JP4942302B2 - Nonaqueous electrolyte secondary battery electrode and method for producing the same - Google Patents
Nonaqueous electrolyte secondary battery electrode and method for producing the same Download PDFInfo
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Description
本発明は、リチウム二次電池などの非水電解質二次電池に用いられる電極及びその製造方法に関するものである。 The present invention relates to an electrode used for a nonaqueous electrolyte secondary battery such as a lithium secondary battery and a method for producing the same.
ケイ素及びケイ素合金などのリチウムと合金化する活物質は、リチウム二次電池の負極活物質として大きな充放電容量を有するものであることから注目されている。しかしながら、ケイ素及びケイ素合金などの活物質は、電気導電性が乏しいことに加えて、リチウムの挿入及び脱離の際に活物質の体積が、炭素負極材料と比較すると大きく増加及び減少する。このため、充放電に伴い電極構造が破壊され、電極内の導電パスが減少し、電池の内部抵抗が増加することにより、充放電効率が低下するという問題点がある。 Active materials that alloy with lithium, such as silicon and silicon alloys, have attracted attention because they have a large charge / discharge capacity as a negative electrode active material for lithium secondary batteries. However, active materials such as silicon and silicon alloys have poor electrical conductivity, and the volume of the active material is greatly increased and decreased when lithium is inserted and desorbed compared to the carbon anode material. For this reason, the electrode structure is destroyed with charge and discharge, the conductive path in the electrode is reduced, and the internal resistance of the battery is increased, resulting in a problem that charge and discharge efficiency is lowered.
電極内の導電性を向上させ、電池の内部抵抗の増加を抑制するため、導電材として炭素材料が混合される場合がある。しかしながら、炭素材料はそれ自身がリチウムを挿入及び脱離して充放電反応を起こすので、導電材としては、リチウムの挿入及び脱離を生じない金属を用いることが好ましい。 A carbon material may be mixed as a conductive material in order to improve conductivity in the electrode and suppress an increase in internal resistance of the battery. However, since the carbon material itself inserts and desorbs lithium to cause a charge / discharge reaction, it is preferable to use a metal that does not cause lithium insertion and desorption as the conductive material.
特許文献１においては、ケイ素やケイ素合金を含む負極活物質と、導電性金属粉末との混合物を導電性金属箔に塗布し、非酸化性雰囲気下で焼結することにより、負極活物質の剥離を防止することが提案されている。 In Patent Document 1, a negative electrode active material containing silicon or a silicon alloy and a mixture of a conductive metal powder are applied to a conductive metal foil and sintered in a non-oxidizing atmosphere, thereby peeling off the negative electrode active material. It has been proposed to prevent this.
また、特許文献２においては、ケイ素やケイ素合金を含む負極活物質を、導電性材料でその表面を被覆し、負極活物質の剥離を防止することが提案されている。 In Patent Document 2, it is proposed that a negative electrode active material containing silicon or a silicon alloy is coated with a conductive material on the surface thereof to prevent peeling of the negative electrode active material.
しかしながら、特許文献１に開示された方法では、導電性金属粉末同士の凝集により、導電材を分散性良く活物質層中に配置することが困難であり、十分に電池の内部抵抗の増加を抑制することができないという問題がある。また、特許文献２においては、集電体上への活物質層の形成後に、表面を被覆することが必要であるため、製造工程が複雑になるという問題がある。
本発明の目的は、電池の内部抵抗を低下させることができる非水電解質二次電池用電極及びその製造方法を提供することにある。 The objective of this invention is providing the electrode for nonaqueous electrolyte secondary batteries which can reduce the internal resistance of a battery, and its manufacturing method.
本発明は、正極と負極と非水電解質とを備える非水電解質二次電池に用いられる電極であり、金属有機化合物を熱処理することによって得られる金属粒子が、正極及び／または負極の活物質を含む活物質層に含まれていることを特徴としている。 The present invention is an electrode used for a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the metal particles obtained by heat-treating a metal organic compound have a positive electrode and / or a negative electrode active material. It is characterized by being contained in the active material layer.
ケイ素またはケイ素合金を活物質として含む負極は、充電時に活物質が膨張し、放電時に活物質が収縮する。リチウムケイ素合金の組成はＬｉ4.4Ｓｉであるので、ケイ素（Ｓｉ）は、満充電後において約４倍の体積に膨張することになる。初期充電において膨張した活物質が放電により収縮すると、電極内の活物質粒子同士の接触箇所が減少するため、電極内部の抵抗が増大する。その際に、導電性微粉末が活物質同士の接触箇所の近傍に存在すると、導電パスの減少を抑制することができる。本発明においては、金属有機化合物を熱処理することによって得られる金属粒子が、電極の活物質層中に含まれている。金属有機化合物を熱処理することによって得られる金属粒子は、微小粒子であり、かつ活物質層において良好な分散性を示す。このため、活物質層中において、活物質粒子に接触している金属粒子の割合が多くなり、活物質層中に効率良く導電パスを形成することができる。このため、電極の内部抵抗を低くすることができ、結果として電池の内部抵抗を低下させ、高い充放電容量を得ることができる。 In a negative electrode containing silicon or a silicon alloy as an active material, the active material expands during charging, and the active material contracts during discharging. Since the composition of the lithium silicon alloy is Li 4.4 Si, silicon (Si) will expand to about four times the volume after full charge. When the active material expanded in the initial charging contracts due to discharge, the number of contact points between the active material particles in the electrode decreases, and the resistance inside the electrode increases. At that time, if the conductive fine powder exists in the vicinity of the contact portion between the active materials, it is possible to suppress a decrease in the conductive path. In this invention, the metal particle obtained by heat-processing a metal organic compound is contained in the active material layer of an electrode. Metal particles obtained by heat-treating a metal organic compound are fine particles and exhibit good dispersibility in the active material layer. For this reason, in the active material layer, the ratio of the metal particles in contact with the active material particles is increased, and a conductive path can be efficiently formed in the active material layer. For this reason, the internal resistance of an electrode can be made low, As a result, the internal resistance of a battery can be reduced and a high charge / discharge capacity can be obtained.
