Hydrogel with cross-linking-spiral network structure, electrode material and preparation method

Abstract

The invention discloses hydrogel with a crosslinking-spiral network structure, an electrode material and a preparation method, the hydrogel with the crosslinking-spiral network structure is mainly composed of a water-soluble polymer material (with a secondary structure) and water, and the water-soluble polymer material generates a spiral winding molecular chain; the spiral winding molecular chains are connected through covalent bonds to form a cross-linked network with fixed cross-linked nodes; the preparation method comprises the following steps: firstly preparing a hydrogel precursor solution containing a water-soluble polymer material, an auxiliary agent and water, then pouring the hydrogel precursor solution into a mold to initiate gelling and initiate the auxiliary agent to play a role at the same time, and finally soaking the hydrogel precursor solution in a structural salt solution; the electrode material is composed of a current collector and a coating located on the surface of the current collector. The coating comprises a water-soluble polymer material, a conductive agent and Si nanoparticles. The preparation method comprises the following steps: coating a mixture on a current collector, soaking in a structural salt solution, and drying to remove a solvent. The cycling stability of the silicon negative electrode material can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and in particular relates to a hydrogel with a "cross-linked-helical" network structure, an electrode material and a preparation method. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in electric vehicles and large-scale energy storage equipment battery systems, and the negative electrode material has an important influence on battery performance. However, the specific capacity of commercial graphite-based carbon-based negative electrode materials is only 372 mAh g -1 , which is difficult to meet the needs of high energy density applications such as electric vehicles. Therefore, researchers began to focus on non-carbon-based negative electrode materials, especially silicon nanomaterials with extremely high theoretical specific capacity values ​​(4200mAh g -1 ). However, silicon nanomaterials have the problem of rapid performance degradation during the charge and discharge cycle. This is because the volume of silicon nanomaterials will expand and contract during the charge and discharge process, causing the electrode material to pulverize or even break. In order to solve this problem, it is necessary to design a high-performance binder system to effectively fix and protect the silicon negative electrode material, thereby improving its overall electrochemical performance.

[0003] In the field of traditional lithium-ion batteries, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) are usually used as binders and solvents for positive and negative electrode materials of lithium-ion batteries. However, PVDF only uses van der Waals forces to bond and fix silicon nanomaterials on the current collector, which cannot effectively buffer the stress generated by the violent lithium expansion of silicon, resulting in serious damage to the electrode structure and a rapid decrease in the capacity of silicon negative electrode materials. In addition, NMP is an organic solvent, which is volatile and polluting, and may have an impact on the environment and human health. In contrast, water-soluble polymer materials are more environmentally friendly and will not cause environmental pollution and health problems. Therefore, water-soluble polymer materials have become a major trend in the development of binders and have broad application prospects.

[0004] Researchers have found that water-soluble polymer materials such as polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), guar gum (GG), chitosan (CS), sodium alginate (Alg), xanthan gum (XG), gelatin (Gel), etc., can form reversible hydrogen bonds with the silicon surface due to the functional groups they contain, thereby improving the cycle stability of silicon negative electrode materials to a certain extent.

[0005] The molecular chain of the water-soluble polymer material with a secondary structure has a reversible spiral secondary structure. When heated, the spiral structure of the molecular chain spontaneously develops to form a solution state; when cooled, the molecular chain re-contracts to form a spirally wound three-dimensional network gel. At the same time, the inventor believes that when the spiral winding of the molecular chain of the water-soluble polymer material with a secondary structure reaches a certain degree, it is expected to spontaneously form a winding network structure without fixed cross-linking nodes. The winding network structure can adapt to the volume expansion of silicon through the extension and deformation of the molecular chain spiral, and form a network structure with a stable mechanical structure through the entanglement of the molecular chain spiral winding. Due to the strong hydrogen bonding between its molecular chains, the material can form a tighter and more uniform bonding network with the active material and the current collector, thereby improving the mechanical strength and electrochemical stability of the electrode sheet. Moreover, these conformations can undergo reversible transformations under changes in temperature, pH or other factors, thereby adjusting the solubility, viscosity and bonding properties of the binder. In addition, its molecular chain has a certain flexibility and elasticity, which can buffer the volume expansion and contraction of the active material during the charge and discharge process, reduce the cracking and peeling of the electrode sheet, and extend the cycle life of the battery.

[0006] At present, the industry and academia have not fully understood the water-soluble polymer binder materials with spiral winding secondary structures. Although there are reports on the use of water-soluble polymer materials with secondary structures as binders for lithium-ion batteries, they mainly use the polar functional groups rich in molecular chains such as carboxyl, hydroxyl, and amino groups as hydrogen bonding sites to interact with the silicon surface oxide layer to improve the interaction between them and silicon, thereby improving the bonding force. It can only improve the volume expansion problem of silicon to a certain extent, and the electrochemical performance still needs to be further improved. Summary of the invention

[0007] The purpose of the present invention is to solve the problems existing in the prior art and to provide a hydrogel, an electrode material and a preparation method having a "cross-linked-helical" network structure.

[0008] In order to achieve the above object, the present invention adopts the following technical scheme:

[0009] A hydrogel with a "cross-linked-helical" network structure, mainly composed of a water-soluble polymer material with a secondary structure and water;

[0010] like Figure 5 As shown in (a), the "cross-linked-helical" network structure means that the water-soluble polymer material with a secondary structure produces a spirally wound molecular chain, and each spirally wound molecular chain is connected by a covalent bond to form a cross-linked network with fixed cross-linking nodes; Figure 5As shown in (b), the spirally wound molecular chains between two adjacent cross-linking nodes constitute a spring group unit, and each spring group unit is connected to one or more other spring group units through the cross-linking nodes at both ends to form a spring group system with a series-parallel hybrid structure; when the spring group system is subjected to external force, the stress generated will be distributed to a large number of parallel spring group units through the cross-linking nodes for dissipation, and the strain generated will be buffered by the tensile deformation of a large number of series spring group units. Therefore, the hydrogel with a "cross-linking-helical" network structure exhibits excellent tensile strength, Young's modulus, ductility and deformation ability, and resilience.

[0011] The present invention also provides a method for preparing a hydrogel having a "cross-linked-helical" network structure as described above, firstly preparing a hydrogel precursor solution containing a water-soluble polymer material having a secondary structure, an auxiliary agent and water, wherein the auxiliary agent is a catalyst and / or a cross-linking agent, wherein the catalyst is used to catalyze a self-cross-linking reaction of the water-soluble polymer material having a secondary structure, and the cross-linking agent is used to connect molecular chains of different water-soluble polymer materials having a secondary structure, then pouring the hydrogel precursor solution into a mold to initiate gelation and simultaneously initiate the auxiliary agent to function, thereby obtaining a hydrogel semi-finished product having a primary cross-linked network structure with fixed cross-linking nodes, and finally soaking the hydrogel semi-finished product in a structural salt solution to obtain a hydrogel, wherein the main component of the structural salt is a kosmotropic salt in the Hofmeister sequence; in this process, the Hofmeister salting-out effect prompts the water-soluble polymer material having a secondary structure to produce a large number of spirally wound molecular chains, thereby forming a "cross-linked-helical" network in which the molecular chains have a large number of spirally wound secondary structures.

[0012] The present invention also provides a method for preparing an electrode material, comprising coating a mixture of a water-soluble polymer material having a secondary structure, water, a conductive agent, and Si nanoparticles on a current collector, soaking the mixture in a structural salt solution, and drying to remove the solvent, thereby obtaining the electrode material, wherein the main component of the structural salt is a kosmotropic salt in the Hofmeister sequence.

