JP2009123402A - Method of manufacturing negative electrode for lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily prevent the capacity of a lithium secondary battery from being reduced since a surface of a thin film of a negative electrode active material is oxidized when manufacturing a negative electrode for the lithium secondary battery in which the thin film of the negative electrode active material is formed on a negative electrode current collector. <P>SOLUTION: The method includes: a step of forming the thin film 1b of the negative electrode active material by discharging the negative electrode active material to store or release lithium into a gas phase under a reduced pressure, and supplying it on the lengthy sheet state negative electrode current collector 1a; and a step of winding up the negative electrode current collector in which the thin film of the negative electrode active material is formed. Before winding up the negative electrode current collector in which the thin film of the negative electrode active material is formed, the negative electrode current collector is cooled down to a temperature lower than room temperature, and an inert gas is adsorbed on a surface of the thin film of the negative electrode active material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a negative electrode for a lithium secondary battery used for a negative electrode of a lithium secondary battery, and in particular, a lithium secondary in which a thin film of a negative electrode active material is formed on a sheet-like negative electrode current collector. When a negative electrode for a battery is manufactured, when the negative electrode for a lithium secondary battery is taken out into the atmosphere, the surface of the thin film of the negative electrode active material is appropriately prevented from being oxidized, and the capacity of the lithium secondary battery is reduced. This is characterized in that it is possible to suppress the decrease in the thickness.

  In recent years, as a new secondary battery with high output and high energy density, a high electromotive force lithium secondary battery using a non-aqueous electrolyte and utilizing oxidation and reduction of lithium has come to be used.

  Here, in such a lithium secondary battery, various battery characteristics such as charge / discharge voltage, charge / discharge cycle characteristics, and storage characteristics are greatly influenced by the electrodes used.

  And, in the negative electrode in such a lithium secondary battery, lithium metal has been conventionally used as the negative electrode active material, but when repeated charging and discharging, lithium is deposited in a dendrite shape on the negative electrode, There was a problem that an internal short circuit occurred.

  For this reason, in recent years, as the negative electrode, a sheet-shaped negative electrode current collector formed by forming a thin film of a negative electrode active material such as aluminum, silicon, and tin that is electrochemically alloyed with lithium during charging, Proposals have been made in which lithium is prevented from dendrite-like precipitation to prevent internal short-circuiting.

  In forming a thin film of a negative electrode active material such as aluminum, silicon, or tin alloyed with lithium on a sheet-like negative electrode current collector as described above, conventionally, as shown in Patent Document 1 A thin film of a negative electrode active material formed of a microcrystalline silicon thin film or an amorphous silicon thin film on a sheet-like negative electrode current collector by a thin film forming method such as a CVD method or a sputtering method; As disclosed in Patent Document 2, an interface layer is formed on a negative electrode current collector by sputtering, and a negative electrode active material layer is formed on the interface layer by a vapor deposition method. .

  When a lithium secondary battery is manufactured using a negative electrode in which a thin film of a negative electrode active material is formed on the negative electrode current collector in this way, the negative electrode thus prepared is generally taken out into the atmosphere and the lithium secondary battery is extracted. The next battery was made.

  However, when the negative electrode is taken out into the atmosphere, the surface of the negative electrode active material formed on the negative electrode current collector is oxidized, and a lithium secondary battery is manufactured using such a negative electrode. In addition, since the oxidized negative electrode active material is reduced, lithium is unnecessarily consumed and the battery capacity is reduced.

  For this reason, recently, as shown in Patent Document 3, the negative electrode in which the thin film of the negative electrode active material is formed on the negative electrode current collector as described above is used as the first preliminary in which an inert atmosphere or a vacuum atmosphere is used. The negative electrode is accommodated in a sealed container provided in the spare chamber, and the sealed container in which the negative electrode is accommodated in this manner is guided to a second preliminary chamber in an inert atmosphere or a vacuum atmosphere. A proposal has been made in which a negative electrode is taken out from the above-mentioned sealed container in two preliminary chambers and led to an apparatus for producing a lithium secondary battery.

