JP5055702B2 - Positive electrode active material and manufacturing method thereof - Google Patents
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Description
本発明は、正極活物質及びその製造方法に関する。 The present invention relates to a positive electrode active material and a method for producing the same.
リチウム二次電池に代表される非水系電解質電池は、高いエネルギー密度を有することから小型携帯端末や移動体通信装置等への電源として広く使用されている。一般的なリチウムイオン電池は、充放電に伴いリチウムイオンを放出・吸蔵しうる正極活物質を備えた正極と、充放電に伴いリチウムイオンを吸蔵・放出しうる負極と、溶質としてリチウム塩が非水溶媒に溶解している非水電解質を備えている。 Non-aqueous electrolyte batteries represented by lithium secondary batteries are widely used as a power source for small portable terminals and mobile communication devices because of their high energy density. A typical lithium ion battery includes a positive electrode having a positive electrode active material capable of releasing and storing lithium ions upon charging and discharging, a negative electrode capable of storing and releasing lithium ions upon charging and discharging, and a lithium salt as a solute. A non-aqueous electrolyte dissolved in an aqueous solvent is provided.
現在、リチウム二次電池の正極活物質には、層状構造を有するＬｉＭＯ2（Ｍは遷移金属元素）で表される組成のリチウム含有遷移金属酸化物、スピネル構造を有するＬｉＭ2Ｏ4（Ｍは遷移金属元素）で表される組成のリチウム含有遷移金属酸化物、ＬｉＭＰＯ4（Ｍは遷移金属元素）で表される組成のリチウム含有遷移金属ポリリン酸化合物等が知られている。とりわけ層状構造を有するＬｉＭＯ2型リチウム含有遷移金属酸化物であるＬｉＣｏＯ2は高いエネルギー密度を示すことから携帯通信機器用の非水系電解質電池用正極活物質材料として広く使用されている。 At present, the positive electrode active material of a lithium secondary battery includes a lithium-containing transition metal oxide having a composition represented by LiMO 2 (M is a transition metal element) having a layered structure, and LiM 2 O 4 (M is a spinel structure). A lithium-containing transition metal oxide having a composition represented by (transition metal element), a lithium-containing transition metal polyphosphate compound having a composition represented by LiMPO 4 (M is a transition metal element), and the like are known. In particular, LiCoO 2 , which is a LiMO 2 type lithium-containing transition metal oxide having a layered structure, is widely used as a positive electrode active material for non-aqueous electrolyte batteries for portable communication devices because of its high energy density.
近年、原料コスト低減や特性向上を目的として、ＬｉＣｏＯ2に対して、Ｃｏの一部をＮｉやＭｎで置換した構造のリチウム含有遷移金属酸化物についても広く検討されている。特に、Ｃｏの一部をＮｉ及びＭｎで置換した構造のリチウム含有遷移金属酸化物について、充電時の熱安定性に優れる系が紹介されている（例えば非特許文献１，２、特許文献１，３〜６参照）。 In recent years, lithium-containing transition metal oxides having a structure in which part of Co is substituted with Ni or Mn for LiCoO 2 have been widely studied for the purpose of reducing raw material costs and improving characteristics. In particular, systems having excellent thermal stability during charging have been introduced for lithium-containing transition metal oxides having a structure in which a part of Co is substituted with Ni and Mn (for example, Non-patent Documents 1 and 2, Patent Document 1). 3-6).
一方、活物質の表面を異種元素で改質して性能を改善する試みも各種提案されている。特許文献７〜１０には、活物質の表面をアルミニウムで被覆することで電子伝導度が向上することが記載されている。しかしながら、この方法によれば確かに粒子表面の電子伝導性は向上するものの正極場での電解質の酸化分解を抑制する目的には不十分であった。 On the other hand, various attempts have been proposed to improve the performance by modifying the surface of the active material with a different element. Patent Documents 7 to 10 describe that the electron conductivity is improved by coating the surface of the active material with aluminum. However, although this method certainly improves the electron conductivity of the particle surface, it is insufficient for the purpose of suppressing the oxidative decomposition of the electrolyte in the positive electrode field.
また、特許文献２には、Ｉｎ、Ｍｇ、Ａｌ、Ｂａ、Ｓｒ、Ｃａ、Ｚｎ、Ｓｎ、Ｂｉ、Ｃｅ、Ｙｂの金属導電層を母材粒子表面に形成した正極材料が記載されている。しかしながら、０価金属を表面に配置すると、サイクル性能が必ずしも良好なものとはならなかった。これは、充放電に伴う活物質粒子の膨張・収縮に対する金属導電層の追随が不充分であるためではないかと推察される。さらに、金属導電層を表面に形成させるには、同文献の実施例記載のように還元雰囲気で処理を行う必要があり、このような雰囲気で処理を行うと、正極活物質からの酸素脱離等が起こり活物質の結晶構造の崩れが生じやすく、電池性能を低下させるといった問題点があった。また、特許文献１には、Ｌｉ−Ｍｎ−Ｎｉ−Ｃｏ系複合酸化物母材粒子の表面近傍に結晶構造を崩さない程度の微小量の異種元素（Ａｌ、Ｍｇ、Ｃａ、Ｓｒ、Ｙ、Ｙｂ）をドープすることにより、耐熱性や電子伝導性を上げる試みがなされている。ここに開示された異種元素の付与方法は、共沈で得られた遷移金属酸化物及び水酸化リチウムと共に焼成するときに適量の水酸化アルミニウムなどのアルミニウム源を同時に混合することにより、アルミニウムは正極活物質の表面近傍のみにドープされるというものである（同文献段落００３７参照）。しかしながら、本発明者らの検討によれば、この技術を用いても、正極場での電解質の酸化分解を抑制するには不十分であった。
非水電解質電池は、充電状態で長時間放置されると、放電性能等電池としての特性を悪化させるという問題があった。特に、充放電を多数回繰り返した非水電解質電池に対して充電状態での長時間放置を行うと、特性の悪化は特に顕著に認められた。この原因について本発明者らが解析したところ、特性が悪化した非水系電解質電池では、炭素材料を用いた負極の作動電位領域が上昇していることが見いだされた。このことから、本発明者らは、特性悪化の原因を次のように推察した。即ち、正極にかかる電位によって正極近傍の電解質が分解して炭酸根を主とする分解生成物が発生し、これが負極側に泳動することで負極表面に炭酸根を主とする被膜が生成し、負極インピーダンスを上昇させる。すると、実質的に負極電位が上昇することによって、負極の作動電位領域が高電位側にシフトし、これに伴い、正極の作動電位領域が高電位側にシフトする。このため、正極にはより高電位がかかることになり、上記現象がより加速され、より電池特性を悪化させる。 When the nonaqueous electrolyte battery is left in a charged state for a long time, there is a problem that the characteristics as a battery such as discharge performance are deteriorated. In particular, when the nonaqueous electrolyte battery that was repeatedly charged and discharged many times was left in the charged state for a long time, the deterioration of the characteristics was particularly noticeable. When the present inventors analyzed this cause, it was found that in the non-aqueous electrolyte battery having deteriorated characteristics, the working potential region of the negative electrode using the carbon material was increased. From this, the present inventors inferred the cause of the characteristic deterioration as follows. That is, the electrolyte in the vicinity of the positive electrode is decomposed by the potential applied to the positive electrode to generate a decomposition product mainly containing carbonate radicals, and this migrates to the negative electrode side to produce a film mainly containing carbonate radicals on the negative electrode surface. Increase negative impedance. Then, when the negative electrode potential substantially increases, the negative working potential region shifts to the high potential side, and accordingly, the positive working potential region shifts to the high potential side. For this reason, a higher potential is applied to the positive electrode, the above phenomenon is further accelerated, and the battery characteristics are further deteriorated.
本発明の課題は、上記問題点に鑑み、充電電位で長時間放置されても性能劣化の小さい正極活物質とその製造方法を提供すること、充電状態で長時間放置されても容量低下の小さい電池とすることのできる正極を提供すること、充電状態で長時間放置されても容量低下の小さい電池を提供することにある。
なお、本発明者らは、上記課題を解決する目的で、水中に母材粒子を分散し、３族元素化合物の水溶液を滴下する方法により、リチウムイオンを吸蔵および放出し得る母材粒子の電解質と接触し得る部分の少なくとも一部の上に周期律表の３族の元素が存在する正極活物質を作製した。この方法の詳細は「比較例２」として本願明細書中に記載した。この方法によっても、充電状態で長時間放置されても容量低下の小さい電池とすることのできる正極活物質を提供することができたものの、電池の初期放電容量が低下してしまうといった問題点があった。本発明は、かかる課題をも解決しようとするものである。
In view of the above problems, an object of the present invention is to provide a positive electrode active material having a small performance deterioration even when left at a charging potential for a long time, and a method for manufacturing the same. An object of the present invention is to provide a positive electrode that can be used as a battery, and to provide a battery with a small capacity drop even when left in a charged state for a long time.
In order to solve the above-mentioned problems, the inventors of the present invention have disclosed a matrix particle electrolyte that can occlude and release lithium ions by a method in which matrix particles are dispersed in water and an aqueous solution of a Group 3 element compound is dropped. A positive electrode active material in which a group 3 element of the periodic table is present on at least a part of a portion that can come into contact with the cathode was prepared. Details of this method are described in the present specification as “Comparative Example 2”. Although this method can provide a positive electrode active material that can be a battery with a small capacity drop even when left in a charged state for a long time, there is a problem that the initial discharge capacity of the battery is reduced. there were. The present invention is also intended to solve such a problem.
