JP2007280657A - Manufacturing method of positive electrode for lithium secondary battery, positive electrode and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode for a lithium secondary battery which is excellent in the binding capability among positive electrode active materials and the adhesion property of a positive electrode active material and a current collector, and which prevents drop in the charge-discharge capacity of the battery performance or degradation in the load characteristics, while having no adverse effects on the environmental loads. <P>SOLUTION: The manufacturing method is intended for a positive electrode for a lithium secondary battery which has a positive electrode active material with its top surface processed by the hydrophilic treatment, a conductive material, a binding agent, and a thickening agent. A mixture of poly(oxyethylene) tridecile ether and water is used as a surface active agent, of which ratio of the additive amount to the total amount of the positive electrode active material and conductive material is 0.1 to 5% in weight. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement in a positive electrode for a lithium secondary battery.

Conventionally, regarding the production of lithium secondary batteries, in addition to a method of producing a paste by simultaneously blending and kneading a lithium-based metal oxide material, a conductive material, and a binder in a thickener aqueous solution, By defining the shearing force, there was an improvement in dispersibility with the active material, the conductive material and the thickener (see, for example, Patent Document 1). Moreover, what improved dispersibility by coat | covering surfactant on the surface of a electrically conductive material is also reported (for example, refer patent document 2).
Japanese Patent Application Laid-Open No. 11-213989 JP 2002-134101 A

  However, in the electrode plate produced by the manufacturing method of Patent Document 1, the degree of mixing of the positive electrode active material, the binder, and the thickener in the paste state has been improved. A phenomenon sometimes occurred. As a result, the adhesion between the active materials after coating and drying and the adhesion with the current collector are deteriorated, and during active storage and repeated charge and discharge, the active material is peeled off or detached from the current collector. There has been a problem that the charge / discharge characteristics are deteriorated and the load characteristics are deteriorated.

  In addition, since the production method of Patent Document 2 is intended to cover only the conductive material, depending on the lithium-based metal oxide material, the dispersion may be insufficient, and agglomerates may be generated during paste preparation. was there. As a result, the binding property between the active materials and the adhesion of the current collector are poor, and the positive electrode active material peels off from the current collector during high-temperature storage or repetitive charge / discharge use, resulting in reduced discharge characteristics and load. There was a problem of promoting deterioration of characteristics.

  Furthermore, depending on the drying temperature, harmful organic aromatic compounds such as benzene may be released into the air, which increases the environmental load.

  The present invention has been made in view of such problems, and its purpose is excellent in binding force between the positive electrode active materials, adhesion between the positive electrode active material and the current collector, and reduction in charge / discharge characteristics. An object of the present invention is to provide a positive electrode for a lithium secondary battery that prevents deterioration of load characteristics and is also environmentally friendly.

  The method for producing a positive electrode for a lithium secondary battery according to the present invention is a method for producing a positive electrode for a lithium secondary battery in which a surface is subjected to a hydrophilic treatment, and a conductive material has a binder and a thickener. A kneading step of kneading the positive electrode active material, the conductive material, the binder, the thickener and water to produce a positive electrode paste; and applying the positive electrode paste to a current collector to form a positive electrode precursor The manufacturing method of the positive electrode for lithium secondary batteries which consists of the application | coating process which obtains, and the drying process which dries the said positive electrode precursor is characterized.

According to the method for producing a positive electrode for a lithium secondary battery of the present invention, deterioration of charge / discharge characteristics and deterioration of load characteristics can be suppressed to an extremely low level in repeated use of charge / discharge. In addition, deterioration of charge / discharge characteristics and load characteristics can be minimized even under severe conditions such as leaving for a long time at high temperatures.

  In addition, since the adhesion is also improved, the positive electrode active material is not dropped during the battery assembly process, and the workability can be improved. Furthermore, since the structural formula does not have a benzene ring, there is no risk of releasing harmful organic aromatic compounds such as benzene into the air in the drying step, and the environmental load can be reduced.

