Silicon negative electrode supramolecular binder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electrochemical energy storage, and discloses a silicon negative electrode supramolecular binder as well as a preparation method and application thereof. The silicon negative electrode supramolecular binder is prepared from the following raw materials: a polyacrylamide derivative, a water-soluble polymer containing-COOH and-OH, inorganic ferric salt, hydroxylated silicon particles, a conductive agent and water. According to the silicon negative electrode supramolecular binder provided by the invention, a water-soluble high-molecular polymer rich in carboxyl (-COOH) and hydroxyl (-OH) and polyacrylamide rich in amide (-CONH2) are used as main raw materials, and a metal ion Fe < 3 + > of inorganic salt is used as a reversible connection point between two high-molecular chains; the three-dimensional supramolecular binder has multiple hydrogen bonds and ion-dipole dual reversible supramolecular action and can be dissociated and self-recovered, the cross-linked network structure of the binder has flexible adaptability to the volume change of a silicon-based material, and the stability of an electrode structure in the electrochemical reaction process is maintained.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a silicon negative electrode supramolecular binder, a preparation method thereof, and applications thereof. Background Art

[0002] At present, the energy density of lithium-ion batteries still cannot meet the needs of electronic devices, power batteries and power grids, and the commercial graphite anode materials of lithium-ion batteries are close to their theoretical capacity (372mAh / g), so there is an urgent need to explore high-energy anode materials. Silicon-based materials have become very promising lithium-ion battery anode materials due to their ultra-high theoretical capacity (4200mAh / g). However, the alloying process of silicon-based materials in electrode reactions is accompanied by a dramatic volume expansion (>300%). The repeated volume stress during the cycle will cause the silicon particles to break, and the exposed new interface will consume the electrolyte to form an excessively thick solid electrolyte interface film (SEI), causing the capacity of the silicon anode to decay rapidly or even fail. These electrochemical-mechanical coupling failure problems have seriously hindered the practical application of high-energy-density silicon anodes in the field of energy storage and conversion.

[0003] Developing advanced binders is one of the effective ways to solve the above problems. The binder accounts for a small proportion of the total mass of the electrode, but it plays the role of bonding the active material, conductive agent and current collector together. Studies have shown that linear polymers such as sodium alginate, carboxymethyl cellulose, polyacrylamide and polyvinyl alcohol are rich in carboxyl groups, hydroxyl groups or amides, which can form hydrogen bonds with the modified silicon surface and thus show high adhesion to silicon particles. However, the tensile properties of the above linear one-dimensional polymers are poor or brittle, and the covalent bond strength of the polymer is strong, which makes it difficult to recover after breaking, resulting in the silicon electrode being easily failed due to irreversible fracture.

[0004] Therefore, providing a binder that conforms to the stress of the silicon negative electrode to solve the problem that silicon-based materials are prone to volume expansion, resulting in poor battery cycle stability and decreased battery specific capacity, is of great significance for promoting the development of silicon negative electrode lithium-ion batteries and meeting the market demand for high energy density lithium-ion batteries. Summary of the Invention

[0005] The present invention aims to solve at least one of the above-mentioned technical problems in the prior art. To this end, one of the objectives of the present invention is to provide a supramolecular binder for silicon negative electrodes.

[0006] A second object of the present invention is to provide a method for preparing the silicon negative electrode supramolecular binder.

[0007] A third object of the present invention is to provide a silicon negative electrode plate.

[0008] A fourth object of the present invention is to provide a lithium-ion battery.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A first aspect of the present invention provides a silicon negative electrode supramolecular binder, which is prepared from the following raw materials: a polyacrylamide derivative, a water-soluble polymer containing -COOH and -OH, an inorganic iron salt, hydroxylated silicon particles, a conductive agent and water.

[0011] In some embodiments of the present invention, in the silicon negative electrode supramolecular binder, the mass ratio of the polyacrylamide derivative to the water-soluble polymer containing -COOH and -OH is 1:(4-8).

[0012] In some specific embodiments of the present invention, in the silicon negative electrode supramolecular binder, the mass ratio of the polyacrylamide derivative to the water-soluble polymer containing -COOH and -OH is 1:(4-6).

