JP2013110105A - Negative electrode for lithium ion secondary battery, and lithium ion secondary battery including the negative electrode - Google Patents
Negative electrode for lithium ion secondary battery, and lithium ion secondary battery including the negative electrode Download PDFInfo
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- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 54
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 53
- 239000002245 particle Substances 0.000 claims abstract description 103
- 239000007773 negative electrode material Substances 0.000 claims abstract description 53
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 74
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- 229910004298 SiO 2 Inorganic materials 0.000 claims description 12
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 10
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- VZCYOOQTPOCHFL-OWOJBTEDSA-N Fumaric acid Chemical compound OC(=O)\C=C\C(O)=O VZCYOOQTPOCHFL-OWOJBTEDSA-N 0.000 description 2
- 229910013063 LiBF 4 Inorganic materials 0.000 description 2
- 229910013684 LiClO 4 Inorganic materials 0.000 description 2
- 229910013870 LiPF 6 Inorganic materials 0.000 description 2
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- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 1
- JAHNSTQSQJOJLO-UHFFFAOYSA-N 2-(3-fluorophenyl)-1h-imidazole Chemical compound FC1=CC=CC(C=2NC=CN=2)=C1 JAHNSTQSQJOJLO-UHFFFAOYSA-N 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- 229910015015 LiAsF 6 Inorganic materials 0.000 description 1
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 1
- 229910013872 LiPF Inorganic materials 0.000 description 1
- 229910001228 Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) Inorganic materials 0.000 description 1
- 101150058243 Lipf gene Proteins 0.000 description 1
- CERQOIWHTDAKMF-UHFFFAOYSA-N Methacrylic acid Chemical compound CC(=C)C(O)=O CERQOIWHTDAKMF-UHFFFAOYSA-N 0.000 description 1
- 229910016485 Mn1/3Ni1/3Co1/3 Inorganic materials 0.000 description 1
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- 238000001069 Raman spectroscopy Methods 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
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- 125000005370 alkoxysilyl group Chemical group 0.000 description 1
- 239000002194 amorphous carbon material Substances 0.000 description 1
- 229910021486 amorphous silicon dioxide Inorganic materials 0.000 description 1
- 239000006183 anode active material Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- CKFRRHLHAJZIIN-UHFFFAOYSA-N cobalt lithium Chemical compound [Li].[Co] CKFRRHLHAJZIIN-UHFFFAOYSA-N 0.000 description 1
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- 230000004927 fusion Effects 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 1
- 150000002334 glycols Chemical class 0.000 description 1
- 150000003949 imides Chemical class 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 230000002687 intercalation Effects 0.000 description 1
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- HSZCZNFXUDYRKD-UHFFFAOYSA-M lithium iodide Inorganic materials [Li+].[I-] HSZCZNFXUDYRKD-UHFFFAOYSA-M 0.000 description 1
- PAZHGORSDKKUPI-UHFFFAOYSA-N lithium metasilicate Chemical compound [Li+].[Li+].[O-][Si]([O-])=O PAZHGORSDKKUPI-UHFFFAOYSA-N 0.000 description 1
- 229910052912 lithium silicate Inorganic materials 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- VZCYOOQTPOCHFL-UPHRSURJSA-N maleic acid Chemical compound OC(=O)\C=C/C(O)=O VZCYOOQTPOCHFL-UPHRSURJSA-N 0.000 description 1
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- LVHBHZANLOWSRM-UHFFFAOYSA-N methylenebutanedioic acid Natural products OC(=O)CC(=C)C(O)=O LVHBHZANLOWSRM-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- 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
Abstract
Description
本発明は、リチウムイオン二次電池用負極及びその負極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 for a lithium ion secondary battery and a lithium ion secondary battery using the negative electrode.
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でき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。現在、一般的に用いられている負極活物質として黒鉛などの炭素材料がある。黒鉛などを負極活物質とする炭素負極は、インターカレーション反応を有することから、サイクル特性は良いものの、高容量化が困難とされている。そこで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. Currently, there is a carbon material such as graphite as a negative electrode active material generally used. A carbon negative electrode using graphite or the like as a negative electrode active material has an intercalation reaction, and thus has high cycle characteristics but is difficult to increase in capacity. Thus, 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できる。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できる。 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 and discharge can be suppressed more than silicon.
また、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。 Further, 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 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. Further, the SiO 2 phase covering the Si phase has a function of suppressing decomposition of the electrolytic solution. Therefore, the secondary battery using the negative electrode active material made of SiO x decomposed into Si and SiO 2 has excellent cycle characteristics.
しかしＳｉＯｘは導電性が低いため、導電材として黒鉛や非晶質の炭素材料を混合し、導電材粉末とＳｉＯｘ粉末を点又は面で接触させることにより負極に導電性をもたせている。例えば特開平１１−３１２５１８号公報には、ケイ酸リチウム粉末と天然黒鉛粉末との混合物からなる負極材料を用いたリチウムイオン二次電池はサイクル特性が向上することが記載されている。ところが、ＳｉＯｘと黒鉛粉末との混合物からなる負極材料を用いたリチウムイオン二次電池は、充放電に伴ってＳｉＯｘの膨張収縮が繰り返されることにより、体積膨張差によってクラックが進展し、集電体と負極活物質層との間で剥離が生じるという問題があった。 However, since SiO x has low conductivity, graphite or an amorphous carbon material is mixed as a conductive material, and the negative electrode is made conductive by bringing the conductive material powder and the SiO x powder into contact with each other at points or surfaces. For example, Japanese Patent Application Laid-Open No. 11-31518 discloses that a lithium ion secondary battery using a negative electrode material made of a mixture of lithium silicate powder and natural graphite powder has improved cycle characteristics. However, in a lithium ion secondary battery using a negative electrode material made of a mixture of SiO x and graphite powder, cracks develop due to a difference in volume expansion due to repeated expansion and contraction of SiO x with charge and discharge. There has been a problem that peeling occurs between the electric body and the negative electrode active material layer.
