Double-conduction composite material, double-conduction slurry, and preparation method and application of double-conduction composite material and double-conduction slurry

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a double-conduction composite material, double-conduction slurry and a preparation method and application of the double-conduction composite material and the double-conduction slurry. The preparation method of the double-conduction composite material comprises the following steps: carrying out a coating reaction on a high-temperature purified carbon nanotube I and dopamine hydrochloride under an alkaline condition to obtain a carbon nanotube II coated with polydopamine on the surface, and carrying out a hydrothermal reaction on the carbon nanotube II and a carbohydrate carbon source to obtain a carbon nanotube III with a carbon coating layer on the surface; mixing the carbon nano tube III with a precursor material of an oxide type solid electrolyte, a chelating agent and water, performing sol-gel reaction, and drying to obtain dry gel; and carrying out secondary calcination treatment on the dry gel in an atmosphere with the oxygen content being less than or equal to 10vol% and an inert atmosphere in sequence to obtain the double-conduction composite material. The double-conduction composite material prepared by the method provided by the invention or the slurry thereof is used as an additive of a positive electrode material or a negative electrode material, so that the rate capability of a lithium ion battery under a low-temperature condition can be remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and particularly relates to a double-conductive composite material and a double-conductive slurry as well as a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have advantages in cost and energy density and thus occupy a dominant position in new energy. However, the rate performance of lithium ion batteries under low temperature conditions is poor, especially the performance under high rate is significantly reduced, mainly because under low temperature conditions, the viscosity of the electrolyte increases and the fluidity decreases, which slows down the ion conduction rate, directly affecting the rate performance of the battery. Most of the existing technologies are to improve the rate discharge performance of the battery by improving the electronic conduction, such as adding a certain proportion of conductive carbon material in the positive material / negative material, but the effect of improving the rate performance of lithium ion batteries under low temperature conditions is not significant. Furthermore, as described in Chinese Patent Document CN116469601B, a nanocarbon material and inorganic solid electrolyte particles are prepared into a conductor dispersion liquid by grinding, and then the conductor dispersion liquid is used as a positive electrode additive to improve the electronic and ionic conduction in the battery. However, this conventional mechanical mixing method is very easy to cause uneven dispersion of the carbon material and the solid electrolyte, and when the additive is added to the electrode material, the distribution in the electrode material will also be uneven, thereby limiting the performance of the battery and having limited effect on improving the low temperature performance. SUMMARY

[0003] One of the purposes of the present application is to provide a preparation method of a double-conductive composite material in view of the poor effect of existing positive / negative electrode additives on improving the low temperature rate performance of lithium ion batteries.

[0004] Specifically, the preparation method of the double-conductive composite material comprises the following steps: S1. Coating reaction of high-temperature purified carbon nanotubes I and hydrochloric acid dopamine under alkaline conditions to obtain carbon nanotubes II coated with polydopamine on the surface; and then hydrothermal reaction of the carbon nanotubes II coated with polydopamine on the surface and a sugar carbon source to obtain carbon nanotubes III with a carbon coating layer derived from polydopamine and the sugar carbon source on the surface; S2. Mixing the carbon nanotubes III obtained in step S1 with a precursor material of an oxide-type solid electrolyte, a chelating agent and water, and then performing a sol-gel reaction to obtain a dry gel after drying; S3. First calcination treatment of the dry gel obtained in step S2 in an atmosphere containing oxygen in an amount of ≤10 vol%, and then second calcination treatment of the obtained product in an inert atmosphere to obtain a double-conductive composite material of carbon nanotubes and an 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 saccharide 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, dopamine hydrochloride and the saccharide carbon source is 10:(4~8):(30~60).

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

[0009] In a preferred embodiment, in step S1, the alkaline condition is achieved by providing a Tris-HCl buffer solution with a pH value of 8.0~9.0.

[0010] In a preferred embodiment, in step S1, the time of the coating reaction is 20~30h.

