JP2005196990A

JP2005196990A - Nonaqueous electrolyte secondary battery

Info

Publication number: JP2005196990A
Application number: JP2003435421A
Authority: JP
Inventors: Yuichi Ito; 裕一伊藤
Original assignee: Sanyo Electric Co Ltd; Sanyo GS Soft Energy Co Ltd
Current assignee: Sanyo Electric Co Ltd; Sanyo GS Soft Energy Co Ltd
Priority date: 2003-12-26
Filing date: 2003-12-26
Publication date: 2005-07-21
Anticipated expiration: 2023-12-26
Also published as: JP4359139B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery excellent in high efficiency discharging capacity characteristics without generating cut-off of a positive electrode. <P>SOLUTION: The nonaqueous electrolyte secondary battery 1 uses a positive electrode activator composed of lithium-cobalt complex oxide. The positive electrode activator of which, the diameter of the grain constituting the positive electrode-the grain diameter obtained by dividing the volume fraction property of a volume fraction by a corresponding grain diameter-(volume fraction/grain diameter) property does not have local maximum at the area of the grain diameter of less than 5μm; and BET specific area is 0.30 m<SP>2</SP>/g or more and 1.00 m<SP>2</SP>/g or less. An electrode group 2 is manufactured by winding a negative electrode plate 3 and a positive electrode plate 4 using the above positive electrode activator through a separator 5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は、リチウムコバルト複合酸化物からなる正極活物質を用いた非水電解質二次電池に関する。 The present invention relates to a non-aqueous electrolyte secondary battery using a positive electrode active material made of a lithium cobalt composite oxide.

近年、携帯電話、ノート型パーソナルコンピュータ、ビデオカメラなどの携帯可能な電子機器の高性能化、小型軽量化が進んでおり、これら電子機器に使用する高エネルギー密度の電池に対する要求が高まっている。このような要求を満たす二次電池として、リチウムイオン電池をあげることができ、例えば正極活物質の粒径−累積体積分率特性を調整して体積容量密度、安全性、均一塗工性、充放電サイクル耐久性、低温特性などの向上を図ったものが提案されている（例えば、特許文献１参照）。
国際公開第０１／０９２１５８号パンフレット In recent years, portable electronic devices such as mobile phones, notebook personal computers, and video cameras have been improved in performance and reduced in size and weight, and the demand for high energy density batteries used in these electronic devices is increasing. As a secondary battery satisfying such requirements, a lithium ion battery can be cited, for example, by adjusting the particle size-cumulative volume fraction characteristic of the positive electrode active material, volume capacity density, safety, uniform coating property, chargeability. The thing which aimed at the improvement of discharge cycle durability, a low temperature characteristic, etc. is proposed (for example, refer patent document 1).
International Publication No. 01/092158 Pamphlet

リチウムイオン電池においては、正極板と負極板とをセパレータを介して扁平巻状、円巻状、楕円巻状などに巻回した構成のものがあるが、正極板を巻回する際、正極板の柔軟性が低い場合は、正極板が切断するという問題がある。特に、巻回した正極板の最内周部はほぼ１８０度近く折れ曲がった状態となるため切断が生じやすい。切断によって分離された部分は充放電に関与できなくなり、放電容量が低下するという問題が生じる。 Some lithium ion batteries have a configuration in which a positive electrode plate and a negative electrode plate are wound in a flat winding shape, a circular winding shape, an elliptical winding shape, etc. via a separator. When the positive electrode plate is wound, the positive electrode plate If the flexibility is low, there is a problem that the positive electrode plate is cut. In particular, the innermost peripheral portion of the wound positive electrode plate is bent almost by 180 degrees, so that cutting is likely to occur. The part separated by cutting cannot participate in charging / discharging, resulting in a problem that the discharge capacity decreases.

なお、上述した特許文献１では、正極板の柔軟性不足による切断は考慮されておらず、巻回時に正極板の切断が起こる可能性がある。また、粒子径が大きく、ＢＥＴ比表面積が小さい正極活物質を用いた場合、正極板が柔軟になると予想できる。しかし、粒子の凝集状態によっては極板の柔軟性が改善されない場合もあり、単に粒子径が大きく、ＢＥＴ比表面積が小さい正極活物質を用いただけでは上述した問題は解決できない。 In Patent Document 1 described above, cutting due to insufficient flexibility of the positive electrode plate is not considered, and the positive electrode plate may be cut during winding. Further, when a positive electrode active material having a large particle diameter and a small BET specific surface area is used, it can be expected that the positive electrode plate becomes flexible. However, the flexibility of the electrode plate may not be improved depending on the aggregation state of the particles, and the above-described problem cannot be solved only by using a positive electrode active material having a large particle diameter and a small BET specific surface area.

本発明は斯かる事情に鑑みてなされたものであり、正極板の切断が生じず、高率放電容量特性に優れた非水電解質二次電池を提供することを目的とする。 The present invention has been made in view of such circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery excellent in high-rate discharge capacity characteristics without causing the positive electrode plate to be cut.

