JP4055241B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

【００３５】
（化１）の反応で生成したＮｉは、負極活物質の充放電される電位領域では化学的かつ電気化学的に安定で、負極が放電される場合、酸化されることはなく不可逆性で金属状態を保つ。このように金属酸化物が初充電時に金属を生成することにより、負極極板中の導電性を著しく向上させるため、負極の内部抵抗、分極を低減でき、高容量化が実現できる。
【００３６】
また、還元生成物はいわゆるリチウムとの化合物を作らないため、（化１）の反応は不可逆反応であり、リチウム放出反応は起こらない。
【００３７】
本発明におけるＡｇ₂Ｏ、ＰｂＯ、Ｎｉ₂Ｏ ₃ 、ＴｉＯ₂、Ｂｉ₂Ｏ₃、Ｓｂ₂Ｏ₃、Ｃｒ₂Ｏ₃、ＳｅＯ₂、ＴｅＯ₂、ＭｎＯ ₂ においてもいずれも同様に不可逆反応が進行し同様の効果が得られることを確認した。
【００３８】
このように炭素質材料中に添加剤としてリチウムイオンを吸蔵もしくは含有しえる化合物を添加する例が報告されているが、（例えばＦｅＯ、ＦｅＯ₂、Ｆｅ₂Ｏ₃、ＳｎＯ、ＳｎＯ₂、ＭｏＯ₂、Ｖ₂Ｏ₅、Ｂｉ₂Ｓｎ₃Ｏ₉、ＷＯ₂、ＷＯ₃、Ｎｂ₂Ｏ₅：特開平７−１９２７２３号公報、リチウムを含有しうる金属酸化物、硫化物、水酸化物、セレン化物、実施例ではリチウムを含有（または結合）したＣｕ、Ｆｅ、Ｍｏ、Ｔｉ、Ｖ、Ｎｂ、Ｍｎ、Ｃｏ、Ｎｉ等の酸化物でリチウム塩と混合した後、熱処理して得られる化合物でＬｉＣｕＯ₃、ＬｉＦｅＯ₂、ＬｉＭｏＯ₃、ＬｉＴｉＯ₂、ＬｉＶＯ₂、ＬｉＮｂＯ₂、Ｌｉ₂ＭｎＯ₄、ＬｉＣｏＯ₂、ＬｉＮｉＯ₂：特開平８−２１３０５３、リチウムを吸蔵・放出できる遷移金属酸化物でＬｉ_pＮｉ_qＶ_1-qＯ_r，ｐ＝０．４〜３，ｑ＝０〜１，ｒ＝１．２〜５．５：特開平６−４４９７２号公報）、これらのリチウムイオンを吸蔵もしくは含有しえる化合物を負極に添加した報告例はいずれも放電末期、もしくは過放電時の負極電位の上昇による銅芯材の溶解などを防止し、負極安定性向上を図るために添加されており、いずれも可逆性が要求されるものである。
【００３９】
本発明のように、初充電する事によって金属まで電気化学的に且つ不可逆的に還元される金属酸化物とは目的、効果とも全く相違するものである。また、これらのリチウムイオンを吸蔵もしくは含有しえる化合物後の初充電後の状態はリチウム含有化合物であるため本発明のような導電性向上の効果が得られない。
【００４０】
【発明の実施の形態】
本発明による添加剤を用いた場合、リチウムと反応すると不可逆であるのでこれにより負極より大きい不可逆容量分を負極添加剤により充電消費させることにより、正負極において可逆な充放電容量を全て構成した二次電池の容量として設計できるため更に高エネルギー密度を持ち、且つサイクル特性の良好な電池が実現可能となる。
【００４１】
また、初充電において正極の不可逆容量のリチウムイオンと反応する事によって生成する化合物（例えばＮｉＯの場合ならＮｉ）によって負極板の導電性が向上し、放電特性が向上する。
【００４２】
本発明における負極材料に添加する添加剤は、還元反応によりリチウムイオンと不可逆に反応する化合物であり、Ａｇ₂Ｏ、ＰｂＯ、ＮｉＯ、Ｎｉ₂Ｏ ₃ 、ＴｉＯ₂、Ｂｉ₂Ｏ₃、Ｓｂ₂Ｏ₃、Ｃｒ₂Ｏ₃、ＳｅＯ₂、ＴｅＯ₂、ＭｎＯ ₂ のいずれかまたは混合物である。
【００４３】
前記化合物の添加量は電気容量として正負極の不可逆容量の差と同じ容量程度であることが望ましく、負極活物質である炭素質材料と化合物の総量に対して０．２重量％〜２０重量％の範囲である場合に最もその効果を発揮できる。
【００４４】
また、前記正極活物質はリチウム含有金属化合物であり、リチウムイオンを放出し、吸蔵する化合物であれば良いが、特に充放電効率（吸蔵量／放出量×１００（％））が７５〜９５％の範囲である化合物においてより効果的である。
【００４５】
特に、前記正極活物質はＬｉＮｉ_xＭ_1-xＯ₂（ＭはＣｏ、Ｍｎ、Ｃｒ、Ｆｅ、Ｖ、Ａｌからなる群から選ばれた少なくとも１種類であり、ｘ：１≧ｘ≧０．５）で示されるリチウム含有ニッケル酸化物である場合に不可逆容量が大きく、本発明の効果が大きい。
【００４６】
このようなＬｉＮｉ_xＭ_1-xＯ₂（ＭはＣｏ、Ｍｎ、Ｃｒ、Ｆｅ、Ｖ、Ａｌからなる群から選ばれた少なくとも１種類であり、ｘ：１≧ｘ≧０．５）で示されるリチウム含有ニッケル酸化物は７５０℃〜９００℃の温度範囲で合成されたものである場合により効果的である。
【００４７】
【実施例】
以下、図面とともに本発明を具体的な実施例に沿って説明する。
【００４８】
（実施例１）
図３に本実施例１で用いた円筒系電池の縦断面図を示す。図３において１は耐有機電解液性のステンレス鋼板を加工した電池ケース、２は安全弁を設けた封口板、３は絶縁パッキングを示す。４は極板群であり、正極板５および負極板６がセパレータ７を介して複数回渦巻状に巻回されてケース内に収納されている。そして上記正極板５からは正極アルミリード５ａが引き出されて封口板２に接続され、負極板６からは負極ニッケルリード６ａが引き出されて電池ケース１の底部に接続されている。８は絶縁リングで極板群４の上下部にそれぞれ設けられている。
【００４９】
以下、正極活物質の合成法について詳しく説明する。
硫酸ニッケル、硫酸コバルト、水酸化ナトリウム溶液を用い、硫酸ニッケル溶液、硫酸コバルト溶液を一定流量で容器内に導入し、十分撹拌しながら、水酸化ナトリウム溶液を添加した。
