Core-shell structure slow-release lithium supplement agent and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a core-shell structure slow-release lithium supplement agent and a preparation method and application thereof. The invention relates to a core-shell structure slow-release lithium supplement agent, which comprises: a LiN nanoparticle inner core, the average particle size D50 of which is 80 + / -30 nm, and the specific surface area of which is greater than or equal to 30 m / g; the Li-PEC shell layer is coated on the surface of the LiN inner core through atomic layer deposition (ALD), the thickness of the shell layer is 5-15 nm, and the shell layer is formed by ethylene carbonate (EC) through ring opening polymerization. According to the core-shell structure slow-release lithium supplement agent and the preparation method thereof, the performance of a battery is improved, the cycle life of the battery is prolonged, side reactions are reduced, the stability of the material and the feasibility of large-scale production are improved, and the core-shell structure slow-release lithium supplement agent and the preparation method thereof have important significance in promoting industrialization of high-energy-density lithium ion batteries and have wide application prospects. And meanwhile, the method has a remarkable promotion effect on technical upgrading of the electric automobile and energy storage industry.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and particularly to a core-shell structure sustained-release lithium supplement agent, a preparation method thereof, and an application thereof. Background Art

[0002] Since the commercialization of lithium-ion batteries in 1990, with their advantages such as high energy density, long cycle life, and low self-discharge rate, they have rapidly become the core power source for consumer electronics, electric vehicles (EVs), and energy storage systems. According to data from global market research institution SNE Research, the global installed capacity of power batteries exceeded 680 GWh in 2023, a year-on-year increase of 45%. Among them, high-nickel ternary (NCM / NCA) and lithium iron phosphate (LFP) systems dominate. However, with the continuous increase in the demand for electric vehicles for driving range (>500 km) and fast charging performance (charged to 80% in 30 minutes), the energy density bottleneck of traditional lithium-ion batteries (the highest current mass-produced batteries are about 300 Wh / kg) has gradually emerged. To achieve higher energy density, the industry is accelerating the advancement of two major technical routes: 1) High-capacity cathode materials: including ultra-high nickel (Ni≥90%, such as NCM90, NCA), lithium-rich manganese-based (Li-rich, such as Li1.2Ni0. 13 Co0. 13 Mn0. 54 O2), and sulfur-based cathodes (theoretical energy density ≈ 2600 Wh / kg); 2) High-capacity anode materials: represented by silicon-based anodes (SiOx / C, theoretical specific capacity ≈ 4200 mAh / g) and lithium metal anodes (3860 mAh / g). However, during the first charge and discharge process of these high-activity materials, the first Coulombic efficiency (ICE) of the battery will decrease significantly due to irreversible lithium loss (such as the ICE of silicon-based anodes is only 70 - 85%, and the ICE of lithium-rich cathodes < 80%). The irreversible consumption of active lithium mainly stems from the oxidative decomposition of the electrolyte at high voltage on the cathode side (especially > 4.3 V vs. Li / Li + ), the continuous formation and rupture of the solid electrolyte interface film (SEI film) on the anode side, and the accumulation of dead lithium caused by uneven lithium deposition / stripping leading to the growth of lithium dendrites. If the irreversible lithium loss cannot be effectively compensated, the actual capacity of the battery will be significantly lower than the theoretical value, and the cycle life will decay rapidly. Therefore, developing efficient lithium supplementation technology has become one of the key paths to break through the industrialization bottleneck of high-energy density batteries.

[0003] The core function of the lithium supplement agent is to inject active lithium (Li + or Li 0 ) into the battery system in a controllable manner to offset irreversible lithium loss, improve ICE, and extend the cycle life. According to the action mechanism and addition position of the lithium supplement agent, the existing technologies can be divided into the following three categories: The positive electrode lithium supplement agent decomposes and releases Li during the first charge by introducing a lithium-rich compound into the positive electrode sheet, compensating for the loss of active lithium in the positive electrode. Common positive electrode lithium supplement agents include decomposable lithium salts (such as Li2O2, Li5FeO4, Li6CoO4, etc.) and decomposable lithium salts (such as Li2CO3, LiNO3, etc.). Representative patents include CN113437343A: It is proposed to use Li2O2 as the positive electrode lithium supplement agent, but a high-voltage electrolyte (>4.5 V) needs to be used to activate the decomposition, resulting in an oxygen generation (O2) side reaction and causing battery swelling problems; US20180241042A1: The positive electrode material is coated with nano-Li3PO4, and Li and a phosphate interface layer are generated after decomposition, but the lithium supplement capacity is limited (<200 mAh / g). + , compensating for the loss of active lithium in the positive electrode. Common positive electrode lithium supplement agents include decomposable lithium compounds (such as Li2O2, Li5FeO4, Li6CoO4, etc.) and decomposable lithium salts (such as Li2CO3, LiNO3, etc.). Representative patents include CN113437343A: It is proposed to use Li2O2 as the positive electrode lithium supplement agent, but a high-voltage electrolyte (>4.5 V) needs to be used to activate the decomposition, resulting in an oxygen generation (O2) side reaction and causing battery swelling problems; US20180241042A1: The positive electrode material is coated with nano-Li3PO4, and Li + and a phosphate interface layer are generated after decomposition, but the lithium supplement capacity is limited (<200 mAh / g).

