JP6376884B2 - Negative electrode active material for lithium ion secondary battery, method for producing the same, negative electrode and battery - Google Patents
Negative electrode active material for lithium ion secondary battery, method for producing the same, negative electrode and battery Download PDFInfo
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- 239000007773 negative electrode material Substances 0.000 title claims description 133
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims description 53
- 229910001416 lithium ion Inorganic materials 0.000 title claims description 53
- 238000004519 manufacturing process Methods 0.000 title claims description 21
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 105
- 239000010703 silicon Substances 0.000 claims description 104
- 239000010949 copper Substances 0.000 claims description 88
- 229910052710 silicon Inorganic materials 0.000 claims description 86
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 claims description 61
- 238000010298 pulverizing process Methods 0.000 claims description 58
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 47
- 229910052802 copper Inorganic materials 0.000 claims description 44
- 238000000034 method Methods 0.000 claims description 36
- 239000005751 Copper oxide Substances 0.000 claims description 34
- 229910000431 copper oxide Inorganic materials 0.000 claims description 34
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 30
- 229910001868 water Inorganic materials 0.000 claims description 29
- 239000000203 mixture Substances 0.000 claims description 25
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 24
- 238000002441 X-ray diffraction Methods 0.000 claims description 23
- 229910052760 oxygen Inorganic materials 0.000 claims description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 16
- 239000001301 oxygen Substances 0.000 claims description 16
- 238000002156 mixing Methods 0.000 claims description 15
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical compound [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 claims description 11
- 239000002245 particle Substances 0.000 claims description 10
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 claims description 8
- 239000011149 active material Substances 0.000 claims description 8
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- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 239000007858 starting material Substances 0.000 description 6
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- 238000012360 testing method Methods 0.000 description 5
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- 238000006243 chemical reaction Methods 0.000 description 4
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- 238000001228 spectrum Methods 0.000 description 4
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
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- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
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- 230000008859 change Effects 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 239000011889 copper foil Substances 0.000 description 2
- PTVDYARBVCBHSL-UHFFFAOYSA-N copper;hydrate Chemical compound O.[Cu] PTVDYARBVCBHSL-UHFFFAOYSA-N 0.000 description 2
- 229910021419 crystalline silicon Inorganic materials 0.000 description 2
- 239000007772 electrode material Substances 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
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- 229910052744 lithium Inorganic materials 0.000 description 2
- 239000007774 positive electrode material Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
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- JJLJMEJHUUYSSY-UHFFFAOYSA-L Copper hydroxide Chemical compound [OH-].[OH-].[Cu+2] JJLJMEJHUUYSSY-UHFFFAOYSA-L 0.000 description 1
- 239000005750 Copper hydroxide Substances 0.000 description 1
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
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- XWROUVVQGRRRMF-UHFFFAOYSA-N F.O[N+]([O-])=O Chemical compound F.O[N+]([O-])=O XWROUVVQGRRRMF-UHFFFAOYSA-N 0.000 description 1
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
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- 229910000676 Si alloy Inorganic materials 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
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- 229910001956 copper hydroxide Inorganic materials 0.000 description 1
- WCCJDBZJUYKDBF-UHFFFAOYSA-N copper silicon Chemical compound [Si].[Cu] WCCJDBZJUYKDBF-UHFFFAOYSA-N 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 210000001787 dendrite Anatomy 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
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- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
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- JEGUKCSWCFPDGT-UHFFFAOYSA-N h2o hydrate Chemical compound O.O JEGUKCSWCFPDGT-UHFFFAOYSA-N 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
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- 229910052759 nickel 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
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- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
本発明はリチウムイオン二次電池等の二次電池用の負極活物質に関するものであり、特にケイ素、銅、酸素を主要な構成元素とする二次電池用負極活物質およびその製造方法、並びに、その負極活物質を用いた二次電池用負極およびその負極を用いた二次電池に関する。 The present invention relates to a negative electrode active material for a secondary battery such as a lithium ion secondary battery, and in particular, a negative electrode active material for a secondary battery containing silicon, copper and oxygen as main constituent elements, a method for producing the same, and The present invention relates to a negative electrode for a secondary battery using the negative electrode active material and a secondary battery using the negative electrode.
近年、携帯型の電子機器、通信機器等の著しい発展に伴い、経済性と機器の小型化、軽量化の観点から、高エネルギー密度のリチウムイオン二次電池が強く要望されている。従来、この種のリチウムイオン二次電池の高容量化の方策として、正極および正極活物質の改善、負極および負極活物質の改善等、様々な方法が検討されている。負極および負極活物質の改善として、負極活物質にケイ素（シリコン、Ｓｉ）またはケイ素化合物を用いる方法が検討されている。ケイ素は現在実用化されている炭素材料の理論容量３７２ｍＡｈ／ｇより遙かに高い理論容量４２００ｍＡｈ／ｇを示すことから、電池の小型化と高容量化において期待が大きい材料である。また、ケイ素はリチウムと合金化することが可能なため、充放電時のデンドライト発生による内部短絡が起こらない負極材として優れた特長を持っている。 In recent years, with the remarkable development of portable electronic devices, communication devices, and the like, a high energy density lithium ion secondary battery has been strongly demanded from the viewpoint of economy and downsizing and weight reduction of devices. Conventionally, various methods, such as improvement of a positive electrode and a positive electrode active material, improvement of a negative electrode and a negative electrode active material, are examined as a policy of high capacity | capacitance of this kind of lithium ion secondary battery. As an improvement of the negative electrode and the negative electrode active material, a method using silicon (silicon, Si) or a silicon compound as the negative electrode active material has been studied. Since silicon shows a theoretical capacity of 4200 mAh / g, which is much higher than the theoretical capacity of 372 mAh / g of carbon materials currently in practical use, it is a material that is highly expected in miniaturization and increase in capacity of batteries. Further, since silicon can be alloyed with lithium, it has an excellent feature as a negative electrode material that does not cause an internal short circuit due to generation of dendrites during charging and discharging.
例えば、特開平５−０７４４６３号公報（特許文献１）には、単結晶ケイ素を負極活物質の支持体として使用したリチウムイオン二次電池が開示されている。また、負極材に導電性を付与することを目的として、特開２０００−２４３３９６号公報（特許文献２）には、酸化ケイ素と黒鉛とをメカニカルアロイングした後、炭化処理する技術が、特開２０００−２１５８８７号公報（特許文献３）には、ケイ素粒子表面を化学蒸着法により炭素層で被覆する技術が、それぞれ開示されている。これらの従来技術の場合、ケイ素粒子表面に炭素層を設けることにより、負極材の導電性を改善することは可能であるが、充放電に伴う大きな体積変化に起因するケイ素負極活物質の低いサイクル特性という課題を解決することはできなかった。
ケイ素はリチウムと合金化した場合、体積が最大４倍程度に膨張する。そのため、充放電サイクルを繰り返すと、ケイ素粒子内に大きな内部歪が生じ、ケイ素粒子が微粉化することによりサイクル特性が低下すると考えられている。ケイ素負極活物質のもつ低いサイクル特性という課題を解決するために、様々な方法が検討されている。特開２００４−３３５２７１号公報（特許文献４）には、ケイ素とチタン、ニッケル、銅等の金属をボールミルでメカニカルアロイし、負極活物質を得る技術が開示されている。特開２０１０−２４４７６７号公報（特許文献５）には、ケイ素粒子と銅粒子を乾式アトライタで処理して、負極活物質を得る技術が開示されている。特開２０１２−１１３９４５号公報（特許文献６）には、ケイ素の粗粉をビーズミルで破砕し、引き続き導電性基材粉として銅粉を加え、せん断応力を加えることにより凝集体を得る技術が開示されている。しかし、これらの技術を用いても、負極活物質単位質量あたりの電池容量やサイクル特性等の、負極活物質に起因する電池特性の改良は現時点では十分とは言えず、ケイ素を用いた負極活物質を使用した二次電池が広く使用されるには至っていないのが現状である。
For example, JP-A-5-074463 (Patent Document 1) discloses a lithium ion secondary battery using single crystal silicon as a support for a negative electrode active material. In addition, for the purpose of imparting conductivity to the negative electrode material, Japanese Patent Laid-Open No. 2000-243396 (Patent Document 2) discloses a technique in which silicon oxide and graphite are mechanically alloyed and then carbonized. Japanese Patent Application Laid-Open No. 2000-215887 (Patent Document 3) discloses a technique of coating the surface of silicon particles with a carbon layer by a chemical vapor deposition method. In the case of these prior arts, it is possible to improve the conductivity of the negative electrode material by providing a carbon layer on the surface of the silicon particles, but the low cycle of the silicon negative electrode active material due to the large volume change accompanying charge / discharge The problem of characteristics could not be solved.
