JP4053657B2 - Lithium secondary battery and manufacturing method thereof - Google Patents
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- JP4053657B2 JP4053657B2 JP14410298A JP14410298A JP4053657B2 JP 4053657 B2 JP4053657 B2 JP 4053657B2 JP 14410298 A JP14410298 A JP 14410298A JP 14410298 A JP14410298 A JP 14410298A JP 4053657 B2 JP4053657 B2 JP 4053657B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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Description
【０００１】
【発明の属する技術分野】
本発明はリチウム二次電池に関する。更に詳しくは、従来の液体状電解質に代えて、ポリマー電解質（電解質をポリマーに含浸又は保持されたものも含む）を用いたリチウム二次電池に関し、サイクル特性に優れ、外部からの圧力、曲げに対して耐えうる優れたリチウム二次電池に関する。
【０００２】
【従来の技術】
近年、カメラ一体型ＶＴＲ装置、オーディオ機器、携帯型コンピュータ、携帯電話等様々な機器の小型化、軽量化が進んでおり、これら機器の電源としての電池に対する高性能化要請が高まっている。中でも電気自動車の動力源としての電池として高電圧、高エネルギー密度で、且つ優れたサイクル特性の実現が可能なリチウム二次電池の開発が盛んになっている。
【０００３】
リチウム二次電池は概ね、リチウムイオンを吸蔵放出可能な正極及び負極、並びに非水電解質液とからなっており、例えば正極にコバルト酸リチウムを含む電極、負極に炭素材料を含む電極、及び電解質液を用いた二次電池の場合には、充電中に正極中からリチウムイオンが電解液を介して負極中に吸蔵され、放電時には負極中からリチウムイオンが放出され電解液を介して正極中に吸蔵されるというものである。この電極に要求される特性として、電極へのリチウムイオンの吸蔵能力及び放出能力が大きく、これら吸蔵・放出の繰り返し（サイクル）による各能力の低下を抑えることである。
【０００４】
このような優れたリチウム二次電池の正極に要求される特性としては正極層内での導電性が挙げられる。正極に用いる、リチウムイオンを吸蔵放出可能な化合物は導電性が殆ど無い酸化物を用いることが多く、これのみでは正極として機能しないので、通常炭素等の導電性物質を用いて導電性を付与し、正極として用いている。又、電解液としては従来、高電圧を得る為に非水系の電解液が用いられてきた。一方、非水系電解液を用いた際には液状であるが故に濾液、これに伴なう発火の危険を有していることから、近年では安全性を向上させるために非水電解液を、例えばゲル状ポリマーに含浸又は保持させたものや、ポリマー自体が電解質として働く、いわゆるポリマー電解質の開発が行われている。
【０００５】
特にリチウム二次電池においては電解質液を用いた際に生ずるリチウムのデンドライト析出による内部短絡による発熱、発火が問題となっており、優れたポリマー電解質の開発とその応用が望まれていた。
さらに上述のポリマー電解質は、それ自体が二次電池系で使用されるセパレーターの代用を勤めることが可能となるので、従来のようにセパレータを用いずとも、このポリマー電解質を挟んで正極と負極を接合させることで電池を構成できる。この様にポリマー電解質を用いることで軽量、形状柔軟性が向上するので、例えばシート状の如き薄膜化が可能であり、軽量、省スペースな電池が作成可能となる有利な点がある。
また、ポリマー電解質は、電池の内部抵抗低下やエネルギー密度向上のため、内部短絡をしない範囲で、薄いことが望まれている。
【０００６】
【発明が解決しようとする課題】
ポリマー電解質は電極の活物質層上に設けるが、この際、ポリマー電解質が活物質層内に含浸したり、又、独立に層を形成する場合等がある。ポリマー電解質としてゲルのごとき機械的強度の弱いものを用いる際には、特にポリマー電解質を薄膜化した場合に、ポリマー電解質層と接する正極又は負極の活物質層表面が荒れていると外部からのわずかな圧力でも正負極の内部短絡の原因となったり、電流の集中のためデンドライトの発生の起点となり、サイクル特性を劣化させるという問題があった。また、活物質表面を完全に平坦にしてしまうと、ポリマー電解質層との接着性が低下し、容易に剥離を招き、ポリマー電池の特徴たる可撓性を損なうという問題があった。
【０００７】
【課題を解決するための手段】
本発明は上記実状に鑑みて為されたものであり、サイクル特性に優れたリチウム二次電池を得るために鋭意検討した結果、正極、負極の活物質層表面粗度を特定範囲にすることにより、又、さらにはポリマー電解質層の表面粗度を特定範囲とすることにより、内部短絡しにくく、且つサイクル特性のよい、可撓性に優れたリチウム二次電池を得られることを見いだし、完成したものである。
【０００８】
【発明の実施の形態】
以下に、本発明を詳細に説明する。
本発明でいう表面粗度とは、任意の方法で算出できるが例えば、非接触もしくは接触式の表面粗度計を用いて測定された粗さ曲線から求めることができる。また、例えばポリマー電解質層の活物質層との接触面の表面粗度とは、界面を剥離し、表面粗度として測定しても良いし、あるいは、切断面をＳＥＭ等の顕微鏡により観察し、粗さ曲線を求め、算出してもよい。Ｒｐ、Ｒｖについては、例えば上述の如き方法により得られた粗さ曲線より、最小二乗法を用いて平均線を求める。Ｒｐ値（平均線高さ）とは、平均線と粗さ曲線の最高山頂の間隔、また、Ｒｖ値（平均線深さ）とは、平均線と最深谷底の間隔である。
【０００９】