[0004] The negative electrode lithium supplement agent directly introduces a lithium source (such as lithium powder, lithium alloy) into the negative electrode, and compensates for the lithium consumption for the formation of the SEI film through a lithiation reaction. Typical solutions include lithium metal powders (such as nano-lithium powder or pre-lithiation of lithium foil); lithium alloys (such as Li-Si, Li-Al alloys). Representative patents include CN112467214A: LiF is used to coat the lithium powder to inhibit side reactions, but the lithium powder still has problems of poor dispersibility and high short-circuit risk; KR102345678B1: Controllable lithium release is achieved through Li-Mg alloy powder, but the alloy preparation process is complex and the cost is high.

[0005] The lithium supplement agent is directly added to the electrolyte, and lithium is continuously supplemented during the cycle through electrochemical or chemical decomposition. This type of technology has the advantages of strong process compatibility and no need to modify the electrode structure, but it is necessary to solve the compatibility with the electrolyte: avoid side reactions between the lithium supplement agent and the solvent / lithium salt. Although the electrolyte lithium supplement agent has significant application potential, the existing technologies still have the following key defects. For example, it is easy to react with the electrolyte solvent (such as EC, DEC) to generate gas, resulting in battery swelling and even failure; the oxygen generated by decomposition is easy to cause electrolyte oxidation, and it is necessary to add additional reducing additives to capture oxygen, increasing the complexity of the formulation. For electrolyte lithium supplement agents, the patents disclosed in recent years mainly focus on material modification (such as coating, nanosizing) and composite system design, but still have not broken through the balance problem of "lithium supplement efficiency - side reaction inhibition". Summary of the Invention

[0006] The purpose of this application is to address the deficiencies of current technologies and provide a core-shell structure slow-release lithium supplement agent, its preparation method and application. Through the innovation of the core-shell structure slow-release lithium supplement agent material design and preparation process, the following breakthroughs are achieved: 1) The staged lithium supplement mechanism: the outer shell layer (Li-PEC): decomposes preferentially during the first charge, quickly compensating for the loss of active lithium in the positive electrode and increasing the initial Coulombic efficiency ICE to >90%; the inner core (Li3N): is triggered by local high voltage / high temperature at the electrode interface during the cycle and gradually releases Li+ , extend the cycle life; 2) Side reaction inhibition strategy: The outer shell Li-PEC isolates Li3N from the electrolyte contact, reducing NH3 generation (gas production is reduced by 60%); The decomposition products of Li-PEC (such as polycarbonate) participate in the formation of a stable SEI film, reducing the interfacial impedance; 3) Feasibility of large-scale preparation: The solvothermal method combined with the atomic layer deposition ALD coating process can achieve the batch synthesis of 50-100 nm particles; The addition amount of the lithium supplement agent is low (0.5-2 wt%), which is compatible with the existing electrolyte. The core-shell structure slow-release lithium supplement agent prepared in this application is expected to provide core material support for the industrialization of high-energy density lithium-ion batteries, promote the technological upgrading of the electric vehicle and energy storage industries, and has significant technical effects and industrialization advantages.

[0007] In the first aspect, this application provides a core-shell structure slow-release lithium supplement agent, adopting the following technical solutions: A core-shell structure slow-release lithium supplement agent, comprising: a Li3N nanoparticle core with an average particle size D50 of 80±30 nm and a specific surface area ≥30 m² / g; a Li-PEC outer shell layer coated on the surface of the Li3N core by atomic layer deposition (ALD), with the outer shell layer thickness of 5-15 nm, formed by ring-opening polymerization of ethylene carbonate (EC).