When silicon is alloyed with lithium, the volume expands up to about 4 times. For this reason, it is considered that when the charge / discharge cycle is repeated, a large internal strain is generated in the silicon particles, and the cycle characteristics are deteriorated by pulverization of the silicon particles. In order to solve the problem of low cycle characteristics of the silicon negative electrode active material, various methods have been studied. Japanese Patent Application Laid-Open No. 2004-335271 (Patent Document 4) discloses a technique for obtaining a negative electrode active material by mechanically alloying silicon and a metal such as titanium, nickel, copper and the like with a ball mill. Japanese Unexamined Patent Application Publication No. 2010-244767 (Patent Document 5) discloses a technique for obtaining a negative electrode active material by treating silicon particles and copper particles with a dry attritor. Japanese Patent Laid-Open No. 2012-113945 (Patent Document 6) discloses a technique for obtaining an agglomerate by crushing coarse silicon powder with a bead mill, subsequently adding copper powder as a conductive base material powder, and applying shear stress. Has been. However, even with these technologies, improvement of battery characteristics due to the negative electrode active material, such as battery capacity per unit mass of the negative electrode active material and cycle characteristics, cannot be said to be sufficient at present. At present, secondary batteries using materials have not been widely used.
ケイ素またはケイ素化合物を用いる負極活物質は、その高い理論容量から、電池の小型化と高容量化において期待が大きいが、負極活物質単位質量あたりの電池容量とサイクル特性を同時に一定以上の水準にすることは、現時点ではできていない。本発明で解決しようとする課題は、サイクル特性が良好であり、リチウムイオン二次電池用負極活物資として実用可能な程度に大きな電池容量を持つ負極活物質とその製造方法を提供することである。また、この負極活物質を用いた負極および二次電池、およびこれらの製造方法を提供することである。 Negative electrode active materials using silicon or silicon compounds are highly expected in terms of battery miniaturization and capacity increase due to their high theoretical capacity, but the battery capacity per unit mass of negative electrode active material and cycle characteristics are simultaneously at a certain level or higher. This is not possible at this time. The problem to be solved by the present invention is to provide a negative electrode active material having good cycle characteristics and a battery capacity large enough to be practically used as a negative electrode active material for a lithium ion secondary battery, and a method for producing the same. . Moreover, it is providing the negative electrode and secondary battery which used this negative electrode active material, and these manufacturing methods.
本発明者らが鋭意検討した結果、ケイ素と酸化銅（２）を粉砕手段に投入し粉砕処理を行うと同時に、粉砕物を混合することにより、また、ケイ素と金属銅（すなわち銅（０））および水を粉砕手段に投入し粉砕処理を行うと同時に、粉砕物を混合することにより、ケイ素、銅、酸素を主要な構成元素とする二次電池用負極活物質得られ、この本発明の二次電池用負極活物質は、サイクル特性が良好であり、リチウムイオン二次電池用負極活物資として実用可能な程度に大きな電池容量を持つ負極活物質であることを見出し、本発明を完成するに至った。なお、酸化銅のあとのカッコ内の数字は、酸化数を表すもので、本来、ローマ数字で表記すべきものである。
特許文献４〜６に記載されているケイ素と金属銅に対してせん断力を加えることにより得られる負極活物質と比較して、本発明の負極活物質のサイクル特性が良好である理由は現時点で特定できていないが、本発明者らは、以下のように推定している。
本発明の負極活物質は、ケイ素および酸化銅、またはケイ素と金属銅と水とを粉砕手段中に投入し、粉砕と混合を同時に行うことにより得られるが、この粉砕および混合の過程において、原料としてケイ素と酸化銅を用いた場合には、ケイ素が酸化銅を一部還元し、ケイ素自体は一部酸化すると考えられる。また、原料としてケイ素、酸化銅と水とを用いた場合には、ケイ素が水と反応し、一部酸化するものと考えられる。すなわち、このケイ素が一部酸化した反応生成物が負極活物質中に存在することにより、サイクル特性が向上していると考えられる。
As a result of intensive studies by the present inventors, silicon and copper oxide (2) are put into a pulverizing means and pulverized, and at the same time, by mixing the pulverized material, silicon and metal copper (ie, copper (0)) ) And water are added to the pulverizing means, and at the same time, the pulverized product is mixed to obtain a negative electrode active material for a secondary battery containing silicon, copper, and oxygen as main constituent elements. The negative electrode active material for secondary batteries has good cycle characteristics, and is found to be a negative electrode active material having a battery capacity large enough for practical use as a negative electrode active material for lithium ion secondary batteries, thereby completing the present invention. It came to. The number in parentheses after the copper oxide represents the oxidation number, and should be originally expressed in Roman numerals.
The reason why the cycle characteristics of the negative electrode active material of the present invention are good compared to the negative electrode active material obtained by applying a shearing force to silicon and metallic copper described in Patent Documents 4 to 6 at present is Although not specified, the present inventors presume as follows.
The negative electrode active material of the present invention can be obtained by adding silicon and copper oxide, or silicon, metallic copper and water into a pulverizing means, and performing pulverization and mixing at the same time. When silicon and copper oxide are used, it is considered that silicon partially reduces copper oxide and silicon itself is partially oxidized. Further, when silicon, copper oxide and water are used as raw materials, it is considered that silicon reacts with water and is partially oxidized. That is, it is considered that the cycle characteristics are improved by the presence of the reaction product in which the silicon is partially oxidized in the negative electrode active material.
上記の目的を達成するために、本発明は、以下を提供する。すなわち、
Ｃｕ3ＳｉおよびＸ線回折法により測定されるＳｉの平均結晶子径（Ｄx）が５０ｎｍ以下、好ましくは２０ｎｍ以下のケイ素の微粒子を含み、モル比で 示される元素組成比Ｃｕ／（Ｓｉ＋Ｃｕ＋Ｏ）およびＯ／（Ｓｉ＋Ｃｕ＋Ｏ）が、０.０２〜０.３０、好ましくは０.０４〜０.２０、さらに好ましくは０.０５〜０.１２であり、ＸＲＤの測定結果から算出されるピーク強度比（Ｃｕ3Ｓｉ／Ｓｉ）が０.０５から１.５であるリチウムイオン二次電池用負極活物質が提供される。このリチウムイオン二次電池用負極活物質は、その構成物質として非晶質のケイ素酸化物を含むものであって良く、その場合、ＸＰＳの測定結果から算出される負極活物質のピーク面積比（ＳｉＯx／Ｓｉ（０））は０.０６〜０.７２のものであっても良い。
また、本発明においては、リチウムイオン二次電池用負極活物質の製造方法として、以下が提供される。すなわち、第一の実施形態においては、リチウムイオン二次電池用負極活物質の原料として、ケイ素および酸化銅（２）を粉砕手段中に投入し、ケイ素および酸化銅（２）を粉砕するとともに、粉砕されたケイ素および酸化銅（２）を混合する工程を含む、リチウムイオン二次電池用負極活物質の製造方法が提供される。
第二の実施形態においては、リチウムイオン二次電池用負極活物質の原料として、ケイ素、金属銅および水を粉砕手段中に投入し、ケイ素および金属銅を粉砕するとともに、粉砕されたケイ素および金属銅を混合する工程を含む、リチウムイオン二次電池用負極活物質の製造方法が提供される。
また、本発明のリチウムイオン二次電池用負極活物質には、上述の第一および第二の実施形態の製造方法により製造される負極活物質が全て含まれる。
本発明により得られる負極活物質を用いてリチウムイオン二次電池用負極が、またそのリチウムイオン二次電池用負極を用いて、リチウムイオン二次電池を製造することができる。
In order to achieve the above object, the present invention provides the following. That is,
Elemental composition ratio Cu / (Si + Cu + O) represented by molar ratio including fine particles of silicon having an average crystallite diameter (D x ) of 50 nm or less, preferably 20 nm or less, measured by Cu 3 Si and X-ray diffraction method And O / (Si + Cu + O) is 0.02 to 0.30, preferably 0.04 to 0.20, more preferably 0.05 to 0.12, and the peak intensity ratio calculated from the measurement result of XRD Provided is a negative electrode active material for a lithium ion secondary battery having (Cu 3 Si / Si) of 0.05 to 1.5. The negative electrode active material for a lithium ion secondary battery may include an amorphous silicon oxide as a constituent material, and in that case, the peak area ratio of the negative electrode active material calculated from the XPS measurement result ( SiO x / Si (0)) may be from 0.06 to 0.72.
Moreover, in this invention, the following is provided as a manufacturing method of the negative electrode active material for lithium ion secondary batteries. That is, in the first embodiment, as raw materials for the negative electrode active material for the lithium ion secondary battery, silicon and copper oxide (2) are charged into the pulverizing means, and silicon and copper oxide (2) are pulverized. There is provided a method for producing a negative electrode active material for a lithium ion secondary battery, comprising a step of mixing pulverized silicon and copper oxide (2).
In the second embodiment, silicon, metallic copper and water are charged into the pulverizing means as raw materials for the negative electrode active material for the lithium ion secondary battery, and the pulverized silicon and metal are pulverized. There is provided a method for producing a negative electrode active material for a lithium ion secondary battery, comprising a step of mixing copper.
Moreover, the negative electrode active material for lithium ion secondary batteries of the present invention includes all negative electrode active materials produced by the production methods of the first and second embodiments described above.
