JP4507284B2 - Non-aqueous electrolyte secondary battery - Google Patents
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【０００１】
【発明の属する技術分野】
本発明は、非水電解液二次電池の、とくにその正極に添加する導電材に関するものである。
【０００２】
【従来の技術】
近年、ＡＶ機器あるいはパソコン等の電子機器のポータブル化、コードレス化が急速に進んでおり、これらの駆動用電源として小型、軽量で高エネルギー密度を有する二次電池への要求が高い。この中でリチウム金属を活物質とする負極を用いたリチウム二次電池はとりわけ高電圧、高エネルギー密度を有する電池として期待が大きいが、安全性、信頼性の点からも現在実用化はされていない。
【０００３】
安全性低下の原因は、充放電の繰り返しにより、リチウム金属負極が樹枝状（デンドライト状）の形態に変化し、内部短絡の可能性が生ずることや電解液とデンドライト状リチウムとの発熱反応が起こるためであると考えられている。
【０００４】
そこで、リチウムを可逆的にインターカレート、デインターカレートできる炭素材料を負極に用い、ＬｉＣｏＯ2 、ＬｉＮｉＯ2 、ＬｉＭｎ2Ｏ4等のリチウム含有遷移金属酸化物等を正極に用いるリチウムイオン二次電池が提案されている。
【０００５】
このリチウムイオン二次電池では、充電時にリチウムが負極の炭素材料中にインターカレートされるために、負極板上でリチウムが析出することは原理的に起こらず、電池の内部短絡を抑え電池の安全性、信頼性に優れるという利点がある。
【０００６】
【発明が解決しようとする課題】
しかしながら、リチウムを可逆的にインターカレート、デインターカレートし得る炭素材料を負極に用いたリチウムイオン二次電池の場合でも、充放電を繰り返すにつれ徐々に負極板上へのリチウムの析出が起こり、サイクル寿命末期において電池の安全性、信頼性が低下するこという課題があった。
【０００７】
本発明はこのような課題を解決するものであり、サイクル寿命末期において負極板上にリチウムが析出することを防止して、充放電サイクル寿命特性や安全性、信頼性の高い電池を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、再充電可能な正極、負極とセパレータ、および非水電解液を具備し、前記正極の導電材として、ケッチェンブラックと鱗片状黒鉛の混合物、または、ケッチェンブラックとアセチレンブラックの混合物を用い、正極活物質１００重量部に対する前記導電材の添加量を、ケッチェンブラックと鱗片状黒鉛の混合物の場合にはケッチェンブラックを０．２〜１．０重量部とし、かつ、ケッチェンブラックの添加量をｘ重量部、鱗片状黒鉛の添加量ｙ重量部とすると、３ｘ＋（３／８）ｙの値が１．０以上３．５以下とし、さらにケッチェンブラックとアセチレンブラックの混合物の場合にはケッチェンブラックを０．２〜１．０重量部とし、かつケッチェンブラックの添加量をｘ重量部、アセチレンブラックの添加量をｚ重量部とすると、３ｘ＋ｚの値が１．１以上３．５以下とするものであって、前記ケッチェンブラックのＤＢＰ吸油量は、３６０ｍｌ／１００ｇ以上であり、前記正極の活物質は、リチウム含有遷移金属カルコゲン化合物である。
【０００９】
充放電サイクルを繰り返した際の電池容量の低下はほとんど負極に起因しており、負極板上にリチウムが析出しておこることがわかっている。
【００１０】
さらに、充電電流が極板中央部分に集中することにより、負極板上へのリチウム析出は、極板の幅方向の中央部分に起こり易く、幅方向の両端部分にはリチウム析出が起こりにくい。したがって、極板における電解液の拡散を均一に行うことができるように、電解液の吸液に優れたケッチェンブラックを用い、さらにこれに鱗片状黒鉛またはアセチレンブラックを加える。また、これらの添加により極板の強度を向上させることができる。
【００１１】
【発明の実施の形態】
ケッチェンブラック等のカーボンブラックの物性の指標としてフタル酸ジブチル吸油量（ＤＢＰ吸油量）が用いられている。このＤＢＰ吸油量が電解液の吸液性に対応すると考えられ、ＤＢＰ吸油量の高いカーボンブラックを導電材として正極に用いると、電解液の吸液性が向上し、極板の幅方向の電解液の拡散が確保されてサイクル特性が向上すると考えられる。ＤＢＰ吸油量はケッチェンブラック（ＥＣ）で３６０ｍｌ／１００ｇ、ケッチェンブラック（ＥＣ６００ＪＤ）で５００ｍｌ／１００ｇ、アセチレンブラックで１２０ｍｌ／１００ｇである。
