JP2017139077A - Positive electrode active material for lithium ion secondary battery - Google Patents
Positive electrode active material for lithium ion secondary battery Download PDFInfo
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- 239000007774 positive electrode material Substances 0.000 title claims abstract description 49
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 36
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 36
- 239000000203 mixture Substances 0.000 claims abstract description 42
- 150000001875 compounds Chemical class 0.000 claims abstract description 36
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 26
- 239000002245 particle Substances 0.000 claims abstract description 16
- 229910013733 LiCo Inorganic materials 0.000 claims description 27
- 238000012423 maintenance Methods 0.000 claims description 26
- 238000007599 discharging Methods 0.000 claims description 16
- 239000006104 solid solution Substances 0.000 claims description 5
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 claims 1
- 229910012820 LiCoO Inorganic materials 0.000 abstract 1
- 230000000007 visual effect Effects 0.000 abstract 1
- 239000011572 manganese Substances 0.000 description 88
- 239000011575 calcium Substances 0.000 description 78
- 238000000034 method Methods 0.000 description 25
- 230000000052 comparative effect Effects 0.000 description 21
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 18
- 239000013078 crystal Substances 0.000 description 14
- 238000000634 powder X-ray diffraction Methods 0.000 description 13
- 239000002994 raw material Substances 0.000 description 11
- 238000002156 mixing Methods 0.000 description 10
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 9
- 230000014759 maintenance of location Effects 0.000 description 9
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 6
- 238000003991 Rietveld refinement Methods 0.000 description 6
- 238000004458 analytical method Methods 0.000 description 6
- 238000011156 evaluation Methods 0.000 description 6
- 229910052744 lithium Inorganic materials 0.000 description 6
- 238000013507 mapping Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 229910020599 Co 3 O 4 Inorganic materials 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- 229910052791 calcium Inorganic materials 0.000 description 3
- 238000012790 confirmation Methods 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000010304 firing Methods 0.000 description 3
- 239000011888 foil Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000004570 mortar (masonry) Substances 0.000 description 3
- 239000002002 slurry Substances 0.000 description 3
- 235000011121 sodium hydroxide Nutrition 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 229910018871 CoO 2 Inorganic materials 0.000 description 2
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 2
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 2
- 229910013859 LiCo0.8Mn0.2O2 Inorganic materials 0.000 description 2
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 2
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- UBEWDCMIDFGDOO-UHFFFAOYSA-N cobalt(2+);cobalt(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[O-2].[Co+2].[Co+3].[Co+3] UBEWDCMIDFGDOO-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000001027 hydrothermal synthesis Methods 0.000 description 2
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 2
- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- -1 that is Substances 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- 239000006230 acetylene black Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- VSGNNIFQASZAOI-UHFFFAOYSA-L calcium acetate Chemical compound [Ca+2].CC([O-])=O.CC([O-])=O VSGNNIFQASZAOI-UHFFFAOYSA-L 0.000 description 1
- 239000001639 calcium acetate Substances 0.000 description 1
- 235000011092 calcium acetate Nutrition 0.000 description 1
- 229960005147 calcium acetate Drugs 0.000 description 1
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 229910000428 cobalt oxide Inorganic materials 0.000 description 1
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(ii) oxide Chemical compound [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 238000007580 dry-mixing Methods 0.000 description 1
- 239000011267 electrode slurry Substances 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229940099596 manganese sulfate Drugs 0.000 description 1
- 239000011702 manganese sulphate Substances 0.000 description 1
- 235000007079 manganese sulphate Nutrition 0.000 description 1
- SQQMAOCOWKFBNP-UHFFFAOYSA-L manganese(II) sulfate Chemical compound [Mn+2].[O-]S([O-])(=O)=O SQQMAOCOWKFBNP-UHFFFAOYSA-L 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000012916 structural analysis Methods 0.000 description 1
- 230000005469 synchrotron radiation 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
Landscapes
- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
本発明は、コバルト酸リチウム系正極活物質に関し、特に、高電圧充電を繰り返しても放電容量が低下しにくく、長寿命のリチウムイオン二次電池を提供できる正極活物質に関する。 The present invention relates to a lithium cobaltate-based positive electrode active material, and more particularly, to a positive electrode active material that can provide a long-life lithium ion secondary battery that is less likely to have a reduced discharge capacity even after repeated high-voltage charging.
リチウムイオン二次電池の正極活物質として、従来、コバルト酸リチウム（ＬｉＣｏＯ2）が用いられている。
図１（Ａ）は、リチウムイオン二次電池の充放電の際の正極活物質（ＬｉＣｏＯ2）の挙動を模式的に示す説明図であり、図１（Ｂ）の点線で囲んである部分は、（Ａ）に示したＬｉＣｏＯ2の単位格子の模式図である。
Conventionally, lithium cobaltate (LiCoO 2 ) has been used as a positive electrode active material for lithium ion secondary batteries.
FIG. 1 (A) is an explanatory view schematically showing the behavior of the positive electrode active material (LiCoO 2 ) during charging / discharging of a lithium ion secondary battery, and the portion surrounded by the dotted line in FIG. 1 (B) 2A is a schematic diagram of a unit cell of LiCoO 2 shown in FIG.
図１（Ａ）に示すように、ＬｉＣｏＯ2の結晶構造は、酸化コバルト（ＣｏＯ2）層とリチウム（Ｌｉ）層とが交互に積み重なった構造を呈しており、充電時には、Ｌｉ層からＬｉ+が脱離して負極に移動し、放電時には、逆に負極からＬｉ+がＣｏＯ2層間に戻る。
非特許文献１では、充電時のリチウムの脱離量は、充電電圧が高くなるほど増加するので、該脱離量が閾値を超えると、前記結晶構造が変化、崩壊する結果、正極活物質としての機能を失うと報告されている。この結晶構造の変化の程度は、粉末Ｘ線回折法とリートベルト法を用いた構造解析によって、図１（Ｂ）に示す単位格子の格子定数や体積を算出することで評価できる。
As shown in FIG. 1 (A), the crystal structure of LiCoO 2 is exhibited and cobalt oxide (CoO 2) layer and the lithium (Li) layer is stacked in alternating structure, at the time of charging, the Li layer Li + Desorbs and moves to the negative electrode. At the time of discharge, Li + returns from the negative electrode to the CoO 2 layer.
In Non-Patent Document 1, the amount of lithium desorbed at the time of charging increases as the charging voltage increases. Therefore, when the amount of desorbed exceeds a threshold value, the crystal structure changes and collapses. Reported loss of function. The degree of change in the crystal structure can be evaluated by calculating the lattice constant and volume of the unit cell shown in FIG. 1B by structural analysis using a powder X-ray diffraction method and a Rietveld method.
