JP5551101B2 - Negative electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents
Negative electrode for lithium ion secondary battery and lithium ion secondary battery Download PDFInfo
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Description
本発明は、高容量でサイクル特性が高いリチウムイオン二次電池用の負極およびかかる負極を備えるリチウムイオン二次電池に関する。 The present invention relates to a negative electrode for a lithium ion secondary battery having high capacity and high cycle characteristics, and a lithium ion secondary battery including such a negative electrode.
リチウムイオン二次電池は、負極に吸蔵されたリチウムがリチウムイオンと電子として放出され、該リチウムイオンはセパレータを通して、一方、電子は回路を通して、それぞれ正極に供給されることで放電する。一方、使用後は、正極が電子と共に放出するリチウムイオンを負極が吸蔵することで充電する仕組みである。通常、リチウムイオン二次電池の負極は、負極活物質からなる粒子（負極活物質粒子）、カーボンブラック等の導電助剤および樹脂製の結着剤とからなるスラリーを、金属箔上に塗布・乾燥したものが用いられている。充電時においては、正極の放出するリチウムイオンが負極表面の負極活物質と結合することで吸蔵される。負極活物質としては通常グラファイトが用いられているが、充電量を増やしてリチウムイオン二次電池の連続使用時間を伸ばすため、リチウムイオンの吸蔵量が高い（すなわち高容量の）負極活物質が求められている。 In the lithium ion secondary battery, lithium occluded in the negative electrode is released as lithium ions and electrons, and the lithium ions are discharged through the separator, while the electrons are supplied to the positive electrode through the circuit. On the other hand, after use, the negative electrode occludes lithium ions released together with electrons, and the negative electrode occludes charging. Usually, a negative electrode of a lithium ion secondary battery is formed by applying a slurry made of particles made of a negative electrode active material (negative electrode active material particles), a conductive auxiliary agent such as carbon black, and a resin binder onto a metal foil. A dry one is used. At the time of charging, lithium ions released from the positive electrode are occluded by combining with the negative electrode active material on the negative electrode surface. In general, graphite is used as the negative electrode active material. However, in order to increase the amount of charge and extend the continuous use time of the lithium ion secondary battery, a negative electrode active material having a high lithium ion storage amount (ie high capacity) is required. It has been.
グラファイトよりも高容量の負極活物質として、シリコンが注目されている。しかしながら、シリコンはリチウムイオンを吸蔵すると約４倍に体積が膨張するため、充放電に伴う膨張と収縮を繰り返すことによってシリコンからなる負極活物質粒子が破壊され、負極から脱落する傾向にある。このためシリコンを負極活物質として用いると、リチウムイオン二次電池の繰り返し使用性（サイクル特性）が悪化するという問題があった。 Silicon is attracting attention as a negative electrode active material having a higher capacity than graphite. However, since the volume of silicon expands by about 4 times when lithium ions are occluded, negative electrode active material particles made of silicon tend to be destroyed and fall off from the negative electrode by repeating expansion and contraction associated with charge and discharge. For this reason, when silicon is used as the negative electrode active material, there is a problem in that the repetitive usability (cycle characteristics) of the lithium ion secondary battery is deteriorated.
そこで、充放電に伴う膨張と収縮の繰り返しによる負極活物質粒子の破壊を抑制するために、シリコンの表面を弾性の高いカーボンナノファイバで被覆した負極活物質粒子が提案されている(特許文献１参照)。かかる負極活物質粒子は膨張と収縮を繰り返しても表面を被覆するカーボンナノファイバによって破壊が抑制される。しかしながら、かかる負極活物質粒子は膨張と収縮によって結着剤から剥離しやすくなり、負極から脱落する傾向となるため、リチウムイオン二次電池のサイクル特性向上には繋がり難い。 Accordingly, negative electrode active material particles in which the surface of silicon is coated with highly elastic carbon nanofibers have been proposed in order to suppress destruction of the negative electrode active material particles due to repeated expansion and contraction associated with charge and discharge (Patent Document 1). reference). Even if the negative electrode active material particles are repeatedly expanded and contracted, the carbon nanofiber covering the surface suppresses the breakage. However, such negative electrode active material particles tend to peel from the binder due to expansion and contraction, and tend to fall off from the negative electrode, so that it is difficult to improve the cycle characteristics of the lithium ion secondary battery.