A negative electrode for a lithium ion secondary battery can be manufactured using the negative electrode active material obtained by the present invention, and a lithium ion secondary battery can be manufactured using the negative electrode for lithium ion secondary battery.
以上、本発明においては、ケイ素と酸化銅（２）、またはケイ素と金属銅と水とを粉砕処理すると同時に粉砕物を混合することにより、ケイ素、銅および酸素を主要な構成元素とするリチウムイオン二次電池用負極活物質が得ることができる。この二次電池用負極活物質は、サイクル特性が良好であり、かつ、リチウムイオン二次電池用負極活物資として実用可能な程度に大きな電池容量を持つ。また、その負極活物質を用いたリチウムイオン二次電池用負極およびリチウムイオン二次電池を得ることができる。 As mentioned above, in the present invention, silicon and copper oxide (2), or silicon, metallic copper and water are pulverized and mixed with the pulverized material, so that lithium ions containing silicon, copper and oxygen as main constituent elements are mixed. A negative electrode active material for a secondary battery can be obtained. This negative electrode active material for a secondary battery has good cycle characteristics and has a battery capacity large enough to be practical as a negative electrode active material for a lithium ion secondary battery. Moreover, the negative electrode for lithium ion secondary batteries and the lithium ion secondary battery using the negative electrode active material can be obtained.
［負極活物質］
本発明のリチウムイオン二次電池用負極活物質は、原料であるケイ素と酸化銅（２）、またはケイ素と金属銅と水とを、公知の粉砕手段中で粉砕処理を行うと同時に、粉砕された原料を混合することにより得られる。原料投入のタイミングは、使用する原料の大きさに依存し、必ずしも同時に投入することを要さないが、後述するケイ素の表面酸化反応の観点から、ケイ素と酸化銅（２）もしくはケイ素と金属銅の粉砕および混合が同時に起こっている時間が必要であり、原料物質を同時に投入することが好ましい。
[Negative electrode active material]
The negative electrode active material for a lithium ion secondary battery of the present invention is pulverized at the same time as pulverization treatment of silicon and copper oxide (2) or silicon, metal copper and water as raw materials in a known pulverizing means. Obtained by mixing the raw materials. The timing of raw material charging depends on the size of the raw material used and does not necessarily need to be charged simultaneously. However, from the viewpoint of the surface oxidation reaction of silicon described later, silicon and copper oxide (2) or silicon and metallic copper The time during which the pulverization and mixing are simultaneously performed is necessary, and it is preferable to add the raw materials simultaneously.
ケイ素と酸化銅（２）を粉砕、混合処理する前の試料についてのＸ線回折（ＸＲＤ）パターンでは酸化銅（２）に対応するピークが観察されるが、各実施例により得られた負極活物質のＸＲＤパターンには、酸化銅（２）に対応するピークは認められない。このことは、粉砕手段中での粉砕、混合処理の際、酸化銅（２）がケイ素により還元され、酸素の一部または全部を失ったためと考えられる。各実施例により得られた負極活物質のＸＲＤパターンには、２θが４４.８°付近にピークが認められ、これはＣｕ3Ｓｉが存在することを示している。また、ケイ素に対応するピークの半値幅が、粉砕処理により増大し、粉砕処理によりケイ素が微結晶化していることが判る。
ケイ素と金属銅と水とを投入して粉砕、混合処理した場合にも、ケイ素に対応するピークの半値幅の増大が観察されるので、この場合にもケイ素の微結晶化が起こっていることは明らかである。
図１に、後述する実施例２および実施例５において得られた負極活物質について、Ｘ線光電子分光分析法（ＸＰＳ）により得られた、ケイ素の２ｐピークのスペクトルを示す。Ｓｉ２ｐスペクトル中には金属状態のケイ素（Ｓｉ（０））に対応するピーク以外に、酸化状態の異なる複数の酸化物に対応するピークが観察され、低級酸化物を含むケイ素の酸化物、すなわちＳｉＯx（ただし０＜ｘ＜２）が存在していることが判る。すなわち、ケイ素と酸化銅（２）を粉砕、混合処理すると、ケイ素は還元剤として作用し、酸化銅（２）の酸素の一部または全部を奪って、ケイ素自体は酸化したものと考えられる。なお、図２は、試料表面をシリコン基板が１０ｎｍの深さでエッチングされる条件でスパッタエッチング行った後に、光電子の取り出し角度４５°で測定を行っている。同様なＳｉ２ｐスペクトルは、ケイ素と金属銅と水とを投入して粉砕、混合処理した場合にも得られており、この場合は、ケイ素と水が反応したものと考えてよい。
In the X-ray diffraction (XRD) pattern of the sample before pulverizing and mixing the silicon and copper oxide (2), a peak corresponding to the copper oxide (2) is observed. No peak corresponding to copper oxide (2) is observed in the XRD pattern of the substance. This is presumably because copper oxide (2) was reduced by silicon and lost part or all of oxygen during pulverization and mixing in the pulverizing means. In the XRD pattern of the negative electrode active material obtained in each example, 2θ has a peak around 44.8 °, which indicates that Cu 3 Si is present. Further, it can be seen that the half width of the peak corresponding to silicon is increased by the pulverization treatment, and silicon is microcrystallized by the pulverization treatment.
Even when silicon, metallic copper, and water are added and pulverized and mixed, an increase in the half-width of the peak corresponding to silicon is observed. In this case, too, silicon microcrystallization occurs. Is clear.
FIG. 1 shows the 2p peak spectrum of silicon obtained by X-ray photoelectron spectroscopy (XPS) for the negative electrode active materials obtained in Examples 2 and 5 described later. In the Si2p spectrum, peaks corresponding to a plurality of oxides having different oxidation states are observed in addition to a peak corresponding to silicon (Si (0)) in the metal state, and an oxide of silicon including a lower oxide, that is, SiO. It can be seen that x (where 0 <x <2) exists. That is, when silicon and copper oxide (2) are pulverized and mixed, silicon acts as a reducing agent, depriving part or all of oxygen in copper oxide (2), and silicon itself is considered to be oxidized. In FIG. 2, the surface of the sample is subjected to sputter etching under the condition that the silicon substrate is etched to a depth of 10 nm, and then the measurement is performed at a photoelectron take-off angle of 45 °. A similar Si2p spectrum is also obtained when pulverized and mixed with silicon, metallic copper, and water. In this case, it may be considered that silicon and water have reacted.
以上の測定結果より、本発明の粉砕および混合処理により得られる電極活物質のサイクル特性が向上する機構は、現在のところ不明であるが、例えば以下の様な機構が推定される。
本発明を実施して得られる負極活物質の複合体には、粉砕処理により微結晶化されたケイ素とともに、やはり粉砕処理によりケイ素と原料中の銅が反応して生成したＣｕ3Ｓｉ等の銅−ケイ素化合物が含まれる。このほかに、酸化銅または水の酸素とケイ素が反応して生成したケイ素酸化物が一定以上存在する。後述する比較例２から、従来技術であるケイ素と金属銅を粉砕処理して得られる負極活物質でも、微結晶化されたケイ素とともに、やはり粉砕処理によりケイ素と原料中の銅が反応して生成したＣｕ3Ｓｉ等の銅−ケイ素化合物を含むことがわかる。これらのことから、微結晶化されたケイ素とともに銅元素および酸素元素を一定以上含むことにより、リチウムイオンの吸放出に基づくケイ素の体積膨張、収縮に伴う応力を緩和するものと考えられるが、その詳細な機構は現時点では不明である。本発明の負極活物質に含まれるＣｕ3Ｓｉは、ＸＲＤの測定結果から後述する方法で得られるピーク強度比（Ｃｕ3Ｓｉ／Ｓｉ）が０.０５〜１.５の範囲であることが好ましい。ピーク強度比（Ｃｕ3Ｓｉ／Ｓｉ）が０.０５未満の場合には、サイクル特性が十分向上しない場合があり、１.５を超える場合には、負極活物質に含まれる結晶性のＳｉの割合が少なくなり、初期放電容量が十分得られない場合がある。本発明の電極活物質の複合体には、処理中に還元されない酸化銅（２）の微粒子が極少量含まれることも考えられるが、その存在自体は特に問題とならない。
ケイ素結晶を微細化すると、ケイ素微結晶の体積変動の絶対値が小さくなるため、リチウムイオンの吸放出に伴うケイ素微結晶の体積変化に基づく電池特性の劣化を抑制する観点から、ケイ素結晶をより微細化することが好ましいと考えられる。
本発明において得られるリチウムイオン二次電池用負極活物質中に含まれるケイ素微結晶の平均粒子径は、後述するＸ線回折法（ＸＲＤ）により測定される平均結晶子径（Ｄx）で５０ｎｍ以下が好ましく、より良好なサイクル特性（容量維持率）を得るためには２０ｎｍ以下であることがさらに好ましい。結晶子径が５０ｎｍを超える場合には、サイクル特性が十分向上しない場合があるので、好ましくない。Ｄxの下限は特に限定されないが、粉砕処理によって１ｎｍ未満にすることは困難であり、現実的には１ｎｍ以上となる。
From the above measurement results, the mechanism for improving the cycle characteristics of the electrode active material obtained by the pulverization and mixing treatment of the present invention is currently unknown. For example, the following mechanism is estimated.
