Ternary positive electrode fiber composite material and preparation method therefor

Abstract

The present application relates to the field of battery materials, and provides a ternary positive electrode fiber composite material and a preparation method therefor. According to the preparation me

Description

The present application relates to the field of battery materials, and specifically relates to a ternary positive electrode fiber composite and a preparation method thereof. BACKGROUND A ternary positive electrode material is a lithium nickel cobalt manganese oxide material prepared from nickel, manganese and cobalt sources with a ratio adjusted to actual needs, which has the advantages of low cost, high unit capacity and good safety. However, with the increasing diversification of application scenarios, simple ternary positive electrode material cannot meet the needs of all users due to its shortcomings of poor heat resistance, short service life and poor rate capability. In view of the inherent defects of simple ternary positive electrode material, some modifications have been used to optimize the material, mainly including elemental doping and structural modification. The structural modification of ternary positive electrode material, especially giving special morphology to the material, can effectively improve the thermal stability and electrochemical performance of the material just by physical approaches. In the prior art, electrospinning is a conventional method to modify and construct the lithium-ion battery material. In the method, electrified substances are accelerated under electric field by high-voltage static electricity, overcome the influence of surface tension and form a jet; when the jet is sprayed out, the solvent will evaporates or the substances will be cured and finally falls on a collector to form a non-woven-like fiber felt. Such three-dimensional fiber composite structure can effectively improve the stress resistance and significantly increase the specific surface area, which can be easily wetted by electrolyte and have more lithium deintercalation-intercalation sites, effectively improving the overall electrochemical activity of the material. However, due to the long electrospinning process, the raw material having solid-liquid phase is prone to separate into layers when standing and thus clogs the needle during the spinning process. Hence, the existing prepared electrospinning raw material is mostly only liquid phase. For the ternary positive electrode material, although soluble salts can be used as raw materials for electrospinning structure construction, these precursor raw materials will have obvious crystallization behavior in the subsequent sintering process, resulting in internal shrinkage of the pre-constructed fiber structure and eventually breakage. SUMMARY The following is a summary of subjects described in detail herein. The summary is not intended to limit the scope of protection of the claims. In view of the problems in the prior art, the present application is to provide a method for preparing a ternary positive electrode fiber composite, in which a coaxial fiber precursor with core-shell structure is pre-constructed by the coaxial electrospinning method, and then the fiber is coated with a nitrogen-containing polymer layer on the surface by the polymer grafting method. After high-temperature sintering, the two layers of the fiber precursor fuse together to form a ternary positive electrode carbon composite, and the outer nitrogen-containing polymer coating is converted into a nitrogen-containing carbon layer that effectively preserves the fiber morphology while effectively enhancing the overall material conductivity. To achieve the object, the present disclosure adopts the following technical solutions. A preparation method of a ternary positive electrode fiber composite is provided, including the following steps: (1) dissolving a cobalt source, a nickel source, a manganese source and a structural polymer in solvent A to prepare spinning solution I, and dissolving a lithium source and a structural polymer in solvent Ato prepare spinning solution II; (2) performing electrospinning treatment by using coaxial needles and with the spinning solution I as inner spinning solution and the spinning solution II as outer spinning solution, and drying a prepared fabric to obtain coaxial fiber precursor a; (3) dissolving a nitrogen-containing polymerization monomer in solvent B, then impregnating the coaxial fiber precursor a with the solution completely, adding a catalyst to initiate polymerization reaction of the nitrogen-containing polymerization monomer, performing filtering and drying after the reaction is complete to obtain a coaxial fiber precursor b; the cobalt source, the nickel source, the manganese source, the lithium source and the structural polymer are insoluble in solvent B; and (4) calcining the coaxial fiber precursor b at 700-900 °C for 10-15 h under protective atmosphere to obtain the ternary positive electrode fiber composite. In the preparation method of a ternary positive electrode fiber composite of the present application, the coaxial fiber precursor is prepared by the coaxial electrospinning method with cobalt, nickel and manganese sources as the inner layer and lithium