Positive pole piece, preparation method thereof and battery

Abstract

The invention provides a positive pole piece and a preparation method thereof and a battery, the positive pole piece comprises a positive pole layer and a positive pole lithium supplement agent layer, the positive pole lithium supplement agent layer is compounded on one side, close to a battery electrolyte, of the positive pole layer, and the positive pole lithium supplement agent layer comprises a positive pole lithium supplement agent, a first solid electrolyte, a conductive agent and a binder, and the positive electrode layer comprises a positive electrode active material and a second solid electrolyte. The positive electrode lithium supplement layer has a lithium supplement function, and after lithium supplement is completed, inactive substances generated by the lithium supplement agent still exist in the positive electrode lithium supplement agent layer. However, the solid electrolyte in the positive electrode lithium supplement layer can play a role in conducting ions, and the conductive agent can still play a role in conducting electrons. And the lithium supplementing layer is gradually converted into an ion and electron conductive interface layer between the positive electrode and the electrolyte from an initial lithium supplementing functional layer. The interface layer can prevent the active material in the positive electrode layer from further reacting with the electrolyte in the cycle process, the active part of the positive electrode layer is not affected, and the first coulombic efficiency and cycle life of the all-solid-state battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly relates to a positive electrode sheet, a preparation method thereof, and a battery. Background Art

[0002] In all-solid-state batteries, during the first charge and discharge, a solid electrolyte interface film formed on the surface of the negative electrode by lithium ions loses a large amount of active lithium, resulting in a low Coulomb efficiency in the first cycle and reducing the capacity and energy density of the all-solid-state lithium-ion battery. The irreversible capacity loss of the most widely used graphite negative electrode is greater than 6%, and for a silicon-based alloy negative electrode with a high specific capacity, the irreversible capacity loss is even as high as more than 10% - 20%.

[0003] By using the lithium supplementation technology, the active lithium lost in the first cycle can be compensated, the shortcoming of low initial efficiency can be improved, the advantage of its high capacity can be fully exerted, and the energy density of the lithium-ion battery can be increased. However, the negative electrode lithium supplementation technology has problems such as demanding production environment requirements and complex and difficult-to-control processes in terms of process, the risk of easily forming lithium dendrites in terms of safety, and high raw material costs and large equipment investments in terms of cost. The positive electrode lithium supplementation technology generally disperses the positive electrode lithium supplementing agent in the positive electrode. When the lithium supplementing agent undergoes one or more charge and discharge cycles, inactive substances that are neither conducive to ion conduction nor electron conduction are generated, thereby hindering the normal conduction of ions and electrons and affecting the cycle life of the battery, which is particularly prominent in the case of no electrolyte infiltration in the solid-state battery.

[0004] Therefore, how to improve the cycle life of the solid-state battery is an urgent problem to be solved. Summary of the Invention

[0005] The present application provides a positive electrode sheet, a preparation method thereof, and a battery, which are used to solve the problem that the existing positive electrode sheet disperses the positive electrode lithium supplementing agent in the positive electrode layer, generating inactive substances that affect the positive electrode active material and resulting in a low cycle life of the solid-state battery.

[0006] In a first aspect, the present application provides a positive electrode sheet, which includes a positive electrode layer and a positive electrode lithium supplementing agent layer. The positive electrode lithium supplementing agent layer is compounded on one side of the positive electrode layer close to the battery electrolyte. The positive electrode lithium supplementing agent layer includes a positive electrode lithium supplementing agent, a first solid electrolyte, a conductive agent, and a binder. The positive electrode layer includes a positive electrode active material and a second solid electrolyte.

[0007] Optionally, the thickness of the positive electrode lithium supplementing agent layer is 1 - 10 μm.

[0008] Optionally, the mass percentage of the first solid electrolyte in the positive electrode lithium supplementing agent layer is 4.9% - 29.4%, and / or the mass percentage of the positive electrode lithium supplementing agent in the positive electrode lithium supplementing agent layer is 63% - 93.1%.

[0009] Optionally, the first solid electrolyte is a sulfide electrolyte, a halide electrolyte or a polymer electrolyte.

[0010] Optionally, the cathode lithium supplement is selected from one or more of Li5FeO4, Li6CoO4, Li2NiO2, Li2MnO3, Li6MnO4, Li5ReO6, Li 4+x V2O5 (0≤x≤1), Li2O, Li2O2, Li3N.

[0011] Optionally, the thickness of the cathode layer is 60-180 μm.

[0012] In a second aspect, the present application provides a method for preparing a cathode electrode sheet, the preparation method being used to prepare the cathode electrode sheet according to any one of the first aspect, and the preparation method comprising:

[0013] Using a first solid electrolyte, a cathode lithium supplement, a conductive agent, a binder and an organic solvent as raw materials to perform dispersion mixing to prepare a lithium supplement slurry;

[0014] Using a second solid electrolyte, a cathode active material, a conductive agent, and a binder as raw materials to perform dispersion mixing by a dry process or a wet process to prepare a cathode mixture;

[0015] Preparing a cathode layer on the surface of a carbon-coated foil by passing the cathode mixture through a wet process or a dry process;

[0016] Directly coating the lithium supplement slurry on the surface of the cathode layer to obtain a composite layer;

[0017] Performing high-temperature heat treatment and densification treatment on the composite layer to obtain the cathode electrode sheet.

