A negative electrode, a preparation method thereof, and a battery

Abstract

The present application discloses a negative electrode, a preparation method and a battery. Titanium niobate and a conductive agent are mixed, and then a solvent containing a binder and a thickening agent is added and mixed to obtain an electrode paste. The electrode paste is printed on a current collector by 3D printing to obtain a negative electrode. The pore size of the negative electrode gradually decreases from the side far from the current collector towards the side close to the current collector. The present invention can shorten the diffusion distance of lithium ions in the material body. When lithium ions are rapidly embedded on the surface, ion and electron conduction are further enhanced, thereby improving the cycle stability and rate performance. Moreover, the electrode with a gradually changing pore structure maximally guarantees the energy density compared with the traditional porous electrode, and can maximize the performance of the battery.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a negative electrode, a preparation method and a battery. Background Art

[0002] In recent years, with the rapid development of new energy vehicles, electronic communication devices, etc., consumers' demand for lithium-ion batteries with characteristics of high capacity, long life, high stability and high power density has been increasing day by day. The electrode is the key factor determining the above performance of the battery. At present, the research on electrodes in lithium-ion batteries mainly focuses on electrode material modification, development of new electrode materials and electrode structure design, etc.

[0003] Many scholars have conducted relevant research on electrode material modification. For traditional cathode materials such as high-nickel ternary materials and lithium-rich manganese-based materials, modification is mostly carried out in the form of coating and doping. For the negative electrode, especially the modification of silicon-based materials, most of them are nano-sized or silicon-carbon composite to relieve the uneven stress distribution during the cycle, thereby improving their performance. In addition to traditional electrode materials, new electrode materials also need to be developed for high-energy-density lithium-ion batteries.

[0004] Considerable progress has been made in material modification and development of new materials. In addition to electrode materials, electrode structure design is also one of the means to improve battery performance. In a porous electrode, the performance of the electrode is closely related to the electronic conductive network composed of solid-phase conductive particles and the liquid-phase ion transport network formed by the electrolyte in the pores. The electronic conductive network and the ion transport network are affected by the structural parameters of the porous electrode, that is, the microscopic structural parameters of the electrode such as porosity, pore size and distribution, tortuosity and electrode component distribution are the key factors determining the performance of the electrode and the battery. A good pore structure and a suitable electrode component distribution can improve the performance of the electrode, but there are still some problems with high-energy-density electrodes. Especially for thick electrodes and high-capacity positive and negative electrodes, affected by the microscopic structural parameters, there are problems such as low ion transport efficiency and poor structural stability during the cycle. Therefore, optimizing the electrode structure design and developing new electrode preparation technologies have become important technical ways to improve the comprehensive performance of high-energy-density lithium-ion batteries. At the same time, on the basis of material modification and new material development, optimizing the electrode structure design and developing new electrode preparation technologies can further ensure the energy density while ensuring the battery performance. To further improve the power characteristics of the battery, the porous electrode technology was born, but for traditional porous electrodes, the pore size is not easy to adjust, and the porous structure loses energy density.

[0005] CN111668452B relates to a negative electrode with active material layers having different porosities and pore sizes and a lithium-ion secondary battery including the negative electrode. The first active material layer is the layer close to the current collector, and the second active material layer is the layer far from the current collector. The first active material layer uses high-porosity and high-pore-size elliptical porous particles as the active material, greatly increasing the electron conduction ability.

[0006] Professor Teng Li from the University of Maryland, USA, and the team of Academician Daining Fang from Peking University obtained highly stretchable electrodes through 3D printing technology and applied them to flexible lithium-ion batteries. The research result was published in the international renowned journal Energy Storage Materials under the title of "3D-printed highly deformable electrodes for flexible lithium ion batteries (LIBs)". As a kind of 3D printing process, direct ink writing (DIW), various printed electrode materials have been developed for the LIBs field. Serpentine ribbons can withstand greater stretching compared to straight ribbons. Designing a planar serpentine network can maintain large in-plane stretching in all directions. An efficient strategy combining direct ink writing technology with structured pattern design is used to prepare highly deformable stretchable lithium-ion battery electrodes.

