CN115986314A - Composite diaphragm and secondary battery - Google Patents
Composite diaphragm and secondary battery Download PDFInfo
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- CN115986314A CN115986314A CN202211709479.7A CN202211709479A CN115986314A CN 115986314 A CN115986314 A CN 115986314A CN 202211709479 A CN202211709479 A CN 202211709479A CN 115986314 A CN115986314 A CN 115986314A
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Abstract
The invention belongs to the technical field of secondary batteries, and particularly relates to a composite diaphragm and a secondary battery, which comprise a base film and a modified coating layer arranged on the surface of the base film, wherein the modified coating layer comprises a first polymer or a mixture of the first polymer and a second polymer, the first polymer is a polyacrylate polymer, the second polymer is a low-melting-point polymer, and the melting point of the second polymer is 80-135 ℃. The first polymer and the second polymer are arranged in the modified coating layer, and the first polymer can effectively improve the cycle resolution of lithium, improve the capacity retention rate and reduce the thickness increase rate of the battery cell; the second polymer can reduce the melting point of the coating and improve the passing rate of the hot box.
Description
Technical Field
The invention belongs to the technical field of secondary batteries, and particularly relates to a composite diaphragm and a secondary battery.
Background
The diaphragm is an important component of the lithium ion battery, is arranged between the anode and the cathode of the battery, plays an important role in preventing the anode and the cathode from contacting to generate short circuit, and can provide an ion transmission channel. The prior experience shows that the safety of the battery core and the properties of the circulating interface and the diaphragm have certain correlation. In the field of soft package batteries of digital mainstream, in order to ensure enough battery cell hardness, commercial diaphragms generally need to be coated with one or two adhesive layers to increase the adhesion to pole pieces. The glue coating process has two main processes, one is an oily process, and the other is a water-based process. The oil process is characterized in that the oil process is mainly characterized in that PVDF-HFP polymer resin, such as LBG of Acomat, is adopted as a raw material, and is dissolved and extracted by NMP or DMAC or acetone and other organic solvents to form a uniform adhesive layer. The solvent of the water-based process is deionized water, and the gluing raw material mainly uses the AFL resin of Ruikang to form a gap glue layer. Along with the circulation, the corner position can be extruded by the expansion of the pole piece of the battery cell, so that the electrolyte is extruded or the backflow is blocked, and the lithium separation is easily caused, thereby increasing the thickness of the battery and reducing the capacity retention rate, and particularly in a quick charging system, the accelerated consumption of the electrolyte can catalyze the lithium separation. At present, the phenomenon of corner lithium precipitation cannot be effectively improved by commercial separators, such as oil separators or water-based separators.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, the composite diaphragm is provided, and the lithium precipitation condition can be effectively improved, and the pass rate of a hot box is improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a composite diaphragm comprises a base film and a modified coating layer arranged on the surface of the base film, wherein the modified coating layer comprises a first polymer or a mixture of the first polymer and a second polymer, the first polymer is a polyacrylate polymer, the second polymer is a low-melting-point polymer, and the melting point of the second polymer is 80-135 ℃.
The modified coating layer comprises a first coating layer, a second coating layer or a third coating layer, the first coating layer comprises a polyacrylate polymer, the second coating layer comprises the polyacrylate polymer, a second polymer and a ceramic material, and the third coating layer comprises the polyacrylate polymer and the second polymer.
Wherein the mass ratio of the ceramic material, the first polymer and the second polymer in the second coating layer is 1-2.
Wherein the mass ratio of the first polymer to the second polymer in the third coating layer is 0.2-0.5.
Wherein the surface density of the first coating layer is 0.05-0.5 g/m 2 The thickness of the coating is 0.5-3 mu m; the surface density of the second coating layer is 0.05-0.5 g/m 2 The thickness of the coating is 2-5 mu m; the surface density of the third coating layer is 0.05-0.5 g/m 2 The thickness of the coating is 2-5 mu m.
Wherein the particle diameter D50 of the ceramic material is 0.2-2 μm. The ceramic material comprises one or more of alumina, boehmite, magnesium hydroxide, aluminum hydroxide, calcium oxide and silicon dioxide.
