JP2012174434A - Method for manufacturing battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a battery with improved production efficiency and yield.SOLUTION: The manufacturing method includes steps for forming an active material layer on a collector, and manufacturing a strip electrode having a non-coated part, at which the collector is exposed, at an end parallel to a longitudinal direction; rolling the strip electrode; tension-annealing the rolled strip electrode; and laminating the tension-annealed strip electrode on a counter electrode via a separator, and manufacturing a group of electrodes.

Description

  Embodiments described herein relate generally to a battery manufacturing method.

  In recent years, non-aqueous electrolyte secondary batteries have attracted attention as power sources for hybrid electric vehicles and as power storage devices for generators using natural energy such as sunlight and wind power. The electrode group provided in the nonaqueous electrolyte secondary battery has a configuration in which a positive electrode and a negative electrode are stacked via a separator. Electrodes such as a positive electrode and a negative electrode are rolled and formed in the manufacturing process, and this rolling causes distortion of the electrodes. When the electrodes are distorted, there are problems that the production efficiency when manufacturing the electrode group is lowered and the yield is lowered.

JP 62-99430 A JP-A-8-227958

  A battery manufacturing method with improved production efficiency and yield is provided.

  According to the embodiment, a method for manufacturing a battery is provided. The method includes forming an active material layer on a current collector, producing a strip electrode having an uncoated portion with the current collector exposed at an end parallel to the longitudinal direction, and rolling the strip electrode Treatment, tension annealing of the strip electrode after the rolling treatment, and laminating the strip electrode after the tension annealing treatment with a counter electrode through a separator to manufacture an electrode group.

The perspective view which shows the external appearance of the nonaqueous electrolyte battery of embodiment. The expansion | deployment perspective view of the battery of FIG. The expansion | deployment perspective view of the electrode group with which the battery of FIG. 1 is equipped. The conceptual diagram which shows the amount of bending.

  Hereinafter, the battery manufactured by this embodiment is demonstrated with reference to drawings. The battery manufactured according to the present embodiment is not limited to this, but may be a nonaqueous electrolyte secondary battery.

  FIG. 1 is an external view of a square nonaqueous electrolyte battery 1. FIG. 2 is a developed perspective view of the nonaqueous electrolyte battery 1 of FIG. As shown in FIG. 2, the nonaqueous electrolyte battery 1 includes a flat electrode group 2.

  The electrode group 2 is accommodated in the outer can 3. A lid 4 is attached to the opening of the outer can 3, thereby sealing the outer can 3. The lid 4 includes a positive electrode terminal 5 and a negative electrode terminal 6.

  Inside the outer can 3, a positive electrode lead 7 and a negative electrode lead 8 are provided. Each of the positive electrode lead 7 and the negative electrode lead 8 includes a connection plate having a through-hole, and a strip-shaped current collecting portion that branches off from the connection plate and extends downward.

  The positive electrode terminal 5 is attached to the lid 4 via an insulating gasket 9 by, for example, caulking. The positive electrode terminal 5 is also caulked and fixed to the through hole of the positive electrode lead 7. Thereby, the positive electrode lead 7 is fixed to the lid 4, and the positive electrode terminal 5 and the positive electrode lead 7 are electrically connected.

  The negative electrode terminal 6 is attached to the lid 4 via an insulating gasket 10 by, for example, caulking. The negative electrode terminal 6 is also caulked and fixed to the through hole of the negative electrode lead 8. Thereby, the negative electrode lead 8 is fixed to the lid 4, and the negative electrode terminal 6 and the negative electrode lead 8 are electrically connected.

  FIG. 3 is a developed perspective view of the electrode group 2. The electrode group 2 has a configuration in which a positive electrode 11 and a negative electrode 12 are stacked via a separator 13 and wound into a flat shape.

  The positive electrode 11 includes a positive electrode current collector 11a and a positive electrode active material layer 11b. The positive electrode active material layer 11b is formed on one side or both sides of the positive electrode current collector 11a. The positive electrode active material layer 11 b is formed leaving an end parallel to the longitudinal direction of the positive electrode 11. Thereby, the non-coating part which the positive electrode electrical power collector 11a exposed is formed in the edge part parallel to the longitudinal direction of a positive electrode. This non-coated part is used as the positive electrode current collecting tab 11c. The positive electrode current collecting tab 11c may be formed at both ends of the positive electrode, but is preferably formed only at one end.