The composite of the negative electrode active material obtained by carrying out the present invention includes Cu 3 Si and the like produced by the reaction of silicon and copper in the raw material by the pulverization process together with the silicon crystallized by the pulverization process. -Silicon compounds are included. In addition, there is a certain amount or more of silicon oxide formed by reaction of copper oxide or water oxygen with silicon. From the comparative example 2 described later, the negative electrode active material obtained by pulverizing silicon and metallic copper, which is a conventional technique, is produced by reacting silicon and copper in the raw material by pulverization with the microcrystallized silicon. It can be seen that it contains a copper-silicon compound such as Cu 3 Si. From these facts, it is considered that the stress accompanying the volume expansion and contraction of silicon based on the absorption and release of lithium ions is relieved by including copper element and oxygen element in a certain amount together with microcrystallized silicon. The detailed mechanism is unknown at this time. Cu 3 Si contained in the negative electrode active material of the present invention preferably has a peak intensity ratio (Cu 3 Si / Si) in the range of 0.05 to 1.5 obtained by the method described later from the XRD measurement results. . When the peak intensity ratio (Cu 3 Si / Si) is less than 0.05, the cycle characteristics may not be sufficiently improved, and when it exceeds 1.5, the crystalline Si contained in the negative electrode active material The ratio decreases and the initial discharge capacity may not be sufficiently obtained. Although it is conceivable that the electrode active material composite of the present invention contains a very small amount of copper oxide (2) fine particles that are not reduced during the treatment, its presence is not particularly problematic.
When the silicon crystal is refined, the absolute value of the volume fluctuation of the silicon microcrystal is reduced. Therefore, from the viewpoint of suppressing the deterioration of battery characteristics due to the volume change of the silicon microcrystal accompanying the absorption and release of lithium ions, the silicon crystal is more It is considered preferable to reduce the size.
The average particle diameter of the silicon microcrystals contained in the negative electrode active material for lithium ion secondary batteries obtained in the present invention is 50 nm as an average crystallite diameter (D x ) measured by an X-ray diffraction method (XRD) described later. The following is preferable, and in order to obtain better cycle characteristics (capacity maintenance ratio), the thickness is more preferably 20 nm or less. When the crystallite diameter exceeds 50 nm, the cycle characteristics may not be sufficiently improved, which is not preferable. The lower limit of the D x is not particularly limited, it is difficult to less than 1nm by milling processing, and more 1nm in reality.
本発明のリチウムイオン二次電池用負極活物質は、ケイ素、銅、酸素を主要な構成元素とするものであり、これらの元素のモル比で示される元素組成比Ｃｕ／（Ｓｉ＋Ｃｕ＋Ｏ）およびＯ／（Ｓｉ＋Ｃｕ＋Ｏ）が、それぞれ０.０２〜０.３０であることが好ましい。元素組成比としては、０.０４〜０.２０であることがさらに好ましく、０.０５〜０.１２であることがより好ましい。前記元素組成比が、０.０２未満の場合には、サイクル特性が十分向上しない場合があり、前記元素組成比が、０.３０を超える場合には、活物質単位質量あたりの電池容量が小さくなる場合があるので好ましくない。サイクル特性と活物質単位質量あたりの容量を同時に高くする観点から、前記元素組成比は、０.０４〜０.２０であることが好ましく、０.０５〜０.１２であることが更に好ましい。これらの値は、原料の配合比率を変化させることにより制御することができる。
ケイ素と酸化銅（２）、またはケイ素と銅と水を、ボールミル、ビーズミル等の粉砕手段により、同時に粉砕処理することにより得られる本発明の負極活物質に、ケイ素、銅、酸素以外の構成元素を含む物質が混入していても、その混入量が一定以下であれば、本発明の効果を奏することが可能である。前記のケイ素、銅および酸素を主要な構成元素とするリチウムイオン二次電池用負極活物質とは、負極活物質中のケイ素、銅、酸素の含有量が合計で７０質量％以上であることを意味する。前記含有量は、８０質量％以上が好ましく、９０質量％以上が更に好ましい。
The negative electrode active material for a lithium ion secondary battery of the present invention contains silicon, copper, and oxygen as main constituent elements, and the elemental composition ratios Cu / (Si + Cu + O) and O / (Si + Cu + O) is preferably 0.02 to 0.30, respectively. The elemental composition ratio is more preferably 0.04 to 0.20, and more preferably 0.05 to 0.12. When the elemental composition ratio is less than 0.02, the cycle characteristics may not be sufficiently improved. When the elemental composition ratio exceeds 0.30, the battery capacity per unit active material mass is small. Since it may become, it is not preferable. From the viewpoint of simultaneously increasing the cycle characteristics and the capacity per unit mass of the active material, the elemental composition ratio is preferably 0.04 to 0.20, and more preferably 0.05 to 0.12. These values can be controlled by changing the mixing ratio of the raw materials.
The negative electrode active material of the present invention obtained by simultaneously pulverizing silicon and copper oxide (2), or silicon and copper and water simultaneously by a pulverizing means such as a ball mill and a bead mill, and other constituent elements other than silicon, copper and oxygen Even if a substance containing odor is mixed, the effect of the present invention can be obtained as long as the mixed amount is not more than a certain level. The negative electrode active material for a lithium ion secondary battery having silicon, copper and oxygen as main constituent elements means that the total content of silicon, copper and oxygen in the negative electrode active material is 70% by mass or more. means. The content is preferably 80% by mass or more, and more preferably 90% by mass or more.
［出発物質］
ケイ素
本発明のリチウムイオン二次電池用負極活物質の製造に用いられる出発物質のケイ素としては、ケイ素からなるものであればその形態は特に問わない。市販のシリコン基板（単結晶、多結晶）、原料用多結晶や非晶質ケイ素を始めとした純ケイ素以外に、ケイ素合金も用いることができる。本発明の負極活物質の製造方法には、粉砕手段による粉砕のステップが含まれるので、出発物質のケイ素の大きさは特に規定するものではないが、作業性の観点から、１ｍｍ以下とすることが好ましい。
酸化銅（２）
ケイ素と酸化銅（２）とを、粉砕手段を用いて粉砕と同時に混合することにより、本発明の負極活物質を得ることができる。粉砕処理することによりサイクル特性と電池容量が向上する理由については、現在のところ不明であるが、粉砕の過程で、上述の様に原料のケイ素が微細化するとともに、原料のケイ素と酸化銅中の酸素が部分的に反応することによる反応生成物が生じ、負極活物質中に存在するためと考えられる。出発物質の酸化銅（２）としては、市販の酸化銅（２）粉等、いかなるものでも用いることができる。
金属銅および水
ケイ素と金属銅と水とを、粉砕手段を用いて粉砕すると同時に混合ことにより、本発明の負極活物質を得ることができる。粉砕処理することによりサイクル特性と電池容量が向上する理由についても、現在のところ不明であるが、粉砕の過程で、原料のケイ素が微細化するとともに、銅の存在下で原料のケイ素と水の酸素が部分的に反応することによる反応生成物が生じ負極活物質中に存在するためと考えられる。出発物質の金属銅としては、市販の金属銅粉等を用いることができる。なお、ケイ素と金属銅と水とを原料物質として用いる場合、粉砕の過程において金属銅の表面が水と反応して、一部水酸化銅または酸化銅が生成することも考えられるが、それらを含めて金属銅と称する。
水の純度については、特に規定しないが、不純物低減の観点から、イオン交換水、逆浸透水、蒸留水などの、純度の高い水を用いることが好ましい。粉砕手段に投入する水の量が過剰であると、得られる粉砕処理して得られる負極活物質の元素組成比Ｏ／（Ｓｉ＋Ｃｕ＋Ｏ）が大きくなりすぎることがある。具体的には、ケイ素に対する水の質量比（Ｈ2Ｏ／Ｓｉ）は、０.５以下が好ましく、０.２以下が更に好ましい。
[Starting material]
Silicon The starting silicon used in the production of the negative electrode active material for a lithium ion secondary battery of the present invention is not particularly limited as long as it is made of silicon. In addition to commercially available silicon substrates (single crystal, polycrystal), raw material polycrystal and amorphous silicon, silicon alloys can also be used. Since the method for producing a negative electrode active material of the present invention includes a pulverizing step by a pulverizing means, the size of silicon as a starting material is not particularly specified, but from the viewpoint of workability, it should be 1 mm or less. Is preferred.
Copper oxide (2)
The negative electrode active material of the present invention can be obtained by mixing silicon and copper oxide (2) simultaneously with pulverization using a pulverizing means. The reason why the cycle characteristics and battery capacity are improved by pulverization is currently unknown, but in the process of pulverization, the raw silicon becomes finer as described above, and the raw silicon and copper oxide It is considered that a reaction product is generated by partial reaction of oxygen and is present in the negative electrode active material. As the starting copper oxide (2), any commercially available copper oxide (2) powder or the like can be used.
