Positive electrode sheet, solid-state battery containing same, and preparation method

Abstract

The present invention provides a positive electrode plate, a solid-state battery containing the same, and a preparation method. The positive electrode plate includes a positive electrode current collector, a first coating layer and a second coating layer, wherein the first coating layer is on the surface of the positive electrode current collector, and the materials of the first coating layer include a positive electrode material, a conductive agent, a binder and a gel polymer; the second coating layer is on a surface of the first coating layer away from the positive electrode current collector, and the materials of the second coating layer include a positive electrode material, a conductive agent, a binder and an oxide solid electrolyte. The positive electrode plate of the present application constructs a multilayer electrode, which can increase the lithium ion current density close to the current collector side; the oxide solid electrolyte in the second coating layer can bidirectionally regulate the lithium ion current density and the electron current density. The construction of the ion channel and the electron channel by the first coating layer and the second coating layer containing specific components can significantly improve the electrical performance of the battery. At the same time, the positive electrode plate of the present application can also significantly improve the safety of the battery.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a positive electrode plate, a solid-state battery containing the same, and a preparation method thereof. Background Art

[0002] Currently, batteries are widely used in mobile electronic devices, electric vehicles, and energy storage devices. In the field of mobile electronic devices, such as smartphones, tablets, and laptops, batteries are widely used as a power source for electric vehicles; in the field of energy storage devices, batteries are used to store renewable energy such as solar and wind energy.

[0003] With the rapid growth of the electric vehicle and energy storage equipment markets, the demand for batteries is also increasing. At the same time, with the advancement of technology, the energy density and cycle life of batteries are constantly improving, and with the continuous reduction of their costs, their application in various fields is becoming more and more extensive.

[0004] However, batteries have limited energy density, relatively small capacity, and some safety risks, which restrict their application. At the same time, some new battery technologies are under development, such as solid-state batteries, which are expected to further promote the development of batteries.

[0005] Semi-solid-state batteries use solid or semi-solid electrolytes, which are safer than traditional liquid batteries and less prone to thermal runaway or explosion. The electrolytes are more stable, extending the battery's cycle life and service life. Furthermore, the production process is more mature than that of all-solid-state batteries.

[0006] How to develop semi-solid-state batteries with higher electrical and safety performance is of great significance to meeting the current market demand for high energy density and high safety batteries. Summary of the Invention

[0007] The main purpose of the present invention is to provide a positive electrode plate, a solid-state battery containing the same and a preparation method, so as to solve the problem of how to further improve the safety and electrical performance of the battery in the prior art.

[0008] In order to achieve the above-mentioned object, according to one aspect of the present invention, a positive electrode plate is provided, which includes a positive electrode collector, a first coating layer and a second coating layer, wherein the first coating layer is on the surface of the positive electrode collector, and the materials of the first coating layer include a positive electrode material, a conductive agent, a binder and a gel polymer; the second coating layer is on a surface of the first coating layer away from the positive electrode collector, and the materials of the second coating layer include a positive electrode material, a conductive agent, a binder and an oxide solid electrolyte.

[0009] Furthermore, the gel-state polymer is formed by in-situ polymerization of monomers under the action of an initiator and a cross-linking agent;

[0010] The monomers include any one or more of vinyl acetate, dimethyl allyl dicarboxylate, diethyl allyl malonate, methallyl carbonate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, methyl methacrylate, butyl methacrylate, vinylene carbonate, vinyl ethylene carbonate, methyl vinyl sulfone, ethyl vinyl sulfone, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate;

[0011] The initiator includes any one or more of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, stannous octoate, lithium acetate, triethyl phosphine, triphenyl phosphine, tri-n-butyl phosphine, tributyltin oxide, tetrabutyl titanate, tetrabutyl zirconate, trialkyltin alkoxide, dialkyltin oxide, N-methylethylenediamine, dimethylformamide, triethyleneethylenediamine, methyldiethylene glycolamine, triethylenediamine, aluminum trifluoromethanesulfonate, magnesium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and tin trifluoromethanesulfonate;

[0012] The crosslinking agent includes any one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, methyl formate and polyether acrylate.

[0013] Furthermore, the oxide solid electrolyte includes any one or more of a NASICON solid electrolyte, a perovskite solid electrolyte, a LISICON solid electrolyte, and a garnet solid electrolyte.

[0014] Furthermore, the mass ratio of the conductive agent to the positive electrode material in the first coating layer is m1, and the mass ratio of the conductive agent to the positive electrode material in the second coating layer is m2, wherein m1 is smaller than m2.

[0015] Furthermore, in the first coating layer, the mass ratio of the positive electrode material, the conductive agent, and the binder is (93-97.5):(1-2.8):(0.5-1.2);

[0016] In the second coating, the mass ratio of the positive electrode material, the conductive agent, the binder and the oxide solid electrolyte is: (93-97.5):(1.5-3.8):(0.5-1.2):(0.5-2).

[0017] Furthermore, the total thickness of the first coating layer and the second coating layer on the same side of the positive electrode current collector is 50-90 μm;

[0018] The absolute value of the difference between the thickness of the first coating layer and the thickness of the second coating layer on the same side of the positive electrode current collector is 0-15 μm.

[0019] In order to achieve the above-mentioned object, according to one aspect of the present invention, a solid-state battery is provided, comprising a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet is any one of the positive electrode sheets mentioned above.

