CN117810459B

CN117810459B - Stainless steel positive electrode current collector, preparation method thereof, positive plate and sodium ion battery

Info

Publication number: CN117810459B
Application number: CN202410232667.8A
Authority: CN
Inventors: 蔡明军
Original assignee: Zhejiang Huangneng New Energy Technology Co ltd
Current assignee: Zhejiang Huangneng New Energy Technology Co ltd
Priority date: 2024-03-01
Filing date: 2024-03-01
Publication date: 2024-07-05
Anticipated expiration: 2044-03-01
Also published as: CN117810459A

Abstract

The invention belongs to the technical field of positive current collectors, and provides a stainless steel positive current collector, a preparation method thereof, a positive plate and a sodium ion battery, comprising the following steps: mixing sodium alginate with nano cellulose solution; mixing graphene oxide dispersion liquid, polyvinyl alcohol solution, catalyst and cross-linking agent; mixing the first precursor solution and the second precursor solution, and then performing gel drying to obtain composite aerogel powder; mixing the composite aerogel powder, the binder and the solvent to obtain conductive slurry, and coating the conductive slurry on the surface of the conductive nickel coating. The invention also provides a stainless steel positive electrode current collector and a sodium ion battery comprising the same, and the stainless steel positive electrode current collector comprises a stainless steel base material, a conductive nickel coating and an aerogel guide layer which are sequentially laminated. The sodium ion battery in the prior art has lower cycle life, and the aerogel guide layer with the double interpenetrating porous network structure is arranged, so that sodium ions in the electrolyte are guided to be uniformly deposited on the surface of the conductive nickel coating, and the cycle life of the sodium ion battery is greatly prolonged.

Description

Stainless steel positive electrode current collector, preparation method thereof, positive plate and sodium ion battery

Technical Field

The invention belongs to the technical field of positive electrode current collectors, and relates to a stainless steel positive electrode current collector, a preparation method thereof, a positive electrode plate and a sodium ion battery.

Background

With the rapid development of human society, renewable clean energy sources including wind energy, solar energy and nuclear energy are becoming the main energy sources of power systems, and the demand for energy storage devices is increasing to obtain stable power supply. The development of lithium ion batteries in the past three decades has become the first energy storage device for hybrid electric vehicles, mobile electronic equipment and off-peak energy storage, supporting the high informatization and digitization of modern society. The continuous growth of new energy automobiles means that the demands of the future society for large-scale energy storage equipment are increasing, and the limitations of the lithium ion batteries restrict the application prospect of the lithium ion batteries in the future large-scale energy storage field. The lithium ion battery anode material applied to new energy automobiles at present is mainly a ternary system, and the main components of lithium, cobalt and other metal resources in the material have small reserves in nature, so that the lithium ion battery has certain potential safety hazard on one hand, and on the other hand, the lithium ion battery anode material has higher cost in practical application and is difficult to meet the market demand of future sustainable development. Aiming at solving the inherent defect problems of the lithium ion battery, research and exploration of a novel secondary battery system which is safer, more environment-friendly and more economical are imperative. The water-based sodium ion battery is considered to be one of the most potential low-cost energy storage technologies due to the advantages of low price, safety, environmental protection and the like.

However, in the process of assembling and applying the aqueous sodium ion battery, the positive electrode current collector of the battery is one of core components of the battery core, and plays a role of a mechanical carrier serving as an electrode active material and providing an electron migration channel. At present, the working environment of the positive current collector of the water-based sodium ion battery is bad, on one hand, the positive active material of the water-based sodium ion battery contains alkali with high pH value, and reacts into slurry containing high-concentration sodium hydroxide after meeting water, while the traditional positive active material is coated on the surface of an aluminum foil, and the aluminum foil can be dissolved when meeting sodium hydroxide; on the other hand, the positive current collector of the water-based sodium ion battery not only needs to cope with oxidation under higher working potential in the saline solution electrolyte, but also overcomes chemical and electrochemical corrosion, which not only limits the capacity exertion of a battery system, but also is unfavorable for long-term working of the battery and seriously affects the cycle life of the battery. In addition, if the positive current collector is improperly selected, the battery will be directly disabled.

Therefore, there is a need to design a new positive current collector suitable for aqueous sodium ion batteries to solve the above-mentioned technical problems.

Disclosure of Invention

Aiming at the defects existing in the prior art, the invention aims to provide a stainless steel positive electrode current collector, a preparation method thereof, a positive electrode plate and a sodium ion battery.

To achieve the purpose, the invention adopts the following technical scheme:

In a first aspect, the present invention provides a method for preparing a stainless steel positive electrode current collector, the method comprising:

Uniformly mixing sodium alginate and a nanocellulose solution, and centrifuging to remove foam to obtain a first precursor solution; dispersing graphene oxide in deionized water to form graphene oxide dispersion liquid, dropwise adding an ammonia water solution into the graphene oxide dispersion liquid to adjust the graphene oxide dispersion liquid to be alkaline, and mixing the graphene oxide dispersion liquid, a polyvinyl alcohol solution, a catalyst and a crosslinking agent to obtain a second precursor solution; mixing, heating and stirring a first precursor solution and a second precursor solution, and performing hydrothermal reduction on graphene oxide to obtain reduced graphene oxide, so as to finally form transparent composite sol;

(II) dripping the composite sol obtained in the step (I) into a gel induction solution to enable the composite sol droplets to be subjected to physical gelation so as to form granular composite hydrogel; then, soaking the composite hydrogel in absolute ethyl alcohol, and performing alcohol-water displacement to obtain composite alcohol gel; introducing supercritical carbon dioxide fluid into the composite alcohol gel, performing supercritical drying on the composite alcohol gel, and finally, crushing and grinding to obtain composite aerogel powder;

(III) mixing nickel salt, a reducing agent, a surfactant and deionized water to obtain a composite plating solution, and adding a pH regulator into the composite plating solution to regulate the composite plating solution to be acidic; then, immersing the stainless steel substrate in the composite plating solution, and depositing a conductive nickel plating layer with the thickness on the surface of the stainless steel substrate through an electrochemical deposition process; and finally, uniformly mixing the composite aerogel powder obtained in the step (II), a binder and a solvent to obtain conductive slurry, coating the conductive slurry on the surface of the conductive nickel coating, and forming an aerogel guide layer after vacuum drying to obtain the stainless steel anode current collector.

The stainless steel positive electrode current collector provided by the invention is formed by sequentially laminating the stainless steel base material, the conductive nickel coating and the aerogel guide layer, and in the charging process, the aerogel guide layer is provided with a double interpenetrating porous network structure, so that the diffusion, penetration and infiltration of electrolyte to the aerogel guide layer can be improved, sodium ions in the electrolyte are guided to be uniformly deposited on the surface of the conductive nickel coating, the growth of sodium dendrites is inhibited, the short-circuit risk of a sodium ion battery is effectively reduced, and the cycle life of the sodium ion battery is greatly prolonged.

The composite aerogel powder prepared by the supercritical drying method has a three-dimensional ordered interpenetrating porous network structure, the structure has a higher specific surface area and abundant micropore quantity, the infiltration, the flow and the diffusion of electrolyte in an aerogel guide layer are facilitated, the aerogel guide layer can provide abundant active sites, the full contact of the electrolyte and a conductive nickel coating is realized, and the electrochemical reaction efficiency is further improved; in addition, the three-dimensional ordered porous structure also imparts excellent mechanical strength and flexibility to the aerogel guide layer, which is beneficial to assembly applications of the stainless steel positive electrode current collector.

According to the invention, the nano cellulose is adopted in the first precursor solution as a multifunctional framework material for constructing a three-dimensional ordered porous structure, the nano cellulose has rich oxygen-containing functional groups (such as-OH and COOH), and also has higher mechanical strength and stronger toughness, and after the nano cellulose is compounded with graphene oxide, the stacking of the graphene oxide can be effectively reduced, and the mechanical strength of a graphene oxide carbon layer can be enhanced; meanwhile, the stability and the conductivity of the three-dimensional porous structure of the composite aerogel powder can be effectively maintained, so that the mechanical property and the electrochemical property of the aerogel guide layer are effectively improved.

In the invention, the polyvinyl alcohol is adopted as a basic framework material in the second precursor solution, and plays a role of connecting and supporting a framework in the composite sol, and in addition, the hydrophilicity of the polyvinyl alcohol enables the polyvinyl alcohol to absorb a large amount of water to dissolve sodium ions, so that the ionic conductivity of the aerogel guide layer can be greatly improved. In the hydrothermal reaction process, graphene oxide is reduced to obtain reduced graphene oxide, and oxygen-containing functional groups in the reduced graphene oxide interact with hydroxyl groups on a polyvinyl alcohol molecular chain and crosslink, so that a large number of uniformly distributed fold structures are formed on the surface of the finally obtained composite hydrogel, the specific surface area and the conductivity of the composite aerogel powder are greatly improved, and the electrochemical performance of the composite aerogel powder can be effectively improved.

Because sodium alginate and polyvinyl alcohol are both strong hydrophilic polymers, a large number of hydroxyl groups are contained in molecules, a large number of hydrogen bonds exist in the first precursor solution and the second precursor solution, and after the sodium alginate and the polyvinyl alcohol are mixed, stronger hydrogen bond action can be generated between the sodium alginate and the polyvinyl alcohol. Meanwhile, the nanocellulose in the first precursor solution is of a fiber-shaped structure with a higher length-diameter ratio, and the polyvinyl alcohol in the second precursor solution is subjected to polymerization reaction under the action of a catalyst and a cross-linking agent to obtain a high-molecular polymer with a longer molecular chain. In the mixing process of the first precursor solution and the second precursor solution, physical cross winding is generated between the fiber filaments of the nanocellulose and the polyvinyl alcohol polymer molecular chains, and the mechanical strength and flexibility of the aerogel guide layer can be greatly improved through the chemical bond action and physical winding of the first precursor solution and the second precursor solution. On the basis, the composite hydrogel with excellent mechanical properties is prepared by means of the sol/gel transition characteristic of sodium alginate in a metal ion solution.

