Lithium supplement material, positive pole piece and secondary battery

Abstract

The invention discloses a lithium supplement material, a positive pole piece and a secondary battery, and belongs to the technical field of electrochemical energy storage, the material takes a carbon nanotube doped porous lithium supplement agent with depth gradient aperture as an inner core, and meanwhile, an intermediate layer with temperature-sensitive characteristic and an outer protective layer with a self-repairing function are arranged on the surface of the inner core; and when applied to a positive pole piece, the lithium ion battery can effectively realize high stability and high lithium supplement efficiency, and finally improves the overall performance of the battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to lithium replenishment materials, positive electrode sheets, and secondary batteries. Background Technology

[0002] During the first charge, lithium-ion rechargeable batteries consume some active lithium ions due to the formation of the SEI film, resulting in a decrease in coulombic efficiency and capacity loss. Lithium replenishment materials are often added to the positive electrode. However, existing lithium replenishment materials have poor conductivity, affecting the lithium replenishment effect. They also often have low lithium replenishment efficiency and poor stability, making it impossible to achieve rapid lithium ion transport. Furthermore, they may cause lithium ions to rapidly detach due to high environmental activity, leading to uncontrolled lithium replenishment. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of the existing technology and provide a lithium replenishment material. This material uses a porous lithium replenishment agent doped with carbon nanotubes with a deep gradient pore size as the core, and at the same time, it is provided with a temperature-sensitive intermediate layer and an outer protective layer with self-healing function on its surface. When applied to the positive electrode, it can effectively achieve high stability and high lithium replenishment efficiency, and ultimately improve the overall performance of the battery.

[0004] To achieve the above objectives, in a first aspect of this application, this application provides a lithium replenishment material comprising, from the inside out, a core, an intermediate layer, and an outer protective layer; The core comprises a lithium supplement and carbon nanotubes; The average pore size at the surface of the core is 0.5~0.6μm, the average pore size at a depth of 0.5μm at the surface is 0.3~0.45μm, and the average pore size at a depth of 1μm at the surface is ≤0.2μm. The intermediate layer comprises a temperature-sensitive organic material and a fast ion conductor; The outer protective layer comprises self-healing organic matter and lithium-containing inorganic salt, wherein the average particle size of the lithium-containing inorganic salt is ≤1nm.

[0005] In some embodiments, the carbon nanotubes have a mass content of 5-8 wt% in the core.

[0006] In some embodiments, the average length of the carbon nanotubes is 2 to 50 nm.

[0007] In some embodiments, the average thickness of the intermediate layer is 0.5 to 0.8 μm.

[0008] In some embodiments, the temperature-sensitive organic material includes at least one of poly(N-isopropylacrylamide), poly(N-ethylacrylamide), and poly(N-isopropylmethacrylamide).

[0009] In some embodiments, the fast ion conductor includes at least one of lithium lanthanum zirconium oxide, lanthanum zirconium oxide salt, lithium aluminum titanium oxide, lithium aluminum titanium phosphate, lithium gallium titanium oxide, and lithium gallium titanium phosphate.

[0010] In some embodiments, the fast ion conductor has a mass content of 5-10 wt% in the intermediate layer.

[0011] In some embodiments, the intermediate layer also includes hydrophobic organic materials.

[0012] In some embodiments, the average thickness of the outer protective layer is 0.3 to 0.6 μm.

[0013] In some embodiments, the self-healing organic material includes at least one of polyurethane resin, epoxy resin, and polyolefin resin, and the self-healing organic material includes at least one of disulfide bond structure, acylhydrazine-carbonyl structure, and hydrogen bond structure.

[0014] In some embodiments, the lithium-containing inorganic salt includes at least one of lithium carbonate, lithium bicarbonate, lithium hydroxide, and lithium dioxaphosphate.

[0015] In some embodiments, the lithium-containing inorganic salt has a mass content of 15-20 wt% in the outer protective layer.

[0016] In a second aspect, this application provides a positive electrode sheet comprising the lithium replenishment material described in this application.

[0017] In a third aspect, this application provides a secondary battery, including the positive electrode described in this application.

[0018] The beneficial effects of this application are as follows: This application provides a lithium replenishment material, which uses a porous lithium replenishment agent doped with carbon nanotubes of varying depth gradient pore size as the core, and simultaneously sets a temperature-sensitive intermediate layer and a self-healing outer protective layer on its surface. When applied to the positive electrode, it can effectively achieve high stability and high lithium replenishment efficiency, ultimately improving the overall performance of the battery. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0021] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0022] The present application is further illustrated below with specific embodiments: A lithium supplement material comprising, from the inside out, a core, an intermediate layer, and an outer protective layer; The core comprises a lithium supplement and carbon nanotubes; The average pore size at the surface of the core is 0.5~0.6μm, the average pore size at a depth of 0.5μm at the surface is 0.3~0.45μm, and the average pore size at a depth of 1μm at the surface is ≤0.2μm. The intermediate layer comprises a temperature-sensitive organic material and a fast ion conductor; The outer protective layer comprises self-healing organic matter and lithium-containing inorganic salt, wherein the average particle size of the lithium-containing inorganic salt is ≤1nm.

