Ni-CeO2-CNT (at) rGO conductive agent as well as preparation method and application thereof

Abstract

The invention discloses a Ni-CeO2-CNT (at) rGO conductive agent as well as a preparation method and application thereof, and relates to the technical field of batteries. The Ni-CeO2-CNT (at) rGO conductive agent is composed of rGO of a three-dimensional network structure and CNT vertically growing on the surface of the rGO, and one end, far away from the rGO, of the CNT is connected with Ni-CeO2 nanoparticles. The conductive agent provided by the invention has better dispersion performance in electrode slurry, can provide abundant and easily available redox active sites, and is helpful for improving the diffusion rate of lithium ions in the lithium ion battery, thereby improving the rate capability and cycle performance of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a Ni-CeO 2 -CNT@rGO conductive agent and its preparation method and application. Background Art

[0002] To facilitate the implementation of the "dual carbon" strategy and promote the continuous innovation of the new energy industry, the requirements for energy storage systems are getting higher and higher, and rechargeable batteries represented by lithium-ion batteries and lead-acid batteries have achieved certain technological developments. Among them, as an important component of electrode materials, conductive agents can reduce the internal resistance of electrodes and accelerate the lithium-ion conduction rate, which plays an important role in improving the rate performance and capacity of lithium-ion batteries.

[0003] Common conductive agents include graphene, carbon black, and carbon nanotubes (CNT). As one of the representative one-dimensional materials in the carbon material family, CNT has high conductivity and a unique hollow tubular structure, which plays an important role in lithium-ion batteries. However, due to its large aspect ratio and flexibility, the lengths of free-growing carbon nanotubes are often different, and they are prone to aggregation and entanglement, causing problems such as capacity attenuation and poor cycling in lithium-ion batteries. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a Ni-CeO 2 -CNT@rGO conductive agent and its preparation method and application. The conductive agent of the present invention has better dispersion performance in the electrode paste, can provide rich and easily accessible redox active sites, helps to improve the diffusion rate of lithium ions in lithium-ion batteries, and thus improves the rate performance and cycling performance of lithium-ion batteries.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] In the first aspect, the present invention provides a Ni-CeO 2 -CNT@rGO conductive agent, which is composed of rGO with a three-dimensional network structure and CNT vertically grown on the surface of rGO, and Ni-CeO 2 nanoparticles are connected to one end of the CNT away from the rGO.

[0007] The present invention constructs a Ni-CeO 2 -CNT@rGO conductive agent with a three-dimensional nano-hybrid heterostructure composed of two carbonaceous nano-materials, reduced graphene oxide (rGO) and carbon nanotubes (CNT), which can inhibit the aggregation of CNT. Compared with pure rGO or CNT, Ni-CeO 2-CNT@rGO has better dispersion performance in the electrode paste, can provide rich and easily accessible redox active sites, helps to improve the diffusion rate of lithium ions in the lithium-ion battery, and thus improves the rate performance and cycling performance of the lithium-ion battery.

[0008] Preferably, the CNT has a tube diameter of 30 - 80 nm, a tube length of 1 - 2 μm, and a specific surface area of 60 - 150 m 2 / g.

[0009] More preferably, the tube diameter of the CNT can be any one or the range value of two of 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm; the tube length of the CNT can be any one or the range value of two of 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm; the specific surface area of the CNT can be any one or the range value of two of 60 m 2 / g, 70 m 2 / g, 80 m 2 / g, 90 m 2 / g, 100 m 2 / g, 110 m 2 / g, 120 m 2 / g, 130 m 2 / g, 140 m 2 / g, 150 m 2 / g.

[0010] Preferably, the sheet diameter of the three-dimensional network-structured rGO is 8 - 15 μm, the number of layers is 1 - 6 layers, and the thickness is 0.5 - 2 nm.

[0011] More preferably, the sheet diameter of the three-dimensional network-structured rGO can be any one or the range value of two of 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm; the number of layers of the rGO can be any one of 1, 2, 3, 4, 5, 6; the thickness of the rGO can be any one or the range value of two of 0.5 nm, 1 nm, 1.5 nm, 2 nm.