The preparation method adopts two-step crosslinking reaction, so that the inside of the prepared composite hydrogel forms a double interpenetrating network structure, first, the first-step crosslinking reaction occurs in a second precursor solution, the covalent crosslinking reaction occurs between the polyvinyl alcohol and a crosslinking agent through the initiation of a catalyst, and a covalent crosslinking network is formed. And then, performing a second-step crosslinking reaction in the gel induction solution, immersing the composite sol in the gel induction solution, and after the liquid drops contact the gel induction solution, immediately performing an ion gel reaction on the surface molecules of the liquid drops, wherein metal ions in the gel induction solution and-COO-in sodium alginate molecules are chelated to form a tetradentate egg-box structure, so that an ion crosslinking network is formed. Finally, the composite hydrogel with a double interpenetrating network structure, which consists of a covalent cross-linked network and an ionic cross-linked network, is obtained.

According to the invention, the hydrothermal reaction is carried out in the mixing process of the first precursor solution and the second precursor solution, so that the graphene oxide is reduced to obtain the reduced graphene oxide, and on one hand, the reduced graphene oxide has excellent conductivity, and the electrochemical performance of the composite hydrogel can be further improved. On the other hand, the reduced graphene oxide also has high-content oxygen-containing functional groups, and can participate in the assembly of sodium alginate and polyvinyl alcohol in the composite hydrogel through the hydrogen bond effect in the composite hydrogel, and the lamellar structure of the reduced graphene oxide can also serve as a physical cross-linking agent to play an additional role in cross-linking in the composite hydrogel system, so that the double interpenetrating network structure of the composite hydrogel is further optimized.

How to effectively remove the ethanol in the pores of the composite aerogel and keep the original porous network structure of the composite aerogel intact, so that the dried composite aerogel does not generate phenomena such as bending, cracking, deformation and the like, and is a key process for preparing the composite aerogel. The conventional drying method still has a gas-liquid interface in the drying process, the existence of the gas-liquid interface is that the surface tension effect exists, and when the evaporation of ethanol in the pore structure of the composite alcohol gel is reduced, the gas-liquid interface is bent, so that capillary pressure is generated, the porous structure of the dried composite aerogel is collapsed, and the surface is cracked and deformed. Therefore, the invention adopts the supercritical carbon dioxide fluid to carry out drying treatment on the composite alcohol gel, the carbon dioxide has lower viscosity, larger diffusion coefficient and stronger dissolution capacity under the supercritical state, and no surface tension exists, compared with other organic solvents, the supercritical carbon dioxide can be rapidly diffused and permeated into the pore structure of the composite alcohol gel, so that the ethanol in the pore canal of the composite alcohol gel is exchanged with the supercritical carbon dioxide and dissolved in the supercritical carbon dioxide fluid, and the ethanol in the composite alcohol gel is completely extracted and separated by the supercritical carbon dioxide; after depressurization, the ethanol is carried out by the carbon dioxide fluid, and the carbon dioxide becomes gas, so that the purpose of thoroughly drying the composite alcohol gel is achieved.

The stainless steel brand used for the stainless steel substrate is not particularly limited and may be, for example, 201, 202, 301, 316, 304, 309s, 310s, 410, 420, 430, etc. Among them, 201, 202, 301, 304, 309s belong to austenitic stainless steel, contain no magnetism, can resist various medium corrosion, is suitable for being used as the base material of the positive current collector. 410. 420, 430 are martensitic stainless steel, have magnetic properties, and are not suitable for use as a base material for a positive electrode current collector. From the viewpoint of cost, the present invention preferably employs 304 stainless steel as the stainless steel substrate, and the thickness of the stainless steel substrate may be 0.001 to 0.1mm.

The nanocellulose solution used in the present invention is preferably a cellulose nanofiber solution.

In a preferred embodiment of the present invention, in the step (i), the mass fraction of the nanocellulose solution is 1.5-3wt%, for example 1.5wt%、1.6wt%、1.7wt%、1.8wt%、1.9wt%、2.0wt%、2.1wt%、2.2wt%、2.3wt%、2.4wt%、2.5wt%、2.6wt%、2.7wt%、2.8wt%、2.9wt% or 3.0wt%, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the mass ratio of sodium alginate to nanocellulose solution is 1 (70-80), for example, 1:70, 1:71, 1:72, 1:73, 1:74, 1:75, 1:6, 1:77, 1:78, 1:79, or 1:80, but not limited to the recited values, other non-recited values within the range of values are equally applicable.

The invention particularly limits the mass ratio of sodium alginate to nanocellulose solution to 1 (70-80), and in the mass ratio range, the tensile strength of the aerogel guide layer is gradually improved along with the increase of the dosage of nanocellulose, because hydroxyl groups in the nanocellulose molecular structure are associated with hydroxyl groups on a polyvinyl alcohol molecular chain, a strong bonding effect can be generated between the two molecules under the action of hydrogen bonds, and the stress generated in the stretching process is shared by both polyvinyl alcohol and nanocellulose, and the nanocellulose has higher mechanical strength, so that the finally prepared stainless steel positive electrode current collector has good mechanical properties. When the amount of nanocellulose exceeds the upper limit of the numerical range defined by the invention, the mechanical properties of the stainless steel positive current collector tend to decrease, which is related to the agglomeration of nanocellulose in the aerogel guiding layer.

In addition, as the amount of the nanocellulose increases, the elongation at break of the stainless steel positive electrode current collector gradually decreases, because as the amount of the nanocellulose increases, the interfacial compatibility of the aerogel guiding layer and the conductive nickel plating layer becomes poor, and the nanocellulose whisker can limit the movement of the polyvinyl alcohol molecular chain, so that the flexibility of the aerogel guiding layer decreases and the brittleness increases; in addition, when the amount of nanocellulose exceeds the upper limit of the range defined by the present invention, agglomeration phenomenon occurs in the aerogel guiding layer, and thus stress concentration and brittle fracture are easily caused.

In some alternative examples, the mixing time of the sodium alginate and the nanocellulose solution is 1-2h, for example, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the rotational speed of the centrifugal defoaming is 5000-6000rpm, which may be, for example, 5000rpm, 5100rpm, 5200rpm, 5300rpm, 5400rpm, 5500rpm, 5600rpm, 5700rpm, 5800rpm, 5900rpm, or 6000rpm, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the time for the centrifugal defoaming is 5-10min, for example, may be 5.0min, 5.5min, 6.0min, 6.5min, 7.0min, 7.5min, 8.0min, 8.5min, 9.0min, 9.5min or 10min, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In a preferred embodiment of the present invention, in the step (I), the concentration of the graphene oxide dispersion liquid is 1 to 5mg/mL, for example, 1.0mg/mL, 1.5mg/mL, 2.0mg/mL, 2.5mg/mL, 3.0mg/mL, 3.5mg/mL, 4.0mg/mL, 4.5mg/mL or 5.0mg/mL, but the concentration is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned numerical range are applicable.

In some alternative examples, the concentration of the aqueous ammonia solution is 5-6mol/L, for example, but not limited to, 5.0mol/L, 5.1mol/L, 5.2mol/L, 5.3mol/L, 5.4mol/L, 5.5mol/L, 5.6mol/L, 5.7mol/L, 5.8mol/L, 5.9mol/L, or 6.0mol/L, and other non-recited values within this range are equally applicable.

In some alternative examples, an aqueous ammonia solution is added dropwise to adjust the pH of the graphene oxide dispersion to 10-11, which may be, for example, 10, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, or 11, but is not limited to the recited values, and other non-recited values within this range are equally applicable.

In some alternative examples, the concentration of the polyvinyl alcohol solution is 2-3mol/L, for example, 2.0mol/L, 2.1mol/L, 2.2mol/L, 2.3mol/L, 2.4mol/L, 2.5mol/L, 2.6mol/L, 2.7mol/L, 2.8mol/L, 2.9mol/L, or 3.0mol/L, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the mass ratio of graphene oxide in the graphene oxide dispersion to polyvinyl alcohol in the polyvinyl alcohol solution is (0.05-0.15): 1, which may be, for example, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, or 0.15:1, but is not limited to the recited values, as other non-recited values within this range of values are equally applicable.

The invention is particularly limited in that the mass ratio of graphene oxide to polyvinyl alcohol is (0.05-0.15): 1, the tensile strength of the aerogel guiding layer is improved and reduced with the increase of the dosage of the graphene oxide, because the oxygen-containing functional group of the graphene oxide and the hydroxyl on the molecular chain of the polyvinyl alcohol form intermolecular acting force, the aerogel guiding layer shows good tensile property, the nano-scale graphene oxide sheets are uniformly dispersed in the polyvinyl alcohol, the specific surface area is large, the nano-scale graphene oxide sheets have good compatibility with the polyvinyl alcohol, and the mechanical property of the aerogel guiding layer is improved. When the amount of graphene oxide exceeds the upper limit of the range defined by the present invention, the tensile strength of the aerogel guiding layer tends to decrease, because the amount of graphene oxide is excessive, which results in aggregation in the second precursor solution, and further stress concentration occurs inside the prepared aerogel guiding layer. In addition, too high an amount of graphene oxide can also lead to a decrease in elongation at break of the aerogel guiding layer, because the graphene oxide lamellae can limit the movement of the polyvinyl alcohol molecular chain, resulting in a decrease in flexibility of the aerogel guiding layer, an increase in brittleness, and a tendency to brittle fracture.

