Positive electrode sheet, method for manufacturing the same, battery, and electric device

Abstract

This application provides a positive electrode sheet, its preparation method, a battery, and an electrical device. The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer includes a slip release portion and an active material portion. The slip release portion includes a first sub-positive active material layer and a slip release layer. The first sub-positive active material layer is disposed on at least one side of the positive current collector, and the slip release layer is disposed on one side of the positive current collector. The slip release layer includes a first crosslinked polymer. The active material portion includes a second sub-positive active material layer, which is disposed on at least one side of the positive current collector and connected to the first sub-positive active material layer. The slip release portion provided in this application provides a preset local relative displacement path within the positive active material layer, allowing slippage to preferentially occur within the slip release portion, maintaining the structural integrity of the positive active material layer, and improving the cycle performance of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode sheet and its preparation method, a battery, and an electrical device. Background Technology

[0002] Batteries are widely used in electric vehicles, energy storage systems, and other fields. In battery manufacturing, positive electrode sheets, separators, and negative electrode sheets are wound or stacked to form a cell. The cell is placed inside a casing, and insulating components and end cap assemblies are installed at the openings at both ends of the casing along the height of the cell.

[0003] During battery charging and discharging, lithium ions are extracted and inserted into the positive electrode active material, causing the overall volume of the positive electrode material and positive electrode sheet to expand and contract. Especially during the lithium insertion process, the positive electrode active material expands in volume, generating expansion stress inside the battery cell.

[0004] This expansion stress can cause cell expansion and internal stress accumulation, which in turn leads to fluctuations in the contact state between positive electrode materials, between positive electrode materials and electrolyte, and between active material layer and current collector, as well as changes in internal pressure, thereby affecting battery life and safety reliability. Summary of the Invention

[0005] This application provides a positive electrode sheet and its preparation method, a battery, and an electrical device, aiming to solve the problems of cell expansion and internal stress accumulation during battery charging and discharging.

[0006] To solve the above problems, this application provides the following technical solution: This application discloses a positive electrode sheet, which includes a positive current collector and a positive active material layer, wherein the positive active material layer includes: The sliding release section includes a first sub-positive electrode active material layer and a sliding release layer. The first sub-positive electrode active material layer is disposed on at least one side of the positive electrode current collector, and the sliding release layer is disposed on the side of the first sub-positive electrode active material layer opposite to the positive electrode current collector. The sliding release layer includes a first crosslinked polymer, which is generated by a first polymer matrix and a first crosslinking substance. The active material portion includes a second sub-positive electrode active material layer, which is disposed on at least one side of the positive electrode current collector and connected to the first sub-positive electrode active material layer.

[0007] In this application, the positive electrode current collector provides conductive support and structural substrate for the positive electrode active material layer. The first sub-positive electrode active material layer and the second sub-positive electrode active material layer are interconnected, maintaining the continuity of the positive electrode active material layer in electrochemical function. Meanwhile, the slip release layer includes a first cross-linked polymer, which is disposed on the surface of the first sub-positive electrode active material layer, so that the slip release part and the active material part have a difference in friction coefficient, surface energy or bonding strength. When expansion and stress accumulation occur in the battery, the slip release part provides a preset local relative displacement path in the positive electrode active material layer, so that slippage occurs preferentially in the slip release part, while the active material part still maintains structural stability. At the same time, when slippage occurs in the slip release part, the first cross-linked polymer absorbs part of the strain energy through the extension and retraction of molecular chains, avoiding peeling or damage to the slip interface due to excessive displacement, avoiding the breakage of positive electrode material particles, increased interface impedance or contact failure caused by uncontrolled slippage, and mitigating the pressure fluctuation in the casing caused by stress concentration.

[0008] In some embodiments, the positive electrode sheet has a first direction and a second direction perpendicular to each other, and along the first direction, the positive current collector includes a first edge and a second edge opposite to each other, at least one of the first edge and the second edge being used to connect to the tab; The sliding release section and the active material section each include multiple portions, and along the second direction, the multiple sliding release sections and the multiple active material sections are alternately arranged.

[0009] In some embodiments, the ratio of the area of ​​the slip release layer to the sum of the areas of the first sub-positive electrode active material layer and the second sub-positive electrode active material layer is 5% to 70%. And / or, the ratio of the area of ​​the second sub-positive electrode active material layer to the sum of the areas of the first sub-positive electrode active material layer and the second sub-positive electrode active material layer is 30% to 95%.

[0010] In some embodiments, the positive electrode sheet further has a third direction, wherein the first direction, the second direction, and the third direction are mutually perpendicular, and the third direction is the thickness direction of the positive electrode sheet. The positive electrode sheet satisfies at least one of the following conditions: (1) Along the first direction, the ratio of the size of the slip release layer to the size of the first sub-positive electrode active material layer is (1~10):10; (2) Along the third direction, the ratio of the size of the slip release layer to the size of the first sub-positive electrode active material layer is (0.1~3.5):10.

[0011] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions: (1) Along the second direction, the size of the slip release layer is 0.2~20mm; (2) Along the third direction, the size of the slip release layer is 0.5~20μm; (3) Along the second direction, the interval between two adjacent slip release layers is 0.5~50mm.

[0012] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions: (1) The first polymer matrix includes at least one of fluoropolymers, polyacrylates, polyimides, polyurethanes and polyethers having active sites; (2) The first crosslinking substance includes at least one of the following: an epoxy-containing compound, an isocyanate-containing compound, a maleimide-containing compound, an alkenyl double bond-containing compound, and a compound containing a thermally activated crosslinking group; (3) The mass ratio of the first polymer matrix to the first crosslinking substance is 100: (1~30).

[0013] In some embodiments, the slip release layer further includes a first solidified substance, wherein the first solidified substance comprises inorganic particles.

[0014] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions: (1) The particle size D50 of the first solidified material is 5~200nm; (2) The inorganic particles include at least one of alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, molecular sieves and porous carbon materials; (3) The mass ratio of the first polymer matrix to the first cured substance is 100: (1~20).

[0015] In some embodiments, the first sub-positive electrode active material layer and the second sub-positive electrode active material layer each comprise a positive electrode active material, wherein the positive electrode active material comprises: The core includes a positive electrode material; A coating layer is disposed on the surface of the core. The coating layer includes a second crosslinked polymer, which is generated by the reaction of a second polymer matrix and a second crosslinked substance. The crosslinking density of the second crosslinked polymer gradually increases from the core toward the coating layer.

[0016] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions: (1) The mass ratio of the coating layer to the core is (0.05~10):100; (2) The particle size D50 of the kernel is 2~20μm; (3) The thickness of the coating layer is 5~500nm.

[0017] In some embodiments, the coating layer further includes a second curing substance, which comprises inorganic particles.

[0018] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions: (1) The particle size D50 of the second solidified material is 5~200nm; (2) The inorganic particles include at least one of alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, molecular sieve and porous carbon material.

[0019] In some embodiments, in the second polymer matrix, the second crosslinking substance and the second curing substance, the mass percentage of the second crosslinking substance is 0.05~20wt%, the mass percentage of the second curing substance is 0.01~10wt%, and the remainder is the second polymer matrix; The mass ratio of the core to the second polymer matrix is ​​100:(0.5~10).

[0020] In some embodiments, the first sub-positive electrode active material layer and the second sub-positive electrode active material layer further comprise microcapsule carriers, the microcapsule carriers comprising: The core material comprises at least one of inorganic particles and organic amine oligomers; An outer shell, which covers the surface of the core material, comprising a polymer.

[0021] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions: (1) The particle size D50 of the core material is 5~200nm; (2) The particle size D50 of the microcapsule carrier is 0.2~5μm; (3) The polymer includes at least one of polyurea, polyurethane, melamine-formaldehyde resin and urea-formaldehyde resin.

[0022] Secondly, embodiments of this application provide a method for preparing a positive electrode sheet, comprising the following steps: A positive electrode slurry is disposed on at least one side of a positive electrode current collector to form a first sub-positive electrode active material layer and a second sub-positive electrode active material layer that are interconnected. A first cross-linked polymer precursor is disposed on the side of the first sub-positive electrode active material layer away from the positive electrode current collector, wherein the first cross-linked polymer precursor includes a first polymer matrix and a first cross-linked material; The first cross-linked polymer precursor is cured to generate a first cross-linked polymer, and a slip release layer is formed on the side of the first sub-positive electrode active material layer away from the positive electrode current collector to obtain a positive electrode sheet, wherein the slip release layer and the first sub-positive electrode active material layer constitute a slip release part, and the second sub-active material layer constitutes an active material part.