[0020] According to another aspect of the present application, a preparation method for the above-mentioned solid-state battery is provided, which comprises: mixing a positive electrode material, a conductive agent, a binder and a monomer to obtain a first coating slurry; mixing a positive electrode material, a conductive agent, a binder and an oxide solid electrolyte to obtain a second coating slurry; arranging the first coating slurry and the second coating slurry on the surface of the positive electrode collector to form a first coating layer and a second coating layer, respectively, to obtain a prefabricated positive electrode sheet; making the prefabricated positive electrode sheet, the separator and the negative electrode sheet into a battery cell; injecting an electrolyte precursor solution into the battery cell, sealing, aging, thermally polymerizing, and standing to obtain a solid-state battery; wherein the electrolyte precursor solution comprises a solvent, a lithium salt, an additive, an initiator and a cross-linking agent.

[0021] Furthermore, the content of the initiator in the electrolyte precursor is 2-10 wt %, and the content of the cross-linking agent in the electrolyte precursor solution is 0.5-2 wt %.

[0022] Furthermore, in the first coating slurry, the mass ratio of the positive electrode material, the conductive agent, the binder, and the monomer is: (93-97.5): (1-2.8): (0.5-1.2): (1-3).

[0023] Furthermore, the temperature of the thermal polymerization is 40° C.-80° C., and preferably, the time of the thermal polymerization is 3 h to 24 h.

[0024] By applying the technical solution of the present invention, the positive electrode sheet of the present application constructs a multilayer electrode, wherein the first coating layer adjacent to the current collector contains a gel-state polymer that effectively regulates lithium ion transmission, avoiding the problem of conventional liquid lithium-ion batteries where the electrolyte near the current collector is easily consumed, resulting in a weakened transmission power that affects ion transmission, thereby increasing the lithium ion current density near the current collector. Furthermore, the oxide solid electrolyte in the second coating layer can bidirectionally regulate the lithium ion current density and the electron current density. By constructing the ion channel and the electron channel through the first coating layer and the second coating layer containing specific components, the electrical performance of the battery can be significantly improved. At the same time, the positive electrode sheet of the present application can also significantly improve the safety of the battery. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0026] As analyzed in the background technology of this application, the demand for battery safety and electrical performance in the prior art is increasing. In order to solve this problem, this application provides a positive electrode plate, a solid-state battery containing the same, and a preparation method.

[0027] According to a typical embodiment of the present application, a positive electrode plate is provided, which includes a positive electrode collector, a first coating and a second coating, wherein the first coating is on the surface of the positive electrode collector, and the materials of the first coating include positive electrode material, a conductive agent, a binder and a gel polymer; the second coating is on a surface of the first coating away from the positive electrode collector, and the materials of the second coating include positive electrode material, a conductive agent, a binder and an oxide solid electrolyte.

[0028] Because the amount of lithium ion transmission (or lithium ion current density, electrolyte current density) decreases from the separator to the current collector, while the amount of electron transmission (or electron current density, electrode current density) increases, the lithium ion current density is highest at the separator and lowest at the electron current density; the lithium ion current density is lowest at the interface between the active coating and the current collector, while the electron current density is highest. Based on the above principles, the positive electrode plate of the present application constructs a multilayer electrode. The first coating layer adjacent to the current collector contains a gel-like polymer that effectively regulates lithium ion transmission, avoiding the weakening of transmission power caused by the easy consumption of electrolyte near the current collector in conventional liquid lithium-ion batteries, thereby increasing the lithium ion current density near the current collector. Furthermore, the oxide solid electrolyte in the second coating layer can bidirectionally regulate the lithium ion current density and the electron current density. By constructing ion and electron channels through the first and second coating layers containing specific components, the battery's electrical performance can be significantly improved. At the same time, the positive electrode plate of the present application can also significantly enhance battery safety.

[0029] The aforementioned gel-state polymer can be selected from existing technologies. In some typical embodiments of the present application, the aforementioned gel-state polymer is formed by in-situ polymerization of monomers under the action of an initiator and a cross-linking agent. The gel-state polymer obtained by in-situ polymerization is more evenly distributed in the first coating layer, which can better exert the function of the gel-state polymer and further improve the safety and electrical performance of the battery.

[0030] In some preferred embodiments of the present application, the above monomers include any one or more of vinyl acetate, dimethyl allyl dicarboxylate, diethyl allyl malonate, methyl allyl carbonate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, methyl methacrylate, butyl methacrylate, vinylene carbonate, ethylene vinylene carbonate, methyl vinyl sulfone, ethyl vinyl sulfone, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate, which is beneficial to further improve the current density in the first coating of the positive electrode sheet, the formed polymer has better weather resistance, and further improves the safety of the battery containing the positive electrode sheet.

[0031] The initiator and crosslinking agent for the above in-situ polymerization can be selected from the prior art. Considering the convenience of preparing the positive electrode sheet and the safety of the sheet, preferably, the initiator includes any one or more of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, stannous octoate, lithium acetate, triethyl phosphine, triphenyl phosphine, tri-n-butyl phosphine, tributyltin oxide, tetrabutyl titanate, tetrabutyl zirconate, trialkyltin alkoxide, dialkyltin oxide, N-methylethylenediamine, dimethylformamide, triethylenediamine, methyldiethylene glycolamine, triethylenediamine, aluminum trifluoromethanesulfonate, magnesium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and tin trifluoromethanesulfonate; preferably, the crosslinking agent includes any one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, methyl formate, and polyether acrylate; which is beneficial to further improve the safety and electrical performance of the battery.

[0032] The oxide solid electrolyte in the above second coating can be selected from the prior art. In some preferred embodiments of the present application, the oxide solid electrolyte includes any one or more of NASICON-type solid electrolyte, perovskite-type solid electrolyte, LISICON-type solid electrolyte, and garnet-type solid electrolyte.

