A bicontinuous composite material and a bicontinuous paste, and a preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a double-conducting composite material and double-conducting slurry as well as a preparation method and application thereof. The preparation method of the double-conducting composite material comprises the following steps: performing a coating reaction on high-temperature purified carbon nanotubes I and hydrochloric acid dopamine under alkaline conditions to obtain carbon nanotubes II with a surface coated with polydopamine, and then performing a hydrothermal reaction on the carbon nanotubes II with a sugar carbon source to obtain carbon nanotubes III with a carbon coating layer on the surface; mixing the carbon nanotubes III, a precursor material of an oxide solid electrolyte, a chelating agent and water, and then performing a sol-gel reaction to obtain dry gel after drying; and performing secondary calcination treatment on the dry gel in an atmosphere with an oxygen content of less than or equal to 10 vol% and an inert atmosphere to obtain the double-conducting composite material. The double-conducting composite material or the slurry prepared by the method provided in the application can be used as an additive of a positive electrode or a negative electrode material, and can significantly improve the rate performance of a lithium ion battery under low-temperature conditions.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a dual-conductivity composite material and a dual-conductivity slurry, their preparation methods, and applications. Background Technology

[0002] Lithium-ion batteries have become mainstream among new energy sources due to their advantages in cost and energy density. However, their rate performance is poor at low temperatures, especially at high rates, where performance drops significantly. This is mainly because low temperatures increase electrolyte viscosity and reduce fluidity, slowing down ion conduction and directly affecting the battery's rate performance. Most existing research focuses on improving electronic conduction to enhance rate discharge performance, such as adding a certain proportion of conductive carbon material to the positive / negative electrode materials. However, this method has not significantly improved the rate performance of lithium-ion batteries at low temperatures. Furthermore, as described in Chinese patent document CN116469601B, a conductive dispersion is prepared by grinding nano-carbon materials and inorganic solid electrolyte particles, and then used as a positive electrode additive to improve electronic and ion conduction. However, this conventional mechanical mixing method easily leads to uneven dispersion of carbon materials and solid electrolytes. When added as an additive to the electrode material, its distribution within the electrode material is also uneven, thus limiting battery performance and having limited effectiveness in improving low-temperature performance. Summary of the Invention

[0003] One of the objectives of this invention is to address the problem that existing positive / negative electrode additives are ineffective in improving the low-temperature rate performance of lithium-ion batteries, and to provide a method for preparing a dual-conductivity composite material.

[0004] Specifically, the preparation method of the dual-conducting composite material includes the following steps: S1. Carbon nanotubes I purified at high temperature are coated with dopamine hydrochloride under alkaline conditions to obtain carbon nanotubes II coated with polydopamine; then the carbon nanotubes II coated with polydopamine are subjected to hydrothermal reaction with a sugar carbon source to obtain carbon nanotubes III with a carbon coating layer derived from polydopamine and sugar carbon source on the surface. S2. The carbon nanotubes III obtained in step S1 are mixed with the precursor material of the oxide-type solid electrolyte, a chelating agent, and water, and then subjected to a sol-gel reaction. After drying, a dry gel is obtained. S3. The dry gel obtained in step S2 is first calcined in an atmosphere with an oxygen content ≤10 vol%, and the resulting product is then calcined in an inert atmosphere to obtain a dual-conducting composite material of carbon nanotubes and oxide-type solid electrolyte.

[0005] In a preferred embodiment, in step S1, the carbon nanotube I is selected from at least one of multi-walled carbon nanotubes, oligo-walled carbon nanotubes, and single-walled carbon nanotubes.

[0006] In a preferred embodiment, in step S1, the carbohydrate carbon source is selected from at least one of glucose, fructose, sucrose, maltose, and chitosan.

[0007] In a preferred embodiment, in step S1, the mass ratio of the carbon nanotube I to dopamine hydrochloride and the sugar carbon source is 10:(4~8):(30~60).

[0008] In a preferred embodiment, in step S1, the pH value of the alkaline condition is 8.0 to 9.0.

[0009] In a preferred embodiment, in step S1, the alkaline conditions are achieved by providing a Tris-HCl buffer solution with a pH of 8.0 to 9.0.

[0010] In a preferred embodiment, in step S1, the coating reaction takes 20-30 hours.

[0011] In a preferred embodiment, in step S1, the conditions for the hydrothermal reaction include: a temperature of 160~200℃ and a time of 10~15h.

[0012] In a preferred embodiment, in step S2, the amount of carbon nanotubes III is 5 to 20 wt% of the oxide-type solid electrolyte.

[0013] In a preferred embodiment, in step S2, the oxide-type solid electrolyte is selected from at least one of LLZO, LATP, and LLTO.

[0014] In a preferred embodiment, in step S2, the precursor material of LLZO solid electrolyte includes a lithium source, a lanthanum source, and a zirconium source; the precursor material of LATP solid electrolyte includes a lithium source, an aluminum source, a titanium source, and a phosphorus source; and the precursor material of LLTO solid electrolyte includes a lithium source, a lanthanum source, and a titanium source.

[0015] In a preferred embodiment, in step S2, the chelating agent is selected from at least one of citric acid, ethylenediaminetetraacetic acid, oxalic acid, and tartaric acid.

