Lithium replenishing agent and its preparation method, positive electrode sheet, battery

Abstract

This invention belongs to the field of battery technology and discloses a lithium replenishing agent and its preparation method, a positive electrode sheet, and a battery. The lithium replenishing agent includes a lithium replenishing agent body and a coating layer formed on at least a portion of the surface of the lithium replenishing agent body. The coating layer includes a carbon material and at least two metal elements selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg, with the metal elements dispersed in the carbon material. The lithium replenishing agent provided by this invention has excellent specific capacity, thereby improving the capacity retention rate of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a lithium replenishing agent and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0002] During the first charge of a lithium-ion battery, the formation of the SEI film (solid electrolyte interphase), the shedding of negative electrode material particles, and the irreversible deposition of lithium metal are inevitable processes that consume active lithium ions from the positive electrode material, resulting in a reduction in the battery's usable energy. Currently, the most widely used graphite negative electrode experiences an irreversible capacity loss of >6%, while for silicon-based and tin-based alloy negative electrodes with high specific capacity, the irreversible capacity loss can even reach 10%–20% or more. Pre-lithiation technology includes negative electrode pre-lithiation and positive electrode lithium replenishment, i.e., adding lithium replenishing agents to the positive electrode and adding lithium replenishing agents to the negative electrode. There are many types of positive electrode lithium replenishing agents; however, existing positive electrode lithium replenishing agents generally suffer from poor conductivity, thus affecting the specific capacity performance of the lithium replenishing agent at lower charging voltages, and consequently affecting the capacity retention rate of batteries containing them. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a lithium replenishing agent and its preparation method, a positive electrode sheet, and a battery. The lithium replenishing agent provided in this application has excellent specific capacity, thereby improving the capacity retention rate of the battery.

[0004] In a first aspect, the present invention provides a lithium replenishing agent comprising a lithium replenishing agent body and a coating layer formed on at least a portion of the surface of the lithium replenishing agent body, the coating layer comprising a carbon material and at least two metal elements selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg, the metal elements being dispersed in the carbon material.

[0005] According to the lithium replenishing agent of the above embodiments of the present invention, the at least two metal elements and carbon material in the coating layer can enhance the conductivity and surface stability of the lithium replenishing agent, reduce the delithiation potential of the lithium replenishing agent, effectively improve the delithiation reaction kinetics, thereby increasing the specific capacity of the lithium replenishing agent, and thus improving the capacity retention rate of the battery.

[0006] In addition, the lithium replenishing agent according to the above embodiments of the present invention may also have the following additional technical features:

[0007] In some embodiments of the present invention, the coating layer comprises the carbon material and two metal elements selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg. Therefore, the lithium replenisher exhibits excellent specific capacity and can improve the battery's capacity retention.

[0008] In some embodiments of the present invention, the carbon material and two metal elements selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg are obtained by calcining and carbonizing a bimetallic organic framework compound. As a result, the lithium replenisher exhibits excellent specific capacity and can improve the battery's capacity retention.

[0009] In some embodiments of the present invention, the lithium replenishing agent comprises at least one of Li5FeO4, Li6CoO4, Li2NiO2, Li3N, Li2O, and LiF. Therefore, the lithium replenishing agent exhibits excellent specific capacity and can improve the battery's capacity retention.

[0010] In some embodiments of the present invention, the average thickness of the coating layer is 2 nm-5 nm. Therefore, the lithium replenisher exhibits excellent specific capacity and can improve the capacity retention of the battery.

[0011] In some embodiments of the present invention, the coating layer accounts for 5%-20% of the total mass of the lithium replenishing agent. Therefore, the lithium replenishing agent exhibits excellent specific capacity and can improve the battery's capacity retention.

[0012] In a second aspect, the present invention provides a method for preparing the aforementioned lithium replenishing agent. According to an embodiment of the present invention, the method includes: dispersing a soluble metal salt of at least two metals selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg, and an organic ligand in a solvent; mixing the solvent with a lithium replenishing agent bulk; and performing a solvothermal reaction to obtain an intermediate; and calcining and carbonizing the intermediate under a protective atmosphere to obtain the lithium replenishing agent. Therefore, the lithium replenishing agent prepared according to the embodiments of the present invention has excellent specific capacity and can improve the capacity retention of the battery.

