JP5515343B2 - Active material manufacturing method, active material, electrode, and lithium ion secondary battery - Google Patents
Active material manufacturing method, active material, electrode, and lithium ion secondary battery Download PDFInfo
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Description
本発明は、活物質の製造方法、活物質、電極及びリチウムイオン二次電池に関する。 The present invention relates to an active material manufacturing method, an active material, an electrode, and a lithium ion secondary battery.
LiVOPO4は、リチウムイオンを可逆的に挿入脱離することができる正極活物質であり、リチウムイオン二次電池の正極が備える活物質層に用いられる。このLiVOPO4は、三斜晶(α型結晶)、斜方晶(β型結晶)等の複数の結晶構造を示し、その結晶構造に応じて異なる電気化学特性を有することが知られている(下記特許文献1、2、非特許文献1〜3参照)。
LiVOPO 4 is a positive electrode active material that can reversibly insert and desorb lithium ions, and is used for an active material layer included in a positive electrode of a lithium ion secondary battery. This LiVOPO 4 has a plurality of crystal structures such as triclinic crystal (α-type crystal) and orthorhombic crystal (β-type crystal), and is known to have different electrochemical characteristics depending on the crystal structure ( (See the following
LiVOPO4のβ型結晶(以下、場合により「β―LiVOPO4」と記す。)は、LiVOPO4のα型結晶(以下、場合により「α―LiVOPO4」と記す。)に比べて、リチウムイオンを可逆的に挿入脱離する特性(以下、場合により「可逆性」と記す。)に優れる。そのため、活物質としてβ―LiVOPO4を用いた電池は、α―LiVOPO4を用いた電池に比べて、大きな充放電容量を有し、レート特性及びサイクル特性に優れる。このような理由から、β―LiVOPO4は、α―LiVOPO4に比べて、活物質として好適である。そのため、β―LiVOPO4の選択的合成方法の開発が望まれる。 Beta-form crystals of LiVOPO 4 (hereinafter also referred to as "beta-LiVOPO 4".) Is, alpha-form crystals of LiVOPO 4 (hereinafter also referred to as "alpha-LiVOPO 4".) As compared to a lithium ion Is reversibly inserted and released (hereinafter, referred to as “reversible” in some cases). Therefore, a battery using β-LiVOPO 4 as an active material has a large charge / discharge capacity and excellent rate characteristics and cycle characteristics compared to a battery using α-LiVOPO 4 . For these reasons, β-LiVOPO 4 is more suitable as an active material than α-LiVOPO 4 . Therefore, development of a selective synthesis method of β-LiVOPO 4 is desired.
しかしながら、β―LiVOPO4は、α―LiVOPO4に比べて、熱的に不安定である。すなわち、β―LiVOPO4は準安定相であり、α―LiVOPO4が安定相である。このことから推測されるように、β―LiVOPO4の選択的な合成を試みても、生成物にα―LiVOPO4が混入する傾向がある。例えば、LiVOPO4の原料となる固体を混合粉砕して焼成する方法や、LiVOPO4の原料を水に溶かした後に蒸発乾固する方法のような従来の方法では、β―LiVOPO4の選択的に合成することは困難である。また、従来の製造方法により得られるβ―LiVOPO4のイオン伝導度及び電子伝導度は必ずしも高くなく、従来のβ―LiVOPO4を活物質として用いた電池の放電容量は、理論容量に比べて十分に大きくなかった。そのため、電極材料として適したβ―LiVOPO4は実現されていない。 However, β-LiVOPO 4 is thermally unstable compared to α-LiVOPO 4 . That is, β-LiVOPO 4 is a metastable phase, and α-LiVOPO 4 is a stable phase. As estimated from this, even when selective synthesis of β-LiVOPO 4 is attempted, α-LiVOPO 4 tends to be mixed into the product. For example, a method of firing the mixed pulverized solid which is a raw material of LiVOPO 4, in the conventional methods, such as evaporation to dryness the material of the LiVOPO 4 after dissolved in water, optionally in the beta-LiVOPO 4 It is difficult to synthesize. In addition, the ionic conductivity and electronic conductivity of β-LiVOPO 4 obtained by the conventional manufacturing method are not necessarily high, and the discharge capacity of the battery using the conventional β-LiVOPO 4 as an active material is sufficiently higher than the theoretical capacity. It was not big. Therefore, β-LiVOPO 4 suitable as an electrode material has not been realized.
本発明は、上記従来技術の有する課題に鑑みてなされたものであり、β―LiVOPO4を選択的に合成することが可能な活物質の製造方法、当該活物質の製造方法により得られ、リチウムイオン二次電池の放電容量を向上させることが可能な活物質、当該活物質を用いた電極及び当該電極を用いたリチウムイオン二次電池を提供することを目的とする。 The present invention has been made in view of the above-described problems of the prior art, and is obtained by a method for producing an active material capable of selectively synthesizing β-LiVOPO 4 , a method for producing the active material, and lithium It is an object to provide an active material capable of improving the discharge capacity of an ion secondary battery, an electrode using the active material, and a lithium ion secondary battery using the electrode.
上記目的を達成するために、本発明に係る活物質の製造方法は、リチウム源とリン酸源とバナジウム源と水とを含み、pHが7以下である混合物を、加圧下で加熱する水熱合成工程と、水熱合成工程において加圧下で加熱した後の混合物を焼成する焼成工程と、を備える。 In order to achieve the above object, a method for producing an active material according to the present invention is a hydrothermal method in which a mixture containing a lithium source, a phosphate source, a vanadium source, and water and having a pH of 7 or less is heated under pressure. A synthesis step and a firing step of firing the mixture after heating under pressure in the hydrothermal synthesis step.
水熱合成の出発原料である混合物のpHを7以下とすることによって、β−LiVOPO4を選択的に合成することが可能となる。また、水熱合成によってβ−LiVOPO4を合成するため、β−LiVOPO4の体積平均一次粒径を微小化し、且つ粒度分布をシャープにすることが可能となる。 By setting the pH of the mixture, which is a starting material for hydrothermal synthesis, to 7 or less, β-LiVOPO 4 can be selectively synthesized. Moreover, since β-LiVOPO 4 is synthesized by hydrothermal synthesis, the volume average primary particle size of β-LiVOPO 4 can be reduced and the particle size distribution can be sharpened.
上記本発明に係る活物質の製造方法では、水熱合成工程において、加熱前の混合物に、硝酸、塩酸又は硫酸の少なくともいずれかを添加する。 The method of manufacturing an active material according to the present invention, in the hydrothermal synthesis step, to the mixture before heating, added nitric, at least one of hydrochloric acid or sulfuric acid.
これにより、加熱前の混合物のpHを7以下の所望の値に調整し易くなる。 Thereby, it becomes easy to adjust the pH of the mixture before heating to a desired value of 7 or less.
