A positive electrode lithium supplement additive, a preparation method thereof, and a positive electrode material and a secondary battery

Abstract

The application relates to the technical field of lithium ion battery additives, and provides a positive electrode lithium supplement additive, which comprises a lithium supplement material and a coating layer coated on the surface of the lithium supplement material, and the material of the coating layer contains carbon and / or nitrogen. The positive electrode lithium supplement additive provided by the application contains the lithium supplement material for supplementing lithium, so that the lithium supplement material can supplement lithium ions consumed by the formation of an SEI film of a negative electrode during the first charging process of a battery, lithium ions in the battery system are kept sufficient, and the first charging efficiency and the overall electrochemical performance of the battery are improved. The coating layer contained in the application is coated on the surface of the lithium supplement material, can isolate the lithium supplement material from air, avoids the corrosion of water, oxygen and carbon dioxide in the air on the lithium supplement material, and therefore improves the stability of the lithium supplement material. In addition, the coating layer has conductivity, can increase the conductivity of the whole positive electrode lithium supplement additive, and therefore can ensure that the voltage change is relatively stable during the charging process.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery cathode additive technology, and particularly relates to a cathode lithium replenishment additive, its preparation method, cathode material, and secondary battery. Background Technology

[0002] With the rapid development of the new energy field, improving battery energy density is an urgent problem to be solved in the field of rechargeable lithium-ion batteries (LIBs), including power batteries, energy storage batteries, and 3C digital consumer batteries. The electrode materials of the battery are the main factor restricting the improvement of battery energy density. During the first charge and discharge process, an electrochemical reaction occurs at the anode interface of a rechargeable lithium-ion battery, forming an inert interface film (SEI). The lithium ions consumed in this process are converted into an inert layer and lose their activity, causing an irreversible decrease in the overall capacity of the lithium-ion battery. At the anode, widely used graphite or hard carbon materials exhibit an irreversible capacity loss of about 10% during the first charge and discharge process. For silicon anodes with higher theoretical capacity, the irreversible capacity loss during the first charge and discharge reaches about 15%. Therefore, adding lithium-rich compounds as cathode lithium replenishment additives in the lithium-ion battery manufacturing process can compensate for the capacity loss caused by the formation of the SEI film. Binary lithium compounds have attracted widespread attention due to their relatively high theoretical capacity. Among them, Li3N, with a theoretical capacity of 2309 mAh / g, has become an ideal cathode lithium replenishment additive.

[0003] However, Li3N is strongly alkaline, which easily causes polyvinylidene fluoride (PVDF) to de-HF and gel during traditional homogenization processes; in addition, Li3N has poor conductivity, resulting in severe polarization. Therefore, the widespread application of Li3N is limited. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode lithium replenishment additive, its preparation method, positive electrode material, and secondary battery, aiming to solve the problem of high process difficulty in the practical application of existing positive electrode lithium replenishment additives.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] In a first aspect, this application provides a positive electrode lithium replenishment additive, which includes a lithium replenishment material and a coating layer covering the surface of the lithium replenishment material, wherein the material of the coating layer contains carbon and / or nitrogen.

[0007] Secondly, this application provides a method for preparing a cathode lithium supplement additive, comprising the following steps:

[0008] Provides lithium supplementation materials, nitrogen and / or carbides of transition metals;

[0009] Nitrogen and / or carbides of transition metals are dispersed in a solvent to form a nitrogen and / or carbide dispersion of transition metals.

[0010] The lithium-replenishing material is mixed with a nitrogen and / or carbide dispersion of transition metals, and then subjected to a first calcination treatment and a first ball milling treatment in sequence to obtain a positive electrode lithium-replenishing additive.

[0011] Thirdly, this application provides a cathode material containing the cathode lithium supplementation additive provided in this application and / or the cathode lithium supplementation additive prepared by the preparation method provided in this application.

[0012] Fourthly, this application provides a secondary battery containing the positive electrode material provided in this application.

[0013] Compared with the prior art, this application has the following technical effects:

[0014] The positive electrode lithium replenishment additive provided in the first aspect of this application includes a lithium replenishment material and a coating layer covering the surface of the lithium replenishment material. The coating layer contains carbon and / or nitrogen. Because this positive electrode lithium replenishment additive contains a lithium replenishment material, during the first charge cycle, the lithium replenishment material can replenish the lithium ions consumed in the formation of the SEI film at the negative electrode, ensuring a sufficient supply of lithium ions within the battery system, thereby improving the first charge efficiency and overall electrochemical performance. Since the coating layer is applied to the surface of the lithium replenishment material, it isolates the material from air, preventing corrosion of the highly active lithium replenishment material by water, oxygen, and carbon dioxide in the air, thus improving the stability of the lithium replenishment material.

