Carbon-complexed transition metal fluoride positive electrode material, preparation method and application thereof

Abstract

The embodiment of the present application relates to a kind of carbon composite transition metal fluoride positive electrode material and its preparation method and application, the preparation method includes: under vacuum condition, transition metal element is heat treated, so that transition metal element is gasified as gaseous metal nanoparticle, obtain transition metal vapor;Transition metal vapor and fluorine source gas are introduced into the reaction container containing porous carbon substrate, transition metal vapor and fluorine source gas occur gas phase reaction, generate transition metal fluoride nanoparticles, and in situ deposit on the surface of porous carbon substrate, obtain carbon composite transition metal fluoride positive electrode material.The carbon composite transition metal fluoride positive electrode material prepared by the preparation method of the present application has good electrochemical performance.

Description

Carbon composite transition metal fluoride cathode materials, their preparation methods and applications Technical Field

[0001] This invention relates to the field of cathode materials for secondary batteries, and more particularly to a carbon composite transition metal fluoride cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have advantages such as high energy conversion efficiency and long lifespan, and are widely used in portable mobile devices, electric vehicles, and other applications. However, the low specific capacity of traditional intercalated electrode materials cannot meet the urgent need for high-capacity cathode materials.

[0003] Transition metal fluorides are considered highly promising candidates for next-generation cathode materials due to their advantages such as high operating voltage and capacity, low cost, wide availability, good thermal stability, and environmental friendliness. For example, iron fluoride (FeF3) has a high capacity of up to 712 mAh g / L. -1 Transition metal fluorides have been extensively studied due to their theoretical capacity and operating potential greater than 3.0V. However, the large bandgap of transition metal fluorides results in poor electronic conductivity, which greatly limits the storage capacity of lithium. In addition, the structural collapse caused by the conversion reaction easily leads to problems such as battery capacity decay and poor cycle stability, which restricts the commercial development of transition metal fluorides.

[0004] To overcome the aforementioned problems, researchers have attempted to prepare carbon-based transition metal fluorides using solvothermal methods, precipitation methods, and ball milling methods. However, each of these methods has its limitations. For example, ball milling produces composite materials with large particle sizes, low tap density, small specific surface area, and poor electrochemical performance. Solvothermal methods are time-consuming, produce large particles, and often contain difficult-to-remove water of crystallization, resulting in poor cycling performance. In summary, the electrode materials obtained by these methods require further improvement in reversible specific capacity, rate performance, and cycling performance. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a carbon composite transition metal fluoride cathode material, its preparation method, and its application. The carbon composite transition metal fluoride cathode material prepared by this method overcomes the problems of low reversible capacity and rapid capacity decay of transition metal fluoride cathode materials, thereby improving electrochemical performance.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a carbon composite transition metal fluoride cathode material, the method comprising:

[0007] Under vacuum conditions, the transition metal element is heat-treated to vaporize into gaseous metal nanoparticles, thus obtaining transition metal vapor.

[0008] The transition metal vapor and fluorine source gas are introduced into a reaction vessel containing a porous carbon substrate. The transition metal vapor and fluorine source gas undergo a gas-phase reaction to generate transition metal fluoride nanoparticles, which are then deposited in situ on the surface of the porous carbon substrate to obtain a carbon composite transition metal fluoride cathode material.

[0009] Preferably, the vacuum condition specifically is: a vacuum degree of less than 10. -3 pa; the heat treatment temperature is 300℃-3000℃, and the different transition metal elements correspond to different heat treatment temperatures.

[0010] Preferably, the heat treatment includes any one of resistance heating, high-frequency induction heating, laser heating, electron beam heating, microwave heating, or electric arc heating.

[0011] Preferably, the gas flow rates of the transition metal vapor and the fluorine source gas are both 10 mL / min to 30 mL / min; and the reaction time of the gas phase reaction is 0.5 h to 6 h.

[0012] Preferably, the molar ratio of the metal element in the transition metal vapor to the fluorine element in the fluorine source gas is 1:1 to 1:6.

[0013] Preferably, the transition metal element includes any one of the metal elements Fe, Co, Mn, Ni, Cu, Zn, Nb, or Ti; and the purity of the transition metal element is greater than 99.8%.

[0014] Preferably, the fluorine source gas is nitrogen trifluoride or carbon tetrafluoride.

[0015] In a second aspect, the present invention provides a carbon composite transition metal fluoride cathode material, wherein the carbon composite transition metal fluoride cathode material is prepared by any of the preparation methods described in the first aspect above.