[0013] In some embodiments of the present invention, the lithium replenishing agent comprises Li5FeO4, and the preparation method of Li5FeO4 includes: mixing a lithium source and an iron source at a lithium to iron molar ratio of (5-7):1, ball milling, and sintering under a protective atmosphere to obtain Li5FeO4. The resulting lithium replenishing agent exhibits excellent specific capacity and can improve the capacity retention of the battery.

[0014] In some embodiments of the present invention, the ball milling time is 5-12 hours. As a result, the prepared lithium supplement exhibits excellent specific capacity and can improve the capacity retention of the battery.

[0015] In some embodiments of the present invention, the ball milling speed is 450 rpm / min-550 rpm / min. Therefore, the prepared lithium supplement exhibits excellent specific capacity and can improve the battery's capacity retention.

[0016] In some embodiments of the present invention, the sintering includes: sintering at 400℃-550℃ for 2h-8h, followed by sintering at 800℃-950℃ for 2h-8h. The resulting lithium supplement exhibits excellent specific capacity and can improve the capacity retention of the battery.

[0017] In some embodiments of the present invention, the organic ligand includes at least one selected from dimethylimidazole, 2-aminoterephthalic acid, terephthalic acid, terephthalic acid, isophthalic acid, phthalic acid, isophthalic acid, and imidazole. Therefore, the prepared lithium supplement exhibits excellent specific capacity and can improve the battery's capacity retention.

[0018] In some embodiments of the present invention, the solvent includes at least one selected from dimethylformamide, ethanol, methanol, and isopropanol. Therefore, the prepared lithium replenishment agent exhibits excellent specific capacity and can improve the capacity retention of the battery.

[0019] In some embodiments of the present invention, the mass ratio of the soluble metal salt to the lithium replenishing agent is (0.1-10):(20-65). Therefore, the prepared lithium replenishing agent exhibits excellent specific capacity and can improve the capacity retention of the battery.

[0020] In some embodiments of the present invention, the temperature of the solvothermal reaction is 80°C-200°C. Therefore, the prepared lithium supplement exhibits excellent specific capacity and can improve the capacity retention of the battery.

[0021] In some embodiments of the present invention, the solvothermal reaction time is 4 h to 24 h. Therefore, the prepared lithium replenishing agent exhibits excellent specific capacity and can improve the capacity retention of the battery.

[0022] In some embodiments of the present invention, the calcination and carbonization temperature is 400°C-900°C. Therefore, the prepared lithium supplement exhibits excellent specific capacity and can improve the battery's capacity retention.

[0023] In some embodiments of the present invention, the calcination and carbonization time is 3-15 hours. Therefore, the prepared lithium supplement exhibits excellent specific capacity and can improve the battery's capacity retention.

[0024] In a third aspect, the present invention provides a positive electrode sheet comprising the lithium replenishing agent described in the first aspect of the invention, or a lithium replenishing agent prepared using the method described in the second aspect. Consequently, a battery containing this positive electrode sheet exhibits excellent capacity.

[0025] In a fourth aspect, the present invention provides a battery. According to an embodiment of the invention, the battery includes a positive electrode plate as described in the third aspect. The battery exhibits excellent capacity.

[0026] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0027] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0028] Figure 1 A schematic diagram of the lithium replenishing agent provided by the present invention is shown.

[0029] Figure 2 The image shows a scanning electron microscope (SEM) image of the lithium supplement prepared in Example 1 of this invention.

[0030] Icon labels:

[0031] Lithium supplement 100, lithium supplement body 1, coating layer 2. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0033] In a first aspect, the present invention provides a lithium supplement 100, see [link to relevant documentation]. Figure 1 The lithium replenishing agent 100 includes a lithium replenishing agent body 1 and a coating layer 2 formed on at least a portion of the surface of the lithium replenishing agent body 1. The coating layer 2 includes a carbon material and at least two metal elements selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg, wherein the metal elements are dispersed in the carbon material.

[0034] According to the above embodiments of the present invention, the lithium replenisher 100, with at least two metal elements and carbon material in its coating layer 2, can enhance the conductivity and surface stability of the lithium replenisher 100. Regarding the delithiation potential, the addition of the two metal elements changes the electronic structure of the lithium replenisher body 1, which adjusts the charge distribution of atoms in the lithium replenisher body 1, making it easier for lithium ions to be extracted from the lithium replenisher body 1. From an energy perspective, the addition of metal elements reduces the energy required for lithium ion extraction, thereby reducing the delithiation potential and effectively improving the delithiation reaction kinetics of the lithium replenisher 100, thereby increasing the specific capacity of the lithium replenisher 100 and improving the capacity retention rate of the battery.