Metallic copper and water Silicon, metallic copper and water are pulverized using a pulverizing means and mixed at the same time, whereby the negative electrode active material of the present invention can be obtained. The reason why the cycle characteristics and battery capacity are improved by pulverization is also unclear at present, but in the course of pulverization, the raw material silicon is refined, and in the presence of copper, the raw material silicon and water This is presumably because a reaction product due to partial reaction of oxygen occurs and exists in the negative electrode active material. Commercially available metallic copper powder or the like can be used as the starting metallic copper. In addition, when silicon, metal copper and water are used as raw materials, it is considered that the surface of metal copper reacts with water during the pulverization process to partially produce copper hydroxide or copper oxide. Including it is called copper metal.
The purity of water is not particularly defined, but it is preferable to use high-purity water such as ion-exchanged water, reverse osmosis water, or distilled water from the viewpoint of reducing impurities. If the amount of water charged into the pulverizing means is excessive, the elemental composition ratio O / (Si + Cu + O) of the negative electrode active material obtained by the pulverization process to be obtained may become too large. Specifically, the mass ratio of water to silicon (H 2 O / Si) is preferably 0.5 or less, and more preferably 0.2 or less.
［粉砕手段］
本発明のリチウムイオン二次電池用負極活物質の製造方法においては、ケイ素と酸化銅（２）、またはケイ素と銅と水とを粉砕すると同時に混合するために、粉砕手段を用いる。粉砕手段としては、振動ミル、ボールミル等の公知の粉砕手段のいずれを用いても構わない。なお、使用する原料の大きさが大幅に異なるときは、最初に大きいほうの原料を粉砕し、その後残りの原料を投入し、粉砕と同時に混合処理しても構わない。粉砕メディアも、特に限定されないが、ジルコニアボール等を用いることができる。粉砕手段に、秤量した出発物質のケイ素と酸化銅（２）、またはケイ素と銅と水とを入れ、撹拌しながら出発物質を粉砕することにより、本発明の負極活物質を得ることができる。なお、出発原料、粉砕メディアとともに撹拌用溶媒を粉砕手段に投入して粉砕することもできる。攪拌用溶媒には非極性の有機溶媒を用いることができる。また、粉砕手段でケイ素と酸化銅（２）、またはケイ素と銅と水を入れる容器は、得られる負極活物質の元素組成比（Ｏ／（Ｓｉ＋Ｃｕ＋Ｏ））の制御性を向上するために密封できる構造とすることができる。
前記粉砕処理の際、回転数、振動数、処理時間等の粉砕処理の適切な条件範囲は、原料投入量、装置仕様、粉砕メディア等の条件により変化するので適宜設定すればよい。粉砕メディアを用いて粉砕処理を行った場合、粉砕処理後に、ふるい等を用いて粉砕メディアを除去して、本発明の負極活物質を得る。
[Crushing means]
In the method for producing a negative electrode active material for a lithium ion secondary battery of the present invention, a pulverizing means is used to pulverize and mix silicon and copper oxide (2) or silicon, copper and water at the same time. As the pulverizing means, any known pulverizing means such as a vibration mill and a ball mill may be used. In addition, when the size of the raw material to be used is significantly different, the larger raw material may be pulverized first, and then the remaining raw material may be charged and mixed at the same time as the pulverization. The grinding media is not particularly limited, and zirconia balls or the like can be used. The negative electrode active material of the present invention can be obtained by putting the weighed starting materials of silicon and copper oxide (2) or silicon, copper and water into the pulverizing means and pulverizing the starting materials while stirring. It is also possible to pulverize the starting material and pulverizing medium together with a stirring solvent into the pulverizing means. A nonpolar organic solvent can be used as the stirring solvent. Moreover, the container which puts silicon and copper oxide (2) or silicon, copper and water by the pulverizing means can be sealed in order to improve the controllability of the elemental composition ratio (O / (Si + Cu + O)) of the obtained negative electrode active material. It can be a structure.
In the pulverization process, the appropriate range of conditions for the pulverization process such as the rotation speed, the vibration frequency, and the processing time varies depending on the conditions such as the raw material input amount, the apparatus specifications, the pulverization media, and the like. When the pulverization process is performed using the pulverization medium, the pulverization medium is removed using a sieve or the like after the pulverization process to obtain the negative electrode active material of the present invention.
［リチウムイオン二次電池用負極］
本発明の負極活物質を用いて、公知の方法により、リチウムイオン二次電池用負極を作製することができる。例えば、前記負極活物質に適当なバインダ（結着剤）を混合し、必要に応じて導電性の向上のために適当な導電性粉末を混合する。この混合物にバインダが溶解する溶媒を加え、必要に応じて公知の攪拌機により十分に攪拌してスラリー状にする。この負極活物質を含むスラリーを、ドクターブレードなどを用いて圧延銅箔などの電極基板（集電体）に塗布し、乾燥した後、必要に応じてロール圧延などによって圧密化して、非水電解質二次電池用負極を作製することができる。
[Anode for lithium ion secondary battery]
A negative electrode for a lithium ion secondary battery can be produced by a known method using the negative electrode active material of the present invention. For example, a suitable binder (binder) is mixed with the negative electrode active material, and a suitable conductive powder is mixed as necessary to improve conductivity. A solvent in which the binder is dissolved is added to this mixture, and if necessary, the mixture is sufficiently stirred with a known stirrer to form a slurry. The slurry containing this negative electrode active material is applied to an electrode substrate (current collector) such as a rolled copper foil using a doctor blade, etc., dried, and then consolidated by roll rolling or the like as necessary to obtain a nonaqueous electrolyte. A negative electrode for a secondary battery can be produced.
［リチウムイオン二次電池］
前述のようにして製造された負極を用いてリチウムイオン二次電池を組立てることができるが、他の非水電解質二次電池を作製することも可能である。リチウムイオン二次電池は、基本構造として負極、正極、セパレータおよび非水系の電解質を含んでおり、前述の手順により作製された負極と、公知の正極、セパレータおよび電解質を用いて、リチウムイオン二次電池を組立てることができる。
[Lithium ion secondary battery]
A lithium ion secondary battery can be assembled using the negative electrode produced as described above, but other nonaqueous electrolyte secondary batteries can also be produced. A lithium ion secondary battery includes a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte as a basic structure, and a lithium ion secondary battery using a negative electrode produced by the above-described procedure and a known positive electrode, separator, and electrolyte. The battery can be assembled.
［評価用電池の製造方法］
本発明により得られるリチウムイオン二次電池負極活物質の性能評価は、以下の手順で行った。
得られた粉末（負極活物質）１.０質量部に人造黒鉛（平均粒子径Ｄ50＝４μｍ）０.２９質量部を加え、混合物とした。さらに宇部興産（株）製ポリイミド樹脂（商標名：Ｕ−ワニスＡ、固形分１８質量％）３.１２質量部およびＮ-メチルピロリドン０.８６質量部を加え、撹拌してスラリーを得た。このスラリーを５０μｍのドクターブレードを使用して厚さ１０μｍの銅箔（負極集電体）に塗布し、窒素雰囲気中、７０℃で２０分乾燥後、６５０℃で３時間真空焼成した。焼成後に１９.６ＭＰａ（２００ｋｇｆ／ｃｍ2）で加圧を行った後、１.５ｃｍ2に打ち抜き、負極成型体とした。
評価用電池は、以下の手順で作製した。正極材料としてＬｉＣｏＯ2を活物質とし、正極集電体には、アルミ箔を用いた単層シート（宝泉（株）製）を用いた。非水電解質溶液には、エチレンカーボネート、ジエチルカーボネートおよびジメチルカーボネートの６０：２５：１５（体積比）混合液に、六フッ化リン酸リチウムを１ｍｏｌ／Ｌの濃度で溶解した非水電解質溶液を用い、セパレータに厚さ５０μｍのポリエチレン製微多孔質フィルムを用いてコイン型リチウムイオン二次電池を作製した。得られた評価用電池を用いて、負極成型体の初回充放電効率及びサイクル特性を評価した。
[Method for Manufacturing Evaluation Battery]
The performance evaluation of the lithium ion secondary battery negative electrode active material obtained by the present invention was performed according to the following procedure.
To 1.0 part by mass of the obtained powder (negative electrode active material), 0.29 part by mass of artificial graphite (average particle diameter D 50 = 4 μm) was added to obtain a mixture. Further, 3.12 parts by mass of polyimide resin (trade name: U-varnish A, solid content 18% by mass) manufactured by Ube Industries, Ltd. and 0.86 parts by mass of N-methylpyrrolidone were added and stirred to obtain a slurry. This slurry was applied to a 10 μm thick copper foil (negative electrode current collector) using a 50 μm doctor blade, dried at 70 ° C. for 20 minutes in a nitrogen atmosphere, and then vacuum baked at 650 ° C. for 3 hours. After firing, pressurization was performed at 19.6 MPa (200 kgf / cm 2 ), and then punched out to 1.5 cm 2 to obtain a molded negative electrode.