[0016] In a preferred embodiment, in step S2, the molar ratio of the chelating agent to the metal in the precursor material of the oxide-type solid electrolyte is (1.5~1.8):1.

[0017] In a preferred embodiment, in step S2, the conditions for the sol-gel reaction include: a temperature of 60~80℃ and a time of 10~15h.

[0018] In a preferred embodiment, in step S3, the conditions for the first calcination treatment include: an oxygen content of 5-10 vol%, a temperature of 550-650°C, and a time of 1-3 hours.

[0019] In a preferred embodiment, in step S3, the conditions for the second calcination treatment include: a temperature of 800~900℃ and a time of 3~5h.

[0020] The second objective of this invention is to provide a dual-conducting composite material prepared by the above method.

[0021] A third objective of this invention is to provide a dual-conducting slurry. The dual-conducting slurry comprises the aforementioned dual-conducting composite material, a dispersant, and a solvent.

[0022] In a preferred embodiment, the content of the dual-conducting composite material is 1.0~10.0 wt%, the content of the dispersant is 0.5~5.0 wt%, and the content of the solvent is 85.0~98.5 wt%.

[0023] In a preferred embodiment, the dispersant is selected from at least one of polyvinylpyrrolidone and its derivatives, hydrogenated nitrile butadiene rubber, styrene-maleic anhydride copolymer and its derivatives, polyvinylidene fluoride, and carboxymethyl cellulose.

[0024] In a preferred embodiment, the solvent is selected from at least one of water, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0025] The fourth objective of this invention is to provide the application of the above-mentioned dual-conducting composite material or dual-conducting slurry in lithium-ion batteries.

[0026] Beneficial effects: The key to this invention is to first coat the surface of carbon nanotubes (CNTs) purified at high temperature with a carbon coating layer derived from polydopamine and sugar carbon sources, and then introduce the aforementioned carbon nanotubes during the sol-gel reaction of the precursor material of the oxide-type solid electrolyte with the chelating agent. The resulting dry gel is then calcined in an atmosphere with an oxygen content ≤10 vol% and an inert atmosphere to obtain a dual-conducting composite material of carbon nanotubes and oxide-type solid electrolyte in situ. When this dual-conducting composite material or its slurry is used as an additive for the positive or negative electrode of a lithium-ion battery, the rate performance of the lithium-ion battery under low-temperature conditions can be significantly improved. The reason for this is speculated to be that, due to the properties of polydopamine itself, it can act as a linker between carbon nanotubes and sugar-based carbon sources, resulting in a uniform carbon protective layer coating the surface of carbon nanotubes. This benefits both the thermal stability of CNTs during subsequent calcination, reducing the impact of oxidation on CNT performance, and the uniform dispersion of CNTs in the sol-gel system. This enhances the in-situ composite effect of carbon nanotubes and oxide-based solid electrolytes, ensuring that CNTs are uniformly distributed on the surface of solid electrolyte particles and / or coated inside them, thereby enabling… To improve ion and electron pathways, the resulting dry gel is first calcined in a low oxygen partial pressure atmosphere. This serves three purposes: first, to preliminarily crystallize the solid electrolyte precursor; second, to remove impurities (such as LiCO3) and reduce the internal resistance of the material; and third, to protect CNTs from oxidation. Then, it is calcined at high temperature in an inert atmosphere to obtain a solid electrolyte material with a purer crystalline phase and higher density. That is, by using a two-stage calcination process in a specific atmosphere, not only can the integrity and good performance of the carbon nanotube structure be ensured, but also a pure solid electrolyte can be obtained, and the carbon nanotubes can be tightly bonded to the solid electrolyte.

[0027] In summary, the method provided by this invention yields a dual-conductivity composite material in which carbon nanotubes and oxide-type solid electrolytes are tightly bonded in situ. This dual-conductivity composite material can be directly used as an additive in either the positive or negative electrode material, thereby improving the rate performance of lithium-ion batteries under low-temperature conditions. In a preferred embodiment, preparing the dual-conductivity composite material into a slurry before using it as an additive in both the positive and negative electrode materials further improves its uniform dispersion within the electrodes, better avoiding battery performance loss caused by localized agglomeration within the electrodes, and thus better enhancing the ion and electron conduction rates of lithium-ion batteries at low temperatures. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the dual-conducting composite material provided in an embodiment of the present invention. Detailed Implementation

[0029] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Furthermore, unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present invention.

[0030] The preparation method of the dual-conducting composite material provided by the present invention includes the following steps: S1. Carbon nanotubes I purified at high temperature are coated with dopamine hydrochloride under alkaline conditions to obtain carbon nanotubes II coated with polydopamine; then the carbon nanotubes II coated with polydopamine are subjected to hydrothermal reaction with a sugar carbon source to obtain carbon nanotubes III with a carbon coating layer derived from polydopamine and sugar carbon source on the surface. S2. The carbon nanotubes III obtained in step S1 are mixed with the precursor material of the oxide-type solid electrolyte, a chelating agent, and water, and then subjected to a sol-gel reaction. After drying, a dry gel is obtained. S3. The dry gel obtained in step S2 is first calcined in an atmosphere with an oxygen content ≤10 vol%, and the resulting product is then calcined in an inert atmosphere to obtain a dual-conductivity composite material of carbon nanotubes and oxide-type solid electrolyte. The oxygen content can be 1 vol%, 2 vol%, 3 vol%, 4 vol%, 5 vol%, 6 vol%, 7 vol%, 8 vol%, 9 vol%, 10 vol%, or any value between them.

