JP2004095391A - Battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery having high capacity and excellent cycle characteristics. <P>SOLUTION: A positive electrode 12 contained in a case can 11 and a negative electrode 14 contained in a case cap 13 are stacked through a separator 15. The negative electrode 14 has a structure in which a negative electrode mix layer 14b is provided in a negative electrode collector 14a. The negative electrode mix layer 14b contains composite powder obtained by making carbon black adsorb at least one of sodium salt and ammonium salt of cellulose. The composite powder prevents a conductive network in the negative electrode mix layer 14b from being broken, because of a function as a cushion and a function to secure conductivity by the carbon black. The sodium salt and ammonium salt of cellulose which the carbon black is made to adsorb prevent the carbon black from causing side reaction with electrolyte and lithium ions from being trapped by the carbon black. The rate of the carbon black to the composite powder is preferably 90 mass % or more. <P>COPYRIGHT: (C)2004,JPO

Description

【００６２】
次いで、負極活物質および導電材である人造黒鉛を用意し、銅スズ合金５０ｇと、複合粉末２ｇと、人造黒鉛３８ｇと、結着材であるポリフッ化ビニリデン１０ｇとを混合し、負極合剤を調整した。続いて、この負極合剤を非水溶媒であるＮ−メチル−２−ピロリドンに分散させて負極合剤スラリーとし、厚み１５μｍの銅箔よりなる負極集電体１４ａに塗布して乾燥させ、ロールプレス機で圧縮成型して負極合剤層１４ｂを形成した。そののち、負極合剤層１４ｂが形成された負極集電体１４ａを直径１６．０ｍｍの円板状に打ち抜くことにより、ペレット状の負極１４を作製した。
【００６３】
正極１２および負極１４を作製したのち、外装カップ１３に、負極１４、厚み２５μｍの微孔性ポリプロピレンフィルムからなるセパレータ１５を順次積層し、この上から電解液を注入し、正極１２を入れた外装缶１１を被せたのち、外装カップ１３および外装缶１１の周縁部をガスケット１６を介してかしめることにより、直径２０．０ｍｍ、高さ１．６ｍｍのコイン型の電池を作製した。その際、電解液には、エチレンカーボネート５０容量％とジメチルカーボネート５０容量％とを混合した溶媒にＬｉＰＦ_６を１．０ｍｏｌ／ｌの含有量で溶解させたものを用いた。
【００６４】
得られた実施例１〜６の二次電池について、充放電試験を行い、初回充放電効率および５０サイクル容量維持率を求めた。その際、充電は、２０℃において２ｍＡの定電流で電池電圧が４．２Ｖに達するまで行ったのち、４．２Ｖの定電圧で電流値が２０μＡに達するまで行い、放電は、２ｍＡの定電流で電池電圧が２．５Ｖに達するまで行った。なお、初回充放電効率は、１サイクル目の充電容量に対する１サイクル目の放電容量の比率（％）として算出した。また、５０サイクル容量維持率は、１サイクル目の放電容量に対する５０サイクル目の放電容量の比率（％）として算出した。得られた結果を表１に示す。
【００６５】
実施例１〜６に対する比較例１として、複合粉末に代えて、セルロースのナトリウム塩およびアンモニウム塩を吸着させていないアセチレンブラックを用いたことを除き、他は実施例１〜６と同様にして二次電池を作製した。また、実施例１〜６に対する比較例２として、複合粉末におけるアセチレンブラックの割合を表１に示したように変えたことを除き、他は実施例１〜６と同様にして二次電池を作製した。更に、実施例１〜６に対する比較例３として、複合粉末に代えて、アセチレンブラックと、ＣＭＣ−Ｎａとを混合し、目開き１５０μｍの篩にかけた混合粉末を用いたことを除き、他は実施例１〜６と同様にして二次電池を作製した。その際、混合粉末におけるアセチレンブラックの割合は、９６質量％とした。なお、比較例１のアセチレンブラック、比較例２の複合粉末または比較例３の混合粉末のタップ密度は、表１に示した値であった。また、これらはいずれも、無水エタノールに分散させて目開き１００μｍの篩で分けたときの透過率が９０質量％以上であり、常圧のアルゴン雰囲気下において１２０℃で５時間放置したときの質量減量率が５％以下であった。また、比重１．６０の比重液に浸漬したときに表面に浮かぶ浮遊物の割合は、比較例２の複合粉末は、１質量％未満であり、比較例３の混合粉末は４．２質量％であった。比較例１〜３の二次電池についても、実施例１〜６と同様にして、充放電試験を行い、初回充放電効率および５０サイクル容量維持率を求めた。それらの結果も表１に合わせて示す。
【００６６】
表１において、実施例１〜６と比較例１とを比較すると分かるように、実施例１〜６は、アセチレンブラックのみを用いた比較例１に比べて、初回充放電効率および５０サイクル容量維持率が優れていた。また、実施例４と比較例３とを比較すると分かるように、実施例４は、アセチレンブラックとＣＭＣ−Ｎａとを単に混合した混合粉末を用いた比較例３に比べて、初回充放電効率および５０サイクル容量維持率が優れていた。なお、比較例３は、ＣＭＣ−Ｎａを用いているのにもかかわらず、ＣＭＣ−Ｎａを用いていない比較例１とタップ密度が同じであり、初回充放電効率および５０サイクル容量維持率については比較例１よりも悪化していた。このような結果が得られたのは、混合しただけのＣＭＣ−Ｎａは不導体としての存在でしかなく、導電性を阻害し電池反応を阻害してしまうが、水を用いてアセチレンブラックと混合したＣＭＣ−Ｎａは、アセチレンブラックの表面に部分的に非常に薄い皮膜として存在し、アセチレンブラックが電解液と反応したりリチウムイオンをトラップすることを抑制することができるためと考えられる。更に、実施例１〜６および比較例２から分かるように、複合粉末におけるアセチレンブラックの割合を少なくすると、タップ密度は上昇し、初回充放電効率および５０サイクル容量維持率は大きくなり、極大値を示したのち小さくなる傾向が見られ、９０質量％未満の比較例２では、改善の効果が見られなかった。
【００６７】
すなわち、導電材としてアセチレンブラックにＣＭＣ−Ｎａを吸着させた複合粉末を非水溶媒に分散させると共に、複合粉末におけるアセチレンブラックの割合を９０質量％以上とすれば、容量およびサイクル特性を向上させることができ、複合粉末におけるアセチレンブラックの割合を９４質量％以上９８質量％未満とすれば、より高い効果を得られることが分かった。
【００６８】
（実施例７）
ＣＭＣ−Ｎａの水溶液に代えてカルボキシメチルセルロースのアンモニウム塩（ＣＭＣ−ＮＨ_４）の水溶液を用いて複合粉末を作製したことを除き、他は実施例４と同様にして二次電池を作製した。また、実施例７に対する比較例４，５として、メチルセルロースまたはヒドロキシプロピルメチルセルロースの水溶液を用いて複合粉末を作製したことを除き、他は実施例７と同様にして二次電池を作製した。なお、実施例７および比較例４，５の複合粉末のタップ密度は、表２に示した値であった。また、実施例７および比較例４，５の複合粉末は、いずれも、無水エタノールに分散させて目開き１００μｍの篩で分けたときの透過率が９０質量％以上であった。また、比重１．６０の比重液に浸漬したときに表面に浮かぶ浮遊物の割合が１質量％未満であった。更に、常圧のアルゴン雰囲気下において１２０℃で５時間放置したときの質量減量率が５％以下であった。
【００６９】
実施例７および比較例４，５の二次電池についても、実施例１〜６と同様にして、充放電試験を行い、初回充放電効率および５０サイクル容量維持率を求めた。それらの結果を実施例４の結果と共に表２に示す。
【００７０】
【表２】