[0007] Changyong Liu et al. from the team of Professor Zhangwei Chen of the Institute of Additive Manufacturing, Shenzhen University, designed and prepared an interdigitated three-dimensional lithium-ion battery composed of a high-voltage lithium cobalt oxide positive electrode and a natural graphite negative electrode based on 3D printing technology, exploring a new technical approach to solve the contradiction between energy density and power density. The research result "Design and 3D Printing of Interdigitated Electrode Structures for High-performance Full Lithium-ion Battery" was published in the excellent journal Chinese Journal of Mechanical Engineering: Additive Manufacturing Frontiers.

[0008] At present, the mainstream lithium-ion power batteries are lithium iron phosphate and ternary lithium batteries, whose negative electrodes use graphite materials. The conductivity of graphite decreases with the decrease of temperature, resulting in an increase in charge transfer resistance, an increase in electrode polarization, and difficulty in the insertion / extraction of lithium ions. More seriously, at low temperatures (-20 °C, current density 1C), since the potential of Li+ inserting into graphite is close to the potential of lithium plating (within 100 mV relative to Li+ / Li), when the overpotential exceeds this potential difference, Li+ tends to be reduced on the graphite surface rather than inserted into the graphite layer, and it is extremely easy to precipitate metallic lithium on the graphite surface to form lithium dendrites, piercing the diaphragm and causing short circuits, bringing great potential safety hazards. However, the low-temperature-resistant lithium titanate negative electrode material also has obvious performance shortcomings. Its tap density is low and the theoretical specific capacity is relatively low (175 mAh / g), resulting in too low battery energy density (70-90 Wh / kg), and the application scenarios are limited.

[0009] As a typical anode with high structural stability, high power type and high working potential (~1.6 V vs Li+ / Li), titanium niobate (TiNb2O7) exhibits long life, high power and low-temperature resistance characteristics. During the rapid charge and discharge process of the titanium niobate battery, it has a high lithium insertion / extraction platform, no formation of SEI film, and realizes a high-safety power operation environment with never lithium precipitation, highly ensuring safety. Moreover, due to having multiple redox electron pairs, it has a higher theoretical specific capacity (387.6 mAh / g), far higher than that of lithium titanate. In addition, TiNb2O7 has a high tap density (greater than 2.0 mg / cm 3 , much higher than 1.5 mg / cm of lithium titanate 3 and 1.0 mg / cm of graphite 3 ), and the volumetric energy density of the battery can be higher than that of lithium iron phosphate batteries.

[0010] In recent years, titanium niobate has attracted much attention as a high-capacity negative electrode material for lithium-ion batteries and is expected to replace lithium titanate. As a typical intercalation negative electrode material, its excellent electrochemical performance is mainly attributed to the unique structure of titanium niobate. The disordered arrangement of Nb atoms and Ti atoms respectively occupies the centers of NbO6 and TiO6 octahedrons. At the same time, the NbO6 octahedron and the TiO6 octahedron share edges and vertices and form an open tunnel-type interstitial space that can accommodate the transmission of lithium ions. Due to the structure of titanium niobate, the insertion and extraction of lithium ions are relatively easy, so it has excellent rate performance. Titanium niobate not only has the advantages of conventional lithium titanium materials in terms of cycle stability and long life, but also has multiple redox pairs of Ti 3+ / Ti 4+ , Nb 4+ / Nb 5+ and Nb 3+ / Nb 4+ ). Titanium niobate has a higher theoretical specific capacity (387.6 mA h g-1 , much higher than that of lithium titanate and even higher than that of graphite anodes), with a working potential similar to that of lithium titanate (1.6 V vs Li+ / Li), which can effectively prevent the generation of lithium dendrites and the reductive decomposition of the electrolyte. Compared with traditional batteries, the safety performance is greatly improved. However, there are also serious problems in the application of titanium niobate in batteries. The electronic and ionic conductivities of this material are relatively low. Therefore, there is an urgent need to invent a method that can simultaneously improve the electronic and ionic conductivities of the material.

