JP4212439B2 - How to use lithium secondary battery - Google Patents
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- JP4212439B2 JP4212439B2 JP2003320661A JP2003320661A JP4212439B2 JP 4212439 B2 JP4212439 B2 JP 4212439B2 JP 2003320661 A JP2003320661 A JP 2003320661A JP 2003320661 A JP2003320661 A JP 2003320661A JP 4212439 B2 JP4212439 B2 JP 4212439B2
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- lithium secondary
- secondary battery
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- 229910052744 lithium Inorganic materials 0.000 title claims description 31
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims description 30
- 239000011149 active material Substances 0.000 claims description 26
- 239000010409 thin film Substances 0.000 claims description 22
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 19
- 229910052710 silicon Inorganic materials 0.000 claims description 19
- 239000010703 silicon Substances 0.000 claims description 19
- 238000000034 method Methods 0.000 claims description 16
- 238000007600 charging Methods 0.000 claims description 15
- 238000007599 discharging Methods 0.000 claims description 15
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 8
- 229910052751 metal Inorganic materials 0.000 claims description 7
- 239000002184 metal Substances 0.000 claims description 7
- 238000000151 deposition Methods 0.000 claims description 6
- 229910021417 amorphous silicon Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 239000010949 copper Substances 0.000 claims description 4
- 239000011230 binding agent Substances 0.000 claims description 3
- 239000011856 silicon-based particle Substances 0.000 claims description 3
- 230000000052 comparative effect Effects 0.000 description 7
- 239000008151 electrolyte solution Substances 0.000 description 5
- 230000003746 surface roughness Effects 0.000 description 5
- 229910045601 alloy Inorganic materials 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 4
- 239000011889 copper foil Substances 0.000 description 4
- 238000004544 sputter deposition Methods 0.000 description 4
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 239000007774 positive electrode material Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 229910000881 Cu alloy Inorganic materials 0.000 description 2
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 2
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 229910013870 LiPF 6 Inorganic materials 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 150000005676 cyclic carbonates Chemical class 0.000 description 2
- 230000001351 cycling effect Effects 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 239000010408 film Substances 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 239000012046 mixed solvent Substances 0.000 description 2
- 239000011255 nonaqueous electrolyte Substances 0.000 description 2
- 239000005518 polymer electrolyte Substances 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- ZZXUZKXVROWEIF-UHFFFAOYSA-N 1,2-butylene carbonate Chemical compound CCC1COC(=O)O1 ZZXUZKXVROWEIF-UHFFFAOYSA-N 0.000 description 1
- LZDKZFUFMNSQCJ-UHFFFAOYSA-N 1,2-diethoxyethane Chemical compound CCOCCOCC LZDKZFUFMNSQCJ-UHFFFAOYSA-N 0.000 description 1
- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical compound O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
- 229910015015 LiAsF 6 Inorganic materials 0.000 description 1
- 229910013063 LiBF 4 Inorganic materials 0.000 description 1
- -1 LiCF 3 SO 3 Inorganic materials 0.000 description 1
- 229910013684 LiClO 4 Inorganic materials 0.000 description 1
- 229910013595 LiCo0.5Ni0.5O2 Inorganic materials 0.000 description 1
- 229910015643 LiMn 2 O 4 Inorganic materials 0.000 description 1
- 229910014689 LiMnO Inorganic materials 0.000 description 1
- 229910011669 LiNi0.7Co0.2Mn0.1O2 Inorganic materials 0.000 description 1
- 229910013290 LiNiO 2 Inorganic materials 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- 229920003171 Poly (ethylene oxide) Polymers 0.000 description 1
- 229910018598 Si-Co Inorganic materials 0.000 description 1
- 229910018594 Si-Cu Inorganic materials 0.000 description 1
- 229910008453 Si—Co Inorganic materials 0.000 description 1
- 229910008465 Si—Cu Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 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
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 150000005678 chain carbonates Chemical class 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000010280 constant potential charging Methods 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 125000004177 diethyl group Chemical group [H]C([H])([H])C([H])([H])* 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 239000004210 ether based solvent Substances 0.000 description 1
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910003480 inorganic solid Inorganic materials 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- ACFSQHQYDZIPRL-UHFFFAOYSA-N lithium;bis(1,1,2,2,2-pentafluoroethylsulfonyl)azanide Chemical compound [Li+].FC(F)(F)C(F)(F)S(=O)(=O)[N-]S(=O)(=O)C(F)(F)C(F)(F)F ACFSQHQYDZIPRL-UHFFFAOYSA-N 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229920002239 polyacrylonitrile Polymers 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 239000007784 solid electrolyte Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- 238000007751 thermal spraying Methods 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910000314 transition metal oxide Inorganic materials 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 238000001771 vacuum deposition Methods 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Description
本発明は、シリコンを含む活物質層を集電体上に設けた電極を負極として用いたリチウム二次電池の使用方法及びリチウム二次電池に関するものである。 The present invention relates to a method for using a lithium secondary battery using an electrode in which an active material layer containing silicon is provided on a current collector as a negative electrode, and a lithium secondary battery.
