JP2009224188A - Method of manufacturing lithium-ion secondary battery and its positive electrode plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a positive electrode plate for a lithium-ion secondary battery, which can be carried out by a simple process, and in which a positive electrode active material, a conductive agent, and a binder are uniformly dispersed without corrosion of an aluminum foil when coating a positive electrode paste on the aluminum foil of a current collector and without reducing productivity. <P>SOLUTION: After mixing the conductive agent and the positive electrode active material mainly composed of a lithium-based metal oxide material in a dispersant mixed aqueous solution in which polyoxyethylene alkyl ether that is a surfactant and a thickener aqueous solution are warming-treated in a state maintained at temperatures of ≥20°C and ≤50°C, the lithium-ion secondary battery can be provided which includes an electrode plate for a positive electrode comprised by using a paste for the positive electrode which is obtained by furthermore throwing in, mixing, and dispersing the binder, coating it on the current collector, and drying it. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a lithium ion secondary battery and a positive electrode plate thereof, and more particularly to a preferable method of manufacturing a positive electrode paste.

  In recent years, as a representative of lithium ion secondary batteries used in portable electronic and communication devices such as mobile phones and laptop computers, carbon materials that can occlude and release lithium ions are used as negative electrode active materials, and lithium selected metals. A lithium ion secondary battery using a composite oxide as a positive electrode active material has been put into practical use.

Conventionally, regarding a method for producing a lithium ion secondary battery, in addition to a method for producing a paste by simultaneously blending and kneading a lithium metal oxide material, a conductive agent, and a binder in an aqueous thickener solution, a positive electrode active material A method of improving the dispersibility of the conductive agent and improving the output characteristics of the lithium ion secondary battery by using a slurry in which a conductive agent and a surfactant are kneaded is disclosed (see Patent Document 1). .
JP 2006-302617 A

  However, in the electrode plate produced by the conventional production method, the degree of mixing of the positive electrode active material, the binder and the thickener immediately after the paste production was improved, but the excess interface was reduced during paste storage. In some cases, separation or sedimentation due to reaggregation presumed to be due to the effect of the activator occurred.

  As a result, the adhesion between the active materials after coating and drying and the adhesion of the current collector are poor, and the active material peels off from the current collector during high-temperature storage or repeated charge / discharge use. There has been a problem that the discharge capacity is reduced and the load characteristics are deteriorated.

  The present invention has been made in view of such a technical background, and can be carried out by a simple process. Even if the paste is left as it is, it remains uniformly dispersed without solid-liquid separation and aggregation. The object is to provide a method of coating.

  In order to achieve the above-mentioned object, a method for producing a positive electrode plate for a lithium ion secondary battery according to the present invention comprises a surfactant having a polyoxyethylene alkyl ether and a thickener aqueous solution at a temperature of 20 ° C to 50 ° C. After mixing a positive electrode active material mainly composed of a conductive agent and a lithium-based metal oxide material in a dispersant mixed aqueous solution that is heated in a state of being kept at a high temperature, a binder is further added and mixed and dispersed. The obtained positive electrode paste is used.

  According to the method for producing a positive electrode paste for a lithium ion secondary battery according to the present invention, the surfactant polyoxyethylene alkyl ether and the aqueous thickener solution are added in a state maintained at a temperature of 20 ° C. or higher and 50 ° C. or lower. A positive electrode that is uniformly dispersed by mixing a positive electrode active material mainly composed of a conductive agent and a lithium-based metal oxide material in a temperature-treated dispersant mixed aqueous solution, and then adding a binder to mix and disperse. By using the paste for a lithium ion secondary battery, it is possible to manufacture a positive electrode plate for a lithium ion secondary battery including a positive electrode plate that is applied to a current collector and dried.

  The gist of the present invention is to knead using a mixture with a thickener aqueous solution in a state where the temperature is kept at 20 ° C. or higher and 50 ° C. or lower in advance as a method for preparing the dispersant mixed aqueous solution. The paste that is efficiently and uniformly dispersed can be applied to the surface of the current collector.

  According to the manufacturing method described above, the positive electrode plate is not exposed to the current collector, so that the conductivity is improved. By using these positive electrode plates, a lithium ion secondary battery with improved battery characteristics can be realized.

