Negative electrode material, preparation method and application thereof

Abstract

The application relates to a negative electrode material and a preparation method and application thereof. The negative electrode material comprises lithium fluoride nanowires and lithium metal with a mass ratio of 1: (2-200), and the lithium metal is filled in a framework formed by the lithium fluoride nanowires. The negative electrode material comprises lithium fluoride nanowires and lithium metal in a certain ratio, the lithium metal is filled in a lithium fluoride nanowire framework, the lithium fluoride nanowire framework can hinder the volume expansion of the lithium metal, has a high lithium interface energy, can promote the uniform deposition of lithium ions, inhibit the longitudinal growth of lithium dendrites, meanwhile, the lithium fluoride nanowires have the characteristics of low electron conductivity and a wide electrochemical window, can reduce the side reaction on the lithium metal / electrolyte interface, and thus improve the cycle life of a lithium secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery materials, and in particular to a negative electrode material, its preparation method, and its application. Background Technology

[0002] Currently, with the development of electric vehicles and portable energy storage devices, the demand for high-capacity batteries is increasing, and lithium-ion batteries based on graphite anodes (theoretical specific capacity of 374 mAh / g) are gradually failing to meet these requirements. Lithium metal anodes are among the electrode materials with the highest known specific energy, possessing an ultra-high theoretical specific capacity (3860 mAh / g) and a low standard electrochemical potential (-3.04V vs. standard hydrogen electrode), and have gradually attracted widespread attention. However, the cycle performance of lithium-ion batteries based on lithium metal anodes still needs improvement during continuous charge and discharge. Summary of the Invention

[0003] Based on this, this application provides a negative electrode material, including lithium metal and lithium fluoride nanowires, for use in secondary batteries, which can improve the cycle performance of the battery.

[0004] In addition, this application also provides a method for preparing and applying a negative electrode material.

[0005] A negative electrode material comprising lithium fluoride nanowires and lithium metal in a mass ratio of 1:(2~200), wherein the lithium metal fills a framework formed by the lithium fluoride nanowires.

[0006] Optionally, the mass ratio of the lithium fluoride nanowire to the lithium metal is 1:(50~100).

[0007] Optionally, the lithium fluoride nanowires have an average diameter of 1 nm to 50 nm and an average length of 50 nm to 10 µm.

[0008] A method for preparing a negative electrode material includes the following steps:

[0009] The negative electrode material is prepared by mixing lithium fluoride nanowires with lithium metal and filling the framework formed by the lithium fluoride nanowires with the lithium metal.

[0010] The mass ratio of the lithium fluoride nanowires to the lithium metal is 1:(2~200).

[0011] Optionally, the step of mixing lithium fluoride nanowires with lithium metal, such that the lithium metal fills the framework formed by the lithium fluoride nanowires, includes:

[0012] The lithium fluoride nanowires and lithium metal were mixed uniformly under an inert atmosphere to prepare a mixture;

[0013] The mixture was annealed at 180°C to 600°C for 0.5 to 24 hours under an inert atmosphere.

[0014] Optionally, the annealing temperature is 180℃~200℃; and / or,

[0015] The annealing process takes 6 to 12 hours.

[0016] Optionally, the lithium fluoride nanowires and the lithium metal are mixed uniformly by ball milling;

[0017] Optionally, the ball mill rotation speed is 300 rpm to 400 rpm, and the time is 4 h to 12 h.

[0018] Optionally, the preparation steps of the lithium fluoride nanowires include:

[0019] A precursor solution is prepared by stirring and reacting a mixture containing a lithium source, a fluorine source, and optionally ammonia water and a solvent.

[0020] The precursor solution was freeze-dried to prepare the lithium fluoride nanowires.

[0021] The lithium source includes one or more of lithium chloride, lithium iodide, and lithium bromide; the fluorine source includes one or more of ammonium fluoride and ammonium bifluoride; and the solvent includes one or more of water and ethanol.

[0022] Optionally, in the freeze-drying step, the vacuum degree is 5 kPa to 20 kPa, the temperature is -15℃ to -10℃, and the freeze-drying time is 0.5 h to 24 h.

[0023] Optionally, the step of stirring and reacting a mixture containing a lithium source, a fluorine source, and optionally ammonia and a solvent satisfies one or more of the following conditions:

[0024] (1) In the mixture, the molar ratio of the lithium source, the fluorine source and the ammonia water is (0.5~1):(0.5~1.1):(0~0.3).