  The invention according to claim 1 of the present invention is a method for producing a positive electrode for a lithium secondary battery having a positive electrode active material having a hydrophilic treatment on its surface, a conductive material, and a binder and a thickener. A kneading step of kneading the positive electrode active material, the conductive material, the binder, the thickener, and water to prepare a positive electrode paste, and a coating that applies the positive electrode paste to a current collector to obtain a positive electrode precursor It is a manufacturing method of the positive electrode for lithium secondary batteries which consists of a process and the drying process which dries the said positive electrode precursor.

  According to the method for producing a positive electrode for a lithium secondary battery of the present invention, deterioration of charge / discharge characteristics and deterioration of load characteristics can be suppressed to an extremely low level in repeated use of charge / discharge. In addition, deterioration of charge / discharge characteristics and load characteristics can be minimized even under severe conditions such as leaving for a long time at high temperatures.

  In addition, since the adhesion is also improved, the positive electrode active material is not dropped during the battery assembly process, and the workability can be improved. Furthermore, since it does not have a benzene ring as a structural formula, there is no fear of releasing harmful organic aromatic compounds such as benzene into the air in the drying step, and the environmental burden can be reduced.

  The invention according to claim 2 is a method for producing a positive electrode for a lithium secondary battery, wherein the surface of the positive electrode active material and the conductive material is covered with a surfactant as the hydrophilic treatment. By using a surfactant as the hydrophilic treatment, the same effect as in claim 1 can be obtained.

  Invention of Claim 3 is a manufacturing method of the positive electrode for lithium secondary batteries characterized by being a mixture of poly (oxyethylene) tridecyl ether and water as said surfactant, Thus, the same effect as in the first aspect can be obtained.

  According to a fourth aspect of the present invention, there is provided a positive electrode for a lithium secondary battery in which the addition amount ratio of the surfactant is 0.1 to 5% by weight with respect to the total amount of the positive electrode active material and the conductive material mixed powder. This is a manufacturing method, and as a result, the same effect as in claim 1 can be obtained.

  Invention of Claim 5 is a positive electrode for lithium secondary batteries produced with the manufacturing method of the positive electrode for lithium secondary batteries of Claims 1-4, The invention of Claim 6 is Claim 5 A lithium secondary battery having the positive electrode for a lithium secondary battery described in 1.

  As described above, the positive electrode produced by the method for producing a positive electrode for a lithium secondary battery of the present invention and the lithium secondary battery using the positive electrode are deteriorated in charge / discharge characteristics in repeated charge / discharge use. Deterioration of load characteristics can be suppressed to an extremely small level. In addition, deterioration of charge / discharge characteristics and load characteristics can be minimized even under severe conditions such as leaving for a long time at high temperatures.

In addition, since the adhesion is also improved, the positive electrode active material is not dropped during the battery assembly process, and the workability can be improved. Furthermore, since the structural formula does not have a benzene ring, there is no fear that harmful organic aromatic compounds such as benzene are released into the air in the drying step, and the environmental load can be reduced.

  FIG. 1 is a partially cut cross-sectional view showing a configuration of a cylindrical lithium secondary battery manufactured in an example of the present invention.

  The cylindrical lithium secondary battery shown in FIG. 1 is composed of an electrode plate group made up of the positive electrode plate 5 and the negative electrode plate 6 obtained in the above embodiment, an electrolyte, and a case-main body 8 for containing them. Consists of.

  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, and a positive electrode lead 3, a negative electrode lead 9, an upper insulating plate 4, and a lower insulating plate 10.

  Next, the manufacturing method of the electrode plate 6 for negative electrodes is demonstrated.

  A thickener aqueous solution 23 dissolved in 99 parts by weight of water with respect to 50 parts by weight of flaky graphite powder as an active material of a negative electrode plate, 5 parts by weight of styrene butadiene rubber as a binder, and 1 part by weight of CMC as a thickener. An electrode plate paste for negative electrode is obtained by mixing and dispersing parts by weight.