【００１２】
すなわち、アセチレンブラックに対してケッチェンブラック（ＥＣ）は１／３の量でほぼ同等の電解液の吸液性を示すためにサイクル特性に優れていると考えられる。また、サイクル寿命末期電池を観察したところ、ケッチェンブラックを用いた電池では、極板の幅方向の両端部分におけるセパレータの目詰まりはなく、また、中央部分のリチウム析出も見られなかった。
【００１３】
しかしながら、アセチレンブラックではその添加量を増加して吸液性を向上させても、ケッチェンブラックほどのサイクル特性の向上は得られなかった。アセチレンブラックの場合には、正極合剤作製時の混練工程で、機械的ストレスによってその鎖状の高次構造が破壊されるために吸液性が低下していると推察される。
【００１４】
ケッチェンブラック、アセチレンブラック等のカーボンブラックはその物性値および構造が多様であり、ＤＢＰ吸油量だけでなく様々な特性が電解液の吸液性に影響を与えているものと推察されるが詳細は不明である。つまり、カーボンブラックの様々な特性が最適化され、それを用いて作製した正極としての吸液性が確保されることでサイクル特性が向上するものと考えられる。現在のところ、サイクル特性の大きな向上が見られたのはケッチェンブラックのみであった。
【００１５】
このケッチェンブラックの特徴を以下に列挙する。
（１）外側に薄くグラファイト結晶が寄り集まったような中空シェル構造
（２）表面積（窒素吸着法） １０００ｍ2／ｇ
（３）ＤＢＰ吸油量 ３６０ｍｌ／１００ｇ
（４）ヨウ素吸着量 ９５０ｍｇ／ｇ
（５）揮発分 １％
（６）ＰＨ９．５
（７）多孔度 ６９．３％
（８）揮発分 ０．５％
（９）見かけ比重 １５０ｇ／ｌ
さらに、正極活物質１００重量部に対する導電材の添加量を、ケッチェンブラック単独の場合０．３〜１．２重量部とする。
【００１６】
ケッチェンブラックと鱗片状黒鉛の混合物を用いた場合には、ケッチェンブラックの添加量を０．２〜１．０重量部とし、かつ、ケッチェンブラックの添加量をｘ重量部、鱗片状黒鉛の添加量ｙ重量部とすると、３ｘ＋（３／８）ｙの値を１．０以上３．５以下とする。ケッチェンブラックとアセチレンブラックの混合物の場合、ケッチェンブラックを０．２〜１．０重量部とし、かつ、アセチレンブラックの添加量をｚ重量部とした時に、３ｘ＋ｚの値を１．１以上３．５以下とする。
【００１７】
これらは、真密度が５ｇ／ｃｍ3程度の正極活物質を用いたときに合剤中の正極活物質密度（以下、単に正極活物質密度とする）が３．０〜３．５ｇ／ｃｍ3程度となるように添加量を規制したものである。
【００１８】
また、ケッチェンブラックと混合する鱗片状黒鉛については天然黒鉛や人造黒鉛等を用いることが可能であり、粒径としては電子導電性の面から３〜１０μｍ程度のものが望ましい。
【００１９】
【実施例】
以下、本発明の実施例を図面を参照しながら説明する。
【００２０】
（参考例１）
図１に本参考例および実施例で用いた円筒形電池の縦断面図を示す。図において、１は耐有機電解液性のステンレス鋼板を加工した電池ケース、２は安全弁を設けた封口板、３は絶縁パッキングを示す。正極４および負極５がセパレータ６を介して複数回渦巻状に巻回されてケース１内に収納されている。そして上記正極からは正極リード７が引き出されて封口板２に接続され、負極からは負極リード８が引き出されて電池ケース１の底部に接続されている。９は絶縁リングで極板群４の上下部にそれぞれ設けられている。以下、正、負極板等について詳しく説明する。
【００２１】
正極はＬｉ2ＣＯ3とＣｏ3Ｏ4とを混合し、９００℃で１０時間焼成して合成したＬｉＣｏＯ2の粉末の重量に対して、ケッチェンブラック（ケッチェンブラックインターナショナル社製 ケッチェンブラックＥＣ）を０．２、０．３、０．５、０．８、１．０、１．２、１．５％混合し、これをフッ素樹脂系結着剤７％とカルボキシメチルセルロース水溶液に懸濁させてペースト状にした。このペーストを厚さ０．０３ｍｍのアルミ箔の両面に塗工し、乾燥後圧延して厚さ０．１８ｍｍ、幅５１ｍｍ、長さ４２０ｍｍの正極板とした。正極板は２５０℃で乾燥を行った。
【００２２】
負極はティムカル社製の人造黒鉛ＫＳ４４を用いた。このＫＳ４４の重量に対して、スチレン／ブタジエンゴム３％を混合した後、カルボキシメチルセルロース水溶液に懸濁させてペースト状にした。そしてこのペーストを厚さ０．０２ｍｍの銅箔の両面に塗工し、乾燥後圧延して、厚さ０．１８ｍｍ、幅５３ｍｍ、長さ４５０ｍｍの負極板とした。
【００２３】
