JP5757148B2 - Negative electrode active material for lithium ion secondary battery and lithium ion secondary battery using the negative electrode active material - Google Patents
Negative electrode active material for lithium ion secondary battery and lithium ion secondary battery using the negative electrode active material Download PDFInfo
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Description
本発明は、リチウムイオン二次電池用負極活物質及びその負極活物質を用いたリチウムイオン二次電池に関するものである。 The present invention relates to a negative electrode active material for a lithium ion secondary battery and a lithium ion secondary battery using the negative electrode active material.
リチウムイオン二次電池は、充放電容量が高く、高出力化が可能な二次電池である。現在、主として携帯電子機器用の電源として用いられており、更に、今後普及が予想される電気自動車用の電源として期待されている。リチウムイオン二次電池は、リチウム（Li）を挿入および脱離することが出来る活物質を正極及び負極にそれぞれ有する。そして、両極間に設けられた電解液内をLiイオンが移動することによって動作する。 A lithium ion secondary battery is a secondary battery having a high charge / discharge capacity and capable of high output. Currently, it is mainly used as a power source for portable electronic devices, and further expected as a power source for electric vehicles that are expected to be widely used in the future. A lithium ion secondary battery has an active material capable of inserting and extracting lithium (Li) in a positive electrode and a negative electrode, respectively. And it operates by moving Li ions in the electrolyte provided between the two electrodes.
リチウムイオン二次電池には、正極の活物質として主にリチウムコバルト複合酸化物等のリチウム含有金属複合酸化物が用いられ、負極の活物質としては多層構造を有する炭素材料が主に用いられている。 In lithium ion secondary batteries, lithium-containing metal composite oxides such as lithium cobalt composite oxide are mainly used as the active material for the positive electrode, and carbon materials having a multilayer structure are mainly used as the active material for the negative electrode. Yes.
リチウムイオン二次電池の性能は、二次電池を構成する正極、負極および電解質の材料に左右される。なかでも活物質を形成する活物質材料の研究開発が活発に行われている。例えば負極活物質材料として炭素よりも高容量なケイ素またはケイ素酸化物が検討されている。 The performance of the lithium ion secondary battery depends on the materials of the positive electrode, the negative electrode, and the electrolyte constituting the secondary battery. In particular, research and development of active material that forms an active material is being actively conducted. For example, silicon or silicon oxide having a higher capacity than carbon has been studied as a negative electrode active material.
ケイ素を負極活物質として用いることにより、炭素材料を用いるよりも高容量の電池とすることが出来る。しかしながらケイ素は、充放電時のLiの吸蔵・放出に伴う体積変化が大きい。そのためケイ素が微粉化して集電体から脱落または剥離し、電池の充放電サイクル寿命が短いという問題点がある。そこでケイ素酸化物を負極活物質として用いることにより、ケイ素よりも充放電時のLiの吸蔵・放出に伴う体積変化を抑制することが出来る。 By using silicon as the negative electrode active material, a battery having a higher capacity than that using a carbon material can be obtained. However, silicon has a large volume change due to insertion and extraction of Li during charge and discharge. Therefore, there is a problem that silicon is pulverized and falls off or peels from the current collector, and the charge / discharge cycle life of the battery is short. Therefore, by using silicon oxide as the negative electrode active material, volume change associated with insertion and extraction of Li during charge / discharge can be suppressed more than silicon.
例えば、負極活物質として、酸化ケイ素（SiOx：ｘは0.5≦ｘ≦1.5程度）の使用が検討されている。SiOxは熱処理されると、SiとSiO2とに分解することが知られている。これは不均化反応といい、SiとOとの比が概ね１：１の均質な固体の一酸化ケイ素SiOであれば、固体の内部反応によりSi相とSiO2相の二相に分離する。分離して得られるSi相は非常に微細である。また、Si相を覆うSiO2相が電解液の分解を抑制する働きをもつ。したがって、SiとSiO2とに分解したSiOxからなる負極活物質を用いた二次電池は、サイクル特性に優れる。 For example, the use of silicon oxide (SiO x : x is about 0.5 ≦ x ≦ 1.5) as a negative electrode active material has been studied. It is known that SiO x decomposes into Si and SiO 2 when heat-treated. This is called a disproportionation reaction, and if it is a homogeneous solid silicon monoxide SiO with a ratio of Si to O of approximately 1: 1, it will be separated into two phases of Si phase and SiO 2 phase by solid internal reaction. . The Si phase obtained by separation is very fine. Further, the SiO 2 phase covering the Si phase has a function of suppressing the decomposition of the electrolytic solution. Therefore, the secondary battery using the negative electrode active material composed of SiO x decomposed into Si and SiO 2 has excellent cycle characteristics.
ところでリチウムイオン二次電池の負極においては、充放電過程においてＳＥＩ(Solid Electrolyte Interface)と称される絶縁被膜が負極の表面に形成される。このＳＥＩは、LiF、LiCO3などを主成分とし、これらは不可逆物質であり充放電に利用可能なリチウム量が減少して不可逆容量となってしまう。 By the way, in the negative electrode of a lithium ion secondary battery, an insulating coating called SEI (Solid Electrolyte Interface) is formed on the surface of the negative electrode in the charge / discharge process. This SEI is mainly composed of LiF, LiCO 3 and the like, and these are irreversible materials, and the amount of lithium available for charge / discharge is reduced, resulting in an irreversible capacity.
そこで負極にＳＥＩが生成しないように、負極活物質の表面を別の物質で被覆することが想起され、下記特許文献1には、リチウムを吸蔵・放出可能な炭素材料の表面の少なくとも一部に、リチウムとの合金化が可能な金属よりなる非晶質な金属化合物を被覆することが提案されている。また下記特許文献2には、炭素または黒鉛粉末に石炭系又は石油系ピッチを表面コートし、表面のピッチを不融化し、解砕し、炭化、黒鉛化することが記載されている。
Therefore, it has been conceived that the surface of the negative electrode active material is coated with another material so that SEI is not generated in the negative electrode. It has been proposed to coat an amorphous metal compound made of a metal that can be alloyed with lithium.
さらに、この初期不可逆容量の対応策として、不可逆容量分をあらかじめ電気化学的に充電しておく電極化成法が試みられている。電極化成法は例えば対極に金属リチウムを用いて半電池を組み、電気化学的にリチウムをドープする方法である。例えば下記特許文献3には、負極と金属リチウムとを電池内で電気化学的に接触させることで、SiOxにリチウムをプリドーピングした材料を含む負極が開示されている。 Furthermore, as a countermeasure for this initial irreversible capacity, an electrode formation method in which the irreversible capacity is electrochemically charged in advance has been attempted. The electrode formation method is, for example, a method of assembling a half cell using metallic lithium as a counter electrode and electrochemically doping lithium. For example, Patent Document 3 below discloses a negative electrode including a material in which lithium is pre-doped in SiO x by electrochemically contacting a negative electrode and metallic lithium in a battery.
