JP2010044963A - Positive electrode active material for nonaqueous electrolyte secondary battery, manufacturing method thereof, and nonaqueous electrolyte secondary battery - Google Patents
Positive electrode active material for nonaqueous electrolyte secondary battery, manufacturing method thereof, and nonaqueous electrolyte secondary battery Download PDFInfo
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- JP2010044963A JP2010044963A JP2008208553A JP2008208553A JP2010044963A JP 2010044963 A JP2010044963 A JP 2010044963A JP 2008208553 A JP2008208553 A JP 2008208553A JP 2008208553 A JP2008208553 A JP 2008208553A JP 2010044963 A JP2010044963 A JP 2010044963A
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- positive electrode
- active material
- secondary battery
- electrode active
- electrolyte secondary
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- 239000007774 positive electrode material Substances 0.000 title claims abstract description 69
- 239000011255 nonaqueous electrolyte Substances 0.000 title claims abstract description 58
- 238000004519 manufacturing process Methods 0.000 title claims description 17
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- RSNHXDVSISOZOB-UHFFFAOYSA-N lithium nickel Chemical compound [Li].[Ni] RSNHXDVSISOZOB-UHFFFAOYSA-N 0.000 claims abstract description 42
- 239000011163 secondary particle Substances 0.000 claims abstract description 31
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- 229910052744 lithium Inorganic materials 0.000 claims abstract description 26
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 23
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- 239000002245 particle Substances 0.000 claims description 37
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- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 description 2
- 150000002697 manganese compounds Chemical class 0.000 description 2
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Inorganic Compounds Of Heavy Metals (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
本発明は、非水系電解質二次電池に関し、特に、該非水系電解質二次電池の正極材料として用いられ、リチウムニッケル複合酸化物からなる正極活物質およびその製造方法に関する。 The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a positive electrode active material that is used as a positive electrode material of the non-aqueous electrolyte secondary battery and is made of a lithium nickel composite oxide and a method for producing the same.
非水系電解質二次電池であるリチウム二次電池は、小型で高容量であることから、携帯電話、ビデオカムおよびＰＤＡ（Personal Digital Assistants）などの小型移動機器の電源として搭載されている。さらに、ハイブリッドカーに代表される自動車への搭載を目指して、研究および開発が進められている。このような背景から、リチウム二次電池に対しては、より高い容量が要求されてきているが、特に、自動車搭載用のリチウム二次電池は、民生用に比べてより高い安全性が要求されている。 Lithium secondary batteries, which are non-aqueous electrolyte secondary batteries, are small and have high capacity, and are therefore mounted as power sources for small mobile devices such as mobile phones, video cams, and PDAs (Personal Digital Assistants). In addition, research and development are underway with the aim of mounting on automobiles represented by hybrid cars. From such a background, a higher capacity has been required for lithium secondary batteries, and in particular, lithium secondary batteries for automobiles are required to have higher safety compared to consumer use. ing.
リチウム二次電池の正極材料の一つであるリチウムニッケル複合酸化物は、現在、主流のリチウムコバルト複合酸化物と比べて、高容量であること、原料であるＮｉがＣｏと比べて安価で、安定して入手可能であることなどの利点を持っていることから、次世代の正極材料として期待され、活発に研究および開発が続けられている。 Lithium nickel composite oxide, which is one of the positive electrode materials for lithium secondary batteries, has a higher capacity than the mainstream lithium cobalt composite oxide, and Ni, which is a raw material, is cheaper than Co. Since it has advantages such as being available stably, it is expected as a next-generation positive electrode material, and research and development are actively continued.
リチウムニッケル複合酸化物（ＬｉＮｉＯ2）は、リチウムコバルト複合酸化物（ＬｉＣｏＯ2）とほぼ同じ理論容量を持ち、リチウムコバルト複合酸化物よりもやや低い電池電圧を示す。このため、電解液の酸化による分解が問題になりにくく、より高容量が期待できることから、開発が盛んに行われている。 Lithium nickel composite oxide (LiNiO 2 ) has almost the same theoretical capacity as lithium cobalt composite oxide (LiCoO 2 ), and shows a slightly lower battery voltage than lithium cobalt composite oxide. For this reason, decomposition | disassembly by oxidation of electrolyte solution does not become a problem, and development is performed actively from expecting higher capacity | capacitance.
しかしながら、リチウムニッケル複合酸化物は、満充電状態で高温環境下に放置しておくと、リチウムコバルト複合酸化物に比べて低い温度からリチウムニッケル複合酸化物の分解による酸素放出を起こすといった問題がある。さらに高温環境下で不安定となったリチウムニッケル複合酸化物中のＮｉが、電解液と接触することにより触媒的な働きをし、放出された酸素との反応を促進し発火し易くなるという安全性の問題がある。 However, when the lithium nickel composite oxide is left in a high temperature environment in a fully charged state, there is a problem that oxygen release occurs due to decomposition of the lithium nickel composite oxide from a lower temperature than the lithium cobalt composite oxide. . In addition, the Ni in the lithium-nickel composite oxide that has become unstable under high-temperature environments acts as a catalyst when it comes into contact with the electrolyte, promoting the reaction with the released oxygen and facilitating ignition. There is a sex problem.
このような問題を解決するために、さまざまな添加元素による電池特性の改善が検討されている。例えば特許文献１では、リチウムイオン二次電池正極材料の熱安定性を向上させることを目的として、ＬｉaＭbＮｉcＣｏdＯe(Ｍは、Ａｌ、Ｍｎ、Ｓｎ、Ｉｎ、Ｆｅ、Ｖ、Ｃｕ、Ｍｇ、Ｔｉ、Ｚｎ、Ｍｏからなる群から選択される少なくとも一種の添加元素であり、かつ０＜ａ＜１．３、０．０２≦ｂ≦０．５、０．０２≦ｄ／ｃ＋ｄ≦０．９、１．８＜ｅ＜２．２の範囲であって、さらにｂ＋ｃ＋ｄ＝１である)で表されるリチウム金属複合酸化物等が提案されている。この場合に添加元素Ｍとして、例えばＡｌを選択した場合、ＮｉからＡｌへの置換量を多くすれば正極活物質の分解反応は抑えられ、熱安定性は向上することが確かめられている。しかしながら、十分な安定性を確保するのに有効なＡｌでＮｉを置換すると、酸化還元反応に寄与するＮｉの量が減少するため、電池性能として最も重要である初期容量が大きく低下するという問題点を有している。 In order to solve such problems, improvement of battery characteristics by various additive elements has been studied. For example, in Patent Document 1, Li a Mb Ni c Co d O e (M is Al, Mn, Sn, In, Fe, V, V) for the purpose of improving the thermal stability of a positive electrode material of a lithium ion secondary battery. , Cu, Mg, Ti, Zn, Mo, and at least one additive element selected from the group consisting of 0 <a <1.3, 0.02 ≦ b ≦ 0.5, 0.02 ≦ d / In the range of c + d ≦ 0.9, 1.8 <e <2.2, and b + c + d = 1), a lithium metal composite oxide or the like has been proposed. In this case, for example, when Al is selected as the additive element M, it is confirmed that if the amount of substitution from Ni to Al is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved. However, if Ni is substituted with Al effective to ensure sufficient stability, the amount of Ni contributing to the oxidation-reduction reaction decreases, so the initial capacity, which is the most important for battery performance, is greatly reduced. have.
一方、添加元素の濃度分布による改善として、特許文献２には、構造的安定性を向上させてサイクル安定性を改善することを目的として、ＬｉＣｏＯ2コアとＡｌ、Ｍｇ、Ｓｎ、Ｃａ、ＴｉおよびＭｎからなる群より選択される金属を含み、この金属が表層から前記コアの中心部まで異なる濃度勾配で分布されていることを特徴とするリチウム二次電池用正極活物質が開示されている。しかしながら、このリチウム二次電池用正極活物質は、構造的安定性を向上させてサイクル安定性を改善することを目的としたものであり、安全性の改善については、考慮されていない。また、リチウムニッケル複合酸化物への適応は考慮されておらず、その効果も不明である。 On the other hand, as an improvement due to the concentration distribution of the additive element, Patent Document 2 describes that LiCoO 2 core and Al, Mg, Sn, Ca, Ti and the like are used for the purpose of improving the structural stability and improving the cycle stability. A positive electrode active material for a lithium secondary battery is disclosed, which contains a metal selected from the group consisting of Mn, and the metal is distributed with different concentration gradients from the surface layer to the center of the core. However, this positive electrode active material for lithium secondary batteries is intended to improve the structural stability and improve the cycle stability, and no consideration is given to improving the safety. Moreover, the application to lithium nickel composite oxide is not considered, and the effect is also unclear.
さらに、特許文献３には、リチウムマンガン複合酸化物からなる種結晶とリチウム塩とマンガン化合物とを湿式粉砕混合してスラリーを調整し、この際に、種結晶中のマンガン原子数に対するリチウム原子数の比をＡ、スラリー中のマンガン化合物に由来するマンガン原子数に対するリチウム塩に由来するリチウム原子数の比をＢとしてＡ＞Ｂとなるように調整し、得られたスラリーをスプレードライヤーで処理し、焼成することにより得られた、粒子内で中心から周辺にかけてリチウム濃度勾配を持つことを特徴とする非水リチウム二次電池用のリチウムマンガン複合酸化物粒子が開示されている。しかしながら、この非水リチウム二次電池用のリチウムマンガン複合酸化物粒子おいても、充放電サイクル特性の改善を目的としたものであり、安全性の改善について考慮したものではない。また、リチウムニッケル複合酸化物への適応は考慮されておらず、さらに、得られた非水リチウム二次電池用のリチウムマンガン複合酸化物粒子は、初期容量が低く、高容量と安全性が両立した非水系電解質二次電池用正極活物質とも言い難い。 Furthermore, in Patent Document 3, a seed crystal comprising a lithium manganese composite oxide, a lithium salt, and a manganese compound are wet pulverized and mixed to prepare a slurry. At this time, the number of lithium atoms relative to the number of manganese atoms in the seed crystal The ratio of A is adjusted so that A> B where B is the ratio of the number of lithium atoms derived from the lithium salt to the number of manganese atoms derived from the manganese compound in the slurry, and the resulting slurry is treated with a spray dryer. A lithium manganese composite oxide particle for a non-aqueous lithium secondary battery obtained by firing and having a lithium concentration gradient from the center to the periphery in the particle is disclosed. However, the lithium manganese composite oxide particles for the non-aqueous lithium secondary battery are also intended to improve the charge / discharge cycle characteristics, and are not intended to improve safety. In addition, application to lithium-nickel composite oxides is not considered, and the obtained lithium manganese composite oxide particles for non-aqueous lithium secondary batteries have a low initial capacity and achieve both high capacity and safety. It is difficult to say that the positive electrode active material for a non-aqueous electrolyte secondary battery.
