JP4238657B2 - Lithium secondary battery and electric vehicle - Google Patents

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【００３６】
（実施例２〜６）
表１に示すように、実施例２〜実施例６では、ＰＶｄＦとＰＶＡとの混合比を変更する以外は実施例１と同様にした。実施例２では、混合比を４０：６０とし、実施例３では、混合比を６０：４０とし、実施例４では、混合比を８０：２０とし、実施例５では、混合比を１０：９０とし、実施例６では、混合比を９０：１０とした。
【００３７】
（実施例７）
表１に示すように、実施例７では、負極活物質に非晶質炭素（呉羽工業（株）製、商品名：ＰＩＣ（Ｆ））を使用し、ＰＶｄＦとＰＶＡとの混合比を４０：６０とした。
【００３８】
（実施例８）
表１に示すように、実施例８では、ＰＶｄＦとＰＶＡとの混合比を１０：９０とする以外は実施例７と同様にした。
【００３９】
（実施例９〜１６）
実施例９〜実施例１６では、実施例１〜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。
【００４０】
（比較例１）
表１に示すように、比較例１では、負極バインダーをＰＶｄＦのみとする以外は実施例１と同様にした。
【００４１】
（比較例２）
表１に示すように、比較例２では、負極バインダーにＰＶＡを単独で用い、バインダーの熱硬化処理を行うために１５０°Ｃで３時間の真空乾燥・熱処理を施した以外は実施例１と同様にした。
【００４２】
（比較例３〜４）
比較例３〜比較例４では、比較例１〜比較例２の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。
【００４３】
＜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。
【００４４】
実施例及び比較例の各電池は初充電を行い、試験環境温度２５±１°Ｃの雰囲気で初期放電容量を測定した。充電条件は、４．２Ｖ定電圧、制限電流５Ａ、４．５時間とした。放電条件は、５Ａ定電流、終止電圧２．７Ｖとした。
【００４５】
また、初充電後に、同じ環境温度の雰囲気で充電状態の電池の放電出力を測定した。測定条件は、１Ａ、３Ａ、６Ａ、各放電電流で５秒目の電圧を読み取り、横軸電流値に対して縦軸に電圧値をプロットし、３点を結ぶ近似直線より初期直流抵抗値（ＤＣＲ）を求めた。
【００４６】
更に、実施例及び比較例の各電池について、２５°Ｃ及び６０°Ｃの雰囲気で電流値１Ｃ（５Ａ）にて充放電を１００回繰り返すサイクル試験を行った。２５°Ｃの雰囲気では電流値１０Ｃ（４０Ａ）のサイクル試験も行った。サイクル試験後、同様にして直流抵抗値及び放電容量を測定し、初期直流抵抗値及び初期放電容量に対するサイクル試験後の直流抵抗値及び放電容量の割合をそれぞれ百分率で求め、それぞれを直流抵抗上昇率及び容量維持率とした。当然のことながら、容量維持率が高く、直流抵抗上昇率が低いほうが寿命特性に優れることを示している。各電池の試験結果を下表２に示す。
【００４７】
ゴルフカートの試験では、満充電状態の電池を搭載して発進し、ゴルフカートが１０ｋｍ／ｈ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、上述したサイクル試験を行った後、再びゴルフカートに搭載して加速時間を同様に測定した。初期の加速時間に対するサイクル試験後の加速時間の増加率（％）を求めた。ゴルフカートの試験結果を下表３に示す。
【００４８】
【表２】

【００４９】
表２に示すように、ＰＶｄＦとＰＶＡとの混合比を変えて作製した実施例１〜実施例６の電池では、ＰＶＡを６０％、すなわちＰＶｄＦを４０％使用したときに（実施例２の電池）、容量維持率が最大となる変曲点があることが判った。また、直流抵抗上昇率も同様に、ＰＶＡ６０％のときに直流抵抗の上昇が最も抑制されていることが判った。容量維持率、直流抵抗上昇率共に、サイクル試験の電流値を１０Ｃと高くした試験においても、同様の結果を示した。これに対して比較例１〜比較例２の電池では、容量維持率が低下し、直流抵抗上昇率が増加した。従って、ＰＶｄＦとＰＶＡとの混合比は、体積比で８０：２０〜２０：８０とすることが好ましく、より好ましくは６０：４０〜４０：６０の範囲であることが判明した。
【００５０】
また、ＰＶＡのみを用いた比較例２の電池では、ＰＶｄＦのみを用いた比較例１の電池より、容量維持率が高い値を示し、直流抵抗上昇率が低い値を示した。従って、ＰＶＡが容量維持率、直流抵抗上昇率の向上に有効であることが判明したが、比較例２では、負極作製時に熱硬化処理を行っており、ＰＶＡを単独で使用するには製造上の問題がある。
【００５１】
更に、負極活物質に非晶質炭素を用いた実施例７及び実施例８の電池では、ＰＶｄＦとＰＶＡとの体積比を４０：６０とした実施例７の電池の方が体積比を１０：９０とした実施例８の電池より容量維持率、直流抵抗上昇率共に優れた結果を示した。しかし、実施例７の電池と、負極活物質に塊状黒鉛を用いた実施例２の電池とを比較すると実施例２の電池の方が優れた結果を示している。従って、負極活物質に非晶質炭素を用いた場合でも、ＰＶＡとＰＶｄＦとを体積比８０：２０〜２０：８０で混合することで、容量維持率、直流抵抗上昇率を向上させることは可能であるが、負極活物質を塊状黒鉛とすることで、容量維持率、直流抵抗上昇率をより向上させることが可能であることが判った。
【００５２】
【表３】

【００５３】
表３に示すように、実施例１〜実施例８の電池をそれぞれ搭載した実施例９〜実施例１６のゴルフカート３０では、比較例１〜比較例２の電池をそれぞれ搭載した比較例３〜比較例４のゴルフカートと比べて、仮想的な充電、走行（放電）の繰り返しに相当するサイクル試験後の加速時間増加率が低く抑えられ、高性能なゴルフカートとなった。また、ゴルフカートの加速時間増加率は、電池の放電容量、直流抵抗値に大きく依存することが判明し、負極バインダにＰＶｄＦとＰＶＡとを混合して用いることで加速性能の低下を抑制できることが判明した。
【００５４】
本実施形態の円筒型リチウムイオン電池２０は、負極バインダとしてＰＶｄＦを混合して使用するので、電流値を１０Ｃとした高率充放電を繰り返しても、容量維持率、直流抵抗上昇率共に優れた電池を得ることができる。また、ＰＶＡを混合して使用することで、負極合剤と負極集電体との結着性が向上するので、充放電を繰り返しても、負極合剤の剥離・脱落が防止され、容量維持率、直流抵抗上昇率を向上させることができる。また、ＰＶＡとＰＶｄＦとの体積比が８０：２０を超えると抵抗成分が増大（直流抵抗上昇率が増大）して出力が低下し、２０：８０に満たないと結着性が不十分なため容量維持率が低下する。このため、ＰＶＡとＰＶｄＦとの体積比は、８０：２０〜２０：８０とすることが好ましい。更に、ＰＶＡを単独で使用するときには、負極合剤と負極集電体との結着性を向上させるために熱処理が必要なため、製造上の問題点があるが、ＰＶＡとＰＶｄＦとの混合物を使用することで、製造上の問題点を克服することができる。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。
【００５５】
（第２実施形態）
次に、本発明をハイブリッド電気自動車の補助電源として用いられる円筒型リチウムイオン電池に適用した第２の実施の形態について説明する。本実施形態では、円筒型リチウムイオン電池を、主電池となる鉛電池を充電する補助電池として用いるものである。なお、本実施形態において、第１の実施形態と同一の構成には同一の符号を付してその説明を省略し、異なる箇所のみ説明する。
【００５６】
図３に示すように、本実施形態のハイブリッド電気自動車４０は、内燃機関エンジン及び車両全体への電力を供給する電源システム５０を備えている。
【００５７】
図４に示すように、電源システム５０は、車両駆動モータ等の機能を有するモータジェネレータ５３、照明類、ワイパ、ラジオ等の負荷５４、並びに、モータジェネレータ５３及び負荷５４へ電力を供給する充放電システム部６０を有している。
【００５８】
モータジェネレータ５３は、図示を省略した車両制御システムにより３つの機能が切替制御され、車両始動から低速走行時には、充放電システム部６０からの電力により作動し車両駆動及びエンジンの始動を行うモータとして、エンジン駆動中には、エンジンの回転力により発電し充放電システム部６０の充電及び負荷５４への電力供給が可能なオルタネータ（発電機）として、車両制動時には、回生エネルギーを電気エネルギーに変換し後述する補助電池５２の充電及び負荷５４への電力供給が可能な高出力のジェネレータとして、それぞれ機能する。
【００５９】
充放電システム部６０は、車両への電力供給の主電源となる主電池５１、主電池５１への充電電力を供給する補助電池５２、補助電池５２の電圧を昇圧するＤＣ−ＤＣコンバータ等の電圧昇圧部５５、並びに、主電池５１及び補助電池５２の充放電状態を制御する充放電制御部５６を有している。
【００６０】
主電池５１には、鉛電池が用いられている。鉛電池の電槽には、内部を１８個のセル室に画定したモノブロック電槽が用いられている。各セル室には、複数の正極板と負極板とをガラス繊維セパレータを介して積層した極板群が１組ずつ収容されており、電解液（希硫酸）が注液されている。各セル室はモノブロック電槽の開口を一体に覆う蓋で密閉されており、各セル室上部に制御弁が配設され密閉化されている。各セル室間は導電性の接続部材により直列に接続されている。