[0018] In a third aspect, the present application provides a method for preparing a cathode electrode sheet, the preparation method being used to prepare the cathode electrode sheet according to any one of the first aspect, and the preparation method comprising:

[0019] Using a first solid electrolyte, a cathode lithium supplement, a conductive agent, a binder and an organic solvent as raw materials to perform dispersion mixing to prepare a lithium supplement slurry;

[0020] Using a second solid electrolyte, a cathode active material, a conductive agent, and a binder as raw materials to perform dispersion mixing by a dry process or a wet process to prepare a cathode mixture;

[0021] Preparing a cathode layer on the surface of a carbon-coated foil by passing the cathode mixture through a wet process or a dry process;

[0022] Coating the lithium supplement slurry on a substrate to obtain a lithium supplement composite tape, transferring the lithium supplement composite tape to the surface of the cathode layer, and removing the substrate to obtain a composite layer;

[0023] The composite layer is subjected to high-temperature heat treatment and densification treatment to obtain the positive electrode sheet.

[0024] In a fourth aspect, the present application provides a battery, which includes the positive electrode sheet, negative electrode sheet, and electrolyte as described in any item of the first aspect.

[0025] Optionally, the electrolyte is a liquid electrolyte or a solid electrolyte.

[0026] The present application provides a positive electrode sheet, a preparation method thereof, and a battery. The positive electrode sheet includes a positive electrode layer and a positive electrode lithium supplement layer. The positive electrode lithium supplement layer is laminated on one side of the positive electrode layer close to the battery electrolyte. The positive electrode lithium supplement layer includes a positive electrode lithium supplement, a first solid electrolyte, a conductive agent, and a binder. The positive electrode layer includes a positive electrode active material and a second solid electrolyte. The lithium supplement layer has charge and discharge capabilities and can provide a lithium supplement function. After lithium supplementation is completed, the inactive substances generated by the lithium supplement still remain in the positive electrode lithium supplement layer. However, the solid electrolyte in the lithium supplement layer can play the role of conducting ions, and the conductive agent can still play the role of conducting electrons. The lithium supplement layer gradually changes from an initial lithium supplement functional layer to an ion- and electron-conducting interface layer between the positive electrode and the electrolyte. Such an arrangement does not affect the active part of the positive electrode layer. This interface layer can prevent further reaction between the active material in the positive electrode layer and the electrolyte during cycling, improving the first Coulomb efficiency and cycle life of the all-solid-state battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0028] Figure 1 It is a schematic structural diagram of the all-solid-state positive electrode provided by the present application.

[0029] Through the above drawings, specific embodiments of the present application have been shown, and there will be more detailed descriptions hereinafter. These drawings and textual descriptions are not intended to limit the scope of the concept of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Here, the exemplary embodiments will be described in detail, and the examples are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0031] In all-solid-state batteries, a large amount of active lithium is lost during the first charge and discharge due to the formation of the solid electrolyte interface film (SEI film) or the occurrence of side reactions, resulting in a low Coulombic efficiency (ICE) in the first cycle and reducing the capacity and energy density of all-solid-state lithium-ion batteries.

[0032] The lithium supplement agent is a material used to make up for the loss of lithium ions in the battery, providing an additional lithium source to supplement this loss, thereby improving the Coulombic efficiency and capacity in the first cycle.

[0033] The usage methods of the lithium supplement agent can be divided into two categories: the positive electrode lithium supplement agent and the negative electrode lithium supplement agent. The positive electrode lithium supplement agent is mainly used to provide an additional lithium source in the positive electrode part of the battery. Usually, the lithium supplement agent is dispersed in the positive electrode material to supplement the loss of lithium ions.

[0034] When the positive electrode lithium supplement agent participates in the reaction during one or more charge and discharge processes, some inactive substances (such as inorganic salts or some oxides, etc.) will be generated. These inactive substances usually do not participate in the electrochemical reaction, which is not only unfavorable for the ionic conductivity but also hinders the flow of electrons, affecting the overall conductivity of the battery. As the amount of inactive substances increases, the cycle performance of the battery is affected.

[0035] When the positive electrode lithium supplement agent is dispersed in the positive electrode active material to supplement the loss of lithium ions, the generated inactive substances will affect the positive electrode active material and hinder the flow of lithium ions.

[0036] In view of this, the present application proposes a positive electrode plate. The positive electrode plate includes a separate positive electrode lithium supplement layer. The positive electrode lithium supplement layer includes a lithium supplement agent, a solid electrolyte, a conductive agent, and a binder. The lithium supplement layer has the ability of charge and discharge and provides the lithium supplement function. After the lithium supplement is completed, the inactive substances generated by the lithium supplement agent still exist in the positive electrode lithium supplement layer, but the solid electrolyte in the lithium supplement layer can still play the role of guiding ions, and the conductive agent can still play the role of guiding electrons. At this time, the lithium supplement layer gradually changes from the initial lithium supplement functional layer to an interface layer that can conduct ions and electrons between the positive electrode and the electrolyte. Such a setting will not affect the active part of the positive electrode layer, and this interface layer can prevent the further reaction between the active material in the positive electrode layer and the electrolyte during the cycle, improving the first Coulombic efficiency and cycle life of the all-solid-state battery.

[0037] In the first aspect of the present application, a positive electrode plate is provided. The positive electrode plate includes a positive electrode layer and a positive electrode lithium supplement layer. The positive electrode lithium supplement layer is laminated on the side of the positive electrode layer close to the battery electrolyte. The positive electrode lithium supplement layer includes a positive electrode lithium supplement agent, a first solid electrolyte, a conductive agent, and a binder. The positive electrode layer includes a positive electrode active material and a second solid electrolyte.

