JP2020095967A - Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery, and lithium ion battery - Google Patents
Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery, and lithium ion battery Download PDFInfo
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- 239000007774 positive electrode material Substances 0.000 title claims abstract description 54
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 51
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 51
- 238000006073 displacement reaction Methods 0.000 claims abstract description 115
- 239000011163 secondary particle Substances 0.000 claims abstract description 82
- 239000011164 primary particle Substances 0.000 claims abstract description 22
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 13
- 238000003825 pressing Methods 0.000 claims abstract description 12
- 229910052749 magnesium Inorganic materials 0.000 claims abstract description 11
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 11
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 11
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 11
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 11
- 229910052726 zirconium Inorganic materials 0.000 claims abstract description 11
- 229910052715 tantalum Inorganic materials 0.000 claims abstract description 10
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 9
- 230000004931 aggregating effect Effects 0.000 abstract description 3
- 239000002245 particle Substances 0.000 description 30
- 229910052751 metal Inorganic materials 0.000 description 13
- 239000002184 metal Substances 0.000 description 13
- 239000000843 powder Substances 0.000 description 13
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 12
- 239000000203 mixture Substances 0.000 description 11
- 230000008602 contraction Effects 0.000 description 9
- 238000011156 evaluation Methods 0.000 description 9
- 238000010304 firing Methods 0.000 description 9
- 239000002002 slurry Substances 0.000 description 7
- 230000014759 maintenance of location Effects 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 239000011230 binding agent Substances 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 238000007599 discharging Methods 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 238000001694 spray drying Methods 0.000 description 4
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 3
- 239000003513 alkali Substances 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 239000004020 conductor Substances 0.000 description 3
- 239000011888 foil Substances 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 239000003595 mist Substances 0.000 description 3
- 239000012266 salt solution Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 2
- 229910002651 NO3 Inorganic materials 0.000 description 2
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 2
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 description 2
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 2
- 238000000975 co-precipitation Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 150000004679 hydroxides Chemical class 0.000 description 2
- 229910052744 lithium Inorganic materials 0.000 description 2
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 2
- 229910052808 lithium carbonate Inorganic materials 0.000 description 2
- 150000002642 lithium compounds Chemical class 0.000 description 2
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 150000002823 nitrates Chemical class 0.000 description 2
- 239000003960 organic solvent Substances 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910001868 water Inorganic materials 0.000 description 2
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 1
- 229910015643 LiMn 2 O 4 Inorganic materials 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 239000011149 active material Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052789 astatine Inorganic materials 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 239000002482 conductive additive Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000009616 inductively coupled plasma Methods 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical group [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
- VROAXDSNYPAOBJ-UHFFFAOYSA-N lithium;oxido(oxo)nickel Chemical compound [Li+].[O-][Ni]=O VROAXDSNYPAOBJ-UHFFFAOYSA-N 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229910000030 sodium bicarbonate Inorganic materials 0.000 description 1
- 235000017557 sodium bicarbonate Nutrition 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910000314 transition metal oxide Inorganic materials 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
Classifications
-
- 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、リチウムイオン電池用正極活物質、リチウムイオン電池用正極、及び、リチウムイオン電池に関する。 The present invention relates to a positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery.
リチウムイオン電池の正極活物質には、一般にリチウム含有遷移金属酸化物が用いられている。具体的には、コバルト酸リチウム（ＬｉＣｏＯ2）、ニッケル酸リチウム（ＬｉＮｉＯ2）、マンガン酸リチウム（ＬｉＭｎ2Ｏ4）等であり、特性改善（高容量化、サイクル特性、保存特性、内部抵抗低減、レート特性）や安全性を高めるためにこれらを複合化することが進められている。車載用やロードレベリング用といった大型用途におけるリチウムイオン電池には、これまでの携帯電話用やパソコン用とは異なった特性が求められている。 A lithium-containing transition metal oxide is generally used as a positive electrode active material of a lithium ion battery. Specifically, it is lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganate (LiMn 2 O 4 ), etc., and has improved characteristics (higher capacity, cycle characteristics, storage characteristics, reduced internal resistance). , Rate characteristics) and compounding these in order to improve safety. Lithium-ion batteries for large-scale applications such as in-vehicle and load-leveling are required to have characteristics different from those for conventional mobile phones and personal computers.
このようなリチウムイオン電池において求められる電池特性の向上について、従来、種々の研究・開発が行われている（特許文献１〜３）。 Conventionally, various researches and developments have been carried out to improve the battery characteristics required in such lithium ion batteries (Patent Documents 1 to 3).
例えば、正極活物質のＮｉ組成比を大きくすることで、高容量化する技術があるが、Ｎｉ組成比が大きくなればなるほど、繰り返し充放電した時の容量維持率、いわゆるサイクル特性が悪くなる。これは、充放電での膨張収縮で活物質間接触が減少し、導電パスが喪失し、抵抗が増加するためである。 For example, there is a technique for increasing the capacity by increasing the Ni composition ratio of the positive electrode active material. However, the higher the Ni composition ratio, the worse the capacity retention ratio after repeated charging and discharging, that is, the so-called cycle characteristics. This is because the contact between the active materials decreases due to expansion and contraction during charge and discharge, the conductive path is lost, and the resistance increases.
また、一般に、正極活物質を導電材と共に、バインダーを含む有機溶剤に混合した後、電極用金属箔にプレスすることで正極が作製されるが、このときのプレスに対して正極活物質の粒子形状が追従できず、正極活物質の粒子間の隙間が増加し、導電パス喪失が大きくなり、その結果、抵抗増加、サイクル特性劣化が大きくなる。 In addition, generally, the positive electrode active material is mixed with an electrically conductive material in an organic solvent containing a binder, and then the positive electrode is produced by pressing on a metal foil for an electrode. The shape cannot follow, the gap between the particles of the positive electrode active material increases, the loss of the conductive path increases, and as a result, the resistance increases and the cycle characteristics deteriorate.