[0025] (2) In the mixture, the total concentration of cations is 1 mol / L to 10 mol / L;

[0026] (3) The stirring reaction time is 1h~48h;

[0027] Optionally, the stirring reaction time is 1 hour to 6 hours.

[0028] A negative electrode sheet includes the negative electrode material described above or includes a negative electrode material prepared by the preparation method described above.

[0029] A secondary battery comprising the aforementioned negative electrode.

[0030] An electrical device comprising the aforementioned secondary battery.

[0031] The inventors discovered that lithium metal anode-based secondary batteries experience severe volume expansion and non-uniform lithium-ion deposition during cycling, leading to lithium dendrite formation. Furthermore, the intrinsic thermodynamic instability of lithium metal with respect to the electrolyte causes continuous side reactions between the lithium anode and the electrolyte, resulting in poor cycle performance. Therefore, the anode material provided in this application comprises a specific ratio of lithium fluoride nanowires and lithium metal. The lithium metal is filled within the framework formed by the lithium fluoride nanowires. This lithium fluoride nanowire framework hinders the volume expansion of lithium metal and possesses a high lithium interface energy, promoting uniform lithium-ion deposition and inhibiting the longitudinal growth of lithium dendrites. Simultaneously, the lithium fluoride nanowires exhibit low electronic conductivity and a wide electrochemical window, reducing side reactions at the lithium metal / electrolyte interface and thus improving the cycle life of the lithium secondary battery. Therefore, the above-mentioned anode material, when used in secondary batteries, can effectively improve the cycle performance of the secondary battery. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a process flow diagram of a method for preparing a negative electrode material in some embodiments of this application. Detailed Implementation

[0034] To facilitate understanding of this application, a more comprehensive description of the application will be provided below in conjunction with specific embodiments. Preferred embodiments of the application are given in the specific embodiments. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] Unless otherwise stated or in case of conflict, the terms or phrases used in this application shall have the following meanings:

[0037] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" and "second" may explicitly or implicitly include at least one of those features.

[0038] In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise expressly and specifically limited.

[0039] In this application, "one or more" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0040] Unless otherwise specified, all percentage concentrations mentioned in this application refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0041] The terms "optionally" and similar expressions used in this application refer to embodiments of this application that may provide certain beneficial effects under certain circumstances. However, other embodiments may also be optional in the same or other circumstances. Furthermore, the description of one or more optional embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this application.

[0042] When a numerical range is disclosed in this application, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any and all subranges to which they are included.

[0043] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0044] The terms "comprising" and "having," and any variations thereof, used in the embodiments of this application, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or components inherent to such processes, methods, products, or devices.

[0045] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0046] In this application, unless otherwise specified, room temperature refers to a temperature of 10℃ to 30℃. For example, room temperature may be, but is not limited to, 10℃, 12℃, 15℃, 18℃, 20℃, 22℃, 25℃, 28℃, 30℃, or any combination of these values. Optionally, room temperature refers to a temperature of 20℃ to 25℃.

[0047] The first aspect of this application provides a negative electrode material comprising lithium fluoride nanowires and lithium metal in a mass ratio of 1:(2~200), wherein the lithium metal is filled in a framework formed by the lithium fluoride nanowires.

[0048] In some embodiments, the mass ratio of lithium fluoride nanowires to lithium metal may be, but is not limited to, 1:2, 1:5, 1:10, 1:20, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:120, 1:140, 1:150, 1:160, 1:180, 1:200, or any range of two of these values. Optionally, the mass ratio of lithium fluoride nanowires to lithium metal is 1:(50~100).

[0049] In this document, nanowires refer to one-dimensional structures having a radial diameter limited to less than 100 nm. For example, the average diameter of a nanowire can be 1 nm to 100 nm. In some embodiments, the average diameter of a lithium fluoride nanowire is 1 nm to 50 nm, and the average length is 50 nm to 10 µm. In a specific example, the average diameter of a lithium fluoride nanowire can be, but is not limited to, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any combination of these values. The average length of a lithium fluoride nanowire can be, but is not limited to, 50 nm, 100 nm, 200 nm, 400 nm, 500 nm, 800 nm, 1 µm, 2 µm, 5 µm, 10 µm, or any combination of these values.