[0012] In a second aspect, the present invention also provides a preparation method of a Ni-CeO 2 -CNT@rGO conductive agent, comprising the following steps:

[0013] (1) Mix the nickel source, cerium source, H 3BTC is dissolved in a first solvent and mixed to obtain a mixed solution; GO is dissolved in a second solvent to obtain a GO dispersion; the mixed solution is then mixed with the GO dispersion to obtain a synthetic solution, and the synthetic solution is poured into a closed container for a hydrothermal reaction; after the reaction is completed, the product is cooled to room temperature, centrifuged, washed, and dried to prepare a precursor Ce-Ni-BTC@GO;

[0014] (2) The carbon source and the precursor Ce-Ni-BTC@GO are placed in a tube furnace for calcination to perform a CVD deposition reaction. After the reaction is complete, Ni-CeO 2 -CNT@rGO conductive agent.

[0015] like Figure 2 As shown, the precursor Ce-Ni-BTC@GO prepared in the above step (1) includes spherical Ce-Ni-BTC and three-dimensional network structure of graphene oxide (GO), and GO can provide abundant nucleation sites for the growth of Ce-Ni-BTC and provide a template for the subsequent vertical growth of CNTs.

[0016] The spherical Ce-Ni-BTC is composed of nickel source, cerium source and trimesic acid (H 3 Ce-Ni-BTC is a metal organic framework (MOFs) material prepared by using Ce-Ni-BTC as raw material. It has many advantages such as hollow structure, high surface area, permanent pores and stable morphology. It does not undergo drastic volume changes and exhibits rapid ion diffusion ability, and has excellent recyclability. Ce-Ni-BTC synthesized by hydrothermal method in the present invention has a uniform spherical morphology with a diameter in the range of 50-100nm. Compared with Fe-based or Co-based MOFs materials, this "ball-to-plate" nanostructure can produce a synergistic effect and increase the contact area. In addition, H 3 While forming the MOFs material framework, BTC also acts as a catalyst for the hydrothermal reaction and provides a small amount of carbon source for the subsequent in-situ vertical growth of CNTs. 2+ The electronegative oxygen functional groups in GO can be adsorbed through electrostatic interactions.

[0017] like Figure 2As shown, in the above step (2), the carbon source and the precursor Ce-Ni-BTC@GO are calcined in a tubular furnace for CVD deposition reaction. After calcination, GO in the precursor Ce-Ni-BTC@GO is reduced to rGO using the carbon source as a reducing agent. At the same time, Ce-Ni-BTC in the precursor Ce-Ni-BTC@GO can serve as the active site for the in-situ vertical growth of CNT on the rGO surface. More specifically, the nickel in Ce-Ni-BTC is the active site for the in-situ vertical growth of CNT on the rGO surface. After the in-situ vertical growth of CNT on the rGO surface, the spherical Ce-Ni-BTC in the precursor Ce-Ni-BTC@GO is transformed into Ni-CeO 2 nanoparticles, and Ni-CeO 2 nanoparticles are connected to one end of the CNT away from the rGO, finally forming Figure 1 the shown Ni-CeO 2 -CNT@rGO conductive agent.

[0018] It can be understood that the three-dimensional network structure of rGO is formed by reducing the three-dimensional network structure of GO. Since the size of rGO basically does not change after GO is reduced to rGO, and the size of GO depends on the size of GO in the raw material GO dispersion, the size of the three-dimensional network structure of rGO in the Ni-CeO 2 -CNT@rGO conductive agent and the size of the three-dimensional network structure of GO in the precursor Ce-Ni-BTC@GO are both the same as the size of GO in the raw material GO dispersion.

[0019] In the present invention, through the hydrothermal method and the chemical vapor deposition (CVD) method, using the Ce-Ni-BTC@GO formed by growing the MOF material Ce-Ni-BTC doped with nickel metal and cerium metal on the GO surface as a precursor, GO is reduced to rGO, and then CNT is in-situ vertically grown on the rGO surface to prepare the Ni-CeO 2 -CNT@rGO conductive agent. This conductive agent has a three-dimensional structure and can provide abundant and easily accessible redox active sites, which helps to improve the diffusion rate of lithium ions in lithium-ion batteries, thereby improving the rate performance and cycling performance of lithium-ion batteries. Moreover, this preparation method has a simple process, low energy consumption, and is green and environmentally friendly.

[0020] Preferably, in the step (1), the molar ratio of Ni 2+ : Ce 3+ : H 3 BTC is (0.5 - 4):1:(0.1 - 3).

