Heteroatom-doped carbon-coated NiF2-based positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of thermal battery materials, and particularly relates to a heteroatom-doped carbon-coated NiF2-based positive electrode material as well as a preparation method and application thereof. According to the positive electrode material, a NiF2-based heterojunction is adopted as a core structure, heteroatom-doped carbon is adopted as a shell structure, and a composite material positive electrode is prepared through the steps of low-temperature polymerization reaction-pyrolysis; according to the composite material, due to the existence of the carbon coating layer, the dissolution of NiF2 in electrolyte can be inhibited, and the electronic conductivity is improved, so that the discharge time of the battery and the utilization rate of an active material are improved, and the advantages of high voltage, long discharge time, excellent rate capability and the like can be maintained when the composite structure positive electrode material is applied to a thermal battery; and miniaturization and light-weight development of the thermal battery is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal battery materials, and specifically relates to a heteroatom-doped carbon-coated nickel fluoride-based cathode material, a preparation method thereof, and its application in thermal battery cathode materials. Background Art

[0002] A thermal battery is a disposable reserve battery, which has the advantages of long storage time, high specific energy, high specific power, and maintenance-free. At room temperature, its electrolyte is a non-conductive solid; when in use, the internal heating sheet of the battery is ignited by a firing head to rapidly increase the temperature, and the electrolyte turns into an ionic conductor with high electrical conductivity characteristics under high-temperature conditions, and the positive and negative active materials undergo redox reactions to discharge. With the continuous development of science and technology, there are requirements for miniaturization, lightweight, and intelligence of thermal batteries. At present, there is an urgent need for thermal batteries with higher energy density and higher power density. As the core component of a thermal battery, the cathode should have the characteristics of high discharge voltage, high electronic conductivity, and good compatibility with the electrolyte.

[0003] Nickel fluoride (NiF 2 ) as a cathode material has a relatively high theoretical voltage and specific capacity, and is one of the ideal choices for high-power thermal battery cathode materials. However, its poor conductivity, solubility with the electrolyte, etc. limit its application and development. To solve the above problems, currently, researchers mostly adopt the method of constructing nickel fluoride into a multi-metal compound composite structure to inhibit the electrolyte immersion problem. However, this method cannot solve the problems of low conductivity and immersion at the same time, and there is still a need to explore a method and strategy that can solve the above problems simultaneously.

[0004] The patent with the publication number CN115411253B proposed a strategy for a carbon-coated one-dimensional iron fluoride cathode material to solve the problems that the FeF 2 electrode will react with the electrolyte and the electrode has poor conductivity during charge and discharge, and utilized the nano-characteristics, conductivity, and structural toughness of one-dimensional carbon materials to improve the electrochemical activity, intrinsic conductivity, and structural stability of transition metal fluorides. However, the preparation method reported in this patent is costly and not conducive to mass production of energy. At the same time, since no carbon material coating layer is formed, its effect of inhibiting the reaction between fluorides and electrolytes is limited.

[0005] The patent with the publication number CN115241453A, Yolk-shell structured metal fluoride / carbon composite materials and their preparation methods, also mentioned the problems of active substance dissolution and poor conductivity, but the preparation process involved is complex, and using highly corrosive fluorine-containing gas as the fluorine source during the pyrolysis process reduces safety and increases costs. At the same time, the above patents did not optimize the intrinsic reaction activity of fluorides, and the optimization effect is too single.

[0006] However, due to the unstable chemical properties of nickel fluoride, factors such as the carbon material precursor for coating and the coating process will greatly affect the final electrochemical performance of the material. Therefore, it is of great significance to explore the surface modification of nickel fluoride materials in order to improve the conductivity of nickel fluoride materials and inhibit the mutual solubility between nickel fluoride and the electrolyte. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art and to achieve the technical objectives of the present invention, the present invention provides a heteroatom-doped carbon-coated nickel fluoride-based cathode material, its preparation method and application.

[0008] Specifically, it is achieved through the following technical solutions:

[0009] The first object of the present invention is to provide: a heteroatom-doped carbon-coated NiF 2 -based cathode material, the cathode material is composed of a heteroatom-doped carbon as the shell structure and a NiF 2 -based heterojunction as the core structure, and the heteroatom is any one or more of nitrogen, sulfur, fluorine, and selenium.