【００７１】
表２において、実施例４，７と比較例４，５とを比較すると分かるように、イオン性のセルロース類を用いた実施例４，７は、分子性のセルロース類を用いた比較例４，５に比べて、初回充放電効率および５０サイクル容量維持率の両方について優れていた。これは、分子性のセルロース類が、アセチレンブラックに吸着しにくいことや、電解液に膨潤してしまうことによるものと考えられる。すなわち、イオン性であるセルロースのナトリウム塩およびアンモニウム塩を用いれば、容量およびサイクル特性を向上させることができることが分かった。
【００７２】
（実施例８〜１０）
Ｃｕ−Ｓｎに代えて、銅とケイ素との合金（Ｃｕ−Ｓｉ）、マグネシウムと鉛との合金（Ｍｇ−Ｐｂ）、またはゲルマニウムとマグネシウムとの合金（Ｇｅ−Ｍｇ）を用いて負極１４を作製したことを除き、他は実施例４と同様にして二次電池を作製した。その際、Ｃｕ−Ｓｉは銅８０質量部とケイ素２０質量部とにより作製し、Ｍｇ−Ｐｂはマグネシウム１９質量部と鉛８１質量部とにより作製し、Ｇｅ−Ｍｇはゲルマニウム６０質量部とマグネシウム４０質量部とにより作製した。また、実施例８〜１０に対する比較例６〜８として、複合粉末に代えてアセチレンブラックのみを用いたことを除き、他は実施例８〜１０と同様にして二次電池を作製した。
【００７３】
実施例８〜１０および比較例６〜８についても、実施例１〜６と同様にして、充放電試験を行い、初回充放電効率および５０サイクル容量維持率を求めた。それらの結果を表３〜５に示す。
【００７４】
【表３】

【００７５】
【表４】

【００７６】
【表５】

【００７７】
表３〜５から分かるように、実施例８〜１０は、実施例４と同様に、対応する比較例６〜８に比べて、初回充放電効率および５０サイクル容量維持率の両方について優れていた。すなわち、他の合金を用いた場合にも容量およびサイクル特性を向上させることができることが分かった。
【００７８】
（実施例１１〜１３）
無水エタノールに分散させて目開き１００μｍの篩で分けたときの透過率が表６に示した値の粉末を用いたことを除き、他は実施例４と同様にして二次電池を作製した。なお、実施例１１では、アセチレンブラックとＣＭＣ−Ｎａとの固形物を目開き１８０μｍの篩にかけることにより複合粉末を作製した。また、実施例１２では、実施例４の複合粉末とアセチレンブラックとを混合したものを用いた。また、実施例１３では、アセチレンブラックとＣＭＣ−Ｎａとの固形物を目開き９０μｍの篩にかけることにより複合粉末を作製した。実施例１１〜１３の二次電池についても、実施例１〜６と同様にして、充放電試験を行い、５０サイクル容量維持率を求めた。それらの結果を表６に示す。
【００７９】
【表６】

