A modified lithium supplement, its modification method and application

Abstract

The application provides a modified lithium supplement agent and a modification method and application thereof. The modified lithium supplement agent comprises a lithium supplement substrate and a protective layer coated on the surface of the lithium supplement substrate; the protective layer comprises a cross-linked polymer; and the reaction raw material of the cross-linked polymer comprises a polyvinyl alcohol polymer and an isocyanate monomer. The cross-linked polymer formed by cross-linking of the polyvinyl alcohol polymer and the isocyanate monomer in the modified lithium supplement agent improves the compactness of the surface of the lithium supplement substrate, insulates air, improves the instability of the lithium supplement material in air, and has excellent lithium supplement effect.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a modified lithium replenishing agent, its modification method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in various aspects of life, such as power supplies for mobile devices, new energy vehicles, and backup power for energy storage stations. These applications leverage the excellent performance of lithium batteries, such as high capacity and long battery life. However, during the first charge, a SEI film forms at the interface between the negative electrode and the electrolyte. This process consumes lithium, damages the positive electrode, and affects battery capacity and lifespan. Lithium replenishment agents, as an effective method, can provide a lithium source for the formation of the SEI film and reduce the loss of positive electrode material.

[0003] The prior art discloses a lithium supplement additive for battery positive electrode, a positive electrode sheet, its preparation method and a lithium-ion battery. The preparation method of the lithium supplement additive for battery positive electrode includes: mixing a lithium source and a nickel source and calcining them to obtain a lithium-rich material, mixing the lithium-rich material with water and washing it with water, and then drying it to obtain the lithium supplement additive for battery positive electrode.

[0004] Existing lithium supplements have extremely poor conductivity and air stability. They produce lithium compound impurities when exposed to even a small amount of water in the air at room temperature, leading to a decline in material performance. Furthermore, the high cost and difficulty in material preparation have increased the need for large-scale industrial production and application.

[0005] Typically, the stability of lithium-rich lithium iron ferrite is improved by coating it with a carbon layer to isolate it from air, while the carbon layer also ensures the extraction of lithium source. For example, CN115719808A relates to a method for preparing a lithium iron ferrite supplement and its application. The method for preparing the lithium iron ferrite supplement includes the following steps: mixing a carbon source, iron oxide, and an organic lubricant and performing a first grinding to obtain a first mixture; mixing the first mixture with an organic lithium source and performing a second grinding to obtain a second mixture; and sintering the second mixture to obtain the lithium iron ferrite supplement. However, this method usually has disadvantages such as the need to prepare a precursor and high heating energy consumption.

[0006] Therefore, how to ensure that lithium replenishment materials can exist stably in the air and have a good lithium replenishment effect is an urgent technical problem to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a modified lithium supplement agent, its modification method, and its application. In the modified lithium supplement agent provided by the present invention, the cross-linked polymer, formed by cross-linking polyvinyl alcohol polymers and isocyanate monomers, improves the surface density of the lithium supplement substrate, isolates it from air, and alleviates the instability of the lithium supplement material in air, resulting in excellent lithium supplementation performance.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a modified lithium supplement agent, the modified lithium supplement agent comprising a lithium supplement substrate and a protective layer coating the surface of the lithium supplement substrate; the protective layer comprising a crosslinked polymer; the reaction raw materials of the crosslinked polymer comprising a polyvinyl alcohol polymer and an isocyanate monomer.

[0010] The modified lithium supplement provided by this invention uses a cross-linked polymer composed of polyvinyl alcohol polymers and isocyanate monomers to improve the density of the lithium supplement substrate surface, isolate it from air, and allow the hydroxyl groups of the organic outer layer to absorb moisture, thus improving the instability of the lithium supplement material in air and providing excellent lithium supplementation effect.

[0011] In this invention, the cross-linking of isocyanate monomers with polyvinyl alcohol polymers acts as a cross-linking protective layer, thereby obtaining a densely coated lithium supplement. If the coating is made of pure polyvinyl alcohol polymer, the stability in air cannot be solved.

[0012] The crosslinked polymer has the structure shown in Formula I:

[0013]

[0014] R1 is selected from any one of the following: the non-functional portion of hexamethylene diisocyanate, the non-functional portion of isophorone diisocyanate, the non-functional portion of dicyclohexylmethane diisocyanate, the non-functional portion of lysine diisocyanate, the non-functional portion of 2,6-toluene diisocyanate, the non-functional portion of diphenylmethane diisocyanate, or the non-functional portion of naphthalene-1,5-diisocyanate.

