Positive pole piece, preparation method thereof and all-solid-state battery

Abstract

The embodiment of the invention provides a positive pole piece, a preparation method thereof and an all-solid-state battery, and relates to the technical field of batteries. The preparation method comprises the following steps: carrying out gradient layering treatment on mixed powder of a positive electrode material to obtain first outer-layer powder and first inner-layer powder, then adding sulfide solid electrolyte into the first outer-layer powder, adding a binder into the first inner-layer powder, and respectively and uniformly mixing to obtain second outer-layer powder and second inner-layer powder, and finally, carrying out pole piece forming treatment on the second outer layer powder and the second inner layer powder to obtain the positive pole piece. The prepared positive pole piece comprises a gradient composite structure composed of an outer layer and an inner layer, wherein the outer layer contains mixed powder of a positive electrode material and sulfide solid electrolyte; and the inner layer contains mixed powder of the positive electrode material and a binder. Through the method, the lithium ion transmission efficiency is improved, the problem of poor interface contact is improved, the stability of the positive pole piece structure is enhanced, and the overall performance of the battery is improved.

Description

Technical Field

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

[0002] All-solid-state batteries have become the core direction of the next generation of battery technology due to their high energy density and high safety. Ternary active materials have important application prospects in all-solid-state batteries due to their high specific capacity.

[0003] In the related technologies for preparing positive electrode sheets using ternary active materials, traditional wet processes have problems such as solvent residue and poor interface contact, which restrict the improvement of battery performance. The dry process mixes the ternary active materials with conductive agents and binders in a certain proportion through mechanical mixing, and then presses the mixed powder into a tablet press. This ensures close contact between the powder particles, forming a positive electrode sheet with sufficient mechanical strength and conductivity.

[0004] However, although the dry process can avoid the use of solvents, during the assembly process of all-solid-state batteries, it still faces the problem of rigid contact between the positive electrode and the solid electrolyte, which leads to obstruction of lithium ion transmission and subsequent poor interface contact. Summary of the Invention

[0005] The embodiments of the present application provide a positive electrode plate, a preparation method thereof, and an all-solid-state battery, which are used to improve the problem of poor interface contact caused by the rigid contact between the positive electrode plate and the solid electrolyte, which hinders lithium ion transmission.

[0006] In a first aspect, an embodiment of the present application provides a positive electrode sheet, comprising: a gradient composite structure consisting of an outer layer and an inner layer;

[0007] Wherein, the outer layer contains a mixed powder of positive electrode materials and a sulfide solid electrolyte;

[0008] The inner layer contains mixed powder of positive electrode materials and a binder.

[0009] In a possible implementation, the mass of the sulfide solid electrolyte is 2% to 5% of the mass of the mixed powder.

[0010] In one possible embodiment, the binder includes a fibrous binder and a non-fibrous binder;

[0011] Wherein, the mass of the fibrous binder is 2% to 3% of the mass of the mixed powder;

[0012] The mass of the non-fibrous binder is 1.5% to 2% of the mass of the mixed powder.

[0013] In a possible embodiment, the mixed powder includes a ternary active material, an oxide solid electrolyte, a conductive agent, and a eutectic electrolyte.

[0014] In one possible embodiment, the eutectic electrolyte is LiTFSI-urea-acetamide.

[0015] In a possible implementation, the filling porosity of the positive electrode sheet is 30% to 50%.

[0016] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode sheet as described in any possible aspect of the first aspect, comprising:

[0017] Performing a gradient layering process on the mixed powder of the positive electrode material to obtain a first outer layer powder and a first inner layer powder;

[0018] Adding a sulfide solid electrolyte to the first outer layer powder and mixing them evenly to obtain a second outer layer powder;

[0019] Adding a binder to the first inner layer powder and mixing them evenly to obtain a second inner layer powder;

[0020] The second outer layer powder and the second inner layer powder are subjected to a pole piece forming process to obtain a positive pole piece.

[0021] In a possible implementation, the mass of the sulfide solid electrolyte is 2% to 5% of the mass of the mixed powder.

[0022] In one possible embodiment, the binder includes a fibrous binder and a non-fibrous binder;

[0023] The mass of the fibrous binder is 2% to 3% of the mass of the mixed powder;

[0024] The mass of the non-fibrous binder is 1.5% to 2% of the mass of the mixed powder.

[0025] In one possible implementation, the method further includes:

[0026] Soaking the positive electrode sheet in a eutectic electrolyte solution to obtain a soaked positive electrode sheet;

[0027] The soaked positive electrode sheet is vacuum dried to obtain a new positive electrode sheet, wherein the filling porosity of the new positive electrode sheet is 30% to 50%.

[0028] In a possible embodiment, during the vacuum drying process, the drying temperature is 60-80° C., and / or the drying time is 8-12 hours.

[0029] In a possible embodiment, before performing the gradient layering process on the mixed powder of the positive electrode material, the method further includes:

[0030] The ternary active material, the oxide solid electrolyte and the conductive agent are mixed evenly, and the eutectic electrolyte is added to obtain a mixed powder.

[0031] In one possible embodiment, the eutectic electrolyte is LiTFSI-urea-acetamide.

[0032] In a third aspect, an embodiment of the present application provides an all-solid-state battery, comprising a positive electrode, a negative electrode, and a solid electrolyte, wherein the positive electrode is any possible positive electrode sheet described in the first aspect or a positive electrode sheet prepared by any possible method described in the second aspect.