[0016] Thirdly, the present invention provides a positive electrode sheet, wherein the positive electrode sheet comprises the carbon composite transition metal fluoride positive electrode material described in the second aspect above.

[0017] Fourthly, the present invention provides a secondary battery, characterized in that the secondary battery includes the positive electrode sheet described in the third aspect above.

[0018] The method for preparing carbon-composite transition metal fluoride cathode material provided in this invention involves heat treatment to gasify the transition metal element, followed by a gas-phase reaction with a fluorine source gas, and then deposition onto a porous carbon substrate to obtain the carbon-composite transition metal fluoride cathode material. This carbon-composite transition metal fluoride cathode material possesses the high specific capacity advantage of transition metal fluorides, and the in-situ composite of transition metal fluorides and carbon constructs an electron transport conductive network between nanoparticles, significantly improving the electronic conductivity of the carbon-composite transition metal fluoride cathode material. The porous carbon substrate provides an effective buffer space for the volume expansion and contraction of the carbon-composite transition metal fluoride cathode material, thereby giving it excellent cycle performance and rate performance. Attached Figure Description

[0019] Figure 1 is a flowchart of the preparation method of carbon composite transition metal fluoride cathode material provided in the embodiment of the present invention;

[0020] Figure 2 is a charge-discharge curve of the carbon composite iron fluoride cathode material prepared in Example 1 of the present invention;

[0021] Figure 3 shows the cycle performance of the carbon composite iron fluoride cathode material prepared in Example 1 of the present invention;

[0022] Figure 4 is a charge-discharge curve of the carbon composite copper fluoride cathode material prepared in Example 2 of the present invention;

[0023] Figure 5 shows the cycle performance of the carbon composite copper fluoride cathode material prepared in Example 2 of the present invention;

[0024] Figure 6 is a charge-discharge curve of the carbon composite cobalt fluoride cathode material prepared in Example 3 of the present invention;

[0025] Figure 7 shows the cycle performance of the carbon composite cobalt fluoride cathode material prepared in Example 3 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] This invention provides a method for preparing a carbon composite transition metal fluoride cathode material, the process of which is shown in Figure 1 and includes the following steps:

[0028] Step 110: Under vacuum conditions, the transition metal element is heat-treated to vaporize into gaseous metal nanoparticles, thus obtaining transition metal vapor.

[0029] This step primarily involves gasifying the transition metal element. The vacuum level under these conditions is less than 10. -3 The heat treatment method can specifically include any one of resistance heating, high-frequency induction heating, laser heating, electron beam heating, microwave heating, or electric arc heating. The heat treatment temperature can specifically range from 300℃ to 3000℃, with different transition metal elements corresponding to different heat treatment temperatures. The transition metal elements can specifically include any one of the following metallic elements: Fe, Co, Mn, Ni, Cu, Zn, Nb, or Ti. The purity of the transition metal element is greater than 99.8%.

[0030] Step 120: Transition metal vapor and fluorine source gas are introduced into a reaction vessel containing a porous carbon substrate. The transition metal vapor and fluorine source gas undergo a gas-phase reaction to generate transition metal fluoride nanoparticles, which are then deposited in situ on the surface of the porous carbon substrate to obtain a carbon composite transition metal fluoride cathode material.

[0031] Specifically, the fluorine source gas can be nitrogen trifluoride or carbon tetrafluoride. The molar ratio of the metal element in the transition metal vapor to the fluorine in the fluorine source gas is 1:1 to 1:6. The gas flow rate of the transition metal vapor and the fluorine source gas can be 10 mL / min to 30 mL / min. The reaction time of the gas-phase reaction is 0.5 h to 6 h. The porous carbon substrate can be any one of carbon fiber, carbon nanorod, carbon nanowire, carbon nanotube, single-walled carbon nanotube, multi-walled carbon nanotube, graphite, graphene, carbon cloth, carbon paper, biomass-derived carbon, or metal-organic framework (MOF) / polymer-derived porous carbon. The transition metal fluoride generated by the gas-phase reaction can specifically include any one of FeF2, FeF3, CoF2, CoF3, MnF2, MnF3, NiF2, NiF3, CuF2, ZnF2, NbF5, and TiF4.

[0032] Atomic-level mixing was achieved through a gas-phase reaction between transition metal vapor and fluorine source gas, resulting in a shorter reaction time and a more complete reaction. The carbon in the porous carbon substrate surrounding the gaseous metal nanoparticles acted as a micro-reactor during the reaction, limiting the aggregation of transition metal fluoride particles and resulting in smaller transition metal fluoride particles with a larger specific surface area and controllable morphology.

