High-entropy metal phosphide / carbon composite lithium ion battery negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses a high-entropy metal phosphide / carbon composite lithium ion battery negative electrode material as well as a preparation method and application thereof, and relates to the technical field of lithium ion battery material preparation. The negative electrode material comprises a high-entropy metal phosphide and a conductive carbon material, the molecular formula of the high-entropy metal phosphide is CuaGebSncZndPx, the cocktail effect of the high-entropy metal phosphide realizes high electronic conductivity and high capacity, the high-entropy effect improves the disorder degree of a system, the potential platform of the negative electrode material is reduced, and the performance of the negative electrode material is improved. And a high-energy-density battery system can be realized. The problem that a high-performance alloy-based negative electrode material is lacked in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery material preparation, and in particular to a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material, a preparation method and application thereof. Background Art

[0002] In recent years, lithium-ion batteries (LIBs) and other advanced energy storage devices have been extensively researched, supporting the rapid development of emerging portable electronic devices and electric vehicles. However, limited by the low discharge capacity of traditional graphite anodes (372 mAh / g), the energy density of current LIBs still needs to be improved and cannot meet the range requirements of electric vehicles. As one of the key components, the anode material is a key factor in improving the energy density of LIBs and determining battery performance. Therefore, the development of high-capacity and high-performance anode materials is a major goal.

[0003] Compared with commercial graphite, phosphorus (P)-based anode materials have extremely high theoretical specific capacity (2596 mAh / g) and are considered to be ideal high energy density battery anode materials. However, red phosphorus (RP) faces the problem of poor conductivity (<1×10 -14 S / cm), low initial Coulombic efficiency, and significant volume changes during ion insertion and extraction, leading to rapid battery degradation, hinder the practical application and industrial development of phosphorus-based alloy anode materials. Currently, phosphorus-based anode materials can be enhanced in conductivity and mitigated in volume expansion by combining them with carbon materials. However, carbon materials have low lithium storage capacity, deviating from the high specific energy characteristics of alloy-based anodes. Alternatively, some have synthesized metal phosphides using lithium-storage-active metal elements such as Ge and Sn, demonstrating high conductivity and reversible capacity. However, existing technologies primarily rely on simple solid-phase ball milling, making it difficult to obtain highly alloyed materials and requiring further high-temperature sintering. The metal phase diagram indicates that at high temperatures, Si-P compounds vaporize above 429°C, forming a mixture of metal phosphide and silicon phosphide rather than a homogeneous, single-phase high-entropy metal phosphide. Therefore, the elemental composition of synthesized high-entropy metal phosphides requires further optimization. In addition, more importantly, as the application end gradually increases the requirements for battery energy density, the higher thermodynamic equilibrium potential of electrochemical lithiation of phosphorus-based negative electrodes (0.7 V vsLi + The problem of lithium-ion battery (Li) has not yet been solved, which is not conducive to achieving a high-energy-density full-battery system. Therefore, current technology still cannot meet the needs of alloy-based anode materials in practical applications. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material and its preparation method and application, so as to solve the problem of lack of high performance alloy-based negative electrode materials in the prior art.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: Provide a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material, including high entropy metal phosphide and conductive carbon material, the molecular formula of the high entropy metal phosphide is Cu a Ge b Sn c Zn d P x , among them, a+b+c+d≤x≤4 (a+b+c+d), a>0, b>0, c>0, d>0.

[0006] The beneficial effects of the present invention are: the present invention has a low electrochemical de- / intercalation thermodynamic equilibrium potential. The present invention changes the reaction path through the high entropy effect, which is beneficial to alleviate the volume expansion of the alloy-based negative electrode material during the lithium insertion process and improve the battery cycle stability. Thanks to the cocktail synergistic effect, the active elements Ge, Sn, Zn, and P in the material can provide high lithium insertion capacity, while the highly conductive element Cu is conducive to the rapid conduction of electrons, thereby improving the fast charging performance of the battery. The high entropy effect also reduces the discharge and charging platform of the alloy-based negative electrode material, which is beneficial to the realization of a high energy density full battery system.

[0007] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore, the molecular formula of the high entropy metal phosphide is CuGeSnZnP4.

[0008] Furthermore, the mass ratio of the high entropy metal phosphide to the conductive carbon material is 50-70:30-50.

[0009] The beneficial effects of adopting the above-mentioned further technical solution are: the combination of carbide material and red phosphorus improves conductivity and mitigates volume expansion. Phosphide has a high theoretical capacity, with carbon primarily serving as an electron conduction path. If the carbon ratio is too low, electronic conductivity may decrease. If the carbon ratio is too high, the phosphide ratio is relatively small, and good capacity characteristics may not be achieved.

[0010] Furthermore, the conductive carbon material is at least one of graphite, reduced graphene oxide, short multi-walled carbon nanotubes and Ketjen black.