ケイ素またはケイ素合金を活物質として用いる場合、一般に負極活物質として用いられるので、金属粒子は負極の活物質層に含まれる。この場合、一般に、負極活物質層は、活物質としてのケイ素またはケイ素合金と、金属粒子と、結着材とを含む。 When silicon or a silicon alloy is used as an active material, it is generally used as a negative electrode active material, so that the metal particles are included in the active material layer of the negative electrode. In this case, generally, the negative electrode active material layer includes silicon or a silicon alloy as an active material, metal particles, and a binder.
本発明における金属粒子は、金属有機化合物を熱処理することによって得られるものであり、微小粒子として形成することができる。一般に、本発明における金属粒子の平均粒子径は１μｍ以下であることが好ましい。平均粒子径が１μｍ以下であることにより、より良好な導電パスを形成することができ、電池の内部抵抗をより低下させることができる。金属粒子の平均粒子径は、電子顕微鏡写真などで金属粒子の粒子径を測定することなどにより求めることができる。金属粒子の平均粒子径の下限値は特に限定されるものではないが、一般には０．０１μｍ以上である。 The metal particles in the present invention are obtained by heat-treating a metal organic compound and can be formed as fine particles. In general, the average particle diameter of the metal particles in the present invention is preferably 1 μm or less. When the average particle diameter is 1 μm or less, a better conductive path can be formed, and the internal resistance of the battery can be further reduced. The average particle diameter of the metal particles can be determined by measuring the particle diameter of the metal particles with an electron micrograph or the like. The lower limit of the average particle diameter of the metal particles is not particularly limited, but is generally 0.01 μm or more.
本発明において、金属粒子は、金属粒子と活物質の合計に対して、１〜５０重量％となるように活物質中に含まれていることが好ましい。金属粒子のさらに好ましい含有量は、金属粒子と活物質の合計に対して５〜５０重量％である。金属粒子の含有量が少な過ぎると、導電パスを良好に形成することができず、電池の内部抵抗を低下させるという本発明の効果が十分に得られない場合がある。金属粒子の含有量が多過ぎると、相対的に活物質の量が減少するため、充放電容量が低下する。 In this invention, it is preferable that the metal particle is contained in the active material so that it may become 1 to 50 weight% with respect to the sum total of a metal particle and an active material. The more preferable content of the metal particles is 5 to 50% by weight with respect to the total of the metal particles and the active material. If the content of the metal particles is too small, the conductive path cannot be formed satisfactorily, and the effect of the present invention that reduces the internal resistance of the battery may not be sufficiently obtained. When there is too much content of a metal particle, since the quantity of an active material reduces relatively, charging / discharging capacity | capacitance falls.
本発明における金属粒子は、金属有機化合物を熱処理することによって得られるものであり、一般には、金属有機化合物の熱分解温度以上の温度で金属有機化合物を熱処理することにより金属粒子とすることができる。金属有機化合物は、熱処理により金属粒子とすることができるものであれば、特に限定されるものではない。金属有機化合物をスラリーに含有させる場合、スラリー中に溶解するものであってもよいし、溶解せずに粉末状に分散するものであってもよい。金属の種類としては、例えば、ニッケル、コバルト、銅、亜鉛、鉄、マンガンなどが挙げられる。金属有機化合物の形態としては、ギ酸金属、酢酸金属などの有機酸の金属塩や、金属メトキシド、金属エトキシドなどの金属アルコキシドや、アルキル金属などの有機金属化合物などが挙げられる。比較的低温で熱分解し、大気中での取り扱いが容易であるという観点から、ギ酸金属、酢酸金属などの有機酸の金属塩が好ましく用いられる。酢酸金属の熱分解温度は、一般に２００℃〜３５０℃である。 The metal particles in the present invention are obtained by heat-treating a metal organic compound. In general, the metal particles can be formed by heat-treating the metal organic compound at a temperature equal to or higher than the thermal decomposition temperature of the metal organic compound. . The metal organic compound is not particularly limited as long as it can be converted into metal particles by heat treatment. When the metal organic compound is contained in the slurry, it may be dissolved in the slurry, or may be dispersed in a powder form without being dissolved. As a kind of metal, nickel, cobalt, copper, zinc, iron, manganese etc. are mentioned, for example. Examples of the form of the metal organic compound include metal salts of organic acids such as metal formate and metal acetate, metal alkoxides such as metal methoxide and metal ethoxide, and organic metal compounds such as alkyl metals. From the viewpoint of thermal decomposition at a relatively low temperature and easy handling in the air, metal salts of organic acids such as metal formate and metal acetate are preferably used. The thermal decomposition temperature of metal acetate is generally 200 ° C to 350 ° C.
