Secondary battery, its preparation method, energy storage system and electrical equipment

Abstract

The present invention provides a secondary battery, a preparation method thereof, an energy storage system and an electrical equipment, relating to the technical field of energy storage. The preparation method includes: mixing a molybdenum source, a sulfur source, polyvinylpyrrolidone and water and then carrying out a synthesis reaction to obtain MoS2; mixing raw materials including MoS2, an iron source, imidazole, benzimidazole and an organic solvent, and then successively carrying out a hydrothermal reaction and a calcination treatment to obtain an Fe-N-C coated MoS2 material, mixing, coating and rolling with a positive electrode active material, a conductive agent and a binder in sequence to obtain a positive electrode sheet; manufacturing a bare battery cell from the positive electrode sheet, a separator and a negative electrode sheet, assembling with a housing and a top cover, and then injecting an electrolyte to obtain a secondary battery; the molar ratio of MoS2, the iron source, imidazole and benzimidazole is (0.01~1):(0.02~0.2):(0.25~10):(0.05~2). The secondary battery of the present application has a lower DC internal resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage, and in particular, to a secondary battery, a preparation method thereof, an energy storage system, and an electrical device. Background Art

[0002] Lithium-ion batteries are widely used in fields such as electric vehicles, energy storage, and consumer electronics. During the charging process, lithium ions are removed from the positive electrode material, transferred through the electrolyte to the negative electrode, and embedded in the negative electrode carbon material; at the same time, electrons are released from the positive electrode, reach the negative electrode through the external circuit, and maintain the balance of the chemical reaction. During the discharging process, lithium ions are removed from the negative electrode, reach the positive electrode through the electrolyte, and at the same time, the negative electrode releases electrons, which reach the positive electrode through the external circuit to provide energy for the outside world. During the charge and discharge process of the battery, the hindrance suffered by electrons and ions is collectively referred to as the DC internal resistance. The conductivity of the positive electrode material directly affects the DC internal resistance, and further affects the energy efficiency, cycle life, and safety of the battery. At present, lithium batteries usually 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 not ideal enough. Summary of the Invention

[0003] The main object of the present invention is to provide a secondary battery, a preparation method thereof, an energy storage system, and an electrical device to solve the problem of large DC internal resistance of secondary batteries in the prior art.

[0004] To achieve the above object, according to one aspect of the present invention, a preparation method of a secondary battery is provided, including: S1, mixing a molybdenum source, a sulfur source, polyvinylpyrrolidone, and water, and then performing a synthesis reaction to obtain MoS2; S2, mixing raw materials including MoS2, an iron source, imidazole, benzimidazole, and an organic solvent, then performing a hydrothermal reaction, and then performing a calcination treatment under a protective gas to obtain an Fe-N-C coated MoS2 material; S3, mixing, coating, and rolling the Fe-N-C coated MoS2 material, a positive electrode active material, a conductive agent, and a binder in sequence to obtain a positive electrode sheet; S4, manufacturing a bare battery cell from the positive electrode sheet, a separator, and a negative electrode sheet, assembling the bare battery cell with a housing and a top cover, and then injecting an electrolyte to obtain a secondary battery; wherein, the molar ratio of MoS2, the iron source, imidazole, and benzimidazole is (0.01~1):(0.02~0.2):(0.25~10):(0.05~2).

[0005] Further, the temperature of the above 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 heat preservation time of the calcination treatment is 2~3h.

[0006] Further, the mass ratio of the above Fe-N-C coated MoS2 material, the cathode 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.

[0007] Further, the molar ratio of the above molybdenum source, sulfur source, and polyvinylpyrrolidone 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 h.

[0008] Further, the number average molecular weight of the above polyvinylpyrrolidone is 10000~60000 Da; and / or, the molybdenum source is selected from any one or more of (NH4)6Mo7O 24 ·4H2O, Na2MoO4·2H2O, and (NH4)2MoS4; and / or, the sulfur source is selected from any one or more of NH2CSNH2, C2H5NS, and C3H7NO2S.

[0009] According to another aspect of the present invention, a secondary battery is provided, which includes a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet. The positive electrode sheet includes a current collector and a positive electrode active layer. The material of the positive electrode active layer includes a Fe-N-C coated MoS2 material, a cathode active material, a conductive agent, and a binder; wherein, the Fe-N-C coated MoS2 material is distributed on the surface of the cathode active material; the mass ratio of MoS2 to Fe-N-C in the Fe-N-C coated MoS2 material is 1:(0.2~1), the molar ratio of Fe element, N element, and C element in Fe-N-C is (1~2):(2~4):(50~100), the structure of MoS2 is a layered structure, and the structure of Fe-N-C is a porous structure.

[0010] Further, the mass ratio of the above Fe-N-C coated MoS2 material, the cathode active material, the conductive agent, and the binder is (0.3~1.2):(94.3~98.2):(0.5~1.5):(1~3).

[0011] Further, the powder resistivity of the above Fe-N-C coated MoS2 material is 10 -2 ~1 Ω·cm; and / or, the average pore diameter of the Fe-N-C coated MoS2 material is 2~20 nm; and / or, the porosity of the Fe-N-C coated MoS2 material is 50~70%.

[0012] According to another aspect of the present invention, there is provided an energy storage system including unit cells, where the unit cells are secondary batteries prepared by the preparation method of the aforementioned secondary batteries or the aforementioned secondary batteries.

[0013] According to another aspect of the present invention, there is provided an electrical equipment including the aforementioned energy storage system, and the energy storage system is used to provide power for the electrical equipment.