[0011] The beneficial effects of adopting the above-mentioned further technical solution are as follows: Graphite has a well-developed pore structure and a large specific surface area. It can form point-to-point contact with the active material, helping to improve the compaction density of the electrode particles and significantly enhance ionic and electronic conductivity. Graphene has a two-dimensional, sheet-like structure that can form point-to-surface contact with the active material. This maximizes the effectiveness of the conductive agent, thereby reducing the amount of conductive agent used, thereby increasing the proportion of active material and improving the capacity of the lithium battery. Carbon nanotubes have a fibrous structure that can form point-to-line contact with the active material, forming a continuous conductive network within the active material of the electrode, acting as a "wire," helping to improve the battery's capacity, rate capability, cycle life, and reduce the battery's interfacial impedance. Ketjen black has a unique branched morphology. The advantage of this morphology is that the conductor has many conductive contact points, and the branches form a large number of conductive pathways, thus achieving extremely high conductivity with only a small amount of addition.

[0012] The present invention also provides a method for preparing the high entropy metal phosphide / carbon composite lithium ion battery negative electrode material, comprising the following steps: (1) Copper powder, germanium powder, tin powder, zinc powder and red phosphorus powder are mixed according to a molar ratio to obtain a mixed powder, and then solid phase ball milling is performed to prepare a high entropy metal phosphide precursor; (2) sintering the high entropy metal phosphide precursor obtained in step (1) and cooling it to room temperature to obtain a high entropy metal phosphide; (3) The high entropy metal phosphide prepared in step (2) and the conductive carbon material are mixed to obtain a mixture, and then solid-phase ball milling is performed to obtain a high entropy metal phosphide / carbon composite lithium-ion battery negative electrode material.

[0013] Furthermore, in step (1) and step (3), solid phase ball milling is performed under an argon atmosphere.

[0014] The beneficial effect of this further technical solution is that during the ball milling process, the impact, shear, and friction of the grinding balls continuously expose new active sites on the powder particle surface. These active sites are susceptible to oxidation reactions with oxygen in the air, thus affecting the properties and quality of the powder. The introduction of argon gas can expel the air from the ball mill, creating an oxygen-free environment, effectively isolating the oxygen and preventing oxidation of the powder.

[0015] Furthermore, in step (1), during solid phase ball milling, the mass ratio of ball milling beads to mixed powder is 20-30:1.

[0016] The beneficial effect of adopting the above-mentioned further technical solution is that when the ball-to-material ratio is optimal, the impact, grinding and shearing effects of the grinding body on the material reach a dynamic balance, which not only ensures sufficient impact kinetic energy to penetrate the material layer to achieve coarse crushing, but also completes fine grinding through the material friction between the grinding bodies, and the energy distribution efficiency is the highest.

[0017] Furthermore, in step (1), during solid phase ball milling, the mass ratio of the ball milling beads to the mixed powder is 20:1.

[0018] Furthermore, the diameter of the ball milling beads is 0.5-15 mm.

[0019] Furthermore, in step (1) and step (3), during solid-phase ball milling, the ball milling speed is 320-400 rpm / min, the single ball milling time is 30-60 min, the interval between two adjacent ball millings is 5-10 min, and the ball milling is repeated 16-20 times.

[0020] Furthermore, in step (1), during solid-phase ball milling, the ball milling speed is 400 rpm / min, the single ball milling time is 60 min, the interval between two adjacent ball millings is 10 min, and the ball milling is repeated 20 times.

[0021] Furthermore, in step (2), the sintering is performed at 450-550° C. for 2-5 hours.

[0022] The beneficial effect of adopting the above further technical solution is that the high entropy metal phosphide material requires sufficient sintering time due to its complex crystal structure.

[0023] Furthermore, in step (2), the sintering is performed at 525° C. for 5 h.

[0024] Furthermore, in step (2), the heating rate during sintering is 3-8°C / min.

[0025] Furthermore, in step (2), the heating rate during sintering is 5°C / min.

[0026] Furthermore, in step (3), during solid phase ball milling, the mass ratio of the ball milling beads to the mixed material is 20-30:1.

[0027] Furthermore, in step (3), during solid phase ball milling, the mass ratio of the ball milling beads to the mixed material is 20:1.

[0028] Furthermore, the diameter of the ball milling beads is 0.5-15 mm.

[0029] Furthermore, in step (3), during solid-phase ball milling, the ball milling speed is 400 rpm / min, the single ball milling time is 10 min, the interval between two adjacent ball millings is 10 min, and the ball milling is repeated 16 times.

[0030] The present invention also provides the use of the high entropy metal phosphide / carbon composite lithium ion battery negative electrode material in the preparation of lithium ion batteries.

[0031] Furthermore, the composition of the lithium-ion battery includes a positive electrode, a negative electrode, a separator and an electrolyte, the negative electrode includes a negative electrode collector and a negative electrode material coated on the negative electrode collector, and the negative electrode material is the above-mentioned high entropy metal phosphide / carbon composite lithium-ion battery negative electrode material.

[0032] The present invention has the following beneficial effects: Phosphorus-based alloy anode materials have high theoretical specific capacity and are considered ideal anode materials. Ge, Sn, and Zn have high theoretical specific capacity, while Cu has high electrical conductivity, which is conducive to the rapid transmission of electrons.