さらに、正極活物質を用いた二次電池の充放電サイクルでの膨張収縮に正極活物質の粒子形状が追従できず、正極活物質の粒子間の隙間が増加し、導電パス喪失が大きくなり、その結果、抵抗増加、サイクル特性劣化が大きくなる。 Furthermore, the particle shape of the positive electrode active material cannot follow the expansion and contraction in the charge/discharge cycle of the secondary battery using the positive electrode active material, the gap between the particles of the positive electrode active material increases, and the loss of the conductive path increases. As a result, resistance increases and cycle characteristic deterioration increases.
このような問題に鑑みて、本発明は、充放電サイクルでの抵抗上昇を抑制し、電池の寿命を長くすることが可能な、電池特性に優れたリチウムイオン電池用正極活物質を提供することを課題とする。 In view of such a problem, the present invention provides a positive electrode active material for a lithium-ion battery, which is capable of suppressing an increase in resistance during charge/discharge cycles and extending the life of the battery, and which has excellent battery characteristics. Is an issue.
本発明者は、上記問題を解決するため種々の検討を行った結果、高Ｎｉ組成を有する正極活物質において、二次粒子に所定の荷重をかけたときに、二次粒子変位量と荷重とが共に増加する領域が２段階となるように制御することで、電極作製時のプレス、及び、二次電池の充放電サイクルでの膨張収縮に対し、正極活物質の粒子が変形しやすくなり、当該プレス及び膨張収縮に良好に追従することができることを見出した。そして、その結果、導電パス喪失を抑制し、抵抗増加及びサイクル特性劣化を抑制することができることを見出した。 As a result of various studies to solve the above problems, the present inventors have found that in a positive electrode active material having a high Ni composition, when a predetermined load is applied to the secondary particles, the amount of displacement of the secondary particles and the load By controlling such that the region where both increase together is in two stages, the particles of the positive electrode active material are easily deformed against pressing during electrode production and expansion/contraction during charge/discharge cycles of the secondary battery. It was found that the press and expansion/shrinkage can be followed well. As a result, they have found that loss of conductive paths can be suppressed and resistance increase and cycle characteristic deterioration can be suppressed.
上記知見を基礎にして完成した本発明は一側面において、組成式：ＬｉaＮｉbＣｏcＺdＡeＯ2（前記式において、１．００≦ａ≦１．０８、ｂ≧０．８、ｂ＋ｃ＋ｄ＝１、０．０２＜ｄ≦０．１０、０．００１≦ｅ≦０．０２、ＺはＭｎまたはＡｌである。ＡはＺがＭｎの場合、Ａｌ、Ｍｇ、Ｔｉ、Ｚｎ、Ｚｒ、Ｎｂ、Ｖ及びＴａから選ばれる少なくとも１種の元素であり、ＺがＡｌの場合、Ｍｇ、Ｔｉ、Ｚｎ、Ｚｒ、Ｎｂ、Ｖ及びＴａから選ばれる少なくとも１種の元素である。）で表され、一次粒子、及び、前記一次粒子を複数集合させて形成した二次粒子で構成され、前記二次粒子に圧子を負荷速度０．５３２ｍＮ／秒で押し付けることで荷重をかけたとき、二次粒子変位量と荷重が共に増加する第１段変位が生じ、続いて二次粒子変位量が増加した後、二次粒子変位量と荷重が共に増加する第２段変位が生じるリチウムイオン電池正極活物質である。 In one aspect, the present invention completed based on the above findings has a composition formula: Li a Ni b Co c Z d A e O 2 (in the above formula, 1.00≦a≦1.08, b≧0.8. , B+c+d=1, 0.02<d≦0.10, 0.001≦e≦0.02, Z is Mn or Al. A is Al, Mg, Ti, Zn, Zr when Z is Mn. , Nb, V and Ta, and when Z is Al, it is at least one element selected from Mg, Ti, Zn, Zr, Nb, V and Ta). A primary particle and a secondary particle formed by aggregating a plurality of the primary particles. When a load is applied to the secondary particle by pressing an indenter at a load speed of 0.532 mN/sec, the secondary particle A first stage displacement in which both the particle displacement amount and the load increase occurs, and subsequently, a secondary particle displacement amount increases, and then a second stage displacement in which both the secondary particle displacement amount and the load increase occur. It is a substance.
本発明に係るリチウムイオン電池用正極活物質は一実施形態において、前記第１段変位の二次粒子変位量をΔＸ１としたとき、ΔＸ１≧Ｄ５０×０．０７となる。 In one embodiment of the positive electrode active material for a lithium ion battery according to the present invention, ΔX1≧D50×0.07, where ΔX1 is the amount of displacement of the secondary particles in the first stage displacement.
本発明に係るリチウムイオン電池用正極活物質は別の一実施形態において、前記第２段変位の二次粒子変位量をΔＸ２としたとき、ΔＸ２≧Ｄ５０×０．０３となる。 In another embodiment of the positive electrode active material for a lithium ion battery according to the present invention, ΔX2≧D50×0.03, where ΔX2 is the amount of secondary particle displacement in the second stage displacement.
本発明に係るリチウムイオン電池用正極活物質は更に別の一実施形態において、前記第１段変位の荷重の最大値が６０ＭＰａ以下である。 In still another embodiment of the positive electrode active material for a lithium ion battery according to the present invention, the maximum value of the load of the first stage displacement is 60 MPa or less.
本発明に係るリチウムイオン電池用正極活物質は更に別の一実施形態において、前記第２段変位の荷重の最大値が１１０ＭＰａ以下である。 In still another embodiment of the positive electrode active material for a lithium ion battery according to the present invention, the maximum value of the load of the second stage displacement is 110 MPa or less.
本発明に係るリチウムイオン電池用正極活物質は更に別の一実施形態において、前記二次粒子を構成する一次粒子の径が０．１〜１．０μｍである。 In still another embodiment of the positive electrode active material for a lithium ion battery according to the present invention, the diameter of the primary particles constituting the secondary particles is 0.1 to 1.0 μm.
本発明に係るリチウムイオン電池用正極活物質は更に別の一実施形態において、前記二次粒子の平均空隙率が５〜２０％である。 In still another embodiment of the positive electrode active material for a lithium ion battery according to the present invention, the average porosity of the secondary particles is 5 to 20%.