[0038] The function of the lithium supplement agent in the positive electrode lithium supplement agent layer is to supplement lithium, the function of the conductive agent is to improve conductivity, the function of the first solid electrolyte is to form a lithium ion conduction channel, and the function of the binder is to bond the above-mentioned various substances together.

[0039] The first solid electrolyte can be a sulfide electrolyte, a halide electrolyte or a polymer electrolyte.

[0040] In some embodiments, the first solid electrolyte is a sulfide electrolyte, and the sulfide electrolyte can be a binary Li2S-P2S5 system sulfide solid electrolyte, a thioargentite-type sulfide solid electrolyte or a thio-LISICON-type sulfide solid electrolyte. The chemical formulas of the binary sulfide and the thioargentite-type sulfide can be expressed as xLi2S·(100-x-z)A y S n ·zB, 0 < x < 100, y is 0, 1 or 2, n is 2y or 2y + 1, 0 ≤ z < 100 - x, A is B 3+ 、Si 4+ 、P 3+ 、P 5+ or Ge 4+ ,and B is LiCl, LiBr, LiI, Li3PO4, GeS2, P2O5, Li4SiO4 or P2S3.

[0041] In some embodiments, the first solid electrolyte is a halide electrolyte, and the chemical formula of the halide electrolyte can be expressed as Li a MX b ,1 ≤ a ≤ 10, 1 ≤ b ≤ 10, M is selected from one or more of the Group III metals, and X is selected from one or more of Cl, Br, I, F, O.

[0042] In some embodiments, the first solid-state electrolyte is a polymer electrolyte, and the polymer electrolyte itself can serve as a binder, i.e., no additional binder needs to be added. The following polymers can all be used as raw materials for the polymer electrolyte: one or more of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyurethane (PU), polyethylene oxide or polyvinylidene fluoride (PVDF). When the first solid-state electrolyte is a polymer electrolyte, a lithium salt can be added to the cathode lithium compensation layer to improve ionic conductivity. The lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium hexafluoroborate, lithium perchlorate, lithium difluoro(oxalato)borate, lithium triethylborohydride, lithium diisopropylamide, lithium acetoacetate, lithium bis(trimethylsilyl), lithium pentamethylcyclopentadienyl, 4,5-dicyano-2-trifluoromethylimidazole, lithium (perfluoro-n-butanesulfonyl)fluorosulfonate, and tert-butyl lithium. In addition, inorganic fillers can be added to the polymer electrolyte to increase the amorphous region of the electrolyte, thereby improving the ionic conductivity of the polymer electrolyte. The inorganic fillers include inactive materials such as alumina and silica, oxide electrolytes such as LATP and LLZO, and active materials such as the sulfide and halide electrolytes mentioned above.

[0043] In a all-solid-state battery, in addition to the cathode active material coated on the cathode layer of the cathode electrode sheet, a solid-state electrolyte is also added. The added solid-state electrolyte can form an effective ion channel, improve the ion migration rate, and enhance the charge and discharge performance of the battery. Therefore, a second solid-state electrolyte is also added to the cathode layer. The second solid-state electrolyte can be a sulfide electrolyte, a halide electrolyte, or a polymer electrolyte. The specific materials that can be selected for the sulfide electrolyte, the halide electrolyte, or the polymer electrolyte are the same as the aforementioned material classifications and will not be elaborated here. To improve the conductivity of the cathode layer, a conductive agent is also added. To improve the binding force of the cathode layer, a binder is also added.

[0044] The mass percentage of the second solid-state electrolyte in the cathode layer is 4.5% - 29.6%. Exemplarily, it can be 4.5%, 8.5%, 15.5%, 20.5%, 24.5%, 29.2%, or the range composed of any two of the above values.

[0045] It should be noted that the first solid-state electrolyte and the second solid-state electrolyte can be made of the same material.

[0046] The cathode lithium supplement agent can be selected from one or more of Li5FeO4, Li6CoO4, Li2NiO2, Li2MnO3, Li6MnO4, Li5ReO6, Li 4+ x xV2O5 (0 ≤ x ≤ 1), Li2O, Li2O2, Li3N.

[0047] In some embodiments, the thickness of the cathode lithium supplement layer is 1-10 μm. Exemplarily, the thickness of the cathode lithium supplement layer is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range composed of any two of the above values.

[0048] In some embodiments, the mass ratio of the first solid electrolyte in the cathode lithium supplement layer is 4.9%-29.4%. Exemplarily, the mass ratio of the first solid electrolyte in the cathode lithium supplement layer can be 4.9%, 8%, 15%, 20%, 25%, 29.4%, or a range composed of any two of the above values.

[0049] In some embodiments, the mass ratio of the cathode lithium supplement in the cathode lithium supplement layer is 63%-93.1%. Exemplarily, the mass ratio of the cathode lithium supplement in the cathode lithium supplement layer can be 63%, 65%, 70%, 75%, 80%, 85%, 90%, 93.1%, or a range composed of any two of the above values.

[0050] In some embodiments, the mass ratio of the conductive agent in the cathode lithium supplement layer can be 1%-5%. Exemplarily, the mass ratio of the conductive agent in the cathode lithium supplement layer can be 1%, 2%, 3%, 4%, 5%, or a range composed of any two of the above values.

