Chiral polymer coated hard carbon / silicon dioxide composite material and preparation method and application thereof, sodium ion battery

Abstract

The present invention discloses a chiral polymer-coated hard carbon / silicon dioxide composite material, a preparation method and application thereof, and a sodium ion battery, and relates to the technical field of sodium ion batteries. The preparation method comprises the following steps: (1) using silicate as a raw material, in situ generating silicon dioxide in the pores of hard carbon by a sol-gel method, to obtain a hard carbon / silicon dioxide composite material; (2) coating a chiral polymer on the surface of the hard carbon / silicon dioxide composite material by an in situ polymerization method, to obtain a chiral polymer-coated hard carbon / silicon dioxide composite material. Using the chiral polymer-coated hard carbon / silicon dioxide composite material of the present invention as a negative electrode material for a sodium ion battery can well solve the problems of low first coulomb efficiency, poor cycle performance, and low discharge capacity of a sodium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a chiral polymer-coated hard carbon / silicon dioxide composite material, a preparation method and application thereof, and a sodium ion battery. Background Art

[0002] Energy, as an indispensable resource, is an important material basis for human civilization and economic development. However, the current energy structure of countries around the world is still mainly based on traditional fossil energy, supplemented by new energy. The use of large amounts of fossil energy generally causes severe environmental pollution and serious energy crises. The best strategy to solve this problem is to use new renewable energy to replace traditional fossil energy.

[0003] Among the numerous new energy systems, wind energy, solar energy, hydropower and tidal energy are being developed and used. However, such new energy sources are usually affected by regions, environments and seasons, making it difficult to achieve sustainable and large-scale energy supply. An effective way to solve the above problems is to use efficient energy storage devices to store, transport and utilize the above energy sources.

[0004] Among the developed energy storage technologies, lithium-ion batteries have been widely used due to their safety, pollution-free, long cycle life, and high energy density, which has greatly improved the production and living standards of human beings. However, due to the contradiction between the rapid growth of demand for lithium-ion batteries and the shortage of lithium resources and rising costs, people are constantly looking for and developing new rechargeable batteries. Sodium, which is in the same main group as lithium, has similar physical and chemical properties, and sodium is cheap and abundant in resources. Therefore, sodium-ion batteries are considered by scientists to be one of the most promising new energy storage systems to replace lithium-ion batteries.

[0005] The positive and negative electrode materials of sodium-ion batteries are the key to determining battery performance. Among them, the negative electrode material has an important influence on the battery's safety, cycle life, energy density and other performance. In sodium-ion batteries, graphite is the most commercially mature and widely used negative electrode material, which has a low working potential and excellent cycle stability. However, the specific capacity of graphite has almost reached the theoretical limit and is difficult to break through. In addition, the radius of the solvated sodium ions is large and it is difficult to embed them into the graphite. Therefore, there are great limitations in using graphite as the negative electrode material for sodium-ion batteries. Therefore, hard carbon materials have successfully occupied a place in the negative electrode materials of sodium-ion batteries with their good cycle stability, good sodium ion transport ability and high specific capacity. However, the surface defects of the current hard carbon cause the material to have the following problems:

[0006] (1) The low first coulombic efficiency of hard carbon materials is mainly due to the consumption of more sodium to form SEI film;

[0007] (2) During the high-temperature carbonization process, coal easily forms a microcrystalline structure with a high degree of graphitization, which limits the insertion and extraction of sodium ions and leads to a low sodium storage capacity;

[0008] (3) The structure in hard carbon materials is unstable and may collapse and mechanically deform.

[0009] In order to solve the above problems, hard carbon and silicon dioxide are generally compounded in the prior art, but the composite material will produce huge volume changes during the charge and discharge process, thus affecting the performance of the battery. The core-shell type negative electrode material prepared by coating the surface of the above carbon / silicon dioxide material with a conductive polymer can cope with the huge volume changes during the charge and discharge process to a certain extent; however, the core-shell type negative electrode material may be affected by environmental factors during application, resulting in structural instability, thereby affecting its electrochemical performance. Summary of the invention

[0010] In order to solve the problems of low initial coulombic efficiency, poor cycle performance and low discharge capacity of sodium ion batteries, the present invention provides a chiral polymer-coated hard carbon / silicon dioxide composite material, a preparation method and application thereof, and a sodium ion battery.

[0011] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0012] One of the purposes of the present invention is to provide a chiral polymer coated hard carbon / silicon dioxide composite material, comprising a core and a shell, wherein the core is a hard carbon / silicon dioxide composite material, the shell is a chiral polymer, and the hard carbon / silicon dioxide composite material is porous hard carbon filled with nano-silicon dioxide.

[0013] The second object of the present invention is to provide a method for preparing the chiral polymer-coated hard carbon / silicon dioxide composite material, comprising the following steps:

[0014] (1) Using silicate as raw material, silicon dioxide is in situ generated in the pores of hard carbon by a sol-gel method to obtain a hard carbon / silicon dioxide composite material;

[0015] (2) coating the surface of the hard carbon / silicon dioxide composite material with a chiral polymer by an in-situ polymerization method to obtain a chiral polymer coated hard carbon / silicon dioxide composite material.