[0035] According to an embodiment of the present invention, the coating layer 2 comprises carbon material and two metal elements selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg. Thus, the two metal elements work synergistically. In the bimetallic coating layer, the metal elements act as catalysts, and the synergistic effect between the two metals optimizes the electronic structure of the catalytic active sites, thereby improving the adsorption and desorption of reaction intermediates, accelerating reaction kinetics, and lowering the energy barrier. The charge transfer between the metals in the bimetallic catalyst enhances the adsorption capacity of reactants and lowers the reaction energy barrier, which can further improve the conductivity of the lithium replenishment agent 1, reduce the delithiation potential, and give the lithium replenishment agent 100 excellent specific capacity, thus improving the battery capacity retention rate.

[0036] According to embodiments of the present invention, carbon materials and two metal elements from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg are obtained by calcining and carbonizing a bimetallic organic framework compound. Thus, this application first coats the surface of the lithium replenishment agent 1 with a bimetallic organic framework compound (bimetallic MOFs) and then calcines and carbonizes it. This in-situ generated bimetallic doped carbon material, with the metal elements dispersed within the carbon material, results in a more uniform distribution of the two metal elements and the carbon material on the surface of the lithium replenishment agent 1. The large contact area with the lithium replenishment agent 1 further enhances the conductivity and surface stability of the lithium replenishment agent 100, resulting in a superior specific capacity and improved battery capacity retention.

[0037] Taking Zn and Co as examples, doping two different metal elements into MOFs-derived porous NC catalysts can construct nitrogen-coordinated bimetallic active sites. This structure can not only increase the number of active sites, but also optimize the electronic structure of the catalytic material.

[0038] According to some embodiments of the present invention, the lithium replenishing agent body 1 includes at least one of Li5FeO4, Li6CoO4, Li2NiO2, Li3N, Li2O, and LiF. By combining the above-mentioned lithium replenishing agent body 1 with a carbon material coating layer 2 containing two metal elements, the conductivity of the lithium replenishing agent body 1 can be further improved, the delithiation potential can be reduced, and the lithium replenishing agent 100 can exhibit excellent specific capacity, thereby improving the battery's capacity retention rate.

[0039] According to some embodiments of the present invention, the average thickness of the coating layer 2 is 2nm-5nm, for example, it can be 2nm, 3nm, 4nm, 5nm, etc. Controlling the average thickness of the coating layer 2 within the above range is sufficient to improve the overall conductivity of the lithium replenishment agent 100, reduce the delithiation potential, and prevent the coating layer 2 from being too thick, which would affect the specific capacity of the lithium replenishment agent 100. This results in the lithium replenishment agent 100 having excellent specific capacity and improving the capacity retention rate of the battery.

[0040] According to some embodiments of the present invention, based on the total mass of the lithium replenisher 100, the mass percentage of the coating layer 2 is 5%-20%. For example, it can be 5%, 10%, 15%, 20%, etc. Controlling the mass percentage of the coating layer 2 within the above range is sufficient to improve the overall conductivity of the lithium replenisher 100, reduce the delithiation potential, and prevent the coating layer 2 from being too large and affecting the specific capacity of the lithium replenisher 100. This results in the lithium replenisher 100 having excellent specific capacity and improving the capacity retention of the battery.

[0041] In a second aspect of the invention, a method for preparing the lithium supplement agent described in the first aspect is provided, comprising:

[0042] S1. Disperse soluble metal salts and organic ligands of at least two metals selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg in a solvent, mix with the lithium supplement bulk, and react with a solvothermal agent to obtain an intermediate.

[0043] In this step, the lithium supplement is added to a solution containing metal salts and organic ligands beforehand, and a solvothermal reaction is used to form a bimetallic organic framework compound on the surface of the lithium supplement, resulting in better uniformity of the coating layer.

[0044] According to some embodiments of the present invention, the lithium supplement body comprises Li5FeO4, and the preparation method of Li5FeO4 includes:

[0045] S10. Mix lithium source and iron source with a lithium element to iron element molar ratio of (5-7):1, ball mill, and sinter under a protective atmosphere to obtain Li5FeO4.

[0046] As an example, the molar ratio of lithium to iron can be 5:1, 6:1, 7:1, etc.

[0047] The Li5FeO4 prepared by the above method has a moderate ratio of lithium to iron, which can reduce the increase of side reactions caused by excessive lithium, resulting in incomplete lithium salt reaction. It can also reduce the loss of lithium salt due to volatilization during the reaction process caused by insufficient lithium salt, which affects the performance of the final product. This makes the lithium supplement agent have excellent specific capacity and can improve the capacity retention rate of the battery.