[0031] In this invention, the source of the high-temperature purified carbon nanotubes in step S1 is not specifically limited; they can be purchased or prepared using existing methods. The high-temperature purified carbon nanotubes can be selected from at least one of multi-walled carbon nanotubes, oligo-walled carbon nanotubes, and single-walled carbon nanotubes.

[0032] In this invention, the specific type of carbohydrate carbon source in step S1 is not particularly limited, as long as it is a carbon-containing substance that can react with polydopamine to be attached to carbon nanotubes. Specific examples include, but are not limited to, at least one of glucose, fructose, sucrose, maltose, and chitosan.

[0033] In this invention, in step S1, the preferred mass ratio of carbon nanotube I to dopamine hydrochloride and carbohydrate carbon source is 10:(4~8):(30~60). Based on 10 parts by weight of carbon nanotube I, the preferred amount of dopamine hydrochloride is 4~8 parts by weight, such as 4, 5, 6, 7, 8 parts by weight or any value between them; the preferred amount of carbohydrate carbon source is 30~60 parts by weight, such as 30, 35, 40, 45, 50, 55, 60 parts by weight or any value between them.

[0034] In this invention, in step S1, the pH value of the alkaline condition is preferably 8.0 to 9.0, such as 8.0, 8.2, 8.5, 8.8, 9.0, or any value between them. The method of achieving the alkaline condition is not particularly limited, but it is preferably achieved by providing a Tris-HCl buffer solution with a pH value of 8.0 to 9.0.

[0035] In this invention, in step S1, the coating reaction is preferably carried out at room temperature, such as 15°C, 18°C, 20°C, 22°C, 25°C, 28°C, 30°C, or any value between them. The coating reaction time is preferably 20~30h, such as 20h, 22h, 25h, 28h, 30h, or any value between them.

[0036] In one specific embodiment, the coating reaction process can be as follows: first, high-temperature purified carbon nanotubes I are mixed and dispersed with a Tris-HCl buffer solution with a pH of 8.0~9.0, then dopamine hydrochloride is added and stirred at room temperature for 20~30 hours. The reaction product is collected, washed, and dried to obtain carbon nanotubes II (PDA@CNTs) coated with polydopamine.

[0037] In this invention, the hydrothermal reaction conditions in step S1 preferably include: a temperature of 160~200℃, such as 160℃, 170℃, 180℃, 190℃, 200℃ or any value between them; and a time of 10~15h, such as 10h, 11h, 12h, 13h, 14h, 15h or any value between them.

[0038] In this invention, in step S2, the mass of the oxide-type solid electrolyte is calculated based on the theoretical mass obtained from the stoichiometric ratio of the precursor materials. The amount of carbon nanotubes III is preferably 5-20 wt% of the oxide-type solid electrolyte, such as 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, or any value between them. This is more conducive to the uniform dispersion of carbon nanotubes in the oxide-type solid electrolyte, achieving a good balance between the conductivity and dispersion of carbon nanotubes in the dual-conductivity composite material (too little carbon nanotube content will result in insufficient conductivity, while too much content will cause them to entangle and affect dispersion). In this invention, in step S2, the oxide-type solid electrolyte is preferably at least one of LLZO, LATP, and LLTO. Specifically, the general chemical formula of LLZO solid electrolyte is Li. 3+x La3Zr2O 12wherein 3.5≤x≤5.5, which can be 3.5, 4.0, 4.5, 5.0, 5.5 or any value between any of the foregoing. The precursor materials of the LLZO solid electrolyte preferably comprise a lithium source, a lanthanum source and a zirconium source. The general chemical formula of the LATP solid electrolyte is Li 1+y Al y Ti 2-y (PO4)3, wherein 0<y≤0.5, and y can be 0.1, 0.2, 0.3, 0.4, 0.5 or any value between any of the foregoing. The precursor materials of the LATP solid electrolyte preferably comprise a lithium source, an aluminum source, a titanium source and a phosphorus source. The general chemical formula of the LLTO solid electrolyte is Li 3z La 2 / 3-z TiO3, wherein 0.04≤z≤0.16, and z can be 0.04, 0.05, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16 or any value between any of the foregoing. The precursor materials of the LLTO solid electrolyte preferably comprise a lithium source, a lanthanum source and a titanium source. The lithium source in the above materials can each be independently selected from any one or more of LiNO3 (lithium nitrate), CH3COOLi (lithium acetate), LiOH (lithium hydroxide) and LiCl (lithium chloride). The lanthanum source in the above materials can be La(NO3)3 (lanthanum nitrate) and / or La(CH3COO)3 (lanthanum acetate). The zirconium source in the above materials can be ZrO(NO3)2 (zirconyl nitrate) and Zr(OC2H5)4 (zirconium alkoxide). The aluminum source in the above materials can be selected from any one or more of Al(NO3)3 (aluminum nitrate), Al(CH3COO)3 (aluminum acetate) and AlCl3 (aluminum chloride). The titanium source in the above materials can be selected from any one or more of TiCl4 (titanium tetrachloride) and Ti(OC4H9)4 (tetrabutyl titanate). The phosphorus source in the above materials can be selected from any one or more of H3PO4 (phosphoric acid), (NH4)3PO4 (ammonium phosphate), NH4H2PO4 (ammonium dihydrogen phosphate), (NH4)2HPO4 (diammonium hydrogen phosphate), (CH3O)3PO (trimethyl phosphate) and (CH3O)3P (trimethyl phosphite).