一方、シリコンの結着剤からの剥離を避けるため、ＣＶＤ法、レーザー蒸着などによってシリコンを金属箔上に成膜する方法が提案されている（特許文献２、特許文献３参照）。これらの方法によれば、シリコンは結着剤などを介さず、高密度のシリコン膜が直接金属箔上に製膜される。 On the other hand, in order to avoid peeling of silicon from the binder, a method of forming a film of silicon on a metal foil by a CVD method, laser deposition, or the like has been proposed (see Patent Document 2 and Patent Document 3). According to these methods, silicon is formed directly on the metal foil without using a binder or the like.
しかしながら、ＣＶＤ法、レーザー蒸着などによってシリコンを金属箔上に成膜した場合、高容量化すべくシリコン膜の厚さを厚くすると、充放電に伴う膨張と収縮の繰り返しによって金属箔から剥離しやすくなる。このため高容量化とサイクル特性の両立が困難であった。 However, when silicon is deposited on the metal foil by CVD, laser deposition, etc., if the thickness of the silicon film is increased in order to increase the capacity, it becomes easy to peel off from the metal foil due to repeated expansion and contraction associated with charge / discharge. . For this reason, it is difficult to achieve both high capacity and cycle characteristics.
本発明の目的は、高容量と高いサイクル特性を実現するリチウムイオン二次電池用の負極およびかかる負極を備えるリチウムイオン二次電池を提供することにある。 The objective of this invention is providing the lithium ion secondary battery provided with the negative electrode for lithium ion secondary batteries which implement | achieves a high capacity | capacitance and high cycling characteristics, and this negative electrode.
本発明によれば、上記の目的は金属箔上に、炭素単体を１０〜１００００ｐｐｍ含有するシリコンからなる気孔率３〜２０％のシリコン膜を備えるリチウムイオン二次電池用の負極、およびかかる負極を備えるリチウムイオン二次電池を提供することによって達成される。本発明の負極が備える上記シリコン膜の厚さは１〜５０μｍの範囲であることが好ましい。 According to the present invention, the above object is to provide a negative electrode for a lithium ion secondary battery comprising a silicon film having a porosity of 3 to 20% made of silicon containing 10 to 10,000 ppm of carbon alone on a metal foil, and such a negative electrode. This is achieved by providing a lithium ion secondary battery comprising the same. The thickness of the silicon film provided in the negative electrode of the present invention is preferably in the range of 1 to 50 μm.
本発明によれば、高容量で高いサイクル特性を実現できるリチウムイオン二次電池用の負極およびかかる負極を備えるリチウムイオン二次電池を提供できる。 ADVANTAGE OF THE INVENTION According to this invention, a lithium ion secondary battery provided with the negative electrode for lithium ion secondary batteries which can implement | achieve a high capacity | capacitance and high cycling characteristics, and this negative electrode can be provided.
本発明に用いるシリコン中の炭素単体の含有率は１０〜１００００ｐｐｍの範囲であり、好ましくは１０〜８０００ｐｐｍの範囲である。炭素単体は、シリコンに添加、混合しても良いし、シリコンウエハ製造時に切削された炭素単体を含むシリコン屑のように、炭素単体がシリコン上に付着したものを本発明で用いてもよい。また本発明で用いるシリコンは、鉄、ニッケルなどの微量の遷移金属、ホウ素、リンなどを含んでいてもよい。かかるシリコンから形成されるシリコン膜は、導電性が良好である。 The content of carbon alone in silicon used in the present invention is in the range of 10 to 10000 ppm, preferably in the range of 10 to 8000 ppm. The carbon simple substance may be added to and mixed with silicon, or the carbon simple substance attached on the silicon, such as silicon scrap containing the carbon simple substance cut at the time of manufacturing the silicon wafer, may be used in the present invention. Silicon used in the present invention may contain a trace amount of transition metals such as iron and nickel, boron, phosphorus and the like. A silicon film formed from such silicon has good conductivity.
上記炭素単体としては、グラファイト、カーボンナノチューブ、フラーレン、アモルファスカーボンなどが挙げられ、導電性、入手性の観点からグラファイトが好ましい。 Examples of the carbon simple substance include graphite, carbon nanotube, fullerene, amorphous carbon, and the like, and graphite is preferable from the viewpoint of conductivity and availability.