[0023] In some embodiments, the positive electrode slurry includes a positive electrode active material, and the preparation method of the positive electrode active material includes: A second cross-linked polymer precursor is disposed on the surface of the core, and after curing, a positive electrode active material precursor is obtained. The core includes a positive electrode material, and the second cross-linked polymer precursor includes a second polymer matrix and a second cross-linked substance. The positive electrode active material precursor is subjected to a triggering treatment to form a second crosslinked polymer precursor, and a coating layer is formed on the surface of the core to obtain the positive electrode active material. The crosslinking density of the second crosslinked polymer gradually increases from the core toward the coating layer along the thickness direction of the coating layer. The triggering treatment includes high potential plateau holding triggering and / or pulse triggering.

[0024] In some embodiments, the high-potential platform maintains a trigger voltage of 4.0~4.5V, and maintains the trigger for 1~240 minutes. And / or, the pulse current of the pulse trigger is 0.05~1.0C, the pulse width is 1~120 s, the pulse interval is 1~600 s, the number of pulses is 1~500, and the pulse trigger voltage window is 3.5~4.5V.

[0025] Thirdly, embodiments of this application provide a battery, the battery comprising the above-described positive electrode sheet or a positive electrode sheet prepared by the above-described method for preparing the positive electrode sheet.

[0026] Fourthly, embodiments of this application provide an electrical device, which includes the battery described above. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet provided in the embodiments of this application; Figure 2 This is a schematic diagram of the battery structure provided in the embodiments of this application; Figure 3 This is a schematic diagram of the structure of the positive electrode active material provided in the embodiments of this application.

[0028] Explanation of reference numerals in the attached figures: 1. Positive electrode sheet; 11. Positive current collector; 111. First edge; 112. Second edge; 12. Positive active material layer; 121. Slip release section; 1211. First sub-positive active material layer; 1212. Slip release layer; 122. Active material section; 13. Tab; 2. Shell; 3. Winded cell; 4. Battery; 5. Positive active material; 51. Core; 52. Coating layer; X, First direction; Y, Second direction; Z, Third direction; L, Radial; H, Axial. Detailed Implementation

[0029] To make the technical problems solved, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0030] Reference Figure 1 This application provides a positive electrode 1 including a positive current collector 11 and a positive active material layer 12. The positive active material layer 12 is disposed on at least one side of the positive current collector 11, and the positive active material layer 12 includes a sliding release portion 121 and an active material portion 122.

[0031] The sliding release section 121 includes a first sub-positive electrode active material layer 1211 and a sliding release layer 1212. The first sub-positive electrode active material layer 1211 is disposed on at least one side of the positive electrode current collector 11, and the sliding release layer 1212 is disposed on the side of the first sub-positive electrode active material layer 1211 away from the positive electrode current collector 11. The sliding release layer 1212 includes a first cross-linked polymer, which is generated by a first polymer matrix and a first cross-linked substance.

[0032] The active material section 122 includes a second sub-positive electrode active material layer, which is disposed on at least one side of the positive electrode current collector 11 and connected to the first sub-positive electrode active material layer 1211.

[0033] In this embodiment, the positive current collector provides conductive support and structural substrate for the positive active material layer, ensuring efficient electron transport during charging and discharging.

[0034] The positive electrode active material layer includes a slip release section and an active material section. The first sub-positive electrode active material layer of the slip release section and the second sub-positive electrode active material layer of the active material section are interconnected, maintaining the continuity of the positive electrode active material layer in electrochemical function and enabling lithium ions to migrate freely between the slip release section and the active material section.

[0035] The slip release section includes a first sub-positive electrode active material layer and a slip release layer disposed on the side of the first sub-positive electrode active material layer facing away from the positive electrode current collector. The slip release layer includes a first cross-linked polymer. By controlling the degree of cross-linking, the first cross-linked polymer creates a difference in friction coefficient, surface energy, or bonding strength between the slip release section and surrounding components (such as adjacent active material sections, separators, and electrolytes). Compared to active material sections without a slip release layer, the surface of the slip release section has lower shear resistance or weaker interfacial bonding strength, thus reducing the critical shear stress required for slippage. Therefore, when the battery expands and accumulates internal stress due to changes in the volume of the positive electrode material, interfacial side reactions, and gas generation, the entire positive electrode active material layer is subjected to shear stress. However, because the interfacial shear strength in the area where the slip release section is located is lower, the critical stress required for shear slippage is also lower. Therefore, the slip release section provides a preset local relative displacement path within the positive electrode active material layer, allowing slippage to preferentially occur in the slip release section, while the active material section, due to its higher interfacial shear strength, helps maintain structural stability.

[0036] Furthermore, when slippage occurs in the slip release section, the first cross-linked polymer imparts appropriate elastic modulus and toughness to the slip release layer. The extension and retraction of the molecular chains of the first cross-linked polymer can absorb some strain energy, preventing the slip interface from peeling or being damaged due to excessive displacement. After the stress is released, the first cross-linked polymer can partially restore its original state, maintaining the structural integrity of the slip release section and enabling it to continuously provide a preset local relative displacement path in subsequent cycles. This avoids the breakage of positive electrode material particles, increased interface impedance, or failure of contact between electrodes caused by uncontrollable slippage, thereby improving the structural stability of the positive electrode active material layer and alleviating the pressure fluctuations inside the shell caused by stress concentration.

[0037] In some embodiments, the first crosslinked polymer is formed by a first polymer matrix and a first crosslinking reaction, and has a three-dimensional network structure.

[0038] In some embodiments, the first polymer matrix comprises at least one of a fluoropolymer having active sites, a polyacrylate, a polyimide, a polyurethane, and a polyether.

[0039] In some embodiments, the first crosslinking substance includes at least one of an epoxy-containing compound, an isocyanate-containing compound, a maleimide-containing compound, an alkenyl double bond-containing compound, and a compound containing a thermally activated crosslinking group.

[0040] In some embodiments, the mass ratio of the first polymer matrix to the first crosslinking substance is controlled within the range of 100:(1~30). Within this ratio range, the crosslinked network has sufficient crosslinking points to maintain the structural integrity of the slip release layer, while the chain segment lengths between the crosslinking points are moderate, giving the slip release layer suitable flexibility and elastic recovery capability. When expansion stress is generated inside the battery, the first crosslinked polymer can absorb part of the strain energy and return to its original state after stress release, so that the slip release layer and the surrounding area form a stable difference in crosslinking degree, friction coefficient, or bonding strength. Thus, it continuously serves as a local relative displacement path for stress release during long-term cycling, realizing controllable slip release of expansion stress.

[0041] In some embodiments, XRD (X-ray diffraction analysis) can detect that the positive electrode active material layer 12 contains a slip release layer 1212.

[0042] During the assembly of battery 4, the positive electrode 1, separator, and negative electrode 1 are wound or stacked to form a wound cell 3 or a stacked cell, which is then installed inside the housing 2. Subsequently, base plates and end cap assemblies are installed at both ends of the housing 2 along the height direction of the cell. The base plates and end cap assemblies are fixed to both ends of the housing 2 by mechanical pressing or welding, applying a compressive preload force to the cell along the height direction, thereby achieving reliable fixation of the cell in the height direction and suppressing volume fluctuations and movement of the cell in the height direction.

[0043] To further constrain and release the expansion stress generated by the cell during cycling due to changes in the volume of the positive electrode material, interfacial side reactions, and gas generation, this embodiment provides multiple slip release units 121 and multiple active material units 122, which are alternately arranged along the second direction Y. In a wound battery, this expansion stress mainly manifests as stress extending outward along the radial direction L of the wound cell 3; in a stacked battery, this expansion stress mainly manifests as stress extending outward along the stacking direction. Whether it is a wound battery or a stacked battery, the cell is installed inside the housing 2. The constraint stiffness provided by the sidewall of the housing 2 in the radial direction of the cell (wound battery) or the stacking direction (stacked battery) is relatively limited. This embodiment, by alternately arranging multiple slip release units 121 and multiple active material units 122 along the second direction Y, makes the second direction Y correspond to the radial direction L of the wound cell or the stacking direction of the stacked battery, thereby providing stress relief units in the radial direction or stacking direction of the cell. When expansion stress is generated along this direction, it is preferentially released in the corresponding area of ​​the sliding release part 121 in a controllable sliding manner, which makes up for the deficiency of insufficient constraint stiffness of the side wall of the shell 2.