[0013] In some embodiments of the present invention, in the silicon negative electrode supramolecular binder, the ratio of the total mass of the polyacrylamide derivative and the water-soluble polymer containing -COOH and -OH to the mass of the inorganic iron salt is (100-500):1.

[0014] In some specific embodiments of the present invention, in the silicon negative electrode supramolecular binder, the ratio of the total mass of the polyacrylamide derivative and the water-soluble polymer containing -COOH and -OH to the mass of the inorganic iron salt is (100-200):1.

[0015] In some embodiments of the present invention, in the silicon negative electrode supramolecular binder, the ratio of the mass of the hydroxylated silicon particles, the total mass of the polyacrylamide derivative, the water-soluble polymer containing -COOH and -OH and the inorganic iron salt, and the mass of the conductive agent is (6-9):(1-4):1.

[0016] In some specific embodiments of the present invention, in the silicon negative electrode supramolecular binder, the ratio of the mass of the hydroxylated silicon particles, the total mass of the polyacrylamide derivative, the water-soluble polymer containing -COOH and -OH and the inorganic iron salt, and the mass of the conductive agent is (6-8):(1-3):1.

[0017] In some embodiments of the present invention, the polyacrylamide derivative is selected from at least one of anionic polyacrylamide, cationic polyacrylamide, and nonionic polyacrylamide.

[0018] In some embodiments of the present invention, the water-soluble polymer containing -COOH and -OH is selected from at least one of sodium alginate, carboxymethyl cellulose, carrageenan, lignin, and hyaluronic acid.

[0019] In some embodiments of the present invention, the inorganic iron salt is selected from at least one of ferric sulfate, ferric chloride, and ferric nitrate.

[0020] In some embodiments of the present invention, the conductive agent is selected from at least one of acetylene black, carbon fiber, carbon nanotube, and conductive carbon black (Super P).

[0021] In some embodiments of the present invention, the particle size of the hydroxylated silicon particles is 30 nm-10 μm.

[0022] In some specific embodiments of the present invention, the particle size of the hydroxylated silicon particles is 50 nm-5 μm.

[0023] In some embodiments of the present invention, the hydroxylated silicon particles are prepared by a method comprising the following steps:

[0024] The silicon particles are mixed with the piranha solution and modified to obtain the hydroxylated silicon particles.

[0025] In some embodiments of the present invention, the piranha solution is composed of 96 wt%-98 wt% concentrated sulfuric acid and 28 wt%-30 wt% hydrogen peroxide in a volume ratio of (6-8):1.

[0026] In some embodiments of the present invention, the mass ratio of the silicon particles to the piranha solution is 1:(20-100).

[0027] In some embodiments of the present invention, the modification time is 0.5-3 hours.

[0028] The second aspect of the present invention provides a method for preparing the silicon negative electrode supramolecular binder according to the first aspect of the present invention, comprising the following steps:

[0029] S1. Dissolving a polyacrylamide derivative, a water-soluble polymer containing -COOH and -OH, and an inorganic iron salt in water, respectively, to obtain solution A, solution B, and solution C;

[0030] S2, adding the solution B and solution C dropwise to the solution A in sequence to obtain a supramolecular system D;

[0031] S3, the hydroxylated silicon particles and the conductive agent are first mixed by ball milling, and then mixed with the supramolecular system D by ultrasonication and ball milling to obtain the silicon negative electrode supramolecular binder.

[0032] In some embodiments of the present invention, in step S1, the concentration of solution A is 0.2 wt%-10 wt%.

[0033] In some specific embodiments of the present invention, in step S1, the concentration of solution A is 3 wt%-8 wt%.

[0034] In some embodiments of the present invention, in step S1, the concentration of solution B is 0.2 wt%-10 wt%.

[0035] In some specific embodiments of the present invention, in step S1, the concentration of solution B is 3 wt%-8 wt%.

[0036] In some embodiments of the present invention, in step S1, the concentration of the solution C is 0.02 wt%-5 wt%.

[0037] In some specific embodiments of the present invention, in step S1, the concentration of the solution C is 3 wt%-5 wt%.

[0038] In some embodiments of the present invention, in step S2, the dropwise addition process is supplemented with stirring.

[0039] In some embodiments of the present invention, in step S2, solution B and solution C are sequentially added dropwise to solution A, and stirring is continued for 0.5-5 hours.

