Lithium composite compound particles and process for producing the same, and non-aqueous electrolyte secondary battery
The present invention aims to provide lithium composite compound particles which can exhibit good cycle characteristics and an excellent high-temperature storage property when used as a positive electrode active substance of a secondary battery, and a secondary battery using the lithium composite compound particles. The present invention relates to lithium composite compound particles having a composition represented by the compositional formula: Li 1+x Ni 1−y−z−a Co y Mn z M a O 2 , in which the lithium composite compound particles have an ionic strength ratio A (LiO − /NiO 2 − ) of not more than 0.5 and an ionic strength ratio B (Li 3 CO 3 + /Ni + ) of not more than 20 as measured on a surface of the respective lithium composite compound particles using a time-of-flight secondary ion mass spectrometer.
1. Lithium composite compound particles having a composition represented by the following compositional formula 1, which particles have an ionic strength ratio A (LiO − /NiO 2 − ) of not more than 0.5 and an ionic strength ratio B (Li 3 CO 3 + /Ni + ) of not more than 20 as measured on a surface of the respective lithium composite compound particles using a time-of-flight secondary ion mass spectrometer:
Li 1+x Ni 1−y−z−a CO y Mn z M a O 2 Compositional formula 1:
wherein M is at least one element selected from the group consisting of Ti, Bi, Sb, Al and Zr; and x, y, z and a satisfy −0.02≦x≦0.05, 0<y≦0.40, 0<z≦0.40 and 0≦a≦0.01, respectively.
2. The lithium composite compound particles according to claim 1 , wherein the lithium composite compound particles have an average secondary particle diameter of 1.0 to 30 μm.
3. The lithium composite compound particles according to claim 1 , wherein the lithium composite compound particles have a powder pH value of not more than 11.0 as measured in a 2% by weight suspension prepared by dispersing the lithium composite compound particles in water.
4. The lithium composite compound particles according to claim 1 , wherein the lithium composite compound particles have a carbon content of not more than 200 ppm.
5. The lithium composite compound particles according to claim 1 , wherein the lithium composite compound particles have a sulfur content of not more than 100 ppm, an ionic strength ratio C (LiSO 3 − /NiO 2 − ) of not more than 0.4 and a sodium content of not more than 100 ppm.
6. The lithium composite compound particles according to claim 1 , wherein the lithium composite compound particles have a lithium carbonate content of not more than 0.10% by weight and a lithium hydroxide content of not more than 0.15% by weight.
7. The lithium composite compound particles according to claim 1 , wherein the lithium composite compound particles have a specific surface area of 0.05 to 0.70 m 2 /g.
8. A process for producing the lithium composite compound particles as defined in claim 1 , comprising the steps of:
(1) washing raw lithium composite compound particles with a water solvent to remove impurities therefrom; and
(2) subjecting the lithium composite compound particles treated in the step (1) to heat treatment,
a ratio of a total molar amount of lithium to a total molar amount of the transition elements and the element M in the lithium composite compound particles used in the step (1) being not less than 1.00 and not more than 1.10.
9. The process according to claim 8 , wherein when suspending the particles in the water solvent in the step (1), an ionic solution comprising the element M is added to deposit the element M on the respective particles.
10. The process according to claim 8 , wherein the heat treatment in the step (2) is conducted in a temperature range of 500 to 850° C. in air or an oxygen atmosphere having a carbonate concentration of not more than 100 ppm.
11. A non-aqueous electrolyte secondary battery comprising the lithium composite compound particles as defined in claim 1 .