JP4798952B2 - Method for manufacturing lithium secondary battery - Google Patents

Method for manufacturing lithium secondary battery Download PDF

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JP4798952B2
JP4798952B2 JP2004078016A JP2004078016A JP4798952B2 JP 4798952 B2 JP4798952 B2 JP 4798952B2 JP 2004078016 A JP2004078016 A JP 2004078016A JP 2004078016 A JP2004078016 A JP 2004078016A JP 4798952 B2 JP4798952 B2 JP 4798952B2
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aqueous electrolyte
carbon dioxide
electrolyte
secondary battery
lithium secondary
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JP2005268016A (en
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博之 南
弘雅 八木
勝信 佐山
善雄 加藤
茂樹 松田
丸男 神野
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Sanyo Electric Co Ltd
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    • YGENERAL 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
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    • YGENERAL 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
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Description

本発明は、リチウム二次電池の製造方法に関するものであり、詳細にはシリコン非結晶薄膜またはシリコンを主成分とする非結晶薄膜を集電体上に堆積させた負極を用いたリチウム二次電池の製造方法に関するものである。   The present invention relates to a method for manufacturing a lithium secondary battery, and more specifically, a lithium secondary battery using a negative electrode in which a silicon amorphous thin film or an amorphous thin film mainly composed of silicon is deposited on a current collector. It is related with the manufacturing method.

近年、高出力及び高エネルギー密度の新型二次電池の1つとして、非水電解液を用い、リチウムイオンを正極と負極との間で移動させて充放電を行うリチウム二次電池が利用されている。   In recent years, a lithium secondary battery that uses a non-aqueous electrolyte and charges and discharges by moving lithium ions between a positive electrode and a negative electrode has been used as one of the new secondary batteries with high output and high energy density. Yes.

このようなリチウム二次電池用負極として、リチウムと合金化する材料を負極活物質として用いたものが検討されている。リチウムと合金化する材料としては、例えばシリコンが検討されている。しかしながら、シリコン等のリチウムと合金化する材料は、リチウムを吸蔵・放出する際に、活物質の体積が膨張・収縮するため、充放電に伴い活物質が微粉化したり、活物質が集電体から脱離する。このため、電極内の集電性が低下し、充放電サイクル特性が悪くなるという問題があった。   As such a negative electrode for a lithium secondary battery, a material using a material alloyed with lithium as a negative electrode active material has been studied. As a material alloyed with lithium, for example, silicon has been studied. However, materials that alloy with lithium, such as silicon, expand and contract the volume of the active material when occluding and releasing lithium, so that the active material is pulverized with charge and discharge, or the active material is a current collector Detach from. For this reason, there existed a problem that the current collection property in an electrode fell and charging / discharging cycling characteristics worsened.

本出願人は、シリコンを活物質とし、良好な充放電サイクル特性を示すリチウム二次電池用電極として、スパッタリング法、化学気相堆積法(CVD法)、及び蒸着法などの薄膜形成方法により、集電体上にシリコンの非結晶薄膜を形成した電極を提案している(特許文献1)。また、シリコンにコバルトなどの他の元素を添加したリチウム二次電池用電極を提案している(特許文献2)。一方、炭素材料または金属リチウムなどを負極活物質としたリチウム二次電池においては、非水電解質に二酸化炭素を溶解させることが提案されている(例えば、特許文献3〜13)。   The present applicant uses silicon as an active material, and as an electrode for a lithium secondary battery exhibiting good charge / discharge cycle characteristics, by a thin film formation method such as sputtering, chemical vapor deposition (CVD), and vapor deposition, An electrode in which an amorphous thin film of silicon is formed on a current collector has been proposed (Patent Document 1). Further, an electrode for a lithium secondary battery in which another element such as cobalt is added to silicon has been proposed (Patent Document 2). On the other hand, in a lithium secondary battery using a carbon material or metallic lithium as a negative electrode active material, it has been proposed to dissolve carbon dioxide in a nonaqueous electrolyte (for example, Patent Documents 3 to 13).

本出願人が提案している上記リチウム二次電池は、充放電容量が大きく、サイクル特性に優れる電池であるが、充放電の繰り返しにより活物質層が多孔質化し、活物質層の厚みが増加するという問題があった。   The lithium secondary battery proposed by the present applicant is a battery having a large charge / discharge capacity and excellent cycle characteristics, but the active material layer becomes porous due to repeated charge / discharge, and the thickness of the active material layer increases. There was a problem to do.