近年、二次電池に対する高容量化の要求は高まる一方であるが、安全性を確保するために容量を犠牲にすることは、リチウムニッケル複合酸化物の高容量のメリットを失うことになり高容量化の要求に応えられなくなる。また、リチウムイオン二次電池を大型二次電池に用いようという動きも盛んであり、中でもハイブリッド自動車用、電気自動車用の電源としての期待が大きい。このように自動車用の電源として用いられる場合、安全性に劣るというリチウムニッケル複合酸化物の問題点の解消は大きな課題である。 In recent years, the demand for higher capacity for secondary batteries has been increasing, but sacrificing capacity to ensure safety will lose the merit of high capacity of lithium nickel composite oxide. It will not be possible to meet the demands of computerization. In addition, a movement to use a lithium ion secondary battery for a large-sized secondary battery is also prominent. In particular, there is a great expectation as a power source for a hybrid vehicle and an electric vehicle. Thus, when used as a power source for automobiles, it is a big problem to solve the problem of the lithium nickel composite oxide that is inferior in safety.
以上のように、高い充放電容量と安全性を両立させたリチウム金属複合酸化物は見出されておらず、これらの問題を解決した非水系電解質二次電池が望まれている。
本発明は、かかる問題点に鑑みてなされたものであって、安全性が高く、かつ、高い充放電容量を有するという２つの特性を両立させた非水系電解質二次電池、および、かかる特性を有する非水系電解質二次電池を実現することが可能な正極活物質を提供することを目的とする。さらに詳しくは、特にハイブリッドカーに代表される自動車への搭載の場合に生じる不安定なモード、特に熱が加わる状況・環境においても高い安全性と高容量を両立させうる非水系電解質二次電池用正極活物質および非水系電解質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 such problems, and is a non-aqueous electrolyte secondary battery that has both the high safety and high charge / discharge capacity, and the above characteristics. It aims at providing the positive electrode active material which can implement | achieve the nonaqueous electrolyte secondary battery which has. More specifically, for non-aqueous electrolyte secondary batteries that can achieve both high safety and high capacity even in unstable modes that occur especially when mounted on automobiles typified by hybrid cars, especially in situations and environments where heat is applied. An object is to provide a positive electrode active material and a non-aqueous electrolyte secondary battery.
本発明に係る非水系電解質二次電池用正極活物質は、Ｃｏ、ＡｌおよびＭｎからなる群から選ばれる１種以上の添加元素Ｍ1と、Ａｌ、Ｍｎ、ＴｉおよびＭｇからなる群から選ばれるＭ1以外の１種以上の添加元素Ｍ2とを含む、ＬｉとＮｉとを主成分とするリチウムニッケル複合酸化物からなる非水系電解質二次電池用正極活物質であって、前記正極活物質の二次粒子の表層部と中心部とにおける前記添加元素Ｍ2の原子濃度比が１．２５〜３であることを特徴とする。 The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention includes at least one additive element M1 selected from the group consisting of Co, Al and Mn, and M1 selected from the group consisting of Al, Mn, Ti and Mg. A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium nickel composite oxide containing Li and Ni as main components and containing one or more additional elements M2 other than The atomic concentration ratio of the additive element M2 in the surface layer portion and the central portion of the particle is 1.25 to 3.
前記リチウムニッケル複合酸化物は、一般式：ＬｉzＮｉ1-x-yＣｏxＭyＯ2（ただし、式中のｘ、ｙ、ｚの値の範囲は、０．１０≦ｘ≦０．２１、０．０５≦ｙ≦０．０８、０．９８≦ｚ≦１．１０である。）で表されるものであることが好ましい。 The lithium nickel composite oxide represented by the general formula: Li z Ni 1-xy Co x M y O 2 ( here, x in the formula, y, a range of values of z is 0.10 ≦ x ≦ 0.21, 0.05 ≦ y ≦ 0.08 and 0.98 ≦ z ≦ 1.10.).
前記リチウムニッケル複合酸化物の二次粒子の平均粒径は５〜１５μｍであることが好ましい。 The average particle diameter of the secondary particles of the lithium nickel composite oxide is preferably 5 to 15 μm.
さらに、本発明の非水系電解質二次電池は、前記のいずれかの非水系電解質二次電池用正極活物質を正極として用いたものである。 Furthermore, the non-aqueous electrolyte secondary battery of the present invention uses any of the positive electrode active materials for non-aqueous electrolyte secondary batteries as a positive electrode.
一方、本発明の非水系電解質二次電池用正極活物質の製造方法は、Ｃｏ、ＡｌおよびＭｎからなる群から選ばれる１種以上の添加元素Ｍ1と、Ａｌ、Ｍｎ、ＴｉおよびＭｇからなる群から選ばれるＭ1以外の１種以上の添加元素Ｍ2を含む、リチウムとニッケルとを主成分とするリチウムニッケル複合酸化物からなる非水系電解質二次電池用正極活物質の製造方法に係る。 On the other hand, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention includes at least one additive element M1 selected from the group consisting of Co, Al and Mn, and a group consisting of Al, Mn, Ti and Mg. The present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium-nickel composite oxide containing lithium and nickel as main components and containing one or more additional elements M2 other than M1 selected from
特に、本発明では、Ｎｉと添加元素Ｍ1との複合水酸化物の粒子表面に、添加元素Ｍ2の化合物を吸着させ、該添加元素Ｍ2が表面に吸着した前記複合水酸化物を６５０〜７５０℃の温度で酸化焙焼して、Ｎｉと添加元素Ｍ1と添加元素Ｍ2との複合酸化物を得て、該複合酸化物とリチウム塩とを混合し、得られた混合物を６５０〜７５０℃の温度で焼成することにより、前記リチウムニッケル複合酸化物を得ることを特徴とする。 In particular, in the present invention, the compound hydroxide of the additive element M2 is adsorbed on the particle surface of the composite hydroxide of Ni and the additive element M1, and the complex hydroxide adsorbed on the surface of the additive element M2 is 650 to 750 ° C. The composite oxide of Ni, additive element M1, and additive element M2 is obtained by oxidizing and roasting at a temperature of, and the composite oxide and lithium salt are mixed. The resulting mixture is heated to a temperature of 650-750 ° C. The lithium nickel composite oxide is obtained by firing at
本発明に係る非水系電解質二次電池用正極活物質は、高い安全性と高容量を同時に達成できるものであり、この正極活物質を正極に使用した非水系電解質二次電池は、自動車の搭載用として好適である。よって、本発明の工業的価値は極めて大きい。 The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention can achieve high safety and high capacity at the same time, and the non-aqueous electrolyte secondary battery using this positive electrode active material as a positive electrode is mounted on an automobile. Suitable for use. Therefore, the industrial value of the present invention is extremely large.
本発明者らは、高い安全性と高容量とを両立させた非水系電解質二次電池用正極活物質について、鋭意研究した結果、リチウムニッケル複合酸化物の二次粒子内部において、安全性を改善するために添加されるＡｌ、Ｍｎ、Ｔｉ、Ｍｇ等の添加元素の濃度分布に、粒子半径に対する特定の濃度勾配を持たせることで、高い安全性と高容量とを両立させることが可能であることとの知見を得て、本発明を完成するに至ったものである。 As a result of earnest research on the positive electrode active material for a non-aqueous electrolyte secondary battery that achieves both high safety and high capacity, the present inventors have improved safety within the secondary particles of the lithium nickel composite oxide. It is possible to achieve both high safety and high capacity by providing a specific concentration gradient with respect to the particle radius in the concentration distribution of additive elements such as Al, Mn, Ti, Mg, etc. to be added The present invention has been completed with the knowledge of the above.
以下に、非水系電解質二次電池用正極活物質、当該正極活物質の製造方法および当該正極活物質を正極として用いた非水系電解質二次電池のそれぞれについて説明する。 Below, each of the positive electrode active material for nonaqueous electrolyte secondary batteries, the manufacturing method of the said positive electrode active material, and the nonaqueous electrolyte secondary battery using the said positive electrode active material as a positive electrode is demonstrated.
１．正極活物質
本発明の非水系電解質二次電池用正極活物質を構成するリチウムニッケル複合酸化物においては、安全性を改善するために、さまざまな添加元素による改善が検討されている。かかる添加元素がリチウムニッケル複合酸化物の結晶中に均一に拡散されると、該複合酸化物の結晶構造が安定化する。しかしながら、安全性を改善するために添加元素を増加させると、酸化還元反応に寄与するＮｉの量が減少するため、電池性能として最も重要である初期容量が大きく低下する結果となってしまう。したがって、安全性を改善するために添加される元素の添加量は可能な限り少なくする必要がある。
1. Cathode Active Material In the lithium nickel composite oxide constituting the cathode active material for a non-aqueous electrolyte secondary battery of the present invention, improvements by various additive elements are being studied in order to improve safety. When such an additive element is uniformly diffused into the crystal of the lithium nickel composite oxide, the crystal structure of the composite oxide is stabilized. However, when the additive element is increased in order to improve safety, the amount of Ni that contributes to the oxidation-reduction reaction decreases, resulting in a significant decrease in the initial capacity, which is most important as battery performance. Therefore, it is necessary to reduce the amount of elements added to improve safety as much as possible.
