Graphene composite lithium ion battery negative electrode material and preparation method thereof

Abstract

The application discloses a kind of graphene composite lithium ion battery negative material and preparation method thereof, belong to battery processing technical field, for solving the technical problems that the cycle stability and conductivity of graphene composite lithium ion battery negative material in prior art need to be further improved, specifically including the following raw materials by portion: 80-100 parts composite aerogel, 2-5 parts conductive agent and 2-5 modified binder;The application is that composite aerogel, conductive agent and modified binder are prepared by grinding to obtain mixed slurry, the mixed slurry is coated on aluminum foil with doctor blade, is scraped flat, is dried, obtains negative material, not only improves the cycle stability and conductivity of graphene composite lithium ion battery negative material, but also improves its charge specific capacity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery processing, in particular to a graphene composite lithium ion battery negative electrode material and a preparation method thereof. BACKGROUND

[0002] In recent years, with the increasing demand for lithium ion batteries in the fields of electric vehicles, portable electronic devices and large-scale energy storage, the research on high-performance negative electrode materials has become the key to improving the rate performance and cycle stability of the batteries.

[0003] Graphene, as a two-dimensional carbon nanomaterial, is widely studied for modification of lithium ion battery negative electrode materials due to its excellent electrical conductivity, high specific surface area and good mechanical properties. By compounding graphene with active substances such as silicon-based, tin-based and transition metal oxides, the problem of low theoretical specific capacity of traditional negative electrode materials can be effectively alleviated. At the same time, the use of graphene's conductive network can accelerate electron transmission and inhibit the volume expansion of active substances during charging and discharging. Currently, the research on graphene composite negative electrode materials has gradually moved from the laboratory stage to industrial application, and various modification strategies such as three-dimensional porous structure, surface functionalization modification and hetero-element doping have been derived to further optimize the electrochemical performance of the materials.

[0004] However, the traditional graphene composite lithium ion battery negative electrode material still has some shortcomings. In the prior art, the lithium storage capacity of the graphene negative electrode material itself is poor, resulting in insufficient specific capacity of the prepared lithium ion battery. In order to improve the capacity of the battery, graphene is often combined with other active substances that can improve the capacity of the battery.

[0005] However, the interface bonding strength between graphene and active substances is insufficient, which leads to the easy detachment of active substances from the conductive network during long-term cycling, resulting in rapid capacity decay. In addition, the agglomeration tendency of graphene further reduces the electrochemical performance of the battery. The volume expansion of the added active materials such as nano-silicon particles during charging and discharging causes the destruction of the electrode structure, further leading to the lack of stable electron transport channels between graphene and active substances, resulting in increased charge transfer impedance and limited rate performance. SUMMARY

[0006] The present application relates to the technical field of battery processing, in particular to a graphene composite lithium ion battery negative electrode material and a preparation method thereof.

[0007] The purpose of the present application can be achieved by the following technical solution: a graphene composite lithium ion battery negative electrode material, comprising the following raw materials in parts by weight: 80-100 parts of composite aerogel, 2-5 parts of conductive agent and 2-5 parts of modified binder.

[0008] The composite aerogel is prepared by the following steps:

[0009] A1, the nano-silicon particles, deionized water, ethanol and gamma-glycidyloxypropyltrimethoxysilane are placed in a reaction kettle, heated to 50-60 DEG C, and the epoxy-modified nano-silicon is obtained after treatment;

[0010] The preparation reaction principle of the epoxy-modified nano-silicon is:

[0011] During the reaction, in ethanol and deionized water, the ethoxy group of gamma-glycidyloxypropyltrimethoxysilane is hydrolyzed to form silanol, and the silanol and the silicon hydroxyl group on the surface of the nano-silicon particles form a stable Si-O-Si covalent bond through dehydration condensation, and a terminal epoxy group is introduced, to obtain the epoxy-modified nano-silicon.

[0012] A2, the epoxy-modified nano-silicon and N,N-dimethylformamide are placed in a reaction kettle, ultrasonic dispersion is carried out for 15-30 min, the modified graphene hydrogel is impregnated, zinc chloride is added, and the temperature is raised to 50-60 DEG C, and the reaction is kept for 4-6 h, and vacuum drying is carried out for 1-2 h, and the modified aerogel precursor is obtained after treatment;

[0013] The preparation reaction principle of the composite aerogel precursor is:

[0014] During the reaction, the three-dimensional porous structure of the modified graphene hydrogel adsorbs the epoxy-modified nano-silicon through capillary action, realizing uniform loading of the nano-silicon between the graphene layers, and under the catalysis of the Lewis acid zinc chloride, the amino group of dopamine in the modified graphene hydrogel reacts with the epoxy group in the epoxy-modified nano-silicon to form a covalent bond, and the modified aerogel precursor is obtained.

[0015] A3, the composite aerogel precursor is placed in a tube furnace protected by nitrogen atmosphere, heated to 800 DEG C, kept for 0.5-1.5 h, ground, and passed through a 200-mesh sieve, to obtain the composite aerogel.

[0016] The preparation reaction principle of the composite aerogel is:

[0017] During the reaction, at high temperature, the graphene oxide in the hydrogel is further reduced to redox graphene, the carbon skeleton is rearranged through graphitization to form an sp2 hybrid carbon network, the conductivity is significantly improved, and the polydopamine is decomposed at high temperature to form amorphous carbon and nitrogen-doped carbon, and the nitrogen atoms are embedded in the carbon skeleton in the form of pyridine nitrogen and pyrrole nitrogen, to obtain the composite aerogel.