[0014] 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, polyvinylpyrrolidone and water are mixed and then subjected to a synthesis reaction. The addition of polyvinylpyrrolidone helps to prepare MoS2 with a layered structure. In S2, the obtained MoS2 with a layered structure, an iron source, imidazole, benzimidazole and an organic solvent raw material 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 in-situ grow and form an iron-based metal-organic framework material on the surface of MoS2. After that, a calcination treatment is carried out to obtain an Fe-N-C coated MoS2 material. Compared with directly mixing MoS2 with an iron-based metal-organic framework material and then carrying out a calcination treatment, in-situ growth helps to improve the binding force between MoS2 and Fe-N-C, thereby helping to improve the conductivity between MoS2 and Fe-N-C. Fe-N-C has high conductivity, and the coating of Fe-N-C on the surface of MoS2 helps to improve the conductivity of MoS2. The layered structure of MoS2 helps to provide channels for rapid ion insertion and extraction, and the Fe-N-C formed by the iron-based metal-organic framework material has a porous structure, which is beneficial to the penetration of the electrolyte and ion diffusion. Adding the Fe-N-C coated MoS2 material to the positive electrode sheet helps to improve the conductivity of the positive electrode sheet and improve the ion transport performance of the positive electrode sheet. Assembling the positive electrode sheet into a secondary battery helps to reduce the internal resistance of the secondary battery, thereby helping to improve the rate performance of the secondary battery. Description of the Drawings

[0015] The specification drawings forming a part of the present application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0016] Figure 1 Shows the process flow chart of the secondary battery preparation of the present application. Detailed Embodiments

[0017] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0018] As analyzed in the background art of this application, there is a problem of relatively large DC internal resistance of secondary batteries in the prior art. To solve this problem, this application provides a secondary battery, a preparation method thereof, an energy storage system, and an electrical equipment.

[0019] In a typical embodiment of this application, a preparation method of a secondary battery is provided. As Figure 1 shown, it includes: S1, mixing a molybdenum source, a sulfur source, polyvinylpyrrolidone, and water and then carrying out a synthesis reaction to obtain MoS2; S2, mixing raw materials including MoS2, an iron source, imidazole, benzimidazole, and an organic solvent and then carrying out a hydrothermal reaction, and then carrying out a calcination treatment under a protective gas to obtain an Fe-N-C coated MoS2 material; S3, mixing, coating, and rolling the Fe-N-C coated MoS2 material, a positive electrode active material, a conductive agent, and a binder in sequence to obtain a positive electrode sheet; S4, fabricating a bare battery cell from the positive electrode sheet, a separator, and a negative electrode sheet, assembling the bare battery cell with a casing and a top cover, and then injecting an electrolyte to obtain a secondary battery; wherein, the molar ratio of MoS2, the iron source, imidazole, and benzimidazole is (0.01~1):(0.02~0.2):(0.25~10):(0.05~2).

[0020] In S1 of this application, after mixing the molybdenum source, the sulfur source, polyvinylpyrrolidone, and water and carrying out a synthesis reaction, the addition of polyvinylpyrrolidone helps to prepare MoS2 with a layered structure. In S2, after mixing the obtained MoS2 with a layered structure, the iron source, imidazole, benzimidazole, and the raw materials of the organic solvent and carrying out a hydrothermal reaction, and controlling the molar ratio of MoS2, the iron source, imidazole, and benzimidazole within the above range, it helps to in-situ grow and form an iron-based metal-organic framework material on the surface of MoS2. After that, a calcination treatment is carried out to obtain an Fe-N-C coated MoS2 material. Compared with directly mixing MoS2 with an iron-based metal-organic framework material and then carrying out a calcination treatment, in-situ growth helps to improve the binding force between MoS2 and Fe-N-C, thereby helping to improve the conductivity between MoS2 and Fe-N-C. Fe-N-C has high conductivity, and Fe-N-C coating on the surface of MoS2 helps to improve the conductivity of MoS2. The layered structure of MoS2 helps to provide channels for rapid ion insertion and extraction, and the Fe-N-C formed from the iron-based metal-organic framework material has a porous structure, which is beneficial to the penetration of the electrolyte and ion diffusion. Adding the Fe-N-C coated MoS2 material to the positive electrode sheet helps to improve the conductivity of the positive electrode sheet and improve the ion transport performance of the positive electrode sheet. Assembling the positive electrode sheet into a secondary battery helps to reduce the internal resistance of the secondary battery, thereby helping to improve the rate performance of the secondary battery.

[0021] It should be noted that the positive electrode active material, the separator, the negative electrode sheet, and the electrolyte of this application can all be obtained by purchasing or through the prior art.

[0022] Including but not limited to, the above conductive agent is selected from any one or more of Super-P, carbon nanotubes, graphene, and carbon fiber; the above binder is selected from any one or more of polyvinylidene fluoride, polyvinylidene difluoride, styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid.

[0023] The function of the protective gas is to reduce the contact between the Fe-N-C coated MoS2 material and oxygen in the air. Including but not limited to, the above protective gas is selected from any one or more of nitrogen, helium, and argon.

[0024] In order to improve the uniformity of the dispersion of the Fe-N-C coated MoS2 material on the surface of the cathode active material, and thus further improve the conductivity and ion transport performance of the cathode sheet. In one embodiment of the present application, in S3 above, the cathode active material, conductive agent, and binder are first mixed, and then the Fe-N-C coated MoS2 material is added and mixed continuously to obtain a mixed material. The mixed material is successively coated and roll-pressed to obtain a cathode sheet.

[0025] In one embodiment of the present application, the temperature of the hydrothermal reaction is 140~180 °C; and / or, the time of the hydrothermal reaction is 24~28 h; 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 heat preservation time of the calcination treatment is 2~3 h.