本出願人は、上記問題を解消するため、二酸化炭素を溶解させた非水電解質を用いることを提案している(特願2003−163692号)。非水電解質に二酸化炭素を溶解させることにより、充放電反応に伴って生じる活物質層の多孔質化を抑制することができる。従って、充放電による活物質層の厚みの増加を少なくすることができ、リチウム二次電池の体積エネルギー密度を高めることができるとともに、充放電サイクル特性を高めることができる。しかしながら、非水電解質に溶解できる二酸化炭素量は、温度依存性を有するため、常温常圧下で二酸化炭素を溶解させた非水電解質は、高温時に二酸化炭素の溶解量が低下し、非水電解質中に溶解していた二酸化炭素がガスとして発生する場合がある。このようなガスが、正極及び負極の間で発生すると、ガスと接触している電極の部分は、充放電に関与しなくなり、大幅に充放電容量が低下する。また、電池内部にガスが充満して電池の厚みが増加するという問題を生じる。このような問題を低減するため、非水電解質中に溶解させる二酸化炭素の量を少なくすることが考えられるが、充放電サイクル特性向上の効果は、溶解する二酸化炭素の量に比例するものであるため、二酸化炭素の溶解量を少なくすると、それに伴って充放電サイクル特性が低下する。
国際公開第01/29913号パンフレット 国際公開第02/071512号パンフレット 米国特許第4853304号明細書 特開平6−150975号公報 特開平6−124700号公報 特開平7−176323号公報 特開平7−249431号公報 特開平8−64246号公報 特開平9−63649号公報 特開平10−40958号公報 特開2001−307771号公報 特開2002−329502号公報 特開2003−86243号公報
In order to solve the above problem, the present applicant has proposed to use a non-aqueous electrolyte in which carbon dioxide is dissolved (Japanese Patent Application No. 2003-163692). By dissolving carbon dioxide in the non-aqueous electrolyte, it is possible to prevent the active material layer from becoming porous due to the charge / discharge reaction. Therefore, an increase in the thickness of the active material layer due to charge / discharge can be reduced, the volume energy density of the lithium secondary battery can be increased, and charge / discharge cycle characteristics can be improved. However, since the amount of carbon dioxide that can be dissolved in the non-aqueous electrolyte is temperature-dependent, a non-aqueous electrolyte in which carbon dioxide is dissolved under normal temperature and normal pressure has a low carbon dioxide solubility at high temperatures. Carbon dioxide dissolved in the gas may be generated as a gas. When such a gas is generated between the positive electrode and the negative electrode, the portion of the electrode that is in contact with the gas is not involved in charge / discharge, and the charge / discharge capacity is significantly reduced. In addition, there is a problem that the battery is filled with gas and the thickness of the battery increases. In order to reduce such problems, it is conceivable to reduce the amount of carbon dioxide dissolved in the non-aqueous electrolyte, but the effect of improving the charge / discharge cycle characteristics is proportional to the amount of dissolved carbon dioxide. For this reason, if the amount of carbon dioxide dissolved is reduced, the charge / discharge cycle characteristics are reduced accordingly.
International Publication No. 01/29913 Pamphlet International Publication No. 02/071512 Pamphlet U.S. Pat. No. 4,853,304 JP-A-6-150975 JP-A-6-124700 JP 7-176323 A Japanese Patent Laid-Open No. 7-249431 JP-A-8-64246 Japanese Patent Laid-Open No. 9-63649 Japanese Patent Laid-Open No. 10-40958 JP 2001-307771 A JP 2002-329502 A JP 2003-86243 A

本発明の目的は、非水電解質中に溶解している二酸化炭素の量が少なくても、良好な充放電サイクル特性を示すリチウム二次電池を製造することができる方法を提供することにある。   An object of the present invention is to provide a method capable of producing a lithium secondary battery exhibiting good charge / discharge cycle characteristics even when the amount of carbon dioxide dissolved in a non-aqueous electrolyte is small.

本発明は、シリコン非結晶薄膜またはシリコンを主成分とする非結晶薄膜を集電体上に堆積させた負極と、正極と、非水電解質とを備えるリチウム二次電池の製造方法であり、二酸化炭素を溶解させた第1の非水電解質に負極及び正極を接触させて少なくとも1サイクルの充放電を行う工程と、該充放電後に、第1の非水電解質よりも二酸化炭素の溶解量が少ない第2の非水電解質を用いて、最終的な電池を組み立てる工程とを備えることを特徴としている。   The present invention is a method for producing a lithium secondary battery comprising a negative electrode obtained by depositing a silicon amorphous thin film or an amorphous thin film mainly composed of silicon on a current collector, a positive electrode, and a non-aqueous electrolyte. A step of charging and discharging at least one cycle by bringing the negative electrode and the positive electrode into contact with the first nonaqueous electrolyte in which carbon is dissolved, and the amount of carbon dioxide dissolved after the charge and discharge is less than that of the first nonaqueous electrolyte And a step of assembling a final battery using the second non-aqueous electrolyte.

本発明においては、第1の非水電解質と第2の非水電解質を用いており、まず相対的に二酸化炭素の溶解量が多い第1の非水電解質中で、少なくとも1サイクルの充放電を行う。その後、第1の非水電解質よりも二酸化炭素の溶解量が相対的に少ない第2の非水電解質を用いて最終的な電池を組み立てる。このように最終的な電池における電解質が、二酸化炭素の溶解量が少ないものであっても、二酸化炭素の溶解量の多い非水電解質中で少なくとも1サイクルの充放電を行うことにより、最終的な電池において二酸化炭素の溶解量が多い非水電解質を用いたものと同程度の充放電サイクル特性向上の効果が得られる。この理由については、以下のように考えられる。   In the present invention, the first non-aqueous electrolyte and the second non-aqueous electrolyte are used. First, at least one cycle of charging / discharging in the first non-aqueous electrolyte having a relatively large amount of dissolved carbon dioxide. Do. Thereafter, a final battery is assembled using a second nonaqueous electrolyte in which the amount of dissolved carbon dioxide is relatively smaller than that of the first nonaqueous electrolyte. Thus, even if the electrolyte in the final battery has a small amount of dissolved carbon dioxide, the final battery is charged and discharged in a non-aqueous electrolyte with a large amount of dissolved carbon dioxide, so that the final The effect of improving the charge / discharge cycle characteristics comparable to that using a non-aqueous electrolyte with a large amount of carbon dioxide dissolved in the battery can be obtained. The reason for this is considered as follows.

すなわち、二酸化炭素の溶解量が相対的に多い第1の非水電解質中で少なくとも1サイクルの充放電を行うことにより、負極の薄膜表面に、リチウムイオン伝導性の良好な安定な被膜が形成されるため、その後の充放電サイクルにおいて、非水電解質中の二酸化炭素の溶解量が少なくても、良好な充放電サイクル特性を示すことができると考えられる。   That is, by performing at least one cycle of charge / discharge in the first non-aqueous electrolyte in which the amount of carbon dioxide dissolved is relatively large, a stable coating with good lithium ion conductivity is formed on the thin film surface of the negative electrode. Therefore, it is considered that good charge / discharge cycle characteristics can be exhibited even if the amount of carbon dioxide dissolved in the nonaqueous electrolyte is small in the subsequent charge / discharge cycle.

