Positive electrode sheet, positive electrode sheet electrochemical performance evaluation method, solid-state battery and electrical equipment

Abstract

The present application provides a positive electrode sheet, a method for evaluating the electrochemical performance of a positive electrode sheet, a solid-state battery, and an electrical device. The positive electrode sheet includes a positive electrode active material layer and a positive electrode electrolyte, and pores are present in the positive electrode active material layer. In a vertical cross-section of the positive electrode active material layer, the total length of the contact interface between the positive electrode active material and the positive electrode electrolyte is defined as the first type of contact interface total length L1, the total length of the contact interface between the positive electrode active material and the positive electrode active material is the second type of contact interface total length L2, and the total length of the contact interface between the positive electrode active material and the pores is the third type of contact interface total length L3. The length ratio of L1, L2, and L3 satisfies: L1: L2: L3 = (80-99): (1-20): (0-5), and the sum of L1, L2, and L3 is 100. The positive electrode sheet has excellent comprehensive electrochemical performance, a simple evaluation method process, a wide range of applications, and can be used to quickly evaluate the electrochemical performance of the positive electrode sheet.

Description

Technical Field

[0001] The present application relates to the field of batteries, and specifically to positive electrode sheets, methods for evaluating the electrochemical performance of positive electrode sheets, solid-state batteries, and electrical equipment. Background Art

[0002] Currently, solid-state batteries are attracting much attention due to their high energy density and high safety. In solid-state batteries, the contact between solid particles within the positive electrode determines the construction of ion and electron pathways, which directly affects the electrical performance of solid-state batteries. Related technologies have mostly focused on the contact between the positive electrode and the solid electrolyte layer, ignoring the contact state of particles within the positive electrode active material layer of the positive electrode. There is also no effective method to evaluate the construction of ion and electron pathways in the positive electrode active material layer. Summary of the Invention

[0003] In view of this, the present application provides a positive electrode sheet, a method for evaluating the electrochemical performance of a positive electrode sheet, a solid-state battery, and an electrical device. The positive electrode sheet has low resistance, high specific capacity, and high ionic conductivity, resulting in excellent electrochemical performance and beneficial for improving the performance of solid-state batteries. The electrochemical performance evaluation method for a positive electrode sheet is simple and has a wide range of applications. It classifies and evaluates the contact state of particles within the positive electrode sheet, ensuring a good ionic conduction path and excellent specific capacity, thereby improving the electrochemical performance of the positive electrode sheet.

[0004] In a first aspect, the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material and a positive electrode electrolyte, and pores are present in the positive electrode active material layer;

[0005] Taking at least one vertical cross-section of the positive electrode active material layer, defining the total length of the contact interface between the positive electrode active material and the positive electrode electrolyte in the at least one vertical cross-section as a first-type total contact interface length L1, the total length of the contact interface between the positive electrode active material and the positive electrode active material as a second-type total contact interface length L2, and the total length of the contact interface between the positive electrode active material and the pores as a third-type total contact interface length L3;

[0006] Among them, the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface satisfies: L1:L2:L3=(80-99):(1-20):(0-5), and the sum of L1, L2 and L3 is 100.

[0007] In an embodiment of the present application, the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface satisfies: L1:L2:L3=(85-95):(5-15):(0-2), and the sum of L1, L2 and L3 is 100.

[0008] In the embodiment of the present application, the mass percentage of the positive electrode active material in the positive electrode active material layer is 50%-90%, and the mass percentage of the positive electrode electrolyte in the active positive electrode material layer is 10%-50%.

[0009] In the embodiment of the present application, the volume percentage of the pores in the positive electrode active material layer is less than or equal to 5%, and the pore diameter is 0.1 μm-5 μm.

[0010] In an embodiment of the present application, the positive electrode active material includes at least one of lithium iron phosphate, lithium cobaltate, lithium manganate, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganate and lithium nickel manganate, and the positive electrode electrolyte includes at least one of an oxide electrolyte, a sulfide electrolyte and a polymer electrolyte.

[0011] In the embodiment of the present application, the sulfide electrolyte includes Li3PS4, Li 5.5 PS 4.5 Cl 1.5 、Li7P3S 11 、Li 11 GeP2S 12 、Li6PS5Cl、Li7P2S8I、Li 10 SnP2S 12 He Li 3.25 Ge 0.25 P 0.75 At least one of S4.

[0012] The positive electrode sheet provided in the present application controls the three types of contacts in the positive electrode active material layer, namely, the contact between the positive electrode active material and the positive electrode electrolyte, the contact between the positive electrode active material and the positive electrode active material, and the contact between the positive electrode active material and the pores, within a suitable proportion range. This enables the positive electrode sheet to have a larger number of ion conduction pathways, thereby improving the ion conductivity, which is beneficial to increasing the specific capacity of the positive electrode sheet and improving the electrochemical performance of the positive electrode sheet.

[0013] In a second aspect, the present application provides a method for evaluating the electrochemical performance of a positive electrode sheet, comprising:

[0014] Providing a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material and a positive electrode electrolyte, and pores existing in the positive electrode active material layer;

[0015] The positive electrode sheet is cut along the thickness direction of the positive electrode sheet to obtain a vertical cross section of the positive electrode active material layer; at least one vertical cross section of the positive electrode active material layer is taken, and the total length of the contact interface between the positive electrode active material and the positive electrode electrolyte in the at least one vertical cross section is defined as a first type of contact interface total length L1, the total length of the contact interface between the positive electrode active material and the positive electrode active material is defined as a second type of contact interface total length L2, and the total length of the contact interface between the positive electrode active material and the pore is defined as a third type of contact interface total length L3;

[0016] The total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface in the vertical cross-section of the positive electrode active material layer are obtained by characterization means, and the ratio L1:L2:L3 of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface are calculated. The electrochemical performance of the positive electrode sheet is evaluated by judging whether L1:L2:L3 satisfies: L1:L2:L3=(80-99):(1-20):(0-5), and the sum of L1, L2 and L3 is 100.

