Composite negative electrode lithium supplement agent, preparation method thereof and lithium ion battery

Abstract

The invention discloses a composite negative electrode lithium supplementing agent, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium supplementing agent materials, and the composite negative electrode lithium supplementing agent comprises a silicon lithium compound, and a lithium nitride layer, a lithium-containing inorganic salt layer and a conductive agent layer which sequentially coat the surface of the silicon lithium compound. The negative electrode lithium supplementing agent is high in stability, and the service life of the battery can be effectively prolonged.

Description

Technical Field

[0001] This application relates to the field of lithium replenishment materials technology, and in particular to composite negative electrode lithium replenishment agents and their preparation methods, and lithium-ion batteries. Background Technology

[0002] With the rapid development of the lithium battery market, lithium-ion batteries have gradually become a popular choice for next-generation high-energy-density batteries due to their high energy density and low electrode potential. Currently, the performance of lithium-ion batteries is nearing its limit. To further improve energy density and cycle performance, using lithium replenishment agents is a promising development direction, and negative electrode lithium replenishment is a very direct and efficient method. Silicon-based materials can themselves be used as negative electrode materials for lithium-ion batteries, possessing very high capacity, with a theoretical capacity reaching 4200 mAh / g. However, silicon-based negative electrodes experience significant volume expansion during charging, which easily damages the SEI film, leading to rapid cycle decay and severely impacting their practical application.

[0003] Lithium silicon compounds (Li x Lithium silicon (Si) has very high capacity, making it a promising candidate for use as a negative electrode lithium replenisher. However, silicon itself has poor conductivity, and lithium silicon compounds exhibit very poor stability in the natural environment. In practical applications of lithium-ion batteries, this leads to rapid lithium-ion loss, thus affecting the battery's lifespan.

[0004] The above content is only used to help understand the technical solution of this application and does not represent an admission that the above content is prior art. Summary of the Invention

[0005] The main objective of this application is to provide a composite negative electrode lithium replenishing agent and its preparation method, as well as a lithium-ion battery, in order to solve the technical problem that the poor stability of existing negative electrode lithium replenishing agents leads to a short service life of lithium-ion batteries.

[0006] To achieve the above objectives, this application proposes a composite negative electrode lithium replenishing agent, which includes a lithium silicon compound and a lithium nitride layer, a lithium-containing inorganic salt layer, and a conductive agent layer sequentially coated on the surface of the lithium silicon compound.

[0007] In one feasible embodiment, the lithium-containing inorganic salt in the lithium-containing inorganic salt layer includes at least one of lithium sulfate, lithium sulfite, lithium phosphate, lithium carbonate, lithium fluoride, lithium nitrate, and lithium nitrite; And / or, the conductive agent in the conductive agent layer includes at least one of carbon nanotubes, carbon black, flake graphite, and graphene.

[0008] In one feasible embodiment, the particle size of the composite negative electrode lithium replenishing agent is 1~2μm.

[0009] This application also provides a method for preparing a composite negative electrode lithium replenishing agent, the preparation method comprising the following steps: Lithium metal is heated to a molten state, and silicon-based materials are added to obtain a lithium silicon compound; Nitrogen gas was introduced into the silicon-lithium compound and reacted at a constant temperature. After cooling, the compound was pulverized to obtain a silicon-lithium compound coated with a lithium nitride layer. The lithium nitride-coated silicon-lithium compound is mixed with a lithium-containing inorganic salt and calcined to form a material having the lithium-containing inorganic salt layer. A composite negative electrode lithium replenishing agent is prepared by uniformly mixing a slurry containing a conductive agent with a material having a lithium-containing inorganic salt layer by spraying.

[0010] In one feasible embodiment, the mass ratio of the lithium nitride-coated silicon-lithium compound to the lithium-containing inorganic salt is 100:(1~5); And / or, the mass ratio of the material having the lithium-containing inorganic salt layer to the slurry containing the conductive agent is 10:(1~2).

[0011] In one feasible embodiment, the silicon-based material includes at least one of elemental silicon, silicon suboxide, and silicon dioxide; And / or, the particle size of the silicon-based material is 50~500 nm; And / or, the heating temperature of the lithium metal is 220~250℃; And / or, the molar ratio of the silicon-based material to lithium metal is 1:(4.5~5.0). And / or, the reaction time to obtain the silicon-lithium compound is 12–36 h.

[0012] In one feasible embodiment, the temperature of the isothermal reaction after nitrogen gas is introduced is 400~500 °C; And / or, the isothermal reaction time after nitrogen gas is introduced is 4~8 h; And / or, the particle size of the lithium silicon compound coated by the lithium nitride layer is 0.5~2μm.

[0013] In one feasible embodiment, after the lithium nitride-coated silicon-lithium compound is mixed with a lithium-containing inorganic salt, the calcination temperature is 700~900℃ and the calcination time is 4~8h.