[0033] Preferably, the molecular formula of the above NASICON-type solid electrolyte is Li 1+x Ti 2-x M x (PO4)3 or Li 1+x Ge 2-x M x (PO4)3, where 0.1 < x < 0.7, and M includes at least one of Al, Ga, In, and Sc; preferably, the molecular formula of the above perovskite-type solid electrolyte is Li 3yLa (2 / 3)-y TiO3, where 0 < y < 0.16; Preferably, the molecular formula of the above LISICON-type solid electrolyte is Li 14 ZnGe4O 16 ; Preferably, the molecular formula of the above garnet-type solid electrolyte is Li5La3M2O 12 or Li7La3Zr2O 12 , where M includes at least one of Ta and Nb.

[0034] In some preferred embodiments of the present application, the particle size D50 of the oxide solid electrolyte is 100 nm - 2 μm, and more preferably 200 nm - 600 nm, which helps the oxide electrolyte to better exert its performance.

[0035] The cathode materials, conductive agents, and binders in the above first coating and second coating can all be selected from the prior art, and there are no special requirements in the present application, so no detailed introduction will be given here one by one.

[0036] As an example, the binder can be any one of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyimide (PI), polytetrafluoroethylene (PTFE), and polystyrene (PS).

[0037] As an example, the conductive agents in the first coating and the second coating independently include any one or more of conductive carbon black, carbon nanotubes, and superconducting carbon. In some preferred embodiments of the present application, the conductive agents in the first coating and the second coating independently are any one or more of conductive carbon black and carbon nanotubes. In particular, the composite use of conductive carbon black and carbon nanotubes can better exert the synergistic effect of the first coating and the second coating, and increase the safety of the battery.

[0038] In some typical embodiments of the present application, in order to further improve the performance of the cathode electrode sheet, the mass ratio of the conductive agent to the cathode material in the above first coating is m1, and the mass ratio of the conductive agent to the cathode material in the second coating is m2, where m1 is less than m2. By increasing the mass ratio of the conductive agent in the second coating relative to the cathode active material, the electron current density of the second coating is increased, thereby improving the safety and electrical performance of the battery containing the cathode electrode sheet. )

[0039] In some embodiments of the present application, in order to better exert the synergistic effect of the components in the first coating and at the same time increase the lithium ion current density in the first coating, the mass ratio of the cathode material, conductive agent, and binder in the first coating is (93 - 97.5):(1 - 2.8):(0.5 - 1.5), preferably (93 - 97.5):(1 - 2.8):(0.5 - 1.2).

[0040] In some embodiments of the present application, in order to better exert the synergistic effect of the components in the second coating and at the same time increase the electron current density in the second coating, the mass ratio of the positive electrode material, the conductive agent, the binder and the oxide solid electrolyte in the second coating is (93-97.5):(1.5-3.8):(0.5-1.2):(0.5-2).

[0041] In some typical embodiments of the present application, the total thickness of the first coating layer and the second coating layer on the same side of the positive electrode current collector is 50-90 μm, and the positive electrode sheet has good comprehensive performance.

[0042] In some preferred embodiments of the present application, the absolute value of the difference between the thickness of the first coating layer and the thickness of the second coating layer on the same side of the positive electrode current collector is 0-15 um.

[0043] Since the lithium ion current density is usually the largest and the electron current density is the smallest at the diaphragm; the lithium ion current density is the smallest and the electron current density is the largest at the interface between the active coating and the current collector, the electron current density and the ion current density tend to decrease or increase in a gradient between the current collector and the diaphragm. Controlling the difference in thickness of the first coating and the second coating on the same side of the positive electrode current collector within the above range can more effectively prevent rapid performance degradation caused by excessive reduction in current density.

[0044] According to another typical embodiment of the present application, a solid-state battery is provided, which includes a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet is any one of the positive electrode sheets mentioned above.

[0045] Because the aforementioned positive electrode sheet constructs a multilayer electrode, the first coating layer adjacent to the current collector contains a gel-like polymer, significantly increasing the lithium ion current density near the current collector. Furthermore, the oxide solid electrolyte in the second coating layer can bidirectionally regulate the lithium ion current density and the electron current density. By constructing ion and electron channels through the first and second coating layers containing specific components, the battery's electrical performance can be significantly improved. Furthermore, compared to ordinary lithium-ion batteries, the safety of solid-state batteries containing the aforementioned positive electrode sheet has also been significantly improved.

[0046] The solid electrolyte and negative electrode plate in the above-mentioned solid-state battery can be selected from the existing technology. There are no special requirements for this application and they will not be introduced in detail here.

[0047] According to another typical embodiment of the present application, a preparation method of the above-mentioned solid-state battery is provided, which comprises: mixing a positive electrode material, a conductive agent, a binder and a monomer to obtain a first coating slurry; mixing a positive electrode material, a conductive agent, a binder and an oxide solid electrolyte to obtain a second coating slurry; arranging the first coating slurry and the second coating slurry on the surface of the positive electrode collector to form a first coating and a second coating, respectively, to obtain a prefabricated positive electrode sheet; making the prefabricated positive electrode sheet, the separator and the negative electrode sheet into a battery cell; injecting an electrolyte precursor solution into the battery cell, sealing, aging, thermally polymerizing, and standing to obtain a solid-state battery; wherein the electrolyte precursor solution comprises a solvent, a lithium salt, an additive, an initiator and a cross-linking agent.

[0048] During the solid-state battery preparation process using the aforementioned method, an initiator and a crosslinker are placed in an electrolyte precursor solution. After the electrolyte precursor solution is injected, it polymerizes with the monomers in the first coating layer, facilitating the construction of ion and electron channels in the first and second coating layers. Because the positive electrode sheet prepared using this method forms a multilayer electrode, the first coating layer adjacent to the current collector contains a gel-like polymer, significantly increasing the lithium ion current density near the current collector. Furthermore, the oxide solid electrolyte in the second coating layer can bidirectionally regulate the lithium ion current density and the electron current density, significantly improving the battery's electrical performance.