[0018] Further, in step A1, the ratio of the amounts of the nano-silicon particles, deionized water, ethanol and γ-glycidoxypropyltrimethoxysilane is 3-5 g:5-10 mL:50-100 mL:1-1.5 g, and the post-treatment step comprises: after the reaction is completed, the reaction solution is cooled to room temperature, filtered, the filter cake is washed with deionized water and ethanol for 2-3 times, and then transferred to an oven with a temperature of 60-70°C for drying until the weight is constant to obtain the epoxy-modified nano-silicon;

[0019] Further, in step A2, the ratio of the amounts of the epoxy-modified nano-silicon, N,N-dimethylformamide and zinc chloride is 2-4 g:100-150 mL:0.5-1 g, the impregnation ratio is 1:30-35, the vacuum drying step comprises: transferring the reaction solution to a vacuum drying box with a temperature of 70-80°C, and drying for 1-2 h at a vacuum degree of 0-0.2 MPa, and the post-treatment step comprises: after the reaction is completed, the product is taken out and washed with deionized water for 2-3 times to obtain the graphene hydrogel precursor; in step A3, the heating rate is 5-10°C / min.

[0020] Further, the modified graphene hydrogel is prepared by the following steps:

[0021] B1, the graphite is placed in a reaction kettle, ice-bathed to 0-5°C, and then concentrated sulfuric acid, deionized water and potassium permanganate are slowly added in sequence under stirring, after stirring for 5-10 min, the temperature is raised to 35-45°C, and then the reaction is kept for 1-2 h, deionized water is added, the temperature is raised to 90-100°C, and then the reaction is kept for 5-15 min, and the post-treatment is performed to obtain the graphene oxide;

[0022] The preparation principle of the graphene oxide is as follows:

[0023] During the reaction, the concentrated sulfuric acid acts as a strong acid and an intercalation agent, and is embedded between the graphite layers through intermolecular forces and electrostatic attraction to form a first-order sulfuric acid-graphite intercalation compound, expand the layer spacing, and the potassium permanganate acts as a strong oxidizing agent to further damage the conjugated π bond of the graphite, convert the carbon atoms from sp² hybridization to sp³ hybridization, introduce hydroxyl, carboxyl and other oxygen-containing functional groups between the graphite layers, high temperature accelerates the oxidation reaction to further stabilize the oxygen-containing functional groups between the graphite layers, and the heat generated by the reaction of sulfuric acid with water promotes the diffusion and removal of the sulfuric acid between the graphene layers, the hydrogen peroxide in the post-treatment reacts with the residual potassium permanganate to generate oxygen and water, and the oxidation reaction is terminated, and finally the graphene oxide is obtained.

[0024] B2, the graphene oxide and deionized water are placed in a single-neck flask, ultrasonic dispersion is performed for 1-2 h, the dopamine hydrochloride solution is added, the ammonia solution is added to adjust the pH to 8.5-9, the temperature is raised to 60-70°C, and then the reaction is kept for 10-12 h to obtain the modified graphene hydrogel.

[0025] The reaction principle of the preparation of the modified graphene hydrogel is as follows:

[0026] During the reaction, the cavitation effect of the ultrasonic wave destroys the van der Waals force between the graphene oxide layers, so that the graphene oxide is uniformly dispersed in water and can fully contact with the dopamine hydrochloride, and the ammonia water provides an alkaline condition, so that the ortho-phenol group in the dopamine hydrochloride molecule is oxidized into a quinone structure, and then an intramolecular or intermolecular cross-linking reaction occurs, and self-polymerization occurs, and meanwhile, under the high-temperature condition, the esterification reaction occurs between the ortho-phenol group of dopamine and the carboxyl group on the surface of the graphene oxide, and a covalent bond is formed, that is, the cross-linking of dopamine connects the graphene oxide layers to form a three-dimensional network structure, and meanwhile, the GO layers also form a layered structure through the π-π stacking effect in the self-assembly process, and a modified graphene hydrogel with a stable three-dimensional network structure is further obtained.

[0027] Further, in step B1, the amount ratio of the graphite, concentrated sulfuric acid, deionized water, potassium permanganate and deionized water is 1-2g:70-80mL:10-15mL:3-4g:100-120mL, and the post-treatment step comprises: after the reaction is completed, the reaction solution is cooled to room temperature, the reaction solution is added into 200-250mL of deionized water, 5-10mL of 20-30wt% hydrogen peroxide aqueous solution is added dropwise, the filter cake is washed with deionized water for 2-3 times, and then the filter cake is transferred to a vacuum freeze-drying box with a temperature of-60℃, the vacuum degree is 0-0.1MPa, and the freeze-drying is performed until the constant weight is obtained, so as to obtain the graphene oxide;

[0028] Further, in step B2, the amount ratio of the graphene oxide, deionized water and dopamine hydrochloride solution is 2-4g:1-2L:1-2L, the dopamine hydrochloride solution is composed of dopamine hydrochloride and Tris buffer solution with an amount ratio of 2-4g:1-2L, and the concentration of the ammonia water solution is 20-30wt%.

[0029] Further, the modified binder is prepared by the following steps:

[0030] C1, polyethylene glycol, 1,4-butanediol, dibutyltin dilaurate and N,N-dimethylformamide are placed in a reaction kettle protected by a nitrogen atmosphere, stirred uniformly, a calculated amount of 4,4'-diisocyanato-3,3'-dimethyldiphenylmethane is added into the reaction kettle, the temperature is raised to 90-100℃, and the reaction is kept for 2-4h, and then the modified binder precursor is obtained through post-treatment;

[0031] C2, the modified binder precursor, 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt, stannous octoate and N,N-dimethylformamide are placed in a reaction kettle, the temperature is raised to 80-100℃, the reaction is kept for 4-8h, and then the modified binder is obtained through post-treatment.