【００５０】
生成した沈澱物を、水洗、乾燥しニッケル−コバルトの共沈水酸化物を得た。得られたニッケル−コバルト共沈水酸化物の化学組成は、Ｎｉ_0.85Ｃｏ_0.15（ＯＨ）₂であった。
【００５１】
得られたニッケル−コバルト共沈水酸化物と水酸化リチウムとを混合し、酸化雰囲気下において８００℃で１０時間焼成してＬｉＮｉ_0.85Ｃｏ_0.15Ｏ₂を合成した。
【００５２】
以後、正極板の製造法を説明する。
正極板は、まず正極材料であるＬｉＮｉ_0.85Ｃｏ_0.15Ｏ₂の粉末１０重量部に、アセチレンブラック３重量部、フッ素樹脂系結着剤５重量部を混合し、Ｎ−メチルピロリドン溶液に懸濁させてペースト状にする。このペーストを厚さ０．０２０ｍｍのアルミ箔の両面に塗着し、乾燥後厚み０．１３０ｍｍ、幅３５ｍｍ、長さ２７０ｍｍの正極板５を作成した。また正極リードとしてアルミニウム片を取り付けた。
【００５３】
以下、負極板６の作製法について詳しく説明する。
負極板６は、黒鉛粉１００重量部に、Ａｇ₂Ｏ、ＰｂＯ、ＮｉＯ、Ｎｉ₂Ｏ₃、ＣｏＯ、Ｃｏ₂Ｏ₃、Ｃｏ₃Ｏ₄、ＴｉＯ₂、Ｂｉ₂Ｏ₃、Ｓｂ₂Ｏ₃、Ｃｒ₂Ｏ₃、ＳｅＯ₂、ＴｅＯ₂、ＭｎＯ₂、Ｆｅ₃Ｏ₄をそれぞれ炭素質材料と添加剤の総量に対し９．０６，８．７５，３．１０，６．６５，３．１１，６．６５，１０．３１，６．４１，１６．６７，１１．１１，６．１２，４．５５，６．４１，６．９５，９．０２重量％を添加した後、スチレン−ブタジエンゴム系結着剤を混合し、カルボキシメチルセルロース水溶液に懸濁させてペースト状にした。なお、各物質の添加量は各物質の還元反応で消費される電気容量と、炭素質材料の不可逆容量の総和が正極の不可逆容量と等しくなるように理論容量から計算して添加した。
【００５４】
そしてこのペーストを厚さ０．０１５ｍｍの銅箔の両面に塗着し、乾燥後厚み０．２ｍｍ、幅３７ｍｍ、長さ３００ｍｍの負極板を作成した。
【００５５】
そして正極板と負極板を、セパレータを介して渦巻き状に巻回し、直径１３．８ｍｍ、高さ５０ｍｍの電池ケース内に収納した。
【００５６】
電解液には炭酸エチレンと炭酸エチルメチルの等体積混合溶媒に、六フッ化リン酸リチウム１モル／ｌの割合で溶解したものを用いて極板群４に注入した後、電池を密封口し、試験電池とした。
【００５７】
（実施例２）
第２実施例として、ニッケル−コバルト共沈水酸化物を水酸化リチウムと混合し、酸化雰囲気下において合成する温度を７００、７５０、８５０、９００、９５０℃で１０時間焼成する以外は全て実施例１と同じ条件で正極板を作製した。
【００５８】
負極添加剤としてＮｉＯを実施例１と同様に３．１０％添加して負極板を作製して電池１７〜２１を作製した。
【００５９】
（比較例１）
比較例１として、負極に添加剤を入れない他は実施例１と同様に電池を構成した。上記比較例１における電池を電池１６とした。
【００６０】
（比較例２）
比較例２として、負極に添加剤を入れない他は実施例２と同様に電池を構成した。上記比較例２における電池を電池２２〜２６とした。
【００６１】
以上の電池を充放電電流１００ｍＡで充電終始電圧４．２Ｖ、放電終止電圧２．５Ｖで充放電サイクルを行った。
【００６２】
サイクル試験を行い、放電容量が３サイクル目の放電容量に対し、７０％の容量に減少したサイクルを寿命サイクルとした。
【００６３】
これらの電池の初充電、初放電容量及び寿命サイクルを（表１）に示した。
【００６４】
【表１】

【００６５】
実施例１および比較例１の電池において、１サイクル目の充電容量と放電容量の差は電池１〜１６においてほとんど同じであることがわかる。
【００６６】
これは、いずれの場合も正極の不可逆容量が大きい為、正極の可逆容量によって電池の容量が決定されていることがわかる。
【００６７】
しかしながら、これらの電池のサイクル試験を行うと比較例の添加剤を加えていない電池に比べ、添加剤を加えている本発明の電池１〜１５のサイクル寿命は著しく向上していることがわかる。
【００６８】
サイクル劣化後の電池（Ｎｏ．１６）を分解し観察した結果、添加剤を加えていない比較例１の電池の負極表面には金属光沢を有するリチウム金属が析出していることがわかった。
【００６９】
この結果から、電池自体の容量は同じであっても正極の不可逆容量分（図１のＡの容量）が負極の負荷となっているため、充電によって負極の可逆な充放電容量を越えて充電されたため負極板表面に金属リチウムが析出し、放電容量が著しく減少したものと考えられた。
【００７０】
電池における正極量を減ずるか、充電電圧を下げる事によって、負極の負荷を小さくすればサイクル特性の良好な電池は実現できるが、この場合は放電容量自体が小さくなるため電池の高容量化が実現できない。
【００７１】
これに対し本発明の電池１〜１５はＡに相当する充放電に関与できない容量を添加した化合物で消費するために（図２のＢの容量）正極の可逆容量と負極可逆容量が最大限利用でき、サイクル寿命も良好な電池が得られる。
【００７２】
なお、還元反応によりリチウムイオンと反応する時の充電電気量は、以下の方法によって測定することが可能である。
【００７３】
添加する化合物（例えばＮｉＯ）に対し重量比で３０％程度のアセチレンブラックを添加、混合した後２５０ｋｇ／ｃｍ²でペレットを作製しステンレス集電体に固定し作用極とする。
【００７４】
対極および参照極に金属リチウムを用い、リチウム極に対して０Ｖに達するまで定電流で放電し電気量を測定する。この際にアセチレンブラックがリチウムと反応する電気量についてはあらかじめ測定しておき、得られた電気量から減じなければならない。