[0014] In one feasible embodiment, the mass ratio of conductive agent, polyvinylidene fluoride, dispersant and N-methylpyrrolidone in the slurry is (0.5-10):(0.5-1):(0.3-1):(88-98.7).

[0015] This application also provides a lithium-ion battery, which contains a composite negative electrode lithium replenishing agent as described above, or a composite negative electrode lithium replenishing agent prepared by the method described above.

[0016] One or more technical solutions proposed in this application have at least the following technical effects: the composite negative electrode lithium replenisher includes a lithium silicon compound and a lithium nitride layer, a lithium-containing inorganic salt layer, and a conductive agent layer sequentially coated on the surface of the lithium silicon compound. Lithium nitride can replenish lithium and has good stability; its combination with the lithium silicon compound increases the stability of the core and suppresses structural changes in the core under slight stress or temperature variations. The dense, continuous, and uniform lithium-containing inorganic salt layer reduces the contact between the core and air and moisture, improving the stability of the lithium replenisher. The conductive agent layer reduces the material's contact with air and moisture and ensures that the lithium replenisher can release lithium ions uniformly and efficiently during discharge, further improving the material's stability. The core-shell structured composite negative electrode lithium replenisher provided in the embodiments of this application has good stability and can improve the service life of lithium-ion batteries. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

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

[0019] Figure 1 A schematic flowchart illustrating the preparation method of the composite negative electrode lithium replenishing agent provided in an embodiment of this application; Figure 2 XRD pattern of a composite negative electrode lithium replenishing agent provided in an embodiment of this application; Figure 3 The cycling performance diagram of a full battery with added lithium supplement provided in an embodiment of this application.

[0020] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] The composite negative electrode lithium replenishing agent and its preparation method, as well as embodiments of the lithium-ion battery, of this application are disclosed in detail below with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0023] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0024] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0025] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0026] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0027] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0028] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0029] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the technical solution of this application is further described below in conjunction with the accompanying drawings and embodiments. However, this application is not limited to the listed embodiments, but should also include any other well-known modifications within the scope of the claims made in this application.

[0030] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0031] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0032] In conventional technologies, lithium silicon compounds (Li x Si has very high capacity, making it a promising candidate for use as a lithium supplement in negative electrodes. However, silicon itself has relatively poor conductivity, and lithium silicon compounds (Li...) x Si has very poor stability in the natural environment. In the actual application of lithium-ion batteries, it will continuously lose lithium ions, thus affecting the service life of lithium-ion batteries.

[0033] This application provides a solution whereby a composite negative electrode lithium replenisher comprises a lithium silicon compound and, sequentially coated on the surface of the lithium silicon compound, a lithium nitride layer, a lithium-containing inorganic salt layer, and a conductive agent layer. Lithium nitride serves two purposes: lithium replenishment and good stability. When combined with the lithium silicon compound, it increases the stability of the core and suppresses structural changes in the core under slight stress or temperature variations. The dense, continuous, and uniform lithium-containing inorganic salt layer reduces the contact between the core and air and moisture, improving the stability of the lithium replenisher. The conductive agent layer further reduces the material's contact with air and moisture and ensures that the lithium replenisher releases lithium ions uniformly and efficiently during discharge, further enhancing the material's stability. The core-shell structured composite negative electrode lithium replenisher provided in this application exhibits good stability and can improve the lifespan of lithium-ion batteries.

[0034] Based on this, the first aspect of the present application provides a composite negative electrode lithium replenishing agent, the composite negative electrode lithium replenishing agent comprising a lithium silicon compound and a lithium nitride layer, a lithium-containing inorganic salt layer and a conductive agent layer sequentially coated on the surface of the lithium silicon compound.

[0035] In one feasible embodiment, the lithium silicon compound is the core component of the composite negative electrode lithium replenishment agent. Silicon has a high theoretical specific capacity (approximately 4200 mAh / g), and the lithium silicon compound formed with lithium can serve as a lithium source, releasing lithium during battery charging and discharging to replenish the battery with lithium elements, thereby improving the battery's energy density.

[0036] In one feasible embodiment, lithium nitride (Li3N) is coated onto the surface of the lithium silicon compound to form a coating layer. Lithium nitride possesses excellent ionic conductivity, which promotes the transport of lithium ions between the inside and outside of the composite negative electrode lithium replenishment agent, improving lithium replenishment efficiency. Simultaneously, it can also protect the lithium silicon compound to a certain extent, preventing it from reacting with substances in the external environment and improving the stability of the composite negative electrode lithium replenishment agent.

[0037] In one feasible embodiment, a lithium-containing inorganic salt layer serves as a coating layer, further encapsulating the lithium nitride layer. The lithium-containing inorganic salt can provide an additional lithium source, increasing the lithium content of the composite negative electrode lithium replenishment agent. Furthermore, these inorganic salts can improve the surface properties of the composite negative electrode lithium replenishment agent, enhance its compatibility with the electrode material, and contribute to improving battery performance.

