Modified graphite-niobium tungstate@carbon composite material, and preparation and use thereof

Abstract

The present invention relates to the field of battery materials, and specifically relates to a modified graphite-niobium tungstate@carbon composite material, and preparation and use thereof. The composite material has a core-shell structure, wherein the core comprises graphite modified with a functional group a and niobium tungstate modified with a functional group b, the shell is composed of amorphous carbon, and the functional group a and the functional group b are independently at least one of a hydroxyl group, a carboxyl group, an amino group, an acyl group, and an ester group. The present invention provides a modified graphite-based negative electrode active material, in which innovatively, graphite is pre-modified with a functional group a and is further compositely modified with niobium tungstate modified with a functional group b. In this way, the hydrogen-bonding and / or chemical-bonding effect of niobium tungstate and the functional group b thereof on the functional group a of graphite improves the composite morphology of graphite and niobium tungstate, optimizes ion and electron transport modes, reduces impedance, and, in combination with subsequent carbon coating, further optimizes the low-temperature and fast-charging performance of the composite material.

Description

Modified graphite-niobium tungstate@carbon composites and their preparation and application Technical Field

[0001] This invention relates to the field of anode materials, and more specifically to the field of graphite-based anode materials. Background Technology

[0002] For lithium-ion batteries, the anode material is often the main factor limiting the rate performance. Among the many anodes currently available, many alloy-type and conversion-type anodes with high theoretical specific capacity exhibit high specific capacity, but suffer from significant volume expansion, leading to severe capacity decay during cycling and low first-cycle coulombic efficiency. In contrast, metal oxide intercalation anode materials possess higher rate performance and are more suitable as anode materials for high-power lithium-ion batteries compared to other types. Niobium tungsten oxide (Nb) 18 W 16 O 93 and Nb 16 W5O 55 These are crystals with tungsten bronze structure and Wadsley-Roth crystal shear plane structure, respectively, and are recently reported active materials with good application prospects.

[0003] For example, Chinese patent document CN116404236A discloses a niobium-based low-temperature lithium-ion battery, specifically describing the addition of a niobium-based compound to the negative electrode active material, and further describing that the niobium-based compound is at least one of niobium oxide and / or niobium tungstate, heteroatom-doped niobium oxide and / or niobium tungstate, carbon-coated niobium oxide and / or niobium tungstate, and carbon-coated heteroatom-doped niobium oxide and / or niobium tungstate.

[0004] Patent document with publication number EP3804005B1 discloses a method for charging and / or discharging an electrochemical cell at a high rate, specifically describing that its working electrode comprises niobium tungsten oxide and / or niobium molybdenum oxide.

[0005] Chinese patent document CN112397709A also describes a niobium tungstate material for high-safety lithium-ion batteries, specifically describing the molecular formula of the niobium tungstate material as Nb. 14 W3O 44 It is prepared by uniformly mixing niobium oxalate hydrate, ammonium metatungstate and fuel in an inorganic acid, and then reacting them in an air atmosphere at 1050-1250℃ through a self-propagating combustion reaction. Technical issues

[0006] In summary, existing technologies have reported some schemes for using niobium tungsten oxide as a negative electrode, but the existing schemes all use niobium tungstate as an active material and conductive agent to prepare batteries. This scheme is difficult to effectively solve the interfacial interaction problems between niobium tungstates and between niobium tungstate and conductive particles, making it difficult to fully utilize its performance and obtain materials that balance ultra-low temperature stability and fast charging performance. Technical solutions

[0007] To address the problems of the prior art, the primary objective of this invention is to provide a modified graphite-niobium tungstate@carbon composite material, which aims to improve the interfacial interaction between graphite and niobium tungstate, thereby improving the low-temperature and fast-charging performance of the composite material.

[0008] The second objective of this invention is to provide a method for preparing and applying the modified graphite-niobium tungstate@carbon composite material.

[0009] The third objective of this invention is to provide an alkali metal secondary battery containing the modified graphite-niobium tungstate@carbon composite material, as well as its negative electrode and negative electrode material.

[0010] A modified graphite-niobium tungstate@carbon composite material has a core-shell structure, wherein the core comprises modified graphite modified with functional group a and modified niobium tungstate modified with functional group b, and the shell is amorphous carbon.

[0011] The functional groups a and b are individually at least one of hydroxyl, carboxyl, amino, acyl, and ester groups.

[0012] This invention provides a modified graphite-based anode active material, which innovatively pre-modifies graphite with functional group a, and innovatively uses niobium tungstate modified with functional group b to perform composite modification. In this way, the hydrogen bonding and / or chemical bonding of niobium tungstate and its functional group b with the functional group a of graphite improves the composite morphology, optimizes the ion and electron conduction mode, reduces impedance, and further optimizes the low-temperature and fast-charging performance of the composite material by subsequent carbon coating.