[0015] It should be noted that in this invention, "non-functional group part" refers to the part of the compound with the isocyanate group removed. For example, the non-functional group part of hexamethylene diisocyanate is hexamethylene, and the non-functional group part of diphenylmethane diisocyanate is diphenylmethane.

[0016] Preferably, the polyvinyl alcohol polymer includes any one or a combination of at least two of polyvinyl alcohol, polyvinyl alcohol copolymers, or polyvinyl alcohol blends.

[0017] Preferably, the polyvinyl alcohol copolymer is formed by copolymerizing polyvinyl alcohol and a second polymer, wherein the second polymer includes any one or a combination of at least two of the following: acrylate copolymers, acrylate blends, vinyl ether copolymers, vinyl ether blends, epoxy polymers, polylactone polymers, vinyl polymers, polyvinylidene fluoride, polyvinyl acetate epoxy polymers, polylactone polymers, vinyl polymers, polyvinylidene fluoride, or polyvinyl acetate.

[0018] Preferably, the organic compounds other than polyvinyl alcohol in the polyvinyl alcohol blend include any one or a combination of at least two of the following: acrylate copolymers, acrylate blends, vinyl ether copolymers, vinyl ether blends, epoxy polymers, polylactone polymers, vinyl polymers, polyvinylidene fluoride, polyvinyl acetate epoxy polymers, polylactone polymers, vinyl polymers, polyvinylidene fluoride, or polyvinyl acetate.

[0019] In this invention, the introduction of other polymers besides polyvinyl alcohol can improve the affinity of the electrolyte and establish a good ion pathway.

[0020] Preferably, the isocyanate monomer comprises any one or a combination of at least two of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, lysine diisocyanate, 2,6-toluene diisocyanate, diphenylmethane diisocyanate, or naphthalene-1,5-diisocyanate.

[0021] Preferably, the lithium-supplementing substrate comprises any one or a combination of at least two of Li5FeO4, LiNiO2, Li2O2, Li2O, or Li3N.

[0022] Preferably, the molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, and isocyanate monomer is 1:0.5:(0.1-2), such as 1:0.5:0.1, 1:0.5:0.3, 1:0.5:0.5, 1:0.5:0.8, 1:0.5:1, 1:0.5:1.3, 1:0.5:1.5, 1:0.5:1.8, or 1:0.5:0.1-2, etc.

[0023] It should be noted that the proportion of polyvinyl alcohol polymers in this invention is calculated based on the molar ratio of polyvinyl alcohol structural units.

[0024] In this invention, if the molar ratio of lithium-supplemented substrate, polyvinyl alcohol polymer, and isocyanate monomer is too large, i.e., too much isocyanate monomer, it will lead to excessive cross-linking and may cause gelation, resulting in insufficient local reaction. If the molar ratio is too small, i.e., too little isocyanate monomer is added, it will lead to low cross-linking, insufficient surface density, and poor stability in air.

[0025] Preferably, the reaction raw materials of the crosslinked polymer also include a latent curing agent.

[0026] In this invention, a latent curing agent is introduced based on the crosslinking reaction of polyvinyl alcohol polymers and isocyanate monomers. The latent curing agent reacts with water at a faster rate than isocyanate, preferentially consuming the adsorbed water and generating alkanolamine compounds. Alkanolamine compounds can act as crosslinking agents, reacting with isocyanates and polyvinyl alcohol; on the other hand, they also have a certain ability to absorb carbon dioxide. This achieves a continuous crosslinking reaction, encapsulating the lithium-supplementing substrate in the crosslinking system to avoid direct contact with air, reducing the adsorption of carbon dioxide and reaction with water by the lithium-supplementing substrate. At the same time, the outer polymer layer also adsorbs water on the outer layer, preventing it from contacting the lithium-supplementing substrate; thus greatly improving the stability of the lithium-supplementing substrate in air.

[0027] Preferably, the latent curing agent comprises an oxazolidine compound.

[0028] Preferably, the oxazolidine compound comprises 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine.