[0010] The cathode material of the present invention uses a heteroatom-doped carbon material to coat nickel fluoride. Its shell structure has excellent conductivity, can increase the chemical reaction sites, reduce the chemical reaction barrier, and can also inhibit the infiltration of NiF 2 . The core structure is a NiF 2 -based heterostructure, specifically a multiphase structure of NiF 2 and other nickel-based materials, which can increase the concentration of active electrons in the outer layer and reduce its electrochemical reaction barrier.

[0011] The second object of the present invention is to provide: a preparation method of the aforementioned heteroatom-doped carbon-coated NiF 2 -based cathode material, including the following steps:

[0012] (1) Low-temperature polymerization reaction

[0013] Weigh commercial NiF 2 and place it in an ethanol solution. Ultrasonically treat the mixed solution for 10 min in an environment with a temperature <5°C and then stir for 10 min to form a mixed solution with a NiF 2 concentration of 0.1 - 0.3 g / mL. Then add the polymer monomer and continue to stir for 20 min to obtain a NiF 2 solution; Take the polymerization reaction initiator and dissolve it fully in deionized water to obtain the polymerization reaction initiator solution;

[0014] Mix the polymerization reaction initiator solution with a concentration of 3 - 5 g / mL with NiF 2Mix the solutions and continue stirring for 3 - 6 h, then wash several times with ethanol to remove excess ions to obtain a solid precursor;

[0015] Vacuum dry the solid precursor at 60 - 80 °C for 12 h, and then grind it to obtain NiF 2 @polymer pyrolysis precursor;

[0016] The volume ratio of water to ethanol in the ethanol solution is 1:2 to 1:4;

[0017] The dropping amount of the polymer monomer is 0.005 - 0.01 mL of the polymer monomer per 100 mL of the mixed solution;

[0018] The polymer monomer is pyrrole or aniline monomer;

[0019] The polymerization initiator is ammonium persulfate or anhydrous ferric chloride;

[0020] (2) Pyrolysis

[0021] Place the NiF 2 @polymer pyrolysis precursor prepared in step (1) in a porcelain boat, add or not add heteroatom substances to the porcelain boat, then place the porcelain boat in the middle of a tube furnace and pyrolyze it under an inert gas atmosphere. After the pyrolysis is completed, let it cool to room temperature naturally to obtain a heteroatom-doped carbon-coated NiF 2 -based cathode material; the pyrolysis conditions are: the heating rate is 3 - 10 °C / min, the pyrolysis temperature is 500 - 600 °C, and the pyrolysis time is 2 - 6 h.

[0022] The heteroatom substances include but are not limited to any one or more of sulfur powder, sodium thiosulfate, ammonium fluoride, ammonium bifluoride, selenium powder.

[0023] The mass ratio of the NiF 2 @polymer pyrolysis precursor to the heteroatom substance is 1:1 to 1:3.

[0024] The NiF 2 @polymer pyrolysis precursor and the heteroatom substance are placed at the downstream end and the upstream end of the porcelain boat respectively, and the upstream end of the porcelain boat refers to the end where the inert gas enters.

[0025] In the preparation process of the present invention, water and ethanol are used as the mixed solution to disperse the NiF 2 material, which can avoid the partial oxidation problem caused by using pure deionized water; combined with temperature control, it effectively slows down the problem of NiF 2 being slightly soluble in water.

[0026] Use a polymerization initiator to initiate the polymerization reaction of pyrrole or aniline monomer to coat a layer of polymer on the outside of NiF 2 @.

[0027] Heteroatom-doped carbon-coated NiF was prepared by introducing heteroatom substances during pyrolysis. 2 The pyrolysis process has multiple effects: (1) promoting the doping of heteroatoms into the carbon material structure and carbonizing the polymer precursor to form a highly conductive and active nitrogen and / or heteroatom-doped carbon coating layer; (2) removing NiF 2 The water adsorbed during the polymerization process; (3) the coating layer can react with NiF during the pyrolysis process 2 React to form NiF with better electrochemical activity 2 Based heterostructure, as NiF 2 Protective layer, with NiF inhibiting 2 The effect of miscibility between materials and electrolytes.

[0028] The third object of the present invention is to provide: a carbon-coated NiF for thermal batteries 2 Application of base cathode materials in the preparation of thermal batteries.

