A lithium ion battery positive electrode sheet, a preparation method thereof and a lithium battery

Abstract

The application provides a lithium ion battery positive electrode sheet, a preparation method thereof and a lithium battery. The preparation method comprises the following steps: (1) coating a mixed solution on a release film, and obtaining an intermediate film after heat treatment; the mixed solution comprises a solvent and a solid electrolyte; (2) bonding the intermediate film obtained in the step (1) with an electrode sheet, removing the release film after rolling, and obtaining the lithium ion battery positive electrode sheet. The preparation method of the lithium ion battery positive electrode sheet provided by the application obtains a lithium ion battery positive electrode sheet with a composite electrolyte film. The thickness of the electrolyte film on the lithium ion battery positive electrode sheet can reach below 5 microns. The electrolyte film will not curl on the surface of the electrode sheet, so that the lithium ion battery positive electrode sheet has a high yield. After the intermediate film is obtained through heat treatment, the intermediate film is in contact with the surface of the electrode sheet, which reduces the damage of the solvent to the surface of the lithium ion battery positive electrode sheet, and the yield of the lithium ion battery positive electrode sheet is increased from 70% to above 95%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion battery materials, and relates to a preparation method of a lithium ion battery positive electrode sheet, in particular to a lithium ion battery positive electrode sheet, a preparation method thereof and a lithium battery. BACKGROUND

[0002] Slurry coating is the next process after the preparation of slurry. The main purpose of this process is to uniformly coat the slurry with good stability, good viscosity and good fluidity on the positive and negative current collectors. The coating of the lithium ion battery positive electrode sheet is of great significance to the capacity, consistency and safety of the lithium battery. According to incomplete statistics, the battery failure caused by the coating process of the lithium ion battery positive electrode sheet accounts for more than 10% of the total causes of lithium battery failure. When a solid electrolyte film is prepared by directly coating a solid electrolyte slurry on the surface of a lithium ion battery positive electrode sheet, it is difficult to make a thin film, especially an electrolyte film below 10 microns, regardless of transfer coating or extrusion coating, due to equipment limitations. Moreover, the solvent problem will damage the surface layer of the electrode sheet, affecting the performance of the battery. Furthermore, the electrode sheet edge is prone to curling during drying of the electrolyte film, affecting the yield.

[0003] CN112909436A discloses a lithium ion battery composite separator and a preparation method thereof, and a lithium ion battery. The lithium ion battery composite separator comprises a base film and a coating layer, and the coating layer is composed of exfoliated boron nitride nanosheets and P(VDF-HFP) powder. However, the lithium ion battery composite separator and the preparation method thereof only use a micro-concave roller coating method to prepare the lithium ion battery composite separator, which makes it difficult to prepare a separator below 10 microns, and the solvent will damage the surface layer of the electrode sheet, thereby affecting the performance of the battery.

[0004] CN108807806A discloses a battery separator and a preparation method thereof, comprising a base film, an aramid / ceramic composite film and a PVDF film connected in sequence. The battery separator provided by the application is a multi-layer composite separator, which can ensure high temperature resistance of the separator, improve the adhesion of the base film and the coating layer and the adhesion between the separator and the electrode sheet, reduce the gap between the separator and the electrode sheet, reduce the interface resistance and improve the hardness of the battery cell. However, the preparation method of the battery separator uses a micro-concave roller coating process or a spraying process, which makes it difficult to prepare a separator below 10 microns, and the solvent used is also likely to damage the surface layer of the electrode sheet.

[0005] CN109817872A discloses a non-full-coverage coating separator, a preparation method and device thereof. The non-full-coverage coating separator comprises a base film and a non-full-coverage coating layer coated on at least one surface of the base film, wherein the non-full-coverage coating layer is uniformly distributed in the form of uniform dots with consistent size and shape. However, the non-full-coverage coating separator, the preparation method and device thereof are relatively complex and have high preparation cost, which is not conducive to large-scale popularization and use.

[0006] Currently available methods for preparing lithium-ion battery cathodes all have certain drawbacks, including difficulty in preparing electrolyte films smaller than 10 micrometers, solvent damage to the electrode surface, edge curling, and high production costs. Therefore, developing a novel method for preparing lithium-ion battery cathodes is crucial. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a lithium-ion battery positive electrode sheet, its preparation method, and a lithium battery. The preparation method of the lithium-ion battery positive electrode sheet of the present invention yields a lithium-ion battery positive electrode sheet with a composite electrolyte membrane. The electrolyte layer thickness on the lithium-ion battery positive electrode sheet can reach less than 5 micrometers. The edges of the lithium-ion battery positive electrode sheet do not curl. The yield rate of the lithium-ion battery positive electrode sheet is increased from 70% to over 95%. The preparation method is simple, low in cost, and suitable for large-scale production.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a positive electrode sheet for a lithium-ion battery, the method comprising the following steps:

[0010] (1) The mixture is coated onto a release film and heat-treated to obtain an intermediate film; the mixture includes a solvent and a solid electrolyte.

[0011] (2) The intermediate film obtained in step (1) is bonded to the electrode sheet, and the release film is removed after rolling to obtain the positive electrode sheet of the lithium-ion battery; the rolling temperature is below 40°C.

[0012] The rolling temperature described in this invention is below 40°C, for example, it can be 39°C, 37°C, 35°C, 33°C, 31°C, 29°C, 25°C, 20°C, 15°C, 10°C or 5°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] Preferably, the rolling temperature is less than 25°C, for example, it can be 25°C, 22°C, 20°C, 18°C, 16°C, 14°C, 12°C, 10°C, 8°C, 6°C, 4°C or 2°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] Coating a micron-sized (greater than 500 nm) solid electrolyte layer on the positive electrode surface is advantageous, but an excessively thick solid electrolyte layer reduces the battery's energy density and reduces the thickness space of the positive electrode active material layer; therefore, it is essential to develop a positive electrode solid electrolyte layer preparation technology to prepare an ultrathin solid electrolyte layer.

[0015] This invention first coats a release film to obtain an intermediate film, which then carries a solid electrolyte layer. The intermediate film is then bonded to the positive electrode of a lithium-ion battery. Because the adhesion between the release film and the solid electrolyte material is much less than the adhesion between the solid electrolyte material and the positive electrode active material layer, the release film on the other side can be easily removed after the intermediate film is bonded to the electrode. After removing the release film, a lithium-ion battery positive electrode with an electrolyte film on its surface is obtained.

