JP4250809B2

JP4250809B2 - Lithium secondary battery and method of manufacturing positive electrode plate thereof

Info

Publication number: JP4250809B2
Application number: JP14991699A
Authority: JP
Inventors: 達也橋本; 頼人大花; 英也浅野; 祐之村井; 博松野
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1998-05-28
Filing date: 1999-05-28
Publication date: 2009-04-08
Anticipated expiration: 2019-05-28
Also published as: JP2000048822A

Description

【０００１】
【発明の属する技術分野】
本発明は、リチウム二次電池とその極板に関するものである。
【０００２】
【従来の技術】
従来、繰り返し充放電の使用や電池組立工程注中の集電体からの活物質の剥離を防ぐために集電体表面にクロメート処理やコロナ放電処理を施すことが提案されている。（特開昭５６−５７２６１号公報、特開平７−１３５０２３号公報）また、リチウムイオン二次電池の極板製造に関して、活物質と結着剤及び増粘剤の濡れ性を改良する方法として、界面活性剤存在下で混練分散を行う方法が示されている。（特開平８−１９０９１２号公報）
【０００３】
【発明が解決しようとする課題】
しかしながら、上記の電池用極板においては、活物質と結着剤及び増粘剤との濡れ性を改良すると共に、活物質を塗布した後の集電体と活物質との密着性を満足させることは困難であった。そのため、高温保存後や充放電を繰り返すうちに集電体から活物質が剥離、脱落して充放電容量が低下するといった問題があった。
【０００４】
そこで、本発明は前記する従来からの課題を解決して活物質による集電体の腐食が少く、集電体からの活物質の剥離や、脱落が少くて放電容量が大きいリチウム二次電池を提供しようとするものである。
【０００５】
【課題を解決するための手段】
本発明は、上記のような課題を解決するもので、集電体上への活物質を主成分とする合剤から成るペーストの塗布に先行して集電体表面にベーマイト処理を行うことを特徴とする電池用極板とそれを用いた電池を提供するものである。
【０００６】
また、本発明は、金属箔よりなる集電体に正極活物質を含んだペーストを塗布した後に乾燥して製造するリチウム二次電池用極板の製造方法において、前記のペーストの塗布に先行して、表面にクロム酸化物層を形成するクロメート処理をした集電体を用いることとしたものである。
【０００７】
【発明の実施の形態】
本発明は、正、負極のいずれか一方の極板の集電体表面にベーマイト処理を施すか、あるいは正極板の集電体表面にクロメート処理を施し、ついで集電体上に電極活物質を含んだ合剤から成るペーストを塗布した後、乾燥して極板を得るものである。この極板を使用した電池は充放電を繰り返して使用しても、充放電容量の劣化や負荷特性の劣化を小さく抑えることが可能である。
【０００８】
【実施例】
以下、本発明の実施例として、リチウムイオン電池用正極集電体にベーマイト処理を施した場合について説明する。
【０００９】
（実施例１）
本発明のリチウム二次電池の一実施の形態は図１に示すような円筒形リチウム二次電池で前記本発明により得られた極板群と電解液とこれらを収容する電池ケース４からなる。極板群は、シート状の前記正極用極板１とシート状の負極用極板２と正極用極板１と負極用極板２との間を絶縁するシート状のセパレータ３と正極リード７と負極リード８と上部絶縁板９と下部絶縁板１０とからなる。セパレータ３は多孔質ポリエチレンフィルムであり、これらが重ねられ渦巻き状に巻回されて、円筒形の電池ケース４内に収容されている。
【００１０】