[0011] In a preferred embodiment, in step S1, the hydrothermal reaction is performed under the condition of a temperature of 160~200℃ and a time of 10~15h.

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

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

[0014] In a preferred embodiment, in step S2, the precursor material of the LLZO solid-state electrolyte comprises a lithium source, a lanthanum source and a zirconium source; the precursor material of the LATP solid-state electrolyte comprises a lithium source, an aluminum source, a titanium source and a phosphorus source; and the precursor material of the LLTO solid-state electrolyte comprises 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-state electrolyte is (1.5~1.8):1.

[0017] In a preferred embodiment, in step S2, the conditions of 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 of the first calcination treatment include an oxygen content of 5-10vol%, a temperature of 550-650℃ and a time of 1-3h.

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

[0020] The second object of the present application is to provide a dual-conductive composite prepared by the above method.

[0021] The third object of the present application is to provide a dual-conductive slurry. The dual-conductive slurry comprises the above dual-conductive composite, a dispersant and a solvent.

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

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

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

[0025] The fourth object of the present application is to provide the use of the above dual-conductive composite or dual-conductive slurry in a lithium ion battery.

[0026] Beneficial effects: The key of the present application is to coat the surface of high-temperature purified carbon nanotubes (CNTs) with a carbon coating layer derived from polydopamine and a saccharide carbon source, and then introduce the above-mentioned carbon nanotubes in the sol-gel reaction process of the precursor material of the oxide-type solid electrolyte and the chelating agent. After the obtained xerogel is subjected to calcination treatment in an atmosphere containing oxygen ≤10 vol% and an inert atmosphere in turn, a double-conductive composite material in which carbon nanotubes are in-situ combined with the oxide-type solid electrolyte is obtained. When the double-conductive composite material or its slurry is used as an additive of the positive electrode or negative electrode of a lithium ion battery, the rate performance of the lithium ion battery under low temperature conditions can be significantly improved. It is speculated that the reason may be as follows: due to the nature of polydopamine, it can be used as a connecting agent between carbon nanotubes and saccharide carbon sources, so that the surface of the carbon nanotubes is uniformly coated with a carbon protective layer. On the one hand, it is beneficial to improve the thermal stability of CNTs in the subsequent calcination process, reduce the influence of oxidation on the performance of CNTs, and on the other hand, it can promote the uniform dispersion of CNTs in the sol-gel system, improve the in-situ combination effect of CNTs and the oxide-type solid electrolyte, so that CNTs are uniformly distributed on the surface of the solid electrolyte particles and / or coated inside the solid electrolyte particles, thereby improving the good ion and electron paths; the obtained xerogel is first calcined in an atmosphere with low oxygen partial pressure. Firstly, the solid electrolyte precursor is preliminarily crystallized, secondly, impurities (such as LiCO3) are removed to reduce the internal resistance of the material, and thirdly, CNTs are protected from oxidation. Then, through high-temperature calcination in an inert atmosphere, a solid electrolyte material with a more pure crystal phase and a higher density is obtained. That is, by using the two-step calcination process in a specific atmosphere, the integrity of the carbon nanotube structure and good performance can be ensured, and at the same time, a pure solid electrolyte can be obtained, and the carbon nanotube and the solid electrolyte are tightly combined.

[0027] In summary, the double-conductive composite material in which carbon nanotubes are in-situ tightly combined with the oxide-type solid electrolyte is prepared by the method provided by the present application. The double-conductive composite material can be directly used as an additive of the positive electrode material or the negative electrode material, and the rate performance of the lithium ion battery under low temperature conditions can be improved. In a preferred embodiment, the double-conductive composite material is prepared into a slurry and then used as an additive in the positive electrode material and the negative electrode material, which can further improve the uniform dispersibility of the double-conductive composite material in the electrode, and better avoid the performance loss of the battery caused by local aggregation in the electrode, thereby better improving the ion and electron conduction rates of the lithium ion battery under low temperature conditions. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a structural schematic diagram of the double-conductive composite material provided by the embodiments of the present application. DETAILED DESCRIPTION

[0029] Embodiments of the present application are described in detail below. The embodiments described below are exemplary only, and are not intended to be limiting of the present application. In addition, unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other, and such technical solutions should be considered to be included in the disclosure of the present application.

