JP3956478B2

JP3956478B2 - Method for manufacturing lithium ion secondary battery

Info

Publication number: JP3956478B2
Application number: JP08730898A
Authority: JP
Inventors: 浩二川本
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1998-03-31
Filing date: 1998-03-31
Publication date: 2007-08-08
Anticipated expiration: 2018-03-31
Also published as: JPH11288739A

Description

【０００１】
【発明の属する技術分野】
本発明はリチウムイオン２次電池の製造方法、特にサイクル特性に優れたリチウムイオン２次電池の製造方法に関する。
【０００２】
【従来の技術】
従来、リチウム２次電池用電極を集電体上に形成する際、電極活物質と結着剤を混合した電極材に集電体を配し、これにプレスを施すことにより電極活物質の密度を上げ、電流密度を上げる技術がある。
【０００３】
例えば、特開昭６２−２２６５６３号公報には、リチウムと合金化可能な金属の粉末に黒鉛粉末及び熱可塑性樹脂を混合した負極材を、ステンレスネットからなる負極集電体をその内底面にスポット溶接して固着した負極缶に盛込み、１５０℃，１ton／cm²の条件でホットプレスする技術が記載されている。
【０００４】
このように電極材にホットプレスを施すことにより、電極材中の結着剤を溶融させることができ、電極活物質間及び電極活物質と集電体との結着力を増加させることができる。
しかし、このようにホットプレスを施した電極をセパレータを介して容器内に配した場合、容器に電解液を注入しても電極はほとんど膨潤しない為、電極及びセパレータと容器との密着力が高められることにより生じる容器からの電極及びセパレータへの圧縮応力は働かない。よって、電極とセパレータとの密着性が悪く、正負極間の厚さがセパレータ厚と一致せず不均一になる。
この正負極間の厚さの不均一により、電池の容量が安定せずサイクル特性が十分でないという問題があった。
【０００５】
また、ホットプレスではなくコールドプレスを施した場合は、プレスにより電極材中に歪み応力が残留し（ホットプレスでは加工中の熱により与えられた歪み応力が除去される。）、電解液を注入した際、電極が膨潤することにより容器と電極及びセパレータとの密着力が高められ、容器から電極及びセパレータへ圧縮応力が働き、正負極間の厚さが均一になる。
しかし、電極材にコールドプレスを施しただけでは電極材中の結着剤を溶融させることができない為、電極活物質間及び電極活物質と集電体との結着力は小さい。
この為、充放電による電極活物質の膨張収縮に伴い、繰り返し使ううちに電極活物質間及び電極活物質と集電体との間で剥離が生じ界面抵抗が増大してしまい、ホットプレスと同様にサイクル特性が十分でないという問題があった。
【０００６】
【発明が解決しようとする課題】
リチウムイオン２次電池のサイクル特性を向上させることを課題とする。
【０００７】
【課題を解決するための手段】
上記課題を解決する請求項１に記載のリチウムイオン２次電池の製造方法の特徴は、電極活物質と結着剤とを含む電極材を集電体に配する行程と、該電極材が配された集電体を前記結着剤が溶融する温度でホットプレスし、電極充填率が３０〜６０体積％となる電極を製造する行程と、該電極にコールドプレスを施し該電極に歪み応力を与え、電極充填率を４０〜７０体積％とする行程と、該歪み応力が与えられた電極を含む正極及び負極をセパレータを介して対向させ倦回する倦回式電極を円筒容器内に配する行程と、該容器内に電解液を注入することにより前記電極を膨潤させ前記容器との間で圧縮応力を発生させる行程と、を有することである。
【０００８】