そこで特開２００４−３６２７８９号公報には、Ｌｉ吸蔵粒子と黒鉛粒子とを含む負極材料において、Ｘ線回折法による（００２）面間隔ｄ（００２）が０．３３５４ｎｍ以上０．３３８ｎｍ以下、かつラマン分光分析によるＧピークとＤピークの面積比がＧ／Ｄ≧９である黒鉛粒子を用いることが提案されている。そしてＬｉ吸蔵粒子としてＳｉ又はＳｉＯを用いることが記載され、Ｓｉ又はＳｉＯをこのような黒鉛粒子と共に用いることで二次電池のサイクル特性が向上することが記載されている。 In view of this, Japanese Patent Application Laid-Open No. 2004-362789 discloses that in a negative electrode material containing Li storage particles and graphite particles, a (002) plane distance d (002) by an X-ray diffraction method is 0.3354 nm or more and 0.338 nm or less, and Raman. It has been proposed to use graphite particles in which the area ratio of G peak to D peak by spectroscopic analysis is G / D ≧ 9. It is described that Si or SiO is used as the Li storage particles, and that the cycle characteristics of the secondary battery are improved by using Si or SiO together with such graphite particles.
また特開２００３−３０３５８８号公報には、ＳｉなどのＬｉと合金化可能な元素を含む材料と、黒鉛などの導電性材料とからスプレードライ法などで複合体粒子を形成し、その複合体粒子が内部に空隙を有し、複合体粒子の空隙体積占有率を所定範囲とした負極材料が提案されている。このように空隙体積占有率を最適範囲とした複合体粒子を負極材料として用いることで、複合体粒子内に膨張分を吸収する隙間が存在し電極特性の劣化を防止できる。また隙間が多くなり過ぎることがないので、導電ネットワークが十分に構築され非水二次電池の充放電容量の低下を防止できる。 Japanese Patent Laid-Open No. 2003-303588 discloses that composite particles are formed from a material containing an element that can be alloyed with Li, such as Si, and a conductive material, such as graphite, by a spray drying method or the like. Has proposed a negative electrode material having voids inside and having a void volume occupation ratio of the composite particles within a predetermined range. As described above, by using the composite particles having the void volume occupation ratio in the optimum range as the negative electrode material, there is a gap for absorbing the expansion in the composite particles, and deterioration of the electrode characteristics can be prevented. Moreover, since there are not too many gaps, a conductive network is sufficiently constructed, and a decrease in charge / discharge capacity of the nonaqueous secondary battery can be prevented.
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、Ｌｉ吸蔵粒子と炭素系粒子とを含む負極材料において、充放電時の体積変化を緩和することで集電体と負極活物質層との界面の剥離を防止するとともに、その負極を用いたリチウムイオン二次電池のサイクル特性を向上させることにある。 The present invention has been made in view of the above-described circumstances, and the main object of the present invention is to reduce the volume change during charge and discharge in a negative electrode material including Li storage particles and carbon-based particles. It is to prevent peeling at the interface between the negative electrode active material layer and the cycle characteristics of a lithium ion secondary battery using the negative electrode.
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の特徴は、集電体と、集電体に形成された負極活物質層と、からなるリチウムイオン二次電池用負極であって、負極活物質層には炭素系粒子と、リチウムイオンを吸蔵可能なＬｉ吸蔵粒子と、を含み、炭素系粒子のＤ５０（Ｄ１）とＬｉ吸蔵粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）が１を超えかつ２以下であり、炭素系粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）が１／４以上かつ５／６以下であることにある。なお、Ｄ５０とはレーザー回析法による粒度分布測定における体積分布の積算値が５０％に相当する粒子径を指す。つまり、Ｄ５０とは、体積基準で測定したメディアン径を指す。 The negative electrode for a lithium ion secondary battery of the present invention that solves the above problems is a negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer formed on the current collector, the ratio of the negative electrode active material layer and the carbon-based particles, anda storage capable Li occluding particles lithium ions, D 50 of D 50 (D 1) and Li occlusion particles of the carbon-based particles (D 2) ( D 1 / D 2 ) exceeds 1 and is 2 or less, and the ratio (D 1 / t) between D 50 (D 1 ) of the carbon-based particles and the thickness (t) of the negative electrode active material layer is 1/4 It is above and below 5/6. D 50 refers to a particle diameter corresponding to an integrated volume distribution value of 50% in particle size distribution measurement by laser diffraction. That is, the D 50, it refers to the median diameter measured by volume.
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、本発明の負極を用いたことにある。 The feature of the lithium ion secondary battery of the present invention that solves the above problems is that the negative electrode of the present invention is used.
炭素系粒子とＬｉ吸蔵粒子との混合物からなる負極活物質層には、粒子どうしの間に必然的に気孔が含まれている。この気孔によって膨張・収縮時の応力が吸収されるのであるが、大きな気孔が小数のものより小さな気孔が多数のものの方が応力吸収性に優れている。また気孔の形状は、真球に近いほど応力集中を回避することができクラックを防止できると考えられる。 The negative electrode active material layer made of a mixture of carbon-based particles and Li storage particles necessarily includes pores between the particles. Although the pores absorb the stress during expansion / contraction, the larger pores have a larger number of smaller pores than the smaller ones, and the stress absorption is superior. Further, it is considered that as the shape of the pore is closer to a true sphere, stress concentration can be avoided and cracks can be prevented.
ところがＬｉ吸蔵粒子として代表的なＳｉＯｘのＤ５０は標準品で約６．５μｍ程度であるのに対し、炭素系粒子として代表的な黒鉛の粒子径は１０μｍ〜２０μｍの範囲にある。そのためＳｉＯｘと人造黒鉛との混合物からなる負極材料においては、粒径差が大きくなり小さな気孔を多数有するようにすることは困難となっていた。 However, the typical SiO x D 50 as a Li-occlusion particle is about 6.5 μm as a standard product, whereas the typical graphite particle size as a carbon-based particle is in the range of 10 μm to 20 μm. Therefore, in a negative electrode material made of a mixture of SiO x and artificial graphite, it is difficult to have a large particle size difference and have many small pores.