[0030] The present application provides a preparation method of the double-conductive composite material, which comprises the following steps: S1. The high-temperature purified carbon nanotube I is subjected to a coating reaction with dopamine hydrochloride under alkaline conditions to obtain a carbon nanotube II coated with polydopamine on the surface; and then the carbon nanotube II coated with polydopamine on the surface is subjected to a hydrothermal reaction with a saccharide carbon source to obtain a carbon nanotube III having a carbon coating layer derived from polydopamine and the saccharide carbon source on the surface; S2. The carbon nanotube III obtained in step S1 is mixed with a precursor material of an oxide solid electrolyte, a chelating agent and water, and then subjected to a sol-gel reaction to obtain a dry gel after drying; S3. The dry gel obtained in step S2 is subjected to a first calcination treatment in an atmosphere containing oxygen in an amount of ≤10 vol%, and then subjected to a second calcination treatment in an inert atmosphere to obtain a double-conductive composite material in which the carbon nanotube is combined with the oxide 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 therebetween.

[0031] In the present application, the source of the high-temperature purified carbon nanotube in step S1 is not specifically limited, and can be purchased or prepared according to the existing method. The high-temperature purified carbon nanotube can be selected from at least one of multi-walled carbon nanotubes, oligo-walled carbon nanotubes and single-walled carbon nanotubes.

[0032] In the present application, the specific type of the saccharide carbon source in step S1 is not specifically limited, as long as it is a kind of carbon-containing substance that can react with polydopamine to be connected to the carbon nanotube. Specific examples include, but are not limited to, at least one of glucose, fructose, sucrose, maltose and chitosan.

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

[0034] In the present application, in step S1, the pH value of the alkaline condition is preferably 8.0-9.0, such as 8.0, 8.2, 8.5, 8.8, 9.0 or any value between them. The implementation of the alkaline condition is not particularly limited, and is preferably achieved by providing a Tris-HCl buffer solution with a pH value of 8.0-9.0.

[0035] In the present application, in step S1, the coating reaction is preferably carried out at room temperature, such as 15℃, 18℃, 20℃, 22℃, 25℃, 28℃, 30℃ or any value between them. The time of the coating reaction is preferably 20-30h, such as 20h, 22h, 25h, 28h, 30h or any value between them.

[0036] In a specific embodiment, the process of the coating reaction can be as follows: first, mix and disperse the high-temperature purified carbon nanotube I with the Tris-HCl buffer solution with a pH value of 8.0-9.0, then add hydrochloric acid dopamine, stir at room temperature for 20-30h, collect the reaction product, wash and dry, to obtain the carbon nanotube II coated with polydopamine (PDA@CNTs).

[0037] In the present application, in step S1, the conditions of the hydrothermal reaction are preferably as follows: temperature is 160-200℃, such as 160℃, 170℃, 180℃, 190℃, 200℃ or any value between them; time is 10-15h, such as 10h, 11h, 12h, 13h, 14h, 15h or any value between them.

