A high-capacity lithium-ion battery for drones and its preparation method

Abstract

The present invention discloses a high-capacity lithium-ion battery for an unmanned aerial vehicle and a preparation method thereof. The method includes the following steps: Step 1: Uniformly coat the positive electrode slurry on the surface of the positive electrode current collector, dry, roll, and punch to obtain a positive electrode sheet; Step 2: Uniformly coat the negative electrode slurry on the surface of the negative electrode current collector, dry, roll, and punch to obtain a negative electrode sheet; Step 3: Place the polyolefin separator in acetone for washing, transfer it to an acrylamide solution, and under a nitrogen atmosphere, set the dose rate to 1.5-2 kGy / h and the irradiation dose to 2-5 kGy, 60 Co-γ ray irradiation grafting; obtain a separator; Step 4: Stack the positive electrode sheet, separator, and negative electrode sheet to make an electric core, put it into a packaging shell, inject an electrolyte solution, and seal to obtain a high-capacity lithium-ion battery. Beneficial effects: The negative electrode active material is prepared to significantly improve the lithium storage capacity; and combined with a composite binder and a compound conductive agent, a negative electrode sheet is obtained; the energy density and cycle stability of the lithium-ion battery are increased.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a high-capacity lithium-ion battery for unmanned aerial vehicles and a preparation method thereof. Background Art

[0002] With the development of science and technology, the applications of unmanned aerial vehicles have expanded to multiple civilian industries such as infectious disease monitoring, disaster rescue, express delivery, mapping, and ionization inspection. The battery of an unmanned aerial vehicle is the source of power for the unmanned aerial vehicle. All unmanned aerial vehicles on the market use lithium polymer batteries. Compared with ordinary batteries, lithium polymer batteries have the advantages of high rate, high energy ratio, high performance, high safety, long life, environmental protection and no pollution, and light weight. In terms of shape, lithium polymer batteries have the characteristics of ultra-thinness and can be made into batteries with different shapes and capacities according to the needs of some products.

[0003] In the prior art, the primary concern of the unmanned aerial vehicle battery is the capacity problem of performance. The polymer lithium-ion battery loses power very quickly on the unmanned aerial vehicle; its rapid discharge in a short period of time will also cause the battery temperature to rise rapidly, reduce the stability of the electrolyte, and cause the electrolyte to react with the electrode material, resulting in an increase in internal resistance, a decrease in capacity, and a decrease in cycle stability. On the other hand, the adhesion problem between the electrode plate and the separator is also one of the concerns. The affinity between the separator and the electrode plate is relatively low. During the process of cyclic charge and discharge, the problem of cell swelling and deformation is likely to occur, thus triggering safety problems; at the same time, it will also increase the thickness of the cell, resulting in a decrease in energy density.

[0004] In summary, to solve the above problems, it is of great significance to prepare a high-capacity lithium-ion battery for unmanned aerial vehicles. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-capacity lithium-ion battery for unmanned aerial vehicles and a preparation method thereof to solve the problems raised in the above background art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A preparation method of a high-capacity lithium-ion battery for unmanned aerial vehicles, characterized by comprising the following steps:

[0008] Step 1: Uniformly coat the positive electrode slurry on the surface of the positive electrode current collector, dry, roll, and punch to obtain a positive electrode plate;

[0009] Step 2: Uniformly coat the negative electrode slurry on the surface of the negative electrode current collector, dry, roll, and punch to obtain a negative electrode plate;

[0010] Step 3: Wash the polyolefin separator in acetone, transfer it to the acrylamide solution, and under a nitrogen atmosphere, set the dose rate to 1.5 - 2 kGy / h and the irradiation dose to 2 - 5 kGy, and irradiate with 60Co-γ rays for grafting; obtain the separator.

[0011] Step 4: Stack and assemble the positive electrode sheet, separator, and negative electrode sheet to make an electric core, place it in a packaging shell, inject the electrolyte solution, and seal it to obtain a high-capacity lithium-ion battery.

