JP4140198B2 - Lithium secondary battery - Google Patents
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- JP4140198B2 JP4140198B2 JP2000398723A JP2000398723A JP4140198B2 JP 4140198 B2 JP4140198 B2 JP 4140198B2 JP 2000398723 A JP2000398723 A JP 2000398723A JP 2000398723 A JP2000398723 A JP 2000398723A JP 4140198 B2 JP4140198 B2 JP 4140198B2
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- 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】
【発明の属する技術分野】
本発明はリチウム二次電池に関し、詳しくは、低温出力等の低温性能が改善されたリチウム二次電池に関する。
【０００２】
【従来の技術】
リチウム二次電池は、正極活物質としてリチウム含有酸化物等を用い、負極活物質としては炭素質材料等を用い、また電解液としてはリチウム電解質を溶解させた非水電解液等を用いて構成される。このリチウム二次電池は、充電時には正極活物質中のリチウムイオンが電解液を介して負極活物質側へと移動して吸蔵され、放電時には逆に負極から放出されたリチウムイオンが正極活物質側へと移動して捕捉される。
【０００３】
上記のようなリチウム二次電池に用いられる正極活物質は、一般にあまり電気伝導性の大きなものではないため、通常は上記正極活物質の粉体にカーボンブラック等の導電化材を添加して、正極活物質層中における電子伝導性を向上させることにより電池の内部抵抗を低減させている。また、特開平１１−２８３６１２号公報には、この正極活物質粉体の少なくとも一部の表面に金属被膜を形成するかあるいは金属粒子を固着させることにより内部抵抗を低減し、これにより充放電サイクル特性の改善および高出力化を図ったリチウム二次電池が開示されている。金属被膜または金属粒子としては、アルミニウム、チタン、金、白金のうち少なくとも一種以上の金属からなるものが好ましいとされている。
【０００４】
【発明が解決しようとする課題】
ところで、電池の内部抵抗は直流抵抗と反応抵抗とに分けられる。常温における電池反応では反応抵抗は小さく、内部抵抗の大部分は直流抵抗により占められる。上記公報に記載の二次電池における内部抵抗の低減は、電子伝導性の向上にともなう直流抵抗の減少により達成されたものと考えられる。
これに対して、電池の低温（例えば−３０℃）使用時においては、内部抵抗の大部分は反応抵抗により占められる。したがって、上記公報のような電子伝導性の向上によっては、低温における電池性能、例えば低温出力を改善する効果を得ることはできない。
【０００５】
本発明の目的は、低温出力等の低温性能が改善されたリチウム二次電池を提供することにある。
【０００６】
【課題を解決するための手段】
上記課題を解決するために、請求項１記載のリチウム二次電池は、還元触媒作用をもつ金属が正極に担持されているリチウム二次電池であって、上記還元触媒作用をもつ金属は、上記正極活物質層を構成する正極活物質粉体の表面に担持されており、上記還元触媒作用をもつ金属の担持量は、正極活物質の表面積１ｍ２あたり１５〜７００μｇであり、上記還元触媒作用をもつ金属はＲｈ、ＲｕおよびＩｒの少なくとも一種であることを特徴とする。
このように、還元触媒作用をもつ金属を正極に担持させることにより、内部抵抗のうち特に反応抵抗が低減されて、低温における電池性能（例えば低温出力）が改善される。これは、上記金属のもつ還元触媒作用による、正極またはその近傍におけるリチウムイオンの移動性の向上および／または正極におけるリチウムイオンの電池反応（還元反応）の促進によるものと推察される。
【０００７】
この還元触媒作用をもつ金属は、本発明では、正極活物質からなる粉体（正極活物質粉体）の表面に担持されている。なお、上記正極活物質層は、上記正極活物質粉体にバインダおよび溶媒、さらに必要に応じて導電化材等を混合してなるペーストを正極集電体に塗布する等の方法により形成することができる。また、一般に正極活物質粉体は正極活物質の微粉末（以下、「正極活物質微粉」ともいう。）が凝集してなる二次粒子であるが、この正極活物質微粉（一次粒子）の表面に上記金属を担持させてもよい。
【０００８】
上記還元触媒作用をもつ金属は、金属被膜の形状で正極に担持されてもよく、金属微粉末（粒子）の形状で担持されてもよい。