[0044] It should be noted that the following description uses the radial expansion stress generated inside a battery composed of a wound cell 3 as an example. For stacked batteries, the cells also generate expansion stress along the stacking direction during charging and discharging, and this stress is physically equivalent to the radial expansion stress of the wound cell. The structural improvement of the positive electrode 1 in this application, namely, the alternating arrangement of the slip release part 121 and the active material part 122 along the second direction Y, is also applicable to stacked batteries, where the second direction Y corresponds to the stacking direction of the stacked battery. Therefore, the technical solution described in this application is universal for both wound and stacked batteries. Although the following description uses a wound cell as an example, it should not be construed as a limitation on the scope of protection of this application.

[0045] Reference Figure 2 The positive electrode 11 has a first direction X, a second direction Y and a third direction Z that are perpendicular to each other. The first direction X is the height direction of the positive electrode 11, which is also equivalent to the height direction of the battery cell (i.e., the axial direction H of the wound battery cell 33 or the height direction of the stacked battery cell).

[0046] Along the first direction X, the positive electrode current collector 11 includes opposing first edges 111 and second edges 112, at least one of the first edges 111 and second edges 112 being used to connect to a tab 13, which is used to electrically connect the positive electrode 11 to the external terminal of the battery 4. The third direction Z is the thickness direction of the positive electrode 11.

[0047] In this embodiment, multiple first sub-positive active material layers 1211 and multiple second sub-positive active material layers are arranged alternately along the second direction Y. Each first sub-positive active material layer 1211 has a slip release layer 121 on the side opposite to the positive current collector 11, thereby forming slip release portions 121 and active material portions 122 alternately distributed along the second direction Y in the positive active material layer 12. The multiple slip release portions 121 and active material portions 122 are alternately arranged along the second direction Y, which can preferentially disperse the radial L expansion stress into the multiple slip release portions 121 for release, avoiding excessive stress accumulation in local areas, thereby alleviating problems such as cell deformation, fluctuation of interlayer contact state of electrode sheets, and cycle life decay caused by the inability to release radial L expansion stress.

[0048] In some embodiments, the ratio of the area of ​​the slip release layer to the sum of the areas of the first sub-positive electrode active material layer and the second sub-positive electrode active material layer is 5% to 70%; the ratio of the area of ​​the second sub-positive electrode active material layer to the sum of the areas of the first sub-positive electrode active material layer and the second sub-positive electrode active material layer is 30% to 95%.

[0049] In this embodiment, the area ratio of the slip release layer is controlled within the range of 5% to 70%, and the area ratio of the active material portion is controlled within the range of 30% to 95%. This ensures that a sufficient number of slip release portions are distributed in the positive electrode active material layer, which can form multiple stress release units to release radial expansion stress in segments and avoid excessive stress accumulation in local areas. At the same time, a sufficient area of ​​active material portion is retained to ensure that the positive electrode sheet has a continuous and stable lithium-ion insertion / extraction path and electron conduction network, maintaining the high energy density and good rate performance of the battery.

[0050] In some embodiments, along the first direction X, the ratio of the size of the slip release layer to the size of the first sub-positive electrode active material layer is (1~10):10. Within this range, the slip release layer can provide a sufficient local relative displacement path for radial expansion stress while avoiding slip discontinuity due to insufficient coverage.

[0051] In some embodiments, along the third direction Z, the ratio of the size of the slip release layer to the size of the first sub-positive electrode active material layer is (0.1~3.5):10. This ensures that the slip release layer has sufficient structural matrix in the third direction, which can effectively combine with the first sub-positive active material layer and achieve the control of properties such as friction coefficient, surface energy or bonding strength of the slip release part. At the same time, it will not cause a significant increase in the overall thickness of the positive electrode or an excessive extension of the ion transport path due to excessive thickness, thereby achieving a balance between stress release effect, cycle stability and energy density.

[0052] In some embodiments, the size of the sliding release layer along the second direction Y is 0.2 to 20 mm. For example, the size of the sliding release layer is any one of 0.2 mm, 0.5 mm, 1 mm, 5 mm, 10 mm, 15 mm and 20 mm or the midpoint of two adjacent values.

[0053] In some embodiments, the size of the slip release layer along the third direction Z is 0.5~20μm. Exemplarily, along the third direction, the size of the slip release layer is any one of 0.5μm, 1μm, 2μm, 5μm, 10μm, 15μm and 20μm or an intermediate value of two adjacent values.

[0054] In some embodiments, the spacing between two adjacent slip-release layers along the second direction Y is 0.5~50mm. This spacing corresponds to the size of the active material portion between two adjacent slip-release portions in the positive electrode active material layer. This is because: the size of the slip-release layer along the second direction is equal to the size of the first sub-positive electrode active material layer, and the slip-release layer completely covers the surface of the first sub-positive electrode active material layer. In this case, the spacing between two adjacent slip-release layers is the size of the active material portion. However, when the size of the slip-release layer in the second direction is smaller than the size of the first sub-positive electrode active material layer, the slip-release layer only partially covers the first sub-positive electrode active material layer. In this case, the spacing between two adjacent slip-release layers includes the second sub-positive electrode active material layer and the portion of the first sub-positive electrode active material layer not covered by the slip-release layer. However, this uncovered portion is electrochemically identical to the second sub-positive electrode active material layer and still belongs to the active material portion. Therefore, along the second direction, the spacing between two adjacent slip-release layers corresponds to the size of the active material portion.

[0055] Meanwhile, by controlling the spacing between 0.5 and 50 mm, the active material portion has a moderate width, which ensures that the positive electrode has a sufficient capacity contribution area and that the radial expansion stress can reach the sliding release portion and be released in a controlled manner within a short transmission distance after it is generated, thus avoiding excessive accumulation of radial expansion stress inside the positive electrode active material layer.

[0056] In some embodiments, the slip release layer further includes a first curing substance, wherein the first curing substance comprises inorganic particles.

[0057] During battery charging and discharging, the electrolyte undergoes oxidative decomposition at higher potentials, generating CO2, CO, phosphorus-containing decomposition products, fluorinated acidic components, and oligomerized byproducts such as carbonates. These byproducts are characterized by strong migration capabilities and high chemical reactivity. To restrict these byproducts and prevent their diffusion to the surface of the cathode material, which would exacerbate interfacial side reactions, leading to cathode material structural degradation, transition metal dissolution, and increased battery internal resistance, this embodiment introduces a second solidification material into the slip release layer as a site for capturing and immobilizing interfacial byproducts. This restricts the morphology and migration path of the interfacial byproducts, immobilizing them within the slip release layer and thus reducing their diffusion into the electrolyte bulk and their further erosion of the cathode material surface.

[0058] In some embodiments, the mass ratio of the first polymer matrix to the first cured substance is 100:(1~20), so that a sufficient number of capture and immobilization sites are uniformly distributed in the slip release layer, which can effectively capture and immobilize CO2, fluorinated acid components and carbonate oligomer byproducts generated by the oxidative decomposition of the electrolyte, limit their migration path, reduce the diffusion and erosion of byproducts to the surface of the positive electrode material, thereby maintaining interface stability and extending battery cycle life.

[0059] In some embodiments, the particle size D50 of the first solidified material is 5~200nm, which enables the first solidified material to be uniformly dispersed in the slip release layer, forming a by-product immobilization interface with a high specific surface area, improving the capture and immobilization efficiency, while avoiding unevenness or local stress concentration on the surface of the slip release layer due to excessively large particles.

[0060] Reference Figure 2 The first sub-positive electrode active material layer 1211 and the second sub-positive electrode active material layer each include positive electrode active material 5. The positive electrode active material 5 includes a core 51 and a coating layer 52. The core 51 includes a positive electrode material. The coating layer 52 is disposed on the surface of the core 51. The coating layer 52 includes a second crosslinked polymer. The crosslinking density of the second crosslinked polymer gradually increases from the core 51 to the coating layer 52. The second crosslinked polymer is generated from a second polymer matrix and a second crosslinked material.

[0061] The cathode material is the core material that determines the battery's energy density, cycle life, and safety. It mainly includes lithium iron phosphate, ternary cathode materials, lithium cobalt oxide, and lithium manganese oxide. During battery charging, the cathode material undergoes a delithiation reaction, resulting in changes in lattice parameters and surface stress. When charging reaches a higher potential range, interfacial side reactions occur in the contact area between the cathode material surface and the electrolyte, generating interfacial byproducts. Because the coating layer is located on the outer surface of the cathode material, it can prevent direct contact between the electrolyte and the cathode material, reducing the sites for interfacial side reactions and thus suppressing them.

[0062] Meanwhile, the coating layer has a crosslinking gradient structure in which the crosslinking density gradually increases from the core towards the coating layer. That is, the second crosslinking polymer has a lower crosslinking density on the side closer to the core (hereinafter referred to as the inner side), and the molecular chain moves relatively freely. This can buffer the volume change and surface stress generated by the cathode material during delithiation, and prevent the coating layer from cracking. On the other hand, the second crosslinking polymer has a higher crosslinking density on the side closer to the electrolyte (hereinafter referred to as the outer side), which can block the diffusion and penetration of solvent molecules and active substances in the electrolyte to the core surface, further suppressing interfacial side reactions and improving the structural stability and interfacial chemical stability of the cathode material.

