Lithium supplement, preparation method thereof, positive electrode sheet and battery

Abstract

The application provides a lithium supplement agent, a preparation method of the lithium supplement agent, a positive plate and a battery. The lithium supplement agent comprises a core and a shell. The core comprises lithium oxalate, and the shell comprises a catalyst. The catalyst comprises a carbon matrix and a composite catalyst material loaded on the carbon matrix. The composite catalyst material comprises M single elements and an M oxide layer formed on the surface of the M single elements. M is a transition metal element. An M / M oxide layer heterojunction structure is formed between the M single elements and the M oxide layer. The lithium supplement agent has a low decomposition potential and a high capacity.

Description

Technical Field

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

[0002] During the initial charging of a lithium-ion battery, the organic electrolyte undergoes reduction and decomposition on the surface of negative electrode materials such as graphite, forming a solid electrolyte interphase (SEI) film. This SEI film effectively inhibits electrolyte decomposition and improves the cycle life of the lithium-ion battery. However, this SEI film leads to irreversible lithium loss in the positive electrode material, causing capacity decay during cycling. Therefore, when using ternary materials / phosphate materials as positive electrode materials in lithium batteries, a certain amount of lithium replenishment agent is often needed to compensate for the irreversible lithium loss during the first cycle, thereby improving the battery's total capacity and energy density.

[0003] To compensate for the irreversible loss of active lithium caused by the formation of a solid electrolyte interphase (SEI) film during the first charge and discharge of lithium-ion batteries, and to improve the battery's initial coulombic efficiency and energy density, pre-lithiation technology has become a key process. Among various lithium replenishing agents, lithium oxalate (Li2C2O4) is considered a highly promising cathode lithium replenishing material due to its high theoretical lithium replenishment capacity (approximately 580 mAh / g), relatively low cost, and relatively clean decomposition products (mainly Li2CO3 and CO2).

[0004] However, the high thermal decomposition temperature of lithium oxalate (typically above 450°C in air or an inert atmosphere) severely limits its practical applications. During the preparation of the positive electrode, the conventional electrode drying and heat treatment temperatures generally do not exceed 200°C in order to remove binders (such as PVDF) and form a good electrode structure. Therefore, lithium oxalate requires a relatively high voltage to decompose during charge and discharge, i.e., a high decomposition potential.

[0005] Existing technologies attempt to reduce the decomposition potential of lithium oxalate by introducing catalysts, but these are mostly concentrated on single transition metals or their oxides, which have problems such as high cost, limited catalytic efficiency, or poor compatibility with battery material systems.

[0006] Therefore, providing a high-capacity lithium oxalate lithium supplement material with low decomposition potential has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] This application provides a lithium replenishing agent and its preparation method, a positive electrode sheet, and a battery. The lithium replenishing agent of this application has a low decomposition potential and a high capacity.

[0008] In a first aspect, this application provides a lithium replenishing agent, the lithium replenishing agent comprising a core and a shell, the core comprising lithium oxalate, and the shell comprising a catalyst;

[0009] The catalyst comprises a carbon matrix and a composite catalytic material supported on the carbon matrix. The composite catalytic material comprises element M and an M oxide layer formed on the surface of the element M. M is a transition metal element, and an M / M oxide layer heterogeneous interface structure is formed between the element M and the M oxide.

[0010] In one possible implementation, M includes at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Mo.

[0011] In one possible implementation, the thickness of the M oxide layer is 2-20 nm;

[0012] And / or; in the transmission electron microscope cross-sectional image of the composite catalytic material, the perimeter of the outer contour of the composite catalytic material is A, the perimeter of the contour formed by the junction of the M element and the M oxide layer is B, and 0.5≤B / A<1;

[0013] And / or; in the catalyst, the loading of element M is 5-30 wt%.

[0014] In one possible implementation, the mass ratio of the core to the outer shell is (4-15):1.

[0015] In one possible implementation, the specific surface area of ​​the lithium supplement is 50-200 m². 2 / g.

[0016] Secondly, this application provides a method for preparing a lithium supplement, the method comprising:

[0017] S1: Element M, or M oxide, or precursor salt containing element M, and carbon-based support are dispersed in a solvent, rotary evaporated, dried, and sintered in a reducing atmosphere to obtain element M loaded on a carbon-based support.

[0018] S2: The product obtained in S1 is heat-treated in an oxygen-containing atmosphere to form an oxide layer of M on element M, thereby obtaining the catalyst; the heat treatment temperature is 100-400℃ and the heat treatment time is 10min-70min.

[0019] S3: Disperse the catalyst and lithium oxalate in a solvent and spray dry to obtain the lithium supplement agent.

[0020] In one possible implementation, in step S2, the temperature of the heat treatment is 150-350°C, and the heat treatment time is 20-60 minutes.

[0021] In one possible implementation, the particle size of the element M is 30-500 nm.

[0022] In one possible implementation, the carbon-based support in step S1 includes at least one of Ketjen black, hard carbon, conductive carbon black, acetylene black, carbon nanotubes, and graphene.

[0023] Thirdly, this application provides a positive electrode sheet, which includes the aforementioned lithium replenishing agent.

[0024] Fourthly, this application provides a battery with the aforementioned positive electrode.