本発明は別の一側面において、本発明のリチウムイオン電池用正極活物質を備えたリチウムイオン電池用正極である。 The present invention, in another aspect, is a positive electrode for a lithium ion battery, comprising the positive electrode active material for a lithium ion battery of the present invention.
本発明は更に別の一側面において、本発明のリチウムイオン電池用正極を備えたリチウムイオン電池である。 In yet another aspect, the present invention is a lithium ion battery including the positive electrode for a lithium ion battery of the present invention.
本発明によれば、充放電サイクルでの抵抗上昇を抑制し、電池の寿命を長くすることが可能な、電池特性に優れたリチウムイオン電池用正極活物質を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material for lithium ion batteries which can suppress the resistance rise in a charging/discharging cycle and can prolong a battery life can be provided.
（リチウムイオン電池用正極活物質の構成）
本発明のリチウムイオン電池用正極活物質は、組成式：ＬｉaＮｉbＣｏcＺdＡeＯ2
（前記式において、１．００≦ａ≦１．０８、ｂ≧０．８、ｂ＋ｃ＋ｄ＝１、０．０２＜ｄ≦０．１０、０．００１≦ｅ≦０．０２、ＺはＭｎまたはＡｌである。ＡはＺがＭｎの場合、Ａｌ、Ｍｇ、Ｔｉ、Ｚｎ、Ｚｒ、Ｎｂ、Ｖ及びＴａから選ばれる少なくとも１種の元素であり、ＺがＡｌの場合、Ｍｇ、Ｔｉ、Ｚｎ、Ｚｒ、Ｎｂ、Ｖ及びＴａから選ばれる少なくとも１種の元素である。）で表され、一次粒子、及び、一次粒子を複数集合させて形成した二次粒子で構成されている。
(Structure of positive electrode active material for lithium ion battery)
The positive electrode active material for a lithium ion battery of the present invention has a composition formula: Li a Ni b Co c Z d A e O 2
(In the above formula, 1.00≦a≦1.08, b≧0.8, b+c+d=1, 0.02<d≦0.10, 0.001≦e≦0.02, Z is Mn or Al. A is at least one element selected from Al, Mg, Ti, Zn, Zr, Nb, V and Ta when Z is Mn, and Mg, Ti, Zn and Zr when Z is Al. , Nb, V and Ta)), and is composed of primary particles and secondary particles formed by aggregating a plurality of primary particles.
リチウムイオン電池用正極活物質における全金属に対するリチウムの比率が１．０〜１．０８であるが、これは、１．０未満では、安定した結晶構造を保持し難く、１．０８超では電池の高容量が確保できなくなるためである。
また、リチウムイオン電池用正極活物質におけるニッケルの組成が０．８以上であるため、当該リチウムイオン電池用正極活物質を用いたリチウムイオン電池の容量、出力、安全性の三つがバランスよく向上する。リチウムイオン電池用正極活物質におけるニッケルの組成は好ましくは０．８〜０．９である。
The ratio of lithium to all metals in the positive electrode active material for a lithium ion battery is 1.0 to 1.08, but if it is less than 1.0, it is difficult to maintain a stable crystal structure, and if it exceeds 1.08, the battery is difficult to maintain. This is because the high capacity of can not be secured.
Further, since the composition of nickel in the positive electrode active material for a lithium ion battery is 0.8 or more, the capacity, output, and safety of the lithium ion battery using the positive electrode active material for a lithium ion battery are improved in a well-balanced manner. .. The composition of nickel in the positive electrode active material for lithium ion batteries is preferably 0.8 to 0.9.
本発明のリチウムイオン電池用正極活物質は、図１に示すように、二次粒子に圧子を負荷速度０．５３２ｍＮ／秒で押し付けることで荷重をかけたとき、二次粒子変位量と荷重（強度）が共に増加する第１段変位が生じ、続いて二次粒子変位量が増加した後、二次粒子変位量と荷重が共に増加する第２段変位が生じる。当該第２段階変位によって、最終的に二次粒子は破断する。なお、第１段変位と第２段変位との間の二次粒子変位量が増加する区間では、当該区間の荷重／変位の傾きが、第１段目変位の荷重／変位の傾きの大きさ以下、且つ、第２段目変位の荷重／変位の傾きの大きさ以下である。また、第１段変位と第２段変位との間の二次粒子変位量が増加する区間の荷重／変位の傾きは、第１段目変位の荷重／変位の傾きの１／１０以下の大きさ、且つ、第２段目変位の荷重／変位の傾きの１／１０以下の大きさであるのが好ましく、図１に示すように当該区間の荷重／変位の傾きが一定であるのがより好ましい。 The positive electrode active material for a lithium ion battery of the present invention, as shown in FIG. 1, when a load is applied by pressing an indenter against a secondary particle at a load speed of 0.532 mN/sec, the secondary particle displacement amount and the load ( The second stage displacement occurs in which both the secondary particle displacement amount and the load increase after the first stage displacement in which the strength) increases and the secondary particle displacement amount subsequently increases. The secondary particles eventually break due to the second-stage displacement. In the section in which the amount of secondary particle displacement between the first-stage displacement and the second-stage displacement increases, the load/displacement slope in the section is the magnitude of the load/displacement slope in the first-stage displacement. It is less than or equal to the magnitude of the load/displacement inclination of the second stage displacement. The gradient of the load/displacement in the section in which the secondary particle displacement amount increases between the first-stage displacement and the second-stage displacement is 1/10 or less of the load/displacement gradient of the first-stage displacement. It is preferable that the load/displacement slope of the second stage displacement is 1/10 or less, and it is more preferable that the load/displacement slope in the section is constant as shown in FIG. preferable.