[0026] 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 while not damaging the material, forming a uniform and stable iron-based metal-organic framework material coated on the MoS2 material. Controlling the heating rate of the calcination treatment within the above range helps to reduce the stress generated inside the material, thus helping to form a stable Fe-N-C 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 an Fe-N-C coating layer with appropriate thickness, pore size, and porosity, and helps to improve the structural stability and conductivity of the Fe-N-C coated MoS2 material while increasing the purity of the Fe-N-C coated MoS2 material, thus helping to further improve the conductivity and ion transport performance of the cathode sheet, and further helping to reduce the internal resistance of the secondary battery.

[0027] In an embodiment of the present application, the mass ratio of the above Fe-N-C coated MoS2 material, the cathode 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.

[0028] The Fe-N-C coated MoS2 material provides an additional conduction path and ion transport channels, the cathode active material provides energy storage, the addition of the conductive agent helps to improve the electron conduction ability of the cathode material, and the presence of the binder helps to have good contact between the electrode material and the current collector, as well as improve the mechanical stability of the cathode sheet. Controlling the mass ratio of the Fe-N-C coated MoS2 material, the cathode active material, the conductive agent, and the binder within the above range helps to improve the mutual synergistic effect among the components, 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.

[0029] In an embodiment of the present application, the molar ratio of the above molybdenum source, sulfur source, and polyvinylpyrrolidone 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 h.

[0030] Controlling the molar ratio of the molybdenum source, sulfur source, and polyvinylpyrrolidone within the above range helps to promote the formation of the MoS2 layered structure, making it have good ion intercalation and deintercalation channels. Controlling the temperature and time of the synthesis reaction within the above range helps to improve the integrity and stability of the MoS2 layered structure, thereby helping to improve the ion transport efficiency of the Fe-N-C coated MoS2 material, and further helping to reduce the internal resistance of the secondary battery and improve the rate performance of the secondary battery.

[0031] In an embodiment of the present application, the number average molecular weight of the above polyvinylpyrrolidone is 10000~60000 Da, specifically it can be 10000 Da, 20000 Da, 30000 Da, 40000 Da, 50000 Da, 60000 Da, and the range values between any two numerical values; and / or, the molybdenum source is selected from any one or more of (NH4)6Mo7O 24 ·4H2O, Na2MoO4·2H2O, and (NH4)2MoS4; and / or, the sulfur source is selected from any one or more of NH2CSNH2, C2H5NS, and C3H7NO2S.

[0032] Controlling the number-average molecular weight of polyvinylpyrrolidone within the above range helps, on the one hand, to provide better dispersion and stability for the synthesis reaction system and helps to reduce the agglomeration of MoS2; on the other hand, it helps to control the formation of the layered structure of MoS2, thus contributing to further improving the conductivity, ion transport efficiency and stability of the Fe-N-C coated MoS2 material. Controlling the types of molybdenum source and sulfur source within the above range helps to enhance the interaction between the two and promotes the formation of the layered structure of MoS2, thereby contributing to further improving the conductivity, ion transport efficiency and stability of the Fe-N-C coated MoS2 material.

[0033] In another typical embodiment of the present application, a secondary battery is provided, which includes a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet. The positive electrode sheet includes a current collector and a positive electrode active layer. The material of the positive electrode active layer includes an Fe-N-C coated MoS2 material, a positive electrode active material, a conductive agent and a binder; wherein, the Fe-N-C coated MoS2 material is distributed on the surface of the positive electrode active material; the mass ratio of MoS2 to Fe-N-C in the Fe-N-C coated MoS2 material is 1:(0.2 - 1), specifically it can be 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 the range values between any two ratios. The molar ratio of Fe element, N element and C element in Fe-N-C is (1 - 2):(2 - 4):(50 - 100). The structure of MoS2 is a layered structure, and the structure of Fe-N-C is a porous structure.

[0034] Fe-N-C has high conductivity. Coating Fe-N-C on the surface of MoS2 helps to improve the conductivity of MoS2. The layered structure of MoS2 helps to provide channels for rapid ion insertion and extraction, and Fe-N-C has a porous structure, which is beneficial to the penetration of the electrolyte and ion diffusion. Since the above positive electrode sheet contains Fe-N-C coated on MoS2, therefore, the positive electrode sheet has high conductivity and ion transport performance. Having this positive electrode sheet in the secondary battery helps to reduce the internal resistance of the secondary battery, thus contributing to improving the rate performance of the secondary battery.

[0035] In an embodiment of the present application, the mass ratio of the above Fe-N-C 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).

[0036] The Fe-N-C coated MoS2 material has high electrical conductivity and ion transport performance. Controlling the mass ratio of the Fe-N-C coated MoS2 material, the cathode active material, the conductive agent, and the binder within the above range helps to improve the interaction between the components, improve the electrical conductivity and ion transport performance of the cathode sheet without reducing the structural stability of the cathode 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.

[0037] In one embodiment of the present application, the powder resistivity of the above Fe-N-C coated MoS2 material is 10 -2 ~1 Ω·cm; and / or, the average pore size of the Fe-N-C coated MoS2 material is 2~20 nm; and / or, the porosity of the Fe-N-C coated MoS2 material is 50~70%.

[0038] The Fe-N-C coated MoS2 material with the above powder resistivity is located on the surface of the cathode active material, which helps to improve the electrical conductivity of the cathode 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. Controlling the average pore size and porosity of the Fe-N-C coated MoS2 material within the above range helps to promote the penetration of the electrolyte and the diffusion of ions, shorten the ion transport path, thereby helping to accelerate the diffusion rate of ions and improve the charge and discharge rate of the secondary battery.

[0039] In one embodiment of the present application, the thickness of the Fe-N-C coating layer in the above Fe-N-C coated MoS2 material is 5~20 nm.