[0033] The in-situ carbon composite of transition metal fluoride particles and porous carbon substrate constructs an electron transport conductive network between nanoparticles, which can improve the electronic conductivity of the material. During the lithium-ion insertion and extraction process, the porous carbon substrate can provide an effective buffer space for the volume expansion and contraction of the cathode material, thus exhibiting excellent cycle performance and rate performance. This overcomes the problems of low reversible capacity and fast capacity decay of transition metal fluoride cathode materials and improves electrochemical performance.

[0034] The method for preparing carbon-composite transition metal fluoride cathode material provided in this invention involves heat treatment to gasify the transition metal element, followed by a gas-phase reaction with a fluorine source gas, and then deposition onto a porous carbon substrate to obtain the carbon-composite transition metal fluoride cathode material. This carbon-composite transition metal fluoride cathode material possesses the high specific capacity advantage of transition metal fluorides, and the in-situ composite of transition metal fluorides and carbon constructs an electron transport conductive network between nanoparticles, significantly improving the electronic conductivity of the carbon-composite transition metal fluoride cathode material. The porous carbon substrate provides an effective buffer space for the volume expansion and contraction of the carbon-composite transition metal fluoride cathode material, thereby giving it excellent cycle performance and rate performance.

[0035] The carbon composite transition metal fluoride cathode material provided by this invention can be used as the cathode material in secondary batteries. By using carbon composite transition metal fluorides as the cathode material for lithium-ion batteries, the dependence on lithium resources is reduced, and the problems of resource shortage and high price of elements such as nickel and cobalt in lithium-ion battery cathode materials are solved.

[0036] To better understand the technical solution provided by the present invention, the following uses several specific examples to illustrate the specific process of preparing carbon composite transition metal fluoride cathode materials using the method provided in the above embodiments of the present invention, as well as the electrochemical characteristics of the prepared carbon composite transition metal fluoride cathode materials.

[0037] Example 1

[0038] The first step is to use a vacuum of 4×10 -4 Under the condition of Pa, metallic iron with a purity of 99.9% is placed in a resistance heater and heated to 1300℃ by resistance, so that the metallic iron is vaporized into gaseous iron nanoparticles, and iron vapor is obtained and collected.

[0039] In the second step, iron vapor and nitrogen trifluoride gas are introduced into the reactor at a molar ratio of 1:3 for iron to fluorine and a gas flow rate of 10 ml / min. The reaction time is 2 hours to generate iron fluoride nanoparticles, which are then deposited in situ on the surface of a carbon fiber substrate to obtain a carbon composite iron fluoride cathode material. After cooling, the material is collected.

[0040] The obtained carbon composite iron fluoride cathode material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a mass ratio of 90:5:5. The mixture was stirred until it reached the required viscosity for coating. Then, the mixture was evenly coated onto aluminum foil using a coating machine. It was then vacuum dried at 80°C for 12 hours.

[0041] The dried electrode sheets were then cut into 12mm diameter discs, with each disc having an active substance loading of 2mg / cm³. 2 .

[0042] Using the prepared electrode sheet as the positive electrode, a lithium sheet as the negative electrode, and Celgard 2500 as the separator, the CR2032 coin cell was assembled entirely within an argon-filled glove box. The electrolyte for the assembled CR2032 coin cell was 1 mol / L lithium hexafluorophosphate (LiPF6), and the solvents were ethylene carbonate (EC) and dimethyl carbonate (DMC), with a volume ratio of EC to DMC of 1:1.

[0043] After assembly, the coin cells were left to stand for 8 hours at room temperature. Then, charge-discharge and cycle tests were performed on the Blue Battery Testing System (CT2001A) with a test voltage of 2.2-4.2V and a current density of 0.1C to evaluate their electrochemical performance.

[0044] Example 2

[0045] The first step is to use a vacuum of 1×10⁻⁶. -4 Under the condition of Pa, 99.95% pure metallic copper is placed in an inductor made of hollow metal tubes and heated to 1100℃ by high-frequency induction heating, so that the metallic copper is vaporized into gaseous copper nanoparticles, and copper vapor is obtained and collected.

[0046] The second step involves introducing copper vapor and carbon tetrafluoride gas into a reactor at a molar ratio of 1:2 (copper to fluorine) and a flow rate of 15 mL / min. The reaction time is 3 hours, which generates copper fluoride nanoparticles. These nanoparticles are then deposited in situ on the surface of a multi-walled carbon nanotube substrate to obtain a carbon composite copper fluoride cathode material, which is then collected after cooling.