[0029] Preferably, the molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer, and latent curing agent is 1:0.5:(0.1-2):(1-4), such as 1:0.5:0.1:1, 1:0.5:0.1:2, 1:0.5:0.1:4, 1:0.5:1:1, 1:0.5:1:2, 1:0.5:1:4, 1:0.5:2:1, 1:0.5:2:2, or 1:0.5:2:4, etc.

[0030] In this invention, if the amount of latent curing agent added is too small, it will cause the diisocyanate to react directly with water, producing a side reaction and affecting the lithium replenishment effect.

[0031] Preferably, when the raw materials of the crosslinked polymer further include a latent curing agent, the crosslinked polymer has the structure shown in Formula II:

[0032]

[0033] R2 and R3 are each independently selected from any one of the following non-functional groups: hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, lysine diisocyanate, 2,6-toluene diisocyanate, diphenylmethane diisocyanate, or naphthalene-1,5-diisocyanate.

[0034] Preferably, the protective layer further includes a second lithium replenishing agent.

[0035] In this invention, a second lithium replenishing agent is added to the protective layer. On the one hand, it can better adsorb carbon dioxide, and on the other hand, it can also be used as a lithium replenishing material to improve the lithium replenishment effect.

[0036] Preferably, the second lithium supplement comprises lithium silicate.

[0037] In this invention, lithium silicate is selected as the second lithium replenishing agent. Lithium silicate can both adsorb carbon dioxide and improve air stability, and can also be used as a lithium replenishing material to enhance the lithium replenishment effect.

[0038] Preferably, the molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer, and second lithium-supplementing agent is 1:0.5:(0.1-2):(0.1-0.5), such as 1:0.5:0.1:0.1, 1:0.5:0.1:0.5, 1:0.5:1:0.1, 1:0.5:1:0.5, 1:0.5:2:0.1, or 1:0.5:2:0.5, etc.

[0039] Preferably, the molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer, latent curing agent, and second lithium-supplementing agent is 1:0.5:(0.1-2):(1-4):(0.1-0.5), for example, 1:0.5:0.1:1:0.1, 1:0.5:0.1:2:0.5, 1:0.5:0.1:4:0.1, 1:0.5:1:1:0.5, 1:0.5:1:2:0.1, 1:0.5:1:4:0.5, 1:0.5:2:1:0.1, 1:0.5:2:2:0.5, or 1:0.5:2:4:0.5, etc.

[0040] In this invention, adding too much of the second lithium supplement will affect the performance of the main lithium supplement and weaken the lithium supplementation effect; while adding too little will not be conducive to improving air stability.

[0041] Secondly, a method for modifying a modified lithium supplement as described in the first aspect, the method comprising the following steps:

[0042] In an oxygen-free environment, lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer and solvent are mixed and reacted to obtain the modified lithium-supplementing agent.

[0043] The preparation method provided by this invention is simple to operate, and the modification of lithium-supplemented substrates can be achieved through simple cross-linking coating.

[0044] Preferably, the isocyanate monomer is added at least twice during the mixing process.

[0045] In this invention, the isocyanate monomer is added in batches, which can avoid the gelation of the slurry and thus improve the cross-linking coating effect.

[0046] Preferably, the solvent includes any one or a combination of at least two of acetonitrile, ethanol, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, or toluene.

[0047] Preferably, the molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, and isocyanate monomer is 1:0.5:(0.1-2).

[0048] Preferably, the reaction temperature is 80-100°C, such as 80°C, 85°C, 90°C, 95°C, or 100°C.

[0049] Preferably, the reaction time is 20 to 50 hours, such as 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, or 50 hours.

[0050] Preferably, the mixed raw materials also include a second lithium supplement agent.

[0051] As a preferred technical solution, the modification method includes the following steps:

[0052] In an oxygen-free environment, a lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer, latent curing agent, second lithium-supplementing agent and solvent are mixed and reacted at 80-100°C for 20-50 hours to obtain the modified lithium-supplementing agent.

[0053] The molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer, latent curing agent, and second lithium-supplementing agent is 1:0.5:(0.1-2):(1-4):(0.1-0.5).

[0054] For example, the present invention provides the following modification methods:

[0055] Option 1: Under anaerobic conditions, polyvinyl alcohol (PVA) is mixed with lithium-supplementing substrate and latent curing agent at a molar ratio of 1:0.5:(1~4). The PVA solution is an acetonitrile solution with a concentration of 20 g / L. After drying, the mixture is reacted at 80-100℃ under anaerobic conditions for 20-50 h. The material powder is then immersed in liquid diisocyanate and reacted for 24 h. After filtration, the mixture is dried at 200℃ to obtain the modified lithium-supplementing material.