[0040] Controlling the thickness of the Fe-N-C coating layer in the Fe-N-C 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 transport efficiency while improving the stability of the Fe-N-C coating layer.

[0041] In one embodiment of the present application, the layered structure of the above MoS2 is formed by stacking MoS2 nanosheets. The average thickness of the MoS2 nanosheets is 1.2~4.0 nm, and the average planar diameter of the MoS2 nanosheets is 100~300 nm.

[0042] Controlling the thickness and planar diameter of the MoS2 nanosheets within the above range, on the one hand, helps to shorten the ion transport 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, enabling ions to contact the MoS2 material more fully, thereby helping to improve the specific capacity of the cathode sheet and further helping to improve the energy density of the secondary battery.

[0043] In one embodiment of the present application, the resistivity of the above-mentioned positive electrode sheet is 207.4412 - 248.7414 Ω·mm, and the conductivity is 0.004232 - 0.004732 S / mm.

[0044] In another typical embodiment of the present application, an energy storage system is provided, including a unit cell, which is a secondary battery prepared by the preparation method of the aforementioned secondary battery or the aforementioned secondary battery.

[0045] Since the energy storage system contains the secondary battery of the present application, the energy storage system has high rate performance and cycle stability.

[0046] In another typical embodiment of the present application, an electrical device is provided, including the aforementioned energy storage system, and the energy storage system is used to provide power for the electrical device.

[0047] Since the energy storage system of the above-mentioned electrical device contains the secondary battery of the present application, the electrical device has high rate performance, cycle stability and safety.

[0048] The beneficial effects of the present application will be further described below in conjunction with embodiments.

[0049] Example 1

[0050] The preparation process flow of the secondary battery is as Figure 1 shown. Specifically, 0.03M of (NH4)6Mo7O 24·4H2O, 0.4 M of NH2CSNH2, 0.3 mM of polyvinylpyrrolidone (number-average molecular weight of 40,000 Da) were dissolved in 60 mL of deionized water, and magnetically stirred for 30 min to form a homogeneous solution; the solution was transferred to a 100 mL Teflon liner, placed in a reaction kettle, and synthesized at 210 °C for 24 h; after cooling to room temperature, the obtained product was centrifuged, washed several times with water and ethanol, and vacuum dried at 50 °C for 12 h to obtain MoS2 with a layered structure. The layered structure was formed by stacking MoS2 nanosheets. The average thickness of the MoS2 nanosheets was 2.0 nm, and the average planar diameter of the MoS2 nanosheets was 200 nm; 0.02 M of Fe(NO3)3·6H2O, 0.25 M of imidazole, 0.05 M of benzimidazole, and 0.01 M of MoS2 were dissolved in 60 mL of N,N-dimethylformamide, magnetically stirred for 30 min, the mixture was transferred to a 100 mL Teflon liner, placed in a reaction kettle, and hydrothermally reacted at 140 °C for 24 h. After natural cooling, the obtained liquid was centrifuged and washed 3 times with ethanol, and dried to obtain a Fe-based metal-organic framework material coated with MoS2. Then, it was calcined at 650 °C for 2 h in an argon atmosphere with a heating rate of 2 °C / min to obtain a Fe-N-C coated MoS2 material, and the powder resistivity was 10 -1 Ω·cm; wherein, the mass ratio of MoS2 to Fe-N-C is 1:0.6, the molar ratio of Fe element, N element and C element in Fe-N-C is 2:2:50, the average pore diameter of the Fe-N-C coated MoS2 material is 10 nm, the porosity is 60%, and the thickness of the Fe-N-C coating layer in the Fe-N-C coated MoS2 material is 12 nm.

[0051] Lithium iron phosphate, Super-P and polyvinylidene fluoride were first mixed, and then the above-prepared Fe-N-C coated MoS2 material was added and mixed continuously. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. Then, after coating, rolling, slitting, tab forming and blanking, a positive electrode sheet was obtained. After stacking the positive electrode sheet, the graphite negative electrode sheet and the polyethylene separator into a bare battery cell, the bare battery cell was successively subjected to tab welding, encapsulation, electrolyte injection, formation and air extraction and edge sealing to obtain a secondary battery.

[0052] Example 2

[0053] 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. Finally, a Fe-N-C coated MoS2 material was obtained, and the powder resistivity was 10 -2Ω·cm, where the mass ratio of MoS2 to Fe-N-C is 1:1, the molar ratio of Fe element, N element and C element in Fe-N-C is 1:4:100, and the thickness of the Fe-N-C coating layer in the Fe-N-C coated MoS2 material is 20 nm.

[0054] First, mix lithium iron phosphate, Super-P and polyvinylidene fluoride, and then add the prepared Fe-N-C coated MoS2 material above to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, through coating, rolling, slitting, tab forming and sheet cutting, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation and gas extraction and edge sealing to obtain a secondary battery.

[0055] Example 3

[0056] 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 finally an Fe-N-C coated MoS2 material is obtained with a powder resistivity of 1 Ω·cm. Among them, the mass ratio of MoS2 to Fe-N-C is 1:0.2, the molar ratio of Fe element, N element and C element in Fe-N-C is 2:2:50, and the thickness of the Fe-N-C coating layer in the Fe-N-C coated MoS2 material is 5 nm.

[0057] First, mix lithium iron phosphate, Super-P and polyvinylidene fluoride, and then add the prepared Fe-N-C coated MoS2 material above to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, through coating, rolling, slitting, tab forming and sheet cutting, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation and gas extraction and edge sealing to obtain a secondary battery.