[0048] According to some embodiments of the present invention, the ball milling time is 5h-12h, for example, it can be 5h, 7h, 9h, 10h, 12h, etc. Controlling the ball milling time within the above range can make the lithium and iron elements uniformly mixed, which is convenient to obtain Li5FeO4 with excellent performance, reduce the delithiation potential, make the lithium replenishing agent have excellent specific capacity, and improve the capacity retention rate of the battery.

[0049] According to some embodiments of the present invention, the rotation speed of the ball mill is 450 rpm / min-550 rpm / min, for example, it can be 450 rpm / min, 500 rpm / min, 550 rpm / min, etc. Controlling the rotation speed of the ball mill within the above range can make the lithium and iron elements mix uniformly, which is conducive to obtaining Li5FeO4 with excellent performance, reducing the delithiation potential, making the lithium replenishing agent have excellent specific capacity, and improving the capacity retention rate of the battery.

[0050] According to some embodiments of the present invention, the sintering includes: sintering at 400℃-550℃ for 2h-8h, and then sintering at 800℃-950℃ for 2h-8h. For example, the sintering temperature at low temperature (400℃-550℃) can be 400℃, 450℃, 500℃, 550℃, etc., and the sintering time at low temperature can be 2h, 4h, 5h, 7h, 8h, etc., and the sintering temperature at high temperature (800℃-950℃) can be 800℃, 850℃, 900℃, 950℃, etc., and the sintering time at high temperature can be 2h, 4h, 5h, 7h, 8h, etc. Thus, sintering at low temperature first, followed by sintering at high temperature, is beneficial for Li5FeO4 nucleation at low temperature and for growth at high temperature, ultimately yielding Li5FeO4 with better morphology. This can further reduce the delithiation potential, resulting in excellent specific capacity of the lithium replenishment agent and improving the capacity retention rate of the battery.

[0051] According to some embodiments of the present invention, the organic ligand includes at least one selected from dimethylimidazole, 2-aminoterephthalic acid, terephthalic acid, terephthalic acid, isophthalic acid, phthalic acid, isophthalic acid, and imidazole. The above-mentioned organic ligand readily reacts with two soluble metal salts under solvent heating conditions to form a bimetallic organic framework compound, which coats the surface of the lithium replenishment substrate. After calcination and carbonization, a uniform coating layer containing bimetallic elements and carbon materials is formed on the surface of the lithium replenishment substrate, which can further reduce the delithiation potential, resulting in excellent specific capacity of the lithium replenishment and improved battery capacity retention.

[0052] According to some embodiments of the present invention, the solvent includes at least one of dimethylformamide, ethanol, methanol, and isopropanol. The above solvents are easy to dissolve soluble metal salts and are compatible with organic ligands, which facilitates the formation of bimetallic organic framework compounds that coat the surface of the lithium replenishing agent. After calcination and carbonization, a uniform coating layer containing bimetallic elements and carbon materials is formed on the surface of the lithium replenishing agent, which can further reduce the delithiation potential, so that the lithium replenishing agent has excellent specific capacity and can improve the capacity retention of the battery.

[0053] According to some embodiments of the present invention, the mass ratio of the soluble metal salt to the lithium replenishing agent body is (0.1-10):(20-65), for example, it can be 0.1:20, 0.1:50, 0.1:65, 10:20, 10:40, 10:65, etc. Controlling the mass ratio of the soluble metal salt to the lithium replenishing agent body within the above range makes it easier to obtain a lithium replenishing agent with a reasonable ratio of lithium replenishing agent body and coating layer, which is sufficient to improve the overall conductivity of the lithium replenishing agent, reduce the delithiation potential, and avoid excessive coating layer that would affect the specific capacity of the lithium replenishing agent. This results in the lithium replenishing agent having excellent specific capacity and improving the capacity retention rate of the battery.

[0054] According to some embodiments of the present invention, the temperature of the solvothermal reaction is 80℃-200℃. For example, the solvothermal reactor temperature can be 80℃, 100℃, 150℃, 200℃, etc. Controlling the temperature of the solvothermal reaction within the above range is more conducive to generating bimetallic organic framework compounds that coat the surface of the lithium replenishing agent. After calcination and carbonization, a uniform coating layer containing bimetallic elements and carbon materials is formed on the surface of the lithium replenishing agent, which can further reduce the delithiation potential, so that the lithium replenishing agent has excellent specific capacity and can improve the capacity retention rate of the battery.