[0039] In the present invention, in step S2, specific examples of the chelating agent include, but are not limited to: at least one of citric acid, oxalic acid, and tartaric acid.

[0040] In the present invention, in step S2, the molar ratio of the chelating agent to the metal in the precursor material of the oxide-type solid electrolyte is preferably (1.5~1.8):1, such as 1.5:1, 1.6:1, 1.7:1, 1.8:1, or any value between any of the foregoing.

[0041] In this invention, the conditions for the sol-gel reaction in step S2 preferably include: a temperature of 60~80℃, such as 60℃, 65℃, 70℃, 75℃, 80℃ or any value between them; and a time of 10~15h, such as 10h, 11h, 12h, 13h, 14h, 15h or any value between them.

[0042] In one specific embodiment, the sol-gel reaction process can be as follows: carbon nanotubes III are mixed with water to obtain a dispersion, the precursor material of the oxide-type solid electrolyte, the chelating agent, and water are mixed with the above dispersion, and the sol-gel reaction is carried out at 60~80℃ for 10~15h, and the dry gel is obtained after drying.

[0043] In this invention, the preferred conditions for the first calcination treatment in step S3 include: an oxygen content of 3-7 vol%, such as 3 vol%, 4 vol%, 5 vol%, 6 vol%, 7 vol%, or any value between them. This is beneficial for the thermal stability of carbon nanotubes and ensures that the carbon coating on the surface of the carbon nanotubes is fully or partially retained, thereby improving the dispersibility of the dual-conducting composite material in the slurry; a temperature of 550-650℃, such as 550℃, 580℃, 600℃, 620℃, 650℃, or any value between them; and a time of 1-3 h, such as 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or any value between them. Controlling the oxygen content, temperature, and time of the first calcination treatment within the above-mentioned preferred ranges is more conducive to improving the purity of the initial crystallization of the solid electrolysis precursor, while ensuring the structural integrity and excellent performance of the carbon nanotubes.

[0044] In this invention, the conditions for the second calcination treatment in step S3 preferably include: a temperature of 800~900℃, such as 800℃, 820℃, 850℃, 880℃, 900℃ or any value between them; and a time of 3~5h, such as 3h, 3.5h, 4h, 4.5h, 5h or any value between them. The inert atmosphere can be nitrogen and / or argon.

[0045] The present invention provides a dual-conducting composite material prepared by the above method.

[0046] The dual-conductive slurry provided by the present invention includes the above-mentioned dual-conductive composite material, dispersant and solvent.

[0047] In this invention, the content of the dual-conducting composite material is preferably 1.0~10.0 wt%, such as 1.0 wt%, 2.0 wt%, 5.0 wt%, 8.0 wt%, 10.0 wt%, or any value between them. The content of the dispersant is preferably 0.5~5.0 wt%, such as 0.5 wt%, 1.0 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt%, 5.0 wt%, or any value between them. The content of the solvent is preferably 85.0~98.5 wt%, such as 85.0 wt%, 88.0 wt%, 90.0 wt%, 92.0 wt%, 95.0 wt%, 96.0 wt%, 97.0 wt%, 98.5 wt%, or any value between them.

[0048] In this invention, specific examples of the dispersant include, but are not limited to, at least one of: polyvinylpyrrolidone and its derivatives, hydrogenated nitrile butadiene rubber, styrene-maleic anhydride copolymer and its derivatives, polyvinylidene fluoride, and carboxymethyl cellulose. Specific examples of the solvent include, but are not limited to, at least one of: water, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0049] In this invention, the dual-conductive slurry can be obtained by mixing a dual-conductive composite material, a dispersant, and a solvent, followed by grinding. The preferred grinding conditions include: a grinding time of 1-2 hours, such as 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, or any value between these; a zirconium bead diameter of 0.2-1.0 mm, such as 0.2 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, or any value between these; and a milling speed of 1000-3000 rpm, such as 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, or any value between these.

[0050] The present invention will be described in detail below through specific embodiments. These embodiments are intended to explain the invention and should not be construed as limiting it. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0051] Example 1 This embodiment illustrates the preparation of a dual-conductive composite material and a dual-conductive slurry, and the specific process is as follows: 1. Carbon nanotube coating: (1) Take 10g of high-temperature purified carbon nanotubes (from Yong'an Kaina New Material Technology Co., Ltd., tube diameter 5~10nm, tube length ≥1μm), add them to 500mL of Tris-HCl buffer solution with pH 8.5, sonicate in an ice-water bath for 30min to fully disperse them, then add 6g of dopamine hydrochloride to the solution and stir magnetically at room temperature for 24h. After the reaction is completed, centrifuge to collect the black product, wash it 8 times with deionized water to remove unreacted monomers, and dry it under vacuum at 60℃ to obtain carbon nanotubes coated with polydopamine, denoted as PDA@CNTs.