[0012] Preferably, the raw materials of the negative electrode paste include the following components: by weight, 84 - 90 parts of negative electrode active material, 5 - 8 parts of binder, and 5 - 8 parts of conductive agent; the negative electrode active material is prepared from porous graphene, sodium citrate, cobalt nitrate, and urea with a mass ratio of 1:1:(0.25 - 0.35):2.

[0013] Preferably, the preparation method of the negative electrode active material: ultrasonically disperse porous graphene in a 12 - 15 wt% cobalt nitrate solution, and add a 20 - 25 wt% sodium citrate solution; add urea and stir for 20 - 30 minutes to obtain a dispersion; heat the dispersion at a heating rate of 1 °C / min to 70 - 75 °C, stir and dry for 1 - 2 hours; transfer it to an oven, set the temperature to 80 - 85 °C and dry for 24 hours; transfer it to a tube furnace, under a nitrogen atmosphere, set the temperature to 600 - 800 °C and anneal for 1 - 1.5 hours, and cool it to room temperature with the furnace; wash it successively with perchloric acid and deionized water, and dry it to obtain the negative electrode active material.

[0014] Preferably, the preparation method of the porous graphene is: disperse graphene oxide in deionized water, add potassium permanganate, and stir evenly to obtain a dispersion; place it in a ball milling tank and ball mill for 15 - 20 minutes; take it out and freeze-dry it, and anneal it at 800 - 850 °C for 1 - 1.5 hours; after cooling, place it in a 1 mol / L hydrochloric acid solution and soak for 3 - 4 days, wash and dry it to obtain porous graphene.

[0015] Preferably, the binder is prepared by compounding tannic acid, polyacrylic acid, polyacrylamide, and pretreated porous graphene with a mass ratio of (0.12 - 0.15):1:(3 - 4):(0.2 - 0.3).

[0016] Preferably, the preparation method of the binder is: stir evenly a 1 - 2 wt% tannic acid solution and a 3 - 4 wt% polyacrylic acid solution to obtain a mixed solution A for standby; disperse polyacrylamide and N-methylpyrrolidone in an N,N-dimethylacetamide-aqueous solution in turn, add solution A, set the stirring speed to 500 - 600 rpm and stir for 2 - 3 hours; add pretreated porous graphene, set the speed to 1000 - 1200 rpm, and stir for 10 - 12 hours; obtain the composite binder.

[0017] More preferably, the preparation method of the pretreated porous graphene is as follows: dispersing the porous graphene in a mixed solvent of isopropanol and water to obtain a mixed solution of 5-10 wt%; under a nitrogen atmosphere, using 60 Co-γ ray irradiation with a dose rate of 3-5 kGy / h and an irradiation dose of 80-120 kGy, filtering and drying to obtain the pretreated porous graphene.

[0018] More preferably, the conductive agent is obtained by compounding nano-graphene and carbon nanotubes with a mass ratio of 1:3.

[0019] More preferably, the raw materials of the electrolyte include the following components: 16-18 wt% lithium salt, 1-1.5 wt% tris(trimethylsilyl) phosphite, 0.5-1 wt% trimethyl borate, 1-1.5 wt% p-hydroxybenzoic acid, and the rest is solvent.

[0020] More preferably, a high-capacity lithium-ion battery prepared by a preparation method of a high-capacity lithium-ion battery for an unmanned aerial vehicle.

[0021] In this technical solution, by preparing the negative electrode active material, the lithium storage capacity is significantly improved; and in combination with the composite binder and the compounded conductive agent, the negative electrode sheet is obtained; the energy density and cycle stability of the lithium-ion battery are increased. And acrylamide is grafted on the surface of the separator to increase the affinity and adhesion between the separator and the negative electrode sheet, thereby reducing the interface and polarization impedance; improving the battery performance.

[0022] (1) In the solution, a single graphene is used as the negative electrode active material, and the volume density is relatively low, and the lithium storage capacity is not high; therefore, in the solution, by loading cobalt oxide, the lithium insertion sites are increased; however, during the in-situ generation of cobalt oxide on the surface of graphene, there is an agglomeration phenomenon; at the same time, there are problems of poor conductivity and volume change of cobalt oxide; therefore, in the solution, sodium citrate and urea are added, one is to increase the dispersibility, and the other is to increase the active sites, thereby improving the lithium insertion sites and the rate of insertion and extraction of lithium ions, and improving the battery performance.