[0021] If Ni 2+ and H 3If the dosage of BTC is too high, it will cause an increase in the particle size of the spherical MOF material Ce-Ni-BTC and a decrease in the specific surface area, resulting in a reduction in the number of contact sites on GO; if Ni 2+ and H 3 If the dosage of BTC is too low, it will limit the in-situ vertical growth of subsequent CNTs. Therefore, in the present invention, by controlling the molar ratio of Ni 2+ :Ce 3+ :H 3 BTC to be (0.5 - 4):1:(0.1 - 3), it is beneficial to improve the rate performance and cycling performance of the lithium-ion battery.

[0022] More preferably, in the step (1), the molar ratio of Ni 2+ :Ce 3+ :H 3 BTC is (1 - 3):1:(1 - 2).

[0023] Preferably, in the step (1), the nickel source includes any one or a combination of Ni(NO 3 ) 2 ·6H 2 O, anhydrous nickel chloride, NiCl 2 ·6H 2 O.

[0024] Preferably, in the step (1), the cerium source includes any one or a combination of Ce(NO 3 ) 3 ·6H 2 O, CeCl 3 ·6H 2 O.

[0025] Preferably, in the step (1), the first solvent is N,N-dimethylformamide (DMF), and the second solvent is deionized water.

[0026] Preferably, in the step (1), the temperature of the hydrothermal reaction is 140°C - 160°C, and the time of the hydrothermal reaction is 12 - 36 h.

[0027] If the temperature of the hydrothermal reaction is too low or too high, it will affect the formation of the spherical MOF material Ce-Ni-BTC. Therefore, in the present invention, by controlling the temperature of the hydrothermal reaction to be 140°C - 160°C, it is beneficial to improve the rate performance and cycling performance of the lithium-ion battery.

[0028] Preferably, in the step (2), the mass ratio of the carbon source to the precursor Ce-Ni-BTC@GO is (5 - 20):1.

[0029] More preferably, in the step (2), the mass ratio of the carbon source to the precursor Ce-Ni-BTC@GO is (6-15):1.

[0030] Further preferably, the mass ratio of the carbon source to the precursor Ce-Ni-BTC@GO is any one or the range value of two of 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1.

[0031] Preferably, the carbon source in the step (2) includes any one or a combination of more of DMF and melamine.

[0032] Preferably, in the step (2), the calcination temperature is 500-800 °C, the calcination time is 0.5-2 h, and the heating rate of the calcination is 1-3 °C / min.

[0033] If the calcination temperature is too high, it will cause the hetero-structure of the Ni-CeO 2 -CNT@rGO conductive agent to collapse or cause the in-situ vertically grown CNTs to agglomerate, while increasing energy consumption; if the calcination temperature is too low, it will limit the subsequent in-situ vertical growth of CNTs. If the calcination time is too long, it will cause the CNTs to grow too densely, thus restricting the transport of lithium ions and ultimately reducing the capacity of the battery; if the calcination time is too short, it will cause the CNTs to grow unevenly, thus resulting in a decrease in the stability of the Ni-CeO 2 -CNT@rGO conductive agent. Therefore, by controlling the calcination temperature at 500-800 °C and the calcination time at 0.5-2 h, the present invention is beneficial to improving the rate performance and cycle performance of lithium-ion batteries.

[0034] In the third aspect, the present invention also provides a cathode material, including the Ni-CeO 2 -CNT@rGO conductive agent prepared as described above.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) By constructing the three-dimensional nano-hybrid hetero-structure Ni-CeO 2 -CNT@rGO conductive agent composed of two carbonaceous nano-materials, rGO and CNT, the aggregation of CNTs can be inhibited. Compared with pure rGO or CNT, the Ni-CeO 2 -CNT@rGO conductive agent has better dispersion performance in the electrode slurry, can provide rich and easily accessible redox active sites, helps to improve the diffusion rate of lithium ions in lithium-ion batteries, and thus improves the rate performance and cycle performance of lithium-ion batteries.

[0037] (2) The present invention uses a hydrothermal method and a chemical vapor deposition (CVD) method. Ce-Ni-BTC@GO formed by growing an MOF material Ce-Ni-BTC doped with nickel metal and cerium metal on the surface of GO is used as a precursor. GO is reduced to rGO, and then CNTs are vertically grown in situ on the surface of rGO to obtain a Ni-CeO 2 -CNT@rGO conductive agent. This conductive agent has a three-dimensional structure, can provide abundant and easily accessible redox active sites, helps to improve the diffusion rate of lithium ions in lithium-ion batteries, and thus improves the rate performance and cycling performance of lithium-ion batteries. Moreover, this preparation method has a simple process, low energy consumption, and is environmentally friendly. Description of the Drawings

[0038] Figure 1 is a schematic structural diagram of the Ni-CeO 2 -CNT@rGO conductive agent provided by the present invention.