[0013] In this invention, functional group a and functional group b interact with each other through hydrogen bonds, chemical bonds, etc. Preferably, functional group a and functional group b can form ester groups and / or amide groups. For example, in an optional embodiment of this invention, functional group a may contain hydroxyl groups, carboxyl groups, etc., and functional group b may contain amino groups. In this invention, the interaction of functional group a and functional group b through the aforementioned ester groups and / or amide groups can further strengthen the interface between the two, reduce impedance, and improve electron and ion conduction pathways, thus contributing to further enhancing the low-temperature and fast-charging performance of the composite material.

[0014] In this invention, the niobium tungstate in the modified niobium tungstate is preferably a homologous heterostructure Nb. 16W5O 55 / Nb 18 W8O 69 Phase materials. Studies have shown that using this preferred niobium tungstate modified with the dual modification scheme of this invention can achieve better synergy and better low-temperature and fast-charging performance.

[0015] Preferably, the weight ratio of modified graphite to modified niobium tungstate is 100:1~20; more preferably, it is 100:3~5.

[0016] The present invention also provides a method for preparing the modified graphite-niobium tungstate@carbon composite material, wherein modified graphite modified with functional group a and modified niobium tungstate modified with functional group b are mixed, and then mixed with a carbon source for carbonization treatment to obtain the composite material.

[0017] As an optional embodiment of the present invention, the functional group a in the modified graphite includes hydroxyl and / or carboxyl groups; it is obtained by modifying graphite in a modification solution.

[0018] Preferably, the modified solution includes at least one modifier selected from nitric acid, hydrofluoric acid, perchloric acid, and hydrogen peroxide.

[0019] Preferably, the concentration of the modifier in the modified solution is above 10 wt.%, and more preferably 30-70 wt.%. Alternatively, the modified solution can be a mixed solution of hydrochloric acid with a concentration of 20-40 wt.% and nitric acid with a concentration of 20-40 wt.% in a volume ratio of 1:0.5-2.

[0020] Preferably, the weight ratio of the modifier to graphite in the modified solution is 1:4~10.

[0021] The temperature during the modification stage is 400~600℃, and the modification time is 2~4h.

[0022] Preferably, the graphite is artificial graphite, which can be an existing commercial product or obtained by crushing, shaping, and graphitizing coke raw materials.

[0023] In this invention, niobium tungstate is obtained by heat treatment with a tungsten source and a niobium source. The tungsten source is an oxide of tungsten. The niobium source is an oxide of niobium. The Nd / W molar ratio in the tungsten and niobium sources is 1.5~6:1; preferably 1.9~5.6:1, and more preferably 2~4.5:1. The heat treatment temperature is 1300~1400℃, and the heat treatment holding time is 20~30h.

[0024] In one optional embodiment of the present invention, the functional group b in the modified niobium tungstate includes an amino group.

[0025] Preferably, the modified niobium tungstate is obtained by modifying niobium tungstate with an aminosilane. The steps include, for example, placing niobium tungstate in a solution containing an aminosilane and carrying out a modification reaction under acidic conditions. The pH of the modification reaction stage is 4-6.5, more preferably 5-6, and the mass ratio of niobium tungstate to aminosilane is 10:1-5, more preferably 10:1-2. During the treatment process, the concentration of aminosilane in the initial solution is not particularly required, for example, it can be 0.5-3%.

[0026] In this invention, modified graphite and modified niobium tungstate can be conventionally mixed, such as by VC mixing, before subsequent coating treatment. Preferably, the modified graphite and modified niobium tungstate are mixed using acoustic resonance. Research in this invention shows that the interaction of modified graphite and modified niobium tungstate under acoustic resonance can further optimize the hydrogen bonding and other interactions of the active groups between the materials, contributing to further optimization of the physicochemical properties of the material and further enhancing the low-temperature and fast-charging performance of the prepared material.

[0027] In this invention, the carbon source includes one or more of asphalt, phenolic resin, petroleum resin and epoxy resin.

[0028] Preferably, the carbonization temperature is 1000~1300℃, and more preferably 1100~1200℃.

[0029] In this invention, a pre-carbonization process is allowed before carbonization. The pre-carbonization process includes, for example, a first pre-carbonization process at a temperature of 300-400°C and a second pre-carbonization process at a temperature of 550-650°C.

[0030] The carbonization time is 2 to 6 hours. When a pre-carbonization process is present, the pre-carbonization time can be, for example, 2 to 6 hours.

[0031] The present invention also provides an application of the modified graphite-niobium tungstate@carbon composite material described above, using it as a negative electrode active material to prepare an alkali metal secondary battery.

[0032] The present invention also provides a negative electrode for an alkali metal secondary battery, comprising a current collector and a negative electrode material composite thereon, wherein the negative electrode material comprises a negative electrode active material, and the negative electrode active material comprises the modified graphite-niobium tungstate@carbon composite material.

