A Composite Lithium-Complementary Additive, Its Preparation Method and Application

Abstract

The present invention relates to a composite lithium supplement additive, its preparation method and application, including: a core, the core includes porous carbon and a first rigid coating disposed on at least a part of the surface of the porous carbon; a functional coating layer coated on the surface of the core, the functional coating layer contains a lithium supplement agent, the functional coating layer is a porous structure, the lithium supplement agent is disposed in some pores of the porous structure, and a second rigid coating is disposed in at least some pores; and a rigid coating layer disposed on the surface of the functional coating layer. In the present invention, porous carbon is used as the core, which can effectively adsorb the gas generated in the battery. The lithium supplement agent accommodated in some pores of the functional coating layer can improve the initial efficiency of the battery, and can further increase the porosity of the functional coating layer after lithium supplementation, which is beneficial to lithium ion transmission. At the same time, the presence of the rigid coating and the rigid coating layer can effectively improve the conductivity and structural stability of the additive, thereby effectively improving the battery safety and electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a composite lithium supplement additive, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of electric vehicles, portable electronic devices, and energy storage systems, the demand for high-energy-density lithium batteries is increasing day by day. High-nickel cathodes (such as NCM, NCA) and silicon-based anodes (such as silicon-carbon composites) are regarded as key materials for the next generation of lithium-ion batteries due to their high theoretical specific capacity. However, these materials still face significant challenges in practical applications. For example: High-nickel cathodes are prone to side reactions with electrolytes during cycling, releasing gases such as oxygen, and the gas production will increase with the increase of nickel content, thus seriously affecting the electrochemical performance and safety performance of lithium batteries; while silicon-based anodes expand violently during charge and discharge, resulting in repeated rupture and regeneration of the solid electrolyte interface (SEI). On the one hand, it exacerbates the decomposition of the electrolyte, generating gases such as hydrogen and alkanes, and at the same time, it will increase the consumption of active lithium, affecting the initial efficiency and cycle performance of the battery.

[0003] At present, the main solutions to the above problems include optimizing electrolyte additives, coating and modifying electrode materials, adding lithium supplement agents, etc., but it is difficult to balance gas production inhibition and lithium compensation efficiency. Among them, by introducing an active lithium source into the positive or negative electrode, although the lithium loss in the first cycle can be compensated and the total reversible capacity of the battery can be improved, existing lithium supplement materials (such as lithium-rich compounds, lithium metal oxides, etc.) have problems such as violent oxidation decomposition side reactions and large gas production during application, which will further deteriorate the safety performance of the battery, and the conductivity of such lithium supplement materials is poor, and it will further exacerbate the contact impedance after the lithium supplement structure fails, affecting the rate performance of the battery, etc.

[0004] Therefore, there is an urgent need to develop a new type of composite lithium supplement additive that can not only efficiently supplement lithium, but also absorb gases in the system, and at the same time stabilize the electrode interface through structural design, so as to comprehensively improve the comprehensive performance of high-nickel silicon-based batteries. Summary of the Invention

[0005] To solve the above problems, the present invention provides a composite lithium supplement additive, its preparation method and application. The composite lithium supplement agent has a core-shell structure, with porous carbon as the inner core, which can effectively adsorb the gas generated in the battery. The lithium supplement agent contained in some pores of the functional coating layer can improve the initial efficiency of the battery, and can further increase the porosity of the functional coating layer after lithium supplementation, which is beneficial to lithium ion transmission. At the same time, the presence of the first rigid coating provided on at least part of the surface of the porous carbon, the second rigid coating provided in at least part of the pores of the functional coating layer, and the rigid coating layer can effectively improve the conductivity and structural stability of the composite lithium supplement additive, thereby effectively improving the battery safety and electrochemical performance. Through the synergistic effect of the above material and structure design, the high-nickel silicon-based battery containing the composite lithium supplement agent can effectively solve the problems of battery gas generation and low initial efficiency, and exhibits better rate performance and cycle stability.

[0006] Specifically, the following technical solutions are provided:

[0007] In the first aspect of the present invention, a composite lithium supplement additive is provided. The composite lithium supplement additive has a core-shell structure and includes: an inner core, a functional coating layer, and a rigid coating layer;

[0008] The inner core includes porous carbon and a first rigid coating provided on at least part of the surface of the porous carbon;

[0009] The functional coating layer is coated on the surface of the inner core. The functional coating layer contains a lithium supplement agent. The functional coating layer is a porous structure. The lithium supplement agent is provided in some pores of the porous structure, and a second rigid coating is provided in at least part of the pores;

[0010] The rigid coating layer is coated on the surface of the functional coating layer;

[0011] The first rigid coating, the second rigid coating, and the rigid coating layer all contain metal carbides and / or metal nitrides.

[0012] Further, the porous carbon includes MOF-based porous carbon derivatives and / or COF-based porous carbon derivatives.

[0013] Further, the lithium supplement agent is a decomposition-type lithium supplement agent, including one or more of Li2O, Li2O2, and Li2N.

[0014] Further, the functional coating layer further contains carbon and a conductive agent.

[0015] Further, the metal elements in the metal carbides and metal nitrides are selected from one or more of titanium, tungsten, zirconium, tantalum, chromium, and vanadium.

[0016] Further, the diameter of the core is preferably 1-3 μm, and the thickness of the first rigid coating is preferably 50-100 nm.

[0017] Further, the thickness of the functional coating layer is preferably 1-3 μm, the particle size of the lithium supplement agent is preferably 500-1000 nm, and the thickness of the second rigid coating is preferably 50-100 nm.

[0018] Further, the thickness of the rigid coating layer is preferably 50-100 nm.

