JP2021120937A - Positive electrode active material for lithium ion secondary battery, positive electrode and lithium ion secondary battery - Google Patents
Positive electrode active material for lithium ion secondary battery, positive electrode and lithium ion secondary battery Download PDFInfo
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- JP2021120937A JP2021120937A JP2020014122A JP2020014122A JP2021120937A JP 2021120937 A JP2021120937 A JP 2021120937A JP 2020014122 A JP2020014122 A JP 2020014122A JP 2020014122 A JP2020014122 A JP 2020014122A JP 2021120937 A JP2021120937 A JP 2021120937A
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- positive electrode
- active material
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- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 54
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- Y02E60/10—Energy storage using batteries
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Abstract
Description
本発明は、リチウムイオン二次電池用正極活物質、正極、及びリチウムイオン二次電池に関する。 The present invention relates to a positive electrode active material for a lithium ion secondary battery, a positive electrode, and a lithium ion secondary battery.
近年、携帯電話やノート型パソコン等の携帯機器の普及にともない、高いエネルギー密度を有する小型かつ軽量な二次電池の開発が強く望まれている。また、ＸＥＶと呼ばれる環境対応自動車においても高容量な二次電池が求められており、高容量の二次電池の需要は、今後、大幅に増加することが予想されている。さらに、環境対応自動車における１回の充電当たりの走行距離の向上や小型化の必要性が増し、更なる高容量化が求められている。 In recent years, with the widespread use of mobile devices such as mobile phones and notebook computers, the development of compact and lightweight secondary batteries having a high energy density has been strongly desired. In addition, high-capacity secondary batteries are also required for environment-friendly automobiles called XEVs, and the demand for high-capacity secondary batteries is expected to increase significantly in the future. Further, there is an increasing need for improvement of the mileage per charge and miniaturization of environment-friendly automobiles, and further increase in capacity is required.
このような要求を満たす二次電池として、リチウムイオン二次電池などのリチウムイオン二次電池がある。リチウムイオン二次電池は、負極および正極と電解液等で構成され、負極および正極の活物質として、リチウムを脱離および挿入することが可能な材料が用いられている。 As a secondary battery satisfying such a requirement, there is a lithium ion secondary battery such as a lithium ion secondary battery. The lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of desorbing and inserting lithium is used as an active material for the negative electrode and the positive electrode.
リチウムイオン二次電池については、現在研究開発が盛んに行われているところであるが、中でも、層状またはスピネル型のリチウム金属複合酸化物を正極材料に用いたリチウムイオン二次電池は、４Ｖ級の高い電圧が得られるため、高いエネルギー密度を有する電池として実用化が進んでいる。 Currently, research and development are being actively carried out on lithium-ion secondary batteries. Among them, lithium-ion secondary batteries using a layered or spinel-type lithium metal composite oxide as a positive electrode material are of the 4V class. Since a high voltage can be obtained, it is being put into practical use as a battery having a high energy density.
かかるリチウムイオン二次電池の正極材料として、これまで主に提案されている材料として、合成が比較的容易なリチウムコバルト複合酸化物（ＬｉＣｏＯ２）や、コバルトよりも安価なニッケルを用いたリチウムニッケル複合酸化物（ＬｉＮｉＯ２）、リチウムニッケルコバルトマンガン複合酸化物（ＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２）、マンガンを用いたリチウムマンガン複合酸化物（ＬｉＭｎ２Ｏ４）、リチウムニッケルマンガン複合酸化物（ＬｉＮｉ０．５Ｍｎ０．５Ｏ２）などのリチウム複合酸化物が提案されている。このうちリチウムニッケルコバルトマンガン複合酸化物は、比較的安価で工業的に扱いやすく、比較的高容量であり安全性も比較的が高い材料として注目されている。 Lithium cobalt composite oxide (LiCoO 2 ), which is relatively easy to synthesize, and lithium nickel using nickel, which is cheaper than cobalt, have been mainly proposed as positive electrode materials for such lithium ion secondary batteries. Composite oxide (LiNiO 2 ), lithium nickel cobalt manganese composite oxide (LiNi 1/3 Co 1/3 Mn 1/3 O 2 ), lithium manganese composite oxide using manganese (LiMn 2 O 4 ), lithium nickel Lithium composite oxides such as manganese composite oxides (LiNi 0.5 Mn 0.5 O 2) have been proposed. Of these, lithium nickel-cobalt-manganese composite oxide is attracting attention as a material that is relatively inexpensive, industrially easy to handle, has a relatively high capacity, and has relatively high safety.
高容量を得るための方法の一つとして、正極活物質の充填性を高めることが挙げられる。正極活物質の充填性を高めることで、合剤正極の単位体積当たりの正極活物質量を高め、体積エネルギー密度（Ｗｈ／Ｌ）に優れるリチウムイオン二次電池を得ることができる。正極活物質の充填性はタップ密度で評価され、タップ密度が高いほど充填性が高く、体積エネルギー密度（Ｗｈ／Ｌ）に優れるリチウムイオン二次電池を得ることができる。 One of the methods for obtaining a high capacity is to improve the filling property of the positive electrode active material. By increasing the filling property of the positive electrode active material, the amount of the positive electrode active material per unit volume of the mixed positive electrode can be increased, and a lithium ion secondary battery having an excellent volume energy density (Wh / L) can be obtained. The filling property of the positive electrode active material is evaluated by the tap density, and the higher the tap density, the higher the filling property, and a lithium ion secondary battery having an excellent volume energy density (Wh / L) can be obtained.
一方で、上記のリチウムイオン二次電池の中には、急速で充放電を行う用途を必要とする二次電池が含まれ、このような用途においては、高出力が求められる。しかし、正極活物質のタップ密度を高めただけでは、高出力は得られない。高出力を得るためには、例えば、正極活物質の表面積をできるだけ大きく製造し、リチウムイオンの挿入脱離反応サイトを増やせばよい。これにより、正極抵抗を低くすることができ、より好適に高出力を得ることができる。 On the other hand, the above-mentioned lithium ion secondary battery includes a secondary battery that requires an application for rapid charging and discharging, and high output is required in such an application. However, high output cannot be obtained simply by increasing the tap density of the positive electrode active material. In order to obtain high output, for example, the surface area of the positive electrode active material may be manufactured as large as possible, and the number of lithium ion insertion / desorption reaction sites may be increased. As a result, the positive electrode resistance can be lowered, and a higher output can be obtained more preferably.
正極活物質の表面積を大きくする公知の技術としては、例えば、特許文献１〜３に開示される技術を挙げることができる。前記の技術は、正極活物質の前駆体となる遷移金属複合水酸化物粒子を、主として核生成を行う核生成工程と、主として粒子成長を行う粒子成長工程の２段階に明確に分離した晶析反応において、反応雰囲気中の酸素濃度を調整することにより、出力特性に優れた中心部に空洞（中空構造）を有する層状構造の正極活物質を製造する技術である。 As a known technique for increasing the surface area of the positive electrode active material, for example, the techniques disclosed in Patent Documents 1 to 3 can be mentioned. The above-mentioned technique clearly separates the transition metal composite hydroxide particles, which are precursors of the positive electrode active material, into two stages, a nucleation step mainly for nucleation and a particle growth step for mainly particle growth. In the reaction, by adjusting the oxygen concentration in the reaction atmosphere, it is a technique for producing a positive electrode active material having a layered structure having a cavity (hollow structure) in the central portion having excellent output characteristics.
リチウムイオン二次電池用の正極活物質として、高容量であり、かつ、高出力である正極活物質が求められている。しかしながら、特許文献１〜３に開示される技術では、高出力が得られるものの、正極活物質の内部に空洞（中空構造）を有しているため、タップ密度を十分に高めることができず、より高容量とすることが難しかった。 As a positive electrode active material for a lithium ion secondary battery, a positive electrode active material having a high capacity and a high output is required. However, although the techniques disclosed in Patent Documents 1 to 3 can obtain high output, the tap density cannot be sufficiently increased because the positive electrode active material has a cavity (hollow structure) inside. It was difficult to increase the capacity.
本発明は、このような実情に鑑みてなされたものであり、高容量であるとともに、高出力を示す、リチウムニッケル複合酸化物を含むリチウムイオン二次電池用正極活物質を提供するものである。 The present invention has been made in view of such circumstances, and provides a positive electrode active material for a lithium ion secondary battery containing a lithium nickel composite oxide, which has a high capacity and a high output. ..
本発明の第１の態様では、第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂとを含むリチウムイオン二次電池用の正極活物質であって、第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂは、六方晶系の層状構造を有するリチウムニッケル複合酸化物であり、かつ、複数の一次粒子が凝集した二次粒子で構成され、第１の正極活物質粒子Ａは、中実構造を有し、タップ密度が２．１ｇ／ｃｍ３以上３．０ｇ／ｃｍ３以下であり、かつ、平均粒径（Ｄ５０）が８μｍ以上３０μｍ以下であり、第２の正極活物質粒子Ｂは、中空構造を有し、タップ密度が１．８ｇ／ｃｍ３以下であり、平均粒径（Ｄ５０）が１μｍ以上８μｍ以下、かつ、第１の正極活物質粒子Ａの平均粒径（Ｄ５０）より小さく、正極活物質を含む正極材料をロールプレスにて線圧２００Ｎ／ｍｍで圧下したとき、圧下後の正極材料の断面で観察される第２の正極活物質粒子Ｂのうち、断面長径が３μｍ以上であり、かつ、二次粒子内で確認される空隙長径が０．３μｍ以上の空隙を有する二次粒子において、空隙長径（Ｌ）と空隙短径（Ｗ）の比である平均アスペクト比（Ｗ／Ｌ）が０．５以下であり、第１の正極活物質粒子Ａの質量（ＷＡ）と第２の正極活物質粒子Ｂの質量（ＷＢ）との比率が以下の関係式（１）を満たす、リチウムイオン二次電池用正極活物質が提供される。
０．００１≦ＷＢ／（ＷＡ＋ＷＢ）≦０．５・・・（１）
In the first aspect of the present invention, the positive electrode active material for a lithium ion secondary battery containing the first positive positive active material particles A and the second positive positive active material particles B, and is the first positive positive active material. The particles A and the second positive electrode active material particles B are lithium nickel composite oxides having a hexagonal layered structure, and are composed of secondary particles in which a plurality of primary particles are aggregated. The positive electrode active material particles A have a solid structure, a tap density of 2.1 g / cm 3 or more and 3.0 g / cm 3 or less, and an average particle size (D50) of 8 μm or more and 30 μm or less. The second positive positive active material particles B have a hollow structure, a tap density of 1.8 g / cm 3 or less, an average particle size (D50) of 1 μm or more and 8 μm or less, and the first positive positive active material particles. When a positive electrode material having a particle size smaller than the average particle size (D50) of A and containing a positive electrode active material is reduced by a roll press at a linear pressure of 200 N / mm, the second positive electrode active material observed in the cross section of the positive electrode material after reduction is observed. Among the particles B, in the secondary particles having a cross-sectional major axis of 3 μm or more and a void major axis confirmed in the secondary particle having a void major axis of 0.3 μm or more, the void major axis (L) and the void minor axis (W) the average aspect ratio is the ratio of) (W / L) is 0.5 or less, the mass of the first cathode active material particles a (W a) and the second positive electrode active material particles B mass (W B) Provided is a positive particle active material for a lithium ion secondary battery, wherein the ratio of and to satisfies the following relational expression (1).
0.001 ≦ W B / (W A + W B) ≦ 0.5 ··· (1)
また、第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂの組成が、金属元素として、リチウム（Ｌｉ）と、ニッケル（Ｎｉ）と、コバルト（Ｃｏ）と、任意に、マンガン（Ｍｎ）、及び、Ｗ、Ｚｒ、Ｖ、Ｍｇ、Ｍｏ、Ｎｂ、Ｔｉ、Ｓｉ、及び、Ａｌからなる群から選ばれる少なくとも１種の元素（Ｍ）と、を含有し、それぞれの金属元素の物質量比がＬｉ：Ｎｉ：Ｃｏ：Ｍｎ：Ｍ＝ｓ：（１−ｘ−ｙ−ｚ）：ｘ：ｙ：ｚ（ただし、０．０５≦ｘ≦０．５０、０≦ｙ≦０．３５、０≦ｚ≦０．０５、０．９５＜ｓ＜１．２０）で表されることが好ましい。また、第１の正極活物質粒子Ａの粒度分布のばらつきを示す（ｄ９０−ｄ１０）／ＭＶの値が０．６５以上１．２以下であり、第２の正極活物質粒子Ｂの粒度分布のばらつきを示す（ｄ９０−ｄ１０）／ＭＶの値が０．６５以下であることが好ましい。また、上記正極活物質のタップ密度が１．９ｇ／ｃｍ３以上３ｇ／ｃｍ３以下であることが好ましい。 Further, the composition of the first positive electrode active material particle A and the second positive positive active material particle B is, as metal elements, lithium (Li), nickel (Ni), cobalt (Co), and optionally manganese. (Mn) and at least one element (M) selected from the group consisting of W, Zr, V, Mg, Mo, Nb, Ti, Si, and Al, and each metal element. The material amount ratio is Li: Ni: Co: Mn: M = s: (1-x−y−z): x: y: z (where 0.05 ≦ x ≦ 0.50, 0 ≦ y ≦ 0. It is preferably represented by 35, 0 ≦ z ≦ 0.05, 0.95 <s <1.20). Further, the value of (d90-d10) / MV showing the variation in the particle size distribution of the first positive electrode active material particle A is 0.65 or more and 1.2 or less, and the particle size distribution of the second positive electrode active material particle B. The value of (d90-d10) / MV showing variation is preferably 0.65 or less. Further, it is preferable that the tap density of the positive electrode active material is 1.9 g / cm 3 or more and 3 g / cm 3 or less.
本発明の第２の態様では、第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂとを含むリチウムイオン二次電池用の正極であって、第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂは、六方晶系の層状構造を有するリチウムニッケル複合酸化物であり、複数の一次粒子が凝集した二次粒子で構成され、金属元素として、リチウム（Ｌｉ）と、コバルト（Ｃｏ）と、ニッケル（Ｎｉ）と、任意に、マンガン（Ｍｎ）、及び、Ｗ、Ｚｒ、Ｖ、Ｍｇ、Ｍｏ、Ｎｂ、Ｔｉ、Ｓｉ、及び、Ａｌから選ばれる少なくとも１種の元素（Ｍ）と、を含有し、それぞれの金属元素の物質量比がＬｉ：Ｎｉ：Ｃｏ：Ｍｎ：Ｍ＝ｓ：（１−ｘ−ｙ−ｚ）：ｘ：ｙ：ｚ（ただし、０．０５≦ｘ≦０．５０、０≦ｙ≦０．３５、０≦ｚ≦０．０５、０．９５＜ｓ＜１．２０）で表され、第１の正極活物質粒子Ａは、中実構造を有し、タップ密度が２．１ｇ／ｃｍ３以上３．０ｇ／ｃｍ３以下であり、かつ、平均粒径（Ｄ５０）が８μｍ以上３０μｍ以下であり、第２の正極活物質粒子Ｂは、中空構造を有し、タップ密度が１．８ｇ／ｃｍ３以下であり、平均粒径（Ｄ５０）が１μｍ以上８μｍ以下、かつ、第１の正極活物質粒子Ａの平均粒径（Ｄ５０）より小さく、正極の断面で観察される第２の正極活物質粒子Ｂのうち、断面長径が３μｍ以上であり、かつ、二次粒子内で観察される空隙長径が０．３μｍ以上の空隙を有する二次粒子において、空隙長径（Ｌ）と空隙短径（Ｗ）との比である平均アスペクト比（Ｗ／Ｌ）が０．５以下であり、第１の正極活物質粒子Ａの質量（ＷＡ）と第２の正極活物質粒子Ｂの質量（ＷＢ）との比率が以下の関係式（１）を満たす、リチウムイオン二次電池用の正極が提供される。
０．００１≦ＷＢ／（ＷＡ＋ＷＢ）≦０．５・・・（１）
In the second aspect of the present invention, it is a positive electrode for a lithium ion secondary battery containing the first positive positive active material particles A and the second positive positive active material particles B, and is the first positive positive active material particles A. The second positive electrode active material particles B are lithium nickel composite oxides having a hexagonal layered structure, and are composed of secondary particles in which a plurality of primary particles are aggregated, and lithium (Li) is used as a metal element. ), Cobalt (Co), nickel (Ni), optionally manganese (Mn), and at least one selected from W, Zr, V, Mg, Mo, Nb, Ti, Si, and Al. Element (M) and the substance amount ratio of each metal element are Li: Ni: Co: Mn: M = s: (1-x−y—z): x: y: z (However, Represented by 0.05 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.05, 0.95 <s <1.20), the first positive electrode active material particle A is It has a solid structure, a tap density of 2.1 g / cm 3 or more and 3.0 g / cm 3 or less, an average particle size (D50) of 8 μm or more and 30 μm or less, and a second positive electrode active material particle. B has a hollow structure, a tap density of 1.8 g / cm 3 or less, an average particle size (D50) of 1 μm or more and 8 μm or less, and an average particle size (D50) of the first positive electrode active material particle A. ), Among the second positive electrode active material particles B observed in the cross section of the positive electrode, voids having a cross-sectional major axis of 3 μm or more and a void major axis observed in the secondary particles of 0.3 μm or more. The average aspect ratio (W / L), which is the ratio of the void major axis (L) to the void minor axis (W), is 0.5 or less, and the mass of the first positive electrode active material particle A ( W a) and the ratio of the mass of the second positive electrode active material particles B (W B) satisfies the relation (1) below, a positive electrode for a lithium ion secondary battery is provided.
0.001 ≦ W B / (W A + W B) ≦ 0.5 ··· (1)
本発明の第３の態様では、上記のリチウムイオン二次電池用の正極の製造方法であって、第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂとを含む正極材料を圧下して、第２の正極活物質粒子Ｂの平均アスペクト比（Ｗ／Ｌ）が０．５以下となるように調整する工程、を含む、正極の製造方法が提供される。 In the third aspect of the present invention, in the above method for manufacturing a positive electrode for a lithium ion secondary battery, a positive electrode material containing a first positive electrode active material particle A and a second positive electrode active material particle B is provided. A method for producing a positive electrode is provided, which comprises a step of reducing the pressure so that the average aspect ratio (W / L) of the second positive electrode active material particles B is 0.5 or less.
本発明の第４の態様では、正極、負極、及び、非水系電解質を備え、正極は、上記の正極活物質を含む、リチウムイオン二次電池が提供される。 In a fourth aspect of the present invention, a lithium ion secondary battery is provided that includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode contains the above-mentioned positive electrode active material.
本発明によれば、二次電池において高い電池容量と、低い正極抵抗による高出力との両立を実現できる正極活物質を提供することができる。また、本発明は、このような正極活物質を、工業規模の生産において容易に製造することが可能であり、工業的価値は極めて大きいものといえる。 According to the present invention, it is possible to provide a positive electrode active material capable of achieving both a high battery capacity and a high output due to a low positive electrode resistance in a secondary battery. Further, according to the present invention, such a positive electrode active material can be easily produced in industrial scale production, and it can be said that the industrial value is extremely large.
以下、図面を参照して、実施形態に係る（１）リチウムイオン二次電池用正極活物質と（２）その製造方法、（３）この正極活物質を含む正極、及び、（４）この正極活物質を含むリチウムイオン二次電池の一例について説明する。ただし、本発明は以下に説明する実施形態に限定されるものではない。また、図面においては、適宜、模式的に表現することや、縮尺を変更して表現することがある。 Hereinafter, with reference to the drawings, (1) a positive electrode active material for a lithium ion secondary battery and (2) a method for producing the same, (3) a positive electrode containing the positive electrode active material, and (4) this positive electrode according to the embodiment. An example of a lithium ion secondary battery containing an active material will be described. However, the present invention is not limited to the embodiments described below. Further, in the drawings, it may be represented schematically or the scale may be changed as appropriate.
（１）リチウムイオン二次電池用正極活物質
リチウムイオン二次電池（以下、単に「二次電池」ともいう。）の性能は、正極に採用される正極活物質の特性により大きく影響を受ける。よって、二次電池の性能を向上させるためには、正極活物質の選択が重要である。本発明者は、高容量化と高出力化とを両立させた正極活物質を得ることを目的として、鋭意検討をしたところ、平均粒径、粒子構造、及び、タップ密度が異なる２種類の正極活物質粒子を特定の割合で混合することにより、高い電池容量と、低い正極抵抗を有することによる高い出力特性と、を共に実現できることを見出して、本発明を完成させた。
(1) Positive Electrode Active Material for Lithium Ion Secondary Battery The performance of a lithium ion secondary battery (hereinafter, also simply referred to as “secondary battery”) is greatly affected by the characteristics of the positive electrode active material used for the positive electrode. Therefore, in order to improve the performance of the secondary battery, it is important to select the positive electrode active material. The present inventor has conducted diligent studies for the purpose of obtaining a positive electrode active material having both high capacity and high output, and as a result, two types of positive electrodes having different average particle size, particle structure, and tap density are obtained. The present invention has been completed by finding that both high battery capacity and high output characteristics due to having a low positive electrode resistance can be realized by mixing the active material particles in a specific ratio.
図１は、本実施形態に係る正極活物質の一例を模式的に示す図である。図１に示すように、正極活物質１００は、中実構造を有し、かつ、特定の平均粒径、及び、タップ密度を有する第１の正極活物質粒子Ａと、粒子内部に中空１０を有する構造（中空構造）を有し、かつ、特定の平均粒径、及び、タップ密度を有する第２の正極活物質粒子Ｂとを含む。
FIG. 1 is a diagram schematically showing an example of a cathode active material according to the present embodiment. As shown in FIG. 1, the positive electrode
ここで、第２の正極活物質粒子Ｂは、第１の正極活物質粒子Ａとともに所定の力（２００Ｎ／ｍｍ）にて加圧されたときに観察される二次粒子断面において、断面長径が３μｍ以上であり、かつ、二次粒子内で確認される空隙長径が０．３μｍ以上の空隙を有するもののうち、空隙長径（Ｌ）と空隙短径（Ｗ）との比である平均アスペクト比（Ｗ／Ｌ）が０．５以下となる粒子である。このような第２の正極活物質粒子Ｂを含むことにより、正極作製時の加圧によって、中空構造を有する第２の正極活物質粒子Ｂが圧下されて変形し、第１の正極活物質粒子Ａ又は第２の正極活物質粒子Ｂを単独で用いた場合よりも電極密度を向上させることができると考えられる。電極密度が向上することにより、高い充放電容量（電池容量）と出力特性の向上とを両立するリチウムイオン二次電池を得ることができる。 Here, the second positive electrode active material particles B have a cross-sectional major axis in the secondary particle cross section observed when pressed together with the first positive electrode active material particles A with a predetermined force (200 N / mm). The average aspect ratio (W), which is the ratio of the void major axis (L) and the void minor axis (W), among those having voids of 3 μm or more and the void major axis confirmed in the secondary particles of 0.3 μm or more. W / L) is 0.5 or less. By including such a second positive electrode active material particle B, the second positive electrode active material particle B having a hollow structure is reduced and deformed by the pressurization at the time of producing the positive electrode, and the first positive electrode active material particle It is considered that the electrode density can be improved as compared with the case where A or the second positive electrode active material particle B is used alone. By improving the electrode density, it is possible to obtain a lithium ion secondary battery that has both a high charge / discharge capacity (battery capacity) and an improvement in output characteristics.
