JPWO2012081534A1 - Anode for non-aqueous electrolyte secondary battery - Google Patents

Anode for non-aqueous electrolyte secondary battery Download PDF

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JPWO2012081534A1
JPWO2012081534A1 JP2012543374A JP2012543374A JPWO2012081534A1 JP WO2012081534 A1 JPWO2012081534 A1 JP WO2012081534A1 JP 2012543374 A JP2012543374 A JP 2012543374A JP 2012543374 A JP2012543374 A JP 2012543374A JP WO2012081534 A1 JPWO2012081534 A1 JP WO2012081534A1
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井上　大輔
大輔 井上
春香 清水
春香 清水
松嶋　英明
英明 松嶋
仁彦 井手
仁彦 井手
なつみ 柴村
なつみ 柴村
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Mitsui Mining and Smelting Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
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  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

充放電によるリチウムイオンの挿入・脱離時における負極活物質の膨張収縮が緩和され、電池の充放電サイクル特性が向上した非水電解液二次電池用負極を提供すること。非水電解液二次電池用負極は、ケイ素を含有する負極活物質の粒子を含む負極活物質層を備える。前記活物質層においては、ポリイミド、ポリアミド又はポリアミドイミドが、前記粒子の表面の少なくとも一部に固着している。かつポリイミド、ポリアミド又はポリアミドイミドを介して複数の前記粒子が連結した状態になっている。To provide a negative electrode for a non-aqueous electrolyte secondary battery in which expansion and contraction of a negative electrode active material during insertion / extraction of lithium ions due to charge / discharge is mitigated and charge / discharge cycle characteristics of the battery are improved. A negative electrode for a nonaqueous electrolyte secondary battery includes a negative electrode active material layer including particles of a negative electrode active material containing silicon. In the active material layer, polyimide, polyamide or polyamideimide is fixed to at least a part of the surface of the particle. In addition, a plurality of the particles are connected via polyimide, polyamide or polyamideimide.

Description

本発明は、リチウム二次電池等の非水電解液二次電池に用いられる負極に関する。更に本発明は、該負極を備えた非水電解液二次電池に関する。   The present invention relates to a negative electrode used for a nonaqueous electrolyte secondary battery such as a lithium secondary battery. Furthermore, this invention relates to the non-aqueous electrolyte secondary battery provided with this negative electrode.

非水電解液二次電池の負極は一般に、充電によってリチウムイオンを挿入可能な材料からなる活物質の粒子を、バインダ、導電材及び溶剤と混合し、それによって得られた合剤を集電体の表面の塗布した後、塗膜を乾燥させ、更にプレス加工を施して製造される。活物質としては、従来グラファイト等の炭素系材料が用いられてきたが、近年では容量が更に高い材料であるケイ素系活物質やスズ系活物質等の使用も検討されている。   The negative electrode of a non-aqueous electrolyte secondary battery is generally prepared by mixing particles of an active material made of a material capable of inserting lithium ions by charging with a binder, a conductive material, and a solvent, and using the resulting mixture as a current collector After coating the surface of the film, the coating film is dried and further pressed to produce. Conventionally, carbon-based materials such as graphite have been used as the active material, but in recent years, the use of silicon-based active materials and tin-based active materials, which are materials with higher capacities, has been studied.

これら高容量の活物質は、リチウムイオンの挿入脱離による体積変化が大きいことから、充放電を繰り返すにつれて活物質層からの脱落が起こりやすいという不都合がある。この不都合を解消するための手段の一つとして、本出願人は先に、活物質の粒子を含む活物質層を備え、該粒子間にリチウム化合物の形成能の低い金属材料が電解めっきによって析出しており、該活物質層の表面が、該金属材料と同種の金属材料からなる表面層によって連続に又は不連続に被覆されている非水電解液二次電池用負極を提案した（特許文献１）。   Since these high-capacity active materials have a large volume change due to the insertion and desorption of lithium ions, there is a disadvantage that the active material layer is likely to fall off as charging and discharging are repeated. As one means for solving this inconvenience, the present applicant has previously provided an active material layer containing active material particles, and a metal material having a low lithium compound forming ability is deposited between the particles by electrolytic plating. And proposed a negative electrode for a non-aqueous electrolyte secondary battery in which the surface of the active material layer is continuously or discontinuously covered with a surface layer made of the same metal material as the metal material (Patent Document) 1).

特許第４０５３５７６号公報Japanese Patent No. 4053576

前記の文献の記載の負極によれば、充放電によって該粒子が膨張収縮することに起因して微粉化しても、その脱落が起こりづらくなるという利点がある。しかも、非水電解液が活物質層へ容易に到達するので、初期充電の過電圧を低くすることができるという利点もある。しかし、非水電解液二次電池に要求される性能はますます厳しくなっており、高容量で、高サイクル特性を有する非水電解液二次電池が求められている。   According to the negative electrode described in the above literature, there is an advantage that even if the particles are pulverized due to expansion / contraction due to charge / discharge, the particles are less likely to fall off. In addition, since the non-aqueous electrolyte easily reaches the active material layer, there is an advantage that the overvoltage of the initial charge can be lowered. However, the performance required for non-aqueous electrolyte secondary batteries is becoming more severe, and there is a demand for non-aqueous electrolyte secondary batteries having high capacity and high cycle characteristics.

したがって本発明の課題は、前述した従来技術の負極よりも各種の性能が一層向上した非水電解液二次電池用負極を提供することにある。   Accordingly, an object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery in which various performances are further improved as compared with the negative electrode of the prior art described above.

本発明は、ケイ素を含有する負極活物質の粒子を含む負極活物質層を備え、
前記活物質層においては、ポリイミド、ポリアミド又はポリアミドイミドが、前記粒子の表面の少なくとも一部に固着しており、かつポリイミド、ポリアミド又はポリアミドイミドを介して複数の前記粒子が連結した状態になっていることを特徴とする非水電解液二次電池用負極を提供するものである。The present invention comprises a negative electrode active material layer containing particles of a negative electrode active material containing silicon,
In the active material layer, polyimide, polyamide or polyamideimide is fixed to at least a part of the surface of the particles, and a plurality of the particles are connected via the polyimide, polyamide or polyamideimide. The present invention provides a negative electrode for a nonaqueous electrolyte secondary battery.

本発明によれば、充放電によるリチウムイオンの挿入・脱離時における負極活物質層の膨張収縮が緩和され、電池の充放電サイクル特性が向上する。   According to the present invention, the expansion and contraction of the negative electrode active material layer during insertion / extraction of lithium ions due to charge / discharge is alleviated, and the charge / discharge cycle characteristics of the battery are improved.

実施例１で得られた負極の活物質層の縦断面における集電体の界面付近の走査型顕微鏡像である。2 is a scanning microscope image in the vicinity of an interface of a current collector in a longitudinal section of a negative electrode active material layer obtained in Example 1. FIG. 実施例及び比較例で得られた負極を用いたリチウム二次電池の初回充放電時の電池厚みの変化を表すグラフである。It is a graph showing the change of the battery thickness at the time of the first charge / discharge of the lithium secondary battery using the negative electrode obtained by the Example and the comparative example. 実施例及び比較例で得られた負極を用いたリチウム二次電池に対して充放電を繰り返したときの電池厚みの変化を表すグラフである。It is a graph showing the change of battery thickness when charging / discharging is repeated with respect to the lithium secondary battery using the negative electrode obtained by the Example and the comparative example. 実施例及び比較例で得られた負極を用いたリチウム二次電池の充放電サイクル特性を表すグラフである。It is a graph showing the charge / discharge cycle characteristic of the lithium secondary battery using the negative electrode obtained by the Example and the comparative example. 上方の写真は、実施例５で得られた負極の活物質層の縦断面における集電体の界面付近の走査型顕微鏡像であり、下方の写真は、その一部を拡大した走査型顕微鏡像である。The upper photograph is a scanning microscope image near the interface of the current collector in the longitudinal section of the negative electrode active material layer obtained in Example 5, and the lower photograph is an enlarged scanning microscope image of a part thereof. It is. 実施例５及び比較例２で得られた負極を使用して作成したコインセルについて、初回充放電時における容量と電圧の関係を示したグラフである。It is the graph which showed the relationship between the capacity | capacitance at the time of first time charge / discharge, and the voltage about the coin cell produced using the negative electrode obtained in Example 5 and Comparative Example 2. FIG. 実施例５及び比較例２で得られた負極を使用して作成したコインセルについて、充放電を繰り返したときの容量の変化を示したグラフである。It is the graph which showed the change of the capacity | capacitance when charging / discharging was repeated about the coin cell produced using the negative electrode obtained in Example 5 and Comparative Example 2. FIG.

以下本発明を、その好ましい実施形態に基づき説明する。
本発明の負極は、リチウム二次電池等の非水電解液二次電池に用いられるものである。この負極は、活物質層の構造に特徴の一つを有するものである。
活物質層は、ケイ素を含有する負極活物質の粒子を含んでいる。ケイ素を含有する負極活物質としては、充放電によってリチウムイオンの挿入脱離が可能な材料が用いられる。そのような材料としては、例えば純ケイ素；ＳｉＯやＳｉＯ2等のケイ素酸化物；ＳｉＢ4、ＳｉＢ6、Ｃｕ5Ｓｉ、ＦｅＳｉ2、Ｍｇ2Ｓｉ等のケイ素合金；ホウ素、リン、鉄が固溶したケイ素固溶体等のケイ素固溶体；Ｓｉ3Ｎ4やＳｉＣ等のケイ素化合物などが挙げられる。Hereinafter, the present invention will be described based on preferred embodiments thereof.
The negative electrode of the present invention is used for a nonaqueous electrolyte secondary battery such as a lithium secondary battery. This negative electrode has one of the characteristics in the structure of the active material layer.
The active material layer includes particles of a negative electrode active material containing silicon. As the negative electrode active material containing silicon, a material capable of inserting and extracting lithium ions by charging and discharging is used. Examples of such materials include pure silicon; silicon oxides such as SiO and SiO 2 ; silicon alloys such as SiB 4 , SiB 6 , Cu 5 Si, FeSi 2 , and Mg 2 Si; boron, phosphorus, and iron are solid solutions. And silicon solid solutions such as silicon solid solution; silicon compounds such as Si 3 N 4 and SiC;

負極活物質粒子の形状は、本発明において特に臨界的でなく、様々な形状の粒子を用いることができる。例えば球状、多面体状、紡錘状、板状若しくは不定形又はそれらの組み合わせを用いることができる。
負極活物質粒子の粒径は、電池の具体的な用途に応じて適切な大きさを選択することができる。一般的には、レーザー回折散乱法によって測定されたＤ50の値が０．１〜１０μｍ、特に２μｍ以上或いは５μｍ以下のものが好適に用いられる。The shape of the negative electrode active material particles is not particularly critical in the present invention, and particles having various shapes can be used. For example, a spherical shape, a polyhedral shape, a spindle shape, a plate shape, an amorphous shape, or a combination thereof can be used.
The particle size of the negative electrode active material particles can be selected as appropriate depending on the specific use of the battery. In general, those having a D 50 value measured by a laser diffraction scattering method of 0.1 to 10 μm, particularly 2 μm or more or 5 μm or less are preferably used.

