Composite lithium supplementing additive, preparation method and application thereof

Abstract

This application belongs to the field of battery materials technology, and particularly relates to a composite lithium replenishment additive, its preparation method, and its application. The composite lithium replenishment additive includes a core containing an amorphous lithium replenishment additive and an encapsulation layer covering the outer surface of the core. The composite lithium replenishment additive provided in this application has a low activation barrier, high lithium extraction efficiency at lower voltages, and high lithium replenishment specific capacity. In the composite lithium replenishment additive provided in the embodiments of this application, the amorphous lithium replenishment additive in the core has less polarization and a lower voltage plateau during charging, which can effectively reduce the activation barrier of the lithium replenishment additive and significantly improve the lithium-ion insertion / extraction efficiency, thereby achieving a high lithium replenishment specific capacity. The encapsulation layer not only improves the stability of the lithium replenishment additive but also effectively improves the electronic and ion conduction properties of the lithium replenishment material in the core, enhancing the stability of the lithium replenishment additive and achieving a stable lithium replenishment effect.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, and in particular relates to a composite lithium supplementation additive, its preparation method and application. Background Technology

[0002] With the rapid development of energy storage technology and the increasing use of portable digital devices and vehicle power supplies, the demand for battery energy density is rising, making the development of high-capacity, long-life, and safe rechargeable batteries imperative. During the first charge and discharge cycle of lithium-ion batteries, an SEI film forms at the interface of the negative electrode material. Studies have shown that the main components of SEI are lithium salts such as LiF, Li₂CO₃, R-COOLi, and R-CH₂OLi. SEI formation is an irreversible process, and the Li₂ used to form the SEI... + During the discharge process, it can no longer be embedded into the positive electrode material, which will cause a loss of battery capacity.

[0003] Studies have found that the formation of the SEI film consumes some of the Li in the cathode material. + This leads to irreversible capacity loss in the electrode material. Therefore, this capacity loss can be compensated for by pre-lithiation. Pre-lithiation technology mainly falls into two categories: one is lithium replenishment technology for negative electrode materials, which has high requirements for the operating environment and typically uses lithium metal foil and inert lithium powder as the replenishing agent; the other is lithium replenishment technology for positive electrode materials, which has relatively lower requirements and is simpler to implement. Lithium replenishment additives such as Li2S have high theoretical specific capacity, reaching 1166 mAh / g, and do not produce gas after delithiation, making them a promising positive electrode lithium replenishment additive.

[0004] However, crystalline lithium-ion additives such as Li₂S have poor electronic and ionic conductivity, and commercially available Li₂S particles are generally in the micrometer range, creating a significant activation barrier during the initial charging process, making it difficult for lithium ions to escape and resulting in a low actual specific capacity. Currently, a common solution is to nanoscale crystalline lithium-ion additives such as Li₂S, which can reduce the activation barrier to some extent, making it easier for lithium ions to escape and improving the specific capacity of crystalline lithium-ion additives such as Li₂S. However, this solution cannot completely eliminate this activation barrier. Summary of the Invention

[0005] The purpose of this application is to provide a composite lithium replenishing additive, its preparation method and application, which aims to solve to some extent the problem that existing crystalline lithium replenishing additives have a large activation barrier during the first charging process, making it difficult for lithium ions to be removed.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, this application provides a composite lithium replenishing additive, the composite lithium replenishing additive comprising a core containing an amorphous lithium replenishing additive and an encapsulation layer covering the outer surface of the core.

[0008] Furthermore, the amorphous lithium supplement additive is selected from at least one of the following: amorphous lithium sulfide, amorphous lithium nitride, amorphous lithium oxide, amorphous lithium fluoride, and amorphous lithium phosphide.

[0009] Furthermore, in the X-ray diffraction pattern of the amorphous lithium supplementation additive, there is at least one characteristic peak between 2θ and 30°, and the peak width of at least one characteristic peak is 2 to 8°.

[0010] Furthermore, the encapsulation layer includes at least one of an isolation encapsulation layer, an ion conductor encapsulation layer, and an electronic conductor encapsulation layer.

[0011] Furthermore, in the core, the content of the amorphous lithium supplementation additive is not less than 20%.

[0012] Furthermore, in the core, the mass ratio of the amorphous lithium supplementing additive to the crystalline lithium supplementing additive is (20-60):(40-80).

[0013] Furthermore, the core has a particle size D50 of 40–60 nm, and the encapsulation layer has a thickness of 5–15 nm.

[0014] Furthermore, the positive electrode prepared by the composite lithium-supplementing additive, conductive agent and binder, after being stored at an ambient humidity of 25% for 20 hours, has a capacity decay rate of no more than 30% compared to the capacity decay rate after 0.5 hours of storage.

[0015] Furthermore, the positive electrode prepared by the composite lithium-supplementing additive, conductive agent and binder, when stored for 20 hours under ambient humidity of 20%, has a capacity decay rate of no more than 25% compared to the capacity decay rate after 0.5 hours of storage.

[0016] Furthermore, the capacity decay rate of the positive electrode sheet prepared by the positive electrode lithium supplementation additive, conductive agent and binder after 20 hours of storage at 10% ambient humidity is no more than 20% compared with the capacity decay rate after 0.5 hours of storage.

[0017] Secondly, this application provides a method for preparing a composite lithium supplement additive, comprising the following steps:

[0018] Prepare a core containing an amorphous lithium-supplementing additive;

[0019] An encapsulation layer is prepared on the outer surface of the core to obtain a composite lithium supplementation additive.

[0020] Furthermore, the core contains at least one amorphous lithium supplementing additive selected from at least one of amorphous lithium sulfide, amorphous lithium nitride, amorphous lithium oxide, amorphous lithium fluoride, and amorphous lithium phosphide.