本発明に係る非水電解質二次電池は、リチウムコバルト複合酸化物からなる正極活物質を用いた非水電解質二次電池において、正極活物質を構成する粒子の粒径−体積分率特性の体積分率を対応する粒径で除した粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもたず、正極活物質のＢＥＴ比表面積は、０．３０ｍ²／ｇ以上、１．００ｍ²／ｇ以下であることを特徴とする。 The nonaqueous electrolyte secondary battery according to the present invention is a nonaqueous electrolyte secondary battery using a positive electrode active material made of a lithium cobalt composite oxide, and the volume of the particle size-volume fraction characteristic of the particles constituting the positive electrode active material. The particle size- (volume fraction / particle size) characteristic obtained by dividing the fraction by the corresponding particle size does not have a maximum value in a region where the particle size is less than 5 μm, and the BET specific surface area of the positive electrode active material is 0. 30 m ² / g or more, and equal to or less than 1.00 m ² / g.

本発明においては、構成粒子の粒径−体積分率特性の体積分率を対応する粒径で除した粒径−（体積分率／粒径）特性において粒径が５μｍ未満の領域に極大値をもたず、しかも、ＢＥＴ比表面積が０．３０ｍ²／ｇ以上、１．００ｍ²／ｇ以下の正極活物質を生成し、生成した正極活物質を用いて正極板を作製する。粒径−（体積分率／粒径）特性は、横軸が粒径、縦軸が（横軸の粒径に対応する体積分率）／（横軸の粒径）のグラフで表せる。ＢＥＴ比表面積が同じ場合は、粒径−（体積分率／粒径）特性が５μｍ未満の領域で極大値をもたない方が正極板の切断は生じ難くなる傾向がある。また、ＢＥＴ比表面積が０．３０ｍ²／ｇよりも小さい場合には、正極板の切断は生じ難いが、高率放電容量特性が低下する傾向にあり、ＢＥＴ比表面積が１．００ｍ²／ｇより大きい場合には、高率放電容量特性は良好であるが、正極板の切断が生じる傾向がある。 In the present invention, the particle size of the constituent particles—the volume fraction of the volume fraction characteristic divided by the corresponding particle diameter— (volume fraction / particle diameter) characteristic has a maximum value in the region where the particle diameter is less than 5 μm. the no, moreover, BET specific surface area of 0.30 m ² / g or more, to produce the following positive electrode active material 1.00 m ² / g, to prepare a positive electrode plate using the generated positive electrode active material. The particle size- (volume fraction / particle size) characteristic can be represented by a graph in which the horizontal axis represents the particle size and the vertical axis represents (volume fraction corresponding to the particle size on the horizontal axis) / (particle size on the horizontal axis). When the BET specific surface area is the same, the positive electrode plate is less likely to be cut if the particle size- (volume fraction / particle size) characteristic does not have a maximum value in the region of less than 5 μm. Further, when the BET specific surface area is smaller than 0.30 m ² / g, the positive electrode plate is hardly cut, but the high rate discharge capacity characteristic tends to be lowered, and the BET specific surface area is 1.00 m ² / g. If it is larger, the high rate discharge capacity characteristics are good, but the positive electrode plate tends to be cut.

本発明によれば、構成粒子の粒径−（体積分率／粒径）特性において粒径が５μｍ未満の領域に極大値をもたず、しかも、ＢＥＴ比表面積が０．３０ｍ²／ｇ以上、１．００ｍ²／ｇ以下の正極活物質を用いることにより、正極板の切断が生じず、高率放電容量特性に優れた非水電解質二次電池を得ることができる。 According to the present invention, in the particle size- (volume fraction / particle size) characteristics of the constituent particles, there is no maximum value in the region where the particle size is less than 5 μm, and the BET specific surface area is 0.30 m ² / g or more. By using a positive electrode active material of 1.00 m ² / g or less, it is possible to obtain a nonaqueous electrolyte secondary battery excellent in high-rate discharge capacity characteristics without being cut by the positive electrode plate.

以下、本発明をその実施の形態を示す図面に基づいて具体的に説明する。
（実施例１）
図１は、本発明に係る角型の非水電解質二次電池の概略断面図である。非水電解質二次電池１は、銅集電体に負極合剤を塗布してなる負極板３、及びアルミ集電体に正極合剤を塗布してなる正極板４がセパレータ５を介して巻回された扁平巻状の電極群２と、非水電解液とを電池ケース６に収納してなる幅３０ｍｍ、高さ４８ｍｍ、厚さ４．２ｍｍのものである。電池ケース６は、底を囲む側壁の開口部に、安全弁８及び負極端子９を備えた電池蓋７がレーザー溶接によって取り付けられている。また、負極端子９は負極リード１０を介して負極板３と接続され、正極板４は電池ケース６の側壁内面と接触して電気的に接続されている。 Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
(Example 1)
FIG. 1 is a schematic cross-sectional view of a rectangular nonaqueous electrolyte secondary battery according to the present invention. The non-aqueous electrolyte secondary battery 1 includes a negative electrode plate 3 formed by applying a negative electrode mixture to a copper current collector, and a positive electrode plate 4 formed by applying a positive electrode mixture to an aluminum current collector through a separator 5. The flat electrode group 2 that has been rotated and the nonaqueous electrolyte solution are housed in a battery case 6 and have a width of 30 mm, a height of 48 mm, and a thickness of 4.2 mm. In the battery case 6, a battery lid 7 having a safety valve 8 and a negative electrode terminal 9 is attached to the opening of the side wall surrounding the bottom by laser welding. The negative electrode terminal 9 is connected to the negative electrode plate 3 through the negative electrode lead 10, and the positive electrode plate 4 is in contact with and electrically connected to the inner surface of the side wall of the battery case 6.

