JP4624589B2

JP4624589B2 - Vanadium-based composite positive electrode for solid-state lithium polymer battery and lithium polymer battery using the same

Info

Publication number: JP4624589B2
Application number: JP2001096504A
Authority: JP
Inventors: 聡井上; 外志雄村永; 哲男境
Original assignee: Daiso Co Ltd; National Institute of Advanced Industrial Science and Technology AIST
Current assignee: National Institute of Advanced Industrial Science and Technology AIST; Osaka Soda Co Ltd
Priority date: 2001-03-29
Filing date: 2001-03-29
Publication date: 2011-02-02
Anticipated expiration: 2021-03-29
Also published as: JP2002298844A

Description

【０００１】
【発明の属する技術分野】
本発明はリチウムポリマー電池用複合正極、およびその正極を用いたリチウムポリマー電池およびその使用方法に関するものである。
【０００２】
【従来の技術】
リチウム二次電池に関して、最近活発に研究がなされており、電池構成材料や組み立てについて多くの提案がなされている。例えば正極活物質としてLiCoO₂、LiNiO₂、LiMn₂O₄、V₂O₅、V₆O₁₃、TiS₂等が用いられ、負極活物質としてリチウム、リチウム-アルミニウム合金、カーボン(ハードカーボン、天然黒鉛、メソフェーズカーボンマイクロビーズ、メソフェーズカーボンファイバー)等を用いる二次電池が提案されている。
これらのリチウム二次電池においては、電解液として、リチウムイオンの移動できるプロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート、1,2-ジメトキシエタン等の1種以上の非プロトン性有機溶媒にLiClO₄、LiBF₄、LiAsF₆、LiPF₆、LiCF₃SO₃、LiN(CF₃SO₂)₂等のリチウム塩を溶解させた電解液が使用されている。しかし、これらの電解液は可燃性であるためこれらの電解液を使用したリチウム二次電池は発火や爆発の危険性がある。またリチウム金属やリチウム合金を負極として使用すると、負極上で生成するリチウムデントライトが正極に達して短絡する危険性もある。これらの問題点は電解液に有機溶媒を使用していることに起因する。
【０００３】
これらの問題点を解決するため電解液をポリマーでゲル化し固定したリチウムポリマー電池の開発が進められているが、まだ電解液の漏液の問題や60℃以上の高温環境下での使用に耐えるものではない。そこで、完全固体電解質ポリマーを用いた固体型リチウム電池の研究が進められている。夏らによって、正極の結着剤兼イオン導電体として分子量約2000のポリエチレングリコールを使用した正極と高分子固体電解質、リチウム金属を組み合わせたリチウムポリマー電池が60℃において、優れた電池特性を示すことがJ. Electorchem. Soc., 147, 2050(2000) に報告されている。しかしながら、この分子量約2000のポリエチレングリコールを正極に使用したリチウムポリマー電池はより高温(80℃以上)では、特に電池のサイクル特性が大きく劣化する欠点を持っている。また、60℃以上の高温下において、このポリエチレングリコールは液体であるため、正極活物質および導電剤との結着力が弱く、正極内に多量に添加する必要があり、その量は正極活物質粒子100重量部に対して50重量部以上必要である。このため、複合正極中における活物質の割合が減少し、複合正極の持つエネルギー密度が小さくなってしまう。このよう欠点のためいまだ実用に耐えうるリチウムポリマー電池用正極は開発されていない。また、特願平10-85890において、正極活物質としてV₂O₅を用いたリチウムポリマー電池用の正極に関する特許が述べられている。この特許においてV₂O₅を活物質とした正極を用いた電池は充電時の上限電圧が3.0Vと低く、このときの電池の放電容量はV₂O₅を用いた電池としては小さい。
【０００４】
【発明が解決しようとする課題】
本発明の目的は小型軽量で充放電容量の大きいリチウムポリマー電池を提供しうるリチウムポリマー電池用複合正極およびその正極を用いたリチウムポリマー電池を提供することにある。
【０００５】
【課題を解決するための手段】
小型軽量で充放電容量の大きいリチウムポリマー電池を得るためには高電圧で充電できる方が望ましいがバナジウム酸化物の場合従来3.5 Vが上限であったが4.2 Vまで充電できる複合正極を見いだした。
【０００６】
即ち、本発明はエチレンオキシド30〜95モル％、側鎖に重合度1〜12のエチレンオキシド単位を有するグリシジルエーテル5〜70モル%からなる重量平均分子量が100万以上の共重合体に電解質塩としてリチウム塩を溶解した高分子固体電解質、正極活物質粒子としてバナジウム系酸化物V_XO₅(X=2〜2.5)、および導電性粒子からなる複合体を集電体上に塗着したことを特徴とする複合正極である。更に本発明は上記複合正極およびリチウム金属あるいはリチウム金属合金からなる負極、ならびにエチレンオキシド30〜94モル％、側鎖に重合度1〜12のエチレンオキシド単位を有するグリシジルエーテル5〜69モル%とアリルグリシジルエーテル1〜5モル％からなる重量平均分子量が100万以上の共重合体にリチウム塩を溶解した高分子固体電解質を架橋させた膜からなるリチウムポリマー電池を提供し、その充電方法を提供するものである。
【０００７】
本発明における複合正極において使用することが望ましい高分子固体電解質はエチレンオキシドと側鎖に重合度1〜12のエチレンオキシド単位を有するグリシジルエーテルからなる重量平均分子量が100万以上の共重合体に電解質塩としてリチウム塩を添加した高分子固体電解質である。この固体電解質は分子量約2000のポリエチレングリコールに比べ、分子量が高いため、機械的強度に優れている。さらに融点が高いため、60℃以上の高温下においても正極活物質粒子および導電性粒子との結着性に優れている。結着性に優れたこの高分子固体電解質を複合正極に用いることにより、複合正極中の高分子固体電解質の量を少なくすることができる。これにより、複合正極のエネルギー密度を向上させることができる。また80℃以上の高温下においても固体であることから、平均分子量約2000のポリエチレングリコールを用いて作製した複合正極にくらべ、正極の劣化が起こりにくい。このことから、この高分子を用いた正極のリチウムポリマー電池は60℃だけでなく、さらに高温(80℃以上)下でも高い電池性能を発揮することができる。
本発明において複合正極は高分子固体電解質、正極活物質粒子、導電性粒子の複合体を集電体上に塗着することにより作製される。集電体としてはアルミニウム、白金、炭素からなる箔、メッシュ、発泡などの形状のものが使用できる。
【０００８】
エチレンオキシドと側鎖に重合度1〜12のエチレンオキシド単位を有するグリシジルエーテルにさらにアリルグリシジルエーテルを共重合させた共重合体に電解質塩としてリチウム塩を溶解させた高分子固体電解質は架橋させることにより、さらに高分子固体電解質の強度を上げることができる。このため、この高分子固体電解質、正極活物質粒子、導電性粒子の複合体を集電体上に塗着したのち、架橋を行うと高分子固体電解質と正極活物質粒子および導電性粒子との結着性をさらにあげることが可能である。このときの架橋方法としては、有機過酸化物、アゾ化合物等から選ばれるラジカル開始剤、紫外線、電子線等の活性エネルギー線を用いることができる。
複合正極中に平均分子量が500以上2000以下のポリエチレングリコールまたはそのエーテル化合物を添加することができる。ポリエチレングリコールのエーテル化合物としてはモノまたはジメチルエーテル、及びモノまたはジエチルエーテルが良い。複合正極中の高分子固体電解質を架橋することにより、正極活物質粒子および導電性粒子との結着性が強くなる。このため複合正極中に結着性に劣るポリエチレングリコールまたはそのエーテル化合物を添加しても、充放電サイクルを繰り返すことによる正極の劣化を減少させることができる。また、平均分子量が500以上2000以下のポリエチレングリコールまたはそのエーテル化合物は高温下(60℃以上)でのイオン導電性に優れるため、正極中に添加すると、特に大電流時における電池の充放電特性を改善することが可能となる。
【０００９】