In some alternative examples, the mass ratio of polyvinyl alcohol, catalyst and cross-linking agent in the polyvinyl alcohol solution is 1 (0.05-0.2): (0.1-0.4), such as 1:0.05:0.1、1:0.06:0.15、1:0.07:0.2、1:0.08:0.25、1:0.09:0.3、1:0.1:0.35、1:0.11:0.4、1:0.12:0.1、1:0.13:0.15、1:0.14:0.2、1:0.15:0.25、1:0.16:0.3、1:0.17:0.35、1:0.18:0.4、1:0.19:0.3 or 1:0.2:0.4, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the graphene oxide dispersion, polyvinyl alcohol solution, catalyst and cross-linking agent are mixed for a period of time ranging from 12 to 24 hours, such as 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours or 24 hours, although not limited to the recited values, and other non-recited values within this range are equally applicable.

In some alternative examples, the graphene oxide dispersion, the polyvinyl alcohol solution, the catalyst, and the crosslinking agent may be mixed at a temperature of 70-80 ℃, such as 70 ℃, 71 ℃, 72 ℃, 73 ℃, 74 ℃, 75 ℃, 76 ℃, 77 ℃, 78 ℃, 79 ℃, or 80 ℃, but are not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the catalyst is any one or a combination of at least two of hydrazine hydrate, triethylamine, and n-propylamine.

In some alternative examples, the cross-linking agent is any one or a combination of at least two of glyoxal, succinaldehyde, glutaraldehyde.

As a preferred embodiment of the present invention, in the step (i), the volume ratio of the first precursor solution and the second precursor solution is (0.5-0.6): 1, for example, may be 0.5:1, 0.51:1, 0.52:1, 0.53:1, 0.54:1, 0.55:1, 0.56:1, 0.57:1, 0.58:1, 0.59:1 or 0.6:1, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.

The composite aerogel prepared by the method has a three-dimensional porous network structure formed by the reduced graphene oxide sheets, and a large number of vertically-through nano holes are formed in the reduced graphene oxide sheets so as to be communicated with different sheets, so that the composite hydrogel prepared by the method has an interpenetrating network structure, the specific surface area of an aerogel guide layer is greatly increased, rich active sites are provided for electrochemical reaction, and sufficient channels are provided for electron transmission.

In order to obtain a clear three-dimensional porous structure with an interpenetrating network, the invention particularly limits the volume ratio of the first precursor solution to the second precursor solution to (0.5-0.6): 1 when the first precursor solution and the second precursor solution are mixed, and the ratio of the graphene oxide to the network structure inside the composite aerogel is clearer along with the increase of the dosage of the second precursor solution. When the amount of the second precursor solution exceeds the upper limit of the range defined in the present invention, collapse of the internal pore structure of the composite aerogel occurs because the amount of the second precursor solution is too high, and the excessive oxidized graphene is agglomerated inside the gel, resulting in destruction of the network structure inside the composite aerogel. Therefore, when the volume ratio of the first precursor solution to the second precursor solution is in the range of (0.5-0.6): 1, the network structure of the resulting composite hydrogel is more developed, and more active sites and electron transport channels can be provided.

In addition, as the addition amount of the second precursor solution is increased, the equilibrium swelling ratio of the composite hydrogel is increased, because the graphene oxide in the second precursor solution contains a large amount of oxygen-containing functional groups, the hydrophilicity of the composite hydrogel pellets can be increased to promote the permeation and rapid diffusion of water molecules; in addition, graphene oxide is used as a physical cross-linking agent, so that the cross-linking sites of the composite hydrogel can be increased, and more pore channel structures are formed inside the composite hydrogel pellets. However, as the addition amount of the second precursor solution is continuously increased, when the upper limit of the range defined by the invention is exceeded, the graphene oxide in the composite sol is excessive, so that the crosslinking sites in the composite hydrogel are increased, the crosslinking density of the composite hydrogel is greatly improved, the entanglement phenomenon of molecular chains in the composite hydrogel is obviously increased, the swelling capacity of the composite hydrogel is weakened, and the equilibrium swelling ratio of the composite hydrogel is reduced.

In addition, as the amount of the first precursor solution increases, the higher the concentration of the nanocellulose in the composite sol is, the more easily the composite hydrogel with a complete spherical structure is formed, because under the condition that the charge promotion effect is the same in unit volume, the higher the concentration of the nanocellulose is, the higher the number of hydroxyl groups is, the higher probability and the faster the hydrogen bond framework is formed, the hydrogen bond framework can be regarded as the 'reinforcing points' of connecting fibers and fibers in the porous network framework structure of the composite hydrogel, the greater the number of hydrogen bonds in unit volume is, the greater the number of reinforcing points is, the higher the strength of the composite hydrogel is, and thus the composite hydrogel with a porous structure with high strength is formed, and the lower the drying shrinkage rate of the composite hydrogel is in the subsequent supercritical drying process.

When the dosage of the first precursor solution is lower than the lower limit of the range defined by the invention, the content of nanocellulose in the composite sol is lower, the number of hydrogen bonds which can be formed in unit volume is smaller, the number of reinforcing points is too small, and a three-dimensional network framework cannot be built, so that the pore structure of the finally prepared composite hydrogel is not compact, the strength is relatively lower, and the shrinkage rate balance point is higher. When the amount of the first precursor solution exceeds the upper limit of the range defined by the present invention, the number of reinforcing points in the composite sol reaches a saturated state, and further increasing the amount of the first precursor solution not only increases the production cost, but also does not have an obvious effect of inhibiting the shrinkage of the composite hydrogel.

In some alternative examples, the mixing heating temperature of the first precursor solution and the second precursor solution is 120-180 ℃, for example, 120 ℃, 125 ℃, 130 ℃, 135 ℃, 140 ℃, 145 ℃, 150 ℃, 155 ℃, 160 ℃, 165 ℃, 170 ℃, 175 ℃, or 180 ℃, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

The graphene oxide has poor conductivity, and the reduced graphene oxide is obtained by performing hydrothermal reduction at 120-180 ℃ to remove part of oxygen-containing functional groups in the graphene oxide. The reduced graphene oxide has a large specific surface area, good conductivity and excellent capacitance. After the reduced graphene oxide is added, a large number of folds can be observed on the surface of the prepared aerogel guide layer, the fold structure provides a large number of active sites, and in addition, a large number of holes can be formed in the aerogel guide layer, so that the structure is favorable for infiltration between the aerogel guide layer and electrolyte and provides an ion transmission channel.

In some alternative examples, the mixing time of the first precursor solution and the second precursor solution is 12-24h, for example, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, or 24h, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.

As a preferable technical scheme of the invention, in the step (II), the gel inducing solution is a calcium chloride solution or a sodium sulfate solution.

The calcium chloride solution is preferably adopted as the gel inducing solution, because the calcium chloride solution contains divalent calcium ions, compared with monovalent sodium ions in the sodium sulfate solution, the calcium chloride solution has higher charge number in unit volume, has stronger action capability on the composite sol, is easier to flocculate the composite sol, has higher gel rate, and immediately diffuses into the liquid drops when the liquid drops of the composite sol with smaller volume are dripped into the calcium chloride solution, the charges act on the interface layers, repulsive potential energy among particles is reduced and mutually approaching, hydrogen bond connection is immediately formed among interface hydroxyl groups, the original spherical particle shape of the liquid drops of the composite sol is maintained, and a three-dimensional network framework is formed to gel.

Compared with a single sodium alginate sol/gel system, the composite hydrogel pellet prepared by the composite sol/gel system has an ellipsoidal structure, has higher specific surface area and smaller volume, and can form a compact porous structure inside. On one hand, the composite sol/gel system adopted by the invention has higher coagulation speed and lower viscosity, so that the composite sol can form ellipsoidal structure gel pellets with smaller volume after being dripped into the gel induction solution, and a large amount of hydroxyl groups contained in the polyvinyl alcohol firstly form intermolecular hydrogen bonding with carboxyl groups and hydroxyl groups in the sodium alginate to be well composited with the carboxyl groups and the hydroxyl groups along with the addition of the polyvinyl alcohol, and the increased free hydroxyl groups in the composite sol/gel system accelerate metal ions in the gel induction solution to enter the composite sol/gel system, so that the coagulation speed of composite sol liquid drops containing the sodium alginate and the polyvinyl alcohol in the gel induction solution is accelerated, and the composite sol liquid drops dripped into the gel induction solution can generate certain deformation in the stirring process, but the deformation of the composite sol liquid drops is not recovered, namely the composite hydrogel pellets in the coagulation solidification state are formed; in addition, the polyvinyl alcohol is an excellent dispersing agent, and can play a good dispersing role on the sodium alginate solution, so that the viscosity of the composite sol is lower than that of a single sodium alginate solution, and the composite sol drops are easier to deform and have larger deformation degree in the stirring process, so that the formed composite hydrogel pellets are of an ellipsoidal structure, and compared with the spherical structure, the composite hydrogel pellets of the ellipsoidal structure have higher specific surface area. On the other hand, the graphene oxide contains a large amount of oxygen-containing functional groups, and can form more hydrogen bonds with sodium alginate and polyvinyl alcohol, so that the crosslinking density of a double-network system in the composite sol is increased; meanwhile, the layered structure of the graphene oxide can be used as a physical cross-linking agent to participate in the assembly process of the hydrogel network, so that the formation of the double-network composite hydrogel porous structure is promoted. By combining the two factors, the regularity of the prepared composite hydrogel pellets is improved, the particle size is reduced, the internal pore diameter is reduced, the pores are compact and uniform, and the permeation, infiltration and diffusion of electrolyte are facilitated.