活物質層においては、活物質粒子どうしの結着剤としてポリイミド、ポリアミド又はポリアミドイミド（以下、これらを総称して「ポリイミド等」とも言う。）が用いられている。
ポリイミド等は、活物質粒子の表面の少なくとも一部に固着している。
ポリイミド等の固着の形態として特に好ましい形態は、活物質粒子の表面を少なくとも一部おいて面状に固着している形態である。「面状」とは、膜状と同義であり、点状に散在している状態と対極にある状態である。また、当該技術分野においてしばしば用いられる結着剤であるスチレンブタジエンゴム（ＳＢＲ）もまた、活物質粒子の表面において、面状に存在しておらず、散点状に存在していることが、本発明者らの検討の結果判明している。また、「固着」とは、活物質粒子とポリイミド等との間に機械的な結合力（例えば係合や嵌合等のアンカー効果）又は化学的な結合力が生じるような状態で結合している状態であり、活物質粒子とポリイミド等とを単に混合して両者が結果的に接触しているだけ状態は「固着」に当たらない。
活物質粒子の表面にポリイミド等を面状に固着させるための方法については後述する。In the active material layer, polyimide, polyamide, or polyamideimide (hereinafter collectively referred to as “polyimide or the like”) is used as a binder between the active material particles.
Polyimide or the like is fixed to at least a part of the surface of the active material particles.
A particularly preferable form of fixing of polyimide or the like is a form in which the surface of the active material particles is fixed in a planar shape with at least a part of the surface thereof. “Surface shape” is synonymous with film shape, and is in a state opposite to a state in which dots are scattered. In addition, the styrene butadiene rubber (SBR), which is a binder often used in the technical field, is not present in a planar shape on the surface of the active material particles, and is present in a scattered shape. As a result of the study by the present inventors, it has been found. In addition, “adhesion” refers to bonding in a state where a mechanical bonding force (for example, an anchor effect such as engagement or fitting) or a chemical bonding force is generated between the active material particles and polyimide. The state where the active material particles and polyimide are simply mixed and both are in contact with each other as a result is not “fixed”.
A method for fixing polyimide or the like on the surface of the active material particles in a planar shape will be described later.

ポリイミド等は、活物質粒子の表面の全域を被覆しているのではなく、該表面にポリイミド等の非固着域を一部残すような態様で、該表面に固着していることが好ましい。活物質粒子は、隣接する粒子の互いの非固着域において接触すると共に、その接触点の周辺にポリイミド等が固着して連結しているのが好ましい。このように該非固着域を通じて活物質粒子どうしが接触することで電子伝導性を確保することができる。   The polyimide or the like preferably does not cover the entire surface of the active material particles but is fixed to the surface in such a manner that a part of the non-fixed region such as polyimide remains on the surface. It is preferable that the active material particles are in contact with each other in the non-fixed region of the adjacent particles, and polyimide or the like is fixed and connected around the contact point. Thus, the electronic conductivity can be ensured by bringing the active material particles into contact with each other through the non-adhering region.

活物質粒子の表面に面状に固着しているポリイミド等は、当該粒子と隣り合う別の活物質の表面に固着しているポリイミド等からなる連結部位を介して一体的に連結している。すなわち、上述したように、活物質粒子は隣接する粒子同士接触すると共に、その接触点の周辺に固着したポリイミド等が互いに連結して連結部位を形成している。
ポリイミド等からなる該連結部位は、活物質粒子にリチウムイオンが挿入され膨張するときに、該粒子との固着状態を維持したままで伸長が可能である。このことによって、膨張に起因する活物質粒子の活物質層からの脱落が効果的に防止され、充放電のサイクル特性が向上する。また、このことは、充電に伴う電池の厚みの増加の抑制にも寄与する。充電に伴う電池の厚みの増加の抑制は、本発明の負極を、携帯電話用の電池のように、電池収容スペースが限られている場面で用いられる電池に適用した場合に特に有効である。The polyimide or the like that is fixed to the surface of the active material particles in a planar shape is integrally connected via a connecting portion made of polyimide or the like that is fixed to the surface of another active material adjacent to the particles. That is, as described above, the active material particles are in contact with adjacent particles, and polyimide and the like fixed around the contact point are connected to each other to form a connection part.
When the lithium ion is inserted into the active material particles and expands, the connecting portion made of polyimide or the like can be stretched while maintaining a fixed state with the particles. This effectively prevents the active material particles from falling off the active material layer due to expansion, and improves the charge / discharge cycle characteristics. This also contributes to suppression of an increase in battery thickness associated with charging. The suppression of the increase in the thickness of the battery accompanying charging is particularly effective when the negative electrode of the present invention is applied to a battery used in a situation where the battery accommodation space is limited, such as a battery for a mobile phone.

一方、放電によって活物質粒子からリチウムイオンが脱離すると該粒子は収縮するところ、連結部位も該粒子の収縮に伴い収縮が可能である。このように、ポリイミド等からなる連結部位は、活物質粒子どうしをあたかもバネのように連結しているので、該粒子が活物質層から脱落することが効果的に防止される。   On the other hand, when lithium ions are desorbed from the active material particles by discharge, the particles contract, and the connection site can also contract as the particles contract. Thus, since the connection part which consists of polyimides etc. has connected active material particle | grains like a spring, it is prevented effectively that this particle | grain falls out of an active material layer.

活物質粒子どうしが、ポリイミド等からなる連結部位を介して連結していることに加え、該粒子の連結の態様も、本発明の特徴の一つである。すなわち、活物質層の縦断面を観察したときに、活物質の粒子は、その複数個が、前記の連結部位を介して連結している。粒子どうしの連結の形態に特に制限はない。
特に好ましい形態においては、複数個の粒子が、前記の連結部位を介して数珠状に連結している。
好ましい形態である数珠状の連結は、直線状でもよく、あるいは蛇行状でもよい。また、数珠状の連結は、文字どおり環状になっていてもよく、あるいは非環状でもよい。
更に、数珠状の連結は、一本の線となる態様でもよく、あるいは枝分かれの態様であってもよい。複数の活物質粒子が数珠状に連結していることで、活物質粒子の膨張による体積の増加が、数珠状の連結の再配置によって一層緩和され、充電に伴う電池の厚みの増加が一層抑制される。
このように複数個の活物質粒子が数珠状に連結するようにするには、例えば負極合剤を集電体に塗布した後、後述するように、比較的低温で加熱して乾燥させるようにすればよい。但し、この方法に限定するものではない。急激に乾燥させるのではなく、緩やかに乾燥させることにより、溶媒が揮発する経路が生じ、この経路に沿って活物質粒子が配列されるのではないか、と考えることができる。In addition to the active material particles being connected to each other via a connecting portion made of polyimide or the like, the connection mode of the particles is also one of the features of the present invention. That is, when the longitudinal section of the active material layer is observed, a plurality of particles of the active material are connected via the connecting portion. There are no particular restrictions on the form of connection between the particles.
In a particularly preferable embodiment, a plurality of particles are connected in a bead shape through the connection site.
The bead-like connection which is a preferred form may be linear or serpentine. Also, the beaded connection may literally be annular or non-annular.
Further, the bead-like connection may be a single line or a branched aspect. By connecting multiple active material particles in a bead shape, the increase in volume due to expansion of the active material particles is further mitigated by the rearrangement of the bead shape connection, and the increase in battery thickness associated with charging is further suppressed. Is done.
In order to connect a plurality of active material particles in a bead shape as described above, for example, after applying a negative electrode mixture to a current collector, as described later, it is heated and dried at a relatively low temperature. do it. However, it is not limited to this method. It can be considered that a path through which the solvent volatilizes is generated by gently drying instead of drying rapidly, and the active material particles are arranged along this path.