[0033] The present invention also provides an alkali metal secondary battery comprising the negative electrode described herein.

[0034] In this invention, lithium-ion batteries and their negative electrodes and materials can be prepared from the recycled negative electrode active material using known processes. For example, the negative electrode active material obtained in this invention is combined with a binder and selectively with a conductive agent to form a negative electrode material. Further, the negative electrode material is slurried and coated onto a current collector using known methods to form a negative electrode. Even further, the negative electrode is combined with a separator and a positive electrode to form a lithium-ion battery. The binder, conductive agent, separator, current collector, and positive electrode described in this invention can all be conventionally available in the industry.

[0035] The present invention also provides a negative electrode for a lithium-ion battery, comprising a current collector and a negative electrode material composite thereon, wherein the negative electrode material comprises a negative electrode active material prepared by regeneration according to the present invention.

[0036] The present invention also provides a lithium-ion battery comprising a negative electrode, a separator, and a positive electrode sequentially composited, wherein the negative electrode is the negative electrode of the present invention containing the regenerated negative electrode active material. Beneficial effects

[0037] This invention provides a modified graphite-based anode active material, which innovatively pre-modifies graphite with functional group a, and innovatively uses niobium tungstate modified with functional group b to perform composite modification. In this way, the hydrogen bonding and / or chemical bonding of niobium tungstate and its functional group b with the functional group a of graphite improves the composite morphology, optimizes the ion and electron conduction mode, reduces impedance, and further optimizes the low-temperature and fast-charging performance of the composite material by subsequent carbon coating. Attached Figure Description

[0038] Figure 1 is a picture of the negative electrode product of Example 1.

[0039] Figure 2 shows the interface of the negative electrode sheet of the lithium-ion battery prepared as the negative electrode material in Example 4 under 3C full charge in a -40°C environment. Embodiments of the present invention

[0040] To better understand the present invention, the following description, in conjunction with embodiments, further illustrates the present invention; however, the implementation of the present invention is not limited thereto.

[0041] The present invention provides an optional method for preparing the modified graphite-niobium tungstate@carbon composite material, comprising the following steps:

[0042] Step 1: The coke raw material is coarsely crushed and pulverized to obtain primary granules with Dv50 = 5~10μm.

[0043] Step 2: Mix the first-stage material obtained in Step 1 with the binder in a VC high-speed mixer at a certain mass ratio, then place it in a reaction kettle for granulation, cooling, and discharge to obtain secondary granules of the second-stage material with Dv50=12~20μm.

[0044] Step 3: Place the two-stage material obtained in Step 2 into a graphitization furnace for high-temperature graphitization, and then depolymerize to obtain a three-stage material with Dv50=9~18μm;

[0045] Step 4: Prepare a modifier aqueous solution of a certain concentration, then spray the modifier solution evenly onto the three-section material obtained in Step 3 according to a certain mass ratio and mix evenly. Then place it in an atmosphere furnace and keep it at a certain temperature and atmosphere for heat treatment. Then cool down and discharge the material and wash it with deionized water until neutral (pH=6.5~7.0 neutral). Dry it to obtain the four-section material.

[0046] Step 5: Place nano-niobium oxide and nano-tungsten oxide in a ball mill at a certain mass ratio for ball milling and drying;

[0047] Step 6: Place the ball-milled and dried nano-niobium oxide and nano-tungsten oxide mixture in an atmosphere furnace and calcine it under an oxygen-containing atmosphere. Then cool it down and discharge it to obtain NWO.

[0048] Step 7: Prepare an aqueous solution of aminosilane and catalyst with a certain concentration, then disperse NWO in the aminosilane aqueous solution, react at a certain temperature, and then filter, wash and dry to obtain aminoNWO.

[0049] Step 8: Place the four-segment material obtained in Step 4 and amino NWO in a resonance device at a certain mass ratio and resonate at a certain temperature, so that amino NWO enters the graphite micropores and surface, thereby obtaining a five-segment material.

[0050] Step 9: Mix the five-segment material obtained in Step 8 with the coating agent in a VC high-speed mixer at a certain mass ratio, then place it in a reaction vessel for medium-temperature heat treatment, and then place it in a high-temperature heat treatment device for high-temperature heat treatment. After cooling and discharging, a low-temperature fast-charging artificial graphite anode with Dv50=9~18μm is obtained.

