JP2004134369A - Lithium secondary battery and electric automobile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery having a long service life with suppressed reduction in maintaining rate for capacity or output associated with charge/discharge cycles. <P>SOLUTION: This cylindrical lithium ion battery uses a positive electrode made of a lithium manganate powder having a layered rock-salt type crystal structure, and a negative electrode made of a graphite powder having a specific surface area of 2.4m<SP>2</SP>/g. A negative electrode binder is prepared by mixing a thermosetting polyvinylalcohol-based resin with an acrylic resin-based plasticizer, and mixed into a negative electrode mixture in an amount of 5.8volume%. Separation or dropping-off of the negative electrode mixture associated with charge/discharge of the cylindrical lithium ion battery is thereby prevented. <P>COPYRIGHT: (C)2004,JPO

Description

【００３４】
（実施例２〜６）
表１に示すように、実施例２〜実施例６では、黒鉛の比表面積及びＰＶＡの含有量を種々変更した以外は実施例１と同様にした。実施例２では、黒鉛の比表面積を３．９ｍ^２／ｇ、バインダ含有量を４．１％とし、実施例３では、黒鉛の比表面積を２．４ｍ^２／ｇ、バインダ含有量を５．８％とし、実施例４では、黒鉛の比表面積を６．４ｍ^２／ｇ、バインダ含有量を５．８％とし、実施例５では、黒鉛の比表面積を２．３ｍ^２／ｇ、バインダ含有量を９．０％とし、実施例６では、黒鉛の比表面積を３．１ｍ^２／ｇ、バインダ含有量を１１．３％とした。
【００３５】
（実施例７）
表１に示すように、実施例７では、正極活物質にスピネル結晶構造を有するマンガン酸リチウム（ＬｉＭｎ_２Ｏ_４）粉末を用い、負極活物質に比表面積が２．６ｍ^２／ｇの黒鉛粉末を用い、負極バインダにＰＶＡを用いた。バインダ含有量を５．８％とした。
【００３６】
（実施例８）
表１に示すように、実施例８では、正極活物質に層状岩塩型結晶構造を有するマンガン酸リチウム（ＬｉＭｎＯ_２）粉末を用い、負極活物質に比表面積が２．４ｍ^２／ｇの黒鉛粉末を用い、負極バインダにＰＶＡを用いた。バインダ含有量を５．８％とした。
【００３７】
（実施例９〜１３）
実施例９〜実施例１３では、実施例２、実施例３、実施例５、実施例７及び実施例８の円筒型リチウムイオン電池２０をそれぞれ７２本直列に接続してゴルフカート３０に搭載した。
【００３８】
（比較例１）
表１に示すように、比較例１では、負極バインダにＰＶＤＦを用いた以外は、実施例３と同様にして円筒型リチウムイオン電池を作製した。
【００３９】
（比較例２）
表１に示すように、比較例２では、正極活物質にスピネル結晶構造を有するマンガン酸リチウム（ＬｉＭｎ_２Ｏ_４）粉末を用い、負極バインダにＰＶＤＦを用いた以外は、実施例３と同様にして円筒型リチウムイオン電池を作製した。
【００４０】
（比較例３）
表１に示すように、比較例３では、正極活物質に層状岩塩型結晶構造を有するマンガン酸リチウム（ＬｉＭｎＯ_２）粉末を用い、負極バインダにＰＶＤＦを用いた以外は、実施例３と同様にして円筒型リチウムイオン電池を作製した。
【００４１】
（比較例４〜６）
比較例４〜比較例６では、比較例１〜比較例３で作製した円筒型リチウムイオン電池をそれぞれ７２本直列に接続してゴルフカートに搭載した。
【００４２】
＜試験・評価＞
次に、以上のようにして作製した実施例及び比較例の各電池及びゴルフカートについて、以下の一連の試験を行った。
【００４３】
実施例及び比較例の各電池を充電した後放電し、環境温度２５±２°Ｃの雰囲気において、放電容量を測定した。充電条件は、４．１Ｖ定電圧、制限電流５Ａ、２．５時間とし、放電条件は、１Ａ定電流、終止電圧２．７Ｖとした。初期及び後述するパルスサイクル試験後の放電容量を測定し、初期の放電容量に対するパルスサイクル試験後の放電容量の割合を百分率で求め、容量維持率とした。
【００４４】
また、各電池を上述した充電条件で充電（満充電状態）した後、環境温度２５±２°Ｃの雰囲気において、出力を測定した。測定条件は、１０Ａ、３０Ａ、９０Ａの電流値で各１０秒間放電し、横軸電流値に対して、各５秒目の電池電圧値を縦軸にプロットし、３点を直線近似した直線が終止電圧である２．７Ｖと交差する点の電流値を読み取り、この電流値と２．７Ｖとの積をその電池の出力とした。初期及びパルスサイクル試験後の出力を測定し、初期の出力に対するパルスサイクル試験後の出力の割合を百分率で求め、出力維持率とした。
【００４５】
各電池のパルスサイクル試験は、５０±３°Ｃの雰囲気において各電池に約５０Ａの高負荷電流を充電方向及び放電方向ともに約５秒間通電し、休止時間も含め１サイクル約３０秒のパルスサイクル試験を連続して１０万回繰り返した。
【００４６】
ゴルフカートの試験では、満充電状態の電池を搭載して定速走行を開始し、ゴルフカートが定速を維持することができなくなるまでの連続走行距離を測定した。また、満充電状態の電池を搭載して発進し、ゴルフカートが所定速度に達するまでの所要時間を測定し、加速時間とした。電池をゴルフカートからはずし、上述したパルスサイクル試験を行った後、再びゴルフカートに搭載して連続走行距離及び加速時間を同様に測定した。初期の連続走行距離及び加速時間に対するパルスサイクル試験後の連続走行距離及び加速時間の割合を百分率で求め、連続走行距離維持率及び加速時間変化率とした。
【００４７】
各電池の試験結果を下表２に、ゴルフカートの試験結果を下表３にそれぞれ示す。
【００４８】
【表２】

【００４９】
表２に示すように、正極活物質にコバルト酸リチウムを用い、負極バインダにＰＶＡを用いた実施例１〜実施例６の各電池では、容量維持率が８４％以上、出力維持率も９０％以上を示した。また、正極活物質にスピネル結晶構造を有するマンガン酸リチウムを用い、負極バインダにＰＶＡを用いた実施例７の電池では、初期放電容量、初期出力、容量維持率及び出力維持率がいずれも高い結果を示した。更に、正極活物質に層状岩塩型結晶構造を有するマンガン酸リチウムを用い、負極バインダにＰＶＡを用いた実施例８の電池では、初期放電容量、初期出力及び容量維持率、出力維持率がいずれにおいても優れた値を示した。これに対して、負極バインダにＰＶＤＦを用いた比較例１〜比較例３の各電池では、容量維持率及び出力維持率がともに７０％以下となり、十分な性能を得ることができなかった。従って、実施例１〜実施例８の各電池は、長寿命の電池である。
【００５０】
また、バインダ含有量が体積比４％未満の実施例１の電池では、容量維持率、出力維持率は良好なものの、初期放電容量が３．３８Ａｈと若干低い値となった。また、バインダ含有量が体積比９％より大きい実施例６の電池では、初期出力が８９０Ｗと若干低い結果となった。従って、ＰＶＡの含有量は負極合剤中の体積比４％〜９％の範囲とすることが好ましいことが分かった。
【００５１】
更に、黒鉛の比表面積が４ｍ^２／ｇより大きい実施例４の電池では、初期放電容量が３．３２Ａｈと若干低い値を示した。従って、黒鉛の比表面積は４ｍ^２／ｇ以下とすることが好ましいことが分かった。