[0019] The second aspect of the present invention provides a preparation method of the composite lithium supplement additive described in the first aspect, including the following steps:

[0020] S1. Mix ammonium bicarbonate and the first binder evenly to obtain a first mixture, and evenly coat the first mixture on the surface of the lithium supplement agent to obtain a modified lithium supplement agent;

[0021] S2. Mix the modified lithium supplement agent, the conductive agent, and the second binder evenly to obtain a second mixture, and evenly coat the second mixture on the surface of the porous material to obtain an additive precursor, and further bake to obtain a porous additive precursor; the porous material is porous carbon and / or a porous carbon precursor;

[0022] S3. Disperse the porous additive precursor into a metal salt solution, separate the solid particles after sufficient impregnation; the metal element in the metal salt is selected from one or more of titanium, tungsten, zirconium, tantalum, chromium, and vanadium;

[0023] S4. Heat-treat the solid particles under a mixed atmosphere to obtain the composite lithium supplement additive; the mixed atmosphere includes a protective gas and an alkane gas.

[0024] Further, in step S1, the mass ratio of the ammonium bicarbonate to the first binder is preferably (40-95):(5-60).

[0025] Further, in step S1, the first binder is a binder commonly used in the art, including but not limited to polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, etc.

[0026] Further, in step S1, in the coating step: first mix the first mixture with a first solvent evenly to obtain a first slurry, and then evenly spray the first slurry onto the surface of the lithium supplement agent by spray coating to obtain a modified lithium supplement agent; the first solvent is preferably N-methylpyrrolidone.

[0027] Further, in step S1, the modified lithium supplementing agent includes a lithium supplementing agent and an ammonium bicarbonate coating layer provided on the surface of the lithium supplementing agent. The thickness of the ammonium bicarbonate coating layer is preferably 100-500 nm.

[0028] Further, in step S2, the mass ratio of the modified lithium supplementing agent, the conductive agent, and the second binder is preferably (92-96):(1-3):(3-5).

[0029] Further, in step S2, the second binder is a binder conventionally used in the art, including but not limited to polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, etc.; the conductive agent is a conductive agent conventionally used in the art, including but not limited to conductive carbon black, graphite, carbon nanotubes, etc.

[0030] Further, in step S2, in the coating step: first, the second mixture is mixed with a second solvent to obtain a second slurry, and then the second slurry is evenly sprayed onto the surface of the porous material by spray coating to obtain an additive precursor; the second solvent is preferably N-methylpyrrolidone.

[0031] Further, in step S2, the additive precursor includes a porous material and a functional layer coated on the surface of the porous material. The thickness of the functional layer is preferably 1-3 μm.

[0032] Further, in step S2, the baking temperature is preferably 100-150 °C, and the time is preferably 8-12 h.

[0033] Further, in step S2, the porous carbon precursor includes a porous MOF material and / or a porous COF material.

[0034] Further, in step S3, the metal salt is selected from one or more of hydrochlorides, sulfates, and nitrates; preferably, the concentration of the metal salt solution is 0.01-0.5 mol / L, and the solvent of the metal salt solution is selected from one or more of benzene, toluene, ethanol, methanol, and chloroform.

[0035] Further, in step S3, the porous additive precursor is fully impregnated in the metal salt solution by stirring; the stirring is carried out under vacuum, and the stirring time is preferably 2-4 h.

[0036] Further, in step S3, the protective gas is selected from one or more of nitrogen, argon, helium, and neon, and the alkane gas is selected from one or more of methane, ethane, and propane.

[0037] Further, in step S3, the temperature of the heat treatment is preferably 800-1400 °C, and the time is preferably 2-6 h.

[0038] The third aspect of the present invention provides a positive electrode sheet, which contains the composite lithium supplement additive described in the first aspect or the composite lithium supplement additive prepared by the preparation method described in the second aspect.

[0039] Further, the positive electrode sheet includes a current collector and a positive electrode active layer provided on at least one surface of the current collector along the thickness direction. The positive electrode active layer contains the composite lithium supplement additive and a high-nickel ternary material; the mass ratio of the composite lithium supplement additive in the positive electrode active layer is preferably 1%-8%.

[0040] Further, the positive electrode active layer further contains a binder and a conductive agent. The mass ratio of the high-nickel ternary material, the composite lithium supplement additive, the binder, and the conductive agent in the positive electrode active layer is preferably (90-95):(1-8):(1-2):(1-2).

[0041] The fourth aspect of the present invention provides a lithium-ion battery, which contains the positive electrode sheet described in the second aspect.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] The present invention provides a composite lithium supplement additive, which uses porous carbon as the core. Its high specific surface area and rich pore structure can effectively adsorb the gas generated in the battery. The lithium supplement agent contained in some pores of the functional coating layer on the outer surface of the porous carbon can provide an additional lithium source to supplement the lithium loss during the cyclic charge and discharge process of the battery, improve the initial efficiency and cycle stability of the battery, and further increase the porosity of the functional coating layer after lithium supplementation, which is beneficial to lithium ion transmission; in addition, the presence of the first rigid coating provided on at least part of the surface of the porous carbon, the second rigid coating provided in at least part of the pores of the functional coating layer, and the outermost rigid coating layer can effectively improve the conductivity and structural stability of the composite lithium supplement additive, so that the composite lithium supplement additive can still maintain its original structure after lithium supplementation, avoiding the deterioration of the contact impedance due to structural failure, thereby effectively improving the battery safety and electrochemical performance.