また、負極活物質として酸化ケイ素を用いたリチウムイオン二次電池の場合には、高温保存試験を行うと電池特性が低下するという不具合があった。この原因は、高温保存中にＳＥＩの一部が電解液中に溶出し、表出した負極活物質の表面に再びＳＥＩが生成することで、結果的にＳＥＩ量が多くなるためと考えられている。 In addition, in the case of a lithium ion secondary battery using silicon oxide as the negative electrode active material, there is a problem in that battery characteristics deteriorate when a high temperature storage test is performed. This is thought to be due to the fact that part of SEI elutes into the electrolyte during high-temperature storage and SEI is generated again on the surface of the exposed negative electrode active material, resulting in an increase in the amount of SEI. Yes.
ところが非晶質な金属化合物で被覆する方法では、金属化合物は電気抵抗が大きいため負荷特性の低下が懸念される。また黒鉛で被覆された負極では、黒鉛自体の絶縁性が低いためＳＥＩの生成を抑制する効果が小さいことが懸念される。 However, in the method of coating with an amorphous metal compound, since the metal compound has a large electric resistance, there is a concern that the load characteristics are deteriorated. Moreover, in the negative electrode coated with graphite, there is a concern that the effect of suppressing the generation of SEI is small because the graphite itself has low insulation.
本発明は、上記した事情に鑑みてなされたものであり、その主な目的は、ＳＥＩの生成を確実に抑制できるリチウムイオン二次電池用負極活物質を提供するとともに、その負極活物質を用いたリチウムイオン二次電池を提供することにある。 The present invention has been made in view of the above circumstances, and its main object is to provide a negative electrode active material for a lithium ion secondary battery that can reliably suppress the formation of SEI, and to use the negative electrode active material. It is to provide a lithium ion secondary battery.
上記課題を解決する本発明のリチウムイオン二次電池用負極活物質の特徴は、SiOx(0.3≦x≦1.6)で表されるケイ素酸化物からなる粒子と、その粒子の表面を被覆する樹脂被膜と、からなり、樹脂被膜はカルボキシル基を含む樹脂からなることにある。 The negative electrode active material for a lithium ion secondary battery of the present invention that solves the above problems is characterized by particles made of silicon oxide represented by SiOx (0.3 ≦ x ≦ 1.6) and a resin film that covers the surface of the particles If, Tona is, the resin film is in Rukoto such a resin containing a carboxyl group.
また上記課題を解決する本発明のリチウムイオン二次電池の特徴は、SiOx(0.3≦x≦1.6)で表されるケイ素酸化物からなる粒子と、その粒子の表面を被覆する樹脂被膜と、からなり、樹脂被膜はカルボキシル基を含む樹脂からなる負極活物質から形成されてなる負極を用いたことにある。 Further, the lithium ion secondary battery of the present invention that solves the above problems is characterized by: particles made of silicon oxide represented by SiOx (0.3 ≦ x ≦ 1.6), and a resin film covering the surface of the particles. Do Ri, resin coating is to using a negative electrode formed by forming a negative electrode active material that Do a resin containing a carboxyl group.
本発明のリチウムイオン二次電池用負極活物質は、SiOx(0.3≦x≦1.6)で表されるケイ素酸化物からなる粒子と、その粒子の表面を被覆する樹脂被膜と、からなる。すなわち負極活物質である粒子の表面に予め絶縁被膜が形成されている状態となるため、LiF、LiCO3などのＳＥＩの生成が抑制される。したがって本発明のリチウムイオン二次電池によれば、負極の不可逆容量を低減することができ、初期効率が向上するとともにサイクル特性も向上する。 The negative electrode active material for a lithium ion secondary battery of the present invention comprises particles made of silicon oxide represented by SiO x (0.3 ≦ x ≦ 1.6) and a resin film covering the surface of the particles. That is, since an insulating coating is formed in advance on the surface of the particles that are the negative electrode active material, the generation of SEI such as LiF and LiCO 3 is suppressed. Therefore, according to the lithium ion secondary battery of the present invention, the irreversible capacity of the negative electrode can be reduced, the initial efficiency is improved, and the cycle characteristics are also improved.
本発明のリチウムイオン二次電池用負極活物質は、SiOx(0.3≦x≦1.6)で表されるケイ素酸化物からなる粒子と、その粒子の表面を被覆する樹脂被膜と、からなり、樹脂被膜で被覆された粒子の集合体である粉末状態をなす。このケイ素酸化物からなる粒子は、不均化反応によって微細なSiと、Siを覆うSiO2とに分解したSiOxからなる。ｘが下限値未満であると、Si比率が高くなるため充放電時の体積変化が大きくなりすぎてサイクル特性が低下する。またｘが上限値を超えると、Si比率が低下してエネルギー密度が低下するようになる。0.5≦x≦1.5の範囲が好ましく、0.7≦x≦1.2の範囲がさらに望ましい。 The negative electrode active material for a lithium ion secondary battery of the present invention comprises a particle made of silicon oxide represented by SiO x (0.3 ≦ x ≦ 1.6), and a resin film covering the surface of the particle, and a resin It forms a powder that is an aggregate of particles coated with a coating. The particles made of silicon oxide are composed of SiO x decomposed into fine Si and SiO 2 covering Si by a disproportionation reaction. When x is less than the lower limit, the Si ratio increases, so that the volume change during charge / discharge becomes too large, and the cycle characteristics deteriorate. When x exceeds the upper limit value, the Si ratio is lowered and the energy density is lowered. A range of 0.5 ≦ x ≦ 1.5 is preferable, and a range of 0.7 ≦ x ≦ 1.2 is more desirable.
一般に、酸素を断った状態であれば800℃以上で、ほぼすべてのSiOが不均化して二相に分離すると言われている。具体的には、非結晶性のSiO粉末を含む原料酸化ケイ素粉末に対して、真空中または不活性ガス中などの不活性雰囲気中で800〜1200℃、1〜5時間の熱処理を行うことで、非結晶性のSiO2相および結晶性のSi相の二相を含むケイ素酸化物粉末が得られる。 In general, when oxygen is turned off, it is said that almost all SiO disproportionates and separates into two phases at 800 ° C. or higher. Specifically, the raw material silicon oxide powder containing amorphous SiO powder is subjected to heat treatment at 800 to 1200 ° C. for 1 to 5 hours in an inert atmosphere such as in a vacuum or an inert gas. A silicon oxide powder containing two phases of an amorphous SiO 2 phase and a crystalline Si phase is obtained.
またケイ素酸化物からなる粒子として、SiOxに対し炭素材料を1〜50質量％で複合化した粒子を用いることもできる。炭素材料を複合化することで、サイクル特性が向上する。炭素材料の複合量が1質量％未満では導電性向上の効果が得られず、50質量％を超えるとSiOxの割合が相対的に減少して負極容量が低下してしまう。炭素材料の複合量は、SiOxに対して5〜30質量％の範囲が好ましく、5〜20質量％の範囲がさらに望ましい。SiOxに対して炭素材料を複合化するには、ＣＶＤ法などを利用することができる。 Further, as a particle made of silicon oxide, a particle in which a carbon material is compounded at 1 to 50% by mass with respect to SiO x can also be used. By combining carbon materials, cycle characteristics are improved. If the composite amount of the carbon material is less than 1% by mass, the effect of improving the conductivity cannot be obtained, and if it exceeds 50% by mass, the proportion of SiO x is relatively decreased and the negative electrode capacity is decreased. The composite amount of the carbon material is preferably in the range of 5 to 30% by mass, more preferably in the range of 5 to 20% by mass with respect to SiO x . In order to combine the carbon material with SiO x , a CVD method or the like can be used.
