JP4507345B2

JP4507345B2 - Method for producing lithium polymer secondary battery

Info

Publication number: JP4507345B2
Application number: JP2000097318A
Authority: JP
Inventors: 英之植田; きよみ神月; 透大島; 積大畠
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2000-03-31
Filing date: 2000-03-31
Publication date: 2010-07-21
Anticipated expiration: 2020-03-31
Also published as: JP2001283916A

Description

【０００１】
【発明の属する技術分野】
本発明は、高分子固体電解質に電解液を保持させたリチウムポリマー二次電池の製造方法に関するものである。
【０００２】
【従来の技術】
近年、携帯型情報機器の小型軽量化、高性能化の急速な進展により、その駆動電源として超薄型高容量電池が要望されるようになった。超薄型高容量電池としては、電解液の代わりに高分子固体電解質に電解液を含浸させたゲル状ポリマー電解質を用い、アルミニウム箔と樹脂フィルムとを積層したラミネート材料を電池外装体として利用したリチウムポリマー二次電池（ゲル状ポリマー電解質電池）が有望であり、その開発、実用化が積極的に行われている。
【０００３】
ゲル状ポリマー電解質は、ゲル化によりポリマーの三次元網目構造内に電解液を保持させたものであり、イオン導電性を確保するとともに電解液の固定化による漏液を防止することができるという優れた特徴を有している。
【０００４】
従来、このようなリチウムポリマー二次電池を作製する方法としては、電解液と重合性化合物と重合開始剤を含むプレゲル電解質溶液を正極及び／または負極に塗布した後、加熱もしくは紫外線、電子線等を照射することにより電極表面にゲル状ポリマー電解質膜を形成し、その後、多孔質体を介して得られた複合電極を対向させる方法や、予め作製したゲル状ポリマー電解質膜もしくは多孔質体と一体化させたゲル状ポリマー電解質膜を正極と負極との間に挟み込む方法が提案されている。
【０００５】
また特開平１１−２１４０３８号公報及び特開平１１−２８３６７３号公報には、多孔質体を介して正極とカーボン負極とが対向してなる発電体が収容された外装体内に重合性化合物と電解液と特定の重合開始剤を含むプレゲル溶液を一括注入した後、これを外装体内部で加熱重合（ゲル化）させることでリチウムポリマー二次電池を作製する構成が開示されている。
【０００６】
【発明が解決しようとする課題】
しかしながら上記した従来の構成では、高性能なリチウムポリマー二次電池を効率的に生産することは困難であり、多くの問題が生じている。
【０００７】
プレゲル電解質溶液を極板上に塗布した後にゲル化させ、その後、多孔質体を介して得られた複合電極を対向させる構成ならびに予め作製したゲル状ポリマー電解質膜もしくは多孔質体と一体化させたゲル状ポリマー電解質膜を正極と負極との間に挟み込む構成では、製造する際の外部環境因子（例えば、湿度、酸素濃度等）の影響を受けやすく、性状及び膜厚の均一なゲル状ポリマー電解質膜を量産レベルで得ることは極めて困難であった。しかもゲル状ポリマー電解質が製造装置を損傷・腐食させるといった問題も有していた。
【０００８】
またプレゲル電解質溶液を一括注入して、電池内部で加熱重合（ゲル化）させる構成では、プレゲル電解質溶液の粘性が高く、正極、カーボン負極、多孔体への溶液の浸透性が悪化するため、ゲル化が電池内部で不均一に生じ、その結果、電池の充放電特性が大幅に低下するといった問題が発生した。さらに電解液中の重合性化合物の加熱重合（ゲル化）反応は、酸素が多量に存在する大気中では抑制されるため、充電時に残存している重合開始剤が負極表面で還元分解し、電池反応を阻害する原因となる問題も有していた。
【０００９】
本発明は上記した従来の課題を解決するものであり、高性能なリチウムポリマー二次電池を効率的に生産するための製造方法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
上記目的を達成するために本発明のリチウムポリマー二次電池の製造方法は、正極、負極、多孔質体からなる発電要素を外装体内に収容する工程と、外装体内に第１の電解液を注入し減圧含浸する工程と、この工程後に、第２の電解液と重合性化合物と熱重合開始剤を少なくとも含むプレゲル電解質溶液を注入し減圧含浸する工程と、このプレゲル電解質溶液が注入された外装体を減圧雰囲気下で密封する工程と、この外装体を加熱してプレゲル電解質溶液をゲル化させる工程とを備える構成とする。
【００１１】
このように従来のプレゲル電解質溶液の一括注入とは異なり、まず電解液のみを注入減圧含浸し、その後、プレゲル電解質溶液を注入減圧含浸することにより、正極／多孔質膜／負極からなる極板群の内部にプレゲル電解質溶液が充分に浸透し電池内部で加熱重合（ゲル化）が均一に生ずるために、優れた充放電特性を有するリチウムポリマー二次電池を提供することが可能となる。
【００１２】
【発明の実施の形態】
以下、本発明の実施の形態について、図１、図２を用いて説明する。
【００１３】
図１は、本発明のリチウムポリマー二次電池の構成を示す概略図である。また図２は、本発明のゲル状ポリマー電解質膜４を形成するための製造プロセスの中で、電解液及びプレゲル電解質溶液の発電要素への注入含浸を行うための製造装置の一例を示す概念図である。
【００１４】
図１中、１は正極、２は負極、３は多孔質膜、４はゲル状ポリマー電解質膜、５は正極リード、６は負極リード、７は外装体、８は上シール部、９は下シール部、１０は絶縁保護フィルムである。図２中、１１は真空槽であり、真空ポンプ１２、電磁弁１３を用いて真空槽１１内部の圧力を調整している。真空槽１１内には、加熱ヒータ入りの電池ホルダー１４が設置されており、その温度は温度コントローラー１５により制御されている。７は正極１、負極２、多孔質体３からなる発電要素が収容された外装体であり、上シール部８のみが封口されている。電解液及びプレゲル電解質溶液は外装体７の下シール部９側より注入される。１６は電解液用の貯蔵タンクであり、電解液は計量後に注入ノズル１７より外装体７内部に供給される。また１８はプレゲル電解質溶液用の貯蔵タンクであり、プレゲル電解質溶液は計量後に注入ノズル１９より外装体７内部に供給される。
【００１５】
本発明は、▲１▼正極１、負極２、多孔質体３からなる発電要素を外装体７に収容する工程、▲２▼外装体７内に第１の電解液を注入し減圧含浸する工程、▲３▼外装体７内に第２の電解液と重合性化合物と熱重合開始剤を少なくとも含むプレゲル電解質溶液を注入し減圧含浸する工程、▲４▼プレゲル電解質溶液が注入された外装体７を減圧雰囲気下で密封する工程、▲５▼外装体７を加熱してプレゲル電解質溶液をゲル化させる工程、からなる。以下、各工程について詳細に説明する。
【００１６】
▲１▼正極１、負極２、多孔質体３からなる発電要素を外装体７に収容する工程
正極１、負極２、多孔質膜３からなる発電要素の作製方法及び発電要素の外装体７内への収容について説明する。
【００１７】
正極１は、正極活物質に導電材と結着剤等を所定比で混合し、水系もしくは有機系溶媒によりペースト化した後、上記ペーストを集電体（Ａｌ箔）の両面にダイコーター等で均一に塗布、乾燥、圧延し、所定の大きさに切断することで得られる。正極１には正極リード５を集電体の端部に溶接する。尚、正極活物質としては、ＬｉＣｏＯ₂、ＬｉＮｉＯ₂、ＬｉＭｎ₂Ｏ₄、ＬｉＦｅＯ₂等のリチウム含有遷移金属酸化物を使用することができる。
【００１８】
負極２は、負極活物質に導電材と結着剤等を所定比で混合し、水系もしくは有機系溶媒によりペースト化した後、上記ペーストを集電体（Ｃｕ箔）の両面にダイコーター等で均一に塗布、乾燥、圧延し、所定の大きさに切断することで得られる。負極２には負極リード６を集電体の端部に溶接する。尚、負極活物質としては、リチウムイオンを電気化学的に吸蔵・放出し得るカーボン材料、好ましくは、天然黒鉛、人造黒鉛、黒鉛化メソフェーズ小球体等の黒鉛材料を使用することができる。
【００１９】
上記の正極１と負極２とを多孔質膜３を介して重ね合わせ、図１中にあるような楕円状又は円形状に捲回する。多孔質膜３としては、ポリエチレン、ポリプロピレン等のポリオレフィン系樹脂の微多孔質膜を用いており、その膜厚は、電池特性、実用信頼性の観点から、５〜３０μｍが好ましい。
【００２０】
正極１、負極２、多孔質膜３からなる発電要素を作製した後、外装体７に収容する。外装体７としては、例えば、Ａｌ箔を中間の１層とし、その内側にポリプロピレンフィルムを、外側にポリエチレンテレフタレートフィルムとナイロンフィルムを積層し一体化したＡｌラミネート材からなる偏平状の袋を使用することができる。この発電要素が収納された後、正極リード５と負極リード６の先端部が外部に突出した状態で外装体７の上シール部８を封口する。尚、リードの上シール部８に接する部分に絶縁保護フィルム１０を貼りつけるとよい。この絶縁保護フィルム１０は、正極リード５、負極リード６の先端部を外部に突出させた状態で外装体７の開口部を熱融着等で封口する際に、正負の電極間の電気的絶縁と電池内部の気密性を確保するために設けた部材である。
【００２１】
▲２▼外装体７内に第１の電解液を注入し減圧含浸する工程
正極１、負極２、多孔質体３からなる発電要素が収容された外装体７内に第１の電解液を注入し減圧含浸する工程を説明する。
【００２２】
図２の注入含浸装置の真空槽１１内部に設置してある加熱ヒータ入りの電池ホルダー１４に、発電要素が収納されている外装体７を、封口した上シール部８を下にした状態で挿入する。その後、電池ホルダー１４の温度を温度コントローラ１５により適温に設定する。この温度は常温よりも高くすることが望ましく、特に４０〜６０℃が好ましい。
【００２３】
さらに真空槽１１内部の真空圧を真空ポンプ１２により３．０×１０⁴Ｐａ以下となるように真空排気する。その後、電解液用の注入ノズル１７より外装体７の内部に第１の電解液を注入し減圧含浸させる。この電解液は、例えば、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ビニレンカーボネート（ＶＣ）等の環状カーボネート類とジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）等の鎖状カーボネート類との混合有機溶媒中に、ＬｉＰＦ₆、ＬｉＣｌＯ₄、ＬｉＢＦ₄等の支持電解質を溶解させたものを使用することができる。尚、電解液への注入含浸時の真空圧は３×１０⁴Ｐａ以下であることが好ましい。さらに好ましくは、２×１０³Ｐａ以下である。
【００２４】
▲３▼外装体７内に第２の電解液と重合性化合物と熱重合開始剤を少なくとも含むプレゲル電解質溶液を注入し減圧含浸する工程
第１の電解液を注入し減圧含浸した後、プレゲル電解質溶液を注入ノズル１９より注入し減圧含浸させる。第１の電解液を注入する工程と、プレゲル電解質溶液を注入する工程は連続している必要はないが、連続して行うことが好ましい。
【００２５】
プレゲル電解質溶液は第２の電解液と重合性化合物と熱重合開始剤を少なくとも含む。電解液としては、第１の電解液と同様のものが使用できるが、有機溶媒の種類、組成を変化させてもよい。重合性化合物としては、例えば、ポリエチレンオキシド（ＰＥＯ）末端アクリレート変性タイプのポリマー材料、アクリレート系ポリマー材料等を用いることができる。熱重合開始剤としては、ｔ−へキシルパーオキシピパレート、ｔ−ブチルパーオキシネオデカノエート等の有機過酸化物を適用することができる。尚、プレゲル電解質溶液の発電要素への注入含浸時の真空圧は、３×１０⁴Ｐａ以下であることが好ましい。さらに好ましくは、２×１０³Ｐａ以下である。注入含浸時の温度は４０℃〜６０℃であると好適である。
【００２６】
▲４▼プレゲル電解質溶液が注入された外装体７を減圧雰囲気下で密封する工程
プレゲル電解質溶液を注入し減圧含浸した後、減圧封口装置を用いて、真空圧３．０×１０⁴Ｐａ以下、さらに好ましくは２×１０³Ｐａ以下の条件にて、外装体７の下シール部９を封口する。
【００２７】
▲５▼外装体７を加熱してプレゲル電解質溶液をゲル化させる工程
外装体７を加熱することにより、プレゲル電解質溶液を電池内部で加熱重合（ゲル化）させ、ゲル状ポリマー電解質膜４とする。この温度は、プレゲル電解質溶液中の重合性化合物が三次元架橋する温度であればよく、重合性化合物と熱重合開始剤により適温を選択する。例えば、上記した重合性化合物と熱重合開始剤であれば、４０〜８０℃が好ましい。また、加熱時間についても適切な時間に設定すればよい。
【００２８】
尚、捲回型のリチウムポリマー二次電池について説明したが、これに限定されるものではなく、正極、多孔質膜、負極を順次重ね合わせた積層型のリチウムポリマー二次電池等にも適用することができる。
【００２９】
【実施例】
次に実施例により本発明をさらに詳細に説明する。
【００３０】
（実施例１）
１．正極の作製
正極活物質として、ＬｉＣｏＯ₂を用い、これに導電材（アセチレンブラック）と結着剤（ポリビニリデンフルオライド（ＰＶＤＦ））を９０：７：３の重量比で混合し、有機溶媒（Ｎ−メチルピロリドン）によりペースト化した。次にダイコーターを用いて集電体（Ａｌ箔）の両面に均一に塗布し乾燥させることで正極用の原反を作製した。さらにこの原反をロールプレス機により圧延した後、所定の大きさに切断して厚みが０．１６ｍｍの正極１を作製した。次に正極１の集電体の端部に正極リード５を溶接した。
【００３１】
２．負極の作製
負極活物質として、天然黒鉛粉末を用い、これに結着剤（ポリビニリデンフルオライド（ＰＶＤＦ））を９７：３の重量比で混合し、有機溶媒（Ｎ−メチルピロリドン）によりペースト化した。次にダイコーターを用いて集電体（Ｃｕ箔）の両面に均一に塗布し乾燥させることで負極用の原反を作製した。さらにこの原反をロールプレス機により圧延した後、所定の大きさに切断して厚みが０．１６ｍｍの負極２を作製した。次に負極２の集電体の端部に負極リード６を溶接した。
【００３２】
３．第１の電解液及びプレゲル電解質溶液の調製
第１の電解液は、エチレンカーボネート（ＥＣ）とエチルメチルカーボネート（ＥＭＣ）を１：３の体積比で混合した有機溶媒中に、支持電解質ＬｉＰＦ₆を１．２ｍｏｌ／ｌの濃度となるように溶解することにより調製した。またプレゲル電解質溶液は、第１の電解液と同一組成である第２の電解液、ポリエーテルアクリレート（分子量：１万）を９０：１０の重量比で混合した後、熱重合開始剤（ｔ−へキシルパーオキシピパレート）を上記混合溶液に対して０．３重量％添加することにより調製した。
【００３３】
４．リチウムポリマー二次電池の作製
上記した方法で作製した正極１と負極２をポリエチレン製の多孔質体３（膜厚：２７μｍ）を介して重ね合わせ捲回することで楕円状の発電要素を作製する。次にこの発電要素をＡｌラミネート材からなる偏平状の外装体７に挿入し、正極リード５、負極リード６の先端部が外部に突出した状態で外装体７の上シール部８を封口する。
【００３４】
次に図２に示した注入含浸装置の真空槽１１内部に設置してある加熱ヒータ入りの電池ホルダー１４に外装体７を封口した上シール部８を下にした状態で挿入した後、電池ホルダー１４の温度を４０℃に設定する。真空槽１１内部の真空圧を２．８×１０⁴Ｐａとなるように真空排気した後、電解液用の注入ノズル１７より外装体７の内部に上記電解液を１．６ｇ注入し、１０分間減圧含浸させる。さらに連続的にプレゲル電解質溶液用の注入ノズル１９より外装体７の内部に上記プレゲル電解質溶液を２．０ｇ注入し、１０分間減圧含浸させる。
【００３５】
次に減圧封口装置を用い、真空圧２．８×１０⁴Ｐａの条件にて、外装体７の下シール部９を封口した後、８０℃にて１時間加熱することにより、プレゲル電解質溶液を電池内部で加熱重合（ゲル化）させ、リチウムポリマー二次電池を作製した。この電池を電池Ａとする。
【００３６】
また比較のために、プレゲル電解質溶液の一括注入、即ち、第１の電解液の注入・減圧含浸工程を省いた以外は、電池Ａと同様な方法でリチウムポリマー二次電池を作製した。この電池を電池Ｚ１とする。尚、この場合のプレゲル電解質溶液の注入量は３．６ｇである。
【００３７】
５．ハイレート放電特性
作製した各電池について、室温（２５℃）において定電流４２０ｍＡ（０．７Ｃ）で４．２Ｖまで充電した後、４．２Ｖの定電圧にて２時間充電する。その後、室温にて１２０ｍＡ（０．２Ｃ）の放電容量で終止電圧が３．０Ｖになるまで放電させ、放電時間より放電容量を算出した。また上記同一条件にて充電した各電池を室温にて１２００ｍＡ（２Ｃ）の放電容量で終止電圧が３．０Ｖになるまで放電させ、放電時間より放電容量を算出した。以上得られた測定データより、０．２Ｃでの放電容量に対する２Ｃでの放電容量の割合（百分率）を算出し、この値をハイレート放電特性と定義した。
【００３８】
６．低温放電特性
作製した各電池について、２５℃において定電流４２０ｍＡ（０．７Ｃ）で４．２Ｖまで充電した後、４．２Ｖの定電圧にて２時間充電する。その後、２５℃にて６００ｍＡ（１Ｃ）の放電容量で終止電圧が３．０Ｖになるまで放電させ、放電時間より放電容量を算出した。また上記同一条件にて充電した各電池を−１０℃にて６００ｍＡ（１Ｃ）の放電容量で終止電圧が３．０Ｖになるまで放電させ、放電時間より放電容量を算出した。以上得られた測定データより、２５℃での放電容量に対する−１０℃での放電容量の割合（百分率）を算出し、この値を低温放電特性と定義した。
【００３９】
７．耐漏液性
耐漏液性としては、加熱重合後の電池を分解し、相分離した電解液の存在有無を目視観察した。評価は漏液が認められないものを○とし、電解液が漏れ出ているものを×とした。
【００４０】
作製したリチウムポリマー二次電池のハイレート放電特性、低温放電特性、耐漏液性の評価結果を（表１）に示す。
【００４１】
【表１】