リチウムニッケル複合酸化物は、満充電状態で高温環境下に放置しておくと、リチウムコバルト複合酸化物に比べて低い温度から酸素を放出し、さらに高温環境下で不安定となったリチウムニッケル複合酸化物中のＮｉが、電解液と接触することにより触媒的な働きをし、放出された酸素との反応を促進し発火し易くなる。以上のことから、リチウムニッケル複合酸化物の安全性に対しては、リチウムニッケル複合酸化物粒子の表層部の影響が大きい。 Lithium nickel composite oxide releases oxygen from a lower temperature than lithium cobalt composite oxide when left in a fully charged state in a high temperature environment, and further becomes unstable in a high temperature environment. When Ni in the oxide comes into contact with the electrolytic solution, it acts as a catalyst, accelerates the reaction with the released oxygen, and easily ignites. From the above, the surface layer portion of the lithium nickel composite oxide particles has a great influence on the safety of the lithium nickel composite oxide.
したがって、少なくともリチウムニッケル複合酸化物の粒子の表層部の酸素放出およびニッケルの不安定化を改善することによって、リチウムニッケル複合酸化物は大きく改善される。このため、本発明の非水系電解質二次電池用正極活物質においては、粒子の表層部では、安全性を改善するために十分な添加元素濃度とし、粒子の中心部においては、容量を確保するため添加元素濃度を最低限の量とする必要がある。 Accordingly, the lithium nickel composite oxide is greatly improved by improving oxygen release and nickel destabilization at least in the surface layer portion of the particles of the lithium nickel composite oxide. For this reason, in the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the additive element concentration is sufficient in the surface layer portion of the particle to improve safety, and the capacity is ensured in the central portion of the particle. Therefore, it is necessary to make the additive element concentration a minimum amount.
すなわち、Ｃｏ、ＡｌおよびＭｎからなる群から選ばれる１種以上の添加元素Ｍ1と、Ａｌ、Ｍｎ、ＴｉおよびＭｇからなる群から選ばれるＭ1以外の１種以上の添加元素Ｍ2とを含む、リチウムニッケル複合酸化物からなる非水系電解質二次電池用正極活物質において、正極活物質の二次粒子の内部にわたって添加元素Ｍ2が存在するものの、該正極活物質の二次粒子の表層部と中心部における添加元素Ｍ2の原子濃度比（表層部濃度／中心部濃度）を１．２５〜３となるように、該添加元素Ｍ2の二次粒子内部における濃度勾配を規制する。ここで、前記原子濃度比が１．２５未満であると、高容量が得られるが安全性が低下する。一方、原子濃度比が３を超えると、安全性は確保されるが容量が低下してしまう。したがって、原子濃度比を１．２５〜３の範囲とすることで高い安全性と高容量とを両立させることができる。なお、ここで、表層部とは、最表面から半径の１０％の深さまでの部分をいい、中心部とは、粒子の中心から半径の３０％以内の部分をいう。なお、該正極活物質の二次粒子の表層部と中心部における添加元素Ｍ2の原子濃度は、活物質を収束イオンビーム（ＦＩＢ）などで断面を露出させ、電子線マイクロアナライザー（ＥＰＭＡ）の線分析等により測定できる。 That is, lithium containing one or more additive elements M1 selected from the group consisting of Co, Al and Mn, and one or more additional elements M2 other than M1 selected from the group consisting of Al, Mn, Ti and Mg In the positive electrode active material for a non-aqueous electrolyte secondary battery made of a nickel composite oxide, although the additive element M2 is present inside the secondary particles of the positive electrode active material, the surface layer portion and the central portion of the secondary particles of the positive electrode active material The concentration gradient in the secondary particles of the additive element M2 is regulated so that the atomic concentration ratio (surface layer portion concentration / center portion concentration) of the additive element M2 in 1.25 is 1.25-3. Here, when the atomic concentration ratio is less than 1.25, a high capacity can be obtained, but safety is lowered. On the other hand, when the atomic concentration ratio exceeds 3, safety is ensured but the capacity decreases. Therefore, it is possible to achieve both high safety and high capacity by setting the atomic concentration ratio in the range of 1.25 to 3. Here, the surface layer portion refers to a portion from the outermost surface to a depth of 10% of the radius, and the central portion refers to a portion within 30% of the radius from the center of the particle. The atomic concentration of the additive element M2 in the surface layer portion and the central portion of the secondary particle of the positive electrode active material is determined by exposing the cross section of the active material with a focused ion beam (FIB) or the like, and using the electron microanalyzer (EPMA) line. It can be measured by analysis.
このうち、添加元素Ｍ1は、サイクル特性の向上に寄与する元素である。かかる添加元素Ｍ1としては、Ｃｏ、Ａｌ、Ｍｎ等を挙げることができる。ただし、これらのうち、少ない添加量でサイクル特性改善効果の特に高い添加元素Ｍ1としてはＣｏを用いることが好ましい。 Among these, the additive element M1 is an element that contributes to improvement of cycle characteristics. Examples of the additive element M1 include Co, Al, and Mn. However, among these, it is preferable to use Co as the additive element M1 having a particularly high effect of improving the cycle characteristics with a small addition amount.
一方、添加元素Ｍ2は、特に限定されるものではないが、安全性の改善に効果がある元素であればよいが、Ａｌ、Ｍｎ、ＴｉおよびＭｇから選ばれる１種以上の金属元素とすることが好ましく、ＡｌまたはＭｎが特に好ましい。ＡｌまたはＭｎ、あるいはその両方を添加することが安全性改善面の効果が大きい。添加元素Ｍ2が、リチウムニッケル複合酸化物中の結晶中に拡散されると、リチウムニッケル複合酸化物中の結晶構造が安定化する。このことにより、非水系電解質二次電池の熱安定性を高めることができる。また、本発明における二次粒子の表層部と中心部での添加元素Ｍ2の原子濃度比を制御する観点から、強固な酸化物を形成するＡｌが添加元素Ｍ2として特に好適である。 On the other hand, the additive element M2 is not particularly limited, but may be any element that is effective in improving safety, but should be one or more metal elements selected from Al, Mn, Ti, and Mg. Are preferred, and Al or Mn is particularly preferred. Addition of Al, Mn, or both has a great effect on safety improvement. When the additive element M2 is diffused into the crystal in the lithium nickel composite oxide, the crystal structure in the lithium nickel composite oxide is stabilized. As a result, the thermal stability of the non-aqueous electrolyte secondary battery can be enhanced. Further, from the viewpoint of controlling the atomic concentration ratio of the additive element M2 in the surface layer portion and the central portion of the secondary particles in the present invention, Al forming a strong oxide is particularly suitable as the additive element M2.
具体的には、前記リチウムニッケル複合酸化物は、一般式：ＬｉzＮｉ1-x-yＣｏxＭ2yＯ2（ただし、式中のｘ、ｙ、ｚの値の範囲は、０．１０≦ｘ≦０．２１、０．０５≦ｙ≦０．０８、０．９８≦ｚ≦１．１０である。）で表される組成であることが好ましい。 Specifically, the lithium nickel composite oxide has a general formula: Li z Ni 1-xy Co x M 2 y O 2 (where x, y, and z are in the range of 0.10 ≦ x ≦ 0.21, 0.05 ≦ y ≦ 0.08, and 0.98 ≦ z ≦ 1.10.
このうち、添加元素Ｍ1の添加量を示すｘの値が０．１０よりも小さいと、十分なサイクル特性を得ることはできず、容量維持率も低下してしまう。また、ｘの値が０．２１を超えると、初期放電容量の低下が大きくなってしまうだけでなく、高価なＣｏの量が増加することとなり、コストの観点からも実用的でないものとなる。 Of these, if the value of x indicating the amount of additive element M1 added is less than 0.10, sufficient cycle characteristics cannot be obtained, and the capacity retention rate will also decrease. On the other hand, if the value of x exceeds 0.21, not only will the initial discharge capacity decrease, but the amount of expensive Co will increase, making it impractical from a cost standpoint.
また、添加元素Ｍ2の添加量を示すｙの値が０．０５よりも少ないと、結晶構造の安定化が認められず、ｙが０．０８を超えると、結晶構造の安定化はより向上するが、初期放電容量の低下が大きくなってしまうため、好ましくない。 Further, if the value of y indicating the amount of additive element M2 added is less than 0.05, stabilization of the crystal structure is not recognized, and if y exceeds 0.08, stabilization of the crystal structure is further improved. However, it is not preferable because the initial discharge capacity is greatly reduced.
本発明において、リチウムニッケル複合酸化物は、一次粒子が凝集した球状の二次粒子の形態であり、二次粒子の平均粒径は、５〜１５μｍである。平均粒径が５μｍ未満であると、タップ密度が下がり、単位体積当たりの電池容量が低下し、一方、平均粒径が１５μｍを超えると、粒子内部でのリチウムの拡散が進まず、正極活物質の利用率が下がってしまう。なお、平均粒径の測定には、レーザー散乱方式の粒度分布測定装置が用いられる。 In the present invention, the lithium nickel composite oxide is in the form of spherical secondary particles in which primary particles are aggregated, and the average particle size of the secondary particles is 5 to 15 μm. When the average particle size is less than 5 μm, the tap density decreases and the battery capacity per unit volume decreases. On the other hand, when the average particle size exceeds 15 μm, the diffusion of lithium inside the particles does not progress, and the positive electrode active material The usage rate of will decrease. For measuring the average particle size, a laser scattering type particle size distribution measuring device is used.