[0023] To overcome the stability and lithium replenishment efficiency issues of existing lithium replenishment materials, this application constructs a core structure using a lithium replenishing agent and highly conductive carbon nanotubes. The entire structure is designed as a porous structure with a specific gradient pore size range of less than 1 μm from the inside out. This design allows for higher lithium ion transport rates, shorter transport paths, and lower resistance. Furthermore, the larger pores in the outer layers allow for the containment of more lithium ions released from the center, achieving continuous lithium replenishment and a greater total lithium replenishment volume. Secondly, to improve the product's stability during lithium replenishment, an intermediate layer containing a temperature-sensitive organic compound and a fast ion conductor is further constructed on the surface of the lithium replenishing agent core. The temperature-sensitive organic compound undergoes a phase transition under abnormal temperature changes (e.g., abnormal temperature rise of the electrode during lithium replenishment), significantly increasing its density and suppressing lithium ion diffusion, thus preventing uncontrolled lithium replenishment due to excessive temperature. The fast ion conductor ensures smooth lithium ion transport between the core and the electrode, preventing a decrease in lithium ion transport efficiency caused by the intermediate layer. Finally, an additional outer protective layer is provided on the outer layer of the intermediate layer. Due to the self-healing organic matter contained in this layer, when the product is damaged by external stress or thermal stress and cracks appear, it can refill and repair the cracks based on the mechanism of hydrogen bond recombination and covalent bond breakage / reconnection, thus maintaining the integrity of the structure. Meanwhile, the nano-sized lithium-containing inorganic salt can be fully dispersed in the micro-gaps of the outer protective layer, improving the interfacial bonding force. This substance will also participate in the lithium replenishment process, improving the lithium replenishment efficiency of the product.

[0024] The inventors discovered that if the core structure does not contain carbon nanotubes, or if the pore size distribution is improperly set, the ideal lithium replenishment efficiency cannot be achieved. Furthermore, if the intermediate layer or outer protective layer is improperly set, in addition to affecting the lithium replenishment efficiency, it may also lead to reliability-related problems such as uncontrolled lithium replenishment, ultimately resulting in a significant decrease in the cycle life of the corresponding secondary battery.

[0025] It should be noted that, in the scheme described in this application, the average pore size range at different depths of the core surface in the lithium replenishment material can be confirmed by, but is not limited to, the following methods: The lithium replenishment material particles are directionally cut using a LEICA EM TIC 3X ion beam cutting instrument. The cut particles are then observed beforehand using a scanning electron microscope (SEM). The thickness and size of the core particles are identified by the carbon nanotube morphology. Depth measurements (surface, 0.5 μm, 1 μm) are performed using a distance measurement tool on the SEM, with the center of the core plane as the center. Within the observation area at each depth, at least 20 independent pores are randomly selected, and the equivalent diameter of each pore is measured. The average value is calculated, and outliers are identified. The above observations and measurements are performed at the same depth in three different core particles at each depth. Finally, the average of the three sets of average values ​​is taken as the final average pore size at that depth.

[0026] In some embodiments, the average pore size at the core surface (i.e., at a depth of 0 μm) is a value ranging from one or any two of 0.5 μm, 0.52 μm, 0.55 μm, 0.56 μm, 0.58 μm, and 0.6 μm; the average pore size at a depth of 0.5 μm at the surface is a value ranging from one or any two of 0.3 μm, 0.32 μm, 0.35 μm, 0.38 μm, 0.4 μm, and 0.45 μm; and the average pore size at a depth of 1 μm at the surface is a value ranging from one or any two of 0.2 μm, 0.15 μm, 0.1 μm, 0.08 μm, 0.05 μm, 0.02 μm, and 0.01 μm.

[0027] In some embodiments, the lithium supplement includes Li4Ti5O 12 Li₂Ti₃O₇, Li₂Ti₆O 13 At least one of them.

[0028] In some embodiments, the carbon nanotubes have a mass content of 5-8 wt% in the core.

[0029] In some embodiments, the carbon nanotubes in the core have a mass content of 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, or any combination thereof.

[0030] More preferably, the carbon nanotubes in the core have a mass content of 6-7 wt%.

[0031] In a core with a gradient porous structure, the amount of carbon nanotubes has a certain impact on the overall conductivity and lithium replenishment capacity of the core. The higher the carbon nanotube content, the better the conductivity provided by the three-dimensional network structure, but the overall lithium replenishment capacity of the lithium replenishing agent decreases and it will block some of the pore structure. When the carbon nanotube content is preferably within the above range, the lithium replenishment efficiency of the lithium replenishing material is better.

[0032] It should be noted that the mass content of carbon nanotubes in the core of this application can be confirmed by, but is not limited to, the following methods: The carbon content in the core is compared with the carbon nanotube content in the core. A LEICA EMTIC 3X ion beam cutting instrument is used to directionally cut the lithium-supplementing material particles. The cut samples are then transferred to a ZEISS Sigma 500 field emission scanning electron microscope for observation. At magnification of 50,000–80,000, the core region where the carbon nanotubes are located is pre-identified. Using the geometric center of the core in the slice as the observation point, three independent observation regions (2×2 μm in area) are delineated. 2The carbon nanotubes are uniformly distributed in the core center (0.5 μm and 1 μm from the surface). The elemental mass fraction of each region was observed using an EDS spectrometer, and the mass fraction of carbon was extracted. The average value of the three regions is taken as the mass content of carbon nanotubes in the core.

[0033] In some embodiments, the average length of the carbon nanotubes is 2 to 50 nm.