そして、正極板にはアルミニウム製、負極板にはニッケル製のリードをそれぞれ取り付け、厚さ０．０２５ｍｍ、幅５９ｍｍ、長さ１２００ｍｍのポリプロピレン製セパレータを介して渦巻状に巻回し、直径１８．０ｍｍ、高さ６５ｍｍの電池ケースに納入した。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）とプロピオン酸メチル（ＭＰ）とを３０：５０：２０の体積比で混合した溶媒に１モル／リットルのＬｉＰＦ６を溶解したものを用い、これを注液した後封口し、参考の電池Ａとした。
【００２４】
（実施例１）
（参考例１）と同様にして合成したＬｉＣｏＯ２の粉末の重量に対して、ケッチェンブラックを０．１、０．２、０．３、０．５、０．８、１．０％、および鱗片状黒鉛（ティムカル社製ＫＳ１０）を０．５、１．０、２．０、３．０、４．０％混合し、これをフッ素樹脂系結着剤７％とカルボキシメチルセルロース水溶液に懸濁させてペースト状にした。このペーストを厚さ０．０３ｍｍのアルミ箔の両面に塗工し、乾燥後圧延して厚さ０．１８ｍｍ、幅５１ｍｍ、長さ４２０ｍｍの正極板とした以外は（参考例１）と同様の電池を構成し、これを本発明の電池Ｂとした。
【００２５】
（実施例２）
（参考例１）と同様にして合成したＬｉＣｏＯ２の粉末の重量に対して、ケッチェンブラックを０．１、０．２、０．３、０．５、０．８、１．０％、およびアセチレンブラック（電気化学工業社製）を０．３、０．５、１．０、１．５、２．０％混合し、これをフッ素樹脂系結着剤７％とカルボキシメチルセルロース水溶液に懸濁させてペースト状にした。このペーストを厚さ０．０３ｍｍのアルミ箔の両面に塗工し、乾燥後圧延して厚さ０．１８ｍｍ、幅５１ｍｍ、長さ４２０ｍｍの正極板とした以外は（参考例１）と同様の電池を構成し、これを本発明の電池Ｃとした。
【００２６】
（比較例）
（参考例１）と同様にして合成したＬｉＣｏＯ２の粉末の重量に対して、アセチレンブラックを３％混合し、これをフッ素樹脂系結着剤７％とカルボキシメチルセルロース水溶液に懸濁させてペースト状にした。このペーストを厚さ０．０３ｍｍのアルミ箔の両面に塗工し、乾燥後圧延して厚さ０．１８ｍｍ、幅５１ｍｍ、長さ４２０ｍｍの正極板とした以外は（参考例１）と同様の電池を構成し、これを比較の電池Ｄとした。
【００２７】
次に、参考の電池Ａおよび本発明の電池Ｂ、Ｃと比較の電池Ｄを各５セルずつ用意してインピーダンス（交流１ｋＨｚ）を測定後、充放電サイクル寿命試験を行った。充放電条件は２０℃において充電は充電電圧４．２Ｖ、制限電流８００ｍＡ、充電時間２時間の定電圧定電流充電を行い、放電は放電電流１２００ｍＡ、放電終止電圧３．０Ｖの定電流放電を行った。そして、それぞれ１０サイクル目の放電容量を初期容量とし、初期容量の半分の容量に低下した時点をサイクル寿命末期とした。正極活物質密度、初期容量、インピーダンス、サイクル数の結果を（表１）、（表２）、（表３）に示す。
【００２８】
【表１】
【表２】
【表３】
（表１）より、参考の電池Ａのサイクル特性は、比較の電池Ｄと比べて向上している。また、ケッチェンブラックの添加量としては０．３重量部から１．２重量部が望ましく、０．２重量部の場合には正極の集電性が低下し電池のインピーダンスが高くなり、１．５重量部の場合では、合剤中の正極活物質密度が低下し電池容量が１１５０ｍＡｈ以下となった。
【００３２】
（表２）より、本発明の電池Ｂのサイクル特性は、比較の電池Ｄと比べて向上している。また、ケッチェンブラックの添加量が０．１重量部の場合にはサイクル特性の大きな向上はなく、正極の集電性が低下し電池のインピーダンスが高くなり、ケッチェンブラックの添加量をｘ重量部、鱗片状黒鉛の添加量をｙ重量部とした時、３ｘ＋（３／８）ｙの値が１より小さい時には、電池のインピーダンスが高く、３．５より大きいときは正極活物質密度が低下し電池容量が１１５０ｍＡｈ以下となった。従って、ケッチェンブラックの添加量を０．２〜１．０重量部とし、かつ、ケッチェンブラックの添加量をｘ重量部、鱗片状黒鉛の添加量ｙ重量部とした時の３ｘ＋（３／８）ｙの値が１．０以上３．５以下とすると初期容量が高く、インピーダンスが低く、かつ、サイクル特性に優れた電池が得られた。
【００３３】