図２は、従来のＬｉＣｏＯ2を正極活物質とするリチウムイオン二次電池における、充電電圧（Ｖ）と、１００回の充放電を繰り返した後（以下、「１００サイクル目」と言うことがある）の放電容量維持率（％）との関係を示す棒グラフである。
図２に示すように、１００サイクル目の放電容量維持率を７０％以上とするためには、すなわち、リチウムイオン二次電池の一定の寿命を保つためには、充電電圧の上限は、４．２〜４．３Ｖに制限されているのが現状である。なお、本明細書において、１００サイクル目の放電容量維持率とは、１回目（初期放電時）の放電容量に対する１００回目の充放電を終えた際の放電容量の割合（％）を示す。
FIG. 2 shows a charge voltage (V) in a conventional lithium ion secondary battery using LiCoO 2 as a positive electrode active material, and after repeating 100 charge / discharge cycles (hereinafter, referred to as “100th cycle”). ) Is a bar graph showing the relationship with the discharge capacity retention rate (%).
As shown in FIG. 2, in order to make the discharge capacity maintenance rate at the 100th cycle 70% or more, that is, to maintain a constant life of the lithium ion secondary battery, the upper limit of the charging voltage is 4. The current situation is limited to 2 to 4.3V. In the present specification, the discharge capacity maintenance rate at the 100th cycle indicates the ratio (%) of the discharge capacity when the 100th charge / discharge is completed with respect to the discharge capacity at the first time (during initial discharge).
一方、非特許文献２には、ＬｉＣｏＯ2にマンガン（Ｍｎ）を添加し、固溶させることが記載されている。
この記載によれば、４．３Ｖの充電電圧下で、１００サイクル目の放電容量維持率を９０％前後に引き上げることができるものの、４．４Ｖないし４．５Ｖの充電電圧下では、９０％を超すことは困難である。
On the other hand, Non-Patent Document 2 describes that manganese (Mn) is added to LiCoO 2 to cause solid solution.
According to this description, the discharge capacity maintenance rate at the 100th cycle can be raised to around 90% under a charging voltage of 4.3V, but 90% under a charging voltage of 4.4V to 4.5V. It is difficult to exceed.
他方、非特許文献３には、ＬｉＣｏＯ2にカルシウム（Ｃａ）を添加し、ＬｉＣｏＯ2の結晶構造を安定化させる手法が開示されている。
この手法は、水熱法によって、ＬｉＣｏＯ2のＬｉ層中にＣａを挿入し、結晶構造の変化抑制を試みたものであるが、製造に要する時間や手間、コスト等を考慮すれば、工業的には実用性に乏しく、量産に適さない。
On the other hand, Non-Patent Document 3, the addition of calcium (Ca) in LiCoO 2, method of stabilizing discloses the crystal structure of LiCoO 2.
This method tried to suppress the change in crystal structure by inserting Ca into the LiCoO 2 Li layer by the hydrothermal method. However, considering the time, labor, cost, etc. required for production, Is not practical and is not suitable for mass production.
本発明は、リチウムイオン二次電池に用いた際に、高電圧での充電を繰り返しても放電容量が低下しにくく、長寿命化が実現でき、しかも工業的に容易な操作で製造できるＬｉＣｏＯ2系正極活物質の提供を課題とする。 When the present invention is used in a lithium ion secondary battery, LiCoO 2 that is less likely to have a reduced discharge capacity even when it is repeatedly charged at a high voltage, can achieve a long life, and can be manufactured by an industrially easy operation. An object is to provide a positive electrode active material.
本発明者らは、上記の課題を解決するために検討を重ねた結果、ＬｉＣｏＯ2の結晶構造の変化を抑制することが、電池の寿命改善の重要なカギであるとの基本に立ち、これを実現する上で、ＭｎとＣａの両方を添加することに着目し、ＭｎとＣａをそれぞれ特定量ずつ含有しているＬｉＣｏ1-xＭｎxＯ2（０．０１＜ｘ＜０．２）とＣａ化合物との混合体であれば、水熱法を用いることなく工業的に容易な操作で上記結晶構造の変化が極めて少ない構造体が得られ、結果、これを用いたリチウムイオン二次電池においては、充電電圧４．３Ｖ以上で充放電を繰り返しても結晶構造が変化しにくいことを見出した。このとき、上記のＬｉＣｏ1-xＭｎxＯ2は、Ｍｎが固溶しているものが好ましいことも見出している。 As a result of repeated studies to solve the above-mentioned problems, the present inventors have been based on the principle that suppressing the change in the crystal structure of LiCoO 2 is an important key for improving the battery life. in order to realize, Mn and focused on the addition of both Ca, LiCo contains a Mn and Ca by each particular amount 1-x Mn x O 2 ( 0.01 <x <0.2) And a Ca compound, a structure having very little change in the crystal structure can be obtained by an industrially easy operation without using a hydrothermal method. As a result, a lithium ion secondary battery using the structure is obtained. In, it was found that the crystal structure hardly changes even when charging and discharging are repeated at a charging voltage of 4.3 V or higher. At this time, it has also been found that the above LiCo 1-x Mn x O 2 is preferably one in which Mn is dissolved.
次いで、このような知見を基に更なる検討を重ねたところ、上記ＬｉＣｏ1-xＭｎxＯ2（０．０１＜ｘ＜０．２）において、特定のサイズのＣａ化合物が偏在している場合に、例えば充電電圧４．５Ｖ程度の条件で充放電を繰り返しても、１００サイクル目の放電容量維持率を確実に７０％以上にできることを見出し、本発明を完成するに至った。 Then, when further examination was repeated based on such knowledge, in the LiCo 1-x Mn x O 2 (0.01 <x <0.2), a Ca compound of a specific size is unevenly distributed. In this case, for example, even when charging / discharging was repeated under the condition of a charging voltage of about 4.5 V, it was found that the discharge capacity maintenance rate at the 100th cycle could be reliably increased to 70% or more, and the present invention was completed.
すなわち、本発明のリチウムイオン二次電池用正極活物質は、ＬｉＣｏ1-xＭｎxＯ2（０．０１＜ｘ＜０．２）とＣａ化合物との混合体からなり、
Ｍｎ含有量が、ＣｏとＭｎの合計量に対し１〜２０モル％
Ｃａ含有量が、ＣｏとＭｎの合計量に対し１〜１５モル％
であることを特徴とする。上記のＬｉＣｏ1-xＭｎxＯ2は、Ｍｎが固溶しているものが好ましい。
この正極活物質を用いたリチウムイオン二次電池は、２０℃の雰囲気下、１６０ｍＡ／ｇを１Ｃとして算出した電流密度（以下、単に電流密度と記す）０．５Ｃで電圧が４．３Ｖ〜４．５Ｖの範囲内の何れかになるまで充電した後、上記電流密度０．５Ｃで電圧３．０Ｖまで放電する操作を、１００回繰り返したときの放電容量維持率が、７０％以上であることが好ましい（この、充放電を１００回繰り返す操作を、以下「サイクル試験」と呼ぶことがある）。
また、本発明の正極活物質の、任意の粒子の断面を、エネルギー分散型Ｘ線分析装置（ＥＤＳ）によって、粒子全体が視野に収まるように、例えば倍率５０００倍、すなわち視野２４×１８μｍの範囲で組成をマッピングした場合、Ｃｏが占める領域とＭｎが占める領域が一致している、すなわちＭｎがＣｏに固溶しており、更に、径１〜１０μｍの《偏在》したＣａが占める領域が３〜６０個存在することが好ましい。このＣａが占める領域に、Ｃａ化合物が存在する。
That is, the positive electrode active material for a lithium ion secondary battery of the present invention consists of a mixture of LiCo 1-x Mn x O 2 (0.01 <x <0.2) and Ca compound,
Mn content is 1-20 mol% with respect to the total amount of Co and Mn
Ca content is 1 to 15 mol% with respect to the total amount of Co and Mn.
