Positive electrode plate and lithium-ion battery comprising the positive electrode plate
Disclosed are a positive electrode plate and a lithium-ion battery including the same. The positive plate includes a positive electrode current collector and a positive electrode coating layer; and the positive electrode coating layer includes a first coating layer and a second coating layer, wherein the first coating layer is coated on the positive electrode current collector surface, and the second coating layer is coated on the first coating layer surface. The lithium-ion battery has a good safety performance, and when mechanical misuse (needling, weight impact) occurs, the probability of battery fire failure is significantly reduced.
1 . A positive electrode plate, comprising a positive electrode current collector and a positive electrode coating layer; wherein:
the positive electrode coating layer comprises a first coating layer and a second coating layer, the first coating layer is coated on the positive electrode current collector surface, and the second coating layer is coated on the first coating layer surface; the first coating layer comprises an inorganic filler, a first conductive agent and a first binder; the second coating layer comprises a positive electrode active material, a second conductive agent and a second binder;
a content of the first binder relative to a total weight of the first coating layer is greater than a content of the second binder relative to a total weight of the second coating layer;
a median particle size D50 of the inorganic filler is smaller than a median particle size D50 of the positive active material and the positive electrode active material in the second coating layer is embedded in the first coating layer; a median particle size D50 of the inorganic filler is 0.05~8 μm; a median particle size D50 of the positive electrode active material is 10~20 μm; and
the positive electrode plate satisfies the following conditions after the positive electrode coating layer of the positive electrode plate is peeled off, a maximum thickness of the positive electrode coating layer remaining on the positive electrode current collector is greater than or equal to a thickness of the first coating layer;
wherein the positive electrode coating layer of the positive electrode plate is peeled off by the following method: at a temperature of 25±3° C., the positive electrode plate is stuck on a tape, and then a tensile machine is used to test a 180 degree peeling.
2 . The positive electrode plate according to claim 1 , wherein a bonding force between the first coating layer and the positive electrode current collector is greater than or equal to 35 N/m and less than or equal to 300 N/m; the bonding force is tested by the following method: at a temperature of 25±3° C., the positive electrode plate is stuck on a tape, and then a tensile machine is used to test a 180 degree peeling, which automatically records the tensile force value that changes with the peeling displacement; the curve of tensile force as a function of the peeling displacement is drawn, in which the abscissa is the peeling displacement and the ordinate is the tensile force value; and the bonding force is defined as the tensile force value where the curve is flat and the peeling displacement is greater than 5 mm.
3 . The positive electrode plate according to claim 1 , wherein a mass percentage of each component in the first coating layer is: 40~93 wt % of the inorganic filler, 2~15 wt % of the first conductive agent, and 5~ 58 wt % of the first binder.
4 . The positive electrode plate according to claim 3 , wherein a mass percentage of each component in the first coating layer is: 60~91 wt % of the inorganic filler, 3-10 wt % of the first conductive agent, and 8~30 wt % of the first binder.
5 . The positive electrode plate according to claim 1 , wherein a mass percentage of each component in the second coating layer is: 93~99 wt % of the positive electrode active material, 0.5~5 wt % of the second conductive agent, and 0.5~2 wt % of the second binder.
6 . The positive electrode plate according to claim 1 , wherein the first binder and the second binder are the same or different, and are at least one independently selected from the group consisting of polyvinylidene fluoride and modified polyvinylidene fluoride; and/or
a crystallinity of the first binder is less than 40%.
7 . The positive electrode plate according to claim 6 , wherein the modified polyvinylidene fluoride is acrylate-modified polyvinylidene fluoride.
8 . The positive electrode plate according to claim 1 , wherein the inorganic filler is selected from lithium-containing transition metal oxides; or
the inorganic filler is selected from ceramic materials; or
the inorganic filler is selected from a mixture of at least one lithium-containing transition metal oxide and at least one ceramic material.
9 . The positive electrode plate according to claim 8 , wherein the lithium-containing transition metal oxides comprise at least one selected from the group consisting of lithium cobalt oxide, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, nickel cobalt manganese aluminum quaternary material, lithium ferrous phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium manganate and lithium rich manganese bases.
10 . The positive electrode plate according to claim 8 , wherein the ceramic materials comprise at least one selected from the group consisting of alumina, boehmite, magnesium oxide, and magnesium hydroxide.
11 . The positive electrode plate according to claim 1 , wherein the positive electrode active material is at least one selected from the group consisting of lithium cobalt oxide, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, nickel cobalt manganese aluminum quaternary material, lithium ferrous phosphate, lithium manganese phosphate, lithium vanadium phosphate and lithium manganate.
12 . The positive electrode plate according to claim 8 , wherein the inorganic filler is lithium ferrous phosphate, the positive electrode active material is lithium cobalt oxide, and after the positive electrode coating layer of the positive electrode plate is peeled off, Co and O elements on the surface of the positive electrode coating layer remaining on the positive electrode current collector are detected by EDS.
13 . The positive electrode plate according to claim 1 , wherein the thickness of the first coating layer is 2~10 μm.
14 . The positive electrode plate according to claim 1 , wherein a thickness of the second coating layer is 30~80 μm.
15 . A lithium-ion battery, comprising the positive electrode plate according to claim 1 .
16 . The positive electrode plate according to claim 1 , wherein the positive electrode current collector is bonded with a part of the first binder, and a part of the positive electrode active material is bonded with another part of the first binder.
17 . The positive electrode plate according to claim 1 , wherein a bonding force between the first coating layer and the positive electrode current collector is greater than 30 N/m; the positive electrode coating layer of the positive electrode plate is peeled off by the following method: at a temperature of 25±3° C., the positive electrode plate is stuck on a tape, and then a tensile machine is used to test a 180 degree peeling.
18 . The positive electrode plate according to claim 17 , wherein the positive electrode plate satisfies at least one of the following conditions (1) to (2):
(1) a bonding force between the first coating layer and the positive electrode current collector is greater than a bonding force between the first coating layer and the second coating layer;
(2) a bonding force between the first coating layer and the positive electrode current collector is greater than a bonding force between positive electrode active material particles of the second coating layer.
19 . The positive electrode plate according to claim 1 , wherein the positive electrode plate satisfies at least one of the following conditions (3) to (6):
(3) after the positive electrode coating layer of the positive electrode plate is peeled off, a maximum thickness of the positive electrode coating layer remaining on the positive electrode current collector is greater than or equal to 2 μm;
(4) a thickness of the positive electrode coating layer remaining on the positive electrode current collector after the positive electrode coating layer of the positive electrode plate is peeled off accounts for more than 5% of a thickness of the positive electrode coating layer on the positive electrode current collector before peeling off;
(5) a total mass of the positive electrode coating layer remaining on the positive electrode current collector after the positive electrode coating layer of the positive electrode plate is peeled off accounts for more than 10% of a total mass of the positive electrode coating layer on the positive electrode current collector before peeling off; and
(6) a total area of the positive electrode coating layer remaining on the positive electrode current collector after the positive electrode coating layer of the positive electrode plate is peeled off accounts for more than 70% of a total area of the positive electrode coating layer before peeling off.