【００８０】
表６から分かるように、無水エタノールに分散させて目開き１００μｍの篩で分けたときの透過率が９０質量％以上の実施例１１，１２は、５０サイクル容量維持率が８５質量％以上であった。これに対して、透過率が９０質量％未満の実施例１３は、５０サイクル容量維持率が８５質量％未満であった。すなわち、複合粉末としては、無水エタノールに分散させて目開き１００μｍの篩で分けたときの透過率が９０質量％以上のものを用いることが好ましいことが分かった。
【００８１】
なお、上記実施例では、セルロースのナトリウム塩およびアンモニウム塩として、ＣＭＣ−ＮａおよびＣＭＣ−ＮＨ_４を例に挙げて説明したが、他のセルロースのナトリウム塩およびアンモニウム塩を用いても同様の結果を得ることができる。
【００８２】
以上、実施の形態および実施例を挙げて本発明を説明したが、本発明は上記実施の形態および実施例に限定されるものではなく、種々変形可能である。例えば、上記実施の形態および実施例では、溶媒に液状の電解質である電解液を用いる場合について説明したが、電解液に代えて、他の電解質を用いるようにしてもよい。他の電解質としては、例えば、電解液を高分子化合物に保持させたゲル状の電解質、イオン伝導性を有する固体電解質、固体電解質と電解液とを混合したもの、あるいは固体電解質とゲル状の電解質とを混合したものが挙げられる。
【００８３】
なお、ゲル状の電解質には電解液を吸収してゲル化するものであれば種々の高分子化合物を用いることができる。そのような高分子化合物としては、例えば、ポリフッ化ビニリデンあるいはフッ化ビニリデンとヘキサフルオロプロピレンとの共重合体などのフッ素系高分子化合物、ポリエチレンオキサイドあるいはポリエチレンオキサイドを含む架橋体などのエーテル系高分子化合物、またはポリアクリロニトリルなどが挙げられる。特に、酸化還元安定性の点からは、フッ素系高分子化合物が望ましい。
【００８４】
固体電解質には、例えば、イオン伝導性を有する高分子化合物に電解質塩を分散させた有機固体電解質、またはイオン伝導性ガラスあるいはイオン性結晶などよりなる無機固体電解質を用いることができる。このとき、高分子化合物としては、例えば、ポリエチレンオキサイドあるいはポリエチレンオキサイドを含む架橋体などのエーテル系高分子化合物、ポリメタクリレートなどのエステル系高分子化合物、アクリレート系高分子化合物を単独あるいは混合して、または分子中に共重合させて用いることができる。また、無機固体電解質としては、窒化リチウムあるいはヨウ化リチウムなどを用いることができる。
【００８５】
また、上記実施の形態および実施例では、コイン型の二次電池を具体的に挙げて説明したが、本発明は、円筒型、ボタン型、角型あるいはラミネートフィルムなどの外装部材を用いた他の形状を有する二次電池、または正極および負極を電解質を介して巻回した巻回構造などの他の構造を有する二次電池についても同様に適用することができる。また、二次電池に限らず、一次電池などの他の電池についても適用することができる。
【００８６】
【発明の効果】
以上説明したように請求項１ないし請求項６のいずれか１項に記載の電池、または、請求項７ないし請求項１４のいずれか１項に記載の電池の製造方法によれば、リチウムを吸蔵・放出可能な金属，半金属，合金および化合物からなる群のうちの少なくとも１種を含有する負極活物質粉末と、カーボンブラックにセルロースのナトリウム塩およびアンモニウム塩のうちの少なくとも一方を吸着させた複合粉末とを含む負極合剤を、非水溶媒に分散させるようにしたので、セルロースのナトリウム塩およびアンモニウム塩がカーボンブラックから分離することなく、複合粉末が負極活物質粉末中に分散される。よって、カーボンブラックと電解質との副反応や、カーボンブラックによるリチウムイオンのトラップがセルロースのナトリウム塩およびアンモニウム塩により抑制されると共に、リチウムを吸蔵・放出可能な金属，半金属，合金または化合物の膨張・収縮による導電ネットワークの破壊がカーボンブラックにより防止される。特に、複合粉末におけるカーボンブラックの割合が９０質量％以上となるようにしたので、セルロースのナトリウム塩およびアンモニウム塩によるカーボンブラックの凝集が強固とならず、複合粉末が負極合剤中に均一に微分散し、導電ネットワークの破壊が十分に防止される。従って、容量および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】本発明の一実施の形態に係る二次電池の構成を表す断面図である。
【図２】図１に示した負極の製造工程を表す流れ図である。
【図３】図１に示した負極の構成を模式的に表す断面図である。
【図４】セルロースのナトリウム塩またはアンモニウム塩を増粘材として用いた場合の負極の構成を模式的に表す断面図である。
【符号の説明】
１１…外装缶、１２…正極、１２ａ…正極集電体、１２ｂ…正極合剤層、１３…外装カップ、１４…負極、１４ａ…負極集電体、１４ｂ…負極合剤層、１５…セパレータ、１６…ガスケット[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a battery provided with an electrolyte together with a positive electrode and a negative electrode, and a method for manufacturing the same, and more particularly to a battery using lithium (Li) or the like as an electrode reactive species and a method for manufacturing the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, many portable electronic devices such as a camera-integrated VTR (Videotape Recorder), a mobile phone, and a laptop computer have appeared, and their size and weight have been reduced. Along with this, research and development for improving the energy density of batteries, particularly secondary batteries, as portable power supplies for portable electronic devices have been actively promoted. Above all, lithium ion secondary batteries are highly expected because they can obtain a higher energy density than lead batteries or nickel cadmium batteries, which are conventional aqueous electrolyte secondary batteries.
[0003]
As a negative electrode active material used in a lithium ion secondary battery, a carbonaceous material such as non-graphitizable carbon or graphite is widely used because it has a relatively high capacity and exhibits good cycle characteristics.
[0004]
However, with the increase in capacity in recent years, further increase in capacity of the negative electrode has been desired, and research and development have been promoted. For example, Japanese Patent Application Laid-Open No. 8-315825 reports that a high capacity was achieved using a carbonaceous material obtained by selecting a carbonization raw material and production conditions. However, this negative electrode had a high discharge potential of 0.8 V to 1.0 V with respect to lithium, and the battery discharge voltage when a battery was formed was low, so that a significant improvement in battery energy density could not be expected. Furthermore, this negative electrode has a drawback that the charge-discharge curve shape has a large hysteresis and the energy efficiency at each charge-discharge cycle is low.
[0005]
On the other hand, as a negative electrode active material capable of realizing a higher capacity, for example, a material which utilizes the fact that a certain kind of lithium metal is reversibly generated and decomposed by an electrochemical reaction has been studied. Specifically, a LiAl alloy has been known for a long time, and a Si alloy has been reported in US Pat. No. 4,950,566. D. Lacher et al. Reported that Cu is used as a negative electrode active material capable of obtaining a high capacity. ₆ Sn ₅ (See Journal of The Electrochemical Society, 147 (5) 1658-1662 (2000)).
[0006]
However, LiAl alloy, Si alloy or Cu ₆ Sn ₅ Since they expand and contract with charge and discharge and become finer each time charge and discharge are repeated, there has been a problem that when used for a negative electrode of a battery, the cycle characteristics of the battery are deteriorated.
[0007]
Therefore, in order to prevent this deterioration, there has been proposed a negative electrode active material in which a part is replaced with an element which does not participate in expansion and contraction accompanying occlusion and release of lithium. For example, Japanese Unexamined Patent Publication No. 6-325765 discloses LiSi _a O _b (0 ≦ a, 0 <b <2) are disclosed in Japanese Patent Application Laid-Open No. 7-230800. _c Si _1-d M _d O _e (M represents a metal excluding an alkali metal or a similar metal excluding silicon, and 0 ≦ c, 0 <d <1, 0 <e <2). However, JP-A-7-288130 discloses a LiAgTe-based alloy. Has been described. However, even with these negative electrode active materials, since the conductive network is destroyed by expansion and contraction, the charge / discharge cycle characteristics are greatly deteriorated, and the fact that the features of high capacity cannot be fully utilized is a reality.
[0008]
Therefore, attempts have been made to improve the charge / discharge cycle characteristics by coating the surface of the particles of the negative electrode active material with a conductive material, thereby preventing the destruction of the conductive network due to the expansion and contraction of the particles. For example, Japanese Patent Application Laid-Open No. 2000-285919 discloses a technique in which a part or the whole of the surface of a negative electrode active material is coated with a conductive material using a mechanochemical reaction. In addition, Japanese Patent Application Laid-Open No. Hei 10-322226 discloses that lithium can be inserted and extracted by CVD (chemical vapor deposition) or by coating an organic substance and firing it to carbonize the organic substance. A method of coating the surface of a simple alloy with a layer made of carbon is disclosed.
[0009]
[Problems to be solved by the invention]
However, in these methods, since the conductive material is merely provided on the particle surface, in a situation where the particles expand in the charging process, the contact resistance with the adjacent particles is reduced, but the discharging process, In particular, there is a problem in that once the expanded particles contract, as in the last stage of discharge, the coating layer made of a conductive material follows the contraction, and the contact resistance with adjacent particles gradually increases. That is, the destruction of the conductive network due to expansion and contraction of the particles of the negative electrode active material cannot be completely prevented.
[0010]
In Japanese Patent Application Laid-Open No. 2000-223117, a method of coating the surface of an aluminum powder or an aluminum alloy powder with a conductive polymer having high flexibility together with carbon to improve the followability to expansion and contraction has been attempted. Even with this, a sufficient effect cannot be obtained. It is also considered that a conductive material having a large specific surface area such as carbon black is added to the negative electrode to secure conductivity while having a role of a cushion. As a result, lithium ion tracks are liable to occur, resulting in a decrease in battery performance.
[0011]
The present invention has been made in view of such a problem, and an object thereof is to provide a battery having a high capacity and excellent cycle characteristics.
[0012]
[Means for Solving the Problems]
A battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes at least one selected from the group consisting of metals, metalloids, alloys, and compounds capable of inserting and extracting lithium. An active material powder and a negative electrode mixture containing a composite powder obtained by adsorbing at least one of a sodium salt and an ammonium salt of cellulose on carbon black, are obtained by dispersing in a non-aqueous solvent, The proportion of carbon black in the powder is at least 90% by mass.
[0013]
The method for producing a battery according to the present invention is for producing a battery provided with an electrolyte together with a positive electrode and a negative electrode, and comprises at least one selected from the group consisting of metals, metalloids, alloys and compounds capable of inserting and extracting lithium. A negative electrode mixture comprising: a negative electrode active material powder containing, and a composite powder obtained by adsorbing at least one of a sodium salt and an ammonium salt of cellulose on carbon black to form a negative electrode by dispersing the mixture in a non-aqueous solvent. And using a composite powder having a carbon black ratio of 90% by mass or more as the composite powder.
[0014]
In the battery and the method of manufacturing the battery according to the present invention, the negative electrode active material powder containing at least one selected from the group consisting of metals, metalloids, alloys, and compounds capable of occluding and releasing lithium; Since the negative electrode mixture containing the composite powder having at least one of a salt and an ammonium salt adsorbed therein is dispersed in a non-aqueous solvent, the sodium powder and the ammonium salt of cellulose are not separated from the carbon black, and the composite powder is Dispersed in the negative electrode active material powder. Thus, the side reaction between carbon black and the electrolyte and the trapping of lithium ions by the carbon black are suppressed by the sodium and ammonium salts of cellulose, and the expansion of metals, metalloids, alloys or compounds capable of occluding and releasing lithium. -Destruction of the conductive network due to shrinkage is prevented by the carbon black. In particular, since the ratio of carbon black in the composite powder is 90% by mass or more, the aggregation of the carbon black by the sodium salt and the ammonium salt of cellulose does not become strong, and the composite powder is finely dispersed uniformly in the negative electrode mixture. The destruction of the conductive network is sufficiently prevented.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 1 shows a cross-sectional structure of a secondary battery according to one embodiment of the present invention. This secondary battery is a so-called coin type. A disc-shaped positive electrode 12 housed in an outer can 11 and a disc-shaped negative electrode 14 housed in an outer cup 13 are interposed via a separator 15. Are stacked. An electrolytic solution, which is a liquid electrolyte, is injected into the outer can 11 and the outer cup 13 and impregnated in the separator 15. The peripheral edges of the outer can 11 and the outer cup 13 are hermetically sealed by being caulked via an insulating gasket 16. The outer can 11 and the outer cup 13 are each made of a metal such as stainless steel or aluminum (Al).
[0017]
The positive electrode 12 has, for example, a structure in which a positive electrode mixture layer 12b is provided on a positive electrode current collector 12a having a pair of opposing surfaces. The positive electrode current collector 12a is made of, for example, a metal foil such as an aluminum foil, a nickel (Ni) foil, or a stainless steel foil. The positive electrode mixture layer 12b includes, for example, a positive electrode active material. As the positive electrode active material, for example, a metal oxide, a metal sulfide, a specific polymer material, or the like is preferable, and one or more of them are selected according to the purpose of use of the battery.
[0018]
As the metal oxide, Li _x MIO ₂ -Based lithium composite oxide or lithium-free V ₂ O ₅ Is mentioned. In particular, a lithium composite oxide is preferable because a high voltage can be generated and the energy density can be increased. In the above composition formula, MI is preferably at least one kind of a group consisting of one or more transition metals, particularly cobalt (Co), nickel and manganese (Mn). The value of x differs depending on the charge / discharge state of the battery, and is usually 0.05 ≦ x ≦ 1.10. As a specific example of such a lithium composite oxide, LiCoO ₂ , LiNiO ₂ , Li _y Ni _z Co _1-z O ₂ (Y and z are different depending on the charge / discharge state of the battery and are usually 0 <y <1, 0.7 <z <1.02) or LiMn having a spinel structure ₂ O ₄ And the like.
[0019]