本発明の負極は、金属箔の少なくとも片面に上記シリコン膜を備える。 The negative electrode of the present invention includes the silicon film on at least one surface of a metal foil.
本発明の負極が備えるシリコン膜の気孔率は３〜２０％の範囲であり、好ましくは５〜１８％の範囲である。気孔率が２０％を超えると、金属箔の接点が減少することで剥離しやすくなり、気孔率が３％を下回ると、充放電に伴う膨張と収縮の繰り返しによって金属箔から剥離しやすくなる。 The porosity of the silicon film provided in the negative electrode of the present invention is in the range of 3 to 20%, preferably in the range of 5 to 18%. If the porosity exceeds 20%, the contact of the metal foil is reduced, so that the metal foil is easily peeled. If the porosity is less than 3%, the metal foil is easily peeled due to repeated expansion and contraction associated with charge / discharge.
本発明の負極が備えるシリコン膜の厚さは、好ましくは１〜５０μｍ、より好ましくは１〜４０μｍの範囲である。シリコン膜の厚さが５０μｍを超えると、充放電に伴う膨張と収縮によって金属箔から剥離しやすくなる場合がある。一方、シリコン膜の厚さが１μｍを下回ると、リチウムイオンの吸蔵量が少なくなるだけでなく、シリコン膜の均一性低下による局所的な過電流が引き起こされる。 The thickness of the silicon film provided in the negative electrode of the present invention is preferably 1 to 50 μm, more preferably 1 to 40 μm. If the thickness of the silicon film exceeds 50 μm, it may be easily peeled off from the metal foil due to expansion and contraction associated with charge / discharge. On the other hand, when the thickness of the silicon film is less than 1 μm, not only the amount of occlusion of lithium ions is reduced, but also a local overcurrent is caused by a decrease in the uniformity of the silicon film.
本発明の負極が備えるシリコン膜は金属箔へのシリコンの溶射によって形成できる。溶射の方法としては、フレーム溶射、爆発溶射、電気式溶射、ガス溶射、コールドスプレーなどが挙げられ、このうち操作性、原材料の選択の観点から、電気式溶射が好ましい。電気式溶射としては、アーク溶射方式、減圧プラズマ式溶射方式、大気プラズマ溶射方式、水プラズマ式溶射方式が挙げられ、このうち操作性、緻密性制御の観点から、大気プラズマ溶射方式が好ましい。 The silicon film provided in the negative electrode of the present invention can be formed by thermal spraying of silicon on a metal foil. Examples of the thermal spraying method include flame spraying, explosive spraying, electric spraying, gas spraying, and cold spraying. Of these, electrical spraying is preferable from the viewpoint of operability and selection of raw materials. Examples of the electric spraying include an arc spraying method, a low-pressure plasma spraying method, an atmospheric plasma spraying method, and a water plasma spraying method. Of these, the atmospheric plasma spraying method is preferable from the viewpoint of operability and denseness control.
上記シリコン膜を溶射によって形成する場合、溶射ガンで発生したプラズマ炎の中にシリコン粒子を供給口よりアルゴンあるいは窒素ガス圧により投入し、金属箔の表面に吹き付ける。シリコン膜の気孔率は溶射ガンの出力および溶射ガンと金属箔との距離（溶射距離）によって調整できる。プラズマ溶射を行う場合、一般に、溶射ガンの出力は１〜８０ｋＷ、溶射距離１００〜５００ｍｍの条件で行われる。出力が高い場合および溶射距離が近い場合は、気孔率が低下する傾向となり、出力が低い場合および溶射距離が遠い場合は、気孔率が上昇する傾向となる。 When the silicon film is formed by thermal spraying, silicon particles are put into a plasma flame generated by a spray gun by argon or nitrogen gas pressure from a supply port and sprayed on the surface of the metal foil. The porosity of the silicon film can be adjusted by the output of the spray gun and the distance between the spray gun and the metal foil (spray distance). When performing plasma spraying, generally the output of a spray gun is performed on the conditions of 1-80 kW and the spraying distance of 100-500 mm. When the output is high and the spraying distance is short, the porosity tends to decrease, and when the output is low and the spraying distance is long, the porosity tends to increase.