[0063] In some embodiments, the second polymer matrix comprises at least one of a fluoropolymer having active sites, a polyacrylate, a polyimide, a polyurethane, and a polyether.

[0064] In some embodiments, the second crosslinking substance includes at least one of an epoxy-containing compound, an isocyanate-containing compound, a maleimide-containing compound, an alkenyl double bond-containing compound, and a compound containing a thermally activated crosslinking group.

[0065] It should be noted that the fluoropolymers with active sites described in the above embodiments include at least one of polyvinylidene fluoride-hexafluoropropylene copolymer and polyvinylidene fluoride; polyacrylates include at least one of polymethyl methacrylate and polyhydroxyethyl methacrylate; polyimides include at least one of polyamic acid and polyether imide; polyurethanes include at least one of polyether polyurethane and polyester polyurethane; and polyethers include at least one of polyethylene glycol, polyethylene oxide and polypropylene glycol.

[0066] The epoxy-containing compounds described in the above embodiments include at least one of glycidyl methacrylate, trimethylolpropane triglycidyl ether, and triglycidyl isocyanurate; the isocyanate-containing compounds include at least one of triallyl isocyanurate and hexamethylene diisocyanate trimer; the maleimide-containing compounds include at least one of N,N'-m-phenylenebismaleimide and N,N'-diphenylmethanebismaleimide; the alkenyl double bond-containing compounds include at least one of triallyl isocyanurate, trimethylallyl isocyanurate, and triallyl cyanurate; and the thermally activated crosslinking group-containing compounds include polyfunctional blocked isocyanates, such as imidazole blocked isocyanates.

[0067] The second polymer matrix reacts with the second crosslinking substance to form a coating layer, which restricts interfacial side reactions and buffers the volume expansion of the positive electrode material.

[0068] In this embodiment, the second polymer matrix reacts with the second crosslinking substance to generate a coating layer with a crosslinking gradient structure. This process is achieved through a triggering process during the battery formation stage. The triggering process includes high-potential plateau holding triggering, pulse triggering, or a combination of both. Its function is to establish a difference in reaction conditions from the outside to the inside on the second crosslinking polymer precursor, thereby driving the crosslinking reaction to exhibit a non-uniform distribution in the coating layer thickness direction, ultimately forming a crosslinking gradient structure with high crosslinking density on the outside and low crosslinking density on the inside.

[0069] Specifically, a second cross-linked polymer precursor, formed by a second polymer matrix and a second cross-linking substance, is coated onto the surface of the cathode material particles. After assembly into a battery, during the triggering process, the side of the second cross-linked polymer precursor closer to the core (inner side) and the side closer to the electrolyte (outer side) are in different chemical and electrochemical environments. The outer side, in direct contact with the electrolyte, is preferentially exposed to a higher interfacial electric field under higher potential conditions. Therefore, the second polymer matrix and the second cross-linking substance on the outer side exhibit a higher reaction rate and a higher reaction conversion rate. Conversely, the potential conditions on the inner side are lower than those on the outer side, resulting in a lower reaction conversion rate. This difference in interfacial reaction and mass transfer from the outside to the inside is a key condition for the formation of the cross-linked gradient structure.

[0070] In some embodiments, the trigger voltage for high-potential platform holding trigger is 4.0~4.5V, and the holding trigger time is 1~240min. High-potential platform holding trigger is to maintain a stable high potential for a long time, so that the outer region continuously experiences the trigger condition, which is beneficial to forming a continuous and gentle crosslinking density distribution with high outer and low inner.

[0071] The pulse current for pulse triggering is 0.05~1.0C, the pulse width is 1~120s, the pulse interval is 1~600s, the number of pulses is 1~500, and the pulse triggering voltage window is 3.5~4.5V. Pulse triggering generates a strong interfacial reaction driving force in a short time through transient high polarization conditions, which is beneficial to enhance the preferential reaction in the outer region and shorten the continuous residence time, thus forming a significant cross-linking gradient structure in a short time.

[0072] Combined triggering first establishes the outer layer reaction basis through a high-potential platform, enabling the outer region to achieve preliminary cross-linking transformation, and then enhances the local transformation through pulse triggering, making the cross-linking gradient structure more significant, thus combining the advantages of continuous outer layer triggering and transient enhancement triggering.

[0073] In some embodiments, the mass ratio of the coating layer to the core is (0.05~10):100, so that the coating layer uniformly coats the core surface with a suitable thickness, forming a stable physical barrier between the electrolyte and the positive electrode material, while maintaining low lithium-ion transport impedance and high energy density.

[0074] In some embodiments, the core particle size D50 is 2~20μm, which gives the cathode material a moderate specific surface area and lithium-ion solid-phase diffusion path, which is beneficial to achieving high rate performance and long cycle stability.

[0075] In some embodiments, the thickness of the coating layer is 5~500nm, which can form a continuous and complete structure, effectively blocking interfacial side reactions while maintaining lithium-ion interfacial transport dynamics, so that the cathode material can maintain a stable interfacial chemical environment at high potentials.

[0076] In some embodiments, the coating layer further includes a second curing substance, which includes at least one of inorganic particles and organic amine oligomers, and the second curing substance is uniformly dispersed in the coating layer.

[0077] During battery charging and discharging, the electrolyte undergoes oxidative decomposition at higher potentials, generating CO2, CO, phosphorus-containing decomposition products, fluorinated acidic components, and oligomerized byproducts such as carbonates. These byproducts are characterized by strong migration capabilities and high chemical reactivity. To restrict these byproducts and prevent their diffusion to the surface of the cathode material, which could exacerbate interfacial side reactions and lead to problems such as cathode material structural degradation, transition metal dissolution, and increased battery internal resistance, this embodiment introduces a second curing substance into the coating layer as a site for capturing and immobilizing interfacial byproducts. This restricts the morphology and migration path of the interfacial byproducts, immobilizing them within the polymer coating layer, thereby reducing their diffusion into the electrolyte bulk and their further erosion of the cathode material surface.

[0078] In some embodiments, the particle size D50 of the second solidified material is 5~200nm, which is beneficial to uniformly disperse the second solidified material in the coating layer, forming a by-product immobilization interface with a high specific surface area, improving the capture efficiency, and avoiding unevenness or local stress concentration on the surface of the coating layer due to excessively large particles.

[0079] In some embodiments, the components for preparing the second crosslinked polymer include a second polymer matrix, a second crosslinking substance, and a second curing substance, wherein the second crosslinking substance accounts for 0.05 to 20 wt% of the mass of the second polymer matrix, the second crosslinking substance, and the second curing substance, and the remaining amount is the second polymer matrix.

[0080] In this embodiment, the mass ratio of the second curing substance is set to 0.01~10wt%, which can form sufficient capture and immobilization sites in the coating layer, effectively adsorb or react to fix interface by-products, while maintaining the structural integrity and ion conduction performance of the coating layer. The mass ratio of the second crosslinking substance is set to 0.05~20wt%, which can react with the second polymer matrix under the triggering treatment conditions to form a coating layer with a crosslinking gradient structure.

[0081] In some embodiments, the mass ratio of the core to the second polymer matrix is ​​set to 100:(0.5~10). Within this ratio range, the amount of the second polymer matrix is ​​sufficient to form a continuous and complete coating layer on the surface of the cathode material particles, effectively blocking the direct contact between the electrolyte and the cathode material and suppressing interfacial side reactions. At the same time, the coating layer thickness is moderate and will not excessively increase the lithium-ion transport impedance, ensuring the rate performance and capacity of the cathode material particles.

[0082] In some embodiments, the first sub-positive electrode active material layer and the second sub-positive electrode active material layer further include microcapsule carriers, the microcapsule carriers including a core material and a shell, the core material including at least one of inorganic particles and organic amine oligomers, the shell covering the surface of the core material, and the shell including a polymer.

[0083] In this embodiment, the outer casing isolates the core material from the external environment, preventing premature exposure and loss of its capture and immobilization capabilities. During battery charging and discharging, interface byproducts gradually diffuse through the casing and contact the core material, ensuring that the core material begins to perform its capture and immobilization functions when needed, thus avoiding early and ineffective consumption.

[0084] It should be noted that the first curing substance, the second curing substance, and the inorganic particles included in the core material are independently selected from at least one of alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, molecular sieves, and porous carbon materials.