また、正極活物質１００は、第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂとを特定の質量比率で含むことにより、リチウムイオン二次電池用の正極活物質として好適に用いることができる。
Further, the positive electrode
以下、本実施形態に係る正極活物質に含まれる、各正極活物質粒子について説明する。 Hereinafter, each positive electrode active material particle contained in the positive electrode active material according to the present embodiment will be described.
［第１の正極活物質粒子Ａ］
第１の正極活物質粒子Ａは、六方晶系の層状構造を有するリチウムニッケル複合酸化物であり、複数の一次粒子が凝集した二次粒子で構成される。以下、第１の正極活物質粒子Ａの各特性について説明する。
[First positive electrode active material particle A]
The first positive electrode active material particle A is a lithium nickel composite oxide having a hexagonal layered structure, and is composed of secondary particles in which a plurality of primary particles are aggregated. Hereinafter, each characteristic of the first positive electrode active material particle A will be described.
（組成）
第１の正極活物質粒子Ａは、リチウムニッケル複合酸化物であり、六方晶系の層状構造を有する。なお、リチウムニッケル複合酸化物とは、少なくともリチウムとニッケルとを含む酸化物をいい、これらの元素以外の他の元素を含んでもよい。第１の正極活物質粒子Ａは、さらにコバルトを含む、リチウムニッケルコバルト複合酸化物であってもよく、さらにマンガンを含む、リチウムニッケルコバルトマンガン複合酸化物であってもよい。第１の正極活物質粒子Ａがニッケル以外の元素を含むことにより、電池特性を向上させることができる。
(composition)
The first positive electrode active material particle A is a lithium nickel composite oxide and has a hexagonal layered structure. The lithium nickel composite oxide means an oxide containing at least lithium and nickel, and may contain elements other than these elements. The first positive electrode active material particle A may be a lithium nickel cobalt composite oxide further containing cobalt, or may be a lithium nickel cobalt manganese composite oxide further containing manganese. When the first positive electrode active material particle A contains an element other than nickel, the battery characteristics can be improved.
第１の正極活物質粒子Ａは、金属元素としてリチウム（Ｌｉ）と、ニッケル（Ｎｉ）と、コバルト（Ｃｏ）と、任意に、マンガン（Ｍｎ）及びＷ、Ｚｒ、Ｖ、Ｍｇ、Ｍｏ、Ｎｂ、Ｔｉ、Ｓｉ、Ａｌからなる群から選ばれる少なくとも１種の元素（Ｍ）と、を含有し、それぞれの上記金属元素の物質量の比がＬｉ：Ｎｉ：Ｃｏ：Ｍｎ：Ｍ＝ｓ：（１−ｘ−ｙ−ｚ）：ｘ：ｙ：ｚ（ただし、０．０５≦ｘ≦０．５０、０≦ｙ≦０．３５、０≦ｚ≦０．０５、０．９５＜ｓ＜１．２０）で表されることが好ましい。）なお、上記金属元素は半金属元素を含むものとする。 The first positive electrode active material particles A include lithium (Li), nickel (Ni), cobalt (Co) as metal elements, and optionally manganese (Mn) and W, Zr, V, Mg, Mo, Nb. , Ti, Si, Al, and at least one element (M) selected from the group, and the ratio of the amount of each of the above metal elements is Li: Ni: Co: Mn: M = s :( 1-x-y-z): x: y: z (where 0.05 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.05, 0.95 <s <1 It is preferably represented by .20). ) The metal element is assumed to include a metalloid element.
上記物質量の比において、Ｌｉ以外の上記元素の物質量比の合計は１となるため、Ｌｉの物質量の比を示すｓは、リチウムと、リチウム以外の上記元素（Ｍｅ）との物質量比（以下「Ｌｉ／Ｍｅ」ともいう）に対応する。上記の物質量比において、リチウムの含有量を示すｓは、０．９５を超え１．２０未満の範囲である。ｓが０．９５未満である場合、得られた正極活物質を用いたリチウムイオン二次電池における正極の正極抵抗が大きくなり、電池の出力が悪化する。一方、ｓが１．２０を超える場合も、上記正極活物質を電池の正極に用いた場合の初期放電容量が低下するとともに、正極の正極抵抗も増加してしまうため、好ましくない。 In the ratio of the amount of substance, the total amount of substance ratio of the above elements other than Li is 1, so s indicating the ratio of the amount of substance of Li is the amount of substance of lithium and the above element (Me) other than lithium. Corresponds to the ratio (hereinafter also referred to as "Li / Me"). In the above substance amount ratio, s indicating the lithium content is in the range of more than 0.95 and less than 1.20. When s is less than 0.95, the positive electrode resistance of the positive electrode in the obtained lithium ion secondary battery using the positive electrode active material becomes large, and the output of the battery deteriorates. On the other hand, when s exceeds 1.20, the initial discharge capacity when the positive electrode active material is used for the positive electrode of the battery decreases, and the positive electrode resistance of the positive electrode also increases, which is not preferable.
上記の物質量比において、コバルトの含有量を示すｘは、０．０５以上０．５以下の範囲である。コバルトは埋蔵量が少なく高価な元素であるため、ｘが０．５を超える場合、コストが増大してしまい好ましくない。 In the above substance amount ratio, x indicating the cobalt content is in the range of 0.05 or more and 0.5 or less. Since cobalt is an expensive element with a small reserve, if x exceeds 0.5, the cost increases, which is not preferable.
上記の物質量比において、マンガンの含有量を示すｙは、０以上０．３５以下の範囲である。ｙが０．３５を超えると、電池の正極に用いた場合の充放電容量が低下してしまう。 In the above substance amount ratio, y indicating the manganese content is in the range of 0 or more and 0.35 or less. If y exceeds 0.35, the charge / discharge capacity when used for the positive electrode of the battery decreases.
上記の物質量比において、Ｍは、任意にＷ、Ｚｒ、Ｖ、Ｍｇ、Ｍｏ、Ｎｂ、Ｔｉ、Ｓｉ、Ａｌから選ばれる少なくとも１種の元素を示す。また、上記の物質量比において、元素（Ｍ）の含有量を示すｚは、０以上０．０５以下の範囲である。ｚが０．０５を超える場合、Ｒｅｄｏｘ反応に貢献する金属元素が減少し、容量が悪化するため好ましくない。 In the above substance amount ratio, M represents at least one element arbitrarily selected from W, Zr, V, Mg, Mo, Nb, Ti, Si and Al. Further, in the above substance amount ratio, z indicating the content of the element (M) is in the range of 0 or more and 0.05 or less. When z exceeds 0.05, the amount of metal elements contributing to the Redox reaction decreases and the capacitance deteriorates, which is not preferable.
また、第１の正極活物質粒子Ａは、上記のＮｉ、Ｃｏ、Ｍｎ以外の元素（Ｍ）を含有することが好ましい。すなわち、上記の物質量比における、ｚは、０を超えることが好ましく、より好ましくは０．０１以上０．０４以下の範囲である。第１の正極活物質粒子Ａが元素（Ｍ）を含有する場合、これを含む正極活物質を用いた二次電池の耐久特性や出力特性を向上させることができる。 Further, the first positive electrode active material particle A preferably contains an element (M) other than the above-mentioned Ni, Co, and Mn. That is, z in the above substance amount ratio preferably exceeds 0, and more preferably is in the range of 0.01 or more and 0.04 or less. When the first positive electrode active material particle A contains an element (M), the durability characteristics and output characteristics of a secondary battery using the positive electrode active material containing the element (M) can be improved.
特に、上記の元素（Ｍ）が、第１の正極活物質粒子Ａの表面または内部に均一に分布する場合、粒子全体で上記効果を得ることができ、少量の元素（Ｍ）の添加により、効果が得られるとともに電池容量の低下を抑制できる。さらに、より少ない元素（Ｍ）の添加量で効果を得るという観点から、第１の正極活物質粒子Ａの粒子内部より粒子表面において元素Ｍの濃度を高めてもよい。 In particular, when the above element (M) is uniformly distributed on the surface or inside of the first positive electrode active material particles A, the above effect can be obtained for the entire particles, and by adding a small amount of the element (M), The effect can be obtained and the decrease in battery capacity can be suppressed. Further, from the viewpoint of obtaining the effect with a smaller amount of the element (M) added, the concentration of the element M may be increased on the particle surface from the inside of the particles of the first positive electrode active material particle A.
なお、第１の正極活物質粒子Ａは、上述した金属元素（Ｌｉ、Ｎｉ、Ｍｎ、Ｃｏ、元素Ｍ）及び酸素以外の元素を、本発明の効果を阻害しない範囲で少量含んでもよい。また、第１の正極活物質粒子Ａは、二次粒子以外に、単独の一次粒子を少量含んでもよい。 The first positive electrode active material particle A may contain a small amount of elements other than the above-mentioned metal elements (Li, Ni, Mn, Co, element M) and oxygen as long as the effects of the present invention are not impaired. Further, the first positive electrode active material particle A may contain a small amount of a single primary particle in addition to the secondary particle.
（粒子構造）
第１の正極活物質粒子Ａは、中実構造を有する。なお、中実構造とは、空隙率（二次粒子の断面積に対する二次粒子の内部の空隙面積）が、１５％未満の粒子構造のことをいう。また、第１の正極活物質粒子Ａの空隙率は、好ましくは１０％以下、さらに好ましくは５％以下である。
(Particle structure)
The first positive electrode active material particle A has a solid structure. The solid structure refers to a particle structure in which the porosity (the void area inside the secondary particles with respect to the cross-sectional area of the secondary particles) is less than 15%. The porosity of the first positive electrode active material particles A is preferably 10% or less, more preferably 5% or less.
なお、空隙率は、第１の正極活物質粒子Ａの任意断面（平均粒径（Ｄ５０）±２０％の断面長径を有する二次粒子の断面）を、走査型電子顕微鏡を用いて観察し、画像解析することによって測定できる。例えば、複数の第１の正極活物質粒子Ａを樹脂などに埋め込み、クロスセクションポリッシャ加工などにより該粒子の断面観察が可能な状態とした後、画像解析ソフト：ＷｉｎＲｏｏｆ ６．１．１等により、上記二次粒子内の空隙部（一次粒子が存在しない部分）を黒として測定し、二次粒子輪郭内の緻密部（一次粒子が存在する部分）を白として測定し、任意の２０個以上の粒子に対して、［黒部分／（黒部分＋白部分）］の面積を計算することで空隙率を求めることができる。 The porosity was determined by observing an arbitrary cross section of the first positive electrode active material particle A (cross section of a secondary particle having a cross-sectional major axis of average particle size (D50) ± 20%) using a scanning electron microscope. It can be measured by image analysis. For example, after embedding a plurality of first positive electrode active material particles A in a resin or the like and making it possible to observe the cross section of the particles by cross-section polisher processing or the like, image analysis software: WinRof 6.1.1 or the like is used. The voids (parts where the primary particles do not exist) in the secondary particles are measured as black, and the dense parts (parts where the primary particles exist) in the contour of the secondary particles are measured as white, and any 20 or more are measured. The void ratio can be obtained by calculating the area of [black part / (black part + white part)] with respect to the particles.
（タップ密度）
第１の正極活物質粒子Ａは、タップ密度が２．１ｇ／ｃｍ３以上３．０ｇ／ｃｍ３以下である。第１の正極活物質粒子Ａのタップ密度が２．１ｇ／ｃｍ３未満である場合、得られる正極活物質において、充填性を十分に高めることができず、高い充放電容量が得られない。一方で、第１の正極活物質粒子Ａのタップ密度が３．０ｇ／ｃｍ３を超える場合、第１の正極活物質粒子Ａに混入する微粒子や粗大粒子が増加してしまう。微粒子や粗大粒子を含む正極活物質を用いて正極を形成した場合、微粒子の局所的な反応が起こったり、正極抵抗が上昇したりすることがある。また、微粒子が選択的に劣化し、サイクル特性が悪化してしまうことがある。
(Tap density)
The first positive electrode active material particle A has a tap density of 2.1 g / cm 3 or more and 3.0 g / cm 3 or less. When the tap density of the first positive electrode active material particles A is less than 2.1 g / cm 3 , the filling property of the obtained positive electrode active material cannot be sufficiently improved, and a high charge / discharge capacity cannot be obtained. On the other hand, when the tap density of the first positive electrode active material particles A exceeds 3.0 g / cm 3 , the number of fine particles and coarse particles mixed in the first positive electrode active material particles A increases. When a positive electrode is formed using a positive electrode active material containing fine particles or coarse particles, a local reaction of the fine particles may occur or the positive electrode resistance may increase. In addition, the fine particles may be selectively deteriorated and the cycle characteristics may be deteriorated.
（平均粒径）
第１の正極活物質粒子Ａの平均粒径（Ｄ５０）は、８μｍ以上３０μｍ以下であり、好ましくは１０μｍ以上２０μｍ以下である。ここで、第１の正極活物質粒子Ａの平均粒径（Ｄ５０）が８μｍ未満である場合、タップ密度を２．１ｇ／ｃｍ３以上にすることが困難となる。一方で、第１の正極活物質粒子Ａの平均粒径（Ｄ５０）が３０μｍを超える場合、第１の正極活物質粒子Ａの粒度分布が広がってしまい、第１の正極活物質粒子Ａに混入する微粒子や粗大粒子が増加したり、正極抵抗が上昇したりすることがある。なお、平均粒径Ｄ５０は、レーザー回折散乱法に基づく測定による体積基準のメジアン径（Ｄ５０：５０％体積平均粒径）として求めることができる。
(Average particle size)
The average particle size (D50) of the first positive electrode active material particles A is 8 μm or more and 30 μm or less, preferably 10 μm or more and 20 μm or less. Here, when the average particle size (D50) of the first positive electrode active material particles A is less than 8 μm, it becomes difficult to make the tap density 2.1 g / cm 3 or more. On the other hand, when the average particle size (D50) of the first positive electrode active material particles A exceeds 30 μm, the particle size distribution of the first positive electrode active material particles A is widened and mixed with the first positive electrode active material particles A. Fine particles and coarse particles may increase, and positive electrode resistance may increase. The average particle size D50 can be obtained as a volume-based median diameter (D50: 50% volume average particle size) measured based on the laser diffraction / scattering method.
（粒度分布）
第１の正極活物質粒子Ａの粒度分布のばらつきの指標である（ｄ９０−ｄ１０）／ＭＶの値は、０．６５以上１．２以下であることが好ましい。上述した平均粒径（Ｄ５０）とあわせて、粒度分布をこの範囲に調整することによって、より好適にタップ密度を２．１ｇ／ｃｍ３以上にすることができる。
(Particle size distribution)
The value of (d90-d10) / MV, which is an index of the variation in the particle size distribution of the first positive electrode active material particles A, is preferably 0.65 or more and 1.2 or less. By adjusting the particle size distribution to this range in combination with the above-mentioned average particle size (D50), the tap density can be more preferably 2.1 g / cm 3 or more.
上記（Ｄ９０−Ｄ１０）／ＭＶにおいて、Ｄ１０は、各粒径における粒子数を粒径の小さい側から累積し、その累積体積が全粒子の合計体積の１０％となる粒径を、Ｄ９０は、同様に粒子数を累積し、その累積体積が全粒子の合計体積の９０％となる粒径をそれぞれ意味している。また、ＭＶは、体積平均粒径ＭＶを示し、体積で重みづけされた平均粒径を意味する。体積平均粒径ＭＶや、Ｄ９０及びＤ１０は、レーザー光回折散乱式粒度分析計を用いて測定することができる。 In the above (D90-D10) / MV, D10 is a particle size in which the number of particles in each particle size is accumulated from the smaller particle size side, and the cumulative volume is 10% of the total volume of all particles. Similarly, it means a particle size in which the number of particles is accumulated and the accumulated volume is 90% of the total volume of all particles. Further, MV indicates a volume average particle size MV, and means an average particle size weighted by volume. The volume average particle size MV and D90 and D10 can be measured using a laser light diffraction / scattering type particle size analyzer.
（粒子の形状）
第１の正極活物質粒子Ａの形状（外形）は、上記特性を満たす粒子であれば特に限定されず、楕円形状の粒子や粒子表面に凹凸がある粒子であってよいが、球状であることが好ましい。
(Particle shape)
The shape (outer shape) of the first positive electrode active material particle A is not particularly limited as long as it is a particle satisfying the above characteristics, and may be an elliptical particle or a particle having irregularities on the particle surface, but it must be spherical. Is preferable.
ここで、第１の正極活物質粒子Ａの形状は、平均アスペクト比によって評価することができる。すなわち、複数の第１の正極活物質粒子Ａのアスペクト比の平均値を求めることによって、粒子の集合体全体の粒子形状を評価することができる。第１の正極活物質粒子Ａは、例えば、平均アスペクト比が０．７以上である場合、得られる正極活物質の充填性をより向上させることができる。 Here, the shape of the first positive electrode active material particle A can be evaluated by the average aspect ratio. That is, the particle shape of the entire aggregate of particles can be evaluated by obtaining the average value of the aspect ratios of the plurality of first positive electrode active material particles A. The first positive electrode active material particles A can further improve the filling property of the obtained positive electrode active material, for example, when the average aspect ratio is 0.7 or more.
なお、個々の粒子におけるアスペクト比は、走査型電子顕微鏡による二次粒子の画面上の外観観察において、二次粒子の外縁上の点から最大長さとなる他の外縁上の点の距離を測定粒径として、二次粒子において最大の測定粒径に対する最小の測定粒径の比を計測することにより求めることができる。また、平均アスペクト比は、任意の２０個以上の二次粒子について求めたアスペクト比を個数平均することで得られる。 The aspect ratio of each particle is measured by measuring the distance from the point on the outer edge of the secondary particle to the point on the other outer edge that is the maximum length when observing the appearance of the secondary particle on the screen with a scanning electron microscope. The diameter can be determined by measuring the ratio of the minimum measured particle size to the maximum measured particle size of the secondary particles. Further, the average aspect ratio can be obtained by averaging the number of aspect ratios obtained for any 20 or more secondary particles.
［第２の正極活物質粒子Ｂ］
第２の正極活物質粒子Ｂは、六方晶系の層状構造を有するリチウムニッケル複合酸化物であり、複数の一次粒子が凝集した二次粒子で構成される。以下、第２の正極活物質粒子Ｂの各特性について説明する。
[Second positive electrode active material particle B]
The second positive electrode active material particle B is a lithium nickel composite oxide having a hexagonal layered structure, and is composed of secondary particles in which a plurality of primary particles are aggregated. Hereinafter, each characteristic of the second positive electrode active material particle B will be described.
（組成）
第２の正極活物質粒子Ｂは、リチウムニッケル複合酸化物であり、六方晶系の層状構造を有する。なお、リチウムニッケル複合酸化物とは、少なくともリチウムとニッケルとを含む酸化物をいい、これらの元素以外の他の元素を含んでもよい。第２の正極活物質粒子Ｂは、さらにコバルトを含む、リチウムニッケルコバルト複合酸化物であってもよく、さらにマンガンを含む、リチウムニッケルコバルトマンガン複合酸化物であってもよい。第２の正極活物質粒子Ｂがニッケル以外の元素を含むことにより、電池特性を向上させることができる。
(composition)
The second positive electrode active material particle B is a lithium nickel composite oxide and has a hexagonal layered structure. The lithium nickel composite oxide means an oxide containing at least lithium and nickel, and may contain elements other than these elements. The second positive electrode active material particle B may be a lithium nickel cobalt composite oxide further containing cobalt, or may be a lithium nickel cobalt manganese composite oxide further containing manganese. When the second positive electrode active material particle B contains an element other than nickel, the battery characteristics can be improved.
第２の正極活物質粒子Ｂは金属元素として、リチウム（Ｌｉ）と、コバルト（Ｃｏ）と、ニッケル（Ｎｉ）と、任意に、マンガン（Ｍｎ）及びＷ、Ｚｒ、Ｖ、Ｍｇ、Ｍｏ、Ｎｂ、Ｔｉ、Ｓｉ、Ａｌからなる群から選ばれる少なくとも１種の元素（Ｍ）と、を含有し、それぞれの上記金属元素の物質量の比がＬｉ：Ｎｉ：Ｃｏ：Ｍｎ：Ｍ＝ｓ：（１−ｘ−ｙ−ｚ）：ｘ：ｙ：ｚ（ただし、０．０５≦ｘ≦０．５０、０≦ｙ≦０．３５、０≦ｚ≦０．０５、０．９５＜ｓ＜１．２０）で表されることが好ましい。なお、上記金属元素は半金属元素を含むものとする。 The second positive electrode active material particle B contains lithium (Li), cobalt (Co), nickel (Ni), and optionally manganese (Mn) and W, Zr, V, Mg, Mo, Nb as metal elements. , Ti, Si, Al, and at least one element (M) selected from the group, and the ratio of the amount of each of the above metal elements is Li: Ni: Co: Mn: M = s :( 1-x-y-z): x: y: z (where 0.05 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.05, 0.95 <s <1 It is preferably represented by .20). The metal element is assumed to include a metalloid element.
第２の正極活物質粒子Ｂにおける各元素の物質量比の説明、及び、好ましい範囲は、上述の第１の正極活物質粒子Ａにおける各元素の物質量比の説明、及び、好ましい範囲と同様であるので、記載を省略する。なお、第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂとの組成は、同一であってもよく、異なっていてもよい。 The description of the substance amount ratio of each element in the second positive electrode active material particle B and the preferable range are the same as the description of the substance amount ratio of each element in the first positive electrode active material particle A and the preferable range. Therefore, the description is omitted. The composition of the first positive electrode active material particle A and the second positive electrode active material particle B may be the same or different.
なお、第２の正極活物質粒子Ｂは、上述した元素（Ｌｉ、Ｎｉ、Ｍｎ、Ｃｏ、元素Ｍ）及び酸素以外の元素を、本発明の効果を阻害しない範囲で少量含んでもよい。また、第２の正極活物質粒子Ｂは、二次粒子以外に、単独の一次粒子を少量含んでもよい。 The second positive electrode active material particle B may contain a small amount of elements other than the above-mentioned elements (Li, Ni, Mn, Co, element M) and oxygen as long as the effects of the present invention are not impaired. Further, the second positive electrode active material particle B may contain a small amount of a single primary particle in addition to the secondary particle.