従って、非水電解質における二酸化炭素の溶解量は、初期の充放電サイクルにおいて重要であることがわかる。本発明においては、最終的な電池における非水電解質中の二酸化炭素溶解量を少なくしているので、従来問題となった、二酸化炭素ガス発生による充放電容量の低下、電池厚みの増加などの問題の発生を防止することができる。   Therefore, it can be seen that the amount of carbon dioxide dissolved in the nonaqueous electrolyte is important in the initial charge / discharge cycle. In the present invention, since the amount of carbon dioxide dissolved in the non-aqueous electrolyte in the final battery is reduced, problems such as a decrease in charge / discharge capacity due to the generation of carbon dioxide gas and an increase in battery thickness have been problems. Can be prevented.

本発明においては、第2の非水電解質として、第1の非水電解質よりも二酸化炭素の溶解量が少ないものを用いる。このような第2の非水電解質は、例えば第1の非水電解質の少なくとも一部を第1の非水電解質よりも二酸化炭素の溶解量が少ない非水電解質に入れ替えることにより調製することができる。   In the present invention, a second nonaqueous electrolyte having a smaller amount of carbon dioxide than that of the first nonaqueous electrolyte is used. Such a second non-aqueous electrolyte can be prepared, for example, by replacing at least a part of the first non-aqueous electrolyte with a non-aqueous electrolyte that dissolves less carbon dioxide than the first non-aqueous electrolyte. .

また、第1の非水電解質を用いた充放電後に、減圧して第1の非水電解質中の二酸化炭素を放出させて、二酸化炭素の濃度を低下させ、第2の非水電解質としてもよい。この減圧によって非水電解質中の成分が蒸発して減少する場合には、二酸化炭素の溶解量の少ない非水電解質あるいは蒸発した溶媒等の成分を補充してもよい。   Further, after charge / discharge using the first non-aqueous electrolyte, the pressure may be reduced to release carbon dioxide in the first non-aqueous electrolyte, and the concentration of carbon dioxide may be lowered to form the second non-aqueous electrolyte. . When the components in the non-aqueous electrolyte are evaporated and reduced by this pressure reduction, components such as a non-aqueous electrolyte with a small amount of dissolved carbon dioxide or an evaporated solvent may be replenished.

また、第1の非水電解質を用いた充放電後に、非水電解質の温度を上げ、これによって溶解している二酸化炭素を放出させ、その溶解量を低減してもよい。また、第1の非水電解質を用いた充放電後に、窒素ガスや不活性ガスなどを第1の非水電解質中に吹き込むことにより、第1の非水電解質中に溶解している二酸化炭素の量を低減させて、第2の非水電解質としてもよい。   Further, after charging / discharging using the first non-aqueous electrolyte, the temperature of the non-aqueous electrolyte may be raised to release dissolved carbon dioxide, thereby reducing the amount of dissolution. In addition, after charging / discharging using the first non-aqueous electrolyte, nitrogen gas, inert gas, or the like is blown into the first non-aqueous electrolyte, so that the carbon dioxide dissolved in the first non-aqueous electrolyte is discharged. The amount may be reduced to form the second nonaqueous electrolyte.

本発明において、第1の電解質に溶解させる二酸化炭素の量は、0.01重量%以上であることが好ましく、さらに好ましくは0.1重量%以上である。通常は、飽和するまで二酸化炭素を溶解させることが好ましい。   In the present invention, the amount of carbon dioxide dissolved in the first electrolyte is preferably 0.01% by weight or more, more preferably 0.1% by weight or more. Usually, it is preferable to dissolve carbon dioxide until saturation.

ここで、二酸化炭素の溶解量には、不可避的に非水電解質に溶解されている二酸化炭素は含まれない。すなわち、通常の製造工程で非水電解質中に溶解する二酸化炭素は含まれない。従って、上記二酸化炭素の溶解量は、例えば、二酸化炭素を溶解させた後の非水電解質の重量と、二酸化炭素を溶解させる前の非水電解質の重量を測定することにより求めることができる。具体的には、以下の式により求めることができる。   Here, the amount of carbon dioxide dissolved does not include carbon dioxide inevitably dissolved in the nonaqueous electrolyte. That is, carbon dioxide that dissolves in the non-aqueous electrolyte in a normal manufacturing process is not included. Therefore, the amount of carbon dioxide dissolved can be determined, for example, by measuring the weight of the non-aqueous electrolyte after dissolving carbon dioxide and the weight of the non-aqueous electrolyte before dissolving carbon dioxide. Specifically, it can be obtained by the following equation.

非水電解質中の二酸化炭素の溶解量(重量%)=〔(二酸化炭素を溶解させた後の非水電解質の重量)−(二酸化炭素を溶解させる前の非水電解質の重量)〕/(二酸化炭素を溶解させた後の非水電解質の重量)×100
本発明において、第2の非水電解質中に溶解されている二酸化炭素の量は、第1の非水電解質よりも少なければよいが、好ましくは、二酸化炭素を溶解させていない非水電解質を第2の非水電解質として用いる。
Dissolved amount of carbon dioxide in non-aqueous electrolyte (% by weight) = [(weight of non-aqueous electrolyte after dissolving carbon dioxide) − (weight of non-aqueous electrolyte before dissolving carbon dioxide)] / (dioxide Weight of non-aqueous electrolyte after dissolving carbon) × 100
In the present invention, the amount of carbon dioxide dissolved in the second non-aqueous electrolyte should be less than that of the first non-aqueous electrolyte, but preferably the non-aqueous electrolyte in which carbon dioxide is not dissolved is used in the first non-aqueous electrolyte. 2 as a non-aqueous electrolyte.

