JP2004047448A - Positive electrode activator for nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode activator with an excellent cycle property, load property, preservation property, and little swelling. <P>SOLUTION: The positive electrode activator for the nonaqueous electrolyte secondary battery contains at least lithium transition metal complex oxide of spinel structure. The lithium transition metal complex oxide exists in a form of a primary grain and/or secondary grain as an aggregate of the primary grain. When a regression line intersecting the original of coordinate plane is drawn, depending on the coordinates of respective grains, denoting cubic roots of light emission voltages due to a transition metal and lithium as two-dimensional coordinates, an absolute error deviation of the respective coordinates against the regression line is 0.25 or less. <P>COPYRIGHT: (C)2004,JPO

Description

【０１２８】
３．正極活物質の評価
上記で得られた各正極活物質を用いて、負極がリチウム金属である試験用二次電池、負極がカーボンである試験用二次電池および円筒電池を作製して、以下のようにして評価した。
【０１２９】
Ａ．負極がリチウム金属である試験用二次電池を用いた評価
負極がリチウム金属である試験用二次電池は以下のように作製した。
正極活物質の粉末９０重量部と、導電剤となる炭素粉末５重量部と、ポリフッ化ビニリデンのノルマルメチルピロリドン溶液（ポリフッ化ビニリデン量として５重量部）とを混練してペーストを調製し、これを正極集電体に塗布し乾燥させて正極板とした。得られた正極板を用い、負極がリチウム金属である試験用二次電池を作製した。
【０１３０】
（１）初期放電容量
充電電位４．３Ｖ、放電電位２．８５Ｖ、放電負荷０．２Ｃ（なお、１Ｃは、１時間で放電が終了する電流負荷である。以下、同じ。）の条件で、負極がリチウム金属である試験用二次電池を放電させた。このときの放電容量を０．２Ｃ初期放電容量とした。
また、充電電位４．３Ｖ、放電電位３．０Ｖ、放電負荷０．２４Ｃの条件で、負極がリチウム金属である試験用二次電池を放電させた。このときの放電容量を０．２４Ｃ初期放電容量とした。
【０１３１】
（２）放電末期の膨れの評価
０．２Ｃ初期放電容量の測定時に、３．３Ｖから２．８５Ｖまで放電する間の容量変化を測定し、放電末期の膨れを評価した。放電末期の膨れが小さいほどサイクル特性に優れると言える。
【０１３２】
（３）初期効率
充電電位４．３Ｖ、放電電位２．８５Ｖ、放電負荷０．２Ｃの条件で、負極がリチウム金属である試験用二次電池を放電させた。このとき、放電容量の値を初期放電容量とし、充電容量の値を初期充電容量とした。得られた初期放電容量の値を初期充電容量で除して、初期効率を求めた。
【０１３３】
（４）負荷放電容量
充電電位４．３Ｖ、放電電位２．８５Ｖ、放電負荷２．０Ｃの条件で、負極がリチウム金属である試験用二次電池を放電させた。このときの放電容量を負荷放電容量とした。
【０１３４】
（５）負荷効率（負荷容量維持率）
負極がリチウム金属である試験用二次電池を用いて、充電電位４．３Ｖ、放電電位２．８５Ｖ、放電負荷０．２Ｃの条件で、初期放電容量を測定した後、充電電位４．３Ｖ、放電電位２．８５Ｖ、放電負荷２．０Ｃの条件で、負荷放電容量を測定した。得られた負荷放電容量の値を初期放電容量で除して、放電負荷２．０Ｃのときの負荷効率を求めた。
【０１３５】
また、負極がリチウム金属である試験用二次電池を用いて、充電電位４．３Ｖ、放電電位２．８５Ｖ、放電負荷０．２４Ｃの条件で、初期放電容量を測定した後、充電電位４．３Ｖ、放電電位２．８５Ｖ、放電負荷３．５Ｃの条件で、負荷放電容量を測定した。得られた負荷放電容量の値を初期放電容量で除して、放電負荷３．５Ｃのときの負荷効率を求めた。
【０１３６】
結果を第２表に示す。なお、表中、「−」は、該当する項目を測定していないことを示す。
第２表から明らかなように、本発明の正極活物質は、初期放電容量および負荷放電容量のいずれにも優れ、初期効率および負荷効率のいずれにも優れ、かつ、サイクル特性に優れていた。
【０１３７】
【表２】

【０１３８】
Ｂ．負極がカーボンである試験用二次電池を用いた評価
負極がリチウム金属である試験用二次電池の場合と同様の方法により、正極板を得た。得られた正極板を用い、負極がカーボンである試験用二次電池を作製した。
【０１３９】
（１）放電容量
充電電位４．２Ｖ、放電電位２．７５Ｖ、放電負荷０．２Ｃの条件で、負極がカーボンである試験用二次電池の充放電を４３サイクル行った。４３サイクル後の放電容量を測定した。
【０１４０】
（２）放電末期膨れ
４３サイクル後の放電容量の測定時に、３．３Ｖから２．８５Ｖまで放電する間の容量変化を測定し、放電末期の膨れを評価した。放電末期の膨れが小さいほどサイクル特性に優れると言える。
【０１４１】
（３）Ｍｎ溶出量
４３サイクル充放電を行った後、負極がカーボンである試験用二次電池を分解し、負極およびセパレーターを取り出し、負極およびセパレーターに付着したＭｎを溶解させて濃縮し、ＩＣＰ分光分析法によりＭｎ溶出量（負極およびセパレーターから溶解させたＭｎ元素の重量）を測定した。Ｍｎ溶出量が少なければ、サイクル特性および保存特性に優れると言える。
【０１４２】
（４）４３サイクル後の放電容量維持率
充電電位４．２Ｖ、放電電位２．７５Ｖ、放電負荷１．０Ｃの条件で充放電を繰り返し行い、４３サイクル後の放電容量を測定した。得られた４３サイクル後の放電容量の値を１サイクル後の放電容量の値で除して、４３サイクル後の放電容量維持率を求め、サイクル特性を評価した。
【０１４３】
結果を第３表に示す。なお、表中、「−」は、該当する項目を測定していないことを示す。
第３表から明らかなように、本発明の正極活物質は、サイクル特性および保存特性に優れていた。
【０１４４】
【表３】

【０１４５】
Ｃ．円筒電池を用いた評価
円筒電池は、以下のようにして作製した。
負極がリチウム金属である試験用二次電池の場合と同様の方法により、正極板を得た。また、負極活物質として炭素材料を用い、正極板の場合と同様にして負極集電体に塗布し乾燥させて負極板とした。セパレーターには多孔性プロピレンフィルムを用いた。電解液には、エチレンカーボネート／メチルエチルカーボネート＝３／７（体積比）の混合溶媒にＬｉＰＦ_６を１ｍｏｌ／Ｌの濃度になるように溶解させた溶液を用いた。正極板、負極板およびセパレーターを薄いシート状に成形し、これを巻回させて金属円筒形の電池ケースに収納し、電池ケース内に電解液を注入して、リチウムイオン電池の円筒電池を得た。
【０１４６】
（１）２００サイクル後の放電容量維持率
充電電位４．２Ｖ、放電電位２．７５Ｖ、放電負荷２Ｃの条件で充放電を繰り返し行い、２００サイクル後の放電容量を測定した。得られた２００サイクル後の放電容量の値を１サイクル後の放電容量の値で除して、２００サイクル後の放電容量維持率を求め、サイクル特性を評価した。
【０１４７】
（２）高温放電容量維持率
６０℃において、充電電位４．２Ｖ、放電電位２．７５Ｖ、放電負荷２Ｃの条件で充放電を繰り返し行い、２００サイクル後の放電容量を測定した。得られた２００サイクル後の放電容量の値を１サイクル後の放電容量の値で除して、高温放電容量維持率を求め、高温サイクル特性を評価した。
【０１４８】
（３）負荷効率（負荷容量維持率）
充電電位４．２Ｖ、放電電位２．７５Ｖ、放電負荷０．２Ｃの条件で、初期放電容量を測定した後、充電電位４．２Ｖ、放電電位２．７５Ｖ、放電負荷２．０Ｃの条件で、負荷放電容量を測定した。得られた負荷放電容量の値を初期放電容量で除して、放電負荷２．０Ｃのときの負荷効率を求めた。
【０１４９】
（４）平均電位
充電電位４．２Ｖ、放電電圧２．７５Ｖ、放電負荷０．２Ｃの条件で、初期放電容量および電力量を測定した。得られた電力量の値を初期放電容量で除して、平均電位を求めた。
【０１５０】
結果を第４表に示す。なお、表中、「−」は、該当する項目を測定していないことを示す。
第４表から明らかなように、本発明の正極活物質は、サイクル特性および高温サイクル特性のいずれにも優れ、かつ、負荷時の平均電位が高く、負荷容量維持率に優れていた。
【０１５１】
【表４】

【０１５２】
【発明の効果】
以上説明したように、本発明の正極活物質を用いることにより、非水電解液二次電池のサイクル特性、負荷特性、保存特性等の電池特性を向上させることができる。これにより従来達成できなかった優れた電池特性の非水電解液二次電池を実用化することができ、種々の分野への応用が可能となる。
【図面の簡単な説明】
【図１】図１は、本発明の正極活物質（実施例１）において、リチウムマンガン複合酸化物粒子のマンガン原子に起因する発光電圧値の三乗根をＸ値とし、リチウム原子に起因する発光電圧値の三乗根をＹ値としたときの（Ｘ，Ｙ）の分布を表す散布図である。
【図２】図２は、従来のリチウムイオン二次電池用正極活物質（比較例１）において、リチウムマンガン複合酸化物粒子のマンガン原子に起因する発光電圧値の三乗根をＸ値とし、リチウム原子に起因する発光電圧値の三乗根をＹ値としたときの（Ｘ，Ｙ）の分布を表す散布図である。
【図３】図３は、一次回帰直線に対する各点の誤差の具体的な求め方の説明図である。
【図４】図４は、スピネル構造のリチウム遷移金属複合酸化物の結晶構造を示す模式図である。
【図５】図５は、正極の模式的な断面図である。
【図６】図６は、円筒型電池の模式的な断面図である。
【図７】図７は、コイン型電池の模式的な部分断面図である。
【図８】図８は、角型電池の模式的な斜視図である。
【図９】実施例１で得られた正極活物質についてＥＰＭＡによるライン分析をして得られた、マグネシウムの存在状態を示すチャートである。
【図１０】比較例１で得られた正極活物質についてＥＰＭＡによるライン分析をして得られた、マグネシウムの存在状態を示すチャートである。
【符号の説明】
１　８ａサイト
２　３２ｅサイト
３　１６ｄサイト
４　結着剤
５　正極活物質
１１　負極
１２　集電体
１３　正極
１４　セパレーター
２０　円筒型電池
３０　コイン型電池
４０　角型電池[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery (hereinafter, also simply referred to as “positive electrode active material”). More specifically, the present invention relates to a positive electrode active material having a lithium-transition metal composite oxide having a spinel structure and excellent in cycle charge / discharge characteristics (cycle characteristics), storage characteristics, load characteristics, and the like.