【００４２】
（表１）から明らかなように、本実施例のリチウムポリマー二次電池（電池Ａ）は、プレゲル電解質溶液が発電要素に充分に浸透し、外装体内部で加熱重合（ゲル化）が均一に生ずるために、ハイレート放電特性、低温放電特性が、比較電池（電池Ｚ）より大幅に向上した。これは、第１の電解液の注入減圧含浸により発電要素内部を予め電解液で湿潤させることができるため、プレゲル電解質溶液の浸透性が改善されたためである。
【００４３】
比較電池（電池Ｚ１）では、第１の電解液を注入せずに、プレゲル電解質溶液を一括注入しているために、プレゲル電解質溶液の発電要素への含浸性が改善されず、ハイレート放電特性、低温放電特性が低下する結果となった。
【００４４】
（実施例２）
次に電解液及びプレゲル電解質溶液の発電要素への注入含浸時の真空圧を変化させた場合について検討を行った。
【００４５】
注入含浸時の真空圧を、１．３×１０⁴Ｐａ、２．８×１０⁴Ｐａ、４．２×１０⁴Ｐａとし、これ以外は実施例１と同様な方法によりリチウムポリマー二次電池を作製した。この電池を電池Ｂ〜Ｄとする。尚、電池Ａと電池Ｃは同一条件で作製された電池である。また比較のために、プレゲル電解質溶液の一括注入、即ち、第１の電解液の注入・減圧含浸工程を省いた以外は、電池Ｂ〜Ｄと同様な方法でリチウムポリマー二次電池を作製した。この電池を電池Ｚ２〜Ｚ４とする。尚、電池Ｚ１と電池Ｚ３は同一条件で作製された電池である。さらにプレゲル電解質溶液を大気圧（０．１ＭＰａ）にて一括注入すること、即ち、プレゲル電解質溶液を一括注入し、且つ、減圧含浸を行わないこと以外は、電池Ａと同様な方法でリチウムポリマー二次電池を作製した。この電池を電池Ｚ５とする。作製したリチウムポリマー二次電池のハイレート放電特性、低温放電特性、耐漏液性の評価結果を（表２）に示す。
【００４６】
【表２】