このように、本発明のリチウムイオン電池用正極活物質は、二次粒子が破断するまで荷重をかけたときの二次粒子変位が、２段階に分けて発生する。二次粒子変位が２段階に分けて発生するのは、二次粒子内部の空隙と関係がある。この二次粒子内部の空隙により、粒子に荷重をかけた際、まずこの空隙が圧縮され二次粒子が変形することで１段目の変位（第１段変位）が発生し、続いて二次粒子変位量が増加した後、二次粒子変位量と荷重が共に増加する第２段変位が生じる。そして、最終的に二次粒子が破断する。 As described above, in the positive electrode active material for a lithium ion battery of the present invention, the displacement of the secondary particles when a load is applied until the secondary particles are broken occurs in two stages. The occurrence of secondary particle displacement in two stages is related to the voids inside the secondary particles. When a load is applied to the particles due to the voids inside the secondary particles, the voids are first compressed and the secondary particles are deformed to cause the first-stage displacement (first-stage displacement). After the amount of particle displacement increases, a second stage displacement occurs in which both the amount of secondary particle displacement and the load increase. Then, the secondary particles finally break.
本発明のような高Ｎｉ組成を有する正極活物質において、二次粒子が破断するまで荷重をかけたときの二次粒子の変位をこのように２段階に制御することで、電極作製時のプレス、及び、二次電池の充放電サイクルでの膨張収縮に対し、正極活物質の粒子が変形しやすくなり、当該プレス及び膨張収縮に良好に追従することができる。その結果、導電パス喪失を抑制し、抵抗増加及びサイクル特性劣化を良好に抑制することができる。 In the positive electrode active material having a high Ni composition as in the present invention, the displacement of the secondary particles when a load is applied until the secondary particles are broken is controlled in this manner in two stages, thereby pressing at the time of manufacturing an electrode. Moreover, the particles of the positive electrode active material are easily deformed with respect to expansion and contraction in the charge and discharge cycle of the secondary battery, and the press and expansion and contraction can be favorably followed. As a result, loss of conductive paths can be suppressed, and resistance increase and cycle characteristic deterioration can be suppressed well.
なお、従来のような単に変位量と荷重とが最後まで（二次粒子が破断するまで）比例して変化する場合に比べ、２段階で変位量と荷重が変化することで、充放電時の粒子の膨張収縮に追従しやすくなり、二次粒子間に発生する隙間が少なくなり、導電パス喪失が抑制される。これは、１段目の変位が二次粒子内部の隙間が圧縮されることで生じるため、比較的小さい荷重で変位し、且つ、粒子形状変化の自由度が大きく、周囲の二次粒子の形状に追従しやすいためである。また、本発明の正極活物質は、二次粒子の平均空隙率が５〜２０％であるのが好ましく、７〜１８％であるのがより好ましい。 It should be noted that, compared with the conventional case where the displacement amount and the load are changed proportionally until the end (until the secondary particles are broken), the displacement amount and the load are changed in two steps. The expansion and contraction of the particles are easily followed, the gaps generated between the secondary particles are reduced, and the loss of the conductive path is suppressed. This is because the displacement of the first stage occurs due to the compression of the gap inside the secondary particles, so the displacement is relatively small and the degree of freedom of changing the particle shape is large, and the shape of the surrounding secondary particles is large. This is because it is easy to follow. Further, in the positive electrode active material of the present invention, the average porosity of the secondary particles is preferably 5 to 20%, more preferably 7 to 18%.
第１段変位の二次粒子変位量をΔＸ１としたとき、ΔＸ１≧Ｄ５０×０．０７となるのが好ましい。また、第２段変位の二次粒子変位量をΔＸ２としたとき、ΔＸ２≧Ｄ５０×０．０３となるのが好ましい。このような構成によれば、電極作製時のプレス、及び、二次電池の充放電サイクルでの膨張収縮に対し、正極活物質の粒子がより変形しやすくなり、当該プレス及び膨張収縮により良好に追従することができる。その結果、導電パス喪失をより抑制し、抵抗増加及びサイクル特性劣化をより良好に抑制することができる。第１段変位の二次粒子変位量をΔＸ１としたとき、ΔＸ１≧Ｄ５０×０．０８となるのがより好ましい。また、第２段変位の二次粒子変位量をΔＸ２としたとき、ΔＸ２≧Ｄ５０×０．０４となるのがより好ましい。 When the secondary particle displacement amount of the first stage displacement is ΔX1, ΔX1≧D50×0.07 is preferable. Further, when the secondary particle displacement amount of the second stage displacement is ΔX2, it is preferable that ΔX2≧D50×0.03. According to such a configuration, the particles of the positive electrode active material are more likely to be deformed with respect to the press at the time of manufacturing the electrode and the expansion/contraction in the charge/discharge cycle of the secondary battery, and the pressing and the expansion/contraction are more favorable. You can follow. As a result, it is possible to further suppress the loss of the conductive path, and it is possible to better suppress the increase in resistance and the deterioration in cycle characteristics. It is more preferable that ΔX1≧D50×0.08, where ΔX1 is the secondary particle displacement amount of the first stage displacement. Further, when the secondary particle displacement amount of the second stage displacement is ΔX2, it is more preferable that ΔX2≧D50×0.04.
第１段変位の荷重の最大値が６０ＭＰａ以下であるのがより好ましく、５０ＭＰａ以下であるのがより好ましく、４５ＭＰａ以下であるのが更により好ましい。また、第２段変位の荷重の最大値が１１０ＭＰａ以下であるのがより好ましく、１００ＭＰａ以下であるのがより好ましく、９０ＭＰａ以下であるのが更により好ましい。このように第１段変位、第２段変位の荷重の最大値を小さくすることで、電極プレス時に粒子が変形しやすく、粒子間の接触面積が多くなる。その結果、充放電時の膨張収縮に追従しやすくサイクル後の粒子間接触を維持しやすくなり、充放電サイクルでの抵抗上昇をより良好に抑制することができる。 The maximum value of the load of the first stage displacement is more preferably 60 MPa or less, more preferably 50 MPa or less, and even more preferably 45 MPa or less. Further, the maximum value of the load of the second stage displacement is more preferably 110 MPa or less, more preferably 100 MPa or less, and even more preferably 90 MPa or less. By reducing the maximum value of the load of the first-stage displacement and the second-stage displacement in this way, the particles are easily deformed during electrode pressing, and the contact area between the particles is increased. As a result, it is easy to follow expansion and contraction during charging and discharging, and it is easy to maintain contact between particles after cycling, and it is possible to better suppress an increase in resistance during charging and discharging cycles.