[0015] The method for preparing a cathode lithium-replenishing additive provided in the second aspect of this application involves first dispersing nitrogen and / or carbides of a transition metal in a solvent to form a nitrogen and / or carbide dispersion of the transition metal; then adding a lithium-replenishing material to the nitrogen and / or carbide dispersion and mixing it, followed by a first calcination treatment and a first ball milling treatment to obtain the cathode lithium-replenishing additive. This preparation process is simple, easy to implement, and has low production costs. Furthermore, the lithium-replenishing additive prepared by this method exhibits good material stability and electrochemical performance, which is beneficial for improving the first-charge efficiency and overall electrochemical performance of the battery.

[0016] The cathode material provided in the third aspect of this application contains the cathode lithium supplementation additive provided in this application or the cathode lithium supplementation additive prepared by the preparation method provided in this application. Therefore, the cathode material has good material stability and electrochemical performance, and can ensure that the voltage change of the battery is stable during the charging process.

[0017] The secondary battery provided in the fourth aspect of this application contains the positive electrode material provided in this application. Therefore, during the first charging process, the lithium replenishing additive contained in the secondary battery can act as a lithium source, releasing lithium ions to achieve lithium replenishment, thereby maintaining an abundance of lithium ions in the battery system and improving the first charging efficiency and overall charge and discharge performance of the battery. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating the preparation process of the positive electrode lithium supplementation additive provided in the embodiments of this application;

[0020] Figure 2 These are XRD patterns of the lithium nitride core, the solid solution layer formed on the surface of the lithium nitride core, and the coating layer formed on the surface of the solid solution layer, provided in Embodiment 5 of this application.

[0021] Figure 3 This is a capacity-voltage diagram of a coin cell after the positive electrode lithium supplementation additives provided in Examples 1, 5, 9 and Comparative Example 1 of this application are added to the positive electrode of lithium iron phosphate. Detailed Implementation

[0022] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0024] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0025] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0026] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0027] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0028] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0029] The first aspect of this application provides a positive electrode lithium replenishment additive, which includes a lithium replenishment material and a coating layer covering the surface of the lithium replenishment material, wherein the material of the coating layer contains carbon and / or nitrogen.

[0030] The positive electrode lithium replenishment additive provided in this application includes a lithium replenishment material and a coating layer covering the surface of the lithium replenishment material. The coating layer material includes nitrogen and / or carbides of transition metals. Because this positive electrode lithium replenishment additive contains a lithium replenishment material, during the first charge cycle, the lithium replenishment material can replenish the lithium ions consumed in the formation of the SEI film at the negative electrode, ensuring a sufficient supply of lithium ions within the battery system, thereby improving the first charge efficiency and overall electrochemical performance. Since the coating layer is applied to the surface of the lithium replenishment material, it isolates the material from air, preventing corrosion of the highly active lithium replenishment material by water, oxygen, and carbon dioxide in the air, thus improving the stability of the lithium replenishment material.

[0031] In this embodiment, the coating material includes carbon materials. These carbon materials include, but are not limited to, at least one of carbon black, graphite, carbon nanotubes, graphene, and amorphous carbon. In a specific embodiment, the carbon material may be amorphous carbon.

[0032] In this embodiment, the coating material includes nitrogen and / or carbides of transition metals. The nitrogen and / or carbides of transition metals can include any one of three types: nitrides of transition metals, carbides of transition metals, or nitrogen-carbides of transition metals. The coating provided in this embodiment is a nitrogen and / or carbide of transition metals, which is conductive and can increase the overall conductivity of the positive electrode lithium-filling additive, thus ensuring relatively stable voltage changes during charging.

[0033] In the embodiments, the general formula for nitrogen and / or carbides of transition metals is M. x B y Wherein, 1≤x≤5; 1≤y≤3, M is selected from any one of Ti, Zr, Ta, W, and Mo, and B includes at least one of C and N. In a specific embodiment, M... x B y The nitrogen and / or carbides of transition metals include at least one of TiN, TiC, TiCN, ZrN, ZrC, ZrCN, TaN, TaC, and TaCN.

[0034] In this embodiment, the coating layer comprises 0.5-10% of the total weight of the positive electrode lithium supplementation additive, with the total weight being 100%. The coating layer thickness is 0.1-10 μm. Within the range of coating layer percentage and thickness provided in this embodiment, complete coating of the lithium supplementation material is ensured, thereby optimizing the conductivity and stability of the lithium supplementation additive. In specific embodiments, the coating layer percentage can be, but is not limited to, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, and 40%. The coating layer thickness can be, but is not limited to, 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm.