[0049] In the above preparation method, the first coating slurry is used to prepare the first coating layer of the prefabricated positive electrode sheet, and the second coating slurry is used to prepare the second coating layer of the prefabricated positive electrode sheet. The components of the first coating slurry and the second coating slurry can be determined according to the above introduction to the positive electrode sheet and mixed in the corresponding proportions. In some typical embodiments of the present application, in the first coating slurry, the mass ratio of the positive electrode material, the conductive agent, the binder and the monomer is (93-97.5):(1-2.8):(0.5-1.5):(1-3), preferably (93-97.5):(1-2.8):(0.5-1.2):(1-3).

[0050] The method for setting the above-mentioned first coating slurry and second coating slurry can be selected from the existing technology, such as coating the two slurries simultaneously through a double-layer coating machine to obtain a double-layer composite positive electrode sheet, or using an ordinary conventional coating machine to coat them twice.

[0051] In some preferred embodiments of the present application, the content of the initiator in the electrolyte precursor solution is 2~10wt%, and preferably, the content of the cross-linking agent in the electrolyte precursor is 0.5~2wt%, which can not only fully polymerize the monomer to obtain a gel polymer with a suitable molecular weight, but also does not affect the performance of the electrolyte, which is beneficial to further improve the safety and electrical performance of the battery.

[0052] The solvent and lithium salt in the electrolyte precursor solution can be selected from the prior art. Preferably, the solvent includes any one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methylpropyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, propyl acetate, γ-butyrolactone, fluoroethylene carbonate, fluoropropylene carbonate, 4-trifluoromethylethylene carbonate, methyl trifluoroethyl carbonate and bistrifluoroethyl carbonate. Preferably, the lithium salt includes any one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium nitrate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium tetrafluoroborate, bisfluorosulfonyl imide lithium salt and bisfluorosulfonyl imide lithium.

[0053] The additive in the electrolyte precursor solution includes at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), propane sultone (PS), DTD, LIBOB, and LIDFOB.

[0054] Those skilled in the art can select the above-mentioned separator or negative electrode plate from the existing technology, or prepare it according to the method in the existing technology. This application is not limited to this and will not be described in detail here.

[0055] In some preferred embodiments of the present application, the thermal polymerization temperature is 40°C-80°C, and the thermal polymerization time is preferably 3 hours to 24 hours. Preferably, the aging temperature is 35°C-50°C, and the time is 3 hours to 12 hours; preferably, the static temperature is 35°C-50°C, and the time is 5 hours to 24 hours.

[0056] The following examples and comparative examples will further illustrate the beneficial effects that can be achieved by the present application.

[0057] Example 1

[0058] Provided is a method for preparing a semi-solid lithium-ion battery, the battery comprising a positive electrode, a negative electrode, and an electrolyte;

[0059] The preparation method of the prefabricated positive electrode sheet is as follows: the preparation method of the positive electrode slurry close to the current collector side is as follows: the NCM811 positive electrode active material, the conductive agent carbon black (sp), the conductive agent carbon nanotubes, the binder polyvinylidene fluoride, and the monomer-dimethyl allyl dicarboxylate are mixed in a mass ratio of 93.5:1.5:0.5:0.9:2.7 (ie, m1 is 0.021), and then dissolved in NMP and mixed evenly to form a positive electrode slurry, that is, the first coating slurry; the preparation method of the positive electrode slurry away from the current collector side is as follows: the NCM811 positive electrode active material, the conductive agent carbon black (sp), the conductive agent carbon nanotubes, the binder polyvinylidene fluoride, and the oxide solid electrolyte LATP (Beiterry New Materials Group Co., Ltd., BEO-1P, particle size D50 is 200nm) are mixed in a mass ratio of 94.2 :2:1:0.9:1 mix (i.e. m2 is 0.031), and then dissolve it in NMP to evenly form a positive electrode slurry, i.e. the second coating slurry; apply the above on one side of the current collector aluminum foil (wherein the first coating slurry is applied on the surface of the current collector to form a first coating; the second coating slurry is applied on a surface of the first coating away from the positive electrode current collector to form a second coating), after drying and rolling at 110°C, the positive electrode slurry is applied and dried on the other side of the aluminum foil according to the above method, and then the prepared aluminum foil with a positive electrode active material layer on both sides is roll-pressed; after trimming and cutting, a lithium-ion battery positive electrode sheet is made; wherein the thickness of the single-side first coating close to the current collector side is 37.5μm: the thickness of the single-side second coating away from the current collector side is 37.5μm;

[0060] The negative electrode sheet preparation method includes the following steps: a silicon-carbon negative electrode active material (Lanxi Zhide New Energy Materials Co., Ltd., model S0332), a conductive agent superconducting carbon, a binder polyacrylic acid, and a binder styrene-butadiene rubber are mixed in a mass ratio of 94:1.5:3.0:1.5, and then dissolved in water to form a negative electrode slurry. The mixture is then coated on a current collector copper foil and dried at 105°C for winding. The negative electrode slurry is then coated and dried on the other side of the copper foil according to the above method. The prepared copper foil with the negative electrode active material layer on both sides is then roll-pressed to obtain a negative electrode sheet.

[0061] A 9 μm thick polyethylene porous film was selected as the separator. The positive electrode sheet, separator, and negative electrode sheet were wound into a battery cell with a capacity of approximately 10 Ah. The separator was located between adjacent positive and negative electrode sheets. The positive electrode was spot-welded with an aluminum tab, and the negative electrode was spot-welded with a nickel tab.

