JP4841125B2 - Method for manufacturing lithium secondary battery - Google Patents

Description

  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.

  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.

  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.

  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). Further, as a method for further improving the charge / discharge cycle characteristics, a method of adding vinylene carbonate or the like to the nonaqueous electrolyte has been proposed (Patent Document 3). 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 5 to 15).

  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.

In order to solve the above problem, the present applicant has proposed using a non-aqueous electrolyte in which carbon dioxide is dissolved (Patent Document 4). 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. A possible reason for suppressing the porosity of the active material layer is that a film is formed on the surface of the active material layer by a reaction between carbon dioxide dissolved in the non-aqueous electrolyte and the active material layer. Carbon dioxide in the non-aqueous electrolyte is consumed due to the formation of such a coating. In some cases, it could not be improved sufficiently.
International Publication No. 01/29913 Pamphlet International Publication No. 02/071512 Pamphlet International Publication No. 02/058182 Pamphlet Unpublished PCT application PCT / JP2004 / 007691 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

  An object of the present invention is to deposit a silicon amorphous thin film or an amorphous thin film containing silicon as a main component on a current collector, comprising a negative electrode using the amorphous thin film as an active material, a positive electrode, and a nonaqueous electrolyte, An object of the present invention is to provide a method capable of efficiently producing a lithium secondary battery having excellent charge / discharge cycle characteristics.

  The present invention relates to a lithium secondary comprising: a non-crystalline silicon film or a non-crystalline thin film mainly composed of silicon deposited on a current collector; a negative electrode using the non-crystalline thin film as an active material; a positive electrode; and a non-aqueous electrolyte. A method for producing a battery, comprising a step of producing a lithium secondary battery in an open state in which a negative electrode, a positive electrode, and a nonaqueous electrolyte are put in a container and not sealed, and an open state in a gas atmosphere containing carbon dioxide A step of charging the lithium secondary battery and a step of sealing the charged lithium secondary battery.

  In the present invention, a lithium secondary battery in an open state that is not sealed is once manufactured, and this lithium secondary battery is charged in a gas atmosphere containing carbon dioxide, and then the lithium secondary battery is sealed. When charging a lithium secondary battery in an open state in a gas atmosphere containing carbon dioxide, carbon dioxide dissolves in the nonaqueous electrolyte of the lithium secondary battery, and the reaction between the carbon dioxide and the amorphous thin film results in an active material. A film is formed on the surface of the amorphous thin film. Carbon dioxide in the nonaqueous electrolyte is consumed by the formation of the coating, but since carbon dioxide is continuously supplied from the gas atmosphere, a thick and stable coating can be formed on the surface of the thin film. Since a thick and stable film can be formed on the surface of the thin film, it is possible to suppress a decrease in charge / discharge capacity due to a structural change of the amorphous thin film during the charge / discharge cycle, and to improve charge / discharge cycle characteristics. .

  In the present invention, the lithium secondary battery is sealed after at least one charge in a gas atmosphere containing carbon dioxide. The charging of the lithium secondary battery in the open state is more preferably a charge / discharge cycle with discharge. Therefore, it is more preferable to charge and discharge the lithium secondary battery in an open state at least once. It is known that a non-crystalline thin film is formed with a cut in the thickness direction by charge / discharge to form a columnar structure. By such a columnar structure, the surface of a new active material thin film appears. The film formed by the reaction between carbon dioxide and the thin film is preferably formed on the surface of such a new columnar thin film.

  Carbon dioxide dissolved in the nonaqueous electrolyte of the lithium secondary battery in an open state is proportional to the pressure or partial pressure of carbon dioxide in the gas atmosphere. Therefore, the higher the pressure or partial pressure of carbon dioxide in the gas atmosphere, the more carbon dioxide dissolves in the non-aqueous electrolyte. The pressure or partial pressure of carbon dioxide in the gas atmosphere is preferably, for example, atmospheric pressure or higher. By setting the pressure to atmospheric pressure or higher, more carbon dioxide can be dissolved in the non-aqueous electrolyte, and the coating formed on the thin film surface can be made thicker and more stable.

  Moreover, in this invention, it is preferable to give a vibration to the lithium secondary battery of an open state in the gas atmosphere containing a carbon dioxide. By giving vibration to the lithium secondary battery, more carbon dioxide in the gas atmosphere can be dissolved in the non-aqueous electrolyte. Therefore, more excellent charge / discharge cycle characteristics can be obtained.

  In the present invention, it is preferable to reduce the amount of carbon dioxide dissolved in the nonaqueous electrolyte before sealing the lithium secondary battery after charging. By reducing the amount of carbon dioxide dissolved in the non-aqueous electrolyte, it is possible to suppress an increase in internal gas pressure at a high temperature in the sealed lithium secondary battery. For this reason, it can suppress that the thickness of a battery increases at the time of high temperature. As a method for reducing the amount of carbon dioxide dissolved in the nonaqueous electrolyte, a method for reducing the pressure or partial pressure of carbon dioxide in the gas atmosphere is preferably used.