In some alternative examples, the mass fraction of the gel inducing solution is 2-3wt%, such as 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, or 3.0wt%, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

Because the nanocellulose, sodium alginate, polyvinyl alcohol and the like in the composite sol contain a large amount of hydroxyl groups, the hydrogel can be spontaneously formed by means of hydrogen bond action among the hydroxyl groups after the nanocellulose, the sodium alginate, the polyvinyl alcohol and the like are directly dispersed in water, but the strength of the hydrogel formed by the nanocellulose is relatively low, and in the process of alcohol-water replacement, the pore structure of the hydrogel can be damaged, so that shrinkage deformation is caused; in the case of the supercritical drying of the alcogel, there may be a large shrinkage, also because of the low strength of the alcogel. In order to maintain the mechanical strength of the hydrogel and further ensure the stability of the pore canal structure of the hydrogel in the alcohol-water displacement and supercritical drying processes, the invention adopts gel induction solution to carry out gel induction on the composite sol. Under the induction and promotion actions of inorganic salt, hydrogen bonds are formed between hydroxyl groups in the composite sol, and the composite hydrogel is spontaneously formed by virtue of the action of the hydrogen bonds. In the gel preparation process, the mass fraction of the gel inducing solution is an important factor influencing the gel forming effect, and the mass fraction of the gel inducing solution is particularly limited to 2-3wt%.

The higher the mass fraction of the gel-induced solution, the more remarkable the promotion effect on the gel forming process of the composite sol, and the lower the concentration of the gel-induced solution, the weaker the charge promotion effect and the lower the flocculation capability due to the fact that the metal cations distributed in the unit volume of the gel-induced solution are less, so that the composite hydrogel with complete spherical particles cannot be formed, and flocculent precipitate can only be formed in the salt solution; along with the gradual increase of the mass fraction of the gel-induced solution, the charge promoting effect is gradually enhanced, and substrate particles are easier to approach each other, so that more opportunities and faster rates exist between hydroxyl groups in composite sol drops dripped into the gel-induced solution to form hydrogen bond frameworks, the composite hydrogel gradually changes from lamellar hydrogel into complete spherical granular hydrogel, the mechanical strength of the formed composite hydrogel is also gradually enhanced, the original shape of the composite hydrogel pellets can be maintained without collapsing and deforming after the composite hydrogel pellets are taken out of the gel-induced solution, and the shrinkage rate of the composite hydrogel pellets can reach the shrinkage rate balance point in the subsequent supercritical drying process.

In some alternative examples, the drop volume of each drop of the composite sol is 0.1-0.3mL, for example, 0.1mL, 0.12mL, 0.14mL, 0.16mL, 0.18mL, 0.2mL, 0.22mL, 0.24mL, 0.26mL, 0.28mL or 0.3mL, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the composite hydrogel is immersed in the absolute ethanol for a period of time ranging from 1 to 5 hours, such as 1.0 hour, 1.5 hours, 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, or 5.0 hours, although not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the supercritical carbon dioxide fluid has a temperature of 50-60 ℃, such as 50 ℃, 51 ℃, 52 ℃, 53 ℃, 54 ℃, 55 ℃, 56 ℃, 57 ℃, 58 ℃, 59 ℃, or 60 ℃, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the supercritical carbon dioxide fluid has a pressure of 20-30MPa, such as 20MPa, 21MPa, 22MPa, 23MPa, 24MPa, 25MPa, 26MPa, 27MPa, 28MPa, 29MPa, or 30MPa, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

The whole mass transfer process of the supercritical carbon dioxide drying composite alcogel can be divided into the following four stages: (1) The supercritical carbon dioxide diffuses into the pore structure of the composite alcohol gel; (2) The ethanol has solvation effect with supercritical carbon dioxide in the composite alcohol gel and is dissolved in the supercritical carbon dioxide; (3) Ethanol dissolved in the supercritical carbon dioxide fluid diffuses into the supercritical carbon dioxide through the pore structure of the composite alcohol gel; (4) Ethanol and supercritical carbon dioxide are mass transferred in the fluid extraction zone.

The pressure of the supercritical carbon dioxide fluid is one of key factors influencing the dissolving capacity of the supercritical carbon dioxide fluid, the pressure of the supercritical carbon dioxide fluid is particularly limited to be 20-30MPa, when the pressure of the supercritical carbon dioxide fluid is lower than 20MPa, the carbon dioxide fluid does not reach a stable supercritical state, and ethanol is mainly volatilized from pores of the composite alcohol gel instead of being extracted and removed, so that the shrinkage rate of the composite alcohol gel is larger, and pores in the finally prepared composite aerogel are smaller or even completely free. Along with the pressure rise of the supercritical carbon dioxide fluid, the carbon dioxide fluid gradually tends to a stable supercritical state, the higher the density of the supercritical carbon dioxide fluid is, the solubility of ethanol in the supercritical carbon dioxide fluid is increased sharply, the influence of the pressure on the dissolving capacity of the carbon dioxide fluid on the ethanol is dominant in the pressure range of 20-30MPa, more ethanol can be dissolved in the carbon dioxide fluid in unit time, the extraction efficiency of the ethanol is obviously improved, and the shrinkage rate of the composite alcohol gel is gradually reduced. However, when the pressure exceeds 30MPa, the effect of the pressure on the increase in density of the supercritical carbon dioxide fluid is reduced, and accordingly, the effect of the increase in solubility of ethanol by the supercritical carbon dioxide fluid is also reduced.

In some alternative examples, the supercritical carbon dioxide fluid has a flow rate of 20-30L/h, such as 20L/h, 21L/h, 22L/h, 23L/h, 24L/h, 25L/h, 26L/h, 27L/h, 28L/h, 29L/h, or 30L/h, although not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In a preferred embodiment of the present invention, in the step (III), the concentration of the nickel salt in the composite plating solution is 10 to 20g/L, for example, 10g/L, 11g/L, 12g/L, 13g/L, 14g/L, 15g/L, 16g/L, 17g/L, 18g/L, 19g/L or 20g/L, but the present invention is not limited to the above-mentioned values, and other values not shown in the above-mentioned value range are equally applicable.

In some alternative examples, the concentration of the reducing agent in the composite plating solution is 0.1-0.5g/L, and may be, for example, 0.1g/L, 0.15g/L, 0.2g/L, 0.25g/L, 0.3g/L, 0.35g/L, 0.4g/L, 0.45g/L, or 0.5g/L, although not limited to the recited values, other non-recited values within the range of values are equally applicable.

In some alternative examples, the concentration of the surfactant in the composite plating solution is 20-30mg/L, for example, 20mg/L, 21mg/L, 22mg/L, 23mg/L, 24mg/L, 25mg/L, 26mg/L, 27mg/L, 28mg/L, 29mg/L or 30mg/L, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the nickel salt is any one or a combination of at least two of nickel sulfate, nickel chloride, nickel nitrate, nickel bromide.

In some alternative examples, the reducing agent is any one or a combination of at least two of sodium borohydride, citric acid, hydroxylamine hydrochloride, formaldehyde.

In some alternative examples, the surfactant is any one or a combination of at least two of sodium dodecyl sulfate, cetyltrimethylammonium bromide, and sodium dodecyl sulfonate.

In some alternative examples, the pH adjuster is added to adjust the pH of the composite plating solution to 4-5, which may be, for example, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5.0, but is not limited to the recited values, and other non-recited values within this range are equally applicable.

In some alternative examples, the pH adjuster is any one or a combination of at least two of boric acid, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid.

In a preferred embodiment of the present invention, in the step (III), the temperature of the composite plating solution is 60 to 70 ℃, for example, 60 ℃, 61 ℃, 62 ℃, 63 ℃, 64 ℃, 65 ℃, 66 ℃, 67 ℃, 68 ℃, 69 ℃, or 70 ℃, but the present invention is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned value range are applicable.

In some alternative examples, the current density of the electrochemical deposition process is 1-10A/dm ², which may be 1A/dm²、2A/dm²、3A/dm²、4A/dm²、5A/dm²、6A/dm²、7A/dm²、8A/dm²、9A/dm² or 10A/dm ², for example, but is not limited to the recited values, and other non-recited values within this range are equally applicable.

In some alternative examples, the electrochemical deposition process has a voltage of 5-15V, which may be, for example, 5V, 6V, 7V, 8V, 9V, 10V, 11V, 12V, 13V, 14V, or 15V, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the electrochemical deposition process may be performed for a period of time ranging from 5 to 10 minutes, such as, but not limited to, 5.0 minutes, 5.5 minutes, 6.0 minutes, 6.5 minutes, 7.0 minutes, 7.5 minutes, 8.0 minutes, 8.5 minutes, 9.0 minutes, 9.5 minutes, or 10.0 minutes, although other non-recited values within the range of values may be equally suitable.

In some alternative examples, the thickness of the conductive nickel plating layer is 40-50 μm, and may be, for example, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, or 50 μm, although not limited to the recited values, other non-recited values within the range of values are equally applicable.

In the step (iii), the mass ratio of the composite aerogel powder, the binder and the solvent is (96-98): (1-2): (1-2), and may be, for example, 96:2:2, 97:2:1, 97:1:2 or 98:1:1, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the binder is any one or a combination of at least two of polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, polyimide, sodium polyacrylate, chitosan, polyvinylidene fluoride, and polyvinylidene fluoride.

In some alternative examples, the solvent is any one or a combination of at least two of water, methanol, ethanol, N-methylpyrrolidone, N-dimethylformamide, dimethyl sulfoxide.