ケイ素酸化物からなる粒子は平均粒径が1μｍ〜10μｍの範囲にあることが望ましい。平均粒径が10μｍより大きいとリチウムイオン二次電池の充放電特性が低下し、平均粒径が1μｍより小さいと樹脂の被覆時に凝集して粗大な粒子となるため同様にリチウムイオン二次電池の充放電特性が低下する場合がある。 The particles made of silicon oxide preferably have an average particle size in the range of 1 μm to 10 μm. When the average particle size is larger than 10 μm, the charge / discharge characteristics of the lithium ion secondary battery are deteriorated. When the average particle size is smaller than 1 μm, the particles are aggregated to become coarse particles when coated with the resin. Charge / discharge characteristics may deteriorate.
ケイ素酸化物からなる粒子に被覆される樹脂としては、電気絶縁性であり、かつリチウムイオンの移動が可能なものであれば特に制約されない。この樹脂被膜の形成量は、ケイ素酸化物からなる粒子100質量部に対して1質量部〜100質量部の範囲が望ましい。樹脂被膜の形成量が1質量部未満では、ケイ素酸化物からなる粒子の全表面を被覆することが困難となり、ケイ素酸化物からなる粒子が表出する表面においてＳＥＩが生成する場合がある。また樹脂被膜の形成量が100質量部を超えると、樹脂被膜による抵抗が増大し電池特性が悪化する場合がある。 The resin coated on the particles made of silicon oxide is not particularly limited as long as it is electrically insulating and can move lithium ions. The amount of the resin film formed is desirably in the range of 1 to 100 parts by mass with respect to 100 parts by mass of the silicon oxide particles. When the amount of the resin coating formed is less than 1 part by mass, it is difficult to coat the entire surface of the particles made of silicon oxide, and SEI may be generated on the surface where the particles made of silicon oxide are exposed. On the other hand, when the amount of the resin coating formed exceeds 100 parts by mass, the resistance due to the resin coating increases and the battery characteristics may deteriorate.
樹脂被膜を形成できる樹脂としては、ポリフッ化ビニリデン（PVDF）、ポリテトラフルオロエチレン（PTFE）等のフッ素系ポリマー、スチレンブタジエンゴム（SBR）等のゴム、ポリイミド等のイミド系ポリマー、アルコキシルシリル基含有樹脂、ポリアクリル酸、ポリメタクリル酸、ポリイタコン酸などが例示される。またアクリル酸と、メタクリル酸、イタコン酸、フマル酸、マレイン酸などの酸モノマーとの共重合物を用いることもできる。中でもポリアクリル酸など、カルボキシル基を含有する樹脂が特に望ましく、カルボキシル基の含有量が多い樹脂ほど好ましい。 Resins that can form resin coatings include fluoropolymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubbers such as styrene butadiene rubber (SBR), imide polymers such as polyimide, and alkoxysilyl groups. Examples thereof include resin, polyacrylic acid, polymethacrylic acid, and polyitaconic acid. A copolymer of acrylic acid and an acid monomer such as methacrylic acid, itaconic acid, fumaric acid or maleic acid can also be used. Among them, a resin containing a carboxyl group such as polyacrylic acid is particularly desirable, and a resin having a higher carboxyl group content is more preferable.
ポリアクリル酸を用いる場合、平均分子量が100,000〜5,000,000のものが好ましく、600,000〜1,000,000のものが特に望ましい。 When polyacrylic acid is used, those having an average molecular weight of 100,000 to 5,000,000 are preferred, and those having 600,000 to 1,000,000 are particularly desirable.
ケイ素酸化物からなる粒子に樹脂被膜を形成するには、樹脂を溶媒に溶解した溶液中にケイ素酸化物粉末を混合し、よく撹拌した後に溶媒を乾燥させる方法を採用することができる。溶媒を乾燥させるには単に加熱するだけでもよいが、スプレードライ法などを用いることも好ましい。 In order to form a resin coating on particles made of silicon oxide, a method of mixing a silicon oxide powder in a solution in which a resin is dissolved in a solvent, thoroughly stirring, and then drying the solvent can be employed. In order to dry the solvent, it may be simply heated, but it is also preferable to use a spray drying method or the like.
この樹脂は、負極形成時のバインダーの一部又は全部を構成することもできる。しかし負極形成時に用いられるスラリーは、負極活物質に加えて炭素粉末などの導電助剤を含むのが一般的であるため、単に混合するのみではケイ素酸化物からなる粒子の全表面に樹脂被膜を形成することが困難となる場合がある。したがって、先ず樹脂被膜を形成する樹脂を溶媒に溶解した溶液中にケイ素酸化物粉末を混合し、よく撹拌した後に導電助剤と残りのバインダー成分を加え、さらに混練してスラリーを調製することが望ましい。 This resin can also constitute a part or all of the binder when forming the negative electrode. However, since the slurry used for forming the negative electrode generally contains a conductive additive such as carbon powder in addition to the negative electrode active material, a resin film is formed on the entire surface of the particles made of silicon oxide simply by mixing. It may be difficult to form. Therefore, the silicon oxide powder is first mixed in a solution in which the resin for forming the resin film is dissolved in a solvent, and after stirring well, the conductive additive and the remaining binder components are added, and further kneaded to prepare a slurry. desirable.
本発明のリチウムイオン二次電池用負極活物質の他の構成要素は、特に限定されず、公知のものが使用できる。 The other component of the negative electrode active material for lithium ion secondary batteries of this invention is not specifically limited, A well-known thing can be used.
本発明のリチウムイオン二次電池の負極は、SiOx(0.3≦x≦1.6)で表されるケイ素酸化物からなる粒子と、その粒子の表面を被覆する樹脂被膜と、からなる負極活物質から形成されてなる。この負極は、集電体と、集電体上に結着された活物質層と、を有する。活物質層は、活物質、導電助剤、バインダー樹脂、及び必要に応じ適量の有機溶剤を加えて混合しスラリーにしたものを、ロールコート法、ディップコート法、ドクターブレード法、スプレーコート法、カーテンコート法などの方法で活物質上に塗布し、バインダー樹脂を硬化させることによって作製することができる。この活物質層中には、樹脂被膜をもちケイ素酸化物からなる粒子が負極活物質として含まれている。 The negative electrode of the lithium ion secondary battery of the present invention comprises a negative electrode active material comprising a particle made of silicon oxide represented by SiO x (0.3 ≦ x ≦ 1.6) and a resin film covering the surface of the particle. Formed. The negative electrode includes a current collector and an active material layer bound on the current collector. The active material layer is made by adding an active material, a conductive additive, a binder resin, and an appropriate amount of an organic solvent as necessary, and mixing them into a slurry. A roll coating method, a dip coating method, a doctor blade method, a spray coating method, It can be produced by applying on the active material by a method such as curtain coating and curing the binder resin. In the active material layer, particles made of silicon oxide having a resin film are contained as a negative electrode active material.