Wherein the thickness of the base film is 3-10 μm, the porosity is 25-55%, and the air permeability is 70-200 s/100cc. The base film comprises any one or more of polyethylene, polypropylene, polyvinylidene fluoride, polyimide, polyamide and polyacrylonitrile.
Wherein the particle size of the second polymer is 0.5-3 μm.
The second polymer comprises at least one of polyethylene, polyethylene wax, polyvinylidene fluoride, polymethyl methacrylate, polyimide, polystyrene and polyacrylamide.
The second purpose of the invention is: in order to overcome the defects of the prior art, the secondary battery has good heat resistance and safety performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a secondary battery comprises the composite diaphragm.
Compared with the prior art, the invention has the beneficial effects that: the composite diaphragm is provided with the modified coating layer, the modified coating layer comprises a first polymer or a mixture of the first polymer and a second polymer, the first polymer is a polyacrylate polymer, the second polymer is a low-melting-point polymer, the melting point of the second polymer is 80-135 ℃, the first polymer can effectively improve the condition of lithium precipitation, improve the capacity retention rate and reduce the thickness increase rate of a battery cell, and the second polymer can effectively reduce the melting point of the coating and improve the pass rate of a hot box.
Drawings
Fig. 1 is a schematic structural view of a composite diaphragm according to a first embodiment of the present invention.
Fig. 2 is a schematic structural view of a composite separator according to a second embodiment of the present invention.
Fig. 3 is a schematic structural view of a composite separator according to a third embodiment of the present invention.
Fig. 4 is a schematic structural view of a composite separator according to a fourth embodiment of the present invention.
Fig. 5 is a schematic structural view of a composite separator according to example five of the present invention.
Fig. 6 is a schematic structural view of a composite separator according to a sixth embodiment of the present invention.
Wherein: 1. a base film; 2. an oily coating; 3. a first coating layer; 4. a second coating layer; 5. and a third coating layer.
Detailed Description
The present invention will be described in further detail with reference to the following detailed description and the accompanying drawings, but the present invention is not limited thereto.
A composite diaphragm comprises a base film 1 and a modified coating layer arranged on the surface of the base film 1, wherein the modified coating layer comprises a first polymer or a mixture of the first polymer and a second polymer, the first polymer is a polyacrylate polymer, the second polymer is a low-melting-point polymer, and the melting point of the second polymer is 80-135 ℃.
The composite diaphragm is provided with the modified coating layer, the modified coating layer comprises a first polymer or a mixture of the first polymer and a second polymer, the first polymer is a polyacrylate polymer, the second polymer is a low-melting-point polymer, the melting point of the second polymer is 80-135 ℃, the first polymer can effectively improve the condition of lithium precipitation, improve the capacity retention rate and reduce the thickness increase rate of a battery cell, and the second polymer can effectively reduce the melting point of the coating and improve the pass rate of a hot box. In the hot box test, the temperature gradually rises, when the temperature rises to 100-125 ℃, the second polymer is heated and starts to enter a molten state, and when the temperature is higher than or equal to 130 ℃, the temperature is higher than the melting point of the second polymer, the second polymer is basically dissolved and covers the surface pores of the coating, namely the second polymer is molten before the closed pore temperature of the substrate, the effect of closing the pores of the substrate is achieved, meanwhile, the second polymer can absorb partial heat, and the second polymer and the closed pore temperature are matched to improve the passing rate of the hot box.
In some embodiments, the modified coating layer comprises a first coating layer 3, a second coating layer 4, or a third coating layer 5, the first coating layer 3 comprising a polyacrylate polymer, the second coating layer 4 comprising a polyacrylate polymer, a second polymer, and a ceramic material, the third coating layer 5 comprising a polyacrylate polymer and a second polymer. The polyacrylic acid polymer forms a gap coating with relatively scattered points distributed through a water-based process, and after pole pieces are bonded in a composite mode, electrolyte infiltration and backflow at corner positions can be increased through gaps of the coating, and the lithium precipitation risk at the later cycle stage is reduced, so that the capacity retention rate of the battery is improved, and the thickness growth rate of the battery is reduced.