正極活物質粉体の表面に上記金属が被膜の状態で担持される場合、この金属被膜は各正極活物質粉体の表面全体を覆ってもよく、粉体の一部表面のみを覆ってもよい。上記金属を担持させた正極活物質粉体を用いて正極活物質層を形成する場合には、この金属を担持させた正極活物質粉体のみを使用してもよく、金属を担持させた正極活物質粉体と金属を担持させていない正極活物質粉体とを任意の割合に混合して用いてもよい。
【０００９】
正極活物質粉体の表面に、上記金属からなる被膜を形成する方法としては、蒸着法、スパッタ法、プラズマコーティング、めっき法、含浸担持法等を採用することができる。また、上記粉体の表面に上記金属の粒子を固着させる方法としては、熱プラズマコーティング、メカニカルグラインディング等の方法を用いることができる。
【００１０】
上記還元触媒作用をもつ金属の担持量は、正極活物質の表面積１ｍ２あたり１５〜７００μｇ（以下、「μｇ／ｍ２」と表す。）であり、より好ましくは３０〜６００μｇ／ｍ２、さらに好ましくは５０〜５００μｇ／ｍ２である。上記金属の担持量が１５μｇ／ｍ２未満では、低温性能の向上効果が不十分となる場合がある。一方、上記金属の担持量が７００μｇ／ｍ２を超えると、この金属の存在によってリチウムイオンの移動がむしろ妨げられる等の要因により電池低能が低下する場合がある。なお、上述のように金属を担持させた正極活物質粉体と金属を担持させていない正極活物質粉体とを混合して用いる場合の担持量は、この正極活物質層の形成に用いられた正極活物質全体に対する平均の担持量をいうものとする。
【００１１】
上記還元触媒作用をもつ金属としては、一種の金属のみを用いてもよく、二種以上の金属の合金を用いてもよく、また二種以上の金属または合金を別個に使用（例えば、金属Ａを担持させた正極活物質粉体と、金属Ｂを担持させた正極活物質粉体とを混合して用いる等）してもよい。この還元触媒作用をもつ金属としては、本発明ではＲｈ、ＲｕおよびＩｒの少なくとも一種が用いられる。上記還元触媒作用をもつ貴金属のうち、Ｒｈを使用することが特に好ましい。
【００１２】
本発明のリチウム二次電池における正極活物質としては、請求項２記載のように、リチウム含有酸化物を用いることが好ましい。このリチウム含有酸化物の例としては、ＬｉＭｎ２Ｏ４等のリチウムマンガン酸化物、ＬｉＮｉＯ２等のリチウムニッケル酸化物、ＬｉＣｏＯ２等のリチウムコバルト酸化物、ＬｉＦｅＯ２等のリチウム鉄酸化物等の、従来のリチウム二次電池の正極活物質に用いられている化合物等が挙げられる。
【００１３】
本発明のリチウム二次電池に用いられる電解液としては、従来のリチウム二次電池に用いられる各種非プロトン性溶媒から選択される一種または二種以上、例えばエチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、γ−ブチロラクトン、１，２−ジメチルエタン、テトラヒドロフラン、１，３−ジオキサン、酢酸メチル、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）、ジメチルカーボネート（ＤＭＣ）等を用いることができる。また電解質としては、従来のリチウムイオン二次電池に用いられる各種リチウム塩、例えばＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣＦ3ＳＯ3、ＬｉＣｌＯ4、ＬｉＡｓＦ6、ＬｉＳｂＦ6、ＬｉＣ4Ｆ9ＳＯ3、ＬｉＮ（ＣＦ3ＳＯ2）2、ＳｉＣ（ＣＦ3ＳＯ2）3等を用いることができ、これらのうちＬｉＰＦ6、ＬｉＢＦ4が好ましい。電解液中における電解質濃度は通常０．０５〜１０ｍｏｌ／Ｌ程度であり、好ましくは０．１〜５ｍｏｌ／Ｌ程度である。
【００１４】
本発明のリチウム二次電池を構成する他の材料についても、従来のリチウム二次電池に用いられる材料等から適宜選択して使用すればよい。例えば、正極または負極用の集電体としてはアルミニウム箔、ニッケル箔、銅箔等の金属箔を、正極活物質層または負極活物質層を形成するためのバインダとしてはポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等を用いることができる。負極活物質としてはアモルファスカーボン、グラファイト等の炭素材料あるいはＳｉ、Ｓｎ、Ｉｎ等の金属とＬｉとの合金または酸化物等を用いることができる。あるいは、負極として金属リチウムを用いてもよい。
【００１５】