[0051] The conductive agent in the cathode lithium supplement or the conductive agent in the cathode layer can be selected from one or more of conductive carbon black (SP), carbon nanotubes (CNT), vapor-grown carbon fibers (VGCF), and graphene. The conductive agent in the cathode lithium supplement and the conductive agent in the cathode layer can be the same or different.

[0052] In some embodiments, the mass ratio of the binder in the cathode lithium supplement layer can be 1%-5%. Exemplarily, the mass ratio of the binder in the cathode lithium supplement layer can be 1%, 2%, 3%, 4%, 5%, or a range composed of any two of the above values.

[0053] The binder can be a polymer, selected from at least one of poly(tetrafluoroethylene) (PTFE), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), and styrene-butadiene-styrene copolymer (SBS). The binder in the cathode lithium supplement and the binder in the cathode layer can be the same or different.

[0054] It should be noted that the sum of the mass ratios of the conductive agent, binder, first solid electrolyte, and lithium supplement in the above cathode lithium supplement layer is less than or equal to 100%.

[0055] The positive electrode active material in the positive electrode layer is selected from any one of lithium-rich manganese-based, lithium cobalt oxide (LiCoO2), high-nickel ternary materials (such as LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.83 Co 0.12 Mn 0.05 O, LiNi 0.92 Co 0.06 Mn 0.02 O, etc.).

[0056] The thickness of the positive electrode layer is 60 - 180 μm. Exemplarily, the thickness of the positive electrode layer can be 60 μm, 70 μm, 80 μm, 100 μm, 120 μm, 140 μm, 180 μm, or a range composed of any two of the above values.

[0057] The positive electrode tab can be single-sided coated or double-sided coated.

[0058] Exemplarily, referring to Figure 1 , a carbon bottom layer, a positive electrode layer, and a positive electrode lithium supplement layer are sequentially coated above one side of the foil.

[0059] The positive electrode tab can also be double-sided coated. A carbon bottom layer, a positive electrode layer, and a positive electrode lithium supplement layer are sequentially coated above one side of the foil, and a carbon bottom layer, a positive electrode layer, and a positive electrode lithium supplement layer are also sequentially coated on the other side of the foil.

[0060] In the second aspect of the present application, a method for preparing a positive electrode tab is provided. This preparation method is used to prepare the positive electrode tab as described in the first aspect above. This preparation method prepares the positive electrode tab by coating, and includes:

[0061] S1. Using a first solid electrolyte, a positive electrode lithium supplement agent, a conductive agent, a binder, and an organic solvent as raw materials, disperse and mix them to prepare a lithium supplement slurry.

[0062] Among them, the organic solvent is selected from linear alkanes, branched alkanes, cycloalkanes, aromatic hydrocarbons, alkenes, cycloalkenes, and other weakly polar solvents. The linear alkanes include at least one of n-hexane, n-pentane, isopentane, n-heptane, n-octane, isooctane, trichlorotrifluoroethane, dichloromethane, and chloroform; the branched alkanes include at least one of 2-methylpentane, 2,2-dimethylpentane, 3-methylpentane, 2,3-dimethylpentane, 2-methylhexane, 2,2-dimethylhexane, 3-methylhexane, 2,3-dimethylhexane, and 3-ethylhexane; the cycloalkanes include at least one of cyclohexane, cycloheptane, methylcyclohexane, tert-butylcyclohexane, and tetrahydrofuran; the aromatic hydrocarbons include at least one of benzene, toluene, 1,2-xylene, 1,3-xylene, 1,4-xylene, chlorobenzene, and o-dichlorobenzene; the alkenes include at least one of 1-hexene, 2-hexene, 1-heptene, 2-heptene, 1-octene, 2-octene, and dichloroethylene; the cycloalkenes include at least one of cyclopentene, cyclohexene, 1-methylcyclohexene, 4-methylcyclohexene, 1-ethylcyclohexene, and 1,4-dimethylcyclohexene; the other weakly polar solvents include one or more of petroleum ether, trifluoroacetic acid, butyl chloride, trichloroethylene, carbon tetrachloride, propyl ether, diethyl ether, butyl acetate, and ethyl acetate.

[0063] The mass fraction of the electrolyte in the lithium supplement slurry (excluding the solvent) is 4.9% - 29.4%, the mass fraction of the positive electrode lithium supplement agent is 63% - 93.1%, the mass fraction of the conductive carbon is 1% - 5%, and the mass fraction of the polymer is 1% - 5%.

[0064] The solid content of the lithium supplement slurry is 15% - 60%; for example, the solid content can be 15%, 20%, 25%, 30%, 40%, 50%, 60%, or the range composed of any two of the above values.

[0065] S2. Using the second solid electrolyte, the positive electrode active material, the conductive agent, and the binder as raw materials, disperse and mix them by dry or wet process to prepare the positive electrode mixture.

[0066] In the wet process, raw materials such as the positive electrode active material, the conductive agent, the binder, and the second solid electrolyte are mixed with a solvent (such as water or an organic solvent). By methods such as stirring, ultrasonic treatment, or high-shear mixing, ensure that the solid raw materials are uniformly dispersed in the liquid solvent to form a uniform slurry.

[0067] The dry process is a mixing process carried out without a solvent or liquid medium, using mechanical force to promote the mixing of materials. Uniformly mix dry powder raw materials such as the positive electrode active material, the conductive agent, the binder, and the solid electrolyte through equipment such as high-speed stirring, rollers, or ball mills.