[0023] Specifically: In the solution, the surface of graphene oxide is impregnated with cobalt ions, and sodium citrate and urea are bound to the surface at the same time, increasing the dispersibility of graphene sheets. During the carbonization process, cobalt ions on the surface of graphene turn into cobalt oxide; while sodium citrate and urea are carbonized with graphene as the framework to form a three-dimensional structure. Among them, cobalt oxide is embedded in the carbon of the three-dimensional structure, which is beneficial to the increase of carbon density; the high porosity of the three-dimensional structure increases the active sites and inhibits the agglomeration of surface cobalt oxide; at the same time, this structure can effectively buffer the volume change of cobalt oxide during the insertion and extraction of lithium ions. On the other hand, in the solution, nitrogen in urea is not only doped into the carbon material; but also part of cobalt oxide is transformed into cobalt oxynitride; through the effective doping of nitrogen atoms, the surface properties of the active material are increased, the wettability of the electrolyte is increased, and the battery performance is improved.

[0024] In addition, in order to further enhance the insertion and extraction of lithium ions, porous graphene is used in the solution; in the solution, graphene oxide is mixed with potassium permanganate, ball-milled, calcined, and acid-etched to form graphene with pores on the surface; the lithium insertion sites and the efficient transport of lithium ions are increased, and the energy density is improved.

[0025] (2) In the solution, polyacrylic acid (PAA) is simply used as the binder, which is rigid and easy to break, and is not conducive to the cycle stability of the battery. Therefore, through treatment with tannic acid and then compounding with polyacrylamide and porous graphene, a binder with good viscoelasticity is formed. By first mixing tannic acid with polyacrylic acid, the viscosity of polyacrylic acid is increased through multiple hydrogen bond forces. At the same time, using the benzene ring in tannic acid, the electrolyte resistance and fracture toughness of polyacrylic acid are increased without reducing the liquid absorption property; it is beneficial to improve the cycle stability and service life of the battery. On the other hand, through the physical cross-linking between the modified polyacrylic acid, polyacrylamide, and porous graphene, a double hydrogen bond network is formed; the internal resistance is effectively reduced, and the charge transfer is promoted; and the viscoelasticity of the binder is improved, which is beneficial to buffering the expansion stress caused by temperature during charging or use and reducing the expansion of the battery cell. At the same time, good liquid absorption property effectively inhibits the growth of dendrites and the deposition of by-products on the electrode. The increase in the negative electrode adhesion helps the stability of the electrolyte.

[0026] (3) In the solution, by irradiating and grafting the surface of the separator, the wettability of the surface electrolyte is increased; more importantly, the affinity with the negative electrode sheet is increased, the interfacial adhesion is increased, the pores between the negative electrode sheet and the separator are reduced, the lithium ion transport path is increased, the interfacial impedance is reduced, and the volume expansion and surface dendrite growth are inhibited.

[0027] (4) In the solution, three additives, namely tris(trimethylsilyl) phosphite, trimethyl borate, and p-hydroxybenzoic acid, are added to the electrolyte. Among them, tris(trimethylsilyl) phosphite and trimethyl borate react with HF and LiF through self-decomposition reactions to reduce the by-products on the surface of the electrode sheet and improve the capacitance. While p-hydroxybenzoic acid can increase the stability of the electrolyte. It can form hydrogen bonds with the lithium salt, reduce the free molecules in the electrolyte, inhibit the decomposition of the solvent, and increase the stability of the electrolyte. The three work together to effectively reduce the interfacial impedance during the cycling process, form a stable negative electrode SEI layer, effectively reduce the interfacial and polarization impedance, thereby increasing the cycling stability and ensuring excellent energy density of the polymer lithium battery. Detailed implementation mode

[0028] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] In the following embodiments, the graphene oxide is prepared by treating graphene through the Hummers method. For the specific reaction, refer to the method of graphite oxide in Example 1 in CN201510819900.3.

