High-performance fluoride composite material for thermal battery and preparation method of high-performance fluoride composite material

Abstract

The invention belongs to the technical field of thermal battery materials, and relates to a high-performance fluoride composite material for a thermal battery and a preparation method thereof, the composite material is a composite material of a binary transition metal fluoride and fluorine-doped carbon or a ternary transition metal fluoride and fluorine-doped carbon, the prepared material can utilize the excellent synergistic effect between different metals to increase the activity and maintain the advantage of high voltage, and the fluorine-doped carbon has excellent conductivity, thermal stability and catalytic activity. In the aspect of the preparation process, a carbon source is introduced in the preparation process of the composite material, so that a fluoride precursor and a carbon precursor can be fully fused, the structural advantage can still be maintained after pyrolysis is completed, the interface resistance between the fluoride and the carbon material is greatly reduced, and the maximum utilization rate of the active material is realized. In conclusion, the composite material has the advantages of high voltage platform, low resistance, excellent thermal stability and high reaction activity, and a thermal battery assembled by using the composite material as a positive electrode material has excellent performance.

Description

Technical Field

[0001] This invention belongs to the field of thermal battery materials technology, specifically relating to a method for preparing a high-performance fluoride composite material and its application in thermal batteries. Background Technology

[0002] Thermal batteries possess advantages such as high specific power, high specific energy, high current output, wide operating temperature range, and long storage life. Chinese patent application CN119080080A discloses a method for preparing and applying a high-performance metal sulfide-carbon composite cathode material. This method involves mixing a precursor containing transition metals and carbon with sulfur-containing substances, followed by high-temperature pyrolysis to obtain a composite material of ternary transition metal sulfides and sulfur-doped carbon. However, sulfides, as cathode materials, suffer from low voltage plateaus and poor thermal stability, gradually failing to meet the current development needs of thermal batteries. Fluorides, compared to sulfides, have higher discharge plateau voltages and are increasingly attracting researchers' attention. However, the poor conductivity and low decomposition temperature of fluorides significantly reduce their utilization rate.

[0003] To address the aforementioned issues, numerous published patents have provided corresponding solutions. Among these, the most effective and rapid method is to construct composite materials using metal fluorides and carbon materials. For example, Chinese patent application CN115241453A discloses a core-shell structured metal fluoride / carbon composite material and its preparation method, employing metal fluoride as the core and carbon material as the outer shell, with a cavity structure between the two materials. This structural feature can improve the material's conductivity. However, the cavity structure increases the contact resistance and ion transport distance between the two materials. Furthermore, the use of fluorine-containing gas in the gas-solid phase reaction presents certain safety and reaction completion issues. Patent CN116779814A discloses a preparation method and application of a calcium titanium fluoride / carbon nanofiber composite material. This material is prepared using a liquid-phase precursor method combined with electrospinning, which can reduce contact resistance. However, the electrospinning method suffers from high cost and low general applicability. Patent CN118954487A discloses an in-situ grown transition metal fluoride / carbon nanotube composite material, its preparation method, and its application. This composite material combines the two materials through in-situ growth, which can reduce interfacial resistance. However, the low-resistance portion only exists at the interface between the two materials; the excellent conductivity of carbon materials is not fully utilized within the material itself.

[0004] Furthermore, during the activation phase of a thermal battery, the thermal shock generated by the heating material typically exceeds 1000℃. The thermal decomposition temperature of low-valence transition metal fluorides is generally around 500℃, while that of high-valence transition metal fluorides is around 400℃. This relatively low decomposition temperature makes them ill-suited to withstand the thermal shock from the heating material. Simultaneously, the operating temperature of thermal batteries is generally 500-550℃. This temperature range leads to the decomposition of some fluorides, reducing material utilization and specific capacity, making them unsuitable for use in thermal battery products. Therefore, further research is needed on the application of fluorides in thermal batteries.

