Preparation method of molybdate nanosheet compound coated modified positive electrode material with three-dimensional stacking structure

Abstract

The application discloses a preparation method of a three-dimensional stacked structure iron molybdate nanosheet compound coated modified positive electrode material, and the positive electrode material is mixed and deposited with a molybdate solution and an iron salt solution through a reverse microemulsion method, and after reaction, separation, washing and drying treatment, microwave carbonization is carried out to obtain the three-dimensional stacked structure iron molybdate nanosheet compound coated modified positive electrode material; the iron molybdate nanosheet compound has various possible stoichiometric compositions and crystal morphologies, and also has an amorphous core-shell structure arranged orthorhombic Li super ionic conductor structure, so that the coated material has high electrochemical activity; compared with metal oxides, the iron molybdate nanosheet compound has significant cycle performance; the unique morphology, low charge transfer resistance and high ion diffusion rate of the Fe2(MoO4)3 nanosheet can effectively improve the electrochemical reaction kinetics; the positive electrode material has better sphericity, and the crystal structure is more obvious, so that the stability of the positive electrode material structure is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of modification of positive electrode materials, and particularly relates to a preparation method of a three-dimensional stacked structure of a molybdate iron nanosheet compound coated modified positive electrode material. BACKGROUND

[0002] The global energy demand is growing rapidly, and people's dependence on efficient and environmentally friendly energy storage solutions continues to rise. As the world's traditional energy is becoming increasingly tight, it is necessary to choose a safer and more reliable energy alternative. In today's electrical age, lithium-ion batteries (LIBs) as a rapidly developing efficient energy storage technology have become a research hotspot due to their excellent portability, high energy density and stable cycle performance, and are widely used in portable electronic products, automobiles and aerospace fields. Although the current battery technology has made significant progress, its endurance and cost are still the main obstacles existing at present.

[0003] The positive electrode material is a key determinant of the performance of lithium-ion batteries, and the current development focus is on improving its safety, economic efficiency, long cycle performance and capacity. Lithium cobaltate, lithium manganate, lithium iron phosphate and ternary positive electrode materials (such as NCM and NCA) are the main choices of existing positive electrode materials, each of which carries different characteristics and challenges. Lithium cobaltate has an ideal ion diffusion rate and electronic conductivity, which makes the battery have high performance. Its high specific capacity (theoretical specific capacity is as high as 274 mAh / g) and stable working voltage bring great advantages. However, in actual situation, lithium cobaltate can only release about 140 mAh / g of specific capacity, because more than 50% of lithium ions are removed during discharge, and the monoclinic crystal structure of the crystal structure is replaced by the original crystal structure, so the actual specific capacity is seriously affected. Therefore, the capacity can be released at most 50% during use, that is, the actual specific capacity is about 140 mAh / g. Lithium cobaltate also has good rate performance, excellent cycle stability and simple synthesis process, but its actual working specific capacity is deviated, there is a risk of thermal runaway, the synthesis cost is high, and it has a certain damage to the environment, so its application scene is greatly limited, mainly used in small or medium-sized electronic products. The unique spinel structure of lithium iron phosphate can protect Li + When excessive diffusion occurs, Fe 2+The stability of the support material structure is not so strong as to cause the crystal structure to be destroyed. LiFePO4 has abundant raw material reserves and is inexpensive, has a working voltage that meets most working requirements and is stable, a theoretical specific capacity of 170 mAh / g, a structure that remains stable during cycling, can meet more high and low temperature applications and long cycle stability, and many other advantages, far superior to other positive electrode materials, is environmentally friendly, and even if a fire occurs, it will not explode and has a series of other advantages. However, the relatively low electronic conductivity and poor ion diffusion rate also have disadvantages, which make the material unable to meet the demand for fast charging and discharging.