[0050] The inventors discovered that during cycling, secondary batteries based on lithium metal anodes experience severe volume expansion and non-uniform lithium-ion deposition, leading to the formation of lithium dendrites. Furthermore, the intrinsic thermodynamic instability of lithium metal with respect to the electrolyte causes continuous side reactions between the lithium anode and the electrolyte, resulting in a high-resistivity interface. These factors contribute to the poor cycle performance of secondary batteries based on lithium metal anodes. Therefore, the anode material provided in this application comprises lithium fluoride nanowires and lithium metal in a specific ratio. The lithium metal is filled within the framework formed by the lithium fluoride nanowires. This lithium fluoride nanowire framework hinders the volume expansion of lithium metal and possesses a high lithium interface energy, promoting uniform lithium-ion deposition and inhibiting the longitudinal growth of lithium dendrites. Simultaneously, the lithium fluoride nanowires also exhibit low electronic conductivity (~10). -12 The aforementioned anode material possesses characteristics such as a wide electrochemical window (0~6.3V), which can reduce side reactions at the lithium metal / electrolyte interface, thereby improving the cycle life of lithium secondary batteries. Therefore, the use of the above-mentioned anode material in secondary batteries can effectively improve the cycle performance of the batteries.

[0051] Furthermore, during continuous charging and discharging, lithium-ion secondary batteries based on lithium metal anodes can experience internal short circuits due to lithium dendrite growth on the anode side, leading to severe thermal runaway or even combustion and explosion. In contrast, the lithium fluoride nanowires in the anode materials of some embodiments of this application possess high lithium interface energy, which uniformly guides lithium-ion deposition, inhibits the longitudinal growth of lithium dendrites, and reduces the risk of internal short circuits in lithium-ion secondary batteries.

[0052] In traditional technologies, to address the issue of declining cycle performance in secondary batteries based on lithium metal anodes, researchers have added surface modification layers, such as lithium fluoride modification layers, to the surface of lithium metal anodes. While this improves cycle performance to some extent compared to lithium metal anodes, there is still room for improvement. In some embodiments of this application, lithium fluoride nanowires are combined with lithium metal, allowing the lithium metal to fill the framework formed by the lithium fluoride nanowires. This further improves cycle performance compared to adding a surface modification layer to the lithium metal surface, providing a new lithium metal-containing anode material.

[0053] A second aspect of this application provides a method for preparing a negative electrode material, comprising the following steps:

[0054] A negative electrode material is prepared by mixing lithium fluoride nanowires with lithium metal, allowing the lithium metal to fill the framework formed by the lithium fluoride nanowires.

[0055] The mass ratio of lithium fluoride nanowires to lithium metal is 1:(2~200).

[0056] In some embodiments, the step of mixing lithium fluoride nanowires with lithium metal to fill the framework formed by the lithium fluoride nanowires includes:

[0057] A mixture was prepared by uniformly mixing lithium fluoride nanowires with lithium metal under an inert atmosphere.

[0058] The mixture was annealed at 180℃~600℃ for 0.5h~24h under an inert atmosphere.

[0059] In some embodiments, lithium fluoride nanowires and lithium metal are mixed uniformly using ball milling. Specifically, the ball milling speed is 300 rpm to 400 rpm, and the time is 4 h to 12 h. Ball milling the lithium fluoride nanowires and lithium metal helps to fully and uniformly disperse the lithium fluoride nanowires and lithium metal. It is understood that the method of mixing the lithium fluoride nanowires and lithium metal is not limited to ball milling; other methods can be used to mix them uniformly.

[0060] In some embodiments, the annealing temperature is 180°C to 600°C. Annealing at these temperatures melts the lithium metal while leaving the lithium fluoride nanowires unmelted, allowing the lithium metal to fill the framework formed by the lithium fluoride nanowires. For example, the annealing temperature can be, but is not limited to, 180°C, 200°C, 220°C, 250°C, 280°C, 300°C, 320°C, 350°C, 380°C, 400°C, 450°C, 500°C, 550°C, 600°C, or any combination of these values. Optionally, the annealing temperature is 180°C to 200°C.

[0061] In some embodiments, the annealing time is 0.5h to 24h. For example, the annealing time may be, but is not limited to, 0.5h, 1h, 2h, 5h, 6h, 9h, 12h, 15h, 18h, 21h, 24h, or any range of two of these values. Optionally, the annealing time is 6h to 12h.

[0062] In some embodiments, the inert atmosphere may be, but is not limited to, an argon atmosphere.

[0063] In some embodiments, the preparation steps of lithium fluoride nanowires include:

[0064] A precursor solution is prepared by stirring and reacting a mixture containing a lithium source, a fluorine source, and optionally ammonia water and a solvent.

[0065] Lithium fluoride nanowires were prepared by freeze-drying the precursor solution.