[0005] Based on this, the present invention uses binary or ternary transition metal fluorides as active materials and fluorine-doped carbon as an electron transport network to improve the conductivity and thermal stability of the composite material. A "precursor preparation-pyrolysis" method is used to ensure complete contact between the two materials, reducing interfacial contact resistance and increasing the thermal decomposition temperature. The composite material prepared using this method can construct a comprehensive "active material-conductive agent" contact interface between the carbon material and the fluoride, reducing contact resistance. The thermal battery assembled from this composite material has the advantages of high voltage from fluorides and high conductivity and excellent thermal stability from carbon materials, making it widely applicable to the development of high-voltage, high-energy-density thermal batteries. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by proposing a high-performance fluoride composite material for thermal batteries and its preparation method. The preparation method of this invention aims to prepare a composite material with advantages such as high discharge voltage, low resistance, excellent reactivity, and high thermal decomposition temperature, and apply it to thermal batteries. This composite cathode can reduce the interfacial contact resistance between fluoride and carbon materials, improve the thermal stability and conductivity of the composite material, and the assembled thermal battery has the advantages of high voltage, long discharge time, and high capacity.

[0007] The technical solution of this invention is as follows:

[0008] A high-performance fluoride composite material for thermal batteries is a composite material of binary transition metal fluorides and fluorine-doped carbon, or a composite material of ternary transition metal fluorides and fluorine-doped carbon. Specifically, it uses binary or ternary transition metal fluorides as the active material and fluorine-doped carbon as the conductive material. The active material utilizes the excellent synergistic effect between different metals to increase activity and maintain a high voltage advantage. The conductive material has superior conductivity, thermal stability, and catalytic activity compared to pure carbon materials. In terms of the preparation process, the introduction of a carbon source during the preparation of the composite material precursor allows the fluoride precursor and carbon precursor to fully fuse together. The pyrolysis products maintain this structural advantage, greatly reducing the interfacial resistance between the fluoride and carbon materials and increasing the thermal decomposition temperature of the composite material. On the other hand, the fluorine-containing gas generated by the fluoride precursor can introduce fluorine atoms into the carbon structure, further increasing the reaction efficiency of the composite material and maximizing the utilization rate of the active material. Furthermore, the fluorine-containing gas in this invention is generated by the thermal decomposition of the fluoride precursor, which significantly improves the safety factor compared to the traditional method of introducing fluorine sources using fluorine gas or hydrofluoric acid.

[0009] This invention provides a method for preparing a high-performance fluoride composite material for thermal batteries, comprising the following steps:

[0010] Step 1: Synthesis of precursors

[0011] Under low temperature conditions, a transition metal salt is dissolved in ethanol and stirred for 0.5-1.5 h to form solution A; under room temperature conditions, a fluorine source and a carbon source are added to deionized water and stirred for 0.5-1.5 h to form solution B; under low temperature conditions, solution B is added dropwise to solution A to obtain a mixed solution and stirring is continued for 20-40 h; the precipitate after the reaction is completed is washed several times with ethanol by centrifugation, then vacuum dried, and the product is collected to obtain the precursor; the low temperature is <5℃;

[0012] The metal ions of the transition metal salt are any two or three of iron, cobalt, nickel, copper and zinc, and the anions are at least one of nitrate, chloride, acetate, phosphate, sulfate and carbonate.

[0013] The total concentration of the metal ions in the mixed solution is 0.15 mol / L-0.3 mol / L, and the content of each metal ion in the mixed solution accounts for not less than 30% of the total ion content;

[0014] The fluorine source is either ammonium fluoride or ammonium bifluoride.

[0015] The carbon source includes, but is not limited to, at least one of citric acid, sodium citrate, glucose, sucrose, cellulose, and fructose;

[0016] The concentrations of the fluoride source and carbon source in deionized water are 0.45 mol / L-0.9 mol / L and 0.02 mol / L-0.08 mol / L, respectively.

[0017] In the mixed solution, solution A accounts for 60%-80% of the volume.

[0018] The vacuum drying process conditions are: temperature 90-110℃, time 12-20h;

[0019] Step 2: Preparation of high-performance fluoride composite materials

[0020] The precursor obtained in step one is placed in a tube furnace. Under a protective gas atmosphere, the pyrolysis temperature is 600-750℃, the holding time is 4-8h, and the heating rate is 1-3℃ / min. After natural cooling to room temperature, the sample is collected to obtain the high-performance fluoride composite material.