[0033] At the same time, according to the Hume–Rothery rule, regarding the difference in atomic radius and electronegativity, if ΔR<30%, Δ x Under the condition of P < 40%, it can crystallize in a single phase and share equiatomic sites. Common metals such as Fe, Mg and other elements have atomic radius and electronegativity that are quite different from P, while the electronegativity of Cu (1.90), Ge (2.01), Sn (1.96), Zn (1.65) and atomic radius of Cu (1.28 Å), Ge (1.22 Å), Sn (1.58 Å), Zn (1.39Å) are similar to P (see Figure 1 ), therefore, it is easier to form a single-phase solid solution.

[0034] In addition, in order to obtain highly alloyed high entropy negative electrode materials, the present invention further adopts high temperature sintering treatment. According to the binary metal phase diagram (see Figure 2 ), at a given ratio and set sintering temperature, taking Sn as an example, metal phosphide solid solution can be formed.

[0035] However, according to the phase diagram (see Figure 3 ) shows that Si-P compounds vaporize above 429°C, which is lower than the given sintering temperature. Therefore, if silicon is used, a mixture of metal phosphide and silicon phosphide is likely to form, rather than a uniform, single-phase high-entropy metal phosphide. Therefore, the Cu-Ge-Sn-Zn-P high-entropy phosphide material was chosen for synthesis.

[0036] Due to the unique cocktail synergistic effect and entropy stabilization effect of the high entropy system, the negative electrode material of the present invention significantly improves the capacity, rate performance and cycle stability of the battery. According to formula (1), the configuration entropy of RP, CuP, CuGeP and CuGeSnZnP was calculated (see Figure 4 ), CuGeSnZnP material has the highest initial disorder of the system.

[0037] (1) Where S is the material configuration entropy, c i are the concentrations of different components.

[0038] In addition, the high configurational entropy of the negative electrode material reduces the entropy change coefficient proportional to ΔS in the electrochemical lithiation process (see Figure 5 According to formula (3) derived from formula (2), therefore, the discharge equilibrium potential of the alloy-based negative electrode material is reduced, which is beneficial to realize a high-energy-density full-cell system.

[0039] ΔH-TΔS = ΔG = -zFE (2) (3) The negative electrode material of the present application has a high specific capacity and excellent rate performance and cycle stability. In addition, the reduced potential platform is beneficial to realize a high-energy-density battery system.

[0040] 1. The preparation method of the present application is simple, low in cost and easy to mass-produce and synthesize.

[0041] 2. The present application uses abundant and low-cost Zn, Cu, Sn, P and other elements to replace expensive transition metal elements (Co, Mn, Ni, etc.), Sn, Ge, P and other elements have lithium intercalation activity, and high-conductivity element Cu is beneficial to the rapid conduction of electrons, which not only obtains excellent electrochemical performance, but also greatly reduces the material cost, which is beneficial to mass production and application.

[0042] 3. The present application uses high-energy ball milling combined with tube furnace high-temperature sintering to prepare high-entropy metal phosphide / carbon composite lithium ion battery negative electrode material Cu a Ge b Sn c Zn d P x / C, which has high yield, high product purity, is easy to mass-produce and apply. The high conductivity and high flexibility of carbon promote the electron transport process in the electrochemical process, and at the same time, the volume expansion of the alloy-type negative electrode is relieved, which greatly improves the fast-charging performance and cycle stability of the battery.

[0043] 4. The high-entropy metal phosphide / carbon composite lithium ion battery negative electrode material of the present application has a high reversible capacity and excellent reversibility, which can release a specific capacity of 2064.6 mAh g -1 and a high first-cycle coulombic efficiency of 83.3% (see Figure 10 ), which has a high application prospect.

[0044] 5. The high-entropy metal phosphide Cu a Ge b Sn c Zn d P xThe "cocktail effect" realizes high electronic conductivity and high capacity, and the "high entropy effect" improves the confusion degree of the system and reduces the potential platform of the negative electrode material, which is beneficial to realize high energy density battery system.

[0045] 6、The high-entropy metal phosphide Cu a Ge b Sn c Zn d P x The element composition and proportion can be adjusted, which is beneficial to wide practical application. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 It is an atomic radius and electronegativity data graph of different elements; Figure 2 It is a tin-phosphorus binary phase diagram; Figure 3 It is a silicon-phosphorus binary phase diagram; Figure 4 It is a configuration entropy data graph of RP, CuP, CuGeP and CuGeSnZnP; Figure 5 It is an entropy coefficient data graph of RP, CuP, CuGeP and CuGeSnZnP; Figure 6 It is an XRD data graph of the phosphorus materials of Example 1 and Comparative Examples 1-5; Figure 7 It is an XRD data graph of the high-entropy metal phosphides of Examples 1-3; Figure 8 It is a mapping data graph of the high-entropy metal phosphide of Example 1; Figure 9 It is an SEM spectrum of the negative electrode materials of Example 1 and Comparative Example 1 before and after 300 cycles; Figure 10 It is a first cycle charge-discharge curve graph of Example 1 and Comparative Examples 1 and 6; Figure 11 It is a cyclic voltammetry curve graph of Example 1 and Comparative Example 1; Figure 12 It is a cycle performance graph of the negative electrode material lithium ion battery of Examples 1-3 at a current density of 1300 mA / g; Figure 13 It is a variable scan rate cyclic voltammetry test data graph of the negative electrode material lithium ion battery of Example 1 and Comparative Example 1; Figure 14 It is a rate performance graph of the negative electrode material lithium ion battery of Example 1 and Comparative Examples 1, 2 and 5; Figure 15 It is an average voltage graph of the negative electrode material lithium ion battery of Example 1 and Comparative Examples 1, 2 and 5; Figure 16 The cycle performance diagram of the full battery assembled with the negative electrode materials of Example 1 and Comparative Example 1 and LiCoO2; Figure 17 The rate performance of the full battery assembled with the negative electrode materials of Examples 1-3 and Comparative Example 1 and LiCoO2. DETAILED DESCRIPTION

