Lithium iron manganese phosphate positive electrode material and preparation method thereof

Abstract

The application provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof. The lithium manganese iron phosphate positive electrode material comprises a positive electrode material core and a coating layer coated on the surface of the positive electrode material core; the chemical general formula of the positive electrode material core is LiMn x Fe 1‑x PO4, wherein 0.5<=x<=0.8; the coating layer comprises an inner coating layer and an outer coating layer which are sequentially stacked, and the inner coating layer is arranged in contact with the positive electrode material core; the inner coating layer comprises a carbon layer; and the outer coating layer comprises poly (3,4-ethylenedioxythiophene) : polystyrene sulfonate and silver nanowires. The silver nanowires can improve the conductivity of the lithium manganese iron phosphate positive electrode material; and the poly (3,4-ethylenedioxythiophene) : polystyrene sulfonate has flexibility and can relieve the volume expansion of the lithium manganese iron phosphate active material during the charging and discharging process. The lithium manganese iron phosphate positive electrode material has the performance advantages of low resistance, high capacity, high compaction and high cycle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium manganese iron phosphate cathode material, in particular to a lithium manganese iron phosphate cathode material and a preparation method thereof. BACKGROUND

[0002] At present, the cathode material of lithium ion battery mainly includes lithium cobalt oxide (LCO), ternary material (NCM) and lithium iron phosphate (LFP). With the popularity of electric vehicles and the gradual increase in demand for energy storage batteries, the safety of batteries is gradually improved. In addition to the improvement of battery design technology (such as blade battery, CTP technology, etc.), the research and development of new materials is also particularly important. LFP gradually becomes the main cathode material of electric vehicles or energy storage batteries due to its high safety, but the development of energy density of LFP battery has almost reached its limit, and there is little room for performance improvement. The crystal structure of lithium manganese iron phosphate (LMFP) is similar to that of LFP, and LMFP also has the characteristics of stable chemical properties and excellent safety performance. At the same time, the manganese element doped in LMFP can increase the charging voltage of the cathode material, which can increase the charging voltage from 3.4V of LFP to 4.1V, so that the theoretical energy density of LMFP battery is increased by 15-20%, thereby further expanding the cruising range of lithium ion battery. At the same time, not only the safety performance of LMFP is better than that of NCM, but also the energy density of LMFP is higher than that of LFP, and the dependence of LMFP on rare metals is low, which can be produced in line with LFP, so that the cost advantage is obvious. However, the problems of LMFP compared with iron lithium material, such as poor conductivity, low compaction density and poor cycle performance caused by manganese dissolution in the cycle process, become the bottleneck of large-scale application. At present, it is urgent to develop a lithium manganese iron phosphate material with low resistance, high capacity and high compaction performance to meet the demand of high energy density lithium ion battery cathode material. SUMMARY

[0003] The main purpose of the present application is to provide a lithium manganese iron phosphate cathode material and a preparation method thereof, so as to solve the problems of poor conductivity, low capacity and compaction density and poor cycle performance caused by manganese dissolution in the cycle process of the lithium manganese iron phosphate cathode material in the prior art.

[0004] In order to achieve the above purpose, according to one aspect of the present application, a lithium manganese iron phosphate cathode material is provided, which includes a cathode material core and a coating layer coated on the surface of the cathode material core; the chemical formula of the cathode material core is LiMn x Fe 1-xPO4, wherein 0.5≤x≤0.8; the coating layer comprises an inner coating layer and an outer coating layer which are stacked in sequence, the inner coating layer is arranged in contact with the inner core of the positive electrode material; the inner coating layer comprises a carbon layer; and the outer coating layer comprises poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and silver nanowires.

[0005] The coating layer of the lithium iron manganese phosphate positive electrode material comprises an inner coating layer and an outer coating layer which are stacked in sequence, wherein the inner coating layer is arranged in contact with the inner core of the positive electrode material, and the inner coating layer comprises a carbon layer, which can improve the compaction density of the lithium iron manganese phosphate positive electrode material. The outer coating layer comprises poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and silver nanowires, which can reinforce the surface structure of the lithium iron manganese phosphate positive electrode material, thereby preventing the dissolution of manganese in the lithium iron manganese phosphate, and further improving the cycle performance of the lithium iron manganese phosphate positive electrode material. The lithium iron manganese phosphate positive electrode material has the performance advantages of low resistance, high capacity, high compaction, high cycle, etc.

[0006] Further, the carbon layer comprises carbon fibers; and / or, the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate has a network structure, the silver nanowires have a linear structure, and the silver nanowires are inserted into the network structure of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate; and / or, the mass ratio of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate to the silver nanowires is 3-3.2:1.8-2.1.

[0007] Preferably, the carbon layer comprises carbon fibers, which not only have regular shape and dense texture, but also have unique fiber structure, thereby further improving the compaction density of the lithium iron manganese phosphate positive electrode material. Preferably, the mass ratio of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate to the silver nanowires and the structure of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and the silver nanowires are within the above ranges, and the silver nanowires are inserted into the network structure of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, thereby further reinforcing the surface structure of the lithium iron manganese phosphate positive electrode material, further reducing the dissolution of manganese in the lithium iron manganese phosphate, and further improving the cycle performance of the lithium iron manganese phosphate positive electrode material.

[0008] Further, the mass ratio of the inner coating layer, the outer coating layer and the inner core of the positive electrode material is 0.5-1.2:0.8-1.1:7.8-8.2.

[0009] Preferably, the mass ratio of the inner coating layer, the outer coating layer and the inner core of the positive electrode material is controlled within the above ranges, thereby improving the synergistic effect of the inner coating layer, the outer coating layer and the inner core of the positive electrode material, and further improving the structural stability of the lithium iron manganese phosphate positive electrode material.

[0010] Further, the diameter of the silver nanowires is 30-200 nm, and / or the length of the silver nanowires is 10-30 μm.

[0011] Preferably, the diameter and length of the silver nanowires are controlled in the above range, which not only helps to further improve the conductivity of the lithium iron manganese phosphate positive electrode material, but also helps to improve the synergistic effect with the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and the silver nanowires, thereby further reinforcing the surface structure of the lithium iron manganese phosphate positive electrode material.