[0011] The progress of high-tech applications represented by 3D printing has brought new possibilities for the miniaturization, customization, and refinement of lithium-ion batteries. Designing a unique electrode structure using 3D printing is of great significance for improving the capacity, energy, and power density of lithium-ion batteries. The existing 3D printing technology for lithium-ion battery electrodes is to print porous electrodes. Although this technology improves the rate performance of the battery, it undoubtedly sacrifices the energy density of the lithium-ion battery. Summary of the Invention

[0012] The present invention discloses a negative electrode, a preparation method, and a battery to solve the problems of low electronic and ionic conductivities of batteries made of existing titanium niobate materials and low energy density of 3D printed porous electrodes.

[0013] To achieve the above object, the embodiments of this specification adopt the following technical solutions:

[0014] In the first aspect, a negative electrode is provided. The material of the negative electrode includes titanium niobate, and the pore size of the negative electrode gradually decreases from the side far away from the current collector towards the side close to the current collector.

[0015] In the second aspect, a preparation method of a negative electrode is provided, including the following steps:

[0016] Mix titanium niobate and a conductive agent, and then add a solvent containing a binder and a thickener to mix to obtain an electrode slurry;

[0017] Print the electrode slurry on a current collector by 3D printing to obtain a negative electrode.

[0018] Optionally, the mass ratio of the titanium niobate, the conductive agent, the binder, and the thickener is 80-90:3-8:3-8:2-4.

[0019] Optionally, the volume ratio of the solvent to the total weight of the titanium niobate, the conductive agent, the binder, and the thickener is 2-5 mL:1 g.

[0020] Optionally, the conductive agent is one or a combination of acetylene black, carbon nanotubes, and reduced graphene oxide.

[0021] Optionally, the binder is one or a combination of two of a mixture of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR), and a mixture of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR).

[0022] Optionally, the thickener is one or a combination of multiple of sodium polyacrylate, polyacrylamide, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0023] Optionally, the solvent is one or a combination of multiple of N,N-dimethylformamide (DMF), tetrahydrofuran, N-methylpyrrolidone (NMP), ethanol, and distilled water.

[0024] Optionally, the parameters of the 3D printing are: the extrusion pressure is 0.05 - 0.2 MPa; and / or

[0025] the single-point time is 50 - 100 ms; and / or

[0026] the printing working speed is 120 - 200 mm / s; and / or

[0027] the printed structure is designed as a 3D pore size gradient structure; and / or

[0028] the number of printed layers is set to 5 - 8 layers; and / or

[0029] the single-layer interval time is 6 - 16 s.

[0030] Optionally, after the electrode paste is printed on the current collector by 3D printing and dried, the drying temperature is 160 - 200 °C, and the drying time is 8 - 12 hours.

[0031] In a third aspect, a battery is provided, which includes the negative electrode mentioned in the first aspect or the negative electrode prepared by the preparation method described in the second aspect.

[0032] The above at least one technical solution adopted in the embodiments of the present application can achieve the following beneficial effects:

[0033] For the negative electrode, preparation method and battery of the present invention, in the electrode with a pore size gradient, the electrolyte is completely infiltrated, the distance for lithium ions in the electrolyte to reach the material is shorter, and the lithium ion diffusion is faster, thereby greatly improving the rate performance. It can shorten the diffusion distance of lithium ions in the material body. When lithium ions are rapidly embedded on the surface, the ion and electron conduction are further enhanced, thereby improving the cycle stability and rate performance. Moreover, the electrode with a gradient pore structure can ensure the energy density to the greatest extent compared with the traditional porous electrode, and can maximize the battery performance. Description of the Drawings

[0034] The accompanying drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0035] Figure 1 It is a schematic structural diagram of the negative electrode obtained in Example 1 of the present invention;

[0036] Figure 2 It is a comparison chart of the rate performance of the negative electrode obtained in Examples 1-6 of the present invention and the negative electrode sheet obtained in Comparative Example 1;

[0037] Figure 3 It is a comparison chart of the cycle performance of the negative electrode obtained in Examples 1-6 of the present invention and the negative electrode sheet obtained in Comparative Example 1. Detailed Embodiments

[0038] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0039] According to an embodiment of the present application, a negative electrode is provided. The material of the negative electrode includes titanium niobate, and the pore size of the negative electrode gradually decreases from the side far from the current collector towards the side close to the current collector.