[0047] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0048] Example 1: A high-entropy metal phosphide / carbon composite lithium-ion battery negative electrode material comprises a high-entropy metal phosphide and a conductive carbon material (mass ratio is 7:3), the molecular formula of the high-entropy metal phosphide is CuGeSnZnP4, and the conductive carbon material is Ketjen black.

[0049] A method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material comprises the following steps: (1) According to the molar ratio, 317.75 mg of copper powder, 363.2 mg of germanium powder, 593.5 mg of tin powder, 327 mg of zinc powder and 619.4 mg of red phosphorus powder were weighed and mixed to obtain a mixed powder. The mixed powder was added to a zirconia ball mill in an argon atmosphere glove box (anhydrous and oxygen-free, with water and oxygen contents of <0.1 ppm) and packaged. The ball mill was taken out of the glove box and fixed on a ball mill. Then, solid-phase ball milling was performed. The mass ratio of zirconia balls to mixed powder was 20:1. The diameter of the zirconia balls was 10 mm. The ball mill speed was set to 400 rpm / min. The single ball milling time was 60 min. The interval between two adjacent ball millings was 10 min. The ball milling was repeated 20 times to obtain a high-entropy metal phosphide precursor. (2) The high entropy metal phosphide precursor prepared in step (1) is sealed in a quartz tube using a vacuum tube sealer, and sintered at high temperature in a tube furnace at a heating rate of 5°C / min to 525°C, kept at this temperature for 5 hours, and naturally cooled to room temperature to obtain a high entropy metal phosphide; (3) The high entropy metal phosphide prepared in step (2) and the conductive carbon material (Ketjen black) were mixed (mass ratio of 7:3) to obtain a mixture. The mixture was added to a zirconia ball mill in an argon atmosphere glove box (anhydrous and oxygen-free, with water and oxygen contents of <0.1 ppm), and then solid-phase ball milling was performed. The mass ratio of zirconia balls to the mixture was 20:1, the diameter of the zirconia balls was 10 mm, the ball mill speed was set to 400 rpm / min, the single ball milling time was 60 min, the interval between two adjacent ball millings was 10 min, and the process was repeated 16 times to obtain a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material (CuGeSnZnP4 / C).

[0050] Example 2: A high-entropy metal phosphide / carbon composite lithium-ion battery negative electrode material, the molecular formula of the high-entropy metal phosphide is CuGeSnZnP5, and the rest is the same as in Example 1.

[0051] A method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material comprises the following steps: In step (1), 774.25 mg of red phosphorus powder was used to prepare a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material (CuGeSnZnP5 / C), and the rest was the same as in Example 1.

[0052] Example 3: A high-entropy metal phosphide / carbon composite lithium-ion battery negative electrode material, the molecular formula of the high-entropy metal phosphide is CuGeSnZnP6, and the rest is the same as in Example 1.

[0053] A method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material comprises the following steps: In step (1), 929.1 mg of red phosphorus powder was used to prepare a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material (CuGeSnZnP6 / C), and the rest was the same as in Example 1.

[0054] Example 4: A high-entropy metal phosphide / carbon composite lithium-ion battery negative electrode material, the molecular formula of the high-entropy metal phosphide is CuGeSnZnP2, and the rest is the same as in Example 1.

[0055] A method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material comprises the following steps: In step (1), 309.7 mg of red phosphorus powder was used to prepare a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material (CuGeSnZnP2 / C), and the rest was the same as in Example 1.

[0056] Example 5: A high-entropy metal phosphide / carbon composite lithium-ion battery negative electrode material, the same as Example 1.

[0057] A method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material comprises the following steps: In step (1), the process was repeated 16 times to obtain a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material (CuGeSnZnP4 / C-1), and the rest was the same as in Example 1.

[0058] Example 6: A high-entropy metal phosphide / carbon composite lithium-ion battery negative electrode material, the same as Example 1.

[0059] A method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material comprises the following steps: In step (3), the process was repeated 20 times to obtain a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material (CuGeSnZnP4 / C-2), and the rest was the same as in Example 1.

