AQUEOUS POSITIVE ELECTRODE SHEET, AND SECONDARY BATTERY INCLUDING THE ELECTRODE SHEET, AND POWER CONSUMPTION APPARATUS
The present application relates to an aqueous positive electrode sheet, which may include a current collector and a positive electrode active substance layer provided on at least one surface of the current collector, the positive electrode active substance layer may include an aqueous binder, where the porosity of a surface area of the positive electrode active substance layer may be greater than the porosity of an inner area of the positive electrode active substance layer, and the average particle size of the positive electrode active material in the surface area may be greater than the average particle size of the positive electrode active material in the inner area. The present application further relates to a secondary battery including the aqueous positive electrode sheet, a battery pack including the secondary battery, and a power consumption apparatus including the battery pack.
1 . An aqueous positive electrode sheet, comprising a current collector and a positive electrode active substance layer provided on at least one surface of the current collector, the positive electrode active substance layer comprising an aqueous binder,
wherein a porosity of a surface area of the positive electrode active substance layer is greater than a porosity of an inner area of the positive electrode active substance layer, and an average particle size of a positive electrode active material in the surface area is greater than an average particle size of the positive electrode active material in the inner area.
2 . The positive electrode sheet according to claim 1 , wherein the thickness of the positive electrode active substance layer is H, a ratio of the porosity in an area of H/3 from a surface in the positive electrode substance material layer to the porosity in an area of H/3 from the current collector in the positive electrode active substance layer is r 1 , and r 1 is 1.05-6.5.
3 . The positive electrode sheet according to claim 2 , wherein the porosity in the area of H/3 from the surface in the positive electrode active substance layer is 10%-30%, and/or
the porosity in the area of H/3 from the current collector in the positive electrode active substance layer is 5%-25%.
4 . The positive electrode sheet according to claim 1 , wherein the thickness of the positive electrode active substance layer is H, a ratio of the average particle size of the positive electrode active material in the area of H/3 from the surface in the positive electrode active substance layer to the average particle size of the positive electrode active material in the area of H/3 from the current collector in the positive electrode active substance layer is r 2 , and r 2 is 1.05-5.
5 . The positive electrode sheet according to claim 4 , wherein the average particle size of the positive electrode active material in the area of H/3 from the surface in the positive electrode active substance layer is 0.8-2.5 μm, and/or
the average particle size of the positive electrode active material in the area of H/3 from the current collector in the positive electrode active substance layer is 0.5-1.5 μm.
6 . The positive electrode sheet according to claim 4 , wherein a value of r 1 ×r 2 is 1.2 to 50.
7 . The positive electrode sheet according to claim 4 , wherein a ratio of r 1 /r 2 is 0.3 to 1.5.
8 . The positive electrode sheet according to claim 1 , wherein the positive electrode active substance layer comprises a conductive agent, the layer in the area of H/3 from the surface in the positive electrode active substance layer comprises the aqueous binder of 1 to 5 parts by weight and the conductive agent of 1 to 5 parts by weight, based on the total weight of the layer in the area.
9 . The positive electrode sheet according to claim 1 , wherein the positive electrode active substance layer comprises the conductive agent, the layer in the area of H/3 from the current collector in the positive electrode active substance layer comprises the aqueous binder of 2 to 6 parts by weight and the conductive agent of 1 to 5 parts by weight, based on the total weight of the layer in the area.
10 . The positive electrode sheet according to claim 1 , wherein the conductive agent comprises one or more of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, Ketjen black, graphene, or carbon nanotubes.
11 . The positive electrode sheet according to claim 1 , wherein the positive electrode active substance layer further comprises the positive electrode active material, and the positive electrode active material comprises one or more of lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.
12 . The positive electrode sheet according to claim 1 , wherein the aqueous binder comprises soluble polysaccharides and derivatives thereof, water-soluble or water-dispersed high polymers or mixtures thereof.
13 . The positive electrode sheet according to claim 1 , wherein the aqueous binder is methylcellulose and salt thereof, xanthan gum and salt thereof, chitosan and salt thereof, alginate and salt thereof, polyethyleneimine and salt thereof, polyacrylamide, acrylonitrile-acrylic acid copolymers and derivatives thereof, or mixtures thereof.
14 . The positive electrode sheet according to claim 1 , wherein the aqueous binder is a compound mixture of the xanthan gum and the polyethyleneimine, a ratio of the xanthan gum to the polyethyleneimine is 2:1-1:15; optionally, the average molecular weight Mn of the xanthan gum is 300000-2000000 g/mol, and the average molecular weight Mn of the polyethyleneimine is 2000-50000 g/mol.
15 . The positive electrode sheet according to claim 1 , wherein a membrane resistance of the positive electrode sheet is 0.3 to 2Ω.
16 . The positive electrode sheet according to claim 1 , wherein the positive electrode active substance layer is formed by multi-layer die head extrusion coating process.
17 . A secondary battery, comprising the aqueous positive electrode sheet according to claim 1 .
18 . A battery pack, comprising the secondary battery according to claim 17 .
19 . A power consumption apparatus, comprising the battery pack according to claim 18 .