However, in this case, the first and second spare chambers are required, which increases the size and cost of the device, and further increases the number of steps required to manufacture the lithium secondary battery, resulting in poor productivity. was there.
International Publication WO01 / 29913 JP 2002-289181 A JP 2003-7343 A

  The present invention produces a negative electrode for a lithium secondary battery in which a thin film of a negative electrode active material is formed on a sheet-like negative electrode current collector as a negative electrode for a lithium secondary battery used for a negative electrode of a lithium secondary battery. The negative electrode active material formed on the negative electrode current collector when the negative electrode for a lithium secondary battery is taken out into the atmosphere. It is an object of the present invention to appropriately prevent the surface of the thin film from being oxidized and to suppress the reduction in the capacity of the lithium secondary battery.

  In the method for producing a negative electrode for a lithium secondary battery according to the present invention, in order to solve the above problems, a negative electrode active material that occludes and releases lithium is released into the gas phase under reduced pressure to form a long sheet. A negative electrode active material formed on the negative electrode current collector, and a negative electrode active material thin film formed on the negative electrode current collector. Before winding the negative electrode current collector on which the thin film is formed, the negative electrode current collector is cooled to a temperature lower than room temperature, and an inert gas is adsorbed on the surface of the thin film of the negative electrode active material. .

  As in the method for producing a negative electrode for a lithium secondary battery in the present invention, a negative electrode active material that occludes and releases lithium is released into a gas phase under reduced pressure and supplied onto a negative electrode current collector that is in the form of a long sheet. After forming the negative electrode active material thin film, when winding the negative electrode current collector formed with the negative electrode active material thin film, the negative electrode current collector is cooled to a temperature lower than room temperature, and the When the inert gas is adsorbed on the surface of the negative electrode active material thin film, when the negative electrode current collector wound up in this way is taken out into the atmosphere, the above-mentioned negative This inert gas prevents oxygen and moisture in the atmosphere from coming into contact with the surface of the negative electrode active material thin film, and the inert gas is adsorbed in the cooled state as described above. Gas expands, oxygen and moisture Contacting the negative electrode active surface of the thin film of the material of the serial is to be further prevented.

  As a result, when the negative electrode for a lithium secondary battery is manufactured as described above, the negative electrode current collector wound as described above is taken out into the atmosphere as it is and led to an apparatus for manufacturing a lithium secondary battery. However, the surface of the thin film of the negative electrode active material formed on the negative electrode current collector is prevented from being oxidized, and the capacity of the lithium secondary battery is prevented from being reduced. Thus, there is no need to provide the first and second spare chambers, and the apparatus does not increase in size or cost.

  Next, an embodiment of a method for producing a negative electrode for a lithium secondary battery according to the present invention will be specifically described. In addition, the manufacturing method of the negative electrode for lithium secondary batteries in this invention is not limited to what was shown to the following embodiment, In the range which does not change the summary, it can implement suitably.

  The method for producing a negative electrode for a lithium secondary battery according to the present invention comprises a negative electrode active material that occludes and releases lithium as described above on a negative electrode current collector formed into a long sheet by releasing it into the gas phase under reduced pressure. After the negative electrode active material thin film is formed, the negative electrode current collector formed with the negative electrode active material thin film is wound up, and the negative electrode current collector is cooled to a temperature lower than room temperature. The inert gas is adsorbed on the surface of the thin film of the negative electrode active material.

  Here, in the method for producing a negative electrode for a lithium secondary battery according to the present invention, the negative electrode active material is effective when a material which is easily oxidized by contact with oxygen or moisture in the atmosphere is used. This is effective when a material alloyed with lithium, which tends to oxidize more easily than a carbon material widely used as a negative electrode active material, is used.

  As the negative electrode active material that is alloyed with lithium in this way, for example, silicon, germanium, tin, zinc, aluminum, or the like can be used. In particular, from the point of forming a thin film as described above, silicon or It is preferable to use a negative electrode active material containing germanium as a main component, and it is more preferable to use a negative electrode active material containing silicon as a main component from the viewpoint of obtaining a lithium secondary battery having a high charge / discharge capacity.

  In addition, when the negative electrode for a lithium secondary battery is used for a lithium secondary battery and charged / discharged, the thin film of the negative electrode active material is prevented from being finely powdered. It is preferably an amorphous thin film or a microcrystalline thin film.