The evaluation battery was produced by the following procedure. As the positive electrode material, LiCoO 2 was used as an active material, and a single layer sheet (made by Hosen Co., Ltd.) using aluminum foil was used as the positive electrode current collector. As the non-aqueous electrolyte solution, a non-aqueous electrolyte solution obtained by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a 60:25:15 (volume ratio) mixed solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate is used. A coin-type lithium ion secondary battery was produced using a polyethylene microporous film having a thickness of 50 μm as a separator. Using the obtained evaluation battery, the initial charge / discharge efficiency and cycle characteristics of the molded negative electrode were evaluated.
［電池容量、サイクル特性評価方法］
作製した評価用リチウムイオン二次電池は、室温で３時間放置した後、充放電装置（（株）北斗電工製）を用い、テストセルの電圧が０.０２Ｖに達するまで０.３ｍＡの定電流で充電を行い、０.０２Ｖに達した後は、セル電圧を０.０２Ｖで一定に保つように電流を減少させて充電を行った。そして、電流値が１０μＡを下回った時点で充電を終了した。放電は０.３ｍＡの定電流で行い、セル電圧が３.８Ｖを上回った時点で放電を終了し、放電容量を求めた。
以上の充放電試験を５０回繰り返し、評価用リチウムイオン二次電池の５０サイクルの充放電試験を行った。後述の実施例および比較例の評価結果を表１に示す。表１では、１サイクル後の放電容量を初期放電容量とし、この初期放電容量に対する５０サイクル後の放電容量の比率を、５０サイクル後容量維持率（％）として示した。ここで、充放電容量は、負極活物質の単位質量あたりの容量を示す。なお、実施例１および比較例１では、１００サイクルの充放電試験も実施しており、その結果も表１に併せて示した。
[Battery capacity and cycle characteristics evaluation method]
The prepared lithium ion secondary battery for evaluation was allowed to stand at room temperature for 3 hours, and then charged and discharged with a constant current of 0.3 mA until the test cell voltage reached 0.02 V using a charge / discharge device (Hokuto Denko). After reaching 0.02V, charging was performed by reducing the current so that the cell voltage was kept constant at 0.02V. Then, the charging was terminated when the current value fell below 10 μA. Discharging was performed at a constant current of 0.3 mA. When the cell voltage exceeded 3.8 V, the discharging was terminated and the discharge capacity was determined.
The above charge / discharge test was repeated 50 times, and a 50-cycle charge / discharge test of the lithium ion secondary battery for evaluation was performed. Table 1 shows the evaluation results of Examples and Comparative Examples described later. In Table 1, the discharge capacity after one cycle was taken as the initial discharge capacity, and the ratio of the discharge capacity after 50 cycles to this initial discharge capacity was shown as the capacity retention rate (%) after 50 cycles. Here, the charge / discharge capacity indicates the capacity per unit mass of the negative electrode active material. In Example 1 and Comparative Example 1, a 100-cycle charge / discharge test was also performed, and the results are also shown in Table 1.
［負極活物質の元素組成比測定方法］
得られた負極活物質の元素組成比は、走査型電子顕微鏡（Ｈｉｔａｃｈｉ ＳＵ−８０００）および電子顕微鏡用エネルギー分散型Ｘ線分析システム（サーモフィッシャーサイエンティフィック社製ＮＯＲＡＮ Ｓｙｓｔｅｍ ７、ＮＳＳ３１２Ｅ）を用いて、以下の方法で測定した。
測定領域を２００μｍ×２００μｍとし、加速電圧１０ｋＶで、試料の異なる１０箇所について、Ｓｉ、Ｃｕ、Ｏの元素組成比を測定し、得られた１０個の測定値の平均値から元素組成比（Ｓｉ／（Ｓｉ＋Ｃｕ＋Ｏ）、（Ｏ／（Ｓｉ＋Ｃｕ＋Ｏ）、Ｃｕ／（Ｓｉ＋Ｃｕ＋Ｏ））を計算した。
局所的な元素組成比は、以下の方法により測定した。
得られた負極活物質について、収束イオンビーム装置（ＦＩＢ装置）を用いて厚さ１００ｎｍの試料を作成した。この試料をＳＴＥＭ−ＥＤＸ（日立製作所社製、型番ＨＤ−２７００）を用いて、加速電圧２００ｋＶの測定条件で、局所的な元素組成比を測定した。
[Method for measuring elemental composition ratio of negative electrode active material]
The element composition ratio of the obtained negative electrode active material was determined using a scanning electron microscope (Hitachi SU-8000) and an energy dispersive X-ray analysis system for electron microscope (NORAN System 7, NSS312E manufactured by Thermo Fisher Scientific). Measured by the following method.
The measurement region is 200 μm × 200 μm, the acceleration voltage is 10 kV, the element composition ratio of Si, Cu, and O is measured at 10 different locations of the sample, and the element composition ratio (Si / (Si + Cu + O), (O / (Si + Cu + O), Cu / (Si + Cu + O)) were calculated.
The local elemental composition ratio was measured by the following method.
About the obtained negative electrode active material, the sample of thickness 100nm was created using the focused ion beam apparatus (FIB apparatus). The local elemental composition ratio of this sample was measured using STEM-EDX (manufactured by Hitachi, Ltd., model number HD-2700) under measurement conditions of an acceleration voltage of 200 kV.
［負極活物質のＸ線回折評価方法］
得られた負極活物質について、Ｘ線回折装置（株式会社リガク製、ＲＩＮＴ−２０００）によりＣｕ線源（４０ｋＶ／２０ｍＡ）の条件で測定して、Ｘ線回折（ＸＲＤ）の評価を行い、Ｘ線回折パターンを得た。
ＸＲＤの測定結果からＳｉの平均結晶子径（Ｄx）を算出する場合には、Ｘ線回折パターンから得られたＳｉ相の（１１１）面の半値幅βを用いて、Ｓｃｈｅｒｒｅｒの式 Ｄ＝（Ｋ・λ）／（β・ｃｏｓθ）を用いて結晶子径（Ｄx）を算出した。なお、Ｓｃｈｅｒｒｅｒの式において、Ｄは結晶子径（ｎｍ）、λは測定Ｘ線波長（ｎｍ）、βは結晶子による回折幅の広がり（半値幅、ラジアン）、θは回折角のブラッグ角、ＫはＳｃｈｅｒｒｅｒ定数を示し、この式中の測定Ｘ線波長λを０.１５４ｎｍ、Ｓｃｈｅｒｒｅｒ定数Ｋを０.９とした。
ＸＲＤの測定結果から、分子をＣｕ3Ｓｉに対応するピーク高さ、分母をＳｉに対応するピーク高さとしたピーク強度比（Ｃｕ3Ｓｉ／Ｓｉ）を以下の方法で算出した。Ｃｕ3Ｓｉに対応するピーク高さは、２θが４４.８°付近にピークがあるＣｕ3Ｓｉに対応するピークと２θが４７.４°付近にピークがあるＳｉに対応するピークをピーク分離し、ピーク分離の結果得られた２θが４４.８°付近にピークがあるプロファイルのピーク高さをＣｕ3Ｓｉに対応するピーク高さとし、２θが２８.４°付近にピークがあるピークの高さをＳｉに対応するピーク高さとして、これらのピーク高さからピーク強度比（Ｃｕ3Ｓｉ／Ｓｉ）を算出した。
[X-ray diffraction evaluation method for negative electrode active material]
About the obtained negative electrode active material, it measures on condition of Cu ray source (40kV / 20mA) with X-ray-diffraction apparatus (Rigaku Corporation make, RINT-2000), X-ray diffraction (XRD) evaluation is performed, X A line diffraction pattern was obtained.
When calculating the average crystallite diameter (D x ) of Si from the XRD measurement results, the Scherrer equation D = is used, using the half width β of the (111) plane of the Si phase obtained from the X-ray diffraction pattern. The crystallite diameter (D x ) was calculated using (K · λ) / (β · cos θ). In the Scherrer equation, D is the crystallite diameter (nm), λ is the measured X-ray wavelength (nm), β is the diffraction width broadened by the crystallite (half-value width, radians), θ is the Bragg angle of the diffraction angle, K represents a Scherrer constant. In this equation, the measured X-ray wavelength λ was 0.154 nm, and the Scherrer constant K was 0.9.
From the XRD measurement results, the peak intensity ratio (Cu 3 Si / Si) with the peak height corresponding to Cu 3 Si as the numerator and the peak height corresponding to Si as the denominator was calculated by the following method. Cu corresponding peak height 3 Si is, 2 [Theta] is a peak separation of peaks peak and 2 [Theta] corresponding to Si having a peak near 47.4 ° corresponding to a peak Cu 3 Si around 44.8 ° The peak height of the profile with 2θ peaked around 44.8 ° obtained as a result of peak separation is the peak height corresponding to Cu 3 Si, and the peak height with 2θ peaked at about 28.4 ° Was the peak height corresponding to Si, and the peak intensity ratio (Cu 3 Si / Si) was calculated from these peak heights.
