JP6296278B2 - Nonaqueous electrolyte secondary battery - Google Patents
Nonaqueous electrolyte secondary battery Download PDFInfo
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- JP6296278B2 JP6296278B2 JP2013246346A JP2013246346A JP6296278B2 JP 6296278 B2 JP6296278 B2 JP 6296278B2 JP 2013246346 A JP2013246346 A JP 2013246346A JP 2013246346 A JP2013246346 A JP 2013246346A JP 6296278 B2 JP6296278 B2 JP 6296278B2
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- negative electrode
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- 239000011255 nonaqueous electrolyte Substances 0.000 title claims description 27
- 239000007773 negative electrode material Substances 0.000 claims description 66
- 239000011230 binding agent Substances 0.000 claims description 62
- 239000002245 particle Substances 0.000 claims description 38
- 150000003377 silicon compounds Chemical class 0.000 claims description 17
- 238000009826 distribution Methods 0.000 claims description 16
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- PPBRXRYQALVLMV-UHFFFAOYSA-N Styrene Chemical compound C=CC1=CC=CC=C1 PPBRXRYQALVLMV-UHFFFAOYSA-N 0.000 claims description 6
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- BFKJFAAPBSQJPD-UHFFFAOYSA-N tetrafluoroethene Chemical group FC(F)=C(F)F BFKJFAAPBSQJPD-UHFFFAOYSA-N 0.000 description 2
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- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
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- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 1
- 229910052808 lithium carbonate Inorganic materials 0.000 description 1
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Classifications
-
- 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
Description
本発明は、非水電解質二次電池に関し、詳しくは、負極活物質にシリコン系化合物を用いる非水電解質二次電池に関する。 The present invention relates to a non-aqueous electrolyte secondary battery , and more particularly to a non-aqueous electrolyte secondary battery using a silicon compound as a negative electrode active material.
非水電解質電池（非水電解質二次電池）の負極には、炭素材料に代表されるリチウムイオンを吸蔵・放出可能な物質が負極活物質として用いられている。そして、この負極は、ＣＭＣ／ＳＢＲやＰＶＤＦよりなる結着剤で負極活物質を結着した負極合材層を負極集電体の表面に形成している。 For the negative electrode of a non-aqueous electrolyte battery (non-aqueous electrolyte secondary battery), a substance capable of inserting and extracting lithium ions typified by a carbon material is used as a negative electrode active material. In this negative electrode, a negative electrode mixture layer formed by binding a negative electrode active material with a binder made of CMC / SBR or PVDF is formed on the surface of the negative electrode current collector.
近年では、高エネルギー密度で良好な充放電サイクル特性を得るための負極活物質として、ケイ素（Ｓｉ）を含むシリコン系化合物を適用することの検討が進められている。 In recent years, studies have been made to apply a silicon-based compound containing silicon (Si) as a negative electrode active material for obtaining good charge / discharge cycle characteristics at a high energy density.
シリコン系化合物は、充放電時に大きな体積変化（膨脹・収縮）を生じる。炭素材料の場合に利用されている結着剤を、シリコン系化合物の場合に適用すると、充放電時の負極活物質の大きな体積変化により、電極内の導電ネットワークの崩壊が発生し、電池容量が急激に減少してしまうという問題があった。この不具合に対して、シリコン系化合物を負極活物質に使用する場合には、ポリアクリル酸系の結着剤が利用されている。 Silicon compounds cause large volume changes (expansion and contraction) during charge and discharge. When the binder used in the case of a carbon material is applied to a silicon compound, a large volume change of the negative electrode active material during charge / discharge causes collapse of the conductive network in the electrode, and the battery capacity is reduced. There was a problem that it decreased rapidly. In response to this problem, when a silicon-based compound is used as the negative electrode active material, a polyacrylic acid-based binder is used.
ポリアクリル酸系の結着剤では、重量平均分子量が小さいため結着力が低く、架橋型構造を有するため吸湿性が高く電池内への水分混入が起きてしまうという問題があった。この問題に対して、特許文献１には、重量平均分子量が３０万〜３００万の非架橋型ポリアクリル酸を結着剤として用いる技術が記載されている。 The polyacrylic acid-based binder has a problem that the binding force is low because the weight average molecular weight is small, and the moisture absorption is high due to the cross-linked structure, so that moisture is mixed into the battery. In order to solve this problem, Patent Document 1 describes a technique using non-crosslinked polyacrylic acid having a weight average molecular weight of 300,000 to 3,000,000 as a binder.
しかしながら、特許文献１に記載の結着剤では、重量平均分子量が３０万〜３００万と大きく、その結果、結着剤の粘度が高くなっていた。その結果、負極活物質（シリコン系化合物）が均一に分散しにくくなるとともに、塗工に手間がかかるようになっていた。 However, the binder described in Patent Document 1 has a large weight average molecular weight of 300,000 to 3,000,000, and as a result, the binder has a high viscosity. As a result, the negative electrode active material (silicon compound) is difficult to uniformly disperse, and the coating is troublesome.
更に、シリコン系化合物は、負極活物質として使用するときに、粒子径を小さくする必要があった。シリコン系化合物の粒子径が大きいと、大きな体積変化に起因する微細化（微粉化）が進行する。このため、粒子径の小さな負極活物質を用いる必要があった。そして、粒子径の小さな負極活物質は、凝集を生じやすいという特性を備えており、均一な分散がより困難になっていた。負極活物質が凝集を生じると、負極活物質が凝集した部分で体積変化に起因する電極内の導電ネットワークの崩壊が発生する。 Furthermore, when the silicon-based compound is used as a negative electrode active material, it is necessary to reduce the particle size. When the particle size of the silicon compound is large, refinement (micronization) due to a large volume change proceeds. For this reason, it was necessary to use a negative electrode active material having a small particle size. And the negative electrode active material with a small particle diameter was equipped with the characteristic that it is easy to produce aggregation, and uniform dispersion | distribution became more difficult. When the negative electrode active material aggregates, the conductive network in the electrode collapses due to the volume change at the portion where the negative electrode active material aggregates.
加えて、シリコン系化合物の粒径を小さくすると、微細粒子の表面に吸着する吸着水との間で反応を生じる（Ｓｉ＋２Ｈ２Ｏ→ＳｉＯ２＋４Ｈ＋）。そして、負極活物質及び結着剤が含まれる合剤のｐＨが低下する。ｐＨが低下すると、結着剤の分子量が意図しない状態で小さくなる（制御不可能な状態で分子量が減少する）。また、ｐＨが低下すると、合剤に含まれる金属（合金）が損傷を生じる。 In addition, when the particle size of the silicon compound is reduced, a reaction occurs with the adsorbed water adsorbed on the surface of the fine particles (Si + 2H 2 O → SiO 2 + 4H + ). And pH of the mixture containing a negative electrode active material and a binder falls. When the pH is lowered, the molecular weight of the binder decreases in an unintended state (the molecular weight decreases in an uncontrollable state). Moreover, when pH falls, the metal (alloy) contained in a mixture will damage.
以上のように、従来の結着剤をシリコン系化合物に適用した場合、負極活物質の分散性及び結着力の低下に起因する二次電池の性能の低下が生じていた。
本発明は上記実状に鑑みてなされたものであり、性能の低下が抑えられた非水電解質二次電池を提供することを課題とする。
As described above, when the conventional binder is applied to the silicon-based compound, the performance of the secondary battery is deteriorated due to the dispersibility and the binding force of the negative electrode active material.
This invention is made | formed in view of the said actual condition, and makes it a subject to provide the nonaqueous electrolyte secondary battery by which the fall of performance was suppressed.
上記課題を解決するために本発明者等は、負極活物質にシリコン系化合物を用いる二次電池の負極の結着剤について検討を重ねた結果、本発明をなすに至った。 In order to solve the above-mentioned problems, the present inventors have studied the binder for the negative electrode of a secondary battery using a silicon-based compound as the negative electrode active material, and as a result, have reached the present invention.