As metal sulfide, TiS ₂ Or MoS ₂ And the like. Examples of the polymer material include polyacetylene and polypyrrole. In addition to these positive electrode active materials, NbSe ₂ Etc. can be used.
[0020]
Positive electrode mixture layer 12b also contains a conductive material. Examples of the conductive material include carbonaceous materials such as graphite and carbon black, and one or more of these materials are used in combination. In addition to the carbonaceous material, a metal material or a conductive polymer material may be used as long as the material has conductivity.
[0021]
The positive electrode mixture layer 12b may further include a binder as needed. Examples of the binder include polyvinylidene fluoride.
[0022]
The negative electrode 14 has, for example, a structure in which a negative electrode mixture layer 14b is provided on a negative electrode current collector 14a having a pair of opposing surfaces, and is obtained by a manufacturing method described later. The negative electrode current collector 14a is made of, for example, a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil. The negative electrode mixture layer 14b is configured to include the negative electrode active material powder, and may be configured to include the same binder as the positive electrode mixture layer 12b as necessary.
[0023]
The negative electrode active material powder preferably contains at least one of a metal, a metalloid, an alloy, and a compound capable of inserting and extracting lithium. This is because a high capacity can be obtained. Note that in this specification, a metalloid refers to a simple substance of a metalloid element. Further, in this specification, an alloy includes an alloy composed of one or more metal elements and one or more metalloid elements in addition to an alloy composed of two or more metal elements. The structure includes a solid solution, a eutectic (eutectic mixture), an intermetallic compound, and a structure in which two or more of them coexist.
[0024]
Metals or metalloids capable of inserting and extracting lithium include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), and bismuth (Bi). , Cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf) Is mentioned.
[0025]
Examples of alloys and compounds capable of occluding and releasing lithium include, for example, those represented by the chemical formula Ma _p Mb _q Mc _r Are represented. In these chemical formulas, Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mb represents at least one of nonmetal elements, and Mc represents a metal element and a metalloid other than Ma. Represents at least one of the elements. The values of p, q, and r are p> 0, q ≧ 0, and r ≧ 0, respectively.
[0026]
Among them, the chemical formula Ms _a Mt _b (Ms represents at least one selected from the group consisting of tin, silicon, germanium, and lead, and Mt represents at least one selected from elements other than Ms).
[0027]
Chemical formula Ms _a Mt _b Specific examples of the intermetallic compound represented by are AsSn, AuSn, and CaSn. ₃ , CeSn ₃ , CoCu ₂ Sn, Co ₂ MnSn, CoNiSn, CoSn ₂ , Co ₃ Sn ₂ , CrCu ₂ Sn, Cu ₂ FeSn, CuMgSn, Cu ₂ MnSn, Cu ₄ MnSn, Cu ₂ NiSn, CuSn, Cu ₃ Sn, Cu ₆ Sn ₅ , FeSn ₂ , IrSn, IrSn ₂ , LaSn ₃ , MgNi ₂ Sn, Mg ₂ Sn, MnNi ₂ Sn, MnSn ₂ , Mn ₂ Sn, Mo ₃ Sn, Nb ₃ Sn, NdSn ₃ , NiSn, Ni ₃ Sn ₂ , PdSn, Pd ₃ Sn, Pd ₃ Sn ₂ , PrSn ₃ , PtSn, PtSn ₂ , Pt ₃ Sn, PuSn ₃ , RhSn, Rh ₃ Sn ₂ , RuSn ₂ , SbSn, SnTi ₂ , Sn ₃ U, SnV ₃ , As ₃ Li ₅ Si, BeSiZr, CoSi ₂ , Β-Cr ₃ Si, Cu ₃ Mg ₂ Si, Fe ₃ Si, Li ₅ P ₃ Si, Mg ₂ Si, MoSi ₂ , Nb ₃ Si, NiSi ₂ , Θ-Ni ₂ Si, β-Ni ₃ Si, ReSi ₂ , Α-RuSi, SiTa ₂ , Si ₂ Th, Si ₂ U, β-Si ₂ U, Si ₃ U, SiV ₃ , Si ₂ W, SiZr ₂ , As ₃ GeLi ₅ , CoFeGe, CoGeMn, FeGe ₂ , Fe _1.7 Ge, FeGeMn, FeGeNi, GeLi ₅ P ₃ , GeMg ₂ , GeMnNi, GeMo ₃ , Β'-Ge ₂ Mo, GeNb ₃ , GeNi _1.7 , GeNi ₃ , Ge ₃ Pu, Ge ₃ U, GeV ₃ , AuPb ₂ , Au ₂ Pb, CaPb ₃ , IrPb, KPb ₂ , LaPb ₃ , Β-LiPb, Mg ₂ Pb, PbPd ₃ , Pb ₂ Pd, Pb ₂ Pd ₃ , Pb ₃ Pr, PbPt, PbPu ₃ , Pb ₂ Rh, Pb ₃ U or PbV ₃ and so on.
[0028]
Note that such a negative electrode active material is produced by, for example, a mechanical alloying method or a method in which raw materials are mixed and heat-treated in an inert atmosphere or a reducing atmosphere.
[0029]
The negative electrode active material powder may further include, in addition to at least one selected from the group consisting of metals, metalloids, alloys, and compounds capable of occluding and releasing lithium, and carbonaceous materials capable of occluding and releasing lithium. May be included. Examples of the carbonaceous material include non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbons, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and the like. And carbon blacks. Among them, cokes include pitch coke, needle coke, petroleum coke, etc. An organic polymer compound fired body is obtained by firing a polymer material such as phenolic resin or furan resin at an appropriate temperature to carbonize. Means what you do.
[0030]
The absorption of lithium into the negative electrode active material may be performed electrochemically in the battery after the battery is manufactured, and may be supplied from the positive electrode 12 or a lithium source other than the positive electrode 12 after or before the battery is manufactured. And may be performed electrochemically. Further, it may be performed by including it during the synthesis of the negative electrode active material.
[0031]
The negative electrode mixture layer 14b also contains, as a conductive material, a composite powder obtained by adsorbing at least one of a sodium salt and an ammonium salt of cellulose on carbon black. This composite powder is obtained by coating at least a portion of at least one of a sodium salt and an ammonium salt of cellulose by granulation, and has a function as a cushion by carbon black and a function of securing conductivity. The conductive network in the negative electrode mixture layer 14b is prevented from being broken. The sodium salt and the ammonium salt of cellulose adsorbed on the carbon black are for preventing a side reaction between the carbon black and the electrolytic solution and trapping lithium ions by the carbon black. The ratio of carbon black in the composite powder is preferably 90% by mass or more. If the content is less than 90% by mass, the composite powder is difficult to be finely dispersed in the negative electrode mixture during the preparation of the negative electrode mixture described later, so that the destruction of the conductive network cannot be sufficiently prevented.
[0032]
Examples of the cellulose include carboxymethylcellulose, carboxymethylethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose and hydroxypropylmethylcellulose.
[0033]
Examples of the carbon black include those prepared by a thermal method, an acetylene decomposition method, a contact method, a lamp / pine smoke method, a gas furnace method, or an oil furnace method. Specific examples of those obtained by these production methods include acetylene black, Ketjen black, thermal black and furnace black. Among these, those having a dibutyl phthalate (DBP) oil absorption of 100 ml / 100 g to 300 ml / 100 g are particularly preferable. If the DBP oil absorption is less than 100 ml / 100 g, the effect of imparting conductivity is small. If the DBP oil absorption is more than 300 ml / 100 g, the pores increase, and the mass ratio of the sodium salt or ammonium salt of cellulose adsorbed on the surface increases. This is because the battery capacity is reduced, and the conductivity of the cellulose salt or the ammonium salt may be significantly reduced due to local thickening of the coating.
[0034]
The negative electrode mixture layer 14b may further include another conductive material. Other conductive materials include carbon black to which sodium and ammonium salts of cellulose are not adsorbed, metal powder such as copper or nickel which does not react with lithium electrically, or other carbonaceous materials.
[0035]
The separator 15 separates the positive electrode 12 and the negative electrode 14 and allows lithium ions to pass therethrough while preventing current short circuit due to contact between the two electrodes. The separator 15 is made of, for example, a synthetic resin porous film made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. A structure in which a plurality of types of porous films are stacked may be employed.
[0036]
The electrolytic solution impregnated in the separator 15 includes, for example, a solvent and a lithium salt that is an electrolyte salt. The solvent dissolves and dissociates the electrolyte salt. As the solvent, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4- Methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, acetate, butyrate or propionate, etc., and one or more of these are mixed. You may use it.
[0037]
As the lithium salt, for example, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl or LiBr are mentioned, and any one of them or a mixture of two or more thereof may be used.
[0038]
This secondary battery can be manufactured, for example, as follows.
[0039]
First, the positive electrode 12 is manufactured. First, for example, a positive electrode mixture is prepared by mixing a positive electrode active material, a conductive material, and a binder, and the positive electrode mixture is dispersed in a non-aqueous solvent such as N-methyl-2-pyrrolidone to form a paste. Positive electrode mixture slurry. Subsequently, this positive electrode mixture slurry is applied to the positive electrode current collector 12a, and after drying the non-aqueous solvent, compression molding is performed by a roll press or the like to form a positive electrode mixture layer 12b. The formed positive electrode current collector 12a is punched into a predetermined shape. Thereby, the positive electrode 12 is formed.
[0040]
Next, the negative electrode 14 is manufactured. FIG. 2 is a flowchart showing a manufacturing process of the negative electrode 14. First, for example, at least one of a sodium salt and an ammonium salt of cellulose and carbon black are mixed using a solvent such as water, and then dried to produce a composite powder as a conductive material (step S101). ). Specifically, a composite powder is prepared by dispersing carbon black in a water-soluble solution in which at least one of a sodium salt and an ammonium salt of cellulose is dissolved, and then drying the carbon black. A solvent other than water in which the sodium or ammonium salt of cellulose is dissolved may be used. At this time, in order to efficiently produce the composite powder, it is preferable to use a general wet granulation technique. Wet granulation includes spray drying granulation, fluidized granulation, stirring granulation, mixed granulation, freeze drying granulation and the like.
[0041]
It is preferable that the mixing ratio of at least one of the sodium salt and the ammonium salt of cellulose and the carbon black is such that the ratio of the carbon black in the composite powder is 90% by mass or more. When the ratio of carbon black in the composite powder is low and the sodium and ammonium salts of cellulose are high, the aggregation of the chain structures of the carbon black becomes strong due to the action of the sodium and ammonium salts of cellulose, and the tap density increases. This is because the composite powder cannot be uniformly finely dispersed in the negative electrode mixture layer 14b.
[0042]
Preferably, the tap density of the composite powder is 0.05 g / ml or more and 0.2 g / ml or less. When the tap density of the composite powder is larger than 0.2 g / ml, it is difficult to uniformly and finely disperse the composite powder as described above, and when the tap density is less than 0.05 g / ml, the sodium salt or ammonium salt of cellulose is reduced. This is because the carbon black is not sufficiently adsorbed, so that a side reaction with the electrolytic solution and an irreversible reaction with lithium are likely to occur. When the composite powder is used by mixing with carbon black on which at least one of the sodium salt and the ammonium salt of cellulose is not adsorbed, the tap density in the mixed state is 0.05 g / ml or more. It is preferably at most 0.2 g / ml.
[0043]
Here, the tap density of the composite powder is measured, for example, by a method for measuring the bulk density of acetylene black specified in JIS K1469. In this measurement method, a sample is taken in a measuring cylinder, dropped on a rubber plate, and compressed to obtain a bulk density. The specific operation method is described below.
[0044]
First, 100 ml of a dry sample is gradually introduced with a spoon while a measuring cylinder having a known mass is inclined, and the mass is weighed to a unit of 10 mg. Next, after a rubber stopper is attached to the measuring cylinder, the sample cylinder is dropped 50 times from a height of about 5 cm on the rubber plate to compress the sample, and the volume of the compressed sample is read. After that, the bulk density is calculated by Equation 1.
[0045]
(Equation 1)
D = m / V
In the formula, D represents the bulk density (g / ml), m represents the mass (g) of the sample, and V represents the volume (ml) of the sample after falling 50 times.
[0046]
