Lithium battery positive electrode material based on high-entropy oxide, preparation method of lithium battery positive electrode material and lithium battery

Abstract

The invention relates to the field of lithium batteries, in particular to a lithium battery positive electrode material based on a high-entropy oxide, a preparation method of the lithium battery positive electrode material and a lithium battery. In the lithium battery positive electrode material provided by the invention, Fe and Ni elements can construct abundant active sites and provide rapid electron transfer, so that the high-entropy effect can be improved, and a stable single-phase solid solution structure can be formed; the Co element can generate a slow diffusion effect, different atoms are mutually hindered, diffusion of surface atoms is inhibited, the trend of generating small HEOs particles in the HEOs forming process is caused, and therefore the specific surface area and the active surface area are increased; the Cu element can better improve the conductivity; the Mg element can be used as a structure stabilizer, stabilizes a single-phase solid solution through size matching and an entropy increasing effect, and optimizes electrochemical, catalytic and corrosion-resistant properties at the same time; the CC is subjected to acid treatment, so that the formation of nanocrystallized HEO is effectively induced, and the contact area of the electrolyte is increased; and meanwhile, through high-temperature air annealing, lithium ion de-intercalation active sites are provided.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a lithium battery positive electrode material based on high entropy oxide, a preparation method thereof, and a lithium battery. Background Art

[0002] Lithium-ion batteries are widely used in new energy electric vehicles and energy storage fields due to their advantages such as good cycle stability, high energy density, and stable electrochemical platform. Lithium batteries are mainly composed of positive electrodes, negative electrodes, electrolytes, and separators. With the rapid growth in demand for lithium batteries, the challenges they face are becoming increasingly prominent. Resource limitations: The reserves of key metal resources such as cobalt, nickel, and lithium in positive electrode materials are limited and unevenly distributed, resulting in high raw material costs and unstable supply. Performance bottleneck: Existing positive electrode materials still have room for improvement in energy density, rate performance, and cycle stability, and it is difficult to meet higher performance requirements. To meet these challenges, efforts have been made to develop new positive electrode materials and improve preparation processes, such as high entropy alloy (HEOs) positive electrode materials and lithium-rich manganese-based materials, in order to improve battery performance and reduce costs.

[0003] Cathode materials are key components that determine the energy density, cycle life, and safety of lithium batteries. Currently, commonly used cathode materials such as lithium cobalt oxide, lithium iron phosphate, and ternary materials have drawbacks such as low capacity, high cost, and poor thermal stability. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies in the prior art and to provide a lithium battery positive electrode material based on high entropy oxide, a preparation method thereof, and a lithium battery.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention is to provide a method for preparing a lithium battery positive electrode material based on high entropy oxide, the steps comprising:

[0007] S1, pre-treating the carbon cloth and then cutting it to obtain a substrate;

[0008] S2. Weigh C4H6CoO4·4H2O, C4H7FeO5·nH2O, Ni(CH3COO)2·4H2O, C4H6CuO4, Mg(CH3COO)2 and 2,5-dihydroxyterephthalic acid, dissolve them in a mixed solvent, and mix them by ultrasonication to obtain a mixture;

[0009] S3, placing the substrate and the mixture in an autoclave for reaction, and then washing and drying the reactants to obtain a high entropy compound FeCoNiCuMg MOFs / CC;

[0010] S4. The high entropy compound FeCoNiCuMg MOFs / CC is placed in a tube furnace for pre-calcination, calcination and annealing to obtain the lithium battery positive electrode material FeCoNiCuMg HEO / CC.

[0011] Preferably, in step S1, the pretreatment comprises: placing the carbon in an oil bath containing H2SO4 at 80°C for 2 hours, and then transferring the carbon to an oil bath containing H2O2 at 80°C for 2 hours.

[0012] Preferably, in step S2, the mixed solvent includes: N,N-dimethylformamide, anhydrous ethanol and deionized water.

[0013] More preferably, in the mixed solution, the volume ratio of N,N-dimethylformamide, anhydrous ethanol and deionized water is (18-22):(1-2):1.

[0014] Preferably, in step S2, the mass ratio of C4H6CoO4·4H2O, C4H7FeO5·nH2O, Ni(CH3COO)2·4H2O, C4H6CuO4, Mg(CH3COO)2 and 2,5-dihydroxyterephthalic acid is (1-2):1:(1-2):(0.8-1):(1-2):(2-4).

[0015] Preferably, in step S3, the reaction conditions are 110-130° C. for 12-24 hours.

[0016] Preferably, in step S4, the pre-calcination treatment comprises: calcining at 300-400° C. for 0.5-1 h.