集電体は、放電或いは充電の間、電極に電流を流し続けるための化学的に不活性な電子高伝導体のことである。集電体は箔、板等の形状を採用することが出来るが、目的に応じた形状であれば特に限定されない。集電体として、例えば銅箔やアルミニウム箔を好適に用いることができる。 A current collector is a chemically inert electronic high conductor that keeps current flowing through an electrode during discharging or charging. The current collector can adopt a shape such as a foil or a plate, but is not particularly limited as long as it has a shape according to the purpose. As the current collector, for example, a copper foil or an aluminum foil can be suitably used.
導電助剤は、電極の導電性を高めるために添加される。導電助剤として、炭素質微粒子であるカーボンブラック、黒鉛、アセチレンブラック（AB）、ケッチェンブラック（KB）、気相法炭素繊維（Vapor Grown Carbon Fiber：VGCF）等を単独でまたは二種以上組み合わせて添加することが出来る。導電助剤の使用量については、特に限定的ではないが、例えば、活物質100質量部に対して、20〜100質量部程度とすることができる。導電助剤の量が20質量部未満では効率のよい導電パスを形成できず、100質量部を超えると電極の成形性が悪化するとともにエネルギー密度が低くなる。なお炭素材料が複合化されたケイ素酸化物を活物質として用いる場合は、導電助剤の添加量を低減あるいは無しとすることができる。 The conductive assistant is added to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used alone or in combination as a conductive additive. Can be added. The amount of the conductive aid used is not particularly limited, but can be, for example, about 20 to 100 parts by mass with respect to 100 parts by mass of the active material. If the amount of the conductive auxiliary is less than 20 parts by mass, an efficient conductive path cannot be formed, and if it exceeds 100 parts by mass, the moldability of the electrode deteriorates and the energy density decreases. Note that when the silicon oxide combined with the carbon material is used as the active material, the amount of the conductive auxiliary agent added can be reduced or eliminated.
バインダー樹脂は、活物質及び導電助剤を集電体に結着するための結着剤として用いられる。バインダー樹脂はなるべく少ない量で活物質等を結着させることが求められ、その量は活物質、導電助材、及びバインダー樹脂を合計したものの0.5wt％〜50wt％が望ましい。バインダー樹脂量が0.5wt％未満では電極の成形性が低下し、50wt％を超えると電極のエネルギー密度が低くなる。なお、バインダー樹脂としては前述した各種樹脂を用いることができる。 The binder resin is used as a binder for binding the active material and the conductive additive to the current collector. The binder resin is required to bind the active material or the like in as small an amount as possible, and the amount is preferably 0.5 wt% to 50 wt% of the total of the active material, the conductive additive, and the binder resin. When the amount of the binder resin is less than 0.5 wt%, the moldability of the electrode is lowered, and when it exceeds 50 wt%, the energy density of the electrode is lowered. In addition, various resin mentioned above can be used as binder resin.
本発明のリチウムイオン二次電池における負極を構成するケイ素酸化物には、リチウムがプリドーピングされていることが望ましい。負極にリチウムをドープするには、例えば対極に金属リチウムを用いて半電池を組み、電気化学的にリチウムをドープする電極化成法などを利用することができる。リチウムのドープ量は特に制約されず、例えば特許文献3に記載の範囲とすることができる。 It is desirable that lithium be pre-doped in the silicon oxide constituting the negative electrode in the lithium ion secondary battery of the present invention. In order to dope lithium into the negative electrode, for example, an electrode formation method in which a half battery is assembled using metallic lithium as the counter electrode and electrochemically doped with lithium can be used. The doping amount of lithium is not particularly limited, and can be in the range described in Patent Document 3, for example.
上記した負極を用いる本発明のリチウムイオン二次電池は、特に限定されない公知の正極、電解液、セパレータを用いることが出来る。正極は、リチウムイオン二次電池で使用可能なものであればよい。正極は、集電体と、集電体上に結着された正極活物質層とを有する。正極活物質層は、正極活物質と、バインダーとを含み、さらには導電助剤を含んでも良い。正極活物質、導電助材およびバインダーは、特に限定はなく、リチウムイオン二次電池で使用可能なものであればよい。 The positive electrode, electrolyte solution, and separator which are not specifically limited can be used for the lithium ion secondary battery of this invention using the above-mentioned negative electrode. The positive electrode may be anything that can be used in a lithium ion secondary battery. The positive electrode has a current collector and a positive electrode active material layer bound on the current collector. The positive electrode active material layer includes a positive electrode active material and a binder, and may further include a conductive additive. The positive electrode active material, the conductive additive, and the binder are not particularly limited as long as they can be used in the lithium ion secondary battery.
正極活物質としては、金属リチウム、LiCoO2、LiNi1/3Co1/3Mn1/3O2、Li2MnO2、硫黄などが挙げられる。集電体は、アルミニウム、ニッケル、ステンレス鋼など、リチウムイオン二次電池の正極に一般的に使用されるものであればよい。導電助剤は上記の負極で記載したものと同様のものが使用できる。 Examples of the positive electrode active material include metallic lithium, LiCoO 2 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 , Li 2 MnO 2 , and sulfur. The current collector is not particularly limited as long as it is generally used for the positive electrode of a lithium ion secondary battery, such as aluminum, nickel, and stainless steel. As the conductive auxiliary agent, the same ones as described in the above negative electrode can be used.
電解液は、有機溶媒に電解質であるリチウム金属塩を溶解させたものである。電解液は、特に限定されない。有機溶媒として、非プロトン性有機溶媒、たとえばプロピレンカーボネート（PC）、エチレンカーボネート（EC）、ジメチルカーボネート（DMC）、ジエチルカーボネート（DEC）、エチルメチルカーボネート（EMC）等から選ばれる一種以上を用いることができる。また、溶解させる電解質としては、LiPF6、LiBF4、LiAsF6、LiI、LiClO4、LiCF3SO3等の有機溶媒に可溶なリチウム金属塩を用いることができる。 The electrolytic solution is obtained by dissolving a lithium metal salt as an electrolyte in an organic solvent. The electrolytic solution is not particularly limited. As the organic solvent, an aprotic organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) or the like is used. Can do. As the electrolyte to be dissolved, a lithium metal salt soluble in an organic solvent such as LiPF 6 , LiBF 4 , LiAsF 6 , LiI, LiClO 4 , LiCF 3 SO 3 can be used.
例えば、エチレンカーボネート、ジメチルカーボネート、プロピレンカーボネート、ジメチルカーボネートなどの有機溶媒にLiClO4、LiPF6、LiBF4、LiCF3SO3等のリチウム金属塩を0.5mol/lから1.7mol/l程度の濃度で溶解させた溶液を使用することが出来る。 For example, an organic solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate is mixed with a lithium metal salt such as LiClO 4 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 at a concentration of about 0.5 mol / l to 1.7 mol / l. A dissolved solution can be used.