[0016] In existing technologies, a solid electrolyte layer is coated onto the positive electrode sheet directly. However, due to the evaporation of the solvent in the solid electrolyte layer upon heating, the tension difference on both sides of the positive electrode sheet causes curling, making the industrialization of solid electrolyte layers extremely difficult. By first preparing a release film and then transferring the solid electrolyte layer through the release film, curling on the electrode surface is avoided, resulting in a higher yield.

[0017] The method for preparing the positive electrode of a lithium-ion battery described in this invention yields a positive electrode of a lithium-ion battery with a composite electrolyte membrane. The thickness of the electrolyte membrane on the positive electrode of the lithium-ion battery can reach less than 5 micrometers, and in particular, less than 3 micrometers.

[0018] Preferably, the coating method in step (1) includes coating with a micro-grooved roller.

[0019] The micro-grooved roller coating method described in this invention is a known coating method, similar to a traditional anilox roller. The roller surface of the micro-grooved roller is also engraved with cavities. The size of the cavities is used to control the amount of adhesive transferred from the adhesive tray. Excess material is scraped off by a doctor blade, and the remaining material in the cavities is transferred to the substrate in a certain proportion. The micro-grooved roller coating method of this invention is not particularly limited. As long as the coating requirements are met, any known micro-grooved roller coating method can be used in this invention.

[0020] The micro-concave roller described in this invention can coat a relatively thin electrolyte membrane. However, if the micro-concave roller is used directly to coat the surface of the positive electrode sheet, the interaction between the solid electrolyte membrane and the positive active material on the surface of the battery electrode sheet due to the surface properties of the battery electrode sheet (such as roughness) amplifies the defects in processes such as homogenization and active material coating. The ultra-thin solid electrolyte membrane is not easy to form stably, resulting in a low yield of the positive electrode sheet. Therefore, this invention combines the micro-concave roller with a release film to prepare a lithium-ion battery positive electrode sheet covered with an electrolyte membrane of relatively small thickness and a high yield.

[0021] The volume of the mixture coated by the micro-concave roller in this invention is determined according to the thickness of the electrolyte membrane to be obtained.

[0022] Preferably, the solid electrolyte in step (1) is an inorganic solid electrolyte.

[0023] The inorganic solid electrolyte of the present invention is at least one of oxides, sulfides, halides, and borates. As an illustrative example, oxides include at least one garnet ceramic, LISICON type oxide, NASICON type oxide, or perovskite type ceramic.

[0024] Garnet ceramics are selected from the following components: Li 6.5 La3Zr 1.75 Te 0.25 O 12 Li7La3Zr2O 12 Li 6.2 Ga 0.3 La 2.95 Rb 0.05 Zr2O 12 Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 Li 6.25 Al 0.25 La3Zr2O 12 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 Or Li 6.75 La3Zr 1.75 Nb 0.25 O 12 At least one of them.

[0025] LISICON type oxides are selected from: Li 14 Zn(GeO4)4, Li 3+x (P 1-x Si x O4 or Li 3+x Ge x V 1-x At least one of O4, wherein 0 <x<1。

[0026] NASICON-type oxides are selected from: LiMM′(PO4)3, Li 1+x Al x Ge 2-x (PO4)3(LAGP), Li 1+x Al x Ti 2-x (PO4)3(LATP), Li 1+x Y x Zr 2-x (PO4)3(LYZP), Li 1.3 Al0.3 Ti 1.7 At least one of (PO4)3, LiTi2(PO4)3, LiGeTi(PO4)3, LiGe2(PO4)3 or LiHf2(PO4)3, wherein M and M′ are independently selected from Al, Ge, Ti, Sn, Hf, Zr or La, and 0 ≤ x ≤ 2.

[0027] The perovskite-type ceramic is selected from: Li 3.3 La 0.53 TiO3, LiSr 1.65 Zr 1.3 Ta 1.7 O9, Li 2x-y Sr 1-x Ta y Zr 1-y O3 (where x = 0.75y and 0.60 < y < 0.75), Li 3 / 8 Sr 7 / 16 Nb 3 / 4 Zr 1 / 4 O3 or Li 3x La (2 / 3-x) TiO3 (where 0 < x < 0.25). In one variant, one or more of the oxide-based materials have an ionic conductivity of ≥10 -5 S / cm to ≤10 -1 S / cm; the above oxide solid electrolyte is only a schematic example, and any known type of inorganic solid electrolyte can be used in the present invention without departing from the technical concept of the present invention.

[0028] Preferably, the solvent in step (1) includes any one or a combination of at least two of N-methylpyrrolidone, dimethylacetamide, acetone, N,N-dimethylformamide or dimethyl sulfoxide. For example, it can be a combination of N-methylpyrrolidone and dimethylacetamide, a combination of dimethylacetamide and acetone, a combination of N,N-dimethylformamide and dimethyl sulfoxide, a combination of N-methylpyrrolidone, dimethylacetamide and acetone, or a combination of N-methylpyrrolidone, dimethylacetamide, acetone and N,N-dimethylformamide.

[0029] The solid electrolyte of the present invention is insoluble in the solvent.

[0030] Preferably, the mixture in step (1) further includes a film-forming agent.

[0031] Preferably, the film-forming agent comprises any one or a combination of at least two of sodium alginate, sodium carboxymethyl cellulose, polyvinyl alcohol, gum arabic, starch, sodium silicate, diethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, or dipropylene glycol monoalkyl ether. For example, it may be a combination of sodium alginate and sodium carboxymethyl cellulose, a combination of sodium carboxymethyl cellulose and polyvinyl alcohol, a combination of polyvinyl alcohol and gum arabic, a combination of starch and sodium silicate, a combination of sodium silicate and diethylene glycol monoalkyl ether, a combination of propylene glycol monoalkyl ether and dipropylene glycol monoalkyl ether, a combination of sodium alginate, sodium carboxymethyl cellulose and polyvinyl alcohol, or a combination of sodium alginate, sodium carboxymethyl cellulose, polyvinyl alcohol and gum arabic.