  The negative electrode 12 includes a negative electrode current collector 12a and a negative electrode active material layer 12b. The negative electrode active material layer 12b is formed on one side or both sides of the negative electrode current collector 12a. The negative electrode active material layer 12 b is formed leaving an end parallel to the longitudinal direction of the negative electrode 12. Thereby, the non-coating part which the negative electrode collector 12a exposed is formed in the edge part parallel to the longitudinal direction of a negative electrode. This non-coated portion is used as the negative electrode current collecting tab 12c. The negative electrode current collecting tab 12c may be formed at both ends of the negative electrode, but is preferably formed only at one end.

  The positive electrode 11 and the negative electrode 12 are arranged such that the positive electrode current collecting tab 11c protrudes from the separator 13 in the winding axis direction of the electrode group, and the negative electrode current collecting tab 12c protrudes from the separator 13 in the opposite direction. The 12 positions are overlapped and wound. Thereby, as shown in FIG. 2, the electrode group 2 has a positive current collecting tab 11c wound spirally from one end face and a negative current collecting tab wound spirally from the other end face. 12c protrudes. In order to secure the electrode group 2 and to insulate the electrode group 2 and the outer can 3, it is preferable that the outermost periphery is covered with an insulating tape 14 as shown in FIG. 2.

  As shown in FIG. 2, the positive electrode current collecting tab 11 c is joined to the positive electrode lead 7. Thereby, the positive electrode 11, the positive electrode lead 7, and the positive electrode terminal 5 are electrically connected. Similarly, the negative electrode current collecting tab 12 c is joined to the negative electrode lead 8. Thereby, the negative electrode 12, the negative electrode lead 8, and the negative electrode terminal 6 are electrically connected. The joining of the positive and negative current collecting tabs 11c and 12c and the positive and negative electrode leads 7 and 8 can be performed by, for example, ultrasonic welding.

  After the positive and negative electrode leads 7 and 8 and the positive and negative electrode current collecting tabs 11 c and 12 c are joined, the electrode group 2 is accommodated in the outer can 3, and the lid 4 is joined to the opening of the outer can 3. The joining can be performed, for example, by seam welding using a laser. Next, the electrolytic solution is injected into the outer can 3 from the liquid injection port 15 provided in the lid 4.

  The outer can 3 and the lid 4 may be formed of a metal such as aluminum, aluminum alloy, iron, and stainless steel, respectively. The outer can 3 and the lid 4 may be formed of different types of metal, but are preferably formed of the same type of metal.

  The positive electrode current collector 11a is preferably formed from an aluminum foil or an aluminum alloy foil containing one or more elements selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The negative electrode current collector 12a is preferably formed from an aluminum foil, an aluminum alloy foil containing one or more elements selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu and Si, or a copper foil. .

  Next, the method for manufacturing the battery according to the present embodiment will be described. The manufacturing method includes forming an active material layer on a current collector, producing a strip-shaped electrode having an uncoated portion where the current collector is exposed at an end parallel to a longitudinal direction; and Rolling treatment, subjecting the strip electrode after the rolling treatment to tension annealing, and laminating the strip electrode after the tension annealing treatment with a counter electrode through a separator to manufacture an electrode group.

  In the electrode group, at least one of the positive electrode and the negative electrode may be processed according to the present embodiment, but both electrodes are preferably processed according to the present embodiment.

  First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. Next, the prepared slurry is applied to one or both sides of the current collector and dried to form an active material layer. At this time, the slurry is applied leaving a portion corresponding to the end parallel to the longitudinal direction of the electrode. Thereby, the non-coating part which the electrical power collector exposed is obtained. This non-coated part is used as a current collecting tab. The non-coated portion may be formed at both ends of the electrode, but is preferably formed only at one end. Next, if necessary, the current collector on which the active material layer is formed is cut into a strip shape. Here, an electrode having a strip shape is referred to as a strip electrode.

  Next, the strip electrode is rolled to compress the active material layer. The rolling process can be performed by, for example, a roller press process. A roller press process can be implemented using the roller press apparatus which loads a strip | belt-shaped electrode with a roller. In the rolling process, when the load is applied at a time, the distortion of the electrode increases. Therefore, it is preferable to apply a step-wise changing load to the strip electrode, and it is preferable to gradually increase the load for rolling.