本発明において、活物質の平均粒子径は１０μｍ以下であることが好ましい。活物質の平均粒子径が１０μｍ以下であると、活物質の比表面積が大きくなるため、他の活物質粒子や金属粒子及び集電体との接触面積が増え、内部抵抗の増加が抑制し易くなることが期待できる。平均粒子径の下限値は特に限定されるものではないが、一般に入手が容易なものは、１μｍ以上である。活物質の平均粒子径は、例えば、レーザー回折式粒度分布測定装置などにより測定することができる。 In the present invention, the average particle diameter of the active material is preferably 10 μm or less. When the average particle diameter of the active material is 10 μm or less, the specific surface area of the active material increases, so that the contact area with other active material particles, metal particles, and current collectors increases, and an increase in internal resistance is easily suppressed. Can be expected. The lower limit value of the average particle diameter is not particularly limited, but generally available is 1 μm or more. The average particle diameter of the active material can be measured by, for example, a laser diffraction particle size distribution measuring apparatus.
本発明の製造方法は、上記本発明の非水電解質二次電池用電極を製造することができる方法である。 The production method of the present invention is a method by which the electrode for a nonaqueous electrolyte secondary battery of the present invention can be produced.
本発明の第１の局面に従う製造方法は、熱処理により金属粒子となる金属有機化合物と、活物質と、結着材とを含むスラリーを調製する工程と、スラリーを集電体の上に塗布して活物質層を形成する工程と、活物質層を熱処理することにより、活物質層に含まれている金属有機化合物を金属粒子にする工程とを備えることを特徴としている。 The manufacturing method according to the first aspect of the present invention includes a step of preparing a slurry containing a metal organic compound that becomes metal particles by heat treatment, an active material, and a binder, and applying the slurry onto a current collector. A step of forming an active material layer, and a step of heat-treating the active material layer to convert the metal organic compound contained in the active material layer into metal particles.
本発明の第１の局面に従う製造方法においては、スラリー中に金属有機化合物を含有させ、活物質層を形成した後、活物質層を熱処理することにより、活物質層に含まれている金属有機化合物を金属粒子にしている。 In the manufacturing method according to the first aspect of the present invention, the metal organic compound contained in the active material layer is formed by heat-treating the active material layer after forming the active material layer in the slurry by containing the metal organic compound. The compound is made into metal particles.
本発明の第２の局面に従う製造方法は、熱処理により金属粒子となる金属有機化合物と、活物質とを混合して混合粉末を調製する工程と、この混合粉末を熱処理して金属有機化合物を金属粒子にする工程と、金属粒子及び活物質からなる熱処理後の混合粉末を結着材と混合してスラリーを調製する工程と、スラリーを集電体の上に塗布して活物質を形成する工程とを備えることを特徴としている。 The manufacturing method according to the second aspect of the present invention includes a step of preparing a mixed powder by mixing a metal organic compound that becomes metal particles by heat treatment and an active material, and heat-treating the mixed powder to convert the metal organic compound into a metal. A step of preparing particles, a step of preparing a slurry by mixing a mixed powder after heat treatment composed of metal particles and an active material with a binder, and a step of forming an active material by applying the slurry on a current collector It is characterized by comprising.
本発明の第２の局面に従う製造方法においては、予め金属有機化合物と活物質とを混合して混合粉末を調製し、混合粉末の段階で熱処理して金属有機化合物を金属粒子にしている。このため、活物質粒子間に金属粒子を分散性良く混合することができる。この金属粒子と活物質の混合粉末をスラリーに用いることにより、容易に金属粒子を分散させることができ、金属粒子が良好な状態で分散した活物質層を形成することができる。 In the manufacturing method according to the second aspect of the present invention, a metal organic compound and an active material are mixed in advance to prepare a mixed powder, and the metal organic compound is converted into metal particles by heat treatment at the stage of the mixed powder. For this reason, metal particles can be mixed with good dispersibility between the active material particles. By using the mixed powder of the metal particles and the active material for the slurry, the metal particles can be easily dispersed, and an active material layer in which the metal particles are dispersed in a good state can be formed.
本発明において、活物質層に含有させる結着材としては、特に限定されないが、熱処理後も分解せずに残存しているものが好ましい。結着材としては、例えば、ポリビニリデンフルオライド、ポリテトラフルオロエチレン、パーフルオロアルコキシアルカンなどのフッ素樹脂や、エポキシ樹脂、ポリイミド樹脂などが挙げられる。これらの中でも、密着性が高く、耐熱性の高いポリイミド樹脂がより好ましく用いられる。ポリイミド樹脂は、ポリアミド酸を熱処理することによっても得ることができる。この熱処理により、ポリアミド酸が脱水縮合して、ポリイミドが生成する。ポリイミドを結着材として用いる場合、ポリイミドが分解しない６００℃以下の温度で熱処理することが好ましい。従って、このような場合、６００℃以下で分解する金属有機化合物を用いることが好ましい。 In the present invention, the binder contained in the active material layer is not particularly limited, but a binder that remains without being decomposed after heat treatment is preferable. Examples of the binder include fluorine resins such as polyvinylidene fluoride, polytetrafluoroethylene, and perfluoroalkoxyalkane, epoxy resins, and polyimide resins. Among these, a polyimide resin having high adhesion and high heat resistance is more preferably used. A polyimide resin can also be obtained by heat-treating polyamic acid. By this heat treatment, the polyamic acid is dehydrated and condensed to produce polyimide. When using polyimide as a binder, it is preferable to perform heat treatment at a temperature of 600 ° C. or less at which the polyimide does not decompose. Therefore, in such a case, it is preferable to use a metal organic compound that decomposes at 600 ° C. or lower.