[0058] Example 4

[0059] The difference from Example 1 is that the hydrothermal reaction temperature is 180 °C and the hydrothermal reaction time is 28 h. Finally, an Fe-N-C coated MoS2 material is obtained with a powder resistivity of 0.08 Ω·cm. Among them, the average pore diameter of the Fe-N-C coated MoS2 material is 5 nm, the porosity is 50%, and the thickness of the Fe-N-C coating layer in the Fe-N-C coated MoS2 material is 15 nm.

[0060] Mix lithium iron phosphate, Super-P and polyvinylidene fluoride first, then add the prepared Fe-N-C coated MoS2 material above and continue to mix. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, through coating, rolling, slitting, tab forming and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation and air extraction and edge sealing to obtain a secondary battery.

[0061] Example 5

[0062] The difference from Example 1 is that the temperature of the hydrothermal reaction is 200 °C, the time of the hydrothermal reaction is 30 h, and finally the Fe-N-C coated MoS2 material is obtained. The powder resistivity is 0.05 Ω·cm. Among them, the average pore diameter of the Fe-N-C coated MoS2 material is 1 nm, the porosity is 45%, and the thickness of the Fe-N-C coating layer in the Fe-N-C coated MoS2 material is 18 nm.

[0063] Mix lithium iron phosphate, Super-P and polyvinylidene fluoride first, then add the prepared Fe-N-C coated MoS2 material above and continue to mix. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, through coating, rolling, slitting, tab forming and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation and air extraction and edge sealing to obtain a secondary battery.

[0064] Example 6

[0065] The difference from Example 1 is that the heating rate of the calcination treatment is 3 °C / min, the temperature of the calcination treatment is 750 °C, and the holding time of the calcination treatment is 3 h. Finally, the Fe-N-C coated MoS2 material is obtained. The powder resistivity is 0.12 Ω·cm. Among them, the average pore diameter of the Fe-N-C coated MoS2 material is 13 nm, the porosity is 63%, and the thickness of the Fe-N-C coating layer in the Fe-N-C coated MoS2 material is 11 nm.

[0066] Mix lithium iron phosphate, Super-P, and polyvinylidene fluoride first, and then add the prepared Fe-N-C coated MoS2 material to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, it undergoes coating, rolling, slitting, tab forming, and blanking to obtain the positive electrode sheet. Stack the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare battery cell, and then successively perform tab welding, encapsulation, liquid injection, formation, and gas extraction and edge sealing on the bare battery cell to obtain a secondary battery.

[0067] Example 7

[0068] The difference from Example 1 is that the heating rate of the calcination treatment is 4 °C / min, the temperature of the calcination treatment is 800 °C, and the holding time of the calcination treatment is 4 h. Finally, the Fe-N-C coated MoS2 material is obtained, with a powder resistivity of 0.09 Ω·cm. Among them, the average pore size of the Fe-N-C coated MoS2 material is 1.5 nm, the porosity is 48%, and the thickness of the Fe-N-C coating layer in the Fe-N-C coated MoS2 material is 9 nm.

[0069] Mix lithium iron phosphate, Super-P, and polyvinylidene fluoride first, and then add the prepared Fe-N-C coated MoS2 material to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, it undergoes coating, rolling, slitting, tab forming, and blanking to obtain the positive electrode sheet. Stack the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare battery cell, and then successively perform tab welding, encapsulation, liquid injection, formation, and gas extraction and edge sealing on the bare battery cell to obtain a secondary battery.

[0070] Example 8

[0071] The difference from Example 1 is that lithium iron phosphate, Super-P, and polyvinylidene fluoride are mixed first, and then the prepared Fe-N-C coated MoS2 material is added to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 0.3:98.2:1.5:3. After that, it undergoes coating, rolling, slitting, tab forming, and blanking to obtain the positive electrode sheet. Stack the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare battery cell, and then successively perform tab welding, encapsulation, liquid injection, formation, and gas extraction and edge sealing on the bare battery cell to obtain a secondary battery.

[0072] Example 9

[0073] The difference from Example 1 is that lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the prepared Fe-N-C coated MoS2 material is added to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 0.1:98.2:1.5:3. Then, through coating, rolling, slitting, tab forming and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, the graphite negative electrode sheet and the polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation and air extraction and edge sealing to obtain a secondary battery.

[0074] Example 10

[0075] The difference from Example 1 is that the molar ratio of (NH4)6Mo7O 24 ·4H2O, NH2CSNH2 and polyvinylpyrrolidone is 0.3:4:0.01. The temperature of the synthesis reaction is 220 °C, and the time of the synthesis reaction is 12 h to obtain layered MoS2. The layered structure is formed by stacking MoS2 nanosheets. The average thickness of the MoS2 nanosheets is 3 nm, and the average planar diameter of the MoS2 nanosheets is 250 nm. The Fe-N-C coated MoS2 material is prepared using the above MoS2.

[0076] Lithium iron phosphate, Super-P and polyvinylidene fluoride are first mixed, and then the prepared Fe-N-C coated MoS2 material is added to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. Then, through coating, rolling, slitting, tab forming and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, the graphite negative electrode sheet and the polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation and air extraction and edge sealing to obtain a secondary battery.

[0077] Example 11

[0078] The difference from Example 1 is that the molar ratio of (NH4)6Mo7O 24 ·4H2O, NH2CSNH2 and polyvinylpyrrolidone is 0.3:4:0.02. The temperature of the synthesis reaction is 200 °C, and the time of the synthesis reaction is 10 h to obtain layered MoS2. The layered structure is formed by stacking MoS2 nanosheets. The average thickness of the MoS2 nanosheets is 5 nm, and the average planar diameter of the MoS2 nanosheets is 350 nm. The Fe-N-C coated MoS2 material is prepared using the above MoS2.