Therefore, the negative electrode active material thin film formed on the negative electrode current collector includes an amorphous silicon thin film, a microcrystalline silicon thin film, an amorphous germanium thin film, a microcrystalline germanium thin film, an amorphous silicon germanium alloy foil film, a fine film It is preferably a crystalline silicon germanium alloy foil film, more preferably an amorphous silicon thin film or a microcrystalline silicon thin film. In the amorphous silicon thin film, a peak in the vicinity of 520 cm ⁻¹ corresponding to the crystalline region is not substantially detected in Raman spectroscopic analysis, and a peak in the vicinity of 480 cm ⁻¹ corresponding to the amorphous region is substantially not detected. In the Raman spectroscopic analysis, the microcrystalline silicon thin film substantially has both a peak near 520 cm ⁻¹ corresponding to the crystalline region and a peak near 480 cm ⁻¹ corresponding to the amorphous region. It is a thin film to be detected.

  In order to prevent the negative electrode active material from being oxidized, it is preferable to reduce the oxygen concentration in the thin film of the negative electrode active material. However, from the viewpoint of production, oxygen is contained in the thin film of the negative electrode active material. However, there is no problem if the oxygen concentration in the thin film of the negative electrode active material is about 7% by weight or less. Note that the oxygen concentration in the thin film of the negative electrode active material can be obtained by ICP emission spectrometry (Inductively Coupled Plasma Spectrometry).

  When the negative electrode active material is discharged into the gas phase under reduced pressure to form a thin film of the negative electrode active material on the negative electrode current collector, for example, PVD (Physical Vapor Deposition) such as sputtering or vapor deposition is used. The CVD (Chemical Vapor Deposition) method such as the plasma CVD method can be used. From the viewpoint of increasing the film formation rate, it is preferable to use a vapor deposition method such as an electron beam evaporation method.

  Also, for the purpose of increasing the adhesion strength of the negative electrode active material thin film to the negative electrode current collector, the negative electrode active material interface layer is formed by sputtering before forming the negative electrode active material thin film on the negative electrode current collector. After that, it is preferable to form a thin film of the negative electrode active material thereon.

  As the inert gas adsorbed on the surface of the negative electrode active material thin film before winding the negative electrode current collector on which the thin film of the negative electrode active material is formed in this way, a rare gas such as helium gas or argon gas is used. A gas, nitrogen gas, or the like can be used, and a rare gas is preferably used from the viewpoint of preventing the thin film of the negative electrode active material from being oxidized, and argon gas is more preferably used from the viewpoint of cost.

  In addition, when winding the negative electrode current collector on which the negative electrode active material thin film is formed as described above, the negative electrode current collector in which the inert gas adsorbed on the surface of the negative electrode active material thin film is wound is appropriately used. In order to prevent the negative electrode current collector from being damaged, the tension at the time of winding the negative electrode current collector on which the thin film of the negative electrode active material is wound is set to the width of the negative electrode current collector. A range of 4 to 40 N per cm is preferable.

  In addition, when the negative electrode current collector on which the thin film of the negative electrode active material is formed as described above, the above-described inert gas is sufficiently adsorbed on the surface of the negative electrode active material thin film, and the wound negative electrode In order to sufficiently hold the current collector, the pressure of the atmosphere when winding the negative electrode current collector by adsorbing an inert gas on the surface of the thin film of the negative electrode active material should be 3 Pa or more. preferable.

  In addition, when the negative electrode current collector wound by adsorbing the inert gas on the surface of the negative electrode active material thin film as described above is taken out into the atmosphere, the inert gas expands and oxygen and moisture are In order to further suppress the contact with the surface of the thin film of the material, when the negative electrode current collector is cooled to a temperature lower than room temperature before winding, the temperature of the negative electrode current collector is lower by 5 ° C. or more than room temperature. It is preferable to cool it. However, when the negative electrode current collector is cooled to a temperature lower by 15 ° C. or more than room temperature, when this negative electrode current collector is taken out into the atmosphere, there is a possibility that dew condensation may occur on the negative electrode current collector, etc. It is preferable to heat the negative electrode current collector before taking it out into the atmosphere.

  In the present invention, the negative electrode current collector forming the thin film of the negative electrode active material is preferably a material that is not alloyed with lithium and has a high electrical conductivity, It is preferable to use a metal composed of a metal having high thermal conductivity so that the negative electrode current collector can be easily cooled or heated as described above. For example, copper or copper as a main material. An alloy, nickel, stainless steel, or the like can be used, or a laminate of two or more of these materials may be used. The conductivity of the negative electrode current collector is preferably about 40% or more of IACS, and the thermal conductivity is preferably 150 W / m · K or more. In addition, the thermal conductivity in the vicinity of 0 ° C. of normal oxygen-free copper is about 400 W / m · K.