次に、正極活物質について説明する。図２は、正極活物質を構成する粒子の粒径−（体積分率／粒径）特性の例を示す図である。粒径−（体積分率／粒径）特性は、図２に示すように、横軸が粒径、縦軸が体積分率／粒径のグラフで表される。このような正極活物質は以下のように調製した。水酸化コバルトCo(OH)₂を６００℃で３時間焼成して、酸化コバルトCo₃O₄を得た。この酸化コバルトと炭酸リチウムLi₂CO₃とを、リチウムとコバルトとのモル比が１：１となるように混合した後、９５０℃で３時間焼成し、コバルト酸リチウムLiCoO₂を得た。このコバルト酸リチウムの活物質粒子を粉砕器で粉砕し、さらに多段ふるいによって分級し、また必要に応じてこれらを再混合することによって、ＢＥＴ比表面積が０．３０ｍ²／ｇであり、しかも、図２に示すように、粒径−体積分率特性の体積分率を対応する粒径で除した粒径−（体積分率／粒径）特性において、５μｍ未満の領域に極大値をもたない正極活物質を得た。 Next, the positive electrode active material will be described. FIG. 2 is a diagram showing an example of the particle size- (volume fraction / particle size) characteristics of the particles constituting the positive electrode active material. As shown in FIG. 2, the particle size- (volume fraction / particle size) characteristic is represented by a graph of the particle size on the horizontal axis and the volume fraction / particle size on the vertical axis. Such a positive electrode active material was prepared as follows. Cobalt hydroxide Co (OH) ₂ was calcined at 600 ° C. for 3 hours to obtain cobalt oxide Co ₃ O ₄ . The cobalt oxide and lithium carbonate Li ₂ CO ₃ were mixed so that the molar ratio of lithium to cobalt was 1: 1, and then calcined at 950 ° C. for 3 hours to obtain lithium cobalt oxide LiCoO ₂ . The lithium cobaltate active material particles are pulverized by a pulverizer, further classified by a multistage sieve, and remixed as necessary, so that the BET specific surface area is 0.30 m ² / g, As shown in FIG. 2, in the particle size- (volume fraction / particle size) characteristic obtained by dividing the volume fraction of the particle size-volume fraction characteristic by the corresponding particle size, a maximum value is given in a region of less than 5 μm. No positive electrode active material was obtained.

ここで、ＢＥＴ比表面積は、定圧窒素吸着量測定法により、多点数の測定（多点法）に基づいて窒素ガスの吸着量から計算される測定サンプルの表面積を、測定サンプルの重量で除して、測定サンプルの比表面積を算出した。 Here, the BET specific surface area is obtained by dividing the surface area of the measurement sample calculated from the adsorption amount of nitrogen gas based on the multipoint measurement (multipoint method) by the constant pressure nitrogen adsorption amount measurement method by the weight of the measurement sample. The specific surface area of the measurement sample was calculated.

また、粒径−体積分率特性における体積分率（％）は、全粒径の累積体積に対する各粒径の体積の比率（％）を表す。体積分率の測定にはレーザー回折式粒度分布測定装置を用い、０．１３３μｍ〜７０４μｍの範囲の１００点の粒径の体積分率を測定した。測定原理は、粒子にレーザー光を当てたときに起こる光の散乱現象を利用したものであり、この散乱光の強度及び散乱角度が、粒子の大きさに大きく依存していることを利用して、この散乱光の強度及び散乱角度を光学検出器により測定し、コンピュータで処理することによって、粒径とその粒径に対応する体積分率との関係を示す粒径−体積分率特性を得るものである。この粒径−体積分率特性の体積分率を対応する粒径で除して、粒径−（体積分率／粒径）特性を得た。 The volume fraction (%) in the particle size-volume fraction characteristic represents the ratio (%) of the volume of each particle size to the cumulative volume of all particle sizes. For measuring the volume fraction, a laser diffraction particle size distribution measuring device was used to measure the volume fraction of 100 particle diameters in the range of 0.133 μm to 704 μm. The measurement principle uses the light scattering phenomenon that occurs when a laser beam is applied to the particle, and the fact that the intensity and angle of the scattered light greatly depends on the size of the particle. The intensity and the scattering angle of the scattered light are measured by an optical detector and processed by a computer to obtain a particle size-volume fraction characteristic indicating the relationship between the particle size and the volume fraction corresponding to the particle size. Is. By dividing the volume fraction of the particle diameter-volume fraction characteristic by the corresponding particle diameter, a particle diameter- (volume fraction / particle diameter) characteristic was obtained.