一次粒子径が０．１〜１．０μｍであるのが好ましい。一次粒子径が０．１μｍより小さい場合は、結晶性が不十分となり、充放電能力が小さくなるおそれがある。一次粒子径が１．０μｍよりも大きい場合は、二次粒子内の空隙が分散しにくく、空隙が局所的に存在しやすくなり、二次粒子に荷重をかけたときの変位が２段階にならない場合がある。一次粒子径は、０．２〜０．６μｍであるのがより好ましい。 The primary particle size is preferably 0.1 to 1.0 μm. When the primary particle size is smaller than 0.1 μm, the crystallinity becomes insufficient and the charge/discharge capacity may be reduced. When the primary particle size is larger than 1.0 μm, the voids in the secondary particles are difficult to disperse, the voids are likely to exist locally, and the displacement when the load is applied to the secondary particles does not have two stages. There are cases. The primary particle diameter is more preferably 0.2 to 0.6 μm.
（リチウムイオン電池用正極及びそれを用いたリチウムイオン電池の構成）
本発明の実施形態に係るリチウムイオン電池用正極は、例えば、上述の構成のリチウムイオン電池用正極活物質と、導電助剤と、バインダーとを混合して調製した正極合剤をアルミニウム箔等からなる集電体の片面または両面に設けた構造を有している。また、本発明の実施形態に係るリチウムイオン電池は、このような構成のリチウムイオン電池用正極を備えている。
(Constitution of positive electrode for lithium-ion battery and lithium-ion battery using the same)
The positive electrode for a lithium ion battery according to the embodiment of the present invention is, for example, a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion battery having the above-described configuration, a conductive additive, and a binder from an aluminum foil or the like. The current collector has a structure provided on one side or both sides. The lithium-ion battery according to the embodiment of the present invention includes the lithium-ion battery positive electrode having such a configuration.
（リチウムイオン電池用正極活物質の製造方法）
次に、本発明の実施形態に係るリチウムイオン電池用正極活物質の製造方法について詳細に説明する。
まず、金属塩溶液を作製する。当該金属は、Ｎｉ、及び、ＭｎまたはＡｌ、及びＣｏである。また、金属塩は硫酸塩、塩化物、硝酸塩、酢酸塩等を用いることができる。金属塩に含まれる各金属は、所望のモル比率となるように調整しておく。これにより、正極活物質中の各金属のモル比率が決定する。当該金属塩溶液とアルカリ溶液とを十分攪拌しながら、金属塩溶液とアルカリ溶液とを同一の槽に徐々に添加しながら撹拌して共沈反応させ、ろ過、洗浄を行い、ケーキを得る。反応は常法に従うことができる。
(Method for producing positive electrode active material for lithium ion battery)
Next, a method for manufacturing the positive electrode active material for a lithium ion battery according to the embodiment of the present invention will be described in detail.
First, a metal salt solution is prepared. The metals are Ni, Mn or Al, and Co. Further, as the metal salt, sulfate, chloride, nitrate, acetate or the like can be used. Each metal contained in the metal salt is adjusted to have a desired molar ratio. This determines the molar ratio of each metal in the positive electrode active material. The metal salt solution and the alkali solution are sufficiently stirred, and the metal salt solution and the alkali solution are gradually added to the same tank while stirring to cause a coprecipitation reaction, filtration, and washing to obtain a cake. The reaction can follow a conventional method.
次に、洗浄した後のケーキに、リチウム化合物（例えば、炭酸リチウム、硝酸リチウム、水酸化リチウムなど）と、ＺがＭｎの場合、Ａｌ、Ｍｇ、Ｔｉ、Ｚｎ、Ｚｒ、Ｎｂ、Ｖ及びＴａから選ばれる少なくとも１種の元素Ａの化合物（例えば、酸化物、水酸化物、炭酸塩、硝酸塩等があるが、特に酸化物が好ましい）、ＺがＡｌの場合、Ｍｇ、Ｔｉ、Ｚｎ、Ｚｒ、Ｎｂ、Ｖ及びＴａから選ばれる少なくとも１種の元素Ａの化合物（例えば、酸化物、水酸化物、炭酸塩、硝酸塩等があるが、特に酸化物が好ましい）と水とを加えてスラリーとし、当該スラリーを乾燥する。このとき添加するリチウム化合物と元素Ａの化合物との量によって、生成する正極活物質中のＬｉ及び元素Ａの含有量を制御することができる。 Next, in the cake after washing, from a lithium compound (for example, lithium carbonate, lithium nitrate, lithium hydroxide, etc.), and when Z is Mn, Al, Mg, Ti, Zn, Zr, Nb, V and Ta A compound of at least one element A selected (for example, oxides, hydroxides, carbonates, nitrates, etc., but particularly preferably oxides), when Z is Al, Mg, Ti, Zn, Zr, At least one compound of element A selected from Nb, V, and Ta (for example, oxides, hydroxides, carbonates, nitrates, etc., but oxides are particularly preferable) and water are added to form a slurry, The slurry is dried. The contents of Li and element A in the produced positive electrode active material can be controlled by the amounts of the lithium compound and the compound of element A added at this time.