[0055] According to some embodiments of the present invention, the solvothermal reaction time is 4h-24h, for example, it can be 4h, 5h, 10h, 20h, 24h, etc. Controlling the solvothermal reaction time within the above range is more conducive to generating bimetallic organic framework compounds, which coat the surface of the lithium replenishing agent body. After calcination and carbonization, a uniform coating layer containing bimetallic elements and carbon materials is formed on the surface of the lithium replenishing agent body, which can further reduce the delithiation potential, so that the lithium replenishing agent has excellent specific capacity and can improve the capacity retention rate of the battery.

[0056] According to some embodiments of the present invention, the calcination and carbonization temperature is 400℃-900℃. For example, the calcination temperature can be 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, etc. Controlling the calcination temperature within the above range can fully carbonize the bimetallic organic framework compound generated on the surface of the lithium replenishing agent, resulting in uniformly distributed metal elements and carbon materials without damaging the structure of the lithium replenishing agent. This can further reduce the delithiation potential, giving the lithium replenishing agent excellent specific capacity and improving the battery capacity retention rate.

[0057] According to some embodiments of the present invention, the calcination and carbonization time is 3h-15h. For example, it can be 3h, 5h, 7h, 10h, 15h, etc. Controlling the calcination time within the above range can fully carbonize the bimetallic organic framework compound generated on the surface of the lithium replenishing agent, resulting in uniformly distributed metal elements and carbon materials, without damaging the structure of the lithium replenishing agent. This can further reduce the delithiation potential, giving the lithium replenishing agent excellent specific capacity and improving the battery capacity retention rate.

[0058] In a third aspect of the invention, the present invention provides a positive electrode sheet comprising the lithium replenishing agent described in the first aspect of the invention, or a lithium replenishing agent prepared by the method described in the second aspect of the invention.

[0059] Therefore, batteries using this positive electrode have excellent capacity.

[0060] Typically, a positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, wherein the positive active material layer includes a positive active material.

[0061] In some embodiments of this application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite positive electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0062] As an example, the positive electrode active material includes, but is not limited to, at least one of metal oxide positive electrode active materials, polyanionic positive electrode active materials, transition metal positive electrode active materials, and organic positive electrode active materials.

[0063] As an example, the metal oxide cathode active materials include, but are not limited to, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium-rich manganese-based materials, lithium manganese oxide (LiMn2O4), and lithium nickel-manganese oxide (LiNi). 0.5 Mn 1.5 At least one of O4, iron(III) oxide (Fe3O4), and lithium vanadate.

[0064] As an example, the polyanionic cathode active material includes, but is not limited to, at least one of lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium manganese iron phosphate, lithium vanadium phosphate (Li3V2(PO4)3), lithium vanadium oxyphosphate (LiVOPO4), lithium cobalt phosphate (LiCoPO4), lithium nickel phosphate (LiNiPO4), lithium iron silicate (Li2FeSiO4), lithium iron fluorosulfate (LiFeSO4F), lithium iron borate (LiFeBO3), and lithium iron titanate (Li2FeTiO4).

[0065] As an example, the transition metal cathode active material includes, but is not limited to, at least one of iron trifluoride (FeF3), cobalt trifluoride (CoF3), nickel trifluoride (NiF3), titanium disulfide (TiS2), iron disulfide (FeS2), molybdenum disulfide (MoS2), and niobium triselenide (NbSe3).

[0066] As an example, the organic positive electrode active material includes, but is not limited to, at least one of quinone-based organic materials and nitrogen-containing organic materials.

[0067] As an example, the quinone molecular organic material includes at least one of benzoquinone, anthraquinone, phenanthrenequinone, dithiophenebenzoquinone, dipyridinobenzoquinone, difuranobenzoquinone, lithium 2,6-dicarboxylate anthraquinone, lithium 2,7-dicarboxylate phenanthrenequinone, and lithium 2,7-dicarboxylate pyrene-4,5,9,10-tetraone.

[0068] As an example, the nitrogen-containing organic material includes, but is not limited to, at least one of pteridine, phenolazine, pteridine derivatives and phenolazine derivatives.

[0069] According to some embodiments of the present invention, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] According to some embodiments of the present invention, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0071] According to some embodiments of the present invention, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, and binder, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive current collector, and obtaining the positive electrode sheet after drying, cold pressing, and other processes.