【００６１】
補助電池５２は、１０個の円筒型リチウムイオン電池２０を直列に接続して構成されている。補助電池５２と電圧昇圧部５５とは直列に接続されている。なお、補助電池５２の電圧が主電池５１の電圧より高いときは、電圧昇圧部５５を接続しないようにしてもよい。
【００６２】
主電池５１の正極外部端子は、電圧昇圧部５５の一端に接続されている。モータジェネレータ５３の一端及び負荷５４の一端は、主電池５１の正極外部端子に接続されている。主電池５１及び補助電池５２の負極外部端子は、グランドに接続されている。モータジェネレータ５３及び負荷５４の他端は、それぞれグランドに接続されている。従って、主電池５１、電圧昇圧部５５と直列に接続された補助電池５２、モータジェネレータ５３及び負荷５４は、並列接続可能とされている。
【００６３】
本実施形態の電源システム５０では、補助電池５２を構成するリチウムイオン電池２０は、車両制動時の回生電力により充電される。主電池５１は、電力受入性が低いため、回生電力による充電は行われない。主電池５１の残存容量が低下したときは、補助電池５２に蓄えられた電力が主電池５１へ供給され、主電池５１が充電される。補助電池５２の電圧が低下したときは、電圧昇圧部５５により補助電池５２の電圧が昇圧され主電池５１に供給される。
【００６４】
また、本実施形態の電源システム５０では、補助電池５２が、モータジェネレータ５３からの回生電力を蓄え、蓄えた電力により主電池５１を穏やかに充電するので、主電池５１の寿命特性を向上させることができる。また、補助電池５２が、寿命特性の改善されたリチウムイオン電池２０で構成されているので、電源システム全体の寿命特性を向上させることができる。
【００６５】
なお、上記実施形態では、ゴルフカート用電源及びハイブリッド電気自動車用補助電源に用いられるリチウムイオン電池について例示したが、電池の大きさ、電池容量には限定されるものではなく、電池容量としておおむね３Ａｈ乃至１００Ａｈ程度の電池に対して本発明は効果を著しく発揮することが確認されている。従って、リチウムイオン電池２０は（純粋）電気自動車にも使用可能である。また、上記実施形態では、正負極板を捲回して用いた円筒型の電池について例示したが、本発明は電池の形状についても限定されるものではなく、角形、その他の多角形の電池や、正負極板を積層した積層タイプの電池にも適用可能である。更に、本発明の適用可能な形状としては、上述した有底筒状容器（缶）に電池上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極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。また、電気自動車やハイブリッド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るものではない。
【００６６】
また、上記実施形態では、負極バインダの熱硬化性可塑化ポリビニルアルコール樹脂組成物の作製に、平均重合度約２０００のポリビニルアルコール系樹脂、コハク酸無水物、重量平均分子量約３１００のラウリルアクリレート／アクリル酸共重合物、ビスフェノールＡ型エポキシ樹脂を用いる例を示したが、本発明はこれらに限定されるものではなく、平均重合度の異なるポリビニルアルコール系樹脂や重量平均分子量の異なるラウリルアクリレート／アクリル酸共重合物を用いてもよい。この場合には、反応時の当量比や反応条件により所望の物性の熱硬化性可塑化ポリビニルアルコール樹脂組成物を得ることができる。
【００６７】
更に、上記実施形態では、正極活物質にマンガン酸リチウムを例示したが、本発明はこれに限定されるものではなく、上記実施形態以外で用いることのできる正極活物質としては、リチウムを挿入・脱離可能な材料であり、予め十分な量のリチウムを挿入したリチウム遷移金属複酸化物であればよく、遷移金属としてＭｎ、Ｎｉ、Ｃｏ等の単体又は２種以上を主成分とした材料を用いてもよい。また、スピネル結晶構造や層状結晶構造等の結晶構造についても特に制限されるものではない。更に、結晶中の遷移金属やリチウムの一部をそれら以外の例えば、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｒ、Ａ１、Ｍｇ、等の元素で置換あるいはドープした材料、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。これら以外に、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。なお、一般に、マンガン酸リチウムは、炭酸リチウム等の適当なリチウム塩と二酸化マンガン等の酸化マンガンとを混合、焼成して合成することができるが、リチウム塩と酸化マンガンの仕込み比を制御することによって所望のＬｉ／Ｍｎ比とすることができる。
【００６８】
また更に、上記実施形態では、正極のバインダにＰＶｄＦを例示したが、上記実施形態以外で用いることのできる正極用バインダとしては、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリエチレン、ポリスチレン、ポリブタジエン、ブチルゴム、ニトリルゴム、スチレン／ブタジエンゴム、多硫化ゴム、ニトロセルロ−ス、シアノエチルセルロース、各種ラテックス、アクリロニトリル、フッ化ビニル、フッ化ビニリデン、フッ化プロピレン、フッ化クロロプレン等の重合体及びこれらの混合体などが挙げられる。
【００６９】
更にまた、上記実施形態では、負極活物質に塊状黒鉛を用いた例を示したが、本発明で用いることのできる負極活物質としては、上記特許請求の範囲に記載した事項以外に特に制限はない。例えば、天然黒鉛や、人造の各種黒鉛材、コークス、非晶質炭素などの炭素質材料等であればよく、黒鉛質炭素であれば更によい。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。
【００７０】
また、上記実施形態では、正極の導電材に黒鉛粉末、アセチレンブラックを用い、負極の導電材に炭素繊維を用いる例を示したが、本発明はこれに限定されるものではなく、通常用いられているいずれの導電材も使用可能である。
【００７１】
更に、上記実施形態では、非水電解液にエチレンカーボネートとジメチルカーボネートとジエチルカーボネートとの体積比１：１：１の混合溶媒中へ６フッ化リン酸リチウムを１モル／リットル溶解したものを例示したが、本発明はこれに限定されるものではなく、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ることができる。用いられるリチウム塩や有機溶媒は特に制限されない。例えば、電解質としては、ＬｉＣｌ０_４、ＬｉＡｓＦ_６、ＬｉＰＦ_６、ＬｉＢＦ_４、ＬｉＢ（Ｃ_６Ｈ_５）_４、ＣＨ_３Ｓ０_３Ｌｉ、ＣＦ_３Ｓ０_３Ｌｉ等やこれらの混合物を用いることができる。非水電解液有機溶媒としては、プロピレンカーボネート、エチレンカーボネート、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−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またはこれら２種類以上の混合溶媒を用いるようにしてもよく、混合配合比についても限定されるものではない。更に、固体電解質を用いてもよい。
【００７２】
また更に、上記実施形態では、絶縁被覆に、基材がポリイミドで、その片面にヘキサメタアクリレートからなる粘着剤を塗布した粘着テープを用いた例を示したが、例えば、基材がポリプロピレンやポリエチレン等のポリオレフィンで、その片面又は両面にヘキサメタアクリレートやブチルアクリレート等のアクリル系粘着剤を塗布した粘着テープや、粘着剤を塗布しないポリオレフィンやポリイミドからなるテープ等も好適に使用することができる。
【００７３】
【発明の効果】
以上説明したように、本発明によれば、バインダにポリフッ化ビニリデンが混合されているので、高率充放電での電池性能に優れると共に、バインダに熱硬化性可塑化ポリビニルアルコール系樹脂組成物が混合されているので、負極混合材と負極集電体との結着性が向上し、充放電を繰り返しても負極混合材の剥離・脱落を防止することができ、得られるリチウム二次電池の容量や出力の維持率の低下を抑制することができる、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第１実施形態の円筒型リチウムイオン電池を動力用電源として搭載したゴルフカートを模式的に示す側面図である。
【図２】第１実施形態の円筒型リチウムイオン電池の断面図である。
【図３】本発明が適用可能な円筒型リチウムイオン電池を補助電源として搭載したハイブリッド電気自動車を模式的に示す側面図である。
【図４】ハイブリッド電気自動車の電源システムの概略ブロック図である。
【符号の説明】
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
４０ ハイブリッド電気自動車（電気自動車）