[0040] In some specific embodiments of the present invention, in step S2, the solution B and solution C are sequentially added dropwise to the solution A, and stirring is continued for 1-3 hours.

[0041] In the present invention, solution A, solution B and solution C are mixed by dropping and stirring, which can avoid the aggregation of the components and improve the mixing uniformity, so that the -COOH, -OH, -CONH2 and Fe 3+ Uniform reversible multiple hydrogen bonds and reversible ion-dipole supramolecular interactions are formed between them.

[0042] In some embodiments of the present invention, in step S3, the temperature of the ultrasound is 25-80° C., and the time is 0.5-6 h.

[0043] In some specific embodiments of the present invention, in step S3, the temperature of the ultrasound is 25-30° C., and the time is 1-2 h.

[0044] In some embodiments of the present invention, in step S3, the ball milling time is selected from 0.5-6 hours.

[0045] In some specific embodiments of the present invention, in step S3, the ball milling time is selected from 0.5-1 h.

[0046] In some embodiments of the present invention, the ball milling method is selected from planetary ball milling or vibrating ball milling.

[0047] In the present invention, the hydroxylated silicon particles and the conductive agent are first ball-milled and dispersed in the supramolecular system D, and then ultrasonically and ball-milled together. This operation sequence can make the active material more evenly dispersed in the slurry, and during the electrode reaction, it can better maintain the cohesive force between the silicon particles and stabilize the electrode structure.

[0048] A third aspect of the present invention provides a silicon negative electrode plate, which is prepared from the following raw materials: a current collector, and the silicon negative electrode supramolecular binder according to the first aspect of the present invention.

[0049] In some embodiments of the present invention, the current collector is selected from a copper foil current collector, a nickel current collector or a stainless steel current collector.

[0050] In some embodiments of the present invention, the silicon negative electrode plate is prepared by a method comprising the following steps:

[0051] The silicon negative electrode supramolecular binder is coated on a current collector and solidified to obtain the silicon negative electrode plate.

[0052] In some embodiments of the present invention, the curing temperature is 50-150° C. and the curing time is 5-30 hours.

[0053] In some embodiments of the present invention, the curing method is selected from at least one of vacuum drying curing and air drying curing.

[0054] In some embodiments of the present invention, the active material loading of the silicon negative electrode plate is 0.3-5.0 mg / cm 2 .

[0055] In some specific embodiments of the present invention, the active material loading of the silicon negative electrode plate is 0.7-2.0 mg / cm 2 .

[0056] A fourth aspect of the present invention provides a lithium-ion battery, comprising the silicon negative electrode sheet according to the third aspect of the present invention.

[0057] In some embodiments of the present invention, the specific capacity of the lithium-ion battery under the test conditions of a potential window of 0.01-2.0 V and a current density of 1 A / g is 1300-1800 mAh / g.

[0058] The basic principles of the present invention are described as follows:

[0059] 1) Supramolecular interactions such as intermolecular van der Waals forces, hydrogen bonds, π-π stacking, and ion-dipole interactions have the properties of reversible bonds, showing a dynamic and flexible mechanism. Under the action of external forces, supramolecular interactions tend to dissociate rather than break, and can recover after stress is eliminated. This interaction is beneficial for silicon particles to maintain interparticle cohesion under huge volume changes; compared with one-dimensional linear molecular polymer binders, three-dimensional network structure binders have better effects on anchoring silicon particles, and at the same time exhibit strong adhesion, high modulus and high elasticity, which helps to adapt to or inhibit the large volume deformation of silicon negative electrodes during the cycle process. Therefore, based on reversible supramolecular interactions such as multiple hydrogen bonds and ion-dipole interactions, the present invention provides a three-dimensional supramolecular binder that can dissociate and self-recover, and is applied to lithium-ion battery silicon negative electrodes to solve the volume effect problem of silicon electrodes;