In some alternative examples, the vacuum drying temperature is 150-180 ℃, such as 150 ℃, 152 ℃, 154 ℃, 156 ℃, 158 ℃, 160 ℃, 162 ℃, 164 ℃, 166 ℃, 168 ℃, 170 ℃, 172 ℃, 174 ℃, 176 ℃, 178 ℃, or 180 ℃, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.

In some alternative examples, the vacuum drying time is 4-6 hours, such as 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, or 6.0 hours, but is not limited to the recited values, and other non-recited values within the range are equally applicable.

In some alternative examples, the aerogel guide layer has a thickness of 400-500 μm, such as 400 μm, 410 μm, 420 μm, 430 μm, 440 μm, 450 μm, 460 μm, 470 μm, 480 μm, 490 μm, or 500 μm, although not limited to the recited values, other non-recited values within the range of values are equally applicable.

The invention provides a preparation method of a stainless steel positive electrode current collector, which comprises the following steps:

(1) Mixing sodium alginate with 1.5-3wt% of nano cellulose solution for 1-2h, wherein the mass ratio of sodium alginate to nano cellulose solution is 1 (70-80), and centrifuging at 5000-6000rpm for defoaming for 5-10min to obtain a first precursor solution;

Dispersing graphene oxide in deionized water to form graphene oxide dispersion liquid with the concentration of 1-5mg/mL, and dropwise adding ammonia water solution with the concentration of 5-6mol/L into the graphene oxide dispersion liquid to adjust the pH value of the graphene oxide dispersion liquid to 10-11; mixing graphene oxide dispersion liquid, 2-3mol/L polyvinyl alcohol solution, a catalyst and a cross-linking agent for 12-24 hours at 70-80 ℃ to obtain a second precursor solution; wherein, the mass ratio of graphene oxide to polyvinyl alcohol is (0.05-0.15) 1, and the mass ratio of polyvinyl alcohol, catalyst and cross-linking agent is (1) (0.05-0.2) 0.1-0.4;

mixing the first precursor solution and the second precursor solution according to the volume ratio of (0.5-0.6): 1, stirring for 12-24 hours at 120-180 ℃, and carrying out hydrothermal reduction on graphene oxide to obtain reduced graphene oxide, so as to finally form transparent composite sol;

(2) Dripping the composite sol obtained in the step (1) into a gel induction solution with the weight percent of 2-3%, wherein the volume of the liquid drops of the composite sol is 0.1-0.3mL each time, so that the liquid drops of the composite sol are subjected to physical gelation to form granular composite hydrogel;

Soaking the composite hydrogel in absolute ethyl alcohol for 1-5h, and performing alcohol-water displacement to obtain composite alcohol gel; introducing supercritical carbon dioxide fluid with the temperature of 50-60 ℃ and the pressure of 20-30MPa into the composite alcohol gel at the flow of 20-30L/h, performing supercritical drying on the composite alcohol gel, and finally, crushing and grinding to obtain composite aerogel powder;

(3) Mixing nickel salt, a reducing agent, a surfactant and deionized water to obtain a composite plating solution, wherein the concentration of the nickel salt in the composite plating solution is 10-20g/L, the concentration of the reducing agent is 0.1-0.5g/L, and the concentration of the surfactant is 20-30mg/L;

Adding a pH regulator into the composite plating solution to regulate the pH value of the composite plating solution to 4-5; then, immersing the stainless steel substrate with the thickness of 0.05-0.1mm in a composite plating solution at the temperature of 60-70 ℃, depositing a conductive nickel plating layer with the thickness of 40-50 mu m on the surface of the stainless steel substrate through an electrochemical deposition process, setting the current density to be 1-10A/dm ², setting the voltage to be 5-15V, and setting the deposition time to be 5-10min;

Uniformly mixing the composite aerogel powder obtained in the step (2), a binder and a solvent according to the mass ratio of (96-98): 1-2 to obtain conductive slurry, coating the conductive slurry on the surface of a conductive nickel coating, and vacuum drying for 4-6 hours at 150-180 ℃ to form an aerogel guide layer with the thickness of 400-500 mu m, thereby obtaining the stainless steel positive electrode current collector.

In a second aspect, the invention provides a stainless steel positive electrode current collector prepared by the preparation method in the first aspect, wherein the stainless steel positive electrode current collector comprises a stainless steel base material, a conductive nickel coating and an aerogel guide layer which are sequentially laminated.

In some alternative examples, the stainless steel substrate has a thickness of 0.05-0.1mm, such as 0.05mm, 0.055mm, 0.06mm, 0.065mm, 0.07mm, 0.075mm, 0.08mm, 0.085mm, 0.09mm, 0.095mm, or 0.1mm, although not limited to the recited values, other non-recited values within this range of values are equally applicable.

In a third aspect, the present invention provides a sodium ion battery comprising a positive electrode sheet, a separator and a negative electrode sheet laminated in sequence; the positive plate of the sodium ion battery comprises the stainless steel positive electrode current collector of the second aspect and a positive electrode active material layer positioned on the surface of the stainless steel positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, a binder and a solvent.

Compared with the prior art, the invention has the beneficial effects that:

The invention adopts two-step crosslinking reaction to lead the interior of the prepared composite hydrogel to form a double interpenetrating network structure, firstly, the first-step crosslinking reaction is carried out in a second precursor solution, the ethylene functional group of the polyvinyl alcohol is initiated to be opened through a catalyst, then the covalent crosslinking reaction is carried out with the vinyl at the tail end of the crosslinking agent to realize chain growth, and a covalent crosslinking network is formed. And then, performing a second-step crosslinking reaction in the gel induction solution, immersing the composite sol in the gel induction solution, and after the liquid drops contact the gel induction solution, immediately performing an ion gel reaction on the surface molecules of the liquid drops, wherein metal ions in the gel induction solution and-COO-in sodium alginate molecules are chelated to form a tetradentate egg-box structure, so that an ion crosslinking network is formed. Finally, the composite hydrogel with a double interpenetrating network structure, which consists of a covalent cross-linked network and an ionic cross-linked network, is obtained.

Drawings

FIG. 1 is a flow chart of the process for preparing stainless steel positive electrode current collectors according to examples 1 to 5 and comparative examples 1 to 8 of the present invention;

FIG. 2 is a schematic structural view of stainless steel positive electrode current collectors prepared in examples 1 to 5 and comparative examples 1 to 8 according to the present invention;

wherein, 1-stainless steel base material; 2-conductive nickel plating; a 3-aerogel guiding layer;

FIG. 3 is a surface electron micrograph of an aerogel guide layer prepared in accordance with example 1 of the present invention;

FIG. 4 is a cross-sectional electron microscope of the aerogel guide layer prepared in example 1 of the present invention at a large scale;

FIG. 5 is a cross-sectional electron micrograph of an aerogel guide layer prepared in example 1 of the present invention at a mesoscale;

FIG. 6 is a cross-sectional electron microscope of the aerogel guide layer prepared in example 1 of the present invention at a small scale;

fig. 7 is an infrared spectrum of the composite sol prepared in example 1 of the present invention, including sodium alginate and graphene oxide.

Detailed Description

The technical scheme of the application is described in detail below with reference to specific embodiments and attached drawings. The examples described herein are specific embodiments of the present application for illustrating the concept of the present application; the description is intended to be illustrative and exemplary in nature and should not be construed as limiting the scope of the application in its aspects. In addition to the embodiments described herein, those skilled in the art can adopt other obvious solutions based on the disclosure of the claims and the specification thereof, including those adopting any obvious substitutions and modifications to the embodiments described herein.

Example 1

The embodiment provides a preparation method of a stainless steel positive electrode current collector, as shown in fig. 1, comprising the following steps:

(1) Mixing sodium alginate with 1.5wt% of nano cellulose solution for 1h, wherein the mass ratio of the sodium alginate to the nano cellulose solution is 1:80, and then centrifugally defoaming for 10min at a rotation speed of 5000rpm to obtain a first precursor solution;

Dispersing graphene oxide in deionized water to form graphene oxide dispersion liquid with the concentration of 1mg/mL, and dropwise adding ammonia water solution with the concentration of 5mol/L into the graphene oxide dispersion liquid to adjust the pH value of the graphene oxide dispersion liquid to 10; mixing graphene oxide dispersion liquid, 2mol/L polyvinyl alcohol solution, hydrazine hydrate and glyoxal at 70 ℃ for 24 hours to obtain a second precursor solution; wherein the mass ratio of graphene oxide to polyvinyl alcohol is 0.05:1, and the mass ratio of polyvinyl alcohol, hydrazine hydrate and glyoxal is 1:0.05:0.1;

mixing the first precursor solution and the second precursor solution according to the volume ratio of 0.5:1, stirring for 24 hours at 120 ℃, and performing hydrothermal reduction on graphene oxide to obtain reduced graphene oxide, so as to finally form transparent composite sol;

(2) Dripping the composite sol obtained in the step (1) into a sodium sulfate solution with the weight percent of 2, wherein the volume of the liquid drops of the composite sol is 0.1mL each time, so that the liquid drops of the composite sol are subjected to physical gelation to form granular composite hydrogel;

Soaking the composite hydrogel in absolute ethyl alcohol for 1h, and performing alcohol-water displacement to obtain composite alcohol gel; introducing supercritical carbon dioxide fluid with the temperature of 50 ℃ and the pressure of 30MPa into the composite alcohol gel at the flow of 20L/h, performing supercritical drying on the composite alcohol gel, and finally, crushing and grinding to obtain composite aerogel powder;

(3) Mixing nickel sulfate, sodium borohydride, sodium dodecyl sulfate and deionized water to obtain a composite plating solution, wherein the concentration of the nickel sulfate in the composite plating solution is 10g/L, the concentration of the sodium borohydride is 0.1g/L, and the concentration of the sodium dodecyl sulfate is 20mg/L;

Adding boric acid into the composite plating solution to adjust the pH value of the composite plating solution to 4; then, immersing the stainless steel substrate 1 with the thickness of 0.05mm in a composite plating solution at 60 ℃, depositing a conductive nickel plating layer 2 with the thickness of 40 mu m on the surface of the stainless steel substrate 1 through an electrochemical deposition process, setting the current density to be 1A/dm ², setting the voltage to be 5V, and setting the deposition time to be 5min;

Uniformly mixing the composite aerogel powder obtained in the step (2), polytetrafluoroethylene and water according to the mass ratio of 96:2:2 to obtain conductive slurry, coating the conductive slurry on the surface of the conductive nickel coating 2, and vacuum drying at 150 ℃ for 6 hours to form an aerogel guide layer 3 with the thickness of 400 mu m, thereby obtaining the stainless steel positive electrode current collector shown in figure 2.