２．正極活物質の製造方法
本発明の非水系電解質二次電池用正極活物質の製造方法について、リチウムニッケル複合酸化物が、一般式：ＬｉzＮｉ1-x-yＣｏxＭ2yＯ2（ただし、式中のｘ、ｙ、ｚの値の範囲は、０．１０≦ｘ≦０．２１、０≦ｙ≦０．０８、０．９８≦ｚ≦１．１０である）で表される場合（Ｍ1がＣｏの場合）を例として、以下に詳細に説明する。
2. Method for Producing Positive Electrode Active Material Regarding the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the lithium nickel composite oxide is represented by the general formula: Li z Ni 1-xy Co x M 2 y O 2 The range of the values of x, y, z in the case is expressed as 0.10 ≦ x ≦ 0.21, 0 ≦ y ≦ 0.08, 0.98 ≦ z ≦ 1.10. The case will be described in detail below, taking as an example.
なお、本発明に係る非水系電解質二次電池用正極活物質の製造方法は、本明細書に記載されている製造方法に特に限定されるものではなく、以下に記載されている製造方法に照らして、当業者の知識に基づき種々の変更、改良を施した形態で実施することができることはいうまでもない。 In addition, the manufacturing method of the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is not particularly limited to the manufacturing method described in this specification, and in light of the manufacturing method described below. Needless to say, various modifications and improvements can be made based on the knowledge of those skilled in the art.
（ニッケルコバルト複合水酸化物の製造）
まず、ニッケルコバルト複合水酸化物を製造する。ニッケルコバルト複合水酸化物は公知の技術により製造が可能である。例えば、所定割合に配合されたニッケル塩とコバルト塩を含む水溶液にアルカリ水溶液を添加してｐＨを調整し、ニッケルとコバルトの水酸化物を共沈させることでニッケルコバルト複合水酸化物が得られる。ニッケル塩としては、水に溶けやすいという理由から、塩化ニッケルや硫酸ニッケルが好ましく、特に、不純物の制御が容易という点から、硫酸ニッケルが好ましい。また、コバルト塩としては、水に溶けやすいという理由から、塩化コバルトや硫酸コバルトが好ましく、特に、不純物の制御が容易という点から硫酸コバルトが好ましい。水溶液中のＮｉとＣｏの割合は、最終的に得ようとするリチウムニッケル複合酸化物の組成に基づいて適宜決定することができる。また、共沈条件としては、液温５０〜８０℃、ｐＨが１０.０〜１２．５とすることが好ましく、アンモニウムイオン供給体などの錯化剤を水溶液に添加してもよい。
(Manufacture of nickel cobalt composite hydroxide)
First, nickel cobalt composite hydroxide is manufactured. Nickel-cobalt composite hydroxide can be produced by a known technique. For example, a nickel-cobalt composite hydroxide can be obtained by adjusting the pH by adding an aqueous alkaline solution to an aqueous solution containing nickel salt and cobalt salt blended in a predetermined ratio and coprecipitating nickel and cobalt hydroxides. . As the nickel salt, nickel chloride or nickel sulfate is preferable because it is easily dissolved in water, and nickel sulfate is particularly preferable because it is easy to control impurities. Further, as the cobalt salt, cobalt chloride and cobalt sulfate are preferable because they are easily dissolved in water, and cobalt sulfate is particularly preferable because impurities can be easily controlled. The ratio of Ni and Co in the aqueous solution can be appropriately determined based on the composition of the lithium nickel composite oxide to be finally obtained. The coprecipitation conditions are preferably a liquid temperature of 50 to 80 ° C. and a pH of 10.0 to 12.5, and a complexing agent such as an ammonium ion supplier may be added to the aqueous solution.
得られるニッケルコバルト複合水酸化物は、一次粒子が凝集した二次粒子であるが、二次粒子の形状は球形であることが好ましく、最終的に得られる正極活物質における好適な粉体特性を考慮して、平均粒径は５〜１５μｍとすることが好ましい。このような形状および平均粒径を有する二次粒子は、上記水溶液とアルカリ水溶液の混合速度、共沈条件を制御することで得ることができる。 The nickel-cobalt composite hydroxide obtained is a secondary particle in which primary particles are aggregated, but the shape of the secondary particle is preferably spherical, and suitable powder characteristics in the finally obtained positive electrode active material are obtained. Considering this, the average particle size is preferably 5 to 15 μm. Secondary particles having such a shape and average particle diameter can be obtained by controlling the mixing speed and coprecipitation conditions of the aqueous solution and the alkaline aqueous solution.
得られたニッケルコバルト複合水酸化物について、ろ過、水洗および乾燥を行なうが、これらの処理は通常に行われる方法でよい。 The obtained nickel cobalt composite hydroxide is filtered, washed with water, and dried, and these treatments may be performed by ordinary methods.
上記製造方法は添加元素としてＣｏを選択した場合であるが、Ｃｏ以外の添加元素Ｍ1としてＡｌ、Ｍｎを選択した場合には、コバルト塩に代えて、添加しようとする元素の水溶性塩を用いることにより、同様の方法で得られる。 In the above manufacturing method, Co is selected as the additive element, but when Al and Mn are selected as the additive element M1 other than Co, a water-soluble salt of the element to be added is used instead of the cobalt salt. Can be obtained in the same manner.
（添加元素Ｍ2の化合物の吸着）
次に、得られたニッケルコバルト複合水酸化物の粒子表面に、添加元素Ｍ2であるＡｌ、Ｍｎ、ＴｉおよびＭｇからなる群から選ばれる１種以上の添加元素の化合物を吸着させる。かかる吸着は、ニッケルコバルト複合水酸化物の二次粒子をスラリーとし、ｐＨを調整しながらスラリーを撹拌しつつ、添加元素Ｍ2の金属塩を含む水溶液を添加することにより行なう。または、スラリーに所望の量の該金属塩を含む水溶液を混合した後、ｐＨを調整して、これにニッケルコバルト複合水酸化物を添加して、その二次粒子の表面に添加元素Ｍ2の化合物を吸着させてもよい。
(Adsorption of compound of additive element M2)
Next, a compound of one or more additive elements selected from the group consisting of Al, Mn, Ti, and Mg, which are additive elements M2, is adsorbed on the particle surfaces of the obtained nickel-cobalt composite hydroxide. Such adsorption is performed by adding an aqueous solution containing a metal salt of the additive element M2 while stirring the slurry while adjusting the pH while making secondary particles of nickel-cobalt composite hydroxide as a slurry. Alternatively, after mixing an aqueous solution containing the desired amount of the metal salt into the slurry, the pH is adjusted, and nickel cobalt composite hydroxide is added thereto, and the compound of the additive element M2 is added to the surface of the secondary particles. May be adsorbed.
金属塩の添加量は、最終的に得ようとするリチウムニッケル複合酸化物の一般式における添加元素Ｍ2の割合と金属Ｍ2の金属塩からの化合物析出率とから容易に決定することができる。通常は、金属塩からほぼ全量が化合物として析出するため、リチウムニッケル複合酸化物の化学式における添加元素Ｍ2の割合から、金属塩の添加量を求めればよい。 The addition amount of the metal salt can be easily determined from the ratio of the additive element M2 in the general formula of the lithium nickel composite oxide to be finally obtained and the compound precipitation rate from the metal salt of the metal M2. Usually, since almost the whole amount is precipitated as a compound from the metal salt, the addition amount of the metal salt may be determined from the ratio of the additive element M2 in the chemical formula of the lithium nickel composite oxide.
添加元素Ｍ2としてＡｌを選択した場合、添加されるアルミニウム塩としては、アルミン酸のアルカリ塩を用いることができる。アルミン酸のアルカリ塩としては、アルミン酸ナトリウム、アルミン酸カリウムが好ましい。アルミン酸のアルカリ塩を用いることでニッケルコバルト複合水酸化物の二次粒子の表面に中和により生成した水酸化アルミニウムが吸着するとともに、ろ過後の洗浄時にもニッケルコバルト複合水酸化物から分離せず、ニッケルコバルト複合水酸化物の周囲に水酸化アルミニウムが均一に分散する。 When Al is selected as the additive element M2, an alkali salt of aluminate can be used as the added aluminum salt. As the alkali salt of aluminate, sodium aluminate and potassium aluminate are preferable. By using alkali salt of aluminate, aluminum hydroxide produced by neutralization is adsorbed on the surface of secondary particles of nickel-cobalt composite hydroxide, and it can be separated from nickel-cobalt composite hydroxide during washing after filtration. The aluminum hydroxide is uniformly dispersed around the nickel cobalt composite hydroxide.
その他、金属塩として硝酸塩、硫酸塩などが挙げられ、添加元素Ｍ2としてＭｎを選択した場合、添加されるマンガン塩としては硫酸マンガン、Ｔｉを選択した場合、添加されるＴｉ塩としては硫酸チタニル、Ｍｇを選択した場合、添加されるマグネシウム塩としては硫酸マグネシウムなどを用いることができる。 In addition, nitrates and sulfates can be cited as metal salts. When Mn is selected as the additive element M2, manganese sulfate is added as the added manganese salt, and when Ti is selected, titanyl sulfate is added as the added Ti salt. When Mg is selected, magnesium sulfate or the like can be used as the magnesium salt to be added.
ニッケル金属複合水酸化物の二次粒子表面に添加元素Ｍ2の化合物（水酸化物）を吸着させた後、ろ過、水洗および乾燥を行なう。ろ過、水洗および乾燥は、ニッケルコバルト複合水酸化物の製造と同様の方法でよい。 After adsorbing the compound (hydroxide) of the additive element M2 on the secondary particle surface of the nickel metal composite hydroxide, filtration, washing and drying are performed. Filtration, water washing and drying may be performed in the same manner as in the production of nickel cobalt composite hydroxide.
