Positive electrode for use in lithium cell and lithium cell using the same

Abstract

A positive electrode for use in a lithium battery using water as a dispersion medium, not causing a problem of deteriorating the battery performance due to corrosion of a collector or the like and not forming unevenness on the coating surface, as well as a lithium battery using the positive electrode, the positive electrode used being formed from a positive electrode paste containing a positive electrode active material represented by the following formula (I), a binder ingredient comprising a water dispersible elastomer and a water soluble polymer as a viscosity improver, water as a dispersion medium and a dispersing agent: LixMPO4   (I) (in the general formula (I) above, M represents a metal atom containing at least one of metal atoms selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B and Mo, and 0<x<2).

Description

BACKGROUND OF THE INVENTION [0001] The present invention concerns a positive electrode for use in lithium cell and a lithium cell using the same. [0002] As electrode materials for lithium secondary cell, it is generally to use carbon compounds such as graphite for a negative electrode and a composite oxide as an electrode active material for a positive electrode. Such positive and negative electrodes are manufactured, for example, by slurryfying an electrode active material, a binder and a electrically conducting agent such as conductive carbon used optionally for improving the electron conductivity with a dispersion medium to prepare a paste or a coating solution, coating the same to an electrode collector by a coater and evaporating the dispersion medium. [0003] An organic dispersion medium such as N-methyl-2-pyrrolidone has been used as the dispersion medium for manufacturing the coating solution but it involves a problem of toxicity in the manufacturing premise, a problem in vie...

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Benefits of technology

[0016] In the invention, since a lithium phosphate compound such as LiFePO4 is used as the positive electrode active material and a specified positive electrode material composition containing a dispersing agent is adopted, even in a case where water is used as a dispersion medium in the positive electrode preparing step, corrosion of a collector less occurs and the problem of degrading the cell performance can be overcome without covering the collector differently from the prior art, and the problem for the occurrence of unevenness during paste coating can also be overcome. Further, the lithium phosphate compound is an active material capable of solving the problems in view of the resource, cost and safety of existent electrode active materials, being inexpensive and having high safety. Accordingly, a positive electrode for use in a lithium cell having high thermal stability as the cell characteristics and also excellent in the rate characteristic and the cycle characteristic can be provided at a reduce cost.

[0017] That is, according to the invention, a lithium cell of high performance can be provided, as well as an effect in view of the manufacture capable of using safe water instead of organic dispersion media having high risk and involving various problems in view of handling can be obtained and it is also advantageous in view of the raw material.

Problems solved by technology

An organic dispersion medium such as N-methyl-2-pyrrolidone has been used as the dispersion medium for manufacturing the coating solution but it involves a problem of toxicity in the manufacturing premise, a problem in view of safety, effects of the dispersion medium wastes on environments, a problem of processing cost, etc.

On the other hand, in the manufacture of the positive electrode, while LiCoO2 has been widely used generally as the positive electrode active material, when water is used as the dispersion medium upon preparing a positive electrode by a positive electrode paste using LiCoO2 as the positive electrode active material, this results in a problem that LiOR, etc. are formed by reaction of lithium ion in the active material and water to cause corrosion of a collector and deteriorate the cell performance.

However, the positive electrodes described above are not still sufficient in view of the cell performance and since they require a step of covering the collector, etc., they involve a problem that they are disadvantageous also in view of the cost.

However, it has been found that the positive electrode active material agglomerates upon preparing the paste, tending to cause unevenness on the paste coated surface.

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