[0039] Figure 2 is a process flow diagram of the preparation method of the Ni-CeO 2 -CNT@rGO conductive agent provided by the present invention. Detailed Embodiments

[0040] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the protection scope and implementation manners of the present invention are not limited thereto.

[0041] The materials, reagents, etc. used in the following embodiments are commercially available reagents and materials unless otherwise specified.

[0042] Example 1

[0043] A preparation method of a Ni-CeO 2 -CNT@rGO conductive agent, comprising the following steps:

[0044] (1) Dissolve Ni(NO 3 ) 2 ·6H 2 O, Ce(NO 3 ) 3 ·6H 2 O, and H 3 BTC in DMF. After ultrasonic treatment for 15 minutes, it becomes a light green transparent solution to obtain a mixed solution; in the mixed solution, Ni(NO 3 ) 2 ·6H 2 O, Ce(NO 3 ) 3 ·6H 2 O, and H 3The total concentration of BTC is 0.01 mol / L, and Ni 2+ : Ce 3+ : H 3 The molar ratio of BTC is 2:1:1; then the original GO dispersion with a concentration of 5 mg / mL (the solvent is deionized water) is mixed with 45 mL of H 2 O, and stirred at 600 rpm for 10 h to obtain a GO dispersion;

[0045] The mixed solution is then mixed and stirred with the GO dispersion for 3 h to obtain a synthesis solution. The synthesis solution is poured into a stainless-steel autoclave lined with polytetrafluoroethylene, sealed and placed in an oven for hydrothermal reaction. The hydrothermal temperature is 150 °C and the hydrothermal time is 24 h; after the reaction is completed, the autoclave is allowed to cool naturally to room temperature, the product is collected by centrifugation, washed with absolute ethanol, and placed in a vacuum drying oven at 60 °C for 12 h to dry, thus preparing the precursor Ce-Ni-BTC@GO.

[0046] (2) DMF and the precursor Ce-Ni-BTC@GO with a mass ratio of 10:1 are placed in two porcelain boats at the upstream and downstream of a tube furnace respectively for CVD deposition reaction by calcination. The calcination temperature is 650 °C, the heating rate of calcination is 2 °C / min, and it is maintained for 1 h in an argon atmosphere. After cooling to room temperature, Ni-CeO 2 -CNT@rGO conductive agent is obtained.

[0047] In the Ni-CeO 2 -CNT@rGO conductive agent prepared in this example, the diameter of CNT is 30 - 40 nm, the tube length is 1.5 - 2 μm, and the specific surface area is 100 - 110 m 2 / g; the sheet diameter of the three-dimensional network structure of rGO is 8 - 15 μm, the number of layers is 1 - 6 layers, and the thickness is 0.5 - 2 nm.

[0048] Example 2

[0049] A preparation method of a Ni-CeO 2 -CNT@rGO conductive agent, comprising the following steps:

[0050] (1) Ni(NO 3 ) 2 ·6H 2 O, Ce(NO 3 ) 3 ·6H 2 O, H 3 BTC are dissolved in DMF, and after ultrasonic treatment for 15 min, it becomes a light green transparent solution to obtain a mixed solution; in the mixed solution, Ni(NO 3 ) 2 ·6H 2O, Ce(NO 3 ) 3 ·6H 2 O, H 3 The total concentration of HBTC is 0.01 mol / L, and the molar ratio of Ni 2+ : Ce 3+ : H 3 BTC is 1:1:0.1; then the original GO dispersion with a concentration of 5 mg / mL (the solvent is deionized water) is mixed with 45 mL of H 2 O, and stirred at 600 rpm for 10 h to obtain a GO dispersion;

[0051] Then the mixed solution is mixed and stirred with the GO dispersion for 3 h to obtain a synthesis solution, and then the synthesis solution is poured into a stainless-steel autoclave lined with polytetrafluoroethylene, sealed and placed in an oven for hydrothermal reaction. The hydrothermal temperature is 140 °C and the hydrothermal time is 36 h; after the reaction is completed, wait for the autoclave to cool naturally to room temperature, collect the product by centrifugation, wash it with absolute ethanol, and place it in a vacuum drying oven at 60 °C for drying for 12 h to prepare the precursor Ce-Ni-BTC@GO.