結着材の活物質層中における量は特に限定されるものではないが、一般には、結着材と活物質の合計に対して、１〜２０重量％の範囲内であることが好ましい。 The amount of the binder in the active material layer is not particularly limited, but generally it is preferably in the range of 1 to 20% by weight with respect to the total of the binder and the active material.
本発明の非水電解質二次電池は、本発明の非水電解質二次電池用電極からなる負極と、正極と、非水電解質とを備えることを特徴としている。 The nonaqueous electrolyte secondary battery of the present invention is characterized by comprising a negative electrode comprising the electrode for a nonaqueous electrolyte secondary battery of the present invention, a positive electrode, and a nonaqueous electrolyte.
本発明の非水電解質二次電池に用いられる非水電解質としては、特に限定されるものではなく、リチウムイオン導電性を発現させる溶質としてのリチウム化合物と、これを溶解・保持する溶媒とが電池の充放電反応時あるいは保存時の電圧で分解しない限り、公知の非水電解質を制約なく用いることができる。 The nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and the battery includes a lithium compound as a solute that develops lithium ion conductivity and a solvent that dissolves and holds the lithium compound. Any known non-aqueous electrolyte can be used without restriction as long as it is not decomposed at the voltage at the time of charge / discharge reaction or storage.
本発明において、非水電解質には、各種添加剤を添加してもよい。例えば、負極活物質としてケイ素またはケイ素合金を用いた場合に、二酸化炭素を溶媒に溶解させると、活物質表面で形成される被膜が良質なものとなり、充放電反応に伴う活物質の割れにより生じる新生面での被膜形成に消費されるリチウム量を減少させることができ、充放電効率の低下を抑制することができる。また、非水電解質に二酸化炭素を溶解させることにより、充放電反応で活物質表面に形成される被膜が、リチウムイオン伝導性に優れた被膜となる。このため、活物質内での充放電反応の分布を均一化することができる。また、活物質の体積の膨張・収縮の偏りによって発生する歪みを低減でき、活物質の割れを抑制することができるので、新生面の発生を抑えることができ、充放電効率を向上させることができる。二酸化炭素の溶解量としては、０．１重量％以上であることが好ましく、上限値は二酸化炭素の溶解飽和量である。 In the present invention, various additives may be added to the nonaqueous electrolyte. For example, when silicon or a silicon alloy is used as the negative electrode active material, if carbon dioxide is dissolved in a solvent, the coating film formed on the surface of the active material will be of good quality, and will be generated by cracking of the active material accompanying the charge / discharge reaction. The amount of lithium consumed for film formation on the new surface can be reduced, and a decrease in charge / discharge efficiency can be suppressed. In addition, by dissolving carbon dioxide in the nonaqueous electrolyte, a film formed on the surface of the active material by the charge / discharge reaction becomes a film excellent in lithium ion conductivity. For this reason, the distribution of the charge / discharge reaction in the active material can be made uniform. Moreover, since distortion generated due to uneven expansion and contraction of the volume of the active material can be reduced and cracking of the active material can be suppressed, generation of a new surface can be suppressed and charge / discharge efficiency can be improved. . The dissolved amount of carbon dioxide is preferably 0.1% by weight or more, and the upper limit is the dissolved saturation amount of carbon dioxide.
また、電池の充放電効率を向上させるための添加剤として、二酸化炭素の他に、ビニレンカーボネート等のカーボネート系化合物、ヨウ化物、臭化物、塩化物等の金属ハロゲン化物や、アミン類、アンモニウム塩、五酸化ニリンなどが挙げられる。 Moreover, as an additive for improving the charge / discharge efficiency of the battery, in addition to carbon dioxide, carbonate compounds such as vinylene carbonate, metal halides such as iodide, bromide and chloride, amines, ammonium salts, Nilin pentoxide and the like.
負極活物質としてケイ素またはケイ素合金などを用いる場合の正極活物質は、特に限定されるものではなく、従来より一般的な正極活物質を用いることができる。例えば、コバルト酸リチウムなどのリチウム含有遷移金属複合酸化物を用いることができる。 The positive electrode active material in the case of using silicon or a silicon alloy as the negative electrode active material is not particularly limited, and a conventional positive electrode active material can be used. For example, a lithium-containing transition metal composite oxide such as lithium cobaltate can be used.
本発明に従えば、電池の内部抵抗を低下させることができ、充放電容量を高めることができる。 According to the present invention, the internal resistance of the battery can be reduced, and the charge / discharge capacity can be increased.
以下、本発明を実施例に基づいてさらに詳細に説明するが、本発明は以下の実施例に限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施することが可能なものである。 Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications within a range that does not change the gist thereof. It is.