[0012] According to another aspect of the present application, a preparation method of the above lithium iron manganese phosphate positive electrode material is provided, which comprises: step S1, sequentially performing first mixing, first drying and sintering on raw materials comprising a carbon source, a first solvent, a lithium source, an iron source, a manganese source and a phosphorus source to obtain a precursor; step S2, performing second mixing on raw materials comprising the precursor and a second solvent to obtain a precursor mixed solution; step S3, performing third mixing on raw materials comprising poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, silver nanowires and a third solvent to obtain a first mixed solution; and step S4, sequentially performing coaxial electrospinning and second drying on raw materials comprising the precursor mixed solution and the first mixed solution to obtain the lithium iron manganese phosphate positive electrode material; wherein the coaxial electrospinning is completed in a coaxial double-layer syringe, the coaxial double-layer syringe comprises, from the axis outward, an inner layer containing cavity and an outer layer containing cavity which are sequentially arranged in the same axial direction; the precursor mixed solution is used as a core layer solution, and the core layer solution is located in the inner layer containing cavity; the first mixed solution is used as a shell layer solution, and the shell layer solution is located in the outer layer containing cavity.

[0013] The process of electrospinning in step S4 can prepare the lithium iron manganese phosphate positive electrode material with nanoscale fibers, and the fibers are in contact with each other to form a good conductive network, and the coaxial design can achieve better coating of the coating layer, thereby providing better protection for the lithium iron manganese phosphate positive electrode material. Specifically, in step S4, the precursor mixed solution is used as a core layer solution, and the first mixed solution is used as a shell layer solution, which are respectively injected into the inner layer containing cavity and the outer layer containing cavity of the coaxial double-layer syringe, so that the coaxial electrospinning can be completed in the coaxial double-layer syringe, thereby achieving a better coating effect. The preparation method of the present application not only has simple steps, but also has low cost.

[0014] Further, step S1 above also includes: step S11, mixing a carbon source with a first solvent to obtain a first solution; and step S12, sequentially performing a first mixing, a first drying, and sintering on raw materials including the first solution, a lithium source, an iron source, a manganese source, and a phosphorus source to obtain a precursor; wherein the mass ratio of the carbon source to the volume of the first solvent is 1.2–3.1 g / L; and / or, based on lithium in the lithium source, iron in the iron source, manganese in the manganese source, and phosphorus in the phosphorus source, the molar ratio of the lithium source, iron source, manganese source, and phosphorus source is 1.01–1.03:0.2–0.5:0.5–0.8:1; and / or, the first mixing... The mixing speed is 80-1000 rpm; and / or, the first mixing time is 40-90 min; and / or, the first mixing temperature is 20-40℃; preferably, the first mixing is carried out at a speed of 80-150 rpm for 30-60 min, followed by a further mixing at a speed of 500-1000 rpm for 10-30 min; and / or, the first drying method is drying, preferably at a temperature of 45℃-100℃, and / or, the drying time is 8-10 h; and / or, the sintering temperature is 500-700℃; and / or, the sintering time is 3-5 h; and / or, the sintering atmosphere is nitrogen and / or argon.

[0015] A first solution is obtained by mixing a carbon source and a first solvent. The first solution is then mixed with a lithium source, an iron source, a manganese source, and a phosphorus source. Preferably, the rotation speed, time, and temperature of the first mixing are controlled within the aforementioned ranges. This helps to improve the mixing uniformity of the raw materials, thereby facilitating the formation of a uniformly coated carbon layer on the surface of the cathode material core. Further preferably, the mass ratio of the carbon source to the volume of the first solvent, the molar ratio of the lithium source, iron source, manganese source, and phosphorus source, the first drying method being drying, and the drying temperature and time, as well as the sintering temperature, time, and atmosphere being within the aforementioned ranges, help to form a regularly shaped and dense carbon layer, thereby further improving the compaction density of the lithium manganese iron phosphate cathode material.

[0016] Further, the carbon source is selected from any one or more of polyacrylonitrile, glucose, and acetic acid; and / or, the first solvent, the second solvent, and the third solvent are each independently selected from any one or more of water, ethanol, and N,N-dimethylformamide; and / or, the lithium source is selected from any one or more of lithium carbonate, lithium dihydrogen phosphate, lithium hydrogen phosphate, and lithium hydroxide; and / or, the iron source is selected from any one or more of ferric oxide, ferric phosphate, and ferrous oxalate; and / or, the manganese source is selected from any one or more of manganese carbonate, manganese phosphate, manganese trioxide, and manganese tetroxide; and / or, the phosphorus source is selected from any one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, ferric phosphate, and manganese phosphate.

[0017] Preferring carbon, lithium, iron, manganese, and phosphorus sources, and selecting first, second, and third solvents within the aforementioned ranges helps to further improve the structural stability and compaction density of the precursor.

[0018] Further, in step S2 above, the ratio of the mass of the precursor to the volume of the second solvent is 1.9 to 4.2 g / L; and / or, the temperature of the second mixing is 20 to 45°C; and / or, the rotation speed of the second mixing is 80 to 150 rpm; and / or, the time of the second mixing is 30 to 60 min.

[0019] Preferably controlling the mass of the precursor, the volume ratio of the second solvent, the temperature, rotation speed, and time of the second mixing within the above ranges helps to uniformly disperse the precursor in the second solvent, thereby facilitating subsequent coaxial electrospinning.

[0020] Further, in step S3 above, the mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires is 3-3.2:1.8-2.1; and / or, the ratio of the total mass of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires to the volume of the third solvent is 1.2-3.3 g / L; and / or, the temperature of the third mixing is 20-40°C; and / or, the rotation speed of the third mixing is 80-300 rpm; and / or, the time of the third mixing is 30-60 min.