[0002]
[Prior art]
2. Description of the Related Art Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are widely used as power supplies for mobile electronic devices such as mobile phones and notebook computers. Recently, application to large-capacity power supplies such as batteries for electric vehicles is expected.
[0003]
At present, various functions are provided to mobile electronic devices such as mobile phones, and accordingly, a non-aqueous electrolyte secondary battery as a power source is required to further improve load characteristics.
When a non-aqueous electrolyte secondary battery is used in an electric vehicle, a battery life of 5 years or more is required, and it is necessary to improve cycle characteristics. Further, in that case, it is necessary to discharge a large current, and further improvement in load characteristics is required.
[0004]
Non-aqueous electrolyte secondary batteries are characterized by having a higher operating voltage and higher energy density than conventional nickel cadmium secondary batteries and the like, and are widely used as power supplies for electronic devices. As the positive electrode active material of this nonaqueous electrolyte secondary battery, LiMn ₂ O ₄ , LiCoO ₂ And LiNiO ₂ And lithium transition metal composite oxides.
[0005]
Of these, LiMn ₂ O ₄ Has a problem that a gas is generated due to charge and discharge and the battery swells. In addition, there is a problem that cycle characteristics at a practical level cannot be obtained. Since these problems are particularly prominent at high temperatures, they cannot be put to practical use, for example, for applications such as mobile devices expected to be used at high temperatures.
[0006]
One of the causes of the above problem is that LiMn ₂ O ₄ The manganese ion is eluted into the electrolyte from the crystal structure of Hereinafter, a specific description will be given.
Manganese ions eluted in the electrolyte precipitate on the surface of the negative electrode, hindering insertion of lithium ions into the negative electrode material and desorption from the negative electrode material, resulting in an increase in internal resistance. As a result, when the charge and discharge are repeatedly performed, the discharge capacity is reduced.
Further, LiMn constituting the positive electrode ₂ O ₄ The elution of manganese ions from the crystals into the electrolyte is accompanied by deterioration and deterioration of the positive electrode and the electrolyte. Deterioration and deterioration of each material constituting such a battery cause deterioration of cycle characteristics.
Further, there is a theory that manganese ions eluted in the electrolytic solution promote the decomposition reaction of the ester compound in the electrolytic solution. By the decomposition of the ester compound, CO 2 ₂ And other gases are generated, causing swelling of the battery.
It is known that the elution of manganese ions occurs not only when charging and discharging are performed, but also when the manganese ions are left alone.
[0007]
[Problems to be solved by the invention]
The present inventors have proposed LiMn ₂ O ₄ It was considered that if the elution of manganese ions can be suppressed in the positive electrode active material using, the discharge capacity can be improved, the cycle characteristics can be improved, and the swelling of the battery can be prevented.
Further, as the positive electrode active material, a material which does not elute manganese ions even during storage of the nonaqueous electrolyte secondary battery and has excellent storage characteristics is preferable.
Furthermore, what has been described above is that LiMn using manganese as a transition metal ₂ O ₄ In addition, the same can be said for a lithium transition metal composite oxide having a spinel structure using another transition metal (for example, titanium).
Accordingly, an object of the present invention is to provide a positive electrode active material for a nonaqueous electrolyte secondary battery having at least a lithium-transition metal composite oxide having a spinel structure, and to improve battery characteristics, in particular, cycle characteristics, load characteristics, storage characteristics, and the like. An object of the present invention is to provide a positive electrode active material which is excellent and has little battery swelling.
[0008]
[Means for Solving the Problems]
That is, the present invention provides the following (1) to (9).
[0009]
(1) A positive electrode active material for a non-aqueous electrolyte secondary battery having at least a lithium transition metal composite oxide having a spinel structure,
The lithium transition metal composite oxide is present in the form of particles composed of one or both of primary particles and secondary particles that are aggregates thereof,
Each of the particles is given a two-dimensional coordinate having a coordinate component of each of the cube roots of the emission voltage values caused by the transition metal and lithium in each of the particles, expressed as a point on a coordinate plane, and linearly regressed through the origin. When finding a straight line,
A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein an absolute deviation of an error at each point with respect to the first linear regression line is 0.25 or less.
[0010]
In other words, the positive electrode active material for a non-aqueous electrolyte secondary battery having at least a lithium transition metal composite oxide having a spinel structure, wherein the lithium transition metal composite oxide is a transition metal of a lithium transition metal composite oxide particle The X-value is the cube root of the light-emitting voltage caused by the above, and the Y-value is the cube root of the light-emitting voltage caused by the lithium. The lithium transition metal composite oxide has an absolute deviation of an error of the oxide particle group of 0.25 or less.
[0011]
The present inventors have conducted intensive studies to achieve the above object, and as a result, by reducing the variation in the composition ratio of each particle of the lithium transition metal composite oxide having a spinel structure, elution of transition metal ions is suppressed. As a result, it was found that the cycle characteristics and the storage characteristics were improved, and that the swelling of the battery was suppressed.
The inventor further noted that the variation in the composition ratio of each particle of the lithium transition metal composite oxide is such that each particle has a coordinate component of each of the cube roots of the emission voltage values caused by the transition metal and lithium in each of the particles. Given two-dimensional coordinates, represented as a point on the coordinate plane, when obtaining a linear regression line passing through the origin, it can be represented by the absolute deviation of the error of each point with respect to the linear regression line, and, It has been found that when the absolute deviation of the error is 0.25 or less, the elution of transition metal ions is suppressed to such an extent that the cycle characteristics, storage characteristics and battery swelling become practical.
The present inventor has completed the above-mentioned positive electrode active material (1) based on these findings.
[0012]
According to the findings of the present inventors, by reducing the variation of the composition ratio of each particle and increasing the uniformity of the composition ratio at the particle level, the insertion and desorption of lithium ions in the entire positive electrode are average. It is considered that the unevenness of the current density does not occur and the load characteristics are improved.
Furthermore, according to the knowledge of the present inventors, by suppressing the variation in the composition ratio of each particle and increasing the uniformity of the composition ratio at the particle level, the discharge potential under load increases, and the capacity retention rate under load increases. Therefore, it is considered that the output characteristics are also improved.
[0013]
(2) In the particle size distribution of the particles, when the particle diameters at which the volume cumulative frequency reaches 10%, 50%, and 90% are D10, D50, and D90, respectively,
0.1 ≦ (D10 / D50) <1,
1 <(D90 / D50) ≦ 3 and
5 μm ≦ D50 ≦ 40 μm
The positive electrode active material for a nonaqueous electrolyte secondary battery according to the above (1), which satisfies all of the following.
[0014]
The present inventors not only reduce the variation in the composition ratio of each particle, but also impair the improvement of cycle characteristics, storage characteristics, load characteristics and output characteristics by controlling the variation in the size of each particle. Without, and without impairing the suppression of battery swelling, improve the electrode plate density when applying the positive electrode active material of the present invention to the positive electrode plate, thereby improving the charge / discharge capacity per unit volume of the battery By finding that it is possible, and by satisfying a specific relational expression relating to the volume cumulative frequency of the particle size distribution, it is possible to achieve both improvement in cycle characteristics, storage characteristics, load characteristics, and output characteristics, and improvement in electrode plate density. They have found that this is possible, and based on these findings, completed the positive electrode active material of (2) above.
[0015]
(3) The positive electrode active material for a non-aqueous electrolyte secondary battery according to (1) or (2), wherein in the particle size distribution of the particles, the standard deviation of the particle diameter is 0.4 or less.
[0016]
The present inventor can also improve the cycle characteristics, storage characteristics, load characteristics and output characteristics and improve the electrode plate density by setting the standard deviation of the particle diameter to 0.4 or less. They found that it was possible and completed the above-mentioned positive electrode active material (3).
[0017]
(4) The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of (1) to (3), wherein the transition metal is manganese.
[0018]
When the transition metal is manganese, the nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention becomes particularly excellent in cycle characteristics, storage characteristics and load characteristics, and thus is used in mobile phones, power tools and the like. Can be particularly preferably used. In addition, since it also has excellent output characteristics, it can be particularly suitably used for electric vehicles.
[0019]
(5) The positive electrode active material for a non-aqueous electrolyte secondary battery according to (4), wherein the lithium transition metal composite oxide is a lithium manganese composite oxide having aluminum and / or magnesium and boron.
[0020]
The present inventor can stabilize the crystal structure by using a lithium manganese composite oxide in which part of manganese of lithium manganate is substituted with aluminum and / or magnesium, and can preserve storage characteristics, load characteristics and output power. It has been found that the cycle characteristics can be further improved and the swelling of the battery can be further suppressed without impairing the characteristics.
In addition, the present inventor has found that since boron acts as a flux and increases crystallinity, the addition of boron further improves the cycle characteristics without impairing the storage characteristics, load characteristics, and output characteristics. .
The present inventor has completed the above-mentioned (5) positive electrode active material based on these findings.
[0021]
(6) The lithium transition metal composite oxide has a general formula Li _{1 + a} M _b Mn _2-ab B _c O _{4 + d} (M represents aluminum and / or magnesium, a represents a number satisfying −0.2 ≦ a ≦ 0.2, b represents a number satisfying 0 ≦ b ≦ 0.2, and c represents 0 ≦ c ≦ The positive electrode active material for a non-aqueous electrolyte secondary battery according to the above (4), wherein the positive electrode active material represents a number satisfying 0.02, and d represents a number satisfying -0.5 ≦ d ≦ 0.5. .
