Lithium-ion secondary battery, battery apparatus, electrical apparatus, preparation method for positive electrode active material, and preparation method for positive electrode plate

A preparation method for a positive electrode plate, wherein the preparation method comprising:

• providing a positive electrode active material comprising lithium-containing transition metal phosphate particles, at least some surfaces of which are provided with a carbon coated material, wherein the positive electrode active material comprises a mixture of a first group of ground particles and a second group of ground particles, a volume median particle size DV50 of the first group of ground particles is 0.8 μm to 1.2 μm, a volume median particle size DV50 of the second group of ground particles is 0.30 μm to 0.5 μm, and a mass ratio of the first group of ground particles to the second group of ground particles is 60:40 to 80:20;
• sequentially adding a binder, a conductive agent, and the positive electrode active material, dry mixing, adding a solvent, stirring, and adjusting a viscosity, to obtain a delivery slurry;
• transfer-coating at least one side of a current collector with the delivery slurry, drying, and hot pressing, to obtain a positive electrode film layer;
• wherein the drying is at a temperature ranging from 95° C. to 105° C. and a speed ranging from 2.0 m/min to 2.3 m/min,
• wherein the hot pressing comprises at least three times of hot rolling with hot rolling pressures sequentially increased and sequentially ranging from 20 metric tons to 50 metric tons, 50 metric tons to 70 metric tons, and 70 metric tons to 90 metric tons, a hot rolling temperature ranges from 40° C. to 80° C., and before entering hot rolling for a first time, the electrode plate is heated at 40° C. to 50° C.,
• wherein in a cross section of the positive electrode film layer in an electrode plate thickness direction, DA90 of particles ranges from 1400 nm to 2100 nm and (DA90−DA10)/DA50 ranges from 1.855 to 2.375.

A lithium-ion 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 arranged on at least one side of the positive electrode current collector, the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector;

• the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises lithium-containing transition metal phosphate particles and a titanium element, at least some surfaces of which are provided with a carbon coated material, and a mass content of the titanium element based on the total mass of the positive electrode active material ranges from 4000 ppm to 8000 ppm;
• and
• the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises artificial graphite;
• wherein the positive electrode active material comprises a mixture of a first group of ground particles and a second group of ground particles, a volume median particle size DV50 of the first group of ground particles is 0.8 μm to 1.2 μm, a volume median particle size DV50 of the second group of ground particles is 0.30 μm to 0.45 μm, and a mass ratio of the first group of ground particles to the second group of ground particles is 60:40 to 80:20,
• wherein in a cross section of the positive electrode film layer in an electrode plate thickness direction, DA90 of the particles ranges from 1400 nm to 2100 nm, DA50 of the particles in the cross section of the positive electrode film layer in the electrode plate thickness direction ranges from 708 nm to 785 nm, DA10 of the particles in the cross section of the positive electrode film layer in the electrode plate thickness direction ranges from 122 nm to 262 nm, and a particle size concentration ratio (DA90−DA10)/DA50 ranges from 1.855 to 2.375, wherein DA90, DA50, and DA10 refer to corresponding particle sizes of particles when area cumulative distributions of the particles reach 90%, 50%, and 10% in an area cumulative distribution curve of the particles,
• wherein a graphitization degree C value cumulative distribution curve of the positive electrode film layer that is obtained in a laser micro-confocal Raman spectrometer surface scanning mode, a graphitization degree median C50 ranges from 1.02 to 1.07;
• and a graphitization degree C value is IG/ID, wherein IG represents an intensity of a G peak at 1580±100 cm−1 of a Raman spectrum, and ID represents an intensity of a D peak at 1350±100 cm−1 of the Raman spectrum,
• wherein in the sphericity area cumulative distribution curve of the particles that are obtained from the cross section of the positive electrode film layer in the electrode plate thickness direction, the sphericity median LA50 ranges from 0.709 to 0.751.