（粒子構造）
第２の正極活物質粒子Ｂは、例えば、図１に示すように、粒子内部に中空１０を有する構造（中空構造）を有してもよい。中空構造とは、空隙率（二次粒子２の断面積に対する二次粒子２の内部の空隙面積）が、例えば、１５％以上であり、且つ、明確な空洞（空隙）が観察される構造のことをいう。第２の正極活物質粒子Ｂの空隙率は、好ましくは２０％以上、さらに好ましくは２５％以上である。なお、明確な空洞（空隙）とは、例えば二次粒子の断面積の１０％以上を占める、一又は複数の空隙をいう。
(Particle structure)
The second positive electrode active material particle B may have a structure (hollow structure) having a hollow 10 inside the particle, as shown in FIG. 1, for example. The hollow structure is a structure in which the porosity (the area of voids inside the secondary particles 2 with respect to the cross-sectional area of the secondary particles 2) is, for example, 15% or more, and clear cavities (voids) are observed. Say that. The porosity of the second positive electrode active material particles B is preferably 20% or more, more preferably 25% or more. The clear cavity (void) means, for example, one or more voids that occupy 10% or more of the cross-sectional area of the secondary particles.
（タップ密度）
第２の正極活物質粒子Ｂは、タップ密度が１．８ｇ／ｃｍ３以下である。第２の正極活物質粒子Ｂを中空構造とし、かつ、タップ密度が上記範囲である場合、反応表面積を大きくすることができる。また、粒子内部の中空側の一次粒子表面における反応界面でも、二次粒子の表面の一次粒子間の粒界あるいは空隙から電解液が浸入するようになるため、リチウムの挿脱入が行われ、Ｌｉイオン及び電子の移動が妨げられず、正極抵抗を低減し、二次電池の出力を高くすることができる。なお、タップ密度の下限は特に限定されないが、例えば、０．９ｇ／ｃｍ３以上である。
(Tap density)
The second positive electrode active material particle B has a tap density of 1.8 g / cm 3 or less. When the second positive electrode active material particles B have a hollow structure and the tap density is in the above range, the reaction surface area can be increased. Further, even at the reaction interface on the surface of the primary particles on the hollow side inside the particles, the electrolytic solution enters from the grain boundaries or voids between the primary particles on the surface of the secondary particles, so that lithium is inserted and removed. The movement of Li ions and electrons is not hindered, the positive electrode resistance can be reduced, and the output of the secondary battery can be increased. The lower limit of the tap density is not particularly limited, but is, for example, 0.9 g / cm 3 or more.
（平均粒径）
第２の正極活物質粒子Ｂの平均粒径（Ｄ５０）は、１μｍ以上８μｍ以下であり、好ましくは３μｍ以上７μｍ以下である。また、第２の正極活物質粒子Ｂの平均粒径（Ｄ５０）は、第１の正極活物質粒子Ａの平均粒径より小さい。第２の正極活物質粒子Ｂの平均粒径（Ｄ５０）が上記範囲である場合、第１の正極活物質粒子Ａの粒子間の隙間に第２の正極活物質粒子Ｂを配置することが可能となり、正極活物質１００全体の充填性を高くすることができる。
(Average particle size)
The average particle size (D50) of the second positive electrode active material particles B is 1 μm or more and 8 μm or less, preferably 3 μm or more and 7 μm or less. Further, the average particle size (D50) of the second positive electrode active material particles B is smaller than the average particle size of the first positive electrode active material particles A. When the average particle size (D50) of the second positive electrode active material particles B is within the above range, the second positive electrode active material particles B can be arranged in the gaps between the particles of the first positive electrode active material particles A. Therefore, the filling property of the entire positive electrode
第２の正極活物質粒子Ｂの平均粒径（Ｄ５０）が１μｍ未満である場合、第２の正極活物質粒子Ｂに充放電時の電流が集中することにより、微粒子の局所的な反応に起因して、正極抵抗が上昇したり、発熱して熱安定が低下したり、微粒子が選択的に劣化するのでサイクル特性が悪化したりする恐れがある。一方、第２の正極活物質粒子Ｂの平均粒径が８μｍを超える場合、電解液と正極活物質との反応面積が十分に取れず正極抵抗の増加により出力が低下したり、第１の正極活物質粒子Ａの粒子間の隙間に配置される第２の正極活物質粒子Ｂが減少したりして、正極活物質の充填性が高いものとならないため好ましくない。 When the average particle size (D50) of the second positive electrode active material particles B is less than 1 μm, the current is concentrated on the second positive electrode active material particles B during charging and discharging, which is caused by the local reaction of the fine particles. As a result, the positive electrode resistance may increase, heat may be generated to reduce thermal stability, and the fine particles may be selectively deteriorated, resulting in deterioration of cycle characteristics. On the other hand, when the average particle size of the second positive electrode active material particles B exceeds 8 μm, the reaction area between the electrolytic solution and the positive electrode active material cannot be sufficiently obtained, and the output decreases due to an increase in the positive electrode resistance, or the first positive electrode It is not preferable because the number of the second positive electrode active material particles B arranged in the gaps between the particles of the active material particles A is reduced and the filling property of the positive electrode active material is not high.
さらに、第２の正極活物質粒子Ｂの平均粒径（Ｄ５０）は、第１の正極活物質粒子Ａの平均粒径（Ｄ５０）に対する比で０．５以下とすることが好ましく、０．３以下とすることがより好ましい。これにより、第１の正極活物質粒子Ａの粒子の間隔を狭くするとともに第１の正極活物質粒子Ａの粒子間に第２の正極活物質粒子Ｂを多く配することが可能となり、正極活物質の充填性を一層高めることができる。 Further, the average particle size (D50) of the second positive electrode active material particles B is preferably 0.5 or less as a ratio to the average particle size (D50) of the first positive electrode active material particles A, and is 0.3. The following is more preferable. As a result, the distance between the particles of the first positive electrode active material particles A can be narrowed, and a large amount of the second positive electrode active material particles B can be arranged between the particles of the first positive electrode active material particles A. The filling property of the substance can be further improved.
（粒度分布）
第２の正極活物質粒子Ｂの粒度分布のばらつきの指標である（ｄ９０−ｄ１０）／ＭＶの値は、０．６５以下であることが好ましく、０．６０以下であることがより好ましい。（ｄ９０−ｄ１０）／ＭＶの値が０．６５以下であることにより、微粒子や粗大粒子の混入を抑制すること可能であり、正極活物質の電池特性の低下を抑制するとともに、充填性をより好適に向上させることができる。
(Particle size distribution)
The value of (d90-d10) / MV, which is an index of the variation in the particle size distribution of the second positive electrode active material particles B, is preferably 0.65 or less, and more preferably 0.60 or less. When the value of (d90-d10) / MV is 0.65 or less, it is possible to suppress the mixing of fine particles and coarse particles, suppress the deterioration of the battery characteristics of the positive electrode active material, and improve the filling property. It can be preferably improved.
（ｄ９０−ｄ１０）／ＭＶの値が０．６５を超える場合、微粒子あるいは粗大粒子が存在するようになり、微粒子の局所的な反応に起因して発熱して安全性が低下し、さらに、微粒子が選択的に劣化するので、サイクル特性が悪化する恐れがある。また、粗大粒子の存在によって、電解液と正極活物質との反応面積が十分に取れず、正極抵抗が増加して出力が低下する。そして、第１の正極活物質粒子Ａの粒子間の隙間に配される第２の正極活物質粒子Ｂが減少して、正極活物質の充填性が高いものとならないため好ましくない。 When the value of (d90-d10) / MV exceeds 0.65, fine particles or coarse particles will be present, heat will be generated due to the local reaction of the fine particles, and safety will be reduced, and further, fine particles will be present. Is selectively deteriorated, so that the cycle characteristics may be deteriorated. Further, due to the presence of coarse particles, the reaction area between the electrolytic solution and the positive electrode active material cannot be sufficiently obtained, the positive electrode resistance increases, and the output decreases. Then, the number of the second positive electrode active material particles B arranged in the gaps between the particles of the first positive electrode active material particles A is reduced, and the filling property of the positive electrode active material is not improved, which is not preferable.
（粒子の形状）
第２の正極活物質粒子Ｂの形状（外形）は、上記特性を満たす粒子であれば特に限定されないが、球状であることが好ましい。第２の正極活物質粒子Ｂの形状が球状である場合、第１の正極活物質粒子Ａの粒子間に第２の正極活物質粒子Ｂを配置することが容易になるとともに、正極活物質内の各粒子の間隔を狭めることができ、正極活物質の充填性を高くすることができる。
(Particle shape)
The shape (outer shape) of the second positive electrode active material particle B is not particularly limited as long as it is a particle satisfying the above characteristics, but it is preferably spherical. When the shape of the second positive electrode active material particle B is spherical, it becomes easy to arrange the second positive electrode active material particle B between the particles of the first positive electrode active material particle A, and in the positive electrode active material. The distance between each of the particles can be narrowed, and the filling property of the positive electrode active material can be improved.
（空隙の平均アスペクト比）
本実施形態における第２の正極活物質粒子Ｂは、二次電池用の正極を作製する際に、本実施形態に係る正極活物質を含む正極材料を圧下することによって変形することが好ましい。
(Average aspect ratio of voids)
The second positive electrode active material particles B in the present embodiment are preferably deformed by reducing the positive electrode material containing the positive electrode active material according to the present embodiment when producing a positive electrode for a secondary battery.
ここで、第２の正極活物質粒子Ｂの変形の程度の評価は、圧下後の第２の正極活物質粒子Ｂにおける空隙の平均アスペクト比を測定することにより行うことができる。圧下後の空隙のアスペクト比は、例えば、圧下後の正極材料が埋め込まれた樹脂を、圧下後の正極材料に対して加圧された面と垂直な断面で切り出し、この断面を研磨してＳＥＭ断面写真を撮影し、画像解析することによって行うことができる。具体的には、ＳＥＭ断面写真の画像解析において、二次粒子の断面長径が３μｍ以上であり、かつ、粒子内部の空隙長径が０．３μｍ以上の空隙を有する第２の正極活物質粒子Ｂ２０個以上に対して、縦断面の空隙長径（Ｌ）と空隙短径（Ｗ）を各々測定して求めた空隙アスペクト比（Ｗ／Ｌ）の個数平均（以下、「空隙の平均アスペクト比」とも呼ぶ。）を算出することによって評価する。なお、同一の粒子に測定対象の空隙が複数含まれる場合には、その粒子の中で最も大きな空隙を測定する。 Here, the degree of deformation of the second positive electrode active material particles B can be evaluated by measuring the average aspect ratio of the voids in the second positive electrode active material particles B after reduction. For the aspect ratio of the voids after reduction, for example, a resin in which the positive electrode material after reduction is embedded is cut out with a cross section perpendicular to the surface pressed with respect to the positive electrode material after reduction, and this cross section is polished to SEM. This can be done by taking a cross-sectional photograph and analyzing the image. Specifically, in the image analysis of the SEM cross-sectional photograph, 20 second positive electrode active material particles B having a cross-sectional major axis of the secondary particles of 3 μm or more and a void major axis of 0.3 μm or more inside the particles. In contrast to the above, the number average of the void aspect ratios (W / L) obtained by measuring the void major axis (L) and the void minor axis (W) in the vertical cross section (hereinafter, also referred to as "average aspect ratio of voids"). ) Is calculated. When the same particle contains a plurality of voids to be measured, the largest void among the particles is measured.
本実施形態における第２の正極活物質粒子Ｂは、本実施形態に係る正極活物質を含む正極材料をロールプレスにて線圧２００Ｎ／ｍｍで加圧したとき、正極材料の断面で観察される第２の正極活物質粒子Ｂのうち、断面長径が３μｍ以上であり、かつ、二次粒子内で確認される空隙長径（Ｌ）が０．３μｍ以上の空隙を有する二次粒子において、空隙の平均アスペクト比（Ｗ／Ｌ）が０．５以下である。なお、線圧とは、ロール幅方向の単位長さ当たりの成形圧力のことを意味する。 The second positive electrode active material particles B in the present embodiment are observed in the cross section of the positive electrode material when the positive electrode material containing the positive electrode active material according to the present embodiment is pressed with a roll press at a linear pressure of 200 N / mm. Among the second positive electrode active material particles B, in the secondary particles having voids having a cross-sectional major axis of 3 μm or more and a void major axis (L) confirmed in the secondary particles of 0.3 μm or more, the voids The average aspect ratio (W / L) is 0.5 or less. The linear pressure means the forming pressure per unit length in the roll width direction.
なお、画像解析の対象とする断面は、クロスセクションポリッシャ加工などによって形成してもよい。空隙の平均アスペクト比（Ｗ／Ｌ）が上記範囲である場合、二次電池の正極において、第２の正極活物質粒子Ｂの内部の表面積が変わらず、その空洞が圧下により圧縮されるので、正極活物質全体の充填性が向上し、単位面積当たりの電池容量を向上させることができる。また、高い初期充放電容量を維持しつつ、正極抵抗を顕著に低減した二次電池を得ることができる。なお、第２の正極活物質粒子Ｂにおける空隙の平均アスペクト比（Ｗ／Ｌ）の下限は特に限定されないが、例えば、０．０５以上であり、０．１以上であってもよい。 The cross section to be analyzed may be formed by cross-section polisher processing or the like. When the average aspect ratio (W / L) of the void is in the above range, the surface area inside the second positive electrode active material particle B does not change in the positive electrode of the secondary battery, and the cavity is compressed by reduction. The filling property of the entire positive electrode active material is improved, and the battery capacity per unit area can be improved. Further, it is possible to obtain a secondary battery in which the positive electrode resistance is remarkably reduced while maintaining a high initial charge / discharge capacity. The lower limit of the average aspect ratio (W / L) of the voids in the second positive electrode active material particles B is not particularly limited, but may be, for example, 0.05 or more and 0.1 or more.
なお、二次粒子の断面長径は、走査型電子顕微鏡観察上において測定される、二次粒子の外縁の点から他の外縁上の点の距離のうち、最大長となる長さを意味する。また、空隙長径（Ｌ）は、走査型電子顕微鏡観察上において測定される、二次粒子の空隙（中空）の外縁の点から他の外縁上の点の距離のうち、最大長となる長さを意味する。また、空隙短径（Ｗ）は、空隙長径（Ｌ）の方向と直交する方向における、二次粒子の空隙（中空）の外縁の点から他の外縁上の点のうち、最大長となる長さを意味する。図２は、圧下後の第２の正極活物質粒子Ｂの空隙長径（Ｌ）、及び、空隙短径（Ｗ）の測定部位の一例を模式的に示した図である。 The cross-sectional major axis of the secondary particle means the length that is the maximum length among the distances from the point on the outer edge of the secondary particle to the point on the other outer edge, which is measured by observing with a scanning electron microscope. The void major axis (L) is the maximum length of the distance from the outer edge point of the void (hollow) of the secondary particle to the point on the other outer edge, which is measured by scanning electron microscope observation. Means. Further, the void minor axis (W) is the length that is the maximum length from the point on the outer edge of the void (hollow) of the secondary particles to the point on the other outer edge in the direction orthogonal to the direction of the void major axis (L). Means FIG. 2 is a diagram schematically showing an example of a measurement site of the void major axis (L) and the void minor axis (W) of the second positive electrode active material particle B after reduction.
なお、正極を作製する際に用いる圧下する力（圧下力）は、作製する二次電池に応じて、適宜調整できる。後述する本実施形態の正極においては、圧下率が５％以上となる荷重で加圧することが好ましい。これにより、圧下後に観察される空隙の平均アスペクト比を容易に０．５以下にすることができる。ここで、圧下率とは、圧下前の正極活物質を含む正極材料を塗布して得られる膜（塗布膜）の厚みに対する加圧後の膜（正極）の厚みの減少量を意味する。例えば、正極活物質を含む正極合材ペーストを集電体上に塗布し、乾燥して塗布膜（乾燥膜）を得た後、この塗布膜を加圧して正極（正極膜）を得る工程において、集電体上に塗布された塗布膜の厚みの加圧による減少量の、加圧前の塗布膜の厚みに対する割合のことを意味する。 The reducing force (reducing force) used when manufacturing the positive electrode can be appropriately adjusted according to the secondary battery to be manufactured. In the positive electrode of the present embodiment described later, it is preferable to pressurize with a load such that the reduction rate is 5% or more. As a result, the average aspect ratio of the voids observed after reduction can be easily reduced to 0.5 or less. Here, the reduction rate means the amount of decrease in the thickness of the film (positive electrode) after pressurization with respect to the thickness of the film (coating film) obtained by applying the positive electrode material containing the positive electrode active material before reduction. For example, in a step of applying a positive electrode mixture paste containing a positive electrode active material on a current collector and drying it to obtain a coating film (dry film), and then pressurizing the coating film to obtain a positive electrode (positive electrode film). It means the ratio of the amount of decrease in the thickness of the coating film applied on the current collector due to pressurization to the thickness of the coating film before pressurization.
なお、後述する実施例のように、評価用の二次電池として２０３２型コイン型電池（図４参照）を用いる場合、塗布膜は、例えば、正極材料として、正極活物質とアセチレンブラックなどの導電材とＰＶＤＦ（ポリフッ化ビニリデン）などの結着剤とを質量比８５：１０：５の割合で含んでもよい。また、塗布膜は、上記正極材料を溶剤に分散させて得られた正極合材ペーストを集電体上に塗布し、乾燥して得てもよい。加圧後の膜の厚みは、例えば、約１００μｍであってもよい。また、加圧を複数回行った場合には、通算の圧下率とする。 When a 2032 type coin type battery (see FIG. 4) is used as the secondary battery for evaluation as in the examples described later, the coating film is, for example, a positive electrode active material and conductivity such as acetylene black as the positive electrode material. The material and a binder such as PVDF (polyvinylidene fluoride) may be contained in a mass ratio of 85:10: 5. Further, the coating film may be obtained by applying a positive electrode mixture paste obtained by dispersing the positive electrode material in a solvent onto a current collector and drying it. The thickness of the film after pressurization may be, for example, about 100 μm. In addition, when pressurization is performed a plurality of times, the total reduction rate is used.
また、二次電池を作製する際に用いる圧下力に応じて、第２の正極活物質粒子Ｂを上述した特性を有する範囲内において適宜選択することができる。なお、第２の正極活物質粒子Ｂが、特許文献３に記載されるような多層構造を有する場合、空隙の平均アスペクト比は、最外殻直下にある中空部に対する、空隙短径（Ｗ）、空隙長径（Ｌ）を用いて算出される。 Further, the second positive electrode active material particles B can be appropriately selected within the range having the above-mentioned characteristics according to the reducing force used when manufacturing the secondary battery. When the second positive electrode active material particle B has a multilayer structure as described in Patent Document 3, the average aspect ratio of the voids is the minority of the voids (W) with respect to the hollow portion directly under the outermost shell. , Calculated using the void major axis (L).
なお、圧下前の第２の正極活物質粒子Ｂの空隙の平均アスペクト比（Ｗ／Ｌ）は、例えば、０．５超であり、０．７以上であってもよい。圧下前の空隙の平均アスペクト比は、圧下前の第２の正極活物質粒子Ｂの断面を用いる以外は、上記の空隙の平均アスペクト比の測定と同様の方法で測定することができる。 The average aspect ratio (W / L) of the voids of the second positive electrode active material particles B before reduction is, for example, more than 0.5 and may be 0.7 or more. The average aspect ratio of the voids before reduction can be measured by the same method as the above-mentioned measurement of the average aspect ratio of the voids, except that the cross section of the second positive electrode active material particle B before reduction is used.
［正極活物質］
本実施系に係る正極活物質は、上記の第１の正極活物質粒子Ａと第２の正極活物質粒子Ｂとを含む。正極活物質中、上記の第１の正極活物質粒子Ａと第２の正極活物質粒子Ｂとは、粉体としての性状を維持しつつ、各粒子が偏在しないように所定の割合で含まれることが好ましい。
[Positive electrode active material]
The positive electrode active material according to the present embodiment includes the above-mentioned first positive electrode active material particles A and the second positive electrode active material particles B. Among the positive electrode active materials, the first positive electrode active material particles A and the second positive electrode active material particles B are contained in a predetermined ratio so that the particles are not unevenly distributed while maintaining the properties as powder. Is preferable.
本実施系に係る正極活物質は、第１の正極活物質粒子Ａの質量（ＷＡ）と第２の正極活物質粒子Ｂの質量（ＷＢ）との比率が以下の関係式（１）を満たし、以下の関係式（２）を満たすことがより好ましく、下記の関係式（３）を満たすことがより好ましい。
０．００１≦ＷＢ／（ＷＡ＋ＷＢ）≦０．５ ・・・（１）
０．１≦ＷＢ／（ＷＡ＋ＷＢ）≦０．３５・・・（２）
０．１≦ＷＢ／（ＷＡ＋ＷＢ）≦０．２５・・・（３）
Positive electrode active material according to the present exemplary system, the first positive electrode active material particle mass A (W A) and the second cathode active mass of material particles B (W B) and the ratio of the following relational expression (1) It is more preferable to satisfy the following relational expression (2), and it is more preferable to satisfy the following relational expression (3).
0.001 ≦ W B / (W A + W B) ≦ 0.5 ··· (1)
0.1 ≦ W B / (W A + W B) ≦ 0.35 ··· (2)
0.1 ≦ W B / (W A + W B) ≦ 0.25 ··· (3)
また、本実施系に係る正極活物質の平均粒径（Ｄ５０）は、５μｍ以上２７μｍ以下の範囲であることが好ましい。正極活物質（Ｄ５０）の平均粒径は、第１の正極活物質粒子Ａと第１の正極活物質粒子Ａとの混合割合を上記範囲で適宜調整することにより、上記範囲とすることができる。 The average particle size (D50) of the positive electrode active material according to this embodiment is preferably in the range of 5 μm or more and 27 μm or less. The average particle size of the positive electrode active material (D50) can be set in the above range by appropriately adjusting the mixing ratio of the first positive electrode active material particles A and the first positive electrode active material particles A in the above range. ..
また、本実施系に係る正極活物質のタップ密度は、１．９ｇ／ｃｍ３以上３ｇ／ｃｍ３以下の範囲であることが好ましい。正極活物質のタップ密度が上記範囲である場合、二次電池において高容量と、高出力とを共に実現することができる。なお、本実施形態に係る正極活物質は、第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂ以外の化合物を含んでもよい。 The tap density of the positive electrode active material according to this embodiment is preferably in the range of 1.9 g / cm 3 or more and 3 g / cm 3 or less. When the tap density of the positive electrode active material is within the above range, both high capacity and high output can be realized in the secondary battery. The positive electrode active material according to the present embodiment may contain compounds other than the first positive electrode active material particles A and the second positive electrode active material particles B.