シリコンは、リチウムを合金化することにより吸蔵することができる材料であり、その理論容量が大きいことから高エネルギー密度化が図れるリチウム二次電池の電極材料として注目されている。しかしながら、シリコンを活物質として用いた電極は、サイクル特性において黒鉛などの炭素材料に比べて劣るという問題があった。この原因の１つとして、充放電における活物質の膨張収縮が大きいため、その際に生じる応力により活物質が微粉化したり、あるいは活物質が集電体から脱離するなどにより、集電性が低下することが考えられる。 Silicon is a material that can be occluded by alloying lithium, and because of its large theoretical capacity, silicon is attracting attention as an electrode material for lithium secondary batteries that can achieve high energy density. However, an electrode using silicon as an active material has a problem that the cycle characteristics are inferior to a carbon material such as graphite. One of the causes is that the active material expands and contracts during charge and discharge, and the active material is pulverized due to the stress generated at that time, or the active material is detached from the current collector. It is thought that it falls.
本出願人は、非晶質シリコン薄膜などを銅箔などの集電体上に堆積して形成した電極が、充放電によって薄膜の厚み方向に切れ目が形成され、この切れ目によって薄膜が柱状に分離することにより、良好なサイクル特性を示すことを見出した（特許文献１など）。 The applicant has formed an electrode formed by depositing an amorphous silicon thin film on a current collector such as a copper foil, and a cut is formed in the thickness direction of the thin film by charging and discharging, and the thin film is separated into a columnar shape by this cut. As a result, it has been found that good cycle characteristics are exhibited (Patent Document 1, etc.).
しかしながら、上記電極の良好なサイクル特性をさらに高めることができる充放電条件の詳細に関しては、未だ提案されていない。
本発明の目的は、シリコンを含む活物質層を集電体上に設けた電極を負極として用いたリチウム二次電池の使用方法において、サイクル特性を高めることができる使用方法を提供することにある。 An object of the present invention is to provide a usage method capable of improving cycle characteristics in a usage method of a lithium secondary battery using an electrode in which an active material layer containing silicon is provided on a current collector as a negative electrode. .
本発明は、リチウムと合金化しない金属からなる集電体の上に、シリコンを含む活物質層を設けた電極を負極として用いたリチウム二次電池の使用方法であり、初回の充電時を除き、負極の電位が０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下である範囲で充放電することを特徴としている。 The present invention is a method for using a lithium secondary battery using an electrode provided with an active material layer containing silicon on a current collector made of a metal that is not alloyed with lithium as a negative electrode, except during the first charge. In addition, charging and discharging are performed in a range where the potential of the negative electrode is 0.8 V (vs. Li / Li + ) or less.
本発明に従い、負極の電位が０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下である範囲で充放電することにより、サイクル特性を向上させることができる。 According to the present invention, cycle characteristics can be improved by charging and discharging in a range where the potential of the negative electrode is 0.8 V (vs. Li / Li + ) or less.