[0021] The protective gas atmosphere refers to at least one of nitrogen and argon.

[0022] This invention also provides an application of high-performance fluoride composite materials in the preparation of positive electrodes for thermal batteries.

[0023] The application method includes the following steps:

[0024] 1) Fabrication of the positive electrode: In a glove box, the fluoride composite material is pressed into a sheet to obtain the positive electrode;

[0025] 2) In the glove box, place the positive electrode, LiCl-KCl electrolyte sheet and lithium negative electrode sheet on the stainless steel lead sheet in sequence and fix them to form a single thermal battery.

[0026] Beneficial effects:

[0027] This invention discloses a method for preparing a high-performance fluoride composite material for thermal batteries. It uses binary or ternary transition metal fluorides as active materials and fluorine-doped carbon materials as conductive agents. This composite material possesses advantages such as a high voltage platform, low resistance, excellent thermal stability, and high reactivity. When used as a cathode material, it results in thermal batteries with excellent performance. The invention also offers the following beneficial effects in terms of preparation process and battery performance improvement:

[0028] (1) The composite material preparation process of the present invention is simple, the material cost is low and the risk factor is low. The prepared composite material can effectively promote the application of fluorides in thermal batteries and has good benefits.

[0029] (2) The fluoride prepared by this invention is a multi-element transition metal fluoride. The heterogeneous metal atoms can generate a strong synergistic effect, which increases the reactivity of the active material and maintains the advantage of high voltage of the fluoride.

[0030] (3) The fluorine-doped carbon material prepared by this invention has high conductivity, thermal stability and catalytic activity. The introduction of fluorine atoms does not require an additional fluorination step, and it is safe and environmentally friendly.

[0031] (4) This invention enables the formation of fluoride precursors within the carbon precursor structure, maintaining this structural advantage after pyrolysis and effectively reducing the interfacial resistance between the two. Furthermore, the fluorine-containing gas generated by the fluoride precursor can introduce fluorine atoms into the carbon structure, increasing the reaction efficiency. Attached Figure Description

[0032] Figure 1 SEM images and elemental distributions of the sample prepared in Example 1 are shown; where (a) is the SEM image and (b)-(e) are the elemental distributions.

[0033] Figure 2 Thermal decomposition characteristics of the sample prepared in Example 1;

[0034] Figure 3 The battery performance test results of the sample prepared in Example 1 are shown; where (a) is the discharge curve and (b)-(c) are the pulse test results.

[0035] Figure 4 SEM images and elemental distributions of the samples prepared in Example 2 are shown; where (a) is the SEM image and (b)-(e) are the elemental distributions.

[0036] Figure 5 Thermal decomposition characteristics of the sample prepared in Example 2;

[0037] Figure 6 The battery performance test results of the sample prepared in Example 2 are shown; where (a) is the discharge curve and (b)-(c) are the pulse test results.

[0038] Figure 7 The battery performance test results of the sample prepared in Example 3 are shown; where (a) is the discharge curve and (b)-(c) are the pulse test results.

[0039] Figure 8 SEM images and elemental distributions of the sample prepared in Example 4 are shown; where (a) is the SEM image and (b)-(e) are the elemental distributions.

[0040] Figure 9 Thermal decomposition characteristics of the sample prepared in Example 4;

[0041] Figure 10 The battery performance test results of the sample prepared in Example 4 are shown; where (a) is the discharge curve and (b)-(c) are the pulse test results.

[0042] Figure 11 Thermal decomposition characteristics of the sample prepared in Example 5;

[0043] Figure 12 The battery performance test results of the sample prepared in Example 5 are shown; where (a) is the discharge curve and (b)-(c) are the pulse test results. Detailed Implementation

[0044] The specific embodiments of the present invention will be described in further detail below, but the present invention is not limited to these embodiments. Any improvements or substitutions based on the basic spirit of these embodiments shall still fall within the scope of protection claimed by the claims of the present invention.