[0056] Option 2: Polyvinyl alcohol (PVA), isocyanate monomer, and latent curing agent are reacted in a molar ratio (PVA as the structural unit) of 1:(0.2-4):(2-8). The PVA solution is an organic solution with a concentration of 20 g / L. The reaction is pretreated by heating at 80-100℃ for 20-50 h under anaerobic conditions. The reaction product is then thoroughly stirred with the lithium-supplementing substrate to obtain a modified lithium-supplementing agent. The pretreated product and the positive electrode slurry are simultaneously added to a dual planetary mixer.

[0057] Option 3: The lithium-supplementing substrate is reacted with polyvinyl alcohol (PVA) and a latent curing agent at a molar ratio (PVA as the structural unit) of 1:0.5:(1-4) in an organic solution with a PVA concentration of 20 g / L under anhydrous and oxygen-free conditions at 80-100℃ for 20-50 hours as a pretreatment. Simultaneously, a certain amount of isocyanate is added in batches to prevent severe gelation. After the reaction is complete, the resulting slurry is coated onto the coated electrode to form a lithium-supplementing layer.

[0058] Option 4: The lithium-supplemented substrate, polyvinyl alcohol (PVA), isocyanate, latent curing agent, and lithium silicate material (Li4SiO4) are mixed and stirred at an oxygen-free temperature of 80-100℃ for 20-50 hours under a molar ratio (PVA as the structural unit) of 1:0.5:(0.1-2):(1-4):(0.1-0.5). The PVA solution concentration is 20 g / L, and the solvent can be one of acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide (DMAC), or toluene.

[0059] Thirdly, the present invention provides a lithium replenishing electrode sheet, wherein the lithium replenishing electrode sheet includes the modified lithium replenishing agent as described in the first aspect or the modified lithium replenishing agent obtained by the modification method described in the second aspect.

[0060] The lithium replenishing electrode sheet provided by the present invention includes a lithium replenishing positive electrode sheet and a lithium replenishing negative electrode sheet, which can be adapted to the actual needs of those skilled in the art; furthermore, the modified lithium replenishing agent can exist as a separate lithium replenishing layer in the lithium replenishing electrode sheet, or it can be directly mixed into the electrode slurry for mixed lithium replenishment, which can be adapted and adjusted by those skilled in the art.

[0061] Fourthly, the present invention also provides a lithium-ion battery, the lithium-ion battery comprising the lithium-filling electrode sheet as described in the third aspect.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] The modified lithium replenishing agent provided by this invention uses a cross-linked polymer composed of polyvinyl alcohol polymers and isocyanate monomers to improve the density of the lithium replenishing substrate surface, isolate it from air, improve the instability of the lithium replenishing material in air, and has excellent lithium replenishing effect. Detailed Implementation

[0064] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be construed as limiting the invention.

[0065] Example 1

[0066] This embodiment provides a modified lithium supplement agent, comprising a lithium supplement substrate (lithium-rich lithium iron ferrite (LFO)) and a protective layer coating the surface of the lithium supplement substrate; the protective layer comprises a crosslinked polymer; the reaction raw materials of the crosslinked polymer include PVA (polyvinyl alcohol), hexamethylene diisocyanate, and a latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine. The structural formula of the crosslinked polymer is shown in Formula-1:

[0067]

[0068] R2 and R3 are the non-functional group (hexamethylene) in hexamethylene diisocyanate.

[0069] The modification method of the modified lithium supplement is as follows:

[0070] Lithium-rich lithium ferrite (LFO), polyvinyl alcohol (PVA), hexamethylene diisocyanate, and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine were mixed in a molar ratio (PVA as the structural unit) of 1:0.5:1:2. The mixture was stirred for 48 hours under anaerobic conditions at 90°C. The PVA solution concentration was 20 g / L (solvent: N-methylpyrrolidone) to obtain the modified lithium supplement.

[0071] Example 2

[0072] The difference between this embodiment and Example 1 is that the molar ratio of lithium iron ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as the structural unit) is 1:0.5:2:2.

[0073] The remaining preparation methods and parameters are consistent with those in Example 1.