[0060] Example 7: A high-entropy metal phosphide / carbon composite lithium-ion battery negative electrode material comprises a high-entropy metal phosphide and a conductive carbon material (mass ratio is 5:5), the molecular formula of the high-entropy metal phosphide is CuGeSnZnP4, and the conductive carbon material is graphite.

[0061] A method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material comprises the following steps: (1) According to the molar ratio, 317.75 mg of copper powder, 363.2 mg of germanium powder, 593.5 mg of tin powder, 327 mg of zinc powder and 619.4 mg of red phosphorus powder were weighed and mixed to obtain a mixed powder. The mixed powder was added to a zirconia ball mill in an argon atmosphere glove box (anhydrous and oxygen-free, with water and oxygen contents of <0.1 ppm) and packaged. The ball mill was taken out of the glove box and fixed on a ball mill. Then, solid-phase ball milling was performed. The mass ratio of zirconia balls to mixed powder was 25:1. The diameter of the zirconia balls was 0.5 mm. The ball mill speed was set to 320 rpm / min. The single ball milling time was 30 min. The interval between two adjacent ball millings was 5 min. The ball milling was repeated 16 times to obtain a high-entropy metal phosphide precursor. (2) The high entropy metal phosphide precursor prepared in step (1) is sealed in a quartz tube using a vacuum tube sealing machine, and sintered at high temperature in a tube furnace at a heating rate of 3°C / min to 450°C, kept at this temperature for 5 hours, and naturally cooled to room temperature to obtain a high entropy metal phosphide; (3) The high entropy metal phosphide prepared in step (2) and the conductive carbon material (graphite) were mixed (mass ratio of 5:5) to obtain a mixture. The mixture was added to a zirconia ball mill in an argon atmosphere glove box (anhydrous and oxygen-free, with water and oxygen contents of <0.1 ppm), and then solid-phase ball milling was performed. The mass ratio of zirconia balls to the mixture was 25:1, the diameter of the zirconia balls was 0.5 mm, the ball mill speed was set to 320 rpm / min, the single ball milling time was 30 min, the interval between two adjacent ball millings was 5 min, and the process was repeated 20 times to obtain a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material (CuGeSnZnP4 / C-3).

[0062] Example 8: A high-entropy metal phosphide / carbon composite lithium-ion battery negative electrode material comprises a high-entropy metal phosphide and a conductive carbon material (mass ratio is 6:4), the molecular formula of the high-entropy metal phosphide is CuGeSnZnP4, and the conductive carbon material is reduced graphene oxide.

[0063] A method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material comprises the following steps: (1) According to the molar ratio, 317.75 mg of copper powder, 363.2 mg of germanium powder, 593.5 mg of tin powder, 327 mg of zinc powder and 619.4 mg of red phosphorus powder were weighed and mixed to obtain a mixed powder. The mixed powder was added to a zirconia ball mill in an argon atmosphere glove box (anhydrous and oxygen-free, with water and oxygen contents of <0.1 ppm) and packaged. The ball mill was taken out of the glove box and fixed on a ball mill. Then, solid-phase ball milling was performed. The mass ratio of zirconia balls to mixed powder was 30:1. The diameter of the zirconia balls was 15 mm. The ball mill speed was set to 350 rpm / min. The single ball milling time was 40 min. The interval between two adjacent ball millings was 8 min. The ball milling was repeated 18 times to obtain a high-entropy metal phosphide precursor. (2) The high entropy metal phosphide precursor prepared in step (1) is sealed in a quartz tube using a vacuum tube sealer, and sintered at high temperature in a tube furnace at a heating rate of 8°C / min to 550°C, kept at this temperature for 2 hours, and naturally cooled to room temperature to obtain a high entropy metal phosphide; (3) The high entropy metal phosphide prepared in step (2) and the conductive carbon material (reduced graphene oxide) were mixed (mass ratio of 6:4) to obtain a mixture. The mixture was added to a zirconia ball mill in an argon atmosphere glove box (anhydrous and oxygen-free, with water and oxygen contents of <0.1 ppm), and then solid-phase ball milling was performed. The mass ratio of zirconia balls to the mixture was 30:1, the diameter of the zirconia balls was 15 mm, the ball mill speed was set to 350 rpm / min, the single ball milling time was 40 min, the interval between two adjacent ball millings was 8 min, and the process was repeated 18 times to obtain a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material (CuGeSnZnP4 / C-4).

[0064] Comparative Example 1: A phosphorus / carbon composite negative electrode material, the preparation method of which comprises the following steps: The high entropy metal phosphide in step (3) was replaced by red phosphorus (Aladdin, 99.999%), and the rest was the same as in Example 1 to prepare a phosphorus / carbon composite negative electrode material (RP / C).

[0065] Comparative Example 2: A metal phosphide / carbon composite negative electrode material, the preparation method of which comprises the following steps: In step (1), the raw material powders are: 1271 mg of copper powder and 309.7 mg of red phosphorus, and the rest are the same as in Example 1, to obtain a metal phosphide / carbon composite material CuP / C.

[0066] Comparative Example 3: A metal phosphide / carbon composite negative electrode material, the preparation method of which comprises the following steps: In step (1), the raw material powders are: 1452.8 mg of germanium powder and 309.7 mg of red phosphorus, and the rest are the same as in Example 1, to obtain a metal phosphide / carbon composite material GeP / C.