５２ 補助電池（補助駆動用電源）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium secondary battery and an electric vehicle, and in particular, a positive electrode using a lithium transition metal double oxide as a positive electrode active material and a negative electrode mixture containing a negative electrode active material and a binder on a negative electrode current collector. The present invention relates to a lithium secondary battery having a negative electrode and an electric vehicle using the lithium secondary battery as a driving power source or an auxiliary driving power source.
[0002]
[Prior art]
Lithium ion secondary batteries, which are representative of lithium secondary batteries, are mainly used as power sources for portable devices such as VTR cameras, laptop computers, and mobile phones, taking advantage of the high energy density. The internal structure of this battery is usually a wound structure as shown below. The electrode has a strip shape in which the active material is applied to the metal foil with a binder (binder) for both the positive electrode and the negative electrode, and the cross section is spirally wound so that the positive electrode and the negative electrode are not in direct contact with the separator interposed therebetween. It forms a group of times. The wound group is accommodated in a cylindrical battery can serving as a battery container, and sealed after injecting the electrolyte.
[0003]
A general cylindrical lithium ion secondary battery has a diameter of 18 mm and a height of 65 mm, which is called 18650 type, and is widely used as a small-sized consumer lithium ion secondary battery. The positive electrode active material of the 18650 type lithium ion secondary battery mainly uses lithium cobaltate, which is characterized by high capacity and long life. The battery capacity is approximately 1.3 Ah to 2.0 Ah, and the output is approximately 10 W. Degree.
[0004]
On the other hand, in the automobile industry, in order to respond to environmental problems, the development of electric vehicles that have no exhaust gas and the power source is completely battery-powered, and hybrid electric vehicles that use both internal combustion engine and battery as power sources Has been accelerated and part of it is now in practical use. Recently, an alternative power source for golf carts using lead batteries has been developed.
[0005]
Batteries that serve as power sources for electric vehicles are naturally required to have higher output that influences higher capacity and acceleration performance, especially high energy by reducing internal resistance of the battery, etc. Lithium ion secondary batteries are attracting attention. For the popularization of electric vehicles, it is essential to reduce the price of the battery. For this purpose, a low-cost battery material is required. For example, in the case of a positive electrode active material, a resource-rich manganese oxide is used. Particular attention has been paid to improvements aimed at improving battery performance. Further, in order to use a lithium ion secondary battery as a power source for an electric vehicle, it is strongly required to extend the life of the battery in order to cope with a long use period of the electric vehicle. The extension of the life here means that not only the battery capacity but also the decrease in output maintenance rate is suppressed and the electric energy supply capability necessary for running the electric vehicle is satisfied over a long period of use.
[0006]
However, in the lithium ion secondary battery, the active material of the positive and negative electrodes repeatedly expands and contracts along with charge and discharge, so that there is a problem that the active material is peeled off from the current collector and dropped and the capacity and output are reduced. In particular, when graphitic carbon is used as the negative electrode active material, it shows a large volume change with expansion and contraction, so that peeling and dropping easily occur. In order to solve this, a technique for ensuring the binding property of the positive and negative electrode active materials to the current collector by limiting the weight average molecular weight of polyvinylidene fluoride used as a binder is disclosed (for example, a patent Reference 1).