（実施例１）
〔負極の作製〕
負極集電体として、厚み３５μｍ、表面における算術平均粗さＲａ１．０μｍの銅箔を用いた。ここで、表面粗さＲａは、日本工業規格（ＪＩＳ Ｂ ０６０１−１９９４）に定められており、例えば、表面粗さ計により測定することができる。
Example 1
(Production of negative electrode)
As the negative electrode current collector, a copper foil having a thickness of 35 μm and an arithmetic average roughness Ra of 1.0 μm on the surface was used. Here, the surface roughness Ra is defined in Japanese Industrial Standard (JIS B 0601-1994), and can be measured by, for example, a surface roughness meter.
負極活物質として、平均粒子径３．３μｍのケイ素粉末を用いた。このケイ素粉末７３．４重量部と、結着材であるポリイミド８．２重量部に対して、コバルトが１８．４重量部となるように、酢酸コバルト無水物を混合し、これにＮ−メチル−２−ピロリドンを加え、３０００ｒｐｍで５分間攪拌を行うことにより、スラリーを調製した。 As the negative electrode active material, silicon powder having an average particle size of 3.3 μm was used. Cobalt acetate anhydride was mixed with 73.4 parts by weight of the silicon powder and 8.2 parts by weight of the polyimide as a binder so that cobalt would be 18.4 parts by weight, and this was mixed with N-methyl. 2-Pyrrolidone was added and a slurry was prepared by stirring at 3000 rpm for 5 minutes.
このスラリーを、上記銅箔からなる負極集電体の片面にドクターブレード法により塗布し、乾燥後、圧延した。次に、これをアルゴン雰囲気中において、４００℃で１時間熱処理し、その後これを切断して、横３０ｍｍ、縦２５ｍｍ、厚み５７μｍの負極Ａ１を得た。 This slurry was applied to one side of the negative electrode current collector made of the copper foil by a doctor blade method, dried and rolled. Next, this was heat-treated at 400 ° C. for 1 hour in an argon atmosphere, and then cut to obtain a negative electrode A1 having a width of 30 mm, a length of 25 mm and a thickness of 57 μm.
（比較例１）
酢酸コバルト無水物に代えて、平均粒子径１．６μｍのコバルト粉末１８．４重量部を用いる以外は、実施例１と同様にして厚み５２μｍの負極Ｂ１を得た。
(Comparative Example 1)
A negative electrode B1 having a thickness of 52 μm was obtained in the same manner as in Example 1 except that 18.4 parts by weight of cobalt powder having an average particle diameter of 1.6 μm was used instead of cobalt acetate anhydride.
（実施例２）
酢酸コバルト無水物に代えて、亜鉛が１８．４重量部となるように、酢酸亜鉛を用いる以外は、実施例１と同様にして、厚み６５μｍの負極Ａ２を得た。
(Example 2)
A negative electrode A2 having a thickness of 65 μm was obtained in the same manner as in Example 1 except that zinc acetate was used so that zinc was 18.4 parts by weight instead of cobalt acetate anhydride.
（実施例３）
ケイ素粉末８８．２重量部と、ポリイミド９．８重量部に対して、コバルト２．０重量部となるように、酢酸コバルト無水物を混合した以外は、実施例１と同様にして、厚み５３μｍの負極Ａ′１を得た。
(Example 3)
A thickness of 53 μm was obtained in the same manner as in Example 1 except that cobalt acetate anhydride was mixed so as to be 2.0 parts by weight of cobalt with respect to 88.2 parts by weight of silicon powder and 9.8 parts by weight of polyimide. Negative electrode A′1 was obtained.
（実施例４）
酢酸コバルト無水物に代えて、亜鉛２．０重量部となるように、酢酸亜鉛を用いる以外は、実施例３と同様にして、厚み５３μｍの負極Ａ′２を得た。
Example 4
A negative electrode A′2 having a thickness of 53 μm was obtained in the same manner as in Example 3 except that zinc acetate was used instead of cobalt acetate anhydride so as to be 2.0 parts by weight of zinc.
（実施例５）
実施例１と同様のケイ素粉末を用い、このケイ素粉末８０重量部に、熱処理後のコバルトが２０重量部となるように酢酸コバルト無水物を混合し、１５分間乳鉢にてらいかいを行った後、この混合粉末を、アルゴン雰囲気中で４００℃、１０時間熱処理した。
(Example 5)
After using the same silicon powder as in Example 1, 80 parts by weight of this silicon powder was mixed with cobalt acetate anhydride so that the cobalt after the heat treatment was 20 parts by weight, and after scouring in a mortar for 15 minutes The mixed powder was heat-treated at 400 ° C. for 10 hours in an argon atmosphere.