[0047] The obtained carbon composite copper fluoride cathode material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a mass ratio of 90:5:5. The mixture was stirred until it reached the required viscosity for coating. Then, the mixture was evenly coated onto aluminum foil using a coating machine. It was then vacuum dried at 80°C for 12 hours.

[0048] The dried electrode sheets were then cut into 12mm diameter discs, with each disc having an active material loading of 3mg / cm³. 2 .

[0049] Using the prepared electrode sheet as the positive electrode, a lithium sheet as the negative electrode, and Celgard 2500 as the separator, the CR2032 coin cell was assembled entirely within an argon-filled glove box. The electrolyte for the assembled CR2032 coin cell was 1 mol / L lithium hexafluorophosphate (LiPF6), and the solvents were ethylene carbonate (EC) and dimethyl carbonate (DMC), with a volume ratio of EC to DMC of 1:1.

[0050] After assembly, the coin cells were left to stand for 8 hours at room temperature. Then, charge-discharge and cycle tests were performed on the Blue Battery Testing System (CT2001A) with a test voltage of 1.5-4.4V and a current density of 0.1C to evaluate their electrochemical performance.

[0051] Example 3

[0052] The first step is to use a vacuum of 1×10⁻⁶. -5 Under the conditions of Pa, metallic cobalt with a purity of 99.98% was placed on a flat graphite plate and heated to 1350℃ by laser, causing the metallic cobalt to vaporize into gaseous cobalt nanoparticles, thus obtaining cobalt vapor, which was then collected.

[0053] In the second step, cobalt vapor and carbon tetrafluoride gas are introduced into the reactor at a molar ratio of cobalt to fluorine of 1:2 and a gas flow rate of 20 ml / min. The reaction time is 2.5 hours to generate cobalt fluoride nanoparticles, which are then deposited in situ on the surface of a graphene substrate to obtain a carbon composite cobalt fluoride cathode material. After cooling, the material is collected.

[0054] The obtained carbon composite cobalt fluoride cathode material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a mass ratio of 90:5:5. The mixture was stirred until it reached the required viscosity for coating. Then, the mixture was evenly coated onto aluminum foil using a coating machine. It was then vacuum dried at 80°C for 12 hours.

[0055] The dried electrode sheets were then cut into discs with a diameter of 12 mm, each disc having an active substance loading of approximately 2.5 mg / cm³. 2 .

[0056] Using the prepared electrode sheet as the positive electrode, a lithium sheet as the negative electrode, and Celgard 2500 as the separator, the CR2032 coin cell was assembled entirely within an argon-filled glove box. The electrolyte for the assembled CR2032 coin cell was 1 mol / L lithium hexafluorophosphate (LiPF6), and the solvents were ethylene carbonate (EC) and dimethyl carbonate (DMC), with a volume ratio of EC to DMC of 1:1.

[0057] After assembly, the coin cells were left to stand for 8 hours at room temperature. Then, charge-discharge and cycle tests were performed on the Blue Battery Testing System (CT2001A) with a test voltage of 1.0-4.0V and a current density of 0.1C to evaluate their electrochemical performance.

[0058] Figures 2-7 are curves obtained from the first-cycle charge-discharge test and cycle test of the coin cells prepared in the above three embodiments at a current density of 0.1C.

[0059] As shown in Figure 2, the carbon composite iron fluoride cathode material prepared in Example 1 has a first-cycle charge specific capacity of 248.5 mAh / g and a discharge specific capacity of 270.2 mAh / g. As shown in Figure 3, after 100 cycles, the discharge specific capacity is 261.0 mAh / g, with a capacity retention of 96.6%.

[0060] As shown in Figure 4, the carbon composite copper fluoride cathode material prepared in Example 2 has a first-cycle charge specific capacity of 411.8 mAh / g and a discharge specific capacity of 562.3 mAh / g. As shown in Figure 5, after 50 cycles, the discharge specific capacity is 489.2 mAh / g, with a capacity retention of 87.0%.

[0061] As shown in Figure 6, the carbon composite cobalt fluoride cathode material prepared in Example 3 has a first-cycle charge specific capacity of 443.5 mAh / g and a discharge specific capacity of 455.2 mAh / g. As shown in Figure 7, after 50 cycles, the discharge specific capacity is 396.6 mAh / g, with a capacity retention of 87.1%.

[0062] Therefore, the preparation method proposed in this invention can improve the conductivity of the material, achieve rapid electron transport and ion migration, reduce internal stress of the electrode, and reduce volume expansion. The carbon composite transition metal fluoride material prepared has high initial capacity and relatively stable cycling performance, without the adverse situation of rapid capacity decay. It improves the problems of poor conductivity, slow reaction kinetics leading to voltage hysteresis, low reversible capacity and rapid decay of transition metal fluorides.