  Here, as the negative electrode current collector, it is particularly preferable to use a copper foil or a copper alloy foil having high electrical conductivity and high thermal conductivity. In addition, as an element other than copper added to the copper alloy, one or more elements selected from tin, zirconium, iron, nickel, silicon, zinc, chromium and magnesium can be used. The amount of element added is preferably 5% by weight or less.

  In the above negative electrode current collector, the surface area is increased to increase the amount of the inert gas adsorbed on the negative electrode active material thin film, and the inert gas is introduced into the gap between the wound negative electrode current collector. In order to ensure proper incorporation, it is preferable to use a surface roughened surface, and the surface roughness Ra defined in Japanese Industrial Standard (JIS B 0601-1994) is in the range of 0.01 to 1 μm. It is preferable to use one having a surface roughness Ra in the range of 0.1 to 1 μm.

  Further, regarding the thickness of the negative electrode current collector, when the thickness is increased, the amount of the negative electrode active material is relatively decreased and the battery capacity is reduced. On the other hand, when the thickness is too thin, the negative electrode current collector is wound up as described above. Since the body easily breaks and the electrical resistance increases, the thickness of the negative electrode current collector is preferably in the range of 5 to 50 μm.

  Next, a specific manufacturing apparatus for manufacturing a negative electrode for a lithium secondary battery as described above will be described with reference to the accompanying drawings.

  In this manufacturing apparatus, as shown in FIG. 1, the inside of the apparatus body 10 is maintained in a vacuum state, and the partition wall 11 in which a slit 11a for passing the negative electrode current collector 1a is formed in the apparatus body 10 is provided. Provided in the apparatus main body 10 is a current collector supply chamber 10A for setting a supply roll 12 around which a long sheet-like negative electrode current collector 1a is wound, and an interface layer on one surface of the negative electrode current collector 1a. The first interface layer forming chamber 10B to be formed, the first active material layer forming chamber 10C for forming the negative electrode active material layer on the interface layer formed on one surface of the negative electrode current collector 1a, and thus the interface layer A guide chamber 10D for reversing and transporting the front and back of the negative electrode current collector 1a on which the negative electrode active material layer is formed, and a negative electrode current collector in which the front and back are reversed and the interface layer and the negative electrode active material layer are not formed Second interface layer type for forming an interface layer on the opposite surface of the body 1a A chamber 10E, a second active material layer forming chamber 10F for forming a negative electrode active material layer on the interface layer formed on the opposite surface of the negative electrode current collector 1a, and an interface layer and The negative electrode current collector 1a on which the negative electrode active material layer is formed is partitioned into a take-out chamber 10G for taking up the take-up roll 13 and taking it out.

  The first and second interface layer forming chambers 10B and 10E are each provided with a high-frequency magnetron sputtering device 16 via a can roll 14 and shielding plates 15 on both sides thereof, and the first and second active materials described above. The layer forming chambers 10C and 10F are each provided with an electron beam evaporation device 17 via a can roll 14 and shielding plates 15 on both sides thereof, and a take-up roll 13 for taking up the negative electrode current collector 1a is taken into the take-out chamber 10G. Also, a temperature adjusting roll 18 is provided at an upstream position, and a temperature adjusting medium is supplied to each of the can rolls 14 and the temperature adjusting roll 18 so that the temperature can be adjusted.

  Here, in producing a negative electrode for a lithium secondary battery using the above production apparatus, a predetermined tension is applied to the long sheet-like negative electrode current collector 1a wound around the supply roll 12, The negative electrode current collector 1a is passed through a slit 11a provided in the partition wall 11, from the current collector supply chamber 10A to the first interface layer forming chamber 10B, the first active material layer forming chamber 10C, the guide chamber 10D, and the second interface layer forming chamber. 10E, the second active material layer forming chamber 10F, and the take-out chamber 10G are guided by the guide roll 19 in this order.

  Then, in the first interface layer forming chamber 10B, an interface layer is formed on one surface of the negative electrode current collector 1a guided to the bottom of the can roll 14 by the high-frequency magnetron sputtering apparatus 16, and then the first interface is formed. In the active material layer forming chamber 10 </ b> C, a negative electrode active material layer is formed by the electron beam vapor deposition device 17 on the interface layer formed on the negative electrode current collector 1 a led to the bottom of the can roll 14.