[0021] Preferred control of the mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires, the ratio of the total mass of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires to the volume of the third solvent, and the temperature, rotation speed and time of the third mixing within the above ranges helps to further improve the uniformity of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires, thereby helping to form a structurally reinforced coating layer, which in turn helps to reduce the dissolution of manganese in lithium manganese iron phosphate.

[0022] Furthermore, step S4 further includes: introducing the core layer solution and the shell layer solution into the inner layer receiving cavity and the outer layer receiving cavity, respectively; connecting the coaxial double-layer syringe with the matching coaxial needle and performing coaxial electrospinning; wherein, the coaxial needle includes an inner needle and an outer needle that are sequentially wrapped around the same axis from the axis outward; preferably, the inner diameter of the inner needle is 0.01-0.1 mm; preferably, the inner diameter of the outer needle is 0.2-0.3 mm; and / or, the mass ratio of the first mixture to the precursor mixture is 1:1.2-1.8; and / or, the voltage of the coaxial electrospinning is 25-30 KV; and / or, the second drying method is drying, preferably the drying temperature is 45-100℃, and / or, the drying time is 8-10 h.

[0023] Step S4 above facilitates the construction of the carbon layer coating and conductive network, achieving one-step coating with excellent electrical performance. Preferably, controlling the inner diameter of the inner needle within the above range helps to further regulate particle size, thereby improving compaction size, coating uniformity, and coating thickness of the inner coating layer. Preferably, controlling the inner diameter of the outer needle within the above range helps to further regulate the thickness of the carbon coating and conductive network, appropriately suppressing the growth of the main material, and regulating the coating uniformity and coating thickness of the outer coating layer. Preferably, the inner diameters of both the inner and outer needles are within the above ranges, which helps to obtain lithium manganese iron phosphate cathode material with controllable particle size through their synergistic effect.

[0024] Applying the technical solution of this invention, the coating layer of the lithium manganese iron phosphate cathode material of this application includes an inner coating layer and an outer coating layer stacked sequentially. The inner coating layer is in contact with the core of the cathode material and includes a carbon layer. This carbon layer is not only regularly shaped but also densely packed, thereby increasing the compaction density of the lithium manganese iron phosphate cathode material. The outer coating layer includes poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires. The silver nanowires possess excellent conductivity, which can improve the conductivity of the lithium manganese iron phosphate cathode material. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate is a high-molecular-weight polymer that not only has better coating capabilities but also possesses high conductivity and high stability. Furthermore, it is flexible, which can alleviate the volume expansion of the lithium manganese iron phosphate active material during charging and discharging, thereby stabilizing the overall structure of the lithium manganese iron phosphate active material. Furthermore, on the one hand, the outer coating layer can prevent the corrosion of hydrofluoric acid and suppress side reactions generated on the particle surface during cycling, thereby reducing the charge transfer resistance on the surface of the lithium manganese iron phosphate active material. On the other hand, in the microstructure of the outer coating layer, the combination of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires can strengthen the surface structure of the lithium manganese iron phosphate cathode material, thereby preventing the dissolution of manganese from lithium manganese iron phosphate and improving the cycling performance of the lithium manganese iron phosphate cathode material. In summary, the lithium manganese iron phosphate cathode material of the present invention has advantages such as low resistance, high capacity, high compaction, and high cycling performance. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0026] As analyzed in the background section of this application, the prior art has problems such as poor conductivity, low capacity and compaction density of lithium manganese iron phosphate cathode materials, and poor cycle performance due to manganese leaching. In order to solve the above problems, this application provides a lithium manganese iron phosphate cathode material and its preparation method.

[0027] In a typical embodiment of this application, a lithium manganese iron phosphate cathode material is provided, comprising a cathode material core and a coating layer covering the surface of the cathode material core; the general chemical formula of the cathode material core is LiMn. x Fe 1-x PO4, wherein 0.5≤x≤0.8; the coating layer includes an inner coating layer and an outer coating layer stacked sequentially, the inner coating layer being in contact with the core of the positive electrode material; the inner coating layer includes a carbon layer; the outer coating layer includes poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires.

[0028] The lithium manganese iron phosphate cathode material coating layer of this application includes an inner coating layer and an outer coating layer stacked sequentially. The inner coating layer is in contact with the core of the cathode material and includes a carbon layer. This carbon layer is not only regularly shaped but also densely packed, thereby increasing the compaction density of the lithium manganese iron phosphate cathode material. The outer coating layer includes poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires. The silver nanowires possess excellent conductivity, which improves the conductivity of the lithium manganese iron phosphate cathode material. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate is a high-molecular-weight polymer that not only has better coating capabilities but also high conductivity and high stability. Furthermore, it is flexible, which can alleviate the volume expansion of the lithium manganese iron phosphate active material during charging and discharging, thereby stabilizing the overall structure of the lithium manganese iron phosphate active material. Furthermore, on the one hand, the outer coating layer can prevent the corrosion of hydrofluoric acid and suppress side reactions generated on the particle surface during cycling, thereby reducing the charge transfer resistance on the surface of the lithium manganese iron phosphate active material. On the other hand, in the microstructure of the outer coating layer, the combination of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires can strengthen the surface structure of the lithium manganese iron phosphate cathode material, thereby preventing the dissolution of manganese from lithium manganese iron phosphate and improving the cycling performance of the lithium manganese iron phosphate cathode material. In summary, the lithium manganese iron phosphate cathode material of the present invention has advantages such as low resistance, high capacity, high compaction, and high cycling performance.

[0029] In one embodiment of this application, the carbon layer comprises carbon fibers; and / or, the structure of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate is a network, and the structure of the silver nanowires is linear, with the silver nanowires interspersed in the network structure of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate; and / or, the mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate to silver nanowires is 3-3.2:1.8-2.1.

[0030] The preferred carbon layer comprises carbon fibers, which are not only regularly shaped and densely packed, but also possess a unique fibrous structure, thereby contributing to further improving the compaction density of the lithium manganese iron phosphate cathode material. The preferred mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires, as well as the structure of the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires within the aforementioned range, with the silver nanowires interspersed within the network structure of the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, helps to further strengthen the surface structure of the lithium manganese iron phosphate cathode material, thereby helping to further reduce the dissolution of manganese in lithium manganese iron phosphate, and thus further contributing to improving the cycle performance of the lithium manganese iron phosphate cathode material.