[0060] 2) The silicon negative electrode supramolecular binder provided by the present invention uses a water-soluble polymer rich in carboxyl (-COOH) and hydroxyl (-OH) and a polyacrylamide rich in amide (-CONH2) as main raw materials. During the preparation process, when the polymer solution containing -COOH and -OH (B solution) is added dropwise to the polyacrylamide solution (A solution), multiple intermolecular hydrogen bonds are formed between -COOH, -OH and -CONH2. These hydrogen bonds have certain flexibility and reversibility, and can buffer the stress generated by the volume change of the silicon negative electrode to a certain extent. Then, an iron-containing inorganic salt solution (C solution) is added, wherein Fe 3+ It will replace some of the hydrogen bonding sites between polymers and serve as reversible ion-dipole interaction points between molecular chains. This ion-dipole interaction is also reversible. When the silicon particles expand or contract, it can flexibly dissociate and self-recover, and together with multiple hydrogen bonds, it constructs a three-dimensional reversible cross-linked network structure, which enhances the sliding flexibility between molecular chains, thereby effectively adapting to the huge volume changes of the silicon negative electrode during the cycle.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] 1) The silicon anode supramolecular binder provided by the present invention is mainly composed of a water-soluble polymer rich in carboxyl (-COOH) and hydroxyl (-OH) and a polyacrylamide rich in amide (-CONH2), and an inorganic salt metal ion Fe 3+ As a reversible connection point between two polymer chains, it is a dissociable and self-recovering three-dimensional supramolecular binder with multiple hydrogen bonds and ion-dipole dual reversible supramolecular interactions. Its cross-linked network structure has flexible adaptability to the volume changes of silicon-based materials, maintaining the stability of the electrode structure during electrochemical reactions. Compared with one-dimensional linear molecular polymer binders, it can better adapt to or inhibit the large volume deformation of the silicon negative electrode during the cycle process.

[0063] 2) The silicon anode supramolecular binder provided by the present invention regulates the two polymer chains and metal ions (Fe 3+ ) ratio, and then rationally construct the multiple hydrogen bonds between organic groups (-COOH, -OH and -CONH2), the interchain metal ions (Fe 3+ ) reversible connection point, using hydroxylated silicon as raw material, can enhance its hydrogen bonding effect with the organic groups on the polymer chain;

[0064] 3) The preparation method of the silicon anode supramolecular binder provided by the present invention has simple steps. The stirring and dropping method can effectively avoid local aggregation and entanglement during the polymer mixing process. The hydroxylated silicon and the conductive agent are first ball-milled and then dispersed into the supramolecular system for ultrasonication and ball-milling, which can effectively improve the dispersion uniformity of the active material in the slurry.

[0065] 4) The silicon negative electrode provided by the present invention has a discharge capacity far higher than the theoretical capacity of the graphite negative electrode, good electrochemical activity and cycle stability, and can use a silicon negative electrode supramolecular binder containing micron silicon, which greatly reduces the cost compared with nano-silicon.

[0066] 5) The lithium-ion battery provided by the present invention adopts a silicon negative electrode plate, has a higher mass specific capacity and better cycle stability, and can better meet the market demand for high energy density batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is a scanning electron microscope image of the silicon negative electrode supramolecular binder prepared in Example 1 after drying;

[0068] Figure 2 This is a cyclic voltammetry test diagram of a button cell assembled with the silicon negative electrode piece in Example 1;

[0069] Figure 3 This is a constant current charge and discharge diagram of the button battery assembled with the silicon negative electrode piece in Example 1;

[0070] Figure 4 This is a constant current charge and discharge diagram of the button battery assembled with the silicon negative electrode piece in Comparative Example 1;

[0071] Figure 5 This is a constant current charge and discharge diagram of the button battery assembled with the silicon negative electrode piece in Comparative Example 2;

[0072] Figure 6 The cycle performance test results of the battery assembled with the silicon negative electrode sheet in Example 2 are as follows;

[0073] Figure 7 This is a comparison chart of the cycle performance of batteries assembled with silicon negative electrode sheets in Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0074] The present invention is further described in detail below using specific examples. Unless otherwise specified, the raw materials, reagents, and apparatus used in the examples and comparative examples are available from conventional commercial sources or by conventional methods. Unless otherwise specified, all experimental or testing methods are conventional in the art.