本発明において、非水電解質に二酸化炭素を溶解させる方法としては、非水電解質に二酸化炭素を接触させることにより二酸化炭素を溶解させる方法が挙げられる。このような方法としては、非水電解質に気体状の二酸化炭素を吹き込む方法が挙げられる。この方法により、効率的に容易に二酸化炭素を溶解した非水電解質を得ることができる。その他の方法としては、二酸化炭素中で非水電解質を撹拌する方法、高圧の二酸化炭素を非水電解質に接触させるなどの方法が挙げられる。また、二酸化炭素を発生する物質を非水電解質に添加することにより、非水電解質に二酸化炭素を溶解させてもよい。二酸化炭素を発生する物質としては、例えば、重炭酸塩及び炭酸塩などが挙げられる。また、ドライアイスなどを用いてもよい。   In the present invention, examples of the method for dissolving carbon dioxide in the non-aqueous electrolyte include a method for dissolving carbon dioxide by bringing carbon dioxide into contact with the non-aqueous electrolyte. As such a method, a method of blowing gaseous carbon dioxide into the non-aqueous electrolyte can be mentioned. By this method, a non-aqueous electrolyte in which carbon dioxide is dissolved can be obtained efficiently and easily. Other methods include a method of stirring the non-aqueous electrolyte in carbon dioxide and a method of bringing high-pressure carbon dioxide into contact with the non-aqueous electrolyte. Further, carbon dioxide may be dissolved in the non-aqueous electrolyte by adding a substance that generates carbon dioxide to the non-aqueous electrolyte. Examples of the substance that generates carbon dioxide include bicarbonate and carbonate. Also, dry ice or the like may be used.

本発明において、第1の非水電解質中で行う充放電は、第1の非水電解質に負極及び正極を接触させた状態で行う。この段階で作製する電池は、最終的な電池ではないので、電池の外装体の一部を開放した状態で行うことが好ましい。このような状態で充放電を行った後、外装体内の第1の非水電解質の少なくとも一部を入れ替えるなどの方法により、外装体内の非水電解質を第2の非水電解質とし、その後外装体を封止するなどして、最終的な電池を組み立てる。   In the present invention, charging / discharging performed in the first nonaqueous electrolyte is performed in a state where the negative electrode and the positive electrode are in contact with the first nonaqueous electrolyte. Since the battery manufactured at this stage is not a final battery, it is preferable to carry out the battery with a part of the battery outer body opened. After charging / discharging in such a state, the nonaqueous electrolyte in the exterior body is made the second nonaqueous electrolyte by a method such as replacing at least a part of the first nonaqueous electrolyte in the exterior body, and then the exterior body. As a result, the final battery is assembled.

本発明においては、シリコン非結晶薄膜、またはシリコンを主成分とする非結晶薄膜を集電体上に堆積させた負極が用いられる。本発明において、非結晶とは、非晶質及び結晶子サイズが100nm以下の微結晶を意味する。非晶質であるか否かの判定及び微結晶薄膜中の結晶子サイズの測定は、X線回折スペクトル中のピークの有無、及びピークの半値幅をScherrerの式に適用することによって行うことができる。上記の非結晶の定義から明らかなように、本発明における非結晶薄膜には、単結晶薄膜及び多結晶薄膜は含まれない。   In the present invention, a negative electrode in which a silicon amorphous thin film or an amorphous thin film mainly composed of silicon is deposited on a current collector is used. In the present invention, non-crystalline means amorphous and fine crystals having a crystallite size of 100 nm or less. The determination of whether or not it is amorphous and the measurement of the crystallite size in the microcrystalline thin film can be performed by applying the presence or absence of a peak in the X-ray diffraction spectrum and the half-width of the peak to the Scherrer equation. it can. As is clear from the above definition of amorphous, the amorphous thin film in the present invention does not include a single crystal thin film and a polycrystalline thin film.

シリコンを主成分とする非結晶薄膜とは、シリコンを50原子%以上含む非結晶合金薄膜である。具体的には、Si−Co合金薄膜、Si−Fe合金薄膜、Si−Zn合金薄膜、Si−Zr合金薄膜などが挙げられる。   The amorphous thin film mainly composed of silicon is an amorphous alloy thin film containing 50 atomic% or more of silicon. Specific examples include Si—Co alloy thin films, Si—Fe alloy thin films, Si—Zn alloy thin films, Si—Zr alloy thin films, and the like.

本発明において、非結晶薄膜を集電体上に形成する方法としては、気相から原料を供給して非結晶薄膜を堆積させる方法が好ましく用いられる。このような方法として、例えば、スパッタリング法、CVD法、及び蒸着法などが挙げられる。   In the present invention, as a method of forming the amorphous thin film on the current collector, a method of depositing the amorphous thin film by supplying the raw material from the gas phase is preferably used. Examples of such a method include a sputtering method, a CVD method, and a vapor deposition method.

本発明において、薄膜が堆積される集電体表面の算術平均粗さRaは、0.1μm以上であることが好ましい。算術平均粗さRaは、日本工業規格(JIS B 0601−1994)に定められている。算術平均粗さRaは、例えば触針式表面粗さ計により測定することができる。このような大きな凹凸を有する集電体の上に薄膜を堆積させることにより、薄膜の表面に、集電体表面の凹凸に対応した凹凸を形成することができる。表面に大きな凹凸を有する非結晶薄膜を活物質として充放電を行うと、薄膜の膨張・収縮に伴う応力が薄膜の凹凸の谷部に集中して膜厚方向に切れ目が形成され、上述のように薄膜が柱状に分離される。この結果、充放電によって発生する応力が分散され、非結晶薄膜の可逆的な構造変化が容易になる。   In the present invention, the arithmetic average roughness Ra of the current collector surface on which the thin film is deposited is preferably 0.1 μm or more. The arithmetic average roughness Ra is defined in Japanese Industrial Standard (JIS B 0601-1994). The arithmetic average roughness Ra can be measured by, for example, a stylus type surface roughness meter. By depositing a thin film on the current collector having such large unevenness, unevenness corresponding to the unevenness of the current collector surface can be formed on the surface of the thin film. When charging / discharging using an amorphous thin film with large irregularities on the surface as an active material, the stress accompanying expansion and contraction of the thin film concentrates on the valleys of the irregularities of the thin film, and a cut is formed in the film thickness direction as described above. The thin film is separated into columns. As a result, stress generated by charging / discharging is dispersed, and reversible structural change of the amorphous thin film is facilitated.