また、正極活物質層の形成においては、導電化材としてカーボンブラック、黒鉛、ピッチコークス等を使用することができる。正極活物質層において十分な電子伝導性が確保できれば、この正極活物質層には特に導電化材を含有させなくてもよい。また、正極活物質層の電子伝導性を高める等の目的で、上記導電化材等と併用して、あるいは上記導電化材等に代えて、正極活物質層に還元触媒作用をもたない金属を含有させてもよい。この還元触媒作用をもたない金属は、正極活物質粉体と単に混合して用いてもよく、正極活物質粉体の表面に形成された金属被膜として用いてもよく、また正極活物質粉体に固着された金属粒子として用いてもよい。還元触媒作用をもたない金属の好ましい例としては、アルミニウム、チタン、金、白金等から選択される一種または二種以上が挙げられる。
【００１６】
本発明のリチウム二次電池のうち、還元触媒作用をもつ金属を正極活物質粉体の表面に担持させたものは、例えば以下の方法により製造することができる。すなわち、正極活物質粉体の表面に還元触媒作用をもつ金属を担持させ、次いでこの金属担持正極活物質粉体にバインダ、溶媒および必要に応じて導電化材等を混合して正極活物質ペーストを調製する。この正極活物質ペーストを正極集電体上に塗布して正極活物質層を形成させることにより正極を作製する。この正極を用いてリチウム二次電池を構成すればよい。
本発明のリチウム二次電池によると、還元触媒作用をもつ金属が正極に担持されていない点以外は同様の構成を有するリチウム二次電池と比較した場合において、ＳＯＣ５０％の条件で−３０℃における低温出力（Ｗ）を１．５倍以上とすることができ、より好ましい実施態様では１．８倍以上、さらに好ましい態様では２倍以上の低温出力を得ることが可能である。
【００１７】
【発明の実施の形態】
以下、実施例により本発明をさらに具体的に説明する。
【００１８】
（１）リチウム二次電池の作製
正極活物質粉体として平均粒子径１０μｍのニッケル酸リチウムを使用した。また、還元触媒作用をもつ金属としてロジウム（Ｒｈ）を、還元触媒作用をもたない（酸化触媒機能をもつ）金属として白金（Ｐｔ）を使用した。含浸担持法により、上記正極活物質粉体の表面に１〜６００μｇ／ｍ2のＲｈまたはＰｔを担持させた。正極集電体としてのアルミニウム箔に、この金属担持粉体を用いて調製されたペーストを塗布して正極活物質層を作製し、リチウム二次電池用の正極を得た。なお、この正極活物質層には、導電化材としてのカーボンブラックが含有されている。
一方、負極集電体として銅箔、負極活物質としてグラファイトを用いて負極を作製した。また、セパレータとしては多孔質ポリエチレンフィルムを、電解液としては１ｍｏｌ／ＬのＬｉＰＦ6を含むＥＣとＤＥＣとの重量比＝３：７の混合溶媒を用いた。これらの材料を用いてコイン型のリチウム二次電池を構成した。
【００１９】
（２）低温出力の評価
上記により得られたリチウム二次電池をＳＯＣ５０％に調整し、１０秒間出力のＩＶ法により、−３０℃における出力を測定した。その結果を、金属（ＲｈまたはＰｔ）の担持量と低温出力との関係として図１に示す。
図１から判るように、還元触媒活性をもつＲｈを正極に５０μｇ／ｍ2、１００μｇ／ｍ2または５００μｇ／ｍ2担持させたリチウム二次電池では、低温出力が明らかに向上した。これに対して、酸化触媒活性をもつＰｔを担持させた場合には、担持量にかかわらず低温出力の向上効果はみられなかった。
【００２０】
（３）常温出力の評価
上記により得られたリチウム二次電池をＳＯＣ５０％に調整し、１０秒間出力のＩＶ法により、２５℃における出力を測定した。その結果を、金属の担持量と常温出力との関係として図２に示す。
図２から判るように、還元触媒活性をもつＲｈを正極に５０μｇ／ｍ2、１００μｇ／ｍ2または５００μｇ／ｍ2担持させたリチウム二次電池では、常温出力が同等あるいはやや向上した。すなわち、これらの電池によると、常温出力を同等以上に維持しつつ、低温出力を明らかに向上させることができた。一方、酸化触媒活性をもつＰｔを担持した場合には出力の向上効果はみられなかった。
【００２１】
なお、上記実施例ではコイン型のリチウム二次電池を用いて作製したが、本発明はコイン型以外の形状、例えば巻回型のリチウム二次電池にも適用することができる。
【００２２】
【発明の効果】
本発明によると、還元触媒作用をもつ金属が正極に担持されていることにより、常温出力等の常温性能を同等以上に維持しつつ、低温出力等の低温性能を向上させることができる。
【図面の簡単な説明】
【図１】金属の担持量と低温出力との関係を示す特性図である。
【図２】金属の担持量と常温出力との関係を示す特性図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery with improved low-temperature performance such as low-temperature output.