本発明においては、正、負極における活物質表面のＲｐ値が０．１μｍ〜２０μｍであり、Ｒｖ値は０．１μｍ〜５０μｍであることが好ましい。Ｒｐ値は、特に１〜１０μｍとすることが好ましい。Ｒｐ値が２０μｍを超えると、電池が内部短絡を起こしやすくなったり、局部的な電流集中によるサイクル特性の低下や、デンドライトの発生につながることがある。また、０．１μｍに満たないとポリマー電解質との接着性が低下し、電池の可撓性を損なうことがある。また、Ｒｖ値は、特に、１μｍ〜２０μｍであることが好ましい。Ｒｖ値が５０μｍを超えると電池の容量低下につながり、０．１μｍに満たないと、ポリマー電解質との接着性に悪影響を与えることがある。
【００１０】
さらに、本発明においては、ポリマー電解質層が活物質層とは独立して層を形成する際に、ポリマー電解質層の活物質層との接触面のＲｐ値が０．１μｍ〜５０μｍ、Ｒｖ値が０．１μｍ〜２０μｍであることが好ましい。Ｒｐ値は、特に１〜１０μｍであることが好ましい。Ｒｐ値が５０μｍを超えると、電池の容量低下につながることがあり、０．１μｍに満たないと、電解質との接着性に悪影響を与えることがある。Ｒｖ値は、特に１μｍ〜１０μｍとすることが好ましい。Ｒｖ値が２０μｍを超えると、電池が内部短絡を起こしやすくなったり、局部的な電流集中を起こし、サイクル特性の低下や、デンドライト発生につながることがある。また、０．１μｍに満たないと、正、負極活物質層との接着性が低下し、電池の可撓性を損なうことがある。
【００１１】
本発明のリチウム二次電池においてはこのように電極活物質層やポリマー電解質層表面の粗さを特定範囲とすることで、特にポリマー電解質（層）の厚さを５０μｍ以下とした薄膜化されたリチウム二次電池においても好適なものが得られるのである。ポリマー電解質（層）の厚さは任意であるが、通常、１０〜５０μｍである。
【００１２】
また、このようなＲｐと短絡との関係は電解質厚さにも依存する。近年、エネルギー密度に対する向上要求は高まってきており、電解質層の平均厚さ（ｄ）と活物質層表面の平均線高さ（Ｒｐ）と、電池特性の関係を検討した結果、Ｒｐ／ｄが０．３以下、中でも０．３〜０．００２、特に０．２５〜０．０５であれば、収率よく良好な特性が得られることを見い出した。Ｒｐ／ｄが０．３をこえると、局部的な電流集中により３７００ｍＶ以上の高電位部でデンドライトの発生による短縮を生じたり、大電流充放電において、サイクル特性の低下をひきおこす原因となるのである。
【００１３】
本発明のリチウム二次電池は正極、負極及びポリマー電解質を主たる構成要件とする。
まず本発明のリチウム二次電池における電極について説明する。一般的に、リチウム二次電池における正極や負極は、アルミニウム箔や銅箔の様な集電体上に正極（負極）活物質、結合樹脂（バインダー）、導電材料及び溶媒等を含有する電極の活物質層を形成する塗料を塗布、乾燥して製造する。
【００１４】
本発明における正極に用いる活物質である、リチウムイオンを吸蔵放出可能な化合物としては、無機化合物としてはＦｅ、Ｃｏ、Ｎｉ、Ｍｎ等の遷移金属の遷移金属酸化物、リチウムと遷移金属との複合酸化物、遷移金属硫化物等が挙げられる。具体的には、ＭｎＯ、Ｖ2 Ｏ5 、Ｖ6 Ｏ13、ＴｉＯ2 等の遷移金属酸化物粉末、ニッケル酸リチウム、コバルト酸リチウムなどのリチウムと遷移金属との複合酸化物粉末、ＴｉＳ2 、ＦｅＳなどの遷移金属硫化物粉末等が挙げられる。有機化合物としては、例えばポリアニリン等の導電性ポリマー等が挙げられる。又、これら無機化合物、有機化合物を任意の割合で混合しても良い。
【００１５】
負極活物質材料としては、Ｌｉ金属箔の他にリチウムイオンを吸蔵放出可能な化合物としてグラファイトやコークス等を用いるが、特に安全性の面からコークスが好ましい。これら正極、負極の活物質の粒径は電池のその他の構成要件とのかねあいで適宜選択すればよいが、通常、平均粒径１〜３０μｍ、特に１〜１０、中でも３〜８μｍとすることで、請求項記載の表面粗度が得られやすくなる。さらには、空隙率を容易に制御することが可能であるという効果があるので好ましい。
【００１６】
バインダーとしては、電解液等に対して安定である必要があり耐候性、耐薬品性、耐熱性、難燃性等が望まれる。さらにイオン伝導性に優れた材料が望ましく例えば架橋性のポリエチレンオキシド樹脂等が挙げられる。さらに好ましくは、ポリエチレンオキシド樹脂末端にアクリル基、メタアクリル基等を導入し熱や紫外線等により架橋させたものが好ましい。
【００１７】
導電性物質としては、リチウムを吸蔵放出可能な化合物粉末に適量混合して導電性を付与できるものであれば特に制限は無いが、アセチレンブラック、カーボンブラック、黒鉛などの炭素質粉末や、使用する電極電位で安定な金属粉末などが挙げられる。
これら導電性物質のＤＢＰ吸油量は１００〜５００ｃｃ／１００ｇ、特に１５０〜３００ｃｃ／１００ｇが好ましい。又、平均粒径は１〜１００［ｎｍ］、特に１０〜５０［ｎｍ］が好ましい。活物質と導電性物質との重量比は、９８／２〜９０／１０の範囲が好ましい。
【００１８】
正極を形成する塗料の溶媒としては、前記バインダーを分散、溶解可能で、且つ容易に乾燥するものが好ましい。例えばアクリロニトリル、ジメチルカーボネート等が挙げられる。
正極の集電体としては、一般的にアルミ箔を用いる。負極の集電体としては、銅箔を用いる。これら集電体においては、活物質層を設ける表面を予め粗面化処理を行うと結着効果が高くなるので好ましい。表面の粗面化方法としては、機械的研磨法、電解研磨法または化学研磨法が挙げられる。機械的研磨法としては、研磨剤粒子を固着した研磨布紙、砥石、エメリバフ、鋼線などを備えたワイヤーブラシなどで集電体表面を研磨する方法が挙げられる。
【００１９】
集電体への正極及び負極の形成方法は、特に限定されるものではないが、塗料の粘度が高いことからコンマリバースコート、スクイーズコート、リップコート等の塗布方式を用いるのが好ましい。正極及び負極の各活物質層の厚み（平均厚さ）は夫々通常、２０〜２００μｍ程度である。
正、負極における活物質層の表面粗度をコントロールするためには、活物質粒子径を変えたり、活物質層形成塗料を基材上に塗布・乾燥した後、塗膜にプレス処理をする方法や塗料の溶媒の種類、量を制御するという種々の方法が有る。例えば、正、負極の活物質層を集電体上に形成した後に、圧力を１〜５０００〔ｋｇ／ｃｍ２ 〕、好ましくは１〜１０００〔ｋｇ／ｃｍ２ 〕、温度を室温〜２００〔℃〕、好ましくは室温〜１５０〔℃〕でカレンダーにより圧力をかけることで成し得る。
【００２０】