【００４７】
（表２）から明らかなように、真空圧が１．３×１０⁴Ｐａ、２．８×１０⁴Ｐａである電池Ｂ及び電池Ｃは、ハイレート放電特性、低温放電特性において、真空圧が４．２×１０⁴Ｐａである電池Ｄより良好な結果を示した。これは真空圧が小さいほど電解液及びプレゲル電解質溶液の発電要素への含浸性が向上し、発電要素内部でゲル化が均一に生じているためである。
【００４８】
（実施例３）
電解液及びプレゲル電解質溶液の発電要素への注入含浸を行う際の外装体の温度を変化させた場合について検討を行った。
【００４９】
注入含浸時の外装体の温度を、２０℃、４０℃、６０℃、８０℃とし、注入含浸時の真空圧を１．３×１０⁴Ｐａとした以外は実施例１と同様な方法によりリチウムポリマー二次電池を作製した。この電池を電池Ｅ〜Ｈとする。尚、電池Ｂと電池Ｆは同一条件で作製された電池である。作製したリチウムポリマー二次電池のハイレート放電特性、低温放電特性、耐漏液性の評価結果を（表３）に示す。
【００５０】
【表３】

【００５１】
（表３）から明らかなように、注入含浸時の外装体の温度を４０〜６０℃に設定した場合に良好な電池特性が得られることが判明した。これは外装体を加温することによりプレゲル電解質溶液の粘度が低下し、発電要素への含浸性が向上したためである。しかしながら、電池Ｈが電池Ｇよりも良好な結果が得られなかった原因としては、▲１▼支持電解質ＬｉＰＦ₆の熱分解、▲２▼プレゲル電解質溶液の部分的なゲル化による発電要素への含浸性の悪化、等が考えられる。
【００５２】
（実施例４）
外装体を密封する際の真空圧を変化させた場合について検討を行った。
【００５３】
外装体を密封する際の真空圧を、１．３×１０⁴Ｐａ、２．８×１０⁴Ｐａ、４．２×１０⁴Ｐａとし、これ以外は実施例１と同様な方法によりリチウムポリマー二次電池を作製した。この電池を電池Ｉ〜Ｋとする。尚、電池Ａと電池Ｊは同一条件で作製された電池である。また比較のために、外装体を密封する際の真空圧を大気圧（０．１ＭＰａ）とし、これ以外は電池Ｚ１と同様な方法によりリチウムポリマー二次電池を作製した。この電池を電池Ｚ６とする。作製したリチウムポリマー二次電池のハイレート放電特性、低温放電特性、耐漏液性の評価結果を（表４）に示す。
【００５４】
【表４】