[0066] The lithium source includes one or more of lithium chloride, lithium iodide and lithium bromide, the fluorine source includes one or more of ammonium fluoride and ammonium bifluoride, and the solvent includes one or more of water and ethanol.

[0067] It is understandable that in the step of stirring and reacting a mixture containing lithium source, fluorine source, optional ammonia and solvent, "optional ammonia" means that ammonia is optional in the mixed solution, that is, it is not necessary to add it, but can be added selectively. This includes two options: (1) stirring and reacting a mixture containing lithium source, fluorine source and solvent (i.e., without adding ammonia); (2) stirring and reacting a mixture containing lithium source, fluorine source, ammonia and solvent (i.e., with adding ammonia).

[0068] In some embodiments, the molar ratio of lithium source, fluorine source, and ammonia in the mixture is (0.5~1):(0.5~1.1):(0~0.3). For example, the molar ratio of lithium source, fluorine source, and ammonia is 0.5:0.5:0.1, 0.7:0.7:0.3, or 1:1:0.2. It is understood that in some embodiments, the mixture may not contain ammonia.

[0069] In some embodiments, the total concentration of cations in the mixture is 1 mol / L to 10 mol / L. For example, the total concentration of cations in the mixture may be, but is not limited to, 1 mol / L, 2 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 8 mol / L, 10 mol / L, or any combination of these values. It is understood that cations include lithium ions and ammonium ions.

[0070] In some embodiments, the stirring reaction step takes place over a period of 1 to 48 hours. The stirring reaction time can be, but is not limited to, 1 hour, 3 hours, 6 hours, 9 hours, 12 hours, 15 hours, 18 hours, 21 hours, 24 hours, 30 hours, 36 hours, 42 hours, 48 ​​hours, or any combination of these values. Optionally, the stirring reaction time is 1 to 6 hours. In practice, the reaction is stopped when a colorless and transparent liquid is obtained by stirring.

[0071] In some embodiments, during the stirring reaction step, the stirring speed is 100 rpm to 1200 rpm. For example, the stirring speed may be, but is not limited to, 100 rpm, 200 rpm, 400 rpm, 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, or any combination of these values.

[0072] In some embodiments, during the freeze-drying step, the vacuum level is 5 kPa to 20 kPa, the temperature is -15°C to -10°C, and the freeze-drying time is 0.5 h to 24 h. For example, during the freeze-drying step, the vacuum level is 5 kPa, 6 kPa, 8 kPa, 10 kPa, 12 kPa, 14 kPa, 15 kPa, 16 kPa, 18 kPa, 20 kPa, or any combination of these values. During the freeze-drying step, the temperature can be, but is not limited to, -15°C, -14°C, -13°C, -12°C, -11°C, -10°C, or any combination of these values. The freeze-drying time can be, but is not limited to, 0.5 h, 1 h, 2 h, 5 h, 6 h, 9 h, 12 h, 15 h, 18 h, 21 h, 24 h, or any combination of these values. Optionally, the freeze-drying time is 6 h to 12 h. Freeze-drying facilitates the preparation of lithium fluoride nanowires, while water-soluble components such as lithium and fluorine sources are removed as the water evaporates.

[0073] In some embodiments, after freeze-drying, the lithium fluoride nanowires can be cleaned, for example, with water and / or ethanol. Since lithium fluoride is insoluble in water and ethanol, while other impurities in the precursor solution, such as lithium halides, are soluble in water and ethanol, washing helps to further remove these impurities and improve the purity of the lithium fluoride nanowires.

[0074] In a specific example, the freeze-drying step is carried out inside a freeze dryer.

[0075] In some of these embodiments, please refer to Figure 1 The preparation method of the negative electrode material includes the following steps:

[0076] Step S110: Stir and react a mixture containing a lithium source, a fluorine source, and optionally ammonia and a solvent to prepare a precursor solution.

[0077] The lithium source includes one or more of lithium chloride, lithium iodide and lithium bromide, the fluorine source includes one or more of ammonium fluoride and ammonium bifluoride, and the solvent includes one or more of water and ethanol.

[0078] Step S120: Freeze-dry the precursor solution to prepare lithium fluoride nanowires.

[0079] Step S130: Under an inert atmosphere, lithium fluoride nanowires are mixed uniformly with lithium metal to prepare a mixture.

[0080] Step S140: Under an inert atmosphere, the mixture is annealed at 180℃~600℃ for 0.5h~24h to prepare the negative electrode material.

[0081] The specific processes for each step are as described above and will not be repeated here.