[0031] In one embodiment of this application, the mass ratio of the inner coating layer, the outer coating layer, and the cathode material core is 0.5–1.2: 0.8–1.1: 7.8–8.2.

[0032] Preferably controlling the mass ratio of the inner coating layer, outer coating layer, and cathode material core within the above range helps to improve the synergistic effect of the inner coating layer, outer coating layer, and cathode material core, thereby further improving the structural stability of lithium manganese iron phosphate cathode material.

[0033] In one embodiment of this application, the diameter of the silver nanowire is 30-200 nm, and / or the length of the silver nanowire is 10-30 μm.

[0034] Preferably controlling the diameter and length of silver nanowires within the aforementioned range not only helps to further improve the conductivity of lithium manganese iron phosphate cathode materials, but also helps to enhance the synergistic effect with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires, thereby further strengthening the surface structure of lithium manganese iron phosphate cathode materials.

[0035] In another typical embodiment of this application, a method for preparing the above-mentioned lithium manganese iron phosphate cathode material is provided. The method includes: step S1, sequentially mixing, drying, and sintering raw materials comprising a carbon source, a first solvent, a lithium source, an iron source, a manganese source, and a phosphorus source to obtain a precursor; step S2, mixing the raw materials comprising the precursor and a second solvent to obtain a precursor mixture; and step S3, mixing the raw materials comprising poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, silver nanowires, and a third solvent... A third mixing process is performed to obtain a first mixture; and in step S4, the raw materials including the precursor mixture and the first mixture are sequentially subjected to coaxial electrospinning and a second drying to obtain lithium manganese iron phosphate cathode material; wherein, the coaxial electrospinning is completed in a coaxial double-layer syringe, and the coaxial double-layer syringe includes an inner layer cavity and an outer layer cavity that are sequentially arranged around the same axis from the axis outward; the precursor mixture is used as the core layer solution, and the core layer solution is located in the inner layer cavity; the first mixture is used as the shell layer solution, and the shell solution is located in the outer layer cavity.

[0036] This application utilizes the electrospinning process in step S4 to prepare lithium manganese iron phosphate cathode materials with nanoscale fibers. The fibers form a good conductive network through mutual contact, and the coaxial design allows for better coating, thus providing better protection for the lithium manganese iron phosphate cathode material. Specifically, in step S1, a first mixing of carbon source, first solvent, lithium source, iron source, manganese source, and phosphorus source ensures uniform dispersion of the raw materials. After a first drying and sintering process, a cathode material core with a certain crystal structure and an inner coating carbon layer covering the surface of the cathode material core can be rapidly formed. In step S2, a second mixing of raw materials including the precursor and second solvent facilitates subsequent coaxial electrospinning. Step S3 ensures uniform mixing of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires, thereby forming a uniform coating layer. In step S4, the precursor mixture is used as the core layer solution, and the first mixture is used as the shell layer solution. These are injected into the inner and outer accommodating cavities of the coaxial double-layer syringe, respectively. This allows for further coaxial electrospinning within the syringe, resulting in a better coating effect. The preparation method described in this application is not only simple in its steps but also low in cost.

[0037] In one embodiment of this application, step S1 further includes: step S11, mixing a carbon source with a first solvent to obtain a first solution; and step S12, sequentially performing a first mixing, a first drying, and a sintering of raw materials including the first solution, a lithium source, an iron source, a manganese source, and a phosphorus source to obtain a precursor; wherein the mass ratio of the carbon source to the volume of the first solvent is 1.2–3.1 g / L; and / or, based on lithium in the lithium source, iron in the iron source, manganese in the manganese source, and phosphorus in the phosphorus source, the molar ratio of the lithium source, iron source, manganese source, and phosphorus source is 1.01–1.03:0.2–0.5:0.5–0.8:1; and / or The first mixing speed is 80-1000 rpm; and / or the first mixing time is 40-90 min; and / or the first mixing temperature is 20-40°C; preferably, the first mixing is carried out at a speed of 80-150 rpm for 30-60 min, followed by mixing at a speed of 500-1000 rpm for 10-30 min; and / or the first drying method is drying, preferably at a temperature of 45°C-100°C, and / or at a drying time of 8-10 h; and / or the sintering temperature is 500-700°C; and / or the sintering time is 3-5 h; and / or the sintering atmosphere is nitrogen and / or argon.

[0038] A first solution is obtained by mixing a carbon source and a first solvent. The first solution is then mixed with a lithium source, an iron source, a manganese source, and a phosphorus source. Preferably, the rotation speed, time, and temperature of the first mixing are controlled within the aforementioned ranges. This helps to improve the mixing uniformity of the raw materials, thereby facilitating the formation of a uniformly coated carbon layer on the surface of the cathode material core. Further preferably, the mass ratio of the carbon source to the volume of the first solvent, the molar ratio of the lithium source, iron source, manganese source, and phosphorus source, and the first drying method being drying, with the drying temperature and time, as well as the sintering temperature, time, and atmosphere within the aforementioned ranges, help to form a regularly shaped and dense carbon layer, thereby further improving the compaction density of the lithium manganese iron phosphate cathode material.

[0039] To further improve the structural stability and compaction density of the precursor, in one embodiment of this application, the carbon source is selected from any one or more of polyacrylonitrile (PAN), glucose, and acetic acid; and / or, the first solvent, the second solvent, and the third solvent are each independently selected from any one or more of water, ethanol, and N,N-dimethylformamide (DMF); and / or, the lithium source is selected from any one or more of lithium carbonate, lithium dihydrogen phosphate, lithium hydrogen phosphate, and lithium hydroxide; and / or, the iron source is selected from any one or more of ferric oxide, ferric phosphate, and ferrous oxalate; and / or, the manganese source is selected from any one or more of manganese carbonate, manganese phosphate, manganese trioxide, and manganese tetroxide; and / or, the phosphorus source is selected from any one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, ferric phosphate, and manganese phosphate.