[0030] Graphene (2000 mesh) is purchased from Macklin; carbon nanotubes (with a thickness of 1-2 nm) are purchased from Macklin; nano-graphene (conductivity: ≥1600 S / cm) is purchased from Macklin; polyacrylic acid (M.W 450,000) is purchased from Macklin; polyacrylamide (M.W 5,000,000) is purchased from Macklin.

[0031] In the N,N-dimethylacetamide-aqueous solution, the mass ratio of N,N-dimethylacetamide to deionized water is 1:1; in the isopropanol-water mixed solvent, the mass ratio of isopropanol to water is 1:1.

[0032] Example 1:

[0033] Step 1: Material preparation:

[0034] (1) Disperse graphene oxide in deionized water, add potassium permanganate, stir evenly to obtain a dispersion; place it in a ball milling tank, ball mill for 18 minutes; take it out and freeze-dry, anneal it at 800 °C for 1 hour; after cooling, place it in a 1 mol / L hydrochloric acid solution and soak for 3-4 days, wash and dry to obtain porous graphene.

[0035] (2) Weigh porous graphene, sodium citrate, cobalt nitrate, and urea according to a mass ratio of 1:0.3:1:2; ultrasonically disperse the porous graphene in a 20 wt% sodium citrate solution, and add a 12 wt% cobalt nitrate solution; add urea and stir for 25 minutes to obtain a dispersion; heat the dispersion to 70 °C at a heating rate of 1 °C / min, stir and dry for 1.5 hours; transfer it to an oven, set the temperature to 80 °C and dry for 24 hours; transfer it to a tube furnace, under a nitrogen atmosphere, set the temperature to 700 °C and anneal for 1 hour, and cool it to room temperature with the furnace; wash it successively with 0.1 mol / L perchloric acid and deionized water, and dry it to obtain the negative electrode active material.

[0036] (3) Disperse the porous graphene in a mixed solvent of isopropanol - water to obtain an 8 wt% mixture; place it under a nitrogen atmosphere and use 60 Co - γ ray irradiation with a dose rate of 5 kGy / h and an irradiation dose of 100 kGy, filter and dry to obtain pretreated porous graphene for standby;

[0037] Weigh tannic acid, polyacrylic acid, polyacrylamide, and pretreated porous graphene according to a mass ratio of 0.12:1:3.5:0.23; stir a 1.5 wt% tannic acid solution and a 3.5 wt% polyacrylic acid solution evenly to obtain a mixed solution A for standby; disperse polyacrylamide and N - methylpyrrolidone successively in an N,N - dimethylacetamide - aqueous solution, add solution A, set the stirring speed to 550 rpm and stir for 2 hours; add the pretreated porous graphene, set it to 1200 rpm, and stir for 12 hours; obtain a composite binder.

[0038] (4) Prepare the electrolyte: By mass percentage, 17 wt% lithium salt, 1 wt% tris(trimethylsilyl) phosphite, 0.5 wt% trimethyl borate, 1.5 wt% p - hydroxybenzoic acid, and the rest is the solvent. Among them, the lithium salt includes lithium hexafluorophosphate and difluorooxalate borate with a mass ratio of 3:1, and the solvent is diethyl carbonate, ethylene carbonate, and propylene carbonate with a mass ratio of 2:2:1.

[0039] Step 2: Mix 94 parts of lithium cobaltate, 4 parts of conductive agent (obtained by mixing 1 part of nano - graphene and 3 parts of carbon nanotubes), 2 parts of polyvinylidene fluoride, and 65 parts of N - dimethylpyrrolidone evenly to obtain a positive electrode paste; coat it on porous aluminum foil, and after drying, rolling, and punching, obtain a positive electrode sheet with a compaction density of 4 g / m 3 of the positive electrode sheet.

[0040] Step 3: Mix 86 parts of negative electrode active material, 8 parts of binder, 4 parts of conductive agent (obtained by mixing 1 part of nano-graphene and 3 parts of carbon nanotubes), and 65 parts of N-dimethylpyrrolidone evenly to obtain a negative electrode slurry; coat it on a porous copper foil, and after drying, rolling, and punching, obtain a negative electrode sheet with a compaction density of 1.5 g / m 3 of the negative electrode sheet.