すなわち、本発明の非水電解質二次電池は、負極活物質と、負極活物質を結着する結着剤と、を備えた負極を用いる非水電解質二次電池において、負極活物質は、粒度分布特性値Ｍ（Ｍ＝（Ｄ９０−Ｄ１０）／Ｄ５０）が１．２以上であるＳｉＯで表されるシリコン系化合物と、粒度分布特性値Ｍ（Ｍ＝（Ｄ９０−Ｄ１０）／Ｄ５０）が１．２未満である炭素質材料と、を有し、結着剤は、重量平均分子量が２０万以下の架橋型構造を有しているポリアクリル酸塩、ＰＴＦＥ，ＰＶＤＦ，フッ素樹脂共重合体（四フッ化エチレン・六フッ化プロピレン共重合体），ＳＢＲ，アクリル系ゴム，フッ素系ゴム，ポリビニルアルコール（ＰＶＡ），スチレン・マレイン酸樹脂，ＣＭＣより選ばれる１種以上のうち、少なくとも該ポリアクリル酸塩を有することを特徴とする。
本発明の非水電解質二次電池は、負極活物質としてシリコン系化合物を用いることから、高エネルギー密度で良好な充放電サイクル特性を発揮する。
That is, a non-aqueous electrolyte secondary battery of the present invention includes a negative electrode active material, a binder for binding the negative electrode active material, a nonaqueous electrolyte secondary battery using a negative electrode having a negative electrode active material, the particle size A silicon compound represented by SiO having a distribution characteristic value M (M = (D90-D10) / D50) of 1.2 or more and a particle size distribution characteristic value M (M = (D90-D10) / D50) are 1. A carbonaceous material having a weight average molecular weight of 200,000 or less, and a binder having a crosslinked structure such as polyacrylate, PTFE, PVDF, fluororesin copolymer ( At least the polyacrylic of at least one selected from tetrafluoroethylene / hexafluoropropylene copolymer), SBR, acrylic rubber, fluorine rubber, polyvinyl alcohol (PVA), styrene / maleic resin, and CMC. Acid salt Characterized in that it.
Since the nonaqueous electrolyte secondary battery of the present invention uses a silicon compound as the negative electrode active material, it exhibits good charge / discharge cycle characteristics at a high energy density.
そして、結着剤として、重量平均分子量が２０万以下の架橋型構造を有しているポリアクリル酸系の化合物を有する。この結着剤は、重量平均分子量が小さいことで負極活物質の分散性に優れ、架橋型構造を有していることで負極活物質を強固に結着することができる。そして、負極活物質を強固に結着することで、負極活物質の変移を長期間にわたって抑えることができる。
この結果、本発明の非水電解質二次電池は、高い電池性能を長期間にわたって発揮できる効果を示す。
And it has a polyacrylic acid type compound which has a crosslinked structure whose weight average molecular weight is 200,000 or less as a binder. This binder is excellent in dispersibility of the negative electrode active material because of its low weight average molecular weight, and can firmly bind the negative electrode active material because of its cross-linked structure. Then, by firmly binding the negative electrode active material, the transition of the negative electrode active material can be suppressed over a long period of time.
As a result, the nonaqueous electrolyte secondary battery of the present invention exhibits the effect that high battery performance can be exhibited over a long period of time.
以下、本発明の非水電解質二次電池の実施形態を、リチウムイオン二次電池を用いて説明する。
本実施形態のリチウムイオン二次電池は、正極，負極及び非水電解質を有する。
（負極）
負極は、負極活物質と、負極活物質を結着する結着剤と、を備えている。
Hereinafter, an embodiment of a nonaqueous electrolyte secondary battery of the present invention will be described using a lithium ion secondary battery.
The lithium ion secondary battery of this embodiment has a positive electrode, a negative electrode, and a nonaqueous electrolyte.
(Negative electrode)
The negative electrode includes a negative electrode active material and a binder that binds the negative electrode active material.
負極活物質は、ＳｉＭｘＬｙ（Ｍ；Ａｌ，Ａｓ，Ｂａ，Ｃ，Ｃａ，Ｃｅ，Ｃｏ，Ｃｒ，Ｃｕ，Ｅｒ，Ｆｅ，Ｇｄ，Ｈｆ，Ｌｕ，Ｍｇ，Ｍｎ，Ｍｏ，Ｎｂ，Ｎｄ，Ｎｉ，Ｐ，Ｐｄ，Ｐｒ，Ｐｔ，Ｐｕ，Ｒｅ，Ｒｈ，Ｒｕ，Ｓｃ，Ｓｍ，Ｓｒ，Ｔａ，Ｔｅ，Ｔｈ，Ｔｉ，Ｔｍ，Ｕ，Ｖ，Ｗ，Ｙ，Ｙｂ，Ｚｎ，Ｚｒより選ばれる少なくとも一種、Ｌ；Ｎ，Ｏより選ばれる少なくとも一種、０≦ｘ≦１、０≦ｙ≦２）で表されるシリコン系化合物のうち、ＳｉＯで表されるシリコン系化合物を有する。ここで、ＳｉＭｘＬｙで表されるシリコン系化合物は、ＳｉＭｘ，ＳｉＬｙで表される化合物あっても、何らの問題はない。負極活物質がシリコン系化合物を有することで、本形態のリチウムイオン二次電池は、高エネルギー密度で良好な充放電サイクル特性を有するようになる。 The negative electrode active material is SiM x L y (M; Al, As, Ba, C, Ca, Ce, Co, Cr, Cu, Er, Fe, Gd, Hf, Lu, Mg, Mn, Mo, Nb, Nd, Ni, P, Pd, Pr, Pt, Pu, Re, Rh, Ru, Sc, Sm, Sr, Ta, Te, Th, Ti, Tm, U, V, W, Y, Yb, Zn, Zr At least one selected from L; N; O, at least one selected from the group consisting of 0 ≦ x ≦ 1, 0 ≦ y ≦ 2) has a silicon compound represented by SiO . Here, there is no problem even if the silicon compound represented by SiM x L y is a compound represented by SiM x , SiL y . When the negative electrode active material has a silicon-based compound, the lithium ion secondary battery of this embodiment has high charge density and good charge / discharge cycle characteristics.
結着剤は、重量平均分子量が２０万以下の架橋型構造を有しているポリアクリル酸塩を少なくとも有している。 The binder has at least a polyacrylate having a crosslinked structure having a weight average molecular weight of 200,000 or less.
結着剤が、ポリアクリル酸，ポリアクリル酸塩，ポリアクリル酸共重合体より選ばれる少なくとも一種（以下、ポリアクリル酸系化合物と総称する）のうち、ポリアクリル酸塩を有することで、シリコン系化合物よりなる負極活物質を結着できる。 Of the at least one selected from the group consisting of polyacrylic acid, polyacrylic acid salt, and polyacrylic acid copolymer (hereinafter collectively referred to as polyacrylic acid compound) , the binder has a polyacrylic acid salt , so that silicon A negative electrode active material made of a base compound can be bound.
ポリアクリル酸は、アクリル酸の重合体であり、そのモノマー種がアクリル酸であれば限定されるものではない。また、ポリアクリル酸塩は、ポリアクリル酸のカルボキシル基の水素が、陽イオン（たとえば、Ｌｉイオン，Ｎａイオン，Ｋイオン等の陽イオンをあげることができる）で置換された構成の化合物である。 Polyacrylic acid is a polymer of acrylic acid, and is not limited as long as the monomer type is acrylic acid. The polyacrylate is a compound having a structure in which the hydrogen of the carboxyl group of polyacrylic acid is replaced with a cation (for example, a cation such as Li ion, Na ion, K ion, etc.). .
ポリアクリル酸共重合体は、アクリル酸と、他の一種以上のモノマーとの重合体である。ポリアクリル酸共重合体のモノマーとしてのアクリル酸は、アクリル酸塩であってもよい。さらに、他の一種以上のモノマーは、アクリル酸と共重合体を形成可能なモノマーであれば限定されない。たとえば、マレイン酸，フマル酸等のカルボン酸（鎖状不飽和ジカルボン酸），ビニルアルコール等のアルコールをあげることができる。 The polyacrylic acid copolymer is a polymer of acrylic acid and one or more other monomers. The acrylic acid as the monomer of the polyacrylic acid copolymer may be an acrylate. Furthermore, the other one or more monomers are not limited as long as they are monomers capable of forming a copolymer with acrylic acid. Examples thereof include carboxylic acids (chain unsaturated dicarboxylic acids) such as maleic acid and fumaric acid, and alcohols such as vinyl alcohol.
