JP3552361B2

JP3552361B2 - Lithium ion secondary battery

Info

Publication number: JP3552361B2
Application number: JP24992695A
Authority: JP
Inventors: 信浩藤原; 康夫雪田; 幸夫野田; 和也小島
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1995-09-27
Filing date: 1995-09-27
Publication date: 2004-08-11
Anticipated expiration: 2015-09-27
Also published as: JPH0992336A

Description

【０００１】
【発明の属する技術分野】
本発明は例えば、電気自動車、ＵＰＳ（無停電電源装置）、ロードレベリング等に使用して好適な大容量のリチウムイオン二次電池に関する。
【０００２】
【従来の技術】
従来、リチウムイオン二次電池は電気自動車、ＵＳＰ、ロードレベリングをはじめ、環境問題に関連する多くの分野において研究開発が進められ、大容量、高出力、高電圧、長期保存性に優れたものが要求されている。
【０００３】
このリチウムイオン二次電池は、充電時はリチウムが正極電極の正極活物質からセパレータ中の電解液中にリチウムイオンとして溶け出し、負極電極の負極活物質に入り込み、放電時はこの負極電極の負極活物質中に入り込んだリチウムイオンが電解液中に放出され、この正極電極の正極活物質中に再び戻ることによって充放電動作を行っている。
【０００４】
従来の小型のリチウムイオン二次電池はエネルギー密度を上げるため、活物質を金属箔の集電体の表裏両面に塗布し、シート状の正及び負極電極を作成し、ポリエチレンもしくはポリプロピレンのセパレータを介して所定の大きさの電極対を多数順次積層した角型電池、あるいは長尺の正及び負極電極をポリエチレンもしくはポリプロピレンのセパレータを介して巻回した円筒型電池構造のものがほとんどであった。
【０００５】
【発明が解決しようとする課題】
ところで、大容量のリチウムイオン二次電池を上述小型のリチウムイオン二次電池と同様に活物質を集電体両面に塗布した正及び負極電極を順次積層して構成したときには、大容量のために、内部短絡を起こすとその個所が発熱し、隣接する正及び負極電極間のセパレータが熱溶融し、内部ショートが拡大する結果、多量の熱を周囲に放出し、多量のガスが噴出するおそれがあるという問題があった。
【０００６】
一般に電池の内部ショートの模擬試験として、電池外部から釘を刺し、人為的に正及び負極電極をショートさせる、釘刺し試験が行われている。本発明者は、上述の如き大容量のリチウムイオン二次電池が釘刺し時に多量のガス噴出に至る過程では、釘刺し部分の抵抗による発熱が火種となり、隣接する正及び負極電極間のセパレータが熱溶融し、正及び負極電極間の直接反応による発熱が生じ、次の隣接電極間のセパレータの熱溶融という逐次的発熱が起こり、最終的には全電極の反応による大発熱に至るとともに、対向する正、負極電極間の微多孔性のポリオレフィン樹脂フィルムよりなるセパレータがシャットダウンする温度を超えてしまい、完全に熱溶融し、更に熱分解し正及び負極電極が直接ショートする事によって内部ショートが拡大し多量の熱を周囲に放出し多量のガスが噴出することを見出した。
【０００７】
本発明は斯る点に鑑み、大容量のリチウムイオン二次電池の内部短絡による影響が隣接する正及び負極電極間に波及することを防ぎ、更に正極電極及び負極電極の直接ショートを防止するようにし、内部ショートの拡大による電池自体の損傷及び周囲への影響を最小限に抑えることを目的とする。
【０００８】
【課題を解決するための手段】
本発明リチウムイオン二次電池は正極集電体の片面もしくは両面に正極活物質を塗布したシート状の正極電極と、負極集電体の片面もしくは両面に負極活物質を塗布したシート状の負極電極とをセパレータを介して積層して成るリチウムイオン二次電池において、この正及び負極電極が対向しない界面を設け、この界面に金属酸化物の粉体を溶射してなる耐熱層を設けたものである。
【０００９】
【作用】
本発明によれば、正極集電体の片面もしくは両面に正極活物質を塗布したシート状の正極電極と、負極集電体の片面もしくは両面に負極活物質を塗布したシート状の負極電極とをセパレータを介して積層して成るリチウムイオン二次電池において、この正及び負極電極が対向しない界面を設け、この界面に金属酸化物の粉体を溶射してなる耐熱層を設けているので、内部ショートが発生しても、隣接する正及び負極電極間にショートが波及することを防ぐことができ、更にセパレータが熱溶融又は熱分解しても正及び負極電極間の電気的絶縁性が確保されると共にこの正及び負極電極の直接ショートを防止し、このショートの拡大による大発熱及びガス噴出が抑制される。
【００１０】
【発明の実施の形態】
以下、図面を参照して本発明リチウムイオン二次電池の実施例につき説明しよう。
図３において、１０はステンレス板よりなる所定形状の密閉型の偏平角型電池容器を示し、この偏平角型電池容器１０内にシート状の正極電極２及びシート状の負極電極３をセパレータ８を介して積層した積層体１４を収納する如くする。
【００１１】
本例においては、このシート状の正極電極２は次のようにして製作した。
炭酸リチウムと炭酸コバルトをＬｉ／Ｃｏ（モル比）＝１になるように混合し、空気中で９００℃、５時間焼成して正極活物質（ＬｉＣｏＯ_２）を合成した。この正極活物質を自動乳鉢を用いて粉砕し、ＬｉＣｏＯ_２粉末を得た。
【００１２】
このようにして得られたＬｉＣｏＯ_２粉末９５重量％と炭酸リチウム５重量％とを混合して得られた混合物を９１重量％、導電体材としてグラファイト６重量％、結着剤としてポリフッ化ビニリデン３重量％の割合で正極合剤を作成し、これをＮ−メチル−２−ピロリドンに分散してスラリー状とする。