[0032] Preferably, the mass fraction of the film-forming agent is 0.5 to 5 wt%, based on the mass of the mixture, for example, it can be 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, based on the mass of the mixture, the mass fraction of the solid electrolyte in step (1) is 30-50 wt%, for example, it can be 30 wt%, 32 wt%, 35 wt%, 38 wt%, 40 wt%, 42 wt%, 45 wt%, 47 wt%, or 50 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The mass fraction of the solid electrolyte will affect the coating efficiency, the performance of the electrode material, and the capacity retention rate of the battery. When the mass fraction of the solid electrolyte is too low, it is not conducive to coating because the solid content of the mixture is too low, the solvent is difficult to dry, and the coating is uneven. When the mass fraction of the solid electrolyte is too high, the solid content of the coating mixture is too high, which makes coating difficult and easily damages the micro-roller.

[0034] Preferably, the viscosity of the mixture in step (1) is 6000 to 14000 cps, for example, it can be 6000 cps, 7000 cps, 8000 cps, 9000 cps, 10000 cps, 11000 cps, 12000 cps, 13000 cps or 14000 cps, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the coating environment in step (1) is a dew point humidity below -20°C, for example, it can be -21°C, -25°C, -30°C, -35°C, -40°C or -45°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the release film in step (1) includes any one or a combination of at least two of PET film, PE film or OPP film, such as a combination of PET film and PE film, a combination of PE film and OPP film, a combination of ET film and OPP film, or a combination of PET film, PE film and OPP film.

[0037] The adhesive force between the release film and the solid electrolyte material is less than the adhesive force between the solid electrolyte material and the positive electrode active material layer. When the adhesive force between the release film and the solid electrolyte material is less than the adhesive force between the solid electrolyte material and the positive electrode active material layer, the release film can be peeled off from the positive electrode sheet by manual labor or equipment during actual production or use.

[0038] Preferably, the heat treatment in step (1) includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment performed sequentially.

[0039] Preferably, the temperature of the first heat treatment is 70-90°C and the time is 0.5-1h.

[0040] The present invention specifies that the temperature of the first heat treatment is 70 to 90°C, for example, it can be 70°C, 72°C, 75°C, 77°C, 80°C, 82°C, 85°C, 87°C or 90°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] The present invention specifies that the time for the first heat treatment is 30 to 60 minutes, for example, it can be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the temperature of the second heat treatment is 100-120°C and the time is 30-60 min.

[0043] The present invention specifies that the temperature of the second heat treatment is 100 to 120°C, for example, it can be 100°C, 102°C, 105°C, 107°C, 110°C, 112°C, 115°C, 117°C or 120°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] The present invention specifies that the time for the second heat treatment is 30 to 60 minutes, for example, it can be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, the temperature of the third heat treatment is 120–140°C, and the time is 30–60 min.

[0046] The present invention specifies that the temperature of the third heat treatment is 120 to 140°C, for example, it can be 120°C, 122°C, 125°C, 127°C, 130°C, 132°C, 135°C, 137°C or 140°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] The present invention specifies that the time for the third heat treatment is 30 to 60 minutes, for example, it can be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the temperature of the fourth heat treatment is 70–90°C and the time is 30–60 min.

[0049] The present invention specifies that the temperature of the fourth heat treatment is 70 to 90°C, for example, it can be 70°C, 72°C, 75°C, 77°C, 80°C, 82°C, 85°C, 87°C or 90°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] The present invention specifies that the time for the fourth heat treatment is 30 to 60 minutes, for example, it can be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Under the conditions of the first, second, third, and fourth heat treatments of the present invention, the solvent in the solid electrolyte layer coated on the release film evaporates upon heating, and the intermediate film after the solvent evaporates upon heating is in an incompletely dried state; the incompletely dried state refers to the solid electrolyte layer on the surface of the intermediate film exhibiting fluid characteristics under pressure.

[0052] Preferably, step (2) further includes drying between the rolling and the removal of the release film.

[0053] The intermediate film described in this invention is completely dry after drying. After complete drying, the release film is removed, and the electrolyte film that is attached to the surface of the positive electrode of the lithium-ion battery is not easily detached.

[0054] Preferably, step (2) further includes hot rolling between rolling and drying.

[0055] This invention limits the hot rolling temperature to 60–180°C, for example, it can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, or 180°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. When the hot rolling temperature is too low, the solvent cannot be completely removed, resulting in a lower capacity retention rate and lower yield of the battery prepared using the lithium-ion battery positive electrode sheet. When the hot rolling temperature is too high, it can easily lead to damage to the positive electrode layer material, resulting in a lower capacity retention rate of the battery prepared using the lithium-ion battery positive electrode sheet.

[0056] The preferred temperature for hot rolling in this invention is 80 to 120°C, for example, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] Preferably, the intermediate film after hot rolling includes an electrolyte film and a release film. The thickness of the electrolyte film is 0.5 to 3 μm, for example, it can be 0.5 μm, 0.7 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2 μm, 2.2 μm, 2.5 μm, 2.7 μm or 3 μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] This invention does not impose any particular limitations on conventional parameters of the hot rolling process, such as rolling time and rolling pressure. Any hot rolling process obtained by adjusting parameters such as rolling pressure and rolling time using conventional methods without departing from the concept of this invention is within the scope of protection of this invention.

[0059] The solvent in the micro-concave roller of this invention is not completely evaporated during the heat treatment after coating on the micro-concave roller, resulting in an intermediate film in a partially dried state, which can be hot rolled. The adhesion between the fully cured solid electrolyte film and the positive electrode active material layer is poor. Existing research shows that when the solid electrolyte layer is not completely dry, rolling between the solid electrolyte layer and the active material layer is beneficial to improve the adhesion between the two layers. In this invention, room temperature rolling is performed when the solid electrolyte layer is not completely dry to promote the adhesion between the two. The bonded positive electrode semi-finished product is then hot rolled again to remove the remaining solvent. Since the amount of solvent involved in the subsequent hot rolling and baking processes is small, the positive electrode will not curl due to solvent evaporation.

[0060] Preferably, the intermediate film after hot rolling includes an electrolyte film and a release film. The thickness of the electrolyte film is 0.5 to 3 μm, for example, it can be 0.5 μm, 0.7 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2 μm, 2.2 μm, 2.5 μm, 2.7 μm or 3 μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0061] In a second aspect, the present invention provides a positive electrode sheet for a lithium-ion battery, wherein the positive electrode sheet for the lithium-ion battery is obtained by the preparation method described in the first aspect.