電池ケース４は、耐有機電解液性のステンレス鋼板を深絞り成形して得ており、極板群、電解液挿入後、開口部は封口板５と電池ケース４との間を絶縁しガスシールするガスケット６により封口されている。
【００１１】
まず、ベーマイト処理として正極集電体である３０μｍのアルミニウム箔上にトリエタノールアミン１２ｃｃ／ｌ溶液中に浸漬した後、１００℃で４時間乾燥させ、表面改質させ、酸化被膜を形成した。このとき、被膜の厚みは０．５〜５．０μｍが望ましい。これは、被膜の厚みが０．５μｍより薄い場合は、表面を改質した効果が十分得られず、活物質との密着性がそれほどよくならないためであり、５．０μｍより厚い場合は、同じ大きさの電池ケースに挿入できる活物質量が減少することによる電池容量の低下の影響が大きくなってしまうためである。
【００１２】
次に、正極用極板１の製造方法を説明する。正極活物質としてＬｉＣｏＯ₂粉末を５０重量部、導電剤としてアセチレンブラックを１．５重量部、結着剤としてＰＴＦＥ５０重量部水溶液を７重量部、そして、増粘剤としてカルボキシメチルセルロース１重量部水溶液を４１．５重量部を配合し、混合分散して正極用の活物質を主成分とする合剤から成るペーストを得た。この正極用ペーストを本発明のベーマイト処理をしたアルミニウム箔上にダイコーターを用いて両面に塗布して、乾燥後、さらにＰＴＦＥの溶融温度である２００〜３００℃で正極用極板を加熱して集電体と正極合剤層の密着性を改良させる。この後、厚み０．１８ｍｍに圧延し、切断して本発明のシート状の正極用極板１を作成した。
【００１３】
負極用極板２の製造方法を説明する。負極活物質として鱗片状黒鉛粉末５０重量部、増粘剤としてカルボキシメチルセルロース１重量部を水９９重量部に溶解した水溶液４５重量部、そして、結着剤としてスチレンブタジエンゴム５重量部を配合し混合分散して負極用ペーストを作成した。得られた負極用ペーストをダイコーターを用いて厚さ４０μｍの銅箔からなる負極用極板２を作成した。
【００１４】
電解液は、炭酸エチレン３０ｖｏｌ％と炭酸ジエチル５０ｖｏｌ％とプロピオン酸メチル２０ｖｏｌ％との混合液にＬｉＰＦ₆を１ｍｏｌ／ｌの濃度に溶解したものからなる。この電解液は、電池ケース内に収容され、正極活物質層および負極活物質層内に含浸されて、電池反応において、多孔質セパレータ３の微小孔を通して正極用極板１と負極用極板２との間のリチウムイオンの移動を担う。
【００１５】
前記正極用極板１を用いて電池を作成し、そのサイクル特性を確認した。電池は、直径１７ｍｍ、高さ５０ｍｍのサイズのものを作成した。
【００１６】
その比較例として、正極集電体表面にベーマイト処理を行わず無処理である他は同様にして電池を作成した。
【００１７】
本発明の電池と比較例の電池について、充電は４．１Ｖまで５００ｍＡの定電流で行い、４．１Ｖになった時点で４．１Ｖの定電圧充電に切り換え、充電時間の合計を２時間とし、放電は、２０℃中で７２０ｍＡで行い、放電電位が３．０Ｖになった時点で放電を終了して１サイクルとし、次の充電を開始した。このようにして、充放電を繰り返したときの前記本発明の電池と比較例の電池のサイクル寿命特性を縦軸に容量維持率、横軸にサイクル数をとって図２に示した。図２より本発明の電池は比較例の電池より充放電を繰り返しても容量の劣化が少なくサイクル特性に優れていることがわかった。
【００１８】
これは、本発明の電池において、正極集電体表面にベーマイト処理を行うことで集電体表面が針状構造を有し、この部位に高分子であるＰＴＦＥが三次元的にからまり、アンカー効果が発現することで集電体と活物質を主成分とする合剤層との密着性が改良されるためと考えられる。これにより、充放電を繰り返して活物質を含む合剤層が膨張収縮しても合剤層が集電体からはがれにくくなる。
【００１９】
また、これら本発明の電池と比較例の電池を充電状態で６０℃中に２０日間保存した後、常温で数回充放電を繰り返し、７２０ｍＡで放電し、電圧が３．０Ｖに達するまでの容量を求め、その保存前の容量に対する割合を（表１）に示した。
【００２０】
【表１】