以上の有利な効果を一層顕著なものとする観点から、活物質層中に含まれるポリイミド等の割合は、活物質粒子の重量に対して１〜１５重量％、特に２重量％以上或いは１０重量％以下であることが好ましい。活物質層に含まれるポリイミド等の割合は以下の方法により測定することができる。
本発明の負極は、ポリイミド等以外の有機物は含んでいない。したがって、負極の重量から負極に含まれている有機物以外の元素の重量、すなわちＳｉ、Ｃｕ、Ａｌ、Ｆｅ、Ｃａ、Ｆ、Ｐ及びＣ等の無機物の重量を差し引くことで有機物の重量を求め、その有機物の重量を活物質層の重量で除することで活物質層中に含まれるポリイミド等の割合を算出することができる。具体的には次の操作を行う。
先ず負極の重量を測定する。また、負極から活物質層を除去して集電体の重量を測定する。次に、負極を完全溶解させて無機物の全重量を、ＩＣＰ発光分析装置を用いて測定する。そして、負極の重量から無機物の全重量を差し引き有機物の重量を算出する。また、無機物の全重量のうち、集電体以外の構成材料の重量を算出し、算出された値と有機物の重量とを足し合わせて活物質層の重量を算出する。そして、有機物の重量を活物質層の重量で除し、更に１００を乗じることで、活物質層に含まれるポリイミド等の割合を算出する。From the viewpoint of making the above advantageous effects more prominent, the proportion of polyimide or the like contained in the active material layer is 1 to 15% by weight, particularly 2% by weight or more or 10% by weight based on the weight of the active material particles. % Or less is preferable. The proportion of polyimide or the like contained in the active material layer can be measured by the following method.
The negative electrode of the present invention does not contain organic substances other than polyimide. Therefore, the weight of the organic substance is determined by subtracting the weight of the element other than the organic substance contained in the negative electrode from the weight of the negative electrode, that is, the weight of the inorganic substance such as Si, Cu, Al, Fe, Ca, F, P, and C. By dividing the weight of the organic material by the weight of the active material layer, the ratio of polyimide or the like contained in the active material layer can be calculated. Specifically, the following operation is performed.
First, the weight of the negative electrode is measured. Further, the active material layer is removed from the negative electrode, and the weight of the current collector is measured. Next, the negative electrode is completely dissolved, and the total weight of the inorganic substance is measured using an ICP emission analyzer. Then, the total weight of the inorganic substance is subtracted from the weight of the negative electrode to calculate the weight of the organic substance. In addition, the weight of the constituent material other than the current collector is calculated out of the total weight of the inorganic material, and the weight of the active material layer is calculated by adding the calculated value and the weight of the organic material. Then, the weight of the organic material is divided by the weight of the active material layer, and further multiplied by 100, thereby calculating the proportion of polyimide or the like contained in the active material layer.

本発明においては、結着剤として、ポリイミド、ポリアミド及びポリアミドイミドのうちのいずれを用いてもよい。これらは単独で用いてもよく、あるいは２種以上を組み合わせてもよい。更にこれらの結着剤以外の結着剤を更に併用してもよい。   In the present invention, any of polyimide, polyamide, and polyamideimide may be used as the binder. These may be used alone or in combination of two or more. Furthermore, you may use together binders other than these binders further.

本発明において用いることのできるポリイミド等としては、市販のものを制限なく用いることができる。特にポリアミドとしては、２００〜４００℃のガラス転移点Ｔｇを有するものを用いることが好ましい。ポリアミドイミドとしても、２００〜４００℃のガラス転移点Ｔｇを有するものを用いることが好ましい。   As the polyimide and the like that can be used in the present invention, commercially available products can be used without limitation. In particular, it is preferable to use a polyamide having a glass transition point Tg of 200 to 400 ° C. It is preferable to use a polyamideimide having a glass transition point Tg of 200 to 400 ° C.

活物質層中には、活物質粒子及びポリイミド等に加え、導電材が含まれていてもよい。
導電材としては、例えば金属微粉や、アセチレンブラック等の導電性炭素材料の粉末等を用いることができる。導電材として金属微粉を用いる場合には、Ｓｎ、Ｚｎ、Ａｇ及びＩｎ等のリチウムイオン伝導性有する金属又はこれらの金属の合金等の微粉を用いることが好ましい。In the active material layer, in addition to the active material particles and polyimide, a conductive material may be included.
As the conductive material, for example, metal fine powder, powder of conductive carbon material such as acetylene black, or the like can be used. When metal fine powder is used as the conductive material, it is preferable to use fine powder such as a metal having lithium ion conductivity such as Sn, Zn, Ag and In or an alloy of these metals.

活物質粒子は、その表面のうち、ポリイミド等が固着していない部位に、リチウム化合物の形成能の低い金属が固着していることも好ましい（以下、この金属を「固着金属」という）。固着金属によって、活物質粒子間の電子伝導性がさらに良好となり、電極の機能低下をさらに防止することができる。
ここでいう「固着」とは、上述したポリイミド等の固着と同義であり、活物質粒子と固着金属との間に機械的な結合力（例えば係合や嵌合等のアンカー効果）又は化学的な結合力が生じるような状態で結合している状態をいう。したがって、活物質粒子と金属粒子とを単に混合して両者が結果的に接触しているだけの状態は「固着」に当たらない。
また「リチウム化合物の形成能が低い」とは、リチウムと金属間化合物若しくは固溶体を形成しないか、又は形成したとしてもリチウムが微量であるか若しくは非常に不安定であることを意味する。It is also preferable that the active material particles have a metal having a low lithium compound forming ability fixed to a portion of the surface where polyimide or the like is not fixed (hereinafter, this metal is referred to as “fixed metal”). The fixed metal further improves the electronic conductivity between the active material particles, and can further prevent the electrode from deteriorating.
The term “adhesion” used herein is synonymous with the above-mentioned fixation of polyimide or the like, and mechanical bonding force (for example, anchor effect such as engagement or fitting) or chemical between the active material particles and the fixed metal. It means a state of being connected in a state where a strong binding force is generated. Therefore, a state in which the active material particles and the metal particles are simply mixed and both are in contact with each other does not correspond to “fixing”.
In addition, “low ability to form a lithium compound” means that lithium does not form an intermetallic compound or solid solution, or even if formed, the amount of lithium is very small or very unstable.

固着金属は、活物質粒子の表面において、該固着金属からなる複数の小粒状体が緻密に固着して、複数の該小粒状体全体として面状に存在していることが好ましい。かつ、活物質粒子は、隣り合う活物質粒子と粒子同士接触すると共に、その接触点の周辺に固着したポリイミド等が互いに連結して連結部位を形成し、さらにまた、部分的には、固着金属からなる１又は複数の小粒状体を介しても連結していることが好ましい。この連結は、上述したポリイミド等からなる連結部位を介した活物質粒子の連結を補強するような態様であることが好ましい。   The fixed metal preferably has a plurality of small particles made of the fixed metal densely fixed on the surface of the active material particles, and is present in a planar shape as a whole of the plurality of small particles. In addition, the active material particles are in contact with adjacent active material particles, and polyimide or the like fixed around the contact point is connected to each other to form a connection part. It is preferable to connect also through the 1 or several small granule which consists of. It is preferable that this connection is an aspect which reinforces the connection of the active material particle through the connection part which consists of a polyimide etc. mentioned above.

固着金属は、該固着金属からなる複数の小粒状体が緻密に集合して、活物質層の厚み方向全域にわたって三次元の網目構造を形成していることが好ましい。「緻密に集合」とは、複数の小粒状体が直接に隙間なく寄り集まり、かつ隣り合う小粒状体間において機械的な結合力（例えば係合や嵌合等のアンカー効果）又は化学的な結合力が生じるような状態で存在していることをいう。したがって、活物質粒子と金属粒子とを単に混合しただけの状態においては、該金属粒子は緻密に集合した状態になっていない。   The fixed metal preferably has a plurality of small particles made of the fixed metal densely gathered to form a three-dimensional network structure over the entire thickness direction of the active material layer. “Dense assembly” means that a plurality of small particles are gathered directly without gaps, and a mechanical coupling force (for example, an anchor effect such as engagement or fitting) or chemical between adjacent small particles. It means that it exists in a state where a binding force is generated. Therefore, in a state where the active material particles and the metal particles are simply mixed, the metal particles are not in a densely assembled state.

固着金属としては、上述のとおり、リチウム化合物の形成能の低い金属が用いられる。そのような金属としては、例えばＣｕ、Ｎｉ、Ｆｅ、Ｃｏ等又はこれらの金属の合金等が挙げられる。
固着金属からなる小粒状体は、その粒径が、活物質粒子の粒径よりも小さい。小粒状体の平均粒径は０．０６〜１μｍ程度、特に０．０６〜０．５μｍ程度であることが好ましい。ここでいう粒径とは、活物質層の電子顕微鏡像から測定された直径のことである。As the fixing metal, a metal having a low ability to form a lithium compound is used as described above. Examples of such metals include Cu, Ni, Fe, Co and the like, and alloys of these metals.
The small granular material made of the fixed metal has a particle size smaller than that of the active material particles. The average particle size of the small particles is preferably about 0.06 to 1 μm, particularly about 0.06 to 0.5 μm. The particle diameter here is a diameter measured from an electron microscopic image of the active material layer.

活物質粒子に固着金属が固着しているか否かにかかわらず、活物質層中には、非水電解液の流通が可能な空隙が存在していることが好ましい。この空隙は、活物質層の厚み方向全域にわたる三次元網目状であることが好ましい。このような空隙の存在によって、活物質層の全体を有効に利用できる。   Regardless of whether or not the fixed metal is fixed to the active material particles, it is preferable that the active material layer has a void through which the non-aqueous electrolyte can flow. The voids are preferably a three-dimensional network over the entire thickness direction of the active material layer. Due to the presence of such voids, the entire active material layer can be effectively utilized.

本発明の負極は、ポリイミドを用いる場合には、次に述べる方法によって好適に製造される。
まず、負極合剤を、Ｃｕ等からなる集電体の表面に塗布する。負極合剤は、活物質粒子及びポリイミドの前駆体化合物を含む。この前駆体化合物としては、ポリイミドの技術分野においてよく知られている化合物であるポリアミック酸（ポリアミド酸）を用いることができる。負極合剤は、必要に応じ、更に金属微粉やアセチレンブラック等の導電材、前駆体化合物を重合させるための触媒、Ｎ−メチル−２−ピロリドン等の有機溶媒等を含んでいてもよい。特に、導電材として金属微粉、とりわけＳｎ、Ｚｎ、Ａｇ及びＩｎなどのリチウムイオン伝導性の高い金属又はこれらの金属の合金等の微粉を用いることが好ましい。この製造方法においては、負極合剤に、ポリイミドそのものではなく、重合によってポリイミドを生成する化合物である前駆体化合物を含有させる点が重要である。そして、活物質層の形成過程において前駆体化合物を重合させてポリイミドを生成させることで、所望の構造を有する活物質層が得られる。When using polyimide, the negative electrode of the present invention is preferably produced by the following method.
First, the negative electrode mixture is applied to the surface of a current collector made of Cu or the like. The negative electrode mixture includes active material particles and a precursor compound of polyimide. As this precursor compound, polyamic acid (polyamide acid) which is a compound well known in the technical field of polyimide can be used. The negative electrode mixture may further contain a conductive material such as metal fine powder and acetylene black, a catalyst for polymerizing the precursor compound, an organic solvent such as N-methyl-2-pyrrolidone, and the like, if necessary. In particular, it is preferable to use metal fine powder as the conductive material, particularly fine powder such as a metal having high lithium ion conductivity such as Sn, Zn, Ag and In or an alloy of these metals. In this production method, it is important that the negative electrode mixture contains not a polyimide itself but a precursor compound that is a compound that forms a polyimide by polymerization. And the active material layer which has a desired structure is obtained by superposing | polymerizing a precursor compound in the formation process of an active material layer, and producing | generating a polyimide.