[0035] In this embodiment, the lithium replenishing material includes a lithium replenishing core and a solid solution bonded to the surface of the lithium replenishing core. The lithium replenishing material provided in this embodiment contains a solid solution bonded to the surface of the lithium replenishing core. The solid solution can reduce the interfacial alkalinity of the lithium replenishing core, preventing gelation under alkaline conditions with widely used N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) during homogenization, thus improving its stability. Furthermore, the solid solution has a low melting point, acting as a binder to ensure a tight bond between the lithium replenishing core and the coating layer, increasing the tightness and integrity of the coating layer, and further improving the stability of the lithium replenishing additive.

[0036] In the embodiments, a solid solution is incorporated into the surface of the lithium-replenishing core to form a solid solution layer that fully or partially covers the lithium-replenishing core. The solid solution layer can fully or partially cover the lithium-replenishing core. Ideally, it is fully covered, which minimizes the surface alkalinity of the lithium-replenishing core while increasing the tightness between the lithium-replenishing core and the coating layer, thereby optimizing the stability of the lithium-replenishing additive.

[0037] In the embodiment, the general formula of the lithium-replenishing core is Li. e E f Wherein, 1≤e≤3, 1≤f≤3, and E is selected from any one of F, S, N, B, P, O, and Se. Because this lithium-replenishing core contains a lithium-replenishing material rich in lithium, it can provide abundant lithium, acting as a "sacrificial agent" during the first charging cycle to release as many lithium ions as possible at once. This replenishes the irreversible lithium ions consumed in the formation of the SEI film at the negative electrode, thereby maintaining a sufficient supply of lithium ions within the battery system and improving the battery's initial efficiency and overall electrochemical performance. In a specific embodiment, the Li... e E f The lithium-replenishing core includes at least one of LiF, Li2S, Li3N, Li3B, Li3P, and Li2Se. These lithium-replenishing materials have high lithium content and good stability.

[0038] In the embodiments, the general formula of the solid solution is Li a Rb A c Wherein, 1≤a≤13; 1≤b≤5; 1≤c≤4, R is selected from any one of Ti, F, S, N, B, P, O, and Se, and A is selected from any one of F, Cl, Br, and I. Because this solid solution is rich in lithium, it can release lithium ions during the first charging cycle, enhancing the lithium replenishment effect of the lithium replenishment additive. Furthermore, its low melting point allows for a tight connection between the lithium replenishment core and the coating layer, which is beneficial for increasing the uniformity and integrity of the coating layer, thereby improving the stability of the lithium replenishment additive. In a specific embodiment, this Li... a R b A c Solid solutions include Li3SF, Li3SCl, Li3SBr, Li3SI, Li4NF, Li4NCl, Li5NBr2, Li4NI, Li4BF, Li4BCl, Li4BBr, Li4BI, Li4PF, Li4PCl, Li4PBr, Li4PI, Li3SeF, Li3SeCl, Li3SeBr, Li3SeI, Li 0.33 Ti 0.33 At least one of Cl and Li5TiN. These solid solutions have low melting points and good adhesive properties.

[0039] In this embodiment, the solid solution layer comprises 1-3% of the positive electrode lithium replenishment additive. The thickness of the solid solution layer is 0.1-10 μm. Within the range of solid solution layer content and thickness provided in this embodiment, it ensures complete coating of the lithium replenishment core, minimizes the surface alkalinity of the lithium replenishment core, and enhances the stability of the lithium replenishment additive; simultaneously, it increases the tightness between the lithium replenishment core and the coating layer, further enhancing the stability of the lithium replenishment additive, thereby achieving optimal stability performance. Specifically, the percentage content of the solid solution layer can be, but is not limited to, 0.1%, 1%, 1.5%, 2%, 2.5%, 3%, 10%, 20%, 30%, and 40%. The thickness of the coating layer can be, but is not limited to, 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm.

[0040] In the embodiments, the percentage content of the lithium-replenishing core is 87-98.5%, calculated based on the total weight of the positive electrode lithium-replenishing additive as 100%. In specific embodiments, the percentage content of the lithium-replenishing core can be, but is not limited to, 87%, 89%, 92%, 94%, 96%, and 98.5%. By controlling and optimizing the content of the lithium-replenishing core, the lithium-replenishing core can fully exert its lithium-replenishing function, thereby maintaining an abundance of lithium ions in the battery system and improving the battery's initial efficiency and overall electrochemical performance.

