JP3650016B2 - Lithium battery - Google Patents
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- JP3650016B2 JP3650016B2 JP2000297333A JP2000297333A JP3650016B2 JP 3650016 B2 JP3650016 B2 JP 3650016B2 JP 2000297333 A JP2000297333 A JP 2000297333A JP 2000297333 A JP2000297333 A JP 2000297333A JP 3650016 B2 JP3650016 B2 JP 3650016B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Description
【０００１】
【発明が属する技術分野】
本発明は、リチウム電池に係わり、詳しくは、充電状態での保存特性（以下、「充電保存特性」と称する場合がある。）が良いリチウム電池を提供することを目的とした、正極の改良に関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
近年、リチウム電池が、エネルギー密度が高いことから、ワープロ、パソコン等の携帯機器の駆動用電源及びメモリバックアップ用電源として、広く使用されている。
【０００３】
しかしながら、従来のリチウム電池には、充電状態で保存すると正極活物質と非水電解液とが反応して、非水電解液が大量に分解するという問題があった。
【０００４】
したがって、本発明は、充電保存特性の良いリチウム電池を提供することを目的とする。
【０００５】
【課題を解決するための手段】
本発明に係るリチウム電池（本発明電池）は、正極活物質、導電剤及び結着剤を含有する正極と、負極と、非水電解液とを備え、前記正極が、赤リンを含有する。
【０００６】
本発明電池は、充電保存特性が良い。この理由は、正極活物質の表面の活性サイトに、正極に含有せしめた赤リンと非水電解液との安定な反応生成物が付着し、この反応生成物が、正極活物質と非水電解液との副反応を抑制するためと考えられる。
【０００７】
正極の赤リン含有量は、０．０１〜２重量％が好ましく、０．０５〜１重量％がより好ましい。赤リン含有量が０．０１〜２重量％の範囲を外れた場合は、充電保存特性を充分に向上させることが困難になる。
【０００８】
赤リンの平均粒径は、１０〜３０μｍが好ましい。平均粒径がこの範囲を外れた場合は、赤リンを正極に均一に含有せしめることが困難になるために、充電保存特性を充分に向上させることが困難になる。
【０００９】
導電剤としては、リチウム電池用として従来公知の導電剤を使用することができるが、導電剤の一部として、膨張黒鉛を使用することが好ましい。但し、この明細書において、膨張黒鉛とは、層間にインターカラントを挿入して体積膨張させた黒鉛であって、ｃ軸方向の結晶子の大きさ（Ｌｃ）が２００Å以下で、ＢＥＴ法による比表面積が１５ｍ2 ／ｇ以上のものをいうものとする。正極活物質の表面の活性サイトに赤リンと非水電解液との反応生成物が付着すると、正極活物質粒子間の電子伝導性の低下を招き、負荷特性が若干低下する。しかし、正極に赤リンを含有せしめた場合であって、導電剤の一部として膨張黒鉛を使用したときは、負荷特性が向上する。膨張黒鉛は嵩密度が小さいので、電池の導電剤としては一般的には不適当と考えられているが、赤リンを正極に含有せしめる本発明においては、意外なことではあるが、導電剤の一部として、膨張黒鉛を使用することが好ましいのである。このように負荷特性が向上するのは、膨張黒鉛と正極活物質との密着性が、通常の黒鉛と正極活物質との密着性に比べて良いために、電子伝導性及びイオン伝導性が向上するためと考えられる。正極の膨張黒鉛含有量は、０．１〜３重量％が好ましい。正極の膨張黒鉛含有量が、０．１重量％未満の場合は電子伝導性及びイオン伝導性が充分に向上しないために、一方３重量％を越えた場合は余剰の膨張黒鉛がリチウムイオンの拡散を阻害するために、いずれの場合も負荷特性の極めて良いリチウム電池を得ることが困難になる。
【００１０】