（２）リチウムイオン二次電池用正極活物質の製造方法
本実施系に係る正極活物質は、図３に示すように、第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂとを混合すること（混合工程：ステップＳ１０）、を備える方法により製造することができる。以下、混合工程（ステップＳ１０）について説明する。
(2) Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery As shown in FIG. 3, the positive electrode active material according to the present implementation system is a first positive electrode active material particle A and a second positive electrode active material particle B. And can be produced by a method comprising mixing (mixing step: step S10). Hereinafter, the mixing step (step S10) will be described.
［混合工程（ステップＳ１０）］
第１の正極活物質粒子Ａと第２の正極活物質粒子Ｂとの混合は、各粒子が粉体としての性状を維持しつつ、各粒子が偏在しないように混合することが好ましい。
[Mixing step (step S10)]
It is preferable that the first positive electrode active material particles A and the second positive electrode active material particles B are mixed so that the particles are not unevenly distributed while maintaining the properties of the powder as a powder.
第１の正極活物質粒子Ａと第２の正極活物質粒子Ｂの質量混合比（ＷＡ：ＷＢ）は、例えば、５０：５０〜９９．９：０．１であり、好ましくは７５：２５〜９０：１０である。質量混合比（ＷＡ：ＷＢ）が上記範囲である場合、大きな平均粒径を有する第１の正極活物質粒子Ａの粒子間に、比較的小さな平均粒径を有する第２の正極活物質粒子Ｂを十分な量で配置することができ、正極活物質の充填性をさらに向上させることができる。 The first positive electrode active material particles A and the mass mixing ratio of the second positive electrode active material particles B (W A: W B) are, for example, 50: 99.9: 0.1, preferably 75: It is 25 to 90:10. Mass mixing ratio (W A: W B) is between the particles of the first cathode active material particles A having a case within the above range, a larger average particle diameter, the second cathode active material having a relatively small average particle size The particles B can be arranged in a sufficient amount, and the filling property of the positive electrode active material can be further improved.
これらの粒子の混合には、一般的な混合機を使用することができ、例えば、シェーカーミキサー、レーディゲミキサー、ジュリアミキサー、Ｖブレンダーなどを用いることができる。混合は、混合前の各粒子の性状が破壊されない程度で、各粒子が十分に混合されればよい。なお、混合工程（Ｓ１０）では、第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂのみを混合してもよく、第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂ以外の他の粒子を混合してもよい。 A general mixer can be used for mixing these particles, and for example, a shaker mixer, a Ladyge mixer, a Julia mixer, a V blender, and the like can be used. For mixing, it is sufficient that each particle is sufficiently mixed so that the properties of each particle before mixing are not destroyed. In the mixing step (S10), only the first positive electrode active material particles A and the second positive electrode active material particles B may be mixed, and the first positive electrode active material particles A and the second positive electrode active material particles A may be mixed. Particles other than the positive electrode active material particles B may be mixed.
以下、混合に用いる第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂの製造方法の一例について説明する。 Hereinafter, an example of a method for producing the first positive electrode active material particles A and the second positive electrode active material particles B used for mixing will be described.
［第１の正極活物質粒子Ａの製造方法］
第１の正極活物質粒子Ａは、上記の特性を満たす粒子が得られれば、特に限定されず、公知の方法で製造することができる。第１の正極活物質粒子Ａは、例えば、ニッケル複合水酸化物、及び、ニッケル複合酸化物の少なくとも一方と、リチウム化合物と、を混合した後、焼成して得ることができる。以下、第１の正極活物質粒子Ａの製造方法の一例について説明する。
[Method for Producing First Positive Electrode Active Material Particles A]
The first positive electrode active material particles A are not particularly limited as long as particles satisfying the above characteristics can be obtained, and can be produced by a known method. The first positive electrode active material particles A can be obtained, for example, by mixing at least one of a nickel composite hydroxide and a nickel composite oxide with a lithium compound and then firing the particles. Hereinafter, an example of a method for producing the first positive electrode active material particles A will be described.
（晶析工程）
ニッケル複合水酸化物の製造方法としては、特に限定されず、公知の方法を用い得ることができるが、所望の組成と粒子構造を有し、かつ、所望の粒径と粒度分布のものを使用するという観点から、晶析法を用いることが好ましく、連続晶析法を用いることがより好ましい。晶析法により得られたニッケル複合水酸化物は、一次粒子が凝集した二次粒子によって構成され、粒子全体で組成を容易に均一とすることができる。
(Crystalization process)
The method for producing the nickel composite hydroxide is not particularly limited, and a known method can be used, but a method having a desired composition and particle structure and a desired particle size and particle size distribution is used. From the viewpoint of this, it is preferable to use the crystallization method, and it is more preferable to use the continuous crystallization method. The nickel composite hydroxide obtained by the crystallization method is composed of secondary particles in which primary particles are aggregated, and the composition can be easily made uniform in the entire particles.
ここで、連続晶析法とは、金属塩を含む混合水溶液を連続的に供給しながら中和剤を供給して、ｐＨを制御しつつ、ニッケル複合水酸化物の粒子を生成し、ニッケル複合水酸化物の粒子をオーバーフローにより回収する晶析法である。連続晶析法は、粒度分布の広い粒子が容易に得られ、充填性の高い二次粒子が得られやすい。また、連続晶析法は、大量生産に向いており、工業的にも有利な製造方法となる。 Here, in the continuous crystallization method, a neutralizing agent is supplied while continuously supplying a mixed aqueous solution containing a metal salt to generate nickel composite hydroxide particles while controlling the pH, and the nickel composite is produced. This is a crystallization method in which hydroxide particles are recovered by overflow. In the continuous crystallization method, particles having a wide particle size distribution can be easily obtained, and secondary particles having a high packing property can be easily obtained. Further, the continuous crystallization method is suitable for mass production and is an industrially advantageous production method.
ニッケル複合水酸化物の製造方法として連続晶析法を用いる場合、晶析工程において、晶析反応を連続的に継続させることにより、得られるニッケル複合水酸化物の二次粒子の平均粒径を所望の粒径（例えば８．０μｍ〜３０．０μｍ）まで好適に成長させることができる。なお、ニッケル複合水酸化物は、二次粒子以外に、単独の一次粒子を少量含んでもよい。以下、晶析工程について説明する。 When the continuous crystallization method is used as the method for producing the nickel composite hydroxide, the average particle size of the secondary particles of the nickel composite hydroxide obtained by continuously continuing the crystallization reaction in the crystallization step can be obtained. It can be suitably grown to a desired particle size (for example, 8.0 μm to 30.0 μm). The nickel composite hydroxide may contain a small amount of single primary particles in addition to the secondary particles. Hereinafter, the crystallization step will be described.
晶析工程では、まず、水酸化ナトリウム水溶液などのアルカリ水溶液、アンモニウムイオン供給体を含むアンモニア水溶液、および水を反応槽に供給し、混合して水溶液を形成する。そして、この水溶液（以下、「反応前水溶液」という）について、ｐＨが液温２５℃基準で１０．０〜１３．０の範囲となるように、且つアンモニウムイオンの濃度が５ｇ／Ｌ〜２０ｇ／Ｌとなるように調節する。ここで、ｐＨとアンモニウムイオン濃度の調節は、ｐＨを調節する場合には、アルカリ水溶液の供給量を調整し、アンモニウムイオン濃度を調節する場合には、アンモニア水溶液の供給量を調整することにより行う。また、温度についても、４０℃〜７０℃となるように調節する。 In the crystallization step, first, an alkaline aqueous solution such as an aqueous sodium hydroxide solution, an aqueous ammonia solution containing an ammonium ion feeder, and water are supplied to the reaction vessel and mixed to form an aqueous solution. Then, with respect to this aqueous solution (hereinafter referred to as "pre-reaction aqueous solution"), the pH is in the range of 10.0 to 13.0 based on the liquid temperature of 25 ° C., and the concentration of ammonium ions is 5 g / L to 20 g /. Adjust so that it becomes L. Here, the pH and the ammonium ion concentration are adjusted by adjusting the supply amount of the alkaline aqueous solution when adjusting the pH, and by adjusting the supply amount of the ammonia aqueous solution when adjusting the ammonium ion concentration. .. The temperature is also adjusted to be 40 ° C to 70 ° C.
次に、調整された反応前水溶液に対して、ニッケル複合水酸化物の粒子における金属の原子比に対応する金属の原子比となるように、金属化合物を所定の割合で水に溶解させた原料水溶液を供給する。これにより、反応槽内には、反応前水溶液と原料水溶液とが混合した、反応水溶液が形成される。この場合、反応水溶液の温度は、４０〜７０℃を保持することが好ましい。４０℃未満では、体積平均粒径が所望の範囲から外れやすく、その制御が困難となる傾向があり、７０℃を超えると、アンモニアの揮発が多く、ニッケルアンミン錯体濃度が安定しない。 Next, the raw material in which the metal compound was dissolved in water at a predetermined ratio so as to have the atomic ratio of the metal corresponding to the atomic ratio of the metal in the particles of the nickel composite hydroxide with respect to the adjusted pre-reaction aqueous solution. Supply an aqueous solution. As a result, a reaction aqueous solution in which the pre-reaction aqueous solution and the raw material aqueous solution are mixed is formed in the reaction vessel. In this case, the temperature of the reaction aqueous solution is preferably maintained at 40 to 70 ° C. Below 40 ° C, the volume average particle size tends to deviate from the desired range, and its control tends to be difficult. Above 70 ° C, ammonia volatilizes a lot and the nickel ammine complex concentration is not stable.
ここで、アンモニウムイオン供給体については、特に限定されるものではなく、例えば、アンモニア、硫酸アンモニウム、塩化アンモニウム、炭酸アンモニウム、フッ化アンモニウムなどを使用することができる。また、ｐＨを調整するアルカリ水溶液についても、特に限定されるものではなく、たとえば、水酸化ナトリウム、水酸化カリウムなどのアルカリ金属水酸化物水溶液を用いることができる。このようなアルカリ金属水酸化物の場合、直接、反応水溶液中に供給してもよいが、反応槽内における反応水溶液のｐＨ値制御の容易さから、水溶液として反応槽内の反応水溶液に添加することが好ましい。 Here, the ammonium ion feeder is not particularly limited, and for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like can be used. Further, the alkaline aqueous solution for adjusting the pH is not particularly limited, and for example, an alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. In the case of such an alkali metal hydroxide, it may be directly supplied into the reaction aqueous solution, but it is added as an aqueous solution to the reaction aqueous solution in the reaction tank because of the ease of controlling the pH value of the reaction aqueous solution in the reaction tank. Is preferable.
また、ニッケル複合水酸化物に元素Ｍを含ませる場合、例えば、上記の晶析工程を行うときに、元素ＭをＮｉ、Ｃｏ、Ｍｎと共に晶析させ、ニッケル複合水酸化物中に均一に分散させてもよいし、元素Ｍを含まないニッケル複合水酸化物を晶析法により形成した後、元素Ｍを含む化合物を、得られたニッケル複合酸化物粒子の表面に被覆したり、リチウム化合物の添加と同時に添加して混合したりしてもよい。 When the nickel composite hydroxide contains the element M, for example, when the above crystallization step is performed, the element M is crystallized together with Ni, Co, and Mn and uniformly dispersed in the nickel composite hydroxide. Alternatively, the nickel composite hydroxide containing no element M may be formed by a crystallization method, and then a compound containing the element M may be coated on the surface of the obtained nickel composite oxide particles, or a lithium compound may be formed. It may be added and mixed at the same time as the addition.
（酸化焙焼）
さらに、得られたニッケル複合水酸化物を酸化焙焼してもよい。酸化焙焼により、ニッケル複合水酸化物の一部、又は、全部がニッケル複合酸化物に変換される。以下、酸化焙焼を行う場合の好ましい条件について記載する。
(Oxidation roasting)
Further, the obtained nickel composite hydroxide may be oxidatively roasted. Oxidative roasting converts some or all of the nickel composite hydroxide into nickel composite oxides. Hereinafter, preferable conditions for performing oxidative roasting will be described.
酸化焙焼の温度は、例えば、３５０℃以上８００℃以下、好ましくは６００℃以上８００℃以下である。酸化焙焼の温度が３５０℃未満である場合、得られる前駆体に多くの水分が残留する場合があり好ましくない。一方、酸化焙焼の温度が８００℃超の場合、前駆体中の水分は除去されるが、コスト、処理時間等の観点から、工業的に適当でないだけでなく、ニッケル複合酸化物自身の結晶成長が進み、リチウム化合物との反応性が低下してしまうことがあり、この場合も好ましくない。 The temperature of oxidative roasting is, for example, 350 ° C. or higher and 800 ° C. or lower, preferably 600 ° C. or higher and 800 ° C. or lower. When the temperature of oxidative roasting is less than 350 ° C., a large amount of water may remain in the obtained precursor, which is not preferable. On the other hand, when the temperature of oxidative roasting exceeds 800 ° C., the water content in the precursor is removed, but it is not industrially suitable from the viewpoint of cost, treatment time, etc., and the nickel composite oxide itself crystallizes. Growth may proceed and the reactivity with the lithium compound may decrease, which is also not preferable.
酸化焙焼の時間は、２時間以上８時間以下で行うことが好ましく、６時間以上８時間以下で行ってもよい。 The oxidative roasting time is preferably 2 hours or more and 8 hours or less, and may be 6 hours or more and 8 hours or less.
（混合工程）
次いで、得られたニッケル複合水酸化物、及び、ニッケル複合酸化物の少なくとも一方（以下、これらをまとめて「ニッケル化合物」ともいう）と、リチウム化合物と混合して、リチウム混合物を形成する。リチウム化合物は、特に限定されることはなく、たとえば、水酸化リチウム、硝酸リチウム、炭酸リチウム、又は、これらの混合物を用いることができる。リチウム化合物は、取り扱いの容易さ、品質の安定性を考慮すると、水酸化リチウム、又は、炭酸リチウムを用いることがより好ましい。
(Mixing process)
Next, the obtained nickel composite hydroxide and at least one of the nickel composite oxides (hereinafter, collectively referred to as "nickel compound") are mixed with the lithium compound to form a lithium mixture. The lithium compound is not particularly limited, and for example, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof can be used. As the lithium compound, it is more preferable to use lithium hydroxide or lithium carbonate in consideration of ease of handling and stability of quality.
ニッケル化合物とリチウム化合物とは、リチウム混合物中のリチウムと、リチウム、酸素、及び、水素以外の上記の元素（Ｍｅ）の物質量比（Ｌｉ／Ｍｅ）が０．９５以上１．２０未満であることが好ましい。すなわち、後述する焼成工程の前後でＬｉ／Ｍｅは変化しないので、この混合工程で混合するＬｉ／Ｍｅが正極活物質におけるＬｉ／Ｍｅとなるため、リチウム混合物におけるＬｉ／Ｍｅが、得ようとする正極活物質におけるＬｉ／Ｍｅと同じになるように混合される。 The nickel compound and the lithium compound have a substance amount ratio (Li / Me) of lithium in the lithium mixture and the above-mentioned element (Me) other than lithium, oxygen, and hydrogen of 0.95 or more and less than 1.20. Is preferable. That is, since Li / Me does not change before and after the firing step described later, the Li / Me mixed in this mixing step becomes Li / Me in the positive electrode active material, so that Li / Me in the lithium mixture is to be obtained. It is mixed so as to be the same as Li / Me in the positive electrode active material.
（焼成工程）
次いで、リチウム混合物を焼成して、第１の正極活物質粒子Ａを得る。焼成は、例えば、酸化性雰囲気中で、６５０℃以上１１００℃以下で行い、６５０℃以上９５０℃以下で行ってもよい。焼成時間は、特に限定されないが、３時間以上４８時間以下であってもよく、２４時間以下であってもよい。なお、焼成温度、焼成雰囲気、焼成時間は、用いたニッケル化合物の組成や物性、リチウム化合物の種類等により適宜調整することができる。
(Baking process)
The lithium mixture is then calcined to give the first positive electrode active material particles A. The firing may be carried out, for example, in an oxidizing atmosphere at 650 ° C. or higher and 1100 ° C. or lower, and at 650 ° C. or higher and 950 ° C. or lower. The firing time is not particularly limited, but may be 3 hours or more and 48 hours or less, or 24 hours or less. The firing temperature, firing atmosphere, and firing time can be appropriately adjusted depending on the composition and physical properties of the nickel compound used, the type of lithium compound, and the like.
［第２の正極活物質粒子Ｂの製造方法］
第２の正極活物質粒子Ｂは、上記の特性を満たす粒子が得られれば、特に限定されず、公知の方法で製造することができる。第２の正極活物質粒子Ｂは、例えば、ニッケル複合水酸化物、及び、ニッケル複合酸化物の少なくとも一方と、リチウム化合物と、を混合した後、焼成して得ることができる。以下、第２の正極活物質粒子Ｂの製造方法の一例について説明する。
[Method for Producing Second Positive Electrode Active Material Particles B]
The second positive electrode active material particle B is not particularly limited as long as particles satisfying the above characteristics can be obtained, and can be produced by a known method. The second positive electrode active material particles B can be obtained, for example, by mixing at least one of a nickel composite hydroxide and a nickel composite oxide with a lithium compound and then firing the particles. Hereinafter, an example of a method for producing the second positive electrode active material particles B will be described.
（晶析工程）
ニッケル複合水酸化物の製造方法としては、特に限定されず、公知の方法を用いることができるが、所望の組成と粒子構造を有し、かつ、所望の粒径と粒度分布のものを使用するという観点から、例えば、特許文献１〜３に開示される晶析工程を採用することができる。
(Crystalization process)
The method for producing the nickel composite hydroxide is not particularly limited, and a known method can be used, but a method having a desired composition and particle structure and a desired particle size and particle size distribution is used. From this point of view, for example, the crystallization step disclosed in Patent Documents 1 to 3 can be adopted.
これらの晶析工程では、連続晶析法のように、核生成反応と粒子成長反応とが同じ槽内で同じ時期に進行するのではなく、主として低密度部（核）を形成する、核生成反応（核生成工程）が生じる時期と、主として高密度部を形成する、粒子成長反応（粒子成長工程）が生じる時期とが異なる時期となるように、それぞれの工程が明確に分離されている。 In these crystallization steps, the nucleation reaction and the particle growth reaction do not proceed at the same time in the same tank as in the continuous crystallization method, but mainly form a low density part (nucleus). Each step is clearly separated so that the time when the reaction (nucleation step) occurs and the time when the particle growth reaction (particle growth step), which mainly forms a high-density portion, occur are different.
核生成工程と粒子成長工程との分離をより確実に行うことにより、各工程における反応水溶液の状態を、各工程に最適な条件とすることができ、粒子成長工程で形成されるニッケル複合水酸化物を、より粒度分布の範囲が狭く、かつ、均質なものとすることができる。 By more reliably separating the nucleation step and the particle growth step, the state of the reaction aqueous solution in each step can be set to the optimum conditions for each step, and the nickel composite hydroxide formed in the particle growth step can be set. The material can be made more uniform with a narrower particle size distribution range.
＜核生成工程＞
核生成工程では、まず、水酸化ナトリウム水溶液などのアルカリ水溶液、アンモニウムイオン供給体を含むアンモニア水溶液、および水を反応槽に供給、混合して水溶液を形成する。そして、この水溶液（以下、「反応前水溶液」という）について、ｐＨが液温２５℃基準で１２．０〜１４．０の範囲となるように、そして、アンモニウムイオンの濃度が３ｇ／Ｌ〜２５ｇ／Ｌとなるように調節する。ここで、ｐＨとアンモニウムイオン濃度の調節は、ｐＨを調節する場合には、アルカリ水溶液の供給量を調整し、アンモニウムイオン濃度を調節する場合には、アンモニア水溶液の供給量を調整することにより行う。また、温度についても、２０℃〜６０℃となるように調節する。
<Nucleation process>
In the nuclear production step, first, an alkaline aqueous solution such as an aqueous sodium hydroxide solution, an aqueous ammonia solution containing an ammonium ion feeder, and water are supplied to the reaction vessel and mixed to form an aqueous solution. Then, for this aqueous solution (hereinafter referred to as "pre-reaction aqueous solution"), the pH should be in the range of 12.0 to 14.0 based on the liquid temperature of 25 ° C., and the concentration of ammonium ions should be 3 g / L to 25 g. Adjust to / L. Here, the pH and the ammonium ion concentration are adjusted by adjusting the supply amount of the alkaline aqueous solution when adjusting the pH, and by adjusting the supply amount of the ammonia aqueous solution when adjusting the ammonium ion concentration. .. The temperature is also adjusted to be 20 ° C to 60 ° C.
次に、調整された反応前水溶液に対して、ニッケルコバルトマンガン複合水酸化物の粒子における金属の原子比に対応する金属の原子比となるように、金属化合物を所定の割合で水に溶解させた原料水溶液を供給する。これにより、反応槽内には、反応前水溶液と原料水溶液とが混合した、反応水溶液である核生成用水溶液が形成され、この核生成用水溶液中において複合水酸化物の微細な核が生成されることになる。そして、核生成用水溶液の液温２５℃におけるｐＨを、１２．０〜１４．０の範囲に制御する。これにより、核の成長を抑制してほぼ核生成のみを起こすことができ、形成される核が均質かつ粒度分布の範囲が狭いものとすることができる。 Next, the metal compound is dissolved in water at a predetermined ratio so that the atomic ratio of the metal corresponds to the atomic ratio of the metal in the particles of the nickel-cobalt-manganese composite hydroxide with respect to the adjusted pre-reaction aqueous solution. Supply the raw material aqueous solution. As a result, a nucleation aqueous solution, which is a reaction aqueous solution, is formed in the reaction vessel by mixing the pre-reaction aqueous solution and the raw material aqueous solution, and fine nuclei of the composite hydroxide are generated in the nucleation aqueous solution. Will be. Then, the pH of the nucleation aqueous solution at a liquid temperature of 25 ° C. is controlled in the range of 12.0 to 14.0. As a result, the growth of nuclei can be suppressed and almost only nucleation can occur, and the nuclei formed can be made homogeneous and the range of particle size distribution can be narrowed.
ここで、アンモニウムイオン供給体については、特に限定されるものではなく、例えば、アンモニア、硫酸アンモニウム、塩化アンモニウム、炭酸アンモニウム、フッ化アンモニウムなどを使用することができる。また、反応水溶液中のｐＨを調整するアルカリ水溶液についても、特に限定されるものではなく、たとえば、水酸化ナトリウム、水酸化カリウムなどのアルカリ金属水酸化物水溶液を用いることができる。このようなアルカリ金属水酸化物の場合、直接、反応水溶液中に供給してもよいが、反応槽内における反応水溶液のｐＨ値制御の容易さから、水溶液として反応槽内の反応水溶液に添加することが好ましい。 Here, the ammonium ion feeder is not particularly limited, and for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like can be used. Further, the alkaline aqueous solution for adjusting the pH in the reaction aqueous solution is not particularly limited, and for example, an alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. In the case of such an alkali metal hydroxide, it may be directly supplied into the reaction aqueous solution, but it is added as an aqueous solution to the reaction aqueous solution in the reaction tank because of the ease of controlling the pH value of the reaction aqueous solution in the reaction tank. Is preferable.