[0004] With the iteration and progress of lithium ion battery technology, LiNiO2 has high specific capacity, LiMnO2 has high safety and low cost, and LiCoO2 has good cycle stability. LiNi x Co y Mn 1-x-y O2(NCM) material was invented, which covers the advantages of the three materials and avoids the disadvantages, making it have an advantage in the field of electric vehicles and other high energy density requirements. At the same time, NCM material has a high working voltage, which means it can provide higher power output under the same current, thus meeting the application scenarios with high power output requirements. NCM material also has good cycle life and stable long cycle performance, which is crucial for the service life and reliability of the battery. However, the current ternary positive electrode material battery also has many problems: low electronic conductivity and diffusion coefficient, poor rate performance; the electrolyte is severely catalyzed and decomposed by the active material at a voltage above 4.3V, resulting in serious gas production during the charging and discharging process of the nickel-rich positive electrode; the active material is easily deliquescent, which will seriously affect the cycle life of the battery; the mechanical properties of the secondary spherical particles are poor, and under high pressure, volume internal strain, expansion and contraction can cause microcracks and particle damage, microcracks react between the active material and the electrolyte, accelerating the disintegration of large particles and the decomposition of the electrolyte, and the crushed particles cannot participate in the electrochemical reaction, resulting in rapid capacity decay.

[0005] To solve these problems, researchers have made a lot of efforts on the modification of ternary materials, mainly through surface coating, ion doping and single crystal treatment to improve performance. Surface coating technology can reduce the direct contact with electrolyte by forming a protective layer on the surface of the electrode material, improve the chemical stability of the material and prevent the occurrence of side reactions, thereby improving the electrochemical performance of the positive electrode material. Ion doping can stabilize the lattice structure, enhance the battery capacity and improve its cycle stability; while single crystal treatment optimizes the microstructure of the material, improves the migration efficiency of lithium ions. The single crystal of ternary positive electrode material can make the particle size smaller, the surface smooth, increase the contact between the material and the electrolyte and the adhesive, and improve the diffusion rate of lithium ions in the material. However, although the modification of carbon materials and metal oxides has achieved certain results, the modification effect still needs to be optimized, and more efficient modification strategies still need to be explored to further promote the application of ternary positive electrode materials, especially in high-demand electric vehicle batteries. SUMMARY

[0006] The present application provides a preparation method of a three-dimensional stacked structure of iron molybdate nanosheet compound coated modified positive electrode material, which aims to solve the problems of rapid capacity attenuation, low stability and low activity of conventional positive electrode materials during the charging and discharging cycle process. The activity, surface stability and cycle performance of the conventional positive electrode material are improved by coating with iron molybdate nanosheet compound.

[0007] The technical scheme of the present application is as follows:

[0008] A preparation method of a three-dimensional stacked structure of iron molybdate nanosheet compound coated modified positive electrode material, the specific steps are as follows:

[0009] (1) The oil phase, surfactant and co-surfactant are added to a round-bottom flask in proportion, stirred until completely transparent to obtain a continuous phase, and the positive electrode material is added to the continuous phase and mixed quickly;

[0010] (2) The molybdate and iron salt are dissolved in water to obtain a mixed solution, which is added to the continuous phase containing the positive electrode material of step (1) to obtain a reverse microemulsion of mixed positive electrode material of molybdenum ions and iron ions, and the mixed material is stirred and reacted to deposit the mixed material with molybdenum ions and iron ions;

[0011] (3) After the mixed material in step (2) is separated, washed and dried, it is subjected to microwave carbonization under nitrogen atmosphere in a microwave to obtain a three-dimensional stacked structure of iron molybdate nanosheet compound coated modified positive electrode material.

[0012] The oil phase in step (1) can be composed of various water-insoluble organic substances, including but not limited to cyclohexane, n-hexane, n-octane, etc. (mainly C6-C 10 The surfactant can be composed of various ionic surfactants, including but not limited to sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, cetyltrimethylammonium bromide, etc., or various non-ionic surfactants, including but not limited to Triton X series, Span series, octylphenol polyoxyethylene ether, etc. The co-surfactant can be composed of various water-soluble alcohols, including but not limited to n-hexanol, n-butanol, n-pentanol, etc. in the continuous phase. The volume ratio of the oil phase, the surfactant, and the co-surfactant is 10:2:3.