[0051] Preferably, the coke raw material is one or more of petroleum coke, coal-based coke, needle coke, pitch coke, and anthracite; the binder is one or more of pitch, phenolic resin, petroleum resin, and epoxy resin; the reactor is a vertical reactor, a horizontal reactor, or a rotary kiln; the modifier is one or more of hydrochloric acid, nitric acid, hydrofluoric acid, sulfuric acid, perchloric acid, and hydrogen peroxide; the niobium oxide is one or more of niobium dioxide and niobium pentoxide; the tungsten oxide is one or more of tungsten dioxide and tungsten trioxide; the aminosilane is one or more of γ-aminopropyltriethoxysilane (APTES), N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (AEAPS), N-phenyl-γ-aminopropyltrimethoxysilane (PhAPTS), N-cyclohexyl-3-aminopropyltrimethoxysilane, and bis(triethoxysilylpropyl)amine (BTESPA); and the coating agent is one or more of pitch, phenolic resin, petroleum resin, and epoxy resin.

[0052] Preferably, in step 1, Dv50 = 5~15μm.

[0053] Preferably, in step 2, the binder is asphalt, the mass ratio of the primary material to asphalt is 100:2~15, the heat treatment atmosphere is an inert atmosphere, and the specific heating steps are as follows: heating from room temperature to 300~400℃ at 5℃ / min, holding for 1~2h, and then continuing to heat to 500~650℃ at 5℃ / min, holding for 2~4h.

[0054] Preferably, in step 3, the graphitization furnace is an Atchison crucible graphitization furnace with a graphitization temperature ≥3000℃ and a power consumption per ton ≥7000 kWh. The graphitization time is, for example, 15~25 hours.

[0055] Preferably, in step 4, the modifier is a mixture of hydrochloric acid, nitric acid, hydrofluoric acid, sulfuric acid, perchloric acid, and hydrogen peroxide. The concentration of the aqueous solution of the modifier is 20-70 wt%, the mass ratio of the modifier to graphite is 1:5-10, the heat treatment heating step is to heat to 400-600℃ at a rate of 5℃ / min, and then hold at that temperature for 2-4 hours, and the heat treatment atmosphere is an oxygen-containing atmosphere (air, a mixture of oxygen and inert gas).

[0056] Preferably, in step 5, the niobium oxide is one or more of niobium dioxide or niobium pentoxide, and the tungsten oxide is one or more of tungsten dioxide or tungsten trioxide. More preferably, it is niobium dioxide and tungsten dioxide, with a mass ratio of niobium dioxide to tungsten dioxide of 2.25~3.20; or it is niobium pentoxide and tungsten trioxide, with a mass ratio of niobium pentoxide to tungsten trioxide of 1.125~1.600. The ball mill is a high-energy ball mill with a rotation speed of 300~500 r / min and a milling time of 10~20 h.

[0057] Preferably, in step 6, the heat treatment atmosphere is an oxygen-containing atmosphere, the heating rate is 5℃ / min, the temperature is raised to 1300~1400℃, and the holding time is 22~30h.

[0058] Preferably, in step 7, the aminosilane is one or more of γ-aminopropyltriethoxysilane (APTES), N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (AEAPS), N-phenyl-γ-aminopropyltrimethyloxysilane (PhAPTS), N-cyclohexyl-3-aminopropyltrimethoxysilane, and bis(triethoxysilylpropyl)amine (BTESPA). The aqueous solution solubility of the aminosilane is 0.5-5%, the catalyst is an organic acid such as acetic acid, and the pH is adjusted to 4-6.5 by adding an appropriate amount of organic acid. The mass ratio of NWO to aminosilane is 10:1-5. The reaction temperature is 25-60°C, and the reaction time is 6-15 h.

[0059] Preferably, in step 8, the mass ratio of the four-segment material to amino NWO is 100:1~20, and the resonance time is 2~20h.

[0060] Preferably, in step 9, the medium-temperature heat treatment reactor is a vertical reactor, a horizontal reactor, or a rotary kiln; the coating agent is one or more of asphalt, phenolic resin, petroleum resin, and epoxy resin; the mass ratio of the primary material to the binder is 100:2~10; the medium-temperature heat treatment atmosphere is an inert atmosphere; and the specific heating steps for the medium-temperature heat treatment are: heating from room temperature to 300~400℃ at 5℃ / min, holding for 1~2 hours, and then continuing to heat at 5℃ / min to 500~650℃, holding for 2~4 hours. The high-temperature heat treatment equipment is an atmosphere furnace, a roller kiln, a tunnel kiln, or a pusher kiln; the high-temperature heat treatment atmosphere is an inert atmosphere; and the specific heating steps for the high-temperature heat treatment are: heating from room temperature to 1100~1200℃ at 5℃ / min, holding for 4~6 hours.

[0061] The present invention also provides an application of the negative electrode active material prepared by the method described above, for the preparation of lithium-ion batteries;

[0062] Preferably, it is used to prepare the negative electrode of a lithium-ion battery;

[0063] Further optimization will allow it to be used as a negative electrode material for lithium-ion batteries;

[0064] Further optimization involves combining it with binders and conductive agents to prepare negative electrode materials for lithium-ion batteries.