上記本発明に係る活物質の製造方法では、リチウム源が、LiNO3、Li2CO3、LiOH、LiCl、Li2SO4及びCH3COOLiからなる群より選ばれる少なくとも一種であり、リン酸源が、H3PO4、NH4H2PO4、(NH4)2HPO4及びLi3PO4からなる群より選ばれる少なくとも一種であり、バナジウム源が、V2O5及びNH4VO3からなる群より選ばれる少なくとも一種であることが好ましい。 In the method for producing an active material according to the present invention, the lithium source is at least one selected from the group consisting of LiNO 3 , Li 2 CO 3 , LiOH, LiCl, Li 2 SO 4 and CH 3 COOLi, and a phosphate source Is at least one selected from the group consisting of H 3 PO 4 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 and Li 3 PO 4 , and the vanadium source is V 2 O 5 and NH 4 VO 3. It is preferably at least one selected from the group consisting of
これらのリチウム源、リン酸源及びバナジウム源を適宜組み合わせて用いることにより、加熱前の混合物のpHを7以下の所望の値に調整し易くなる。 By appropriately combining these lithium source, phosphoric acid source and vanadium source, it becomes easy to adjust the pH of the mixture before heating to a desired value of 7 or less.
上記本発明に係る活物質の製造方法では、リチウム源がLi2CO3であり、リン酸源がH3PO4であり、バナジウム源がV2O5であることが好ましい。 In the method for producing an active material according to the present invention, it is preferable that the lithium source is Li 2 CO 3 , the phosphoric acid source is H 3 PO 4 , and the vanadium source is V 2 O 5 .
これにより、β−LiVOPO4を選択的に合成し易くなる。 Thereby, it becomes easy to selectively synthesize β-LiVOPO 4 .
本発明に係る活物質は、LiVOPO4のβ型結晶構造を有し、体積平均一次粒径が121〜500nmである粒子群を備える。 The active material according to the present invention includes a particle group having a β type crystal structure of LiVOPO 4 and having a volume average primary particle size of 121 to 500 nm.
本発明に係る電極は、集電体と、上記本発明に係る活物質を含有し、集電体上に設けられた活物質層と、を備える。 The electrode according to the present invention includes a current collector, and an active material layer containing the active material according to the present invention and provided on the current collector.
本発明に係るリチウムイオン二次電池は、上記本発明に係る電極を備える。 The lithium ion secondary battery according to the present invention includes the electrode according to the present invention.
LiVOPO4のβ型結晶構造を有する粒子群(以下、場合により「β−LiVOPO4粒子群」と記す。)は、LiVOPO4のα型結晶構造を有する粒子群に比べて、可逆性(Liイオンの放出効率及び取り込み効率)に優れる。 A particle group having a β type crystal structure of LiVOPO 4 (hereinafter sometimes referred to as “β-LiVOPO 4 particle group”) is reversible (Li ion) compared to a particle group having an α type crystal structure of LiVOPO 4 . Is excellent in the release efficiency and the uptake efficiency.
また、本発明では、β−LiVOPO4粒子群の体積平均一次粒径が、121〜500nmであり、従来のα−LiVOPO4の粒子群又は従来のβ−LiVOPO4の粒子群に比べて小さい。そのため、本発明では、従来の活物質に比べて、イオンの伝導経路の密度が増加すると共に、粒子内でのLiイオンの拡散距離が短縮され、Liイオンの拡散能が高くなる。また、本発明では、β−LiVOPO4粒子群の比表面積が従来に比べて大きくなるため、可逆性が向上すると共に、集電体と粒子群との接触面積、及び活物質に一般的に含まれる導電剤と粒子との接触面積が増加し、電子の伝導経路の密度が増加する。 In the present invention, the β-LiVOPO 4 particle group has a volume average primary particle size of 121 to 500 nm, which is smaller than the conventional α-LiVOPO 4 particle group or the conventional β-LiVOPO 4 particle group. . Therefore, in the present invention, compared to the conventional active material, the density of the ion conduction path is increased, the diffusion distance of Li ions in the particles is shortened, and the diffusibility of Li ions is increased. In the present invention, since the specific surface area of the β-LiVOPO 4 particle group is larger than the conventional one, the reversibility is improved, and the contact area between the current collector and the particle group, and generally included in the active material The contact area between the conductive agent and the particles increases, and the density of the electron conduction path increases.
以上の理由から、本発明に係る活物質では、従来の活物質に比べて、イオン並びに電子の伝導性及び容量密度が向上する。そのため、本発明に係る活物質を用いたリチウムイオン二次電池では、従来のLiVOPO4の粒子群を用いた場合に比べて、放電容量が向上する。 For the above reasons, the active material according to the present invention improves the conductivity and capacity density of ions and electrons as compared with the conventional active material. Therefore, in the lithium ion secondary battery using the active material according to the present invention, the discharge capacity is improved as compared with the case of using the conventional LiVOPO 4 particle group.
上記本発明に係る活物質では、粒子群の比表面積が1〜10m2/gであることが好ましい。 In the active material according to the present invention, the specific surface area of the particle group is preferably 1 to 10 m 2 / g.
これにより、β−LiVOPO4粒子群の可逆性がより向上する。 Thus, reversibility of beta-LiVOPO 4 particles is further improved.
上記本発明に係る電極では、活物質層における粒子群の含有率が80〜97質量%であることが好ましい。 In the electrode according to the present invention, the content of the particle group in the active material layer is preferably 80 to 97% by mass.
これにより、リチウムイオン二次電池の放電容量を向上させ易くなる。 Thereby, it becomes easy to improve the discharge capacity of the lithium ion secondary battery.
本発明によれば、β―LiVOPO4を選択的に合成することが可能な活物質の製造方法、当該活物質の製造方法により得られ、リチウムイオン二次電池の放電容量を向上させることが可能な活物質、当該活物質を用いた電極及び当該電極を用いたリチウムイオン二次電池を提供することができる。 According to the present invention, it is possible to improve the discharge capacity of a lithium ion secondary battery obtained by an active material manufacturing method capable of selectively synthesizing β-LiVOPO 4 and the active material manufacturing method. An active material, an electrode using the active material, and a lithium ion secondary battery using the electrode can be provided.
(活物質の製造方法)
以下では、本発明の一実施形態に係る活物質の製造方法について説明する。本実施形態では、活物質がβ−LiVOPO4の粒子群のみから構成される場合について説明する。すなわち、本実施形態では、活物質とβ−LiVOPO4の粒子群とは同義である。なお、本発明の他の実施形態では、活物質は粒子群に加えて更に導電剤等を含有してもよい。
(Method for producing active material)
Below, the manufacturing method of the active material which concerns on one Embodiment of this invention is demonstrated. In the present embodiment, a case where the active material is composed of only β-LiVOPO 4 particle groups will be described. That is, in this embodiment, the active material and the β-LiVOPO 4 particle group are synonymous. In another embodiment of the present invention, the active material may further contain a conductive agent in addition to the particle group.
本実施形態に係る活物質の製造方法は、リチウム源とリン酸源とバナジウム源と水とを含み、pHが7以下である混合物を、加圧下で加熱する水熱合成工程と、水熱合成工程において加圧下で加熱した後の混合物を焼成する焼成工程と、を備える。 The method for producing an active material according to the present embodiment includes a hydrothermal synthesis step in which a mixture containing a lithium source, a phosphate source, a vanadium source, and water and having a pH of 7 or less is heated under pressure, and hydrothermal synthesis. A firing step of firing the mixture after being heated under pressure in the step.