  Then, the negative electrode current collector 1a having the interface layer and the negative electrode active material layer formed on one side in this manner is reversed in the guide chamber 10D, and the above-mentioned canister is formed in the second interface layer formation chamber 10E. An interfacial layer is formed on the opposite surface of the negative electrode current collector 1a led to the bottom of the roll 14 by the high frequency magnetron sputtering apparatus 16, and then the can roll 14 is formed in the second active material layer forming chamber 10F. A negative electrode active material layer is formed by an electron beam evaporation device 17 on the interface layer formed on the negative electrode current collector 1 a led to the bottom of the electrode.

  Next, the negative electrode current collector 1a having the interface layer and the negative electrode active material layer formed on both sides as described above is introduced into the extraction chamber 10G, and an inert gas is supplied to the extraction chamber 10G from the gas supply port 20. The negative electrode current collector is made to adsorb an inert gas on the surface of the negative electrode active material layer and supply a refrigerant to the temperature adjusting roll 18 to cool the negative electrode current collector 1a to room temperature or lower. The la is wound around the winding roll 13 with an appropriate tension applied.

  In addition, after winding the negative electrode current collector 1a on the take-up roll 13 in this way, when taking out the take-up roll 13 to the outside, a heating medium is supplied to the temperature adjusting roll 18 and the take-up roll 13 is taken up. After the negative electrode current collector 1a wound around the roll 13 is heated to some extent, dry air is introduced into the take-out chamber 10G, and then the take-up roll 13 is taken out.

  In this way, the inert gas adsorbed on the surface of the negative electrode active material as described above expands, and this inert gas prevents oxygen and moisture in the atmosphere from contacting the surface of the negative electrode active material. Will come to be.

  Next, the case where the negative electrode for a lithium secondary battery of the example is manufactured using the above manufacturing apparatus and the case where the negative electrode for a lithium secondary battery of the comparative example is manufactured will be specifically described, and manufactured in this way. The negative electrode for the lithium secondary battery of the example was compared with the negative electrode for the lithium secondary battery of the comparative example. In the negative electrode for the lithium secondary battery of the example, oxidation of the negative electrode active material was suppressed, and the lithium secondary battery It will be clarified that the charge and discharge efficiency of the is improved.

Example 1
In Example 1, copper was deposited on both surfaces of a rolled copper alloy foil containing 0.02% by weight of Zr as a negative electrode current collector by an electrolytic method, the surface roughness Ra was 0.5 μm, the width was 20 cm, and the thickness was What became 26 micrometers was used. The negative electrode current collector had a tensile strength of 400 N / mm ² , an electric conductivity of 97% IACS, and a thermal conductivity of about 370 W / m · K.

Then, the negative electrode current collector 1a is wound around the supply roll 12 as described above and set in the current collector supply chamber 10A, and the inside of the apparatus main body 10 is exhausted by a vacuum exhaust device (not shown). The pressure in the first and second active material layer forming chambers 10C and 10F was set to 5 × 10 ⁻³ Pa or less.

  Then, the negative electrode current collector 1a is fed at a feed rate of 0.2 m / min in a state where a predetermined tension is applied, and in the first interface layer forming chamber 10B, the negative electrode current collector 1a is placed on one surface. The interface layer was formed by the high frequency magnetron sputtering apparatus 16 described above.

  Here, in forming the interface layer on one side of the negative electrode current collector 1a, argon gas is used as the atmosphere gas, and a silicon single crystal having a purity of 99.999% is used as the target, and sputtering is performed under the sputtering conditions shown in Table 1 below. And an interface layer having a thickness of 0.1 μm was formed. When the negative electrode current collector 1a is wound around the can roll 14 and guided to the position of the high-frequency magnetron sputtering apparatus 16, a tension of 300 N is applied to the negative electrode current collector 1a, and the negative electrode current collector 1a has a width of 1 cm. The negative electrode current collector 1a immediately after the interface layer is formed by supplying a refrigerant to the can roll 14 and controlling the temperature of the surface of the can roll 14 to 20 ° C. The surface temperature was set to 150 ° C. or lower.

  Next, in the first active material layer forming chamber 10C, a negative electrode active material layer was formed by the electron beam evaporation apparatus 17 on the interface layer formed on one surface of the negative electrode current collector 1a as described above.