[0013] As the preferred technical solution:

[0014] In the above-mentioned method for preparing an electrode material, the main component of the structural salt is one or more of ammonium sulfate, potassium phosphate, sodium carbonate and sodium acetate.

[0015] According to the above-mentioned method for preparing an electrode material, the concentration of the structural salt solution is 6 to 20 wt %; the immersion temperature is 1 to 60° C., and the immersion time is 0.1 to 48 hours; the concentration of the structural salt solution will affect the modification effect. Generally speaking, the higher the concentration of the structural salt solution, the greater the tensile strength of the water-soluble polymer material with a secondary structure; however, the present invention finds that for electrode materials, the higher the concentration of the structural salt solution, the greater the tensile strength of the binder material. Too high a salt solution solubility will cause the electrode material to be too rigid, so that it has no elasticity and cannot deform with the violent physical and chemical expansion of silicon, and cannot It plays a buffering role, but causes the cycle stability of silicon negative electrode materials to decrease instead of increase; the immersion temperature and time are also important factors affecting the modification effect of structural salts. Generally speaking, the higher the temperature and the longer the time, the more obvious the modification effect. This is because temperature and time will affect the reaction kinetics and equilibrium constants between structural salts and water-soluble polymer materials. However, the higher the temperature and time, the better. Too high temperature and too long time may cause degradation or deterioration of water-soluble polymer materials. Therefore, when determining the concentration of the structural salt solution, the immersion temperature and time, it should be optimized according to the characteristics and needs of the target material.

[0016] In the preparation method of an electrode material as described above, the mixture also contains 0.1 to 20 wt% of an auxiliary agent, which is a catalyst and / or a cross-linking agent. The catalyst is used to catalyze the self-cross-linking reaction of the water-soluble polymer material with a secondary structure, and the cross-linking agent is used to connect the molecular chains of different water-soluble polymer materials with a secondary structure; before immersion in the structural salt solution, the auxiliary agent is triggered to take effect.

[0017] When the mixture contains an auxiliary agent, the process of preparing the electrode material of the present invention is to use the hydrogel with a "cross-linked-helical" network structure as a binder for the silicon negative electrode of a lithium-ion battery. When the Si nanoparticles expand upon lithiation, the "cross-linked-helical" network can maintain the stability of the electrode structure and transfer the stress and strain to the spring group unit. The stress is dissipated by stretching the parallel spring group units and the deformation is buffered by extending the series spring group units. The hydrogel with a "cross-linked-helical" network structure can better match the characteristics of the severe lithiation expansion of the silicon material, thereby greatly improving the cycle stability of the silicon negative electrode.

[0018] The present invention controls the content of the auxiliary agent in the mixture to be 0.1-20wt%. The amount of the auxiliary agent added to the mixture is positively correlated with the crosslinking degree and mechanical properties of the mixture. However, when the amount of the auxiliary agent added exceeds a certain threshold, the mechanical properties of the mixture decrease instead. This may be because excessive addition of the auxiliary agent leads to excessive and uneven crosslinking bonds between the molecules of the mixture, making the mixture gel too dense and hardened, and losing a certain elasticity and toughness. Therefore, the amount of the auxiliary agent added to the mixture has a certain range.

[0019] In the preparation method of an electrode material as described above, the auxiliary agent is TG enzyme (catalyst, the enzymatic reaction can form covalent bonds between water-soluble polymer molecules with a secondary structure, thereby increasing the molecular weight and degree of polymerization of the water-soluble polymer with a secondary structure, and forming cross-linking nodes to connect molecular chains with a spiral structure to form a network framework), aldehyde cross-linking agent (such as glutaraldehyde, formaldehyde, etc.), epoxy compound cross-linking agent (such as epichlorohydrin, epichlorohydrin, polyethyleneimine, etc.), boric acid cross-linking agent or more.

[0020] The preparation method of an electrode material as described above is to place the electrode material at 5 to 80° C. for 0.1 to 10 hours before immersing it in a structural salt solution; before immersing it in the structural salt solution, when the mixture contains a cross-linking agent or a catalyst, the molecular chains of the water-soluble polymer material with a secondary structure are cross-linked to form a cross-linked network with fixed cross-linking nodes, and the temperature will also affect the degree of spiral winding of the molecular chains of the water-soluble polymer material with a secondary structure. When immersed in the structural salt solution, the Hofmeister salting-out effect prompts the molecular chains of the water-soluble polymer material with a secondary structure to produce a large amount of spiral winding, so that the binder material with a spirally wound secondary structure, which originally has general performance, can greatly improve the charge and discharge cycle stability of the silicon negative electrode material.

[0021] In the preparation method of an electrode material as described above, after drying and removing the solvent, the material is kept warm at 300-600°C for 5-600 minutes under the protection of nitrogen or inert gas, so that part of the molecular chains in the water-soluble polymer material with a secondary structure can be carbonized to form a rigid skeleton. If the molecular chain contains amino and carboxyl functional groups, part of the polar functional groups such as amino and carboxyl groups also undergo condensation reactions, thereby fixing and strengthening the network.

[0022] The preparation method of the electrode material as described above, the water-soluble polymer material with a secondary structure includes proteins and their derivatives and polysaccharides and their derivatives, such as gelatin, xanthan gum, guar gum, polyaspartic acid, etc.; the conductive agent is one or more of carbon black, graphite, graphene, carbon nanotubes, Ketjen black, metal fibers and carbon fibers; the average particle size of Si nanoparticles is 30 to 200 nm; in the mixture, the content of the water-soluble polymer material with a secondary structure is 1 to 20 wt%, the content of the conductive agent is 1 to 20 wt%, and the content of the Si nanoparticles is 50 to 90 wt%; the current collector is copper foil, aluminum foil, etc. Foil, stainless steel, nickel foam, carbon paper, carbon ash, molybdenum mesh or tungsten sheet; the amount of Si nanoparticles, water-soluble polymer materials with secondary structure and conductive agent mainly depends on the properties of Si nanoparticles (type, shape, particle size), the properties of water-soluble polymer materials with secondary structure (type, shape, particle size), the properties of conductive agent (type, shape, particle size) and the preparation process of slurry and other factors. Among them, the amount of water-soluble polymer materials with secondary structure should be as small as possible, but it should not affect the stability and integrity of the electrode; the amount of conductive agent should also be as small as possible, but it should not affect the conductive network and contact effect of the electrode.

[0023] In the above-mentioned method for preparing an electrode material, the mixture is only coated on a single surface of a current collector, the thickness of the current collector is 4 to 100 μm, and the coating thickness is 50 to 200 μm.

[0024] The present invention also provides an electrode material prepared by the method for preparing an electrode material as described in any one of the above items, which comprises a current collector and a coating located on the surface of the current collector, wherein the coating comprises a water-soluble polymer material having a secondary structure, a conductive agent, and Si nanoparticles;

[0025] The conductive agent is dispersed between Si nanoparticles to form a primary conductive network, providing an electron transmission channel on a macroscopic scale;

[0026] The molecular chains of the water-soluble polymer material with a secondary structure are spirally wound around each other to form a spiral winding network, and are wrapped around the surface of Si nanoparticles and conductive agents to form a secondary conductive network, providing electronic coupling at the microscopic scale;

[0027] The water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds, ensuring the mechanical stability and conductivity of the entire electrode.

[0028] As the preferred technical solution:

[0029] For the electrode material as described above, the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of more than 60% of the initial specific capacity after 300 cycles, and an first efficiency (ICEs) of more than 70%.