【００１３】
このスラリー状の正極合剤を正極集電体５である帯状のアルミニウム箔の片面に塗布し、乾燥後、ローラープレス機で圧縮成形して、図２Ａに示す如き、正極集電体５の片面に正極合剤４が被着された正極電極原反を作成した。
【００１４】
この正極電極原反を図２Ａに示す如く、大きさ１０７ｍｍ×２６５ｍｍに型抜きして一枚の正極電極２とした。
【００１５】
本例では図２Ａに示す如く、この正極電極２の集電体５の正極合剤４が被着されていない面に平均粒径２０μｍのアルミナ（Ａｌ_２Ｏ_３）のセラミック粉体を溶射、例えばプラズマ溶射して、耐熱断熱性皮膜２０を形成する。
【００１６】
ところで、溶射とは燃料−酸素の燃焼、電気エネルギー等による熱源を用いて、金属、金属酸化物等の溶射材料を加熱し、溶融またはそれに近い状態にした粒子を基材に吹き付けて、皮膜を形成する技術であり、大きく分けてガス式溶射、電気式溶射の２方式に分類される。
【００１７】
このガス式溶射にはフレーム溶射、爆発溶射が含まれ、電気式溶射には、アーク溶射、プラズマ溶射、線爆溶射の３方式がある。これらの溶射の中でも、プラズマ溶射は非常に高温なプラズマジェットを使用していることから、ガス式溶射では溶射困難なセラミック、サーメット等の高融点材料を容易に溶射することができる。
【００１８】
プラズマ溶射は、溶射ガン、溶射材料供給装置、電源、高周波ステーター、冷却水供給ポンプ及び制御装置から構成され、プラズマジェット（１００００℃〜２００００℃）で溶融された粒径数１０ミクロンの粒子が高速で基材に衝突して、非常に短時間（１０ｍｓｅｃのオーダー）で冷却されて液相から固相になり、このような粒子が積層して皮膜が形成される。
【００１９】
また溶射材料としては、金属、金属酸化物、金属炭化物、金属窒化物等種々なものが使用できるが、特に２０００℃以上の耐熱性及び電気絶縁性を有し、電気化学的に電池材料として、使用できる材料としてはアルミナ（Ａｌ_２Ｏ_３）、ジルコニア（ＺｒＯ_２）、アルミナジルコニア（Ａｌ_２Ｏ_３−ＺｒＯ_２）、ジルコン酸マグネシウム（ＭａＺｒＯ_３）等の金属酸化物のセラミック粉体が適している。
【００２０】
また、本例においては、このシート状の負極電極３は次のようにして製作した。
出発物質に石油ピッチを用い、これに酸素を含む官能基を１０〜２０％導入（いわゆる酸素架橋）した後、不活性ガス中１０００℃で焼成してガラス状炭素に近い性質の難黒鉛化炭素材料を得た。
【００２１】
この炭素材料（負極活物質）を９０重量％、結着剤としてポリフッ化ビニリデン１０重量％の割合で混合して負極合剤を作成し、これをＮ−メチル−２−ピロリドンに分散してスラリー状とする。
【００２２】
このスラリー状の負極合剤を負極集電体７である帯状銅箔の両面に塗布し、乾燥後、ローラープレス機で圧縮成形して、図２Ｂに示す如き、負極集電体７の両面に負極合剤６が被着された負極電極原反を作成した。
【００２３】
この負極電極原反を図２Ｂに示す如く、大きさ１０９ｍｍ×２７０ｍｍに型抜きして一枚の負極電極３とした。
【００２４】
本例においては、図２Ｂに示す如く、この負極電極３をポリプロピレン製の微多孔性のフィルムのセパレータ８を２枚貼り合せた袋状セパレータに挿入する如くする。
【００２５】
この片面に耐熱断熱性皮膜２０が形成された正極電極２の６０枚と袋状セパレータ８に挿入された負極電極３の３０枚とを図１に示す如く負極電極３を２枚の正極電極２で溶射皮膜が無い正極合剤４が被着された面で挟む込む様にして順次正極集電体５の正極合剤４が被着されていない耳部５ａ同志及び負極集電体７の負極合剤６が被着されていない耳部７ａ同志が夫々重なり合う如く積層して積層体１４を形成する。
【００２６】
この場合、図１に示す如く、正極電極２、袋状セパレータ８に挿入した負極電極３及び正極電極２で電極ペア３０を構成し、この電極ペア３０と電極ペア３０との間に正極電極２同志が対接し、正極電極２と負極電極３とが対向しない界面３０ａが形成され、この界面３０ａに耐熱断熱性皮膜２０が存在するものとなる。
【００２７】
図４に示す如く、この積層体１４の正極集電体５の耳部５ａを束ねて正極端子１１に超音波溶接にて溶着すると共にこの積層体１４の負極集電体７の耳部７ａを束ねて負極端子１２に超音波溶接にて溶着する如くする。
【００２８】
この正極端子１１及び負極端子１２が設けられた図４に示す如き積層体１４を偏平角型電池容器１０内に挿入し、その後電解液注入口１３を有するステンレススチールの天板１０ａをこの偏平角型電池容器１０にレーザー溶接して蓋する如くする。
【００２９】
その後、この電解液注入口１３よりプロピレンカーボネート、ジェチルカーボネートの混合溶媒の中にＬｉＰＦ_６を１モル／１の割合で溶解した有機電解液を注入し、この正極合剤４及び負極合剤６間にこの有機電解液を充填する如くする。
【００３０】
その後、この電解液注入口１３に安全弁として、厚さ例えば５μｍのステンレス箔の破裂板１３ａを破裂板ホルダ１３ｂで密閉固定する如くする。
【００３１】
本例によるリチウムイオン二次電池の充放電を行った結果、３５Ａｈの放電容量が得られ、充放電特性は良好であった。
【００３２】
また本例によるリチウムイオン二次電池を充電電圧４．２Ｖで満充電し、この電池について釘刺し試験を行った結果、表１に実施例１として示す如くガスの噴出はほとんど無く、電解液の減少即ち重量減少率も２８％と少なく、内部ショートに対して安全性が向上することがわかった。
【００３３】
即ち、本例によれば、内部ショートが発生しても、電極ペア３０の１ペアおきに正極電極２及び負極電極３が対向しない界面３０ａを設け、この界面３０ａに溶射による耐熱層２０を設けたので、内部短絡が発生しても、隣接する電極ペア３０に波及することを防ぐことができ、この電池自体の損傷及び周囲への影響を最小限に抑えることができる利益がある。