[0040] The main component of the negative electrode is the titanium niobate negative electrode material. The pore size of the negative electrode is gradually changing. The pore size is larger on the side far from the current collector. The structure of the negative electrode enables the electrolyte to be fully infiltrated, shortens the bulk diffusion distance of lithium ions, reduces the diffusion energy barrier of lithium ions, and maximizes the rate performance. The smaller pore size structure on the side close to the current collector ensures that the energy density is not excessively lost.

[0041] In the embodiments of this specification, more preferably, the pore size of the negative electrode uniformly changes from 4 um to 0.8 um. The pore sizes on the side of the electrode electrolyte interface and the side close to the current collector are 4 um and 0.8 um respectively. This pore size range facilitates the full infiltration of the electrolyte and shortens the lithium ion diffusion path. Furthermore, it improves the power density of the battery cell without excessively losing the energy density of the battery cell. Moreover, the porosity of the porous electrode with a gradually changing pore size is close to 10%. The rate of change of the pore size of the negative electrode is related to the electrode thickness. For example, for a negative electrode with an electrode thickness of 40 um (excluding the current collector), the rate of change of the pore size is 0.08 ((4 - 0.8) / 40 = 0.08).

[0042] According to an embodiment of the present application, a method for preparing a negative electrode is provided, comprising the following steps:

[0043] Mix titanium niobate and a conductive agent, and then add a solvent containing a binder and a thickener and mix to obtain an electrode paste;

[0044] Print the electrode paste on a current collector by 3D printing to obtain a negative electrode.

[0045] In the embodiments of this specification, there is no limitation on the mixing method in "mix titanium niobate and a conductive agent, and then add a solvent containing a binder and a thickener and mix", as long as it can make titanium niobate, the conductive agent, the binder, the thickener, and the solvent evenly mixed, and the present invention does not limit this. Preferably, after mixing titanium niobate and the conductive agent, dry grinding is used to make titanium niobate and the conductive agent uniform; after adding the solvent containing the binder and the thickener and mixing, high-speed ball milling and stirring are used to obtain a paste-like electrode paste for 3D printing.

[0046] In the embodiments of this specification, the ratios of the titanium niobate, the conductive agent, the binder, and the thickener are not limited, and the ratio of the volume of the solvent to the total weight of the titanium niobate, the conductive agent, the binder, and the thickener is not limited, as long as the effects of the negative electrode of the present invention can be achieved. Preferably, the mass ratio of the titanium niobate, the conductive agent, the binder, and the thickener is 80-90:3-8:3-8:2-4; the ratio of the volume of the solvent to the total weight of the titanium niobate, the conductive agent, the binder, and the thickener is 2-5 mL:1 g.

[0047] In the embodiments of this specification, the types of the conductive agent, the binder, the thickener, and the solvent are not limited, as long as the effects of the negative electrode of the present invention can be achieved. Preferably, the conductive agent is one or a combination of acetylene black, carbon nanotubes, and reduced graphene oxide; the binder is one or a combination of a mixture of polyvinylidene fluoride PVDF and styrene-butadiene rubber SBR, and a mixture of carboxymethyl cellulose CMC and styrene-butadiene rubber SBR; the thickener is one or a combination of sodium polyacrylate, polyacrylamide, hydroxyethyl cellulose, and hydroxypropyl cellulose; the solvent is one or a combination of N,N-dimethylformamide DMF, tetrahydrofuran, N-methylpyrrolidone NMP, ethanol, and distilled water.