[0052] (2) Put DMF and the precursor Ce-Ni-BTC@GO with a mass ratio of 5:1 in two porcelain boats at the upstream and downstream of a tube furnace for CVD deposition reaction. The calcination temperature is 500 °C, the heating rate of calcination is 2 °C / min, and it is maintained in an argon atmosphere for 2 h. Wait until it cools to room temperature to obtain the Ni-CeO 2 -CNT@rGO conductive agent.

[0053] In the Ni-CeO 2 -CNT@rGO conductive agent prepared in this example, the tube diameter of CNT is 50 - 60 nm, the tube length is 1 - 1.5 μm, and the specific surface area is 80 - 90 m 2 / g; the sheet diameter of the three-dimensional network structure rGO is 8 - 15 μm, the number of layers is 1 - 6 layers, and the thickness is 0.5 - 2 nm.

[0054] Example 3

[0055] A preparation method of a Ni-CeO 2 -CNT@rGO conductive agent, comprising the following steps:

[0056] (1) Mix Ni(NO 3 ) 2 ·6H 2 O, Ce(NO 3 ) 3 ·6H 2 O, H 3BTC was dissolved in DMF. After ultrasonic treatment for 15 min, it became a light green transparent solution, and a mixed solution was obtained. In the mixed solution, the total concentration of Ni(NO 3 ) 2 ·6H 2 O, Ce(NO 3 ) 3 ·6H 2 O, and H 3 BTC was 0.01 mol / L, and the molar ratio of Ni 2+ :Ce 3+ :H 3 BTC was 4:1:3. Then, the original GO dispersion (with deionized water as the solvent) with a concentration of 5 mg / mL was mixed with 45 mL of H 2 O and stirred at 600 rpm for 10 h to obtain a GO dispersion;

[0057] The mixed solution was then mixed with the GO dispersion and stirred for 3 h to obtain a synthesis solution. The synthesis solution was poured into a stainless-steel autoclave lined with polytetrafluoroethylene, sealed, and placed in an oven for hydrothermal reaction. The hydrothermal temperature was 160 °C, and the hydrothermal time was 12 h. After the reaction, the autoclave was allowed to cool naturally to room temperature. The product was collected by centrifugation, washed with absolute ethanol, and dried in a vacuum drying oven at 60 °C for 12 h to prepare the precursor Ce-Ni-BTC@GO.

[0058] (2) DMF and the precursor Ce-Ni-BTC@GO with a mass ratio of 20:1 were placed in two porcelain boats at the upstream and downstream of a tube furnace for CVD deposition reaction. The calcination temperature was 800 °C, the heating rate of calcination was 2 °C / min, and it was maintained in an argon atmosphere for 0.5 h. After cooling to room temperature, the Ni-CeO 2 -CNT@rGO conductive agent was obtained.

[0059] In the Ni-CeO 2 -CNT@rGO conductive agent prepared in this example, the tube diameter of CNT was 35 - 45 nm, the tube length was 1.5 - 2 μm, and the specific surface area was 90 - 100 m 2 / g; the sheet diameter of the three-dimensional network structure rGO was 8 - 15 μm, the number of layers was 1 - 6 layers, and the thickness was 0.5 - 2 nm.

[0060] Example 4

[0061] A preparation method of a Ni-CeO 2 -CNT@rGO conductive agent, which is different from that in Example 1 in that in step (1), the molar ratio of Ni 2+ :Ce 3+ :H 3 BTC was 0.4:1:0.09.

[0062] The Ni-CeO 2 -CNT@rGO conductive agent prepared in this example has a CNT diameter of 70-80 nm, a tube length of 1-1.5 μm, and a specific surface area of 70-80 m 2 / g; the rGO with a three-dimensional network structure has a sheet diameter of 8-15 μm, 1-6 layers, and a thickness of 0.5-2 nm.

[0063] Example 5

[0064] A preparation method of a Ni-CeO 2 -CNT@rGO conductive agent, different from that of Example 1 in that in step (1), the molar ratio of Ni 2+ :Ce 3+ :H 3 :BTC is 4.5:1:3.5.

[0065] The Ni-CeO 2 -CNT@rGO conductive agent prepared in this example has a CNT diameter of 40-50 nm, a tube length of 1.5-2 μm, and a specific surface area of 90-100 m 2 / g; the rGO with a three-dimensional network structure has a sheet diameter of 8-15 μm, 1-6 layers, and a thickness of 0.5-2 nm.