[0082] Figure 1 This is a schematic flowchart of a method for preparing a negative electrode material according to an embodiment of this application. It should be understood that, although Figure 1 The steps in the flowchart shown are displayed sequentially according to the arrows. However, these steps are not necessarily performed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order requirement for the execution of these steps; they can be executed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. Their execution order is not necessarily sequential, but can be executed in turn or alternately with at least some of other steps or other sub-steps or stages.

[0083] The above-mentioned anode material has a simple preparation process and the raw materials are easy to obtain, making it suitable for large-scale production.

[0084] A third aspect of this application provides a negative electrode sheet comprising the aforementioned negative electrode material.

[0085] It is understandable that the above-mentioned negative electrode material can be in block form, and negative electrode sheets can be prepared by rolling or cutting.

[0086] A fourth aspect of this application provides a secondary battery including the aforementioned negative electrode.

[0087] It is understood that the positive electrode, electrolyte, separator, etc. in secondary batteries can be those commonly used in this field, and no special limitation is made here.

[0088] The fifth aspect of this application provides an electrical device including the aforementioned secondary battery.

[0089] Specifically, electrical equipment can be, but is not limited to, electronic devices such as mobile phones, tablets, and laptops, or vehicles such as electric vehicles.

[0090] To make the objectives and advantages of this application clearer, the negative electrode material and its effects are further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining this application and should not be used to limit this application. Unless otherwise specified, the following embodiments do not include components other than unavoidable impurities. Unless otherwise specified, the drugs and instruments used in the embodiments are conventional choices in the art. Experimental methods in the embodiments that do not specify specific conditions are implemented according to conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0091] Example 1

[0092] This embodiment provides a negative electrode material comprising lithium fluoride nanowires and lithium metal in a mass ratio of 1:150, with the lithium metal filling the framework formed by the lithium fluoride nanowires. The preparation steps are as follows:

[0093] (1) Prepare a mixture of lithium chloride, ammonium fluoride, ammonia and water in a molar ratio of 0.5:0.5:0.1. The total cation concentration in the mixture is 5 mol / L.

[0094] (2) Place the mixture in a polytetrafluoroethylene bottle, turn on the magnetic stirrer, stir at 400 rpm for 8 hours to react until a colorless and transparent liquid is formed, and obtain the precursor solution.

[0095] (3) The precursor solution was placed in a freeze dryer, the vacuum degree of the freeze dryer was controlled at 10 kPa, the temperature was -15℃, the freezing time was 12h, and the solution was restored to room temperature to obtain lithium fluoride nanowires.

[0096] (4) In a glove box filled with argon, lithium fluoride nanowires and lithium metal with a mass ratio of 1:150 were placed in a vacuum ball mill jar, the ball milling speed was set to 300 rpm, the ball milling time was 4 h, and the lithium fluoride nanowire-lithium metal composite was obtained.

[0097] (5) The composite was placed in a muffle furnace in a glove box filled with argon gas, and the annealing temperature was set to 200°C and the annealing time was 12h. After the annealing was completed and the temperature was restored to room temperature, the negative electrode material of this embodiment was obtained.

[0098] The coin-type lithium secondary batteries assembled using the negative electrode material of Example 1 were tested for cycle performance at 0.5C and 1.0C rates. The results are as follows: at 0.5C, the first discharge specific capacity was 145 mAh / g, the first-cycle efficiency was 94%, and the capacity retention rate after 50 cycles was 89%; at 1.0C, the first discharge specific capacity was 140 mAh / g, the first-cycle efficiency was 89%, and the capacity retention rate after 50 cycles was 87%.

[0099] Example 2

[0100] This embodiment provides a negative electrode material comprising lithium fluoride nanowires and lithium metal in a mass ratio of 1:8, with the lithium metal filling the framework formed by the lithium fluoride nanowires. The preparation steps are as follows:

[0101] (1) Prepare a mixture of lithium bromide, ammonium bifluoride, ammonia and ethanol in a molar ratio of 0.7:0.7:0.3. The total cation concentration in the mixture is 10 mol / L.

[0102] (2) Place the mixture in a polytetrafluoroethylene bottle, turn on the magnetic stirrer, stir at 700 rpm for 8 hours to react until a colorless and transparent liquid is formed, and obtain the precursor solution.

[0103] (3) The precursor solution was placed in a freeze dryer, and the vacuum degree of the freeze dryer was controlled at 7 kPa, the temperature at -10℃, and the freezing time was 4 h. After freezing, the solution was restored to room temperature to obtain lithium fluoride nanowires.