【００３４】
【表１】

【００３５】
次に、この表１に示す実施例２につき説明するに、この実施例２は図５に、示す如く上述実施例１と同様の負極電極３の両面に平均粒径１８μｍのアルミナジルコニア（Ａｌ_２Ｏ_３−ＺｒＯ_２）のセラミック粉体をプラズマ溶射して、この負極電極３の両面の負極合剤６の表面上に溶射皮膜即ち耐熱断熱性皮膜２０ａを形成した。
ここで、溶射皮膜２０ａの構造は溶射粒子どうしが結合した連通孔を有したポーラス（気孔率０〜２０％程度）な焼結体に近いものとなっており、イオンの透過性がある。
斯る耐熱断熱性皮膜２０ａは溶射粒子どうしが、結合した連通孔を有したぽーらすな焼結体に近いものであり、この厚さを例えば約３０μｍとしたとき、空孔率が１０〜２０％のものが得られる。
【００３６】
またこの実施例２においては、上述実施例１と同様の集電体５の正極合剤４の被着されていない面に溶射皮膜２０の形成された正極電極２をプリプロピレン製の微多孔性フィルムのセパレータ８を２枚貼り合せた袋状セパレータに挿入する如くする。
【００３７】
この実施例２においてはこの両面に耐熱断熱性皮膜２０ａ形成された負極電極３の３０枚と袋状セパレータ８に挿入された正極電極２の６０枚とを負極電極３を２枚の正極電極２の正極合剤４が被着された面で挟み込む様にして順次積層して積層体１４を形成する。その他は、実施例１と同様に構成する。
【００３８】
この場合、図５に示す如く、負極電極３を袋状セパレータ８に挿入した２枚の正極電極２で挟む構成で電極ペア３０を構成し、電極ペア３０と電極ペア３０との間に正極電極２同志が対接し、正極電極２と負極電極３とが対向しない界面３０ａが形成され、この界面３０ａに耐熱断熱性皮膜２０が存在し、また正極電極２と負極電極３との間に耐熱断熱性皮膜２０ａが存するものとなる。
【００３９】
斯る実施例２のリチウムイオン二次電池の充放電を行った結果、３５Ａｈの放電容量が得られ、充放電特性は良好であった。
【００４０】
また本例による溶射してなる耐熱断熱性皮膜は微細な連通孔を有しているので、この連通孔を通してリチウムイオンが移動できるので、通常の充放電機能には問題は生じない。
【００４１】
また、実施例２によるリチウムイオン二次電池を充電電圧４．２Ｖで満充電し、この電池について、釘刺し試験を行った結果、表１に示す如くガスの噴出がほとんど無く、電解液の減少即ち重量減少率も１８％と少なく、内部ショートに対して安全性が向上することがわかった。この実施例２においては正極電極２と負極電極３との間に耐熱断熱性皮膜２０ａが存するので、実施例１よりも更に内部ショートの拡大が防止されている。
【００４２】
従って、この実施例２においても、上述実施例１と同様の作用効果が得られることは容易に理解できよう。
【００４３】
また実施例３は図６に示す如き円筒型の大容量のリチウムイオン二次電池の例を示す。この実施例３は図７に示す如く実施例１同様に負極集電体７の両面に負極合剤６が被着された帯状の（２８３ｍｍ×１７５０ｍｍ）の大きさの負極電極３を作製すると共に正極集電体５の片面に正極合剤４が塗布された帯状の（２８０ｍｍ×１７４５ｍｍ）大きさの正極電極２を作製する。
【００４４】
この負極電極３の一側のリード部にニッケル製の負極リード２１の一端を抵抗溶接により溶着し、また正極電極２の他側のリード部にアルミニウム製の正極リード２２の一端を抵抗溶接により溶着する。
【００４５】
また、この正極電極２の集電体５の正極合剤４が被着されていない面に平均粒径１８μｍのアルミナ（Ａｌ_２Ｏ_３）のセラミック粉体をプラズマ溶射して、この正極電極２の集電体５の正極合剤４が被着されていない表面上に厚さ３０μｍの溶射皮膜即ち耐熱断熱性皮膜２０を形成する。
【００４６】
この実施例３においては、図７に示す如く、この正極電極２及び厚さ２５μｍ、大きさ（２８７ｍｍ×１７５５ｍｍ）のポリプロピレン製の微多孔性フィルムのセパレータ８、負極電極３、セパレータ８及び正極電極２を順次に積層（電極ペア３０）してから渦巻状に多数回巻回して渦巻状積層体２３を形成する。
【００４７】
この場合、この渦巻状積層体２３においては図７に示す如く正極電極２の集電体５の面同志が対向する界面３０ａの間にアルミナよりなる６０μｍ厚の耐熱断熱性皮膜２０が存在することとなる。
【００４８】
また、ニッケルメッキを施した鉄製の円筒型電池容器２４の底部に絶縁板を挿入し、その後、この渦巻状積層体２３を収納する。そして負極端子２６、正極端子２７及び電解液注入口２８を有するニッケルメッキを施した鉄製の電池蓋２５の負極端子２６に負極リード２１の他端を溶接すると共に正極端子２７に正極リード２２の他端を溶接する。
【００４９】
そして電解液注入口２８よりプロピレンカーボネートの５０容量％とジエチルカーボネートの５０重量％の混合溶媒中にＬｉＰＦ_６を１モル／１の割合で溶解した有機電解液を注入し、この正極合剤４及び負極合剤６間にこの有機電解液を充填する如くする。
【００５０】
その後、この電解液注入口２８に安全弁として厚さ例えば５μｍのステンレス箔の破裂板２８ａを破裂板ホルダ２８ｂで密封固定する如くする。そしてこの電池蓋２５と円筒型電池容器２４とをレーザー溶接で固定し、直径５０ｍｍ、高さ３００．５ｍｍの円筒型のリチウムイオン二次電池を作製した。
【００５１】
この円筒型のリチウムイオン二次電池を充放電した結果、２０Ａｈの放電容量が得られ、良好な充放電特性が得られた。
【００５２】
またこの実施例３によるリチウムイオン二次電池を充電電圧４．２Ｖ満充電し、この電池について、釘刺し試験を行った結果、表１に示す如く、ガスの噴出はほとんど無く、電解液の減少即ち重量減少も２１％と少なく、内部ショートとに対して安全性が向上することがわかった。
【００５３】
従って、この実施例３においても、上述実施例１と同様の作用効果が得られることは容易に理解できよう。