<水熱合成工程>
水熱合成工程では、まず、内部を加熱、加圧する機能を有する反応容器(例えば、オートクレーブ等)内に、上述したリチウム源、リン酸源、バナジウム源、及び水を投入して、これらが分散した混合物(水溶液)を調製する。なお、混合物を調製する際は、例えば、最初に、リン酸源、バナジウム源及び水を混合したものを還流した後、これにリチウム源を加えてもよい。この還流により、リン酸源及びバナジウム源の複合体を形成することができる。
<Hydrothermal synthesis process>
In the hydrothermal synthesis process, first, the above-described lithium source, phosphate source, vanadium source, and water are put into a reaction vessel (for example, an autoclave) having a function of heating and pressurizing the inside, and these are dispersed. A prepared mixture (aqueous solution) is prepared. In preparing the mixture, for example, first, a mixture of a phosphate source, a vanadium source and water may be refluxed, and then a lithium source may be added thereto. By this reflux, a complex of a phosphate source and a vanadium source can be formed.
混合物のpHは7以下に調整する。これによりβ−LiVOPO4を選択的に合成することが可能となる。なお、混合物のpHは1.0以上であることが好ましく、1.8〜6.7であることがより好ましい。混合物のpHが小さ過ぎる場合、β−LiVOPO4に不純物が混入し易くなる傾向があり、混合物のpHが大き過ぎる場合、α−LiVOPO4が生成する傾向がある。 The pH of the mixture is adjusted to 7 or less. This makes it possible to selectively synthesize β-LiVOPO 4 . In addition, it is preferable that pH of a mixture is 1.0 or more, and it is more preferable that it is 1.8-6.7. When the pH of the mixture is too low, impurities tend to be mixed into β-LiVOPO 4 , and when the pH of the mixture is too high, α-LiVOPO 4 tends to be generated.
混合物のpHを7以下に調整する方法としては、様々な方法を採用し得るが、混合物に硝酸、塩酸又は硫酸の少なくともいずれかを添加する。これらの添加量は、混合物の量、並びにリチウム源、リン酸源及びバナジウム源の種類及び配合比に応じて適宜調整すればよい。 As a method of pH adjusting to the 7 or less of the mixture, but may employ various methods, nitric acid mixture, you add at least one of hydrochloric acid or sulfuric acid. What is necessary is just to adjust these addition amounts suitably according to the quantity of a mixture, and the kind and compounding ratio of a lithium source, a phosphoric acid source, and a vanadium source.
混合物のpHを7以下に調整する他の方法としては、特定のリチウム源、リン酸源及びバナジウム源を組み合わせることが好ましい。すなわち、β−LiVOPO4の原料として、特定のリチウム源、リン酸源及びバナジウム源を組み合わせて混合物に含有させることにより、混合物のpHを7以下の所望の値に調整することが容易となる。 As another method of adjusting the pH of the mixture to 7 or less, it is preferable to combine a specific lithium source, phosphate source and vanadium source. That is, as a raw material of β-LiVOPO 4 , a specific lithium source, a phosphoric acid source, and a vanadium source are combined and contained in the mixture, so that the pH of the mixture can be easily adjusted to a desired value of 7 or less.
具体的には、リチウム源として、LiNO3、Li2CO3、LiOH、LiCl、Li2SO4及びCH3COOLiからなる群より選ばれる少なくとも一種を用い、リン酸源として、H3PO4、NH4H2PO4、(NH4)2HPO4及びLi3PO4からなる群より選ばれる少なくとも一種を用い、バナジウム源として、V2O5及びNH4VO3からなる群より選ばれる少なくとも一種を用いることが好ましい。リチウム源、リン酸源及びバナジウム源の組合せと、それによって実現する混合物のpHを表1に示す。なお、リチウム源、リン酸源及びバナジウム源のみでpHを7以下に調整する場合、表1に示す組合せのうち、pHが7以下となる組合せを採用すればよい。 Specifically, at least one selected from the group consisting of LiNO 3 , Li 2 CO 3 , LiOH, LiCl, Li 2 SO 4 and CH 3 COOLi is used as the lithium source, and H 3 PO 4 , At least one selected from the group consisting of NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 and Li 3 PO 4 is used, and the vanadium source is at least selected from the group consisting of V 2 O 5 and NH 4 VO 3. It is preferable to use one kind. The combinations of lithium source, phosphate source and vanadium source, and the pH of the mixture realized thereby are shown in Table 1. In addition, what is necessary is just to employ | adopt the combination from which the pH becomes 7 or less among the combinations shown in Table 1 when adjusting pH to 7 or less only with a lithium source, a phosphate source, and a vanadium source.
上記の化合物の中でも、リチウム源としてLi2CO3を用い、リン酸源としてH3PO4を用い、バナジウム源としてV2O5を用いることが好ましい。これにより、β−LiVOPO4を選択的に合成し易くなる。 Among the above compounds, it is preferable to use Li 2 CO 3 as the lithium source, use H 3 PO 4 as the phosphate source, and use V 2 O 5 as the vanadium source. Thereby, it becomes easy to selectively synthesize β-LiVOPO 4 .
なお、混合物におけるリチウム源、リン酸源及びバナジウム源の配合比は、得られる粒子群が、LiVOPO4で表される組成となるように調整すればよい。例えば、Li2CO3、V2O5及びH3PO4は1:1:2のバランスで配合すればよい。 Incidentally, the lithium source in the mixture, the mixing ratio of phosphoric acid source and vanadium source, group the resulting particles may be adjusted so as to have the composition represented by the LiVOPO 4. For example, Li 2 CO 3 , V 2 O 5 and H 3 PO 4 may be blended in a balance of 1: 1: 2.
また、硝酸、塩酸又は硫酸の添加によるpHの調整方法と、リチウム源、リン酸源及びバナジウム源の組合せによるpHの調整方法とを併用してもよい。これによりpHの微調整が可能となる。また、二種以上のリチウム源、二種以上のリン酸源又は二種以上のバナジウム源を併用してもよい。これによりpHの微調整が可能となる。また、表1に示す組合せ1〜9のうち、二通り以上の組合せを併用してもよい。 Moreover, you may use together the adjustment method of pH by addition of nitric acid, hydrochloric acid, or a sulfuric acid, and the adjustment method of pH by the combination of a lithium source, a phosphate source, and a vanadium source. Thereby, fine adjustment of pH becomes possible. Two or more lithium sources, two or more phosphate sources, or two or more vanadium sources may be used in combination. Thereby, fine adjustment of pH becomes possible. Moreover, you may use 2 or more types of combinations among the combinations 1-9 shown in Table 1 together.
次に、反応容器を密閉して、混合物を加圧しながら加熱することにより、混合物の水熱反応を進行させる。これにより、β−LiVOPO4粒子群の前駆体が水熱合成される。 Next, the reaction vessel is sealed, and the mixture is heated while being pressurized, thereby causing the hydrothermal reaction of the mixture to proceed. Thereby, the precursor of the β-LiVOPO 4 particle group is hydrothermally synthesized.
水熱合成工程において混合物に加える圧力は、0.2〜1MPaとすることが好ましい。混合物に加える圧力が低過ぎると、最終的に得られるβ−LiVOPO4粒子群の結晶性が低下し、活物質の容量密度が減少する傾向がある。混合物に加える圧力が高過ぎると、反応容器に高い耐圧性が求められ、活物質の製造コストが増大する傾向がある。混合物に加える圧力を上記の範囲内とすることによって、これらの傾向を抑制できる。 The pressure applied to the mixture in the hydrothermal synthesis step is preferably 0.2 to 1 MPa. When the pressure applied to the mixture is too low, the crystallinity of the finally obtained β-LiVOPO 4 particle group is lowered, and the volume density of the active material tends to be reduced. If the pressure applied to the mixture is too high, the reaction vessel is required to have high pressure resistance, and the production cost of the active material tends to increase. By setting the pressure applied to the mixture within the above range, these tendencies can be suppressed.