It is characterized by being. The LiCo 1-x Mn x O 2 is preferably one in which Mn is dissolved.
The lithium ion secondary battery using this positive electrode active material has a current density calculated from 160 mA / g as 1 C in an atmosphere of 20 ° C. (hereinafter simply referred to as current density) of 0.5 C and a voltage of 4.3 V to 4 V. The discharge capacity maintenance rate is 70% or more when the operation of discharging to a voltage of 3.0 V at a current density of 0.5 C is repeated 100 times after charging to be within a range of 0.5 V. (This operation of repeating charging and discharging 100 times may be hereinafter referred to as a “cycle test”).
Further, the cross section of an arbitrary particle of the positive electrode active material of the present invention is, for example, in a magnification of 5000 times, that is, in a range of 24 × 18 μm, so that the entire particle can be accommodated by an energy dispersive X-ray analyzer (EDS) When the composition is mapped with, the region occupied by Co is the same as the region occupied by Mn, that is, Mn is solid-solved in Co, and further, there are 3 regions occupied by <Eccentricity> Ca having a diameter of 1 to 10 μm. There are preferably ˜60. A Ca compound is present in the area occupied by Ca.
本発明の、特にＭｎが固溶しているＬｉＣｏ1-xＭｎxＯ2とＣａ化合物との混合体である正極活物質は、例えば、リチウムイオン二次電池に使用した場合に、充電電圧の上限が４．３Ｖ以上、４．５Ｖ以下の範囲内になるように充放電を繰り返しても１００サイクル目の放電容量維持率が極めて高く、長寿命のリチウムイオン二次電池とすることができる。
また、本発明の正極活物質は、Ｃａ化合物が均一に分散せずに偏在している場合に、高い放電容量維持率をより確実に得ることができる。
The positive electrode active material according to the present invention, in particular, a mixture of LiCo 1-x Mn x O 2 and Ca compound in which Mn is dissolved, for example, when used in a lithium ion secondary battery, Even when charging and discharging are repeated so that the upper limit is in the range of 4.3 V or more and 4.5 V or less, the discharge capacity maintenance rate at the 100th cycle is extremely high, and a long-life lithium ion secondary battery can be obtained.
Moreover, the positive electrode active material of this invention can obtain a high discharge capacity maintenance factor more reliably, when Ca compound is unevenly distributed without disperse | distributing uniformly.
本発明の正極活物質は、ＬｉＣｏ1-xＭｎxＯ2（０．０１＜ｘ＜０．２）、特にＭｎが固溶しているＬｉＣｏ1-xＭｎxＯ2（０．０１＜ｘ＜０．２）と、Ｃａ化合物との混合体からなり、
Ｍｎ含有量が、ＣｏとＭｎの合計量に対し１〜２０モル％
Ｃａ含有量が、ＣｏとＭｎの合計量に対し１〜１５モル％である。
The positive electrode active material of the present invention is LiCo 1-x Mn x O 2 (0.01 <x <0.2), particularly LiCo 1-x Mn x O 2 (0.01 <x <0.2) and a mixture of Ca compound,
Mn content is 1-20 mol% with respect to the total amount of Co and Mn
Ca content is 1-15 mol% with respect to the total amount of Co and Mn.
上記混合体において、Ｍｎ含有量が、ＣｏとＭｎの合計量に対し少なすぎれば放電容量維持率が低下しやすくなり、結果として長寿命を得ることができず、多すぎると、放電容量自体が低下する虞があるため、１〜２０モル％、好ましくは５〜１１モル％とする。
また、Ｃａ含有量が、ＣｏとＭｎの合計量に対し少なすぎても多すぎても、Ｍｎと同様であるため、１〜１５モル％、好ましくは１〜５モル％とする。
In the above mixture, if the Mn content is too small with respect to the total amount of Co and Mn, the discharge capacity retention rate tends to be lowered, and as a result, a long life cannot be obtained. Since there exists a possibility that it may fall, it is 1-20 mol%, Preferably you may be 5-11 mol%.
Moreover, since it is the same as Mn, even if Ca content is too little or too much with respect to the total amount of Co and Mn, it is 1-15 mol%, Preferably you may be 1-5 mol%.
図３（Ａ）に、本発明のＭｎが固溶しているＬｉＣｏ1-xＭｎxＯ2とＣａ化合物との混合体（Ｘ＝０．０５、ＣｏとＭｎの合計量に対するＣａ含有量が３モル％の場合）の粒子断面のＳＥＭ画像を示す。
図３（Ｂ）〜（Ｄ）は、図３（Ａ）に示した混合体の粒子断面をＥＤＳによって組成マッピングした画像であり、（Ｂ）がＣｏ、（Ｃ）がＭｎ、（Ｄ）がＣａの各分散状態を示している。
FIG. 3A shows a mixture of LiCo 1-x Mn x O 2 and Ca compound in which Mn of the present invention is dissolved (X = 0.05, the Ca content relative to the total amount of Co and Mn is The SEM image of the particle | grain cross section of the case of 3 mol% is shown.
3 (B) to 3 (D) are images obtained by EDS composition mapping of the particle cross section of the mixture shown in FIG. 3 (A), where (B) is Co, (C) is Mn, and (D) is Each dispersion state of Ca is shown.