[0021] Furthermore, the step of preparing the encapsulation layer on the outer surface of the core includes: forming at least one of an isolation encapsulation layer, an ion conductor encapsulation layer, and an electronic conductor encapsulation layer on the outer surface of the core.

[0022] Furthermore, the step of preparing the amorphous lithium sulfide includes:

[0023] Elemental sulfur is dissolved in an organic solvent to obtain a first reaction solution; wherein the organic solvent has an amino group at the end.

[0024] Under reflux conditions, the first reaction solution is mixed with elemental lithium and reacted to obtain amorphous lithium sulfide.

[0025] Furthermore, the organic solvent is selected from at least one of propylenediamine and ethylenediamine.

[0026] Furthermore, the step of mixing the first reaction solution with elemental lithium includes: mixing the first reaction solution with elemental lithium by dropwise addition and reacting.

[0027] Furthermore, the ratio of the elemental sulfur to the organic solvent is (1-2) g: (50-80) mL.

[0028] Furthermore, the mass ratio of the lithium element to the sulfur element is 1:(2-4).

[0029] Thirdly, this application provides a cathode material, including a cathode active material and the above-mentioned composite lithium supplementation additive.

[0030] Furthermore, the mass percentage of the composite lithium-supplementing additive in the cathode material is 0.1% to 4%.

[0031] Fourthly, this application provides a positive electrode sheet, wherein the positive electrode sheet contains the aforementioned positive electrode material.

[0032] Fifthly, this application provides a secondary battery, which includes the above-mentioned positive electrode plate.

[0033] The composite lithium replenishment additive provided in the first aspect of this application includes a core containing an amorphous lithium replenishment additive and a carbon encapsulation layer covering the outer surface of the core. The amorphous lithium replenishment additive in the core has lower polarization and a lower voltage plateau during charging, which can effectively reduce the activation barrier of the lithium replenishment additive and significantly improve the lithium-ion insertion / extraction efficiency, thereby achieving a high lithium replenishment specific capacity of the additive. The encapsulation layer not only improves the stability of the lithium replenishment additive, but also effectively improves the electronic and ion conduction performance of the lithium replenishment material in the core, increases lithium extraction during charging, and also plays a certain role in isolating water and oxygen, thereby improving the stability of the lithium replenishment additive and achieving a stable lithium replenishment effect.

[0034] The second aspect of this application provides a method for preparing a composite lithium-replenishing additive, which involves preparing a core containing an amorphous lithium-replenishing additive to impart high lithium-ion insertion / extraction efficiency to the composite lithium-replenishing additive; then, an encapsulation layer is prepared on the outer surface of the core to obtain the composite lithium-replenishing additive. The method for preparing the composite lithium-replenishing additive provided by this application is simple, efficient, and suitable for large-scale industrial production and application. Furthermore, the prepared composite lithium-replenishing additive has a low activation barrier and can essentially completely extract lithium ions at relatively low voltages, achieving a high specific capacity for lithium replenishment.

[0035] The cathode material provided in the third aspect of this application includes a cathode active material and the aforementioned composite lithium-replenishing additive. This additive has a low activation barrier and can essentially completely extract lithium ions at relatively low voltages, achieving a high lithium-replenishing specific capacity. Therefore, it can play a good lithium-replenishing role in the cathode material. When the cathode material is applied to a battery, it can compensate for the active lithium ions consumed during the first charge due to the formation of the SEI film, thereby effectively maintaining the specific capacity of the cathode and improving the capacity retention rate of the cathode.

[0036] The positive electrode provided in the fourth aspect of this application contains the aforementioned composite lithium replenishing additive. This additive has a low activation barrier and can essentially completely extract lithium ions at a lower voltage, thus achieving a higher lithium replenishing specific capacity. Therefore, it can play a good lithium replenishing role in the positive electrode, making up for the active lithium ions consumed by the formation of the SEI film during the first charge of the battery, thereby effectively maintaining the specific capacity of the positive electrode and improving the capacity retention rate of the positive electrode.

[0037] The secondary battery provided in the fifth aspect of this application, because it contains the aforementioned positive electrode sheet, which is supplemented with the aforementioned composite lithium-replenishing additive, can effectively compensate for the active lithium ions consumed during the first charge of the battery due to the formation of the SEI film, effectively maintaining the specific capacity of the positive electrode sheet and improving the capacity retention rate of the positive electrode sheet. Therefore, the secondary battery provided in this application has high energy density and good capacity retention rate. Attached Figure Description

[0038] 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.

[0039] Figure 1 This is a schematic flowchart of the preparation method of the composite lithium supplementation additive provided in the embodiments of this application;

[0040] Figure 2 This is an X-ray diffraction (XRD) test pattern of amorphous lithium sulfide provided in Embodiment 1 of this application. Detailed Implementation

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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" and "the" as 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.

[0046] 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 in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as μg, mg, g, or kg.

[0047] 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.

[0048] The first aspect of this application provides a composite lithium supplement additive, including a core containing an amorphous lithium supplement additive and an encapsulation layer covering the outer surface of the core.

[0049] The composite lithium replenishing additive provided in the first aspect of this application includes a core containing an amorphous lithium replenishing additive and a carbon encapsulation layer covering the outer surface of the core. The amorphous lithium replenishing additive in the core has lower polarization and a lower voltage plateau during charging, which can effectively reduce the activation barrier of the lithium replenishing additive and significantly improve the lithium ion insertion / extraction efficiency, thereby achieving a high lithium replenishment specific capacity of the additive. The encapsulation layer not only improves the stability of the lithium replenishing additive, but also effectively improves the electronic and ion conduction performance of the lithium replenishing material in the core, increases lithium extraction during charging, and also plays a certain role in isolating water and oxygen, thereby improving the stability of the lithium replenishing additive and achieving a stable lithium replenishment effect.