[0002]
[Prior art]
The lithium secondary battery is composed of a lithium-containing oxide or the like as the positive electrode active material, a carbonaceous material or the like as the negative electrode active material, and a nonaqueous electrolytic solution in which a lithium electrolyte is dissolved as the electrolytic solution. Is done. In this lithium secondary battery, lithium ions in the positive electrode active material move to the negative electrode active material side through the electrolytic solution during charging and are occluded. On the other hand, lithium ions released from the negative electrode are discharged from the negative electrode during discharge. Moved to and captured.
[0003]
Since the positive electrode active material used for the lithium secondary battery as described above is generally not a material having a large electrical conductivity, a conductive material such as carbon black is usually added to the powder of the positive electrode active material, The internal resistance of the battery is reduced by improving the electron conductivity in the positive electrode active material layer. Japanese Patent Application Laid-Open No. 11-283612 discloses that the internal resistance is reduced by forming a metal film or fixing metal particles on at least a part of the surface of the positive electrode active material powder, thereby charging and discharging cycles. A lithium secondary battery with improved characteristics and higher output is disclosed. As the metal coating or metal particles, those made of at least one metal among aluminum, titanium, gold and platinum are preferred.
[0004]
[Problems to be solved by the invention]
Incidentally, the internal resistance of the battery is divided into a direct current resistance and a reaction resistance. In the battery reaction at room temperature, the reaction resistance is small, and most of the internal resistance is occupied by DC resistance. The reduction of the internal resistance in the secondary battery described in the above publication is considered to be achieved by the reduction of the direct current resistance accompanying the improvement of the electron conductivity.
On the other hand, when the battery is used at a low temperature (for example, −30 ° C.), most of the internal resistance is occupied by the reaction resistance. Therefore, the effect of improving battery performance at a low temperature, for example, low temperature output, cannot be obtained by improving the electronic conductivity as described in the above publication.
[0005]
An object of the present invention is to provide a lithium secondary battery with improved low-temperature performance such as low-temperature output.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the lithium secondary battery according to
As described above, by supporting the metal having a reduction catalytic action on the positive electrode, the reaction resistance, particularly the internal resistance, is reduced, and the battery performance (for example, low temperature output) at a low temperature is improved. This is presumably due to the improvement of lithium ion mobility at or near the positive electrode and / or the promotion of the lithium ion battery reaction (reduction reaction) at the positive electrode due to the reduction catalytic action of the metal.
[0007]
In the present invention, the metal having the reduction catalytic action is supported on the surface of a powder made of a positive electrode active material (positive electrode active material powder) . In addition, the positive electrode active material layer is formed by a method such as applying a paste obtained by mixing the positive electrode active material powder with a binder and a solvent, and further, if necessary, a conductive material to the positive electrode current collector. Can do. In general, the positive electrode active material powder is a secondary particle formed by agglomerating fine powder of the positive electrode active material (hereinafter also referred to as “positive electrode active material fine powder”). The metal may be supported on the surface.
[0008]
The metal having the reduction catalytic action may be supported on the positive electrode in the form of a metal film, or may be supported in the form of metal fine powder (particles).
When the metal is supported on the surface of the positive electrode active material powder in the form of a film, the metal film may cover the entire surface of each positive electrode active material powder, or may cover only a part of the surface of the powder. Good. When forming the positive electrode active material layer using the positive electrode active material powder supporting the metal, only the positive electrode active material powder supporting the metal may be used, or the positive electrode supporting the metal. You may mix and use active material powder and the positive electrode active material powder which is not carrying | supporting a metal in arbitrary ratios.