【００２１】
（表１）に示すとおり、高温保存においても本発明の電池は容量の劣化が少ないことがわかった。
【００２２】
本実施例ではリチウム二次電池用の正極用集電体にベーマイト処理を施した場合を示したが、ベーマイト処理を施すのは負極用集電体でもよくまた、他の電池系の極板に適用しても同様の効果が得られる。
【００２３】
（実施例２）
正極用極板１の製造は実施例１のベーマイト処理したアルミニウム箔の代わりに、あらかじめクロム酸化物層を表面に形成するクロメート処理をしたアルミニウム箔を用いた以外は実施例１と同様に行った。
【００２４】
負極用極板２に用いる負極用ペーストの製造は実施例１と同様に行った。得られた負極用ペーストをダイコーターを用いて厚さ５０μｍの銅箔からなる負極集電体の両面に塗布乾燥し、厚み０．２ｍｍに圧延し、切断してシート状の負極用極板２を作製した。
【００２５】
また、電解液は実施例１と同様のものを用いた。
【００２６】
前記の正極用極板１を用いて実施例１と同様に電池を作製し、そのサイクル特性を確認した。電池は、直径１７ｍｍ，高さ５０ｍｍの寸法のものを作製した。
【００２７】
また、比較例として、正極集電体の表面にクロメート処理を行わず無処理である他は同じ製造方法で作製した正極板を用いたリチウム二次電池と、本発明の製造法により製造した正極板を備えたリチウム二次電池のサイクル寿命特性を図３に示す。
【００２８】
実施例１と同様に、充電は５００ｍＡの定電流で行い４．１Ｖになった時点で４．１Ｖの定電圧充電に切り換え、合計２時間充電を行った。放電は２０℃７２０ｍＡで行い、放電電位が３．０Ｖになった時点で放電を終了し次の充電を開始した。この図より本発明の製造方法によるリチウム二次電池の正極用極板を備えた電池は、従来の方法により製造したリチウム二次電池の正極用極板を有する電池と比較して、充放電を繰り返しても容量の劣化が少なくサイクル特性に優れていることがわかる。
【００２９】
これは、本発明の製造方法により得たリチウム二次電池の正極用極板を備えた電池は、正極集電体表面をクロメート処理を行うことで、クロメート処理した集電体表面の被膜は腐食するものの活物質を主成分とする合剤層が集電体に直接には接しないため合剤層による集電体の腐食を低減し、腐食反応時に界面付近で発生する水素ガスの生成を抑制することができるので正極合剤層と集電体との密着性が改良されたためで、これにより、充放電での正極合剤層の膨脹収縮によっても正極合剤層が集電体から剥れ難くなったことが原因である。
【００３０】
また、正極集電体にアルミニウム箔を用いるとクロメート処理により、表面が適度に腐食されるため、その結果、表面にアンカー効果を生じ正極合剤層との密着が格段に改良される。他方、集電体に鉄箔を用いた場合にはクロメート処理によるアンカー効果は小さい。
【００３１】
これらの正極用極板を備えたリチウム二次電池を充電状態で６０℃２０日間保存し、その後常温にて数回充放電を行った後、７２０ｍＡで放電を行い電圧が３．０Ｖに達するまでの容量を求め、その保存前の容量に対する割合を（表２）に示した。
【００３２】
【表２】