セパレータは、リチウムイオン二次電池に使用されることが出来るものであれば特に限定されない。セパレータは、正極と負極とを分離し電解液を保持するものであり、ポリエチレン、ポリプロピレン等の薄い微多孔膜を用いることができる。 A separator will not be specifically limited if it can be used for a lithium ion secondary battery. The separator separates the positive electrode and the negative electrode and holds the electrolytic solution, and a thin microporous film such as polyethylene or polypropylene can be used.
本発明のリチウムイオン二次電池は、形状に特に限定はなく、円筒型、積層型、コイン型等、種々の形状を採用することができる。いずれの形状を採る場合であっても、正極および負極にセパレータを挟装させ電極体とし、正極集電体および負極集電体から外部に通ずる正極端子および負極端子までの間を、集電用リード等を用いて接続した後、この電極体を電解液とともに電池ケースに密閉して電池となる。 The lithium ion secondary battery of the present invention is not particularly limited in shape, and various shapes such as a cylindrical shape, a stacked shape, and a coin shape can be adopted. Regardless of the shape, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the space between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal is used for current collection. After connecting using a lead or the like, the electrode body is sealed in a battery case together with an electrolytic solution to form a battery.
以下、実施例を挙げて本発明を更に詳しく説明する。 Hereinafter, the present invention will be described in more detail with reference to examples.
＜リチウムイオン二次電池用負極の作製＞
先ずSiO粉末（シグマ・アルドリッチ・ジャパン社製、平均粒径5μｍ）を900℃で２時間熱処理し、平均粒径5μｍのSiOx粉末を調製した。この熱処理によって、SiとOとの比が概ね１：１の均質な固体の一酸化ケイ素SiOであれば、固体の内部反応によりSi相とSiO2相の二相に分離する。分離して得られるSi相は非常に微細である。
<Preparation of negative electrode for lithium ion secondary battery>
First, SiO powder (manufactured by Sigma-Aldrich Japan, average particle size 5 μm) was heat-treated at 900 ° C. for 2 hours to prepare SiO x powder having an average particle size of 5 μm. By this heat treatment, if the ratio of Si to O is a homogeneous solid silicon monoxide SiO of approximately 1: 1, it is separated into two phases of Si phase and SiO 2 phase by the internal reaction of the solid. The Si phase obtained by separation is very fine.
すなわち得られたSiOx粉末は、図1の左側に示すSiOx粒子1の集合体であり、このSiOx粒子1は、SiO210のマトリックス中に微細なSi粒子11が分散した構造となっている。
That is, the obtained SiO x powder is an aggregate of SiO x particles 1 shown on the left side of FIG. 1, and this SiO x particle 1 has a structure in which
次に、ポリアクリル酸（「H-AS」日本触媒社製）をN-メチル-2-ピロリドン(NMP)に8質量％となるように混合し、溶解してポリアクリル酸溶液を調製した。このポリアクリル酸溶液の380質量部中に、上記のSiOx粉末48質量部を混合し、混練機を用いてよく混練した。 Next, polyacrylic acid (“H-AS” manufactured by Nippon Shokubai Co., Ltd.) was mixed with N-methyl-2-pyrrolidone (NMP) at 8% by mass and dissolved to prepare a polyacrylic acid solution. In 380 parts by mass of this polyacrylic acid solution, 48 parts by mass of the above-mentioned SiO x powder were mixed and well kneaded using a kneader.
この混練時には、図1に示したSiOx粒子1の表面の全面にポリアクリル酸溶液が付着し、後述の集電体に塗布して乾燥後には、図1の右側に示すように、SiOx粒子1の表面にはポリアクリル酸からなる薄い樹脂被膜2が形成される。
During this kneading, the entire surface polyacrylic acid solution SiO x particles 1 surface is attached as shown in Figure 1, after drying by coating the current collector described below, as shown on the right side of FIG. 1, SiO x A
得られた混練物に、導電助剤としての黒鉛粉末34.4質量部とケッチェンブラック（KB）粉末2.6質量部とを混合し、スラリーを調製した。スラリー中の各成分の組成比は固形分として、SiOx粉末：黒鉛粉末：ケッチェンブラック：ポリアクリル酸＝48：34.4：2.6：15である。このスラリーを、厚さ20μｍの電解銅箔（集電体）の表面にドクターブレードを用いて塗布し、銅箔上に負極活物質層を形成した。 The obtained kneaded product was mixed with 34.4 parts by mass of graphite powder as a conductive additive and 2.6 parts by mass of ketjen black (KB) powder to prepare a slurry. The composition ratio of each component in the slurry is SiO x powder: graphite powder: ketchen black: polyacrylic acid = 48: 34.4: 2.6: 15 as a solid content. This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of 20 μm using a doctor blade to form a negative electrode active material layer on the copper foil.
その後、80℃で20分間乾燥し、負極活物質層から有機溶媒を揮発させて除去した。乾燥後、ロールプレス機により、集電体と負極活物質層を強固に密着接合させた。これを200℃で2時間加熱硬化させて、活物質層の厚さが15μｍ程度の負極を形成した。 Then, it dried at 80 degreeC for 20 minute (s), and the organic solvent was volatilized and removed from the negative electrode active material layer. After drying, the current collector and the negative electrode active material layer were firmly and closely joined with a roll press. This was heat-cured at 200 ° C. for 2 hours to form a negative electrode having an active material layer thickness of about 15 μm.
なお、負極としてリチウムがドーピングされている負極を用いてもよい。 Note that a negative electrode doped with lithium may be used as the negative electrode.
＜リチウムイオン二次電池の作製＞
上記の手順で作製した電極を評価極として用い、リチウムイオン二次電池（ハーフセル）を作製した。対極は、金属リチウム箔（厚さ500μｍ）とした。
<Production of lithium ion secondary battery>
A lithium ion secondary battery (half cell) was produced using the electrode produced by the above procedure as an evaluation electrode. The counter electrode was a metal lithium foil (
対極をφ13mm、評価極をφ11mmに裁断し、セパレータ（ヘキストセラニーズ社製ガラスフィルターおよびcelgard2400）を両者の間に挟装して電極体電池とした。この電極体電池を電池ケース（宝泉株式会社製CR2032コインセル）に収容した。また、電池ケースには、エチレンカーボネートとジエチルカーボネートとを1：1（体積比）で混合した混合溶媒にLiPF6を1Mの濃度で溶解した非水電解質を注入し、電池ケースを密閉して、リチウムイオン二次電池を得た。 The counter electrode was cut to φ13 mm, the evaluation electrode was cut to φ11 mm, and a separator (Hoechst Celanese glass filter and celgard2400) was sandwiched between them to form an electrode body battery. This electrode body battery was accommodated in a battery case (CR2032 coin cell manufactured by Hosen Co., Ltd.). Also, in the battery case, a nonaqueous electrolyte in which LiPF 6 was dissolved at a concentration of 1M was injected into a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a 1: 1 ratio (volume ratio), and the battery case was sealed, A lithium ion secondary battery was obtained.
