Negative electrode plate and secondary battery
The present application relates to a negative electrode plate and a secondary battery. Specifically, the present application provides a negative electrode plate comprising a negative electrode current collector and an negative electrode film coated on at least one surface of the negative electrode current collector and containing the negative active material, wherein the negative electrode plate satisfies 0.6≤0.7×P×(D90−D10)/D50+B/3≤8.0, wherein P refers to the porosity of the negative electrode film; B refers to the active specific surface area of the negative electrode film, and the unit thereof is m 2 /g; D10 refers to the particle size corresponding to the cumulative volume percentage of the negative active material reaching 10%, D90 refers to the particle size corresponding to the cumulative volume percentage of the negative active material reaching 90%, and D50 refers to the particle size corresponding to the cumulative volume percentage of the negative active material reaching 50%.
1. A secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film coated on at least one surface of the negative electrode current collector and containing a negative active material, wherein the negative electrode plate satisfies the following Formula I:
1.2≤0.7× P ×( D 90− D 10)/ D 50+ B/ 3≤4.0 (Formula I)
wherein,
P refers to a porosity of the negative electrode film;
B refers to an active specific surface area of the negative electrode film, and the unit thereof is cm 2 /g;
D10 refers to a particle size corresponding to the cumulative volume percentage of the negative active material reaching 10%; D90 refers to a particle size corresponding to the cumulative volume percentage of the negative active material reaching 90%, and D50 refers to a particle size corresponding to the cumulative volume percentage of the negative active material reaching 50%, i.e. the median particle size of the volume distribution, the units of D10, D90, and D50 are all μm;
wherein the active specific surface area B of the negative electrode film is obtained as follows:
the negative electrode plate was used as a cathode, and a lithium metal sheet was used as an anode, and ferrocene having a concentration of 50 mmol/L was added to the electrolyte, then assembled into a button half battery; four parallel samples were scanned at sweep speeds of 0.1 mV/s, 0.3 mV/s, 0.5 mV/s, and 1 mV/s, respectively, to obtain cyclic voltammetry curves at different sweep speeds, which were extracted by using EC-Lab software to obtain the peak current ip of the cyclic voltammetry curve; taking the square root √{square root over (v)} of the sweep velocity v as the abscissa and the peak current ip as the ordinate, a linear graph of the cyclic volt-ampere curve ip vs. √{square root over (v)} was obtained, and then the slope K was obtained; according to the Randles-Sevick equation i p =2.69×10 5 n 3/2 Ac√{square root over (D)}√{square root over (v)}, as can be seen that the slope was K=2.69×10 5 n 3/2 Ac√{square root over (D)}, where n was the number of electron transfer, which was related to the molecular type of the probe; here, n was given a value of 1, c was the concentration of ferrocene, and here c was given a value of 50 mmol/L, and D was the diffusion coefficient of ferrocene, and here D was given a value of 2.1×10 −6 cm 2 /s; thus the active surface area of the negative electrode plate was A=K/(2.69×10 5 n 3/2 c√{square root over (D)}); then the ratio of the active surface area A of the negative electrode film to the weight m of the negative electrode film was calculated, which represented the active specific surface area B of the negative electrode film;
wherein the negative active material has a specific surface area of from 1.1 m 2 /g to 2.9 m 2 /g;
wherein the active specific surface area B of the negative electrode film satisfies 3.5 cm 2 /g≤B≤10 cm 2 /g; and
wherein the negative active material is graphite material.
2. The secondary battery according to claim 1 , further comprising a positive electrode plate which contains a positive active material, wherein the positive active material comprises lithium iron phosphate.
3. The secondary battery according to claim 1 , wherein the porosity P of the negative electrode film satisfies 20%≤P≤60%.
4. The secondary battery according to claim 1 , wherein the porosity P of the negative electrode film satisfies 25%≤P≤45%.
5. The secondary battery according to claim 1 , wherein the active specific surface area B of the negative electrode film satisfies 4 cm 2 /g≤B≤10 cm 2 /g.
6. The secondary battery according to claim 1 , wherein the negative active material satisfies: 10 μm≤D90≤60 μm; and/or
4 μm≤D50≤20 μm; and/or
1 μm≤D10≤15 μm.
7. The secondary battery according to claim 1 , wherein the negative active material satisfies: 15 μm≤D90≤40 μm; and/or
5 μm≤D50≤14 μm; and/or
3 μm≤D10≤10 μm.
8. The secondary battery according to claim 1 , wherein the negative active material satisfies 0.3≤(D90−D10)/D50≤8.
9. The secondary battery according to claim 1 , wherein the negative active material satisfies 0.8≤(D90−D10)/D50≤3.
10. The secondary battery according to claim 1 , wherein a packed density PD of the negative electrode film satisfies 0.8 g/cm 3 ≤PD≤2.0 g/cm 3 .
11. The secondary battery according to claim 10 , wherein the packed density PD of the negative electrode film satisfies 1.0 g/cm 3 ≤PD≤1.8 g/cm 3 .
12. The secondary battery according to claim 1 , wherein a coating weight CW per unit area of the negative electrode film satisfies 2 mg/cm 2 ≤CW≤13 mg/cm 2 .
13. The secondary battery according to claim 12 , wherein the coating weight CW per unit area of the negative electrode film satisfies 5 mg/cm 2 ≤CW≤10 mg/cm 2 .