[0029] Furthermore, the thermal battery is carbon-coated NiF 2 The base positive electrode material is used as the positive electrode active material of the thermal battery.

[0030] Furthermore, the application, the specific method comprises the following steps:

[0031] Step 1: Prepare the positive electrode

[0032] Carbon-coated NiF for thermal batteries 2 The base cathode material and LiCl / KCl separator were weighed and ground at a mass ratio of 80:20, and 0.20 g of powder was placed in a circular mold with a diameter of 20 mm, and a molding pressure of 20 to 30 MPa was applied. After demolding, the cathode sheet used for the single-body test was obtained;

[0033] Step 2: Prepare the diaphragm

[0034] 0.45 g of the prepared LiCl / KCl membrane was placed in a circular mold with a diameter of 20 mm, and a molding pressure of 15-25 MPa was applied. After demolding, the electrolyte sheet used for the monomer test was obtained;

[0035] Step 3: Battery assembly and testing

[0036] In the glove box, the positive electrode sheet, the diaphragm sheet and the commercial lithium-boron alloy are placed on the guide bar in order to form a single thermal battery. After being taken out, they are placed on a single tester for testing.

[0037] Beneficial effects:

[0038] A heteroatom-doped carbon-coated NiF protected by the present invention 2 Base cathode, using NiF 2 The base heterojunction is used as the core structure, and the polymer-derived carbon doped with heterogeneous atoms is used as the shell structure. The composite material is prepared through the steps of "low-temperature polymerization coating-pyrolysis carbonization doping". This material has the following beneficial effects in the preparation process and battery performance improvement:

[0039] (1) The composite material has a simple preparation process, low material cost, and little environmental pollution. In addition, the prepared material can significantly improve battery performance and has a good benefit effect.

[0040] (2) The carbon coating can effectively inhibit NiF 2 The material dissolves in the electrolyte and improves electronic conductivity, increasing battery discharge time and active material utilization.

[0041] (3) Heterogeneous heteroatoms (N, F, S, Se) in carbon materials can serve as electrochemical reaction sites, reducing the reaction barrier and increasing the reaction rate.

[0042] (4)NiF 2 Compared with pure NiF 2 The material has better reactivity and can regulate NiF 2 The outer electrons are arranged so that the discharge process can be carried out more fully.

[0043] (5) The excellent thermal stability of carbon materials increases the decomposition temperature of the battery, can resist stronger thermal shock, and reduce the decomposition rate of active materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 NiF doped with nitrogen atom prepared in Example 1 2 XRD pattern of the base cathode material;

[0045] Figure 2 NiF doped with nitrogen atom prepared in Example 1 2 SEM image and element distribution map of the base positive electrode material; (a) is the SEM image, and (b) is the element distribution map;

[0046] Figure 3 NiF doped with nitrogen atom prepared in Example 1 2 Discharge curves of base cathode materials under different current density conditions;

[0047] Figure 4 The sulfur and nitrogen atom-doped carbon-coated NiF prepared in Example 2 2 XRD pattern of the base cathode material;

[0048] Figure 5 SEM images and elemental distribution maps of the sulfur, nitrogen co-doped carbon-coated NiF-based cathode material prepared in Example 2; where (a) is the SEM image and (b-f) are the elemental distribution maps; 2

[0049] Figure 6 SEM images and elemental distribution maps of the sulfur, nitrogen co-doped carbon-coated NiF-based cathode material prepared in Example 2; where (a) is the SEM image and (b-f) are the elemental distribution maps; 2 Discharge curves of the sulfur, nitrogen co-doped carbon-coated NiF-based cathode material prepared in Example 2 at different current densities;

[0050] Figure 7 XRD pattern of the fluorine, nitrogen co-doped carbon-coated NiF-based cathode material prepared in Example 3; 2

[0051] Figure 8 SEM images and elemental distribution maps of the fluorine, nitrogen co-doped carbon-coated NiF-based cathode material prepared in Example 3; where (a) is the SEM image and (b) is the elemental distribution map; 2

[0052] Figure 9 Discharge curves of the fluorine, nitrogen co-doped carbon-coated NiF-based cathode material prepared in Example 3 at different current densities; 2

[0053] Figure 10 SEM images and elemental distribution maps of the selenium, nitrogen co-doped carbon-coated NiF-based cathode material prepared in Example 4; where (a) is the SEM image and (b-f) are the elemental distribution maps; 2

[0054] Figure 11 Discharge curves of the selenium, nitrogen co-doped carbon-coated NiF-based cathode material prepared in Example 4 at different current densities; 2 Detailed Description of the Invention

[0055] The following further elaborates on the specific embodiments of the present invention. However, the present invention is not limited to these embodiments. Any improvement or substitution based on the basic spirit of these embodiments still falls within the scope protected by the claims of the present invention.