（表３）より、本発明の電池Ｃのサイクル特性は、比較の電池Ｄと比べて向上している。また、ケッチェンブラックの添加量が０．１重量部の場合にはサイクル特性の大きな向上はなく、正極の集電性が低下し電池のインピーダンスが高くなった。ケッチェンブラックの添加量をｘ重量部、アセチレンブラックの添加量をｚ重量部とした時、３ｘ＋ｚの値が１．１より小さい時には、電池のインピーダンスが高く、３．５より大きいときは正極活物質密度が低下し電池容量が１１５０ｍＡｈ以下となった。従って、ケッチェンブラックの添加量を０．２〜１．０重量部とし、かつ、ケッチェンブラックの添加量をｘ重量部、アセチレンブラックの添加量ｚ重量部とした時に３ｘ＋ｚの値が１．１以上３．５以下とした時に初期容量が高く、インピーダンスが低く、かつ、サイクル特性に優れた電池が得られる。
【００３４】
ケッチェンブラックと混合する鱗片状黒鉛について、天然黒鉛や人造黒鉛等を用いることが可能であり、粒径としては電子導電性の面から３〜１５μｍ程度のものが望ましいと考えられる。
【００３５】
また、本実施例では正極活物質としてＬｉＣｏＯ2について示したが、ＬｉＮｉＯ2やＬｉＭｎ2Ｏ4等のその他のリチウム含有遷移金属カルコゲン化合物を用いても同様の効果が得られることは明らかである。
【００３６】
【発明の効果】
以上のように本発明では、正極の導電材として、ケッチェンブラックと鱗片状黒鉛の混合物、または、ケッチェンブラックとアセチレンブラックの混合物をそれぞれ所定量、正極活物質に添加することによって、サイクル特性に優れ、かつ、サイクル寿命末期においても安全性の高い電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例および比較例における円筒形電池の縦断面図
【符号の説明】
１ 電池ケース
２ 封口板
３ 絶縁パッキング
４ 極板群
５ 正極リード
６ 負極リード
７ 絶縁リング[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductive material added to a positive electrode of a non-aqueous electrolyte secondary battery, in particular.
[0002]
[Prior art]
In recent years, electronic devices such as AV devices and personal computers are rapidly becoming portable and cordless, and there is a high demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. Among them, lithium secondary batteries using a negative electrode made of lithium metal as an active material are particularly expected as batteries having high voltage and high energy density, but are currently put into practical use from the viewpoint of safety and reliability. Absent.
[0003]
The reason for the decrease in safety is that the lithium metal negative electrode changes into a dendritic (dendritic) form due to repeated charge and discharge, which may cause an internal short circuit, and an exothermic reaction between the electrolyte and the dendritic lithium occurs. It is thought to be because.
[0004]
Therefore, a lithium ion secondary using a carbon material capable of reversibly intercalating and deintercalating lithium for the negative electrode and using a lithium-containing transition metal oxide such as LiCoO 2 , LiNiO 2 , LiMn 2 O 4 for the positive electrode Batteries have been proposed.