【００５４】
また表１に示す比較例１は実施例１のリチウムイオン二次電池において、正極電極２の片面に溶射皮膜即ち耐熱断熱性皮膜２０を形成しないもので、その他は実施例１と同様に構成したものである。この比較例１のリチウムイオン二次電池の放電容量は３５Ａｈであった。
【００５５】
この比較例１によるリチウムイオン二次電池を充電電圧４．２Ｖで満充電し、この電池について、釘刺し試験を行った結果、表１に示す如く多量のガス噴出があり、電解液の減少即ち重量減少が１１０％と大きかった。
【００５６】
また比較例２は実施例３の円筒型のリチウムイオン二次電池において、帯状の正極電極２の片面に溶射皮膜即ち耐熱断熱性皮膜２０を形成しないもので、その他は実施例３と同様に構成したものである。この比較例２のリチウムイオン二次電池の放電容量は２０Ａｈであった。
【００５７】
この比較例２によるリチウムイオン二次電池を充電電圧４．２Ｖで満充電し、この電池について、釘刺し試験を行った結果、表１に示す如く多量のガスの噴出があり、電解液の減少即ち重量減少が１１５％と大きかった。
【００５８】
尚、上述実施例においては耐熱断熱性皮膜を正極電極又は負極電極の一方の電極面に形成した例につき述べたが、この皮膜を両方に設けるようにしても良いことは勿論である。また上述実施例では溶射材料として、アルミナ、アルミナジルコニアを用いた例につき述べたが、その他の、金属酸化物、金属炭化物、金属窒化物等が使用できる。
【００５９】
また上述実施例では電極ペア毎に界面３０ａを設け、この界面３０ａに溶射皮膜を設けたが、この代わりに数電極ペア毎に界面３０ａを設け、これに溶射皮膜を設けても上述実施例同様の作用効果が得られることは容易に理解できよう。
【００６０】
また本発明は上述実施例に限らず、本発明の要旨を逸脱することなくその他種々の構成が採り得ることは勿論である。
【００６１】
【発明の効果】
本発明によれば、内部ショートが発生しても、電極ペアの１ペアもしくは数ペアおきに正及び負極電極対向しない界面を設け、この界面に金属酸化物の粉体の溶射皮膜による耐熱層を設けているので、内部短絡が発生しても、隣接する電極ペアに波及することを防ぐことができ、電池自体の損傷及び周囲への影響を最小限に抑えることができる利益がある。
【００６２】
更に、セパレータが熱溶融又は熱分解した場合でも、この正極電極及び負極電極の対向する界面に耐熱断熱性皮膜を形成しているので正及び負極電極間の電気的絶縁性が確保されると共にこの正及び負極電極の直接ショートを防止し、このショートの拡大による大発熱及びガス噴出が抑制される利益がある。
【図面の簡単な説明】
【図１】本発明リチウムイオン二次電池の一実施例の要部の例を示す断面図である。
【図２】図１の説明に供する線図である。
【図３】リチウムイオン二次電池の一例を示す斜視図である。
【図４】図３のリチウムイオン二次電池の例の説明に供する斜視図である。
【図５】本発明の他の実施例の要部を示す断面図である。
【図６】リチウムイオン二次電池の他の例を示す分解斜視図である。
【図７】本発明の他の実施例の要部を示す一部切欠断面図である。
【符号の説明】
２正極電極
３負極電極
４正極合剤
５正極集電体
６負極合剤
７負極集電体
８セパレータ
２０，２０ａ耐熱断熱性皮膜（溶射皮膜）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a large-capacity lithium ion secondary battery suitable for use in, for example, electric vehicles, UPS (uninterruptible power supply), load leveling, and the like.
[0002]
[Prior art]
Conventionally, lithium ion secondary batteries have been researched and developed in many fields related to environmental issues such as electric vehicles, USP, road leveling, etc., and those with excellent capacity, high output, high voltage, and long-term storage characteristics have been developed. Is required.
[0003]
In this lithium ion secondary battery, when charging, lithium dissolves as lithium ions from the positive electrode active material of the positive electrode into the electrolyte solution in the separator, enters the negative electrode active material of the negative electrode, and discharges the negative electrode of the negative electrode. The lithium ions that have entered the active material are released into the electrolytic solution, and return to the positive electrode active material of the positive electrode to perform a charge / discharge operation.