また請求項２に記載のリチウムイオン２次電池の製造方法の特徴は、電極活物質と結着剤とを含む電極材を集電体に配する行程と、該電極材が配された集電体をコールドプレスする行程と、該電極材を前記結着剤が溶融する温度で加熱し、電極充填率が３０〜６０体積％となる電極を製造する行程と、該電極にコールドプレスを施し該電極に歪み応力を与え、電極充填率を４０〜７０体積％とする行程と、該歪み応力が与えられた電極を含む正極及び負極をセパレータを介して対向させ倦回する倦回式電極を円筒容器内に配する行程と、該容器内に電解液を注入することにより前記電極を膨潤させ前記容器との間で圧縮応力を発生させる行程と、を有することである。
【０００９】
【発明の実施の形態】
以下、本件の実施の形態（以下実施形態という）について説明する。
【００１０】
実施形態１．
本発明のリチウムイオン２次電池の製造方法では、電極活物質と結着剤とを含む電極材を集電体に配したものにホットプレスを行った後に結着剤が溶融する温度で加熱することにより、電極活物質間及び電極活物質と集電体との十分な結着力を得ることができる。
また、その後こうして得られた電極にコールドプレスを施すことにより、電極に歪み応力を残留させ、この電極を容器内に挿入した後、電解液を注入することにより電極が膨潤し、容器との密着力が向上する。
電極と容器との密着力が向上することにより、容器から電極へ圧縮応力が生じ、電極間厚さを均一に保つことができるようになる。
【００１１】
即ち、本発明により電極活物質間及び電極活物質と集電体との十分な結着力の確保と、電極間厚さの均一化が両立でき、サイクル特性を向上させることができる。
【００１２】
ここで、ホットプレス又はコールドプレス後加熱し、その後コールドプレスを施す処理は正極及び負極のいずれか一方以上に行えば効果を有し、両方に行えば一方に行ったものよりもなおいっそうの効果を有する。
【００１３】
また、上記ホットプレスまたはコールドプレス後に加熱を施す工程は、電極活物質間及び電極活物質と集電体との密着力を向上させる為、結着剤の融点以上の温度となるようにし、電極の充填率が３０〜６０体積％（空孔率が４０〜７０体積％）となるように条件を設定するのが望ましい。
【００１４】
更に、その後のコールドプレス工程は、電解液注入後に電極が膨潤するよう電極の充填率が４０〜７０体積％となるようにプレスするのが望ましい。
【００１５】
実施形態２．
実施形態１でホットプレスを行う代わりに、コールドプレスを行い、その後結着剤が溶融する温度で加熱して電極を製造することもできる。
この場合はコールドプレスで電極材中に歪み応力が残留するが、加熱によりこの歪み応力が除去される為、実施形態１と同様にこの後の処理で電極に歪み応力を付与する為のコールドプレスが必要である。
実施形態２も１と同様の理由で、サイクル特性を向上させることができる。
【００１６】
以下に、上記実施形態の具体例を実施例として説明する。
【実施例】
（実施例１）
図１に本件発明に係る実施例１のリチウムイオン２次電池製造過程のフローチャートを示す。
図１において、ステップ１００では、集電箔上に電極活性物質と結着剤と溶剤からなるペーストを塗布する。
【００１７】
正極の場合、８５ｗｔ％のＬｉＭｎ２Ｏ４を電極活性物質とし、１０ｗｔ％のカーボンブラックを導電化材として、結着剤ＰＶＤＦを５ｗｔ％溶かしたＮ−メチルピロリドン（ＮＭＰ）溶液中に混合，混練してペースト状とした。このペーストをアルミニウム集電箔上に塗布した。
【００１８】
負極の場合、９０ｗｔ％の天然黒鉛を電極活性物質とし、結着剤ＰＶＤＦを１０ｗｔ％溶かしたＮ−メチルピロリドン（ＮＭＰ）溶液中に混合，混練してペースト状とした。このペーストを銅集電箔上に塗布した。
【００１９】
ステップ１０１では、上記ペーストを集電箔上で乾燥した。
【００２０】
ステップ１０２は、ホットプレス工程を表す。
正極は０．５ton／cm²、負極は０．１ton／cm²の圧力をかけ、両者ともＰＶＤＦが溶融する１７５℃でホットプレスを行った。
この工程で結着剤は溶融し、電極活物質間及び電極活物質と集電箔との結着力が向上するとともに、電極内部の応力は緩和される。
【００２１】
ステップ１０３は、コールドプレス工程を表す。
正極は１ton／cm²、負極は０．２ton／cm²の圧力をかけ、常温でコールドプレスを行った。
この工程でのコールドプレスの加圧力は、後の工程で電解液を注入し電極を膨張させることにより容器との間で発生させたい応力量とする。
【００２２】
ステップ１０４では、こうして出来上がった正極及び負極をセパレータを介して対向させ捲回することにより捲回式電極を得た。
【００２３】