水熱合成工程における混合物の温度は、150〜200℃とすることが好ましい。混合物の温度が低過ぎると、最終的に得られるβ−LiVOPO4粒子群の結晶性が低下し、活物質の容量密度が減少する傾向がある。混合物の温度が高過ぎると、反応容器に高い耐熱性が求められ、活物質の製造コストが増大する傾向がある。混合物の温度を上記の範囲内とすることによって、これらの傾向を抑制できる。 The temperature of the mixture in the hydrothermal synthesis step is preferably 150 to 200 ° C. When the temperature of the mixture is too low, the crystallinity of the finally obtained β-LiVOPO 4 particle group is lowered, and the volume density of the active material tends to be reduced. When the temperature of the mixture is too high, the reaction vessel is required to have high heat resistance, and the production cost of the active material tends to increase. By setting the temperature of the mixture within the above range, these tendencies can be suppressed.
<焼成工程>
焼成工程では、水熱合成工程において加圧下で加熱した後の混合物(β−LiVOPO4粒子群の前駆体)を焼成する。これにより、β−LiVOPO4粒子群が得られる。
<Baking process>
In the firing step, the mixture (precursor of β-LiVOPO 4 particle group) after being heated under pressure in the hydrothermal synthesis step is fired. Thereby, a β-LiVOPO 4 particle group is obtained.
焼成工程における混合物の焼成温度は600〜700℃とすることが好ましい。焼成温度が低過ぎる場合、β−LiVOPO4の結晶成長が不十分となり、活物質の容量密度が低下する傾向がある。焼成温度が高過ぎる場合、β−LiVOPO4の粒成長が進み、粒径が増加する結果、活物質におけるリチウムの拡散が遅くなり、活物質の容量密度が減少する傾向がある。焼成温度を上記の範囲内とすることによって、これらの傾向を抑制できる。 The firing temperature of the mixture in the firing step is preferably 600 to 700 ° C. When the firing temperature is too low, the crystal growth of β-LiVOPO 4 becomes insufficient, and the capacity density of the active material tends to decrease. When the firing temperature is too high, the grain growth of β-LiVOPO 4 proceeds and the particle diameter increases, so that the diffusion of lithium in the active material becomes slow, and the capacity density of the active material tends to decrease. By setting the firing temperature within the above range, these tendencies can be suppressed.
混合物の焼成時間は、3〜20時間とするこが好ましい。また、混合物の焼成雰囲気は、窒素雰囲気、アルゴン雰囲気、又は空気雰囲気とすることが好ましい。 The firing time of the mixture is preferably 3 to 20 hours. The firing atmosphere of the mixture is preferably a nitrogen atmosphere, an argon atmosphere, or an air atmosphere.
なお、水熱合成工程で得られる混合物を、焼成工程で焼成する前に60〜150℃程度で1〜30時間程度、加熱処理してもよい。この加熱処理により、混合物が粉体となる。この粉体状の混合物を焼成してもよい。これにより、混合物から余計な水分や有機溶媒が除去され、β−LiVOPO4型粒子の結晶中に不純物が取り込まれることを防ぎ、粒子形状を均一化することが可能となる。 In addition, you may heat-process the mixture obtained at a hydrothermal synthesis process at about 60-150 degreeC for about 1 to 30 hours, before baking at a baking process. By this heat treatment, the mixture becomes powder. This powdery mixture may be fired. This removes excess water and organic solvent from the mixture, prevents impurities from being taken into the crystals of β-LiVOPO 4 type particles, and makes the particle shape uniform.
上述した本実施形態に係る活物質の製造方法では、β−LiVOPO4粒子群を選択的に得ることが可能となる。即ち、本実施形態では、α−LiVOPO4の生成を防止し、β−LiVOPO4粒子群の収率及び純度を向上させることが可能となる。また、本実施形態に係る活物質の製造方法では、β−LiVOPO4粒子群の粒度分布をシャープにすることも可能となる。 In the method for producing an active material according to this embodiment described above, it is possible to selectively obtain a β-LiVOPO 4 particle group. That is, in this embodiment, it is possible to prevent the production of α-LiVOPO 4 and improve the yield and purity of the β-LiVOPO 4 particle group. In the manufacturing method of the active material in accordance with this embodiment, it is possible to sharpen the particle size distribution of beta-LiVOPO 4 particles.
なお、従来の活物質の製造方法としては、例えば、LiVOPO4の原料となる固体を混合、粉砕したものを焼成して、LiVOPO4の粒子を形成し、これを炭素とを混合する方法や、LiVOPO4の原料を水に溶かし、蒸発乾固してLiVOPO4の粒子を形成し、これを炭素とを混合する方法が知られている。しかし、これらの方法では、β−LiVOPO4粒子群を選択的に合成することは困難であり、ましてや、β−LiVOPO4粒子群の体積平均一次粒径を微小化することも困難である。 As the manufacturing method of the conventional active material, for example, a method of mixing a solid as a raw material for LiVOPO 4, and calcined what was pulverized to form particles of LiVOPO 4, which is mixed with carbon, A method is known in which a raw material of LiVOPO 4 is dissolved in water and evaporated to dryness to form LiVOPO 4 particles, which are mixed with carbon. However, in these methods, to selectively synthesize beta-LiVOPO 4 particles is difficult, let alone, it is difficult to infinitesimal the volume average primary particle size of beta-LiVOPO 4 particles.
(活物質)
次に、本発明の一実施形態に係る活物質について説明する。本実施形態に係る活物質は、上述した本実施形態に係る活物質の製造方法によって製造することができる。
(Active material)
Next, an active material according to an embodiment of the present invention will be described. The active material which concerns on this embodiment can be manufactured with the manufacturing method of the active material which concerns on this embodiment mentioned above.
本発明に係る活物質は、LiVOPO4のβ型結晶構造を有する粒子群を備える。粒子群の体積平均一次粒径は121〜500nmである。なお、粒子群の体積平均一次粒径は、レーザー散乱法で測定すればよい。 The active material according to the present invention includes a particle group having a β-type crystal structure of LiVOPO 4 . The volume average primary particle diameter of the particles is Ru one hundred and twenty-one to five hundred nm der. Na us, volume average primary particle diameter of the particles may be measured by a laser scattering method.
LiVOPO4のβ型結晶構造は、α型結晶構造に比べて直線的で短いイオン伝導経路を有するため、β型結晶構造を有する粒子群は、α型結晶構造を有する場合に比べて可逆性に優れる。 Since the β-type crystal structure of LiVOPO 4 has a linear and shorter ionic conduction path than the α-type crystal structure, the particles having the β-type crystal structure are more reversible than the case of having the α-type crystal structure. Excellent.