本発明は、従来のリチウム電池の充電保存特性を改善するべく、正極に赤リンを含有せしめた点に特徴がある。したがって、正極活物質、負極活物質、非水電解液などの電池構成材料には、従来公知のものを特に制限なく使用することができる。
【００１１】
正極活物質としては、遷移金属の酸化物、硫化物、窒化物又はこれらのリチウム化物（リチウム含有化合物）が例示され、具体例としては、ＬｉＣｏＯ2 、ＬｉＮｉＯ2 、ＬｉＮｉx Ｃｏ1-x Ｏ2 （０＜ｘ＜１）、ＬｉＭｎ2 Ｏ4 、ＬｉＭｎＯ2 、ＬｉＣｏ0.5 Ｎｉ0.3 Ｍｎ0.2 Ｏ2 、ＭｎＯ2 が挙げられる。なお、充電状態での保存中に非水電解液を分解させ易い、充電電位が４．０Ｖ（vs. Ｌｉ／Ｌｉ+ ）以上になる高電位型正極活物質を使用した場合に、本発明の効果が顕著に認められる。
【００１２】
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及び放出することが可能な物質及びリチウム金属が挙げられる。リチウムイオンを電気化学的に吸蔵及び放出することが可能な物質としては、ＳｎＯ2 等の金属酸化物；ＴｉＳ2 等の金属硫化物；黒鉛、コークス、有機物焼成体等の炭素材料；リチウム−アルミニウム合金、リチウム−マグネシウム合金、リチウム−インジウム合金、リチウム−アルミニウム−マンガン合金等のリチウム合金が例示される。
【００１３】
非水電解液の溶媒としては、エチレンカーボネート、プロピレンカーボネート、１，２−ブチレンカーボネート、２，３−ブチレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート、メチルプロピルカーボネート、メチルイソプロピルカーボネート、ジメトキシエタン、ジエトキシエタン、テトラヒドロフラン、γ−ブチロラクトン及びこれらの２種以上の混合溶媒が例示される。
【００１４】
非水電解液の溶質としては、ＬｉＰＦ6 、ＬｉＢＦ4 、ＬｉＣＦ3 ＳＯ3 、ＬｉＮ（ＣＦ3 ＳＯ2 ）2 、ＬｉＮ（Ｃ2 Ｆ5 ＳＯ2 ）2 、ＬｉＮ（ＣＦ3 ＳＯ2 ）（Ｃ4 Ｆ9 ＳＯ2 ）、ＬｉＣ（ＣＦ3 ＳＯ2 ）3 、ＬｉＣ（Ｃ2 Ｆ5 ＳＯ2 ）3 が例示される。これらのリチウム塩は一種単独を使用してもよく、必要に応じて、２種以上を併用してもよい。
【００１５】
【実施例】
本発明を実施例に基づいてさらに詳細に説明するが、本発明は下記実施例に何ら限定されるものではなく、その要旨を変更しない範囲で適宜変更して実施することが可能なものである。
【００１６】
（実験１）
本発明電池及び比較電池を作製し、充電保存特性を比較した。
【００１７】
（実施例１）
〔正極の作製〕
正極活物質としてのＬｉＣｏＯ2 と、導電剤としての人造黒鉛と、結着剤としてのＰＶｄＦ（ポリフッ化ビニリデン）と、平均粒径２０μｍの赤リンとを、重量比８９．５：５：５：０．５で混合し、さらにＮＭＰ（Ｎ−メチル−２−ピロリドン）を加えて混合してスラリーを調製し、このスラリーを正極芯体（集電体）としての厚さ２０μｍのアルミニウム箔の両面にドクターブレード法により塗布し、１２０°Ｃで２時間真空下にて乾燥し、圧延して、幅４０ｍｍの帯状の正極を正極芯体と一体的に作製した。
【００１８】
〔負極の作製〕
格子面（００２）面の面間隔（ｄ002 ）が３．３５Åであり、ｃ軸方向の結晶子の大きさ（Ｌｃ）が１０００Å以上である黒鉛粉末と、結着剤としてのＰＶｄＦとを、重量比９０：１０で混合し、さらにＮＭＰを加えて混合してスラリーを調製し、このスラリーを負極芯体（集電体）としての厚さ２０μｍの銅箔の両面にドクターブレード法により塗布し、１２０°Ｃで２時間真空下にて乾燥し、圧延して、幅４２ｍｍの帯状の負極を負極芯体と一体的に作製した。
【００１９】
〔非水電解液の調製〕
エチレンカーボネートとジエチルカーボネートとの体積比２：３の混合溶媒にＬｉＰＦ6 を１モル／リットル溶かして、非水電解液を調製した。
【００２０】
〔リチウム二次電池の作製〕
上記の正極、負極及び非水電解液を使用して、直径１４．２ｍｍ、高さ５０．０ｍｍの円筒形のリチウム二次電池Ａ１（本発明電池）を作製した。セパレータには、ポリプロピレンフィルムを使用した。図１は、作製したリチウム二次電池Ａ１の断面図であり、図示のリチウム二次電池Ａ１は、正極１、負極２、これらを離間するセパレータ３、正極リード４、負極リード５、正極蓋６、負極缶７などからなる。正極１及び負極２は、セパレータ３を間に介在させた状態で渦巻き状に巻き取られて負極缶７内に収納されており、正極１は正極リード４を介して正極蓋６に、負極２は負極リード５を介して負極缶７に、それぞれ接続され、充放電が可能な構造になっている。