[0007]
[Patent Document 1]
JP 2002-270182 A
[0008]
[Problems to be solved by the invention]
However, when polyvinylidene fluoride is used alone for the negative electrode binder, the battery performance at high rate (high rate charge / discharge) is excellent because the polyvinylidene fluoride has excellent binding properties to graphitic carbon. Because it is plastic, it softens in a high-temperature environment, so the binding property between the negative electrode mixture and the negative electrode current collector decreases, so the negative electrode mixture peels off and falls off, degrading battery performance. is there. On the other hand, when a thermosetting polyvinyl alcohol resin is used alone for the negative electrode binder, the binding property between the negative electrode mixture and the negative electrode current collector is improved as compared with the case of polyvinylidene fluoride. Therefore, the life characteristics are improved, but on the other hand, there is a problem that the output is lowered because of the large iR drop (voltage drop) at high rate charge / discharge. Furthermore, in order to further improve the binding property between the negative electrode mixture and the negative electrode current collector, there is a manufacturing problem that heat treatment is necessary.
[0009]
In view of the above-described case, the present invention suppresses a decrease in capacity and output retention rate associated with a charge / discharge cycle, and has a long-life lithium secondary battery and the lithium secondary battery mounted as a driving power source or an auxiliary driving power source. It is an object to provide an electric vehicle.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, a first aspect of the present invention is to apply a positive electrode using a lithium transition metal double oxide as a positive electrode active material and a negative electrode mixture containing a negative electrode active material and a binder to a negative electrode current collector. A lithium secondary battery having a negative electrode attached thereto is characterized in that a main component of the binder is a mixture of a thermosetting plasticized polyvinyl alcohol-based resin composition and polyvinylidene fluoride.
[0011]
In the first aspect, since polyvinylidene fluoride is mixed in the binder, the battery performance at high rate charge / discharge is excellent, and the thermosetting plasticized polyvinyl alcohol resin composition is mixed in the binder. The binding property between the negative electrode mixture and the negative electrode current collector is improved, and the negative electrode mixture can be prevented from peeling and dropping even after repeated charge and discharge, and the capacity and output retention rate of the obtained lithium secondary battery Can be suppressed.
[0012]
In the first embodiment, when the volume ratio of the polyvinyl alcohol-based resin composition and polyvinylidene fluoride exceeds 80:20, the resistance component increases and the output decreases. Since the life is reduced because it is sufficient, the volume ratio is preferably in the range of 80:20 to 20:80. The polyvinyl alcohol-based resin composition may include a first resin component made of a thermosetting polyvinyl alcohol-based resin and a second resin component made of an acrylic resin-based plasticizer. At this time, a thermosetting polyvinyl alcohol resin obtained by reacting a polyvinyl alcohol resin with a cyclic acid anhydride can be used as the first resin component, and a lauryl acrylate / acrylic acid copolymer can be used as the second resin component. An acrylic resin plasticizer obtained by reacting a product with a bifunctional epoxy resin can be used. The negative electrode active material is preferably graphitic carbon. Furthermore, if the lithium transition metal double oxide of the positive electrode active material has a spinel crystal structure, the spinel crystal structure is excellent in thermal stability, so that high capacity and high output can be maintained even in a high temperature environment. Alternatively, if the lithium transition metal double oxide has a layered crystal structure, since the layered crystal has a two-dimensional lithium ion diffusion path, the lithium ion diffusibility is excellent, and thus a high output is secured. be able to.
[0013]
A second aspect of the present invention is an electric vehicle on which the lithium secondary battery according to the first aspect described above is mounted as a driving power source or an auxiliary driving power source. According to this aspect, since the lithium secondary battery that suppresses the decrease in the output and capacity maintenance ratio is used as the driving power supply or the auxiliary driving power supply, the acceleration performance is reduced even when charging and running (discharging) are repeated. A long-life electric vehicle can be realized.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
Hereinafter, a first embodiment in which the present invention is applied to a cylindrical lithium ion battery used as a power source for power of a golf cart will be described with reference to the drawings.
[0015]
As shown in FIG. 1, the golf cart 30 of this embodiment includes a chassis 31 serving as a base. A battery box 36 containing a plurality of cylindrical lithium ion batteries 20 (described later) connected in series is fixed to a substantially central portion of the chassis 31. A cushion 35 is disposed on the battery case 36, and the battery case 36 and the cushion 35 constitute a front seat.
[0016]
In front of the chassis 31, a motor that uses the cylindrical lithium ion battery 20 as a power source and a power transmission mechanism that transmits the rotational driving force of the motor shaft to the wheels are fixed to the chassis 31, and the power transmission mechanism rotates the tire. It is supposed to be a structure to let you. An acceleration pedal 37 that adjusts the forward speed of the golf cart 30 is disposed at the position of the foot of the driver seated on the front seat. The acceleration pedal 37 is connected to a variable resistor that is linked to the depression amount, and the golf cart 30 has a structure that advances according to the depression amount when the driver steps on the acceleration pedal 37.
[0017]
The cylindrical lithium ion battery 20 accommodated in the battery box 36 is manufactured as follows.
[0018]
(Preparation of positive electrode)
As shown in FIG. 2, the positive electrode active material is lithium manganate (LiMn) as a lithium transition metal double oxide.₂O₄)It was used. Graphite powder of conductive material (manufactured by Nippon Graphite Industry Co., Ltd., trade name: J-SP) and acetylene black (trade name: Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) and polyvinylidene fluoride of binder (binder) (Hereinafter referred to as PVdF) was mixed at a mass ratio of 85: 8: 2: 5 to obtain a positive electrode mixture. If necessary, a dispersion solvent N-methyl-2-pyrrolidone (hereinafter referred to as NMP) was added, and the kneaded 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 with a width of 30 mm was left on one side edge in the positive electrode longitudinal direction.
[0019]
Thereafter, drying, pressing, and cutting were performed to obtain a positive electrode having a width of 82 mm, a predetermined length, and a predetermined thickness of the positive electrode mixed material application portion. The bulk density of the positive electrode mixture layer W2 is 2.65 g / cm.³It was. A notch was left in the uncoated portion left on the side edge, and the remaining notch was used as the positive electrode lead piece 2. Adjacent positive electrode lead pieces 2 were spaced 50 mm apart, and the width of the positive electrode lead pieces 2 was 5 mm.