[0038] In one feasible embodiment, the conductive agent layer is the outermost coating layer. The conductive agent can improve the electronic conductivity of the composite negative electrode lithium replenishment agent, ensuring that electrons can be smoothly transferred during battery charging and discharging, reducing the battery's internal resistance, and improving the battery's charge and discharge efficiency and rate performance.

[0039] In one feasible embodiment, the lithium-containing inorganic salt in the lithium-containing inorganic salt layer includes at least one of lithium sulfate, lithium sulfite, lithium phosphate, lithium carbonate, lithium fluoride, lithium nitrate, and lithium nitrite; In one feasible embodiment, the conductive agent in the conductive agent layer includes at least one of carbon nanotubes, carbon black, flake graphite, and graphene.

[0040] Alternatively, carbon nanotubes possess excellent one-dimensional electrical conductivity and a high aspect ratio, enabling them to form a well-conducting network.

[0041] Alternatively, carbon black is a commonly used conductive additive with a high specific surface area and good dispersibility.

[0042] Alternatively, flake graphite has a good layered structure and electrical conductivity; graphene has extremely high electron mobility and electrical conductivity.

[0043] Optionally, selecting different conductive agents or combinations thereof can optimize the conductivity of the composite negative electrode lithium replenishment agent.

[0044] In one feasible implementation, the particle size of the composite negative electrode lithium replenishing agent is 1~2μm.

[0045] Optionally, the particle size of the composite negative electrode lithium replenishing agent can be 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, etc.

[0046] Optionally, a suitable particle size is crucial for the performance of composite negative electrode lithium replenishing agents. Particles that are too small may lead to agglomeration, affecting their dispersibility in the electrode material; while particles that are too large may affect the diffusion rate of lithium ions and the electronic conduction efficiency. A particle size range of 1–2 μm can provide suitable lithium ion diffusion paths and electronic conduction channels while ensuring good dispersibility, which is beneficial for improving battery performance.

[0047] The composite negative electrode lithium replenisher in this embodiment includes a lithium silicon compound and a lithium nitride layer, a lithium-containing inorganic salt layer, and a conductive agent layer sequentially coated on the surface of the lithium silicon compound. Lithium nitride serves two purposes: lithium replenishment and good stability. Combined with the lithium silicon compound, it increases the stability of the core and suppresses structural changes in the core under slight stress or temperature variations. The dense, continuous, and uniform lithium-containing inorganic salt layer reduces the contact between the core and air and moisture, improving the stability of the lithium replenisher. The conductive agent layer further reduces the material's contact with air and moisture and ensures that the lithium replenisher releases lithium ions uniformly and efficiently during discharge, further enhancing the material's stability. The core-shell structured composite negative electrode lithium replenisher provided in this embodiment exhibits good stability and can improve the lifespan of lithium-ion batteries.

[0048] Based on this, the second aspect of this application provides a method for preparing a composite negative electrode lithium replenishing agent, referring to... Figure 1 The preparation methods of composite negative electrode lithium replenishing agents include: Step S10: Heat lithium metal to a molten state, add silicon-based material, and obtain a lithium silicon compound; In one feasible embodiment, metallic lithium becomes molten after being heated to a certain temperature. At this point, it exhibits high activity and can chemically react with silicon-based materials to form lithium silicon compounds. These lithium silicon compounds, as the core of the composite negative electrode lithium replenishment agent, are the main source of lithium storage and release.

[0049] In one feasible embodiment, the silicon-based material includes at least one of elemental silicon, silicon suboxide, and silicon dioxide; In one feasible implementation, the particle size of the silicon-based material is 50~500 nm; Optionally, the particle size of the silicon-based material can be 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, etc.

[0050] Optionally, nanoscale silicon-based materials possess a large specific surface area, increasing the contact area with molten lithium metal, thereby enhancing reactivity and allowing the reaction to proceed more fully and rapidly, which is beneficial for forming uniform lithium silicon compounds. If the particle size of the silicon-based material is too small, its surface energy is too high, making it prone to agglomeration, leading to uneven reaction and affecting the quality of the formed lithium silicon compound. If the particle size of the silicon-based material is too large, its specific surface area decreases, reducing the contact area with lithium metal, decreasing reactivity, slowing the reaction rate, and potentially causing incomplete reaction, affecting the yield and quality of the lithium silicon compound. It also makes dispersion in molten lithium difficult, easily leading to localized uneven reaction and unstable performance of the resulting lithium silicon compound. An appropriate particle size range helps the silicon-based material to disperse uniformly in molten lithium, avoiding agglomeration, ensuring the reaction proceeds uniformly throughout the system, and obtaining a stable lithium silicon compound.