[比較例1]
N-メチル-2-ピロリドン（NMP）にバインダー樹脂としてのポリアミドイミド−シリカハイブリッド樹脂(荒川化学工業製、溶剤組成：NMP／キシレン＝4/1、硬化残分30.0％、硬化残分中のシリカ：2％（割合は全て質量比）、粘度8700mPa・S/25℃)を溶解させた。この溶液と、実施例1と同様のSiOx粉末、導電助剤としての黒鉛粉末、ケッチェンブラック（KB）粉末を混合し、スラリーを調製した。スラリー中の各成分の組成比は固形分として、SiOx粉末：黒鉛粉末：ケッチェンブラック：バインダー樹脂＝48：34.4：2.6：15である。このスラリーを、厚さ20μｍの電解銅箔（集電体）の表面にドクターブレードを用いて塗布し、銅箔上に負極活物質層を形成した。
[Comparative Example 1]
N-methyl-2-pyrrolidone (NMP) and polyamideimide-silica hybrid resin as binder resin (Arakawa Chemical Industries, solvent composition: NMP / xylene = 4/1, cured residue 30.0%, silica in cured residue : 2% (all ratios are mass ratios), viscosity 8700 mPa · S / 25 ° C.) was dissolved. This solution was mixed with the same SiO x powder as in Example 1, graphite powder as a conductive aid, and ketjen black (KB) powder to prepare a slurry. The composition ratio of each component in the slurry is SiO x powder: graphite powder: ketchen black: binder resin = 48: 34.4: 2.6: 15 as a solid content. This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of 20 μm using a doctor blade to form a negative electrode active material layer on the copper foil.
その後、80℃で20分間乾燥し、負極活物質層から有機溶媒を揮発させて除去した。乾燥後、ロールプレス機により、集電体と負極活物質層を強固に密着接合させた。これを200℃で2時間加熱硬化させて、活物質層の厚さが15μｍ程度の負極を形成した。 Then, it dried at 80 degreeC for 20 minute (s), and the organic solvent was volatilized and removed from the negative electrode active material layer. After drying, the current collector and the negative electrode active material layer were firmly and closely joined with a roll press. This was heat-cured at 200 ° C. for 2 hours to form a negative electrode having an active material layer thickness of about 15 μm.
この負極を用い、実施例1と同様にしてリチウムイオン二次電池を作製した。 Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1.
＜リチウムイオン二次電池の充放電特性＞
作製したリチウムイオン二次電池に対して充放電試験を行い、結果を図2に示す。なお充放電試験は、25℃の温度環境のもと、金属Li基準で放電終止電圧0.01Vまで0.05mAの定電流で充電を行った後、充電終止電圧2Vまで0.05mAの定電流で放電を行った。「充電」は評価極の活物質がLiを吸蔵する方向、「放電」は評価極の活物質がLiを放出する方向、である。
<Charge / discharge characteristics of lithium ion secondary battery>
A charge / discharge test was performed on the fabricated lithium ion secondary battery, and the results are shown in FIG. In the charge / discharge test, the battery was charged at a constant current of 0.05 mA up to a discharge end voltage of 0.01 V under a temperature environment of 25 ° C. up to a discharge end voltage of 0.01 V, and then discharged at a constant current of 0.05 mA up to a charge end voltage of 2 V. went. “Charge” is the direction in which the active material of the evaluation electrode occludes Li, and “discharge” is the direction in which the active material of the evaluation electrode releases Li.
実施例1と比較例1のリチウムイオン二次電池の1サイクル目の充放電曲線を図2に示した。図2から1Vでの初期放電容量および2Vでの初期放電容量をそれぞれ読み取り、初期効率を算出した。結果を表１に示す。初期効率は、初期放電容量を初期充電容量で除した値の百分率（（初期放電容量）／（初期充電容量）×100）で求められる値である。 The charge / discharge curves for the first cycle of the lithium ion secondary batteries of Example 1 and Comparative Example 1 are shown in FIG. The initial discharge capacity at 1V and the initial discharge capacity at 2V were read from FIG. 2, and the initial efficiency was calculated. The results are shown in Table 1. The initial efficiency is a value obtained as a percentage of a value obtained by dividing the initial discharge capacity by the initial charge capacity ((initial discharge capacity) / (initial charge capacity) × 100).
図2において、実施例1の放電曲線に比べて、比較例1の放電曲線はなだらかに電圧が低下している。これは、比較例1のリチウムイオン二次電池では負極にＳＥＩが生成したことを示している。また表1から、実施例1のリチウムイオン二次電池は比較例1に比べて高い初期効率を示し、これは負極におけるＳＥＩの生成が抑制されたことによる効果であると考えられる。 In FIG. 2, compared with the discharge curve of Example 1, the voltage of the discharge curve of Comparative Example 1 is gradually decreased. This indicates that in the lithium ion secondary battery of Comparative Example 1, SEI was generated on the negative electrode. Also, from Table 1, the lithium ion secondary battery of Example 1 shows a higher initial efficiency than that of Comparative Example 1, which is considered to be an effect due to the suppression of SEI generation in the negative electrode.
すなわち各実施例のリチウム二次電池によれば、負極活物質であるSiOxの粒子の表面にポリアクリル酸からなる樹脂被膜が形成されているため、負極におけるＳＥＩの生成が抑制され、その結果、初期効率が向上したと考えられる。 That is, according to the lithium secondary battery of each example, since the resin film made of polyacrylic acid is formed on the surface of the SiO x particles as the negative electrode active material, the generation of SEI in the negative electrode is suppressed, and as a result The initial efficiency is considered to have improved.
＜リチウムイオン二次電池用負極の作製＞
ポリアクリル酸（「H-AS」日本触媒社製）6.7質量部と、ポリアミドイミドシリカ樹脂（「H900-2」荒川化学工業社製）10質量部と、実施例１と同様にして調製されたSiOx粉末83質量部とを混合し、混練機を用いてよく混練した。この際、粘度調整のためにN-メチル-2-ピロリドン(NMP)を混合した。この混練によって、SiOx粒子の表面の全面に樹脂溶液が付着する。
<Preparation of negative electrode for lithium ion secondary battery>
6.7 parts by mass of polyacrylic acid (“H-AS” manufactured by Nippon Shokubai Co., Ltd.) and 10 parts by mass of polyamideimide silica resin (“H900-2” manufactured by Arakawa Chemical Industries) were prepared in the same manner as in Example 1. 83 parts by mass of SiO x powder was mixed and well kneaded using a kneader. At this time, N-methyl-2-pyrrolidone (NMP) was mixed for viscosity adjustment. By this kneading, the resin solution adheres to the entire surface of the SiO x particles.
得られた混練物に、導電助剤としての黒鉛粉末とケッチェンブラック（KB）粉末とを混合し、スラリーを調製した。スラリー中の各成分の組成比は固形分として、SiOx粉末：黒鉛粉末：ケッチェンブラック：ポリアクリル酸：ポリアミドイミド＝50：37：3：4：6である。このスラリーを、厚さ20μｍの電解銅箔（集電体）の表面にドクターブレードを用いて塗布し、銅箔上に負極活物質層を形成した。 The obtained kneaded product was mixed with graphite powder as a conductive additive and Ketjen black (KB) powder to prepare a slurry. The composition ratio of each component in the slurry is SiO x powder: graphite powder: Ketjen black: polyacrylic acid: polyamideimide = 50: 37: 3: 4: 6 as a solid content. This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of 20 μm using a doctor blade to form a negative electrode active material layer on the copper foil.