得られたニッケル金属複合水酸化物について、ろ過、水洗および乾燥を行なうが、これらの処理は通常に行われる方法でよい。 The obtained nickel metal composite hydroxide is filtered, washed with water and dried, and these treatments may be carried out by ordinary methods.
（酸化焙焼）
次に、二次粒子の表面に添加元素Ｍ2の化合物を吸着したニッケル金属複合水酸化物を酸化焙焼する。酸化焙焼することによって、最終的に、二次粒子の表層部と中心部における添加元素Ｍ2の原子濃度比（表層部濃度／中心部濃度）が１．２５〜３であるリチウムニッケル複合酸化物が得られる。酸化焙焼より二次粒子の表層部と中心部における添加元素Ｍ2の原子濃度が異なるリチウムニッケル複合酸化物が得られる理由は不明であるが、以下のように推測される。
(Oxidation roasting)
Next, the nickel metal composite hydroxide having the compound of the additive element M2 adsorbed on the surface of the secondary particles is oxidized and roasted. Lithium nickel composite oxide in which the atomic concentration ratio (surface layer concentration / center concentration) of the additive element M2 in the surface layer portion and the center portion of the secondary particles is finally 1.25 to 3 by oxidative roasting Is obtained. The reason why the lithium nickel composite oxide having different atomic concentrations of the additive element M2 in the surface layer portion and the central portion of the secondary particles is not clear by oxidative roasting, but is presumed as follows.
表面に添加元素Ｍ2の化合物を吸着させたニッケル金属複合水酸化物粒子を酸化焙焼することで、ニッケル金属複合水酸化物が複合酸化物に転換するとともに、その表面の添加元素Ｍ2の化合物も酸化物となって複合酸化物粒子表面に被膜を形成する。その後にリチウム塩と混合してリチウム金属複合酸化物を得るための焼成を行なっても、酸化物被膜となった添加元素Ｍ2は、固相拡散によってのみ複合酸化物粒子内部に拡散するため、拡散速度が遅く均一な濃度となり難く、二次粒子の表層部と中心部とで異なる原子濃度となる。 By oxidizing and roasting nickel metal composite hydroxide particles with adsorbed element M2 compound adsorbed on the surface, the nickel metal composite hydroxide is converted to composite oxide, and the additive element M2 compound on the surface is also converted. It becomes an oxide and forms a film on the surface of the composite oxide particle. Even if the mixture is then baked to obtain a lithium metal composite oxide by mixing with a lithium salt, the additive element M2 that has become an oxide film diffuses only inside the composite oxide particles by solid phase diffusion. The speed is low and it is difficult to obtain a uniform concentration, and the atomic concentration differs between the surface layer portion and the central portion of the secondary particles.
一方、酸化焙焼を行なわず焼成のみによってリチウム金属複合酸化物を得た場合には、焼成時の加熱により溶融したリチウム塩が、二次粒子の表層部から一次粒子間の空隙等を伝って内部に浸透する際に、表層部に存在する金属Ｍ2の化合物も、溶融したリチウム塩とともに内部に浸透する。このため、原子濃度を均一にするまでの拡散距離が短くなり、内部まで添加元素の原子濃度が均一となると考えられる。 On the other hand, when the lithium metal composite oxide is obtained only by firing without oxidative roasting, the lithium salt melted by heating during firing travels from the surface layer portion of the secondary particles through the voids between the primary particles. When penetrating into the interior, the metal M2 compound present in the surface layer also penetrates into the interior together with the molten lithium salt. For this reason, it is considered that the diffusion distance until the atomic concentration becomes uniform is shortened, and the atomic concentration of the additive element becomes uniform to the inside.
以上の理由より、正極活物質の二次粒子の表層部と中心部で異なる原子濃度とするためには、添加元素Ｍ2は、強固な酸化物を形成するＡｌ、Ｍｎ、ＴｉおよびＭｇからなる群から選ばれる１種以上の金属元素が原子濃度比を制御するために好ましい。中でも、Ａｌが特に好ましい。 For the above reasons, in order to obtain different atomic concentrations in the surface layer portion and the central portion of the secondary particles of the positive electrode active material, the additive element M2 is a group consisting of Al, Mn, Ti and Mg forming a strong oxide. One or more metal elements selected from are preferable for controlling the atomic concentration ratio. Among these, Al is particularly preferable.
また、酸化焙焼温度は、６５０〜７５０℃が好ましく、７００〜７５０℃がより好ましい。６５０℃未満では、表面に形成される酸化被膜が十分でなく、７５０℃を超えると添加元素Ｍ2の粒子内への拡散が起こるため好ましくない。 Moreover, 650-750 degreeC is preferable and the oxidation roasting temperature has more preferable 700-750 degreeC. If the temperature is lower than 650 ° C., the oxide film formed on the surface is not sufficient.
酸化焙焼の雰囲気は、非還元性雰囲気であれば問題なく、大気雰囲気あるいは酸素雰囲気が好ましい。酸化焙焼時間は特に限定されるものでなく、処理する量および酸化焙焼温度に基づいて適宜決定することができる。 The oxidation roasting atmosphere has no problem as long as it is a non-reducing atmosphere, and is preferably an air atmosphere or an oxygen atmosphere. The oxidation roasting time is not particularly limited, and can be appropriately determined based on the amount to be processed and the oxidation roasting temperature.
（リチウムの添加）
Ｌｉを添加するため、上記酸化焙焼により得られたニッケルコバルト複合酸化物をリチウム塩と混合する。混合するリチウム塩の量は、最終的に得ようとするリチウムニッケル複合酸化物から決めればよく、例えば、一般式ＬｉzＮｉ1-x-yＣｏxＭ2yＯ2（ただし、Ｍ2は、Ａｌ、Ｍｎ、ＴｉおよびＭｇから選ばれる少なくとも１種の金属元素、０．１０≦ｘ≦０．２１、０．０５≦ｙ≦０．０８、０．９８≦ｚ≦１．１０）で表されるリチウムニッケル複合酸化物の場合、組成式から容易にリチウム塩の量を決めることができる。
(Addition of lithium)
In order to add Li, the nickel cobalt composite oxide obtained by the oxidative roasting is mixed with a lithium salt. The amount of lithium salt to be mixed may be determined from the lithium nickel composite oxide to be finally obtained. For example, the general formula Li z Ni 1-xy Co x M 2 y O 2 (where M 2 is Al, Mn Lithium nickel represented by at least one metal element selected from Ti, Mg, 0.10 ≦ x ≦ 0.21, 0.05 ≦ y ≦ 0.08, 0.98 ≦ z ≦ 1.10. In the case of a composite oxide, the amount of lithium salt can be easily determined from the composition formula.
混合するリチウム塩としては、硝酸リチウムや水酸化リチウム、炭酸リチウム等を用いることができるが、コスト的な観点や、融点が比較的低いという観点から、特に水酸化リチウムを用いることが好ましい。 As the lithium salt to be mixed, lithium nitrate, lithium hydroxide, lithium carbonate, or the like can be used, but lithium hydroxide is particularly preferably used from the viewpoint of cost and a relatively low melting point.
上記混合は、Ｖブレンダーやスパルタンリューザー、あるいはバーチカルグラニュエーターといった乾式混合機や混合造粒機を用いて行うことができ、均一に混合される適切な時間の範囲で行うことが好ましい。 The mixing can be performed using a dry mixer or a mixing granulator such as a V blender, a Spartan rewinder, or a vertical granulator, and is preferably performed within a suitable time range for uniform mixing.
（焼成）
リチウム塩と上記ニッケルコバルト複合酸化物を混合した後、混合物を焼成して非水系電解質二次電池用正極活物質であるリチウム金属複合酸化物を得る。ここで、焼成温度は６５０〜７５０℃とすることが好ましく、７００〜７５０℃とすることがより好ましい。焼成時間としては、特に限定されるものではなく、１０〜２０時間程度とすることが好ましい。また、焼成時の雰囲気としては、酸素雰囲気等の酸化性雰囲気とすることが好ましい。
(Baking)
After mixing the lithium salt and the nickel cobalt composite oxide, the mixture is fired to obtain a lithium metal composite oxide that is a positive electrode active material for a non-aqueous electrolyte secondary battery. Here, the firing temperature is preferably 650 to 750 ° C, and more preferably 700 to 750 ° C. The firing time is not particularly limited, and is preferably about 10 to 20 hours. In addition, the firing atmosphere is preferably an oxidizing atmosphere such as an oxygen atmosphere.
焼成温度が６５０℃未満では、リチウム化合物との反応が十分に進まず、層状構造で結晶性の良いリチウムニッケル複合酸化物を合成することが難しくなるとともに、上記原子濃度比が３を超えてしまう。一方、７５０℃を超えると、添加元素Ｍ2が粒子内へ拡散して、上記原子濃度比が１．２５未満となってしまう。 When the firing temperature is less than 650 ° C., the reaction with the lithium compound does not proceed sufficiently, it becomes difficult to synthesize a lithium nickel composite oxide having a layered structure and good crystallinity, and the atomic concentration ratio exceeds 3. . On the other hand, when the temperature exceeds 750 ° C., the additive element M2 diffuses into the particles and the atomic concentration ratio becomes less than 1.25.
３．非水系電解質二次電池
本発明の非水系電解質二次電池は、正極、負極および非水系電解液などからなり、一般の非水系電解質二次電池と同様の構成要素により構成される。なお、以下で説明する実施形態は例示に過ぎず、本発明の非水系電解質二次電池は、本明細書に記載されている実施形態に照らして、当業者の知識に基づき種々の変更、改良を施した形態で実施することができることはいうまでもない。また、本発明の非水系電解質二次電池は、その用途を特に限定するものではない。
3. Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte solution, and the like, and includes the same components as those of a general non-aqueous electrolyte secondary battery. The embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present invention is variously modified and improved based on the knowledge of those skilled in the art in light of the embodiment described in the present specification. Needless to say, it can be carried out in the form of the above. Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.