[0033] The embodiments of the present application provide a positive electrode plate, a preparation method thereof, and an all-solid-state battery. The method comprises performing a gradient layering process on a mixed powder of a positive electrode material to obtain a first outer layer of powder and a first inner layer of powder. A sulfide solid electrolyte is then added to the first outer layer of powder, and a binder is added to the first inner layer of powder. The two layers are mixed evenly to obtain a second outer layer of powder and a second inner layer of powder. Finally, the second outer layer of powder and the second inner layer of powder are subjected to a plate forming process to obtain a positive electrode plate. The prepared positive electrode plate comprises: a gradient composite structure consisting of an outer layer and an inner layer; wherein the outer layer contains a mixed powder of a positive electrode material and a sulfide solid electrolyte; and the inner layer contains a mixed powder of a positive electrode material and a binder. Through the above method, the ion transmission efficiency is improved, the problem of poor interface contact is improved, and the stability of the plate structure is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0035] Figure 1 A schematic diagram of a process for preparing a positive electrode sheet provided in this application Figure 1 ;

[0036] Figure 2 A schematic diagram of a process for preparing a positive electrode sheet provided in this application Figure 2 .

[0037] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0038] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0039] First, the application background of this application is explained as follows:

[0040] As a next-generation energy storage technology, all-solid-state batteries, which replace the liquid electrolytes in traditional lithium-ion batteries with solid-state electrolytes, have attracted much attention due to their potential high energy density and safety. In all-solid-state battery research, ternary active materials have become a hot topic due to their excellent cycle life and high specific capacity, which can achieve longer battery life.

[0041] In the conventional wet process for preparing positive electrode sheets from ternary active materials to form all-solid-state batteries, the traditional wet process involves mixing the ternary active materials with a conductive agent and a binder in an organic solvent to form a uniform slurry. This slurry is then evenly coated on an aluminum foil current collector. The slurry is then dried at high temperature to accelerate solvent evaporation, followed by roller pressing to produce the positive electrode sheet. Finally, the positive electrode sheet is stacked with a solid electrolyte layer and a negative electrode material layer to form a battery cell. The conventional wet process suffers from issues such as solvent residue and poor interfacial contact. The dry process achieves uniform dispersion by mechanically mixing the ternary active materials with the conductive agent and binder through dry mixing (e.g., ball milling or drum mixing). This process eliminates the need for solvent intervention and avoids the impact of solvent residue on the ionic conductivity of the solid electrolyte. The mixed powder is then stacked on an aluminum foil current collector and formed by cold or hot pressing. This involves pressing the powder under a certain pressure (typically tens to hundreds of MPa) and temperature to form a compact positive electrode sheet. Finally, the positive electrode sheet is stacked and assembled with the solid electrolyte layer and negative electrode sheet to form the all-solid-state battery structure. However, although the dry process can avoid the use of solvents, it still faces the problem of rigid contact between the positive electrode and the solid electrolyte during the assembly of the all-solid-state battery, which leads to obstructed lithium ion transmission and thus poor interface contact. In addition, the existing dry process for preparing positive electrode sheets also faces problems such as interface debonding and irregular pore structure of the positive electrode sheets. Some pores are too large or have poor connectivity, which affects ion transmission and interface stability. At the same time, the dry mixing process is complex and it is difficult to achieve uniform dispersion of the ternary active material, solid electrolyte and conductive agent, which in turn affects the performance of the positive electrode sheet.

[0042] In summary, providing a method for preparing a positive electrode sheet that can improve the poor interface contact between the positive electrode sheet and the solid electrolyte and the low ion transfer efficiency and achieve high energy density and high cycle stability is a technical problem that needs to be solved urgently.

[0043] Based on the above technical problems, the inventors discovered in the process of studying the preparation method of the positive electrode sheet that by performing a gradient layering process on the mixed powder obtained by uniformly mixing the ternary active material, the conductive agent, and the binder by dry mechanical mixing, an inner layer powder and an outer layer powder are obtained, and a sulfide electrolyte is added to the inner layer powder and a binder is added to the outer layer powder, thereby preparing a positive electrode sheet with a gradient composite structure. This can effectively solve the problem of poor interface contact caused by the rigid contact between the positive electrode sheet and the solid electrolyte during the assembly process of the all-solid-state battery, thereby improving the ion transmission efficiency, reducing the problems of high porosity of the positive electrode sheet and interface debonding, and thus optimizing the performance of the positive electrode sheet. Based on this, the present application provides a positive electrode sheet, a preparation method thereof, and an all-solid-state battery.

[0044] The following specific embodiments describe in detail the technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0045] Figure 1 A schematic diagram of a process for preparing a positive electrode sheet provided in this application Figure 1 ,like Figure 1 As shown, the method includes:

[0046] S101: performing gradient layering processing on the mixed powder of the positive electrode material to obtain a first outer layer powder and a first inner layer powder.

[0047] In this step, gradient stratification treatment refers to the operation process of separating the mixed powder into different levels according to a certain gradient law in terms of physical or chemical properties based on the differences in particle size, density, morphology or composition distribution of the mixed powder particles of the positive electrode material through specific process means (such as air flow classification, centrifugal separation, etc.). Through gradient stratification treatment, the mixed powder forms a gradient functional distribution, thereby improving battery performance.

[0048] Exemplarily, the mixed powder of the positive electrode material is evenly separated into a first outer layer powder and a first inner layer powder by centrifugal separation, which serve as the base powders of the outer layer and the inner layer, respectively.

[0049] S102: Add sulfide solid electrolyte to the first outer layer powder and mix them evenly to obtain a second outer layer powder.

[0050] In this step, the sulfide solid electrolyte has high ion conductivity and is usually composed of lithium, sulfur and other elements, and has good flexibility and processing properties. Among them, nano-scale sulfide electrolyte refers to a sulfide solid electrolyte with a particle size of nanometer scale (usually 1 to 100 nanometers), which has a large specific surface area and can optimize the ion transmission path. At the same time, the nano-scale structure can effectively reduce the grain boundary resistance and shorten the lithium ion migration distance. The ion conductivity of some materials can reach 10 -3 S / cm, approaching or even exceeding the level of liquid electrolyte.

[0051] Exemplarily, nano-scale sulfide electrolyte Li6PS5Cl is added to the first outer layer powder and mixed evenly to obtain the second outer layer powder.

[0052] By adding nano-scale sulfide electrolyte to the first outer layer powder, not only can the grain boundary resistance be effectively reduced and the ion transmission efficiency be improved, but also the good flexible filling ability of nano-scale sulfide electrolyte nanoparticles can reduce the interface gap and reduce the interface impedance.