そこで本発明のリチウムイオン二次電池用負極は、炭素系粒子のＤ５０（Ｄ１）とＬｉ吸蔵粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）が１を超えかつ２以下としているので、Ｄ１とＤ２とが近く負極活物質層には小さな気孔が多数含まれるようになる。 So the negative electrode for a lithium ion secondary battery of the present invention, D 50 (D 1) and the ratio between D 50 of Li occlusion particle (D 2) (D 1 / D 2) is greater than 1 and 2 of the carbon-based particles since the less, so small pores is contained a number in the D 1 and D 2 and is close to the negative electrode active material layer.
一方、負極活物質層の厚さは電気抵抗値を小さくするためになるべく薄いことが望ましいが、負極活物質層の厚さを薄くすると、炭素系粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）も大きくなり、そうなると気孔の分散性が低下してしまう。 On the other hand, the thickness of the negative electrode active material layer is desirably as thin as possible in order to reduce the electrical resistance value. However, when the thickness of the negative electrode active material layer is reduced, the D 50 (D 1 ) of the carbon-based particles and the negative electrode active material The ratio (D 1 / t) to the layer thickness (t) also increases, and the dispersibility of the pores decreases.
そこで本発明では、炭素系粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）を１／４以上かつ５／６以下としているので、Ｄ１に対してｔが十分に大きく、気孔の分散性がよい。 Therefore, in the present invention, the ratio (D 1 / t) between D 50 (D 1 ) of the carbon-based particles and the thickness (t) of the negative electrode active material layer is set to 1/4 or more and 5/6 or less. T is sufficiently larger than 1 , and the dispersibility of the pores is good.
したがって本発明の負極を用いた本発明のリチウムイオン二次電池は、負極活物質層に含まれる小さくて分散性が高い気孔によって充放電時の体積変化による応力を緩和することができ、クラックや剥離を防止できるためサイクル特性が向上する。 Therefore, the lithium ion secondary battery of the present invention using the negative electrode of the present invention can relieve the stress caused by the volume change during charge and discharge by the small and highly dispersible pores contained in the negative electrode active material layer. Since peeling can be prevented, cycle characteristics are improved.
本発明のリチウムイオン二次電池用負極は、炭素系粒子とＬｉ吸蔵粒子とを含む。炭素系粒子としては、天然黒鉛、人造黒鉛、コークス、メソフェーズ炭素、気相成長炭素繊維、ピッチ系炭素繊維、ＰＡＮ系炭素繊維などが例示されるが、緩衝性能に優れ、かつＤ５０が１μｍ〜１５μｍの範囲にある黒鉛が好ましい。この炭素系粒子のＤ５０は、Ｌｉ吸蔵粒子として下記のＳｉＯｘを用いた場合には、１μｍ〜１０μｍであることが特に望ましい。 The negative electrode for a lithium ion secondary battery of the present invention includes carbon-based particles and Li storage particles. Examples of the carbon-based particles include natural graphite, artificial graphite, coke, mesophase carbon, vapor-grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber, etc., and have excellent buffer performance and D 50 of 1 μm to Graphite in the range of 15 μm is preferred. The D 50 of the carbon-based particles is particularly preferably 1 μm to 10 μm when the following SiO x is used as the Li storage particles.
Ｌｉ吸蔵粒子としては、ケイ素、錫、ゲルマニウム、鉛、インジウム、酸化ケイ素、酸化錫、などを用いることができるが、ＳｉＯｘ（０．３≦ｘ≦１．６）で表されるケイ素酸化物からなるＳｉＯ系粒子を用いることが望ましい。このＳｉＯ系粒子は、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。 As the Li storage particles, silicon, tin, germanium, lead, indium, silicon oxide, tin oxide, or the like can be used, and silicon oxide represented by SiO x (0.3 ≦ x ≦ 1.6). It is desirable to use SiO-based particles made of The SiO-based particles 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珪素粉末に対して、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時間〜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ＳｉＯｘ粒子からなる粉末が得られる。 In general, when oxygen is turned off, it is said that almost all SiO is disproportionated and separated 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 ° C. to 1200 ° C. for 1 hour to 5 hours in an inert atmosphere such as in a vacuum or an inert gas. Thus, a powder composed of SiO x particles including two phases of an amorphous SiO 2 phase and a crystalline Si phase is obtained.
またＬｉ吸蔵粒子は、ＳｉＯ系粒子と、炭素材料からなりＳｉＯ系粒子の表面を被覆する被覆層と、からなることが望ましい。被覆層を有することでＳｉＯ系粒子とフッ酸などとの反応をさらに防止することができ、リチウムイオン二次電池のサイクル特性が向上する。被覆層の炭素材料としては、天然黒鉛、人造黒鉛、コークス、メソフェーズ炭素、気相成長炭素繊維、ピッチ系炭素繊維、ＰＡＮ系炭素繊維などを用いることができる。また被覆層を形成するには、珪素酸化物と炭素材料前駆体とを混合して焼成するとよい。炭素材料前駆体としては、糖類、グリコール類、ポリピロール等のポリマーなどの有機化合物やアセチレンブラックなど、焼成により炭素材料に転化しうる有機化合物が使用可能である。その他、特許文献１に記載されたメカノフュージョンなどの機械的表面融合処理法、ＣＶＤなどの蒸着法を用いても、被覆層を形成することができる。 The Li storage particles are preferably composed of SiO-based particles and a coating layer made of a carbon material and covering the surface of the SiO-based particles. By having the coating layer, the reaction between the SiO-based particles and hydrofluoric acid can be further prevented, and the cycle characteristics of the lithium ion secondary battery are improved. As the carbon material for the coating layer, natural graphite, artificial graphite, coke, mesophase carbon, vapor-grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber, or the like can be used. In order to form the coating layer, silicon oxide and a carbon material precursor are mixed and fired. As the carbon material precursor, an organic compound that can be converted into a carbon material by firing, such as an organic compound such as a polymer such as sugars, glycols, or polypyrrole, or acetylene black can be used. In addition, the coating layer can be formed using a mechanical surface fusion treatment method such as mechanofusion described in Patent Document 1 or a vapor deposition method such as CVD.