[0032] The preparation reaction formula of the modified adhesive is:

[0033]

[0034] The preparation reaction principle of the modified adhesive is:

[0035] In the reaction process, the isocyanate groups in 4,4'-diisocyanato-3,3'-dimethyl diphenyl methane are added to the hydroxyl groups at both ends of 1,4-butanediol and 1,4-butanediol to form a urethane bond, forming a hydroxyl-terminated prepolymer, obtaining a modified adhesive precursor, and under the action of high temperature and a catalyst, the ester groups of the modified adhesive precursor and the amino groups of 2-[(2-aminoethyl)amino] ethanesulfonic acid sodium salt are subjected to an ester exchange reaction to obtain the modified adhesive.

[0036] Further, in step C1, the amount of dibutyltin dilaurate and N,N-dimethylformamide is 0.5-1g:200-300mL, in the reaction, the amount of 4,4'-diisocyanato-3,3'-dimethyl diphenyl methane added is 0.35 times the molar amount of hydroxyl groups in the system, and the weight ratio of polyethylene glycol and 1,4-butanediol is 1-2:2-4; in step C2, the amount of the modified adhesive precursor, 2-[(2-aminoethyl)amino] ethanesulfonic acid sodium salt, stannous octoate and N,N-dimethylformamide is 2-4g:1-2g:0.2-0.5g:150-200mL, and the post-treatment step includes: after the reaction is completed, the temperature is raised to 150-160℃, and the pressure is reduced to distill until no liquid is produced, to obtain the modified adhesive.

[0037] The application further provides a preparation method of the graphene composite lithium ion battery negative electrode material.

[0038] S1, under a nitrogen atmosphere, the composite aerogel, the conductive agent and the modified adhesive are placed in a mortar and ground uniformly to obtain a mixed slurry;

[0039] S2, under a nitrogen atmosphere, the mixed slurry is coated on an aluminum foil sheet with a doctor blade, is scraped flat, and is dried to obtain the negative electrode material.

[0040] Further, in step S1, the conductive agent is acetylene black; in step S2, the coating thickness is 10-50μm, and the drying temperature is 80-100℃, and the drying time is 6-10h.

[0041] The application has the following beneficial effects:

[0042] 1. The present application is prepared by dopamine self-polymerization and graphene oxide to prepare modified graphene hydrogel, and the modified graphene hydrogel is further combined with epoxy modified nano silicon to form a composite aerogel, and a modified binder modified with sulfonic acid groups is prepared by nucleophilic reaction and ester exchange reaction, the composite aerogel, the conductive agent and the modified binder are prepared into a mixed slurry by grinding, the mixed slurry is coated on the aluminum foil by a doctor blade, and the aluminum foil is dried to obtain a negative electrode material; the present application prepares graphene oxide, controls dopamine to occur self-polymerization reaction, and generates modified graphene hydrogel with three-dimensional network structure by covalent bonding with graphene oxide; graphene itself has excellent conductivity, but there is strong interaction between layers, which is easy to agglomerate or stack, and is difficult to disperse uniformly in the composite material; the self-polymerization of dopamine hydrochloride and graphene oxide can form a three-dimensional network structure of hydrogel, promote the uniform dispersion of graphene in the negative electrode material, avoid the occurrence of agglomeration phenomenon, and the dopamine modified graphene hydrogel has higher chemical stability and mechanical strength, can maintain the integrity of the structure during the charging and discharging process of the battery, prolong the service life of the battery, and the surface of the dopamine modified graphene hydrogel provides more active sites, which can be chemically bonded with subsequent epoxy modified nano silicon, improve the interface stability of the negative electrode material, improve the cycle stability and rate performance of the lithium battery, and the active sites can adsorb more lithium ions during the operation of the lithium battery, increase the capacity of the lithium battery.

[0043] 2. The present application is prepared by epoxy modification of nano silicon particles, and the modified graphene hydrogel is immersed in a reaction solution composed of epoxy modified nano silicon and Lewis acid, and nano silicon particles are generated in the hydrogel by nucleophilic reaction, and the composite aerogel is obtained by calcination; the epoxy group on the surface of the epoxy modified nano silicon and the amino group on the dopamine coated graphene hydrogel occur nucleophilic ring-opening reaction under the catalysis of Lewis acid to generate stable C-N bond; this chemical bonding significantly enhances the binding force between nano silicon and graphene, effectively inhibits the shedding problem caused by the volume expansion of silicon during charging and discharging, improves the cycle stability of the lithium battery, and uniformly disperses the nano silicon in the graphene network to increase the active sites and improve the charging specific capacity of the lithium ion battery; in the composite aerogel, the graphene layers are connected to form a continuous three-dimensional conductive network, providing a fast transmission channel for electrons; the addition of nano silicon is chemically bonded with graphene to ensure efficient migration of electrons in the material, reduce the interface contact resistance, make the transmission of electrons at the interface more efficient, and further improve the conductivity of the lithium ion battery.

[0044] 3、The application is by taking 4,4'-diisocyanate-3,3'-dimethyl diphenyl methane as a hard segment, taking polyethylene glycol as a soft segment, and taking 1,4-butanediol as a chain extender to obtain a modified adhesive precursor, and further preparing a modified adhesive modified with a sulfonic acid group through an ester exchange reaction, the soft and hard segment design of the polyurethane structure endows the adhesive with excellent mechanical strength and elasticity, can effectively buffer the volume expansion of the negative electrode material in the lithiation / delithiation process, reduce electrode pulverization and crack formation, thereby improving the conductivity, rate performance and charge specific capacity of the lithium battery, the sulfonic acid group has strong polarity and hydrophilicity, can form strong adhesion with the graphene, nanosilicon particles and polydopamine surface in the composite aerogel through hydrogen bonding and ionic interaction, improve the bonding strength of the internal components of the aerogel, prevent the aggregation or shedding of the nanoparticles in the cycle process, maintain the integrity of the three-dimensional porous structure, improve the structural stability of the negative electrode material, and further improve the cycle stability of the lithium battery prepared from the negative electrode material. DETAILED DESCRIPTION