  In the present invention, the lithium secondary battery after charging is sealed. Needless to say, “after charging” may be after charging and discharging.

  In the present invention, carbon dioxide may be dissolved in advance in a non-aqueous electrolyte that is put in an open container. That is, a nonaqueous electrolyte in which carbon dioxide is dissolved in advance may be placed in an open container. Examples of the method for dissolving carbon dioxide in advance include a method in which carbon dioxide is blown into the non-aqueous electrolyte by a hub ring or the like, and a method in which carbon dioxide having a relatively high pressure is brought into contact with the non-aqueous electrolyte.

  In the present invention, the amount of carbon dioxide previously dissolved in the nonaqueous electrolyte is preferably 0.01% by weight or more, and more preferably 0.1% by weight or more. Usually, it is preferable to dissolve carbon dioxide until saturation.

  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.

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, 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.

  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.

  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.

  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.

  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.

  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.

  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.

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、耐熱性銅合金箔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 foil as the current collector, it is possible to prevent a decrease in mechanical strength due to a temperature change, and to ensure sufficient conductivity.

  As described above, the current collector used in the present invention preferably has large irregularities on the surface thereof. For this reason, when the arithmetic average roughness Ra of the heat resistant copper alloy foil is not sufficiently large, a large unevenness may be provided on the surface by providing an electrolytic copper layer or an electrolytic copper alloy layer on the foil surface. . The electrolytic copper layer and the electrolytic copper alloy layer can be formed by an electrolytic method.

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, as the electrolyte, a gel polymer electrolyte in which a polymer electrolyte such as polyethylene oxide or polyacrylonitrile is impregnated with an electrolytic solution is exemplified. 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.

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.

  According to the present invention, carbon dioxide can be dissolved in the nonaqueous electrolyte by charging an open lithium secondary battery in a gas atmosphere containing carbon dioxide. A stable film can be formed on the surface of the amorphous thin film by the dissolved carbon dioxide, and charge / discharge cycle characteristics can be improved. Therefore, according to the present invention, a lithium secondary battery excellent in charge / discharge cycle characteristics can be efficiently produced.

  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.

(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 31 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.

  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.

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.

薄膜を厚み５μｍとなるまで堆積させた後、集電体の他方面の上にも同様にして非結晶シリコン薄膜を堆積させ、集電体の両面上に非結晶シリコン薄膜を形成した。次に、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４ｃｍ×３０ｃｍ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 the thin film was deposited to a thickness of 5 μm, an amorphous silicon thin film was similarly deposited on the other side of the current collector to form an amorphous silicon thin film on both sides of the current collector. Next, the current collector was removed from the substrate holder 2, and both the thin film and the current collector were cut into a size of 4 cm × 30 cm, and a negative electrode tab was attached thereto to produce a negative electrode.

[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 in a 5% by weight N-methylpyrrolidone aqueous solution containing 5 parts by weight of polytetrafluoroethylene as a binder, and a positive electrode mixture A slurry was obtained. This slurry was applied on a 4 cm × 30 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. Two positive electrodes were used for each lithium secondary battery.

[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 designated as nonaqueous electrolyte a1.

  Carbon dioxide was blown into the nonaqueous electrolyte a1 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 b1. 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.

[Preparation of an open lithium secondary battery]
A resin separator is stacked on both sides of the negative electrode, and the two positive electrodes are stacked on the outer sides of the separator. The positive electrode active material layer and the amorphous silicon thin film of the negative electrode are arranged to face each other. Produced. The electrode structure was folded and inserted into an exterior body made of an aluminum laminate film. The positive electrode tab and the negative electrode tab are taken out from the end of the welded outer body. This exterior body has a structure that can be sealed by welding all ends, but the electrode structure is inserted into a bag-like exterior body without welding only one portion of the end. Further, a non-aqueous electrolyte was injected to produce an open lithium secondary battery that was not sealed.

  The non-aqueous electrolyte a1 was used for the batteries A2 to A9 of Examples 1 to 8 and the battery A1 of Comparative Example 1.

  The non-aqueous electrolyte b1 was used for the batteries B2 and B3 of Examples 9 and 10 and the battery B1 of Comparative Example 2. The non-aqueous electrolyte b1 is a non-aqueous electrolyte in which carbon dioxide is dissolved in advance by blowing carbon dioxide gas as described above.

[Initial charging / discharging of an open lithium secondary battery]
About each battery of Examples 1-10, in the atmosphere of the carbon dioxide pressure shown in Table 3, initial charge or initial stage charge / discharge was performed on the conditions shown in Table 3. In addition, 4 ml of each nonaqueous electrolyte was injected.