It is preferable that the obtained composite powder is sufficiently dried to sufficiently reduce the water content. If the water content of the composite powder is high, when a non-water-soluble binder is used in preparing a negative electrode slurry described later, problems such as solidification of the binder occur, and the battery is assembled and charged. This is because if moisture remains up to the step of performing, the battery performance will decrease. Specifically, at normal pressure (1.013 × 10 ⁵ It is desirable to dry until the weight loss rate when left at 120 ° C. for 5 hours in an argon atmosphere of Pa) is 10% or less, and more desirably to 5% by weight or less.
[0047]
Further, the composite powder may be adjusted so that the transmittance when carbon black is dispersed in a solvent that does not dissolve or swell cellulose such as anhydrous ethanol and sieved with a sieve having an opening of 100 μm is 90% by mass or more. Preferably, the transmittance is more preferably adjusted to be 90% by mass or more when divided by a sieve having an opening of 75 μm. Also, when used in combination with carbon black to which at least one of the sodium salt and the ammonium salt of cellulose is not adsorbed, the carbon black is dispersed in a solvent that does not dissolve or swell cellulose such as anhydrous ethanol, and the mesh is opened. It is preferable to adjust the transmittance so as to be 90% by mass or more when divided by a 100 μm sieve, and more preferably to adjust the transmittance so as to be 90% by mass or more when divided by a sieve having an opening of 75 μm. preferable. If this range is significantly exceeded, the secondary particles contained in the composite powder become lump (coagulated material) in the negative electrode slurry and are difficult to be uniformly dispersed, and the negative electrode slurry is placed on the negative electrode current collector 14a as described later. This becomes an obstacle when the negative electrode mixture layer 14b is formed by applying the negative electrode mixture layer, and a problem such as the formation of an uncoated portion is likely to occur.
[0048]
In addition, the ratio of the sodium salt and the ammonium salt of cellulose separated without being adsorbed on the carbon black contained in the composite powder is preferably 1% by mass or less. This is because sodium salts and ammonium salts of cellulose that do not completely adhere to carbon black are regarded as nonconductors in a battery reaction system and cause a factor to increase resistance.
[0049]
The proportion of cellulose not adsorbed on carbon black can be determined, for example, by measuring the mass of suspended matter floating on the surface when immersed in a specific gravity liquid having a specific gravity of 1.60 at 25 ° C. Is calculated. This is because the true specific gravity of carbon black is 1.75 to 1.90, and the true specific gravity of carbon black on which a sodium salt or ammonium salt of cellulose is adsorbed is 1.68 or more, whereas sodium salt and ammonium of cellulose are used. The fact that the true specific gravity of the salt is 1.55 or less is used. The mass of the suspended matter is specifically measured as follows. First, the composite powder is sieved with a sieve having an opening of 100 μm, 1 g is weighed from the passed composite powder, and the mixture is put into a 100 ml colorimetric tube. Next, 100 ml of a specific gravity liquid having a specific gravity of 1.60 is further added to the colorimetric tube, and the mixture is thoroughly stirred, and the composite powder is sufficiently impregnated with the specific gravity liquid and allowed to stand for 12 hours. Subsequently, 5 ml is separated from the surface of the specific gravity liquid together with the suspended matter. This separated liquid is again added to 90 ml of a clean specific gravity liquid having a specific gravity of 1.60, stirred well, and left to stand for 12 hours. After that, 5 ml of the specific gravity liquid is again separated from the surface of the specific gravity liquid, dried and taken out of the suspended matter, and the mass of the suspended matter is measured. At this time, as the specific gravity liquid having a specific gravity of 1.60, for example, carbon tetrachloride (CCl ₄ ) And bromoform (CHBr) ₃ ) Can be used in a desired mixing ratio.
[0050]
After preparing a composite powder, a negative electrode active material powder containing at least one selected from the group consisting of metals, metalloids, alloys and compounds capable of occluding and releasing lithium is mixed with the composite powder and a binder. Thus, a negative electrode mixture is prepared, and this negative electrode mixture is dispersed in a non-aqueous solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry (step S102). Thereby, the composite powder is uniformly dispersed in the negative electrode active material powder. The non-aqueous solvent is used, because the aqueous solvent dissolves and separates the sodium or ammonium salt of cellulose adsorbed on carbon black, and the effect of suppressing side reactions between the carbon black and the electrolytic solution is reduced. Not only that, but also because the sodium salt or the ammonium salt of cellulose evenly covers the battery reaction contributing substances such as the negative electrode active material, thereby inhibiting the battery reaction. Subsequently, the negative electrode mixture slurry is applied to the negative electrode current collector 14a, the non-aqueous solvent is dried, and then compression-molded by a roll press or the like to form a negative electrode mixture layer 14b (step S103). The negative electrode current collector 14a on which the agent layer 14b is formed is punched into a predetermined shape (Step S104). Thereby, the negative electrode 14 is formed. FIG. 3 schematically shows the configuration of the negative electrode 14. As shown in FIG. 3, the sodium salt or ammonium salt of cellulose adsorbed on the carbon black is not dissolved in the solvent at the time of preparing the slurry, and therefore exists as a deposited film on the negative electrode constituent material such as the negative electrode active material 14b1. And exists as complex 14b2.
[0051]
In addition, the sodium salt and the ammonium salt of cellulose may be used as a thickener of the negative electrode mixture slurry by dissolving it in water to form a paste when preparing the negative electrode mixture slurry, for example. In this case, for example, a sodium salt or an ammonium salt of cellulose is mixed with a negative electrode active material, a conductive material such as carbon black, a binder, and water, then applied to a negative electrode current collector, and dried to obtain a mixture shown in FIG. As shown in (1), it precipitates on the surface or between particles of the negative electrode constituting material such as the negative electrode active material 14b1, the negative electrode current collector 14a or the conductive material 14b3, and contributes to adhesion. However, the sodium or ammonium salt 14b4 of cellulose here also functions as a non-conductor, and is a factor that impedes the battery reaction by uniformly covering the battery reaction contributing substances such as the negative electrode active material 14b1 or the negative electrode current collector 14a. Also. That is, in the present embodiment, unlike this case, the inhibition on the battery reaction is extremely small. In FIG. 4, the same components as those shown in FIG. 3 are denoted by the same reference numerals.
[0052]
After producing the positive electrode 12 and the negative electrode 14, for example, the negative electrode 14, the separator 15 impregnated with the electrolytic solution, and the positive electrode 12 are laminated, placed in the outer cup 13 and the outer can 11, and caulked. Thereby, the secondary battery shown in FIG. 1 is completed.
[0053]
This secondary battery operates as follows.
[0054]
In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 12 and occluded in the negative electrode 14 via the electrolytic solution impregnated in the separator 15. When the discharge is performed, for example, lithium ions are released from the negative electrode 14 and occluded in the positive electrode 12 through the electrolytic solution impregnated in the separator 15. At this time, the composite powder in which at least one of the sodium salt and the ammonium salt of cellulose is adsorbed on the carbon black secures the conductivity between the particles of the negative electrode active material powder while serving as a cushion. Further, at least one of the sodium salt and the ammonium salt of cellulose adsorbed on the carbon black suppresses a side reaction between the carbon black and the electrolytic solution and a trap of lithium ions by the carbon black.
[0055]
As described above, according to the present embodiment, the negative electrode active material powder containing at least one selected from the group consisting of metals, metalloids, alloys, and compounds capable of occluding and releasing lithium; Since the negative electrode mixture containing the composite powder having at least one of the salt and the ammonium salt adsorbed therein is dispersed in the non-aqueous solvent, the sodium and ammonium salts of cellulose are not separated from the carbon black, The composite powder is dispersed in the negative electrode active material powder. Therefore, the side reaction between carbon black and the electrolyte and the trapping of lithium ions by the carbon black are suppressed by the sodium and ammonium salts of cellulose, and the metal, metalloid, alloy or compound capable of occluding and releasing lithium is suppressed. Breakage of the conductive network due to expansion and contraction is prevented by the carbon black. In particular, since the ratio of carbon black in the composite powder is 90% by mass or more, the aggregation of carbon black by the sodium salt and ammonium salt of cellulose does not become strong, and the composite powder is uniformly finely dispersed in the negative electrode mixture. It is dispersed and the destruction of the conductive network is sufficiently prevented. Therefore, capacity and cycle characteristics can be improved.
[0056]
【Example】
Further, a specific embodiment of the present invention will be described in detail with reference to FIG.
[0057]
(Examples 1 to 6)
First, lithium carbonate (Li ₂ CO ₃ ) And cobalt carbonate (CoCO ₃ ) Were mixed at a ratio of lithium carbonate: cobalt carbonate = 0.5: 1 (molar ratio) and calcined in air at 900 ° C. for 5 hours to obtain a lithium-cobalt composite oxide (LiCoO 2) as a positive electrode active material. ₂ ) Got. Next, 91 parts by mass of the lithium-cobalt composite oxide, 6 parts by mass of graphite as a conductive material, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone which is a non-aqueous solvent to form a positive electrode mixture slurry, which is uniformly applied to a 20 μm-thick aluminum foil positive electrode current collector 12a, and dried. Then, the mixture was compression-molded with a roll press to form a positive electrode mixture layer 12b. Thereafter, the positive electrode current collector 12a on which the positive electrode mixture layer 12b was formed was punched into a disc having a diameter of 15.5 mm, thereby producing a pellet-shaped positive electrode 12.
[0058]
Further, copper and tin were weighed so as to have a ratio of copper: tin = 50: 50 (parts by mass), placed in a quartz tube, and melted in a high-frequency melting furnace in an argon atmosphere. Thereafter, this was cast on a rotating disk made of copper having a diameter of 200 mm, a width of 20 mm, and a rotation speed of 3000 rpm, and rapidly cooled to obtain a ribbon-shaped copper-tin (Cu-Sn) alloy piece. The obtained ribbon-shaped copper-tin alloy piece was pulverized using a ball mill under an argon atmosphere to obtain powder. Next, the obtained powder was classified with a sieve having a mesh size of 63 μm to obtain a negative electrode active material powder. The average particle size of the negative electrode active material powder obtained by the classification was 25 μm.
[0059]
Next, the average particle diameter is 35 nm, and the specific surface area is 68 m. ² / G, acetylene black having an oil absorption of 175 ml / 100 g of dibutyl phthalate and a 4% aqueous solution of a sodium salt of carboxymethylcellulose (CMC-Na) having an average degree of polymerization of 120, an average molecular weight of 30,000 and an etherification degree of 0.6 are mixed, Pure water was appropriately added thereto, and the mixture was further mixed, heated and dried to obtain a solid. The obtained solid was crushed in an agate mortar, sieved through a 150 μm mesh sieve, and then 1.33 × 10 ³ It dried at 100 degreeC under reduced pressure of Pa or less for 12 hours, and obtained the composite powder which made CMC-Na adsorb | suck to acetylene black.
[0060]
At that time, the ratio of acetylene black in the composite powder was changed as shown in Table 1 in Examples 1 to 6. The tap densities of the obtained composite powders of Examples 1 to 6 specified in JIS K1469 were as shown in Table 1. In addition, all of the composite powders of Examples 1 to 6 had a transmittance of 90% by mass or more when dispersed in anhydrous ethanol and sieved with a sieve having openings of 100 µm. In addition, the ratio of suspended matter floating on the surface when immersed in a specific gravity liquid having a specific gravity of 1.60 was less than 1% by mass. Further, the mass loss rate when left at 120 ° C. for 5 hours under an argon atmosphere at normal pressure was 5% or less.
[0061]
[Table 1]