[0044] The present invention also provides a method for preparing the above-mentioned composite lithium supplement additive. Through multi-layer coating, baking, impregnation, and heat treatment, a composite lithium supplement additive with a core-shell structure and provided with a first rigid coating, a second rigid coating, and a rigid coating layer can be prepared. The preparation process is simple in operation and easy to control in conditions, and is suitable for batch production; more importantly, the composite lithium supplement additive prepared by the above method not only can provide the lithium supplement function, but also has excellent properties such as gas generation adsorption in the battery, good conductivity, and stable structure, and has a good application prospect in high-nickel silicon-based batteries.

[0045] The high-nickel silicon-based lithium battery prepared by using the above composite lithium supplement additive as a cathode lithium supplement additive can effectively reduce the gas volume in the battery and increase the battery thermal failure temperature, thereby being beneficial to improving the safety performance of the battery. In addition, the high-nickel silicon-based lithium battery containing the above composite lithium supplement additive has a higher energy density while also showing better rate performance and cycling performance. Brief Description of the Drawings

[0046] Figure 1 It is a schematic structural diagram of a composite lithium supplement additive provided by the present invention;

[0047] Figure 2 It is an SEM image of a partial cross-sectional area of the composite lithium supplement additive prepared in Example 1 at the maximum compaction density;

[0048] Figure 3 It is an SEM image of a partial cross-sectional area of the composite lithium supplement additive prepared in Comparative Example 2 at the maximum compaction density;

[0049] In the figure: 1 is the inner core, 11 is the porous carbon, 111 is the pore structure in the porous carbon, 12 is the first rigid coating, 2 is the functional coating layer, 21 is the lithium supplement agent, 22 is a partial pore structure in the functional layer, 23 is the second rigid coating, and 3 is the rigid coating layer. Detailed Description of the Embodiments

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items. The "including" or "comprising" described in the present invention can also be replaced by the closed "being" or "consisting of...".

[0051] As described in the background art, high-nickel silicon-based lithium batteries with high theoretical specific capacity have problems such as serious gas production, low initial efficiency, and poor cycling performance. Existing solutions such as optimizing electrolyte additives, coating and modifying electrode materials, and adding lithium supplement agents are difficult to balance gas production inhibition and lithium compensation efficiency. Moreover, the lithium supplement agent will not only further exacerbate the gas production problem during application, but also its poor conductivity and structural collapse after lithium supplementation will deteriorate the battery internal resistance and affect the battery rate performance.

[0052] To solve the above problems, some embodiments of the present invention provide a composite lithium supplement additive. The composite lithium supplement additive has a core-shell structure and includes: a core 1, a functional coating layer 2, and a rigid coating layer 3; wherein, the core 1 includes porous carbon 11 and a first rigid coating 12 provided on at least a part of the surface of the porous carbon; the functional coating layer 2 is coated on the surface of the core 1, the functional coating layer 2 contains a lithium supplement agent 21, the functional coating layer 2 is a porous structure, the lithium supplement agent 21 is disposed in some pores 22 of the porous structure, and a second rigid coating 23 is disposed in at least some pores 22; the rigid coating layer 3 is coated on the surface of the functional coating layer 2; the first rigid coating 12, the second rigid coating 23, and the rigid coating layer 3 all contain metal carbides and / or metal nitrides.

[0053] In the existing high-nickel silicon-based battery system, there are problems such as serious gas generation, low initial efficiency, and poor cycle performance. By adding a lithium supplement agent, although the problem of low initial efficiency can be improved, it will further exacerbate the gas generation problem, and its poor conductivity and structural collapse after lithium supplementation will deteriorate the battery internal resistance, which will instead affect the battery rate performance. To solve the above problems, the present invention provides a composite lithium supplement additive with a core-shell structure. Among them, porous carbon is used as the core, and its high specific surface area and rich pore structure can effectively adsorb the gas generated in the battery. The lithium supplement agent accommodated in some pores of the functional coating layer on the outer surface of the porous carbon can provide an additional lithium source to supplement the lithium loss during the cyclic charge and discharge process of the battery, improve the battery initial efficiency and cycle stability, and further increase the porosity of the functional coating layer after lithium supplementation, which is beneficial to lithium ion transmission; in addition, the presence of the first rigid coating provided on at least a part of the surface of the porous carbon, the second rigid coating provided in at least some pores of the functional coating layer, and the outermost rigid coating layer can effectively improve the conductivity and structural stability of the composite lithium supplement additive, so that the composite lithium supplement additive can still maintain its original structure after lithium supplementation, avoiding the deterioration of the battery internal resistance due to structural failure, thereby effectively improving the battery safety and electrochemical performance. Through the dual design of the above materials and structures, the composite lithium supplement additive of the present invention not only provides a lithium supplementation function, but also has characteristics such as adsorbing battery gas, good conductivity, and stable structure, thus effectively solving the problems of gas generation and low initial efficiency of high-nickel silicon-based batteries, and the lithium battery containing the composite lithium supplement additive exhibits better rate performance and cycle stability.

[0054] In some preferred embodiments of the present invention, the porous carbon is a MOF-based porous carbon derivative and / or a COF-based porous carbon derivative; compared with other porous carbon materials, such MOF-based porous carbon derivatives and COF-based porous carbon derivatives have a higher specific surface area and excellent pore structures, so as to provide more adsorption sites and increase the gas adsorption capacity.

[0055] In the present invention, the lithium supplementing agent includes one or more of Li2O, Li2O2, and Li2N, and can also be other conventional decomposition-type lithium supplementing agents used in the art. After decomposition of the lithium supplementing agent, the porosity of the functional coating layer can be increased, which is beneficial to promoting the transport of lithium ions.

[0056] In the present invention, the functional coating layer further contains carbon and a conductive agent, which is beneficial to further improving the conductivity of the composite lithium supplementing additive.