[0065] The resonant mixing described in this invention is a conventional mixing device that uses sound waves as the mixing source. For example, as an example of an alternative solution, the resonant device in the following case is the HAM500 resonator manufactured by Shenzhen Sound Enhancement Technology Co., Ltd.

[0066] Example 1

[0067] Step 1: The needle coke raw material is coarsely crushed and pulverized to obtain primary granules with Dv50 = 6~8μm.

[0068] Step 2: Mix the first-stage material obtained in Step 1 with asphalt at a mass ratio of 100:10 in a VC high-speed mixer until homogeneous. Then place the mixture in a reaction vessel and heat it to 350°C at 5°C / min. Hold the temperature for 1 hour. Then continue to heat it to 600°C at 5°C / min and hold the temperature for 2 hours. Finally, cool it down to below 50°C and discharge the material to obtain the second-stage material.

[0069] Step 3: Place the two-stage material obtained in Step 2 into the Atchison graphitization furnace for high-temperature graphitization at a temperature of 3100℃ (graphitization time of 20h). Cool down, discharge, and depolymerize to obtain the three-stage material.

[0070] Step 4: Select hydrochloric acid and nitric acid as modifiers. Prepare a 30wt% solution of hydrochloric acid and a 30wt% solution of nitric acid. The mass ratio of hydrochloric acid to nitric acid is 1:1, and the mass ratio of the three-stage material to the modifier is 5:1. Spray the prepared modifier aqueous solution evenly into the three-stage material and mix it evenly. Then place the evenly mixed material in an atmosphere furnace and heat it to 400℃ at 5℃ / min. Hold it at this temperature for 2 hours. Then cool it down, discharge it, and wash it with deionized water until it is neutral (pH=6.5~7.0). Dry it to obtain the four-stage material.

[0071] Step 5: Place nano-niobium pentoxide and nano-tungsten trioxide in a high-energy ball mill with a mass ratio of nano-niobium pentoxide: nano-tungsten trioxide equal to 1.2:1 (Nd / W molar ratio is 2:1). Use ethanol as the dispersant, and mill at 400 r / min for 12 h. Then discharge and dry the material.

[0072] Step 6: Place the ball-milled and dried nano-niobium pentoxide and nano-tungsten trioxide mixture in an atmosphere furnace, introduce compressed air, heat to 1350℃ at 5℃ / min, hold for 24h, then cool to below 50℃ at a rate of 10℃ / min, discharge the material to obtain NWO, and then use a nano-sand mill to sand mill the NWO to obtain nano-NWO.

[0073] Step 7: First, prepare a 1 wt% aqueous solution of γ-aminopropyltriethoxysilane (APTES). Then, add nano NWO to the APTES aqueous solution at a mass ratio of nano NWO:APTES = 10:1. Add acetic acid to the mixed solution to adjust the pH to 6. Mix thoroughly at 35°C for 8 hours. Then wash until neutral and dry to obtain nano amino NWO.

[0074] Step 8: Place the four-segment material obtained in Step 4 and nano-amino NWO at a mass ratio of four-segment material: nano-amino NWO = 100: 5 into a resonance device for resonance for 4 hours. After resonance is completed, collect the material to obtain five-segment material.

[0075] Step 9: Mix the five-section material obtained in Step 8 with asphalt at a certain mass ratio of five-section material: asphalt = 100:4 in a VC high-speed mixer until homogeneous. Then, place the mixture in a reactor and heat it to 400°C at 5°C / min under nitrogen protection, hold it at that temperature for 1.5 hours, then continue to heat it to 650°C at 5°C / min, hold it at that temperature for 2 hours, cool it down to below 50°C, and discharge the material. Then, place the mixture in an atmosphere furnace and heat it to 1150°C at 5°C / min under nitrogen protection, hold it at that temperature for 4 hours, cool it down to below 50°C, and discharge the material.

[0076] Example 2

[0077] Step 1: The needle coke raw material is coarsely crushed and pulverized to obtain primary granules with Dv50 = 6~8μm.

[0078] Step 2: Mix the first-stage material obtained in Step 1 with asphalt at a mass ratio of 100:6 in a VC high-speed mixer until homogeneous. Then place the mixture in a reaction vessel and heat it to 300°C at 5°C / min. Hold the temperature for 2 hours. Then continue to heat it to 550°C at 5°C / min and hold the temperature for 4 hours. Finally, cool it down to below 50°C and discharge the material to obtain the second-stage material.

[0079] Step 3: Place the two-stage material obtained in Step 2 into the Atchison graphitization furnace for high-temperature graphitization at a temperature of 3000℃ (graphitization time of 24h). Cool down, discharge, and depolymerize to obtain the three-stage material.