[0008] By adopting the above technical solutions, through designing a specific outer shell layer (Li-PEC) and core (Li3N) structure, a staged lithium ion replenishment mechanism is realized. The outer shell layer preferentially decomposes during the first charge, quickly compensating for the loss of active lithium in the positive electrode, thereby increasing the initial Coulombic efficiency (ICE) to more than 90%. The core gradually releases Li during the cycling process. +, extend the cycle life of the battery. This staged lithium supplementation mechanism enables the battery to respond quickly and reach a high efficiency during the first charge, while continuously supplementing lithium ions during subsequent cycles to maintain battery performance. The outer shell layer Li-PEC can effectively isolate the contact between Li3N and the electrolyte, reduce the generation of harmful products such as NH3, and at the same time, the decomposition products of Li-PEC participate in the formation of a stable SEI film to reduce the interfacial impedance. This strategy helps to improve the safety and stability of the battery and reduce the occurrence of side reactions inside the battery. Through the solvothermal method combined with the atomic layer deposition (ALD) process, the batch synthesis of 50-100 nm particles is achieved. At the same time, the addition amount of the lithium supplement is low (0.5-2 wt%), and it has good compatibility with the existing electrolyte, which provides feasibility for large-scale production and commercial application. The synergistic effect of Li3N and Li-PEC not only improves the first charge-discharge efficiency and cycle life of the battery, but also improves the overall performance of the battery by reducing harmful side reactions and lowering the interfacial impedance. This synergistic effect makes the application of the core-shell structure slow-release lithium supplement in high-energy-density lithium-ion batteries have significant technical effects and industrialization advantages. In summary, the core-shell structure slow-release lithium supplement provides core material support for the industrialization of high-energy-density lithium-ion batteries through its unique staged lithium supplementation mechanism and side reaction inhibition strategy, as well as good large-scale preparation feasibility, and promotes the technological upgrading of the electric vehicle and energy storage industries.

[0009] Preferably, the thickness of the Li-PEC outer shell layer is 8 ± 2 nm, and the growth rate of each cycle of atomic layer deposition (ALD) is 0.15 - 0.18 nm / cycle.

[0010] By adopting the above technical solution, the thickness of the Li-PEC outer shell layer directly affects its performance during the battery cycle. When the outer shell layer thickness is 8 ± 2 nm, this thickness can ensure that the outer shell layer decomposes preferentially during the first charge and quickly compensates for the loss of active lithium in the positive electrode, while not overly hindering the release of Li from the inner core Li3N + . This balance ensures high efficiency (ICE is increased to 92%) of the battery during the first charge and good performance during subsequent cycles. If the outer shell layer is too thick (such as 13 nm), although it can provide better protection, it will also hinder the release of Li from Li3N +, which leads to a reduction in the cycle life and ICE of the battery. On the contrary, if the outer shell layer is too thin or there is no outer shell layer, a large amount of active lithium will be released and consumed during the initial cycle of the battery, thus seriously affecting the cycle life of the battery. The growth rate of atomic layer deposition (ALD) per cycle determines the deposition rate and uniformity of the Li-PEC outer shell layer. At a rate of 0.15 - 0.18 nm / cycle, uniform deposition and thickness control of the outer shell layer can be ensured, while avoiding structural defects or non-uniformities caused by too fast deposition rate. This rate can ensure that the outer shell layer can effectively decompose during the first charge and compensate for the loss of active lithium in the positive electrode, while maintaining the ability of the inner core Li3N to gradually release Li + during subsequent cycles. In summary, the thickness and ALD growth rate of the Li-PEC outer shell layer are crucial for the function and synergistic effect of the core-shell structured slow-release lithium supplement agent. By precisely controlling these parameters, rapid response of the outer shell layer during the first charge and continuous lithium supplement effect during subsequent cycles can be achieved, while maintaining the high efficiency and long life of the battery.

[0011] In a second aspect, the present application provides a preparation method of a core-shell structured slow-release lithium supplement agent, adopting the following technical solution: As a general technical concept, the present application also provides the preparation method of the above-mentioned core-shell structured slow-release lithium supplement agent, including the following steps: S31. After cutting the lithium metal sheet, soak it in tetrahydrofuran (THF) to remove the surface oxide, and dry it with nitrogen for standby; S32. In a glove box, add lithium sheet, sodium dodecylbenzenesulfonate (SDBS), ethylenediamine (EDA) and tetrahydrofuran (THF) to the reaction kettle according to the mass ratio of 1 - 100:1 - 100:1 - 100:1 - 100; S33. Fill the reaction kettle with nitrogen, seal it and place it in an oven, heat it to 100 - 200°C at a rate of 1 - 2°C / min, keep the temperature for reaction for 1 - 12 h, naturally cool it to room temperature, centrifuge to separate and collect the precipitate, and wash it 3 times with absolute ethanol to obtain the precipitate; S34. Vacuum dry the precipitate to obtain gray-black Li3N nanoparticles, and gently grind it with a ball mill to break the soft agglomeration to obtain uniformly dispersed Li3N nanoparticles; S35. Uniformly spread the Li3N nanoparticles on the atomic layer deposition ALD sample plate with a thickness <1 mm, and dehydrate it in vacuum at 80 - 200°C for 1 - 12 h; S36. Perform atomic layer deposition ALD coating on the Li3N particles to obtain a core-shell structured slow-release lithium supplement agent.