[0104] (4) In a glove box filled with argon, lithium fluoride nanowires and lithium metal with a mass ratio of 1:8 were placed in a vacuum ball mill jar, the ball milling speed was set to 400 rpm, the ball milling time was 12 h, and the lithium fluoride nanowire-lithium metal composite was obtained.

[0105] (5) The composite was placed in a muffle furnace in a glove box filled with argon, and the annealing temperature was set to 180°C and the annealing time was 24h. After the annealing was completed and the temperature was restored to room temperature, the negative electrode material of this embodiment was obtained.

[0106] The coin-type lithium secondary batteries assembled using the negative electrode material of Example 2 above were tested for cycle performance at 1.0C and 4.0C rates. The results are as follows: at 1.0C, the first discharge specific capacity was 140 mAh / g, the first-cycle efficiency was 88%, and the capacity retention rate was 88% after 50 cycles; at 4.0C, the first discharge specific capacity was 134 mAh / g, the first-cycle efficiency was 86%, and the capacity retention rate was 83% after 200 cycles.

[0107] Example 3

[0108] This embodiment provides a negative electrode material comprising lithium fluoride nanowires and lithium metal in a mass ratio of 1:50, wherein the lithium metal fills the framework formed by the lithium fluoride nanowires. The preparation steps are as follows:

[0109] (1) Prepare a mixture of lithium iodide, ammonium fluoride, ammonia water in a molar ratio of 1:1:0.2 and a mixture of water and ethanol in a volume ratio of 1:1. The total concentration of cations in the mixture is 3 mol / L.

[0110] (2) Place the mixture in a polytetrafluoroethylene bottle, turn on the magnetic stirrer, stir at 1000 rpm for 40 h to react until a colorless and transparent liquid is formed, and obtain the precursor solution.

[0111] (3) The precursor solution was placed in a freeze dryer, and the vacuum degree of the freeze dryer was controlled at 5 kPa, the temperature at -13℃, and the freezing time was 24 h. After the freezing was completed and the temperature was restored to room temperature, lithium fluoride nanowires were obtained.

[0112] (4) In a glove box filled with argon, lithium fluoride nanowires and lithium metal with a mass ratio of 1:50 were placed in a vacuum ball mill jar. The ball milling speed was set to 400 rpm and the ball milling time was 6 h. After the ball milling was completed, the lithium fluoride nanowire-lithium metal composite was obtained.

[0113] (5) The composite was placed in a muffle furnace in a glove box filled with argon, and the annealing temperature was set to 450°C and the annealing time was 8h. After the annealing was completed and the temperature was restored to room temperature, the negative electrode material of this embodiment was obtained.

[0114] The coin-type lithium secondary batteries assembled using the negative electrode material of Example 3 above were tested for cycle performance at 0.1C and 3.0C rates. The results are as follows: at 0.1C, the first discharge specific capacity was 146 mAh / g, the first-cycle efficiency was 95%, and the capacity retention rate after 100 cycles was 95%; at 3.0C, the first discharge specific capacity was 142 mAh / g, the first-cycle efficiency was 90%, and the capacity retention rate after 300 cycles was 89%.

[0115] Example 4

[0116] This embodiment provides a negative electrode material comprising lithium fluoride nanowires and lithium metal in a mass ratio of 1:100, with the lithium metal filling the framework formed by the lithium fluoride nanowires. The preparation steps are as follows:

[0117] (1) Prepare a mixture of lithium chloride, ammonium fluoride, ammonia and water in a molar ratio of 0.5:0.5:0.1. The total cation concentration in the mixture is 5 mol / L.

[0118] (2) Place the mixture in a polytetrafluoroethylene bottle, turn on the magnetic stirrer, stir at 400 rpm for 8 hours to react until a colorless and transparent liquid is formed, and obtain the precursor solution.

[0119] (3) The precursor solution was placed in a freeze dryer, the vacuum degree of the freeze dryer was controlled at 10 kPa, the temperature was -15℃, the freezing time was 12h, and the solution was restored to room temperature to obtain lithium fluoride nanowires.

[0120] (4) In a glove box filled with argon, lithium fluoride nanowires and lithium metal with a mass ratio of 1:100 were placed in a vacuum ball mill jar, the ball milling speed was set to 300 rpm, the ball milling time was 4 h, and the lithium fluoride nanowire-lithium metal composite was obtained.

[0121] (5) The composite was placed in a muffle furnace in a glove box filled with argon gas, and the annealing temperature was set to 200°C and the annealing time was 12h. After the annealing was completed and the temperature was restored to room temperature, the negative electrode material of this embodiment was obtained.