source as the outer layer, and both the inner and outer layers are morphologically fixed with the structural polymer. Then, a nitrogen-containing polymerization monomer is further introduced into the precursor, and a thin nitrogen-containing polymer coating is grafted on the precursor surface with the structural polymer contained in the precursor as grafting sites. When lithium nickel cobalt manganese oxide is generated in the precursor during the high-temperature sintering, the cobalt, nickel and manganese sources of the inner layer and the lithium source of the outer layer are crystallized. However, due to different structural positions, the two layers have opposite stress trends. The overall shrinkage stress of the material is significantly reduced. The inner layer and outer layer fuse together. The nitrogen-containing polymer grafted on the outer layer will, on the one hand, carbonize into a high conductivity nitrogen-containing carbon layer during the high-temperature sintering, and on the other hand, effectively support the coaxial fiber and preserve its morphology. The final ternary positive electrode fiber composite not only has high electrical conductivity, but also maintains relatively complete fiber network structure, and also has large specific surface area, abundant lithium deintercalation-intercalation sites, high proportion of active triad materials, and excellent electrochemical performance. Preferably, the cobalt source, the nickel source and the manganese source are soluble salts; the lithium source is lithium carbonate, the structural polymer is polyimide, and the solvent A is N,N- dimethylformamide (DMF). More preferably, the cobalt source is at least one of cobalt acetate and cobalt nitrate, the nickel source is at least one of nickel acetate and nickel nitrate, and the manganese source is manganese acetate. It should be noted that the cobalt source, the nickel source, the manganese source and the lithium source in the present application can be selected from other soluble salts that are soluble in solvent Ain addition to the preferred ones. As long as the salts can be prepared into solutions for electrospinning and directly produce lithium nickel cobalt manganese oxide subsequently, the salt type is not limited by the preferred range. Preferably, cobalt element in the cobalt source, nickel element in the nickel source and manganese element in the manganese source have a molar ratio of x:y:(l-x-y), in which x = 0.01-0.1. Preferably, the structural polymer has a mass concentration of 5-15wt% in the spinning solution I and in the spinning solution II, cobalt ions, nickel ions and manganese ions have a total concentration of 0.4-0.8 mmol / g in the spinning solution I, and lithium ions have a concentration of 0.4-0.8 mmol / g in the spinning solution II. In the electrospinning process, in addition to shaping the fiber and keeping fiber spraying continuously, the structural polymer introduced also acts as a load for the cobalt and lithium sources in the obtained coaxial fiber precursor a. If the content is too low, various raw material solutions will easily lost during the subsequent processing, and the nitrogen-containing polymerization monomer cannot be fully grafted and polymerized. If the content is too high, the spinning solution will be overly thick, which affects the crystallization and also the synthesis efficiency of lithium nickel cobalt manganese oxide subsequently. Preferably, for the electrospinning treatment in step (2), an outer spinning needle has an inner diameter of 0.8-1.5 mm, an inner spinning needle has an inner diameter of 0.3-0.5 mm, an injection rate is 0.4-0.6 mL / h, a voltage is 18-22 kV, and a spinning collecting distance is 10-25 cm. Preferably, the nitrogen-containing polymerization monomer is pyrrole, the catalyst is ferric chloride, and the solvent B is anhydrous ethanol. Preferably, the structural polymer in the coaxial fiber precursor a and the nitrogen-containing polymerization monomer have a mass ratio of 1:(0.2-0.4). If too much nitrogen-containing polymerization monomer is introduced, although more polypyrrole can be formed during the polymerization process, not all of the polypyrrole can be grafted onto the coaxial fiber precursor a, which has limited effect on improving the stability of the final product and may cause uneven distribution of the active substance in the overall product; if too little is introduced, the nitrogen-containing polymer will be difficult to exert the support effect to guarantee the fiber morphology of the final product; besides, the electrical conductivity improvement of the product will be insufficient with insufficient nitrogen-doped amount. Preferably, the polymerization reaction in step (3) is performed at -5-5 °C. In a second aspect, the present application provides a ternary positive electrode fiber composite which is prepared by the preparation method of a ternary positive electrode fiber composite. In a third aspect, the present application provides a lithium-ion battery positive electrode sheet, which is prepared from the ternary positive electrode fiber composite of the present application. The ternary positive electrode fiber composite of the present application has an excellent three-dimensional fiber structure, a large specific surface