[0012] By adopting the above technical solution, the pretreatment of the lithium metal sheet: soaking the lithium metal sheet in tetrahydrofuran (THF) to remove the surface oxide is to ensure the purity of the lithium sheet during the subsequent reaction process. Nitrogen drying is to prevent the further formation or contamination of oxides. The reaction in the reaction kettle: mixing lithium sheet, sodium dodecylbenzenesulfonate (SDBS), ethylenediamine (EDA) and tetrahydrofuran (THF) for reaction is to form a precursor of Li3N nanoparticles. SDBS and EDA act as surfactants and crosslinking agents during the reaction, which helps to form stable nanoparticles. Collection and washing of the precipitate: centrifugal separation and washing with absolute ethanol are to remove unreacted raw materials and by-products to ensure that the collected precipitate is mainly Li3N nanoparticles. Drying and ball milling: vacuum drying is to remove moisture and solvent residues. Light ball milling by a ball mill to break soft agglomerates is to make the Li3N nanoparticles more evenly dispersed and improve the efficiency and quality of subsequent ALD coating. ALD coating: evenly spreading the Li3N nanoparticles on the ALD sample plate for ALD coating is to form a uniform Li-PEC outer shell layer on the surface of the Li3N particles. This process is a key step to achieve the core-shell structure. Vacuum dehydration: vacuum dehydration at 80-200 °C is to remove moisture and solvent residues on the particle surface to ensure the cleanliness of the particle surface and the smooth progress of the ALD coating process. The result of the synergistic effect of each step is to form a Li3N@Li-PEC core-shell structured lithium supplement agent with a uniform outer shell layer and inner core. This structure enables the lithium supplement agent to quickly compensate for the loss of active lithium during the first charge, and at the same time the inner core gradually releases Li + , extending the battery cycle life. In addition, the outer shell layer also plays a role in isolating the contact between Li3N and the electrolyte, reducing the generation of NH3 and lowering the interfacial impedance. These synergistic effects together improve the battery performance and cycle life.

[0013] Preferably, in step S31, the soaking time is 1-5 h.

[0014] Preferably, in step S33, the pressure of nitrogen charged into the reaction kettle is 4-10 MPa; the centrifugation rate of the centrifugal separation is 7000-9000 rpm, and the centrifugation time is 9-12 min.

[0015] Preferably, in step S34, the conditions for light ball milling by the ball mill include: the rotation speed is 180-220 rpm, and the time is 10-300 min; the temperature of the vacuum drying is 35-60 °C, and the drying time is 1-12 h.

[0016] Preferably, in step S36, the specific process of coating Li3N particles by atomic layer deposition (ALD) is as follows: Place the sample disk in step S35 into the atomic layer deposition equipment, introduce ethylene carbonate vapor at a temperature of 40 - 100 °C until the pressure rises to 0.4 - 0.6 MPa, perform pulsed atomic layer deposition with a pulse time of 0.05 - 0.15 s, then introduce argon at a flow rate of 200 - 300 SCCM for 10 s to remove unreacted ethylene carbonate, and then heat to 145 - 150 °C and keep it warm for a reaction time of 30 - 35 s to cause the ring-opening polymerization of ethylene carbonate on the surface of Li3N particles to form a Li-PEC outer shell layer; then purge with argon for 20 s to remove unreacted by-products, and repeat this cycle 1 - 70 times to end the reaction, obtaining a core-shell structured slow-release lithium supplement agent, denoted as Li3N@Li-PEC powder.

[0017] Thirdly, the present application provides a lithium supplement electrolyte for a lithium battery, adopting the following technical solution: As a general technical concept, the present application also provides the above-mentioned core-shell structured slow-release lithium supplement agent as the lithium supplement electrolyte for a lithium battery. Add Li3N@Li-PEC powder and perfluoropolyether (PFPE) into dimethyl carbonate (DMC), and magnetically stir at a rotation speed of 500 rpm for 30 - 40 min to form a Li3N@Li-PEC dispersion liquid. Mix the Li3N@Li-PEC dispersion liquid with a commercial electrolyte and stir for 2 h to obtain the lithium supplement electrolyte for the lithium battery.

[0018] Preferably, the mass ratio of the Li3N@Li-PEC dispersion liquid to the commercial electrolyte is 0.5 - 2:100; the mass ratio of the Li3N@Li-PEC powder, perfluoropolyether, and dimethyl carbonate is 10:1:100.

[0019] Fourthly, the present application provides an application of a core-shell structured slow-release lithium supplement agent, adopting the following technical solution: As a general technical concept, the present application also provides the above-mentioned application of the core-shell structured slow-release lithium supplement agent in an energy storage system or a power battery for an electric vehicle.

[0020] In summary, the present application includes at least one of the following beneficial technical effects: 1. Improve battery performance: Through the staged lithium supplementation mechanism and the side reaction inhibition strategy, the initial Coulombic efficiency (ICE) and cycle life of the battery are significantly improved. The outer shell layer Li-PEC preferentially decomposes during the first charge, quickly compensating for the loss of active lithium in the positive electrode, increasing the ICE of the battery from 80% to 92%. The inner core Li3N gradually releases Li + , extending the cycle life of the battery.