[0050] In some embodiments, the X-ray diffraction pattern of the amorphous lithium supplement additive has at least one characteristic peak between 2θ and 30°, and the peak width of the at least one characteristic peak is 2 to 8°. Compared with crystalline lithium supplement additives, the characteristic peak of amorphous lithium sulfide is wider.

[0051] In some embodiments, the amorphous lithium supplementation additive is selected from at least one of amorphous lithium sulfide (Li2S), lithium nitride (Li3N), lithium oxide (Li2O), lithium fluoride (LiF), and lithium phosphide (Li3P). These amorphous lithium supplementation additives not only have good lithium supplementation effects, but also have low polarization and low activation barriers, which can significantly improve the lithium ion insertion / extraction efficiency.

[0052] In some embodiments, the encapsulation layer includes at least one of an isolation encapsulation layer, an ion conductor encapsulation layer, and an electronic conductor encapsulation layer. These encapsulation layers can effectively improve the electronic and ion conductivity of the lithium-replenishing material in the core, increasing lithium extraction during charging; they also provide some moisture isolation, improving the stability of the cathode lithium-replenishing additive and achieving a stable lithium-replenishing effect. Furthermore, they can ensure the stability, uniform dispersion, and good processing performance of the cathode lithium-replenishing additive in the electrode active slurry and active layer.

[0053] In some embodiments, the content of amorphous lithium supplementation additive in the core is not less than 20%, further not less than 30%, further not less than 50%, further not less than 80%, etc.

[0054] In some embodiments, the mass ratio of amorphous lithium-replenishing additive to crystalline lithium-replenishing additive in the core is (20-60):(40-80), more specifically (40-60):(40-60), and even more specifically (50-60):(40-50). The content of amorphous lithium-replenishing additive in the core of this application effectively reduces the activation potential of the composite lithium-replenishing additive and improves the lithium-ion insertion / extraction efficiency of the additive, thereby achieving a higher lithium-replenishing specific capacity. The higher the content of amorphous lithium sulfide, the better the lithium-ion insertion / extraction effect of the additive.

[0055] In some embodiments, the core particle size D50 is 40–60 nm, and the encapsulation layer thickness is 5–15 nm. The thickness of the encapsulation layer ensures both the specific capacity and electronic conductivity environment of the composite lithium supplementation additive. If the encapsulation layer is too thick, the overall specific capacity of the additive will be reduced because the encapsulation layer does not contribute lithium ions; if the encapsulation layer is too thin, the encapsulation layer will not completely cover the core, which is not conducive to building a good electronic conductivity environment. In addition, a core particle size D50 of 40–60 nm provides a larger active specific surface area, which is beneficial for lithium ion insertion and extraction. If the core particle size is too small, particle agglomeration will be more severe; if the core particle size is too large, the specific surface area will be reduced, which will decrease the lithium ion insertion and extraction efficiency, resulting in poor lithium supplementation effect of the additive. In some specific embodiments, in the composite lithium supplementation additive, the thickness of the encapsulation layer can be 5-8nm, 8-10nm, 10-13nm, 13-15nm, etc., and the particle size D50 of the core can be 40-45nm, 45-50nm, 50-55nm, 55-60nm, etc.

[0056] Based on the structure and performance of the lithium-replenishing additive in the embodiments of the above application, the lithium-replenishing additive in the above application exhibits excellent storage and processability, as well as stable electrochemical performance. For example, tests show that the capacity decay rate of a positive electrode sheet directly prepared with the lithium-replenishing additive in the embodiments of this application, such as a positive electrode sheet prepared by the lithium-replenishing additive with a binder and a conductive agent, after storage for 20 hours at 25% humidity relative to the capacity decay rate after 0.5 hours of storage, is no greater than 30%, and further no greater than 14.5%; after storage for 20 hours at 20% humidity relative to the capacity decay rate after 0.5 hours of storage, it is no greater than 25%, and further no greater than 12.2%; and after storage for 20 hours at 10% humidity relative to the capacity decay rate after 0.5 hours of storage, it is no greater than 20%, and further no greater than 8.8%. This demonstrates that the lithium-replenishing additive in the embodiments of this application has excellent storage properties, high lithium-replenishing effect, and stable lithium-replenishing performance. Ideally, the lithium-replenishing additive in the above application is stored in a dry, oxygen-free environment, such as a vacuum environment, to maximize the electrochemical performance of the lithium-replenishing additive in the above application.

[0057] As attached Figure 1 As shown, a second aspect of this application provides a method for preparing a composite lithium supplementation additive, comprising the following steps:

[0058] S10. Prepare a core containing an amorphous lithium-supplementing additive;

[0059] S20. An encapsulation layer is prepared on the outer surface of the core to obtain a composite lithium supplementation additive.

[0060] The second aspect of this application provides a method for preparing a composite lithium-replenishing additive, which involves preparing a core containing an amorphous lithium-replenishing additive to impart high lithium-ion insertion / extraction efficiency to the composite lithium-replenishing additive; then, an encapsulation layer is prepared on the outer surface of the core to obtain the composite lithium-replenishing additive. The method for preparing the composite lithium-replenishing additive provided in this application is simple, efficient, and suitable for large-scale industrial production and application. Furthermore, the prepared composite lithium-replenishing additive has a low activation barrier and can essentially completely extract lithium ions at relatively low voltages, achieving a high specific capacity for lithium replenishment.

[0061] This application does not specifically limit the preparation method of amorphous lithium replenishment in step S10 above, as long as the amorphous lithium replenishment additive material can be obtained. In some embodiments, the method for preparing the core containing the amorphous lithium replenishment additive can be atomic layer deposition.

[0062] In some embodiments, the core contains at least one amorphous lithium supplementation additive selected from amorphous lithium sulfide, amorphous lithium nitride, amorphous lithium oxide, amorphous lithium fluoride, and amorphous lithium phosphide; these amorphous lithium supplementation additives not only have good lithium supplementation effects, but also have low polarization and low activation barriers, which can significantly improve the lithium ion insertion / extraction efficiency.