  Here, in forming the negative electrode active material layer on the interface layer formed on the negative electrode current collector 1 a, small granular silicon having a purity of 99.999% was used as the vapor deposition material, and the vapor deposition shown in Table 2 below. Vapor deposition was performed under the conditions to form a negative electrode active material layer having a thickness of 5 μm. When the negative electrode current collector 1a is wound around the can roll 14 and led to the position of the electron beam evaporation apparatus 17, a tension of 300 N is applied to the negative electrode current collector 1a, and the width of the negative electrode current collector 1a is 1 cm. The negative electrode current collector immediately after forming a negative electrode active material layer by allowing a tension of 15 N to act and supplying a refrigerant to the can roll 14 to control the temperature of the surface of the can roll 14 to 20 ° C. The surface temperature of 1a was made to be 150 ° C. or lower.

  And after forming the interface layer and the negative electrode active material layer on one surface of the negative electrode current collector 1a in this way, the front and back of the negative electrode current collector 1a are reversed in the guide chamber 10D, and the second interface layer is formed. In the forming chamber 10E, the interface layer having a thickness of 0.1 μm is formed on the opposite surface of the negative electrode current collector 1a in the same manner as in the case of the first interface layer forming chamber 10B. In the second active material layer forming chamber 10F, the thickness is 5 μm on the interface layer formed on the opposite surface of the negative electrode current collector 1a in the same manner as in the case of the first active material layer forming chamber 10C. A negative electrode active material layer was formed.

  Next, the negative electrode current collector 1a having the interface layer and the negative electrode active material layer formed on both sides in this way is introduced into the extraction chamber 10G, and an inert gas argon gas is introduced into the extraction chamber 10G from the gas supply port 20. Is supplied at a flow rate of 10 sccm, the pressure in the vicinity of the winding roll 13 is set to 5 Pa, and a refrigerant is supplied to the temperature adjusting roll 18 to control the temperature of the surface of the temperature adjusting roll 18 to −25 ° C. The negative electrode current collector 1 a was cooled by the temperature adjusting roll 18, and the negative electrode current collector 1 a thus cooled was wound on the take-up roll 13. In addition, when winding the negative electrode current collector 1a on the take-up roll 13, a tension of 100N was applied so that a tension of 5N was applied per 1 cm width of the negative electrode current collector 1a.

  In addition, after the negative electrode current collector 1a having the interface layer and the negative electrode active material layer formed on both sides in this manner is wound around the take-up roll 13, the take-up roll 13 is taken out to the outside. A heating medium is supplied to the temperature adjusting roll 18 so that the temperature of the surface of the temperature adjusting roll 18 is 20 ° C., and the negative electrode current collector 1 a wound around the winding roll 13 is heated to some extent. The dry air was introduced into the apparatus main body 10 to bring the inside of the apparatus main body 10 to atmospheric pressure, and then the winding roll 13 was taken out to the outside.

(Comparative Example 1)
In Comparative Example 1, the inert gas argon gas is not supplied to the take-out chamber 10G, and the refrigerant is not supplied to the temperature adjusting roll 18, so that the interface layer and the negative electrode active material layer are formed on both sides. The negative electrode current collector 1a formed with and was wound around the take-up roll 13, and the others were the same as in Example 1 above.

(Comparative Example 2)
In Comparative Example 2, the refrigerant is not supplied to the temperature adjusting roll 18, and the negative electrode current collector 1 a having the interface layer and the negative electrode active material layer formed on both sides is wound around the winding roll 13. The others were the same as in the case of Example 1 above.

  Next, the glove box in an atmosphere of 100% argon gas with the negative electrodes for lithium secondary batteries of Example 1 and Comparative Examples 1 and 2 taken out together with the take-up roll 13 as described above in the roll state. In this glove box, a 1 cm square sample for analysis was cut out from the negative electrode for a lithium secondary battery, and a Raman emission analysis and an oxygen concentration were performed on the negative electrode active material formed on each negative electrode for a lithium secondary battery. Analysis was carried out.

Results of Raman emission analysis, the negative electrode active material composed of silicon formed on the negative electrode for the lithium secondary battery described above, while the peak of 480 cm ^-1 vicinity is observed substantially peak of 520 cm ^-1 vicinity substantially It was found that it was amorphous silicon.

  The oxygen concentration in the negative electrode active material was determined from the ratio of the amount of Si determined by ICP emission spectroscopic analysis and the amount of oxygen determined by combustion analysis.