【００３３】
（表２）に示すとおり、高温保存においても本発明の製造方法により製造した正極用極板を備えたリチウム二次電池は容量の劣化が少なくなることが明らかとなった。
【００３４】
【発明の効果】
以上説明したように本発明によれば、充放電を繰り返して使用する際、充放電容量の劣化や保存特性の劣化を極めて小さく抑えることができる。また、高温下に長期間放置するような厳しい条件下においても充放電容量の劣化を小さく抑えることができる。また、電池組立工程中の極板の集電体からの活物質を主成分とする合剤層の剥離が抑えられ、作業性を改善することができる。
【図面の簡単な説明】
【図１】本発明の一実施例による電池の断面図
【図２】サイクル寿命特性を比較した図
【図３】サイクル寿命特性を比較した図
【符号の説明】
１正極用極板
２負極用極板
３セパレータ
４電池ケース
５封口板
６ガスケット
７正極リード
８負極リード
９上部絶縁板
１０下部絶縁板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium secondary battery and its electrode plate.
[0002]
[Prior art]
Conventionally, it has been proposed to perform chromate treatment or corona discharge treatment on the surface of the current collector in order to prevent repeated use of charge / discharge and separation of the active material from the current collector during the battery assembly process. (JP-A-56-57261, JP-A-7-135023) Further, as a method for improving the wettability of the active material, the binder and the thickener with respect to the production of the electrode plate of the lithium ion secondary battery, A method of kneading and dispersing in the presence of a surfactant is shown. (Japanese Patent Laid-Open No. 8-190912)
[0003]
[Problems to be solved by the invention]
However, in the above-described electrode plate for a battery, the wettability between the active material, the binder, and the thickener is improved, and the adhesion between the current collector and the active material after applying the active material is satisfied. It was difficult. For this reason, there is a problem that the active material is peeled off from the current collector and dropped off after being stored at high temperature or repeatedly being charged and discharged, resulting in a decrease in charge / discharge capacity.
[0004]
Accordingly, the present invention solves the above-described conventional problems by providing a lithium secondary battery with a small discharge capacity due to less corrosion of the current collector due to the active material, less detachment of the active material from the current collector, and falling off. It is something to be offered.
[0005]
[Means for Solving the Problems]
The present invention solves the problems as described above, and performs a boehmite treatment on the surface of the current collector prior to application of a paste composed of a mixture mainly composed of an active material on the current collector. The present invention provides a battery electrode plate and a battery using the same.
[0006]
Further, the present invention provides a method for producing an electrode plate for a lithium secondary battery, which is produced by applying a paste containing a positive electrode active material to a current collector made of a metal foil and then drying the paste. Thus, a current collector having a chromate treatment for forming a chromium oxide layer on the surface is used.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the surface of the current collector of either the positive electrode or the negative electrode is subjected to boehmite treatment, or the surface of the current collector of the positive electrode plate is subjected to chromate treatment, and then the electrode active material is placed on the current collector. After applying the paste composed of the mixture, the electrode plate is obtained by drying. Even if the battery using this electrode plate is repeatedly charged and discharged, deterioration of charge / discharge capacity and load characteristics can be kept small.
[0008]
【Example】
Hereinafter, as an example of the present invention, a case where a boehmite treatment is performed on a positive electrode current collector for a lithium ion battery will be described.
[0009]
Example 1
One embodiment of the lithium secondary battery of the present invention comprises a cylindrical lithium secondary battery as shown in FIG. 1 and an electrode plate group obtained by the present invention, an electrolytic solution, and a battery case 4 that accommodates them. The electrode plate group includes a sheet-like positive electrode plate 1, a sheet-like negative electrode plate 2, a sheet-like separator 3 that insulates between the positive electrode plate 1 and the negative electrode plate 2, and a positive electrode lead 7. And a negative electrode lead 8, an upper insulating plate 9, and a lower insulating plate 10. The separator 3 is a porous polyethylene film, and these are overlapped and wound in a spiral shape, and are accommodated in a cylindrical battery case 4.
[0010]
The battery case 4 is obtained by deep-drawing a stainless steel plate resistant to organic electrolyte, and after the electrode plate group and the electrolyte are inserted, the opening is insulated between the sealing plate 5 and the battery case 4 to provide a gas seal. The gasket 6 is sealed.
[0011]