[0041] In this embodiment, the particle size of the lithium replenishment material core is 0.1-50 μm. By controlling the core particle size, this embodiment can, on the one hand, control the content of the lithium replenishment core in the cathode lithium replenishment additive, thereby optimizing the lithium replenishment effect of the cathode lithium replenishment additive; on the other hand, it can, together with the solid solution layer and the coating layer, achieve control over the overall particle size of the cathode lithium replenishment additive. In specific embodiments, the particle size of the lithium replenishment material core can be, but is not limited to, 0.1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm.

[0042] In the embodiments, the particle size of the positive electrode lithium replenishment additive is 0.2-60 μm. Within the particle size range of the positive electrode lithium replenishment additive provided in the embodiments of this application, the conductivity and stability of the positive electrode lithium replenishment additive can be optimized. In specific embodiments, the particle size of the positive electrode lithium replenishment additive can be, but is not limited to, 0.2 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, and 60 μm.

[0043] The second aspect of this application provides a method for preparing a positive electrode lithium supplementation additive, such as... Figure 1 As shown, it includes the following steps:

[0044] S10: Provides lithium supplementation materials, nitrogen and / or carbides of transition metals;

[0045] S20: Dispersing nitrogen and / or carbides of transition metals in a solvent to form a nitrogen and / or carbide dispersion of transition metals;

[0046] S30: The lithium-replenishing material is added to a nitrogen and / or carbide dispersion of transition metals and mixed, and then subjected to a first calcination treatment and a first ball milling treatment in sequence to obtain a positive electrode lithium-replenishing additive.

[0047] The method for preparing the positive electrode lithium-replenishing additive provided in this application involves first dispersing nitrogen and / or carbides of a transition metal in a solvent to form a nitrogen and / or carbide dispersion of the transition metal; then, adding the lithium-replenishing material to the nitrogen and / or carbide dispersion and mixing it, followed by a first calcination treatment and a first ball milling treatment to obtain the positive electrode lithium-replenishing additive. This preparation process is simple, easy to implement, and has low production costs. Furthermore, the lithium-replenishing additive prepared by this method exhibits good material stability and electrochemical performance, which is beneficial for improving the first-charge efficiency and overall electrochemical performance of the battery.

[0048] In step S10, the lithium replenishing material can include two scenarios: the first scenario is that the lithium replenishing material only contains a lithium replenishing core, and the second scenario is that the lithium replenishing material contains a lithium replenishing core and a solid solution layer. The lithium replenishing material containing only a lithium replenishing core is as described above and will not be repeated here. The preparation method of the lithium replenishing material containing a lithium replenishing core and a solid solution layer includes: mixing lithium halide with the lithium replenishing core, and then sequentially performing a second calcination treatment and a second ball milling treatment to obtain the lithium replenishing material. Specifically, the lithium halide can include at least one of LiF, LiCl, LiBr, and LiI. In this embodiment, the lithium halide and the lithium replenishing core are first ball-milled and mixed to uniformly disperse the lithium halide on the surface of the lithium replenishing core. Then, a second calcination treatment is performed to melt and embed the lithium halide into the surface layer of the lithium replenishing core at high temperature to form a solid solution layer. After a second ball milling treatment, a lithium replenishing material that meets the particle size requirements and has uniform size can be obtained.

[0049] In this embodiment, the molar ratio of lithium halide to the lithium-replenishing core is (1-100):1. Within the range of this molar ratio provided in this embodiment, it is beneficial for lithium halide to embed into the surface of the lithium-replenishing core to form a uniform solid solution layer, and it can best coat the lithium-replenishing core, thus achieving optimal stability of the lithium-replenishing material. In specific embodiments, the molar ratio of lithium halide to the lithium-replenishing core can be, but is not limited to, 1:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, and 100:1.

[0050] In the embodiments, the conditions for the second calcination treatment include: a holding temperature of 400-900℃ and a holding time of 1-24h. Within the holding temperature range provided in the embodiments of this application, the sintering temperature is greater than or equal to the melting point of lithium halide, which can promote the melting of lithium halide and the formation of a solid solution layer with the lithium supplementary core surface layer. Within the holding time range provided in the embodiments of this application, it is beneficial for lithium halide to form a uniform solid solution layer on the lithium supplementary core surface layer, and the energy consumption cost is low. In specific embodiments, the holding temperature can be, but is not limited to, 400℃, 500℃, 600℃, 700℃, 800℃, and 900℃. The holding time can be, but is not limited to, 1h, 5h, 10h, 15h, 20h, and 24h.

[0051] In step S20, the transition metal carbide is dispersed in a solvent to form a transition metal carbide dispersion; or, the transition metal nitride is dispersed in a solvent to form a transition metal nitride dispersion; or, the transition metal nitrogen carbide is dispersed in a solvent to form a transition metal nitrogen carbide dispersion. In the embodiments, the solvent may include at least one of N,N-dimethylformamide, tetrahydrofuran, n-hexane, and benzene.