[0004]
In order to increase energy density, conventional small lithium ion secondary batteries apply an active material to both front and back surfaces of a metal foil current collector, create sheet-like positive and negative electrodes, and place them through a polyethylene or polypropylene separator. In many cases, the battery was a prismatic battery in which a large number of electrode pairs of a predetermined size were sequentially laminated, or a cylindrical battery structure in which long positive and negative electrodes were wound via a polyethylene or polypropylene separator.
[0005]
[Problems to be solved by the invention]
By the way, when a large-capacity lithium-ion secondary battery is formed by sequentially laminating positive and negative electrodes coated with an active material on both surfaces of a current collector similarly to the above-mentioned small-sized lithium-ion secondary battery, If an internal short circuit occurs, heat is generated at that location, the separator between the adjacent positive and negative electrodes is thermally melted, and the internal short circuit is expanded.As a result, a large amount of heat may be released to the surroundings and a large amount of gas may be ejected. There was a problem.
[0006]
In general, as a simulation test of a short circuit inside a battery, a nail piercing test is performed in which a nail is pierced from the outside of the battery to artificially short the positive and negative electrodes. The present inventor has found that in the process in which a large-capacity lithium-ion secondary battery leads to a large amount of gas emission at the time of nail penetration as described above, heat generated by the resistance of the nail penetration portion becomes a fire source, and the separator between the adjacent positive and negative electrodes becomes Heat is melted, and heat is generated by the direct reaction between the positive and negative electrodes, and successive heat is generated by heat melting of the separator between the next adjacent electrodes. The temperature of the separator made of the microporous polyolefin resin film between the positive and negative electrodes exceeds the shut-down temperature, complete thermal melting, further thermal decomposition, and the positive and negative electrodes are directly short-circuited, increasing the internal short circuit It was found that a large amount of heat was released to the surroundings and a large amount of gas spouted.
[0007]
In view of the above, the present invention prevents the influence of an internal short circuit of a large-capacity lithium ion secondary battery from spreading between adjacent positive and negative electrodes, and further prevents a direct short circuit between a positive electrode and a negative electrode. The purpose of the present invention is to minimize the damage to the battery itself and the influence on the surroundings due to the expansion of the internal short circuit.
[0008]
[Means for Solving the Problems]
The lithium ion secondary battery of the present invention has a sheet-shaped positive electrode in which a positive electrode active material is coated on one or both surfaces of a positive electrode current collector, and a sheet-shaped negative electrode in which a negative electrode active material is coated on one or both surfaces of a negative electrode current collector. And a lithium ion secondary battery having a positive electrode and a negative electrode facing each other, and a heat-resistant layer formed by spraying metal oxide powder on the interface. is there.
[0009]
[Action]
According to the present invention, a sheet-shaped positive electrode coated with a positive electrode active material on one or both surfaces of a positive electrode current collector, and a sheet-shaped negative electrode coated with a negative electrode active material on one or both surfaces of a negative electrode current collector In a lithium ion secondary battery laminated with a separator interposed therebetween, an interface where the positive and negative electrodes do not face each other is provided, and a heat-resistant layer formed by spraying metal oxide powder is provided on this interface. Even if a short circuit occurs, the short circuit can be prevented from spreading between adjacent positive and negative electrodes, and furthermore, even if the separator is thermally melted or thermally decomposed, electrical insulation between the positive and negative electrodes is ensured. In addition, a direct short circuit between the positive and negative electrodes is prevented, and large heat generation and gas ejection due to the expansion of the short circuit are suppressed.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the lithium ion secondary battery of the present invention will be described with reference to the drawings.
3, 10 denotes a flat rectangular battery container sealed with a predetermined shape ing a stainless plate, a sheet-like positive electrode 2 and negative electrode 3 shaped sheet to the flat rectangular battery container 10 separator 8 To accommodate the laminated body 14 laminated.
[0011]
In this example, the sheet-shaped positive electrode 2 was manufactured as follows.
Lithium carbonate and cobalt carbonate were mixed so that Li / Co (molar ratio) = 1 and fired in air at 900 ° C. for 5 hours to synthesize a positive electrode active material (LiCoO ₂ ). This positive electrode active material was pulverized using an automatic mortar to obtain LiCoO ₂ powder.
[0012]
91% by weight of a mixture obtained by mixing 95% by weight of the LiCoO ₂ powder thus obtained and 5% by weight of lithium carbonate, 6% by weight of graphite as a conductive material, and polyvinylidene fluoride 3 as a binder A positive electrode mixture is prepared at a ratio of weight%, and this is dispersed in N-methyl-2-pyrrolidone to form a slurry.
[0013]
This slurry-like positive electrode mixture is applied to one surface of a belt-shaped aluminum foil as the positive electrode current collector 5, dried, and compression-molded by a roller press to form one surface of the positive electrode current collector 5 as shown in FIG. 2A. To prepare a positive electrode raw material having the positive electrode mixture 4 applied thereto.
[0014]
As shown in FIG. 2A, this positive electrode raw material was die-cut into a size of 107 mm × 265 mm to form one positive electrode 2.
[0015]
In this example, as shown in FIG. 2A, a ceramic powder of alumina (Al ₂ O ₃ ) having an average particle diameter of 20 μm was sprayed on the surface of the current collector 5 of the positive electrode 2 on which the positive electrode mixture 4 was not applied. For example, the plasma-spraying is performed to form the heat-resistant and heat-insulating coating 20.
[0016]
By the way, thermal spraying is a method of heating a thermal spray material such as a metal or a metal oxide using a heat source based on fuel-oxygen combustion, electric energy, etc., and spraying a molten or near-like particle onto a base material to form a coating. It is a technique of forming, and is roughly classified into two types, gas type thermal spraying and electric type thermal spraying.