In some embodiments, the mass ratio of the ceramic material, the first polymer and the second polymer in the second coating layer 4 is 1 to 2. Ceramic materials are added into the second coating layer 4, so that the heat resistance of the coating can be improved, meanwhile, the first polymer improves the circulating corner lithium precipitation, the capacity retention rate is improved, the thickness growth rate of the battery cell is reduced, and the second polymer reduces the melting point of the coating and improves the pass rate of a hot box. Preferably, the mass ratio of the ceramic material, the first polymer and the second polymer in the second coating layer 4 is 1-2. Specifically, the mass ratio of the ceramic material to the first polymer to the second polymer in the second coating layer 4 is 1.
In some embodiments, the mass ratio of the first polymer to the second polymer in the third coating layer 5 is 0.2 to 0.5. The first polymer and the second polymer are added to the third coating layer 5, the first polymer improves the lithium precipitation of the cycling corner, improves the capacity retention rate and reduces the thickness growth rate of the battery cell, and the second polymer reduces the melting point of the coating and improves the passing rate of a hot box. Preferably, the mass ratio of the first polymer to the second polymer is 0.2.
In some embodiments, the first coating layer 3 has an areal density of 0.05 to 0.5g/m 2 The thickness of the coating is 0.5-3 mu m; the surface density of the second coating layer 4 is 0.05-0.5 g/m 2 The thickness of the coating is 2-5 mu m; the surface density of the third coating layer 5 is 0.05-0.5 g/m 2 The thickness of the coating is 2-5 mu m. During preparation, the coating is formed by transfer coating of a gravure roller and drying of the odor and the surface density of each coating layer is set, so that each coating layer can play the respective role. Preferably, the areal density of the first coating layer 3 is 0.05g/m 2 、0.08g/m 2 、0.09g/m 2 、0.1g/m 2 、0.2g/m 2 、0.3g/m 2 、0.4g/m 2 、0.5g/m 2 . The thickness of the first coating layer 3 is 0.5 μm, 0.8 μm, 0.9 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 1.9 μm, 2 μm, 2.3 μm, 2.5 μm, 2.9 μm, 3 μm. The areal density of the second coating layer 4 was 0.05g/m 2 、0.08g/m 2 、0.09g/m 2 、0.1g/m 2 、0.2g/m 2 、0.3g/m 2 、0.4g/m 2 、0.5g/m 2 . The thickness of the second coating layer 4 was 2 μm, 3 μm, 4 μm, 5 μm. The third coating layer 5 had an areal density of 0.05g/m 2 、0.08g/m 2 、0.09g/m 2 、0.1g/m 2 、0.2g/m 2 、0.3g/m 2 、0.4g/m 2 、0.5g/m 2 . The thickness of the third coating layer 5 was 2 μm, 3 μm, 4 μm, 5 μm.
In some embodiments, the ceramic material has a particle size D50 of 0.2 to 2 μm. The ceramic material comprises one or more of aluminum oxide, boehmite, magnesium hydroxide, aluminum hydroxide, calcium oxide and silicon dioxide. Preferably, the particle diameter D50 of the ceramic material is 0.2. Mu.m, 0.5. Mu.m, 0.8. Mu.m, 1.2. Mu.m, 1.5. Mu.m, 1.8. Mu.m, 1.9. Mu.m, 2. Mu.m.
In some embodiments, the base film 1 has a thickness of 3 to 10 μm, a porosity of 25 to 55%, and an air permeability of 70 to 200s/100cc. The base film 1 comprises any one or more of polyethylene, polypropylene, polyvinylidene fluoride, polyimide, polyamide and polyacrylonitrile. Base film 1 sets up certain thickness, can enough provide 1 mechanical strength of base film, also can have certain membrane pore size, is favorable to the removal of active ion. Preferably, the base film 1 has a thickness of 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, a porosity of 25%, 28%, 29%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 55%, and an air permeability of 70s/100cc, 80s/100cc, 90s/100cc, 100s/100cc.
In some embodiments, the particle size of the second polymer is 0.5 to 3 μm. Preferably, the particle size of the second polymer is 0.5 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 3 μm.
In some embodiments, the second polymer comprises at least one of polyethylene, polyethylene wax, polyvinylidene fluoride, polymethyl methacrylate, polyimide, polystyrene, polyacrylamide.
A secondary battery comprises the composite diaphragm. The secondary battery has good heat resistance and safety performance.