負極合剤における前駆体化合物の使用量は、活物質粒子１００重量部に対して１〜１５重量部、特に２重量部以上或いは１０重量部以下であることが好ましい。また、導電材を用いる場合には、該導電材の使用量は、活物質粒子１００重量部に対して１〜１０重量部、特に２重量部以上或いは５重量部以下であることが好ましい。   The amount of the precursor compound used in the negative electrode mixture is preferably 1 to 15 parts by weight, particularly 2 parts by weight or more or 10 parts by weight or less based on 100 parts by weight of the active material particles. Moreover, when using a electrically conductive material, it is preferable that the usage-amount of this electrically conductive material is 1-10 weight part with respect to 100 weight part of active material particles, especially 2 weight part or more or 5 weight part or less.

負極合剤を集電体の表面に塗布したら、次いで塗膜を加熱して有機溶剤を揮発させるとともに前駆体化合物の重合を開始させる。
本製造方法においては、前駆体化合物の重合条件を調整することで、活物質粒子の表面にポリイミドを首尾良く面状に固着させることができる。また、ポリイミドからなる連結部位を首尾良く形成することができる。また、活物質粒子と集電体とをポリイミドからなる連結部位で連結することができる。When the negative electrode mixture is applied to the surface of the current collector, the coating film is then heated to volatilize the organic solvent and start polymerization of the precursor compound.
In this production method, the polyimide can be successfully fixed to the surface of the active material particles in a planar shape by adjusting the polymerization conditions of the precursor compound. Moreover, the connection part which consists of polyimides can be formed successfully. Further, the active material particles and the current collector can be connected to each other at a connecting portion made of polyimide.

前駆体化合物の重合条件として、多段階の加熱を行うことが有利であることが、本発明者らの検討の結果判明した。特に、少なくとも２段階、好適には少なくとも３段階、さらに好ましくは４段階の加熱を行うことが有利である。例えば、２段階の加熱を行う場合には、１段階目の加熱を１００〜１５０℃で行うことが好ましく、２段階目の加熱を２００〜４００℃で行うことが好ましい。
加熱時間に関しては、１段階目の加熱時間を２段階目の加熱時間と同じか又はそれよりも長くすることが好ましい。例えば、１段階目の加熱時間を１２０〜３００分、特に１８０分以上或いは２４０分以下に設定し、２段階目の加熱時間を３０〜１２０分、特に３０〜６０分に設定することが好ましい。As a result of the study by the present inventors, it has been found that it is advantageous to perform multi-stage heating as the polymerization condition of the precursor compound. In particular, it is advantageous to carry out heating in at least 2 stages, preferably at least 3 stages, more preferably 4 stages. For example, when two-stage heating is performed, the first-stage heating is preferably performed at 100 to 150 ° C., and the second-stage heating is preferably performed at 200 to 400 ° C.
Regarding the heating time, it is preferable that the heating time of the first stage is equal to or longer than the heating time of the second stage. For example, the first stage heating time is preferably set to 120 to 300 minutes, particularly 180 minutes or more and 240 minutes or less, and the second stage heating time is set to 30 to 120 minutes, particularly 30 to 60 minutes.

３段階の加熱を行う場合には、上述した２段階の加熱において、１段階目と２段階目の中間の加熱温度を採用することが好ましい。
この中間の加熱は、１５０〜１９０℃で行うことが好ましい。加熱時間は、１段階目及び２段階目の時間と同じか又は１段階目と２段階目の中間の時間とすることが好ましい。つまり、３段階の加熱を行う場合には、各段階で加熱時間を同じにするか、又は段階が進むにつれて加熱時間を短くすることが好ましい。
さらに４段階の加熱を行う場合には、３段階目よりも高い加熱温度を採用することが好ましい。In the case of performing three-stage heating, it is preferable to employ a heating temperature intermediate between the first and second stages in the above-described two-stage heating.
This intermediate heating is preferably performed at 150 to 190 ° C. The heating time is preferably the same as the time of the first stage and the second stage or a time intermediate between the first stage and the second stage. That is, when performing heating in three stages, it is preferable that the heating time be the same in each stage, or that the heating time be shortened as the stages progress.
Furthermore, when performing four steps of heating, it is preferable to employ a higher heating temperature than the third step.

加熱を何段階で行うかにかかわらず、加熱はアルゴン等の不活性雰囲気中で行うことが好ましい。
また、加熱処理のときには、活物質層をガラス板等の押さえ部材で押さえることも好ましい。こうすることで、有機溶媒が潤沢な状態で、つまりポリアミック酸が有機溶媒中にあたかも飽和したような状態で、該ポリアミック酸を重合させることができるので、生成するポリイミドの分子鎖どうしが絡まりやすくなるからである。Regardless of the number of stages of heating, heating is preferably performed in an inert atmosphere such as argon.
In the heat treatment, it is also preferable to hold the active material layer with a pressing member such as a glass plate. By doing so, the polyamic acid can be polymerized in a state where the organic solvent is abundant, that is, in a state where the polyamic acid is saturated in the organic solvent, so that the molecular chains of the resulting polyimide are easily entangled. Because it becomes.

以上の多段階加熱を行うことで、負極合剤に含まれている有機溶媒を徐々に揮発させることができ、それによって前駆体化合物を十分に高分子量化させることが可能になるとともに、活物質粒子の表面の広い範囲にわたりポリイミドを固着させることができる。また、ポリイミドからなる連結部位を首尾良く形成することができる。このように、本製造方法においては、いわばinsituの重合によってポリイミドを生成させることで、目的とする構造の活物質層を得ている。また、以上の操作によって、活物質層中にはその厚み方向全域にわたる三次元網目状の空隙が形成される。   By performing the above multi-stage heating, the organic solvent contained in the negative electrode mixture can be gradually volatilized, thereby making it possible to sufficiently increase the molecular weight of the precursor compound, and the active material Polyimide can be fixed over a wide range of particle surfaces. Moreover, the connection part which consists of polyimides can be formed successfully. Thus, in this manufacturing method, the active material layer having the target structure is obtained by generating polyimide by so-called in-situ polymerization. In addition, through the above operation, a three-dimensional network-like void is formed in the active material layer over the entire thickness direction.

結着剤として、ポリアミド及びポリアミドイミドを用いる場合には、上述したポリイミドの場合と異なり、負極合剤中に、活物質の粒子や、アセチレンブラック及び金属微粉等の導電材等に加えて、ポリアミド及び／又はポリアミドイミドを添加して該合剤を調製し、該合剤を集電体の表面に塗布すればよい。   In the case of using polyamide and polyamideimide as the binder, unlike the above-mentioned polyimide, in addition to the active material particles, conductive materials such as acetylene black and metal fine powder in the negative electrode mixture, polyamide And / or polyamideimide may be added to prepare the mixture, and the mixture may be applied to the surface of the current collector.

特に結着剤としてポリアミド又はポリアミドイミドを用いる場合には、ポリアミド又はポリアミドイミド及び活物質の粒子を含む負極合剤を集電体の表面に塗布し、その後Ｔｇ−１００℃〜Ｔｇ＋１００℃（該Ｔｇはポリアミド又はポリアミドイミドのガラス転移点を表す）の温度範囲、特にＴｇ−１００℃〜Ｔｇの温度範囲で塗膜を乾燥することで活物質層を形成することが好ましい。このような乾燥を行うことでサイクル特性が一層向上することが、本発明者らの検討の結果判明した。サイクル特性の更に一層の向上は、前記の乾燥をＴｇ−５０℃〜Ｔｇ＋５０℃、中でも特にＴｇ−５０℃〜Ｔｇの温度範囲で行うと一層顕著なものとなる。
ポリアミド又はポリアミドイミドのガラス転移点は、ＴＧ−ＤＴＡ６２００（ＳＩＩ（株）社製）を用いて、Ａｒ雰囲気下、走査速度を５℃／ｍｉｎに設定して測定される。In particular, when polyamide or polyamideimide is used as the binder, a negative electrode mixture containing polyamide or polyamideimide and active material particles is applied to the surface of the current collector, and then Tg-100 ° C to Tg + 100 ° C (the Tg Represents the glass transition point of polyamide or polyamideimide), and it is preferable to form the active material layer by drying the coating film in the temperature range of Tg-100 ° C. to Tg. As a result of studies by the present inventors, it has been found that the cycle characteristics are further improved by performing such drying. The further improvement of the cycle characteristics becomes more remarkable when the above-mentioned drying is carried out in the temperature range of Tg-50 ° C to Tg + 50 ° C, particularly Tg-50 ° C to Tg.
The glass transition point of polyamide or polyamideimide is measured using TG-DTA6200 (manufactured by SII Co., Ltd.) under an Ar atmosphere and setting the scanning speed to 5 ° C./min.

前記の乾燥は、Ａｒ雰囲気下に、好ましくは１〜５時間、更に好ましくは１〜３時間行われる。   The drying is preferably performed in an Ar atmosphere for 1 to 5 hours, more preferably 1 to 3 hours.

本発明者らが検討した結果、結着剤としてポリアミド又はポリアミドイミドを用いる場合の塗膜の乾燥によるサイクル特性の向上は、乾燥後に、活物質粒子に固着金属を固着させるか否かにかかわらず観察されることが判明した。   As a result of the study by the present inventors, the improvement of the cycle characteristics by drying the coating film when polyamide or polyamideimide is used as the binder, regardless of whether or not the fixing metal is fixed to the active material particles after drying. It was found to be observed.