[0048] In the embodiments of this specification, the specific steps of printing the electrode paste on the current collector by 3D printing may be as follows: Transfer the paste-like electrode paste as a raw material to the extrusion barrel of a 3D printer, set the printing path pattern and related printing process parameters through the 3D printer encoder. The electrode paste in the extrusion barrel is extruded and formed on the current collector under pressure, and after printing, it is dried to obtain a niobium titanate negative electrode with a gradually changing pore diameter. The negative electrode of the present invention is prepared by using a multi-layer 3D printing technology. By controlling the pore size of each layer, a negative electrode with a gradually changing pore diameter is prepared.

[0049] In the embodiments of this specification, the parameters of the 3D printing can be set according to the ability to obtain a niobium titanate negative electrode with a gradually changing pore diameter, and this specification does not limit it. Optionally, the parameters of the 3D printing are: the extrusion pressure is 0.05 - 0.2 MPa; and / or the single-point time is 50 - 100 ms; and / or the printing working speed is 120 - 200 mm / s; and / or the printing structure is designed as a 3D pore diameter gradually changing structure; and / or the number of printing layers is set to 5 - 8 layers; and / or the single-layer interval time is 10 s. Preferably, the parameters of the 3D printing are: the extrusion pressure is 0.05 - 0.2 MPa, the single-point time is 50 - 100 ms, the printing working speed is 120 - 200 mm / s, the printing structure is designed as a 3D pore diameter gradually changing structure, the number of printing layers is set to 5 - 8 layers, and the single-layer interval time is 6 - 16 s.

[0050] In the embodiments of this specification, after printing the electrode paste on the current collector by 3D printing, it is dried. This specification does not limit the drying method, drying temperature, and time. Preferably, the current collector is dried in a vacuum drying oven; the drying temperature is 160 - 200 degrees Celsius, and the drying time is 8 - 12 hours.

[0051] The method of the present invention can simultaneously have the advantages of a large surface area, a high surface loading density, a short lithium ion diffusion path, and a small ion transport resistance, etc., shortening the lithium ion diffusion path in the material body, thereby improving the cycle stability and rate performance. And the unique electrode with a gradually changing pore diameter structure compared with the traditional porous electrode maximally ensures the electrode energy density, maximally exerts the battery performance, and promotes the application of niobium titanate materials in the high-power field.

[0052] According to an embodiment of the present application, a battery is provided, and the battery includes the above negative electrode or the negative electrode prepared by the above-mentioned preparation method.

[0053] Since the electrode with a gradually changing pore diameter shortens the lithium ion diffusion distance, the lithium ion diffusion rate is increased, which is also beneficial at low temperatures and can promote the research and development of low-temperature new battery swapping niobium titanate battery materials.

[0054] The following will, in conjunction with the accompanying drawings, elaborate in detail on the technical solutions provided by each embodiment of the present application.

[0055] Embodiment 1:

[0056] A method for preparing a negative electrode is provided, including the following steps:

[0057] (1) Weigh 8.5 g of titanium niobate and 0.6 g of acetylene black respectively, and put them into a mortar for grinding until they reach a uniform particle size, and uniformly mix the two solid materials. Then add 40 ml of N,N-dimethylformamide (DMF) solvent containing 1.25 g of a mixture of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR) and 1 g of sodium polyacrylate per 100 ml. After high-speed ball milling and stirring for 40 minutes, a paste-like electrode slurry is obtained for 3D printing, where the mass ratio of PVDF to SBR is 1:1.

[0058] (2) Transfer the paste-like electrode slurry prepared in step (1) as raw material to the extrusion barrel of a 3D printer. Set the printing path pattern and related printing process parameters through the 3D printer encoder. The electrode slurry in the extrusion barrel is extruded and formed on the current collector under pressure. After printing, it is dried in a vacuum drying oven at a drying temperature of 160 °C for 12 hours to obtain a titanium niobate negative electrode with a gradually changing pore size. The structural schematic diagram of the titanium niobate negative electrode with a gradually changing pore size is as Figure 1 shown;

[0059] Among them, the parameters of the 3D printing are: the extrusion pressure is 0.15 MPa, the single-point time is 70 ms, the printing working speed is 150 mm / s, the printing path pattern is designed as a 3D pore size gradually changing structure, the number of printing layers is set to 7 layers, and the single-layer interval time is 10 s.