[0020]
(Preparation of negative electrode)
Lumped graphite of negative electrode active material (manufactured by Hitachi Chemical Co., Ltd., trade name: MAG), vapor-grown carbon fiber of conductive material (trade name: VGCF, manufactured by Showa Denko KK), and PVdF of binder as described later NMP solution of a mixture with a thermosetting plasticized polyvinyl alcohol resin composition (hereinafter referred to as PVA) is mixed at a mass ratio of 87.62: 4.76: 7.62, did. The slurry which added and kneaded the dispersion | distribution solvent NMP as needed was apply | coated to both surfaces of 10-micrometer-thick rolled copper foil W3 (negative electrode collector). At this time, an uncoated part with a width of 30 mm was left on one side edge in the negative electrode longitudinal direction.
[0021]
Thereafter, drying, pressing, and cutting were performed to obtain a negative electrode having a width of 86 mm, a predetermined length, and a predetermined thickness of the mixed material application portion. The negative electrode was compressed so that the porosity of the negative electrode mixture layer W4 was about 35%. A notch was formed in the uncoated part left on the side edge in the same manner as the positive electrode, and the remaining part of the notch was used as the negative electrode lead piece 3. Adjacent negative electrode lead pieces 3 were spaced 50 mm apart, and the width of the negative electrode lead pieces 3 was 5 mm.
[0022]
In PVA, a first resin component made of a thermosetting polyvinyl alcohol resin and a second resin component made of an acrylic resin plasticizer are mixed and dissolved in an appropriate solvent (NMP in this embodiment). I used what is. The thermosetting polyvinyl alcohol resin, which is 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 2000, triethylamine in an organic solvent such as NMP. It is obtained by reacting in a substantially anhydrous state in the presence of a catalyst such as The reaction ratio between the polyvinyl alcohol resin and the cyclic acid anhydride is preferably about 0.1 equivalent of the anhydride group of the cyclic acid anhydride with respect to 1 equivalent of the alcoholic hydroxyl group of the polyvinyl alcohol resin. The acrylic resin plasticizer as the second resin component is suitably a reaction product of a lauryl acrylate / acrylic acid copolymer and a bifunctional epoxy resin.
[0023]
The first resin component was synthesized as follows. A separable flask equipped with a stirrer, thermometer, cooling pipe, distilling pipe, and nitrogen gas introduction pipe was charged with 51 g of polyvinyl alcohol with a saponification degree of about 98%, 650 g of NMP and 10 g of toluene while stirring and bubbling with nitrogen. The temperature was raised to 195 ° C. over about 30 minutes. The mixture was kept at the same temperature for 2 hours, and water was azeotroped by refluxing toluene to distill off the water in the flask. Next, toluene was distilled off, cooled to 120 ° C., and kept at the same temperature, 7.7 g of succinic anhydride was added and reacted for 1 hour (an acid hydroxyl group equivalent to 1 equivalent of polyvinyl alcohol was acidified). About 0.07 equivalents of anhydride groups). The mixture was cooled to room temperature to obtain an NMP solution containing about 8% by mass of the first resin component.
[0024]
The second resin component was synthesized as follows. A separable flask equipped with a stirrer, thermometer, cooling pipe, distilling pipe, nitrogen gas introduction pipe, 110 g of a solvent-free lauryl acrylate / acrylic acid copolymer having a weight average molecular weight of about 3100, and a bisphenol A type epoxy 71 g of resin (about 2 equivalents as an epoxy group with respect to 1 equivalent of a carboxyl group of a 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. Warm up. The reaction was allowed to proceed for 2 hours at the same temperature, and then 78 g of NMP was added and cooled to room temperature to obtain an NMP solution containing about 70% by mass of the second resin component.
[0025]
An NMP solution of 8% by mass of the first resin component and an NMP solution of about 70% by mass 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. It was.
[0026]
(Production of battery)
The produced positive electrode and negative electrode were wound together with a polyethylene separator W5 having a width of 90 mm and a thickness of 40 μm so that the two electrodes do not directly contact each other. A hollow cylindrical shaft core 1 made of polypropylene was used at the center of winding. At this time, the positive electrode lead piece 2 and the negative electrode lead piece 3 were respectively positioned on opposite end surfaces of the wound group (electrode group) 6. Further, the lengths of the positive electrode, the negative electrode, and the separator were adjusted, and the diameter of the wound group 6 was 38 ± 0.1 mm.
[0027]
After deforming the positive electrode lead piece 2, all of them are gathered and brought into contact with the vicinity of the collar portion integrally projecting from the circumference of the positive electrode current collecting ring 4 substantially on the extension line of the axis 1 of the winding group 6. The positive electrode lead piece 2 and the flange periphery were ultrasonically welded to connect the positive electrode lead piece 2 to the flange peripheral surface. On the other hand, the connection operation between the negative electrode current collection ring 5 and the negative electrode lead piece 3 was performed in the same manner as the connection operation between the positive electrode current collection ring 4 and the positive electrode lead piece 2.
[0028]
Thereafter, an insulation coating was applied to the entire circumference of the collar peripheral surface of the positive electrode current collecting ring 4. For this insulation coating, an adhesive tape in which the base material was polyimide and an adhesive made of hexamethacrylate was applied on one side thereof was used. One or more layers of this adhesive tape were wound from the circumferential surface of the collar portion to the outer circumferential surface of the wound group 6 to form an insulating coating, and the wound group 6 was inserted into the battery container 7. As the battery container 7, a steel container having an outer diameter of 40 mm and an inner diameter of 39 mm and plated with nickel was used.
[0029]
A negative electrode lead plate 8 for electrical continuity is welded to the negative electrode current collecting ring 5 in advance, and after inserting the wound group 6 into the battery container 7, the bottom of the battery container 7 and the negative electrode lead plate 8 are welded. .
[0030]
On the other hand, the positive electrode current collecting ring 4 is welded with a positive electrode lead 9 formed by previously superposing a plurality of aluminum ribbons, and a battery for sealing the battery container 7 at the other end of the positive electrode lead 9. Welded to the bottom of the lid. The battery lid is provided with a cleavage valve 11 as an internal pressure release mechanism that cleaves as the internal pressure of the cylindrical lithium ion battery 20 increases. The cleavage pressure of the cleavage valve 11 is about 9 × 10⁵Pa was set. The battery lid includes a lid case 12, a lid cap 13, a valve retainer 14 that keeps airtightness, and a cleavage valve (internal gas discharge valve) 11. These are laminated to caulk the periphery of the lid case 12. It is assembled by doing.
[0031]
A predetermined amount of non-aqueous electrolyte is poured into the battery container 7, and then the battery container 7 is covered with a battery cover so that the positive electrode lead 9 is folded, and then crimped and sealed with an EPDM resin gasket 10. Thus, the cylindrical lithium ion battery 20 was completed.
[0032]
The non-aqueous electrolyte includes lithium hexafluorophosphate (LiPF) in a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1: 1: 1.₆) Was dissolved at 1 mol / liter. Note that the cylindrical lithium ion battery 20 has a PTC (Positive Temperature Coefficient) element that operates electrically in response to an increase in battery temperature, or a positive or negative electrical lead in response to an increase in battery internal pressure. There is no current interrupting mechanism to be disconnected.