このようにして、目的とする構造の活物質層を有する負極が得られる。
活物質層において、活物質粒子に、固着金属を固着させるためには、上述の操作の後に、次に述べる操作を行えばよい。すなわち、上述の操作よって得られた負極を、固着金属のイオンが含まれているめっき液中に浸漬して、活物質粒子間にめっき液を浸透させる。この状態下に電解めっき又は無電解めっきを行い、該活物質層内に固着金属を析出させる。固着金属の析出は、活物質粒子の表面のうち、ポリアミド又はポリアミドイミドが固着していない部位に優先的に生じる。また、固着金属の析出は、該金属の核粒子の発生及び該核粒子の成長を経て行われるので、複数の小粒状体の生成を伴う。その結果、固着金属は、活物質粒子の表面において、該固着金属からなる複数の小粒状体が緻密に固着して、複数の該小粒状体全体として面状に存在するようになる。小粒状体の成長が更に進行すると、隣り合う活物質粒子が、１又は複数の小粒状体を介して連結するようになる。そして、最終的には、固着金属による連続した三次元の網目構造が、活物質層の厚み方向全域にわたって形成される。その結果、活物質の粒子の表面には、ポリアミド又はポリアミドイミドによって被覆されている部位と、固着金属によって被覆されている部位が存在することになる。以上の操作の詳細は、例えば本出願人の先の出願に係る特開２００６−１５５９００号公報に記載されている。In this way, a negative electrode having an active material layer having a target structure is obtained.
In order to fix the fixed metal to the active material particles in the active material layer, the following operation may be performed after the above operation. That is, the negative electrode obtained by the above operation is immersed in a plating solution containing fixed metal ions, and the plating solution is infiltrated between the active material particles. Under this condition, electrolytic plating or electroless plating is performed to deposit a fixed metal in the active material layer. Precipitation of the fixed metal occurs preferentially in a portion of the surface of the active material particles where polyamide or polyamideimide is not fixed. Further, the precipitation of the fixed metal is performed through the generation of the core particles of the metal and the growth of the core particles, and therefore involves the generation of a plurality of small particles. As a result, the fixed metal has a plurality of small particles made of the fixed metal densely fixed on the surface of the active material particles, and the entire fixed particles are present in a planar shape. When the growth of the small granular material further proceeds, adjacent active material particles are connected via one or a plurality of small granular materials. Finally, a continuous three-dimensional network structure made of fixed metal is formed over the entire thickness direction of the active material layer. As a result, on the surface of the active material particles, there are a portion covered with polyamide or polyamideimide and a portion covered with the fixed metal. Details of the above operation are described in, for example, Japanese Patent Application Laid-Open No. 2006-155900 related to an earlier application of the present applicant.

このようにして製造された負極は、正極、セパレータ、非水電解液等とともに用いられて非水電解液二次電池を構成する。
正極は、例えば集電体の少なくとも一面に正極活物質層が形成されてなるものである。正極活物質層には活物質が含まれている。正極活物質としては、当該技術分野において従来知られているものを特に制限なく用いることができる。例えば各種のリチウム遷移金属複合酸化物を用いることができる。そのような物質としては、例えばＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎＯ2、ＬｉＭｎ2Ｏ4、ＬｉＣｏ1/3Ｎｉ1/3Ｍｎ1/3Ｏ2、ＬｉＣｏ0.5Ｎｉ0.5Ｏ2、ＬｉＮｉ0.7Ｃｏ0.2Ｍｎ0.1Ｏ2、Ｌｉ（ＬｉxＭｎ2xＣｏ1-3x）Ｏ2（式中、０＜ｘ＜１／３である）、ＬｉＦｅＰＯ4、ＬｉＭｎ1-zＭzＰＯ4 （式中、０＜ｚ≦０．１であり、ＭはＣｏ、Ｎｉ、Ｆｅ、Ｍｇ、Ｚｎ及びＣｕからなる群から選ばれる少なくとも１種の金属元素である。）などが挙げられる。The negative electrode manufactured in this way is used together with a positive electrode, a separator, a non-aqueous electrolyte and the like to constitute a non-aqueous electrolyte secondary battery.
The positive electrode is formed, for example, by forming a positive electrode active material layer on at least one surface of a current collector. The positive electrode active material layer contains an active material. As a positive electrode active material, what is conventionally known in the said technical field can be especially used without a restriction | limiting. For example, various lithium transition metal composite oxides can be used. Examples of such a material include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiCo 1/3 Ni 1/3 Mn 1/3 O 2 , LiCo 0.5 Ni 0.5 O 2 , LiNi 0.7 Co 0.2 Mn 0.1. O 2 , Li (Li x Mn 2x Co 1-3x ) O 2 (where 0 <x <1/3), LiFePO 4 , LiMn 1-z M z PO 4 (where 0 <z ≦ 0.1 and M is at least one metal element selected from the group consisting of Co, Ni, Fe, Mg, Zn and Cu.

負極及び正極とともに用いられるセパレータとしては、合成樹脂製不織布、ポリエチレンやポリプロピレン等のポリオレフィン、又はポリテトラフルオロエチレンの多孔質フィルム等が好ましく用いられる。   As the separator used together with the negative electrode and the positive electrode, a synthetic resin nonwoven fabric, a polyolefin such as polyethylene or polypropylene, or a polytetrafluoroethylene porous film is preferably used.

非水電解液は、支持電解質であるリチウム塩を有機溶媒に溶解した溶液からなる。有機溶媒としては、例えばエチレンカーボネート、プロピレンカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート等のカーボネート系有機溶媒、フルオロエチレンカーボネート等の前記カーボネート系有機溶媒の一部をフッ素化したフッ素系有機溶媒等の１種又は２種以上の組み合わせが用いられる。具体的には、フルオロエチレンカーボネート、ジエチルフルオロカーボネート、ジメチルフルオロカーボネート等を用いることができる。リチウム塩としては、ＣＦ3ＳＯ3Ｌｉ、（ＣＦ3ＳＯ2）ＮＬｉ、（Ｃ2Ｆ5ＳＯ2）2ＮＬｉ、ＬｉＣｌＯ4、ＬｉＡ１Ｃｌ4、ＬｉＰＦ6、ＬｉＡｓＦ6、ＬｉＳｂＦ6、ＬｉＣｌ、ＬｉＢｒ、ＬｉＩ、ＬｉＣ4Ｆ9ＳＯ3等が例示される。これらは単独で又は２種以上を組み合わせて用いることができる。The nonaqueous electrolytic solution is a solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent. Examples of the organic solvent include carbonate organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, fluorine organic solvents obtained by fluorinating a part of the carbonate organic solvent such as fluoroethylene carbonate, and the like. One type or a combination of two or more types is used. Specifically, fluoroethylene carbonate, diethyl fluorocarbonate, dimethyl fluorocarbonate, or the like can be used. The lithium salt, CF 3 SO 3 Li, ( CF 3 SO 2) NLi, (C 2 F 5 SO 2) 2 NLi, LiClO 4, LiA1Cl 4, LiPF 6, LiAsF 6, LiSbF 6, LiCl, LiBr, LiI And LiC 4 F 9 SO 3 . These can be used alone or in combination of two or more.

なお、本明細書において「Ｘ〜Ｙ」（Ｘ，Ｙは任意の数字）と表現する場合、特にことわらない限り「Ｘ以上Ｙ以下」の意と共に、「好ましくはＸより大きい」或いは「好ましくはＹより小さい」の意も包含する。
また、「Ｘ以上」（Ｘは任意の数字）或いは「Ｙ以下」（Ｙは任意の数字）と表現した場合、「Ｘより大きいことが好ましい」或いは「Ｙ未満であることが好ましい」旨の意図も包含する。In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” or “preferably” with the meaning of “X to Y” unless otherwise specified. Also includes the meaning "is smaller than Y".
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

以下、実施例により本発明を更に詳細に説明する。しかしながら本発明の範囲は、かかる実施例に制限されない。   Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

〔実施例１〕
（１）負極合剤の調製
Ｓｉの粒子からなる紛体(Ｄ50＝２．７μm)を負極活物質として用いた。該負極活物質１００重量部に対して、導電材（アセチレンブラック）１重量部、ポリイミドの前駆体化合物（ポリアミック酸）７重量部を添加した。更に、負極活物質１００重量部に対して、Ｎ−メチル−２−ピロリドン１００重量部を添加した。これらの混合によって負極合剤を得た。[Example 1]
(1) Preparation of negative electrode mixture A powder composed of Si particles (D 50 = 2.7 µm) was used as a negative electrode active material. 1 part by weight of a conductive material (acetylene black) and 7 parts by weight of a polyimide precursor compound (polyamic acid) were added to 100 parts by weight of the negative electrode active material. Furthermore, 100 parts by weight of N-methyl-2-pyrrolidone was added to 100 parts by weight of the negative electrode active material. A negative electrode mixture was obtained by mixing them.

上記のＤ50は、レーザー回折粒度分布測定機用試料循環器（日機装株式会社製「Ｍｉｃｒｏｔｏｒａｃ Ｎｏ．９３２０−Ｘ１００」）を用い、サンプル（粉体）を水溶性溶媒に投入し、４０ｍＬ/ｓｅｃの流速中、３０ｗｔａａｔｓの超音波を１５０秒間照射した後、日機装株式会社製レーザー回折粒度分布測定機「ＨＲＡ（Ｘ１００）」を用いて粒度分布を測定し、得られた体積基準粒度分布のチャートから求めた値である。The D 50 is a sample circulator for laser diffraction particle size distribution measuring instrument (“Microtorac No. 9320-X100” manufactured by Nikkiso Co., Ltd.), and the sample (powder) is charged into a water-soluble solvent, and 40 mL / sec. After irradiating ultrasonic waves of 30 wtats for 150 seconds at a flow rate, the particle size distribution is measured using a laser diffraction particle size distribution measuring instrument “HRA (X100)” manufactured by Nikkiso Co., Ltd., and obtained from the chart of the volume-based particle size distribution obtained. Value.