[0040] In one embodiment of this application, in step S2 above, the mass ratio of the precursor to the volume of the second solvent is 1.9 to 4.2 g / L; and / or, the temperature of the second mixing is 20 to 45°C; and / or, the rotation speed of the second mixing is 80 to 150 rpm; and / or, the time of the second mixing is 30 to 60 min.

[0041] Preferably controlling the mass of the precursor and the volume ratio of the second solvent, as well as the temperature, rotation speed, and time of the second mixing, within the aforementioned ranges helps to uniformly disperse the precursor in the second solvent, thereby facilitating subsequent coaxial electrospinning.

[0042] In one embodiment of this application, in step S3 above, the mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires is 3-3.2:1.8-2.1; and / or, the ratio of the total mass of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires to the volume of the third solvent is 1.2-3.3 g / L; and / or, the temperature of the third mixing is 20-40°C; and / or, the rotation speed of the third mixing is 80-300 rpm; and / or, the time of the third mixing is 30-60 min.

[0043] Preferred control of the mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires, the ratio of the total mass of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires to the volume of the third solvent, and the temperature, rotation speed and time of the third mixing within the above ranges helps to further improve the uniformity of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires, thereby helping to form a structurally reinforced coating layer, which in turn helps to reduce the dissolution of manganese in lithium manganese iron phosphate.

[0044] In one embodiment of this application, step S4 further includes introducing the core layer solution and the shell layer solution into the inner layer receiving cavity and the outer layer receiving cavity, respectively; connecting the coaxial double-layer syringe with the matching coaxial needle, and then performing coaxial electrospinning; wherein, the coaxial needle includes an inner needle and an outer needle that are sequentially wrapped around the same axis from the axis outward; preferably, the inner diameter of the inner needle is 0.01-0.1 mm; preferably, the inner diameter of the outer needle is 0.2-0.3 mm; and / or, the mass ratio of the first mixture to the precursor mixture is 1:1.2-1.8; and / or, the voltage of the coaxial electrospinning is 25-30 KV; and / or, the second drying method is drying, preferably the drying temperature is 45-100°C, and / or, the drying time is 8-10 h.

[0045] By introducing the precursor mixture as the core layer solution and the first mixture as the shell layer solution into the inner and outer accommodating cavities of a coaxial double-layer syringe, respectively, and connecting the coaxial double-layer syringe to a matching coaxial needle, coaxial electrospinning is performed. This facilitates the carbon layer coating and the construction of the conductive network, achieving one-step coating with excellent electrical properties. Preferably, controlling the inner diameter of the inner needle within the aforementioned range helps to further regulate particle size, thereby improving compaction size, coating uniformity, and coating thickness of the inner coating layer. Preferably, controlling the inner diameter of the outer needle within the aforementioned range helps to further regulate the thickness of the carbon coating and the conductive network, appropriately suppressing the growth of the main material, and regulating the coating uniformity and coating thickness of the outer coating layer. Preferably, the inner diameters of both the inner and outer needles are within the aforementioned ranges, which helps to obtain lithium manganese iron phosphate cathode materials with controllable particle size through their synergistic effect. Preferred control of the mass ratio of the first mixture and the precursor mixture, the voltage of coaxial electrospinning, and the first drying method (drying), with the drying temperature and time within the aforementioned ranges, helps to form the nanoscale fiber structure of the lithium manganese iron phosphate cathode material. This facilitates better coating, and the fibers form a good conductive network through mutual contact, thereby improving the conductivity of the lithium manganese iron phosphate cathode material.

[0046] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0047] Example 1

[0048] 1.2 g of carbon source polyacrylonitrile (PAN) was added to 1 L of the first solvent N,N-dimethylformamide (DMF) to obtain the first solution. Based on the elemental composition of lithium source (lithium), iron source (iron), manganese source (manganese), and phosphorus source (phosphorus), lithium hydroxide, iron phosphate, manganese trioxide, and ammonium dihydrogen phosphate were weighed in a molar ratio of 1.01:0.2:0.8:1 and then sequentially mixed with the first solution. The mixture underwent a first mixing, a first drying, and sintering in a nitrogen atmosphere with a purity of 99.99% or higher to obtain the precursor. The first mixing consisted of mixing at 80 rpm for 60 min, followed by a further mixing at 500 rpm for 30 min at a temperature of 20°C. The first drying method was drying at 80°C for 9 h. The sintering temperature was 500°C for 5 h.

[0049] The raw materials, including 1.9g of precursor and 1L of second solvent DMF, were mixed for the second time to obtain a precursor mixture. The temperature of the second mixing was 45℃, the speed of the second mixing was 150rpm, and the time of the second mixing was 30min.

[0050] The raw materials, including 3g of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, 1.8g of silver nanowires and 4L of DMF as a third solvent, were mixed in a third mixture to obtain a first mixture. The third mixing temperature was 20℃, the third mixing speed was 80rpm, and the third mixing time was 60min.

[0051] 1.8g of precursor mixture as the core layer solution and 1g of the first mixture as the shell layer solution were respectively introduced into the inner and outer accommodating cavities of a coaxial double-layer syringe. After connecting the coaxial double-layer syringe to the matching coaxial needle, coaxial electrospinning was completed in the coaxial double-layer syringe, followed by a second drying process to obtain lithium manganese iron phosphate cathode material. The coaxial double-layer syringe includes an inner accommodating cavity and an outer accommodating cavity arranged sequentially around the same axis from the axis outward. The coaxial needle includes an inner needle and an outer needle arranged sequentially around the same axis from the axis outward. The inner diameter of the inner needle is 0.1mm and the inner diameter of the outer needle is 0.3mm. The voltage of coaxial electrospinning is 30KV. The second drying method is drying at a temperature of 80℃ for 9 hours.

[0052] The lithium manganese iron phosphate cathode material includes a cathode material core and a coating layer covering the surface of the cathode material core. The coating layer includes an inner coating layer and an outer coating layer. The inner coating layer includes a carbon layer, and the outer coating layer includes poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires. The mass ratio of the inner coating layer, the outer coating layer and the cathode material core is 0.5:0.8:7.8.