area, and many lithium deintercalation-intercalation sites. Additionally, based on the nitrogen doping, the lithium-ion battery positive electrode sheet that uses the ternary positive electrode fiber composite not only has good lithium deintercalation-intercalation efficiency and high electrical conductivity, but also has good cycling stability and improved service life compared with existing products. The beneficial effect of the present application is as follows. The present application provides a method for preparing a ternary positive electrode fiber composite. In this method, a coaxial fiber precursor with core-shell structure is pre-constructed by the coaxial electrospinning method, and then the fiber is coated with a nitrogen-containing polymer layer on the surface by the polymer grafting method. After high-temperature sintering, the two layers of the fiber precursor fuse together to form a ternary positive electrode carbon composite, and the outer nitrogen-containing polymer coating is converted into a nitrogen-containing carbon layer that effectively preserves the fiber morphology while effectively enhancing the overall material conductivity. The present application also provides a lithium-ion battery positive electrode sheet prepared from the ternary positive electrode fiber composite. Other aspects will become apparent after reading and understanding the drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS The drawings are used to provide a further understanding of the technical solution herein, and constitute a part of the specification, and together with the embodiment of the present application, serve to explain the technical solution herein, and do not constitute a limitation on the technical solution herein. FIG. 1 is a transmission electron microscopy image of a ternary positive electrode fiber composite obtained in Example 1 of the present application. FIG. 2 is a transmission electron microscopy image of a ternary positive electrode fiber composite obtained in Comparative Example 1 of the present application. FIG. 3 is a transmission electron microscopy image of a ternary positive electrode fiber composite obtained in Comparative Example 2 of the present application. DETAILED DESCRIPTION In order to better illustrate the objects, technical solutions and advantages of the present application, the present application is further described below through examples and comparative examples, which is used for a better understanding of the present application but not intended to limit the present application. All other examples obtained by those skilled in the art without creative efforts fall within the protection scope of the present application. Unless otherwise specified, the experimental reagents, raw materials and apparatus involved in the examples and comparative examples of the present application are the conventional experimental reagents, raw materials and apparatus. Preferably, polyimide used in the examples and comparative examples is optionally Matrimid 5218 PI powder, and cobalt element in the cobalt source, nickel element in the nickel source and manganese element in the manganese source have a molar ratio of 0.1:0.8:0.1. It should be noted herein that the examples and comparative examples of the present application are illustrated through some specific feasible embodiments but are not limited to them. It should be apparent to those skilled in the art that, without affecting the feasibility of the overall technical solution, the polyimide can be selected from other sources, and the molar ratio of the nickel, cobalt and manganese elements in the product can be adjusted according to actual needs. Example 1 An example of the ternary positive electrode fiber composite, and the preparation method thereof in the present application is provided, which includes the following steps: (1) a cobalt source of cobalt acetate, a nickel source of nickel acetate, a manganese source of manganese acetate, and a structural polymer of polyimide which was 10wt% of a total solution mass were dissolved in DMF under the condition of water bath at 60-80 °C with stirring to prepare spinning solution I; a lithium source of lithium acetate, and a structural polymer of polyimide which was 10wt% of a total solution mass were dissolved in DMF under the condition of water bath at 60-80 °C with stirring to prepare spinning solution II; cobalt element in the cobalt source, nickel element in the nickel source and manganese element in the manganese source had a molar ratio of x:y:( 1-x-y), in which x = 0.1, and y = 0.8; cobalt ions, nickel ions and manganese ions had a total concentration of 0.6 mmol / g in the spinning solution I; lithium ions had a concentration of 0.6 mmol / g in the spinning solution II; (2) electrospinning treatment was performed by using coaxial needles and with the spinning solution I as inner spinning solution and the spinning solution II as outer spinning solution, and a prepared fabric was dried at 80 °C for 24 h to obtain coaxial fiber precursor a; the specific parameters used included: an outer spinning needle had an inner diameter of 1.2 mm, an inner spinning needle had an inner diameter of 0.3 mm, an injection rate was 0.5 mL / h, a voltage was 19 kV, and a spinning collecting distance was 22 cm; (3) a