【００７５】
測定に用いる電解液は電池に用いるものが最も好ましい。また、充電の際の電流密度は０．１ｍＡ／ｃｍ²以下であることが望ましい。
【００７６】
（表２）に実施例２および比較例２の結果を示す。
【００７７】
【表２】

【００７８】
実施例２の結果から、７５０℃未満の温度で合成した場合では（電池１７、２２）では本発明による添加剤を入れない場合でも、正極のリチウムイオンを放出し、吸蔵する充放電効率（吸蔵量／放出量×１００（％））が９５％以上と高く、正極における不可逆容量が小さいため負極活物質である黒鉛がもつ不可逆容量で十分相殺可能となり、良好なサイクル寿命が得られる。
【００７９】
このため、ＬｉＮｉ_xＭ_1-xＯ₂（ＭはＣｏ、Ｍｎ、Ｃｒ、Ｆｅ、Ｖ、Ａｌからなる群から選ばれた少なくとも１種類であり、ｘ：１≧ｘ≧０．５）を正極活物質とした電池においては７５０℃以上で合成した活物質を正極とした電池に用いた場合に最も大きな効果が得られる。
【００８０】
また、合成温度が７５０℃〜９００℃の合成温度の範囲では本発明の添加剤を加える事によって実施例１と同様にサイクル寿命特性が向上しており、本発明の効果が顕著であることがわかる。
【００８１】
しかし、合成温度が９５０℃を越えると、活物質の結晶構造が六方晶と岩塩構造の２相となることから正極のリチウムイオンを放出し、吸蔵する充放電効率（吸蔵量／放出量×１００（％））が５０％台になり正極の放電特性そのものが劣化するため好ましくない。
【００８２】
このようにＬｉＮｉ_xＭ_1-xＯ₂（ＭはＣｏ、Ｍｎ、Ｃｒ、Ｆｅ、Ｖ、Ａｌからなる群から選ばれた少なくとも１種類であり、ｘ：１≧ｘ≧０．５）を正極活物質とした場合には、７５０℃〜９００℃の温度範囲で合成したものを用いた場合に最も大きな効果が得られる。
【００８３】
なお、本発明における正極のリチウムイオンを放出し、吸蔵する充放電効率（吸蔵量／放出量×１００（％））とは、正確には金属リチウムを負極として通常電池が使用される電位領域である４．３Ｖまで充電し、２．５Ｖまで放電させた場合のそれぞれの電気量から算出することが可能である。
【００８４】
この場合の測定に用いる電解液は、実際の電池で用いる電解液と同じものであることは言うまでもない。
【００８５】
本実施例においては正極活物質としてＬｉＮｉ_xＭ_1-xＯ₂（ＭはＣｏ、Ｍｎ、Ｃｒ、Ｆｅ、Ｖ、Ａｌからなる群から選ばれた少なくとも１種類であり、ｘ：１≧ｘ≧０．５）を用いたが、正極活物質はリチウム含有金属化合物であり、リチウムイオンを放出し、吸蔵する充放電効率（吸蔵量／放出量×１００（％））が７５〜９５％の範囲であれば電池の作動原理は同じであるため同様の効果が得られる。
【００８６】
また、本実施例での正極活物質であるＬｉＮｉ_xＭ_1-xＯ₂の置換金属ＭはＣｏを用いたが、このほかにＭｎ、Ｃｒ、Ｆｅ、Ｖ、Ａｌのいずれであっても同様の効果が得られる。
【００８７】
本発明は正負極の不可逆容量の差を緩和することが目的であるため、実施例では黒鉛材料を負極活物質として用いたがこのような炭素材料の他に例えばスズ化合物、窒化物、珪化物、合金等リチウムを充放電可能な物質であれば同様の効果が得られる。
【００８８】
上記実施例においては円筒型の電池を用いて評価を行ったが、角型など電池形状が異なっても同様の効果が得られる。
【００８９】
また、上記実施例において電解質として六フッ化リン酸リチウムを使用したが、他のリチウム含有塩、例えば過塩素酸リチウム、四フッ化ホウ酸リチウム、トリフルオロメタンスルホン酸リチウム、六フッ化ヒ酸リチウムなどでも同様の効果が得られた。
【００９０】
さらに、上記実施例では炭酸エチレンと炭酸エチルメチルの混合溶媒を用いたが、他の非水溶媒例えば、プロピレンカーボネートなどの環状エステル、テトラヒドロフランなどの環状エーテル、ジメトキシエタンなどの鎖状エーテル、プロピオン酸メチルなどの鎖状エステルなどの非水溶媒や、これらの多元系混合溶媒を用いても同様の効果が得られた。当然の事ながら、本発明には電解質は関係なく、例えば高分子電解質や、固体電解質、ゲル電解質等のいずれの場合にでも適用が可能である。
【００９１】
以上の説明から明らかなように、本発明による負極主要材料に、還元反応によりリチウムイオンと不可逆に反応する化合物としてＡｇ₂Ｏ、ＰｂＯ、ＮｉＯ、
Ｎｉ₂Ｏ₃ 、ＴｉＯ₂、Ｂｉ₂Ｏ₃、Ｓｂ₂Ｏ₃、Ｃｒ₂Ｏ₃、ＳｅＯ₂、ＴｅＯ₂、ＭｎＯ ₂ からなる群から選ばれた少なくとも１種類のいずれかまたは混合物を添加する事により、高容量でサイクル寿命が優れた非水電解質二次電池を提供することが出来る。
【図面の簡単な説明】
【図１】本発明を使用しない場合のリチウム二次電池について一回目の充放電時の電位と容量の様子を示す概念図
【図２】本発明のリチウム二次電池について一回目の充放電時の電位と容量の様子を示す概念図
【図３】本実施例および比較例における円筒型非水電解質二次電池の縦断面図
【符号の説明】
１ 電池ケース
２ 封口板
３ 絶縁パッキング
４ 極板群
５ 正極板
５ａ 正極リード
６ 負極板
６ａ 負極リード
７ セパレータ
８ 絶縁リング[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery, and particularly to improvement of battery characteristics.