[0080] Step 4: Select hydrochloric acid and nitric acid as modifiers. Prepare a 35wt% solution of hydrochloric acid and a 35wt% solution of nitric acid. The mass ratio of hydrochloric acid to nitric acid is 1:1, and the mass ratio of the three-stage material to the modifier is 8:1. Spray the prepared modifier aqueous solution evenly into the three-stage material and mix it evenly. Then place the evenly mixed material in an atmosphere furnace and heat it to 500℃ at 5℃ / min. Hold it at this temperature for 2 hours. Then cool it down, discharge it, and wash it with deionized water until it is neutral (pH=6.5~7.0). Dry it to obtain the four-stage material.

[0081] Step 5: Place nano-niobium pentoxide and nano-tungsten trioxide in a high-energy ball mill at a mass ratio of nano-niobium pentoxide: nano-tungsten trioxide equal to 1.5:1. Use ethanol as the dispersant, and mill at a speed of 400 r / min for 12 h. Then discharge and dry the material.

[0082] Step 6: Place the ball-milled and dried nano-niobium pentoxide and nano-tungsten trioxide mixture in an atmosphere furnace, introduce compressed air, heat to 1300℃ at 5℃ / min, hold for 30h, then cool to below 50℃ at a rate of 10℃ / min, discharge the material to obtain NWO, and then use a nano-sand mill to sand mill the NWO to obtain nano NWO.

[0083] Step 7: First, prepare a 1.5 wt% aqueous solution of γ-aminopropyltriethoxysilane (APTES). Then, add nano-NWO to the APTES aqueous solution at a mass ratio of nano-NWO:APTES = 10:1.5. Add acetic acid to the mixed solution to adjust the pH to 5.5. Mix thoroughly at 35°C for 12 hours. Then wash until neutral and dry to obtain nano-aminoNWO.

[0084] Step 8: Place the four-segment material obtained in Step 4 and nano-amino NWO at a mass ratio of four-segment material: nano-amino NWO = 100: 5 into a resonance device for resonance for 4 hours. After resonance is completed, collect the material to obtain five-segment material.

[0085] Step 9: Mix the five-section material obtained in Step 8 with asphalt at a certain mass ratio of five-section material: asphalt = 100:5 in a VC high-speed mixer until homogeneous. Then, place the mixture in a reactor and heat it to 400°C at 5°C / min under nitrogen protection, hold it at that temperature for 1.5 hours, then continue to heat it to 650°C at 5°C / min, hold it at that temperature for 2 hours, cool it down to below 50°C, and discharge the material. Then, place the mixture in an atmosphere furnace and heat it to 1150°C at 5°C / min under nitrogen protection, hold it at that temperature for 4 hours, cool it down to below 50°C, and discharge the material.

[0086] Example 3

[0087] Step 1: The needle coke raw material is coarsely crushed and pulverized to obtain primary granules with Dv50 = 6~8μm.

[0088] Step 2: Mix the first-stage material obtained in Step 1 with asphalt at a mass ratio of 100:12 in a VC high-speed mixer until homogeneous. Then place the mixture in a reaction vessel and heat it to 400°C at 5°C / min. Hold the temperature for 1 hour. Then continue to heat it to 650°C at 5°C / min and hold the temperature for 2 hours. Finally, cool it down to below 50°C and discharge the material to obtain the second-stage material.

[0089] Step 3: Place the two-stage material obtained in Step 2 into the Atchison graphitization furnace for high-temperature graphitization at a temperature of 3100℃ (holding time of 22h), then cool down, discharge, and depolymerize to obtain the three-stage material.

[0090] Step 4: Select hydrochloric acid and nitric acid as modifiers. Prepare a 30wt% solution of hydrochloric acid and a 30wt% solution of nitric acid. According to the mass ratio of hydrochloric acid:nitric acid = 1:1 and the ratio of three-stage material:modifier = 5:1, spray the prepared modifier aqueous solution evenly into the three-stage material and mix it evenly. Then place the evenly mixed material in an atmosphere furnace, heat it to 550℃ at 5℃ / min, hold it at that temperature for 2 hours, then cool it down and discharge it. Wash it with deionized water until it is neutral (pH = 6.5~7.0 neutral), and dry it to obtain the four-stage material.

[0091] Step 5: Place nano-niobium pentoxide and nano-tungsten trioxide in a high-energy ball mill at a mass ratio of nano-niobium pentoxide: nano-tungsten trioxide equal to 1.6:1. Use ethanol as the dispersant, and mill at a speed of 400 r / min for 12 hours. Then discharge and dry the material.

[0092] Step 6: Place the ball-milled and dried nano-niobium pentoxide and nano-tungsten trioxide mixture in an atmosphere furnace, introduce compressed air, heat to 1400℃ at 5℃ / min, hold for 24h, then cool to below 50℃ at a rate of 10℃ / min, discharge the material to obtain NWO, and then use a nano-sand mill to sand mill the NWO to obtain nano NWO.