  The carbon dioxide pressure shown in Table 3 is an absolute pressure, and 0.1 MPa indicates that carbon dioxide is at atmospheric pressure. For the batteries A8 and A9 of Examples 7 and 8, after initial charge or initial charge / discharge at a carbon dioxide pressure of 0.1 MPa, the carbon dioxide pressure was reduced to 0.05 MPa, and then the batteries were sealed.

  In addition, with respect to the batteries A6 and A7 of Examples 5 and 6, initial charging or initial charging / discharging was performed while applying ultrasonic vibration to the open lithium secondary battery.

  As described above, after performing initial charge or initial charge / discharge in a carbon dioxide gas atmosphere, the lithium secondary battery was sealed by welding the open end. As described above, the batteries A8 and A9 of Examples 7 and 8 were sealed after reducing the carbon dioxide gas pressure to 0.05 MPa and maintaining this pressure for 5 minutes. In addition, the batteries A4 and A5 of Examples 3 and 4 were sealed after reducing the carbon dioxide gas pressure to 0.1 MPa after initial charge or initial charge / discharge.

[Production of Lithium Secondary Battery of Comparative Example]
For the lithium secondary battery of Comparative Example 1, after using the nonaqueous electrolyte a1 in which carbon dioxide is not dissolved and inserting the electrode structure into the exterior body in an argon gas atmosphere, 4 ml of the nonaqueous electrolyte a1 is injected. Then, the open end portion of the outer package was welded to produce a sealed lithium secondary battery A1.

  For the battery of Comparative Example 2, a sealed lithium secondary battery B1 was produced in the same manner as in Comparative Example 1 except that the nonaqueous electrolyte b1 in which carbon dioxide was previously dissolved was used as the nonaqueous electrolyte.

[Charge / discharge cycle test]
A charge / discharge cycle test was performed on the sealed lithium secondary batteries A1 to A9 and B1 to B3 produced as described above. The charge / discharge condition is that the battery is charged at a charge current of 700 mA until the end-of-charge voltage is 4.2 V, and then discharged at a discharge current of 700 mA until the end-of-discharge voltage is 2.75 V. This is one cycle of charge / discharge up to 100 cycles. A charge / discharge test was conducted.

  The maximum discharge capacity through all the cycles is shown in Table 4 as “maximum discharge capacity”. Further, the capacity retention ratio with respect to the discharge capacity and the maximum discharge capacity at the 100th cycle was determined and shown in Table 4. Moreover, after charging / discharging 100 cycles, each battery was heated to 60 degreeC and the thickness of the exterior body was measured. From this measured value and the thickness of the exterior body in the room temperature state before the charge / discharge cycle test, the thickness increase of the exterior body was measured, and the results are shown in Table 4.

表４に示す結果から明らかなように、アルゴンガス雰囲気中で密封し、二酸化炭素ガス雰囲気下で充電または充放電を行っていない比較例１の電池Ａ１は、１００サイクル後の容量維持率が２８．４％と低くなっているのに対し、本発明に従い二酸化炭素ガス雰囲気下で初期充電または初期充放電を行った実施例１〜１０の電池Ａ２〜Ａ９及びＢ２〜Ｂは、１００サイクル後の容量維持率が高く、充放電サイクル特性が向上していることがわかる。また、予め二酸化炭素を溶解していない非水電解質ａ１を用いた実施例１〜８の電池Ａ２〜Ａ９は、予め二酸化炭素が溶解された非水電解質ｂ１用いた比較例２の電池Ｂ１に比べ、高い容量維持率を示しており、充放電サイクル特性に優れていることがわかる。

As is clear from the results shown in Table 4, the battery A1 of Comparative Example 1 that was sealed in an argon gas atmosphere and was not charged or charged / discharged in a carbon dioxide gas atmosphere had a capacity retention rate of 28 after 100 cycles. The batteries A2 to A9 and B2 to B2 of Examples 1 to 10 that were initially charged or initially charged / discharged in a carbon dioxide gas atmosphere in accordance with the present invention were low after 4 cycles. It can be seen that the capacity retention rate is high and the charge / discharge cycle characteristics are improved. Further, the batteries A2 to A9 of Examples 1 to 8 using the nonaqueous electrolyte a1 in which carbon dioxide is not dissolved in advance are compared with the battery B1 of Comparative Example 2 using the nonaqueous electrolyte b1 in which carbon dioxide is dissolved in advance. It shows a high capacity retention rate and is excellent in charge / discharge cycle characteristics.