[0025] This application provides a lithium supplement agent and its preparation method, a positive electrode sheet, and a battery. The method involves coating a catalyst onto a lithium oxalate core. The catalyst comprises a carbon matrix and a composite catalytic material supported on the carbon matrix. The composite catalytic material includes elemental M and an oxide layer of M formed on the surface of elemental M. An M / M oxide heterogeneous interface structure is formed between elemental M and the oxide layer. Specifically, this method offers the following advantages:

[0026] Bifunctional adsorption and activation: Under thermal or electrochemical fields, oxalate ions can be simultaneously adsorbed and activated at different sites on the catalyst surface. The Lewis acid sites provided by the M oxide layer have a strong affinity for the C=O carbonyl oxygen, effectively polarizing and weakening the C-C bond. Simultaneously, elemental M can interact with the π orbitals of the oxalate molecule through its d electrons, providing another activation pathway. This dual-site adsorption lowers the reaction initiation energy barrier.

[0027] Interfacial electron transfer promotes oxygen exchange and carbon-oxygen bond breaking: At the M / M oxide layer heterojunction, due to the Fermi level difference, electrons transfer from the elemental M phase to the oxide layer, increasing the electron cloud density on the oxide layer side and enhancing the activity of its lattice oxygen. This "activated" lattice oxygen or interfacial adsorbed oxygen species can more effectively attack the adsorbed and activated oxalate ions, promoting C / C bond breaking and CO2 removal (decarboxylation). The elemental M phase acts as a rapid electron channel, promoting the entire charge transfer process. In the electrochemical decomposition pathway, the formation of the heterojunction promotes a decrease in the decomposition potential.

[0028] Rapid transfer and stabilization of hydrogen species (protons): Formate (HCOO) may be generated during the decomposition of lithium oxalate. - Hydrogen-containing intermediates such as M and H2. Elemental M is an excellent hydrogenation / dehydrogenation catalyst, capable of rapidly capturing and recombining the hydrogen (H2) released or desired from these intermediates. + / H - This prevents the accumulation or generation of byproducts (such as H2O) that are detrimental to electrode stability, and guides the reaction to generate the target product (Li2CO3) and gas (CO2) in a directional and efficient manner.

[0029] Synergistic catalytic cycle: The M oxide layer is mainly responsible for the adsorption and activation of reactants and the provision of active oxygen sources, while the M element is mainly responsible for the rapid electron conduction and the management of hydrogen intermediates. The two form a closed-loop "catalytic microreactor" at the heterojunction. At the heterojunction, the complex decomposition reaction that originally required a high-potential one-step process is decoupled into multiple elementary steps that can be carried out rapidly at low potentials. This significantly reduces the apparent activation energy of the reaction and achieves efficient low-potential decomposition of lithium oxalate.

[0030] In addition, the catalyst also includes a carbon matrix, which has the following functions: First, it can improve air stability and inhibit the lithium supplement material from reacting with moisture and carbon dioxide in the air to form residual alkali and become ineffective. Second, it improves conductivity, providing a more efficient electron transport channel for electrochemical reactions. Third, it improves electrochemical performance, providing a stable interface and efficient electron transport, thereby significantly improving specific capacity, rate performance, and cycle stability. Finally, it helps suppress gas production; specifically, it can physically isolate the electrolyte, reducing side reactions; and it utilizes the porous carbon layer to physically adsorb reactive oxygen species, reducing oxygen release. Attached Figure Description

[0031] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0032] Figure 1 The lithium supplement provided in Example 1 of this application was dispersed in 5L of water for 3 hours, filtered, washed 3 times, and dried. XRD pattern of the result.

[0033] Figure 2 The lithium supplement provided in Example 1 of this application was dispersed in 5L of water for 3 hours, filtered, washed 3 times, and dried to obtain the following EDS spectrum;

[0034] Figure 3 The lithium supplement provided in Example 1 of this application was dispersed in 5L of water for 3 hours, filtered, washed 3 times, and dried. TEM cross-sectional image of the result.

[0035] Figure 4 SEM cross-sectional view of the lithium supplement agent of Example 1 provided in this application.

[0036] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present invention, this application will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the invention and are not intended to limit its scope. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. When the following description relates to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0038] In a first aspect, this application provides a lithium supplement agent, comprising a core and a shell, wherein the core comprises lithium oxalate and the shell comprises a catalyst;

[0039] The catalyst comprises a carbon matrix and a composite catalytic material supported on the carbon matrix. The composite catalytic material comprises elemental M and an oxide layer of M formed on the surface of elemental M. M is a transition metal element, and an M / M oxide layer heterogeneous interface structure is formed between elemental M and the oxide layer.

[0040] This application involves coating a catalyst onto a lithium oxalate core. The catalyst comprises a carbon matrix and a composite catalytic material supported on the carbon matrix. The composite catalytic material comprises elemental M and an M oxide layer formed on the surface of elemental M. An M / M oxide layer heterogeneous interface structure is formed between elemental M and the M oxide layer, which has the following advantages:

[0041] Bifunctional adsorption and activation: Under thermal or electrochemical fields, oxalate ions can be simultaneously adsorbed and activated at different sites on the catalyst surface. The Lewis acid sites provided by the M oxide layer have a strong affinity for the C=O carbonyl oxygen, effectively polarizing and weakening the C-C bond. Simultaneously, elemental M can interact with the π orbitals of the oxalate molecule through its d electrons, providing another activation pathway. This dual-site adsorption lowers the reaction initiation energy barrier.