  The obtained negative electrode plate paste was continuously coated on a copper foil having a thickness of 40 μm and a width of 150 mm by a die coating method in the same manner as the above-described method for producing a positive electrode plate. After applying and drying on both surfaces of the copper foil so that the negative electrode active material layer is formed to 110 mm, a negative electrode jumbo roll is obtained. Then, it rolls so that the thickness of the one side of a negative mix layer may be set to 0.20 mm, and it cuts so that it may become a predetermined dimension, and the negative electrode plate 6 is produced.

  As the nonaqueous electrolytic solution, a solution obtained by dissolving LiPF6 at a concentration of 1.0 mol / L in a mixed solution of ethylene carbonate 30 vol%, diethyl carbonate 50 vol% and methyl propionate 20 vol% is used. This non-aqueous electrolyte 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 positive electrode plate 5 and the negative electrode electrode through the micropores of the porous separator. Responsible for the movement of Li ions between the plates 6.

  The battery case is composed of a case main body 8 obtained by deep drawing an organic electrolyte resistant stainless steel plate, and an insulating gasket 2 that can insulate between the sealing plate 1, the sealing plate 1, and the battery case 8. Yes.

  The size of the cylindrical lithium secondary battery of this example is 17 mm in diameter and 50 mm in height.

  Hereinafter, the present invention will be described in detail using examples and comparative examples.

(Example 1)
300 parts by weight of an aqueous surfactant solution prepared by dissolving 95 parts by weight of LiCoO ² powder as a positive electrode active material, 5 parts by weight of acetylene black as a conductive material, and 99 parts by weight of water with respect to 1 part by weight of poly (oxyethylene) tridecyl ether The parts were mixed for 60 minutes.

  The mixed solution of the positive electrode active material, the conductive material and the surfactant obtained by mixing in this way is dried at a temperature of 90 ° C. for 180 minutes, and then agglomerates are removed through a 100-mesh sieve to obtain a positive electrode active material. And a mixture product obtained by hydrophilically treating the surface of the conductive material with a surfactant.

4 parts by weight of an aqueous solution containing 50 parts by weight of a solid material of polytetrafluoroethylene (hereinafter abbreviated as PTFE) as a binder in 100 parts by weight of a mixture of a positive electrode active material and a conductive material subjected to hydrophilic treatment, thickening As an agent, 30 parts by weight of an aqueous solution in which carboxymethyl cellulose (hereinafter abbreviated as CMC) was dissolved in 99 parts by weight of water with respect to 1 part by weight was blended, mixed and dispersed to obtain a positive electrode paste.

  Next, a positive electrode active material layer having a thickness of 0.11 mm on one side is formed on an aluminum foil, which is a current collector having a thickness of 15 μm and a width of 150 mm, by continuously applying this positive electrode paste by a die coating method. After applying and drying on both surfaces of the aluminum foil, a positive jumbo roll was obtained.

  After that, jumbo rolls are sequentially drawn and run in a drying furnace set in a range of 250 ° C. to 350 ° C., which is the melting temperature of PTFE, and heated by passage. By carrying out like this, the adhesion layer of aluminum foil and a positive mix layer can be improved. Then, it rolled so that the thickness of the one side of a positive mix layer might be set to 0.09 mm, and it cut | judged so that it might become a predetermined dimension, the positive electrode plate was produced, and it was set as the Example electrode plate 1. FIG. A cylindrical lithium secondary battery using this was designated as Example Battery 1.

(Comparative Example 1)
In the production of the positive electrode plate, a positive electrode plate was produced in the same manner as in Example 1 except that neither the positive electrode active material nor the conductive material was subjected to hydrophilic treatment. And the cylindrical lithium secondary battery using this was made into comparative example battery 1.

(Comparative Example 2)
In the production of the positive electrode plate, a positive electrode plate was produced in the same manner as in Example 1 except that only the positive electrode active material was subjected to a hydrophilic treatment to obtain a comparative electrode plate 2. And the cylindrical lithium secondary battery using this was made into comparative example battery 2.

(Comparative Example 3)
In the production of the positive electrode, a positive electrode plate was produced in the same manner as in Example 1 except that only the conductive material was subjected to the hydrophilic treatment, and a comparative electrode plate 2 was obtained. And the cylindrical battery using this was used as the comparative example electrode plate 3. And the cylindrical lithium secondary battery using this was made into comparative example battery 3.