リチウムポリマー二次電池の3V級正極材料としてはバナジウム系酸化物が広く使われてきた。バナジウム系酸化物は充電がすすむにつれ、電池電圧も単調に増加する。リチウムポリマー電池は電解質として高分子固体電解質を使用するが有機電解液に比べイオン導電性に劣り、充放電時の電圧の分極が大きい。このため、充電できる容量が充電時の分極で減少してしまうことになる。従来の高分子固体電解質としてポリエチレンオキシドを用いた電池では高分子固体電解質が分解することにより充電電圧の限界は3.5Vであった。また、前述した特許(特願平10-85890)においても、充電電圧の上限は3.0Vであった。本発明におけるエチレンオキシド(30〜94モル％)、側鎖に重合度1〜12のエチレンオキシド単位を有するグリシジルエーテル(5〜69モル%)とアリルグリシジルエーテル(1〜5モル％)からなる重量平均分子量が100万以上の共重合体に電解質塩としてリチウム塩を溶解した高分子固体電解質を架橋させた膜を高分子固体電解質膜として使用したリチウムポリマー電池はより高電圧(4.2V)まで充電することが可能であり、これにより従来のリチウムポリマー電池よりも高容量な電池とすることができる。また、満充電時においては電圧が急上昇するため充電終止電圧を設定することで容易に充電制御が行える。
【００１０】
電解質塩としてはLiClO₄、LiBF₄、LiAsF₆、LiPF₆、LiCF₃SO₃、LiN(CF₃SO₂)₂等のリチウム塩を使用することができる。これらのうちで、正極中の高分子固体電解質に使用するリチウム塩としてはLiN(CF₃SO₂)₂がより簡便に使用することができる。これは以下のような理由による。リチウム二次電池に広く使用されているLiPF₆のようなリチウム塩は水分により容易に加水分解し、HFが発生する。この発生したHFは高分子固体電解質を分解してしまう。または、リチウム金属と反応してフッ化リチウムを生成する。一方、LiN(CF₃SO₂)₂は水分による加水分解はほとんどなく、HFも発生しないからである。また、共重合体100重量部に対して加えるLiN(CF₃SO₂)₂の量が5重量部より少ないと高分子固体電解質中のリチウムイオンの濃度が薄すぎ十分なリチウムイオン導電性が得られない。また共重合体100重量部に対し50重量部以上はリチウム塩が共重合体中に溶けきれず加えることができない。このことから高分子固体電解質中のリチウム塩としてはLiN(CF₃SO₂)₂が良く、その量は共重合体100重量部に対して5〜50重量部が良い。
【００１１】
複合正極中に含まれる正極活物質粒子、および高分子固体電解質には電子伝導性はない。そこで複合正極中の正極活物質粒子において酸化還元反応がおこるためには複合正極中に導電性粒子を加えることが不可欠になる。導電性粒子としては少ない添加量で高い電子伝導性を複合正極に与えるケッチェンブラック（登録商標）やアセチレンブラックが適している。複合正極中の導電性粒子は正極活物質100重量部に対して5〜20重量部が良い。これは、正極活物質粒子100重量部に対して5重量部より導電性粒子の添加量が少ないと複合正極に十分な電子導電性を与えることができず、複合正極中の正極活物質粒子における酸化還元反応が十分に起きない。これにより、正極活物質粒子の利用率が低下し、充放電容量は理論値より大きく減少する。一方、正極活物質粒子100重量部に対して20重量部以上添加すると複合正極の電子導電性は確保できるものの、複合正極中の正極活物質の割合が低下する。これにより、複合正極の容量は低下してしまう。
【００１２】
複合正極中には正極活物質粒子100重量部に対して高分子固体電解質が5〜35重量部含まれていることが良い。これは高分子固体電解質が5重量部以下であると正極活物質粒子に対する結着力が弱く複合正極が作製できない。また35重量部以上であると結着力は十分なものの、複合正極中の正極活物質粒子が減少し、複合正極の容量が低下してしまう。
本実施例で使用した共重合体の重量平均分子量はゲルパーミュエーションクロマトグラフィ測定法により、標準ポリスチレン換算により分子量を算出した。ゲルパーミュエーションクロマトグラフィ測定は株式会社島津製作所の測定装置ＲＩＤ−６Ａ、昭和電工株式会社製カラムのショウデックスＫＤ−８０６、ＫＤ−８０６Ｍ、ＫＤ−８０３、及び溶媒ＤＭＦを用いて60℃で行った。
【００１３】
【実施例】
以下、実施例を示し、本発明を具体的に説明する。
実施例1
V₂O₅粉末 1.0g、ケッチェンブラック（登録商標） 0.15gの比率で採取し、乳鉢でよく混合した。一方、エチレンオキシド(88モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(12モル%)の共重合体（重量平均分子量：150万） 0.15g、LiN(CF₃SO₂)₂
0.033gをアセトニトリルに溶解させた。V₂O₅、ケッチェンブラック（登録商標）混合粉末に上記溶液を加え、乳鉢でよく混合し、正極スラリーを得た。このスラリーを厚み20μｍのアルミ箔に塗布したのち、溶媒を80℃の乾燥器中で除去した。これをロールプレスすることにより、正極全体の厚みが40μmの複合正極を作製した。えられた複合正極、高分子固体電解質膜としてエチレンオキシド(80.6モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(17.7モル%)とアリルグリシジルエーテル(1.7モル%)の共重合体100重量部にLiN(CF₃SO₂)₂を30重量部溶解させ架橋処理を行った高分子固体電解質を膜厚50μmに製膜したもの、負極として厚さ100μmのLi金属箔をはりあわせてコイン型セルを作製した。60℃の恒温槽中で0.5C、上限電圧4.1Vで定電流充電、0.2C、下限電圧2.0Vで定電流放電を行った。充放電を繰り返したときの放電容量を図1に示す。この図から、正極活物質1g当り約300mAhの高い初期放電容量を示すことがわかる（以後、mAh/gは正極活物質1g当りの充放電容量を表す）。80サイクル後も200mAh/gと高い放電容量を維持しており、試作した電池は60℃において高いサイクル特性を示すことがわかった。
【００１４】
実施例2
V₂O₅粉末 1.0g、ケッチェンブラック（登録商標） 0.15gの比率で採取し、乳鉢でよく混合した。一方、エチレンオキシド(88モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(12モル%)の共重合体（重量平均分子量：150万）0.20g、LiN(CF₃SO₂)₂
0.067gをアセトニトリルに溶解させた。V₂O₅、ケッチェンブラック（登録商標）混合粉末に上記溶液を加え、乳鉢でよく混合し、正極スラリーを得た。このスラリーを厚み20μｍのアルミ箔に塗布したのち、溶媒を80℃の乾燥器中で除去した。これをロールプレスすることにより、正極全体の厚み40μmの複合正極を作製した。えられた複合正極、高分子固体電解質膜としてエチレンオキシド(80.6モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(17.7モル%)とアリルグリシジルエーテル(1.7モル%)の共重合体100重量部にLiN(CF₃SO₂)₂を30重量部溶解させ架橋処理を行った高分子固体電解質を膜厚50μmに製膜したもの、負極として厚さ100μmのLi金属箔をはりあわせてコイン型セルを作製した。60℃および80℃の恒温槽中で0.2C、上限電圧4.1Vで定電流充電、0.2C、下限電圧2.0Vで定電流放電を行った。電池試験温度が80℃においても60℃のときと同様の高いサイクル特性を示した。
【００１５】
比較例1
V₂O₅粉末 1.0g、ケッチェンブラック（登録商標） 0.13gの比率で採取し、乳鉢でよく混合した。一方、平均分子量約2000のポリエチレングリコールモノメチルエーテル 0.53g、LiN(CF₃SO₂)₂
0.177gをアセトニトリルに溶解させた。V₂O₅、ケッチェンブラック（登録商標）混合粉末に上記溶液を加え、乳鉢でよく混合し、正極スラリーを得た。このスラリーを厚み20μｍのアルミ箔に塗布したのち、溶媒を80℃の乾燥器中で除去した。これをロールプレスすることにより、正極全体の厚み40μmの複合正極を作製した。えられた複合正極、高分子固体電解質膜としてエチレンオキシド(80.6モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(17.7モル%)とアリルグリシジルエーテル(1.7モル%)の共重合体100重量部にLiN(CF₃SO₂)₂を30重量部溶解させ架橋処理を行った高分子固体電解質を膜厚50μmに製膜したもの、負極として厚さ100μmのLi金属箔をはりあわせてコイン型セルを作製した。60℃および80℃の恒温槽中で0.2C、上限電圧4.1Vで定電流充電、0.2C、下限電圧2.0Vで定電流放電を行った。電池試験温度が80℃においては60℃のときに比べ、サイクル特性の劣化が大きくなった。
【００１６】
【表１】