本発明の技術的構成および作用効果は以下の通りである。ただし、作用機構については推定を含んでおり、その作用機構の正否は本発明を制限するものではない。
（１） リチウムを含有しかつリチウムイオンを吸蔵および放出し得る母材粒子の上に、元素Ａの化合物粒子（但し、Ａは周期律表の３族の元素）が配されている正極活物質である。
（２） 前記元素Ａの化合物粒子は前記母材粒子の上に点在して配されている（１）項記載の正極活物質。
（３） 前記母材粒子の上に配されている前記元素Ａの化合物粒子の最大粒径は、該化合物粒子が配されている前記母材粒子の粒径の０．０１倍以上０．１倍以下である（１）項又は（２）項記載の正極活物質。
（４） 前記元素Ａの化合物は、前記母材粒子の重量に対して、元素Ａの酸化物換算で０．５重量％以上５重量％以下配されている（１）項〜（３）項のいずれかに記載の正極活物質。
（５） 前記母材粒子は、α−ＮａＦｅＯ2型結晶構造を有するリチウム含有遷移金属酸化物からなる（１）項〜（４）項のいずれかに記載の正極活物質。
（６） 前記母材粒子は、α−ＮａＦｅＯ2型結晶構造を有し、組成式ＬｉxＭｎaＮｉbＣｏcＯd（但し、０≦ｘ≦１．３、ａ＋ｂ＋ｃ＝１、｜ａ−ｂ｜≦０．０３、０≦ｃ＜１、１．７≦ｄ≦２．３）で表されるリチウム含有遷移金属酸化物からなる（１）項〜（５）項のいずれかに記載の正極活物質。
（７） リチウムを含有しかつリチウムイオンを吸蔵および放出し得る母材粒子と、元素Ａの化合物（但し、Ａは周期律表の３族の元素）粒子とを混合し、熱処理を行うことにより、前記母材粒子の上に元素Ａが存在し得るように元素Ａを付与する正極活物質の製造方法。
（８） 前記元素Ａの化合物粒子の平均粒径は、前記母材粒子の平均粒径の０．０１倍以上０．１倍以下である（７）項記載の正極活物質の製造方法。
（９） 前記母材粒子１００重量部に対して、前記元素Ａの化合物粒子を１重量部以上５重量部以下混合する（７）項又は（８）項記載の正極活物質の製造方法。
（１０） 前記熱処理の温度は９００℃以上である（７）項〜（９）項のいずれかに記載の正極活物質の製造方法。
（１１） 前記母材粒子は、α−ＮａＦｅＯ2型結晶構造を有するリチウム含有遷移金属酸化物の粒子である（７）項〜（１０）項のいずれかに記載の正極活物質の製造方法。
（１２） 前記母材粒子は、α−ＮａＦｅＯ2型結晶構造を有し、組成式ＬｉxＭｎaＮｉbＣｏcＯd（但し、０≦ｘ≦１．３、ａ＋ｂ＋ｃ＝１、｜ａ−ｂ｜≦０．０３、０≦ｃ＜１、１．７≦ｄ≦２．３）で表されるリチウム含有遷移金属酸化物の粒子である（７）項〜（１１）項のいずれかに記載の正極活物質の製造方法。
（１３） （７）項〜（１２）項のいずれかに記載の正極活物質の製造方法によって製造された正極活物質。
（１４） （１）項〜（６）項のいずれか又は（１３）項に記載の正極活物質を備えた正極。
（１５） （１４）項記載の正極を備えた電池。
The technical configuration and operational effects of the present invention are as follows. However, the action mechanism includes estimation, and the correctness of the action mechanism does not limit the present invention.
(1) Cathode active material in which compound particles of element A (where A is a group 3 element of the periodic table) are arranged on base material particles containing lithium and capable of occluding and releasing lithium ions It is.
(2) The positive electrode active material according to (1), wherein the compound particles of the element A are interspersed on the base material particles.
(3) The maximum particle size of the compound particle of the element A arranged on the base material particle is 0.01 times or more of the particle size of the base material particle on which the compound particle is arranged. The positive electrode active material according to the item (1) or (2), which is twice or less.
(4) Item (1) to (3), wherein the compound of element A is arranged in an amount of 0.5 wt% or more and 5 wt% or less in terms of oxide of element A with respect to the weight of the base material particles. The positive electrode active material in any one of.
(5) The positive electrode active material according to any one of (1) to (4), wherein the base material particle is made of a lithium-containing transition metal oxide having an α-NaFeO 2 type crystal structure.
(6) The base material particle has an α-NaFeO 2 type crystal structure and has a composition formula Li x Mn a Ni b Co c O d (where 0 ≦ x ≦ 1.3, a + b + c = 1, | a− b | ≦ 0.03, 0 ≦ c <1, 1.7 ≦ d ≦ 2.3), which is composed of a lithium-containing transition metal oxide represented by any one of items (1) to (5) Positive electrode active material.
(7) By mixing base material particles containing lithium and capable of occluding and releasing lithium ions, and compound of element A (where A is a group 3 element in the periodic table), heat treatment is performed. A method for producing a positive electrode active material, wherein the element A is provided so that the element A can be present on the base material particles.
(8) The method for producing a positive electrode active material according to (7), wherein the average particle diameter of the compound particles of the element A is 0.01 times or more and 0.1 times or less of the average particle diameter of the base material particles.
(9) The method for producing a positive electrode active material according to (7) or (8), wherein 1 to 5 parts by weight of the compound particles of the element A are mixed with 100 parts by weight of the base material particles.
(10) The method for producing a positive electrode active material according to any one of (7) to (9), wherein the temperature of the heat treatment is 900 ° C. or higher.
(11) The method for producing a positive electrode active material according to any one of (7) to (10), wherein the base material particles are particles of a lithium-containing transition metal oxide having an α-NaFeO 2 type crystal structure.
(12) The base material particle has an α-NaFeO 2 type crystal structure and has a composition formula Li x Mn a Ni b Co c O d (where 0 ≦ x ≦ 1.3, a + b + c = 1, | a− b | ≦ 0.03, 0 ≦ c <1, 1.7 ≦ d ≦ 2.3), which is a lithium-containing transition metal oxide particle, The manufacturing method of the positive electrode active material of description.
(13) A positive electrode active material produced by the method for producing a positive electrode active material according to any one of items (7) to (12).
(14) A positive electrode comprising the positive electrode active material according to any one of items (1) to (6) or (13).
(15) A battery comprising the positive electrode according to (14).
上記（１）項において、母材粒子とは、元素Ａの化合物粒子が配されることがなくても、リチウムを含有しかつリチウムイオンを吸蔵および放出し得る粒子である。ここで、元素Ａは周期律表の３族の元素であれば特に限定されないが、Ｙｂ（イットリビウム）又はＣｅ（セリウム）が特に好ましい。 In the above item (1), the base material particle is a particle that contains lithium and can occlude and release lithium ions without the compound particles of the element A being disposed. Here, the element A is not particularly limited as long as it is a group 3 element in the periodic table, but Yb (yttrium) or Ce (cerium) is particularly preferable.
上記（２）項において、「前記元素Ａの化合物粒子は前記母材粒子の上に点在して配されている」とは、前記元素Ａの化合物粒子が配されている一個の母材粒子を観察したとき、前記元素Ａの化合物粒子は該一個の母材粒子の上に点在して配されているように見えることをいう。この様子は、後述するように、走査型電子顕微鏡（ＳＥＭ）観察によって確認することができる。ここで、「一個の」母材粒子とは、リチウムを含有しかつリチウムイオンを吸蔵および放出し得る材料（母材）の最小単位粒子をいう。但し、一般的な「リチウムを含有しかつリチウムイオンを吸蔵および放出し得る材料」においては、前記最小単位粒子は、複数の一次粒子が集合したような二次粒子形態を呈していることが多い。ここで、「複数の一次粒子が集合したような二次粒子形態を呈している」との表現は、母剤粒子の生成過程を限定するものではない。例えば前記母材粒子がα−ＮａＦｅＯ2型結晶構造を有するリチウム含有遷移金属酸化物からなる場合には、該母材粒子はちょうど複数の一次粒子が集合したような二次粒子形態を呈しているのが一般的である。しかしながら、該母材粒子は、実際には元々独立していた一次粒子同士が凝集して形成されたものではない。遷移金属化合物とリチウム化合物を混合して熱処理を経てリチウム含有遷移金属酸化物が生成する過程において、前記遷移金属化合物の粒子が結晶成長してリチウム含有遷移金属酸化物に変化するが、このときの生成したリチウム含有遷移金属酸化物の結晶粒子形態がちょうどあたかも複数の一次粒子が寄り集まってできたかのような形態にみえることから、「複数の一次粒子が集合したような二次粒子形態を呈している」と表現したにすぎない。従って、このような材料の場合、前記「一個の」粒子は、「複数の一次粒子が集合した二次粒子形態を呈している一個の粒子」に相当する。 In the above item (2), “the compound particles of the element A are scattered on the base material particles” means that one base material particle in which the compound particles of the element A are disposed Is observed, the compound particles of the element A appear to be scattered on the single base material particle. This state can be confirmed by observation with a scanning electron microscope (SEM), as will be described later. Here, the “single” matrix particle refers to a minimum unit particle of a material (matrix) containing lithium and capable of inserting and extracting lithium ions. However, in a general “material containing lithium and capable of occluding and releasing lithium ions”, the minimum unit particle often has a secondary particle form in which a plurality of primary particles are aggregated. . Here, the expression “presenting a secondary particle form in which a plurality of primary particles are aggregated” does not limit the generation process of the matrix particles. For example, when the base material particle is made of a lithium-containing transition metal oxide having an α-NaFeO 2 type crystal structure, the base material particle has a secondary particle form in which a plurality of primary particles are aggregated. It is common. However, the base material particles are not actually formed by aggregation of primary particles that were originally independent. In the process of producing a lithium-containing transition metal oxide by mixing a transition metal compound and a lithium compound through heat treatment, the transition metal compound particles grow into crystals and change to a lithium-containing transition metal oxide. Since the crystal particle morphology of the generated lithium-containing transition metal oxide appears to be just as if a plurality of primary particles were gathered together, “a secondary particle morphology as if a plurality of primary particles were aggregated was exhibited. I just expressed. " Therefore, in the case of such a material, the “single particle” corresponds to “a single particle having a secondary particle form in which a plurality of primary particles are aggregated”.