[0063] In some specific embodiments, the steps for preparing amorphous lithium sulfide include:

[0064] S11. Dissolve elemental sulfur in an organic solvent to obtain the first reaction solution; wherein the organic solvent has an amino group at the end.

[0065] S12. Under reflux conditions, the first reaction solution is mixed with elemental lithium and reacted to obtain amorphous lithium sulfide.

[0066] The method for preparing amorphous lithium sulfide provided in this application involves dissolving elemental sulfur in an organic solvent with an amino group at the end. The terminal amino group in the organic solvent undergoes a ring-opening reaction with the S8 molecule to generate an amino polysulfide, i.e., the first reaction solution. Then, the amino polysulfide is mixed with elemental lithium to generate amorphous lithium sulfide. Since this reaction process generates a large amount of heat, in order to avoid the evaporation of the solution affecting the formation of amorphous lithium sulfide, the reaction process is carried out under reflux conditions.

[0067] In some embodiments, in step S11 above, the organic solvent is selected from at least one of propylenediamine and ethylenediamine. The organic solvent used in this application embodiment has an amino group at its end. If the organic solvent is a linear molecule, both ends are amino groups, including but not limited to propylenediamine and ethylenediamine. The amino groups at the beginning and end of the organic solvent undergo a ring-opening reaction with the S8 molecule to generate an amino polysulfide, which then reacts with elemental lithium to generate amorphous lithium sulfide. Furthermore, the organic solvent can adsorb onto the surface of the newly formed lithium sulfide through the terminal amino groups, preventing further growth of lithium sulfide and thus avoiding the formation of a crystalline state.

[0068] In some embodiments, the ratio of elemental sulfur to organic solvent is (1-2) g : (50-80) mL; this ratio sufficiently ensures the reaction between elemental sulfur and organic solvent, while the ratio of organic solvent also facilitates the in-situ conversion into the conditions provided by the carbon encapsulation layer. In some specific embodiments, the ratio of elemental sulfur to organic solvent includes, but is not limited to, 1 g : (50-60) mL, 1 g : (60-70) mL, 1 g : (70-80) mL, 2 g : (50-60) mL, 2 g : (60-70) mL, 2 g : (70-80) mL, etc.

[0069] In some embodiments, step S12 above, the step of mixing the first reaction solution with elemental lithium, includes: mixing the first reaction solution with elemental lithium by dropwise addition and reacting. Since the reaction between amino polysulfides and elemental lithium is very rapid and generates a large amount of heat, to ensure a stable, complete, and sufficient reaction, the first reaction solution is mixed with elemental lithium by dropwise addition under reflux conditions.

[0070] In some embodiments, the mass ratio of elemental lithium to elemental sulfur is 1:(2-4). This ratio ensures sufficient efficiency in the formation of amorphous lithium sulfide. If there is too much elemental lithium or too much elemental sulfur, it will increase by-products and reduce product purity.

[0071] In some embodiments, after the first reaction solution is mixed with elemental lithium, the reaction solution is filtered to obtain a solid precipitate, which is then dried under vacuum at 40–60°C for 10–24 h to obtain amorphous lithium sulfide.

[0072] In some embodiments, step S20 above, the step of preparing an encapsulation layer on the outer surface of the core, includes the step of forming at least one of an isolation encapsulation layer, an ion conductor encapsulation layer, and an electronic conductor encapsulation layer on the outer surface of the core.

[0073] In some embodiments, the material used to prepare the isolation encapsulation layer on the outer surface of the core containing the amorphous lithium supplementation additive includes at least one of ceramic, polymer, or carbon materials.

[0074] In some specific embodiments, when the material of the isolation encapsulation layer is a ceramic layer, the ceramic target can be sputtered and deposited on the surface of the core containing amorphous lithium supplementation additives by magnetron sputtering, but not only, wherein the magnetron sputtering conditions are adjusted according to the specific target properties.

[0075] In another specific embodiment, when the material of the isolation encapsulation layer is a polymer layer, the step of forming the polymer isolation encapsulation layer may be: dispersing the core material in a solution containing the polymer, and then vacuum drying to form a dense polymer isolation encapsulation layer on the core surface. The solvent in the solution is a solvent capable of uniformly dispersing or dissolving the polymer, such as one or more of N-methylpyrrolidone, methanol, ethanol, isopropanol, acetone, tetrahydrofuran, and diethyl ether.

[0076] In another specific embodiment, when the material of the isolation and encapsulation layer is a carbon material layer, the method for forming the carbon material isolation and encapsulation layer includes the following steps: dispersing the core material in a solution containing a carbon source, drying it, and then carbonizing it to form a dense carbon isolation and encapsulation layer on the core surface. The carbon source can be, but is not limited to, PEO, and can also be other carbon sources. Any carbon source capable of forming a coating layer on the core surface is suitable for this application. Specifically, for example, the core material is mixed uniformly with PEO, the PEO reaches its melting point at 300°C, and the mixture is uniformly coated on the core surface. The coated material is then sintered in an inert atmosphere at 600°C for 16 hours, resulting in a dense carbon layer.

[0077] In some embodiments, the material used to prepare the electronic conductor encapsulation layer includes at least one of carbon materials, conductive polymers, or conductive oxides; the carbon materials, conductive polymers, and conductive oxides are all materials used in the electronic conductor encapsulation layer contained in the lithium supplementation additive described above. The methods and conditions for forming the electronic conductor encapsulation layer of carbon materials, conductive polymers, and conductive oxides are specifically formulated according to the methods for forming carbon materials, conductive polymers, or conductive oxides. In some specific embodiments, the method for forming the electronic conductor encapsulation layer may employ chemical deposition, magnetron sputtering, or atomic layer deposition to form an isolated conductive encapsulation layer.