[0066] Example 6

[0067] A preparation method of a Ni-CeO 2 -CNT@rGO conductive agent, different from that of Example 1 in that in step (1), the hydrothermal temperature is 130 °C and the hydrothermal time is 24 h.

[0068] The Ni-CeO 2 -CNT@rGO conductive agent prepared in this example has a CNT diameter of 30-40 nm, a tube length of 1.5-2 μm, and a specific surface area of 100-110 m 2 / g; the rGO with a three-dimensional network structure has a sheet diameter of 8-15 μm, 1-6 layers, and a thickness of 0.5-2 nm.

[0069] Example 7

[0070] A preparation method of a Ni-CeO 2 -CNT@rGO conductive agent, different from that of Example 1 in that in step (1), the hydrothermal temperature is 170 °C and the hydrothermal time is 24 h.

[0071] The Ni-CeO 2- In the -CNT@rGO conductive agent, the diameter of CNT is 30 - 40 nm, the tube length is 1.5 - 2 μm, and the specific surface area is 100 - 110 m 2 / g; the sheet diameter of rGO with a three-dimensional network structure is 8 - 15 μm, the number of layers is 1 - 6 layers, and the thickness is 0.5 - 2 nm.

[0072] Example 8

[0073] A preparation method of Ni-CeO 2 -CNT@rGO conductive agent, different from Example 1 in that in step (2), the calcination temperature is 400 °C and the calcination time is 1 h.

[0074] The Ni-CeO 2 -CNT@rGO conductive agent prepared in this example has a CNT diameter of 35 - 45 nm, a tube length of 1.5 - 2 μm, and a specific surface area of 90 - 100 m 2 / g; the sheet diameter of rGO with a three-dimensional network structure is 8 - 15 μm, the number of layers is 1 - 6 layers, and the thickness is 0.5 - 2 nm.

[0075] Example 9

[0076] A preparation method of Ni-CeO 2 -CNT@rGO conductive agent, different from Example 1 in that in step (2), the calcination temperature is 900 °C and the calcination time is 1 h.

[0077] The Ni-CeO 2 -CNT@rGO conductive agent prepared in this example has a CNT diameter of 50 - 60 nm, a tube length of 1 - 1.5 μm, and a specific surface area of 80 - 90 m 2 / g; the sheet diameter of rGO with a three-dimensional network structure is 8 - 15 μm, the number of layers is 1 - 6 layers, and the thickness is 0.5 - 2 nm.

[0078] Comparative Example 1

[0079] A preparation method of Ni-CeO 2 -CNT@rGO conductive agent, different from Example 1 in that in step (1), 2,3,6,7,10,11-hexahydroxytriphenylene (HTTP) is used to replace H 3 BTC.

[0080] In the conductive agent prepared in this comparative example, CNT does not grow vertically on the surface of rGO; the sheet diameter of rGO with a three-dimensional network structure is 8 - 15 μm, the number of layers is 1 - 6 layers, and the thickness is 0.5 - 2 nm.

[0081] Comparative Example 2

[0082] A kind of C O -CeO 2 -CNT@rGO conductive agent preparation method, different from Example 1, in step (1), C O (NO 3 ) 2 ·6H 2 O is used to replace Ni(NO 3 ) 2 ·6H 2 O.

[0083] In the C O -CeO 2 -CNT@rGO conductive agent prepared in this comparative example, the tube diameter of CNT is 30 - 40 nm, the tube length is 1.5 - 2 μm, and the specific surface area is 100 - 110 m 2 / g; the sheet diameter of the three-dimensional network structure rGO is 8 - 15 μm, the number of layers is 1 - 6 layers, and the thickness is 0.5 - 2 nm.

[0084] Comparative Example 3

[0085] A kind of CeO 2 -CNT@rGO conductive agent preparation method, different from Example 1, in step (1), Ni(NO 3 ) 2 ·6H 2 O is not added.

[0086] In the conductive agent prepared in this comparative example, CNT does not grow vertically on the surface of rGO; the sheet diameter of the three-dimensional network structure rGO is 8 - 15 μm, the number of layers is 1 - 6 layers, and the thickness is 0.5 - 2 nm.