[0034] In some embodiments, the average length of the carbon nanotubes is a range of one or any two of 2nm, 5nm, 10nm, 20nm, 25nm, 30nm, 40nm, 45nm, and 50nm.

[0035] In some embodiments, the average length of the carbon nanotubes is determined by transmission electron microscopy (TEM). The lithium supplement material is dispersed in ethanol, sonicated for 2 hours, and then the particles are observed using TEM. Particles in which carbon nanotubes can be clearly seen are selected, and at least 20 particles are selected. Fifty carbon nanotubes are cut and measured, and their lengths are measured and the average value is calculated.

[0036] In some embodiments, the average particle size of the kernel is 1~5 μm.

[0037] In some embodiments, the average particle size of the kernel is a range of one or any two of the following: 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, and 5 μm. In some embodiments, the average thickness of the intermediate layer is 0.5 to 0.8 μm.

[0038] In some embodiments, the average thickness of the intermediate layer is a range of one or both of 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, and 0.8 μm.

[0039] More preferably, the average thickness of the intermediate layer is 0.6~0.7μm.

[0040] The main function of the intermediate layer is to achieve the temperature sensitivity of the product, that is, to automatically adjust the lithium replenishment rate when thermal anomalies occur in the application scenario, so as to avoid lithium replenishment runaway. When the thickness of the intermediate layer is preferably within the above range, not only can a higher lithium transmission efficiency be guaranteed, but also a higher thermal regulation efficiency. Therefore, the secondary battery corresponding to the lithium replenishment material has higher lithium replenishment efficiency and cycle performance.

[0041] It should be noted that the average core particle size and average thickness of the intermediate layer of the lithium replenishment material described in this application can be confirmed by, but not limited to, the following methods: The lithium replenishment material is sliced ​​using a LEICA EM UC7 ultrathin slicer to ensure that the slices completely present the structure of the core, intermediate layer and outer protective layer. The copper mesh carrying the slices is placed in a FEI Talos F200X transmission electron microscope with a magnification of 30,000 to 50,000 times. Taking the central area of ​​the copper mesh as a reference, 10 independent lithium replenishment material particles are randomly selected, each particle corresponding to an observation field. The core area of ​​each particle is confirmed based on the morphology of carbon nanotubes. Three mutually perpendicular diameters passing through the center of the core are measured, and the average of the three diameters of each core is calculated as the particle size. The arithmetic mean of the particle sizes of the 10 particles is the average core diameter of the lithium replenishment material. Use the same software to mark the inner boundary (core and intermediate layer) and outer boundary (intermediate layer and outer protective layer) of the intermediate layer, ensuring that the marking is perpendicular to the thickness direction of the intermediate layer. Select 5 evenly distributed measurement points for each intermediate layer, record the thickness value of each measurement point, calculate the average of the 5 measurement points of the intermediate layer of each particle, and take it as the intermediate layer thickness of that particle. Then take the arithmetic mean of the intermediate layer thickness data of 10 particles, which is the intermediate layer thickness.

[0042] In some embodiments, the temperature-sensitive organic material includes at least one of poly(N-isopropylacrylamide), poly(N-ethylacrylamide), and poly(N-isopropylmethacrylamide).

[0043] In some embodiments, the fast ion conductor includes at least one of lithium lanthanum zirconium oxide, lanthanum zirconium oxide salt, lithium aluminum titanium oxide, lithium aluminum titanium phosphate, lithium gallium titanium oxide, and lithium gallium titanium phosphate.

[0044] In some embodiments, the fast ion conductor has a mass content of 5-10 wt% in the intermediate layer.

[0045] In some embodiments, the fast ion conductor in the intermediate layer has a mass content of 5 wt%, 6 wt%, 7 wt%, 7.5 wt%, 8 wt%, 9 wt%, 10 wt%, or any combination thereof.

[0046] It should be noted that the mass content of the fast ion conductor in the intermediate layer described in this application can be confirmed by, but is not limited to, the following methods: First, the lithium replenishment material is ultrasonically cleaned with ethanol to remove surface impurities, and the outer protective layer is peeled off using a FEI Helios G4 UX focused ion beam (FIB) device until the smooth surface of the intermediate layer is exposed. The sample is placed in a ThermoScientific K-Alpha+ X-ray photoelectron spectrometer, and the narrow spectrum of characteristic elements is scanned (the type of fast ion conductor and the elements it contains are pre-identified, such as La and Zr). Peak fitting is performed on the narrow spectrum of characteristic elements, and the atomic percentage (At%) of the characteristic elements is calculated. The mass ratio of the characteristic elements in the fast ion conductor is also calculated. The mass content of the fast ion conductor is calculated by dividing the mass fraction corresponding to the atomic percentage of the characteristic element by the mass ratio of the element in the fast ion conductor. The test results of the three regions are repeated for verification, and the arithmetic mean is taken as the final mass content of the fast ion conductor in the intermediate layer.

[0047] In some embodiments, the intermediate layer also includes hydrophobic organic materials.

[0048] In some embodiments, the hydrophobic organic material includes a range of one or any two of polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, and polyvinylidene fluoride.

[0049] Introducing hydrophobic organic matter into the intermediate layer, which serves as the intermediate interface layer, can further prevent water or hydrophilic substances from contaminating and affecting the core, thereby further improving the overall structural stability and lithium replenishment efficiency.

[0050] In some embodiments, the mass ratio of thermosensitive organic matter to hydrophobic organic matter in the intermediate layer is (3:1) to (8:1).