上記（３）項において、「前記母材粒子の上に配されている前記元素Ａの化合物粒子の最大粒径は、該化合物粒子が配されている前記母材粒子の粒径の０．０１倍以上０．１倍以下である」と記載したように、本発明に係る正極活物質は、走査型電子顕微鏡（ＳＥＭ）等によって粒子を観察したとき、母材粒子と前記元素Ａの化合物粒子とが独立して観察されるといった特徴がある。この観察像は、大きな粒子の上に小さな粒子を載置したように見える。したがって、前記観察結果から、前記元素Ａは、母材粒子の内部あるいは表面近傍にドープされているのではないことが強く示唆される。一方、本発明者らの検討によれば、引用文献１記載の方法に倣って正極活物質を作製した場合、即ち、共沈で得られた遷移金属酸化物及び水酸化リチウムと共に焼成してリチウム含有遷移金属酸化物を得る際に前記元素Ａの化合物を混合しておくことによって得られた正極活物質のＳＥＭ像は、前記元素Ａの化合物を混合しないで焼成して得られたリチウム含有遷移金属酸化物からなる正極活物質（前記母材粒子に相当）と見分けがつかなかったことから、引用文献１記載の方法によれば、同文献の段落００３７にも記載されている通り、元素Ａはリチウム含有遷移金属酸化物粒子の上にではなく、リチウム含有遷移金属酸化物の結晶格子内にドープされていることが推察された。なお、前記母材粒子の上に配されている前記元素Ａの化合物粒子は、充分に小さくても本発明の効果が奏されるが、その最大粒径が、該化合物粒子が配されている前記母材粒子の粒径の０．０１倍以上であることによって、ＳＥＭ観察やＥＰＭＡ測定等によって本発明の適用を確認することが容易となる。また、０．１倍以下であることによって、前記元素Ａの化合物が物理的に母材粒子の表面を大きく覆い電池内で電解液との接触を阻害する虞が低減できるほか、電極のエネルギー密度を低下させる虞を低減できるため、好ましい。 In the above item (3), “the maximum particle size of the element A compound particles arranged on the matrix particles is 0.01% of the particle size of the matrix particles on which the compound particles are arranged. As described above, the positive electrode active material according to the present invention can be obtained by observing particles with a scanning electron microscope (SEM) or the like, and base material particles and compound particles of the element A. And are observed independently. This observation image looks like small particles placed on large particles. Therefore, the observation result strongly suggests that the element A is not doped inside or near the surface of the base material particle. On the other hand, according to the study by the present inventors, when a positive electrode active material was produced following the method described in Cited Document 1, that is, calcined with a transition metal oxide and lithium hydroxide obtained by coprecipitation, lithium The SEM image of the positive electrode active material obtained by mixing the compound of the element A when obtaining the contained transition metal oxide is a lithium-containing transition obtained by firing without mixing the compound of the element A Since it was indistinguishable from a positive electrode active material made of a metal oxide (corresponding to the base material particle), according to the method described in the cited document 1, as described in paragraph 0037 of the document, the element A It was speculated that is doped on the crystal lattice of the lithium-containing transition metal oxide, not on the lithium-containing transition metal oxide particles. Note that the effect of the present invention can be obtained even if the compound particles of the element A arranged on the base material particles are sufficiently small, but the maximum particle size of the compound particles is arranged. By being 0.01 times or more of the particle diameter of the base material particles, it becomes easy to confirm the application of the present invention by SEM observation, EPMA measurement or the like. Moreover, by being 0.1 times or less, the compound of the element A physically covers the surface of the base material particles, and the possibility of hindering contact with the electrolytic solution in the battery can be reduced. In addition, the energy density of the electrode This is preferable because the risk of lowering can be reduced.
上記（４）項に記載したように、前記元素Ａの化合物は、前記母材重量に対して、元素Ａの酸化物換算で０．５重量％以上配されていることによって、本発明の効果を十分に発揮させることができる点で好ましい。また、５重量％以下配されていることによって、電極のエネルギー密度を低下させる虞を低減できるため、好ましい。 As described in the above item (4), the compound of the element A is arranged in an amount of 0.5% by weight or more in terms of the oxide of the element A with respect to the base material weight. Is preferable in that it can be sufficiently exhibited. Further, it is preferable that the amount is 5% by weight or less because the risk of lowering the energy density of the electrode can be reduced.
上記（５）項に記載したように、前記母材粒子は、α−ＮａＦｅＯ2型結晶構造を有するリチウム含有遷移金属酸化物の粒子であるものから選択することにより、高い作動電位を有し繰り返し充放電性能にも優れた正極活物質並びに電池とすることができる点で好ましい。このような粒子としては、ＬｉＣｏＯ2粒子、ＬｉＮｉＯ2粒子等が挙げられる。 As described in the above section (5), the base material particles are selected from those containing lithium-containing transition metal oxides having an α-NaFeO 2 type crystal structure, so that they have a high working potential and are repeated. It is preferable at the point which can be set as the positive electrode active material and battery which were excellent also in charging / discharging performance. Examples of such particles include LiCoO 2 particles and LiNiO 2 particles.
上記（６）項に記載したように、なかでも、前記母材粒子は、α−ＮａＦｅＯ2型結晶構造を有し、組成式ＬｉxＭｎaＮｉbＣｏcＯd（但し、０≦ｘ≦１．３、ａ＋ｂ＋ｃ＝１、｜ａ−ｂ｜≦０．０３、０≦ｃ＜１、１．７≦ｄ≦２．３）で表されるリチウム含有遷移金属酸化物の粒子であるものとすることが好ましく、ｃ≠０であることにより本発明の効果が顕著に奏される。ｃの値は０．３付近でも良いが、０．６以上とすることで、長寿命でエネルギー密度が高く、高温熱安定性にも優れた電池を提供できる点で好ましい。ここで、前記母材粒子はＬｉ，Ｍｎ，Ｎｉ，Ｃｏ，Ｏ以外の元素を少量含んでいてもよく、そのようなものについても本発明の範囲内である。
上記（７）項において、元素Ａは周期律表の３族の元素であれば特に限定されないが、Ｙｂ（イットリビウム）又はＣｅ（セリウム）が特に好ましい。前記母材粒子と、元素Ａの化合物粒子とを混合し、熱処理を行うことにより、元素Ａの化合物粒子が前記母材粒子の上に固定される。前記熱処理によって元素Ａの化合物粒子が前記母材粒子の上に固定される機構については必ずしも明らかではないが、一種の「焼結」によるものと推察される。
As described in the above item (6), among these, the base material particles have an α-NaFeO 2 type crystal structure, and have a composition formula Li x Mna a Ni b Co c O d (where 0 ≦ x ≦ 1.3, a + b + c = 1, | a−b | ≦ 0.03, 0 ≦ c <1, 1.7 ≦ d ≦ 2.3) Preferably, the effect of the present invention is remarkably exhibited when c ≠ 0. The value of c may be around 0.3, but is preferably 0.6 or more in that a battery having a long life, high energy density, and excellent high-temperature thermal stability can be provided. Here, the base material particles may contain a small amount of elements other than Li, Mn, Ni, Co, and O, and such particles are also within the scope of the present invention.
In the above item (7), the element A is not particularly limited as long as it is a group 3 element in the periodic table, but Yb (yttrium) or Ce (cerium) is particularly preferable. The base material particles and element A compound particles are mixed and subjected to heat treatment, whereby the element A compound particles are fixed on the base material particles. The mechanism by which the compound particles of element A are fixed on the base material particles by the heat treatment is not necessarily clear, but is presumed to be due to a kind of “sintering”.
本発明の製造方法によれば、充電電位で長時間放置されても性能劣化の小さい正極活物質とその製造方法を提供することができる。また、充電状態で長時間放置されても容量低下の小さい電池とすることのできる正極を提供することができる。また、充電状態で長時間放置されても容量低下の小さい電池を提供することができる。 According to the production method of the present invention, it is possible to provide a positive electrode active material with little performance deterioration even when left at a charging potential for a long time, and a method for producing the same. In addition, it is possible to provide a positive electrode that can be a battery with a small capacity drop even when left in a charged state for a long time. Further, it is possible to provide a battery with a small capacity drop even when left in a charged state for a long time.
本発明に用いる母材粒子は、リチウムコバルト酸化物やリチウムニッケル酸化物等に代表される、α−ＮａＦｅＯ2型の層状結晶構造を有するリチウム遷移金属化合物が好ましい。なかでも、一般式ＬｉxＮｉaＭｎbＣｏcＯdで表され、ｘ、ａ、ｂ、ｃ、ｄが以下に示す関係式を満たす組成であることが好ましい。
０＜ｘ≦１．４
０≦ａ＜１．０
０≦ｂ＜０．６
０≦ｃ＜１
ａ＋ｂ＋ｃ＝１
１．７≦ｄ≦２．３
The base material particles used in the present invention are preferably lithium transition metal compounds having an α-NaFeO 2 type layered crystal structure typified by lithium cobalt oxide and lithium nickel oxide. Among them, it is represented by the general formula Li x Ni a Mn b Co c O d, x, a, b, c, is preferably d is a composition satisfying the relational expression shown below.
0 <x ≦ 1.4
0 ≦ a <1.0
0 ≦ b <0.6
0 ≦ c <1
a + b + c = 1
1.7 ≦ d ≦ 2.3
上記リチウム遷移金属化合物は、α−ＮａＦｅＯ2型層状構造を有するＬｉＮｉＯ2のＮｉサイトの一部をＭｎ、Ｃｏで置換した構造である。Ｎｉサイトの一部をＭｎ、Ｃｏで置換することにより、ＮｉとＭｎ、Ｃｏとの間で配位子である酸素イオンを介して共鳴安定化するため、ＬｉＮｉＯ2よりも熱的安定性が向上する。特に、本発明の課題のように長時間の充電状態に対応させようとする場合には、充電末状態の正極活物質の安定性は極めて重要であり、ＬｉＮｉＯ2よりも充電末安定性の高いＬｉ−Ｎｉ−Ｍｎ（−Ｃｏ）複合酸化物が好適に使用できる。 The lithium transition metal compound has a structure in which a part of the Ni site of LiNiO 2 having an α-NaFeO 2 type layered structure is substituted with Mn and Co. By substituting part of the Ni site with Mn and Co, resonance stabilization is achieved between Ni and Mn and Co via the oxygen ion that is a ligand, so thermal stability is improved over LiNiO 2. To do. In particular, when trying to cope with a long-time charged state as in the problem of the present invention, the stability of the positive electrode active material in the end-of-charge state is extremely important and has higher end-of-charge stability than LiNiO 2. Li—Ni—Mn (—Co) composite oxide can be preferably used.
ＬｉxＮｉaＭｎbＣｏcＯdを合成するに当たり、Ｍｎ量が多い場合、即ちｂ＞０．６の場合には、主に斜方晶のＬｉＭｎＯ2が生成してしまい、層状のα―ＮａＦｅＯ2型結晶構造を取ることができないので、ｂは０．６を超えることができない。従って、０≦ｂ＜０．６が好ましい。特に本発明のような常時高電圧で使用する電池に用いる場合には、ｂの値は０．５５未満がさらに好ましい。 In synthesizing Li x Ni a Mn b Co c O d , when the amount of Mn is large, that is, when b> 0.6, orthorhombic LiMnO 2 is mainly produced, and the layered α- Since the NaFeO 2 type crystal structure cannot be taken, b cannot exceed 0.6. Therefore, 0 ≦ b <0.6 is preferable. In particular, when used in a battery that is always used at a high voltage as in the present invention, the value of b is more preferably less than 0.55.
また、ＭｎがＮｉより多い（ａ／ｂ＞１）場合や、Ｎｉを含まない組成（ａ＝０）では、Ｌｉ2ＭｎＯ3のようなα―ＮａＦｅＯ2型ではない不純相が形成され、層状のα―ＮａＦｅＯ2型結晶構造と共存する。この不純相は４Ｖ領域での電極反応に供しないものであるため、この不純相を多く含むと活物質としての容量は減少し、充放電サイクル時にはこの不純相の存在による構造の不安定化により劣化速度が速くなる。従って、ａ／ｂ≦１、ａ＞０とすることが好ましい。 In addition, when Mn is larger than Ni (a / b> 1) or when the composition does not contain Ni (a = 0), an impure phase that is not α-NaFeO 2 type such as Li 2 MnO 3 is formed, and a layered state is formed. Co-exist with the α-NaFeO 2 type crystal structure. Since this impure phase is not subjected to an electrode reaction in the 4 V region, the capacity as the active material is reduced when a large amount of this impure phase is contained, and the structure is unstable due to the presence of this impure phase during the charge / discharge cycle. Deterioration speed increases. Therefore, it is preferable that a / b ≦ 1 and a> 0.