熱処理後の混合粉末９１．８重量部と、結着材としてのポリイミド８．２重量部に、Ｎ−メチル−２−ピロリドンを加えて、３０００ｒｐｍで５分間攪拌を行い、スラリーを調製した。このスラリーを、実施例１と同様の銅箔からなる負極集電体の片面にドクターブレード法により塗布し、乾燥させた後圧延し、この電極をアルゴン雰囲気中で４００℃、１０時間熱処理し、横３０ｍｍ、縦２５ｍｍ、厚み５０μｍの負極Ａ３を得た。 N-methyl-2-pyrrolidone was added to 91.8 parts by weight of the mixed powder after heat treatment and 8.2 parts by weight of polyimide as a binder, and stirred at 3000 rpm for 5 minutes to prepare a slurry. This slurry was applied to one side of a negative electrode current collector made of the same copper foil as in Example 1 by a doctor blade method, dried and rolled, and this electrode was heat-treated in an argon atmosphere at 400 ° C. for 10 hours, A negative electrode A3 having a width of 30 mm, a length of 25 mm, and a thickness of 50 μm was obtained.
〔反射電子像による電極の観察〕
負極Ａ１、Ｂ１及びＡ３について、走査型電子顕微鏡で、電極断面の反射電子像を観察した。各電極について、アルゴンイオンスパッタにより切断した断面を観察した。
[Observation of electrodes by reflected electron images]
With respect to the negative electrodes A1, B1, and A3, reflected electron images of the electrode cross section were observed with a scanning electron microscope. About each electrode, the cross section cut | disconnected by argon ion sputtering was observed.
図１は、負極Ａ１の電子顕微鏡写真であり、図２は、負極Ｂ１の電子顕微鏡写真であり、図３は、負極Ａ３の電子顕微鏡写真である。反射電子像では、導電性の高い部分が白く、導電性の低い部分が黒く見える。従って、図１、図２及び図３において、最も白い部分が金属粒子である。図１から明らかなように、負極Ａ１においては、活物質層全体において平均粒子径１μｍ以下の金属粒子が均一に存在していることがわかる。これに対し、図２から明らかなように、負極Ｂ１においては、コバルト粒子同士が凝集していることがわかる。また、図３から明らかなように、負極Ａ３においては、負極Ａ１と同様に、平均粒子径１μｍ以下の金属粒子が良好な分散状態で活物質層中に存在していることがわかる。 1 is an electron micrograph of the negative electrode A1, FIG. 2 is an electron micrograph of the negative electrode B1, and FIG. 3 is an electron micrograph of the negative electrode A3. In the reflected electron image, the portion with high conductivity appears white and the portion with low conductivity appears black. Therefore, in FIG. 1, FIG. 2 and FIG. 3, the whitest part is the metal particles. As can be seen from FIG. 1, in the negative electrode A1, metal particles having an average particle diameter of 1 μm or less are uniformly present in the entire active material layer. On the other hand, as is clear from FIG. 2, it can be seen that the cobalt particles are aggregated in the negative electrode B1. As can be seen from FIG. 3, in the negative electrode A3, similarly to the negative electrode A1, it can be seen that metal particles having an average particle diameter of 1 μm or less are present in a well dispersed state in the active material layer.
以上のことから、本発明に従い、金属有機化合物を熱処理することによって得られる金属粒子を用いることにより、より良好な分散状態で活物質層中に導電材を分散させることができる。 From the above, according to the present invention, the conductive material can be dispersed in the active material layer in a better dispersion state by using metal particles obtained by heat-treating the metal organic compound.
〔正極の作製〕
正極活物質としてのＬｉＣｏＯ2と、導電材である黒鉛と、結着材であるポリフッ化ビニリデンとを、９２．５：４．５：３の重量比で混合し、これにＮ−メチル−２−ピロリドンを加えてスラリーを調製した。
[Production of positive electrode]
LiCoO 2 as a positive electrode active material, graphite as a conductive material, and polyvinylidene fluoride as a binder were mixed at a weight ratio of 92.5: 4.5: 3, and this was mixed with N-methyl-2. -A slurry was prepared by adding pyrrolidone.
このスラリーを、厚み２０μｍのアルミニウム箔からなる正極集電体の片面にドクターブレード法により塗布し、乾燥し、圧延した後、これを切断して、横２０ｍｍ、縦２０ｍｍ、厚み８５μｍの正極を得た。 This slurry was applied to one side of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm by a doctor blade method, dried, rolled, and then cut to obtain a positive electrode having a width of 20 mm, a length of 20 mm, and a thickness of 85 μm. It was.
〔非水電解液の作製〕
エチレンカーボネートと、ジエチルカーボネートとを３：７の体積で混合し、この混合溶媒に溶質としてＬｉＰＦ6を１モル／リットルの濃度となるように溶解させた。この非水電解液を５℃まで冷却し、二酸化炭素雰囲気下で、この非水電解液に二酸化炭素ガスを３００ｍｌ／分で２０分間吹き込んだ。これを２５℃に昇温し、非水電解液として用いた。
[Preparation of non-aqueous electrolyte]
Ethylene carbonate and diethyl carbonate were mixed in a volume of 3: 7, and LiPF 6 was dissolved as a solute in this mixed solvent to a concentration of 1 mol / liter. The non-aqueous electrolyte was cooled to 5 ° C., and carbon dioxide gas was blown into the non-aqueous electrolyte at 300 ml / min for 20 minutes in a carbon dioxide atmosphere. This was heated to 25 ° C. and used as a non-aqueous electrolyte.