本発明において、「初回の充電時を除き」とは、初回の充電を開始する際においては、負極の電位が０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）より高い値であってもよいことを意味している。 In the present invention, “except at the first charge” means that the potential of the negative electrode may be higher than 0.8 V (vs. Li / Li + ) when starting the first charge. I mean.
本発明のさらに限定された局面は、リチウムを合金化しない金属からなる集電体の上に、非晶質シリコン薄膜を堆積して設けた電極を負極として用いたリチウム二次電池の使用方法であり、初回の充電時を除き、負極の電位が０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下である範囲で充放電することを特徴としている。 A further limited aspect of the present invention is a method of using a lithium secondary battery in which an electrode provided by depositing an amorphous silicon thin film on a current collector made of a metal that does not alloy lithium is used as a negative electrode. In addition, except for the first charge, charging and discharging are performed in a range where the potential of the negative electrode is 0.8 V (vs. Li / Li + ) or less.
上記局面に従い、負極の電位が０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下である範囲で充放電することにより、サイクル特性を向上させることができる。 In accordance with the above aspect, cycle characteristics can be improved by charging and discharging in a range where the potential of the negative electrode is 0.8 V (vs. Li / Li + ) or less.
本発明においては、負極の電位が０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下である範囲で充放電することにより、サイクル特性を高めている。０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）を超えて充放電を行うと、活物質の構造変化がより大きくなり、活物質の劣化が促進されるため、サイクル特性が悪くなる。すなわち、放電末期において特に活物質の変化の度合いが大きくなり、また放電末期において電解液との反応による被膜が形成され、この被膜の形成がサイクル特性に悪影響を及ぼしているものと考えられる。本発明においては、負極の電位が０．７Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下の範囲で充放電が行われることがさらに好ましい。 In the present invention, cycle characteristics are enhanced by charging and discharging in the range where the potential of the negative electrode is 0.8 V (vs. Li / Li + ) or less. When charging / discharging is performed at a voltage exceeding 0.8 V (vs. Li / Li + ), the structural change of the active material is further increased, and the deterioration of the active material is promoted, resulting in poor cycle characteristics. That is, the degree of change of the active material is particularly large at the end of discharge, and a film is formed by reaction with the electrolytic solution at the end of discharge, and this formation of the film is considered to have an adverse effect on the cycle characteristics. In the present invention, it is more preferable that charging / discharging is performed in a range where the potential of the negative electrode is 0.7 V (vs. Li / Li + ) or less.
負極の電位は、放電の際に上昇する。従って、負極の放電終止電位を０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下とすることにより、本発明に従う充放電を行うことができる。 The potential of the negative electrode rises during discharge. Therefore, charging / discharging according to the present invention can be performed by setting the discharge end potential of the negative electrode to 0.8 V (vs. Li / Li + ) or less.
本発明において、シリコンを含む活物質層は、例えば、シリコンを薄膜状に堆積して形成された層である。薄膜の形成方法としては、ＣＶＤ法、スパッタリング法、真空蒸着法、及び溶射法などが挙げられる。また、本発明においてシリコンを含む活物質層は、シリコン粒子とバインダーを含むスラリーを集電体上に塗布することにより形成された層であってもよい。すなわち、活物質層は、シリコン粒子とバインダーから形成された層であってもよい。シリコンを含む合金としては、例えば、Ｓｉ−Ｃｕ、Ｓｉ−Ｃｏなどが挙げられる。 In the present invention, the active material layer containing silicon is, for example, a layer formed by depositing silicon in a thin film shape. Examples of the method for forming a thin film include a CVD method, a sputtering method, a vacuum evaporation method, and a thermal spraying method. In the present invention, the active material layer containing silicon may be a layer formed by applying a slurry containing silicon particles and a binder onto a current collector. That is, the active material layer may be a layer formed of silicon particles and a binder. Examples of the alloy containing silicon include Si—Cu and Si—Co.