[0013] The cathode material in step (1) is one of LiNi x Co y Mn 1-x-y O2, LiNi x Co y Al 1-x-y O2, LiCoO2, LiMnO2, LiFePO4, LiMn2O4, Li4Ti5O 12 , LiMn 1.5 Ni 0.5 O4, but is not limited to the listed ones; wherein LiNi x Co y Mn 1-x-y O2 is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, etc., LiNi x Co y Al 1-x-y O2 is LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.815 Co 0.15 Al 0.035 O2, etc.; the mol:mL of the cathode material and the continuous phase is 0.05:210-240.

[0014] The stirring speed in step (1) is 200-400 rpm.

[0015] The molybdate in step (2) is Na2MoO4, (NH4)6Mo7O 24 , (NH4)2MoO4, etc. in any proportion.

[0016] The iron salt in step (2) is FeCl3, Fe(NO3)3·9H2O, Fe(NO3)3, etc. in any proportion.

[0017] The molybdate and the iron salt in step (2) are mixed in a ratio to generate iron molybdate, and the molar ratio of the positive electrode material to the iron molybdate is calculated based on 1:0.01 to 1:0.2.

[0018] The stirring speed in step (2) is 200 to 400 rpm, and the reaction time is 2 to 6 hours.

[0019] The washing solvent in step (3) is any one or a mixture of two of ethanol, deionized water, etc.; the drying temperature is 80 to 120°C, and the drying time is 8 to 12 hours.

[0020] The microwave carbonization power in step (3) is 500 to 800 W, and the carbonization time is 10 to 30 minutes.

[0021] The present application has the following advantages:

[0022] (1) The iron molybdate nanosheet compound has various possible stoichiometric compositions, crystal structures, valence states, and nanocrystal morphologies, and is coated on the surface of the positive electrode material, which makes the positive electrode material have high electrochemical activity. In addition, the positive electrode material coated with the iron molybdate nanosheet compound has better electrical conductivity, mechanical properties, and cycle stability.

[0023] (2) The positive electrode material coated with the three-dimensional stacked structure iron molybdate nanosheet compound has better sphericity, and the crystal structure is more obvious, which greatly improves the stability of the positive electrode material structure, reduces the volume change and lattice expansion during the lithium ion insertion / extraction process, and thus optimizes the cycle performance.

[0024] (3) The three-dimensional stacked structure combined with the positive electrode material has a unique composite structure, effectively improves the electronic conductivity of the material and accelerates the diffusion rate of Li + , and provides a reference for the high performance of other low-activity and low-stability electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1(a) uncoated modified polycrystalline commercial NCM811; (b) a detailed magnified view of uncoated modified polycrystalline commercial NCM811; (c) Fe2(MoO4)3nanosheet compound coated modified polycrystalline commercial NCM811 - Example 3; (d) a detailed magnified view of Fe2(MoO4)3nanosheet compound coated modified polycrystalline commercial NCM811 - Example 3. DETAILED DESCRIPTION

[0026] In order to better embody the content of the present application, the present application will be further described in detail below through specific examples, but the scope of protection of the present application is not limited to the content described.