[0022]
Further, the present inventors have found the following.
That is, in order to suppress the elution of manganese ions, it is effective to increase the Li / Mn molar ratio. However, as the Li / Mn molar ratio increases, the charge / discharge capacity decreases. Further, if the composition ratio of the lithium manganese composite oxide varies greatly among particles, manganese ions are eluted from particles having a small Li / Mn molar ratio even when the Li / Mn molar ratio of the average composition is increased.
In the positive electrode active material of the above (1), elution of transition metal ions is suppressed by reducing the variation of the composition ratio of each particle. However, the charge / discharge capacity is not reduced, and The Li / Mn molar ratio can be adjusted to a range where the elution of manganese ions can be effectively suppressed.
The present inventor has determined the preferable range of the Li / Mn molar ratio based on these findings, and has completed the above-mentioned cathode active material (6). Therefore, the positive electrode active material of (6) is excellent in cycle characteristics, load characteristics, storage characteristics and charge / discharge capacity, and has little battery swelling.
[0023]
(7) The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of (1) to (6), wherein the lithium transition metal composite oxide has a (400) crystallite diameter of 600 to 1200 Å.
[0024]
When the (400) crystallite diameter is 600 to 1200 angstroms, more excellent cycle characteristics can be realized without impairing the storage characteristics, load characteristics, and output characteristics.
[0025]
(8) Specific surface area is 0.2 to 1.2 m ² / G, the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of the above (1) to (7).
[0026]
Specific surface area is 0.2-1.2m ² / G can further suppress the expansion coefficient of the battery without impairing the cycle characteristics, storage characteristics, load characteristics, and output characteristics.
[0027]
(9) In the particle size distribution of the particles, the proportion of particles having a volume-based particle size of 50 μm or more is 10% by volume or less of all particles, and the non-aqueous liquid according to any one of (1) to (8) above. Positive active material for electrolyte secondary battery.
[0028]
In the particle size distribution of the particles, when the ratio of the particles having a volume-based particle diameter of 50 μm or more is 10% by volume or less of all the particles, the smoothness is maintained without impairing the cycle characteristics, storage characteristics, load characteristics, and output characteristics. Thus, a positive electrode coated surface having excellent characteristics can be obtained.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the positive electrode active material of the present invention will be described with reference to embodiments, examples, and FIGS. 1 to 10. However, the present invention is not limited to the embodiment, the examples, and FIGS.
[0030]
(Positive electrode active material for non-aqueous electrolyte secondary batteries)
The positive electrode active material of the present invention has at least a lithium transition metal composite oxide having a spinel structure (a spinel-type crystal structure). "Spinel structure" is a compound oxide of AB ₂ O ₄ Is one of the typical crystal structure types found in the type compounds (A and B are metal elements).
FIG. 4 is a schematic diagram showing a crystal structure of a lithium transition metal composite oxide having a spinel structure. In FIG. 4, lithium atom 1 occupies the 8a site tetrahedral site, oxygen atom 2 occupies the 32e site, and transition metal atom 3 (and possibly excess lithium atom) occupies the 16d site octahedral site. Occupy.
[0031]
Examples of the lithium transition metal composite oxide having a spinel structure include a lithium manganese composite oxide and a lithium titanium composite oxide. Especially, a lithium manganese composite oxide is preferable.
[0032]
In the positive electrode active material of the present invention, the lithium transition metal composite oxide exists in the form of particles composed of one or both of primary particles and secondary particles that are aggregates thereof. That is, the lithium transition metal composite oxide exists in the form of particles, and the particles may be composed of only primary particles, or may be composed of only secondary particles that are aggregates of primary particles. It may be composed of both particles and secondary particles.
[0033]
In the positive electrode active material of the present invention, each of the particles is given a two-dimensional coordinate having a coordinate component of each of the cube roots of the emission voltage value caused by the transition metal and lithium in each particle, and a point on a coordinate plane is given. When the primary regression line passing through the origin is obtained, the absolute deviation of the error of each point with respect to the primary regression line is 0.25 or less. The details will be described below.
The `` emission voltage value '' was obtained by introducing particles of a lithium transition metal composite oxide into microwave plasma, decomposing the particles into atoms, exciting the particles, and detecting an emission spectrum emitted by the excited atoms as a voltage. It is the value of time. In the present invention, in each particle of the lithium transition metal composite oxide, a light emission voltage value caused by a transition metal atom and a lithium atom is determined.
[0034]
Hereinafter, the method actually performed by the present inventor will be specifically described by way of example. First, using a fine particle component analyzer (Particle Analyzer PT1000, manufactured by Yokogawa Electric Corporation), manganese and lithium were measured for thousands to tens of thousands of particles of the positive electrode active material of Example 1 and Comparative Example 1 described later. Was subjected to elemental analysis. For manganese, the emission spectrum at an emission wavelength of 257.610 nm was measured at a high-voltage power supply magnification of 1.00, with the channel of the detector of the above device being set to 2. For lithium, the emission spectrum at an emission wavelength of 670.780 nm was measured at a high-voltage power supply magnification of 0.75, with channel 3 of the detector of the above-mentioned device being set to 3. In the present invention, the apparatus is not limited to the above-described apparatus, but may be an apparatus that performs elemental analysis of each particle by using the emission voltage of each element using microwave plasma.
[0035]
For each particle, the X-value is the cube root of the emission voltage value resulting from the obtained manganese atom, the Y-value is the cube root of the emission voltage value obtained from the obtained lithium atom, and the coordinates are given to each particle. Two-dimensional coordinates (X, Y) as components were given and represented as points on a coordinate plane. FIG. 1 is a scatter diagram showing the distribution of (X, Y) for Example 1, and FIG. 2 is a scatter diagram showing the distribution of (X, Y) for Comparative Example 1. Note that particles with Y = 0 and / or X = 0 were excluded because they were particles below the measurement limit. The ratio between the X value and the Y value at each point represents the ratio between the lithium and manganese contents in each particle of the lithium-manganese composite oxide.
Next, a linear regression line (approximate line) passing through the origin represented by Y = aX (a is a constant) was obtained by the least square method, and is shown in FIGS. 1 and 2.
[0036]
Further, the absolute deviation of the error at each point with respect to the linear regression line was determined as follows. In FIGS. 1 and 2, the directed distance between each point and the intersection of the perpendicular line drawn from each point and the approximate straight line (positive when the point is above the approximate straight line, negative when it is below the approximate straight line) ) Is d, and the distance between the intersection and the intersection of the vertical axis drawn from the intersection and the X axis is H. At this time, the error e is represented by the following equation (1).
[0037]
e = d / H (1)
[0038]
FIG. 3 is an explanatory diagram of a specific method of obtaining the error of each point with respect to the linear regression line. In FIG. 3, the distance between the point A and the point B and the intersection of the perpendicular line drawn from the point A and the point B and the approximate straight line is d, respectively. ₁ (> 0) and d ₂ (<0), and the lengths of perpendiculars lowered from the intersection of the approximate straight line and the perpendicular to the X axis are represented by H, respectively. ₁ And H ₂ And At this time, the error e ₁ And e ₂ Is e ₁ = D ₁ / H ₁ (> 0) and e ₂ = D ₂ / H ₂ (<0).
Here, the absolute deviation E of the error is represented by the following equation (2).
[0039]
E = 1 / n · Σ | e−e ′ | (2)
[0040]
In the above formula (2), n represents the number of measured particles, and e 'represents an average value of the error. The absolute deviation E of the error varies in a range of 0 ≦ E ≦ 1.
[0041]
In the positive electrode active material of the present invention, the absolute deviation of the above-mentioned error is 0.25 or less, preferably 0.22 or less. When the absolute deviation of the error is within the above range, the cycle characteristics, load characteristics, storage characteristics, and charge / discharge capacity are excellent without increasing the Li / Mn molar ratio excessively, and the swelling of the battery is suppressed. You.
On the other hand, if the absolute deviation of the error is too large, the composition ratio of each particle of the lithium manganese composite oxide will vary greatly, and manganese ions will easily elute from particles having a small Li / Mn molar ratio. As a result, the cycle characteristics and the storage characteristics are reduced, and the battery may swell.
In the present invention, each of the above effects is realized by controlling the composition ratio of each particle based on the absolute deviation of the error.
[0042]
In the present invention, in the particle size distribution of particles, when the particle diameters at which the volume cumulative frequency reaches 10%, 50%, and 90% are D10, D50, and D90, respectively,
0.1 ≦ (D10 / D50) <1,
1 <(D90 / D50) ≦ 3 and
5 μm ≦ D50 ≦ 40 μm
Is preferably satisfied.
When D10, D50, and D90 satisfy the above relational expressions, the electrode density can be improved without impairing the improvement in cycle characteristics, storage characteristics, load characteristics, and output characteristics, and without impairing suppression of battery swelling. Can be improved.
[0043]
Further, D10, D50 and D90 are represented by more preferable relational expressions according to the purpose and use. For example, in order to further increase the electrode plate density,
0.2 ≦ (D10 / D50) ≦ 0.9,
1.2 ≦ (D90 / D50) ≦ 2 and
7 μm ≦ D50 ≦ 30 μm
Is preferably satisfied.
[0044]
Further, in order for the nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention to be suitably used for stationary use such as for home use and home use,
0.7 ≦ (D10 / D50) <1,
1 <(D90 / D50) ≦ 1.3 and
7μm ≦ D50 ≦ 15μm
Is preferably satisfied. In this case, cycle characteristics, storage characteristics, load characteristics, and output characteristics are particularly excellent.
[0045]
Furthermore, in order for the nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention to be suitably used for applications such as mobile phones, electric tools, and electric vehicles,
0.2 ≦ (D10 / D50) ≦ 0.7,
1.3 ≦ (D90 / D50) ≦ 2 and
15μm ≦ D50 ≦ 36μm
Is preferably satisfied. In this case, the cycle characteristics, the storage characteristics, the load characteristics, and the output characteristics are excellent, and the electrode plate density is more excellent.