[0078] In some embodiments, the material used to prepare the ion conductor encapsulation layer includes at least one of perovskite, NASICON, garnet, or polymer solid electrolytes; the method and conditions for forming the ion conductor encapsulation layer are specifically in accordance with the method for forming perovskite, NASICON, garnet, or polymer solid electrolytes.

[0079] In some specific embodiments, the step of preparing a carbon material encapsulation layer on the outer surface of a core containing an amorphous lithium sulfide additive includes:

[0080] S11. Dissolve elemental sulfur in organic solvents with amino groups such as propylenediamine and ethylenediamine to obtain the first reaction solution;

[0081] S12. Under reflux conditions, the first reaction solution is mixed with elemental lithium and reacted to obtain amorphous lithium sulfide.

[0082] S21. Carbon coating of amorphous lithium sulfide is carried out by calcination to obtain a composite lithium supplement additive.

[0083] The composite lithium supplement additive prepared in this application embodiment contains amorphous lithium sulfide in its core, and Li in an amorphous state... + With S 2- The bonding force of lithium sulfide is much weaker than in the crystalline state, resulting in less polarization and a lower voltage plateau during charging. This effectively lowers the activation barrier of lithium sulfide, significantly improving the lithium-ion insertion / extraction efficiency and thus achieving a higher specific capacity for lithium replenishment. The carbon encapsulation layer effectively increases the conductivity of the additive, further reducing its polarization and facilitating the extraction of lithium ions from lithium sulfide during charging, thereby further enhancing the specific capacity.

[0084] In some embodiments, step S21 above, the step of carbon coating amorphous lithium sulfide by calcination treatment, includes: holding the amorphous lithium sulfide at an inert atmosphere at a temperature of 400-500°C for 1-3 hours to obtain a composite lithium supplement additive. In this embodiment, because amorphous lithium sulfide contains residual organic solvents, sintering in an inert atmosphere can convert them in situ into amorphous carbon that coats the surface of the lithium sulfide, forming a carbon encapsulation layer. If the temperature is too low, carbonization will be incomplete, resulting in low conductivity of the carbon layer. If the temperature is too high, due to the poor thermal stability of amorphous lithium sulfide, excessive conversion of amorphous lithium sulfide into crystals may occur. A sintering temperature of 400-500°C can reduce the proportion of amorphous lithium sulfide converted into lithium sulfide crystals.

[0085] In some embodiments, in the composite lithium replenishment additive, the mass fraction of the encapsulation layer is 20-40%, and the mass fraction of the core is 60-80%. In the composite lithium replenishment additive of this application, the mass ratio of the encapsulation layer and the core simultaneously ensures both the added specific capacity and the electronic conductivity environment. If the encapsulation layer content is too high, the overall specific capacity will be reduced because the encapsulation material does not contribute lithium ions; if the encapsulation layer content is too low, it is not conducive to forming a complete and uniformly thick encapsulation layer on the outer surface of the core, resulting in incomplete encapsulation and hindering the construction of a good electronic conductivity environment. In some specific embodiments, the mass fraction of the encapsulation layer in the composite lithium replenishment additive can be 20%, in which case the mass fraction of the core is 80%; or the mass fraction of the encapsulation layer can be 30%, in which case the mass fraction of the core is 70%; or the mass fraction of the encapsulation layer can be 40%, in which case the mass fraction of the core is 60%, etc. In some specific embodiments, the thickness of the encapsulation layer in the composite lithium replenishment additive is 5-15 nm, and the particle size D50 of the core is 40-60 nm.

[0086] In the core of the composite lithium-replenishing additive in this application embodiment, compared to crystalline lithium sulfide, the amorphous lithium-replenishing additive exhibits less polarization and a lower voltage plateau during charging. Under the same voltage window, it can release more lithium ions, resulting in higher specific capacity. Simultaneously, it produces virtually no gas and exhibits good chemical stability. Therefore, a higher content of amorphous lithium-replenishing additive in the core of the composite lithium-replenishing additive is more conducive to lithium-ion intercalation and deintercalation, thereby giving the additive higher specific capacity and other electrochemical properties.

[0087] In some embodiments, the core of the composite lithium supplement additive contains at least 20% amorphous lithium supplement additive by mass, effectively ensuring improved lithium-ion extraction from the additive, increasing the additive's specific capacity, and thus improving the lithium supplementation effect when added to the positive electrode. In some embodiments, the core of the composite lithium supplement additive contains 20-60% amorphous lithium sulfide by mass and 40-80% crystalline lithium sulfide by mass. Further, the ratio of amorphous lithium sulfide to crystalline lithium sulfide is (40-60):(40-60), and further, the ratio of amorphous lithium sulfide to crystalline lithium sulfide is (50-60):(40-50).

[0088] Thirdly, this application also provides a cathode material. The cathode material of this application includes a cathode active material and the cathode lithium-supplementing additive mentioned above. Thus, the cathode material of this application has excellent lithium-supplementing performance and good processing performance, which can improve the quality of the cathode active material layer, thereby improving the quality of the cathode active material layer and imparting electrochemical performance to the corresponding cathode sheet.

[0089] In the embodiments, the content of the positive electrode lithium supplementation additive in the positive electrode material of the above-mentioned application embodiments can be controlled. The mass content of the positive electrode material in the positive electrode active layer of the above-mentioned application embodiments can be 1.5%-5.5%, and more specifically 2.0%.

[0090] In some embodiments, the mass percentage of the composite lithium-replenishing additive in the cathode material is 0.1% to 4%, a ratio that precisely compensates for the loss of active lithium during the first charge of the battery. If the amount of composite lithium-replenishing additive added to the cathode sheet is too low, the lost active lithium in the cathode material cannot be fully replenished, which is detrimental to improving the battery's energy density and capacity retention. If the amount of composite lithium-replenishing additive added to the cathode material is too high, it may lead to severe lithium plating on the anode and increase costs. In some specific embodiments, the mass percentage of the composite lithium-replenishing additive in the cathode material can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, etc.