[0045] The technical solutions of the application will be described clearly and completely in combination with the embodiments below. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0046] The graphite used in the application is purchased from Qingdao Weijie Graphite Co., Ltd., and the product name is flake graphite, the crystal particle size is 0.05-1.5 mm;

[0047] The polyethylene glycol used in the application is purchased from Nanjing Xinhua Original Chemical Co., Ltd., the molecular weight is 4000, and the execution standard is ISO9001;

[0048] The nanosilicon particles used in the application are purchased from Hebei Leijiang New Material Technology Co., Ltd., the particle size is 200 mesh, and the brand is SF90;

[0049] The positive electrode sheet used in the application is purchased from Dongguan Kelude New Energy Technology Co., Ltd., the product brand is Kelude, the product name is lithium iron phosphate LFP electrode sheet, and the product standard is international;

[0050] The electrolyte used in the application is purchased from Shandong Aite Chemical Co., Ltd., the product name is ethylene carbonate, the execution standard is national standard, and the brand is Aite;

[0051] The gasket used in the application is purchased from Langfang Zhongyang Technology Co., Ltd., and the model is a graphite sealing ring;

[0052] The spring sheet used in the application is purchased from Dongguan Hujie Precision Electronic Technology Co., Ltd., and the specification is 30x20.91mm.

[0053] Example 1

[0054] The embodiment provides a preparation method of modified graphene hydrogel used for composite aerogel for graphene composite lithium ion battery negative material, and comprises the following steps:

[0055] Step I, preparing graphene oxide

[0056] Weighing: 10g of graphite is placed in a reaction kettle, and ice bath is used to cool to 0 DEG C; under the condition of stirring, 700mL of concentrated sulfuric acid, 100mL of deionized water and 30g of potassium permanganate are slowly added in sequence; after stirring for 5min, the temperature is increased to 35 DEG C, and the reaction is kept for 1h; 1000mL of deionized water is added, the temperature is increased to 90 DEG C, and the reaction is kept for 5min; after the reaction is completed, the reaction solution is added into 2000mL of deionized water, 50mL of 20wt% hydrogen peroxide aqueous solution is added dropwise, and the filter cake is washed with deionized water for 2 times; then the filter cake is transferred to a vacuum freeze-drying box with a temperature of-60 DEG C; the vacuum degree is 0MPa; freeze-drying is performed until the weight is constant; and graphene oxide is obtained.

[0057] Step II, preparing modified graphene hydrogel

[0058] Weighing: 20g of dopamine hydrochloride and 10L of deionized water are uniformly mixed to obtain a dopamine hydrochloride solution, which is prepared;

[0059] Weighing: 20g of graphene oxide and 10L of deionized water are ultrasonically dispersed for 1h; 10L of the dopamine hydrochloride solution is added; 20wt% ammonia water solution is added to adjust the pH to 8.5; the temperature is increased to 60 DEG C; and the reaction is kept for 10h; and the modified graphene hydrogel is obtained.

[0060] Example 2

[0061] The embodiment provides a preparation method of modified graphene hydrogel used for composite aerogel for graphene composite lithium ion battery negative material, and comprises the following steps:

[0062] Step I, preparing graphene oxide

[0063] Weighing: graphite 15 g is placed in a reaction kettle, ice bath to 3 ℃, under stirring, concentrated sulfuric acid 750 mL, deionized water 130 mL and potassium permanganate 35 g are slowly added in turn, after stirring for 7 min, the temperature is raised to 40 ℃, and the reaction is kept for 1.5 h, then deionized water 1100 mL is added, the temperature is raised to 95 ℃, and the reaction is kept for 10 min, after the reaction is completed, the reaction liquid is cooled to room temperature, then the reaction liquid is added into 2200 mL of deionized water, 70 mL of 25 wt% hydrogen peroxide aqueous solution is added dropwise, filtration is performed, the filter cake is washed with deionized water for 3 times, and then the filter cake is transferred to a vacuum freeze-drying box with a temperature of -60 ℃, the vacuum degree is 0.05 MPa, and freeze-drying is performed until the weight is constant, to obtain graphene oxide.

[0064] Step II, preparation of modified graphene hydrogel

[0065] Weighing: dopamine hydrochloride 30 g and deionized water 15 L are uniformly mixed to obtain a dopamine hydrochloride solution, which is prepared for use.

[0066] Weighing: graphene oxide 30 g and deionized water 15 L are ultrasonically dispersed for 1.5 h, the dopamine hydrochloride solution 15 L is added, 25 wt% ammonia water solution is added to adjust the pH to 8.7, the temperature is raised to 65 ℃, and the reaction is kept for 11 h, to obtain the modified graphene hydrogel.

[0067] Example 3

[0068] The embodiment provides a preparation method of modified graphene hydrogel for graphene composite lithium ion battery negative electrode material composite aerogel, which comprises the following steps:

[0069] Step I, preparation of graphene oxide

[0070] Weighing: graphite 20 g is placed in a reaction kettle, ice bath to 5 ℃, under stirring, concentrated sulfuric acid 800 mL, deionized water 150 mL and potassium permanganate 40 g are slowly added in turn, after stirring for 10 min, the temperature is raised to 45 ℃, and the reaction is kept for 2 h, then deionized water 1200 mL is added, the temperature is raised to 100 ℃, and the reaction is kept for 15 min, after the reaction is completed, the reaction liquid is cooled to room temperature, then the reaction liquid is added into 2500 mL of deionized water, 100 mL of 30 wt% hydrogen peroxide aqueous solution is added dropwise, filtration is performed, the filter cake is washed with deionized water for 3 times, and then the filter cake is transferred to a vacuum freeze-drying box with a temperature of -60 ℃, the vacuum degree is 0.1 MPa, and freeze-drying is performed until the weight is constant, to obtain graphene oxide.