[0021] 2. Reduction of side reactions: The outer shell Li-PEC isolates Li3N from contacting with the electrolyte, reducing the generation of NH3. At the same time, the decomposition products of Li-PEC participate in the formation of a stable SEI film, reducing the interfacial impedance and the occurrence of side reactions inside the battery.

[0022] 3. Improvement of material stability: The Li3N nanoparticles are coated by atomic layer deposition (ALD) process, improving the stability and uniformity of the material and avoiding the occurrence of soft agglomeration.

[0023] 4. Feasibility of large-scale preparation: The combination of solvothermal method and atomic layer deposition (ALD) process can realize the batch synthesis of 50 - 100 nm particles. Meanwhile, the addition amount of lithium supplement agent is low (0.5 - 2 wt%), and it has good compatibility with the existing electrolyte.

[0024] 5. Economic benefits: Since the preparation method of this lithium supplement agent is simple, low-cost and has remarkable effects, it has high economic benefits and market competitiveness. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings used in the embodiments are briefly introduced below: Figure 1 SEM image of the Li3N powder prepared in Example 1; Figure 2 SEM image of the Li3N powder prepared in Example 2; Figure 3 Cycle stability curve of the battery obtained by preparing the core-shell structure slow-release lithium supplement agent prepared in Example 1 and Comparative Examples 1 - 2 into a lithium supplement electrolyte and adding it to a lithium battery. Detailed Embodiments

[0026] The implementation schemes of the present application will be described in detail below in combination with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0027] Example 1 Step 1: Cut the lithium metal sheet into 5×5 mm fragments, soak them in tetrahydrofuran (THF, volume ratio 1:1) for 5 minutes to remove the surface oxide, and dry them with nitrogen for standby; Step 2: In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), add lithium pieces (2 g), sodium dodecylbenzenesulfonate (SDBS) (0.02 g), ethylenediamine (EDA) (40 mL), and THF (40 mL) to the reaction kettle; Step 3: Fill the reaction kettle with N2 to a pressure of 5 MPa, seal it, and place it in an oven. Heat it to 180°C at a rate of 2°C / min, keep it warm for 12 h, cool it naturally to room temperature, centrifuge (8000 rpm, 10 min) to collect the precipitate, and wash it 3 times with absolute ethanol; Step 4: Vacuum dry the precipitate at 60°C for 12 h to obtain gray-black Li3N nanoparticles. Gently grind (30 min, rotation speed 200 rpm) with a ball mill to break up the soft agglomerates and obtain uniformly dispersed Li3N powder (D50 = 80 nm, BET specific surface area ≈ 35 m² / g); Step 5: Evenly spread the Li3N powder on an ALD sample plate (thickness < 1 mm) and vacuum dehydrate it at 120°C for 2 h; Step 6: Coating a Li-PEC layer on the surface of Li3N by atomic layer deposition (ALD) (the precursor is ethylene carbonate vapor, deposition temperature 80°C, number of cycles 50 times). Introduce ethylene carbonate (EC) vapor (temperature 80°C, pulse time 0.1 s) into the chamber, raise the pressure to 0.5 MPa, introduce argon gas (Ar) (flow rate 200 SCCM, time 10 s) to remove unreacted EC, heat to 150°C to cause the ring-opening polymerization of EC on the surface of Li3N to form a Li-PEC layer (reaction time 30 s); then purge with Ar gas for 20 s to remove unreacted by-products. After 50 such cycles, the reaction ends to prepare Li3N@Li-PEC powder. (The thickness of the outer shell ≈ 8 nm, growth rate per cycle ≈ 0.16 nm / cycle).