[0051] In one feasible implementation, the heating temperature of metallic lithium is 220~250°C; Optionally, the heating temperature of lithium metal can be 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, etc.

[0052] Optionally, lithium metal has a melting point of approximately 180.5°C. Within a temperature range of 220-250°C, lithium can fully melt and exhibits good fluidity, facilitating thorough contact and reaction with silicon-based materials. This temperature range helps prevent lithium volatilization due to excessively high temperatures, reducing lithium loss and minimizing the possibility of other side reactions caused by high temperatures, thus ensuring the safety of the reaction and the purity of the product.

[0053] In one feasible implementation, the molar ratio of silicon-based material to lithium metal is 1:(4.5~5.0). Optionally, the molar ratio of silicon-based material to lithium metal can be 1:4.5, 1:4.6, 1:4.7, 1:4.8, 1:4.9, 1:5, etc.

[0054] Optionally, if the molar ratio of the base material to lithium metal is too low, the amount of lithium metal will be insufficient to react with all the silicon-based materials, resulting in some unreacted silicon-based materials, reducing the yield of the lithium silicon compound. Furthermore, the unreacted silicon-based materials may affect the subsequent coating process and the performance of the final product. If the molar ratio of the base material to lithium metal is too high, excess lithium may remain in the reaction system, increasing the risk of side reactions and wasting lithium resources, thus increasing production costs. Moreover, excess lithium may affect the structure and properties of the lithium silicon compound, making its electrochemical performance unstable. A suitable molar ratio helps control the composition and structure of the lithium silicon compound, enabling it to possess good electrochemical performance and meet the requirements for use as a lithium supplement agent in composite anodes.

[0055] In one feasible embodiment, the reaction time to obtain the lithium silicon compound is 12–36 h.

[0056] Optionally, the reaction time for the lithium silicon compound can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, or 36h.

[0057] Optionally, if the reaction time of the lithium silicon compound is too short, the reaction may be incomplete, resulting in insufficient reaction between the silicon-based material and metallic lithium, leaving some raw material residue. This reduces the yield and purity of the lithium silicon compound, affecting the performance of the final product. Conversely, if the reaction time is too long, it increases energy consumption and production costs, reducing production efficiency. Furthermore, prolonged high-temperature reactions may alter the structure of the product, affecting its electrochemical performance and increasing the likelihood of side reactions. The aforementioned time range balances reaction quality with production efficiency, avoiding excessively long reaction times that lead to extended production cycles and increased production costs.

[0058] Step S20: Nitrogen gas is introduced into the lithium silicon compound and the reaction is carried out at a constant temperature. After cooling, the mixture is pulverized to obtain a lithium silicon compound coated with a lithium nitride layer. In one feasible embodiment, at high temperature, lithium on the surface of the lithium silicon compound reacts with nitrogen gas to generate lithium nitride, thereby forming a lithium nitride layer on the surface of the lithium silicon compound. Lithium nitride has good ionic conductivity, which can promote the transport of lithium ions while protecting the lithium silicon compound.

[0059] In one feasible implementation, the temperature of the isothermal reaction after nitrogen gas is introduced is 400~500 °C; Optionally, the temperature of the isothermal reaction after nitrogen gas is introduced can be 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, etc.

[0060] Optionally, if the isothermal reaction temperature is too low after nitrogen is introduced, the activity of lithium atoms will be insufficient, and the reaction rate with nitrogen will be significantly reduced. This may lead to incomplete formation or uneven thickness of the lithium nitride coating, affecting the protective effect of the lithium nitride layer on the lithium silicon compound and the lithium-ion conductivity. If the isothermal reaction temperature is too high after nitrogen is introduced, it may trigger some side reactions. For example, the structure of the lithium silicon compound itself may change, affecting its performance as a lithium supplement. Excessively high temperatures may also make the structure of the lithium nitride coating layer loose, reducing its protective ability on the lithium silicon compound, and may also affect ion conductivity. A temperature of 400~500℃ can promote the reaction of lithium with nitrogen to form lithium nitride, while avoiding other unnecessary side reactions caused by excessively high temperatures, ensuring the purity and performance of the product.

[0061] In one feasible implementation, the isothermal reaction time after nitrogen gas introduction is 4-8 hours; Optionally, the isothermal reaction time after nitrogen gas is introduced can be 4h, 5h, 6h, 7h, 8h, etc.

[0062] Optionally, if the isothermal reaction time after nitrogen introduction is too short, the reaction may be incomplete, resulting in insufficient thickness of the lithium nitride coating layer. This would fail to effectively protect the lithium silicon compound and hinder its ability to fully promote lithium-ion transport. Conversely, if the isothermal reaction time after nitrogen introduction is too long, it will increase production costs and energy consumption, reduce production efficiency, and prolonged high-temperature reactions may also cause structural changes in the lithium nitride layer, such as grain growth, thereby affecting its performance.