被覆層の形成量は、ＳｉＯ系粒子と被覆層の合計に対して１質量％〜５０質量％とすることができる。被覆層が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。被覆層の形成量は５質量％〜３０質量％の範囲が好ましく、５質量％〜２０質量％の範囲がさらに望ましい。なお、ＳｉＯ系粒子の表面に炭素材料からなる被覆層を備える場合において、ＳｉＯ系粒子の質量には被覆層の質量を含む。被覆層をなす炭素材料は炭素系粒子とは区別される。 The amount of the coating layer formed can be 1% by mass to 50% by mass with respect to the total of the SiO-based particles and the coating layer. If the coating layer is less than 1% by mass, the effect of improving the electrical conductivity cannot be obtained. If the coating layer exceeds 50% by mass, the proportion of SiO x is relatively decreased and the negative electrode capacity is decreased. The formation amount of the coating layer is preferably in the range of 5% by mass to 30% by mass, and more preferably in the range of 5% by mass to 20% by mass. In addition, when providing the coating layer which consists of carbon materials on the surface of SiO type particle | grains, the mass of a coating layer is included in the mass of SiO type particle | grains. The carbon material forming the coating layer is distinguished from carbon-based particles.
Ｌｉ吸蔵粒子はＤ５０が１μｍ〜１０μｍの範囲にあることが望ましい。Ｄ５０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、Ｄ５０が１μｍより小さいと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。 Li occlusion particles is desirably D 50 is in the range of 1 m to 10 m. When D 50 is larger than 10 μm, the charge / discharge characteristics of the lithium ion secondary battery are deteriorated. When D 50 is smaller than 1 μm, the particles are aggregated into coarse particles, so that the charge / discharge characteristics of the lithium ion secondary battery are similarly decreased. There is a case.
炭素系粒子とＬｉ吸蔵粒子との混合比率は、質量比で炭素系粒子：Ｌｉ吸蔵粒子＝５５：２７〜４５：３７の範囲とするのが好ましい。質量比で炭素系粒子：Ｌｉ吸蔵粒子＝５５：２７より炭素系粒子の質量比が大きくなると容量が減少するため好ましくなく、炭素系粒子：Ｌｉ吸蔵粒子＝４５：３７より炭素系粒子の質量比が小さくなるとサイクル特性が悪化するため好ましくない。炭素系粒子とＬｉ吸蔵粒子との混合物と、導電助剤と、バインダー樹脂とを合計した質量を１００質量％とした時、炭素系粒子は４０質量％以上６５質量％以下の範囲で混合されていることが好ましい。炭素系粒子が４０質量％未満では、リチウムイオン二次電池のサイクル特性の向上を図ることが困難となる。また炭素系粒子が６５質量％を超えて混合されても、理由は不明であるが、炭素系粒子が６５質量％以下の場合に比べてリチウムイオン二次電池のサイクル特性が低下する。さらに炭素系粒子の混合量は、４５質量％〜６５質量％の範囲がより最適である。 The mixing ratio of the carbon-based particles and the Li storage particles is preferably in the range of carbon-based particles: Li storage particles = 55: 27 to 45:37 by mass ratio. When the mass ratio of carbon-based particles: Li occluded particles = 55: 27 is larger than the mass ratio, the capacity decreases, which is not preferable. Carbon-based particles: Li occluded particles = 45: 37. If becomes small, the cycle characteristics deteriorate, which is not preferable. When the total mass of the mixture of carbon-based particles and Li storage particles, the conductive additive, and the binder resin is 100% by mass, the carbon-based particles are mixed in the range of 40% by mass to 65% by mass. Preferably it is. When the carbon-based particles are less than 40% by mass, it is difficult to improve the cycle characteristics of the lithium ion secondary battery. Even if the carbon-based particles are mixed in excess of 65% by mass, the reason is unknown, but the cycle characteristics of the lithium ion secondary battery are deteriorated as compared with the case where the carbon-based particles are 65% by mass or less. Furthermore, the mixing amount of the carbon-based particles is more optimal in the range of 45% by mass to 65% by mass.
炭素系粒子のＤ５０（Ｄ１）とＬｉ吸蔵粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）は、１を超えかつ２以下とする。この比が２を超えると粒径差が大きくなり、負極活物質層が小さな気孔を多数有するようにすることが困難となる。 The ratio of D 50 (D 2) of the D 50 (D 1) and Li occlusion particles of the carbon-based particles (D 1 / D 2) shall be greater than 1 and 2 below. When this ratio exceeds 2, the particle size difference becomes large, and it becomes difficult for the negative electrode active material layer to have many small pores.
気孔は真球に近い形状であることが望ましく、気孔の短径（ａ）と長径（ｂ）との比（ａ／ｂ）が１に近いことが望ましい。このようにすることで応力集中が防止でき、クラックや剥離を防止することができる。また負極活物質層における気孔の合計容積は、Ｌｉ吸蔵粒子の合計体積より小さいことが望ましい。気孔の合計容積がＬｉ吸蔵粒子の合計体積より大きくなると、電極の体積あたりの容量が低下するとともに容量維持率が低下する。 The pores preferably have a shape close to a true sphere, and the ratio (a / b) between the short diameter (a) and the long diameter (b) of the pores is preferably close to 1. By doing so, stress concentration can be prevented, and cracking and peeling can be prevented. The total volume of pores in the negative electrode active material layer is desirably smaller than the total volume of Li storage particles. When the total volume of the pores is larger than the total volume of the Li storage particles, the capacity per volume of the electrode is lowered and the capacity maintenance rate is lowered.