[0053] S103: Adding a binder to the first inner layer powder and mixing them evenly to obtain a second inner layer powder.

[0054] In this step, the binder is used to generate adhesion between the powder particles in the first inner layer, thereby bonding the dispersed particles into a whole and giving the material a certain formability and mechanical strength. That is, the first inner layer powder particles are firmly bonded through the viscosity of the binder, ensuring that the positive electrode material is not easy to fall off after being prepared into a pole piece and maintains a stable structure.

[0055] Binders include fibrous binders and non-fibrous binders. Fibrous binders have a one-dimensional fiber structure with a large aspect ratio. They can tightly connect particles through physical entanglement and mechanical interlocking, thereby providing strong structural support and mechanical strength to the material. Non-fibrous binders do not have a fibrous long-chain structure and usually exist in the form of particles, colloids, or molecular chains. They mainly rely on intermolecular forces (such as van der Waals forces and hydrogen bonds) or chemical reactions to bind to powder particles. They have good dispersibility and can evenly coat the surface of particles. Commonly used non-fibrous binders include polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), etc.

[0056] For example, a fibrous binder polytetrafluoroethylene (PTFE) and a non-fibrous binder polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) are added to the first inner layer powder and mixed evenly to obtain the second inner layer powder.

[0057] By adding a binder to the first inner layer powder, the structural integrity and mechanical strength of the positive electrode material can be significantly enhanced, ensuring that after the positive electrode material is prepared into a positive electrode sheet, its particles are not easy to fall off and maintain good structural stability.

[0058] S104: performing a pole piece forming process on the second outer layer powder and the second inner layer powder to obtain a positive pole piece.

[0059] In this step, the electrode sheet forming process involves preparing the second outer layer powder and the second inner layer powder into an electrode sheet with a specific shape and properties through a specific process. The resulting positive electrode sheet comprises a gradient composite structure consisting of an outer layer and an inner layer. The outer layer contains a mixed powder of the positive electrode material and a sulfide solid electrolyte, while the inner layer contains a mixed powder of the positive electrode material and a binder. The outer layer facilitates the construction of ion transport channels, while the inner layer enhances ion transport efficiency and the structural integrity and mechanical strength of the positive electrode material.

[0060] The embodiment of the present application provides a method for preparing a positive electrode plate, which comprises performing a gradient layering process on a mixed powder of a positive electrode material to obtain a first outer layer of powder and a first inner layer of powder, then adding a sulfide solid electrolyte to the first outer layer of powder and a binder to the first inner layer of powder, mixing them evenly to obtain a second outer layer of powder and a second inner layer of powder, and finally performing a plate forming process on the second outer layer of powder and the second inner layer of powder to obtain a positive electrode plate. The prepared positive electrode plate has a gradient distribution function, and the sulfide electrolyte in the outer layer constructs a continuous ion channel, improves the rigid contact between the positive electrode plate and the solid electrolyte, improves the ion transmission efficiency, and improves the problem of poor interface contact; the binder in the inner layer reduces the problems of high porosity of the positive electrode plate and interface debonding. Through the above method, the active material, solid electrolyte, conductive agent and binder are more evenly dispersed, the stability of the positive electrode plate structure is enhanced, and the overall performance of the positive electrode plate is improved.

[0061] exist Figure 1 Based on the examples, in one possible implementation manner, the mass of the sulfide solid electrolyte is 2% to 5% of the mass of the mixed powder.

[0062] That is to say, when a sulfide solid electrolyte is added to the first outer layer powder, the mass of the sulfide solid electrolyte can be 2%, 3%, 4% or 5% of the mass of the mixed powder. In actual application, it can be appropriately adjusted according to specific needs, and this application does not make specific limitations.

[0063] exist Figure 1 Based on the examples, in a possible implementation manner, the mass of the fibrous binder is 2% to 3% of the mass of the mixed powder, and the mass of the non-fibrous binder is 1.5% to 2% of the mass of the mixed powder.

[0064] That is to say, when a fibrous binder is added to the first inner layer powder, the mass of the fibrous binder can be 2%, 2.5%, 2.8% or 3% of the mass of the mixed powder; when a non-fibrous binder is added to the first inner layer powder, the mass of the non-fibrous binder can be 1.5%, 1.7%, 1.8% or 2% of the mass of the mixed powder. In actual application, it can be appropriately adjusted according to specific needs, and this application does not make specific limitations.

[0065] exist Figure 1 Based on the embodiment, in a possible implementation manner, before the mixed powder of the positive electrode material is subjected to gradient layering treatment, the method for preparing the positive electrode plate further includes: uniformly mixing the ternary active material, the oxide solid electrolyte and the conductive agent, and adding the eutectic electrolyte to obtain a mixed powder.

[0066] In one possible embodiment, the eutectic electrolyte is LiTFSI-urea-acetamide.

[0067] Ternary active materials usually refer to composite metal oxides composed of three transition metal elements and are an important type of positive electrode material for lithium-ion batteries. Its chemical formula can be expressed as LiNi x Co y Mn z O2, in which three metal elements, nickel (Ni), cobalt (Co), and manganese (Mn), are combined in different proportions. Nickel is used to increase the specific capacity of the material, cobalt is used to improve the conductivity and structural stability of the material, and manganese is used to enhance the safety of the material and reduce costs.

[0068] Oxide solid electrolytes are solid ion conducting materials based on metal oxides, which are used to provide a conductive path for lithium ions. Commonly used oxide solid electrolytes include garnet type (Li7La3Zr2O 12 , LLZO), perovskite type (Li 3x La 2 / 3-x TiO3, LLTO).

[0069] Conductive agents are added to the positive electrode materials to connect with each other to form an efficient electronic conductive network. Commonly used conductive agents include carbon black, carbon nanotubes and graphene. Eutectic electrolyte is a mixture of two or more components with a melting point lower than the individual melting points of each component. The use of eutectic electrolyte can reduce interfacial impedance and improve the overall performance of the battery.

