Secondary battery and preparation method thereof, energy storage system and electric equipment

Abstract

The invention provides a secondary battery and a preparation method thereof, an energy storage system and electric equipment, and relates to the technical field of energy storage. The preparation method comprises the following steps: mixing a molybdenum source, a sulfur source, polyvinyl pyrrolidone and water, and carrying out a synthetic reaction to obtain MoS2; the preparation method comprises the following steps: mixing raw materials including MoS2, an iron source, imidazole, benzimidazole and an organic solvent, sequentially carrying out hydrothermal reaction and calcination treatment to obtain a Fe-N-C coated MoS2 material, and sequentially mixing, coating and rolling the Fe-N-C coated MoS2 material with a positive active material, a conductive agent and a binder to obtain a positive plate; and preparing the positive plate, the diaphragm and the negative plate into a naked battery cell, assembling the naked battery cell with the shell and the top cover, and then injecting electrolyte to obtain the secondary battery. The secondary battery provided by the invention has relatively low direct-current internal resistance.

Description

[0001] This invention is a divisional application of the invention patent application with the application date of April 25, 2025, application number 202510537278.0, and the invention name being "Secondary battery and its preparation method, energy storage system and electrical equipment". Technical Field

[0002] The present invention relates to the field of energy storage technology, and in particular to a secondary battery and a preparation method thereof, an energy storage system and electrical equipment. Background Art

[0003] Lithium-ion batteries are widely used in electric vehicles, energy storage, consumer electronics and other fields. During the charging process, lithium ions are released from the positive electrode material, transferred to the negative electrode through the electrolyte, and embedded in the negative electrode carbon material; at the same time, electrons are released from the positive electrode and reach the negative electrode from the external circuit, maintaining the balance of the chemical reaction. During the discharge process, lithium ions are released from the negative electrode and reach the positive electrode through the electrolyte. At the same time, the negative electrode releases electrons and reaches the positive electrode from the external circuit, providing energy to the outside world. The obstacles encountered by electrons and ions during the battery's charging and discharging process are collectively referred to as the DC internal resistance. The conductivity of the positive electrode material directly affects the DC internal resistance, which in turn affects the battery's energy efficiency, cycle life and safety. Currently, lithium batteries generally use conductive carbon black and graphene / carbon nanotubes to reduce the resistance of the positive electrode sheet, reduce the DC internal resistance, and improve the performance of the battery cell, but the improvement effect is less than ideal. Summary of the Invention

[0004] The main purpose of the present invention is to provide a secondary battery and a preparation method thereof, an energy storage system and an electrical device, so as to solve the problem of large DC internal resistance of secondary batteries in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing a secondary battery is provided, comprising: S1, mixing a molybdenum source, a sulfur source, polyvinyl pyrrolidone and water, and conducting a synthesis reaction to obtain MoS2; S2, mixing raw materials including MoS2, an iron source, imidazole, benzimidazole and an organic solvent, and conducting a hydrothermal reaction, and then calcining under a protective gas to obtain a Fe-NC coated MoS2 material; S3, sequentially mixing, coating and rolling the Fe-NC coated MoS2 material, a positive electrode active material, a conductive agent and a binder to obtain a positive electrode sheet; S4, making the positive electrode sheet, the diaphragm and the negative electrode sheet into a bare cell, assembling the bare cell with a shell and a top cover, and then injecting an electrolyte to obtain a secondary battery; wherein the molar ratio of MoS2, the iron source, the imidazole and the benzimidazole is (0.01~1):(0.02~0.2):(0.25~10):(0.05~2).

[0006] Furthermore, the temperature of the hydrothermal reaction is 140-180°C; and / or the time of the hydrothermal reaction is 24-28h; and / or the heating rate of the calcination treatment is 2-3°C / min; and / or the temperature of the calcination treatment is 650-750°C; and / or the holding time of the calcination treatment is 2-3h.

[0007] Furthermore, the mass ratio of the above-mentioned Fe-NC coated MoS2 material, positive electrode active material, conductive agent and binder is (0.3~1.2):(94.3~98.2):(0.5~1.5):(1~3); and / or, the iron source is selected from any one or more of Fe(NO3)3·6H2O, FeCl3·6H2O and FeSO4·7H2O; and / or, the organic solvent is selected from any one or more of N,N-dimethylformamide, acetonitrile and ethanol.

[0008] Furthermore, the molar ratio of the molybdenum source, sulfur source and polyvinyl pyrrolidone is (0.3-1):(4-8):(0.003-0.01); and / or the synthesis reaction temperature is 210-220° C.; and / or the synthesis reaction time is 12-24 h.

[0009] Furthermore, the number average molecular weight of the polyvinyl pyrrolidone is 10,000 to 60,000 Da; and / or the molybdenum source is selected from (NH4)6Mo7O 24 ·Any one or more of 4H2O, Na2MoO4·2H2O and (NH4)2MoS4; and / or, the sulfur source is selected from any one or more of NH2CSNH2, C2H5NS and C3H7NO2S.

[0010] According to another aspect of the present invention, a secondary battery is provided, comprising a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode active layer, the material of the positive electrode active layer comprising Fe-NC coated MoS2 material, a positive electrode active material, a conductive agent and a binder; wherein the Fe-NC coated MoS2 material is distributed on the surface of the positive electrode active material; the mass ratio of MoS2 to Fe-NC in the Fe-NC coated MoS2 material is 1:(0.2~1), the molar ratio of Fe element, N element and C element in Fe-NC is (1~2):(2~4):(50~100), the structure of MoS2 is a layered structure, and the structure of Fe-NC is a porous structure.