[0033]
【Example】
  Next, examples of the cylindrical lithium ion battery 20 and the golf cart 30 manufactured by changing the mixing ratio of PVdF and PVA of the negative electrode binder according to the present embodiment will be described. Hereinafter, with respect to the cylindrical lithium ion battery 20, the first embodiment to the first embodiment.8In addition, the embodiment for the golf cart 309~Example16It will be described in detail. In addition, it describes together about the battery and golf cart of the comparative example produced for the comparison.
[0034]
Example 1
As shown in Table 1 below, in Example 1, bulk graphite was used as the negative electrode active material, and the volume ratio of PVdF and PVA as the negative electrode binder was 20:80.
[0035]
[Table 1]

[0036]
(Example 26)
  As shown in Table 1, Example 2 to Example6Then, it carried out similarly to Example 1 except changing the mixing ratio of PVdF and PVA. In Example 2, the mixing ratio is 40:60, in Example 3, the mixing ratio is 60:40, and in Example 4, the mixing ratio is 80:20.In Example 5, the mixing ratio was 10:90, and in Example 6, the mixing ratio was 90:10.It was.
[0037]
(Example 7)
  As shown in Table 1,Example 7Then, amorphous carbon (made by Kureha Kogyo Co., Ltd., trade name: PIC (F)) was used as the negative electrode active material, and the mixing ratio of PVdF and PVA was 40:60.
[0038]
(Example 8)
  As shown in Table 1,Example 8Then, except that the mixing ratio of PVdF and PVA is 10:90Example 7And so on.
[0039]
(Example9~16)
  Example9~Example16Then, Example 1- Example8The 72 cylindrical lithium ion batteries 20 were connected in series and mounted on the golf cart 30.
[0040]
(Comparative example1)
  As shown in Table 1, comparative examples1IsNegative electrode binderPVdFOnlyThe same as Example 1 except that.
[0041]
(Comparative example2)
  As shown in Table 1, comparative examples2Then, PVA was used alone as the negative electrode binder, and the same procedure as in Example 1 was performed except that vacuum drying and heat treatment were performed at 150 ° C. for 3 hours in order to perform thermosetting treatment of the binder.
[0042]
(Comparative example3~4)
  Comparative example3~ Comparative example4Then, Comparative Example 1 to Comparative Example272 cylindrical lithium ion batteries were connected in series and mounted on a golf cart.
[0043]
<Test and evaluation>
Next, the following series of tests were performed on the batteries and golf carts of Examples and Comparative Examples produced as described above.
[0044]
Each battery of the examples and comparative examples was initially charged, and the initial discharge capacity was measured in an atmosphere at a test environment temperature of 25 ± 1 ° C. The charging conditions were a 4.2 V constant voltage, a limiting current of 5 A, and 4.5 hours. The discharge conditions were a 5 A constant current and a final voltage of 2.7 V.
[0045]
Moreover, the discharge output of the battery in a charged state was measured in the atmosphere at the same environmental temperature after the initial charge. The measurement conditions are 1A, 3A, 6A, the voltage at 5 seconds is read for each discharge current, the voltage value is plotted on the vertical axis against the current value on the horizontal axis, and the initial DC resistance value ( DCR) was determined.
[0046]
Further, each battery of the example and the comparative example was subjected to a cycle test in which charging and discharging were repeated 100 times at an electric current value of 1C (5A) in an atmosphere of 25 ° C and 60 ° C. In an atmosphere of 25 ° C., a cycle test with a current value of 10 C (40 A) was also performed. After the cycle test, the DC resistance value and the discharge capacity are measured in the same manner, and the ratio of the DC resistance value and the discharge capacity after the cycle test with respect to the initial DC resistance value and the initial discharge capacity is obtained as a percentage, respectively. And capacity retention rate. Naturally, the higher the capacity retention rate and the lower the DC resistance increase rate, the better the life characteristics. The test results of each battery are shown in Table 2 below.
[0047]
In the golf cart test, the vehicle was started with a fully charged battery, and the time required for the golf cart to reach 10 km / h was measured to determine the acceleration time. After removing the battery from the golf cart and performing the cycle test described above, the battery was mounted on the golf cart again and the acceleration time was measured in the same manner. The increase rate (%) of the acceleration time after the cycle test with respect to the initial acceleration time was determined. The test results of the golf cart are shown in Table 3 below.
[0048]
[Table 2]

[0049]
  As shown in Table 2, Examples 1 to Examples produced by changing the mixing ratio of PVdF and PVA6It was found that there was an inflection point at which the capacity retention rate was maximum when 60% of PVA, that is, 40% of PVdF was used (battery of Example 2). Similarly, it was found that the DC resistance increase rate was most suppressed when the PVA was 60%. Similar results were shown in both the capacity maintenance rate and the DC resistance increase rate in the test in which the current value of the cycle test was increased to 10C. In contrast, Comparative Examples 1 to 12In this battery, the capacity retention rate decreased and the DC resistance increase rate increased. Therefore, the mixing ratio of PVdF and PVA is preferably 80:20 to 20:80, more preferably 60:40 to 40:60 in volume ratio.
[0050]
  Moreover, the comparative example using only PVA2This battery showed a higher capacity retention rate and a lower DC resistance increase rate than the battery of Comparative Example 1 using only PVdF. Therefore, it has been found that PVA is effective in improving the capacity maintenance rate and the DC resistance increase rate.2Then, the thermosetting treatment is performed at the time of producing the negative electrode, and there is a manufacturing problem in using PVA alone.
[0051]
  Furthermore, amorphous carbon was used as the negative electrode active material.Example 7as well asExample 8In the battery, the volume ratio of PVdF to PVA was set to 40:60.Example 7The battery has a volume ratio of 10:90.Example 8Both the capacity retention rate and the DC resistance increase rate were superior to those of the batteries. But,Example 7When the battery of Example 2 was compared with the battery of Example 2 using massive graphite as the negative electrode active material, the battery of Example 2 showed better results. Therefore, even when amorphous carbon is used as the negative electrode active material, it is possible to improve the capacity retention rate and the DC resistance increase rate by mixing PVA and PVdF at a volume ratio of 80:20 to 20:80. However, it has been found that the capacity retention rate and the DC resistance increase rate can be further improved by using the graphite as the negative electrode active material.
[0052]
[Table 3]

[0053]
  As shown in Table 3, Example 1 to Example8Example with each battery9~Example16In the golf cart 30 of Comparative Example 1 to Comparative Example2Comparative example with each battery3~ Comparative example4Compared to golf carts, the rate of increase in acceleration time after a cycle test corresponding to repeated virtual charging and running (discharging) was kept low, resulting in a high-performance golf cart. Further, it has been found that the acceleration time increase rate of the golf cart greatly depends on the discharge capacity and DC resistance value of the battery. By using a mixture of PVdF and PVA in the negative electrode binder, it is possible to suppress a decrease in acceleration performance. found.