[0068] The mass fraction of the electrolyte in the positive electrode mixture (excluding solvent) is 4.5% - 29.6%, the mass fraction of the positive electrode lithium supplement is 63% - 93.8%, the mass fraction of the conductive carbon is 1% - 5%, and the mass fraction of the polymer is 0.25% - 5%.

[0069] If it is prepared by the wet process, the solid content is 25% - 70%. Exemplarily, the solid content can be 25%, 35%, 45%, 55%, 60%, 65%, 70%, or the range composed of any two of the above values.

[0070] If it is prepared by the dry process, the dispersion equipment is planetary ball mill, homogenizing emulsifier, defoamer, planetary homogenizer, magnetic stirring, high-speed disperser, etc., and the dispersion time is 30 min - 360 min.

[0071] S3. Prepare a positive electrode layer on the surface of the carbon-coated foil by wet or dry process using the positive electrode mixture.

[0072] For the wet process, use a coater, knife die coating, etc. to evenly coat the prepared slurry on the surface of the pre-prepared current collector material (such as aluminum foil). During coating, it is necessary to ensure that the slurry evenly covers the entire surface of the current collector to reach the required thickness. After coating, remove the solvent by drying.

[0073] For the dry process, evenly coat the dry mixed powder on the surface of the current collector by electrostatic spraying, roll coating, brush coating, etc.

[0074] S4. Directly coat a lithium supplement slurry on the surface of the positive electrode layer to obtain a composite layer.

[0075] The coating methods involved in S3 and S4 can be one of gravure coating, knife roll coating, metering rod coating, and slot die coating.

[0076] After coating in S3 and S4, drying treatment is required. For the drying treatment involved, the treatment temperature is 40 - 80 °C and the time is 30 min - 720 min.

[0077] S5. Perform high-temperature heat treatment and densification treatment on the composite layer to obtain a positive electrode plate.

[0078] The composite layer after coating with the lithium supplement slurry needs to undergo high-temperature heat treatment and densification treatment to ensure its structural stability and enhance the performance of the battery.

[0079] High-temperature heat treatment helps to improve the stability of the composite layer, enabling it to better fuse with the positive electrode material and preventing the lithium supplement material from falling off during use. The high-temperature heat treatment temperature is 60 - 150 °C and the time is 5 min - 180 min.

[0080] The densification process is one or more of isostatic pressing and roll pressing. The limit of roll pressing is that the compaction density of the composite cathode is 2.1 g / cm 3 - 3.6 g / cm 3 , and the applied pressure is 100 MPa - 600 MPa.

[0081] The above embodiments provide a method for preparing a positive electrode sheet by coating a lithium supplement agent slurry on a positive electrode layer.

[0082] The third aspect of the present application provides a method for preparing a positive electrode sheet. This preparation method is used to prepare the positive electrode sheet in the above embodiments. This preparation method is prepared by transfer printing and specifically includes:

[0083] S1. Using a first solid electrolyte, a positive electrode lithium supplement agent, a conductive agent, a binder, and an organic solvent as raw materials, disperse and mix them to prepare a lithium supplement slurry.

[0084] S2. Using a second solid electrolyte, a positive electrode active material, a conductive agent, and a binder as raw materials, disperse and mix them by a dry process or a wet process to prepare a positive electrode mixture.

[0085] S3. Prepare a positive electrode layer on the surface of the carbon-coated foil by a wet process or a dry process.

[0086] The processes of the above steps S1 - S3 are the same as those of S1 - S3 in the second aspect embodiment and will not be elaborated here.

[0087] S4. Coat the lithium supplement slurry on a substrate to obtain a lithium supplement composite tape, transfer the lithium supplement composite tape to the surface of the positive electrode layer, and remove the substrate to obtain a composite layer.

[0088] The transfer substrate can be one or more of a PET film, a PET release film, a PI film, an aluminum foil, and a stainless steel foil. The transfer temperature is 60 - 150 °C, and the time is 5 min - 60 min.

[0089] Specifically, uniformly coat the lithium supplement slurry on the surface of a pre-prepared substrate material. Common methods include roll coating, knife coating, or spraying, etc., to ensure uniform distribution of the slurry. After coating, the lithium supplement slurry needs to be dried or heat-treated to remove the solvent and cure it to form a tough lithium supplement composite tape. At this time, the composite tape already has good adhesion and can be operated in the subsequent transfer process. Align the prepared lithium supplement composite tape with the surface of the positive electrode layer, and make the composite tape in close contact with the surface of the positive electrode layer through a certain pressure or temperature. Usually, this step can be achieved by hot pressing, roll pressing, etc. After the composite tape is successfully transferred and adhered to the positive electrode layer, slowly remove the substrate material. Since the substrate material is usually selected to have good separation performance from the lithium supplement material, the substrate can be easily peeled off from the composite tape, leaving a complete lithium supplement composite layer.

[0090] S5. Subject the composite layer to high-temperature heat treatment and densification treatment to obtain the positive electrode sheet.

[0091] This step is the same as the S5 process in the embodiment of the foregoing second aspect, and will not be elaborated here.

[0092] The above embodiment introduces the transfer of the lithium supplement layer to the positive electrode layer by means of transfer printing.

[0093] The third aspect of the present application provides a battery, which includes the positive electrode sheet according to any one of the first aspect, or the positive electrode sheet prepared by the second aspect or the third aspect. The battery further includes a negative electrode sheet and an electrolyte.

[0094] The negative electrode material is selected from one or more of graphite, silicon carbide, silicon, tin, and red phosphorus.