【００１７】
実施例3
V₂O₅粉末 1.0g、ケッチェンブラック（登録商標） 0.15gの比率で採取し、乳鉢でよく混合した。一方、エチレンオキシド(88モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(12モル%)の共重合体（重量平均分子量：150万）0.15g、LiN(CF₃SO₂)₂
0.05gをアセトニトリルに溶解させた。V₂O₅、ケッチェンブラック（登録商標）混合粉末に上記溶液を加え、乳鉢でよく混合し、正極スラリーを得た。このスラリーを厚み20μｍのアルミ箔に塗布したのち、溶媒を80℃の乾燥器中で除去した。これをロールプレスすることにより、正極全体の厚み40μmの複合正極を作製した。えられた複合正極、高分子固体電解質膜としてエチレンオキシド(80.6モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(17.7モル%)とアリルグリシジルエーテル(1.7モル%)の共重合体100重量部にLiN(CF₃SO₂)₂を30重量部溶解させ架橋処理を行った高分子固体電解質を膜厚50μmに製膜したもの、負極として厚さ100μmのLi金属箔をはりあわせてコイン型セルを作製した。60℃の恒温槽中で0.2C、上限電圧を3.2、3.5、3.8、4.1、4.4Vと変化させて定電流充電、0.2C、下限電圧2.0Vで定電流放電を行った。上限電圧が3.6V以上でも、問題なく充電を行うことができた。それぞれの上限電圧における放電容量を図2に示す。これから、高い電圧まで充電することで電池の放電容量を増加させることができた。図3に充放電サイクルを10サイクル目の充放電容量と電池電圧の関係を示す。この図から満充電にあたる容量270mAh/g付近で電池電圧が急上昇していることがわかる。充電終止電圧を4.0〜4.2Vに設定することにより簡単に充電を制御することができることがわかった。
【００１８】
実施例4
V₂O₅粉末 1.0g、ケッチェンブラック（登録商標） 0.15gの比率で採取し、乳鉢でよく混合した。一方、エチレンオキシド(88モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(12モル%)の共重合体（重量平均分子量：150万）0.10g、LiN(CF₃SO₂)₂
0.033gをアセトニトリルに溶解させた。V₂O₅、ケッチェンブラック（登録商標）混合粉末に上記溶液を加え、乳鉢でよく混合し、正極スラリーを得た。このスラリーを厚み20μｍのアルミ箔に塗布したのち、溶媒を80℃の乾燥器中で除去した。これをロールプレスすることにより、正極全体の厚み40μmの複合正極を作製した。えられた複合正極、高分子固体電解質膜としてエチレンオキシド(80.6モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(17.7モル%)とアリルグリシジルエーテル(1.7モル%)の共重合体100重量部にLiN(CF₃SO₂)₂を30重量部溶解させ架橋処理を行った高分子固体電解質を膜厚50μmに製膜したもの、負極として厚さ100μmのLi金属箔をはりあわせてコイン型セルを作製した。60℃の恒温槽中で上限電圧4.1Vで定電流充電、下限電圧2.0Vで定電流放電を行った。0.2Cの電流で充放電を200サイクル繰り返したとき、電池の容量は初期容量の76％となった。また、0.5Cで充放電を行うと0.2Cで充放電を行ったときの容量の約68％となった。
【００１９】
実施例5
V₂O₅粉末 1.0g、ケッチェンブラック（登録商標） 0.15gの比率で採取し、乳鉢でよく混合した。一方、エチレンオキシド(82モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(18モル%)とアリルグリシジルエーテル(1.7モル%)の共重合体（重量平均分子量：150万）0.10g、LiN(CF₃SO₂)₂ 0.033g、過酸化ベンゾイル0.005gをアセトニトリルに溶解させた。V₂O₅、ケッチェンブラック（登録商標）混合粉末に上記溶液を加え、乳鉢でよく混合し、正極スラリーを得た。このスラリーを厚み20μｍのアルミ箔に塗布したのち、溶媒を80℃の乾燥器中で除去した。これをロールプレスすることにより、正極全体の厚み40μmの複合正極を作製した。この複合正極をアルゴンガス中、100℃、3時間加熱処理を行うことにより複合正極中の重合体の架橋を行った。高分子固体電解質膜としてエチレンオキシド(80.6モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(17.7モル%)とアリルグリシジルエーテル(1.7モル%)の共重合体100重量部にLiN(CF₃SO₂)₂を30重量部溶解させ架橋処理を行った高分子固体電解質を膜厚50μmに製膜したもの、負極として厚さ100μmのLi金属箔をはりあわせてコイン型セルを作製した。60℃の恒温槽中で上限電圧4.1Vで定電流充電、下限電圧2.0Vで定電流放電を行った。0.2Cの電流で充放電を200サイクル繰り返したとき、電池の容量は初期容量の81％となった。また、0.5Cで充放電を行うと0.2Cで充放電を行ったときの容量の約63％となった。これは、複合正極中の重合体を架橋処理することにより、正極活物質粒子および導電性粒子との結着性があがったため電池のサイクル寿命が伸び、架橋処理により複合正極中の高分子固体電解質のイオン導電性が低下したために0.5Cでの容量の低下が大きかったと考えられる。
【００２０】
実施例6
V₂O₅粉末 1.0g、ケッチェンブラック（登録商標） 0.15gの比率で採取し、乳鉢でよく混合した。一方、エチレンオキシド(82モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(18モル%)とアリルグリシジルエーテル(1.7モル%)の共重合体（重量平均分子量：150万）0.10g、分子量約2000のポリエチレングリコールジメチルエーテル 0.05g、LiN(CF₃SO₂)₂
0.033g、過酸化ベンゾイル 0.005gをアセトニトリルに溶解させた。V₂O₅、ケッチェンブラック（登録商標）混合粉末に上記溶液を加え、乳鉢でよく混合し、正極スラリーを得た。このスラリーを厚み20μｍのアルミ箔に塗布したのち、溶媒を80℃の乾燥器中で除去した。これをロールプレスすることにより、正極全体の厚み40μmの複合正極を作製した。この複合正極をアルゴンガス中、100℃、3時間加熱処理を行うことにより複合正極中の重合体の架橋を行った。高分子固体電解質膜としてエチレンオキシド(80.6モル%)と2-(2-メトキシエトキシ)エチルグリシジルエーテル(17.7モル%)とアリルグリシジルエーテル(1.7モル%)の共重合体100重量部にLiN(CF₃SO₂)₂を30重量部溶解させ架橋処理を行った高分子固体電解質を膜厚50μmに製膜したもの、負極として厚さ100μmのLi金属箔をはりあわせてコイン型セルを作製した。60℃の恒温槽中で上限電圧4.1Vで定電流充電、下限電圧2.0Vで定電流放電を行った。0.2Cの電流で充放電を200サイクル繰り返したとき、電池の容量は初期容量の79％となった。また、0.5Cで充放電を行うと0.2Cで充放電を行ったときの容量の約72％となった。これは、複合正極中の重合体を架橋処理することにより、正極活物質粒子および導電性粒子との結着性があがったため電池のサイクル寿命が伸び、複合正極中に添加したポリエチレングリコールジメチルエーテルにより、イオン導電性が向上したため0.5Cでの容量の低下が小さくなったと考えられる。
【００２１】
【表２】