【００５２】
【表３】

【００５３】
表３に示すように、実施例２、実施例３、実施例５、実施例７及び実施例８の電池をそれぞれ搭載した実施例９〜実施例１３のゴルフカート３０は、比較例１、比較例２及び比較例３の電池をそれぞれ搭載した比較例４、比較例５及び比較例６のゴルフカートに比べて、連続走行距離維持率及び加速時間変化率共に高い値を示した。仮想的な充電、走行の繰り返しに相当するパルスサイクル試験後においても連続走行距離及び加速時間の低下が極めて低く抑えられ、高性能なゴルフカートとなった。また、表２及び表３から、電池の容量維持率とゴルフカートの連続走行距離維持率、電池の出力維持率とゴルフカートの加速時間変化率は、それぞれ相関があることが判明した。
【００５４】
本実施形態の円筒型リチウムイオン電池２０は、負極のバインダにＰＶＡを用いることで、負極活物質の黒鉛表面がＰＶＡで適切に被覆されるので、ガス化などの副反応を発生する反応点が減少して初期の放電容量を向上させることができる。また、充放電による黒鉛の膨張・収縮に対して抵抗力が増加されるため、負極合剤の剥離・脱落（崩壊）が抑制されるので、容量及び出力の低下を抑制し長寿命の電池を得ることができる。また、ＰＶＡの含有量が負極合剤の体積比４％未満では黒鉛表面の被覆が不十分なため副反応が生じて容量が減少し、反対に体積比９％を超えると抵抗成分が増大するため出力が低下する。このため、ＰＶＡの含有量は負極合剤の体積比で４％〜９％の範囲が好ましい。更に、負極活物質である黒鉛の比表面積が４ｍ^２／ｇを超えると副反応が発生しやすくなるため初期放電容量が低下する。このため、黒鉛の比表面積は４ｍ^２／ｇ以下とすることが好ましい。
【００５５】
また、正極活物質にスピネル結晶構造を有するマンガン酸リチウム（ＬｉＭｎ_２Ｏ_４）を用いた場合、スピネル結晶構造を有するマンガン酸リチウムは充電によって収縮する特性があり、充電時には、負極に捲回圧がかからなくなり、特に高温では負極合剤の剥離・脱落が起こりやすくなる。従来使用されているＰＶＤＦを負極バインダに用いたときは、負極合剤の剥離・脱落が起こり易いため、高温サイクル、高温保存時の容量の低下、出力の低下ともに大きい。負極バインダにＰＶＡを用いたときは、負極合剤の剥離・脱落が抑制されるので、正極活物質に収縮性の大きなスピネル結晶構造を有するマンガン酸リチウムを用いても、長寿命の電池を得ることができる。又は、正極活物質に層状結晶構造を有するマンガン酸リチウム（ＬｉＭｎＯ_２）を用いた場合、層状結晶構造を有するマンガン酸リチウムは、充電によりリチウムイオンを放出すると酸素間斥力のために層間距離が拡大する特性があり、負極にかかる捲回圧が増大する。このため、充電時には、負極合剤の剥離・脱落が抑制されると共に、負極バインダにＰＶＡを用いることにより負極合剤が確実に保持されるので、容量、出力ともに維持することができ長寿命の電池を得ることができる。これらの電池を搭載したゴルフカート３０は、充電、走行を繰り返しても連続走行距離、加速時間の低下が少なく、高性能なゴルフカートとすることができる。
【００５６】
なお、本実施形態では、円筒型リチウムイオン電池２０について例示したが、本発明は電池の形状については限定されず、角形、その他の多角形の電池にも適用可能である。また、本発明の適用可能な構造としては、上述した電池容器に電池蓋がカシメによって封口されている構造の電池以外であっても構わない。このような構造の一例として正負極外部端子が電池蓋を貫通し、電池容器内で軸芯を介して正負外部端子が押し合っている状態の電池を挙げることができる。更に本発明は、正極及び負極を捲回式の構造とせず、積層式の構造としたリチウム二次電池にも適用可能である。
【００５７】
また、本実施形態では、正極活物質にコバルト酸リチウム（ＬｉＣｏＯ_２）、スピネル結晶構造を有するマンガン酸リチウム（ＬｉＭｎ_２Ｏ_４）、層状岩塩型結晶構造を有するマンガン酸リチウム（ＬｉＭｎＯ_２）を用いた例を示したが、本発明のリチウム二次電池用正極活物質としては、リチウムイオンを挿入・脱離可能な材料であり、予め十分な量のリチウムイオンを挿入したリチウム遷移金属複酸化物であればよい。例えば、リチウムマンガン複酸化物、リチウムコバルト複酸化物、リチウムニッケル複酸化物等でも同様の効果が得られる。さらにこれらのリチウム遷移金属複酸化物結晶中の遷移金属やリチウムの一部をそれら以外の元素、例えば、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｒ、Ａ１、Ｍｇ、等の元素で置換あるいはドープした材料や結晶中の酸素の一部をＳ、Ｐ等の元素で置換あるいはドープした材料を使用するようにしてもよい。更には、電池電圧として５Ｖ級が可能なリチウムマンガン複酸化物を用いても、本発明の効果には変わりない。
【００５８】
更に、本実施形態では、負極活物質に黒鉛を用いた例を示したが、本発明はこれに限定されるものではなく、黒鉛質炭素であればよい。ここでいう黒鉛質炭素は、必ずしも高結晶性の黒鉛を示すのではなく、メソフェーズ系黒鉛のような、Ｘ線回折による層間距離ｄ_００２が０．３３５４ｎｍを超える黒鉛でもよい。Ｘ線回折で、ｈｋｌ指数付けが可能な回折線が現れるものでもよい。また、粒子形状においても、鱗片状、球状、繊維状、塊状等、特に制限されるものではない。
【００５９】
また更に、本実施形態では、エチレンカーボネート、ジメチルカーボネート、ジエチルカーボネートを体積比１：１：１で混合した混合溶媒にＬｉＰＦ_６を溶解した非水電解液を例示したが、一般的なリチウム塩を電解質とし、これを有機溶媒に溶解した非水電解液を用いてもよく、本発明は用いられるリチウム塩や有機溶媒には特に制限されない。例えば、電解質としては、ＬｉＣｌＯ_４、ＬｉＡｓＦ_６、ＬｉＢＦ_４、ＬｉＢ（Ｃ_６Ｈ_５）_４、ＣＨ_３ＳＯ_３Ｌｉ、ＣＦ_３ＳＯ_３Ｌｉ等やこれらの混合物を用いることができる。また、有機溶媒としては、プロピレンカーボネート、１，２−ジメトキシエタン、１，２−ジエトキシエタン、γ−ブチロラクトン、テトラヒドロフラン、１，３−ジオキソラン、４−メチル−１，３−ジオキソラン、ジエチルエーテル、スルホラン、メチルスルホラン、アセトニトリル、プロピオニトリル等、又はこれらの２種類以上を混合した混合溶媒を用いることができ、更に、混合配合比についても限定されるものではない。このような非水電解液を用いることにより電池容量の向上や寒冷地での使用にも適合させることが可能となる。更に、固体電解質を用いてもよい。
【００６０】
更にまた、上記実施形態では、円筒型リチウムイオン電池２０のみを動力源としたゴルフカート３０を例示したが、本発明はこれに限定されることはなく、内燃機関エンジンと併用するようにしてもよい。また、電気自動車に搭載する電池の本数は、所望の出力、容量により適宜組み合わせればよく、電池の設置場所についても特に制限されない。
【００６１】
そして、本実施形態では、正極、負極集電体に金属箔（アルミニウム箔、銅箔）を用いた例を示したが、本発明はこれに限定されるものではなく、メッシュ状の金属集電体を用いてもよい。
【００６２】
【発明の効果】
以上説明したように、本発明によれば、負極のバインダに熱硬化性を有し可塑化されたポリビニルアルコール系樹脂を用いることで、黒鉛質炭素の膨張・収縮に対する抵抗力が増加して負極合剤の剥離・脱落が抑制されるので、得られるリチウム二次電池の容量維持率、出力維持率の低下を抑制することができると共に、熱硬化性を有し可塑化されたポリビニルアルコール系樹脂により黒鉛質炭素の表面が適切に被覆され、初充電時に電解液又は固体電解質の液成分の分解による黒鉛質炭素の表面でのガス化などの副反応の発生が抑制されるので、リチウム二次電池の電池容量の初期低下を防止することができる、という効果を得ることができる。
【図面の簡単な説明】
【図１】本発明が適用可能な実施形態のゴルフカートを模式的に示す側面図である。
【図２】本発明が適用可能な実施形態の円筒型リチウムイオン電池の断面図である。
【符号の説明】
６　捲回群（電極群）
２０　円筒型リチウムイオン電池（リチウム二次電池）
３０　ゴルフカート（電気自動車）
３５　前部座席
