Method of producing active material particles with lithium transition metal oxide secondary particles
Active material particles are provided that exhibit performance suitable for increasing the output of a lithium secondary battery and little deterioration due to charge-discharge cycling. The active material particles provided by the present invention have a hollow structure having secondary particles including an aggregate of a plurality of primary particles of a lithium transition metal oxide, and a hollow portion formed inside the secondary particles, and through holes that penetrates to the hollow portion from the outside are formed in the secondary particles. BET specific surface area of the active material particles is 0.5 to 1.9 m 2 /g.
1. A method of producing active material particles having a holed hollow structure having secondary particles including an aggregate of a plurality of primary particles of a lithium transition metal oxide, and a hollow portion formed inside the secondary particles, with through holes that penetrate to the hollow portion from the outside being formed in the secondary particles,
the method comprising:
a raw material hydroxide formation step of supplying ammonium ions to an aqueous solution of a transition metal compound, and precipitating particles of the transition metal hydroxide from the aqueous solution, with the aqueous solution containing at least one transition metal element that composes the lithium transition metal oxide;
a mixing step of mixing the transition metal hydroxide with a lithium compound to prepare an unfired mixture, and
a calcining step of calcining the mixture to obtain the active material particles, wherein
the raw material hydroxide formation step includes a nucleation stage in which the transition metal hydroxide is precipitated from the aqueous solution at a pH of 12 or higher and an ammonium ion concentration of 25 g/L or less, and a particle growth stage in which the precipitated transition metal hydroxide is grown at a pH of less than 12 and an ammonium ion concentration of 3 g/L or more.
2. The method according to claim 1 , wherein the calcining step is carried out such that the maximum calcining temperature is 800° C. to 1100° C.
3. The method according to claim 1 , wherein the calcining step includes a first calcining stage, in which the mixture is fired at a temperature T1 of 700° C. to 900° C., and a second calcining stage, in which the result of the first calcining stage is fired at a temperature T2 of 800° C. to 1100° C. that is higher than the firing temperature T1 of the first calcining stage.
4. The method according to claim 1 , wherein the particle growth stage is carried out at the ammonium ion concentration of 15 g/L or less.
5. The method according to claim 1 , wherein an aqueous solution of a transition metal compound contains nickel.
6. A method according to claim 1 , wherein the pH of the particle growth stage is 11.8 or lower.
7. A method according to claim 1 , wherein the pH of the particle growth stage is 0.5 or more lower than the pH of the nucleation stage.
8. A method according to claim 1 , wherein the calcining step is the step to obtain the active material particles with a BET specific surface area of from 0.5 to 1.9 m 2 /g.
9. A method according to claim 1 , wherein the calcining step is the step to obtain the active material particles with 1 to 20 through holes per particle of the active material particles on average.
10. A method according to claim 1 , wherein the average hardness of the active material particles, as obtained by measuring dynamic hardness under conditions of a loading speed of 0.5 mN/sec to 3 mN/sec using a flat diamond indenter having a diameter of 50 μm, is 0.5 MPa or more.
11. A method according to claim 1 , wherein, the primary particles that compose the secondary particles are sintered in the calcining step in the portion of the secondary particles that surrounds the hollow portion, with the exception of the portions having the through holes.