ステップ１０５では、上記捲回式電極を円筒型容器に挿入した。
【００２４】
ステップ１０６では、容器内にエチレンカーボネート（ＥＣ）とジエチレンカーボネート（ＤＥＣ）を体積比１：１で混合した溶媒に１mol／lのＬｉＢＦ４を溶解させた電解液を注入した。
電解液を注入することによって、電極が膨張し電極と容器とが密着することにより電極間に圧縮応力が発生した。
【００２５】
（実施例２）
図２に本件発明に係る実施例２の製造過程のフローチャートを示す。
【００２６】
実施例２では実施例１のステップ１０２のホットプレス代わりにステップ２０２として第１のコールドプレスを行い、ステップ２０３として電極の加熱工程が加わったのみで、他は実施例１と同様の条件で製造した。
【００２７】
ステップ２０２では、正極は１ton／cm²、負極は０．２ton／cm²の圧力をかけ、常温でコールドプレスを行った。
また、ステップ２０３では、正極及び負極をＰＶＤＦが溶融する１７５℃で加熱した。
（比較例１）
比較例１では、電極にホットプレスのみを施した例を示す。
比較例１では、実施例１のステップ１０３のコールドプレスを行わなかった他は実施例１と同様の条件で製造した。
【００２８】
（比較例２）
比較例２では、電極にコールドプレスのみを施した例を示す。
比較例２では、実施例２のステップ２０３の加熱工程及びステップ２０４の第２のコールドプレスを行わなかった他は実施例２と同様の条件で製造した。
【００２９】
（評価）
これら作製されたリチウムイオン２次電池のサイクル特性を評価した。
【００３０】
表１には、サイクル特性の評価結果が示させる。
サイクル特性は、（１／３）Ｃ、すなわち３時間で満充電できる定電流を充放電させる工程を１サイクルとし、初期容量に対する２００サイクル後の容量で評価した。
【００３１】
【表１】

【００３２】
表１から分かるように、本実施例はいずれの比較例に比べてもサイクル特性が大きく向上していることが分かる。
【００３３】
比較例１でサイクル特性が低いのは、正負極間の厚さが不均一である為、充放電容量が安定しないことによると考えられる。
また、比較例２でサイクル特性が低いのは、電極活物質間及び電極活物質と集電箔との結着力が小さく、繰り返し使ううちに電極活物質間及び電極活物質と集電箔との間で剥離が生じ界面抵抗が増大してしまうことによると考えられる。
【００３４】
これに対して、実施例１及び２のサイクル特性が高いのは、正負極間の厚さの均一化と電極活物質間及び電極活物質と集電箔との結着力向上が両立している為だと考えられる。
【００３５】
【発明の効果】
即ち、本発明のリチウムイオン2次電池の製造方法では、電極活物質間及び電極活物質と集電体との十分な結着力が得られるとともに、容器から電極へ圧縮応力を生じさせ、正負極間の厚さを均一化することができ、サイクル特性を向上させることができる。
【図面の簡単な説明】
【図１】本発明実施例１の製造過程のフローチャートを示す図である。
【図２】本発明実施例２の製造過程のフローチャートを示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a lithium ion secondary battery, and more particularly to a method for producing a lithium ion secondary battery having excellent cycle characteristics.
[0002]
[Prior art]
Conventionally, when forming an electrode for a lithium secondary battery on a current collector, the current collector is disposed on an electrode material in which an electrode active material and a binder are mixed, and the density of the electrode active material is determined by pressing the current collector. To increase the current density.