[0042] Interfacial electron transfer promotes oxygen exchange and carbon-oxygen bond breaking: At the M / M oxide layer heterojunction, due to the Fermi level difference, electrons transfer from the elemental M phase to the oxide layer, increasing the electron cloud density on the oxide layer side and enhancing the activity of its lattice oxygen. This "activated" lattice oxygen or interfacial adsorbed oxygen species can more effectively attack the adsorbed and activated oxalate ions, promoting C / C bond breaking and CO2 removal (decarboxylation). The elemental M phase acts as a rapid electron channel, promoting the entire charge transfer process. In the electrochemical decomposition pathway, the formation of the heterojunction promotes a decrease in the decomposition potential.

[0043] Rapid transfer and stabilization of hydrogen species (protons): Formate (HCOO) may be generated during the decomposition of lithium oxalate. -Hydrogen-containing intermediates such as M and H2. Elemental M is an excellent hydrogenation / dehydrogenation catalyst, capable of rapidly capturing and recombining the hydrogen (H2) released or desired from these intermediates. + / H - This prevents the accumulation or generation of byproducts (such as H2O) that are detrimental to electrode stability, and guides the reaction to generate the target product (Li2CO3) and gas (CO2) in a directional and efficient manner.

[0044] Synergistic catalytic cycle: The M oxide layer is mainly responsible for the adsorption and activation of reactants and the provision of active oxygen sources, while the M element is mainly responsible for the rapid electron conduction and the management of hydrogen intermediates. The two form a closed-loop "catalytic microreactor" at the heterojunction. At the heterojunction, the complex decomposition reaction that originally required a high-potential one-step process is decoupled into multiple elementary steps that can be carried out rapidly at low potentials. This significantly reduces the apparent activation energy of the reaction and achieves efficient low-potential decomposition of lithium oxalate.

[0045] In addition, the catalyst also includes a carbon matrix, which has the following functions: First, it can improve air stability and inhibit the lithium supplement material from reacting with moisture and carbon dioxide in the air to form residual alkali and become ineffective. Second, it improves conductivity, providing a more efficient electron transport channel for electrochemical reactions. Third, it improves electrochemical performance, providing a stable interface and efficient electron transport, thereby significantly improving specific capacity, rate performance, and cycle stability. Finally, it helps suppress gas production; specifically, it can physically isolate the electrolyte, reducing side reactions; and it utilizes the porous carbon layer to physically adsorb reactive oxygen species, reducing oxygen release.

[0046] In one possible implementation, M includes at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Mo.

[0047] In one possible implementation, the thickness of the M oxide layer is 2-20 nm. The thickness of the M oxide layer in this application is within this range, ensuring sufficient heterogeneous interfaces between the elemental M and the M oxide layer in the catalyst. This guarantees adequate surface active sites while avoiding excessive thickness that could block electron conduction pathways, thereby better achieving the synergistic catalytic effect of the M / M oxide layers.

[0048] Understandably, the thickness of the M oxide layer is 2-20 nm, for example, 2 nm, 5 nm, 10 nm, 15 nm, 20 nm or a range between two of these.

[0049] In one possible implementation, a transmission electron microscope (TEM) cross-sectional sample is prepared using focused ion beam (FIB) technology. The cross-section is observed using high-resolution transmission electron microscopy (HRTEM) at 500,000x magnification. In the TEM cross-sectional image of the composite catalytic material, the perimeter of the outer contour of the composite catalytic material is A, and the perimeter of the contour formed by the junction of the M elemental layer and the M oxide layer is B, where 0.5 ≤ B / A < 1. This application controls B / A within the above range to ensure that the heterogeneous interface provides sufficient active sites.

[0050] It is understandable that 0.5 ≤ B / A < 1, such as 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or a range of two of these values.

[0051] In one possible implementation, the loading of element M in the catalyst is 5-30 wt%. The loading of element M in the catalyst of this application is within this range, which provides sufficient catalytic active sites and improves the dispersion of element M, thus enabling better low-potential and efficient decomposition of lithium oxalate. If the loading of element M is too low, there will be too few metal active sites, resulting in poor catalytic performance. If the loading of element M is too high, the active metal will be poorly dispersed, and agglomeration will affect catalytic performance. Simultaneously, it will reduce the proportion of carbon matrix, affecting the impedance and electronic conductivity of the material, and consequently affecting electrochemical performance.

[0052] It is understood that the loading of element M in the catalyst is 5-30 wt%, for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, or a range between two of these.

[0053] In one possible implementation, the mass ratio of the core to the shell is (4-15):1. The mass ratio of the inner shell to the outer shell in the lithium supplement of this application is within the above range, which ensures that the theoretical capacity of the final product is at a higher level and that sufficient capacity can be achieved in practice. Simultaneously, the catalyst is sufficient in quantity and has ample catalytic sites, enabling better low-potential and efficient decomposition of lithium oxalate.