（正極）
前述のように得られた非水系電解質二次電池用正極活物質を用いて、例えば、以下のようにして、非水系電解質二次電池の正極を作製する。
(Positive electrode)
Using the positive electrode active material for a non-aqueous electrolyte secondary battery obtained as described above, for example, a positive electrode of a non-aqueous electrolyte secondary battery is produced as follows.
まず、粉末状の正極活物質、導電材、結着剤を混合し、さらに必要に応じて活性炭、粘度調整等の目的の溶剤を添加し、これを混練して正極合材ペーストを作製する。正極合材ペースト中のそれぞれの混合比も、非水系電解質二次電池の性能を決定する重要な要素となる。溶剤を除いた正極合材の固形分の全質量を１００質量部とした場合、一般の非水系電解質二次電池の正極と同様、正極活物質の含有量を６０〜９５質量部とし、導電材の含有量を１〜２０質量部とし、結着剤の含有量を１〜２０質量部とすることが望ましい。 First, a powdered positive electrode active material, a conductive material, and a binder are mixed, and, if necessary, a target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare a positive electrode mixture paste. Each mixing ratio in the positive electrode mixture paste is also an important factor for determining the performance of the non-aqueous electrolyte secondary battery. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass in the same manner as the positive electrode of a general non-aqueous electrolyte secondary battery, and the conductive material It is desirable to set the content of 1 to 20 parts by mass and the content of the binder to 1 to 20 parts by mass.
得られた正極合材ペーストを、例えば、アルミニウム箔製の集電体の表面に塗布し、乾燥して、溶剤を飛散させる。必要に応じ、電極密度を高めるべく、ロールプレス等により加圧することもある。このようにして、シート状の正極を作製することができる。シート状の正極は、目的とする電池に応じて適当な大きさに裁断等をして、電池の作製に供することができる。ただし、正極の作製方法は、前記例示のものに限られることなく、他の方法によってもよい。 The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, an aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.
正極の作製にあたって、導電剤としては、例えば、黒鉛（天然黒鉛、人造黒鉛、膨張黒鉛など）や、アセチレンブラック、ケッチェンブラックなどのカーボンブラック系材料などを用いることができる。 In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used.
結着剤は、活物質粒子をつなぎ止める役割を果たすもので、例えば、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、フッ素ゴム、エチレンプロピレンジエンゴム、スチレンブタジエン、セルロース系樹脂、ポリアクリル酸などを用いることができる。 The binder plays a role of holding the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin, polyacrylic. An acid or the like can be used.
必要に応じ、正極活物質、導電材、活性炭を分散させ、結着剤を溶解する溶剤を正極合材に添加する。溶剤としては、具体的には、Ｎ−メチル−２−ピロリドン等の有機溶剤を用いることができる。また、正極合材には、電気二重層容量を増加させるために、活性炭を添加することができる。 If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.
（負極）
負極には、金属リチウムやリチウム合金等、あるいは、リチウムイオンを吸蔵および脱離できる負極活物質に、結着剤を混合し、適当な溶剤を加えてペースト状にした負極合材を、銅等の金属箔集電体の表面に塗布し、乾燥し、必要に応じて電極密度を高めるべく圧縮して形成したものを使用する。
(Negative electrode)
For the negative electrode, metallic lithium, lithium alloy, or the like, or a negative electrode active material capable of occluding and desorbing lithium ions mixed with a binder, and an appropriate solvent is added to form a paste for the negative electrode mixture, such as copper It is applied to the surface of the metal foil current collector, dried, and compressed to increase the electrode density as necessary.
負極活物質としては、例えば、天然黒鉛、人造黒鉛、フェノール樹脂等の有機化合物焼成体、コークス等の炭素物質の粉状体を用いることができる。この場合、負極結着剤としては、正極同様、ＰＶＤＦ等の含フッ素樹脂等を用いることができ、これらの活物質および結着剤を分散させる溶剤としては、Ｎ−メチル−２−ピロリドン等の有機溶剤を用いることができる。 As the negative electrode active material, for example, natural graphite, artificial graphite, a fired organic compound such as phenol resin, or a powdery carbon material such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used as in the case of the positive electrode, and as a solvent for dispersing these active materials and the binder, N-methyl-2-pyrrolidone or the like can be used. Organic solvents can be used.
（セパレータ）
正極と負極との間には、セパレータを挟み込んで配置する。セパレータは、正極と負極とを分離し、電解質を保持するものであり、ポリエチレン、ポリプロピレン等の薄い膜で、微少な孔を多数有する膜を用いることができる。
(Separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene and a film having many minute holes can be used.
（非水系電解液）
非水系電解液は、支持塩としてのリチウム塩を有機溶媒に溶解したものである。
(Non-aqueous electrolyte)
The nonaqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.
有機溶媒としては、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、トリフルオロプロピレンカーボネート等の環状カーボネート、また、ジエチルカーボネート、ジメチルカーボネート、エチルメチルカーボネート、ジプロピルカーボネート等の鎖状カーボネート、さらに、テトラヒドロフラン、２−メチルテトラヒドロフラン、ジメトキシエタン等のエーテル化合物、エチルメチルスルホン、ブタンスルトン等の硫黄化合物、リン酸トリエチル、リン酸トリオクチル等のリン化合物等から選ばれる１種を単独で、あるいは２種以上を混合して用いることができる。 Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.
支持塩としては、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4、ＬｉＡｓＦ6、ＬｉＮ（ＣＦ3ＳＯ2）2等、およびそれらの複合塩を用いることができる。 As the supporting salt, LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiN (CF 3 SO 2 ) 2 , or a composite salt thereof can be used.
さらに、非水系電解液は、ラジカル捕捉剤、界面活性剤および難燃剤等を含んでいてもよい。 Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.
（電池の形状および構成）
以上のように説明してきた正極、負極、セパレータおよび非水系電解液で構成される本発明の非水系電解質二次電池の形状は、円筒型、積層型等、種々のものとすることができる。
(Battery shape and configuration)
The shape of the non-aqueous electrolyte secondary battery of the present invention composed of the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte described above can be various, such as a cylindrical type and a laminated type.
いずれの形状を採る場合であっても、正極および負極を、セパレータを介して積層させて電極体とし、得られた電極体に、非水系電解液を含浸させ、正極集電体と外部に通ずる正極端子との間、および、負極集電体と外部に通ずる負極端子との間を、集電用リード等を用いて接続し、電池ケースに密閉して、非水系電解質二次電池を完成させる。 In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like and sealed in a battery case to complete a non-aqueous electrolyte secondary battery. .
（実施例１）
Ｎｉ／Ｃｏのモル比が０．８５／０．１５になるように、硫酸ニッケル（和光純薬工業株式会社製、試薬特級）および硫酸コバルト（和光純薬工業株式会社製、試薬特級）を調合し、純水に溶解して得た水溶液に、２５％アンモニア水溶液（和光純薬工業株式会社製、試薬特級）を少量ずつ滴下しながら、ｐＨ＝１１〜１３、４０〜５０℃の温度で反応させることで、Ｎｉ0.83Ｃｏ0.17（ＯＨ）2で表される球状二次粒子の水酸化物を得た。
Example 1
Nickel sulfate (made by Wako Pure Chemical Industries, Ltd., reagent grade) and cobalt sulfate (made by Wako Pure Chemical Industries, Ltd., reagent grade) are prepared so that the molar ratio of Ni / Co is 0.85 / 0.15. Then, a 25% aqueous ammonia solution (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent) was added dropwise to the aqueous solution obtained by dissolving in pure water, while reacting at a temperature of pH = 11-13 and 40-50 ° C. Thus, a hydroxide of spherical secondary particles represented by Ni 0.83 Co 0.17 (OH) 2 was obtained.
得られた水酸化物を純水に入れて攪拌しながら、モル比でＡｌ／（Ｎｉ＋Ｃｏ＋Ａｌ）＝０．０３となるように、ＮａＡｌＯ2（和光純薬工業株式会社製、試薬特級）を添加した後、硫酸を用いてｐＨ９．５を目標値として中和した。中和後の水酸化物の組成はＮｉ0.82Ｃｏ0.15Ａｌ0.03（ＯＨ）2であった。 While stirring the resulting hydroxide in pure water, NaAlO 2 (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent) was added so that the molar ratio was Al / (Ni + Co + Al) = 0.03. Thereafter, the mixture was neutralized with sulfuric acid at a pH value of 9.5. The composition of the neutralized hydroxide was Ni 0.82 Co 0.15 Al 0.03 (OH) 2 .
次いで、得られた中和後の水酸化物を電気炉（ＡＤＶＡＮＴＥＣ社製、電気マッフル炉 特ＦＵＭ３７３）で、大気雰囲気中７００℃にて酸化焙焼して酸化物を得た。得られた酸化物と水酸化リチウムとを、モル比でＬｉ／（Ｎｉ＋Ｃｏ＋Ａｌ）＝１．０６となるように調合し、シェーカーミキサー装置（ＷＡＢ社製、ＴＵＲＢＵＬＡ ＴｙｐｅＴ２Ｃ）を用いて混合し、混合物とした。 Next, the obtained neutralized hydroxide was oxidized and roasted in an air atmosphere at 700 ° C. in an electric furnace (ADVANTEC, electric muffle furnace, special FUM373) to obtain an oxide. The obtained oxide and lithium hydroxide were prepared so that the molar ratio was Li / (Ni + Co + Al) = 1.06, mixed using a shaker mixer (WAB, TURBULA Type T2C), and the mixture did.
さらに、前述の電気炉を用いて、混合物を酸素雰囲気中７３０℃にて焼成し、正極活物質を得た。 Furthermore, the mixture was fired at 730 ° C. in an oxygen atmosphere using the electric furnace described above to obtain a positive electrode active material.