[0030] Beneficial effects:

[0031] (1) The present invention further promotes the molecular chain of the water-soluble polymer material with a secondary structure to produce spiral winding through the Hofmeister salting-out effect, adjusts the secondary structure of the molecular chain segment, and thus improves the buffering effect of the water-soluble polymer material with a secondary structure on the volume expansion of silicon (which is difficult to achieve by traditional molecular chain segment design, chemical modification of the water-soluble polymer material with a secondary structure, or cross-linking), so that the stability of the spirally wound material with ordinary performance to the silicon negative electrode material is greatly improved. Specifically, Si nanoparticles are dispersed in the water-soluble polymer material with a secondary structure. When the volume of the Si nanoparticles expands, the spirally wound molecular chain segments in the water-soluble polymer material with a secondary structure can expand with the volume expansion of silicon to adapt to the deformation of silicon, and dissipate the stress generated by the deformation of silicon, thereby improving the buffering effect of the water-soluble polymer material with a secondary structure on the Si nanoparticles, and further improving the cycle stability of the silicon negative electrode material.

[0032] (2) When the present invention uses a water-soluble polymer material with a secondary structure as a binder to prepare an electrode material, the Hofmeister salting-out effect causes the molecular chains of the water-soluble polymer material with a secondary structure to spirally wind, and a large amount of spiral winding forms a spiral winding network without fixed cross-linking nodes. The cross-linking reaction causes the molecular chains of the water-soluble polymer material with a secondary structure to cross-link, forming a cross-linked network with fixed cross-linking nodes. In the final electrode material, a large number of spirally wound molecular chains are connected in series and in parallel by cross-linking nodes to form a "cross-linked-spiral" network, which is similar to a spring group composed of a large number of spring groups connected in series and in parallel;

[0033] When the volume of Si nanoparticles or other particles dispersed therein expands, the water-soluble polymer material with a secondary structure maintains the stability of the network through the cross-linked network framework, and transmits its stress and strain to each spirally wound molecular chain in the framework. The stress generated can be evenly distributed and dissipated by the spirally wound molecular chains similar to a parallel spring group, and the strain generated can be stretched and deformed by a large number of spirally wound molecular chains to adapt to it similar to a series spring group. Since the framework of the network is formed by cross-linking and has stability, and the molecular chains are spirally wound and have resilience, the network has resilience. When the volume of silicon shrinks, the network also returns to its original shape, so that it is always in close contact with the Si nanoparticles to prevent them from falling off.

[0034] In addition, some water-soluble polymer materials with secondary structures, such as gelatin, are rich in polar functional groups such as amino and carboxyl groups. These polar functional groups can form hydrogen bonds with Si nanoparticles and with each other. Even if the "cross-linking-helix" network is damaged, it can be repaired to a certain extent through the reversibility of bonding. Through this special "cross-linking-helix" synergistic effect, the new three-dimensional network is expected to better match Si nanoparticles or other materials with volume changes.

[0035] (3) The present invention further optimizes the performance of the binder by keeping the binder at 300-600°C for 5-600 min (i.e., low-temperature heat treatment) under the protection of nitrogen or inert gas, so that part of the molecular chains in the water-soluble polymer material with a secondary structure are carbonized to form a rigid skeleton. If the water-soluble polymer material also has amino and carboxyl groups, part of its polar functional groups such as amino and carboxyl groups undergo condensation reactions, thereby fixing and strengthening the network. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The performance comparison diagrams of gelatin (Examples 22-23 and Comparative Examples 8-9) under different conditions, wherein (a) is a stress-strain curve diagram of gelatin gel under different preparation conditions; (b) is a maximum tensile stress diagram corresponding to the four gels in (a); (c) is a Young's modulus diagram corresponding to the four gels in (a); (d) is the 1st, 5th and 10th loading-unloading curves of the gel prepared under the conditions of Gel+TG+(NH4)2SO4 in (a);

[0037] Figure 2 The figure is a comparison chart of specific capacity-cycle number of silicon negative electrode half cells (Examples 6 to 8 and Comparative Examples 1 to 2) made of different gelatins;

[0038] Figure 3 It is a comparison chart of the specific capacity of silicon negative electrode half-cells (Examples 6 to 8 and Comparative Examples 1 to 2) made of different gelatins at different current densities;

[0039] Figure 4 It is a comparison chart of the specific capacity of silicon negative electrode half-cells corresponding to Examples 9 to 11 and Comparative Examples 3 to 4 at different cycle times;

[0040] Figure 5 Schematic diagram of hydrogel, wherein (a) is a schematic diagram of the "cross-linked-helical" network structure; and (b) is a schematic diagram of the spring group system. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0042] The sources of the related substances in the examples are as follows:

[0043] Gelatin: manufacturer is Sigma, cas is 9000-70-8;

[0044] Konjac gum: manufacturer is Aladdin, cas is 37220-17-0;

[0045] Xanthan gum: manufacturer is Aladdin, cas is 11138-66-2;

[0046] Guar gum: manufacturer is Aladdin, cas is 9000-30-0;

[0047] Polyaspartic acid-potassium salt: manufacturer is Sigma, cas is 26936-41-4;

[0048] Carbon black: manufacturer is Shanghai Xianding Biotechnology, cas is 1333-86-4;

[0049] Graphite: manufacturer is Sigma, cas is 7782-42-5;

[0050] Graphene: The manufacturer is CLOUD, the product code is MA-LO-TW-01022V;

[0051] Carbon nanotubes: manufacturer is Sigma, cas is 308068-56-6;

[0052] Ketchen Black: Manufacturer is Lion, cas is 1333-86-4;

[0053] Nickel-plated fiber: the manufacturer is Jusheng Carbon Fiber (Guangdong) Co., Ltd., the product number is T300;

[0054] Carbon fiber: manufacturer is Turing, cas is 768-74-5;

[0055] Copper foil: manufacturer is Desco Electronic Technology;

[0056] Aluminum foil: Manufacturer: McLean;

[0057] Stainless steel: manufacturer is Boyangte, model is SUS430;

[0058] Nickel foam: manufacturer is Desco Electronic Technology, model number is LC-PMN-009;

[0059] Foam copper: manufacturer is Fuhuili, model is FHL-21, thickness is 100μm;

[0060] Carbon paper: manufacturer is Lihua, brand number is N0S1005;

[0061] Carbon cloth: manufacturer is Shibang, brand is SHB-A501;

[0062] Molybdenum mesh: manufacturer is Aegis Metal, model is AGSW1121, mesh number is 100 mesh;

[0063] Tungsten foil: manufacturer is Fujiede, brand name is W1, mesh number is 200 mesh.

[0064] The silicon negative electrode half-cell assembled from the prepared electrode material in the present invention is a CR2025 button cell.

[0065] Method for detecting relevant performance of silicon negative electrode half-cell assembled from the prepared electrode material in the embodiment:

[0066] Constant current charge and discharge method: Use a battery charge and discharge tester to connect the half-cell to the two-electrode system, set the charge and discharge rate and cut-off potential, start the constant current charge and discharge cycle, and record the charge and discharge capacity and coulomb efficiency to analyze the lithium storage capacity and cycle stability of the electrode.

[0067] After 300 cycles, the specific capacity was tested by using the LANHE-CT3002A battery test system to perform constant current charge and discharge tests on the assembled half-cell. The specific test process is as follows: stand for 8 hours → 0.5Ag -1 Discharge test with current density of 0.5A -1 Carry out charging test with current density → Cycle 300 times in the mode of discharge first and then charge. After the cycle, open the data and check the cycle-specific capacity to get the specific capacity of the half battery after 300 cycles.