[0011] Furthermore, the mass ratio of the above-mentioned Fe-NC coated MoS2 material, positive electrode active material, conductive agent and binder is (0.3~1.2):(94.3~98.2):(0.5~1.5):(1~3).

[0012] Furthermore, the powder resistivity of the Fe-NC coated MoS2 material is 10 -2 ~1Ω·cm; and / or, the average pore size of the Fe-NC coated MoS2 material is 2 to 20 nm; and / or, the porosity of the Fe-NC coated MoS2 material is 50 to 70%.

[0013] According to another aspect of the present invention, there is provided an energy storage system, comprising a unit cell, wherein the unit cell is a secondary battery prepared by the aforementioned method for preparing a secondary battery or the aforementioned secondary battery.

[0014] According to another aspect of the present invention, there is provided an electrical device comprising the aforementioned energy storage system, wherein the energy storage system is used to provide power to the electrical device.

[0015] By applying the technical solution of the present application, the beneficial effects of the present application are as follows: in S1 of the present application, a molybdenum source, a sulfur source, polyvinyl pyrrolidone and water are mixed and subjected to a synthesis reaction, and the addition of polyvinyl pyrrolidone helps to prepare MoS2 with a layered structure. In S2, the raw materials of the obtained layered structure MoS2, an iron source, imidazole, benzimidazole and an organic solvent are mixed and subjected to a hydrothermal reaction, and the molar ratio of MoS2, the iron source, imidazole and benzimidazole is controlled within the above range, which helps to in situ grow an iron-based metal organic framework material on the surface of MoS2, and then calcinate it to obtain a Fe-NC coated MoS2 material. Compared with directly mixing MoS2 with an iron-based metal organic framework material and then calcining it, the in situ growth helps to improve the bonding force between MoS2 and Fe-NC, thereby helping to improve the electrical conductivity between MoS2 and Fe-NC. Fe-NC has high conductivity. Fe-NC coating on the surface of MoS2 helps improve MoS2's conductivity. MoS2's layered structure provides channels for rapid ion insertion and extraction. Furthermore, the Fe-NC formed from an iron-based metal-organic framework material has a porous structure, which facilitates electrolyte penetration and ion diffusion. Adding Fe-NC-coated MoS2 material to the positive electrode sheet helps improve the sheet's conductivity and ion transport properties. Assembling this positive electrode sheet into a secondary battery helps reduce the battery's internal resistance, thereby improving the battery's rate capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 The flowchart of the secondary battery preparation process of the present application is shown. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0019] As analyzed in the background technology of this application, the existing technology has the problem of large DC internal resistance of secondary batteries. In order to solve this problem, this application provides a secondary battery and its preparation method, energy storage system and electrical equipment.

[0020] In a typical embodiment of the present application, a method for preparing a secondary battery is provided, such as Figure 1 As shown, it includes: S1, mixing a molybdenum source, a sulfur source, polyvinyl pyrrolidone and water and conducting a synthesis reaction to obtain MoS2; S2, mixing raw materials including MoS2, an iron source, imidazole, benzimidazole and an organic solvent and conducting a hydrothermal reaction, and then calcining under a protective gas to obtain a Fe-NC coated MoS2 material; S3, mixing, coating and rolling the Fe-NC coated MoS2 material, a positive electrode active material, a conductive agent and a binder in sequence to obtain a positive electrode sheet; S4, making the positive electrode sheet, the diaphragm and the negative electrode sheet into a bare battery cell, assembling the bare battery cell with the outer shell and the top cover, and then injecting the electrolyte to obtain a secondary battery; wherein the molar ratio of MoS2, the iron source, the imidazole and the benzimidazole is (0.01~1):(0.02~0.2):(0.25~10):(0.05~2).

[0021] In S1 of the present application, a molybdenum source, a sulfur source, polyvinyl pyrrolidone and water are mixed and then subjected to a synthesis reaction. The addition of polyvinyl pyrrolidone helps to prepare MoS2 with a layered structure. In S2, the raw materials of the obtained layered structure MoS2, an iron source, imidazole, benzimidazole and an organic solvent are mixed and then subjected to a hydrothermal reaction, and the molar ratio of MoS2, the iron source, imidazole and benzimidazole is controlled within the above range, which helps to form an iron-based metal organic framework material in situ growth on the surface of MoS2, and then calcination treatment is performed to obtain Fe-NC coated MoS2 material. Compared with directly mixing MoS2 with an iron-based metal organic framework material and then calcining treatment, the in situ growth helps to improve the bonding force between MoS2 and Fe-NC, thereby helping to improve the electrical conductivity between MoS2 and Fe-NC. Fe-NC has high conductivity. Fe-NC coating on the surface of MoS2 helps improve MoS2's conductivity. MoS2's layered structure provides channels for rapid ion insertion and extraction. Furthermore, the Fe-NC formed from an iron-based metal-organic framework material has a porous structure, which facilitates electrolyte penetration and ion diffusion. Adding Fe-NC-coated MoS2 material to the positive electrode sheet helps improve the sheet's conductivity and ion transport properties. Assembling this positive electrode sheet into a secondary battery helps reduce the battery's internal resistance, thereby improving the battery's rate capability.

[0022] It should be noted that the positive electrode active material, separator, negative electrode sheet and electrolyte of the present application can all be purchased or prepared using existing technologies.

[0023] Including but not limited to, the above-mentioned conductive agent is selected from any one or more of Super-P, carbon nanotubes, graphene and carbon fiber; the above-mentioned binder is selected from any one or more of polyvinylidene fluoride, polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose and polyacrylic acid.