上記溶射に用いるシリコン粒子の粒径は、通常０．０５〜１０μｍであり、好ましくは０．０５〜６μｍの範囲である。粒径が１０μｍよりも大きいと目的の膜厚に制御することが難しく、０．０５μｍよりも小さいと膜厚ムラが生じやすい。 The particle size of the silicon particles used for the thermal spraying is usually 0.05 to 10 μm, preferably 0.05 to 6 μm. When the particle size is larger than 10 μm, it is difficult to control the film thickness to a target, and when it is smaller than 0.05 μm, film thickness unevenness is likely to occur.
本発明で用いる金属箔としては、銅、ニッケル、アルミニウムなどの金属箔が挙げられるが、銅箔が好ましい。また、金属箔の表面を機械加工などで粗面化することが、シリコン膜との剥離を抑制する上で好ましい。 As metal foil used by this invention, metal foil, such as copper, nickel, aluminum, is mentioned, Copper foil is preferable. In addition, it is preferable to roughen the surface of the metal foil by machining or the like in order to suppress peeling from the silicon film.
本発明で用いる金属箔の厚さは、通常０．１〜１００μｍの範囲であり、好ましくは１〜５０μｍの範囲である。金属箔の厚さが０．１μｍを下回ると溶射による熱によって金属箔が収縮、変形する傾向にあり、１００μｍを上回るとリチウムイオン二次電池に占める負極の体積が大きくなり、電池容量が小さくなる。 The thickness of the metal foil used in the present invention is usually in the range of 0.1 to 100 μm, and preferably in the range of 1 to 50 μm. When the thickness of the metal foil is less than 0.1 μm, the metal foil tends to shrink and deform due to heat generated by thermal spraying. When the thickness is more than 100 μm, the volume of the negative electrode in the lithium ion secondary battery increases and the battery capacity decreases. .
次に、本発明のリチウムイオン二次電池の製造方法を説明する。かかるリチウムイオン二次電池は、電池ケース内に、正極と負極との間にセパレータを配置してなる電池構造体とともに、電解液を入れてなる。 Next, the manufacturing method of the lithium ion secondary battery of this invention is demonstrated. In such a lithium ion secondary battery, an electrolytic solution is put in a battery case together with a battery structure in which a separator is disposed between a positive electrode and a negative electrode.
本発明のリチウムイオン二次電池が備える正極は、通常、正極活物質、導電助剤、樹脂製の結着剤、増粘剤及び溶媒を混合してスラリーを調製し、アルミ箔などの金属箔の少なくとも片面に塗布・乾燥することで製造できる。 The positive electrode provided in the lithium ion secondary battery of the present invention is usually prepared by mixing a positive electrode active material, a conductive additive, a resin binder, a thickener and a solvent to prepare a slurry, and a metal foil such as an aluminum foil. Can be produced by applying and drying on at least one side.
正極活物質としては、通常、リチウム金属酸化物が用いられ、かかるリチウム金属酸化物としては、ＬｉＣｏＯ２、ＬｉＭｎ２Ｏ４、ＬｉＭｎＯ２、ＬｉＮｉＯ２、ＬｉＦｅＯ２、ＬｉＦｅＰＯ４、Ｌｉ２ＦｅＰＯ４Ｆ、ＬｉＣｏ１/３Ｎｉ１/３Ｍｎ１/３Ｏ２が挙げられる。 As the positive electrode active material, a lithium metal oxide is usually used. As the lithium metal oxide, LiCoO 2 , LiMn 2 O 4 , LiMnO 2 , LiNiO 2 , LiFeO 2 , LiFePO 4 , Li 2 FePO 4 F, LiCo 1/3 Ni 1/3 Mn 1/3 O 2 may be mentioned.
上記導電助剤としてはカーボンブラックが挙げられる。上記結着剤としてはフッ化ビニリデン／ヘキサフルオロプロピレンコポリマー、ポリフッ化ビニリデン、ポリアクリロニトリル、ポリメチルメタクリレート、ポリテトラフルオロエチレン、およびスチレンブタジエンゴム系ポリマーが挙げられる。上記増粘剤としてはポリビニルアルコール、カルボキシメチルセルロースなどが挙げられる。また、正極活物質の組成物に用いる溶媒としてはＮ−メチルピロリドン（ＮＭＰ）、アセトン、および水が挙げられる。 Examples of the conductive aid include carbon black. Examples of the binder include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, and a styrene butadiene rubber-based polymer. Examples of the thickener include polyvinyl alcohol and carboxymethyl cellulose. Moreover, N-methylpyrrolidone (NMP), acetone, and water are mentioned as a solvent used for the composition of a positive electrode active material.