The secondary battery may be a lithium ion battery, a sodium ion battery, a magnesium ion battery, a calcium ion battery, a potassium ion battery, or the like. Preferably, the following secondary battery is exemplified by a lithium ion battery, which includes a positive plate, a negative plate, a separator, an electrolyte, and a case, wherein the separator separates the positive plate from the negative plate, and the case is used for mounting the positive plate, the negative plate, the separator, and the electrolyte. The diaphragm is the composite diaphragm.
The positive plate comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, wherein the positive active material layer comprises a positive active material, and the positive active material can be a compound including but not limited to a chemical formula such as Li a Ni x Co y M z O 2-b N b (wherein 0.95. Ltoreq. A. Ltoreq.1.2. X>0,y is more than or equal to 0, z is more than or equal to 0, and x + y + z =1,0 is more than or equal to b is less than or equal to 1, M is selected from one or more of Mn and Al, N is selected from one or more of F, P and S), the positive active material can also be selected from one or more of LiCoO 2 、LiNiO 2 、LiVO 2 、LiCrO 2 、LiMn 2 O 4 、LiCoMnO 4 、Li 2 NiMn 3 O 8 、LiNi 0.5 Mn 1.5 O 4 、LiCoPO 4 、LiMnPO 4 、LiFePO 4 、LiNiPO 4 、LiCoFSO 4 、CuS 2 、FeS 2 、MoS 2 、NiS、TiS 2 And the like. The positive electrode active material may be further modified, and the method of modifying the positive electrode active material is known to those skilled in the art, for example, the positive electrode active material may be modified by coating, doping, and the like, and the material used in the modification may be one or a combination of more of Al, B, P, zr, si, ti, ge, sn, mg, ce, W, and the like. While the positive current collector is generally a structure or part that collects current, the positive current collector may be any of various materials in the art suitable for use as a positive current collector in a lithium ion battery, for example, the positive electrodeThe current collector may be, but is not limited to, a metal foil, etc., and more particularly, may be, but is not limited to, an aluminum foil, etc.
The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material can be one or more of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate or other metals capable of forming an alloy with lithium. Wherein, the graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material can be one or more selected from simple substance silicon, silicon-oxygen compound, silicon-carbon compound and silicon alloy; the tin-based material can be one or more selected from simple substance tin, tin oxide compound and tin alloy. The negative electrode current collector is generally a structure or a part for collecting current, and the negative electrode current collector may be any material suitable for use as a negative electrode current collector of a lithium ion battery in the art, for example, the negative electrode current collector may include, but is not limited to, a metal foil, and the like, and more specifically, may include, but is not limited to, a copper foil, and the like.
The electrolyte comprises an organic solvent, electrolyte lithium salt and an additive. Wherein the electrolyte lithium salt may be LiPF used in a high-temperature electrolyte 6 And/or LiBOB; or LiBF used in low-temperature electrolyte 4 、LiBOB、LiPF 6 At least one of; or LiBF used in anti-overcharge electrolyte 4 、LiBOB、LiPF 6 At least one of, liTFSI; may also be LiClO 4 、LiAsF 6 、LiCF 3 SO 3 、LiN(CF 3 SO 2 ) 2 At least one of (1). And the organic solvent may be a cyclic carbonate including PC, EC; or chain carbonates including DFC, DMC, or EMC; and also carboxylic acid esters including MF, MA, EA, MP, etc. And additives include, but are not limited to, film forming additives, conductive additives, flame retardant additives, overcharge prevention additives, control of H in the electrolyte 2 Of additives with O and HF contents, additives for improving low-temperature properties, multifunctional additivesAt least one of them.
Wherein, the material of casing is one of stainless steel, plastic-aluminum membrane.
Example 1
Preparing a composite diaphragm:
the composite separator of the present embodiment includes a porous substrate, an oily coating layer 2, and a first coating layer 3, as shown in fig. 1. The oily coating 2 was a commercial ceramic and PVDF-HFP mixed coating having a coating thickness of 1 μm, coated on one side of the substrate, and then the first coating layer 3 slurry was coated on the other side of the substrate. The oily coating 2 of the diaphragm faces to the anode, the first coating layer 3 faces to the cathode, and the anode, the cathode and the electrolyte are assembled into the lithium ion battery. The coating areal density of the first coating layer 3 was 0.1g/m 2 The slurry was milled using a milling apparatus to a particle size of 3 μm to obtain a coating thickness of 2.5 μm. The base film 1 had a thickness of 5 μm, a porosity of 40% and an air permeability of 90s/100cc.
