Non-aqueous electrolyte secondary battery and production method thereof

Abstract

A method for producing a non-aqueous electrolyte secondary battery comprising the steps of: (i) mixing a positive electrode active material, a first binder A and a dispersion medium to prepare a paste A, the active material comprising a lithium-containing transition metal oxide; (ii) mixing a conductive agent, a second binder B and a dispersion medium to prepare a paste B, the conductive agent comprising carbon black; (iii) mixing the paste A and the paste B to prepare a positive electrode material paste C; (iv) applying the positive electrode material paste C onto a positive electrode core member and rolling and drying the resultant member to prepare a positive electrode; and (v) fabricating a battery using the positive electrode, a negative electrode and a non-aqueous electrolyte, wherein contact angle θA between the non-aqueous electrolyte and the binder A and contact angle θB between the non-aqueous electrolyte and the binder B satisfy the formula (1): θB−θA≧15°.

Description

BACKGROUND OF THE INVENTION[0001]With the rapidly growing trend toward cordless and more portable consumer electronic products, there is an increasing demand for batteries that are small and lightweight but have high energy density as the power source for such electronic products. From this viewpoint, non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are commonly used in such appliances as notebook computers, mobile phones and audiovisual equipment as batteries having high voltage and high energy density.[0002]Because of the use in such appliances, these non-aqueous electrolyte secondary batteries are required to have good discharge characteristics while maintaining high capacity. In order to satisfy the requirement, it is essential to improve permeability of an electrolyte into a positive electrode.[0003]The permeability of the electrolyte into the positive electrode can be improved, for example, by a process of adding a proper amount of flu...

AI Technical Summary

Benefits of technology

[0010]An object of the present invention is to realize a non-aqueous electrolyte secondary battery comprising a lithium-containing transition metal oxide as a positive electrode active material which has both a high capacity and improved characteristics. Specifically, the present invention uses two kinds of binders having a different affinity for a non-aqueous electrolyte used in production of the battery in different steps and thereby enables a reduction in amount of a conductive agent and the binders, which has conventionally been difficult to achieve. As a result, the present invention can improve the active material density of a positive electrode without impairing characteristics in terms of charge / discharge and cycle life.

[0011]Another object of the present invention is to control, in a preferable range, the bulk density of the conductive agent contained in the positive electrode material paste and thereby form an excellent electroconductive network within the positive electrode material layer. The use of such a positive electrode makes it possible to provide a non-aqueous electrolyte secondary battery having excellent characteristics in terms of charge / discharge and cycle life.

Problems solved by technology

The above-described conventional method of positive electrode production, however, has a problem that the conductive agent tends to form agglomerated particles including the fluorocarbon resin.

This causes a shortage of the binder in the vicinity of the positive electrode active material particles to hinder smooth permeation of the electrolyte to be ensured by the presence of the binder, so that electrode reactions are hampered, resulting in lowered discharge characteristics.

Also, with the formation of the agglomerated particles, because of the shortage of the binding effects of the binder, there arises another problem that the positive electrode material layer separates from the positive electrode core member.

On the other hand, when an excessive amount of binder is added in order to ensure that the electrode sheet is bound firmly, it is difficult to heighten the battery capacity.

Resultantly, it becomes difficult to realize a non-aqueous electrolyte secondary battery having a higher capacity.

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