図３（Ｂ）〜（Ｄ）に示すように、図３（Ａ）の混合体において、ＣｏとＭｎは、均一に分散しているのに対し、Ｃａは、偏在している。このことから、Ｍｎは固溶しているが、Ｃａは固溶することなく、Ｃａ由来の副生成物が生成していると考えられる。粉末Ｘ線回折法による分析の結果、このときの副生成物はＣａ3Ｃｏ2Ｏ6であることが確認されている。
一般に、添加元素が「固溶」せず、「混合体」として存在していると、電池性能は悪いと言われている。しかし、意外なことに、本発明者らは「Ｍｎが固溶したＬｉＣｏ1-xＭｎxＯ2（０．０１＜ｘ＜０．２）に、Ｃａが（固溶することなく）Ｃａ化合物として偏在した混合体」となっていると、高電圧の充電によりＬｉの脱離量が閾値を超えた場合においても、前述のような結晶構造が崩壊することはなく、結果として、長寿命という優れた電池性能が得られることを見出し、本発明ではこれを正極活物質とすることとしている。
As shown in FIGS. 3B to 3D, in the mixture of FIG. 3A, Co and Mn are uniformly dispersed, whereas Ca is unevenly distributed. From this, Mn is dissolved, but Ca is not dissolved, and it is considered that a Ca-derived by-product is generated. As a result of analysis by a powder X-ray diffraction method, it is confirmed that the by-product at this time is Ca 3 Co 2 O 6 .
In general, it is said that the battery performance is poor when the additive element does not “solid solution” but exists as a “mixture”. Surprisingly, however, the present inventors have stated that “Ca compounds (without solid solution) are contained in LiCo 1-x Mn x O 2 (0.01 <x <0.2) in which Mn is dissolved. When the amount of Li desorption exceeds a threshold value due to high voltage charging, the crystal structure as described above does not collapse, resulting in long life. It has been found that excellent battery performance can be obtained, and in the present invention, this is used as a positive electrode active material.
なお、ＬｉＣｏ1-xＭｎxＯ2（０．０１＜ｘ＜０．２）の単位格子（特に、Ｍｎが固溶している該ＬｉＣｏ1-xＭｎxＯ2）は、図１（Ｂ）に模式的に示したＬｉＣｏＯ2の単位格子と同様に、長さ方向に垂直の断面が菱形形状を有する柱状６面体をなしていると考えられる。
このように、本発明の正極活物質（特にＭｎが固溶しているＬｉＣｏ1-xＭｎxＯ2とＣａ化合物との混合体）は、リチウムイオン二次電池の正極材料として使用した場合、高電圧での充放電を繰り返しても、放電容量が低下し難いリチウムイオン二次電池とすることができる。
The unit cell of LiCo 1-x Mn x O 2 (0.01 <x <0.2) (particularly, the LiCo 1-x Mn x O 2 in which Mn is dissolved) is shown in FIG. As in the LiCoO 2 unit cell schematically shown in FIG. 5), it is considered that the cross section perpendicular to the length direction forms a columnar hexahedron having a rhombus shape.
Thus, when the positive electrode active material of the present invention (particularly, a mixture of LiCo 1-x Mn x O 2 and Ca compound in which Mn is dissolved) is used as a positive electrode material of a lithium ion secondary battery, Even if charging / discharging at a high voltage is repeated, a lithium ion secondary battery in which the discharge capacity does not easily decrease can be obtained.
さらに、本発明の正極活物質の、任意の粒子の断面を、粒子全体が視野に収まるように、例えば倍率５０００倍、すなわち視野２４×１８μｍの範囲でＥＤＳによって組成のマッピングを行うと、この視野範囲において、Ｃｏの占める領域と、Ｍｎの占める領域が一致していることが解る。このことから、ＭｎはＣｏに固溶していることが好ましいことが解る。
しかも、径１〜１０μｍの《偏在》したＣａの占める領域が３〜６０個存在することが好ましいことも解る。なお、このＣａが占める領域に、Ｃａ化合物が存在することは明白である。《偏在》したＣａが占める領域の径は、小さすぎても、大きすぎても、放電容量維持率を大幅に高くすることができず、結果長寿命化が達成できない。より好ましい径は２〜５μｍである。また、視野２４×１８μｍ当たりの《偏在》したＣａが占める領域の数は、少なすぎれば、放電容量維持率を大幅に高くすることができず、結果長寿命化が達成できず、多すぎれば不純物となって放電容量を低下させるため、３〜６０個程度が好ましく、より好ましくは５〜４０個程度である。このように、特定サイズの《偏在》したＣａの占める領域が特定の数であれば、高い放電容量維持率をより確実に得ることができる正極活物質となる。
Furthermore, when the composition of the positive electrode active material of the present invention is mapped by EDS in a range of, for example, a magnification of 5000 times, that is, a field of view of 24 × 18 μm so that the entire particle can be within the field of view, this field of view can be obtained. In the range, it can be seen that the region occupied by Co and the region occupied by Mn coincide. From this, it is understood that Mn is preferably dissolved in Co.
In addition, it can be seen that it is preferable that there are 3 to 60 regions that are occupied by Ca unevenly distributed and having a diameter of 1 to 10 μm. It is obvious that a Ca compound is present in the area occupied by Ca. If the diameter of the region occupied by the unevenly distributed Ca is too small or too large, the discharge capacity maintenance rate cannot be significantly increased, and as a result, a long life cannot be achieved. A more preferable diameter is 2 to 5 μm. In addition, if the number of Ca unevenly distributed Ca areas per field of view 24 × 18 μm is too small, the discharge capacity maintenance rate cannot be significantly increased, and as a result, a long life cannot be achieved. In order to reduce the discharge capacity as an impurity, the number is preferably about 3 to 60, more preferably about 5 to 40. In this way, when the area occupied by a specific size of << unevenly distributed Ca >> is a specific number, it becomes a positive electrode active material capable of obtaining a high discharge capacity retention rate more reliably.
本発明の正極活物質（ＬｉＣｏ1-xＭｎxＯ2（０．０１＜ｘ＜０．２）、特にＭｎが固溶している該ＬｉＣｏ1-xＭｎxＯ2と、Ｃａ化合物との混合体）は、例えば、（１）Ｃｏ原料と粒径５μｍ未満のＭｎ原料を混合する工程と、（２）（１）で得られた材料とＣａ原料を混合する工程と、（３）（２）で得られた材料とＬｉ原料を混合する工程と、（４）得られた混合体を焼成して解砕する工程を行うことによって製造することができる。
（１）のＣｏ原料とＭｎ原料を混合する方法の好ましい例としては、Ｃｏ原料を水に分散させたスラリーに、Ｍｎ塩の水溶液と苛性ソーダ水溶液を滴下する手法が挙げられる。（２）のＣａ原料を混合する方法の好ましい例としては、Ｃａ塩水溶液を用いた湿式混合法が挙げられる。（３）のＬｉ原料を混合する方法の好ましい例としては、ニューグラマシンやコンテナミキサー等を用いた乾式混合法が挙げられる。解砕方法の例としては、乳鉢で粉砕する方法やピンミルを用いた方法が挙げられる。（４）の混合体の焼成は、好ましくは、空気中、９００〜１１００℃、３０〜３６０分間の条件で行い、焼成後の解砕は、好ましくはピンミルによる解砕が挙げられる。
The positive electrode active material of the present invention (LiCo 1-x Mn x O 2 (0.01 <x <0.2), in particular, the LiCo 1-x Mn x O 2 in which Mn is dissolved, and a Ca compound) For example, (mixture) includes (1) a step of mixing a Co raw material and a Mn raw material having a particle size of less than 5 μm, a step of (2) mixing the material obtained in (1) and a Ca raw material, and (3) ( It can be manufactured by mixing the material obtained in 2) and the Li raw material, and (4) firing and crushing the obtained mixture.