[0091] In other embodiments, the positive electrode active material contained in the positive electrode material of this application embodiment can be a phosphate positive electrode active material and a ternary positive electrode active material. In specific embodiments, it includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0092] The fourth aspect of this application provides a positive electrode sheet containing a composite lithium supplement additive prepared by the above method, or containing the above-described composite lithium supplement additive.

[0093] The positive electrode provided in the fourth aspect of this application contains the above-mentioned composite lithium replenishing additive. This additive has a low activation barrier and can basically completely extract lithium ions at a low voltage, thus achieving a high lithium replenishing specific capacity. Therefore, it can play a good lithium replenishing effect in the positive electrode, making up for the active lithium ions consumed by the formation of the SEI film during the first charge of the battery, thereby effectively maintaining the specific capacity of the positive electrode and improving the capacity retention rate of the positive electrode.

[0094] In some embodiments, the positive electrode includes a current collector and an active material layer laminated together. The mass percentage of the composite lithium-replenishing additive in the active material layer is 0.1% to 4%, a ratio that precisely compensates for the loss of active lithium during the first charge of the battery. If the amount of composite lithium-replenishing additive in the positive electrode is too low, the lost active lithium in the positive electrode material cannot be fully replenished, which is detrimental to improving the battery's energy density and capacity retention. If the amount of composite lithium-replenishing additive in the positive electrode is too high, it may lead to severe lithium plating on the negative electrode and increase costs. In some specific embodiments, the mass percentage of the composite lithium-replenishing additive in the active material layer of the positive electrode can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, etc.

[0095] In some embodiments, the positive electrode active material in the positive electrode sheet includes, but is not limited to, at least one of lithium iron phosphate, lithium cobalt oxide, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. These positive electrode materials have high specific capacity, which is beneficial to improving the energy density of the battery.

[0096] In some embodiments, the positive electrode sheet may also include a positive current collector, and the positive electrode active layer may also include components such as conductive agents and binders. The embodiments of this application do not specifically limit these materials, and appropriate materials can be selected according to actual application requirements.

[0097] In some embodiments, the positive current collector includes, but is not limited to, any one of copper foil and aluminum foil.

[0098] In some embodiments, the binder content in the positive electrode active layer is 2wt%-4wt%. In specific embodiments, the binder content can be typical but not limited to 2wt%, 3wt%, 4wt%, etc. In specific embodiments, the binder includes one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0099] In some embodiments, the conductive agent content in the positive electrode active layer is 3wt%-5wt%. In specific embodiments, the conductive agent content can be a typical but not limited content such as 3wt%, 4wt%, or 5wt%. In specific embodiments, the conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes.

[0100] In some embodiments, the preparation process of the positive electrode sheet is as follows: the positive electrode active material, composite lithium supplementation additive, conductive agent and binder are mixed to obtain an electrode slurry, the electrode slurry is coated on the current collector, and the positive electrode sheet is prepared by drying, rolling and die cutting.

[0101] The fifth aspect of this application provides a secondary battery, which includes the above-described positive electrode sheet.

[0102] The secondary battery provided in the fifth aspect of this application includes the aforementioned positive electrode sheet, which contains the aforementioned composite lithium-replenishing additive. This effectively compensates for the active lithium ions consumed during the first charge due to the formation of the SEI film, effectively maintaining the specific capacity of the positive electrode sheet and improving its capacity retention rate. Therefore, the secondary battery provided in this application provides high energy density and good capacity retention rate.

[0103] The secondary battery in this application embodiment can be a lithium-ion battery or a lithium metal battery.

[0104] The negative electrode, electrolyte, separator, etc. of the secondary battery in this application embodiment are not specifically limited and can be applied to any battery system.

[0105] To enable those skilled in the art to clearly understand the above-described implementation details and operations, and to demonstrate the significant improvement in the performance of the composite lithium-replenishing additive, its preparation method, positive electrode, and secondary battery in the embodiments of this application, the following examples illustrate the above technical solutions.

[0106] Example 1

[0107] A composite Li2S lithium supplementary additive, the preparation of which includes the following steps:

[0108] 1 g of elemental sulfur was dissolved in 50 mL of propylenediamine. After complete dissolution, the solution was slowly added dropwise to a flask containing approximately 0.5 g of lithium bars. The solution was refluxed to prevent solvent loss until all lithium was consumed. The reaction solution was filtered to obtain amorphous lithium sulfide. The precipitate was then vacuum dried for 12 hours. The dried precipitate was placed in a corundum boat, and argon gas was introduced into a tube furnace. The temperature was raised to 400 °C and held for 2 hours to obtain a carbon-coated composite lithium supplement, denoted as H-Li2S@C-1.

[0109] A lithium-ion battery includes the following preparation steps:

[0110] ① Preparation of positive electrode sheet: The composite lithium supplement additive and lithium cobalt oxide are mixed at a mass ratio of 5:90 to obtain a mixture. The mixture is then mixed with SP:PVDF at a mass ratio of 95:2:3 and ball-milled for 60 minutes. The speed is set to 30Hz. After homogenization, coating, drying and cutting, positive electrode sheets are prepared. The positive electrode sheets are baked in a vacuum oven at 100℃ to remove trace amounts of water.

[0111] ② Negative electrode: A lithium metal sheet with a diameter of 16mm;

[0112] ③ Electrolyte: 1 mol / L LiPF6 solution, the solvent is composed of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1;

[0113] ④Separator: Polypropylene microporous diaphragm.

[0114] ⑤ Lithium-ion battery assembly: Assemble lithium-ion batteries in an inert atmosphere glove box according to the assembly sequence of lithium metal sheet-separator-electrolyte-positive electrode.

[0115] Example 2

[0116] A composite Li2S lithium supplement additive, which differs from Example 1 in that the organic solvent is replaced with ethylenediamine, and the product is labeled as H-Li2S@C-2.