[0053] Example 2

[0054] 2g of glucose was added to 1L of ethanol as the first solvent to obtain the first solution. Based on the lithium element in the lithium source, the iron element in the iron source, the manganese element in the manganese source, and the phosphorus element in the phosphorus source, lithium carbonate, ferric oxide, manganese trioxide, and ammonium dihydrogen phosphate were weighed in a molar ratio of 1.02:0.3:0.7:1 and then mixed with the first solution sequentially. The mixture underwent a first mixing, a first drying, and sintering in an argon atmosphere with a purity of 99.99% or higher to obtain the precursor. The first mixing consisted of mixing at 100 rpm for 45 min, followed by mixing at 700 rpm for 20 min at a temperature of 30°C. The first drying method was drying at 45°C for 10 h. The sintering temperature was 600°C for 4 h.

[0055] The raw materials, including 2.5g of precursor and 1L of second solvent ethanol, were mixed for the second time to obtain a precursor mixture. The temperature of the second mixing was 30℃, the speed of the second mixing was 120rpm, and the time of the second mixing was 45min.

[0056] The raw materials, including 3.1g of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, 1.9g of silver nanowires and 4L of ethanol as the third solvent, were mixed in a third mixture to obtain a first mixture. The temperature of the third mixing was 30°C, the speed of the third mixing was 200 rpm, and the time of the third mixing was 45 min.

[0057] 1.5g of precursor mixture as the core layer solution and 1g of the first mixture as the shell layer solution were respectively introduced into the inner and outer accommodating cavities of a coaxial double-layer syringe. After connecting the coaxial double-layer syringe to the matching coaxial needle, coaxial electrospinning was completed in the coaxial double-layer syringe, followed by a second drying process to obtain lithium manganese iron phosphate cathode material. The inner diameter of the inner needle was 0.05mm, the inner diameter of the outer needle was 0.25mm, the voltage of coaxial electrospinning was 28KV, and the second drying method was drying at a temperature of 45℃ for 10h.

[0058] The lithium manganese iron phosphate cathode material includes a cathode material core and a coating layer covering the surface of the cathode material core. The coating layer includes an inner coating layer and an outer coating layer. The inner coating layer includes a carbon layer, and the outer coating layer includes poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires. The mass ratio of the inner coating layer, the outer coating layer and the cathode material core is 0.8:1:8.

[0059] Example 3

[0060] 3.1 g of acetic acid was added to 1 L of water as the first solvent to obtain the first solution. Based on the lithium element in the lithium source, the iron element in the iron source, the manganese element in the manganese source, and the phosphorus element in the phosphorus source, lithium dihydrogen phosphate, ferrous oxalate, manganese trioxide, and ammonium dihydrogen phosphate were weighed in a molar ratio of 1.03:0.5:0.5:1 and then mixed with the first solution sequentially. The mixture underwent a first mixing, a first drying, and sintering in an argon atmosphere with a purity of 99.99% or higher to obtain the precursor. The first mixing consisted of mixing at 150 rpm for 30 min, followed by mixing at 500 rpm for another 30 min at a temperature of 40°C. The first drying method was drying at 100°C for 8 h. The sintering temperature was 700°C for 3 h.

[0061] The raw materials, including 4.2g of precursor and 1L of second solvent water, were mixed for the second time to obtain a precursor mixture. The temperature of the second mixing was 20℃, the speed of the second mixing was 80rpm, and the time of the second mixing was 60min.

[0062] The raw materials, including 3.2g of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, 2.1g of silver nanowires and 4L of water as a third solvent, were mixed in a third mixture to obtain a first mixture. The temperature of the third mixing was 40℃, the speed of the third mixing was 300rpm, and the time of the third mixing was 60min.

[0063] 1.2g of precursor mixture as the core layer solution and 1g of the first mixture as the shell layer solution were introduced into the inner and outer accommodating cavities of a coaxial double-layer syringe, respectively. After connecting the coaxial double-layer syringe to the matching coaxial needle, coaxial electrospinning was completed in the coaxial double-layer syringe, followed by a second drying process to obtain lithium manganese iron phosphate cathode material. The inner diameter of the inner needle was 0.01mm, the inner diameter of the outer needle was 0.2mm, the voltage of coaxial electrospinning was 25KV, the second drying method was baking, the baking temperature was 100℃, and the first drying time was 8h.

[0064] The lithium manganese iron phosphate cathode material includes a cathode material core and a coating layer covering the surface of the cathode material core. The coating layer includes an inner coating layer and an outer coating layer. The inner coating layer includes a carbon layer, and the outer coating layer includes poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires. The mass ratio of the inner coating layer, the outer coating layer and the cathode material core is 1.2:1.1:8.2.

[0065] Example 4

[0066] The difference from Example 1 is that the mass ratio of the inner coating layer, the outer coating layer, and the cathode material core is 1.2:1.1:8.2, and the lithium manganese iron phosphate cathode material is finally obtained.

[0067] Example 5

[0068] The difference from Example 1 is that the mass ratio of the inner coating layer, the outer coating layer, and the cathode material core is 0.4:0.5:8.2, resulting in lithium manganese iron phosphate cathode material.

[0069] Example 6

[0070] The difference from Example 1 is that the mass ratio of the carbon source PAN to the volume ratio of the first solvent DMF is 3.1 g / L, and the lithium manganese iron phosphate cathode material is finally obtained.

[0071] Example 7

[0072] The difference from Example 1 is that the mass ratio of the carbon source PAN to the volume ratio of the first solvent DMF is 1 g / L, and the final product is lithium manganese iron phosphate cathode material.

[0073] Example 8

[0074] The difference from Example 1 is that the sintering temperature is 700°C and the sintering time is 3 hours, ultimately yielding lithium manganese iron phosphate cathode material.

[0075] Example 9

[0076] The difference from Example 1 is that the sintering temperature is 800℃ and the sintering time is 2h, and finally lithium manganese iron phosphate cathode material is obtained.