[0027] Example 1

[0028] A method for preparing a high-nickel NCM811 cathode material by coating modification of a three-dimensional stacked structure of a ferromolybdate nanosheet compound, the specific steps being as follows:

[0029] (1) 150 mL of cyclohexane, 30 mL of octylphenol polyoxyethylene ether (OP-10), and 45 mL of n-hexanol were weighed into a round-bottom flask, respectively, and stirred at 200 rpm until completely transparent to prepare a continuous phase. 4.86 g of commercial high-nickel cathode material LiNi0.80Co0.10Mn0.10O2powder was added to the continuous phase to obtain a mixed phase; 0.8 Co 0.1 Mn 0.1 O2powder was added to the continuous phase and stirred to obtain a mixed phase;

[0030] (2) 1.09 g of sodium molybdate Na2MoO4and 0.488 g of iron chloride FeCl3were weighed in a molar ratio (NCM811: Fe2(MoO4)3) of 1:0.03, dissolved in 20 mL of water, and then added dropwise to the mixed phase of step (1) to form a reverse microemulsion, and reacted at a speed of 200 rpm for 6 h to obtain a mixed material with molybdenum ions and iron ions deposited thereon;

[0031] (3) After the mixed material obtained in step (2) was separated and washed with ethanol, it was dried at 80°C for 12 h, and then carbonized by radiation heating in a microwave reactor under a nitrogen atmosphere at a power of 650 W for 25 min to obtain a three-dimensional stacked structure of Li(Ni0.80Co0.10Mn0.10)O2@3at%Fe2(MoO4)3high-nickel cathode material. 0.8 Co 0.1 Mn 0.1 )O2@3at%Fe2(MoO4)3high-nickel cathode material.

[0032] Example 2

[0033] A method for preparing a high-nickel NCM811 cathode material by coating modification of a three-dimensional stacked structure of a ferromolybdate nanosheet compound, the specific steps being as follows:

[0034] (1) Respectively take 150 mL of cyclohexane, 30 mL of octylphenol polyoxyethylene ether (OP-10) and 45 mL of n-hexanol into a round-bottom flask, stir at 300 rpm until completely transparent to prepare a continuous phase, weigh 4.86 g of commercial nickel-rich positive material LiNi 0.8 Co 0.1 Mn 0.1 O2 powder into the continuous phase to obtain a mixed phase;

[0035] (2) Take 0.882 g of ammonium molybdate (NH4)2MoO4 and 0.726 g of iron nitrate Fe(NO3)3 with a molar ratio (NCM811:Fe2(MoO4)3) of 1:0.03, add 20 mL of water to dissolve completely; Then add dropwise to the mixed phase of step (1) to form a reverse microemulsion, and react at a speed of 300 rpm for 5 h to obtain a mixed material with molybdenum ions and iron ions deposited;

[0036] (3) After the mixed material obtained in step (2) is separated and washed with water and ethanol, it is dried at 100°C for 10h, then irradiated and heated in a microwave reactor under a nitrogen atmosphere at a power of 800W for 10min to obtain a three-dimensional stacked structure Li(Ni 0.8 Co 0.1 Mn 0.1 )O2@3at%Fe2(MoO4)3 nickel-rich positive material.

[0037] Example 3

[0038] A method for preparing a high-nickel NCM811 positive material by coating modification of a three-dimensional stacked structure of a molybdate iron nanosheet compound, the specific steps are as follows:

[0039] (1) Respectively take 150 mL of cyclohexane, 30 mL of octylphenol polyoxyethylene ether (OP-10) and 45 mL of n-hexanol into a round-bottom flask, stir at 400 rpm until completely transparent to prepare a continuous phase, weigh 4.86 g of commercial nickel-rich positive material LiNi 0.8 Co 0.1 Mn 0.1 O2 powder into the continuous phase to obtain a mixed phase;

[0040] (2) Take 0.882 g of ammonium molybdate (NH4)2MoO4 and 0.726 g of iron nitrate Fe(NO3)3 with a molar ratio (NCM811:Fe2(MoO4)3) of 1:0.03, add 30 mL of water to dissolve completely; Then add dropwise to the mixed phase of step (1) to form a reverse microemulsion, and react at a speed of 400 rpm for 4 h to obtain a mixed material with molybdenum ions and iron ions deposited;

[0041] (3) The mixed material obtained in step (2) is separated, washed with water and ethanol, and dried at 120°C for 8h. Then, in a microwave reactor, under a nitrogen atmosphere, the carbonization is carried out by irradiation heating with a power of 650W for 25min to obtain a three-dimensional stacked structure Li(Ni 0.8 Co 0.1 Mn 0.1 )O2@3at%Fe2(MoO4)3 nickel-rich positive electrode material.