（２）負極合剤の塗布及び加熱処理
負極合剤を、厚み１８μｍの電解銅箔上に片面塗布した。次いで、減圧Ａｒ雰囲気下において塗膜を加熱して前駆体化合物の重合を行った。加熱は３段階で行った。１段階目の加熱は、１２０℃で２４０分間行った。２段階目の加熱は、１８０℃で６０分間行った。３段階目の加熱は、２００℃で６０分間行った。加熱の間、塗膜が形成された集電体を、２枚のガラス板に挟持しておいた。
この際、活物質層中に含まれるポリイミドの割合は、活物質粒子の重量に対して７重量％であった。(2) Application of negative electrode mixture and heat treatment The negative electrode mixture was applied on one side of an electrolytic copper foil having a thickness of 18 µm. Next, the coating was heated in a reduced pressure Ar atmosphere to polymerize the precursor compound. Heating was performed in three stages. The first stage heating was performed at 120 ° C. for 240 minutes. The second stage heating was performed at 180 ° C. for 60 minutes. The third stage heating was performed at 200 ° C. for 60 minutes. During the heating, the current collector on which the coating film was formed was sandwiched between two glass plates.
At this time, the ratio of the polyimide contained in the active material layer was 7% by weight with respect to the weight of the active material particles.

（３）固着金属の析出
本出願人の先の出願に係る特開２００６−１５５９００号公報に記載の方法にしたがい固着金属を析出させた。前項（２）で処理された塗膜を、集電体ごと、以下の浴組成を有するピロリン酸銅浴に浸漬させた。そして電解によって、塗膜に対して銅のめっきを行った。電解の条件は以下のとおりとした。陽極にはＤＳＥを用いた。電源は直流電源を用いた。電解めっきは、塗膜の厚み方向全域にわたって銅が析出した時点で終了させた。このようにして固着金属の析出を行い、目的とする負極を得た。ピロリン酸銅浴におけるＰ2Ｏ7の重量とＣｕの重量との比（Ｐ2Ｏ7／Ｃｕ）は７とした。
・ピロリン酸銅三水和物：１０５ｇ／ｌ
・ピロリン酸カリウム：４５０ｇ／ｌ
・硝酸カリウム：３０ｇ／ｌ
・浴温度：５０℃
・電流密度：３Ａ／ｄｍ2
・ｐＨ：アンモニア水とポリリン酸を添加してｐＨ８．２になるように調整した。(3) Precipitation of fixed metal The fixed metal was deposited according to the method described in Japanese Patent Application Laid-Open No. 2006-155900 related to the applicant's previous application. The coating film treated in the previous item (2) was immersed in a copper pyrophosphate bath having the following bath composition together with the current collector. And the copper plating was performed with respect to the coating film by electrolysis. The electrolysis conditions were as follows. DSE was used for the anode. A DC power source was used as the power source. The electrolytic plating was terminated when copper was deposited over the entire thickness direction of the coating film. In this way, the fixed metal was deposited to obtain a target negative electrode. The ratio (P 2 O 7 / Cu) between the weight of P 2 O 7 and the weight of Cu in the copper pyrophosphate bath was 7.
Copper pyrophosphate trihydrate: 105 g / l
-Potassium pyrophosphate: 450 g / l
・ Potassium nitrate: 30 g / l
・ Bath temperature: 50 ° C
・ Current density: 3 A / dm 2
-PH: Ammonia water and polyphosphoric acid were added to adjust to pH 8.2.

このようにして得られた負極の活物質層の縦断面における集電体の界面付近の走査型顕微鏡像を図１に示す。同図から明らかなように、ポリイミド（ＰＩ）はＳｉからなる活物質粒子の表面に面状に固着していた。また、隣り合う活物質粒子どうしが互いに接触すると共に、ポリイミド（ＰＩ）からなる連結部位によって隣り合う活物質粒子どうしが連結し、数珠状になっていた。更に、活物質粒子と集電体も、ポリイミド（ＰＩ）からなる連結部位によって連結していた。   FIG. 1 shows a scanning microscope image near the interface of the current collector in the longitudinal section of the negative electrode active material layer thus obtained. As is clear from the figure, polyimide (PI) was fixed in a planar shape on the surface of the active material particles made of Si. Adjacent active material particles were in contact with each other, and adjacent active material particles were connected by a connecting portion made of polyimide (PI) to form a bead shape. Furthermore, the active material particles and the current collector were also connected by a connecting portion made of polyimide (PI).

また、Ｓｉからなる活物質粒子の表面には、Ｃｕからなる固着金属の小粒状体が多数固着していた。小粒状体は緻密に集合していた。更に、隣り合う活物質粒子は、ポリイミド（ＰＩ）からなる連結部位によって連結すると共に、一部では、Ｃｕからなる固着金属の１個又は複数個の小粒状体を介しても連結していた。   In addition, many small particles of fixed metal made of Cu were fixed on the surface of the active material particles made of Si. The small granules were densely assembled. Further, adjacent active material particles are connected by a connecting portion made of polyimide (PI), and in some cases, the active material particles are also connected through one or a plurality of small particles of fixed metal made of Cu.

〔実施例２〕
実施例１で調製した負極合剤において、前駆体化合物及び導電材の使用量を、負極活物質１００重量部に対してそれぞれ２．５重量部及び３．５重量部とした。これ以外は実施例１と同様にして負極を得た。ポリイミド（ＰＩ）の固着状態は、実施例１と同様であった。
この際、活物質層中に含まれるポリイミドの割合は、活物質粒子の重量に対して３重量％であった。[Example 2]
In the negative electrode mixture prepared in Example 1, the usage amounts of the precursor compound and the conductive material were 2.5 parts by weight and 3.5 parts by weight, respectively, with respect to 100 parts by weight of the negative electrode active material. A negative electrode was obtained in the same manner as in Example 1 except for this. The fixing state of polyimide (PI) was the same as in Example 1.
At this time, the ratio of the polyimide contained in the active material layer was 3% by weight with respect to the weight of the active material particles.

〔比較例１〕
実施例１で調製した負極合剤において、前駆体化合物に代えてスチレンブタジエンゴムを用いた。その使用量は、負極活物質１００重量部に対して２．５重量部とした。また、導電材の使用量を、負極活物質１００重量部に対して３．５重量部とした。これ以外は実施例１と同様にして、負極を得た。実施例１と同様の固着状態であった。得られた負極の活物質層の縦断面における集電体の界面付近を走査型顕微鏡で拡大観察したところ、スチレンブタジエンゴムは、活物質粒子の表面に散点状に固着していた。また、スチレンブタジエンゴムは、隣り合う活物質粒子どうしを連結していなかった。[Comparative Example 1]
In the negative electrode mixture prepared in Example 1, styrene butadiene rubber was used instead of the precursor compound. The amount used was 2.5 parts by weight with respect to 100 parts by weight of the negative electrode active material. Moreover, the usage-amount of the electrically conductive material was 3.5 weight part with respect to 100 weight part of negative electrode active materials. Except this, it carried out similarly to Example 1, and obtained the negative electrode. The fixed state was the same as in Example 1. When the vicinity of the current collector interface in the longitudinal section of the obtained negative electrode active material layer was magnified and observed with a scanning microscope, the styrene-butadiene rubber was fixed to the surface of the active material particles in the form of dots. Moreover, the styrene butadiene rubber did not connect adjacent active material particles.

〔評価〕
実施例及び比較例で得られた負極を用いてリチウム二次電池を作製し、充放電を繰り返したときの電池の膨張収縮の程度を測定した。また、充放電のサイクル特性を測定した。二次電池を次の手順で作製した。正極活物質として、ＬｉＮｉ1/3Ｍｎ1/3Ｃｏ1/3Ｏ2に、Ｌｉ1.05Ｎｉ0.7Ｔｉ0.2（Ｍｎ2/3Ｌｉ1/3）0.1Ｏ2を２０重量％添加したものを用いた。これを、アセチレンブラック及びポリフッ化ビニリデンとともに、溶媒であるＮ−メチル−２−ピロリドンに懸濁させ正極合剤を得た。配合の重量比は、正極活物質：アセチレンブラック：ポリフッ化ビニリデン＝８８：６：６とした。この正極合剤をアルミニウム箔（厚さ２０μｍ）からなる集電体にアプリケータを用いて塗布し、１２０℃で乾燥した後、荷重０．５ｔｏｎ／ｃｍのロールプレスを行い、正極を得た。電解液として、エチレンカーボネートとジエチルカーボネートの１：１体積比混合溶媒に１ｍｏｌ／ｌのＬｉＰＦ6を溶解した溶液を用いた。セパレータとして、ポリプロピレン製多孔質フィルムを用いた。これらを用いて得られたラミネートセル（電極サイズ：負極４２ｍｍ×３１ｍｍ、正極４０ｍｍ×２９ｍｍ）を得た。[Evaluation]
Lithium secondary batteries were produced using the negative electrodes obtained in Examples and Comparative Examples, and the degree of expansion and contraction of the batteries when charging and discharging were repeated was measured. Moreover, the charge / discharge cycle characteristics were measured. A secondary battery was produced by the following procedure. As a positive electrode active material, a LiNi 1/3 Mn 1/3 Co 1/3 O 2 , used was a Li 1.05 Ni 0.7 Ti 0.2 (Mn 2/3 Li 1/3) 0.1 O 2 was added 20 wt% . This was suspended in N-methyl-2-pyrrolidone as a solvent together with acetylene black and polyvinylidene fluoride to obtain a positive electrode mixture. The weight ratio of the blending was positive electrode active material: acetylene black: polyvinylidene fluoride = 88: 6: 6. This positive electrode mixture was applied to a current collector made of an aluminum foil (thickness 20 μm) using an applicator, dried at 120 ° C., and then roll-pressed with a load of 0.5 ton / cm to obtain a positive electrode. As an electrolytic solution, a solution obtained by dissolving 1 mol / l LiPF 6 in a 1: 1 volume ratio mixed solvent of ethylene carbonate and diethyl carbonate was used. A polypropylene porous film was used as the separator. A laminate cell (electrode size: negative electrode 42 mm × 31 mm, positive electrode 40 mm × 29 mm) obtained using these was obtained.