[0068] The test method of first effect (ICEs) after 300 cycles: the assembled half-cell is tested by constant current charge and discharge using the LANHE-CT3002A battery test system; the specific test process is as follows: stand for 8 hours → 0.5Ag -1 Discharge test with current density of 0.5A -1 → Cycle 300 times in the mode of discharge first and then charge. After the cycle is completed, open the data and check the cycle-efficiency. The first coulombic efficiency value is the first efficiency (ICEs) of the half-battery after 300 cycles.

[0069] Example 1

[0070] A method for preparing an electrode material, the specific steps are as follows:

[0071] (1) Prepare materials:

[0072] Water-soluble polymer materials with secondary structure: gelatin;

[0073] Conductive agent: carbon black;

[0074] Si nanoparticles: average particle size is 100nm;

[0075] Structural salt solution: the solute is ammonium sulfate, the solvent is water, and the concentration is 12wt%;

[0076] Current collector: copper foil with a thickness of 12 μm;

[0077] Deionized water;

[0078] (2) Preparation of mixture:

[0079] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent and Si nanoparticles are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent and the water-soluble polymer material with a secondary structure is 3:1:1;

[0080] (3) Coating:

[0081] The mixture prepared in step (2) is coated on one side of the current collector; after coating, it is placed at 5° C. for 8 hours; wherein the coating thickness is 100 μm;

[0082] (4) Soaking:

[0083] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 450° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0084] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 70.5% of the initial specific capacity after 300 cycles, and an initial efficiency (ICEs) of 89%.

[0085] Example 2

[0086] A method for preparing an electrode material, the specific steps are as follows:

[0087] (1) Prepare materials:

[0088] Water-soluble polymer material with secondary structure: konjac gum;

[0089] Conductive agent: graphite;

[0090] Si nanoparticles: average particle size 80nm;

[0091] Structural salt solution: the solute is ammonium sulfate, the solvent is water, and the concentration is 8wt%;

[0092] Current collector: nickel foam with a thickness of 100 μm;

[0093] Deionized water;

[0094] (2) Preparation of mixture:

[0095] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent and Si nanoparticles are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent and the water-soluble polymer material with a secondary structure is 3:1:1;

[0096] (3) Coating:

[0097] The mixture prepared in step (2) is coated on one side of the current collector; after coating, the mixture is placed at 5° C. for 10 hours; wherein the coating thickness is 80 μm;

[0098] (4) Soaking:

[0099] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 550° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0100] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 71% of the initial specific capacity after 300 cycles, and an initial efficiency (ICEs) of 87%.

[0101] Example 3

[0102] A method for preparing an electrode material, the specific steps are as follows:

[0103] (1) Prepare materials:

[0104] Water-soluble polymer materials with secondary structure: xanthan gum;

[0105] Conductive agent: graphene;

[0106] Si nanoparticles: average particle size 80nm;

[0107] Structural salt solution: the solute is sodium carbonate, the solvent is water, and the concentration is 10wt%;

[0108] Current collector: 12 μm thick copper foam;

[0109] Deionized water;

[0110] (2) Preparation of mixture:

[0111] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent and Si nanoparticles are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent and the water-soluble polymer material with a secondary structure is 3:1:1;

[0112] (3) Coating:

[0113] The mixture prepared in step (2) is coated on one side of the current collector; after coating, it is placed at 80° C. for 0.1 h; wherein the coating thickness is 100 μm;

[0114] (4) Soaking:

[0115] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 450° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0116] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 69% of the initial specific capacity after 300 cycles, and an initial efficiency (ICEs) of 85%.

[0117] Example 4

[0118] A method for preparing an electrode material, the specific steps are as follows:

[0119] (1) Prepare materials:

[0120] Water-soluble polymer materials with secondary structure: gelatin;

[0121] Conductive agent: carbon nanotubes;

[0122] Si nanoparticles: average particle size is 100nm;

[0123] Structural salt solution: the solute is potassium phosphate, the solvent is water, and the concentration is 12wt%;

[0124] Current collector: aluminum foil with a thickness of 20 μm;

[0125] Deionized water;

[0126] (2) Preparation of mixture:

[0127] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent and Si nanoparticles are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent and the water-soluble polymer material with a secondary structure is 3:1:1;

[0128] (3) Coating:

[0129] The mixture prepared in step (2) is coated on one side of the current collector; after coating, it is placed at 80° C. for 8 hours; wherein the coating thickness is 100 μm;

[0130] (4) Soaking:

[0131] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 550° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0132] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 68% of the initial specific capacity after 300 cycles, and an initial efficiency (ICEs) of 88%.

[0133] Example 5

[0134] A method for preparing an electrode material, the specific steps are as follows:

[0135] (1) Prepare materials:

[0136] Water-soluble polymer materials with secondary structure: guar gum;

[0137] Conductive agent: Ketjen black;

[0138] Si nanoparticles: average particle size 80nm;

[0139] Structural salt solution: the solute is a mixture of ammonium sulfate and potassium phosphate in a mass ratio of 1:1, the solvent is water, and the concentration is 10wt%;

[0140] Current collector: stainless steel with a thickness of 20 μm;

[0141] Deionized water;

[0142] (2) Preparation of mixture:

[0143] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent and Si nanoparticles are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent and the water-soluble polymer material with a secondary structure is 3:1:1;

[0144] (3) Coating:

[0145] The mixture prepared in step (2) is coated on one side of the current collector; after coating, the mixture is placed at 5° C. for 8 hours; wherein the coating thickness is 80 μm;

[0146] (4) Soaking:

[0147] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 450° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0148] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 62% of the initial specific capacity after 300 cycles, and an first efficiency (ICE) of 73%.

[0149] Example 6

[0150] A method for preparing an electrode material, the specific steps are as follows:

[0151] (1) Prepare materials:

[0152] Water-soluble polymer materials with secondary structure: gelatin;

[0153] Conductive agent: carbon black;

[0154] Si nanoparticles: average particle size is 100nm;

[0155] Structural salt solution: the solute is ammonium sulfate, the solvent is water, and the concentration is 12wt%;

[0156] Current collector: copper foil with a thickness of 12 μm;

[0157] Auxiliary agent: TG enzyme;

[0158] Deionized water;

[0159] (2) Preparation of mixture:

[0160] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent, Si nanoparticles and an additive are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent, the additive and the water-soluble polymer material with a secondary structure is 7:1:1:1;

[0161] (3) Coating:

[0162] The mixture prepared in step (2) is coated on one side of the current collector; after coating, it is placed at 5° C. for 8 hours; wherein the coating thickness is 100 μm;

[0163] (4) Soaking:

[0164] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 450° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0165] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are cross-linked to form a cross-linked network with fixed cross-linking nodes; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 74% of the initial specific capacity after 300 cycles, and an initial efficiency (ICEs) of 91%.

[0166] Example 7

[0167] A method for preparing an electrode material is basically the same as that of Example 6, except that in step (4), the process ends after drying and removing the solvent.

[0168] Example 8

[0169] A method for preparing an electrode material is basically the same as Example 7, except that: in step (1), no auxiliary agent is prepared; and in step (2), no auxiliary agent is added.

[0170] Comparative Example 1

[0171] A method for preparing an electrode material is basically the same as Example 7, except that: in step (1), a structured salt solution is not prepared; and there is no step (4).