[0056] Example 1

[0057] A method for preparing a nitrogen-doped carbon-coated NiF-based cathode material and a method for assembling a battery thereof, comprising the following steps: 2

[0058] (1) Low-temperature polymerization

[0059] ​​​​​​​Take ammonium persulfate and fully dissolve it in deionized water to prepare an ammonium persulfate solution with a concentration of 3g / mL; take 33mL of water and 67mL of ethanol to form an ethanol solution, weigh 10g of commercial NiF 2 The mixed solution was placed in 100 mL of ethanol solution to form a mixed solution. The mixed solution was ultrasonically treated for 10 min in an environment with a temperature of less than 5°C and then stirred for 10 min. Subsequently, 0.005 mL of pyrrole monomer was added and the stirring was continued for 20 min to obtain NiF 2 Solution; Take 3 mL of ammonium persulfate solution with a concentration of 3 g / mL and add NiF 2 The solution was mixed evenly, and the stirring was continued for 3 hours to carry out the polymerization reaction. After the polymerization reaction was completed, it was washed several times with ethanol to remove excess ions, and then vacuum dried at 60°C for 12 hours, and then ground to obtain NiF 2 @Polypyrrole pyrolysis precursor;

[0060] (2) Pyrolysis

[0061] The NiF prepared in step (1) 2 The polypyrrole pyrolysis precursor was placed in a porcelain boat and placed in a tube furnace. Under an argon atmosphere, the temperature was raised to 500°C at 3°C / min. After pyrolysis for 2 hours, nitrogen-doped carbon-coated NiF was obtained after the temperature dropped to room temperature. 2 Base cathode material.

[0062] (3) Nitrogen-doped carbon-coated NiF 2 Application of base cathode materials in the preparation of thermal batteries;

[0063] Step 1: Prepare the positive electrode

[0064] Nitrogen-doped carbon coated NiF 2 The base cathode material and LiCl / KCl separator were weighed and ground at a mass ratio of 80:20, and 0.20 g of powder was placed in a circular mold with a diameter of 20 mm. A molding pressure of 20 MPa was applied, and the cathode sheet used for the single-body test was obtained after demolding;

[0065] Step 2: Prepare the diaphragm

[0066] 0.45 g of the prepared LiCl / KCl membrane was placed in a circular mold with a diameter of 20 mm, and a molding pressure of 15 MPa was applied. After demolding, the electrolyte sheet used for the monomer test was obtained;

[0067] Step 3: Battery assembly and testing

[0068] In the glove box, the positive electrode, diaphragm and commercial lithium-boron alloy are placed on the guide bar in order to form a single thermal battery. After being taken out, they are placed on a single tester for testing.

[0069] The phase composition of the prepared material is as follows Figure 1 shown. By comparing with the standard card, it is found that the material has a high coincidence with NiF 2 (PDF#24 - 0792) and NiF 3 (PDF#50 - 1313), indicating that the prepared material is a composite material of NiF 2 -NiF 3 . The reason may be that during the high-temperature carbonization process, an oxidation-reduction reaction occurs when polypyrrole is converted into carbon material, resulting in the conversion of part of NiF 2 to NiF 3 . In the low diffraction angle region, there is a certain bulge in the pattern, indicating that the material contains amorphous carbon material. The morphology of the material is as shown in Figure 2 (a). The nitrogen-doped carbon-coated NiF 2 -NiF 3 material presents a granular structure, and no obvious structural differences are found, indicating that carbon completely coats the NiF 2 -NiF 3 -based composite material. Further, the corresponding element distribution( Figure 2 b) shows that the four elements of Ni, F, C, and N are evenly distributed on the surface of the material. The composite material is assembled into a thermal battery and discharged at different current densities, and the corresponding results are as shown in Figure 3 . When the cut-off voltage is 1.5V, the discharge specific capacities at current densities of 100mA / cm 2 and 200mA / cm 2 are 144.1mAh / g and 146.4mAh / g respectively. At low current density, the discharge voltage plateau is about 2.48V; at high current density, the discharge voltage plateau is about 2.35V, indicating that the composite material has good rate performance and conductivity.