核生成工程における雰囲気は、反応槽内の空間の酸素濃度が１容量％を超える酸化性雰囲気とする必要がある。酸素濃度が１０容量％を超える酸化性雰囲気が好ましく、制御が容易な大気雰囲気（酸素濃度：２１容量％）とすることが特に好ましい。酸素濃度が１容量％を超える雰囲気とすることで、平均粒径が０．０１μｍ〜０．３μｍの範囲内にある微細一次粒子を好適に形成することができる。酸素濃度が１容量％以下では、中心部の一次粒子の平均粒径が０．３μｍを超えてしまう恐れがある。微細一次粒子の平均粒径が０．３μｍを超えると、焼成時における収縮が低温域で進行せず、中心部および高密度部との収縮差が少なり、得られる正極活物質において、十分な大きさの空間部を形成できない場合があり、好ましくない。酸素濃度の上限は、特に限定されるものではないが、３０容量％を超えると、一次粒子の平均粒径が０．０１μｍ未満となり、十分な大きさの低密度部が形成されない恐れがあるため、この場合も好ましくない。 The atmosphere in the nucleation step needs to be an oxidizing atmosphere in which the oxygen concentration in the space in the reaction vessel exceeds 1% by volume. An oxidizing atmosphere having an oxygen concentration of more than 10% by volume is preferable, and an air atmosphere (oxygen concentration: 21% by volume) that is easy to control is particularly preferable. By setting the atmosphere in which the oxygen concentration exceeds 1% by volume, fine primary particles having an average particle size in the range of 0.01 μm to 0.3 μm can be suitably formed. When the oxygen concentration is 1% by volume or less, the average particle size of the primary particles in the central portion may exceed 0.3 μm. When the average particle size of the fine primary particles exceeds 0.3 μm, the shrinkage during firing does not proceed in the low temperature region, and the shrinkage difference between the central portion and the high density portion becomes small, which is sufficient for the obtained positive electrode active material. It may not be possible to form a space portion of a size, which is not preferable. The upper limit of the oxygen concentration is not particularly limited, but if it exceeds 30% by volume, the average particle size of the primary particles becomes less than 0.01 μm, and a low density portion having a sufficient size may not be formed. , This case is also not preferable.
雰囲気中の酸素濃度は、例えば、窒素などの不活性ガスを用いて調整することができる。雰囲気中の酸素濃度が所定の濃度となるように調節するための手段としては、例えば、当該雰囲気中に常に雰囲気中に流通させる方法を挙げることができる。 The oxygen concentration in the atmosphere can be adjusted using, for example, an inert gas such as nitrogen. As a means for adjusting the oxygen concentration in the atmosphere to a predetermined concentration, for example, a method of constantly circulating in the atmosphere can be mentioned.
＜粒子成長工程＞
粒子成長工程では、核生成工程の終了後、前記核生成用水溶液のｐＨ値を、液温２５℃基準でｐＨ値が１０．５〜１２．０となるように調整して、粒子成長工程における反応水溶液である粒子成長用水溶液を得る。この際、アルカリ水溶液の供給のみを停止することでｐＨ値を調整することができるが、粒度分布の狭い複合水酸化物粒子を得る観点から、一旦、すべての水溶液の供給を停止した上で、ｐＨ値を調整することが好ましい。なお、ｐＨ値の調整は、核生成用水溶液に、原料となる金属化合物を構成する酸と同種の無機酸、たとえば、原料として硫酸塩を使用する場合には、硫酸を供給することで行うことができる。
<Particle growth process>
In the particle growth step, after the completion of the nucleation step, the pH value of the aqueous solution for nucleation is adjusted to be 10.5 to 12.0 based on the liquid temperature of 25 ° C., and the particle growth step is performed. An aqueous solution for particle growth, which is a reaction aqueous solution, is obtained. At this time, the pH value can be adjusted by stopping only the supply of the alkaline aqueous solution, but from the viewpoint of obtaining composite hydroxide particles having a narrow particle size distribution, once the supply of all the aqueous solutions is stopped, the pH value can be adjusted. It is preferable to adjust the pH value. The pH value is adjusted by supplying an aqueous solution for nucleation with an inorganic acid of the same type as the acid constituting the metal compound as a raw material, for example, when sulfate is used as a raw material, sulfuric acid is supplied. Can be done.
次に、この粒子成長用水溶液を撹拌しながら、混合水溶液の供給を再開する。この際、粒子成長用水溶液のｐＨ値は上述した範囲にあるため、新たな核はほとんど生成せず、核（粒子）成長が進行し、所定の粒径を有する複合水酸化物粒子が形成される。 Next, the supply of the mixed aqueous solution is restarted while stirring the particle growth aqueous solution. At this time, since the pH value of the aqueous solution for particle growth is in the above range, almost no new nuclei are generated, the nuclei (particles) grow, and composite hydroxide particles having a predetermined particle size are formed. NS.
そして、この粒子成長工程の途中で、反応雰囲気を、上記の酸化性雰囲気から、弱酸化性〜非酸化性の範囲の雰囲気、具体的には、反応槽内空間の酸素濃度が１容量％以下である雰囲気に切り替える。好ましくは、酸素濃度が０．５容量％以下、より好ましくは０．２容量％以下となるように制御する。反応槽内空間の酸素濃度を１容量％以下にして粒子成長させることで、粒子の不要な酸化を抑制し、一次粒子の成長を促して、平均粒径０．３μｍ〜３μｍの板状一次粒子で粒度が揃った、緻密で高密度の外殻部を有する二次粒子を得ることができる。 Then, in the middle of this particle growth step, the reaction atmosphere is changed from the above-mentioned oxidizing atmosphere to an atmosphere in the range of weakly oxidizing to non-oxidizing, specifically, the oxygen concentration in the reaction tank space is 1% by volume or less. Switch to an atmosphere that is. Preferably, the oxygen concentration is controlled to be 0.5% by volume or less, more preferably 0.2% by volume or less. By growing the particles by reducing the oxygen concentration in the reaction tank space to 1% by volume or less, unnecessary oxidation of the particles is suppressed, the growth of the primary particles is promoted, and the plate-shaped primary particles having an average particle size of 0.3 μm to 3 μm are promoted. It is possible to obtain secondary particles having a dense and high-density outer shell portion having a uniform particle size.
なお、この粒子成長工程においては、金属イオンは、核または複合水酸化物となって晶出するので、それぞれの反応水溶液中の金属成分に対する液体成分の割合が増加する。この場合、見かけ上、供給する混合水溶液の濃度が低下したようになり、特に粒子成長工程において、複合水酸化物が十分に成長しない可能性がある。したがって、反応水溶液中の液体成分の増加を抑制するため、核生成工程終了後から粒子成長工程の途中で、反応水溶液、特に粒子成長用水溶液中の液体成分の一部を反応槽外に排出することが好ましい。具体的には、粒子成長用水溶液に対する混合水溶液、アルカリ水溶液およびアンモニア水溶液の供給および攪拌を停止して、核や複合水酸化物を沈降させて、粒子成長用水溶液の上澄み液を排出する。これにより、粒子成長用水溶液における混合水溶液の相対的な濃度を高めることができる。 In this particle growth step, the metal ions crystallize as nuclei or composite hydroxides, so that the ratio of the liquid component to the metal component in each reaction aqueous solution increases. In this case, the concentration of the supplied mixed aqueous solution apparently decreases, and there is a possibility that the composite hydroxide does not grow sufficiently, especially in the particle growth step. Therefore, in order to suppress the increase of the liquid component in the reaction aqueous solution, a part of the liquid component in the reaction aqueous solution, particularly the particle growth aqueous solution, is discharged to the outside of the reaction vessel during the particle growth step after the nucleation step is completed. Is preferable. Specifically, the supply and stirring of the mixed aqueous solution, the alkaline aqueous solution and the ammonia aqueous solution with respect to the aqueous solution for particle growth are stopped, the nuclei and the composite hydroxide are precipitated, and the supernatant of the aqueous solution for particle growth is discharged. Thereby, the relative concentration of the mixed aqueous solution in the aqueous solution for particle growth can be increased.
上述のようにして得られるニッケル複合水酸化物の粒径は、粒子成長工程や核生成工程の時間、核生成用水溶液や粒子成長用水溶液のｐＨ値や、原料水溶液の供給量により制御することができる。例えば、核生成工程におけるｐＨ値を高い値とすることにより、または、粒子生成工程の時間を長くすることにより、得られる複合水酸化物粒子の粒径を小さくすることができる。反対に、核生成工程における核の生成量を抑制することで、得られる複合水酸化物粒子の粒径を大きくすることができる The particle size of the nickel composite hydroxide obtained as described above is controlled by the time of the particle growth step and the nucleation step, the pH value of the nucleation aqueous solution and the particle growth aqueous solution, and the supply amount of the raw material aqueous solution. Can be done. For example, the particle size of the obtained composite hydroxide particles can be reduced by increasing the pH value in the nucleation step or by lengthening the time in the particle formation step. On the contrary, by suppressing the amount of nucleation produced in the nucleation step, the particle size of the obtained composite hydroxide particles can be increased.
また、ニッケル複合水酸化物に元素Ｍを含ませる場合、例えば、上記の核生成工程と粒子成長工程を行うときに、元素ＭをＮｉや、任意にＣｏ、Ｍｎと共に晶析させ、ニッケル複合水酸化物中に均一に分散させてもよいし、元素Ｍを含まないニッケル複合水酸化物を晶析法により形成した後、元素Ｍを含む化合物を、得られたニッケル複合酸化物粒子の表面に被覆したり、リチウム化合物の添加と同時に添加して混合したりしてもよい。 When the nickel composite hydroxide contains the element M, for example, when the above-mentioned nucleation formation step and particle growth step are performed, the element M is crystallized together with Ni and optionally Co and Mn to form nickel composite water. It may be uniformly dispersed in the oxide, or a nickel composite hydroxide containing no element M is formed by a crystallization method, and then a compound containing the element M is applied to the surface of the obtained nickel composite oxide particles. It may be coated or added and mixed at the same time as the addition of the lithium compound.
（酸化焙焼）
得られたニッケル複合水酸化物に対して酸化焙焼を行って、ニッケル複合酸化物にしてもよい。ここで、酸化焙焼の条件は、上記の第１の正極活物質粒子Ａの製造方法における酸化焙焼の条件と同様であるので、ここでの記載は省略する。
(Oxidation roasting)
The obtained nickel composite hydroxide may be oxidatively roasted to obtain a nickel composite oxide. Here, since the conditions for oxidative roasting are the same as the conditions for oxidative roasting in the above-mentioned method for producing the positive electrode active material particles A, the description here is omitted.
（混合工程、焼成工程）
次いで、得られたニッケル複合水酸化物、及び、ニッケル複合酸化物の少なくとも一方と、リチウム化合物と混合して、リチウム混合物を形成した後、リチウム混合物を焼成して、第２の正極活物質粒子Ｂを得る。ここで、混合工程、及び、焼成工程の条件は、上記の第１の正極活物質粒子Ａの製造方法における混合工程、及び、焼成工程の条件と同様であるので、ここでの記載は省略する。なお、焼成温度、焼成雰囲気、焼成時間は、用いたニッケル化合物の組成や物性、リチウム化合物の種類等により適宜調整することができる。
(Mixing process, firing process)
Next, the obtained nickel composite hydroxide and at least one of the nickel composite oxides are mixed with a lithium compound to form a lithium mixture, and then the lithium mixture is fired to produce a second positive electrode active material particle. Get B. Here, the conditions of the mixing step and the firing step are the same as the conditions of the mixing step and the firing step in the above-mentioned method for producing the positive electrode active material particles A, and thus the description thereof is omitted here. .. The firing temperature, firing atmosphere, and firing time can be appropriately adjusted depending on the composition and physical properties of the nickel compound used, the type of lithium compound, and the like.
（３）リチウムイオン二次電池用の正極
本実施形態に係る正極は、第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂとを含み、リチウムイオン二次電池に好適に用いることができる。
(3) Positive Electrode for Lithium Ion Secondary Battery The positive electrode according to the present embodiment contains a first positive electrode active material particle A and a second positive electrode active material particle B, and is suitably used for a lithium ion secondary battery. be able to.
第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂは、六方晶系の層状構造を有するリチウムニッケル複合酸化物であり、複数の一次粒子が凝集した二次粒子で構成され、金属元素として、リチウム（Ｌｉ）と、コバルト（Ｃｏ）と、ニッケル（Ｎｉ）と、任意に、マンガン（Ｍｎ）、及び、Ｗ、Ｚｒ、Ｖ、Ｍｇ、Ｍｏ、Ｎｂ、Ｔｉ、Ｓｉ、及び、Ａｌから選ばれる少なくとも１種の元素（Ｍ）と、を含有し、それぞれの上記金属元素の物質量比がＬｉ：Ｎｉ：Ｃｏ：Ｍｎ：Ｍ＝ｓ：（１−ｘ−ｙ−ｚ）：ｘ：ｙ：ｚ（ただし、０．０５≦ｘ≦０．５０、０≦ｙ≦０．５００．３５、０≦ｚ≦０．０５、０．９５＜ｓ＜１．２０）で表される。ここで、上記金属元素は半金属元素を含むものとする。なお、第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂのそれぞれの金属元素の物質量比は、上記範囲を満たしていれば、それぞれ同一であってもよく、異なっていてもよい。 The first positive electrode active material particle A and the second positive positive active material particle B are lithium nickel composite oxides having a hexagonal layered structure, and are composed of secondary particles in which a plurality of primary particles are aggregated. , As metal elements, lithium (Li), cobalt (Co), nickel (Ni), optionally manganese (Mn), and W, Zr, V, Mg, Mo, Nb, Ti, Si, and , Al contains at least one element (M), and the substance amount ratio of each of the above metal elements is Li: Ni: Co: Mn: M = s :( 1-x-y-z). : X: y: z (where 0.05 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.500.35, 0 ≦ z ≦ 0.05, 0.95 <s <1.20) NS. Here, it is assumed that the metal element includes a metalloid element. The material amount ratios of the metal elements of the first positive electrode active material particles A and the second positive electrode active material particles B may be the same or different as long as they satisfy the above range. You may.
第１の正極活物質粒子Ａは、中実構造を有し、タップ密度が２．１ｇ／ｃｍ３以上３．０ｇ／ｃｍ３以下であり、かつ、平均粒径（Ｄ５０）が８μｍ以上３０μｍ以下である。 The first positive electrode active material particle A has a solid structure, a tap density of 2.1 g / cm 3 or more and 3.0 g / cm 3 or less, and an average particle size (D50) of 8 μm or more and 30 μm or less. Is.
第２の正極活物質粒子Ｂは、中空構造を有し、タップ密度が１．８ｇ／ｃｍ３以下であり、平均粒径（Ｄ５０）が１μｍ以上８μｍ以下、かつ、第１の正極活物質粒子Ａの平均粒径（Ｄ５０）より小さい。 The second positive electrode active material particle B has a hollow structure, a tap density of 1.8 g / cm 3 or less, an average particle size (D50) of 1 μm or more and 8 μm or less, and a first positive electrode active material particle. It is smaller than the average particle size (D50) of A.
第１の正極活物質粒子Ａの質量（ＷＡ）と第２の正極活物質粒子Ｂの質量（ＷＢ）との比率が以下の関係式（１）を満たす。
０．００１≦ＷＢ／
（ＷＡ＋ＷＢ）≦０．５・・・（１）
Ratio of the first positive electrode active material particles A of the mass (W A) and the second positive electrode active material particles B mass (W B) satisfies the relation (1) below.
0.001 ≦ W B /
(W A + W B) ≦ 0.5 ··· (1)
また、第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂの好ましい組成や特性は、上記の正極活物質の項目で記載したものと同様である。 Further, the preferable compositions and characteristics of the first positive electrode active material particles A and the second positive electrode active material particles B are the same as those described in the above item of positive electrode active material.
また、正極断面で観察される第２の正極活物質粒子Ｂのうち、断面長径が３μｍ以上であり、かつ、二次粒子内で観察される空隙長径が０．３μｍ以上の空隙を有する二次粒子において、空隙長径（Ｌ）と空隙短径（Ｗ）との比である平均アスペクト比（Ｗ／Ｌ）（以下、「空隙の平均アスペクト比」とも呼ぶ。）が０．５以下である。 Further, among the second positive electrode active material particles B observed in the positive electrode cross section, the secondary has a void with a cross-sectional major axis of 3 μm or more and a void major axis observed in the secondary particle of 0.3 μm or more. In the particles, the average aspect ratio (W / L) (hereinafter, also referred to as “average aspect ratio of the voids”), which is the ratio of the major void diameter (L) to the minority void diameter (W), is 0.5 or less.
平均アスペクト比が上記範囲である場合、内部の表面積が変わらず、空洞が圧下により圧縮されるので、充填性が向上し、単位面積当たりの電池容量を向上させることができるため、高い電池容量を維持しつつ、正極抵抗を顕著に低減することができる。なお、平均アスペクト比（Ｗ／Ｌ）の下限は特に限定されないが、例えば、０．１以上であり、０．２以上であってもよい。 When the average aspect ratio is in the above range, the internal surface area does not change and the cavity is compressed by reduction, so that the filling property can be improved and the battery capacity per unit area can be improved, so that a high battery capacity can be obtained. The positive electrode resistance can be significantly reduced while maintaining the positive electrode resistance. The lower limit of the average aspect ratio (W / L) is not particularly limited, but may be, for example, 0.1 or more and 0.2 or more.
正極断面における第２の正極活物質粒子Ｂの空隙のアスペクト比は、正極作製時に加圧された面に垂直な断面のＳＥＭ写真を画像解析したとき、観察される二次粒子の断面長径が３μｍ以上であり、かつ、粒子内部の空隙長径が０．３μｍ以上の空隙を有する第２の正極活物質粒子Ｂ２０個以上における、縦断面の空隙長径（Ｌ）と空隙短径（Ｗ）を各々測定して求めた空隙アスペクト比（Ｗ／Ｌ）の個数平均を算出して得ることができる。なお、同一の粒子に測定対象の空隙が複数含まれる場合には、その粒子の中で最も大きな空隙を測定する。 The aspect ratio of the voids of the second positive electrode active material particles B in the positive electrode cross section is such that the cross-sectional major axis of the secondary particles observed when the SEM photograph of the cross section perpendicular to the pressurized surface at the time of producing the positive electrode is image-analyzed is 3 μm. The void major axis (L) and the void minor axis (W) in the vertical cross section of 20 or more second positive electrode active material particles B having voids of 0.3 μm or more inside the particles are measured. It can be obtained by calculating the number average of the void aspect ratios (W / L) obtained in the above steps. When the same particle contains a plurality of voids to be measured, the largest void among the particles is measured.
正極において、第２の正極活物質粒子Ｂの空隙の平均アスペクト比を０．５以下に調整するためには、例えば、第２の正極活物質粒子Ｂを含む正極材料を圧下率が５％以上となる荷重で加圧すればよい。例えば、ロールプレスを用いて、正極材料が塗布された面を加圧する場合には、２００Ｎ／ｍｍの線圧で加圧してもよく、それ以上の線圧で加圧してもよい。なお、線圧とは、ロール幅方向の単位長さ当たりの成形圧力のことを意味する。 In order to adjust the average aspect ratio of the voids of the second positive electrode active material particles B to 0.5 or less in the positive electrode, for example, the reduction rate of the positive electrode material containing the second positive electrode active material particles B is 5% or more. It suffices to pressurize with the load that becomes. For example, when the surface coated with the positive electrode material is pressed by using a roll press, the pressure may be applied with a linear pressure of 200 N / mm, or may be pressurized with a linear pressure higher than that. The linear pressure means the forming pressure per unit length in the roll width direction.
ここで、圧下率とは、圧下前の正極活物質を含む正極材料を塗布して得られる膜（塗布膜）の厚みに対する加圧後の膜（正極）の厚みの減少量を意味する。例えば、正極活物質を含む正極合材ペーストを集電体上に塗布し、乾燥して塗布膜（乾燥膜）を得た後、この塗布膜を加圧して正極（正極膜）を得る工程において、集電体上に塗布された塗布膜の厚みの加圧による減少量の、加圧前の塗布膜の厚みに対する割合のことを意味する。また、加圧を複数回行った場合には、通算の圧下率とする。これにより、正極における正極活物質の充填性を高めることができる。 Here, the reduction rate means the amount of decrease in the thickness of the film (positive electrode) after pressurization with respect to the thickness of the film (coating film) obtained by applying the positive electrode material containing the positive electrode active material before reduction. For example, in a step of applying a positive electrode mixture paste containing a positive electrode active material on a current collector and drying it to obtain a coating film (dry film), and then pressurizing the coating film to obtain a positive electrode (positive electrode film). It means the ratio of the amount of decrease in the thickness of the coating film applied on the current collector due to pressurization to the thickness of the coating film before pressurization. In addition, when pressurization is performed a plurality of times, the total reduction rate is used. Thereby, the filling property of the positive electrode active material in the positive electrode can be improved.
なお、二次粒子の断面長径は、走査型電子顕微鏡の断面観察上において測定される、二次粒子の外縁の点から他の外縁上の点の距離のうち、最大長となる長さを意味する。また、空隙長径（Ｌ）は、走査型電子顕微鏡の断面観察上において測定される、二次粒子の空隙（中空）の外縁の点から他の外縁上の点の距離のうち、最大長となる長さを意味する。また、空隙短径（Ｗ）は、空隙長径（Ｌ）の方向と直交する方向における、二次粒子の空隙（中空）の外縁の点から他の外縁上の点の距離のうち、最大長となる長さを意味する。 The cross-sectional major axis of the secondary particle means the length that is the maximum length among the distances from the point on the outer edge of the secondary particle to the point on the other outer edge, which is measured on the cross-sectional observation of the scanning electron microscope. do. Further, the void major axis (L) is the maximum length among the distances from the outer edge point of the void (hollow) of the secondary particles to the point on the other outer edge, which is measured on the cross-sectional observation of the scanning electron microscope. Means length. Further, the void minor axis (W) is defined as the maximum length of the distance from the point on the outer edge of the void (hollow) of the secondary particles to the point on the other outer edge in the direction orthogonal to the direction of the void major axis (L). Means the length.
正極の製造方法は、特に限定されないが、例えば、上記の第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂと、を含む正極活物質を用いて、以下のように製造される。 The method for producing the positive electrode is not particularly limited, but for example, it is produced as follows using the positive electrode active material containing the first positive electrode active material particles A and the second positive electrode active material particles B. NS.