[0054] Understandably, the mass ratio of the core to the shell is (4-15):1, such as 4:1, 6:1, 8:1, 10:1, 12:1, 15:1 or a range of values ​​between the two.

[0055] In one possible implementation, the specific surface area of ​​the lithium supplement is 50-200 m². 2 / g, the specific surface area of ​​the lithium supplement agent in this application is within the above range, which can ensure that the M metal is sufficiently dispersed, thereby providing sufficient catalytic active sites to promote the efficient decomposition of lithium oxalate, while avoiding the difficulties in battery homogenization caused by excessive specific surface area.

[0056] It is understandable that the specific surface area of ​​lithium supplements is 50-200 m². 2 / g, for example 50m 2 / g, 100m 2 / g, 150m 2 / g、200m 2 / g or a range of values ​​between the two.

[0057] Secondly, this application provides a method for preparing a lithium supplement, comprising:

[0058] S1: Element M, or M oxide, or precursor salt containing element M, and carbon-based support are dispersed in a solvent, rotary evaporated, dried, and sintered in a reducing atmosphere to obtain element M loaded on a carbon-based support.

[0059] S2: The product obtained in S1 is heat-treated in an oxygen-containing atmosphere to form an oxide layer of M on elemental M, thereby obtaining a catalyst; the heat treatment temperature is 100-400℃ and the heat treatment time is 10min-70min.

[0060] S3: Disperse the catalyst and lithium oxalate in a solvent and spray dry to obtain a lithium supplement.

[0061] This application first loads elemental M onto a carbon-based support, which improves the dispersibility of elemental M during the subsequent preparation of the lithium supplement. Secondly, the product obtained in S1 is heat-treated in an oxygen-containing atmosphere, with the temperature and time of the heat treatment controlled to manage the degree of oxidation. The aim is to form an M oxide layer on the surface of the M particles, preventing excessive oxidation that would cause all of the elemental M to be converted into M oxide. Since the M oxide layer is formed only on the surface of the M particles, an M / M oxide heterogeneous interface can be constructed. Finally, the catalyst and lithium oxalate are spray-dried to form a catalyst coating layer on the surface of the lithium oxalate.

[0062] It is understood that the heat treatment temperature is 100-400℃, such as 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, 400℃ or a range between two of these.

[0063] It is understandable that the heat treatment time is 10 min to 70 min, such as 10 min, 20 min, 40 min, 60 min, 70 min or a range between two of these.

[0064] In one possible implementation, in step S2, the heat treatment temperature is 150-350°C and the heat treatment time is 20-60 minutes.

[0065] In one possible implementation, the particle size of elemental M is 30-500 nm. The particle size of elemental M within this range ensures sufficient dispersion of metal M, thereby providing adequate catalytic active sites, while avoiding over-oxidation of elemental M during subsequent oxidation processes due to excessively small particle size.

[0066] It is understandable that the particle size of element M is 30-500 nm, such as 30 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm or a range between two of these.

[0067] In one possible implementation, the carbon-based support in step S1 includes at least one of Ketjen black, hard carbon, conductive carbon black, acetylene black, carbon nanotubes, and graphene.

[0068] In one possible implementation, in step S1, the temperature of rotary evaporation is 60-90°C.

[0069] In one possible implementation, in step S1, the drying temperature is 80-110°C and the drying time is 5-10 hours.

[0070] In one possible implementation, in step S1, the mass ratio of element M to carbon-based support is 1:(2.5-20).

[0071] It is understandable that the mass ratio of element M to carbon-based support is 1:(2.5-20), such as 1:2.5, 1:5, 1:10, 1:15, 1:20 or a range between the two.

[0072] In one possible implementation, the sintering temperature in step S1 is 300-600°C.

[0073] Understandably, the sintering temperature is 300-600℃, such as 300℃, 400℃, 500℃, 600℃ or a range between two of these.

[0074] In one possible implementation, the heating rate of the heat treatment in step S2 is greater than or equal to 5°C / min.

[0075] In one possible implementation, in step S2, after heat treatment, the temperature is reduced to room temperature by blowing air.

[0076] In one possible implementation, the outlet air temperature of the spray dryer is 90-110°C.

[0077] Thirdly, this application provides a positive electrode sheet, which includes the aforementioned lithium supplement agent.

[0078] In the specific preparation of the positive electrode sheet, for example, the positive electrode material, the lithium supplement agent of this application, the conductive agent and the binder can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and cutting, the positive electrode sheet is obtained.

[0079] The positive current collector can be made of at least one of aluminum foil or nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0080] Fourthly, this application provides a battery with the aforementioned positive electrode.

[0081] It is conceivable that, in addition to the aforementioned positive electrode, the battery of this application also includes a negative electrode, an electrolyte, and a separator.

[0082] This application does not strictly limit the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in lithium-ion batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), and tin-based negative electrode materials (mainly including tin and tin alloy).

[0083] This application does not strictly limit the choice of electrolyte, which may include one or more solvents commonly used in lithium-ion battery electrolytes, as well as lithium salts commonly used in lithium-ion electrolytes. For example, the solvent may be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0084] This application does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0085] In battery manufacturing, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare battery, which is then packaged into a pre-stamped aluminum-plastic film bag or steel casing. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete battery manufacturing.