[0054]
Since the cylindrical lithium ion battery 20 of the present embodiment is used by mixing PVdF as a negative electrode binder, both the capacity retention rate and the DC resistance increase rate are excellent even when high rate charge / discharge with a current value of 10 C is repeated. A battery can be obtained. Moreover, since the binding property between the negative electrode mixture and the negative electrode current collector is improved by mixing and using PVA, the negative electrode mixture is prevented from being peeled off or dropped even after repeated charge and discharge, and the capacity is maintained. Rate and DC resistance increase rate can be improved. In addition, when the volume ratio of PVA to PVdF exceeds 80:20, the resistance component increases (DC resistance increase rate increases) and the output decreases. When the volume ratio is less than 20:80, the binding property is insufficient. Capacity maintenance rate decreases. For this reason, it is preferable that the volume ratio of PVA and PVdF shall be 80: 20-20: 80. Furthermore, when PVA is used alone, heat treatment is required to improve the binding property between the negative electrode mixture and the negative electrode current collector, and thus there is a manufacturing problem, but a mixture of PVA and PVdF is used. By using it, manufacturing problems can be overcome. The golf cart 30 equipped with these batteries can be a high-performance golf cart with little decrease in acceleration time even when charging and running are repeated.
[0055]
(Second Embodiment)
Next, a second embodiment in which the present invention is applied to a cylindrical lithium ion battery used as an auxiliary power source for a hybrid electric vehicle will be described. In this embodiment, a cylindrical lithium ion battery is used as an auxiliary battery for charging a lead battery as a main battery. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described.
[0056]
As shown in FIG. 3, the hybrid electric vehicle 40 of this embodiment includes a power supply system 50 that supplies electric power to the internal combustion engine and the entire vehicle.
[0057]
As shown in FIG. 4, the power supply system 50 includes a motor generator 53 having functions such as a vehicle drive motor, a load 54 such as lighting, a wiper, and a radio, and charge / discharge for supplying power to the motor generator 53 and the load 54. A system unit 60 is included.
[0058]
The motor generator 53 has three functions switched and controlled by a vehicle control system (not shown). The motor generator 53 is driven by electric power from the charge / discharge system unit 60 to drive the vehicle and start the engine during low-speed running from the start of the vehicle. During engine driving, as an alternator (generator) capable of generating electric power by the rotational force of the engine and charging the charge / discharge system unit 60 and supplying electric power to the load 54, regenerative energy is converted into electric energy when the vehicle is braked. Function as a high-output generator capable of charging the auxiliary battery 52 and supplying power to the load 54.
[0059]
The charge / discharge system unit 60 includes a main battery 51 serving as a main power source for supplying power to the vehicle, an auxiliary battery 52 that supplies charging power to the main battery 51, and a voltage of a DC-DC converter that boosts the voltage of the auxiliary battery 52. The booster 55 has a charge / discharge controller 56 that controls the charge / discharge states of the main battery 51 and the auxiliary battery 52.
[0060]
As the main battery 51, a lead battery is used. As a battery case for a lead battery, a monoblock battery case whose interior is defined by 18 cell chambers is used. Each cell chamber accommodates a pair of electrode plates in which a plurality of positive electrode plates and negative electrode plates are laminated via a glass fiber separator, and an electrolytic solution (dilute sulfuric acid) is injected therein. Each cell chamber is sealed with a lid that integrally covers the opening of the monoblock battery case, and a control valve is disposed above each cell chamber and sealed. The cell chambers are connected in series by a conductive connecting member.
[0061]
The auxiliary battery 52 is configured by connecting ten cylindrical lithium ion batteries 20 in series. The auxiliary battery 52 and the voltage booster 55 are connected in series. When the voltage of the auxiliary battery 52 is higher than the voltage of the main battery 51, the voltage booster 55 may not be connected.
[0062]
A positive external terminal of the main battery 51 is connected to one end of the voltage booster 55. One end of the motor generator 53 and one end of the load 54 are connected to the positive external terminal of the main battery 51. The negative external terminals of the main battery 51 and the auxiliary battery 52 are connected to the ground. The other ends of the motor generator 53 and the load 54 are each connected to the ground. Therefore, the main battery 51, the auxiliary battery 52 connected in series with the voltage booster 55, the motor generator 53, and the load 54 can be connected in parallel.
[0063]
In the power supply system 50 of the present embodiment, the lithium ion battery 20 constituting the auxiliary battery 52 is charged by regenerative power during vehicle braking. Since the main battery 51 has low power acceptability, charging with regenerative power is not performed. When the remaining capacity of the main battery 51 is reduced, the power stored in the auxiliary battery 52 is supplied to the main battery 51 and the main battery 51 is charged. When the voltage of the auxiliary battery 52 decreases, the voltage of the auxiliary battery 52 is boosted by the voltage booster 55 and supplied to the main battery 51.
[0064]
Further, in the power supply system 50 of the present embodiment, the auxiliary battery 52 stores the regenerative power from the motor generator 53 and gently charges the main battery 51 with the stored power, so that the life characteristics of the main battery 51 are improved. Can do. Further, since the auxiliary battery 52 is composed of the lithium ion battery 20 with improved life characteristics, the life characteristics of the entire power supply system can be improved.
[0065]
In the above embodiment, the lithium ion battery used for the power source for the golf cart and the auxiliary power source for the hybrid electric vehicle is exemplified. However, the size and battery capacity of the battery are not limited, and the battery capacity is approximately 3 Ah. It has been confirmed that the present invention exerts a remarkable effect on a battery of about 100 Ah. Therefore, the lithium ion battery 20 can also be used for a (pure) electric vehicle. Further, in the above embodiment, the cylindrical battery using the positive and negative electrode plates wound up is exemplified, but the present invention is not limited to the shape of the battery, and a rectangular battery, other polygonal batteries, The present invention can also be applied to a laminate type battery in which positive and negative electrode plates are laminated. Furthermore, the shape to which the present invention can be applied may be other than a battery having a structure in which the upper lid of the battery is sealed by caulking in the above-described bottomed cylindrical container (can). As an example of such a structure, a battery in which the positive and negative external terminals penetrate through the battery lid and the positive and negative external terminals are pressed through the shaft core in the battery container can be cited. Further, the number of batteries mounted on the electric vehicle or the hybrid electric vehicle may be appropriately combined depending on the desired output and capacity, and the battery installation location is not particularly limited.
[0066]
In the above-described embodiment, the thermosetting plasticized polyvinyl alcohol resin composition of the negative electrode binder is prepared by using a polyvinyl alcohol resin having an average polymerization degree of about 2000, succinic anhydride, and a lauryl acrylate / acrylic having a weight average molecular weight of about 3100. Examples of using acid copolymer and bisphenol A type epoxy resin have been shown, but the present invention is not limited to these, polyvinyl alcohol resins having different average polymerization degrees and lauryl acrylate / acrylic acid having different weight average molecular weights. A copolymer may be used. In this case, a thermosetting plasticized polyvinyl alcohol resin composition having desired physical properties can be obtained depending on the equivalent ratio and reaction conditions during the reaction.