[0002]
[Prior art]
In recent years, consumer electronic devices have become increasingly portable and cordless. Conventionally, nickel-cadmium batteries or sealed small lead-acid batteries have played a role as power sources for driving these electronic devices. However, as the use of portable and cordless batteries has progressed and become established, they will become power sources for driving. There is a strong demand for higher energy density and smaller size and weight of secondary batteries.
[0003]
From such a situation, a lithium transition metal composite oxide exhibiting a high charge / discharge voltage such as LiCoO ₂ (for example, JP-A-55-136131), LiNiO ₂ aimed at a higher capacity (for example, US Pat. No. 4,302,518), composite oxides of a plurality of metal elements lithium (e.g. _{Li y Ni x Co 1-x} O 2: JP 63-299056 _{JP, Li x M y N z O} 2 ( where, M is Fe, Co, Ni And at least one selected from Ti, V, Cr, and Mn): JP-A-3-267053) is used as the positive electrode active material, and lithium ions are inserted and released. A non-aqueous electrolyte secondary battery using a battery has been proposed.
[0004]
In particular, LiNiO ₂ is actively researched and developed because the supply amount of Ni, which is a raw material, is stable, is inexpensive, and high capacity is expected.
[0005]
In addition, as a negative electrode active material for such a non-aqueous electrolyte secondary battery, graphite that absorbs and releases lithium ions and has a high charge / discharge efficiency (discharge capacity / storage capacity × 100 (%)) of 80% or more is shown. Such carbonaceous materials, tin compounds, nitrides, silicides, alloys and the like are used.
[0006]
[Problems to be solved by the invention]
However, the positive electrode active materials reported so far (particularly LiNi _x M _1-x O ₂ (M is at least one selected from the group consisting of Co, Mn, Cr, Fe, V, Al, and x: 1 ≧ x ≧ 0.5), the first charge (lithium release reaction) and discharge (lithium insertion reaction) in the potential region (4.3 V to 2 V with respect to Li) normally used as a battery (For example, A. Rougier et al. Solid State Ionics 90 , 83 (1996).) A graphite-based carbon material having the same theoretical capacity as such a positive electrode material is used. The potential behavior of the positive electrode and the negative electrode during the initial charge and initial discharge of the battery used for the negative electrode is schematically shown in FIG.
[0007]
In FIG. 1, (A-B) is the initial charge electricity amount of the positive electrode, (BC) is the initial discharge capacity of the positive electrode, and (C-A) is the irreversible capacity of the positive electrode.
[0008]
(A′-B ′) is the initial charge electricity amount of the negative electrode, which is the same as that of the positive electrode (AB). (B′-C ′) is the initial dischargeable capacity of the negative electrode, and (C′-A ′) is the irreversible capacity of the negative electrode. Since the initial discharge capacity (B′-C ′) of the negative electrode is larger by (C′-D) than the positive discharge capacity (BC) of the positive electrode, the initial discharge capacity of the battery is the initial discharge capacity of the positive electrode. It is regulated by the capacity (B-C). In the charge / discharge cycle after the initial discharge, the reaction proceeds reversibly between (B-C) for the positive electrode and between (B'-D) having the same capacity as (BC) for the negative electrode. Therefore, (C′-D) equivalent lithium of the negative electrode remains in the negative electrode as “dead lithium” that cannot contribute to the charge / discharge reaction of the battery, and contributes to the battery capacity increase without participating in the charge / discharge reaction. It is impossible.
[0009]
Accordingly, when the theoretical capacity of the positive and negative electrodes is adjusted by increasing the filling amount of the positive and negative electrodes so that the initial discharge capacities of the positive and negative electrodes after the initial charge are the same, (C-A) and (C (C′−D) equivalent to “dead lithium” of the negative electrode of the difference from “−A”) overcharges the negative electrode.
[0010]
However, there is a limit to the reversible charge capacity of the negative electrode active material. For example, when graphite is used as the negative electrode active material, 372 mAh / g corresponding to C ₆ Li is the limit.
[0011]
In addition, when a material other than graphite is charged beyond the limit amount, it is deposited as metallic lithium on the surface of the negative electrode plate, and the safety of the battery is significantly impaired.
[0012]
In addition, when metallic lithium is deposited on the negative electrode surface, the deposited lithium reacts with the electrolytic solution to inactivate, reducing charge / discharge efficiency and cycle life characteristics.
[0013]
Therefore, it can be said that such positive and negative electrode capacity settings are inappropriate.
In order to increase the capacity of the lithium ion secondary battery, it is necessary to select a positive and negative electrode material having as high initial charge / discharge efficiency as possible and a large reversible capacity portion by charge / discharge. Then, the irreversible capacity portions of the positive electrode and the negative electrode and “dead lithium” should be made as small as possible, and care must be taken so that the negative electrode is not excessively overcharged and metallic lithium is not deposited.
[0014]
However, when the positive electrode has a larger initial charge / discharge efficiency than the negative electrode, it is difficult to design and configure the battery under the above-described conditions.
[0015]
In the present invention, the adjustment of the theoretical capacity of the positive and negative electrodes of the battery design and various appropriate negative electrode additives have been studied, and the conventional problems have been specifically solved to achieve a high capacity technology.
[0016]
[Means for Solving the Problems]
As a result of thorough examinations by the present inventors, the main material that is the negative electrode active material is a non-material composed of a mixture obtained by adding an oxide of the metal that is electrochemically reduced to the metal by charging. By using a water electrolyte secondary battery, the battery has been successfully designed and configured so that “dead lithium” that cannot participate in the charge / discharge reaction does not remain and the negative electrode is not overcharged. With such a configuration, it is possible to provide a high-capacity nonaqueous electrolyte secondary battery with excellent cycle life.