【００５５】
（表４）から明らかなように、外装体を密封する際の真空圧が小さいほど、ハイレート放電特性、低温放電特性、耐漏液性が向上する結果となった。これは外装体内部を酸素遮断雰囲気とすることにより、重合性化合物の三次元架橋反応が促進され、電解液をポリマーマトリックス内に多量に取り込むことが可能となったためと考えられる。
【００５６】
【発明の効果】
以上のように本発明は、ゲル状ポリマー電解質を含有した多孔質体を介して正極と負極とが対向してなる発電要素を外装体内に収容させたリチウムポリマー二次電池の製造方法において、正極、負極、多孔質体からなる発電要素を前記外装体内に収容する工程と、前記外装体内に第１の電解液を注入し減圧含浸する工程と、前記外装体内に第２の電解液と重合性化合物と熱重合開始剤を少なくとも含むプレゲル電解質溶液を注入し減圧含浸する工程と、前記プレゲル電解質溶液が注入された前記外装体を減圧雰囲気下で密封する工程と、前記外装体を加熱して前記プレゲル電解質溶液をゲル化させる工程とを備えることにより、プレゲル電解質溶液が発電要素に充分に浸透し、外装体内部で加熱重合（ゲル化）が均一に生ずるために、優れたハイレート放電特性、低温放電特性を有し、且つ、耐漏液性の良好なリチウムポリマー二次電池を効率よく提供することが可能となり、その実用上の価値は大なるものがある。
【図面の簡単な説明】
【図１】本発明のリチウムポリマー二次電池の構成を示す概略図
【図２】電解液及びプレゲル電解質溶液の注入含浸装置を示す図
【符号の説明】
１．正極
２．負極
３．多孔質膜
４．ゲル状ポリマー電解質膜
５．正極リード
６．負極リード
７．外装体
８．上シール部
９．下シール部
１０．絶縁保護フィルム
１１．真空槽
１２．真空ポンプ
１３．電磁弁
１４．電池ホルダー
１５．温度コントローラー
１６．電解液用の貯蔵タンク
１７．注入ノズル
１８．プレゲル電解質溶液用の貯蔵タンク
１９．注入ノズル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a lithium polymer secondary battery in which an electrolytic solution is held in a polymer solid electrolyte.
[0002]
[Prior art]
In recent years, with the rapid progress of miniaturization and weight reduction and high performance of portable information equipment, an ultra-thin high-capacity battery has been demanded as a driving power source. As an ultra-thin high-capacity battery, a gel polymer electrolyte in which a polymer solid electrolyte is impregnated with an electrolyte solution is used instead of the electrolyte solution, and a laminate material in which an aluminum foil and a resin film are laminated is used as a battery outer package. Lithium polymer secondary batteries (gel polymer electrolyte batteries) are promising, and their development and practical application are being actively carried out.
[0003]
Gel polymer electrolyte is an electrolyte that is retained in the three-dimensional network structure of the polymer by gelation, and it has excellent ionic conductivity and can prevent leakage due to immobilization of the electrolyte. It has the characteristics.
[0004]
Conventionally, as a method for producing such a lithium polymer secondary battery, a pregel electrolyte solution containing an electrolytic solution, a polymerizable compound, and a polymerization initiator is applied to the positive electrode and / or the negative electrode, and then heated, ultraviolet, electron beam, etc. The gel polymer electrolyte membrane is formed on the surface of the electrode by irradiating the electrode, and then the composite electrode obtained through the porous body is opposed to the gel polymer electrolyte membrane or the porous body prepared in advance. A method has been proposed in which a gelled polymer electrolyte membrane is sandwiched between a positive electrode and a negative electrode.
[0005]
Japanese Patent Application Laid-Open No. 11-214038 and Japanese Patent Application Laid-Open No. 11-283673 disclose a polymerizable compound and an electrolytic solution in an exterior body in which a power generation body in which a positive electrode and a carbon negative electrode are opposed to each other through a porous body. And a pregel solution containing a specific polymerization initiator are collectively injected, and then this is heated and polymerized (gelled) inside the outer package to produce a lithium polymer secondary battery.
[0006]
[Problems to be solved by the invention]
However, with the above-described conventional configuration, it is difficult to efficiently produce a high-performance lithium polymer secondary battery, and many problems arise.
[0007]
The pregel electrolyte solution was applied on the electrode plate and then gelled, and then the composite electrode obtained through the porous body was opposed to each other and integrated with a previously prepared gel polymer electrolyte membrane or porous body. In the structure in which the gel polymer electrolyte membrane is sandwiched between the positive electrode and the negative electrode, the gel polymer electrolyte is easily affected by external environmental factors (for example, humidity, oxygen concentration, etc.), and has a uniform property and film thickness. It was extremely difficult to obtain a film at a mass production level. Moreover, the gel polymer electrolyte has a problem of damaging and corroding the manufacturing apparatus.
[0008]
In addition, in the configuration in which the pregel electrolyte solution is collectively injected and heated and polymerized (gelled) inside the battery, the viscosity of the pregel electrolyte solution is high, and the permeability of the solution to the positive electrode, the carbon negative electrode, and the porous body deteriorates. As a result, a problem arises in that the charge / discharge characteristics of the battery are significantly reduced. Furthermore, since the heat polymerization (gelation) reaction of the polymerizable compound in the electrolyte is suppressed in the atmosphere containing a large amount of oxygen, the polymerization initiator remaining at the time of charging is reduced and decomposed on the negative electrode surface. It also had problems that caused the reaction to be inhibited.
[0009]
The present invention solves the above-described conventional problems, and an object thereof is to provide a production method for efficiently producing a high-performance lithium polymer secondary battery.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a lithium polymer secondary battery of the present invention includes a step of housing a power generation element composed of a positive electrode, a negative electrode, and a porous body in an exterior body, and injecting a first electrolyte into the exterior body A step of impregnating under reduced pressure, a step of injecting a pregel electrolyte solution containing at least a second electrolytic solution, a polymerizable compound and a thermal polymerization initiator after this step and impregnating under reduced pressure, and an outer package in which the pregel electrolyte solution is injected Are sealed in a reduced-pressure atmosphere, and the outer body is heated to gel the pregel electrolyte solution.
[0011]
Thus, unlike the conventional batch injection of the pregel electrolyte solution, the electrode plate group consisting of positive electrode / porous membrane / negative electrode is prepared by first injecting only the electrolyte solution and impregnating under reduced pressure and then injecting the pregel electrolyte solution under reduced pressure. Since the pregel electrolyte solution sufficiently penetrates into the inside of the battery and heat polymerization (gelation) occurs uniformly inside the battery, it is possible to provide a lithium polymer secondary battery having excellent charge / discharge characteristics.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0013]
FIG. 1 is a schematic view showing the configuration of the lithium polymer secondary battery of the present invention. FIG. 2 is a conceptual diagram showing an example of a manufacturing apparatus for performing injection impregnation of the electrolytic solution and the pregel electrolyte solution into the power generation element in the manufacturing process for forming the gel polymer electrolyte membrane 4 of the present invention. It is.
[0014]
In FIG. 1, 1 is a positive electrode, 2 is a negative electrode, 3 is a porous membrane, 4 is a gel polymer electrolyte membrane, 5 is a positive electrode lead, 6 is a negative electrode lead, 7 is an exterior body, 8 is an upper seal portion, and 9 is a lower portion. The seal part 10 is an insulating protective film. In FIG. 2, 11 is a vacuum chamber, and the pressure inside the vacuum chamber 11 is adjusted using a vacuum pump 12 and an electromagnetic valve 13. A battery holder 14 with a heater is installed in the vacuum chamber 11, and its temperature is controlled by a temperature controller 15. Reference numeral 7 denotes an outer package in which a power generation element composed of the positive electrode 1, the negative electrode 2, and the porous body 3 is accommodated, and only the upper seal portion 8 is sealed. The electrolyte solution and the pregel electrolyte solution are injected from the lower seal portion 9 side of the outer package 7. Reference numeral 16 denotes a storage tank for the electrolytic solution, and the electrolytic solution is supplied into the exterior body 7 from the injection nozzle 17 after measurement. Reference numeral 18 denotes a storage tank for the pregel electrolyte solution, and the pregel electrolyte solution is supplied into the exterior body 7 from the injection nozzle 19 after measurement.
[0015]
The present invention includes (1) a step of housing a power generation element composed of a positive electrode 1, a negative electrode 2, and a porous body 3 in an exterior body 7, and (2) a step of injecting a first electrolyte into the exterior body 7 and impregnating it under reduced pressure. (3) A step of injecting a pregel electrolyte solution containing at least a second electrolytic solution, a polymerizable compound and a thermal polymerization initiator into the outer package 7 and impregnating under reduced pressure, and (4) an outer package 7 in which the pregel electrolyte solution is injected. And (5) heating the exterior body 7 to gel the pregel electrolyte solution. Hereinafter, each step will be described in detail.
[0016]
(1) Step of housing the power generation element composed of the positive electrode 1, the negative electrode 2, and the porous body 3 in the exterior body 7 A method for producing the power generation element composed of the positive electrode 1, the negative electrode 2 and the porous film 3, and the inside of the exterior body 7 of the power generation element The housing will be described.
[0017]
In the positive electrode 1, a conductive material and a binder are mixed with a positive electrode active material at a predetermined ratio and made into a paste with an aqueous or organic solvent, and then the paste is placed on both sides of a current collector (Al foil) with a die coater or the like. It is obtained by uniformly coating, drying, rolling, and cutting into a predetermined size. A positive electrode lead 5 is welded to the positive electrode 1 at the end of the current collector. As the positive electrode active material, lithium-containing transition metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and LiFeO ₂ can be used.
[0018]
The negative electrode 2 is prepared by mixing a negative electrode active material with a conductive material and a binder at a predetermined ratio and forming a paste with an aqueous or organic solvent, and then applying the paste to both sides of a current collector (Cu foil) with a die coater or the like. It is obtained by uniformly coating, drying, rolling, and cutting into a predetermined size. A negative electrode lead 6 is welded to the end of the current collector. As the negative electrode active material, a carbon material capable of electrochemically occluding and releasing lithium ions, preferably a graphite material such as natural graphite, artificial graphite, graphitized mesophase spherules or the like can be used.
[0019]
The positive electrode 1 and the negative electrode 2 are overlapped via the porous film 3 and wound into an elliptical shape or a circular shape as shown in FIG. As the porous film 3, a microporous film of polyolefin resin such as polyethylene or polypropylene is used, and the film thickness is preferably 5 to 30 μm from the viewpoint of battery characteristics and practical reliability.
[0020]