[0038] In the present application, in step S2, the mass of the oxide-type solid electrolyte is calculated based on the theoretical mass according to the stoichiometric ratio of the precursor material, and the amount of the carbon nanotube III is preferably 5-20wt% of the oxide-type solid electrolyte, such as 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt% or any value between them. At this time, it is more beneficial for the carbon nanotubes to be uniformly dispersed in the oxide-type solid electrolyte, so that the conductivity and dispersibility of the carbon nanotubes in the double-conductive composite material achieve a good balance (too little carbon nanotube content will result in insufficient conductivity, and too much carbon nanotube content will entangle with each other, affecting the dispersion). In the present application, in step S2, the oxide-type solid electrolyte is preferably at least one selected from LLZO, LATP and LLTO. Specifically, the chemical formula of the 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 them. The precursor material of the LLZO solid-state electrolyte preferably comprises a lithium source, a lanthanum source, a zirconium source. The chemical general formula of the LATP solid-state electrolyte is Li 1+y Al y Ti 2-y (PO4)3, wherein 0<y≤0.5, which can be 0.1, 0.2, 0.3, 0.4, 0.5 or any value between them. The precursor material of the LATP solid-state electrolyte preferably comprises a lithium source, an aluminum source, a titanium source, a phosphorus source. The chemical general formula of the LLTO solid-state electrolyte is Li 3z La 2 / 3-z TiO3, wherein 0.04≤z≤0.16, which can be 0.04, 0.05, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16 or any value between them. The precursor material of the LLTO solid-state electrolyte preferably comprises a lithium source, a lanthanum source, a titanium source. The lithium source in the above-mentioned materials can be independently selected from any one or more of LiNO3 (lithium nitrate), CH3COOLi (lithium acetate), LiOH (lithium hydroxide), LiCl (lithium chloride). The lanthanum source in the above-mentioned materials can be La(NO3)3 (lanthanum nitrate) and / or La(CH3COO)3 (lanthanum acetate). The zirconium source in the above-mentioned materials can be ZrO(NO3)2 (zirconyl nitrate), Zr(OC2H5)4 (zirconium alkoxide). The aluminum source in the above-mentioned materials can be selected from any one or more of Al(NO3)3 (aluminum nitrate), Al(CH3COO)3 (aluminum acetate), AlCl3 (aluminum chloride). The titanium source in the above-mentioned materials can be selected from any one or more of TiCl4 (titanium chloride), Ti(OC4H9)4 (titanium acid tetrabutyl ester). The phosphorus source in the above-mentioned materials can be selected from any one or more of H3PO4 (phosphoric acid), (NH4)3PO4 (ammonium phosphate), NH4H2PO4 (diammonium hydrogen phosphate), (NH4)2HPO4 (diammonium hydrogen phosphate), (CH3O)3PO (trimethyl phosphate), (CH3O)3P (trimethyl phosphite).

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

[0040] In the present application, in step S2, the molar ratio of the chelating agent to the metal in the precursor material of the oxide-type solid-state 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 them.

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

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

[0043] In the present application, in step S3, the conditions of the first calcination treatment preferably include: an oxygen content of 3-7vol%, such as 3vol%, 4vol%, 5vol%, 6vol%, 7vol% or any value between them, which is more conducive to the thermal stability of the carbon nanotubes on the one hand, and makes the carbon coating on the surface of the carbon nanotubes completely or partially remain, thereby making the dual-conductive composite have better dispersibility in the slurry; a temperature of 550-650℃, such as 550℃, 580℃, 600℃, 620℃, 650℃ or any value between them; a time of 1-3h, such as 1h, 1.5h, 2h, 2.5h, 3h or any value between them. When the oxygen content, temperature and time of the first calcination treatment are controlled within the above preferred ranges, it is more conducive to improving the purity of the preliminary crystallization of the solid electrolyte precursor, while ensuring the structural integrity and excellent performance of the carbon nanotubes.

[0044] In the present application, in step S3, the conditions of the second calcination treatment preferably include: a temperature of 800-900℃, such as 800℃, 820℃, 850℃, 880℃, 900℃ or any value between them; 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 application provides a dual-conductive composite prepared by the above method.

[0046] The present application provides a dual-conductive slurry, which comprises the above dual-conductive composite, a dispersant and a solvent.

[0047] In the present application, the content of the dual-conductive composite 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 therebetween. 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 therebetween. 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 therebetween.