このラミネートセルについて以下の方法で充放電を繰り返し行い、厚みの変化を測定した。初回充放電時の厚みの変化を図２に示す。また、繰り返し充放電を行ったときの厚みの変化を図３に示す。更に、充放電のサイクル特性を図４に示す。充電は、４．２Ｖまで行い、定電流、定電圧（ＣＣ−ＣＶ）のモードで電流値がＣ／５となったところで充電完了とした。放電は２．７Ｖまで行い、定電流（ＣＣ）のモードとした。充電及び放電のレートは、１回目は０．０５Ｃ、２〜５回目は０．１Ｃ、６回目以降は０．５Ｃとした。ラミネートセルの厚みは、その最大幅広面の中央部の位置においてマイクロメータを用いて測定した。充放電サイクル特性の測定においては、初期の容量に対する各サイクルの容量を百分率で表示した（容量維持率）。   The laminate cell was repeatedly charged and discharged by the following method, and the change in thickness was measured. The change in thickness during the first charge / discharge is shown in FIG. Moreover, the change of the thickness when charging / discharging is repeated is shown in FIG. Furthermore, the charge / discharge cycle characteristics are shown in FIG. Charging was performed up to 4.2 V, and charging was completed when the current value reached C / 5 in the constant current and constant voltage (CC-CV) mode. Discharging was performed up to 2.7 V, and a constant current (CC) mode was set. The charge and discharge rates were 0.05C for the first time, 0.1C for the second to fifth times, and 0.5C for the sixth and subsequent times. The thickness of the laminate cell was measured using a micrometer at the position of the central portion of the maximum wide surface. In the measurement of the charge / discharge cycle characteristics, the capacity of each cycle relative to the initial capacity was displayed as a percentage (capacity maintenance ratio).

図２及び図３に示す結果から明らかなとおり、実施例の負極を用いた電池は、比較例の負極を用いた電池よりも、充放電に起因する電池の厚みの変化が小さいことが判った。また、図４に示す結果から明らかなとおり、実施例の負極を用いた電池は、比較例の負極を用いた電池よりも、良好なサイクル特性を示すことが判った。   As is clear from the results shown in FIGS. 2 and 3, it was found that the battery using the negative electrode of the example had a smaller change in the thickness of the battery due to charging / discharging than the battery using the negative electrode of the comparative example. . Further, as is apparent from the results shown in FIG. 4, it was found that the battery using the negative electrode of the example exhibited better cycle characteristics than the battery using the negative electrode of the comparative example.

〔実施例３及び４〕
（１）負極合剤の調製
Ｓｉの粒子からなる紛体(Ｄ50＝２．７μm)を負極活物質として用いた。該負極活物質１００重量部に対して、導電材１重量部、ポリアミドイミド（Ｔｇ＝３２５℃）１０重量部を添加した。更に、負極活物質１００重量部に対して、Ｎ−メチル２−ピロリドン１００重量部を添加した。これらの混合によって負極合剤を得た。[Examples 3 and 4]
(1) Preparation of negative electrode mixture A powder composed of Si particles (D 50 = 2.7 µm) was used as a negative electrode active material. 1 part by weight of a conductive material and 10 parts by weight of polyamideimide (Tg = 325 ° C.) were added to 100 parts by weight of the negative electrode active material. Furthermore, 100 parts by weight of N-methyl 2-pyrrolidone was added to 100 parts by weight of the negative electrode active material. A negative electrode mixture was obtained by mixing them.

（２）負極合剤の塗布及び加熱処理
負極合剤を、厚み１８μｍの電解銅箔上に片面塗布した。次いで、Ａｒ雰囲気下において塗膜を１時間加熱乾燥した。乾燥温度は３００℃（実施例３）及び３５０℃（実施例４）とした。
この際、活物質層中に含まれるポリイミドの割合は、活物質粒子の重量に対して１０重量％であった。(2) Application of negative electrode mixture and heat treatment The negative electrode mixture was applied on one side of an electrolytic copper foil having a thickness of 18 µm. Subsequently, the coating film was heat-dried for 1 hour in Ar atmosphere. The drying temperature was 300 ° C. (Example 3) and 350 ° C. (Example 4).
At this time, the ratio of the polyimide contained in the active material layer was 10% by weight with respect to the weight of the active material particles.

〔評価〕
実施例３及び４並びに比較例１で得られた負極を用いてリチウム二次電池を作製し、充放電を繰り返したときのサイクル特性を測定した。二次電池は次の手順で作製した。正極活物質としては金属リチウムを用いた。電解液として、エチレンカーボネートとジエチルカーボネートの１：１体積比混合溶媒に１ｍｏｌ／ｌのＬｉＰＦ6を溶解した溶液を用いた。セパレータとして、ポリプロピレン製多孔質フィルムを用いた。これらを用いて得られたコインセル（電極サイズ：負極１４ｍｍφ、正極１５ｍｍφ）を得た。[Evaluation]
Lithium secondary batteries were produced using the negative electrodes obtained in Examples 3 and 4 and Comparative Example 1, and the cycle characteristics when charging and discharging were repeated were measured. The secondary battery was produced by the following procedure. Metallic lithium was used as the positive electrode active material. As an electrolytic solution, a solution obtained by dissolving 1 mol / l LiPF 6 in a 1: 1 volume ratio mixed solvent of ethylene carbonate and diethyl carbonate was used. A polypropylene porous film was used as the separator. Coin cells (electrode size: negative electrode 14 mmφ, positive electrode 15 mmφ) obtained using these were obtained.

このコインセルについて以下の方法で充放電を繰り返し行い、サイクル特性を測定した。充電は、０．００１Ｖまで行い、定電流・定電圧（ＣＣ−ＣＶ）のモードで電流値が０．２Ｃとなったところで充電完了とした。放電は１．５Ｖまで行い、定電流（ＣＣ）のモードとした。充電及び放電のレートは、１回目は０．０５Ｃ、２回目以降は０．１Ｃとした。その結果、１０サイクル充放電後の容量維持率は、実施例３で得られた負極を用いた場合には８６％、実施例４では９１％であるのに対して、比較例１で得られた負極を用いた場合には、５５％という低い値になった。また、実施例３及び４の負極を用いた電池において１サイクル充放電後に電池を解体して負極の状態を電子顕微鏡観察したところ、集電体と活物質粒子との間の結着剤による結合状態は、実施例３及び４で大差はなかった。活物質粒子どうしの結合状態は、実施例３では結着剤による活物質粒子どうしの面状の結合状態が確認されたが、実施例４では結着剤の剥離が一部観察された。   This coin cell was repeatedly charged and discharged by the following method to measure cycle characteristics. Charging was performed up to 0.001 V, and charging was completed when the current value reached 0.2 C in the constant current / constant voltage (CC-CV) mode. Discharging was performed up to 1.5 V, and a constant current (CC) mode was set. The charge and discharge rates were 0.05C for the first time and 0.1C for the second and subsequent times. As a result, the capacity retention rate after 10 cycles of charge / discharge was 86% when the negative electrode obtained in Example 3 was used, and 91% in Example 4, whereas it was obtained in Comparative Example 1. When a negative electrode was used, the value was as low as 55%. Moreover, in the battery using the negative electrode of Examples 3 and 4, the battery was disassembled after one cycle of charge and discharge, and the state of the negative electrode was observed with an electron microscope. As a result, the binding between the current collector and the active material particles by the binder The state was not much different between Examples 3 and 4. Regarding the bonding state between the active material particles, in Example 3, a planar bonding state between the active material particles by the binder was confirmed, but in Example 4, some peeling of the binder was observed.

〔実施例５〕
（１）負極合剤の調製
Ｓｉの粒子からなる紛体(Ｄ50＝２．７μm)を負極活物質として用いた。該負極活物質１００重量部に対して、導電材（アセチレンブラック）５重量部、ポリイミドの前駆体化合物（ポリアミック酸）５重量部を添加した。さらに、負極活物質１００重量部に対して、Ｎ-メチル-ピロリドン１００重量部を添加した。これらを混合して負極合剤を得た。Example 5
(1) Preparation of negative electrode mixture A powder composed of Si particles (D 50 = 2.7 µm) was used as a negative electrode active material. 5 parts by weight of a conductive material (acetylene black) and 5 parts by weight of a polyimide precursor compound (polyamic acid) were added to 100 parts by weight of the negative electrode active material. Further, 100 parts by weight of N-methyl-pyrrolidone was added to 100 parts by weight of the negative electrode active material. These were mixed to obtain a negative electrode mixture.

（２）負極合剤の塗布及び加熱処理
上記の如く得られた負極合剤を、厚み１８μｍの電解銅箔上に片面塗布した。次いで、減圧Ａｒ雰囲気下において塗膜を加熱して前駆体化合物の重合を行い、負極を作製した。この際、加熱は４段階で行った。１段階目の加熱は１２０℃で２４０分間行った。２段階目の加熱は１８０℃で６０分間行った。３段階目の加熱は２００℃で６０分間行った。４段階目の加熱は３００℃で６０分間行った。加熱の間、塗膜が形成された集電体を２枚のガラス板に挟持しておいた。
この際、活物質層中に含まれるポリイミドの割合は、活物質粒子の重量に対して５重量％であった。(2) Application of negative electrode mixture and heat treatment The negative electrode mixture obtained as described above was applied on one side onto an electrolytic copper foil having a thickness of 18 µm. Next, the coating film was heated in a reduced pressure Ar atmosphere to polymerize the precursor compound, thereby preparing a negative electrode. At this time, heating was performed in four stages. The first stage heating was performed at 120 ° C. for 240 minutes. The second stage heating was performed at 180 ° C. for 60 minutes. The third stage heating was performed at 200 ° C. for 60 minutes. The fourth stage heating was performed at 300 ° C. for 60 minutes. During the heating, the current collector on which the coating film was formed was sandwiched between two glass plates.
At this time, the ratio of the polyimide contained in the active material layer was 5% by weight with respect to the weight of the active material particles.

このようにして得られた負極の活物質層の縦断面における集電体の界面付近を走査型顕微鏡で観察したところ、隣り合う活物質粒子どうしが互いに接触すると共に、ポリイミド（ＰＩ）からなる連結部位によって隣り合う活物質粒子どうしが連結し、数珠状になっていた。更に、活物質粒子と集電体も、ポリイミド（ＰＩ）からなる連結部位によって連結していた。   When the vicinity of the current collector interface in the longitudinal section of the active material layer of the negative electrode thus obtained was observed with a scanning microscope, adjacent active material particles were in contact with each other and connected with polyimide (PI). The active material particles adjacent to each other were connected to each other depending on the part, forming a bead shape. Furthermore, the active material particles and the current collector were also connected by a connecting portion made of polyimide (PI).