[0077] Example 10

[0078] The difference from Example 1 is that the ratio of the mass of the precursor to the volume of the second solvent DMF is 4.2 g / L, and the lithium manganese iron phosphate cathode material is finally obtained.

[0079] Example 11

[0080] The difference from Example 1 is that the ratio of the mass of the precursor to the volume of the second solvent DMF is 5 g / L, and the lithium manganese iron phosphate cathode material is finally obtained.

[0081] Example 12

[0082] The difference from Example 1 is that the mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires is 3.2:2.1, which ultimately yields lithium manganese iron phosphate cathode material.

[0083] Example 13

[0084] The difference from Example 1 is that the mass ratio of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires is 3.5:2.1, which ultimately yields lithium manganese iron phosphate cathode material.

[0085] Example 14

[0086] The difference from Example 1 is that the ratio of the total mass of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires to the volume of the third solvent DMF is 3.3 g / L, ultimately yielding lithium manganese iron phosphate cathode material.

[0087] Example 15

[0088] The difference from Example 1 is that the ratio of the total mass of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires to the volume of the third solvent DMF is 1 g / L, ultimately yielding lithium manganese iron phosphate cathode material.

[0089] Example 16

[0090] The difference from Example 1 is that the mass ratio of the first mixture to the precursor mixture is 1:1.2, and the final product is lithium manganese iron phosphate cathode material.

[0091] Example 17

[0092] The difference from Example 1 is that the mass ratio of the first mixture to the precursor mixture is 1:2, and the final product is lithium manganese iron phosphate cathode material.

[0093] Example 18

[0094] The difference from Example 1 is that the inner diameter of the inner needle is 0.01 mm and the inner diameter of the outer needle is 0.2 mm, ultimately yielding lithium manganese iron phosphate cathode material.

[0095] Example 19

[0096] The difference from Example 1 is that the inner diameter of the inner needle is 0.15 mm and the inner diameter of the outer needle is 0.15 mm, ultimately yielding lithium manganese iron phosphate cathode material.

[0097] Example 20

[0098] The difference from Example 1 is that the second drying method is drying, the drying temperature is 100°C and the drying time is 8 hours, and finally lithium manganese iron phosphate cathode material is obtained.

[0099] Example 21

[0100] The difference from Example 1 is that the second drying method is drying, the drying temperature is 105°C and the drying time is 11 hours, and finally lithium manganese iron phosphate cathode material is obtained.

[0101] Comparative Example 1

[0102] The difference from Example 1 is that the precursor solution is subjected to coaxial electrospinning and then drying in sequence to obtain lithium manganese iron phosphate cathode material.

[0103] Comparative Example 2

[0104] The difference from Example 1 is that, based on the lithium element in the lithium source, the iron element in the iron source, the manganese element in the manganese source, and the phosphorus element in the phosphorus source, lithium hydroxide (lithium source), iron phosphate (iron source), manganese trioxide (manganese source), and ammonium dihydrogen phosphate (phosphorus source) are weighed in a molar ratio of 1.01:0.8:0.2:1 and then mixed for the first time to finally obtain lithium manganese iron phosphate cathode material.

[0105] Test method:

[0106] The lithium manganese iron phosphate cathode materials prepared in the above examples and comparative examples were subjected to performance tests, and the test results are shown in Table 1.

[0107] Button cell preparation and testing: Lithium manganese iron phosphate cathode material, PVDF binder, and acetylene black were mixed in 10 mL of N-methylpyrrolidone at a mass ratio of 8:1:1 and thoroughly stirred to form a slurry. This slurry was then coated onto the surface of aluminum foil using a coating machine and naturally dried under vacuum at 60°C before being cut. Using lithium foil as the anode and lithium hexafluorophosphate solution as the electrolyte, button cells were assembled in an argon-protected glove box using a 2032-type button cell casing. Electrochemical performance was tested at room temperature within a voltage range of 2.8–4.3V at 25°C.

[0108] Powder resistivity and compaction density test: The powder resistivity and compaction density of lithium manganese iron phosphate cathode material were measured in accordance with GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0109] Table 1

[0110]

[0111]

[0112] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0113] The lithium manganese iron phosphate cathode material coating layer of this application includes an inner coating layer and an outer coating layer stacked sequentially. The inner coating layer is in contact with the core of the cathode material and includes a carbon layer. This carbon layer is not only regularly shaped but also densely packed, thereby increasing the compaction density of the lithium manganese iron phosphate cathode material. The outer coating layer includes poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires. The silver nanowires possess excellent conductivity, which improves the conductivity of the lithium manganese iron phosphate cathode material. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate is a high-molecular-weight polymer that not only has better coating capabilities but also high conductivity and high stability. Furthermore, it is flexible, which can alleviate the volume expansion of the lithium manganese iron phosphate active material during charging and discharging, thereby stabilizing the overall structure of the lithium manganese iron phosphate active material. Furthermore, on the one hand, the outer coating layer can prevent the corrosion of hydrofluoric acid and suppress side reactions generated on the particle surface during cycling, thereby reducing the charge transfer resistance on the surface of the lithium manganese iron phosphate active material. On the other hand, in the microstructure of the outer coating layer, the combination of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires can strengthen the surface structure of the lithium manganese iron phosphate cathode material, thereby preventing the dissolution of manganese from lithium manganese iron phosphate and improving the cycling performance of the lithium manganese iron phosphate cathode material. In summary, the lithium manganese iron phosphate cathode material of the present invention has advantages such as low resistance, high capacity, high compaction, and high cycling performance.