[0045] Example 1

[0046] Step 1: Synthesis of precursors

[0047] Cobalt nitrate and nickel nitrate were dissolved in 60 mL of ethanol, resulting in a cobalt ion concentration of 0.075 mol / L and a nickel ion concentration of 0.075 mol / L. The solution was stirred at low temperature (<5℃) for 0.5 h to form solution A. Ammonium fluoride and citric acid were added to 40 mL of deionized water, resulting in an ammonium fluoride concentration of 0.45 mol / L and a citric acid concentration of 0.02 mol / L. The solution was stirred at room temperature for 0.5 h to form solution B. Solution B was added dropwise to solution A at low temperature, and stirring continued for 40 h to ensure complete reaction. The precipitate was washed several times with ethanol by centrifugation, then placed in a vacuum drying oven and kept at 90℃ for 12 h. The collected product was the precursor.

[0048] Step 2: Preparation of high-performance fluoride composite materials

[0049] The precursor obtained in step one is placed in a tube furnace and heated to a pyrolysis temperature of 600°C at a rate of 1°C / min in an argon atmosphere. The temperature is held for 4 hours. After natural cooling to room temperature, the sample is collected, which is the fluoride composite material for thermal batteries.

[0050] Step 3: Application of composite cathodes in thermal batteries

[0051] In the glove box, the composite material is pressed into a sheet and used as the positive electrode sheet. The positive electrode sheet, LiCl-KCl electrolyte sheet and lithium negative electrode sheet are placed on the stainless steel lead sheet in sequence to form a single thermal battery. After being taken out, it is placed on a single cell tester for testing.

[0052] like Figure 1 (a) shows the SEM image of the prepared material, which exhibits an irregular blocky structure with diverse sizes. The corresponding elemental distribution is as follows: Figure 1As shown in (be), C, F, Co, and Ni atoms are uniformly distributed on the material surface. The thermal decomposition characteristics of the prepared material are as follows: Figure 2 As shown, the material's mass loss is 14.6% when the temperature rises from 100℃ to 800℃, exhibiting excellent thermal stability. The discharge curve of the assembled thermal battery is shown below. Figure 3 As shown in (a), at 100 mA / cm 2 At a current density of 1.5V, the battery's initial discharge voltage is 2.44V. When the discharge cutoff voltage is 1.5V, the battery's discharge specific capacity reaches 206.2mAh / g. The battery's pulse discharge curve is shown below. Figure 3 As shown in (b), it can be seen that the internal resistance of the battery increases with the increase of discharge time. The calculated internal resistance value of the battery is as follows: Figure 3 As shown in (c), the initial internal resistance of the battery is 0.219Ω, which gradually increases to 0.340Ω. Although the internal resistance of the battery shows an increasing trend, its value remains relatively small.

[0053] Example 2

[0054] Step 1: Synthesis of precursors

[0055] Ferric nitrate, nickel chloride, and cobalt acetate were dissolved in 80 mL of ethanol, resulting in a solution with iron ion concentrations of 0.1 mol / L, nickel ion concentrations of 0.1 mol / L, and cobalt ion concentrations of 0.1 mol / L. The solution was stirred at low temperature (<5℃) for 1.5 h to form solution A. Ammonium fluoride and citric acid were added to 20 mL of deionized water, resulting in a solution with ammonium fluoride concentrations of 0.9 mol / L and citric acid concentrations of 0.08 mol / L. The solution was stirred at room temperature for 1.5 h to form solution B. Solution B was then added dropwise to solution A at low temperature, and the mixture was stirred for another 20 h to ensure complete reaction. The precipitate was washed several times with ethanol by centrifugation, then placed in a vacuum drying oven and kept at 110℃ for 20 h. The collected product was the precursor.

[0056] Step 2: Preparation of high-performance fluoride composite materials

[0057] The precursor obtained in step one was placed in a tube furnace and heated to a pyrolysis temperature of 750°C at a rate of 3°C / min in a nitrogen atmosphere. The temperature was held for 8 hours. After naturally cooling to room temperature, the sample was collected, which is the fluoride composite material.

[0058] Step 3: Application of composite cathodes in thermal batteries

[0059] In the glove box, the composite material is pressed into sheets, and the positive electrode sheet, LiCl-KCl electrolyte sheet and lithium negative electrode sheet are placed on the stainless steel lead sheet in sequence to form a single thermal battery. After being taken out, it is placed on a single cell tester for testing.