一方、上記したＬｉ2ＭｎＯ3のような不純相の形成は、焼成時にＬｉをやや過剰に仕込むこと、すなわち、組成中のＬｉ比を１．０＜ｘとすることで抑制することができる。これはＬｉを過剰にするとＬｉが遷移金属サイトに入り込むことで不純相の形成を阻害し、構造を安定化させているものと思われる。 On the other hand, the formation of an impure phase such as Li 2 MnO 3 described above can be suppressed by charging Li slightly slightly during firing, that is, by setting the Li ratio in the composition to 1.0 <x. This is presumably because when Li is excessive, Li enters the transition metal site to inhibit the formation of an impure phase and stabilize the structure.
特に、Ｍｎ組成比率（ｂの値）を高い（例えば０．５５≦ｂ≦０．６０）ものとする場合には、ｘの値を１．３〜１．４とすることで、Ｌｉ2ＭｎＯ3の生成を抑え構造を安定化させる効果を有効に発揮でき、特に、本発明の課題である長時間の充電状態に対応させようとする場合には、ｘの値を１．３〜１．４とすることによる構造安定化の効果を有効に享受できる。従って、組成中のＬｉ比を１．０＜ｘ≦１．４とすることが好ましい。 In particular, when the Mn composition ratio (value of b) is high (for example, 0.55 ≦ b ≦ 0.60), by setting the value of x to 1.3 to 1.4, Li 2 MnO 3 can be effectively exhibited and the structure can be effectively stabilized. In particular, when trying to cope with the long-time charged state, which is the subject of the present invention, the value of x is set to 1.3 to 1. It is possible to effectively enjoy the effect of stabilizing the structure. Therefore, the Li ratio in the composition is preferably 1.0 <x ≦ 1.4.
リチウムコバルト酸化物では、正極電位が４．５Ｖを越えたあたりから結晶構造が六方晶から単斜晶へと変化すると伴に酸素層間が開きすぎることでＬｉイオンの静電トラップ効果が働き結晶内のＬｉイオン拡散が阻害され、放電時の高率放電が悪くなると言われている。また、同時に充放電効率やサイクル性能が極端に悪くなるためリチウムコバルト酸化物を正極活物質に使用した電池の高電圧使用は好ましくない。この観点から、Ｃｏ組成比率（ｃの値）は１でも良いが、ｃ＜１とすることが好ましく、なかでもｃ≦０．８４とすることで母材粒子の構造安定性が飛躍的に向上するので、本発明に適用すると高性能な非水系電解質電池用正極活物質が得られる。Ｍｎ、Ｎｉの比については、１：１に近い組成（｜ａ−ｂ｜＜０．０３）の活物質とすることで最も構造が安定し、充放電サイクル性能に優れた正極活物質となるので、最も好ましい。 In lithium cobalt oxide, when the positive electrode potential exceeds 4.5V, the crystal structure changes from hexagonal to monoclinic, and the oxygen layer opens too much, thereby causing an electrostatic trapping effect of Li ions. Li ion diffusion is inhibited, and it is said that high-rate discharge during discharge deteriorates. At the same time, the charge / discharge efficiency and the cycle performance are extremely deteriorated, so it is not preferable to use a high voltage battery using lithium cobalt oxide as the positive electrode active material. From this point of view, the Co composition ratio (value of c) may be 1. However, it is preferable that c <1, and in particular, the structural stability of the base material particles is dramatically improved by setting c ≦ 0.84. Therefore, when applied to the present invention, a high-performance positive electrode active material for a non-aqueous electrolyte battery can be obtained. With regard to the ratio of Mn and Ni, by using an active material having a composition close to 1: 1 (| ab− <0.03), the structure is most stable, and a positive electrode active material having excellent charge / discharge cycle performance is obtained. So most preferred.
リチウムニッケルマンガンコバルト複合酸化物を合成するにあたっては、Ｌｉがα−ＮａＦｅＯ2構造の６ａサイトに、Ｃｏ、ＭｎおよびＮｉが６ｂサイトに、そしてＯが６ｃサイトにそれぞれ過不足なく占有されるならば、製造方法は特に限定されるものではない。現実的には、Ｌｉ化合物、Ｍｎ化合物、Ｎｉ化合物およびＣｏ化合物を粉砕・混合し、熱的に分解混合させる方法、沈殿反応させる方法、または加水分解させる方法によって好適に合成することが可能である。なかでも、ＭｎとＮｉとＣｏとの複合沈殿化合物（以下「前駆体」ともいう）とＬｉ化合物とを原料とし、それらを混合・熱処理する方法が均一な母材粒子を合成する上で好ましい。 In the synthesis of the lithium nickel manganese cobalt composite oxide, if Li is occupied in the 6a site of the α-NaFeO 2 structure, Co, Mn and Ni are occupied in the 6b site, and O is occupied in the 6c site without excess or deficiency. The production method is not particularly limited. Actually, it can be suitably synthesized by a method in which Li compound, Mn compound, Ni compound, and Co compound are pulverized and mixed, thermally decomposed and mixed, precipitated, or hydrolyzed. . In particular, a method of mixing and heat-treating a composite precipitation compound of Mn, Ni and Co (hereinafter also referred to as “precursor”) and a Li compound as raw materials is preferable for synthesizing uniform base material particles.
前記前駆体は、ＭｎとＮｉとＣｏとが均一に混合された化合物であることが好ましい。この条件を満たす限りにおいては、前記Ｍｎ−Ｎｉ−Ｃｏ混合物前駆体の製法は特に限定されないが、本発明に係るリチウムニッケルマンガンコバルト複合酸化物の元素の構成範囲では、Ｌｉの脱離・挿入による結晶構造の安定性が高いことが要求されるため、「Ｍｎ、ＮｉおよびＣｏの酸性水溶液を水酸化ナトリウム水溶液等のアルカリ水溶液で沈澱させる共沈製法」を採用してもよく、この方法により作製された前駆体を用いれば、とりわけ高い電池性能を示す正極活物質を作製することができる。このとき、これらＭｎ、ＮｉおよびＣｏの金属イオン量に対して、反応系内のアンモニウムイオン量を過剰量とした条件下で結晶成長の核を発生させると、極めて均質で嵩高い前駆体粒子の作製が可能となり、好ましい。アンモニウムイオンが存在しないと、これらの金属イオンが酸−塩基反応によって急速に沈殿形成するため、結晶配向が無秩序となって嵩密度の低い沈殿が形成されるので好ましくない。アンモニウムイオンが存在することにより、前記沈殿反応速度が金属−アンミン錯体形成反応を経由することで緩和され、結晶配向性がよく、嵩高くて一次粒子結晶の発達した沈殿を作製することが可能となるので好ましい。また、反応器形状や回転翼の種類といった装置因子や、反応槽内に沈殿物が滞在する時間、反応槽温度、総イオン量、液ｐＨ、アンモニアイオン濃度、酸化数調整剤の濃度などの諸因子を選択することで、前記共沈化合物の粒子形状や嵩密度、表面積などの物性を制御することも可能となる。 The precursor is preferably a compound in which Mn, Ni, and Co are uniformly mixed. As long as this condition is satisfied, the method for producing the Mn—Ni—Co mixture precursor is not particularly limited. However, in the constituent range of the elements of the lithium nickel manganese cobalt composite oxide according to the present invention, Li desorption / insertion is performed. Since the crystal structure is required to have high stability, the “coprecipitation method in which an acidic aqueous solution of Mn, Ni and Co is precipitated with an alkaline aqueous solution such as an aqueous sodium hydroxide solution” may be employed. By using the prepared precursor, a positive electrode active material exhibiting particularly high battery performance can be produced. At this time, if the nucleus of crystal growth is generated under the condition that the amount of ammonium ions in the reaction system is excessive with respect to the amount of metal ions of Mn, Ni, and Co, extremely homogeneous and bulky precursor particles It is possible to manufacture and is preferable. In the absence of ammonium ions, these metal ions are rapidly precipitated by an acid-base reaction, which is undesirable because the crystal orientation is disordered and precipitates with low bulk density are formed. Due to the presence of ammonium ions, the precipitation reaction rate is relaxed by going through a metal-ammine complex formation reaction, and it is possible to produce a precipitate with good crystal orientation, bulky and developed primary particle crystals. This is preferable. Also, various factors such as equipment factors such as reactor shape and type of rotor blades, time for sediment to stay in the reaction tank, reaction tank temperature, total ion amount, liquid pH, ammonia ion concentration, concentration of oxidation number regulator, etc. By selecting a factor, it becomes possible to control physical properties such as particle shape, bulk density, and surface area of the coprecipitation compound.
前記Ｍｎ−Ｎｉ−Ｃｏ混合物前駆体の原料は、Ｍｎ化合物としては酸化マンガン、炭酸マンガン、硫酸マンガン、硝酸マンガン等を、Ｎｉ化合物としては、水酸化ニッケル、炭酸ニッケル、硫酸ニッケル、硝酸ニッケル等を、Ｃｏ化合物としては、硫酸コバルト、硝酸コバルト等を、アンモニウム源としては、硫酸アンモニウム、アンモニア水等を一例として挙げることができる。 The raw material of the Mn-Ni-Co mixture precursor is manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, etc. as the Mn compound, and nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, etc. as the Ni compound. Examples of the Co compound include cobalt sulfate and cobalt nitrate, and examples of the ammonium source include ammonium sulfate and aqueous ammonia.
前記Ｍｎ−Ｎｉ−Ｃｏ混合物前駆体の作製に用いる原料としては、アルカリ水溶液と沈殿反応を形成するものであればどのような形態のものでも使用することができるが、好ましくは溶解度の高い金属塩を用いるとよい。この場合、Ｍｎは複数の酸化数をとりうるが、沈殿形成時は２価の状態で結晶内に取り込まれることが好ましい。沈殿形成時にマンガンが酸化されると、結晶内に水が取り込まれやすくなり、焼結工程で不純相が生成する可能性がある。前記不純相としてはＬｉＭｎ2Ｏ3が挙げられ、該ＬｉＭｎ2Ｏ3は活物質としては４Ｖ付において電気的に不活性であり、容量低下の要因となる。この問題を解決する手段として、反応溶液へヒドラジン等の還元剤を入れたり、反応容器内を不活性ガスで満たして、酸素を取り除いたりする方法が採られる。なお、水酸化物の共存下で沈澱形成を行った場合、その形態は水酸化物が主たる生成物となるが、Ｍｎなどは沈殿前駆体の乾燥工程で酸化物の形態となることもある。 As a raw material used for the preparation of the Mn—Ni—Co mixture precursor, any material can be used as long as it forms a precipitation reaction with an alkaline aqueous solution, but preferably a highly soluble metal salt. Should be used. In this case, although Mn can take a plurality of oxidation numbers, it is preferably taken into the crystal in a divalent state at the time of precipitation formation. If manganese is oxidized during the formation of the precipitate, water is easily taken into the crystal, and an impure phase may be generated in the sintering process. Examples of the impure phase include LiMn 2 O 3 , and the LiMn 2 O 3 is electrically inactive at 4 V as an active material, which causes a decrease in capacity. As a means for solving this problem, a method of putting a reducing agent such as hydrazine into the reaction solution or filling the reaction vessel with an inert gas to remove oxygen is adopted. In addition, when precipitation is formed in the presence of hydroxide, the form is the main product of hydroxide, but Mn and the like may be in the form of oxide in the drying step of the precipitation precursor.