[0062] Prepare an electrolyte precursor solution: Azobisisobutyronitrile (ABI) and polyethylene glycol diacrylate (PEGDA) as a crosslinker are stirred for 4 hours and then added to a solvent (the solvent formula is a mixed solution of propylene carbonate (PC): ethylene carbonate (EC): dimethyl carbonate (DMC) with a volume ratio of 1:1:1). 15 wt% lithium hexafluorophosphate (LiPF6) and 7.5 wt% FEC additive are then added and stirred thoroughly. The electrolyte precursor solution contains 5 wt% of the reaction initiator and 1.2 wt% of the crosslinker.

[0063] The battery cell obtained in the above steps is placed in an aluminum-plastic packaging bag, baked, injected with the above electrolyte precursor solution, sealed, formed, aged at 50°C for 8 hours, heated to 60°C for thermal polymerization for 6 hours, cooled to 50°C and allowed to stand for 24 hours to obtain a semi-solid lithium-ion battery.

[0064] Example 2

[0065] Provided is a method for preparing a semi-solid lithium-ion battery, the battery comprising a positive electrode, a negative electrode, and an electrolyte.

[0066] The preparation method of the prefabricated positive electrode sheet is as follows: the preparation method of the positive electrode slurry close to the current collector side is as follows: NCM811 positive electrode active material, conductive agent carbon black (sp), conductive agent carbon nanotubes, binder polyvinylidene fluoride, monomer-vinylene carbonate (VC) are mixed in a mass ratio of 95:0.5:0.5:0.5:1 (i.e., m1 is 0.01), and then dissolved in NMP and mixed evenly to form a positive electrode slurry, i.e., the first coating slurry; the preparation method of the positive electrode slurry away from the current collector side is as follows: NCM811 positive electrode active material, conductive agent carbon black (sp), conductive agent carbon nanotubes, binder polyvinylidene fluoride, oxide solid electrolyte LLTO (LanGu New Energy Technology Co., Ltd., LG1522 , particle size D50 is 200nm) are mixed in a mass ratio of 93:1:1:0.5:0.7 (i.e., m2 is 0.021) to uniformly form a positive electrode slurry, i.e., a second coating slurry; the above-mentioned slurry is coated on one side of the current collector aluminum foil (wherein, the first coating slurry is coated on the surface of the current collector to form a first coating; the second coating slurry is coated on a surface of the first coating away from the positive electrode current collector to form a second coating), after drying and rolling at 110°C, the positive electrode slurry is coated and dried on the other side of the aluminum foil according to the above method, and then the prepared aluminum foil with a positive electrode active material layer on both sides is cold pressed; after trimming and cutting, a lithium-ion battery positive electrode sheet is made; wherein the thickness of the single-side first coating close to the current collector side is 37.5μm: the thickness of the single-side second coating away from the current collector side is 25.5μm.

[0067] The negative electrode sheet preparation method is exactly the same as that in Example 1, and the same separator as in Example 1 is selected to prepare the battery cell using the same process.

[0068] Prepare an electrolyte precursor solution: Azobisisobutyronitrile (ABI) and trimethylolpropane trimethacrylate (TMP) as a reaction initiator are stirred for 4 hours and then added to a solvent (the solvent formula is a mixed solution of propylene carbonate (PC): ethylene carbonate (EC): dimethyl carbonate (DMC) in a volume ratio of 1:1:1). 15 wt% lithium hexafluorophosphate (LiPF6) and 7.5 wt% FEC additive are then added and stirred thoroughly. The electrolyte precursor solution contains 10 wt% of the reaction initiator and 2 wt% of the crosslinker.

[0069] The battery cell obtained in the above steps is placed in an aluminum-plastic packaging bag, baked, injected with the above electrolyte precursor solution, sealed, formed, aged at 50°C for 24 hours, thermally polymerized at 45°C for 12 hours, and allowed to stand at 50°C for 24 hours to obtain the semi-solid lithium ion battery.

[0070] Example 3

[0071] Provided is a method for preparing a semi-solid lithium-ion battery, the battery comprising a positive electrode, a negative electrode, and an electrolyte.

[0072] The preparation method of the prefabricated positive electrode sheet is as follows: the preparation method of the positive electrode slurry close to the current collector side is as follows: NCM811 positive electrode active material, conductive agent carbon black (sp), conductive agent carbon nanotubes, binder polyvinylidene fluoride, and monomer pentaerythritol triacrylate are mixed in a mass ratio of 97:1.5:0.7:1.2:2 (i.e., m1 is 0.02), and then dissolved in NMP and mixed evenly to form a positive electrode slurry, i.e., the first coating slurry; the preparation method of the positive electrode slurry away from the current collector side is as follows: NCM811 positive electrode active material, conductive agent carbon black (sp), conductive agent carbon nanotubes, binder polyvinylidene fluoride, oxide solid electrolyte LLTO (LanGu New Energy Technology Co., Ltd., LG1522 , particle size D50 is 200nm) are mixed in a mass ratio of 97:2:1.5:1.2:1.8 (i.e., m2 is 0.036) to uniformly form a positive electrode slurry, i.e., a second coating slurry; the above-mentioned slurry is coated on one side of the current collector aluminum foil (wherein, the first coating slurry is coated on the surface of the current collector to form a first coating; the second coating slurry is coated on a surface of the first coating away from the positive electrode current collector to form a second coating), after drying and rolling at 110°C, the positive electrode slurry is coated and dried on the other side of the aluminum foil according to the above method, and then the prepared aluminum foil with a positive electrode active material layer on both sides is cold pressed; after trimming and cutting, a lithium-ion battery positive electrode sheet is made; wherein the thickness of the single-side first coating close to the current collector side is 37μm: the thickness of the single-side second coating away from the current collector side is 30μm.