[0028] Example 2 Step 1: Cut the metallic lithium pieces into 5×5 mm fragments, soak them in tetrahydrofuran (THF, volume ratio 1:1) for 5 minutes to remove the surface oxides, and dry them with nitrogen for standby; Step 2: In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), add lithium pieces (2 g), sodium dodecylbenzenesulfonate (SDBS) (0.02 g), ethylenediamine (EDA) (40 mL), and THF (40 mL) to the reaction kettle; Step 3: Fill the reaction kettle with N2 to a pressure of 10 MPa, seal it and place it in an oven. Heat it to 180 °C at a rate of 2 °C / min, keep it warm for 12 h, naturally cool it to room temperature, and centrifuge (8000 rpm, 10 min) to collect the precipitate, and wash it 3 times with absolute ethanol; Step 4: Vacuum dry the precipitate at 60 °C for 12 h to obtain gray-black Li3N nanoparticles. Gently grind it (30 min, rotation speed 200 rpm) with a ball mill to break the soft agglomeration and obtain a uniformly dispersed Li3N powder (D50 = 105 nm, BET specific surface area ≈ 31 m² / g); Step 5: Evenly spread the Li3N powder on an ALD sample plate (thickness < 1 mm), and vacuum dehydrate it at 120 °C for 2 h; Step 6: Coating a Li-PEC layer on the surface of Li3N by atomic layer deposition (ALD) (the precursor is ethylene carbonate vapor, deposition temperature 80 °C, number of cycles 50 times). Introduce ethylene carbonate (EC) vapor (temperature 80 °C, pulse time 0.1 s) into the chamber, increase the pressure to 0.5 MPa, introduce argon (Ar) (flow rate 200 SCCM, time 10 s) to remove unreacted EC, heat it to 150 °C to cause the ring-opening polymerization of EC on the surface of Li3N to form a Li-PEC layer (reaction time 30 s); then purge with Ar gas for 20 s to remove unreacted by-products. After 50 such cycles, the reaction ends to prepare Li3N@Li-PEC powder. (The thickness of the outer shell ≈ 8 nm, growth rate per cycle ≈ 0.16 nm / cycle).

[0029] Example 3 Step 1: Cut the lithium metal sheet into 5×5 mm fragments, soak them in tetrahydrofuran (THF, volume ratio 1:1) for 1 minute to remove the surface oxide, and dry them with nitrogen for standby; Step 2: In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), add lithium flakes (2 g), sodium dodecylbenzenesulfonate (SDBS) (0.02 g), ethylenediamine (EDA) (40 mL) and THF (40 mL) to the reaction kettle; Step 3: Fill the reaction kettle with N2 to a pressure of 10 MPa, seal it and place it in an oven. Heat it to 100 °C at a rate of 1 °C / min, keep it warm for 1 h, naturally cool it to room temperature, and centrifuge (7000 rpm, 12 min) to collect the precipitate, and wash it 3 times with absolute ethanol; Step 4: The precipitate was dried in vacuum at 35 °C for 1 h to obtain gray-black Li3N nanoparticles. The soft agglomerates were broken by gently milling with a ball mill (300 min, rotation speed 220 rpm) to obtain uniformly dispersed Li3N powder (D50 = 81 nm, BET specific surface area ≈ 35 m² / g); Step 5: The Li3N powder was evenly spread on an ALD sample plate (thickness < 1 mm) and dehydrated in vacuum at 120 °C for 2 h; Step 6: A Li-PEC layer was coated on the surface of Li3N by atomic layer deposition (ALD) (the precursor was ethylene carbonate vapor, deposition temperature 40 °C, number of cycles 20). Ethylene carbonate (EC) vapor (temperature 40 °C, pulse time 0.15 s) was introduced into the chamber, the pressure was increased to 0.6 MPa, argon (Ar) (flow rate 300 SCCM, time 10 s) was introduced to remove unreacted EC, and it was heated to 145 °C to cause the ring-opening polymerization of EC on the surface of Li3N to form a Li-PEC layer (reaction time 35 s); then it was purged with Ar gas for 20 s to remove unreacted by-products. After 20 such cycles, the reaction was terminated to prepare Li3N@Li-PEC powder. (The shell thickness ≈ 3.6 nm, growth rate per cycle ≈ 0.18 nm / cycle).

[0030] Comparative Example 1: (The coating layer is too thick, resulting in the inability of LI3N to be released and low capacity) Step 1: Lithium metal sheets were cut into 5×5 mm fragments, soaked in tetrahydrofuran (THF, volume ratio 1:1) for 5 minutes to remove surface oxides, and dried with nitrogen for later use; Step 2: In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), lithium flakes (2 g), sodium dodecylbenzenesulfonate (SDBS) (0.02 g), ethylenediamine (EDA) (40 mL), and THF (40 mL) were added to the reaction kettle; Step 3: The reaction kettle was filled with N2 to a pressure of 5 MPa, sealed and placed in an oven, heated to 180 °C at a rate of 2 °C / min, kept warm for 12 h, naturally cooled to room temperature, and the precipitate was collected by centrifugation (8000 rpm, 10 min) and washed 3 times with absolute ethanol; Step 4: The precipitate was dried in vacuum at 60 °C for 12 h to obtain gray-black Li3N nanoparticles. The soft agglomerates were broken by gently milling with a ball mill (30 min, rotation speed 200 rpm) to obtain uniformly dispersed Li3N powder (D50 = 80 nm, BET specific surface area ≈ 35 m² / g); Step 5: The Li3N powder was evenly spread on an ALD sample plate (thickness < 1 mm) and dehydrated in vacuum at 120 °C for 2 h; Step 6: Coating the surface of Li3N with a Li-PEC layer by atomic layer deposition (ALD) (the precursor is ethylene carbonate vapor, deposition temperature 80 °C, number of cycles 80 times). Introduce ethylene carbonate (EC) vapor (temperature 80 °C, pulse time 0.1 s) into the chamber, raise the pressure to 0.5 MPa, introduce argon (Ar) (flow rate 200 SCCM, time 10 s) to remove unreacted EC, heat to 150 °C to cause the ring-opening polymerization of EC on the surface of Li3N to form a Li-PEC layer (reaction time 30 s); then purge with Ar gas for 20 s to remove unreacted by-products. After 80 such cycles, the reaction ends, and Li3N@Li-PEC powder is prepared. (Shell thickness ≈ 13 nm, growth rate per cycle ≈ 0.16 nm / cycle).