[0071] Step II, preparation of modified graphene hydrogel

[0072] Weighing: dopamine hydrochloride 40 g and deionized water 20 L are uniformly mixed to obtain a dopamine hydrochloride solution, which is prepared for use.

[0073] Take: graphene oxide 40 g and deionized water 20 L ultrasonic dispersion 2 h, add dopamine hydrochloride solution 20 L, add 30 wt% ammonia solution to adjust pH = 9, heat to 70℃, keep the reaction for 12 h, get modified graphene hydrogel.

[0074] Example 4

[0075] The embodiment provides a preparation method of a composite aerogel for graphene composite lithium ion battery negative electrode material, comprising the following steps:

[0076] Step 1, preparation of epoxy modified nano silicon

[0077] Take: nano silicon particles 300 g, deionized water 50 mL, ethanol 500 mL and γ-glycidoxypropyltrimethoxysilane 10 g are placed in a reaction kettle, heated to 50℃, after the reaction is completed, the reaction liquid is cooled to room temperature, filtered, the filter cake is washed with deionized water and ethanol for 2 times, transferred to an oven with a temperature of 60℃, dried to constant weight, and the epoxy modified nano silicon is obtained.

[0078] Step 2, preparation of composite aerogel precursor

[0079] Take: epoxy modified nano silicon 20 g and N,N-dimethylformamide 1000 mL are placed in a reaction kettle, ultrasonic dispersion is carried out for 150 min, the modified graphene hydrogel prepared in example 1 is impregnated, the impregnation ratio is 1:30, zinc chloride 5 g is added, heated to 50℃, and kept for 4 h, the reaction liquid is transferred to a vacuum drying oven with a temperature of 70℃, dried for 1 h, the vacuum degree is 0 MPa, after the reaction is completed, the product is taken out and washed with deionized water for 2 times, and the modified composite aerogel precursor is obtained.

[0080] Step 3, preparation of composite aerogel

[0081] Take: the composite aerogel precursor is placed in a tube furnace protected by nitrogen atmosphere, heated to 800℃ at a rate of 5℃ / min, kept for 0.5 h, ground, and screened through a 200 mesh sieve, and the composite aerogel is obtained.

[0082] Example 5

[0083] The embodiment provides a preparation method of a composite aerogel for graphene composite lithium ion battery negative electrode material, comprising the following steps:

[0084] Step 1, preparation of epoxy modified nano silicon

[0085] Take: nano-silicon particles 40 g, deionized water 70 mL, ethanol 700 mL and γ-glycidyl ether oxygen propyl trimethoxysilane 12 g are placed in the reaction kettle, and the temperature is raised to 55℃. After the reaction is completed, the reaction liquid is cooled to room temperature, filtered, and the filter cake is washed with deionized water and ethanol for 3 times, and then transferred to an oven with a temperature of 65℃. Dry to constant weight to obtain epoxy-modified nano-silicon.

[0086] Step 2, preparation of composite aerogel precursor

[0087] Take: epoxy-modified nano-silicon 30 g and N,N-dimethylformamide 1200 mL are placed in the reaction kettle, ultrasonic dispersion for 20 min, then modified graphene hydrogel prepared in Example 2 is impregnated, the impregnation ratio is 1:32, 7 g of zinc chloride is added, and the temperature is raised to 55℃. Keep the reaction for 5h, then transfer the reaction liquid to a vacuum drying oven with a temperature of 75℃. Dry for 1.5h, the vacuum degree is 0.1MPa. After the reaction is completed, the product is taken out and washed with deionized water for 3 times to obtain a modified composite aerogel precursor.

[0088] Step 3, preparation of composite aerogel

[0089] Take: composite aerogel precursor is placed in a tube furnace protected by nitrogen atmosphere, and the temperature is raised to 800℃ at a rate of 7℃ / min, and kept for 1h. Grind and pass through a 200 mesh sieve to obtain a composite aerogel.

[0090] Example 6

[0091] The present embodiment provides a method for preparing a composite aerogel for graphene composite lithium ion battery negative electrode material, comprising the following steps:

[0092] Step 1, preparation of epoxy-modified nano-silicon

[0093] Take: nano-silicon particles 40 g, deionized water 70 mL, ethanol 700 mL and γ-glycidyl ether oxygen propyl trimethoxysilane 12 g are placed in the reaction kettle, and the temperature is raised to 55℃. After the reaction is completed, the reaction liquid is cooled to room temperature, filtered, and the filter cake is washed with deionized water and ethanol for 3 times, and then transferred to an oven with a temperature of 65℃. Dry to constant weight to obtain epoxy-modified nano-silicon.

[0094] Step 2, preparation of composite aerogel precursor

[0095] Take: epoxy modified nanometer silicon 40 g and N, N-dimethylformamide 1500 mL in the reaction kettle, ultrasonic dispersion for 30 min, add the modified graphene hydrogel prepared in example 3 to impregnate, the impregnation ratio is 1:35, add zinc chloride 10 g, heating to 60℃, keep the reaction for 6 h, the reaction liquid is transferred to the vacuum drying oven with the temperature of 80℃, drying for 2 h, the vacuum degree is 0.2 MPa, after the reaction is completed, the product is taken out and washed with deionized water for 3 times to obtain the modified aerogel precursor.

[0096] Step 3, preparation of composite aerogel

[0097] Take: composite aerogel precursor is placed in a tube furnace protected by nitrogen atmosphere, heated to 800℃ at a rate of 10℃ / min, and kept for 1.5 h, ground and sieved through a 200 mesh sieve to obtain the composite aerogel.