[0046]
In the present invention, examples of a method for measuring the particle size distribution of particles include a sieving method, an image analysis method, a sedimentation method, a laser diffraction scattering method, and an electrical detection method.
[0047]
In the positive electrode active material of the present invention, in the particle size distribution of the particles, the standard deviation of the particle diameter is preferably 0.4 or less, more preferably 0.36 or less, and 0.07 or more. Is preferred. Within the above range, the electrode plate density can be further increased without impairing the cycle characteristics, storage characteristics, load characteristics, and output characteristics.
[0048]
In the positive electrode active material of the present invention, the transition metal is preferably manganese. When the transition metal is manganese, the nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention becomes particularly excellent in cycle characteristics, storage characteristics and load characteristics, and thus is used in mobile phones, power tools and the like. Can be particularly preferably used. In addition, since it also has excellent output characteristics, it can be particularly suitably used for electric vehicles.
[0049]
In the positive electrode active material of the present invention, preferred embodiments of the lithium transition metal composite oxide include the following (i) to (viii).
[0050]
(I) An embodiment in which the lithium transition metal composite oxide is a lithium manganese composite oxide having aluminum and / or magnesium and boron.
[0051]
Aspect (i) is excellent in cycle characteristics, load characteristics, storage characteristics and charge / discharge capacity, and has little battery swelling. The reason is described below.
When having aluminum and / or magnesium, the crystal structure is stabilized, so that the cycle characteristics are excellent without impairing the storage characteristics, load characteristics and output characteristics, and the swelling of the battery can be further suppressed. it can. In addition, boron acts as a flux, promoting crystal growth, and further improving cycle characteristics and storage characteristics.
[0052]
In the embodiment (i), the composition ratio of Li, Mn and O of the lithium manganese composite oxide is represented by the general formula Li _{1 + a} Mn _2-a O _{4 + d} It is preferable that a represents a number satisfying −0.2 ≦ a ≦ 0.2 and d represents a number satisfying −0.5 ≦ d ≦ 0.5. The same applies to embodiments (iii), (v) and (vii) described below.
a is preferably larger than 0, and is preferably 0.15 or less. It is thought that the synergistic effect of lithium in excess of the stoichiometric ratio and aluminum and / or magnesium further stabilizes the crystal structure and further improves the cycle characteristics.
[0053]
(Ii) The lithium transition metal composite oxide has a general formula Li _{1 + a} M _b Mn _2-ab B _c O _{4 + d} (M represents aluminum and / or magnesium, a represents a number satisfying −0.2 ≦ a ≦ 0.2, b represents a number satisfying 0 ≦ b ≦ 0.2, and c represents 0 ≦ c ≦ Represents a number that satisfies 0.02, and d represents a number that satisfies −0.5 ≦ d ≦ 0.5.)
[0054]
Mode (ii) is excellent in cycle characteristics, load characteristics, storage characteristics and charge / discharge capacity, and has little battery swelling.
In embodiment (ii), a is preferably greater than 0. It is considered that the cycle characteristics are improved by partially replacing manganese with lithium.
In the embodiment (ii), b is preferably larger than 0, and more preferably 0.05 or more. When having aluminum and / or magnesium, the crystal structure is stabilized, so that the cycle characteristics are excellent without impairing the storage characteristics, load characteristics and output characteristics, and the swelling of the battery can be further suppressed. it can. b is preferably 0.15 or less. If b is too large, the discharge capacity decreases.
In the embodiment (ii), c is preferably larger than 0, and more preferably 0.001 or more. Boron acts as a flux, promoting crystal growth and further improving cycling and storage characteristics. c is preferably 0.01 or less. If c is too large, the cycle characteristics deteriorate.
[0055]
(Iii) An embodiment in which the lithium transition metal composite oxide is a lithium manganese composite oxide containing aluminum and / or magnesium, at least one selected from the group consisting of fluorine, chlorine, bromine and iodine, and boron.
[0056]
The halogen element has an effect of turning the lithium manganese composite oxide powder into a spherical powder having a uniform particle size. This makes it possible to form a positive electrode coated surface having excellent surface smoothness, low internal resistance, and excellent binding properties without impairing cycle characteristics, storage characteristics, load characteristics, and output characteristics. As the halogen element, fluorine and / or chlorine are preferable.
[0057]
(Iv) The lithium transition metal composite oxide has the general formula Li _{1 + a} M _c Mn _2-ac O ₄ ・ Li _b X _d B _e O _f (M represents aluminum and / or magnesium, X represents at least one selected from the group consisting of fluorine, chlorine, bromine and iodine, a represents a number satisfying 0 <a ≦ 0.1, and b represents 0 ≦ b ≦ 0.1, c represents a number satisfying 0 <c ≦ 0.2, d represents a number satisfying 0 <d ≦ 0.05, and e represents 0 <e ≦ 0. 02 represents a number satisfying 02, and f represents a number satisfying 0 ≦ f <0.1).
[0058]
In the embodiment (iv), the lithium transition metal composite oxide is Li _{1 + a} M _c Mn _2-ac O ₄ A cubic spinel-type lithium manganese composite oxide represented by _b X _d B _e O _f And an impurity phase composed of at least one compound represented by the following formula:
In the embodiment (iv), a is preferably 0.02 or more, and more preferably 0.08 or less. For the same reason as in the case of the mode (ii).
In embodiment (iv), X is preferably fluorine and / or chlorine. d is preferably 0.01 or more, and more preferably 0.03 or less. For the same reason as in the case of mode (iii).
In the embodiment (iv), e is preferably 0.001 or more, and more preferably 0.01 or less. For the same reason as in the case of the mode (ii).
[0059]
(V) The lithium transition metal composite oxide is a lithium manganese composite oxide having aluminum and / or magnesium, at least one selected from the group consisting of fluorine, chlorine, bromine and iodine, boron and sulfur. Aspects.
[0060]
In the aspect (v), it is considered that the cycle characteristics and the load characteristics are further improved because the passage of electrons is improved by the presence of sulfur.
The content of sulfur is preferably 0.03 to 0.3% by weight based on the total of the lithium transition metal composite oxide and sulfur. If the amount is less than 0.03% by weight, the electron transfer resistance may not be easily reduced. If the content is more than 0.3% by weight, the battery may swell due to moisture adsorption.
[0061]
Sulfur may be present in any form. For example, it may be present in the form of sulfate.
The sulfate group contains a sulfate ion, a group of atoms obtained by removing the charge from the sulfate ion, and a sulfo group. It is preferably based on at least one selected from the group consisting of alkali metal sulfates, alkaline earth metal sulfates, organic sulfates, and organic sulfonic acids and salts thereof.
Above all, it is preferably based on at least one selected from the group consisting of alkali metal sulfates and alkaline earth metal sulfates, and more preferably based on alkali metal sulfates. This is because these are chemically stable because they consist of a strong acid-strong base bond.
[0062]
The reason for having an element other than sulfur in the aspect (v) is the same as in the aspects (i) to (iv).
In the aspect (v), by having each of the above elements, a positive electrode plate having a high charge / discharge capacity and excellent in binding property and surface smoothness can be obtained due to a synergistic effect of each element.
[0063]
(Vi) The lithium transition metal composite oxide has the general formula Li _{1 + a} M _b Mn _2-ab X _c B _d S _e O _{4 + f} (M represents aluminum and / or magnesium, X represents at least one selected from the group consisting of fluorine, chlorine, bromine and iodine, a represents a number satisfying -0.2 ≦ a ≦ 0.2, b represents a number satisfying 0 <b ≦ 0.2, c represents a number satisfying 0 ≦ c ≦ 0.05, d represents a number satisfying 0 <d ≦ 0.02, and e represents 0 ≦ e. Represents a number that satisfies ≦ 0.1, and f represents a number that satisfies −0.5 ≦ f ≦ 0.5.)
[0064]
In embodiment (vi), e is preferably greater than 0. For the same reason as in the case of the mode (v).
Further, e is more preferably 0.0017 or more, and preferably 0.02 or less. If e is too small, the electron transfer resistance may be low. If e is too large, the battery may swell due to moisture adsorption.
Other points are the same as in the case of the mode (v).
[0065]
(Vii) the lithium transition metal composite oxide has aluminum and / or magnesium, at least one selected from the group consisting of fluorine, chlorine, bromine and iodine, boron, sulfur, and sodium and / or calcium An embodiment which is a lithium manganese composite oxide.
[0066]
In the embodiment (vii), by having sodium and / or calcium, the elution of manganese ions can be further suppressed by the synergistic effect of boron (preferably, boron and sulfur), and the cycle is excellent at a practical level. Characteristics can be realized.
The reason for having an element other than sodium and / or calcium in the embodiment (vii) is the same as in the embodiments (i) to (vi).
[0067]
(Viii) a lithium transition metal composite oxide represented by the general formula Li _{1 + a} M _b Mn _2-ab X _c B _d S _e A _g O _{4 + f} (M represents aluminum and / or magnesium, X represents at least one selected from the group consisting of fluorine, chlorine, bromine and iodine, A represents sodium and / or calcium, and a represents -0.2 ≦ a Represents a number satisfying ≦ 0.2, b represents a number satisfying 0 <b ≦ 0.2, c represents a number satisfying 0 ≦ c ≦ 0.05, and d represents 0 <d ≦ 0.02. E represents a number satisfying 0 ≦ e ≦ 0.1, f represents a number satisfying −0.5 ≦ f ≦ 0.5, and g represents 0.00004 ≦ g ≦ 0.015. Represents the number to be satisfied.).
[0068]
The reason why the embodiment (viii) is preferable is the same as that in the embodiment (vii).
In the embodiment (viii), e is preferably 0.0017 or more, and more preferably 0.02 or less. If e is too small, the electron transfer resistance may be low. If e is too large, the battery may swell due to moisture adsorption.
Other points are the same as in the case of the embodiment (vii).
[0069]
The lithium transition metal composite oxide preferably has an iron content of 25 ppm or less, more preferably 20 ppm or less, and even more preferably 18 ppm or less. If the iron content is too high, it may cause an internal short circuit in the battery.
