JP4291901B2

JP4291901B2 - Organic electrolyte battery

Info

Publication number: JP4291901B2
Application number: JP24565698A
Authority: JP
Inventors: 誠筒江; 一成木下; 明子石田; 賢西村; 信夫江田
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1998-02-18
Filing date: 1998-08-31
Publication date: 2009-07-08
Anticipated expiration: 2018-08-31
Also published as: JPH11307101A

Description

【０００１】
【発明の属する技術分野】
本発明は、有機電解質電池、特に電極およびセパレータが有機電解液を吸収保持するポリマーを含み、電極とセパレータが熱融着により一体化できる有機電解質二次電池に関するものである。
【０００２】
【従来の技術】
近年、携帯電話やノート型コンピューター等の携帯機器の普及に伴い、小型、軽量で、高エネルギー密度の二次電池が切望されている。このような要望に応えるために、各種二次電池の開発が進められている。リチウムを負極活物質とするリチウム二次電池は、高エネルギー密度が期待できることから注目されている。なかでも正極、負極およびセパレータ部分にポリマーを含み、このポリマーに有機電解液を吸収保持させた、いわゆるポリマー電解質二次電池が注目されている。
このポリマー電解質二次電池は、ポリマーとしてフッ化ビニリデンと六フッ化プロピレンの共重合体を用い、正極、セパレータおよび負極を熱融着により一体化できることから、薄型電池の実用化に最も近い電池系として注目されている（特表平８−５０７４０７号公報）。
【０００３】
上記ポリマー電解質二次電池は、たとえば、次のようにして製造される。まず、コバルト酸リチウムや球状黒鉛粒子などの電極活物質粉末と導電剤粉末の混合物に、ポリマーの有機溶媒溶液と造孔剤のフタル酸ジ−ｎ−ブチルを添加してペーストを調製する。このペーストを集電体に塗着した後、乾燥し前記有機溶媒を除去して電極シートを得る。こうして得られた正極シートと負極シートとの間に、造孔剤を含むポリマーのシートからなるセパレータシートを介在させ、加熱下で加圧することにより熱融着一体化して電池素子シートを得る。次いで、この電池素子シートをたとえば抽出溶媒のジエチルエーテル中に浸漬して造孔剤を抽出除去して多孔性化し、しかる後細孔部分とポリマー自身に有機電解液を含浸させる。
【０００４】
【発明が解決しようとする課題】
上記のようにして得られるポリマー電解質電池の容量密度は、電極中のポリマーの配合割合および電極の多孔度に大きく左右される。すなわち、電極中のポリマーの割合が高ければ活物質の量が相対的に減少するし、ポリマーの割合が低ければ電極強度が低下する。上記の電極材料のペーストを集電体に塗着した後、圧延するなどにより活物質の充填密度を上げるのが好ましい。しかし、ポリマーの割合が高くなるとゴム状になり、十分に圧延することができなくなる。さらに、電極の集電体としてラス板などを用いると、圧延するときに集電体も一緒に延びて甚だしいときには集電体が引きちぎられるなどにより、活物質の充填密度を上げることができない。また、ポリマーの割合が少ないと、電極とセパレータとを一体に熱融着することができず、電極とセパレータとの間に隙間ができ、電池の内部抵抗が高くなり、安定した電池性能が得られない。従って、従来においては、電極の活物質混合物層のポリマー含量は２０重量％程度が適切とされていた。
【０００５】
本発明は、以上に鑑み、電極中のポリマー含量を適切に設定することにより、容量密度の大きいポリマー電解質電池を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明の有機電解質電池は、電解液を吸収保持するポリマーを含む活物質混合物層と活物質混合物層を支持する集電体からなる正、負の電極、電解液を吸収保持するポリマーからなる多孔性のセパレータ、並びに前記両電極およびセパレータに吸収保持された有機電解液を具備し、前記正、負の電極と前記セパレータとが熱融着により一体化されており、前記正極の活物質混合物層のポリマー含量が５〜１０重量％、前記負極の活物質混合物層のポリマー含量が７〜１６重量％であることを特徴とする。