上記スラリーの乾燥は、乾燥粉の内部に空隙ができるようにマイクロミストドライヤーで噴霧乾燥させる。マイクロミストドライヤーの給気温度を５００℃以上、排気温度を２５０℃以上とすることで、乾燥粉内部で急激にガスを発生させ、乾燥粉内部に小さな空隙を分散して生成することができる。給気温度、排気温度については特に上限は設けないが、装置の都合により上限を定めれば良い。これまでの一般的な噴霧乾燥技術では、例えば、特開２００３−１１９０２６に記載されるように、給気温度３００℃以下、排気温度２００℃以下で乾燥しているものが大半であったが、このときに生じる空隙は大きな空隙が局所的に存在してしまう。これに対し、本発明のように給気温度５００℃以上、排気温度２５０℃以上で乾燥した場合の空隙は、比較的小さな空隙が分散して存在する。これにより、二次粒子に荷重をかけたときに、小さな空隙が分散して存在することで空隙が圧縮されて１段目の変位が発生し、その後更に加重を加えたときは破断するまで粒子変形が起こり、２段目の変位が発生する。なお、大きな空隙が局所的に存在するものは、空隙が圧縮されると同時に粒子破断が起こるため、変位が一段となる。 The slurry is dried by spray drying with a micro mist dryer so that voids are formed inside the dried powder. By setting the air supply temperature of the micro mist dryer to 500° C. or higher and the exhaust temperature to 250° C. or higher, gas can be rapidly generated inside the dry powder, and small voids can be dispersed and generated inside the dry powder. There is no particular upper limit for the supply air temperature and the exhaust temperature, but the upper limit may be set for the convenience of the device. In general spray drying techniques up to now, for example, as described in JP-A-2003-119026, most of them are dried at a supply temperature of 300° C. or lower and an exhaust temperature of 200° C. or lower. Large voids locally exist in the voids generated at this time. On the other hand, as in the present invention, when air is dried at a supply temperature of 500° C. or higher and an exhaust temperature of 250° C. or higher, relatively small voids are dispersed. As a result, when a load is applied to the secondary particles, the voids are compressed due to the presence of dispersed small voids, and the displacement of the first stage occurs. Deformation occurs and a second-stage displacement occurs. In the case where large voids are locally present, the voids are compressed and the particles are broken at the same time, so that the displacement is further increased.
続いて、生成した乾燥粉を、焼成温度７４０〜８００℃、焼成保持時間１０〜２０時間で焼成する。二次粒子内部に空隙をつくり、そして、焼成温度を８００℃以下とし、一次粒子同士の焼結を抑え、二次粒子が荷重を受けたときの変位量を制御することができる。一次粒子径は焼成温度、二次粒子が荷重を受けたときの変位量は噴霧乾燥条件および焼成温度が重要なパラメータとなる。焼成温度が７４０℃未満の場合は、一次粒子径が小さ過ぎてしまう。また、焼成温度が８００℃超の場合は、一次粒子同士の焼結が進行し、二次粒子が荷重を受けたときの変位量が小さくなってしまう。 Then, the produced dry powder is fired at a firing temperature of 740 to 800° C. and a firing holding time of 10 to 20 hours. By forming voids inside the secondary particles and setting the firing temperature to 800° C. or lower, it is possible to suppress the sintering of the primary particles and to control the displacement amount of the secondary particles when a load is applied. The primary particle size is the firing temperature, and the displacement amount when the secondary particles are subjected to the load are the spray drying conditions and the firing temperature. If the firing temperature is lower than 740°C, the primary particle diameter will be too small. Further, when the firing temperature is higher than 800° C., the sintering of the primary particles progresses, and the displacement amount when the secondary particles receive a load becomes small.
次に、焼成した粉(焼成粉)を、必要であれば、ロールミル、パルべライザー等を用いて解砕し、所定の平均粒子径を有する正極活物質を得る。 Next, if necessary, the calcined powder (calcined powder) is crushed by using a roll mill, a pulverizer or the like to obtain a positive electrode active material having a predetermined average particle diameter.
以下、本発明及びその利点をより良く理解するための実施例を提供するが、本発明はこれらの実施例に限られるものではない。 Examples are provided below for better understanding of the present invention and its advantages, but the present invention is not limited to these examples.
（実施例１〜３２、比較例１〜１６）
Ｎｉ、及び、ＭｎまたはＡｌ、及びＣｏの硝酸塩溶液と、アルカリとして炭酸水素ナトリウムとを混合して十分攪拌しながら、共沈反応させ、ろ過、洗浄を行い、ケーキを得た。次に、洗浄した後のケーキに炭酸リチウムと、Ａｌ、Ｍｇ、Ｔｉ、Ｚｎ、Ｚｒ、Ｎｂ、Ｖ及びＴａから選ばれる少なくとも１種の元素Ａの酸化物と水とを加えてスラリーとし、当該スラリーを乾燥した。
(Examples 1 to 32, Comparative Examples 1 to 16)
A nitrate solution of Ni, Mn or Al, and Co and sodium hydrogen carbonate as an alkali were mixed and sufficiently stirred to cause a coprecipitation reaction, filtration and washing to obtain a cake. Next, lithium carbonate, an oxide of at least one element A selected from Al, Mg, Ti, Zn, Zr, Nb, V, and Ta and water are added to the washed cake to form a slurry, The slurry was dried.
上記スラリーの乾燥は、乾燥粉の内部に空隙ができるように、表１に示す給気温度及び排気温度にて、マイクロミストドライヤーで噴霧乾燥させた。 The slurry was dried by spray drying with a micro mist dryer at the air supply temperature and the exhaust temperature shown in Table 1 so that voids were formed inside the dried powder.
続いて、生成した乾燥粉を、焼成温度：７８０℃、焼成保持時間：１８時間で焼成した。次に、焼成した粉(焼成粉)を、パルべライザーで解砕し、正極活物質を得た。 Subsequently, the produced dry powder was fired at a firing temperature of 780° C. and a firing holding time of 18 hours. Next, the calcined powder (calcined powder) was crushed with a pulverizer to obtain a positive electrode active material.
（評価）
−正極材組成の評価−
各正極材中の金属含有量は、誘導結合プラズマ発光分光分析装置（ＩＣＰ−ＯＥＳ）で測定し、各金属の組成比（モル比）を算出した。各金属の組成比は、表１に記載の通りであることを確認した。
(Evaluation)
-Evaluation of positive electrode material composition-
The metal content in each positive electrode material was measured by an inductively coupled plasma optical emission spectrometer (ICP-OES), and the composition ratio (molar ratio) of each metal was calculated. It was confirmed that the composition ratio of each metal is as shown in Table 1.