[0031] Comparative Example 2: (Uncoated) Step 1: Cut the lithium metal sheet into 5×5 mm pieces, soak them in tetrahydrofuran (THF, volume ratio 1:1) for 5 minutes to remove surface oxides, and dry them with nitrogen for later use. Step 2: In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), add lithium flakes (2 g), sodium dodecylbenzenesulfonate (SDBS, 0.1 wt%) (0.02 g), ethylenediamine (EDA) (40 mL), and THF (40 mL) to the reaction kettle. Step 3: Fill the reaction kettle with N2 to a pressure of 5 MPa, seal it and place it in an oven, heat it to 180 °C at a rate of 2 °C / min, keep it warm for 12 h, naturally cool to room temperature, centrifuge (8000 rpm, 10 min) to collect the precipitate, and wash it 3 times with absolute ethanol.

[0032] Step 4: Vacuum-dry the precipitate at 60 °C for 12 h to obtain gray-black Li3N nanoparticles, and gently grind them with a ball mill (30 min, rotation speed 200 rpm) to break up soft agglomerates, obtaining uniformly dispersed Li3N powder (D50 = 80 nm, BET specific surface area ≈ 35 m² / g).

[0033] Performance detection test 1. Samples were taken from the core-shell structure slow-release lithium supplement agents prepared in Examples 1 - 2 and tested with a scanning electron microscope (SEM). The test results are as Figure 1 and Figure 2 shown.

[0034] 2. Preparation and testing of coin cells Preparation of lithium supplement electrolyte (1) 1 g of the core-shell structured slow-release lithium supplement (Li3N@Li-PEC powder or Li3N powder) prepared in Example 1 and Comparative Examples 1-2 and 0.1 g of perfluoropolyether were separately added to 10 g of dimethyl carbonate, and magnetically stirred at 500 rpm for 35 min to form a lithium supplement dispersion liquid. The lithium supplement dispersion liquid was mixed with a commercial electrolyte according to a mass ratio of 1-25, and after stirring for 2 h, a lithium supplement electrolyte for a lithium battery was obtained. Among them, the specific formula of the commercial electrolyte was 1 M LiPF6 / EC+DMC (3:7, volume ratio), containing 1 wt% VC (vinyl carbonate).

[0035] (2) Assemble a coin cell. The assembly sequence of the cell is the positive electrode case, LiNi0.5Co0.2Mn0.3O2 (523 positive electrode material), PE separator, silicon-oxygen negative electrode, gasket and negative electrode case. The entire assembly process is carried out in a glove box under an argon atmosphere; the coin cell is kept in an incubator at 60 °C for 12 h and then tested, and charged and discharged at a constant current of 50 mAh to detect the cycle stability of the coin cell. The test results are as Figure 3 shown.

[0036] Figure 3 The cycle stability curve graph of the battery obtained by using the core-shell structured slow-release lithium supplement prepared in Example 1 and Comparative Examples 1-2 to prepare a lithium supplement electrolyte and adding it to a lithium battery. From Figure 3 it can be seen that Li3N@Li-PEC particles with a suitable coating layer thickness have the effect of significantly improving the cycle life of the battery. During the battery cycle, the outer shell Li-PEC decomposes preferentially and compensates a large amount of active lithium during the first charge, so the ICE of the battery increases from 80% to 92%. During the subsequent cycle process, the inner core Li3N gradually releases Li + during the cycle, so the capacity retention rate is optimal after multiple cycles. For the battery prepared in Comparative Example 1, when the number of ALD cycles is increased to 80 times (the outer shell is 13 nm), due to its too thick coating layer, the outer shell blocks the release of Li3N, so the cycle life and ICE of its battery are the second. For the battery prepared in Comparative Example 2, when Li3N is not coated and acts in the battery, due to the absence of a coating layer, a large amount of active lithium is released and consumed in large quantities during the initial cycle of the battery, so the cycle life of the battery is the worst.

[0037] The above embodiments are only used to explain and illustrate the technical solutions of the present application rather than to limit them. Although the above embodiments have specifically described the present application, those skilled in the art should understand that the specific implementation manners of the present application can still be modified or equivalently replaced, and any modification and equivalent replacement without departing from the spirit and scope of the present application should be covered by the protection scope of the present application.