その後、80℃で20分間乾燥し、負極活物質層から有機溶媒を揮発させて除去した。乾燥後、ロールプレス機により、集電体と負極活物質層を強固に密着接合させた。これを200℃で2時間加熱硬化させて、活物質層の厚さが15μｍ程度の負極を形成した。 Then, it dried at 80 degreeC for 20 minute (s), and the organic solvent was volatilized and removed from the negative electrode active material layer. After drying, the current collector and the negative electrode active material layer were firmly and closely joined with a roll press. This was heat-cured at 200 ° C. for 2 hours to form a negative electrode having an active material layer thickness of about 15 μm.
＜リチウムイオン二次電池用対極活物質の作製＞
0.30molの水酸化リチウム一水和物LiOH・H2O(12.6ｇ)と0.10molの硝酸リチウムLiNO3(6.9ｇ)とを混合して溶融塩原料を調製した。ここに金属化合物原料として前駆体(1.0ｇ)を加えて原料混合物を調製した。以下に、前駆体の合成手順を説明する。
<Preparation of counter electrode active material for lithium ion secondary battery>
A molten salt raw material was prepared by mixing 0.30 mol of lithium hydroxide monohydrate LiOH.H 2 O (12.6 g) and 0.10 mol of lithium nitrate LiNO 3 (6.9 g). The precursor (1.0g) was added here as a metal compound raw material, and the raw material mixture was prepared. Below, the synthesis | combining procedure of a precursor is demonstrated.
0.67molのＭn(NO3)2・６H2O(192.3ｇ)と、0.16molのCo(NO3)2・６H2O(46.6ｇ)と、0.16molのNi(NO3)2・６H2O(46.5ｇ)とを500mLの蒸留水に溶解させて金属塩含有水溶液を作製した。この水溶液を氷浴中でスターラーを用いて撹拌しながら、50ｇ(1.2mol)のLiOH・H2Oを300mLの蒸留水に溶解させたものを2時間かけて滴下して水溶液をアルカリ性とし、金属水酸化物の沈殿を析出させた。この沈殿溶液を5℃に保持したまま酸素雰囲気下で1日熟成を行った。得られた沈殿物を濾過、蒸留水を用いて洗浄することによりMn：Co：Ni＝0.67：0.16：0.16の前駆体を得た。 0.67 mol of Mn (NO 3 ) 2 · 6H 2 O (192.3 g), 0.16 mol of Co (NO 3 ) 2 · 6H 2 O (46.6 g), and 0.16 mol of Ni (NO 3 ) 2 · 6H 2 O (46.5 g) was dissolved in 500 mL of distilled water to prepare a metal salt-containing aqueous solution. While stirring this aqueous solution with a stirrer in an ice bath, 50 g (1.2 mol) of LiOH.H 2 O dissolved in 300 mL of distilled water was added dropwise over 2 hours to make the aqueous solution alkaline. A hydroxide precipitate was deposited. The precipitation solution was aged for 1 day in an oxygen atmosphere while being kept at 5 ° C. The obtained precipitate was filtered and washed with distilled water to obtain a precursor of Mn: Co: Ni = 0.67: 0.16: 0.16.
なお、得られた前駆体は、Ｘ線回折測定により、Mn3O4、Co3O4およびNiOの混合相からなることが確認された。そのため、この前駆体1ｇの遷移金属元素含有量は0.013molである。このとき、前駆体の遷移金属が全て目的生成物に供給されたと仮定して、（目的生成物のLi）／（溶融塩原料のLi）は、0.0195mol／0.4mol＝0.04875であった。 The obtained precursor was confirmed to be composed of a mixed phase of Mn 3 O 4 , Co 3 O 4 and NiO by X-ray diffraction measurement. Therefore, the transition metal element content of 1 g of this precursor is 0.013 mol. At this time, assuming that all of the precursor transition metals were supplied to the target product, (Li of target product) / (Li of molten salt raw material) was 0.0195 mol / 0.4 mol = 0.04875.
原料混合物は坩堝にいれて、真空乾燥器内において120℃で12時間真空乾燥した。その後、乾燥器を大気圧に戻し、原料混合物の入った坩堝を取り出し、直ちに450℃に熱せられた電気炉に移し、酸素雰囲気中450℃で4時間加熱した。このとき原料混合物は融解して溶融塩となり、黒色の生成物が沈殿していた。 The raw material mixture was put in a crucible and vacuum-dried at 120 ° C. for 12 hours in a vacuum dryer. Thereafter, the dryer was returned to atmospheric pressure, the crucible containing the raw material mixture was taken out, immediately transferred to an electric furnace heated to 450 ° C., and heated in an oxygen atmosphere at 450 ° C. for 4 hours. At this time, the raw material mixture melted to form a molten salt, and a black product was precipitated.
次に、溶融塩の入った坩堝を電気炉から取り出し、室温にて冷却した。溶融塩が十分に冷却されて固体化した後、坩堝ごと200mLのイオン交換水に浸し、攪拌することで、固体化した溶融塩を水に溶解した。黒色の生成物は水に不溶性であるため、水は黒色の懸濁液となった。黒色の懸濁液を濾過すると、透明な濾液と、濾紙上に黒色固体の濾物と、が得られた。得られた濾物をさらにイオン交換水を用いて十分に洗浄しながら濾過した。洗浄後の黒色固体を120℃で6時間、真空乾燥した後、乳鉢と乳棒を用いて粉砕した。得られた黒色粉末についてCuＫα線を用いたＸＲＤ測定を行った。ＸＲＤによれば、得られた化合物は層状岩塩構造であることがわかった。また、ICPおよびMnの平均価数分析によれば、組成は0.5(Li2MnO3)・0.5(LiCo1/3Ni1/3Mn1/3O2)であると確認された。 Next, the crucible containing the molten salt was taken out of the electric furnace and cooled at room temperature. After the molten salt was sufficiently cooled and solidified, the crucible was immersed in 200 mL of ion exchange water and stirred to dissolve the solidified molten salt in water. Since the black product was insoluble in water, the water became a black suspension. Filtration of the black suspension yielded a clear filtrate and a black solid residue on the filter paper. The obtained filtrate was further filtered while thoroughly washing with ion exchange water. The black solid after washing was vacuum-dried at 120 ° C. for 6 hours and then pulverized using a mortar and pestle. XRD measurement using CuKα rays was performed on the obtained black powder. According to XRD, the obtained compound was found to have a layered rock salt structure. The average valence analysis of ICP and Mn confirmed that the composition was 0.5 (Li 2 MnO 3 ) · 0.5 (LiCo 1/3 Ni 1/3 Mn 1/3 O 2 ).