[0070]
When the lithium transition metal composite oxide has magnesium, it is preferable that the proportion of magnesium on the surface of the particles is 20% or more. The proportion of magnesium present on the surface of the particles is more preferably at least 40%, even more preferably at least 60%, even more preferably at least 80%.
When the proportion of magnesium on the surface of the lithium transition metal composite oxide particles is within the above range, magnesium is uniformly present on the surface of the particles, so that the effect of suppressing elution of transition metal ions is excellent.
In the present invention, the presence state of magnesium on the surface of the particles is not particularly limited.
[0071]
In the present invention, the “magnesium content on the surface of the lithium transition metal composite oxide particles” is determined as follows.
First, the presence state of magnesium on the surface of particles of a lithium transition metal composite oxide is observed using an electron beam microanalyzer (EPMA) equipped with a wavelength dispersive X-ray spectrometer (WDX). Then, in the observation visual field, a portion having the largest amount of magnesium per unit area (a portion having the largest peak of magnesium) is selected, and a line is drawn along a line segment (for example, a line segment having a length of 300 μm) passing through this portion. Perform analysis. In the line analysis, the quotient obtained by dividing the total length of the portion where the peak was 4% or more when the value of the peak in the portion having the largest amount of magnesium per unit area as 100% was divided by the length of the line segment. Is defined as “the ratio of magnesium present on the surface of the lithium transition metal composite oxide particles”. Note that it is preferable to use the average value of “the ratio of magnesium present on the surface of the lithium transition metal composite oxide particles” by performing the line analysis a plurality of times (for example, 10 times).
In the above method, a portion where the peak of magnesium is less than 4% has a large difference from a portion where the amount of magnesium is the largest, and thus is regarded as a portion where magnesium does not exist.
[0072]
The above-mentioned “magnesium abundance ratio on the surface of the lithium transition metal composite oxide particles” indicates whether magnesium is uniformly present or unevenly present on the surface of the lithium transition metal composite oxide particles. be able to.
[0073]
In the positive electrode active material of the present invention, the lithium transition metal composite oxide preferably has a (400) crystallite diameter (crystallite diameter in the (400) vector direction) of 600 to 1200 angstroms. The (400) crystallite diameter is more preferably 700 Å or more, and more preferably 1100 Å or less.
[0074]
Here, “crystallite” means the maximum set considered to be a single crystal, and “crystallite diameter” means the size of a crystallite.
Therefore, the larger the crystallite diameter, the better the crystallinity and the less the distortion of the crystal structure. In a lithium transition metal composite oxide having a spinel structure as used in the present invention, the degree of regularity of the arrangement of unit cells can be indicated by the following (400) crystallite diameter.
[0075]
The (400) crystallite diameter of the lithium transition metal composite oxide can be determined, for example, by an X-ray diffraction method. The X-ray diffraction method can be performed, for example, under the conditions of a tube current of 100 mA and a tube voltage of 40 kV. The crystallite diameter is calculated from the diffraction peak attributable to the (400) plane obtained by the X-ray diffraction method according to Scherrer's formula represented by the following formula (3).
[0076]
D = Kλ / (βcosθ) (3)
[0077]
In the above formula, D represents the size (Å) of the crystallite, K represents the Scherrer constant (1.05 when β is calculated from the integration width), and λ represents the wavelength of the X-ray source (in the case of CuKα1). Represents 1.554062 °), β represents the width of the spread of the diffraction line depending on the size of the crystallite (radian), and θ represents the diffraction angle (degree).
[0078]
In the positive electrode active material of the present invention, the specific surface area is 0.2 to 1.2 m ² / G is preferred. Specific surface area is 0.25m ² / G or more, more preferably 0.9 m ² / G or less. If the specific surface area is too small, the discharge capacity decreases. If the specific surface area is too large, the cycle characteristics will not be excellent. The specific surface area can be measured by a nitrogen gas adsorption method.
[0079]
In the positive electrode active material of the present invention, in the particle size distribution of the particles, the proportion of particles having a volume-based particle diameter of 50 μm or more is preferably 10% by volume or less of all particles, and is preferably 7% by volume or less. Is more preferred.
By controlling the particle size distribution of the particles as described above, coarse particles composed of secondary aggregates can be prevented from being included, so that a positive electrode coated surface with excellent smoothness can be obtained.
[0080]
Although the production method of the positive electrode active material of the present invention is not particularly limited, it can be produced, for example, as in the following (1) and (2).
[0081]
(1) Preparation of raw material mixture
The compounds described below are mixed so that each constituent element has a predetermined composition ratio to obtain a raw material mixture. The compound used in the raw material mixture is selected according to the elements constituting the desired composition.
The method of mixing is not particularly limited. For example, a method in which a powdery compound is directly mixed to form a raw material mixture; mixed in a slurry using water and / or an organic solvent, and then dried to obtain a raw material mixture. Method: a method in which an aqueous solution of the above-described compound is mixed and precipitated, and the obtained precipitate is dried to form a raw material mixture; a method in which these are used in combination.
[0082]
Hereinafter, the compounds used in the raw material mixture will be exemplified.
Although the lithium compound is not particularly limited, for example, Li ₂ CO ₃ , LiOH, LiOH.H ₂ O, Li ₂ O, LiCl, LiNO ₃ , Li ₂ SO ₄ , LiHCO ₃ , Li (CH ₃ COO), lithium fluoride, lithium bromide, lithium iodide, and lithium peroxide. Among them, Li ₂ CO ₃ , LiOH, LiOH.H ₂ O, Li ₂ O, LiCl, LiNO ₃ , Li ₂ SO ₄ , LiHCO ₃ , Li (CH ₃ COO) is preferred.
[0083]
The manganese compound is not particularly limited. For example, manganese metal, oxide (for example, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ ), Hydroxides, nitrates, carbonates (MnCO ₃ ), Chloride salts (eg, MnCl ₂ ), Manganese iodide, manganese sulfate, manganese nitrate (eg, MnSO ₄ ). Among them, manganese metal, MnCO ₃ , MnSO ₄ , MnCl ₂ Is preferred.
The manganese compound has a particle size distribution of 10%, 50%, and 90% in the particle size distribution of the particles, when d10, d50, and d90, respectively, d10 is 5 to 25 μm, d50 is 7 to 40 μm, It is preferable to use those having a d90 of 10 to 60 μm. In order to obtain a manganese compound having such a particle size distribution, a mortar, a ball mill, a vibration mill, a jet mill, or the like can be used. Also, various classifiers can be used.
[0084]
Although the magnesium compound is not particularly limited, for example, MgO, MgCO ₃ , Mg (OH) ₂ , MgCl ₂ , MgSO ₄ , Mg (NO ₃ ) ₂ , Mg (CH ₃ COO) ₂ , Magnesium iodide and magnesium perchlorate. Among them, MgSO ₄ , Mg (NO ₃ ) ₂ Is preferred.
The aluminum compound is not particularly limited. ₂ O ₃ , Al (NO ₃ ) ₃ , Al ₂ (SO ₄ ) ₃ , Al ₂ (CO ₃ ) ₃ , Al (CH ₃ COO) ₃ Is mentioned.
[0085]
The boron compound is not particularly limited. ₂ O ₃ (Melting point 460 ° C), H ₃ BO ₃ (Decomposition temperature: 173 ° C.), lithium boron composite oxide, orthoboric acid, boron oxide, and boron phosphate. Above all, H ₃ BO ₃ , B ₂ O ₃ Is preferred.
The halogen compound is not particularly limited. ₄ F, NH ₄ Cl, NH ₄ Br, NH ₄ I, LiF, LiCl, LiBr, LiI, MnF ₂ , MnCl ₂ , MnBr ₂ , MnI ₂ , Hydrogen fluoride, oxygen fluoride, hydrofluoric acid, hydrogen chloride, hydrochloric acid, chlorine oxide, chlorine fluoride oxide, bromine oxide, bromine fluorosulfate, hydrogen iodide, iodine oxide, and periodic acid. Among them, NH ₄ F, NH ₄ Cl, NH ₄ Br, NH ₄ I, LiF, LiCl, LiBr, LiI, MnF ₂ , MnCl ₂ , MnBr ₂ , MnI ₂ Is preferred.
[0086]
Although the sulfur compound is not particularly limited, for example, Li ₂ SO ₄ , MnSO ₄ , (NH ₄ ) ₂ SO ₄ , Al ₂ (SO ₄ ) ₃ , MgSO ₄ , Sulfide, sulfur iodide, hydrogen sulfide, sulfuric acid and its salts, and nitrogen sulfide. Among them, Li ₂ SO ₄ , MnSO ₄ , (NH ₄ ) ₂ SO ₄ , Al ₂ (SO ₄ ) ₃ , MgSO ₄ Is preferred.
[0087]
The sodium compound is not particularly limited. ₂ CO ₃ , NaOH, Na ₂ O, NaCl, NaNO ₃ , Na ₂ SO ₄ , NaHCO ₃ , CH ₃ COONa.
[0088]
Although the calcium compound is not particularly limited, for example, CaO, CaCO ₃ , Ca (OH) ₂ , CaCl ₂ , CaSO ₄ , Ca (NO ₃ ) ₂ , Ca (CH ₃ COO) ₂ Is mentioned.
Further, a compound containing two or more of the above-described elements may be used.
[0089]
Hereinafter, a preferred method for obtaining the raw material mixture will be specifically described with reference to a positive electrode active material that is a lithium manganese composite oxide having magnesium and boron as an example.
An aqueous solution containing a manganese ion and a magnesium ion having a predetermined composition ratio and prepared from the above-described manganese compound and magnesium compound is dropped into pure water being stirred.
Then, an aqueous solution of ammonium bicarbonate is added dropwise to precipitate manganese and magnesium to obtain a manganese and magnesium salt. Instead of the aqueous ammonium hydrogen carbonate solution, an alkaline solution such as an aqueous sodium hydroxide solution, an aqueous sodium hydrogen carbonate solution, an aqueous potassium hydroxide solution, or an aqueous lithium hydroxide solution can also be used.
[0090]
Next, the aqueous solution is filtered to collect a precipitate, the collected precipitate is washed with water, heat-treated, and then mixed with the above-mentioned lithium compound and boron compound to obtain a raw material mixture.