[0122] The coin-type lithium secondary batteries assembled using the negative electrode material of Example 4 above were tested for cycle performance at 0.5C and 1.0C rates. The results are as follows: at 0.5C, the first discharge specific capacity was 143 mAh / g, the first-cycle efficiency was 93%, and the capacity retention rate after 50 cycles was 89%; at 1.0C, the first discharge specific capacity was 140 mAh / g, the first-cycle efficiency was 89%, and the capacity retention rate after 50 cycles was 91%.

[0123] Comparative Example 1

[0124] The negative electrode material in Comparative Example 1 is lithium metal.

[0125] The cycle performance of coin-type lithium secondary batteries assembled with lithium metal anode materials was tested at 0.5C and 1.0C rates. The results are as follows: at 0.5C, the first discharge specific capacity was 140 mAh / g, the first-cycle efficiency was 88%, and the capacity retention rate after 50 cycles was 32%; at 1.0C, the first discharge specific capacity was 132 mAh / g, the first-cycle efficiency was 85%, and the capacity retention rate after 50 cycles was 17%.

[0126] Comparative Example 2

[0127] Comparative Example 2 provides a negative electrode material, comprising a lithium metal sheet and a lithium fluoride modification layer disposed on the surface of the lithium metal sheet, and the preparation steps are as follows:

[0128] (1) Prepare an ammonium fluoride solution by mixing dimethyl sulfoxide and ammonium fluoride in a volume ratio of 10:1 and ultrasonically disperse for 15 min. Then add 2 g of dehydrating molecular sieve to remove water.

[0129] (2) Place the lithium metal sheet on a spin coater in an argon-filled glove box, and add 0.1 mL of ammonium bifluoride solution at a rate of 1100 rpm to the surface of the lithium metal sheet with a stable rotation speed for 1 min to obtain a lithium metal sheet with a liquid film formed on the surface.

[0130] (3) The lithium metal sheet with a liquid film formed on its surface is placed in a dielectric barrier discharge device (DBD device). The gas path in the dielectric barrier discharge device is opened, and argon gas is introduced for 5 minutes to clean the pipeline. Then, a mixture of argon gas and hydrogen fluoride gas with a volume ratio of 95:5 is introduced. The power of the dielectric barrier discharge device is adjusted to 60W and the working voltage is 24V. The frequency of the DBD device is adjusted to stabilize the current at 2.5A. The in-situ synthesis reaction is carried out for 30 minutes. After the reaction is completed, the dielectric barrier discharge device is turned off to obtain a lithium metal anode containing a lithium fluoride surface modification layer, which is the anode material of Comparative Example 2.

[0131] The coin-type lithium secondary batteries assembled using the lithium metal anode with the lithium fluoride surface modification layer were tested at 0.5C and 1.0C rates. The results are as follows: at 0.5C, the first discharge specific capacity was 141 mAh / g, the first-cycle efficiency was 90%, and the capacity retention rate after 50 cycles was 66%; at 1.0C, the first discharge specific capacity was 140 mAh / g, the first-cycle efficiency was 90%, and the capacity retention rate after 50 cycles was 54%.

[0132] Comparative Example 3

[0133] Comparative Example 3 provides an anode material comprising lithium fluoride nanowires and lithium metal in a mass ratio of 1:150, and the preparation steps are as follows:

[0134] (1) Prepare a mixture of lithium chloride, ammonium fluoride, ammonia and water in a molar ratio of 0.5:0.5:0.1. The total cation concentration in the mixture is 5 mol / L.

[0135] (2) Place the mixture in a polytetrafluoroethylene bottle, turn on the magnetic stirrer, stir at 400 rpm for 8 hours to react until a colorless and transparent liquid is formed, and obtain the precursor solution.

[0136] (3) The precursor solution was placed in a freeze dryer, the vacuum degree of the freeze dryer was controlled at 10 kPa, the temperature was -15℃, the freezing time was 12h, and the solution was restored to room temperature to obtain lithium fluoride nanowires.

[0137] (4) In a glove box filled with argon, lithium fluoride nanowires and lithium metal with a mass ratio of 1:150 were placed in a vacuum ball mill jar. The ball milling speed was set to 300 rpm and the ball milling time was 4 h. The lithium fluoride nanowire-lithium metal composite anode material was obtained, which is the anode material of Comparative Example 3.