[0114] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium iron manganese phosphate cathode material, characterized in that, The preparation method comprises: Step S1, raw materials comprising a carbon source, a first solvent, a lithium source, an iron source, a manganese source, and a phosphorus source are sequentially subjected to first mixing, first drying, and sintering to obtain a precursor; the molar ratio of the lithium source, the iron source, the manganese source, and the phosphorus source, in terms of lithium elements in the lithium source, iron elements in the iron source, manganese elements in the manganese source, and phosphorus elements in the phosphorus source, is 1.01-1.03:0.2-0.5:0.5-0.8:1; Step S2, raw materials comprising the precursor and a second solvent are subjected to second mixing to obtain a precursor mixed solution; Step S3, raw materials comprising poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, silver nanowires, and a third solvent are subjected to third mixing to obtain a first mixed solution; and Step S4, raw materials comprising the precursor mixed solution and the first mixed solution are sequentially subjected to coaxial electrospinning and second drying to obtain the lithium manganese iron phosphate positive electrode material; The coaxial electrospinning is completed in a coaxial double-layer injector, and the coaxial double-layer injector comprises, from the axis outward, an inner layer containing cavity and an outer layer containing cavity which are sequentially arranged on the same axis; The precursor mixed solution is used as a core layer solution, and the core layer solution is located in the inner layer containing cavity; the first mixed solution is used as a shell layer solution, and the shell layer solution is located in the outer layer containing cavity; The lithium manganese iron phosphate positive electrode material comprises a positive electrode material inner core and a coating layer coated on the surface of the positive electrode material inner core; The chemical general formula of the positive material inner core is LiMn x Fe 1-x PO4, wherein 0.5≤x≤0.8; The coating layer comprises an inner coating layer and an outer coating layer which are sequentially arranged, and the inner coating layer is arranged in contact with the positive electrode material inner core; The inner coating layer comprises a carbon layer; The outer coating layer comprises poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and silver nanowires.

2. The production method according to claim 1, characterized by, The step S1 further comprises: Step S11, the carbon source is mixed with the first solvent to obtain a first solution; and Step S12, raw materials comprising the first solution, the lithium source, the iron source, the manganese source, and the phosphorus source are sequentially subjected to the first mixing, the first drying, and the sintering to obtain the precursor; The ratio of the mass of the carbon source to the volume of the first solvent is 1.2-3.1 g / L; The rotation speed of the first mixing is 80-1000 rpm; the time of the first mixing is 40-90 min; and the temperature of the first mixing is 20-40℃; The drying mode of the first drying is baking, and the time of the baking is 8-10 h; the temperature of the sintering is 500-700℃; the time of the sintering is 3-5 h; and the atmosphere of the sintering is nitrogen and / or argon.

3. The preparation method according to claim 2, characterized in that, The first mixing is mixing at a rotation speed of 80-150 rpm for 30-60 min, and then continuing mixing at a rotation speed of 500-1000 rpm for 10-30 min.

4. The production method according to claim 2, characterized by, The temperature of the baking is 45℃-100℃.

5. The preparation method according to claim 1, characterized in that, The carbon source is selected from any one or more of polyacrylonitrile, glucose and acetic acid; and / or, the first solvent, the second solvent and the third solvent are each independently selected from any one or more of water, ethanol and N,N-dimethylformamide; and / or, the lithium source is selected from any one or more of lithium carbonate, lithium dihydrogen phosphate, lithium hydrogen phosphate and lithium hydroxide; and / or, the iron source is selected from any one or more of diiron trioxide, iron phosphate and ferrous oxalate; and / or, the manganese source is selected from any one or more of manganese carbonate, manganese phosphate, manganese trioxide and manganese tetraoxide; and / or, the phosphorus source is selected from any one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate and manganese phosphate.

6. The method of claim 1, wherein, In the step S2, the ratio of the mass of the precursor to the volume of the second solvent is 1.9-4.2 g / L; and / or, the temperature of the second mixing is 20-45℃; and / or, the rotating speed of the second mixing is 80-150 rpm; and / or, the time of the second mixing is 30-60 min.

7. The preparation method according to claim 1, characterized in that, In the step S3, the mass ratio of the poly(3,4-ethylenedioxythiophene) : polystyrene sulfonate to the silver nanowire is 3-3.2:1.8-2.1; and / or, the ratio of the total mass of the poly(3,4-ethylenedioxythiophene) : polystyrene sulfonate and the silver nanowire to the volume of the third solvent is 1.2-3.3 g / L; and / or, the temperature of the third mixing is 20-40℃; and / or, the rotating speed of the third mixing is 80-300 rpm; and / or, the time of the third mixing is 30-60 min.

8. The method of claim 1, wherein, The step S4 further comprises: passing the core layer solution and the shell layer solution into the inner layer containing cavity and the outer layer containing cavity, respectively; connecting the coaxial double-layer syringe with the matched coaxial needle, and then performing the coaxial electrospinning; wherein the coaxial needle comprises an inner needle and an outer needle which are sequentially arranged on the same axis from the axis to the outside; and / or, the mass ratio of the first mixed solution to the precursor mixed solution is 1:1.2-1.8; and / or, the voltage of the coaxial electrospinning is 25-30 KV; and / or, the second drying mode is drying, and / or, the time of the drying is 8-10 h.

9. The production method according to claim 8, characterized by, The inner diameter of the inner needle is 0.01-0.1 mm.

10. The method of claim 8, wherein, The inner diameter of the outer needle is 0.2-0.3 mm.

11. The preparation method according to claim 8, characterized in that, The temperature of the drying is 45-100℃.

12. The method of claim 1, wherein, The carbon layer comprises carbon fibers; and / or, the structure of the poly(3,4-ethylenedioxythiophene) : polystyrene sulfonate is reticular, the structure of the silver nanowire is linear, and the silver nanowire is inserted into the reticular structure of the poly(3,4-ethylenedioxythiophene) : polystyrene sulfonate; and / or, the mass ratio of the poly(3,4-ethylenedioxythiophene) : polystyrene sulfonate to the silver nanowire is 3-3.2:1.8-2.

1.

13. The method of claim 1, wherein, The mass ratio of the inner cladding layer, the outer cladding layer and the positive material core is 0.5-1.2:0.8-1.1:7.8-8.

2.

14. The method of claim 12, wherein, The silver nanowires have a diameter of 30-200 nm, and / or the silver nanowires have a length of 10-30 μm. The silver nanowires have a diameter of 30-200 nm, and / or the silver nanowires have a length of 10-30 μm.

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