このようにして作製したＭｎ−Ｎｉ−Ｃｏ混合物前駆体とＬｉ化合物とを混合し、熱処理することにより、本発明に係る母剤粒子として好ましいリチウムニッケルマンガンコバルト複合酸化物を好適に作製することができる。前記Ｌｉ化合物としては、水酸化リチウム、炭酸リチウムを用いることで好適に製造することができる。 By mixing the Mn—Ni—Co mixture precursor thus prepared and the Li compound and performing a heat treatment, it is possible to suitably produce a lithium nickel manganese cobalt composite oxide that is preferable as the base particle according to the present invention. it can. As said Li compound, it can manufacture suitably by using lithium hydroxide and lithium carbonate.
この時の熱処理条件としては、酸素雰囲気下、７００℃以上１０００℃以下の温度範囲を採用すれば好適に製造することができる。前記熱処理温度が７００℃を下回ると、固相反応が進行せず、また、１０００℃より高いと固相反応が過度に進行する結果、極度に焼結化が進行するので好ましくない。８００℃以上１０００℃以下の温度範囲であれば高い性能を有するリチウムニッケルマンガンコバルト複合酸化物を得ることができるのでより好ましい。 As a heat treatment condition at this time, it can be suitably manufactured by adopting a temperature range of 700 ° C. or higher and 1000 ° C. or lower in an oxygen atmosphere. If the heat treatment temperature is lower than 700 ° C., the solid phase reaction does not proceed, and if it is higher than 1000 ° C., the solid phase reaction proceeds excessively, resulting in extreme progress of sintering. If it is the temperature range of 800 degreeC or more and 1000 degrees C or less, since the lithium nickel manganese cobalt complex oxide which has high performance can be obtained, it is more preferable.
本発明に係る正極活物質を製造するにあたっては、上記（７）項に記載したように、リチウムを含有しかつリチウムイオンを吸蔵および放出し得る母材粒子と、元素Ａのカルコゲン化合物（但し、Ａは周期律表の３族の元素）粒子とを混合し、熱処理を行うことにより、前記母材粒子の上に元素Ａが存在し得るように元素Ａを付与することができる。ここで用いる元素Ａの化合物としては、例えばＹｂ2Ｏ3やＣｅＯ2等を用いることができる。但し、０価金属を用い、母材粒子上に０価金属の状態で存在させようとすると、特許文献２にも記載されているように、不活性ガス等の還元雰囲気で熱処理を行う必要がある。ところが、還元雰囲気で熱処理を行うと、母材粒子を構成しているカルコゲン原子が熱処理の過程で脱落し易くなる。例えば、層状岩塩型結晶構造を有するＬｉxＭｎaＮｉbＣｏcＯ2組成で表される母材粒子の場合には、酸素原子が脱落して組成比の崩れを導き、その結果、正極活物質としての特性を著しく低下させる虞がある。従って、０価金属は好ましくない。これに対し、母材粒子上に存在させる元素Ａの化合物が酸化物である場合には、還元雰囲気で熱処理を行う必要がないのでこのような問題がない。従って、元素Ａの化合物は酸化物が好ましい。 In producing the positive electrode active material according to the present invention, as described in the above section (7), base material particles containing lithium and capable of occluding and releasing lithium ions, and a chalcogen compound of element A (however, The element A can be added so that the element A can be present on the base material particle by mixing A and particles and performing a heat treatment. For example, Yb 2 O 3 or CeO 2 can be used as the compound of element A used here. However, if a zero-valent metal is used and is allowed to exist in the state of a zero-valent metal on the base material particle, it is necessary to perform heat treatment in a reducing atmosphere such as an inert gas as described in Patent Document 2. is there. However, when heat treatment is performed in a reducing atmosphere, chalcogen atoms constituting the base material particles are likely to fall off during the heat treatment. For example, in the case of a base material particle having a layered rock salt type crystal structure and represented by a composition of Li x Mn a Ni b Co c O 2 , oxygen atoms are dropped off, leading to a collapse of the composition ratio. There is a possibility that the properties as a substance may be significantly reduced. Accordingly, zero-valent metals are not preferred. On the other hand, when the compound of element A present on the base material particles is an oxide, there is no such problem because it is not necessary to perform heat treatment in a reducing atmosphere. Therefore, the compound of element A is preferably an oxide.
前記母材粒子と元素Ａのカルコゲン化合物との混合にあたっては、両者を水または有機溶剤等の媒体で攪拌することによってもよいが、水の使用を避けることにより、母材粒子表面に水酸化物が形成され、正極活物質の電気抵抗を増大させる虞を避けることができるため、好ましい。また、乾式による混合を採用すれば、前記混合工程を簡略化できるため、好ましい。 In mixing the base particle and the chalcogen compound of element A, both may be stirred with a medium such as water or an organic solvent. However, by avoiding the use of water, a hydroxide is formed on the surface of the base particle. Is formed, and the possibility of increasing the electrical resistance of the positive electrode active material can be avoided. Moreover, it is preferable to employ dry mixing because the mixing step can be simplified.
本発明に係る前記熱処理の雰囲気としては特に限定されるものではなく、空気雰囲気とすれば製造コストを低減できる点で好ましい。 The atmosphere of the heat treatment according to the present invention is not particularly limited, and an air atmosphere is preferable in that the manufacturing cost can be reduced.
熱処理時間は、５時間以上１５時間以下とすることが好ましい。熱処理時間を５時間以上とすることにより、元素Ａの化合物粒子の母材粒子への付与が充分となる点で好ましく。１５時間以下とすることにより、該熱処理工程に係るコストを最小限とすることができる点で好ましい。 The heat treatment time is preferably 5 hours or more and 15 hours or less. By making the heat treatment time 5 hours or more, it is preferable in that the compound particles of the element A are sufficiently applied to the base material particles. By setting it as 15 hours or less, it is preferable at the point which can minimize the cost concerning this heat processing process.
上記（８）項に記載したように、前記元素Ａのカルコゲン化合物粒子の平均粒径は、前記母材粒子の平均粒径の０．０１倍以上０．１倍以下とすることが好ましい。０．０１倍以上とすることにより、前記母材粒子と前記元素Ａの化合物粒子を混合するときに粒子が細かすぎて舞い上がり作業性が低下する虞を軽減できる点で好ましい。また、０．１倍以下であることによって、前記元素Ａの化合物が物理的に母材粒子の表面を大きく覆い電池内で電解液との接触を阻害する虞が低減できるほか、電極のエネルギー密度を低下させる虞を低減できるため、好ましい。 As described in item (8) above, the average particle size of the chalcogen compound particles of the element A is preferably 0.01 to 0.1 times the average particle size of the base material particles. It is preferable that the ratio is 0.01 times or more in that the possibility that particles may be too fine to be lifted and workability may be reduced when the base material particles and the compound particles of the element A are mixed. Moreover, by being 0.1 times or less, the compound of the element A physically covers the surface of the base material particles, and the possibility of hindering contact with the electrolytic solution in the battery can be reduced. In addition, the energy density of the electrode This is preferable because the risk of lowering can be reduced.
前記母材粒子と元素Ａのカルコゲン化合物との混合比率は、上記（９）項に記載したように、前記母材粒子１００重量部に対して、前記元素Ａのカルコゲン化合物粒子を１重量部以上とすることによって、本発明の効果を十分に発揮させることができる点で好ましい。また、５重量部以下とすることによって、電極のエネルギー密度を低下させる虞を低減できるため、好ましい。 The mixing ratio of the base material particles and the chalcogen compound of element A is 1 part by weight or more of the chalcogen compound particles of element A with respect to 100 parts by weight of the base material particles as described in the above section (9). It is preferable in that the effects of the present invention can be sufficiently exhibited. Further, the content of 5 parts by weight or less is preferable because the risk of lowering the energy density of the electrode can be reduced.
前記熱処理の温度は、上記（１０）項に記載したように、化合物粒子の母材粒子への付与を充分とすることができるため、９００℃以上であることが好ましい。また、該熱処理温度は１１００℃以下とすることにより、母材粒子が酸素欠損を生じる虞を低減できるため、好ましい。 As described in the above item (10), the temperature of the heat treatment is preferably 900 ° C. or higher because the compound particles can be sufficiently applied to the base material particles. Further, it is preferable to set the heat treatment temperature to 1100 ° C. or lower because the possibility that the base material particles may cause oxygen deficiency can be reduced.
本発明の正極活物質を用いた正極は、前記正極活物質を主要構成成分とし、正極活物質を、導電剤および結着剤、さらに必要に応じてフィラーと混練して正極合剤とした後、この正極合剤を集電体としての箔やラス板等に塗布、または圧着して５０℃〜２５０℃程度の温度で、２時間程度加熱処理することにより好適に作製される。正極活物質の正極に対する含有量は、８０重量％〜９９重量％が好ましく、８５重量％〜９７重量％がより好ましい。 The positive electrode using the positive electrode active material of the present invention has the positive electrode active material as a main constituent, and the positive electrode active material is kneaded with a conductive agent and a binder, and further, if necessary, a filler to form a positive electrode mixture. The positive electrode mixture is applied to a foil, a lath plate or the like as a current collector, or press-bonded, and then heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. The content of the positive electrode active material with respect to the positive electrode is preferably 80% by weight to 99% by weight, and more preferably 85% by weight to 97% by weight.
なお、導電剤および結着剤、フィラー、集電体としては、当該技術分野において、自明のものを、自明の処方で用いることができる。 In addition, as a conductive agent, a binder, a filler, and a current collector, those that are obvious in the technical field can be used in obvious formulas.
上記正極を非水電解質電池に適用する場合には、正極と、負極と、非水系電解質とを具備し、一般的には、正極と負極との間に、非水系電解質電池用セパレータが設けられる。非水系電解質は、電解質塩が非水溶媒に含有されてなる形態を好適に例示できる。 When the positive electrode is applied to a non-aqueous electrolyte battery, the positive electrode includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. In general, a separator for a non-aqueous electrolyte battery is provided between the positive electrode and the negative electrode. . The non-aqueous electrolyte is preferably exemplified by a form in which an electrolyte salt is contained in a non-aqueous solvent.