３６　電池箱[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium secondary battery and an electric vehicle, and in particular, includes a negative electrode in which a negative electrode mixture containing graphitic carbon and a binder is substantially evenly applied to both surfaces of a metal current collector, and a positive electrode. The present invention relates to a lithium secondary battery and an electric vehicle using the lithium secondary battery as a power source for power.
[0002]
[Prior art]
Lithium secondary batteries are mainly used as power supplies for portable devices such as VTR cameras, notebook computers, and mobile phones, taking advantage of their high energy density. The internal structure of this battery is usually of a wound type as shown below. The electrode is a belt-shaped electrode in which the active material is coated on the metal foil with a binder (binder) for both the positive electrode and the negative electrode. The cross section is spirally wound so that the positive and negative electrodes do not come into direct contact with each other across the separator. Form a group. The wound group is housed in a cylindrical battery can serving as a battery container, and is sealed after the electrolyte is injected.
[0003]
A general cylindrical lithium secondary battery has a size of 18650, a diameter of 18 mm and a height of 65 mm, and is widely used as a small consumer lithium ion battery. As the positive electrode active material of the 18650 type lithium secondary battery, lithium cobalt oxide having high capacity and long life is mainly used. The battery capacity is approximately 1.3 Ah to 1.7 Ah, and the output is about 10 W. It is.
[0004]
On the other hand, in the automotive industry, in order to cope with environmental problems, an electric vehicle (EV) having no exhaust gas and a power source entirely using only batteries, and a hybrid (power source using both an internal combustion engine and a battery) ( The development of electric vehicles has been accelerated and some of them have been put into practical use. In order to use a lithium secondary battery as a power source of such an electric vehicle, not only high capacity but also high output which affects acceleration performance and the like, that is, reduction in internal resistance of the battery is required. In addition, it is required to extend the life of the battery in order to cope with a long use period of the electric vehicle. To extend the life here means to suppress not only a decrease in the battery capacity but also a decrease in output, and to satisfy the electric energy supply capacity necessary for running an electric vehicle for a long period of time.
[0005]
However, in the lithium secondary battery, the active material of the positive and negative electrodes repeatedly expands and contracts with the charge / discharge cycle, so that the active material is separated and dropped from the current collector. In addition, since the pressure (winding pressure) applied between the positive and negative electrodes changes due to expansion and contraction of the active material, the active material tends to peel off and fall off particularly in a high-temperature environment, and the capacity and output decrease. is there. A technique has been disclosed for securing the binding property of the positive and negative electrode mixture to the current collector by limiting the weight average molecular weight of polyvinylidene fluoride used as a binder in order to suppress peeling and falling off of the active material. (For example, see Patent Document 1).