nitrogen-containing polymerization monomer of pyrrole was dissolved in anhydrous ethanol, and then the coaxial fiber precursor a was impregnated with the solution completely; the solution was cooled down to 0 °C, and added with an appropriate amount of ferric chloride to initiate polymerization reaction of the nitrogen-containing polymerization monomer of pyrrole; after the reaction was complete, the reaction system was filtered and dried at 60 °C for 24 h to obtain coaxial fiber precursor b; an addition amount of pyrrole was: a total addition mass of polyimide : an addition mass of pyrrole = 1:0.3; and (4) the coaxial fiber precursor b was calcined at 850 °C for 15 h under protective atmosphere to obtain the ternary positive electrode fiber composite. Example 2 An example of the ternary positive electrode fiber composite, and the preparation method thereof in the present application is provided. This example differs from Example 1 only in that: polyimide had a mass concentration of 15wt% in the spinning solution I and in the spinning solution II in step (1), cobalt ions, nickel ions and manganese ions had a total concentration of 0.4 mmol / g in the spinning solution I, and lithium ions had a concentration of 0.4 mmol / g in the spinning solution II. Example 3 An example of the ternary positive electrode fiber composite, and the preparation method thereof in the present application is provided. This example differs from Example 1 only in that: polyimide had a mass concentration of 5wt% in the spinning solution I and in the spinning solution II in step (1), cobalt ions, nickel ions and manganese ions had a total concentration of 0.8 mmol / g in the spinning solution I, and lithium ions had a concentration of 0.8 mmol / g in the spinning solution II. Example 4 An example of the ternary positive electrode fiber composite, and the preparation method thereof in the present application is provided. This example differs from Example 1 only in that: polyimide had a mass concentration of 20wt% in the spinning solution I and in the spinning solution II in step (1), cobalt ions, nickel ions and manganese ions had a total concentration of 0.2 mmol / g in the spinning solution I, and lithium ions had a concentration of 0.2 mmol / g in the spinning solution II. Example 5 An example of the ternary positive electrode fiber composite, and the preparation method thereof in the present application is provided. This example differs from Example 1 only in that: polyimide had a mass concentration of 3wt% in the spinning solution I and in the spinning solution II in step (1), cobalt ions, nickel ions and manganese ions had a total concentration of 1 mmol / g in the spinning solution I, and lithium ions had a concentration of 1 mmol / g in the spinning solution II. Example 6 An example of the ternary positive electrode fiber composite, and the preparation method thereof in the present application is provided. This example differs from Example 1 only in that: an addition amount of pyrrole in step (3) was: a total addition mass of polyimide : an addition mass of pyrrole = 1:0.2. Example 7 An example of the ternary positive electrode fiber composite, and the preparation method thereof in the present application is provided. This example differs from Example 1 only in that: an addition amount of pyrrole in step (3) was: a total addition mass of polyimide : an addition 8 mass of pyrrole = 1:0.4. Example 8 An example of the ternary positive electrode fiber composite, and the preparation method thereof in the present application is provided. This example differs from Example 1 only in that: an addition amount of pyrrole in step (3) was: a total addition mass of polyimide : an addition mass of pyrrole = 1:0.1. Example 9 An example of the ternary positive electrode fiber composite, and the preparation method thereof in the present application is provided. This example differs from Example 1 only in that: an addition amount of pyrrole in step (3) was: a total addition mass of polyimide : an addition mass of pyrrole = 1:0.5. Comparative Example 1 A ternary positive electrode fiber composite and a preparation method thereof include the following steps: (1) a lithium source of lithium acetate, a cobalt source of cobalt acetate, a nickel source of nickel acetate, a manganese source of manganese acetate, and a structural polymer of polyimide which was 20wt% of a total solution mass were dissolved in DMF under the condition of water bath at 60-80 °C with stirring to prepare spinning solution; cobalt element in the cobalt source, nickel element in the nickel source and manganese element in the manganese source had a molar ratio of x:y:(l-x-y), in which x = 0.1, and y = 0.8; cobalt ions, nickel ions and manganese ions had a total concentration of 0.6 mmol / g in the spinning solution I; lithium ions had a concentration of 0.6 mmol / g; (2) electrospinning treatment was performed with the spinning solution, and a prepared fabric was dried at 80 °C for 24 h to obtain fiber precursor a; the specific parameters used included: a spinning needle had an inner diameter, an injection rate was 0.3 mL / h, a voltage was 20 kV, and a spinning collecting distance was 22 cm; (3) a nitrogen-containing polymerization monomer of pyrrole was dissolved in anhydrous ethanol, and then