[0017]
Specifically, the present invention adds an oxide of the metal that is electrochemically reduced to the metal by a reduction reaction.
[0018]
Examples of the compound to be added include Ag ₂ O, PbO, NiO, Ni ₂ O ₃ , TiO ₂ , Bi ₂ O ₃ , and Sb ₂ O ₃ that react with lithium ions in a potential region between the positive electrode and the negative electrode. is to add a _{Cr 2 O 3, SeO 2,} TeO 2, any or a mixture of MnO _2.
[0019]
FIG. 2 is a schematic diagram showing the potential behavior of both the positive and negative electrodes in the initial charge and initial discharge of the nonaqueous electrolyte secondary battery according to the present invention.
[0020]
In FIG. 2, (A-B) is the initial charge electricity amount of the positive electrode, (BC) is the initial discharge capacity of the positive electrode, and (C-A) is the irreversible capacity of the positive electrode.
[0021]
(A′-B ′) is the initial charge electricity amount of the negative electrode, which is the same as that of the positive electrode (AB). In the initial charging of the negative electrode, first, the metal oxide added to the carbon material, which is the main material of the negative electrode, is electrochemically reduced (A′-C ′), and then the lithium ion is added to the main carbon material. Is occluded and charged.
[0022]
The initial charge electricity amount of the carbon material corresponds to (B′−C ′). The initial discharge capacity (B′-D) of the negative electrode is the same as (BC) of the positive electrode.
[0023]
The initial discharge capacities of these positive and negative electrodes are the respective reversible capacities. Note that (C′-D) is the irreversible capacity of the carbon material itself of the negative electrode.
[0024]
As can be fully understood from FIG. 2, in the present invention, the amount of metal oxide added to the carbon material, which is the main material of the negative electrode, varies from the irreversible capacity (CA) of the positive electrode to the irreversible of the carbon material, which is the main material of the negative electrode. A value (A′−C ′) corresponding to the capacity excluding the capacity is applied.
[0025]
Metal oxides that are added to the negative electrode, electrochemically reduced by charging, and irreversibly produce metal are usually added to the negative electrode because they have a higher bulk specific gravity than carbon materials such as graphite powder. However, the increase in volume is negligible.
[0026]
As described above, the reversible capacity of the positive electrode and the negative electrode is maximized by adding a metal oxide that is electrochemically reduced by charging, particularly the first charge, and irreversibly generates metal to the negative electrode. Since the capacity can be increased and the negative electrode is substantially prevented from being overcharged in charge and discharge after the second cycle, the cycle life is not deteriorated.
[0027]
The amount of the compound may be added by the amount of consuming the irreversible capacity of the positive electrode, usually in the range of 0.2% to 20% by weight relative to the total amount of the anode mix.
[0028]
The present invention can be more effective when a lithium-containing metal oxide based on a lithium-containing nickel oxide having an initial charge / discharge efficiency of only 75 to 95% is used as the positive electrode material.
[0029]
Further, if the positive electrode active material is a lithium-containing metal compound, it may be any lithium-containing compound that releases lithium ions such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, etc. A particularly large effect is obtained when (occlusion amount / release amount × 100 (%)) is in the range of 75 to 95%.
[0030]
Among _{this, LiNi x M 1-x O} 2 (M as the positive electrode active material is at least one selected Co, Mn, Cr, Fe, V, from the group consisting of Al, x: 1 ≧ x ≧ 0. The lithium-containing nickel oxide shown in 5) is particularly preferable because the charge / discharge efficiency (occlusion amount / release amount × 100 (%)) in the first cycle is small.
[0031]
When the positive electrode active material is synthesized at a high temperature, the charge / discharge efficiency (occlusion amount / release amount × 100 (%)) in the first cycle becomes extremely small as 75% or less, and the discharge characteristics as the active material deteriorate. It is most effective when it is synthesized in a temperature range of 750 ° C. to 900 ° C.
[0032]
Such an additive to the negative electrode is preferably an oxide known as a positive electrode active material for a lithium primary battery mainly using metallic lithium as a negative electrode (for example, Tsutomu Obata, Zenichiro Takehara, Shiro Yoshizawa, Electrochemical 46, 411 (1978).).
[0033]
For example, if these compounds are NiO, metallic nickel is produced by a reduction reaction as shown in (Chemical Formula 1).
[0034]
[Chemical 1]

[0035]
Ni produced by the reaction of (Chemical Formula 1) is chemically and electrochemically stable in the potential region where the negative electrode active material is charged and discharged. When the negative electrode is discharged, it is not oxidized and is irreversible. Keep state. Thus, since the metal oxide generates a metal at the time of initial charge, the conductivity in the negative electrode plate is remarkably improved, so that the internal resistance and polarization of the negative electrode can be reduced, and high capacity can be realized.
[0036]
In addition, since the reduction product does not form a compound with so-called lithium, the reaction of (Chemical Formula 1) is an irreversible reaction, and no lithium releasing reaction occurs.
[0037]
Ag ₂ O in the present _{invention, PbO, Ni 2 O 3,} TiO 2, Bi 2 O 3, Sb 2 O 3, Cr 2 O 3, SeO 2, TeO 2, both also Oite the MnO ₂ Similarly irreversible reaction It has been confirmed that the same effect can be obtained.
[0038]
As described above, an example of adding a compound capable of occluding or containing lithium ions as an additive to a carbonaceous material has been reported (for example, FeO, FeO ₂ , Fe ₂ O ₃ , SnO, SnO ₂ , MoO _2). V ₂ O ₅ , Bi ₂ Sn ₃ O ₉ , WO ₂ , WO ₃ , Nb ₂ O ₅ : Japanese Patent Laid-Open No. 7-192723, metal oxide, sulfide, hydroxide, selenide that may contain lithium In this example, LiCuO ₃ is a compound obtained by heat treatment after mixing lithium salt with an oxide such as Cu, Fe, Mo, Ti, V, Nb, Mn, Co, or Ni containing lithium (or bonding). _{, LiFeO 2, LiMoO 3, LiTiO} 2, LiVO 2, LiNbO 2, Li 2 MnO 4, LiCoO 2, LiNiO 2: JP-a 8-213053, a transition metal oxide lithium can absorbing and desorbing Objects in _{Li p Ni q V 1-q} O r, p = 0.4~3, q = 0~1, r = 1.2~5.5: JP 6-44972), these lithium ion All reported examples of adding a compound capable of occluding or containing copper to the negative electrode were added to improve the stability of the negative electrode by preventing the dissolution of the copper core due to the increase in the negative electrode potential at the end of discharge or during overdischarge. In any case, reversibility is required.