[0062]
Next, a negative electrode active material and artificial graphite as a conductive material were prepared, and 50 g of a copper-tin alloy, 2 g of composite powder, 38 g of artificial graphite, and 10 g of polyvinylidene fluoride as a binder were mixed, and a negative electrode mixture was prepared. It was adjusted. Subsequently, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone, which is a non-aqueous solvent, to form a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a negative electrode current collector 14a made of a copper foil having a thickness of 15 μm, and dried. The negative electrode mixture layer 14b was formed by compression molding with a press. Thereafter, the negative electrode current collector 14a on which the negative electrode mixture layer 14b was formed was punched into a disk having a diameter of 16.0 mm, thereby producing a pellet-shaped negative electrode 14.
[0063]
After producing the positive electrode 12 and the negative electrode 14, the negative electrode 14 and the separator 15 made of a microporous polypropylene film having a thickness of 25 μm are sequentially laminated on the external cup 13, and an electrolyte is injected from above, and the external container is filled with the positive electrode 12. After covering the can 11, the outer peripheral portion of the outer cup 13 and the outer can 11 was swaged via a gasket 16 to produce a coin-type battery having a diameter of 20.0 mm and a height of 1.6 mm. At this time, the electrolyte was made of LiPF in a mixed solvent of 50% by volume of ethylene carbonate and 50% by volume of dimethyl carbonate. ₆ Was dissolved at a content of 1.0 mol / l.
[0064]
The obtained secondary batteries of Examples 1 to 6 were subjected to a charge / discharge test to determine an initial charge / discharge efficiency and a 50-cycle capacity retention rate. At this time, charging was performed at 20 ° C. at a constant current of 2 mA until the battery voltage reached 4.2 V, and then at a constant voltage of 4.2 V until the current value reached 20 μA, and discharging was performed at a constant current of 2 mA. And until the battery voltage reached 2.5V. The initial charge / discharge efficiency was calculated as a ratio (%) of the first cycle discharge capacity to the first cycle charge capacity. The 50-cycle capacity retention rate was calculated as the ratio (%) of the 50th cycle discharge capacity to the 1st cycle discharge capacity. Table 1 shows the obtained results.
[0065]
As Comparative Example 1 with respect to Examples 1 to 6, except that acetylene black not adsorbing cellulose sodium and ammonium salts was used in place of the composite powder, the same procedures as in Examples 1 to 6 were repeated. A secondary battery was manufactured. Further, as Comparative Example 2 with respect to Examples 1 to 6, a secondary battery was fabricated in the same manner as in Examples 1 to 6, except that the ratio of acetylene black in the composite powder was changed as shown in Table 1. did. Further, as Comparative Example 3 for Examples 1 to 6, except that a mixed powder obtained by mixing acetylene black and CMC-Na and sieving with a 150 μm mesh was used instead of the composite powder. A secondary battery was manufactured in the same manner as in Examples 1 to 6. At that time, the ratio of acetylene black in the mixed powder was 96% by mass. The tap density of the acetylene black of Comparative Example 1, the composite powder of Comparative Example 2, or the mixed powder of Comparative Example 3 was the value shown in Table 1. All of these have a transmittance of 90% by mass or more when dispersed in anhydrous ethanol and sieved with a sieve having an opening of 100 μm, and the mass when left at 120 ° C. for 5 hours in an argon atmosphere at normal pressure. The weight loss rate was 5% or less. In addition, the ratio of suspended matter floating on the surface when immersed in a specific gravity liquid having a specific gravity of 1.60 is less than 1% by mass for the composite powder of Comparative Example 2 and 4.2% by mass for the mixed powder of Comparative Example 3 Met. For the secondary batteries of Comparative Examples 1 to 3, a charge / discharge test was performed in the same manner as in Examples 1 to 6, and the initial charge / discharge efficiency and the 50-cycle capacity retention rate were determined. The results are also shown in Table 1.
[0066]
In Table 1, as can be seen by comparing Examples 1 to 6 with Comparative Example 1, Examples 1 to 6 have an initial charge / discharge efficiency and a 50-cycle capacity retention as compared to Comparative Example 1 using only acetylene black. The rate was excellent. Further, as can be seen by comparing Example 4 and Comparative Example 3, Example 4 has an initial charge / discharge efficiency and an initial charge / discharge efficiency that are lower than Comparative Example 3 using a mixed powder obtained by simply mixing acetylene black and CMC-Na. The 50-cycle capacity retention rate was excellent. Note that Comparative Example 3 had the same tap density as Comparative Example 1 not using CMC-Na, despite using CMC-Na. It was worse than Comparative Example 1. Such a result was obtained because CMC-Na which was just mixed was present only as a non-conductor, and inhibited the conductivity and the battery reaction, but was mixed with acetylene black using water. It is considered that the CMC-Na thus present partially exists as a very thin film on the surface of acetylene black, and can suppress the reaction of acetylene black with the electrolytic solution and the trapping of lithium ions. Furthermore, as can be seen from Examples 1 to 6 and Comparative Example 2, when the ratio of acetylene black in the composite powder is reduced, the tap density increases, the initial charge / discharge efficiency and the 50-cycle capacity retention ratio increase, and the maximum value increases. After that, a tendency to decrease was observed, and in Comparative Example 2 having less than 90% by mass, no improvement effect was observed.
[0067]
That is, when the composite powder obtained by adsorbing CMC-Na on acetylene black as a conductive material is dispersed in a non-aqueous solvent, and the proportion of acetylene black in the composite powder is 90% by mass or more, the capacity and cycle characteristics are improved. It was found that a higher effect could be obtained if the ratio of acetylene black in the composite powder was 94% by mass or more and less than 98% by mass.
[0068]
(Example 7)
Instead of the aqueous solution of CMC-Na, ammonium salt of carboxymethyl cellulose (CMC-NH ₄ A secondary battery was fabricated in the same manner as in Example 4, except that a composite powder was fabricated using the aqueous solution of (2). Further, as Comparative Examples 4 and 5 with respect to Example 7, secondary batteries were manufactured in the same manner as Example 7 except that a composite powder was manufactured using an aqueous solution of methylcellulose or hydroxypropylmethylcellulose. The tap densities of the composite powders of Example 7 and Comparative Examples 4 and 5 were the values shown in Table 2. In addition, each of the composite powders of Example 7 and Comparative Examples 4 and 5 had a transmittance of 90% by mass or more when dispersed in anhydrous ethanol and sieved with a sieve having openings of 100 μm. In addition, the ratio of suspended matter floating on the surface when immersed in a specific gravity liquid having a specific gravity of 1.60 was less than 1% by mass. Further, the mass loss rate when left at 120 ° C. for 5 hours under an argon atmosphere at normal pressure was 5% or less.
[0069]
For the secondary batteries of Example 7 and Comparative Examples 4 and 5, a charge / discharge test was performed in the same manner as in Examples 1 to 6, and the initial charge / discharge efficiency and the 50-cycle capacity retention rate were determined. The results are shown in Table 2 together with the results of Example 4.
[0070]
[Table 2]