the fiber precursor a was impregnated with the solution completely; the solution was cooled down to 0 °C, and added with an appropriate amount of ferric chloride to initiate polymerization reaction of the nitrogen-containing polymerization monomer of pyrrole; after the reaction was complete, the reaction system was filtered and dried at 60 °C for 24 h to obtain coaxial fiber precursor b; an addition amount of pyrrole was: a total addition mass of polyimide : an addition mass of pyrrole = 1:0.3; (4) the coaxial fiber precursor b was calcined at 850 °C for 15 h under protective atmosphere to obtain the ternary positive electrode fiber composite. Comparative Example 2 A ternary positive electrode fiber composite and a preparation method thereof include the following steps: (1) a cobalt source of cobalt acetate, a nickel source of nickel acetate, a manganese source of manganese acetate, and a structural polymer of polyimide which was 10wt% of a total solution mass were dissolved in DMF under the condition of water bath at 60-80 °C with stirring to prepare spinning solution I; a lithium source of lithium acetate, and a structural polymer of polyimide which was 10wt% of a total solution mass were dissolved in DMF under the condition of water bath at 60-80 °C with stirring to prepare spinning solution II; cobalt element in the cobalt source, nickel element in the nickel source and manganese element in the manganese source had a molar ratio of x:y:(l-x-y), in which x = 0.1, and y = 0.8; cobalt ions, nickel ions and manganese ions had a total concentration of 0.6 mmol / g in the spinning solution I; lithium ions had a concentration of 0.6 mmol / g in the spinning solution II; (2) electrospinning treatment was performed by using coaxial needles and with the spinning solution I as inner spinning solution and the spinning solution II as outer spinning solution, and a prepared fabric was dried at 80 °C for 24 h to obtain coaxial fiber precursor a; the specific parameters used included: an outer spinning needle had an inner diameter of 1.2 mm, an inner spinning needle had an inner diameter of 0.3 mm, an injection rate was 0.5 mL / h, a voltage was 19 kV, and a spinning collecting distance was 22 cm; and (3) the coaxial fiber precursor a was calcined at 850 °C for 15 h under protective atmosphere to obtain the ternary positive electrode fiber composite. Comparative Example 3 A ternary positive electrode fiber composite and a preparation method thereof include the following steps: (1) a cobalt source of cobalt acetate, a nickel source of nickel acetate, a manganese source of manganese acetate, and a structural polymer of polyimide which was 10wt% of a total solution mass were dissolved in DMF under the condition of water bath at 60-80 °C with stirring to prepare spinning solution I; a lithium source of lithium acetate, and a structural polymer of polyimide which was 10wt% of a total solution mass were dissolved in DMF under the condition of water bath at 60-80 °C with stirring to prepare spinning solution II; cobalt element in the cobalt source, nickel element in the nickel source and manganese element in the manganese source had a molar ratio of x:y:(l-x-y), in which x = 0.1, and y = 0.8; cobalt ions, nickel ions and manganese ions had a total concentration of 0.6 mmol / g in the spinning solution I; lithium ions had a concentration of 0.6 mmol / g in the spinning solution II; (2) electrospinning treatment was performed by using coaxial needles and with the spinning solution I as inner spinning solution and the spinning solution II as outer spinning solution, and a prepared fabric was dried at 80 °C for 24 h to obtain coaxial fiber precursor a; the specific parameters used included: an outer spinning needle had an inner diameter of 1.2 mm, an inner spinning needle had an inner diameter of 0.3 mm, an injection rate was 0.5 mL / h, a voltage was 19 kV, and a spinning collecting distance was 22 cm; (3) reduced graphene oxide (rGO) prepare by HUMMER method was added into anhydrous ethanol, and then the coaxial fiber precursor a was impregnated with the solution completely; the rGO and the coaxial fiber precursor a were mixed uniformly under the ultrasonic condition with stirring at 50 rpm, filtered and dried at 60 °C for 24 h to obtain coaxial fiber precursor b; an addition amount of pyrrole was: a total addition mass of polyimide : an addition mass of pyrrole = 1:0.3; and (4) the coaxial fiber precursor b was calcined at 850 °C for 15 h under protective atmosphere to obtain the ternary positive electrode fiber composite. Effect Example 1 In order to verify the preferability of the preparation method of the ternary positive electrode fiber composite of the present application, the products of Example 1, Comparative Example 1 and Comparative Example 2 were observed by transmission electron microscopy. The characterization results are shown in FIGs. 1-3. It can be seen that, by the preferred preparation method of the present application, the prepared product has good fiber morphology, and the integral fiber structure is not collapsed during the sintering process of forming the ternary positive electrode material due to the two polymers; by comparison, the coaxial spinning process was not used during the preparation of the product of Comparative Example 