【００２２】
【発明の効果】
本発明によれば、小型軽量で充放電容量の大きいリチウムポリマー電池を供する複合正極ならびにその正極を用いたリチウムポリマー電池がえられる。本発明の電池は高い電圧まで充電することが可能であり、このことにより高容量を達成しうる。
本発明の電池は高温下においても安定に作動するため、電池温度が上がりやすい電気自動車やハイブリッド自動車、ロードレベリング用電池等として使用できる。
【図面の簡単な説明】
【図１】V₂O₅複合正極を用いた全固体リチウムポリマー電池の放電容量とサイクル特性との関係を示す。
【図２】V₂O₅複合正極を用いたリチウムポリマー電池の充電時の上限電圧と放電容量との関係を示す。
【図３】V₂O₅複合正極を用いたリチウムポリマー電池の充放電容量と電池電圧の関係を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a composite positive electrode for a lithium polymer battery, a lithium polymer battery using the positive electrode, and a method of using the lithium polymer battery.
[0002]
[Prior art]
Recently, active research has been conducted on lithium secondary batteries, and many proposals have been made on battery constituent materials and assembly. For example, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , V ₆ O ₁₃ , TiS ₂ etc. are used as the positive electrode active material, and lithium, lithium-aluminum alloy, carbon (hard carbon, natural Secondary batteries using graphite, mesophase carbon microbeads, mesophase carbon fibers) and the like have been proposed.
In these lithium secondary batteries, as an electrolytic solution, one or more aprotic organic solvents such as propylene carbonate, ethylene carbonate, diethyl carbonate, 1,2-dimethoxyethane capable of transferring lithium ions are used as LiClO ₄ , LiBF _4. An electrolytic solution in which a lithium salt such as LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , or LiN (CF ₃ SO ₂ ) ₂ is dissolved is used. However, since these electrolytes are flammable, lithium secondary batteries using these electrolytes have a risk of ignition or explosion. Further, when lithium metal or a lithium alloy is used as the negative electrode, there is a risk that the lithium dentlite produced on the negative electrode reaches the positive electrode and short-circuits. These problems are caused by using an organic solvent in the electrolytic solution.
[0003]
In order to solve these problems, development of a lithium polymer battery in which the electrolyte is gelled and fixed with a polymer is in progress, but it still can withstand the problem of electrolyte leakage and use in a high-temperature environment of 60 ° C or higher. It is not a thing. Therefore, research on solid-state lithium batteries using a completely solid electrolyte polymer is underway. According to Natsu et al., A lithium polymer battery combining a positive electrode using polyethylene glycol having a molecular weight of about 2000 as a positive electrode binder and ionic conductor, a polymer solid electrolyte, and lithium metal exhibits excellent battery characteristics at 60 ° C. Is reported in J. Electorchem. Soc., 147, 2050 (2000). However, a lithium polymer battery using polyethylene glycol having a molecular weight of about 2000 as a positive electrode has a drawback that the cycle characteristics of the battery are greatly deteriorated at a higher temperature (80 ° C. or higher). In addition, since this polyethylene glycol is a liquid at a high temperature of 60 ° C. or higher, the binding force between the positive electrode active material and the conductive agent is weak, and it is necessary to add a large amount in the positive electrode. 50 parts by weight or more is necessary for 100 parts by weight. For this reason, the ratio of the active material in a composite positive electrode reduces, and the energy density which a composite positive electrode has will become small. Due to such drawbacks, a positive electrode for a lithium polymer battery that can withstand practical use has not yet been developed. Japanese Patent Application No. 10-85890 describes a patent relating to a positive electrode for a lithium polymer battery using V ₂ O ₅ as a positive electrode active material. In this patent, a battery using a positive electrode using V ₂ O ₅ as an active material has a low upper limit voltage of 3.0 V during charging, and the discharge capacity of the battery at this time is small as a battery using V ₂ O ₅ .
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a composite positive electrode for a lithium polymer battery and a lithium polymer battery using the positive electrode, which can provide a small and light lithium polymer battery having a large charge / discharge capacity.
[0005]
[Means for Solving the Problems]
In order to obtain a small and light lithium polymer battery with a large charge / discharge capacity, it is desirable to be able to charge at a high voltage. However, in the case of vanadium oxide, a composite positive electrode capable of charging up to 4.2 V was found, although 3.5 V was the upper limit.
[0006]
That is, the present invention provides a copolymer having a weight average molecular weight of 5 to 70 mol% having 30 to 95 mol% ethylene oxide and 5 to 70 mol% glycidyl ether having a degree of polymerization of 1 to 12 in the side chain as an electrolyte salt. A solid polymer electrolyte in which salt is dissolved, vanadium-based oxide V _X O ₅ (X = 2 to 2.5) as positive electrode active material particles, and a composite composed of conductive particles are coated on the current collector. And a composite positive electrode. Furthermore, the present invention relates to the above composite positive electrode and a negative electrode comprising lithium metal or lithium metal alloy, and 30 to 94 mol% of ethylene oxide, 5 to 69 mol% of glycidyl ether having an ethylene oxide unit of 1 to 12 in the side chain, and allyl glycidyl ether. Provided is a lithium polymer battery comprising a membrane obtained by crosslinking a solid polymer electrolyte in which a lithium salt is dissolved in a copolymer having a weight average molecular weight of 1 to 5 mol% and having a weight average molecular weight of 1 million or more. is there.
[0007]
The polymer solid electrolyte desirably used in the composite positive electrode in the present invention is an electrolyte salt formed on a copolymer having a weight average molecular weight of 1 million or more, which is composed of ethylene oxide and a glycidyl ether having a degree of polymerization of 1 to 12 in the side chain. This is a polymer solid electrolyte to which a lithium salt is added. Since this solid electrolyte has a higher molecular weight than polyethylene glycol having a molecular weight of about 2000, it has excellent mechanical strength. Furthermore, since the melting point is high, the binding property with the positive electrode active material particles and the conductive particles is excellent even at a high temperature of 60 ° C. or higher. By using this solid polymer electrolyte excellent in binding property for the composite positive electrode, the amount of the solid polymer electrolyte in the composite positive electrode can be reduced. Thereby, the energy density of a composite positive electrode can be improved. In addition, since it is solid even at a high temperature of 80 ° C. or higher, the cathode is less likely to deteriorate than a composite cathode produced using polyethylene glycol having an average molecular weight of about 2000. Thus, a positive electrode lithium polymer battery using this polymer can exhibit high battery performance not only at 60 ° C. but also at higher temperatures (80 ° C. or higher).