本発明のリチウムイオン二次電池の負極は、集電体と、集電体上に結着された負極活物質層と、を有する。負極活物質層は、炭素系粒子とＬｉ吸蔵粒子との混合物と、導電助剤と、バインダー樹脂と、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集電体上に塗布し、プレスして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。この負極活物質層の厚さ（ｔ）は、従来と同様に１０μｍ〜２０μｍとすることができる。 The negative electrode of the lithium ion secondary battery of the present invention has a current collector and a negative electrode active material layer bound on the current collector. The negative electrode active material layer is prepared by adding a mixture of carbon-based particles and Li occlusion particles, a conductive additive, a binder resin, and an appropriate amount of an organic solvent, and mixing them into a slurry. It can be produced by coating on a current collector by a method such as a coating method, a doctor blade method, a spray coating method, or a curtain coating method, and pressing to cure the binder resin. The thickness (t) of this negative electrode active material layer can be set to 10 μm to 20 μm as in the conventional case.
炭素系粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）は、１／４以上かつ５／６以下とする。この比（Ｄ１／ｔ）が１／４未満では、負極活物質層の電気抵抗が大きくなってリチウムイオン二次電池の充放電効率が低下し、５／６を超えると負極活物質層にクラックや剥離が生じやすくなる。この比（Ｄ１／ｔ）は、１／２以上かつ２／３以下とすることが特に望ましい。 The ratio (D 1 / t) between D 50 (D 1 ) of the carbon-based particles and the thickness (t) of the negative electrode active material layer is set to ¼ or more and 5/6 or less. If this ratio (D 1 / t) is less than ¼, the electrical resistance of the negative electrode active material layer increases, and the charge / discharge efficiency of the lithium ion secondary battery decreases. Cracks and peeling easily occur. This ratio (D 1 / t) is particularly preferably 1/2 or more and 2/3 or less.
また、Ｌｉ吸蔵粒子のＤ５０（Ｄ２）と負極活物質層の厚さ（ｔ）との比（Ｄ２／ｔ）は、上述した炭素系粒子のＤ５０（Ｄ１）とＬｉ吸蔵粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）と、炭素系粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）との関係から、１／８以上かつ２／３以下とする。 In addition, the ratio (D 2 / t) between D 50 (D 2 ) of the Li storage particles and the thickness (t) of the negative electrode active material layer is such that D 50 (D 1 ) of the carbon-based particles and the Li storage particles described above. the ratio of D 50 (D 2) of (D 1 / D 2), and the ratio of D 50 (D 1) and the anode active material layer thickness of the carbon-based particles (t) (D 1 / t ) From the above relationship, it should be 1/8 or more and 2/3 or less.
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できるが、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。上記した炭素系粒子も導電助剤として機能するが、炭素質微粒子であるカーボンブラック、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できる。導電助剤の使用量については、特に限定されない。なお炭素材料からなる被覆層をもつLi吸蔵粒子を用いる場合は、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. The carbon-based particles described above also function as a conductive additive, but carbon black, acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used. It can add individually or in combination of 2 or more types. There is no particular limitation on the amount of conductive aid used. When Li storage particles having a coating layer made of a carbon material are used, the amount of 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、その量は炭素系粒子とＬｉ吸蔵粒子との混合物と、導電助剤と、バインダー樹脂とを合計したものの０．５質量％〜５０質量％が望ましい。バインダー樹脂量が０．５質量％未満では電極の成形性が低下し、５０質量％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、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、ポリアミドイミド、ポリアミドイミドシリカハイブリッド等のイミド系ポリマー、アルコキシシリル基含有樹脂、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。中でも結着性に優れた高結着性バインダーが好ましく、ポリアミドイミド樹脂、ポリアミドイミドシリカハイブリッド及びポリアクリル酸から選ばれる少なくとも一種が特に望ましい。 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 little amount as possible, and the amount is 0.5 mass of the total of the mixture of carbon-based particles and Li storage particles, the conductive auxiliary agent, and the binder resin. % To 50% by mass is desirable. When the amount of the binder resin is less than 0.5% by mass, the moldability of the electrode is deteriorated. In addition, as binder resins, fluorinated polymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubbers such as styrene butadiene rubber (SBR), imides such as polyimide, polyamideimide, and polyamideimide silica hybrid Examples thereof include polymers, alkoxysilyl group-containing resins, 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 high binding binder having excellent binding properties is preferable, and at least one selected from a polyamideimide resin, a polyamideimide silica hybrid, and polyacrylic acid is particularly desirable.
本発明のリチウムイオン二次電池における負極には、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ない。 The negative electrode in the lithium ion secondary battery of the present invention is desirably pre-doped with lithium. 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 amount of lithium doped is not particularly limited.
リチウムをドープすることにより、あるいは本発明の第２の実施形態のリチウムイオン二次電池の初回充電後には、負極活物質のＳｉＯ系粒子のＳｉＯ２相にＬｉｘＳｉｙＯｚで表される酸化物系化合物が含まれている。ＬｉｘＳｉｙＯｚとしては、例えばｘ＝０、ｙ＝１、ｚ＝２のＳｉＯ２、ｘ＝２、ｙ＝１、ｚ＝３のＬｉ２ＳｉＯ３、ｘ＝４、ｙ＝１、ｚ＝４のＬｉ４ＳｉＯ４などが例示される。例えばｘ＝４、ｙ＝１、ｚ＝４のＬｉ４ＳｉＯ４は下記の反応により生成し、クーロン効率は約７７％と計算される。
２ＳｉＯ ＋ ８.６Ｌｉ＋ ＋ ８.６ｅ− → １.５Ｌｉ４.４Ｓｉ ＋ １/２Ｌｉ４ＳｉＯ４
By doping lithium or after the initial charging of the lithium ion secondary battery of the second embodiment of the present invention, the SiO 2 phase of the SiO-based particles of the negative electrode active material is expressed as Li x Si y O z Oxide compounds are included. As Li x Si y O z , for example, x = 0, y = 1, z = 2 SiO 2 , x = 2, y = 1, z = 3 Li 2 SiO 3 , x = 4, y = 1, Examples thereof include Li 4 SiO 4 with z = 4. For example, Li 4 SiO 4 with x = 4, y = 1 and z = 4 is produced by the following reaction, and the Coulomb efficiency is calculated to be about 77%.