[0017] The electrochemical performance evaluation method for positive electrode sheets provided in this application is novel, has a simple evaluation process, and has a wide range of applications, and can quickly evaluate the electrochemical performance of positive electrode sheets.

[0018] In a third aspect, the present application provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material and a positive electrode electrolyte, and the positive electrode active material layer having pores;

[0019] In the positive electrode active material layer, the total area of ​​the contact interface between the positive electrode active material and the positive electrode electrolyte is defined as the first type of contact interface total area S1, the total area of ​​the contact interface between the positive electrode active material and the positive electrode active material is defined as the second type of contact interface total area S2, and the total area of ​​the contact interface between the positive electrode active material and the pores is defined as the third type of contact interface total area S3;

[0020] Among them, the area ratio of the total area S1 of the first type of contact interface, the total area S2 of the second type of contact interface, and the total area S3 of the third type of contact interface satisfies: S1:S2:S3=(80-99):(1-20):(0-5), and the sum of S1, S2 and S3 is 100.

[0021] The positive electrode sheet provided in the present application controls the three types of contacts in the positive electrode active material layer, namely, the contact between the positive electrode active material and the positive electrode electrolyte, the contact between the positive electrode active material and the positive electrode active material, and the contact between the positive electrode active material and the pores, within a suitable proportion range. This enables the positive electrode sheet to have a larger number of ion conduction pathways, thereby improving the ion conductivity, which is beneficial to increasing the specific capacity of the positive electrode sheet and improving the electrochemical performance of the positive electrode sheet.

[0022] In a fourth aspect, the present application provides a solid-state battery, comprising a positive electrode sheet and a solid electrolyte layer arranged on the surface of the positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode sheet described in the first aspect or the third aspect.

[0023] In an embodiment of the present application, the solid electrolyte layer includes at least one of an oxide electrolyte, a sulfide electrolyte, and a polymer electrolyte.

[0024] The solid-state battery provided in this application has excellent electrochemical performance and high safety performance, which is conducive to the widespread application of solid-state batteries.

[0025] In a fifth aspect, the present application provides an electrical device, which includes the solid-state battery described in the fourth aspect.

[0026] The electrical equipment provided in this application has excellent comprehensive performance and strong market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] Figure 1 A schematic cross-sectional view of a positive electrode sheet provided in one embodiment of the present application;

[0029] Figure 2 for Figure 1 Enlarged view of the middle dashed area;

[0030] Figure 3 A schematic diagram of a cross-sectional structure of a solid-state battery provided in one embodiment of the present application;

[0031] Figure 4 This is a scanning electron microscope (SEM) image of the cross section of the positive electrode active material layer provided in Example 1 of the present application. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0033] In the related art, solid-state batteries mostly focus on the contact between the positive electrode and the solid electrolyte layer, ensuring the ionic conductivity path between the positive electrode and the solid electrolyte layer. However, for the positive active material layer of the positive electrode, there are no research reports on how to measure the contact state of the particles within the positive active material layer, nor how to ensure the effective construction of the ion and electron pathways in the positive active material layer. Currently, there are still problems such as increased resistance, reduced specific capacity, and decreased electrochemical performance of solid-state batteries caused by the unbalanced construction of the ion and electron pathways in the positive electrode.

[0034] In order to solve the above technical problems, the present application provides a positive electrode sheet and a method for evaluating the electrochemical performance of a positive electrode sheet. The positive electrode sheet has the advantages of low resistance, high specific capacity and high ionic conductivity, and has excellent comprehensive performance. The method for evaluating the electrochemical performance of a positive electrode sheet is simple, and the contact state of the internal particles in the positive electrode active material layer in the positive electrode sheet is classified and evaluated, and the electrochemical performance of the positive electrode sheet can be further evaluated quickly and effectively.

[0035] See also Figure 1 and Figure 2 , Figure 1 This is a schematic cross-sectional view of a positive electrode sheet provided in one embodiment of the present application. Figure 2 for Figure 1Enlarged view of the dotted area. The positive electrode sheet 10 includes a positive electrode current collector 12 and a positive electrode active material layer 11 disposed on the surface of the positive electrode current collector 12. The positive electrode active material layer 11 includes a positive electrode active material 110 and a positive electrode electrolyte 111, and there are pores 112 in the positive electrode active material layer; the contact interface between the positive electrode active material 110 and the positive electrode electrolyte 111 is defined as a first type of contact interface 113, the contact interface between the positive electrode active material 110 and the positive electrode active material 110 is defined as a second type of contact interface 114, and the contact interface between the positive electrode active material 110 and the pores 112 is defined as a third type of contact interface 115; take at least one vertical section of the positive electrode active material layer, and define the total length of the contact interface between the positive electrode active material 110 and the positive electrode electrolyte 111 in at least one vertical section, That is, the total length of the first type of contact interface 113 is the total length L1 of the first type of contact interface, the total length of the contact interface between the positive electrode active material 110 and the positive electrode active material 110; that is, the total length of the second type of contact interface 114 is the total length L2 of the second type of contact interface, the total length of the contact interface between the positive electrode active material 110 and the pore 112; that is, the total length of the third type of contact interface 115 is the total length L3 of the third type of contact interface, wherein the length ratio of L1:L2:L3 satisfies: L1:L2:L3=(80-99):(1-20):(0-5), and the sum of L1, L2 and L3 is 100.