  In addition, Examples 3 and 4 in which the carbon dioxide pressure during initial charge or initial charge / discharge was 0.6 MPa had a higher capacity retention rate than Examples 1 and 2 in which the carbon dioxide pressure was 0.1 MPa. It has become. This is considered to be because the dissolution of carbon dioxide in the non-aqueous electrolyte was promoted by increasing the pressure or partial pressure of carbon dioxide during the initial charge or initial charge / discharge, so that the charge / discharge cycle characteristics were improved.

  In addition, Examples 5 and 6 (batteries A6 and A7) to which ultrasonic vibration was applied during initial charge or initial charge / discharge were compared with Examples 1 and 2 (batteries A2 and A3) to which ultrasonic vibration was not applied. The capacity maintenance rate is high. This is considered to be because dissolution of carbon dioxide in the nonaqueous electrolyte was promoted by applying ultrasonic vibration during initial charge or initial charge / discharge.

  Further, in Examples 7 and 8 (batteries A8 and A9) in which the pressure of carbon dioxide was reduced from 0.1 MPa to 0.05 MPa after the initial charge or initial charge / discharge, the increase in the thickness of the outer package at high temperatures was caused by It is smaller than 1 and 2 (batteries A2 and A3). This is because the amount of carbon dioxide dissolved in the non-aqueous electrolyte is reduced by lowering the pressure of carbon dioxide after the initial charge or initial charge / discharge, so that the amount of carbon dioxide generated from the non-aqueous electrolyte at high temperatures is reduced. This is thought to be due to the decrease.

  Examples 9 and 10 (batteries B2 and B3) using a non-aqueous electrolyte b1 in which carbon dioxide was dissolved in advance as the non-aqueous electrolyte were examples 1 and 10 using the non-aqueous electrolyte a1 in which carbon dioxide was not dissolved in advance. Compared to 2 (batteries A2 and A3), the capacity retention rate is higher. This is considered to be because the amount of carbon dioxide dissolved in the nonaqueous electrolyte is increased by using a nonaqueous electrolyte in which carbon dioxide is dissolved in advance as the nonaqueous electrolyte.

The schematic diagram which shows the sputtering device used in the Example according to this invention.

Explanation of symbols

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 (11)

A non-crystalline silicon thin film or a non-crystalline alloy thin film containing 50 atomic% or more of silicon is deposited on a current collector, and includes a negative electrode using the non-crystalline thin film or the non-crystalline alloy thin film as an active material, a positive electrode, and a non-aqueous electrolyte. A method for manufacturing a lithium secondary battery, comprising:
Placing the negative electrode, the positive electrode, and the non-aqueous electrolyte in a container to produce an unsealed lithium secondary battery;
Charging the open lithium secondary battery in a gas atmosphere containing carbon dioxide;
Sealing the lithium secondary battery after charging ,
The method for producing a lithium secondary battery, wherein the pressure or partial pressure of carbon dioxide in the gas atmosphere is atmospheric pressure or higher .   The method for producing a lithium secondary battery according to claim 1, wherein the lithium secondary battery in the open state is charged and discharged at least once in a gas atmosphere containing carbon dioxide. Method for producing a lithium secondary battery according to claim 1 or 2, characterized in that in a gas atmosphere containing carbon dioxide further comprises the step of applying vibration to the lithium secondary battery of the open state. Before sealing the lithium secondary battery after the charging, lithium according to any one of claims 1 to 3, characterized in that reducing the amount of carbon dioxide dissolved in the said non-aqueous electrolyte A method for manufacturing a secondary battery. 5. The lithium secondary battery according to claim 4 , wherein the amount of carbon dioxide dissolved in the non-aqueous electrolyte is reduced by reducing the pressure or partial pressure of carbon dioxide in the gas atmosphere. Manufacturing method. Method for producing a lithium secondary battery according to any one of claims 1 to 5, characterized in that pre-dioxide in the nonaqueous electrolyte to put into the container is dissolved. Method for producing a lithium secondary battery according to any one of claims 1 to 6, the arithmetic mean roughness Ra of the current collector surface, characterized in that at 0.1μm or more. Method for producing a lithium secondary battery according to any one of claims 1 to 7, wherein the current collector is characterized in that it is a foil containing a heat-resistant copper alloy. Any one of claims 1 to 8, the current collector is characterized in that it is a metallic foil having a metal foil or an electrolytic copper alloy layer provided an electrolytic copper layer on the surface of the foil containing a heat-resistant copper alloy The manufacturing method of the lithium secondary battery as described in 2 .. The deposition of amorphous thin film or the amorphous alloy thin film, a manufacturing method of a lithium secondary battery according to any one of claims 1 to 9, characterized in that by supplying the material from the gas phase. The method of manufacturing a lithium secondary battery according to claim 10 , wherein the amorphous thin film or the amorphous alloy thin film is deposited by an evaporation method, a sputtering method, or a chemical vapor deposition method.

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