[0057] In the present invention, the metal elements in the above-mentioned metal carbides and metal nitrides are selected from one or more of titanium, tungsten, zirconium, tantalum, chromium, and vanadium. The metal carbides and metal nitrides formed by these metals not only have excellent mechanical strength but also good conductivity, which is beneficial to further improving the structural stability and conductivity of the composite lithium supplementing additive.

[0058] In the present invention, the diameter of the core of the composite lithium supplementing additive is preferably 1-3 μm, such as 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, etc., including but not limited to the diameter sizes listed above; the thickness of the first rigid coating is preferably 50-100 nm, such as 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc., including but not limited to the thickness values listed above.

[0059] In the present invention, the thickness of the functional coating layer is preferably 1-3 μm, such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, etc., and the particle size of the lithium supplementing agent accommodated in some pores of the functional coating layer is preferably 500-1000 nm, such as 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, etc., including but not limited to the particle size sizes listed above, and the thickness of the second rigid coating provided on the inner surface of some pores is preferably 50-100 nm, such as 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc., including but not limited to the thickness values listed above.

[0060] In some preferred embodiments of the present invention, a second rigid coating is provided on the inner surface of some pores in the functional coating layer where the lithium supplementing agent is provided, so that the composite lithium supplementing additive can still maintain its original structure after lithium supplementation, and the contact resistance is prevented from increasing due to the collapse of the structure of the lithium supplementing agent.

[0061] In the present invention, the thickness of the rigid coating layer is preferably 50 - 100 nm, such as 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc., including but not limited to the thickness values listed above. If the thicknesses of the above-mentioned first rigid coating, second rigid coating and rigid coating layer are too thick, it will affect gas adsorption and lithium supplementation effect. If they are too thin, they cannot effectively support the structure and improve the conductivity. Therefore, preferably, the thicknesses of the above-mentioned rigid coatings and rigid coating layer are controlled in the range of 50 - 100 nm, so as to improve the conductivity and structural stability of the composite lithium supplementation additive while reducing the influence on gas adsorption and lithium supplementation effect.

[0062] The embodiment part of the present invention also provides a preparation method of the above-mentioned composite lithium supplementation additive, including the following steps:

[0063] S1. Mix ammonium bicarbonate and the first binder evenly to obtain a first mixture, and evenly coat the first mixture on the surface of the lithium supplementation agent to obtain a modified lithium supplementation agent;

[0064] S2. Mix the modified lithium supplementation agent, a conductive agent and the second binder evenly to obtain a second mixture, and evenly coat the second mixture on the surface of the porous material to obtain an additive precursor, and further bake it to obtain a porous additive precursor; the porous material is porous carbon and / or a porous carbon precursor;

[0065] S3. Disperse the porous additive precursor into a metal salt solution, separate the solid particles after sufficient impregnation; the metal element in the metal salt is selected from one or more of titanium, tungsten, zirconium, tantalum, chromium, and vanadium;

[0066] S4. Heat-treat the solid particles under a mixed atmosphere to obtain the composite lithium supplementation additive; the mixed atmosphere contains a protective gas and an alkane gas.

[0067] In the present invention, ammonium bicarbonate is used to coat the surface of the lithium supplement agent with a first binder to prepare a modified lithium supplement agent. Then, a conductive agent and the modified lithium supplement agent are coated on the surface of a porous material with a second binder to prepare an additive precursor. Subsequently, by baking, ammonium bicarbonate in the modified lithium supplement agent in the surface functional layer of the additive precursor is thermally decomposed, thereby forming a pore structure around the lithium supplement agent, making the functional layer have a porous structure, and obtaining the above-mentioned porous additive precursor. Then, the porous additive precursor is fully mixed and impregnated with a metal salt solution, so that the metal salt solution can enter the interior of the porous additive precursor through the porous structure of the functional layer and the pore structure of the porous material. After high-temperature carbonization, a rigid coating is formed on the partial surface of the carbonized porous material and the inner surface of the partial pore structure of the functional coating layer, and a rigid coating layer is formed on the outer surface of the functional coating layer, obtaining a composite lithium supplement additive with a core-shell structure and provided with a first rigid coating, a second rigid coating, and a rigid coating layer. The above method has simple operation and easy control of preparation conditions, and is suitable for industrial production.

[0068] In step S1 of the present invention, the mass ratio of the ammonium bicarbonate to the first binder is preferably (40 - 95):(5 - 60), such as 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, 95:5, etc., including but not limited to the mass ratios listed above.

[0069] In step S1 of the present invention, the first binder used is a binder commonly used in the art, including but not limited to polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, etc.

[0070] In step S1 of the present invention, in the coating step: first, the first mixture is uniformly mixed with the first solvent to obtain a first slurry, and then it is uniformly sprayed onto the surface of the lithium supplement agent by spray coating to obtain a modified lithium supplement agent; wherein, the first solvent is preferably N-methylpyrrolidone; other coating treatments can also be used, such as liquid-phase mixing and stirring, etc.

[0071] In step S1 of the present invention, the modified lithium supplement agent includes a lithium supplement agent and an ammonium bicarbonate coating layer provided on the surface of the lithium supplement agent. Among them, the thickness of the ammonium bicarbonate coating layer is preferably 100 - 500 nm, such as 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc., so that after ammonium bicarbonate decomposes, a sufficiently large pore structure can be formed around the lithium supplement agent, and after impregnation and heat treatment, a second rigid coating with an appropriate thickness can be formed.

[0072] In step S2 of the present invention, the mass ratio of the modified lithium supplement agent to the conductive agent and the second binder is preferably (92 - 96):(1 - 3):(3 - 5), such as 95:2:3, etc.