正極は、例えば、正極活物質を含有する正極合材ペーストを集電体の表面に塗布し、乾燥した後、これを加圧して形成することができる。集電体は、例えば、アルミニウム箔製である。本実施形態においては、電極密度を高めるべくロールプレス等により加圧する。 The positive electrode can be formed, for example, by applying a positive electrode mixture paste containing a positive electrode active material to the surface of a current collector, drying it, and then pressurizing it. The current collector is made of, for example, aluminum foil. In this embodiment, pressure is applied by a roll press or the like in order to increase the electrode density.
そして、加圧された正極に対して、加圧された方向に平行な第２の正極活物質粒子ＢのＳＥＭ断面写真を画像解析したとき、観察される断面長径が３μｍ以上であり、かつ、粒子内部の空隙長径が０．３μｍ以上の空隙を有する第２の正極活物質粒子Ｂ２０個以上に対する、空隙の平均アスペクト比が０．５以下である。 Then, when the SEM cross-sectional photograph of the second positive electrode active material particle B parallel to the pressurized positive electrode is image-analyzed, the observed cross-sectional major axis is 3 μm or more and the cross-sectional major axis is 3 μm or more. The average aspect ratio of the voids is 0.5 or less with respect to 20 or more second positive electrode active material particles B having voids having a void major axis of 0.3 μm or more inside the particles.
このようにして得られた正極は、シート状（膜状）であり、シート状の正極（正極膜）を目的とする電池に応じて適当な大きさに裁断等し、電池の作製に供することができる。なお、正極の作製方法は、上記以外の方法を用いてもよい。 The positive electrode thus obtained is in the form of a sheet (film), and the sheet-like positive electrode (positive electrode film) is cut into an appropriate size according to the target battery and used for manufacturing the battery. Can be done. As a method for producing the positive electrode, a method other than the above may be used.
正極合材ペーストは、例えば、正極合材に、必要に応じて活性炭、及び／又は、溶剤を添加して、混練して形成される。正極合材は、例えば、粉末状の正極活物質と、導電材と、結着剤とを混合して形成される。 The positive electrode mixture paste is formed, for example, by adding activated carbon and / or a solvent to the positive electrode mixture, if necessary, and kneading the paste. The positive electrode mixture is formed by mixing, for example, a powdered positive electrode active material, a conductive material, and a binder.
正極合材に含まれる導電材は、電極に適当な導電性を与える。導電材としては、特に限定されず、例えば、黒鉛（天然黒鉛、人造黒鉛および膨張黒鉛など）や、アセチレンブラックやケッチェンブラックなどのカーボンブラック系材料を用いることができる。 The conductive material contained in the positive electrode mixture imparts appropriate conductivity to the electrode. The conductive material is not particularly limited, and for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) or a carbon black material such as acetylene black or ketjen black can be used.
正極合材に含まれる結着剤は、正極活物質を構成する粒子同士をつなぎ止めることができる。正極合材に含まれる結着剤としては、特に限定されないが、たとえば、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、フッ素ゴム、エチレンプロピレンジエンゴム、スチレンブタジエン、セルロース系樹脂、ポリアクリル酸などを用いることができる。なお、正極合材には、活性炭などを添加してもよく、活性炭などを添加することによって、正極の電気二重層容量を増加させることができる。 The binder contained in the positive electrode mixture can hold the particles constituting the positive electrode active material together. The binder contained in the positive electrode mixture is not particularly limited, and is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, and poly. Acrylic acid or the like can be used. Activated carbon or the like may be added to the positive electrode mixture, and the electric double layer capacity of the positive electrode can be increased by adding activated carbon or the like.
正極合材ペーストの製造に用いられる溶剤は、結着剤を溶解して、正極活物質、導電材および活性炭などを結着剤中に分散させる。また、溶剤は、正極合材ペーストの粘度を調整することができる。溶剤としては、特に限定されないが、たとえば、Ｎ−メチル−２−ピロリドンなどの有機溶剤を用いることができる。 The solvent used in the production of the positive electrode mixture paste dissolves the binder and disperses the positive electrode active material, the conductive material, activated carbon and the like in the binder. Further, the solvent can adjust the viscosity of the positive electrode mixture paste. The solvent is not particularly limited, but for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.
目的とする二次電池の性能に応じて、正極合材ペースト中のそれぞれの材料の混合比は、適宜、調整することができる。例えば、溶剤を除いた正極合材の固形分を１００質量部とした場合、正極活物質の含有量を６０質量部以上９５質量部以下、導電材の含有量を１質量部以上２０質量部以下とし、結着剤の含有量を１質量部以上２０質量部以下としてもよい。 The mixing ratio of each material in the positive electrode mixture paste can be appropriately adjusted according to the performance of the target secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass or more and 95 parts by mass or less, and the content of the conductive material is 1 part by mass or more and 20 parts by mass or less. The content of the binder may be 1 part by mass or more and 20 parts by mass or less.
（４）リチウムイオン二次電池
本実施形態に係るリチウムイオン二次電池（以下、「二次電池」ともいう。）は、上述した正極と、負極と、非水系電解質とを備える。二次電池は、例えば、正極、負極、及び非水系電解液を備える。また、二次電池は、例えば、正極、負極、及び固体電解質を備えてもよい。また、二次電池は、リチウムイオンの脱離及び挿入により、充放電を行う二次電池であればよく、例えば、非水系電解液二次電池であってもよく、全固体リチウム二次電池であってもよい。なお、以下に説明する実施形態は例示にすぎず、本実施形態に係る二次電池は、本明細書に記載されている実施形態を基づいて、種々の変更、改良を施した形態に適用してもよい。
(4) Lithium Ion Secondary Battery The lithium ion secondary battery according to the present embodiment (hereinafter, also referred to as “secondary battery”) includes the above-mentioned positive electrode, negative electrode, and non-aqueous electrolyte. The secondary battery includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte solution. Further, the secondary battery may include, for example, a positive electrode, a negative electrode, and a solid electrolyte. The secondary battery may be a secondary battery that charges and discharges by removing and inserting lithium ions. For example, a non-aqueous electrolyte secondary battery may be used, and an all-solid-state lithium secondary battery may be used. There may be. It should be noted that the embodiments described below are merely examples, and the secondary battery according to the present embodiment is applied to an embodiment in which various modifications and improvements have been made based on the embodiments described in the present specification. You may.
本実施形態に係るリチウムイオン二次電池は、正極材料として上記の正極活物質を用いたこと以外は、一般的なリチウムイオン二次電池と実質的に同様の構造を備えてもよい。 The lithium ion secondary battery according to the present embodiment may have substantially the same structure as a general lithium ion secondary battery except that the above-mentioned positive electrode active material is used as the positive electrode material.
例えば、非水系電解液二次電池の場合、ケースと、このケース内に収容された正極、負極、非水系電解液およびセパレータを備えた構造を有している。具体的にいえば、セパレータを介して正極と負極とを積層させて電極体とし、得られた電極体に非水系電解液を含浸させ、正極の正極集電体と外部に通ずる正極端子との間、および、負極の負極集電体と外部に通ずる負極端子との間を、それぞれ集電用リードなどを用いて接続し、ケースに密閉することによって、本発明の二次電池は形成される。 For example, a non-aqueous electrolyte secondary battery has a structure including a case and a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator housed in the case. Specifically, a positive electrode and a negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte solution to form a positive electrode current collector of the positive electrode and a positive electrode terminal communicating with the outside. The secondary battery of the present invention is formed by connecting the space and between the negative electrode current collector of the negative electrode and the negative electrode terminal leading to the outside by using a current collecting lead or the like and sealing the case. ..
以下、本発明のリチウムイオン二次電池について詳細に説明するが、本発明の二次電池の構造は、上記例に限定されないのはいうまでもなく、また、その外形も筒形や積層形など、種々の形状を採用することができる。 Hereinafter, the lithium ion secondary battery of the present invention will be described in detail, but it goes without saying that the structure of the secondary battery of the present invention is not limited to the above example, and the outer shape thereof is also tubular or laminated. , Various shapes can be adopted.
［負極］
負極は、銅などの金属箔集電体の表面に、負極合材ペーストを塗布し、乾燥して形成されたシート状の部材である。負極活物質は、例えば、金属リチウムやリチウム合金などのリチウムを含有する物質や、リチウムイオンを吸蔵および脱離できる吸蔵物質を採用することができる。吸蔵物質は、特に限定されないが、例えば、天然黒鉛、人造黒鉛、フェノール樹脂などの有機化合物焼成体、およびコークスなどの炭素物質の粉状体を用いることができる。
[Negative electrode]
The negative electrode is a sheet-like member formed by applying a negative electrode mixture paste to the surface of a metal leaf current collector such as copper and drying it. As the negative electrode active material, for example, a material containing lithium such as metallic lithium or a lithium alloy, or a storage material capable of storing and desorbing lithium ions can be adopted. The occlusal substance is not particularly limited, and for example, a calcined product of an organic compound such as natural graphite, artificial graphite, or phenol resin, and a powdered material of a carbon substance such as coke can be used.
［セパレータ］
セパレータは、例えば、ポリエチレンやポリプロピレンなどの薄い膜で、微細な孔を多数有する膜を用いることができる。なお、セパレータの機能を有するものであれば、特に限定されない。
[Separator]
As the separator, for example, a thin film such as polyethylene or polypropylene, which has a large number of fine pores, can be used. It is not particularly limited as long as it has a separator function.
［非水系電解質］
非水系電解質としては、例えば非水系電解液を用いることができる。非水系電解液は、支持塩としてのリチウム塩を有機溶媒に溶解したものである。有機溶媒としては、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、トリフルオロプロピレンカーボネートなどの環状カーボネート；ジエチルカーボネート、ジメチルカーボネート、エチルメチルカーボネート、ジプロピルカーボネートなどの鎖状カーボネート；テトラヒドロフラン、２−メチルテトラヒドロフラン、ジメトキシエタンなどのエーテル化合物；エチルメチルスルホンやブタンスルトンなどの硫黄化合物；リン酸トリエチルやリン酸トリオクチルなどのリン化合物などから選ばれる１種を、単独で、あるいは２種以上を混合して用いることができる。支持塩としては、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＮ（ＣＦ３ＳＯ２）２およびそれらの複合塩などを用いることができる。
[Non-aqueous electrolyte]
As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used. The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; tetrahydrofuran, 2-methyltetraethane and dimethoxy. One selected from ether compounds such as ethane; sulfur compounds such as ethylmethyl sulfone and butane sulton; phosphorus compounds such as triethyl phosphate and trioctyl phosphate can be used alone or in admixture of two or more. .. As the supporting salt, LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiN (CF 3 SO 2 ) 2, and a composite salt thereof and the like can be used.
また、非水系電解質としては、固体電解質を用いてもよい。固体電解質は、高電圧に耐えうる性質を有する。固体電解質としては、無機固体電解質、有機固体電解質が挙げられる。 Moreover, you may use a solid electrolyte as a non-aqueous electrolyte. The solid electrolyte has a property of being able to withstand a high voltage. Examples of the solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte.
無機固体電解質としては、酸化物系固体電解質、硫化物系固体電解質等が挙げられる。 Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.
酸化物系固体電解質としては、特に限定されず、例えば酸素（Ｏ）を含有し、かつリチウムイオン伝導性と電子絶縁性とを有するものを好適に用いることができる。酸化物系固体電解質としては、例えば、リン酸リチウム（Ｌｉ３ＰＯ４）、Ｌｉ３ＰＯ４ＮＸ、ＬｉＢＯ２ＮＸ、ＬｉＮｂＯ３、ＬｉＴａＯ３、Ｌｉ２ＳｉＯ３、Ｌｉ４ＳｉＯ４−Ｌｉ３ＰＯ４、Ｌｉ４ＳｉＯ４−Ｌｉ３ＶＯ４、Ｌｉ２Ｏ−Ｂ２Ｏ３−Ｐ２Ｏ５、Ｌｉ２Ｏ−ＳｉＯ２、Ｌｉ２Ｏ−Ｂ２Ｏ３−ＺｎＯ、Ｌｉ１＋ＸＡｌＸＴｉ２−Ｘ（ＰＯ４）３（０≦Ｘ≦１）、Ｌｉ１＋ＸＡｌＸＧｅ２−Ｘ（ＰＯ４）３（０≦Ｘ≦１）、ＬｉＴｉ２（ＰＯ４）３、Ｌｉ３ＸＬａ２／３−ＸＴｉＯ３（０≦Ｘ≦２／３）、Ｌｉ５Ｌａ３Ｔａ２Ｏ１２、Ｌｉ７Ｌａ３Ｚｒ２Ｏ１２、Ｌｉ６ＢａＬａ２Ｔａ２Ｏ１２、Ｌｉ３．６Ｓｉ０．６Ｐ０．４Ｏ４等から選択された１種類以上を用いることができる。 The oxide-based solid electrolyte is not particularly limited, and for example, one containing oxygen (O) and having lithium ion conductivity and electron insulating property can be preferably used. Examples of the oxide-based solid electrolyte include lithium phosphate (Li 3 PO 4 ), Li 3 PO 4 N X , LiBO 2 N X , LiNbO 3 , LiTaO 3 , Li 2 SiO 3 , Li 4 SiO 4- Li 3 PO 4 , Li 4 SiO 4- Li 3 VO 4 , Li 2 O-B 2 O 3- P 2 O 5 , Li 2 O-SiO 2 , Li 2 O-B 2 O 3- ZnO, Li 1 + X Al X Ti 2-X (PO 4 ) 3 (0 ≦ X ≦ 1), Li 1 + X Al X Ge 2-X (PO 4 ) 3 (0 ≦ X ≦ 1), LiTi 2 (PO 4 ) 3 , Li 3X La 2 / 3-X TiO 3 (0 ≤ X ≤ 2/3), Li 5 La 3 Ta 2 O 12 , Li 7 La 3 Zr 2 O 12 , Li 6 BaLa 2 Ta 2 O 12 , Li 3.6 Si 0.6 One or more types selected from P 0.4 O 4 and the like can be used.
硫化物系固体電解質としては、特に限定されず、例えば硫黄（Ｓ）を含有し、かつリチウムイオン伝導性と電子絶縁性とを有するものを好適に用いることができる。硫化物系固体電解質としては、例えば、Ｌｉ２Ｓ−Ｐ２Ｓ５、Ｌｉ２Ｓ−ＳｉＳ２、ＬｉＩ−Ｌｉ２Ｓ−ＳｉＳ２、ＬｉＩ−Ｌｉ２Ｓ−Ｐ２Ｓ５、ＬｉＩ−Ｌｉ２Ｓ−Ｂ２Ｓ３、Ｌｉ３ＰＯ４−Ｌｉ２Ｓ−Ｓｉ２Ｓ、Ｌｉ３ＰＯ４−Ｌｉ２Ｓ−ＳｉＳ２、ＬｉＰＯ４−Ｌｉ２Ｓ−ＳｉＳ、ＬｉＩ−Ｌｉ２Ｓ−Ｐ２Ｏ５、ＬｉＩ−Ｌｉ３ＰＯ４−Ｐ２Ｓ５等から選択された１種類以上を用いることができる。 The sulfide-based solid electrolyte is not particularly limited, and for example, one containing sulfur (S) and having lithium ion conductivity and electron insulating property can be preferably used. The sulfide-based solid electrolyte, for example, Li 2 S-P 2 S 5, Li 2 S-SiS 2, LiI-Li 2 S-SiS 2, LiI-Li 2 S-P 2 S 5, LiI-Li 2 S-B 2 S 3, Li 3 PO 4 -Li 2 S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O One or more selected from 5 , LiI-Li 3 PO 4- P 2 S 5 and the like can be used.
なお、無機固体電解質としては、上記以外のものを用いてよく、例えば、Ｌｉ３Ｎ、ＬｉＩ、Ｌｉ３Ｎ−ＬｉＩ−ＬｉＯＨ等を用いてもよい。 As the inorganic solid electrolyte, an electrolyte other than the above may be used, and for example, Li 3 N, LiI, Li 3 N-LiI-LiOH or the like may be used.
有機固体電解質としては、イオン伝導性を示す高分子化合物であれば、特に限定されず、例えば、ポリエチレンオキシド、ポリプロピレンオキシド、これらの共重合体などを用いることができる。また、有機固体電解質は、支持塩（リチウム塩）を含んでいてもよい。 The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof and the like can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt).
なお、非水系電解液に代わり固体電解質を用いて二次電池を構成することも可能である。固体電解質は高電位でも分解しないので、非水系電解液で見られるような充電時の電解液の分解によるガス発生や熱暴走が無いため、高い熱安定性を有している。そのため、本発明による正極活物質を用いたリチウムイオン二次電池に用いた場合、より熱安定性の高い二次電池を得ることができる。 It is also possible to construct a secondary battery by using a solid electrolyte instead of the non-aqueous electrolyte solution. Since the solid electrolyte does not decompose even at a high potential, it has high thermal stability because there is no gas generation or thermal runaway due to decomposition of the electrolyte during charging as seen in non-aqueous electrolytes. Therefore, when used in a lithium ion secondary battery using the positive electrode active material according to the present invention, a secondary battery with higher thermal stability can be obtained.
（二次電池の形状、構成）
二次電池の構成は、特に限定されず、上述したように正極、負極、セパレータ、非水系電解質などで構成されてもよく、正極、負極、固体電解質などで構成されもよい。また、二次電池の形状は、特に限定されず、円筒形や積層形など、種々の形状にすることができる。例えば、二次電池が非水系電解液二次電池である場合、正極および負極を、セパレータを介して積層させて電極体とし、得られた電極体に、非水系電解液を含浸させ、正極集電体と外部に通ずる正極端子との間、および、負極集電体と外部に通ずる負極端子との間を、集電用リードなどを用いて接続し、電池ケースに密閉して、二次電池を完成させる。
(Shape and configuration of secondary battery)
The configuration of the secondary battery is not particularly limited, and may be composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, or the like as described above, or may be composed of a positive electrode, a negative electrode, a solid electrolyte, or the like. Further, the shape of the secondary battery is not particularly limited, and various shapes such as a cylindrical shape and a laminated shape can be used. For example, when the secondary battery is a non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with the non-aqueous electrolyte solution to collect positive electrodes. The secondary battery is connected between the electric body and the positive electrode terminal that communicates with the outside, and between the negative electrode current collector and the negative electrode terminal that communicates with the outside by using a current collecting lead or the like, and is sealed in a battery case. To complete.
なお、本実施形態に係る二次電池は非水系電解質として非水系電解液を用いた形態に限定されるものではなく、例えば固体の非水系電解質を用いた二次電池、すなわち全固体電池とすることもできる。全固体電池とする場合、正極活物質以外の構成は必要に応じて変更することができる。 The secondary battery according to the present embodiment is not limited to a mode in which a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, and is, for example, a secondary battery using a solid non-aqueous electrolyte, that is, an all-solid-state battery. You can also do it. In the case of an all-solid-state battery, the configurations other than the positive electrode active material can be changed as needed.
本実施形態に係る二次電池は、高い熱安定性を低コストで実現できる。また、二次電池に用いられる正極活物質は、上述した工業的な製造方法で得ることができる。また、二次電池は、常に高容量を要求される小型携帯電子機器（ノート型パーソナルコンピュータや携帯電話端末など）の電源に好適である。また、二次電池は、従来のリチウムコバルト系酸化物あるいはリチウムニッケル系酸化物の正極活物質を用いた電池との比較においても、容量のみならず、耐久性及び過充電時の熱安定性に優れている。そのため、小型化、高容量化が可能であることから、搭載スペースに制約を受ける電気自動車用電源として好適である。なお、二次電池は、純粋に電気エネルギーで駆動する電気自動車用の電源のみならず、ガソリンエンジンやディーゼルエンジンなどの燃焼機関と併用するいわゆるハイブリット車用の電源としても用いることができる。 The secondary battery according to the present embodiment can realize high thermal stability at low cost. Further, the positive electrode active material used in the secondary battery can be obtained by the above-mentioned industrial manufacturing method. Further, the secondary battery is suitable as a power source for small portable electronic devices (notebook personal computers, mobile phone terminals, etc.) that are always required to have a high capacity. In addition, the secondary battery has not only capacity but also durability and thermal stability during overcharging, even when compared with conventional batteries using a positive electrode active material of lithium cobalt oxide or lithium nickel oxide. Are better. Therefore, since it is possible to reduce the size and increase the capacity, it is suitable as a power source for electric vehicles whose mounting space is restricted. The secondary battery can be used not only as a power source for an electric vehicle driven by purely electric energy, but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.
なお、本発明の技術範囲は、上述の実施形態などで説明した態様に限定されるものではない。上述の実施形態などで説明した要件の１つ以上は、省略されることがある。また、上述の実施形態などで説明した要件は、適宜組み合わせることができる。また、法令で許容される限りにおいて、本明細書で引用した全ての文献の内容を援用して本文の記載の一部とする。 The technical scope of the present invention is not limited to the embodiments described in the above-described embodiments. One or more of the requirements described in the above embodiments and the like may be omitted. In addition, the requirements described in the above-described embodiments and the like can be combined as appropriate. In addition, to the extent permitted by law, the contents of all documents cited in this specification shall be incorporated as part of the description of the main text.
以下に、本発明の実施例及び比較例によって、本発明をさらに詳細に説明するが、本発明は、これらの実施例によってなんら限定されるものではない。なお、実施例及び比較例における正極活物質に含有される金属の分析方法及び正極活物質の各種評価方法は、以下の通りである。 Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples. The method for analyzing the metal contained in the positive electrode active material and the various evaluation methods for the positive electrode active material in Examples and Comparative Examples are as follows.
［平均粒径および粒度分布の測定］
平均粒径（Ｄ５０）および粒度分布（〔（ｄ９０−ｄ１０）／平均粒径〕値）は、レーザー回折散乱式粒度分布測定装置（日機装株式会社製、マイクロトラックＨＲＡ）を用いて測定した体積積算値から算出した。
[Measurement of average particle size and particle size distribution]
The average particle size (D50) and the particle size distribution ([(d90-d10) / average particle size] value) are volume integrated measured using a laser diffraction / scattering type particle size distribution measuring device (Microtrac HRA, manufactured by Nikkiso Co., Ltd.). Calculated from the value.
［タップ密度］
ＪＩＳ Ｚ−２５０４に準拠して、容器に採取した試料粉末に対して、１００回のタッピングを行った後、振とう比重測定器を用いてかさ密度（タップ密度）を測定した。
[Tap Density]
According to JIS Z-2504, the sample powder collected in the container was tapped 100 times, and then the bulk density (tap density) was measured using a shaking bulk density measuring instrument.
［組成分析］
試料を溶解した後、ＩＣＰ発光分光法（ＩＣＰ：Ｉｎｄｕｃｔｉｖｅｌｙ Ｃｏｕｐｌｅｄ ＰｌＡｓｍＡ）により分析した。
[Composition analysis]
After the sample was dissolved, it was analyzed by ICP: Inductively Coupled Plasma (ICP).