次に、ポリマー電解質について説明する。
ポリマー電解質としては、それ自体電解質を構成するものであってもよく、ゲル状ポリマー中に電解液を含有するものであっもよいが、後者の場合には、一般的にはゲル状ポリマーに含有させる電解液は非水電解液が好適であり、これは非水溶媒に電解質を溶解させたものを用いるのが一般的である。
【００２１】
ポリマー電解質作成に用いる電解質としては、電解質として正極活物質及び負極活物質に対して安定であり、且つリチウムイオンが前記正極活物質あるいは負極活物質と電気化学反応をするための移動を行い得るものであればいずれのものでも使用することができる。
具体的にはＬｉＰＦ6 、ＬｉＡｓＦ6 、ＬｉＳｂＦ6 、ＬｉＢＦ4 、ＬｉＣｌＯ4 、ＬｉＩ、ＬｉＢｒ、ＬｉＣｌ、ＬｉＡｌＣｌ、ＬｉＨＦ2 、ＬｉＳＣＮ、ＬｉＳＯ3 ＣＦ2 等が挙げられる。これらのうちでは特にＬｉＰＦ6 、ＬｉＣｌＯ4 が好ましい。
【００２２】
これら電解質の電解液における含有量は、一般的に０．５〜２．５ｍｏｌ／ｌである。
この電解質を溶解する溶媒は特に限定されないが、比較的高誘電率の溶媒が好適に用いられる。具体的にはエチレンカーボネート、プロピレンカーボネート等の環状カーボネート類、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネートなどの非環状カーボネート類、テトラヒドロフラン、２−メチルテトラヒドロフラン、ジメトキシエタン等のエーテル類、γ−ブチルラクトン等のラクトン類、スルフォラン等の硫黄化合物、アセトニトリル等のニトリル類が挙げられる。又、これらの２種以上を、任意の割合で混合して用いてもよい。これらの中でも特にエチレンカーボネート、プロピレンカーボネート等の環状カーボネート類、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネートなどの非環状カーボネート類から選ばれた１種又は任意の割合からなる２種以上の混合溶液が好ましい。
【００２３】
ポリマー電解質は、電解質溶解液をゲルを形成するポリマー、例えばポリエチレンオキサイド、ポリプロピレンオキサイド、ポリエチレンオキサイドのイソシアネート架橋体、フェニレンオキシド、フェニレンスルフィド系ポリマー等の重合体に含浸させゲル状のポリマー電解質を作成する。必要に応じてアクリル基など重合性の官能基を持つ化合物を電解質溶液と混合し、ＵＶなどのエネルギー線を照射し重合したり、混合物を熱により重合させて、ポリマー電解質を得てもよい。
電解質の電解質溶解液における含有量は一般に０．５〜２．５ｍｏｌ／ｌである。また、この場合のゲルを構成するポリマーの強度としてはピン刺し強度＜１ｍｍφ０．５ｒの球面座圧触試験として通常１〜５０ｇ・Ｆ程度のものが用いられる。なお、補強材として、不織布あるいは多孔質膜等を組合せて用いてもよく、この場合の前記ピン刺し強度としては、１００〜５００ｇ・Ｆ程度である。
【００２４】
ポリマー電解質層を形成する塗料の粘度は塗工方法や塗料形成材料にもよるが、１００００ｃｐ以下とするのが好ましい。この範囲であれば、正、負極の活物質層表面の凹凸に電解質を容易に入り込ませることができるので、電解質層の表面粗度、正極負極層との界面粗度は、接触している正極負極層の表面粗度を逆に写し取った大きさとなる。即ち、活物質層表面のＲｐ、Ｒｖ値がこの表面に接触するポリマー電解質層表面のＲｖ、Ｒｐ値となるので好ましい。また、逆に電解質溶液の粘度が１０００００ｃｐを超えるような高粘度の場合、容易に正、負極の活物質層表面の凹凸になじまないことがある。
【００２５】
本発明の特徴は上述した如く、ポリマー電解質を用いたリチウム二次電池において正、負極の活物質層、ポリマー電解質層の表面を特定範囲とすることによりサイクル特性や外部からの圧力による曲げ等の変形に強く、カード型等の薄膜化二次電池を提供することが可能となる。
以下、本発明を具体的に説明する。
【００２６】
以下に実施例を示し、本発明を更に具体的に説明するが、本発明はその要旨を越えない限り、以下に示す実施例に制限されるものではない。
実施例１
以下に示す組成に従い正極用塗料を作成しアルミ基材上に塗布してリチウム二次電池用の正極とし評価した。正極用塗料の原料としては以下のものを使用した。
【００２７】
正極活物資材 ＬｉＣｏＯ2 平均粒径：５μｍ（ＦＭＣ社製）
導電材 アセチレンブラック 平均粒径：４０ｎｍ（電気化学工業製）
バインダー Ｐｈｏｔｏｍｅｒ４０５０（Ｈｅｎｋｅｌ社製）
溶剤 ＤＭＣ：ジメチルカーボネート（三菱化学）
架橋開始剤 Ｔｒｉｇｎｏｘ４２（Ａｋｕｚｏ Ｎｏｂｅｌ社製）
【００２８】
上記正極用材料を下記の割合で、秤量後、混練・分散処理を行い塗料化した。
ＬｉＣｏＯ2 ５９．０ｗｔ％
アセチレンブラック ８．０ｗｔ％
Ｐｈｏｔｏｍｅｒ４０５０ ８．０ｗｔ％
Ｔｒｉｇｎｏｘ４２ ０．１ｗｔ％
ＰＣ ２４．９ｗｔ％
【００２９】
この塗料を、厚さ２０μｍのアルミ箔上にドクターブレードを用いて、膜厚が１５０μｍになるよう塗布した。次にプレス圧が１０ｋｇｆ／ｃｍ2となるようプレスを行い、１２０℃で架橋させて電極材が塗布されたシートを得た。
【００３０】
次に以下に示す組成に従い負極用塗料を作成し鋼基材上に塗布してＬｉ電池用の正極とし評価した。負極塗料の原料としては以下のものを使用した。
負極活物資材 人造黒鉛粉ＫＳ６ 平均粒径：５μｍ（ＬＯＮＺＡ社製）
上記負極用材料を下記の割合で、秤量後、混練・分散処理を行い塗料化した。
ＫＳ６ ４５．０ｗｔ％
Ｐｈｏｔｏｍｅｒ４０５０ １０．９ｗｔ％
Ｔｒｉｇｎｏｘ４２ ０．１ｗｔ％
ＰＣ ２２．０ｗｔ％
ＥＣ ２２．０ｗｔ％
【００３２】
この塗料を、厚さ２０μｍの銅箔上にドクターブレードを用い膜厚が１５０μｍになるよう塗布した。次にプレス圧が１０ｋｇｆ／ｃｍ2となるようプレスを行い、１２０℃で架橋させて電極材が塗布されたシートを得た。
次に以下に示す組成に従いポリマー電解質を作製した。原料としては以下のものを使用した。
上記材料を下記の割合で、秤量後、攪拌溶解し、ポリマー電解質溶液を得た。
Ｐｈｏｔｏｍｅｒ４０５０ ６．０ｗｔ％
Ｐｈｏｔｏｍｅｒ４１５８ ４．０ｗｔ％
ポリエチレンオキシド ０．５ｗｔ％
ＰＣ ７９．０ｗｔ％
ＬｉＣｌＯ4 １０．０ｗｔ％