After the power generation element composed of the positive electrode 1, the negative electrode 2, and the porous film 3 is produced, it is accommodated in the outer package 7. As the outer package 7, for example, a flat bag made of an Al laminate material in which an Al foil is an intermediate layer, a polypropylene film is laminated on the inside, and a polyethylene terephthalate film and a nylon film are laminated on the outside is used. be able to. After the power generation element is housed, the upper seal portion 8 of the outer package 7 is sealed with the leading ends of the positive electrode lead 5 and the negative electrode lead 6 protruding to the outside. Insulating protective film 10 may be attached to a portion in contact with upper seal portion 8 of the lead. This insulating protective film 10 is used to electrically insulate between positive and negative electrodes when the opening of the outer package 7 is sealed by thermal fusion or the like with the leading ends of the positive electrode lead 5 and the negative electrode lead 6 protruding to the outside. And a member provided to ensure airtightness inside the battery.
[0021]
(2) Step of injecting the first electrolytic solution into the exterior body 7 and impregnating under reduced pressure Injecting the first electrolyte into the exterior body 7 in which the power generation elements composed of the positive electrode 1, the negative electrode 2, and the porous body 3 are accommodated Next, the step of impregnating under reduced pressure will be described.
[0022]
Inserted into the battery holder 14 with a heater installed in the vacuum chamber 11 of the injection impregnation apparatus of FIG. 2, the exterior body 7 containing the power generation element is inserted with the sealed upper seal 8 facing down. To do. Thereafter, the temperature of the battery holder 14 is set to an appropriate temperature by the temperature controller 15. This temperature is desirably higher than room temperature, and is preferably 40 to 60 ° C.
[0023]
Further, the vacuum pressure in the vacuum chamber 11 is evacuated by the vacuum pump 12 so as to be 3.0 × 10 ⁴ Pa or less. Thereafter, the first electrolytic solution is injected into the exterior body 7 from the injection nozzle 17 for electrolytic solution and impregnated under reduced pressure. Examples of the electrolytic solution include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC), and dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). A solution obtained by dissolving a supporting electrolyte such as LiPF ₆ , LiClO ₄ , LiBF _{4 in} a mixed organic solvent with a chain carbonate can be used. In addition, it is preferable that the vacuum pressure at the time of the injection | pouring impregnation to electrolyte solution is 3 * 10 < ⁴ > Pa or less. More preferably, it is 2 × 10 ³ Pa or less.
[0024]
(3) A step of injecting a pregel electrolyte solution containing at least a second electrolytic solution, a polymerizable compound and a thermal polymerization initiator into the outer package 7 and impregnating under reduced pressure After injecting the first electrolytic solution and impregnating under reduced pressure, the pregel electrolyte The solution is injected from the injection nozzle 19 and impregnated under reduced pressure. The step of injecting the first electrolytic solution and the step of injecting the pregel electrolyte solution need not be continuous, but are preferably performed continuously.
[0025]
The pregel electrolyte solution includes at least a second electrolyte solution, a polymerizable compound, and a thermal polymerization initiator. As the electrolytic solution, the same one as the first electrolytic solution can be used, but the type and composition of the organic solvent may be changed. As the polymerizable compound, for example, a polyethylene oxide (PEO) terminal acrylate-modified polymer material, an acrylate polymer material, or the like can be used. As the thermal polymerization initiator, organic peroxides such as t-hexyl peroxypiparate and t-butyl peroxyneodecanoate can be applied. The vacuum pressure during the impregnation of the pregel electrolyte solution into the power generation element is preferably 3 × 10 ⁴ Pa or less. More preferably, it is 2 × 10 ³ Pa or less. The temperature during the impregnation is preferably 40 ° C to 60 ° C.
[0026]
(4) A process of sealing the exterior body 7 injected with the pregel electrolyte solution in a reduced pressure atmosphere After injecting the pregel electrolyte solution and impregnating under reduced pressure, using a vacuum sealing device, a vacuum pressure of 3.0 × 10 ⁴ Pa or less, More preferably, the lower seal portion 9 of the outer package 7 is sealed under the condition of 2 × 10 ³ Pa or less.
[0027]
(5) Step of heating the exterior body 7 to gel the pregel electrolyte solution By heating the exterior body 7, the pregel electrolyte solution is heated and polymerized (gelled) inside the battery to obtain the gel polymer electrolyte membrane 4. . This temperature may be a temperature at which the polymerizable compound in the pregel electrolyte solution is three-dimensionally cross-linked, and an appropriate temperature is selected depending on the polymerizable compound and the thermal polymerization initiator. For example, if it is an above-described polymeric compound and a thermal-polymerization initiator, 40-80 degreeC is preferable. Further, the heating time may be set to an appropriate time.
[0028]
The wound type lithium polymer secondary battery has been described. However, the present invention is not limited to this, and the present invention is also applicable to a laminated type lithium polymer secondary battery in which a positive electrode, a porous film, and a negative electrode are sequentially stacked. be able to.
[0029]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0030]
Example 1
1. Preparation of positive electrode LiCoO ₂ was used as a positive electrode active material, and a conductive material (acetylene black) and a binder (polyvinylidene fluoride (PVDF)) were mixed at a weight ratio of 90: 7: 3, and an organic solvent ( N-methylpyrrolidone). Next, the raw material for positive electrodes was produced by apply | coating uniformly on both surfaces of a collector (Al foil) using a die coater, and making it dry. Furthermore, this raw fabric was rolled by a roll press machine, and then cut into a predetermined size to produce a positive electrode 1 having a thickness of 0.16 mm. Next, the positive electrode lead 5 was welded to the end of the current collector of the positive electrode 1.
[0031]
2. Fabrication of negative electrode Natural graphite powder is used as the negative electrode active material, and binder (polyvinylidene fluoride (PVDF)) is mixed in a weight ratio of 97: 3 and pasted with an organic solvent (N-methylpyrrolidone). did. Next, the raw material for negative electrodes was produced by apply | coating uniformly on both surfaces of a collector (Cu foil) using a die coater, and making it dry. Furthermore, this raw fabric was rolled by a roll press and then cut into a predetermined size to produce a negative electrode 2 having a thickness of 0.16 mm. Next, the negative electrode lead 6 was welded to the end of the current collector of the negative electrode 2.
[0032]
3. Preparation of First Electrolyte Solution and Pregel Electrolyte Solution The first electrolyte solution comprises a supporting electrolyte LiPF ₆ in an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 1: 3. It was prepared by dissolving to a concentration of 1.2 mol / l. The pregel electrolyte solution is prepared by mixing a second electrolyte solution having the same composition as the first electrolyte solution and polyether acrylate (molecular weight: 10,000) at a weight ratio of 90:10, and then adding a thermal polymerization initiator (t- Hexylperoxypiparate) was prepared by adding 0.3% by weight to the above mixed solution.
[0033]
4). Production of lithium polymer secondary battery The positive electrode 1 and the negative electrode 2 produced by the above-described method are overlapped and wound through a polyethylene porous body 3 (film thickness: 27 μm) to produce an elliptical power generation element. . Next, this power generation element is inserted into a flat outer package 7 made of an Al laminate material, and the upper seal portion 8 of the outer package 7 is sealed with the tip portions of the positive electrode lead 5 and the negative electrode lead 6 protruding outside.
[0034]
Next, the battery holder 14 is inserted into the battery holder 14 with a heater installed inside the vacuum tank 11 of the injection impregnation apparatus shown in FIG. The temperature of 14 is set to 40 ° C. After evacuating the vacuum pressure inside the vacuum chamber 11 to 2.8 × 10 ⁴ Pa, 1.6 g of the electrolyte solution is injected into the exterior body 7 from the injection nozzle 17 for electrolyte solution, and 10 minutes. Impregnation under reduced pressure. Further, 2.0 g of the pregel electrolyte solution is continuously injected into the exterior body 7 from the injection nozzle 19 for the pregel electrolyte solution and impregnated under reduced pressure for 10 minutes.
[0035]
Next, after sealing the lower seal portion 9 of the outer package 7 under a vacuum pressure of 2.8 × 10 ⁴ Pa using a vacuum sealing device, the pregel electrolyte solution is heated at 80 ° C. for 1 hour. Heat polymerization (gelation) was performed inside the battery to produce a lithium polymer secondary battery. This battery is referred to as battery A.
[0036]
For comparison, a lithium polymer secondary battery was produced in the same manner as battery A, except that the pre-gel electrolyte solution batch injection, that is, the first electrolyte injection / vacuum impregnation step was omitted. This battery is referred to as a battery Z1. In this case, the injection amount of the pregel electrolyte solution is 3.6 g.
[0037]
5). Each battery fabricated with high-rate discharge characteristics is charged to 4.2 V at a constant current of 420 mA (0.7 C) at room temperature (25 ° C.) and then charged at a constant voltage of 4.2 V for 2 hours. Thereafter, the battery was discharged at room temperature with a discharge capacity of 120 mA (0.2 C) until the final voltage reached 3.0 V, and the discharge capacity was calculated from the discharge time. Each battery charged under the same conditions was discharged at room temperature with a discharge capacity of 1200 mA (2C) until the final voltage reached 3.0 V, and the discharge capacity was calculated from the discharge time. From the measurement data obtained above, the ratio (percentage) of the discharge capacity at 2C to the discharge capacity at 0.2C was calculated, and this value was defined as the high rate discharge characteristic.
[0038]
6). About each battery which produced the low-temperature discharge characteristic, it charges to 4.2V with the constant current 420mA (0.7C) at 25 degreeC, Then, it charges for 2 hours with the constant voltage of 4.2V. Thereafter, the battery was discharged at 25 ° C. with a discharge capacity of 600 mA (1 C) until the final voltage reached 3.0 V, and the discharge capacity was calculated from the discharge time. Further, each battery charged under the same conditions was discharged at −10 ° C. with a discharge capacity of 600 mA (1C) until the end voltage reached 3.0 V, and the discharge capacity was calculated from the discharge time. From the measurement data obtained above, the ratio (percentage) of the discharge capacity at −10 ° C. to the discharge capacity at 25 ° C. was calculated, and this value was defined as the low temperature discharge characteristics.
[0039]
7). As the leakage resistance, the battery after heat polymerization was disassembled, and the presence or absence of the phase separated electrolyte was visually observed. In the evaluation, a case where no leakage was observed was rated as “◯”, and a case where electrolyte was leaking was rated as “X”.
[0040]
Table 1 shows the evaluation results of the high-rate discharge characteristics, low-temperature discharge characteristics, and leakage resistance of the produced lithium polymer secondary battery.
[0041]
[Table 1]