[0005]
In this lithium ion secondary battery, since lithium is intercalated in the carbon material of the negative electrode during charging, lithium does not precipitate on the negative electrode plate in principle, and the internal short circuit of the battery is suppressed. There is an advantage that it is excellent in safety and reliability.
[0006]
[Problems to be solved by the invention]
However, even in the case of a lithium ion secondary battery using a carbon material capable of reversibly intercalating and deintercalating lithium as the negative electrode, lithium deposition gradually occurs on the negative electrode plate as charging and discharging are repeated. Therefore, there is a problem that the safety and reliability of the battery decrease at the end of the cycle life.
[0007]
The present invention solves such problems, and prevents lithium from being deposited on the negative electrode plate at the end of the cycle life, thereby providing a battery with high charge / discharge cycle life characteristics, safety and reliability. With the goal.
[0008]
[Means for Solving the Problems]
The present invention, rechargeable positive electrode, comprising a negative electrode and the separator, and the nonaqueous electrolyte, wherein the positive electrode of electrically conductive material, a mixture of Ketjen black and flake graphite, or a mixture of Ketjen black and acetylene black the use, the amount of the conductive material for the positive electrode active material 100 parts by weight, and 0.2 to 1.0 parts by weight of ketjen black in the case of a mixture of Ke Tsu Chen black and flake graphite, and Ketjen If the addition amount of chain black is x parts by weight and the addition amount of scaly graphite is y parts by weight, the value of 3x + (3/8) y is 1.0 or more and 3.5 or less, and further, ketjen black and acetylene black In the case of a mixture, the amount of ketjen black is 0.2 to 1.0 part by weight, the amount of ketjen black added is x parts by weight, and the amount of acetylene black added is z parts by weight. The value of 3x + z is 1.1 or more and 3.5 or less, the DBP oil absorption of the ketjen black is 360 ml / 100 g or more, and the positive electrode active material is a lithium-containing transition metal chalcogen compound It is.
[0009]
It has been found that the decrease in battery capacity when the charge / discharge cycle is repeated is mostly due to the negative electrode, and lithium is deposited on the negative electrode plate.
[0010]
Furthermore, when the charging current is concentrated at the center portion of the electrode plate, lithium deposition on the negative electrode plate is likely to occur at the center portion in the width direction of the electrode plate, and lithium deposition is unlikely to occur at both end portions in the width direction. Therefore, ketjen black, which is excellent in absorbing the electrolyte solution, is used so that the electrolyte solution can be diffused uniformly on the electrode plate, and further, flaky graphite or acetylene black is added thereto. Further, the addition of these can improve the strength of the electrode plate.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Dibutyl phthalate oil absorption (DBP oil absorption) is used as an indicator of the physical properties of carbon black such as ketjen black. This DBP oil absorption is considered to correspond to the liquid absorption of the electrolytic solution. When carbon black having a high DBP oil absorption is used for the positive electrode as the conductive material, the liquid absorption of the electrolytic solution is improved, and electrolysis in the width direction of the electrode plate is achieved. It is considered that the diffusion of the liquid is secured and the cycle characteristics are improved. The DBP oil absorption is 360 ml / 100 g for ketjen black (EC), 500 ml / 100 g for ketjen black (EC600JD), and 120 ml / 100 g for acetylene black.
[0012]
In other words, ketjen black (EC) is considered to be excellent in cycle characteristics because it exhibits substantially the same liquid absorbency of the electrolytic solution in an amount of 1/3 with respect to acetylene black. Further, when the end-of-cycle-life battery was observed, the battery using Ketjen Black had no clogging of the separator at both end portions in the width direction of the electrode plate, and no lithium deposition was observed at the center portion.
[0013]
However, even when the amount of acetylene black added is increased to improve the liquid absorption, the cycle characteristics as improved as ketjen black were not obtained. In the case of acetylene black, it is presumed that in the kneading step at the time of preparing the positive electrode material mixture, the chain-like higher-order structure is destroyed by mechanical stress, so that the liquid absorbency is lowered.
[0014]
Carbon blacks such as ketjen black and acetylene black have various physical properties and structures, and it is speculated that not only the DBP oil absorption but also various characteristics affect the liquid absorption of the electrolyte. Is unknown. That is, it is considered that the cycle characteristics are improved by optimizing various characteristics of the carbon black and ensuring the liquid absorption as the positive electrode produced using the carbon black. At present, the only significant improvement in cycle characteristics has been seen with Ketjen Black.