[0087] Positive electrode slurry preparation

[0088] The Ni-CeO 2 -CNT@rGO conductive agents prepared in the above Examples 1 - 9 and Comparative Examples 1 - 3 are respectively weighed with conductive carbon black, polyvinylidene fluoride (PVDF) and lithium iron phosphate positive electrode material according to a mass ratio of 1.0:1.5:2.5:95, and N-methylpyrrolidone (NMP) solvent is added to prepare a positive electrode slurry, and the solid content of the positive electrode slurry is 54 ± 3%.

[0089] Button cell preparation

[0090] The above positive electrode slurry is coated on the surface of aluminum foil, dried and roll-pressed to obtain a positive electrode plate. Using a lithium metal sheet as the negative electrode plate and a polypropylene film as the separator, dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1, and then lithium hexafluorophosphate (LiPF 6) to obtain an electrolyte with a concentration of 1 M of LiPF 6 Then a coin cell was fabricated, and the entire process was assembled in a super-clean glove box filled with an argon atmosphere.

[0091] Performance testing

[0092] 1. Cathode slurry viscosity test:

[0093] Pour the above-mentioned cathode slurry into a 150 ml beaker, keep the temperature of the cathode slurry at 25 ± 1 °C, then place the rotor into the prepared cathode slurry, set the parameters: 64# rotor, rotation speed 30 rpm, turn on the rotational viscometer to start the test, and obtain the viscosity of the cathode slurry.

[0094] 2. Cathode sheet resistivity test:

[0095] Coat the above-mentioned cathode slurry on a polyethylene terephthalate (PET) film with a thickness of 70 - 80 μm (excluding the PET film), and after cooling, use a manual slicing machine to cut out thin round pieces (pore diameter 15 mm) as test samples, and then use a four-probe tester (RTE-8 type) for testing. Each test sample is tested 5 times and the average value is taken.

[0096] 3. Variable-rate charge and discharge performance test:

[0097] Perform electrochemical performance tests on the above-mentioned coin cells respectively. The test conditions are as follows: at 25 °C, perform variable-rate charge and discharge tests, and the process is as follows:

[0098] (1) First, charge at a rate of 0.2C to 3.65V, then discharge at a rate of 0.2C to 2.5V. This is taken as one cycle, and a total of 5 cycles are performed;

[0099] (2) Charge at a rate of 1C to 3.65V, then discharge at a rate of 1C to 2.5V. This is taken as one cycle, and a total of 5 cycles are performed;

[0100] (3) Charge at a rate of 2C to 3.65V, then discharge at a rate of 2C to 2.5V. This is taken as one cycle, and a total of 5 cycles are performed;

[0101] (4) Charge at a rate of 5C to 3.65V, then discharge at a rate of 5C to 2.5V. This is taken as one cycle, and a total of 5 cycles are performed;

[0102] (5) Charge at a rate of 0.2C to 3.65V, then discharge at a rate of 0.2C to 2.5V. This is taken as one cycle, and a total of 5 cycles are performed to obtain the final variable-rate capacity retention rate.

[0103] 4. Cycle performance test

[0104] Charge it at a rate of 1C to 3.65V and then discharge it at a rate of 1C to 2.5V. Take this as one cycle. After 200 cycles, its 200-cycle retention rate is obtained.

[0105] The test results are shown in Table 1.

[0106] Table 1

[0107]

[0108]

[0109] According to Table 1, it can be seen that the Ni-CeO 2 -CNT@rGO conductive agent prepared by the present invention as a conductive agent for the positive electrode material of a lithium-ion battery can provide rich and easily accessible redox active sites, which helps to improve the diffusion rate of lithium ions in the lithium-ion battery, thereby improving the rate performance and cycling performance of the lithium-ion battery.

[0110] Compared with Example 1, in Comparative Example 1, 2,3,6,7,10,11-hexahydroxytriphenylene (HTTP) is used to replace H 3 BTC. The formed MOFs material has a partial pore structure that is insufficient to provide a growth environment for CNTs, and it will completely decompose under the calcination conditions, resulting in structural collapse and affecting the uniformity of CNT growth. Therefore, the viscosity of the positive electrode paste prepared from the conductive agent of this comparative example is too high, the resistivity of the positive electrode sheet is too high, and the variable-rate capacity retention rate and 200-cycle retention rate of the lithium-ion battery are too poor.

