JP2010170854A - Method of manufacturing positive electrode for nonaqueous electrolyte battery, positive electrode for nonaqueous electrolyte battery, and nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a positive electrode for nonaqueous electrolyte battery by a green sheet sintering method in which a nonaqueous electrolyte battery having a sufficiently small electric resistance and a sufficiently high battery capacity can be obtained, a positive electrode for nonaqueous electrolyte battery, and a nonaqueous electrolyte battery. <P>SOLUTION: The method of manufacturing the positive electrode for nonaqueous electrolyte battery includes a slurry preparation step of preparing slurry containing powder of a positive electrode material having mainly a lithium compound oxide and a solvent, a coating film preparation step in which the slurry is coated on a substrate and by removing the solvent, a coating film is prepared, and a sintering step in which the coating film is pressurized with a prescribed condition and heated and sintered. The positive electrode for nonaqueous electrolyte battery contains a sintered compact which has mainly a lithium compound oxide and has at least one face of a surface with surface roughness Ra of 10 nm or less. The nonaqueous electrolyte battery has a solid electrolyte which is opposed to the surface of a sintered compact having mainly a lithium compound oxide with the surface roughness Ra of 10 nm or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a positive electrode for a non-aqueous electrolyte battery in which electrical resistance with the non-aqueous electrolyte is reduced, a positive electrode for a non-aqueous electrolyte battery, and a non-aqueous electrolyte battery.

  In recent years, non-aqueous electrolyte batteries using lithium or a lithium alloy as a negative electrode and a non-aqueous electrolyte such as a non-aqueous electrolyte or a solid electrolyte have been required to be thinner and have a higher output. As a positive electrode for a nonaqueous electrolyte battery to meet such a demand, there is a sintered positive electrode for a nonaqueous electrolyte battery (hereinafter also simply referred to as “positive electrode”).

  Conventional sintered positive electrodes have been manufactured by sintering powdered compacts of positive electrode materials. Specifically, lithium composite oxide powder, lithium composite oxide raw material powder, etc. are filled in a mold and press-molded, and the obtained molded body is sintered at a predetermined temperature. It was.

  However, in the sintering method for sintering the molded body (hereinafter also referred to as “molded body sintering method”), for example, it is difficult to produce a thickness of about 60 μm or less. It was not possible to provide a nonaqueous electrolyte battery satisfying the above.

  In addition, in this method, since it is difficult to uniformly fill the positive electrode material powder in the mold, the sintering reaction does not proceed uniformly, and it is difficult to ensure a uniform density distribution of the obtained sintered body. Therefore, the nonaqueous electrolyte battery using the positive electrode according to this method has a problem that the battery capacity is inferior.

  In order to solve the problem of the positive electrode due to the above-mentioned green body sintering method, a coating method (green sheet) is formed by the green sheet method, and the formed coating film is sintered (hereinafter referred to as “green sheet sintering method”). The positive electrode is also proposed (for example, claim 2 of Patent Document 1).

  In the green sheet sintering method, a slurry obtained by kneading the positive electrode material powder together with a binder, a dispersant, a solvent, etc. is thinly applied onto a substrate, and the coating film obtained by removing the solvent is sintered. This method is suitable for the production of a thin positive electrode and has an advantage that a more uniform filling can be obtained as compared with the molded body.

JP 2001-143687 A

  However, the positive electrode by the green sheet sintering method as described above cannot be said to be a non-aqueous electrolyte battery having a sufficiently low electric resistance and a sufficiently high battery capacity.

  Therefore, the present invention provides a method for producing a positive electrode for a non-aqueous electrolyte battery by a green sheet sintering method, which can obtain a non-aqueous electrolyte battery having a sufficiently low electric resistance and a sufficiently high battery capacity as compared with the prior art. And a positive electrode for a non-aqueous electrolyte battery and a non-aqueous electrolyte battery.

  In view of the above problems, the present inventors have intensively researched and found a method for solving the above problems by heating while applying pressure in the sintering process, and have completed the present invention.

(A) The method for producing the positive electrode for a non-aqueous electrolyte battery of the present invention comprises:
A slurry preparation step of preparing a slurry containing a powder of a positive electrode material mainly composed of lithium composite oxide and a solvent;
A coating film preparation step of applying the slurry on a substrate and removing the solvent to prepare a coating film;
It has the sintering process which heats and heat-sinters the said coating film, and is sintered.