[0070] Commonly used ternary active materials include lithium nickel cobalt manganese oxide (LiNi xCoMnO2, NCM), lithium nickel cobalt aluminate (LiNiCoAlO2, NCA), among which commonly used NCMs include NCM811, NCM622 and NCM712. NCM811 refers to a molar ratio of nickel, cobalt and manganese of 8:1:1. The high nickel content makes NCM811 have a higher energy density; NCM622 refers to a molar ratio of nickel, cobalt and manganese of 6:2:2. Compared with NCM811, NCM622 has better thermal stability and cycle life; NCM712 refers to a molar ratio of nickel, cobalt and manganese of 7:1:2. The performance of NCM712 is between NCM811 and NCM622. Compared with NCM811, NCM712 improves the stability of the material by increasing the proportion of manganese while still maintaining a higher energy density.

[0071] LiTFSI-urea-acetamide is a eutectic electrolyte formed through the synergistic action of three components: LiTFSI, urea, and acetamide. Lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), a commonly used lithium salt, serves as a lithium ion source in the electrolyte. Its anionic structure has low coordination ability and good chemical stability, which facilitates the dissociation and migration of lithium ions. Urea (CO(NH2)2), a nitrogen-containing organic compound, coordinates with lithium ions in the lithium salt through its amino groups, promoting lithium salt dissolution and ion conduction. Acetamide (CH3CONH2), an organic compound, forms a low-melting-point eutectic mixture with LiTFSI and urea. The carbonyl and amino groups in its molecules interact with lithium ions, regulating the melting point, viscosity, and ion conductivity of the eutectic system. The eutectic electrolyte LiTFSI-urea-acetamide forms a eutectic system with a specific phase diagram and physicochemical properties through the synergistic action of the three components. Its eutectic properties avoid the high melting point disadvantages of a single component, while optimizing the ion transport environment through interactions between the components, thereby enhancing battery performance.

[0072] Exemplarily, the ternary active material NCM811, the oxide solid electrolyte LLZO and the conductive agent graphene are uniformly mixed in a mass ratio of 85:10:5, and the eutectic electrolyte LiTFSI-urea-acetamide is added, and stirred at a speed of 5000 r / min in a high-speed mixer for 30 minutes to obtain a mixed powder.

[0073] Figure 2 A schematic diagram of a process for preparing a positive electrode sheet provided in this application Figure 2 ,like Figure 2 As shown, in Figure 1 Based on the embodiment, in S104, the second outer layer powder and the second inner layer powder are subjected to a pole piece forming process to obtain a positive pole piece, which specifically includes the following steps:

[0074] S201: performing a fiberization treatment on the second outer layer powder and the second inner layer powder to obtain pre-fiberized powder.

[0075] In this step, fiberization treatment refers to the process of forming a fibrous structure of the second outer layer powder particles and the second inner layer powder particles through physical or chemical processes. Common methods include electrospinning, melt spinning, sol-gel spinning, etc. During this process, the sulfide electrolyte particles in the second outer layer powder and the binder molecules in the second inner layer powder will be evenly dispersed in the fiber structure, forming an interpenetrating network through intermolecular forces or chemical bonding.

[0076] Exemplarily, the second outer layer powder and the second inner layer powder are placed in a stirring tank, stirred at a low speed of 200 r / min for 10 minutes at a low temperature (0°C~10°C), and kept at 90°C for 2 hours to pre-fiberize the binder to obtain pre-fiberized powder.

[0077] By fiberizing the second outer layer powder and the second inner layer powder, the ion conduction characteristics of the sulfide electrolyte are retained and the mechanical strength of the material is enhanced through the fiber network. At the same time, the pores between the fibers can provide a buffer space for the volume change of the electrode, and can also optimize the wettability of the solid electrolyte, laying the foundation for subsequent coating, rolling and other processes during the electrode forming process, so that the final positive electrode sheet has both ion transmission efficiency and structural stability.

[0078] S202: performing supersonic airflow dispersion treatment on the pre-fiberized powder using a supersonic airflow to obtain a second mixed powder.

[0079] Supersonic airflow refers to high-speed airflow exceeding the speed of sound. It is typically generated by accelerating high-pressure gas through a Laval nozzle and possesses extremely high kinetic energy and turbulence intensity. Supersonic airflow dispersion utilizes the strong shear, impact, and turbulence effects of supersonic airflow to fully disperse pre-fiberized powder particles within the airflow. Specifically, when pre-fiberized powder enters the supersonic airflow field, the high-speed airflow drags the particles, generating enormous kinetic energy. This leads to high-frequency collisions between particles and with the walls of the equipment. Simultaneously, the shear forces generated by the strong turbulence disrupt entanglements and agglomerates between fibers, dissociating previously adherent fibrous structures into a more evenly dispersed state.

[0080] Exemplarily, the pre-fiberized powder material is placed in a supersonic airflow mill, and a supersonic airflow (supersonic airflow velocity is greater than 300 m / s) is used to drag the pre-fiberized powder particles by the high-speed airflow to obtain huge kinetic energy, so that the binder is coated on the surface of the positive electrode active material to obtain a fiberized and coated second mixed powder.

[0081] By subjecting the pre-fiberized powder to supersonic airflow dispersion treatment, the resulting fiberized coated second mixed powder has better fluidity and uniformity, facilitating subsequent mixing with other components or processes such as electrode forming. It can also reduce problems such as local resistance anomalies or uneven ion conduction caused by powder agglomeration.

[0082] S203: stacking the outer layer powder and the inner layer powder in the second mixed powder in sequence on a carbon-coated aluminum foil current collector and performing hot roller pressing to obtain a positive electrode sheet.