Preparing a positive plate:
lithium cobaltate, conductive agent superconducting carbon (Super-P) and binder polyvinylidene fluoride (PVDF) are mixed according to the mass ratio of 97:1.5:1.5, uniformly mixing to prepare lithium ion battery anode slurry with certain viscosity, coating the slurry on a current collector aluminum foil, drying at 85 ℃, and then carrying out cold pressing; then trimming, cutting into pieces, slitting, drying for 4 hours at 110 ℃ under the vacuum condition after slitting, and welding the tabs to prepare the positive plate.
Preparing a negative plate:
graphite, conductive agent superconducting carbon (Super-P), thickening agent carboxymethyl cellulose sodium (CMC) and binder Styrene Butadiene Rubber (SBR) are mixed according to a mass ratio of 96:2.0:1.0:1.0, preparing slurry, coating the slurry on a current collector copper foil, drying at 85 ℃, cutting edges, cutting pieces, dividing strips, drying for 4 hours at 110 ℃ under a vacuum condition after dividing the strips, and welding tabs to prepare a negative plate.
Preparing an electrolyte:
mixing lithium hexafluorophosphate (LiPF) 6 ) Dissolving the mixture in a mixed solvent composed of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) (the mass ratio of the three is 1:2: 1) Obtaining electrolysis with a concentration of 1mol/LAnd (4) liquid.
Preparing a lithium ion battery:
winding the positive plate, the prepared diaphragm and the negative plate into a battery cell, wherein the oily diaphragm is positioned between the positive plate and the negative plate, the positive electrode is led out by spot welding of an aluminum tab, and the negative electrode is led out by spot welding of a nickel tab; and then placing the battery cell in an aluminum-plastic packaging bag, injecting the electrolyte, and carrying out procedures of packaging, formation, capacity and the like to prepare the lithium ion battery.
Example 2
The difference from the embodiment 1 is that: unlike the composite separator, the composite separator of the present embodiment includes a porous substrate, an oily coating layer 2, and a second coating layer 4, as shown in fig. 2. The oil coating 2 and the second coating layer 4 are respectively coated on two sides of the base material, wherein the oil coating is a commercial ceramic and PVDF-HFP mixed coating, the thickness of the coating is 1 mu m, and when the lithium ion battery is formed, the oil coating 2 faces to the positive electrode, and the second coating layer 4 faces to the negative electrode. In the second coating layer 4, ceramic: polymer A: the polymer B is mixed according to the mass ratio of 1.
The process is the same as that of embodiment 1, and is not described herein again.
Example 3
The difference from the embodiment 1 is that: unlike the composite separator, the composite separator of the present embodiment includes a porous substrate, an oily coating layer 2, and a third coating layer 5, as shown in fig. 3. The oil coating is a commercial ceramic and PVDF-HFP mixed coating, the thickness of the coating is 1 mu m, the oil coating 2 and the third coating 5 are respectively coated on two sides of the base material, and when the lithium ion battery is formed, the oil coating 2 faces to the positive electrode, and the third coating 5 faces to the negative electrode. In the third coating layer 5, polymer a: polymer B was mixed and dispersed in water at a mass ratio of 0.3.
The rest is the same as embodiment 1, and the description is omitted here.
Example 4
The difference from example 1 is that: the composite separator is different from the composite separator, the composite of the embodiment includes a porous substrate, a first coating layer 3 coated on one side of the porous substrate film 1, and a second coating layer 4 coated on the other side of the porous substrate film 1, as shown in fig. 4, when the lithium ion battery is composed, the first coating layer 3 faces a positive electrode, the second coating layer 4 faces a negative electrode, and the mass ratio of the ceramic material, the first polymer and the second polymer in the second coating layer 4 is 1.5.
The rest is the same as embodiment 1, and the description is omitted here.