ここにおいて、正極の活物質混合物層のポリマー含量は５〜７重量％、負極の活物質混合物層のポリマー含量は９〜１２重量％の範囲にあることがより好ましい。
【０００７】
【発明の実施の形態】
本発明者らは、活物質混合物層中のポリマーの配合割合を従来より削減して、なおかつ電極およびセパレータを一体に熱融着することができ、安定した性能を発揮できる条件を探索した結果、上記のように正極および負極における活物質混合物層の各ポリマー含量の最適値において活物質の充填密度および放電性能の優れた電池が得られることを見いだした。なお、このポリマー含量の算出には電解質を含めないものとする。
本発明によるポリマー電解質電池の電極は、以下のようにして作製することが好ましい。まず、電極活物質粉末、必要に応じて加える導電剤粉末、ポリマーの有機溶媒溶液および造孔剤を混合してペーストを調製する。このペーストを集電体に塗着し乾燥した後、加圧ローラーにより圧延し、所定の寸法に切断して電極シートを得る。セパレータは、造孔剤を含むポリマーのシートとして用意する。そして、このようにして得られた電極およびセパレータのシート状態で、または正極、負極およびセパレータを一体に熱融着して電池素子に組み立てた状態において、造孔剤を抽出することによりポリマー部分に電解液を浸透保持させる細孔を形成する。
【０００８】
このような製造方法により得られる電極の性能は、活物質混合物層の多孔度によっても影響される。活物質混合物層の多孔度は、前記の加圧ローラーによる圧延の度合い、およびポリマーに対する造孔剤の添加割合によって調整することができる。造孔剤によって定まる多孔度は、電解液をポリマー部分に浸透保持させるための最低限のものであるから、活物質に対するポリマーの配合量が決まれば、ポリマーに対する最適な造孔剤の添加割合は自ずから決まる。
ここで、活物質混合物層の多孔度は、（活物質混合物層の空間部分の総体積）／（活物質混合物層の総体積）×１００（％）で表される。
本発明は、以上の観点から以下の実施例に示すように、電極を構成する活物質量を一定とし、ポリマーと造孔剤との比を一定としながらポリマーの量を変えて得られる電極の充填密度、同電極を用いた電池の放電容量、内部抵抗などから最適なポリマー含量を決定した。なお、ポリマーに対する造孔剤の重量比は、１〜２倍の範囲が好ましい。
【０００９】
本発明の電極およびセパレータに用いるポリマーは、フッ化ビニリデンと六フッ化プロピレンとの共重合体、また造孔剤はフタル酸ージ−ｎーブチルがそれぞれ好適であるが、これらに限定されるものではない。
正極活物質としては、ＬｉＣｏＯ₂、ＬｉＮｉＯ₂、ＬｉＭｎ₂Ｏ₄など充放電によりリチウムイオンを可逆的に出し入れできる化合物、特に遷移金属含有リチウム酸化物が用いられる。また、負極活物質としては、充放電によりリチウムイオンを可逆的に出し入れできる炭素材料、なかでも炭素質メソフェーズ粒体を炭素化および黒鉛化して得られた球状黒鉛粒子が好適に用いられる。
【００１０】
正極の集電体には、アルミニウム、チタン、ステンレス鋼などの箔、穴あき板、ラス板、網体など、また負極の集電体には、銅、ステンレス鋼などの箔、穴あき板、ラス板、網体などがそれぞれ用いられる。セルを多層に積層する構成をとるときは、穴あき板などの多孔板を用いるのが好ましい。
有機電解液には、ＬｉＣｌＯ₄、ＬｉＢＦ₄、ＬｉＰＦ₆、ＬｉＣＦ₃ＳＯ₃など溶質とエチレンカーボネート、プロピレンカーボネート、ジメトキシエタンなどの有機溶媒との組み合わせなど、有機電解質電池に用いるものとして知られているもののなかから適宜選択して用いられる。
【００１１】
本発明の好適な実施形態において、ポリマーはフッ化ビニリデンと六フッ化プロピレンとの共重合体であり、電極の活物質混合物中にはカーボンブラックなどの炭素質導電剤を含み、活物質混合物はポリマー含量が５〜１６重量％、多孔度が３０〜６０％である。