  In this rolling process, the current collector is also rolled together with the active material layer. However, since the diameter of the roller is constant, the roller does not contact the non-coated portion (that is, the current collecting tab) where the slurry is not applied and the active material layer is not formed. Therefore, the current collector in the portion where the active material layer is formed is rolled, while the current collector in the non-coated portion is not rolled. As a result, a residual stress is generated at the boundary between these portions, and the entire electrode is distorted.

  When the electrodes are distorted, the production efficiency and the yield are reduced when the electrodes are stacked to produce an electrode group. Therefore, in this embodiment, the strip electrode after the rolling process is further subjected to a tension annealing process to correct the distortion of the electrode.

  The tension annealing treatment can be performed using, for example, a rewinding device including a brewing device and a winding device. The rewinding device can control the tensile stress applied to the electrode by adjusting the braking force of the unwinding device and the winding force of the winding device. By passing the strip-shaped electrode after the rolling treatment through a rewinding device and unwinding and winding it while controlling the tension, an appropriate tensile stress can be applied to the strip-shaped electrode and the distortion can be corrected.

  The tensile stress applied to the strip electrode is preferably in the range of 10 MPa to 200 MPa. By setting the tensile stress to 10 MPa or more, the distortion of the strip electrode can be effectively corrected. Moreover, by setting the tensile stress to 200 MPa or less, the strip electrode can be prevented from being broken. The tensile stress applied to the strip electrode is more preferably in the range of 100 MPa to 150 MPa.

  When performing the tension annealing treatment, the strip electrode or the current collecting tab may be heated. By heating, the distortion of the electrode can be corrected with a smaller tension. Further, by heating, moisture in the electrode can be evaporated and drying can be promoted. Therefore, it is possible to shorten the time for vacuum drying the electrode group in the subsequent process, and to further improve the production efficiency.

  The heating temperature is preferably in the range of 50 ° C to 150 ° C. By heating at 50 ° C. or higher, the electrode can be corrected more effectively. Further, by setting the heating temperature to 150 ° C. or lower, it is possible to prevent the binder contained in the active material layer from being decomposed.

  The longer the heating time, the higher the distortion correction effect, and the variation in the degree of distortion tends to decrease. On the other hand, a shorter heating time is preferable from the viewpoint of productivity and cost. Therefore, the heating time is appropriately determined by the tensile stress and the heating temperature.

  Furthermore, the tension annealing treatment is preferably performed in a reduced pressure atmosphere. Under a reduced pressure atmosphere, heating of the strip electrode is easy, and evaporation of moisture is further promoted. The pressure in the reduced-pressure atmosphere is not limited to this, but is preferably 100 Pas or less, for example, in absolute pressure.

  By such a tension annealing treatment, the residual stress generated at the boundary between the current collector in the part where the active material layer is formed and the current collector in the non-coated part is eliminated, and the distortion and curvature are corrected. An electrode can be obtained. Therefore, production efficiency and yield can be significantly improved in the stacking process for manufacturing the electrode group.

Since the strained electrode is curved, the strain of the electrode can be evaluated by measuring the amount of bending. FIG. 4 shows a conceptual diagram of the bending amount. Of the two sides parallel to the longitudinal direction of the electrode, the longer side is referred to as the outer edge. This outer edge is usually a side of the end opposite to the end where the current collecting tab is located, and is a side that is longer than the side on the side of the current collecting tab when the electrode is rolled. The straight line connecting the points P ₁ and P ₂ on the outer edge to the reference line. The points P ₁ and P ₂ are set so that the distance X of the straight line connecting these points is constant. In the present embodiment, to set the linear distance X of the point _{P 1} and _{P 2} and 1000 mm. Between the point P ₁ and P _2, the maximum distance Y is bending amount between the reference line and the outer edge.

  The amount of bending can be measured at an arbitrary plurality of locations of the strip electrode, and can be evaluated as a range of measured values obtained. For example, the number of measurement points can be three at intervals of 0.5 m per 2 m, but is not limited thereto.

  Next, the strip electrode manufactured by the above method is laminated with a counter electrode via a separator to manufacture an electrode group. That is, when the manufactured strip electrode is a positive electrode, it is laminated with a negative electrode, and when the manufactured strip electrode is a negative electrode, it is laminated with a positive electrode. In addition, as above-mentioned, it is preferable that both the positive electrode and the negative electrode are manufactured by the said method. When manufacturing a wound electrode group, a positive electrode and a negative electrode are laminated with a separator interposed therebetween and wound. When manufacturing a laminated electrode, a strip electrode is cut into a desired size and stacked in a stack with a separator interposed therebetween.