As a preferred example of the method (1) of mixing the Co raw material and the Mn raw material, a method in which an aqueous solution of Mn salt and an aqueous caustic soda solution are dropped into a slurry in which the Co raw material is dispersed in water. A preferable example of the method (2) of mixing the Ca raw material is a wet mixing method using an aqueous Ca salt solution. As a preferable example of the method of mixing the Li raw material of (3), a dry mixing method using a Newgra machine, a container mixer or the like can be mentioned. Examples of the crushing method include a method of pulverizing with a mortar and a method using a pin mill. Firing of the mixture of (4) is preferably performed in air at 900 to 1100 ° C. for 30 to 360 minutes, and crushing after firing is preferably crushing with a pin mill.
以上のような本発明の正極活物質を正極に用いる以外は、従来からの一般的なリチウムイオン二次電池と同様、金属リチウム箔を負極に用いて調製したリチウムイオン二次電池は、２０℃の雰囲気下、電流密度０．５Ｃで電圧４．３Ｖ〜４．５Ｖまで充電し、電流密度０．５Ｃで電圧３．０Ｖまで放電する操作を１００回繰り返したときの放電容量維持率が７０％以上であることが好ましく、より好ましくは、９１％以上である。 Except for using the positive electrode active material of the present invention as described above for the positive electrode, a lithium ion secondary battery prepared using a metal lithium foil as a negative electrode is 20 ° C. as in the case of a conventional general lithium ion secondary battery. The discharge capacity maintenance rate is 70% when the operation of charging to a voltage of 4.3 V to 4.5 V at a current density of 0.5 C and discharging to a voltage of 3.0 V at a current density of 0.5 C is repeated 100 times. Preferably, it is 91% or more.
以下に挙げる例において、結晶構造の変化の評価以外の粉末Ｘ線回折法は、株式会社リガク製粉末Ｘ線回折装置ＲＩＮＴ１４００を用いて測定した。 In the following examples, powder X-ray diffraction methods other than the evaluation of the change in crystal structure were measured using a powder X-ray diffraction apparatus RINT1400 manufactured by Rigaku Corporation.
参考例１
〔ＬｉＣｏＯ2〕
正極活物質として従来のＬｉＣｏＯ2を用いて、正極活物質９０重量％に、アセチレンブラック５重量％及びＰＶＤＦ（ポリフッ化ビニリデン）５重量％をＮ−メチル−２−ピロリドンに添加して混練し、正極スラリーを作製した。作製したスラリーをアルミニウム箔の上に塗布した後乾燥し、その後圧延ロールを用いて圧延し、直径１１ｍｍの円板状に打ち抜いて正極とした。この正極と、負極としての金属リチウム箔と、セパレータとしてのガラス繊維ろ紙と、電解液としての、ＥＣ（エチレンカーボネイト）とＤＥＣ（ジエチルカーボネイト）を体積比１：１となるよう混合した溶媒に、ヘキサフルオロリン酸リチウム（ＬｉＰＦ6）を１モル／Ｌの濃度となるように溶解した溶液とを用いてリチウムイオン二次電池を作成した。これを参考例１とした。
Reference example 1
[LiCoO 2 ]
Using conventional LiCoO 2 as a positive electrode active material, 90% by weight of the positive electrode active material, 5% by weight of acetylene black and 5% by weight of PVDF (polyvinylidene fluoride) are added to N-methyl-2-pyrrolidone and kneaded. A positive electrode slurry was prepared. The prepared slurry was applied on an aluminum foil, dried, then rolled using a rolling roll, and punched into a disk shape having a diameter of 11 mm to obtain a positive electrode. In a solvent in which EC (ethylene carbonate) and DEC (diethyl carbonate) as an electrolyte solution are mixed at a volume ratio of 1: 1, this positive electrode, a metal lithium foil as a negative electrode, a glass fiber filter paper as a separator, A lithium ion secondary battery was prepared using a solution in which lithium hexafluorophosphate (LiPF 6 ) was dissolved to a concentration of 1 mol / L. This was designated as Reference Example 1.
比較例１〜３
〔ＬｉＣｏ1-xＭｎxＯ2の作成〕
四酸化三コバルト（Ｃｏ3Ｏ4）を水に分散させてスラリー化したものに、Ｃｏ：Ｍｎのモル比が、それぞれ９５：５、９２：８、８９：１１、となるように、硫酸マンガン（ＭｎＳＯ4）水溶液と、ＭｎＳＯ4の２．２モル当量にあたる苛性ソーダ（ＮａＯＨ）水溶液を滴下してＣｏ3Ｏ4にＭｎ化合物を付着させ、ＣｏとＭｎの混合物を得た。付着したＭｎ化合物の径は５μｍ以下であった。これに炭酸リチウム（Ｌｉ2ＣＯ3）を乾式法で混合した後、空気雰囲気中にて１０００℃で４時間焼成し、乳鉢で解砕して、ＬｉＣｏ1-xＭｎxＯ2を得た。
ＣｏとＭｎの合計量に対しＭｎ含有量が５モル％のものを比較例１、８モル％のものを比較例２、１１モル％のものを比較例３とした。
Comparative Examples 1-3
[Production of LiCo 1-x Mn x O 2 ]
Manganese sulfate was prepared by dispersing tricobalt tetroxide (Co 3 O 4 ) in water so that the molar ratio of Co: Mn was 95: 5, 92: 8, and 89:11, respectively. A (MnSO 4 ) aqueous solution and a caustic soda (NaOH) aqueous solution corresponding to 2.2 molar equivalents of MnSO 4 were dropped to attach a Mn compound to Co 3 O 4 to obtain a mixture of Co and Mn. The diameter of the deposited Mn compound was 5 μm or less. Lithium carbonate (Li 2 CO 3 ) was mixed with this by a dry method, and then calcined at 1000 ° C. for 4 hours in an air atmosphere, and pulverized in a mortar to obtain LiCo 1-x Mn x O 2 .
Comparative Example 1 was used with a Mn content of 5 mol% relative to the total amount of Co and Mn, Comparative Example 2 was used with 8 mol%, and Comparative Example 3 was 11 mol%.