[0172] Comparative Example 2

[0173] A method for preparing an electrode material is basically the same as that of comparative example 1, except that: in step (1), no auxiliary agent is prepared; and in step (2), no auxiliary agent is added.

[0174] The electrode materials of Examples 7-8 and Comparative Examples 1-2 were assembled into silicon negative electrode half-cells and tested in the same manner as in Example 6.

[0175] The present invention discusses the specific capacity of the silicon negative electrode half-cells corresponding to Examples 6 to 8 and Comparative Examples 1 to 2 at different cycle times, such as Figure 2 As shown, the specific capacity of the silicon negative electrode half-cell corresponding to Comparative Example 2 decreased to 23.4 mAh g after 100 cycles. -1 ;

[0176] Due to the improvement of the performance of water-soluble polymer materials with secondary structures by enzymatic crosslinking, the cycle stability of the silicon negative electrode half-cell corresponding to Example 1 was slightly improved, and the specific capacity decreased to 165 mAh g after 100 cycles. -1 ;

[0177] Due to the improvement of the performance of the water-soluble polymer material with a secondary structure by the Hofmeister salting-out effect, the cycle stability of the silicon negative electrode half-cell corresponding to Example 8 was slightly improved, and the specific capacity decreased to 624 mAh g after 100 cycles. -1 ;

[0178] Due to the improvement of the performance of the water-soluble polymer material with a secondary structure by the Hofmeister salting-out effect and the synergistic effect of cross-linking, the cycle stability of the silicon negative electrode half-cell corresponding to Example 7 was greatly improved, and the specific capacity was as high as 1760 mAh g after 100 cycles. -1 This indicates that the synergistic effect of the two is more significant than using the Hofmeister salting-out effect or cross-linking alone to improve the cycle stability of silicon negative electrode half-cells;

[0179] In addition, the specific capacity of the silicon negative electrode half-cell corresponding to Example 6 is as high as 2670 mAh g after 100 cycles. -1 , which is significantly higher than that of Example 7. This is because after the “cross-linked-helical” network is subjected to low-temperature heat treatment, the primary and secondary structures of the molecular chains are further solidified.

[0180] The present invention also discusses the specific capacity of the silicon negative electrode half-cells corresponding to Examples 6 to 8 and Comparative Examples 1 to 2 at different current densities and cycle times, such as Figure 3 As shown in Figure 2, when the silicon negative electrode half-cell corresponding to Comparative Example 2 is restored to a rate of 0.25C, its specific capacity reaches 94 mAh g -1 ;

[0181] Due to the improvement of the performance of water-soluble polymer materials with secondary structures by enzymatic crosslinking, the specific capacity of the silicon negative electrode half-cell corresponding to Comparative Example 1 reached 620 mAh g when the rate was restored to 0.25C. -1 ;

[0182] Due to the improvement of the performance of the water-soluble polymer material with a secondary structure due to the Hofmeister salting-out effect, the specific capacity of the silicon negative electrode half-cell corresponding to Example 8 reached 1509 mAh g when the rate was restored to 0.25C. -1 ;

[0183] Due to the improvement of the performance of the water-soluble polymer material with a secondary structure due to the Hofmeister salting-out effect and the synergistic effect of cross-linking, the specific capacity of the silicon negative electrode half-cell corresponding to Example 7 is as high as 1566 mAh g when the rate is restored to 0.25C.-1 , indicating that the “cross-linked-helical” network structure has a good buffering effect on the volume expansion of silicon;

[0184] In addition, the silicon anode half-cell corresponding to Example 6 exhibited the best rate performance, maintaining 1576 mAh g even at 1C rate. -1 The specific capacity is much higher than other silicon negative electrode half-cells. When it is restored to 0.25C rate, its specific capacity is as high as 2537mAh g -1 , which is significantly higher than that of Example 7. This is because after the “cross-linked-helical” network is subjected to low-temperature heat treatment, the primary and secondary structures of the molecular chains are further solidified.

[0185] Example 9

[0186] A method for preparing an electrode material, the specific steps are as follows:

[0187] (1) Prepare materials:

[0188] Water-soluble polymer material with secondary structure: polyaspartic acid-potassium salt;

[0189] Conductive agent: carbon fiber;

[0190] Si nanoparticles: average particle size 50nm;

[0191] Structural salt solution: the solute is sodium carbonate, the solvent is water, and the concentration is 10wt%;

[0192] Current collector: carbon paper with a thickness of 15 μm;

[0193] Additives: glutaraldehyde;

[0194] Deionized water;

[0195] (2) Preparation of mixture:

[0196] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent, Si nanoparticles and an additive are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent, the additive and the water-soluble polymer material with a secondary structure is 7:1:1:1;

[0197] (3) Coating:

[0198] The mixture prepared in step (2) is coated on one side of the current collector; after coating, it is placed at 80° C. for 10 hours; wherein the coating thickness is 100 μm;

[0199] (4) Soaking:

[0200] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 450° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0201] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are cross-linked to form a cross-linked network with fixed cross-linking nodes; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 70% of the initial specific capacity after 300 cycles, and an initial efficiency (ICEs) of 87%.

[0202] Example 10

[0203] A method for preparing an electrode material is basically the same as that of Example 9, except that in step (4), the process ends after drying and removing the solvent.

[0204] Embodiment 11

[0205] A method for preparing an electrode material is basically the same as Example 10, except that: in step (1), no auxiliary agent is prepared; and in step (2), no auxiliary agent is added.

[0206] Comparative Example 3

[0207] A method for preparing an electrode material is basically the same as Example 10, except that: in step (1), a structured salt solution is not prepared; and there is no step (4).

[0208] Comparative Example 4

[0209] A method for preparing an electrode material is basically the same as that of Comparative Example 3, except that: in step (1), no auxiliary agent is prepared; and in step (2), no auxiliary agent is added.

[0210] The electrode materials of Examples 10 to 11 and Comparative Examples 3 to 4 were assembled into silicon negative electrode half-cells and tested in the same manner as in Example 9.

[0211] The present invention discusses the specific capacity of the silicon negative electrode half-cells corresponding to Examples 9 to 11 and Comparative Examples 3 to 4 at different cycle times, such as Figure 4As shown, the specific capacity of the silicon negative electrode half-cell corresponding to Comparative Example 4 drops to 50 mAh g-1 after 100 cycles;

[0212] Due to the improvement of the performance of the water-soluble polymer material with a secondary structure by the glutaraldehyde crosslinking agent, the cycle stability of the silicon negative electrode half-cell corresponding to Comparative Example 3 was slightly improved, and the specific capacity decreased to 327 mAh g-1 after 100 cycles;

[0213] Due to the improvement of the performance of the water-soluble polymer material with a secondary structure by the Hofmeister salting-out effect, the cycle stability of the silicon negative electrode half-cell corresponding to Example 11 was slightly improved, and the specific capacity decreased to 893 mAh g-1 after 100 cycles;

[0214] Due to the improvement of the performance of the water-soluble polymer material with a secondary structure by the synergistic effect of the Hofmeister salting-out effect and the cross-linking, the cycle stability of the silicon negative electrode half-cell corresponding to Example 10 is greatly improved, and the specific capacity is as high as 1453 mAh g-1 after 100 cycles, which shows that compared with the Hofmeister salting-out effect or the cross-linking alone to improve the cycle stability of the silicon negative electrode half-cell, the synergistic effect of the two is more significant;

[0215] In addition, the specific capacity of the silicon negative electrode half-cell corresponding to Example 9 is as high as 1894 mAh g-1 after 100 cycles, which is significantly higher than that of Example 10. This is because the primary and secondary structures of the molecular chains of the "cross-linked-helical" network are further solidified after low-temperature heat treatment.