粒子群の体積平均一次粒径が小さ過ぎる場合、放電容量が低下する傾向がある。粒子群の体積平均一次粒径が大き過ぎる場合、可逆性、Liイオンの拡散能、及びイオン並びに電子の伝導経路の密度が低下する傾向がある。本実施形態では、粒子群の体積平均一次粒径を上記の範囲内とすることにより、これらの傾向を抑制できる。 When the volume average primary particle size of the particle group is too small, the discharge capacity tends to decrease. When the volume average primary particle size of the particle group is too large, the reversibility, the diffusion capacity of Li ions, and the density of ion and electron conduction paths tend to decrease. In this embodiment, these tendencies can be suppressed by setting the volume average primary particle size of the particle group within the above range.
β−LiVOPO4粒子群の比表面積は1〜10m2/gであることが好ましい。比表面積が小さ過ぎる場合、可逆性、Liイオンの拡散能、及びイオン並びに電子の伝導経路の密度が低下する傾向があり、比表面積が大き過ぎる場合、活物質及び電池の耐熱性が低下する傾向がある。本実施形態では、β−LiVOPO4粒子群の比表面積を上記の範囲内とすることにより、これらの傾向を抑制できる。なお、比表面積はBET法により求めればよい。 The specific surface area of the β-LiVOPO 4 particle group is preferably 1 to 10 m 2 / g. If the specific surface area is too small, the reversibility, Li ion diffusivity, and the density of the ion and electron conduction paths tend to decrease, and if the specific surface area is too large, the heat resistance of the active material and the battery tends to decrease. There is. In this embodiment, these tendencies can be suppressed by setting the specific surface area of the β-LiVOPO 4 particle group within the above range. The specific surface area may be determined by the BET method.
(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は、互いに対向する板状の負極及び板状の正極と、負極と正極との間に隣接して配置される板状のセパレータと、を備える発電要素と、リチウムイオンを含む電解質溶液と、これらを密閉した状態で収容するケースと、負極に一方の端部が電気的に接続されると共に他方の端部がケースの外部に突出される負極リードと、正極に一方の端部が電気的に接続されると共に他方の端部がケースの外部に突出される正極リードとを備える。
(Lithium ion secondary battery)
A lithium ion secondary battery according to the present embodiment includes a plate-shaped negative electrode and a plate-shaped positive electrode facing each other, and a plate-shaped separator disposed adjacently between the negative electrode and the positive electrode; An electrolyte solution containing lithium ions, a case containing them in a sealed state, a negative electrode lead having one end electrically connected to the negative electrode and the other end protruding outside the case, One end is electrically connected to the positive electrode, and the other end is provided with a positive electrode lead protruding outside the case.
負極は、負極集電体と、負極集電体上に形成された負極活物質層と、を有する。また、正極は、正極集電体と、正極集電体上に形成された正極活物質層と、を有する。セパレータは、負極活物質層と正極活物質層との間に位置している。 The negative electrode has a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The separator is located between the negative electrode active material layer and the positive electrode active material layer.
正極活物質層は、体積平均一次粒径が121〜500nmであるβ−LiVOPO4粒子群を含有する。なお、正極活物質層が、更に、活性炭、カーボンブラック(黒鉛)、ソフトカーボン、ハードカーボン等の導電剤を含有していてもよい。 The positive electrode active material layer contains a β-LiVOPO 4 particle group having a volume average primary particle size of 121 to 500 nm. Note that the positive electrode active material layer may further contain a conductive agent such as activated carbon, carbon black (graphite), soft carbon, or hard carbon.
本実施形態では、正極活物質層が、従来の活物質に比べてイオン並びに電子の伝導性及び容量密度に優れるβ−LiVOPO4粒子群を含有するため、リチウムイオン二次電池の放電容量、レート特性及びサイクル特性が従来に比べて向上する。 In this embodiment, since the positive electrode active material layer contains β-LiVOPO 4 particles that are superior in ion conductivity and electron conductivity and capacity density as compared with the conventional active material, the discharge capacity and rate of the lithium ion secondary battery The characteristics and cycle characteristics are improved as compared with the prior art.
正極活物質層におけるβ−LiVOPO4粒子群の含有率は、80〜97質量%であることが好ましい。β−LiVOPO4粒子群の含有率が小さ過ぎる場合、イオン並びに電子の伝導性及び容量密度が低下して、電池の放電容量が低下する傾向がある。β−LiVOPO4粒子群の含有率が大き過ぎる場合、正極活物質層に占める導電剤の割合が小さくなり、正極活物質層の電子伝導性が低下する傾向がある。本実施形態では、正極活物質層におけるβ−LiVOPO4粒子群の含有率の上記の範囲内とすることにより、これらの傾向を抑制できる。 The content of the β-LiVOPO 4 particle group in the positive electrode active material layer is preferably 80 to 97% by mass. When the content of the β-LiVOPO 4 particle group is too small, the conductivity and capacity density of ions and electrons are lowered, and the discharge capacity of the battery tends to be lowered. When the content of the β-LiVOPO 4 particle group is too large, the proportion of the conductive agent in the positive electrode active material layer tends to be small, and the electron conductivity of the positive electrode active material layer tends to be reduced. In this embodiment, these tendencies can be suppressed by setting the content of the β-LiVOPO 4 particle group in the positive electrode active material layer within the above range.
以上、本発明の活物質及び活物質の製造方法の好適な一実施形態について詳細に説明したが、本発明は上記実施形態に限定されるものではない。 As mentioned above, although one suitable embodiment of the active material of this invention and the manufacturing method of an active material was described in detail, this invention is not limited to the said embodiment.
例えば、本発明の活物質は、リチウムイオン二次電池以外の電気化学素子の電極材料としても用いることができる。このような、電気化学素子としては、金属リチウム二次電池(カソードに本発明の複合粒子を含む電極を用い、アノードに金属リチウムを用いたもの)等のリチウムイオン二次電池以外の二次電池や、リチウムキャパシタ等の電気化学キャパシタ等が挙げられる。これらの電気化学素子は、自走式のマイクロマシン、ICカードなどの電源や、プリント基板上又はプリント基板内に配置される分散電源の用途に使用することが可能である。 For example, the active material of the present invention can also be used as an electrode material for electrochemical devices other than lithium ion secondary batteries. As such an electrochemical element, a secondary battery other than a lithium ion secondary battery, such as a metallic lithium secondary battery (which uses an electrode containing the composite particles of the present invention as a cathode and metallic lithium as an anode). And electrochemical capacitors such as lithium capacitors. These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.
以下、実施例及び比較例に基づいて本発明をより具体的に説明するが、本発明は以下の実施例に限定されるものではない。 EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.