[0041] Step 4: Wash the polyolefin separator in acetone, transfer it to an acrylamide solution, and under a nitrogen atmosphere, set the dose rate to 1.5 kGy / h and the irradiation dose to 4 kGy, 60 and irradiate it with Co-γ rays for grafting; obtain the separator;

[0042] Step 5: Stack the positive electrode sheet, separator, and negative electrode sheet to make an electric core, install it in a packaging shell, inject an electrolyte solution, and seal it to obtain a high-capacity lithium-ion battery.

[0043] Example 2:

[0044] Step 1: Material preparation:

[0045] (1) Disperse graphene oxide in deionized water, add potassium permanganate, and stir evenly to obtain a dispersion; place it in a ball milling tank and ball mill for 15 minutes; take it out and freeze-dry it, then anneal it at 800 °C for 1.5 hours; after cooling, place it in a 1 mol / L hydrochloric acid solution and soak for 4 days, wash and dry it to obtain porous graphene.

[0046] (2) Weigh porous graphene, sodium citrate, cobalt nitrate, and urea according to a mass ratio of 1:0.25:1:2; ultrasonically disperse the porous graphene in a 20 wt% sodium citrate solution, and add a 12 wt% cobalt nitrate solution; add urea and stir for 30 minutes to obtain a dispersion; heat the dispersion at a heating rate of 1 °C / min to 70 °C, stir and dry for 2 hours; transfer it to an oven, set the temperature to 80 °C and dry for 24 hours; transfer it to a tubular furnace, under a nitrogen atmosphere, set the temperature to 600 °C and anneal for 1.5 hours, and cool it to room temperature with the furnace; wash it successively with perchloric acid and deionized water, and dry it to obtain the negative electrode active material.

[0047] (3) Disperse the porous graphene in a mixed solvent of isopropanol and water to obtain a 5 wt% mixture; place it under a nitrogen atmosphere and use 60 Co-γ rays for irradiation, with a dose rate of 3 kGy / h and an irradiation dose of 80 kGy, filter and dry it to obtain pretreated porous graphene for standby;

[0048] Weigh tannic acid, polyacrylic acid, polyacrylamide, and pretreated porous graphene according to a mass ratio of 0.12:1:3:0.2; put 1 wt% tannic acid solution into 4 wt% polyacrylic acid solution, stir evenly to obtain a mixed solution A for standby; disperse polyacrylamide and N-methylpyrrolidone in N,N-dimethylacetamide-aqueous solution in sequence, add solution A, set the stirring speed at 500 rpm and stir for 3 hours; add pretreated porous graphene, set at 1000 rpm and stir for 12 hours; obtain a composite binder.

[0049] (4) Prepare the electrolyte: by mass percentage, 16 wt% lithium salt, 1.5 wt% tris(trimethylsilyl) phosphite, 1 wt% trimethyl borate, 1.5 wt% p-hydroxybenzoic acid, and the rest is solvent. The lithium salt includes lithium hexafluorophosphate and difluorooxalate borate with a mass ratio of 3:1, and the solvent is diethyl carbonate, ethylene carbonate, and propylene carbonate with a mass ratio of 2:2:1.

[0050] Step 2: Mix 94 parts of lithium cobaltate, 4 parts of conductive agent (obtained by mixing 1 part of nano-graphene and 3 parts of carbon nanotubes), 2 parts of polyvinylidene fluoride, and 65 parts of N-dimethylpyrrolidone evenly to obtain a positive electrode paste; coat it on porous aluminum foil, and after drying, rolling, and punching, obtain a positive electrode sheet with a tap density of 4 g / m 3 of the positive electrode sheet.