ポリアクリル酸系化合物の重量平均分子量が２０万以下となることで、結着剤の粘度が低下し、負極活物質の分散性が向上する。すなわち、結着剤が、負極活物質粒子が均一に分散した状態で結着することができる。また、粘度が低下することで、結着剤の塗工性が向上する。ポリアクリル酸系化合物の重量平均分子量が２０万を超えて大きくなると、結着剤の粘度が高くなり、負極活物質粒子を均一に分散することが難しくなる（分散性が低下する）。好ましい重量平均分子量は、１万程度以上、１５万程度以下であり、更に好ましい重量平均分子量は、１５万程度である。なお、１万程度及び１５万程度とは、それぞれ±２０％程度を示す。 When the weight average molecular weight of the polyacrylic acid compound is 200,000 or less, the viscosity of the binder is lowered, and the dispersibility of the negative electrode active material is improved. That is, the binder can be bound in a state where the negative electrode active material particles are uniformly dispersed. Moreover, the coating property of a binder improves because a viscosity falls. When the weight average molecular weight of the polyacrylic acid compound exceeds 200,000, the viscosity of the binder increases, and it becomes difficult to uniformly disperse the negative electrode active material particles (dispersibility decreases). A preferred weight average molecular weight is about 10,000 or more and about 150,000 or less, and a more preferred weight average molecular weight is about 150,000. In addition, about 10,000 and about 150,000 show about +/- 20%, respectively.
結着剤を構成するポリアクリル酸系化合物が架橋型構造を有していることで、負極活物質をより強固に結着できる。具体的には、架橋型の結着剤と非架橋型の結着剤とを比較すると、架橋型の結着剤は網目構造となり、非架橋型では直鎖状の構造となる。網目構造の場合、１箇所の結合が切れても、切れた結合の末端の分子（単量体）は、複数箇所で他の分子（単量体）との結合が維持される。すなわち、結着剤の剥離が生じない。対して、非架橋型の場合、他の結合が維持されることで、結着剤の構造が維持される。対して、非架橋型では、１箇所の結合が切れると、１箇所の結合が切れると、切れた結合の末端の分子（単量体）は、他の分子（単量体）との結合が１箇所のみとなり、結着剤の構造が維持されなくなる。このように、ポリアクリル酸系化合物が架橋型構造となることで、より強固に負極活物質を結着できる。 Since the polyacrylic acid compound constituting the binder has a cross-linked structure, the negative electrode active material can be bound more firmly. Specifically, when a crosslinked binder and a non-crosslinked binder are compared, the crosslinked binder has a network structure, and the non-crosslinked binder has a linear structure. In the case of a network structure, even if the bond at one place is broken, the molecule (monomer) at the end of the broken bond maintains the bond with another molecule (monomer) at a plurality of places. That is, the binder does not peel off. On the other hand, in the case of the non-crosslinked type, the structure of the binder is maintained by maintaining other bonds. On the other hand, in the non-crosslinked type, when one bond is broken and one bond is broken, the molecule (monomer) at the end of the broken bond is bonded to another molecule (monomer). There is only one place, and the structure of the binder is not maintained. As described above, the polyacrylic acid-based compound has a cross-linked structure, so that the negative electrode active material can be bound more firmly.
ポリアクリル酸系化合物の架橋構造を、ポリアクリル酸を用いて具体的に説明する。ポリアクリル酸は、化１で示される。そして、架橋型ポリアクリル酸は、化１中のカルボン酸が脱水縮合して架橋する。この結果、架橋型ポリアクリル酸は、網目構造を形成し、強固に結合できる。なお、ポリアクリル酸系化合物の架橋構造は、架橋剤を用いて架橋構造としてもよい。 The cross-linked structure of the polyacrylic acid compound will be specifically described using polyacrylic acid. Polyacrylic acid is represented by Chemical Formula 1: The crosslinked polyacrylic acid is crosslinked by dehydration condensation of the carboxylic acid in Chemical Formula 1. As a result, the cross-linked polyacrylic acid forms a network structure and can be firmly bonded. The crosslinked structure of the polyacrylic acid compound may be a crosslinked structure using a crosslinking agent.
結着剤は、ｐＨが３．０〜９．０の溶液であることが好ましい。結着剤が所定のｐＨの溶液であることで、結着性と分散性に優れた結着剤となる。ｐＨが３．０未満となると、ｐＨが低くなりすぎて結着剤の架橋構造が切断されるようになる。この架橋構造の切断は、ランダムに発生し、シリコン系化合物の分子量（重量平均分子量）に大きなバラツキが生じるようになる。そして、結着性の低下や、負極活物質粒子の分散性の低下を招く。
また、ｐＨが低くなりすぎると、含まれる金属系化合物（特に、負極活物質のシリコン系化合物）を酸化（損傷）するようになる。
The binder is preferably a solution having a pH of 3.0 to 9.0. When the binder is a solution having a predetermined pH, the binder has excellent binding properties and dispersibility. When the pH is less than 3.0, the pH becomes too low and the crosslinked structure of the binder is cut. This cutting of the cross-linked structure occurs randomly and causes a large variation in the molecular weight (weight average molecular weight) of the silicon compound. And it causes a decrease in binding properties and a decrease in dispersibility of the negative electrode active material particles.
Moreover, when pH becomes low too much, the metal type compound (especially silicon type compound of a negative electrode active material) contained will be oxidized (damaged).
溶液のｐＨが９．０を超えて大きくなると、結着剤の溶液（ポリアクリル酸系化合物の溶液）が高粘度となり、負極活物質粒子の分散性の低下を招く。更に、ポリアクリル酸系化合物の固形分が多くなる。 When the pH of the solution exceeds 9.0, the binder solution (polyacrylic acid compound solution) becomes highly viscous, leading to a decrease in the dispersibility of the negative electrode active material particles. Furthermore, the solid content of the polyacrylic acid compound increases.
ここで、結着剤は、ポリアクリル酸系化合物の溶液であればよく、ポリアクリル酸系化合物が溶解した溶液であっても、ポリアクリル酸系化合物が分散してなる溶液であっても、ポリアクリル酸系化合物そのものの溶液（溶融液）であっても、いずれでもよい。好ましくは、ポリアクリル酸系化合物が溶媒に溶解した溶液である。 Here, the binder may be a solution of a polyacrylic acid compound, whether it is a solution in which a polyacrylic acid compound is dissolved or a solution in which a polyacrylic acid compound is dispersed, It may be either a solution (melt) of the polyacrylic acid compound itself. A solution in which a polyacrylic acid compound is dissolved in a solvent is preferable.
結着剤は、ポリアクリル酸系化合物が溶媒に溶解した溶液（又は分散媒に分散した分散溶液）であるときに、固形分が３０ｍａｓｓ％で含まれる溶液であることが好ましい。このとき、ポリアクリル酸系化合物と溶媒の合計の質量が１００ｍａｓｓ％に相当する。なお、ポリアクリル酸系化合物の溶液は、固形分が３０ｍａｓｓ％の溶液であることが好ましいが、これ以外の溶液を使用してもよい。その場合、本発明のそれぞれの好ましい条件は、変更（算出した条件に変更）することが好ましい。 When the binder is a solution in which a polyacrylic acid compound is dissolved in a solvent (or a dispersion solution dispersed in a dispersion medium), the binder is preferably a solution containing a solid content of 30 mass%. At this time, the total mass of the polyacrylic acid compound and the solvent corresponds to 100 mass%. In addition, although it is preferable that the solution of a polyacrylic acid type compound is a solution whose solid content is 30 mass%, you may use solutions other than this. In that case, each preferable condition of the present invention is preferably changed (changed to the calculated condition).