[0015]
The characteristics of this ketjen black are listed below.
(1) Hollow shell structure with thin graphite crystals gathered outside (2) Surface area (nitrogen adsorption method) 1000 m 2 / g
(3) DBP oil absorption 360ml / 100g
(4) Iodine adsorption amount 950 mg / g
(5) Volatile content 1%
(6) PH9.5
(7) Porosity 69.3%
(8) Volatile content 0.5%
(9) Apparent specific gravity 150g / l
Furthermore, the addition amount of the conductive material with respect to 100 parts by weight of the positive electrode active material is 0.3 to 1.2 parts by weight in the case of ketjen black alone.
[0016]
When a mixture of ketjen black and flaky graphite is used, the amount of ketjen black added is 0.2 to 1.0 part by weight, the amount of ketjen black added is x parts by weight, and flaky graphite is added. When the added amount is y parts by weight, the value of 3x + (3/8) y is set to 1.0 or more and 3.5 or less. In the case of a mixture of ketjen black and acetylene black, when the ketjen black is 0.2 to 1.0 part by weight and the addition amount of acetylene black is z part by weight, the value of 3x + z is 1.1 or more and 3 .5 or less.
[0017]
These materials have a positive electrode active material density (hereinafter simply referred to as positive electrode active material density) of 3.0 to 3.5 g / cm 3 in the mixture when a positive electrode active material having a true density of about 5 g / cm 3 is used. The amount of addition is regulated so as to be about.
[0018]
In addition, as the flaky graphite mixed with ketjen black, natural graphite or artificial graphite can be used, and the particle size is preferably about 3 to 10 μm from the viewpoint of electronic conductivity.
[0019]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0020]
( Reference Example 1)
FIG. 1 is a longitudinal sectional view of a cylindrical battery used in the present reference example and examples. In the figure, 1 is a battery case obtained by processing a stainless steel plate resistant to organic electrolyte, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. The positive electrode 4 and the
[0021]
The positive electrode was mixed with Li 2 CO 3 and Co 3 O 4 and baked at 900 ° C. for 10 hours to synthesize the weight of LiCoO 2 powder. ) 0.2, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5%, and this is suspended in a fluororesin binder 7% and a carboxymethylcellulose aqueous solution. To make a paste. This paste was applied to both sides of a 0.03 mm thick aluminum foil, dried and rolled to obtain a positive electrode plate having a thickness of 0.18 mm, a width of 51 mm, and a length of 420 mm. The positive electrode plate was dried at 250 ° C.
[0022]
Artificial graphite KS44 manufactured by Timcal Co. was used for the negative electrode. After mixing 3% of styrene / butadiene rubber with respect to the weight of KS44, it was suspended in an aqueous carboxymethylcellulose solution to make a paste. This paste was applied to both sides of a 0.02 mm thick copper foil, dried and rolled to obtain a negative electrode plate having a thickness of 0.18 mm, a width of 53 mm, and a length of 450 mm.
[0023]
A lead made of aluminum is attached to the positive electrode plate and a nickel lead is attached to the negative electrode plate, respectively, wound in a spiral shape through a polypropylene separator having a thickness of 0.025 mm, a width of 59 mm, and a length of 1200 mm, and a diameter of 18.0 mm. Supplied to a battery case with a height of 65 mm. As the electrolytic solution, a solution obtained by dissolving 1 mol / liter of LiPF 6 in a solvent in which ethylene carbonate (EC), diethyl carbonate (DEC), and methyl propionate (MP) are mixed at a volume ratio of 30:50:20 is used. Then, after pouring this, it was sealed and used as a reference battery A.
[0024]
(Example 1 )
Ketjen Black is 0.1, 0.2, 0.3, 0.5, 0.8, 1.0% with respect to the weight of the LiCoO 2 powder synthesized in the same manner as in ( Reference Example 1). In addition, 0.5, 1.0, 2.0, 3.0, and 4.0% of flaky graphite (KS10 manufactured by Timcal Corporation) were mixed and suspended in a fluororesin binder 7% and a carboxymethylcellulose aqueous solution. It was made turbid and pasty. Coating the paste on both sides of an aluminum foil having a thickness of 0.03 mm, dried rolled to a thickness of 0.18 mm, width 51 mm, except that the positive electrode plate of length 420mm is similar to (Reference Example 1) A battery was constructed and designated as battery B of the present invention.