[0017] Preferably, in step S4, the calcination treatment comprises: heating to 500-600° C. at a heating rate of 3-6° C. / min and then calcining for 2 hours.

[0018] The second aspect of the present invention is to provide a lithium battery positive electrode material based on high entropy oxide, which is prepared using the above-mentioned preparation method.

[0019] A third aspect of the present invention is to provide a lithium battery, comprising: a positive electrode sheet and a negative electrode sheet;

[0020] Among them, the positive electrode sheet adopts the lithium battery positive electrode material prepared by the above preparation method.

[0021] The present invention adopts the above technical solution, which has the following technical effects compared with the prior art:

[0022] (1) In the lithium battery positive electrode material of the present invention, Fe and Ni elements can construct abundant active sites, provide rapid electron transfer, provide good stability and activity, help to improve the high entropy effect, increase the mixed configuration entropy, and facilitate the formation of a stable single-phase solid solution structure, thereby improving stability; Co element can produce a slow diffusion effect, allowing different atoms to hinder each other, inhibiting the diffusion of surface atoms, resulting in a trend of producing small HEOs particles during the HEOs formation process, thereby increasing the specific surface area and the active surface area; Cu element can better improve the electrical conductivity; Mg element can act as a structural stabilizer, stabilizing the single-phase solid solution through size matching and entropy increase effect, while optimizing the electrochemical, catalytic and corrosion resistance properties.

[0023] (2) The non-precious metal elements used in the lithium battery positive electrode material of the present invention are cheap and widely available, which can effectively reduce production costs and significantly improve production efficiency.

[0024] (3) Carbon paper (CC) itself has good conductivity, and the addition of HEO further improves the overall conductivity, which helps to improve the charge and discharge efficiency of the battery; the porous structure of carbon paper provides a larger specific surface area, increases the loading amount of active materials, and improves the energy density of the battery; carbon paper has good flexibility and mechanical strength, can withstand volume changes during charge and discharge, reduce the shedding of electrode materials, and extend battery life.

[0025] (4) The multi-element synergistic effect of HEO enhances the structural stability and electrochemical performance of the material, improves the cycle stability and rate performance of the battery; the multi-element combination of HEO provides abundant redox reaction sites, enhances the electrochemical activity of the electrode material, and improves the specific capacity and energy density of the battery. 2+ / Fe 3+ 、Co 2 + / Co 3+ ) may provide a richer electron transfer path. The solid solution structure of HEO can inhibit the volume expansion and phase separation during the charge and discharge process, reduce the collapse of the electrode structure, and improve the cycle stability. The metal properties of HEO (especially the introduction of Cu and Ni) can significantly improve the electronic conductivity, reduce the internal resistance of the electrode, and improve the rate performance. In HEO, Fe 2+ / Fe 3+ 、Co 2+ / Co 3+ 、Ni 2+ / Ni 3 + :These variable valence metal ions are transferred by reversible electrons (such as ) participate in charge compensation and directly store / release lithium ions Lithium intercalation and deintercalation can be achieved in the range of 3.0-4.5V vs.Li+ / Li, forming a sufficient voltage difference with the negative electrode.

[0026] (5) Acid treatment of CC provides an excellent nucleation site for metal ions. The CC surface forms a strong interaction with HEO through chemical bonds (such as MOC, where M is HEO metal). Acid treatment can effectively remove organic pollutants, metal impurities or oxides on the CC surface, avoiding their interference with high-entropy alloy loading or subsequent reactions. At the same time, oxygen-containing functional groups (such as carboxyl-COOH, hydroxyl-OH, carbonyl-C=O, etc.) are introduced on the carbon cloth surface. The functional groups enhance the wettability of the carbon cloth, promote the penetration of the electrolyte or reactants, effectively induce the formation of nano-HEO, increase the electrolyte contact area, and shorten the Li + Diffusion path; at the same time, high temperature air annealing is used to form (FeCoNiCuMg) on ​​the HEO surface x O γ The oxide layer provides active sites for lithium ion deintercalation and insertion; the Fe / Co / Ni redox reaction may provide a discharge platform of 2.5-4.0V; the synergistic effect of CC substrate and HEO can improve the cycle performance; the coexistence of multiple metals broadens the redox potential range, making the material active within a wide voltage window; the HEO formed by air annealing is a rock salt or spinel structure, and the rock salt structure has octahedral sites for lithium storage, Li + It can be embedded in the gaps between transition metal octahedrons, accompanied by changes in the valence state of metal ions; the spinel structure has a 3D lithium ion diffusion channel, and at the same time, partial oxygen deficiency forms oxygen vacancies during the annealing process, which can serve as a fast channel for lithium ion migration and enhance electron conduction; the grain boundaries or surface amorphous layers of HEO can provide additional lithium storage sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is an XRD pattern of FeCoNiCuMg HEO / CC cathode material;