[0024] The function of the protective gas is to reduce the contact between the Fe-NC coated MoS2 material and oxygen in the air, including but not limited to, the above-mentioned protective gas is selected from any one or more of nitrogen, helium and argon.

[0025] In order to improve the uniformity of the dispersion of the Fe-NC coated MoS2 material on the surface of the positive electrode active material, thereby further improving the conductivity and ion transport performance of the positive electrode sheet, in one embodiment of the present application, in the above S3, the positive electrode active material, the conductive agent and the binder are first mixed, and then the Fe-NC coated MoS2 material is added and continued to be mixed to obtain a mixture, and the mixture is coated and rolled in sequence to obtain a positive electrode sheet.

[0026] In one embodiment of the present application, the temperature of the above-mentioned hydrothermal reaction is 140-180°C; and / or, the time of the hydrothermal reaction is 24-28h; and / or, the heating rate of the calcination treatment is 2-3°C / min; and / or, the temperature of the calcination treatment is 650-750°C; and / or, the holding time of the calcination treatment is 2-3h.

[0027] Controlling the temperature and time of the hydrothermal reaction within the above range helps to promote the reaction between MoS2 and the Fe source, imidazole and benzimidazole without destroying the material, thereby forming a uniform and stable iron-based metal-organic framework material coated MoS2 material. Controlling the heating rate of the calcination treatment within the above range helps to reduce the stress generated inside the material, thereby helping to form a stable Fe-NC coated MoS2 material. Controlling the temperature and time of the calcination treatment within the above range helps to promote the carbonization of the iron-based metal-organic framework material, forming a Fe-NC coating layer with suitable thickness, pore size and porosity, and helps to improve the structural stability and conductivity of the Fe-NC coated MoS2 material while improving the purity of the Fe-NC coated MoS2 material, thereby helping to further improve the conductivity and ion transport performance of the positive electrode sheet, and then helping to reduce the internal resistance of the secondary battery.

[0028] In one embodiment of the present application, the mass ratio of the above-mentioned Fe-NC coated MoS2 material, positive electrode active material, conductive agent and binder is (0.3~1.2):(94.3~98.2):(0.5~1.5):(1~3); and / or, the iron source is selected from any one or more of Fe(NO3)3·6H2O, FeCl3·6H2O and FeSO4·7H2O; and / or, the organic solvent is selected from any one or more of N,N-dimethylformamide, acetonitrile and ethanol.

[0029] The Fe-NC-coated MoS2 material provides additional conductive pathways and ion transport channels, while the positive electrode active material provides energy storage. The addition of a conductive agent helps improve the electron conductivity of the positive electrode material. The presence of a binder helps ensure good contact between the electrode material and the current collector, as well as improve the mechanical stability of the positive electrode sheet. Controlling the mass ratio of the Fe-NC-coated MoS2 material, the positive electrode active material, the conductive agent, and the binder within the aforementioned range helps enhance the synergistic effect between the components, thereby helping to reduce the internal resistance of the secondary battery and improve the capacity, rate capability, cycle stability, and safety of the secondary battery.

[0030] In one embodiment of the present application, the molar ratio of the above-mentioned molybdenum source, sulfur source and polyvinyl pyrrolidone is (0.3~1):(4~8):(0.003~0.01); and / or the temperature of the synthesis reaction is 210~220℃; and / or the time of the synthesis reaction is 12~24h.

[0031] Controlling the molar ratio of the molybdenum source, sulfur source, and polyvinyl pyrrolidone within the aforementioned range helps promote the formation of a MoS2 layered structure, providing it with good ion insertion and extraction channels. Controlling the temperature and time of the synthesis reaction within the aforementioned range helps improve the integrity and stability of the MoS2 layered structure, thereby helping to improve the ion transport efficiency of the Fe-NC-coated MoS2 material, thereby helping to reduce the internal resistance of the secondary battery and improve the rate performance of the secondary battery.

[0032] In one embodiment of the present application, the number average molecular weight of the polyvinyl pyrrolidone is 10,000 to 60,000 Da, specifically 10,000 Da, 20,000 Da, 30,000 Da, 40,000 Da, 50,000 Da, 60,000 Da, and a range between any two values; and / or the molybdenum source is selected from (NH4)6Mo7O 24 ·Any one or more of 4H2O, Na2MoO4·2H2O and (NH4)2MoS4; and / or, the sulfur source is selected from any one or more of NH2CSNH2, C2H5NS and C3H7NO2S.

[0033] Controlling the number-average molecular weight of polyvinyl pyrrolidone within the aforementioned range not only helps provide better dispersion and stability for the synthesis reaction system, helping to reduce MoS2 agglomeration, but also helps control the formation of a layered structure in MoS2, thereby further improving the conductivity, ion transport efficiency, and stability of the Fe-NC-coated MoS2 material. Controlling the types of molybdenum and sulfur sources within the aforementioned ranges helps enhance the interaction between the two, promoting the formation of a layered structure in MoS2, thereby further improving the conductivity, ion transport efficiency, and stability of the Fe-NC-coated MoS2 material.

[0034] In another typical embodiment of the present application, a secondary battery is provided, comprising a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode active layer, the material of the positive electrode active layer comprising Fe-NC coated MoS2 material, a positive electrode active material, a conductive agent and a binder; wherein the Fe-NC coated MoS2 material is distributed on the surface of the positive electrode active material; the mass ratio of MoS2 to Fe-NC in the Fe-NC coated MoS2 material is 1:(0.2~1), specifically 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1 and a range value between any two ratios, the molar ratio of Fe element, N element and C element in Fe-NC is (1~2):(2~4):(50~100), the structure of MoS2 is a layered structure, and the structure of Fe-NC is a porous structure.