[0042] Example 4

[0043] A method for preparing a high-nickel NCM811 positive electrode material by coating modification of a three-dimensional stacked structure iron molybdate nanosheet compound, the specific steps are as follows:

[0044] (1) 150mL of cyclohexane, 30mL of octylphenol polyoxyethylene ether (OP-10), and 45mL of n-hexanol are weighed into a round-bottom flask, stirred at 400rpm until completely transparent to prepare a continuous phase. 4.86g of commercial nickel-rich positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2 powder is added to the continuous phase to obtain a mixed phase;

[0045] (2) 7.26g of sodium molybdate Na2MoO4 and 3.25g of iron chloride FeCl3 are weighed in a molar ratio (NCM811:Fe2(MoO4)3) of 1:0.2, and dissolved in 25mL of water. Then, it is added dropwise to the mixed phase of step (1) to form a reverse microemulsion, and reacted at a speed of 400rpm for 4h to obtain a mixed material with molybdenum ions and iron ions deposited;

[0046] (3) The mixed material obtained in step (2) is separated, washed with ethanol, and dried at 80°C for 12h. Then, in a microwave reactor, under a nitrogen atmosphere, the carbonization is carried out by irradiation heating with a power of 650W for 25min to obtain a three-dimensional stacked structure Li(Ni 0.8 Co 0.1 Mn 0.1 )O2@20at%Fe2(MoO4)3 nickel-rich positive electrode material.

[0047] Example 5

[0048] A method for preparing a high-nickel NCM811 positive electrode material by coating modification of a three-dimensional stacked structure iron molybdate nanosheet compound, the specific steps are as follows:

[0049] (1) Respectively take 165 mL of cyclohexane, 33 mL of octylphenol polyoxyethylene ether (OP-10) and 45.5 mL of n-hexanol, add them into a round-bottom flask, stir at 350 rpm until completely transparent to prepare a continuous phase, and weigh 4.86 g of commercial nickel-rich positive material LiNi 0.8 Co 0.1 Mn 0.1 O2 powder into the continuous phase to obtain a mixed phase by stirring;

[0050] (2) Take 0.795 g of ammonium molybdate (NH4)6Mo7O 24 ·4H2O and 1.21 g of iron nitrate nonahydrate Fe(NO3)3·9H2O, add them into 25 mL of water to dissolve completely, then add them dropwise into the mixed phase of step (1) to form a reverse microemulsion, and react at a speed of 300 rpm for 5 h to obtain a mixed material with molybdenum ions and iron ions deposited;

[0051] (3) After the mixed material obtained in step (2) is separated and washed with water and ethanol, it is dried at 100°C for 10 h, then irradiated and heated in a microwave reactor under a nitrogen atmosphere at a power of 650 W for 25 min to obtain a three-dimensional stacked structure Li(Ni 0.8 Co 0.1 Mn 0.1 )O2@3at%Fe2(MoO4)3 nickel-rich positive material.

[0052] Example 6

[0053] A method for preparing a high-nickel NCM811 positive material by coating modification of a three-dimensional stacked structure of a molybdate iron nanosheet compound, the specific steps are as follows:

[0054] (1) Respectively take 135 mL of cyclohexane, 27 mL of octylphenol polyoxyethylene ether (OP-10) and 40.5 mL of n-hexanol, add them into a round-bottom flask, stir at 350 rpm until completely transparent to prepare a continuous phase, and weigh 4.86 g of commercial nickel-rich positive material LiNi 0.8 Co 0.1 Mn 0.1 O2 powder into the continuous phase to obtain a mixed phase by stirring;

