JP5018055B2 - Method for producing positive electrode plate of lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a method for producing a positive electrode plate used in a lithium ion secondary battery, and more particularly to a suitable heat treatment thereof.

  In recent years, consumer electronic devices have become increasingly portable and cordless. Conventionally, nickel-cadmium batteries, nickel-hydrogen batteries, or sealed small lead-acid batteries have played a role as power sources for driving these electronic devices. There is a strong demand for higher energy density, smaller size, and lighter weight of secondary batteries as power sources. In recent years, there has been a demand for a battery that can be charged and discharged at a high rate as represented by the rapid market expansion of small personal computers and communication devices.

  Under such circumstances, lithium ion secondary batteries using lithium cobalt composite oxide showing a high rate charge / discharge voltage, for example, LiCoO 2 as a positive electrode active material and utilizing insertion and detachment of lithium ions have become mainstream.

  Such a battery is produced by forming a spiral structure in which a separator is interposed between a positive electrode plate and a negative electrode plate in order to realize high rate charge / discharge. The positive electrode plate used here is obtained by applying and drying a positive electrode mixture on both surfaces of a positive electrode current collector made of a strip-shaped aluminum foil when producing the positive electrode plate in order to obtain efficient charge / discharge characteristics. In the heat treatment furnace, heat treatment is performed at a temperature higher than the melting point of the binder (Example of FEP binder: 300 ° C .: 15 minutes) to improve the binding force between the current collector and the active material mixture. (See, for example, Patent Document 1).

However, because only the heat treatment before pressing reduces battery performance due to the effects of thickeners and surfactant residues contained in the mixture that could not be decomposed by moisture adsorption or heat treatment in the steps after the heat treatment step, By performing heat treatment for 8 hours in a drying furnace at 250 ° C. higher than the softening point of the binder and thickener, the electrode plate cut into a predetermined width in the longitudinal direction after pressing and wound into a hoop shape The thickener residue and adsorbed moisture of the positive electrode plate are decomposed to stabilize the electrode plate resistance and improve battery performance (see, for example, Patent Document 2).
JP 2001-216957 A JP 2003-223899 A

However, in the conventional technology, when the heat treatment time is shortened to improve productivity, there is a problem that the battery performance is deteriorated due to the influence of the thickener or the residue of the surfactant. Moreover, when the electrode plate cut in the longitudinal direction and wound up in a hoop shape is dried at 250 ° C. for 8 hours in a drying furnace, the residual stress due to the press in the previous process is changed by heating and the electrode mixture is changed. As the thickness of the compressed electrode plate is restored due to the alteration of the binder contained, external pressure is applied in the hoop outer peripheral direction, the aluminum foil of the electrode plate on the outer peripheral portion is stretched, and the outer periphery side and the core side of the hoop A difference in length per electrode plate occurs.

Further, if the thickness of the cut electrode plate in the width direction is different, the thicker aluminum foil is stretched by tension from the thinner side, and a bending phenomenon occurs. Due to the difference in the length of one electrode plate between the outer peripheral side and the winding core side of this hoop and the bending phenomenon, the winding misalignment failure in the step of winding with a separator between the positive electrode plate and the negative electrode plate in the next step In addition, when the lead is welded, a defect in which the lead position is shifted occurs, and the defect loss increases and the operating rate of the winding process decreases.

  An object of the present invention is to solve such problems and improve the productivity of the heat treatment process, stabilize the process in the winding process, and improve the battery performance.

  In order to solve the above-mentioned problems, the present invention performs a heat treatment on a positive electrode plate dried by applying an electrode mixture on both sides of an aluminum foil current collector in a range of 340 ° C. to 400 ° C. for 60 seconds to 300 seconds. It is characterized by that.

  In addition, after the heat-treated positive electrode plate is pressed to a predetermined thickness, it is cut into a predetermined width in the longitudinal direction, and the electrode plate wound up in a hoop shape is further heated in a range of 110 ° C. to 200 ° C. in a drying furnace. The drying is performed for 4 hours or more and 12 hours or less.

  As in the present invention, the heat treatment is performed by heat-treating the electrode plate for a positive electrode, which has been dried by applying an electrode mixture on both sides of an aluminum foil current collector, in a range of 340 ° C. to 400 ° C. for 60 seconds to 300 seconds. In the process, the remaining additive other than the active material, conductive agent, and binder in the electrode mixture can be made 0.3% or less.