[0073] The negative electrode sheet preparation method is exactly the same as that in Example 1, and the same separator as in Example 1 is selected to prepare the battery cell using the same process.

[0074] Prepare an electrolyte precursor solution: A reaction initiator, aluminum trifluoromethanesulfonate (Al(OTf)3), and a cross-linker, methyl formate, are stirred for 4 hours and then added to a solvent (the solvent formula is a mixed solution of propylene carbonate (PC): ethylene carbonate (EC): dimethyl carbonate (DMC) with a volume ratio of 1:1:1). 15 wt% lithium hexafluorophosphate (LiPF6) and 7.5 wt% FEC additive are then added and stirred thoroughly. The electrolyte precursor solution contains 2 wt% of the reaction initiator and 0.5 wt% of the cross-linker.

[0075] The battery cell obtained in the above steps is placed in an aluminum-plastic packaging bag, baked, injected with the above electrolyte precursor solution, sealed, formed, aged at 50°C for 8 hours, heated to 80°C for thermal polymerization for 4 hours, cooled to 50°C and allowed to stand for 24 hours to obtain the semi-solid lithium-ion battery.

[0076] Example 4

[0077] The only difference between this embodiment and embodiment 1 is that the thickness of the single-side first coating layer close to the current collector side is 37.5 μm, and the thickness of the single-side second coating layer away from the current collector side is 54.5 μm (that is, the difference between the thickness of the first coating layer and the thickness of the second coating layer on the same side of the positive electrode current collector is greater than 15 μm).

[0078] Example 5

[0079] The only difference from Example 1 is that in the first coating, the NCM811 positive electrode active material, the conductive agent carbon black (sp), the conductive agent carbon nanotubes, the binder polyvinylidene fluoride, and the monomer-dimethyl allyldicarboxylate are mixed in a mass ratio of 93.5:1.5:1.3:0.9:2.7 (i.e., m1 is 0.03), and in the second coating, the NCM811 positive electrode active material, the conductive agent carbon black (sp), the conductive agent carbon nanotubes, the binder polyvinylidene fluoride, and the oxide solid electrolyte LATP are mixed in a mass ratio of 94.2:1:0.5:0.9:1 (i.e., m2 is 0.15).

[0080] Example 6

[0081] The difference from Example 1 is that the NCM811 positive electrode active material, the conductive agent carbon black (sp), the conductive agent carbon nanotubes, the binder polyvinylidene fluoride, and the monomer-dimethyl allyl dicarboxylate are mixed in a mass ratio of 93.5:1.5:0.5:0.9:4.

[0082] Example 7

[0083] The difference from Example 1 is that the NCM811 positive electrode active material, the conductive agent carbon black (sp), the conductive agent carbon nanotubes, the binder polyvinylidene fluoride, and the monomer-dimethyl allyl dicarboxylate are mixed in a mass ratio of 93.5:1.5:0.5:0.9:0.5.

[0084] Comparative Example 1

[0085] A semi-solid lithium-ion battery is used to improve the positive electrode current density, the battery comprising a positive electrode, a negative electrode and an electrolyte;

[0086] The positive electrode sheet is prepared by uniformly mixing NCM811 positive electrode active material, conductive agent carbon black (sp), conductive agent carbon nanotubes, and binder polyvinylidene fluoride in a mass ratio of 93.5:1.5:0.5:0.9 to form a positive electrode slurry; coating the positive electrode slurry on one side of a current collector aluminum foil, drying and rolling it at 110°C, and then coating and drying the positive electrode slurry on the other side of the aluminum foil according to the above method; and then cold pressing the prepared aluminum foil with the positive electrode active material layer coated on both sides; trimming and cutting to form a lithium-ion battery positive electrode sheet; wherein the thickness of the positive electrode active material layer on one side is 75 μm;

[0087] The negative electrode sheet preparation method is exactly the same as that in Example 1, and the same separator as in Example 1 is selected to prepare the battery cell using the same process.

[0088] Prepare an electrolyte precursor solution: Add 1 mol / L LiPF6 and 7.5 wt% FEC additive to a solvent (the solvent formula is a mixed solution of propylene carbonate (PC): ethylene carbonate (EC): dimethyl carbonate (DMC) in a volume ratio of 1:1:1) and stir thoroughly to obtain an electrolyte solution;

[0089] The battery cell obtained in the above steps is placed in an aluminum-plastic packaging bag, baked, injected with the above electrolyte precursor solution, sealed, formed, and aged at 50° C. for 8 hours to obtain a lithium-ion battery.

[0090] Comparative Example 2

[0091] Preparation method of prefabricated positive electrode sheet: The positive electrode slurry preparation method is as follows: NCM811 positive electrode active material, conductive agent carbon black (sp), conductive agent carbon nanotube, binder polyvinylidene fluoride, monomer dimethyl allyl dicarboxylate, oxide solid electrolyte LATP (Beiterui New Materials Group Co., Ltd., BEO-1P, D50 particle size 200nm) are mixed in a mass ratio of 93.5:1.5:0.5:0.9:2.7, and then dissolved in NMP and mixed evenly to form a positive electrode slurry, and the above positive electrode slurry is coated on one side of the current collector aluminum foil, dried and rolled at 110°C, and then the positive electrode slurry is coated and dried on the other side of the aluminum foil according to the above method, and then the prepared aluminum foil with a positive electrode active material layer on both sides is cold pressed; after trimming and cutting, a lithium-ion battery positive electrode sheet is made; the coating thickness is 75μm;

[0092] Subsequently, a semi-solid-state battery was prepared in the same manner as in Example 1.