[0073] In step S2 of the present invention, the second binder used is a binder commonly used in the art, including but not limited to polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, etc.; the conductive agent used is a conductive agent commonly used in the art, including but not limited to conductive carbon black, graphite, carbon nanotubes, etc.

[0074] In step S2 of the present invention, in the coating step: first, the second mixture is uniformly mixed with the second solvent to obtain a second slurry, and then it is uniformly sprayed onto the surface of the porous material by spray coating to obtain an additive precursor; wherein, the second solvent is preferably N-methylpyrrolidone; other coating treatments can also be used, such as liquid-phase mixing and stirring, etc.

[0075] In step S2 of the present invention, the above-mentioned additive precursor includes a porous material and a functional layer coated on the surface of the porous material, wherein the thickness of the functional layer is preferably 1-3 μm, such as 1 μm, 2 μm, 3 μm, etc., to accommodate sufficient lithium supplement agent to ensure the lithium supplement effect.

[0076] In step S2 of the present invention, the baking temperature is preferably 100-150 °C, such as 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, etc., and the time is preferably 8-12 h, such as 8 h, 9 h, 10 h, 11 h, 12 h, etc.

[0077] In step S2 of the present invention, the porous carbon precursor includes a porous MOF material and / or a porous COF material. The porous MOF material and the porous COF material are heat-treated to form corresponding derivatives, which not only have a high specific surface area and a rich pore structure, but also have excellent electrical conductivity.

[0078] In step S3 of the present invention, the metal salt is selected from one or more of hydrochlorides, sulfates, nitrates; preferably, the concentration of the metal salt solution is 0.01-0.5 mol / L, such as 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, etc., including but not limited to the concentrations listed above; the solvent of the metal salt solution can be selected from one or more of benzene, toluene, ethanol, methanol, chloroform.

[0079] In step S3 of the present invention, the porous additive precursor is fully impregnated in the metal salt solution by stirring treatment; the stirring treatment is carried out under vacuum, and the time of the stirring treatment is preferably 2-4 h, such as 2 h, 3 h, 4 h, etc.

[0080] In step S3 of the present invention, the protective gas in the above-mentioned mixed atmosphere may be selected from one or more of nitrogen, argon, helium, and neon, and the alkane gas in the mixed atmosphere may be selected from one or more of methane, ethane, and propane.

[0081] In step S3 of the present invention, the temperature of the heat treatment is preferably 800 - 1400 °C, such as 800 °C, 900 °C, 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C, etc., and the time is preferably 2 - 6 h, such as 2 h, 3 h, 4 h, 5 h, 6 h, etc.

[0082] In addition, the embodiment part of the present invention also provides a positive electrode sheet, which contains the composite lithium supplement additive prepared by the above preparation method.

[0083] In the present invention, the above-mentioned positive electrode sheet includes a current collector and a positive electrode active layer provided on at least one surface of the current collector along the thickness direction. The positive electrode active layer contains the above-mentioned composite lithium supplement additive and a high-nickel ternary material; wherein, the mass ratio of the composite lithium supplement additive in the positive electrode active layer is preferably 1% - 8%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc., including but not limited to the mass ratios listed above.

[0084] In the present invention, the positive electrode active layer further contains a binder and a conductive agent. The mass ratio of the high-nickel ternary material, the composite lithium supplement additive, the binder, and the conductive agent in the positive electrode active layer is preferably (90 - 95):(1 - 8):(1 - 2):(1 - 2), such as 93:5:1:1, etc.

[0085] The embodiment part of the present invention also provides a lithium-ion battery, which contains the above-mentioned positive electrode sheet; this lithium-ion battery not only has a higher thermal failure temperature, but also has less gas volume in the battery and higher safety performance; in addition, this lithium-ion battery also exhibits better rate performance and cycle performance while having a high energy density.

[0086] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited do not limit the present invention. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not specified for the manufacturers, they are all conventional products that can be obtained through commercial purchase.

[0087] Example 1

[0088] This example relates to the preparation of a composite lithium supplement additive, which specifically includes the following steps:

[0089] (1)Preparation of porous material: Cobalt nitrate and 2-methylimidazole were uniformly mixed in water at a mass ratio of 1:4 to prepare a mixed solution with a concentration of 20 g / L. The temperature was slowly raised to 130 °C and stirred for 4 h to obtain a porous material ZIF with a particle size of 1.5 μm.

[0090] (2)Preparation of modified lithium supplement agent: The lithium supplement agent Li2O particles were ground into particles with a particle size of 500 nm, and an ammonium bicarbonate slurry was prepared. The ammonium bicarbonate particles and the binder (polyvinylidene fluoride) were uniformly mixed at a mass ratio of 95:5 and stirred for 2 h. Subsequently, it was uniformly sprayed onto the surface of the lithium supplement agent by spray coating, with a thickness of about 200 nm.

[0091] (3)Preparation of porous additive precursor: The binder (polyvinylidene fluoride), conductive agent (conductive carbon black), and modified lithium supplement agent were uniformly mixed at a mass ratio of 3:2:95. The additive precursor was obtained by uniformly spraying it onto the surface of the core porous material by spray coating. The thickness of the functional layer here was 1.5 μm. Then, it was baked at 120 °C for 8 h to obtain the porous additive precursor.

[0092] (4)Preparation of rigid coating and rigid coating layer: After grinding the prepared porous additive precursor into particles of appropriate size, it was uniformly dispersed in titanium tetrachloride solution with a concentration of 0.1 mol / L, stirred under vacuum for 2 h, and then the soaked material was taken out by filtration. Under the protection of N2, an alkane gas was introduced and reacted at 1000 °C for 4 h to obtain the composite lithium supplement additive.