[0039]
Unlike the metal oxide which is electrochemically and irreversibly reduced to the metal by first charging as in the present invention, the object and effect are completely different. Moreover, since the state after the initial charge after the compound that can occlude or contain these lithium ions is a lithium-containing compound, the effect of improving conductivity as in the present invention cannot be obtained.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
When the additive according to the present invention is used, it is irreversible when it reacts with lithium, so that the irreversible capacity larger than that of the negative electrode is charged and consumed by the negative electrode additive, so that all the reversible charge / discharge capacities in the positive and negative electrodes are constituted. Since it can be designed as the capacity of the secondary battery, a battery having higher energy density and good cycle characteristics can be realized.
[0041]
In addition, the compound (for example, Ni in the case of NiO) generated by reacting with the irreversible capacity lithium ion of the positive electrode in the first charge improves the conductivity of the negative electrode plate and improves the discharge characteristics.
[0042]
Additives to be added to the negative electrode material of the invention, Ri compounds der reacting lithium ion and irreversible by _{reduction, Ag 2 O, PbO, NiO} , Ni 2 O 3, TiO 2, Bi 2 O 3, Sb 2 _{O 3, Cr 2 O 3,} SeO 2, TeO 2, Ru or or mixtures der of MnO _2.
[0043]
The amount of the compound added is preferably about the same as the difference between the irreversible capacities of the positive and negative electrodes in terms of electric capacity, and is 0.2 wt % to 20 wt % with respect to the total amount of the carbonaceous material and the compound as the negative electrode active material If it is in the range, the effect can be exhibited most.
[0044]
The positive electrode active material is a lithium-containing metal compound, and may be any compound that releases and occludes lithium ions. In particular, the charge / discharge efficiency (occlusion / release x 100 (%)) is 75 to 95%. It is more effective in the compound which is the range.
[0045]
In particular, the positive electrode active material is _{LiNi x M 1-x O 2} (M is at least one selected Co, Mn, Cr, Fe, V, from the group consisting of Al, x: 1 ≧ x ≧ 0. In the case of the lithium-containing nickel oxide shown in 5), the irreversible capacity is large, and the effect of the present invention is great.
[0046]
Such LiNi _x M _1-x O ₂ (M is at least one selected from the group consisting of Co, Mn, Cr, Fe, V, and Al, and x: 1 ≧ x ≧ 0.5) The lithium-containing nickel oxide is more effective when it is synthesized at a temperature range of 750 ° C. to 900 ° C.
[0047]
【Example】
Hereinafter, the present invention will be described with reference to the accompanying drawings along with specific examples.
[0048]
Example 1
FIG. 3 shows a longitudinal sectional view of the cylindrical battery used in the first embodiment. In FIG. 3, 1 is a battery case obtained by processing an organic electrolyte resistant stainless steel plate, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. Reference numeral 4 denotes an electrode plate group, in which a positive electrode plate 5 and a negative electrode plate 6 are wound in a spiral shape through a separator 7 and accommodated in a case. A positive electrode aluminum lead 5 a is drawn from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode nickel lead 6 a is drawn from the negative electrode plate 6 and connected to the bottom of the battery case 1. Insulating rings 8 are provided at the upper and lower portions of the electrode plate group 4, respectively.
[0049]
Hereinafter, the synthesis method of the positive electrode active material will be described in detail.
Using nickel sulfate, cobalt sulfate, and sodium hydroxide solution, the nickel sulfate solution and the cobalt sulfate solution were introduced into the container at a constant flow rate, and the sodium hydroxide solution was added with sufficient stirring.
[0050]
The formed precipitate was washed with water and dried to obtain a nickel-cobalt coprecipitated hydroxide. The chemical composition of the obtained nickel-cobalt coprecipitated hydroxide was Ni _0.85 Co _0.15 (OH) ₂ .
[0051]
The obtained nickel-cobalt coprecipitated hydroxide and lithium hydroxide were mixed and baked at 800 ° C. for 10 hours in an oxidizing atmosphere to synthesize LiNi _0.85 Co _0.15 O ₂ .
[0052]
Hereinafter, a method for manufacturing the positive electrode plate will be described.
The positive electrode plate is prepared by first mixing 10 parts by weight of the powder of the positive electrode material LiNi _0.85 Co _0.15 O ₂ with 3 parts by weight of acetylene black and 5 parts by weight of a fluororesin binder and suspending it in an N-methylpyrrolidone solution. And paste it. This paste was applied to both sides of an aluminum foil having a thickness of 0.020 mm, and after drying, a positive electrode plate 5 having a thickness of 0.130 mm, a width of 35 mm, and a length of 270 mm was produced. An aluminum piece was attached as a positive electrode lead.
[0053]
Hereinafter, a method for producing the negative electrode plate 6 will be described in detail.
The negative electrode plate 6 is composed of 100 parts by weight of graphite powder, Ag ₂ O, PbO, NiO, Ni ₂ O ₃ , CoO, Co ₂ O ₃ , Co ₃ O ₄ , TiO ₂ , Bi ₂ O ₃ , Sb ₂ O ₃ , _{cr 2 O 3, SeO 2,} TeO 2, MnO 2, Fe 3 O 4 , respectively 9.06,8.75,3.10,6.65,3.11 the total amount of additives and carbonaceous material, After adding 6.65, 10.31, 6.41, 16.67, 11.11, 6.12, 4.55, 6.41, 6.95, 9.02 wt%, styrene-butadiene rubber The system binder was mixed and suspended in an aqueous carboxymethyl cellulose solution to make a paste. The amount of each substance added was calculated from the theoretical capacity so that the sum of the electric capacity consumed in the reduction reaction of each substance and the irreversible capacity of the carbonaceous material was equal to the irreversible capacity of the positive electrode.