[0098] Example 7

[0099] The present embodiment provides a preparation method of a modified binder for graphene composite lithium ion battery negative electrode material, comprising the following steps:

[0100] Step 1, preparation of modified binder precursor

[0101] Take: polyethylene glycol 10 g, 1, 4-butanediol 20 g, dibutyltin dilaurate 5 g and N, N-dimethylformamide 2000 mL are placed in a reaction kettle protected by nitrogen atmosphere, stirred uniformly, 0.35 times of 4, 4'-diisocyanate-3, 3'-dimethyl diphenyl methane of the molar amount of hydroxyl in the reaction kettle is added, heated to 90℃, and kept for 2 h, and then treated to obtain the modified binder precursor.

[0102] Step 2, preparation of modified binder

[0103] Take: modified binder precursor 20 g, 2-[(2-aminoethyl) amino] ethanesulfonic acid sodium salt 10 g, stannous octoate 2 g and N, N-dimethylformamide 1500 mL are placed in a reaction kettle, heated to 80℃, kept for 4 h, after the reaction is completed, heated to 150℃, distilled under reduced pressure until no liquid is collected, to obtain the modified binder.

[0104] Example 8

[0105] The present embodiment provides a preparation method of a modified binder for graphene composite lithium ion battery negative electrode material, comprising the following steps:

[0106] Step 1, preparation of modified binder precursor

[0107] Take: polyethylene glycol 15 g, 1,4-butanediol 30 g, dibutyltin dilaurate 7 g and N, N-dimethylformamide 2500 mL is placed in the reaction kettle under the protection of nitrogen atmosphere, stirring, adding 0.35 times of 4,4'-diisocyanato-3,3'-dimethyl diphenyl methane in the system of hydroxyl molar amount to the reaction kettle, heating to 95℃, keeping for 3h, post-processing to obtain modified adhesive precursor.

[0108] Step 2, preparation of modified adhesive

[0109] Take: modified adhesive precursor 30 g, 2-[(2-aminoethyl) amino] ethanesulfonic acid sodium salt 15 g, stannous octoate 3.5 g and N, N-dimethylformamide 1700 mL is placed in the reaction kettle, heating to 90℃, keeping for 6h, after the reaction is completed, heating to 155℃, distillation under reduced pressure until no liquid is produced, to obtain the modified adhesive.

[0110] Example 9

[0111] The embodiment provides a preparation method of a modified adhesive for graphene composite lithium ion battery negative electrode material, comprising the following steps:

[0112] Step 1, preparation of modified adhesive precursor

[0113] Take: polyethylene glycol 20 g, 1,4-butanediol 40 g, dibutyltin dilaurate 10 g and N, N-dimethylformamide 3000 mL is placed in the reaction kettle under the protection of nitrogen atmosphere, stirring, adding 0.35 times of 4,4'-diisocyanato-3,3'-dimethyl diphenyl methane in the system of hydroxyl molar amount to the reaction kettle, heating to 100℃, keeping for 4h, post-processing to obtain modified adhesive precursor.

[0114] Step 2, preparation of modified adhesive

[0115] Take: modified adhesive precursor 40 g, 2-[(2-aminoethyl) amino] ethanesulfonic acid sodium salt 20 g, stannous octoate 5 g and N, N-dimethylformamide 2000 mL is placed in the reaction kettle, heating to 100℃, keeping for 8h, after the reaction is completed, heating to 160℃, distillation under reduced pressure until no liquid is produced, to obtain the modified adhesive.

[0116] Example 10

[0117] The embodiment provides a preparation method of a graphene composite lithium ion battery negative electrode material, comprising the following steps:

[0118] Step 1, preparation of mixed slurry

[0119] The mixed slurry was prepared by placing 80 parts of the composite aerogel prepared in Example 4, 2 parts of acetylene black and 2 parts of the modified binder prepared in Example 7 in a mortar under a nitrogen atmosphere and grinding uniformly.

[0120] Step II, preparation of the negative electrode material

[0121] The mixed slurry was coated on an aluminum foil with a doctor blade under a nitrogen atmosphere, leveled, and the coating thickness was 10 μm. The coated aluminum foil was placed in an oven at 80°C and dried for 6 h to obtain the negative electrode material.

[0122] Example 11

[0123] The present example provides a method for preparing a graphene composite negative electrode material for lithium ion batteries, comprising the following steps:

[0124] Step I, preparation of the mixed slurry

[0125] The mixed slurry was prepared by placing 90 parts of the composite aerogel prepared in Example 5, 3.5 parts of acetylene black and 3.5 parts of the modified binder prepared in Example 8 in a mortar under a nitrogen atmosphere and grinding uniformly.

[0126] Step II, preparation of the negative electrode material

[0127] The mixed slurry was coated on an aluminum foil with a doctor blade under a nitrogen atmosphere, leveled, and the coating thickness was 25 μm. The coated aluminum foil was placed in an oven at 90°C and dried for 8 h to obtain the negative electrode material.

[0128] Example 12

[0129] The present example provides a method for preparing a graphene composite negative electrode material for lithium ion batteries, comprising the following steps:

[0130] Step I, preparation of the mixed slurry

[0131] The mixed slurry was prepared by placing 100 parts of the composite aerogel prepared in Example 6, 5 parts of acetylene black and 5 parts of the modified binder prepared in Example 9 in a mortar under a nitrogen atmosphere and grinding uniformly.

[0132] Step II, preparation of the negative electrode material

[0133] The mixed slurry was coated on an aluminum foil with a doctor blade under a nitrogen atmosphere, leveled, and the coating thickness was 50 μm. The coated aluminum foil was placed in an oven at 100°C and dried for 10 h to obtain the negative electrode material.