[0079] First, mix lithium iron phosphate, Super-P, and polyvinylidene fluoride, and then add the prepared Fe-N-C coated MoS2 material above to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, through coating, rolling, slitting, tab forming, and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and gas extraction and edge sealing to obtain a secondary battery.

[0080] Example 12

[0081] The difference from Example 1 is that the number-average molecular weight of polyvinylpyrrolidone is 10000 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 planar diameter of the MoS2 nanosheets is 100 nm. The Fe-N-C coated MoS2 material is prepared using the above MoS2.

[0082] First, mix lithium iron phosphate, Super-P, and polyvinylidene fluoride, and then add the prepared Fe-N-C coated MoS2 material above to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, through coating, rolling, slitting, tab forming, and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and gas extraction and edge sealing to obtain a secondary battery.

[0083] Example 13

[0084] The difference from Example 1 is that the number-average molecular weight of polyvinylpyrrolidone is 60000 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 planar diameter of the MoS2 nanosheets is 300 nm. The Fe-N-C coated MoS2 material is prepared using the above MoS2.

[0085] First, mix lithium iron phosphate, Super-P, and polyvinylidene fluoride, and then add the prepared Fe-N-C coated MoS2 material to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. Then, through coating, rolling, slitting, tab forming, and sheet cutting, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and air extraction and edge sealing to obtain a secondary battery.

[0086] Example 14

[0087] The difference from Example 1 is that the number-average molecular weight of polyvinylpyrrolidone is 80,000 Da, and layered 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 planar diameter of the MoS2 nanosheets is 360 nm. The Fe-N-C coated MoS2 material is prepared using the above MoS2.

[0088] First, mix lithium iron phosphate, Super-P, and polyvinylidene fluoride, and then add the prepared Fe-N-C coated MoS2 material to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. Then, through coating, rolling, slitting, tab forming, and sheet cutting, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and air extraction and edge sealing to obtain a secondary battery.

[0089] Comparative Example 1

[0090] The difference from Example 1 is that the addition of the Fe-N-C coated MoS2 material is cancelled, and lithium iron phosphate, Super-P, and polyvinylidene fluoride are mixed. The mass ratio of lithium iron phosphate, Super-P, and polyvinylidene fluoride is 96.1:0.7:2. Then, through coating, rolling, slitting, tab forming, and sheet cutting, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and air extraction and edge sealing to obtain a secondary battery.

[0091] Comparative Example 2

[0092] 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 finally an Fe-N-C coated MoS2 material is obtained. The powder resistivity is 1.8 Ω·cm. Among them, the mass ratio of MoS2 to Fe-N-C is 1:0.11, and the molar ratio of Fe element, N element and C element in Fe-N-C is 2:2:50. The thickness of the Fe-N-C coating layer in the Fe-N-C coated MoS2 material is 2 nm.

[0093] First, mix lithium iron phosphate, Super-P and polyvinylidene fluoride, and then add the above-prepared Fe-N-C coated MoS2 material to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. Then, through coating, rolling, slitting, tab forming and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation and air extraction and edge sealing to obtain a secondary battery.

[0094] Comparative Example 3

[0095] 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 finally an Fe-N-C coated MoS2 material is obtained. The powder resistivity is 0.007 Ω·cm. Among them, the mass ratio of MoS2 to Fe-N-C is 1:2.3, and the molar ratio of Fe element, N element and C element in Fe-N-C is 1:4:100. The thickness of the Fe-N-C coating layer in the Fe-N-C coated MoS2 material is 25 nm.

[0096] First, mix lithium iron phosphate, Super-P and polyvinylidene fluoride, and then add the above-prepared Fe-N-C coated MoS2 material to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P and polyvinylidene fluoride is 1.2:96.1:0.7:2. Then, through coating, rolling, slitting, tab forming and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet and polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation and air extraction and edge sealing to obtain a secondary battery.

[0097] Comparative Example 4

[0098] The difference from Example 1 is that the addition of polyvinylpyrrolidone is cancelled to obtain MoS2, and the Fe-N-C coated MoS2 material is prepared using the above MoS2.

[0099] First, mix lithium iron phosphate, Super-P, and polyvinylidene fluoride, and then add the prepared Fe-N-C coated MoS2 material to continue mixing. The mass ratio of the Fe-N-C coated MoS2 material, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, through coating, rolling, slitting, tab forming, and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare cell, the bare cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and air extraction and edge sealing to obtain a secondary battery.

[0100] Comparative Example 5

[0101] The difference from Example 1 is that the addition of MoS2 is cancelled. Dissolve 0.02 M of Fe(NO3)3·6H2O, 0.25 M of imidazole, and 0.05 M of benzimidazole in 60 mL of N,N-dimethylformamide, stir magnetically for 30 min, transfer the mixture to a 100 mL Teflon liner, place it in a reaction kettle, and carry out hydrothermal reaction at 140 °C for 24 h. After natural cooling, centrifuge the obtained liquid and wash it with ethanol three times, and dry it to obtain an iron-based metal-organic framework material. Then, calcine it at 650 °C for 2 h under an argon atmosphere with a heating rate of 2 °C / min to obtain Fe-N-C.

[0102] First, mix lithium iron phosphate, Super-P, and polyvinylidene fluoride, and then add the prepared Fe-N-C material to continue mixing. The mass ratio of Fe-N-C, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, through coating, rolling, slitting, tab forming, and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare cell, the bare cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and air extraction and edge sealing to obtain a secondary battery.