[0036] The positive electrode sheet provided in the present application has a high proportion of the total length L1 of the first type of contact interface, that is, the contact interface between the positive electrode active material and the positive electrode electrolyte in the active material layer is relatively large, the range of ion transfer is wide, and the ion insertion and extraction paths are increased, thereby improving the ionic conductivity and specific capacity of the positive electrode sheet; an appropriate total length L2 of the second type of contact interface, that is, an appropriate amount of contact interface formed between the positive electrode active materials, provides an appropriate number of electronic conduction pathways, and maintains a low positive electrode sheet resistance; the total length L3 of the third type of contact interface reflects the contact state between the positive electrode active material and the pores. This type of contact cannot participate in the construction of electronic conduction and ion conduction pathways, is an invalid contact, and cannot play an effective role in the electrochemical properties of the positive electrode sheet. Controlling the proportion of the total length L3 of the third type of contact interface to be low is beneficial to improving the performance of the positive electrode sheet. The positive electrode sheet provided in the present application can increase the number of ion conduction pathways in the positive electrode sheet, control the appropriate number of electronic conduction pathways, improve the ion conductivity and specific capacity, reduce the resistance of the positive electrode sheet, and thus improve the comprehensive electrochemical performance of the positive electrode sheet by controlling the proportion range of the three types of contacts in the positive electrode active material layer: the contact between the positive electrode active material and the positive electrode electrolyte, the contact between the positive electrode active material and the positive electrode active material layer, and the contact between the positive electrode active material layer and the pores.

[0037] In the present application, at least one vertical cross-section of the positive electrode active material layer is taken to perform statistics on the proportion of the total length of the first type of contact interface, the total length of the second type of contact interface, and the total length of the third type of contact interface. The at least one vertical cross-section can be one or more (two or more) vertical cross-sections. Among them, taking cross-sections of multiple positive electrode active material layers to perform statistics on the total length of the first type of contact interface, the total length of the second type of contact interface, and the total length of the third type of contact interface is conducive to obtaining a positive electrode active material layer with better performance. Specifically, the number of vertical cross-sections of the positive electrode active material layer taken can be, but is not limited to, 1, 2, 3, 5, 8, 10, 15, 20 or 50, etc. In one embodiment of the present application, the number of vertical cross-sections of the positive electrode active material layer taken can be 2-10.

[0038] It should be noted that when multiple vertical cross-sections are taken, the total length L1 of the first type of contact interface is obtained by adding the lengths of all first type of contact interfaces 113 in the multiple vertical cross-sections; the total length L2 of the second type of contact interface is obtained by adding the lengths of all second type of contact interfaces 114 in the multiple vertical cross-sections; and the total length L3 of the third type of contact interface is obtained by adding the lengths of all third type of contact interfaces 115 in the multiple vertical cross-sections. When multiple vertical cross-sections are taken, the multiple vertical cross-sections can be evenly spaced in the positive electrode active material layer.

[0039] In this application, the total length of the contact interface between the positive electrode active material and the positive electrode electrolyte in at least one vertical cross section is defined as the total length of the first type of contact interface L1. In the positive electrode active material layer, the positive electrode active material and the positive electrode electrolyte are in contact with each other, and the contact position is the main position where ions are transferred. In other words, the larger the area of ​​the contact portion, the higher the ion mobility and the higher the ion conductivity. For the convenience of characterization, this application evaluates the contact interface length between the positive electrode active material and the positive electrode electrolyte in the vertical cross section of the positive electrode active material layer, and statistically calculates the total length of the contact interface between the positive electrode active material and the positive electrode electrolyte in the vertical cross section to reflect the contact state between the positive electrode active material and the positive electrode electrolyte in the positive electrode active material layer.

[0040] In the present application, the total length of the contact interface between the positive electrode active material and the positive electrode active material in at least one vertical cross section is defined as the total length L2 of the second type of contact interface. In the positive electrode active material layer, the positive electrode active material and the positive electrode active material are in contact with each other, and the contact position provides a transmission channel for electrons in the positive electrode sheet. However, excessively high electronic conductivity will lead to aggravated electrolyte side effects and increased resistance of the positive electrode sheet. Therefore, it is necessary to control the contact area between the positive electrode active material and the positive electrode active material to ensure that the positive electrode sheet has a low resistance and a certain electronic conductivity. For the convenience of characterization, this application evaluates the contact interface length between the positive electrode active material and the positive electrode active material in the vertical cross section of the positive electrode active material layer, and statistically calculates the total length of the contact interface between the positive electrode active material and the positive electrode active material in the vertical cross section to reflect the contact state between the positive electrode active material and the positive electrode active material in the positive electrode active material layer.