[0060] like Figure 4 (a) shows a SEM image of the material prepared in Example 2. Compared to Example 1, the material is smaller in size, possibly due to a shorter stirring time, which did not allow sufficient time for crystal growth. However, the material also exhibits an irregular blocky structure. The corresponding elemental distribution is as follows: Figure 4 As shown in (bf), C, F, Fe, Co, and Ni atoms are uniformly distributed on the material surface. The thermal decomposition characteristics of the prepared material are as follows: Figure 5 As shown, the material's mass loss is 23.6% when the temperature rises from 100℃ to 800℃. The discharge curve of the assembled thermal battery is shown below. Figure 6 As shown in (a), at 100 mA / cm 2 At a current density of [value missing], the battery's peak discharge voltage is 2.40V. When the discharge cutoff voltage is 1.5V, the battery's discharge specific capacity reaches 166.3mAh / g. The battery's pulse performance is as follows: Figure 6 As shown in (b), it can be seen that the battery's internal resistance decreases with increasing discharge time. The calculated internal resistance value of the battery is as follows: Figure 6 As shown in (c), the initial internal resistance of the battery is 0.363Ω, which then gradually decreases to 0.186Ω.

[0061] Example 3

[0062] Step 1: Synthesis of precursors

[0063] Ferric chloride and copper acetate were dissolved in 70 mL of ethanol, resulting in a solution with ferric ion concentrations of 0.1 mol / L and copper ion concentrations of 0.1 mol / L. The solution was stirred at low temperature (<5℃) for 1 h to form solution A. Ammonium fluoride and citric acid were added to 30 mL of deionized water, resulting in a solution with ammonium fluoride concentrations of 0.7 mol / L and citric acid concentrations of 0.05 mol / L. The solution was stirred at room temperature for 1 h to form solution B. Solution B was added dropwise to solution A at low temperature, and the mixture was stirred for another 30 h to ensure complete reaction. The precipitate was washed several times with ethanol by centrifugation, then placed in a vacuum drying oven and kept at 100℃ for 16 h. The collected product was the precursor.

[0064] Step 2: Preparation of high-performance fluoride composite materials

[0065] The precursor obtained in step one was placed in a tube furnace and heated to a pyrolysis temperature of 650°C at a rate of 2°C / min in an argon atmosphere. The temperature was held for 6 hours. After natural cooling to room temperature, the sample was collected, which is the fluoride composite material.

[0066] Step 3: Application of composite cathodes in thermal batteries

[0067] In the glove box, the composite material is pressed into sheets, and the positive electrode sheet, LiCl-KCl electrolyte sheet and lithium negative electrode sheet are placed in sequence on the stainless steel lead sheet to form a single thermal battery. After being taken out, it is placed on a single cell tester for testing.

[0068] The discharge curve of the thermal battery assembled from the prepared materials is as follows: Figure 7 As shown in (a), at 100 mA / cm 2 At a current density of [value missing], the battery's peak discharge voltage is 2.53V. When the discharge cutoff voltage is 1.5V, the battery's discharge specific capacity reaches 232.4mAh / g. The battery's pulse performance is as follows: Figure 7 As shown in (b), it can be seen that the battery's internal resistance decreases with increasing discharge time. The calculated internal resistance value of the battery is as follows: Figure 7 As shown in (c), the initial internal resistance of the battery is 0.398Ω, which then gradually decreases to 0.243Ω.

[0069] Example 4

[0070] Step 1: Synthesis of precursors

[0071] Ferric chloride, nickel chloride, and copper chloride were dissolved in 65 mL of ethanol, resulting in a solution with ferric ion concentrations of 0.05 mol / L, nickel ion concentrations of 0.05 mol / L, and copper ion concentrations of 0.05 mol / L. The solution was stirred at low temperature (<5℃) for 0.5 h to form solution A. Ammonium fluoride and citric acid were added to 35 mL of deionized water, resulting in a solution with ammonium bifluoride concentrations of 0.45 mol / L and sodium citrate concentrations of 0.08 mol / L. The solution was stirred at room temperature for 0.5 h to form solution B. Solution B was then added dropwise to solution A at low temperature, and the mixture was stirred for another 40 h to ensure complete reaction. The precipitate was washed several times with ethanol by centrifugation, then placed in a vacuum drying oven and kept at 110℃ for 12 h. The collected product was the precursor.