[0085] Among them, inorganic particles such as alumina, silicon oxide, titanium oxide, zirconium oxide and magnesium oxide can chemically adsorb or react with fluorine-containing acidic components to form stable surface immobilization products, transforming active acidic species into inert substances and preventing them from further corroding the cathode material.

[0086] Inorganic particles such as molecular sieves and porous carbon materials have high specific surface area and abundant pore structure, which can physically adsorb low molecular weight byproducts such as CO2 and CO, confining them inside the pores and inhibiting their diffusion into the electrolyte.

[0087] The core material also includes organic amine oligomers, which include oligomers with a number average molecular weight between 200 and 3000 g / mol, such as polyethyleneimine, polyallylamine, and aliphatic polyamines such as ethylenediamine and diethylenetriamine. These organic amine oligomers have short molecular chains and low viscosity, making them more likely to react with active groups in interfacial byproducts. Their physical form is usually a viscous liquid, resinous or waxy solid, and they are covered with a shell to ensure their morphological stability. When the battery is charged and discharged, the organic amine oligomers undergo surface chemical reactions with carbonates and other substances in the interfacial byproducts to form a non-migrating immobilized phase, converting the mobile organic byproducts into stable products fixed in the positive electrode active material layer.

[0088] In some embodiments, the particle size D50 of the core material is 5~200nm, which is beneficial for rapid and sufficient contact with interface byproducts and adsorption or reaction after the shell is opened, thus ensuring the capture and immobilization capability of the microcapsule carrier after triggering.

[0089] In some embodiments, the particle size D50 of the microcapsule carrier is 0.2~5μm, which enables the microcapsule carrier to be uniformly dispersed in the positive electrode active material layer and to form good contact with the positive electrode active material. This ensures sufficient core material capacity to capture interfacial byproducts while avoiding unevenness or stress concentration on the surface of the positive electrode active material layer due to excessively large particle size.

[0090] The shell includes at least one of polyurea, polyurethane, melamine-formaldehyde resin and urea-formaldehyde resin. These polymers have a dense network structure and good chemical stability, which can effectively encapsulate the core material and prevent the core material from being exposed and consumed prematurely. At the same time, during the triggering process or long-term cycling, the core material’s capture and immobilization function can be controlled by means of shell penetration, local cracking or surface exposure, so as to capture and fix interface by-products.

[0091] This application also provides a method for preparing a positive electrode sheet, including the following steps: S10. The positive electrode slurry is coated on at least one side of the positive electrode current collector to form a first sub-positive electrode active material layer and a second sub-positive electrode active material layer that are interconnected.

[0092] The positive electrode slurry is made by mixing positive electrode active material, conductive agent, and binder. After coating, it is dried at 90-110°C for 20-30 minutes, then re-dried at 70-80°C for 1-2 hours. Subsequently, it is rolled at 50-60°C under a rolling pressure of 110-120 kN / m to form an interconnected first and second sub-positive electrode active material layer on the surface of the positive electrode current collector. This step ensures good adhesion and uniform thickness distribution between the positive electrode active material layer and the current collector.

[0093] S11. The first cross-linked polymer precursor is disposed on the side of the first sub-positive electrode active material layer away from the positive electrode current collector, wherein the first cross-linked polymer precursor includes a first polymer matrix and a first cross-linked material.

[0094] In this embodiment, the first crosslinked polymer precursor further includes a wetting and dispersing agent and a solvent.

[0095] The setting method includes coating or selective surface treatment. The coating method involves directly coating the first cross-linked polymer precursor onto the side of the first sub-positive electrode active material layer away from the positive electrode current collector. The selective surface treatment method involves depositing the first cross-linked polymer precursor in the form of atomization or microdroplets onto the side of the first sub-positive electrode active material layer away from the positive electrode current collector.

[0096] S13. The first cross-linked polymer precursor is cured to generate the first cross-linked polymer, and a slip release layer is formed on the side of the first sub-positive electrode active material layer away from the positive electrode current collector to obtain the positive electrode sheet, wherein the slip release layer and the first sub-positive electrode active material layer constitute the slip release part, and the second sub-active material layer constitutes the active material part.

[0097] In this embodiment, the curing temperature for curing the first crosslinked polymer precursor to generate the first crosslinked polymer is 100~120℃ and the time is 30~60min, so that the first crosslinked polymer forms a stable and moderate crosslinked network in the slip release layer.

[0098] In some embodiments, the positive electrode slurry includes a positive electrode active material, and the preparation method of the positive electrode active material includes the following steps: S20. A second cross-linked polymer precursor is disposed on the surface of the core, and after curing, a positive electrode active material precursor is obtained, wherein the core includes a positive electrode material, and the second cross-linked polymer precursor includes a second polymer matrix and a second cross-linked substance.

[0099] In this embodiment, the second cross-linked polymer precursor is disposed on the core surface in two ways: Method 1 involves mixing the second polymer matrix and the second crosslinking substance to obtain a first premix; the first premix is ​​then placed on the core surface and subjected to a curing reaction (reaction temperature 150~170°C, reaction time 50~70 min) to form a second crosslinking polymer precursor on the core surface, thereby obtaining a positive electrode active material precursor.

[0100] Method 2 involves mixing the second polymer matrix with the core to obtain a second premix, then mixing the second premix with the second crosslinked substance and subjecting it to a curing reaction (reaction temperature 150~170°C, reaction time 50~70 min) to form a second crosslinked polymer precursor on the surface of the core, thereby obtaining a positive electrode active material precursor.

[0101] Under the curing reaction conditions of Method 1 and Method 2 above, the morphology of the second crosslinked polymer precursor on the core surface is mainly fixed and a partial crosslinking reaction occurs, so that the coating layer is initially shaped and has a certain degree of pre-crosslinked structure. The main crosslinking reaction is still reserved until the triggering process to ensure that a second crosslinked polymer with a crosslinked gradient structure is formed during the battery formation process.

[0102] S21. The positive electrode active material precursor is subjected to a triggering treatment to form a second cross-linked polymer precursor, forming a coating layer on the core surface to obtain the positive electrode active material. The cross-linking density of the second cross-linked polymer gradually increases from the core towards the coating layer. The triggering includes high-potential plateau holding triggering and / or pulse triggering.

[0103] After assembling the battery, high-potential plateau hold triggering and / or pulse triggering are performed. The trigger voltage for high-potential plateau hold triggering is 4.0~4.5V, and the hold triggering time is 1~240min. The pulse current for pulse triggering is 0.05~1.0C, the pulse width is 1~120 s, the pulse interval is 1~600 s, the number of pulses is 1~500, and the pulse triggering voltage window is 3.5~4.5V. For the beneficial effects of high-potential plateau holding triggering and / or pulse triggering, please refer to the description in the positive electrode embodiment.

[0104] In some embodiments, the assembled battery may undergo a first charge-discharge process before the triggering process. The first charge-discharge process is used to establish an initial interface state, complete the full wetting after liquid injection, the initial remodeling of the electrode interface, and the formation of the initial interface film, so that the subsequent triggering process can be carried out under relatively stable initial interface conditions.

[0105] The first charge / discharge process uses either constant current or constant current / constant voltage charging methods.

[0106] When using constant current mode, the constant current charging rate is 0.01C to 0.20C, and the constant current charging cutoff voltage is 0.1V to 0.5V below the upper cutoff voltage.

[0107] When using a constant current and constant voltage method, the constant current charging rate is 0.01C to 0.20C, and the constant current charging cutoff voltage is 0.1V to 0.5V below the upper cutoff voltage. Then, constant voltage charging is performed at this voltage, with a constant voltage holding time of 1 to 180 minutes, or a constant voltage cutoff current of 0.005 to 0.05C. The first charge-discharge process uses constant current discharge, with a discharge rate of 0.01 to 0.20C and a discharge cutoff voltage equal to the lower cutoff voltage. After the first charge-discharge process, a resting period of 10 to 720 minutes is performed. After the first charge-discharge process is completed, triggering can proceed.

[0108] In some embodiments, after the triggering process is completed, the battery may undergo a second charge-discharge process. The second charge-discharge process is used to further electrochemically stabilize the formed coating layer and slip release layer, and to confirm that the cell assembly state and interface state have entered a repeatable cycle state.

[0109] The second charge / discharge process uses a constant current or constant current / constant voltage charging method.

[0110] When using constant current mode, the constant current charging rate is 0.05~0.5C, and the constant current charging cutoff voltage is the upper cutoff voltage.