[0041] In this application, the total length of the contact interface between the positive electrode active material and the pores in at least one vertical cross section is defined as the total length of the third type of contact interface L3, see Figure 2 The positive electrode active material and the pores are in contact with each other, that is, a portion of the positive electrode active material is exposed in the pores and forms a complete pore boundary with other particles, participating in the formation of the pore boundary. The portion of the positive electrode active material exposed in the pores is the contact interface between the positive electrode active material and the pores, namely the third type of contact interface. In the positive electrode active material layer, processes such as mixing and coating will cause pores to appear in the positive electrode active material layer. The pores cannot participate in the construction of ion and electron pathways and cannot contribute to the electrochemical performance of the positive electrode sheet. Controlling the total area of ​​this type of contact between the positive electrode active material and the pores within a small range can reduce the adverse effects of the pores on the positive electrode sheet. The contact state between the positive electrode active material and the pores is evaluated by using the length of the contact interface between the positive electrode active material and the pores in the vertical cross section of the positive electrode active material layer. The total length of the contact interface between the positive electrode active material and the pores in the vertical cross section is statistically calculated to reflect the contact state between the positive electrode active material and the pores in the positive electrode active material layer.

[0042] In this application, the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface satisfies: L1:L2:L3=(80-99):(1-20):(0-5), and the sum of L1, L2 and L3 is 100. Specifically, the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface can be, but is not limited to, 80:(1-20):(0-5), 85:(1-20):(0-5), 90:(1-20):(0-5), 95:(1-20):(0-5), 99:(1-20):(0-5), (80-99):5:(0-5), (80-99):15:(0-5), (80-99):20:(0-5), (80-99):(1-20):0, (80-99):(1-20):2 or (80-99):(1-20):5, etc. In one embodiment of the present application, the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface satisfies: L1:L2:L3=(85-95):(5-10):(0-2), which can improve the ionic conductivity and specific capacity of the positive electrode sheet.

[0043] In one embodiment of the present application, the positive electrode active material can aggregate a large number of ions, thereby improving the ionic and electronic conductivity of the positive electrode sheet. Specifically, the positive electrode active material can include, but is not limited to, at least one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese oxide. In one embodiment of the present application, the positive electrode active material can be lithium iron phosphate. In another embodiment of the present application, the positive electrode active material can be lithium manganese oxide.

[0044] In one embodiment of the present application, the positive electrode electrolyte provides sites for ion extraction and insertion, increasing the number of ion pathways. Specifically, the positive electrode electrolyte may include, but is not limited to, at least one of an oxide electrolyte, a sulfide electrolyte, and a polymer electrolyte. For example, the sulfide electrolyte may include, but is not limited to, Li3PS4, Li 5.5 PS 4.5 Cl 1.5 、Li7P3S 11 、Li 11 GeP2S 12 、Li6PS5Cl、Li7P2S8I、Li 10 SnP2S 12 He Li 3.25 Ge 0.25 P 0.75 In one embodiment of the present application, when the positive electrode electrolyte is a sulfide electrolyte, the positive electrode electrolyte is Li 11 GeP2S12 In another embodiment of the present application, the positive electrode electrolyte may be an oxide electrolyte. In one embodiment of the present application, the positive electrode current collector may include, but is not limited to, at least one of copper, aluminum, nickel, and stainless steel. In one embodiment of the present application, the positive electrode current collector may be aluminum foil.

[0045] In one embodiment of the present application, the positive electrode active material layer further includes a binder to enhance the bonding between the positive electrode active material layer and the positive electrode current collector. Specifically, the binder may include, but is not limited to, at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polybutadiene, acrylic resin, epoxy resin, polyethylene oxide, sodium carboxymethyl cellulose, and styrene-butadiene latex. In one embodiment of the present application, the binder may be sodium carboxymethyl cellulose. In another embodiment of the present application, the binder may be epoxy resin.

[0046] In one embodiment of the present application, the mass percentage of the positive electrode active material in the positive electrode active material layer is 50%-90%. Specifically, the mass percentage of the positive electrode active material in the positive electrode active material layer may be, but is not limited to, 50%, 55%, 60%, 70%, 80%, or 90%. In one embodiment of the present application, the mass percentage of the positive electrode active material in the positive electrode active material layer may be 50%-75%. In another embodiment of the present application, the mass percentage of the positive electrode active material in the positive electrode active material layer may be 70%-90%.

[0047] In one embodiment of the present application, the D50 particle size of the positive electrode active material is 2μm-6μm, which can improve the specific capacity and ionic conductivity of the positive electrode sheet. Specifically, the particle size D50 of the positive electrode active material can be, but is not limited to, 2μm, 3μm, 4μm, 5μm, or 6μm. In one embodiment of the present application, the particle size D50 of the positive electrode active material can be 2μm-4μm. In another embodiment of the present application, the particle size D50 of the positive electrode active material can be 3μm-6μm.

[0048] In one embodiment of the present application, the mass percentage of the positive electrode electrolyte in the positive electrode active material layer is 10%-50%. Specifically, the mass percentage of the positive electrode electrolyte in the positive electrode active material layer can be, but is not limited to, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or 50%. In one embodiment of the present application, the mass percentage of the positive electrode electrolyte in the positive electrode active material layer can be 10%-45%. In another embodiment of the present application, the mass percentage of the positive electrode electrolyte in the positive electrode active material layer can be 20%-50%.

[0049] In one embodiment of the present application, the particle size D50 of the positive electrode electrolyte is 1 μm-5 μm, which can improve the specific capacity and ionic conductivity of the positive electrode sheet. Specifically, the particle size D50 of the positive electrode electrolyte can be, but is not limited to, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm. In one embodiment of the present application, the particle size D50 of the positive electrode electrolyte can be 1 μm-4 μm. In another embodiment of the present application, the particle size D50 of the positive electrode electrolyte can be 2 μm-5 μm.