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

Example 1
The lithium ion secondary battery of the present invention is a cylindrical lithium ion secondary battery as shown in FIG. 1 and comprises an electrode plate group, an electrolytic solution, and a battery case that houses them. The electrode plate group includes a sheet-like positive electrode plate 5, a sheet-like negative electrode plate 6, a sheet-like separator 7 that insulates between the positive electrode plate 5 and the negative electrode plate 6, a positive electrode lead 3, a negative electrode lead 9, and an upper portion. It consists of an insulating plate 4 and a lower insulating plate 10. The positive electrode plate 5 is formed by coating on both surfaces of an aluminum foil. The separator 7 is a porous polypropylene film, and these are overlapped and wound in a spiral shape, and are tightly accommodated in a cylindrical case body 8.

  As the size of the cylindrical battery in this example, a cylindrical lithium ion secondary battery having a diameter of 17 mm, a height of 50 mm, and a nominal capacity of 1440 mAh was manufactured.

  First, the manufacturing method of the positive electrode plate 5 is demonstrated in detail using sectional drawing of the lithium ion secondary battery used for this invention of FIG.

  99 parts by weight of water per 1 part by weight of carboxymethyl cellulose (Serogen EP by Daiichi Kogyo Seiyaku Co., Ltd.) as a thickener for 1 part by weight of polyoxyethylene alkyl ether (manufactured by NOF Corporation) as a surfactant 30 parts by weight of the aqueous solution dissolved in is mixed and heated to 35 ° C.

  In the thus-heated thickener aqueous solution and dispersant mixed aqueous solution, 1.5 parts by weight of industrial acetylene black (manufactured by Denka Co., Ltd.) as the conductive agent and LiCoO 2 powder (Nichia Chemical) as the positive electrode active material 50 parts by weight of Kogyo Co., Ltd.) is mixed for 20 minutes. After mixing, 5 parts by weight of an aqueous solution of 50 parts by weight of PTFE (polyflon D-1 manufactured by Daikin Industries, Ltd.) as a binder was mixed and dispersed to obtain a positive electrode paste.

  Next, this positive electrode paste is applied to an aluminum foil having a thickness of 20 μm (1085 material manufactured by Showa Denko KK) using a die coater to a thickness of 180 μm on one side and dried, and then a melting temperature of PTFE of 200 to 300 The positive electrode plate is heated at 0 ° C. to improve the adhesion layer between the current collector and the positive electrode mixture layer. After that, it was rolled to a thickness of 0.18 mm and cut to a predetermined width to obtain a positive electrode plate.

  One embodiment of the lithium secondary battery of the present invention is a cylindrical lithium secondary battery as shown in FIG. 1, and an electrode plate group using the positive electrode plate 5 obtained by the method for producing a positive electrode paste of the present invention; And an electrolyte solution and a battery case containing them. The electrode plate group includes a sheet-like positive electrode plate 5, a sheet-like negative electrode plate 6, a sheet-like separator 7 that insulates between the positive electrode plate 5 and the negative electrode plate 6, a positive electrode lead 3, a negative electrode lead 9, It consists of an upper insulating plate 4 and a lower insulating plate 10.

The positive electrode plate 5 is formed by coating on both surfaces of an aluminum foil. The separator 7 is a porous polypropylene film, and these are overlapped and wound in a spiral shape, and are tightly accommodated in a cylindrical battery case.

  Next, a method for manufacturing the negative electrode plate 6 will be described.

  First, flaky graphite powder (manufactured by Kansai Thermochemical Co., Ltd.) 50 parts by mass, styrene butadiene rubber (manufactured by JSR Co., Ltd.) 5 parts by mass as a binder, and carboxylmethylcellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a thickener. A paste for negative electrode was obtained by mixing and dispersing 23 parts by mass of an aqueous solution dissolved in 99 parts by mass of water with respect to 1 part by mass of (Serogen EP). The obtained negative electrode paste was applied to and dried on both sides of a negative electrode current collector made of a 10 μm thick copper foil (Fukuda Metal Foil Powder Co., Ltd.) using a die coater, rolled to a thickness of 0.2 mm, and cut. Thus, a sheet-like negative electrode plate 6 was produced.

As an electrolytic solution (manufactured by Mitsubishi Chemical Corporation), a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / liter in a mixed solution of ethylene carbonate 30 vol%, diethyl carbonate 50 vol%, and methyl propionate 20 vol% at 25 ° C. was used. . This electrolytic solution is accommodated in the battery case, impregnated in the positive electrode active material layer and the negative electrode active material layer, and in the battery reaction, the Li between the positive electrode plate 5 and the negative electrode plate 6 passes through the minute holes of the porous separator 7. Responsible for the movement of ions.

  The battery case includes a case main body 8 obtained by deep drawing an organic electrolyte resistant stainless steel plate, a sealing plate 1, and an insulating gasket 2 that insulates the sealing plate 1 from the case main body 8.