[0086] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0087] Example 1

[0088] The preparation method of the lithium supplement in this embodiment is as follows:

[0089] S1: Disperse 100g of conductive carbon black (Super P) in ethanol.

[0090] S2: Add 100g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O) to S1, stir and disperse for 4 hours, evaporate by rotary evaporation at 70°C, and dry at a constant temperature in an oven at 90°C for 6 hours to obtain catalyst material A with precursor support. The mass ratio of nickel to carbon-based support is 1:5.

[0091] S3: The product obtained in S2 is placed in a tube furnace and heated to 550°C at a rate of 2°C / min in an H2 / Ar atmosphere with a hydrogen volume ratio of 10%. The temperature is held for 4 hours to ensure the decomposition of the precursor. After natural cooling, nickel element supported on a carbon-based support (Ni / C) is obtained, wherein the particle size of the metallic nickel element is 330nm.

[0092] S4: The product of S3 is placed in a furnace with 20% oxygen by volume in O2 / N2 (flow rate 50 sccm), heated to 250°C at 5°C / min and heat-treated for 30 minutes. Then, it is cooled to room temperature by blowing gas to obtain the target catalyst (denoted as Cat-A).

[0093] S5: Disperse Li2C2O4 and Cat-A in water at a mass ratio of 6:1, then pump the well-stirred mixture into a spray drying tower, atomize it into micron-sized droplets through centrifugation or pressure nozzles, dry it under the action of hot air (inlet temperature 220°C, outlet temperature 100°C), and dry it in an oven at 105°C for 3 hours to obtain the lithium supplement agent of this embodiment, denoted as LCO-s1.

[0094] Figure 1The image shows the XRD pattern of the lithium supplement material of Example 1 after dispersion in 5L of water for 3 hours, filtration, washing 3 times, and drying. As can be seen from the figure, after the lithium supplement material is dispersed in water and filtered, lithium oxalate is dissolved and removed by filtration, and the remaining material is the catalyst. The phase analysis shows that the catalyst material contains both NiO and Ni phases, and the synergistic effect of the two can promote the decomposition of lithium oxalate.

[0095] Figure 2 The lithium supplement material of Example 1 was dispersed in 5L of water for 3 hours, filtered, washed 3 times, and dried. The resulting EDS spectrum shows that the nickel particles are relatively evenly distributed in the catalyst.

[0096] Figure 3 The lithium supplement material of Example 1 was dispersed in 5L of water for 3 hours, filtered, washed 3 times, and dried. The TEM cross-sectional image shows that there is a NiO layer on the surface of Ni.

[0097] Figure 4 SEM cross-sectional view of the lithium supplement agent of Example 1 provided in this application.

[0098] Example 2

[0099] The preparation method of the lithium supplement in this embodiment is as follows:

[0100] S1: Elemental nickel with a particle size of 330 nm and conductive carbon black were dispersed in an ethanol solution (where the mass ratio of nickel to carbon-based support was 1:5), stirred for 4 hours, rotary evaporated at 70°C, and dried in a 90°C oven for 6 hours. Then, the solution was placed in a tube furnace and heated to 550°C at a rate of 2°C / min under an H2 / Ar atmosphere with a hydrogen volume percentage of 10%, held for 4 hours, and then naturally cooled to obtain elemental nickel loaded on a carbon-based support.

[0101] S2: The product obtained in S1 is placed in a furnace with 20% oxygen by volume in O2 / N2 (flow rate 50 sccm), and heated to 250°C at 5°C / min for 30 minutes. Then, it is cooled to room temperature by blowing gas to obtain the catalyst.

[0102] S3: Disperse Li2C2O4 and catalyst in water at a mass ratio of 6:1. Then, pump the well-stirred mixture into a spray drying tower and atomize it into micron-sized droplets through centrifugation or pressure nozzles. Dry it under the action of hot air (inlet temperature 220°C, outlet temperature 100°C) and dry it in an oven at 105°C for 3 hours to obtain the lithium supplement agent of this embodiment.

[0103] Example 3

[0104] The preparation method of the lithium supplement in this embodiment is as follows:

[0105] S1: 350 nm nano-nickel oxide and conductive carbon black were dispersed in an ethanol solution (the mass ratio of nickel to carbon-based support was controlled to be 1:5). The mixture was stirred and dispersed for 4 hours, then rotary evaporated at 70°C and dried in a 90°C oven for 6 hours to obtain nickel oxide loaded on a carbon-based support.

[0106] S2: The product obtained in S1 was placed in a tube furnace and heated to 550°C at a rate of 2°C / min under an H2 / Ar atmosphere with a hydrogen volume ratio of 10%. The temperature was held for 4 hours and then naturally cooled to obtain nickel elemental supported on a carbon-based support (Ni / C), wherein the particle size of the metallic nickel elemental was 330 nm.

[0107] S3: Place the product of S2 in a furnace with 20% oxygen by volume in O2 / N2 (flow rate 50 sccm), heat it to 250°C at 5°C / min for 30 minutes, and then cool it down to room temperature by blowing gas to obtain the catalyst.