[0093] Step 7: First, prepare a 1 wt% aqueous solution of the treatment agent (γ-aminopropyltriethoxysilane (APTES)). Then, add nano NWO to the APTES aqueous solution at a mass ratio of nano NWO:APTES = 10:1. Add acetic acid to the mixed solution to adjust the pH to 5. Mix thoroughly at 45°C for 10 h. Then wash until neutral and dry to obtain nano amino NWO.

[0094] Step 8: Place the four-segment material obtained in Step 4 and nano-amino NWO at a mass ratio of four-segment material: nano-amino NWO = 100: 5 into a resonance device for resonance for 4 hours. After resonance is completed, collect the material to obtain five-segment material.

[0095] Step 9: Mix the five-section material obtained in Step 8 with asphalt at a certain mass ratio of five-section material: asphalt = 100:4 in a VC high-speed mixer until homogeneous. Then, place the mixture in a reactor and heat it to 350°C at 5°C / min under nitrogen protection, hold it at that temperature for 1.5 hours, then continue to heat it to 550°C at 5°C / min, hold it at that temperature for 3 hours, cool it down to below 50°C, and discharge the material. Then, place the mixture in an atmosphere furnace and heat it to 1200°C at 5°C / min under nitrogen protection, hold it at that temperature for 4 hours, cool it down to below 50°C, and discharge the material.

[0096] Example 4

[0097] Compared with Example 1, the only difference is that in step 4, the composition of the modifier is changed, specifically: 30wt% hydrochloric acid and 30wt% nitric acid are replaced with 30wt% hydrochloric acid and 30wt% oxalic acid; other operations and parameters are the same as in Example 1.

[0098] Example 5

[0099] Compared with Example 1, the only difference is that in step 5, the preparation of NWO is changed. Specifically, niobium pentoxide is replaced with niobium dioxide, tungsten trioxide is replaced with tungsten dioxide, and niobium dioxide and tungsten dioxide are prepared in a mass ratio of niobium dioxide:tungsten dioxide equal to 2.5:1. Other operations and parameters are the same as in Example 1.

[0100] Example 6

[0101] Compared with Example 1, the only difference is that in step 8, the mass ratio of the four-stage material to amino NWO is 100:3, and the other operations and parameters are the same as in Example 1.

[0102] Example 7

[0103] Compared with Example 1, the only difference is that in step 7, oxalic acid is selected as the treatment agent, and oxalic acid is prepared into an aqueous solution with a concentration of 1 mol / L. The nano NWO is dispersed in the oxalic acid solution according to the mass ratio of nano NWO to oxalic acid solution of 1:1. The mixture is thoroughly mixed at 80°C for 8 hours, then cooled to below 50°C, washed until neutral and dried to obtain nano carboxyl NWO.

[0104] Example 8

[0105] Compared with Example 1, the only difference is that in step 8, the resonance treatment is replaced by VC mixing, while other operations and parameters are the same as in Example 1.

[0106] Comparative Example 1

[0107] Compared with Example 1, the only difference is that step 4 is omitted, and the three-section material is directly replaced with the four-section material for step 8. Other operations and parameters are the same as in Example 1.

[0108] Comparative Example 2

[0109] Compared with Example 1, the only difference is that step 7 is omitted, and the NWO prepared in step 6 is directly processed in step 8. Other operations and parameters are the same as in Example 1.

[0110] Comparative Example 3

[0111] Compared with Example 1, the only difference is that in step 6, the heat treatment temperature is 800℃, the holding time is 2h, and no NWO phase material is obtained. This material is used to replace NWO in subsequent treatments. Other operations and parameters are the same as in Example 1.

[0112] Comparative Example 4

[0113] Compared with Example 1, the only difference is that nano-niobium pentoxide is missing in step 5. All other operations and parameters are the same as in Example 1 to obtain tungsten-modified graphite material.

[0114] Electrodes were fabricated using the materials described in the embodiments and comparative examples, and tests were conducted, specifically as follows:

[0115] Half-battery test:

[0116] A half-cell was fabricated using a lithium metal sheet as the counter electrode. The electrode slurry formulation was as follows: PVDF:SP = 91.6:6.6:1.8. The initial lithium removal specific capacity and initial coulombic efficiency of the half-cell were tested using a Landian testing system manufactured by Wuhan Landian Electronics Co., Ltd.