[0050] In one embodiment of the present application, the mass ratio of the positive electrode active material to the positive electrode electrolyte is 1:(0.1-1). Specifically, the mass ratio of the positive electrode active material to the positive electrode electrolyte may be, but is not limited to, 1:0.1, 1:0.2, 1:0.4, 1:0.5, 1:0.7, 1:0.8, 1:0.9 or 1:1, etc. In one embodiment of the present application, the mass ratio of the positive electrode active material to the positive electrode electrolyte may be 1:(0.1-0.5). In another embodiment of the present application, the mass ratio of the positive electrode active material to the positive electrode electrolyte may be 1:(0.3-1).

[0051] In one embodiment of the present application, the pores have a pore diameter of 0.1 μm-5 μm. The smaller the pore diameter, the shorter the total length L3 of the third type contact interface, and the less adverse effect of the pores on the positive electrode sheet. Specifically, the pore diameter may be, but is not limited to, 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm. In one embodiment of the present application, the pore diameter may be 0.1 μm-3 μm. In another embodiment of the present application, the pore diameter may be 2 μm-5 μm. The volume and pore diameter of the pores can be tested by SEM images.

[0052] In one embodiment of the present application, the volume percentage of the pores in the positive electrode active material layer is less than or equal to 5%. In the positive electrode active material layer, the smaller the pore volume, the shorter the total length L3 of the third type contact interface, thereby improving the electrochemical performance of the positive electrode sheet. Specifically, the volume percentage of the pores in the positive electrode active material layer may be, but is not limited to, less than or equal to 5%, less than or equal to 4.5%, less than or equal to 3%, less than or equal to 3.5%, or less than or equal to 2%. In one embodiment of the present application, the volume percentage of the pores in the positive electrode active material layer may be less than or equal to 3.5%.

[0053] This application also provides a method for evaluating the electrochemical performance of a positive electrode sheet, including:

[0054] Providing a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material and a positive electrode electrolyte, and pores exist in the positive electrode active material layer;

[0055] The positive electrode sheet is cut along the thickness direction of the positive electrode sheet to obtain a vertical cross section of the positive electrode active material layer; at least one vertical cross section of the positive electrode active material layer is taken, and the total length of the contact interface between the positive electrode active material and the positive electrode electrolyte in the at least one vertical cross section is defined as the first type of contact interface total length L1, the total length of the contact interface between the positive electrode active material and the positive electrode active material is defined as the second type of contact interface total length L2, and the total length of the contact interface between the positive electrode active material and the pore is defined as the third type of contact interface total length L3;

[0056] The total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface in the vertical cross-section of the positive electrode active material layer are obtained by characterization means, and the ratio L1:L2:L3 of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface are calculated. The electrochemical performance of the positive electrode sheet is evaluated by judging whether L1:L2:L3 satisfies: L1:L2:L3=(80-99):(1-20):(0-5), and the sum of L1, L2 and L3 is counted as 100.

[0057] The electrochemical performance evaluation method for positive electrode sheets provided in this application is novel, has a simple evaluation process, and has a wide range of applications, and can be used to quickly evaluate the electrochemical performance of positive electrode sheets.

[0058] In one embodiment of the present application, an ion mill is used to cut the positive electrode sheet along the thickness direction of the positive electrode sheet to obtain a vertical cross-section of the positive electrode active material layer; at least one vertical cross-section of the positive electrode active material layer is taken, and it is defined that in at least one vertical cross-section, the total length of the contact interface between the positive electrode active material and the positive electrode electrolyte is the first type of contact interface total length L1, the total length of the contact interface between the positive electrode active material and the positive electrode active material is the second type of contact interface total length L2, and the total length of the contact interface between the positive electrode active material and the pore is the third type of contact interface total length L3; using analysis software or manual The particle distribution characterization of the vertical cross-section of the positive electrode active material layer is calculated to obtain the total length L1 of the contact interface between the positive electrode active material and the positive electrode electrolyte, the total length L2 of the contact interface between the positive electrode active material and the positive electrode active material, and the total length L3 of the contact interface between the positive electrode active material and the pores. With the sum of L1, L2, and L3 being 100, the ratio L1:L2:L3 of the three is calculated. The electrochemical performance of the positive electrode sheet is evaluated by determining whether L1:L2:L3 satisfies the following relationship: L1:L2:L3=(80-99):(1-20):(0-5). If L1:L2:L3 satisfies the following relationship: L1:L2:L3=(80-99):(1-20):(0-5), the positive electrode sheet has high ionic conductivity, high specific capacity, low resistance, and excellent overall electrochemical performance. If L1:L2:L3 does not satisfy: L1:L2:L3=(80-99):(1-20):(0-5), the positive electrode sheet has poor ionic conductivity, low specific capacity, high resistance, and poor overall electrochemical performance.

[0059] In the present application, at least one vertical cross-section of the positive electrode active material layer is taken to perform statistical analysis on the proportion of the total length of the first type of contact interface, the total length of the second type of contact interface, and the total length of the third type of contact interface. The at least one vertical cross-section can be one or more (two or more) vertical cross-sections. Among them, taking multiple vertical cross-sections for statistical analysis is conducive to more accurate evaluation of the electrochemical performance of the positive electrode sheet. The vertical cross-section can be a vertical cross-section along the length direction of the positive electrode active material layer, or a vertical cross-section along the width direction of the positive electrode active material layer, or a vertical cross-section across the central axis of the positive electrode active material layer. In some embodiments of the present application, the vertical cross-section of the positive electrode active material layer can be obtained by cutting across the central axis of the positive electrode active material layer. When multiple cuts are performed and the cutting interval is small enough to obtain enough vertical cross-sections, the statistical accuracy of various contact conditions in the positive electrode sheet can be further improved, and the obtained L1:L2:L3 is also closer to the actual total area ratio of the three types of contacts in the positive electrode active material layer.