  The oxygen concentration in the negative electrode active material was measured at the initial stage when each negative electrode for a lithium secondary battery was produced as described above and when each negative electrode for a lithium secondary battery was left in the atmosphere for one month. The results are shown in Table 3 below.

  As is apparent from the results, the negative electrode for a lithium secondary battery manufactured as shown in Example 1 was manufactured in comparison with the negative electrode for a lithium secondary battery manufactured as shown in Comparative Examples 1 and 2. It was found that the oxygen concentration in the negative electrode active material at the initial stage was greatly reduced, and the negative electrode active material was prevented from being oxidized. In addition, when left in the atmosphere for one month, the difference in oxygen concentration in the negative electrode active materials of Example 1 and Comparative Examples 1 and 2 was small.

  Next, the negative electrodes for lithium secondary batteries of Example 1 and Comparative Examples 1 and 2 manufactured as described above, and the negative electrodes for lithium secondary batteries of Example 1 and Comparative Examples 1 and 2 as described above, respectively. Lithium secondary batteries were manufactured using the negative electrodes for lithium secondary batteries of Reference Example 1 and Reference Comparative Examples 1 and 2 that were left in the atmosphere for 1 month, and the charge and discharge efficiencies of the lithium secondary batteries were compared. did.

  Here, in manufacturing each lithium secondary battery, a positive electrode and a non-aqueous electrolyte prepared as described below were used.

[Production of positive electrode]
Li ₂ CO ₃ and CoCO ₃ are weighed so that the atomic ratio of Li: Co is 1: 1 and mixed in a mortar. The mixture is pressure-molded using a mold press having a diameter of 17 mm, and then air It was fired at 800 ° C. for 24 hours to obtain a fired body made of LiCoO ₂ .

Next, this fired body was pulverized with a mortar until the average particle size became 20 μm, to obtain a LiCoO ₂ powder as a positive electrode active material.

Then, 90 parts by weight of the LiCoO ₂ powder of the positive electrode active material obtained as described above, 5 parts by weight of the artificial graphite powder of the conductive agent, and 5 parts by weight of the polytetrafluoroethylene binder are included. The mixture was mixed with a weight% N-methylpyrrolidone aqueous solution to obtain a positive electrode mixture slurry.

  And this slurry is apply | coated on the 20 micrometer-thick aluminum foil which is a positive electrode collector by the doctor blade method, This is dried, The positive electrode by which the positive electrode active material layer was formed in the single side | surface of a positive electrode collector was produced. did.

[Preparation of non-aqueous electrolyte]
LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 to a concentration of 1 mol / liter to prepare a non-aqueous electrolyte.

  Here, in manufacturing the lithium secondary battery, as shown in FIGS. 2 and 3, in the negative electrode 1 in which the negative electrode active material layer 1b is formed on both surfaces of the negative electrode current collector 1a, the negative electrode current collector 1a is formed. While attaching the negative electrode current collection tab 1c, the positive electrode current collection tab 2c was attached to the positive electrode current collector 2a in the positive electrode 2 in which the positive electrode active material layer 2b was formed on one surface of the positive electrode current collector 2a.

  The positive electrode active material layer 2b and the positive electrode active material layer 2b are respectively connected to the inside of the outer package 3 made of an aluminum laminate film, on both sides of the negative electrode 1 with a separator 4 made of porous polyethylene having a thickness of 35 μm. In the state where the non-aqueous electrolyte 5 is injected and the negative electrode current collecting tab 1c and the positive electrode current collecting tab 2c are extended to the outside while being arranged so as to face the material layer 1b. Each lithium using the negative electrode for each lithium secondary battery of Example 1 and Comparative Examples 1 and 2, and each of the negative electrodes for lithium secondary batteries of Reference Example 1 and Reference Comparative Examples 1 and 2, with the outer package 3 sealed. A secondary battery was produced.

  Next, each of the lithium secondary batteries prepared as described above was charged in a 20 ° C. atmosphere at a charging current of 100 mA until the battery voltage reached 4.2 V, and the charge capacity Q1 was determined. The battery was discharged at a discharge current of 100 mA until the battery voltage reached 2.75 V, the discharge capacity Q2 was determined, the charge / discharge efficiency (%) in each lithium secondary battery was determined by the following formula, and the results are shown in the table below. This is shown in FIG.