  Thus, a cylindrical lithium ion secondary battery was produced, and its initial discharge capacity and cycle characteristics were confirmed. Moreover, before producing a battery, the mass of the positive electrode plate used for the battery was measured and compared with the initial discharge capacity. The above battery was designated as battery 1 of this example.

(Example 2)
Other than blending 30 parts by weight of an aqueous solution in which 99 parts by weight of water is dissolved in 99 parts by weight of water with respect to 1 part by weight of carboxymethyl cellulose as a thickener with respect to 1 part by weight of polyoxyethylene alkyl ether as a surfactant, and heating to 22 ° C The positive electrode paste produced under exactly the same conditions as in Example 1 was used as paste 2 in this Example 2, and the positive electrode plate produced using this paste was used as the electrode plate 2 in this Example 2, and a battery using this. Was used as the battery 2 of Example 2.

(Example 3)
Other than blending 30 parts by weight of an aqueous solution in which 99 parts by weight of water is dissolved in 99 parts by weight of water with respect to 1 part by weight of carboxymethyl cellulose as a thickener, 1 part by weight of polyoxyethylene alkyl ether as a surfactant, and heating to 48 ° C Is a paste for positive electrode produced under the same conditions as in Example 1 and paste 3 of Example 3, and a positive electrode plate prepared using this paste is used as electrode plate 3 of Example 3, and a battery using this is used. The battery 3 of Example 3 was obtained.

(Comparative Example 1)
A positive electrode paste prepared by using the paste 1 of this comparative example 1, this positive electrode paste prepared under exactly the same conditions as in Example 1 except that the surfactant polyoxyethylene alkyl ether was not added. Was the electrode plate 1 of Comparative Example 1, and the battery using this was the battery 1 of Comparative Example 1.

(Comparative Example 2)
Except for blending 30 parts by weight of an aqueous solution in which 99 parts by weight of water is dissolved in 99 parts by weight of water with respect to 1 part by weight of carboxymethylcellulose as a thickener with respect to 1 part by weight of polyoxyethylene alkyl ether as a surfactant, The positive electrode paste produced under exactly the same conditions as in Example 1 was used as Paste 2 in this Comparative Example 2, and the positive electrode plate produced using this paste was used as the Electrode 2 in this Comparative Example 2, and a battery using this was used. The battery 2 of Comparative Example 2 was obtained.

(Comparative Example 3)
Other than blending 30 parts by weight of an aqueous solution in which 99 parts by weight of water is dissolved in 99 parts by weight of water with respect to 1 part by weight of carboxymethylcellulose as a thickener with respect to 1 part by weight of polyoxyethylene alkyl ether as a surfactant, and heating to 60 ° C The positive electrode paste produced under exactly the same conditions as in Example 1 was used as paste 3 of this comparative example 3, and the positive electrode plate produced using this paste was used as the electrode plate 3 of this comparative example 3, and a battery using this. Was designated as Battery 2 of Comparative Example 2.

(Evaluation)
The positive electrode pastes obtained in Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 were evaluated as shown below.

(Viscosity evaluation of positive electrode paste)
100 g of the positive electrode paste was put in a 200 cc container and allowed to stand for 3 days from the date of paste preparation, and the paste viscosity was measured with a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) for 3 days from the date of preparation and every other day. The measurement conditions were measured at ○ rpm using a ○ rotor. The results are shown in Table 1.

  When the dispersion of the surfactant is insufficient, the binder and the conductive material are segregated, so that sedimentation occurs in the positive electrode paste, so that only the solvent component becomes a supernatant and the viscosity is remarkably lowered.

  Moreover, when the paste for positive electrodes becomes high temperature, it becomes highly alkaline, and the viscosity of the paste is remarkably lowered by cutting the carboxymethyl cellulose molecular chain with a thickener.

  Comparative Examples 1, 2, and 3 shown in Table 1 show the state remarkably, and a drop in paste viscosity is observed during the period of 3 days from the production date. That is, the state of the finished paste is unstable, and it can be said that there are significant problems in terms of productivity and quality.

  On the other hand, in Examples 1, 2, and 3, no change in paste viscosity was observed even when left for 3 days from the day of paste preparation, the state as a finished paste was extremely stable, and excellent in terms of productivity and quality. It is clear that

(Evaluation of surface quality of positive electrode plate)
Agglomerates and pinholes present on the surface of the produced positive electrode plate 1000 cm ² were visually counted and are shown in Table 2.