Fig. 3 shows the surface microstructure of the aerogel guide layer 3 prepared in this example, and it can be seen that there are a large number of pleat structures on the surface of the aerogel guide layer 3 added, and the pleat structures provide active sites.

Fig. 4, fig. 5 and fig. 6 show the cross-sectional micro-morphology of the aerogel guiding layer 3 prepared in this embodiment, and as can be seen from fig. 4 and fig. 5, the inside of the aerogel guiding layer 3 presents a three-dimensional ordered porous structure, which has a relatively high specific surface area and a rich micropore number, is favorable for the infiltration, flow and diffusion of the electrolyte in the aerogel guiding layer 3, and the aerogel guiding layer 3 can provide rich active sites, and realizes the sufficient contact of the electrolyte with the conductive nickel plating layer 2, thereby improving the electrochemical reaction efficiency. As can be seen from fig. 6, the carbon layer at the cross section of the aerogel guiding layer 3 has a large number of vertically penetrating nanopores with an average pore diameter of about 100nm, which are formed by dehydration of cellulose chains during supercritical drying of the composite hydrogel. The existence of the nano-pores can be communicated with different carbon layers, and the structure is beneficial to infiltration and permeation between the aerogel guide layer 3 and the electrolyte and provides an ion transmission channel.

Fig. 7 is an infrared spectrum of sodium alginate, graphene oxide and the composite sol prepared in example 1 of the present invention, and it can be seen from the figure that in the infrared spectrum of sodium alginate, the stretching vibration peaks at 1595cm ^-1、1418cm^-1 and 1026cm ^-1 correspond to stretching vibration of c= C, C-OH and C-O-C, respectively. In the infrared spectrum of graphene oxide, the broad peak band at 3200-3400cm ^-l corresponds to the stretching vibration of-OH, the absorption peak at 1224cm ^-l corresponds to the stretching vibration of C-O-C, and the absorption peak at 1718cm ^-l corresponds to the stretching vibration of C=O. In the infrared spectrum of the composite sol, the stretching vibration peaks at 3289cm ^-1、1601cm^-1、1418cm^-1 and 1025cm ^-1 correspond to stretching vibration of-OH, C= C, C-OH and C-O-C respectively, which indicates that sodium alginate and graphene oxide have been successfully compounded.

Example 2

(1) Mixing sodium alginate with 1.8wt% of nano cellulose solution for 1.2h, wherein the mass ratio of the sodium alginate to the nano cellulose solution is 1:78, and then centrifuging and defoaming for 8min at the rotating speed of 5200rpm to obtain a first precursor solution;

Dispersing graphene oxide in deionized water to form 2mg/mL graphene oxide dispersion liquid, and dropwise adding 5.2mol/L ammonia water solution into the graphene oxide dispersion liquid to adjust the pH value of the graphene oxide dispersion liquid to 10.2; mixing graphene oxide dispersion liquid, 2.2mol/L polyvinyl alcohol solution, triethylamine and glyoxal at 72 ℃ for 22 hours to obtain a second precursor solution; wherein the mass ratio of graphene oxide to polyvinyl alcohol is 0.08:1, and the mass ratio of polyvinyl alcohol, triethylamine and glyoxal is 1:0.08:0.2;

Mixing the first precursor solution and the second precursor solution according to the volume ratio of 0.52:1, stirring for 22 hours at 130 ℃, and performing hydrothermal reduction on graphene oxide to obtain reduced graphene oxide, so as to finally form transparent composite sol;

(2) Dripping the composite sol obtained in the step (1) into 2.2 weight percent of calcium chloride solution, wherein the volume of the liquid drops of the composite sol is 0.15mL each time, so that the liquid drops of the composite sol are subjected to physical gelation to form granular composite hydrogel;

Soaking the composite hydrogel in absolute ethyl alcohol for 2 hours, and performing alcohol-water displacement to obtain composite alcohol gel; introducing supercritical carbon dioxide fluid with the temperature of 52 ℃ and the pressure of 28MPa into the composite alcohol gel at the flow of 22L/h, performing supercritical drying on the composite alcohol gel, and finally, crushing and grinding to obtain composite aerogel powder;

(3) Mixing nickel sulfate, citric acid, sodium dodecyl sulfate and deionized water to obtain a composite plating solution, wherein the concentration of the nickel sulfate in the composite plating solution is 12g/L, the concentration of the citric acid is 0.2g/L, and the concentration of the sodium dodecyl sulfate is 22mg/L;

Adding sulfuric acid into the composite plating solution to adjust the pH value of the composite plating solution to 4.2; then, immersing the stainless steel substrate 1 with the thickness of 0.06mm in a composite plating solution at 62 ℃, depositing a conductive nickel plating layer 2 with the thickness of 42 mu m on the surface of the stainless steel substrate 1 through an electrochemical deposition process, setting the current density to be 3A/dm ², setting the voltage to be 8V, and setting the deposition time to be 6min;

uniformly mixing the composite aerogel powder obtained in the step (2), styrene-butadiene rubber and methanol according to the mass ratio of 97:1:2 to obtain conductive slurry, coating the conductive slurry on the surface of the conductive nickel coating 2, and vacuum drying at 160 ℃ for 5.5 hours to form an aerogel guide layer 3 with the thickness of 420 mu m, thereby obtaining the stainless steel positive electrode current collector shown in figure 2.

Example 3

(1) Mixing sodium alginate with 2wt% of nano cellulose solution for 1.5h, wherein the mass ratio of the sodium alginate to the nano cellulose solution is 1:75, and then centrifuging and defoaming for 7min at the rotating speed of 5500rpm to obtain a first precursor solution;

dispersing graphene oxide in deionized water to form a graphene oxide dispersion liquid with the concentration of 3mg/mL, and dropwise adding an ammonia water solution with the concentration of 5.5mol/L into the graphene oxide dispersion liquid to adjust the pH value of the graphene oxide dispersion liquid to 10.5; mixing graphene oxide dispersion liquid, 2.5mol/L polyvinyl alcohol solution, triethylamine and succinaldehyde for 20 hours at 75 ℃ to obtain a second precursor solution; wherein the mass ratio of graphene oxide to polyvinyl alcohol is 0.1:1, and the mass ratio of polyvinyl alcohol, triethylamine and succinaldehyde is 1:0.1:0.3;

Mixing the first precursor solution and the second precursor solution according to the volume ratio of 0.55:1, stirring for 20 hours at 150 ℃, and performing hydrothermal reduction on graphene oxide to obtain reduced graphene oxide, so as to finally form transparent composite sol;

(2) Dripping the composite sol obtained in the step (1) into 2.5wt% of calcium chloride solution, wherein the volume of the liquid drops of the composite sol is 0.2mL each time, so that the liquid drops of the composite sol are subjected to physical gelation to form granular composite hydrogel;

Soaking the composite hydrogel in absolute ethyl alcohol for 3 hours, and performing alcohol-water displacement to obtain composite alcohol gel; introducing supercritical carbon dioxide fluid with the temperature of 55 ℃ and the pressure of 25MPa into the composite alcohol gel at the flow rate of 25L/h, performing supercritical drying on the composite alcohol gel, and finally, crushing and grinding to obtain composite aerogel powder;

(3) Mixing nickel chloride, hydroxylamine hydrochloride, cetyl trimethyl ammonium bromide and deionized water to obtain a composite plating solution, wherein the concentration of the nickel chloride in the composite plating solution is 15g/L, the concentration of the hydroxylamine hydrochloride is 0.3g/L, and the concentration of the cetyl trimethyl ammonium bromide is 25mg/L;

Adding hydrochloric acid into the composite plating solution to adjust the pH value of the composite plating solution to 4.5; then, immersing the stainless steel substrate 1 with the thickness of 0.08mm in a composite plating solution at 65 ℃, depositing a conductive nickel plating layer 2 with the thickness of 45 mu m on the surface of the stainless steel substrate 1 through an electrochemical deposition process, setting the current density to be 5A/dm ², setting the voltage to be 10V, and setting the deposition time to be 7min;

Uniformly mixing the composite aerogel powder obtained in the step (2), polyacrylate and ethanol according to the mass ratio of 97:2:1 to obtain conductive slurry, coating the conductive slurry on the surface of the conductive nickel coating 2, and vacuum drying at 170 ℃ for 5 hours to form an aerogel guide layer 3 with the thickness of 450 mu m, thereby obtaining the stainless steel positive electrode current collector shown in figure 2.