【００２１】
（比較例１）
ＬｉＣｏＯ2 と、人造黒鉛と、ＰＶｄＦとを、重量比９０：５：５で混合し、さらにＮＭＰ（Ｎ−メチル−２−ピロリドン）を加えて混合してスラリーを調製し、このスラリーを正極芯体としての厚さ２０μｍのアルミニウム箔の両面にドクターブレード法により塗布し、１２０°Ｃで２時間真空下にて乾燥し、圧延して、幅４０ｍｍの帯状の正極を正極芯体と一体的に作製した。次いで、この正極を使用したこと以外は実施例１と同様にして、正極のみが本発明電池Ａ１と異なるリチウム二次電池Ｘ（比較電池）を作製した。
【００２２】
〈各電池の充電保存特性〉
各電池を、１００ｍＡで４．１Ｖまで充電し、１００ｍＡで２．７Ｖまで放電して、保存前の放電容量Ｃp １（ｍＡｈ）を求めた。続けて、１００ｍＡで４．１Ｖまで充電し、６０°Ｃで１４日間保存した後、１００ｍＡで２．７Ｖまで放電して、保存後の放電容量Ｃp ２（ｍＡｈ）を求め、保存前の放電容量Ｃp １に対する保存後の放電容量Ｃp ２の比率Ｐ（Ｐ（％）＝（Ｃp ２／Ｃp １）×１００）を求めた。比率Ｐの値が大きいほど、充電保存特性が良い。結果を表１に示す。
【００２３】
【表１】
表１に示すように、本発明電池Ａ１は、比較電池Ｘに比べて、充電保存特性が良い。
【００２５】
（実験２）
正極の赤リン含有量と充電保存特性の関係を調べた。
【００２６】
ＬｉＣｏＯ2 と、人造黒鉛と、ＰＶｄＦと、平均粒径２０μｍの赤リンとを、表２に示す重量比で混合し、さらにＮＭＰを加えて混合してスラリーを調製し、このスラリーを正極芯体としての厚さ２０μｍのアルミニウム箔の両面にドクターブレード法により塗布し、１２０°Ｃで２時間真空下にて乾燥し、圧延して、幅４０ｍｍの帯状の７種の正極を正極芯体と一体的に作製した。次いで、これらの各正極を使用したこと以外は実施例１と同様にして、正極のみが本発明電池Ａ１と異なるリチウム二次電池Ｂ１〜Ｂ７（本発明電池）を作製した。
【００２７】
各電池について、実験１で行ったものと同じ条件の電池試験を行い、充電保存特性を調べた。結果を表２に示す。表２には、本発明電池Ａ１の結果も表１より転記して示してある。
【００２８】
【表２】
表２より、充電保存特性が良いリチウム二次電池を得る上で、正極の赤リン含有量は、０．０１〜２重量％が好ましく、０．０５〜１重量％がより好ましいことが分かる。
【００３０】
（実験３）
導電剤の一部として膨張黒鉛を使用した電池、及び、導電剤として膨張黒鉛を全く使用しなかった電池の充電保存特性及び負荷特性を調べた。
【００３１】
ＬｉＣｏＯ2 と、人造黒鉛と、Ｌｃ１２０Å、ＢＥＴ法による比表面積２６ｍ2 ／ｇの膨張黒鉛と、ＰＶｄＦと、平均粒径２０μｍの赤リンとを、表３に示す重量比で混合し、さらにＮＭＰを加えて混合してスラリーを調製し、このスラリーを正極芯体としての厚さ２０μｍのアルミニウム箔の両面にドクターブレード法により塗布し、１２０°Ｃで２時間真空下にて乾燥し、圧延して、幅４０ｍｍの帯状の正極を正極芯体と一体的に作製した。なお、膨張黒鉛としては、黒鉛と、濃硫酸９０％と濃硝酸１０％とからなる１００°Ｃに加熱した混酸とを反応させた後、水洗し、乾燥し、５００°Ｃで加熱処理することにより作製したものを使用した。次いで、この正極を使用したこと以外は実施例１と同様にして、正極のみが本発明電池Ａ１と異なるリチウム二次電池Ｃ１（本発明電池）を作製した。
【００３２】
本発明電池Ｃ１について、実験１で行ったものと同じ条件の電池試験を行い、充電保存特性を調べた。また、本発明電池Ｃ１、本発明電池Ａ１及び比較電池Ｘについて、各電池を、１００ｍＡで４．１Ｖまで充電し、１００ｍＡで２．７Ｖまで放電して、低率放電での放電容量Ｃp ３（ｍＡｈ）を求めた。続けて、１００ｍＡで４．１Ｖまで充電した後、５００ｍＡで２．７Ｖまで放電して、高率放電での放電容量Ｃp ４（ｍＡｈ）を求め、低率放電での放電容量Ｃp ３に対する高率放電での放電容量Ｃp ４の比率Ｑ（Ｑ（％）＝（Ｃp ４／Ｃp ３）×１００）を求めた。比率Ｑの値が大きいほど、負荷特性が良い。結果を表３に示す。