[0003]
For example, in Japanese Patent Laid-Open No. 62-226563, a negative electrode material in which graphite powder and a thermoplastic resin are mixed with metal powder that can be alloyed with lithium is spotted on a negative electrode current collector made of a stainless steel net on its inner bottom surface. A technique is described in which a negative electrode can fixed by welding is loaded and hot pressed under conditions of 150 ° C. and 1 ton / cm ² .
[0004]
By performing hot pressing on the electrode material in this manner, the binder in the electrode material can be melted, and the binding force between the electrode active materials and between the electrode active material and the current collector can be increased.
However, when an electrode subjected to hot pressing in this way is placed in a container through a separator, the electrode hardly swells even when an electrolyte is injected into the container, so that the adhesion between the electrode and the separator and the container is increased. The compressive stress from the container to the electrode and the separator caused by being applied does not work. Therefore, the adhesion between the electrode and the separator is poor, and the thickness between the positive and negative electrodes does not match the thickness of the separator and becomes non-uniform.
Due to the uneven thickness between the positive and negative electrodes, there is a problem that the capacity of the battery is not stable and the cycle characteristics are not sufficient.
[0005]
In addition, when cold pressing is performed instead of hot pressing, strain stress remains in the electrode material due to pressing (in hot pressing, strain stress applied by heat during processing is removed), and an electrolytic solution is injected. When the electrode is swollen, the adhesion between the container, the electrode, and the separator is enhanced, and a compressive stress acts from the container to the electrode and the separator, so that the thickness between the positive and negative electrodes becomes uniform.
However, since the binder in the electrode material cannot be melted only by performing a cold press on the electrode material, the binding force between the electrode active materials and between the electrode active material and the current collector is small.
For this reason, as the electrode active material expands and contracts due to charge and discharge, peeling between the electrode active materials and between the electrode active material and the current collector occurs during repeated use, increasing the interface resistance. However, there is a problem that the cycle characteristics are not sufficient.
[0006]
[Problems to be solved by the invention]
It is an object to improve the cycle characteristics of a lithium ion secondary battery.
[0007]
[Means for Solving the Problems]
The feature of the manufacturing method of the lithium ion secondary battery according to claim 1 for solving the above-described problem is that a step of arranging an electrode material including an electrode active material and a binder on a current collector, and the electrode material is disposed. And hot-pressing the collected current collector at a temperature at which the binder melts to produce an electrode having an electrode filling rate of 30 to 60% by volume , and cold-pressing the electrode to apply strain stress to the electrode. give, distribution electrode filling rate and the stroke shall be the 40 to 70% by volume, the倦回type electrodes倦回are opposed through a separator positive electrode and a negative electrode comprising electrodes strained stress is given to a cylindrical vessel And a step of causing the electrode to swell by injecting an electrolytic solution into the container and generating a compressive stress between the container and the container.
[0008]
The method for producing a lithium ion secondary battery according to claim 2 is characterized in that an electrode material including an electrode active material and a binder is disposed on a current collector, and a current collector on which the electrode material is disposed. A step of cold pressing the body, a step of heating the electrode material at a temperature at which the binder melts, and manufacturing an electrode having an electrode filling rate of 30 to 60% by volume; distorts stress on the electrode, and the stroke you an electrode filling factor and 40 to 70 vol%, the倦回type electrodes倦回are opposed through a separator positive electrode and a negative electrode comprising electrodes strained stress is given A process of arranging in a cylindrical container, and a process of injecting an electrolytic solution into the container to swell the electrode and generate a compressive stress between the container and the container.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention (hereinafter referred to as an embodiment) will be described.
[0010]
Embodiment 1. FIG.
In the method for producing a lithium ion secondary battery of the present invention, an electrode material containing an electrode active material and a binder is placed on a current collector, and hot pressing is performed at a temperature at which the binder melts. Thus, a sufficient binding force between the electrode active materials and between the electrode active material and the current collector can be obtained.
Also, after that, the electrode thus obtained is subjected to a cold press to leave strain stress in the electrode, and after inserting the electrode into the container, the electrode is swollen by injecting the electrolytic solution, so that the electrode is in close contact with the container. Power is improved.