[0070] Example 2

[0071] A preparation method of a sulfur and nitrogen-doped carbon-coated NiF 2 -based cathode material and its battery assembly method, including the following steps:

[0072] (1) Low-temperature polymerization

[0073] Take ammonium persulfate and dissolve it fully in deionized water to make an ammonium persulfate solution with a concentration of 5g / mL; take 20mL of water and 80mL of ethanol and mix them to form an ethanol solution. Weigh 20g of commercial NiF 2 and place it in 100mL of ethanol solution to form a mixed solution. Ultrasonically treat the mixed solution for 10min in an environment with a temperature < 5°C and then stir it for 10min. Subsequently, add 0.01mL of pyrrole monomer and continue to stir it for 20min to obtain NiF 2Take 5mL of 5g / mL ammonium persulfate solution and add the above NiF 2 The solution was mixed evenly and stirred for 3 hours to carry out polymerization reaction. After the polymerization reaction was completed, it was washed several times with ethanol to remove excess ions, and then vacuum dried at 60°C for 12 hours, and then ground to obtain NiF. 2 @Polypyrrole pyrolysis precursor.

[0074] (2) Pyrolysis

[0075] The NiF prepared in step (1) 2 @After weighing the polypyrrole pyrolysis precursor and sulfur powder in a mass ratio of 1:3, sulfur powder, NiF 2 @Polypyrrole pyrolysis precursor was placed at the upstream and downstream ends of the porcelain boat. The porcelain boat was placed in a tube furnace and the upstream end was placed at the argon inlet, that is, the upstream end was closer to the inlet than the downstream end. In an argon atmosphere, the temperature was raised at 10°C / min to a pyrolysis temperature of 550°C. The pyrolysis time was 6h. After the temperature dropped to room temperature, sulfur- and nitrogen-doped carbon-coated NiF was obtained. 2 Base cathode material.

[0076] (3) Sulfur and nitrogen doped carbon coated NiF 2 Application of base cathode in thermal battery

[0077] Step 1: Prepare the positive electrode

[0078] Sulfur and nitrogen doped carbon coated NiF 2 The base cathode material and LiCl / KCl separator were weighed and ground at a mass ratio of 80:20, and 0.20 g of powder was placed in a circular mold with a diameter of 20 mm. A molding pressure of 30 MPa was applied, and the cathode sheet used for the single-body test was obtained after demolding;

[0079] Step 2: Prepare the diaphragm

[0080] 0.45 g of the prepared LiCl / KCl membrane was placed in a circular mold with a diameter of 20 mm, and a molding pressure of 25 MPa was applied. After demolding, the electrolyte sheet used for the monomer test was obtained;

[0081] Step 3: Battery assembly and testing

[0082] In the glove box, the positive electrode, diaphragm and commercial lithium-boron alloy are placed on the guide bar in order to form a single thermal battery. After being taken out, they are placed on a single tester for testing.

[0083] The phase composition of the prepared materials is Figure 4 As shown, after comparison with the standard card, it was found that the diffraction peak of this material is similar to that of NiF 2(PDF#24-0792), NiS (PDF#02-1280) and NiS 2 (PDF#11-0099) has a high overlap, indicating that the prepared material is NiF 2 -NiS-NiS 2 composite material. The reason may be that during the high-temperature carbonization process, the introduced sulfur powder is doped into the carbon material structure and reacts with NiF 2 to form nickel-based sulfide. In the low diffraction angle region, there is an obvious region with increased diffraction intensity in the spectrum, indicating that the material contains amorphous carbon material. The morphology of the material is as Figure 5 (a) shows that sulfur and nitrogen-doped carbon-coated NiF 2 -NiS-NiS 2 composite material presents a granular structure, and no obvious structural differences are found, indicating that the morphology has not changed during the pyrolysis process of introducing the sulfur element precursor. Further, the corresponding element distribution ( Figure 5 (b-f)) shows that the five elements of Ni, F, C, N, and S are evenly distributed on the surface of the material. Assembling the composite material into a thermal battery and discharging it at different current densities, the corresponding results are as Figure 6 shown. When the cut-off voltage is 1.5V, the discharge specific capacities at current densities of 100 mA / cm 2 and 200 mA / cm 2 are 224.5 mAh / g and 207.5 mAh / g respectively. Compared with the nitrogen-doped carbon-coated NiF 2 thermal battery, there is a certain improvement in the discharge specific capacity, which may be due to the fact that dual-atom doping can improve the reaction activity of NiF 2 and the conductivity of the carbon material, and the formed three-phase structure is more conducive to the progress of the electrochemical reaction, thereby increasing the discharge specific capacity.