しかしながら、一方で薄膜が柱状に分離されることにより、薄膜と非水電解質との接触面積が飛躍的に増大する。上述のように、従来の電極においては、非水電解質と接触する薄膜の表面から活物質が変質し、薄膜が多孔質化することがわかっている。本発明に従えば、このような多孔質化を抑制することができ、充放電サイクル特性を向上させることができるとともに、薄膜の厚みの増加を抑制して、電池における体積エネルギー密度を向上させることができる。   However, when the thin film is separated into columns, the contact area between the thin film and the nonaqueous electrolyte is dramatically increased. As described above, in the conventional electrode, it is known that the active material is altered from the surface of the thin film that is in contact with the nonaqueous electrolyte, and the thin film becomes porous. According to the present invention, such porous formation can be suppressed, charge / discharge cycle characteristics can be improved, and an increase in the thickness of the thin film can be suppressed to improve the volume energy density in the battery. Can do.

集電体表面の算術平均粗さRaの上限値は、特に限定されるものではないが、集電体の厚みが10〜100μmの範囲であることが好ましいので、集電体表面の算術平均粗さRaの上限値は実質的に10μm以下であることが好ましい。   The upper limit value of the arithmetic mean roughness Ra of the current collector surface is not particularly limited, but it is preferable that the current collector has a thickness in the range of 10 to 100 μm. The upper limit of the thickness Ra is preferably substantially 10 μm or less.

本発明においては、集電体として耐熱性銅合金箔を用いることが好ましい。ここで、耐熱性銅合金とは、200℃1時間の焼鈍後の引張強度が300MPa以上である銅合金を意味している。このような耐熱性銅合金としては、例えば、表1に挙げたものを使用することができる。   In the present invention, it is preferable to use a heat-resistant copper alloy foil as the current collector. Here, the heat resistant copper alloy means a copper alloy having a tensile strength of 300 MPa or more after annealing at 200 ° C. for 1 hour. As such a heat-resistant copper alloy, for example, those listed in Table 1 can be used.

Figure 0004798952
Figure 0004798952

本発明における負極の作製においては、集電体上に薄膜を形成する際の温度変化によって、集電体の機械的強度が低下し、電池を作製する際の加工が困難になる場合がある。集電体として、耐熱性銅合金薄を用いることにより、温度変化による機械的強度の低下を防止することができ、十分な導電性を確保することができる。   In the production of the negative electrode in the present invention, the mechanical strength of the current collector may be reduced due to a temperature change when forming a thin film on the current collector, which may make it difficult to process the battery. By using a heat-resistant copper alloy thin film as the current collector, it is possible to prevent a decrease in mechanical strength due to a temperature change, and to ensure sufficient conductivity.

上述のように、本発明において用いる集電体は、その表面に大きな凹凸を有することが好ましい。このため、耐熱性銅合金箔の算術平均粗さRaが十分に大きくない場合には、その箔表面に電解銅または電解銅合金を設けることにより、その表面に大きな凹凸を設けてもよい。電解銅層及び電解銅合金層は、電解法により形成することができる。   As described above, the current collector used in the present invention preferably has large irregularities on the surface thereof. For this reason, when arithmetic mean roughness Ra of heat-resistant copper alloy foil is not large enough, you may provide a large unevenness | corrugation in the surface by providing electrolytic copper or an electrolytic copper alloy in the foil surface. The electrolytic copper layer and the electrolytic copper alloy layer can be formed by an electrolytic method.

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(C25SO2)2、LiN(CF3SO2)(C49SO2)、LiC(CF3SO2)3、LiC(C25SO2)3、LiAsF6、LiClO4、Li210Cl10、Li212Cl12など及びそれらの混合物が例示される。特に、LiXFy(式中、XはP、As、Sb、B、Bi、Al、Ga、またはInであり、XがP、AsまたはSbのときyは6であり、XがBi、Al、Ga、またはInのときyは4である)、リチウムペルフルオロアルキルスルホン酸イミドLiN(Cm2m+1SO2)(Cn2n+1SO2)(式中、m及びnはそれぞれ独立して1〜4の整数である)またはリチウムペルフルオロアルキルスルホン酸メチドLiN(Cp2p+1SO2)(Cq2q+1SO2)(Cr2r+1SO2)(式中、p、q及びrはそれぞれ独立して1〜4の整数である)などの溶質が好ましく用いられる。これらの中でも、LiPF6が特に好ましく用いられる。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。本発明のリチウム二次電池の電解質は、イオン導電性を発現させる溶質としてのリチウム化合物とこれを溶解・保持する溶媒が電池の充電時や放電時あるいは保存時の電圧で分解しない限り、制約なく用いることができる。 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. In particular, LiXF y (wherein X is P, As, Sb, B, Bi, Al, Ga, or In, y is 6 when X is P, As, or Sb, and X is Bi, Al, Ga or y when in is 4), lithium perfluoroalkyl sulfonic acid imide LiN (C m F 2m + 1 SO 2) (C n F 2n + 1 SO 2) ( wherein, m and n are each independently, to an integer of 1 to 4) or lithium perfluoroalkyl sulfonic acid methide LiN (C p F 2p + 1 SO 2) (C q F 2q + 1 SO 2) (C r F 2r + 1 SO 2) ( wherein Among them, solutes such as p, q and r are each independently an integer of 1 to 4 are preferably used. Among these, LiPF 6 is particularly preferably used. 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. The electrolyte of the lithium secondary battery of the present invention is not limited as long as the lithium compound as a solute that exhibits ionic conductivity and the solvent that dissolves and retains the lithium compound do not decompose at the time of battery charging, discharging, or storage. Can be used.