[0009]
As a method for forming a film made of the above metal on the surface of the positive electrode active material powder, an evaporation method, a sputtering method, a plasma coating, a plating method, an impregnation supporting method, or the like can be employed. In addition, as a method for fixing the metal particles to the surface of the powder, methods such as thermal plasma coating and mechanical grinding can be used.
[0010]
The amount of the metal having the reduction catalytic action is 15 to 700 μg (hereinafter referred to as “μg / m 2 ”) per 1 m 2 of the surface area of the positive electrode active material, more preferably 30 to 600 μg / m 2 , Preferably it is 50-500 microgram / m < 2 >. When the amount of the metal supported is less than 15 μg / m 2 , the effect of improving the low temperature performance may be insufficient. On the other hand, if the amount of the metal supported exceeds 700 μg / m 2 , battery low performance may be reduced due to factors such as the movement of lithium ions being rather hindered by the presence of the metal. As described above, when the positive electrode active material powder supporting metal and the positive electrode active material powder not supporting metal are mixed and used, the supported amount is used for forming this positive electrode active material layer. The average supported amount with respect to the whole positive electrode active material.
[0011]
As the metal having the reduction catalytic action, only one kind of metal may be used, or an alloy of two or more kinds of metals may be used, or two or more kinds of metals or alloys may be used separately (for example, metal A Or a mixture of a positive electrode active material powder supporting metal B and a positive electrode active material powder supporting metal B may be used. In the present invention, at least one of Rh, Ru and Ir is used as the metal having the reduction catalytic action. Of the noble metals having a reduction catalytic action, it is particularly preferable to use Rh.
[0012]
As the positive electrode active material in the lithium secondary battery of the present invention, it is preferable to use a lithium-containing oxide as described in
[0013]
As an electrolytic solution used in the lithium secondary battery of the present invention, one or more selected from various aprotic solvents used in conventional lithium secondary batteries, for example, ethylene carbonate (EC), propylene carbonate (PC ), Γ-butyrolactone, 1,2-dimethylethane, tetrahydrofuran, 1,3-dioxane, methyl acetate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and the like. As the electrolyte, various lithium salts used in the conventional lithium ion secondary battery, for example LiPF 6, LiBF 4, LiCF 3 SO 3, LiClO 4, LiAsF 6, LiSbF 6, LiC 4 F 9 SO 3, LiN (CF 3 SO 2 ) 2 , SiC (CF 3 SO 2 ) 3 or the like can be used, and among these, LiPF 6 and LiBF 4 are preferable. The electrolyte concentration in the electrolytic solution is usually about 0.05 to 10 mol / L, preferably about 0.1 to 5 mol / L.
[0014]
Other materials constituting the lithium secondary battery of the present invention may be appropriately selected from materials used for conventional lithium secondary batteries. For example, as a current collector for a positive electrode or a negative electrode, a metal foil such as an aluminum foil, a nickel foil, or a copper foil, and as a binder for forming a positive electrode active material layer or a negative electrode active material layer, polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE) or the like can be used. As the negative electrode active material, a carbon material such as amorphous carbon or graphite, or an alloy or oxide of Li and a metal such as Si, Sn, or In can be used. Alternatively, metallic lithium may be used as the negative electrode.
[0015]
In the formation of the positive electrode active material layer, carbon black, graphite, pitch coke, or the like can be used as a conductive material. As long as sufficient electron conductivity can be secured in the positive electrode active material layer, the positive electrode active material layer may not contain a conductive material. In addition, for the purpose of increasing the electron conductivity of the positive electrode active material layer, a metal that does not have a reduction catalytic action on the positive electrode active material layer in combination with the conductive material or the like or instead of the conductive material. May be included. The metal having no reduction catalytic action may be used by simply mixing with the positive electrode active material powder, or may be used as a metal film formed on the surface of the positive electrode active material powder. It may be used as metal particles fixed to the body. Preferable examples of the metal having no reduction catalytic action include one or more selected from aluminum, titanium, gold, platinum and the like.