本発明のリチウムイオン二次電池が備えるセパレータとしては、正極と負極の電子伝導を絶縁する機能を有する、リチウムイオン二次電池で通常用いられるものを使用できる。かかるセパレータの例としては、多孔質ポリプロピレン層／多孔質ポリエチレン層／多孔質ポリプロピレン層の３層からなる複層膜が挙げられる。かかるセパレータの厚さは、電解質のイオン移動に対する抵抗の低さ、リチウムイオン二次電池の容量向上の観点から、好ましくは０．５〜３０μｍ以下、より好ましくは１〜２０μｍである。 As a separator with which the lithium ion secondary battery of this invention is equipped, what is normally used with the lithium ion secondary battery which has a function which insulates the electronic conduction of a positive electrode and a negative electrode can be used. An example of such a separator is a multilayer film composed of three layers of a porous polypropylene layer / a porous polyethylene layer / a porous polypropylene layer. The thickness of the separator is preferably 0.5 to 30 μm, more preferably 1 to 20 μm, from the viewpoint of low resistance to ion migration of the electrolyte and improvement in capacity of the lithium ion secondary battery.
本発明のリチウムイオン二次電池に用いる電解液としては、炭酸プロピレン、炭酸エチレン、炭酸ブチレン、ベンゾニトリル、アセトニトリル、テトラヒドロフラン、２−メチルテトラヒドロフラン、γ−ブチロラクトン、ジオキソラン、４−メチルオキソラン、Ｎ，Ｎ−ジメチルホルムアミド、ジメチルアセトアミド、ジメチルスルホキシド、ジオキサン、１，２−ジメトキシエタン、スルホラン、ジクロロエタン、クロロベンゼン、ニトロベンゼン、炭酸ジメチル、炭酸メチルエチル、炭酸ジエチル、炭酸メチルプロピル、炭酸メチルイソプロピル、炭酸エチルプロピル、炭酸ジプロピル、炭酸ジブチル、ジエチレングリコール、ジメチルエーテルなどから選ばれる溶媒または混合溶媒にＬｉＰＦ６、ＬｉＢＦ４、ＬｉＳｂＦ６、ＬｉＡｓＦ６、ＬｉＣｌＯ４、ＬｉＣＦ３ＳＯ３、Ｌｉ（ＣＦ３ＳＯ２）２Ｎ、ＬｉＣ４Ｆ９ＳＯ３、ＬｉＡｌＯ４、ＬｉＡｌＣｌ４、ＬｉＮ（ＣｘＦ２ｘ＋１ＳＯ２）（ＣｙＦ２ｙ＋１ＳＯ２）（ただし、ｘ，ｙは自然数）、ＬｉＣｌ、ＬｉＩなどのリチウム塩からなる電解質の少なくとも１種を溶解した溶液を用いる。 Examples of the electrolyte used for the lithium ion secondary battery of the present invention include propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyloxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, LiPF 6, LiBF 4 dipropyl carbonate, dibutyl carbonate, diethylene glycol, a solvent or a mixed solvent selected from such as dimethyl ether, LiSbF 6, L AsF 6, LiClO 4, LiCF 3 SO 3, Li (CF 3 SO 2) 2 N, LiC 4 F 9 SO 3, LiAlO 4, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F 2y + 1 SO 2 (Where x and y are natural numbers), a solution in which at least one electrolyte composed of a lithium salt such as LiCl or LiI is dissolved is used.
上記した正極と負極との間にセパレータを配置して、電池構造体を形成する。このような電池構造体を巻くか、または折って円筒形の電池ケースや角形の電池ケースに入れた後、電解液を注入して、リチウムイオン二次電池とする。 A separator is disposed between the positive electrode and the negative electrode described above to form a battery structure. Such a battery structure is wound or folded and put into a cylindrical battery case or a rectangular battery case, and then an electrolytic solution is injected to obtain a lithium ion secondary battery.