Example 4

(1) Mixing sodium alginate with 2.5wt% of nano cellulose solution for 1.8h, wherein the mass ratio of the sodium alginate to the nano cellulose solution is 1:72, and then centrifuging and defoaming for 6min at the rotating speed of 5800rpm to obtain a first precursor solution;

Dispersing graphene oxide in deionized water to form a graphene oxide dispersion liquid with the concentration of 4mg/mL, and dropwise adding an ammonia water solution with the concentration of 5.8mol/L into the graphene oxide dispersion liquid to adjust the pH value of the graphene oxide dispersion liquid to 10.8; mixing graphene oxide dispersion liquid, 2.8mol/L polyvinyl alcohol solution, hydrazine hydrate and succinaldehyde for 15 hours at 78 ℃ to obtain a second precursor solution; wherein the mass ratio of graphene oxide to polyvinyl alcohol is 0.12:1, and the mass ratio of polyvinyl alcohol, hydrazine hydrate and succinyl aldehyde is 1:0.15:0.3;

mixing the first precursor solution and the second precursor solution according to the volume ratio of 0.58:1, stirring for 15 hours at 160 ℃, and performing hydrothermal reduction on graphene oxide to obtain reduced graphene oxide, so as to finally form transparent composite sol;

(2) Dripping the composite sol obtained in the step (1) into 2.8wt% of calcium chloride solution, wherein the volume of the liquid drops of the composite sol is 0.25mL each time, so that the liquid drops of the composite sol are subjected to physical gelation to form granular composite hydrogel;

Soaking the composite hydrogel in absolute ethyl alcohol for 4 hours, and performing alcohol-water displacement to obtain composite alcohol gel; introducing supercritical carbon dioxide fluid with the temperature of 58 ℃ and the pressure of 23MPa into the composite alcohol gel at the flow of 28L/h, performing supercritical drying on the composite alcohol gel, and finally, crushing and grinding to obtain composite aerogel powder;

(3) Mixing nickel nitrate, formaldehyde, hexadecyl trimethyl ammonium bromide and deionized water to obtain a composite plating solution, wherein the concentration of the nickel nitrate in the composite plating solution is 18g/L, the concentration of the formaldehyde is 0.4g/L, and the concentration of the hexadecyl trimethyl ammonium bromide is 28mg/L;

adding nitric acid into the composite plating solution to adjust the pH value of the composite plating solution to 4.8; then, immersing the stainless steel substrate 1 with the thickness of 0.09mm in a composite plating solution at 68 ℃, depositing a conductive nickel plating layer 2 with the thickness of 48 mu m on the surface of the stainless steel substrate 1 through an electrochemical deposition process, setting the current density to be 7A/dm ², setting the voltage to be 12V, and setting the deposition time to be 8min;

Uniformly mixing the composite aerogel powder obtained in the step (2), polyimide and N-methyl pyrrolidone according to the mass ratio of 98:1.5:1.5 to obtain conductive slurry, coating the conductive slurry on the surface of the conductive nickel coating 2, and vacuum drying at 170 ℃ for 4.5 hours to form an aerogel guide layer 3 with the thickness of 480 mu m, thereby obtaining the stainless steel positive electrode current collector shown in figure 2.

Example 5

(1) Mixing sodium alginate with 3wt% of nano cellulose solution for 2 hours, wherein the mass ratio of the sodium alginate to the nano cellulose solution is 1:70, and then centrifuging and defoaming for 5 minutes at a rotating speed of 6000rpm to obtain a first precursor solution;

Dispersing graphene oxide in deionized water to form a graphene oxide dispersion liquid with the concentration of 5mg/mL, and dropwise adding an ammonia water solution with the concentration of 6mol/L into the graphene oxide dispersion liquid to adjust the pH value of the graphene oxide dispersion liquid to 11; mixing graphene oxide dispersion liquid, a polyvinyl alcohol solution with the concentration of 3mol/L, n-propylamine and glutaraldehyde for 12 hours at the temperature of 80 ℃ to obtain a second precursor solution; wherein the mass ratio of graphene oxide to polyvinyl alcohol is 0.15:1, and the mass ratio of polyvinyl alcohol, n-propylamine and glutaraldehyde is 1:0.2:0.4;

Mixing the first precursor solution and the second precursor solution according to the volume ratio of 0.6:1, stirring for 12 hours at 180 ℃, and performing hydrothermal reduction on graphene oxide to obtain reduced graphene oxide, so as to finally form transparent composite sol;

(2) Dripping the composite sol obtained in the step (1) into a 3wt% calcium chloride solution, wherein the volume of the liquid drops of the composite sol is 0.3mL each time, so that the liquid drops of the composite sol are subjected to physical gelation to form granular composite hydrogel;

soaking the composite hydrogel in absolute ethyl alcohol for 5 hours, and performing alcohol-water displacement to obtain composite alcohol gel; introducing supercritical carbon dioxide fluid with the temperature of 60 ℃ and the pressure of 20MPa into the composite alcohol gel at the flow of 30L/h, performing supercritical drying on the composite alcohol gel, and finally, crushing and grinding to obtain composite aerogel powder;

(3) Mixing nickel bromide, sodium borohydride, sodium dodecyl sulfate and deionized water to obtain a composite plating solution, wherein the concentration of the nickel bromide in the composite plating solution is 20g/L, the concentration of the sodium borohydride is 0.5g/L, and the concentration of the sodium dodecyl sulfate is 30mg/L;

adding phosphoric acid into the composite plating solution to adjust the pH value of the composite plating solution to 5; then, immersing the stainless steel substrate 1 with the thickness of 0.1mm in a composite plating solution at 70 ℃, depositing a conductive nickel plating layer 2 with the thickness of 50 mu m on the surface of the stainless steel substrate 1 through an electrochemical deposition process, setting the current density to be 10A/dm ², setting the voltage to be 15V, and setting the deposition time to be 10min;

Uniformly mixing the composite aerogel powder obtained in the step (2), sodium polyacrylate and N, N-dimethylformamide according to the mass ratio of 98:1:1 to obtain conductive slurry, coating the conductive slurry on the surface of the conductive nickel coating 2, and vacuum drying for 4 hours at 180 ℃ to form an aerogel guide layer 3 with the thickness of 500 mu m, thereby obtaining the stainless steel positive electrode current collector shown in figure 2.

Comparative example 1

The comparative example provides a preparation method of a stainless steel positive electrode current collector, which is different from the embodiment 1 in that in the step (1), the mass ratio of sodium alginate to nanocellulose solution is adjusted to be 1:60, and other process parameters and operation steps are identical to those of the embodiment 1.

Comparative example 2

The comparative example provides a preparation method of a stainless steel positive electrode current collector, which is different from the embodiment 1 in that in the step (1), the mass ratio of sodium alginate to nanocellulose solution is adjusted to be 1:90, and other process parameters and operation steps are identical to those of the embodiment 1.

Comparative example 3

The comparative example provides a preparation method of a stainless steel positive electrode current collector, which is different from the embodiment 1 in that in the step (1), the mass ratio of graphene oxide to polyvinyl alcohol is adjusted to be 0.01:1, and other process parameters and operation steps are identical to those of the embodiment 1.

Comparative example 4

The comparative example provides a preparation method of a stainless steel positive electrode current collector, which is different from the embodiment 1 in that in the step (1), the mass ratio of graphene oxide to polyvinyl alcohol is adjusted to be 0.2:1, and other process parameters and operation steps are identical to those of the embodiment 1.

Comparative example 5

The comparative example provides a method for preparing a stainless steel positive electrode current collector, which is different from example 1 in that in the step (1), the volume ratio of the first precursor solution to the second precursor solution is adjusted to be 0.4:1, and other process parameters and operation steps are identical to those of example 1.

Comparative example 6

The comparative example provides a method for preparing a stainless steel positive electrode current collector, which is different from example 1 in that in the step (1), the volume ratio of the first precursor solution to the second precursor solution is adjusted to be 0.7:1, and other process parameters and operation steps are identical to those of example 1.

Comparative example 7

The comparative example provides a method for preparing a stainless steel positive electrode current collector, which is different from example 1 in that in the step (2), the pressure of the supercritical carbon dioxide fluid is adjusted to 15MPa, and other process parameters and operation steps are exactly the same as those of example 1.

Comparative example 8

The comparative example provides a method for preparing a stainless steel positive electrode current collector, which is different from example 1 in that in the step (2), the pressure of the supercritical carbon dioxide fluid is adjusted to 35MPa, and other process parameters and operation steps are exactly the same as those of example 1.

Comparative example 9

This comparative example uses a conventional aluminum foil (thickness of 0.05 mm) as the positive electrode current collector.

The positive electrode sheets were prepared by using the positive electrode current collectors provided in examples 1 to 5 and comparative examples 1 to 9, and the specific preparation process was as follows:

Coating the positive electrode slurry on the surface of a positive electrode current collector, drying at 95 ℃, and rolling to obtain a positive electrode plate; wherein, the positive electrode slurry comprises 94wt% of NaFe _1/3Ni_1/3Mn_1/3O₃, 3wt% of a conductive agent Super P and 3wt% of a binder PVDF.

And slitting and winding the positive electrode plate, and assembling the 26650 cylindrical sodium ion battery.

The maximum compacted density of the positive electrode sheet, the sheet resistance and the cycle life of the sodium ion battery were tested.

The testing process and the calculating method of the maximum compaction density of the positive pole piece are as follows:

(1) Cutting a stainless steel positive electrode current collector into a wafer-shaped current collector sample of 100cm ² by using a sampler and weighing, cutting a positive electrode plate into a wafer-shaped plate sample of 100cm ² by using the sampler and weighing;

(2) Extruding the cut pole piece sample by a roller for multiple times until the pole piece sample is compact and crisp but is folded in half and cannot be broken;

(3) And respectively measuring the thickness of the extruded pole piece sample and the thickness of the current collector sample by using a screw micrometer.