[0062] Thirdly, the present invention provides a lithium-ion battery comprising a positive electrode, an electrolyte, and a negative electrode stacked sequentially, wherein the positive electrode comprises the lithium-ion battery positive electrode described in the second aspect.

[0063] The lithium-ion battery described in this invention does not have any special requirements for the selection of the negative electrode. Any known negative electrode can be used in this invention without departing from the technical concept of this invention.

[0064] The electrolyte includes a non-aqueous liquid electrolyte solution and / or a solid electrolyte, wherein the non-aqueous liquid electrolyte solution includes an organic solvent and a lithium salt dissolved in the organic solvent.

[0065] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0066] The method for preparing the positive electrode sheet of a lithium-ion battery according to the present invention yields a positive electrode sheet of a lithium-ion battery with a composite electrolyte membrane. The thickness of the electrolyte membrane on the positive electrode sheet can reach less than 5 micrometers. Since the electrode membrane is rolled after being bonded to the electrode sheet, curling does not occur on the surface of the electrode sheet, resulting in a high yield. After the solvent is heat-treated to obtain an intermediate film, the intermediate film contacts the surface of the electrode sheet, and the solvent does not come into direct contact with the electrode sheet. This reduces the damage of the solvent to the surface of the positive electrode sheet of the lithium-ion battery, and increases the yield of the positive electrode sheet of the lithium-ion battery from 70% to over 95%. The preparation method is simple, low-cost, and suitable for large-scale production. Detailed Implementation

[0067] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0068] In one specific embodiment, the present invention provides a method for preparing a positive electrode sheet for a lithium-ion battery, the method comprising the following steps:

[0069] (1) The mixture is coated onto a release film and heat-treated to obtain an intermediate film; the mixture includes a solvent and a solid electrolyte.

[0070] (2) The intermediate film obtained in step (1) is bonded to the electrode sheet, and the release film is removed after rolling to obtain the positive electrode sheet of the lithium-ion battery; during the rolling process, the rolling temperature is less than 40°C.

[0071] The rolling temperature of the present invention is less than 30°C, and more preferably, the rolling temperature is less than 25°C.

[0072] The present invention has the advantage of coating a micron-level (greater than 500 nm) solid electrolyte layer on the surface of the positive electrode, but an excessively thick solid electrolyte layer reduces the energy density of the battery and reduces the thickness space of the positive electrode active material layer; therefore, it is necessary to develop a positive electrode solid electrolyte layer preparation technology to prepare an ultra-thin solid electrolyte layer.

[0073] This invention first coats a release film to obtain an intermediate film, which then carries a solid electrolyte layer. The intermediate film is then bonded to the positive electrode of a lithium-ion battery. Because the adhesion between the release film and the solid electrolyte material is much less than the adhesion between the solid electrolyte material and the positive electrode active material layer, the release film on the other side can be easily removed after the intermediate film is bonded to the electrode. After removing the release film, a lithium-ion battery positive electrode with an electrolyte film on its surface is obtained.

[0074] The method for preparing the positive electrode of a lithium-ion battery described in this invention yields a positive electrode of a lithium-ion battery with a composite electrolyte membrane. The thickness of the electrolyte membrane on the positive electrode of the lithium-ion battery can reach less than 5 micrometers, and in particular, less than 3 micrometers.

[0075] Existing technologies coat solid electrolyte layers onto positive electrode sheets via direct coating. However, the solvent in the solid electrolyte layer evaporates upon heating, causing tension differences on both sides of the positive electrode sheet and resulting in curling. Therefore, industrializing solid electrolyte layers is extremely difficult. This embodiment prepares a release film first, and then transfers the solid electrolyte layer using the release film, preventing curling on the electrode surface and achieving a higher yield.

[0076] After the solvent is heat-treated to obtain an intermediate film, the intermediate film comes into contact with the electrode surface, and the solvent does not come into direct contact with the electrode. This reduces the damage of the solvent to the surface of the lithium-ion battery positive electrode, and increases the yield of the lithium-ion battery positive electrode from 70% to over 95%. The preparation method is simple, low-cost, and suitable for large-scale production.

[0077] Furthermore, the coating method described in step (1) includes coating using a micro-grooved roller.

[0078] The micro-grooved roller coating method described in this invention is a known coating method, similar to a traditional anilox roller. The roller surface of the micro-grooved roller is also engraved with cavities. The size of the cavities is used to control the amount of adhesive transferred from the adhesive tray. Excess material is scraped off by a doctor blade, and the remaining material in the cavities is transferred to the substrate in a certain proportion. The micro-grooved roller coating method of this invention is not particularly limited. Any known micro-grooved roller coating method can be used in this invention as long as the coating requirements are met.

[0079] The micro-concave roller described in this invention can coat a relatively thin electrolyte membrane. However, if the micro-concave roller is used directly to coat the surface of the positive electrode sheet, the interaction between the solid electrolyte membrane and the positive active material on the surface of the battery electrode sheet due to the surface properties of the battery electrode sheet (such as roughness) amplifies the defects in processes such as homogenization and active material coating. The ultra-thin solid electrolyte membrane is not easy to form stably, resulting in a low yield of the positive electrode sheet. Therefore, this invention combines the micro-concave roller with a release film to prepare a lithium-ion battery positive electrode sheet covered with an electrolyte membrane of relatively small thickness and a high yield.

[0080] The volume of the mixture coated by the micro-concave roller in this invention is determined according to the thickness of the electrolyte membrane to be obtained.

[0081] Furthermore, the solid electrolyte in step (1) is an inorganic solid electrolyte.

[0082] The inorganic solid electrolyte of the present invention is at least one of oxides, sulfides, halides, and borates. As an illustrative example, oxides include at least one garnet ceramic, LISICON type oxide, NASICON type oxide, or perovskite type ceramic.

[0083] Garnet ceramics are selected from the following components: Li 6.5 La3Zr 1.75 Te 0.25 O 12 Li7La3Zr2O 12 Li 6.2 Ga 0.3 La 2.95 Rb 0.05 Zr2O 12 Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 Li 6.25 Al 0.25 La3Zr2O 12 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 Or Li6.75 La3Zr 1.75 Nb 0.25 O 12 at least one of

[0084] The LISICON-type oxide is selected from: Li 14 Zn(GeO4)4, Li 3+x (P 1-x Si x )O4 or Li 3+x Ge x V 1-x O4, where 0 < x < 1.

