A high-voltage high-entropy metal fluoride positive electrode, a preparation method and applications thereof

Abstract

A high-voltage high-entropy metal fluoride positive electrode, a preparation method and applications thereof belong to the technical field of lithium ion batteries. Copper fluoride, iron fluoride, cobalt fluoride, nickel fluoride and manganese fluoride are mixed, sodium alginate is added, and high-entropy metal fluoride material uniformly fused with sodium alginate is obtained under argon protection ball milling; then, ketjen black is added under argon protection, and ball milling is carried out under the same conditions; the powder obtained by ball milling is mixed with a Mxene aqueous dispersion, coated on a titanium foil after ball milling, and dried to obtain a high-entropy metal fluoride positive electrode combined with a conductive binder. The application of high-entropy materials and high-conductivity cross-linked binders to copper fluoride positive electrodes utilizes the improvement of the two on the conductive capacity and the protection effect on copper fluoride, as well as the cross-linking effect among CuF2, SA and MXene, improves the conductive performance and cycle stability of the positive electrode, and enables the average discharge voltage of the full battery to break through 2.5V, so that it can be used for assembling full batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a high-voltage, high-entropy metal fluoride cathode for lithium-fluoride batteries, its preparation method, and its application in assembling full cells. Background Technology

[0002] In recent years, with the development and infrastructure construction of new energy sources such as solar, wind, and nuclear power, the country's demand for energy storage and conversion systems that address the temporal and regional limitations of new energy sources has been increasing. Therefore, novel energy storage batteries, as a key component of energy storage systems, have attracted much attention. Currently, due to the need for large-scale energy storage, the development of commercial lithium-ion battery cathodes faces problems such as low average discharge voltage, low energy density, and rising costs. Furthermore, the most advanced intercalated cathodes have reached their theoretical limits. Developing novel high-energy-density battery cathodes has become a key focus and hot topic in academic research.

[0003] Currently, the discharge process of conversion-type fluoride cathodes involves multiple electron transfers and exhibits high specific capacity. Among them, iron fluoride cathodes, with their high energy density and low cost, are candidate cathodes for novel large-scale energy storage lithium-ion battery systems. However, due to its poor electron conductivity, the actual average discharge voltage of iron fluoride cathodes is far lower than the theoretical value, limiting its energy density. Copper fluoride cathodes, on the other hand, are advantageous because of their relatively low energy density compared to Li / Li... + With a high theoretical potential of 3.55V and higher energy density, copper fluoride (CFD) cathodes hold promise as a new direction for the development of fluoride cathode systems, potentially replacing iron fluoride cathodes. However, CFD cathodes also suffer from significant volume expansion during discharge, poor conductivity, and copper nanoparticle aggregation during charge and discharge, severely impacting their cycle life. Furthermore, the severe dissolution of the active material copper fluoride during battery loading leads to irreversible capacity loss, further limiting the development of CFD cathodes.

[0004] To address these challenges, researchers have conducted extensive studies. However, only limited progress has been made. Currently, using nanoscale copper fluoride-carbon composite cathodes or iron doping can improve the initial performance of copper fluoride cathodes, but the cycling performance cannot exceed 10 cycles; using copper fluoride-sodium alginate composite cathodes can stabilize battery cycling, but the average discharge voltage still cannot reach 2.5V. Summary of the Invention

[0005] The purpose of this invention is to provide a high-voltage, high-entropy metal fluoride cathode for lithium-fluoride batteries, its preparation method, and its application in assembling full batteries.

[0006] The preparation method of the high-voltage, high-entropy metal fluoride cathode (HE-CuF2-SA-M) for lithium-fluoride batteries according to the present invention firstly involves mixing 0.9–1.2 g of anhydrous copper fluoride, 0.04–0.1 g of anhydrous iron fluoride, 0.04–0.1 g of anhydrous cobalt fluoride, 0.04–0.1 g of anhydrous nickel fluoride, and 0.04–0.1 g of anhydrous manganese fluoride, and then adding 0.2–0.4 g of anhydrous sodium alginate (SA). The mixture is then ball-milled for 1 hour under argon protection at 400–600 rpm. After 3 hours, a high-entropy metal fluoride material uniformly fused with sodium alginate was obtained. Then, under argon protection, 0.25–0.8 g of Ketjen black was added, and ball milling was performed under the same conditions for 2–8 hours to uniformly disperse the high-entropy metal fluoride material in the carbon framework. The ball-milled powder was mixed with 2–10 wt% Mxene aqueous dispersion at a mass ratio of 1–10:1, and ball milling was continued for 0.5–1.5 hours. Finally, the mixture was coated onto titanium foil, with a high-entropy metal fluoride material loading of 0.5–1 mg / cm³. 3 Then, it is dried at 70-90°C under vacuum for 18-36 hours to obtain the high-entropy metal fluoride cathode with conductive binder described in this invention.