[0083] In this step, the hot rolling temperature is 120-250°C, the hot rolling pressure is 5-15 MPa, and the hot rolling speed is 3-10 m / min. In other words, in actual hot rolling processing, the hot rolling temperature can be 120°C, 150°C, 180°C, 200°C, or 250°C, the hot rolling pressure can be 5 MPa, 8 MPa, 10 MPa, 13 MPa, or 15 MPa, and the hot rolling speed can be 3 m / min, 5 m / min, 8 m / min, or 10 m / min. These can be adjusted appropriately according to specific needs in actual applications.

[0084] Exemplarily, the outer layer powder and the inner layer powder of the fiberized coated second mixed powder are stacked in sequence on the carbon-coated aluminum foil current collector, and are rolled at a heating roller working temperature of 150°C, a pressure of 10 MPa, and a speed of 8 m / min to obtain a gradient-distributed positive electrode sheet.

[0085] During the hot roller pressing process, the eutectic electrolyte forms a stable solid electrolyte interface (SEI) in situ at the interface of the positive electrode sheet. This is a solid film that is ionically conductive but electronically insulating. This film evenly covers the interface between the active material and the solid electrolyte, improving interfacial contact and reducing interfacial impedance, which plays a key role in the battery's cycle life and safety. During the in-situ film formation process, hot pressing promotes the reaction of the eutectic electrolyte at the interface, forming an SEI film that adheres tightly to the surface of the positive electrode sheet, optimizing ion transport pathways and improving battery performance.

[0086] The embodiment of the present application provides a method for preparing a positive electrode plate, which performs a fiberization treatment on the second outer layer powder and the second inner layer powder to form a fibrous structure, and then uses a supersonic airflow to disperse the pre-fiberized powder, thereby enhancing the fluidity and uniformity of the powder and reducing the problems of local resistance anomalies or uneven ion conduction caused by powder agglomeration. Finally, the outer layer powder and the inner layer powder of the fiberized coated second mixed powder are stacked in sequence on a carbon-coated aluminum foil current collector and hot rolled to form a gradient-distributed positive electrode plate. During the hot rolling process, the solid electrolyte interface (SEI) film formed in situ improves the interface contact, reduces the interface impedance, and improves the cycle life and safety of the battery. Overall, the above method improves the ion transmission efficiency and structural stability of the positive electrode plate, thereby improving the overall performance and reliability of the battery.

[0087] Based on the above embodiment, the method for preparing the positive electrode sheet further includes:

[0088] In a possible implementation, the positive electrode sheet is immersed in a eutectic electrolyte solution to obtain an immersed positive electrode sheet.

[0089] Exemplarily, LiTFSI, urea, and acetamide are mixed and dissolved in an inert atmosphere at a specific molar ratio (for example, LiTFSI: urea: acetamide = 1:2:3) to obtain a LiTFSI, urea, and acetamide eutectic electrolyte solution, and the positive electrode sheet is soaked in the eutectic electrolyte solution at 25°C to 60°C for 30 minutes to 2 hours to allow the solution to fully penetrate into the inter-fiber pores and particle gaps of the positive electrode sheet, thereby obtaining a soaked positive electrode sheet.

[0090] In a possible implementation, the soaked positive electrode sheet is vacuum dried to obtain a new positive electrode sheet, and the filling porosity of the new positive electrode sheet is 30% to 50%.

[0091] In a possible embodiment, during the vacuum drying process, the drying temperature is 60-80° C., and / or the drying time is 8-12 hours.

[0092] That is to say, in the actual vacuum drying process, the drying temperature can be 60°C, 65°C, 70°C, 75°C or 80°C, and the drying time can be 8h, 9h, 10h, 11h or 12h, etc., which can be appropriately adjusted according to specific needs in actual applications.

[0093] Exemplarily, after the soaking is completed, the soaked positive electrode plate is vacuum dried at 60°C for 8 hours to remove excess electrolyte solution and retain an appropriate amount of electrolyte, for example, the residual amount is controlled to 5% to 10% of the plate mass, such as 5%, 7%, 8% or 10%, etc., to obtain a new positive electrode plate.

[0094] Porosity is a parameter that measures the internal pore structure of the positive electrode material; it is the ratio of the pore volume of the positive electrode to the total volume of the positive electrode. The eutectic electrolyte solution permeates the interfiber pores and intergranular spaces of the positive electrode. After vacuum drying, the eutectic electrolyte solution that has permeated the interfiber pores and intergranular spaces of the positive electrode solidifies, effectively filling the originally irregular pores and forming a uniform pore structure that is conducive to ion transport. The new positive electrode has a filling porosity of 30% to 50%. That is, by controlling the residual amount of eutectic electrolyte in the electrode, the porosity of the new positive electrode can reach 30%, 35%, 40%, 45%, or 50%.

[0095] The present application provides a positive electrode sheet, comprising: a gradient composite structure consisting of an outer layer and an inner layer, wherein the gradient composite structure of the positive electrode sheet specifically comprises:

[0096] In a possible embodiment, the outer layer contains a mixed powder of the positive electrode material and a sulfide solid electrolyte, and the inner layer contains a mixed powder of the positive electrode material and a binder.

[0097] As described in the above embodiments, the mixed powder includes a ternary active material, an oxide solid electrolyte, a conductive agent, and a eutectic electrolyte. For example, the ternary active material may be NCM, NCA, etc., the oxide solid electrolyte may be LLZO, LLTO, etc., the conductive agent may be carbon black, carbon nanotubes, graphene, etc., and the eutectic electrolyte may be LiTFSI-urea-acetamide, etc.

[0098] The gradient composite structure of the mixed powder is a gradient structure including an inner layer base powder and an outer layer base powder obtained by subjecting the mixed powder to a specific separation process.

[0099] Among them, the outer layer contains a mixed powder of positive electrode materials and a sulfide solid electrolyte, that is, a sulfide solid electrolyte is added to the outer layer basic powder; the inner layer contains a mixed powder of positive electrode materials and a binder, that is, a binder is added to the inner layer basic powder.