なお、活物質の原料は、上記の例に限るものではなく、炭酸リチウム、水酸化リチウム、硝酸リチウム等に代表されるリチウム化合物と、酸化コバルト、水酸化コバルト、炭酸コバルト、硝酸コバルト塩等に代表されるコバルト化合物とを用いてもよい。また、活物質中の微量元素として、例えば、マグネシウムＭｇ、アルミニウムＡｌ、カルシウムＣａ、マンガンＭｎ、鉄Ｆｅ、ニッケルＮｉ、ストロンチウムＳｒ、ナトリウムＮａ、フッ素Ｆ、硫黄Ｓなどを含んでもよい。また、活物質粒子のＢＥＴ比表面積、及び、粒径−（体積分率／粒径）特性は、リチウム原料やコバルト原料の粒子形状等を制御したり、リチウム原料とコバルト原料との混合比の調整、混合原料の造粒、あるいはコバルト酸リチウムの焼成条件、他元素添加などによって制御してもよい。 In addition, the raw material of an active material is not restricted to said example, Lithium compound represented by lithium carbonate, lithium hydroxide, lithium nitrate etc., and cobalt oxide, cobalt hydroxide, cobalt carbonate, cobalt nitrate salt etc. You may use the cobalt compound represented. As trace elements in the active material, for example, magnesium Mg, aluminum Al, calcium Ca, manganese Mn, iron Fe, nickel Ni, strontium Sr, sodium Na, fluorine F, sulfur S and the like may be included. In addition, the BET specific surface area and particle size- (volume fraction / particle size) characteristics of the active material particles control the particle shape of the lithium raw material and the cobalt raw material, or the mixing ratio of the lithium raw material and the cobalt raw material. You may control by adjustment, granulation of a mixed raw material, or the baking conditions of lithium cobaltate, addition of other elements.

このようにして得られた活物質粒子と、導電剤としてのアセチレンブラックと、バインダーとしてのポリフッ化ビニリデン（ＰＶＤＦ）とを重量比で９１：３：６となるように混合し、これに溶媒であるＮ−メチル−２−ピロリドン（ＮＭＰ）を適量加えて撹拌することで、正極ペーストを得た。正極板４は、上記の正極ペーストを、ＮＭＰを除いた合剤の重量が片面につき０．０２５ｇ／ｃｍ²となるように、ドクターブレードを用いて厚さ１５μｍのアルミ箔集電体の両面に塗布し、乾燥させ、厚さ１７５μｍとなるようにプレスして作製した。 The active material particles thus obtained, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were mixed at a weight ratio of 91: 3: 6, and this was mixed with a solvent. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and stirred to obtain a positive electrode paste. The positive electrode plate 4 is formed on both surfaces of an aluminum foil current collector having a thickness of 15 μm using a doctor blade so that the weight of the mixture excluding NMP is 0.025 g / cm ² per side. It was applied, dried, and pressed to a thickness of 175 μm.

また、グラファイト（黒鉛）、およびバインダーとしてのポリフッ化ビニリデン（ＰＶＤＦ）を重量比で９０：１０とした負極合剤に、Ｎ−メチル−２−ピロリドン（ＮＭＰ）を適量加えて負極ペーストを得た。負極板３は、前記負極ペーストを、ＮＭＰを除いた合剤の重量が片面につき０．０１２ｇ／ｃｍ²となるように、ドクターブレードを用いて厚さ１０μｍの銅箔集電体の両面に塗布し、乾燥させ、厚さ１７５μｍとなるようにプレスして作製した。 Further, a negative electrode paste was obtained by adding an appropriate amount of N-methyl-2-pyrrolidone (NMP) to a negative electrode mixture in which graphite (graphite) and polyvinylidene fluoride (PVDF) as a binder were in a weight ratio of 90:10. . For the negative electrode plate 3, the negative electrode paste was applied to both sides of a 10 μm thick copper foil current collector using a doctor blade so that the weight of the mixture excluding NMP was 0.012 g / cm ² per side. And dried and pressed to a thickness of 175 μm.

セパレータ５には、ポリエチレン製微多孔膜を用いた。また、電解液には、エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）との体積比が３：７の混合溶媒に、LiPF₆を１ｍｏｌ／ｌ溶解させたものを用いた。 For the separator 5, a polyethylene microporous film was used. As the electrolytic solution, a solution obtained by dissolving 1 mol / l of LiPF ₆ in a mixed solvent having a volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) of 3: 7 was used.