[0095] In some embodiments, the electrolyte is a solid electrolyte. The solid electrolyte can be selected from one of sulfide electrolytes, halide electrolytes, oxide electrolytes, and polymer-based electrolytes.

[0096] In some embodiments, the electrolyte is a liquid electrolyte.

[0097] After obtaining the positive electrode sheet, the preparation processes of the solid-state battery and the liquid battery are the same as those of the prior art, and will not be elaborated here.

[0098] The following will be introduced with specific examples.

[0099] Example 1

[0100] Figure 1 It is a schematic structural diagram of the all-solid positive electrode provided by the present application. As Figure 1 shown, it includes an S1 - foil; an S2 - carbon bottom layer; an S3 - positive electrode layer; and an S4 - lithium supplement layer, which are sequentially arranged from bottom to top.

[0101] Positive electrode preparation:

[0102] S1. Weigh 19.2 g of sulfide electrolyte Li6PS5Cl 0.5 Br 0.5 19.2 g, 76.8 g of positive electrode lithium supplement Li5FeO4, 2 g of conductive carbon VGCF, and 2 g of polymer SEBS, and mix and disperse them evenly in the organic solvent p - xylene through a homogenizing emulsifier. The solid content is 30% to prepare a lithium supplement slurry.

[0103] S2. 19.2 g of halide electrolyte Li3InCl6, positive electrode active material LiNi 0.92 Co 0.06 Mn 0.02 O 76.8 g, 2 g of conductive carbon VGCF, 2 g of polymer SEBS, were uniformly mixed and dispersed in organic solvents p-xylene and butyl acetate (mass ratio 2:1) by a defoaming machine, with a solid content of 55%, to prepare the positive electrode paste.

[0104] S3. The obtained positive electrode paste was coated on carbon-coated foils S1 and S2, and dried at 60 °C for 4 h to prepare the positive electrode layer.

[0105] S4. The obtained lithium supplement paste was coated on a PET film, dried at 50 °C for 4 h to obtain a lithium supplement composite tape, which was laminated on the positive electrode layer S3 at 80 °C for 30 min, and then the composite tape substrate was peeled off.

[0106] S5. The positive electrode composite layer was roll-pressed at a temperature of 90 °C, and the compaction density was 2.6 g / cm 3 , to obtain the positive electrode of the all-solid-state battery; the thicknesses of each layer in the finished all-solid-state positive electrode are: S1 - foil: 12 μm, S2 - carbon bottom layer: 2 μm, S3 - positive electrode layer: 146 μm, S4 - lithium supplement layer: 3.3 μm.

[0107] Assembly of all-solid-state battery:

[0108] Electrolyte layer: Li 5.5 PS 4.5 Cl 1.5 : PTFE = 99.5:0.5, thickness 45 μm.

[0109] Negative electrode layer: Si:Li 5.5 PS 4.5 Cl 1.5 : VGCF:SEBS = 67:28:3:2, thickness 20 μm.

[0110] Battery assembly: The above electrode units were die-cut into the designed size, stacked in the order of negative electrode - electrolyte - positive electrode, and then hot-pressed at 120 °C and 1 MPa for 120 s. The bare battery core was encapsulated in a soft package and isostatically pressed at 500 MPa for 10 min to form the final all-solid-state lithium battery.

[0111] Example 2

[0112] The difference from Example 1 is only that:

[0113] S1. The formulation was adjusted to 23.9 g of sulfide electrolyte Li3PS4, 71.6 g of positive electrode lithium supplement agent Li5FeO4, 3 g of conductive carbon CNT, and 1.5 g of polymer SBS.

[0114] S2. 19.2 g of sulfide electrolyte Li6PS5Cl, positive electrode active material LiNi 0.9 Co 0.06 Mn0.04 O 76.8 g, 2 g of conductive carbon VGCF, 2 g of polymer SEBS.

[0115] S5. The thickness of the lithium supplement layer is adjusted to 8 μm.

[0116] Example 3

[0117] The difference from Example 1 is only that:

[0118] S1. The formulation is adjusted to sulfide electrolyte Li6PS5Cl 0.5 Br 0.5 4.9 g, 93.1 g of positive electrode lithium supplement agent Li5FeO4, 1 g of conductive carbon VGCF, 1 g of polymer SEBS.

[0119] S5. The thickness of the lithium supplement layer is adjusted to 2 μm.

[0120] Example 4

[0121] The difference from Example 1 is only that:

[0122] S1. The formulation is adjusted to sulfide electrolyte Li6PS5Cl 0.5 Br 0.5 27 g, 63 g of positive electrode lithium supplement agent Li5FeO4, 5 g of conductive carbon VGCF, 5 g of polymer SEBS.

[0123] S5. The thickness of the lithium supplement layer is adjusted to 4 μm.

[0124] Example 5

[0125] The difference from Example 1 is only that:

[0126] S1. The mixture is uniformly mixed and dispersed by a planetary ball mill in an organic solvent isobutyl isobutyrate, and the solid content is 40%.

[0127] S4. The obtained lithium supplement slurry is coated on aluminum foil, dried at 60 °C for 8 h, and then adhered to the positive electrode layer S3 and treated at 80 °C for 30 min.

[0128] Example 6

[0129] The difference from Example 1 is only that:

[0130] S5. The positive electrode composite layer is roll-pressed at a temperature of 150 °C, and the compaction density is 2.8 g / cm 3 .