[0052] (2) The PDA@CNTs obtained above were dispersed in 500 mL of 0.5 M glucose solution and sonicated in an ice-water bath for 30 min. Then the mixed solution was transferred to a high-pressure reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 180 °C for 12 h. After cooling, the product was collected by centrifugation, washed 8 times with deionized water, and dried under vacuum at 60 °C to obtain carbon nanotubes with carbon coatings on the surface derived from polydopamine and glucose, which were denoted as C-PDA@CNTs.

[0053] 2. Preparation of C-PDA@CNTs / LLZO precursor by sol-gel method: (1) Weigh 0.42 g of C-PDA@CNTs and disperse them in 50 mL of deionized water. Sonicate for 30 min to form a uniform and stable dispersion. (The amount of carbon nanotubes added is 10 wt% of LLZO) (2) According to the chemical formula of LLZO, Li7La3Zr2O 12 The stoichiometric ratios of 6.82 g LiNO3·6H2O (38.5 mmol), 6.50 g La(NO3)3·6H2O (15 mmol), and 2.68 g ZrO(NO3)2·2H2O (10 mmol) were weighed out and dissolved in deionized water. Then, 21.84 g citric acid monohydrate (104 mmol) was added to the precursor metal salt solution, and the mixture was stirred at 70 °C to dissolve. While stirring, a C-PDA@CNTs dispersion was slowly added dropwise to form a black sol. The black sol was stirred at 70 °C for 12 h to obtain a black gel. The black gel was then dried in a 120 °C oven for 12 h to obtain a black dry gel.

[0054] 3. Preparation of CNTs / LLZO composite materials by calcination: (1) First calcination treatment: The dry gel prepared in the previous step was placed in a tube furnace and calcined at 600℃ for 2h with a heating rate of 3℃ / min. Atmosphere: 95vol% N2 + 5vol% O2 (which can be achieved by controlling the N2:O2 flow rate ratio = 95:5).

[0055] (2) Second calcination treatment: turn off O2, purge with N2 for 30 min, continue to heat to 850℃, calcinate for 4 h at a heating rate of 3℃ / min, cool to room temperature to obtain CNTs / LLZO composite material.

[0056] 4. Preparation of CNTs / LLZO composite slurry Weigh 20g of CNTs / LLZO composite powder, 5g of polyvinylpyrrolidone K30 and 475g of NMP solvent (N-methylpyrrolidone), and grind them in a sand mill for 90min (zirconium bead diameter is 0.8mm, sand mill speed is 2000rpm). After sand milling, a uniform CNTs / LLZO dual-guide slurry is obtained.

[0057] The structural schematic diagram of the obtained CNTs / LLZO composite material is shown below. Figure 1 As shown, CNTs are embedded inside the solid electrolyte particles and wrapped around the particle surface, meaning that CNTs and solid electrolyte particles are in-situ composites.

[0058] Example 2 This embodiment illustrates the preparation of a dual-conductive composite material and a dual-conductive slurry, and the specific process is as follows: 1. Carbon nanotube coating: (1) Take 10g of high-temperature purified carbon nanotubes (from Yong'an Kaina New Material Technology Co., Ltd., with a diameter of 30~80nm and a length of ≥1μm), add them to 500mL of Tris-HCl buffer solution with pH 8.0, and sonicate in an ice-water bath for 30min to ensure thorough dispersion. Then add 4g of dopamine hydrochloride to the solution and stir magnetically at room temperature for 24h. After the reaction is complete, collect the black product by centrifugation, wash it 8 times with deionized water to remove unreacted monomers, and dry it under vacuum at 60℃ to obtain carbon nanotubes coated with polydopamine, denoted as PDA@CNTs.

[0059] (2) The PDA@CNTs obtained above were dispersed in 500 mL of 0.3 M sucrose solution and sonicated in an ice-water bath for 30 min. Then the mixed solution was transferred to a high-pressure reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 180 °C for 12 h. After cooling, the product was collected by centrifugation, washed 8 times with deionized water, and dried under vacuum at 60 °C to obtain carbon nanotubes with carbon coatings on the surface derived from polydopamine and sucrose, which were denoted as C-PDA@CNTs.

[0060] 2. Preparation of C-PDA@CNTs / LLZO precursor by sol-gel method: (1) Weigh 0.21g of C-PDA@CNTs and disperse them in 50mL of deionized water. Sonicate for 30min to form a uniform and stable dispersion. (The amount of carbon nanotubes added in this scheme is 5wt% of LLZO) (2) According to the chemical formula of LLZO, Li7La3Zr2O 12 The stoichiometric ratios of 6.82 g LiNO3·6H2O (38.5 mmol), 6.50 g La(NO3)3·6H2O (15 mmol), and 2.68 g ZrO(NO3)2·2H2O (10 mmol) were weighed out and dissolved in deionized water. Then, 14.40 g tartaric acid (96 mmol) was added to the precursor metal salt solution, and the mixture was stirred at 60 °C to dissolve. While stirring, a C-PDA@CNTs dispersion was slowly added dropwise to form a black sol. The black sol was stirred at 60 °C for 12 h to obtain a black gel. The black gel was then dried in an oven at 120 °C for 12 h to obtain a black dry gel.