[0093] Example 2

[0094] This example relates to the preparation of a composite lithium supplement additive. The difference from Example 1 is only that: in step (1), the particle size of the porous material ZIF is 2.5 μm, and the other conditions are the same, and the corresponding composite lithium supplement additive is prepared.

[0095] Example 3

[0096] This example relates to the preparation of a composite lithium supplement additive. The difference from Example 1 is only that: in step (2), the particle size of the lithium supplement agent particles is 1000 nm, and the other conditions are the same, and the corresponding composite lithium supplement additive is prepared.

[0097] Example 4

[0098] This example relates to the preparation of a composite lithium supplement additive. The difference from Example 1 is only that: in step (3), the thickness of the functional layer is 2.5 μm, and the other conditions are the same, and the corresponding composite lithium supplement additive is prepared.

[0099] Example 5

[0100] This example relates to the preparation of a composite lithium supplement additive. The difference from Example 1 is only that: the lithium supplement agent in step (2) is Li2N, and the rest of the conditions are the same, and the corresponding composite lithium supplement additive is prepared.

[0101] Comparative Example 1

[0102] This comparative example relates to the preparation of a composite lithium supplement additive. The difference from Example 1 is only that: the temperature of the heat treatment in step (4) is 600 °C, and the rest of the conditions are the same, and the corresponding composite lithium supplement additive is prepared.

[0103] Comparative Example 2

[0104] This comparative example relates to the preparation of a composite lithium supplement additive. The difference from Example 1 is only that: step (4) does not include the step of stirring treatment in the titanium tetrachloride solution, and the rest of the conditions are the same, and the corresponding composite lithium supplement additive is prepared.

[0105] Comparative Example 3

[0106] This comparative example relates to the preparation of a composite lithium supplement additive. The difference from Example 1 is only that: it does not include the step of modifying the lithium supplement agent in step (2), and the rest of the conditions are the same, and the corresponding composite lithium supplement additive is prepared.

[0107] Application and Performance Test

[0108] (1) The following performance tests are carried out on the composite lithium supplement additives prepared in the above examples and comparative examples:

[0109] Specific surface area test: Take samples of the same mass, and use the N2 adsorption method to characterize the specific surface area contained in the material through the adsorption amount of gas;

[0110] Maximum compaction density and crushing situation of the composite lithium supplement additive under the maximum compaction density: Place 1 g of the target product powder in the sample bin, extrude it under a pressure of 3 T, take the extruded sample, and use a planar scanning electron microscope and CP (cross-section scanning electron microscope) to judge whether the composite lithium supplement additive is broken, and record the maximum compaction density corresponding to no breakage of the structure. Compaction density = surface density / thickness (surface density = 1 g / sample bin area, thickness = powder compaction thickness when the lithium supplement additive is broken).

[0111] Conductivity test: Take the composite lithium supplement additives of the same mass, extrude them into blocks of the same thickness, and then place them on a four-probe resistivity tester to test the electrical conductivity of the material.

[0112] The test results are shown in Table 1 below:

[0113] Table 1

[0114]

[0115] As can be seen from Table 1, the composite lithium supplement additives prepared in Examples 1-5 all have high specific surface area, tap density and conductivity, and the composite lithium supplement additives do not crack or break under the maximum tap density, which is beneficial to optimizing the energy density, rate performance and cycle performance of the battery.

[0116] As can be seen from Example 1 and Comparative Examples 1 and 2, the presence of the first and second rigid coatings and the rigid coating layer can effectively improve the structural strength of the composite lithium supplement additive. For example Figure 2 , 3 shown, under the extrusion of 3 T pressure, the SEM image of the local area of the cross-section of the composite lithium supplement additive prepared in Example 1 after extrusion at the maximum tap density shows no obvious cracking or breaking problems, while the SEM image of the local area of the cross-section of the composite lithium supplement additive in Comparative Example 2 after extrusion at the maximum tap density shows obvious cracking and breaking phenomena, and the maximum tap density of the composite lithium supplement additive prepared in Example 1 is higher than that of the composite lithium supplement additive prepared in Comparative Example 1. It can be seen from this that the presence of the rigid coating / coating layer is beneficial to improving the overall tap density and is beneficial to the high energy density system; too low sintering temperature of the rigid coating / coating layer (Comparative Example 2) will result in poor structural strength and low conductivity of the whole composite lithium supplement additive, because too low sintering temperature cannot form a dense and high-hardness rigid coating and rigid coating layer.

[0117] In addition, as can be seen from Example 1 and Comparative Example 3, the specific surface area of the composite lithium supplement additive prepared without ammonium bicarbonate coating modification (Comparative Example 3) is significantly lower than that of the composite lithium supplement additive prepared in Example 1. This is because the lithium supplement agent modified by ammonium bicarbonate coating in some pores of the functional coating layer can be decomposed by baking treatment to form pores, thereby effectively increasing the specific surface area of the composite lithium supplement additive, and the metal salt solution can form a metal salt adsorption layer on the inner wall of the pores through these pores, and a rigid coating is obtained after sintering, which is beneficial to improving the conductivity of the composite lithium supplement additive. At the same time, due to the presence of the rigid coating, the inner wall of the pores accommodating the lithium supplement agent can still maintain its original structure after the lithium supplement agent decomposes during lithium supplementation, effectively avoiding the problem of increasing the contact resistance due to the collapse of the structure of the lithium supplement agent.