Example 5
The difference from example 1 is that: the composite separator is different from the composite separator, the composite of the embodiment includes a porous substrate, a first coating layer 3 coated on one side of the porous substrate film 1, and a third coating layer 5 coated on the other side of the porous substrate film 1, as shown in fig. 5, when the lithium ion battery is composed, the first coating layer 3 faces a positive electrode, the third coating layer 5 faces a negative electrode, and the mass ratio of the first polymer to the second polymer in the third coating layer 5 is 0.4.
The rest is the same as embodiment 1, and the description is omitted here.
Example 6
The difference from example 1 is that: the composite separator is different from the composite separator, the composite of the embodiment includes a porous substrate, a second coating layer 4 coated on one side of the porous substrate film 1, and a third coating layer 5 coated on the other side of the porous substrate film 1, as shown in fig. 6, when the lithium ion battery is composed, the second coating layer 4 faces a positive electrode, the third coating layer 5 faces a negative electrode, and the mass ratio of the ceramic material, the first polymer and the second polymer in the second coating layer 4 is 1.5. The mass ratio of the first polymer to the second polymer in the third coating layer 5 is 0.4.
The rest is the same as embodiment 1, and the description is omitted here.
Example 7
The difference from example 1 is that: the mass ratio of the ceramic material, the first polymer and the second polymer in the second coating layer 4 is 1.
The rest is the same as embodiment 1, and the description is omitted here.
Example 8
The difference from example 1 is that: the mass ratio of the ceramic material, the first polymer and the second polymer in the second coating layer 4 is 1.
The rest is the same as embodiment 1, and the description is omitted here.
Example 9
The difference from example 1 is that: the mass ratio of the ceramic material to the first polymer to the second polymer in the second coating layer 4 is 1.5.
The rest is the same as embodiment 1, and the description is omitted here.
Example 10
The difference from example 1 is that: the mass ratio of the first polymer to the second polymer in the third coating layer 5 is 0.2.
The rest is the same as embodiment 1, and the description is omitted here.
Example 11
The difference from example 1 is that: the mass ratio of the first polymer to the second polymer in the third coating layer 5 is 0.3.
The rest is the same as embodiment 1, and the description is omitted here.
Example 12
The difference from example 1 is that: the mass ratio of the first polymer to the second polymer in the third coating layer 5 is 0.4.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 1
The difference from the embodiment 1 is that: the composite diaphragm comprises a porous base membrane 1 and oily coatings 2 coated on the two side surfaces of the porous base membrane 1, wherein the oily coatings 2 are coated on the two sides, and the thickness of a single-side coating is about 1.5 mu m.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 2
The difference from the example 1 is that: the composite diaphragm comprises a porous base film 1 and commercial double-sided water system diaphragms coated on the surfaces of the two sides of the porous base film 1, heat-resistant ceramic and double-sided AFL glue are coated, the particle size of the AFL is 0.6 mu m, and the total thickness of a coating is about 3 mu m.
The rest is the same as embodiment 1, and the description is omitted here.
The separators obtained in examples 1 to 12 and comparative examples 1 to 2 were assembled into cells as described in the examples, taking a lithium ion pouch battery as an example:
(1) Cycle performance: recording the thickness of the battery cell in the half-electricity state before testing at 25 ℃, taking the thickness as the initial thickness standard, keeping the constant current and the constant voltage of the lithium ion battery at 0.05 ℃ to 4.48V, and taking the discharge capacity of 0.2 ℃ as the initial capacity. And then, charging the lithium ion battery to 4.35V by using a 3C constant current, charging the lithium ion battery to 4.48V by using a 1.8C constant current and a constant voltage, wherein the cut-off current is 0.05C, then discharging the lithium ion battery to 3.0V by using 0.7C, carrying out 1000-time cycle test on the lithium ion battery according to the method, recording the capacity retention rate of the 800 th cycle, and then fully charging the lithium ion battery to record the thickness of the battery cell.
(2) Performance of the hot box: and (3) putting the fully-filled battery cell into an oven, heating the temperature of the oven to 132 ℃ at the speed of 5 +/-2 ℃/min, keeping the temperature for 30min, and stopping.
The test results are given in table 1 below:
TABLE 1
As can be seen from table 1, the composite separator prepared according to the present invention has better safety performance and electrochemical performance, higher hot box pass rate, higher capacity retention rate at 3C rate, and lower thickness growth rate, compared to the composite separator of comparative example 1 or 2.