[0017]
The gas spraying includes flame spraying and explosive spraying, and the electric spraying includes three types of arc spraying, plasma spraying, and line explosion spraying. Among these thermal sprays, since plasma spray uses a very high temperature plasma jet, it is possible to easily spray high melting point materials such as ceramics and cermets, which are difficult to spray by gas type thermal spraying.
[0018]
Plasma spraying consists of a spray gun, a spray material supply device, a power supply, a high-frequency stator, a cooling water supply pump, and a control device. Particles of several tens of microns in diameter that are melted by a plasma jet (10000 ° C. to 20,000 ° C.) are high-speed. Then, it is cooled in a very short time (on the order of 10 msec) and changes from a liquid phase to a solid phase, and such particles are laminated to form a film.
[0019]
As the thermal spray material, various materials such as metal, metal oxide, metal carbide, and metal nitride can be used, and in particular, have heat resistance of 2000 ° C. or more and electrical insulation, and are electrochemically used as battery materials. As a usable material, ceramic powder of a metal oxide such as alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), alumina zirconia (Al ₂ O ₃ —ZrO ₂ ), magnesium zirconate (MaZrO ₃ ) is suitable. I have.
[0020]
In this example, the sheet-like negative electrode 3 was manufactured as follows.
After using petroleum pitch as a starting material and introducing 10 to 20% of a functional group containing oxygen (so-called oxygen cross-linking) into this, it is calcined at 1000 ° C. in an inert gas and is hardly graphitized carbon having properties similar to glassy carbon. The material was obtained.
[0021]
This carbon material (negative electrode active material) was mixed at a ratio of 90% by weight and polyvinylidene fluoride as a binder at a ratio of 10% by weight to prepare a negative electrode mixture, which was dispersed in N-methyl-2-pyrrolidone and slurry. State.
[0022]
This slurry-like negative electrode mixture is applied to both sides of the strip-shaped copper foil as the negative electrode current collector 7, dried, and compression-molded with a roller press, and is applied to both sides of the negative electrode current collector 7 as shown in FIG. 2B. A negative electrode raw material to which the negative electrode mixture 6 was applied was prepared.
[0023]
As shown in FIG. 2B, this negative electrode material was cut into a size of 109 mm × 270 mm to form one negative electrode 3.
[0024]
In this example, as shown in FIG. 2B, the negative electrode 3 is inserted into a bag-like separator formed by laminating two polypropylene microporous film separators 8.
[0025]
As shown in FIG. 1, 60 positive electrodes 2 each having a heat-resistant and heat-insulating film 20 formed on one surface and 30 negative electrodes 3 inserted into the bag-like separator 8 were replaced with two positive electrodes 2 as shown in FIG. The ear 5a of the positive electrode current collector 5 where the positive electrode mixture 4 is not applied and the negative electrode of the negative electrode current collector 7 are successively sandwiched between the surfaces where the positive electrode mixture 4 having no thermal spray coating is applied. The laminated body 14 is formed by laminating the ear portions 7a to which the mixture 6 is not applied so that they overlap each other.
[0026]
In this case, as shown in FIG. 1, an electrode pair 30 is constituted by the positive electrode 2, the negative electrode 3 and the positive electrode 2 inserted in the bag-shaped separator 8, and the positive electrode 2 is disposed between the electrode pair 30 and the electrode pair 30. An interface 30a is formed in which the positive electrode 2 and the negative electrode 3 do not face each other, and the heat-resistant and heat-insulating coating 20 exists on the interface 30a.
[0027]
As shown in FIG. 4, the ears 5a of the positive electrode current collector 5 of the laminate 14 are bundled and welded to the positive electrode terminal 11 by ultrasonic welding, and the ears 7a of the negative electrode current collector 7 of the laminate 14 are They are bundled and welded to the negative electrode terminal 12 by ultrasonic welding.
[0028]
The laminated body 14 as shown in FIG. 4 provided with the positive electrode terminal 11 and the negative electrode terminal 12 is inserted into the oblong-shaped battery case 10, and then the stainless steel top plate 10 a having the electrolyte injection port 13 is moved to the oblique angle. It is laser-welded to the type battery container 10 so as to cover it.
[0029]
Thereafter, an organic electrolyte obtained by dissolving LiPF ₆ at a ratio of 1 mol / 1 into a mixed solvent of propylene carbonate and getyl carbonate is injected from the electrolyte injection port 13, and the positive electrode mixture 4 and the negative electrode mixture 6 are mixed. During this time, the organic electrolytic solution is filled.
[0030]
Thereafter, as a safety valve, a rupture plate 13a made of stainless steel and having a thickness of, for example, 5 μm is hermetically fixed to the electrolyte injection port 13 with a rupture plate holder 13b.
[0031]
As a result of charging and discharging the lithium ion secondary battery according to this example, a discharge capacity of 35 Ah was obtained, and the charge and discharge characteristics were good.
[0032]
Further, the lithium ion secondary battery according to this example was fully charged at a charging voltage of 4.2 V, and a nail penetration test was performed on the battery. As a result, as shown in Example 1 in Table 1, there was almost no gas ejection, and The reduction, that is, the weight reduction rate was as small as 28%, and it was found that the safety against internal short circuit was improved.
[0033]
That is, according to this example, even if an internal short circuit occurs, the interface 30a where the positive electrode 2 and the negative electrode 3 do not face each other is provided for every other pair of the electrode pairs 30, and the heat-resistant layer 20 by thermal spraying is provided on this interface 30a. Therefore, even if an internal short circuit occurs, it can be prevented from spreading to the adjacent electrode pair 30, and there is an advantage that damage to the battery itself and its influence on the surroundings can be minimized.