[0111] When using a constant current and constant voltage method, the constant current charging rate is 0.05~0.5C, and the constant current charging cutoff voltage is the upper cutoff voltage. Then, constant voltage charging is performed at this voltage, with a constant voltage cutoff current of 0.01~0.10C, or a constant voltage holding time of 5~240 minutes. The second charge-discharge process uses constant current discharge, with a discharge rate of 0.05~0.5C and a discharge cutoff voltage of the lower cutoff voltage. The number of charge-discharge cycles in the second charge-discharge process is 1~10. After the second charge-discharge process is completed, the system is left to stand for 10~1440 minutes.

[0112] In some embodiments, the lower cutoff voltage is 2.5~3.0V and the upper cutoff voltage is 4.0~4.5V.

[0113] This application also provides a battery, which includes a positive electrode sheet or a positive electrode sheet prepared by the above-described method for preparing a positive electrode sheet.

[0114] The above-described battery embodiment includes the aforementioned positive electrode sheet and achieves the same technical effect. To avoid repetition, it will not be described again here. For relevant details, please refer to the description of the positive electrode sheet embodiment.

[0115] This application embodiment also provides an electrical device, which includes the battery described above, and the battery is used to provide electrical energy to the electrical device.

[0116] To make the inventive objectives, technical solutions, and beneficial effects of this application clearer, the present application is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0117] The present application will be described in detail below through embodiments.

[0118] Unless otherwise specified, the techniques or conditions described in the literature in this field or the product instructions shall be followed. Reagents or instruments whose manufacturers are not specified are all commercially available standard products.

[0119] Example 1 (1) Preparation of positive electrode active material precursor S11 selects LiNi as the cathode material. 0.6 Co 0.2 Mn 0.2 O2 with a particle size D50 of 6~12μm was used to vacuum dry the cathode material at 120°C for 12h.

[0120] S12, by mass fraction, adds 93 parts of the second polymer matrix, polyvinylidene fluoride-hexafluoropropylene copolymer (weight average molecular weight 3 × 10⁻⁶), to an appropriate amount of solvent N-methylpyrrolidone. 5 ~6×105 Stir and disperse at 2000 rpm for 60 min; then add 5 parts of the second crosslinking material triallyl isocyanurate (TAIC), 1 part of the initiator azobisisobutyronitrile, and 2 parts of the second curing material alumina with a particle size D50 of 50~100 nm, stir evenly to obtain the premix.

[0121] S13 The dried cathode material is added to the premix, and the mass ratio of cathode material to second polymer matrix is ​​100:2. The mixture is stirred at 25°C for 120 min to form an adsorption deposition system. The adsorption deposition system is centrifuged at 4000 rpm for 10 min to obtain a solid. The obtained solid is pre-dried at 80°C for 2 h and then vacuum-dried at 100 Pa and 120°C for 12 h.

[0122] S14 First Curing Process: The obtained solid is cured at 150℃ for 60 minutes to form a coating layer precursor including a second crosslinked polymer precursor on the surface of the positive electrode material core, thus obtaining the positive electrode active material precursor. The thickness of the coating layer precursor is 100 nm.

[0123] (2) Preparation of positive electrode slurry The positive electrode slurry was prepared according to the following mass proportions: 94 parts of positive electrode active material precursor, 3 parts of conductive agent (carbon black), 3 parts of binder (polyvinylidene fluoride), and an appropriate amount of solvent N-methylpyrrolidone. The solid content of the positive electrode slurry was 60 wt%. The positive electrode slurry was prepared by the following steps: premixing at 500 rpm for 15 min, dispersing at 3000 rpm for 45 min, and degassing at 500 Pa for 20 min.

[0124] (3) Preparation of positive electrode sheet S31 involves coating the positive electrode slurry onto the positive electrode current collector, resulting in a wet film thickness of 150 μm; drying at 100°C for 20 min, followed by re-drying at 80°C for 2 h; and then rolling at a rolling temperature of 60°C and a rolling line pressure of 120 kN / m to form a coating with a thickness of 60 μm.

[0125] S32, by mass fraction, takes 100 parts of the first polymer matrix polyvinylidene fluoride-hexafluoropropylene copolymer, 15 parts of the second crosslinking substance triallyl isocyanurate, 2 parts of the wetting and dispersing aid polyester modified polysiloxane, and an appropriate amount of solvent N-methylpyrrolidone. After mixing the above components, disperse them at a stirring speed of 2000 rpm for 60 min, and obtain a uniform coating liquid by filtration.

[0126] S33 divides the coating into multiple alternating first sub-positive active material layers and multiple second sub-positive active material layers along the second direction. The size of the first sub-positive active material layer along the second direction is 5 mm, the spacing between two adjacent first sub-positive active material layers along the second direction is 10 mm, and the size of the first sub-positive active material layer along the first direction is equal to 80% of the size of the first positive electrode sheet. The coating liquid is uniformly applied to the side of the first sub-positive active material layer away from the positive current collector and cured (temperature is 120℃ and time is 30 min) to form a slip release layer with a thickness (along the third direction) of 10 μm.

[0127] (4) Battery preparation The positive electrode, separator, and negative electrode (the negative electrode is a graphite negative electrode) prepared in step (3) are wound into an electrode roll with a winding tension of 30N. The electrode roll is then placed into a cylindrical shell (aluminum shell or steel shell) to form a radial pre-compression ratio of 3%. An electrolyte is injected, which includes lithium salt and solvent, with a concentration of 1mol / L. The lithium salt is LiPF6, and the solvent is a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1:1). The injection volume is 2.5g / Ah. The electrode is then immersed and allowed to stand at 45°C for 12h. After sealing, the electrode is allowed to stand at 25°C for 12h.

[0128] (5) Hierarchical formation triggering procedure A graded formation triggering procedure was performed at 25°C, with a lower cutoff voltage of 2.8V and an upper cutoff voltage of 4.3V, including the following steps: S51 first charge / discharge process: charge to 3.9V with constant current at 0.1C; let stand for 120 minutes; discharge to 2.8V with constant current at 0.1C; let stand for 120 minutes.

[0129] S52 triggering process: High-potential plateau holding triggering is performed within a voltage range of 4.25~4.30V for 60 minutes; followed by resting for 240 minutes. During the triggering process, the second latent crosslinking unit undergoes a crosslinking reaction, forming a crosslinking gradient structure in the coating layer. Along the thickness direction of the coating layer, the crosslinking density of this crosslinking gradient structure gradually increases from the inside to the outside.

[0130] S53 second charge-discharge process: Charge at a constant current of 0.2C to 4.3V, then charge at a constant voltage until the current drops to 0.05C; let stand for 120 minutes; discharge at a constant current of 0.2C to 2.8V; let stand for 120 minutes. After two cycles, let stand for 12 hours to complete the formation.

[0131] Example 2 The difference from Example 1 is as follows: The cathode material in S11 is LiCoO2.

[0132] S12 and S13 were modified as follows: 85 parts by mass of the second polymer matrix methyl methacrylate and 1 part by mass of the initiator azobisisobutyronitrile were added to an appropriate amount of solvent N-methylpyrrolidone, stirred and dispersed evenly, and then the dried positive electrode material was added. The mixture was stirred at 25°C for 120 min to form an adsorption deposition system. The adsorption deposition system was centrifuged at 4000 rpm for 10 min. After pre-drying at 80°C for 2 h, it was vacuum dried at 100 Pa and 120°C for 12 h. 15 parts by mass of the second crosslinking substance glycidyl methacrylate were added to obtain a solid.

[0133] In S33, the size of the first sub-positive electrode active material layer along the second direction is 3 mm, the spacing between two adjacent first sub-positive electrode active material layers along the second direction is 8 mm, and the size of the first sub-positive electrode active material layer along the first direction is equal to 70% of the size of the first positive electrode sheet.

[0134] The step-by-step formation triggering procedure (5) is modified as follows: The step-by-step formation triggering procedure is performed at 30°C with a lower cutoff voltage of 2.8V and an upper cutoff voltage of 4.4V, including the following steps: First charge / discharge process: Charge to 3.9V at 0.1C; let stand for 120 minutes; Discharge to 2.8V at 0.1C; let stand for 120 minutes.

[0135] Triggering process: pulse current 0.5C, pulse width 10s, pulse interval 30s, pulse count 100, pulse trigger voltage window 3.8~4.4V; rest for 240min.

[0136] Third charge-discharge process: Charge to 4.4V at 0.2C and keep constant at 0.05C; Discharge to 2.8V at 0.2C; Cycle twice; Let stand for 12 hours.

[0137] Example 3 The difference from Example 1 is as follows: The cathode material in S11 is LiFePO4.

[0138] In S12, the second polymer matrix, polyvinylidene fluoride-hexafluoropropylene copolymer, comprises 85 parts by mass, the second crosslinking substance, triallyl isocyanurate, comprises 10 parts by mass, and the second curing substance, alumina, comprises 5 parts by mass.