［負極活物質のＸ線光電子分光分析評価方法］
負極活物質のＸ線光電子分光分析評評価は、Ｘ線源としてモノクロメーターにより単色化されたＡｌＫα線を用い、測定領域φ０.６２ｍｍ、光電子の取り出し角度４５°の条件で測定を行った。測定前に、試料表面をシリコン基板が１００ｎｍの深さでエッチングされる条件でＡｒスパッタエッチングを行った。Ｓｉ２ｐスペクトル中には金属状態のケイ素（Ｓｉ（０））に対応するピーク以外に、高結合エネルギー側にシフトした複数のピークが観察された。この高結合エネルギー側にシフトした複数のピークは酸化状態の異なる複数の酸化物（低級酸化物を含むケイ素の酸化物、すなわちＳｉＯx（ただし０＜ｘ＜２））に対応するピークと判断される。Ｓｉ（０）、ＳｉＯxに対応するピークをピーク分離し、分子をＳｉＯxに対応する各ピークの面積の和、分母をＳｉ（０）に対応するピークの面積としたピーク面積比（ＳｉＯx／Ｓｉ（０））を算出した。
[X-ray photoelectron spectroscopic analysis evaluation method of negative electrode active material]
For evaluation evaluation of the negative electrode active material by X-ray photoelectron spectroscopic analysis, AlKα ray monochromatized by a monochromator was used as an X-ray source, and measurement was performed under conditions of a measurement region φ0.62 mm and a photoelectron extraction angle of 45 °. Before the measurement, Ar sputter etching was performed on the sample surface under the condition that the silicon substrate was etched at a depth of 100 nm. In the Si2p spectrum, in addition to a peak corresponding to silicon (Si (0)) in the metal state, a plurality of peaks shifted to the high binding energy side were observed. The plurality of peaks shifted to the higher binding energy side are judged to be peaks corresponding to a plurality of oxides having different oxidation states (silicon oxides including lower oxides, that is, SiO x (where 0 <x <2)). The Peak areas corresponding to Si (0) and SiO x are separated, the numerator is the sum of the areas of the peaks corresponding to SiO x , and the denominator is the area of the peak corresponding to Si (0) (SiO x / Si (0)) was calculated.
［実施例１］
平均粒径が５μｍである粒状Ｓｉ（高純度化学研究所製、純度９９.９％）１.５６ｇとＣｕＯ粉（株式会社レアメタリック製、純度９９.９質量％、平均粒径１μｍ）０.４４ｇと直径１５ｍｍのジルコニアボール７個を粉砕ポット（ステンレス製、容量４５ｃｍ3）に入れ密封した。この粉砕ポットを遊星ボールミル（Ｆｒｉｔｓｃｈ社製、Ｐｕｌｖｅｒｉｓｅｔｔｅ−７）にセットし、回転速度６００ｒｐｍの条件で、３時間粉砕処理を実施した。粉砕ポットの内容物から、ジルコニアボールを分離し、負極活物質を得た。得られた負極活物質の元素組成比、ＸＲＤのＳｉ（１１１）ピークの半値幅および結晶子径、ピーク強度比（Ｃｕ3Ｓｉ／Ｓｉ）を表１に示し、走査型電子顕微鏡写真を図２に示す。実施例１〜１３により得られた負極活物質のＸＲＤパターン（図３）には、２θが４４.８°付近にピークが認められ、Ｃｕ3Ｓｉが存在することを示していた。
図４に、負極活物質の透過電子顕微鏡（ＳＴＥＭ）暗視野像を示す。ＳＴＥＭ暗視野像中で白っぽく見える３点（矢印部）の元素組成をＳＴＥＭ−ＥＤＸで測定した結果は、Ｃｕ／Ｓｉのモル比が２.７３〜３.２７であり、Ｃｕ3Ｓｉが生成していることが確認された。
図５（ａ）、図５（ｂ）に、実施例１により得られた負極活物質のＳＴＥＭ像を示す。図５（ａ）が明視野ＳＴＥＭ像で図５（ｂ）が暗視野ＳＴＥＭ像である。この暗視野ＳＴＥＭ像は、写真の下半分の部分にはＣｕ3Ｓｉが生成していないことを示している。金属状態のＳｉは良好な結晶性を示すが、その周辺に結晶格子の乱れた非晶質な領域が存在しており、この領域がアモルファス状のＳｉ酸化物であると考えられる。この明視野ＳＴＥＭ像の下右部分には結晶性のＳｉが存在し、下左部分にはアモルファス状のＳｉ酸化物が存在していると考えられる。
得られた負極活物質を用い、前述の手順で評価用電池を作製し、負極活物質の性能を評価した。充放電試験の結果を表１に示す。なお、表１には、実施例２〜１３および比較例１および２についての結果も併せて示してある。
[Example 1]
1.56 g of granular Si (manufactured by High-Purity Chemical Laboratory, purity 99.9%) with an average particle diameter of 5 μm and CuO powder (manufactured by Rare Metallic, purity 99.9% by mass, average particle diameter 1 μm) 44 g and 7 zirconia balls having a diameter of 15 mm were put in a crushing pot (made of stainless steel, capacity 45 cm 3 ) and sealed. This pulverization pot was set in a planetary ball mill (manufactured by Fritsch, Pulverisete-7), and pulverization was performed for 3 hours under the condition of a rotational speed of 600 rpm. Zirconia balls were separated from the contents of the grinding pot to obtain a negative electrode active material. The element composition ratio, the XRD Si (111) peak half width and crystallite diameter, and peak intensity ratio (Cu 3 Si / Si) of the obtained negative electrode active material are shown in Table 1, and a scanning electron micrograph is shown in FIG. Shown in In the XRD pattern (FIG. 3) of the negative electrode active materials obtained in Examples 1 to 13, a peak was observed around 24.8 of 44.8 °, indicating that Cu 3 Si was present.
FIG. 4 shows a transmission electron microscope (STEM) dark field image of the negative electrode active material. The elemental composition of three points (arrows) that look whitish in the STEM dark field image was measured with STEM-EDX. The Cu / Si molar ratio was 2.73 to 3.27, and Cu 3 Si was produced. It was confirmed that
5A and 5B show STEM images of the negative electrode active material obtained in Example 1. FIG. FIG. 5A is a bright field STEM image, and FIG. 5B is a dark field STEM image. This dark field STEM image shows that Cu 3 Si is not generated in the lower half of the photograph. Although Si in a metal state exhibits good crystallinity, an amorphous region with a disordered crystal lattice exists around it, and this region is considered to be an amorphous Si oxide. It is considered that crystalline Si is present in the lower right portion of the bright field STEM image, and amorphous Si oxide is present in the lower left portion.
Using the obtained negative electrode active material, an evaluation battery was prepared according to the procedure described above, and the performance of the negative electrode active material was evaluated. The results of the charge / discharge test are shown in Table 1. In Table 1, the results for Examples 2 to 13 and Comparative Examples 1 and 2 are also shown.
［実施例２］
負極活物質製造の際、粒状Ｓｉの量を１.５６ｇから１.０７７ｇに変更し、ＣｕＯ粉の量を０.４４ｇから０.９２３ｇに変更した以外は、実施例１と同様にして、負極活物質およびそれを用いた電池を作製し、評価を行った。
得られた負極活物質をＸＰＳで分析した。得られたＳｉ２ｐピークを図１に示す。Ｓｉ２ｐピークは、酸化数０〜４に対応する５つのピークに分離することができた。このことは、得られた負極活物質には酸化数の異なるＳｉ酸化物が存在していることを示している。ピーク面積比（ＳｉＯx／Ｓｉ（０））は０.５７であった。実施例１〜１３で得られた負極活物質のピーク面積比（ＳｉＯx／Ｓｉ（０））は、０.０６〜０.７２の範囲であった。
実施例１〜６の粉砕前の粒状ＳｉとＣｕＯ粉の混合物をＸＲＤで測定した場合、２θが３５.４°および３８.４°付近にＣｕＯのピークが認められるが、粉砕後には、それらのピークは認められない。更に、実施例１〜６で得られた負極活物質のＸＲＤ測定結果では、Ｓｉ酸化物によるピークは認められなかった。これらのことは、本発明の負極活物質中の酸素原子は、アモルファス状のＳｉ酸化物の形態で存在しているものと考えられる。
[Example 2]
The negative electrode active material was manufactured in the same manner as in Example 1 except that the amount of granular Si was changed from 1.56 g to 1.077 g and the amount of CuO powder was changed from 0.44 g to 0.923 g. An active material and a battery using the active material were prepared and evaluated.
The obtained negative electrode active material was analyzed by XPS. The obtained Si2p peak is shown in FIG. The Si2p peak could be separated into 5 peaks corresponding to oxidation numbers 0-4. This indicates that Si oxides having different oxidation numbers are present in the obtained negative electrode active material. The peak area ratio (SiO x / Si (0)) was 0.57. The peak area ratio (SiO x / Si (0)) of the negative electrode active materials obtained in Examples 1 to 13 was in the range of 0.06 to 0.72.
When the mixture of granular Si and CuO powder before pulverization of Examples 1 to 6 was measured by XRD, 2θ was 35.4 ° and 38.4 °, and CuO peaks were observed. No peak is observed. Furthermore, in the XRD measurement results of the negative electrode active materials obtained in Examples 1 to 6, no peak due to Si oxide was observed. These things are considered that the oxygen atom in the negative electrode active material of this invention exists in the form of amorphous Si oxide.