  According to the invention of (A), a positive electrode for a non-aqueous electrolyte battery is manufactured by a green sheet sintering method, which can obtain a non-aqueous electrolyte battery having a sufficiently low electric resistance and a sufficiently high battery capacity as compared with the prior art. can do.

  As a result of examining the cause of the electrical resistance not being sufficiently lowered in the non-aqueous electrolyte battery using the positive electrode by the conventional green sheet sintering method described above, the electrical resistance at the interface between the positive electrode and the non-aqueous electrolyte was determined. This is because the surface roughness of the sintered body contained in the positive electrode is large.

  As a result of further investigation, when producing a sintered body of a positive electrode by a green sheet method, it is usually simply sintered, but by heating and sintering while applying pressure, the surface roughness of the sintered body is reduced. It was found that it can be made sufficiently small. The reason why the surface roughness can be sufficiently reduced in this way is presumed to be that the contact between the powders (particles) is increased and the sinterability is improved by heating and sintering while applying pressure. Then, by using the positive electrode for a non-aqueous electrolyte battery including a sintered body having a reduced surface roughness in this way, it becomes difficult to inhibit the diffusion of lithium ions at the interface between the positive electrode and the non-aqueous electrolyte. A non-aqueous electrolyte battery with reduced can be obtained. Specifically, the surface roughness Ra of the sintered body can be reduced to 10 nm or less, usually about 6 nm, by heating and sintering while applying pressure.

  Furthermore, it was found that by heating while applying pressure as described above, the porosity of the sintered body can be reduced to about 5%, and the packing density of the active material can be improved. That is, it has been found that the effect of improving the energy density can be obtained by heating and sintering while applying pressure.

In addition, as the powder of the positive electrode material, a material mainly composed of lithium composite oxide powder in which a part of Co in LiCoO ₂ or LiCoO ₂ is substituted with another metal is used. A metal oxide such as ₃ O ₄ or a conductive agent may be contained.

  Moreover, a binder, a dispersant, or the like may be added to the slurry. As the solvent, for example, various organic solvents such as various alcohols and N-methyl-2-pyrrolidone are preferably used.

  In the “coating film preparation step”, heating may be performed to promote the removal of the solvent of the coating film. In the case of heating, it is preferable to heat the coating film in an open atmosphere such as the air after applying the slurry on the substrate in terms of completely evaporating the solvent. In addition to removing the solvent to solidify the coating film, for example, when a binder is used, it is preferable to perform temporary baking to decompose and remove the binder contained in the coating film. In addition, the thickness of the coating film is preferably 500 μm or less for improving the drying property of the coating film and improving the binder removal property.

  The atmosphere, applied pressure, temperature, and the like in the “sintering step” are appropriately set so that the coating is sufficiently performed in the sintering of the coating film using various positive electrode material powders. Specifically, the atmosphere is preferably an inert gas atmosphere, and a reduced pressure atmosphere having an absolute pressure of about 0.5 atm is preferable in order to suppress decomposition of the material powder. The applied pressure is preferably about 10 to 200 MPa, particularly 30 to 50 MPa in order to increase the particle indirect point during firing. The sintering temperature is preferably about 950 ° C. ± 100 ° C. Furthermore, the heating for sintering is preferably performed by energization heating in terms of ensuring uniformity and adjusting the atmosphere.

(B) The positive electrode for a non-aqueous electrolyte battery of the present invention is
It includes a sintered body mainly composed of a lithium composite oxide and having at least one surface with a surface roughness Ra of 10 nm or less.

  In the invention of (B), since the sintered body has at least one surface with a surface roughness Ra of 10 nm or less, such a surface is used facing the nonaqueous electrolyte, The diffusion of lithium ions at the non-aqueous electrolyte interface is hardly inhibited, and the electrical resistance at the interface between the positive electrode and the non-aqueous electrolyte can be sufficiently reduced.

(C) The nonaqueous electrolyte battery of the present invention is
A nonaqueous electrolyte battery comprising a positive electrode for a nonaqueous electrolyte battery comprising a sintered body mainly comprising a lithium composite oxide and having a surface roughness Ra of at least one surface of 10 nm or less, and a solid electrolyte,
The solid electrolyte is opposed to the surface of the sintered body having a surface roughness Ra of 10 nm or less.