First, after being immersed in a 12 cc / l solution of triethanolamine on a 30 μm aluminum foil as a positive electrode current collector as a boehmite treatment, it was dried at 100 ° C. for 4 hours and surface-modified to form an oxide film. At this time, the thickness of the coating is preferably 0.5 to 5.0 μm. This is because when the thickness of the coating is thinner than 0.5 μm, the effect of modifying the surface is not sufficiently obtained, and the adhesion with the active material is not so good. This is because the effect of a decrease in battery capacity due to a decrease in the amount of active material that can be inserted into a battery case having a large size is increased.
[0012]
Next, a method for manufacturing the positive electrode plate 1 will be described. 50 parts by weight of LiCoO ₂ powder as a positive electrode active material, 1.5 parts by weight of acetylene black as a conductive agent, 7 parts by weight of an aqueous solution of 50 parts by weight of PTFE as a binder, and an aqueous solution of 1 part by weight of carboxymethyl cellulose as a thickener 41.5 parts by weight was blended, mixed and dispersed to obtain a paste composed of a mixture mainly composed of a positive electrode active material. This positive electrode paste was applied to both sides of the boehmite-treated aluminum foil of the present invention using a die coater, dried, and further heated at a positive electrode plate at 200 to 300 ° C., which is the melting temperature of PTFE. Improves the adhesion between the current collector and the positive electrode mixture layer. Thereafter, the sheet was rolled to a thickness of 0.18 mm and cut to prepare the sheet-like positive electrode plate 1 of the present invention.
[0013]
A method for manufacturing the negative electrode plate 2 will be described. Mix and mix 50 parts by weight of scaly graphite powder as a negative electrode active material, 45 parts by weight of an aqueous solution in which 1 part by weight of carboxymethylcellulose is dissolved in 99 parts by weight of water, and 5 parts by weight of styrene butadiene rubber as a binder. A negative electrode paste was prepared by dispersing. A negative electrode plate 2 made of a copper foil having a thickness of 40 μm was prepared from the obtained negative electrode paste using a die coater.
[0014]
The electrolytic solution is composed of LiPF ₆ dissolved at a concentration of 1 mol / l in a mixed solution of ethylene carbonate 30 vol%, diethyl carbonate 50 vol%, and methyl propionate 20 vol%. This electrolytic solution is accommodated in the battery case, impregnated in the positive electrode active material layer and the negative electrode active material layer, and in the battery reaction, the positive electrode plate 1 and the negative electrode plate 2 through the micropores of the porous separator 3. It is responsible for the movement of lithium ions between the two.
[0015]
A battery was prepared using the positive electrode plate 1 and its cycle characteristics were confirmed. A battery having a diameter of 17 mm and a height of 50 mm was prepared.
[0016]
As a comparative example, a battery was prepared in the same manner except that the boehmite treatment was not performed on the surface of the positive electrode current collector.
[0017]
For the battery of the present invention and the battery of the comparative example, charging is performed at a constant current of 500 mA up to 4.1 V, and when it reaches 4.1 V, switching to a constant voltage charging of 4.1 V is performed, and the total charging time is 2 hours. The discharge was performed at 20 ° C. at 720 mA, and when the discharge potential reached 3.0 V, the discharge was terminated to one cycle, and the next charge was started. Thus, the cycle life characteristics of the battery of the present invention and the battery of the comparative example when charging and discharging are repeated are shown in FIG. 2 with the capacity retention rate on the vertical axis and the number of cycles on the horizontal axis. From FIG. 2, it was found that the battery of the present invention was superior in cycle characteristics with less capacity deterioration even when charging and discharging were repeated as compared with the battery of the comparative example.
[0018]
In the battery of the present invention, the surface of the current collector has a needle-like structure by performing boehmite treatment on the surface of the positive electrode current collector, and PTFE which is a polymer is entangled three-dimensionally at this site, It is considered that the adhesiveness between the current collector and the mixture layer containing the active material as a main component is improved due to the effect. Thereby, even if charging / discharging is repeated and the mixture layer containing an active material expands and contracts, the mixture layer is difficult to peel off from the current collector.
[0019]
In addition, after storing the battery of the present invention and the battery of the comparative example in a charged state at 60 ° C. for 20 days, the battery is repeatedly charged and discharged several times at room temperature, discharged at 720 mA, and the capacity until the voltage reaches 3.0V. (Table 1) shows the ratio to the capacity before storage.
[0020]
[Table 1]