[0060] The present application also provides a positive electrode sheet, which includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material and a positive electrode electrolyte, and there are pores in the positive electrode active material layer. It is defined that in the positive electrode active material layer, the contact area between the positive electrode active material and the positive electrode electrolyte is the first type of total contact interface area S1, the contact area between the positive electrode active material and the positive electrode active material is the second type of total contact interface area S2, and the contact area between the positive electrode active material and the pores is the third type of total contact interface area S3; wherein, the area ratio of the first type of total contact interface area S1, the second type of total contact interface area S2, and the third type of total contact interface area S3 satisfies: S1:S2:S3=(80-99):(1-20):(0-5), and the sum of S1, S2 and S3 is 100.

[0061] The total area S1 of the first type of contact interface of the positive electrode sheet provided in the present application accounts for a high proportion, that is, the contact interface between the positive electrode active material and the positive electrode electrolyte in the active material layer is large, the range of ion transfer is wide, the ion insertion and extraction paths are increased, and the ionic conductivity and specific capacity of the positive electrode sheet are improved; the appropriate total area S2 of the second type of contact interface, that is, the contact interface between the positive electrode active materials, provides an appropriate number of electronic conduction pathways, and maintains a low positive electrode sheet resistance; the total area S3 of the third type of contact interface reflects the contact area between the positive electrode active material and the pores, which cannot participate in the construction of electronic conduction and ion conduction pathways, is an invalid contact, and cannot play an effective role in the electrochemical properties of the positive electrode sheet, so the total area S3 of the third type of contact interface is low. The positive electrode sheet provided in the present application can increase the number of ion conduction pathways in the positive electrode sheet, control the appropriate number of electronic conduction pathways, improve the ion conductivity and specific capacity, reduce the resistance of the positive electrode sheet, and thus improve the comprehensive electrochemical performance of the positive electrode sheet by controlling the contact ratio range of the contact area between the positive electrode active material and the positive electrode electrolyte, the contact area between the positive electrode active material and the positive electrode active material, and the contact area between the positive electrode active material and the pores in the positive electrode active material layer.

[0062] The present application provides a solid-state battery, which comprises a positive electrode provided by any one of the above embodiments and a solid electrolyte layer provided on the surface of the positive electrode. The solid-state battery provided by the present application has high specific capacity, good safety performance, and excellent electrochemical performance. Figure 3 , is a schematic diagram of the cross-sectional structure of a solid-state battery provided in one embodiment of the present application. The solid-state battery includes a positive electrode sheet 10, a negative electrode sheet 30, and a solid electrolyte layer 20 arranged between the positive electrode sheet 10 and the negative electrode sheet 30. The negative electrode sheet 30 includes a negative electrode current collector 32 and a negative electrode active material layer 31 arranged on the surface of the negative electrode current collector 32.

[0063] In one embodiment of the present application, a solid electrolyte layer can improve the safety of a solid-state battery, and the solid electrolyte layer includes a solid electrolyte and a binder. The binder can improve the binding ability of the components in the solid electrolyte layer and improve the binding ability between the solid electrolyte layer and the negative electrode and the positive electrode. Specifically, the binder can be, but is not limited to, at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polybutadiene, acrylic resin, epoxy resin, polyethylene oxide, sodium carboxymethyl cellulose and styrene-butadiene latex. In one embodiment of the present application, the binder can be polyvinylidene fluoride. In another embodiment of the present application, the binder can be sodium carboxymethyl cellulose.

[0064] In one embodiment of the present application, the solid electrolyte may include, but is not limited to, at least one of an organic polymer, an oxide, and a sulfide. The organic polymer may include, but is not limited to, at least one of polyethylene oxide, polypropylene oxide, polyvinylidene chloride, and polyvinylidene fluoride; the oxide may include, but is not limited to, at least one of lithium-titanium oxide, lithium-zirconium oxide, and a fast ion conductor; the sulfide may include, but is not limited to, at least one of lithium-containing sulfide, aluminum-containing sulfide, phosphorus-containing sulfide, silicon-containing sulfide, and tin-containing sulfide. In one embodiment of the present application, the solid electrolyte may include, but is not limited to, a lithium-containing sulfide, and the lithium-containing sulfide electrolyte may include, but is not limited to, Li3PS4, Li 5.5 PS 4.5 Cl 1.5 、Li7P3S 11 、Li 11 GeP2S 12 、Li6PS5Cl、Li7P2S8I、Li 10 SnP2S 12 He Li 3.25 Ge 0.25 P 0.75 In another embodiment of the present application, the solid electrolyte may be polyoxypropylene.

[0065] In one embodiment of the present application, the particle size of the solid electrolyte particles is 1 nm to 5 μm. Specifically, the particle size of the solid electrolyte particles may be, but is not limited to, 1 nm, 20 nm, 100 nm, 1.5 μm, 2 μm, 3 μm, or 5 μm. In one embodiment of the present application, the particle size of the solid electrolyte particles may be 1 nm to 500 nm. In another embodiment of the present application, the particle size of the solid electrolyte particles may be 1 μm to 5 μm.