［空隙率］
測定対象の正極活物質粒子を樹脂に埋め込み、クロスセクションポリッシャ加工によって断面観察が可能な状態とした後、走査型電子顕微鏡を用いて観察し、画像解析により評価した。画像解析ソフトはＷｉｎＲｏｏｆ ６．１．１を使用し、空隙率は、二次粒子中の空隙部を黒として測定し、二次粒子輪郭内の緻密部を白として測定し、任意の２０個以上の粒子に対して、［黒部分／（黒部分＋白部分）］の面積を計算して求めた。
[Porosity]
After embedding the positive electrode active material particles to be measured in a resin and making it possible to observe the cross section by cross-section polisher processing, the particles were observed using a scanning electron microscope and evaluated by image analysis. The image analysis software uses WinRof 6.1.1, and the void ratio is measured by measuring the voids in the secondary particles as black and the dense parts in the contour of the secondary particles as white, and 20 or more arbitrary particles. The area of [black part / (black part + white part)] was calculated and obtained for the particles of.
［空隙の平均アスペクト比］
空隙の平均アスペクト比は、後述する方法により、ロールプレスして得られた正極ＰＥを樹脂に埋め込み、その樹脂を前記プレス成型後の正極ＰＥのプレス面に対して垂直な断面で切り出し、この断面を研磨してＳＥＭ断面写真を撮影して画像解析したときに、断面長径が３μｍ以上であり、かつ、粒子内部の空隙長径が０．３μｍ以上の空隙を有する第２の正極活物質粒子Ｂ２０個以上に対して、縦断面の空隙長径（Ｌ）と空隙短径（Ｗ）を各々測定して求めたアスペクト比（Ｗ／Ｌ）を個数平均することによって求めた。なお、同一の粒子に測定対象の空隙が複数含まれる場合には、その粒子の中で最も大きな空隙を測定した。
[Average aspect ratio of voids]
The average aspect ratio of the voids is determined by embedding the positive electrode PE obtained by roll pressing in a resin by a method described later, and cutting out the resin in a cross section perpendicular to the pressed surface of the positive electrode PE after press molding. 20 second positive electrode active material particles B having a cross-sectional major axis of 3 μm or more and a void major axis of 0.3 μm or more inside the particles when the SEM cross-sectional photograph was taken and the image was analyzed. With respect to the above, it was obtained by averaging the number of aspect ratios (W / L) obtained by measuring the void major axis (L) and the void minor axis (W) in the vertical cross section. When the same particle contained a plurality of voids to be measured, the largest void among the particles was measured.
［電池評価］
電池評価には、図４に示す２０３２型コイン電池（以下、コイン型電池ＣＢＡという）を作製して用いた。
[Battery evaluation]
For the battery evaluation, a 2032 type coin battery (hereinafter referred to as a coin type battery CBA) shown in FIG. 4 was produced and used.
図４に示すように、コイン型電池ＣＢＡは、ケース（正極缶ＰＣ、負極缶ＮＣ）と、このケース内に収容された電極（正極ＰＥ、負極ＮＥ）とから構成されている。ケースは、中空かつ一端が開口された正極缶ＰＣと、この正極缶ＰＣの開口部に配置される負極缶ＮＣとからなり、負極缶ＮＣを正極缶ＰＣの開口部に配置すると、負極缶ＮＣと正極缶ＰＣとの間に電極を収容する空間が形成されるように構成されている。 As shown in FIG. 4, the coin-type battery CBA is composed of a case (positive electrode can PC, negative electrode can NC) and electrodes (positive electrode PE, negative electrode NE) housed in the case. The case consists of a positive electrode can PC that is hollow and has one end opened, and a negative electrode can NC that is arranged in the opening of the positive electrode can PC. When the negative electrode can NC is arranged in the opening of the positive electrode can PC, the negative electrode can NC. It is configured so that a space for accommodating the electrodes is formed between the positive electrode can PC and the positive electrode can PC.
電極は、正極ＰＥおよび負極ＮＥとからなり、正極ＰＥと負極ＮＥの間にはセパレータＳＥが挿入されて積層されており、正極ＰＥが正極缶ＰＣの内面に接触し、負極ＮＥが負極缶ＮＣの内面に接触するようにケースに収容されている。 The electrode is composed of a positive electrode PE and a negative electrode NE, and a separator SE is inserted and laminated between the positive electrode PE and the negative electrode NE, the positive electrode PE contacts the inner surface of the positive electrode can PC, and the negative electrode NE is the negative electrode can NC. It is housed in a case so that it comes into contact with the inner surface of the electrode.
なお、ケースはガスケットＧＡを備えており、このガスケットＧＡによって、正極缶ＰＣと負極缶ＮＣとの間が電気的に絶縁状態を維持するように固定されている。また、ガスケットＧＡは、正極缶ＰＣと負極缶ＮＣとの隙間を密封してケース内と外部との間を気密および液密に遮断する機能も有している。コイン型電池ＣＢＡは、以下のようにして製作した。 The case is provided with a gasket GA, and the gasket GA is used to fix the positive electrode can PC and the negative electrode can NC so as to maintain an electrically insulated state. Further, the gasket GA also has a function of sealing the gap between the positive electrode can PC and the negative electrode can NC to airtightly and liquid-tightly block the space between the inside and the outside of the case. The coin-type battery CBA was manufactured as follows.
まず、リチウムイオン二次電池用正極活物質をアセチレンブラック（導電材）とＰＶＤＦ（ポリフッ化ビニリデン）を質量比８５：１０：５となるように混合し、ＮＭＰ（Ｎ−メチル−２−ピロリドン）中に分散させてスラリー化した。この正極スラリーを、厚さ２０μｍのアルミニウム箔（正極集電体）にアプリケーターを用い、単位面積当たり７ｍｇ／ｃｍ２に塗工した。その後、送風乾燥機で１２０℃×３０分乾燥し、ロールプレスにて圧延し正極ＰＥ（電極）を得た。ここで、上記の圧延は、後述する実施例と比較例において、所望の空隙のアスペクト比が得られるような荷重で加圧することにより行った。その後、一角に幅１０ｍｍの帯状部が突き出た３ｃｍ×５ｃｍの長方形に打ち抜き成型して、直径１１ｍｍ、厚さ１００μｍの正極ＰＥとした。 First, the positive electrode active material for a lithium ion secondary battery is mixed with acetylene black (conductive material) and PVDF (polyvinylidene fluoride) so as to have a mass ratio of 85:10: 5, and NMP (N-methyl-2-pyrrolidone). It was dispersed in the slurry to form a slurry. This positive electrode slurry was applied to an aluminum foil (positive electrode current collector) having a thickness of 20 μm at 7 mg / cm 2 per unit area using an applicator. Then, it was dried in a blower dryer at 120 ° C. for 30 minutes and rolled by a roll press to obtain a positive electrode PE (electrode). Here, the above-mentioned rolling was carried out by pressurizing with a load so as to obtain a desired aspect ratio of voids in Examples and Comparative Examples described later. Then, it was punch-molded into a rectangle of 3 cm × 5 cm in which a strip-shaped portion having a width of 10 mm protruded in one corner to obtain a positive electrode PE having a diameter of 11 mm and a thickness of 100 μm.
この正極ＰＥと、負極ＮＥ、セパレータＳＥおよび電解液とを用いて、コイン型電池ＣＢＡを、露点が−８０℃に管理されたＡｒ雰囲気のグローブボックス内で作製した。なお、負極ＮＥには、直径１４ｍｍの円盤状に打ち抜かれた平均粒径２０μｍ程度の黒鉛粉末とポリフッ化ビニリデンが銅箔に塗布された負極シートを用いた。また、セパレータＳＥには膜厚２５μｍのポリエチレン多孔膜を用いた。 Using this positive electrode PE, the negative electrode NE, the separator SE, and the electrolytic solution, a coin-type battery CBA was produced in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C. As the negative electrode NE, a graphite powder having an average particle diameter of about 20 μm punched into a disk shape having a diameter of 14 mm and a negative electrode sheet coated with polyvinylidene fluoride on a copper foil were used. Further, a polyethylene porous membrane having a film thickness of 25 μm was used for the separator SE.
電解液には、１ＭのＬｉＣｌＯ４を支持電解質とするエチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）の等量混合液（富山薬品工業株式会社製）を用いた。
作製したコイン型電池ＣＢＡの性能評価を、初期放電容量、正極抵抗について、以下のように定義した。
As the electrolytic solution, an equal amount mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO 4 as a supporting electrolyte (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used.
The performance evaluation of the produced coin-type battery CBA was defined as follows for the initial discharge capacity and the positive electrode resistance.
（初期放電容量）
コイン型電池ＣＢＡを作製してから２４時間程度放置し、開回路電圧ＯＣＶ（ｏｐｅｎ ｃｉｒｃｕｉｔ ｖｏｌｔＡｇｅ）が安定した後、正極に対する電流密度を０．５ｍＡ／ｃｍ２としてカットオフ電圧４．４Ｖまで充電し、１時間の休止後、カットオフ電圧３．０Ｖまで放電したときの容量を初期放電容量とした。
(Initial discharge capacity)
After producing the coin-type battery CBA, leave it for about 24 hours, and after the open circuit voltage OCV (open discharge voltage) stabilizes, charge the current density to the positive electrode to 0.5 mA / cm2 and charge it to a cutoff voltage of 4.4 V. The capacity when discharged to a cutoff voltage of 3.0 V after a one-hour rest was defined as the initial discharge capacity.
（正極抵抗）
正極抵抗は、コイン型電池ＣＢＡを充電電位４．１Ｖで充電して、周波数応答アナライザおよびポテンショガルバノスタット（ソーラトロン製、１２５５Ｂ）を使用して交流インピーダンス法により測定して、図５に示すナイキストプロットを作成する。このナイキストプロットは、溶液抵抗、負極抵抗とその容量、および、正極抵抗とその容量を示す特性曲線の和として表しているため、このナイキストプロットに基づき等価回路を用いてフィッティング計算して、正極抵抗の値を算出した。
(Positive electrode resistance)
The positive electrode resistance is measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) by charging the coin-type battery CBA at a charging potential of 4.1 V, and the Nyquist plot shown in FIG. To create. Since this Nyquist plot is expressed as the sum of the solution resistance, the negative electrode resistance and its capacitance, and the positive electrode resistance and its capacitance, the fitting calculation is performed using an equivalent circuit based on this Nyquist plot, and the positive electrode resistance is calculated. The value of was calculated.
［実施例１］
（第１の正極活物質粒子Ａの製造）
反応槽（５Ｌ）内に、水を９００ｍｌ入れて、撹拌しながら、槽内温度を６０℃に設定した。さらに、反応槽内の水に２５％水酸化ナトリウム水溶液と２５％アンモニア水４０ｍｌを適量加えることにより、液温２５℃におけるｐＨとして、槽内の反応液のｐＨが１１．０となるように反応前水溶液を調整した。
[Example 1]
(Production of First Positive Electrode Active Material Particle A)
900 ml of water was placed in the reaction vessel (5 L), and the temperature in the vessel was set to 60 ° C. with stirring. Further, by adding an appropriate amount of 25% sodium hydroxide aqueous solution and 40 ml of 25% ammonia water to the water in the reaction tank, the reaction was carried out so that the pH of the reaction liquid in the tank was 11.0 as the pH at a liquid temperature of 25 ° C. The pre-aqueous solution was adjusted.
一方、各原料（Ｎｉ、Ｃｏ、Ｍｎ）の硫酸塩を水に溶かして、１．８ｍｏｌ／Ｌの原料水溶液を得た。なお、原料水溶液中の各原料の物質量比は、表１に示す範囲内となるように調整した。反応槽内の反応前水溶液を撹拌しながら、得られた原料水溶液を反応槽内の反応前水溶液に加え、同時に、２５質量％アンモニア水および２５質量％水酸化ナトリウム水溶液を連続的に加えて、中和晶析を行った。なお、晶析反応の時間、反応溶液のｐＨ、アンモニウムイオン供給体の量等は、表１に示される特性を有する第１の正極活物質粒子Ａが得られるように、適宜調整した。 On the other hand, the sulfates of each raw material (Ni, Co, Mn) were dissolved in water to obtain a 1.8 mol / L raw material aqueous solution. The substance amount ratio of each raw material in the raw material aqueous solution was adjusted to be within the range shown in Table 1. While stirring the pre-reaction aqueous solution in the reaction vessel, the obtained raw material aqueous solution was added to the pre-reaction aqueous solution in the reaction vessel, and at the same time, 25% by mass ammonia water and 25% by mass sodium hydroxide aqueous solution were continuously added. Neutralization crystallization was performed. The time of the crystallization reaction, the pH of the reaction solution, the amount of the ammonium ion feeder, and the like were appropriately adjusted so that the first cathode active material particles A having the characteristics shown in Table 1 could be obtained.
得られたニッケル複合水酸化物に対してリチウム化合物をＬｉ/Ｍｅ比１．１となるように混合した後、８５０℃で焼成して、平均粒径が１６．５μｍ、タップ密度が２．６３ｇ／ｃｍ３である、表１に示す特性を有する第１の正極活物質粒子Ａを得た。 A lithium compound was mixed with the obtained nickel composite hydroxide so as to have a Li / Me ratio of 1.1, and then calcined at 850 ° C. to have an average particle size of 16.5 μm and a tap density of 2.63 g. A first positive electrode active material particle A having the characteristics shown in Table 1 having a value of / cm 3 was obtained.
（第２の正極活物質粒子Ｂの製造）
反応槽（３４Ｌ）内に水を１７Ｌ入れて撹拌しながら、槽内温度を４０℃に設定し、大気雰囲気（酸素濃度：２１容量％）とした。反応槽内の水に２５％水酸化ナトリウム水溶液と２５％アンモニア水を適量加えることにより、液温２５℃におけるｐＨとして、槽内の反応前水溶液のｐＨが１２．６となるように調整した。また、反応前水溶液中のアンモニウムイオン濃度を１５ｇ／Ｌに調節した。
(Manufacture of Second Positive Electrode Active Material Particle B)
While 17 L of water was placed in the reaction tank (34 L) and stirred, the temperature in the tank was set to 40 ° C. to create an atmospheric atmosphere (oxygen concentration: 21% by volume). By adding an appropriate amount of 25% sodium hydroxide aqueous solution and 25% ammonia water to the water in the reaction tank, the pH of the pre-reaction aqueous solution in the tank was adjusted to 12.6 as the pH at a liquid temperature of 25 ° C. In addition, the ammonium ion concentration in the pre-reaction aqueous solution was adjusted to 15 g / L.
次いで、各原料の硫酸塩を水に溶かして各原料の物質量比が表１に示す比率となるように調整した１．８ｍｏｌ／Ｌの原料水溶液を、反応槽内の反応前水溶液に８８ｍｌ／分で加えた。同時に、２５質量％アンモニア水および２５質量％水酸化ナトリウム水溶液も反応槽内の反応前水溶液に一定速度で加えていき、得られた反応水溶液中のアンモニウムイオン濃度を１５ｇ／Ｌとなるように保持した状態で、ｐＨを１２．６に制御しながら２分３０秒間晶析を行って、核生成を行った。 Next, a 1.8 mol / L raw material aqueous solution prepared by dissolving the sulfate of each raw material in water so that the substance amount ratio of each raw material had the ratio shown in Table 1 was added to the pre-reaction aqueous solution in the reaction vessel at 88 ml /. Added in minutes. At the same time, 25% by mass aqueous ammonia and 25% by mass aqueous sodium hydroxide solution are also added to the pre-reaction aqueous solution in the reaction vessel at a constant rate to maintain the ammonium ion concentration in the obtained reaction aqueous solution at 15 g / L. In this state, crystallization was carried out for 2 minutes and 30 seconds while controlling the pH to 12.6 to generate nuclei.
次に、核生成終了後、液温２５℃における反応水溶液ｐＨが１１．６（粒子成長ｐＨ）になるまで、２５質量％水酸化ナトリウム水溶液の供給のみを一時停止した。反応水溶液のｐＨ値が１１．６に到達した後、再度、２５質量％水酸化ナトリウム水溶液の供給を再開し、液温２５℃基準でｐＨ値を１１．６に制御したまま、３０分間の晶析を継続し粒子成長を行った後、全ての給液を一旦停止し、反応槽内空間の酸素濃度が０．２容量％以下となるまで窒素ガスを５Ｌ／ｍｉｎで流通させた。その後、給液を再開し、粒子成長開始からあわせて２時間晶析を行った。 Next, after the completion of nucleation, only the supply of the 25 mass% sodium hydroxide aqueous solution was suspended until the pH of the reaction aqueous solution at a liquid temperature of 25 ° C. reached 11.6 (particle growth pH). After the pH value of the reaction aqueous solution reached 11.6, the supply of the 25 mass% sodium hydroxide aqueous solution was restarted, and the crystals were crystallized for 30 minutes while the pH value was controlled to 11.6 based on the liquid temperature of 25 ° C. After continuing the analysis and growing the particles, all the liquid supplies were temporarily stopped, and nitrogen gas was circulated at 5 L / min until the oxygen concentration in the reaction vessel space became 0.2% by mass or less. Then, the liquid supply was restarted, and crystallization was carried out for a total of 2 hours from the start of particle growth.
反応槽内が満液になったところで水酸化ナトリウム溶液の供給を停止するとともに撹拌を止めて静置することにより、生成物の沈殿を促した。その後、反応槽から上澄み液を半量抜き出した後、水酸化ナトリウム溶液の供給を再開し、０．５時間晶析を行った後（計２．５時間）、粒子の成長を終了させた。そして、得られた生成物を水洗、濾過、乾燥させることにより、ニッケル複合水酸化物を回収した。なお、粒子成長工程の時間、核生成工程のｐＨと金属化合物の量等は、表１に示される特性を有する第２の正極活物質粒子Ｂが得られるように、適宜調整した。 When the inside of the reaction vessel became full, the supply of the sodium hydroxide solution was stopped, the stirring was stopped, and the mixture was allowed to stand to promote the precipitation of the product. Then, half of the supernatant was withdrawn from the reaction vessel, the supply of the sodium hydroxide solution was restarted, crystallization was performed for 0.5 hours (2.5 hours in total), and then the growth of the particles was terminated. Then, the obtained product was washed with water, filtered, and dried to recover the nickel composite hydroxide. The time of the particle growth step, the pH of the nucleation step, the amount of the metal compound, and the like were appropriately adjusted so as to obtain the second positive electrode active material particles B having the characteristics shown in Table 1.
得られたニッケルコバルトマンガン複合水酸化物に対してリチウム化合物をＬｉ／Ｍｅ比１．１となるように混合した後、８００℃で焼成して、平均粒径が４．８μｍ、タップ密度が１．５８ｇ／ｃｍ３である、表１に示す特性を有する第２の正極活物質粒子Ｂを得た。 A lithium compound was mixed with the obtained nickel-cobalt-manganese composite hydroxide so as to have a Li / Me ratio of 1.1, and then calcined at 800 ° C. to have an average particle size of 4.8 μm and a tap density of 1. A second positive electrode active material particle B having the characteristics shown in Table 1 at .58 g / cm 3 was obtained.
（第１の正極活物質粒子Ａと第２の正極活物質粒子Ｂとの混合）
上記により得られた、第１の正極活物質粒子Ａと第２の正極活物質粒子Ｂとを、Ａ：Ｂ＝９０：１０の比率にて混合し、正極活物質を得た。
(Mixing of the first positive electrode active material particle A and the second positive electrode active material particle B)
The first positive electrode active material particles A and the second positive electrode active material particles B obtained as described above were mixed at a ratio of A: B = 90:10 to obtain a positive electrode active material.
（電池の製造、性能評価）
ロールプレスにて線圧２００Ｎ／ｍｍの荷重で圧延し、正極（電極）を得た。圧下率は５％以上であった。正極ＰＥに対する断面観察において、第２の正極活物質粒子Ｂにおける、断面長径が３μｍ以上であり、かつ、二次粒子内で確認される空隙長径が０．３μｍ以上の空隙を有する二次粒子の、空隙長径（Ｌ）と空隙短径（Ｗ）との比である平均アスペクト比（Ｗ／Ｌ）は０．４３であった。得られた正極活物質を用いた正極を有するコイン型電池ＣＢＡを作成し、電池評価を行った。表１に電池評価の詳細結果を示す。
(Battery manufacturing, performance evaluation)
A positive electrode was obtained by rolling with a roll press under a load of 200 N / mm. The reduction rate was 5% or more. In the cross-sectional observation of the positive electrode PE, the secondary particles of the second positive electrode active material particle B having a cross-sectional major axis of 3 μm or more and a void major axis confirmed in the secondary particles of 0.3 μm or more. The average aspect ratio (W / L), which is the ratio of the void major axis (L) to the void minor axis (W), was 0.43. A coin-type battery CBA having a positive electrode using the obtained positive electrode active material was prepared, and the battery was evaluated. Table 1 shows the detailed results of battery evaluation.
［実施例２〜６］
表１に示す条件となるように、原料となる金属化合物を溶解させた混合水溶液中に溶解させる各金属元素の割合、粒子成長工程の時間、核生成工程のｐＨと金属化合物の量、第１の正極活物質粒子Ａと第２の正極活物質粒子Ｂとの混合比率を調整した以外は、実施例１と同様の条件で正極活物質を得た。得られた正極活物質を用いた正極を有するコイン型電池ＣＢＡを作成し、電池評価を行った。表１に電池評価の詳細結果を示す。
[Examples 2 to 6]
According to the conditions shown in Table 1, the ratio of each metal element to be dissolved in the mixed aqueous solution in which the metal compound as a raw material is dissolved, the time of the particle growth step, the pH of the nucleation step and the amount of the metal compound, the first A positive electrode active material was obtained under the same conditions as in Example 1 except that the mixing ratio of the positive electrode active material particles A and the second positive electrode active material particles B was adjusted. A coin-type battery CBA having a positive electrode using the obtained positive electrode active material was prepared, and the battery was evaluated. Table 1 shows the detailed results of battery evaluation.