二酸化炭素ガス吹き込み後の電解液の重量を二酸化炭素ガス雰囲気下で測定し、二酸化炭素ガス吹き込み前後の電解液の重量変化を測定することにより、電解液に溶解している二酸化炭素ガスを算出した。二酸化炭素の電解液への溶解量は、０．４重量％であった。 Carbon dioxide gas dissolved in the electrolyte was calculated by measuring the weight of the electrolyte after carbon dioxide gas was blown in a carbon dioxide gas atmosphere and measuring the change in the weight of the electrolyte before and after carbon dioxide gas was blown. . The amount of carbon dioxide dissolved in the electrolytic solution was 0.4% by weight.
〔リチウム二次電池の作製〕
アルミニウムからなる金属シートの両面にポリプロピレンを被覆したラミネートフィルムを用いて、電池容器を作製し、この電池容器内に、図４で示すように、上記正極と負極をこれらの間にポリエチレン性微多孔膜からなるセパレータを挟んだ状態で収容した。正極集電体１ｂの上には、正極活物質層１ａが形成されており、正極集電体１ｂには、アルミニウムからなる正極タブ１ｃが取り付けられている。また、負極集電体３ｂの上には、負極活物質層３ａが形成されており、負極集電体３ｂには、ニッケルからなる負極タブ３ｃが取り付けられている。正極活物質層１ａと負極活物質層３ａとの間にセパレータ２が配置されている。正極タブ１ｃ及び負極タブ３ｃが外部に出た状態となるように電池容器内に収納した後、この電池容器内に上記非水電解液を注入し、この状態で電池容器の周囲を熱融着させて封止し、薄型のリチウム二次電池を作製した。負極Ａ１、Ａ２、Ａ′１、Ａ′２、Ａ３、Ｂ１、及びＢ２を用いて作製した電池を、それぞれ電池ａ１、ａ２、ａ′１、ａ′２、ａ３、ｂ１、及びｂ２とした。
[Production of lithium secondary battery]
A battery container is prepared using a laminate film in which polypropylene is coated on both sides of a metal sheet made of aluminum, and the positive electrode and the negative electrode are interposed between the positive electrode and the negative electrode in the battery container as shown in FIG. It was accommodated in a state of sandwiching a separator made of a membrane. A positive electrode active material layer 1a is formed on the positive electrode current collector 1b, and a positive electrode tab 1c made of aluminum is attached to the positive electrode current collector 1b. A negative electrode active material layer 3a is formed on the negative electrode current collector 3b, and a negative electrode tab 3c made of nickel is attached to the negative electrode current collector 3b. A separator 2 is disposed between the positive electrode active material layer 1a and the negative electrode active material layer 3a. After the positive electrode tab 1c and the negative electrode tab 3c are accommodated in the battery container so as to come out, the non-aqueous electrolyte is injected into the battery container, and in this state, the periphery of the battery container is thermally fused Then, a thin lithium secondary battery was produced. Batteries produced using the negative electrodes A1, A2, A′1, A′2, A3, B1, and B2 were designated as batteries a1, a2, a′1, a′2, a3, b1, and b2, respectively.
〔内部抵抗の測定〕
作製した各電池について、２５℃にて１４ｍＡで４．２Ｖまで定電流で充電し、０．７ｍＡまで定電圧で充電した後、１４ｍＡで２．７５Ｖまで放電した。この充放電後、周波数１ｋＨｚで電池の内部抵抗を測定した。測定結果を表１に示す。
[Measurement of internal resistance]
About each produced battery, after charging with constant current to 4.2V at 14mA at 25 degreeC, and charging with constant voltage to 0.7mA, it discharged to 2.75V at 14mA. After this charging / discharging, the internal resistance of the battery was measured at a frequency of 1 kHz. The measurement results are shown in Table 1.
表１に示すように、本発明に従う電極を用いた電池ａ１、ａ２、ａ′１、ａ′２、及びａ３は、比較の電池ｂ１及びｂ２に比べ、内部抵抗が低くなっていることがわかる。これは、本発明に従い、金属有機化合物を熱処理することによって得られる金属粒子を活物質層に含有させることにより、充放電後における導電パスの減少を抑制することができ、結果として内部抵抗を低下させることができたためと考えられる。すなわち、本発明に従う金属粒子は、図１及び図３に示すように、良好な分散状態でかつ微小な粒子として存在しているため、図２に示す比較電極に比べ、導電パスを多く形成できると考えられる。 As shown in Table 1, it can be seen that the batteries a1, a2, a′1, a′2, and a3 using the electrodes according to the present invention have lower internal resistance than the comparative batteries b1 and b2. . According to the present invention, the active material layer contains metal particles obtained by heat-treating a metal organic compound, thereby suppressing a decrease in the conductive path after charge / discharge, resulting in a decrease in internal resistance. It is thought that it was possible to make it. That is, since the metal particles according to the present invention exist as fine particles in a well dispersed state as shown in FIGS. 1 and 3, a larger number of conductive paths can be formed than the comparative electrode shown in FIG. it is conceivable that.
また、表１に示す結果から、金属粒子の含有量は、２重量％の場合よりも、２０重量％の方が、内部抵抗の低減効果が高いことがわかる。 In addition, the results shown in Table 1 show that the effect of reducing internal resistance is higher when the content of metal particles is 20% by weight than when the content is 2% by weight.
