Positive electrode active material and preparation method therefor, positive electrode sheet, secondary battery, and electrical device
A positive electrode active material and a preparation method therefor, a positive electrode sheet, a secondary battery, and an electric device, wherein the positive electrode active material comprises hollow secondary particles, the hollow secondary particles comprising Li a Ni x Co y Mn z A q M p O b , 0.25≤a≤1.2, 1.8≤b≤2, 0.3≤x≤0.6, 0≤y≤0.4, 0<z≤0.4, 0≤q≤0.02, and 0<p≤0.02, the atomic percentage of element M at grain boundaries being greater than or equal to the atomic percentage of element M in bulk phase parts of primary particles, and element A being distributed in the hollow secondary particles in the form of bulk phase doping. The positive electrode active material comprises the hollow secondary particles, element M is mainly distributed at the grain boundary of the hollow secondary particles, and element A can be optionally doped, thereby keeping good cycle performance while effectively improving the power performance.
1 . A positive electrode active material, comprising hollow secondary particles; and, wherein
the hollow secondary particles comprise Li a Ni x Co y Mn z A q M p O b , wherein 0.2≤a≤1.2, 1.8≤b≤2, 0.3≤x≤0.6, 0≤y≤0.4, 0≤z≤0.4, 0≤q≤0.02, and 0<p≤0.02, element A comprises one or more of Al, Ti, Zr, Sr, B, La and Y, and element M comprises one or more of W, Mo, Nb, Y, Ta, La, Zr and Co; and
atomic percent of the element M at grain boundaries is greater than or equal to atomic percent of the element M in the bulk-phase part of primary particles, and a distance from the bulk-phase part to the surface of the primary particles is equal to a volume average particle size Dv50 of the primary particles multiplied by 5%; and the element A is distributed in the hollow secondary particles by bulk doping.
2 . The positive electrode active material of claim 1 , wherein residual alkali in the positive electrode active material comprises Li 2 CO 3 and LiOH; in the positive electrode active material, content of Li 2 CO 3 is s, and content of LiOH is t, wherein 0.05 wt %<s<3wt %, and 0<t<0.4wt %.
3 . The positive electrode active material of claim 2 , wherein at least one of the following conditions (a1) and (a2) is satisfied:
(a1) 0.05wt %≤s≤0.4wt %; and
(a2) 0<t≤0.25wt %.
4 . The positive electrode active material of claim 1 , wherein 0<q≤0.005.
5 . The positive electrode active material of claim 1 , wherein 0<p≤0.01.
6 . The positive electrode active material of claim 1 , wherein at least one of the following conditions (b1) to (b5) is satisfied:
(b1) the volume average particle size Dv50 of the hollow secondary particles is 2-5 μm;
(b2) the volume average particle size Dv50 of the hollow secondary particles is 2.5-3.5 μm;
(b3) the hollow secondary particles have a wall thickness of 0.2-1.6 μm;
(b4) a ratio of cavity diameter of the hollow secondary particles to the volume average particle size Dv50 of the hollow secondary particles is k, wherein 0.1≤k≤0.8; and
(b5) the ratio of the cavity diameter of the hollow secondary particles to the volume average particle size Dv50 of the hollow secondary particles is k, wherein 0.5≤k≤0.8.
7 . The positive electrode active material of claim 1 , wherein the positive electrode active material further comprises a coating layer, the coating layer is distributed on at least a part of the surface of the hollow secondary particles; and
the coating layer contains element Al and/or element B.
8 . The positive electrode active material of claim 7 , wherein in the positive electrode active material, a ratio of total content of the element Al and/or element B in the coating layer to mass of the positive electrode active material is b, satisfying at least one of the following conditions (c1) and (c2):
(c1) 0<b≤5wt %; and
(c2) 0.1wt %<b<2wt %.
9 . The positive electrode active material of claim 7 , wherein in the coating layer, at least one of the following conditions (d1) and (d2) is satisfied:
(d1) a mass ratio of Al to B is 1-5; and
(d2) the mass ratio of Al to B is 2-2.5.
10 . The positive electrode active material of claim 1 , wherein the positive electrode active material has a true density of≥4.6g/cm 3 .
11 . A positive electrode plate, comprising the positive electrode active material of claim 1 .
12 . A secondary battery, comprising the positive electrode plate of claim 11 .
13 . An electrical device, comprising the secondary battery of claim 12 .
14 . A preparation method for the positive electrode active material of claim 1 , comprising:
heating a solution containing transition metal salts to form a carbonate core;
performing a precipitation reaction on the surface of the carbonate core so as to obtain a precursor having a carbonate-containing core and a hydroxide-containing shell; and
mixing the precursor, a lithium salt, a material containing element A and a raw material containing element M, and sintering to obtain hollow secondary particles.
15 . The preparation method of claim 14 , wherein at least one of the following conditions (e1) to (e3) is satisfied:
(e1) the pH value of the solution containing transition metal salts is 10.5-12;
(e2) the time for heating the solution containing transition metal salts is 14-25 h;
(e3) the time for the precipitation reaction is 20-28 h; and
(e4) a molar ratio of the precursor to the lithium salt is 1:(1-1.2).
16 . The preparation method of claim 14 , wherein the preparation method further comprises:
mixing the hollow secondary particles with a raw material of a coating layer, and sintering to obtain a positive electrode active material having the coating layer distributed on at least a part of the surface of the hollow secondary particles; wherein the coating layer comprises element Al and/or element B.