【００３３】
【表３】
本発明電池Ａ１の負荷特性と本発明電池Ｃ１のそれとの比較から、導電剤の一部として膨張黒鉛を使用することにより、負荷特性が向上することが分かる。本発明電池Ａ１の負荷特性が比較電池Ｘに比べて若干良くないのは、赤リンと非水電解液との反応生成物により、正極活物質粒子間の電子伝導性が若干低下したからである。
【００３５】
（実験４）
導電剤の一部として膨張黒鉛を使用した電池について、正極の膨張黒鉛含有量と充電保存特性及び負荷特性の関係を調べた。
【００３６】
ＬｉＣｏＯ2 と、人造黒鉛と、Ｌｃ１２０Å、ＢＥＴ法による比表面積２６ｍ2 ／ｇの膨張黒鉛と、ＰＶｄＦと、平均粒径２０μｍの赤リンとを、表４に示す重量比で混合し、さらにＮＭＰを加えて混合してスラリーを調製し、このスラリーを正極芯体としての厚さ２０μｍのアルミニウム箔の両面にドクターブレード法により塗布し、１２０°Ｃで２時間真空下にて乾燥し、圧延して、幅４０ｍｍの帯状の４種の正極を正極芯体と一体的に作製した。次いで、この正極を使用したこと以外は実施例１と同様にして、正極のみが本発明電池Ａ１と異なるリチウム二次電池Ｄ１〜Ｄ４（本発明電池）を作製した。
【００３７】
各電池について、実験３で行ったものと同じ条件の２種の電池試験を行い、充電保存特性及び負荷特性を調べた。結果を表４に示す。
【００３８】
【表４】
表４より、負荷特性が良いリチウム二次電池を得る上で、正極の膨張黒鉛含有量は、０．１〜３重量％が好ましいことが分かる。
【００４０】
（実験５）
赤リンの平均粒径と充電保存特性の関係を調べた。
【００４１】
正極の作製において、平均粒径２０μｍの赤リンに代えて、表５に示す平均粒径の赤リンを使用したこと以外は実施例１と同様にして、正極のみが本発明電池Ａ１と異なる４種のリチウム二次電池Ｅ１〜Ｅ４（本発明電池）を作製した。
【００４２】
各電池について、実験１で行ったものと同じ条件の電池試験を行い、充電保存特性を調べた。結果を表５に示す。表５には、本発明電池Ａ１の結果も表１より転記して示してある。
【００４３】
【表５】
表５より、充電保存特性が良いリチウム二次電池を得る上で、平均粒径１０〜３０μｍの赤リンが好ましいことが分かる。
【００４５】
上記の実施例では、本発明を円筒形のリチウム電池に適用する場合を例に挙げて説明したが、本発明は、電池の形状に制限は無く、扁平形等の種々の形状のリチウム電池に適用可能である。また、上記の実施例では、本発明をリチウム二次電池に適用する場合について検討したが、本発明はリチウム一次電池にも適用することが可能である。
【００４６】
【発明の効果】
充電保存特性の良いリチウム電池が提供される。
【図面の簡単な説明】
【図１】実施例で作製した円筒形のリチウム二次電池の断面図である。
【符号の説明】
Ａ１ リチウム二次電池
１ 正極
２ 負極
３ セパレータ
４ 正極リード
５ 負極リード
６ 正極蓋
７ 負極缶[0001]
[Technical field to which the invention belongs]
The present invention relates to a lithium battery, and more particularly, to an improvement in a positive electrode for the purpose of providing a lithium battery having good storage characteristics in a charged state (hereinafter sometimes referred to as “charge storage characteristics”). .
[0002]
[Prior art and problems to be solved by the invention]
In recent years, lithium batteries have been widely used as power sources for driving portable devices such as word processors and personal computers and power sources for memory backup because of their high energy density.