非水系電解質、負極、セパレータとしては、一般にリチウム電池等への使用が提案されている自明のものを、自明の処方で使用可能である。ここで、前記非水電解質としては、液状電解質（電解液）、ゲル電解質、（無機、有機）固体電解質などを適宜選択して使用可能である。 As the non-aqueous electrolyte, the negative electrode, and the separator, obvious ones that are generally proposed for use in lithium batteries and the like can be used in obvious formulas. Here, as the non-aqueous electrolyte, a liquid electrolyte (electrolytic solution), a gel electrolyte, a (inorganic, organic) solid electrolyte, or the like can be appropriately selected and used.
非水電解質電池は、非水電解質を、例えば、セパレータと正極と負極とを積層する前または積層した後に注液し、最終的に、外装材で封止することによって好適に作製される。また、正極と負極とがセパレータを介して積層された発電要素を巻回してなる電池においては、非水電解質は、前記巻回の前後に発電要素に注液されるのが好ましい。注液法としては、常圧で注液することも可能であるが、真空含浸方法や加圧含浸方法も使用可能である。 The nonaqueous electrolyte battery is suitably produced by injecting a nonaqueous electrolyte, for example, before or after laminating the separator, the positive electrode, and the negative electrode, and finally sealing with a packaging material. Further, in a battery formed by winding a power generation element in which a positive electrode and a negative electrode are laminated via a separator, the nonaqueous electrolyte is preferably injected into the power generation element before and after the winding. As the injection method, it is possible to inject at normal pressure, but a vacuum impregnation method and a pressure impregnation method can also be used.
電池の外装体の材料としては、当該技術分野において、自明のものを、自明の処方で用いることができる。 As the material of the battery outer package, a material that is obvious in the technical field can be used in a self-evident formula.
以下に、実施例に基づき本発明をさらに詳細に説明するが、本発明は以下の記載により限定されるものではない。 Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following description.
５リットル密閉型反応槽に水を３．５リットル入れた。さらにｐＨ＝１１．６±０．１となるよう、３２％水酸化ナトリウム水溶液を加えた。パドルタイプの攪拌羽根を備えた攪拌機を用いて１２００ｒｐｍの回転速度で攪拌し、外部ヒーターにより反応槽内溶液温度を５０℃に保った。また、前記反応槽内溶液にアルゴンガスを吹き込んで、溶液内の溶存酸素を除去した。 3.5 liters of water was placed in a 5 liter sealed reactor. Further, a 32% aqueous sodium hydroxide solution was added so that pH = 11.6 ± 0.1. The mixture was stirred at a rotational speed of 1200 rpm using a stirrer equipped with a paddle type stirring blade, and the solution temperature in the reaction vessel was kept at 50 ° C. by an external heater. Further, argon gas was blown into the reaction tank solution to remove dissolved oxygen in the solution.
一方、原料溶液である遷移金属元素が溶解している水溶液を調整した。マンガン濃度が０．２９３ｍｏｌ／リットル、ニッケル濃度が０．２９３ｍｏｌ／リットル、コバルト濃度が１．１７２ｍｏｌ／リットル及びヒドラジン濃度が０．０１０１ｍｏｌ／リットルとなるように、硫酸マンガン・５水和物水溶液、硫酸ニッケル・６水和物水溶液、硫酸コバルト・７水和物水溶液及びヒドラジン１水和物水溶液を混合して得た。 On the other hand, an aqueous solution in which a transition metal element as a raw material solution was dissolved was prepared. Manganese sulfate pentahydrate aqueous solution, sulfuric acid so that the manganese concentration is 0.293 mol / liter, the nickel concentration is 0.293 mol / liter, the cobalt concentration is 1.172 mol / liter, and the hydrazine concentration is 0.0101 mol / liter. A nickel hexahydrate aqueous solution, a cobalt sulfate heptahydrate aqueous solution and a hydrazine monohydrate aqueous solution were mixed to obtain.
該原料溶液を３．１７ｍｌ／ｍｉｎの流量で前記反応槽に連続的に滴下した。これと同期して、１２ｍｏｌ／リットルのアンモニア溶液を０．２２ｍｌ／ｍｉｎの流量で滴下混合した。なお、滴下の開始以降、前記反応槽内溶液のｐＨが１１．４±０．１と一定になるよう、３２％水酸化ナトリウム水溶液を断続的に投入した。また、前記反応槽内の溶液温度が５０℃と一定になるよう断続的にヒーターで制御した。また、前記反応槽内が還元雰囲気となるよう、アルゴンガスを液中に直接吹き込んだ。また、反応槽内の溶液量が３．５リットルと常に一定量となるよう、フローポンプを使ってスラリーを系外に排出した。 The raw material solution was continuously added dropwise to the reaction vessel at a flow rate of 3.17 ml / min. In synchronization with this, a 12 mol / liter ammonia solution was dropped and mixed at a flow rate of 0.22 ml / min. In addition, 32% sodium hydroxide aqueous solution was intermittently thrown in after the start of dripping so that pH of the said solution in a reaction tank might become fixed with 11.4 +/- 0.1. Further, the temperature of the solution in the reaction vessel was intermittently controlled with a heater so as to be constant at 50 ° C. In addition, argon gas was blown directly into the liquid so that the inside of the reaction vessel had a reducing atmosphere. Further, the slurry was discharged out of the system by using a flow pump so that the amount of the solution in the reaction tank was always constant at 3.5 liters.
前記滴下の開始から６０時間経過後、そこから５時間の間に、前記滴下を継続しながら、反応晶析物であるＮｉ−Ｍｎ−Ｃｏ複合酸化物のスラリーを採取した。採取したスラリーを水洗、ろ過し、８０℃で一晩乾燥させ、Ｎｉ−Ｍｎ−Ｃｏ共沈前駆体の乾燥粉末を得た。 After the elapse of 60 hours from the start of the dropping, a slurry of Ni—Mn—Co composite oxide as a reaction crystallized product was collected while continuing the dropping for 5 hours. The collected slurry was washed with water, filtered, and dried overnight at 80 ° C. to obtain a dry powder of a Ni—Mn—Co coprecipitation precursor.
得られたＮｉ−Ｍｎ−Ｃｏ共沈前駆体粉末を７５μｍ未満に篩い分け、水酸化リチウム一水塩（ＬｉＯＨ・Ｈ2Ｏ）粉末をＬｉ／（Ｎｉ＋Ｍｎ＋Ｃｏ）＝１．０２となるように秤量し、遊星型混練器を用いて混合した。これをアルミナ製こう鉢に充てんし、電気炉を用いて、ドライエア流通下、１００℃／ｈの昇温速度で８５０℃まで昇温し、８５０℃の温度を１５ｈ保持し、次いで、１００℃／ｈの冷却速度で２００℃まで冷却し、その後放冷した。得られた粉体を７５μｍ以下に篩い分けした。エックス線回折測定の結果、得られた粉末は空間群Ｒ３−ｍに帰属される単一相であることがわかった。ＩＣＰ発光分光分析の結果、ＬｉＭｎ0.167Ｎｉ0.167Ｃｏ0.667Ｏ2組成を確認した。このようにして母材粒子を作製し、以下の実施例及び比較例に用いた。 The obtained Ni—Mn—Co coprecipitation precursor powder was sieved to less than 75 μm, and the lithium hydroxide monohydrate (LiOH.H 2 O) powder was weighed so that Li / (Ni + Mn + Co) = 1.02. Then, they were mixed using a planetary kneader. This was filled in an alumina pot and heated to 850 ° C. at a heating rate of 100 ° C./h under a flow of dry air using an electric furnace, maintained at a temperature of 850 ° C. for 15 h, and then 100 ° C. / It cooled to 200 degreeC with the cooling rate of h, and stood to cool after that. The obtained powder was sieved to 75 μm or less. As a result of X-ray diffraction measurement, the obtained powder was found to be a single phase belonging to the space group R3-m. As a result of ICP emission spectroscopic analysis, the composition of LiMn 0.167 Ni 0.167 Co 0.667 O 2 was confirmed. Base material particles were prepared in this way and used in the following examples and comparative examples.
（実施例１）
母材粒子として、上記にて得られたＬｉＭｎ0.167Ｎｉ0.167Ｃｏ0.667Ｏ2（平均粒径１μｍ）と、元素Ａのカルコゲン化合物として平均粒径０．１μｍのＹｂ2Ｏ3を９７：３の重量比で混合し、空気中９００℃にて１２時間焼成し、粉末を得た。走査型電子顕微鏡（ＳＥＭ）観察及びＥＰＭＡ測定の結果、得られた粉末は、平均粒径０．１μｍの酸化物が平均粒径１μｍの母材表面に付着したような形態を呈していた。これを実施例１に係る正極活物質とする。エックス線回折測定の結果、得られた粉末は空間群Ｒ３−ｍに帰属される単一相を依然として保っていた。ＩＣＰ発光分光分析の結果、ＬｉＭｎ0.167Ｎｉ0.167Ｃｏ0.667Ｏ2組成の存在を確認した。元素分析の結果から、配されたＹｂの量は、Ｙｂ2Ｏ3換算で、母材粒子に対して２．５重量％であった。該正極活物質のＳＥＭ写真を図１，２に示す。ここで、図１は、５０００倍の設定で撮影したＳＥＭ観察像であり、下部の白いバーの長さが１０μｍであることを示している。また、図２は、７５００倍の設定で撮影したＳＥＭ観察像であり、下部の白いバーの長さが１０μｍであることを示している。
Example 1
As the base material particles, LiMn 0.167 Ni 0.167 Co 0.667 O 2 (average particle size 1 μm) obtained above and Yb 2 O 3 with an average particle size of 0.1 μm as the chalcogen compound of element A at a weight of 97: 3 The mixture was mixed at a ratio and baked in air at 900 ° C. for 12 hours to obtain a powder. As a result of observation with a scanning electron microscope (SEM) and EPMA measurement, the obtained powder had a form in which an oxide having an average particle size of 0.1 μm adhered to the surface of a base material having an average particle size of 1 μm. This is referred to as a positive electrode active material according to Example 1. As a result of X-ray diffraction measurement, the obtained powder still maintained a single phase belonging to the space group R3-m. As a result of ICP emission spectroscopic analysis, the presence of a LiMn 0.167 Ni 0.167 Co 0.667 O 2 composition was confirmed. From the results of elemental analysis, the amount of Yb provided was 2.5% by weight with respect to the base material particles in terms of Yb 2 O 3 . SEM photographs of the positive electrode active material are shown in FIGS. Here, FIG. 1 is an SEM observation image taken at a setting of 5000 times, and shows that the length of the lower white bar is 10 μm. FIG. 2 is an SEM observation image taken at a setting of 7500 times, and shows that the length of the lower white bar is 10 μm.