[0063] In one feasible embodiment, the particle size of the lithium silicon compound coated with the lithium nitride layer is 0.5~2μm.

[0064] Optionally, the particle size of the lithium silicon compound coated with the lithium nitride layer can be 0.5μm, 0.6μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2μm, etc.

[0065] Optionally, if the particle size of the lithium silicon compound coated with the lithium nitride layer is too small, the specific surface area of ​​the lithium silicon compound coated with the lithium nitride layer will be too large, resulting in high surface energy and a tendency to agglomerate. This leads to uneven dispersion during electrode preparation, affecting the consistency of battery performance. Too small a particle size may also increase side reactions with the electrolyte, reducing the battery's cycle stability. Conversely, if the particle size of the lithium silicon compound coated with the lithium nitride layer is too large, the specific surface area of ​​the lithium silicon compound coated with the lithium nitride layer will be reduced, decreasing the contact area with the electrolyte. This will affect the lithium-ion transport rate, leading to a decrease in battery charge-discharge efficiency. Large particle sizes may also cause localized stress concentration in the electrode, easily leading to electrode structure damage during charge-discharge processes and affecting the battery's cycle life.

[0066] In one feasible embodiment, the temperature is raised after the dry nitrogen gas is introduced for 30-60 minutes, and the heating rate is controlled at 1-5°C / min.

[0067] Step S30: The lithium nitride-coated silicon-lithium compound is mixed with a lithium-containing inorganic salt and calcined to form a material with a lithium-containing inorganic salt layer. In one feasible embodiment, through a calcination process, the lithium-containing inorganic salt is tightly bonded to the lithium silicon-lithium compound coated with the lithium nitride layer, forming a lithium-containing inorganic salt layer on its surface. This lithium-containing inorganic salt layer can provide an additional lithium source, improving the surface properties of the composite negative electrode lithium replenishment agent.

[0068] In one feasible embodiment, the lithium nitride-coated silicon-lithium compound is mixed with a lithium-containing inorganic salt and then calcined at a temperature of 700-900°C for 4-8 hours.

[0069] Optionally, the calcination temperature can be 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, 820℃, 840℃, 860℃, 88℃, 900℃, etc.

[0070] Optionally, the calcination time can be 4h, 5h, 6h, 7h, 8h, etc.

[0071] Step S40: The slurry containing the conductive agent is uniformly mixed with the material containing the lithium inorganic salt layer by spraying to obtain the composite negative electrode lithium replenishing agent.

[0072] In one feasible embodiment, a spraying method can uniformly disperse the conductive agent-containing slurry on the surface of a coating material having a lithium-containing inorganic salt layer, forming a conductive agent layer. This conductive agent layer can improve the electronic conductivity of the composite negative electrode lithium replenishment agent.

[0073] In one feasible embodiment, the mass ratio of conductive agent, polyvinylidene fluoride, dispersant and N-methylpyrrolidone in the slurry is (0.5-10):(0.5-1):(0.3-1):(88-98.7).

[0074] Optionally, the mass ratio of the conductive agent, polyvinylidene fluoride, dispersant, and N-methylpyrrolidone can be 0.5:0.5:0.3:98.7, 2:0.6:0.4:97, 4:0.7:0.5:94.8, 6:0.8:0.6:92.6, 8:0.9:0.7:90.4, 10:1:0.8:88.2, 3:0.5:0.9:95.6, 7:0.7:1:91.3, etc.

[0075] In one feasible embodiment, the mass ratio of the lithium silicon compound coated with the lithium nitride layer to the lithium-containing inorganic salt is 100:(1~5).

[0076] In one feasible embodiment, the ratio of the lithium silicon compound coated with the lithium nitride layer to the lithium-containing inorganic salt is within a suitable range, which can form a dense interface that continuously covers the lithium nitride layer. If the ratio is too low, it cannot fully fill the microscopic defects of the lithium nitride layer, which can easily lead to electrolyte penetration and side reactions; if the ratio is too high, the excessive thickness of the inorganic salt layer will increase the lithium-ion diffusion resistance and reduce the battery capacity.

[0077] Optionally, the mass ratio of the lithium silicon compound coated with the lithium nitride layer to the lithium-containing inorganic salt can be 100:1, 100:2, 100:3, 100:4, 100:5, etc.

[0078] In one feasible embodiment, the mass ratio of the material having the lithium-containing inorganic salt layer to the slurry containing the conductive agent is 10:(1~2).

[0079] In one feasible embodiment, when the ratio of the material with the lithium-containing inorganic salt layer to the slurry containing the conductive agent is within a suitable range, a continuous conductive path can be constructed on the surface of the lithium silicon compound. If the ratio is too low, the internal resistance of the electrode increases significantly, leading to a decrease in rate performance; if the ratio is too high, it will over-cover the active material, reducing the energy density.