[0131] The thickness of each layer in the all-solid-state cathode finished product is adjusted to: S1-foil: 10 μm, S2-carbon bottom layer: 1.5 μm, S3-cathode layer: 136 μm, S4-lithium supplement layer: 3.1 μm.

[0132] Example 7

[0133] The difference from Example 1 is only that:

[0134] Cathode preparation:

[0135] S1. Weigh 3.2 g of alumina, 76.8 g of cathode lithium supplement agent Li5FeO4, 2 g of conductive carbon VGCF, 6 g of polymer PEO, and 12 g of lithium salt lithium bis(trifluoromethanesulfonyl)imide respectively, and mix and disperse them evenly in the organic solvent acetonitrile through a homogenizing emulsifier. The solid content is 20%, and a lithium supplement slurry is prepared.

[0136] S4. Coat the obtained lithium supplement slurry on a PET film, dry it at 50 °C for 4 h to obtain a lithium supplement composite tape, attach it to the cathode layer S3, keep it at 60 °C for 30 min, and then remove the composite tape substrate.

[0137] S5. Roll press the cathode composite layer at a temperature of 60 °C.

[0138] Example 8

[0139] Cathode preparation:

[0140] S1. Weigh 96 g of cathode lithium supplement agent Li5FeO4, 1.6 g of SP, 0.4 g of CNT, and 2 g of polymer PVDF respectively, and mix and disperse them evenly in the organic solvent N-methylpyrrolidone (NMP) through a homogenizing emulsifier. The solid content is 40%, and a lithium supplement slurry is prepared.

[0141] S2. Cathode active material LiNi 0.92 Co 0.06 Mn 0.02 O 96 g, 1.6 g of SP, 0.4 g of CNT, and 2 g of polymer PVDF, and mix and disperse them evenly in the organic solvent NMP through a defoamer. The solid content is 65%, and a cathode slurry is prepared.

[0142] S3. Coat the obtained cathode slurry on the carbon-coated foil S1 and S2, and dry it at 90 °C for 6 h to prepare a cathode layer.

[0143] S4. Coat the obtained lithium supplement slurry on the dried cathode film, and dry it at 90 °C for 6 h.

[0144] S5. Roll press the cathode composite layer at a temperature of 90 °C, and the compaction density is 3.5 g / cm 3, a positive electrode of a all - solid - state battery is obtained; the thicknesses of each layer in the finished all - solid - state positive electrode are as follows: S1 - foil: 12 μm, S2 - carbon bottom layer: 1 μm, S3 - positive electrode layer: 57 μm, S4 - lithium - supplementing layer: 1.8 μm.

[0145] Battery assembly:

[0146] Electrolyte: ethylene carbonate (EC): 30%, propylene carbonate (PC): 20%, diethyl carbonate (DEC): 20%, dimethyl carbonate (DMC): 20%, lithium hexafluorophosphate (LiPF6): 10%.

[0147] Separator: PE separator, 12 μm.

[0148] Negative electrode layer: Si:SP:CNT:PAA = 96.5:0.7:0.3:2.5, thickness 11 μm.

[0149] Battery assembly: The above electrode units are die - cut into the designed size, stacked and encapsulated in the order of negative electrode - separator - positive electrode, and the electrolyte is injected at 2 g / Ah.

[0150] Comparative Example 1

[0151] The difference from Example 1 is only that:

[0152] S5, the thickness of the lithium - supplementing layer is adjusted to 25 μm.

[0153] Comparative Example 2

[0154] The difference from Example 1 is only that:

[0155] S1, the formula is adjusted to sulfide electrolyte Li6PS5Cl 0.5 Br 0.5 3 g, positive electrode lithium - supplementing agent Li5FeO4 96 g, conductive carbon VGCF 0.5 g, polymer SEBS 0.5 g.

[0156] Comparative Example 3

[0157] The difference from Example 1 is only that:

[0158] S1, the formula is adjusted to sulfide electrolyte Li6PS5Cl 0.5 Br 0.5 44 g, positive electrode lithium - supplementing agent Li5FeO4 40 g, conductive carbon VGCF 8 g, polymer SEBS 8 g.

[0159] Comparative Example 4

[0160] The difference from Example 1 is only that:

[0161] There is no lithium - supplementing layer, that is, there is no S1 process.

[0162] Comparative Example 5

[0163] It is only different from Example 1 in that:

[0164] The lithium supplement layer is cancelled, and the lithium supplement agent is added to the positive electrode layer.

[0165] S2. The formula is the sulfide electrolyte Li6PS5Cl 0.5 Br 0.5 19.2 g, the positive electrode active material LiNi 0.92 Co 0.06 Mn 0.02 O 76.8 g, the positive electrode lithium supplement agent Li5FeO4 1.536 g, the conductive carbon VGCF 2 g, the polymer SEBS 2 g.

[0166] Battery testing

[0167] Test the cycle performance of the solid-state batteries of the examples and comparative examples. The specific test method is as follows:

[0168] The test method for cycle performance is as follows: The test temperature is 25°C, the equivalent pressure under pressure is 75 MPa. First, perform constant current charging at a current of 0.1C until 4.4V, then perform constant voltage charging until the current is cut off at 0.05C. Then, after standing for 20 min, discharge at a current of 0.1C until 2V, and stand for 20 min to complete one cycle. Repeat the charge and discharge 2 cycles in this way, and then perform charge and discharge cycle testing at a current of 0.33C.