[0054]
This paste was applied to both sides of a 0.015 mm thick copper foil, and after drying, a negative electrode plate having a thickness of 0.2 mm, a width of 37 mm, and a length of 300 mm was prepared.
[0055]
Then, the positive electrode plate and the negative electrode plate were spirally wound through a separator and housed in a battery case having a diameter of 13.8 mm and a height of 50 mm.
[0056]
The electrolyte was injected into the electrode plate group 4 using a solution of ethylene carbonate and ethyl methyl carbonate in an equal volume mixed solvent at a rate of 1 mol / l lithium hexafluorophosphate, and the battery was sealed. A test battery was obtained.
[0057]
(Example 2)
As a second example, Example 1 is used except that nickel-cobalt coprecipitated hydroxide is mixed with lithium hydroxide and synthesized at 700, 750, 850, 900, and 950 ° C. for 10 hours under an oxidizing atmosphere. A positive electrode plate was produced under the same conditions as those described above.
[0058]
As a negative electrode additive, 3.10% of NiO was added in the same manner as in Example 1 to prepare a negative electrode plate, thereby preparing batteries 17 to 21.
[0059]
(Comparative Example 1)
As Comparative Example 1, a battery was constructed in the same manner as in Example 1 except that no additive was added to the negative electrode. The battery in Comparative Example 1 was referred to as Battery 16.
[0060]
(Comparative Example 2)
As Comparative Example 2, a battery was constructed in the same manner as in Example 2 except that no additive was added to the negative electrode. The batteries in Comparative Example 2 were designated as batteries 22 to 26.
[0061]
The above battery was charged / discharged at a charge / discharge current of 100 mA at a charge end voltage of 4.2 V and a discharge end voltage of 2.5 V.
[0062]
A cycle test was performed, and a cycle in which the discharge capacity was reduced to 70% of the discharge capacity in the third cycle was defined as a life cycle.
[0063]
The initial charge, initial discharge capacity and life cycle of these batteries are shown in Table 1.
[0064]
[Table 1]

[0065]
In the batteries of Example 1 and Comparative Example 1, it can be seen that the difference between the charge capacity and the discharge capacity in the first cycle is almost the same in the batteries 1-16.
[0066]
This indicates that the capacity of the battery is determined by the reversible capacity of the positive electrode because the irreversible capacity of the positive electrode is large in any case.
[0067]
However, when the cycle test of these batteries is performed, it can be seen that the cycle life of the batteries 1 to 15 of the present invention to which the additive is added is remarkably improved as compared with the battery to which the additive of the comparative example is not added.
[0068]
As a result of disassembling and observing the battery after cycle deterioration (No. 16), it was found that lithium metal having metallic luster was deposited on the negative electrode surface of the battery of Comparative Example 1 in which no additive was added.
[0069]
From this result, even if the capacity of the battery itself is the same, since the irreversible capacity of the positive electrode (the capacity of A in FIG. 1) is a negative load, the charge exceeds the reversible charge / discharge capacity of the negative electrode by charging. Therefore, it was considered that metallic lithium was deposited on the surface of the negative electrode plate, and the discharge capacity was remarkably reduced.
[0070]
If the negative electrode load is reduced by reducing the amount of positive electrode in the battery or lowering the charging voltage, a battery with good cycle characteristics can be realized, but in this case, the discharge capacity itself becomes small, so the capacity of the battery is increased. Can not.
[0071]
On the other hand, since the batteries 1 to 15 of the present invention are consumed by a compound added with a capacity that does not participate in charge / discharge corresponding to A (the capacity of B in FIG. 2), the reversible capacity of the positive electrode and the reversible capacity of the negative electrode are utilized to the maximum. Battery with good cycle life.
[0072]
In addition, the amount of charged electricity when reacting with lithium ions by a reduction reaction can be measured by the following method.
[0073]
After adding and mixing acetylene black of about 30% by weight with respect to the compound to be added (for example, NiO), pellets are prepared at 250 kg / cm ² and fixed to a stainless steel current collector to form a working electrode.
[0074]
Metal lithium is used for the counter electrode and the reference electrode, and the amount of electricity is measured by discharging at a constant current until reaching 0 V with respect to the lithium electrode. At this time, the amount of electricity with which acetylene black reacts with lithium must be measured in advance and subtracted from the obtained amount of electricity.
[0075]
The electrolyte used for the measurement is most preferably used for the battery. In addition, the current density during charging is preferably 0.1 mA / cm ² or less.
[0076]
Table 2 shows the results of Example 2 and Comparative Example 2.
[0077]
[Table 2]

[0078]
From the results of Example 2, when synthesized at a temperature lower than 750 ° C. (Batteries 17 and 22), even when the additive according to the present invention is not added, the lithium ion of the positive electrode is released and occluded (occlusion). (Amount / discharge amount × 100 (%)) is as high as 95% or more, and since the irreversible capacity at the positive electrode is small, the irreversible capacity of graphite as the negative electrode active material can be sufficiently offset, and a good cycle life can be obtained.
[0079]
Therefore, LiNi _x M _1-x O ₂ (M is at least one selected from the group consisting of Co, Mn, Cr, Fe, V, and Al, and x: 1 ≧ x ≧ 0.5) is the positive electrode. In the case of a battery using an active material, the greatest effect can be obtained when the active material synthesized at 750 ° C. or higher is used for a battery using a positive electrode.
[0080]
In addition, in the synthesis temperature range of 750 ° C. to 900 ° C., the addition of the additive of the present invention improves the cycle life characteristics as in Example 1, and the effect of the present invention is remarkable. Recognize.
[0081]
However, when the synthesis temperature exceeds 950 ° C., the crystal structure of the active material becomes a two-phase structure of hexagonal crystal and rock salt structure. Therefore, the lithium ion of the positive electrode is released and stored, and the charge / discharge efficiency (storage amount / discharge amount × 100 (%)) Is in the 50% range, and the discharge characteristics of the positive electrode itself deteriorate, which is not preferable.