−二次粒子の変位量と荷重−
二次粒子の変位量と荷重は、島津製作所製微小圧縮試験機MCT-211にて測定を行った。測定は試料台に分散させた粉末サンプルを置き、顕微鏡で粒径が「Ｄ５０の粒径−１．０μｍ」から「Ｄ５０の粒径＋１．０μｍ」の範囲にある粒子を選択し、その二次粒子一粒の中心を狙い、２０μｍの径の圧子を負荷速度０．５３２ｍＮ／秒で押し付け、第１段変位の荷重最大値および変位量、第２段変位の荷重最大値および変位量をＮ＝１０で測定し、その平均値を各サンプルの第１段変位の荷重最大値および変位量、第２段変位の荷重最大値および変位量とした。
− Secondary Particle Displacement and Load −
The displacement amount and load of the secondary particles were measured with a micro compression tester MCT-211 manufactured by Shimadzu Corporation. For the measurement, the dispersed powder sample is placed on a sample table, and a particle having a particle size in the range of “D50 particle size−1.0 μm” to “D50 particle size+1.0 μm” is selected by a microscope, and the secondary particle is selected. Aiming at the center of each particle, an indenter with a diameter of 20 μm is pressed at a load speed of 0.532 mN/sec, and the load maximum value and displacement amount of the first stage displacement and the load maximum value and displacement amount of the second stage displacement are N= The measurement was performed at 10, and the average value was used as the load maximum value and displacement amount of the first stage displacement and the load maximum value and displacement amount of the second stage displacement of each sample.
−一次粒子径及び二次粒子径の評価−
一次粒子径は、該当の正極活物質（二次粒子）を樹脂埋め後、研磨加工により断面を出し、SIMまたはSEM観察を実施した。その観察写真からランダムに１００個の一次粒子を選び、長軸径、短軸径を測定し、その平均値を一次粒子径とした。
二次粒子径は、日機装株式会社製のマイクロトラックＭＴ３０００ＥＸ IIで測定した粒度分布における５０％径とした。
-Evaluation of primary particle size and secondary particle size-
Regarding the primary particle size, after filling the relevant positive electrode active material (secondary particle) with a resin, a cross section was taken out by polishing, and SIM or SEM observation was carried out. From the observation photograph, 100 primary particles were randomly selected, the major axis diameter and the minor axis diameter were measured, and the average value was used as the primary particle diameter.
The secondary particle size was 50% in the particle size distribution measured by Microtrac MT3000EX II manufactured by Nikkiso Co., Ltd.
−二次粒子変位量の二次粒子の平均粒径Ｄ５０に対する割合−
二次粒子変位量は、島津製作所製微小圧縮試験機MCT-211にて測定を行った。測定は試料台に分散させた粉末サンプルを置き、顕微鏡で粒径が「Ｄ５０の粒径−１．０μｍ」から「Ｄ５０の粒径＋１．０μｍ」の範囲にある粒子を選択し、その二次粒子一粒の中心を狙い、２０μｍの径の圧子を負荷速度０．５３２ｍＮ／秒で押し付けた。粒子に荷重がかかったところを第１段変位の始点とした。その後、変位量増加とともに荷重も増加したが、あるところで、変位量は増加するが荷重が増加しなくなる領域が発生した。このときの変位量は増加するが荷重は増加しなくなる開始点を第１段変位の終点とした。次に更に変位量を増加させていくと荷重が増加する領域が発生した（第２段変位）。このときの開始点を第２段変位の始点とし、粒子が最終的に破断すると変位量は増加するが荷重は増加しなくなった。このときの変位量は増加するが荷重は増加しなくなる開始点を第２段変位の終点とした。
-Ratio of secondary particle displacement amount to average particle diameter D50 of secondary particles-
The amount of secondary particle displacement was measured by a micro compression tester MCT-211 manufactured by Shimadzu Corporation. For the measurement, the dispersed powder sample is placed on a sample table, and a particle having a particle size in the range of “D50 particle size−1.0 μm” to “D50 particle size+1.0 μm” is selected by a microscope, and the secondary particle is selected. A 20 μm diameter indenter was pressed at a load speed of 0.532 mN/sec aiming at the center of each particle. The point where the particles were loaded was taken as the starting point of the first stage displacement. After that, the load increased as the displacement increased, but at some point, a region where the displacement increased but the load did not increase occurred. At this time, the starting point where the amount of displacement increases but the load does not increase is the end point of the first stage displacement. Next, when the amount of displacement was further increased, a region where the load increased occurred (second stage displacement). The starting point at this time was set as the starting point of the second stage displacement, and when the particles finally broke, the displacement amount increased but the load did not increase. At this time, the starting point where the amount of displacement increases but the load does not increase is set as the end point of the second stage displacement.
−二次粒子内部の平均空隙率の評価−
サンプルの粉末を樹脂に埋め、５０μｍ×７０μｍの観察視野にて撮影した電子顕微鏡による観察写真について、二次粒子内部の空隙率を目視で評価した。二次粒子内部の空隙率は、二次粒子の面積に対する、当該二次粒子内部の空隙の面積の割合とした。これらの観察を１つのサンプルに対して１０観察視野分行い、それらの平均値を算出し、これを二次粒子内部の平均空隙率とした。
-Evaluation of average porosity inside secondary particles-
The powder of the sample was embedded in a resin, and the porosity inside the secondary particles was visually evaluated with respect to an observation photograph by an electron microscope taken in an observation visual field of 50 μm×70 μm. The porosity inside the secondary particles was defined as the ratio of the area of the voids inside the secondary particles to the area of the secondary particles. These observations were carried out for 10 observation fields of view for one sample, and the average value thereof was calculated and used as the average porosity inside the secondary particles.