[0216] Example 12

[0217] A method for preparing an electrode material, the specific steps are as follows:

[0218] (1) Prepare materials:

[0219] Water-soluble polymer material with secondary structure: konjac gum;

[0220] Conductive agent: nickel-plated fiber;

[0221] Si nanoparticles: average particle size is 30nm;

[0222] Structural salt solution: the solute is a mixture of ammonium sulfate and sodium acetate in a mass ratio of 1:1, the solvent is water, and the concentration is 12wt%;

[0223] Current collector: carbon cloth with a thickness of 100 μm;

[0224] Auxiliary agent: epichlorohydrin;

[0225] Deionized water;

[0226] (2) Preparation of mixture:

[0227] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent, Si nanoparticles and an additive are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent, the additive and the water-soluble polymer material with a secondary structure is 7:1:1:1;

[0228] (3) Coating:

[0229] The mixture prepared in step (2) is coated on one side of the current collector; after coating, the mixture is placed at 80° C. for 10 hours; wherein the coating thickness is 80 μm;

[0230] (4) Soaking:

[0231] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 550° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0232] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are cross-linked to form a cross-linked network with fixed cross-linking nodes; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 65% of the initial specific capacity after 300 cycles, and an initial efficiency (ICEs) of 78%.

[0233] Embodiment 13

[0234] A method for preparing an electrode material is basically the same as that of Example 12, except that in step (4), the process ends after drying and removing the solvent.

[0235] Embodiment 14

[0236] A method for preparing an electrode material is basically the same as Example 13, except that: in step (1), no auxiliary agent is prepared; in step (2), no auxiliary agent is added; and the concentration of the structural salt solution in step (1) is changed to obtain a series of electrode materials.

[0237] Comparative Example 5

[0238] A method for preparing an electrode material is basically the same as Example 13, except that: in step (1), no structural salt solution is prepared; there is no step (4); and the amount of additive added in step (2) is changed to obtain a series of electrode materials.

[0239] The electrode materials of Example 13, Example 14 and Comparative Example 5 were assembled into silicon negative electrode half-cells and tested in the same manner as in Example 12.

[0240] The present invention discusses the specific capacity of the silicon negative electrode half-cells corresponding to Example 13, Example 14 and Comparative Example 5 at different cycle times, and the results show that:

[0241] The specific capacity of the silicon negative electrode half-cell corresponding to Example 13 after 100 cycles is 1368 mAh g -1 ;

[0242] The cycle stability of the silicon negative electrode half-cell corresponding to Example 14 increases first and then decreases with the increase of the concentration of the structured salt solution. The maximum specific capacity of the silicon negative electrode half-cell corresponding to Example 14 is 904 mAh g after 100 cycles. -1 ;

[0243] The cycle stability of the silicon negative electrode half-cell corresponding to Comparative Example 5 increases first and then decreases with the increase of the amount of additive added. The maximum specific capacity of the silicon negative electrode half-cell corresponding to Comparative Example 5 is 412 mAh g after 100 cycles. -1 ;

[0244] By comparison, it can be seen that this shows that compared with the Hofmeister salting-out effect or the cross-linking alone to improve the cycle stability of the silicon negative electrode half-cell, the synergistic effect of the two is more significant;

[0245] The synergistic effect of Hofmeister salting-out effect and cross-linking can achieve effects that cannot be achieved by using Hofmeister salting-out effect or cross-linking alone.

[0246] Embodiment 15

[0247] A method for preparing an electrode material, the specific steps are as follows:

[0248] (1) Prepare materials:

[0249] Water-soluble polymer materials with secondary structure: xanthan gum;

[0250] Conductive agent: graphene;

[0251] Si nanoparticles: average particle size is 200nm;

[0252] Structural salt solution: the solute is potassium phosphate, the solvent is water, and the concentration is 12wt%;

[0253] Current collector: Molybdenum mesh with a thickness of 20 μm;

[0254] Auxiliary agent: a mixture of TG enzyme and boric acid in a mass ratio of 1:1;

[0255] Deionized water;

[0256] (2) Preparation of mixture:

[0257] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent, Si nanoparticles and an additive are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent, the additive and the water-soluble polymer material with a secondary structure is 7:1:1:1;

[0258] (3) Coating:

[0259] The mixture prepared in step (2) is coated on one side of the current collector; after coating, the mixture is placed at 80° C. for 8 hours; wherein the coating thickness is 80 μm;

[0260] (4) Soaking:

[0261] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 350° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0262] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are cross-linked to form a cross-linked network with fixed cross-linking nodes; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled with the electrode material has a specific capacity of 66% of the initial specific capacity after 300 cycles, and an initial efficiency (ICEs) of 81%.

[0263] Example 16

[0264] A method for preparing an electrode material is basically the same as that of Example 15, except that in step (4), the process ends after drying and removing the solvent.

[0265] Embodiment 17

[0266] A method for preparing an electrode material is basically the same as Example 16, except that: in step (1), no auxiliary agent is prepared; in step (2), no auxiliary agent is added; and the concentration of the structural salt solution in step (1) is changed to obtain a series of electrode materials.

[0267] Comparative Example 6

[0268] A method for preparing an electrode material is basically the same as Example 16, except that: in step (1), no structural salt solution is prepared; there is no step (4); and the amount of additive added in step (2) is changed to obtain a series of electrode materials.

[0269] The electrode materials of Example 16, Example 17 and Comparative Example 6 were assembled into silicon negative electrode half-cells and tested in the same manner as in Example 15.

[0270] The present invention discusses the specific capacity of the silicon negative electrode half-cells corresponding to Example 16, Example 17 and Comparative Example 6 at different cycle times, and the results show that:

[0271] The specific capacity of the silicon negative electrode half-cell corresponding to Example 16 after 100 cycles is 1260 mAh g -1 ;

[0272] The cycle stability of the silicon negative electrode half-cell corresponding to Example 17 increases first and then decreases with the increase of the concentration of the structured salt solution. The maximum specific capacity of the silicon negative electrode half-cell corresponding to Example 17 is 846 mAh g after 100 cycles. -1 ;

[0273] The cycle stability of the silicon negative electrode half-cell corresponding to Comparative Example 6 first increases and then decreases with the increase of the amount of additive added. The maximum specific capacity of the silicon negative electrode half-cell corresponding to Comparative Example 6 is 371 mAh g after 100 cycles. -1 ;

[0274] By comparison, it can be seen that this shows that compared with the Hofmeister salting-out effect or the cross-linking alone to improve the cycle stability of the silicon negative electrode half-cell, the synergistic effect of the two is more significant;

[0275] The synergistic effect of Hofmeister salting-out effect and cross-linking can achieve effects that cannot be achieved by using Hofmeister salting-out effect or cross-linking alone.