[0052] In step S30, the above-mentioned lithium replenishing material is first added to a transition metal carbide dispersion and stirred until homogeneous. Then, a first calcination treatment is performed to evaporate the solvent in the dispersion, resulting in a positive electrode lithium replenishing additive with transition metal carbide coating. Alternatively, the above-mentioned lithium replenishing material is first added to a transition metal nitride dispersion and stirred until homogeneous. Then, a first calcination treatment is performed to evaporate the solvent in the dispersion, resulting in a positive electrode lithium replenishing additive with transition metal nitride coating. Alternatively, the above-mentioned lithium replenishing material is first added to a transition metal nitride carbide dispersion and stirred until homogeneous. Then, a first calcination treatment is performed to evaporate the solvent in the dispersion, resulting in a positive electrode lithium replenishing additive with transition metal nitride carbide coating. Finally, a first ball milling treatment is performed to obtain a positive electrode lithium replenishing additive that meets the particle size requirements and has uniform size.

[0053] In the embodiments, the conditions for the first calcination treatment include: a holding temperature of 400-900℃ and a holding time of 1-24h. Within the holding temperature range provided in the embodiments of this application, the sintering temperature is greater than or equal to the melting point of the solid solution, which promotes the wetting of the solid solution layer and the coating layer, and is beneficial to forming a uniformly coated lithium-replenishing additive for the positive electrode. Within the holding time range provided in the embodiments of this application, complete wetting of the solid solution layer and the coating layer is ensured, thereby forming a uniform coating layer on the surface of the solid solution layer, and the energy consumption cost is low. In specific embodiments, the holding temperature can be, but is not limited to, 400℃, 500℃, 600℃, 700℃, 800℃, and 900℃. The holding time can be, but is not limited to, 1h, 5h, 10h, 15h, 20h, and 24h.

[0054] Thirdly, this application provides a cathode material containing the cathode lithium supplementation additive provided in this application and / or the cathode lithium supplementation additive prepared by the preparation method provided in this application.

[0055] The cathode material provided in this application embodiment contains the cathode lithium supplementation additive provided in this application or the cathode lithium supplementation additive prepared by the preparation method provided in this application. Therefore, the cathode material has good material stability and electrochemical performance, and can ensure that the battery voltage changes steadily during the charging process.

[0056] Fourthly, this application provides a secondary battery containing the positive electrode material provided in this application.

[0057] The secondary battery provided in this application contains the positive electrode material provided in this application. Therefore, during the first charge, the lithium replenishing additive contained in the secondary battery can act as a lithium source, releasing lithium ions to achieve lithium replenishment, thereby maintaining an abundance of lithium ions in the battery system and improving the first charge efficiency and overall charge and discharge performance of the battery.

[0058] The following description is based on specific embodiments.

[0059] 1. Lithium supplementation additive for positive electrode and its preparation method:

[0060] Example 1

[0061] This embodiment provides a cathode lithium replenishment additive and its preparation method. The cathode lithium replenishment additive includes a LiN lithium replenishment core and a TiN coating layer on the surface of the lithium replenishment core, namely LiN@TiN.

[0062] The preparation method of the positive electrode lithium supplementation additive in this embodiment includes the following steps:

[0063] S10: Provides LiN lithium supplementation core and TiN;

[0064] S20: Add TiN to N,N-dimethylformamide solvent and ultrasonically disperse for 1-10 h to obtain a TiN dispersion with a mass fraction of 5-20%;

[0065] S30: Add the LiN lithium core to the TiN dispersion and stir to form a mixed slurry. Then, load the mixed slurry into an alumina boat and place it in a tube furnace under inert gas protection. Heat the furnace to 400-900℃ and hold for 1-24 hours. Then, allow it to cool naturally and finally ball mill it to obtain the TiN-coated LiN lithium core positive electrode lithium supplement additive.

[0066] Testing revealed that the LiN lithium-replenishing core has a particle size of 1-8 μm, the TiN coating layer has a thickness of 10-30 nm, and the lithium-replenishing additive has a particle size of 1.01-8.05 μm.

[0067] Example 2

[0068] This embodiment provides a cathode lithium replenishment additive and its preparation method. The cathode lithium replenishment additive includes a LiN lithium replenishment core and a TiC coating layer on the surface of the lithium replenishment core, namely LiN@TiC.

[0069] The preparation method of the lithium supplement additive in this embodiment differs from that in Example 1 in that, in step S10 of this embodiment, a LiN lithium supplement core and TiC are provided.