  Thereafter, pressing to a predetermined thickness, cutting to a predetermined width in the longitudinal direction, and drying the electrode plate wound in a hoop shape in a drying furnace in the range of 110 ° C. to 200 ° C. for 4 hours or more and 12 hours or less is performed. By doing this, the productivity of the heat treatment process can be improved, the winding process can be stabilized, and the yield can be improved.

  Furthermore, a lithium ion secondary battery with improved battery performance can be provided.

The method for producing a positive electrode plate for a lithium ion secondary battery according to the first aspect of the present invention comprises an electrode assembly comprising an active material, a conductive agent, a binder, a thickener, and a surfactant on both sides of a current collector. A coating drying step of creating a positive electrode plate by applying an agent and drying, a heat treatment step of performing a heat treatment in the range of 340 ° C. to 400 ° C. for 60 seconds to 300 seconds , A pressing step for pressing the electrode plate to a predetermined thickness, a cutting step for cutting the pressed electrode plate into a predetermined width in the longitudinal direction, and winding the electrode plate in a hoop shape; and an electrode wound in a hoop shape And a hoop drying step for drying the plate in a drying oven in the range of 110 ° C. to 200 ° C. for 4 hours or more and 12 hours or less, and the residue in the electrode plate excluding the active material, the conductive material, and the binder Is characterized by being 0.10% to 0.30% by weight It is intended.

  In the positive electrode plate manufactured by such a manufacturing method, the electrode plate coated with the electrode mixture on both surfaces of the aluminum foil current collector and dried is 340 ° C to 400 ° C in the range of 60 seconds to 300 seconds, By performing the heat treatment, it is possible to reduce the remaining amount of additives other than the active material, the conductive agent, and the binder in the electrode mixture to 0.3% or less in the heat treatment step. Moreover, the softening of the aluminum foil can be compensated for, and the adhesion between the mixture and the current collector can be secured.

In the first invention of the present invention, the thickness of the electrode plate compressed by the press can suppress the restoration, and the adsorbed moisture can also be decomposed. By suppressing the restoration of the electrode plate, the length of the electrode plate on the outer peripheral side and the core side of the hoop is made uniform, and the bending phenomenon can be suppressed. Here, if the drying time exceeds 12 hours, for example, 20 hours or more, the production efficiency of the drying process is lowered.

The second lithium ion secondary battery, the inventor of the present invention has employed the positive electrode plates produced by the production method of the present invention, to improve the stability of the winding process of the step and battery performance Is possible.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a process diagram in a manufacturing process of a positive electrode plate according to an embodiment of the present invention, in which a kneading process 1, a coating drying process 2, a heat treatment process 3 according to the manufacturing method, and a pressing process are performed in the order of steps. 4 shows a cutting process 5 and a hoop drying process 6 according to the present invention.

  Next, the detail of the Example of the said battery electrode plate is demonstrated.

Example 1
The positive electrode active material is 100 parts by weight of lithium cobaltate, 3 parts by weight of acetylene black as a conductive agent, 4 parts by weight of a dispersion mainly composed of FEP as a binder, and 0.8% of CMC. Part by weight and 0.2 part by weight of a surfactant were added, and 30 parts by weight of water was kneaded as a solvent to obtain a paste. This kneaded paste-like active material is disposed on a current collecting core made of a strip-shaped rolled aluminum foil having a thickness of 15 μm and a width of 490 mm, with a coating width of 470 mm, a coating portion of 560 mm in the longitudinal direction, and an uncoated portion of 116 mm. The electrode mixture part was formed by performing intermittent application continuously and then drying and solidifying. Next, the pasty active material was intermittently applied to the coated back surface in the same manner as described above.

  This coated and dried electrode plate was subjected to heat treatment in a continuous heat treatment furnace having a furnace length of 10 m. As heat treatment conditions, the furnace temperature was set to 340 ° C., and the treatment speed was 10 m / min (furnace residence time 60 seconds).

  The electrode plate after the heat treatment was subjected to compression molding until a predetermined thickness was obtained with a roll press, so that the thickness of the electrode plate was 0.147 mm. The rolling was performed by a constant pressure rolling method, and the pressing force was rolled twice at a linear pressure of 1500 kg / cm. Then, it cut | judged by taking 8 rows by 56.5 mm width in a longitudinal direction, and wound about 700 electrode plates on the reel per row.