本発明において、集電体は、リチウムと合金化しない金属から形成される。このような金属としては、銅、ニッケル、鉄、チタン、コバルト、モリブデン、タングステン、タンタル等の金属及びこれらの合金などが挙げられ、特に好ましくは、銅、銅合金が用いられる。また活物質層を設ける面に凹凸が形成されている集電体が好ましく用いられる。このような観点からは、電解銅箔及び電解銅合金箔などが好ましく用いられる。 In the present invention, the current collector is formed from a metal that does not alloy with lithium. Examples of such metals include metals such as copper, nickel, iron, titanium, cobalt, molybdenum, tungsten, and tantalum, and alloys thereof, and copper, copper alloys are particularly preferably used. Further, a current collector in which irregularities are formed on the surface on which the active material layer is provided is preferably used. From such a viewpoint, electrolytic copper foil, electrolytic copper alloy foil, and the like are preferably used.
本発明において、活物質層がシリコン薄膜である場合には、その厚み方向に形成された切れ目によって柱状にシリコン薄膜が分離されており、該柱状部分の底部が集電体と密着していることが好ましい。このような柱状構造を有することにより、柱状部分の周囲に形成された隙間によって、充放電反応の際の薄膜の体積の膨張・収縮を吸収することができ、体積膨張によって生じる応力を緩和させることができる。このため、活物質の微粉化や集電体からの脱離を防止することができ、サイクル特性を高めることができる。 In the present invention, when the active material layer is a silicon thin film, the silicon thin film is separated in a columnar shape by a cut formed in the thickness direction, and the bottom of the columnar portion is in close contact with the current collector. Is preferred. By having such a columnar structure, the gap formed around the columnar part can absorb the expansion and contraction of the volume of the thin film during the charge / discharge reaction, and relieve the stress caused by the volume expansion. Can do. For this reason, pulverization of the active material and desorption from the current collector can be prevented, and cycle characteristics can be improved.
集電体の表面には、上述のように凹凸が形成されていることが好ましい。薄膜が形成されている面に凹凸を設けることにより、初回以降の充放電によって活物質薄膜が柱状に分離され、上記の柱状構造が形成される。集電体表面の表面粗さＲａは、０．０１〜２μｍ程度であることが好ましく、さらに好ましくは、０．１〜２μｍ程度である。表面粗さＲａは、日本工業規格（ＪＩＳ Ｂ ０６０１−１９９４）に定められている。例えば、表面粗さ計により表面粗さを測定することができる。 The surface of the current collector is preferably formed with irregularities as described above. By providing irregularities on the surface on which the thin film is formed, the active material thin film is separated into columns by charge and discharge after the first time, and the columnar structure is formed. The surface roughness Ra of the current collector surface is preferably about 0.01 to 2 μm, and more preferably about 0.1 to 2 μm. The surface roughness Ra is defined in Japanese Industrial Standard (JIS B 0601-1994). For example, the surface roughness can be measured with a surface roughness meter.
本発明のリチウム二次電池の正極活物質としては、リチウム二次電池の正極活物質として用いることができるものであれば特に限定されるものではなく、例えば、従来より正極活物質として用いられているＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎ2Ｏ4、ＬｉＭｎＯ2、ＬｉＣｏ0.5Ｎｉ0.5Ｏ2、ＬｉＮｉ0.7Ｃｏ0.2Ｍｎ0.1Ｏ2などのリチウム含有遷移金属酸化物や、ＭｎＯ2などのリチウムを含有していない金属酸化物が例示される。また、この他にも、リチウムを電気化学的に挿入、脱離する物質であれば、制限なく用いることができる。 The positive electrode active material of the lithium secondary battery of the present invention is not particularly limited as long as it can be used as the positive electrode active material of a lithium secondary battery. For example, it has been conventionally used as a positive electrode active material. Does not contain lithium-containing transition metal oxides such as LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiMnO 2 , LiCo 0.5 Ni 0.5 O 2 , LiNi 0.7 Co 0.2 Mn 0.1 O 2 or lithium such as MnO 2 Metal oxide is exemplified. In addition, any substance that electrochemically inserts and desorbs lithium can be used without limitation.