(参考例1)
<水熱合成工程>
23.13g(0.2mol)のH3PO4水溶液(分子量:98.00、ナカライテスク社製、特級、純度:85重量%)、503gのH2O(ナカライテスク社製、HPLC(高速液体クロマトグラフィー)用)、18.37g(0.1mol)のV2O5(分子量:181.88、ナカライテスク社製、特級、純度:99重量%)、及び7.40g(0.1mol)のLi2CO3(分子量:73.89、ナカライテスク社製、特級、純度:99重量%)を、この順序で1.5Lオートクレーブ容器に導入して、pHが3.5である混合物を調製した。これらの原料の量は、化学量論的に約30g(0.2mol)のLiVOPO4(分子量:168.85)を生成させる量に相当する。
( Reference Example 1)
<Hydrothermal synthesis process>
23.13 g (0.2 mol) of an H 3 PO 4 aqueous solution (molecular weight: 98.00, manufactured by Nacalai Tesque, special grade, purity: 85% by weight), 503 g of H 2 O (manufactured by Nacalai Tesque, HPLC (high performance liquid) Chromatography)), 18.37 g (0.1 mol) of V 2 O 5 (molecular weight: 181.88, manufactured by Nacalai Tesque, special grade, purity: 99 wt%), and 7.40 g (0.1 mol). Li 2 CO 3 (molecular weight: 73.89, manufactured by Nacalai Tesque, special grade, purity: 99% by weight) was introduced in this order into a 1.5 L autoclave vessel to prepare a mixture having a pH of 3.5. . The amount of these raw materials corresponds to the amount of stoichiometrically producing about 30 g (0.2 mol) of LiVOPO 4 (molecular weight: 168.85).
容器を密閉して、混合物を室温下で約30分攪拌した後に、容器内の圧力を0.5MPaにし、160℃/200rpmで16時間還流し、水熱合成反応を進行させた。水熱合成反応後の混合物のpHは2.3であった。 The vessel was sealed, and the mixture was stirred at room temperature for about 30 minutes, and then the pressure in the vessel was brought to 0.5 MPa and refluxed at 160 ° C./200 rpm for 16 hours to proceed the hydrothermal synthesis reaction. The pH of the mixture after the hydrothermal synthesis reaction was 2.3.
水熱合成反応後の混合物に水を加えた後に、混合物をバットに開けて、90℃で約21時間蒸発乾固させた。蒸発乾固後の混合物を粉砕して、深橙色の粉体(活物質の前躯体)を得た。 After adding water to the mixture after the hydrothermal synthesis reaction, the mixture was opened in a vat and evaporated to dryness at 90 ° C. for about 21 hours. The mixture after evaporation to dryness was pulverized to obtain a deep orange powder (active material precursor).
<焼成工程>
5.00gの前駆体をアルミナ坩堝に入れて、600℃で4時間焼成した後、急冷させた。なお、粉体の焼成は空気雰囲気中で行った。また、焼成工程では、焼成温度を45分かけて室温から450℃まで昇温させた。この焼成工程により、くすんだ緑色の粒子群(参考例1の活物質)を4.27g得た。
<Baking process>
5.00 g of the precursor was put in an alumina crucible, baked at 600 ° C. for 4 hours, and then rapidly cooled. The powder was fired in an air atmosphere. In the firing step, the firing temperature was raised from room temperature to 450 ° C. over 45 minutes. By this firing step, 4.27 g of a dull green particle group (active material of Reference Example 1) was obtained.
<結晶構造の測定>
粉末X線回折(XRD)に基づくリートベルト解析の結果から、参考例1の活物質は、LiVOPO4の粒子群を備え、粒子群中に存在するLiVOPO4のα型結晶相(以下、場合により「α相」と記す。)のモル数αと粒子群中に存在するLiVOPO4のβ型結晶相(以下、場合により「β相」と記す。)のモル数βとの比率α/βが、0.01であることが確認された。
<Measurement of crystal structure>
From the results of Rietveld analysis based on the powder X-ray diffraction (XRD), the active material of Reference Example 1 has a particle group of LiVOPO 4, alpha-type crystalline phase of the LiVOPO 4 present in the particles (hereinafter, optionally The ratio α / β between the number of moles α of “α phase” and the number of moles β of the β-type crystal phase of LiVOPO 4 present in the particle group (hereinafter sometimes referred to as “β phase”) is , 0.01 was confirmed.
<粒度分布の測定>
参考例1の活物質の粒度分布をレーザー散乱法(動的光散乱法)で測定した。粒度分布の測定には、Malvern社製の装置を用いた。参考例1の活物質の光強度基準の粒度分布Cを図1Aに示す。参考例1の活物質の体積基準の粒度分布Cを図1Bに示す。参考例1の活物質の粒子数基準の粒度分布Cを図1Cに示す。
<Measurement of particle size distribution>
The particle size distribution of the active material of Reference Example 1 was measured by a laser scattering method (dynamic light scattering method). An apparatus made by Malvern was used for measurement of the particle size distribution. The light intensity standard particle size distribution C of the active material of Reference Example 1 is shown in FIG. 1A. The volume-based particle size distribution C of the active material of Reference Example 1 is shown in FIG. 1B. The particle size distribution C based on the number of particles of the active material of Reference Example 1 is shown in FIG. 1C.
参考例1の加熱前の前駆体の光強度基準の粒度分布Aを図1Aに示す。参考例1の加熱前の前駆体の体積基準の粒度分布Aを図1Bに示す。参考例1の加熱前の前駆体の粒子数基準の粒度分布Aを図1Cに示す。 The particle size distribution A based on the light intensity of the precursor before heating in Reference Example 1 is shown in FIG. 1A. The volume-based particle size distribution A of the precursor before heating in Reference Example 1 is shown in FIG. 1B. The particle size distribution A based on the number of particles of the precursor before heating in Reference Example 1 is shown in FIG. 1C.
参考例1の前駆体を600℃で4時間焼成して得られた粉体(以下、「粉体B」と記す。)の光強度基準の粒度分布Bを図1Aに示す。粉体Bの体積基準の粒度分布Bを図1Bに示す。粉体Bの粒子数基準の粒度分布Bを図1Cに示す。 FIG. 1A shows the light intensity-based particle size distribution B of a powder obtained by firing the precursor of Reference Example 1 at 600 ° C. for 4 hours (hereinafter referred to as “powder B”). The volume-based particle size distribution B of the powder B is shown in FIG. 1B. A particle size distribution B based on the number of particles of the powder B is shown in FIG. 1C.
体積基準の粒度分布から参考例1の活物質の体積平均一次粒径を算出した。 The volume average primary particle size of the active material of Reference Example 1 was calculated from the volume-based particle size distribution .
<放電容量の測定>
参考例1の活物質と、バインダーであるポリフッ化ビニリデン(PVDF)とアセチレンブラックを混合したものを、溶媒であるN−メチル−2−ピロリドン(NMP)中に分散させてスラリーを調製した。なお、スラリーにおいて活物質とアセチレンブラックとPVDFとの重量比が84:8:8となるように、スラリーを調製した。このスラリーを集電体であるアルミニウム箔上に塗布し、乾燥させた後、圧延を行い、参考例1の活物質を含む活物質層が形成された電極(正極)を得た。
<Measurement of discharge capacity>
A slurry was prepared by dispersing the active material of Reference Example 1, polyvinylidene fluoride (PVDF) as a binder, and acetylene black in N-methyl-2-pyrrolidone (NMP) as a solvent. The slurry was prepared so that the weight ratio of the active material, acetylene black, and PVDF was 84: 8: 8 in the slurry. This slurry was applied on an aluminum foil as a current collector, dried, and then rolled to obtain an electrode (positive electrode) on which an active material layer containing the active material of Reference Example 1 was formed.