1, and the pre-constructed fiber morphology was destroyed during the sintering and crystallization process of the ternary positive electrode material; due to the absence of the outer coating of nitrogen-containing polymer, the product of Comparative Example 2 also fails to maintain a good three-dimensional fiber network structure during the high-temperature sintering and shows obvious fiber breakage after sintering. Effect Example 2 In order to verify the performance preferability of the ternary positive electrode fiber composite of the present application, the products of each examples and comparative examples were used in the preparation of lithium-ion battery positive electrode sheets: the products of each examples and comparative examples were mixed with carbon black and PVDF at a mass ratio of 8:1:1, stirred to prepare slurry, and then coated on aluminum foils and cut to prepare electrode sheets. The obtained electrode sheets were used as the positive electrode sheet, and lithium sheets were used as the counter electrode sheet, and button lithium-ion half batteries were prepared by using commercial separators and commercial lithium hexafluorophosphate electrolyte. The obtained batteries were charged and discharged for 100 cycles at a working voltage of 3-4.5 V and at 0.1 C; meanwhile, another batch of samples were prepared in parallel for rate capability test: the batteries were charged and discharged for 10 cycles at the same voltage and at 0.1 C, then charged and discharged for 50 cycles at a high rate of 2 C and then returned to 0.1 C to calculate the capacity retention rate. The test results are shown in Table 1. Table 1 Product Initial discharge specific capacity at 0.1 C (mAh / g) Discharge specific capacity after 100 cycles at 0.1 C (mAh / g) Capacity retention rate after rate capability (%) Example 1 177.5 163.3 89.6 Example 2 168.2 159 91.5 Example 3 183.6 162.7 84.6 Example 4 160.5 152 92 Example 5 185 148.9 76.5 Example 6 175.6 162.8 87 Example 7 175.1 162.4 91 Example 8 170.9 146 83.2 Example 9 173.8 160.6 91 Comparative Example 1 176.5 124.7 58.5 Comparative Example 2 136.1 105.2 68.4 Comparative Example 3 165.2 126.8 71 As can be seen from Table 1, based on the coaxial spinning treatment in the precursor preparation as well as the stabilizing effect of the structural polymer and conductive polymer, the lithium nickel cobalt manganese oxide in the material can realize in situ crystallization during the sintering preparation process, which has few influences on the fiber structure of the 5 product. The entire product has large specific surface area, good three-dimensional fiber structure, high stability and many lithium deintercalation-intercalation sites, and can be effectively wetted by the electrolyte. Meanwhile, the conductivity of the product is improved by doping with nitrogen. The initial discharge specific capacity of the ternary positive electrode fiber composite can reach 160-185 mAh / g during the cycles at low rate, and the discharge 10 specific capacity after 100 cycles can also reach 140-165 mAh / g. After the rate capability test, the capacity retention rate is up to 92%. As can be seen from the comparison between Example 1 and Examples 2-9, in the case where the addition proportion of the structural polymer, conductive polymer (i.e., polypyrrole) or ternary material, no matter what it is, is changed, the discharge capacity, cycling stability and rate capability of the final product will change, and 15 thereby, the addition proportion should be maintained within an appropriate range. By comparison, the coaxial spinning method was not used to prepare the precursor for the product of Comparative Example 1, the product fails to maintain the pre-constructed fiber structure after the subsequent loading and sintering steps, and the cycle stability and rate capability of the product are poor. Although the coaxial spinning method was used to prepare the precursor in Comparative Example 2, the outer coating of nitrogen-containing polymer was not further introduced, and thus the obtained product has an unsatisfactory morphology and structure; meanwhile, due to the absence of the doped nitrogen, the product has insufficient conductivity 5 and low discharge capacity. Comparative Example 3 uses reduced graphene oxide, a conventional modified carbon material, to prepare the product instead of the polypyrrole coating. However, the reduced graphene is difficult to bond to the precursor just based on physical dispersion. Therefore, although the integral performance of the product is improved to a certain extent compared with Comparative Example 2, the overall effect is still less satisfying than the 10 products of the examples. Finally, it should be noted that the above examples are intended to illustrate the technical solutions of the present application but should not be regard as a limitation to the protection scope of the present application. Although the present application has been described in detail with reference to the preferred examples, it should be apparent to those skilled in the art that the 15 technical solutions of the present application can be modified or replaced by equivalent solutions without departing from the conception and scope of the technical solutions of the present application.