2SiO + 8.6Li + + 8.6e− → 1.5Li 4.4 Si + 1 / 2Li 4 SiO 4
また上記反応が途中で停止した場合には、下記の反応のようにｘ＝２、ｙ＝１、ｚ＝３のＬｉ２ＳｉＯ３とｘ＝４、ｙ＝１、ｚ＝４のＬｉ４ＳｉＯ４の両者が生成し、この場合のクーロン効率も約７７％と計算される。
２ＳｉＯ ＋ ７.３５Ｌｉ＋ ＋ ７.３５ｅ− → １.４２Ｌｉ４Ｓｉ ＋ １/３Ｌｉ２ＳｉＯ３ ＋ １/４Ｌｉ４ＳｉＯ４
Further, when the reaction is stopped halfway, x = 2, y = 1 , z = 3 of Li 2 SiO 3 and x = 4, y = 1, z = 4 in Li 4 SiO as the following reaction 4 is generated, and the Coulomb efficiency in this case is also calculated to be about 77%.
2SiO + 7.35Li + + 7.35e− → 1.42Li 4 Si + 1 / 3Li 2 SiO 3 + 1 / 4Li 4 SiO 4
上記反応によって生成するＬｉ４ＳｉＯ４は、充放電時の電極反応に関与しない不活性な物質であり、充放電時の活物質の体積変化を緩和する働きをする。したがってＳｉＯ系粒子のＳｉＯ２相にＬｉｘＳｉｙＯｚで表される酸化物系化合物が含まれる場合には、本発明のリチウムイオン二次電池はサイクル特性がさらに向上する。 Li 4 SiO 4 produced by the above reaction is an inert substance which does not participate in the electrode reaction during charging and discharging and relieve a volume change of the active material during charging and discharging. Therefore, when the oxide compound represented by Li x Si y O z is contained in the SiO 2 phase of the SiO-based particles, the cycle characteristics of the lithium ion secondary battery of the present invention are further improved.
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できる。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、Ｌｉ２ＭｎＯ３、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 lithium metal, LiCoO 2 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 , Li 2 MnO 3 , 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、たとえばフルオロエチレンカーボネート（ＦＥＣ）、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）、メチルエチルカーボネート（ＭＥＣ）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, from aprotic organic solvents such as fluoroethylene carbonate (FEC), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), etc. One or more selected can be used. As the electrolyte to be dissolved, a lithium metal salt that is 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できる。 For example, a lithium metal salt such as LiClO 4 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 or the like in an organic solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate is about 0.5 mol / l to 1.7 mol / l. A solution dissolved in a concentration 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でき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 electrolyte 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＞
ＳｉＯ粉末を９００℃で２時間熱処理し、Ｄ５０が６．５μｍ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>
The SiO powder was heat-treated at 900 ° C. for 2 hours to prepare a SiO x powder having a D 50 of 6.5 μm. With this heat treatment, if the silicon monoxide SiO is a homogeneous solid having a ratio of Si to O of approximately 1: 1, it is separated into two phases of Si phase and SiO 2 phase by solid internal reaction. The Si phase obtained by separation is very fine.
得られたＳｉＯｘ粉末３２質量部と、Ｄ５０が９．２μｍの黒鉛粉末５０質量部と、カーボンブラック８質量部と、バインダー溶液１０質量部とを混合してスラリーを調製した。バインダー溶液は、ポリアミドイミド樹脂をＮ-メチル-２-ピロリドン（ＮＭＰ）に溶解したものを用いた。このスラリーを、厚さ約２０μｍ〜３０μｍ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。その後、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。これを真空乾燥し、負極活物質層の厚さが１５μｍの負極を形成した。 A slurry was prepared by mixing 32 parts by mass of the obtained SiO x powder, 50 parts by mass of graphite powder having a D 50 of 9.2 μm, 8 parts by mass of carbon black, and 10 parts by mass of a binder solution. As the binder solution, a polyamideimide resin dissolved in N-methyl-2-pyrrolidone (NMP) was used. This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of about 20 μm to 30 μm by using a doctor blade to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely joined by a roll press. This was vacuum dried to form a negative electrode having a negative electrode active material layer thickness of 15 μm.
この負極において、黒鉛粒子のＤ５０（Ｄ１）とＳｉＯｘ粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）は１．４２であり、黒鉛粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）は０．６１である。 In this negative electrode, the ratio of D 50 (D 2) of D 50 (D 1) and SiO x particles of the graphite particles (D 1 / D 2) is 1.42, D 50 of the graphite particles (D 1) And the thickness (t) of the negative electrode active material layer (D 1 / t) is 0.61.
＜正極の作製＞
正極活物質としてのＬ３３３（Ｌｉ［Ｍｎ１／３Ｎｉ１／３Ｃｏ１／３］Ｏ２）と、導電助剤としてのアセチレンブラック（ＡＢ）と、バインダー樹脂としてのポリフッ化ビニリデン（ＰＶＤＦ）とを混合し、スラリー状の正極合材を調製した。スラリー中の各成分（固形分）の組成比は、Ｌ３３３：ＡＢ：ＰＶＤＦ＝８８：６：６（質量比）であった。このスラリーを集電体に塗布し、集電体上に正極合材層を積層形成した。具体的には、ドクターブレードを用いてこのスラリーを厚さ２０μｍのアルミニウム箔（集電体）の表面に塗布した。
<Preparation of positive electrode>
L333 (Li [Mn 1/3 Ni 1/3 Co 1/3 ] O 2 ) as a positive electrode active material, acetylene black (AB) as a conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as a binder resin Were mixed to prepare a slurry-like positive electrode mixture. The composition ratio of each component (solid content) in the slurry was L333: AB: PVDF = 88: 6: 6 (mass ratio). This slurry was applied to a current collector, and a positive electrode mixture layer was laminated on the current collector. Specifically, this slurry was applied to the surface of an aluminum foil (current collector) having a thickness of 20 μm using a doctor blade.