The areal density of the positive pole piece is calculated by adopting the following formula:

Wherein ρ _A is the areal density of the positive pole piece (g/cm ²）;m_a is the mass (g) of the pole piece sample, m _b is the mass (g) of the current collector sample, and S is the area (cm ²) of the pole piece sample.

The maximum compaction density of the positive pole piece is calculated by adopting the following formula:

Wherein ρ _B is the maximum compacted density of the positive electrode sheet (g/cm ³）;ρ_A is the areal density of the positive electrode sheet (g/cm ²）;h_a is the thickness (μm) of the sheet sample; h _b is the thickness (μm) of the current collector sample).

The impedance of the positive electrode sheet is tested as follows:

The AC impedance value of the button cell was measured using a CHI-660-E electrochemical analyzer. The test frequency is set to 10 ^-2-10⁵ Hz, the maximum value of the applied voltage is 5mV, and the test temperature is 25 ℃; the sodium ion batteries subjected to the impedance test were each charged to a half-charged state (soc=50%) after 5 times of charge/discharge cycles of 0.1C.

The cycle life of the sodium ion battery was tested as follows:

And (3) carrying out cyclic test on the prepared sodium ion battery, circularly charging and discharging n times, recording the discharge capacity of the nth and the 1 st batteries, calculating the discharge retention rate, stopping the test when the discharge retention rate reaches 80%, and recording the cycle times, wherein the discharge retention rate is calculated as n discharge capacity/1 st discharge capacity multiplied by 100%. The test results are shown in Table 1.

TABLE 1

From the test data of example 1, comparative example 1 and comparative example 2, it can be seen that when the mass ratio of sodium alginate to nanocellulose solution exceeds the numerical range defined by the present invention, the maximum compaction density of the positive electrode sheet is reduced, resulting in an increase in the impedance of the positive electrode sheet, and the cycle life of the prepared sodium ion battery is deteriorated.

From the test data of example 1, comparative example 3 and comparative example 4, it can be seen that when the mass ratio of graphene oxide to polyvinyl alcohol is out of the numerical range defined by the present invention, the maximum compaction density of the positive electrode sheet is reduced, resulting in an increase in the impedance of the positive electrode sheet, and the cycle life of the prepared sodium ion battery is deteriorated.

From the test data of example 1, comparative example 5 and comparative example 6, it can be seen that when the volume ratio of the first precursor solution to the second precursor solution is out of the numerical range defined in the present invention, the maximum compacted density of the positive electrode sheet is reduced, resulting in an increase in the impedance of the positive electrode sheet, and the cycle life of the prepared sodium ion battery is deteriorated.

From the test data of example 1, comparative example 7 and comparative example 8, it can be seen that when the pressure of the supercritical carbon dioxide fluid exceeds the numerical range defined by the present invention, the maximum compacted density of the positive electrode sheet is reduced, resulting in an increase in the resistance of the positive electrode sheet, and the cycle life of the prepared sodium ion battery is deteriorated.

As can be seen from the test data of example 1 and comparative example 9, compared with the sodium ion battery prepared by using the conventional aluminum foil, the sodium ion battery prepared by using the positive electrode current collector provided by the invention has the advantages that the maximum compaction density, the battery capacity and the cycle life of the positive electrode plate are greatly improved.

The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.

Claims

1. The preparation method of the stainless steel positive electrode current collector is characterized by comprising the following steps of:

Uniformly mixing sodium alginate and a nanocellulose solution, and centrifuging to remove foam to obtain a first precursor solution; dispersing graphene oxide in deionized water to form graphene oxide dispersion liquid, dropwise adding an ammonia solution into the graphene oxide dispersion liquid to adjust the graphene oxide dispersion liquid to be alkaline, and mixing the graphene oxide dispersion liquid, a polyvinyl alcohol solution, a catalyst and a cross-linking agent to obtain a second precursor solution, wherein the catalyst is any one or a combination of at least two of hydrazine hydrate, triethylamine and n-propylamine, and the cross-linking agent is any one or a combination of at least two of glyoxal, succinaldehyde and glutaraldehyde; mixing, heating and stirring a first precursor solution and a second precursor solution, and performing hydrothermal reduction on graphene oxide to obtain reduced graphene oxide, so as to finally form transparent composite sol;

Dripping the composite sol obtained in the step (I) into a gel induction solution to enable the composite sol droplets to be subjected to physical gelation to form granular composite hydrogel, wherein the gel induction solution is a calcium chloride solution or a sodium sulfate solution; then, soaking the composite hydrogel in absolute ethyl alcohol, and performing alcohol-water displacement to obtain composite alcohol gel; introducing supercritical carbon dioxide fluid into the composite alcohol gel, performing supercritical drying on the composite alcohol gel, and finally, crushing and grinding to obtain composite aerogel powder;

2. The method according to claim 1, wherein in the step (i), the mass fraction of the nanocellulose solution is 1.5-3wt%;

The mass ratio of the sodium alginate to the nanocellulose solution is 1 (70-80);

the mixing time of the sodium alginate and the nano cellulose solution is 1-2h;

the rotational speed of the centrifugal defoaming is 5000-6000rpm;

The time for centrifugal defoaming is 5-10min.

3. The method of claim 1, wherein in step (i), the graphene oxide dispersion has a concentration of 1-5mg/mL;

The concentration of the ammonia water solution is 5-6mol/L;

Dropwise adding an ammonia water solution to adjust the pH value of the graphene oxide dispersion liquid to 10-11;

The concentration of the polyvinyl alcohol solution is 2-3mol/L;

the mass ratio of graphene oxide in the graphene oxide dispersion liquid to polyvinyl alcohol in the polyvinyl alcohol solution is (0.05-0.15) 1;

The mass ratio of the polyvinyl alcohol, the catalyst and the cross-linking agent in the polyvinyl alcohol solution is 1 (0.05-0.2) (0.1-0.4);

the mixing time of the graphene oxide dispersion liquid, the polyvinyl alcohol solution, the catalyst and the cross-linking agent is 12-24 hours;

the mixing temperature of the graphene oxide dispersion liquid, the polyvinyl alcohol solution, the catalyst and the cross-linking agent is 70-80 ℃.

4. The method of claim 1, wherein in step (i), the volume ratio of the first precursor solution to the second precursor solution is (0.5-0.6): 1;

The mixing heating temperature of the first precursor solution and the second precursor solution is 120-180 ℃;

The mixing and stirring time of the first precursor solution and the second precursor solution is 12-24h.

5. The method according to claim 1, wherein in step (ii), the mass fraction of the gel inducing solution is 2-3wt%;

The volume of the liquid drop of the composite sol is 0.1-0.3mL each time;

the soaking time of the composite hydrogel in the absolute ethyl alcohol is 1-5h;

the temperature of the supercritical carbon dioxide fluid is 50-60 ℃;

the pressure of the supercritical carbon dioxide fluid is 20-30MPa;

the flow rate of the supercritical carbon dioxide fluid is 20-30L/h.

6. The method according to claim 1, wherein in the step (iii), the concentration of the nickel salt in the composite plating solution is 10 to 20g/L;

The concentration of the reducing agent in the composite plating solution is 0.1-0.5g/L;

The concentration of the surfactant in the composite plating solution is 20-30mg/L;

The nickel salt is any one or the combination of at least two of nickel sulfate, nickel chloride, nickel nitrate and nickel bromide;

the reducing agent is any one or the combination of at least two of sodium borohydride, citric acid, hydroxylamine hydrochloride and formaldehyde;

the surfactant is any one or a combination of at least two of sodium dodecyl sulfate, cetyltrimethylammonium bromide and sodium dodecyl sulfonate;

adding the pH regulator to regulate the pH value of the composite plating solution to 4-5;

the pH regulator is any one or the combination of at least two of boric acid, sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid.

7. The method according to claim 1, wherein in the step (iii), the temperature of the composite plating solution is 60 to 70 ℃;

The current density of the electrochemical deposition process is 1-10A/dm ²;

the voltage of the electrochemical deposition process is 5-15V;

The time of the electrochemical deposition process is 5-10min;

the thickness of the conductive nickel coating is 40-50 mu m.

8. The method of claim 1, wherein in step (iii), the mass ratio of the composite aerogel powder, binder, and solvent is (96-98): 1-2;

the binder is any one or a combination of at least two of polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, polyimide, sodium polyacrylate, chitosan, polyvinylidene fluoride and polyvinylidene fluoride;

The solvent is any one or the combination of at least two of water, methanol, ethanol, N-methylpyrrolidone, N-dimethylformamide and dimethyl sulfoxide;

the temperature of the vacuum drying is 150-180 ℃;

the time of vacuum drying is 4-6h;

the aerogel guide layer has a thickness of 400-500 μm.

9. A stainless steel positive electrode current collector prepared by the preparation method according to any one of claims 1 to 8, characterized in that the stainless steel positive electrode current collector comprises a stainless steel base material, a conductive nickel plating layer and an aerogel guiding layer which are laminated in sequence;

the thickness of the stainless steel base material is 0.05-0.1mm;

The thickness of the conductive nickel coating is 40-50 mu m;

the aerogel guide layer has a thickness of 400-500 μm.

10. The sodium ion battery is characterized by comprising a positive plate, a diaphragm and a negative plate which are sequentially laminated; the positive plate of the sodium ion battery comprises the stainless steel positive electrode current collector and a positive electrode active material layer positioned on the surface of the stainless steel positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, a binder and a solvent.