In the present invention, the composite positive electrode is produced by coating a composite of a solid polymer electrolyte, positive electrode active material particles, and conductive particles on a current collector. As the current collector, a foil, mesh, foam or the like made of aluminum, platinum or carbon can be used.
[0008]
By cross-linking a solid polymer electrolyte in which a lithium salt is dissolved as an electrolyte salt in a copolymer obtained by copolymerizing allyl glycidyl ether with ethylene oxide and a glycidyl ether having a degree of polymerization of 1 to 12 in the side chain, Furthermore, the strength of the polymer solid electrolyte can be increased. For this reason, after the polymer solid electrolyte, the positive electrode active material particles, and the conductive particle composite are coated on the current collector and then crosslinked, the polymer solid electrolyte, the positive electrode active material particles, and the conductive particles It is possible to further increase the binding property. As a crosslinking method at this time, a radical initiator selected from organic peroxides, azo compounds and the like, and active energy rays such as ultraviolet rays and electron beams can be used.
Polyethylene glycol having an average molecular weight of 500 or more and 2000 or less or an ether compound thereof can be added to the composite positive electrode. The ether compound of polyethylene glycol is preferably mono or dimethyl ether, and mono or diethyl ether. By cross-linking the solid polymer electrolyte in the composite positive electrode, the binding property with the positive electrode active material particles and the conductive particles becomes strong. For this reason, even if polyethylene glycol or its ether compound having poor binding properties is added to the composite positive electrode, the deterioration of the positive electrode due to repeated charge / discharge cycles can be reduced. In addition, polyethylene glycol having an average molecular weight of 500 or more and 2000 or less and its ether compound is excellent in ionic conductivity at high temperature (60 ° C. or more). It becomes possible to improve.
[0009]
Vanadium-based oxides have been widely used as 3V cathode materials for lithium polymer secondary batteries. As the charging of vanadium oxide proceeds, the battery voltage increases monotonously. A lithium polymer battery uses a solid polymer electrolyte as an electrolyte, but is inferior in ionic conductivity as compared with an organic electrolyte and has a large voltage polarization during charge and discharge. For this reason, the chargeable capacity is reduced due to polarization during charging. In a battery using polyethylene oxide as a conventional polymer solid electrolyte, the charging voltage limit was 3.5 V due to decomposition of the polymer solid electrolyte. In the above-mentioned patent (Japanese Patent Application No. 10-85890), the upper limit of the charging voltage was 3.0V. Weight average molecular weight comprising ethylene oxide (30 to 94 mol%), glycidyl ether (5 to 69 mol%) having an ethylene oxide unit having a polymerization degree of 1 to 12 in the side chain and allyl glycidyl ether (1 to 5 mol%) in the present invention Lithium polymer batteries using a solid polymer electrolyte membrane cross-linked with a polymer solid electrolyte in which a lithium salt is dissolved as an electrolyte salt in a copolymer of 1 million or more must be charged to a higher voltage (4.2V). Accordingly, a battery having a higher capacity than that of a conventional lithium polymer battery can be obtained. Further, since the voltage rapidly rises at the time of full charge, the charge control can be easily performed by setting the charge end voltage.
[0010]
As the electrolyte salt, lithium salts such as LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used. Of these, LiN (CF ₃ SO ₂ ) ₂ can be more easily used as the lithium salt used for the polymer solid electrolyte in the positive electrode. This is due to the following reasons. Lithium salts such as LiPF ₆ widely used in lithium secondary batteries are easily hydrolyzed by moisture to generate HF. The generated HF decomposes the solid polymer electrolyte. Alternatively, it reacts with lithium metal to produce lithium fluoride. On the other hand, LiN (CF ₃ SO ₂ ) ₂ is hardly hydrolyzed by moisture and HF is not generated. Also, if the amount of LiN (CF ₃ SO ₂ ) ₂ added to 100 parts by weight of the copolymer is less than 5 parts by weight, the lithium ion concentration in the polymer solid electrolyte is too thin and sufficient lithium ion conductivity is obtained. I can't. Further, 50 parts by weight or more with respect to 100 parts by weight of the copolymer cannot be added because the lithium salt is not completely dissolved in the copolymer. For this reason, LiN (CF ₃ SO ₂ ) ₂ is good as the lithium salt in the polymer solid electrolyte, and the amount is preferably 5 to 50 parts by weight with respect to 100 parts by weight of the copolymer.
[0011]
The positive electrode active material particles and the polymer solid electrolyte contained in the composite positive electrode do not have electronic conductivity. Therefore, in order for the redox reaction to occur in the positive electrode active material particles in the composite positive electrode, it is indispensable to add conductive particles in the composite positive electrode. As the conductive particles, ketjen black (registered trademark) or acetylene black which imparts high electron conductivity to the composite positive electrode with a small addition amount is suitable. The conductive particles in the composite positive electrode are preferably 5 to 20 parts by weight with respect to 100 parts by weight of the positive electrode active material. This is because if the amount of conductive particles added is less than 5 parts by weight based on 100 parts by weight of the positive electrode active material particles, the composite positive electrode cannot be provided with sufficient electronic conductivity, and the positive electrode active material particles in the composite positive electrode The redox reaction does not occur sufficiently. Thereby, the utilization factor of the positive electrode active material particles is reduced, and the charge / discharge capacity is greatly reduced from the theoretical value. On the other hand, when 20 parts by weight or more is added with respect to 100 parts by weight of the positive electrode active material particles, the electronic conductivity of the composite positive electrode can be secured, but the ratio of the positive electrode active material in the composite positive electrode decreases. Thereby, the capacity | capacitance of a composite positive electrode will fall.