[0072] In a fourth aspect, the present invention provides a battery comprising the battery of the third aspect of the present invention, thereby providing a battery with excellent capacity.

[0073] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0074] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0075] According to some embodiments of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0076] According to some embodiments of the present invention, the negative electrode active material includes, but is not limited to, at least one of graphite, graphene, soft carbon, hard carbon, elemental silicon, silicon-oxygen materials, silicon-carbon materials, silicon-nitrogen composite materials, silicon-based alloys, elemental tin, tin oxides, tin-based alloys, lithium metal, lithium alloys, lithium titanium oxides, transition metal oxides, and transition metal sulfides.

[0077] According to some embodiments of the present invention, the negative electrode active material layer may optionally include a binder. The binder may include at least one selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0078] According to some embodiments of the present invention, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0079] According to some embodiments of the present invention, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0080] According to some embodiments of the present invention, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0081] This invention does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0082] According to some embodiments of the present invention, the material of the separator may include at least one of glass fiber, non-woven fabric, polyolefin membrane, aromatic polyamide membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane.

[0083] According to some embodiments of the present invention, the thickness of the isolation membrane can be 10μm-12μm, for example, 10μm, 11μm, 12μm, etc.

[0084] According to some embodiments of the present invention, the electrolyte may be liquid or solid.

[0085] When the electrolyte is in liquid form, it may include organic solvents, lithium salts, and optionally additives.

[0086] According to some embodiments of the present invention, the organic solvent is selected from at least one of C3-C6 carbonate compounds, C3-C8 carboxylic acid ester compounds, sulfone compounds, and ether compounds. More preferably, the C3-C6 carbonate compounds are selected from at least one of ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; the C3-C8 carboxylic acid ester compounds are selected from at least one of γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, and propyl propionate; the sulfone compounds are selected from sulfolane; and the ether compounds are selected from at least one of triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0087] According to some embodiments of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, and lithium bis(trifluoromethanesulfonyl)imide.

[0088] When the electrolyte is solid, the electrolyte includes solid electrolytes and lithium salts.

[0089] As an example, the solid electrolyte includes, but is not limited to, at least one of oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, boride solid electrolytes, and ionic liquids.

[0090] The present disclosure will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0091] Example 1

[0092] Step 1: Lithium hydroxide and ferric oxide were premixed in a ball mill for 5 hours at a Li:Fe molar ratio of 5.5:1 at a ball mill speed of 450 rpm / min. Then, the mixture was calcined at a first temperature of 500℃ for 4 hours under a nitrogen atmosphere, followed by sintering at a second temperature of 900℃ for 6 hours at a heating rate of 2℃ / min. The resulting lithium-rich lithium iron ferrite material was then crushed and sieved to obtain lithium-rich lithium iron ferrite material with a particle size Dv50 of 10 micrometers.

[0093] Step 2: Dissolve 10 mmol of zinc nitrate hexahydrate Zn(NO3)2·6H2O and 20 mmol of cobalt nitrate hexahydrate Co(NO3)2·6H2O in 80 ml of ethanol solution, with a molar ratio of Zn(NO3)2·6H2O to Co(NO3)2·6H2O of 1:2. Stir to dissolve, and then add 4 g of lithium-rich lithium ferrite material to form the first solution.

[0094] Step 3: Dissolve 4g of dimethylimidazole in 40ml of ethanol solution and stir to prepare a second solution. Add the first solution to the second solution and then add it to a high-pressure reactor and react in an 80℃ oven for 8 hours.

[0095] Step 4: The Zn / Co MOFs core-shell coated lithium iron ferrite material prepared in step 3 is placed in a tube furnace and carbonized at 800°C for 9 hours under a nitrogen atmosphere to finally prepare a Zn / Co bimetallic lithium supplement coated with carbon material.

[0096] Example 2

[0097] Step 1: Lithium hydroxide and ferric oxide were premixed in a ball mill at a ratio of Li:Fe of 6:1 for 6 hours at a ball mill speed of 500 rpm / min. Then, the mixture was calcined at a first temperature of 500℃ for 4 hours under a nitrogen atmosphere, followed by sintering at a second temperature of 900℃ for 6 hours at a heating rate of 2℃ / min to finally prepare lithium-rich lithium iron ferrite material. The material was then crushed and sieved to obtain lithium-rich lithium iron ferrite material with a particle size Dv50 of 10 micrometers.