[0074] Example 3

[0075] The difference between this embodiment and Example 1 is that the molar ratio of lithium iron ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as the structural unit) is 1:0.5:0.5:2.

[0076] The remaining preparation methods and parameters are consistent with those in Example 1.

[0077] Example 4

[0078] The difference between this embodiment and Example 1 is that the molar ratio of lithium iron ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as the structural unit) is 1:0.5:0.1:2.

[0079] The remaining preparation methods and parameters are consistent with those in Example 1.

[0080] Example 5

[0081] The difference between this embodiment and Example 1 is that the molar ratio of lithium iron ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as the structural unit) is 1:0.5:0.5:1.

[0082] The remaining preparation methods and parameters are consistent with those in Example 1.

[0083] Example 6

[0084] The difference between this embodiment and Example 1 is that the molar ratio of lithium iron ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as the structural unit) is 1:0.5:0.5:4.

[0085] The remaining preparation methods and parameters are consistent with those in Example 1.

[0086] Example 7

[0087] This embodiment provides a modified lithium supplement agent, which includes a lithium supplement substrate (lithium-rich lithium iron ferrite (LFO)) and a protective layer coated on the surface of the lithium supplement substrate; the protective layer includes a crosslinked polymer; the reaction raw materials of the crosslinked polymer include PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine.

[0088] The modification method of the modified lithium supplement is as follows:

[0089] Lithium-rich lithium ferrite (LFO), polyvinyl alcohol (PVA), and a latent curing agent were mixed and stirred at a molar ratio of 1:0.5:2 under anaerobic conditions at 80°C for 48 hours. The PVA solution (acetonitrile) had a mass concentration of 20 g / L. After drying under anaerobic conditions, the mixture was immersed in a concentrated hexamethylene diisocyanate solution (lithium-rich lithium ferrite (LFO), PVA, hexamethylene diisocyanate, and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine in a molar ratio (PVA as the structural unit) of 1:0.5:1:2) and reacted at 80°C for 24 hours to obtain the modified lithium supplement.

[0090] Example 8

[0091] The difference between this embodiment and Example 7 is that the molar ratio of lithium iron ferrite (LFO), PVA (polyvinyl alcohol), and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as a structural unit) is 1:0.5:1.

[0092] The remaining preparation methods and parameters are consistent with those in Example 7.

[0093] Example 9

[0094] The difference between this embodiment and Example 7 is that the molar ratio of lithium iron ferrite (LFO), PVA (polyvinyl alcohol), and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as a structural unit) is 1:0.5:4.

[0095] The remaining preparation methods and parameters are consistent with those in Example 7.

[0096] Example 10

[0097] This embodiment provides a modified lithium supplement agent, which includes a lithium supplement substrate (lithium-rich lithium iron ferrite (LFO)) and a protective layer coating the surface of the lithium supplement substrate; the protective layer includes a crosslinked polymer and a second lithium supplement agent (lithium silicate); the reaction raw materials of the crosslinked polymer include PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine.

[0098] The modified lithium supplement is prepared as follows:

[0099] Lithium-rich lithium iron ferrite (LFO), polyvinyl alcohol (PVA), hexamethylene diisocyanate, oxazolidine latent curing agent, and lithium silicate material (Li4SiO4) were mixed in a molar ratio (PVA as the structural unit) of 1:0.5:1:2:0.1. The mixture was stirred at 90°C for 48 hours in an oxygen-free environment. The solution concentration of polyvinyl alcohol (PVA) was 20 g / L of organic solution (N-methylpyrrolidone) to obtain the modified lithium supplement.

[0100] Example 11

[0101] This embodiment provides a modified lithium supplement agent, which includes a lithium supplement substrate (lithium-rich lithium iron ferrite (LFO)) and a protective layer coated on the surface of the lithium supplement substrate; the protective layer includes a crosslinked polymer; the reaction raw materials of the crosslinked polymer include PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine.

[0102] The modification method of the modified lithium supplement is as follows:

[0103] PVA (polyvinyl alcohol), hexamethylene diisocyanate, and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine were mixed in a molar ratio (PVA as the structural unit) of 1:1:4 and stirred for 48 hours under anaerobic conditions at 90°C. The PVA (polyvinyl alcohol) solution concentration was 20 g / L in an organic solution (N-methylpyrrolidone as the solvent). A crosslinked polymer was obtained. The crosslinked polymer was then pretreated with lithium-rich lithium ferrite (LFO) (lithium-rich lithium ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate, and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine in a molar ratio (PVA as the structural unit) of 1:0.5:0.5:2) to obtain the modified lithium supplement.