  Thereafter, the electrode plate hoop cut and wound in a batch drying furnace was dried at 110 ° C. for 4 hours to prepare a positive electrode plate.

  In addition, when the drying time was less than 4 hours, the surface temperature of the positive electrode hoop core portion did not reach the specified temperature.

(Example 2)
The coated and dried electrode plate used in Example 1 was heat-treated in a continuous heat treatment furnace having a furnace length of 10 m as in Example 1. As heat treatment conditions, the temperature in the furnace was set to 340 ° C., and the treatment speed was 2 m / min (residence time in the furnace 300 seconds).

  Note that a speed of less than 2 m / min (residence time in the furnace of 300 seconds) was not carried out because the productivity of the heat treatment process was lowered.

  After heat treatment, pressing and cutting were performed with the same dimensions as in Example 1, and about 700 electrode plates were wound on a reel per row.

  Thereafter, the electrode plate hoop cut and wound in a batch drying furnace was dried at 110 ° C. for 4 hours to prepare a positive electrode plate.

(Example 3)
As the heat treatment conditions for the coated and dried electrode plate used in Example 1, the furnace temperature was set to 400 ° C., and the treatment speed was 10 m / min (furnace residence time 60 seconds). A heat treatment was performed in the same manner as in Example 1 except that.

  Pressing and cutting were performed with the same dimensions as in Example 1 after the heat treatment, and about 700 electrode plates were wound on a reel per row.

  Thereafter, the electrode plate hoop cut and wound in a batch drying furnace was dried at 110 ° C. for 4 hours to prepare a positive electrode plate.

Example 4
As the heat treatment conditions for the coated and dried electrode plate used in Example 1, the furnace temperature was set to 400 ° C., and the treatment speed was 2 m / min (furnace residence time 300 seconds). A heat treatment was performed in the same manner as in Example 1 except that.

  Pressing and cutting were performed with the same dimensions as in Example 1 after the heat treatment, and about 700 electrode plates were wound on a reel per row.

  Thereafter, the electrode plate hoop cut and wound in a batch drying furnace was dried at 110 ° C. for 4 hours to prepare a positive electrode plate.

(Example 5)
The coated and dried electrode plate used in Example 1 was subjected to the same heat treatment conditions as in Example 3 (furnace temperature: 400 ° C., treatment rate: 10 m / min (furnace residence time 60 seconds)). Except for the above, heat treatment was performed in the same manner as in Example 1.

  Pressing and cutting were performed with the same dimensions as in Example 1 after the heat treatment, and about 700 electrode plates were wound on a reel per row.

  Thereafter, the electrode plate hoop cut and wound in a batch drying furnace was dried at 200 ° C. for 12 hours to prepare a positive electrode plate.

  If the drying time exceeds 12 hours, the production efficiency of the drying process is greatly reduced, so 12 hours was the limit.

(Comparative Example 1)
Next, as Comparative Example 1, the electrode plate coated and dried in the same manner as in Example 1 was subjected to heat treatment conditions, the furnace temperature was set to 300 ° C., and the treatment speed was 2 m / min (furnace residence time 300 seconds). The heat treatment was performed in the same manner as in Example 1 except that the above was performed.

  Pressing and cutting were performed with the same dimensions as in Example 1 after the heat treatment, and about 700 electrode plates were wound on a reel per row.

  Thereafter, the electrode plate hoop cut and wound in a batch drying furnace was dried at 110 ° C. for 4 hours to prepare a positive electrode plate.

(Comparative Example 2)
Next, in Comparative Example 2, coating, heat treatment, pressing and cutting were performed under the same conditions as in Comparative Example 1, and the hoop wound on the reel was dried in a batch drying furnace at 220 ° C. for 4 hours to form a positive electrode A board was created.

(Comparative Example 3)
Next, as Comparative Example 3, the electrode plate coated and dried in the same manner as in Example 1 was subjected to heat treatment conditions, the furnace temperature was set to 420 ° C., and the treatment speed was 10 m / min (furnace residence time 60 seconds). The heat treatment was performed in the same manner as in Example 1 except that the above was performed.

  This was compression-molded by a roll press machine until the thickness became 0.145 mm. However, since the mixture applied from the aluminum foil frequently occurred during the press, the process could not proceed to the next step. This is because the adhesive strength between the mixture and the aluminum foil was lowered because the binder (FEP) contained in the mixture was decomposed by setting the heat treatment temperature to 420 ° C.