[0075] Example 1

[0076] In this embodiment, a silicon negative electrode supramolecular binder is prepared and used to prepare a silicon negative electrode plate. The steps are as follows:

[0077] Preparation of supramolecular binder for silicon anode:

[0078] S11, weighing an appropriate amount of anionic polyacrylamide and dissolving it in water to obtain a solution A with a concentration of 5 wt%, weighing an appropriate amount of sodium alginate and dissolving it in water to obtain a solution B with a concentration of 5 wt%, and weighing an appropriate amount of ferric sulfate and dissolving it in water to obtain a solution C with a concentration of 5 wt%;

[0079] S21. Under stirring conditions, solution B and solution C were sequentially added dropwise to solution A. After the addition was completed, stirring was continued for 3 h to obtain a supramolecular system D, wherein the mass ratio of cationic polyacrylamide to sodium alginate was 1:4, and the mass ratio of the total mass of cationic polyacrylamide and sodium alginate to the mass ratio of ferric sulfate was 100:1;

[0080] S31, mixing 0.35 g of silicon particles with a particle size of 50 nm with 10 g of piranha solution (98 wt % concentrated sulfuric acid and 30 wt % hydrogen peroxide, 7:1, v / v), and slowly stirring for 0.5 h to obtain hydroxylated silicon particles;

[0081] S32. The hydroxylated silicon particles and acetylene black were ball-milled for 0.5 h, dispersed in the supramolecular system D, and then ultrasonicated at 25°C for 1 h and ball-milled for 0.5 h to obtain a silicon negative electrode supramolecular binder, wherein the mass ratio of the hydroxylated silicon particles, the solute in the supramolecular system D, and the acetylene black was 7:2:1.

[0082] Preparation of silicon negative electrode:

[0083] The silicon anode supramolecular binder was coated on the copper foil current collector and cured at 100 °C for 15 h to obtain an active material loading of 1.2 mg / cm 2 Silicon negative electrode.

[0084] Example 2

[0085] In this embodiment, a silicon negative electrode supramolecular binder is prepared and used to prepare a silicon negative electrode plate. The steps are as follows:

[0086] Preparation of supramolecular binder for silicon anode:

[0087] S11. Weigh an appropriate amount of cationic polyacrylamide and dissolve it in water to obtain a 6 wt % solution A; weigh an appropriate amount of hyaluronic acid and dissolve it in water to obtain a 5 wt % solution B; weigh an appropriate amount of ferric nitrate and dissolve it in water to obtain a 3 wt % solution C;

[0088] S21. Under stirring, solution B and solution C were sequentially added dropwise to solution A. After the addition was completed, stirring was continued for 3 h to obtain a supramolecular system D, wherein the mass ratio of cationic polyacrylamide to hyaluronic acid was 1:6, and the mass ratio of the total mass of cationic polyacrylamide and hyaluronic acid to ferric nitrate was 200:1;

[0089] S31, mixing 0.35 g of silicon particles with a particle size of 1 μm with 10 g of piranha solution (98 wt % concentrated sulfuric acid and 30 wt % hydrogen peroxide, 7:1, v / v), and slowly stirring for 3 h to obtain hydroxylated silicon particles;

[0090] S32. The hydroxylated silicon particles and the conductive carbon black were ball-milled for 0.5 h, dispersed in the supramolecular system D, and then ultrasonicated at 30°C for 1 h and ball-milled for 1 h to obtain a silicon negative electrode supramolecular binder, wherein the mass ratio of the hydroxylated silicon particles, the solute in the supramolecular system D, and the conductive carbon black was 8:3:1.

[0091] Preparation of silicon negative electrode:

[0092] The silicon anode supramolecular binder was coated on the copper foil current collector and cured at 100 °C for 15 h to obtain an active material loading of 1.8 mg / cm 2 Silicon negative electrode.

[0093] Comparative Example 1

[0094] This comparative example prepares a silicon negative electrode supramolecular binder. The difference from Example 1 is that Solution C is replaced with the same volume of deionized water, and the silicon negative electrode supramolecular binder is used to prepare a silicon negative electrode plate. The steps are as follows:

[0095] Preparation of supramolecular binder for silicon anode:

[0096] S11, weighing an appropriate amount of anionic polyacrylamide and dissolving it in water to obtain a solution A with a concentration of 5 wt%, weighing an appropriate amount of sodium alginate and dissolving it in water to obtain a solution B with a concentration of 5 wt%, and using deionized water as solution C;

[0097] S21. Under stirring conditions, solution B and solution C were sequentially added dropwise to solution A. After the addition was completed, stirring was continued for 3 h to obtain a supramolecular system D, wherein the mass ratio of cationic polyacrylamide to sodium alginate was 1:4;