実施例１〜３≪Ｃａ含有量が３モル％≫
〔ＬｉＣｏ1-xＭｎxＯ2とＣａ化合物との混合体の作成〕
酢酸カルシウム（Ｃａ（ＣＨ3ＣＯＯ）2）水溶液と、比較例１〜３の作成途中で得たＣｏとＭｎの混合物を混合してスラリーとし、水分を蒸発させてＣｏとＭｎとＣａの混合物を得た。なお、Ｃａ（ＣＨ3ＣＯＯ）2は、ＣｏとＭｎの合計量に対し、Ｃａ含有量が３モル％となるように秤量した。
上記のようにして得られた混合物と炭酸リチウム（Ｌｉ2ＣＯ3）を乾式法で混合した後、空気雰囲気中にて１０００℃で４時間焼成し、乳鉢で解砕してＬｉＣｏ1-xＭｎxＯ2とＣａ化合物との混合体を得た。
ＣｏとＭｎの合計量に対し、Ｍｎ含有量が５モル％のものを実施例１、８モル％のものを実施例２、１１モル％のものを実施例３とした。Ｃａ含有量は、いずれもＣｏとＭｎの合計量に対し３モル％である。粉末Ｘ線回折法による分析の結果、実施例１〜３に含まれるＣａ化合物はＣａ3Ｃｏ2Ｏ6であった。
Examples 1-3 << Ca content is 3 mol% >>
[Preparation of mixture of LiCo 1-x Mn x O 2 and Ca compound]
A calcium acetate (Ca (CH 3 COO) 2 ) aqueous solution and a mixture of Co and Mn obtained during the preparation of Comparative Examples 1 to 3 were mixed to form a slurry, and the water was evaporated to obtain a mixture of Co, Mn and Ca. Obtained. Ca (CH 3 COO) 2 was weighed so that the Ca content was 3 mol% with respect to the total amount of Co and Mn.
The mixture obtained as described above and lithium carbonate (Li 2 CO 3 ) were mixed by a dry method, then calcined in an air atmosphere at 1000 ° C. for 4 hours, crushed in a mortar, and LiCo 1-x Mn A mixture of x O 2 and a Ca compound was obtained.
Example 1 shows that the Mn content is 5 mol% with respect to the total amount of Co and Mn, Example 2 shows that the content of 8 mol% is Example 2, and Example 3 shows that with 11 mol%. The Ca content is 3 mol% with respect to the total amount of Co and Mn. As a result of analysis by powder X-ray diffractometry, the Ca compound contained in Examples 1 to 3 was Ca 3 Co 2 O 6 .
〔分散《偏在》状態の確認〕
分散《偏在》状態の確認は、走査型電子顕微鏡（ＳＥＭ）として日本電子株式会社製ＪＳＭ６７００Ｆを、エネルギー分散型Ｘ線分析装置（ＥＤＳ）として日本電子株式会社製ＪＥＤ２３００Ｆを用いて行った。
正極活物質の、径８〜２０μｍの範囲内の任意の粒子の、ほぼ二等分した断面を、ＥＤＳによって組成マッピングしたところ、Ｃａは、実施例１〜３のいずれも図３（Ｄ）のような偏在状態であった。
また、この《偏在》したＣａが占める領域の大きさと数を目視により数えたところ、実施例１〜３のいずれも、径１〜５μｍの範囲内の粒子は、５〜４０個程度であった。
さらに、Ｃｏが占める領域と、Ｍｎが占める領域は、いずれも一致していた。
[Confirmation of distributed (unevenly distributed) state]
Confirmation of the dispersed << uneven distribution >> state was performed using JSM6700F manufactured by JEOL Ltd. as a scanning electron microscope (SEM) and JED2300F manufactured by JEOL Ltd. as an energy dispersive X-ray analyzer (EDS).
When the composition of an almost bisected cross section of an arbitrary particle having a diameter of 8 to 20 μm in the positive electrode active material was subjected to composition mapping by EDS, Ca in each of Examples 1 to 3 is shown in FIG. It was the uneven distribution state.
Moreover, when the size and the number of the area occupied by the << unevenly distributed Ca >> were visually counted, all of Examples 1 to 3 had about 5 to 40 particles having a diameter of 1 to 5 μm. .
Furthermore, the region occupied by Co and the region occupied by Mn all coincided.
〔放電容量維持率の評価〕
比較例１〜３および実施例１〜３で得られたものを、正極活物質として使用する以外は参考例１と同様にしてリチウムイオン二次電池を作製した。
参考例１、比較例１〜３、実施例１〜３の各リチウムイオン二次電池について、２０℃の雰囲気下、電流密度０．５Ｃで電圧４．３Ｖと、４．５Ｖに充電し、電流密度０．５Ｃで電圧３．０Ｖまで放電する操作をそれぞれ１００回繰り返した後（１００サイクル目）の放電容量維持率（％）を求めた。
図４（Ａ）が充電電圧４．３Ｖ、（Ｂ）が充電電圧４．５Ｖの各場合の放電容量維持率を示している。
[Evaluation of discharge capacity maintenance rate]
Lithium ion secondary batteries were produced in the same manner as in Reference Example 1 except that the materials obtained in Comparative Examples 1 to 3 and Examples 1 to 3 were used as the positive electrode active material.
For each of the lithium ion secondary batteries of Reference Example 1, Comparative Examples 1 to 3, and Examples 1 to 3, the battery was charged to a voltage of 4.3 V and 4.5 V at a current density of 0.5 C in an atmosphere of 20 ° C. The discharge capacity maintenance rate (%) after each operation of discharging to a voltage of 3.0 V at a density of 0.5 C was repeated 100 times (100th cycle).
FIG. 4 (A) shows the discharge capacity maintenance rate when the charging voltage is 4.3V and FIG. 4 (B) is the charging voltage of 4.5V.
〔結晶構造の変化の評価〕
比較例１〜３および実施例１〜３で得られた正極活物質について、結晶構造の変化を評価するために、次の要領で粉末Ｘ線回折を行った。
充放電サイクルを行う前の正極活物質と、充電電圧４．５Ｖまでの充放電サイクル試験を１００回行った後の電池を解体して取り出した正極活物質について、公益財団法人高輝度光科学研究センター運営の大型放射光施設ＳＰｒｉｎｇ−８（ビームラインＢＬ１９Ｂ２、波長λ＝０．７Å）を用い、回折角２θ＝０°〜７０°の範囲で行った。
[Evaluation of changes in crystal structure]
In order to evaluate the change in the crystal structure of the positive electrode active materials obtained in Comparative Examples 1 to 3 and Examples 1 to 3, powder X-ray diffraction was performed as follows.
High-intensity photochemical research on the positive electrode active material before charge / discharge cycle and the positive electrode active material taken out after disassembling the battery after 100 times of charge / discharge cycle test up to 4.5V charge voltage Using a large synchrotron radiation facility SPring-8 (beam line BL19B2, wavelength λ = 0.7 mm) operated by the center, the diffraction angle was 2θ = 0 ° to 70 °.