本形態において、ポリアクリル酸系化合物よりなる結着剤とは、ポリアクリル酸系化合物のみからなる結着剤だけでなく、従来公知の添加剤を添加した結着剤を含む。たとえば、結着剤がポリアクリル酸系化合物が溶解した溶液である場合に、粘度やｐＨ等を調整する調整剤を添加剤として添加していてもよい。 In this embodiment, the binder made of a polyacrylic acid compound includes not only a binder made only of a polyacrylic acid compound but also a binder added with a conventionally known additive. For example, when the binder is a solution in which a polyacrylic acid compound is dissolved, a regulator for adjusting viscosity, pH and the like may be added as an additive.
負極活物質は、粒度分布特性値Ｍ（Ｍ＝（Ｄ９０−Ｄ１０）／Ｄ５０）が１．２以上である。粒度分布特性値Ｍは、粒度分布を測定したときの粒度の広がり（バラツキ）を示す。具体的には、粒度分布特性値Ｍが大きくなることは、（Ｄ９０−Ｄ１０）が大きくなることを示し、粒子径のバラツキの大きな負極活物質粉末となることを示す。また、負極活物質の粒度分布曲線を測定したときに、ピーク幅がブロードとなる。 The negative electrode active material has a particle size distribution characteristic value M (M = (D90−D10) / D50) of 1.2 or more . The particle size distribution characteristic value M indicates the spread (variation) of the particle size when the particle size distribution is measured. Specifically, an increase in the particle size distribution characteristic value M indicates that (D90-D10) is increased, indicating that the negative electrode active material powder has a large variation in particle diameter. Moreover, when the particle size distribution curve of the negative electrode active material is measured, the peak width becomes broad.
本形態（本発明）に用いられる結着剤は高い分散性を持つものであるため、凝集性の高い負極活物質であっても、均一に分散させることができる。すなわち、粒度分布特性値Ｍが１．２以上となるような粒子径のバラツキが大きな分散性の低い負極活物質であっても、均一に分散させることができる。 Since the binder used in this embodiment (the present invention) has a high dispersibility, even a highly cohesive negative electrode active material can be uniformly dispersed. That is, even a negative electrode active material having a large particle size variation and a low dispersibility such that the particle size distribution characteristic value M is 1.2 or more can be uniformly dispersed.
負極活物質は、シリコン系化合物を有すること以外は、従来公知の負極活物質と同様とすることができる。すなわち、シリコン系化合物よりなる負極活物質だけでなく、別の材質よりなる負極活物質との混合物であってもよい。別の材質からなる負極活物質は、たとえば、Ｌｉ，Ｓｎ，Ｓｂ，Ｇｅ，Ｃの少なくともひとつの元素を挙げることができる。 The negative electrode active material can be the same as a conventionally known negative electrode active material except that it has a silicon-based compound. That is, not only a negative electrode active material made of a silicon-based compound but also a mixture with a negative electrode active material made of another material may be used. Examples of the negative electrode active material made of another material include at least one element of Li, Sn, Sb, Ge, and C.
これらの負極活物質のうち、Ｃは、リチウムイオン二次電池の電解質イオンを吸蔵・脱離可能な（Ｌｉ吸蔵能がある）炭素質材料であることが好ましく、アセチレンブラック，ケッチェンブラック，カーボンブラック，黒鉛，アモルファスコート黒鉛などの炭素質材料を挙げることができる。本形態では、負極活物質は、炭素質材料を有することが好ましい。 Among these negative electrode active materials, C is preferably a carbonaceous material capable of occluding and desorbing electrolyte ions of a lithium ion secondary battery (having Li occlusion ability), such as acetylene black, ketjen black, carbon Examples thereof include carbonaceous materials such as black, graphite, and amorphous coated graphite. In this embodiment, the negative electrode active material preferably has a carbonaceous material.
炭素質材料は、粒度分布特性値Ｍ（Ｍ＝（Ｄ９０−Ｄ１０）／Ｄ５０）が１．２未満である。上記のように粒度分布特性値Ｍは、炭素質材料の粒度分布のバラツキを示す。粒度分布特性値Ｍが１．２未満となることで、炭素質材料の粒子径のバラツキが抑えられ、それぞれの粒子のＬｉを吸脱着する量が均一となり、生じる電極反応の反応量にバラツキが生じなくなる。 The carbonaceous material has a particle size distribution characteristic value M (M = (D90−D10) / D50) of less than 1.2 . As described above, the particle size distribution characteristic value M indicates variation in the particle size distribution of the carbonaceous material. When the particle size distribution characteristic value M is less than 1.2, variation in the particle size of the carbonaceous material is suppressed, the amount of adsorption and desorption of Li in each particle becomes uniform, and variation in the reaction amount of the electrode reaction that occurs. No longer occurs.
また、上記の負極活物質のうち、Ｓｎ，Ｓｂ，Ｇｅは、特に、体積変化の多い合金材料である。これらの負極活物質は、Ｔｉ−Ｓｉ，Ａｇ−Ｓｎ，Ｓｎ−Ｓｂ，Ａｇ−Ｇｅ，Ｃｕ−Ｓｎ，Ｎｉ−Ｓｎなどのように、別の金属と合金をなしていてもよい。 Of the above negative electrode active materials, Sn, Sb, and Ge are alloy materials that have a large volume change. These negative electrode active materials may form an alloy with another metal such as Ti—Si, Ag—Sn, Sn—Sb, Ag—Ge, Cu—Sn, and Ni—Sn.
負極活物質は、シリコン系化合物と炭素質材料との混合物よりなることが最も好ましい。この場合、両者の質量比は特に限定されるものではないが、シリコン系化合物が５０ｍａｓｓ％以上であることが好ましい。
本形態の好ましい負極は、ＳｉＯと炭素の混合電極である。
The negative electrode active material is most preferably made of a mixture of a silicon compound and a carbonaceous material. In this case, the mass ratio of the two is not particularly limited, but the silicon compound is preferably 50 mass% or more.
A preferred negative electrode of this embodiment is a mixed electrode of SiO and carbon.
本形態の負極は、負極活物質と、負極活物質を結着する結着剤と、を備えていれば、その形態が限定されるものではない。本形態の負極は、従来公知の負極と同様に、負極活物質と結着剤とを混合して得られた合材を集電体の表面に塗布して活物質層を形成したものを用いることが好ましい。 The form of the negative electrode of this embodiment is not limited as long as it includes a negative electrode active material and a binder that binds the negative electrode active material. As the negative electrode of this embodiment, a negative electrode active material and a binder obtained by mixing a negative electrode active material and a binder are applied to the surface of a current collector to form an active material layer, similarly to a conventionally known negative electrode. It is preferable.
負極合材は、負極活物質を結着剤溶液に分散させて、あるいは更に溶媒を加えて調整される。溶媒としては、溶液状の結着剤に用いられている有機溶媒や、結着剤を溶解可能な有機溶媒を使用できる。たとえば、ＮＭＰ，ジメチルホルムアミド，ジメチルアセトアミド，メチルエチルケトン，シクロヘキサノン，酢酸メチル，アクリル酸メチル，ジエチルトリアミン，Ｎ−Ｎ−ジメチルアミノプロピルアミン，エチレンオキシド，テトラヒドロフランなどを挙げることができるが、これらに限定されない。 The negative electrode mixture is prepared by dispersing the negative electrode active material in a binder solution or further adding a solvent. As the solvent, an organic solvent used for a solution binder or an organic solvent capable of dissolving the binder can be used. Examples thereof include, but are not limited to, NMP, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.