[0071]
In Table 2, as can be seen by comparing Examples 4 and 7 with Comparative Examples 4 and 5, Examples 4 and 7 using ionic celluloses were Comparative Examples 4 and 7 using molecular celluloses. Compared to No. 5, both the initial charge and discharge efficiency and the 50-cycle capacity retention ratio were excellent. This is considered to be due to the fact that molecular celluloses are hardly adsorbed on acetylene black and swell in the electrolytic solution. That is, it was found that capacity and cycle characteristics could be improved by using ionic cellulose sodium and ammonium salts.
[0072]
(Examples 8 to 10)
The negative electrode 14 is manufactured using an alloy of copper and silicon (Cu-Si), an alloy of magnesium and lead (Mg-Pb), or an alloy of germanium and magnesium (Ge-Mg) instead of Cu-Sn. A secondary battery was fabricated in the same manner as in Example 4 except for the above. At that time, Cu-Si was produced by 80 parts by mass of copper and 20 parts by mass of silicon, Mg-Pb was produced by 19 parts by mass of magnesium and 81 parts by mass of lead, and Ge-Mg was produced by 60 parts by mass of germanium and 40 parts by mass of magnesium. Parts by mass. Further, as Comparative Examples 6 to 8 with respect to Examples 8 to 10, secondary batteries were manufactured in the same manner as in Examples 8 to 10, except that only acetylene black was used instead of the composite powder.
[0073]
For Examples 8 to 10 and Comparative Examples 6 to 8, a charge / discharge test was performed in the same manner as in Examples 1 to 6, and the initial charge / discharge efficiency and the 50-cycle capacity retention rate were determined. Tables 3 to 5 show the results.
[0074]
[Table 3]