[0066] In one embodiment of the present application, the negative electrode may be a conventional negative electrode such as a graphite negative electrode, a silicon-based negative electrode, or lithium metal.

[0067] In one embodiment of the present application, the negative electrode active material layer includes a negative electrode active material. The negative electrode active material may include, but is not limited to, at least one of silicon, tin, germanium, lithium, alloys thereof, and a carbon material. The carbon material may include, but is not limited to, at least one of non-graphitizable carbon, graphite, pyrolytic carbon, coke, activated carbon, or acetylene black. In one embodiment of the present application, the negative electrode active material may be a carbon material. In another embodiment of the present application, the negative electrode active material may be a silicon material.

[0068] In one embodiment of the present application, when the negative electrode active material includes a silicon material, the negative electrode active material layer also includes a conductive agent. The conductive agent can increase the electrical conductivity between the active materials and improve electronic conductivity. Specifically, the conductive agent may include, but is not limited to, at least one of graphite, carbon black, acetylene black, and graphene. In one embodiment of the present application, the conductive agent may be graphite. In another embodiment of the present application, the conductive agent may be carbon black.

[0069] In one embodiment of the present application, the negative electrode current collector may include, but is not limited to, at least one of copper, aluminum, nickel, and stainless steel. In one embodiment of the present application, the negative electrode current collector may be copper foil.

[0070] The present application also provides an electrical device, which includes the solid-state battery described in any of the above embodiments. The electrical device provided by this application has excellent comprehensive performance and strong market competitiveness. Electrical devices include mobile phones, tablets, watches, VR glasses, cars, etc. In one embodiment of the present application, the solid-state battery can be used in a car to improve the safety of automobile electricity use. In another embodiment of the present application, the solid-state battery can also be used in a mobile phone to increase the battery capacity of the mobile phone and improve the battery life.

[0071] The effects of the technical solution of this application are further illustrated below through specific examples.

[0072] Example 1

[0073] 1. Positive electrode sheet: The positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2) single crystal) and the positive electrode electrolyte (Li with a particle size of 1 μm 5.5 PS 4.5 Cl 1.5 ) are mixed, the mass ratio of the positive electrode active material to the positive electrode electrolyte is 4:1, a mixed slurry is obtained, and the mixed slurry is coated on the surface of the positive electrode current collector to obtain a positive electrode sheet. A vertical cross section of the positive electrode active material layer along the thickness direction is randomly taken. Figure 4This is a scanning electron microscope (SEM) image of a cross-section of the positive electrode active material layer provided in Example 1 of the present application. The positive electrode active material layer 11 includes a positive electrode active material 110 and a positive electrode electrolyte 111. Pores 112 are present in the positive electrode active material layer. The contact interface between the positive electrode active material 110 and the positive electrode electrolyte 111 is a first type of contact interface 113, the contact interface between the positive electrode active material 110 and the positive electrode active material 110 is a second type of contact interface 114, and the contact interface between the positive electrode active material 110 and the pore 112 is a third type of contact interface 115. The lengths of the three types of contact interfaces in the entire cross-section are statistically calculated, and the ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface is 88:10:2.

[0074] 2. Negative electrode sheet: Take a lithium copper composite foil with a thickness of 20 μm and cut it into the negative electrode sheet of the present invention.

[0075] 3. Solid-state electrolyte layer: 980g of lithium sulfide electrolyte (LPSCl) was dissolved in 600g of a xylene solution containing 20g of a butadiene rubber binder. The solution was then heated and stirred until a stable, uniform solution formed. This solution was then continuously coated onto a release film and dried at 333K to produce a self-supporting electrolyte membrane with a thickness of 40µm. This was then cut into electrolyte layer sheets.

[0076] Example 2

[0077] The difference from Example 1 is that the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface is 93:5:2.

[0078] Example 3

[0079] The difference from Example 1 is that the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface is 80:18:2.

[0080] Example 4

[0081] The difference from Example 1 is that the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface is 85:10:5.

[0082] Example 5

[0083] The difference from Example 1 is that the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface is 98:1:1.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface is 80:10:10.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface is 55:30:15.

[0088] Performance testing

[0089] The positive and negative electrodes and solid electrolyte layers prepared in the above-described embodiments and comparative examples were used to form solid-state batteries, and battery performance testing was performed as follows: Five solid-state batteries prepared in each embodiment and comparative example were taken and subjected to charge-discharge cycle testing at a 0.1C rate on a LAND CT 2001C secondary battery performance testing device. The specific capacity of the positive electrode was calculated and recorded as Q1. A charge-discharge test was then performed at a 0.5C background rate, with the specific capacity recorded as Q2. The 0.5C / 0.1C capacity retention ratio was Q1 / Q2*100%, recorded as the rate performance. This step was repeated. Cycling was terminated when the battery capacity fell below 80% of the initial discharge capacity. This number of cycles was the cycle life of the solid-state battery. The results are shown in Table 1.

[0090] Table 1 Battery performance test results

[0091] Specific capacity (mAh / g) Rate performance (%) Cycle life (cycles) Example 1 202 93.7 178 Example 2 208 87.2 174 Example 3 197 94.1 159 Example 4 195 84.7 151 Example 5 211 82.6 192 Comparative Example 1 192 88.5 147 Comparative Example 2 172 77.1 82

[0092] As can be seen from the data in Table 1, compared with Comparative Examples 1-2, the positive electrode sheets prepared in Examples 1-5 of the present application have high specific capacity, excellent rate performance, long cycle life, and good overall performance. This is because, in Examples 1-5, the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface satisfies: L1: L2: L3 = (80-99): (1-20): (0-5), which can ensure that there are a large number of ion conduction pathways in the positive electrode sheet, while having a suitable number of electronic conduction pathways, effectively improving ion conductivity and specific capacity, and reducing positive electrode sheet resistance. However, Comparative Examples 1-2 do not meet the above ranges and cannot obtain batteries with excellent overall performance.