[0169] Use the above method to test the electrochemical performance of the solid-state batteries respectively. The obtained results are shown in Table 1.

[0170] Table 1 Battery performance

[0171]

[0172] According to the above experimental data, compared with Comparative Example 4, in Comparative Example 5, the lithium supplement agent is dispersedly added to the positive electrode. Due to the function of the lithium supplement agent, the initial Coulomb efficiency is slightly improved, and the cycle retention rate is improved. Compared with Comparative Example 5, in Examples 1-7, by setting a separate lithium supplement agent layer, the Coulomb efficiency is further improved, and the cycle retention rate is significantly improved, which can be increased by more than 50%. The above experimental data show that the lithium supplement agent layer involved in this solution can be used as a lithium source for lithium supplementation during the initial charge and discharge. As the battery cycles, the lithium supplementation functional layer gradually transforms into an interfacial layer that can conduct ions and electrons between the positive electrode and the electrolyte. This interfacial layer can prevent the further reaction between the positive electrode and the electrolyte during the cycle, and improve the cycle life of the all-solid-state battery.

[0173] It can be seen from Example 1 and Comparative Example 1 that the formulation of the lithium supplement layer remains unchanged. The thickness of the lithium supplement layer in Comparative Example 1 is 25 μm, which is too thick and will lead to a decline in the cycling performance of the battery.

[0174] From the data of Comparative Example 2 and Comparative Example 3, it can be known that when the proportion of the solid electrolyte in the formulation of the lithium supplement layer is too high or too low, the cycling performance of the battery will decline.

[0175] The experimental data of Example 8 show that the positive electrode tab with a separate positive electrode lithium supplement layer can be applied in lithium-ion liquid batteries, and the function and principle of the lithium supplement layer are the same as those in all-solid-state batteries.

[0176] Finally, it should be noted that those skilled in the art will easily think of other implementation schemes of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include the common general knowledge or conventional technical means in the technical field not disclosed in the present invention. It is not limited to the precise structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A positive electrode sheet, characterized in that, The positive electrode sheet includes a positive electrode layer and a positive electrode lithium supplement layer. The positive electrode lithium supplement layer is laminated on one side of the positive electrode layer close to the battery electrolyte. The positive electrode lithium supplement layer includes a positive electrode lithium supplement, a first solid electrolyte, a conductive agent, and a binder. The positive electrode layer includes a positive electrode active material and a second solid electrolyte.

2. The positive electrode sheet according to claim 1, characterized in that, The thickness of the positive electrode lithium supplement layer is 1-10 μm.

3. The positive electrode sheet according to claim 1, wherein The mass ratio of the first solid electrolyte in the positive electrode lithium supplement layer is 4.9%-29.4%, and / or the mass ratio of the positive electrode lithium supplement in the positive electrode lithium supplement layer is 63%-93.1%.

4. The positive electrode sheet according to any one of claims 1-3, characterized in that, The first solid electrolyte is a sulfide electrolyte, a halide electrolyte, or a polymer electrolyte.

5. The positive electrode sheet according to any one of claims 1-3, characterized in that, The positive electrode lithium supplement is selected from one or more of Li5FeO4, Li6CoO4, Li2NiO2, Li2MnO3, Li6MnO4, Li5ReO6, Li 4+x V2O5 (0 ≤ x ≤ 1), Li2O, Li2O2, Li3N.

6. The positive electrode sheet according to any one of claims 1-3, characterized in that, The thickness of the positive electrode layer is 60-180 μm.

7. A method for preparing a positive electrode plate, characterized in that, The preparation method is used to prepare the positive electrode sheet according to any one of claims 1-6. The preparation method includes: Using a first solid electrolyte, a positive electrode lithium supplement, a conductive agent, a binder, and an organic solvent as raw materials to perform dispersion mixing to prepare a lithium supplement slurry; Using a second solid electrolyte, a positive electrode active material, a conductive agent, and a binder as raw materials to perform dispersion mixing by a dry process or a wet process to prepare a positive electrode mixture; Preparing the positive electrode layer on the surface of a carbon-coated foil by passing the positive electrode mixture through a wet process or a dry process; Directly coating the lithium supplement slurry on the surface of the positive electrode layer to obtain a composite layer; Performing high-temperature heat treatment and densification treatment on the composite layer to obtain the positive electrode sheet.

8. A method for preparing a positive electrode sheet, characterized in that, The preparation method is used to prepare the positive electrode sheet according to any one of claims 1-6. The preparation method includes: Using a first solid electrolyte, a positive electrode lithium supplement, a conductive agent, a binder, and an organic solvent as raw materials to perform dispersion mixing to prepare a lithium supplement slurry; Using a second solid electrolyte, a positive electrode active material, a conductive agent, and a binder as raw materials to perform dispersion mixing by a dry process or a wet process to prepare a positive electrode mixture; Preparing the positive electrode layer on the surface of a carbon-coated foil by passing the positive electrode mixture through a wet process or a dry process; Coating the lithium supplement slurry on a substrate to obtain a lithium supplement composite tape, transferring the lithium supplement composite tape to the surface of the positive electrode layer, and removing the substrate to obtain a composite layer; Performing high-temperature heat treatment and densification treatment on the composite layer to obtain the positive electrode sheet.

9. A battery, characterized in that, The battery includes the positive electrode sheet, a negative electrode sheet, and an electrolyte according to any one of claims 1-6.

10. The battery according to claim 9, characterized in that, The electrolyte is a liquid electrolyte or a solid electrolyte.

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