[0003]
However, the conventional lithium battery has a problem that when stored in a charged state, the positive electrode active material reacts with the non-aqueous electrolyte and the non-aqueous electrolyte is decomposed in a large amount.
[0004]
Accordingly, an object of the present invention is to provide a lithium battery with good charge storage characteristics.
[0005]
[Means for Solving the Problems]
The lithium battery (present battery) according to the present invention includes a positive electrode containing a positive electrode active material, a conductive agent, and a binder, a negative electrode, and a non-aqueous electrolyte, and the positive electrode contains red phosphorus.
[0006]
The battery of the present invention has good charge storage characteristics. The reason for this is that a stable reaction product of red phosphorus contained in the positive electrode and the nonaqueous electrolytic solution adheres to the active sites on the surface of the positive electrode active material, and this reaction product is separated from the positive electrode active material and the nonaqueous electrolyte. This is considered to suppress the side reaction with the liquid.
[0007]
The red phosphorus content of the positive electrode is preferably 0.01 to 2% by weight, more preferably 0.05 to 1% by weight. When the red phosphorus content is out of the range of 0.01 to 2% by weight, it is difficult to sufficiently improve the charge storage characteristics.
[0008]
The average particle size of red phosphorus is preferably 10 to 30 μm. When the average particle size is outside this range, it becomes difficult to uniformly contain red phosphorus in the positive electrode, so that it is difficult to sufficiently improve the charge storage characteristics.