[0051] More preferably, the mass ratio of the thermosensitive organic compound to the hydrophobic organic compound is (4:1) to (6:1).

[0052] In some embodiments, the average thickness of the outer protective layer is 0.3 to 0.6 μm.

[0053] In some embodiments, the average thickness of the outer protective layer is a range of one or both of 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, and 0.6 μm.

[0054] More preferably, the average thickness of the outer protective layer is 0.4~0.5μm.

[0055] When the thickness of the outer protective layer increases, in addition to improving the overall structural stability and lithium replenishment capacity of the lithium replenishment material, the conductivity of the particles themselves will also change. When the thickness of the outer protective layer is preferably within the above range, the ion transport efficiency and structural stability of the lithium replenishment material can be at a better level.

[0056] It should be noted that the average thickness test method for the outer protective layer of the lithium replenishment material is the same as the average thickness test method for the intermediate layer in this application, and will not be repeated here.

[0057] In some embodiments, the self-healing organic material includes at least one of polyurethane resin, epoxy resin, and polyolefin resin, and the self-healing organic material includes at least one of disulfide bond structure, acylhydrazine-carbonyl structure, and hydrogen bond structure.

[0058] In some embodiments, the lithium-containing inorganic salt includes at least one of lithium carbonate, lithium bicarbonate, lithium hydroxide, and lithium dioxaphosphate.

[0059] In some embodiments, the average particle size of the lithium-containing inorganic salt is 0.3~1 nm.

[0060] More preferably, the average particle size of the lithium-containing inorganic salt is 0.5~0.8 nm.

[0061] In some embodiments, the lithium-containing inorganic salt has a mass content of 15-20 wt% in the outer protective layer.

[0062] In some embodiments, the mass content of the lithium-containing inorganic salt in the outer protective layer is a range of one or any two of 15wt%, 15.5wt%, 16wt%, 16.5wt%, 17wt%, 18wt%, and 20wt%.

[0063] In some embodiments, the lithium replenishing material can be prepared by, but is not limited to, the following methods: (1) The raw materials of lithium supplementation agent are mixed with carbon nanotubes and pore-forming agent and dispersed in a solvent, spray dried, and the resulting particles are heated and sintered to obtain the core. (2) Mix and disperse the temperature-sensitive organic material, fast ion conductor and hydrophobic organic material in a solvent to obtain a mixture. Immerse the core into the mixture and impregnate it by lifting. Then, pre-dry, thermal cross-linking and curing, and impurity removal and shaping treatment are performed on the impregnated core to obtain a core covered with an intermediate layer. (3) The core with the intermediate layer is immersed in a dispersion containing self-healing organic matter and lithium inorganic salt for a pull-in impregnation treatment, dried, and thermally crosslinked to obtain the lithium supplement material.

[0064] In some embodiments, the raw materials of the lithium replenishing agent include a lithium source and a transition metal source.

[0065] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium nitrate.

[0066] In some embodiments, the transition metal source includes at least one selected from titanium dioxide, titanium chloride, tetrabutyl titanate, zirconium oxide, zirconium chloride, gallium oxide, and lanthanum oxide.

[0067] In some embodiments, the pore-forming agent includes at least one of stearic acid and polystyrene.

[0068] In some embodiments, the mass ratio of the raw material of the lithium replenishing agent to the carbon nanotubes and the pore-forming agent is 85~90:5~8:3~7.

[0069] In the scheme described in this application, the mass content of the carbon nanotubes and the pore size at different depths of the core can be controlled by the mass ratio of the above-mentioned raw materials. For example, the more pore-forming agent is added, the larger the pore size will be, but it is not limited to this.

[0070] In some embodiments, the atmosphere during heating and sintering in step (1) is air, the temperature is 750~900℃, and the time is 3~6h.

[0071] In this application, the pore size of the core can also be controlled by the temperature during heating and sintering; for example, the higher the temperature, the larger the pore size.

[0072] In some embodiments, in step (2), the mass ratio of the added thermosensitive organic material, fast ion conductor and hydrophobic organic material is 75~85:5~10:5~15.

[0073] In some embodiments, in step (2), the solvent in the mixture is at least one of N-methylpyrrolidone (NMP), ethanol, and propanol, and the mass concentration of the mixture is 5 to 10 wt%.

[0074] In some embodiments, the pre-drying temperature in step (2) is 30~60℃ and the time is 20~50min. The thermal crosslinking curing includes a first-stage thermal crosslinking curing and a second-stage thermal crosslinking curing. The temperature of the first-stage thermal crosslinking curing is 60~80℃ and the time is 50~80min. The temperature of the second-stage thermal crosslinking curing is 80~90℃ and the time is 2~3h. The impurity removal and shaping treatment uses ethanol reflux extraction for 1~3h, followed by vacuum drying at 40~60℃ for 1~3h.

[0075] In some embodiments, the ratio of the added mass of the core to the volume of the mixture is 1 g : (20~30) mL.

[0076] In some embodiments, the lifting and immersion treatment is performed 1 to 3 times at a rate of 3 to 8 mm / min.

[0077] In this application, the thickness of the intermediate layer and the outer protective layer can be adjusted by the lifting speed and number of times. For example, the slower the lifting speed or the more times the lifting is performed, the greater the thickness. However, this is not the only option. Those skilled in the art can also adjust the thickness in other ways, and this is not a limitation.