［実施例３］
負極活物質製造の際、粒状Ｓｉの量を１.５６ｇから１.８２４ｇに変更し、ＣｕＯ粉の量を０.４４ｇから０.１７６ｇに変更した以外は、実施例１と同様にして、負極活物質及びそれを用いた電池を作製し、評価を行った。
[Example 3]
The negative electrode active material was manufactured in the same manner as in Example 1 except that the amount of granular Si was changed from 1.56 g to 1.824 g and the amount of CuO powder was changed from 0.44 g to 0.176 g. An active material and a battery using the active material were prepared and evaluated.
［実施例４〜６］
負極活物質製造の際、粒状Ｓｉの量を１.５６ｇから表１に記載の値に変更し、ＣｕＯ粉の量を０.４４ｇから表１に記載の値に変更した以外は、実施例１と同様にして、負極活物質及びそれを用いた電池を作製し、評価を行った。実施例５で得られた負極活物質をＸＰＳで分析した。ＸＰＳの結果から得られたピーク面積比（ＳｉＯx／Ｓｉ（０））は０.１９であった。
[Examples 4 to 6]
Example 1 except that the amount of granular Si was changed from 1.56 g to the value shown in Table 1 and the amount of CuO powder was changed from 0.44 g to the value shown in Table 1 during the production of the negative electrode active material. In the same manner as described above, a negative electrode active material and a battery using the same were produced and evaluated. The negative electrode active material obtained in Example 5 was analyzed by XPS. The peak area ratio (SiO x / Si (0)) obtained from the XPS result was 0.19.
［実施例７］
負極活物質製造の際、出発原料を粒状Ｓｉ１.５６ｇとＣｕＯ粉０.４４ｇから、平均粒径が５μｍである粒状Ｓｉ（高純度化学研究所製、純度９９.９％）１.７１ｇとＣｕ粉（金属銅粉（Ａｌｄｒｉｃｈ製、純度９９.７質量％、平均粒径３μｍ）０.２９ｇと水０.０５４ｇに変更した以外は、実施例１と同様にして、負極活物質及びそれを用いた電池を作製し、評価を行った。
[Example 7]
In the production of the negative electrode active material, the starting materials are 1.56 g of granular Si and 0.44 g of CuO powder, 1.71 g of granular Si having an average particle size of 5 μm (purity 99.9%, purity 99.9%) and Cu Powder (Metal copper powder (made by Aldrich, purity 99.7% by mass, average particle size 3 μm)) In the same manner as in Example 1, except for changing to 0.29 g and water 0.054 g, the negative electrode active material and the same were used. A battery was prepared and evaluated.
［実施例８〜１２］
負極活物質製造の際、Ｃｕ粉の量を１.７１ｇから表１に記載の値に変更し、水の量を０.０５４ｇから表１に記載の値に変更した以外は、実施例７と同様にして、負極活物質及びそれを用いた電池を作製し、評価を行った。実施例８により得られた負極活物質の走査型電子顕微鏡写真を図６に示す。
［実施例１３］
負極活物質製造の際、粉砕処理時間を３時間から１時間に変更した以外は、実施例１と同様にして、負極活物質及びそれを用いた電池を作製し、評価を行った。
[Examples 8 to 12]
Example 7 and Example 7 except that the amount of Cu powder was changed from 1.71 g to the value shown in Table 1 and the amount of water was changed from 0.054 g to the value shown in Table 1 during the production of the negative electrode active material. Similarly, a negative electrode active material and a battery using the same were prepared and evaluated. A scanning electron micrograph of the negative electrode active material obtained in Example 8 is shown in FIG.
[Example 13]
A negative electrode active material and a battery using the same were prepared and evaluated in the same manner as in Example 1 except that the pulverization time was changed from 3 hours to 1 hour during the production of the negative electrode active material.
［比較例１］
負極活物質製造の際、粒状Ｓｉの量を１.５８７ｇから２ｇに変更し、ＣｕＯ粉を使用しなかった以外は、実施例１と同様にして、負極活物質及びそれを用いた電池を作製し、評価を行った。
[Comparative Example 1]
During the production of the negative electrode active material, the amount of granular Si was changed from 1.587 g to 2 g, and a negative electrode active material and a battery using the same were produced in the same manner as in Example 1 except that no CuO powder was used. And evaluated.
［比較例２］
負極活物質製造の際、粒状Ｓｉの量を１.５８７ｇから１.６２８ｇに変更し、ＣｕＯ粉０.４１３ｇに代えて、金属銅粉（Ａｌｄｒｉｃｈ製、純度９９.７質量％、平均粒径３μｍ）０.３７２ｇに変更した以外は、実施例１と同様にして、負極活物質及びそれを用いた電池を作製し、評価を行った。
[Comparative Example 2]
In the production of the negative electrode active material, the amount of granular Si was changed from 1.587 g to 1.628 g, and instead of CuO powder 0.413 g, metal copper powder (made by Aldrich, purity 99.7 mass%, average particle size 3 μm) ) A negative electrode active material and a battery using the same were produced and evaluated in the same manner as in Example 1 except that the amount was changed to 0.372 g.
実施例５および実施例８で得られた負極活物質について、以下の方法で成分分析を行った。ＳｉおよびＣｕの含有量は、試料をフッ化水素酸と硝酸の混酸水溶液で溶解後、ＩＣＰ−ＯＥＳ法（ＩＣＰ発光分析法）で含有量を測定した。Ｃｕの含有量測定では、試料をフッ化水素酸−硝酸の混酸水溶液で溶解後、硫酸を添加した後に加熱乾固してＳｉをＳｉＯ2として揮発除去する操作を行った。Ｏ（酸素）含有量はＬＥＣＯ社製、ＯＮＨ８３６を用いて測定した。いずれも負極活物質も、Ｓｉ、Ｃｕ、Ｏの合計の含有量（質量）は、試料質量の９８.５質量％であった。 About the negative electrode active material obtained in Example 5 and Example 8, component analysis was performed with the following method. The contents of Si and Cu were measured by the ICP-OES method (ICP emission analysis method) after dissolving the sample with a mixed acid aqueous solution of hydrofluoric acid and nitric acid. In measuring the Cu content, the sample was dissolved in a mixed acid aqueous solution of hydrofluoric acid-nitric acid, sulfuric acid was added, and the mixture was heated to dryness to volatilize and remove Si as SiO 2 . The O (oxygen) content was measured using ONH836 manufactured by LECO. In any of the negative electrode active materials, the total content (mass) of Si, Cu, and O was 98.5% by mass of the sample mass.
実施例５の負極活物質について、電池容量、サイクル特性評価方法の条件である放電を終了する時点のセル電圧を３.８Ｖから１.６Ｖに変更して充放電負荷を低減した条件（充電深度を１００％から６０％に変更した条件）でサイクル特性評価を行った。結果、５０サイクル後および１００サイクル後の容量維持率は、いずれも９９.５％以上であり、極めて優れたサイクル特性を示した。 For the negative electrode active material of Example 5, the cell voltage at the time of termination of discharge, which is the condition of the battery capacity and cycle characteristic evaluation method, was changed from 3.8 V to 1.6 V (charge depth). The cycle characteristics were evaluated under the condition of changing from 100% to 60%. As a result, the capacity retention ratios after 50 cycles and 100 cycles were both 99.5% or more, indicating extremely excellent cycle characteristics.
本発明の製造方法により得られた負極活物質を用いたリチウムイオン二次電池は、５０サイクル後容量維持率が５８.８％〜１０２.２％であり、優れた性能を示した。 The lithium ion secondary battery using the negative electrode active material obtained by the production method of the present invention had a capacity retention rate of 58.8% to 102.2% after 50 cycles, and exhibited excellent performance.
Claims (9)
ただし、酸素を含むケイ素の単体または固溶体である第一の相と、ケイ素と銅の化合物または銅の単体もしくは固溶体である第二の相が界面を介して接合し、前記第一の相と第二の相が外表面に露出しており、前記第一の相と第二の相が、界面以外が略球面状の表面を有するナノサイズの粒子を除く。 Silicon negative electrode active material for lithium ion secondary batteries having silicon, copper and oxygen as main constituent elements, and having an average crystallite diameter (D x ) of 50 nm or less measured by Cu 3 Si and X-ray diffraction method The element composition ratios Cu / (Si + Cu + O) and O / (Si + Cu + O) represented by a molar ratio including particles and amorphous silicon oxide are 0.02 to 0.30. A negative electrode active material for a lithium ion secondary battery having a calculated peak intensity ratio (Cu 3 Si / Si) of 0.05 to 1.5.
However, the first phase which is a simple substance or solid solution of silicon containing oxygen and the second phase which is a silicon and copper compound or a simple substance or solid solution of copper are bonded via an interface, and the first phase and the first phase Two phases are exposed on the outer surface, and the first phase and the second phase exclude nano-sized particles having a substantially spherical surface except for the interface.
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