[0108] S4: Disperse Li2C2O4 and catalyst in water at a mass ratio of 6:1. Then, pump the well-stirred mixture into a spray drying tower and atomize it into micron-sized droplets through centrifugation or pressure nozzles. Dry it under the action of hot air (inlet temperature 220°C, outlet temperature 100°C) and dry it in an oven at 105°C for 3 hours to obtain the lithium supplement agent of this embodiment.

[0109] Example 4

[0110] The lithium supplement agent in this embodiment is basically the same as that in Example 2, with the only difference being as follows:

[0111] The nickel in S1 was replaced with 30-nanometer cobalt, and the mass ratio of cobalt to carbon-based support was controlled at 1:5.

[0112] Example 5

[0113] The lithium supplement agent in this embodiment is basically the same as that in Example 3, with the only difference being as follows:

[0114] The nano-nickel oxide in S1 was replaced with 500nm nano-molybdenum oxide, and the mass ratio of molybdenum to carbon-based support was controlled to be 1:5.

[0115] The particle size of molybdenum obtained in Example S2 is 480 nm.

[0116] Example 6

[0117] The only difference between this embodiment and Embodiment 1 is that nickel nitrate hexahydrate is replaced with chromium nitrate nonahydrate, and the mass ratio of chromium to carbon-based support is 1:5.

[0118] Example 7

[0119] The only difference between this embodiment and Embodiment 1 is that the mass of nickel nitrate hexahydrate is adjusted so that the mass ratio of nickel to carbon-based support is 1:2.5.

[0120] Example 8

[0121] The only difference between this embodiment and Embodiment 1 is that the mass of nickel nitrate hexahydrate is adjusted so that the mass ratio of nickel to carbon-based support is 1:20.

[0122] Example 9

[0123] The only difference between this embodiment and Embodiment 1 is that the heat treatment temperature in step S4 is 150°C.

[0124] Example 10

[0125] The only difference between this embodiment and Embodiment 1 is that the heat treatment temperature in step S4 is 350°C.

[0126] Example 11

[0127] The only difference between this embodiment and Embodiment 1 is that the heat treatment time in step S4 is 20 minutes.

[0128] Example 12

[0129] The only difference between this embodiment and Embodiment 1 is that the heat treatment time in step S4 is 60 minutes.

[0130] Example 13

[0131] The only difference between this embodiment and Embodiment 1 is that in step S5, Li2C2O4 and the catalyst are mixed in a mass ratio of 4:1.

[0132] Example 14

[0133] The only difference between this embodiment and Embodiment 1 is that in step S5, Li2C2O4 and the catalyst are mixed in a mass ratio of 15:1.

[0134] Example 15

[0135] The only difference between this embodiment and Embodiment 1 is that the heat treatment temperature in step S4 is 100°C.

[0136] Example 16

[0137] The only difference between this embodiment and Embodiment 1 is that the heat treatment temperature in step S4 is 400°C.

[0138] Example 17

[0139] The only difference between this embodiment and Embodiment 1 is that the heat treatment time in step S4 is 10 minutes.

[0140] Example 18

[0141] The only difference between this embodiment and Embodiment 1 is that the heat treatment temperature in step S4 is 70 min.

[0142] Example 19

[0143] The only difference between this embodiment and Example 1 is that the mass ratio of catalyst to lithium oxalate is 1:3.

[0144] Example 20

[0145] The only difference between this embodiment and Example 1 is that the mass ratio of catalyst to lithium oxalate is 1:16.

[0146] Comparative Example 1

[0147] The only difference between this embodiment and Example 1 is that the oxidation treatment of S4 is not performed, resulting in a pure Ni / C catalyst.

[0148] Comparative Example 2

[0149] The only difference between this embodiment and Example 1 is that the sintering temperature in S4 is 500°C and the sintering time is 3 hours, resulting in a pure NiO / C catalyst.

[0150] Application examples

[0151] Lithium oxalate supplement: SP:PVDF at a mass ratio of 96:2:2 is weighed and added to a dual planetary mixer. An appropriate amount of NMP is added and mixed thoroughly to prepare a positive electrode slurry. The positive electrode slurry is coated onto both sides of an aluminum foil. After drying and rolling, a positive electrode coating is formed on both sides of the aluminum foil, yielding a positive electrode sheet. Negative electrode active material (artificial graphite): CMC:SBR:SP at a mass ratio of 94:1:2:3 is weighed and added to a dual planetary mixer. Water is added and mixed to prepare a negative electrode slurry. The negative electrode slurry is coated onto both sides of a copper foil and dried to obtain a negative electrode sheet. The positive electrode, separator (PP / PE / PP three-layer composite separator), and negative electrode are alternately stacked to assemble a stacked cell. The stacked cell is placed in an aluminum-plastic film with the electrolyte injection port remaining. Electrolyte (composed of LiPF6, EC, EMC, and FEC, where the mass ratio of EC to EMC is 7:3, the mass percentage of FEC in the electrolyte is 1%, and the concentration of LiPF6 in the electrolyte is 1 mol / L) is injected into the cell through the injection port. Then the injection port is sealed, and the cell is subjected to aging, formation (cutoff voltage of 4.45V), and aging treatment in sequence to obtain the battery.