[0006]
[Patent Document 1]
JP-A-2002-270182
[Problems to be solved by the invention]
However, in the technique of Patent Document 1 described above, since polyvinylidene fluoride used as a binder has thermoplasticity, it softens at a high temperature of 50 ° C. or higher. For this reason, in a charge / discharge cycle in a high-temperature environment, particularly an environment reaching about 50 ° C. such as an engine room such as an EV, it is possible to sufficiently secure the binding property between the positive and negative electrode mixture and the current collector. Absent. Accordingly, if a long-life lithium secondary battery capable of preventing the positive / negative electrode mixture from peeling and falling off and suppressing the reduction in capacity and output even in a charge / discharge cycle under a high-temperature environment is obtained, the spread of EV and the like is accelerated. Can be expected.
[0008]
The present invention has been made in view of the above circumstances, and provides a long-life lithium secondary battery capable of suppressing a decrease in the capacity and output maintenance rate due to a charge / discharge cycle, and an electric vehicle using the lithium secondary battery as a power supply. That is the task.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, a first aspect of the present invention is a negative electrode in which a negative electrode mixture containing graphitic carbon and a binder is substantially evenly applied to both surfaces of a metal current collector, Wherein the binder is a thermosetting and plasticized polyvinyl alcohol-based resin.
[0010]
If the expansion and contraction of the graphitic carbon, which is the negative electrode active material, is repeated with the occlusion and release of lithium ions by the charge and discharge cycle, the negative electrode mixture peels and falls off, causing a reduction in capacity and output, especially in the engine room. In a high-temperature environment of about 50 ° C. as shown in FIG. In this embodiment, by using a thermosetting and plasticized polyvinyl alcohol-based resin for the binder of the negative electrode, the resistance to expansion and contraction of the graphitic carbon is increased, and the peeling and falling off of the negative electrode mixture is suppressed. Therefore, it is possible to suppress a decrease in the capacity maintenance rate and output maintenance rate of the obtained lithium secondary battery, and to make the surface of the graphitic carbon appropriate by a plasticized polyvinyl alcohol-based resin having thermosetting properties. To prevent the occurrence of side reactions such as gasification on the surface of the graphitic carbon due to the decomposition of the electrolyte component or the liquid component of the solid electrolyte at the time of the first charge, thereby preventing the initial decrease in the battery capacity of the lithium secondary battery. Can be prevented.
[0011]
In this case, when the content of the thermosetting and plasticized polyvinyl alcohol-based resin is less than 4% by volume of the negative electrode mixture, the side surface reaction occurs due to insufficient coating on the surface of the graphitic carbon, and the capacity is reduced. When the content of the plasticized polyvinyl alcohol-based resin having a thermosetting property exceeds 9% by volume of the negative electrode mixture, the resistance component increases and the output decreases, so that the content of the polyvinyl alcohol-based resin is reduced. Is preferably 4 to 9% by volume of the negative electrode mixture. Further, if the specific surface area of the graphitic carbon as the negative electrode active material exceeds 4 m ² / g, a side reaction is likely to occur and the initial capacity decreases, so the specific surface area of the graphitic carbon is set to 4 m ² / g or less. Is preferred.
[0012]
Further, when a lithium transition metal double oxide is used as the positive electrode active material, the winding pressure or lamination pressure applied to the negative electrode changes with expansion and contraction of the lithium transition metal double oxide due to charge and discharge, and particularly at high temperatures. The negative electrode mixture is easily peeled and dropped. By using a thermosetting and plasticized polyvinyl alcohol-based resin for the binder of the negative electrode, peeling and falling off of the negative electrode mixture can be suppressed. Even when an oxide is used, high capacity and high output can be maintained, and a long life of the lithium secondary battery can be realized. As such a positive electrode active material, a lithium transition metal double oxide having a spinel crystal structure may be used. Since the lithium transition metal double oxide having a spinel crystal structure has excellent thermal stability, the capacity and output can be maintained even in a high temperature environment. Alternatively, a lithium transition metal double oxide having a layered crystal structure may be used as the positive electrode active material. The lithium transition metal complex oxide having a layered crystal structure expands the interlayer distance of the crystal due to charging, and expands. Therefore, pressure is applied between the positive and negative electrodes, and peeling and falling off of the negative electrode mixture are suppressed, and the negative electrode binder is removed. Since the binding property of the negative electrode mixture is ensured by the polyvinyl alcohol-based resin, high capacity and high output can be maintained.
[0013]
A second aspect of the present invention is an electric vehicle using the lithium secondary battery of the first aspect as a power source for power. According to this aspect, since the lithium secondary battery whose output and capacity are suppressed from being reduced is used as the power source, even if charging and running (discharging) are repeated, there is little decrease in acceleration performance and continuous running distance. Can be realized.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a cylindrical lithium ion battery used as a power source for driving a golf cart will be described with reference to the drawings.
[0015]
As shown in FIG. 1, the golf cart 30 includes a chassis 31 serving as a base. At a substantially central portion of the chassis 31, a battery box 36 accommodating a plurality of cylindrical lithium ion batteries 20, which will be described later, connected in series is fixed. A cushion 35 is arranged on the battery box 36, and the battery box 36 and the cushion 35 constitute a front seat.
[0016]
In front of the chassis 31, a motor using the cylindrical lithium-ion battery 20 as a power source and a power transmission mechanism for transmitting the rotational driving force of the motor shaft to the wheels are fixed to the chassis 31, and the power transmission mechanism rotates the tires. It is a structure to make it. An acceleration pedal 37 for adjusting the forward speed of the golf cart 30 is arranged at the position of the feet of the driver sitting on the front seat. The acceleration pedal 37 is connected to a variable resistor that is linked to the amount of depression, and the golf cart 30 is structured so that when the driver depresses the acceleration pedal 37, the golf cart 30 moves forward according to the amount of depression.
[0017]
The cylindrical lithium ion battery 20 housed in the battery box 36 is manufactured as follows.