[0103] Comparative Example 6

[0104] The difference from Example 1 is that the coating of Fe-N-C is cancelled. First, mix lithium iron phosphate, Super-P, and polyvinylidene fluoride, and then add the prepared MoS2 material to continue mixing. The mass ratio of MoS2, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. After that, through coating, rolling, slitting, tab forming, and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, graphite negative electrode sheet, and polyethylene separator into a bare cell, the bare cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and air extraction and edge sealing to obtain a secondary battery.

[0105] Comparative Example 7

[0106] The difference from Example 1 is that the calcination treatment is cancelled. First, lithium iron phosphate, Super-P, and polyvinylidene fluoride are mixed, and then the prepared iron-based metal-organic framework material-coated MoS2 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. Then, after coating, rolling, slitting, tab forming, and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, a graphite negative electrode sheet, and a polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and air extraction and edge sealing to obtain a secondary battery.

[0107] Comparative Example 8

[0108] The difference from Example 1 is that the hydrothermal reaction is cancelled. 0.02 M of Fe(NO3)3·6H2O, 0.25 M of imidazole, 0.05 M of benzimidazole, and 0.01 M of MoS2 are dissolved in 60 mL of N,N-dimethylformamide, magnetically stirred for 30 min, and the mixture is dried to obtain a mixed material. Then, it is calcined at 650 °C for 2 h under an argon atmosphere with a heating rate of 2 °C / min to obtain a MoS2 material with Fe, N, and C elements on its surface.

[0109] First, lithium iron phosphate, Super-P, and polyvinylidene fluoride are mixed, and then the prepared MoS2 material with Fe, N, and C elements on its surface is added to continue mixing. The mass ratio of the MoS2 material with Fe, N, and C elements on its surface, lithium iron phosphate, Super-P, and polyvinylidene fluoride is 1.2:96.1:0.7:2. Then, after coating, rolling, slitting, tab forming, and blanking, a positive electrode sheet is obtained. After laminating the positive electrode sheet, a graphite negative electrode sheet, and a polyethylene separator into a bare battery cell, the bare battery cell is successively subjected to tab welding, encapsulation, liquid injection, formation, and air extraction and edge sealing to obtain a secondary battery.

[0110] Comparative Example 9

[0111] The difference from Example 1 is that the addition of Fe(NO3)3·6H2O is cancelled, and finally a secondary battery is obtained.

[0112] Comparative Example 10

[0113] The difference from Example 1 is that the addition of imidazole and benzimidazole is cancelled, and finally a secondary battery is obtained.

[0114] Performance Test

[0115] The resistivity and conductivity of the positive electrode sheets prepared in the examples and comparative examples were tested, and the test results are shown in Table 1. The secondary batteries prepared in the examples and comparative examples were tested for the first discharge specific capacity at 0.5C and the capacity retention rate after 1000 cycles at 0.5P at an ambient temperature of 25°C, and the test results are shown in Table 1.

[0116] Table 1

[0117]

[0118] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0119] As can be seen from Table 1, in Examples 1 to 3, as the mass of the Fe-N-C coating layer increased, the conductivity of the positive electrode sheet was significantly improved. However, it is not that the larger the mass of the Fe-N-C coating layer, the better. From the data of the first discharge specific capacity and the 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 hydrothermal reaction temperature has a significant effect on the average pore diameter and porosity of the Fe-N-C coated MoS2 material. When the hydrothermal reaction temperature is too high, the average pore diameter and porosity of the Fe-N-C coated MoS2 material decrease, affecting the lithium ion transport efficiency, so that the first discharge specific capacity and the capacity retention rate of Examples 1 and 4 are better than those of Example 5. From the comparison results of Examples 1, 6, and 7, it can be seen that the calcination treatment conditions also have a certain effect on the average pore diameter and porosity of the Fe-N-C coated MoS2 material, so that the first discharge specific capacity and the capacity retention rate of Examples 1 and 6 are better than those of Example 7. Examples 1, 8, and 9 are to adjust the proportion of the Fe-N-C coated MoS2 material in the positive electrode material. From the data, it can be seen that the proportion of the Fe-N-C coated MoS2 material significantly affects the first discharge specific capacity and the capacity retention rate of the battery. Examples 1, 10, and 11 control the thickness and surface diameter of the MoS2 nanosheets by controlling the addition amount of polyvinylpyrrolidone. From the data results, it can be seen that adding an appropriate amount of polyvinylpyrrolidone helps to control the thickness and surface diameter of the MoS2 nanosheets within a suitable range, thus helping to improve the first discharge specific capacity and the capacity retention rate of the battery. Examples 1, 12 to 14 regulate the thickness and surface diameter of the MoS2 nanosheets by adjusting the number average molecular weight of polyvinylpyrrolidone. From the data results, it can be seen that polyvinylpyrrolidone with a suitable number average molecular weight helps to regulate the thickness and surface diameter of the MoS2 nanosheets to a suitable range, thus helping to improve the first discharge specific capacity and the capacity retention rate of the battery.