(Comparative Example 4)
The ratio of the addition amount of the surfactant to the total amount of the mixed powder of the positive electrode active material and the conductive material was added by 0.05% by weight. Otherwise, a positive electrode plate was prepared in the same manner as in Example 1 to obtain a comparative electrode plate 4. And the cylindrical lithium secondary battery using this was made into comparative example battery 4.

(Comparative Example 5)
The ratio of the addition amount of the surfactant to the total amount of the mixed powder of the positive electrode active material and the conductive material was added by 7% by weight. Other than that, a positive electrode plate was prepared in the same manner as in Example 1 to obtain a comparative electrode plate 5. And the cylindrical lithium secondary battery using this was made into comparative example battery 5.

(Comparative Example 6)
In the production of the positive electrode, the ratio of the addition amount of the surfactant to the total amount of the mixed powder of the positive electrode active material and the conductive material is the same, but the active material, the conductive material, the binder, the thickener aqueous solution and the surfactant are collectively included. This was added to prepare a positive electrode plate paste. Otherwise, a positive electrode plate was produced in the same manner as in Example 1, and a comparative electrode plate 6 was obtained. A cylindrical lithium secondary battery using this was designated as Comparative Example Battery 6.

The positive electrode plates obtained in Example 1 and Comparative Examples 1 to 6 were evaluated by the methods shown below. The number of agglomerates and pinholes present on the surface of the positive electrode plate 1000 cm ² was visually counted and shown in (Table 1).

  From the results of (Table 1), Comparative Example 1 in which the positive electrode active material and the conductive material are not subjected to hydrophilic treatment in advance has insufficient wettability with the solvent and the binder, resulting in insufficient dispersion and generation of agglomerates. did.

  In addition, when the hydrophilic treatment was performed only on the positive electrode active material of Comparative Example 2 or only on the conductive material of Comparative Example 3, the dispersion of the material that was not applied was insufficient and aggregates were generated.

  About the addition amount of poly (oxyethylene) tridecyl ether which is a surfactant, if it is too small as in Example 4, sufficient dispersibility cannot be obtained, and if added excessively as in Example 5, On the contrary, reaggregation occurs or the paste easily foams, and it is considered difficult to obtain a good positive electrode plate.

  In addition, in the case where the surfactant is added all at once as in Comparative Example 6, the surfactant is adsorbed and dispersed not only on the surface of the conductive agent but also on the binder and the thickener aqueous solution, so that the surface of the conductive agent is sufficiently covered. Therefore, sufficient dispersibility cannot be obtained, and it is considered difficult to obtain a good positive electrode plate.

  Next, in order to evaluate the adhesion between the aluminum foil as the current collector and the positive electrode mixture layer, the surface of the positive electrode mixture layer film was scratched in accordance with the cross cut test method JIS K5400. The cellophane pressure-sensitive adhesive tape was applied to the top and peeled off, and the evaluation was made based on the number of cells remaining in the positive electrode mixture layer. For example, if the adhesion is good, all of the squares remain as the positive electrode mixture layer, which is indicated as 100/100. This was visually counted and shown in Table 2.

  From the results of (Table 2), those in which the positive electrode active material and the conductive material are not subjected to hydrophilic treatment in advance have insufficient wettability with the solvent and the binder, resulting in insufficient dispersion, resulting in decreased adhesion. did.

  In addition, when the hydrophilic treatment was applied only to the positive electrode active material or only the conductive material, the dispersion of the material not applied was insufficient and the adhesion was lowered. If the amount of the poly (oxyethylene) tridecyl ether, which is a surfactant, is too small, sufficient dispersibility cannot be obtained. If it is added excessively, re-agglomeration occurs or the paste foams. It becomes easy and it is thought that it is difficult to obtain a good positive electrode plate.

  In addition, when the surfactant is added all at once, the surfactant is adsorbed and dispersed not only on the surface of the conductive material but also on the binder or thickener aqueous solution, so that the surface of the conductive material cannot be sufficiently covered. Thus, it is considered difficult to obtain a good positive electrode plate.