[0061] 3. Preparation of CNTs / LLZO composite materials by calcination: (1) First calcination treatment: The dry gel prepared in the previous step was placed in a tube furnace and calcined at 650℃ for 2h with a heating rate of 3℃ / min. The atmosphere was 97vol% N2 + 3vol% O2 (which can be achieved by controlling the N2:O2 flow rate ratio = 97:3).

[0062] (2) Second calcination treatment: turn off O2, purge with N2 for 30 min, continue to heat to 800℃, calcine for 4 h at a heating rate of 3℃ / min, cool to room temperature, and obtain CNTs / LLZO composite material.

[0063] 4. Preparation of CNTs / LLZO composite slurry Weigh 50g of CNTs / LLZO composite powder, 10g of polyvinylpyrrolidone K30 and 440g of NMP solvent (N-methylpyrrolidone), and grind them in a sand mill for 90min (zirconium bead diameter is 0.8mm, sand mill speed is 2000rpm). After sand milling, a uniform CNTs / LLZO dual-guide slurry is obtained.

[0064] Example 3 This embodiment illustrates the preparation of a dual-conductive composite material and a dual-conductive slurry, and the specific process is as follows: 1. Carbon nanotube coating: (1) Take 10g of high-temperature purified carbon nanotubes (from Yong'an Kaina New Material Technology Co., Ltd., tube diameter 3~8nm, tube length ≥2μm), add them to 500mL of Tris-HCl buffer solution with pH 9.0, and sonicate in an ice-water bath for 30min to fully disperse them. Then add 8g of dopamine hydrochloride to the solution and stir magnetically at room temperature for 24h. After the reaction is completed, centrifuge to collect the black product, wash it 8 times with deionized water to remove unreacted monomers, and dry it under vacuum at 60℃ to obtain carbon nanotubes coated with polydopamine, denoted as PDA@CNTs.

[0065] (2) The PDA@CNTs obtained above were dispersed in 500 mL of 0.5 M glucose solution and sonicated in an ice-water bath for 30 min. Then the mixed solution was transferred to a high-pressure reactor with a polytetrafluoroethylene liner and hydrothermally reacted at 180 °C for 12 h. After cooling, the product was collected by centrifugation, washed 8 times with deionized water, and dried under vacuum at 60 °C to obtain carbon nanotubes with carbon coatings on the surface derived from polydopamine and glucose, which were denoted as C-PDA@CNTs.

[0066] 2. Preparation of C-PDA@CNTs / LLZO precursor by sol-gel method: (1) Weigh 0.84 g of C-PDA@CNTs and disperse them in 50 mL of deionized water. Sonicate for 30 min to form a uniform and stable dispersion. (The amount of carbon nanotubes added in this scheme is 20 wt% of LLZO) (2) According to the chemical formula of LLZO, Li7La3Zr2O 12 The stoichiometric ratios of 6.82 g LiNO3·6H2O (38.5 mmol), 6.50 g La(NO3)3·6H2O (15 mmol), and 2.68 g ZrO(NO3)2·2H2O (10 mmol) were weighed out and dissolved in deionized water. Then, 23.95 g citric acid monohydrate (114 mmol) was added to the precursor metal salt solution, and the mixture was stirred at 80 °C to dissolve. While stirring, a C-PDA@CNTs dispersion was slowly added dropwise to form a black sol. The black sol was stirred at 80 °C for 12 h to obtain a black gel. The black gel was then dried in a 120 °C oven for 12 h to obtain a black dry gel.

[0067] 3. Preparation of CNTs / LLZO composite materials by calcination: (1) First calcination treatment: The dry gel prepared in the previous step was placed in a tube furnace and calcined at 550℃ for 2h with a heating rate of 3℃ / min. Atmosphere: 93vol% N2 + 7vol% O2 (which can be achieved by controlling the N2:O2 flow rate ratio = 93:7).

[0068] (2) Second calcination treatment: turn off O2, purge with N2 for 30 min, continue to heat to 900℃, calcine for 4 h, heating rate 3℃ / min, cool to room temperature to obtain CNTs / LLZO composite material.

[0069] 4. Preparation of CNTs / LLZO composite slurry Weigh 10g of CNTs / LLZO composite powder, 5g of polyvinylpyrrolidone K30 and 485g of NMP solvent (N-methylpyrrolidone), and grind them in a sand mill for 90min (zirconium bead diameter is 0.8mm, sand mill speed is 2000rpm). After sand milling, a uniform CNTs / LLZO dual-guide slurry is obtained.

[0070] Example 4 This embodiment illustrates the preparation of a dual-conductive composite material and a dual-conductive slurry, and the specific process is as follows: The dual-conducting composite material was prepared according to the method of Example 1, except that the amount of carbon nanotubes added in step 2-(1) was 10 wt% of LATP, and the amount added in step 2-(2) was according to the chemical formula of LATP, Li 1.3 Al 0.3 Ti 1.7 The stoichiometric ratios of LiNO3·6H2O (28.6 mmol), Al(NO3)3 (6 mmol), TiCl4 (34 mmol), and H3PO4 (60 mmol) in (PO4)3 were weighed out respectively, and the remaining conditions were the same as in Example 1, thereby preparing the CNTs / LATP dual-conductor slurry.