[0100] For example, the sulfide solid electrolyte may be a nano-scale sulfide electrolyte Li6PS5Cl, the binder may be a fibrous binder polytetrafluoroethylene (PTFE), and the non-fibrous binder may be a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0101] In one possible embodiment, since a sulfide solid electrolyte is added to the outer layer base powder, it is understandable that the content of the solid electrolyte (including the oxide solid electrolyte and the sulfide solid electrolyte) in the outer layer is greater than the content of the solid electrolyte in the inner layer.

[0102] In another possible embodiment, since a binder is added to the base powder of the inner layer, it can be understood that the total content of the conductive agent and the binder in the inner layer is greater than the total content of the conductive agent and the binder in the outer layer.

[0103] The fibrous binder and non-fibrous binder are evenly coated on the surface of the active material, forming a continuous fibrous coating, which can effectively enhance the bonding between the active materials and between the active materials and the current collector. The fibrous binder can also tightly connect the particles through physical entanglement and mechanical interlocking, building a dense three-dimensional network structure. This not only improves the mechanical strength of the positive electrode sheet, but also reduces the disordered distribution of internal pores, making the positive electrode sheet structure more stable.

[0104] The outer layer is rich in nano-scale sulfide solid electrolyte (Li6PS5Cl) and oxide solid electrolyte (LLZO), while the inner layer contains a higher proportion of conductive agent (graphene) as well as PTFE fibrous binder and PVDF-HFP non-fibrous binder. The high content of graphene conductive agent in the inner layer is interconnected to form an efficient electronic conductive network, which cooperates with the good ion transmission channel in the outer layer to achieve efficient coordination of ion and electron transmission in the positive electrode sheet, thereby improving the overall conductivity of the positive electrode sheet.

[0105] In one possible embodiment, the mass of the sulfide solid electrolyte in the outer layer is 2% to 5% of the mass of the mixed powder.

[0106] That is to say, the mass of the sulfide solid electrolyte in the outer layer can be 2%, 3%, 4% or 5% of the mass of the mixed powder.

[0107] In one possible embodiment, the binder in the inner layer includes a fibrous binder and a non-fibrous binder, wherein the mass of the fibrous binder is 2% to 3% of the mass of the mixed powder, and the mass of the non-fibrous binder is 1.5% to 2% of the mass of the mixed powder.

[0108] That is to say, the mass of the fibrous binder in the inner layer can be 2%, 2.5%, 2.8% or 3% of the mass of the mixed powder; the mass of the non-fibrous binder can be 1.5%, 1.7%, 1.8% or 2% of the mass of the mixed powder.

[0109] In one possible embodiment, the filling porosity of the positive electrode sheet is 30% to 50%.

[0110] As described in the above embodiments, the eutectic electrolyte solution fully penetrates into the inter-fiber pores and particle gaps of the positive electrode plate. After drying, the eutectic electrolyte solution solidifies, effectively filling the originally irregular pores to form a uniform pore structure that is conducive to ion transmission. The filling porosity of the new positive electrode plate is 30% to 50%. For example, the filling porosity of the new positive electrode plate can reach 30%, 35%, 40%, 45% or 50%.

[0111] The present application also provides an all-solid-state battery, comprising a positive electrode, a negative electrode and a solid electrolyte, wherein the positive electrode is the positive electrode sheet described in the above embodiment or a Figure 1 The positive electrode sheet is prepared by the method described in the embodiment.

[0112] The following will introduce the positive electrode plate and its preparation method and all-solid-state battery provided by this application in detail through specific examples.

[0113] Unless otherwise specified, the reagents, materials, and instruments used in the following examples are conventional reagents, conventional materials, and conventional instruments in the art and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0114] Example 1

[0115] This embodiment provides a positive electrode sheet, the preparation method of which includes the following steps:

[0116] (1) The ternary active material NCM811, the oxide solid electrolyte LLZO, and the conductive agent graphene are uniformly mixed, and the eutectic electrolyte powder LiTFSI-urea-acetamide is added to obtain a mixed powder. The mass ratio of NCM811, LLZO, graphene, and LiTFSI-urea-acetamide is 85:10:5:3;

[0117] (2) performing gradient layering on the mixed powder obtained in step (1) to obtain a first outer layer powder and a first inner layer powder;

[0118] (3) Adding sulfide solid electrolyte Li6PS5Cl in an amount of 5% of the mass of the mixed powder to the first outer layer powder obtained in step (2), mixing the mixture evenly, and obtaining a second outer layer powder;

[0119] (4) Adding 3% of the mass of the mixed powder to the first inner layer powder obtained in step (2) is a PTFE fibrous binder and 2% of the mass of the mixed powder to the PVDF-HFP non-fibrous binder, and mixing them evenly to obtain a second inner layer powder;

[0120] (5) placing the second outer layer powder obtained in step (3) and the second inner layer powder obtained in step (4) in a stirring tank, stirring them at a low speed of 200 r / min at 5°C for 10 minutes, and keeping them at 90°C for 2 hours to obtain pre-fiberized powder;

[0121] (6) placing the pre-fiberized powder obtained in step (5) in a supersonic airflow mill, and subjecting it to supersonic airflow dispersion treatment by a supersonic airflow of 340 m / s to obtain a second mixed powder;

[0122] (7) The outer layer powder and the inner layer powder of the second mixed powder obtained in step (6) are stacked on a carbon-coated aluminum foil current collector in sequence, and roller-pressed at a heating roller working temperature of 150°C, a pressure of 10 MPa, and a speed of 5 m / min to obtain a positive electrode sheet with a gradient distribution.

[0123] Example 2

[0124] This embodiment provides a positive electrode sheet, and its preparation method is basically the same as that of Example 1, except that:

[0125] (1) The ternary active material NCM622, the oxide solid electrolyte LLZO, and the conductive agent graphene are uniformly mixed, and the eutectic electrolyte powder LiTFSI-urea-acetamide is added to obtain a mixed powder. The mass ratio of NCM622, LLZO, graphene, and LiTFSI-urea-acetamide is 80:10:5:3;

[0126] (2) to (6) are the same as steps (2) to (6) in Example 1;

[0127] (7) The outer layer powder and the inner layer powder of the second mixed powder obtained in step (6) are stacked in sequence on a carbon-coated aluminum foil current collector, and roller-pressed at a heating roller operating temperature of 180°C, a pressure of 12 MPa, and a speed of 3 m / min to obtain a gradient-distributed positive electrode sheet.