Ｄａｒｏｃｕｒｅ１１７３ ０．５ｗｔ％
【００３４】
この溶液の粘度をＢ型粘度計を用いて測定したところ、２００ｃｐであった。次にこの溶液を、銅基材上に塗布した負極活物質層上に、ドクターブレードを用い膜厚（ｄ）が５０μｍになるように塗布し、１０００Ｊ／ｃｍ2 で紫外線照射を行い、ポリマー電解質層を得た。
なお、このポリマー電解質層を構成するポリマーのピン刺し強度は２０ｇ・ｆであった。このポリマー電解質層付きの負極の反対の面に正極を重ね合わせ、電極を取り付け、アルミ蒸着を施したポリエチレン製の袋内に減圧封入し、リチウム二次電池を得た。ポリマー電解質層の断面を観察したところ、ポリマー電解質はほぼ正、負極の活物質層表面の凹凸に含浸しており、断面を走査型電子顕微鏡により観察し粗さ曲線を求めたところ、正極側の活物質層のＲｐ値は１０μｍ、Ｒｖ値は６μｍ、負極側の活物質層のＲｐ値は１２μｍ、Ｒｖ値は９μｍであった。したがって、Ｒｐ／ｄは正極側０．２、負極側０．２４であった。
【００３５】
このリチウム二次電池を５個充放電試験に供したところ、すべて内部短絡もなく、良好な電池特性を示し、容量が初期容量の８０％以下となるサイクル数をライフと定義すると、サイクルライフは５３回であった。この電池を１００ｍｍＲの曲率で曲げたが、ポリマー電解質と活物質層との剥離は観察されず、良好な接着性を示していた。そしてこのリチウム二次電池に対し、５ｋｇ／ｃｍ２の荷重を加えたが、内部短絡もなく、電池特性上も影響がなかった。
【００３６】
実施例２
負極作製時のプレス圧を２０ｋｇｆ／ｃｍ2 とした以外は実施例１と同様に行い、リチウム二次電池を作製した。実施例１と同様にポリマー電池断面から正、負極活物質層の表面粗度を求めたところ、正極側のＲｐ値は１０μｍ、Ｒｖ値は６μｍ、負極側のＲｐ値は５μｍ、Ｒｖ値は７μｍであった。したがって、Ｒｐ／ｄは正極側０．２、負極側０．１であった。得られた電池５個を充放電試験に供したところ、すべて得られた電池のサイクルライフは、５８回と良好な特性を示し、１００ｍｍＲの曲げ試験に耐える良好な接着性を示した。次いで行った５ｋｇ／ｃｍ2 の荷重試験後も特性は変わらなかった。
【００３７】
比較例１
負極作製時に、プレス処理をすることなく負極層を形成した以外は実施例１と同様に行い、リチウム二次電池サンプルを作製した。実施例１同様にポリマー電池断面から正、負極活物質層の表面粗度を求めたところ、正極側のＲｐ値は１０μｍ、Ｒｖ値は６μｍの負極側のＲｐ値は、３７μｍ、Ｒｖ値は２５μｍであった。したがって、Ｒｐ／ｄは正極側０．２、負極側０．７４であった。得られた電池５個に対し充放電試験を試みたところ、５個のうち１個は、１Ｖ以下で、２個は３．８Ｖ以上の電圧で短絡をおこした。１Ｖ以下で短絡した電池を分解観察したところ、突起が欠け落ちたと思われる微粉が、活物質表面から遊離する形で存在していた。また、３．８Ｖ以上で短絡した電池を分解観察したところ、局部的にリチウムデンドライトの発生がみられ、正極表面まで到達していた。残りの２個について、繰り返し充放電試験をしたところ、サイクルライフは平均１２回であり、５ｋｇ／ｃｍ2 の荷重試験により内部短絡をおこした。
【００３８】
比較例２
負極作製時のプレス圧を５ｋｇｆ／ｃｍ ２ とした以外は、実施例１と同様に行い、リチウム二次電池を作製した。実施例１同様にポリマー電池断面から正、負極活物質層の表面粗度をもとめたところ、正極層のＲｐ値は１０μｍ、Ｒｖ値は６μｍ、負極層のＲｐ値は２５μｍ、Ｒｖ値は２５μｍであった。したがって、Ｒｐ／ｄは、正極層０．２、負極層０．５であった。得られた電池５個を充放電試験に供したところ、５個のうち２個は３．８Ｖ以上の電圧で短絡をおこした。初期充電が正常に行われた３個について、繰り返し充放電試験をしたところ、サイクルライフは平均２０回であった。
【００３９】
比較例３
負極作製時のプレス圧を７ｋｇｆ／ｃｍ2 とした以外は、実施例１と同様に行い、リチウム二次電池を作製した。実施例１同様にポリマー電池断面から正、負極活物質層の表面粗度をもとめたところ、正極層のＲｐ値は１０μｍ、Ｒｖ値は６μｍ、負極層のＲｐ値は２２μｍ、Ｒｖ値は２５μｍであった。したがって、Ｒｐ／ｄは、正極層０．２、負極層０．４４であった。得られた電池５個を充放電試験に供したところ、５個のうち２個は３．８Ｖ以上の電圧で短絡をおこした。初期充電が正常に行われた３個について、繰り返し充放電試験をしたところ、サイクルライフは平均３５回であった。
【００４０】
比較例４
負極作製時のプレス圧を１００ｋｇｆ／ｃｍ2 とした以外は、実施例１と同様に行い、リチウム二次電池を作製した。実施例１同様にポリマー電池断面から正、負極活物質層の表面粗度をもとめたところ、正極層のＲｐ値は１μｍ、Ｒｖ値は２μｍ、負極層のＲｐ値は０．０５μｍ、Ｒｖ値は０．０７μｍであった。得られた電池５個を充放電試験に供したところ、５個とも初期充電が正常に行われた。しかしながら、１００ｍｍＲの曲げ試験を行ったところ、電解質／負極界面での剥離が観察され、界面接着性の乏しいものであった。
【００４１】
【発明の効果】
本発明のリチウム二次電池は、製品収率、サイクル特性に優れ、外部からの圧力や曲げに対して耐えうる優れたものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium secondary battery. More specifically, it relates to a lithium secondary battery using a polymer electrolyte (including an electrolyte impregnated or held in a polymer) in place of a conventional liquid electrolyte, and has excellent cycle characteristics and is suitable for external pressure and bending. The present invention relates to an excellent lithium secondary battery that can withstand this.