[0071] Example 5 This embodiment illustrates the preparation of a dual-conductive composite material and a dual-conductive slurry, and the specific process is as follows: The dual-conducting composite material was prepared according to the method of Example 1, except that the amount of carbon nanotubes added in step 2-(1) was 10 wt% of LLTO, and the amount of carbon nanotubes added in step 2-(2) was according to the chemical formula of LLTO, Li 0.33 La 0.56 The stoichiometric ratios of LiNO3·6H2O (14.5 mmol), La(NO3)3·6H2O (22.4 mmol), and TiCl4 (40 mmol) in TiO3 were weighed out, and the other conditions were the same as in Example 1, thereby preparing CNTs / LLTO dual-conductor slurry.

[0072] Example 6 This embodiment illustrates the preparation of a dual-conductive composite material and a dual-conductive slurry, and the specific process is as follows: The dual-conductive composite material was prepared according to the method of Example 1. The difference was that the atmosphere of the first calcination treatment in step 3-(1) was 90 vol% N2 + 10 vol% O2, and the other conditions were the same as in Example 1. Thus, CNTs / LLZO dual-conductive slurry was prepared.

[0073] Example 7 This embodiment illustrates the preparation of a dual-conductive composite material and a dual-conductive slurry, and the specific process is as follows: The dual-conductive composite material was prepared according to the method of Example 1. The difference was that the atmosphere of the first calcination treatment in step 3-(1) was 99 vol% N2 + 1 vol% O2, and the other conditions were the same as in Example 1. Thus, CNTs / LLZO dual-conductive slurry was prepared.

[0074] Example 8 This embodiment illustrates the preparation of a dual-conductive composite material and a dual-conductive slurry, and the specific process is as follows: The dual-conductive composite material was prepared according to the method of Example 1, except that the amount of carbon nanotubes added in step 2-(1) was 2wt% of LLZO, and the other conditions were the same as in Example 1. Thus, CNTs / LLZO dual-conductive slurry was prepared.

[0075] Example 9 This embodiment illustrates the preparation of a dual-conductive composite material and a dual-conductive slurry, and the specific process is as follows: The dual-conductive composite material was prepared according to the method of Example 1, except that the amount of carbon nanotubes added in step 2-(1) was 40wt% of LLZO, and the other conditions were the same as in Example 1. Thus, the CNTs / LLZO dual-conductive slurry was prepared.

[0076] Comparative Example 1 This comparative example illustrates the preparation of a reference slurry, and the specific process is as follows: 1. Preparation of LLZO precursors using the sol-gel method: A black dry gel was prepared according to the method in step 2 of Example 1.

[0077] 2. Preparation of LLZO materials by calcination: The above-mentioned black dry gel was calcined according to the method in step 3 of Example 1 to obtain LLZO material.

[0078] 3. Weigh 3.33g of high-temperature purified carbon nanotubes (from Yong'an Kaina New Material Technology Co., Ltd., tube diameter 5~10nm, tube length ≥1μm), 16.67g of LLZO material, 5g of polyvinylpyrrolidone K30 and 475g of NMP solvent (N-methylpyrrolidone), and grind them in a sand mill for 90min (zirconium bead diameter 0.8mm, sand mill speed 2000rpm). After sand milling, a uniform reference CNTs / LLZO slurry is obtained.

[0079] Comparative Example 2 This comparative example illustrates the preparation of a reference composite material and a reference slurry, and the specific process is as follows: The reference composite material was prepared according to the method of Example 1, except that step 1 was not performed and the same mass of high-temperature purified carbon nanotubes (from Yong'an Kaina New Material Technology Co., Ltd., with a diameter of 5~10nm and a length of ≥1μm) were used instead of C-PDA@CNTs in step 2. All other conditions were the same as in Example 1. The reference CNTs / LLZO composite material and reference CNTs / LLZO slurry were thus prepared.

[0080] Comparative Example 3 This comparative example illustrates the preparation of a reference composite material and a reference slurry, and the specific process is as follows: The reference composite material was prepared according to the method of Example 1, except that step 1-(1) was not performed. Instead, the high-temperature purified carbon nanotubes were directly dispersed in 500 mL of 0.5 M glucose solution. All other conditions were the same as in Example 1. The reference CNTs / LLZO composite material and reference CNTs / LLZO slurry were thus prepared.

[0081] Comparative Example 4 This comparative example illustrates the preparation of a reference composite material and a reference slurry, and the specific process is as follows: The reference composite material was prepared according to the method of Example 1, except that steps 1-(2) were not performed, and the other conditions were the same as in Example 1. Thus, the reference CNTs / LLZO composite material and the reference CNTs / LLZO slurry were prepared.