負極合剤は、ポリアクリル酸系化合物よりなる結着剤に、更に別の結着剤を混合してもよい。別の結着剤としては、リチウムイオン二次電池の負極に使用されている従来公知の結着剤である。たとえば、ＰＴＦＥ，ＰＶＤＦ，フッ素樹脂共重合体（四フッ化エチレン・六フッ化プロピレン共重合体），ＳＢＲ，アクリル系ゴム，フッ素系ゴム，ポリビニルアルコール（ＰＶＡ），スチレン・マレイン酸樹脂，ポリアクリル酸塩，ＣＭＣなどを挙げることができる。
負極集電体は、従来公知の集電体を用いることができ、銅，ステンレス，チタンあるいはニッケルからなる箔，メッシュなどを用いることができる。
In the negative electrode mixture, another binder may be further mixed with a binder made of a polyacrylic acid compound. Another binder is a conventionally known binder used for the negative electrode of a lithium ion secondary battery. For example, PTFE, PVDF, fluororesin copolymer (tetrafluoroethylene / hexafluoropropylene copolymer), SBR, acrylic rubber, fluororubber, polyvinyl alcohol (PVA), styrene / maleic resin, polyacrylic Examples thereof include acid salts and CMC.
As the negative electrode current collector, a conventionally known current collector can be used, and a foil, mesh, or the like made of copper, stainless steel, titanium, or nickel can be used.
本形態の負極は、脱水処理が施された後に使用に供されることが好ましい。脱水処理が施されることで、負極中に存在する水分の影響をより抑えることができる。脱水処理では、負極中に存在する水分量が少なくなるほど好ましい。脱水処理は、限定されるものではなく、乾燥雰囲気中での保持，加熱，真空乾燥等の処理方法を適宜選択することができる。また、脱水処理は、二次電池の組み付けの前であっても、二次電池を組み立てた条体で行っても、いずれでもよい。
本形態の負極は、電極内水分量が１００ｐｐｍ以下となる乾燥度であることが好ましい。
The negative electrode of this embodiment is preferably used after being subjected to a dehydration treatment. By performing the dehydration treatment, the influence of moisture present in the negative electrode can be further suppressed. In the dehydration treatment, the smaller the amount of moisture present in the negative electrode, the better. The dehydration treatment is not limited, and a treatment method such as holding in a dry atmosphere, heating, and vacuum drying can be appropriately selected. In addition, the dehydration treatment may be performed either before the secondary battery is assembled or may be performed on the strip in which the secondary battery is assembled.
It is preferable that the negative electrode of this embodiment has a dryness such that the moisture content in the electrode is 100 ppm or less.
（正極）
正極は、リチウムイオンを充電時には放出し、かつ放電時には吸蔵することができる正極活物質を備えていれば、その材料構成で特に限定されるものではなく、公知の材料構成のものを用いることができる。特に、正極活物質、導電材及び結着材を混合して得られた合材が集電体に塗布されて活物質層を形成するものを用いることが好ましい。
(Positive electrode)
The positive electrode is not particularly limited in its material configuration as long as it has a positive electrode active material that can release lithium ions during charging and can be occluded during discharging. it can. In particular, it is preferable to use a material in which a mixture obtained by mixing a positive electrode active material, a conductive material, and a binder is applied to a current collector to form an active material layer.
正極活物質は、従来公知の正極活物質を用いることができる。正極活物質は、たとえば、種々の酸化物、硫化物、リチウム含有酸化物、導電性高分子などを用いることができる。正極活物質は、リチウム−遷移金属複合酸化物であることが好ましい。 A conventionally known positive electrode active material can be used as the positive electrode active material. As the positive electrode active material, for example, various oxides, sulfides, lithium-containing oxides, conductive polymers, and the like can be used. The positive electrode active material is preferably a lithium-transition metal composite oxide.
リチウム−遷移金属複合酸化物は、ポリアニオン構造のリチウム金属化合物（ＬｉαＭ０ βＸηＯ４−γＺγ）であることがより好ましい。（なお、Ｍ０：Ｍｎ，Ｃｏ，Ｎｉ，Ｆｅ，Ｃｕ，Ｃｒ，Ｍｇ，Ｃａ，Ｚｎ，Ｔｉより選ばれる１種以上、Ｘ：Ｐ，Ａｓ，Ｓｉ，Ｍｏ，Ｇｅより選ばれる１種以上、Ｚ：Ａｌ，Ｍｇ，Ｃａ，Ｚｎ，Ｔｉより選ばれる１種以上を任意で含有可能、０≦α≦２．０、０≦β≦１．５、１≦η≦１．５、０≦γ≦１．５） Lithium - transition metal composite oxide is preferably a lithium metal compound polyanion structure (Li α M 0 β X η O 4-γ Z γ). (M 0 : one or more selected from Mn, Co, Ni, Fe, Cu, Cr, Mg, Ca, Zn, Ti, one or more selected from X: P, As, Si, Mo, Ge, Z: One or more selected from Al, Mg, Ca, Zn and Ti can be optionally contained, 0 ≦ α ≦ 2.0, 0 ≦ β ≦ 1.5, 1 ≦ η ≦ 1.5, 0 ≦ γ ≦ 1.5)
リチウム−遷移金属複合酸化物は、オリビン構造のリチウム−遷移金属複合酸化物であることが好ましい。このオリビン構造のリチウム−遷移金属複合酸化物としては、ＬｉＦｅＰＯ４，ＬｉＦｅｘＭｎ１−ｘＰＯ４（０≦ｘ＜１）を例示できる。 The lithium-transition metal composite oxide is preferably a lithium-transition metal composite oxide having an olivine structure. Examples of the olivine-structured lithium-transition metal composite oxide include LiFePO 4 and LiFe x Mn 1-x PO 4 (0 ≦ x <1).
導電材は、正極の電気伝導性を確保する。導電材としては、黒鉛の微粒子，アセチレンブラック，ケッチェンブラック，カーボンナノファイバーなどのカーボンブラック，ニードルコークスなどの無定形炭素の微粒子などを使用できるが、これらに限定されない。 The conductive material ensures the electrical conductivity of the positive electrode. Examples of the conductive material include, but are not limited to, graphite fine particles, acetylene black, ketjen black, carbon black such as carbon nanofiber, and amorphous carbon fine particles such as needle coke.
結着剤は、正極活物質粒子や導電材を結着する。結着剤としては、たとえば、ＰＶＤＦ，ＥＰＤＭ，ＳＢＲ，ＮＢＲ，フッ素ゴムなどを使用できるが、これらに限定されない。 The binder binds the positive electrode active material particles and the conductive material. As the binder, for example, PVDF, EPDM, SBR, NBR, fluorine rubber and the like can be used, but are not limited thereto.
正極合材は、溶媒に分散させて集電体に塗布される。溶媒としては、通常は結着剤を溶解する有機溶媒を使用する。たとえば、ＮＭＰ，ジメチルホルムアミド，ジメチルアセトアミド，メチルエチルケトン，シクロヘキサノン，酢酸メチル，アクリル酸メチル，ジエチルトリアミン，Ｎ−Ｎ−ジメチルアミノプロピルアミン，エチレンオキシド，テトラヒドロフランなどを挙げることができるが、これらに限定されない。また、水に分散剤、増粘剤などを加えてＰＴＦＥなどで正極活物質をスラリー化する場合もある。 The positive electrode mixture is dispersed in a solvent and applied to the current collector. As the solvent, an organic solvent that normally dissolves the binder is used. Examples thereof include, but are not limited to, NMP, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. In some cases, a positive electrode active material is slurried with PTFE or the like by adding a dispersant, a thickener, or the like to water.
正極集電体は、たとえば、アルミニウム，ステンレスなどの金属を加工したもの、たとえば板状に加工した箔，網，パンチドメタル，フォームメタルなどを用いることができるが、これらに限定されない。 As the positive electrode current collector, for example, a material obtained by processing a metal such as aluminum or stainless steel, for example, a foil processed into a plate shape, a net, a punched metal, a foam metal, or the like can be used, but is not limited thereto.
（非水電解質）
非水電解質は、その材料構成で特に限定されるものではなく、公知の材料構成のものを用いることができる。非水電解質（一般的には、非水電解液とも称される）は、支持塩が有機溶媒に溶解してなるものを用いることができる。
(Nonaqueous electrolyte)
The non-aqueous electrolyte is not particularly limited by its material structure, and a known material structure can be used. As the non-aqueous electrolyte (generally also referred to as a non-aqueous electrolyte), a solution obtained by dissolving a supporting salt in an organic solvent can be used.