[0035] Fe-NC has high conductivity. Fe-NC coated on the surface of MoS2 helps improve the conductivity of MoS2. MoS2's layered structure helps provide channels for rapid ion insertion and extraction. Fe-NC also has a porous structure, which is conducive to electrolyte penetration and ion diffusion. Because the above-mentioned positive electrode sheet contains Fe-NC coated on MoS2, the positive electrode sheet has high conductivity and ion transport performance. Including this positive electrode sheet in a secondary battery helps reduce the internal resistance of the secondary battery, thereby helping to improve the rate performance of the secondary battery.

[0036] In one embodiment of the present application, the mass ratio of the above-mentioned Fe-NC coated MoS2 material, positive electrode active material, conductive agent and binder is (0.3~1.2):(94.3~98.2):(0.5~1.5):(1~3).

[0037] Fe-NC coated MoS2 material has high conductivity and ion transport performance. Controlling the mass ratio of Fe-NC coated MoS2 material, positive electrode active material, conductive agent and binder within the above range helps to improve the interaction between the components, thereby improving the conductivity and ion transport performance of the positive electrode sheet without reducing the structural stability of the positive electrode sheet, thereby helping to reduce the internal resistance of the secondary battery and improve the capacity, rate performance, cycle stability and safety of the secondary battery.

[0038] In one embodiment of the present application, the powder resistivity of the Fe-NC coated MoS2 material is 10 -2 ~1Ω·cm; and / or, the average pore size of the Fe-NC coated MoS2 material is 2 to 20 nm; and / or, the porosity of the Fe-NC coated MoS2 material is 50 to 70%.

[0039] The Fe-NC-coated MoS2 material with the aforementioned powder resistivity, located on the surface of the positive electrode active material, helps improve the conductivity of the positive electrode sheet, thereby reducing the internal resistance of the secondary battery and improving the capacity, rate capability, cycle stability, and safety of the secondary battery. Controlling the average pore size and porosity of the Fe-NC-coated MoS2 material within the aforementioned ranges helps promote electrolyte penetration and ion diffusion, shortening the ion transport path, thereby accelerating ion diffusion and improving the charge and discharge rates of the secondary battery.

[0040] In one embodiment of the present application, the thickness of the Fe-NC coating layer in the above-mentioned Fe-NC coated MoS2 material is 5 to 20 nm.

[0041] Controlling the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material within the above range, on the one hand, helps to reduce the contact resistance between the MoS2 material and the current collector, thereby helping to reduce the internal resistance of the entire secondary battery; on the other hand, it helps to improve the ion transmission efficiency while improving the stability of the Fe-NC coating layer.

[0042] In one embodiment of the present application, the layered structure of MoS2 is formed by stacking MoS2 nanosheets, the average thickness of the MoS2 nanosheets is 1.2 to 4.0 nm, and the average plane diameter of the MoS2 nanosheets is 100 to 300 nm.

[0043] Controlling the thickness and planar diameter of the MoS2 nanosheets within the above range, on the one hand, helps shorten the ion transmission path, thereby helping to reduce the internal resistance of the secondary battery, and further helping to improve the rate performance of the secondary battery; on the other hand, it helps to increase the active contact area, so that the ions can more fully contact with the MoS2 material, thereby helping to increase the specific capacity of the positive electrode sheet, and further helping to improve the energy density of the secondary battery.

[0044] In one embodiment of the present application, the resistivity of the positive electrode sheet is 207.4412-248.7414 Ω·mm, and the conductivity is 0.004232-0.004732 S / mm.

[0045] In another typical embodiment of the present application, an energy storage system is provided, including a unit cell, wherein the unit cell is a secondary battery prepared by the aforementioned method for preparing a secondary battery or the aforementioned secondary battery.

[0046] Since the above energy storage system contains the secondary battery of the present application, the energy storage system has high rate performance and cycle stability.

[0047] In another typical embodiment of the present application, an electrical device is provided, including the aforementioned energy storage system, where the energy storage system is used to provide power to the electrical device.

[0048] Since the energy storage system of the above-mentioned electrical equipment contains the secondary battery of the present application, the electrical equipment has higher rate performance, cycle stability and safety.

[0049] The beneficial effects of the present application will be further illustrated below with reference to examples.

[0050] Example 1

[0051] The preparation process of secondary batteries is as follows: Figure 1 As shown, specifically, 0.03M (NH4)6Mo7O 24 4H2O, 0.4M NH2CSNH2, and 0.3mM polyvinyl pyrrolidone (number average molecular weight of 40,000Da) were dissolved in 60mL of deionized water and magnetically stirred for 30min to form a homogeneous solution. The solution was transferred to a 100mL Teflon-lined container, placed in a reactor, and subjected to a synthesis reaction at 210°C for 24h. After cooling to room temperature, the resulting product was centrifuged, washed several times with water and ethanol, and dried in vacuo at 50°C for 12h to obtain a layered MoS2 structure. The layered structure is composed of M oS2 nanosheets are stacked to form MoS2 nanosheets with an average thickness of 2.0nm and an average plane diameter of 200nm; 0.02M Fe(NO3)3·6H2O, 0.25M imidazole, 0.05M benzimidazole, and 0.01M MoS2 are dissolved in 60mL of N,N-dimethylformamide and magnetically stirred for 30min. The mixture is transferred to a 100mL Teflon liner and placed in a reactor for hydrothermal reaction at 140°C for 24h. After natural cooling, the resulting liquid is centrifuged and washed with ethanol three times and dried to obtain an iron-based metal organic framework material coated with MoS2. It is then calcined at 650°C for 2h in an argon atmosphere with a heating rate of 2°C / min to obtain a Fe-NC coated MoS2 material with a powder resistivity of 10 -1 Ω·cm; among them, the mass ratio of MoS2 to Fe-NC is 1:0.6, the molar ratio of Fe element, N element and C element in Fe-NC is 2:2:50, the average pore size of Fe-NC coated MoS2 material is 10nm, the porosity is 60%, and the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material is 12nm.