[0002]
[Prior art]
In recent years, various devices such as a camera-integrated VTR device, an audio device, a portable computer, and a mobile phone have been reduced in size and weight, and there is an increasing demand for higher performance of batteries as power sources of these devices. In particular, development of lithium secondary batteries capable of realizing excellent cycle characteristics with high voltage and high energy density as a battery as a power source of an electric vehicle has become active.
[0003]
A lithium secondary battery generally includes a positive electrode and a negative electrode capable of occluding and releasing lithium ions, and a nonaqueous electrolyte solution. For example, an electrode containing lithium cobaltate as a positive electrode, an electrode containing a carbon material as a negative electrode, and an electrolyte solution In the case of a secondary battery using lithium, lithium ions are occluded in the negative electrode through the electrolyte during charging, and lithium ions are released from the negative electrode during discharge and occluded in the positive electrode through the electrolyte. It is to be done. As a characteristic required for this electrode, the ability to occlude and release lithium ions into the electrode is large, and it is necessary to suppress a decrease in each ability caused by repeated (occlusion) of occlusion and release.
[0004]
The characteristics required for the positive electrode of such an excellent lithium secondary battery include conductivity within the positive electrode layer. The compound used for the positive electrode that can occlude and release lithium ions is often an oxide that has almost no electrical conductivity, and this alone does not function as the positive electrode. Therefore, it usually imparts electrical conductivity using a conductive material such as carbon. It is used as a positive electrode. Conventionally, a non-aqueous electrolyte has been used as the electrolyte to obtain a high voltage. On the other hand, when using a non-aqueous electrolyte, since it is liquid, it has a risk of ignition due to the filtrate, and in recent years, in order to improve safety, For example, what has been impregnated or held in a gel polymer and what is called a polymer electrolyte in which the polymer itself functions as an electrolyte have been developed.
[0005]
In particular, in lithium secondary batteries, heat generation and ignition due to internal short circuit due to lithium dendrite precipitation that occurs when an electrolyte solution is used are problematic, and the development and application of excellent polymer electrolytes have been desired.
Furthermore, since the polymer electrolyte described above can serve as a substitute for the separator used in the secondary battery system itself, the positive electrode and the negative electrode are sandwiched by sandwiching the polymer electrolyte without using a separator as in the prior art. A battery can be formed by bonding. By using the polymer electrolyte in this way, the light weight and the shape flexibility are improved, so that, for example, a sheet-like thin film can be formed, and there is an advantage that a light-weight and space-saving battery can be produced.
In addition, the polymer electrolyte is desired to be thin as long as it does not cause an internal short circuit in order to reduce the internal resistance of the battery and improve the energy density.
[0006]
[Problems to be solved by the invention]
The polymer electrolyte is provided on the active material layer of the electrode. At this time, the polymer electrolyte may be impregnated in the active material layer, or the layer may be independently formed. When using a polymer electrolyte with weak mechanical strength such as gel, especially when the polymer electrolyte is thinned, if the surface of the active material layer of the positive electrode or negative electrode in contact with the polymer electrolyte layer is rough, it will be slightly Even if the pressure is high, there is a problem of causing internal short circuit between the positive and negative electrodes, or the generation of dendrites due to the concentration of current, which deteriorates the cycle characteristics. Further, if the surface of the active material is made completely flat, the adhesiveness with the polymer electrolyte layer is lowered, peeling easily occurs, and the characteristic flexibility of the polymer battery is impaired.
[0007]
[Means for Solving the Problems]
The present invention has been made in view of the above circumstances, and as a result of intensive studies to obtain a lithium secondary battery having excellent cycle characteristics, the surface roughness of the active material layer of the positive electrode and the negative electrode is set within a specific range. In addition, it was found that by making the surface roughness of the polymer electrolyte layer in a specific range, it is possible to obtain a lithium secondary battery that is not easily short-circuited internally, has good cycle characteristics, and has excellent flexibility. Is.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The surface roughness referred to in the present invention can be calculated by an arbitrary method, but can be obtained from, for example, a roughness curve measured using a non-contact or contact-type surface roughness meter. Further, for example, the surface roughness of the contact surface of the polymer electrolyte layer with the active material layer may be measured by peeling the interface and measuring the surface roughness, or observing the cut surface with a microscope such as SEM, A roughness curve may be obtained and calculated. For Rp and Rv, for example, an average line is obtained from the roughness curve obtained by the method as described above using the least square method. The Rp value (average line height) is the distance between the average line and the highest peak of the roughness curve, and the Rv value (average line depth) is the distance between the average line and the bottom of the deepest valley.
[0009]
In the present invention, the Rp value on the surface of the active material in the positive and negative electrodes is preferably 0.1 μm to 20 μm, and the Rv value is preferably 0.1 μm to 50 μm. The Rp value is particularly preferably 1 to 10 μm. When the Rp value exceeds 20 μm, the battery is likely to cause an internal short circuit, and the cycle characteristics may be deteriorated due to local current concentration, or dendrite may be generated. On the other hand, when the thickness is less than 0.1 μm, the adhesiveness with the polymer electrolyte is lowered, and the flexibility of the battery may be impaired. Moreover, it is preferable that especially Rv value is 1 micrometer-20 micrometers. When the Rv value exceeds 50 μm, the capacity of the battery is reduced, and when it is less than 0.1 μm, the adhesion to the polymer electrolyte may be adversely affected.
[0010]
Furthermore, in the present invention, when the polymer electrolyte layer forms a layer independently of the active material layer, the Rp value of the contact surface of the polymer electrolyte layer with the active material layer is 0.1 μm to 50 μm, and the Rv value is It is preferable that it is 0.1-20 micrometers. The Rp value is particularly preferably 1 to 10 μm. When the Rp value exceeds 50 μm, the capacity of the battery may be reduced. When the Rp value is less than 0.1 μm, the adhesion with the electrolyte may be adversely affected. The Rv value is particularly preferably 1 μm to 10 μm. When the Rv value exceeds 20 μm, the battery is likely to cause an internal short circuit or local current concentration may occur, leading to deterioration of cycle characteristics and generation of dendrite. On the other hand, when the thickness is less than 0.1 μm, the adhesiveness with the positive and negative electrode active material layers is lowered, and the flexibility of the battery may be impaired.