非水電解質の支持塩は、その種類が特に限定されるものではないが、ＬｉＰＦ６，ＬｉＢＦ４，ＬｉＣｌＯ４及びＬｉＡｓＦ６から選ばれる無機塩，これらの無機塩の誘導体，ＬｉＳＯ３ＣＦ３，ＬｉＣ（ＳＯ３ＣＦ３）３及びＬｉＮ（ＳＯ２ＣＦ３）２，ＬｉＮ（ＳＯ２Ｃ２Ｆ５）２，ＬｉＮ（ＳＯ２ＣＦ３）（ＳＯ２Ｃ４Ｆ９），から選ばれる有機塩、並びにこれらの有機塩の誘導体の少なくとも１種であることが望ましい。これらの支持塩は、電池性能を更に優れたものとすることができ、かつその電池性能を室温以外の温度域においても更に高く維持することができる。支持塩の濃度についても特に限定されるものではなく、用途に応じ、支持塩及び有機溶媒の種類を考慮して適切に選択することが好ましい。 The supporting salt of the non-aqueous electrolyte is not particularly limited, but an inorganic salt selected from LiPF 6 , LiBF 4 , LiClO 4 and LiAsF 6 , derivatives of these inorganic salts, LiSO 3 CF 3 , LiC An organic salt selected from (SO 3 CF 3 ) 3 and LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiN (SO 2 CF 3 ) (SO 2 C 4 F 9 ), In addition, it is desirable to be at least one of these organic salt derivatives. These supporting salts can further improve the battery performance, and can maintain the battery performance higher even in a temperature range other than room temperature. The concentration of the supporting salt is not particularly limited, and it is preferable to appropriately select the supporting salt and the organic solvent in consideration of the use.
支持塩が溶解する有機溶媒（非水溶媒）は、通常の非水電解質に用いられる有機溶媒であれば特に限定されるものではなく、たとえばカーボネート類，ハロゲン化炭化水素，エーテル類，ケトン類，ニトリル類，ラクトン類，オキソラン化合物等を用いることができる。特に、プロピレンカーボネート，エチレンカーボネート，１，２−ジメトキシエタン，ジメチルカーボネート，ジエチルカーボネート，エチルメチルカーボネート，ビニレンカーボネート等及びそれらの混合溶媒が適当である。例に挙げたこれらの有機溶媒のうち、特にカーボネート類，エーテル類からなる群より選ばれた１種以上の非水溶媒を用いることにより、支持塩の溶解性、誘電率及び粘度において優れ、電池の充放電効率が高いので、好ましい。
本形態のリチウムイオン二次電池において、最も好ましい非水電解質は、支持塩が有機溶媒に溶解したものである。
The organic solvent (non-aqueous solvent) in which the supporting salt dissolves is not particularly limited as long as it is an organic solvent used in ordinary non-aqueous electrolytes. For example, carbonates, halogenated hydrocarbons, ethers, ketones, Nitriles, lactones, oxolane compounds and the like can be used. In particular, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate and the like, and mixed solvents thereof are suitable. Among these organic solvents mentioned in the examples, in particular, by using one or more non-aqueous solvents selected from the group consisting of carbonates and ethers, the solubility of the supporting salt, the dielectric constant and the viscosity are excellent, and the battery The charge / discharge efficiency is preferable.
In the lithium ion secondary battery of this embodiment, the most preferable non-aqueous electrolyte is a support salt dissolved in an organic solvent.
（その他の構成）
本形態のリチウムイオン二次電池は、正極，負極及び非水電解質を有すること以外の構成は、特に限定されるものではなく、公知の材料構成のものを用いることができる。
(Other configurations)
The lithium ion secondary battery of this embodiment is not particularly limited except for having a positive electrode, a negative electrode, and a nonaqueous electrolyte, and a known material structure can be used.
たとえば、リチウムイオン二次電池は、正極及び負極がセパレータを介した状態で、非水電解質とともにケースに封入されて形成されることが好ましい。これらの要素以外に、その他必要に応じた要素を有することができる。 For example, the lithium ion secondary battery is preferably formed by being enclosed in a case together with a nonaqueous electrolyte in a state where the positive electrode and the negative electrode are interposed via a separator. In addition to these elements, other elements as required can be included.
セパレータは、正極及び負極を電気的に絶縁し、非水電解質を保持する役割を果たす。セパレータは、たとえば、多孔性合成樹脂膜、特にポリオレフィン系高分子（ポリエチレン、ポリプロピレン）の多孔膜を用いることが好ましい。なおセパレータは、正極と負極との絶縁を担保するため、正極及び負極よりも更に大きい形状とすることが好ましい。 The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the nonaqueous electrolyte. As the separator, for example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film is preferably used. Note that the separator preferably has a shape larger than that of the positive electrode and the negative electrode in order to ensure insulation between the positive electrode and the negative electrode.
リチウムイオン二次電池は、上記の要素以外に、その他必要に応じた要素を有することが好ましい。リチウムイオン二次電池は、その形状には特に制限を受けず、コイン型、円筒型、角型等、種々の形状の電池や、ラミネート外装体に封入した不定形状の電池とすることができる。 The lithium ion secondary battery preferably has other elements as necessary in addition to the above elements. The shape of the lithium ion secondary battery is not particularly limited, and can be a battery of various shapes such as a coin shape, a cylindrical shape, a square shape, or an indefinite shape sealed in a laminate outer package.
以下、実施例を用いて本発明を説明する。
本発明の実施例として、リチウムイオン二次電池の負極及びリチウムイオン二次電池を製造した。
［実施例及び参考例］
（負極）
Hereinafter, the present invention will be described using examples.
As an example of the present invention, a negative electrode of a lithium ion secondary battery and a lithium ion secondary battery were manufactured.
[Examples and Reference Examples ]
(Negative electrode)
リチウムイオン二次電池の負極は、予め準備した負極活物質，結着剤，導電材を表１に示した割合で混合し、適量の水を添加して混練することでペースト状の負極合材を調整した。この負極合材を、厚さ１０μｍの銅箔製負極集電体の表面に塗布、乾燥し、プレス工程を経て、シート状の負極を作製した。ここで、負極合材の塗布後の乾燥は、減圧下での加熱（真空乾燥）により行われた。製造された負極は、負極集電体の表面に負極活物質層が形成されている。負極活物質層は、２．６６ｍｇ／ｃｍ２，１．５ｇ／ｃｍ３で形成されている。 The negative electrode of the lithium ion secondary battery is prepared by mixing a negative electrode active material, a binder, and a conductive material prepared in advance at a ratio shown in Table 1, adding an appropriate amount of water, and kneading to paste a negative electrode mixture. Adjusted. The negative electrode mixture was applied to the surface of a copper foil negative electrode current collector having a thickness of 10 μm, dried, and subjected to a pressing step to produce a sheet-like negative electrode. Here, the drying after application of the negative electrode mixture was performed by heating under reduced pressure (vacuum drying). In the manufactured negative electrode, the negative electrode active material layer is formed on the surface of the negative electrode current collector. The negative electrode active material layer is formed at 2.66 mg / cm 2 and 1.5 g / cm 3 .