[0042]
As is clear from Table 1, in the lithium polymer secondary battery (battery A) of this example, the pregel electrolyte solution sufficiently penetrates into the power generation element, and the heat polymerization (gelation) is uniform inside the outer package. As a result, the high-rate discharge characteristics and the low-temperature discharge characteristics were significantly improved over the comparative battery (battery Z). This is because the permeability of the pregel electrolyte solution is improved because the inside of the power generation element can be preliminarily wetted with the electrolyte solution by injecting the first electrolyte solution under reduced pressure.
[0043]
In the comparative battery (battery Z1), since the pregel electrolyte solution was injected all at once without injecting the first electrolyte solution, the impregnation property of the pregel electrolyte solution into the power generation element was not improved, and high-rate discharge characteristics, As a result, the low-temperature discharge characteristics deteriorated.
[0044]
(Example 2)
Next, the case where the vacuum pressure during the injection impregnation of the electrolytic solution and the pregel electrolyte solution into the power generation element was changed was examined.
[0045]
The vacuum pressure during the impregnation was set to 1.3 × 10 ⁴ Pa, 2.8 × 10 ⁴ Pa, 4.2 × 10 ⁴ Pa, and the lithium polymer secondary battery was prepared in the same manner as in Example 1 except for this. Produced. This battery is referred to as batteries B to D. Battery A and battery C are batteries manufactured under the same conditions. For comparison, lithium polymer secondary batteries were fabricated in the same manner as in batteries B to D except that the pre-gel electrolyte solution batch injection, that is, the first electrolyte injection / vacuum impregnation step was omitted. This battery is referred to as batteries Z2 to Z4. The battery Z1 and the battery Z3 are batteries manufactured under the same conditions. Further, the lithium polymer solution is injected in the same manner as in the battery A except that the pregel electrolyte solution is collectively injected at atmospheric pressure (0.1 MPa), that is, the pregel electrolyte solution is collectively injected and no impregnation under reduced pressure is performed. A secondary battery was produced. This battery is referred to as a battery Z5. Table 2 shows the evaluation results of the high-rate discharge characteristics, low-temperature discharge characteristics, and leakage resistance of the produced lithium polymer secondary battery.
[0046]
[Table 2]