得られた正極活物質をレーザー散乱式粒度測定装置（日機装製、マイクロトラックＨＲＡ）で測定し、平均粒径としてＤ５０（累積分布率５０質量％での粒度）を求めたところ、８．２μｍであった。 The obtained positive electrode active material was measured with a laser scattering particle size measuring device (manufactured by Nikkiso Co., Ltd., Microtrac HRA). there were.
次に、得られた正極活物質の断面をＥＰＭＡで測定することで、二次粒子の表層部と二次粒子の中心部におけるＡｌの原子濃度比を求めた。具体的には、二次粒子の中心を通る直線状でＥＰＭＡによる線分析を行い、二次粒子の中心部と表層部とで得られたＡｌの特性Ｘ線の強度から原子濃度を求めた。この方法により得られた中心部に対する表層部のＡｌの原子濃度比は、１．３であった。 Next, the cross section of the obtained positive electrode active material was measured by EPMA, and thereby the atomic concentration ratio of Al in the surface layer portion of the secondary particles and the central portion of the secondary particles was determined. Specifically, line analysis by EPMA was performed in a straight line passing through the center of the secondary particles, and the atomic concentration was determined from the intensity of characteristic X-rays of Al obtained at the center and the surface layer of the secondary particles. The atomic concentration ratio of Al in the surface layer portion with respect to the central portion obtained by this method was 1.3.
さらに、それぞれの正極活物質を使用して、以下のように、巻回型リチウム二次電池を作製し、電池容量を測定した。 Furthermore, using each positive electrode active material, a wound type lithium secondary battery was produced as follows, and the battery capacity was measured.
先ず、２５℃の正極活物質と、カーボンブラックからなる導電材と、ポリフッ化ビニリデン（ＰＶＤＦ）よりなる結着剤とを、８５：１０：５の質量割合で混合し、Ｎ−メチル−２−ピロリドン（ＮＭＰ）溶液に溶解させ、正極合材ペーストを作製した。得られた正極合材ペーストを、コンマコータにてアルミ箔の両面に塗布し、１００℃で加熱して乾燥させて正極を得た。得られた正極をロールプレス機に通して荷重を加え、電極密度を向上させた正極シートを作製した。 First, a positive electrode active material at 25 ° C., a conductive material made of carbon black, and a binder made of polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 85: 10: 5, and N-methyl-2- A positive electrode mixture paste was prepared by dissolving in a pyrrolidone (NMP) solution. The obtained positive electrode mixture paste was applied to both sides of an aluminum foil with a comma coater, heated at 100 ° C. and dried to obtain a positive electrode. The obtained positive electrode was passed through a roll press to apply a load, and a positive electrode sheet with improved electrode density was produced.
続いて、グラファイトよりなる負極活物質と、結着剤としてのＰＶＤＦとを９２．５：７．５の質量割合でＮＭＰ溶液に溶解させて、負極合材ペーストを得た。得られた負極合材ペーストを、正極と同様に、コンマコータにて銅箔の両面に塗布し、１２０℃で乾燥させて負極を得た。得られた負極をロールプレス機に通して荷重を加え、電極密度を向上させた負極シートを作製した。 Subsequently, a negative electrode active material made of graphite and PVDF as a binder were dissolved in an NMP solution at a mass ratio of 92.5: 7.5 to obtain a negative electrode mixture paste. The obtained negative electrode mixture paste was applied to both surfaces of a copper foil with a comma coater in the same manner as the positive electrode, and dried at 120 ° C. to obtain a negative electrode. The obtained negative electrode was passed through a roll press to apply a load, and a negative electrode sheet with improved electrode density was produced.
得られた正極シートおよび負極シートを、厚さ２５μｍの微多孔性ポリエチレンシートよりなるセパレータを介した状態で巻回させて、巻回型電極体を形成した。正極シートおよび負極シートは、それぞれに設けたリードタブが正極端子あるいは負極端子に接合した状態で、前述の巻回型電極体を電池ケースの内部に挿入した。 The obtained positive electrode sheet and negative electrode sheet were wound with a separator made of a microporous polyethylene sheet having a thickness of 25 μm interposed therebetween to form a wound electrode body. In the positive electrode sheet and the negative electrode sheet, the above-described wound electrode body was inserted into the battery case in a state where the lead tabs provided on the positive electrode sheet and the negative electrode sheet were bonded to the positive electrode terminal or the negative electrode terminal.
さらに、エチレンカーボネート（ＥＣ）とジエチレンカーボネート（ＤＥＣ）とを、３：７の体積比で混合した混合溶液よりなる有機溶媒に、電解液中で１ｍｏｌ／ｄｍ3となるように、リチウム塩としてＬｉＰＦ6を溶解させて、電解液を調整した。 Further, LiPF as a lithium salt is added to an organic solvent composed of a mixed solution in which ethylene carbonate (EC) and diethylene carbonate (DEC) are mixed at a volume ratio of 3: 7 so as to be 1 mol / dm 3 in the electrolytic solution. 6 was dissolved to prepare an electrolytic solution.
得られた電解液を、巻回型電極体が挿入された電池ケース内に注入し、電池ケースの開口部を密閉し、電池ケースを封止した。 The obtained electrolytic solution was poured into the battery case in which the wound electrode body was inserted, the opening of the battery case was sealed, and the battery case was sealed.
作製した電池は、２４時間程度放置し、開路電圧ＯＣＶ（open circuit voltage）が安定した後、正極に対する電流密度を０．５ｍＡ／ｃｍ2としてカットオフ電圧４．３Ｖまで充電して初期充電容量とし、１時間の休止後カットオフ電圧３．０Ｖまで放電したときの容量を初期放電容量とした。初期放電容量は、比較例１の初期放電容量を１００とした容量比で評価した。 The produced battery is left for about 24 hours, and after the open circuit voltage OCV (open circuit voltage) is stabilized, the current density with respect to the positive electrode is set to 0.5 mA / cm 2 and charged to a cutoff voltage of 4.3 V to obtain an initial charge capacity. The capacity when the battery was discharged to a cutoff voltage of 3.0 V after 1 hour of rest was defined as the initial discharge capacity. The initial discharge capacity was evaluated by a capacity ratio with the initial discharge capacity of Comparative Example 1 as 100.
また、正極の安全性の評価は以下のようにして測定した。上述の方法で作製した電池をカットオフ電圧４．５Ｖまで定電流定電圧（ＣＣＣＶ）方式で充電した後、短絡しないように注意しながら解体して正極を取り出した。この電極を３．０ｍｇ計り取り、電解液を１．３ｍｇ加えて、アルミニウム製測定容器に封入し、示差走査熱量計（ＤＳＣ）（リガク社製）を用いて昇温速度１０℃／ｍｉｎで室温から４００℃まで発熱挙動を測定した。 Moreover, the safety evaluation of the positive electrode was measured as follows. The battery produced by the above-described method was charged by a constant current constant voltage (CCCV) method up to a cutoff voltage of 4.5 V, and then disassembled with care so as not to short-circuit, and the positive electrode was taken out. 3.0 mg of this electrode was measured, 1.3 mg of the electrolyte was added, sealed in an aluminum measuring container, and room temperature was measured at a temperature rising rate of 10 ° C./min using a differential scanning calorimeter (DSC) (manufactured by Rigaku) The exothermic behavior was measured from 400 to 400 ° C.
発熱量は、後述する比較例１の発熱量を１００とした発熱量比で評価した。 The calorific value was evaluated by a calorific value ratio with the calorific value of Comparative Example 1 described later as 100.
各評価によって得られた原子濃度比と発熱量比および容量比の関係を図１に示す。 The relationship between the atomic concentration ratio, the calorific value ratio, and the capacity ratio obtained by each evaluation is shown in FIG.
（実施例２）
酸化焙焼温度を７００℃、焼成温度を７１０℃としたこと以外は、実施例１と同様にして正極活物質を得た。得られた正極活物質の平均粒径を実施例１と同様にして求めたところ、８．７μｍであった。また、実施例１と同様にしてＡｌの原子濃度比を求めたところ、１．８であった。
(Example 2)
A positive electrode active material was obtained in the same manner as in Example 1 except that the oxidation roasting temperature was 700 ° C. and the firing temperature was 710 ° C. When the average particle diameter of the obtained positive electrode active material was determined in the same manner as in Example 1, it was 8.7 μm. Further, when the atomic concentration ratio of Al was determined in the same manner as in Example 1, it was 1.8.
さらに、実施例１と同様にして容量比および発熱量比を評価した。各評価によって得られた原子濃度比と発熱量比および容量比の関係を図１に示す。 Furthermore, the capacity ratio and the calorific value ratio were evaluated in the same manner as in Example 1. The relationship between the atomic concentration ratio, the calorific value ratio, and the capacity ratio obtained by each evaluation is shown in FIG.
（実施例３）
酸化焙焼温度を６５０℃、焼成温度を７３０℃としたこと以外は、実施例１と同様にして正極活物質を得た。得られた正極活物質の平均粒径を実施例１と同様にして求めたところ、８．４μｍであった。また、実施例１と同様にしてＡｌの原子濃度比を求めたところ、２．１であった。
(Example 3)
A positive electrode active material was obtained in the same manner as in Example 1 except that the oxidation roasting temperature was 650 ° C. and the firing temperature was 730 ° C. When the average particle diameter of the obtained positive electrode active material was determined in the same manner as in Example 1, it was 8.4 μm. Further, when the atomic concentration ratio of Al was determined in the same manner as in Example 1, it was 2.1.
さらに、実施例１と同様にして容量比および発熱量比を評価した。各評価によって得られた原子濃度比と、発熱量比および容量比との関係を図１に示す。 Furthermore, the capacity ratio and the calorific value ratio were evaluated in the same manner as in Example 1. FIG. 1 shows the relationship between the atomic concentration ratio obtained by each evaluation, the calorific value ratio, and the capacity ratio.