[0078] In some embodiments, the drying temperature in step (3) is 40~50℃ and the time is 30~50min, and the temperature for thermal crosslinking and curing is 60~80℃ and the time is 1~2h.

[0079] In a second aspect, this application provides a positive electrode sheet comprising the lithium replenishment material described in this application.

[0080] In some embodiments, the positive electrode includes a current collector and a positive active material layer, wherein the positive active material layer includes a positive electrode material and a lithium supplement material.

[0081] In some embodiments, the mass percentage of lithium replenishing material in the positive electrode active material layer is 3-8 wt%.

[0082] In some embodiments, the cathode material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium iron phosphate.

[0083] In some embodiments, the positive electrode active material layer further includes a binder and a conductive agent.

[0084] In some embodiments, the mass ratio of the positive electrode material, lithium replenishment material, binder, and conductive agent is 85~92:3~8:2~4:2~4.

[0085] In some embodiments, the adhesive includes at least one selected from polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, and polyvinyl alcohol.

[0086] In some embodiments, the conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the areal density of the positive electrode sheet is 150~220 g / m³. 2 The compacted density is 2.2~2.6 g / cm³. 3 .

[0088] In a third aspect, this application provides a secondary battery, including the positive electrode described in this application.

[0089] In some embodiments, the secondary battery further includes a negative electrode, a separator, and an electrolyte.

[0090] In some embodiments, the negative electrode sheet includes a current collector and a negative electrode active material layer.

[0091] In some embodiments, the negative electrode active material layer includes a negative electrode material, a binder, a thickener, and a conductive agent.

[0092] In some embodiments, the mass ratio of the negative electrode material, conductive agent, thickener, and binder is (94~97):(1~2):(1~2):(1~2).

[0093] In some embodiments, the negative electrode material includes at least one of graphite material and silicon-carbon material.

[0094] It should be noted that the conductive agent in the negative electrode active material layer described in this application is used to provide conductivity, and any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. For example, the conductive agent includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon black is, for example, SP (SuperP), acetylene black, Ketjen black, etc.

[0095] The binders and thickeners in the negative electrode active material layer are used to improve the adhesion between the negative electrode material and the conductive agent particles, and between the negative electrode active material layer and the current collector. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. For example, the binders include, but are not limited to, fluorinated polyolefin binders, including but not limited to polyvinylidene fluoride (PVDF), PVDF copolymers or their modified derivatives (e.g., modified with carboxylic acid, acrylic acid, acrylonitrile, etc.), and styrene-butadiene rubber (SBR). Thickeners include, but are not limited to, carboxymethyl cellulose or its salts.

[0096] In some embodiments, the areal density of the negative electrode sheet is 80~150 g / m². 2 The compacted density is 1.5~1.8 g / cm³. 3 .

[0097] In some embodiments, the electrolyte comprises a solvent and a lithium salt.

[0098] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

[0099] Exemplary examples include, but are not limited to, at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); carboxylic acid ester solvents include, but are not limited to, at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; ether solvents include, at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; sulfone solvents include, at least one of methyl sulfone and dimethyl sulfoxide; nitrile solvents include, at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and phosphate ester solvents include, at least one of trimethyl triphosphate and triethyl phosphate.

[0100] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluoromethanesulfonylimide, lithium ditrifluoromethanesulfonylimide, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0101] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.8~2 mol / L.

[0102] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0103] It should be noted that the separator can be any of the battery separator materials available in the art. For example, the separator may include, but is not limited to, at least one of polypropylene and polyethylene.

[0104] The present invention is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention: Example 1 The embodiments of the lithium replenishment material, positive electrode sheet, and secondary battery described in this application include the following steps in the preparation method of the secondary battery: Preparation of lithium supplementation materials: (1) 100g of lithium supplement raw materials (lithium carbonate and tetrabutyl titanate, wherein the molar ratio of lithium element in lithium titanate to titanium element in tetrabutyl titanate is 4:5) are mixed with 6g of carbon nanotubes (multi-walled carbon nanotubes produced by Hunan Shanshan, which are crushed before use, with an average diameter of 15nm and an average length of 2μm after crushing) and 6g of pore-forming agent stearic acid and dispersed in 50mL of NMP solvent. The mixture is ball-milled at 300r / min for 2h, and then placed in a spray dryer (inlet air temperature 200℃, outlet air temperature 80℃, atomization pressure 0.3MPa) for spray drying. The resulting particles are heated to 850℃ at 5℃ / min in air atmosphere for 4h for heating and sintering to obtain the core. (2) 80g of thermosensitive organic poly(N-isopropylacrylamide) (Maclean CAS25189-55-3), 7g of fast ion conductor LLZO (average particle size 1.5μm) and 13g of hydrophobic organic PVDF were mixed and dispersed in NMP and ethanol in a volume ratio of 3:1 to prepare a 7wt% mixture. The core was immersed in the mixture at a solid-liquid ratio of 1g:25mL and impregnated once by lifting at a rate of 5mm / min. The impregnated core was then pre-dried at 40℃ for 30min, then thermally crosslinked and cured at 60℃ for 60min, then thermally crosslinked and cured at 85℃ for 2h, cooled and refluxed with ethanol for 2h, and then dried at 50℃ in a vacuum environment for 2h to obtain a core coated with an intermediate layer. (3) The core coated with the intermediate layer was immersed in 150 mL of NMP dispersion (5 wt%) containing self-healing organic polycaprolactone-polyethylene glycol block copolymer (HO-PEG-PCL produced by Xi'an Kaixin) and lithium inorganic salt lithium carbonate (mass ratio of the two to 4:1) at a rate of 6 mm / min for two dip-dip treatments, dried at 45 °C for 40 min, and thermally crosslinked and cured at 70 °C in a vacuum environment for 1.5 h to obtain the lithium supplement material. The parameters and product characteristics of the lithium supplement material during preparation are shown in Tables 1 and 2.