[0047]
As is clear from Table 2, the battery B and the battery C having a vacuum pressure of 1.3 × 10 ⁴ Pa and 2.8 × 10 ⁴ Pa have a vacuum pressure of 4 in the high rate discharge characteristics and the low temperature discharge characteristics. Better results than battery D, which is 2 × 10 ⁴ Pa. This is because as the vacuum pressure is smaller, the impregnation property of the electrolytic solution and the pregel electrolyte solution into the power generation element is improved, and gelation occurs uniformly within the power generation element.
[0048]
(Example 3)
The case where the temperature of the exterior body at the time of carrying out the injection | pouring impregnation to the electric power generation element of electrolyte solution and a pregel electrolyte solution was examined.
[0049]
Lithium was prepared in the same manner as in Example 1 except that the temperature of the outer casing during injection impregnation was 20 ° C., 40 ° C., 60 ° C., 80 ° C., and the vacuum pressure during injection impregnation was 1.3 × 10 ⁴ Pa. A polymer secondary battery was produced. This battery is referred to as batteries E to H. Battery B and battery F are batteries manufactured under the same conditions. The evaluation results of the high-rate discharge characteristics, low-temperature discharge characteristics, and liquid leakage resistance of the prepared lithium polymer secondary battery are shown in Table 3.
[0050]
[Table 3]