[0098] Step 2: Dissolve 1.08g FeCl3·6H2O and 0.66g H2BDC (phthalic acid) in 80mL DMF and add 0.19g Cu(NO3)2·3H2O. Stir to dissolve, and then add 2g of lithium iron ferrite material.

[0099] Step 3: Transfer the solution from step 2 to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and heat it at 110 °C for 20 h.

[0100] Step 4: The Fe / Cu MOFs core-shell coated lithium iron ferrite material prepared in step 3 is placed in a tube furnace and carbonized at 700°C for 10 hours under a nitrogen atmosphere to finally prepare the Fe / Cu bimetallic and carbon-coated lithium supplement.

[0101] The lithium supplements in Examples 3-7 and Comparative Examples 1-4 were the same as those in Example 1, except for the different experimental parameters (see Table 1).

[0102] Compared with Example 1, Comparative Example 1 used only 30 mmol of Zn(NO3)2·6H2O and did not use Co(NO3)2·6H2O; Comparative Example 2 did not use either Zn(NO3)2·6H2O or Co(NO3)2·6H2O; Comparative Example 3 did not use dimethylimidazole; and Comparative Example 4 directly used Li5FeO4 as a lithium supplement.

[0103] The experimental parameters of the lithium supplements in Examples 1-7 and Comparative Examples 1-4 are shown in Table 1.

[0104] Table 1

[0105]

[0106]

[0107] " / " indicates no.

[0108] The lithium supplement prepared in Example 1 was analyzed by scanning electron microscopy, and the results were obtained. Figure 2 As can be seen, the lithium supplement particles prepared in Example 1 are relatively regular and have a surface coating layer.

[0109] The specific capacity of the lithium replenishment agents in Examples 1-7 and Comparative Examples 1-4 was tested, and the capacity retention of the batteries was determined.

[0110] Positive electrode preparation: The above-mentioned lithium supplement agent and lithium iron phosphate material were mixed at a ratio of 2:98 to obtain a positive electrode active material composite. This positive electrode active material composite was mixed with conductive carbon and polyvinylidene fluoride binder at a ratio of 92:4:4, and an appropriate amount of NMP solvent was added dropwise. After being ground evenly, the mixture was dispersed and coated onto aluminum foil and then vacuum dried at 110°C. After the aluminum foil was dried at room temperature, it was transferred to a forced-air oven at 120°C and dried for 12 hours. Then, it was cold-pressed and die-cut to form a positive electrode sheet.

[0111] Negative electrode preparation: Spherical hard carbon, binder PVDF, and conductive agent Super-P are mixed together in a mass ratio of 97:2:1 and dispersed in NMP organic solvent to obtain a uniform coating on a copper foil with a thickness of 10 μm. The aluminum foil is dried at 80°C under vacuum for 12 h, and then cold-pressed and die-cut to form the negative electrode.

[0112] Electrolyte preparation: In an argon-filled glove box (moisture content <10ppm, oxygen content <1ppm), solvent EC:EMC was mixed evenly at a mass ratio of 1:1. Sufficiently dried LiPF6 was quickly added to the mixed solution and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1mol / L.

[0113] Separator: A 12μm polyethylene film is used as the separator.

[0114] Secondary battery preparation: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain a bare cell. The tabs are welded on, and the bare cell is placed in an outer package. The electrolyte prepared above is injected into the dried cell. The cells are then encapsulated, left to stand, formed, and shaped to complete the preparation of the secondary battery.

[0115] Testing and Analysis

[0116] Under the same conditions, the lithium replenishing agents and batteries prepared in Examples 1-7 and Comparative Examples 1-4 were tested as follows, and the specific test methods are as follows:

[0117] Lithium supplement specific capacity determination: The lithium supplement, PVDF, and conductive agent Super-P prepared above were mixed at a mass ratio of 6:2:2, then dispersed in NMP solution. After grinding evenly, the mixture was coated onto aluminum foil and vacuum dried at 100°C. After drying the aluminum foil at room temperature, it was transferred to a 120°C forced-air oven for 2 hours of drying. Then, it was cold-pressed and die-cut to form the positive electrode sheet for coin cell assembly. The negative electrode sheet was a lithium sheet.

[0118] After the assembled button cell was left to stand for 12 hours, it was charged to 4.3V with a constant current and constant voltage of 0.05C, and the cutoff current was 0.02C. Then it was left to stand for 5 minutes. It was then discharged to 2.5V with a constant current of 0.05C. The discharged capacity is the specific capacity of the lithium replenisher.