本発明のリチウム二次電池の正極材料としては、LiCoO2、LiNiO2、LiMn24、LiMnO2、LiCo0.5Ni0.52、LiNi0.7Co0.2Mn0.12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。 Examples of the positive electrode material of the lithium secondary battery of the present invention include 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 and other lithium-containing transition metal oxides. Examples thereof include metal oxides that do not contain lithium, such as MnO 2 . In addition, any substance that electrochemically inserts and desorbs lithium can be used without limitation.

本発明によれば、非水電解質中に溶解している二酸化炭素の量が少なくても、良好な充放電サイクル特性を示すリチウム二次電池とすることができる。   According to the present invention, even if the amount of carbon dioxide dissolved in the nonaqueous electrolyte is small, a lithium secondary battery exhibiting good charge / discharge cycle characteristics can be obtained.

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.

(実験1)
〔負極の作製〕
ジルコニウム銅合金(ジルコニウム含有量0.03重量%)からなる耐熱性銅合金圧延箔の表面に、電解法により銅を析出させることにより表面を粗面化した耐熱性銅合金箔(算術平均粗さRa0.25μm、厚み26μm)を集電体として用いた。この集電体の上に、図1に示すスパッタリング装置を用いて非結晶シリコン薄膜を堆積させた。
(Experiment 1)
(Production of negative electrode)
Heat-resistant copper alloy foil (arithmetic mean roughness) roughened by depositing copper on the surface of a heat-resistant copper alloy rolled foil made of zirconium copper alloy (zirconium content 0.03% by weight) by electrolytic method Ra 0.25 μm, thickness 26 μm) was used as a current collector. An amorphous silicon thin film was deposited on the current collector using the sputtering apparatus shown in FIG.

図1に示すように、チャンバー1内に回転可能な円筒状の基板ホルダー2が設けられており、この基板ホルダー2の表面に集電体を取り付けた。また、チャンバー1内にはSiスパッタ源3が設けられており、Siスパッタ源3にDCパルス電源4が接続されている。また、チャンバー1内には、Arガスを導入するためのガス導入口6が設けられており、チャンバー1内を排気するための排気口7が設けられている。   As shown in FIG. 1, a rotatable cylindrical substrate holder 2 is provided in the chamber 1, and a current collector is attached to the surface of the substrate holder 2. A Si sputtering source 3 is provided in the chamber 1, and a DC pulse power source 4 is connected to the Si sputtering source 3. In the chamber 1, a gas introduction port 6 for introducing Ar gas is provided, and an exhaust port 7 for exhausting the inside of the chamber 1 is provided.

排気口7から真空排気することにより、チャンバー内を1×10-4Paまで排気した後、Arガスをガス導入口6からチャンバー1内に導入してガス圧力を安定させ、ガス圧力が安定した状態で、Siスパッタ源3にDCパルス電源4から直流パルスを印加し、プラズマ5を発生させて、基板ホルダー2の表面に取り付けた集電体上に、非結晶シリコン薄膜を堆積させた。具体的な薄膜堆積条件は、表2に示す通りである。 After exhausting the inside of the chamber to 1 × 10 −4 Pa by evacuating from the exhaust port 7, Ar gas was introduced into the chamber 1 from the gas introduction port 6 to stabilize the gas pressure, and the gas pressure was stabilized. In this state, a DC pulse was applied to the Si sputtering source 3 from the DC pulse power source 4 to generate plasma 5, and an amorphous silicon thin film was deposited on the current collector attached to the surface of the substrate holder 2. Specific thin film deposition conditions are as shown in Table 2.

Figure 0004798952
Figure 0004798952

薄膜を厚み5μmとなるまで堆積させた後、集電体を基板ホルダー2から取り外し、薄膜と集電体を共に2.5cm×2.5cmの大きさに切り取り、これに負極タブを取り付けて、負極を作製した。   After depositing the thin film to a thickness of 5 μm, the current collector is removed from the substrate holder 2, the thin film and the current collector are both cut into a size of 2.5 cm × 2.5 cm, and a negative electrode tab is attached thereto. A negative electrode was produced.

〔正極の作製〕
LiCoO2粉末90重量部、及び導電剤としての人造黒鉛粉末5重量部を、結着剤としてのポリフッ化ビニリデン5重量部を含む5重量%のN−メチルピロリドン水溶液に混合し、正極合剤スラリーとした。このスラリーをドクターブレード法により、正極集電体であるアルミニウム箔(厚み18μm)の2cm×2cmの領域の上に塗布した後乾燥し、正極活物質層を形成した。正極活物質層を塗布しなかったアルミニウム箔の領域の上に正極タブを取り付け、正極を作製した。
[Production of positive electrode]
90 parts by weight of LiCoO 2 powder and 5 parts by weight of artificial graphite powder as a conductive agent are mixed with a 5% by weight N-methylpyrrolidone aqueous solution containing 5 parts by weight of polyvinylidene fluoride as a binder, and a positive electrode mixture slurry It was. This slurry was applied on a 2 cm × 2 cm region of an aluminum foil (thickness: 18 μm) as a positive electrode current collector by a doctor blade method and then dried to form a positive electrode active material layer. A positive electrode tab was attached on the region of the aluminum foil where the positive electrode active material layer was not applied, and a positive electrode was produced.