[0007] This invention applies high-entropy metal fluoride materials and highly conductive crosslinking binders to the positive electrode of lithium-ion batteries through ball milling. By utilizing the improved conductivity and protection of copper fluoride by the two materials, as well as the crosslinking effect between CuF2, SA, and MXene, the conductivity and cycle stability of the positive electrode are improved, while the average discharge voltage of the full cell can exceed 2.5V.

[0008] The beneficial effects of this invention are:

[0009] 1) A novel high-entropy metal fluoride cathode has been developed. This method can synthesize high-entropy metal fluorides in just one ball milling step. The process is simple and the average discharge voltage of the product is significantly improved.

[0010] 2) Due to the "cocktail" effect of high-entropy materials (a synergistic effect brought about by the interaction between elements, i.e., a special combination of elements may bring about changes in material properties such as conductivity), the conductivity and cycle stability of the high-entropy metal fluoride materials are significantly improved.

[0011] 3) By using a simple liquid-phase method to crosslink CuF2, SA, and MXene, a highly conductive and protective polymer film is formed on the surface of the active material, which greatly improves the conductivity of the positive electrode and thus increases the average discharge voltage of the material. Attached Figure Description

[0012] To more clearly illustrate the technical solution of this invention and the properties of the materials prepared therefrom, relevant figures are provided below.

[0013] Figure 1 The X-ray diffraction (XRD) pattern of the high-entropy metal fluoride cathode (HE-CuF2-SA-M) prepared in Example 1 is shown. The XRD pattern confirms the successful preparation of the high-entropy metal fluoride, with copper fluoride as the main phase.

[0014] Figure 2 The image shows a scanning electron microscope (SEM) image of the HE-CuF2-SA-M powder prepared from Example 1. The SEM image shows that HE-CuF2-SA-M consists of nanoparticles with a size of 50–200 nm, which are bonded together by a binder composed of SA and Mxene.

[0015] Figure 3 The images show transmission electron microscopy (TEM) image (a) and high-resolution transmission electron microscopy (HRTEM) image (b) of the HE-CuF2-SA-M powder prepared in Example 1. The TEM image shows that the HE-CuF2-SA-M powder is nanoscale in size and is connected together by a binder composed of SA and Mxene, which corresponds to the morphology in the SEM image. In Figure (b), lattice fringes corresponding to copper fluoride can be seen, indicating that the main body of the material is copper fluoride.

[0016] Figure 4 The image shows the transmission electron microscope (TEM) image of the HE-CuF2-SA-M powder prepared in Example 1, and the corresponding X-ray energy dispersive spectroscopy (EDS) image. The uniform distribution of Na and Ti elements and the distributed distribution of Cu and F elements indicate that the binder composed of SA and Mxene successfully bonded the high-entropy fluoride particles together to form a polymer conductive network. Furthermore, the presence of manganese, cobalt, nickel, and iron elements indicates that the main component of the material is copper fluoride, and that the high-entropy components of manganese, cobalt, nickel, and iron fluorides were successfully introduced.

[0017] Figure 5 The figure shows the discharge curve of a full cell assembled with the HE-CuF2-SA-M material cathode prepared in Example 1. As can be seen from the figure, the material has a high initial capacity but a low discharge voltage. After 10 cycles, the discharge voltage increases significantly, and a clear discharge plateau appears at around 2.7V, indicating that ion diffusion and charge transfer gradually increase. This is related to the formation of conductive CEI / SEI and the "cocktail" effect of high-entropy materials on the electrode during the charge-discharge reaction.

[0018] Figure 6 The graph shows the cycling performance of the full cell assembled with the HE-CuF2-SA-M material prepared in Example 1 at 0.05C. The graph consists of two curves; curve 1 represents the discharge specific capacity of the cathode. The full cell containing the HE-CuF2-SA-M cathode can cycle stably for more than 40 cycles, and still retains a capacity of 298.2 mAh g⁻¹.-1 This indicates that the full cell containing the HE-CuF2-SA-M cathode has excellent average discharge voltage and stable cycle performance; Curve 2 is the average discharge voltage curve of this cathode. It can be seen from the figure that after a short activation process, HE-CuF2-SA-M can reach more than 2.5V.

[0019] Figure 7 The image shows a scanning electron microscope (SEM) image of the CuF2-SA-M powder prepared in Example 2. The SEM image shows that the CuF2-SA-M powder is nanoscale in size and is linked together by a binder composed of SA and Mxene, but it exhibits severe aggregation compared to high-entropy materials.

[0020] Figure 8 The image shows the discharge curve of a full cell assembled with the CuF2-SA-M cathode material prepared in Example 2. It can be seen that, compared to HE-CuF2-SA-M, the voltage plateau of the full cell assembled with the CuF2-SA-M cathode material is significantly shortened. This is because the high-entropy fluoride enhances the reaction kinetics of the cathode, making the reaction of copper fluoride more likely to occur at higher potentials.