[0012]
The composite positive electrode preferably contains 5 to 35 parts by weight of a solid polymer electrolyte with respect to 100 parts by weight of the positive electrode active material particles. This is because when the solid polymer electrolyte is 5 parts by weight or less, the binding force to the positive electrode active material particles is weak and a composite positive electrode cannot be produced. If the amount is 35 parts by weight or more, the binding force is sufficient, but the positive electrode active material particles in the composite positive electrode are reduced, and the capacity of the composite positive electrode is reduced.
The weight average molecular weight of the copolymer used in this example was calculated by gel permeation chromatography and calculated in terms of standard polystyrene. Gel permeation chromatography measurement was performed at 60 ° C. using Shimadzu Corporation's measuring device RID-6A, Showa Denko Co., Ltd. column Showdex KD-806, KD-806M, KD-803, and solvent DMF. .
[0013]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
Example 1
V ₂ O ₅ powder was collected at a ratio of 1.0 g and ketjen black (registered trademark) 0.15 g and mixed well in a mortar. On the other hand, a copolymer of ethylene oxide (88 mol%) and 2- (2-methoxyethoxy) ethyl glycidyl ether (12 mol%) (weight average molecular weight: 1.5 million) 0.15 g, LiN (CF ₃ SO ₂ ) ₂
0.033 g was dissolved in acetonitrile. The above solution was added to a mixed powder of V ₂ O ₅ and Ketjen Black (registered trademark) and mixed well in a mortar to obtain a positive electrode slurry. After applying this slurry to an aluminum foil having a thickness of 20 μm, the solvent was removed in a dryer at 80 ° C. By roll pressing this, a composite positive electrode having a total positive electrode thickness of 40 μm was produced. Obtained composite positive electrode, polymer solid electrolyte membrane as ethylene oxide (80.6 mol%), 2- (2-methoxyethoxy) ethyl glycidyl ether (17.7 mol%) and allyl glycidyl ether (1.7 mol%) copolymer 100 weight 30 parts by weight of LiN (CF ₃ SO ₂ ) ₂ dissolved in the part and a solid polymer electrolyte with a cross-linking treatment formed into a film thickness of 50 μm, a 100 μm thick Li metal foil as a negative electrode, and a coin type A cell was made. In a constant temperature bath at 60 ° C., constant current charging was performed at 0.5 C and an upper limit voltage of 4.1 V, and constant current discharging was performed at 0.2 C and a lower limit voltage of 2.0 V. Figure 1 shows the discharge capacity when charging and discharging are repeated. From this figure, it can be seen that a high initial discharge capacity of about 300 mAh per 1 g of the positive electrode active material is shown (hereinafter, mAh / g represents the charge / discharge capacity per 1 g of the positive electrode active material). The high discharge capacity of 200 mAh / g was maintained even after 80 cycles, and the prototype battery was found to exhibit high cycle characteristics at 60 ° C.
[0014]
Example 2
V ₂ O ₅ powder was collected at a ratio of 1.0 g and ketjen black (registered trademark) 0.15 g and mixed well in a mortar. On the other hand, a copolymer of ethylene oxide (88 mol%) and 2- (2-methoxyethoxy) ethyl glycidyl ether (12 mol%) (weight average molecular weight: 1,500,000) 0.20 g, LiN (CF ₃ SO ₂ ) ₂
0.067 g was dissolved in acetonitrile. The above solution was added to a mixed powder of V ₂ O ₅ and Ketjen Black (registered trademark) and mixed well in a mortar to obtain a positive electrode slurry. After applying this slurry to an aluminum foil having a thickness of 20 μm, the solvent was removed in a dryer at 80 ° C. This was roll-pressed to produce a composite positive electrode having a total positive electrode thickness of 40 μm. Obtained composite positive electrode, polymer solid electrolyte membrane as ethylene oxide (80.6 mol%), 2- (2-methoxyethoxy) ethyl glycidyl ether (17.7 mol%) and allyl glycidyl ether (1.7 mol%) copolymer 100 weight 30 parts by weight of LiN (CF ₃ SO ₂ ) ₂ dissolved in the part and a solid polymer electrolyte with a cross-linking treatment formed into a film thickness of 50 μm, a 100 μm thick Li metal foil as a negative electrode, and a coin type A cell was made. In a thermostat bath at 60 ° C. and 80 ° C., constant current charging was performed at 0.2 C and an upper limit voltage of 4.1 V, and constant current discharging was performed at 0.2 C and a lower limit voltage of 2.0 V. Even at a battery test temperature of 80 ° C., high cycle characteristics similar to those at 60 ° C. were exhibited.
[0015]
Comparative Example 1
V ₂ O ₅ powder was collected at a ratio of 1.0 g and ketjen black (registered trademark) 0.13 g, and mixed well in a mortar. Meanwhile, 0.53 g of polyethylene glycol monomethyl ether having an average molecular weight of about 2000, LiN (CF ₃ SO ₂ ) ₂
0.177 g was dissolved in acetonitrile. The above solution was added to a mixed powder of V ₂ O ₅ and Ketjen Black (registered trademark) and mixed well in a mortar to obtain a positive electrode slurry. After applying this slurry to an aluminum foil having a thickness of 20 μm, the solvent was removed in a dryer at 80 ° C. This was roll-pressed to produce a composite positive electrode having a total positive electrode thickness of 40 μm. Obtained composite positive electrode, polymer solid electrolyte membrane as ethylene oxide (80.6 mol%), 2- (2-methoxyethoxy) ethyl glycidyl ether (17.7 mol%) and allyl glycidyl ether (1.7 mol%) copolymer 100 weight 30 parts by weight of LiN (CF ₃ SO ₂ ) ₂ dissolved in the part and a solid polymer electrolyte with a cross-linking treatment formed into a film thickness of 50 μm, a 100 μm thick Li metal foil as a negative electrode, and a coin type A cell was made. In a thermostat bath at 60 ° C. and 80 ° C., constant current charging was performed at 0.2 C and an upper limit voltage of 4.1 V, and constant current discharging was performed at 0.2 C and a lower limit voltage of 2.0 V. When the battery test temperature was 80 ° C., the deterioration of the cycle characteristics was larger than when the battery test temperature was 60 ° C.
[0016]
[Table 1]