[0084] Example 3

[0085] A preparation method of a fluorine and nitrogen-doped carbon-coated NiF 2 -based cathode material and its battery assembly method, including the following steps:

[0086] (1) Low-temperature polymerization

[0087] Dissolve ammonium persulfate sufficiently in deionized water to make an ammonium persulfate solution with a concentration of 4 g / mL; take 25 mL of water and 75 mL of ethanol and mix them to form an ethanol solution. Weigh 20 g of commercial NiF 2 and place it in 100 mL of ethanol solution to form a mixed solution. Ultrasonically treat the mixed solution in an environment with a temperature < 5°C for 10 min and then stir for 10 min. Subsequently, add 0.007 mL of aniline monomer and continue to stir for 20 min to obtain NiF 2Solution; Take 4mL of 4g / mL ammonium persulfate solution and add the aforementioned NiF 2 The solution was mixed evenly and stirred for 3 hours to carry out polymerization reaction. After the polymerization reaction was completed, it was washed several times with ethanol to remove excess ions, and then vacuum dried at 60°C for 12 hours, and then ground to obtain NiF. 2 @Polyaniline pyrolysis precursor.

[0088] (2) Pyrolysis

[0089] The NiF prepared in step (1) 2 @Polyaniline pyrolysis precursor and ammonium fluoride were weighed at a mass ratio of 1:2 and placed at the downstream and upstream ends of the porcelain boat respectively. The porcelain boat was then placed in a tube furnace and the upstream end was kept close to the argon inlet. In an argon atmosphere, the temperature was raised at 5°C / min to a pyrolysis temperature of 600°C. The pyrolysis time was 3h. When the temperature dropped to room temperature, fluorine- and nitrogen-doped carbon-coated NiF was obtained. 2 Base cathode material.

[0090] (3) Fluorine and nitrogen doped carbon coated NiF 2 Application of composite cathode materials in thermal batteries

[0091] Step 1: Prepare the positive electrode

[0092] Fluorine and nitrogen doped carbon coated NiF 2 The composite cathode material and LiCl / KCl separator were weighed and ground at a mass ratio of 80:20, and 0.20 g of powder was placed in a circular mold with a diameter of 20 mm. A molding pressure of 25 MPa was applied, and after demolding, the thermal battery cathode sheet used for the single-cell test was obtained;

[0093] Step 2: Prepare the diaphragm

[0094] 0.45g of the prepared LiCl / KCl membrane was placed in a circular mold with a diameter of 20mm, and a molding pressure of 20MPa was applied. After demolding, the hot battery electrolyte sheet used for the monomer test was obtained;

[0095] Step 3: Battery assembly and testing

[0096] In the glove box, the positive electrode, diaphragm and commercial lithium-boron alloy are placed on the guide bar in order to form a single thermal battery. After being taken out, they are placed on a single tester for testing.

[0097] The phase composition of the prepared materials is Figure 7 As shown, after comparing with the standard card, it was found that the material is NiF 2 -NiF 3The composite material shows a certain degree of bulge in the low diffraction angle region of the spectrum, indicating that the material contains amorphous carbon materials. The morphology of the material is as Figure 8 (a) shows that the fluorine and nitrogen doped carbon coated NiF 2 -NiF 3 -based composite material presents a granular structure and no obvious structural differences are found. Further, the corresponding element distribution ( Figure 8 (b)) shows that the four elements of Ni, F, C, and N are evenly distributed on the surface of the material, and the doped elements are consistent with the anions of the compound, and there are no obvious element distribution differences. The composite material is assembled into a thermal battery and discharged at different current densities, and the corresponding results are as Figure 9 shown. When the cut-off voltage is 1.5V, the discharge specific capacities at current densities of 100 mA / cm 2 and 200 mA / cm 2 are 319.1 mAh / g and 307.8 mAh / g respectively. At low current densities, the discharge voltage plateau is about 2.45V; at high current densities, the discharge voltage plateau is about 2.31V. Although the voltage plateau of the battery decreases at high current densities, its discharge specific capacity does not decrease significantly, that is, this material can improve the battery performance.