[0138] Using the negative electrode metamaterial of Comparative Example 3, the coin-type lithium secondary battery was assembled and tested for cycle performance at 0.5C and 1.0C rates. The results are as follows: at 0.5C, the first discharge specific capacity was 139 mAh / g, the first-cycle efficiency was 89%, and the capacity retention rate after 50 cycles was 63%; at 1.0C, the first discharge specific capacity was 134 mAh / g, the first-cycle efficiency was 87%, and the capacity retention rate after 50 cycles was 53%.

[0139] As can be seen from the comparison of the above embodiments and Comparative Examples 1-2, compared with pure lithium metal anodes or lithium metal anodes modified with lithium fluoride surface modification layers, the composite material including lithium fluoride nanowires and lithium metal used as the anode in the embodiments of this application significantly improves the cycle performance. As can be seen from the comparison of the above embodiments and Comparative Example 3, in the embodiments, the lithium metal anode and lithium fluoride nanowires are ball-milled and then annealed, allowing the lithium metal to fill the framework formed by the lithium fluoride nanowires. Compared with Comparative Example 3, which only uses ball milling for mixing, the cycle performance of the prepared anode material is significantly improved.

[0140] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0141] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A negative electrode material, characterized in that, The mixture comprises lithium fluoride nanowires and lithium metal in a mass ratio of 1:(2~200), wherein the lithium metal fills the framework formed by the lithium fluoride nanowires, and the lithium fluoride nanowires have an average diameter of 1nm~50nm and an average length of 50nm~10µm.

2. The negative electrode material according to claim 1, characterized in that, The mass ratio of the lithium fluoride nanowires to the lithium metal is 1:(50~100).

3. A method for preparing a negative electrode material, characterized in that, Includes the following steps: The negative electrode material is prepared by mixing lithium fluoride nanowires with lithium metal and filling the framework formed by the lithium fluoride nanowires with the lithium metal. The lithium fluoride nanowires are in a mass ratio of 1:(2~200) to lithium metal, and the lithium fluoride nanowires have an average diameter of 1nm~50nm and an average length of 50nm~10µm.

4. The method for preparing the negative electrode material according to claim 3, characterized in that, The step of mixing lithium fluoride nanowires with lithium metal, thereby filling the framework formed by the lithium fluoride nanowires with the lithium metal, includes: The lithium fluoride nanowires and lithium metal were mixed uniformly under an inert atmosphere to prepare a mixture; The mixture was annealed at 180°C to 600°C for 0.5 to 24 hours under an inert atmosphere.

5. The method for preparing the negative electrode material according to claim 4, characterized in that, The annealing temperature is 180℃~200℃; and / or, The annealing process takes 6 to 12 hours.

6. The method for preparing the negative electrode material according to claim 4, characterized in that, The lithium fluoride nanowires and lithium metal were mixed evenly by ball milling.

7. The method for preparing the negative electrode material according to claim 6, characterized in that, The ball mill speed is 300 rpm to 400 rpm, and the time is 4 h to 12 h.

8. The method for preparing the negative electrode material according to any one of claims 3 to 7, characterized in that, The preparation steps of the lithium fluoride nanowires include: A precursor solution is prepared by stirring and reacting a mixture containing a lithium source, a fluorine source, and a solvent. The precursor solution was freeze-dried to prepare the lithium fluoride nanowires. The lithium source includes one or more of lithium chloride, lithium iodide, and lithium bromide; the fluorine source includes one or more of ammonium fluoride and ammonium bifluoride; and the solvent includes one or more of water and ethanol.

9. The method for preparing the negative electrode material according to claim 8, characterized in that, The mixture also contains ammonia.

10. The method for preparing the negative electrode material according to claim 8, characterized in that, In the freeze-drying step, the vacuum degree is 5 kPa to 20 kPa, the temperature is -15℃ to -10℃, and the freeze-drying time is 0.5 h to 24 h.

11. The method for preparing the negative electrode material according to claim 8, characterized in that, The step of stirring and reacting a mixture containing a lithium source, a fluorine source, and a solvent satisfies one or more of the following conditions: (1) In the mixture, the molar ratio of the lithium source, the fluorine source and the ammonia is (0.5~1):(0.5~1.1):(0~0.3). (2) In the mixture, the total concentration of cations is 1 mol / L to 10 mol / L; (3) The stirring reaction time is 1h~48h.

12. The method for preparing the negative electrode material according to claim 11, characterized in that, The stirring reaction time is 1 to 6 hours.

13. A negative electrode sheet, characterized in that, It includes the negative electrode material according to any one of claims 1 to 2 or the negative electrode material prepared by the preparation method according to any one of claims 3 to 12.

14. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 13.

15. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 14.

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