[0021] Figure 9 The graph shows the cycling performance of the full cell assembled with the CuF2-SA-M cathode prepared in Example 2 at 0.05C. Curve 1 is the average discharge voltage curve of this cathode, and curve 2 is the discharge specific capacity curve of this cathode. As can be seen from the figure, although the full cell containing the CuF2-SA-M cathode has a discharge specific capacity similar to that of the HE-CuF2-SA-M cathode, the average discharge voltage can only reach a maximum of about 2.1V. This indicates that the "cocktail" effect of the high-entropy component can optimize the reaction kinetics of the copper fluoride cathode and effectively improve the average discharge voltage of the fluoride cathode.

[0022] Figure 10 The figures show the charge-discharge curves of the full cell assembled with the CuF2-M cathode prepared in Example 3. Curve 1 is the discharge curve, and curve 2 is the charging curve. It can be seen that, compared with the HE-CuF2-SA-M and CuF2-SA-M cathodes, the battery assembled with the pure copper fluoride cathode without sodium alginate cannot be charged to 4.4V after discharge, indicating that sodium alginate has a protective effect on the copper fluoride cathode. Detailed Implementation

[0023] Example 1:

[0024] First, 1g of anhydrous copper fluoride, 0.05g of anhydrous iron fluoride, 0.05g of anhydrous cobalt fluoride, 0.05g of anhydrous nickel fluoride, and 0.05g of anhydrous manganese fluoride were mixed, and then 0.3g of anhydrous sodium alginate was added. The mixture was ball-milled for 2 hours under argon protection at 450 rpm to obtain a high-entropy metal fluoride material uniformly fused with sodium alginate. Then, 0.6g of Ketjen black was added under argon protection, and the mixture was ball-milled for 4 hours under the same conditions to uniformly disperse the high-entropy metal fluoride material in the carbon framework. The ball-milled powder was mixed with 5wt% Mxene aqueous dispersion at a mass ratio of 3:1, and ball-milled for another 1 hour. Finally, the mixture was coated onto a 3cm × 3cm titanium foil, with a high-entropy metal fluoride material loading of 0.8 mg / cm². 3 Then, it is dried in a vacuum oven at 80°C for 24 hours to obtain the high-entropy metal fluoride cathode (HE-CuF2-SA-M) with conductive binder as described in this invention.

[0025] When assembling the full cell, a high-entropy metal fluoride positive electrode with conductive binder is used as the positive electrode, and lithium metal is used as the negative electrode. Whatman 1822-090 is used as the separator, and 60 μL of EC / PC electrolyte (Dodo reagent) with 4M LiClO4 dissolved in it at a volume ratio of 1:1 is added to each side of the separator.

[0026] Example 2:

[0027] The difference between Example 2 and Example 1 is that only copper fluoride and anhydrous sodium alginate were used in the first ball milling step to prepare the CuF2-SA-M cathode. The electrochemical performance testing was similar to that in Example 1.

[0028] Example 3:

[0029] The difference between Example 3 and Example 2 is that anhydrous sodium alginate was not used in the first step of ball milling; instead, copper fluoride and Ketjen Black were used directly for ball milling. The material was then mixed with polyvinylidene fluoride (PVDF) at a mass ratio of 9:1 and coated onto a 3cm × 3cm titanium foil to prepare the CuF2-M cathode. The electrochemical performance testing was similar to that in Example 1.

Claims

1. A method of making a high-voltage high-entropy metal fluoride cathode, the method comprising: First, 0.9-1.2 g of anhydrous copper fluoride, 0.04-0.1 g of anhydrous iron fluoride, 0.04-0.1 g of anhydrous cobalt fluoride, 0.04-0.1 g of anhydrous nickel fluoride and 0.04-0.1 g of anhydrous manganese fluoride are mixed, then 0.2-0.4 g of anhydrous sodium alginate is added, and ball milling is carried out under the protection of argon at 400-600 rpm for 1-3 h to obtain a high-entropy metal fluoride material uniformly fused with sodium alginate; then 0.25-0.8 g of Ketjenblack is added under the protection of argon, and ball milling is carried out at 400-600 rpm for 2-8 h to uniformly disperse the high-entropy metal fluoride material in the carbon skeleton; the powder obtained by ball milling is mixed with 2-10 wt% of a Mxene aqueous dispersion at a mass ratio of 1-10:1, and ball milling is continued for 0.5-1.5 h; finally, the mixture is coated on a titanium foil and dried under vacuum to obtain a high-entropy metal fluoride positive electrode combined with a conductive binder. ​ 2. The method of claim 1, wherein the high voltage high entropy metal fluoride cathode is prepared by: The high-entropy metal fluoride material has a loading of 0.5-1 mg / cm 3 .

3. The method for preparing a high-voltage, high-entropy metal fluoride cathode as described in claim 1, characterized in that: The temperature for vacuum drying is 70-90℃, and the time for vacuum drying is 18-36 h.

4. A high-voltage high-entropy metal fluoride cathode, characterized by: is prepared by the method of claim 1, 2 or 3.

5. Use of a high-voltage high-entropy metal fluoride positive electrode according to claim 4 in assembling a full battery.

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