[0093] In addition, it can be seen from the results of Examples 1-5 that, while satisfying L1:L2:L3=(80-99):(1-20):(0-5), while maintaining a high proportion of the total length L1 of the first type of contact interface, appropriately increasing the proportion of the total length L2 of the second type of contact interface and reducing the proportion of the total length L3 of the third type of contact interface, is conducive to better balancing ionic conductivity and electronic conductivity, so that the positive electrode sheet can better take into account high specific capacity, rate performance and cycle performance.

[0094] The above is a preferred embodiment of the present application, but it should not be construed as limiting the scope of the present application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present application, and such improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material and a positive electrode electrolyte, and pores exist in the positive electrode active material layer; Taking at least one vertical cross-section of the positive electrode active material layer along the thickness direction, define the total length of the contact interface between the positive electrode active material and the positive electrode electrolyte in the at least one vertical cross-section as the first type of contact interface total length L1, the total length of the contact interface between the positive electrode active material and the positive electrode active material as the second type of contact interface total length L2, and the total length of the contact interface between the positive electrode active material and the pores as the third type of contact interface total length L3; Among them, the length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface satisfies: L1:L2:L3=(80-99):(1-20):(0-5), and the sum of L1, L2 and L3 is 100.

2. The positive electrode sheet according to claim 1, wherein: The length ratio of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface satisfies: L1:L2:L3=(85-95):(5-15):(0-2), and the sum of L1, L2 and L3 is 100.

3. The positive electrode sheet according to claim 1, wherein: The mass percentage of the positive electrode active material in the positive electrode active material layer is 50%-90%, and the mass percentage of the positive electrode electrolyte in the positive electrode active material layer is 10%-50%.

4. The positive electrode sheet according to claim 1, wherein: The volume percentage of the pores in the positive electrode active material layer is less than or equal to 5%, and the pore diameter is 0.1 μm-5 μm.

5. The positive electrode sheet according to claim 1, wherein: The positive electrode active material includes at least one of lithium iron phosphate, lithium cobaltate, lithium manganate, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganate and lithium nickel manganate, and the positive electrode electrolyte includes at least one of an oxide electrolyte, a sulfide electrolyte and a polymer electrolyte.

6. The positive electrode sheet according to claim 5, wherein: The sulfide electrolyte includes Li3PS4, Li 5.5 PS 4.5 Cl 1.5、 Li7P3S 11 、Li 11 GeP2S 12 、Li6PS5Cl、Li7P2S8I、Li 10 SnP2S 12 He Li 3.25 Ge 0.25 P 0.75 At least one of S4.

7. A method for evaluating the electrochemical performance of a positive electrode sheet, characterized in that: include: Providing a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material and a positive electrode electrolyte, and pores existing in the positive electrode active material layer; The positive electrode sheet is cut along the thickness direction of the positive electrode sheet to obtain a vertical cross section of the positive electrode active material layer; at least one vertical cross section of the positive electrode active material layer is taken, and the total length of the contact interface between the positive electrode active material and the positive electrode electrolyte in the at least one vertical cross section is defined as a first type of contact interface total length L1, the total length of the contact interface between the positive electrode active material and the positive electrode active material is defined as a second type of contact interface total length L2, and the total length of the contact interface between the positive electrode active material and the pore is defined as a third type of contact interface total length L3; The total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface in the vertical cross-section of the positive electrode active material layer are obtained by characterization means, and the ratio L1:L2:L3 of the total length L1 of the first type of contact interface, the total length L2 of the second type of contact interface, and the total length L3 of the third type of contact interface are calculated. The electrochemical performance of the positive electrode sheet is evaluated by judging whether L1:L2:L3 satisfies the following ratio: L1:L2:L3=(80-99):(1-20):(0-5). The sum of L1, L2, and L3 is 100.

8. A positive electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material and a positive electrode electrolyte, and pores exist in the positive electrode active material layer; The total area of ​​the contact interfaces between the positive electrode active material and the positive electrode electrolyte in the positive electrode active material layer is defined as the first type of contact interface total area S1, the total area of ​​the contact interfaces between the positive electrode active material and the positive electrode active material is defined as the second type of contact interface total area S2, and the total area of ​​the contact interfaces between the positive electrode active material and the pores is defined as the third type of contact interface total area S3; Among them, the area ratio of the total area S1 of the first type of contact interface, the total area S2 of the second type of contact interface, and the total area S3 of the third type of contact interface satisfies: S1:S2:S3=(80-99):(1-20):(0-5), and the sum of S1, S2 and S3 is 100.

9. A solid-state battery, characterized in that: The solid-state battery includes a positive electrode sheet and a solid electrolyte layer arranged on the surface of the positive electrode sheet, and the positive electrode sheet includes the positive electrode sheet according to any one of claims 1 to 6 or claim 8.

10. The solid-state battery according to claim 9, wherein The solid electrolyte layer includes at least one of an oxide electrolyte, a sulfide electrolyte, and a polymer electrolyte.

11. An electrical device, characterized in that: The electrical equipment includes the solid-state battery according to any one of claims 9 to 10.

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