(Comparative Example 4)
Next, as Comparative Example 4, the temperature in the furnace was set to 400 ° C. using the electrode plate coated and dried as in Example 1 as heat treatment conditions, and the treatment speed was 12 m / min (the residence time in the furnace was 50 seconds). The heat treatment was performed in the same manner as in Example 1 except that the above was performed.

  Pressing and cutting were performed with the same dimensions as in Example 1 after the heat treatment, and about 700 electrode plates were wound on a reel per row.

  Thereafter, the electrode plate hoop cut and wound in a batch drying furnace was dried at 110 ° C. for 4 hours to prepare a positive electrode plate.

The heat treatment temperature, residence time and hoop drying temperature, and time conditions of Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 1, and after the heat treatment in Examples 1 to 4 and Comparative Examples 1 and 4 described above. results residue content in the electrode mixture of the measurement was carried out weight loss upon reaching the temperature was elevated 350 ° C. by a heat analysis method shown in Table 2.

From the measurement results, the reduction rate of Example 1 was 0.3%, Example 2 was 0.2%, Example 3 was 0.2%, and Example 4 was 0.1%. On the other hand, Comparative Example 1 is 0.6%, Comparative Example 4 is 0.4%, and the weight reduction rate is large compared to the Examples. Therefore, the active material, the conductive agent and the binder are excluded, and the residue is large. became.

  Next, the length of each of about 700 electrode plates from the outer periphery of the hoop after the hoop drying to the winding core for each of Example 1, Example 5, and Comparative Example 2 was evaluated. The results are shown in Table 3.

  From the test results, the difference in length per electrode plate between the outermost peripheral portion and the innermost peripheral portion of the hoop is that the difference between the maximum value and the minimum value (R) is 5.5 mm and the deviation is 2.4 mm. In Example 1, R1.0 mm and deviation 0.3 mm, and in Example 5 R2.5 mm and deviation 0.7 mm, respectively, the variations in electrode plate length in the hoop were significantly suppressed.

  Next, when the amount of bending of the length of the second and fourth electrode plates from the outermost peripheral portion of the hoop was measured, the comparative example 2 had a bending amount of 9.8 mm. The bend amounts were 0.5 mm and 2.0 mm, respectively, and the bend amount of the outer periphery of the hoop was suppressed. This is because by reducing the drying temperature from 220 ° C. to 110 ° C. to 200 ° C., the restoration of the electrode plate thickness after drying can be suppressed, and the tensile force of the core material applied to the outer periphery of the hoop is suppressed. In addition, the yield of the winding process was 99.8% and 99.4% in Examples 1 and 5, respectively, which was significantly improved from the yield of 97.8% in Comparative Example 2.

  Next, in order to confirm the battery performance, the positive electrode plates of Examples 1 to 5 and Comparative Examples 1, 2, and 4 prepared under the same conditions were wound with the separator and the separator shown in FIG. A lithium ion secondary battery was prepared and the battery characteristics were evaluated.

  First, the structure of the lithium ion secondary battery created in this example will be described.

  FIG. 2 illustrates a longitudinal sectional view of a cylindrical lithium ion secondary battery according to an embodiment of the present invention.

  A positive electrode lead 17 made of aluminum is attached by welding to a lead attachment portion where the electrode mixture portion at the end of the positive electrode plate 12 according to the present invention is not formed. On the other hand, the negative electrode side electrode plate 13 is rolled to a predetermined thickness after intermittently applying and drying a paste-like active material on both sides of a current collecting core made of, for example, a strip-shaped copper foil, like the positive electrode plate. Is provided by providing an electrode mixture portion and cutting it into a sheet having a predetermined length.

In a battery case 19 formed by processing a stainless steel plate resistant to organic electrolyte, the above-described positive electrode plate 12 and negative electrode plate 13 are interposed with a separator 14 made of, for example, polyethylene between them. The electrode group 11 formed by spirally winding in a stacked state is accommodated, the other end of the positive electrode lead 17 is connected to the sealing plate 20 by spot welding, and one end of the negative electrode lead 18 is connected by spot welding. It is connected to the bottom of the battery case 19. Insulating rings 21 and 22 are provided above and below the electrode group 11, respectively. Further, in the battery case 19, a non-aqueous electrolyte solution dissolved in an equal volume mixed solvent of ethylene carbonate and dialkyl carbonate at a ratio of 1 mol / l lithium hexafluorophosphate is injected, and then the safety valve 23. After the sealing plate 20 provided with an insulating packing 24 is caulked into the opening of the battery case 19, the peripheral portion of the opening of the battery case 19 is caulked inward, thereby opening the opening. Is sealed.