[0117] A lithium-ion battery differs from Example 1 in that the lithium-replenishing additive in the positive electrode sheet is the composite lithium-replenishing additive prepared in Example 2.

[0118] Example 3

[0119] A composite Li2S lithium supplement additive, which differs from Example 1 in that the obtained carbon-coated Li2S composite lithium supplement additive is further subjected to secondary carbon coating by a solvothermal method to achieve more complete coating, and the product is labeled as H-Li2S@C-3.

[0120] A lithium-ion battery differs from Example 1 in that the lithium replenishing additive in the positive electrode sheet is the composite lithium replenishing additive prepared in Example 3.

[0121] Example 4

[0122] A composite Li2S lithium supplement additive differs from Example 1 in that the heat treatment temperature of the dried precipitate is reduced from 400°C to 300°C, resulting in a higher proportion of amorphous components in the obtained composite lithium supplement additive. The product is labeled as H-Li2S@C-4.

[0123] A lithium-ion battery differs from Example 1 in that the lithium replenishing additive in the positive electrode sheet is the composite lithium replenishing additive prepared in Example 4.

[0124] Example 5

[0125] A composite LiF lithium supplement additive was developed by radio frequency sputtering (RF power: 30W, via pure argon inflow, ambient pressure maintained at 10). -2 LiF thin films were grown on silicon wafers using mbar. The resulting material was a crystalline / amorphous composite lithium supplement additive. The resulting film was ball-milled, then sieved, and carbon-coated using a solvothermal method to obtain H-LiF@C.

[0126] Example 6

[0127] A composite Li3N lithium supplement additive is prepared by placing purchased Li3N powder (Aladdin, L303263 lithium nitride, 99.9%) in a tantalum boat and evaporating it by resistance heating. The total evaporation pressure in the vacuum chamber is kept constant. At 50 mPa, the temperature of the boat is adjusted to 550-800℃ to achieve the deposition of crystalline / amorphous composite Li3N on a substrate. Then, the powder is ball-milled, sieved, and carbon-coated by solvothermal methods. The resulting sample is denoted as H-Li3N@C.

[0128] Comparative Example 1

[0129] Commercially available crystalline Li2S (Aladdin, L166537, 99.98%) was purchased and mixed with PVP and heat-treated at 700°C to obtain a crystalline Li2S@C-1 composite material.

[0130] Comparative Example 2

[0131] Li2SO4 and PVP were ball-milled and mixed, and then heat-treated at 800℃ in an inert atmosphere to obtain a crystalline Li2S@C-2 composite material.

[0132] Comparative Example 3

[0133] In an inert atmosphere, lithium metal and CoF3 powder are mixed in a molar ratio of 3:1 and heated to 240°C. The lithium becomes molten. The mixture is then mechanically stirred to react and generate a crystalline Co / LiF composite material.

[0134] Comparative Example 4

[0135] A certain amount of lithium foil is placed in a tube furnace, and nitrogen gas at 100 sccm is continuously introduced into it. The furnace is heated to 300°C and held at that temperature for 24 hours to obtain crystalline Li3N. Then, the Li3N is ball-milled and crushed, and carbon is coated using a solvothermal method to obtain crystalline Li3N@C.

[0136] Furthermore, to verify the progressiveness of the embodiments of this application, the materials prepared in Examples 1-6 and Comparative Examples 1-4 were subjected to the following performance tests:

[0137] Related feature tests

[0138] 1. The amorphous lithium sulfide prepared in Example 1 was subjected to XRD testing, and the test results are shown in the attached figure. Figure 2 As shown, the XRD characteristic peaks of the amorphous lithium sulfide prepared in Example 1 are the same as those of the crystalline lithium sulfide. The characteristic peaks of the amorphous lithium sulfide are wider, with obvious characteristic peaks between 2θ and 30°, and at least one characteristic peak has a width of 8°.

[0139] 2. Moisture resistance test of positive electrode lithium supplementation additive:

[0140] To further evaluate the moisture resistance of the aforementioned lithium-replenishing materials, this application separately prepared electrode sheets by mixing the aforementioned composite lithium-replenishing additive, conductive agent, and binder (without adding positive electrode active material). The specific steps are as follows: The lithium-replenishing materials in each example or comparative example were mixed with SP and PVDF at a mass ratio of 80:8:12 and ball-milled for 60 min; the rotation speed was set to 30 Hz; after homogenization-coating-drying-cutting operations, positive electrode sheets were prepared respectively. The positive electrode sheets were baked in a vacuum oven at 100°C to remove trace amounts of water. Except for the positive electrode sheets, the other battery components are consistent with the above description and remain unchanged.

[0141] Here, taking Example 1 as an example and Comparative Example 1 as a reference, we tested the specific capacity of the electrode sheet of Example 1 under different humidity conditions (25%, 20%, 10%) and after different periods of storage. The results are shown in Tables 2, 3, and 4 below:

[0142] Table 2

[0143]

[0144] Table 3

[0145]

[0146]

[0147] Table 4

[0148]

[0149] The test results above show that the specific capacity of the positive electrode sheet (excluding positive electrode active material) prepared by the positive electrode composite lithium supplementation additive in Example 1 of this application does not change significantly when stored under different humidity conditions. Under humidity conditions of 25%, 20%, and 10%, the specific capacity reduction rates after 20 hours of storage relative to 0.5 hours are 14.5%, 12.2%, and 8.8%, respectively. The lower the humidity, the smaller the change in specific capacity. Therefore, the composite lithium supplementation additive in the positive electrode sheet of this application not only has a good lithium supplementation effect but also good stability and stable lithium supplementation.