[0080] Optionally, the mass ratio of the material with the lithium-containing inorganic salt layer to the slurry containing the conductive agent can be 10:1, 10:1.2, 10:1.3, 10:1.4, 10:1.5, 10:1.6, 10:1.7, 10:1.8, 10:1.9, 10:2, etc.

[0081] This embodiment prepares a composite negative electrode lithium replenisher by selecting appropriate process parameters. First, metallic lithium reacts with silicon-based materials to generate a lithium silicon compound, which provides an abundant lithium source and improves the battery's energy density. Nitrogen gas is introduced to form a lithium nitride layer, which protects the lithium silicon compound, enhances its stability, and reduces side reactions with the external environment. The calcination treatment of the lithium-containing inorganic salt layer further optimizes the structure and improves the chemical stability and cycle performance of the lithium replenisher. A conductive agent layer is uniformly mixed by spraying to improve the conductivity of the lithium replenisher and accelerate lithium-ion transport. The preparation method provided in this embodiment is simple and feasible, and the resulting composite negative electrode lithium replenisher can effectively improve battery performance and extend battery life.

[0082] This application also provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises the composite negative electrode lithium replenishing agent in the above embodiments, or the composite negative electrode lithium replenishing agent prepared by the preparation method of the composite negative electrode lithium replenishing agent in the above embodiments.

[0083] To enable those skilled in the art to clearly understand the details and operations of the above embodiments of this application, and to demonstrate the significant improvement in the performance of the lithium metal battery recycling method of this application, the above technical solutions are illustrated below through multiple embodiments.

[0084] Example 1 Step 1: In an argon atmosphere, lithium metal is heated to 230°C and melted. Elemental silicon is then added to obtain a lithium silicon compound, wherein the molar ratio of elemental silicon to lithium metal is 1:4.8. The mixture is stirred at a constant temperature and reacted for 24 hours. Step 2: Nitrogen gas is introduced into the lithium silicon compound and the reaction is carried out at a constant temperature of 450°C for 7 hours. After cooling, the mixture is pulverized to obtain lithium silicon compound coated with lithium nitride. Step 3: Mix lithium nitride-coated lithium silicon compound with lithium carbonate at a mass ratio of 100:3 and calcine at 750°C for 6 hours to form a coating material with a lithium carbonate layer. Step 4: The conductive slurry containing carbon black is uniformly mixed with the coating material with a lithium carbonate layer by spraying to obtain a composite negative electrode lithium replenishing agent, wherein the mass ratio of the coating material with a lithium carbonate layer to the conductive slurry containing carbon black is 10:2; thus, the composite negative electrode lithium replenishing agent is obtained.

[0085] Figure 2 The results show that the composite negative electrode lithium replenishment agent obtained in Example 1 was characterized by XRD (X-ray diffraction), and the Li2CO3 and Li... 21 Characteristic diffraction peaks of various components such as Si5, Li3N, and C were observed, indicating that a composite negative electrode lithium replenishment agent was successfully prepared.

[0086] Example 2 Step 1: In an argon atmosphere, lithium metal is heated to 230°C and melted. Elemental silicon is then added to obtain a silicon-lithium compound, wherein the molar ratio of elemental silicon to lithium metal is 1:4.6. The mixture is stirred at a constant temperature and reacted for 24 hours. Step 2: Nitrogen gas is introduced into the lithium silicon compound and the reaction is carried out at a constant temperature of 450°C for 7 hours. After cooling, the mixture is pulverized to obtain lithium silicon compound coated with lithium nitride. Step 3: Mix lithium nitride-coated lithium silicon compound with lithium carbonate at a mass ratio of 100:3 and calcine at 750°C for 6 hours to form a coating material with a lithium carbonate layer. Step 4: The conductive slurry containing carbon black is uniformly mixed with the coating material with a lithium carbonate layer by spraying to obtain a composite negative electrode lithium replenishing agent, wherein the mass ratio of the coating material with a lithium carbonate layer to the conductive slurry containing carbon black is 10:2; thus, the composite negative electrode lithium replenishing agent is obtained.

[0087] Example 3 Step 1: In an argon atmosphere, metallic lithium is heated to 230°C to become molten, and elemental silicon is added to obtain a silicon-lithium compound, wherein the molar ratio of elemental silicon to metallic lithium is 1:5. The mixture is stirred at a constant temperature and reacted for 24 hours. Step 2: Nitrogen gas is introduced into the lithium silicon compound and the reaction is carried out at a constant temperature of 450°C for 7 hours. After cooling, the mixture is pulverized to obtain lithium silicon compound coated with lithium nitride. Step 3: Mix lithium nitride-coated lithium silicon compound with lithium carbonate at a mass ratio of 100:3 and calcine at 750°C for 6 hours to form a coating material with a lithium carbonate layer. Step 4: The conductive slurry containing carbon black is uniformly mixed with the coating material with a lithium carbonate layer by spraying to obtain a composite negative electrode lithium replenishing agent, wherein the mass ratio of the coating material with a lithium carbonate layer to the conductive slurry containing carbon black is 10:1.5; thus, the composite negative electrode lithium replenishing agent is obtained.