  Subsequently, the battery performance in Examples 1 to 5 and Comparative Examples 1, 2, and 4 was evaluated. As battery performance evaluation, after charging to 4.2 V at 1430 mA, 18 W constant watt discharge was evaluated in an atmosphere of 0 ° C. The results are shown in FIG.

  In FIG. 3, 101 to 105 are discharge curves of Examples 1 to 5, and 111, 112, and 114 are discharge curves of Comparative Example 1, Comparative Example 2, and Comparative Example 4, respectively.

  As is clear from FIG. 3, the discharge curves 101 to 105 of Examples 1 to 5 are smaller in initial voltage drop than the discharge curves 114 and 115 of Comparative Examples 1 and 4, and the battery performance is improved. ing. On the other hand, in Comparative Example 1, the initial voltage drop is large, and the battery performance is clearly degraded.

  In Comparative Example 1, as the heat treatment conditions, the temperature in the furnace is 300 ° C., the processing speed is 2 m / min (residence time in the furnace 600 seconds), and the final electrode plate hoop drying is performed at 110 ° C. for 4 hours. The residual ratio of the additive after the heat treatment was 0.6%, and the performance characteristics of the battery deteriorated due to the fact that the residual additive did not promote decomposition in the final hoop drying step.

  Each of Comparative Examples 4 was also subjected to heat treatment conditions, the furnace temperature was 400 ° C., the treatment speed was 12 m / min (furnace residence time 50 seconds), and the final electrode plate hoop drying was performed at 110 ° C. for 4 hours. However, since the heat treatment time is short, the residual rate after heat treatment is 0.4%, and as in Comparative Example 1, the remaining of the additive is not accelerated in the final hoop drying step, and the battery performance The characteristics have been deteriorated.

  In Examples 1 to 5, the remaining amount of the additive other than the active material, conductive agent, and binder in the electrode mixture is decomposed into a small amount (0.3% or less) by optimizing the heat treatment conditions in the heat treatment step. Therefore, even if the final hoop drying temperature is lowered, the battery performance can be ensured, the dimensional variation of the electrode plate can be suppressed, the winding process can be stabilized, the yield can be improved, and the heat treatment process can be made more efficient.

  The lithium ion secondary battery using the positive electrode plate for a lithium ion secondary battery according to the present invention is useful as a power source for portable electric devices and a driving power source for consumer electronic devices that require high capacity and high reliability. .

The process figure in the manufacture process of the positive electrode plate which concerns on the Example of this invention. 1 is a longitudinal sectional view of a cylindrical lithium ion secondary battery according to an embodiment of the present invention. The figure which shows the relationship between the discharge capacity and voltage in an Example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Kneading process 2 Coating drying process 3 Heat treatment process 4 Pressing process 5 Cutting process 6 Hoop drying process 11 Electrode group
12 Positive electrode plate
13 Negative electrode plate
14 Separator
17 Positive lead
18 Negative lead 19 Battery case
20 Sealing plate
21 Insulating plate 22 Insulating plate 23 Safety valve
24 Insulation gasket

Claims (2)

A coating and drying step in which an electrode mixture composed of an active material, a conductive agent, a binder, a thickener, and a surfactant is applied to both sides of the current collector, and a positive electrode plate is created by drying;
A heat treatment step of heat-treating the electrode plate in a range of 340 ° C. to 400 ° C. for 60 seconds to 300 seconds ;
A pressing step of pressing the electrode plate to a predetermined thickness;
Cutting the pressed electrode plate to a predetermined width in the longitudinal direction, and winding it in a hoop shape,
A hoop drying step of drying the electrode plate wound in a hoop shape in a drying furnace in a range of 110 ° C. to 200 ° C. for 4 hours to 12 hours,
The manufacturing method of the electrode plate for lithium ion secondary battery positive electrodes in which the residue except an active material, a electrically conductive material, and a binder in an electrode plate is 0.10%-0.30% by weight ratio . A lithium ion secondary battery using a positive electrode plate manufactured by the manufacturing method according to claim 1 .

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