[0021]
As shown in (Table 1), it was found that the battery of the present invention had little capacity deterioration even at high temperature storage.
[0022]
In this example, the case where the boehmite treatment was applied to the positive electrode current collector for the lithium secondary battery was shown, but the boehmite treatment may be applied to the negative electrode current collector, or to the electrode plate of another battery system. Even if applied, the same effect can be obtained.
[0023]
(Example 2)
The positive electrode plate 1 was manufactured in the same manner as in Example 1 except that instead of the boehmite-treated aluminum foil of Example 1, a chromate-treated aluminum foil having a chromium oxide layer formed on the surface in advance was used. .
[0024]
The negative electrode paste used for the negative electrode plate 2 was produced in the same manner as in Example 1. The obtained negative electrode paste was applied and dried on both sides of a negative electrode current collector made of a copper foil having a thickness of 50 μm using a die coater, rolled to a thickness of 0.2 mm, cut and cut into a sheet-like negative electrode plate 2 for negative electrode. Was made.
[0025]
Moreover, the electrolyte solution used was the same as in Example 1.
[0026]
A battery was produced using the positive electrode plate 1 in the same manner as in Example 1, and its cycle characteristics were confirmed. A battery having a diameter of 17 mm and a height of 50 mm was produced.
[0027]
Moreover, as a comparative example, a lithium secondary battery using a positive electrode plate manufactured by the same manufacturing method except that the surface of the positive electrode current collector is not subjected to chromate treatment and is not processed, and a positive electrode manufactured by the manufacturing method of the present invention FIG. 3 shows the cycle life characteristics of the lithium secondary battery provided with the plate.
[0028]
As in Example 1, charging was performed at a constant current of 500 mA, and when the voltage reached 4.1 V, the charging was switched to constant voltage charging of 4.1 V, and charging was performed for a total of 2 hours. Discharge was performed at 20 ° C. and 720 mA, and when the discharge potential reached 3.0 V, the discharge was terminated and the next charge was started. From this figure, the battery provided with the positive electrode plate of the lithium secondary battery according to the manufacturing method of the present invention is charged and discharged in comparison with the battery having the positive electrode plate of the lithium secondary battery manufactured by the conventional method. It can be seen that even if it is repeated, the capacity is hardly deteriorated and the cycle characteristics are excellent.
[0029]
This is because the battery provided with the positive electrode plate of the lithium secondary battery obtained by the production method of the present invention is subjected to chromate treatment on the surface of the positive electrode current collector, and the coating on the chromate-treated current collector surface is corroded. However, since the mixture layer containing the active material as the main component does not directly contact the current collector, the corrosion of the current collector by the mixture layer is reduced and the generation of hydrogen gas generated near the interface during the corrosion reaction is suppressed. Because the adhesion between the positive electrode mixture layer and the current collector is improved, the positive electrode mixture layer is peeled off from the current collector due to expansion and contraction of the positive electrode mixture layer during charge and discharge. This is because it became difficult.
[0030]
Further, when an aluminum foil is used for the positive electrode current collector, the surface is appropriately corroded by the chromate treatment. As a result, an anchor effect is generated on the surface, and the adhesion with the positive electrode mixture layer is remarkably improved. On the other hand, when an iron foil is used for the current collector, the anchor effect by chromate treatment is small.
[0031]
Lithium secondary batteries equipped with these positive electrode plates are stored in a charged state at 60 ° C. for 20 days, then charged and discharged several times at room temperature, then discharged at 720 mA until the voltage reaches 3.0V. (Table 2) shows the ratio to the capacity before storage.
[0032]
[Table 2]

[0033]
As shown in (Table 2), it was revealed that the lithium secondary battery including the positive electrode plate manufactured by the manufacturing method of the present invention is less deteriorated in capacity even during high-temperature storage.
[0034]
【The invention's effect】
As described above, according to the present invention, when charging / discharging is used repeatedly, deterioration of charge / discharge capacity and deterioration of storage characteristics can be suppressed to an extremely low level. In addition, the deterioration of the charge / discharge capacity can be suppressed even under severe conditions such as leaving for a long time at a high temperature. Moreover, peeling of the mixture layer containing the active material as a main component from the current collector of the electrode plate during the battery assembly process can be suppressed, and workability can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a battery according to an embodiment of the present invention. FIG. 2 is a diagram comparing cycle life characteristics. FIG. 3 is a diagram comparing cycle life characteristics.
DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 4 Battery case 5 Sealing plate 6 Gasket 7 Positive electrode lead 8 Negative electrode lead 9 Upper insulating plate 10 Lower insulating plate

Claims

A lithium secondary battery using a current collector having a boehmite treatment on at least one of positive and negative electrode plates.

The lithium secondary battery according to claim 1, wherein the thickness of the coating formed on the surface of the current collector by boehmite treatment is 0.5 to 5 µm.