[0085] The NASICON-type oxide is selected from: LiMM′(PO4)3, Li 1+x Al x Ge 2-x (PO4)3 (LAGP), Li 1+x Al x Ti 2-x (PO4)3 (LATP), Li 1+x Y x Zr 2-x (PO4)3 (LYZP), Li 1.3 Al 0.3 Ti 1.7 (PO4)3, LiTi2(PO4)3, LiGeTi(PO4)3, LiGe2(PO4)3 or LiHf2(PO4)3, where M and M′ are independently selected from Al, Ge, Ti, Sn, Hf, Zr or La, 0 ≤ x ≤ 2.

[0086] The perovskite-type ceramic is selected from: Li 3.3 La 0.53 TiO3, LiSr 1.65 Zr 1.3 Ta 1.7 O9, Li 2x-y Sr 1-x Ta y Zr 1-y O3 (where x = 0.75y and 0.60 < y < 0.75), Li 3 / 8 Sr 7 / 16 Nb 3 / 4 Zr 1 / 4 O"3 or Li 3x La (2 / 3-x) TiO3 (where 0 < x < 0.25). In one variant, one or more oxide-based materials have ≥ 10 -5 S / cm to ≤ 10 -1The ionic conductivity S / cm; the above-mentioned oxide solid electrolyte is merely an illustrative example. Without departing from the technical concept of this invention, any known type of inorganic solid electrolyte can be used in this invention.

[0087] Further, the solvent in step (1) includes any one or a combination of at least two of N-methylpyrrolidone, dimethylacetamide, acetone, N,N-dimethylformamide or dimethyl sulfoxide, for example, a combination of N-methylpyrrolidone and dimethylacetamide, a combination of dimethylacetamide and acetone, a combination of N,N-dimethylformamide and dimethyl sulfoxide, a combination of N-methylpyrrolidone, dimethylacetamide and acetone, or a combination of N-methylpyrrolidone, dimethylacetamide, acetone and N,N-dimethylformamide.

[0088] The solid electrolyte described in this invention is insoluble in solvents.

[0089] Furthermore, the mixture in step (1) also includes a film-forming agent.

[0090] Further, the film-forming agent includes any one or a combination of at least two of sodium alginate, sodium carboxymethyl cellulose, polyvinyl alcohol, gum arabic, starch, sodium silicate, diethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, or dipropylene glycol monoalkyl ether. For example, it can be a combination of sodium alginate and sodium carboxymethyl cellulose, a combination of sodium carboxymethyl cellulose and polyvinyl alcohol, a combination of polyvinyl alcohol and gum arabic, a combination of starch and sodium silicate, a combination of sodium silicate and diethylene glycol monoalkyl ether, a combination of propylene glycol monoalkyl ether and dipropylene glycol monoalkyl ether, a combination of sodium alginate, sodium carboxymethyl cellulose and polyvinyl alcohol, or a combination of sodium alginate, sodium carboxymethyl cellulose, polyvinyl alcohol and gum arabic.

[0091] Furthermore, based on the mass of the mixture, the mass fraction of the film-forming agent in step (1) is 0.5–5 wt%.

[0092] Furthermore, based on the mass of the mixture, the mass fraction of the solid electrolyte in step (1) is 30-50 wt%. The mass fraction of the solid electrolyte will affect the coating efficiency, the performance of the electrode material and the capacity retention rate of the battery. When the mass fraction of the solid electrolyte is too low, it is not conducive to coating because the solid content of the mixture is too low, the solvent is difficult to dry, and the coating is uneven. When the mass fraction of the solid electrolyte is too high, the solid content of the coating mixture is too high, which makes coating difficult and easily damages the micro-roller.

[0093] Further, the viscosity of the mixture in step (1) is 6000 to 14000 cps.

[0094] Furthermore, the coating environment in step (1) is a dew point humidity below -20°C.

[0095] Further, the release film in step (1) includes any one or a combination of at least two of PET film, PE film or OPP film.

[0096] The adhesive force between the release film and the solid electrolyte material is less than the adhesive force between the solid electrolyte material and the positive electrode active material layer. When the adhesive force between the release film and the solid electrolyte material is less than the adhesive force between the solid electrolyte material and the positive electrode active material layer, the release film can be peeled off from the positive electrode sheet by manual labor or equipment during actual production or use.

[0097] Furthermore, the heat treatment in step (1) includes a first heat treatment, a second heat treatment, a third heat treatment, and a fourth heat treatment performed sequentially.

[0098] Furthermore, the temperature of the first heat treatment is 70–90°C, and the time is 0.5–1 hour.

[0099] The present invention specifies that the temperature of the first heat treatment is 70 to 90°C.

[0100] The present invention specifies that the time for the first heat treatment is 30 to 60 minutes.

[0101] Furthermore, the temperature of the second heat treatment is 100–120°C, and the time is 30–60 min.

[0102] Furthermore, the temperature of the third heat treatment is 120–140°C, and the time is 30–60 min.

[0103] The present invention specifies that the temperature of the third heat treatment is 120-140°C.

[0104] The present invention specifies that the time for the third heat treatment is 30 to 60 minutes.

[0105] Furthermore, the temperature of the fourth heat treatment is 70–90°C, and the time is 30–60 min.

[0106] The present invention specifies that the temperature of the fourth heat treatment is 70 to 90°C.

[0107] The present invention specifies that the time for the fourth heat treatment is 30 to 60 minutes.

[0108] Under the conditions of the first, second, third, and fourth heat treatments of the present invention, the solvent in the solid electrolyte layer coated on the release film evaporates upon heating, and the solvent is in an incompletely dried state after evaporation; the incompletely dried state refers to the solid electrolyte layer on the surface of the intermediate film exhibiting fluid characteristics under pressure.

[0109] Preferably, step (2) further includes drying between the rolling and the removal of the release film.

[0110] The intermediate film described in this invention is completely dry after drying. After complete drying, the release film is removed, and the electrolyte film that is attached to the surface of the positive electrode of the lithium-ion battery is not easily detached.