[0082]
Thus, LiNi _x M _1-x O ₂ (M is at least one selected from the group consisting of Co, Mn, Cr, Fe, V, and Al, and x: 1 ≧ x ≧ 0.5) is the positive electrode. When the active material is used, the greatest effect can be obtained when a material synthesized in the temperature range of 750 ° C. to 900 ° C. is used.
[0083]
In the present invention, the charge / discharge efficiency (occlusion / release amount × 100 (%)) for releasing and occluding lithium ions of the positive electrode in the present invention is precisely the potential region where a battery is normally used with metallic lithium as the negative electrode. It is possible to calculate from each amount of electricity when charging to 4.3V and discharging to 2.5V.
[0084]
Needless to say, the electrolyte used for the measurement in this case is the same as the electrolyte used in an actual battery.
[0085]
_{LiNi x M 1-x O 2} (M as the positive electrode active material in this embodiment is at least one selected Co, Mn, Cr, Fe, V, from the group consisting of Al, x: 1 ≧ x ≧ 0.5) was used, but the positive electrode active material was a lithium-containing metal compound, and the charge / discharge efficiency (occlusion amount / discharging amount × 100 (%)) for releasing and storing lithium ions was in the range of 75 to 95%. If so, the battery operating principle is the same, so the same effect can be obtained.
[0086]
In addition, although Co is used as the substitution metal M of LiNi _x M _1-x O ₂ which is the positive electrode active material in this example, any of Mn, Cr, Fe, V, and Al may be used in addition to this. The effect is obtained.
[0087]
The purpose of the present invention is to alleviate the difference between the irreversible capacities of the positive and negative electrodes. In the examples, graphite materials were used as negative electrode active materials. In addition to such carbon materials, for example, tin compounds, nitrides, silicides, etc. The same effect can be obtained as long as it is a substance capable of charging and discharging lithium such as an alloy.
[0088]
In the above examples, evaluation was performed using a cylindrical battery, but the same effect can be obtained even if the battery shape is different, such as a rectangular battery.
[0089]
Moreover, although lithium hexafluorophosphate was used as the electrolyte in the above examples, other lithium-containing salts such as lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium hexafluoroarsenate The same effect was also obtained.
[0090]
Further, in the above examples, a mixed solvent of ethylene carbonate and ethyl methyl carbonate was used, but other non-aqueous solvents such as cyclic esters such as propylene carbonate, cyclic ethers such as tetrahydrofuran, chain ethers such as dimethoxyethane, propionic acid, etc. The same effect was obtained even when a non-aqueous solvent such as a chain ester such as methyl or a multicomponent mixed solvent thereof was used. As a matter of course, the present invention is not related to the electrolyte, and can be applied to any case of a polymer electrolyte, a solid electrolyte, a gel electrolyte, and the like.
[0091]
As is clear from the above explanation, the negative electrode main material according to the present invention includes Ag ₂ O, PbO, NiO, as a compound that reacts irreversibly with lithium ions by a reduction reaction.
_{Ni 2 O 3, T iO 2} , Bi 2 O 3, addition of the _{Sb 2 O 3, Cr 2 O} 3, SeO 2, TeO 2, at least one of either or mixtures selected from MnO ₂ or Ranaru group By doing so, a non-aqueous electrolyte secondary battery having a high capacity and an excellent cycle life can be provided.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing the state of potential and capacity during the first charge / discharge of a lithium secondary battery when the present invention is not used. FIG. 2 is the first charge / discharge of the lithium secondary battery of the present invention. Fig. 3 is a conceptual diagram showing the state of the potential and capacity of the electrode. Fig. 3 is a longitudinal sectional view of a cylindrical nonaqueous electrolyte secondary battery in this example and a comparative example.
DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode plate group 5 Positive electrode plate 5a Positive electrode lead 6 Negative electrode plate 6a Negative electrode lead 7 Separator 8 Insulation ring

Claims (7)

A positive electrode using a lithium-containing metal oxide as a positive electrode active material through a separator or solid electrolyte layer impregnated with an organic electrolyte, and a material capable of charging and discharging lithium as a negative electrode active material and having an irreversible capacity during initial charge It is composed of a negative electrode using, in the positive electrode active anode active non-aqueous electrolyte secondary battery is greater than the irreversible capacity of the material of irreversible capacity in the negative electrode material in the positive electrode, a negative electrode, Ri by the be charged electrical chemically reduced Ag ₂ generates a metal _{O, PbO, NiO, Ni 2} O 3, TiO 2, Bi 2 O 3, Sb 2 O 3, Cr 2 O 3, SeO 2, TeO 2, MnO _At least one metal oxide selected from the group consisting of ₂ is added in a range of 0.2 wt% to 20 wt% with respect to the total amount of the negative electrode active material, and the metal oxide is electrochemically reduced. Generated by Metal is chemically and electrochemically stable in the potential region where the charging and discharging of the negative electrode active material is not oxidized in the case where the anode is discharged, characterized by keeping the metallic state in irreversible A non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is a carbon material capable of charging and discharging lithium. Metal oxide content to be added to the negative electrode, the positive electrode and the negative electrode non-aqueous electrolyte secondary cell of claim 1, wherein the value corresponding to the capacitance of the difference between the irreversible capacity can not contribute to the first discharge after the initial charge of the positive electrode and the negative electrode . Lithium-containing metal compound used for the positive electrode, the general formula _{LiNi x M 1-x O 2} (M is Co, Mn, Cr, Fe, V, any one or more of Al, x: 1 ≧ x ≧ 0.5) The nonaqueous electrolyte secondary battery of Claim 1 shown by these.   The initial charge / discharge efficiency (occlusion / release amount × 100 (%)) of the lithium-containing metal compound used for the positive electrode when it is charged for the first time is released and discharged for the first time, and is 75 to 95%. The non-aqueous electrolyte secondary battery according to claim 1, wherein 6. The nonaqueous electrolyte secondary battery according to claim 5 , wherein the lithium-containing metal oxide used for the positive electrode is obtained by mixing lithium hydroxide with the metal hydroxide and synthesizing it by heating. The nonaqueous electrolyte secondary battery according to claim 6 , wherein the synthesis temperature of the lithium-containing metal oxide used for the positive electrode is synthesized in a temperature range of 750C to 900C.

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