上記により調製された正極活物質と、導電助剤としてのアセチレンブラックと、結着材としてのPVdFと、分散剤のPVP（ポリビニルピロリドン(BASF社製)）を、質量比で88：6：5.88：0.12の割合で混合した。次いで、この混合物を集電体であるアルミニウム箔に塗工した。その後、120℃で6時間以上真空乾燥し、活物質層の厚さが約54μｍの正極を形成した。 The positive electrode active material prepared as described above, acetylene black as a conductive additive, PVdF as a binder, and PVP (polyvinylpyrrolidone (manufactured by BASF)) as a weight ratio are 88: 6: 5.88. : Mixed at a ratio of 0.12. Next, this mixture was applied to an aluminum foil as a current collector. Then, it vacuum-dried at 120 degreeC for 6 hours or more, and formed the positive electrode whose thickness of an active material layer is about 54 micrometers.
＜リチウムイオン二次電池の作製＞
上記の手順で作製した負極と正極を用いて、リチウムイオン二次電池を作製した。
<Production of lithium ion secondary battery>
A lithium ion secondary battery was produced using the negative electrode and the positive electrode produced by the above procedure.
正極を7.5mm2、負極を8.06mm2に裁断し、セパレータ（「celgard2400」セルガード社製）を両者の間に挟装して電極体電池とした。この電極体電池をラミネートに収容した。また、ラミネートセルには、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（体積比）で混合した混合溶媒にLiPF6を1Mの濃度で溶解した非水電解質を注入し、ラミネートを密閉して、リチウムイオン二次電池を得た。 7.5 mm 2 The positive electrode was cut to negative electrode 8.06Mm 2, and an electrode assembly battery was sandwiched between them a separator (manufactured by "celgard2400" Celgard Inc.). The electrode body battery was accommodated in a laminate. In addition, a non-aqueous electrolyte in which LiPF 6 is dissolved at a concentration of 1 M is injected into a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 3: 7, and the laminate is sealed in the laminate cell. An ion secondary battery was obtained.
[参考例1]
N-メチル-2-ピロリドン（NMP）にバインダー樹脂としてのポリアミドイミドシリカ樹脂（「H900-2」荒川化学工業社製）を溶解させた。この溶液と、実施例1と同様のSiOx粉末、導電助剤としての黒鉛粉末、ケッチェンブラック（KB）粉末を混合し、スラリーを調製した。スラリー中の各成分の組成比は固形分として、SiOx粉末：黒鉛粉末：ケッチェンブラック：バインダー樹脂＝50：37：3：10である。このスラリーを、厚さ20μｍの電解銅箔（集電体）の表面にドクターブレードを用いて塗布し、銅箔上に負極活物質層を形成した。
[Reference Example 1]
Polyamideimide silica resin (“H900-2” manufactured by Arakawa Chemical Industries, Ltd.) as a binder resin was dissolved in N-methyl-2-pyrrolidone (NMP). This solution was mixed with the same SiO x powder as in Example 1, graphite powder as a conductive aid, and ketjen black (KB) powder to prepare a slurry. The composition ratio of each component in the slurry is SiO x powder: graphite powder: ketchen black: binder resin = 50: 37: 3: 10 as a solid content. This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of 20 μm using a doctor blade to form a negative electrode active material layer on the copper foil.
その後、80℃で20分間乾燥し、負極活物質層から有機溶媒を揮発させて除去した。乾燥後、ロールプレス機により、集電体と負極活物質層を強固に密着接合させた。これを200℃で2時間加熱硬化させて、活物質層の厚さが15μｍ程度の負極を形成した。 Then, it dried at 80 degreeC for 20 minute (s), and the organic solvent was volatilized and removed from the negative electrode active material layer. After drying, the current collector and the negative electrode active material layer were firmly and closely joined with a roll press. This was heat-cured at 200 ° C. for 2 hours to form a negative electrode having an active material layer thickness of about 15 μm.
この負極を用いたこと以外は実施例1と同様にして、リチウムイオン二次電池を作製した。 A lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.
＜リチウムイオン二次電池の高温保存特性＞
実施例2及び参考例1のリチウムイオン二次電池をそれぞれ満充電状態とし、1Cにおける放電容量をそれぞれ測定し保存前放電容量とした。その後再び満充電状態とし、80℃にて5日間保存する保存試験を行った後に、1Cにおける放電容量をそれぞれ測定して保存後放電容量とした。そして保存特性値として100×保存後放電容量／保存前放電容量を算出し、結果を表2に示す。
<High temperature storage characteristics of lithium ion secondary batteries>
The lithium ion secondary batteries of Example 2 and Reference Example 1 were fully charged, and the discharge capacities at 1C were measured to determine the discharge capacities before storage. The battery was then fully charged again and subjected to a storage test for storage at 80 ° C. for 5 days, and then the discharge capacity at 1C was measured to determine the discharge capacity after storage. Then, 100 × discharge capacity after storage / discharge capacity before storage was calculated as a storage characteristic value, and the results are shown in Table 2.
表2より、実施例2に係るリチウムイオン二次電池は高温保存後にも高い放電容量を示し、放電特性に優れている。これは、負極活物質であるSiOx粉末の表面にポリアクリル酸の被膜が形成されていることによる効果であると考えられる。 From Table 2, the lithium ion secondary battery according to Example 2 shows high discharge capacity even after storage at high temperature, and is excellent in discharge characteristics. This is considered to be an effect due to the formation of a polyacrylic acid film on the surface of the SiO x powder, which is the negative electrode active material.
1：SiOx粒子 2：樹脂被膜 10：SiO2 11：Si 1: SiO x particles 2: Resin coating 10: SiO 2 11: Si
Claims (5)
前記樹脂被膜は、ポリアクリル酸、ポリメタクリル酸、若しくは、ポリイタコン酸、又は、アクリル酸と、メタクリル酸、イタコン酸、フマル酸、若しくは、マレイン酸との共重合物からなることを特徴とするリチウムイオン二次電池用負極活物質。 A particle composed of a silicon oxide represented by SiOx (0.3 ≦ x ≦ 1.6), and a resin film covering the entire surface of the particle,
The resin film is made of polyacrylic acid, polymethacrylic acid, polyitaconic acid, or a copolymer of acrylic acid and methacrylic acid, itaconic acid, fumaric acid, or maleic acid. Negative electrode active material for ion secondary battery.
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| JP6548959B2 (en) * | 2015-06-02 | 2019-07-24 | 信越化学工業株式会社 | Negative electrode active material for non-aqueous electrolyte secondary battery, negative electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for producing negative electrode active material particles |
| US20180226637A1 (en) * | 2015-08-10 | 2018-08-09 | Murata Manufacturing Co., Ltd. | Secondary battery-use anode and method of manufacturing the same, secondary battery and method of manufacturing the same, battery pack, electric vehicle, electric power storage system, electric power tool, and electronic apparatus |
| KR102150749B1 (en) | 2015-08-10 | 2020-09-01 | 가부시키가이샤 무라타 세이사쿠쇼 | A negative electrode for a secondary battery and its manufacturing method, a secondary battery and its manufacturing method, and battery packs, electric vehicles, power storage systems, power tools, and electronic devices |
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