[0128] Example 3

[0129] This embodiment provides a positive electrode sheet, and its preparation method is basically the same as that of Example 1, except that:

[0130] (1) The ternary active material NCM712, the oxide solid electrolyte LLZO, and the conductive agent carbon nanotubes were mixed evenly, and the eutectic electrolyte powder LiTFSI-urea-acetamide was added to obtain a mixed powder. The mass ratio of NCM712, LLZO, carbon nanotubes, and LiTFSI-urea-acetamide was 83:12:3:3;

[0131] (2) The same as step (2) in Example 1;

[0132] (3) Adding sulfide solid electrolyte Li6PS5Cl in an amount of 2% of the mass of the mixed powder to the first outer layer powder obtained in step (2), mixing the mixture evenly, and obtaining a second outer layer powder;

[0133] (4) Adding 2.5% of the mass of the mixed powder to the first inner layer powder obtained in step (2) of the PTFE fibrous binder and 1.5% of the mass of the mixed powder to the PVDF-HFP non-fibrous binder, and mixing them evenly to obtain the second inner layer powder;

[0134] (5) to (6) are the same as steps (5) to (6) in Example 1;

[0135] (7) The outer layer powder and the inner layer powder of the second mixed powder obtained in step (6) are stacked on a carbon-coated aluminum foil current collector in sequence, and roller-pressed at a heating roller working temperature of 160°C, a pressure of 11 MPa, and a speed of 4 m / min to obtain a positive electrode sheet with a gradient distribution.

[0136] Example 4

[0137] This embodiment provides a positive electrode sheet, and its preparation method is basically the same as that of Example 1, except that:

[0138] (1) The ternary active material NCA, the oxide solid electrolyte LLZO, and the conductive agent graphene are uniformly mixed, and the eutectic electrolyte powder LiTFSI-urea-acetamide is added to obtain a mixed powder. The mass ratio of NCA, LLZO, graphene, and LiTFSI-urea-acetamide is 80:15:3:3;

[0139] (2) The same as step (2) in Example 1;

[0140] (3) Adding sulfide solid electrolyte Li6PS5Cl in an amount of 2% of the mass of the mixed powder to the first outer layer powder obtained in step (2), mixing the mixture evenly, and obtaining a second outer layer powder;

[0141] (4) Adding PTFE fibrous binder having a mass of 2% of the mass of the mixed powder and PVDF-HFP non-fibrous binder having a mass of 2% of the mass of the mixed powder to the first inner layer powder obtained in step (2), and mixing them evenly to obtain a second inner layer powder;

[0142] (5) to (6) are the same as steps (5) to (6) in Example 1;

[0143] (7) The outer layer powder and the inner layer powder of the second mixed powder obtained in step (6) are stacked on a carbon-coated aluminum foil current collector in sequence, and roller-pressed at a heating roller working temperature of 155°C, a pressure of 10 MPa, and a speed of 5 m / min to obtain a gradient-distributed positive electrode sheet.

[0144] Comparative Example 1

[0145] This embodiment provides a positive electrode sheet, the preparation method of which includes the following steps:

[0146] (1) The ternary active material NCM811, the binder PVDF, the conductive agent carbon black SP and the carbon nanotubes CNT were mixed in an organic solvent N-methylpyrrolidone NMP in a mass ratio of 97.6:1.1:0.9:0.4, and mixed evenly to obtain a positive electrode slurry; wherein the mass of NMP is 70% of the mass of the solid dissolved therein;

[0147] (2) The positive electrode slurry obtained in step (1) is evenly coated on the carbon-coated aluminum foil current collector, vacuum dried at 80°C for 24 hours, and then rolled to obtain a positive electrode sheet.

[0148] Comparative Example 2

[0149] This embodiment provides a positive electrode sheet, the preparation method of which includes the following steps:

[0150] (1) The ternary active material NCM811, the binder PTFE, and the conductive agent vapor-grown carbon fiber VGCF were mixed uniformly in a mass ratio of 96.5:3:0.5 to obtain a positive electrode powder;

[0151] (2) The positive electrode powder obtained in step (1) is stacked on a carbon-coated aluminum foil current collector and subjected to roller pressing at a heating roller operating temperature of 150°C, a pressure of 10 MPa, and a speed of 5 m / min to obtain a positive electrode sheet.

[0152] Assembling the battery

[0153] The positive electrode sheet prepared in Example 1 was used as the positive electrode and assembled with a lithium metal negative electrode and a sulfide solid electrolyte Li6PS5Cl to obtain an all-solid-state battery.

[0154] The positive electrode sheet prepared in Example 2 was used as the positive electrode and assembled with a lithium metal negative electrode and an oxide solid electrolyte LLZO to obtain an all-solid-state battery.

[0155] The positive electrode sheet prepared in Example 3 was used as the positive electrode and assembled with a lithium metal negative electrode and a composite solid electrolyte LLZO-Li6PS5Cl to obtain an all-solid-state battery, wherein the mass ratio of LLZO to Li6PS5Cl was 3:1.

[0156] The positive electrode sheet prepared in Example 4 was used as the positive electrode, and the lithium metal negative electrode and the sulfide solid electrolyte Li 10 GeP2S 12 Assemble to obtain an all-solid-state battery.

[0157] The positive electrode sheet prepared in Comparative Example 1 was used as the positive electrode and assembled with a lithium metal negative electrode and a sulfide solid electrolyte Li6PS5Cl to obtain an all-solid-state battery.

[0158] The positive electrode sheet prepared in Comparative Example 2 was used as the positive electrode and assembled with a lithium metal negative electrode and a sulfide solid electrolyte Li6PS5Cl to obtain an all-solid-state battery.