[0111] In another specific embodiment, the process of rolling and drying in step (2) also includes hot rolling.

[0112] This invention limits the hot rolling temperature to 60–180°C. When the hot rolling temperature is too low, the solvent cannot be completely removed, resulting in a lower capacity retention rate and a lower yield of the battery prepared using the lithium-ion battery positive electrode sheet. When the hot rolling temperature is too high, it can easily lead to damage to the positive electrode layer material, resulting in a lower capacity retention rate of the battery prepared using the lithium-ion battery positive electrode sheet.

[0113] The preferred temperature for hot rolling in this invention is 80–120°C.

[0114] Furthermore, the intermediate film after hot rolling includes an electrolyte film and a release film, wherein the thickness of the electrolyte film is 0.5–3 μm.

[0115] This invention does not impose any particular limitations on conventional parameters of the hot rolling process, such as rolling time and rolling pressure. Any hot rolling process obtained by adjusting parameters such as rolling pressure and rolling time using conventional methods without departing from the concept of this invention is within the scope of protection of this invention.

[0116] The solvent in the micro-concave roller of this invention is not completely evaporated during the heat treatment after coating on the micro-concave roller, resulting in an intermediate film in a partially dried state, which can be hot rolled. The adhesion between the fully cured solid electrolyte film and the positive electrode active material layer is poor. Existing research shows that when the solid electrolyte layer is not completely dry, rolling between the solid electrolyte layer and the active material layer is beneficial to improve the adhesion between the two layers. In this invention, room temperature rolling is performed when the solid electrolyte layer is not completely dry to promote the adhesion between the two. The bonded positive electrode semi-finished product is then hot rolled again to remove the remaining solvent. Since the amount of solvent involved in the subsequent hot rolling and baking processes is small, the positive electrode will not curl due to solvent evaporation.

[0117] Further, the intermediate film after hot rolling in step (2) includes an electrolyte film and a release film, wherein the thickness of the electrolyte film is 0.5 to 3 μm.

[0118] In another specific embodiment, the present invention provides a positive electrode sheet for a lithium-ion battery, wherein the positive electrode sheet for the lithium-ion battery is obtained by the preparation method described in the first aspect.

[0119] In addition to a solid electrolyte layer, the positive electrode sheet of the present invention also includes a current collector and a positive electrode active material layer. The positive electrode current collector can be a metal foil, metal mesh or wire mesh, or mesh metal containing aluminum or any other suitable conductive material known to those skilled in the art.

[0120] The positive electrode active material layer is formed of multiple positive electrode active particles comprising one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof. In some embodiments, the positive electrode active material layer further comprises an electrolyte, such as multiple electrolyte particles. The positive electrode active material layer has a thickness of 1 μm to 1000 μm.

[0121] The positive electrode active material is one of the following: layered oxide cathode, spinel cathode, olivine type cathode, and polyanion cathode.

[0122] Layered oxide cathodes are selected from the following components: LiCoO2 (LCO), LiNi x Mn y Co 1-x-y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi 1-x-y Co x Al y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi x Mn 1-x O2 (where 0 ≤ x ≤ 1), and Li 1+ x MO2 (where M is one of Mn, Ni, Co and Al and 0≤x≤1); the spinel cathode is selected from the following compositions: LiMn2O4 (LMO) and LiNi x Mn 1.5 O4; olivine-type cathodes are selected from the following components: LiMPO4 (where M is at least one of Fe, Ni, Co and Mn); polyanion cathodes are selected from the following components: LiV2(PO4)3, silicates (e.g., LiFeSiO4).

[0123] One or more lithium-based positive electrode active materials may optionally be coated (e.g., by LiNbO3 and / or Al2O3). Furthermore, in some embodiments, one or more lithium-based positive electrode active materials may optionally be mixed with one or more conductive materials that provide an electron conduction path and / or at least one polymeric binder material that improves the structural integrity of the positive electrode. For example, the positive electrode active material layer may comprise 30 wt% to 98 wt% of one or more lithium-based positive electrode active materials, 0 wt% to 30 wt% of conductive materials, 0 wt% to 20 wt% of binder, and 1 wt% to 20 wt% of adhesive.

[0124] The positive electrode active material layer can be mixed with any one or a combination of at least two of the following binders: polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, and lithium alginate. The conductive material can include carbon-based materials, powdered nickel, other metal particles, or conductive polymers. Carbon-based materials can include particles of carbon black, graphite, acetylene black (e.g., KETCHENTM black or DENKATM black), carbon fibers, nanotubes, or graphene. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0125] The positive electrode active material layer also contains conductive agents, such as carbon-based materials, powdered nickel, other metal particles, or conductive polymers. Carbon-based materials may include particles such as carbon black, graphite, SuperP, acetylene black (e.g., KETCHENTM black or DENKATM black), carbon fibers and nanotubes, graphene, etc. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4-ethylenedioxythiophene)polysulfonated styrene, etc.

[0126] In another specific embodiment, the present invention provides a lithium-ion battery comprising a positive electrode, an electrolyte, and a negative electrode stacked sequentially, wherein the positive electrode comprises the lithium-ion battery positive electrode described in the second aspect.

[0127] This invention does not have any special requirements for the selection of the negative electrode. Any known negative electrode can be used in this invention without departing from the technical concept of this invention.

[0128] The electrolyte described in this invention can be a non-aqueous liquid electrolyte solution, which may include an organic solvent and a lithium salt dissolved in the organic solvent; on the other hand, the electrolyte can also be a solid electrolyte or a combination of a non-aqueous liquid electrolyte solution and a solid electrolyte.

[0129] Example 1

[0130] This embodiment prepares a positive electrode sheet for a lithium-ion battery. The preparation method includes the following steps:

[0131] (1) In an environment with a dew point humidity of -30℃, the mixture is coated onto a PET film using a micro-concave roller, and then subjected to a first heat treatment at 85℃ for 45 min, a second heat treatment at 115℃ for 50 min, a third heat treatment at 130℃ for 45 min, and a fourth heat treatment at 85℃ for 50 min to obtain an intermediate film in a partially dried state.

[0132] The mixture comprises N-methylpyrrolidone and LLZO (lithium lanthanum zirconium oxide), with LLZO having a mass fraction of 40 wt% and N-methylpyrrolidone having a mass fraction of 60 wt%, and the viscosity of the mixture is 10000 cps.