[0070] Testing revealed that the LiN lithium-replenishing core has a particle size of 1-8 μm, the TiC coating layer has a thickness of 10-30 nm, and the lithium-replenishing additive has a particle size of 1.01-8.05 μm.

[0071] Example 3

[0072] This embodiment provides a cathode lithium replenishment additive and its preparation method. The cathode lithium replenishment additive includes a LiP lithium replenishment core and a TiC coating layer on the surface of the lithium replenishment core, namely LiP@TiC.

[0073] The preparation method of the lithium supplement additive in this embodiment differs from that in Example 1 in that, in step S10 of this embodiment, a LiP lithium supplement core and TiC are provided.

[0074] Testing revealed that the LiP lithium-replenishing core has a particle size of 1-8 μm, the TiC coating layer has a thickness of 10-30 nm, and the lithium-replenishing additive has a particle size of 1.01-8.05 μm.

[0075] Example 4

[0076] This embodiment provides a cathode lithium replenishment additive and its preparation method. The cathode lithium replenishment additive includes a Li2S lithium replenishment core and a TiNC coating layer on the surface of the lithium replenishment core, namely Li2S@TiNC.

[0077] The preparation method of the lithium supplement additive in this embodiment differs from that in Example 1 in that, in step S10 of this embodiment, a Li2S lithium supplement core and TiNC are provided.

[0078] Testing revealed that the Li2S lithium-replenishing core has a particle size of 1-8 μm, the TiNC coating layer has a thickness of 10-30 nm, and the lithium-replenishing additive has a particle size of 1.01-8.05 μm.

[0079] Example 5

[0080] This embodiment provides a cathode lithium replenishing additive and its preparation method. The cathode lithium replenishing additive includes a LiN lithium replenishing core, and the surface of the lithium replenishing core is sequentially coated with a Li4NCl solid solution layer and a TiN coating layer.

[0081] The preparation method of the positive electrode lithium supplementation additive in this embodiment includes the following steps:

[0082] S10: Provides LiN lithium supplementation core, LiCl, TiN;

[0083] S20: According to the molar ratio of (1-100):1, the LiN lithium core and LiCl are mixed and ball-milled for 1-24h to obtain a mixture. Then, the mixture is loaded into an alumina boat and placed in a tube furnace under inert gas protection. The temperature is raised to 400-900℃ and held for 1-24h. After natural cooling, the mixture is ball-milled to obtain a lithium-replenishing material with a Li4NCl solid solution layer coating a LiN lithium core, namely LiN@Li4NCl.

[0084] S30: Add TiN to N,N-dimethylformamide solvent and ultrasonically disperse for 1-10 h to obtain a TiN dispersion with a mass fraction of 5-20%;

[0085] S30: Add the LiN@Li4NCl obtained in S20 to the TiN dispersion and stir to form a mixed slurry. Then, put the mixed slurry into an alumina boat and place it in a tube furnace under inert gas protection. Heat it to 400-900℃, keep it at that temperature for 1-24 hours, and then let it cool naturally. Finally, ball mill it to obtain the positive electrode lithium supplement additive with TiN coated Li4NCl solid solution layer, namely LiN@Li4NCl@TiN.

[0086] The test results showed that the particle size of the LiN lithium-replenishing core was 1-8 μm, the thickness of the Li4NCl solid solution layer was 10-30 nm, the thickness of the TiN coating layer was 10-30 nm, and the particle size of the lithium-replenishing additive was 1.02-8.1 μm.

[0087] Example 6

[0088] This embodiment provides a cathode lithium replenishing additive and its preparation method. The cathode lithium replenishing additive includes a LiN lithium replenishing core, and the surface of the lithium replenishing core is sequentially coated with a Li5NBr2 solid solution layer and a TiC coating layer.

[0089] The preparation method of the lithium supplement additive in this embodiment differs from that in Example 4 in that, in step S10 of this embodiment, a LiN lithium supplement core, LiBr, and TiC are provided.

[0090] The test results showed that the particle size of the LiN lithium-replenishing core was 1-8 μm, the thickness of the Li5NBr2 solid solution layer was 10-30 nm, the thickness of the TiC coating layer was 10-30 nm, and the particle size of the lithium-replenishing additive was 1.02-8.1 μm.

[0091] Example 7

[0092] This embodiment provides a cathode lithium replenishment additive and its preparation method. The cathode lithium replenishment additive includes a LiP lithium replenishment core, the surface of which is sequentially coated with Li... 0.33 Ti 0.33 Cl solid solution layer, TiC coating layer.

[0093] The preparation method of the lithium supplement additive in this embodiment differs from that in Example 4 in that, in step S10 of this embodiment, a LiP lithium supplement core, LiCl, and TiC are provided.