[0051]
As is clear from (Table 3), it has been found that good battery characteristics can be obtained when the temperature of the outer package during the impregnation is set to 40 to 60 ° C. This is because the viscosity of the pregel electrolyte solution is lowered by heating the exterior body, and the impregnation property to the power generation element is improved. However, the reasons why the battery H did not achieve better results than the battery G are as follows: (1) thermal decomposition of the supporting electrolyte LiPF _{6 and} (2) impregnation of the power generation element by partial gelation of the pregel electrolyte solution Sexual deterioration, etc. can be considered.
[0052]
Example 4
The case where the vacuum pressure at the time of sealing an exterior body was changed was examined.
[0053]
The vacuum pressure at the time of sealing the outer package was set to 1.3 × 10 ⁴ Pa, 2.8 × 10 ⁴ Pa, 4.2 × 10 ⁴ Pa. A secondary battery was produced. This battery is referred to as batteries I to K. Battery A and battery J are batteries manufactured under the same conditions. For comparison, a lithium polymer secondary battery was produced in the same manner as the battery Z1, except that the vacuum pressure when sealing the outer package was atmospheric pressure (0.1 MPa). This battery is referred to as a battery Z6. Table 4 shows the evaluation results of the high-rate discharge characteristics, low-temperature discharge characteristics, and leakage resistance of the produced lithium polymer secondary battery.
[0054]
[Table 4]

[0055]
As is clear from (Table 4), the lower the vacuum pressure when sealing the outer package, the higher the high rate discharge characteristics, the low temperature discharge characteristics, and the liquid leakage resistance. This is presumably because by setting the inside of the outer package to an oxygen-blocking atmosphere, the three-dimensional crosslinking reaction of the polymerizable compound was promoted, and the electrolyte solution could be taken in a large amount into the polymer matrix.
[0056]
【The invention's effect】
As described above, the present invention provides a method for producing a lithium polymer secondary battery in which a power generation element in which a positive electrode and a negative electrode are opposed to each other through a porous body containing a gel polymer electrolyte is accommodated in an outer package. , A step of accommodating a power generation element composed of a negative electrode and a porous body in the exterior body, a step of injecting a first electrolytic solution into the exterior body and impregnating under reduced pressure, and a polymerization property with the second electrolyte solution in the exterior body A step of injecting a pregel electrolyte solution containing at least a compound and a thermal polymerization initiator and impregnating under reduced pressure; a step of sealing the outer body into which the pregel electrolyte solution has been injected in a reduced-pressure atmosphere; and heating the outer body to And the step of gelling the pregel electrolyte solution, the pregel electrolyte solution is sufficiently penetrated into the power generation element, and heat polymerization (gelation) is uniformly generated inside the exterior body. Ireto discharge characteristics, has a low-temperature discharge characteristic, it is possible to efficiently provide excellent lithium polymer secondary battery of the leakage resistance, its practical value is what great made.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of a lithium polymer secondary battery of the present invention. FIG. 2 is a diagram showing an injection impregnation apparatus for an electrolyte solution and a pregel electrolyte solution.
1. Positive electrode 2. Negative electrode 3. Porous membrane 4. 4. Gel-like polymer electrolyte membrane Positive electrode lead 6. 6. Negative electrode lead Exterior body 8. 8. Upper seal part Lower seal part 10. 10. Insulating protective film Vacuum chamber 12. Vacuum pump 13. Solenoid valve 14. Battery holder 15. Temperature controller 16. Storage tank for electrolyte 17. Injection nozzle 18. 18. Storage tank for pregel electrolyte solution Injection nozzle

Claims

A method for producing a lithium polymer secondary battery in which a power generation element in which a positive electrode and a negative electrode are opposed to each other through a porous body containing a gel polymer electrolyte is housed in an exterior body,
A step of accommodating a power generation element composed of a positive electrode, a negative electrode, and a porous body in the exterior body;
Injecting a first electrolyte into the outer package and impregnating under reduced pressure;
Injecting a pregel electrolyte solution containing at least a second electrolyte solution, a polymerizable compound and a thermal polymerization initiator into the outer package and impregnating under reduced pressure;
Sealing the outer package infused with the pregel electrolyte solution under a reduced pressure atmosphere;
Heating the exterior body to gel the pregel electrolyte solution;
A method for producing a lithium polymer secondary battery, comprising:

The lithium polymer secondary battery according to claim 1, wherein the step of injecting the first electrolytic solution and impregnating under reduced pressure and the step of injecting the pregel electrolyte solution and impregnating under reduced pressure are successively performed in this order. Production method.

The lithium polymer according to any one of claims 1 and 2, wherein the impregnation of the first electrolytic solution and the pregel electrolyte solution into the power generation element is performed in a reduced pressure atmosphere having a vacuum pressure of 3 x 10 ⁴ Pa or less. A method for manufacturing a secondary battery.

The lithium polymer secondary battery according to any one of claims 1 to 3, wherein the impregnation of the first electrolytic solution and the pregel electrolyte solution into the power generation element is performed in an environment of 40 ° C to 60 ° C. Production method.

The hermetic body is sealed in a reduced pressure atmosphere of 3 × 10 ⁴ Pa or less, and then the outer body is heated at a temperature of 40 ° C. to 80 ° C. to gel the pregel electrolyte solution. 5. A method for producing a lithium polymer secondary battery according to any one of 4 above.

The method for producing a lithium polymer secondary battery according to claim 1, wherein the first electrolytic solution and the second electrolytic solution have the same composition.

2. The method for producing a lithium polymer secondary battery according to claim 1, wherein the polymerizable compound is either a polyethylene oxide-terminated acrylate-modified polymer material or an acrylate polymer material.

2. The method for producing a lithium polymer secondary battery according to claim 1, wherein the thermal polymerization initiator is an organic peroxide.

9. The method for producing a lithium polymer secondary battery according to claim 8, wherein the organic peroxide is t-hexyl peroxypiparate or t-butyl peroxyneodecanoate.

2. The method for producing a lithium polymer secondary battery according to claim 1, wherein the exterior body is made of a multilayer laminate material mainly composed of a resin film having a metal foil as an intermediate layer and has a flat shape.