［比較例１］
第１の正極活物質粒子Ａの平均粒径が８．０μｍ未満となるように、晶析工程での反応時間、反応溶液のｐＨ、アンモニウムイオン供給体の量を調整した以外は、実施例１と同様に行った。評価結果を表１に示す。
［比較例２］
第１の正極活物質粒子Ａの平均粒径が３０μｍ超となるように、晶析工程での反応時間、反応溶液のｐＨ、アンモニウムイオン供給体の量を調整した以外は、実施例１と同様に行った。評価結果を表１に示す。
［比較例３］
第１の正極活物質粒子Ａのタップ密度が２．１ｇ／ｃｍ３未満となるように、晶析工程での反応時間、反応溶液のｐＨ、アンモニウムイオン供給体の量を調整した以外は、実施例１と同様に行った。
評価結果を表１に示す。
［比較例４］
第１の正極活物質粒子Ａのタップ密度が３．０ｇ／ｃｍ３超となるように、晶析工程での反応時間、反応溶液のｐＨ、アンモニウムイオン供給体の量を調整した以外は、実施例１と同様に行った。評価結果を表１に示す。
［比較例５］
第２の正極活物質粒子Ｂの平均粒径が１．０μｍ未満となるように、晶析工程での反応時間、反応溶液のｐＨ、アンモニウムイオン供給体の量を調整した以外は、実施例１と同様に行った。評価結果を表１に示す。
［比較例６］
第２の正極活物質粒子Ｂの平均粒径が８．０μｍ超となるように、晶析工程での反応時間、反応溶液のｐＨ、アンモニウムイオン供給体の量を調整した以外は、実施例１と同様に行った。評価結果を表１に示す。
［比較例７］
第２の正極活物質粒子Ｂのタップ密度が１．８ｇ／ｃｍ３超となるように、晶析工程での反応時間、反応溶液のｐＨ、アンモニウムイオン供給体の量を調整した以外は、実施例１と同様に行った。評価結果を表１に示す。
［比較例８］
第１の正極活物質粒子Ａと第２の正極活物質粒子Ｂとを、Ａ：Ｂ＝１００：０の比率にて混合した以外は、実施例１と同様に行った。評価結果を表１に示す。
［比較例９］
第１の正極活物質粒子Ａと第２の正極活物質粒子Ｂとを、Ａ：Ｂ＝０：１００の比率にて混合した以外は、実施例１と同様に行った。評価結果を表１に示す。
[Comparative Example 1]
Example 1 except that the reaction time in the crystallization step, the pH of the reaction solution, and the amount of the ammonium ion feeder were adjusted so that the average particle size of the first positive electrode active material particles A was less than 8.0 μm. I went in the same way. The evaluation results are shown in Table 1.
[Comparative Example 2]
Same as in Example 1 except that the reaction time in the crystallization step, the pH of the reaction solution, and the amount of the ammonium ion feeder were adjusted so that the average particle size of the first positive electrode active material particles A was more than 30 μm. I went to. The evaluation results are shown in Table 1.
[Comparative Example 3]
This was carried out except that the reaction time in the crystallization step, the pH of the reaction solution, and the amount of the ammonium ion feeder were adjusted so that the tap density of the first positive electrode active material particles A was less than 2.1 g / cm 3. The procedure was the same as in Example 1.
The evaluation results are shown in Table 1.
[Comparative Example 4]
Except for adjusting the reaction time in the crystallization step, the pH of the reaction solution, and the amount of the ammonium ion feeder so that the tap density of the first positive electrode active material particles A exceeds 3.0 g / cm 3. The procedure was the same as in Example 1. The evaluation results are shown in Table 1.
[Comparative Example 5]
Example 1 except that the reaction time in the crystallization step, the pH of the reaction solution, and the amount of the ammonium ion feeder were adjusted so that the average particle size of the second positive electrode active material particles B was less than 1.0 μm. I went in the same way. The evaluation results are shown in Table 1.
[Comparative Example 6]
Example 1 except that the reaction time in the crystallization step, the pH of the reaction solution, and the amount of the ammonium ion feeder were adjusted so that the average particle size of the second positive electrode active material particles B was more than 8.0 μm. I went in the same way. The evaluation results are shown in Table 1.
[Comparative Example 7]
This was carried out except that the reaction time in the crystallization step, the pH of the reaction solution, and the amount of the ammonium ion feeder were adjusted so that the tap density of the second positive electrode active material particles B was more than 1.8 g / cm 3. The procedure was the same as in Example 1. The evaluation results are shown in Table 1.
[Comparative Example 8]
The same procedure as in Example 1 was carried out except that the first positive electrode active material particles A and the second positive electrode active material particles B were mixed at a ratio of A: B = 100: 0. The evaluation results are shown in Table 1.
[Comparative Example 9]
The same procedure as in Example 1 was carried out except that the first positive electrode active material particles A and the second positive electrode active material particles B were mixed at a ratio of A: B = 0: 100. The evaluation results are shown in Table 1.
［参考例１］
実施例１と同様の正極活物質を用い、正極加圧時の圧下率が５％未満になるように、ロールプレスにて線圧１８０Ｎ／ｍｍの荷重で圧延して正極（電極）を得た以外は、実施例１と同様に行った。評価結果を表１に示す。
[Reference example 1]
Using the same positive electrode active material as in Example 1, a positive electrode was obtained by rolling with a roll press under a load of 180 N / mm so that the reduction rate at the time of pressurizing the positive electrode was less than 5%. Except for the above, the same procedure as in Example 1 was carried out. The evaluation results are shown in Table 1.
［評価結果］
実施例の正極活物質では、以下の結果が得られた。
・初期放電容量が１５１〜１８４ｍＡｈ／ｇ
・正極抵抗が２．９〜５．９Ω（ＳＯＣ２０（％））、１．３〜２．９Ω（ＳＯＣ８０（％））
[Evaluation results]
The following results were obtained with the positive electrode active material of the example.
・ Initial discharge capacity is 151-184mAh / g
-Positive electrode resistance is 2.9 to 5.9Ω (SOC20 (%)), 1.3 to 2.9Ω (SOC80 (%))
以上から、実施例の正極活物質では、初期放電容量が１５０ｍＡｈ／ｇを満たすとともに、正極抵抗が６．０Ω以下（ＳＯＣ２０（％））、３．０Ω以下（ＳＯＣ８０（％））を満たしており、高容量と低い正極抵抗とを兼ね備えた二次電池となっていた。すなわち、実施例の正極活物質を用いた二次電池では、高い電池容量と、低い正極抵抗による高い出力特性とを両立できることが示された。 From the above, in the positive electrode active material of the example, the initial discharge capacity satisfies 150 mAh / g, and the positive electrode resistance satisfies 6.0 Ω or less (SOC20 (%)) and 3.0 Ω or less (SOC80 (%)). It was a secondary battery that had both high capacity and low positive electrode resistance. That is, it was shown that the secondary battery using the positive electrode active material of the example can achieve both high battery capacity and high output characteristics due to low positive electrode resistance.
一方、実施例１、２と同様の第１の正極活物質粒子Ａのみを用いた比較例８の正極活物質では、初期放電容量は高いものの、ＳＯＣ２０％およびＳＯＣ８０％における正極抵抗が高く、高出力が得られない二次電池となっていた。また、実施例１、２と同様の第２の正極活物質粒子Ｂのみを用いた比較例９の正極活物質では、ＳＯＣ２０％およびＳＯＣ８０％における正極抵抗は低いものの、初期放電容量が低かった。 On the other hand, in the positive electrode active material of Comparative Example 8 using only the first positive electrode active material particles A similar to Examples 1 and 2, although the initial discharge capacity is high, the positive electrode resistance at SOC 20% and SOC 80% is high and high. It was a secondary battery with no output. Further, in the positive electrode active material of Comparative Example 9 using only the second positive electrode active material particles B similar to Examples 1 and 2, the positive electrode resistance at SOC 20% and SOC 80% was low, but the initial discharge capacity was low.
以下、図６、及び、図７を参照して、本実施形態に係る正極活物質の正極抵抗の低減効果について説明する。 Hereinafter, the effect of reducing the positive electrode resistance of the positive electrode active material according to the present embodiment will be described with reference to FIGS. 6 and 7.
図６、及び、図７は、実施例１、２と、比較例８、９とのＳＯＣ２０％、及び、ＳＯＣ８０％における正極抵抗を示したグラフである。図６、７に示されるように、中空構造を有する第２の正極活物質粒子Ｂを１０質量％含む実施例１では、第２の正極活物質粒子Ｂのみを含む比較例９の正極活物質の正極抵抗と近い値まで正極抵抗が顕著に低下する。さらに、中空構造を有する第２の正極活物質粒子Ｂを５０質量％含む実施例２では、第２の正極活物質粒子Ｂのみを含む比較例９の正極活物質の正極抵抗よりも、さらに正極抵抗が低下する。この理由の詳細は不明であるが、大きい粒径を有する第１の正極活物質粒子Ａの粒子間の空隙に、小さい粒径を有し、かつ、中空構造を有する第２の正極活物質粒子Ｂが好適に配置されることにより、適度に第２の正極活物質粒子Ｂが圧下され、電極密度が向上したと考えられる。 6 and 7 are graphs showing the positive electrode resistance at SOC 20% and SOC 80% between Examples 1 and 2 and Comparative Examples 8 and 9. As shown in FIGS. 6 and 7, in Example 1 containing 10% by mass of the second positive electrode active material particles B having a hollow structure, the positive electrode active material of Comparative Example 9 containing only the second positive electrode active material particles B. The positive electrode resistance drops significantly to a value close to the positive electrode resistance of. Further, in Example 2 containing 50% by mass of the second positive electrode active material particles B having a hollow structure, the positive electrode is further higher than the positive electrode resistance of the positive electrode active material of Comparative Example 9 containing only the second positive electrode active material particles B. Resistance decreases. The details of the reason for this are unknown, but the second positive electrode active material particles having a small particle size and having a hollow structure in the voids between the particles of the first positive electrode active material particles A having a large particle size. It is considered that when B is appropriately arranged, the second positive electrode active material particles B are appropriately reduced and the electrode density is improved.
また、平均粒径が８μｍ未満である第１の正極活物質粒子Ａを含む比較例１の正極活物質では、タップ密度を高くすることが難しく、初期放電容量が低く、正極抵抗が高かった。また、平均粒径が３０μｍを超えるである第１の正極活物質粒子Ａを含む比較例２の正極活物質では、正極抵抗が高かった。 Further, in the positive electrode active material of Comparative Example 1 containing the first positive electrode active material particles A having an average particle size of less than 8 μm, it was difficult to increase the tap density, the initial discharge capacity was low, and the positive electrode resistance was high. Further, the positive electrode active material of Comparative Example 2 containing the first positive electrode active material particles A having an average particle size of more than 30 μm had a high positive electrode resistance.
また、タップ密度が２．１ｇ／ｃｍ３未満の第１の正極活物質粒子Ａを含む比較例３の正極活物質では、タップ密度を高くすることが難しく、初期放電容量が低かった。また、タップ密度が３．０ｇ／ｃｍ３を超える第１の正極活物質粒子Ａを含む比較例４の正極活物質では、正極抵抗が高かった。 Further, in the positive electrode active material of Comparative Example 3 containing the first positive electrode active material particles A having a tap density of less than 2.1 g / cm 3, it was difficult to increase the tap density and the initial discharge capacity was low. Further, the positive electrode active material of Comparative Example 4 containing the first positive electrode active material particles A having a tap density of more than 3.0 g / cm 3 had a high positive electrode resistance.
また、平均粒径が１μｍ未満の第２の正極活物質粒子Ｂを含む比較例５、および、平均粒径が８μｍを超える第２の正極活物質粒子Ｂを含む比較例６の正極活物質では、正極抵抗が高かった。また、タップ密度が１．８ｇ／ｃｍ３を超える第２の正極活物質粒子Ｂを含む比較例７の正極活物質では、正極抵抗が高かった。 Further, in the positive electrode active material of Comparative Example 5 containing the second positive electrode active material particles B having an average particle size of less than 1 μm and Comparative Example 6 containing the second positive electrode active material particles B having an average particle size of more than 8 μm. , The positive electrode resistance was high. Further, the positive electrode active material of Comparative Example 7 containing the second positive electrode active material particles B having a tap density of more than 1.8 g / cm 3 had a high positive electrode resistance.
また、実施例１の正極活物質を用い、正極作製時の圧下率を通常よりも低く設定した参考例１の正極では、正極断面で観察される第２の正極活物質粒子Ｂの空隙の平均アスペクト比が０．５を超えるため、第１の正極活物質粒子Ａ単独の場合よりも正極抵抗は低減するものの、実施例の正極と比較して、十分に正極抵抗を低減することができず、初期放電容量も十分ではなかった。 Further, in the positive electrode of Reference Example 1 in which the reduction rate at the time of producing the positive electrode was set lower than usual by using the positive electrode active material of Example 1, the average of the voids of the second positive electrode active material particles B observed in the positive electrode cross section was obtained. Since the aspect ratio exceeds 0.5, the positive electrode resistance is reduced as compared with the case of the first positive electrode active material particle A alone, but the positive electrode resistance cannot be sufficiently reduced as compared with the positive electrode of the example. , The initial discharge capacity was also not sufficient.
ＣＢＡ…コイン型電池（評価用電池）
ＰＥ…正極（評価用電極）
ＮＥ…負極
ＳＥ…セパレータ
ＧＡ…ガスケット
ＰＣ…正極缶
ＮＣ…負極缶
CBA: Coin-type battery (evaluation battery)
PE ... Positive electrode (evaluation electrode)
NE ... Negative electrode SE ... Separator GA ... Gasket PC ... Positive electrode can NC ... Negative electrode can
Claims (7)
第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂは、六方晶系の層状構造を有するリチウムニッケル複合酸化物であり、かつ、複数の一次粒子が凝集した二次粒子で構成され、
第１の正極活物質粒子Ａは、中実構造を有し、タップ密度が２．１ｇ／ｃｍ３以上３．０ｇ／ｃｍ３以下であり、かつ、平均粒径（Ｄ５０）が８μｍ以上３０μｍ以下であり、
第２の正極活物質粒子Ｂは、中空構造を有し、タップ密度が１．８ｇ／ｃｍ３以下であり、平均粒径（Ｄ５０）が１μｍ以上８μｍ以下、かつ、第１の正極活物質粒子Ａの平均粒径（Ｄ５０）より小さく、
前記正極活物質を含む正極材料をロールプレスにて線圧２００Ｎ／ｍｍで圧下したとき、前記圧下後の正極材料の断面で観察される第２の正極活物質粒子Ｂのうち、断面長径が３μｍ以上であり、かつ、前記二次粒子内で確認される空隙長径が０．３μｍ以上の空隙を有する二次粒子において、空隙長径（Ｌ）と空隙短径（Ｗ）の比である平均アスペクト比（Ｗ／Ｌ）が０．５以下であり、
第１の正極活物質粒子Ａの質量（ＷＡ）と第２の正極活物質粒子Ｂの質量（ＷＢ）との比率が以下の関係式（１）を満たす、
リチウムイオン二次電池用正極活物質。
０．００１≦ＷＢ／（ＷＡ＋ＷＢ）≦０．５・・・（１） A positive electrode active material for a lithium ion secondary battery containing the first positive electrode active material particles A and the second positive electrode active material particles B.
The first positive electrode active material particles A and the second positive electrode active material particles B are secondary particles in which a hexagonal layered structure is a lithium nickel composite oxide and a plurality of primary particles are aggregated. Configured,
The first positive electrode active material particle A has a solid structure, a tap density of 2.1 g / cm 3 or more and 3.0 g / cm 3 or less, and an average particle size (D50) of 8 μm or more and 30 μm or less. And
The second positive electrode active material particle B has a hollow structure, a tap density of 1.8 g / cm 3 or less, an average particle size (D50) of 1 μm or more and 8 μm or less, and a first positive electrode active material particle. Smaller than the average particle size of A (D50),
When the positive electrode material containing the positive electrode active material is reduced by a roll press at a linear pressure of 200 N / mm, the cross-sectional major axis of the second positive electrode active material particles B observed in the cross section of the positive electrode material after the reduction is 3 μm. The average aspect ratio, which is the ratio of the void major axis (L) and the void minor axis (W), in the secondary particles having the above and the void major axis confirmed in the secondary particle having a void major axis of 0.3 μm or more. (W / L) is 0.5 or less,
Ratio of the first positive electrode active material particles A of the mass (W A) and the second positive electrode active material particles B mass (W B) satisfies the following equation (1),
Positive electrode active material for lithium-ion secondary batteries.
0.001 ≦ W B / (W A + W B) ≦ 0.5 ··· (1)
それぞれの前記金属元素の物質量比がＬｉ：Ｎｉ：Ｃｏ：Ｍｎ：Ｍ＝ｓ：（１−ｘ−ｙ−ｚ）：ｘ：ｙ：ｚ（ただし、０．０５≦ｘ≦０．５０、０≦ｙ≦０．３５、０≦ｚ≦０．０５、０．９５＜ｓ＜１．２０）で表される、
請求項１に記載のリチウムイオン二次電池用正極活物質。 The composition of the first positive electrode active material particle A and the second positive electrode active material particle B comprises lithium (Li), nickel (Ni), cobalt (Co), and optionally manganese (Mn) as metal elements. ), And at least one element (M) selected from the group consisting of W, Zr, V, Mg, Mo, Nb, Ti, Si, and Al.
The amount of substance ratio of each of the metal elements is Li: Ni: Co: Mn: M = s: (1-x−y−z): x: y: z (where 0.05 ≦ x ≦ 0.50, It is represented by 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.05, 0.95 <s <1.20).
The positive electrode active material for a lithium ion secondary battery according to claim 1.
第１の正極活物質粒子Ａ、及び、第２の正極活物質粒子Ｂは、六方晶系の層状構造を有するリチウムニッケル複合酸化物であり、複数の一次粒子が凝集した二次粒子で構成され、金属元素として、リチウム（Ｌｉ）と、コバルト（Ｃｏ）と、ニッケル（Ｎｉ）と、任意に、マンガン（Ｍｎ）、及び、Ｗ、Ｚｒ、Ｖ、Ｍｇ、Ｍｏ、Ｎｂ、Ｔｉ、Ｓｉ、及び、Ａｌから選ばれる少なくとも１種の元素（Ｍ）と、を含有し、それぞれの前記金属元素の物質量比がＬｉ：Ｎｉ：Ｃｏ：Ｍｎ：Ｍ＝ｓ：（１−ｘ−ｙ−ｚ）：ｘ：ｙ：ｚ（ただし、０．０５≦ｘ≦０．５０、０≦ｙ≦０．３５、０≦ｚ≦０．０５、０．９５＜ｓ＜１．２０）で表され、
第１の正極活物質粒子Ａは、中実構造を有し、タップ密度が２．１ｇ／ｃｍ３以上３．０ｇ／ｃｍ３以下であり、かつ、平均粒径（Ｄ５０）が８μｍ以上３０μｍ以下であり、
第２の正極活物質粒子Ｂは、中空構造を有し、タップ密度が１．８ｇ／ｃｍ３以下であり、平均粒径（Ｄ５０）が１μｍ以上８μｍ以下、かつ、第１の正極活物質粒子Ａの平均粒径（Ｄ５０）より小さく、
前記正極の断面で観察される第２の正極活物質粒子Ｂのうち、断面長径が３μｍ以上であり、かつ、前記二次粒子内で観察される空隙長径が０．３μｍ以上の空隙を有する二次粒子において、空隙長径（Ｌ）と空隙短径（Ｗ）との比である平均アスペクト比（Ｗ／Ｌ）が０．５以下であり、
第１の正極活物質粒子Ａの質量（ＷＡ）と第２の正極活物質粒子Ｂの質量（ＷＢ）との比率が以下の関係式（１）を満たす、
リチウムイオン二次電池用の正極。
０．００１≦ＷＢ／（ＷＡ＋ＷＢ）≦０．５・・・（１） A positive electrode for a lithium ion secondary battery containing the first positive electrode active material particles A and the second positive electrode active material particles B.
The first positive electrode active material particle A and the second positive positive active material particle B are lithium nickel composite oxides having a hexagonal layered structure, and are composed of secondary particles in which a plurality of primary particles are aggregated. , As metal elements, lithium (Li), cobalt (Co), nickel (Ni), optionally manganese (Mn), and W, Zr, V, Mg, Mo, Nb, Ti, Si, and , At least one element (M) selected from Al, and the substance amount ratio of each of the metal elements is Li: Ni: Co: Mn: M = s :( 1-x-y-z). : X: y: z (where 0.05 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.05, 0.95 <s <1.20).
The first positive electrode active material particle A has a solid structure, a tap density of 2.1 g / cm 3 or more and 3.0 g / cm 3 or less, and an average particle size (D50) of 8 μm or more and 30 μm or less. And
The second positive electrode active material particle B has a hollow structure, a tap density of 1.8 g / cm 3 or less, an average particle size (D50) of 1 μm or more and 8 μm or less, and a first positive electrode active material particle. Smaller than the average particle size of A (D50),
Among the second positive electrode active material particles B observed in the cross section of the positive electrode, the second positive electrode active material particle B has a void with a cross-sectional major axis of 3 μm or more and a void major axis observed in the secondary particle of 0.3 μm or more. In the next particle, the average aspect ratio (W / L), which is the ratio of the void major axis (L) to the void minor axis (W), is 0.5 or less.
Ratio of the first positive electrode active material particles A of the mass (W A) and the second positive electrode active material particles B mass (W B) satisfies the following equation (1),
Positive electrode for lithium-ion secondary batteries.
0.001 ≦ W B / (W A + W B) ≦ 0.5 ··· (1)
第１の正極活物質粒子Ａと、第２の正極活物質粒子Ｂとを含む正極材料を圧下して、第２の正極活物質粒子Ｂの前記平均アスペクト比（Ｗ／Ｌ）が０．５以下となるように調整する工程、を含む、正極の製造方法。 The method for manufacturing a positive electrode for a lithium ion secondary battery according to claim 5.
The positive electrode material containing the first positive electrode active material particles A and the second positive electrode active material particles B is reduced, and the average aspect ratio (W / L) of the second positive electrode active material particles B is 0.5. A method for manufacturing a positive electrode, which comprises a step of adjusting so as to be as follows.
A lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains the positive electrode active material according to any one of claims 1 to 4.
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| JP7416897B1 (en) | 2022-12-02 | 2024-01-17 | 住友化学株式会社 | Lithium metal composite oxide, positive electrode active material for lithium secondary batteries, positive electrode for lithium secondary batteries, and lithium secondary batteries |
| JP7422121B2 (en) | 2021-12-27 | 2024-01-25 | プライムアースＥｖエナジー株式会社 | Lithium ion secondary battery |
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| JP2017123236A (en) | 2016-01-05 | 2017-07-13 | トヨタ自動車株式会社 | Nonaqueous electrolyte secondary battery |
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| JP7422121B2 (en) | 2021-12-27 | 2024-01-25 | プライムアースＥｖエナジー株式会社 | Lithium ion secondary battery |
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| WO2024048574A1 (en) * | 2022-08-31 | 2024-03-07 | 住友化学株式会社 | Positive electrode active material |
| JP7498374B1 (en) | 2022-08-31 | 2024-06-11 | 住友化学株式会社 | Positive electrode active material |
| WO2024047854A1 (en) * | 2022-09-01 | 2024-03-07 | ビークルエナジージャパン株式会社 | Lithium ion secondary battery positive electrode and lithium ion secondary battery |
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