[0118] (2) The composite lithium supplement additives prepared in the above examples and comparative examples were used to prepare positive electrode sheets and construct corresponding lithium ion batteries. The specific operations are as follows:

[0119] Preparation of the positive electrode sheet: The high-nickel ternary material (LiNi 0.8 Co 0.1 Mn 0.1O2), binder PVDF5130, conductive agent SP, and composite lithium supplement additive are added in a mass ratio of 93:1:1:5, and NMP is added and stirred to form a uniformly mixed and stable positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector (13 μm aluminum foil), and the coating areal density is 195 g / m 2 , and after drying and cold pressing, a positive electrode sheet is obtained. The selected compaction density is 3.4 g / cm 3 .

[0120] Preparation of negative electrode sheet: The negative electrode active material (obtained by mixing graphite and silicon-oxygen material in a mass ratio of 8:2), conductive agent SP, PAA, and SBR are mixed in a mass ratio of 95.5:1.5:2:1, and then deionized water is added and stirred to form a uniformly mixed and stable negative electrode slurry. The negative electrode slurry is uniformly coated on the negative electrode current collector, and the coating areal density is 105 g / m 2 , and after drying, a negative electrode sheet is obtained. The selected compaction density is 1.5 g / cm 3 .

[0121] Separator: Composite ceramic separator (9 μm PP base film + 3 μm ceramic layer).

[0122] Electrolyte: LiPF6 is dissolved in a solvent with a volume ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate of 1:1:1, and the concentration is 1.2 mol / L.

[0123] Arrange the positive electrode sheet, separator, negative electrode sheet, and isolation film in sequence, and the winding method is selected for assembly; inject the electrolyte into the dry battery cell, soak for 24 h, and then carry out formation at 45 °C. The formation process: charge at 0.05 C to 3.4 V, and then charge at 0.2 C to 3.75 V; after aging at room temperature for 24 h, the battery cell production is completed.

[0124] Perform the following electrochemical performance tests on the above lithium-ion batteries containing different composite lithium supplement additives:

[0125] Measurement of the gas volume inside the battery: Take the battery completed by the above aging production and measure its initial volume V0 by the water displacement method; charge at a constant current of 0.5 C to 4.25 V, then charge at a constant voltage of 4.25 V to 0.05 C, let it stand for 30 min, and then discharge at a constant current of 1 C to 2.5 V. Repeat the above charge and discharge operations for 400 cycles, and then measure the volume V1 of the battery after 400 cycles by the water displacement method. The gas volume = measured volume V1 - battery initial volume V0.

[0126] Thermal failure temperature test: Charge at a constant current of 0.5 C until 4.25 V, then charge at a constant voltage of 4.25 V until 0.05 C to fully charge the battery cell. Place it in a thermal chamber, heat it at a rate of 5 °C per minute to 130 °C and hold for half an hour. Observe for half an hour. If there is no fire or smoke, continue to heat at a rate of 5 °C and test the failure temperature every 5 °C until the battery fails. The temperature at this time is the thermal failure temperature.

[0127] 1 C energy density test: Let the battery stand in an environment of 25 °C for 30 min, charge at a constant current of 0.5 C until 4.25 V, then charge at a constant voltage of 4.25 V until 0.05 C, stand for 30 min, discharge at a constant current of 1 C until 2.5 V, collect the discharged capacity and discharged voltage data of the test. At this time, the energy density = discharged capacity × average voltage / battery weight.

[0128] 1 C cycle test: Let the battery stand in an environment of 25 °C for 30 min, charge at a constant current of 0.5 C until 4.25 V, then charge at a constant voltage of 4.25 V until 0.05 C, stand for 30 min, discharge at a constant current of 1 C until 2.5 V, record the discharged capacity of the first cycle as the initial capacity, repeat the above charge and discharge operations, and record the discharged capacity of the 500th cycle; then the capacity retention rate of 500 cycles = (discharged capacity of the 500th cycle / discharged capacity of the first cycle) × 100%.

[0129] Rate retention test: Charge at a constant current of 0.5 C until 4.25 V, then charge at a constant voltage of 4.25 V until 0.05 C; stand for 30 min; discharge at a constant current of 0.5 C to the lower limit voltage of 2.5 V, record the discharged capacity at 0.5 C; stand for 30 min; then charge at a constant current of 0.5 C until 4.25 V, then charge at a constant voltage of 4.25 V until 0.05 C; stand for 30 min; perform a constant current discharge at 5 C and record the discharged capacity at 5 C; then the 5 C rate retention = (discharged capacity at 5 C / discharged capacity at 0.5 C) × 100%.

[0130] The test results are shown in Table 2 below:

[0131] Table 2

[0132]

[0133] As can be seen from Table 2, the lithium-ion batteries constructed by adding the composite lithium supplement additives prepared in Examples 1-5 to the positive electrode not only have high energy density, excellent cycle performance and rate performance, but also after 500 cycles of charge and discharge, the gas volume in the battery is small and the thermal chamber failure temperature is high, and the safety performance of the battery is better.

[0134] As can be seen from Example 1 and Comparative Examples 1 and 2, reducing the carbonization temperature of the rigid coating or directly canceling the preparation of the rigid coating / cladding layer results in a lower structural strength of the prepared composite lithium supplement additive, which not only affects its compaction and conductivity, but also causes a decrease in the energy density of the battery, and deteriorates the rate performance, cycle performance, and thermal box safety performance, etc.

[0135] In addition, for the lithium-ion battery constructed by adding the composite lithium supplement additive (Comparative Example 3) without being coated and modified with ammonium bicarbonate to the positive electrode, compared with Example 1, not only is the energy density low, the cycle performance and rate performance are relatively poor, but also the gas absorption effect is poor, and the thermal box failure temperature also decreases. This is because the composite lithium supplement additive prepared without being coated and modified with ammonium bicarbonate has fewer pores, resulting in a decrease in the gas absorption effect. At the same time, it will affect the transmission of lithium ions. Moreover, since an effective rigid coating cannot be formed on the inner wall of the pores in the composite lithium supplement additive that accommodate the lithium supplement agent, the structural stability and conductivity become poor, leading to deterioration of the overall electrochemical performance of the lithium-ion battery.