[0051] Step 3: Mix 84 parts of negative electrode active material, 10 parts of binder, 6 parts of conductive agent (obtained by mixing 1 part of nano-graphene and 3 parts of carbon nanotubes), and 65 parts of N-dimethylpyrrolidone evenly to obtain a negative electrode paste; coat it on porous copper foil, and after drying, rolling, and punching, obtain a negative electrode sheet with a tap density of 1.5 g / m 3 of the negative electrode sheet.

[0052] Step 4: Wash the polyolefin separator in acetone, transfer it to acrylamide solution, and under a nitrogen atmosphere, set the dose rate at 1.5 kGy / h and the irradiation dose at 2 kGy, 60 Co-γ ray irradiation grafting; obtain the separator;

[0053] Step 5: Stack the positive electrode sheet, separator, and negative electrode sheet to make an electric core, put it into a packaging shell, inject the electrolyte solution, and seal it to obtain a high-capacity lithium-ion battery.

[0054] Example 3:

[0055] Step 1: Material preparation:

[0056] (1)Disperse graphene oxide in deionized water, add potassium permanganate, stir evenly to obtain a dispersion; place it in a ball milling tank, ball mill for 20 minutes; take it out and freeze-dry, anneal it at 850 °C for 1 hour; after cooling, place it in a 1 mol / L hydrochloric acid solution, soak for 3 days, wash and dry to obtain porous graphene.

[0057] (2)Weigh porous graphene, sodium citrate, cobalt nitrate, and urea according to a mass ratio of 1:0.35:1:2; ultrasonically disperse the porous graphene in a 25 wt% sodium citrate solution, and add a 15 wt% cobalt nitrate solution; add urea and stir for 20 minutes to obtain a dispersion; heat the dispersion at a heating rate of 1 °C / min to 75 °C, stir and dry for 1 hour; transfer it to an oven, set the temperature to 80 °C and dry for 24 hours; transfer it to a tubular furnace, under a nitrogen atmosphere, set the temperature to 800 °C and anneal for 1 hour, and cool it to room temperature with the furnace; wash it successively with perchloric acid and deionized water, and dry to obtain the negative electrode active material.

[0058] (3)Disperse the porous graphene in a mixed solvent of isopropanol and water to obtain a 10 wt% mixture; place it under a nitrogen atmosphere and use 60 Co-γ ray irradiation with a dose rate of 5 kGy / h and an irradiation dose of 120 kGy, filter and dry to obtain pretreated porous graphene for standby;

[0059] Weigh tannic acid, polyacrylic acid, polyacrylamide, and pretreated porous graphene according to a mass ratio of 0.15:1:4:0.3; stir evenly in a 2 wt% tannic acid solution and a 3 wt% polyacrylic acid solution to obtain a mixed solution A for standby; disperse polyacrylamide and N-methylpyrrolidone successively in an N,N-dimethylacetamide-aqueous solution, add solution A, set the stirring speed to 600 rpm and stir for 2 hours; add the pretreated porous graphene, set it to 1200 rpm, and stir for 10 hours; obtain the composite binder.

[0060] (4)Prepare the electrolyte: By mass percentage, 18 wt% lithium salt, 1 wt% tris(trimethylsilyl) phosphite, 0.5 wt% trimethyl borate, 1 wt% p-hydroxybenzoic acid, and the rest is the solvent. The lithium salt includes lithium hexafluorophosphate and lithium difluoro(oxalato)borate with a mass ratio of 3:1, and the solvent is diethyl carbonate, ethylene carbonate, and propylene carbonate with a mass ratio of 2:2:1.

[0061] Step 2: Mix 94 parts of lithium cobaltate, 4 parts of conductive agent (a mixture of 1 part of nano-graphene and 3 parts of carbon nanotubes), 2 parts of polyvinylidene fluoride, and 68 parts of N-dimethylpyrrolidone evenly to obtain the positive electrode slurry; coat it on porous aluminum foil, and after drying, rolling, and punching, obtain a positive electrode sheet with a compaction density of 4 g / m 3 of.

[0062] Step 3: Mix 88 parts of negative electrode active material, 6 parts of binder, 6 parts of conductive agent (a mixture of 1.5 parts of nano-graphene and 4.5 parts of carbon nanotubes) and 68 parts of N-dimethylpyrrolidone evenly to obtain a negative electrode slurry; coat it on a porous copper foil, and after drying, rolling and punching, obtain a negative electrode sheet with a compaction density of 1.5 g / m 3 of the negative electrode sheet.