[0063] Example 4

[0064] The first step is to use a vacuum of 2×10⁻⁶. -4Under the conditions of Pa, 99.99% pure metallic nickel was placed in an electron beam evaporation device and heated to 1300℃ by an electron beam, causing the metallic nickel to vaporize into gaseous nickel nanoparticles, thus obtaining nickel vapor, which was then collected.

[0065] In the second step, nickel vapor and nitrogen trifluoride gas are introduced into the reactor at a molar ratio of nickel to fluorine of 1:2.5 and a gas flow rate of 25 ml / min. The reaction time is 2 hours to generate nickel fluoride nanoparticles, which are then deposited in situ on the surface of a biomass-derived carbon substrate to obtain a carbon composite nickel fluoride cathode material. After cooling, the material is collected.

[0066] Example 5

[0067] The first step is to use a vacuum of 3×10⁻⁶. -5 Under the conditions of Pa, 99.95% pure metallic zinc is placed in a microwave heater and heated to 300°C by microwave, causing the metallic zinc to vaporize into gaseous zinc nanoparticles, thus obtaining zinc vapor, which is then collected.

[0068] The second step involves introducing zinc vapor and carbon tetrafluoride gas into a reactor at a molar ratio of 1:2 (zinc to fluorine) and a flow rate of 10 mL / min. The reaction time is 6 hours, which generates zinc fluoride nanoparticles. These nanoparticles are then deposited in situ onto the surface of a carbon paper substrate to obtain a carbon composite zinc fluoride cathode material, which is then collected after cooling.

[0069] Example 6

[0070] The first step is to use a vacuum of 1×10⁻⁶. -4 Under the conditions of Pa, 99.9% pure metallic titanium is placed in a microwave heater and heated to 1400℃ by microwave, causing the metallic titanium to vaporize into gaseous titanium nanoparticles, thus obtaining titanium vapor, which is then collected.

[0071] In the second step, titanium vapor and carbon tetrafluoride gas are introduced into the reactor at a molar ratio of titanium to fluorine of 1:4 and a gas flow rate of 20 ml / min. The reaction time is 3 hours to generate titanium fluoride nanoparticles, which are then deposited in situ on the surface of a metal organic framework (MOF) / polymer-derived porous carbon substrate to obtain carbon composite titanium fluoride cathode material. After cooling, the material is collected.

[0072] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon composite transition metal fluoride cathode material, characterized in that, The preparation method includes: heat-treating a transition metal element under vacuum conditions to vaporize the transition metal element into gaseous metal nanoparticles, thereby obtaining transition metal vapor; introducing the transition metal vapor and fluorine source gas into a reaction vessel containing a porous carbon substrate, wherein the transition metal vapor and fluorine source gas undergo a gas-phase reaction to generate transition metal fluoride nanoparticles, which are then deposited in situ on the surface of the porous carbon substrate to obtain a carbon composite transition metal fluoride cathode material.

2. The preparation method according to claim 1, characterized in that, The vacuum condition specifically refers to a vacuum degree of less than 10. - 3 pa; The heat treatment temperature is 300℃-3000℃, and different transition metal elements correspond to different heat treatment temperatures.

3. The preparation method according to claim 1, characterized in that, The heat treatment includes any one of resistance heating, high-frequency induction heating, laser heating, electron beam heating, microwave heating, or electric arc heating.

4. The preparation method according to claim 1, characterized in that, The gas flow rates of the transition metal vapor and the fluorine source gas are both 10 mL / min to 30 mL / min; the reaction time of the gas phase reaction is 0.5 h to 6 h.

5. The preparation method according to claim 1, characterized in that, The molar ratio of the metal element in the transition metal vapor to the fluorine element in the fluorine source gas is 1:1 to 1:

6.

6. The preparation method according to claim 1, characterized in that, The transition metal element includes any one of the metallic elements Fe, Co, Mn, Ni, Cu, Zn, Nb, or Ti; the purity of the transition metal element is greater than 99.8%.

7. The preparation method according to claim 1, characterized in that, The fluorine source gas is nitrogen trifluoride or carbon tetrafluoride.

8. A carbon composite transition metal fluoride cathode material, characterized in that, The carbon composite transition metal fluoride cathode material is prepared by any one of the preparation methods described in claims 1-7.

9. A positive electrode sheet, characterized in that, The positive electrode sheet comprises the carbon composite transition metal fluoride positive electrode material as described in claim 8.

10. A secondary battery, characterized in that, The secondary battery includes the positive electrode sheet as described in claim 9.

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