[0034]
[Table 1]

[0035]
Next, Example 2 shown in Table 1 will be described. In Example 2, as shown in FIG. 5, alumina zirconia having an average particle diameter of 18 μm (Al ₂ A ceramic powder of O ₃ —ZrO ₂ ) was plasma sprayed to form a thermal spray coating, that is, a heat-resistant and heat-insulating coating 20 a on the surface of the negative electrode mixture 6 on both surfaces of the negative electrode 3.
Here, the structure of the thermal spray coating 20a is close to a porous (porosity of about 0 to 20%) sintered body having communication holes in which thermal spray particles are bonded, and has ion permeability.
The heat-resistant and heat-insulating coating 20a is similar to a plain sintered body having interconnected communication holes, and when the thickness is set to, for example, about 30 μm, the porosity is 10%. ~ 20% is obtained.
[0036]
In the second embodiment, the positive electrode 2 having the thermal spray coating 20 formed on the surface of the current collector 5 on which the positive electrode mixture 4 is not adhered is the same as the first embodiment. The film separator 8 is inserted into a bag-like separator in which two sheets are laminated.
[0037]
In the second embodiment, 30 negative electrodes 3 having heat-resistant and heat-insulating coatings 20 a formed on both surfaces and 60 positive electrodes 2 inserted into the bag-like separator 8 were replaced with two negative electrodes 2. The positive electrode mixture 4 is sequentially laminated so as to be sandwiched between the surfaces to which the positive electrode mixture 4 is applied, to form a laminate 14. Other configurations are the same as those of the first embodiment.
[0038]
In this case, as shown in FIG. 5, the electrode pair 30 is configured such that the negative electrode 3 is sandwiched between two positive electrodes 2 inserted into the bag-shaped separator 8, and the positive electrode 3 is provided between the electrode pairs 30. An interface 30a is formed in which the two electrodes are in contact with each other and the positive electrode 2 and the negative electrode 3 do not face each other. The heat-resistant and heat-insulating film 20 exists on this interface 30a. The conductive film 20a is present.
[0039]
As a result of performing charge and discharge of the lithium ion secondary battery of Example 2, a discharge capacity of 35 Ah was obtained, and the charge and discharge characteristics were good.
[0040]
In addition, since the heat-resistant and heat-insulating coating formed by thermal spraying according to the present embodiment has fine communication holes, lithium ions can move through the communication holes, so that there is no problem in the ordinary charge / discharge function.
[0041]
Further, the lithium ion secondary battery according to Example 2 was fully charged at a charging voltage of 4.2 V, and a nail penetration test was performed on this battery. As a result, as shown in Table 1, almost no gas was blown out, and the electrolyte decreased. That is, it was found that the weight reduction rate was as small as 18%, and the safety against internal short-circuit was improved. In the second embodiment, since the heat-resistant and heat-insulating coating 20a exists between the positive electrode 2 and the negative electrode 3, expansion of the internal short circuit is further prevented as compared with the first embodiment.
[0042]
Therefore, it can be easily understood that the same operation and effect as those of the first embodiment can be obtained in the second embodiment.
[0043]
Embodiment 3 shows an example of a cylindrical large-capacity lithium ion secondary battery as shown in FIG. In the third embodiment, as shown in FIG. 7, a strip-shaped (283 mm × 1750 mm) -sized negative electrode 3 in which the negative electrode mixture 6 is adhered to both surfaces of the negative electrode current collector 7, as in the first embodiment, is manufactured. A positive electrode 2 having a band shape (280 mm × 1745 mm) in which the positive electrode mixture 4 is applied to one surface of the positive electrode current collector 5 is produced.
[0044]
One end of a nickel negative electrode lead 21 is welded to one lead of the negative electrode 3 by resistance welding, and one end of an aluminum positive lead 22 is welded to the other lead of the positive electrode 2 by resistance welding. I do.
[0045]
Also, a ceramic powder of alumina (Al ₂ O ₃ ) having an average particle diameter of 18 μm is plasma-sprayed on the surface of the current collector 5 of the positive electrode 2 on which the positive electrode mixture 4 is not adhered. A 30 μm-thick thermal spray coating, that is, a heat-resistant heat-insulating coating 20 is formed on the surface of the current collector 5 on which the positive electrode mixture 4 is not adhered.
[0046]
In Example 3, as shown in FIG. 7, the positive electrode 2 and a separator 8, a negative electrode 3, a separator 8, and a positive electrode 25 made of a polypropylene microporous film having a thickness of 25 μm and a size (287 mm × 1755 mm) were formed. 2 are sequentially laminated (electrode pair 30) and then spirally wound many times to form a spirally laminated body 23.
[0047]
In this case, in this spiral laminated body 23, as shown in FIG. 7, a heat-resistant and heat-insulating film 20 of alumina having a thickness of 60 μm exists between the interfaces 30a of the current collector 5 of the positive electrode 2 facing each other. It becomes.
[0048]
Further, an insulating plate is inserted into the bottom of the nickel-plated iron cylindrical battery container 24, and thereafter, the spirally stacked body 23 is housed. Then, the other end of the negative electrode lead 21 is welded to the negative electrode terminal 26 of the nickel-plated iron battery cover 25 having the negative electrode terminal 26, the positive electrode terminal 27, and the electrolyte injection port 28, and the other ends of the positive electrode lead 22 are connected to the positive electrode terminal 27. Weld the ends.
[0049]
Then, an organic electrolyte obtained by dissolving LiPF ₆ at a ratio of 1 mol / 1 in a mixed solvent of 50% by volume of propylene carbonate and 50% by weight of diethyl carbonate was injected from the electrolyte injection port 28, and this positive electrode mixture 4 and The organic electrolytic solution is filled between the negative electrode mixture 6.