[0159] Test Case

[0160] First, the all-solid-state battery prepared in the above embodiment is subjected to standard charging. First, it is charged at a set current constant current until the battery voltage reaches the rated value, and then switched to constant voltage charging until the current drops to the specified threshold. After charging is completed, constant current discharge is performed at a rate of 0.5C, and the change in voltage over time during the discharge process is recorded until the voltage drops to the cut-off voltage. The first discharge specific capacity is obtained by calculating the discharge capacity and dividing it by the mass of the active material. After the first charge and discharge is completed, the operation is repeated according to the charge-discharge cycle. Each charge and discharge is maintained at a rate of 0.5C. Each completed charge and discharge is regarded as a cycle. The discharge capacity is recorded regularly during the cycle. When the number of cycles reaches 200, the discharge capacity at this time is measured and compared with the first discharge specific capacity to calculate the capacity retention rate. Constant current condition: 0.1mA / cm 2 The performance test results are shown in Table 1.

[0161] Table 1 Performance test results

[0162]

[0163] According to Table 1, the following conclusions can be drawn:

[0164] As the experimental group, Examples 1 to 4 have higher initial discharge specific capacities at a rate of 0.5C than Comparative Example 1 and Comparative Example 2, wherein the initial discharge specific capacity of Example 4 reaches 185 mAh / g, the highest value among all groups. The initial discharge specific capacities of Examples 1 and 3 are 180 mAh / g and 178 mAh / g, respectively, and that of Example 2 is slightly lower at 172 mAh / g, but still significantly higher than 150 mAh / g of Comparative Example 1 and 160 mAh / g of Comparative Example 2, indicating that the internal lithium ion transmission of the all-solid-state batteries of Examples 1 to 4 is smoother, that is, the interface contact state is better, reducing the transmission resistance caused by rigid contact.

[0165] In terms of capacity retention after 200 cycles, Example 2 performed best, reaching 88%, while Example 1 and Example 3 were 85% and 86% respectively, and Example 4 was 84%. The capacity retention rates of Comparative Example 1 and Comparative Example 2 were only 65% and 70% respectively, which were significantly lower than those of the experimental group, indicating that the interface stability of the all-solid-state batteries of Examples 1 to 4 was stronger, and the lithium ion transmission path was more stable during the cycle, effectively solving the problem of poor interface contact.

[0166] In summary, the positive electrode plate, its preparation method, and all-solid-state battery provided in this application can effectively improve the problem of poor interface contact caused by the rigid contact between the positive electrode plate and the solid electrolyte, which leads to obstruction of lithium ion transmission.

[0167] Finally, it should be noted that those skilled in the art will readily identify other embodiments 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 that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The present invention is not limited to the precise structure described above and illustrated in the accompanying drawings, and various modifications and variations may be made without departing from the scope thereof. The scope of the present invention is limited solely by the appended claims.

Claims

1. A positive electrode plate, characterized in that: include: A gradient composite structure consisting of an outer layer and an inner layer; Wherein, the outer layer contains a mixed powder of positive electrode materials and a sulfide solid electrolyte; The inner layer contains mixed powder of positive electrode materials and a binder.

2. The positive electrode sheet according to claim 1, characterized in that: The mass of the sulfide solid electrolyte is 2% to 5% of the mass of the mixed powder.

3. The positive electrode sheet according to claim 1, characterized in that: The binder includes a fibrous binder and a non-fibrous binder; Wherein, the mass of the fibrous binder is 2% to 3% of the mass of the mixed powder; The mass of the non-fibrous binder is 1.5% to 2% of the mass of the mixed powder.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The mixed powder includes a ternary active material, an oxide solid electrolyte, a conductive agent and a eutectic electrolyte.

5. The positive electrode sheet according to claim 4, characterized in that: The eutectic electrolyte is LiTFSI-urea-acetamide.

6. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The filling porosity of the positive electrode plate is 30% to 50%.

7. A method for preparing a positive electrode sheet according to any one of claims 1 to 6, characterized in that: include: Performing a gradient layering process on the mixed powder of the positive electrode material to obtain a first outer layer powder and a first inner layer powder; Adding a sulfide solid electrolyte to the first outer layer powder and mixing them evenly to obtain a second outer layer powder; Adding a binder to the first inner layer powder and mixing them evenly to obtain a second inner layer powder; The second outer layer powder and the second inner layer powder are subjected to a pole piece forming process to obtain a positive pole piece.

8. The method according to claim 7, characterized in that The mass of the sulfide solid electrolyte is 2% to 5% of the mass of the mixed powder.

9. The method according to claim 7, characterized in that The binder includes a fibrous binder and a non-fibrous binder; The mass of the fibrous binder is 2% to 3% of the mass of the mixed powder; The mass of the non-fibrous binder is 1.5% to 2% of the mass of the mixed powder.

10. The method according to any one of claims 7 to 9, characterized in that The method further comprises: Soaking the positive electrode sheet in a eutectic electrolyte solution to obtain a soaked positive electrode sheet; The soaked positive electrode sheet is vacuum dried to obtain a new positive electrode sheet, wherein the filling porosity of the new positive electrode sheet is 30% to 50%.

11. The method according to claim 10, characterized in that During the vacuum drying process, the drying temperature is 60-80° C., and / or the drying time is 8-12 hours.

12. The method according to any one of claims 7 to 9, characterized in that Before performing the gradient layering process on the mixed powder of the positive electrode material, the method further comprises: The ternary active material, the oxide solid electrolyte and the conductive agent are mixed evenly, and the eutectic electrolyte is added to obtain a mixed powder.

13. The method according to claim 12, characterized in that The eutectic electrolyte is LiTFSI-urea-acetamide.

14. An all-solid-state battery, characterized in that: The invention comprises a positive electrode, a negative electrode and a solid electrolyte, wherein the positive electrode is the positive electrode sheet according to any one of claims 1 to 6 or the positive electrode sheet prepared by the method according to any one of claims 7 to 13.

Images