[0276] Embodiment 18

[0277] A method for preparing an electrode material, the specific steps are as follows:

[0278] (1) Prepare materials:

[0279] Water-soluble polymer materials with secondary structure: guar gum;

[0280] Conductive agent: a mixture of carbon black and graphite in a mass ratio of 1:1;

[0281] Si nanoparticles: average particle size 50nm;

[0282] Structural salt solution: the solute is sodium acetate, the solvent is water, and the concentration is 10wt%;

[0283] Current collector: tungsten foil with a thickness of 20 μm;

[0284] Auxiliary agent: polyethyleneimine;

[0285] Deionized water;

[0286] (2) Preparation of mixture:

[0287] The water-soluble polymer material with a secondary structure, deionized water, a conductive agent, Si nanoparticles and an additive are uniformly mixed to form a mixture; in the mixture, the mass ratio of the Si nanoparticles, the conductive agent, the additive and the water-soluble polymer material with a secondary structure is 7:1:1:1;

[0288] (3) Coating:

[0289] The mixture prepared in step (2) is coated on one side of the current collector; after coating, the mixture is placed at 80° C. for 10 hours; wherein the coating thickness is 80 μm;

[0290] (4) Soaking:

[0291] The current collector coated with the mixture obtained in step (3) is immersed in a structural salt solution at 25° C. for 12 hours, dried to remove the solvent, and kept at 350° C. for 60 minutes under nitrogen or inert gas protection to obtain the electrode material.

[0292] The final electrode material consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; the conductive agent is dispersed between the Si nanoparticles to form a primary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are spirally entangled with each other to form a spirally entangled network, and are wrapped around the surfaces of the Si nanoparticles and the conductive agent to form a secondary conductive network; the molecular chains of the water-soluble polymer material with a secondary structure are cross-linked to form a cross-linked network with fixed cross-linking nodes; the water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds; the silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 70% of the initial specific capacity after 300 cycles, and an initial efficiency (ICEs) of 86%.

[0293] Embodiment 19

[0294] A method for preparing an electrode material is basically the same as Example 18, except that the solute in the structural salt solution used in this example includes not only sodium acetate but also calcium chloride, and the mass ratio of sodium acetate to calcium chloride is 1:1.

[0295] The silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 69% of the initial specific capacity after 300 cycles, and the first efficiency (ICEs) is 85%.

[0296] Embodiment 20

[0297] A method for preparing an electrode material is basically the same as that of Example 18, except that in step (4), the process ends after drying and removing the solvent.

[0298] The silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 64% of the initial specific capacity after 300 cycles, and the first efficiency (ICEs) is 83%.

[0299] By comparing Example 18 with Example 20, it can be seen that low-temperature heat treatment can carbonize part of the molecular chains in the binder material to form a rigid skeleton, thereby fixing and strengthening the network, while the negative electrode material that has not been subjected to low-temperature heat treatment is not sufficient to cope with the volume expansion problem of the silicon negative electrode during long-term half-cell cycling.

[0300] Embodiment 21

[0301] A method for preparing an electrode material is basically the same as Example 20, except that no auxiliary agent is prepared in step (1), and an equal mass of deionized water is used to replace the auxiliary agent in step (2).

[0302] The silicon negative electrode half-cell assembled by the electrode material has a specific capacity of 62.5% of the initial specific capacity after 300 cycles, and the first efficiency (ICEs) is 71%.

[0303] By comparing Example 20 with Example 21, it can be seen that the cycle performance of the electrode material without the addition of additives is poor. The reason is that the addition of additives can add a number of cross-linking nodes to the original 3D network structure of the binder material, which can greatly enhance the mechanical properties of the electrode material. Example 21 does not add additives, so the performance will be relatively reduced.

[0304] Comparative Example 7

[0305] A method for preparing an electrode material is basically the same as Example 21, except that: in step (1), no structural salt solution is prepared, and in step (4), an equal mass of deionized water is used to replace the structural salt solution.

[0306] The silicon negative electrode half-cell assembled from the electrode material has a specific capacity of 43% of the initial specific capacity after 300 cycles, and the first efficiency (ICEs) is 61%.

[0307] By comparing Comparative Example 7 with Example 21, it can be seen that the electrode material subjected to simple low-temperature heat treatment has only one carbonization process and does not form a strong 3D network structure, which is insufficient to alleviate the volume expansion in the silicon negative electrode, and thus exhibits poor cycle performance and first effect.

[0308] Gelatin is a macromolecular hydrophilic colloid and a product of partial hydrolysis of collagen. Collagen molecules are helices formed by three polypeptide chains entangled with each other. Through the process, the collagen molecule helix is ​​denatured and decomposed into an α-component of a single polypeptide chain (α-chain), a β-component composed of two α chains, a γ-component composed of three α chains, and molecular chain fragments in between and smaller than the α-component or larger than the γ-component. It can be seen that gelatin has a small molecular weight due to a series of physical and chemical process treatments, and the molecular chain presents a fragmented polydisperse system. (In existing literature reports, gelatin is used as a binder material for lithium-ion batteries, and the fragmentation of gelatin molecular chains cannot effectively inhibit the volume expansion of silicon, which is not ideal for improving the cycle stability of silicon negative electrodes.)

[0309] In order to systematically explore the effects of the enzymatic reaction of TG enzyme and the Hofmeister salting-out effect on the mechanical properties of gelatin hydrogel, the present invention also prepared untreated gelatin hydrogel (Comparative Example 9), TG enzyme cross-linked gelatin hydrogel (Comparative Example 8), kosmotropic salt solution soaked twisted gelatin hydrogel (Example 23), and cross-linked-helical gelatin hydrogel obtained after first cross-linking and then soaking in salt solution (Example 22), and the tensile and compressive properties of these hydrogels were tested using a universal testing machine (Instron Tester5982); the sample was prepared by a national standard dumbbell type 1 stretching mold of polytetrafluoroethylene, with a size of 35 mm×6 mm×2 mm and a stretching rate of 20 mm / min.

[0310] Embodiment 22

[0311] A method for preparing a hydrogel comprises the following specific steps: preparing a gelatin solution with a solubility of 10% and a TG enzyme solution with a solubility of 10% at the same time, heating and stirring at 60°C until the gelatin solution and the TG enzyme solution are uniformly dissolved, mixing the two and continuing to stir at 45°C for 1 hour, then pouring into a national standard dumbbell type 1 stretching mold made of polytetrafluoroethylene, placing in a 5°C refrigerator for 20 minutes to gel, taking out and placing in a 20wt% concentration ammonium sulfate solution to soak for 12 hours, and obtaining a hydrogel.

[0312] Embodiment 23

[0313] A method for preparing a hydrogel, the specific process is: prepare a gelatin solution with a solubility of 10%, heat and stir at 60°C until the gelatin solution is uniformly dissolved, then pour it into a national standard dumbbell type 1 stretching mold made of polytetrafluoroethylene, put it in a 5°C refrigerator for 20 minutes to gel, take it out and put it in a 20wt% concentration ammonium sulfate solution to soak for 12 hours to obtain the hydrogel.

[0314] Comparative Example 8

[0315] A method for preparing a hydrogel comprises the following specific steps: preparing a 10% gelatin solution and a 10% TG enzyme solution, heating and stirring at 60°C until the gelatin solution and the TG enzyme solution are uniformly dissolved, mixing the two and continuing to stir at 45°C for 1 hour, then pouring the mixture into a national standard dumbbell type 1 stretching mold made of polytetrafluoroethylene, placing the mixture in a 5°C refrigerator for 20 minutes to gel, and obtaining the hydrogel.

[0316] Comparative Example 9

[0317] A method for preparing a hydrogel comprises the following specific steps: preparing a gelatin solution with a solubility of 10%, heating and stirring at 60°C until the gelatin solution is uniformly dissolved, then pouring the solution into a national standard dumbbell type 1 stretching mold made of polytetrafluoroethylene, and placing the mold in a refrigerator at 5°C for 20 minutes to gel, thereby obtaining the hydrogel.