  In the invention of (C), since the solid electrolyte faces the surface having a surface roughness Ra of 10 nm or less of the sintered body which is the positive electrode, it is difficult to inhibit diffusion of lithium ions at the interface between the positive electrode and the solid electrolyte. Since the electric resistance at the interface between the positive electrode and the non-aqueous electrolyte is surely small, a non-aqueous electrolyte battery having a sufficiently low electric resistance can be provided.

  Even in a non-aqueous electrolyte battery using a solid electrolyte that is difficult to adjust to the surface of the positive electrode, the electrical resistance at the interface between the positive electrode and the solid electrolyte can be sufficiently reduced by sufficiently contacting the positive electrode and the solid electrolyte. The invention exhibits a particularly remarkable effect in an all-solid-state nonaqueous electrolyte battery using a solid electrolyte.

The “opposite” in the invention of (C) is not only the case where the positive electrode for the nonaqueous electrolyte battery and the solid electrolyte are in contact with each other, but the positive electrode for the nonaqueous electrolyte battery and the solid electrolyte are nanometers. A layer such as LiNbO ₃ having a thickness of the order (referred to as a buffer layer. The buffer layer is extremely thinner than a positive electrode for a non-aqueous electrolyte battery or a solid electrolyte having a thickness of a micron order) to be opposed to each other. Including cases.

  According to the present invention, a method for producing a positive electrode for a non-aqueous electrolyte battery by a green sheet sintering method and a non-aqueous electrolyte battery capable of obtaining a non-aqueous electrolyte battery having a sufficiently low electric resistance and a sufficiently high battery capacity, and the non-aqueous electrolyte battery A positive electrode for use and a non-aqueous electrolyte battery can be provided.

It is a figure which shows typically the sintering method in the green sheet sintered positive electrode which concerns on the Example of this invention. It is a figure which shows typically the sintering method in the conventional green sheet sintered type positive electrode. It is a figure which shows the image which image | photographed the cross section of the positive electrode of an Example and a comparative example with the scanning electron microscope (SEM). It is a figure which shows the image which image | photographed the surface of the positive electrode of an Example and a comparative example with the scanning electron microscope (SEM).

  Hereinafter, the present invention will be described based on the best mode. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

1. Example This example is an example of a positive electrode for a non-aqueous electrolyte battery made of a sintered body by a green sheet sintering method mainly composed of LiCoO ₂ .
I. Preparation of Slurry First, preparation of a slurry for producing a positive electrode will be described. 100 parts by weight of LiCoO ₂ powder (made by Nippon Kagaku Kogyo Co., Ltd.) which is a lithium composite oxide, 5 parts by weight of PVB resin (made by ESREC) as a binder, and 3 parts by weight of DPB (made by Futaba Chemical) as a plasticizer Then, 26 parts by weight of toluene (manufactured by Kanto Chemical Co., Inc.) as a solvent was kneaded with a ball mill for 24 hours to prepare a slurry in which each material was uniformly dispersed.

B. Preparation of Coating Film The obtained slurry was uniformly applied to a 50 μm thick polyester film with a metal squeegee to a thickness of 150 μm and a diameter of 19 mm.

  Next, after removing the solvent by heating at 120 ° C. for 20 minutes in an atmospheric furnace, it was peeled from the polyester film to obtain a coating film having a thickness of 150 μm and a diameter of 19 mm.

C. Sintering Next, the obtained coating film was sintered. FIG. 1 is a diagram schematically showing a method for producing a positive electrode by sintering a coating film. In FIG. 1, 12 is a positive electrode, 41 is a lower carbon jig, 42 is an upper carbon jig, 51 is a lower electrode and press plate, 52 is an upper electrode and press plate, and 60 is It is a cylindrical carbon jig.

The obtained coating film is inserted into a cylindrical carbon jig 60 and sandwiched between the upper carbon jig 42 and the lower carbon jig 41 from above and below, and the upper carbon jig 42 and the lower carbon jig 41 are also used as the upper electrode. It is sandwiched between the press plate 52 and the lower electrode / press plate 51. Then, the surroundings are set to a reduced-pressure argon (Ar) atmosphere of 0.5 atm, and an alternating current is passed between the upper electrode / press plate 52 and the lower electrode / press plate 51 while being pressurized with a press pressure P of 30 MPa, and 950 ° C. The positive electrode 12 made of a sintered body of LiCoO ₂ having a thickness of 120 μm and a diameter of 16 mm was obtained.