[0117] Full battery test:

[0118] Using the materials described in the examples and comparative examples as the negative electrode active material, low-temperature LFP (lithium iron phosphate) as the positive electrode active material, and low-temperature nitrile electrolyte, soft-pack stacked three-electrode full cells were fabricated, with a total capacity of approximately 900mAh. The positive electrode slurry formulation was LFP:PVDF:SP = 96.0:2.0:2.0, and the negative electrode formulation was the negative electrode active material (for each case): SP:CMC:SBR = 95.3:1.0:1.2:2.5, with a full cell NP ratio of 1.15. The charging performance of the full cells was tested using the Landian testing system manufactured by Wuhan Landian Electronics Co., Ltd. The cells were charged from 0% SOC to 80% maximum charge rate at -40℃. After 10 cycles of 3C charging and 1C discharging at -40℃, the cells were fully charged at 3C, and then the negative electrode interface was observed after disassembly. The low-temperature and fast-charging negative electrode products for each case were tested, and the test results are shown in Table 1.

[0119]

[0120] As shown in Table 1, the resonance treatment described above can unexpectedly improve the interfacial interaction between modified graphite and modified niobium tungstate, which can further improve their performance, especially their ultra-low temperature performance.

[0121] The above embodiments only illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as allowing for various modifications and improvements to be made based on the concept of the present invention. These modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the claims used.

Claims

1. A modified graphite-niobium tungstate@carbon composite material, characterized in that, It has a core-shell structure, wherein the core comprises modified graphite modified with functional group a and modified niobium tungstate modified with functional group b, and the shell is amorphous carbon; The functional groups a and b are individually at least one of hydroxyl, carboxyl, amino, acyl, and ester groups.

2. The modified graphite-niobium tungstate@carbon composite material as described in claim 1, characterized in that, The functional groups a and b can form ester groups and / or amide groups with each other; Preferably, the niobium tungstate in the modified niobium tungstate is a homologous Nb. 16 W5O 55 / Nb 18 W8O 69 Material; Preferably, the weight ratio of modified graphite to modified niobium tungstate is 100:1~20.

3. A method for preparing the modified graphite-niobium tungstate@carbon composite material according to claim 1 or 2, characterized in that, The modified graphite modified with functional group a and the modified niobium tungstate modified with functional group b are mixed, and then mixed with a carbon source for carbonization treatment to obtain the final product.

4. The preparation method of the modified graphite-niobium tungstate@carbon composite material as described in claim 3, characterized in that, The functional group a in the modified graphite includes hydroxyl and / or carboxyl groups; it is obtained by modifying graphite in a modification solution; Preferably, the modified solution includes at least one modifier selected from nitric acid, hydrofluoric acid, perchloric acid, and hydrogen peroxide; Preferably, the concentration of the modifier in the modified solution is above 10 wt.%; Preferably, the weight ratio of the modifier to graphite in the modified solution is 1:4~10; Preferably, the graphite is artificial graphite, which is obtained by crushing, shaping and graphitizing coke raw materials.

5. The preparation method of the modified graphite-niobium tungstate@carbon composite material as described in claim 3, characterized in that, The niobium tungstate is obtained by heat treatment with a tungsten source and a niobium source; Preferably, the tungsten source is tungsten oxide; Preferably, the niobium source is an oxide of niobium; Preferably, the Nd / W molar ratio in the tungsten source and the niobium source is 1.5~6:1; more preferably, it is 1.9~5.6:

1. Preferably, the heat treatment temperature of the tungsten source and niobium source is 1300~1400℃, and the heat treatment holding time is 20~30h.

6. The method for preparing the modified graphite-niobium tungstate@carbon composite material as described in claim 5, characterized in that, The functional group b in the modified niobium tungstate includes amino groups; Preferably, the modified niobium tungstate is obtained by modifying niobium tungstate with an aminosilane; Preferably, the pH during the modification stage is 4 to 6.5, and the mass ratio of niobium tungstate to aminosilane is 10:1 to 5.

7. The method for preparing the modified graphite-niobium tungstate@carbon composite material as described in claim 3, characterized in that, The modified graphite and modified niobium tungstate were mixed by acoustic vibration. Preferably, the carbon source includes one or more of asphalt, phenolic resin, petroleum resin and epoxy resin; Preferably, the carbonization temperature is 1000~1300℃; The carbonization time is 2 to 6 hours.

8. The application of the modified graphite-niobium tungstate@carbon composite material according to any one of claims 1-2 or the modified graphite-niobium tungstate@carbon composite material prepared by the preparation method according to any one of claims 3-7, characterized in that, Using it as the negative electrode active material, an alkali metal secondary battery was prepared.

9. A negative electrode for an alkali metal secondary battery, comprising a current collector and a negative electrode material composited thereon, said negative electrode material comprising a negative electrode active material, characterized in that, The negative electrode active material comprises the modified graphite-niobium tungstate@carbon composite material according to any one of claims 1 to 2 or the modified graphite-niobium tungstate@carbon composite material prepared by the preparation method according to any one of claims 3 to 7.

10. An alkali metal secondary battery, characterized in that, It includes the negative electrode as described in claim 9.

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