〔非水電解質の作製〕
エチレンカーボネートとジエチルカーボネートを3:7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た液を調製し、これを非水電解質b1とした。
[Production of non-aqueous electrolyte]
A solution prepared by dissolving LiPF 6 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 was prepared, and this was used as the nonaqueous electrolyte b1.

非水電解質b1に25℃の温度で30分間二酸化炭素を吹き込み、二酸化炭素を飽和量となるまで溶解させ、これを非水電解質a1とした。二酸化炭素を溶解させる前の重量と、二酸化炭素を溶解させた後の重量を測定し、二酸化炭素の溶解量を求めたところ、0.37重量%であった。   Carbon dioxide was blown into the nonaqueous electrolyte b1 at a temperature of 25 ° C. for 30 minutes to dissolve the carbon dioxide until the saturation amount was reached, and this was designated as the nonaqueous electrolyte a1. The weight before dissolving carbon dioxide and the weight after dissolving carbon dioxide were measured, and the amount of carbon dioxide dissolved was determined to be 0.37% by weight.

非水電解質a1及びb1は、以下の通りである。
非水電解質a1:CO2を溶解させた非水電解質
非水電解質b1:CO2を溶解させていない非水電解質
The nonaqueous electrolytes a1 and b1 are as follows.
Nonaqueous electrolyte a1: Nonaqueous electrolyte in which CO 2 is dissolved Nonaqueous electrolyte b1: Nonaqueous electrolyte in which CO 2 is not dissolved

〔電池の作製〕
二酸化炭素雰囲気において、上記の正極及び負極に、それぞれ正極集電体タブ及び負極集電体タブを取り付けた後、正極及び負極の間に多孔質ポリエチレンからなるセパレータを挟んで電極群とし、この電極群をアルミニウムラミネートからなる外装体内に挿入した。その後、非水電解質a1を600μl注入し、電池A1及び電池B1を作製した。
[Production of battery]
In a carbon dioxide atmosphere, after attaching a positive electrode current collector tab and a negative electrode current collector tab to the positive electrode and the negative electrode, respectively, a separator made of porous polyethylene is sandwiched between the positive electrode and the negative electrode to form an electrode group. The group was inserted into an exterior body made of aluminum laminate. Thereafter, 600 μl of the non-aqueous electrolyte a1 was injected to produce a battery A1 and a battery B1.

〔充放電サイクル試験〕
上記のようにし作製したリチウム二次電池A1及びB1について、充放電サイクル試験を行った。充放電の条件は、25℃において、充電電流13mAで充電終止電圧4.2Vとなるまで充電した後、放電電流13mAで放電終止電圧2.75Vとなるまで放電し、これを1サイクルの充放電とした。
[Charge / discharge cycle test]
The lithium secondary batteries A1 and B1 produced as described above were subjected to a charge / discharge cycle test. The charging / discharging conditions are as follows: At 25 ° C., the battery is charged with a charging current of 13 mA until the charging end voltage is 4.2 V, and then discharged with a discharging current of 13 mA until the discharging end voltage is 2.75 V. It was.

1サイクルの充放電後に、表3に示す条件で、各電池の非水電解質を入れ替え、さらに上記充放電条件でサイクル試験を継続した。   After one cycle of charge and discharge, the nonaqueous electrolyte of each battery was replaced under the conditions shown in Table 3, and the cycle test was continued under the above charge and discharge conditions.

各電池についての最大放電容量及び100サイクル目における放電容量及び容量維持率を表4に示す。なお、最大放電容量は、全てのサイクルの中で最大であった放電容量であり、容量維持率は、この最大放電容量を100%とした値である。   Table 4 shows the maximum discharge capacity, discharge capacity and capacity retention rate at the 100th cycle for each battery. Note that the maximum discharge capacity is the maximum discharge capacity in all the cycles, and the capacity maintenance rate is a value obtained by setting the maximum discharge capacity to 100%.

Figure 0004798952
Figure 0004798952

Figure 0004798952
Figure 0004798952

表4に示すように、1サイクル目の充放電後に、二酸化炭素を溶解していない非水電解質b1に入れ替えた電池A1は、1サイクル目の充放電後に、二酸化炭素を溶解させた非水電解質a1に入れ替えた電池B1と同等の充放電サイクル特性を示した。この理由としては、1サイクル目の充放電サイクルの際に、電極の薄膜表面に良好な被膜が形成されたため、その後に非水電解質を入れ替えても良好なサイクル特性が維持されたと考えられる。なお、二酸化炭素を溶解していない非水電解質b1を最初から用いた電池の100サイクル目の容量維持率は、約18%である。従って、1サイクル目の充放電のみを二酸化炭素を溶解させた非水電解質中で行うことにより、上記のように充放電サイクル特性を顕著に高めることができる。   As shown in Table 4, the battery A1 replaced with the nonaqueous electrolyte b1 in which carbon dioxide was not dissolved after the first cycle charge / discharge was a nonaqueous electrolyte in which carbon dioxide was dissolved after the first cycle charge / discharge. Charge / discharge cycle characteristics equivalent to those of the battery B1 replaced with a1 were shown. This is probably because a good film was formed on the thin film surface of the electrode during the first charge / discharge cycle, and therefore good cycle characteristics were maintained even after the nonaqueous electrolyte was replaced. Note that the capacity maintenance rate at the 100th cycle of the battery using the nonaqueous electrolyte b1 not dissolving carbon dioxide from the beginning is about 18%. Therefore, by performing only the charge / discharge of the first cycle in the nonaqueous electrolyte in which carbon dioxide is dissolved, the charge / discharge cycle characteristics can be remarkably improved as described above.