[0055] (2) Take 0.294 g of ammonium molybdate (NH4)2MoO4 and 0.242 g of iron nitrate Fe(NO3)3, add them into 20 mL of water to dissolve completely, then add them dropwise into the mixed phase of step (1) to form a reverse microemulsion, and react at a speed of 300 rpm for 6 h to obtain a mixed material with molybdenum ions and iron ions deposited;

[0056] (3) After the mixed material obtained in step (2) is separated and washed with water and ethanol, and dried at 120°C for 8h, a three-dimensional stacked structure Li(Ni 0.8 Co 0.1 Mn 0.1 )O2@1at%Fe2(MoO4)3 nickel-rich positive electrode material is obtained by irradiation heating carbonization in a microwave reactor under a nitrogen atmosphere at a power of 500W for 30min.

[0057] Example 7

[0058] A method for preparing a LiFePO4 positive electrode material by coating modification of a three-dimensional stacked structure iron molybdate nanosheet compound is as follows:

[0059] (1) 150mL of cyclohexane, 30mL of octylphenol polyoxyethylene ether (OP-10), and 45mL of n-hexanol are weighed into a round-bottom flask, stirred at 250rpm until completely transparent to prepare a continuous phase, and 7.89g of commercial LiFePO4 powder is added to the continuous phase to obtain a mixed phase;

[0060] (2) 0.882g of ammonium molybdate (NH4)2MoO4 and 0.726g of iron nitrate Fe(NO3)3 are weighed in a molar ratio (LiFePO4:Fe2(MoO4)3) of 1:0.03, dissolved in 20mL of water, then added dropwise to the mixed phase of step (1) to form a reverse microemulsion, and reacted at a speed of 300rpm for 6h to obtain a mixed material with molybdenum ions and iron ions deposited;

[0061] (3) After the mixed material obtained in step (2) is separated and washed with water and ethanol, and dried at 120°C for 8h, a three-dimensional stacked structure LiFePO4@3at%Fe2(MoO4)3 positive electrode material is obtained by irradiation heating carbonization in a microwave reactor under a nitrogen atmosphere at a power of 650W for 25min.

[0062] Comparative Example 1

[0063] A method for preparing a high-nickel NCM811 positive electrode material by coating modification of iron oxide is as follows:

[0064] (1) 150mL of cyclohexane, 30mL of octylphenol polyoxyethylene ether (OP-10), and 45mL of n-hexanol are weighed into a round-bottom flask, stirred at 400rpm until completely transparent to prepare a continuous phase, and 4.86g of commercial nickel-rich positive electrode material LiNi 0.8 Co 0.1 Mn 0.1O2 powder is added to the continuous phase to obtain a mixed phase;

[0065] (2) 0.726 g of iron nitrate Fe(NO3)3 was weighed in a molar ratio (LiFePO4: Fe2O3) of 1:0.03 and added to 30 mL of water to dissolve completely; then it was added dropwise to the mixed phase of step (1) to form a reverse microemulsion, and reacted at a speed of 300 rpm for 5 h to obtain a mixed material with iron ion deposition;

[0066] (3) After the mixed material obtained in step (2) was separated and washed with water and ethanol, and dried at 100°C for 10 h, it was irradiated and heated in a microwave reactor under a nitrogen atmosphere at a carbonization power of 800 W for 10 min to obtain a three-dimensional stacked structure Li(Ni 0.8 Co 0.1 Mn 0.1 )O2@3at%Fe2O3 nickel-rich positive electrode material.