[0088] Example 4 Step 1: In an argon atmosphere, lithium metal is heated to 230°C and melted. Elemental silicon is then added to obtain a lithium silicon compound, wherein the molar ratio of elemental silicon to lithium metal is 1:4.8. The mixture is stirred at a constant temperature and reacted for 24 hours. Step 2: Nitrogen gas is introduced into the lithium silicon compound and the reaction is carried out at a constant temperature of 450°C for 7 hours. After cooling, the mixture is pulverized to obtain lithium silicon compound coated with lithium nitride. Step 3: Mix lithium nitride-coated silicon lithium compound with lithium fluoride at a mass ratio of 100:3, and calcine at 750°C for 6 hours to form a coating material with a lithium fluoride layer. Step four: The conductive slurry containing carbon black is uniformly mixed with the coating material with a lithium fluoride layer by spraying to obtain a composite negative electrode lithium replenishing agent, wherein the mass ratio of the coating material with a lithium fluoride layer to the conductive slurry containing carbon black is 10:2; thus, the composite negative electrode lithium replenishing agent is obtained.

[0089] Example 5 Step 1: In an argon atmosphere, lithium metal is heated to 230°C and melted. Elemental silicon is then added to obtain a lithium silicon compound, wherein the molar ratio of elemental silicon to lithium metal is 1:4.8. The mixture is stirred at a constant temperature and reacted for 24 hours. Step 2: Nitrogen gas is introduced into the lithium silicon compound and the reaction is carried out at a constant temperature of 450°C for 7 hours. After cooling, the mixture is pulverized to obtain lithium silicon compound coated with lithium nitride. Step 3: Mix lithium nitride-coated lithium silicon compound with lithium carbonate at a mass ratio of 100:3 and calcine at 750°C for 6 hours to form a coating material with a lithium carbonate layer. Step 4: The conductive slurry containing carbon black is uniformly mixed with the coating material with a lithium carbonate layer by spraying to obtain a composite negative electrode lithium replenishing agent, wherein the mass ratio of the coating material with a lithium carbonate layer to the conductive slurry containing carbon black is 10:1; thus, the composite negative electrode lithium replenishing agent is obtained.

[0090] Comparative Example 1 Lithium metal was heated to 230°C in an argon atmosphere until it became molten, and elemental silicon was added to obtain a lithium silicon compound, wherein the molar ratio of elemental silicon to lithium metal was 1:4.8. The mixture was stirred at a constant temperature and reacted for 24 hours to obtain a lithium replenishing agent for the negative electrode.

[0091] Comparative Example 2 Lithium metal was heated to 230°C in an argon atmosphere until it became molten, and elemental silicon was added, wherein the molar ratio of elemental silicon to lithium metal was 1:4.8. The mixture was stirred at a constant temperature and reacted for 24 hours to obtain a lithium silicon compound. The obtained lithium silicon compound was mixed with lithium nitride to obtain a lithium replenishing agent for the negative electrode.

[0092] Comparative Example 3 Lithium metal was heated to 230°C in an argon atmosphere until it became molten, and elemental silicon was added, wherein the molar ratio of elemental silicon to lithium metal was 1:4.8. The mixture was stirred at a constant temperature and reacted for 24 hours to obtain a lithium silicon compound. The obtained lithium silicon compound was mixed evenly with lithium nitride and lithium carbonate to obtain a negative electrode lithium replenishing agent.

[0093] The newly prepared negative electrode lithium replenishing agents in Examples 1-5 and Comparative Examples 1-3, as well as the negative electrode lithium replenishing agents placed in a natural environment (temperature around 26°C, relative humidity around 60%) for 12 hours, were used to prepare coin cells. The steps included: After thoroughly mixing the above-mentioned lithium replenishing agent, conductive carbon black, polyvinylidene fluoride, etc. according to the mass ratio, a lithium replenishing agent slurry is obtained. The prepared slurry is coated on copper foil, and after drying and rolling, a negative electrode sheet is obtained. A coin cell is assembled from lithium metal sheets, negative electrode sheets, separators, and electrolytes.