（実施例２）
母材粒子として上記にて得られたＬｉＭｎ0.167Ｎｉ0.167Ｃｏ0.667Ｏ2（平均粒径１μｍ）と、元素Ａのカルコゲン化合物として平均粒径０．１μｍのＣｅＯ2を９７：３の重量比で混合し、空気中９００℃にて１２時間焼成し、粉末を得た。走査型電子顕微鏡（ＳＥＭ）観察及びＥＰＭＡ測定の結果、得られた粉末は平均粒径０．１μｍの酸化物が平均粒径１μｍの母材表面に付着したような形態を呈していた。これを実施例２に係る正極活物質とする。エックス線回折測定の結果、得られた粉末は空間群Ｒ３−ｍに帰属される単一相であることがわかった。ＩＣＰ発光分光分析の結果、ＬｉＭｎ0.167Ｎｉ0.167Ｃｏ0.667Ｏ2組成を確認した。元素分析の結果から、配されたＣｅの量は、ＣｅＯ2換算で、母材粒子に対して２．５重量％であった。
(Example 2)
LiMn 0.167 Ni 0.167 Co 0.667 O 2 (average particle size 1 μm) obtained above as base material particles and CeO 2 having an average particle size of 0.1 μm as a chalcogen compound of element A were mixed at a weight ratio of 97: 3. And calcined in air at 900 ° C. for 12 hours to obtain a powder. As a result of observation with a scanning electron microscope (SEM) and EPMA measurement, the obtained powder had a form in which an oxide having an average particle diameter of 0.1 μm adhered to the surface of a base material having an average particle diameter of 1 μm. This is designated as a positive electrode active material according to Example 2. As a result of X-ray diffraction measurement, the obtained powder was found to be a single phase belonging to the space group R3-m. As a result of ICP emission spectroscopic analysis, the composition of LiMn 0.167 Ni 0.167 Co 0.667 O 2 was confirmed. From the results of elemental analysis, the amount of Ce distributed was 2.5% by weight with respect to the base material particles in terms of CeO 2 .
（比較例１）
上記にて得られたＬｉＭｎ0.167Ｎｉ0.167Ｃｏ0.667Ｏ2（平均粒径１μｍ）を比較例１に係る正極活物質とする。該正極活物質のＳＥＭ写真を図３，４に示す。ここで、図３は、５０００倍の設定で撮影したＳＥＭ観察像であり、下部の白いバーの長さが１０μｍであることを示している。また、図４は、７５００倍の設定で撮影したＳＥＭ観察像であり、下部の白いバーの長さが１０μｍであることを示している。この観察結果から明らかなように、母材粒子の表面に、図１，２で観察されたような直径０．１ｍｍ前後の粒子は全く見られない。
(Comparative Example 1)
LiMn 0.167 Ni 0.167 Co 0.667 O 2 (average particle size 1 μm) obtained above is used as the positive electrode active material according to Comparative Example 1. SEM photographs of the positive electrode active material are shown in FIGS. Here, FIG. 3 is an SEM observation image taken at a setting of 5000 times, and shows that the length of the lower white bar is 10 μm. FIG. 4 is an SEM observation image taken at a setting of 7500 times, and shows that the length of the lower white bar is 10 μm. As is apparent from this observation result, particles having a diameter of around 0.1 mm as observed in FIGS. 1 and 2 are not seen at all on the surface of the base material particles.
（比較例２）
母材粒子として上記にて得られたＬｉＭｎ0.167Ｎｉ0.167Ｃｏ0.667Ｏ2（平均粒径１μｍ）５０ｇを１リットル反応容器に入れ、そこに全量が５００ｇとなるようイオン交換水を入れ、固形分比率１０重量％の懸濁溶液を作製した。一方、Ｙｂ（ＮＯ3）3・４Ｈ2Ｏ（３．３４ｇ）を１００ｍｌイオン交換水に溶解した水溶液（以下単に「析出反応液」ともいう）を作製した。ここで、析出反応液中のＹｂ化合物の量（元素Ａの量）は、母材粒子の重量との和に対してＹｂ2Ｏ3換算で３．０重量％に相当するようにして決定した。前記懸濁溶液をパドル翼を備えた攪拌棒を用いて４５０ｒｐｍの回転速度で攪拌し、外部ヒーターを用いて懸濁溶液の温度を５０℃と一定になるよう制御した。
(Comparative Example 2)
50 g of LiMn 0.167 Ni 0.167 Co 0.667 O 2 (average particle size 1 μm) obtained above as base material particles is put into a 1 liter reaction vessel, and ion-exchanged water is put therein so that the total amount becomes 500 g, and the solid content ratio A 10 wt% suspension solution was made. On the other hand, an aqueous solution (hereinafter also simply referred to as “deposition reaction solution”) in which Yb (NO 3 ) 3 .4H 2 O (3.34 g) was dissolved in 100 ml ion-exchanged water was prepared. Here, the amount of Yb compound (the amount of element A) in the precipitation reaction solution was determined so as to correspond to 3.0% by weight in terms of Yb 2 O 3 with respect to the sum of the weight of the base material particles. . The suspension solution was stirred at a rotation speed of 450 rpm using a stirring rod equipped with a paddle blade, and the temperature of the suspension solution was controlled to be constant at 50 ° C. using an external heater.
前記懸濁溶液に前記析出反応液を３ｍｌ／ｍｉｎの速度で滴下した。析出反応液の滴下と同期して、懸濁溶液のｐＨが１１．０±０．１と一定になるよう１０重量％ＮａＯＨ溶液を断続的に投入した。析出反応液の滴下終了後、懸濁溶液の温度を５０℃に保持したまま、懸濁溶液のｐＨを１２．０±０．１まで増加させ、この状態で３０分保持した。次に、懸濁液をろ過・洗浄し、１１０℃で乾燥後、エアー流通下４００℃で５時間熱処理した。得られた粉体を７５μｍ未満に篩い分けした。これを比較例２に係る正極活物質とする。 The precipitation reaction solution was added dropwise to the suspension solution at a rate of 3 ml / min. In synchronism with the dropping of the precipitation reaction solution, a 10 wt% NaOH solution was intermittently added so that the pH of the suspension solution became constant at 11.0 ± 0.1. After completion of the dropwise addition of the precipitation reaction solution, the pH of the suspension solution was increased to 12.0 ± 0.1 while maintaining the temperature of the suspension solution at 50 ° C., and this state was maintained for 30 minutes. Next, the suspension was filtered and washed, dried at 110 ° C., and then heat treated at 400 ° C. for 5 hours under air flow. The obtained powder was sieved to less than 75 μm. This is a positive electrode active material according to Comparative Example 2.
処理後の粉体のＢＥＴ表面積と平均粒径（Ｄ50）の値は処理前母材粒子の値と一致した。エックス線光電子分光法（ＸＰＳ）により、付与した元素Ａの状態分析を行ったところ、１８５．５ｅＶ付近に４ｄ５スペクトル線が観測された。これは、別途市販のＹｂ2Ｏ3を用いて測定したスペクトル線と完全に一致した。このことから、付与された元素Ａは酸化物の状態で存在していることが示唆された。次に、処理後の粉体の組成をＩＣＰ発光分光分析によって求めたところ、元素Ａの化合物は、全母材重量に対してＹｂ2Ｏ3換算で２．５重量％付与されていることがわかった。エックス線回折測定（ＸＲＤ）の結果、Ｙｂ2Ｏ3に基づく回折線は認められなかった。また、処理前の母材粒子と処理後の粉体との間に格子定数の変動が認められなかったことから、付与された元素Ａは母材中にはドープされず、リチウムイオンを吸蔵および放出し得る母材粒子の電解質と接触し得る部分の少なくとも一部の上に周期律表の３族の元素が存在する正極活物質が得られたことが認められた。しかしながら、走査型電子顕微鏡（ＳＥＭ）観察の結果、上記実施例１や実施例２に係る正極活物質のＳＥＭ観察結果にみられたような、小粒径の酸化物が母材粒子の上に点在して配されている形態は認められなかった。 The values of the BET surface area and the average particle diameter (D 50 ) of the powder after the treatment coincided with the values of the base material particles before the treatment. When the state analysis of the provided element A was performed by X-ray photoelectron spectroscopy (XPS), a 4d5 spectral line was observed in the vicinity of 185.5 eV. This completely coincided with the spectral line measured using separately available Yb 2 O 3 . From this, it was suggested that the provided element A exists in the state of an oxide. Next, the composition of the powder after the treatment was determined by ICP emission spectroscopic analysis. As a result, the compound of element A was given 2.5% by weight in terms of Yb 2 O 3 with respect to the total weight of the base material. all right. As a result of X-ray diffraction measurement (XRD), no diffraction line based on Yb 2 O 3 was observed. In addition, since no change in lattice constant was observed between the base material particles before the treatment and the powder after the treatment, the provided element A was not doped in the base material, and occluded lithium ions. It was confirmed that a positive electrode active material in which the Group 3 element of the Periodic Table was present on at least a part of the portion of the base material particle that could be released and contacted with the electrolyte was obtained. However, as a result of observation by a scanning electron microscope (SEM), an oxide having a small particle size as seen in the SEM observation result of the positive electrode active material according to Example 1 or Example 2 is formed on the base material particle. No scattered form was observed.
実施例１，２及び比較例１に係る正極活物質を用い、以下に示す手順で、非水系電解質電池用正極を作成した後、負極に金属リチウムを用いた非水系電解質電池を作製し、正極活物質の電気化学的評価を行った。なお、現実の用途に用いる非水電解質電池には、現在広く市販されている非水電解質電池と同様に、リチウムイオンを吸蔵放出可能な炭素質材料を備えた負極を用いることが好ましいが、ここでは正極の挙動を中心に評価する目的から、負極には金属リチウムを用いることとしたものである。負極に金属リチウムを用いた電池を用いることにより、定電圧印加試験において印可した電圧は、正極に印可した電位とほぼ等しいと考えることができる。また、本発明の正極活物質を用いた非水電解質電池は、通常４．２〜４．３Ｖの電圧で充電を行う使用方法を想定して設計する場合が多い。本発明はかかる設計によって作製された電池において効果を奏する。以下の評価試験においては、加速試験の観点から、定電圧印加試験に用いる電圧を４．５Ｖとした。本発明の正極活物質を用いた非水電解質電池は、４．５Ｖといった高い電圧で充電を行う使用方法を想定して設計してもよい。充電時の正極電位が４．５Ｖに至って使用する非水電解質電池に本発明の正極活物質を適用すれば、本発明の効果がより顕著に認められる。 Using the positive electrode active materials according to Examples 1 and 2 and Comparative Example 1, a positive electrode for a non-aqueous electrolyte battery was prepared according to the procedure shown below, and then a non-aqueous electrolyte battery using metallic lithium as a negative electrode was prepared. Electrochemical evaluation of the active material was performed. In addition, it is preferable to use a negative electrode provided with a carbonaceous material capable of occluding and releasing lithium ions, as in non-aqueous electrolyte batteries that are currently widely marketed, for non-aqueous electrolyte batteries used in actual applications. Then, for the purpose of evaluating mainly the behavior of the positive electrode, metallic lithium is used for the negative electrode. By using a battery using metallic lithium for the negative electrode, it can be considered that the voltage applied in the constant voltage application test is substantially equal to the potential applied to the positive electrode. Moreover, the nonaqueous electrolyte battery using the positive electrode active material of the present invention is often designed assuming a usage method in which charging is usually performed at a voltage of 4.2 to 4.3 V. The present invention is effective in a battery manufactured by such a design. In the following evaluation tests, the voltage used for the constant voltage application test was set to 4.5 V from the viewpoint of the acceleration test. The nonaqueous electrolyte battery using the positive electrode active material of the present invention may be designed assuming a usage method in which charging is performed at a high voltage of 4.5V. If the positive electrode active material of the present invention is applied to a non-aqueous electrolyte battery that is used with a positive electrode potential of 4.5 V at the time of charging, the effects of the present invention can be recognized more remarkably.