[0133] (2) The intermediate film obtained in step (1) is bonded to the electrode sheet, rolled at room temperature at 25°C, and then hot rolled at 150°C and dried to remove the PET film, finally obtaining a positive electrode sheet with an LLZO film thickness of 2.4 μm.

[0134] Example 2

[0135] This embodiment provides a method for preparing a positive electrode sheet for a lithium-ion battery, the method comprising the following steps:

[0136] (1) In an environment with a dew point humidity of -25℃, the mixture is coated onto a PE film using a micro-concave roller, and then subjected to a first heat treatment at 80℃ for 50 min, a second heat treatment at 110℃ for 40 min, a third heat treatment at 125℃ for 40 min, and a fourth heat treatment at 80℃ for 45 min to obtain an intermediate film in a partially dried state.

[0137] The mixture comprises dimethylacetamide and LLTO (lithium lanthanum titanium oxide), with LLTO having a mass fraction of 45 wt% and dimethylacetamide having a mass fraction of 55 wt%, and the viscosity of the mixture is 12000 cps.

[0138] (2) The intermediate film obtained in step (1) is bonded to the electrode sheet, rolled at room temperature at 25°C, and then hot rolled at 120°C to remove the PE film, finally obtaining a positive electrode sheet with an LLTO film thickness of 1.2 μm.

[0139] Example 3

[0140] This embodiment provides a method for preparing a positive electrode sheet for a lithium-ion battery, the method comprising the following steps:

[0141] (1) In an environment with a dew point humidity of -32℃, the mixture is coated onto the OPP film using a micro-concave roller, and then subjected to a first heat treatment at 75℃ for 40 min, a second heat treatment at 105℃ for 45 min, a third heat treatment at 135℃ for 50 min, and a fourth heat treatment at 75℃ for 40 min to obtain an intermediate film in a partially dried state.

[0142] The mixture comprises acetone, sodium alginate, and LLZTO (lithium lanthanum zirconium tantalum oxide), with LLZTO having a mass fraction of 35 wt%, acetone having a mass fraction of 63 wt%, sodium alginate having a mass fraction of 2 wt%, and the viscosity of the mixture being 8000 cps.

[0143] (2) The intermediate film obtained in step (1) is bonded to the electrode sheet, rolled at room temperature at 25°C, and then hot rolled at 90°C and dried to remove the OPP film, finally obtaining a positive electrode sheet with a thickness of 1.8 μm of LLZTO film.

[0144] Example 4

[0145] This embodiment prepares a positive electrode sheet for a lithium-ion battery. The preparation method includes the following steps:

[0146] (1) In an environment with a dew point humidity of -30℃, the mixture is coated onto a PET film using a micro-concave roller. The film is then subjected to a first heat treatment at 90℃ for 60 min, a second heat treatment at 120℃ for 60 min, a third heat treatment at 135℃ for 60 min, and a fourth heat treatment at 85℃ for 60 min to obtain an intermediate film that is not completely dried.

[0147] The mixture comprises N-methylpyrrolidone and LLZO (lithium lanthanum zirconium oxide), with LLZO having a mass fraction of 40 wt% and N-methylpyrrolidone having a mass fraction of 60 wt%, and the viscosity of the mixture is 10000 cps.

[0148] (2) The intermediate film obtained in step (1) is bonded to the electrode sheet, and after being rolled at room temperature at 25°C, the PET film is dried to remove the electrode sheet, thus obtaining the positive electrode sheet of the lithium-ion battery. Finally, a lithium-ion battery positive electrode sheet with an LLZO film thickness of 3.1 μm is prepared.

[0149] Comparative Example 1

[0150] This comparative example provides a method for preparing a positive electrode sheet for a lithium-ion battery. Except for the method of coating the mixture onto a PET film by scraping, the method is the same as in Example 1. The thickness of the electrolyte film on the obtained positive electrode sheet for the lithium-ion battery is 11 μm.

[0151] Comparative Example 2

[0152] This comparative example provides a method for preparing a positive electrode sheet for a lithium-ion battery, the method comprising the following steps:

[0153] In an environment with a dew point humidity of -30℃, the mixture is directly coated onto the electrode using a micro-concave roller, and then hot-rolled at 150℃ to obtain a lithium-ion battery positive electrode. The thickness of the electrolyte film on the obtained lithium-ion battery positive electrode is 4.6μm.

[0154] The performance of the lithium-ion battery positive electrode sheets obtained in Examples 1-4 and Comparative Examples 1 and 2 was tested:

[0155] The battery manufacturing method is as follows:

[0156] The composition of the positive electrode active material layer is: 95wt% NCM, 3wt% PVDF, and 2wt% super-P;

[0157] The composition of the negative electrode active material layer is: 95wt% graphite, 3wt% (CMC+SBR), and 2wt% super-P; the preparation of the negative electrode sheet is as follows: the negative electrode active material, conductive agent, and binder are mixed in the above proportions and added to the solvent, coated onto the negative electrode current collector, and dried to obtain the negative electrode sheet.

[0158] The positive electrode, negative electrode, and separator are stacked together, and then sequentially processed through liquid injection, formation, and other steps to finally produce a lithium-ion battery.

[0159] I. Cyclic Performance Testing

[0160] Test temperature: 25℃±2℃;

[0161] Testing process:

[0162] (1) Charge to the termination voltage at 1C or the specified current, cut off current 0.05C, and let stand for 30 minutes;

[0163] (2) Discharge at 1C until the final discharge voltage (2.75V), record the discharge capacity, and let stand for 30 minutes;

[0164] Cycle (1) and (2) to calculate the ratio of the discharge capacity in the 500th cycle to the initial discharge capacity:

[0165] Capacity retention rate (%) = discharge capacity at 500th cycle / initial discharge capacity. The results are shown in Table 1.