Claims

1. A core-shell structure sustained-release lithium supplement, characterized in that: include: The Li3N nanoparticle core has an average particle size D50 of 80±30 nm and a specific surface area of ​​≥30 m² / g; the Li-PEC shell layer is coated on the surface of the Li3N core by atomic layer deposition, and the shell layer thickness is 5-15 nm, which is formed by the ring-opening polymerization of ethylene carbonate.

2. A core-shell structure sustained-release lithium supplement according to claim 1, characterized in that: The thickness of the Li-PEC outer layer is 8±2 nm, and the growth rate of each atomic layer deposition cycle is 0.15-0.18 nm / cycle.

3. A method for preparing a core-shell structure sustained-release lithium supplement as claimed in claim 1 or 2, characterized in that: The following steps are involved: S31, cutting the metal lithium sheet, soaking it in tetrahydrofuran to remove surface oxides, and blowing it dry with nitrogen for later use; S32, in a glove box, adding lithium sheet, sodium dodecylbenzenesulfonate, ethylenediamine and tetrahydrofuran into a reaction kettle at a mass ratio of 1-100:1-100:1-100:1-100; S33, filling the reactor with nitrogen, sealing it and placing it in an oven, heating it to 100-200°C at a rate of 1-2°C / min, keeping the temperature for reaction for 1-12 h, naturally cooling it to room temperature, collecting the precipitate by centrifugation, and washing it with anhydrous ethanol three times to obtain a precipitate; S34, vacuum drying the precipitate to obtain gray-black Li3N nanoparticles, and lightly grinding with a ball mill to break up soft agglomerates to obtain evenly dispersed Li3N nanoparticles; S35, Li3N nanoparticles are evenly spread on the atomic layer deposition ALD sample plate with a thickness of <1 mm, and vacuum dehydrated at 80-200°C for 1-12 h; S36. Li3N particles are coated by atomic layer deposition to obtain a core-shell structured sustained-release lithium supplement.

4. The method for preparing a core-shell structure sustained-release lithium supplement according to claim 3, characterized in that: In step S31, the soaking time is 1-5 hours.

5. The method for preparing a core-shell structure sustained-release lithium supplement according to claim 3, characterized in that: In step S33, the pressure of nitrogen filled into the reactor is 4-10 MPa; the centrifugal speed of the centrifugal separation is 7000-9000 rpm, and the centrifugal time is 9-12 min.

6. The method for preparing a core-shell structure sustained-release lithium supplement according to claim 3, characterized in that: In step S34, the conditions for light grinding in the ball mill include: a rotation speed of 180-220 rpm and a time of 10-300 min; a temperature of the vacuum drying is 35-60° C. and a drying time of 1-12 h.

7. The method for preparing a core-shell structure sustained-release lithium supplement according to claim 3, characterized in that: In step S36, the specific process of atomic layer deposition coating of Li3N particles is as follows: placing the sample tray in step S35 into an atomic layer deposition device, introducing ethylene carbonate vapor at a temperature of 40-100°C until the pressure rises to 0.4-0.6 MPa, performing pulsed atomic layer deposition, and the pulse time is 0.05-0.15 s, followed by introducing argon gas at a flow rate of 200-300 SCCM for 10 s to remove unreacted ethylene carbonate, and then heating to 145-150°C for a heat preservation reaction time of 30-35 s to allow ethylene carbonate to ring-open polymerize on the surface of the Li3N particles to form a Li-PEC outer shell layer; then purging with argon gas for 20 s to remove unreacted by-products, and terminating the reaction after 1-70 cycles to obtain a core-shell structure sustained-release lithium supplement, marked as Li3N@Li-PEC powder.

8. A lithium-supplementing electrolyte for a lithium battery, characterized in that: A core-shell structure sustained-release lithium supplement agent comprising the core-shell structure sustained-release lithium supplement agent according to any one of claims 1 to 2, wherein Li3N@Li-PEC powder and perfluoropolyether are added to dimethyl carbonate, and magnetic stirring is performed at a speed of 500 rpm for 30-40 min to form a Li3N@Li-PEC dispersion, and the Li3N@Li-PEC dispersion is mixed with a commercial electrolyte, and stirred for 2 hours to obtain a lithium supplement electrolyte for a lithium battery.

9. The lithium-supplementing electrolyte for a lithium battery according to claim 8, characterized in that: The mass ratio of the Li3N@Li-PEC dispersion to the commercial electrolyte is 0.5-2:100; the mass ratio of the Li3N@Li-PEC powder, perfluoropolyether and dimethyl carbonate is 10:1:

100.

10. A use of the core-shell structure sustained-release lithium supplement as claimed in claim 1 or 2, characterized in that: Application of the core-shell structure sustained-release lithium supplement in energy storage systems or electric vehicle power batteries.

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