[0075]
[Table 4]

[0076]
[Table 5]

[0077]
As can be seen from Tables 3 to 5, Examples 8 to 10 were superior to Comparative Examples 6 to 8 in both the initial charge / discharge efficiency and the 50-cycle capacity retention rate, as in Example 4. . That is, it was found that the capacity and cycle characteristics could be improved even when another alloy was used.
[0078]
(Examples 11 to 13)
A secondary battery was fabricated in the same manner as in Example 4, except that powder having a transmittance shown in Table 6 when dispersed in anhydrous ethanol and sieved with a sieve having an opening of 100 μm was used. In Example 11, a composite powder was prepared by sieving a solid of acetylene black and CMC-Na through a 180-μm mesh sieve. In Example 12, a mixture of the composite powder of Example 4 and acetylene black was used. Further, in Example 13, a composite powder was prepared by sieving a solid of acetylene black and CMC-Na through a sieve having a mesh size of 90 μm. With respect to the secondary batteries of Examples 11 to 13, a charge / discharge test was performed in the same manner as in Examples 1 to 6, and a 50-cycle capacity retention rate was obtained. Table 6 shows the results.
[0079]
[Table 6]

[0080]
As can be seen from Table 6, in Examples 11 and 12 in which the transmittance was 90% by mass or more when dispersed in anhydrous ethanol and sieved with a sieve having an opening of 100 µm, the 50-cycle capacity retention ratio was 85% by mass or more. Was. In contrast, Example 13 having a transmittance of less than 90% by mass had a 50-cycle capacity retention of less than 85% by mass. That is, it was found that it is preferable to use a composite powder having a transmittance of 90% by mass or more when dispersed in anhydrous ethanol and sieved with a sieve having openings of 100 μm.
[0081]
In the above examples, CMC-Na and CMC-NH were used as the sodium and ammonium salts of cellulose. ₄ However, similar results can be obtained by using other sodium salts and ammonium salts of cellulose.
[0082]
As described above, the present invention has been described with reference to the embodiment and the example. However, the present invention is not limited to the above-described embodiment and example, and can be variously modified. For example, in the above-described embodiments and examples, a case has been described in which an electrolytic solution that is a liquid electrolyte is used as a solvent. However, another electrolyte may be used instead of the electrolytic solution. As other electrolytes, for example, a gel electrolyte in which an electrolyte is held by a polymer compound, a solid electrolyte having ionic conductivity, a mixture of a solid electrolyte and an electrolyte, or a solid electrolyte and a gel electrolyte And mixtures thereof.
[0083]
Note that various polymer compounds can be used as the gel electrolyte as long as they absorb the electrolytic solution and gel. Examples of such a polymer compound include fluorine-based polymer compounds such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, and ether-based polymers such as polyethylene oxide or a crosslinked product containing polyethylene oxide. And polyacrylonitrile. In particular, from the viewpoint of oxidation-reduction stability, a fluorine-based polymer compound is desirable.
[0084]
As the solid electrolyte, for example, an organic solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, or an inorganic solid electrolyte made of ion-conductive glass or ionic crystal can be used. At this time, as the polymer compound, for example, an ether-based polymer compound such as polyethylene oxide or a crosslinked body containing polyethylene oxide, an ester-based polymer compound such as polymethacrylate, or an acrylate-based polymer compound alone or as a mixture, Alternatively, they can be used after being copolymerized in the molecule. As the inorganic solid electrolyte, lithium nitride, lithium iodide, or the like can be used.
[0085]
Further, in the above-described embodiment and examples, the coin-type secondary battery was specifically described. However, the present invention is not limited to use of an exterior member such as a cylindrical, button, square, or laminated film. And the secondary battery having another structure such as a wound structure in which a positive electrode and a negative electrode are wound with an electrolyte interposed therebetween can be similarly applied. Further, the invention is not limited to the secondary battery, and can be applied to other batteries such as a primary battery.
[0086]
【The invention's effect】
As described above, according to the method of manufacturing a battery according to any one of claims 1 to 6 or the method of manufacturing a battery according to any one of claims 7 to 14, lithium is absorbed. .A composite in which a negative electrode active material powder containing at least one selected from the group consisting of releasable metals, metalloids, alloys and compounds, and carbon black adsorbing at least one of a sodium salt and an ammonium salt of cellulose. Since the negative electrode mixture containing the powder and the powder is dispersed in the non-aqueous solvent, the composite powder is dispersed in the negative electrode active material powder without separating the sodium salt and the ammonium salt of cellulose from the carbon black. Thus, the side reaction between carbon black and the electrolyte and the trapping of lithium ions by the carbon black are suppressed by the sodium and ammonium salts of cellulose, and the expansion of metals, metalloids, alloys or compounds capable of occluding and releasing lithium. -Destruction of the conductive network due to shrinkage is prevented by the carbon black. In particular, since the ratio of the carbon black in the composite powder is set to 90% by mass or more, the aggregation of the carbon black by the sodium salt and the ammonium salt of cellulose does not become strong, and the composite powder is uniformly finely dispersed in the negative electrode mixture. It is dispersed and the destruction of the conductive network is sufficiently prevented. Therefore, capacity and cycle characteristics can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a manufacturing process of the negative electrode shown in FIG.
FIG. 3 is a cross-sectional view schematically illustrating a configuration of a negative electrode illustrated in FIG.
FIG. 4 is a cross-sectional view schematically showing a configuration of a negative electrode when a sodium salt or an ammonium salt of cellulose is used as a thickener.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Outer can, 12 ... Positive electrode, 12a ... Positive electrode collector, 12b ... Positive electrode mixture layer, 13 ... Outer cup, 14 ... Negative electrode, 14a ... Negative electrode collector, 14b ... Negative electrode mixture layer, 15 ... Separator, 16 ... Gasket

Claims (12)

A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode includes a negative electrode active material powder containing at least one selected from the group consisting of a metal, a metalloid, an alloy, and a compound capable of inserting and extracting lithium; A negative electrode mixture containing at least one of the composite powder adsorbed, is obtained by dispersing in a non-aqueous solvent,
The battery according to claim 1, wherein a ratio of carbon black in the composite powder is 90% by mass or more. The metal, metalloid, alloy, and compound capable of inserting and extracting lithium include at least one selected from the group consisting of tin (Sn), silicon (Si), germanium (Ge), and lead (Pb). The battery according to claim 1, wherein: The battery according to claim 1, wherein the composite powder has a tap density of 0.05 g / ml or more and 0.2 g / ml or less. The battery according to claim 1, wherein the composite powder has a transmittance of 90% by mass or more when dispersed in anhydrous ethanol and sieved with a sieve having an opening of 100 µm. 2. The battery according to claim 1, wherein the composite powder has less than 1% by mass of a floating substance floating on the surface when immersed in a specific gravity liquid having a specific gravity of 1.60. 3. 2. The battery according to claim 1, wherein the composite powder has a weight loss rate of 10% or less when left at 120 ° C. for 5 hours in an argon atmosphere at normal pressure. 3. A method for producing a battery including an electrolyte together with a positive electrode and a negative electrode,
Negative electrode active material powder containing at least one selected from the group consisting of metals, metalloids, alloys and compounds capable of occluding and releasing lithium, and adsorbing at least one of sodium salt and ammonium salt of cellulose on carbon black Including a step of preparing the negative electrode by dispersing the negative electrode mixture containing the composite powder and the non-aqueous solvent,
A method for producing a battery, comprising using the composite powder having a carbon black ratio of 90% by mass or more. As the metal, metalloid, alloy and compound capable of inserting and extracting lithium, those containing at least one selected from the group consisting of tin (Sn), silicon (Si), germanium (Ge) and lead (Pb). The method for producing a battery according to claim 7, wherein the battery is used. The method according to claim 7, wherein the composite powder has a tap density of 0.05 g / ml or more and 0.2 g / ml or less. The method for producing a battery according to claim 7, wherein the composite powder has a transmittance of 90 mass% or more when dispersed in anhydrous ethanol and sieved with a sieve having an opening of 100 µm. The method for producing a battery according to claim 7, wherein the composite powder has a ratio of a floating substance floating on the surface of less than 1% by mass when immersed in a specific gravity liquid having a specific gravity of 1.60. The method according to claim 7, wherein the composite powder has a mass loss rate of 10% or less when left at 120 ° C for 5 hours in an argon atmosphere at normal pressure.

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