[0017]
Example 3
V ₂ O ₅ powder was collected at a ratio of 1.0 g and ketjen black (registered trademark) 0.15 g and mixed well in a mortar. Meanwhile, 0.15 g of a copolymer of ethylene oxide (88 mol%) and 2- (2-methoxyethoxy) ethyl glycidyl ether (12 mol%) (weight average molecular weight: 1,500,000), LiN (CF ₃ SO ₂ ) ₂
0.05 g was dissolved in acetonitrile. The above solution was added to a mixed powder of V ₂ O ₅ and Ketjen Black (registered trademark) and mixed well in a mortar to obtain a positive electrode slurry. After applying this slurry to an aluminum foil having a thickness of 20 μm, the solvent was removed in a dryer at 80 ° C. This was roll-pressed to produce a composite positive electrode having a total positive electrode thickness of 40 μm. Obtained composite positive electrode, polymer solid electrolyte membrane as ethylene oxide (80.6 mol%), 2- (2-methoxyethoxy) ethyl glycidyl ether (17.7 mol%) and allyl glycidyl ether (1.7 mol%) copolymer 100 weight 30 parts by weight of LiN (CF ₃ SO ₂ ) ₂ dissolved in the part and a solid polymer electrolyte with a cross-linking treatment formed into a film thickness of 50 μm, a 100 μm thick Li metal foil as a negative electrode, and a coin type A cell was made. In a constant temperature bath at 60 ° C., 0.2C and the upper limit voltage were changed to 3.2, 3.5, 3.8, 4.1, and 4.4V, and constant current charge was performed at 0.2C and the lower limit voltage was 2.0V. Even if the upper limit voltage was 3.6V or higher, charging was possible without any problems. The discharge capacity at each upper limit voltage is shown in FIG. From this, it was possible to increase the discharge capacity of the battery by charging to a high voltage. FIG. 3 shows the relationship between the charge / discharge capacity and the battery voltage in the 10th charge / discharge cycle. From this figure, it can be seen that the battery voltage rises rapidly at a capacity of 270 mAh / g, which is full charge. It was found that charging can be easily controlled by setting the end-of-charge voltage to 4.0 to 4.2V.
[0018]
Example 4
V ₂ O ₅ powder was collected at a ratio of 1.0 g and ketjen black (registered trademark) 0.15 g and mixed well in a mortar. On the other hand, a copolymer of ethylene oxide (88 mol%) and 2- (2-methoxyethoxy) ethyl glycidyl ether (12 mol%) (weight average molecular weight: 1,500,000) 0.10 g, LiN (CF ₃ SO ₂ ) ₂
0.033 g was dissolved in acetonitrile. The above solution was added to a mixed powder of V ₂ O ₅ and Ketjen Black (registered trademark) and mixed well in a mortar to obtain a positive electrode slurry. After applying this slurry to an aluminum foil having a thickness of 20 μm, the solvent was removed in a dryer at 80 ° C. This was roll-pressed to produce a composite positive electrode having a total positive electrode thickness of 40 μm. Obtained composite positive electrode, polymer solid electrolyte membrane as ethylene oxide (80.6 mol%), 2- (2-methoxyethoxy) ethyl glycidyl ether (17.7 mol%) and allyl glycidyl ether (1.7 mol%) copolymer 100 weight 30 parts by weight of LiN (CF ₃ SO ₂ ) ₂ dissolved in the part and a solid polymer electrolyte with a cross-linking treatment formed into a film thickness of 50 μm, a 100 μm thick Li metal foil as a negative electrode, and a coin type A cell was made. Constant current charging was performed at an upper limit voltage of 4.1 V and constant current discharging was performed at a lower limit voltage of 2.0 V in a constant temperature bath at 60 ° C. When charging and discharging were repeated 200 cycles at a current of 0.2 C, the battery capacity was 76% of the initial capacity. Moreover, when charging / discharging at 0.5C, it became about 68% of the capacity when charging / discharging at 0.2C.
[0019]
Example 5
V ₂ O ₅ powder was collected at a ratio of 1.0 g and ketjen black (registered trademark) 0.15 g and mixed well in a mortar. On the other hand, a copolymer of ethylene oxide (82 mol%), 2- (2-methoxyethoxy) ethyl glycidyl ether (18 mol%) and allyl glycidyl ether (1.7 mol%) (weight average molecular weight: 1,500,000) 0.10 g, LiN (CF ₃ SO ₂ ) ₂ 0.033 g and benzoyl peroxide 0.005 g were dissolved in acetonitrile. The above solution was added to a mixed powder of V ₂ O ₅ and Ketjen Black (registered trademark) and mixed well in a mortar to obtain a positive electrode slurry. After applying this slurry to an aluminum foil having a thickness of 20 μm, the solvent was removed in a dryer at 80 ° C. This was roll-pressed to produce a composite positive electrode having a total positive electrode thickness of 40 μm. The composite positive electrode was heat-treated in argon gas at 100 ° C. for 3 hours to crosslink the polymer in the composite positive electrode. As a polymer solid electrolyte membrane, 100 parts by weight of a copolymer of ethylene oxide (80.6 mol%), 2- (2-methoxyethoxy) ethyl glycidyl ether (17.7 mol%) and allyl glycidyl ether (1.7 mol%) was mixed with LiN (CF ₃ A solid polymer electrolyte obtained by dissolving 30 parts by weight of SO ₂ ) ₂ and cross-linking was formed into a film having a thickness of 50 μm, and a Li metal foil having a thickness of 100 μm was laminated as a negative electrode to prepare a coin-type cell. Constant current charging was performed at an upper limit voltage of 4.1 V and constant current discharging was performed at a lower limit voltage of 2.0 V in a constant temperature bath at 60 ° C. When charging and discharging were repeated 200 cycles at a current of 0.2 C, the battery capacity was 81% of the initial capacity. In addition, when charging / discharging at 0.5C, it was about 63% of the capacity when charging / discharging at 0.2C. This is because the polymer in the composite positive electrode is cross-linked to increase the binding property between the positive electrode active material particles and the conductive particles, thereby extending the cycle life of the battery. It is considered that the decrease in capacity at 0.5C was large due to the decrease in ionic conductivity.
[0020]
Example 6
V ₂ O ₅ powder was collected at a ratio of 1.0 g and ketjen black (registered trademark) 0.15 g and mixed well in a mortar. On the other hand, ethylene oxide (82 mol%), 2- (2-methoxyethoxy) ethyl glycidyl ether (18 mol%) and allyl glycidyl ether (1.7 mol%) copolymer (weight average molecular weight: 1,500,000) 0.10 g, molecular weight Approximately 2000 polyethylene glycol dimethyl ether 0.05 g, LiN (CF ₃ SO ₂ ) ₂
0.033 g and benzoyl peroxide 0.005 g were dissolved in acetonitrile. The above solution was added to a mixed powder of V ₂ O ₅ and Ketjen Black (registered trademark) and mixed well in a mortar to obtain a positive electrode slurry. After applying this slurry to an aluminum foil having a thickness of 20 μm, the solvent was removed in a dryer at 80 ° C. This was roll-pressed to produce a composite positive electrode having a total positive electrode thickness of 40 μm. The composite positive electrode was heat-treated in argon gas at 100 ° C. for 3 hours to crosslink the polymer in the composite positive electrode. As a polymer solid electrolyte membrane, 100 parts by weight of a copolymer of ethylene oxide (80.6 mol%), 2- (2-methoxyethoxy) ethyl glycidyl ether (17.7 mol%) and allyl glycidyl ether (1.7 mol%) was mixed with LiN (CF ₃ A solid polymer electrolyte obtained by dissolving 30 parts by weight of SO ₂ ) ₂ and cross-linking was formed into a film having a thickness of 50 μm, and a Li metal foil having a thickness of 100 μm was laminated as a negative electrode to prepare a coin-type cell. Constant current charging was performed at an upper limit voltage of 4.1 V and constant current discharging was performed at a lower limit voltage of 2.0 V in a constant temperature bath at 60 ° C. When charging and discharging were repeated 200 cycles at a current of 0.2 C, the battery capacity was 79% of the initial capacity. Moreover, when charging / discharging at 0.5C, it became about 72% of the capacity when charging / discharging at 0.2C. This is because the polymer in the composite positive electrode is cross-linked to increase the binding property between the positive electrode active material particles and the conductive particles, thereby extending the cycle life of the battery. By the polyethylene glycol dimethyl ether added to the composite positive electrode, It is thought that the decrease in capacity at 0.5C was reduced because of improved ionic conductivity.
[0021]
[Table 2]