〔比較例２〕
（１）負極合剤の調製
実施例５の負極合剤の調製において、ポリイミドの前駆体化合物に代えてスチレンブタジエンゴムを用いると共に、その添加量を負極活物質１００重量部に対して１０重量部とし、導電材の添加量を負極活物質１００重量部に対して５重量部とした。これ以外は実施例５と同様に負極合剤を調製した。[Comparative Example 2]
(1) Preparation of negative electrode mixture In the preparation of the negative electrode mixture of Example 5, styrene butadiene rubber was used in place of the polyimide precursor compound, and the amount added was 10 parts by weight with respect to 100 parts by weight of the negative electrode active material. The amount of conductive material added was 5 parts by weight with respect to 100 parts by weight of the negative electrode active material. Other than this, a negative electrode mixture was prepared in the same manner as in Example 5.

（２）負極合剤の塗布及び加熱処理
上記の如く得られた負極合剤を、厚み１８μｍの電解銅箔上に片面塗布し、次いで、減圧Ａｒ雰囲気下において１２０℃で２４０分間、塗膜を加熱して負極を作製した。加熱の間、塗膜が形成された集電体を２枚のガラス板に挟持しておいた。(2) Application of negative electrode mixture and heat treatment The negative electrode mixture obtained as described above was applied on one side onto an 18 μm-thick electrolytic copper foil, and then the coating film was applied at 120 ° C. for 240 minutes in a reduced pressure Ar atmosphere. A negative electrode was produced by heating. During the heating, the current collector on which the coating film was formed was sandwiched between two glass plates.

得られた負極の活物質層の縦断面における集電体の界面付近を走査型顕微鏡で拡大観察したところ、スチレンブタジエンゴムは、活物質粒子の表面に散点状に固着していた。また、スチレンブタジエンゴムは、隣り合う活物質粒子どうしを連結していなかった。   When the vicinity of the current collector interface in the longitudinal section of the obtained negative electrode active material layer was magnified and observed with a scanning microscope, the styrene-butadiene rubber was fixed to the surface of the active material particles in the form of dots. Moreover, the styrene butadiene rubber did not connect adjacent active material particles.

〔評価〕
実施例５及び比較例２で得られた負極を直径１４ｍｍの円形に打ち抜き、１６０℃で６時間真空乾燥を施した。そして、アルゴン雰囲気下のグローブボックス内で、２０３２型コインセルを組み立てた。この際、対極としては金属リチウムを用いた。電解液としては、エチレンカーポネートとジエチルカーポネートの１：１体積比混合溶媒に１ｍｏｌ／ＬのＬｉＰＦ6を溶解した溶液を用いた。セバレータとしては、ポリプロピレン製多孔質フィルムを用いた。[Evaluation]
The negative electrodes obtained in Example 5 and Comparative Example 2 were punched into a circle having a diameter of 14 mm, and vacuum-dried at 160 ° C. for 6 hours. Then, a 2032 type coin cell was assembled in a glove box under an argon atmosphere. At this time, metallic lithium was used as the counter electrode. As the electrolytic solution, a solution in which 1 mol / L LiPF 6 was dissolved in a 1: 1 volume ratio mixed solvent of ethylene carbonate and diethyl carbonate was used. A polypropylene porous film was used as the separator.

このようにして得られたコインセルについて、初回充放電時の可逆性を測定した。その結果を図６に示す。また、充放電サイクル特性を測定し、その結果を図７に示す。
これらの試験を行ったときの充電条件は、１サイクル目は０．０５Ｃのレートで０．０１０Ｖまで行い、定電流、定電圧（ＣＣ−ＣＶ）のモードで電流値がＣ／５となったところで充電完了とした。放電条件は０．０５Ｃのレートで１．５Ｖまで行い、定電流（ＣＣ）のモードとした。また、２サイクル目以降は０．１Ｃのレートで行った以外は１サイクル目と同様の条件で行った。Thus, about the coin cell obtained, the reversibility at the time of first charge / discharge was measured. The result is shown in FIG. Further, charge / discharge cycle characteristics were measured, and the results are shown in FIG.
The charging conditions when these tests were performed were performed at a rate of 0.05 C up to 0.010 V in the first cycle, and the current value became C / 5 in the constant current and constant voltage (CC-CV) mode. By the way, charging was completed. Discharging conditions were performed at a rate of 0.05 C up to 1.5 V, and a constant current (CC) mode was set. The second and subsequent cycles were performed under the same conditions as in the first cycle except that the second cycle was performed at a rate of 0.1C.

図６及び図７に示す結果から明らかなように、実施例の負極を用いたコインセルは、比較例の負極を用いたコインセルよりも、初回充放電時の可逆性が高いことが判った。   As is apparent from the results shown in FIGS. 6 and 7, the coin cell using the negative electrode of the example was found to have higher reversibility at the time of first charge / discharge than the coin cell using the negative electrode of the comparative example.

前駆体化合物の重合条件として、多段階の加熱を行うことが有利であることが、本発明者らの検討の結果判明した。特に、少なくとも２段階、好適には少なくとも３段階、さらに好ましくは４段階の加熱を行うことが有利である。例えば、２段階の加熱を行う場合には、１段階目の加熱を１００〜１５０℃で行うことが好ましく、２段階目の加熱を２００〜３００℃で行うことが好ましい。
加熱時間に関しては、１段階目の加熱時間を２段階目の加熱時間と同じか又はそれよりも長くすることが好ましい。例えば、１段階目の加熱時間を１２０〜３００分、特に１８０分以上或いは２４０分以下に設定し、２段階目の加熱時間を３０〜１２０分、特に３０〜６０分に設定することが好ましい。 As a result of the study by the present inventors, it has been found that it is advantageous to perform multi-stage heating as the polymerization condition of the precursor compound. In particular, it is advantageous to carry out heating in at least 2 stages, preferably at least 3 stages, more preferably 4 stages. For example, when two-stage heating is performed, the first-stage heating is preferably performed at 100 to 150 ° C., and the second-stage heating is preferably performed at 200 to 300 ° C.
Regarding the heating time, it is preferable that the heating time of the first stage is equal to or longer than the heating time of the second stage. For example, the first stage heating time is preferably set to 120 to 300 minutes, particularly 180 minutes or more and 240 minutes or less, and the second stage heating time is set to 30 to 120 minutes, particularly 30 to 60 minutes.

Claims (7)

ケイ素を含有する負極活物質の粒子を含む負極活物質層を備え、
前記活物質層においては、ポリイミド、ポリアミド又はポリアミドイミドが、前記粒子の表面の少なくとも一部に固着しており、かつポリイミド、ポリアミド又はポリアミドイミドを介して複数の前記粒子が連結した状態になっていることを特徴とする非水電解液二次電池用負極。A negative electrode active material layer including particles of a negative electrode active material containing silicon,
In the active material layer, polyimide, polyamide or polyamideimide is fixed to at least a part of the surface of the particles, and a plurality of the particles are connected via the polyimide, polyamide or polyamideimide. A negative electrode for a non-aqueous electrolyte secondary battery. 前記活物質層が集電体の表面に形成されており、
前記粒子の表面に面状に固着しているポリイミド、ポリアミド又はポリアミドイミドを介して、該粒子と集電体とが結合している請求項１に記載の非水電解液二次電池用負極。The active material layer is formed on the surface of the current collector,
The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the particles and the current collector are bonded via polyimide, polyamide, or polyamideimide that is fixed in a planar manner to the surfaces of the particles. 前記粒子は、その表面のうち、ポリイミド、ポリアミド又はポリアミドイミドが固着していない部位に、リチウム化合物の形成能の低い金属材料が固着しており、該金属を介して前記粒子どうしが連結している請求項１又は２に記載の非水電解液二次電池用負極。   The particles have a metal material with a low lithium compound forming ability fixed to a portion of the surface where polyimide, polyamide or polyamideimide is not fixed, and the particles are connected via the metal. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1 or 2. ポリイミドは、ポリイミドの前駆体化合物及び前記粒子を含む負極合剤を前記集電体の表面に塗布し、次いで該前駆体を重合させることで生じたものである請求項１ないし３のいずれか一項に記載の非水電解液二次電池用負極。   The polyimide is produced by applying a negative electrode mixture containing a precursor compound of polyimide and the particles to the surface of the current collector, and then polymerizing the precursor. A negative electrode for a non-aqueous electrolyte secondary battery according to Item. ポリアミド又はポリアミドイミドは、該ポリアミド又は該ポリアミドイミド及び前記粒子を含む負極合剤を前記集電体の表面に塗布することで、前記活物質層中に含有されたものである１ないし３のいずれか一項に記載の非水電解液二次電池用負極。   The polyamide or polyamideimide is any one of 1 to 3 which is contained in the active material layer by applying a negative electrode mixture containing the polyamide or the polyamideimide and the particles to the surface of the current collector. A negative electrode for a non-aqueous electrolyte secondary battery according to claim 1. 前記活物質層が、ポリアミド又はポリアミドイミド及び前記粒子を含む負極合剤を前記集電体の表面に塗布し、その後Ｔｇ−１００℃〜Ｔｇ＋１００℃（Ｔｇはポリアミド又はポリアミドイミドのガラス転移点を表す）の温度範囲で塗膜を乾燥して形成されたものである請求項５に記載の非水電解液二次電池用負極。   The active material layer is coated with a negative electrode mixture containing polyamide or polyamideimide and the particles on the surface of the current collector, and then Tg-100 ° C to Tg + 100 ° C (Tg represents a glass transition point of polyamide or polyamideimide). The negative electrode for a nonaqueous electrolyte secondary battery according to claim 5, which is formed by drying the coating film within a temperature range of 請求項１ないし５のいずれかに記載の負極を備えることを特徴とする非水電解液二次電池。   A non-aqueous electrolyte secondary battery comprising the negative electrode according to claim 1.
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