[0011]
In the lithium secondary battery of the present invention, the surface of the electrode active material layer and the polymer electrolyte layer was made into a specific range, and the thickness of the polymer electrolyte (layer) was reduced to 50 μm or less. A suitable lithium secondary battery can also be obtained. The thickness of the polymer electrolyte (layer) is arbitrary, but is usually 10 to 50 μm.
[0012]
Further, the relationship between Rp and short circuit depends on the electrolyte thickness. In recent years, the demand for improvement in energy density has increased, and as a result of examining the relationship between the average thickness (d) of the electrolyte layer, the average line height (Rp) of the active material layer surface, and battery characteristics, Rp / d is It has been found that good characteristics can be obtained with a good yield if it is 0.3 or less, especially 0.3 to 0.002, particularly 0.25 to 0.05. When Rp / d exceeds 0.3, local current concentration causes shortening due to the generation of dendrites at a high potential portion of 3700 mV or higher, or causes deterioration of cycle characteristics in large current charge / discharge. .
[0013]
The lithium secondary battery of the present invention mainly comprises a positive electrode, a negative electrode, and a polymer electrolyte.
First, the electrode in the lithium secondary battery of the present invention will be described. Generally, a positive electrode or a negative electrode in a lithium secondary battery is an electrode containing a positive electrode (negative electrode) active material, a binding resin (binder), a conductive material, a solvent, etc. on a current collector such as an aluminum foil or a copper foil. A coating material for forming the active material layer is applied and dried.
[0014]
As the active material used for the positive electrode in the present invention, the compound capable of occluding and releasing lithium ions includes, as inorganic compounds, transition metal oxides of transition metals such as Fe, Co, Ni and Mn, and composites of lithium and transition metals. Examples thereof include oxides and transition metal sulfides. Specifically, transition metal oxide powders such as MnO, V 2 O 5 , V 6 O 13 and TiO 2 , composite oxide powders of lithium and transition metals such as lithium nickelate and lithium cobaltate, TiS 2 , Examples thereof include transition metal sulfide powders such as FeS. Examples of the organic compound include conductive polymers such as polyaniline. Moreover, you may mix these inorganic compounds and organic compounds in arbitrary ratios.
[0015]
As the negative electrode active material, graphite, coke, or the like is used as a compound capable of occluding and releasing lithium ions in addition to the Li metal foil, and coke is particularly preferable from the viewpoint of safety. The particle size of the active material of these positive and negative electrodes may be appropriately selected in consideration of the other constituent elements of the battery, but is usually set to an average particle size of 1 to 30 μm, particularly 1 to 10, especially 3 to 8 μm. The surface roughness described in the claims can be easily obtained. Furthermore, it is preferable because there is an effect that the porosity can be easily controlled.
[0016]
As the binder, it is necessary to be stable with respect to an electrolytic solution and the like, and weather resistance, chemical resistance, heat resistance, flame retardancy, and the like are desired. Further, a material excellent in ion conductivity is desirable, and examples thereof include a crosslinkable polyethylene oxide resin. More preferably, those obtained by introducing an acrylic group, a methacrylic group or the like at the end of the polyethylene oxide resin and crosslinking with heat or ultraviolet rays are preferred.
[0017]
The conductive substance is not particularly limited as long as it can impart conductivity by mixing an appropriate amount of compound powder capable of occluding and releasing lithium, but carbonaceous powder such as acetylene black, carbon black, graphite, or the like is used. Examples thereof include metal powder that is stable at electrode potential.
The DBP oil absorption of these conductive materials is preferably 100 to 500 cc / 100 g, particularly 150 to 300 cc / 100 g. The average particle size is preferably 1 to 100 [nm], particularly preferably 10 to 50 [nm]. The weight ratio between the active material and the conductive material is preferably in the range of 98/2 to 90/10.
[0018]
As a solvent for the coating material forming the positive electrode, a solvent that can disperse and dissolve the binder and is easily dried is preferable. Examples include acrylonitrile and dimethyl carbonate.
As the positive electrode current collector, an aluminum foil is generally used. A copper foil is used as the current collector for the negative electrode. In these current collectors, it is preferable to roughen the surface on which the active material layer is provided in advance because the binding effect is enhanced. Examples of the surface roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. Examples of the mechanical polishing method include a method of polishing the surface of the current collector with a wire brush equipped with abrasive cloth paper, a grindstone, an emery buff, a steel wire or the like to which abrasive particles are fixed.
[0019]
The method for forming the positive electrode and the negative electrode on the current collector is not particularly limited, but it is preferable to use a coating method such as comma reverse coating, squeeze coating, or lip coating because the viscosity of the coating is high. The thickness (average thickness) of each active material layer of the positive electrode and the negative electrode is usually about 20 to 200 μm.
In order to control the surface roughness of the active material layer in the positive and negative electrodes, the active material layer diameter is changed, or the active material layer-forming coating material is applied and dried on the substrate, and then the coating film is pressed. There are various methods for controlling the type and amount of paint solvent. For example, after forming the positive and negative active material layers on the current collector, the pressure is 1 to 5000 [kg / cm 2 ], preferably 1 to 1000 [kg / cm 2 ], and the temperature is room temperature to 200 [° C. ], preferably it is made by applying a pressure by Carre down Zehnder at room temperature to 150 [℃].
[0020]
Next, the polymer electrolyte will be described.
The polymer electrolyte may be one that constitutes the electrolyte itself, or may contain an electrolytic solution in the gel polymer, but in the latter case, it is generally contained in the gel polymer. The electrolyte solution to be used is preferably a non-aqueous electrolyte solution, which is generally a solution obtained by dissolving an electrolyte in a non-aqueous solvent.
[0021]
As the electrolyte used for preparing the polymer electrolyte, the electrolyte is stable with respect to the positive electrode active material and the negative electrode active material, and lithium ions can move to cause an electrochemical reaction with the positive electrode active material or the negative electrode active material. Any one can be used.
Specific examples include LiPF 6 , LiAsF 6 , LiSbF 6 , LiBF 4 , LiClO 4 , LiI, LiBr, LiCl, LiAlCl, LiHF 2 , LiSCN, LiSO 3 CF 2 and the like. Of these, LiPF 6 and LiClO 4 are particularly preferable.
[0022]
The content of these electrolytes in the electrolytic solution is generally 0.5 to 2.5 mol / l.