正極活物質に上記のような酸化物を用いた場合、正極活物質混合物層中のポリマー含量は５〜１０重量％、多孔度は４０〜５５％がより好ましい。一方、負極は、前記のような球状黒鉛粒子を活物質に用いた場合、活物質混合物層中のポリマー含量は７〜１６重量％、多孔度は３５〜４５％がより好ましい。
【００１２】
【実施例】
以下、本発明をその実施例により詳細に説明する。
《実施例１》
フッ化ビニリデンと六フッ化プロピレンとの共重合体（六フッ化プロピレンの比率：１２重量％）（以下、Ｐ（ＶＤＦ−ＨＦＰ）で表す。）１００ｇをアセトン５００ｇに溶解し、その溶液にフタル酸ージ−ｎーブチル（以下、ＤＢＰで表す。）１５０ｇを添加して混合溶液を得た。この溶液をガラス板上に塗布した後、乾燥してアセトンを除去し、厚さ５０μｍのシートを得た。このシートを切断し、サイズ３５ｍｍ×６５ｍｍのセパレータシートとした。
一方、Ｐ（ＶＤＦ−ＨＦＰ）９０ｇをアセトン１５００ｇに溶解した溶液に、コバルト酸リチウムＬｉＣｏＯ₂９００ｇ、アセチレンブラック５０ｇ、およびＤＢＰ１３５ｇを混合してペーストを調製した。このペーストを集電体のアルミニウムのラス板の片面に塗着し乾燥した後、ロールプレスにより圧延した。こうして厚さ１００μｍのシートを得た。このシートを切断し、サイズ３０ｍｍ×６０ｍｍの正極シートとした。
【００１３】
Ｐ（ＶＤＦ−ＨＦＰ）１２０ｇをアセトン１０００ｇに溶解した溶液に、炭素質メソフェーズ粒体を炭素化および黒鉛化して得られた平均粒径６μｍの球状黒鉛粒子（大阪ガス製）７５０ｇ、導電剤の黒鉛繊維（大阪ガス製）６０ｇ、およびＤＢＰ１８０ｇを混合してペーストを得た。ここに用いた黒鉛繊維は、気相成長法により得た炭素繊維を黒鉛化したものである。このペーストを集電体の銅のラス板の両面に塗着し乾燥した後、ロールプレスにより圧延した。こうして厚さ３００μｍのシートを得た。このシートを切断し、サイズ３０ｍｍ×６０ｍｍの負極シートとした。
なお、上記の正極および負極の集電体は、あらかじめ表面に導電性炭素皮膜を形成したものを用いた。この導電性炭素皮膜は、ポリフッ化ビニリデンのＮーメチルピロリドン溶液（濃度１２重量％）にアセチレンブラックを分散した分散液を集電体表面に塗布した後、８０℃以上の温度で乾燥して形成した。
【００１４】
上記のようにして得た負極シートの両面に、それぞれセパレータシートを介して正極シートを配し、１２０℃に加熱された二本の加圧ローラー間をとおして加圧することにより一体に熱融着して電池素子を得た。この電池素子は、次にジエチルエーテル中に浸漬することによりＤＢＰを抽出除去してポリマー部分を多孔性化した後、５０℃で真空乾燥し、次いで電解液中に浸漬して電極およびセパレータ中の細孔内およびポリマー自身に電解液を含浸保持させた。電解液には、エチレンカーボネートとメチルカーボネートの体積比１：３の混合溶媒に六フッ化リン酸リチウムＬｉＰＦ₆を１モル／ｌの割合で溶解したものである。
このようにして調製した電池素子を、絶縁性樹脂フィルムの中間にアルミニウムフィルムを配したラミネートフィルムで外装して厚さ０．６ｍｍ、大きさ３５ｍｍ×６０ｍｍの電池を得た。
この電池の正極活物質混合物層のポリマー含量（電解液は含めない）は８．７重量％、負極のそれは１２．９重量％であった。
【００１５】
《実施例２》
負極およびセパレータシートは実施例１と同じとし、正極活物質混合物層のポリマーＰ（ＶＤＦ−ＨＦＰ）の量を変えて同様に電池を作製した。ただし、正極活物質のコバルト酸リチウムと導電剤のアセチレンブラックの量は実施例１と同じとし、ＤＢＰの量はＰ（ＶＤＦ−ＨＦＰ）に対する比を一定（１．５倍）とした。これらをＡ群電池という。
【００１６】
《実施例３》
正極およびセパレータシートは実施例１と同じとし、負極活物質混合物層のポリマーＰ（ＶＤＦ−ＨＦＰ）の量を変えて同様に電池を作製した。ただし、負極活物質の球状黒鉛粒子と導電剤の黒鉛繊維の量は実施例１と同じとし、ＤＢＰの量はＰ（ＶＤＦ−ＨＦＰ）に対する比を一定（１．５倍）とした。これらをＢ群電池という。
【００１７】
これらの電極、および電池について特性を比較した結果を以下に説明する。
まず、正極のポリマー含量と活物質層の充填密度との関係を図１に示す。また、負極のポリマー含量と活物質層の充填密度との関係を図２に示す。