[0152] Test example:

[0153] M oxide thickness: The lithium supplement was dispersed in 5L of water for 3 hours, filtered, washed, and dried. 0.2g of the solution was then dispersed in ethanol and dropped onto a copper grid. The solution was dried under UV light for 1 hour to obtain the TEM sample to be tested. The sample was fixed on the sample stage, and a platinum or tungsten protective layer was deposited on the surface of the target cross-section. Then, a U-shaped groove was etched on both sides of the protective layer using a gallium ion beam with a relatively high current, so that only the bottom of the sheet was connected to the substrate. Next, a mechanical probe was moved to the sheet and welded to it using ion beam-assisted deposition. After cutting off the bottom connection, the sheet was extracted and transferred to a special copper grid for fixation. Finally, the ion beam current and voltage were gradually reduced to perform bilateral fine thinning and low-energy final polishing of the sheet until the thickness was less than 100 nm (less than 50 nm for high-resolution observation). An electron-transparent cross-section sample was obtained for TEM analysis. Using a high-resolution transmission electron microscope at 500,000x magnification, 100 composite catalysts were randomly selected, and the M oxide layer thickness of each composite catalyst was measured and the average value was calculated.

[0154] M / M oxide heterostructure size: Lithium supplement was dispersed in 5L water for 3 hours, filtered, washed, and dried. 0.2g of the solution was then dispersed in ethanol and dropped onto a copper grid. The sample was dried under UV light for 1 hour to obtain the TEM sample. The sample was fixed on the sample stage, and a platinum or tungsten protective layer was deposited on the surface of the target cross-section. Then, a U-shaped groove was etched on both sides of the protective layer using a high-current gallium ion beam, ensuring that only the bottom of the sheet was connected to the substrate. Next, a mechanical probe was moved to the sheet and welded using ion beam-assisted deposition. After severing the bottom connection, the sheet was extracted and transferred to a dedicated copper grid for fixation. Finally, the ion beam current and voltage were gradually reduced, and the sheet underwent bilateral fine thinning and low-energy final polishing until the thickness was less than 100 nm (less than 50 nm for high-resolution observation). (nm), to obtain electron-transparent cross-sectional samples for TEM analysis. Using a high-resolution transmission electron microscope at 500,000x magnification, 100 composite catalytic materials were randomly selected. The perimeter A of the outer contour of the composite catalytic material was measured in the transmission electron microscope image of each composite catalytic material. The perimeter B of the contour formed by the junction of the M element and the M oxide layer was calculated. The B / A ratio of each composite catalytic material was calculated. Finally, the average value of B / A of the 100 composite catalytic materials was calculated.

[0155] Measurement of perimeter of heterogeneous interface contour and composite catalytic material perimeter: ImageJ software was used to measure the perimeter of the interface contour of the target particles in the TEM image. First, the TEM image to be measured was opened, and the scale bar in the image was accurately calibrated using the line tool. The global scale was set by Analyze>Set Scale to complete the conversion between pixels and physical size. Then, the polygon selection tool or freehand selection tool was used to manually outline the interface contour of the target particles to form a closed selection area. The Perimeter parameter was checked in Analyze>Set Measurements. Finally, the Analyze>Measure command was executed, and the software automatically calculated and output the perimeter data of the selected contour.

[0156] It should be noted that composite catalytic materials are usually spherical, so in transmission electron microscopy (TEM) images, the outer contour of the composite catalytic material is basically circular. Therefore, A is actually the circumference of the outer contour, which is the circumference of this circular shape. The contour formed by the junction of elemental M and oxide layer M is also basically circular in reality. Therefore, B is actually the circumference of the circular contour formed by the junction of elemental M and oxide layer M.

[0157] Loading of element M: 100g of lithium supplement sample was weighed and dissolved in 5L of water. After stirring for 3 hours, the precipitate was obtained by filtration, washed 3 times, and dried to obtain catalyst B. 0.5g of catalyst B was digested with aqua regia to obtain the test solution. The concentration of element M was measured by inductively coupled plasma optical emission spectrometry (ICP-OES). The loading of element M was calculated based on the dilution factor and sample mass.

[0158] Core-to-shell mass ratio: Weigh 0.5g of lithium supplement sample, digest with aqua regia to obtain the test solution, and measure the Li element concentration using inductively coupled plasma optical emission spectrometry (ICP-OES). Calculate the Li element mass fraction based on the dilution factor and sample mass. The core-to-shell mass ratio is calculated using the formula Y = (X / 0.1362) / (1-(X / 0.1362)), where 0.1362 is the theoretical mass fraction of lithium in lithium oxalate.

[0159] Specific surface area of ​​lithium supplement: Weigh the total weight of the empty small test tube and the stopper. Soak the lithium supplement powder sample to be tested in anhydrous ethanol for 4 hours. Then take out the powder sample and dry it in an oven at 105℃ for half an hour. Next, put the powder sample into the sample tube and weigh the total weight of the powder sample, the small test tube and the stopper to calculate the sample mass. Turn on the degassing station and put the small test tube containing the powder sample into the degassing station at 105℃. Purge with nitrogen (pure nitrogen) for 30 minutes, cool for 15 minutes, and test on the instrument at 25℃ and 60% humidity. Plot P / P0 with points in the range of 0.05~0.25 as the x-axis and P / V (P0-P) as the y-axis. Perform linear fitting by plotting the BET equation to obtain the slope and intercept of the straight line, and then calculate the BET specific surface area of ​​the powder sample.