本発明のリチウム二次電池に用いる非水電解質の溶媒は、特に限定されるものではないが、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ビニレンカーボネートなどの環状カーボネートと、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネートなどの鎖状カーボネートとの混合溶媒が例示される。また、上記環状カーボネートと１，２−ジメトキシエタン、１，２−ジエトキシエタンなどのエーテル系溶媒との混合溶媒も例示される。また、非水電解質の溶質としては、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣＦ3ＳＯ3、ＬｉＮ（ＣＦ3ＳＯ2)2、ＬｉＮ（Ｃ2Ｆ5ＳＯ2)2、ＬｉＮ（ＣＦ3ＳＯ2)(Ｃ4Ｆ9ＳＯ2)、ＬｉＣ（ＣＦ3ＳＯ2)3、ＬｉＣ（Ｃ2Ｆ5ＳＯ2)3、ＬｉＡｓＦ6、ＬｉＣｌＯ4、Ｌｉ2Ｂ10Ｃｌ10、Ｌｉ2Ｂ12Ｃｌ12など及びそれらの混合物が例示される。さらに電解質として、ポリエチレンオキシド、ポリアクリロニトリルなどのポリマー電解質に電解液を含浸したゲル状ポリマー電解質や、ＬｉＩ、Ｌｉ3Ｎなどの無機固体電解質が例示される。 The solvent of the non-aqueous electrolyte used in the lithium secondary battery of the present invention is not particularly limited, but cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl A mixed solvent with a chain carbonate such as carbonate is exemplified. Further, mixed solvents of the above cyclic carbonate and ether solvents such as 1,2-dimethoxyethane and 1,2-diethoxyethane are also exemplified. The solutes of the nonaqueous electrolyte include LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN (CF 3 SO 2 ) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, LiAsF 6, LiClO 4, Li 2 B 10 Cl 10, Li 2 B 12 Cl 12 and the like and their Mixtures are exemplified. Further, examples of the electrolyte include gel polymer electrolytes in which a polymer electrolyte such as polyethylene oxide and polyacrylonitrile is impregnated with an electrolytic solution, and inorganic solid electrolytes such as LiI and Li 3 N.
本発明によれば、シリコンを含む活物質層を集電体上に設けた電極を負極として用いたリチウム二次電池のサイクル特性を高めることができる。 ADVANTAGE OF THE INVENTION According to this invention, the cycling characteristics of the lithium secondary battery using the electrode which provided the active material layer containing silicon on the electrical power collector as a negative electrode can be improved.
以下、本発明を実施例に基づいてさらに詳細に説明するが、本発明は以下の実施例に何ら限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施することが可能なものである。 Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications within a range not changing the gist thereof. Is.
〔電極の作製〕
圧延銅箔（厚み２５μｍ）の表面に電解法で銅を析出することにより、表面に凹凸を形成した銅箔（厚み３０μｍ、表面粗さＲａ＝０．２μｍ）を集電体として用いた。この集電体の上に、厚み３．５μｍの非晶質シリコン薄膜を堆積し、電極を作製した。スパッタリングの条件は、直流パルス周波数：１００ｋＨｚ、直流パルス幅：１８５６ｎｓ、直流パルス電力：２０００Ｗ、アルゴン流量：６０ｓｃｃｍ、ガス圧力：２〜２．５×１０-1Ｐａ、形成時間：１０５分とした。なお、ここでは、スパッタリング用電力として直流パルスを供給しているが、直流や高周波でも同様の条件でスパッタリングすることが可能である。
[Production of electrodes]
A copper foil (thickness 30 μm, surface roughness Ra = 0.2 μm) having irregularities formed on the surface by depositing copper on the surface of the rolled copper foil (thickness 25 μm) was used as a current collector. An amorphous silicon thin film having a thickness of 3.5 μm was deposited on the current collector to produce an electrode. The sputtering conditions were as follows: DC pulse frequency: 100 kHz, DC pulse width: 1856 ns, DC pulse power: 2000 W, argon flow rate: 60 sccm, gas pressure: 2 to 2.5 × 10 −1 Pa, formation time: 105 minutes. Note that although a DC pulse is supplied as sputtering power here, sputtering can be performed under the same conditions even at DC or high frequency.