[0136] The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims

1. A composite lithium supplement additive, characterized in that, The composite lithium supplement additive has a core-shell structure and includes: a core, a functional coating layer, and a rigid coating layer; The core includes porous carbon and a first rigid coating disposed on at least a part of the surface of the porous carbon; The functional coating layer is coated on the surface of the core. The functional coating layer contains a lithium supplement agent. The functional coating layer is a porous structure. The lithium supplement agent is disposed in some pores of the porous structure, and a second rigid coating is disposed in at least some pores; The rigid coating layer is coated on the surface of the functional coating layer; The first rigid coating, the second rigid coating, and the rigid coating layer all contain metal carbides and / or metal nitrides; The preparation method of the composite lithium supplement additive includes the following steps: S1. Mix ammonium bicarbonate and a first binder evenly to obtain a first mixture, and evenly coat the first mixture on the surface of the lithium supplement agent to obtain a modified lithium supplement agent; S2. Mix the modified lithium supplement agent, a conductive agent, and a second binder evenly to obtain a second mixture, and evenly coat the second mixture on the surface of the porous material to obtain an additive precursor, and further bake it to obtain a porous additive precursor; the porous material is porous carbon and / or a porous carbon precursor; S3. Disperse the porous additive precursor into a metal salt solution, separate the solid particles after sufficient impregnation; the metal element in the metal salt is selected from one or more of titanium, tungsten, zirconium, tantalum, chromium, and vanadium; S4. Heat-treat the solid particles under a mixed atmosphere to obtain the composite lithium supplement additive; the mixed atmosphere contains a protective gas and an alkane gas.

2. The composite lithium supplement additive according to claim 1, wherein It at least includes one of the following features: (1) The porous carbon includes MOF-based porous carbon derivatives and / or COF-based porous carbon derivatives; (2) The lithium supplement agent includes one or more of Li2O, Li2O2, and Li2N; (3) The metal element in the metal carbide and the metal nitride is selected from one or more of titanium, tungsten, zirconium, tantalum, chromium, and vanadium; (4) The functional coating layer further contains carbon and a conductive agent.

3. The composite lithium supplement additive according to claim 1, characterized in that, It at least includes one of the following features: (1) The diameter of the core is 1-3 μm; (2) The thickness of the first rigid coating is 50-100 nm; (3) The thickness of the functional coating layer is 1-3 μm; (4) The particle size of the lithium supplement agent is 500-1000 nm; (5) The thickness of the second rigid coating is 50-100 nm; (6) The thickness of the rigid coating layer is 50-100 nm.

4. The composite lithium supplement additive according to claim 1, wherein In step S1, it at least includes one of the following features: (1) The mass ratio of the ammonium bicarbonate to the first binder is (40-95):(5-60); (2) In the coating step: first mix the first mixture with a first solvent evenly to obtain a first slurry, and then evenly spray and coat it on the surface of the lithium supplement agent by a spray coating method to obtain a modified lithium supplement agent; the first solvent is N-methylpyrrolidone; (3)The modified lithium supplement agent includes a lithium supplement agent and an ammonium bicarbonate coating layer provided on the surface of the lithium supplement agent, and the thickness of the ammonium bicarbonate coating layer is 100-500 nm.

5. The composite lithium supplement additive according to claim 1, characterized in that In step S2, it includes at least one of the following features: (1)The mass ratio of the modified lithium supplement agent, the conductive agent, and the second binder is (92-96):(1-3):(3-5); (2)In the coating step: First, the second mixture is uniformly mixed with a second solvent to obtain a second slurry, and then it is uniformly sprayed onto the surface of the porous material by spray coating to obtain an additive precursor; the second solvent is N-methylpyrrolidone; (3)The additive precursor includes a porous material and a functional layer coated on the surface of the porous material, and the thickness of the functional layer is 1-3 μm; (4)The baking temperature is 100-150 °C, and the time is 8-12 h; (5)The porous carbon precursor includes a porous MOF material and / or a porous COF material.

6. The composite lithium supplement additive according to claim 1, wherein In step S3, it includes at least one of the following features: The metal salt is selected from one or more of hydrochlorides, sulfates, and nitrates; The concentration of the metal salt solution is 0.01-0.5 mol / L, and the solvent of the metal salt solution is selected from one or more of benzene, toluene, ethanol, methanol, and chloroform; The porous additive precursor is fully impregnated in the metal salt solution by stirring treatment; the stirring treatment is carried out under vacuum, and the time of the stirring treatment is 2-4 h; The protective gas is selected from one or more of nitrogen, argon, helium, and neon, and the alkane gas is selected from one or more of methane, ethane, and propane; The temperature of the heat treatment is 800-1400 °C, and the time is 2-6 h.

7. A positive electrode sheet, characterized in that, It includes the composite lithium supplement additive according to any one of claims 1-6.

8. The positive electrode sheet according to claim 7, wherein The positive electrode sheet includes a current collector and a positive electrode active layer provided on at least one surface of the current collector along the thickness direction. The positive electrode active layer includes the composite lithium supplement additive and a high-nickel ternary material; the mass ratio of the composite lithium supplement additive in the positive electrode active layer is 1%-8%.

9. A lithium-ion battery, characterized in that, It includes the positive electrode sheet according to claim 7 or 8.

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