次に、得られた電極と、その対極であるLi箔とを、それらの間にポリエチレン微多孔膜からなるセパレータを挟んで積層し、積層体(素体)を得た。この積層体を、アルミラミネーターパックに入れ、このアルミラミネートパックに、電解液として1MのLiPF6溶液を注入した後、真空シールし、参考例1の評価用セルを作製した。 Next, the obtained electrode and the Li foil as the counter electrode were laminated with a separator made of a polyethylene microporous film interposed therebetween to obtain a laminate (element body). This laminate was placed in an aluminum laminator pack, and 1M LiPF 6 solution was injected as an electrolyte into the aluminum laminate pack, followed by vacuum sealing to produce an evaluation cell of Reference Example 1.
参考例1の評価用セルを用いて、放電レートを0.1C(25℃で定電流放電を行ったときに10時間で放電終了となる電流値)とした場合の放電容量(単位:mAh/g)を測定した。測定結果を表2に示す。 Using the evaluation cell of Reference Example 1, the discharge capacity (unit: mAh / unit) when the discharge rate is 0.1 C (current value at which discharge is completed in 10 hours when constant current discharge is performed at 25 ° C.) g) was measured. The measurement results are shown in Table 2.
(参考例2)
水熱合成反応前の混合物に、Li2CO3の代わりとして、20.7gのLiNO3を含有させたこと以外は、参考例1と同様の方法で、参考例2の活物質及び評価用セルを得た。
( Reference Example 2)
The active material and evaluation cell of Reference Example 2 were the same as Reference Example 1 except that 20.7 g of LiNO 3 was contained in the mixture before the hydrothermal synthesis reaction instead of Li 2 CO 3. Got.
(実施例3)
水熱合成反応前の混合物に、Li2CO3の代わりとして、7.2gのLiOHを含有させたこと以外は、参考例1と同様の方法で、実施例3の活物質及び評価用セルを得た。
(Example 3)
The active material and the evaluation cell of Example 3 were prepared in the same manner as in Reference Example 1 except that 7.2 g of LiOH was contained in the mixture before the hydrothermal synthesis reaction instead of Li 2 CO 3. Obtained.
(実施例4)
実施例4では、水熱合成反応前の混合物に、H3PO4の代わりとして(NH4)H2PO4を含有させ、Li2CO3の代わりとして20.7gのLiNO3を含有させた。また、実施例4では、水熱合成反応前の混合物に塩酸を加えて混合物のpHを調整した。以上の事項以外は、参考例1と同様の方法で、実施例4の活物質及び評価用セルを得た。
Example 4
In Example 4, the mixture before the hydrothermal synthesis reaction contained (NH 4 ) H 2 PO 4 instead of H 3 PO 4 and 20.7 g of LiNO 3 instead of Li 2 CO 3 . . In Example 4, hydrochloric acid was added to the mixture before the hydrothermal synthesis reaction to adjust the pH of the mixture. Except for the above, the active material and evaluation cell of Example 4 were obtained in the same manner as in Reference Example 1.
(参考例5)
参考例5では、水熱合成反応前の混合物に、H3PO4の代わりとして(NH4)H2PO4を含有させ、Li2CO3の代わりとして20.7gのLiNO3を含有させた。また、参考例5では、水熱合成反応前の混合物に塩酸を加えて混合物のpHを調整した。以上の事項以外は、参考例1と同様の方法で、参考例5の活物質及び評価用セルを得た。
( Reference Example 5)
In Reference Example 5, the mixture before the hydrothermal synthesis reaction contained (NH 4 ) H 2 PO 4 instead of H 3 PO 4 and 20.7 g of LiNO 3 instead of Li 2 CO 3 . . In Reference Example 5, hydrochloric acid was added to the mixture before the hydrothermal synthesis reaction to adjust the pH of the mixture. Except for the above, the active material and evaluation cell of Reference Example 5 were obtained in the same manner as in Reference Example 1.
(参考例6)
参考例6では、水熱合成反応前の混合物に、H3PO4の代わりとして(NH4)H2PO4を含有させ、Li2CO3の代わりとして20.7gのLiNO3を含有させた。また、参考例6では、水熱合成反応前の混合物に塩酸を加えて混合物のpHを調整した。以上の事項以外は、参考例1と同様の方法で、参考例6の活物質及び評価用セルを得た。
( Reference Example 6)
In Reference Example 6, the mixture before the hydrothermal synthesis reaction contained (NH 4 ) H 2 PO 4 instead of H 3 PO 4 and 20.7 g of LiNO 3 instead of Li 2 CO 3 . . In Reference Example 6, hydrochloric acid was added to the mixture before the hydrothermal synthesis reaction to adjust the pH of the mixture. Except for the above, the active material and evaluation cell of Reference Example 6 were obtained in the same manner as in Reference Example 1.
(比較例1)
LiNO3、V2O5及びH3PO4を、モル比で2:1:2となるように水に溶解させて、これらを80℃で攪拌し、水溶液を調製した。水溶液を蒸発乾固し、更に110℃下で一晩乾燥させた。乾燥後に得られた固形物を粉砕し、空気中において600℃で14時間焼成することにより、比較例1の活物質を得た。また、比較例1の活物質を用いたこと以外は、参考例1の同様の方法で、比較例1の評価用セルを得た。
(Comparative Example 1)
LiNO 3 , V 2 O 5 and H 3 PO 4 were dissolved in water at a molar ratio of 2: 1: 2 and stirred at 80 ° C. to prepare an aqueous solution. The aqueous solution was evaporated to dryness and further dried at 110 ° C. overnight. The solid material obtained after drying was pulverized and fired in air at 600 ° C. for 14 hours to obtain an active material of Comparative Example 1. Moreover, the evaluation cell of Comparative Example 1 was obtained in the same manner as in Reference Example 1 except that the active material of Comparative Example 1 was used.
(比較例2)
水熱合成反応前の混合物に、Li2CO3の代わりとして、20.7gのLiNO3を含有させ、更に濃度が28重量%であるアンモニア水を49.0g添加したこと以外は、参考例1と同様の方法で、比較例2の活物質及び評価用セルを得た。
(Comparative Example 2)
Reference Example 1 except that 20.7 g of LiNO 3 was contained in the mixture before the hydrothermal synthesis reaction instead of Li 2 CO 3 and 49.0 g of ammonia water having a concentration of 28% by weight was added. By the same method, the active material and evaluation cell of Comparative Example 2 were obtained.
(比較例3)
水熱合成反応前の混合物に、Li2CO3の代わりとして、20.7gのLiNO3を含有させ、H3PO4水溶液の代わりとして、39.6gのNH4H2(PO4)を含有させたこと以外は、参考例1と同様の方法で、比較例3の活物質及び評価用セルを得た。
(Comparative Example 3)
The mixture before the hydrothermal synthesis reaction contains 20.7 g of LiNO 3 instead of Li 2 CO 3 , and 39.6 g of NH 4 H 2 (PO 4 ) instead of the aqueous H 3 PO 4 solution. An active material and an evaluation cell of Comparative Example 3 were obtained in the same manner as in Reference Example 1 except that the above procedure was performed.
(比較例4)
水熱合成反応前の混合物に溶媒として濃塩酸を添加したこと以外は参考例2と同様にして、pHが0である混合物を得た。この混合物を用いて、参考例1と同様の方法で活物質の作製を試みた。しかし、不純物が多量に生成したことが原因で、比較例4の活物質を作製することはできなかった。
(Comparative Example 4)
A mixture having a pH of 0 was obtained in the same manner as in Reference Example 2 except that concentrated hydrochloric acid was added as a solvent to the mixture before the hydrothermal synthesis reaction. Using this mixture, an active material was produced in the same manner as in Reference Example 1. However, the active material of Comparative Example 4 could not be produced due to the generation of a large amount of impurities.