以上のように、本発明によれば、最終的な電池において、二酸化炭素の溶解量の少ない非水電解質を用いることができるので、高温保存時において非水電解質からの二酸化炭素の発生の少ないリチウム二次電池とすることができる。従って、ガス発生による充放電容量の低下、電池厚みの増加などの問題の生じないリチウム二次電池とすることができる。   As described above, according to the present invention, since a non-aqueous electrolyte with a small amount of carbon dioxide dissolved can be used in the final battery, lithium that generates little carbon dioxide from the non-aqueous electrolyte during high-temperature storage can be used. It can be set as a secondary battery. Therefore, a lithium secondary battery that does not cause problems such as a decrease in charge / discharge capacity due to gas generation and an increase in battery thickness can be obtained.

上記実施例においては、非水電解質を入れ替える際、全ての非水電解質を入れ替えているが、本発明はこれに限定されるものではなく、非水電解質の一部のみを入れ替えてもよい。   In the above embodiment, when replacing the nonaqueous electrolyte, all the nonaqueous electrolytes are replaced. However, the present invention is not limited to this, and only a part of the nonaqueous electrolyte may be replaced.

本発明に従う実施例において用いたスパッタリング装置を示す模式図。The schematic diagram which shows the sputtering device used in the Example according to this invention.

符号の説明Explanation of symbols

1…チャンバー
2…基板ホルダー
3…Siスパッタ源
4…DCパルス電源
5…プラズマ
6…ガス導入口
7…ガス排気口
DESCRIPTION OF SYMBOLS 1 ... Chamber 2 ... Substrate holder 3 ... Si sputter source 4 ... DC pulse power supply 5 ... Plasma 6 ... Gas introduction port 7 ... Gas exhaust port

Claims (5)

シリコン非結晶薄膜またはシリコンを主成分とする非結晶薄膜を集電体上に堆積させた負極と、正極と、非水電解質とを備えるリチウム二次電池の製造方法であって、
二酸化炭素を溶解させた第1の非水電解質に、前記負極及び正極を接触させて少なくとも1サイクルの充放電を行う工程と、
前記充放電後に、前記第1の非水電解質よりも二酸化炭素の溶解量が少ない第2の非水電解質を用いて、最終的な電池を組み立てる工程とを備えることを特徴とするリチウム二次電池の製造方法。
A method for producing a lithium secondary battery comprising a negative electrode obtained by depositing a silicon amorphous thin film or an amorphous thin film mainly composed of silicon on a current collector, a positive electrode, and a nonaqueous electrolyte,
Charging and discharging at least one cycle by bringing the negative electrode and the positive electrode into contact with a first non-aqueous electrolyte in which carbon dioxide is dissolved;
And a step of assembling a final battery using the second non-aqueous electrolyte in which the amount of carbon dioxide dissolved is smaller than that of the first non-aqueous electrolyte after the charge / discharge. Manufacturing method.
前記第1の非水電解質の少なくとも一部を、前記第1の非水電解質よりも二酸化炭素の溶解量が少ない非水電解質に入れ替えることにより、前記第2の非水電解質とすることを特徴とする請求項1に記載のリチウム二次電池の製造方法。   The second non-aqueous electrolyte is obtained by replacing at least a part of the first non-aqueous electrolyte with a non-aqueous electrolyte that dissolves less carbon dioxide than the first non-aqueous electrolyte. The method for producing a lithium secondary battery according to claim 1. 前記少なくとも1サイクルの充放電を行う工程の後、前記第1の非水電解質中の二酸化炭素を放出させて前記第1の非水電解質中の二酸化炭素濃度を低下させるために減圧する工程を行い、
二酸化炭素濃度が低下された第1の非水電解質を、前記第2の非水電解質として用いることを特徴とする請求項1に記載のリチウム二次電池の製造方法。
After the step of performing at least one cycle of charging and discharging, performing a step of reducing the pressure to release carbon dioxide in the first nonaqueous electrolyte and lower the concentration of carbon dioxide in the first nonaqueous electrolyte. ,
2. The method of manufacturing a lithium secondary battery according to claim 1, wherein the first non-aqueous electrolyte having a reduced carbon dioxide concentration is used as the second non-aqueous electrolyte.
前記少なくとも1サイクルの充放電を行う工程の後、前記第1の非水電解質中の二酸化炭素を放出させて前記第1の非水電解質中の二酸化炭素濃度を低下させるために、前記第1の非水電解質を熱する工程を行い、
二酸化炭素濃度が低下された第1の非水電解質を、前記第2の非水電解質として用いることを特徴とする請求項1に記載のリチウム二次電池の製造方法。
After the step of performing at least one cycle of charging / discharging, in order to release carbon dioxide in the first nonaqueous electrolyte and reduce the carbon dioxide concentration in the first nonaqueous electrolyte, the first a non-aqueous electrolyte performs addition or heat process,
2. The method of manufacturing a lithium secondary battery according to claim 1, wherein the first non-aqueous electrolyte having a reduced carbon dioxide concentration is used as the second non-aqueous electrolyte.
前記少なくとも1サイクルの充放電を行う工程の後、前記第1の非水電解質中の二酸化炭素濃度を低下させるために、前記第1の非水電解質中に窒素ガス又は/及び不活性ガスを吹き込む工程を行い、
二酸化炭素濃度が低下された第1の非水電解質を、前記第2の非水電解質として用いることを特徴とする請求項1に記載のリチウム二次電池の製造方法。
After the step of performing at least one cycle of charging / discharging, nitrogen gas and / or inert gas is blown into the first non-aqueous electrolyte in order to reduce the carbon dioxide concentration in the first non-aqueous electrolyte. Perform the process,
2. The method of manufacturing a lithium secondary battery according to claim 1, wherein the first non-aqueous electrolyte having a reduced carbon dioxide concentration is used as the second non-aqueous electrolyte.
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