  Furthermore, the charge / discharge repeated capacity deterioration characteristics (hereinafter referred to as cycle life characteristics) of the cylindrical lithium secondary battery produced using the positive electrode plate of Example 1 and Comparative Examples 1 to 6 were measured, and the cycle life was measured. FIG. 2 shows a battery characteristic diagram comparing the characteristics.

  The evaluation method of cycle life characteristics is shown below.

  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, and when the discharge potential reached 3.0 V, the discharge was terminated and the next charge was started. From FIG. 2, it was found that the cylindrical lithium secondary battery of the present invention was excellent in cycle characteristics with little capacity deterioration even after repeated charge and discharge.

This is because the cylindrical lithium secondary battery of the present invention causes the positive electrode active material, the conductive material and the binder to agglomerate in the positive electrode paste by applying hydrophilic treatment to both surfaces of the positive electrode active material and the conductive material in advance. Suppressed, improved dispersibility with positive electrode active material, conductive material and binder in paste, and improved adhesion to current collector, so peeling due to expansion and contraction of mixture during charge / discharge The cause is thought to be difficult.

  In addition, these batteries are stored in a charged state at 60 ° C. for 20 days, and then charged and discharged several times at room temperature, then discharged at 720 mA to determine the capacity until the voltage reaches 3.0 V, and before the storage The ratio of the capacity to the capacity is shown in (Table 3).

  As shown in (Table 3), it has been clarified that the product of the present invention has less capacity deterioration even when stored at high temperature.

  As described above, according to the present invention, in repeated use of charge / discharge, deterioration of charge / discharge characteristics and load characteristics can be suppressed extremely small.

  In addition, deterioration of charge / discharge characteristics and load characteristics can be minimized even under severe conditions such as leaving for a long time at high temperatures.

  In addition, since the adhesion is also improved, the positive electrode active material is not dropped during the battery assembly process, and the workability can be improved.

  Furthermore, since the structural formula does not have a benzene ring, there is no risk of releasing harmful organic aromatic compounds such as benzene into the air during the drying process, and the environmental load can be reduced.

The positive electrode produced by the method for producing a positive electrode for a lithium secondary battery of the present invention and the lithium secondary battery using the positive electrode are excellent in binding force between the positive electrode active materials and adhesion between the positive electrode active material and the current collector. In addition, it provides a positive electrode for lithium secondary batteries that prevents the deterioration of charge / discharge characteristics and load characteristics of battery characteristics and is also environmentally friendly, contributing to the manufacture and sale of batteries. It is extremely useful.

Partially cutaway sectional view showing the configuration of a cylindrical lithium secondary battery produced in an example of the present invention Battery characteristics comparing cycle life characteristics

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 Battery case 9 Negative electrode lead 10 Lower insulating plate

Claims (6)

A method for producing a positive electrode for a lithium secondary battery having a binder and a thickener on a positive electrode active material and a conductive material having a hydrophilic treatment on the surface, the positive electrode active material, the conductive material, and the binder A kneading step of kneading the agent, the thickener and water to produce a positive electrode paste, a coating step of applying the positive electrode paste to a current collector to obtain a positive electrode precursor, and drying to dry the positive electrode precursor The manufacturing method of the positive electrode for lithium secondary batteries which consists of a process. 2. The method for producing a positive electrode for a lithium secondary battery according to claim 1, wherein the hydrophilic treatment covers surfaces of the positive electrode active material and the conductive material with a surfactant. The method for producing a positive electrode for a lithium secondary battery according to claim 1, wherein the surfactant is a mixture of poly (oxyethylene) tridecyl ether and water. 4. The method for producing a positive electrode for a lithium secondary battery according to claim 1, wherein a ratio of the surfactant added is 0.1 to 5 wt% with respect to a total amount of the positive electrode active material and the conductive material mixed powder. . The positive electrode for lithium secondary batteries produced with the manufacturing method of the positive electrode for lithium secondary batteries of Claims 1-4. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 5.

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