得られたデータについて、解析プログラムＲＩＥＴＡＮ-ＦＰ（Ｆ.Ｉｚｕｍｉ ａｎｄ Ｋ.Ｍｏｍｍａ,Ｓｏｌｉｄ Ｓｔａｔｅ Ｐｈｅｎｏｍ.,１３０,１５−２０（２００７）参照）により、リートベルト解析を行い、ｃ軸の長さと単位格子の体積を算出した。
充放電を行う前（０（ゼロ）サイクル時）の正極活物質の、リートベルト解析によって算出された“ｃ軸の長さ”に対する、１００サイクル試験後の正極活物質の、リートベルト解析によって算出された“ｃ軸の長さ”の割合を、ｃ軸長維持率（％）とした。
同様に、充放電を行う前（０（ゼロ）サイクル時）の正極活物質の、リートベルト解析によって算出された“単位格子の体積”に対する、サイクル試験後の正極活物質の、リートベルト解析によって算出された“単位格子の体積”の割合を、体積維持率（％）とした。
The obtained data is subjected to Rietveld analysis by the analysis program RIETA-FP (see F. Izumi and K. Mamma, Solid State Phenom., 130, 15-20 (2007)), and the c-axis length and unit cell are analyzed. The volume of was calculated.
Calculated by Rietveld analysis of the positive electrode active material after 100 cycles test against the “c-axis length” calculated by Rietveld analysis of the positive electrode active material before charge / discharge (during 0 (zero) cycle) The ratio of the “c-axis length” obtained was defined as the c-axis length maintenance rate (%).
Similarly, by the Rietveld analysis of the positive electrode active material after the cycle test with respect to the “unit cell volume” calculated by the Rietveld analysis of the positive electrode active material before charging / discharging (during 0 (zero) cycle). The calculated ratio of “unit cell volume” was defined as the volume retention rate (%).
図５（Ａ）に、ｃ軸長維持率（％）を、図５（Ｂ）に、体積維持率（％）をそれぞれ示す。実施例１〜３は、参考例１や比較例１〜３と比べて、ｃ軸長、体積ともに維持率が１００％に近い、すなわち、実施例１〜３の正極活物質は、４．５Ｖという高い電圧で充電を繰り返しても、結晶構造の変化が小さい（充電電圧４．５Ｖ未満の場合、変化がより小さいことは非特許文献１から推測できる）。
以上から、実施例１〜３の正極活物質を正極材料に使用した電池は、サイクル試験において優れた放電容量維持率を示すことが確認できる。
FIG. 5A shows the c-axis length maintenance rate (%), and FIG. 5B shows the volume maintenance rate (%). In Examples 1 to 3, compared with Reference Example 1 and Comparative Examples 1 to 3, both the c-axis length and volume have a maintenance rate close to 100%. That is, the positive electrode active materials of Examples 1 to 3 are 4.5 V. Even when charging is repeated at a high voltage, the change in the crystal structure is small (when the charging voltage is less than 4.5 V, it can be estimated from Non-Patent Document 1 that the change is smaller).
From the above, it can be confirmed that the batteries using the positive electrode active materials of Examples 1 to 3 as the positive electrode material show an excellent discharge capacity retention rate in the cycle test.
比較例４
Ｃｏ3Ｏ4にＭｎ化合物を付着させなかったこと以外は、実施例１〜３と同様にして、ＬｉＣｏＯ2とＣａ化合物との混合体を得た。
粉末Ｘ線回折法による分析の結果、Ｃａ化合物は複数種の混合物であることは判明したが、それらの化合物を粉末Ｘ線回折法によっては特定することができなかった。
Comparative Example 4
A mixture of LiCoO 2 and a Ca compound was obtained in the same manner as in Examples 1 to 3, except that no Mn compound was attached to Co 3 O 4 .
As a result of analysis by the powder X-ray diffraction method, it was found that the Ca compound was a mixture of a plurality of types, but these compounds could not be identified by the powder X-ray diffraction method.
比較例５〜７
Ｍｎ原料を５μｍより大きな粒子を含む二酸化マンガン（ＭｎＯ2）に、Ｃａ原料を水酸化カルシウム（Ｃａ（ＯＨ）2）に、Ｃｏ3Ｏ4との混合方法を乾式法に変更した以外は、実施例１〜３と同様にしてＬｉＣｏ1-xＭｎxＯ2とＣａ化合物との混合体を得た。
ＣｏとＭｎの合計量に対しＭｎ含有量が５モル％のものを比較例５、８モル％のものを比較例６、１１モル％のものを比較例７とした。
粉末Ｘ線回折法による分析の結果、比較例５〜７に含まれるＣａ化合物はＣａ3Ｃｏ2Ｏ6であることが解った。
この混合体について、前記〔分散《偏在》状態の確認〕と同様にして、任意の粒子の断面をＥＤＳによって組成マッピングしたところ、図８（Ｂ）及び図８（Ｃ）に示すように、Ｍｎは一部に偏在し、Ｃｏと固溶していないことが確認された。
また、図８（Ｄ）に示すように、Ｃａが占める領域は斑点状になっておらず、実施例と全く異なる形状を成していることが分かる。
Comparative Examples 5-7
Except for changing the mixing method of manganese raw material to manganese dioxide (MnO 2 ) containing particles larger than 5 μm, Ca raw material to calcium hydroxide (Ca (OH) 2 ), and Co 3 O 4 to the dry method. In the same manner as in Examples 1 to 3, a mixture of LiCo 1-x Mn x O 2 and a Ca compound was obtained.
The Mn content of 5 mol% with respect to the total amount of Co and Mn was Comparative Example 5, 8 mol% was Comparative Example 6, and 11 mol% was Comparative Example 7.
As a result of analysis by the powder X-ray diffraction method, it was found that the Ca compound contained in Comparative Examples 5 to 7 was Ca 3 Co 2 O 6 .
About this mixture, when the cross section of an arbitrary particle was subjected to composition mapping by EDS in the same manner as in [Confirmation of dispersion << uneven distribution >> state], as shown in FIGS. 8B and 8C, Mn Was unevenly distributed in part and was not dissolved in Co.
Further, as shown in FIG. 8D, it can be seen that the area occupied by Ca is not spotted, and has a shape completely different from that of the example.
〔放電容量維持率の評価〕
比較例４〜７で得られたものを、正極活物質として使用する以外は参考例１と同様にしてリチウムイオン二次電池を作製し、実施例１〜３と同様にして放電容量維持率の評価を行った。
比較例４〜７のいずれにおいても、１００サイクル目の放電容量維持率は、充電電圧が４．５Ｖの場合、多くて６０％程度にしかならず、放電容量が低下し易くなっていることがわかる。
従って、比較例４〜７については結晶構造の変化の評価は行わなかった。
[Evaluation of discharge capacity maintenance rate]
A lithium ion secondary battery was produced in the same manner as in Reference Example 1 except that the materials obtained in Comparative Examples 4 to 7 were used as the positive electrode active material. Evaluation was performed.