[0150] 3. Electrochemical performance testing of lithium-ion batteries:

[0151] The composite lithium-replenishing additives prepared in Examples 1-6 and Comparative Examples 1-4 were assembled into identical lithium-ion coin cells under the same conditions (with the composite lithium-replenishing additive as the variable), and their performance was tested according to the following methods:

[0152] Charge the button cell to 4.3V at a constant current and constant voltage rate of 0.05C, cut off the current at 0.01C, let it rest for 5 minutes, and then discharge it to 3.0V at a rate of 0.05C.

[0153] The relevant performance test results are shown in Table 1 below:

[0154] Table 1

[0155]

[0156] As shown in Table 1 above, compared with lithium-ion batteries without lithium replenishment additives (control group) and those with crystalline Li2S@C prepared in Comparative Examples 1-2, lithium-ion batteries with composite Li2S lithium replenishment additives prepared in Examples 1-4 of this application exhibit superior initial charge specific capacity and a higher specific capacity increase. This indicates that lithium ions are more easily extracted from amorphous Li2S, resulting in high lithium ion insertion / extraction efficiency and thus achieving a higher specific capacity for lithium replenishment. Similarly, comparing Example 5 with Comparative Example 3, and Example 6 with Comparative Example 4, similar trends can be observed with LiF and Li3N lithium replenishment additives. These results demonstrate the advantages of amorphous / crystalline composite lithium replenishment additives in terms of lithium removal and performance.

[0157] 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 composite lithium supplementing additive, characterized by, The composite lithium supplement additive includes a core containing an amorphous lithium supplement additive and an encapsulation layer covering the outer surface of the core; the content of the amorphous lithium supplement additive in the core is not less than 20%; the composite lithium supplement additive is a positive electrode lithium supplement additive; the amorphous lithium supplement additive is amorphous lithium sulfide; the mass ratio of the amorphous lithium supplement additive to the crystalline lithium supplement additive in the core is (20~60):(40~80); the particle size D50 of the core is 40~60 nm; the preparation steps of the amorphous lithium sulfide include: dissolving elemental sulfur in an organic solvent to obtain a first reaction solution; wherein the end group of the organic solvent is amino; under reflux conditions, mixing and reacting the first reaction solution with elemental lithium, and separating to obtain the amorphous lithium sulfide; the preparation steps of the encapsulation layer include: calcining the amorphous lithium sulfide in an inert atmosphere at a temperature of 400℃~500℃ to form the encapsulation layer.

2. The composite lithium supplement additive as described in claim 1, characterized in that, In the X-ray diffraction pattern of the amorphous lithium supplementation additive, there is at least one characteristic peak between 2θ and 30°, and the peak width of the at least one characteristic peak is 2 to 8°. And / or, the encapsulation layer includes at least one of an isolation encapsulation layer, an ion conductor encapsulation layer, and an electronic conductor encapsulation layer.

3. The composite lithium supplement additive as described in claim 1, characterized in that, The thickness of the encapsulation layer is 5~15 nm.

4. The composite lithium supplement additive according to any one of claims 1-3, characterized in that, The positive electrode prepared from the composite lithium-supplementing additive, conductive agent, and binder exhibits a capacity decay rate of no more than 30% after 20 hours of storage at 25% ambient humidity compared to 0.5 hours of storage; and / or The positive electrode prepared from the composite lithium-supplementing additive, conductive agent, and binder exhibits a capacity decay rate of no more than 25% after 20 hours of storage at 20% ambient humidity compared to the capacity decay rate after 0.5 hours of storage; and / or The positive electrode sheet prepared by the positive electrode lithium supplementation additive, conductive agent and binder has a capacity decay rate of no more than 20% after 20 hours of storage at an ambient humidity of 10% compared with the capacity decay rate after 0.5 hours of storage.

5. A method for preparing a composite lithium supplement additive as described in any one of claims 1 to 4, characterized in that, Includes the following steps: A core containing an amorphous lithium supplementing additive is prepared; wherein the content of the amorphous lithium supplementing additive in the core is not less than 20%; the amorphous lithium supplementing additive is amorphous lithium sulfide; and the particle size D50 of the core is 40~60 nm. An encapsulation layer is prepared on the outer surface of the core to obtain a composite lithium supplement additive; the composite lithium supplement additive is a positive electrode lithium supplement additive.

6. The method for preparing the composite lithium supplementation additive as described in claim 5, characterized in that, The step of preparing an encapsulation layer on the outer surface of the core includes: forming at least one of an isolation encapsulation layer, an ion conductor encapsulation layer, and an electronic conductor encapsulation layer on the outer surface of the core.

7. The preparation method of the composite lithium supplementation additive as described in claim 6, characterized in that, The steps for preparing the amorphous lithium sulfide include: Elemental sulfur is dissolved in an organic solvent to obtain a first reaction solution; wherein the organic solvent has an amino group at the end. Under reflux conditions, the first reaction solution is mixed with elemental lithium and reacted to obtain amorphous lithium sulfide.

8. The method for preparing the composite lithium supplementation additive as described in claim 7, characterized in that, The organic solvent is selected from at least one of propylenediamine and ethylenediamine; And / or, the step of mixing the first reaction solution with elemental lithium includes: mixing the first reaction solution with elemental lithium by dropwise addition and reacting; And / or, the ratio of the elemental sulfur to the organic solvent is (1~2) g: (50~80) mL; And / or, the mass ratio of the lithium element to the sulfur element is 1:(2~4).

9. A positive electrode material, characterized in that, It includes positive electrode active materials and composite lithium supplementation additives as described in any one of claims 1 to 4, or composite lithium supplementation additives prepared by the method described in any one of claims 5 to 8.

10. The cathode material as described in claim 9, characterized in that, The mass percentage of the composite lithium supplementation additive in the cathode material is 0.1-4%.

11. A positive electrode plate, characterized in that, The positive electrode sheet contains the positive electrode material as described in claim 9.

12. A secondary battery, characterized in that, The secondary battery includes the positive electrode as described in claim 11.

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