参考例1と同様の方法で、参考例2、実施例3、4、参考例5、6、及び比較例2、3の水熱合成反応前後における混合物のpHをそれぞれ測定した。また、参考例1と同様の方法で、参考例2、実施例3、4、参考例5、6、及び比較例1〜3の活物質の結晶構造、体積平均一次粒径、評価用セルの放電容量をそれぞれ求めた。結果を表2に示す。参考例1、2、実施例3、4、参考例5、6、1〜3の活物質のいずれも、LiVOPO4であることが確認された。表2では、α/βが0.05より大きい場合、活物質の結晶構造を「α」と記す。α/βが0.05以下である場合、又はβ相のみが検出され、α相が検出されなかった場合、活物質の結晶構造を「β」と記す。α/βが0.05以下であること、又はβ相のみが検出され、α相が検出されないことは、β−LiVOPO4が選択的に合成されていることを意味する。 In the same manner as in Reference Example 1, the pHs of the mixtures before and after the hydrothermal synthesis reaction of Reference Example 2 , Examples 3, 4, Reference Examples 5, 6, and Comparative Examples 2, 3 were measured. Further, in the same manner as in Reference Example 1, the crystal structures, volume average primary particle sizes, and evaluation cells of the active materials of Reference Example 2 , Examples 3, 4, Reference Examples 5, 6, and Comparative Examples 1 to 3 Each discharge capacity was determined. The results are shown in Table 2. It was confirmed that all of the active materials of Reference Examples 1 and 2, Examples 3 and 4, Reference Examples 5, 6 , and 1 to 3 were LiVOPO 4 . In Table 2, when α / β is larger than 0.05, the crystal structure of the active material is described as “α”. When α / β is 0.05 or less, or when only β phase is detected and α phase is not detected, the crystal structure of the active material is described as “β”. That α / β is 0.05 or less, or that only β phase is detected and α phase is not detected means that β-LiVOPO 4 is selectively synthesized.
表2に示すように、水熱合成反応前の混合物のpHが7以下である参考例1、2、実施例3、4、参考例5、6の活物質は、いずれもLiVOPO4のβ型結晶構造を有し、0.05以下のα/βを示すことが確認された。一方、水熱合成反応前の混合物のpHが7以上である比較例2、3の活物質は、0.12以上のα/βを示し、参考例1、2、実施例3、4、参考例5、6に比べて多量のα相を有することが確認された。 As shown in Table 2, the active materials of Reference Examples 1 and 2, Examples 3, 4 and Reference Examples 5 and 6 in which the pH of the mixture before the hydrothermal synthesis reaction is 7 or less are all β-forms of LiVOPO 4 It was confirmed that it has a crystal structure and exhibits an α / β of 0.05 or less. On the other hand, the active materials of Comparative Examples 2 and 3 in which the pH of the mixture before the hydrothermal synthesis reaction is 7 or more show α / β of 0.12 or more, and Reference Examples 1, 2, Examples 3, 4 and Reference Compared to Examples 5 and 6 , it was confirmed to have a larger amount of α phase.
水熱合成反応を用いずに得た比較例1の活物質は、α型結晶構造とβ型結晶構造の両方を有することが確認された。比較例1の活物質についてリートベルト解析を行ったところ、比較例1の活物質は、約8mol%の割合でα−LiVOPO4を含むことが確認された。 It was confirmed that the active material of Comparative Example 1 obtained without using the hydrothermal synthesis reaction had both an α-type crystal structure and a β-type crystal structure. When Rietveld analysis was performed on the active material of Comparative Example 1, it was confirmed that the active material of Comparative Example 1 contained α-LiVOPO 4 at a ratio of about 8 mol%.
以上のように、参考例1、2、実施例3、4、参考例5、6では、比較例1〜3に比べて、β―LiVOPO4が合成され易いことが確認された。また、参考例1、2、実施例3、4、参考例5、6の評価セルの放電容量は、比較例1〜3に比べて大きいことが確認された。 As described above, it was confirmed that in Reference Examples 1 and 2, Examples 3, 4 and Reference Examples 5 and 6, β-LiVOPO 4 was easily synthesized as compared with Comparative Examples 1 to 3. Moreover, it was confirmed that the discharge capacity of the evaluation cells of Reference Examples 1 and 2, Examples 3, 4 and Reference Examples 5 and 6 is larger than those of Comparative Examples 1 to 3.
d・・・粒径、A・・・参考例1の加熱前の前駆体の粒度分布、B・・・参考例1の前駆体を450℃で焼成して得られた粉体の粒度分布、C・・・参考例1の活物質の粒子分布。 d: particle size, A: particle size distribution of the precursor of Reference Example 1 before heating, B: particle size distribution of the powder obtained by firing the precursor of Reference Example 1 at 450 ° C., C: Particle distribution of the active material of Reference Example 1.
Claims (7)
圧下で加熱する水熱合成工程と、
前記水熱合成工程において加圧下で加熱した後の前記混合物を焼成する焼成工程と、
を備え、
前記水熱合成工程において、加熱前の前記混合物に、硝酸、塩酸又は硫酸の少なくとも
いずれかを添加する、活物質の製造方法。 A hydrothermal synthesis step of heating a mixture containing a lithium source, a phosphate source, a vanadium source, and water and having a pH of 7 or less under pressure;
A firing step of firing the mixture after heating under pressure in the hydrothermal synthesis step;
With
In the hydrothermal synthesis step, a method for producing an active material, wherein at least one of nitric acid, hydrochloric acid, and sulfuric acid is added to the mixture before heating.
びCH3COOLiからなる群より選ばれる少なくとも一種であり、
前記リン酸源が、H3PO4、NH4H2PO4、(NH4)2HPO4及びLi3P
O4からなる群より選ばれる少なくとも一種であり、
前記バナジウム源が、V2O5及びNH4VO3からなる群より選ばれる少なくとも一
種である、請求項1に記載の活物質の製造方法。 The lithium source is at least one selected from the group consisting of LiNO 3 , Li 2 CO 3 , LiOH, LiCl, Li 2 SO 4 and CH 3 COOLi;
The phosphoric acid source is H 3 PO 4 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 and Li 3 P
At least one selected from the group consisting of O 4 ,
The method for producing an active material according to claim 1, wherein the vanadium source is at least one selected from the group consisting of V 2 O 5 and NH 4 VO 3 .
前記リン酸源がH3PO4であり、
前記バナジウム源がV2O5である、請求項1又は2に記載の活物質の製造方法。 The lithium source is Li 2 CO 3 ;
The phosphate source is H 3 PO 4 ;
Wherein the vanadium source is V 2 O 5, method of manufacturing an active material according to claim 1 or 2.
請求項4に記載の活物質を含有し、前記集電体上に設けられた活物質層と、を備
える、電極。 A current collector,
An active material layer containing the active material according to claim 4 and provided on the current collector.
の電極。 The electrode according to claim 5 , wherein a content ratio of the particle group in the active material layer is 80 to 97% by mass.
A lithium ion secondary battery comprising the electrode according to claim 5 .
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