[0111] Compared with Example 1, in Comparative Example 2, C O (NO 3 ) 2 ·6H 2 O is used to replace Ni(NO 3 ) 2 ·6H 2 O, that is, cobalt doping is used to replace nickel doping to prepare the MOFs material. Nickel is the active site for the in-situ vertical growth of CNTs on the surface of rGO. When cobalt doping replaces nickel doping, cobalt can also be the active site for the in-situ vertical growth of CNTs on the surface of rGO, but its effect is far less than that of nickel. Therefore, the resistivity of the positive electrode sheet prepared from the conductive agent of this comparative example is too high, and the variable-rate capacity retention rate and 200-cycle retention rate of the lithium-ion battery are too poor.

[0112] Compared with Example 1, in Comparative Example 3, Ni(NO 3 ) 2 ·6H 2O, that is, there is no nickel doping in the MOF material. Since nickel is the active site for the in-situ vertical growth of CNTs on the rGO surface, CNTs cannot grow vertically on the rGO surface. Therefore, the viscosity of the positive electrode slurry prepared from the conductive agent of this comparative example is too high, the resistivity of the positive electrode sheet is too high, and the variable magnification capacity retention rate and the 200-cycle retention rate of the lithium-ion battery are too poor.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A Ni-CeO2-CNT@rGO conductive agent, characterized in that: The Ni-CeO2-CNT@rGO conductive agent consists of rGO with a three-dimensional network structure and CNTs vertically grown on the surface of rGO, and one end of the CNT away from the rGO is connected with Ni-CeO2 nanoparticles.

2. The Ni-CeO2-CNT@rGO conductive agent according to claim 1, characterized in that: The CNT has a diameter of 30-80 nm, a length of 1-2 μm, and a specific surface area of ​​60-150 m 2 / g.

3. The Ni-CeO2-CNT@rGO conductive agent according to claim 1, characterized in that: The rGO sheet diameter of the three-dimensional network structure is 8-15 μm, the number of layers is 1-6, and the thickness is 0.5-2 nm.

4. The method for preparing the Ni-CeO2-CNT@rGO conductive agent according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) dissolving a nickel source, a cerium source, and H3BTC in a first solvent, and mixing them to obtain a mixed solution; dissolving GO in a second solvent to obtain a GO dispersion; then mixing the mixed solution with the GO dispersion to obtain a synthetic solution, and then pouring the synthetic solution into a closed container for a hydrothermal reaction; after the reaction is completed, cooling to room temperature, centrifuging, washing, and drying the product, thereby preparing a precursor Ce-Ni-BTC@GO; (2) The carbon source and the precursor Ce-Ni-BTC@GO are placed in a tubular furnace for calcination to carry out a CVD deposition reaction. After the reaction is complete, the Ni-CeO2-CNT@rGO conductive agent is obtained.

5. The method for preparing the Ni-CeO2-CNT@rGO conductive agent according to claim 4, characterized in that: In the step (1), Ni 2+ :Ce 3+ : The molar ratio of H3BTC is (0.5-4):1:(0.1-3).

6. The method for preparing the Ni-CeO2-CNT@rGO conductive agent according to claim 4, characterized in that: The temperature of the hydrothermal reaction in step (1) is 140° C.-160° C., and the time of the hydrothermal reaction is 12-36 hours.

7. The method for preparing the Ni-CeO2-CNT@rGO conductive agent according to claim 4, characterized in that: In the step (2), the calcination temperature is 500-800° C., the calcination time is 0.5-2 h; and / or the calcination heating rate is 1-3° C. / min.

8. The method for preparing the Ni-CeO2-CNT@rGO conductive agent according to claim 4, characterized in that: In the step (2), the mass ratio of the carbon source to the precursor Ce-Ni-BTC@GO is (5-20):

1.

9. The method for preparing the Ni-CeO2-CNT@rGO conductive agent according to claim 4, characterized in that: In step (1), the nickel source includes any one or more of Ni(NO3)2·6H2O, anhydrous nickel chloride, and NiCl2·6H2O; and / or, In step (1), the cerium source includes any one or more combinations of Ce(NO3)3·6H2O and CeCl3·6H2O; and / or, The carbon source in step (2) includes any one or more combinations of DMF and melamine.

10. A positive electrode material, comprising the Ni-CeO2-CNT@rGO conductive agent as described in any one of claims 1 to 3 or the Ni-CeO2-CNT@rGO conductive agent obtained by the preparation method of the Ni-CeO2-CNT@rGO conductive agent as described in any one of claims 4 to 9.

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