[0018]
(Production of positive electrode plate)
As shown in FIG. 2, lithium cobalt oxide (LiCoO ₂ ) powder or lithium manganate (LiMn ₂ O ₄ ) powder having a spinel crystal structure or lithium manganate (LiMnO ₂ ) having a layered rock salt type crystal structure as a positive electrode active material The powder, graphite powder and acetylene black as a conductive material, and polyvinylidene fluoride (hereinafter referred to as PVDF) as a binder (binder) are mixed at a mass ratio of 85: 9: 2: 4, and a dispersion solvent is added thereto. N-methyl-2-pyrrolidone (hereinafter referred to as NMP) was added and kneaded, and the slurry was applied to both surfaces of an aluminum foil W1 (positive electrode current collector) having a thickness of 20 μm. At this time, an uncoated portion having a width of 30 mm was left on one side edge in the longitudinal direction of the positive electrode plate. Thereafter, drying, pressing, and cutting were performed to obtain a positive electrode plate having a width of 82 mm, a length of 374 cm, and a thickness of 111 μm in the active material mixture application portion. The bulk density of the positive electrode active material mixture layer W2 was 2.65 g / cm ³ . A notch was made in the uncoated portion left on the side edge, and the remaining notch was used as a positive electrode lead piece 2. Adjacent positive electrode lead pieces 2 were set at intervals of 50 mm, and the width of the positive electrode lead pieces 2 was set at 5 mm.
[0019]
(Production of negative electrode plate)
A graphite powder having a specific surface area as a negative electrode active material and an acetylene black powder as a conductive material are mixed at a mass ratio of 95: 5, and a thermosetting plasticized polyvinyl alcohol is added thereto as described later. A system resin (hereinafter referred to as PVA) was mixed at a predetermined volume ratio as a binder, and NMP as a dispersion solvent was added and kneaded to obtain a slurry. The obtained slurry was uniformly applied to both surfaces of a rolled copper foil W3 (negative electrode current collector) having a thickness of 10 μm. At this time, an uncoated portion having a width of 30 mm was left on one side edge in the longitudinal direction of the negative electrode plate. Thereafter, drying, pressing, and cutting were performed to obtain a negative electrode plate having a width of 86 mm, a length of 386 cm, and a thickness of the active material mixture application portion of 79 μm. The bulk density of the negative electrode active material mixture layer W4 was 1.00 g / cm ³ . A notch was made in the uncoated portion left on the side edge in the same manner as the positive electrode plate, and the remaining notch was used as a negative electrode lead piece 3. Adjacent negative electrode lead pieces 3 were set at intervals of 50 mm, and the width of the negative electrode lead pieces 3 was set at 5 mm.
[0020]
PVA is obtained by mixing and dissolving a first resin component composed of a thermosetting polyvinyl alcohol-based resin and a second resin component composed of an acrylic resin-based plasticizer in an appropriate organic solvent (in this embodiment, NMP). Is done. The thermosetting polyvinyl alcohol resin as the first resin component is obtained by adding a cyclic acid anhydride such as succinic anhydride to a polyvinyl alcohol resin having an average degree of polymerization of about 2,000 in an organic solvent such as NMP and triethylamine. And in the presence of such a catalyst in a substantially anhydrous state. The reaction ratio between the polyvinyl alcohol resin and the cyclic acid anhydride is such that the anhydride group of the cyclic acid anhydride is about 0.1 equivalent to 1 equivalent of the alcoholic hydroxyl group of the polyvinyl alcohol resin. As the acrylic resin-based plasticizer as the second resin component, a reaction product of a lauryl acrylate / acrylic acid copolymer and a bifunctional epoxy resin is suitable.
[0021]
The first resin component was synthesized as follows. In a separable flask equipped with a stirrer, a thermometer, a cooling pipe, a distilling pipe, and a nitrogen gas introducing pipe, 51 g of polyvinyl alcohol having a degree of saponification of about 98%, 650 g of NMP and 10 g of toluene were charged, and the mixture was stirred with nitrogen bubbling and stirring. The temperature was raised to 195 ° C over 30 minutes. The solution was kept at the same temperature for 2 hours, and toluene was refluxed to azeotropically evaporate water, thereby distilling off water in the flask. Then, toluene was distilled off, the mixture was cooled to 120 ° C., and 7.7 g of succinic anhydride was added thereto while keeping the temperature at the same temperature, and the mixture was reacted for 1 hour (per 1 equivalent of alcoholic hydroxyl group of polyvinyl alcohol, acid was added). Anhydride groups are about 0.07 equivalents). After cooling to room temperature, an NMP solution containing about 8% by mass of the first resin component was obtained.
[0022]
The second resin component was synthesized as follows. In a separable flask equipped with a stirrer, a thermometer, a cooling pipe, a distilling pipe, and a nitrogen gas introducing pipe, 110 g of a solventless lauryl acrylate / acrylic acid copolymer having a weight average molecular weight of about 3100, and a bisphenol A type epoxy resin 71 g (about 2 equivalents of epoxy group per 1 equivalent of carboxyl group of the solvent-free lauryl acrylate / acrylic acid copolymer) was added, and the temperature was raised to 150 ° C. over about 15 minutes with nitrogen bubbling and stirring. did. After keeping the temperature at the same temperature for 2 hours to advance the reaction, 78 g of NMP was added thereto and cooled to room temperature to obtain an NMP solution of about 70% by weight of the second resin component.
[0023]
An NMP solution of 8% by weight of the first resin component and an NMP solution of about 70% by weight of the second resin component are mixed at a ratio of 100: 10 in terms of mass of each resin component to obtain an NMP solution of PVA. Was.
[0024]
(Production of battery)
The produced positive electrode plate and negative electrode plate were wound together with a polyethylene separator W5 having a width of 90 mm and a thickness of 40 μm so that these two electrode plates did not come into direct contact with each other. At the center of the winding, a hollow cylindrical shaft core 1 made of polypropylene was used. At this time, the positive electrode lead piece 2 and the negative electrode lead piece 3 were located on both end surfaces of the winding group 6 on the opposite sides. The lengths of the positive electrode plate, the negative electrode plate, and the separator were adjusted, and the diameter of the winding group 6 was set to 38 ± 0.1 mm.
[0025]
After the positive electrode lead pieces 2 are deformed, and all of them are gathered and brought into contact with the vicinity of a flange peripheral surface integrally projecting from the periphery of the positive electrode current collecting ring 4 substantially on the extension of the shaft core 1 of the winding group 6, Then, the positive electrode lead 2 and the flange peripheral surface were ultrasonically welded to connect the positive electrode lead 2 to the flange peripheral surface. On the other hand, the connection operation between the negative electrode current collector ring 5 and the negative electrode lead piece 3 was also performed in the same manner as the connection operation between the positive electrode current collector ring 4 and the positive electrode lead piece 2.