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

[0049] In the present application, the dual-conductive slurry can be obtained by mixing the dual-conductive composite, the dispersant and the solvent and then performing a grinding treatment. The conditions of the grinding treatment preferably include a grinding time of 1-2 h, such as 1 h, 1.2 h, 1.5 h, 1.8 h, 2 h or any value therebetween; 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 therebetween; and a sanding rotation speed of 1000-3000 rpm, such as 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm or any value therebetween.

[0050] The present application will be described in detail below through specific examples. The examples are intended to explain the present application and cannot be understood as limiting the present application. If a specific technique or condition is not specified in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0051] Example 1 This example is used to illustrate the preparation of a dual-conductive composite and a dual-conductive slurry, and the specific process is as follows: 1. Carbon nanotube coating: (1) Take 10 g of high-temperature purified carbon nanotubes (from Yongan City Kaina New Material Technology Co., Ltd., tube diameter 5-10 nm, tube length > 1 μm), add it to 500 mL of Tris-HCl buffer solution with pH 8.5, and ultrasonic in ice water bath for 30 min to make it fully dispersed, then add 6 g of hydrochloric acid dopamine to the solution, and stir magnetically at room temperature for 24 h. After the reaction is completed, the black product is collected by centrifugation, washed with deionized water 8 times to remove unreacted monomers, and dried at 60°C under vacuum to obtain carbon nanotubes coated with polydopamine on the surface, denoted as PDA@CNTs.

[0052] (2) Disperse the PDA@CNTs obtained above in 500 mL of 0.5 M glucose solution, ultrasonic in ice water bath for 30 min, then transfer the mixed solution to a polytetrafluoroethylene-lined high-pressure reaction kettle, and hydrothermal reaction at 180°C for 12 h. After cooling, the product is collected by centrifugation, washed with deionized water 8 times, and dried at 60°C under vacuum to obtain carbon nanotubes with a carbon coating layer derived from polydopamine and glucose on the surface, denoted as C-PDA@CNTs.

[0053] 2. Preparation of C-PDA@CNTs / LLZO precursor by sol-gel method: (1) Take 0.42 g of C-PDA@CNTs and disperse in 50 mL of deionized water, ultrasonic for 30 min to form a uniform and stable dispersion liquid. (The addition amount of carbon nanotubes is 10 wt% of LLZO) (2) According to the stoichiometric ratio of the chemical formula Li7La3Zr2O 12 In the chemical formula Li7La3Zr2O 12 , respectively take 6.82 g of LiNO3·6H2O (38.5 mmol), 6.50 g of La(NO3)3·6H2O (15 mmol), and 2.68 g of ZrO(NO3)2·2H2O (10 mmol), dissolve them in deionized water, then add 21.84 g of citric acid monohydrate (104 mmol) to the precursor metal salt solution, stir and dissolve at 70°C, continue to slowly drop the C-PDA@CNTs dispersion liquid into it under stirring to form a black sol, continue to stir the black sol at 70°C for 12 h to obtain a black gel. Place the black gel in a 120°C oven and dry for 12 h to obtain a black xerogel.

[0054] 3. Preparation of CNTs / LLZO composite material by calcination: (1) First calcination treatment: place the xerogel prepared in the previous step in a tube furnace, calcine at 600°C for 2 h, the heating rate is 3°C / min, the atmosphere is 95 vol% N2+5 vol% O2 (which can be realized by controlling the flow rate ratio of N2:O2=95:5).

[0055] (2) Second calcination treatment: close O2, purged with N2 for 30 min, continue to heat to 850℃, calcination for 4h, heating rate 3℃ / min, cool to room temperature, CNTs / LLZO composite material is obtained.

[0056] 4. Preparation of CNTs / LLZO composite slurry Take 20g CNTs / LLZO composite material powder, 5g polyvinylpyrrolidone K30 and 475g NMP solvent (N-methyl pyrrolidone), put into the sand mill and grind for 90min (zirconium bead diameter is 0.8mm, sand mill rotating speed is 2000rpm), after sand mill grinding, uniform CNTs / LLZO double-conductive slurry is obtained.