[0067]
Furthermore, in the above embodiment, lithium manganate is exemplified as the positive electrode active material. However, the present invention is not limited to this, and the positive electrode active material that can be used in other than the above embodiment includes lithium. A lithium transition metal double oxide in which a sufficient amount of lithium is inserted in advance is sufficient as a detachable material, and a material mainly composed of a single element or two or more of Mn, Ni, Co, etc. as a transition metal. It may be used. Further, the crystal structure such as spinel crystal structure and layered crystal structure is not particularly limited. Further, a material in which a part of transition metal or lithium in the crystal is substituted or doped with other elements such as Fe, Co, Ni, Cr, A1, Mg, etc., a part of oxygen in the crystal is S, A material substituted or doped with an element such as P may be used. In addition to these, the use of lithium manganese complex oxide capable of 5V class as the battery voltage does not change the effect of the present invention. In general, lithium manganate can be synthesized by mixing and baking an appropriate lithium salt such as lithium carbonate and manganese oxide such as manganese dioxide, but the charge ratio of the lithium salt and manganese oxide should be controlled. The desired Li / Mn ratio can be obtained.
[0068]
Furthermore, in the above embodiment, PVdF is exemplified as the positive electrode binder, but as the positive electrode binder that can be used in other than the above embodiment, polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile Polymers such as rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene, and mixtures thereof It is done.
[0069]
Furthermore, in the above embodiment, an example in which massive graphite is used as the negative electrode active material has been shown. However, as the negative electrode active material that can be used in the present invention, there is no particular limitation other than the matters described in the claims. Absent. For example, natural graphite, various artificial graphite materials, carbonaceous materials such as coke, amorphous carbon, etc. may be used, and graphite carbon is better. The graphitic carbon here does not necessarily indicate highly crystalline graphite, but the interlayer distance d by X-ray diffraction, such as mesophase graphite.₀₀₂May be graphite exceeding 0.3354 nm. X-ray diffraction may show diffraction lines that can be indexed by hkl. Also, the particle shape is not particularly limited, such as a scale shape, a spherical shape, a fiber shape, or a lump shape.
[0070]
In the above embodiment, an example is shown in which graphite powder and acetylene black are used for the positive electrode conductive material, and carbon fiber is used for the negative electrode conductive material. However, the present invention is not limited to this and is usually used. Any conductive material can be used.
[0071]
Furthermore, in the said embodiment, what melt | dissolved 1 mol / l of lithium hexafluorophosphate in the mixed solvent of the volume ratio 1: 1: 1 of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in nonaqueous electrolyte solution is illustrated. However, the present invention is not limited to this, and a nonaqueous electrolytic solution in which a general lithium salt is used as an electrolyte and this is dissolved in an organic solvent can be used. The lithium salt and organic solvent used are not particularly limited. For example, as an electrolyte, LiCl0₄, LiAsF₆, LiPF₆, LiBF₄, LiB (C₆H₅)₄, CH₃S0₃Li, CF₃S0₃Li or the like or a mixture thereof can be used. Nonaqueous electrolyte organic solvents include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3- Dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, or a mixed solvent of two or more of these may be used, and the mixing ratio is not limited. Further, a solid electrolyte may be used.
[0072]
Furthermore, in the said embodiment, although the base material was a polyimide and the adhesive tape which apply | coated the adhesive which consists of hexamethacrylate was used for the one side was shown in the insulation coating, for example, a base material is polypropylene and polyethylene. It is also possible to suitably use a pressure-sensitive adhesive tape in which an acrylic pressure-sensitive adhesive such as hexamethacrylate or butyl acrylate is applied on one or both surfaces thereof, or a tape made of polyolefin or polyimide to which no pressure-sensitive adhesive is applied.
[0073]
【The invention's effect】
As described above, according to the present invention, since polyvinylidene fluoride is mixed in the binder, the battery performance at high rate charge / discharge is excellent, and the thermosetting plasticized polyvinyl alcohol resin composition is added to the binder. Since it is mixed, the binding property between the negative electrode mixture and the negative electrode current collector is improved, and the negative electrode mixture can be prevented from peeling and dropping even after repeated charge and discharge. It is possible to obtain an effect that it is possible to suppress a decrease in capacity and output maintenance rate.
[Brief description of the drawings]
FIG. 1 is a side view schematically showing a golf cart equipped with a cylindrical lithium ion battery according to a first embodiment to which the present invention is applicable as a power source for power.
FIG. 2 is a cross-sectional view of the cylindrical lithium ion battery according to the first embodiment.
FIG. 3 is a side view schematically showing a hybrid electric vehicle equipped with a cylindrical lithium ion battery to which the present invention is applicable as an auxiliary power source.
FIG. 4 is a schematic block diagram of a power supply system of a hybrid electric vehicle.
[Explanation of symbols]
20 Cylindrical lithium ion battery (lithium secondary battery)
30 Golf cart (electric car)
35 Front seat
36 Battery box
40 Hybrid electric vehicle (electric vehicle)
52 Auxiliary battery (auxiliary drive power supply)

Claims (9)

  In a lithium secondary battery having a positive electrode using a lithium transition metal complex oxide as a positive electrode active material and a negative electrode obtained by coating a negative electrode current collector with a negative electrode active material and a negative electrode mixed material including a binder. A lithium secondary battery, wherein the component is a mixture of a thermosetting plasticized polyvinyl alcohol-based resin composition and polyvinylidene fluoride.   The lithium secondary battery according to claim 1, wherein a volume ratio of the polyvinyl alcohol-based resin composition to the polyvinylidene fluoride is in a range of 80:20 to 20:80.   The said polyvinyl alcohol-type resin composition contains the 1st resin component which consists of a thermosetting polyvinyl alcohol-type resin, and the 2nd resin component which consists of an acrylic resin-type plasticizer, It is characterized by the above-mentioned. Lithium secondary battery.   The lithium secondary battery according to claim 3, wherein the first resin component is a thermosetting polyvinyl alcohol resin obtained by reacting a cyclic acid anhydride with a polyvinyl alcohol resin.   4. The lithium secondary battery according to claim 3, wherein the second resin component is an acrylic resin plasticizer obtained by reacting a lauryl acrylate / acrylic acid copolymer with a bifunctional epoxy resin. 5.   The lithium secondary battery according to any one of claims 1 to 5, wherein the negative electrode active material is graphitic carbon.   The lithium ion secondary battery according to any one of claims 1 to 6, wherein the lithium transition metal double oxide has a spinel crystal structure.   The lithium ion secondary battery according to any one of claims 1 to 6, wherein the lithium transition metal double oxide has a layered crystal structure.   An electric vehicle comprising the lithium secondary battery according to any one of claims 1 to 8 mounted as a driving power source or an auxiliary driving power source.

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