[0025]
(Example 2 )
Ketjen Black is 0.1, 0.2, 0.3, 0.5, 0.8, 1.0% with respect to the weight of the LiCoO 2 powder synthesized in the same manner as in ( Reference Example 1). And 0.3%, 0.5, 1.0, 1.5, and 2.0% of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) are mixed in 7% of a fluororesin binder and an aqueous carboxymethylcellulose solution. It was made turbid and pasty. Coating the paste on both sides of an aluminum foil having a thickness of 0.03 mm, dried rolled to a thickness of 0.18 mm, width 51 mm, except that the positive electrode plate of length 420mm is similar to (Reference Example 1) A battery was constructed, and this was designated as a battery C of the present invention.
[0026]
(Comparative example)
3% of acetylene black is mixed with respect to the weight of the LiCoO 2 powder synthesized in the same manner as in ( Reference Example 1), and this is suspended in 7% of a fluororesin binder and an aqueous carboxymethyl cellulose solution to form a paste. I made it. Coating the paste on both sides of an aluminum foil having a thickness of 0.03 mm, dried rolled to a thickness of 0.18 mm, width 51 mm, except that the positive electrode plate of length 420mm is similar to (Reference Example 1) A battery was constructed, and this was designated as comparative battery D.
[0027]
Next, the reference battery A, the batteries B and C of the present invention , and the comparative battery D were prepared for each five cells, the impedance (AC 1 kHz) was measured, and then a charge / discharge cycle life test was performed. Charging and discharging conditions are 20 ° C., charging is a charging voltage of 4.2 V, a limiting current of 800 mA, a constant voltage and a constant current charging of 2 hours, and a discharging is a discharging current of 1200 mA and a discharging current of 3.0 V. It was. The discharge capacity at the 10th cycle was set as the initial capacity, and the time when the discharge capacity decreased to half the initial capacity was defined as the end of the cycle life. The results of the positive electrode active material density, initial capacity, impedance, and cycle number are shown in (Table 1), (Table 2), and (Table 3).
[0028]
[Table 1]
[Table 2]
[Table 3]
From (Table 1), the cycle characteristics of the reference battery A are improved as compared with the comparative battery D. Further, the addition amount of ketjen black is preferably 0.3 to 1.2 parts by weight, and when 0.2 part by weight, the current collecting property of the positive electrode is lowered and the impedance of the battery is increased. In the case of 5 parts by weight, the density of the positive electrode active material in the mixture decreased and the battery capacity became 1150 mAh or less.
[0032]
From Table 2, the cycle characteristics of the battery B of the present invention are improved as compared with the comparative battery D. In addition, when the amount of ketjen black added is 0.1 parts by weight, there is no significant improvement in cycle characteristics, and the current collecting performance of the positive electrode is lowered, the battery impedance is increased, and the amount of ketjen black added is x weight. When the added amount of graphite and flaky graphite is y parts by weight, the impedance of the battery is high when the value of 3x + (3/8) y is smaller than 1, and the density of the positive electrode active material decreases when the value is larger than 3.5. The battery capacity was 1150 mAh or less. Therefore, the amount of ketjen black added is 0.2 to 1.0 parts by weight, the amount of ketjen black added is x parts by weight, and the amount of flaky graphite added is y parts by weight. 8) When the value of y was 1.0 or more and 3.5 or less, a battery having high initial capacity, low impedance, and excellent cycle characteristics was obtained.
[0033]
From Table 3, the cycle characteristics of the battery C of the present invention are improved as compared with the comparative battery D. In addition, when the amount of ketjen black added was 0.1 parts by weight, there was no significant improvement in cycle characteristics, and the current collecting property of the positive electrode was lowered and the battery impedance was increased. When the addition amount of ketjen black is x parts by weight and the addition amount of acetylene black is z parts by weight, the impedance of the battery is high when the value of 3x + z is smaller than 1.1, and the positive electrode active when it is larger than 3.5. The material density decreased and the battery capacity became 1150 mAh or less. Therefore, when the addition amount of ketjen black is 0.2 to 1.0 part by weight, the addition amount of ketjen black is x parts by weight, and the addition amount z of acetylene black is z parts by weight, the value of 3x + z is 1. When it is 1 or more and 3.5 or less, a battery having a high initial capacity, a low impedance, and excellent cycle characteristics can be obtained.
[0034]
As the flaky graphite mixed with ketjen black, it is possible to use natural graphite, artificial graphite or the like, and the particle size is considered to be preferably about 3 to 15 μm from the viewpoint of electronic conductivity.