[0067] Comparative Example 4: A metal phosphide / carbon composite negative electrode material, the preparation method of which comprises the following steps: In step (1), the raw material powders are: 2374 mg of tin powder and 309.7 mg of red phosphorus, and the rest are the same as in Example 1, to obtain a metal phosphide / carbon composite material SnP / C.

[0068] Comparative Example 5: A metal phosphide / carbon composite negative electrode material, the preparation method of which comprises the following steps: In step (1), the raw material powders are: 635.5 mg of copper powder, 726.4 mg of germanium powder and 309.7 mg of red phosphorus, and the rest are the same as in Example 1, to obtain a metal phosphide / carbon composite material CuGeP / C.

[0069] Comparative Example 6: A metal phosphide / carbon composite negative electrode material, the preparation method of which comprises the following steps: The metal phosphide / carbon composite material CuGeSiZnP4 / C was prepared by replacing 93.5 mg of tin powder in step (1) with 140.43 mg of silicon powder, with the rest being the same as in Example 1.

[0070] Test example 1. Phase composition 1. X-ray diffraction tests were performed on the high entropy metal phosphide prepared in Example 1, the metal phosphide prepared in Comparative Example 1, and the metal phosphides prepared in Comparative Examples 2-5. The results are shown in FIG. Figure 6 .

[0071] 2. The high entropy metal phosphides prepared in Examples 1-3 were subjected to X-ray diffraction tests. The results are shown in Table 2. Figure 7 .

[0072] Depend on Figure 6-7 The XRD patterns of the high-entropy alloy materials of Examples 1-3 exhibit new diffraction peak morphologies relative to the elemental patterns of the comparative examples, indicating that the interaction between the elements has generated a new structure. Comparison and analysis with standard PDF cards show that the phases of the high-entropy metal phosphides of Examples 1-3 are all F-43m phases.

[0073] 3. The high entropy metal phosphide prepared in Example 1 was characterized by energy spectrum using a scanning electron microscope. The results are shown in Figure 8 .

[0074] Depend on Figure 8 It can be seen that the Cu, Ge, Sn, Zn, and P elements are evenly distributed on the nanoscale without aggregation or separation, indicating that high-entropy metal phosphide is completely formed in Example 1.

[0075] 2. Electrochemical Performance Characterization (1) Half-cell electrochemical performance test In order to verify the effect of the lithium-ion battery prepared by the high-entropy metal phosphide / carbon composite lithium-ion battery negative electrode material of the present invention, the lithium-ion button half-cells prepared by the battery negative electrode materials of Examples 1-6 and Comparative Examples 1-6 were respectively subjected to battery performance tests, specifically using Xinwei and Blue Electric battery testing equipment.

[0076] Battery assembly: The battery negative electrode material, Super P, and sodium alginate were mixed evenly in a mass ratio of 7:2:1 and coated on copper foil. Button cells were assembled in an argon atmosphere glove box. The counter electrode was a lithium sheet, the separator was made of PP, and the electrolyte was a 1 mol / L LiPF6EC / DEC with 5% FEC solution.

[0077] The lithium-ion battery parameters of Examples 1-6 and Comparative Examples 1-6 are shown in Table 1.

[0078] Table 1 Lithium-ion battery parameters

[0079] 1. The specific method of cycle performance test is as follows: At room temperature, the lithium-ion batteries obtained in each embodiment and comparative example were discharged at a constant current rate of 0.1C to a voltage of 0.01V, then allowed to stand for 1 minute, and then charged at a constant current rate of 0.1C to a voltage of 3.0V, and then allowed to stand for 1 minute. This constituted one cycle of charge and discharge, and five cycles were performed. The lithium-ion batteries were then discharged at a constant current rate of 0.5C to 0.01V, then allowed to stand for 1 minute, and then charged at a constant current rate of 0.5C to 3.0V, and then allowed to stand for 1 minute, and this cycle was repeated n times.

[0080] The capacity retention rate (%) of a lithium-ion battery after n cycles = the charging capacity of the lithium-ion battery in the nth cycle / the charging capacity of the lithium-ion battery in the first cycle × 100%.

[0081] See the results Figure 9-13 .

[0082] The negative electrode materials prepared in Example 1 and Comparative Example 1 were assembled into button-type half-cells and subjected to 300 complete charge and discharge cycles, followed by SEM characterization. The results are as follows: Figure 9 (The left side is before the loop, the right side is after the loop).

[0083] Depend on Figure 9 It can be seen that the volume expansion rate of the sample in Example 1 is only 24.5%, and the volume expansion during the cycle is significantly suppressed, which is significantly lower than 145.6% of Comparative Example 1.

[0084] Depend on Figure 10 It can be seen that due to the high entropy effect, the lithium insertion discharge platform of Example 1 is significantly lower than those of Comparative Examples 1 and 6, and the discharge platform of Comparative Example 6 does not show a significant decrease.