[0160] Lithium oxalate decomposition potential: The above battery was charged and discharged once at 0.1C, with a voltage range of 2.0V-4.5V, and the decomposition potential was recorded.

[0161] First charge capacity: Charge and discharge the battery once at 0.1C, with a voltage range of 2.0V-4.5V, and calculate the first charge capacity.

[0162] The test results are detailed in Table 1-2.

[0163] Table 1

[0164]

[0165] Table 2

[0166]

[0167] As can be seen from Tables 1 and 2, comparing Example 15 with Example 1, it can be seen that due to the decrease in heat treatment temperature, the nickel oxide layer thickness is too thin, the nickel surface layer is not completely oxidized, resulting in a low B / A ratio, which cannot better exert the catalytic effect of the nickel-nickel oxide heterointerface, leading to an increase in decomposition potential and a decrease in capacity utilization.

[0168] A comparison of Example 16 and Example 1 shows that, due to the increase in heat treatment temperature, the nickel oxide layer becomes too thick, the B / A ratio decreases, and the number of active sites at the heterostructure interface decreases. At the same time, the interface layer is located in a deep layer and cannot make better contact with lithium oxalate, which hinders the catalytic performance of the heterostructure interface, resulting in an increase in decomposition potential and a decrease in capacity.

[0169] A comparison of Example 17 and Example 1 shows that, due to the decrease in heat treatment time, the nickel oxide layer thickness is too thin, the nickel surface layer is not completely oxidized, the B / A ratio is too small, and the catalytic effect of the nickel-nickel oxide heterostructure interface cannot be better utilized, resulting in an increase in decomposition potential and a decrease in capacity utilization.

[0170] A comparison of Example 18 and Example 1 shows that, due to the increased sintering time, the nickel oxide layer becomes too thick, the B / A ratio decreases, and the number of active sites at the heterostructure interface decreases. At the same time, the interface layer is located in a deep layer and cannot make better contact with lithium oxalate, which hinders the catalytic performance of the heterostructure interface, resulting in an increase in decomposition potential and a decrease in capacity.

[0171] A comparison of Example 19 and Example 1 shows that the decomposition voltage decreases due to the increased mass ratio of catalyst to lithium oxalate, but the capacity utilization decreases due to the decreased proportion of lithium oxalate.

[0172] A comparison of Example 20 and Example 1 shows that the decomposition voltage increases due to the decrease in the mass ratio of catalyst to lithium oxalate and the reduction in active sites.

[0173] Comparative Examples 1-2, lacking either a nickel oxide layer or a nickel elemental layer, were unable to form a heterogeneous interface between nickel and nickel oxide, resulting in a sharp decline in catalytic performance and an excessively high decomposition potential, which prevented them from fully utilizing their capacity at the cutoff potential.

[0174] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A lithium supplement, characterized in that, The lithium replenishing agent includes a core and a shell, the core including lithium oxalate and the shell including a catalyst; The catalyst comprises a carbon matrix and a composite catalytic material supported on the carbon matrix. The composite catalytic material comprises element M and an oxide layer of M formed on the surface of element M. M is a transition metal element, and an M / Oxide layer heterogeneous interface structure is formed between element M and the oxide layer.

2. The lithium supplement of claim 1, wherein, M includes at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Mo.

3. The lithium supplement of claim 1, wherein, The thickness of the M oxide layer is 2-20 nm; And / or; in the transmission electron microscope cross-sectional image of the composite catalytic material, the perimeter of the outer contour of the composite catalytic material is A, the perimeter of the contour formed by the junction of the M element and the M oxide layer is B, and 0.5≤B / A<1; And / or; in the catalyst, the loading of element M is 5-30 wt%.

4. The lithium supplement agent according to claim 1, characterized in that, The mass ratio of the core to the shell is (4-15):

1.

5. The lithium supplement agent according to claim 1, characterized in that, The specific surface area of the lithium supplement is 50-200 m 2 / g.

6. A method for preparing a lithium supplement according to any one of claims 1-5, characterized in that, The method includes: S1: Element M, or M oxide, or precursor salt containing element M, and carbon-based support are dispersed in a solvent, rotary evaporated, dried, and sintered in a reducing atmosphere to obtain element M loaded on a carbon-based support. S2: The product obtained in S1 is heat-treated in an oxygen-containing atmosphere to form an oxide layer of M on element M, thereby obtaining the catalyst; the heat treatment temperature is 100-400℃ and the heat treatment time is 10min-70min. S3: Disperse the catalyst and lithium oxalate in a solvent and spray dry to obtain the lithium supplement agent.

7. The preparation method according to claim 6, characterized in that, In step S2, the heat treatment temperature is 150-350℃ and the heat treatment time is 20min-60min.

8. The preparation method according to claim 6, characterized in that, The carbon-based support in step S1 includes at least one of Ketjen black, hard carbon, conductive carbon black, acetylene black, carbon nanotubes, and graphene. And / or; the particle size of the element M is 30-500 nm.

9. A positive electrode plate, characterized in that, The positive electrode includes a lithium supplement agent according to any one of claims 1-5.

10. A battery comprising a positive electrode according to claim 9.

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