Claims

1. A preparation method of a ternary positive electrode fiber composite, comprising:(1) dissolving a cobalt source, a nickel source, a manganese source and a structural polymer in solvent A to prepare spinning solution I, and dissolving a lithium source and a structural polymer in solvent Ato prepare spinning solution II;(2) performing electrospinning treatment by using coaxial needles and with the spinning solution I as inner spinning solution and the spinning solution II as outer spinning solution, and drying a prepared fabric to obtain coaxial fiber precursor a;(3) dissolving a nitrogen-containing polymerization monomer in solvent B, then impregnating the coaxial fiber precursor a with the solution completely, adding a catalyst to initiate polymerization reaction of the nitrogen-containing polymerization monomer, performing filtering and drying after the reaction is complete to obtain a coaxial fiber precursor b; the cobalt source, the nickel source, the manganese source, the lithium source and the structural polymer are insoluble in solvent B; and(4) calcining the coaxial fiber precursor b at 700-900 °C for 10-15 h under protective atmosphere to obtain the ternary positive electrode fiber composite.

2. The preparation method of a ternary positive electrode fiber composite according to claim 1, wherein the cobalt source, the nickel source and the manganese source are soluble salts; the lithium source is lithium carbonate, the structural polymer is polyimide, and the solvent A is N,N- dimethylformamide.

3. The preparation method of a ternary positive electrode fiber composite according to claim 2, wherein the cobalt source is at least one of cobalt acetate and cobalt nitrate, the nickel source is at least one of nickel acetate and nickel nitrate, and the manganese source is manganese acetate.

4. The preparation method of a ternary positive electrode fiber composite according to claim 3, wherein cobalt element in the cobalt source, nickel element in the nickel source and manganese element in the manganese source have a molar ratio of x:y:( 1-x-y), wherein x = 0.01-0.1.

5. The preparation method of a ternary positive electrode fiber composite according to claim 1, wherein the structural polymer has a mass concentration of 5-15wt% in the spinning solution Iand in the spinning solution II, cobalt ions, nickel ions and manganese ions have a total concentration of 0.4-0.8 mmol / g in the spinning solution I, and lithium ions have a concentration of 0.4-0.8 mmol / g in the spinning solution II.

6. The preparation method of a ternary positive electrode fiber composite according to claim 1, 5 wherein for the electrospinning treatment in step (2), an outer spinning needle has an inner diameter of 0.8-1.5 mm, an inner spinning needle has an inner diameter of 0.3-0.5 mm, an injection rate is 0.4-0.6 mL / h, a voltage is 18-22 kV, and a spinning collecting distance is 10-25 cm.

7. The preparation method of a ternary positive electrode fiber composite according to claim 1, 10 wherein the nitrogen-containing polymerization monomer is pyrrole, the catalyst is ferric chloride, and the solvent B is anhydrous ethanol.

8. The preparation method of a ternary positive electrode fiber composite according to claim 1, wherein the structural polymer in the coaxial fiber precursor a and the nitrogen-containing polymerization monomer have a mass ratio of 1:(0.2-0.4).15 9. A ternary positive electrode fiber composite, which is prepared by the preparation method ofa ternary positive electrode fiber composite according to any one of claims 1 to 8.

10. A lithium-ion battery positive electrode sheet, which is prepared from the ternary positive electrode fiber composite according to claim 9.

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