負極活物質は、ケイ素酸化物（ＳｉＭｘＬｙにおいてｘ＝０，Ｌ＝Ｏに相当，表１中ではＳｉＯと表示）（和光純薬工業株式会社製，商品名：一酸化ケイ素、９９．９％），ケイ素（ＳｉＭｘＬｙにおいてｘ＝０，ｙ＝０に相当，表１中ではＳｉと表示）（和光純薬工業株式会社製，商品名：ケイ素、粉末），Ｓｉ−Ｎｉ−Ｔｉ合金（ＳｉＭｘＬｙにおいてＭ＝Ｎｉ，Ｌ＝Ｔｉに相当，表１中ではＳｉＮｉＴｉと表示）（Ｓｉ（上記市販品）とＮｉ（市販品、和光純薬工業株式会社製、商品名；ニッケル粉末 １４５−００９８２）とＴｉ（市販品、和光純薬工業株式会社製、商品名；チタン粉末 ２００−０５２０２）をメカニカルアロイング法にて室温で３時間混合して製造），黒鉛（和光純薬工業株式会社製，商品名：グラファイト、粉末）から選択した。負極活物質の粒度分布特性値Ｍを、それぞれ表１に合わせて示した。 The negative electrode active material was silicon oxide (corresponding to x = 0, L = O in SiM x L y , indicated as SiO in Table 1) (manufactured by Wako Pure Chemical Industries, Ltd., trade name: silicon monoxide, 99. 9%), silicon (corresponding to x = 0 and y = 0 in SiM x L y , indicated as Si in Table 1) (Wako Pure Chemical Industries, Ltd., trade name: silicon, powder), Si-Ni- Ti alloy (corresponding to M = Ni and L = Ti in SiM x L y , indicated as SiNiTi in Table 1) (Si (commercial product) and Ni (commercial product, manufactured by Wako Pure Chemical Industries, Ltd., trade name); Nickel powder 145-00982) and Ti (commercially available, manufactured by Wako Pure Chemical Industries, Ltd., trade name; titanium powder 200-05202) manufactured by mechanical alloying at room temperature for 3 hours), graphite (Wako Pure) Product name: Graphi It was selected from powder). Table 1 shows the particle size distribution characteristic value M of the negative electrode active material.
結着剤は、架橋型ポリアクリル酸ナトリウム塩（表１中ではＰＡＡＨｘＮａｙと表示）（ポリアクリル酸溶液（市販品、和光純薬工業株式会社製、商品名；ポリアクリル酸溶液（２５％）８０００〜１２０００ ｃｐを架橋剤により架橋して製造，部分的にアクリル酸がナトリウムに置換），架橋型ポリアクリル酸−マレイン酸共重合体（ポリアクリル酸共重合体に相当，表１中ではＰＡＡＨｘＮａｙ−ＭＡと表示）（ポリアクリル酸溶液（上記市販品）を架橋剤により架橋させマレイン酸と共重合して製造），架橋型ポリアクリル酸リチウム塩（表１中ではＰＡＡＨｘＬｉｙと表示）（ポリアクリル酸溶液（上記架橋型ポリアクリル酸）に炭酸リチウム（リチウム源）を加えて製造）及びＣＭＣ（固形分３０ｍａｓｓ％，第一工業製薬製，商品名：ＢＳＨ−６）から選択した。
導電材は、アセチレンブラック（表１中ではＡＢと表示）（電気化学工業製，商品名：デンカブラック）を用いた。
The binder is a cross-linked polyacrylic acid sodium salt (indicated as PAAHxNay in Table 1) (polyacrylic acid solution (commercial product, Wako Pure Chemical Industries, Ltd., trade name; polyacrylic acid solution (25%) 8000). -12000 cp produced by crosslinking with a crosslinking agent, partially substituted with acrylic acid by sodium), crosslinked polyacrylic acid-maleic acid copolymer (corresponding to polyacrylic acid copolymer, in Table 1 PAAHxNay- MA)) (manufactured by cross-linking polyacrylic acid solution (the above-mentioned commercial product) with a crosslinking agent and copolymerizing with maleic acid), cross-linked polyacrylic acid lithium salt (indicated in Table 1 as PAAHxLiy) (polyacrylic acid Solution (produced by adding lithium carbonate (lithium source) to the above-mentioned cross-linked polyacrylic acid) and CMC (solid content 30 mass%, manufactured by Daiichi Kogyo Seiyaku, Ltd. Product name: BSH-6).
As the conductive material, acetylene black (indicated as AB in Table 1) (trade name: Denka Black, manufactured by Denki Kagaku Kogyo) was used.
（リチウムイオン二次電池）
製造された負極と、金属リチウムよりなる正極（対極）と、非水電解質（非水電解液）と、電池ケースと、を用いて、ドライボックス中で本例のコイン型のリチウムイオン二次電池（ＣＲ２０３２タイプ）を組み立てた。なお、負極と正極との間には、多孔質樹脂（ポリプロピレン）よりなるセパレータが配されている。
(Lithium ion secondary battery)
A coin-type lithium ion secondary battery of this example in a dry box using the manufactured negative electrode, a positive electrode (counter electrode) made of metallic lithium, a non-aqueous electrolyte (non-aqueous electrolyte), and a battery case. (CR2032 type) was assembled. A separator made of porous resin (polypropylene) is disposed between the negative electrode and the positive electrode.
なお、非水電解液は、エチレンカーボネート（ＥＣ）３０体積％とジメチルカーボネート（ＤＭＣ）３０体積％とエチルメチルカーボネート（ＥＭＣ）３０体積％との混合溶媒に、ＬｉＰＦ６を１モル／リットルとなるように溶解させて調製されている。また、電解液は、添加剤としてビニレンカーボネート（ＶＣ）が１ｍａｓｓ％となるように添加されている。
以上により、実施例の試料１１，１２，２７及び参考例の試料１〜１０，１３〜２６のリチウムイオン二次電池（ハーフセルタイプ）が作成された。
The non-aqueous electrolyte is mixed with 30% by volume of ethylene carbonate (EC), 30% by volume of dimethyl carbonate (DMC) and 30% by volume of ethyl methyl carbonate (EMC), and LiPF6 is 1 mol / liter. It is prepared by dissolving in. Moreover, the electrolyte solution is added so that vinylene carbonate (VC) may be 1 mass% as an additive.
Thus , lithium ion secondary batteries (half cell type) of Samples 11 , 12, and 27 of Examples and Samples 1 to 10, and 13 to 26 of Reference Examples were prepared.
［比較例］
本比較例は、架橋型ポリアクリル酸ナトリウム塩（ＰＡＡＨｘＮａｙ）に替えて、表２に示した非架橋型ポリアクリル酸ナトリウム塩（表１と同様にＰＡＡＨｘＮａｙと示す）を用いたこと以外は実施例（試料：ＳｉＯ，ＳｉＯと炭素の混合物、Ｓｉ，ＳｉＮｉＴｉ）と同様なリチウムイオン二次電池の負極及びリチウムイオン二次電池を製造した。
本例の試料３１〜３９のリチウムイオン二次電池（ハーフセルタイプ）が得られた。
[Comparative example]
This comparative example is an example except that in place of the crosslinked polyacrylic acid sodium salt (PAAHxNay), the non-crosslinked polyacrylic acid sodium salt shown in Table 2 (shown as PAAHxNay as in Table 1) was used. (Sample: SiO, a mixture of SiO and carbon, Si, SiNiTi) The same negative electrode of lithium ion secondary battery and lithium ion secondary battery were produced.
The lithium ion secondary battery (half cell type) of Samples 31 to 39 of this example was obtained.
また、試料４０として、試料１１の架橋型ポリアクリル酸ナトリウム塩（ＰＡＡＨｘＮａｙ）に替えて、非架橋型ポリアクリル酸ナトリウム塩（ＰＡＡＨｘＮａｙ）を用いた例もあわせて製造した（表２には記載せず）。 Further, as a sample 40, in place of the crosslinked polyacrylic acid sodium salt of the sample 11 (PAAHxNay), examples using non-crosslinked polyacrylic acid sodium salt (PAAHxNay) were also prepared together (not described in Table 2 )
［評価］
実施例、参考例及び比較例（各試料）の評価を下記の通り行った。
[Evaluation]
Examples , reference examples and comparative examples (each sample) were evaluated as follows.
評価として、負極合材における負極活物質の分散性，負極合材のポリアクリル酸の結着性，各試料のリチウムイオン二次電池の容量維持率を求めた。得られた評価結果は、それぞれ表１〜２に合わせて示した。 As evaluation, the dispersibility of the negative electrode active material in the negative electrode mixture, the binding property of polyacrylic acid in the negative electrode mixture, and the capacity retention rate of the lithium ion secondary battery of each sample were determined. The obtained evaluation results are shown in Tables 1 and 2, respectively.
（分散性）
分散性の測定は、ＪＩＳ Ｋ５１０１に準じて行った。
また、試料１１の負極合材及び試料４０の負極合材のＳＥＭ写真を撮影して分散性を確認した。
(Dispersibility)
The dispersibility was measured according to JIS K5101.