[0091]
(2) Firing and grinding of the raw material mixture
Next, the raw material mixture is fired. The firing temperature, time, atmosphere, and the like are not particularly limited, and can be appropriately determined depending on the purpose.
The firing temperature is preferably at least 650 ° C, more preferably at least 700 ° C. If the firing temperature is too low, unreacted raw materials remain in the positive electrode active material, and the original characteristics of the positive electrode active material may not be utilized. Further, the firing temperature is preferably 1100 ° C. or less, more preferably 950 ° C. or less. If the firing temperature is too high, the particle size of the positive electrode active material may become too large, and the battery characteristics may deteriorate. Also, Li ₂ MnO ₃ , LiMnO ₂ And other by-products are likely to be generated, which may cause a decrease in discharge capacity per unit weight, a decrease in cycle characteristics, and a decrease in operating voltage.
Generally, the firing time is preferably from 1 to 24 hours, more preferably from 6 to 12 hours. If the firing time is too short, the diffusion reaction between the raw material particles does not proceed. If the calcination time is too long, calcination after the completion of the diffusion reaction is wasted, and coarse particles may be formed by sintering.
[0092]
The firing atmosphere includes, for example, air, oxygen gas, a mixed gas thereof with an inert gas such as nitrogen gas and argon gas, an atmosphere in which the oxygen concentration (oxygen partial pressure) is controlled, and a weakly oxidizing atmosphere. Above all, an atmosphere in which the oxygen concentration is controlled is preferable.
When calcination is performed in an atmosphere in which the oxygen concentration is controlled, the generation of oxygen deficiency in the crystal structure can be suppressed, the crystal is hardly distorted, and the (400) crystallite diameter is large. Can be produced.
[0093]
Among them, an oxidizing atmosphere having an oxygen concentration of 10% by volume or more is preferable. When calcination is performed in an oxidizing atmosphere having an oxygen concentration of 10% by volume or more, a powder having a (400) crystallite diameter of 600 Å or more is obtained.
In particular, an oxidizing atmosphere having an oxygen concentration of 18% by volume or more is preferable. When calcination is performed in an oxidizing atmosphere having an oxygen concentration of 18% by volume or more, sufficient oxygen is supplied into the crystal structure, and a powder having a (400) crystallite diameter of 600 to 1200 Å is obtained.
[0094]
After firing, if desired, the powder can be pulverized using a mortar, ball mill, vibration mill, pin mill, jet mill, or the like to obtain a powder having a desired particle size. In this way, by pulverizing after firing, the specific surface area can be set in the above-described preferable range.
[0095]
The positive electrode active material of the present invention can be obtained by the above-described manufacturing method.
[0096]
The positive electrode active material of the present invention is suitably used for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery and a lithium ion polymer secondary battery.
The non-aqueous electrolyte secondary battery may use the positive electrode active material of the present invention as at least a part of the positive electrode active material in a conventionally known non-aqueous electrolyte secondary battery, and other configurations are not particularly limited. Hereinafter, a lithium ion secondary battery will be described as an example.
[0097]
As the negative electrode active material, lithium metal, a lithium alloy, or a compound capable of inserting and extracting lithium ions can be used. Examples of the lithium alloy include a LiAl alloy, a LiSn alloy, and a LiPb alloy. Examples of the compound capable of inserting and extracting lithium ions include carbon materials such as graphite and graphite; and oxides such as tin oxide and titanium oxide.
[0098]
The electrolytic solution is not particularly limited as long as it is a compound that does not deteriorate or decompose at the operating voltage.
Examples of the solvent include organic solvents such as dimethoxyethane, diethoxyethane, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, γ-butyrolactone, 2-methyltetrahydrofuran, dimethyl sulfoxide, and sulfolane. Is mentioned. These can be used alone or in combination of two or more.
[0099]
Examples of the electrolyte include lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium tetrafluorophosphate, and lithium trifluoromethane.
The above-mentioned solvent and electrolyte are mixed to form an electrolyte. Here, a gelling agent or the like may be added and used as a gel. Further, it may be used after being absorbed by a hygroscopic polymer. Further, a solid electrolyte having inorganic or organic lithium ion conductivity may be used.
[0100]
Examples of the separator include a porous film made of polyethylene, polypropylene, or the like.
[0101]
Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, polyamide, and acrylic resin.
[0102]
Using the positive electrode active material of the present invention, the above-described negative electrode active material, electrolyte solution, separator and binder, a lithium ion secondary battery can be obtained according to a standard method.
[0103]
A preferred method for producing a positive electrode using the positive electrode active material of the present invention will be described below.
A positive electrode mixture is prepared by mixing a powder of the positive electrode active material of the present invention with a carbon-based conductive agent such as acetylene black or graphite, a binder, and a solvent or a dispersion medium of the binder. The obtained positive electrode mixture is formed into a slurry or a kneaded material, which is applied or supported on a current collector such as an aluminum foil, and is pressed and rolled to form a positive electrode active material layer on the current collector.
FIG. 5 is a schematic cross-sectional view of the positive electrode. As shown in FIG. 5, the positive electrode 13 has the positive electrode active material 5 held on the current collector 12 by the binder 4.
[0104]
It is considered that the positive electrode active material of the present invention is excellent in the mixing property with the conductive agent powder and the internal resistance of the battery is small. Therefore, the charge / discharge characteristics, particularly the discharge capacity, are excellent.
In addition, the positive electrode active material of the present invention has excellent fluidity even when kneaded with a binder, easily entangles with a polymer of the binder, and has excellent binding properties.
Furthermore, since the positive electrode active material of the present invention does not contain coarse particles and is spherical, the surface of the coating surface of the prepared positive electrode has excellent smoothness. For this reason, the coating surface of the positive electrode plate is excellent in binding properties and hardly peels off. Further, since the surface is smooth and lithium ions enter and exit from the surface of the coating film during charging and discharging uniformly, remarkable improvement in cycle characteristics is observed.
[0105]
The shape of the lithium ion secondary battery is not particularly limited, and may be a cylindrical type, a coin type, a square type, a laminate type, or the like.
FIG. 6 is a schematic sectional view of a cylindrical battery. As shown in FIG. 6, in the cylindrical battery 20, the positive electrode 13 in which the positive electrode active material layer is formed on the current collector 12 and the negative electrode 11 in which the negative electrode active material layer is formed on the current collector 12 Are repeatedly laminated via the separator 14.
FIG. 7 is a schematic partial cross-sectional view of a coin-type battery. As shown in FIG. 7, in the coin-type battery 30, the positive electrode 13 in which the positive electrode active material layer is formed on the current collector 12 and the negative electrode 11 are stacked via the separator 14.
FIG. 8 is a schematic perspective view of a prismatic battery. As shown in FIG. 8, in the prismatic battery 40, the positive electrode 13 having the positive electrode active material layer formed on the current collector 12 and the negative electrode 11 having the negative electrode active material layer formed on the current collector 12 Are repeatedly laminated via the separator 14.
[0106]
The use of the nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention is not particularly limited. For example, notebook personal computers, pen input personal computers, pocket personal computers, notebook type word processors, pocket word processors, e-book players, mobile phones, cordless handsets, electronic notebooks, calculators, LCD TVs, electric shavers, electric tools, electronic translators, automobiles Telephone, portable printer, transceiver, pager, handy terminal, portable copy, voice input device, memory card, backup power supply, tape recorder, radio, headphone stereo, handy cleaner, portable compact disc (CD) player, video movie, navigation system, etc. It can be used as a power source for devices.
In addition, lighting equipment, air conditioners, TVs, stereos, water heaters, refrigerators, microwave ovens, dishwashers, washing machines, dryers, game machines, toys, road conditioners, medical equipment, automobiles, electric vehicles, golf carts, It can also be used as a power source for electric carts, power storage systems and the like.
Further, the application is not limited to civilian use, but may be for military use or space use.
[0107]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.
[0108]
1. Preparation of positive electrode active material
[Example 1]
The manganese and magnesium carbonates whose particle diameters (d10, d50 and d90) at which the volume cumulative frequency in the particle size distribution reaches 10%, 50% and 90% are 11 μm, 14 μm and 18 μm, respectively, are washed with water and dried. After that, it was mixed with orthoboric acid and lithium carbonate. The obtained mixture was calcined at about 800 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
The composition of the obtained positive electrode active material is Li _1.09 Mn _1.94 Mg _0.01 B _0.008 O ₄ Met. The content of the sulfate was 0.5% by weight based on the total of the lithium transition metal composite oxide and the sulfate. The Fe content was 7 ppm with respect to the total of the lithium transition metal composite oxide and Fe.
[0109]
[Example 2]
A positive electrode active material was obtained in the same manner as in Example 1, except that the mixing ratio of manganese and magnesium carbonate, orthoboric acid, and lithium carbonate was changed.
The composition of the obtained positive electrode active material is Li _1.08 Mn _1.94 Mg _0.01 B _0.005 O ₄ Met. The content of the sulfate group was 0.4% by weight based on the total of the lithium transition metal composite oxide and the sulfate group. The Fe content was 2 ppm with respect to the total of the lithium transition metal composite oxide and Fe.
[0110]
[Example 3]
A positive electrode active material was obtained in the same manner as in Example 1, except that the mixing ratio of manganese and magnesium carbonate, orthoboric acid, and lithium carbonate was changed.
The composition of the obtained positive electrode active material is Li _1.05 Mn _1.95 Mg _0.01 B _0.005 O ₄ Met. The content of the sulfate group was 0.4% by weight based on the total of the lithium transition metal composite oxide and the sulfate group. The Fe content was 2 ppm with respect to the total of the lithium transition metal composite oxide and Fe.
[0111]
[Example 4]
A positive electrode active material was obtained in the same manner as in Example 1, except that the mixing ratio of manganese and magnesium carbonate, orthoboric acid, and lithium carbonate was changed.
The composition of the obtained positive electrode active material is Li _1.05 Mn _1.95 Mg _0.01 B _0.008 O ₄ Met.