（実施例４）
酸化焙焼温度を６５０℃、焼成温度を６８０℃としたこと以外は、実施例１と同様にして正極活物質を得た。得られた正極活物質の平均粒径を実施例１と同様にして求めたところ、８．８μｍであった。また、実施例１と同様にしてＡｌの原子濃度比を求めたところ、２．８であった。
Example 4
A positive electrode active material was obtained in the same manner as in Example 1 except that the oxidation roasting temperature was 650 ° C. and the firing temperature was 680 ° C. When the average particle diameter of the obtained positive electrode active material was determined in the same manner as in Example 1, it was 8.8 μm. Further, when the atomic concentration ratio of Al was determined in the same manner as in Example 1, it was 2.8.
さらに、実施例１と同様にして容量比および発熱量比を評価した。各評価によって得られた原子濃度比と発熱量比および容量比の関係を図１に示す。 Furthermore, the capacity ratio and the calorific value ratio were evaluated in the same manner as in Example 1. The relationship between the atomic concentration ratio, the calorific value ratio, and the capacity ratio obtained by each evaluation is shown in FIG.
（比較例１）
酸化焙焼温度を７００℃、焼成温度を７８０℃としたこと以外は、実施例１と同様にして正極活物質を得た。得られた正極活物質の平均粒径を実施例１と同様にして求めたところ、７．９μｍであった。また、実施例１と同様にしてＡｌの原子濃度比を求めたところ、Ａｌは、二次粒子内で均一な濃度になっており、原子濃度比は１であった。
(Comparative Example 1)
A positive electrode active material was obtained in the same manner as in Example 1 except that the oxidation roasting temperature was 700 ° C. and the firing temperature was 780 ° C. When the average particle size of the obtained positive electrode active material was determined in the same manner as in Example 1, it was 7.9 μm. Further, when the atomic concentration ratio of Al was determined in the same manner as in Example 1, Al had a uniform concentration within the secondary particles, and the atomic concentration ratio was 1.
さらに、実施例１と同様にして初期放電容量および発熱量を測定した。各評価によって得られた原子濃度比と発熱量比および容量比の関係を図１に示す。 Further, the initial discharge capacity and the calorific value were measured in the same manner as in Example 1. The relationship between the atomic concentration ratio, the calorific value ratio, and the capacity ratio obtained by each evaluation is shown in FIG.
（比較例２）
酸化焙焼温度を７８０℃、焼成温度を７００℃としたこと以外は、実施例１と同様にして正極活物質を得た。得られた正極活物質の平均粒径を実施例１と同様にして求めたところ、８．５μｍであった。また、実施例１と同様にしてＡｌの原子濃度比を求めたところ、１．１であった。
(Comparative Example 2)
A positive electrode active material was obtained in the same manner as in Example 1 except that the oxidation roasting temperature was 780 ° C. and the firing temperature was 700 ° C. When the average particle diameter of the obtained positive electrode active material was determined in the same manner as in Example 1, it was 8.5 μm. Further, when the atomic concentration ratio of Al was determined in the same manner as in Example 1, it was 1.1.
さらに、実施例１と同様にして容量比および発熱量比を評価した。各評価によって得られた原子濃度比と発熱量比および容量比の関係を図１に示す。 Furthermore, the capacity ratio and the calorific value ratio were evaluated in the same manner as in Example 1. The relationship between the atomic concentration ratio, the calorific value ratio, and the capacity ratio obtained by each evaluation is shown in FIG.
（比較例３）
酸化焙焼温度を６００℃、焼成温度を７３０℃としたこと以外は、実施例１と同様にして正極活物質を得た。得られた正極活物質の平均粒径を実施例１と同様にして求めたところ、８．１μｍであった。また、実施例１と同様にしてＡｌの原子濃度比を求めたところ、３．２であった。
(Comparative Example 3)
A positive electrode active material was obtained in the same manner as in Example 1 except that the oxidation roasting temperature was 600 ° C. and the firing temperature was 730 ° C. When the average particle diameter of the obtained positive electrode active material was determined in the same manner as in Example 1, it was 8.1 μm. Further, when the atomic concentration ratio of Al was determined in the same manner as in Example 1, it was 3.2.
さらに、実施例１と同様にして容量比および発熱量比を評価した。各評価によって得られた原子濃度比と発熱量比および容量比の関係を図１に示す。 Furthermore, the capacity ratio and the calorific value ratio were evaluated in the same manner as in Example 1. The relationship between the atomic concentration ratio, the calorific value ratio, and the capacity ratio obtained by each evaluation is shown in FIG.
（比較例４）
酸化焙焼を行わず、焼成温度を６００℃としたこと以外は、実施例１と同様にして正極活物質を得た。得られた正極活物質の平均粒径を実施例１と同様にして求めたところ、８．７μｍであった。また、実施例１と同様にしてＡｌの原子濃度比を求めたところ、４．０であった。
(Comparative Example 4)
A positive electrode active material was obtained in the same manner as in Example 1 except that oxidation roasting was not performed and the firing temperature was 600 ° C. When the average particle diameter of the obtained positive electrode active material was determined in the same manner as in Example 1, it was 8.7 μm. Further, when the atomic concentration ratio of Al was determined in the same manner as in Example 1, it was 4.0.
さらに、実施例１と同様にして容量比および発熱量比を評価した。各評価によって得られた原子濃度比と発熱量比および容量比の関係を図１に示す。 Furthermore, the capacity ratio and the calorific value ratio were evaluated in the same manner as in Example 1. The relationship between the atomic concentration ratio, the calorific value ratio, and the capacity ratio obtained by each evaluation is shown in FIG.
以上より、実施例１〜４は、比較例１と比べて電池容量は２〜５％低いものの、発熱量は１０％以上減少しており、高容量でありながら安全性が高いリチウム二次電池といえる。一方、比較例１および２は、電池容量は高いが、発熱量が多く、安全性に問題がある。また、比較例３および４は、発熱量は改善されているが、電池容量が大幅に減少しており、容量の点で問題がある。 From the above, although Examples 1 to 4 have a battery capacity that is 2 to 5% lower than Comparative Example 1, the calorific value is reduced by 10% or more, and a lithium secondary battery that has high capacity and high safety. It can be said. On the other hand, Comparative Examples 1 and 2 have a high battery capacity but a large amount of heat generation, which is problematic in safety. In Comparative Examples 3 and 4, although the calorific value is improved, the battery capacity is greatly reduced, which is problematic in terms of capacity.
本発明の非水系電解質二次電池は、安全性に優れていながら、高い充放電容量も有しているということから、常に高容量を要求される小型携帯電子機器（ノート型パーソナルコンピュータや、携帯電話端末など）の電源として好適である。 Since the non-aqueous electrolyte secondary battery of the present invention is excellent in safety and has a high charge / discharge capacity, it is a small portable electronic device (a notebook personal computer or a portable computer) that always requires a high capacity. It is suitable as a power source for telephone terminals and the like.
また、電気自動車用の電源においては、電池の大型化による安全性の確保の難しさと、より高度な安全性を確保するための高価な保護回路が必要不可欠である。これに対して、本発明の非水系電解質二次電池は、優れた安全性を有しているため、安全性の確保が容易になるばかりでなく、高価な保護回路を簡略化し、より低コストにできるという点において、電気自動車用電源としても好適である。なお、本発明は、純粋に電気エネルギで駆動する電気自動車用の電源のみならず、ガソリンエンジン、ディーゼルエンジン等の燃焼機関と併用するいわゆるハイブリッド車用の電源としても用いることができる。 Further, in a power source for an electric vehicle, it is indispensable to ensure safety by increasing the size of the battery and an expensive protection circuit for ensuring higher safety. On the other hand, the non-aqueous electrolyte secondary battery of the present invention has excellent safety, so that not only is it easy to ensure safety, but also an expensive protection circuit is simplified to reduce the cost. Therefore, it is also suitable as a power source for electric vehicles. The present invention can be used not only as a power source for an electric vehicle driven purely by electric energy but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.
Claims (5)
前記正極活物質の二次粒子の表層部と中心部とにおける前記添加元素Ｍ2の原子濃度比が１．２５〜３であることを特徴とする、非水系電解質二次電池用正極活物質。 Li and Ni containing one or more additive elements M1 selected from the group consisting of Co, Al and Mn and one or more additive elements M2 other than M1 selected from the group consisting of Al, Mn, Ti and Mg A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium nickel composite oxide containing as a main component,
A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein an atomic concentration ratio of the additive element M2 in a surface layer portion and a center portion of the secondary particles of the positive electrode active material is 1.25 to 3.
Ｎｉと添加元素Ｍ1との複合水酸化物の粒子表面に、添加元素Ｍ2の化合物を吸着させ、該添加元素Ｍ2が表面に吸着した前記複合水酸化物を６５０〜７５０℃の温度で酸化焙焼して、Ｎｉと添加元素Ｍ1と添加元素Ｍ2との複合酸化物を得て、該複合酸化物とリチウム塩とを混合し、得られた混合物を６５０〜７５０℃の温度で焼成することにより、前記リチウムニッケル複合酸化物を得ることを特徴とする、非水系電解質二次電池用正極活物質の製造方法。 Lithium and nickel containing one or more additive elements M1 selected from the group consisting of Co, Al and Mn, and one or more additional elements M2 other than M1 selected from the group consisting of Al, Mn, Ti and Mg A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium nickel composite oxide containing as a main component,
The compound hydroxide of additive element M2 is adsorbed on the particle surface of the composite hydroxide of Ni and additive element M1, and the composite hydroxide adsorbed on the surface of the additive element M2 is oxidized and roasted at a temperature of 650 to 750 ° C. Then, by obtaining a composite oxide of Ni, additive element M1, and additive element M2, mixing the composite oxide and lithium salt, and firing the resulting mixture at a temperature of 650-750 ° C., A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the lithium nickel composite oxide is obtained.
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