  Although it does not specifically limit as a positive electrode active material used for manufacture of a positive electrode, The oxide, sulfide, polymer, etc. which can occlude / release lithium can be used. In particular, lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, and lithium iron phosphate are preferable because a high positive electrode potential can be obtained.

  The negative electrode active material used in the production of the negative electrode is not particularly limited, and metal oxides, metal sulfides, metal nitrides, alloys, and the like that can occlude and release lithium can be used. In particular, a substance having a lithium ion storage / release potential of 0.4 V or more noble with respect to the metal lithium potential is preferable. A negative electrode active material having a lithium ion occlusion / release potential of no less than 0.4 V relative to the metal lithium potential can suppress the reaction between aluminum or an aluminum alloy and lithium. Therefore, the negative electrode current collector and the member related to the negative electrode can be formed of aluminum or an aluminum alloy.

  Examples of negative electrode active materials having a lithium ion occlusion / release potential of no less than 0.4 V with respect to the metal lithium potential include lithium-titanium composite oxides such as titanium oxide and lithium titanate, tungsten oxide, and amorphous tin oxidation. Products, tin silicon oxide, and silicon oxide. In particular, a lithium titanium composite oxide is preferably used.

  The conductive agent contained in the slurry is used to suppress contact resistance between the active material and the current collector. As the conductive agent, for example, a carbonaceous material such as acetylene black, carbon black, and graphite can be used.

  The binder contained in the slurry is used to bind the active material and the conductive agent. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber can be used as the binder.

  The compounding ratio of the positive electrode active material, the conductive agent, and the binder is 80% by weight to 95% by weight for the positive electrode active material, 3% by weight to 18% by weight for the conductive agent, and 2% by weight to 17% by weight for the binder. % Or less is preferable. When the conductive agent is contained in an amount of 3% by weight or more, the above-described effects can be obtained. By including the conductive agent in a range of 18% by weight or less, the decomposition of the nonaqueous electrolyte on the surface of the conductive agent under high temperature storage can be reduced. it can. When the binder is contained in an amount of 2% by weight or more, sufficient electrode strength can be obtained, and when it is contained in the range of 17% by weight or less, the amount of the insulator can be reduced and the internal resistance can be reduced.

  The compounding ratio of the negative electrode active material, the conductive agent and the binder is such that the negative electrode active material is 70% by weight to 96% by weight, the conductive agent is 2% by weight to 28% by weight, and the binder is 2% by weight to 28% by weight. % Or less is preferable. By containing 2% by weight or more of the conductive agent, the current collecting performance of the negative electrode layer can be improved, and the large current characteristics of the battery can be improved. In addition, when the binder is contained in an amount of 2% by weight or more, the binding property between the negative electrode layer and the negative electrode current collector can be improved, and the cycle characteristics can be improved. On the other hand, from the viewpoint of increasing the capacity, it is preferable that the conductive agent and the binder are included in a range of 28% by weight or less.

  For example, N-methylethylpyrrolidone can be used as a solvent for preparing the slurry. The mixing ratio of the total weight of the active material, conductive agent and binder to the weight of the solvent is preferably in the range of 50:50 to 80:20.

  The separator used for the production of the electrode group may be a microporous membrane, a woven fabric or a non-woven fabric, or a combination thereof. The separator may be formed of a material selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymer, and ethylene-butene copolymer.

The electrode group produced as described above is housed in an outer can, and after injecting an electrolyte, it is sealed. As the electrolytic solution, a nonaqueous electrolytic solution prepared by dissolving an electrolyte (for example, lithium salt) in a nonaqueous solvent can be used. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (γ -BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran and the like. Nonaqueous solvents may be used alone or in combination of two or more. Examples of electrolytes include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), trifluorometa Examples thereof include lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ). The electrolyte may be used alone or in combination of two or more. The amount of electrolyte dissolved in the non-aqueous solvent is desirably 0.2 mol / L to 3 mol / L.

  According to the above embodiment, a battery manufacturing method with improved production efficiency and yield can be provided.

  According to the embodiment, an electrode for a lithium ion secondary battery was manufactured.

Example 1
A positive electrode was prepared using lithium cobalt oxide LiCoO ₂ as a positive electrode active material, graphite powder as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder. Each was mixed at a weight ratio of 85: 5: 5: 5 and dispersed in an organic solvent to prepare a slurry. This slurry was applied to a sheet-like aluminum foil having a thickness of 20 μm and dried to form an active material layer. Similarly, the slurry was applied to the back side of the aluminum foil and dried to form an active material layer. The aluminum foil was cut into a strip shape having a width of 100 mm and a current collecting tab width of 10 mm.