本発明のリチウムイオン二次電池は、正極および負極と通電対象をリード線で接続して通電を行う。かかる正極および負極は、リード線との結合を容易にするために、リード線を結んだり、ハンダ付けしたりできる金属製のタブを備えていてもよい。かかるタブに用いる金属としてはアルミニウム、銅、ニッケルなどが挙げられる。 The lithium ion secondary battery of the present invention is energized by connecting the positive electrode and the negative electrode to the energization target with lead wires. The positive electrode and the negative electrode may be provided with a metal tab that can be connected to the lead wire or soldered to facilitate the coupling with the lead wire. Examples of the metal used for the tab include aluminum, copper, and nickel.
以下に実施例を示し、本発明を詳細に説明するが、本発明は以下の実施例に限定されるものではない。
シリコン粒子の粒径測定には堀場製作所製 レーザー回折/散乱式粒子径分布測定装置（商品名：PARTICA LA950）、炭素含量の測定には堀場製作所製 炭素・硫黄分析装置（商品名：EMIA-810W）を使用した
シリコン膜の厚さは薄膜断面を電子顕微鏡（キーエンス製 KEYENCE VE8800）で観察し測定した。
EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.
Laser diffraction / scattering particle size distribution analyzer (trade name: PARTICA LA950) manufactured by HORIBA, Ltd. for silicon particle size measurement, and carbon / sulfur analyzer (product name: EMIA-810W) manufactured by HORIBA, Ltd. for carbon content measurement The thickness of the silicon film was measured by observing the cross section of the thin film with an electron microscope (KEYENCE VE8800 manufactured by Keyence).
［実施例１］
プラズマ溶射ガン（日本ユテク社製テロダインシステム２０００）に、炭素含量２００ｐｐｍ、粒径０．０２〜１．５μｍのシリコン粒子を供給しながら、プラズマ投入電力３０ＫＷ、窒素流量４０リットル／分、シリコン粒子の供給量１ｇ／分の条件で、高温プラズマ発生部と厚さ２０μｍの銅箔との距離１２０ｍｍとして２０秒間溶射処理を行い、銅箔の片面に厚さ１２μｍのシリコン膜を形成した。かかる薄膜の厚さ、使用したシリコンの量、シリコンの密度から算出される気孔率は１１％であった。このようにして本発明の負極を得た。
[Example 1]
While supplying silicon particles having a carbon content of 200 ppm and a particle size of 0.02 to 1.5 μm to a plasma spray gun (Terodyne System 2000 manufactured by Nippon Yutec Co., Ltd.), a plasma input power of 30 KW, a nitrogen flow rate of 40 liters / minute, Thermal spraying was performed for 20 seconds at a distance of 120 mm between the high-temperature plasma generating part and a 20 μm thick copper foil under the condition of a supply rate of 1 g / min, and a 12 μm thick silicon film was formed on one side of the copper foil. The porosity calculated from the thickness of the thin film, the amount of silicon used, and the density of silicon was 11%. Thus, the negative electrode of the present invention was obtained.
［実施例２］
実施例１において、窒素流量を６０リットル／ｍｉｎとした以外は、実施例１と同様に行い、気孔率１５％、厚さ１０μｍのシリコン膜を形成した。このようにして本発明の負極を得た。
[Example 2]
A silicon film having a porosity of 15% and a thickness of 10 μm was formed in the same manner as in Example 1 except that the nitrogen flow rate was changed to 60 liters / min. Thus, the negative electrode of the present invention was obtained.
［比較例１］
実施例１において、プラズマ投入電力を６０ＫＷとした以外は、実施例１と同様に行い、気孔率１％、厚さ１２μｍのシリコン膜を形成した。このようにして本発明の比較例である負極を得た。
[Comparative Example 1]
In Example 1, a silicon film having a porosity of 1% and a thickness of 12 μm was formed in the same manner as in Example 1 except that the plasma input power was 60 kW. In this way, a negative electrode as a comparative example of the present invention was obtained.
［実施例３］
実施例１で得られた負極を２．５ｃｍ×２．５ｃｍの大きさに切り取り、これに銅製導電性テープからなるタブを取り付けた。
[Example 3]
The negative electrode obtained in Example 1 was cut into a size of 2.5 cm × 2.5 cm, and a tab made of a copper conductive tape was attached thereto.