[0016]
Among the lithium secondary batteries of the present invention, a battery in which a metal having a reduction catalytic action is supported on the surface of the positive electrode active material powder can be produced, for example, by the following method. That is, a positive active material paste is prepared by supporting a metal having a reduction catalytic action on the surface of the positive electrode active material powder, and then mixing a binder, a solvent, and a conductive material, if necessary, with the metal supported positive electrode active material powder. To prepare. This positive electrode active material paste is applied onto a positive electrode current collector to form a positive electrode active material layer, thereby producing a positive electrode. What is necessary is just to comprise a lithium secondary battery using this positive electrode.
According to the lithium secondary battery of the present invention, when compared with a lithium secondary battery having the same configuration except that a metal having a reduction catalytic action is not supported on the positive electrode, the temperature is −30 ° C. under the condition of
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described more specifically with reference to examples.
[0018]
(1) Production of Lithium Secondary Battery Lithium nickelate having an average particle size of 10 μm was used as the positive electrode active material powder. Further, rhodium (Rh) was used as a metal having a reduction catalytic action, and platinum (Pt) was used as a metal having no reduction catalytic action (having an oxidation catalytic function). By the impregnation supporting method, 1 to 600 μg / m 2 of Rh or Pt was supported on the surface of the positive electrode active material powder. A paste prepared using this metal-supported powder was applied to an aluminum foil as a positive electrode current collector to produce a positive electrode active material layer, thereby obtaining a positive electrode for a lithium secondary battery. The positive electrode active material layer contains carbon black as a conductive material.
On the other hand, a negative electrode was produced using copper foil as the negative electrode current collector and graphite as the negative electrode active material. Further, a porous polyethylene film was used as the separator, and a mixed solvent of EC / DEC containing 1 mol / L LiPF 6 and a weight ratio of 3: 7 was used as the electrolyte. A coin-type lithium secondary battery was constructed using these materials.
[0019]
(2) Evaluation of low-temperature output The lithium secondary battery obtained as described above was adjusted to
As can be seen from FIG. 1, in the lithium secondary battery in which Rh having reduction catalytic activity is supported on the positive electrode at 50 μg / m 2 , 100 μg / m 2 or 500 μg / m 2 , the low-temperature output is clearly improved. On the other hand, when Pt having oxidation catalyst activity was supported, the effect of improving the low temperature output was not seen regardless of the amount supported.
[0020]
(3) Evaluation of normal temperature output The lithium secondary battery obtained as described above was adjusted to 50% SOC, and the output at 25 ° C. was measured by the IV method of output for 10 seconds. The result is shown in FIG. 2 as the relationship between the metal loading and the room temperature output.
As can be seen from FIG. 2, in the lithium secondary battery in which Rh having reduction catalytic activity is supported on the positive electrode at 50 μg / m 2 , 100 μg / m 2, or 500 μg / m 2 , the normal temperature output is equivalent or slightly improved. That is, according to these batteries, the low temperature output could be clearly improved while maintaining the normal temperature output equal to or higher than that. On the other hand, when Pt having oxidation catalyst activity was supported, no effect of improving the output was observed.
[0021]
In the above embodiment, a coin-type lithium secondary battery is used. However, the present invention can be applied to shapes other than the coin-type, for example, a wound-type lithium secondary battery.
[0022]
【The invention's effect】
According to the present invention, since the metal having a reduction catalytic action is supported on the positive electrode, the low temperature performance such as the low temperature output can be improved while maintaining the normal temperature performance such as the normal temperature output equal to or higher.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing the relationship between the amount of metal carried and low-temperature output.
FIG. 2 is a characteristic diagram showing the relationship between the amount of metal carried and normal temperature output.
Claims (2)
上記還元触媒作用をもつ金属は、上記正極活物質層を構成する正極活物質粉体の表面に担持されており、
上記還元触媒作用をもつ金属の担持量は、正極活物質の表面積１ｍ２あたり１５〜７００μｇであり、
上記還元触媒作用をもつ金属はＲｈ、ＲｕおよびＩｒの少なくとも一種であることを特徴とするリチウム二次電池。A lithium secondary battery in which a metal having a reduction catalytic action is supported on a positive electrode,
The metal having the reduction catalytic action is supported on the surface of the positive electrode active material powder constituting the positive electrode active material layer,
The amount of the metal having the reduction catalytic action is 15 to 700 μg per 1 m 2 of the surface area of the positive electrode active material,
The lithium secondary battery, wherein the metal having a reduction catalytic action is at least one of Rh, Ru, and Ir.
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