（実施例２）
ＢＥＴ比表面積が０．５１ｍ²／ｇであること以外は、実施例１と同様の正極活物質を得た。したがって、図２に示すように、実施例１と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもたない。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Example 2)
A positive electrode active material similar to that of Example 1 was obtained except that the BET specific surface area was 0.51 m ² / g. Therefore, as shown in FIG. 2, as in Example 1, the particle size- (volume fraction / particle size) characteristic does not have a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（実施例３）
ＢＥＴ比表面積が１．００ｍ²／ｇであること以外は、実施例１と同様の正極活物質を得た。したがって、図２に示すように、実施例１と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもたない。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Example 3)
A positive electrode active material similar to that of Example 1 was obtained except that the BET specific surface area was 1.00 m ² / g. Therefore, as shown in FIG. 2, as in Example 1, the particle size- (volume fraction / particle size) characteristic does not have a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（比較例１）
ＢＥＴ比表面積が０．１１ｍ²／ｇであること以外は、実施例１と同様の正極活物質を得た。したがって、図２に示すように、実施例１と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもたない。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Comparative Example 1)
A positive electrode active material similar to that of Example 1 was obtained except that the BET specific surface area was 0.11 m ² / g. Therefore, as shown in FIG. 2, as in Example 1, the particle size- (volume fraction / particle size) characteristic does not have a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（比較例２）
ＢＥＴ比表面積が０．２０ｍ²／ｇであること以外は、実施例１と同様の正極活物質を得た。したがって、図２に示すように、実施例１と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもたない。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Comparative Example 2)
A positive electrode active material similar to that of Example 1 was obtained except that the BET specific surface area was 0.20 m ² / g. Therefore, as shown in FIG. 2, as in Example 1, the particle size- (volume fraction / particle size) characteristic does not have a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（比較例３）
ＢＥＴ比表面積が１．１０ｍ²／ｇであること以外は、実施例１と同様の正極活物質を得た。したがって、図２に示すように、実施例１と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもたない。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Comparative Example 3)
A positive electrode active material similar to that of Example 1 was obtained except that the BET specific surface area was 1.10 m ² / g. Therefore, as shown in FIG. 2, as in Example 1, the particle size- (volume fraction / particle size) characteristic does not have a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（比較例４）
ＢＥＴ比表面積が０．１２ｍ²／ｇであり、図２に示すように、粒径−（体積分率／粒径）特性が、粒径５μｍ未満の領域に極大値をもつこと以外は、実施例１と同様の正極活物質を得た。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Comparative Example 4)
Implemented except that the BET specific surface area is 0.12 m ² / g and the particle size- (volume fraction / particle size) characteristic has a maximum value in the region of less than 5 μm as shown in FIG. A positive electrode active material similar to that in Example 1 was obtained. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（比較例５）
ＢＥＴ比表面積が０．２０ｍ²／ｇであること以外は、比較例４と同様の正極活物質を得た。したがって、図２に示すように、比較例４と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもつ。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Comparative Example 5)
A positive electrode active material similar to that of Comparative Example 4 was obtained except that the BET specific surface area was 0.20 m ² / g. Therefore, as shown in FIG. 2, as in Comparative Example 4, the particle size- (volume fraction / particle size) characteristic has a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（比較例６）
ＢＥＴ比表面積が０．３０ｍ²／ｇであること以外は、比較例４と同様の正極活物質を得た。したがって、図２に示すように、比較例４と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもつ。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Comparative Example 6)
A positive electrode active material similar to that of Comparative Example 4 was obtained except that the BET specific surface area was 0.30 m ² / g. Therefore, as shown in FIG. 2, as in Comparative Example 4, the particle size- (volume fraction / particle size) characteristic has a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（比較例７）
ＢＥＴ比表面積が０．４７ｍ²／ｇであること以外は、比較例４と同様の正極活物質を得た。したがって、図２に示すように、比較例４と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもつ。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Comparative Example 7)
A positive electrode active material similar to that of Comparative Example 4 was obtained except that the BET specific surface area was 0.47 m ² / g. Therefore, as shown in FIG. 2, as in Comparative Example 4, the particle size- (volume fraction / particle size) characteristic has a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（比較例８）
ＢＥＴ比表面積が０．９９ｍ²／ｇであること以外は、比較例４と同様の正極活物質を得た。したがって、図２に示すように、比較例４と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもつ。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Comparative Example 8)
A positive electrode active material similar to that of Comparative Example 4 was obtained except that the BET specific surface area was 0.99 m ² / g. Therefore, as shown in FIG. 2, as in Comparative Example 4, the particle size- (volume fraction / particle size) characteristic has a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

（比較例９）
ＢＥＴ比表面積が１．４５ｍ²／ｇであること以外は、比較例４と同様の正極活物質を得た。したがって、図２に示すように、比較例４と同様、粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもつ。また、実施例１と同様の方法で、正極板および非水電解質二次電池を得た。 (Comparative Example 9)
A positive electrode active material similar to that of Comparative Example 4 was obtained except that the BET specific surface area was 1.45 m ² / g. Therefore, as shown in FIG. 2, as in Comparative Example 4, the particle size- (volume fraction / particle size) characteristic has a maximum value in a region where the particle size is less than 5 μm. In addition, a positive electrode plate and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1.