[0166] Table 1

[0167] Capacity retention rate (%) Yield rate (%) Example 1 93.6％ 96％ Example 2 93.4％ 95％ Example 3 93.1％ 96％ Example 4 92.5％ 96％ Comparative Example 1 90.2％ 95％ Comparative Example 2 92.6％ 71％

[0168] From Table 1, we can obtain:

[0169] (1) The electrolyte film on the lithium-ion battery positive electrode obtained by the preparation method of lithium-ion battery positive electrode in Examples 1-4 is thinner, and the yield of the prepared positive electrode is high and the battery cycle performance is good. This shows that the preparation method of the present invention can prepare a battery with good morphology and thinner thickness, avoiding the influence of coating solid electrolyte layer on battery performance. At the same time, comparing Examples 1 and 4, it can be seen that by using a two-step rolling method to achieve the composite of solid electrolyte film and electrode in the case of incomplete drying, the solid electrolyte layer and active material layer can be better bonded, thus improving cycle performance.

[0170] (2) Comparing Comparative Example 1 and Example 1, it can be seen that the solid electrolyte membrane prepared by coating the release film with the solid electrolyte layer and the positive electrode active material layer by conventional coating method has a larger thickness, which has a greater negative effect on the battery cycle performance.

[0171] (3) Comparing Comparative Example 2 and Example 1, it can be seen that if a micro-concave roller is used to directly coat the solid electrolyte layer on the surface of the positive electrode active material layer, although the thickness of the solid electrolyte layer can be greatly reduced compared to Comparative Example 1, the solid electrolyte film is too thin and is easy to break on the surface of the positive electrode active material, resulting in a low yield and failing to achieve the thickness of the solid electrolyte layer obtained by the preparation method described in this invention.

[0172] In summary, the method for preparing the positive electrode sheet of a lithium-ion battery according to the present invention yields a positive electrode sheet of a lithium-ion battery with a composite electrolyte membrane. The thickness of the electrolyte layer on the positive electrode sheet can reach less than 5 micrometers, and in particular less than 3 micrometers. The edges of the positive electrode sheet of the lithium-ion battery do not curl, the solvent does not damage the surface of the positive electrode sheet of the lithium-ion battery, and the yield of the positive electrode sheet of the lithium-ion battery is increased from 70% to over 95%. The preparation method is simple, low in cost, and suitable for large-scale production.

[0173] The method for preparing the positive electrode sheet of a lithium-ion battery according to the present invention yields a positive electrode sheet of a lithium-ion battery with a composite electrolyte membrane. The thickness of the electrolyte membrane on the positive electrode sheet can reach less than 5 micrometers. Since the electrode film is hot-rolled and bonded to the electrode sheet, curling does not occur on the surface of the electrode sheet, resulting in a high yield. After the solvent is heat-treated to obtain an intermediate film, the intermediate film contacts the surface of the electrode sheet, and the solvent does not directly contact the electrode sheet. This reduces the damage of the solvent to the surface of the positive electrode sheet of the lithium-ion battery, increasing the yield of the positive electrode sheet of the lithium-ion battery from 70% to over 95%. The preparation method is simple, low-cost, and suitable for large-scale production.

[0174] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode sheet for a lithium-ion battery, characterized in that, The preparation method includes the following steps: (1) The mixture is coated onto a release film and then heat-treated to obtain an intermediate film; the mixture includes a solvent and a solid electrolyte; (2) The intermediate film obtained in step (1) is bonded to the electrode sheet, and the release film is removed after rolling to obtain the positive electrode sheet of the lithium-ion battery; the rolling temperature is below 40°C. The coating method described in step (1) includes coating using a micro-grooved roller; The heat treatment in step (1) includes a first heat treatment, a second heat treatment, a third heat treatment and a fourth heat treatment performed sequentially; The temperature of the first heat treatment is 70~90℃, and the time is 30~60min; The second heat treatment is performed at a temperature of 100~120℃ for a time of 30~60 minutes. The third heat treatment is performed at a temperature of 120~140℃ for a time of 30~60 min; The fourth heat treatment is performed at a temperature of 70~90℃ for a time of 30~60min; Under the conditions of the first heat treatment, the second heat treatment, the third heat treatment, and the fourth heat treatment, the solvent in the solid electrolyte layer coated on the release film evaporates upon heating, and the intermediate film after the solvent evaporates upon heating is in an incompletely dry state; the incompletely dry state refers to the solid electrolyte layer on the surface of the intermediate film exhibiting fluid characteristics under pressure.

2. The preparation method according to claim 1, characterized in that, The solid electrolyte in step (1) is an inorganic solid electrolyte.

3. The preparation method according to claim 1, characterized in that, The solvent in step (1) includes any one or a combination of at least two of N-methylpyrrolidone, dimethylacetamide, acetone, N,N-dimethylformamide or dimethyl sulfoxide.

4. The preparation method according to claim 1, characterized in that, The mixture in step (1) also includes a film-forming agent.

5. The preparation method according to claim 4, characterized in that, The film-forming agent includes any one or a combination of at least two of sodium alginate, sodium carboxymethyl cellulose, polyvinyl alcohol, gum arabic, starch, sodium silicate, diethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, or dipropylene glycol monoalkyl ether.

6. The preparation method according to claim 4 or 5, characterized in that, Based on the mass of the mixture, the mass fraction of the film-forming agent is 0.5~5wt%.

7. The preparation method according to claim 1, characterized in that, Based on the mass of the mixture, the mass fraction of the solid electrolyte in step (1) is 30~50 wt%.

8. The preparation method according to claim 1, characterized in that, The viscosity of the mixture in step (1) is 6000~14000 cps.

9. The preparation method according to claim 1, characterized in that, The coating environment in step (1) is a dew point humidity below -20°C.

10. The preparation method according to claim 1, characterized in that, The release film in step (1) includes any one or a combination of at least two of PET film, PE film or OPP film.

11. The preparation method according to claim 1, characterized in that, Step (2) also includes drying between the rolling and the removal of the release film.

12. The preparation method according to claim 11, characterized in that, Step (2) also includes hot rolling between rolling and drying.

13. The preparation method according to claim 12, characterized in that, The temperature of the hot roller pressing is 60~180℃.

14. The preparation method according to claim 13, characterized in that, The temperature of the hot roller pressing is 80~120℃.

15. The preparation method according to any one of claims 12 to 14, characterized in that, The intermediate film after hot rolling includes an electrolyte film and a release film, and the thickness of the electrolyte film is 0.5~3μm.

16. A positive electrode sheet for a lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery is obtained by the preparation method according to any one of claims 1-15.

17. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, an electrolyte, and a negative electrode stacked sequentially, wherein the positive electrode includes the lithium-ion battery positive electrode as described in claim 16.