[0318] Analyze the data of Examples 22 to 23 and Comparative Examples 8 to 9. Figure 1 As shown in Figures (a) to (c), the gelatin hydrogel of Comparative Example 9 has no mechanical strength, while the tensile stress, tensile strain and Young's modulus of the gelatin hydrogel of Comparative Example 8 increase to 141 kPa, 217%, and 65.51 kPa, respectively. This is mainly attributed to the formation of covalent cross-links between gelatin molecules by the enzymatic reaction, which results in a number of cross-linking nodes in the originally disordered gelatin molecular coils, thereby enhancing the stability of the network structure. However, due to the fragmentation of the gelatin molecular chains, even if cross-linked, a relatively complete cross-linked network structure cannot be formed, and thus the tensile strength and Young's modulus are limited. In contrast, the tensile stress, tensile strain and Young's modulus of the gelatin hydrogel of Example 23 increase to 141 kPa, 217%, and 65.51 kPa, respectively. The tensile stress, tensile strain and Young's modulus of the gelatin hydrogel in Example 22 increased to 522 kPa, 414% and 126.65 kPa, respectively. These results indicate that the synergistic effect of enzymatic crosslinking and Hofmeister salting-out effect on the mechanical properties of gelatin hydrogel is significantly better than the effect of using either alone.

[0319] At the same time, in order to verify that the gelatin hydrogel under the synergistic effect of enzymatic crosslinking and Hofmeister salting-out effect has the best anti-fatigue and shape recovery properties, the gelatin hydrogel of Example 22 was subjected to a loading-unloading cycle test. When the tensile strain was set to 100%, after 10 loading-unloading cycle tests, as shown in FIG. Figure 1 As shown in the middle figure (d), after 10 cycles, the gelatin hydrogel did not undergo obvious plastic deformation or strength degradation and had good elasticity and shape recovery properties; this indicates that the application of Hofmeister structural salt with appropriate solubility can significantly improve the mechanical strength and flexibility of gelatin hydrogel.

[0320] In order to explain the principle of greatly improved mechanical properties of gelatin in the "cross-linked-helical" network, the multiple structures of the modified gelatin molecular chain are compared to a spring group model. In the traditional cross-linked network, the network is composed of fixed cross-linked nodes. In the spirally wound network, there are no fixed cross-linked nodes, and it is only composed of the winding of molecular chains. Therefore, it is easy to slip when subjected to force and deformation, and the external force cannot be evenly distributed to each molecular chain. However, in the "cross-linked-helical" network system, every two cross-linked nodes and the spirally wound molecular chains between them constitute a spring group unit, so the entire "cross-linked-helical" network can be regarded as a spring group system composed of a large number of series and parallel springs. When the network is deformed by force, the stress generated will be evenly transmitted to each "spring" through the cross-linked nodes. The generated strain is transmitted to each "spring" molecular chain through the cross-linking nodes, and the strain is buffered by the tensile deformation of the "spring" molecular chain. The higher the degree of cross-linking, the more cross-linking nodes there are in the "cross-linking-helical" network, and the more spring units can be divided. The higher the concentration of Hofmeister salt solution, the higher the degree and number of molecular chain spiral windings, which is equivalent to increasing the effective number of rings and the number of "springs" of each molecular chain. Therefore, under the optimized cross-linking degree and salt effect, the maximum tensile force and deformation of the entire spring group system will be greatly improved. This is mainly due to the increase in the number of stretchable springs in the network and the increase in the effective number of rings of each spring, which reduces the stiffness of the system and improves the deflection and ductility.

Claims

1. A hydrogel having a "cross-linked-helical" network structure, characterized in that: It is mainly composed of water-soluble polymer materials with secondary structures and water; The "cross-linked-helical" network structure means that the water-soluble polymer material with a secondary structure produces a spirally wound molecular chain, and each spirally wound molecular chain is connected by covalent bonds to form a cross-linked network with fixed cross-linking nodes.

2. A method for preparing a hydrogel having a "cross-linked-helical" network structure as claimed in claim 1, characterized in that: First, a hydrogel precursor solution containing a water-soluble polymer material with a secondary structure, an auxiliary agent and water is prepared, wherein the auxiliary agent is a catalyst and / or a cross-linking agent, the catalyst is used to catalyze the self-cross-linking reaction of the water-soluble polymer material with a secondary structure, and the cross-linking agent is used to connect the molecular chains of different water-soluble polymer materials with a secondary structure, then the hydrogel precursor solution is poured into a mold to initiate gelation and simultaneously initiate the auxiliary agent to function, thereby obtaining a hydrogel semi-finished product, and finally the hydrogel semi-finished product is immersed in a structural salt solution to obtain a hydrogel, wherein the main component of the structural salt is a kosmotropic salt in the Hofmeister sequence.

3. A method for preparing an electrode material, characterized in that: After coating a mixture of a water-soluble polymer material with a secondary structure, water, a conductive agent, and Si nanoparticles on a current collector, the current collector is immersed in a structural salt solution, and the solvent is removed by drying to obtain an electrode material, wherein the main component of the structural salt is a kosmotropic salt in the Hofmeister sequence.

4. The method for preparing an electrode material according to claim 3, characterized in that: The main components of the structural salt are one or more of ammonium sulfate, potassium phosphate, sodium carbonate and sodium acetate.

5. The method for preparing an electrode material according to claim 3, characterized in that: The mixture also contains 0.1 to 20 wt% of an auxiliary agent, which is a catalyst and / or a cross-linking agent. The catalyst is used to catalyze the self-cross-linking reaction of the water-soluble polymer material with a secondary structure, and the cross-linking agent is used to connect the molecular chains of different water-soluble polymer materials with a secondary structure. Before immersing in the structural salt solution, the auxiliary agent is triggered to play a role.

6. The method for preparing an electrode material according to any one of claims 3 to 5, characterized in that: Before soaking in the structural salt solution, place it at 5-80℃ for 0.1-10h.

7. The method for preparing an electrode material according to any one of claims 3 to 5, characterized in that: After drying and removing the solvent, the mixture is kept at 300-600°C for 5-600 minutes under the protection of nitrogen or inert gas.

8. The method for preparing an electrode material according to claim 3, characterized in that: The water-soluble polymer material with a secondary structure includes proteins and their derivatives and polysaccharides and their derivatives; the conductive agent is one or more of carbon black, graphite, graphene, carbon nanotubes, Ketjen black, metal fibers and carbon fibers; the average particle size of Si nanoparticles is 30 to 200 nm; in the mixture, the content of the water-soluble polymer material with a secondary structure is 1 to 20 wt%, the content of the conductive agent is 1 to 20 wt%, and the content of the Si nanoparticles is 50 to 90 wt%; the current collector is copper foil, aluminum foil, stainless steel, nickel foam, carbon paper, carbon ash, molybdenum mesh or tungsten sheet.

9. An electrode material prepared by the method for preparing an electrode material according to any one of claims 3 to 8, characterized in that: It consists of a current collector and a coating located on the surface of the current collector, wherein the coating includes a water-soluble polymer material with a secondary structure, a conductive agent, and Si nanoparticles; The conductive agent is dispersed between Si nanoparticles to form a primary conductive network; The molecular chains of the water-soluble polymer material with a secondary structure are spirally wound around each other to form a spirally wound network, and are wrapped around the surface of Si nanoparticles and conductive agents to form a secondary conductive network. The water-soluble polymer material with a secondary structure is connected to the current collector through physical contact or chemical bonds.

10. The electrode material according to claim 9, characterized in that After 300 cycles, the specific capacity of the silicon negative electrode half-cell assembled from the electrode material is more than 60% of the initial specific capacity, and the first efficiency is more than 70%.

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