  The obtained strip electrode was roll-pressed and rolled and then subjected to tension annealing for 1.5 minutes under the conditions of a tensile stress of 100 MPa and a heating temperature of 150 ° C.

(Examples 2 to 16)
An electrode was produced in the same manner as in Example 1 except that the conditions of tensile stress, heating temperature and heating time were changed as shown in Table 1.

(Comparative example)
An electrode was produced in the same manner as in Example 1 except that no tensile stress was applied to the strip electrode and no tension annealing treatment was performed.

(Measurement of bending amount)
The bending amount of the electrodes of Examples 1 to 16 and the comparative example was measured. The measurement was performed at five locations on each electrode (n = 5). The measurement results are shown in Table 1.

(result)
In Examples 1 to 16, the amount of bending was smaller than that of the comparative example in which the tension annealing treatment was not performed. Therefore, it was shown that the strain of the electrode can be corrected by performing the tension annealing treatment.

  From Examples 1 to 5, it was shown that the amount of bending decreases as the tensile stress increases.

  Examples 6 to 8 show that the amount of bending decreases as the heating temperature increases.

  From Examples 9 to 11, it was shown that the longer the heating time, the lower the amount of bending, and the variation in the amount of bending decreased.

  In Example 15 where the tensile stress was 10 MPa, the amount of bending was smaller than that in Example 16 where the tensile stress was 5 MPa, although the heating temperature was lower. From this, it was shown that the tensile stress of 10 MPa or more has a higher effect of correcting the distortion.

  From Examples 13 and 14, it was shown that the effect of reducing the bending amount can be obtained even in a room temperature (25 ° C.) environment. However, from Example 6, it was shown that the amount of bending can be reduced more efficiently by heating at a temperature of 50 ° C. or higher.

(Example 17)
An electrode was produced in the same manner as in Example 1 except that the tensile stress was 300 MPa.

(Measurement of breaking rate)
For the electrodes of Examples 3 to 5, 12 and 17, the ratio of fracture during the tension annealing treatment was examined. The results are shown in Table 2.

  In Examples 12 and 17 in which the tensile stress was 250 MPa or more, although the effect of reducing the bending amount was high, the fracture rate was high. On the other hand, Examples 3 to 5 having a tensile stress of 200 MPa or less had a breaking rate of 0.

  Therefore, it was shown that the tensile stress is preferably 200 MPa or less from the viewpoint of improving production efficiency and yield.

  Although the embodiment of the present invention has been described, the above embodiment has been presented as an example, and is not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Nonaqueous electrolyte battery, 2 ... Electrode group, 3 ... Outer can, 4 ... Cover, 5 ... Positive electrode terminal, 6 ... Negative electrode terminal, 7 ... Positive electrode lead, 8 ... Negative electrode lead, 9, 10 ... Insulating gasket, 11 ... Positive electrode, 11a ... Positive electrode current collector, 11b ... Positive electrode active material layer, 11c ... Positive electrode current collector tab, 12 ... Negative electrode, 12a ... Negative electrode current collector, 12b ... Negative electrode active material layer, 12c ... Negative electrode current collector tab, 13 ... Separator, 14 ... insulating tape, 15 ... liquid inlet.

Claims (6)

Forming an active material layer on the current collector, and producing a strip electrode having an uncoated portion where the current collector is exposed at an end parallel to the longitudinal direction;
Rolling the strip electrode;
Tension annealing the strip-shaped electrode after the rolling process;
Laminating the belt-like electrode after the tension annealing treatment with a counter electrode via a separator to produce an electrode group;
A method for producing a battery, comprising:   The manufacturing method according to claim 1, wherein the tension annealing treatment applies a tensile stress of 10 MPa to 200 MPa to the strip electrode.   The manufacturing method according to claim 2, wherein the tension annealing treatment is performed at a temperature of 50 ° C. or more and 150 ° C. or less.   The manufacturing method according to claim 2, wherein the tension annealing treatment is performed in a reduced-pressure atmosphere.   The manufacturing method according to any one of claims 2 to 4, wherein the tension annealing treatment is performed by winding the strip electrode.   The said rolling process is performed by applying the load which changes to the said strip | belt-shaped electrode in steps, The manufacturing method as described in any one of Claims 2-5 characterized by the above-mentioned.

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