[0139] S13 is modified as follows: In S13, the dried positive electrode material is added to the premix, and the mass ratio of the positive electrode material to the solute in the premix is ​​100:0.5. The coating is carried out by spray drying, with the inlet air temperature of spray drying being 180°C and the outlet air temperature being 90°C. After the premix is ​​uniformly coated on the surface of the positive electrode material, it is vacuum dried at 100Pa and 120°C for 12 hours.

[0140] In S33, the size of the first sub-positive electrode active material layer along the second direction is 2 mm, the spacing between two adjacent first sub-positive electrode active material layers along the second direction is 6 mm, and the size of the first sub-positive electrode active material layer along the first direction is equal to 60% of the size of the first positive electrode sheet.

[0141] The step-by-step formation triggering procedure (5) is modified as follows: The step-by-step formation triggering procedure is performed at 30°C with a lower cutoff voltage of 2.5V and an upper cutoff voltage of 4.1V, including the following steps: First charge / discharge process: Charge to 3.9V at 0.1C; let stand for 120 minutes; Discharge to 2.8V at 0.1C; let stand for 120 minutes.

[0142] Triggering process: First, execute a high-potential platform hold trigger, with a trigger voltage of 4.05–4.10V held for 30 minutes. Then, execute a pulse trigger with a pulse current of 0.2C, a pulse width of 10s, an interval of 30s, and 50 pulses, with a voltage window of 3.6~4.1V. Then, let it stand for 240 minutes.

[0143] The third charge-discharge process: charge at a constant current of 0.2C to 4.1V, then charge at a constant voltage until the current drops to 0.05C; let stand for 120 minutes; discharge at a constant current of 0.2C to 2.5V; let stand for 120 minutes. After two cycles, let stand for 12 hours to complete the formation.

[0144] Example 4 The difference from Example 1 is that S12-S14 are not performed.

[0145] Example 5 The difference from Example 1 is that no second cured alumina particles are added in S12 and S32-S33 are not performed.

[0146] Example 6 The difference from Example 1 is that S32-S33 are not executed.

[0147] Comparative Example 1 The difference from Example 1 is that S12-S14 and S32-S33 are not executed.

[0148] Test Example 1: Test of Change in Shell Outer Diameter Cylindrical batteries prepared in each embodiment and comparative example were used, with 3 batteries in each group as a test sample, for a total of 3 batteries × 6 groups = 18 batteries. The test environment temperature was 25±2℃. Before each measurement, the batteries to be tested were allowed to stand at 25±2℃ for 30min to 120min to allow the battery temperature to reach equilibrium with the ambient temperature. The measuring tools used were a laser diameter gauge or micrometer with a resolution of not less than 10μm. Three measurement positions were determined along the height direction of the battery: near the top insulating part, in the middle of the casing height direction, and near the bottom insulating part. Two measuring points were evenly selected along the circumference of the casing at each measurement position, for a total of 6 measuring points. At each test point, the outer diameter measurement value of each measuring point was recorded, and the arithmetic mean of the outer diameter measurement values ​​of the 6 measuring points was calculated as D = (d1 + d2 + d3 + d4 + d5 + d6) / 6, where d1 to d6 are the outer diameter measurement values ​​of each measuring point, and the unit is millimeters (mm).

[0149] The test nodes include the following five stages: before formation, after formation, after 50 cycles, after 100 cycles, and after 200 cycles. The cycle conditions are set as follows: ambient temperature 25±2°C, charge / discharge voltage window from 2.8V to 4.3V, charging method is constant current charging at a 0.5C rate to the upper cutoff voltage, and discharging method is constant current discharging at a 0.5C rate to the lower cutoff voltage, with 200 consecutive cycles. The change in outer diameter ΔD at each test node is recorded, where ΔD = D. t D0, where D0 represents the outer diameter after sealing and before formation, D t The outer diameter of the test node (after transformation and several cycles) is shown in Table 1. The test results are shown in Table 1.

[0150] Test Example 2: Shell Strain Test Three batteries from each of the embodiments and comparative examples were used, and the test environment temperature was 25±2°C. Resistance strain gauges were used as strain measurement sensors, with a range of 0 to 5000 με. The strain gauges were attached to the center of the outer surface of the battery casing in the height direction, with two strain gauges attached 180° apart along the circumference of the casing, ensuring a tight fit between the strain gauges and the casing surface without air bubbles. The strain gauges were connected to a strain acquisition instrument via wires, and the sampling frequency was set to 1 Hz (which can be selected within the range of 0.1 Hz to 10 Hz according to test requirements). Strain measurements were expressed in microstrain (με), where 1 με represents 10-1... -6 The relative length change. Two strain gauges record their respective strain readings ε1 and ε2. The arithmetic mean of the two strain gauge readings is taken as the strain value ε of the cell at the current moment, calculated by the following formula: ε = (ε1 + ε2) / 2, in με.

[0151] The recording points include the entire formation process and the entire cycling process, and the casing strain values ​​are extracted at each time point after formation, after 50 cycles, after 100 cycles, and after 200 cycles. By comparing the strain values ​​of different embodiments and comparative examples at each test point, the magnitude of the expansion stress borne by the battery casing under radial confinement conditions can be evaluated. The smaller the strain value ε, the more fully the radial expansion stress is released. The test results are shown in Table 2.

[0152] Test Example 3: Battery Internal Pressure Test Three batteries each from Examples 1, 4, and Comparative Example 1 were selected to prepare an experimental battery cell with a pressure sampling structure. This experimental battery cell maintained the same sealed structure for the electrode rolls, casing, and top cover assembly as a normal battery, except that a pressure sensor interface was added to the casing or top cover assembly. A pressure sensor was installed at the interface, and a seal was ensured. The pressure sensor had a range of 0 MPa to 2 MPa and an accuracy of no less than ±0.01 MPa. The pressure sensor was connected to a data acquisition system, and the sampling frequency was set to 1 Hz.

[0153] Test nodes: Before formation, after formation, after 50 cycles, after 100 cycles, and after 200 cycles. Stable readings of the pressure sensor were recorded to obtain the internal pressure value P, in MPa. This test characterizes the pressure changes inside the battery casing during cycling. Increased internal pressure is usually related to electrolyte decomposition and gas production, as well as the accumulation of interfacial side reactions. Lower internal pressure indicates better suppression of interfacial side reactions. The test results are shown in Table 3.

[0154] Test Example 4: Electro-acoustic Impedance Testing (EIS) Three batteries each from Example 1, Example 4, and Comparative Example 1 were used. Before testing, each battery was charged at a constant current rate of 0.5C to the upper cutoff voltage, then charged at a constant voltage rate until the current dropped to 0.05C, and then discharged at a constant current rate of 0.5C to 50% state of charge (i.e., the discharge capacity is half of the rated capacity), so that the battery was in a 50% state of charge state. The batteries were then left to stand at 25±2°C for 60 min to 180 min to allow the internal electrochemical state of the battery to reach equilibrium.

[0155] AC impedance testing was performed using an electrochemical workstation at an ambient temperature of 25±2°C. The frequency scan range was set to 10mHz to 100kHz in logarithmic scan mode, with 10 frequency points acquired every ten octaves. The applied AC disturbance signal was a sinusoidal voltage of 5mV to 10mV (typically 5mV or 10mV was chosen to ensure the response signal remained within the linear range). After the test, the Nyquist plot (x-axis: real impedance Z', y-axis: imaginary impedance Z'') and Bode plot (x-axis: logarithm of frequency, y-axis: impedance magnitude and phase angle) of the battery were recorded. The impedance spectrum was fitted using an equivalent circuit model. A commonly used equivalent circuit is Rs connected in series with Rct and CPE (which are in parallel), and then connected in series with W, denoted as Rs-(Rct / CPE)-W. Here, Rs is the ohmic resistance (including electrolyte resistance, tab resistance, current collector resistance, etc.), Rct is the charge transfer resistance, CPE is a constant phase angle element (used to describe the non-ideal capacitive behavior of the electrode surface), and W is the Warburg impedance (used to describe the diffusion process of lithium ions in the solid phase). After fitting the values ​​of each element, the Rct values ​​of different embodiments and comparative examples were compared at the same test node. A smaller Rct value indicates faster interfacial reaction kinetics and less accumulation of interfacial side reactions.

[0156] The test nodes include before transformation, after transformation, after 100 cycles, and after 200 cycles. The test results of Rct and Rs are shown in Table 4.