[0052] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0053] Example 2

[0054] The difference from Example 1 is that the molar ratio of MoS2, Fe(NO3)3·6H2O, imidazole and benzimidazole is 0.01:0.2:10:2, and the Fe-NC coated MoS2 material is finally obtained, and the powder resistivity is 10 -2 Ω·cm, where the mass ratio of MoS2 to Fe-NC is 1:1, the molar ratio of Fe, N and C in Fe-NC is 1:4:100, and the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material is 20 nm.

[0055] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0056] Example 3

[0057] The difference from Example 1 is that the molar ratio of MoS2, Fe(NO3)3·6H2O, imidazole and benzimidazole is 1:0.02:0.25:0.05, and the final Fe-NC coated MoS2 material is obtained, and the powder resistivity is 1Ω·cm, wherein the mass ratio of MoS2 to Fe-NC is 1:0.2, the molar ratio of Fe element, N element and C element in Fe-NC is 2:2:50, and the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material is 5nm.

[0058] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0059] Example 4

[0060] The difference from Example 1 is that the temperature of the hydrothermal reaction is 180°C, the time of the hydrothermal reaction is 28 hours, and finally the Fe-NC coated MoS2 material is obtained, the powder resistivity is 0.08Ω·cm, wherein the average pore size of the Fe-NC coated MoS2 material is 5nm, the porosity is 50%, and the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material is 15nm.

[0061] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0062] Example 5

[0063] The difference from Example 1 is that the temperature of the hydrothermal reaction is 200°C, the time of the hydrothermal reaction is 30 hours, and finally the Fe-NC coated MoS2 material is obtained, the powder resistivity is 0.05Ω·cm, wherein the average pore size of the Fe-NC coated MoS2 material is 1nm, the porosity is 45%, and the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material is 18nm.

[0064] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0065] Example 6

[0066] The difference from Example 1 is that the heating rate of the calcination treatment is 3°C / min, the calcination temperature is 750°C, and the holding time of the calcination treatment is 3h. Finally, Fe-NC coated MoS2 material is obtained, and the powder resistivity is 0.12Ω·cm. Among them, the average pore size of the Fe-NC coated MoS2 material is 13nm, the porosity is 63%, and the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material is 11nm.

[0067] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0068] Example 7

[0069] The difference from Example 1 is that the heating rate of the calcination treatment is 4°C / min, the calcination temperature is 800°C, and the holding time of the calcination treatment is 4h. Finally, Fe-NC coated MoS2 material is obtained, and the powder resistivity is 0.09Ω·cm. Among them, the average pore size of the Fe-NC coated MoS2 material is 1.5nm, the porosity is 48%, and the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material is 9nm.

[0070] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0071] Example 8

[0072] The difference from Example 1 is that lithium iron phosphate, Super-P and polyvinylidene fluoride are mixed first, and then the Fe-NC coated MoS2 material prepared above is added and continued to mix. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 0.3:98.2:1.5:3. After that, the positive electrode sheet is obtained by coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene diaphragm are stacked into a bare battery cell, and then the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, chemical formation and vacuum sealing to obtain a secondary battery.

[0073] Example 9

[0074] The difference from Example 1 is that lithium iron phosphate, Super-P and polyvinylidene fluoride are mixed first, and then the Fe-NC coated MoS2 material prepared above is added and continued to mix. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 0.1:98.2:1.5:3. After that, the positive electrode sheet is obtained by coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene diaphragm are stacked into a bare battery cell, and then the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, chemical formation and vacuum sealing to obtain a secondary battery.

[0075] Example 10

[0076] The difference from Example 1 is that (NH4)6Mo7O 24 The molar ratio of 4H2O, NH2CSNH2 and polyvinyl pyrrolidone is 0.3:4:0.01, the synthesis reaction temperature is 220℃, and the synthesis reaction time is 12h to obtain MoS2 with a layered structure. The layered structure is formed by stacking MoS2 nanosheets. The average thickness of the MoS2 nanosheets is 3nm, and the average planar diameter of the MoS2 nanosheets is 250nm. The above MoS2 is used to prepare Fe-NC coated MoS2 material.

[0077] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0078] Example 11

[0079] The difference from Example 1 is that (NH4)6Mo7O 24 The molar ratio of 4H2O, NH2CSNH2 and polyvinyl pyrrolidone is 0.3:4:0.02, the synthesis reaction temperature is 200℃, and the synthesis reaction time is 10 hours to obtain MoS2 with a layered structure. The layered structure is formed by stacking MoS2 nanosheets. The average thickness of the MoS2 nanosheets is 5nm, and the average planar diameter of the MoS2 nanosheets is 350nm. The Fe-NC-coated MoS2 material is prepared using the above MoS2.