[0098] Example 4

[0099] A preparation method of a selenium and nitrogen doped carbon coated NiF 2 -based cathode material and its battery assembly method, including the following steps:

[0100] (1) Low-temperature polymerization

[0101] Take ammonium persulfate and dissolve it fully in deionized water to make an ammonium persulfate solution with a concentration of 5 g / mL; take 25 mL of water and 75 mL of ethanol and mix them to form an ethanol solution. Weigh 20 g of commercial NiF 2 and place it in 100 mL of ethanol solution to form a mixed solution. Ultrasonically treat the mixed solution in an environment with a temperature < 5°C for 10 min and then stir for 10 min. Subsequently, add 0.008 mL of pyrrole monomer and continue to stir for 20 min to obtain a NiF 2 solution. Take 3 mL of the ammonium persulfate solution with a concentration of 5 g / mL and add it to the above NiF 2 solution and mix evenly, and continue to stir for 4 h for polymerization reaction. After the polymerization reaction is completed, wash it several times with ethanol to remove excess ions, and then vacuum dry it at 80°C for 12 h, and then grind it to obtain NiF 2 @polypyrrole pyrolysis precursor.

[0102] (2) Pyrolysis

[0103] The NiF prepared in step (1)2 The polypyrrole pyrolysis precursor and selenium powder were weighed according to a mass ratio of 1:2 and placed at the downstream end and upstream end of the porcelain boat respectively. Then the porcelain boat was placed in a tube furnace and ensured that the upstream end was close to the argon inlet. It was heated to the pyrolysis temperature of 550 °C at a rate of 7 °C / min under an argon atmosphere, and the pyrolysis time was 5 h. After the temperature dropped to room temperature, selenium, nitrogen-doped carbon-coated NiF 2 -based cathode composite material was obtained.

[0104] (3) Application of selenium, nitrogen-doped carbon-coated NiF 2 -based cathode in thermal batteries

[0105] The first step: Preparation of the cathode plate

[0106] The selenium, nitrogen-doped carbon-coated NiF 2 -based cathode material and the LiCl / KCl separator were weighed according to a mass ratio of 80:20 and ground thoroughly. 0.20 g of the powder was placed in a circular mold with a diameter of 20 mm, and a forming pressure of 20 MPa was applied. After demolding, the cathode plate of the thermal battery used for single-cell testing was obtained;

[0107] The second step: Preparation of the separator plate

[0108] 0.45 g of the prepared LiCl / KCl separator was placed in a circular mold with a diameter of 20 mm, and a forming pressure of 25 MPa was applied. After demolding, the electrolyte plate of the thermal battery used for single-cell testing was obtained;

[0109] The third step: Assembly and testing of the battery

[0110] In the glove box, the cathode, the separator plate and the commercial lithium-boron alloy were placed on the current collector strip in sequence to form a single-cell thermal battery, which was taken out and placed on a single-cell tester for testing.

[0111] Figure 10 (a) is the SEM image of the selenium, nitrogen-doped carbon-coated NiF 2 composite material. The results show that the particles of the composite material are significantly enlarged and there is obvious agglomeration. Further, the corresponding elemental distribution Figure 10 (b-f) shows that Ni, F, C, N and Se elements are uniformly distributed on the material surface. The selenium, nitrogen-doped carbon-coated NiF 2 -based cathode composite material was assembled into a battery and discharged at different current densities. The corresponding curves are as Figure 11 shown. At a cut-off voltage of 1.5 V, the current densities are 100 mA / cm 2 and 200 mA / cm 2The discharge specific capacities at that time were 260.8 mAh / g and 239.2 mAh / g respectively. At low current density, the discharge voltage plateau was around 2.41 V; at high current density, the discharge voltage plateau was around 2.39 V. The voltage plateau of the battery did not decrease significantly at different current densities, indicating that the composite material had good active material utilization rate.