[0072] Step 2: Preparation of high-performance fluoride composite materials

[0073] The precursor obtained in step one was placed in a tube furnace and heated to a pyrolysis temperature of 600°C at a rate of 3°C / min in a nitrogen atmosphere. The temperature was held for 4 hours. After naturally cooling to room temperature, the sample was collected, which is the fluoride composite material.

[0074] Step 3: Application of composite cathodes in thermal batteries

[0075] In the glove box, the composite material is pressed into sheets, and the positive electrode sheet, LiCl-KCl electrolyte sheet and lithium negative electrode sheet are placed in sequence on the stainless steel lead sheet to form a single thermal battery. After being taken out, it is placed on a single cell tester for testing.

[0076] like Figure 8 (a) shows a SEM image of the material prepared in Example 4. The material is relatively large, indicating that it had sufficient time for crystal growth. The corresponding elemental distribution is as follows: Figure 8 As shown in (bf), C, F, Fe, Ni, and Cu atoms are uniformly distributed on the material surface. The thermal decomposition characteristics of the prepared material are as follows: Figure 9 As shown, the mass loss of the material is 21.6% when the temperature rises from 100℃ to 800℃. The discharge curve of the thermal battery assembled with the prepared material is shown in the figure. Figure 10 As shown in (a), at 100 mA / cm 2 At a current density of [value missing], the battery's initial discharge voltage is 2.52V. When the discharge cutoff voltage is 1.5V, the battery's discharge specific capacity reaches 217.9mAh / g. The battery's pulse performance is as follows: Figure 10 As shown in (b), it can be seen that the battery's internal resistance decreases with increasing discharge time. The calculated internal resistance value of the battery is as follows: Figure 10 As shown in (c), the initial internal resistance of the battery is 0.332Ω, which then gradually decreases to 0.170Ω.

[0077] Example 5

[0078] Step 1: Synthesis of precursors

[0079] Nickel chloride and copper acetate were dissolved in 75 mL of ethanol, resulting in a nickel ion concentration of 0.15 mol / L and a copper ion concentration of 0.15 mol / L. The solution was stirred at low temperature (<5℃) for 1.5 h to form solution A. Ammonium bifluoride and glucose were added to 25 mL of deionized water, resulting in an ammonium fluoride concentration of 0.9 mol / L and a citric acid concentration of 0.02 mol / L. The solution was stirred at room temperature for 0.5 h to form solution B. Solution B was added dropwise to solution A at low temperature, and stirring continued for 20 h to ensure complete reaction. The precipitate was washed several times with ethanol by centrifugation, then placed in a vacuum drying oven and kept at 90℃ for 20 h. The collected product was the precursor.

[0080] Step 2: Preparation of high-performance fluoride composite materials

[0081] The precursor obtained in step one was placed in a tube furnace and heated to a pyrolysis temperature of 750°C at a rate of 1°C / min in an argon atmosphere. The temperature was held for 6 hours. After natural cooling to room temperature, the sample was collected, which is the fluoride composite material.

[0082] Step 3: Application of composite cathodes in thermal batteries

[0083] In the glove box, the composite material is pressed into sheets, and the positive electrode sheet, LiCl-KCl electrolyte sheet and lithium negative electrode sheet are placed on the stainless steel lead sheet in sequence to form a single thermal battery. After being taken out, it is placed on a single cell tester for testing.