〔電解液の作製〕
エチレンカーボネートとジエチルカーボネートを体積比３：７で混合した溶媒に、ＬｉＰＦ6を１モル／リットルとなるように溶解させて、電解液を作製した。
(Preparation of electrolyte)
LiPF 6 was dissolved in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 so as to be 1 mol / liter to prepare an electrolytic solution.
〔小型ラミネートセルの作製〕
上記電極を２ｃｍ×２ｃｍの大きさに切り取ったものを作用極として用い、小型ラミネートセルを作製した。参照極としてはリチウム金属を用い、対極としては、ＬｉＣｏＯ2を用いた。対極は、作用極が０Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）となるのに必要な容量に対し大過剰となる容量のＬｉＣｏＯ2をアルミニウム箔の上に塗布して作製したものを用いた。
[Production of small laminate cells]
A small laminate cell was prepared by using the electrode cut into a size of 2 cm × 2 cm as a working electrode. Lithium metal was used as the reference electrode, and LiCoO 2 was used as the counter electrode. The counter electrode was prepared by applying on the aluminum foil a large excess of LiCoO 2 with respect to the capacity necessary for the working electrode to be 0 V (vs. Li / Li + ).
電解液としては、上記電解液を用いた。 As the electrolytic solution, the above electrolytic solution was used.
〔サイクル試験〕
上記のようにして作製した小型ラミネートセルを、２５℃にて、１１ｍＡで作用極（負極）の電位が０．０７Ｖになるまで定電流充電を行い、さらにその電位を保持したまま０．６ｍＡになるまで定電圧充電行った。その後、１１ｍＡで作用極が表１に示す所定の電位になるまで定電流放電を行い、これを１サイクルとして、１００サイクル充放電を行った。なお、ここでは、作用極の還元を充電とし、作用極の酸化を放電としている。以下の式により、１００サイクル目の容量維持率を算出し、表１に示した。
[Cycle test]
The small laminate cell produced as described above was charged at a constant current of 11 mA at 25 ° C. until the potential of the working electrode (negative electrode) reached 0.07 V, and further maintained at 0.6 mA while maintaining the potential. Constant voltage charging was performed until Then, constant current discharge was performed until the working electrode reached a predetermined potential shown in Table 1 at 11 mA, and this was defined as one cycle, and 100 cycles of charge / discharge were performed. Here, reduction of the working electrode is charging, and oxidation of the working electrode is discharging. The capacity retention rate at the 100th cycle was calculated according to the following formula and shown in Table 1.
１００サイクル目の容量維持率（％）＝（１００サイクル目の放電容量）／（１サイクル目の放電容量）×１００ Capacity maintenance ratio (%) at 100th cycle = (discharge capacity at 100th cycle) / (discharge capacity at the first cycle) × 100
１００サイクル後の実施例１の電極及び比較例３の電極について、活物質薄膜の断面を電子顕微鏡（ＳＥＭ）で観察した。図１（倍率２００００）は実施例１の電極であり、図２（倍率２００００）は比較例３の電極である。 About the electrode of Example 1 and the electrode of Comparative Example 3 after 100 cycles, the cross section of the active material thin film was observed with an electron microscope (SEM). 1 (magnification 20000) is the electrode of Example 1, and FIG. 2 (magnification 20000) is the electrode of Comparative Example 3.