[0035]
In this example, LiCoO 2 was shown as the positive electrode active material. However, it is clear that the same effect can be obtained even when other lithium-containing transition metal chalcogen compounds such as LiNiO 2 and LiMn 2 O 4 are used.
[0036]
【The invention's effect】
In the present invention, as described above, as the conductive material of the positive electrode, a mixture of Ketjen black and flake graphite, or a mixture of each predetermined amount of ketjen black and acetylene black, by adding the positive electrode active material, the cycle characteristics In addition, it is possible to provide a battery having excellent safety and high safety even at the end of the cycle life.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a cylindrical battery in Examples and Comparative Examples of the present invention.
1
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP05466798A JP4507284B2 (en) | 1997-03-11 | 1998-03-06 | Non-aqueous electrolyte secondary battery |
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| JP5583097 | 1997-03-11 | ||
| JP9-55830 | 1997-03-11 | ||
| JP05466798A JP4507284B2 (en) | 1997-03-11 | 1998-03-06 | Non-aqueous electrolyte secondary battery |
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| JP4507284B2 true JP4507284B2 (en) | 2010-07-21 |
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| JP4595145B2 (en) * | 1999-10-27 | 2010-12-08 | ソニー株式会社 | Non-aqueous electrolyte battery |
| KR20010046245A (en) * | 1999-11-11 | 2001-06-05 | 김순택 | Active material composition for lithium secondary battery and lithium secondary battery manufactured using the same |
| JP2001216970A (en) * | 2000-02-04 | 2001-08-10 | Sony Corp | Nonaqueous electrolyte battery |
| JP2002083588A (en) * | 2000-09-08 | 2002-03-22 | Matsushita Electric Ind Co Ltd | Manufacturing method of positive electrode mixture for lithium ion secondary battery |
| JP4839517B2 (en) * | 2001-02-28 | 2011-12-21 | 新神戸電機株式会社 | Nonaqueous electrolyte secondary battery |
| US8709648B2 (en) | 2002-06-04 | 2014-04-29 | Ener1, Inc. | Conductor-mixed active electrode material, electrode structure, rechargeable battery, and manufacturing method of conductor-mixed active electrode material |
| JP2006164689A (en) * | 2004-12-06 | 2006-06-22 | Enerstruct Kk | Electrode structure, secondary battery, and capacitor |
| CN100416897C (en) * | 2005-01-17 | 2008-09-03 | 比亚迪股份有限公司 | Negative electrode of lithium ion secondary cell and lithium ion secondary cell comprising the same |
| JP4826877B2 (en) * | 2005-01-25 | 2011-11-30 | 三菱化学株式会社 | Electrode for electrochemical device and lithium secondary battery using the same |
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| JP5574404B2 (en) * | 2009-07-16 | 2014-08-20 | Ｎｅｃエナジーデバイス株式会社 | Lithium ion secondary battery |
| EP2549569A4 (en) * | 2010-03-18 | 2014-08-06 | Nec Energy Devices Ltd | Lithium ion secondary battery |
| JP2015103332A (en) * | 2013-11-22 | 2015-06-04 | トヨタ自動車株式会社 | Nonaqueous electrolyte secondary battery |
| JP6260834B2 (en) * | 2015-06-22 | 2018-01-17 | トヨタ自動車株式会社 | Non-aqueous electrolyte secondary battery |
| JP2017073334A (en) * | 2015-10-09 | 2017-04-13 | 日立マクセル株式会社 | Nonaqueous electrolyte battery |
| KR102414805B1 (en) | 2016-07-13 | 2022-06-29 | 주식회사 발카 | Perfluoroelastomer composition and sealing material |
| US10910632B2 (en) | 2016-11-22 | 2021-02-02 | Nissan Motor Co., Ltd. | Negative electrode for electric device and electric device using the same |
| JP6952784B2 (en) | 2017-09-14 | 2021-10-20 | 株式会社東芝 | Electrodes and non-aqueous electrolyte batteries |
| JP2019160517A (en) * | 2018-03-12 | 2019-09-19 | Tdk株式会社 | Positive electrode for lithium ion secondary battery, and lithium ion secondary battery |
| KR20210097528A (en) * | 2020-01-30 | 2021-08-09 | 주식회사 엘지화학 | Method for preparing positive electrode active material for lithium secondary battery and positive electrode active material prepared thereby |
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