Negative-electrode active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery
A non-aqueous electrolyte secondary battery that contains a silicon material as a negative-electrode active material has improved initial charge/discharge efficiency. A negative-electrode active material particle ( 10 ) according to an embodiment contains a base particle ( 13 ), which includes a lithium silicate phase ( 11 ) represented by Li 2z SiO (2+z) {0<z<2} and silicon particles ( 12 ) dispersed in the lithium silicate phase ( 11 ). The base particle ( 13 ) has a porosity of 25% or less, preferably 15% or less.
1. A non-aqueous electrolyte secondary battery, comprising:
a negative electrode with a negative-electrode active material including a base particle; a non-aqueous electrolyte; and a positive electrode;
and, wherein the base particle comprises:
a lithium silicate phase represented by Li 2z SiO (2+z) {0<z<2} and
silicon particles are uniformly dispersed in a matrix of the lithium silicate phase,
wherein the base particle has a porosity of 25% or less before initial charging, and
wherein within the negative-electrode active material an area of particles having a particle size of 20 nm or more out of the silicon particles in a cross section of the base particle is 20% or more of an area occupied by the silicon particles before initial charging.
2. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the base particle has a porosity of 15% or less before initial charging.
3. The non-aqueous electrolyte secondary battery according to claim 1 , wherein no SiO 2 peak is observed at 2θ=25 degrees in an XRD pattern obtained by XRD measurement in the negative-electrode active material.
4. The non-aqueous electrolyte secondary battery according to claim 3 , wherein the lithium silicate phase is composed mainly of Li 2 SiO 3 .
5. The non-aqueous electrolyte secondary battery according to claim 4 , wherein the negative-electrode active material after charging and discharging contains no Li 4 SiO 4 .
6. The non-aqueous electrolyte secondary battery according to claim 3 , wherein the negative-electrode active material after charging and discharging contains no Li 4 SiO 4 .
7. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the base particle is covered with an electrically conductive layer.
8. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the silicon particles have an average particle size of 200 nm or less before initial charging.
9. The a non-aqueous electrolyte secondary battery according to claim 1 , wherein the lithium silicate phase is composed mainly of Li 2 SiO 3 .
10. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the lithium silicate phase is composed mainly of Li 2 Si 2 O 5 .
11. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the negative-electrode active material after charging and discharging contains no Li 4 SiO 4 .
12. The non-aqueous electrolyte secondary battery according to claim 1 ,
wherein the non-aqueous electrolyte is at least one of the group consisting of: a non-aqueous solvent with an electrolyte salt dissolved in the non-aqueous solvent and a solid electrolyte containing a gel polymer.