１ａ…正極活物質層
１ｂ…正極集電体
１ｃ…正極タブ
２…セパレータ
３…負極活物質層
３ｂ…負極集電体
３ｃ…負極タブ
DESCRIPTION OF SYMBOLS 1a ... Positive electrode active material layer 1b ... Positive electrode collector 1c ... Positive electrode tab 2 ... Separator 3 ... Negative electrode active material layer 3b ... Negative electrode collector 3c ... Negative electrode tab
Claims (11)
前記負極の活物質層には、負極活物質としてのケイ素またはケイ素合金と、コバルト又は亜鉛を金属成分として含む酢酸金属を熱処理することによって得られる金属粒子と、結着剤とが含まれることを特徴とする非水電解質二次電池用電極。
An electrode used in a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The negative electrode active material layer contains silicon or a silicon alloy as a negative electrode active material, metal particles obtained by heat-treating metal acetate containing cobalt or zinc as a metal component, and a binder. A non-aqueous electrolyte secondary battery electrode.
3. The electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the metal particles are contained in an amount of 1 to 50% by weight based on a total of the metal particles and the negative electrode active material.
The average particle diameter of the said negative electrode active material is 10 micrometers or less, The electrode for nonaqueous electrolyte secondary batteries of any one of Claims 1-3 characterized by the above-mentioned.
The electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the binder is a binder remaining after the heat treatment.
6. The electrode for a nonaqueous electrolyte secondary battery according to claim 5, wherein the binder is polyimide condensed by heat treatment of polyamic acid.
熱処理により、コバルト又は亜鉛を金属成分として含む金属粒子となる酢酸金属と、負
極活物質としてのケイ素またはケイ素合金と、結着剤とを含むスラリーを調製する工程と、
前記スラリーを集電体の上に塗布して負極活物質層を形成する工程と、
前記負極活物質層を熱処理することにより、前記負極活物質層に含まれている前記酢酸金属を金属粒子にする工程とを備えることを特徴とする非水電解質二次電池用電極の製造方法。
A method for producing an electrode for a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
A step of preparing a slurry containing metal acetate which becomes metal particles containing cobalt or zinc as a metal component by heat treatment, silicon or a silicon alloy as a negative electrode active material, and a binder;
Applying the slurry onto a current collector to form a negative electrode active material layer;
And a step of heat-treating the negative electrode active material layer to convert the metal acetate contained in the negative electrode active material layer into metal particles. A method for producing an electrode for a nonaqueous electrolyte secondary battery, comprising:
The method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 7 , wherein the binder is a binder remaining after the heat treatment.
The method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 8 , wherein the binder is polyimide condensed by heat treatment of polyamic acid.
熱処理によりコバルト又は亜鉛を金属成分として含む金属粒子となる酢酸金属と、負極活物質としてのケイ素またはケイ素合金とを混合して混合粉末を調製する工程と、
前記混合粉末を熱処理して、前記酢酸金属を前記金属粒子にする工程と、
前記金属粒子及び前記負極活物質からなる熱処理後の前記混合粉末を結着剤と混合してスラリーを調製する工程と、
前記スラリーを集電体の上に塗布して負極活物質層を形成する工程とを備えることを特徴とする非水電解質二次電池用電極の製造方法。
A method for producing an electrode for a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
A step of preparing a mixed powder by mixing metal acetate to be metal particles containing cobalt or zinc as a metal component by heat treatment and silicon or a silicon alloy as a negative electrode active material;
Heat treating the mixed powder to convert the metal acetate into the metal particles;
A step of preparing a slurry by mixing the mixed powder after heat treatment composed of the metal particles and the negative electrode active material with a binder;
Applying the slurry onto a current collector to form a negative electrode active material layer, and a method for producing an electrode for a nonaqueous electrolyte secondary battery.
A nonaqueous electrolyte secondary battery comprising a negative electrode comprising the electrode according to claim 1, a positive electrode, and a nonaqueous electrolyte.
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| US8951672B2 (en) | 2007-01-30 | 2015-02-10 | Sony Corporation | Anode, method of manufacturing it, battery, and method of manufacturing it |
| JP5360485B2 (en) * | 2009-09-16 | 2013-12-04 | 株式会社豊田自動織機 | Negative electrode for lithium ion secondary battery and method for producing the same |
| WO2015103785A1 (en) * | 2014-01-13 | 2015-07-16 | 孙松华 | Complexing agent and preparation method and use thereof |
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| JPH076761A (en) * | 1993-06-15 | 1995-01-10 | Fuji Photo Film Co Ltd | Nonaqueous secondary battery |
| JP3582161B2 (en) * | 1995-08-11 | 2004-10-27 | ソニー株式会社 | Positive electrode active material and non-aqueous electrolyte secondary battery using the same |
| JPH09245798A (en) * | 1996-03-05 | 1997-09-19 | Matsushita Denchi Kogyo Kk | Lithium secondary battery |
| JP2000173622A (en) * | 1998-12-08 | 2000-06-23 | Hitachi Ltd | Lithium secondary battery |
| JP2001185139A (en) * | 1999-12-22 | 2001-07-06 | Mitsui Mining & Smelting Co Ltd | Positive electrode material for secondary battery using nonaqueous electrolyte and manufacturing method therefor and lithium secondary battery |
| JP4212263B2 (en) * | 2000-09-01 | 2009-01-21 | 三洋電機株式会社 | Negative electrode for lithium secondary battery and method for producing the same |
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