[0067] Comparative Example 2

[0068] A method for preparing a high-nickel NCM811 positive electrode material by coating modification of molybdenum oxide, the specific steps are as follows:

[0069] (1) 150 mL of cyclohexane, 30 mL of octylphenol polyoxyethylene ether (OP-10), and 45 mL of n-hexanol were weighed into a round-bottom flask, stirred at 300 rpm until completely transparent to prepare a continuous phase, and 4.86 g of commercial nickel-rich positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2 powder was added to the continuous phase to obtain a mixed phase;

[0070] (2) 0.294 g of ammonium molybdate (NH4)2MoO4 was weighed in a molar ratio (LiFePO4: MoO3) of 1:0.03 and added to 30 mL of water to dissolve completely; then it was added dropwise to the mixed phase of step (1) to form a reverse microemulsion, and reacted at a speed of 300 rpm for 5 h to obtain a mixed material with molybdenum ion deposition;

[0071] (3) After the mixed material obtained in step (2) was separated and washed with water and ethanol, and dried at 100°C for 10 h, it was irradiated and heated in a microwave reactor under a nitrogen atmosphere at a power of 800 W for 10 min to obtain a three-dimensional stacked structure Li(Ni 0.8 Co 0.1 Mn 0.1 )O2@3at%MoO3 nickel-rich positive electrode material.

[0072] Figure 1(a) Uncoated modified NCM811 cathode material - commercial NCM811; (b) Detail magnification of uncoated modified NCM811 cathode material - commercial NCM811; (c) Polycrystalline NCM811 cathode material coated with Fe2(MoO4)3 nanosheet compound - Example 3; (d) Detail magnification of polycrystalline NCM811 cathode material coated with Fe2(MoO4)3 nanosheet compound - Example 3, as can be seen from the figure, the NCM811 cathode material surface coated with Fe2(MoO4)3 nanosheet compound forms a sheet layer crystal structure, and the crystal coating is relatively uniform and has good consistency.

[0073] The materials prepared in the above examples and commercial NCM811, commercial LiFePO4 were used as cathodes, lithium metal as anode, polypropylene film (Celgard 2400) as separator, and ethylene carbonate containing 1M lithium hexafluorophosphate as electrolyte. The coin cells were assembled in an argon-filled glove box with water content less than 0.01 ppm and oxygen content less than 0.01 ppm. The capacity retention rate of the cathode lithium ion NCM811 battery was tested at 2.8-4.3V, LiFePO4 battery at 2.5-4.2V, and charge-discharge rate at 1C for 50 cycles, and the results are shown in Table 1 below:

[0074] Table 1

[0075]

[0076] Examples 1-3 and Examples 4-6 are NCM811 cathode materials coated with Fe2(MoO4)3 nanosheet compound with three-dimensional stacked structure formed by different molybdenum sources and iron sources, wherein Example 1 and Example 4 use sodium molybdate and ferric chloride as ion sources of Fe2(MoO4)3, Example 2, Example 3 and Example 6 use ammonium molybdate without combined water and ferric nitrate as ion sources of Fe2(MoO4)3, and Example 5 uses ammonium molybdate tetrahydrate and ferric nitrate nonahydrate containing combined water as ion sources of Fe2(MoO4)3; by comparing Example 3 with Example 5, it can be found that Fe2(MoO4)3 formed by ammonium molybdate without combined water and ferric nitrate exhibits higher initial specific discharge capacity and capacity retention rate after 50 cycles, which is because the molybdenum salt and iron salt without combined water are more stable and easier to combine with the ternary cathode material and adhere to the material surface; and by comparing Example 2, Example 3 and Example 6, it can be found that the coating material formed by microwave carbonization power of 650W exhibits higher initial specific capacity, which is because too high power can easily cause the lattice of Fe2(MoO4)3 material to become smaller, hindering the Li + extraction and intercalation process; and too low power can affect the coating quality of the material and cannot achieve complete coating effect.

[0077] It is found from the comparison between Example 2 and Comparative Examples 1-2 that the effect of single iron or molybdenum oxide on the initial capacity and capacity retention of NCM811 material is not as obvious as that of cerium-molybdenum composite oxide, because the formed iron oxide or molybdenum oxide exhibits a dense oxide layer on the surface of the material, which hinders the extraction and embedding of Li + , resulting in capacity decline and capacity retention reduction; while the iron molybdate nanosheet compound as a unique three-dimensional stacked structure coating layer can have a larger specific surface area and porosity to provide more active sites for the extraction and embedding process of Li + .