[0063] Step 4: Place the polyolefin separator in acetone for washing, transfer it to an acrylamide solution, and under a nitrogen atmosphere, set the dose rate to 2 kGy / h and the irradiation dose to 5 kGy, 60 and irradiate it with Co-γ rays for grafting; obtain the separator;

[0064] Step 5: Stack and assemble the positive electrode sheet, separator and negative electrode sheet to make an electric core, put it into a packaging shell, inject an electrolyte solution and seal it to obtain a high-capacity lithium-ion battery.

[0065] Comparative Example 1: Replace the negative electrode active material with a graphene / cobalt oxide composite material. Specifically, refer to the method disclosed in Example 1 of CN201510819900.3 to prepare the graphene / cobalt oxide composite material, and the rest is the same as in Example 1;

[0066] Comparative Example 2: Do not add sodium citrate in the preparation of the negative electrode active material, and the rest is the same as in Example 1;

[0067] Comparative Example 3: Do not add urea in the preparation of the negative electrode active material, and the rest is the same as in Example 1;

[0068] Comparative Example 4: Replace the porous graphene in the preparation of the negative electrode active material with graphene oxide, and the rest is the same as in Example 1;

[0069] Comparative Example 5: Do not introduce tannic acid into the binder, and the rest is the same as in Example 1;

[0070] Comparative Example 6: Do not pre-treat the porous graphene in the binder, and the rest is the same as in Example 1.

[0071] Comparative Example 7: Change the mass ratio of tannic acid, polyacrylic acid, polyacrylamide and pre-treated porous graphene to 0.12:1:3:0.5, and the rest is the same as in Example 1;

[0072] Comparative Example 8: In the electrolyte solution, completely replace trimethyl borate with hydroxybenzoic acid, and the rest is the same as in Example 1;

[0073] Comparative Example 9: In the electrolyte solution, completely replace trimethyl borate with tris(trimethylsilyl) phosphite and do not introduce hydroxybenzoic acid, and the rest is the same as in Example 1;

[0074] Experiment: The lithium-ion batteries prepared in the examples and Comparative Example 2 were subjected to performance testing. At room temperature, between 1.5 and 3 V, a constant current charge and discharge was performed at 0.5 C once, and the initial discharge capacity test was recorded. After 2000 cycles of testing, the discharge capacity was tested again, and the capacity retention rate was calculated. The obtained data are shown below:

[0075]

[0076]

[0077] Conclusion: From the data of the examples and comparative examples, it can be seen that in the solution, a composite material of nitrogen-doped cobalt oxide, graphene, and carbon was prepared, which significantly increased the active sites; and the binder obtained by co-compounding synergistically enhanced the capacitance and cycle stability. Comparative Examples 1 to 4 were related to the characteristic changes of the negative electrode active material. The data showed that sodium citrate, urea, and porous graphene synergistically improved the defects of cobalt oxide, increased the lithium intercalation sites and the efficient transmission of lithium ions, and improved the capacitance. Comparative Examples 5 to 7 were the characteristic changes of the composite binder. The data showed that the modification of tannic acid and the pretreatment of porous graphene enhanced the battery performance, but the introduction amount of the pretreated porous graphene should not be too much, which would increase brittleness and reduce the cycle stability. Comparative Examples 8 to 9 were the changes of the additives in the electrolyte solution, indicating that the addition of the three composite additives could minimize the internal resistance and improve the cycle stability.