[0085] Depend on Figure 11 It can be seen that Example 1 has a lower lithium insertion peak (≈0.3 V).

[0086] Depend on Figure 12 It can be seen that the negative electrode material of the present invention has excellent capacity and cycle stability. Example 1 with the highest configurational entropy is the best, and it still exhibits a capacity of 1431.2 mAh / g and a retention rate of 81.5% after 300 cycles.

[0087] Depend on Figure 13 It can be seen that compared with Comparative Example 1, Example 1 has a higher lithium ion diffusion coefficient.

[0088] 2. The specific method of rate performance test is as follows: At room temperature, the lithium ion batteries obtained in each embodiment and comparative example were discharged to 0.01V at a constant current of 130 mA / g, then allowed to stand for 1 min, and charged to 3.0V at a constant current of 130 mA / g, and then allowed to stand for 1 min, and this was repeated for 5 cycles; discharged to 0.01V at a constant current of 260 mA / g, then allowed to stand for 1 min, and charged to 3.0V at a constant current of 260 mA / g, and then allowed to stand for 1 min, and this was repeated for 5 cycles; discharged to 0.01V at a constant current of 520 mA / g, then allowed to stand for 1 min, and charged to 3.0V at a constant current of 520 mA / g, and then allowed to stand for 1 min, and this was repeated for 5 cycles; discharged to 0.01V at a constant current of 1300 mA / g, then allowed to stand for 1 min, and charged to 3.0V at a constant current of 1300 mA / g, and then allowed to stand for 1 min, and this was repeated for 5 cycles; discharged to 0.01V at a constant current of 2600 mA / g, then allowed to stand for 1 min, and charged to 3.0V at a constant current of 2600 mA / g, and then allowed to stand for 1 min, and this was repeated for 5 cycles; mA / g constant current discharge to 0.01V, then let it stand for 1 min, charge to 3.0V at 2600 mA / g constant current, then let it stand for 1 min, and do 5 cycles; discharge to 0.01V at 3900 mA / g constant current, then let it stand for 1 min, charge to 3.0V at 3900 mA / g constant current, then let it stand for 1 min, and do 5 cycles; discharge to 0.01V at 5200 mA / g constant current, then let it stand for 1 min, charge to 3.0V at 5200 mA / g constant current, then let it stand for 1 min, and do 5 cycles; discharge to 0.01V at 7800 mA / g constant current, then let it stand for 1 min, charge to 3.0V at 7800 mA / g constant current, then let it stand for 1 min, and do 5 cycles; discharge to 0.01V at 10400 mA / g constant current, then let it stand for 1 min, and mA / g constant current charge to 3.0V, then let it stand for 1min, and do this for 5 cycles; discharge at 13000 mA / g constant current to 0.01V, then let it stand for 1min, charge at 13000 mA / g constant current to 3.0V, then let it stand for 1min, and do this for 5 cycles; discharge at 520 mA / g constant current to 0.01V, then let it stand for 1min, charge at 520 mA / g constant current to 3.0V, then let it stand for 1min, and do this for 10 cycles Capacity retention rate = charging capacity of the last cycle / charging capacity of the first cycle × 100%.

[0089] The rate performance test results are shown in Table 2 and Figure 14-15 .

[0090] Table 2 Rate performance test results

[0091] It can be seen from Table 2 that with the increase of the configurational entropy of high-entropy metal phosphides, the rate performance of lithium-ion batteries is improved to varying degrees.

[0092] Depend on Figure 14 It can be seen that with the increase of the configuration entropy of the negative electrode material, the lithium-ion battery exhibits better rate performance.

[0093] Depend on Figure 15 It can be seen that as the configuration entropy of the negative electrode material increases, the average discharge voltage becomes lower.

[0094] (2) Full battery electrochemical performance test Battery assembly: The negative electrode materials of each embodiment and comparative example were assembled with LiCO2 positive electrode to obtain a lithium ion battery.

[0095] 1. Cycle performance test The specific method is as follows: At room temperature, the lithium ion battery obtained by assembling each embodiment and comparative example as the negative electrode material with the LiCO2 positive electrode was charged at a constant current rate of 0.1C to a voltage of 4.2V, then allowed to stand for 1 minute, and discharged at a constant current rate of 0.1C to a voltage of 1.2V, and then allowed to stand for 1 minute. This was a cycle of charge and discharge, and 5 cycles were performed. The lithium ion battery was then charged at a constant current of 0.5C to 4.2V, then allowed to stand for 1 minute, and discharged at a constant current of 0.5C to 1.2V, and then allowed to stand for 1 minute, and the cycle was repeated n times.

[0096] The capacity retention rate (%) of a lithium-ion battery after n cycles = the discharge capacity of the lithium-ion battery in the nth cycle / the discharge capacity of the lithium-ion battery in the first cycle × 100%.

[0097] See the results Figure 16 .

[0098] Depend on Figure 16 It can be seen that the lithium-ion battery obtained by assembling Example 1 as the negative electrode material with the LiCO2 positive electrode exhibits better cycle stability.