その後、８０℃で２０分間乾燥し、正極合材中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、電極密度を調整した。これを真空乾燥炉にて２００℃で２時間加熱硬化させて、集電体の上層に厚さ５０μｍ程度の正極合材層が積層されてなる正極を得た。 Then, it dried at 80 degreeC for 20 minute (s), the organic solvent was volatilized and removed from the positive mix. After drying, the electrode density was adjusted with a roll press. This was heat-cured at 200 ° C. for 2 hours in a vacuum drying furnace to obtain a positive electrode in which a positive electrode mixture layer having a thickness of about 50 μm was laminated on the upper layer of the current collector.
＜リチウムイオン二次電池の作製＞
正極を３０ｍｍ×２５ｍｍ、負極を３１ｍｍ×２６ｍｍに裁断し、ラミネートフィルムで収容した。この正極および負極の間に、セパレータとしてポリプロピレン樹脂からなる矩形状シート(４０ｍｍ×４０ｍｍ角、厚さ３０μｍ）を挟装して極板群とした。この極板群を二枚一組のラミネートフィルムで覆い、三辺をシールした後、袋状となったラミネートフィルムに上記の電解液を注入した。その後、残りの一辺をシールすることで、四辺が気密にシールされ、極板群および電解液が密閉されたラミネートセルを得た。電解液にはＦＥＣ（フルオロエチレンカーボネート）、ＥＣ（エチレンカーボネート）、ＭＥＣ（メチルエチルカーボネート）、ＤＭＣ（ジメチルカーボネート）＝０．４：２．６：３：４（体積比）の混合溶液にＬｉＰＦ６を１モル／Ｌとなる濃度で溶解したものを用いた。正極および負極は外部と電気的に接続可能なタブを備え、このタブの一部はラミネートセルの外側に延出した。以上の工程で、ラミネートセル(２極ポーチセル)状のリチウムイオン二次電池を得た。
<Production of lithium ion secondary battery>
The positive electrode was cut into 30 mm × 25 mm and the negative electrode was cut into 31 mm × 26 mm, and accommodated with a laminate film. A rectangular sheet (40 mm × 40 mm square, thickness 30 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then the above electrolyte was poured into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a laminate cell in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. For the electrolyte, a mixed solution of FEC (fluoroethylene carbonate), EC (ethylene carbonate), MEC (methyl ethyl carbonate), DMC (dimethyl carbonate) = 0.4: 2.6: 3: 4 (volume ratio) is LiPF. 6 was dissolved at a concentration of 1 mol / L. The positive electrode and the negative electrode were provided with a tab that could be electrically connected to the outside, and a part of this tab extended to the outside of the laminate cell. A lithium ion secondary battery in the form of a laminate cell (bipolar pouch cell) was obtained through the above steps.
Ｄ５０が９．２μｍの黒鉛粉末に代えてＤ５０が１２．５μｍの黒鉛粉末を用いたこと以外は実施例１と同様にして負極を形成した。この負極においては、黒鉛粒子のＤ５０（Ｄ１）とＳｉＯｘ粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）は１．９２であり、黒鉛粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）は０．８３である。 A negative electrode was formed in the same manner as in Example 1 except that graphite powder having D 50 of 12.5 μm was used instead of graphite powder having D 50 of 9.2 μm. In this negative electrode, the ratio of the D 50 of the graphite particles (D 1) and D 50 of the SiO x particulate (D 2) (D 1 / D 2) is 1.92, the graphite particles D 50 (D 1 ) And the thickness (t) of the negative electrode active material layer (D 1 / t) is 0.83.
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成した。 Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1.
実施例1と同様のＳｉＯｘ粉末４２質量部と、Ｄ５０が９．２μｍの黒鉛粉末４０質量部と、カーボンブラック３質量部と、バインダー溶液１５質量部とを混合してスラリーを調製した。バインダー溶液は、ポリアミドイミド樹脂をＮ-メチル-２-ピロリドン（ＮＭＰ）に溶解したものを用いた。 Similar SiO x powder 42 parts Example 1, D 50 and the graphite powder 40 parts by weight of 9.2 .mu.m, and carbon black 3 parts by weight, were mixed with a binder solution 15 parts by weight to prepare a slurry. As the binder solution, a polyamideimide resin dissolved in N-methyl-2-pyrrolidone (NMP) was used.
このスラリーを用いたこと以外は実施例１と同様にして負極を形成した。この負極においては、黒鉛粒子のＤ５０（Ｄ１）とＳｉＯｘ粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）は１．９２であり、黒鉛粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）は０．６１である。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成した。 A negative electrode was formed in the same manner as in Example 1 except that this slurry was used. In this negative electrode, the ratio of the D 50 of the graphite particles (D 1) and D 50 of the SiO x particulate (D 2) (D 1 / D 2) is 1.92, the graphite particles D 50 (D 1 ) And the thickness (t) of the negative electrode active material layer (D 1 / t) is 0.61. Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1.
（比較例１）
Ｄ５０が９．２μｍの黒鉛粉末に代えてＤ５０が２０．０μｍの黒鉛粉末を用いたこと以外は実施例１と同様にして負極を形成した。この負極においては、黒鉛粒子のＤ５０（Ｄ１）とＳｉＯｘ粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）は３．０８であり、黒鉛粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）は１．３３である。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成した。
(Comparative Example 1)
A negative electrode was formed in the same manner as in Example 1 except that graphite powder having D 50 of 20.0 μm was used instead of graphite powder having D 50 of 9.2 μm. In this negative electrode, the ratio of the D 50 of the graphite particles (D 1) and D 50 of the SiO x particulate (D 2) (D 1 / D 2) is 3.08, the graphite particles D 50 (D 1 ) And the thickness (t) of the negative electrode active material layer (D 1 / t) is 1.33. Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1.