図１及び図２に示すように、活物質薄膜の縦方向に切れ目が形成されていることがわかる。この切れ目は、シリコン薄膜が充放電反応により膨張・収縮することにより、その厚み方向に形成された切れ目である。この切れ目によりシリコン薄膜は柱状に分離されている。図１と図２の比較から明らかなように、図２に示す比較例３の電極においては、活物質である薄膜の表面に大きな凹凸が存在しており、薄膜の表面が荒れていることがわかる。これは、充放電反応によるシリコン薄膜の構造の変化が大きいことを示す。これに対し、図１に示す実施例１の電極では、このような薄膜表面の状態変化が認められない。 As shown in FIGS. 1 and 2, it can be seen that a cut is formed in the longitudinal direction of the active material thin film. This break is a break formed in the thickness direction by the silicon thin film expanding and contracting due to the charge / discharge reaction. The silicon thin film is separated into columns by the cuts. As is clear from the comparison between FIG. 1 and FIG. 2, in the electrode of Comparative Example 3 shown in FIG. 2, there are large irregularities on the surface of the thin film as the active material, and the surface of the thin film is rough. Recognize. This indicates that the change in the structure of the silicon thin film due to the charge / discharge reaction is large. On the other hand, in the electrode of Example 1 shown in FIG.
図３は、比較例３の１サイクル目の放電曲線を示す図である。図３から明らかなように、０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下の範囲で充放電を行っても、十分な充放電容量が得られることがわかる。 FIG. 3 is a diagram showing a discharge curve in the first cycle of Comparative Example 3. As is apparent from FIG. 3, it is understood that sufficient charge / discharge capacity can be obtained even when charge / discharge is performed in the range of 0.8 V (vs. Li / Li + ) or less.
従って、本発明によれば、充放電容量が高く、かつサイクル特性に優れたリチウム二次電池の充放電方法とすることができる。 Therefore, according to this invention, it can be set as the charging / discharging method of the lithium secondary battery which was high in charge / discharge capacity and excellent in cycling characteristics.
Claims (7)
初回の充電時を除き、前記負極の電位が０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下である範囲で充放電することを特徴とするリチウム二次電池の使用方法。 A method for using a lithium secondary battery in which an electrode provided with an active material layer containing silicon on a current collector made of a metal that is not alloyed with lithium is used as a negative electrode,
A method for using a lithium secondary battery, wherein charging and discharging are performed in a range where the potential of the negative electrode is 0.8 V (vs. Li / Li + ) or less except during the first charge.
初回の充電時を除き、前記負極の電位が０．８Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下である範囲で充放電することを特徴とするリチウム二次電池の使用方法。 A method for using a lithium secondary battery in which an electrode provided by depositing an amorphous silicon thin film on a current collector made of a metal not alloyed with lithium is used as a negative electrode,
A method for using a lithium secondary battery, wherein charging and discharging are performed in a range where the potential of the negative electrode is 0.8 V (vs. Li / Li + ) or less except during the first charge.
The method of using a lithium secondary battery according to claim 1, wherein the current collector is made of copper.
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| US9123928B2 (en) | 2011-05-27 | 2015-09-01 | Nec Corporation | Method for doping and dedoping lithium into and from negative electrode and method for producing negative electrode for lithium secondary battery |
| JP7019840B2 (en) | 2019-01-17 | 2022-02-15 | 三菱電機株式会社 | Semiconductor devices and methods for manufacturing semiconductor devices |
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| EP2267824B1 (en) | 2008-04-18 | 2014-05-07 | Kabushiki Kaisha Toyota Jidoshokki | Negative electrode for lithium-ion secondary battery and manufacturing process for the same |
| CN103943821A (en) * | 2013-01-18 | 2014-07-23 | 苏州宝时得电动工具有限公司 | Negative electrode, battery with negative electrode and negative electrode manufacturing method |
| JP6955660B2 (en) * | 2014-05-09 | 2021-10-27 | ユニチカ株式会社 | Power storage element |
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| US9123928B2 (en) | 2011-05-27 | 2015-09-01 | Nec Corporation | Method for doping and dedoping lithium into and from negative electrode and method for producing negative electrode for lithium secondary battery |
| JP7019840B2 (en) | 2019-01-17 | 2022-02-15 | 三菱電機株式会社 | Semiconductor devices and methods for manufacturing semiconductor devices |
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