[0094] Testing revealed that the LiP lithium-filled cores have a particle size of 1-8 μm, and the Li... 0.33 Ti 0.33The thickness of the Cl solid solution layer is 10-30 nm, the thickness of the TiC coating layer is 10-30 nm, and the particle size of the lithium supplement additive is 1.02-8.1 μm.

[0095] Example 8

[0096] This embodiment provides a cathode lithium replenishment additive and its preparation method. The cathode lithium replenishment additive includes a Li2S lithium replenishment core, and the surface of the lithium replenishment core is sequentially coated with a Li5TiN solid solution layer and a TiNC coating layer.

[0097] The preparation method of the lithium supplement additive in this embodiment differs from that in Example 1 in that, in step S10 of this embodiment, a Li2S lithium supplement core and TiNC are provided.

[0098] The test results showed that the particle size of the Li2S lithium-replenishing core was 1-8 μm, the thickness of the Li5TiN solid solution layer was 10-30 nm, the thickness of the TiNC coating layer was 10-30 nm, and the particle size of the lithium-replenishing additive was 1.02-8.1 μm.

[0099] Example 9

[0100] This embodiment provides a positive electrode lithium replenishment additive and its preparation method. The positive electrode lithium replenishment additive includes a LiN lithium replenishment core and an amorphous carbon layer coated on the surface of the lithium replenishment core, namely LiN@amorphous carbon layer.

[0101] The preparation method of the core-shell cathode lithium supplementation additive in this embodiment includes the following steps:

[0102] S10: Provides a LiN lithium supplementation core;

[0103] S20: The LiN lithium replenishing material is mixed with a carbon source binder and granulated, and then carbonized to form an amorphous carbon coating layer that coats the LiN lithium replenishing core.

[0104] Testing revealed that the LiN lithium-replenishing core has a particle size of 1-8 μm, the amorphous carbon coating layer has a thickness of 10-30 nm, and the lithium-replenishing additive has a particle size of 1.01-8.05 μm.

[0105] Comparative Example 1

[0106] This comparative example provides a LiN lithium supplementation material.

[0107] 2. Relevant characteristic test analysis.

[0108] 1. Structural characterization of the positive electrode lithium supplementation additive:

[0109] X-ray diffraction analysis was performed on the lithium nitride core provided in Example 5, the cathode lithium supplement additive after a solid solution layer was formed on the surface of the lithium nitride core, and the cathode lithium supplement additive after a coating layer was formed on the surface of the solid solution layer. The XRD patterns are shown below. Figure 2 As shown in the figure. The XRD pattern of the lithium nitride core shows that all its diffraction peaks correspond to the characteristic peaks of lithium nitride. The XRD pattern of the lithium nitride core coated with a solid solution layer shows that, except for the diffraction peaks corresponding to the characteristic peaks of lithium nitride, the remaining diffraction peaks correspond exactly to the characteristic peaks of Li₄NCl, indicating that the lithium nitride core is coated with a Li₄NCl solid solution layer. The XRD pattern of the solid solution layer coated with a coating layer shows that, except for the diffraction peaks corresponding to the characteristic peaks of lithium nitride and Li₄NCl, the remaining diffraction peaks correspond exactly to the characteristic peaks of TiN, indicating that the Li₄NCl solid solution layer is coated with a TiN coating layer.

[0110] 2. Electrochemical performance testing and analysis of lithium-ion batteries:

[0111] A slurry was prepared using N-methylpyrrolidone as a solvent, comprising 5% lithium iron phosphate (LFP) as the positive electrode material, 80% polyvinylidene fluoride (PVDF) as the positive electrode binder, 10% carbon black (Super P) as the binder, and homogenized coating to prepare the positive electrode sheet. The coin cell was tested for charge-discharge performance using a 0.1C constant current / constant voltage method, with a voltage range of 2.0-3.7V and a cutoff current of 0.02C.

[0112] Figure 3 Capacity-voltage diagrams of coin cells after adding the cathode lithium supplementation additives provided in Examples 1, 5, 9, and Comparative Example 1 to lithium iron phosphate cathodes, from... Figure 3 It can be seen that after adding the cathode lithium supplement additive, the initial efficiency of LFP is greater than 94%, with Example 5 showing an initial efficiency of 96%. Discharge capacity comparison shows that the specific capacity of LFP is significantly improved after adding the cathode lithium supplement additive. Comparing Example 1 with Comparative Example 1, the presence of the coating layer increased the specific capacity of LFP by 5%. This is attributed to the coating layer reducing the surface alkalinity of the Li3N lithium supplement core, preventing the lithium supplement core from reacting with NMP or PVDF during the homogenization process and resulting in loss. Comparing Example 1 with Example 9, TiN coating is more effective than amorphous carbon coating, thanks to TiN's better conductivity and fewer surface defects. Comparing Example 5 with Example 1, the capacity is improved by 3%, thanks to the synergistic effect of the added solid solution intermediate layer and the surface TiN, resulting in a tighter surface coating of the lithium supplement core and improved stability.