[0080] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0081] Example 12

[0082] The difference from Example 1 is that the number average molecular weight of polyvinyl pyrrolidone is 10,000 Da, and a layered structure of MoS2 is obtained. The layered structure is formed by stacking MoS2 nanosheets. The average thickness of the MoS2 nanosheets is 1.2 nm, and the average plane diameter of the MoS2 nanosheets is 100 nm. The Fe-NC-coated MoS2 material is prepared using the above MoS2.

[0083] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0084] Example 13

[0085] The difference from Example 1 is that the number average molecular weight of polyvinyl pyrrolidone is 60,000 Da, and a layered structure of MoS2 is obtained. The layered structure is formed by stacking MoS2 nanosheets. The average thickness of the MoS2 nanosheets is 4.0 nm, and the average plane diameter of the MoS2 nanosheets is 300 nm. The Fe-NC-coated MoS2 material is prepared using the above MoS2.

[0086] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0087] Example 14

[0088] The difference from Example 1 is that the number average molecular weight of polyvinyl pyrrolidone is 80,000 Da, and a layered structure of MoS2 is obtained. The layered structure is formed by stacking MoS2 nanosheets. The average thickness of the MoS2 nanosheets is 4.8 nm, and the average plane diameter of the MoS2 nanosheets is 360 nm. The Fe-NC-coated MoS2 material is prepared using the above MoS2.

[0089] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that the addition of Fe-NC coated MoS2 material is cancelled, and lithium iron phosphate, Super-P and polyvinylidene fluoride are mixed, and the mass ratio of lithium iron phosphate, Super-P and polyvinylidene fluoride is 96.1:0.7:2. Then, the positive electrode sheet is obtained by coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene diaphragm are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that the molar ratio of MoS2, Fe(NO3)3·6H2O, imidazole and benzimidazole is 2:0.02:0.25:0.05, and the final Fe-NC coated MoS2 material is obtained, the powder resistivity is 1.8Ω·cm, wherein the mass ratio of MoS2 to Fe-NC is 1:0.11, the molar ratio of Fe element, N element and C element in Fe-NC is 2:2:50, and the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material is 2nm.

[0094] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0095] Comparative Example 3

[0096] The difference from Example 1 is that the molar ratio of MoS2, Fe(NO3)3·6H2O, imidazole and benzimidazole is 0.005:0.2:10:2, and the final Fe-NC coated MoS2 material is obtained, the powder resistivity of which is 0.007Ω·cm, wherein the mass ratio of MoS2 to Fe-NC is 1:2.3, the molar ratio of Fe element, N element and C element in Fe-NC is 1:4:100, and the thickness of the Fe-NC coating layer in the Fe-NC coated MoS2 material is 25nm.

[0097] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0098] Comparative Example 4

[0099] The difference from Example 1 is that the addition of polyvinyl pyrrolidone is eliminated to obtain MoS2, and the Fe-NC coated MoS2 material is prepared using the above MoS2.

[0100] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC coated MoS2 material prepared above is added and continued to be mixed. The mass ratio of Fe-NC coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0101] Comparative Example 5

[0102] The difference from Example 1 is that the addition of MoS2 is omitted. Instead, 0.02M Fe(NO3)3·6H2O, 0.25M imidazole, and 0.05M benzimidazole are dissolved in 60mL of N,N-dimethylformamide and magnetically stirred for 30 minutes. The mixture is then transferred to a 100mL Teflon-lined container, placed in a reactor, and hydrothermally reacted at 140°C for 24 hours. After natural cooling, the resulting liquid is centrifuged, washed three times with ethanol, and dried to obtain an iron-based metal-organic framework. This is then calcined at 650°C for 2 hours under an argon atmosphere at a heating rate of 2°C / min to obtain Fe-NC.

[0103] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the Fe-NC material prepared above is added and continued to be mixed. The mass ratio of Fe-NC, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained by coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene separator are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0104] Comparative Example 6

[0105] The difference from Example 1 is that the Fe-NC coating is cancelled, and the lithium iron phosphate, Super-P and polyvinylidene fluoride are mixed first, and then the MoS2 material prepared above is added and continued to mix. The mass ratio of MoS2, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained by coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene diaphragm are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0106] Comparative Example 7

[0107] The difference from Example 1 is that the calcination treatment is cancelled, and the lithium iron phosphate, Super-P and polyvinylidene fluoride are mixed first, and then the iron-based metal organic framework material coated MoS2 prepared above is added to continue mixing. The mass ratio of the iron-based metal organic framework material coated MoS2, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained by coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene diaphragm are stacked into a bare battery cell, and the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, chemical formation and vacuum sealing to obtain a secondary battery.

[0108] Comparative Example 8

[0109] The difference from Example 1 is that the hydrothermal reaction is cancelled, and 0.02M Fe(NO3)3·6H2O, 0.25M imidazole, 0.05M benzimidazole, and 0.01M MoS2 are dissolved in 60mL of N,N-dimethylformamide and magnetically stirred for 30min. The mixture is dried to obtain a mixed material, and then calcined at 650°C for 2h in an argon atmosphere with a heating rate of 2°C / min to obtain a MoS2 material containing Fe, N, and C elements on the surface.

[0110] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the above-prepared MoS2 material containing Fe, N and C elements on the surface is added and continued to be mixed. The mass ratio of MoS2 material containing Fe, N and C elements on the surface, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, the positive electrode sheet is obtained through coating, rolling, slitting, tab forming and cutting. The positive electrode sheet, graphite negative electrode sheet and polyethylene diaphragm are stacked into a bare battery cell, and then the bare battery cell is sequentially subjected to tab welding, packaging, liquid injection, formation and vacuum sealing to obtain a secondary battery.

