Lithium secondary battery

Abstract

In a lithium secondary battery using negative electrode active material particles containing silicon, excellent charge-discharge characteristics are achieved and swelling of the negative electrode is minimized. A lithium secondary battery has a positive electrode containing a positive electrode active material, a negative electrode containing an active material layer and a current collector made of a conductive metal foil, and a non-aqueous electrolyte. The active material layer has a binder and active material particles containing silicon, and is formed by sintering the active material layer on a current collector surface in a non-oxidizing atmosphere. The active material particles have an average particle size of from 7.5-15 μm and a particle size distribution such that 60 volume % or more of the active material particles falls within the ±40% range of the average particle size, and the lithium secondary battery has a negative/positive electrode capacity ratio of 1.7 or greater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the relationship between number of cycles and capacity retention ratio of a battery A3 according to the invention;

FIG. 2 is a plan view illustrating a lithium secondary battery fabricated in the manner described in a later-described Example in the present invention;

FIG. 3 is a cross-sectional view of the lithium secondary battery of FIG. 2 taken along line III-III; and

FIGS. 4( a) and 4(b) are schematic views showing the relationship between the active material particles and the current collector, for illustrating the advantageous effects of the present invention.

Claims

1. A lithium secondary battery comprising: a positive electrode comprising a positive electrode active material;a negative electrode comprising an active material layer; and a current collector made of a conductive metal foil, the active material layer comprising a binder and active material particles that contain silicon, and being formed by sintering the active material layer on a surface of the current collector in a non-oxidizing atmosphere, the active material particles having an average particle size of from 7.5 μm to 15 μm and a particle size distribution such that 60 volume % or more of the active material particles falls within the ±40% range of the average particle size; anda non-aqueous electrolyte, whereinthe lithium secondary battery has a negative/positive electrode capacity ratio of 1.7 or greater, the negative/positive electrode capacity ratio being defined as the ratio of negative electrode specific capacity/positive electrode specific capacity, wherein the negative electrode specific capacity is a negative electrode capacity per unit area that is obtained, using a three-electrode cell in which the negative electrode and Li oppose each other, by passing a current through the three-electrode cell so that the potential changes from 1 m V (vs. Li/Li+) to 1000 mV (vs. Li/Li+), and the positive electrode specific capacity is a positive electrode capacity per unit area that is obtained, using a three-electrode cell in which the positive electrode and Li oppose each other, by passing a current through the three-electrode cell so that the potential changes from 4.4 V (vs. Li/Li+) to 3.0 V (vs. Li/Li+).

2. The lithium secondary battery according to claim 1, wherein the active material particles are silicon particles.

3. The lithium secondary battery according to claim 1, wherein the binder comprises a polyimide.

4. The lithium secondary battery according to claim 2, wherein the binder comprises a polyimide.