次に、ポリマー含量が２、５、７、１０、１５、および２５重量％の正極、およびポリマー含量が５、７、１０、１２、１５、１６および２５重量％の負極について、電極シートを作製する際の電極板の伸び率をそれぞれ図３および図４に示す。
これらの図から明らかなように、正極、負極ともポリマー含量の増加とともに活物質混合物層の充填密度が低下している。また、ポリマー含量の増加により電極を加圧したときの伸び率が大きくなっている。これは、活物質の充填密度を上げるための加圧操作の際、ポリマー含量が多いとポリマーの性質であるゴム状性状が顕著になり、加圧により活物質混合物層が十分加圧されて薄型化する前に集電体が伸びてしまうためである。従って、ポリマー含量が多いと、電極の製造上においても電極の薄型化が困難となり、充填密度が上がらなくなる。
【００１８】
次に、Ａ群電池を放電レート０．２Ｃで終止電圧３．０Ｖまで放電して放電容量を求めた。その結果を図５に示す。同様にＢ群電池について試験した結果を図６に示す。
また、Ａ群電池およびＢ群電池の内部抵抗を交流インピーダンス法（１ＫＨｚ）によって測定した。その結果をそれぞれ図７および図８に示す。
これらの図から明らかなように、正極、負極ともにポリマー含量の増加により電池としての放電容量は低下している。これは、活物質量が一定であるにもかかわらず導電性を持たないポリマーの割合が多くなるためである。ただし、ポリマー含量が低いと、放電容量は大きくともばらつきが大きく放電特性は不安定であり、なかには放電できないものもあった。
【００１９】
電池の内部抵抗を基準にすると、活物質混合物層の最適なポリマー含量は、従来の２０重量％に比べてかなり低いところにあることがわかる。すなわち、内部抵抗が低いところの好ましいポリマー含量は、正極では５〜１０重量％、負極では７〜１６重量％の範囲である。導電性を持たないポリマーの割合が多いところでは電池の内部抵抗が高くなり、ポリマーの割合が少ないところでは電極とセパレータの熱融着が十分できないため、電極とセパレータとの間に隙間が生じていまい、内部抵抗が高くなる。このため、安定した性能が得られず、甚だしい場合は放電できないこともある。
これらの結果より、正極活物質混合物層中のポリマー含量を５〜１０重量％、負極活物質混合物層中のポリマー含量を７〜１６重量％としたとき性能の良い電池が得られ、正極活物質混合物層中のポリマー含量を５〜７重量％、負極活物質混合物層中のポリマー含量を７〜１２重量％としたときより良い性能の電池が得られる。正極活物質混合物層中のポリマー含量を７重量％、負極活物質混合物層中のそれを１０重量％としたとき最も良い性能の電池が得られる。
【００２０】
【発明の効果】
以上のように、本発明によれば、電極の活物質混合物層のポリマーの含量を適切にすることにより、容量密度の大きいポリマー電解質電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例におけるポリマー電解質電池用正極のポリマー含量と充填密度との関係を示す図である。
【図２】同負極のポリマー含量と充填密度との関係を示す図である。
【図３】ポリマー含量の異なる正極を製造する際の電極の厚みと伸び率との関係を示す図である。
【図４】ポリマー含量の異なる負極を製造する際の電極の厚みと伸び率との関係を示す図である。
【図５】正極のポリマー含量と電池の放電容量との関係を示す図である。
【図６】負極のポリマー含量と電池の放電容量との関係を示す図である。
【図７】正極のポリマー含量と電池の内部抵抗との関係を示す図である。
【図８】負極のポリマー含量と電池の内部抵抗との関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electrolyte battery, and more particularly to an organic electrolyte secondary battery in which an electrode and a separator contain a polymer that absorbs and holds an organic electrolyte, and the electrode and the separator can be integrated by heat fusion.