[0134] Comparative Example 1

[0135] The difference between the present comparative example and Example 12 is that dopamine is not used in the preparation of the modified graphene hydrogel in Step II.

[0136] Comparative Example 2

[0137] The difference between this comparative example and Example 12 is that, in the preparation of the composite aerogel precursor in step ii, the epoxy-modified nanosilicon is replaced with an equivalent amount of nanosilicon particles.

[0138] Comparative Example 3

[0139] The difference between this comparative example and Example 12 is that, in the preparation of the mixed slurry in step i, the binder is not used.

[0140] Performance testing:

[0141] The graphene composite lithium-ion battery negative electrode materials prepared in Examples 10-12 and Comparative Examples 1-3 were prepared into test samples according to GB / T 44027.1-2024 “Determination methods for carbon materials Part 1: Determination of initial specific capacity, initial coulombic efficiency, and capacity retention rate at different rates”.

[0142] The rate performance and charge specific capacity of the test samples prepared from the negative electrode materials prepared in Examples 10-12 and Comparative Examples 1-3 were tested according to standard SJ / T 11793-2022 “Electrochemical performance test method for lithium-ion battery electrode materials”.

[0143] The conductivity of the test samples prepared from the negative electrode materials prepared in Examples 10-12 and Comparative Examples 1-3 was tested according to standard SJ / T 11792-2022 “Conductivity test method for lithium-ion battery electrode materials”.

[0144] The method for testing the cycle performance of the test samples prepared from the negative electrode materials is as follows: charge to 4.1 V at 0.5C, then constant voltage charge to 4.1 V with a cutoff current of 0.02C, discharge to 3.0 V at 0.5C, and use the discharge capacity as the cycle discharge capacity for comparison. The highest discharge capacity in the first three cycles is set as 100%. The specific test results are shown in Table 1.

[0145] Table 1. Test results of samples

[0146]

[0147] Data analysis:

[0148] Analysis of the data in Table 1 shows that the conductivity of the coin lithium battery prepared from the negative electrode material prepared in this experiment is 0.0130 S·cm -1 , the capacity retention rate after 100 cycles is 94.8%, the rate performance is 92.3%, and the charge specific capacity is 362.1 mAh·g -1 .

[0149] Comparative analysis of the table data of Example 12 and Comparative Example 1 shows that the capacity retention rate after 100 cycles, the rate performance and the specific charge capacity of Comparative Example 1 decrease significantly, which indicates that the present application controls the self-polymerization of dopamine by preparing graphene oxide, and generates modified graphene hydrogel with three-dimensional network structure through covalent bonding of dopamine and graphene oxide. Graphene itself has excellent conductivity, but there is strong interaction between layers, which is easy to agglomerate or stack, and difficult to disperse uniformly in the composite material. The self-polymerization of dopamine and graphene oxide forms a three-dimensional network structure of hydrogel through covalent bonding, which promotes the uniform dispersion of graphene in the negative electrode material and avoids the occurrence of agglomeration. Moreover, the dopamine-modified graphene hydrogel has higher chemical stability and mechanical strength, which can maintain the integrity of the structure during the charging and discharging process of the battery, prolong the service life of the battery, and provide more active sites on the surface of the dopamine-modified graphene hydrogel. These active sites can form chemical bonds with subsequent epoxy-modified nanosilicon, improve the interface stability of the negative electrode material, and improve the cycle stability and rate performance of the lithium battery. Moreover, these active sites can adsorb more lithium ions during the operation of the lithium battery, increasing the capacity of the lithium battery.

[0150] Comparative analysis of the table data of Example 12 and Comparative Example 2 shows that the electrical conductivity, capacity retention rate after 100 cycles, rate performance and specific charge capacity of Comparative Example 2 decrease significantly, which indicates that the present application modifies nanosilicon particles by epoxy modification, and then immerses the modified graphene hydrogel in a reaction solution composed of epoxy-modified nanosilicon and Lewis acid to generate nanosilicon particles in the hydrogel through nucleophilic reaction. The composite aerogel is obtained by calcination. The epoxy group on the surface of the epoxy-modified nanosilicon and the amino group on the dopamine-coated graphene hydrogel undergo nucleophilic ring-opening reaction under the catalysis of Lewis acid to generate stable C-N bonds. This chemical bonding significantly enhances the binding force between nanosilicon and graphene, effectively inhibits the shedding problem caused by the volume expansion of silicon during the charging and discharging process, and improves the cycle stability of the lithium battery. The nanosilicon is uniformly dispersed in the graphene network, increasing the active sites and improving the specific charge capacity of the lithium ion battery. In the composite aerogel, the graphene layers are connected to form a continuous three-dimensional conductive network, providing a fast transmission channel for electrons. The addition of nanosilicon ensures the efficient migration of electrons in the material through chemical bonding with graphene, reduces the interface contact resistance, and makes the transmission of electrons at the interface more efficient, further improving the electrical conductivity of the lithium ion battery.

[0151] The table data of comparative example 12 and comparative example 3 shows that the conductivity, cycle 100 capacity retention rate, rate performance and specific charge capacity of comparative example 3 are significantly reduced, which indicates that the modified binder precursor is prepared by taking 4,4'-diisocyanate-3,3'-dimethyl diphenyl methane as the hard segment, taking polyethylene glycol as the soft segment, and taking 1,4-butanediol as the chain extender, and the modified binder modified with sulfonic acid group is prepared by ester exchange reaction, the design of soft and hard segments of polyurethane structure gives the binder excellent mechanical strength and elasticity, which can effectively buffer the volume expansion of negative electrode material during lithiation / delithiation process, reduce electrode pulverization and crack formation, thereby improving the conductivity, rate performance and specific charge capacity of lithium battery, the sulfonic acid group has strong polarity and hydrophilicity, which can form strong adhesion with graphene, nano silicon particles and polydopamine surface in the composite aerogel through hydrogen bond and ionic interaction, improve the bonding strength of the internal components of the aerogel, prevent the aggregation or shedding of nano particles during the cycle process, maintain the integrity of the three-dimensional porous structure, improve the structural stability of the negative electrode material, and further improve the cycle stability of the lithium battery prepared by the negative electrode material.