[0093] Comparative Example 3

[0094] Preparation method of positive electrode sheet: The preparation method of positive electrode slurry close to the current collector side is as follows: The preparation method of positive electrode slurry is as follows: NCM811 positive electrode active material, conductive agent carbon black (sp), conductive agent carbon nanotubes, binder polyvinylidene fluoride, oxide solid electrolyte LATP (Beiterui New Materials Group Co., Ltd., BEO-1P, D50 particle size 200nm) are mixed in a mass ratio of 94.2:2:1:0.9:1, and then dissolved in NMP to evenly form a positive electrode slurry; the above-mentioned positive electrode slurry is coated on one side of the current collector aluminum foil, and after drying and rolling at 110°C, the positive electrode slurry is coated and dried on the other side of the aluminum foil according to the above method, and then the prepared aluminum foil with a positive electrode active material layer on both sides is cold pressed; after trimming and cutting, a lithium-ion battery positive electrode sheet is made; the thickness of the coating is 75μm.

[0095] Comparative Example 4:

[0096] The only difference between the positive electrode sheet of this comparative example and Example 1 is that the second coating slurry in Example 1 is applied on the surface of the current collector to form a third coating layer; and the first coating slurry in Example 1 is applied on a surface of the third coating layer away from the positive electrode current collector to form a fourth coating layer.

[0097] Subsequently, a semi-solid-state battery was prepared in the same manner as in Example 1.

[0098] The semi-solid lithium-ion batteries prepared in the above examples and comparative examples were subjected to the following tests, and the test results are listed in Table 1.

[0099] Specific capacity test: Fully charge to 4.2V at 0.33C constant voltage and constant current (CVCC) to 0.05C, then discharge to 2.5V at 1C. Calculate the discharge capacity and divide it by the mass of the positive electrode material in the positive electrode sheet.

[0100] First efficiency test: Under the voltage range of 2.5-4.2V and 0.33C charge and discharge, the first cycle discharge capacity is compared with the charge capacity;

[0101] Diaphragm resistance test: Cut the rolled positive electrode sheet into 4cm*4cm square pieces and place them under the pole of the test box for testing.

[0102] Hot box test: The test temperature starts at 80 degrees Celsius and is increased at a rate of 5°C / min. The temperature is kept at 5°C for half an hour every half an hour until the battery starts to smoke or catch fire or explode. The thermal runaway temperature is recorded.

[0103] Table 1

[0104] Specific capacity / mAh / g First effect / % Positive electrode film resistance / S / cm Thermal runaway temperature / ℃ Example 1 189.4 86.1 0.052 160 Example 2 187.4 85.2 0.048 158 Example 3 187.5 85.7 0.049 157 Example 4 183.7 83.5 0.053 155 Example 5 183.3 83.2 0.068 157 Example 6 184.9 84.0 0.062 155 Example 7 181.9 82.7 0.064 157 Comparative Example 1 175.6 79.8 0.027 130 Comparative Example 2 158.8 72.2 0.069 148 Comparative Example 3 176.6 80.3 0.032 140 Comparative Example 4 173.2 78.7 0.071 130

[0105] From the above description, it can be seen that the above-mentioned embodiments 1-7 of the present invention achieve the following technical effects: the positive electrode sheet of the present application constructs a multilayer electrode, wherein the first coating layer adjacent to the current collector contains a gel-state polymer, which can increase the lithium ion current density near the current collector side; further, the oxide solid electrolyte in the second coating layer can bidirectionally regulate the lithium ion current density and the electron current density. By constructing the ion channel and the electron channel through the first coating layer and the second coating layer containing specific components, the electrical performance of the battery can be significantly improved. At the same time, the positive electrode sheet of the present application can also significantly improve the safety of the battery.

[0106] Among them, compared with Example 1, since the difference in thickness between the first coating layer and the second coating layer on the same side of the positive electrode current collector in Example 4 is greater than 15 μm, whether the electron current density or the ion current density increases or decreases in the electrode in a step-by-step manner, the difference is too large, resulting in a sudden decrease in the current density; thus, compared with Example 1, the battery performance will be slightly affected.

[0107] Compared with Example 1, in Example 5, since m1 is greater than m2, the electronic conductivity of the second coating is smaller than that of the first coating, but the electronic conductivity from the current collector to the diaphragm shows a gradient decreasing trend, so such a design will further reduce the electronic conductivity near the diaphragm, thereby having some impact on the battery performance compared with Example 1; compared with Example 1, in Example 6, due to excessive addition of monomers, the internal polymerization of the first coating is slightly excessive, thereby affecting the migration of lithium ions in the electrode, resulting in the specific capacity of Example 6 being lower than that of Example 1 and the internal resistance being increased.

[0108] Compared with Example 1, Example 7 has insufficient monomer addition, which results in incomplete polymerization within the first coating layer, thereby affecting the conduction of some ions. As a result, compared with Example 1, the specific capacity of Example 7 is lower and the internal resistance is increased.

[0109] Compared with Example 1, in Comparative Example 1, since the first coating and the second coating are not provided, the electronic conductivity and ionic conductivity from the current collector to the separator of the electrode are both gradient distributed, which affects the performance of the electrode.

[0110] Compared with Example 1, in Comparative Example 2, since only the first coating layer is provided and the second coating layer is not provided, the ionic conductivity of the electrode is improved as a whole, but the electronic conductivity still presents a gradient distribution, which affects the performance of the battery.

