SECONDARY BATTERY, AND BATTERY MODULE, BATTERY PACK, AND ELECTRICAL DEVICE COMPRISING THE SAME

1 . A secondary battery, comprising:

a positive electrode sheet having a positive electrode active material; and

a non-aqueous electrolyte;

wherein:

the positive electrode active material comprises a central core material and a modification layer disposed on a surface of the central core material, the modification layer comprising an orthophosphate with a molecular formula A a+ x [PO 4 ] 3− y , where A denotes one or more of Li, Na, K, Rb, Cs, Mg, Ca, Ba, Ni, Fe, Co, Ti, Al, Cr, V, Nb, and W, and 1≤a≤6, and ax=3y; and

the non-aqueous electrolyte comprises a fluorinated phosphate with a molecular formula B b+ m [PO 1+c F 3-c ] c− n , where B denotes one or more of Li, Na, K, Rb, Cs, Mg, Ca, and Ba, 1≤b≤2, c denotes 1 or 2, and bm=cn.

2 . The secondary battery according to claim 1 , wherein a mass percentage C % of the orthophosphate based on a total mass of the positive electrode active material and a mass percentage D % of the fluorinated phosphate based on a total mass of the non-aqueous electrolyte satisfy at least one of following conditions:

C is 0.2-20;

D is 0.1-3; and

C×D is 0.1-15.

3 . The secondary battery according to claim 1 , wherein a ratio of a mass of element P in the modification layer to a total mass of the positive electrode active material is 0.05-6.

4 . The secondary battery according to claim 1 , wherein the positive electrode active material has a voltage plateau ≥3.8V vs Li + /Li.

5 . The secondary battery according to claim 1 , wherein the central core material comprises element Mn.

6 . The secondary battery according to claim 1 , wherein the central core material comprises one or more of spinel-type lithium manganate LiM p Mn 2-p O 4 , lithium manganese phosphate LiN q Mn 1-q PO 4 , and a layered manganese-rich material Li 1+t Mn 1-w L w O 2+t , where 0≤p≤1, 0≤q≤0.5, 0≤t≤1, 0≤w≤0.5, and M, N, and L each independently denotes one or more of Ni, Co, Fe, Cr, V, Ti, Zr, La, Ce, Rb, P, W, Nb, Mo, Sb, B, Al, and Si.

7 . The secondary battery according to claim 1 , wherein the central core material has a monocrystalline or monocrystalline-like morphology.

8 . The secondary battery according to claim 1 , wherein:

A denotes one or more of Li, Na, K, Mg, Ni, Co, Ti, Al, Nb, and W; and/or

B denotes one or more of Li, Na, K, and Mg.

9 . The secondary battery according to claim 1 , wherein c denotes 2.

10 . The secondary battery according to claim 1 , wherein:

the orthophosphate comprises one or more of Li 3 PO 4 , Na 3 PO 4 , K 3 PO 4 , Mg 3 (PO 4 ) 2 , AlPO 4 , Nb 3 (PO 4 ) 5 , LiNiPO 4 , TiLi 2 (PO 4 ) 2 , and LiNi 0.8 Co 0.2 PO 4 ; and/or

the fluorinated phosphate comprises one or more of LiPO 2 F 2 , NaPO 2 F 2 , KPO 2 F 2 , Li 2 PO 3 F, Na 2 PO 3 F, and K 2 PO 3 F.

11 . The secondary battery according to claim 1 , wherein the modification layer is disposed on 50%-100% of a surface of the central core material.

12 . The secondary battery according to claim 1 , wherein:

the positive electrode active material has a specific surface area less than 1.5 m 2 /g; and/or

the positive electrode active material has a volume particle diameter Dv50 of 1 μm-20 μm.

13 . A battery module, comprising the secondary battery according to claim 1 .

14 . A battery pack, comprising the secondary battery according to claim 1 .

15 . An electrical device, comprising the secondary battery according to claim 1 .