[0078] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Preparation method of a high-capacity lithium-ion battery for an unmanned aerial vehicle, characterized in that: It includes the following steps: Step 1: Material preparation; Step 2: Uniformly coat the positive electrode paste on the surface of the positive electrode current collector, dry, roll, and punch to obtain a positive electrode sheet; Step 3: Uniformly coat the negative electrode paste on the surface of the negative electrode current collector, dry, roll, and punch to obtain a negative electrode sheet; Step 4: Place the polyolefin separator in acetone for washing, transfer it to the acrylamide solution, and under a nitrogen atmosphere, set the dose rate to 1.5 - 2 kGy / h and the irradiation dose to 2 - 5 kGy, 60 Irradiate and graft with Co-γ rays; obtain the separator; Step 5: Stack and assemble the positive electrode sheet, separator, and negative electrode sheet to make an electric core, install it in a packaging shell, inject an electrolyte solution, and seal to obtain a high-capacity lithium-ion battery; The raw materials of the negative electrode paste include the following components: by weight, 84-90 parts of negative electrode active material, 5-8 parts of binder, 5-8 parts of conductive agent, and 65-68 parts of solvent; The binder is prepared by compounding tannic acid, polyacrylic acid, polyacrylamide, and pretreated porous graphene with a mass ratio of (0.12-0.15):1:(3-4):(0.2-0.3); The preparation method of the binder is: put 1-2wt% tannic acid solution and 3-4wt% polyacrylic acid solution, stir evenly to obtain a mixed solution A for standby; disperse polyacrylamide and N-methylpyrrolidone in N,N-dimethylacetamide-aqueous solution in turn, add solution A, set the stirring speed to 500-600rpm and stir for 2-3 hours; add pretreated porous graphene, set 1000-1200rpm, and stir for 10-12 hours; obtain a composite binder; The preparation method of the pretreated porous graphene is as follows: Dispersing the porous graphene in a mixed solvent of isopropanol and water to obtain a mixed solution with a concentration of 5-10 wt%; placing it in a nitrogen atmosphere and using 60 Co-γ ray irradiation with a dose rate of 3-5 kGy / h and an irradiation dose of 80-120 kGy, followed by filtration and drying to obtain the pretreated porous graphene.

2. The preparation method of a high-capacity lithium-ion battery for an unmanned aerial vehicle according to claim 1, characterized in that: The negative electrode active material is prepared from porous graphene, sodium citrate, cobalt nitrate, and urea with a mass ratio of 1:(0.25-0.35):1:2; The preparation method of the negative electrode active material: ultrasonically disperse porous graphene in a 20-25wt% sodium citrate solution, add a 12-15wt% cobalt nitrate solution; add urea and stir for 20-30 minutes to obtain a dispersion; heat the dispersion at a heating rate of 1°C / min to 70-75°C, stir and dry for 1-2 hours; transfer to an oven, set the temperature to 80-85°C and dry for 24 hours; transfer to a tubular furnace, under a nitrogen atmosphere, set the temperature to 600-800°C and anneal for 1-1.5 hours, and cool to room temperature with the furnace; wash it successively with perchloric acid and deionized water, and dry to obtain the negative electrode active material.

3. The preparation method of a high-capacity lithium-ion battery for an unmanned aerial vehicle according to claim 1, characterized in that: The preparation method of the porous graphene is: disperse graphene oxide in deionized water, add potassium permanganate, and stir evenly to obtain a dispersion; place it in a ball milling tank and ball mill for 15-20 minutes; take it out and freeze-dry, and anneal it at 800-850°C for 1-1.5 hours; after cooling, soak it in a 1mol / L hydrochloric acid solution for 3-4 days, wash and dry to obtain porous graphene.

4. The preparation method of a high-capacity lithium-ion battery for an unmanned aerial vehicle according to claim 1, characterized in that: The conductive agent is obtained by compounding nanographene and carbon nanotubes with a mass ratio of 1:

3.

5. The preparation method of a high-capacity lithium-ion battery for an unmanned aerial vehicle according to claim 1, characterized in that: The raw materials of the electrolyte solution include the following components: 16-18 wt% lithium salt, 1-1.5 wt% tris(trimethylsilyl) phosphite, 0.5-1 wt% trimethyl borate, 1-1.5 wt% p-hydroxybenzoic acid, and the rest is solvent.

6. A high-capacity lithium-ion battery prepared by the preparation method of a high-capacity lithium-ion battery for an unmanned aerial vehicle according to any one of claims 1-5.

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