[0026]
Thereafter, an insulating coating was applied to the entire periphery of the flange peripheral surface of the positive electrode current collecting ring 4. For this insulating coating, a pressure-sensitive adhesive tape was used in which the base material was polyimide and one side thereof was coated with a pressure-sensitive adhesive composed of hexamethacrylate. This adhesive tape was wound one or more times from the peripheral surface of the flange portion to the outer peripheral surface of the winding group 6 to form an insulating coating, and the winding group 6 was inserted into the battery container 7. A nickel-plated steel container having an outer diameter of 40 mm and an inner diameter of 39 mm was used as the battery container 7.
[0027]
A negative electrode lead plate 8 for electrical conduction is welded to the negative electrode current collecting ring 5 in advance. After the winding group 6 is inserted into the battery container 7, the bottom of the battery container 7 and the negative electrode lead plate 8 are welded. .
[0028]
On the other hand, a positive electrode lead 9 formed by laminating a plurality of aluminum ribbons in advance is welded to the positive electrode current collecting ring 4, and the other end of the positive electrode lead 9 is sealed with a battery for closing the battery container 7. Welded to the underside of the lid. The battery lid is provided with a cleavage valve 11 as an internal pressure release mechanism that is opened in accordance with an increase in the internal pressure of the cylindrical lithium ion battery 20. The cleavage pressure of the cleavage valve 11 was set to about 9 × 10 ⁵ Pa. The battery lid is composed of a lid case 12, a lid cap 13, a valve retainer 14 for keeping airtightness, and a cleavage valve 11, and these are stacked and assembled by caulking the periphery of the lid case 12. I have.
[0029]
A predetermined amount of non-aqueous electrolyte is injected into the battery container 7, and then the battery cover 7 is covered with the battery cover so that the positive electrode lead 9 is folded, and caulked and sealed via an EPDM resin gasket 10. Thus, the cylindrical lithium ion battery 20 was completed.
[0030]
As the non-aqueous electrolyte, a solution prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a mole ratio of 1 mol / L in a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate at a volume ratio of 1: 1: 1 was used.
[0031]
【Example】
Next, examples of the cylindrical lithium ion battery 20 and the golf cart 30 manufactured according to the present embodiment will be described. Hereinafter, the cylindrical lithium-ion battery 20 will be described in detail in Examples 1 to 8, and the golf cart 30 will be described in Examples 9 to 13. A battery and a golf cart of a comparative example produced for comparison are also described.
[0032]
(Example 1)
As shown in Table 1 below, in Example 1, lithium cobalt oxide (LiCoO ₂ ) powder was used for the positive electrode active material, graphite powder having a specific surface area of 3.1 m ² / g was used for the negative electrode active material, and the negative electrode binder was used for the negative electrode binder. PVA was used. The binder content was set to 3.2% by volume of the negative electrode mixture.
[0033]
[Table 1]

[0034]
(Examples 2 to 6)
As shown in Table 1, Examples 2 to 6 were the same as Example 1 except that the specific surface area of graphite and the content of PVA were variously changed. In Example 2, the specific surface area of graphite was 3.9 m ² / g, and the binder content was 4.1%. In Example 3, the specific surface area of graphite was 2.4 m ² / g, and the binder content was 5. In Example 4, the specific surface area of graphite was 6.4 m ² / g and the binder content was 5.8%. In Example 5, the specific surface area of graphite was 2.3 m ² / g and the binder content was In Example 6, the specific surface area was 3.1 m ² / g, and the binder content was 11.3%.
[0035]
(Example 7)
As shown in Table 1, in Example 7, lithium manganate (LiMn ₂ O ₄ ) powder having a spinel crystal structure was used for the positive electrode active material, and graphite powder having a specific surface area of 2.6 m ² / g was used for the negative electrode active material. And PVA was used for the negative electrode binder. The binder content was 5.8%.
[0036]
(Example 8)
As shown in Table 1, in Example 8, a lithium manganate (LiMnO ₂ ) powder having a layered rock salt type crystal structure was used for the positive electrode active material, and a graphite powder having a specific surface area of 2.4 m ² / g was used for the negative electrode active material. And PVA was used for the negative electrode binder. The binder content was 5.8%.
[0037]
(Examples 9 to 13)
In the ninth to thirteenth examples, 72 cylindrical lithium-ion batteries 20 of the second, third, fifth, seventh, and eighth examples were connected in series and mounted on the golf cart 30. .
[0038]
(Comparative Example 1)
As shown in Table 1, in Comparative Example 1, a cylindrical lithium ion battery was manufactured in the same manner as in Example 3, except that PVDF was used as the negative electrode binder.
[0039]
(Comparative Example 2)
As shown in Table 1, Comparative Example 2 was performed in the same manner as in Example 3 except that lithium manganate (LiMn ₂ O ₄ ) powder having a spinel crystal structure was used for the positive electrode active material and PVDF was used for the negative electrode binder. Thus, a cylindrical lithium ion battery was manufactured.
[0040]
(Comparative Example 3)
As shown in Table 1, Comparative Example 3 was performed in the same manner as in Example 3 except that lithium manganate (LiMnO ₂ ) powder having a layered rock salt type crystal structure was used for the positive electrode active material and PVDF was used for the negative electrode binder. Thus, a cylindrical lithium ion battery was manufactured.
[0041]
(Comparative Examples 4 to 6)
In Comparative Examples 4 to 6, 72 cylindrical lithium ion batteries produced in Comparative Examples 1 to 3 were connected in series and mounted on a golf cart.
[0042]
<Test / Evaluation>
Next, the following series of tests were performed on the batteries and golf carts of the examples and comparative examples manufactured as described above.
[0043]
The batteries of the example and the comparative example were discharged after being charged, and the discharge capacity was measured in an atmosphere at an environmental temperature of 25 ± 2 ° C. The charging conditions were a constant voltage of 4.1 V, a limiting current of 5 A, and 2.5 hours, and the discharging conditions were a constant current of 1 A and a final voltage of 2.7 V. The discharge capacity after the pulse cycle test at the initial stage and after the pulse cycle test described later was measured, and the ratio of the discharge capacity after the pulse cycle test to the initial discharge capacity was determined as a percentage, which was defined as the capacity retention ratio.