[0098] S31, mixing 0.35 g of silicon particles with a particle size of 50 nm with 10 g of piranha solution (98 wt % concentrated sulfuric acid and 30 wt % hydrogen peroxide, 7:1, v / v), and slowly stirring for 0.5 h to obtain hydroxylated silicon particles;

[0099] S32. The hydroxylated silicon particles and acetylene black were ball-milled for 0.5 h, dispersed in the supramolecular system D, and then ultrasonicated at 25°C for 1 h and ball-milled for 0.5 h to obtain a silicon negative electrode supramolecular binder, wherein the mass ratio of the hydroxylated silicon particles, the solute in the supramolecular system D, and the acetylene black was 7:2:1.

[0100] Preparation of silicon negative electrode:

[0101] The silicon negative electrode supramolecular binder was coated on the copper foil current collector and cured at 100°C for 15h to obtain a silicon negative electrode sheet.

[0102] Comparative Example 2

[0103] This comparative example prepares a silicon negative electrode binder. The difference from comparative example 1 is that solution B is replaced with the same volume of deionized water, and the silicon negative electrode binder is used to prepare a silicon negative electrode sheet. The steps are as follows:

[0104] Preparation of supramolecular binder for silicon anode:

[0105] S11, weighing an appropriate amount of anionic polyacrylamide and dissolving it in water to obtain a solution A with a concentration of 5 wt%, and using deionized water as solution B and solution C;

[0106] S21, under stirring, solution B and solution C were sequentially added dropwise to solution A. After the addition was completed, stirring was continued for 3 h to obtain system D;

[0107] S31, mixing 0.35 g of silicon particles with a particle size of 50 nm with 10 g of piranha solution (98 wt % concentrated sulfuric acid and 30 wt % hydrogen peroxide, 7:1, v / v), and slowly stirring for 0.5 h to obtain hydroxylated silicon particles;

[0108] S32. The hydroxylated silicon particles and acetylene black were ball-milled for 0.5 h, dispersed in system D, and then ultrasonicated at 25°C for 1 h and ball-milled for 0.5 h to obtain a silicon negative electrode binder, wherein the mass ratio of the hydroxylated silicon particles, anionic polyacrylamide, and acetylene black was 7:2:1.

[0109] Preparation of silicon negative electrode:

[0110] The silicon negative electrode binder was coated on the copper foil current collector and cured at 100° C. for 15 h to obtain a silicon negative electrode sheet.

[0111] Performance Testing

[0112] 1. The silicon anode supramolecular binder prepared in Example 1 was dried and then subjected to scanning electron microscopy testing:

[0113] Figure 1 This is a scanning electron microscope image of the silicon negative electrode supramolecular binder prepared in Example 1 after drying. Figure 1 It can be seen that in the silicon negative electrode supramolecular binder prepared in Example 1, the components are uniformly distributed without obvious agglomeration or local aggregation. This is due to the hydrogen bonding between the organic functional groups (-COOH, -OH, -CONH2) of the polymer and the -OH on the surface of the hydroxylated silicon. This hydrogen bonding enhances the mutual attraction between the different components, allowing them to be evenly dispersed in the slurry system; in addition, the order of preparing the slurry by first ball-milling the hydroxylated silicon and the conductive agent and then adding them to the supramolecular system for ultrasonic and ball-milling mixing also plays a key role. This preparation process ensures that the components are fully contacted and evenly distributed at the microscopic level, laying the foundation for the subsequent preparation and performance improvement of the electrode, and is conducive to maintaining the cohesion between the silicon particles under huge volume changes.

[0114] 2. The silicon negative electrode sheets prepared in Examples 1-3 and Comparative Examples 1 and 2 were respectively assembled with lithium positive electrode sheets into button cells for electrochemical testing:

[0115] 1) Cyclic voltammetry was performed on the battery assembled with the silicon negative electrode piece in Example 1, with a potential window of 0.01-2.0 V and a scan rate of 0.1-1 mV / s:

[0116] Figure 2 This is the cyclic voltammetry test diagram of the button battery assembled with the silicon negative electrode piece in Example 1. Figure 2 It can be seen that at the maximum scanning speed of 1 mV / s, the reduction peak current is 1.9 mA, which is relatively high, indicating that lithium ions can be quickly embedded in the silicon negative electrode material, that is, the electrode structure constructed by the supramolecular binder provided by the present invention is conducive to electron transport and provides a good channel for the embedding of lithium ions; the oxidation peak current is relatively small, but it also reaches 0.57 mA, reflecting that lithium ions can also be smoothly extracted from the silicon negative electrode material; the good redox characteristic peaks indicate that the electrode has good electrochemical reaction kinetics.