  Here, the reason why the AC power supply is used for heating is that uniform pressing and control for heating are easy. The reason why the reduced pressure argon atmosphere is used is that suppression of the decomposition of the material powder is taken into consideration. In order to make the drawing easier to see, in FIG. 1, for convenience, the upper carbon jig 42 and the lower carbon jig 41 are separated from the positive electrode 12.

2. Comparative Example This comparative example is an example in which a positive electrode was produced in the same manner as in the example except that sintering was performed in an air atmosphere without applying pressure. The sintering method of this comparative example will be described below.

  FIG. 2 is a diagram schematically showing a method for producing a positive electrode in a comparative example. In FIG. 2, 11 is a positive electrode, 20 is a heating substrate, and 30 is an atmospheric furnace. The obtained coating film was placed on the heating substrate 20, and as shown in FIG. 2, the positive electrode 11 was produced by heating and sintering without applying pressure using the atmospheric furnace 30.

(Evaluation of positive electrode)
I. Surface Roughness The cross sections of the positive electrode 12 of the example and the positive electrode 11 of the comparative example were photographed with a scanning electron microscope (SEM), and the surface roughness Ra was compared. FIG. 3 shows cross-sectional SEM images of the example and the comparative example. (A) is a comparative example, (b) is an Example.

  From the cross-sectional SEM image of FIG. 3, it can be seen that the surface roughness Ra of the comparative example is 66 nm, whereas the surface roughness Ra of the example is as small as 6 nm. For this reason, when the positive electrode of an Example is used, it becomes difficult to inhibit the spreading | diffusion of lithium ion in the interface of a positive electrode and a solid electrolyte, and a nonaqueous electrolyte battery with small electrical resistance is obtained by extension.

B. Porosity Moreover, the surface of the positive electrode 12 of an Example and the positive electrode 11 of a comparative example was image | photographed with the scanning electron microscope (SEM), and the porosity was compared. The surface SEM image of an Example and a comparative example is shown in FIG. (A) is a comparative example, (b) is an Example.

  From the surface SEM image of FIG. 4, it can be seen that the porosity of the positive electrode is 11% in the comparative example, whereas the example is as small as 5% and is dense. For this reason, when the positive electrode of the example is used, the packing density of the active material of the positive electrode is greatly improved, and thus a non-aqueous electrolyte secondary battery having a sufficiently large energy density can be obtained. Therefore, a small and lightweight non-aqueous electrolyte battery can be obtained.

  Among non-aqueous electrolyte batteries, non-aqueous electrolyte secondary batteries are generally used for applications such as high-power electronic devices, and thus are particularly required to have low electrical resistance. For this reason, this invention exhibits a remarkable effect in a nonaqueous electrolyte secondary battery.

11, 12 Positive electrode 20 Heating substrate 30 Atmospheric furnace 41 Lower carbon jig 42 Upper carbon jig 51 Lower electrode / press plate 52 Upper electrode / press plate 60 Cylindrical carbon jig

Claims (3)

A slurry preparation step of preparing a slurry containing a powder of a positive electrode material mainly composed of lithium composite oxide and a solvent;
A coating film preparation step of applying the slurry on a substrate and removing the solvent to prepare a coating film;
A method for producing a positive electrode for a non-aqueous electrolyte battery, comprising a sintering step of heating and sintering the coating film while applying pressure.   A positive electrode for a non-aqueous electrolyte battery comprising a sintered body mainly composed of a lithium composite oxide and having at least one surface having a surface roughness Ra of 10 nm or less. A nonaqueous electrolyte battery comprising a positive electrode for a nonaqueous electrolyte battery comprising a sintered body mainly comprising a lithium composite oxide and having a surface roughness Ra of at least one surface of 10 nm or less, and a solid electrolyte,
The non-aqueous electrolyte battery, wherein the solid electrolyte is opposed to a surface having a surface roughness Ra of 10 nm or less of the sintered body.