ＬｉＣｏＯ2粉末（宝泉製、ｄ５０ １０μｍ 高容量タイプ）９０質量部、及び導電剤としての人造黒鉛粉末５質量部を、結着剤としてのポリテトラフルオロエチレン５質量部を分散させたＮ−メチルピロリドン２０質量部に混合し、正極活物質の組成物とした。この組成物をドクターブレード法により、アルミニウム箔（厚さ１８μｍ；２ｃｍ×２ｃｍ）の片面に塗布した後乾燥し、正極を形成した。正極活物質層を塗布しなかったアルミニウム箔の背面よりアルミニウム製導電性テープからなるタブを取り付けた。 N-methyl in which 90 parts by mass of LiCoO 2 powder (manufactured by Hosen, d50 10 μm high capacity type) and 5 parts by mass of artificial graphite powder as a conductive agent are dispersed in 5 parts by mass of polytetrafluoroethylene as a binder. It mixed with 20 mass parts of pyrrolidone, and it was set as the composition of the positive electrode active material. This composition was applied to one side of an aluminum foil (thickness 18 μm; 2 cm × 2 cm) by the doctor blade method and then dried to form a positive electrode. A tab made of an aluminum conductive tape was attached from the back surface of the aluminum foil to which the positive electrode active material layer was not applied.
炭酸プロピレンと炭酸エチルを９：１の体積比で混合した溶媒に、ＬｉＰＦ6を１モル／リットルとなるように溶解し、電解液を作製した。 LiPF 6 was dissolved in a solvent in which propylene carbonate and ethyl carbonate were mixed at a volume ratio of 9: 1 so as to be 1 mol / liter to prepare an electrolytic solution.
前記の負極、正極、及び電解液を用いて、リチウム二次電池を作製した。負極のシリコン膜と正極の正極活物質を塗布した面が、セパレータを介して対向するように配置した。セパレータとして、厚さ１０μｍの単層ポリプロピレン製多孔質フィルム（宝泉製、商品名：セルガード）を用いた。これらをアルミニウムラミネートからなる外装体（宝泉製 アルミラミネートフィルムシーラント）に挿入し、上記電解液５００μＬを注液し、外装体の封止部をラミネータにより封止して、リチウムイオン二次電池を作製した。
［実施例４］
実施例３において、実施例２で作製した負極を用いた以外は、実施例３と同様にしてリチウムイオン二次電池を作成した。
［比較例２］
実施例３において、比較例１で作製した負極を用いた以外は、実施例３と同様にしてリチウムイオン二次電池を作成した。
A lithium secondary battery was produced using the negative electrode, the positive electrode, and the electrolytic solution. The negative electrode silicon film and the positive electrode applied with the positive electrode active material were disposed so that the surfaces of the negative electrode film and the positive electrode active material were opposed to each other with a separator interposed therebetween. As a separator, a 10 μm-thick single layer polypropylene porous film (made by Hosen, trade name: Celgard) was used. These are inserted into an outer package made of aluminum laminate (aluminum laminate film sealant made by Hosen), 500 μL of the electrolyte solution is injected, and the sealing part of the outer package is sealed with a laminator, and a lithium ion secondary battery is manufactured. Produced.
[Example 4]
In Example 3, a lithium ion secondary battery was produced in the same manner as in Example 3 except that the negative electrode produced in Example 2 was used.
[Comparative Example 2]
In Example 3, a lithium ion secondary battery was produced in the same manner as in Example 3 except that the negative electrode produced in Comparative Example 1 was used.
実施例３、実施例４、比較例２で作成したリチウムイオン二次電池を、２５℃において、電流値１０ｍＡで４．２Ｖまで充電した後、電流値１０ｍＡで２．７５Ｖまで放電し、これを１サイクルの充放電とした。得られた放電容量から、負極１ｇあたりの放電容量（ｍAh）を算出し、３０サイクル後の放電容量と１回目のサイクルでの放電容量から容量維持率を算出した。結果を表１に示す。 The lithium ion secondary batteries prepared in Example 3, Example 4, and Comparative Example 2 were charged to 4.2 V at a current value of 10 mA at 25 ° C., and then discharged to 2.75 V at a current value of 10 mA. One cycle of charge / discharge was performed. From the obtained discharge capacity, the discharge capacity (mAh) per 1 g of the negative electrode was calculated, and the capacity retention rate was calculated from the discharge capacity after 30 cycles and the discharge capacity in the first cycle. The results are shown in Table 1.
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