[0113] As shown in Table 1 below, compared with Comparative Example 1, the positive electrode lithium replenishment additives in Examples 1 and 2, which contain the coating layer provided in this application, showed significantly lower lithium hydroxide content after being placed in air with a relative humidity of 20% for 24 hours. This indicates that forming a coating layer on the surface of the lithium replenishment core can improve the stability of the lithium replenishment material. Examples 5 and 6, which further contain a positive electrode lithium replenishment additive with an intermediate solid solution layer, showed lower lithium hydroxide content than Examples 1 and 2, and their capacity and the number of lithium nitride delithiations in the first cycle were significantly better than those in Examples 1 and 2. This indicates that the synergistic effect of the solid solution layer and the surface coating layer formed on the surface of the lithium replenishment core can further improve the stability of the lithium replenishment material. Therefore, the battery's first charging efficiency and overall electrochemical performance are better.

[0114] Table 1

[0115]

[0116] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode lithium supplementing additive, characterized by, The positive electrode lithium supplement additive comprises a lithium supplement material and a coating layer coated on the surface of the lithium supplement material, the material of the coating layer contains carbon and / or nitrogen; the lithium supplement material comprises a lithium supplement core and a solid solution combined on the surface layer of the lithium supplement core, the solid solution combined on the surface layer of the lithium supplement core forms a solid solution layer fully or partially coating the lithium supplement core, the lithium supplement core is Li3N, and the general formula of the solid solution is Li a R b A c , wherein 1≤a≤13; 1≤b≤5; 1≤c≤4, R is selected from N, and A is selected from any one of F, Cl, Br and I, the solid solution layer is formed by melting lithium halide and embedding on the surface layer of the lithium supplement core; and the material of the coating layer comprises a nitrogen and / or carbon compound of a transition metal.

2. The positive-electrode lithium supplementing additive according to claim 1, characterized by The general formula of the nitride and / or carbide of the transition metal is M x B y wherein 1≤x≤5; 1≤y≤3, M is selected from any one of Ti, Zr, Ta, W, Mo, and B includes at least one of C, N.

3. The positive-electrode lithium supplementing additive according to claim 1, wherein The percentage content of the coating layer is 0.5-50%, calculated based on the total weight of the positive electrode lithium supplement additive being 100%; and / or The thickness of the coating layer is 0.1-10 μm.

4. The positive-electrode lithium supplementing additive according to claim 1, wherein The percentage content of the solid solution layer in the positive electrode lithium supplement additive is 0.1-40%; and / or The thickness of the solid solution layer is 0.1-10 μm; and / or The particle size of the lithium supplement core is 0.1-50 μm; and / or The particle size of the positive electrode lithium supplement additive is 0.2-60 μm.

5. A method of preparing a positive electrode lithium supplementing additive according to any one of claims 1 to 4, characterized by, The method comprises the following steps: The lithium supplement material, the nitrogen and / or carbide of the transition metal are provided; The nitrogen and / or carbide of the transition metal is dispersed in a solvent to form a dispersion liquid of the nitrogen and / or carbide of the transition metal; The lithium supplement material is added into the dispersion liquid of the nitrogen and / or carbide of the transition metal for mixing, and then first calcination treatment and first ball milling treatment are sequentially performed to obtain the positive electrode lithium supplement additive.

6. The production method according to claim 5, wherein The preparation method of the lithium supplement material comprises: The lithium supplement material is obtained by mixing lithium halide with the lithium supplement core, and then sequentially performing second calcination treatment and second ball milling treatment.

7. The production method according to claim 6, characterized by, The molar ratio of the lithium halide to the lithium supplement core is (1-100):1; and / or The conditions of the first calcination treatment comprise: the holding temperature is 400-900 ℃, and the holding time is 1-24 h; and / or The conditions of the second calcination treatment comprise: the holding temperature is 400-900 ℃, and the holding time is 1-24 h.

8. A positive electrode material, characterized by, The positive electrode material contains the positive electrode lithium supplement additive according to any one of claims 1-4 and / or the positive electrode lithium supplement additive prepared by the preparation method according to any one of claims 5-7.

9. A secondary battery characterized by comprising: The secondary battery contains the positive electrode material according to claim 8.

Images