Charging / discharging efficiency (%) = (Q2 / Q1) × 100

  As is apparent from the results, the lithium secondary battery using the negative electrode for lithium secondary battery of Example 1 was the negative electrode for each lithium secondary battery of Comparative Examples 1 and 2, and Reference Example 1 and Reference Comparative Example 1. Compared with each lithium secondary battery using the negative electrode for each lithium secondary battery of No. 1 and 2, charge / discharge efficiency was greatly improved.

  Moreover, the relationship between the oxygen concentration contained in the negative electrode active material in each said lithium secondary battery and charging / discharging efficiency (%) was shown in FIG.

  As a result, it was found that when the oxygen concentration contained in the negative electrode active material was 7% by weight or less, a lithium secondary battery having a charge / discharge efficiency of 85% or more, which is a good battery standard, was obtained.

It is the schematic explanatory drawing which showed an example of the apparatus which manufactures the negative electrode for lithium secondary batteries of this invention. It is a schematic plan view of the lithium secondary battery produced using each negative electrode for lithium secondary batteries of an Example, a comparative example, a reference example, and a reference comparative example. It is sectional explanatory drawing which showed the internal structure of said lithium secondary battery. It is the figure which showed the relationship between the oxygen concentration contained in the negative electrode active material in each lithium secondary battery of an Example, a comparative example, a reference example, and a reference comparative example, and charging / discharging efficiency (%).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode 1a Negative electrode collector 1b Negative electrode active material layer 1c Negative electrode current collection tab 2 Positive electrode 2a Positive electrode current collector 2b Positive electrode active material layer 2c Positive electrode current collection tab 3 Exterior body 4 Separator 5 Nonaqueous electrolyte 10 Device main body 10A Current collection Body supply chamber 10B first interface layer forming chamber 10C first active material layer forming chamber 10D guide chamber 10E second interface layer forming chamber 10F second active material layer forming chamber 10G take-out chamber 11 partition 11a slit 12 supply roll 13 take-up roll 14 Can Roll 15 Shielding Plate 16 High Frequency Magnetron Sputtering Device 17 Electron Beam Deposition Device 18 Temperature Control Roll 19 Guide Roll 20 Gas Supply Port

Claims (8)

  A process of forming a thin film of a negative electrode active material by discharging a negative electrode active material that absorbs and releases lithium into a gas phase under reduced pressure and supplying the negative electrode active material onto a negative electrode current collector formed into a long sheet; And winding the negative electrode current collector on which the thin film is formed, and before winding the negative electrode current collector on which the thin film of the negative electrode active material is wound, the negative electrode current collector is lower than room temperature. A method for producing a negative electrode for a lithium secondary battery, wherein the negative electrode active material is cooled to a temperature and an inert gas is adsorbed on the surface of the thin film of the negative electrode active material.   2. The method for producing a negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material is a material alloyed with lithium.   The method for producing a negative electrode for a lithium secondary battery according to claim 2, wherein the negative electrode active material is silicon.   4. The method for producing a negative electrode for a lithium secondary battery according to claim 1, wherein the thin film of the negative electrode active material is an amorphous or microcrystalline thin film. A method for producing a negative electrode for a secondary battery.   The method for producing a negative electrode for a lithium secondary battery according to any one of claims 1 to 4, wherein the tension when winding the negative electrode current collector on which the thin film of the negative electrode active material is wound is negative electrode current collector. The manufacturing method of the negative electrode for lithium secondary batteries characterized by being in the range of 4-40N per cm width of a body.     The method for producing a negative electrode for a lithium secondary battery according to any one of claims 1 to 5, wherein an inert gas is adsorbed on the surface of the thin film of the negative electrode active material to wind up the negative electrode current collector. A method for producing a negative electrode for a lithium secondary battery, wherein the atmospheric pressure is 3 Pa or more.   In the manufacturing method of the negative electrode for lithium secondary batteries of any one of Claims 1-6, the negative electrode electrical power collector by which the surface was roughened was used for said negative electrode electrical power collector. A method for producing a negative electrode for a lithium secondary battery.   In the manufacturing method of the negative electrode for lithium secondary batteries of any one of Claims 1-7, after winding up the negative electrode collector in which the thin film of the negative electrode active material was formed, this was made to heat. A method for producing a negative electrode for a lithium secondary battery, wherein the negative electrode is extracted in an environment containing oxygen.

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