−電池特性（充放電容量、サイクル特性）の評価−
正極活物質と、導電材と、バインダー（ＰＶＤＦ）を９４：３：３の割合で秤量し、バインダーを有機溶媒（Ｎ−メチルピロリドン）に溶解したものに、正極活物質と導電材とを混合してスラリー化し、Ａｌ箔上に塗布して乾燥後にプレスして正極とした。続いて、対極をＬｉとした評価用の対極Ｌｉコインセル(ＣＲ２０３２)を準備し、電解液に１Ｍ−ＬｉＰＦ6をＥＣ−ＤＭＣ（３：７）に溶解したものを用いて、２５℃で１Ｃの放電電流で得られた初期放電容量と１０サイクル後の放電容量とを比較することによってサイクル特性（容量維持率）を測定した。具体的な評価条件及び表に記載の容量維持率と直流抵抗増加率の定義を以下に示す。
・初回充放電（初期容量）：２５℃、充電４．２３Ｖ,０．２Ｃ,１０ｈ、放電３．０Ｖ,０．２Ｃ
・１Ｃ充放電サイクル：４５℃、充電４．２３Ｖ,１Ｃ,２．５ｈ、放電３．０Ｖ,１Ｃ
・容量維持率：５５℃雰囲気で充放電サイクル評価（充電４．２３Ｖ,１Ｃ、放電１Ｃ,３．０Ｖｃｕｔ）を行ったときの、１サイクル目に対する１０サイクル目の放電容量の割合。
・直流抵抗増加率：５５℃雰囲気で充放電サイクル評価（充電４．２３Ｖ,１Ｃ、放電１Ｃ,３．０Ｖｃｕｔ）を行ったときの、１サイクル目に対する１０サイクル目の直流抵抗値の割合。
これらの結果を表１〜４に示す。
-Evaluation of battery characteristics (charge/discharge capacity, cycle characteristics)-
The positive electrode active material, the conductive material, and the binder (PVDF) were weighed in a ratio of 94:3:3, and the binder was dissolved in an organic solvent (N-methylpyrrolidone), and the positive electrode active material and the conductive material were mixed. To form a slurry, which was applied onto an Al foil, dried and then pressed to obtain a positive electrode. Subsequently, a counter electrode Li coin cell (CR2032) for evaluation in which the counter electrode was Li was prepared, and 1M-LiPF 6 dissolved in EC-DMC (3:7) was used as an electrolytic solution at 25°C for 1C. The cycle characteristics (capacity retention rate) were measured by comparing the initial discharge capacity obtained by the discharge current with the discharge capacity after 10 cycles. The specific evaluation conditions and the definitions of the capacity retention rate and the DC resistance increase rate described in the table are shown below.
・First charge/discharge (initial capacity): 25°C, charge 4.23V, 0.2C, 10h, discharge 3.0V, 0.2C
・1C charge/discharge cycle: 45°C, charge 4.23V, 1C, 2.5h, discharge 3.0V, 1C
-Capacity maintenance rate: The ratio of the discharge capacity at the 10th cycle to the 1st cycle when charge/discharge cycle evaluation (charge 4.23V, 1C, discharge 1C, 3.0Vcut) was performed in a 55°C atmosphere.
-DC resistance increase rate: The ratio of the DC resistance value at the 10th cycle to the 1st cycle when charge/discharge cycle evaluation (charge 4.23V, 1C, discharge 1C, 3.0Vcut) was performed in a 55°C atmosphere.
The results are shown in Tables 1 to 4.
実施例１〜３２は、いずれも二次粒子に圧子を負荷速度０．５３２ｍＮ／秒で押し付けることで荷重をかけたとき、二次粒子変位量と荷重が共に増加する第１段変位が生じ、続いて二次粒子変位量が増加した後、二次粒子変位量と荷重が共に増加する第２段変位が生じ、充放電サイクルでの抵抗上昇が抑制され、且つ、容量維持率が良好であった。
比較例１〜１６は、いずれも二次粒子に圧子を負荷速度０．５３２ｍＮ／秒で押し付けることで荷重をかけたとき、二次粒子変位量と荷重が共に増加する上記第１段変位、及び、二次粒子変位量と荷重が共に増加する上記第２段変位が生じなかった。このため、充放電サイクルでの抵抗上昇を抑制することができず、且つ、容量維持率が不良であった。
In each of Examples 1 to 32, when a load is applied by pressing the indenter against the secondary particles at a load speed of 0.532 mN/sec, the first stage displacement in which the secondary particle displacement amount and the load are both increased occurs, Then, after the secondary particle displacement amount increases, a second stage displacement occurs in which both the secondary particle displacement amount and the load increase, which suppresses the resistance increase in the charge/discharge cycle and has a good capacity retention ratio. It was
In each of Comparative Examples 1 to 16, when a load is applied by pressing the indenter against the secondary particles at a load speed of 0.532 mN/sec, the secondary particle displacement amount and the load increase together with the first stage displacement, and The second-stage displacement in which the secondary particle displacement amount and the load both increase did not occur. Therefore, it was not possible to suppress an increase in resistance during charge/discharge cycles, and the capacity retention ratio was poor.
Claims (9)
（前記式において、１．００≦ａ≦１．０８、ｂ≧０．８、ｂ＋ｃ＋ｄ＝１、０．０２＜ｄ≦０．１０、０．００１≦ｅ≦０．０２、ＺはＭｎまたはＡｌである。ＡはＺがＭｎの場合、Ａｌ、Ｍｇ、Ｔｉ、Ｚｎ、Ｚｒ、Ｎｂ、Ｖ及びＴａから選ばれる少なくとも１種の元素であり、ＺがＡｌの場合、Ｍｇ、Ｔｉ、Ｚｎ、Ｚｒ、Ｎｂ、Ｖ及びＴａから選ばれる少なくとも１種の元素である。）
で表され、一次粒子、及び、前記一次粒子を複数集合させて形成した二次粒子で構成され、
前記二次粒子に圧子を負荷速度０．５３２ｍＮ／秒で押し付けることで荷重をかけたとき、二次粒子変位量と荷重が共に増加する第１段変位が生じ、続いて二次粒子変位量が増加した後、二次粒子変位量と荷重が共に増加する第２段変位が生じるリチウムイオン電池正極活物質。 Compositional formula: Li a Ni b Co c Z d A e O 2
(In the above formula, 1.00≦a≦1.08, b≧0.8, b+c+d=1, 0.02<d≦0.10, 0.001≦e≦0.02, Z is Mn or Al. A is at least one element selected from Al, Mg, Ti, Zn, Zr, Nb, V and Ta when Z is Mn, and Mg, Ti, Zn and Zr when Z is Al. , At least one element selected from Nb, V, and Ta.)
Represented by, primary particles, and composed of secondary particles formed by collecting a plurality of the primary particles,
When a load is applied by pressing an indenter against the secondary particles at a load speed of 0.532 mN/sec, a displacement of the secondary particles and a first stage displacement in which the load increase together occur, and subsequently the secondary particle displacement amount is A positive electrode active material for a lithium ion battery in which a second-stage displacement occurs in which the secondary particle displacement amount and the load both increase after the increase.
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