By comparing examples 1 to 3 with comparative examples 1 to 2, the capacity retention rate can be effectively improved and the thickness growth rate can be effectively reduced by adding the composite coating containing the polymer A. Further, as can be seen from comparative example 1, when only the oil coating layer 2 was used, the heat resistance of the composite separator could not be increased, and the hot box pass rate was 0. As can be seen from comparative example 2, the heat resistance of the conventional commercially available water-based separator was not increased, resulting in poor heat resistance.
By comparing examples 2-3 with comparative examples 1-2, the composite coating containing the polymer B is added, so that the hot box passing rate can be effectively improved.
Compared with the embodiments 1 to 6, when the first coating layer 3, the second coating layer 4 or the third coating layer 5 in the composite diaphragm is used in a composite mode, the prepared composite diaphragm is better in performance, and still has higher hot box passing rate and capacity retention rate under the condition that the thickness growth rate is kept lower.
Compared with examples 2 and 7 to 9, the composite diaphragm prepared by the method has better performance and higher capacity retention rate when the mass ratio of the ceramic material, the first polymer and the second polymer in the second coating layer 4 in the composite diaphragm is 1.
From comparison of examples 3 and 10 to 12, when the mass ratio of the first polymer to the second polymer in the third coating layer 5 in the composite diaphragm is 0.3.
The present invention includes, but is not limited to, the above embodiments, for example, a first oil coating layer 2 is coated, then a first coating layer 3, a second coating layer 4, or a third coating layer 5 is coated on both sides, or a heat-resistant ceramic is coated on the surface of the porous substrate, then a first coating layer 3, a second coating layer 4, or a third coating layer 5 is coated on one side or both sides, or a plurality of composite coating layers are mixed and combined, or the orientation of the coating layers is opposite to that of the examples, and all of the embodiments belong to the present application.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (10)
1. The composite diaphragm is characterized by comprising a base film and a modified coating layer arranged on the surface of the base film, wherein the modified coating layer comprises a first polymer or a mixture of the first polymer and a second polymer, the first polymer is a polyacrylate polymer, the second polymer is a low-melting-point polymer, and the melting point of the second polymer is 80-135 ℃.
2. The composite separator membrane of claim 1 wherein the modified coating layer comprises one or more of a first coating layer comprising a polyacrylate polymer, a second polymer, and a ceramic material, or a third coating layer comprising a polyacrylate polymer and a second polymer.
3. The composite separator according to claim 2, wherein the mass ratio of the ceramic material, the first polymer and the second polymer in the second coating layer is 1-2.
4. The composite separator according to claim 2 or 3, wherein the mass ratio of the first polymer to the second polymer in the third coating layer is 0.2 to 0.5.
5. The composite separator of claim 4, wherein the areal density of the first coating layer is 0.05 to 0.5g/m 2 The thickness of the coating is 0.5-3 mu m; the surface density of the second coating layer is 0.05-0.5 g/m 2 The thickness of the coating is 2-5 mu m; the surface density of the third coating layer is 0.05-0.5 g/m 2 The thickness of the coating is 2-5 mu m.
6. The composite separator according to claim 2, wherein the particle diameter D50 of the ceramic material is 0.2 to 2 μm.
7. The composite separator according to claim 1, wherein the base film has a thickness of 3 to 10 μm, a porosity of 25 to 55%, and an air permeability of 70 to 200s/100cc.
8. The composite separator according to claim 1, wherein the particle size of the second polymer is 0.5 to 3 μm.
9. The composite separator of claim 1, wherein the second polymer comprises at least one of polyethylene, polyethylene wax, polyvinylidene fluoride, polymethyl methacrylate, polyimide, polystyrene, polyacrylamide.
10. A secondary battery comprising the composite separator according to any one of claims 1 to 9.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117954791A (en) * | 2024-03-26 | 2024-04-30 | 宁德新能源科技有限公司 | Separator, electrochemical device, and electronic apparatus |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117954791A (en) * | 2024-03-26 | 2024-04-30 | 宁德新能源科技有限公司 | Separator, electrochemical device, and electronic apparatus |
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