[0078] The positive electrode material used in Examples 1-6 and Comparative Examples 1-2 is NCM811, and LiFePO4 is used in Example 7. As can be seen from the above table data, whether the positive electrode material is NCM811 or LiFePO4, compared with the corresponding commercial positive electrode material, the initial discharge specific capacity and cycle capacity retention of the coated material are improved to a certain extent, indicating that the coating modification of the iron molybdate nanosheet compound has a certain effect on the performance of NCM811 and LiFePO4. The reaction between the active material and the electrolyte will accelerate the disintegration of large particles and the decomposition of electrolyte, and the crushed particles cannot participate in the electrochemical reaction, resulting in rapid capacity decay. The use of coating method to modify the positive electrode material can reduce the direct contact between the positive electrode material and the electrolyte, and to a certain extent, increase its cycle life. In addition, the iron molybdate nanosheet compound has excellent electrical conductivity, which can improve the electron transport rate in the positive electrode material without the need for a large amount of non-active conductive agent.

[0079] The specific embodiments of the present application are described in detail above with reference to the accompanying drawings, but the present application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application.

Claims

1. A method for preparing a three-dimensional stacked structure of a molybdate iron nanosheet compound-coated modified positive electrode material, characterized by, The specific steps are as follows: (1) The oil phase, surfactant, and co-surfactant are mixed and stirred until completely transparent to obtain a continuous phase, and the positive electrode material is added to the continuous phase for mixing; (2) The molybdate and iron salt are dissolved in water to obtain a mixed solution, which is added to the continuous phase containing the positive electrode material in step (1) to obtain a reverse microemulsion of the mixed positive electrode material of molybdenum ions and iron ions, and stirring is performed to obtain a mixed material with molybdenum ions and iron ions deposited thereon; (3) After the mixed material in step (2) is separated, washed, and dried, microwave carbonization is performed under a nitrogen atmosphere to obtain a positive electrode material coated with a three-dimensional stacked structure of a nanosheet compound of iron molybdate.

2. The preparation method according to claim 1, characterized in that, In step (1), the oil phase is cyclohexane, n-hexane, or n-octane; the surfactant is sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, cetyltrimethylammonium bromide, Triton X series, Span series, or octylphenol polyoxyethylene ether; the co-surfactant is n-hexanol, n-butanol, or n-pentanol; and the volume ratio of the oil phase, surfactant, and co-surfactant in the continuous phase is 10:2:

3.

3. The preparation method according to claim 1, characterized in that, The cathode material in step (1) is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.815 Co 0.15 Al 0.035 O2; the mol:mL of the cathode material and the continuous phase is 0.05:210-240.

4. The preparation method according to claim 1, characterized in that, In step (1), the stirring speed is 200-400 rpm.

5. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. The molybdate salt in step (2) is Na2MoO4, (NH4)6Mo7O 24 • one or more of Na2MoO4, (NH4)6Mo7O 4H2O, (NH4)2MoO4in any ratio.

6. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step (2), the iron salt is one or more of FeCl3, Fe(NO3)3·9H2O, and Fe(NO3)3 in any proportion.

7. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step (2), the molybdate and iron salt are mixed in a proportion to generate iron molybdate, and the molar ratio of the positive electrode material to iron molybdate is 1:0.01-1:0.

2.

8. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step (2), the stirring speed for stirring is 200-400 rpm, and the reaction time is 2-6 h.

9. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step (3), the drying temperature is 80-120°C, and the drying time is 8-12 h.

10. The method of claim 1, wherein, In step (3), the microwave carbonization power is 500-800 W, and the carbonization time is 10-30 min.

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