The solvent for dissolving the electrolyte is not particularly limited, but a solvent having a relatively high dielectric constant is preferably used. Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane, γ-butyllactone, etc. Lactones, sulfur compounds such as sulfolane, and nitriles such as acetonitrile. Moreover, you may mix and use these 2 or more types by arbitrary ratios. Among these, a mixed solution of at least one selected from cyclic carbonates such as ethylene carbonate and propylene carbonate, and noncyclic carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is preferable. .
[0023]
The polymer electrolyte is prepared by impregnating an electrolyte solution with a polymer that forms a gel, such as polyethylene oxide, polypropylene oxide, a crosslinked polymer of polyethylene oxide, a phenylene oxide, a phenylene sulfide polymer, or the like to form a gel polymer electrolyte. . If necessary, a compound having a polymerizable functional group such as an acrylic group may be mixed with an electrolyte solution and irradiated with energy rays such as UV for polymerization, or the mixture may be polymerized by heat to obtain a polymer electrolyte.
The content of the electrolyte in the electrolyte solution is generally 0.5 to 2.5 mol / l. Further, the strength of the polymer constituting the gel in this case is usually about 1 to 50 g · F as a spherical contact pressure test with a pin puncture strength <1 mmφ0.5r. In addition, you may use combining a nonwoven fabric or a porous membrane as a reinforcing material, and the pin stab strength in this case is about 100-500 g * F.
[0024]
Although the viscosity of the coating material forming the polymer electrolyte layer depends on the coating method and the coating material, it is preferably 10000 cp or less. Within this range, the electrolyte can easily enter the irregularities on the surface of the active material layer of the positive and negative electrodes. Therefore, the surface roughness of the electrolyte layer and the interface roughness with the positive electrode negative electrode layer are in contact with the positive electrode. The surface roughness of the negative electrode layer is reversed. That is, the Rp and Rv values on the surface of the active material layer are preferably Rv and Rp values on the surface of the polymer electrolyte layer in contact with the surface. On the other hand, when the viscosity of the electrolyte solution is high such that it exceeds 100,000 cp, the positive and negative active material layer surfaces may not be easily adapted to the unevenness.
[0025]
As described above, the characteristics of the present invention are as follows. In the lithium secondary battery using the polymer electrolyte, the positive and negative electrode active material layers and the surface of the polymer electrolyte layer are set in a specific range so that the cycle characteristics and bending due to external pressure can be reduced. It is possible to provide a thin-film secondary battery such as a card type that is resistant to deformation.
The present invention will be specifically described below.
[0026]
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples shown below unless it exceeds the gist.
Example 1
According to the composition shown below, a positive electrode paint was prepared and applied on an aluminum substrate, and evaluated as a positive electrode for a lithium secondary battery. The following were used as raw materials for the positive electrode paint.
[0027]
Cathode active material LiCoO 2 average particle diameter: 5 μm (FMC)
Conductive material Acetylene black Average particle size: 40 nm (manufactured by Denki Kagaku)
Binder Photomer 4050 (Henkel)
Solvent DMC: Dimethyl carbonate (Mitsubishi Chemical)
Cross-linking initiator Trignox42 (Akuzo Nobel)
[0028]
The positive electrode material was weighed at the following ratio, and then kneaded and dispersed to prepare a paint.
LiCoO 2 59.0 wt%
Acetylene black 8.0wt%
Photomer 4050 8.0 wt%
Trignox42 0.1wt%
PC 24.9wt%
[0029]
This paint was applied onto an aluminum foil having a thickness of 20 μm using a doctor blade so that the film thickness became 150 μm. Next, pressing was performed so that the pressing pressure became 10 kgf / cm 2, and a sheet coated with an electrode material was obtained by crosslinking at 120 ° C.
[0030]
Next, a negative electrode paint was prepared according to the composition shown below and applied on a steel substrate to evaluate as a positive electrode for a Li battery. The following were used as raw materials for the negative electrode paint.
Negative electrode active material Artificial graphite powder KS6 Average particle size: 5 μm (manufactured by LONZA)
The negative electrode material was weighed at the following ratio, and then kneaded and dispersed to form a paint.
KS6 45.0wt%
Photomer 4050 10.9 wt%
Trignox42 0.1wt%
PC 22.0wt%
EC 22.0wt%
[0032]
This paint was applied onto a copper foil having a thickness of 20 μm using a doctor blade so that the film thickness became 150 μm. Next, pressing was performed so that the pressing pressure became 10 kgf / cm 2, and a sheet coated with an electrode material was obtained by crosslinking at 120 ° C.
Next, a polymer electrolyte was produced according to the composition shown below. The following were used as raw materials.
The above materials were weighed in the following proportions, and dissolved by stirring to obtain a polymer electrolyte solution.
Photomer 4050 6.0 wt%
Photomer 4158 4.0 wt%
Polyethylene oxide 0.5wt%
PC 79.0wt%
LiClO 4 10.0 wt%
Darocure 1173 0.5wt%
[0034]
When the viscosity of this solution was measured using a B-type viscometer, it was 200 cp. Next, this solution was applied on the negative electrode active material layer applied on the copper base material using a doctor blade so that the film thickness (d) was 50 μm, and irradiated with ultraviolet rays at 1000 J / cm 2 to obtain a polymer electrolyte. A layer was obtained.
The polymer constituting the polymer electrolyte layer had a pin puncture strength of 20 g · f. A positive electrode was placed on the surface opposite to the negative electrode with the polymer electrolyte layer, an electrode was attached, and the mixture was sealed under reduced pressure in a polyethylene bag subjected to aluminum vapor deposition to obtain a lithium secondary battery. When the cross section of the polymer electrolyte layer was observed, the polymer electrolyte was almost positive and impregnated in the irregularities on the surface of the active material layer of the negative electrode. When the cross section was observed with a scanning electron microscope and the roughness curve was obtained, The Rp value of the active material layer was 10 μm, the Rv value was 6 μm, the Rp value of the active material layer on the negative electrode side was 12 μm, and the Rv value was 9 μm. Therefore, Rp / d was 0.2 on the positive electrode side and 0.24 on the negative electrode side.
[0035]
When five lithium secondary batteries were subjected to a charge / discharge test, all had no internal short circuit and exhibited good battery characteristics. When the number of cycles in which the capacity was 80% or less of the initial capacity was defined as life, the cycle life was 53 times. Although this battery was bent at a curvature of 100 mmR, no peeling between the polymer electrolyte and the active material layer was observed, indicating good adhesion. And with respect to the lithium secondary battery, has been added a load of 5 kg / cm 2, no internal short-circuit had no effect even on battery characteristics.