[0104] Example 12

[0105] The difference between this embodiment and Embodiment 1 is that the raw material of the crosslinked polymer provided in this embodiment does not include a latent curing agent, and the specific structural formula of the crosslinked polymer is shown in Formula 2.

[0106]

[0107] R1 is the nonfunctional group portion of hexamethylene diisocyanate;

[0108] No latent curing agent is added in the preparation method.

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Example 13

[0111] The difference between this embodiment and Embodiment 1 is that the molar ratio of lithium iron ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as a structural unit) in this embodiment is 1:0.5:2.5:2.

[0112] The remaining preparation methods and parameters are consistent with those in Example 1.

[0113] Example 14

[0114] The difference between this embodiment and Embodiment 1 is that the molar ratio of lithium iron ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as the structural unit) in this embodiment is 1:0.5:1:0.5.

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Example 15

[0117] The difference between this embodiment and Embodiment 1 is that the molar ratio of lithium-rich lithium iron ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA is the structural unit) in this embodiment is 1:0.5:1:5.

[0118] The remaining preparation methods and parameters are consistent with those in Example 1.

[0119] Example 16

[0120] The difference between this embodiment and Example 1 is that in the preparation method provided in this embodiment, hexamethylene diisocyanate is added in two separate additions, with the amount added each time remaining consistent. (This ensures that the molar ratio of lithium-rich lithium iron ferrite (LFO), PVA (polyvinyl alcohol), hexamethylene diisocyanate, and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA as the structural unit) is 1:0.5:1:2.)

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Example 17

[0123] The difference between this embodiment and Example 1 is that polyvinyl alcohol-polymethyl methacrylate block copolymer is added to replace polyvinyl alcohol. In this embodiment, the molar ratio of lithium iron ferrite (LFO), PVA-b-PMMA (polyvinyl alcohol-polymethyl methacrylate block copolymer), hexamethylene diisocyanate and latent curing agent 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine (PVA is the structural unit) is 1:0.5:1:2.

[0124] The remaining preparation methods and parameters are consistent with those in Example 1.

[0125] Comparative Example 1

[0126] This comparative example provides a lithium replenishing agent, which is a pure lithium replenishing substrate, lithium iron ferrite (LFO).

[0127] Comparative Example 2

[0128] The difference between this comparative example and Example 1 is that the polymer in this comparative example is polyethylene glycol, and no diisocyanate or latent curing agent was added.

[0129] The remaining preparation methods and parameters are consistent with those in Example 1.

[0130] The lithium replenishing agents (modified or unmodified) provided in Examples 1-17 and Comparative Examples 1-2 were subjected to air stability tests under the following conditions: charge and discharge at 0.1C and 25°C.

[0131] The specific test results are shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] Lithium replenishment was performed at the positive end of the lithium replenishing agents (modified or unmodified) provided in Examples 1-17 and Comparative Examples 1-2.

[0136] The specific lithium replenishment process is as follows:

[0137] Add lithium supplement during the homogenization and dry mixing process, and follow the normal procedure for the other steps.

[0138] The positive electrode sheet after lithium supplementation is used to prepare a coin electrode, with the positive electrode being a lithium-supplemented positive electrode sheet and the negative electrode being a graphite negative electrode.

[0139] The batteries provided in Examples 1-17 and Comparative Examples 1-2 were subjected to electrochemical performance tests. The test conditions were: charge and discharge at 25°C, first cycle at 0.1C, and long cycle at 0.5C for 100 cycles. The test results are shown in Table 2.

[0140] Table 2

[0141]

[0142]

[0143] Combining Table 1 and Table 2, we can see that:

[0144] The data from Examples 1 and 10 show that adding a second lithium replenishing agent to the protective layer can better achieve lithium replenishment and improve the capacity retention rate after first efficiency and long cycle.

[0145] The data results from Examples 1 and 11 show that the order of mixing and coating the crosslinked polymer and the lithium-supplementing substrate provided by the present invention does not affect the density of the coating layer on the lithium-supplementing layer.