[0152] The preferred embodiments of the application disclosed above are only used to help explain the application. The preferred embodiments do not describe all the details and limit the application to the specific embodiments. Obviously, many modifications and variations can be made according to the content of the specification. The specification selects and describes these embodiments in order to better explain the principles and practical applications of the application, so that those skilled in the art can well understand and utilize the application. The application is limited only by the claims and their full scope and equivalents.

Claims

1. A graphene composite lithium-ion battery anode material, characterized in that, The raw materials include the following ingredients by weight: 80-100 parts of composite aerogel, 2-5 parts of conductive agent and 2-5 parts of modified adhesive; The composite aerogel is prepared by the following steps: A1, the nano-silicon particles, deionized water, ethanol and γ-glycidyl ether oxygen propyl trimethoxysilane are placed in a reaction kettle, heated to 50-60℃, and the epoxy modified nano-silicon is obtained after treatment; A2, the epoxy modified nano-silicon and N,N-dimethylformamide are placed in a reaction kettle, ultrasonic dispersion for 15-30min, and the modified graphene hydrogel is impregnated, and zinc chloride is added, heated to 50-60℃, and the modified composite aerogel precursor is obtained after 4-6h of incubation and 1-2h of vacuum drying; A3, the composite aerogel precursor is placed in a tube furnace under nitrogen atmosphere protection, heated to 800℃, incubated for 0.5-1.5h, ground, and sieved through a 200 mesh screen to obtain the composite aerogel; The modified graphene hydrogel is prepared by the following steps: B1, the graphite is placed in a reaction kettle, ice bathed to 0-5℃, and under stirring, concentrated sulfuric acid, deionized water and potassium permanganate are slowly added in sequence, stirred for 5-10min, heated to 35-45℃, incubated for 1-2h, deionized water is added, heated to 90-100℃, incubated for 5-15min, and the graphene oxide is obtained after treatment; B2, the graphene oxide and deionized water are placed in a single-neck flask, ultrasonic dispersion for 1-2h, hydrochloric acid dopamine solution is added, ammonia solution is added to adjust pH=8.5-9, heated to 60-70℃, and the modified graphene hydrogel is obtained after 10-12h of incubation; The modified adhesive is prepared by the following steps: C1, the polyethylene glycol, 1,4-butanediol, dibutyltin dilaurate and N,N-dimethylformamide are placed in a reaction kettle under nitrogen atmosphere protection, stirred uniformly, and a calculated amount of 4,4'-diisocyanato-3,3'-dimethyl diphenyl methane is added to the reaction kettle, heated to 90-100℃, incubated for 2-4h, and the modified adhesive precursor is obtained after treatment; C2, the modified adhesive precursor, 2-[(2-aminoethyl)amino] ethanesulfonic acid sodium salt, stannous octoate and N,N-dimethylformamide are placed in a reaction kettle, heated to 80-100℃, incubated for 4-8h, and the modified adhesive is obtained after treatment.

2. The graphene composite lithium ion battery anode material according to claim 1, characterized in that, In step A1, the amount ratio of the nano-silicon particles, deionized water, ethanol and γ-glycidyl ether oxygen propyl trimethoxysilane is 3-5g:5-10mL:50-100mL:1-1.5g; in step A2, the amount ratio of the epoxy modified nano-silicon, N,N-dimethylformamide and zinc chloride is 2-4g:100-150mL:0.5-1g, and the impregnation ratio is 1:30-35; in step A3, the heating rate is 5-10℃ / min.

3. The graphene composite lithium ion battery anode material according to claim 1, characterized in that, In step B1, the graphite, concentrated sulfuric acid, deionized water, potassium permanganate and deionized water are used in a ratio of 1-2g:70-80mL:10-15mL:3-4g:100-120mL; in step B2, the graphene oxide, deionized water and dopamine hydrochloride solution are used in a ratio of 2-4g:1-2L:1-2L, the dopamine hydrochloride solution is composed of dopamine hydrochloride and Tris buffer solution in a ratio of 2-4g:1-2L, and the concentration of the ammonia solution is 20-30wt%.

4. The graphene composite lithium ion battery anode material of claim 1, wherein, In step C1, the dibutyltin dilaurate and N,N-dimethylformamide are used in a ratio of 0.5-1g:200-300mL, in the reaction, the amount of 4,4'-diisocyanato-3,3'-dimethyl diphenyl methane added is 0.35 times the molar amount of hydroxyl groups in the system, and the weight ratio of polyethylene glycol and 1,4-butanediol is 1-2:2-4; in step C2, the modified binder precursor, 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt, stannous octoate and N,N-dimethylformamide are used in a ratio of 2-4g:1-2g:0.2-0.5g:150-200mL.

5. A method of preparing a graphene composite lithium-ion battery anode material as claimed in any one of claims 1 to 4, characterized in that, The method comprises the following steps: S1, under a nitrogen atmosphere, placing the composite aerogel, conductive agent and modified binder in a mortar and grinding them uniformly to obtain a mixed slurry; S2, under a nitrogen atmosphere, coating the mixed slurry on an aluminum foil sheet with a doctor blade, leveling and drying to obtain a negative electrode material.

6. The method for preparing a graphene composite lithium-ion battery anode material according to claim 5, characterized in that, In step S1, the conductive agent is acetylene black; in step S2, the coating thickness is 10-50μm, the drying temperature is 80-100℃, and the drying time is 6-10h.

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