[0060] Embodiment 2:

[0061] A method for preparing a negative electrode is provided, including the following steps:

[0062] (1) Weigh 8.5 g of titanium niobate and 0.4 g of carbon nanotubes respectively, and put them into a mortar for grinding until they reach a uniform particle size, and uniformly mix the two solid materials. Then add 40 ml of tetrahydrofuran solvent containing 1.25 g of a mixture of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR) and 1 g of polyacrylamide per 100 ml. After high-speed ball milling and stirring for 40 minutes, a paste-like electrode slurry is obtained for 3D printing, where the mass ratio of PVDF to SBR is 1:1.

[0063] (2) Transfer the paste-like electrode slurry prepared in step (1) as a raw material into the extrusion barrel of a 3D printer. Set the printing path pattern and related printing process parameters through the 3D printer encoder. The electrode slurry in the extrusion barrel is extruded and formed on the current collector under pressure. After printing, it is dried in a vacuum drying oven at a drying temperature of 170 °C for 11 hours to obtain a niobium titanate negative electrode with a desired gradually changing pore size. The structural schematic diagram of the niobium titanate negative electrode with a gradually changing pore size is as shown in Figure 1 shown;

[0064] Among them, the parameters of the 3D printing are: the extrusion pressure is 0.05 MPa, the single-point time is 60 ms, the printing working speed is 180 mm / s, the printing path pattern is designed as a 3D pore size gradually changing structure, the number of printing layers is set to 5 layers, and the single-layer interval time is 10 s.

[0065] Example 3:

[0066] Provide a method for preparing a negative electrode, including the following steps:

[0067] (1) Weigh 9.0 g of niobium titanate and 0.6 g of reduced graphene oxide respectively, and put them into a mortar for grinding until they reach a uniform particle size, and evenly mix the two solid materials. Then add 40 ml of N-methylpyrrolidone NMP solvent containing 1.25 g of a mixture of polyvinylidene fluoride PVDF and styrene-butadiene rubber SBR and 1 g of hydroxyethyl cellulose per 100 ml, and stir by high-speed ball milling for 40 minutes to obtain a paste-like electrode slurry for 3D printing, where the mass ratio of PVDF to SBR is 1:1.

[0068] (2) Transfer the paste-like electrode slurry prepared in step (1) as a raw material into the extrusion barrel of a 3D printer. Set the printing path pattern and related printing process parameters through the 3D printer encoder. The electrode slurry in the extrusion barrel is extruded and formed on the current collector under pressure. After printing, it is dried in a vacuum drying oven at a drying temperature of 180 °C for 10 hours to obtain a niobium titanate negative electrode with a desired gradually changing pore size. The structural schematic diagram of the niobium titanate negative electrode with a gradually changing pore size is as shown in Figure 1 shown;

[0069] Among them, the parameters of the 3D printing are: the extrusion pressure is 0.12 MPa, the single-point time is 80 ms, the printing working speed is 140 mm / s, the printing path pattern is designed as a 3D pore size gradually changing structure, the number of printing layers is set to 6 layers, and the single-layer interval time is 10 s.

[0070] Example 4:

[0071] Provide a method for preparing a negative electrode, including the following steps:

[0072] (1) Weigh 8.5 g of titanium niobate, 0.3 g of acetylene black, and 0.3 g of reduced graphene oxide respectively, and put them all into a mortar for grinding until they reach a uniform particle size, and evenly mix the two solid materials. Then add 40 ml of an ethanol solvent containing 1.0 g of a mixture of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR) and 0.8 g of hydroxypropyl cellulose per 100 ml that has been prepared. After high-speed ball milling and stirring for 40 minutes, a paste-like electrode slurry is obtained for 3D printing, where the mass ratio of PVDF to SBR is 1:1.