[0002]
[Prior art]
In recent years, with the widespread use of portable devices such as mobile phones and notebook computers, secondary batteries that are small, lightweight, and have high energy density are desired. In order to meet such demands, various secondary batteries are being developed. Lithium secondary batteries that use lithium as a negative electrode active material are attracting attention because they can be expected to have a high energy density. In particular, a so-called polymer electrolyte secondary battery in which a polymer is contained in the positive electrode, the negative electrode, and the separator portion and an organic electrolyte solution is absorbed and held in the polymer has attracted attention.
This polymer electrolyte secondary battery uses a copolymer of vinylidene fluoride and propylene hexafluoride as a polymer, and the positive electrode, separator, and negative electrode can be integrated by thermal fusion. (Japanese Patent Publication No. 8-507407).
[0003]
The polymer electrolyte secondary battery is manufactured, for example, as follows. First, a paste is prepared by adding a polymer organic solvent solution and a pore-forming agent di-n-butyl phthalate to a mixture of electrode active material powder such as lithium cobaltate and spherical graphite particles and conductive agent powder. The paste is applied to a current collector and then dried to remove the organic solvent to obtain an electrode sheet. A separator sheet made of a polymer sheet containing a pore-forming agent is interposed between the positive electrode sheet and the negative electrode sheet thus obtained, and heat fusion is integrated by applying pressure under heating to obtain a battery element sheet. Next, this battery element sheet is immersed in, for example, diethyl ether as an extraction solvent to extract and remove the pore-forming agent to make it porous. Thereafter, the pore portion and the polymer itself are impregnated with an organic electrolyte.
[0004]
[Problems to be solved by the invention]
The capacity density of the polymer electrolyte battery obtained as described above greatly depends on the blending ratio of the polymer in the electrode and the porosity of the electrode. That is, if the polymer ratio in the electrode is high, the amount of the active material is relatively decreased, and if the polymer ratio is low, the electrode strength is decreased. It is preferable to increase the packing density of the active material by, for example, rolling the electrode material paste after applying the paste to the current collector. However, when the ratio of the polymer becomes high, it becomes rubbery and cannot be sufficiently rolled. Furthermore, when a lath plate or the like is used as the current collector of the electrode, the current collector also extends together when rolling, and the current collector is torn off when it is severe, so the packing density of the active material cannot be increased. In addition, when the polymer ratio is small, the electrode and the separator cannot be thermally fused together, a gap is formed between the electrode and the separator, the internal resistance of the battery is increased, and stable battery performance is obtained. I can't. Therefore, conventionally, the polymer content of the active material mixture layer of the electrode is appropriately about 20% by weight.
[0005]
In view of the above, an object of the present invention is to provide a polymer electrolyte battery having a large capacity density by appropriately setting the polymer content in an electrode.
[0006]
[Means for Solving the Problems]
The organic electrolyte battery of the present invention includes an active material mixture layer containing a polymer that absorbs and holds an electrolytic solution, and a positive and negative electrode comprising a current collector that supports the active material mixture layer, and a porous material comprising a polymer that absorbs and holds an electrolytic solution. Active separator, and the positive electrode active material mixture layer , wherein the positive electrode and the negative electrode are integrated by thermal fusion. The polymer content is 5 to 10% by weight, and the polymer content of the active material mixture layer of the negative electrode is 7 to 16% by weight.
Here, the polymer content of the active material mixture layer of the positive electrode is more preferably 5 to 7% by weight, and the polymer content of the active material mixture layer of the negative electrode is more preferably 9 to 12% by weight.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
As a result of searching for conditions under which the blending ratio of the polymer in the active material mixture layer can be reduced as compared with the conventional method, and the electrode and the separator can be integrally heat-sealed, and stable performance can be exhibited. As described above, it has been found that a battery having an excellent active material packing density and discharge performance can be obtained at an optimum value of each polymer content of the active material mixture layer in the positive electrode and the negative electrode. In addition, the electrolyte content is not included in the calculation of the polymer content.