[0050]
Thereafter, a rupturable plate 28a made of stainless steel and having a thickness of, for example, 5 μm as a safety valve is hermetically fixed to the electrolytic solution inlet 28 with a rupturable plate holder 28b. Then, the battery lid 25 and the cylindrical battery container 24 were fixed by laser welding to produce a cylindrical lithium ion secondary battery having a diameter of 50 mm and a height of 300.5 mm.
[0051]
As a result of charging / discharging this cylindrical lithium ion secondary battery, a discharge capacity of 20 Ah was obtained, and good charge / discharge characteristics were obtained.
[0052]
Further, the lithium ion secondary battery of Example 3 was fully charged at a charging voltage of 4.2 V, and a nail penetration test was performed on this battery. As shown in Table 1, almost no gas was blown out, and the electrolyte decreased. That is, it was found that the weight loss was as small as 21% and the safety against internal short circuit was improved.
[0053]
Therefore, it can be easily understood that the same operation and effect as those of the first embodiment can be obtained in the third embodiment.
[0054]
Comparative Example 1 shown in Table 1 was the same as Example 1 except that the thermal spray coating, that is, the heat-insulating film 20 was not formed on one surface of the positive electrode 2 in the lithium ion secondary battery of Example 1. Things. The discharge capacity of the lithium ion secondary battery of Comparative Example 1 was 35 Ah.
[0055]
The lithium ion secondary battery according to Comparative Example 1 was fully charged at a charging voltage of 4.2 V, and a nail penetration test was performed on the battery. As a result, a large amount of gas was blown out as shown in Table 1, and a decrease in the electrolyte, that is, The weight loss was as large as 110%.
[0056]
Comparative Example 2 was the same as Example 3 except that the thermal spray coating, that is, the heat-resistant and heat-insulating coating 20 was not formed on one surface of the belt-shaped positive electrode 2 in the cylindrical lithium ion secondary battery of Example 3. It was done. The discharge capacity of the lithium ion secondary battery of Comparative Example 2 was 20 Ah.
[0057]
The lithium ion secondary battery according to Comparative Example 2 was fully charged at a charging voltage of 4.2 V, and a nail penetration test was performed on the battery. As a result, as shown in Table 1, a large amount of gas was blown out, and the electrolyte decreased. That is, the weight loss was as large as 115%.
[0058]
In the above-described embodiment, the example in which the heat-resistant and heat-insulating coating is formed on one of the positive electrode and the negative electrode has been described. However, it is needless to say that this coating may be provided on both the electrodes. Further, in the above-described embodiment, an example was described in which alumina and alumina zirconia were used as the thermal spraying material, but other metal oxides, metal carbides, metal nitrides, and the like can be used.
[0059]
In the above-described embodiment, the interface 30a is provided for each electrode pair, and the spray coating is provided on the interface 30a. However, the interface 30a may be provided for every several electrode pairs, and the spray coating may be provided on the interface 30a. It can be easily understood that the operation and effect can be obtained.
[0060]
In addition, the present invention is not limited to the above-described embodiment, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.
[0061]
【The invention's effect】
According to the present invention, even if an internal short circuit occurs, an interface that does not face the positive and negative electrodes is provided every other pair or every few pairs of electrodes, and a heat-resistant layer of a thermal spray coating of metal oxide powder is provided on this interface. Because of the provision, even if an internal short circuit occurs, it can be prevented from spreading to adjacent electrode pairs, and there is an advantage that damage to the battery itself and influence on the surroundings can be minimized.
[0062]
Further, even when the separator is thermally melted or thermally decomposed, since the heat-resistant and heat-insulating film is formed on the facing interface between the positive electrode and the negative electrode, electrical insulation between the positive and negative electrodes is ensured, and There is an advantage that a direct short circuit between the positive and negative electrodes is prevented, and large heat generation and gas ejection due to the expansion of the short circuit are suppressed.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of a main part of an embodiment of a lithium ion secondary battery of the present invention.
FIG. 2 is a diagram for explaining FIG. 1;
FIG. 3 is a perspective view showing an example of a lithium ion secondary battery.
FIG. 4 is a perspective view for explaining an example of the lithium ion secondary battery of FIG. 3;
FIG. 5 is a sectional view showing a main part of another embodiment of the present invention.
FIG. 6 is an exploded perspective view showing another example of the lithium ion secondary battery.
FIG. 7 is a partially cutaway sectional view showing a main part of another embodiment of the present invention.
[Explanation of symbols]
2 Positive electrode 3 Negative electrode 4 Positive electrode mixture 5 Positive electrode current collector 6 Negative electrode mixture 7 Negative current collector 8

Separator

20, 20a Heat-resistant heat-insulating film (sprayed film)

Claims

A sheet-shaped positive electrode having one or both surfaces of a positive electrode current collector coated with a positive electrode active material, and a sheet-shaped negative electrode having one or both surfaces of a negative electrode current collector coated with a negative electrode active material laminated via a separator. And, in the lithium ion secondary battery provided with an interface where the positive and negative electrodes do not face each other, and a heat-resistant layer having electrolyte resistance at the interface.
A lithium ion secondary battery comprising, as the heat-resistant layer, a coating formed by spraying metal oxide powder on the surface of at least one of the interfaces where the positive and negative electrodes do not face each other. .

2. The lithium ion secondary battery according to claim 1, wherein a heat-resistant and heat-insulating film is formed on at least one of the opposing surfaces of the positive electrode and the negative electrode.

2. The lithium ion secondary battery according to claim 1, wherein said thermal spraying is plasma spraying.

2. The lithium ion secondary battery according to claim 1, wherein a film formed by spraying metal oxide powder is formed on at least one surface of the interface where the positive and negative electrodes face each other. Secondary battery.