[0111] Comparative Example 9

[0112] The difference from Example 1 is that the addition of Fe(NO3)3·6H2O is eliminated, and a secondary battery is finally obtained.

[0113] Comparative Example 10

[0114] The difference from Example 1 is that the addition of imidazole and benzimidazole is eliminated, and a secondary battery is finally obtained.

[0115] Performance Testing

[0116] The positive electrode sheets prepared in the examples and comparative examples were subjected to resistivity and conductivity tests, and the test results are shown in Table 1. The secondary batteries prepared in the examples and comparative examples were subjected to first discharge gram capacity tests at 0.5C and capacity retention rate tests after 1000 cycles at 0.5P at an ambient temperature of 25°C. The test results are shown in Table 1.

[0117] Table 1

[0118]

[0119] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0120] It can be seen from Table 1 that in Examples 1 to 3, as the mass of the Fe-NC coating layer increases, the conductivity of the positive electrode sheet is significantly improved, but the greater the mass of the Fe-NC coating layer, the better. From the data of the first discharge gram capacity and capacity retention rate, it can be seen that the effect of Example 1 is better than that of Examples 2 and 3; from the comparison results of Examples 1, 4 and 5, it can be seen that the temperature of the hydrothermal reaction has a more obvious effect on the average pore size and porosity of the Fe-NC coated MoS2 material. If the hydrothermal reaction temperature is too high, the average pore size and porosity of the Fe-NC coated MoS2 material decrease, affecting the transmission efficiency of lithium ions, thereby making the first discharge gram capacity and capacity retention rate of Examples 1 and 4 better than that of Example 5; from the comparison results of Examples 1, 6 and 7, it can be seen that the calcination conditions also have a certain effect on the average pore size and porosity of the Fe-NC coated MoS2 material, thereby making the first discharge gram capacity and capacity retention rate of Examples 1 and 6 better than that of Example 5. Example 7 is better; Examples 1, 8 and 9 are to adjust the proportion of Fe-NC coated MoS2 material in the positive electrode material. It can be seen from the data that the proportion of Fe-NC coated MoS2 material significantly affects the first discharge gram capacity and capacity retention rate of the battery; Examples 1, 10 and 11 regulate the thickness and surface diameter of MoS2 nanosheets by controlling the amount of polyvinyl pyrrolidone added. It can be seen from the data results that adding an appropriate amount of polyvinyl pyrrolidone helps to control the thickness and surface diameter of MoS2 nanosheets within a suitable range, thereby helping to improve the first discharge gram capacity and capacity retention rate of the battery; Examples 1, 12-14 regulate the thickness and surface diameter of MoS2 nanosheets by adjusting the number average molecular weight of polyvinyl pyrrolidone. It can be seen from the data results that polyvinyl pyrrolidone with an appropriate number average molecular weight helps to regulate the thickness and surface diameter of MoS2 nanosheets to a suitable range, thereby helping to improve the first discharge gram capacity and capacity retention rate of the battery.

[0121] From the test results of Example 1 and Comparative Example 1, it can be seen that by canceling the addition of Fe-NC coated MoS2 material, the resistivity of the positive electrode sheet is significantly improved and the conductivity is significantly reduced, which leads to the fact that the first discharge gram capacity and capacity retention rate of the battery of Comparative Example 1 are significantly lower than those of Example 1; by adjusting the mass ratio of MoS2 to Fe-NC in Comparative Examples 2 and 3, it can be seen that a mass ratio of MoS2 to Fe-NC that is too large or too small is not conducive to improving the first discharge gram capacity and capacity retention rate of the battery; in Comparative Example 4, the addition of polyvinyl pyrrolidone is canceled, which affects the morphology and structure of MoS2, thereby affecting the transmission efficiency of lithium ions, and further significantly reduces the first discharge gram capacity and capacity retention rate of the battery; in Comparative Example 5, the addition of MoS2 is canceled, although it has little effect on the resistivity and conductivity of the positive electrode sheet, but affects the lithium ion transmission efficiency of the positive electrode sheet, which also significantly reduces the first discharge gram capacity and capacity retention rate of the battery; in Comparative Example 6, the addition of Fe- The NC coating significantly affects the resistivity and conductivity of the positive electrode sheet, resulting in poor first discharge capacity in grams and capacity retention rate of the battery; in Example 7, the calcination treatment is cancelled, and the Fe-NC coating layer with high conductivity is not formed, which seriously affects the resistivity and conductivity of the positive electrode sheet, resulting in low first discharge capacity in grams and capacity retention rate of the battery; in Example 8, the hydrothermal reaction is cancelled, and the iron-based metal organic framework material is not in situ grown on the MoS2 surface to form an Fe-NC coating layer with high conductivity, so that the Fe-NC coating layer with high conductivity cannot be formed during the calcination process, resulting in a decrease in the first discharge capacity in grams and capacity retention rate of the battery; in Example 9, the addition of Fe(NO3)3·6H2O is cancelled, and in Example 10, the addition of imidazole and benzimidazole is cancelled, so that in Example 9 and Example 10, no iron-based metal organic framework material is formed during the hydrothermal reaction, so that the Fe-NC coating layer with high conductivity cannot be formed during the calcination process, resulting in a decrease in the first discharge capacity in grams and capacity retention rate of the battery.