[0009]
As the conductive agent, a conventionally known conductive agent for lithium batteries can be used, but it is preferable to use expanded graphite as a part of the conductive agent. However, in this specification, expanded graphite refers to graphite that is volume-expanded by inserting an intercalant between layers, and the crystallite size (Lc) in the c-axis direction is 200 mm or less, and the ratio by BET method. The surface area shall mean 15 m 2 / g or more. If the reaction product of red phosphorus and non-aqueous electrolyte adheres to the active site on the surface of the positive electrode active material, the electron conductivity between the positive electrode active material particles is reduced, and the load characteristics are slightly reduced. However, when red phosphorus is contained in the positive electrode and expanded graphite is used as a part of the conductive agent, the load characteristics are improved. Since expanded graphite has a low bulk density, it is generally considered unsuitable as a conductive agent for batteries. However, in the present invention in which red phosphorus is contained in the positive electrode, it is surprising that As part, it is preferred to use expanded graphite. The load characteristics are thus improved because the adhesion between the expanded graphite and the positive electrode active material is better than the adhesion between the normal graphite and the positive electrode active material, so that the electron conductivity and the ionic conductivity are improved. It is thought to do. The expanded graphite content of the positive electrode is preferably 0.1 to 3% by weight. If the expanded graphite content of the positive electrode is less than 0.1% by weight, the electron conductivity and ionic conductivity are not sufficiently improved. On the other hand, if it exceeds 3% by weight, excess expanded graphite diffuses lithium ions. In any case, it becomes difficult to obtain a lithium battery with very good load characteristics.
[0010]
The present invention is characterized in that red phosphorus is contained in the positive electrode in order to improve the charge storage characteristics of a conventional lithium battery. Therefore, conventionally known materials can be used for the battery constituent materials such as the positive electrode active material, the negative electrode active material, and the non-aqueous electrolyte without limitation.
[0011]
Examples of the positive electrode active material include transition metal oxides, sulfides, nitrides, and lithiates (lithium-containing compounds) thereof. Specific examples include LiCoO 2 , LiNiO 2 , LiNi x Co 1-x O 2. (0 <x <1), LiMn 2 O 4 , LiMnO 2 , LiCo 0.5 Ni 0.3 Mn 0.2 O 2 , MnO 2 . In addition, when a high potential positive electrode active material having a charging potential of 4.0 V (vs. Li / Li + ) or more that easily decomposes the non-aqueous electrolyte during storage in a charged state is used, The effect is noticeable.
[0012]
Examples of the negative electrode active material include a material capable of electrochemically inserting and extracting lithium ions and lithium metal. Substances capable of electrochemically inserting and extracting lithium ions include metal oxides such as SnO 2 ; metal sulfides such as TiS 2 ; carbon materials such as graphite, coke, and organic fired bodies; lithium-aluminum Examples include lithium alloys such as alloys, lithium-magnesium alloys, lithium-indium alloys, and lithium-aluminum-manganese alloys.
[0013]
As the solvent of the non-aqueous electrolyte, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dimethoxy ethane, Examples include diethoxyethane, tetrahydrofuran, γ-butyrolactone, and a mixed solvent of two or more thereof.
[0014]
Solutes of the non-aqueous electrolyte include LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN (CF 3 SO 2 ) (C 4 F 9 SO 2), LiC ( CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3 can be exemplified. These lithium salts may be used individually by 1 type, and may use 2 or more types together as needed.
[0015]
【Example】
The present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples, and can be appropriately modified and implemented without departing from the scope of the present invention. .
[0016]
(Experiment 1)
The battery of the present invention and the comparative battery were prepared and the charge storage characteristics were compared.
[0017]
(Example 1)
[Production of positive electrode]
LiCoO 2 as a positive electrode active material, artificial graphite as a conductive agent, PVdF (polyvinylidene fluoride) as a binder, and red phosphorus having an average particle diameter of 20 μm, a weight ratio of 89.5: 5: 5: Then, NMP (N-methyl-2-pyrrolidone) is added and mixed to prepare a slurry. This slurry is used as a positive electrode core (current collector) on both sides of an aluminum foil having a thickness of 20 μm. The film was applied by a doctor blade method, dried under vacuum at 120 ° C. for 2 hours, and rolled to produce a strip-shaped positive electrode having a width of 40 mm integrally with the positive electrode core.