[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the lithium polymer battery using the composite positive electrode which provides a lithium polymer battery with a small and lightweight large charge / discharge capacity and the positive electrode is obtained. The battery of the present invention can be charged to a high voltage, which can achieve a high capacity.
Since the battery of the present invention operates stably even at a high temperature, it can be used as an electric vehicle, a hybrid vehicle, a road leveling battery, and the like that easily raise the battery temperature.
[Brief description of the drawings]
FIG. 1 shows the relationship between the discharge capacity and cycle characteristics of an all-solid lithium polymer battery using a V ₂ O ₅ composite positive electrode.
FIG. 2 shows a relationship between an upper limit voltage and a discharge capacity during charging of a lithium polymer battery using a V ₂ O ₅ composite positive electrode.
FIG. 3 shows the relationship between the charge / discharge capacity of a lithium polymer battery using a V ₂ O ₅ composite positive electrode and the battery voltage.

Claims

A lithium salt dissolved as an electrolyte salt in a copolymer having a weight average molecular weight of 5 to 70 mol% having 30 to 95 mol% ethylene oxide and 5 to 70 mol% glycidyl ether having an ethylene oxide unit having a polymerization degree of 1 to 12 in the side chain. A composite positive electrode in which a composite comprising a molecular solid electrolyte, a vanadium-based oxide V _X O ₅ (X = 2 to 2.5) as positive electrode active material particles, and conductive particles is coated on a current collector, and lithium metal Or the weight average which consists of a negative electrode which consists of a lithium metal alloy, and ethylene oxide 30-94 mol%, glycidyl ether which has an ethylene oxide unit of polymerization degree 1-12 in a side chain, 5-69 mol%, and allyl glycidyl ether 1-5 mol% A film obtained by crosslinking a polymer solid electrolyte in which a lithium salt is dissolved in a copolymer having a molecular weight of 1 million or more. And charging the lithium polymer battery at a high temperature of 60 ° C. or higher in a range of 3.6 to 4.2 V.

A lithium salt dissolved as an electrolyte salt in a copolymer having a weight average molecular weight of 5 to 70 mol% having 30 to 95 mol% ethylene oxide and 5 to 70 mol% glycidyl ether having an ethylene oxide unit having a polymerization degree of 1 to 12 in the side chain. A composite comprising a molecular solid electrolyte, polyethylene glycol having an average molecular weight of 500 or more and 2000 or less, an ether compound thereof, vanadium-based oxide V _X O ₅ (X = 2 to 2.5) as positive electrode active material particles, and conductive particles And a negative electrode made of lithium metal or a lithium metal alloy, and 30 to 94 mol% of ethylene oxide and 5 to 69 glycidyl ether having a degree of polymerization of 1 to 12 in the side chain. Weight average molecular weight consisting of 1 mol% and 1-5 mol% allyl glycidyl ether Charging of a lithium polymer battery comprising a membrane obtained by crosslinking a solid polymer electrolyte in which a lithium salt is dissolved in a copolymer of 1 million or more is completed at a high temperature of 60 ° C. or higher and in the range of 3.6 to 4.2 V And charging the lithium polymer battery.

To a copolymer having a weight average molecular weight of 1 million or more consisting of 30 to 94 mol% of ethylene oxide, 5 to 69 mol% of glycidyl ether having 1 to 12 degree of polymerization of ethylene oxide in the side chain, and 1 to 5 mol% of allyl glycidyl ether. A polymer solid electrolyte in which lithium salt is dissolved as an electrolyte salt, vanadium-based oxide V _X O ₅ (X = 2 to 2.5) as positive electrode active material particles, and conductive particles are formed on a current collector. Coated composite positive electrode, negative electrode made of lithium metal or lithium metal alloy, and 30 to 94 mol% ethylene oxide, 5 to 69 mol% glycidyl ether having an ethylene oxide unit with a polymerization degree of 1 to 12 in the side chain, and allyl glycidyl ether A lithium salt was dissolved in a copolymer consisting of 1 to 5 mol% and having a weight average molecular weight of 1 million or more. A method for charging a lithium polymer battery, characterized in that charging of a lithium polymer battery comprising a film obtained by crosslinking a polymer solid electrolyte is terminated at a high temperature of 60 ° C or higher in a range of 3.6 to 4.2 V.

To a copolymer having a weight average molecular weight of 1 million or more consisting of 30 to 94 mol% of ethylene oxide, 5 to 69 mol% of glycidyl ether having 1 to 12 degree of polymerization of ethylene oxide in the side chain, and 1 to 5 mol% of allyl glycidyl ether. Polymer solid electrolyte in which lithium salt is dissolved as an electrolyte salt, polyethylene glycol having a weight average molecular weight of 500 or more and 2000 or less, or an ether compound thereof, and vanadium oxide V _X O ₅ (X = 2 to 2.5 as positive electrode active material particles) ), And a composite positive electrode obtained by coating a composite made of conductive particles on a current collector, a negative electrode made of lithium metal or a lithium metal alloy, and 30 to 94 mol% of ethylene oxide, and a degree of polymerization of 1 to 12 in the side chain 5 to 69 mol% of glycidyl ether having ethylene oxide units and allyl glycidyl The charging of a lithium polymer battery comprising a film in which a polymer solid electrolyte obtained by dissolving a lithium salt in a copolymer having a weight average molecular weight of 1 to 5 mol% of ether and having a weight average molecular weight of 1 million or more is charged at a high temperature of 60 ° C. or higher. The method for charging the lithium polymer battery, wherein the charging is completed in the range of 3.6 to 4.2 V.

The method for charging a lithium polymer battery according to claim 3 or 4, wherein the solid polymer electrolyte in the composite positive electrode is crosslinked.

The lithium salt used for the polymer solid electrolyte in the composite positive electrode is LiN (CF ₃ SO ₂ ) ₂ , and the lithium salt is used in an amount of 5 to 50 parts by weight based on 100 parts by weight of the copolymer. The method for charging a lithium polymer battery according to any one of claims 1 to 5.

7. The conductive particles in the composite positive electrode are acetylene black, and these conductive particles are used in an amount of 5 to 20 parts by weight with respect to 100 parts by weight of the positive electrode active material particles. The charging method of the lithium polymer battery as described in 2.

The method for charging a lithium polymer battery according to any one of claims 1 to 7, wherein 5 to 35 parts by weight of a polymer solid electrolyte is used in the composite positive electrode with respect to 100 parts by weight of the positive electrode active material particles.