（比較例２）
Ｄ５０が９．２μｍの黒鉛粉末に代えてＤ５０が２０．０μｍの黒鉛粉末を用いたこと以外は実施例３と同様にして負極を形成した。この負極においては、黒鉛粒子のＤ５０（Ｄ１）とＳｉＯｘ粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）は３．０８であり、黒鉛粒子のＤ５０（Ｄ１）と負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）は０．６１である。この負極を用い、実施例３と同様にしてリチウムイオン二次電池を作成した。
(Comparative Example 2)
A negative electrode was formed in the same manner as in Example 3 except that graphite powder having D 50 of 20.0 μm was used instead of graphite powder having D 50 of 9.2 μm. In this negative electrode, the ratio of the D 50 of the graphite particles (D 1) and D 50 of the SiO x particulate (D 2) (D 1 / D 2) is 3.08, the graphite particles D 50 (D 1 ) And the thickness (t) of the negative electrode active material layer (D 1 / t) is 0.61. Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 3.
＜試験＞
実施例２と比較例１で形成された負極の断面をＳＥＭで観察した。そのＳＥＭ像を図１及び図２に示す。比較例１に比べて実施例２の方が小さな気孔が多く形成されていることがわかる。実施例１、２及び比較例１のリチウムイオン二次電池に対し、充放電電流密度０．２ｍＡｃｍ−２にて１サイクル目の定電流充放電試験を行い、２サイクル目以降は充放電電流密度０．５ｍＡｃｍ−２で行った。電位範囲は、リチウム基準電位で０Ｖ〜３．０Ｖであり、試験は室温下で行った。１サイクル目以降は、負極中の活物質であるＳｉＯｘのＳｉＯ２相に、Ｌｉ４ＳｉＯ４を含みＬｉｘＳｉｙＯｚで表される酸化物系化合物が生成している。充放電サイクル試験中の各サイクルにおいて、放電開始から１０秒後における負極の抵抗値（放電ＩＲドロップ）をそれぞれ測定し、４００サイクルまでの結果を図３に示す。
<Test>
The cross section of the negative electrode formed in Example 2 and Comparative Example 1 was observed with SEM. The SEM images are shown in FIGS. It can be seen that many smaller pores are formed in Example 2 than in Comparative Example 1. The lithium ion secondary batteries of Examples 1 and 2 and Comparative Example 1 were subjected to a constant current charge / discharge test in the first cycle at a charge / discharge current density of 0.2 mAcm −2 , and the charge and discharge current densities in the second and subsequent cycles. Performed at 0.5 mA cm −2 . The potential range was 0 V to 3.0 V at the lithium reference potential, and the test was performed at room temperature. After the first cycle, an oxide-based compound containing Li 4 SiO 4 and represented by Li x Si y O z is generated in the SiO 2 phase of SiO x that is the active material in the negative electrode. In each cycle during the charge / discharge cycle test, the resistance value (discharge IR drop) of the negative electrode 10 seconds after the start of discharge was measured, and the results up to 400 cycles are shown in FIG.
＜評価＞
図３から、実施例１及び実施例２の負極は比較例１に比べて放電ＩＲドロップが低いことから、比（Ｄ１／Ｄ２）が１を超えかつ２以下とすることで導電性に優れた負極を形成できることがわかる。しかも実施例１より実施例２の方が抵抗が低いことから、黒鉛の粒径には最適範囲があることが示唆される。
<Evaluation>
From FIG. 3, since the negative electrode of Example 1 and Example 2 has a lower discharge IR drop than that of Comparative Example 1, the ratio (D 1 / D 2 ) is more than 1 and not more than 2 to make it conductive. It can be seen that an excellent negative electrode can be formed. Moreover, since the resistance of Example 2 is lower than that of Example 1, it is suggested that there is an optimum range for the particle size of graphite.
実施例３と比較例２のリチウムイオン二次電池について上記と同様の定電流充放電試験を行い、５００サイクルまでの負極の抵抗値（放電ＩＲドロップ）の測定結果を図４に示す。比較例２では、４００サイクルを超えてからの抵抗値が実施例３より大きく上昇し、５００サイクルに近いある時点から、大きく上下していることがわかる。これは、比較例２の負極において負極活物質層にクラックが発生したり、負極活物質層が集電体から剥離して導電性が大きく低下したことを示している。 The lithium ion secondary batteries of Example 3 and Comparative Example 2 were subjected to the same constant current charge / discharge test as described above, and the measurement results of the negative electrode resistance value (discharge IR drop) up to 500 cycles are shown in FIG. In Comparative Example 2, it can be seen that the resistance value after exceeding 400 cycles is significantly higher than that in Example 3, and greatly increases and decreases from a certain point close to 500 cycles. This indicates that in the negative electrode of Comparative Example 2, cracks occurred in the negative electrode active material layer, or the negative electrode active material layer peeled off from the current collector, resulting in a significant decrease in conductivity.
Claims (7)
該負極活物質層には炭素系粒子と、リチウムイオンを吸蔵可能なＬｉ吸蔵粒子と、を含み、該炭素系粒子のＤ５０（Ｄ１）と該Ｌｉ吸蔵粒子のＤ５０（Ｄ２）との比（Ｄ１／Ｄ２）が１を超えかつ２以下であり、該炭素系粒子の該Ｄ５０（Ｄ１）と該負極活物質層の厚さ（ｔ）との比（Ｄ１／ｔ）が１／４以上かつ５／６以下であることを特徴とするリチウムイオン二次電池用負極。 A negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer formed on the current collector,
The negative electrode active material layer includes carbon-based particles and Li-occlusion particles capable of occluding lithium ions. The carbon-based particles D 50 (D 1 ) and the Li-occlusion particles D 50 (D 2 ) Ratio (D 1 / D 2 ) of more than 1 and 2 or less, and the ratio of D 50 (D 1 ) of the carbon-based particles to the thickness (t) of the negative electrode active material layer (D 1 / A negative electrode for a lithium ion secondary battery, wherein t) is ¼ or more and 5/6 or less.
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| JP2013110104A (en) * | 2011-10-24 | 2013-06-06 | Toyota Industries Corp | Negative electrode for lithium ion secondary battery, and lithium ion secondary battery including the negative electrode |
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| JP2013110104A (en) * | 2011-10-24 | 2013-06-06 | Toyota Industries Corp | Negative electrode for lithium ion secondary battery, and lithium ion secondary battery including the negative electrode |
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