The electrode of the polymer electrolyte battery according to the present invention is preferably produced as follows. First, a paste is prepared by mixing an electrode active material powder, a conductive agent powder added if necessary, an organic solvent solution of a polymer, and a pore former. The paste is applied to a current collector and dried, then rolled with a pressure roller, and cut into a predetermined size to obtain an electrode sheet. The separator is prepared as a polymer sheet containing a pore-forming agent. And in the sheet state of the electrode and separator obtained in this way, or in the state where the positive electrode, the negative electrode and the separator are integrally heat-sealed and assembled into a battery element, the pore former is extracted into the polymer part. Fine pores that permeate and hold the electrolyte are formed.
[0008]
The performance of the electrode obtained by such a manufacturing method is also influenced by the porosity of the active material mixture layer. The porosity of the active material mixture layer can be adjusted by the degree of rolling by the pressure roller and the ratio of the pore former added to the polymer. Since the porosity determined by the pore-forming agent is the minimum for allowing the electrolytic solution to permeate and maintain the polymer part, once the amount of polymer to be blended with the active material is determined, the optimum addition ratio of the pore-forming agent to the polymer is It is decided by itself.
Here, the porosity of the active material mixture layer is expressed by (total volume of the space portion of the active material mixture layer) / (total volume of the active material mixture layer) × 100 (%).
From the above viewpoint, as shown in the following examples, the present invention provides an electrode obtained by changing the amount of the polymer while keeping the amount of the active material constituting the electrode constant and keeping the ratio of the polymer and the pore former constant. The optimum polymer content was determined from the packing density, the discharge capacity of the battery using the same electrode, the internal resistance, and the like. The weight ratio of the pore forming agent to the polymer is preferably in the range of 1 to 2 times.
[0009]
The polymer used for the electrode and separator of the present invention is preferably a copolymer of vinylidene fluoride and propylene hexafluoride, and the pore-forming agent is preferably phthalate-di-n-butyl, but is not limited thereto. is not.
As the positive electrode active material, a compound such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ that can reversibly take in and out lithium ions by charging / discharging, in particular, a transition metal-containing lithium oxide is used. Further, as the negative electrode active material, a carbon material capable of reversibly taking in and out lithium ions by charging / discharging, particularly spherical graphite particles obtained by carbonizing and graphitizing carbonaceous mesophase particles is preferably used.
[0010]
The current collector of the positive electrode is a foil, holed plate, lath plate, net, etc. of aluminum, titanium, stainless steel, etc. The current collector of the negative electrode is a foil, holed plate of copper, stainless steel, etc. A lath plate, a net, or the like is used. When taking a configuration in which cells are laminated in multiple layers, it is preferable to use a porous plate such as a perforated plate.
Organic electrolytes are known for use in organic electrolyte batteries, such as combinations of solutes such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ and organic solvents such as ethylene carbonate, propylene carbonate, and dimethoxyethane. It is appropriately selected from those used.
[0011]
In a preferred embodiment of the present invention, the polymer is a copolymer of vinylidene fluoride and propylene hexafluoride, the electrode active material mixture includes a carbonaceous conductive agent such as carbon black, and the active material mixture is The polymer content is 5 to 16% by weight and the porosity is 30 to 60%.
When the above oxide is used for the positive electrode active material, the polymer content in the positive electrode active material mixture layer is more preferably 5 to 10% by weight, and the porosity is more preferably 40 to 55%. On the other hand, in the negative electrode, when the above spherical graphite particles are used as the active material, the polymer content in the active material mixture layer is more preferably 7 to 16% by weight and the porosity is more preferably 35 to 45%.
[0012]
【Example】
Hereinafter, the present invention will be described in detail by examples.
Example 1
100 g of a copolymer of vinylidene fluoride and propylene hexafluoride (ratio of propylene hexafluoride: 12% by weight) (hereinafter referred to as P (VDF-HFP)) is dissolved in 500 g of acetone, and phthalate is added to the solution. 150 g of acid-di-n-butyl (hereinafter referred to as DBP) was added to obtain a mixed solution. This solution was applied on a glass plate and then dried to remove acetone, thereby obtaining a sheet having a thickness of 50 μm. This sheet was cut into a separator sheet having a size of 35 mm × 65 mm.
On the other hand, a solution prepared by dissolving 90 g of P (VDF-HFP) in 1500 g of acetone was mixed with 900 g of lithium cobaltate LiCoO ₂ , 50 g of acetylene black, and 135 g of DBP to prepare a paste. This paste was applied to one side of an aluminum lath plate as a current collector, dried, and then rolled by a roll press. Thus, a sheet having a thickness of 100 μm was obtained. This sheet was cut into a positive electrode sheet having a size of 30 mm × 60 mm.