これらの各実施例および各比較例の非水電解質二次電池に用いた正極板について、極板の柔軟性を評価した。また、各実施例および各比較例の非水電解質二次電池の高率放電容量特性を評価した。 The flexibility of the electrode plate was evaluated for the positive electrode plate used in the non-aqueous electrolyte secondary battery of each of these Examples and Comparative Examples. Moreover, the high rate discharge capacity characteristic of the nonaqueous electrolyte secondary battery of each Example and each comparative example was evaluated.

正極板４の柔軟性の評価は、正極板４と負極板３とをセパレータ５を介して扁平巻状に巻回した電極群２において、折り曲げる角度がもっとも大きい最内周部の正極板３の折り曲げ部位の切断あるいは亀裂の有無を確認した。試験数は、それぞれの実施例及び比較例に対して１０個の電極群２を作製し、そのうちの一つにでも切断あるいは亀裂が認められた場合には、切断不良（切断あり）とみなした。 The evaluation of the flexibility of the positive electrode plate 4 is based on the fact that the positive electrode plate 3 of the innermost peripheral portion where the angle of bending is the largest in the electrode group 2 in which the positive electrode plate 4 and the negative electrode plate 3 are wound in a flat winding shape via the separator 5 The presence or absence of a cut or crack in the bent part was confirmed. As for the number of tests, 10 electrode groups 2 were prepared for each of the examples and comparative examples, and when cutting or cracking was observed in one of them, it was regarded as defective cutting (with cutting). .

また、高率放電容量特性の評価は、室温２０℃の雰囲気下において、充電電流６００ｍＡ、充電電圧４．２０Ｖの定電流定電圧充電で２．５時間充電した後、放電電流６００ｍＡ、終止電圧２．７５Ｖの条件で放電を行い、放電容量を測定した。続いて、同一の電池を用いて同様に充電し、放電条件を放電電流６００ｍＡから１２００ｍＡに変更した高率放電の放電容量を測定し、測定値を放電電流６００ｍＡの放電容量で除して、高率放電容量比率（％）を算出した。なお、試験電池数は、それぞれの実施例及び比較例に対して３個とし、３個の平均値を求めて、高率放電容量特性（％）の指標に用いた。試験結果を表１に示す。 In addition, the evaluation of the high-rate discharge capacity characteristics was carried out under a room temperature of 20 ° C. in an atmosphere at a charging current of 600 mA and a charging voltage of 4.20 V for 2.5 hours, followed by a charging current of 600 mA and a final voltage of 2 Discharge was performed under the condition of .75 V, and the discharge capacity was measured. Subsequently, the same battery was charged in the same manner, the discharge capacity of the high rate discharge with the discharge condition changed from the discharge current of 600 mA to 1200 mA was measured, and the measured value was divided by the discharge capacity of the discharge current of 600 mA. The rate discharge capacity ratio (%) was calculated. The number of test batteries was three for each of the examples and comparative examples, and the average value of the three was obtained and used as an indicator of high rate discharge capacity characteristics (%). The test results are shown in Table 1.

表１の試験結果から、ＢＥＴ比表面積が小さい方が正極板４の切断は生じ難くなるが、高率放電容量特性は低下する傾向にあり、同じＢＥＴ比表面積では、粒径−（体積分率／粒径）特性が５μｍ未満の領域に極大値をもたない方が正極板の切断は生じ難くなる傾向があることが分かる。 From the test results of Table 1, the smaller the BET specific surface area, the less likely the cutting of the positive electrode plate 4 is, but the high rate discharge capacity characteristics tend to be reduced. It can be seen that there is a tendency that the positive electrode plate is less likely to be cut when there is no maximum value in a region where the / particle size characteristic is less than 5 μm.

比較例１〜３および実施例１〜３の試験結果から、粒径−（体積分率／粒径）特性が粒径５μｍ未満の領域で極大値をもたない場合において、比較例３のようにＢＥＴ比表面積が１．１０ｍ²／ｇと大きい場合には、正極板４の切断が生じたことから、ＢＥＴ比表面積は１．００ｍ²／ｇ以下に抑える必要がある。 From the test results of Comparative Examples 1 to 3 and Examples 1 to 3, when the particle size- (volume fraction / particle size) characteristic does not have a maximum value in the region where the particle size is less than 5 μm, as in Comparative Example 3 In the case where the BET specific surface area is as large as 1.10 m ² / g, the positive electrode plate 4 is cut, so that the BET specific surface area must be suppressed to 1.00 m ² / g or less.