Further, SEM photographs of the negative electrode mixture of sample 11 and the negative electrode mixture of sample 40 were taken to confirm dispersibility.
表１〜２に示したように、実施例の負極合材は、比較例の負極合材よりも、粒ゲージ最大粒子の粒子径が小さくなっている。粒ゲージ最大粒子の粒子径は、シリコン系化合物が凝集を生じて二次粒子を形成すると大きくなる値である。この値が小さいことから、実施例の負極合材は、シリコン系化合物が凝集を生じることが抑えられていることがわかる。 As shown in Tables 1 and 2, the negative electrode composites of the examples have smaller particle diameters of the largest particle gauge particles than the negative electrode composites of the comparative examples. The particle diameter of the largest particle gauge particle is a value that increases when the silicon-based compound aggregates to form secondary particles. Since this value is small, it turns out that the negative electrode compound of an Example has suppressed that a silicon type compound agglomerates.
このことは、二つの負極合材のＳＥＭ写真からも明らかである。試料１１の負極合材のＳＥＭ写真からは、シリコン系化合物粒子がＡＢの周囲に均一に分散していることが確認できた。対して、試料４０の負極合材のＳＥＭ写真からは、シリコン系化合物粒子がＡＢの周囲で凝集していることが確認できた。 This is clear from SEM photographs of the two negative electrode composites. From the SEM photograph of the negative electrode composite material of Sample 11, it was confirmed that the silicon compound particles were uniformly dispersed around the AB. On the other hand, from the SEM photograph of the negative electrode mixture of Sample 40, it was confirmed that the silicon-based compound particles were aggregated around AB.
（結着性）
結着性の測定は、ＪＩＳ Ｋ６８４５に準じて行った。
(Binding property)
The measurement of the binding property was performed according to JIS K6845.
表１〜２に示したように、実施例の負極合材の結着剤は、比較例の結着剤よりも、接着強度が遙かに高くなっている。すなわち、実施例の負極の結着剤（架橋型ポリアクリル酸塩）は、比較例の結着剤（非架橋型ポリアクリル酸塩）よりも高い結着性を備えていることがわかる。 As shown in Tables 1-2, the adhesive strength of the binder of the negative electrode mixture of the example is much higher than that of the comparative example. That is, it can be seen that the negative electrode binder (crosslinked polyacrylate ) of the example has higher binding properties than the comparative binder (non-crosslinked polyacrylate ).
そして、実施例の負極の結着剤（架橋型ポリアクリル酸塩）と比較例の負極の結着剤（非架橋型ポリアクリル酸塩）の相違点は、ポリアクリル酸が架橋型か非架橋型かの点である。すなわち、架橋型ポリアクリル酸塩は、非架橋型ポリアクリル酸塩よりも高い結着性を備えていることがわかる。 The difference between the negative electrode binder (crosslinked polyacrylate ) of the example and the negative electrode binder (non-crosslinked polyacrylate ) of the comparative example is that the polyacrylic acid is crosslinked or non-crosslinked It is a point of type. That is, cross-linked polyacrylic acid salt, it can be seen that with a high binding property than non-cross-linked polyacrylate.
（容量維持率）
まず、充電電流０．１０ｍＡ／ｃｍ２で０．０１Ｖまで定電流充電し、放電電流０．１０ｍＡ／ｃｍ２で１．５Ｖまで定電流放電を行った。この時の放電容量を初期放電容量とした。
次に、初回充放電後、充電電流０．１０ｍＡ／ｃｍ２で０．０１Ｖまで定電流充電し、放電電流０．１０ｍＡ／ｃｍ２で１．５Ｖまで定電流放電のサイクルを６０℃で９０回繰り返して行った。
そして、９０サイクル目の放電容量と初回放電容量とから、下記式により容量維持率（％）を求めた。なお、２５℃の雰囲気で充放電及び放電容量の測定を行った。
容量維持率（％）＝[(９０サイクル目の放電容量)／（初回放電容量）]×１００
表１〜２に示したように、実施例のリチウムイオン二次電池は、比較例のリチウムイオン二次電池よりも、容量維持率が高くなっている。
(Capacity maintenance rate)
First, constant current charging at a charging current 0.10mA / cm 2 to 0.01 V, was constant current discharge to 1.5V at a discharge current 0.10mA / cm 2. The discharge capacity at this time was defined as the initial discharge capacity.
Then, after the initial charge and discharge, the charging current 0.01V to a constant current charge at 0.10mA / cm 2, discharge current 0.10mA / cm 2 in 90 times 60 ° C. The cycle of constant current discharge to 1.5V Repeatedly.
And the capacity | capacitance maintenance factor (%) was calculated | required by the following formula from the discharge capacity of 90th cycle, and initial stage discharge capacity. In addition, the measurement of charging / discharging and discharge capacity was performed in 25 degreeC atmosphere.
Capacity retention rate (%) = [(discharge capacity at 90th cycle) / (initial discharge capacity)] × 100
As shown in Tables 1-2, the capacity retention rate of the lithium ion secondary batteries of the examples is higher than that of the lithium ion secondary batteries of the comparative examples.
すなわち、上記の分散性及び結着性に優れた実施例が、比較例に対して優れた容量維持率を備えていることがわかる。このことは、充放電時の体積変化の大きなシリコン系化合物が均一に分散した状態で結着されていることで、シリコン系化合物に起因する導電ネットワークの崩壊が抑えられたことを示す。 That is, it turns out that the Example excellent in said dispersibility and binding property is equipped with the capacity | capacitance maintenance rate excellent with respect to the comparative example. This indicates that the collapse of the conductive network caused by the silicon compound was suppressed by binding the silicon compound having a large volume change during charge and discharge in a uniformly dispersed state.
また、実施例のリチウムイオン二次電池の負極活物質に用いられるシリコン系化合物は、高エネルギー密度で良好な充放電サイクル特性を発揮することが知られており、実施例のリチウムイオン二次電池においても、この効果を発揮する。
以上に示したように、実施例のリチウムイオン二次電池は、高い電池性能を長期間にわたって発揮できる効果を示している。
In addition, it is known that the silicon-based compound used for the negative electrode active material of the lithium ion secondary battery of the example exhibits good charge / discharge cycle characteristics at a high energy density, and the lithium ion secondary battery of the example Also demonstrates this effect.
As described above, the lithium ion secondary battery of the example shows the effect that high battery performance can be exhibited over a long period of time.
Claims (1)
該負極活物質は、粒度分布特性値Ｍ（Ｍ＝（Ｄ９０−Ｄ１０）／Ｄ５０）が１．２以上であるＳｉＯで表されるシリコン系化合物と、粒度分布特性値Ｍ（Ｍ＝（Ｄ９０−Ｄ１０）／Ｄ５０）が１．２未満である炭素質材料と、を有し、
該結着剤は、重量平均分子量が２０万以下の架橋型構造を有しているポリアクリル酸塩、ＰＴＦＥ，ＰＶＤＦ，フッ素樹脂共重合体，ＳＢＲ，アクリル系ゴム，フッ素系ゴム，ポリビニルアルコール（ＰＶＡ），スチレン・マレイン酸樹脂，ＣＭＣより選ばれる１種以上のうち、少なくとも該ポリアクリル酸塩を有することを特徴とする非水電解質二次電池。 In a nonaqueous electrolyte secondary battery using a negative electrode comprising a negative electrode active material and a binder that binds the negative electrode active material,
The negative electrode active material includes a silicon compound represented by SiO having a particle size distribution characteristic value M (M = (D90−D10) / D50) of 1.2 or more, and a particle size distribution characteristic value M (M = (D90−). A carbonaceous material having D10) / D50) of less than 1.2,
The binder is a polyacrylate having a cross-linked structure having a weight average molecular weight of 200,000 or less, PTFE, PVDF, fluororesin copolymer, SBR, acrylic rubber, fluororubber, polyvinyl alcohol ( A non-aqueous electrolyte secondary battery comprising at least the polyacrylate of at least one selected from PVA), styrene / maleic acid resin, and CMC.
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