[0112]
[Example 5]
The manganese and magnesium carbonates with d10, d50 and d90 of 23 μm, 31 μm and 48 μm, respectively, were washed with water, dried and then mixed with orthoboric acid and lithium carbonate. The obtained mixture was calcined at about 800 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
The composition of the obtained positive electrode active material is Li _1.08 Mn _1.95 Mg _0.01 B _0.0002 O ₄ Met. The content of the sulfate was 0.5% by weight based on the total of the lithium transition metal composite oxide and the sulfate. The Fe content was 8 ppm with respect to the total of the lithium transition metal composite oxide and Fe.
[0113]
[Example 6]
A positive electrode active material was obtained in the same manner as in Example 5, except that the mixing ratio of manganese and magnesium carbonate, orthoboric acid, and lithium carbonate was changed.
The composition of the obtained positive electrode active material is Li _1.08 Mn _1.95 Mg _0.01 B _0.003 O ₄ Met. The content of the sulfate was 0.5% by weight based on the total of the lithium transition metal composite oxide and the sulfate. The Fe content was 5 ppm with respect to the total of the lithium transition metal composite oxide and Fe.
[0114]
[Example 7]
The manganese and magnesium carbonates with d10, d50 and d90 of 20 μm, 29 μm and 41 μm, respectively, were washed with water, dried and then mixed with orthoboric acid and lithium carbonate. The obtained mixture was calcined at about 800 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
The composition of the obtained positive electrode active material is Li _1.08 Mn _1.94 Mg _0.01 B _0.005 O ₄ Met.
[0115]
Example 8
The manganese and magnesium carbonates with d10, d50 and d90 of 10 μm, 13 μm and 18 μm, respectively, were washed with water, dried and then mixed with orthoboric acid and lithium carbonate. The obtained mixture was calcined at about 800 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
The composition of the obtained positive electrode active material is Li _1.08 Mn _1.94 Mg _0.01 B _0.005 O ₄ Met. The content of the sulfate group was 0.4% by weight based on the total of the lithium transition metal composite oxide and the sulfate group. The Fe content was 5 ppm with respect to the total of the lithium transition metal composite oxide and Fe.
[0116]
[Example 9]
Manganese carbonates having d10, d50 and d90 of 9 μm, 12 μm and 16 μm, respectively, were washed with water, dried and then mixed with orthoboric acid, lithium carbonate and aluminum hydroxide. The obtained mixture was calcined at about 800 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
The composition of the obtained positive electrode active material is Li _1.08 Mn _1.94 Al _0.04 B _0.005 O ₄ Met. The content of the sulfate group was 0.4% by weight based on the total of the lithium transition metal composite oxide and the sulfate group. The Fe content was 2 ppm with respect to the total of the lithium transition metal composite oxide and Fe.
[0117]
[Example 10]
A positive electrode active material was obtained in the same manner as in Example 8, except that the mixing ratio of manganese and magnesium carbonate, orthoboric acid, and lithium carbonate was changed.
The composition of the obtained positive electrode active material is Li _1.07 Mn _1.94 Mg _0.04 B _0.005 O ₄ Met. The content of the sulfate group was 0.4% by weight based on the total of the lithium transition metal composite oxide and the sulfate group. The Fe content was 16 ppm based on the total of the lithium transition metal composite oxide and Fe.
[0118]
[Comparative Example 1]
Manganese dioxide having d10, d50 and d90 of 0.4 μm, 9.6 μm and 28.3 μm, lithium carbonate, magnesium carbonate and orthoboric acid were dry-mixed to obtain a powder of a raw material mixture. The obtained raw material mixture was fired at 830 ° C. for 11 hours in the air atmosphere. The obtained fired product was pulverized to obtain a positive electrode active material.
The composition of the obtained positive electrode active material is Li _1.10 Mn _1.93 Mg _0.01 B _0.0083 O ₄ Met. The content of the sulfate was 1.2% by weight based on the total of the lithium transition metal composite oxide and the sulfate. The Fe content was 40 ppm based on the total of the lithium transition metal composite oxide and Fe.
[0119]
In the examples and comparative examples described above, the composition of the positive electrode active material was determined by inductively coupled high frequency plasma spectroscopy (ICP spectroscopy). The contents of sulfate and Fe were determined by ICP spectroscopy.
[0120]
2. Properties of positive electrode active material
(1) Composition of positive electrode active material
The positive electrode active materials obtained in Example 1 and Comparative Example 1 were subjected to line analysis along a 300 μm-long line segment using EPMA equipped with WDX by the method described above. The results are shown in FIGS.
FIG. 9 shows that in the positive electrode active material obtained in Example 1, the presence state of magnesium existing on the surface is uniform. The proportion of magnesium present on the surface of the lithium transition metal composite oxide particles was 84.5%.
FIG. 10 shows that in the positive electrode active material obtained in Comparative Example 1, the presence state of magnesium present on the surface is non-uniform (is uneven). The proportion of magnesium present on the surface of the lithium transition metal composite oxide particles was 2.0%.
[0121]
(2) Absolute deviation of error
Elemental analysis of the obtained positive electrode active material was performed using a particle analyzer “PT-1000” (manufactured by Yokogawa Electric Corporation) that performs elemental analysis by the emission voltage of each element. From the above equations (1) and (2), the absolute deviation of the error based on the emission voltage due to the transition metal and lithium was determined.
[0122]
(3) Specific surface area and particle size distribution of positive electrode active material
The specific surface area of the obtained positive electrode active material was measured by a constant pressure BET adsorption method using nitrogen gas.
Further, the particle size distribution of the obtained positive electrode active material was measured by a laser diffraction scattering method, and D10, D50, D90, the standard deviation of the particle diameter, and the ratio of particles having a volume-based particle diameter of 50 μm or more were determined. Was.
[0123]
(4) (400) crystallite diameter of positive electrode active material
An X-ray diffraction method was performed on the obtained positive electrode active material. The X-ray diffraction method was performed using an X-ray diffractometer (RINT 2500 V, manufactured by Rigaku Denki Co., Ltd.), using CuKα1 as an X-ray source, at a tube current of 100 mA and a tube voltage of 40 kV. Based on the X-ray diffraction pattern obtained by the X-ray diffraction method, the (400) crystallite diameter of the positive electrode active material was determined from Scherrer's formula represented by the above formula (3).
[0124]
(5) Mn elution test of positive electrode active material
After drying the obtained positive electrode active material at 110 ° C. for 15 hours, LiPF was added to a mixed solvent of ethylene carbonate / diethyl carbonate = 3/7. ₆ Was mixed with an electrolyte dissolved at a concentration of 1 mol / L and stored at 85 ° C. for 48 days. After removing the positive electrode active material by filtration with a filter, the elution amount of Mn (the weight of the Mn element with respect to the weight of the electrolytic solution) was measured by ICP spectroscopy. It can be said that the smaller the amount of Mn eluted, the better the storage characteristics.
[0125]
(6) Electrode plate density of positive electrode active material
A paste is prepared by kneading 95 parts by weight of the positive electrode active material powder and a normal methylpyrrolidone solution of polyvinylidene fluoride (5 parts by weight as polyvinylidene fluoride), and applying the paste to an aluminum electrode plate by a doctor blade method, followed by drying. Thus, a positive electrode plate was obtained. Make the positive electrode plate a predetermined size (5 cm ² ), The electrode plate was pressed with a uniaxial press. The electrode density was calculated from the thickness and weight of the electrode after pressing.
[0126]
The results are shown in Table 1. In the table, "-" indicates that the corresponding item was not measured.
As is clear from Table 1, the positive electrode active material of the present invention had a lower Mn elution amount and was superior in storage characteristics as compared with the positive electrode active material of Comparative Example 1. The positive electrode active material of the present invention had the same electrode plate density as the positive electrode active material of Comparative Example 1.
[0127]
[Table 1]

[0128]
3. Evaluation of positive electrode active material
Using each of the positive electrode active materials obtained above, a test secondary battery in which the negative electrode was lithium metal, a test secondary battery in which the negative electrode was carbon, and a cylindrical battery were produced, and evaluated as follows. .
[0129]
A. Evaluation using a test secondary battery in which the negative electrode is lithium metal
A test secondary battery in which the negative electrode was lithium metal was produced as follows.
A paste was prepared by kneading 90 parts by weight of the powder of the positive electrode active material, 5 parts by weight of carbon powder serving as a conductive agent, and a normal methylpyrrolidone solution of polyvinylidene fluoride (5 parts by weight as the amount of polyvinylidene fluoride). Was applied to a positive electrode current collector and dried to obtain a positive electrode plate. Using the obtained positive electrode plate, a test secondary battery in which the negative electrode was lithium metal was produced.
[0130]
(1) Initial discharge capacity
The negative electrode is lithium metal under the conditions of a charge potential of 4.3 V, a discharge potential of 2.85 V, and a discharge load of 0.2 C (1 C is a current load at which discharge is completed in one hour; the same applies hereinafter). The test secondary battery was discharged. The discharge capacity at this time was defined as 0.2 C initial discharge capacity.
Further, under the conditions of a charge potential of 4.3 V, a discharge potential of 3.0 V, and a discharge load of 0.24 C, the test secondary battery whose negative electrode was lithium metal was discharged. The discharge capacity at this time was defined as an initial discharge capacity of 0.24C.
[0131]
(2) Evaluation of swelling at the end of discharge
At the time of measuring the initial discharge capacity at 0.2 C, a change in capacity during discharge from 3.3 V to 2.85 V was measured, and the swelling at the end of discharge was evaluated. It can be said that the smaller the swelling at the end of discharge, the better the cycle characteristics.
[0132]
(3) Initial efficiency
The test secondary battery whose negative electrode was made of lithium metal was discharged under the conditions of a charge potential of 4.3 V, a discharge potential of 2.85 V, and a discharge load of 0.2 C. At this time, the value of the discharge capacity was set as the initial discharge capacity, and the value of the charge capacity was set as the initial charge capacity. The value of the obtained initial discharge capacity was divided by the initial charge capacity to obtain the initial efficiency.
[0133]
(4) Load discharge capacity
The test secondary battery in which the negative electrode was lithium metal was discharged under the conditions of a charge potential of 4.3 V, a discharge potential of 2.85 V, and a discharge load of 2.0 C. The discharge capacity at this time was defined as a load discharge capacity.