[0013]
750 g of spherical graphite particles (manufactured by Osaka Gas) having an average particle diameter of 6 μm obtained by carbonizing and graphitizing carbonaceous mesophase granules in a solution of 120 g of P (VDF-HFP) in 1000 g of acetone, graphite as a conductive agent A paste was obtained by mixing 60 g of fibers (manufactured by Osaka Gas) and 180 g of DBP. The graphite fiber used here is a graphitized carbon fiber obtained by a vapor phase growth method. This paste was applied to both sides of a copper lath plate as a current collector, dried, and then rolled by a roll press. A sheet having a thickness of 300 μm was thus obtained. This sheet was cut into a negative electrode sheet having a size of 30 mm × 60 mm.
In addition, as the current collector for the positive electrode and the negative electrode, those having a conductive carbon film formed on the surface in advance were used. This conductive carbon film is formed by applying a dispersion of acetylene black dispersed in an N-methylpyrrolidone solution of polyvinylidene fluoride (concentration: 12% by weight) to the surface of the current collector and then drying at a temperature of 80 ° C. or higher. did.
[0014]
A positive electrode sheet is disposed on both sides of the negative electrode sheet obtained as described above via a separator sheet, and heat is integrally fused by applying pressure between two pressure rollers heated to 120 ° C. Thus, a battery element was obtained. This battery element is then immersed in diethyl ether to extract and remove DBP to make the polymer part porous, and then vacuum-dried at 50 ° C., and then immersed in an electrolytic solution to saturate the electrode and separator. The electrolyte solution was impregnated and held in the pores and in the polymer itself. The electrolytic solution is obtained by dissolving lithium hexafluorophosphate LiPF ₆ at a ratio of 1 mol / l in a mixed solvent of ethylene carbonate and methyl carbonate in a volume ratio of 1: 3.
The battery element thus prepared was packaged with a laminate film in which an aluminum film was placed in the middle of the insulating resin film to obtain a battery having a thickness of 0.6 mm and a size of 35 mm × 60 mm.
The polymer content (not including the electrolyte) of the positive electrode active material mixture layer of this battery was 8.7% by weight, and that of the negative electrode was 12.9% by weight.
[0015]
Example 2
The negative electrode and the separator sheet were the same as those in Example 1, and batteries were similarly produced by changing the amount of polymer P (VDF-HFP) in the positive electrode active material mixture layer. However, the amount of lithium cobalt oxide as the positive electrode active material and the amount of acetylene black as the conductive agent were the same as those in Example 1, and the amount of DBP was constant (1.5 times) with respect to P (VDF-HFP). These are called Group A batteries.
[0016]
Example 3
The positive electrode and the separator sheet were the same as those in Example 1, and batteries were similarly produced by changing the amount of polymer P (VDF-HFP) in the negative electrode active material mixture layer. However, the amount of spherical graphite particles of the negative electrode active material and the amount of graphite fiber of the conductive agent were the same as in Example 1, and the amount of DBP was constant (1.5 times) with respect to P (VDF-HFP). These are called group B batteries.
[0017]
The results of comparing the characteristics of these electrodes and batteries will be described below.
First, FIG. 1 shows the relationship between the polymer content of the positive electrode and the packing density of the active material layer. FIG. 2 shows the relationship between the polymer content of the negative electrode and the packing density of the active material layer.
Next, electrode sheets were prepared for the positive electrode having a polymer content of 2, 5, 7, 10, 15, and 25% by weight and the negative electrode having a polymer content of 5, 7, 10, 12, 15, 16, and 25% by weight. FIG. 3 and FIG. 4 show the elongation percentage of the electrode plate at the time.
As is clear from these figures, the packing density of the active material mixture layer decreases with increasing polymer content in both the positive electrode and the negative electrode. Moreover, the elongation rate when the electrode is pressurized increases due to the increase in the polymer content. This is because the rubber-like property that is a property of the polymer becomes noticeable when the polymer content is large during the pressurizing operation for increasing the packing density of the active material, and the active material mixture layer is sufficiently pressed by the pressurization and thin. This is because the current collector stretches before it is converted. Therefore, when the polymer content is large, it is difficult to make the electrode thin in manufacturing the electrode, and the packing density cannot be increased.