By improving the adhesion between the electrode and the container, a compressive stress is generated from the container to the electrode, and the thickness between the electrodes can be kept uniform.
[0011]
That is, according to the present invention, sufficient binding force between the electrode active materials and between the electrode active material and the current collector can be ensured and the thickness between the electrodes can be made uniform, and the cycle characteristics can be improved.
[0012]
Here, the process of heating after hot pressing or cold pressing and then performing cold pressing has an effect when performed on one or more of the positive electrode and the negative electrode, and even more effective than that performed on one when both are performed. Have
[0013]
In addition, the step of heating after the hot press or cold press is performed at a temperature equal to or higher than the melting point of the binder in order to improve the adhesion between the electrode active materials and between the electrode active material and the current collector. It is desirable to set the conditions so that the filling ratio is 30 to 60% by volume (the porosity is 40 to 70% by volume).
[0014]
Further, in the subsequent cold pressing step, it is desirable to press the electrode so that the filling rate of the electrode is 40 to 70% by volume so that the electrode swells after the electrolyte solution is injected.
[0015]
Embodiment 2. FIG.
Instead of performing hot pressing in the first embodiment, cold pressing is performed, and then the electrode can be manufactured by heating at a temperature at which the binder melts.
In this case, strain stress remains in the electrode material by cold pressing, but since this strain stress is removed by heating, a cold press for applying strain stress to the electrode in the subsequent processing as in the first embodiment. is required.
In the second embodiment, the cycle characteristics can be improved for the same reason as in the first embodiment.
[0016]
Specific examples of the above embodiment will be described below as examples.
【Example】
Example 1
FIG. 1 shows a flowchart of a process of manufacturing a lithium ion secondary battery of Example 1 according to the present invention.
In FIG. 1, in step 100, a paste made of an electrode active material, a binder, and a solvent is applied on the current collector foil.
[0017]
In the case of the positive electrode, 85 wt% LiMn 2 O 4 is used as the electrode active material, 10 wt% carbon black is used as the conductive material, and the paste is mixed and kneaded in an N-methylpyrrolidone (NMP) solution containing 5 wt% binder PVDF. It was in the shape. This paste was applied onto an aluminum current collector foil.
[0018]
In the case of the negative electrode, 90 wt% of natural graphite was used as an electrode active material, and the mixture was mixed and kneaded in an N-methylpyrrolidone (NMP) solution in which 10 wt% of a binder PVDF was dissolved to form a paste. This paste was applied onto a copper current collector foil.
[0019]
In step 101, the paste was dried on a current collector foil.
[0020]
Step 102 represents a hot press process.
Positive electrode 0.5 ton / cm ^2, the negative electrode applying a pressure of 0.1ton / cm ^2, PVDF both were subjected to hot pressing at 175 ° C. to melt.
In this step, the binder is melted, the binding force between the electrode active materials and between the electrode active material and the current collector foil is improved, and the stress inside the electrode is relaxed.
[0021]
Step 103 represents a cold press process.
The positive electrode was 1 ton / cm ² and the negative electrode was 0.2 ton / cm ² , and cold pressed at room temperature.
The pressure of the cold press in this step is set to the amount of stress desired to be generated between the container by injecting an electrolyte solution and expanding the electrode in the subsequent step.
[0022]
In Step 104, a wound electrode was obtained by winding the positive electrode and the negative electrode thus obtained with a separator interposed therebetween.
[0023]
In step 105, the wound electrode was inserted into a cylindrical container.
[0024]
In step 106, an electrolytic solution in which 1 mol / l LiBF4 was dissolved in a solvent in which ethylene carbonate (EC) and diethylene carbonate (DEC) were mixed at a volume ratio of 1: 1 was injected into the container.
By injecting the electrolytic solution, the electrodes expanded, and the electrodes and the container were brought into close contact with each other, thereby generating a compressive stress between the electrodes.
[0025]
(Example 2)
FIG. 2 shows a flowchart of the manufacturing process of the second embodiment according to the present invention.