[0122] In S1 of the present application, a molybdenum source, a sulfur source, polyvinyl pyrrolidone and water are mixed and then subjected to a synthesis reaction. The addition of polyvinyl pyrrolidone helps to prepare MoS2 with a layered structure. In S2, the raw materials of the obtained layered structure MoS2, an iron source, imidazole, benzimidazole and an organic solvent are mixed and then subjected to a hydrothermal reaction, and the molar ratio of MoS2, the iron source, imidazole and benzimidazole is controlled within the above range, which helps to form an iron-based metal organic framework material in situ growth on the surface of MoS2, and then calcination treatment is performed to obtain Fe-NC coated MoS2 material. Compared with directly mixing MoS2 with an iron-based metal organic framework material and then calcining treatment, the in situ growth helps to improve the bonding force between MoS2 and Fe-NC, thereby helping to improve the electrical conductivity between MoS2 and Fe-NC. Fe-NC has high conductivity. Fe-NC coating on the surface of MoS2 helps improve MoS2's conductivity. MoS2's layered structure provides channels for rapid ion insertion and extraction. Furthermore, the Fe-NC formed from an iron-based metal-organic framework material has a porous structure, which facilitates electrolyte penetration and ion diffusion. Adding Fe-NC-coated MoS2 material to the positive electrode sheet helps improve the sheet's conductivity and ion transport properties. Assembling this positive electrode sheet into a secondary battery helps reduce the battery's internal resistance, thereby improving the battery's rate capability.

[0123] The above are merely embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a secondary battery, characterized in that: include: S1, mixing a molybdenum source, a sulfur source, polyvinyl pyrrolidone and water and performing a synthesis reaction to obtain MoS2; S2, mixing the raw materials including the MoS2, iron source, imidazole, benzimidazole and organic solvent, performing a hydrothermal reaction, and then calcining under a protective gas to obtain a Fe-NC coated MoS2 material; S3, sequentially mixing, coating and rolling the Fe-NC coated MoS2 material, the positive electrode active material, the conductive agent and the binder to obtain a positive electrode sheet; S4, making the positive electrode sheet, the separator and the negative electrode sheet into a bare cell, assembling the bare cell with the outer shell and the top cover, and then injecting the electrolyte to obtain the secondary battery.

2. The method for preparing a secondary battery according to claim 1, wherein: The temperature of the hydrothermal reaction is 140-180° C.; and / or, the time of the hydrothermal reaction is 24-28 hours; and / or, the heating rate of the calcination treatment is 2-3° C. / min; and / or, the temperature of the calcination treatment is 650-750° C.; and / or, the holding time of the calcination treatment is 2-3 hours.

3. The method for preparing a secondary battery according to claim 2, wherein: The mass ratio of the Fe-NC coated MoS2 material, the positive electrode active material, the conductive agent and the binder is (0.3-1.2): (94.3-98.2): (0.5~1.5):(1~3); and / or, the iron source is selected from any one or more of Fe(NO3)3·6H2O, FeCl3·6H2O and FeSO4·7H2O; and / or, the organic solvent is selected from any one or more of N,N-dimethylformamide, acetonitrile and ethanol; and / or, the molar ratio of the MoS2, the iron source, the imidazole and the benzimidazole is (0.01~1):(0.02~0.2):(0.25~10):(0.05~2).

4. The method for preparing a secondary battery according to claim 1, wherein: The molar ratio of the molybdenum source, the sulfur source and the polyvinyl pyrrolidone is (0.3-1):(4-8):(0.003-0.01); and / or the temperature of the synthesis reaction is 210-220° C.; and / or the time of the synthesis reaction is 12-24 hours.

5. The method for preparing a secondary battery according to any one of claims 1 to 4, characterized in that: The number average molecular weight of the polyvinyl pyrrolidone is 10,000 to 60,000 Da; and / or the molybdenum source is selected from (NH4)6Mo7O 24 ·Any one or more of 4H2O, Na2MoO4·2H2O and (NH4)2MoS4; and / or, the sulfur source is selected from any one or more of NH2CSNH2, C2H5NS and C3H7NO2S.

6. A secondary battery comprising a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, wherein the positive electrode sheet comprises a current collector and a positive electrode active layer, characterized in that: The material of the positive electrode active layer includes Fe-NC coated MoS2 material, positive electrode active material, conductive agent, and binder; wherein the Fe-NC coated MoS2 material is distributed on the surface of the positive electrode active material; The structure of the MoS2 is a layered structure, and the structure of the Fe-NC is a porous structure.

7. The secondary battery according to claim 6, characterized in that The mass ratio of the Fe-NC coated MoS2 material, the positive electrode active material, the conductive agent and the binder is (0.3-1.2): (94.3-98.2): (0.5-1.5): (1~3); and / or, the mass ratio of MoS2 to Fe-NC in the Fe-NC coated MoS2 material is 1:(0.2~1).

8. The secondary battery according to claim 6, wherein The powder resistivity of the Fe-NC coated MoS2 material is 10 -2 ~1Ω·cm; and / or, the average pore size of the Fe-NC coated MoS2 material is 2~20nm; and / or, the porosity of the Fe-NC coated MoS2 material is 50~70%; and / or, the molar ratio of Fe element, N element and C element in the Fe-NC is (1~2):(2~4):(50~100).

9. An energy storage system comprising a unit battery, characterized in that: The unit cell is a secondary battery prepared by the method for preparing a secondary battery according to any one of claims 1 to 5 or a secondary battery according to any one of claims 6 to 8.

10. An electrical device, characterized in that: The energy storage system comprises the energy storage system according to claim 9, wherein the energy storage system is used to provide power for the electrical equipment.

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