[0044]
After charging each battery under the above-described charging conditions (fully charged state), the output was measured in an atmosphere at an environmental temperature of 25 ± 2 ° C. The measurement conditions were as follows: the battery was discharged for 10 seconds at current values of 10 A, 30 A, and 90 A, and the battery voltage value at each 5 seconds was plotted on the vertical axis against the horizontal axis current value. A current value at a point crossing 2.7 V, which is the final voltage, was read, and the product of this current value and 2.7 V was used as the output of the battery. The output after the initial cycle and after the pulse cycle test was measured, and the ratio of the output after the pulse cycle test to the initial output was calculated as a percentage, which was defined as the output maintenance rate.
[0045]
In the pulse cycle test of each battery, a high load current of about 50 A is applied to each battery in an atmosphere of 50 ± 3 ° C for about 5 seconds in both the charging direction and the discharging direction, and a pulse cycle of about 30 seconds per cycle including a pause time. The test was repeated 100,000 times continuously.
[0046]
In the golf cart test, the vehicle was driven at a constant speed with a fully charged battery, and the continuous running distance until the golf cart could not maintain the constant speed was measured. The time required for the golf cart to start with the fully charged battery and to reach the predetermined speed was measured and defined as the acceleration time. After removing the battery from the golf cart and performing the pulse cycle test described above, the battery was mounted again on the golf cart, and the continuous running distance and the acceleration time were measured in the same manner. The percentages of the continuous running distance and the acceleration time after the pulse cycle test with respect to the initial continuous running distance and the acceleration time were determined as percentages, and were defined as the continuous running distance maintenance rate and the acceleration time change rate.
[0047]
The test results for each battery are shown in Table 2 below, and the test results for the golf cart are shown in Table 3 below.
[0048]
[Table 2]

[0049]
As shown in Table 2, in each of the batteries of Examples 1 to 6 using lithium cobalt oxide as the positive electrode active material and PVA as the negative electrode binder, the capacity retention rate was 84% or more and the output retention rate was 90%. The above is shown. Further, in the battery of Example 7 using lithium manganate having a spinel crystal structure as the positive electrode active material and using PVA as the negative electrode binder, the initial discharge capacity, the initial output, the capacity retention, and the output retention were all high. showed that. Furthermore, in the battery of Example 8 using lithium manganate having a layered rock salt type crystal structure for the positive electrode active material and using PVA for the negative electrode binder, the initial discharge capacity, the initial output and the capacity retention rate, Also showed excellent values. On the other hand, in each of the batteries of Comparative Examples 1 to 3 using PVDF as the negative electrode binder, both the capacity retention ratio and the output retention ratio were 70% or less, and sufficient performance could not be obtained. Therefore, the batteries of Examples 1 to 8 are long-life batteries.
[0050]
Further, in the battery of Example 1 in which the binder content was less than 4% by volume, the capacity retention ratio and the output retention ratio were good, but the initial discharge capacity was a slightly lower value of 3.38 Ah. In the battery of Example 6 in which the binder content was larger than 9% by volume, the initial output was slightly lower at 890 W. Therefore, it was found that the content of PVA is preferably in the range of 4% to 9% by volume in the negative electrode mixture.
[0051]
Furthermore, in the battery of Example 4 in which the specific surface area of graphite was larger than 4 m ² / g, the initial discharge capacity showed a slightly low value of 3.32 Ah. Therefore, it was found that the specific surface area of graphite is preferably 4 m ² / g or less.
[0052]
[Table 3]

[0053]
As shown in Table 3, the golf carts 30 of Examples 9 to 13 equipped with the batteries of Example 2, Example 3, Example 5, Example 7, and Example 8 respectively correspond to Comparative Example 1 and Comparative Example 1. Both the continuous running distance maintenance rate and the acceleration time change rate showed higher values as compared with the golf carts of Comparative Examples 4, 5 and 6 equipped with the batteries of Example 2 and Comparative Example 3, respectively. Even after the pulse cycle test corresponding to the repetition of virtual charging and running, the reduction of the continuous running distance and the acceleration time was suppressed extremely low, and a high-performance golf cart was obtained. Further, from Tables 2 and 3, it was found that the battery capacity maintenance rate and the golf cart continuous running distance maintenance rate, and the battery output maintenance rate and the golf cart acceleration time change rate had correlations.
[0054]
In the cylindrical lithium-ion battery 20 of the present embodiment, by using PVA for the binder of the negative electrode, the graphite surface of the negative electrode active material is appropriately coated with PVA, so that the reaction point at which a side reaction such as gasification occurs is reduced. Thus, the initial discharge capacity can be improved. In addition, since the resistance to the expansion and contraction of graphite due to charge and discharge is increased, peeling and falling off (collapse) of the negative electrode mixture is suppressed. Obtainable. When the content of PVA is less than 4% by volume of the negative electrode mixture, the graphite surface is insufficiently coated, so that a side reaction occurs to reduce the capacity, and when the content exceeds 9%, the resistance component increases. Therefore, the output decreases. Therefore, the content of PVA is preferably in the range of 4% to 9% by volume of the negative electrode mixture. Further, when the specific surface area of graphite as the negative electrode active material exceeds 4 m ² / g, a side reaction is likely to occur, so that the initial discharge capacity decreases. For this reason, it is preferable that the specific surface area of graphite be 4 m ² / g or less.
[0055]
In addition, when lithium manganate having a spinel crystal structure (LiMn ₂ O ₄ ) is used as the positive electrode active material, lithium manganate having a spinel crystal structure has a property of contracting upon charging. In particular, at high temperatures, the negative electrode mixture tends to peel off or fall off. When a conventionally used PVDF is used for the negative electrode binder, the negative electrode mixture is apt to peel off and fall off, so that both the high-temperature cycle, the reduction in capacity during high-temperature storage, and the reduction in output are large. When PVA is used for the negative electrode binder, peeling and falling off of the negative electrode mixture is suppressed, so that a long-life battery is obtained even when lithium manganate having a large shrinkable spinel crystal structure is used for the positive electrode active material. be able to. Alternatively, when lithium manganate having a layered crystal structure (LiMnO ₂ ) is used as the positive electrode active material, the lithium manganate having the layered crystal structure emits lithium ions upon charging, and the interlayer distance increases due to repulsion between oxygen. And the winding pressure applied to the negative electrode increases. For this reason, at the time of charging, peeling and falling off of the negative electrode mixture are suppressed, and since the negative electrode mixture is reliably held by using PVA for the negative electrode binder, both capacity and output can be maintained, and a long life can be maintained. You can get a battery. The golf cart 30 equipped with these batteries can be a high-performance golf cart with little decrease in continuous running distance and acceleration time even when charging and running are repeated.
