Secondary battery, preparation method thereof, and battery module, battery pack, and apparatus containing secondary battery

1. A secondary battery, comprising a positive electrode plate, a negative electrode plate, and an electrolyte, wherein

the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer being disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, and

the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer being disposed on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material; and, wherein

the positive electrode active material comprises a first material and a second material, the first material contains one or more of layered lithium transition metal oxides and their modified compounds, and the second material contains one or more of an olivine-structured lithium-containing phosphate and its modified compounds;

the secondary battery satisfies

4

≤

d

c

×

l

c

×

d

a

×

l

a

I

e

≤

9

⁢

0

,

wherein

d c is compacted density of the positive electrode film layer and measured in g/cm 3 ;

l c is a mass ratio of the positive electrode active material to the positive electrode film layer;

d a is compacted density of the negative electrode film layer and measured in g/cm 3 ;

l a is a mass ratio of the negative electrode active material to the negative electrode film layer; and

I e is a ratio of a mass of the electrolyte to a total mass of the electrolyte, the positive electrode active material, and the negative electrode active material in the secondary battery, and

the secondary battery further satisfies:

0.03

≤

ε

c

×

ε

a

×

σ

θ

′

≤

8

;

and

wherein σ is ionic conductivity of the electrolyte at 25° C. and measured in mS/cm;

ε c is porosity of the positive electrode film layer;

ε a is porosity of the negative electrode film layer; and

θ′ is an electrolyte contact angle of the positive electrode film layer and measured in radian.

2. The secondary battery according to claim 1 , wherein the secondary battery satisfies:

1

⁢

0

≤

d

c

×

l

c

×

d

a

×

l

a

I

e

≤

55.

3. The secondary battery according to claim 1 , wherein the secondary battery further satisfies one or more of the following (1) to (5):

(1) the compacted density d c of the positive electrode film layer is 2.1 g/cm 3 to 4.2 g/cm 3 ;

(2) the mass ratio l c of the positive electrode active material to the positive electrode film layer is 0.85 to 0.99;

(3) the compacted density d a of the negative electrode film layer is 1.0 g/cm 3 to 2.2 g/cm 3 ;

(4) the mass ratio l a of the negative electrode active material to the negative electrode film layer is 0.85 to 0.99; and

(5) the ratio I e of the mass of the electrolyte to the total mass of the electrolyte, the positive electrode active material, and the negative electrode active material in the secondary battery is 0.1 to 0.5, and optionally 0.1 to 0.3.

4. The secondary battery according to claim 1 , wherein the secondary battery further satisfies one or more of the following (1) to (4):

(1) porosity ε c of the positive electrode film layer is 10% to 50%;

(2) the porosity ε a of the negative electrode film layer is 10% to 50%;

(3) ionic conductivity a of the electrolyte at 25° C. is 0.5 mS/cm to 50 mS/cm; and

(4) electrolyte contact angle θ of the positive electrode film layer satisfies 0°≤θ≤75°.

5. The secondary battery according to claim 1 , wherein a median particle size by volume D v 50 of the first material is 0.1 μm to 30 μm; or

a median particle size by volume D v 50 of the second material is 0.01 μm to 15 μm.

6. The secondary battery according to claim 1 , wherein the first material comprises one or more of single particles and secondary particles.

7. The secondary battery according to claim 1 , wherein the second material comprises secondary particles.

8. The secondary battery according to claim 1 , wherein a mass ratio of the first material to the second material is 99.9:0.1 to 50:50.

9. The secondary battery according to claim 1 , wherein the first material is selected from one or more of a lithium nickel cobalt manganese oxide, a lithium nickel cobalt aluminum oxide, a lithium cobalt oxide, and their respective modified compound; or the second material is selected from one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium iron phosphate, and their respective modified compounds.

10. The secondary battery according to claim 1 , wherein the negative electrode active material contains one or more of artificial graphite, natural graphite, silicon-based material, and tin-based material.

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

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

13. A preparation method of a secondary battery, comprising:

preparing a positive electrode slurry by using a positive electrode active material, wherein the positive electrode active material comprises a first material and a second material, the first material contains one or more of layered lithium transition metal oxides and their modified compounds, and the second material contains one or more of an olivine-structured lithium-containing phosphate and its modified compounds;

applying the positive electrode slurry on at least one surface of a positive electrode current collector to form a positive electrode film layer, to obtain a positive electrode plate; and

assembling the positive electrode plate, a negative electrode plate, and an electrolyte into the secondary battery, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer that is disposed on at least one surface of the negative electrode current collector and that comprises a negative electrode active material;

wherein the secondary battery satisfies

4

≤

d

c

×

l

c

×

d

a

×

l

a

I

e

≤

9

⁢

0

,

wherein

d c is compacted density of the positive electrode film layer and measured in g/cm 3 ;

l c is a mass ratio of the positive electrode active material to the positive electrode film layer;

d a is compacted density of the negative electrode film layer and measured in g/cm 3 ;

l a is a mass ratio of the negative electrode active material to the negative electrode film layer; and

I e is a ratio of a mass of the electrolyte to a total mass of the electrolyte, the positive electrode active material, and the negative electrode active material in the secondary battery; and

wherein the secondary battery further satisfies:

0.03

≤

ε

c

×

ε

a

×

σ

θ

′

≤

8

;

and

wherein σ is ionic conductivity of the electrolyte at 25° C. and measured in mS/cm;

ε c is porosity of the positive electrode film layer;

ε a is porosity of the negative electrode film layer; and

θ′ is an electrolyte contact angle of the positive electrode film layer and measured in radian.

14. The preparation method according to claim 13 , wherein viscosity of the positive electrode slurry is 4000 mPa·s to 15000 mPa·s; or

a solid content in the positive electrode slurry is 60% to 80%.