[0146] The data from Examples 1 and 12 show that the addition of the latent curing agent can prevent the side reaction between isocyanate and water, thereby improving the lithium replenishment effect and air stability. Therefore, although Example 1 has a smaller charging capacity than Example 12 due to the lower proportion of lithium replenishing agent matrix, Example 1 has a larger proportion of latent curing agent and better stability. Its charging capacity, first efficiency, and 100-cycle capacity retention rate after being placed in air for five days are all better than those of Example 12.

[0147] The data from Examples 1 and 13 show that adding too much isocyanate will increase side reactions and affect the lithium replenishment effect.

[0148] The data from Examples 1 and 5, 6, 14 and 15 show that if too little latent curing agent is added, it cannot effectively prevent side reactions. Although Example 14 has a higher initial specific capacity and first-cycle efficiency than Example 1 due to the higher proportion of lithium-replenishing substrate in the modified lithium replenishing agent, its specific capacity retention rate after five days in air is 90%, which is lower than that of Example 1. Compared with Example 1, Example 1 has better storage performance and stronger application performance. Compared with Example 1, Example 15 has a higher proportion of latent curing agent and a relatively lower proportion of lithium replenishing agent. Therefore, the charging specific capacity, first-cycle efficiency and 100-cycle capacity retention rate of Example 1 are all better than those of Example 15.

[0149] The data from Examples 1 and 16 show that adding isocyanate in batches during the preparation process is more conducive to the lithium supplement being more densely coated by the organic cross-linking layer. The gram capacity and first-efficiency of Example 16 are close to those of Example 1, but it has better air stability and cycle stability. Its charging capacity retention rate after being placed in air for five days and its 100-cycle capacity retention rate are significantly improved compared to Example 1.

[0150] The data from Examples 1 and 17 show that, in addition to polyvinyl alcohol, the introduction of other polymers can improve the affinity of the electrolyte and establish a good ion pathway.

[0151] As can be seen from the data results of Example 1 and Comparative Examples 1 and 2, the present invention solves the problem that the lithium supplementation effect of lithium supplementation agents is easily affected by water and carbon dioxide by the re-crosslinking reaction of polyvinyl alcohol polymers.

[0152] In summary, the modified lithium replenishing agent provided by this invention uses a cross-linked polymer composed of polyvinyl alcohol polymers and isocyanate monomers to improve the density of the lithium replenishing substrate surface, isolate it from air, improve the instability of the lithium replenishing material in air, and has excellent lithium replenishing effect.

[0153] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified lithium supplement agent, characterized in that, The modified lithium supplement agent includes a lithium supplement substrate and a protective layer coated on the surface of the lithium supplement substrate; the protective layer includes a crosslinked polymer; the reaction raw materials of the crosslinked polymer include polyvinyl alcohol polymers and isocyanate monomers; When the reactants do not include a latent curing agent, the crosslinked polymer has the formula: The structure shown is as follows: ； Mode ; R1 is selected from any one of the following: the non-functional portion of hexamethylene diisocyanate, the non-functional portion of isophorone diisocyanate, the non-functional portion of dicyclohexylmethane diisocyanate, the non-functional portion of lysine diisocyanate, the non-functional portion of 2,6-toluene diisocyanate, the non-functional portion of diphenylmethane diisocyanate, or the non-functional portion of naphthalene-1,5-diisocyanate. or, The reaction raw materials of the crosslinked polymer also include a latent curing agent; when the raw materials of the crosslinked polymer also include a latent curing agent, the crosslinked polymer has the formula... The structure shown is as follows: ； Mode ; R2 and R3 are each independently selected from any one of the following non-functional groups: hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, lysine diisocyanate, 2,6-toluene diisocyanate, diphenylmethane diisocyanate, or naphthalene-1,5-diisocyanate.

2. The modified lithium supplement agent according to claim 1, characterized in that, The polyvinyl alcohol polymers include any one or a combination of at least two of polyvinyl alcohol, polyvinyl alcohol copolymers, or polyvinyl alcohol blends.

3. The modified lithium supplement agent according to claim 2, characterized in that, The polyvinyl alcohol copolymer is formed by copolymerizing polyvinyl alcohol and a second polymer, wherein the second polymer includes any one or a combination of at least two of the following: acrylate copolymers, acrylate blends, vinyl ether copolymers, vinyl ether blends, epoxy polymers, polylactone polymers, vinyl polymers, polyvinylidene fluoride, polyvinyl acetate epoxy polymers, polylactone polymers, vinyl polymers, polyvinylidene fluoride, or polyvinyl acetate.