[0056]
In the present embodiment, the cylindrical lithium-ion battery 20 has been described as an example. However, the present invention is not limited to the shape of the battery, and can be applied to a square or other polygonal battery. The structure to which the present invention can be applied may be a battery other than the above-described battery container in which the battery lid is sealed by caulking. As an example of such a structure, a battery in a state where positive and negative external terminals penetrate a battery lid and positive and negative external terminals are pressed together via a shaft core in a battery container can be given. Further, the present invention is also applicable to a lithium secondary battery having a stacked structure without using a positive electrode and a negative electrode in a wound structure.
[0057]
In the present embodiment, lithium cobaltate (LiCoO ₂ ), lithium manganate having a spinel crystal structure (LiMn ₂ O ₄ ), and lithium manganate having a layered rock salt type crystal structure (LiMnO ₂ ) are used as the positive electrode active material. The positive electrode active material for a lithium secondary battery of the present invention is a material capable of inserting and removing lithium ions, and a lithium transition metal complex oxide in which a sufficient amount of lithium ions has been inserted in advance. Should be fine. For example, a similar effect can be obtained with a lithium manganese double oxide, a lithium cobalt double oxide, a lithium nickel double oxide, or the like. Further, a material or crystal in which a part of the transition metal or lithium in these lithium transition metal double oxide crystals is substituted or doped with another element such as Fe, Co, Ni, Cr, A1, Mg, or the like. It is also possible to use a material in which a part of the oxygen inside is replaced or doped with an element such as S or P. Further, even if a lithium manganese double oxide capable of providing a battery voltage of 5V class is used, the effect of the present invention is not changed.
[0058]
Furthermore, in the present embodiment, an example in which graphite is used as the negative electrode active material has been described, but the present invention is not limited to this, and any graphite graphite may be used. Graphitic carbon referred to herein do not necessarily indicate highly crystalline graphite, such as mesophase graphite, the interlayer distance d ₀₀₂ by X-ray diffraction may be a graphite exceeds 0.3354 nm. In X-ray diffraction, a diffraction line that can be assigned an hkl index may be used. Also, the particle shape is not particularly limited, such as a flake shape, a spherical shape, a fibrous shape, and a massive shape.
[0059]
Furthermore, in this embodiment, a non-aqueous electrolyte in which LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate mixed at a volume ratio of 1: 1: 1 has been described. As the electrolyte, a non-aqueous electrolyte obtained by dissolving this in an organic solvent may be used, and the present invention is not particularly limited to the lithium salt and the organic solvent used. For example, as the electrolyte, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, or a mixture thereof can be used. Examples of the organic solvent include propylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, Sulfolane, methylsulfolane, acetonitrile, propionitrile, and the like, or a mixed solvent obtained by mixing two or more thereof can be used, and the mixing ratio is not limited. By using such a non-aqueous electrolyte, it is possible to improve the battery capacity and adapt the battery to use in cold regions. Further, a solid electrolyte may be used.
[0060]
Furthermore, in the above-described embodiment, the golf cart 30 using only the cylindrical lithium ion battery 20 as a power source is illustrated, but the present invention is not limited to this, and may be used in combination with an internal combustion engine. Good. Further, the number of batteries mounted on the electric vehicle may be appropriately combined depending on the desired output and capacity, and the location of the batteries is not particularly limited.
[0061]
In the present embodiment, an example in which metal foils (aluminum foil, copper foil) are used for the positive electrode and the negative electrode current collector has been described. However, the present invention is not limited to this, and a mesh-shaped metal current collector is used. A body may be used.
[0062]
【The invention's effect】
As described above, according to the present invention, by using a thermosetting and plasticized polyvinyl alcohol-based resin for the binder of the negative electrode, the resistance to expansion and contraction of the graphitic carbon increases, Since the exfoliation and falling off of the mixture are suppressed, a decrease in the capacity retention rate and output retention rate of the obtained lithium secondary battery can be suppressed, and a thermosetting plasticized polyvinyl alcohol-based resin. This ensures that the surface of the graphitic carbon is appropriately covered, and suppresses the occurrence of side reactions such as gasification on the surface of the graphitic carbon due to decomposition of the electrolytic solution or the liquid component of the solid electrolyte at the time of the first charge. The effect of being able to prevent the initial decrease in the battery capacity of the battery can be obtained.
[Brief description of the drawings]
FIG. 1 is a side view schematically showing a golf cart according to an embodiment to which the present invention can be applied.
FIG. 2 is a sectional view of a cylindrical lithium ion battery according to an embodiment to which the present invention can be applied.
[Explanation of symbols]
6 Winding group (electrode group)
20 Cylindrical lithium-ion battery (lithium secondary battery)
30 golf cart (electric car)
35 Front seat 36 Battery box

Claims (7)

In a lithium secondary battery having a negative electrode in which a negative electrode mixture containing graphitic carbon and a binder is substantially uniformly applied to both surfaces of a metal current collector, and a positive electrode, the binder has thermosetting properties. A lithium secondary battery comprising a plasticized polyvinyl alcohol-based resin. The lithium secondary battery according to claim 1, wherein the content of the polyvinyl alcohol-based resin is 4% by volume or more and 9% by volume or less of the negative electrode mixture. The lithium secondary battery according to claim 1, wherein the specific surface area of the graphitic carbon is 4 m ² / g or less. 4. The lithium secondary battery according to claim 1, wherein the positive electrode active material is a lithium transition metal double oxide. 5. 5. The lithium secondary battery according to claim 1, wherein the active material of the positive electrode is a lithium transition metal double oxide having a spinel crystal structure. 6. The lithium secondary battery according to any one of claims 1 to 4, wherein the active material of the positive electrode is a lithium transition metal double oxide having a layered crystal structure. An electric vehicle using the lithium secondary battery according to any one of claims 1 to 6 as a power source for power.

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