[0084] The thermal decomposition characteristics of the prepared material are as follows: Figure 11 As shown, when the temperature rises from 100℃ to 800℃, the mass loss of the material is only 12.7%, exhibiting the lowest thermal properties compared to previous samples. The discharge curve of the assembled thermal battery is shown below. Figure 12 As shown in (a), at 100 mA / cm 2 At a current density of [value missing], the battery's peak discharge voltage is 2.40V. When the discharge cutoff voltage is 1.5V, the battery's discharge specific capacity reaches 166.3mAh / g. The battery's pulse performance is as follows: Figure 12 As shown in (b), it can be seen that the battery's internal resistance decreases with increasing discharge time. The calculated internal resistance value of the battery is as follows: Figure 12 As shown in (c), the initial internal resistance of the battery is 0.518Ω, which then gradually decreases to 0.300Ω.

[0085] The above results demonstrate that the discharge voltage and specific capacity of the battery can be effectively improved by selecting the precursor and controlling the carbon material. Simultaneously, each battery exhibits low internal resistance and high thermal decomposition temperature, indicating that the complete contact between the two materials results in low contact resistance and improved thermal stability.

[0086] While preferred embodiments of the present invention have been disclosed above, they are not intended to limit the invention. Any researcher in the art can modify and alter the research scheme of the present invention using the design parameters and content of the disclosed embodiments without departing from the spirit and scope of the invention. Therefore, any simple modifications, parameter changes, and alterations made to the above embodiments based on the research essence of the present invention, without departing from the content of the present invention, fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance fluoride composite material for thermal batteries, characterized in that, The following steps are involved: Step 1: Synthesis of precursors Under low temperature conditions, a transition metal salt is dissolved in ethanol and stirred for 0.5-1.5 h to form solution A; under room temperature conditions, a fluorine source and a carbon source are added to deionized water and stirred for 0.5-1.5 h to form solution B; under low temperature conditions, solution B is added dropwise to solution A to obtain a mixed solution and stirring is continued for 20-40 h; the precipitate after the reaction is complete is washed several times with ethanol by centrifugation, then vacuum dried, and the product is collected to obtain the precursor; the low temperature conditions are <5℃; Step 2, Preparation of fluoride composite materials The precursor obtained in step one is placed in a tube furnace. Under a protective gas atmosphere, the pyrolysis temperature is 600-750℃, the holding time is 4-8h, and the heating rate is 1-3℃ / min. After naturally cooling to room temperature, the sample is collected to obtain the fluoride composite material.

2. The method for preparing a high-performance fluoride composite material for thermal batteries as described in claim 1, characterized in that, The metal ions of the transition metal salt are any two or three of iron, cobalt, nickel, copper and zinc, and the anions are at least one of nitrate, chloride, acetate, phosphate, sulfate and carbonate.

3. The method for preparing a high-performance fluoride composite material for thermal batteries as described in claim 1, characterized in that, The total concentration of metal ions in the mixed solution is 0.15 mol / L-0.3 mol / L, and the content of each metal ion in the mixed solution accounts for no less than 30% of the total ion content.

4. The method for preparing a high-performance fluoride composite material for thermal batteries as described in claim 1, characterized in that, The fluorine source is any one of ammonium fluoride and ammonium bifluoride; the carbon source is at least one of citric acid, sodium citrate, glucose, sucrose, cellulose, and fructose.

5. The method for preparing a high-performance fluoride composite material for thermal batteries as described in claim 1, characterized in that, The concentrations of the fluorine source and carbon source in the mixed solution are 0.45 mol / L-0.9 mol / L and 0.02 mol / L-0.08 mol / L, respectively.

6. The method for preparing a high-performance fluoride composite material for thermal batteries as described in claim 1, characterized in that, In the mixed solution, solution A accounts for 60%-80% of the volume.

7. The method for preparing a high-performance fluoride composite material for thermal batteries as described in claim 1, characterized in that, The vacuum drying process conditions are: temperature 90-110℃, time 12-20h.

8. A high-performance fluoride composite material for thermal batteries prepared by the preparation method according to any one of claims 1-7, characterized in that, The fluoride composite material is a composite material of binary transition metal fluorides and fluorine-doped carbon, or a composite material of ternary transition metal fluorides and fluorine-doped carbon.

9. The application of the high-performance fluoride composite material for thermal batteries prepared by the preparation method according to any one of claims 1-7, or the high-performance fluoride composite material according to claim 8, in the preparation of the positive electrode of a thermal battery.

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