[0099] 2. Rate performance test The specific method is as follows: At room temperature, the lithium ion battery obtained by assembling each embodiment and comparative example as the negative electrode material with the LiCoO2 positive electrode was charged at a constant current of 20 mA / g to a voltage of 4.2V, then allowed to stand for 1 min, and discharged at a constant current of 20 mA / g to a voltage of 1.2V, and then allowed to stand for 1 min. This was a cyclic charge and discharge process, and 5 cycles were performed; the voltage was charged at a constant current of 40 mA / g to a voltage of 4.2V, then allowed to stand for 1 min, and discharged at a constant current of 40 mA / g to a voltage of 1.2V, and then allowed to stand for 1 min. This was a cyclic charge and discharge process, and 5 cycles were performed; the voltage was charged at a constant current of 80 mA / g to a voltage of 4.2V, then allowed to stand for 1 min, and discharged at a constant current of 80 mA / g to a voltage of 1.2V, and then allowed to stand for 1 min. This was a cyclic charge and discharge process, and 5 cycles were performed; the voltage was charged at a constant current of 100 mA / g to a voltage of 4.2V, then allowed to stand for 1 min, and discharged at a constant current of 100 mA / g to a voltage of mA / g constant current discharge to the voltage of 1.2V, then let it stand for 1min, this is a cyclic charge and discharge process, and this is done for 5 cycles; charge at a constant current of 200 mA / g to a voltage of 4.2V, then let it stand for 1min, discharge at a constant current of 200 mA / g to a voltage of 1.2V, and then let it stand for 1min, this is a cyclic charge and discharge process, and this is done for 5 cycles; charge at a constant current of 300 mA / g to a voltage of 4.2V, then let it stand for 1min, discharge at a constant current of 300 mA / g to a voltage of 1.2V, and then let it stand for 1min, this is a cyclic charge and discharge process, and this is done for 5 cycles; charge at a constant current of 40 mA / g to a voltage of 4.2V, then let it stand for 1min, discharge at a constant current of 40 mA / g to a voltage of 1.2V, and then let it stand for 1min, this is a cyclic charge and discharge process, and this is done for 10 cycles Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle × 100%.

[0100] See the results Figure 17 .Depend on Figure 17 It can be seen that with the increase of the configuration entropy of the negative electrode material, the lithium-ion battery exhibits higher capacity and better fast charging performance.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high entropy metal phosphide / carbon composite lithium ion battery negative electrode material, characterized in that: It includes high entropy metal phosphide and conductive carbon material, wherein the molecular formula of the high entropy metal phosphide is Cu a Ge b Sn c Zn d P x , among them, a+b+c+d≤x≤4 (a+b+c+d), a>0, b>0, c>0, d>0.

2. The high entropy metal phosphide / carbon composite lithium ion battery negative electrode material according to claim 1, characterized in that The mass ratio of the high entropy metal phosphide to the conductive carbon material is 50-70:30-50.

3. The high entropy metal phosphide / carbon composite lithium ion battery negative electrode material according to claim 1, characterized in that The conductive carbon material is at least one of graphite, reduced graphene oxide, short multi-walled carbon nanotubes and Ketjen black.

4. The method for preparing the high entropy metal phosphide / carbon composite lithium ion battery negative electrode material according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Copper powder, germanium powder, tin powder, zinc powder and red phosphorus powder are mixed according to a molar ratio to obtain a mixed powder, and then solid phase ball milling is performed to prepare a high entropy metal phosphide precursor; (2) sintering the high entropy metal phosphide precursor obtained in step (1) and cooling it to room temperature to obtain a high entropy metal phosphide; (3) The high entropy metal phosphide prepared in step (2) and the conductive carbon material are mixed to obtain a mixture, and then solid-phase ball milling is performed to obtain a high entropy metal phosphide / carbon composite lithium-ion battery negative electrode material.

5. The method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material according to claim 4, characterized in that: In both step (1) and step (3), solid phase ball milling is performed under an argon atmosphere.

6. The method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material according to claim 4, characterized in that: In step (1), during solid phase ball milling, the mass ratio of ball milling beads to mixed powder is 20-30:

1.

7. The method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material according to claim 4, characterized in that: In step (1) and step (3), during solid phase ball milling, the ball milling speed is 320-400 rpm / min, the single ball milling time is 30-60 min, the interval between two adjacent ball millings is 5-10 min, and the ball milling is repeated 16-20 times.

8. The method for preparing a high entropy metal phosphide / carbon composite lithium ion battery negative electrode material according to claim 4, characterized in that: In step (2), sintering is performed at 450-550°C for 2-5 hours.

9. Use of the high entropy metal phosphide / carbon composite lithium ion battery negative electrode material according to any one of claims 1 to 3 in the preparation of lithium ion batteries.

10. Use of the high entropy metal phosphide / carbon composite lithium ion battery negative electrode material according to claim 9 in the preparation of lithium ion batteries, characterized in that: The lithium-ion battery comprises a positive electrode, a negative electrode, a separator and an electrolyte, the negative electrode comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, and the negative electrode material is the high entropy metal phosphide / carbon composite lithium-ion battery negative electrode material according to any one of claims 1 to 3.

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