The agglomerates were counted as defective 1 in the mass of an active material lump of 1 mm or more. The pinhole was 1 mm or more, and a hole or dent penetrating to the current collector was counted as a defect 1.

  When the dispersion of the surfactant is insufficient, segregation of the binder and the conductive material occurs, so that the adhesion between the current collector and the mixture is lowered and the electrode plate is dropped. Further, when the paste for the positive electrode becomes high temperature, corrosion of the aluminum foil is promoted, and hydrogen gas is generated at the interface between the foil and the active material to generate pinholes.

  As is apparent from Table 2, in Examples 1, 2, and 3 of the present invention, the phenomenon as described above was not confirmed, and the generation of aggregates and pinholes was excellent as the surface quality.

  On the other hand, in Comparative Examples 1, 2, and 3, many agglomerates and pinholes are generated, and it can be seen that the surface quality of the electrode plate is remarkably deteriorated.

  More specifically, as in Examples 1, 2 and 3, carboxymethyl cellulose as a surfactant and 1 part by weight of polyoxyethylene alkyl ether as a surfactant was dissolved in 99 parts by weight of water with respect to 1 part by weight. By mixing 30 parts by weight of the aqueous solution at a predetermined temperature, the mixture is sufficiently dispersed as compared with Comparative Example 1 where no surfactant is added and Comparative Example 2 where the temperature during mixing is low. For this reason, no segregation of the binder is observed, so that the active material does not fall off or rise from the foil, and the yield of the coating process is improved.

  On the other hand, when the temperature at the time of mixing is too high as shown in Comparative Example 3, corrosion of the aluminum foil by the alkali component of the positive electrode paste is promoted, and hydrogen gas is generated at the interface between the foil and the active material to increase pinholes. At the same time, the active material dropped from the foil or floated up, causing cracks from the active material to fall off.

(Cycle life characteristics evaluation)
The measurement result of the cycle life characteristic of the cylindrical lithium ion secondary battery produced using these positive electrode plates is shown in FIG.

  FIG. 2 is a diagram showing the relationship between the capacity retention rate and the cycle number of the cylindrical lithium ion secondary battery produced in the example of the present invention, and compares the cycle life characteristics.

  Charging was performed at a constant current of 500 mA. When the voltage reached 4.1 V, charging was replaced with constant voltage charging of 4.1 V, and charging was performed for a total of 2 hours. Discharge was performed at 20 ° C. and 720 mA. When the discharge potential reached 3.0 V, the discharge was terminated and the next charge was started, and 300 cycles were confirmed.

  As is clear from FIG. 2, the batteries of Examples 1, 2, and 3 (101 to 103 in FIG. 2) are charged and discharged compared to Comparative Examples 1, 2, and 3 (104 to 107 in FIG. 2). It was found that there was little deterioration of the capacity even when the process was repeated, and the cycle characteristics were excellent.

  In the battery of this example, the dispersibility of the positive electrode paste was improved, so that the active material was not dropped from the foil or lifted up, and the adhesion of the positive electrode mixture to the current collector was improved. For this reason, it is considered that even when the mixture expands and contracts during charge and discharge, the mixture is difficult to peel off from the current collector, and the current collecting property of the active material is maintained, and the battery characteristics are improved.

  According to the present invention, the current collector is not exposed and the yield of the positive electrode plate is improved. Further, since there is no current collector exposure of the positive electrode plate, a lithium ion secondary battery with improved conductivity and battery characteristics can be realized. Therefore, it is useful as a power source for portable electric devices.

Sectional drawing of the cylindrical lithium ion secondary battery used in the Example of this invention The figure which shows the relationship between the capacity maintenance rate of the cylindrical lithium ion secondary battery used in the Example of this invention, and the cycle number.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sealing plate 2 Insulation gasket 3 Positive electrode lead 4 Upper insulating plate 5 Positive electrode plate 6 Negative electrode plate 7 Separator 8 Case body 9 Negative electrode lead 10 Lower insulating plate

Claims (2)

  A conductive agent and a lithium-based metal oxide material in a dispersant mixed aqueous solution obtained by heating a polyoxyethylene alkyl ether which is a surfactant and a thickener aqueous solution while maintaining a temperature of 20 ° C. or higher and 50 ° C. or lower. Lithium ion provided with a positive electrode plate obtained by mixing a positive electrode active material mainly composed of, then applying a binder and mixing and dispersing the binder to a current collector and drying. A method for producing a positive electrode plate for a secondary battery. The lithium ion secondary battery which comprised the positive electrode plate obtained by the manufacturing method of the positive electrode plate for lithium ion secondary batteries of Claim 1.