[0073] (2) Transfer the paste-like electrode slurry prepared in step (1) as a raw material to the extrusion barrel of a 3D printer, and complete the setting of the printing path pattern and related printing process parameters through the 3D printer encoder. The electrode slurry in the extrusion barrel is extruded and formed on the current collector under pressure, and after printing, it is dried in a vacuum drying oven at a drying temperature of 190 °C for 9 hours to obtain a titanium niobate negative electrode with a gradually changing pore size. The structural schematic diagram of the titanium niobate negative electrode with a gradually changing pore size is as Figure 1 shown;

[0074] Among them, the parameters of the 3D printing are: the extrusion pressure is 0.2 MPa, the single-point time is 70 ms, the printing working speed is 190 mm / s, the printing path pattern is designed as a 3D pore size gradually changing structure, the number of printing layers is set to 7 layers, and the single-layer interval time is 10 s.

[0075] Example 5:

[0076] Provide a method for preparing a negative electrode, including the following steps:

[0077] (1) Weigh 8.5 g of titanium niobate, 0.4 g of carbon nanotubes, and 0.2 g of reduced graphene oxide respectively, and put them all into a mortar for grinding until they reach a uniform particle size, and evenly mix the two solid materials. Then add 40 ml of a distilled water solvent containing 1.25 g of a mixture of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), 0.5 g of sodium polyacrylate, and 0.5 g of polyacrylamide per 100 ml that has been prepared. After high-speed ball milling and stirring for 40 minutes, a paste-like electrode slurry is obtained for 3D printing, where the mass ratio of CMC to SBR is 1:1.

[0078] (2) Transfer the paste-like electrode slurry prepared in step (1) as a raw material to the extrusion barrel of a 3D printer. Set the printing path pattern and related printing process parameters through the 3D printer encoder. The electrode slurry in the extrusion barrel is extruded and formed on the current collector under pressure. After printing, it is dried in a vacuum drying oven at a drying temperature of 200 °C for 8 hours to obtain a niobium titanate negative electrode with a desired gradually changing pore size. The schematic structural diagram of the niobium titanate negative electrode with a gradually changing pore size is as shown in Figure 1 shown;

[0079] Among them, the parameters of the 3D printing are: the extrusion pressure is 0.1 MPa, the single-point time is 60 ms, the printing working speed is 130 mm / s, the printing path pattern is designed as a 3D pore size gradually changing structure, the number of printing layers is set to 8 layers, and the single-layer interval time is 10 s.

[0080] Example 6:

[0081] Provide a method for preparing a negative electrode, including the following steps:

[0082] (1) Weigh 8.5 g of niobium titanate, 0.3 g of acetylene black, and 0.3 g of carbon nanotubes respectively, and put them all into a mortar for grinding until they reach a uniform particle size, and evenly mix the two solid materials. Then add 40 ml of a mixed solvent of ethanol and distilled water containing 1 g of a mixture of carboxymethyl cellulose CMC and styrene-butadiene rubber SBR, 0.5 g of hydroxyethyl cellulose, and 0.5 g of hydroxypropyl cellulose per 100 ml. Stir for 40 minutes by high-speed ball milling to obtain a paste-like electrode slurry for 3D printing, where the mass ratio of CMC to SBR is 1:1.

[0083] (2) Transfer the paste-like electrode slurry prepared in step (1) as a raw material to the extrusion barrel of a 3D printer. Set the printing path pattern and related printing process parameters through the 3D printer encoder. The electrode slurry in the extrusion barrel is extruded and formed on the current collector under pressure. After printing, it is dried in a vacuum drying oven at a drying temperature of 160 °C for 12 hours to obtain a niobium titanate negative electrode with a desired gradually changing pore size. The schematic structural diagram of the niobium titanate negative electrode with a gradually changing pore size is as shown in Figure 1 shown;

[0084] Among them, the parameters of the 3D printing are: the extrusion pressure is 0.2 MPa, the single-point time is 100 ms, the printing working speed is 200 mm / s, the printing path pattern is designed as a 3D pore size gradually changing structure, the number of printing layers is set to 5 layers, and the single-layer interval time is 10 s.