[0018]
Next, the group A batteries were discharged at a discharge rate of 0.2 C to a final voltage of 3.0 V to determine the discharge capacity. The result is shown in FIG. Similarly, the results of testing for the group B battery are shown in FIG.
Moreover, the internal resistance of the A group battery and the B group battery was measured by the alternating current impedance method (1 KHz). The results are shown in FIGS. 7 and 8, respectively.
As is clear from these figures, the discharge capacity as a battery is reduced due to an increase in the polymer content in both the positive electrode and the negative electrode. This is because the proportion of the polymer that does not have conductivity even though the amount of the active material is constant increases. However, when the polymer content is low, even if the discharge capacity is large, the variation is large and the discharge characteristics are unstable, and there are some that cannot be discharged.
[0019]
Based on the internal resistance of the battery, it can be seen that the optimum polymer content of the active material mixture layer is considerably lower than the conventional 20% by weight. That is, the preferred polymer content where the internal resistance is low is in the range of 5 to 10% by weight for the positive electrode and 7 to 16% by weight for the negative electrode. Where there is a large proportion of non-conductive polymer, the internal resistance of the battery is high, and where there is a small amount of polymer, the electrode and the separator cannot be sufficiently heat-sealed, so there is a gap between the electrode and the separator. The internal resistance becomes high. For this reason, stable performance cannot be obtained, and discharge may not be possible in severe cases.
From these results, when the polymer content in the positive electrode active material mixture layer is 5 to 10% by weight and the polymer content in the negative electrode active material mixture layer is 7 to 16% by weight, a battery having good performance can be obtained. When the polymer content in the mixture layer is 5 to 7% by weight and the polymer content in the negative electrode active material mixture layer is 7 to 12% by weight, a battery with better performance can be obtained. When the polymer content in the positive electrode active material mixture layer is 7% by weight and that in the negative electrode active material mixture layer is 10% by weight, the battery with the best performance can be obtained.
[0020]
【The invention's effect】
As described above, according to the present invention, a polymer electrolyte battery having a large capacity density can be provided by making the content of the polymer in the active material mixture layer of the electrode appropriate.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between a polymer content and a packing density of a positive electrode for a polymer electrolyte battery in an example of the present invention.
FIG. 2 is a graph showing the relationship between polymer content and packing density of the negative electrode.
FIG. 3 is a graph showing the relationship between the thickness of an electrode and the elongation when manufacturing positive electrodes with different polymer contents.
FIG. 4 is a diagram showing the relationship between the thickness of an electrode and the elongation when producing negative electrodes with different polymer contents.
FIG. 5 is a graph showing the relationship between the polymer content of the positive electrode and the discharge capacity of the battery.
FIG. 6 is a graph showing the relationship between the polymer content of the negative electrode and the discharge capacity of the battery.
FIG. 7 is a graph showing the relationship between the polymer content of the positive electrode and the internal resistance of the battery.
FIG. 8 is a graph showing the relationship between the polymer content of the negative electrode and the internal resistance of the battery.

Claims

An active material mixture layer containing a polymer that absorbs and holds an organic electrolyte solution, a positive and negative electrode made of a current collector that supports the active material mixture layer, a porous separator made of a polymer that absorbs and holds an organic electrolyte solution, and The positive electrode and the negative electrode and the separator are integrated by thermal fusion, and the polymer content of the active material mixture layer of the positive electrode is 5 to 5. 10% by weight, and the polymer content of the negative electrode active material mixture layer is 7 to 16% by weight.

A positive electrode comprising an active material mixture layer containing a polymer that absorbs and holds an organic electrolyte and a transition metal-containing lithium oxide, and a current collector that supports the active material mixture layer, a polymer that absorbs and holds an organic electrolyte, and lithium ions by charge and discharge An active material mixture layer containing a carbon material capable of entering and exiting, a negative electrode made of a current collector that supports the active material mixture layer, a porous separator made of a polymer that absorbs and holds an organic electrolyte, and the positive electrode, the negative electrode, and An organic electrolyte solution absorbed and held in a separator is provided, and the positive and negative electrodes and the separator are integrated by thermal fusion, and the polymer content of the active material mixture layer of the positive electrode is 5 to 10% by weight An organic electrolyte battery in which the polymer content of the active material mixture layer of the negative electrode is 7 to 16% by weight.