[0057] The structure diagram of the obtained CNTs / LLZO composite material is shown in Figure 1 The CNTs are embedded in the interior of the solid electrolyte particles and wound on the surface of the particles, that is, the CNTs and the solid electrolyte particles are in-situ composite.

[0058] Example 2 This example is used to illustrate the preparation of a double-conductive composite material and a double-conductive slurry, and the specific process is as follows: 1. Carbon nanotube coating: (1) Take 10g high-temperature purified carbon nanotubes (from Yongan City Kaina New Material Technology Co., Ltd., tube diameter 30~80nm, tube length≥1μm), add it into 500mL Tris-HCl buffer solution with pH 8.0, ice water bath ultrasonic for 30min, so that it is fully dispersed, then add 4g hydrochloric acid dopamine into the solution, magnetic stirring at room temperature for 24h. After the reaction is completed, the black product is collected by centrifugation, washed with deionized water for 8 times to remove unreacted monomer, and vacuum dried at 60℃ to obtain polydopamine coated carbon nanotubes, which is recorded as PDA@CNTs.

[0059] (2) Disperse the obtained PDA@CNTs in 500mL 0.3M sucrose solution, ice water bath ultrasonic for 30min, then transfer the mixed solution to a polytetrafluoroethylene lined high-pressure reaction kettle, hydrothermal reaction at 180℃ for 12h, after cooling, centrifugal collection of the product, washed with deionized water for 8 times, vacuum dried at 60℃ to obtain carbon nanotubes with carbon coating layer derived from polydopamine and sucrose on the surface, which is recorded as C-PDA@CNTs.

[0060] 2. Preparation of C-PDA@CNTs / LLZO precursor by sol-gel method: (1) Take 0.21g C-PDA@CNTs and disperse in 50mL deionized water, ultrasonic for 30min to form a uniform and stable dispersion liquid. (The addition amount of carbon nanotubes 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, heating rate 3℃ / min, cool to room temperature to 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: close O2, purge with N2 for 30 min, continue to heat to 900°C, calcine for 4 h, heating rate 3°C / min, cool to room temperature, to obtain CNTs / LLZO composite material.

[0069] 4. Preparation of CNTs / LLZO composite slurry Weigh 10 g of CNTs / LLZO composite material powder, 5 g of polyvinylpyrrolidone K30 and 485 g of NMP solvent (N-methylpyrrolidone), put them into a sand mill and grind for 90 min (zirconium beads with a diameter of 0.8 mm, sand mill speed of 2000 rpm), and obtain a uniform CNTs / LLZO double-conductive slurry after sanding.

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

[0071] Example 5 This example is used to illustrate the preparation of a double-conductive composite material and a double-conductive slurry, and the specific process is as follows: The double-conductive composite material is prepared according to the method of Example 1, except that the amount of carbon nanotubes added in step 2- (1) is 10 wt% of LLZO, and in step 2- (2), the stoichiometric ratio in the chemical formula Li 0.33 La 0.56 TiO3is respectively weighed LiNO3·6H2O (14.5 mmol), La (NO3)3·6H2O (22.4 mmol), TiCl4(40 mmol), and the rest of the conditions are the same as in Example 1, thereby preparing a CNTs / LLTO double-conductive slurry.

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

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

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

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

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

[0077] 2. Preparation of LLZO material by calcination: The above black xerogel was calcined to obtain an LLZO material according to the method of step 3 in Example 1.

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

[0079] Comparative Example 2 This comparative example is used to illustrate the preparation of a reference composite material and a reference slurry, and the specific process is as follows: The reference composite material is prepared according to the method of Example 1, except that step 1 is not performed and the same mass of high-temperature purified carbon nanotubes (from Yongan City Kaina New Material Technology Co., Ltd., tube diameter 5-10 nm, tube length ≥1 μm) is used instead of C-PDA@CNTs in step 2, and the remaining conditions are the same as those of Example 1, thereby preparing a reference CNTs / LLZO composite material and a reference CNTs / LLZO slurry.