[0112] Although the present invention has been disclosed with preferred embodiments as above, it is not intended to limit the present invention. Any researcher in the art can make changes and modifications to the research scheme of the present invention by using the design parameters and content in the above disclosed embodiments without departing from the spirit and scope of the present invention. Therefore, any simple modifications, parameter changes and decorations made to the above embodiments based on the research essence of the present invention without departing from the content of the present invention scheme all fall within the protection scope of the present invention scheme.

Claims

1. A heteroatom-doped carbon-coated NiF2-based positive electrode material, characterized in that: The positive electrode material is composed of heteroatom-doped carbon as a shell structure and NiF2-based heterojunction as a core structure, wherein the heteroatom is any one or more of nitrogen, sulfur, fluorine and selenium.

2. The method for preparing a heteroatom-doped carbon-coated NiF2-based positive electrode material according to claim 1, characterized in that: The following steps are involved: (1) Low temperature polymerization Weigh commercial NiF2 and place it in an ethanol solution, then ultrasonically treat it in an environment with a temperature of less than 5°C and then stir it to obtain a mixed solution, then add a polymer monomer and continue to stir it to obtain a NiF2 solution; mix a polymerization initiator solution with the NiF2 solution, and continue to stir it for 3-6 hours after mixing to perform a polymerization reaction; after the polymerization reaction is completed, wash it with ethanol several times to obtain a solid precursor, and vacuum dry and grind the solid precursor in turn to obtain a NiF2@polymer pyrolysis precursor; (2) Pyrolysis The NiF2@polymer pyrolysis precursor prepared in step (1) is placed in a porcelain boat, heteroatom substances are added or not added to the porcelain boat, and then the porcelain boat is placed in the middle of a tube furnace and pyrolyzed in an inert gas atmosphere at a heating rate of 3 to 10°C / min, a pyrolysis temperature of 500-600°C, and a pyrolysis time of 2-6h. After the pyrolysis is completed, the temperature is cooled to room temperature to obtain a carbon-coated NiF2-based positive electrode material.

3. The method for preparing a heteroatom-doped carbon-coated NiF2-based positive electrode material according to claim 2, characterized in that: The concentration of NiF2 in the ethanol solution is 0.1-0.3 g / mL, and the volume ratio of water to ethanol in the ethanol solution is 1:2-1:

4.

4. The method for preparing a heteroatom-doped carbon-coated NiF2-based positive electrode material according to claim 2, characterized in that: The polymer monomer is a pyrrole or aniline monomer, and the amount of the monomer added dropwise in 100 mL of the mixed solution is 0.005-0.01 mL.

5. The method for preparing a heteroatom-doped carbon-coated NiF2-based positive electrode material according to claim 2, characterized in that: The polymerization initiator is ammonium persulfate or anhydrous ferric chloride, and its concentration in the solution containing the polymerization initiator is 3-5 g / mL.

6. The method for preparing a heteroatom-doped carbon-coated NiF2-based positive electrode material according to claim 2, characterized in that: The heteroatom substances include, but are not limited to, any one or more of sulfur powder, sodium thiosulfate, ammonium fluoride, ammonium bifluoride, and selenium powder.

7. The method for preparing a heteroatom-doped carbon-coated NiF2-based positive electrode material according to claim 2, characterized in that: The mass ratio of the NiF2@polymer pyrolysis precursor to the heteroatom substance is 1:1 to 1:

3.

8. The method for preparing a heteroatom-doped carbon-coated NiF2-based positive electrode material according to claim 2, characterized in that: The NiF2@polymer pyrolysis precursor is placed at the downstream end of the porcelain boat, and the heteroatom substance is placed at the upstream end of the porcelain boat. The upstream end of the porcelain boat is an inert gas inlet end.

9. Use of a heteroatom-doped carbon-coated NiF2-based positive electrode material as claimed in claim 1 or a heteroatom-doped carbon-coated NiF2-based positive electrode material prepared by the preparation method as claimed in any one of claims 2 to 8 in preparing a thermal battery.

10. The heteroatom-doped carbon-coated NiF2-based positive electrode material as claimed in claim 1 or the heteroatom-doped carbon-coated NiF2-based positive electrode material prepared by the preparation method as claimed in any one of claims 2 to 8 is used as a positive electrode active material for a thermal battery.

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