[0134]
(5) Load efficiency (load capacity maintenance rate)
Using a test secondary battery in which the negative electrode is lithium metal, the initial discharge capacity was measured under the conditions of a charge potential of 4.3 V, a discharge potential of 2.85 V, and a discharge load of 0.2 C. The load discharge capacity was measured under the conditions of a discharge potential of 2.85 V and a discharge load of 2.0 C. The obtained load discharge capacity value was divided by the initial discharge capacity to determine the load efficiency at a discharge load of 2.0C.
[0135]
Further, an initial discharge capacity was measured using a test secondary battery in which the negative electrode was lithium metal under the conditions of a charge potential of 4.3 V, a discharge potential of 2.85 V, and a discharge load of 0.24 C. The load discharge capacity was measured under the conditions of 3 V, a discharge potential of 2.85 V, and a discharge load of 3.5 C. The obtained load discharge capacity value was divided by the initial discharge capacity to determine the load efficiency at a discharge load of 3.5C.
[0136]
The results are shown in Table 2. In the table, "-" indicates that the corresponding item was not measured.
As is clear from Table 2, the positive electrode active material of the present invention was excellent in both initial discharge capacity and load discharge capacity, excellent in both initial efficiency and load efficiency, and excellent in cycle characteristics.
[0137]
[Table 2]

[0138]
B. Evaluation using a test secondary battery in which the negative electrode is carbon
A positive electrode plate was obtained in the same manner as in the test secondary battery in which the negative electrode was lithium metal. Using the obtained positive electrode plate, a test secondary battery in which the negative electrode was carbon was produced.
[0139]
(1) Discharge capacity
Under the conditions of a charging potential of 4.2 V, a discharging potential of 2.75 V, and a discharging load of 0.2 C, 43 cycles of charging and discharging of the test secondary battery in which the negative electrode was carbon were performed. The discharge capacity after 43 cycles was measured.
[0140]
(2) Swelling at the end of discharge
At the time of measuring the discharge capacity after 43 cycles, the change in capacity during discharge from 3.3 V to 2.85 V was measured, and the swelling at the end of discharge was evaluated. It can be said that the smaller the swelling at the end of discharge, the better the cycle characteristics.
[0141]
(3) Mn elution amount
After performing 43 cycles of charge and discharge, the test secondary battery in which the negative electrode was carbon was disassembled, the negative electrode and the separator were taken out, Mn attached to the negative electrode and the separator was dissolved and concentrated, and Mn was eluted by ICP spectroscopy. The amount (weight of Mn element dissolved from the negative electrode and the separator) was measured. If the amount of Mn eluted is small, it can be said that the cycle characteristics and the storage characteristics are excellent.
[0142]
(4) Discharge capacity retention rate after 43 cycles
Charge and discharge were repeated under the conditions of a charge potential of 4.2 V, a discharge potential of 2.75 V, and a discharge load of 1.0 C, and the discharge capacity after 43 cycles was measured. The obtained discharge capacity value after 43 cycles was divided by the discharge capacity value after 1 cycle to obtain a discharge capacity retention rate after 43 cycles, and the cycle characteristics were evaluated.
[0143]
The results are shown in Table 3. In the table, "-" indicates that the corresponding item was not measured.
As is clear from Table 3, the positive electrode active material of the present invention was excellent in cycle characteristics and storage characteristics.
[0144]
[Table 3]

[0145]
C. Evaluation using cylindrical batteries
The cylindrical battery was manufactured as follows.
A positive electrode plate was obtained in the same manner as in the test secondary battery in which the negative electrode was lithium metal. In addition, a carbon material was used as a negative electrode active material, and applied to a negative electrode current collector and dried in the same manner as in the case of the positive electrode plate to obtain a negative electrode plate. A porous propylene film was used as a separator. For the electrolyte, LiPF was used in a mixed solvent of ethylene carbonate / methyl ethyl carbonate = 3/7 (volume ratio). ₆ Was used so as to have a concentration of 1 mol / L. The positive electrode plate, the negative electrode plate, and the separator are formed into a thin sheet, wound and stored in a metal cylindrical battery case, and an electrolyte is injected into the battery case to obtain a lithium ion battery cylindrical battery. Was.
[0146]
(1) Discharge capacity retention rate after 200 cycles
Charge and discharge were repeated under the conditions of a charge potential of 4.2 V, a discharge potential of 2.75 V, and a discharge load of 2 C, and the discharge capacity after 200 cycles was measured. The obtained value of the discharge capacity after 200 cycles was divided by the value of the discharge capacity after 1 cycle to obtain a discharge capacity retention rate after 200 cycles, and the cycle characteristics were evaluated.
[0147]
(2) High temperature discharge capacity maintenance rate
At 60 ° C., charge and discharge were repeated under the conditions of a charge potential of 4.2 V, a discharge potential of 2.75 V, and a discharge load of 2 C, and the discharge capacity after 200 cycles was measured. The obtained value of the discharge capacity after 200 cycles was divided by the value of the discharge capacity after one cycle to obtain a high-temperature discharge capacity retention ratio, and the high-temperature cycle characteristics were evaluated.
[0148]
(3) Load efficiency (load capacity maintenance rate)
After measuring the initial discharge capacity under the conditions of a charge potential of 4.2 V, a discharge potential of 2.75 V, and a discharge load of 0.2 C, under the conditions of a charge potential of 4.2 V, a discharge potential of 2.75 V, and a discharge load of 2.0 C, The load discharge capacity was measured. The obtained load discharge capacity value was divided by the initial discharge capacity to determine the load efficiency at a discharge load of 2.0C.
[0149]
(4) Average potential
The initial discharge capacity and the electric energy were measured under the conditions of a charge potential of 4.2 V, a discharge voltage of 2.75 V, and a discharge load of 0.2 C. The obtained electric energy value was divided by the initial discharge capacity to obtain an average potential.
[0150]
The results are shown in Table 4. In the table, "-" indicates that the corresponding item was not measured.
As is clear from Table 4, the positive electrode active material of the present invention was excellent in both cycle characteristics and high-temperature cycle characteristics, had a high average potential under load, and was excellent in load capacity retention.
[0151]
[Table 4]

[0152]
【The invention's effect】
As described above, by using the positive electrode active material of the present invention, battery characteristics such as cycle characteristics, load characteristics, and storage characteristics of a nonaqueous electrolyte secondary battery can be improved. As a result, a non-aqueous electrolyte secondary battery having excellent battery characteristics that could not be achieved conventionally can be put to practical use, and can be applied to various fields.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a graph showing an X value of a positive electrode active material according to the present invention (Example 1), where an X value is a cube root of an emission voltage value of a lithium-manganese composite oxide particle due to a manganese atom. FIG. 9 is a scatter diagram illustrating a distribution of (X, Y) when a cube root of a light emission voltage value is a Y value.
FIG. 2 is a graph showing a relationship between a third root of a light emission voltage value caused by manganese atoms of lithium manganese composite oxide particles in a conventional positive electrode active material for a lithium ion secondary battery (Comparative Example 1); FIG. 9 is a scatter diagram illustrating a distribution of (X, Y) when a cube root of a light emission voltage value caused by a lithium atom is set to a Y value.
FIG. 3 is an explanatory diagram of a specific method of obtaining an error of each point with respect to a linear regression line.
FIG. 4 is a schematic diagram showing a crystal structure of a lithium transition metal composite oxide having a spinel structure.
FIG. 5 is a schematic sectional view of a positive electrode.
FIG. 6 is a schematic sectional view of a cylindrical battery.
FIG. 7 is a schematic partial cross-sectional view of a coin-type battery.
FIG. 8 is a schematic perspective view of a prismatic battery.
FIG. 9 is a chart showing the presence state of magnesium obtained by performing a line analysis by EPMA on the positive electrode active material obtained in Example 1.
FIG. 10 is a chart showing the presence state of magnesium obtained by performing a line analysis by EPMA on the positive electrode active material obtained in Comparative Example 1.
[Explanation of symbols]
18a site
232e site
3 16d site
4 Binder
5 Positive electrode active material
11 Negative electrode
12 current collector
13 Positive electrode
14 Separator
20 Cylindrical battery
30 coin-type battery
40 square battery

Claims (9)

A positive electrode active material for a non-aqueous electrolyte secondary battery having at least a lithium transition metal composite oxide having a spinel structure,
The lithium transition metal composite oxide is present in the form of particles composed of one or both of primary particles and secondary particles that are aggregates thereof,
Each of the particles is given a two-dimensional coordinate having a coordinate component of each of the cube roots of the emission voltage values caused by the transition metal and lithium in each of the particles, expressed as a point on a coordinate plane, and linearly regressed through the origin. When finding a straight line,
A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein an absolute deviation of an error at each point with respect to the first linear regression line is 0.25 or less. In the particle size distribution of the particles, when the particle diameters at which the volume cumulative frequency reaches 10%, 50%, and 90% are D10, D50, and D90, respectively,
0.1 ≦ (D10 / D50) <1,
1 <(D90 / D50) ≦ 3 and 5 μm ≦ D50 ≦ 40 μm
The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, which satisfies all of the following. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein a standard deviation of a particle diameter in the particle size distribution of the particles is 0.4 or less. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the transition metal is manganese. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 4, wherein the lithium transition metal composite oxide is a lithium manganese composite oxide having aluminum and / or magnesium and boron. The lithium transition metal composite oxide is represented by the general formula _{Li 1 + a M b Mn 2} -a-b B c O 4 + d (M represents aluminum and / or magnesium, a is satisfy -0.2 ≦ a ≦ 0.2 Represents a number, b represents a number satisfying 0 ≦ b ≦ 0.2, c represents a number satisfying 0 ≦ c ≦ 0.02, and d represents a number satisfying −0.5 ≦ d ≦ 0.5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, which is represented by: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the (400) crystallite diameter of the lithium transition metal composite oxide is 600 to 1200 Å. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the specific surface area is 0.2 to 1.2 m ² / g. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 8, wherein, in the particle size distribution of the particles, a ratio of particles having a volume-based particle diameter of 50 µm or more is 10% by volume or less of all particles. Positive electrode active material.

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