[0018]
(Production of negative electrode)
A graphite powder having a lattice plane (002) plane spacing (d 002 ) of 3.35 mm and a c-axis direction crystallite size (Lc) of 1000 mm or more, and PVdF as a binder, Mixing at a weight ratio of 90:10, further adding NMP and mixing to prepare a slurry, and applying this slurry to both sides of a 20 μm thick copper foil as a negative electrode core (current collector) by the doctor blade method The film was dried at 120 ° C. under vacuum for 2 hours and rolled to produce a strip-shaped negative electrode having a width of 42 mm integrally with the negative electrode core.
[0019]
(Preparation of non-aqueous electrolyte)
A non-aqueous electrolyte was prepared by dissolving 1 mol / L of LiPF 6 in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 2: 3.
[0020]
[Production of lithium secondary battery]
A cylindrical lithium secondary battery A1 (invention battery) having a diameter of 14.2 mm and a height of 50.0 mm was produced using the positive electrode, the negative electrode, and the nonaqueous electrolytic solution. A polypropylene film was used as the separator. FIG. 1 is a cross-sectional view of the manufactured lithium secondary battery A1, and the illustrated lithium secondary battery A1 includes a positive electrode 1, a
[0021]
(Comparative Example 1)
LiCoO 2 , artificial graphite, and PVdF are mixed at a weight ratio of 90: 5: 5, and NMP (N-methyl-2-pyrrolidone) is added and mixed to prepare a slurry. The aluminum foil having a thickness of 20 μm was coated on both surfaces by a doctor blade method, dried under vacuum at 120 ° C. for 2 hours, and rolled to form a strip-shaped positive electrode having a width of 40 mm integrally with the positive electrode core. Produced. Next, a lithium secondary battery X (comparative battery) in which only the positive electrode was different from the battery A1 of the present invention was produced in the same manner as in Example 1 except that this positive electrode was used.
[0022]
<Charge storage characteristics of each battery>
Each battery was charged to 4.1 V at 100 mA, discharged to 2.7 V at 100 mA, and the discharge capacity C p 1 (mAh) before storage was determined. Subsequently, the battery was charged to 4.1 V at 100 mA, stored at 60 ° C. for 14 days, then discharged to 2.7 V at 100 mA, and the discharge capacity C p 2 (mAh) after storage was determined. The ratio P (P (%) = (
[0023]
[Table 1]
As shown in Table 1, the battery A1 of the present invention has better charge storage characteristics than the comparative battery X.
[0025]
(Experiment 2)
The relationship between the red phosphorus content of the positive electrode and the charge storage characteristics was investigated.
[0026]
LiCoO 2 , artificial graphite, PVdF, and red phosphorus having an average particle diameter of 20 μm are mixed at a weight ratio shown in Table 2, and NMP is added and mixed to prepare a slurry. Is applied to both surfaces of an aluminum foil having a thickness of 20 μm by a doctor blade method, dried under vacuum at 120 ° C. for 2 hours, and rolled to integrate seven positive electrodes having a width of 40 mm with the positive electrode core. Was made. Next, lithium secondary batteries B1 to B7 (invention batteries) that differ from the invention battery A1 only in the positive electrode were produced in the same manner as in Example 1 except that these positive electrodes were used.
[0027]
For each battery, a battery test under the same conditions as in Experiment 1 was performed to examine the charge storage characteristics. The results are shown in Table 2. In Table 2, the results of the battery A1 of the present invention are also transferred from Table 1.
[0028]
[Table 2]
From Table 2, it can be seen that the red phosphorus content of the positive electrode is preferably 0.01 to 2% by weight and more preferably 0.05 to 1% by weight in obtaining a lithium secondary battery with good charge storage characteristics.
[0030]
(Experiment 3)
The charge storage characteristics and load characteristics of a battery using expanded graphite as a part of the conductive agent and a battery using no expanded graphite as the conductive agent were investigated.