[0105] Preparation of the positive electrode sheet: Lithium cobalt oxide (Xiamen Tungsten New Energy, L906, 10μm particle size), the above-mentioned lithium supplementation material, conductive carbon black SP as a conductive agent, and PVDF as a binder are mixed in N-methylpyrrolidone at a mass ratio of 88:5:4:3 to prepare a slurry. This slurry is then coated onto aluminum foil as a current collector and dried to obtain the positive electrode sheet. The areal density of the positive electrode sheet is 200 g / m³. 2 The compacted density is 2.4 g / cm³. 3 ; Preparation of the negative electrode sheet: Artificial graphite, conductive agent acetylene black, thickener sodium carboxymethyl cellulose, and binder SBR are dispersed in water at a mass ratio of 96:2:1:1, then coated onto a current collector copper foil and dried to obtain the negative electrode sheet. The compacted density of the negative electrode sheet is 1.65 g / cm³.3 .

[0106] Preparation of electrolyte: Ethylene carbonate EC, ethyl methyl carbonate EMC, and dimethyl carbonate DMC are mixed in a volume ratio of 1:1:1 as a solvent, and then lithium hexafluorophosphate is added to prepare a concentration of 1 mol / L to obtain the electrolyte.

[0107] The negative electrode, separator, and positive electrode are stacked in sequence, the tabs are welded, and after hot pressing, they are sealed with aluminum-plastic film, liquid is injected, and then sealed again to obtain the secondary battery.

[0108] Examples 2-14, Comparative Examples 1-2, Comparative Example 8 An embodiment of a lithium replenishment material, a positive electrode sheet, and a secondary battery differs from Embodiment 1 only in that the parameters used in the preparation of the lithium replenishment material are different, as shown in Table 1, and the characteristic parameters of the resulting product are shown in Table 2. The mass content of the fast ion conductor in the intermediate layer is controlled by adjusting the amount of fast ion conductor added, while keeping the total amount of thermosensitive organic material, fast ion conductor, and hydrophobic organic material constant, and the mass ratio of thermosensitive organic material to hydrophobic organic material constant. The mass content of lithium-containing inorganic salt in the outer protective layer is controlled by adjusting the amount of lithium-containing inorganic salt added, while keeping the total amount of self-healing organic material and lithium-containing inorganic salt constant. In Example 14, the raw materials of the lithium replenishing agent were replaced with lithium carbonate and tetrabutyl titanate, wherein the molar ratio of lithium element in lithium titanate to titanium element in tetrabutyl titanate was 2:3; the temperature-sensitive organic material was replaced with an equal mass of poly-N-ethylacrylamide (Maclean); the fast ion conductor was replaced with an equal mass of lithium aluminum titanium phosphate LATP (Sichuan Putailai); the self-healing organic polymer was replaced with an equal mass of epoxy resin containing hydrazide-carbon structure (SM-EP-HZ-01 produced by Jiangsu Sanmu, hydrazide-modified bisphenol A epoxy resin); and the lithium-containing inorganic salt was replaced with an equal mass of lithium hydroxide with an average particle size of 0.6 nm.

[0109] Comparative Example 3 A lithium replenishment material, a positive electrode sheet, and a secondary battery differ from Example 1 only in that, in the preparation method of the lithium replenishment material described below, the carbon nanotubes are not added during the preparation of the core in step (1).

[0110] Comparative Example 4 A lithium replenishment material, positive electrode sheet and secondary battery, differing from Example 1 only in that, in the preparation method of the lithium replenishment material, fast ion conductors are not added in step (2), and their addition amount is made up by thermosensitive organic matter and hydrophobic organic matter in the same ratio.

[0111] Comparative Example 5 A lithium replenishment material, a positive electrode sheet, and a secondary battery differ from Example 1 only in that, in the preparation method of the lithium replenishment material, no temperature-sensitive organic material is added in step (2), and its addition amount is supplemented by hydrophobic organic material.

[0112] Comparative Example 6 A lithium replenishment material, positive electrode sheet and secondary battery, differing from Example 1 only in that lithium-containing inorganic salts are not added in step (3), and the amount added is supplemented by self-healing organic matter.