〔正極の作製〕
正極活物質、アセチレンブラック及びポリフッ化ビニリデン（ＰＶｄＦ）を重量比９０：５：５の割合で混合し、分散媒としてＮ−メチルピロリドンを加えて混練分散し、塗布液を調製した。なお、ＰＶｄＦは固形分が溶解分散された液を用い、固形重量換算した。該塗布液を厚さ２０μｍのアルミニウム箔集電体に塗布し、揮発溶剤を除去し、プレスすることによって正極板を作製した。なお、正極板は電池の組み立て前に１５０℃で１２時間減圧乾燥を行った。
[Production of positive electrode]
A positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 90: 5: 5, and N-methylpyrrolidone was added as a dispersion medium and kneaded and dispersed to prepare a coating solution. In addition, PVdF converted into solid weight using the liquid by which solid content was melt | dissolved and disperse | distributed. The coating solution was applied to an aluminum foil current collector having a thickness of 20 μm, the volatile solvent was removed, and pressing was performed to produce a positive electrode plate. The positive electrode plate was dried under reduced pressure at 150 ° C. for 12 hours before assembling the battery.
〔電池の作製〕
厚さ４０μｍの金属リチウム箔を厚さ１０μｍの銅箔集電体に貼付したものを負極板とし、エチレンカーボネート、ジエチルカーボネート及びエチルメチルカーボネートを６：７：７の体積比で混合した溶媒に１ｍｏｌ／ｌの濃度でＬｉＰＦ6を溶解したものを電解質として用い、セパレータにはポリアクリレートで表面改質して電解質の保持性を向上したポリプロピレン製の微孔膜を用いた。外装体には金属樹脂複合フィルムを用いた。実施例１，２及び比較例１，２に係る正極活物質をそれぞれ用いて設計容量１０ｍＡｈの非水系電解質電池を作製し、それぞれ本発明電池１，２及び比較電池１，２とした。
[Production of battery]
A metal lithium foil with a thickness of 40 μm attached to a copper foil current collector with a thickness of 10 μm is used as a negative electrode plate, and 1 mol in a solvent in which ethylene carbonate, diethyl carbonate and ethyl methyl carbonate are mixed at a volume ratio of 6: 7: 7. A solution obtained by dissolving LiPF 6 at a concentration of / l was used as an electrolyte, and a microporous membrane made of polypropylene whose surface was modified with polyacrylate to improve electrolyte retention was used as a separator. A metal resin composite film was used for the exterior body. Using the positive electrode active materials according to Examples 1 and 2 and Comparative Examples 1 and 2, non-aqueous electrolyte batteries having a design capacity of 10 mAh were prepared, and the batteries 1 and 2 of the present invention and the comparative batteries 1 and 2, respectively.
〔定電圧印加試験〕
上記それぞれの電池に対して２０℃の恒温槽中で５サイクル半の初期充放電を行った。充電条件は、充電電圧４．５Ｖ、電流０．１ＩｔＡ、１５時間の定電流定電圧充電とし、放電条件は、電流０．１ＩｔＡ、終止電圧３．０Ｖの定電流放電とした。５サイクル目の放電容量に基づき、正極活物質の単位重量当たりの放電容量（ｍＡｈ／ｇ）を算出し、表１に示した。
[Constant voltage application test]
Each of the batteries was subjected to initial charge and discharge for 5 cycles and a half in a constant temperature bath at 20 ° C. The charging conditions were a charging voltage of 4.5 V, a current of 0.1 ItA, and a constant current constant voltage charging of 15 hours, and the discharging conditions were a constant current discharging of a current of 0.1 ItA and a final voltage of 3.0 V. Based on the discharge capacity at the 5th cycle, the discharge capacity (mAh / g) per unit weight of the positive electrode active material was calculated and shown in Table 1.
６サイクル目の充電後、４．５Ｖの充電電圧を印加したまま、恒温槽の温度を５５℃とし、さらに前記４．５Ｖの定電圧を２００時間連続的に印加した。次に、回路を開放して恒温槽の温度を２０℃に戻し、電池温度が２０℃となるまで充分な時間（１６時間）放置後、上記初期充放電の同一の条件で、６サイクル目の放電、７サイクル目の充電及び７サイクル目の放電を行った。前記５サイクル目の放電容量に対する７サイクル目の放電容量の割合を容量維持率（％）として求め、表１に示した。 After charging at the 6th cycle, the temperature of the thermostatic chamber was set to 55 ° C. while applying a charging voltage of 4.5 V, and the constant voltage of 4.5 V was continuously applied for 200 hours. Next, the circuit is opened, the temperature of the thermostatic chamber is returned to 20 ° C., and after leaving for a sufficient time (16 hours) until the battery temperature reaches 20 ° C., the sixth cycle is performed under the same conditions of the initial charge / discharge. Discharge, 7th cycle charge, and 7th cycle discharge were performed. The ratio of the discharge capacity at the seventh cycle to the discharge capacity at the fifth cycle was determined as a capacity retention rate (%) and is shown in Table 1.
表１に示されているように、リチウム含有遷移金属酸化物の粒子上にＹｂ化合物の粒子又はＣｅ化合物の粒子が配された実施例１又は２に係る正極活物質を備えた正極を用いた本発明電池１，２は、Ｙｂ化合物の粒子又はＣｅ化合物の粒子が配されていない比較例１に係るリチウム含有遷移金属酸化物の粒子を正極活物質として備える正極を用いた比較電池１に比べ、充電状態に長時間放置された後においても充分な電池容量を示すことが確認された。また、前記元素Ａとしては、ＣｅよりもＹｂが好ましいことがわかった。元素Ａの化合物が付与されているものの母材粒子の上に点在して配されている形態がＳＥＭ観察によって確認できなかった比較例２に係る正極活物質を用いた比較電池２においても本発明の効果が認められたものの、放電容量の低下が見られた。これは、前記元素Ａの付与を湿式で行ったため、母材中のリチウムが溶出したことによると考えられる。加えて、本発明の製造方法によれば、比較例２の方法に比べて極めて簡便な方法で本発明に係る正極活物質を製造することができる。 As shown in Table 1, a positive electrode including the positive electrode active material according to Example 1 or 2 in which Yb compound particles or Ce compound particles are arranged on lithium-containing transition metal oxide particles was used. Inventive batteries 1 and 2 are compared with comparative battery 1 using a positive electrode provided with lithium-containing transition metal oxide particles according to Comparative Example 1 in which no Yb compound particles or Ce compound particles are arranged. It was confirmed that a sufficient battery capacity was exhibited even after being left in a charged state for a long time. Further, it was found that Yb is preferable to Ce as the element A. Even in the comparative battery 2 using the positive electrode active material according to the comparative example 2 in which the compound of the element A was provided but the form scattered on the base material particles could not be confirmed by SEM observation. Although the effect of the invention was recognized, a decrease in discharge capacity was observed. This is considered to be due to the elution of lithium in the base material since the application of the element A was performed in a wet manner. In addition, according to the manufacturing method of the present invention, the positive electrode active material according to the present invention can be manufactured by an extremely simple method as compared with the method of Comparative Example 2.
なお、本発明は、その精神又は主要な特徴から逸脱することなく、他のいろいろな形で実施することができる。そのため、上記した実施の形態若しくは実施例はあらゆる点で単なる例示に過ぎず、限定的に解釈してはならない。本発明の範囲は、請求の範囲によって示すものであって、明細書本文にはなんら拘束されない。さらに、請求の範囲の均等範囲に属する変形や変更は、すべて本発明の範囲内のものである。 It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiments or examples are merely examples in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the scope of claims, and is not restricted to the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.
Claims (9)
The method for producing a positive electrode active material according to claim 8, wherein the temperature of the heat treatment is 900 ° C. or higher.
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| CN108886142A (en) * | 2016-03-25 | 2018-11-23 | Ecopro Bm 有限公司 | The manufacturing method of anode for lithium secondary battery active material and thus obtained anode for lithium secondary battery active material |
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| CN101808939B (en) | 2007-09-28 | 2012-10-03 | 3M创新有限公司 | Sintered cathode compositions |
| MA32844B1 (en) * | 2009-06-24 | 2011-12-01 | Reminex | COBALT AND LITHIUM OXIDE PARTICLES DOPED, AND THEIR PREPARATION METHOD FOR POTENTIAL APPLICATIONS AS LITHIUM ION BATTERIES OF HIGH PERFORMANCE IN TERMS OF SAFETY AND ENERIGY |
| EP2660907B1 (en) | 2010-12-27 | 2018-09-26 | GS Yuasa International Ltd. | Positive electrode material for nonaqueous electrolyte rechargeable batteries, method for producing positive electrode material, electrode for nonaqueous electrolyte rechargeable batteries, nonaqueous electrolyte rechargeable batteries and method of production therefor |
| WO2015115547A1 (en) | 2014-01-31 | 2015-08-06 | 住友金属鉱山株式会社 | Nickel-manganese composite hydroxide particles, method for producing same, positive electrode active material for nonaqueous electrolyte secondary batteries, method for producing positive electrode active material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery |
| JP6460575B2 (en) * | 2015-01-06 | 2019-01-30 | 株式会社Ｇｓユアサ | Positive electrode active material for lithium secondary battery, electrode for lithium secondary battery, and lithium secondary battery |
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| CN108886142A (en) * | 2016-03-25 | 2018-11-23 | Ecopro Bm 有限公司 | The manufacturing method of anode for lithium secondary battery active material and thus obtained anode for lithium secondary battery active material |
| US11165061B2 (en) | 2016-03-25 | 2021-11-02 | Ecopro Bm Co., Ltd. | Method of preparing positive electrode active material for lithium secondary battery and positive electrode active material for lithium secondary battery prepared thereby |
| CN108886142B (en) * | 2016-03-25 | 2022-07-22 | Ecopro Bm 有限公司 | Method for manufacturing anode active material for lithium secondary battery and anode active material for lithium secondary battery manufactured thereby |
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