[0157] Table 1 Test results of shell outer diameter variation

[0158] Table 2 Test results of shell strain values

[0159] Table 3 Battery internal pressure test results

[0160] Table 4 Test results of ohmic resistance and charge transfer resistance

[0161] Note: Mean in Tables 1-4 represents the mean, and SD represents the standard deviation.

[0162] Based on the data in Tables 1 to 4, the performance of Comparative Example 1 (battery without structural improvements in this application) is inferior to that of the embodiments, which verifies the advantages of one or more of the slip release part, the cross-linked gradient coating layer and the second cured material in suppressing radial expansion, reducing internal pressure and maintaining interface stability.

[0163] Terminology Explanation In this application, "multiple" refers to two or more.

[0164] The terms “first,” “second,” “third,” “fourth,” etc., in this application (if present) are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0165] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0166] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, if a method includes steps A and B, it means that the method may include steps A and B performed sequentially, or it may include steps B and A performed sequentially. For example, if a method may also include step C, it means that step C may be added to the method in any order. For example, the method may include steps A, B, and C, or it may include steps A, C, and B, or it may include steps C, A, and B, etc.

[0167] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material layer includes: The sliding release section includes a first sub-positive electrode active material layer and a sliding release layer. The first sub-positive electrode active material layer is disposed on at least one side of the positive electrode current collector, and the sliding release layer is disposed on the side of the first sub-positive electrode active material layer opposite to the positive electrode current collector. The sliding release layer includes a first crosslinked polymer, which is generated by a first polymer matrix and a first crosslinking substance. The active material portion includes a second sub-positive electrode active material layer, which is disposed on at least one side of the positive electrode current collector and connected to the first sub-positive electrode active material layer.

2. The positive electrode sheet according to claim 1, characterized in that, The positive electrode sheet has a first direction and a second direction perpendicular to each other. Along the first direction, the positive current collector includes a first edge and a second edge opposite to each other. At least one of the first edge and the second edge is used to connect to the electrode tab. The sliding release section and the active material section each include multiple portions, and along the second direction, the multiple sliding release sections and the multiple active material sections are alternately arranged.

3. The positive electrode sheet according to claim 2, characterized in that, The ratio of the area of ​​the slip release layer to the sum of the areas of the first sub-positive electrode active material layer and the second sub-positive electrode active material layer is 5% to 70%. And / or, the ratio of the area of ​​the second sub-positive electrode active material layer to the sum of the areas of the first sub-positive electrode active material layer and the second sub-positive electrode active material layer is 30% to 95%.

4. The positive electrode sheet according to claim 2, characterized in that, The positive electrode sheet also has a third direction, wherein the first direction, the second direction, and the third direction are perpendicular to each other, and the third direction is the thickness direction of the positive electrode sheet. The positive electrode sheet satisfies at least one of the following conditions: (1) Along the first direction, the ratio of the size of the slip release layer to the size of the first sub-positive electrode active material layer is (1~10):10; (2) Along the third direction, the ratio of the size of the slip release layer to the size of the first sub-positive electrode active material layer is (0.1~3.5):

10.

5. The positive electrode sheet according to claim 4, characterized in that, The positive electrode sheet satisfies at least one of the following conditions: (1) Along the second direction, the size of the slip release layer is 0.2~20mm; (2) Along the third direction, the size of the slip release layer is 0.5~20μm; (3) Along the second direction, the interval between two adjacent slip release layers is 0.5~50mm.

6. The positive electrode sheet according to claim 1, characterized in that, The positive electrode sheet satisfies at least one of the following conditions: (1) The first polymer matrix includes at least one of fluoropolymers, polyacrylates, polyimides, polyurethanes and polyethers having active sites; (2) The first crosslinking substance includes at least one of the following: an epoxy-containing compound, an isocyanate-containing compound, a maleimide-containing compound, an alkenyl double bond-containing compound, and a compound containing a thermally activated crosslinking group; (3) The mass ratio of the first polymer matrix to the first crosslinking substance is 100: (1~30).

7. The positive electrode sheet according to claim 1, characterized in that, The slip release layer further includes a first solidified substance, wherein the first solidified substance comprises inorganic particles.

8. The positive electrode sheet according to claim 7, characterized in that, The positive electrode sheet satisfies at least one of the following conditions: (1) The particle size D50 of the first solidified material is 5~200nm; (2) The inorganic particles include at least one of alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, molecular sieves and porous carbon materials; (3) The mass ratio of the first polymer matrix to the first cured substance is 100: (1~20).

9. The positive electrode sheet according to claim 1, characterized in that, The first sub-positive electrode active material layer and the second sub-positive electrode active material layer each include positive electrode active materials, wherein the positive electrode active materials include: The core includes a positive electrode material; A coating layer is disposed on the surface of the core. The coating layer includes a second crosslinked polymer, which is generated by the reaction of a second polymer matrix and a second crosslinked substance. The crosslinking density of the second crosslinked polymer gradually increases from the core toward the coating layer.

10. The positive electrode sheet according to claim 9, characterized in that, The positive electrode sheet satisfies at least one of the following conditions: (1) The mass ratio of the coating layer to the core is (0.05~10):100; (2) The particle size D50 of the kernel is 2~20μm; (3) The thickness of the coating layer is 5~500nm.

11. The positive electrode sheet according to claim 9, characterized in that, The coating layer further includes a second cured substance, which comprises inorganic particles.

12. The positive electrode sheet according to claim 11, characterized in that, The positive electrode sheet satisfies at least one of the following conditions: (1) The particle size D50 of the second solidified material is 5~200nm; (2) The inorganic particles include at least one of alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, molecular sieve and porous carbon material.

13. The positive electrode sheet according to claim 11, characterized in that, In the second polymer matrix, the second crosslinking substance and the second curing substance, the mass percentage of the second crosslinking substance is 0.05~20wt%, the mass percentage of the second curing substance is 0.01~10wt%, and the remainder is the second polymer matrix; And / or, the mass ratio of the core to the second polymer matrix is ​​100:(0.5~10).

14. The positive electrode sheet according to claim 1, characterized in that, The first sub-positive electrode active material layer and the second sub-positive electrode active material layer further include microcapsule carriers, wherein the microcapsule carriers include: The core material comprises at least one of inorganic particles and organic amine oligomers; An outer shell, which covers the surface of the core material, comprising a polymer.

15. The positive electrode sheet according to claim 14, characterized in that, The positive electrode sheet satisfies at least one of the following conditions: (1) The particle size D50 of the core material is 5~200nm; (2) The particle size D50 of the microcapsule carrier is 0.2~5μm; (3) The polymer includes at least one of polyurea, polyurethane, melamine-formaldehyde resin and urea-formaldehyde resin.

16. A method for preparing a positive electrode sheet, characterized in that, Includes the following steps: A positive electrode slurry is disposed on at least one side of a positive electrode current collector to form a first sub-positive electrode active material layer and a second sub-positive electrode active material layer that are interconnected. A first cross-linked polymer precursor is disposed on the side of the first sub-positive electrode active material layer away from the positive electrode current collector, wherein the first cross-linked polymer precursor includes a first polymer matrix and a first cross-linked material; The first cross-linked polymer precursor is cured to generate a first cross-linked polymer, and a slip release layer is formed on the side of the first sub-positive electrode active material layer away from the positive electrode current collector to obtain a positive electrode sheet, wherein the slip release layer and the first sub-positive electrode active material layer constitute a slip release part, and the second sub-active material layer constitutes an active material part.

17. The method for preparing the positive electrode sheet according to claim 16, characterized in that, The positive electrode slurry includes a positive electrode active material, and the preparation method of the positive electrode active material includes: A second cross-linked polymer precursor is disposed on the surface of the core, and after curing, a positive electrode active material precursor is obtained. The core includes a positive electrode material, and the second cross-linked polymer precursor includes a second polymer matrix and a second cross-linked substance. The positive electrode active material precursor is subjected to a triggering treatment to form a second crosslinked polymer precursor, and a coating layer is formed on the surface of the core to obtain the positive electrode active material. The crosslinking density of the second crosslinked polymer gradually increases from the core toward the coating layer. The triggering treatment includes high potential plateau holding triggering and / or pulse triggering.

18. The method for preparing the positive electrode sheet according to claim 17, characterized in that, The high-potential platform maintains a trigger voltage of 4.0~4.5V for 1~240min. And / or, the pulse current of the pulse trigger is 0.05~1.0C, the pulse width is 1~120 s, the pulse interval is 1~600s, the number of pulses is 1~500, and the pulse trigger voltage window is 3.5~4.5V.

19. A battery, characterized in that, The battery includes a positive electrode sheet prepared by any one of claims 1 to 15 or by any one of claims 16 to 18.

20. An electrical appliance, characterized in that, Includes the battery as described in claim 19.

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