[0111] Compared with Example 1, in Comparative Example 3, since only the second coating layer is provided and the first coating layer is not provided, the overall electronic conductivity of the electrode is improved, but the ionic conductivity still presents a gradient distribution, which affects the performance of the battery.

[0112] Compared with Example 1, Comparative Example 4 improves the electronic conductivity of the electrode near the current collector because the positions of the first coating and the second coating are exchanged. However, the electronic conductivity itself is in an advantageous position near the current collector, which further improves the electronic conductivity, but ignores the influence of ionic conductivity; the ionic conductivity is improved near the diaphragm. Similarly, the ionic conductivity of the diaphragm is better than that of the current collector due to the porous liquid retention performance of the diaphragm. Further setting a gel electrolyte at this position to improve the ionic conductivity cannot solve the problem of the inferior electronic conductivity at the diaphragm, further affecting the battery performance.

[0113] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A solid-state battery comprising a positive electrode sheet, a separator and a negative electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode current collector, a first coating layer and a second coating layer, wherein: The first coating is on the surface of the positive electrode current collector, and the materials of the first coating are positive electrode material, conductive agent, binder and gel polymer; the gel polymer is formed by in-situ polymerization of monomers under the action of initiator and cross-linking agent; The second coating layer is on a surface of the first coating layer away from the positive electrode current collector, and the materials of the second coating layer include a positive electrode material, a conductive agent, a binder and an oxide solid electrolyte; The mass ratio of the conductive agent to the positive electrode material in the first coating layer is m1, and the mass ratio of the conductive agent to the positive electrode material in the second coating layer is m2, wherein m1 is less than m2; In the first coating, the mass ratio of the positive electrode material, the conductive agent and the binder is (93-97.5):(1-2.8):(0.5-1.2); In the second coating, the mass ratio of the positive electrode material, the conductive agent, the binder and the oxide solid electrolyte is (93-97.5):(1.5-3.8):(0.5-1.2):(0.5-2); The total thickness of the first coating layer and the second coating layer on the same side of the positive electrode current collector is 50-90 μm; and / or, the absolute value of the difference between the thickness of the first coating layer and the thickness of the second coating layer on the same side of the positive electrode current collector is 0-15 μm; The preparation method of the solid-state battery includes: Mixing the positive electrode material, the conductive agent, the binder and the monomer to obtain a first coating slurry; in the first coating slurry, the mass ratio of the positive electrode material, the conductive agent, the binder and the monomer is (93-97.5):(1-2.8):(0.5-1.2):(1-3); mixing the positive electrode material, the conductive agent, the binder and the oxide solid electrolyte to obtain a second coating slurry; Disposing the first coating slurry and the second coating slurry on the surface of the positive electrode current collector to form the first coating layer and the second coating layer, respectively, to obtain a prefabricated positive electrode sheet; The prefabricated positive electrode sheet, separator and negative electrode sheet are made into a battery cell; injecting an electrolyte precursor solution into the battery cell, sealing, aging, thermally polymerizing, and allowing to stand to obtain the solid-state battery; The electrolyte precursor solution includes a solvent, a lithium salt, an additive, the initiator and a cross-linking agent. The content of the initiator in the electrolyte precursor is 2-10 wt %, and the content of the cross-linking agent in the electrolyte precursor solution is 0.5-2 wt %.

2. The solid-state battery according to claim 1, characterized in that The monomers include any one or more of vinyl acetate, dimethyl allyl dicarboxylate, diethyl allyl malonate, methallyl carbonate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, methyl methacrylate, butyl methacrylate, vinylene carbonate, vinyl ethylene carbonate, methyl vinyl sulfone, ethyl vinyl sulfone, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate; The initiator includes any one or more of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, stannous octoate, lithium acetate, triethyl phosphine, triphenyl phosphine, tri-n-butyl phosphine, tributyltin oxide, tetrabutyl titanate, tetrabutyl zirconate, trialkyltin alkoxide, dialkyltin oxide, N-methylethylenediamine, dimethylformamide, triethyleneethylenediamine, methyldiethylene glycolamine, triethylenediamine, aluminum trifluoromethanesulfonate, magnesium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide and tin trifluoromethanesulfonate; The crosslinking agent includes any one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, methyl formate and polyether acrylate.

3. The solid-state battery according to claim 1, characterized in that The oxide solid electrolyte includes any one or more of a NASICON solid electrolyte, a perovskite solid electrolyte, a LISICON solid electrolyte and a garnet solid electrolyte.

4. A method for preparing a solid-state battery according to claim 1, characterized in that: include: Mixing the positive electrode material, the conductive agent, the binder and the monomer to obtain a first coating slurry; In the first coating slurry, the mass ratio of the positive electrode material, the conductive agent, the binder, and the monomer is (93-97.5):(1-2.8):(0.5-1.2):(1-3); mixing the positive electrode material, the conductive agent, the binder and the oxide solid electrolyte to obtain a second coating slurry; Disposing the first coating slurry and the second coating slurry on the surface of the positive electrode current collector to form the first coating layer and the second coating layer, respectively, to obtain a prefabricated positive electrode sheet; The prefabricated positive electrode sheet, separator and negative electrode sheet are made into a battery cell; injecting an electrolyte precursor solution into the battery cell, sealing, aging, thermally polymerizing, and allowing to stand to obtain the solid-state battery; The electrolyte precursor solution includes a solvent, a lithium salt, an additive, the initiator and a cross-linking agent. The content of the initiator in the electrolyte precursor is 2-10 wt %, and the content of the cross-linking agent in the electrolyte precursor solution is 0.5-2 wt %.

5. The preparation method according to claim 4, characterized in that The temperature of the thermal polymerization is 40° C.-80° C., and the time of the thermal polymerization is 3 h to 24 h.