[0085] Comparative Example 1:

[0086] Titanium niobate is dispersed in a solvent with a conductive agent and a binder in a mass ratio of 90:5:5 to obtain a negative electrode slurry. The negative electrode slurry is coated on a negative electrode current collector, dried, roll-pressed, and die-cut to obtain a negative electrode sheet. The sheet prepared by this traditional method is pore-free and not conducive to the rapid transmission of lithium ions.

[0087] Performance test:

[0088] 1. Rate performance test

[0089] The negative electrodes prepared in Examples 1-6 and the negative electrode sheet prepared in Comparative Example 1 are respectively assembled into coin cells to test the rate performance. As Figure 2 shown, the negative electrodes prepared in each example exhibit good rate performance and show relatively high capacities at 40C (corresponding to charge and discharge in 1.5 min), all higher than the comparative electrode, indicating that this method has good application prospects in the preparation of high-power electrodes.

[0090] 2. Cycle stability test

[0091] The negative electrodes prepared in Examples 1-6 and the negative electrode sheet prepared in Comparative Example 1 are respectively assembled into coin cells to test the cycle performance at 10C (corresponding to charge and discharge completed in 6 min). As Figure 3 shown, the negative electrodes prepared in each example exhibit good cycle stability at a high current density of 10C, all higher than the comparative electrode, indicating that the electrodes prepared by this method have practical application value.

[0092] The above are only the embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A negative electrode, characterized in that: The material of the negative electrode includes titanium niobate, and the pore size of the negative electrode gradually decreases linearly from the side away from the current collector to the side close to the current collector; Titanium niobate and a conductive agent are mixed, and a solvent containing a binder and a thickener is added and mixed to obtain an electrode slurry; Printing the electrode slurry on a current collector by 3D printing to obtain a negative electrode; The printed structure is designed as a 3D pore gradient structure; and / or The number of printing layers is set at 5-8 layers; and / or The single layer interval time is 6-16s.

2. A method for preparing a negative electrode as claimed in claim 1, characterized in that: The following steps are involved: Titanium niobate and a conductive agent are mixed, and a solvent containing a binder and a thickener is added and mixed to obtain an electrode slurry; Printing the electrode slurry on a current collector by 3D printing to obtain a negative electrode; The printed structure is designed as a 3D pore gradient structure; and / or The number of printing layers is set at 5-8 layers; and / or The single layer interval time is 6-16s.

3. The preparation method according to claim 2, characterized in that: The mass ratio of the titanium niobate, the conductive agent, the binder and the thickener is 80-90:3-8:3-8:2-4; and / or, The ratio of the volume of the solvent to the total weight of the titanium niobate, the conductive agent, the binder and the thickener is 2-5 mL: 1 g.

4. The preparation method according to claim 2, characterized in that: The conductive agent is a combination of one or more of acetylene black, carbon nanotubes, and reduced graphene oxide.

5. The preparation method according to claim 2, characterized in that: The binder is one of a mixture of polyvinylidene fluoride PVDF and styrene butadiene rubber SBR, a mixture of carboxymethyl cellulose CMC and styrene butadiene rubber SBR, or a combination of two thereof.

6. The preparation method according to claim 2, characterized in that: The thickener is a combination of one or more of sodium polyacrylate, polyacrylamide, hydroxyethyl cellulose and hydroxypropyl cellulose.

7. The preparation method according to claim 2, characterized in that: The solvent is a combination of one or more of N,N-dimethylformamide DMF, tetrahydrofuran, N-methylpyrrolidone NMP, ethanol and distilled water.

8. The preparation method according to claim 2, characterized in that: The parameters of the 3D printing are: extrusion pressure of 0.05-0.2MPa; and / or Single point time is 50-100ms; and / or The printing speed is 120-200mm / s.

9. The preparation method according to claim 2, characterized in that: The electrode slurry is printed on the current collector by 3D printing and then dried. The drying temperature is 160-200 degrees Celsius and the drying time is 8-12 hours.

10. A battery, characterized in that: The battery comprises the negative electrode described in claim 1 or the negative electrode prepared by the preparation method described in any one of claims 2-9.

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