また、比較例１〜３および実施例１〜３の試験結果から、粒径−（体積分率／粒径）特性が粒径５μｍ未満の領域で極大値をもたない場合において、比較例１，２のように、ＢＥＴ比表面積が０．１１ｍ²／ｇあるいは０．２０ｍ²／ｇと小さい場合には、高率放電容量特性が著しく劣ったことから、ＢＥＴ比表面積は０．３０ｍ²／ｇ以上にする必要がある。 Further, from the test results of Comparative Examples 1 to 3 and Examples 1 to 3, in the case where the particle size- (volume fraction / particle size) characteristic does not have a maximum value in a region where the particle size is less than 5 μm, Comparative Example 1 , as 2, if the BET specific surface area is small and 0.11 m ² / g or 0.20 m ² / g, since the high-rate discharge capacity characteristics were markedly inferior, BET specific surface area of 0.30 m ² / g or more is necessary.

一方、粒径−（体積分率／粒径）特性が粒径５μｍ未満の領域で極大値をもつ場合については、比較例６〜９のようにＢＥＴ比表面積が０．３０ｍ²／ｇ以上の正極板４には全て切断が生じていた。また、正極板４の切断が生じなかった比較例４，５の電池についても、高率放電容量特性が著しく劣っており、いずれにおいても、良好な電池は得られなかった。 On the other hand, in the case where the particle size- (volume fraction / particle size) characteristic has a maximum value in the region of less than 5 μm, the BET specific surface area is 0.30 m ² / g or more as in Comparative Examples 6 to 9. All the positive electrode plates 4 were cut. In addition, the batteries of Comparative Examples 4 and 5 in which the cutting of the positive electrode plate 4 did not occur were extremely inferior in the high rate discharge capacity characteristics, and in any case, a good battery could not be obtained.

以上のことから、粒径−（体積分率／粒径）特性が粒径５μｍ未満の領域で極大値をもたず、ＢＥＴ比表面積が０．３０〜１．００ｍ²／ｇの正極活物質を用いることにより、柔軟で正極板に破断が生じず、高エネルギー密度で放電特性が優れた電池を得ることができる。 From the above, the positive electrode active material having a particle size- (volume fraction / particle size) characteristic that does not have a maximum value in a region where the particle size is less than 5 μm and the BET specific surface area is 0.30 to 1.00 m ² / g. By using the battery, it is possible to obtain a battery that is flexible and does not break in the positive electrode plate, and has a high energy density and excellent discharge characteristics.

正極板４と負極板３とセパレータ５とからなる電極群２を巻回する際の正極板４の最内周部の折り曲げ部位の切断は、正極板４の柔軟性が低い場合に生じる。これは、電極群２の巻回時に、電極群２の内周ほど折り曲げる角度が大きくなることから、電極群２の内周部の極板の折り曲げ部位の内側には大きな圧縮力が作用しており、柔軟性が低い正極板４では、内側の合剤が変形に耐えられず、アルミ箔を押し広げて破断させるためである。この傾向は、正極板４の合剤の充電密度が高く、極板を折り曲げる角度が大きい角型電池において特に顕著であると考えられるが、円筒型の電池などにおいても、製造の各工程における正極板切断の不具合が減少するため、本発明は有用である。 When the electrode group 2 including the positive electrode plate 4, the negative electrode plate 3, and the separator 5 is wound, cutting of the bent portion of the innermost peripheral portion of the positive electrode plate 4 occurs when the flexibility of the positive electrode plate 4 is low. This is because when the electrode group 2 is wound, the angle at which the inner circumference of the electrode group 2 is bent increases, so that a large compressive force acts on the inner side of the electrode plate bending portion of the inner circumference portion of the electrode group 2. In the positive electrode plate 4 having low flexibility, the inner mixture cannot withstand deformation, and the aluminum foil is spread and broken. This tendency is considered to be particularly noticeable in a rectangular battery in which the charge density of the mixture of the positive electrode plate 4 is high and the angle at which the electrode plate is bent is large, but the positive electrode in each step of manufacturing also in a cylindrical battery or the like. The present invention is useful because the problem of cutting the plate is reduced.

なお、正極活物質のＢＥＴ比表面積が大きくなると、正極板４の柔軟性が低下する原因は明らかになっていないが、ＢＥＴ比表面積が大きい活物質は、バインダーとの接触面積が大きくなるために、正極合剤がより強固に接着されるために、柔軟性が低下すると考えられる。 In addition, when the BET specific surface area of the positive electrode active material is increased, the cause of the decrease in flexibility of the positive electrode plate 4 has not been clarified. However, the active material having a large BET specific surface area has a large contact area with the binder. The positive electrode mixture is more strongly bonded, and thus the flexibility is considered to be lowered.