[0036]
Example 2
A lithium secondary battery was produced in the same manner as in Example 1 except that the pressing pressure during production of the negative electrode was 20 kgf / cm 2 . The surface roughness of the positive and negative electrode active material layers was determined from the cross section of the polymer battery in the same manner as in Example 1. The Rp value on the positive electrode side was 10 μm, the Rv value was 6 μm, the Rp value on the negative electrode side was 5 μm, and the Rv value was 7 μm. Met. Therefore, Rp / d was 0.2 on the positive electrode side and 0.1 on the negative electrode side. When the obtained five batteries were subjected to a charge / discharge test, the cycle life of all the batteries obtained showed good characteristics of 58 times, and showed good adhesion withstanding a bending test of 100 mmR. The characteristics did not change after the 5 kg / cm 2 load test.
[0037]
Comparative Example 1
A lithium secondary battery sample was produced in the same manner as in Example 1 except that the negative electrode layer was formed without pressing during the production of the negative electrode. As in Example 1, the surface roughness of the positive and negative electrode active material layers was determined from the cross section of the polymer battery. The Rp value on the positive electrode side was 10 μm, the Rv value was 6 μm, the Rp value on the negative electrode side was 37 μm, and the Rv value was 25 μm. Met. Therefore, Rp / d was 0.2 on the positive electrode side and 0.74 on the negative electrode side. When a charge / discharge test was attempted on five obtained batteries, one of the five batteries was short-circuited at a voltage of 1 V or less, and two of them were short-circuited at a voltage of 3.8 V or more. When the battery short-circuited at 1 V or less was disassembled and observed, the fine powder that seems to have lost the protrusions was present in a form free from the active material surface. Moreover, when the battery short-circuited at 3.8 V or more was disassembled and observed, generation of lithium dendrite was observed locally and reached the positive electrode surface. When the remaining two were subjected to repeated charge / discharge tests, the cycle life was 12 times on average, and an internal short circuit was caused by a 5 kg / cm 2 load test.
[0038]
Comparative Example 2
A lithium secondary battery was produced in the same manner as in Example 1 except that the press pressure at the time of producing the negative electrode was changed to 5 kgf / cm 2 . As in Example 1, when the surface roughness of the positive and negative electrode active material layers was determined from the cross section of the polymer battery, the Rp value of the positive electrode layer was 10 μm, the Rv value was 6 μm, the Rp value of the negative electrode layer was 25 μm, and the Rv value was 25 μm. there were. Therefore, Rp / d was the positive electrode layer 0.2 and the negative electrode layer 0.5. When the obtained five batteries were used for the charge / discharge test, two of the five batteries were short-circuited at a voltage of 3.8 V or higher. When the charge / discharge test was repeatedly performed on the three pieces that were normally charged initially, the cycle life was 20 times on average.
[0039]
Comparative Example 3
A lithium secondary battery was produced in the same manner as in Example 1 except that the press pressure during the production of the negative electrode was 7 kgf / cm 2 . As in Example 1, when the surface roughness of the positive and negative electrode active material layers was determined from the cross section of the polymer battery, the Rp value of the positive electrode layer was 10 μm, the Rv value was 6 μm, the Rp value of the negative electrode layer was 22 μm, and the Rv value was 25 μm. there were. Therefore, Rp / d was the positive electrode layer 0.2 and the negative electrode layer 0.44. When the obtained five batteries were used for the charge / discharge test, two of the five batteries were short-circuited at a voltage of 3.8 V or higher. When the charge and discharge tests were repeatedly performed on the three pieces that were normally charged initially, the cycle life was 35 times on average.
[0040]
Comparative Example 4
A lithium secondary battery was produced in the same manner as in Example 1 except that the pressing pressure during production of the negative electrode was 100 kgf / cm 2 . As in Example 1, when the surface roughness of the positive and negative electrode active material layers was determined from the cross section of the polymer battery, the Rp value of the positive electrode layer was 1 μm, the Rv value was 2 μm, the Rp value of the negative electrode layer was 0.05 μm, and the Rv value was It was 0.07 μm. When 5 batteries obtained were subjected to a charge / discharge test, initial charge was normally performed for all 5 batteries. However, when a 100 mmR bending test was performed, peeling at the electrolyte / negative electrode interface was observed, and the interface adhesion was poor.
[0041]
【The invention's effect】
The lithium secondary battery of the present invention is excellent in product yield and cycle characteristics, and can withstand external pressure and bending.
Claims (18)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14410298A JP4053657B2 (en) | 1997-05-30 | 1998-05-26 | Lithium secondary battery and manufacturing method thereof |
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| JP14176797 | 1997-05-30 | ||
| JP9-141767 | 1997-05-30 | ||
| JP14410298A JP4053657B2 (en) | 1997-05-30 | 1998-05-26 | Lithium secondary battery and manufacturing method thereof |
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| JP4053657B2 true JP4053657B2 (en) | 2008-02-27 |
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| KR20050111650A (en) * | 1999-11-08 | 2005-11-25 | 나노그램 코포레이션 | Electrodes including particles of specific sizes |
| JP5303817B2 (en) * | 2001-07-25 | 2013-10-02 | ソニー株式会社 | Nonaqueous electrolyte secondary battery |
| JP2004311108A (en) * | 2003-04-03 | 2004-11-04 | Nissan Motor Co Ltd | Total polymer electrolyte battery and manufacturing method |
| JP4920169B2 (en) * | 2003-10-06 | 2012-04-18 | 日産自動車株式会社 | Battery and vehicle equipped with this battery |
| JP5550948B2 (en) * | 2010-03-04 | 2014-07-16 | Ｊｘ日鉱日石金属株式会社 | Method for producing positive electrode for lithium ion battery |
| JP2012174414A (en) * | 2011-02-18 | 2012-09-10 | Toshiba Corp | Nonaqueous electrolyte battery and method of manufacturing the same |
| JP2013077734A (en) * | 2011-09-30 | 2013-04-25 | Asahi Kasei Corp | Electrode and method of manufacturing the same |
| JP5968444B2 (en) * | 2012-08-24 | 2016-08-10 | 日立オートモティブシステムズ株式会社 | Negative electrode for lithium ion secondary battery and method for producing the same |
| JP5664932B2 (en) * | 2012-10-17 | 2015-02-04 | トヨタ自動車株式会社 | Secondary battery |
| KR20210056169A (en) * | 2019-11-08 | 2021-05-18 | 주식회사 엘지화학 | Negative electrode, method for preparing the negative electrode, and secondary battery including the negative electrode |
| JPWO2022202578A1 (en) * | 2021-03-22 | 2022-09-29 | ||
| CN113078287B (en) * | 2021-03-29 | 2022-07-29 | 宁德新能源科技有限公司 | Electrochemical device and electronic device |
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