[0120] From the test results of Example 1 and Comparative Example 1, it can be seen that by canceling the addition of the Fe-N-C coated MoS2 material, the resistivity of the positive electrode sheet increases significantly and the conductivity decreases significantly, resulting in the first discharge specific capacity and capacity retention rate of the battery in Comparative Example 1 being significantly lower than those in Example 1; from Comparative Examples 2 and 3, by adjusting the mass ratio of MoS2 to Fe-N-C, it can be seen that whether the mass ratio of MoS2 to Fe-N-C is too large or too small is not conducive to the improvement of the first discharge specific capacity and capacity retention rate of the battery; in Comparative Example 4, by canceling the addition of polyvinylpyrrolidone, the morphology and structure of MoS2 are affected, thus affecting the lithium ion transport efficiency, and further causing the first discharge specific capacity and capacity retention rate of the battery to decrease significantly; in Comparative Example 5, by canceling the addition of MoS2, although it has little effect on the resistivity and conductivity of the positive electrode sheet, it affects the lithium ion transport efficiency of the positive electrode sheet, also causing the first discharge specific capacity and capacity retention rate of the battery to decrease significantly; in Comparative Example 6, by canceling the Fe-N-C coating, the resistivity and conductivity of the positive electrode sheet are significantly affected, resulting in poor first discharge specific capacity and capacity retention rate of the battery; in Comparative Example 7, by canceling the calcination treatment, a highly conductive Fe-N-C coating layer is not formed, seriously affecting the resistivity and conductivity of the positive electrode sheet, resulting in a lower first discharge specific capacity and capacity retention rate of the battery; in Comparative Example 8, by canceling the hydrothermal reaction, an iron-based metal-organic framework material is not in-situ grown on the surface of MoS2, so that a highly conductive Fe-N-C coating layer cannot be formed during the calcination process, resulting in a decrease in the first discharge specific capacity and capacity retention rate of the battery; in Comparative Example 9, by canceling the addition of Fe(NO3)3·6H2O, and in Comparative Example 10, by canceling the addition of imidazole and benzimidazole, no iron-based metal-organic framework material is formed during the hydrothermal reaction in Comparative Example 9 and Comparative Example 10, so that a highly conductive Fe-N-C coating layer cannot be formed during the calcination process, resulting in a decrease in the first discharge specific capacity and capacity retention rate of the battery.

[0121] In S1 of the present application, a molybdenum source, a sulfur source, polyvinylpyrrolidone, and water are mixed and then subjected to a synthesis reaction. The addition of polyvinylpyrrolidone helps to prepare MoS2 with a layered structure. In S2, the obtained MoS2 with a layered structure, an iron source, imidazole, benzimidazole, and a raw material of an organic solvent are mixed and then subjected to a hydrothermal reaction, and controlling the molar ratio of MoS2, the iron source, imidazole, and benzimidazole within the above range helps to in-situ grow a iron-based metal-organic framework material on the surface of MoS2. After that, a calcination treatment is carried out to obtain an Fe-N-C-coated MoS2 material. Compared with directly mixing MoS2 with an iron-based metal-organic framework material and then carrying out a calcination treatment, in-situ growth helps to improve the binding force between MoS2 and Fe-N-C, thereby helping to improve the conductivity between MoS2 and Fe-N-C. Fe-N-C has high conductivity, and coating Fe-N-C on the surface of MoS2 helps to improve the conductivity of MoS2. The layered structure of MoS2 helps to provide channels for rapid insertion and extraction of ions, and the Fe-N-C formed by the iron-based metal-organic framework material has a porous structure, which is beneficial to the penetration of the electrolyte and ion diffusion. Adding the Fe-N-C-coated MoS2 material to the positive electrode sheet helps to improve the conductivity of the positive electrode sheet and improve the ion transport performance of the positive electrode sheet. Assembling the positive electrode sheet into a secondary battery helps to reduce the internal resistance of the secondary battery, thereby helping to improve the rate performance of the secondary battery.

[0122] The above are only embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a secondary battery, characterized in that, Including: S1. Mix a molybdenum source, a sulfur source, polyvinylpyrrolidone, and water, and then conduct a synthesis reaction to obtain MoS2; S2. Mix raw materials including the MoS2, an iron source, imidazole, benzimidazole, and an organic solvent, conduct a hydrothermal reaction, and then conduct a calcination treatment under a protective gas to obtain an Fe-N-C coated MoS2 material; S3. Mix, coat, and roll press the Fe-N-C coated MoS2 material, a cathode active material, a conductive agent, and a binder in sequence to obtain a cathode sheet; S4. Fabricate a bare battery cell from the cathode sheet, a separator, and an anode sheet, assemble the bare battery cell with a casing and a top cover, and then inject an electrolyte to obtain the secondary battery; wherein, 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).

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 h; 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 heat preservation time of the calcination treatment is 2~3 h.

3. The method for preparing a secondary battery according to claim 1, characterized in that, The mass ratio of the Fe-N-C coated MoS2 material, the cathode 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.

4. The manufacturing method of the secondary battery according to claim 1, characterized in that, The molar ratio of the molybdenum source, the sulfur source, and the polyvinylpyrrolidone 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 h.

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 polyvinylpyrrolidone is 10,000 to 60,000 Da; and / or, the molybdenum source is selected from any one or more of (NH4)6Mo7O 24 ·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 cathode active layer includes an Fe-N-C coated MoS2 material, a cathode active material, a conductive agent, and a binder; wherein, the Fe-N-C coated MoS2 material is distributed on the surface of the cathode active material; the mass ratio of MoS2 to Fe-N-C in the Fe-N-C coated MoS2 material is 1:(0.2~1), the molar ratio of Fe element, N element, and C element in the Fe-N-C is (1~2):(2~4):(50~100), the structure of the MoS2 is a layered structure, and the structure of the Fe-N-C is a porous structure.

7. The secondary battery according to claim 6, wherein The mass ratio of the Fe-N-C coated MoS2 material, the cathode active material, the conductive agent, and the binder is (0.3~1.2):(94.3~98.2):(0.5~1.5):(1~3).

8. The secondary battery according to claim 6 or 7, characterized in that, The powder resistivity of the Fe-N-C coated MoS2 material is 10 -2 ~1 Ω·cm; and / or, the average pore size of the Fe-N-C coated MoS2 material is 2~20 nm; and / or, the porosity of the Fe-N-C coated MoS2 material is 50~70%.

9. A energy storage system, comprising unit cells, 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, It includes the energy storage system according to claim 9, and the energy storage system is used to provide power for the electrical equipment.

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