4. The modified lithium supplement agent according to claim 2, characterized in that, The organic compounds other than polyvinyl alcohol in the polyvinyl alcohol blend include any one or a combination of at least two of the following: acrylate copolymers, acrylate blends, vinyl ether copolymers, vinyl ether blends, epoxy polymers, polylactone polymers, vinyl polymers, polyvinylidene fluoride, polyvinyl acetate epoxy polymers, polylactone polymers, vinyl polymers, polyvinylidene fluoride, or polyvinyl acetate.

5. The modified lithium supplement agent according to claim 1, characterized in that, The isocyanate monomer includes any one or a combination of at least two of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, lysine diisocyanate, 2,6-toluene diisocyanate, diphenylmethane diisocyanate, or naphthalene-1,5-diisocyanate.

6. The modified lithium supplement agent according to claim 1, characterized in that, The lithium-supplementing substrate includes any one or a combination of at least two of Li5FeO4, LiNiO2, Li2O2, Li2O, or Li3N.

7. The modified lithium supplement agent according to claim 1, characterized in that, The molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, and isocyanate monomer is 1:0.5:(0.1~2).

8. The modified lithium supplement agent according to claim 1, characterized in that, The latent curing agent includes oxazolidine compounds.

9. The modified lithium supplement agent according to claim 8, characterized in that, The oxazolidine compound includes 2-isopropyl-3-hydroxyethyl-1,3-oxazolidine.

10. The modified lithium supplement agent according to claim 1, characterized in that, The molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer and latent curing agent is 1:0.5:(0.1~2):(1~4).

11. The modified lithium supplement agent according to claim 1, characterized in that, The protective layer also includes a second lithium replenishing agent.

12. The modified lithium supplement agent according to claim 11, characterized in that, The second lithium supplement includes lithium silicate.

13. The modified lithium supplement agent according to claim 11, characterized in that, The molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer, and second lithium-supplementing agent is 1:0.5:(0.1~2):(0.1~0.5).

14. The modified lithium supplement agent according to claim 11, characterized in that, The molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer, latent curing agent, and second lithium-supplementing agent is 1:0.5:(0.1~2):(1~4):(0.1~0.5).

15. A method for modifying the modified lithium supplement agent according to any one of claims 1-4, characterized in that, The modification method includes the following steps: In an oxygen-free environment, lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer and solvent are mixed and reacted to obtain the modified lithium-supplementing agent.

16. The method for modifying the modified lithium supplement agent according to claim 15, characterized in that, During the mixing process, the isocyanate monomer is added at least twice.

17. The method for modifying the modified lithium supplement agent according to claim 15, characterized in that, The solvent includes any one or a combination of at least two of acetonitrile, ethanol, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, or toluene.

18. The method for modifying the modified lithium supplement agent according to claim 15, characterized in that, The molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, and isocyanate monomer is 1:0.5:(0.1~2).

19. The method for modifying the modified lithium supplement agent according to claim 15, characterized in that, The reaction temperature is 80~100℃.

20. The method for modifying the modified lithium supplement agent according to claim 15, characterized in that, The reaction time is 20-50 hours.

21. The method for modifying the modified lithium supplement agent according to claim 15, characterized in that, The mixed raw materials also include a second lithium supplement.

22. The method for modifying the modified lithium supplement agent according to claim 15, characterized in that, The modification method includes the following steps: In an oxygen-free environment, a lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer, latent curing agent, second lithium-supplementing agent and solvent are mixed and reacted at 80~100℃ for 20~50h to obtain the modified lithium-supplementing agent. The molar ratio of the lithium-supplementing substrate, polyvinyl alcohol polymer, isocyanate monomer, latent curing agent, and second lithium-supplementing agent is 1:0.5:(0.1~2):(1~4):(0.1~0.5).

23. A lithium-filling electrode sheet, characterized in that, The lithium replenishing electrode sheet includes the modified lithium replenishing agent as described in any one of claims 1-14 or the modified lithium replenishing agent obtained by the modification method described in any one of claims 15-22.

24. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium replenishment electrode sheet as described in claim 23.

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