[0094] The negative electrode lithium replenishing agents from Examples 1-5 and Comparative Examples 1-3 were added to the negative electrode at a concentration of 2% each, to prepare full cells. The steps included: After thoroughly mixing the positive electrode active material lithium iron phosphate, conductive carbon black and polyvinylidene fluoride according to the mass ratio, a positive electrode slurry is obtained, which is coated on aluminum foil, and then dried and rolled to obtain a positive electrode sheet. After thoroughly mixing graphite, the above-mentioned lithium supplement, conductive carbon black, polyvinylidene fluoride, etc. according to the mass ratio, a negative electrode slurry is obtained. The prepared slurry is coated on copper foil, and after drying and rolling, a negative electrode sheet is obtained. The positive electrode, negative electrode, separator, and electrolyte are assembled into a full cell.

[0095] The test content includes: 1. The cycle performance of the full cell was tested at a current density of 1C.

[0096] Reference Figure 3 The x-axis represents the number of cycles of the full cell, and the y-axis represents the capacity retention of the full cell. With increasing cycle count, the capacity of the full cells corresponding to Examples 1-5 decreases relatively slowly, maintaining a capacity retention of over 95% after 600 cycles, higher than Comparative Examples 1-3; while the capacity of the full cells prepared with the negative electrode lithium replenishment agent in Comparative Examples 1-3 decreases more rapidly. This indicates that the batteries in Examples 1-5, using a multi-layered composite negative electrode lithium replenishment agent, exhibit good capacity retention and good cycle performance.

[0097] 2. The initial capacity of the button cell was tested, and the results are shown in Table 1 below: Table 1. Capacity of button cells in each embodiment and comparative example

[0098] As can be seen, the composite negative electrode lithium replenishing agent provided in Examples 1-5 of this application exhibits minimal capacity decay after 12 hours of storage, effectively reducing the environmental requirements for subsequent storage and processing, and demonstrating more stable performance. Figure 3 The displayed results are consistent.

Claims

1. A composite negative electrode lithium replenishing agent, characterized in that, The composite negative electrode lithium replenishing agent includes a lithium silicon compound and a lithium nitride layer, a lithium-containing inorganic salt layer, and a conductive agent layer sequentially coated on the surface of the lithium silicon compound.

2. The composite negative electrode lithium replenishing agent as described in claim 1, characterized in that, The lithium-containing inorganic salt in the lithium-containing inorganic salt layer includes at least one of lithium sulfate, lithium sulfite, lithium phosphate, lithium carbonate, lithium fluoride, lithium nitrate, and lithium nitrite. And / or, the conductive agent in the conductive agent layer includes at least one of carbon nanotubes, carbon black, flake graphite, and graphene.

3. The composite negative electrode lithium replenishing agent as described in claim 1, characterized in that, The particle size of the composite negative electrode lithium replenishing agent is 1~2μm.

4. A method for preparing a composite negative electrode lithium replenishing agent as described in any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: Lithium metal is heated to a molten state, and silicon-based materials are added to obtain a lithium silicon compound; Nitrogen gas was introduced into the silicon-lithium compound and reacted at a constant temperature. After cooling, the compound was pulverized to obtain a silicon-lithium compound coated with a lithium nitride layer. The lithium nitride-coated silicon-lithium compound is mixed with a lithium-containing inorganic salt and calcined to form a material having the lithium-containing inorganic salt layer. A composite negative electrode lithium replenishing agent is prepared by uniformly mixing a slurry containing a conductive agent with a material having a lithium-containing inorganic salt layer by spraying.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the lithium nitride-coated silicon-lithium compound to the lithium-containing inorganic salt is 100:(1~5); And / or, the mass ratio of the material having the lithium-containing inorganic salt layer to the slurry containing the conductive agent is 10:(1~2).

6. The preparation method according to claim 4, characterized in that, The silicon-based material includes at least one of elemental silicon, silicon suboxide, and silicon dioxide; And / or, the particle size of the silicon-based material is 50~500nm; And / or, the heating temperature of the lithium metal is 220~250℃; And / or, the molar ratio of the silicon-based material to lithium metal is 1:(4.5~5.0). And / or, the reaction time to obtain the silicon-lithium compound is 12–36 h.

7. The preparation method according to claim 4, characterized in that, The isothermal reaction temperature after nitrogen gas is introduced is 400~500℃; And / or, the isothermal reaction time after nitrogen gas is introduced is 4~8 hours; And / or, the particle size of the lithium silicon compound coated by the lithium nitride layer is 0.5~2μm.

8. The preparation method according to claim 4, characterized in that, After the lithium nitride-coated silicon-lithium compound is mixed with a lithium-containing inorganic salt, the calcination temperature is 700~900℃ and the calcination time is 4~8h.

9. The preparation method according to claim 4, characterized in that, The mass ratio of conductive agent, polyvinylidene fluoride, dispersant and N-methylpyrrolidone in the slurry is (0.5-10):(0.5-1):(0.3-1):(88-98.7).

10. A lithium-ion battery, characterized in that, The lithium-ion battery contains a composite negative electrode lithium replenishing agent as described in any one of claims 1 to 3, or a composite negative electrode lithium replenishing agent prepared by any one of claims 4 to 9.

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