[0117] 2) The batteries assembled with the silicon negative electrode sheets in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to constant current charge and discharge tests, with a potential window of 0.01-2.0 V and a current density of 1 A / g:

[0118] Figure 3 This is the constant current charge and discharge diagram of the button battery assembled with the silicon negative electrode piece in Example 1. Figure 3It can be seen that when the current density reaches 1 A / g, the specific capacity of the button battery assembled with the silicon negative electrode sheet in Example 1 reaches 1334.3 mAh / g, far exceeding the theoretical capacity of the graphite negative electrode (372 mAh / g).

[0119] Figure 4 This is the constant current charge and discharge diagram of the button battery assembled with the silicon negative electrode piece in Comparative Example 1. Figure 4 It can be seen that under the condition of current density of 1A / g, the specific capacity of the button cell assembled with silicon negative electrode in comparative example 1 is only 857.7mAh / g, which is much lower than that in example 1, and the specific capacity has decreased by about 476mAh / g, indicating that the reversible ion-dipole linking effect between chains has a significant effect on the specific capacity of the battery. In the supramolecular binder system, Fe 3+ As a reversible ion-dipole interaction point between chains, it can enhance the interaction between molecular chains and build a more stable three-dimensional network structure. When this effect is removed, the structural stability of the binder system decreases, and it cannot effectively adapt to the volume changes of the silicon negative electrode during the charging and discharging process, causing the silicon particles to be more easily broken, and the active material exposes a new interface to consume the electrolyte to react and form SEI, thereby significantly reducing the specific capacity of the battery.

[0120] Figure 5 This is the constant current charge and discharge diagram of the button battery assembled with the silicon negative electrode piece in Comparative Example 2. Figure 5 It can be seen that under the current density of 1A / g, the specific capacity of the button battery assembled with the silicon negative electrode plate in Comparative Example 1 is only 428.2mAh / g, which is much lower than that in Example 1, indicating that the multiple hydrogen bonding interactions and ion-dipole interactions between polymer chains are crucial to maintaining the high specific capacity of the battery. In the supramolecular binder system, these interactions jointly construct a stable three-dimensional network structure, which can effectively buffer the volume changes of the silicon negative electrode during the charge and discharge process and maintain the integrity and activity of the silicon particles. When these interactions are lost, the silicon particles are easily broken during the volume expansion and contraction process, causing the active material to expose a new interface to react with the electrolyte to form SEI. The loss of active lithium and electrolyte causes the battery specific capacity to drop sharply, which also shows that compared with the one-dimensional linear molecular polymer binder, the three-dimensional network structure binder provided by the present invention is more adaptable to or inhibits the large volume deformation of the silicon negative electrode during the cycle process.

[0121] 3) Cycling performance tests were conducted on batteries assembled with the silicon negative electrode sheets in Example 1, Example 2, and Comparative Example 2. After pre-activation at current densities of 0.2 A / g and 0.8 A / g for 5 and 10 cycles, long cycling was performed at 1 A / g. The cycle retention rate was calculated starting from the 16th cycle:

[0122] Figure 6The cycle performance test results of the battery assembled with the silicon negative electrode piece in Example 2 are as follows: Figure 6 It can be seen that under the test condition of a current density of 1A / g, the battery assembled with the silicon negative electrode sheet in Example 2 has a specific capacity of 1351.5mAh / g after 200 cycles, showing a high discharge specific capacity. Even when performing charge and discharge tests at high currents, the micron silicon electrode designed based on this binder can still adapt to the volume expansion and contraction of micron silicon during the lithium insertion / delithiation process, maintaining good cycle stability. This shows that the dual supramolecular binder prepared based on multiple hydrogen bonds and ion-dipole reconstruction can be used for micron silicon with a huge volume effect. Compared with expensive nano-silicon particles, low-cost micron silicon particles have higher economic application value. This dual supramolecular binder system shows good application prospects.