[0026]
In Example 2, instead of the hot pressing in Step 102 of Example 1, the first cold press is performed as Step 202, and only the electrode heating process is added as Step 203, and the other conditions are the same as in Example 1. did.
[0027]
In step 202, the positive electrode 1 ton / cm ^2, the negative electrode applying a pressure of 0.2ton / cm ^2, was cold pressed at room temperature.
In Step 203, the positive electrode and the negative electrode were heated at 175 ° C. at which PVDF was melted.
(Comparative Example 1)
Comparative Example 1 shows an example in which only hot pressing is applied to the electrode.
Comparative Example 1 was manufactured under the same conditions as in Example 1 except that the cold press in Step 103 of Example 1 was not performed.
[0028]
(Comparative Example 2)
Comparative Example 2 shows an example in which only the cold press is applied to the electrode.
Comparative Example 2 was manufactured under the same conditions as in Example 2 except that the heating process in Step 203 of Example 2 and the second cold press in Step 204 were not performed.
[0029]
(Evaluation)
The cycle characteristics of these produced lithium ion secondary batteries were evaluated.
[0030]
Table 1 shows the evaluation results of the cycle characteristics.
The cycle characteristics were evaluated by (1/3) C, that is, the capacity after 200 cycles with respect to the initial capacity, with the process of charging / discharging a constant current that can be fully charged in 3 hours as one cycle.
[0031]
[Table 1]

[0032]
As can be seen from Table 1, it can be seen that the cycle characteristics of the present example are greatly improved compared to any of the comparative examples.
[0033]
It is considered that the reason why the cycle characteristics are low in Comparative Example 1 is that the charge / discharge capacity is not stable because the thickness between the positive and negative electrodes is not uniform.
In addition, the cycle characteristics in Comparative Example 2 are low because the binding force between the electrode active materials and between the electrode active materials and the current collector foil is small, and between the electrode active materials and between the electrode active materials and the current collector foil during repeated use. This is thought to be due to the fact that separation occurs between them and the interface resistance increases.
[0034]
On the other hand, the high cycle characteristics of Examples 1 and 2 are compatible with the uniformity of the thickness between the positive and negative electrodes and the improvement of the binding force between the electrode active materials and between the electrode active materials and the current collector foil. It is thought to be for the purpose.
[0035]
【The invention's effect】
That is, in the method for producing a lithium ion secondary battery of the present invention, a sufficient binding force between the electrode active materials and between the electrode active material and the current collector can be obtained, and a compressive stress is generated from the container to the electrode, so that the positive and negative electrodes The thickness in between can be made uniform, and the cycle characteristics can be improved.
[Brief description of the drawings]
FIG. 1 is a flowchart of a manufacturing process according to Embodiment 1 of the present invention.
FIG. 2 is a flowchart showing a manufacturing process according to Embodiment 2 of the present invention.

Claims

The step of arranging an electrode material including an electrode active material and a binder on a current collector, and hot pressing the current collector on which the electrode material is arranged at a temperature at which the binder melts , a step of manufacturing an electrode comprising 30 to 60 vol%, giving a strain stress to the electrode subjected to cold pressing to the electrodes, and the stroke you an electrode filling factor and 40 to 70% by volume, given the strain stress A step of disposing a wound type electrode in a cylindrical container that is wound with a positive electrode and a negative electrode that are opposed to each other through a separator , and injecting an electrolyte into the container to swell the electrode and A process for generating a compressive stress between the two, a method for manufacturing a lithium ion secondary battery.

A step of arranging an electrode material including an electrode active material and a binder on a current collector, a step of cold pressing the current collector on which the electrode material is arranged, and the binder melts the electrode material heated to a temperature, a step of manufacturing an electrode in which the electrode filling rate is 30 to 60 vol%, giving a strain stress to the electrode subjected to cold pressing to the electrodes, electrode filling factor and 40 to 70 vol% A stroke, a stroke in which a positive electrode and a negative electrode including an electrode to which a strain stress is applied are opposed to each other through a separator and wound in a cylindrical container, and an electrolyte is injected into the container A process for swelling the electrode and generating a compressive stress with the container.