[0082] Test case The dual-conducting slurries prepared in the above examples and comparative examples were used as additives for the positive electrode material, and assembled into a 400mAh soft-pack battery according to the following method: The slurry formula of the positive electrode sheet was NCM622:PVDF:carbon black:dual-conducting slurry (based on the mass of the dual-conducting composite material contained) = 95:2:1.5:1.5 by mass, and the slurry formula of the negative electrode sheet was graphite:carbon black:CMC:SBR = 94.5:1.5:1.5:2.5 by mass. The solvent of the positive electrode slurry was N-methylpyrrolidone, the solvent of the negative electrode slurry was deionized water, the separator was a PE separator, and the electrolyte was a 1M LiF6 solution (solvent:EC:DMC:EMC = 1:1:1).

[0083] The soft-pack batteries assembled according to the above method were subjected to low-temperature rate performance testing: the test temperature was -20℃, the test voltage range was 3.0~4.2V, and the test rates were 0.2C, 1C, 3C, 5C, and 7C. Then, the discharge capacity at each rate was divided by the discharge capacity at 0.2C to calculate the retention rate of the discharge capacity under different rate conditions compared to the 0.2C rate. The results are shown in Table 1.

[0084] Table 1

[0085] As shown in Table 1, compared with Comparative Examples 1-4, the dual-conducting slurry provided in Examples 1-9 of the present invention can give lithium-ion batteries better rate performance under low temperature conditions (-20℃). As the rate increases, the difference in discharge capacity retention rate between them and the comparative examples becomes more significant.

[0086] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing a dual-conducting composite material, characterized in that, The preparation method includes the following steps: S1. Carbon nanotubes I purified at high temperature are coated with dopamine hydrochloride under alkaline conditions to obtain carbon nanotubes II coated with polydopamine; then the carbon nanotubes II coated with polydopamine are subjected to hydrothermal reaction with a sugar carbon source to obtain carbon nanotubes III with a carbon coating layer derived from polydopamine and sugar carbon source on the surface. S2. The carbon nanotubes III obtained in step S1 are mixed with the precursor material of the oxide-type solid electrolyte, a chelating agent, and water, and then subjected to a sol-gel reaction. After drying, a dry gel is obtained. S3. The dry gel obtained in step S2 is first calcined in an atmosphere with an oxygen content ≤10 vol%, and the resulting product is then calcined in an inert atmosphere to obtain a dual-conducting composite material of carbon nanotubes and oxide-type solid electrolyte. In step S2, the amount of carbon nanotubes III used is 5-20 wt% of the oxide-type solid electrolyte. In step S3, the conditions for the first calcination treatment include: an oxygen content of 3-7 vol%, a temperature of 550-650℃, and a time of 1-3 h; the conditions for the second calcination treatment include: a temperature of 800-900℃ and a time of 3-5 h.

2. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S1, the carbon nanotube I is selected from at least one of multi-walled carbon nanotubes, oligo-walled carbon nanotubes, and single-walled carbon nanotubes.

3. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S1, the carbohydrate carbon source is selected from at least one of glucose, fructose, sucrose, maltose, and chitosan.

4. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S1, the mass ratio of carbon nanotube I to dopamine hydrochloride and sugar carbon source is 10:(4~8):(30~60).

5. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S1, the pH value of the alkaline condition is 8.0~9.

0.

6. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S1, the alkaline conditions are achieved by providing a Tris-HCl buffer solution with a pH of 8.0 to 9.

0.

7. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S1, the coating reaction takes 20-30 hours.

8. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S1, the conditions for the hydrothermal reaction include: a temperature of 160~200℃ and a time of 10~15h.

9. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S2, the oxide-type solid electrolyte is selected from at least one of LLZO, LATP, and LLTO.

10. The method for preparing the dual-conducting composite material according to claim 9, characterized in that, In step S2, the precursor materials for LLZO solid electrolyte include lithium source, lanthanum source, and zirconium source; the precursor materials for LATP solid electrolyte include lithium source, aluminum source, titanium source, and phosphorus source; and the precursor materials for LLTO solid electrolyte include lithium source, lanthanum source, and titanium source.

11. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S2, the chelating agent is selected from at least one of citric acid, ethylenediaminetetraacetic acid, oxalic acid, and tartaric acid.

12. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S2, the molar ratio of the chelating agent to the metal in the precursor material of the oxide-type solid electrolyte is (1.5~1.8):

1.

13. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S2, the conditions for the sol-gel reaction include: a temperature of 60~80℃ and a time of 10~15h.

14. A dual-conducting composite material prepared by the method according to any one of claims 1 to 13.

15. A dual-guided slurry, characterized in that, The dual-conducting slurry comprises the dual-conducting composite material, dispersant, and solvent as described in claim 14.

16. The dual-conductor slurry according to claim 15, characterized in that, The content of the dual-conducting composite material is 1.0~10.0 wt%, the content of the dispersant is 0.5~5.0 wt%, and the content of the solvent is 85.0~98.5 wt%.

17. The dual-conductor slurry according to claim 16, characterized in that, The dispersant is selected from at least one of polyvinylpyrrolidone and its derivatives, hydrogenated nitrile butadiene rubber, styrene-maleic anhydride copolymer and its derivatives, polyvinylidene fluoride, and carboxymethyl cellulose.

18. The dual-conductor slurry according to claim 16, characterized in that, The solvent is selected from at least one of water, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

19. The application of the dual-conducting composite material of claim 14 or the dual-conducting slurry of any one of claims 15 to 18 in lithium-ion batteries.

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