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

[0081] Comparative Example 4 This comparative example is used to illustrate the preparation of a reference composite material and a reference slurry, and the specific process is as follows: The reference composite material is prepared according to the method of Example 1, except that step 1- (2) is not performed, and the remaining conditions are the same as those of Example 1, thereby preparing a reference CNTs / LLZO composite material and a reference CNTs / LLZO slurry.

[0082] Test Example The bi-conductive slurry prepared by the above examples and comparative examples was used as an additive of the positive material, and a 400 mAh soft package battery was assembled according to the following method: the slurry formula of the positive sheet was NCM622: PVDF: carbon black: bi-conductive slurry (by mass of the bi-conductive composite contained) = 95: 2: 1.5: 1.5, the slurry formula of the negative sheet was graphite: carbon black: CMC: SBR = 94.5: 1.5: 1.5: 2.5, the solvent of the positive slurry was N-methyl pyrrolidone, the solvent of the negative 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 package battery assembled according to the above method was subjected to low-temperature rate performance test: the test temperature was -20℃, the test voltage range was 3.0-4.2V, the test rates were 0.2C, 1C, 3C, 5C and 7C, respectively, then the discharge capacity at each rate was divided by the discharge capacity at 0.2C rate, and the discharge capacity retention rate at different rates was calculated. The results are shown in Table 1.

[0084] Table 1

[0085] From the results in Table 1, it can be seen that, compared with Comparative Examples 1-4, the bi-conductive slurry provided by Examples 1-9 of the present application can endow the lithium ion battery with more excellent rate performance under low temperature conditions (-20℃), and the difference in discharge capacity retention rate between the examples and the comparative examples becomes more significant as the rate increases.

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

Claims

1. A method for producing a dual-lead composite material, characterized by, 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.

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; Preferably, the carbohydrate carbon source is selected from at least one of glucose, fructose, sucrose, maltose, and chitosan; Preferably, the mass ratio of the carbon nanotube I to dopamine hydrochloride and the sugar carbon source is 10:(4~8):(30~60).

3. 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; Preferably, the alkaline conditions are achieved by providing a Tris-HCl buffer solution with a pH of 8.0 to 9.0; Preferably, the coating reaction takes 20-30 hours; Preferably, the conditions for the hydrothermal reaction include: a temperature of 160~200℃ and a time of 10~15h.

4. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S2, the amount of carbon nanotubes III used is 5-20 wt% of the oxide-type solid electrolyte. Preferably, the oxide-type solid electrolyte is selected from at least one of LLZO, LATP, and LLTO; Preferably, the precursor materials for LLZO solid electrolyte include lithium, lanthanum, and zirconium sources; the precursor materials for LATP solid electrolyte include lithium, aluminum, titanium, and phosphorus sources; and the precursor materials for LLTO solid electrolyte include lithium, lanthanum, and titanium sources.

5. 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; Preferably, 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; Preferably, the conditions for the sol-gel reaction include: a temperature of 60~80℃ and a time of 10~15h.

6. The method for preparing the dual-conducting composite material according to claim 1, characterized in that, In step S3, the conditions for the first calcination treatment include: oxygen content of 3-7 vol%, temperature of 550-650℃, and time of 1-3 h; Preferably, the conditions for the second calcination treatment include: a temperature of 800~900℃ and a time of 3~5h.

7. A dual-conducting composite material prepared by the method according to any one of claims 1 to 6.

8. A dual-guided slurry, characterized in that, The dual-conductive slurry comprises the dual-conductive composite material, dispersant, and solvent as described in claim 7.

9. The dual-conductor slurry according to claim 8, 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%. Preferably, 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; Preferably, the solvent is selected from at least one of water, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

10. The application of the dual-conducting composite material of claim 7 or the dual-conducting slurry of claim 8 or 9 in lithium-ion batteries.

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