[0031]
LiCoO 2 , artificial graphite, Lc120%, expanded graphite having a specific surface area of 26 m 2 / g by BET method, PVdF, and red phosphorus having an average particle diameter of 20 μm are mixed in a weight ratio shown in Table 3, and NMP is further mixed. In addition, a slurry is prepared by mixing, and this slurry is applied to both surfaces of an aluminum foil having a thickness of 20 μm as a positive electrode core by the doctor blade method, dried at 120 ° C. for 2 hours under vacuum, and rolled. A belt-like positive electrode having a width of 40 mm was produced integrally with the positive electrode core. As expanded graphite, graphite and a mixed acid composed of 90% concentrated sulfuric acid and 10% concentrated nitric acid heated to 100 ° C are reacted, then washed with water, dried, and heat-treated at 500 ° C. What was produced by was used. Next, a lithium secondary battery C1 (invention battery) was produced in the same manner as in Example 1 except that this positive electrode was used.
[0032]
The battery C1 of the present invention was subjected to a battery test under the same conditions as those performed in Experiment 1 to examine the charge storage characteristics. Further, the present invention cell C1, the present invention cells A1 and Comparative Battery X, each battery was charged to 4.1V at 100 mA, and discharged to 2.7V at 100 mA, the
[0033]
[Table 3]
From comparison between the load characteristics of the present invention battery A1 and that of the present invention battery C1, it can be seen that the use of expanded graphite as a part of the conductive agent improves the load characteristics. The reason why the load characteristic of the battery A1 of the present invention is slightly poorer than that of the comparative battery X is that the electron conductivity between the positive electrode active material particles is slightly decreased by the reaction product of red phosphorus and the non-aqueous electrolyte. .
[0035]
(Experiment 4)
Regarding batteries using expanded graphite as a part of the conductive agent, the relationship between the expanded graphite content of the positive electrode, the charge storage characteristics and the load characteristics was examined.
[0036]
LiCoO 2 , artificial graphite, Lc120%, expanded graphite having a specific surface area of 26 m 2 / g by BET method, PVdF, and red phosphorus having an average particle diameter of 20 μm are mixed at a weight ratio shown in Table 4, and NMP is further mixed. In addition, a slurry is prepared by mixing, and this slurry is applied to both surfaces of a 20 μm-thick aluminum foil as a positive electrode core by the doctor blade method, dried at 120 ° C. for 2 hours under vacuum, and rolled. Four types of positive electrodes with a width of 40 mm were produced integrally with the positive electrode core. Next, lithium secondary batteries D1 to D4 (invention batteries) different from the invented battery A1 only in the same manner as in Example 1 except that this positive electrode was used.
[0037]
For each battery, two types of battery tests were performed under the same conditions as those performed in
[0038]
[Table 4]
From Table 4, it can be seen that 0.1 to 3% by weight of the expanded graphite content of the positive electrode is preferable in obtaining a lithium secondary battery with good load characteristics.
[0040]
(Experiment 5)
The relationship between the average particle size of red phosphorus and the charge storage characteristics was investigated.
[0041]
In the production of the positive electrode, only the positive electrode differs from the present invention battery A1 in the same manner as in Example 1, except that red phosphorus having an average particle diameter shown in Table 5 is used instead of red phosphorus having an average particle diameter of 20 μm. Seed lithium secondary batteries E1 to E4 (present invention batteries) were produced.
[0042]
For each battery, a battery test under the same conditions as in Experiment 1 was performed to examine the charge storage characteristics. The results are shown in Table 5. In Table 5, the results of the present invention battery A1 are also transferred from Table 1.
[0043]
[Table 5]
From Table 5, it can be seen that red phosphorus having an average particle size of 10 to 30 μm is preferable in obtaining a lithium secondary battery having good charge storage characteristics.
[0045]
In the above embodiment, the case where the present invention is applied to a cylindrical lithium battery has been described as an example. However, the present invention is not limited to the shape of the battery, and is applicable to lithium batteries having various shapes such as a flat shape. Applicable. In the above embodiments, the case where the present invention is applied to a lithium secondary battery has been studied. However, the present invention can also be applied to a lithium primary battery.
[0046]
【The invention's effect】
A lithium battery having good charge storage characteristics is provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a cylindrical lithium secondary battery manufactured in an example.
[Explanation of symbols]
A1 Lithium secondary battery 1
Claims (5)
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