[0113] Comparative Example 7 A lithium replenishment material, a positive electrode sheet, and a secondary battery, differing from Example 1 only in the preparation of the lithium replenishment material: (1) Same as Example 1; (2) Mix 80g of thermosensitive organic poly(N-isopropylacrylamide) and 20g of hydrophobic organic PVDF and disperse them in NMP and ethanol in a volume ratio of 3:1 to prepare a 7wt% mixture. Immerse the core in the mixture at a solid-liquid ratio of 1g:25mL and impregnate it once at a rate of 5mm / min by lifting. Then, pre-dry the impregnated core at 40℃ for 30min, perform a first-stage thermal crosslinking and curing at 60℃ for 60min, perform a second-stage thermal crosslinking and curing at 85℃ for 2h, reflux with ethanol for 2h after cooling, and then dry at 50℃ under vacuum for 2h to obtain a core coated with an intermediate layer. (3) The core coated with the intermediate layer is immersed in 150 mL of NMP dispersion (concentration 5wt%) containing self-healing organic polycaprolactone-polyethylene glycol block copolymer, lithium carbonate containing lithium inorganic salt and fast ion conductor LLZO (mass ratio of the three is 6:2:2) at a rate of 6 mm / min for two dip-dip treatments, dried at 45°C for 40 min, and thermally crosslinked and cured at 70°C in a vacuum environment for 1.5 h to obtain the lithium replenishing material. The intermediate layer does not contain fast ion conductors, and the outer protective layer contains fast ion conductors.

[0114] Table 1 Table 2 Example of effect 1 To verify the effectiveness of the lithium replenishment material described in this application, the secondary batteries obtained in each embodiment and comparative example were tested as follows. Meanwhile, a control group was prepared using the same preparation method as in Example 1, except that no lithium replenishment material was introduced, and the same tests were performed: (1) First-time efficiency test: The secondary battery was charged at a constant current of 0.1C to the cutoff voltage of 4.2V. When the current dropped to 0.05C, the charging was stopped and the charging capacity was recorded. After standing for 30 minutes, it was discharged at a constant current of 0.1C to the cutoff voltage (2.75V) and the discharge capacity was recorded. The first charge-discharge efficiency (%) of the secondary battery = discharge capacity / charging capacity × 100%. Ten parallel samples were tested in each group and the average value was taken. (2) Long-cycle capacity retention test: The secondary battery is charged with a constant current of 0.5C to the cutoff voltage, charged with a constant voltage until the current is ≤0.05C, left to stand for 5 minutes, discharged with a constant current of 0.5C to 2.75V, left to stand for 5 minutes, and one cycle is completed. The discharge capacity of the first cycle is recorded. The charge and discharge cycles are repeated 100 times, and the discharge capacity of the 100th cycle is recorded. The cycle capacity retention rate (%) = (100th discharge capacity / first discharge capacity) × 100%; (3) Lithium replenishment rate: Charge the battery at a constant current of 0.5C to the cutoff voltage (same as the first-efficiency test), let it stand for 1 hour, and then discharge it to 2.75V to complete the pre-activation; charge it again at a constant current of 0.5C, record the charging capacity every 10 minutes, plot the charging time-charging capacity curve, and calculate the lithium replenishment rate based on the curve fitting. (4) High temperature cycle test: Place the secondary battery in a 45℃ constant temperature chamber and let it stand for 2 hours to ensure that the battery temperature is consistent with the environment. Then charge it with a constant current of 0.5C to the cutoff voltage, charge it with a constant voltage until the current is ≤0.05C, let it stand for 5 minutes, discharge it with a constant current of 0.5C to 2.75V, let it stand for 5 minutes to complete one high temperature cycle, and record the first discharge capacity. Repeat the cycle to 50 times, and record the discharge capacity for each cycle. The high temperature cycle capacity retention rate (%) is calculated as the 50th discharge capacity / the first discharge capacity × 100%. At the same time, record whether there is a sudden drop in capacity during the cycle (single capacity loss > 5%). If so, record it.

[0115] (5) Rate Cycling Test: The secondary battery is first charged at a constant current of 0.2C to the cutoff voltage, then constant voltage to 0.05C, and discharged at 0.2C to 2.75V. The discharge capacity at this rate is recorded. The above charge and discharge process is repeated at a rate of 1C. The discharge capacity at the rate of 1C is recorded as Q1C. The battery is further cycled at a rate of 1C for 50 cycles. The discharge capacity at the 50th cycle (Q50-1C) is recorded. The capacity retention rate at the rate of 1C for 50 cycles (%) is calculated as (Q50-1C / Q1C) × 100%.

[0116] The test results are shown in Table 3.