In any of Comparative Examples 4 to 7, the discharge capacity maintenance rate at the 100th cycle is only about 60% when the charging voltage is 4.5 V, and it can be seen that the discharge capacity tends to decrease.
Therefore, in Comparative Examples 4 to 7, the change in crystal structure was not evaluated.
実施例４
Ｃｏ：Ｍｎのモル比が９９：１に、ＣｏとＭｎの合計量に対し、Ｃａが１モル％となるようにした以外は実施例１と同様にしてＬｉＣｏ0.99Ｍｎ0.01Ｏ2とＣａ化合物との混合体を得た。Ｃａの混合モル比が小さいため、粉末Ｘ線回折法ではＣａ化合物を特定することが極めて困難であった。
Example 4
LiCo 0.99 Mn 0.01 O 2 and the Ca compound were the same as in Example 1 except that the molar ratio of Co: Mn was 99: 1 and Ca was 1 mol% based on the total amount of Co and Mn. A mixture of was obtained. Since the mixing molar ratio of Ca is small, it was very difficult to specify the Ca compound by the powder X-ray diffraction method.
実施例５
Ｃｏ：Ｍｎのモル比が９９：１に、ＣｏとＭｎの合計量に対し、Ｃａが１５モル％となるようにした以外は実施例１と同様にしてＬｉＣｏ0.99Ｍｎ0.01Ｏ2とＣａ化合物との混合体を得た。粉末Ｘ線回折法による分析の結果、このＣａ化合物はＣａ3Ｃｏ2Ｏ6とＣａ9Ｃｏ12Ｏ28であった。
Example 5
LiCo 0.99 Mn 0.01 O 2 and the Ca compound were the same as in Example 1 except that the molar ratio of Co: Mn was 99: 1 and Ca was 15 mol% with respect to the total amount of Co and Mn. A mixture of was obtained. As a result of analysis by a powder X-ray diffraction method, the Ca compounds were Ca 3 Co 2 O 6 and Ca 9 Co 12 O 28 .
実施例６
Ｃｏ：Ｍｎのモル比が８０：２０に、ＣｏとＭｎの合計量に対し、Ｃａが１モル％となるようにした以外は実施例１と同様にしてＬｉＣｏ0.8Ｍｎ0.2Ｏ2とＣａコバルト複合酸化物との混合体を得た。Ｃａの混合モル比が小さいため、粉末Ｘ線回折法ではＣａ化合物を特定することが極めて困難であった。
Example 6
LiCo 0.8 Mn 0.2 O 2 and Ca cobalt composite as in Example 1 except that the molar ratio of Co: Mn is 80:20 and Ca is 1 mol% with respect to the total amount of Co and Mn. A mixture with the oxide was obtained. Since the mixing molar ratio of Ca is small, it was very difficult to specify the Ca compound by the powder X-ray diffraction method.
実施例７
Ｃｏ：Ｍｎのモル比が８０：２０に、ＣｏとＭｎの合計量に対し、Ｃａが１５モル％となるようにした以外は実施例１と同様にしてＬｉＣｏ0.8Ｍｎ0.2Ｏ2とＣａ化合物との混合体を得た。粉末Ｘ線回折法による分析の結果、このＣａ化合物はＣａ3Ｃｏ2Ｏ6であった。
Example 7
LiCo 0.8 Mn 0.2 O 2 and a Ca compound were prepared in the same manner as in Example 1 except that the molar ratio of Co: Mn was 80:20 and Ca was 15 mol% with respect to the total amount of Co and Mn. A mixture of was obtained. As a result of analysis by a powder X-ray diffraction method, this Ca compound was Ca 3 Co 2 O 6 .
実施例４〜７で得られた、Ｍｎが固溶しているＬｉＣｏ1-xＭｎxＯ2（０．０１＜ｘ＜０．２）とＣａ化合物との混合体を正極活物質として使用する以外は、参考例１と同様にしてリチウムイオン二次電池を作製した。
各リチウムイオン二次電池について、測定温度２０℃の条件下、０．５Ｃの電流密度で電圧４．３Ｖあるいは４．５Ｖまで充電し、０．５Ｃの電流密度で電圧３．０Ｖまで放電する操作を、それぞれ１００回繰り返した。
Obtained in Example 4 to 7, Mn uses mixture of LiCo 1-x Mn x O 2 (0.01 <x <0.2) and Ca compounds dissolved as a positive electrode active material A lithium ion secondary battery was produced in the same manner as in Reference Example 1 except for the above.
For each lithium ion secondary battery, an operation of charging to a voltage of 4.3 V or 4.5 V at a current density of 0.5 C under a measurement temperature of 20 ° C. and discharging to a voltage of 3.0 V at a current density of 0.5 C Was repeated 100 times.
〔放電容量維持率の評価〕
充放電を１００回繰り返した後（１００サイクル目）の放電容量維持率（％）を求めた。
図７（Ａ）が充電電圧４．３Ｖ、（Ｂ）が充電電圧４．５Ｖの各場合の放電容量維持率を示しており参考のために参考例１の結果を併せて示している。
[Evaluation of discharge capacity maintenance rate]
The discharge capacity retention rate (%) after charging and discharging 100 times (100th cycle) was determined.
FIG. 7 (A) shows the discharge capacity retention rate in each case where the charging voltage is 4.3V, and FIG. 7 (B) is the charging voltage of 4.5V, and the result of Reference Example 1 is also shown for reference.
本発明の正極活物質は、リチウムイオン二次電池の正極材料として使用することによって、従来のリチウムイオン二次電池に比べて、高い放電容量維持率と長寿命を備えたリチウムイオン二次電池を得ることができる。
よって、本発明の正極活物質によれば、常に高容量を要求されるＥＶ用電源、パソコンや携帯電話用電源、バックアップ電源等をはじめとする公知の各種の用途に用いることが可能である。
By using the positive electrode active material of the present invention as a positive electrode material for a lithium ion secondary battery, a lithium ion secondary battery having a higher discharge capacity retention rate and a longer life than a conventional lithium ion secondary battery can be obtained. Can be obtained.
Therefore, according to the positive electrode active material of the present invention, it can be used for various known applications including a power source for EV, a power source for personal computers and mobile phones, a backup power source and the like that always require a high capacity.
Claims (4)
Ｍｎ含有量が、ＣｏとＭｎの合計量に対し１〜２０モル％
Ｃａ含有量が、ＣｏとＭｎの合計量に対し１〜１５モル％
であることを特徴とするリチウムイオン二次電池用正極活物質。 LiCo 1-x Mn x O 2 (0.01 <x <0.2) and a mixture of Ca compound,
Mn content is 1-20 mol% with respect to the total amount of Co and Mn
Ca content is 1 to 15 mol% with respect to the total amount of Co and Mn.
A positive electrode active material for a lithium ion secondary battery.
2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein LiCo 1-x Mn x O 2 (0.01 <x <0.2) is a solid solution of Mn.
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