[0119] Battery capacity retention test after 100 cycles: 1C charge-discharge cycle test, voltage range 2.75-3.65V, 100 cycles, and the capacity retention rate is measured.

[0120] The test results are shown in Table 2.

[0121] Table 2

[0122] Example 1 712 91.84％ Example 2 710 91.97％ Example 3 709 91.81％ Example 4 701 90.89％ Example 5 687 90.26％ Example 6 690 90.49％ Example 7 722 94.89％ Comparative Example 1 688 88.15％ Comparative Example 2 672 86.67％ Comparative Example 3 645 82.38％ Comparative Example 4 671 85.84％

[0123] Referring to Tables 1 and 2, it can be seen that the lithium replenishing agents used in Examples 1-7 of this application have higher specific capacity, and the batteries containing them exhibit excellent cycle performance. In contrast, Comparative Examples 1-4, which did not use the lithium replenishing agents from the examples of this application, show significantly reduced specific capacity and battery cycle performance. Therefore, the lithium replenishing agent provided by this invention has excellent specific capacity, thereby improving the battery's capacity retention rate.

[0124] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," "some implementations," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0125] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a lithium supplement, characterized in that, The method includes: Soluble metal salts of at least two metals selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg, and organic ligands are dispersed in a solvent and mixed with a lithium supplement bulk. The mixture undergoes a solvothermal reaction to obtain an intermediate. The temperature of the solvothermal reaction is 80℃-110℃. Under solvent heating conditions, the organic ligands and the two soluble metal salts generate a bimetallic organic framework compound, which coats the surface of the lithium supplement bulk. The intermediate is calcined and carbonized under a protective gas atmosphere to obtain the lithium supplement; The lithium replenishing agent includes a lithium replenishing agent body and a coating layer formed on at least a portion of the surface of the lithium replenishing agent body, the coating layer including a carbon material and at least two metal elements selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg; The coating layer comprises an in-situ generated bimetallic doped carbon material, wherein the metal elements are dispersed in the carbon material; The lithium supplementary agent includes at least one of Li5FeO4, Li6CoO4, Li2NiO2, Li3N, Li2O, and LiF.

2. The method according to claim 1, characterized in that, The coating layer comprises the carbon material and two metallic elements selected from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg.

3. The method according to claim 2, characterized in that, The carbon material and two metallic elements from Zn, Co, Mo, Fe, Cu, Ni, Al, and Mg are obtained by calcining and carbonizing a bimetallic organic framework compound.

4. The method according to any one of claims 1-3, characterized in that, The average thickness of the coating layer is 2nm-5nm.

5. The method according to any one of claims 1-3, characterized in that, Based on the total mass of the lithium replenishing agent, the mass percentage of the coating layer is 5%-20%.

6. The method according to claim 1, characterized in that, The lithium supplement agent comprises Li5FeO4, and the preparation method of Li5FeO4 includes: Lithium and iron sources were mixed and ball-milled at a lithium to iron molar ratio of (5-7):1, and then sintered under a protective atmosphere to obtain Li5FeO4.

7. The method according to claim 6, characterized in that, The ball milling time is 5-12 hours.

8. The method according to claim 6, characterized in that, The ball mill rotates at a speed of 450 rpm / min to 550 rpm / min.

9. The method according to claim 6, characterized in that, The sintering process includes: sintering at 400℃-550℃ for 2h-8h, and then sintering at 800℃-950℃ for 2h-8h.

10. The method according to any one of claims 1-9, characterized in that, The organic ligand includes at least one of dimethylimidazole, 2-aminoterephthalic acid, terephthalic acid, phthalic acid, terephthalic acid, isophthalic acid, isophthalic acid, and imidazole.

11. The method according to any one of claims 1-9, characterized in that, The solvent includes at least one of dimethylformamide, ethanol, methanol, and isopropanol.

12. The method according to any one of claims 1-9, characterized in that, The mass ratio of the soluble metal salt to the lithium supplement body is (0.1-10):(20-65).

13. The method according to any one of claims 1-9, characterized in that, The solvothermal reaction time is 4h-24h.

14. The method according to any one of claims 1-9, characterized in that, The calcination and carbonization temperature is 400℃-900℃.

15. The method according to any one of claims 1-9, characterized in that, The calcination and carbonization time is 3h-15h.

16. A positive electrode plate, characterized in that, The positive electrode comprises a lithium supplement prepared by any one of claims 1-15.

17. A battery, characterized in that, The battery includes the positive electrode sheet as described in claim 16.

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