また、粒径−（体積分率／粒径）特性が粒径５μｍ未満の領域に極大値をもつ作用について、その詳細は不明であるが、上記のＢＥＴ比表面積と同様に、バインダーとの接着性の違いが影響しているものと推定される。体積分率は、全粒径の累積体積に対する各粒径の体積の割合であることから、体積分率を粒径で除したものは、表面積（表面積分率）に準じる指標となると考えられ、粒径５μｍ未満の領域に極大値をもつということは、粒径に対する表面積比率が非常に大きい微紛を多量に含むか、あるいは、球形の粒径から想定される以上の表面積を有する粒径５μｍ未満の粒子を含むことを示していると推察される。 Further, the details of the action of the maximum value in the region where the particle size- (volume fraction / particle size) characteristic is less than 5 μm are unclear, but as with the BET specific surface area described above, adhesion to the binder It is presumed that gender differences have an effect. Since the volume fraction is the ratio of the volume of each particle size to the cumulative volume of all particle sizes, the volume fraction divided by the particle size is considered to be an index according to the surface area (surface integral ratio), Having a maximum value in a region having a particle size of less than 5 μm means that a large amount of fine powder having a very large surface area ratio to the particle size or a particle size of 5 μm having a surface area larger than that assumed from a spherical particle size. It is inferred that it contains less than particles.

このような粒子の例としては、より微細な一次粒子が凝縮した二次粒子、それが焼結した表面起伏の大きい一次粒子、それらの中間の粒子、球状ではなく平板状の特異な形状のもの、などが考えられ、このような粒子はバインダーとの接着性に優れているために、極板の柔軟性を低下させていると推定される。本発明は、これらの粒子の形状について規定するものではないが、LiCoO₂の反応の均一性の観点から、各粒子はより均一な粒子形状であることが望ましいと考えられる。このような特異な粒子の有無の判別、分析は困難であり、本発明で示した指標、および、その規定は、非常に有用である。例えばＳＥＭ写真観察で分かる粒子の凝集状態を定量的に判断するのは困難であるが、本発明を用いることにより、定量的な取り扱いが可能となり、よりクリティカルな物性の規定が可能になる。 Examples of such particles include secondary particles with condensed finer primary particles, primary particles with large surface undulations that have been sintered, particles in between, and particles with a unique shape that is flat rather than spherical. These particles are presumed to reduce the flexibility of the electrode plate because they are excellent in adhesiveness with the binder. Although the present invention does not specify the shape of these particles, it is considered that each particle preferably has a more uniform particle shape from the viewpoint of the uniformity of the LiCoO ₂ reaction. It is difficult to discriminate and analyze the presence / absence of such unique particles, and the index and its definition shown in the present invention are very useful. For example, although it is difficult to quantitatively determine the aggregation state of particles that can be seen by SEM photograph observation, by using the present invention, quantitative handling becomes possible and more critical physical properties can be defined.

また、正極活性物質のＢＥＴ比表面積が小さいものは、反応面積が小さいために、高率放電容量特性が劣ると考えられる。また、粒径−（体積分率／粒径）特性の粒径５μｍ未満の領域に極大値をもつ正極活物質の高率放電容量特性が若干劣る理由については不明であるが、粒径が小さく反応性に富む活物質の表面が、バインダーによって覆われているためであると考えられる。 Moreover, it is thought that the thing with a small BET specific surface area of a positive electrode active material is inferior in a high rate discharge capacity characteristic, since the reaction area is small. Further, the reason why the high rate discharge capacity characteristic of the positive electrode active material having a maximum value in the region of the particle size of less than 5 μm in the particle size- (volume fraction / particle size) characteristic is unclear, but the particle size is small. This is probably because the surface of the active material rich in reactivity is covered with a binder.

本発明に係る角型の非水電解質二次電池の概略断面図である。It is a schematic sectional drawing of the square nonaqueous electrolyte secondary battery which concerns on this invention. 正極活物質を構成する粒子の粒径−（体積分率／粒径）特性の例を示す図である。It is a figure which shows the example of the particle size- (volume fraction / particle size) characteristic of the particle | grains which comprise a positive electrode active material.

符号の説明Explanation of symbols

１非水電解質二次電池
２電極群
３負極板
４正極板
５セパレータ
６電池ケース
７電池蓋
８安全弁
９負極端子
１０負極リード DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 3 Negative electrode plate 4 Positive electrode plate 5 Separator 6 Battery case 7 Battery cover 8 Safety valve 9 Negative electrode terminal 10 Negative electrode lead

Claims

リチウムコバルト複合酸化物からなる正極活物質を用いた非水電解質二次電池において、
正極活物質を構成する粒子の粒径−体積分率特性の体積分率を対応する粒径で除した粒径−（体積分率／粒径）特性は、粒径が５μｍ未満の領域に極大値をもたず、
正極活物質のＢＥＴ比表面積は、０．３０ｍ²／ｇ以上、１．００ｍ²／ｇ以下であることを特徴とする非水電解質二次電池。 In a non-aqueous electrolyte secondary battery using a positive electrode active material made of lithium cobalt composite oxide,
The particle size of the positive electrode active material—the volume fraction obtained by dividing the volume fraction of the volume fraction characteristic by the corresponding particle size— (volume fraction / particle size) characteristic is maximum in a region where the particle size is less than 5 μm. No value,
BET specific surface area of the positive electrode active material, 0.30 m ² / g or more, a non-aqueous electrolyte secondary batteries, characterized by at most 1.00 m ² / g.