[0123] Figure 7 The comparison chart of the cycle performance of the battery assembled with the silicon negative electrode sheet in Example 1 and Comparative Example 2 is shown in FIG. Figure 7 It can be seen that under the test conditions of a current density of 1 A / g, the battery assembled with the silicon negative electrode piece in Example 1 has an electrode capacity retention rate of more than 83% after a long cycle of 1200 cycles, and the coulombic efficiency (CE) is stable at more than 97%, while the battery assembled with the silicon negative electrode piece in Comparative Example 2 has no capacity after 903 cycles, which proves that the one-dimensional linear molecular polymer binder in Comparative Example 2 easily causes the silicon electrode to fail due to irreversible fracture, while the reversible dissociation and self-recovery performance of the binder in Example 1 based on the dual supramolecular effect can effectively adapt to the stress generated by repeated volume changes of the silicon negative electrode during the cycle, alleviate the electrochemical-mechanical coupling failure problem of silicon-based materials, and extend the service life of the silicon electrode.

Claims

1. A silicon negative electrode supramolecular binder, characterized in that: The invention is prepared from the following raw materials: a polyacrylamide derivative, a water-soluble polymer containing -COOH and -OH, an inorganic iron salt, hydroxylated silicon particles, a conductive agent and water.

2. The silicon negative electrode supramolecular binder according to claim 1, characterized in that In the silicon negative electrode supramolecular binder, the mass ratio of the polyacrylamide derivative to the water-soluble polymer containing -COOH and -OH is 1:(4-8); And / or, the ratio of the total mass of the polyacrylamide derivative and the water-soluble polymer containing -COOH and -OH to the mass of the inorganic iron salt is (100-500):1; And / or, the ratio of the mass of the hydroxylated silicon particles, the total mass of the polyacrylamide derivative, the water-soluble polymer containing -COOH and -OH and the inorganic iron salt, and the mass of the conductive agent is (6-9):(1-4):

1.

3. The silicon negative electrode supramolecular binder according to claim 1 or 2, characterized in that The polyacrylamide derivative is selected from at least one of anionic polyacrylamide, cationic polyacrylamide, and nonionic polyacrylamide; And / or, the water-soluble polymer containing -COOH and -OH is selected from at least one of sodium alginate, carboxymethyl cellulose, carrageenan, lignin, and hyaluronic acid; And / or, the inorganic iron salt is selected from at least one of ferric sulfate, ferric chloride, and ferric nitrate; And / or, the conductive agent is selected from at least one of acetylene black, carbon fiber, carbon nanotube, and conductive carbon black; And / or, the particle size of the hydroxylated silicon particles is 30 nm-10 μm.

4. The method for preparing the silicon negative electrode supramolecular binder according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Dissolving a polyacrylamide derivative, a water-soluble polymer containing -COOH and -OH, and an inorganic iron salt in water, respectively, to obtain solution A, solution B, and solution C; S2, adding the solution B and solution C dropwise to the solution A in sequence to obtain a supramolecular system D; S3, the hydroxylated silicon particles and the conductive agent are first mixed by ball milling, and then mixed with the supramolecular system D by ultrasonication and ball milling to obtain the silicon negative electrode supramolecular binder.

5. The preparation method according to claim 4, characterized in that In step S3, the temperature of the ultrasound is 25-80°C and the time is 0.5-6h; And / or, the ball milling time is selected from 0.5-6h.

6. A silicon negative electrode plate, characterized in that: The silicon negative electrode supramolecular binder is prepared from the following raw materials: a current collector and the silicon negative electrode supramolecular binder according to any one of claims 1 to 3.

7. The silicon negative electrode plate according to claim 6, characterized in that: The silicon negative electrode plate is prepared by a method comprising the following steps: The silicon negative electrode supramolecular binder is coated on a current collector and solidified to obtain the silicon negative electrode plate.

8. The silicon negative electrode plate according to claim 7, characterized in that: The curing temperature is 50-150° C. and the curing time is 5-30 hours.

9. The silicon negative electrode sheet according to any one of claims 6 to 8, characterized in that: The active material loading of the silicon negative electrode plate is 0.3-5.0 mg / cm 2 .

10. A lithium ion battery, characterized in that: Including the silicon negative electrode sheet as described in any one of claims 6-9.

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