SECONDARY BATTERY, BATTERY MODULE, BATTERY PACK, AND ELECTRIC APPARATUS

1 . A secondary battery, wherein

the secondary battery comprises a positive electrode plate, a negative electrode plate, an electrolyte, and a separator, wherein

the positive electrode plate comprises a positive electrode active material;

the positive electrode active material contains a transition metal element, and a molar ratio of Mn in the transition metal element, r(Mn), satisfies 0.3≤r(Mn)≤1;

the electrolyte contains:

at least one selected from lithium bisoxalate borate serving as a compound, a compound) represented by the following formula (1), and a compound represented by the following formula (2), and a lithium salt;

wherein in formula (1), R 1 and R 2 each are independently a fluorine atom or fluorine-containing alkyl with 1-3 carbon atoms;

wherein in formula (2), 2≤n≤4;

a total mass percentage of the compound, compound, and compound in the electrolyte is W1%, wherein W1% is 0.1% to 5%; and

the lithium salt comprises a compound represented by the following formula (3);

wherein in formula (3), R 3 and R 4 each independently represent alkyl with 1-3 carbon atoms that is substitutable by a fluorine atom, a hydrogen atom, a fluorine atom, or a chlorine atom;

a molar ratio C1 of the compound in the electrolyte satisfies 0.2≤C1≤1.5, wherein C1 is in unit of mol/L; and

the molar ratio of Mn in the transition metal element, r(Mn), of the positive electrode active material, the molar ratio C1 of the compound in the electrolyte, and the total mass percentage W1% of the compound, compound, and compound in the electrolyte satisfy the following relation:

13

≤

(

100

×

W

⁢

1

⁢

%

+

12

⁢

C

⁢

1

)

/

r

⁡

(

Mn

)

≤

20.

2 . The secondary battery according to claim 1 , wherein

1

≤

1

⁢

0

⁢

0

×

W

⁢

1

⁢

%

/

r

⁡

(

Mn

)

≤

2

.

3 . The secondary battery according to claim 1 , wherein

1

≤

C

⁢

1

/

r

⁡

(

Mn

)

≤

1.5

.

4 . The secondary battery according to claim 1 , wherein

the lithium salt further comprises LiPF 6 , and a molar ratio C2 of LiPF 6 in the electrolyte satisfies 0.6≤C2≤1, wherein C2 is in unit of mol/L.

5 . The secondary battery according to claim 4 , wherein

0

.

8

≤

C

⁢

1

+

C

⁢

2

≤

2

.

6 . The secondary battery according to claim 1 , wherein

W1% is 0.5% to 3%.

7 . The secondary battery according to claim 1 , wherein

the compound is lithium borate difluoroxalate.

8 . The secondary battery according to claim 1 , wherein

the compound is at least one selected from lithium difluorosulfonimide, lithium bis(trifluoromethyl) sulfonimide, lithium (fluorosulfonyl)(trifluoromethyl) sulfonimide, lithium (fluorosulfonyl)(perfluoroethyl) sulfonimide, and lithium bis(perfluoroethyl) sulfonimide, optionally at least one selected from lithium difluorosulfonimide and lithium bis(perfluoroethyl) sulfonimide.

9 . The secondary battery according to claim 1 , wherein

an active material contained in the positive electrode plate comprises at least one selected from LiNi x Co y Mn z M1 1-x-y-z O 2 , LiMn 2 O 4 , and Li 2 MnO 3 (1−a)LiM2O 2 ; wherein

M1 is selected from any one of Al, Co, Ni, Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, and Ti, 0≤x<1, 0≤y≤1, 0≤z≤1, and x+y+z≤1;

M2 is Ni, Co, or Mn; and

0

<

a

<

1.

10 . The secondary battery according to claim 1 , wherein

a molar ratio of the transition metal element in the positive electrode active material is 0.15 to 0.4, optionally 0.25 to 0.34.

11 . The secondary battery according to claim 1 , wherein

the positive electrode plate comprises a positive electrode material and a positive electrode current collector, wherein a mass proportion w of water in the positive electrode material satisfies 100 ppm≤w≤400 ppm.

12 . An electric apparatus, characterized by comprising at least one of the secondary battery according to claim 1 .