[0028] FIG2 is a TEM image of a FeCoNiCuMg HEO / CC cathode material;

[0029] Figure 3 Comparison of the cycle-capacity retention rates of FeCoNiCuMg HEO / CC and lithium metal sheets. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0033] Example 1

[0034] This embodiment provides a method for preparing a lithium battery positive electrode material based on high entropy oxide, the steps comprising:

[0035] S1. Place the CC in an 80°C oil bath with 0.1M H2SO4 for 2 hours, then place it in an 80°C oil bath with H2O2 for 2 hours to remove impurities on the CC surface, improve wettability, enhance surface activity, and improve conductivity; cut the pretreated CC into 1*1cm pieces using a cutting machine for subsequent experiments;

[0036] S2. 0.0.249 g (C4H6CoO4·4H2O), 0.190 g (C4H7FeO5·nH2O), 0.249 g (Ni(CH3COO)2·4H2O), 0.1816 g C4H6CuO4, 0.214 g MgC4H6O4, and 0.595 g 2,5-dihydroxyterephthalic acid (H4DOT) were dissolved in 52 mL N,N-dimethylformamide (DMF), 2.5 mL anhydrous ethanol (EtOH), and 2.5 mL deionized (DI) water, and vigorously sonicated to obtain a mixture;

[0037] S3. The mixture was transferred to a 100 mL polytetrafluoroethylene-lined autoclave, and 1*1 cm of CC was added. The mixture was sent to a hydrothermal oven for hydrothermal heating to react CC and the five-component mixture. The mixture was hydrothermally heated to 120°C and maintained for 24 h. The FeCoNiCuMg MOFs / CC was removed and the collected FeCoNiCuMg MOFs / CC was washed with DMF, DI water, and EtOH. The collected FeCoNiCuMg MOFs / CC was sent to a vacuum drying oven at 70°C for drying for 12 h before being removed.

[0038] S4. Pre-calcined the FeCoNiCuMg MOFs / CC at 350°C for 1 h in an air-filled tube furnace, then heated to 500°C at a heating rate of 5°C / min and calcined for 2 h, followed by natural annealing at 500°C for 3 h. The final product, FeCoNiCuMg HEO / CC, was obtained. The FeCoNiCuMg HEO / CC was washed with DI water and EtOH, dried in a drying oven at 70°C for 12 h, and then directly used as a positive electrode sheet for performance testing.

[0039] Comparative Example 1

[0040] This comparative example provides a method for preparing a positive electrode material for a lithium battery. The acid treatment in step S1 of Example 1 is omitted, and the rest is the same as in Example 1.

[0041] Comparative Example 2

[0042] This comparative example provides another method for preparing a positive electrode material for a lithium battery. The annealing treatment in step S4 of Example 1 is omitted, and the rest is the same as in Example 1.

[0043] Comparative Example 3

[0044] Only lithium sheets are used as positive electrode materials.

[0045] Detection Example

[0046] The lithium battery positive electrode materials prepared by the preparation methods described in Example 1 and Comparative Examples 1-2 are respectively used to form a battery, and the steps include:

[0047] In an argon glove box, assemble a button cell in the following order: positive electrode casing → positive electrode sheet → PP separator → 1MLiPF6in EC / DMC electrolyte → copper sheet → gasket → spring sheet → negative electrode casing. Place the numbered positive electrode casing on the assembly table; use tweezers to remove the positive electrode sheet and place it in the center of the positive electrode casing; use a dropper to apply three drops of electrolyte to the sheet; insert the separator and use tweezers to move it to the center of the casing; seal the battery using a button cell sealer and let it sit for 6 hours to allow the electrolyte to fully penetrate.

[0048] The battery capacity was tested by charging it at a constant voltage, leaving it standing, and then discharging it. The results are shown in Table 1 and Figures 1-3.

[0049] Table 1

[0050]

[0051]

[0052] When Comparative Example 1, which has not been acid-treated, is used in a lithium battery, the charging capacity of the positive electrode sheet is only 1.1238 mAh at a current of 0.238 mA, and the discharge capacity of the positive electrode sheet reaches 1.0432 mAh at a discharge current of 0.238 mA. The charge and discharge capacity is very low and the performance is poor; the positive electrode material of Comparative Example 2 does not even show any performance in the lithium battery, indicating that it cannot be used as a positive electrode sheet for a lithium battery; Comparative Example 3, which directly uses a lithium sheet, has a charging capacity of only 1.1179 mAh for the positive electrode sheet at a current of 0.238 mA, and a discharge capacity of 1.0058 mAh for the positive electrode sheet at a discharge current of 0.238 mA; the charge and discharge capacity of the positive electrode material of Example 1 for lithium batteries is significantly higher than that of Comparative Examples 1-3.