[0117] Table 3 As can be seen from the table, the lithium replenishment material described in this application, after being introduced into the positive electrode, can not only effectively improve the initial efficiency of the secondary battery, but also, based on the continuous replenishment of active lithium, significantly improve the cycle performance, high-temperature performance, and rate performance of the secondary batteries in each embodiment compared with the control group. This is mainly due to the special structural design of the material itself: the main core structure is constructed by combining the lithium replenishment agent and highly conductive carbon nanotubes. At the same time, the entire structure is set as a porous structure with a specific gradient pore size range of less than 1μm from the inside to the outside. Through this setting, the lithium ion transport rate of the lithium replenishment agent is not only higher, but the total amount of lithium replenished is also greater, thus achieving continuous lithium replenishment. Secondly, to improve the stability of the product during lithium replenishment, an intermediate layer containing a temperature-sensitive organic material and a fast ion conductor is further constructed on the surface of the core containing the lithium replenishment agent. The temperature-sensitive organic material can undergo a phase transition when the temperature changes abnormally (such as when the temperature of the electrode rises abnormally during the lithium replenishment stage), resulting in a significant increase in density. This suppresses the diffusion of lithium ions, avoids uncontrolled lithium replenishment due to excessive temperature, and improves the cycle, high-temperature, and rate performance of the secondary battery. The fast ion conductor ensures the smooth transport of lithium ions between the core and the electrode, preventing a decrease in lithium ion transport efficiency due to the intermediate layer.Finally, an additional outer protective layer is added outside the intermediate layer. This layer contains self-healing organic matter, which allows the product to repair cracks caused by external or thermal stress through hydrogen bond recombination and covalent bond breakage / reconnection, maintaining structural integrity and further improving the cycle stability of the secondary battery under different scenarios. Meanwhile, nanoscale lithium-containing inorganic salts are fully dispersed in the microscopic gaps of the outer protective layer, enhancing interfacial bonding. This substance also participates in the lithium replenishment process, improving the product's lithium replenishment efficiency. In contrast, Comparative Examples 1 and 2 have improper core design, resulting in poor lithium replenishment effects of the lithium replenishment materials. This also means that the introduction of lithium replenishment does not significantly improve the cycle, high-temperature, and rate performance of the secondary battery compared to the product in the examples. Comparative Example 3's material core does not contain carbon nanotubes, resulting in low initial lithium replenishment efficiency, which also affects the lithium replenishment material's performance in various scenarios. The impact on the subsequent performance of the secondary battery: Comparative Examples 4 and 6 did not incorporate fast ion conductors and lithium-containing inorganic salts, which significantly affected the lithium replenishment efficiency, resulting in insufficient lithium replenishment efficiency. Comparative Example 5 lacked a temperature-sensitive organic layer, leading to poor lithium replenishment efficiency and, due to the damage to the lithium replenishment material during cycling, impacting electrode stability, resulting in poor cycle, high-temperature, and rate performance of the secondary battery. In Comparative Example 7, the fast ion conductor was not paired with the temperature-sensitive organic material; the presence of the intermediate layer actually inhibited ion transport efficiency, and this pairing affected the stability of the lithium replenishment material structure, resulting in lower performance compared to Comparative Example 4, which did not incorporate a fast ion conductor. In Comparative Example 8, the lithium-containing inorganic salt was too large, limiting the improvement in ion conduction efficiency and resulting in low binding to the outer layer, with little difference in performance compared to Comparative Example 6, which did not incorporate a lithium-containing inorganic salt.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this article without departing from the essence and scope of the technical solutions of this article.

Claims

1. Lithium supplementing material, characterized in that, The lithium supplement material comprises an inner core, an intermediate layer and an outer protective layer from inside to outside. The inner core comprises a lithium supplement agent and carbon nanotubes. The average pore size at the surface of the inner core is 0.5-0.6 μm, the average pore size at a depth of 0.5 μm from the surface is 0.3-0.45 μm, and the average pore size at a depth of 1 μm from the surface is ≤0.2 μm. The intermediate layer comprises a temperature-sensitive organic matter and a fast ion conductor. The outer protective layer comprises a self-repairing organic matter and a lithium-containing inorganic salt, and the average particle size of the lithium-containing inorganic salt is ≤1 nm.

2. The lithium supplementing material according to claim 1, wherein The mass content of the carbon nanotubes in the inner core is 5-8 wt%.

3. The lithium supplementing material of claim 1, wherein the lithium supplementing material is represented by the following formula: Li2Mn2Oy, wherein 0 < y < 4. The average length of the carbon nanotubes is 2-50 nm.

4. The lithium supplementing material of claim 1, wherein the lithium supplementing material is represented by the following formula: Li2Mn2Oy, wherein 0 < y < 4. The average thickness of the intermediate layer is 0.5-0.8 μm.

5. The lithium supplementing material of claim 1, wherein the lithium supplementing material is represented by the following formula: Li2Mn2Oy, wherein 0 < y < 4. The temperature-sensitive organic matter comprises at least one of poly-N-isopropyl acrylamide, N-isopropyl acrylamide, poly-N-ethyl acrylamide and poly-N-isopropyl methacrylamide, and / or the fast ion conductor comprises at least one of lithium lanthanum zirconium oxide, lanthanum zirconium oxide salt, lithium aluminum titanium oxide, lithium aluminum titanium phosphate, lithium gallium titanium oxide and lithium gallium titanium phosphate.

6. The lithium supplementing material of claim 1, wherein the lithium supplementing material is represented by the following formula: Li4ZnO4. The mass content of the fast ion conductor in the intermediate layer is 5-10 wt%.

7. The lithium supplementing material of claim 1, wherein the lithium supplementing material is represented by the following formula: Li4ZnO4. The intermediate layer further comprises a hydrophobic organic matter.

8. The lithium supplementing material of claim 1, wherein the lithium supplementing material is represented by the following formula: Li4ZnO4. The average thickness of the outer protective layer is 0.3-0.6 μm.

9. The lithium supplementing material of claim 1, wherein the lithium supplementing material is represented by the following formula: Li4ZnO4. The self-repairing organic matter comprises at least one of polyurethane resin, epoxy resin and polyolefin resin, and the self-repairing organic matter comprises at least one of disulfide bond structure, hydrazine-carbonyl structure and hydrogen bond structure.

10. The lithium supplementing material of claim 1, wherein the lithium supplementing material is represented by the following formula: Li2Mn2Oy, wherein 0 < y < 4. The mass content of the lithium-containing inorganic salt in the outer protective layer is 15-20 wt%.

11. A positive electrode sheet characterized by comprising: The lithium supplement material comprises the lithium supplement material according to any one of claims 1-10.

12. A secondary battery characterized by comprising: The positive electrode plate comprises the positive electrode plate according to claim 11.

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