[0053] As shown in Figure 1, the five-element MOFs have more peak positions and good crystallinity, mainly because there are more metal crystals in the unoxidized MOFs ( Figure 1a ), after oxidation in a tube furnace, the crystallinity of the material decreases, e.g. Figure 1b As shown in the figure, the HEO material after oxidation of the five-element MOFs precursor showed three diffraction peaks at 2θ angles of 45.1°, 51° and 75.7°, indicating that all HEOs have a face-centered cubic (FCC) crystal structure.

[0054] As shown in Figure 2, Figure 2a The red framed area shows that the (202) and (022) crystal planes in the material have large dislocations. Further magnification results show that some areas in the material have no dislocations ( Figure 2b , A area), but there are also some areas with dislocations ( Figure 2b , Area B), through Figure 2b HRTEM image observations of the medium elliptical curve revealed that the nanocrystals were well confined, which can greatly improve the stability of the structure and provide higher specific capacity and rate performance.

[0055] Figure 3 It is a curve chart of the number of cycles and capacity retention of metal lithium sheets and FeCoNiCuMg HEO positive electrode sheets. After 1500 cycles, the capacity retention rate of the metal lithium sheet dropped to 81.78%. After 1750 cycles, the capacity retention rate of the FeCoNiCuMg HEO positive electrode sheet was 92.92%. It can be seen that the FeCoNiCuMg HEO positive electrode sheet can maintain a high number of cycles and a good capacity retention rate.

[0056] In summary, FeCoNiCuMgHEO / CC obtained by acid treatment of CC and combined with tubular furnace annealing can be used as the positive electrode of lithium battery, and can achieve good charge, discharge and cycle performance.

[0057] The above description is only a preferred embodiment of the present invention and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode material for a lithium battery based on a high entropy oxide, characterized in that the steps include: S1, pre-treating the carbon cloth and then cutting it to obtain a substrate; S2. Weigh C4H6CoO4·4H2O, C4H7FeO5·nH2O, Ni(CH3COO)2·4H2O, C4H6CuO4, Mg(CH3COO)2 and 2,5-dihydroxyterephthalic acid, dissolve them in a mixed solvent, and mix them by ultrasonication to obtain a mixture; S3, placing the substrate and the mixture in an autoclave for reaction, and then washing and drying the reactants to obtain a high entropy compound FeCoNiCuMg MOFs / CC; S4. The high entropy compound FeCoNiCuMg MOFs / CC is placed in a tube furnace for pre-calcination, calcination and annealing to obtain the lithium battery positive electrode material FeCoNiCuMg HEO / CC.

2. The preparation method according to claim 1, characterized in that In step S1, the pretreatment includes: placing the carbon in an oil bath containing H2SO4 at 80°C for 2 hours, and then transferring it to an oil bath containing H2O2 at 80°C for 2 hours.

3. The preparation method according to claim 1, characterized in that In step S2, the mixed solvent includes: N,N-dimethylformamide, anhydrous ethanol and deionized water.

4. The preparation method according to claim 3, characterized in that In the mixed solution, the volume ratio of N,N-dimethylformamide, anhydrous ethanol and deionized water is (18-22):(1-2):

1.

5. The preparation method according to claim 1, characterized in that In step S2, the mass ratio of C4H6CoO4·4H2O, C4H7FeO5·nH2O, Ni(CH3COO)2·4H2O, C4H6CuO4, Mg(CH3COO)2 and 2,5-dihydroxyterephthalic acid is (1-2):1:(1-2):(0.8-1):(1-2):(2-4).

6. The preparation method according to claim 1, characterized in that In step S3, the reaction conditions are 110-130° C. for 12-24 hours.

7. The preparation method according to claim 1, characterized in that In step S4, the pre-calcination treatment includes: calcining at 300-400° C. for 0.5-1 h.

8. The preparation method according to claim 1, characterized in that In step S4, the calcination treatment includes: heating to 500-600° C. at a heating rate of 3-6° C. / min and then calcining for 2 hours.

9. A lithium battery positive electrode material based on high entropy oxide, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. A lithium battery, characterized in that: include: Positive electrode and negative electrode; The positive electrode sheet is a lithium battery positive electrode material prepared by the preparation method according to any one of claims 1 to 8.

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