[0016] The third object of the present invention is to provide the application of the chiral polymer-coated hard carbon / silicon dioxide composite material in sodium ion batteries and lithium ion batteries.

[0017] A fourth object of the present invention is to provide a sodium ion battery comprising a positive electrode, a negative electrode and a separator, wherein the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises the chiral polymer-coated hard carbon / silicon dioxide composite material.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention uses anthracite as a raw material for preparing hard carbon materials. Anthracite has the advantages of high carbon content, low volatile matter, dense structure, high hardness and low price, and the preparation process is simple, which is conducive to large-scale production.

[0020] 2. The present invention adopts a chemical activation method to form pores in anthracite. Compared with physical activation method (such as water vapor pore formation), chemical activation method can make anthracite have an ultra-high specific surface area, provide more storage sites for sodium ions, and thus further improve the battery capacity.

[0021] 3. The present invention utilizes an in-situ synthesis method to generate silica in the pores of the hard carbon material, and at the same time, by controlling the condition parameters of the sol-gel method, the particle size of the monodisperse silica particles is reduced to the minimum as much as possible, in order to minimize the volume expansion effect of silica.

[0022] 4. The present invention uses a chiral polymer to coat the hard carbon / silicon dioxide composite material, which can reduce the volume expansion effect of silicon dioxide and the specific surface area of ​​the composite material, thereby improving the first coulombic efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart for preparing the C / SiO2@L-PPy composite material in Example 1;

[0024] Figure 2 The XRD and EDS diagrams of WYM in Example 1 are shown in FIG. Figure 2 (a) is the XRD pattern of WYM before and after activation. Figure 2 (b) is the EDS graph after WYM activation;

[0025] Figure 3 The particle size distribution curve, SEM image, nitrogen adsorption / desorption curve and pore size distribution curve of PCM in Example 1 are shown in FIG. Figure 3 (a) is a SEM image of PCM magnified 150,000 times. Figure 3 (b) is the particle size distribution curve of PCM. Figure 3 (c) is the nitrogen adsorption / desorption curve of PCM (where the cross group curve is the adsorption curve, and the hollow group curve is the desorption curve). Figure 3 (d) is the pore size distribution curve of PCM;

[0026] Figure 4 The SEM images of the C / SiO2 composite material in Example 1 at different magnifications are shown; wherein, Figure 4 (a) is a SEM image of C / SiO2 composite material magnified 50,000 times. Figure 4 (b) is the SEM image of C / SiO2 composite material magnified 120,000 times;

[0027] Figure 5 The sodium ion battery assembled with WYM, PCM and C / SiO2@L-PPy as negative electrode active materials at 0.1 A g -1 Cyclic performance diagram under current density of , where the hollow group curve is the Coulomb efficiency curve, and the solid group curve is the discharge specific capacity curve;

[0028] Figure 6 The SEM images of the C / SiO2@L-PPy composite material in Example 1 and the C / SiO2@PPy composite material in Comparative Example 6; wherein, Figure 6 (a) is a SEM image of C / SiO2@L-PPy composite material magnified 20,000 times. Figure 6 (b) is a SEM image of the C / SiO2@L-PPy composite material magnified 3,000 times. Figure 6 (c) is a SEM image of the C / SiO2@PPy composite material magnified 20,000 times. Figure 6 (d) is a SEM image of the C / SiO2@PPy composite material magnified 3,000 times. DETAILED DESCRIPTION

[0029] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments and diagrams.

[0030] The invention provides a chiral polymer coated hard carbon / silicon dioxide composite material, comprising a core and a shell, wherein the core is a hard carbon / silicon dioxide composite material, the shell is a chiral polymer, and the hard carbon / silicon dioxide composite material is porous hard carbon filled with nano-silicon dioxide.

[0031] The present invention also provides a method for preparing the chiral polymer-coated hard carbon / silicon dioxide composite material, comprising the following steps:

[0032] (1) Using silicate as raw material, silicon dioxide is in situ generated in the pores of hard carbon by a sol-gel method to obtain a hard carbon / silicon dioxide composite material;

[0033] (2) coating the surface of the hard carbon / silicon dioxide composite material with a chiral polymer by an in-situ polymerization method to obtain a chiral polymer coated hard carbon / silicon dioxide composite material.

[0034] In step (1), the mass ratio of the hard carbon to the silicate is (1-3): (1-3), wherein the mass of the silicate is calculated as silicon dioxide, for example, it can be 1:1, 1:2, 1:3, 2:1, 2:3, 3:1, 3:2 or any value in the range formed by any two of the above ratios. Preferably, the mass ratio of the hard carbon to the silicate is (1-2): (1-2), wherein the mass of the silicate is calculated as silicon dioxide.

[0035] In step (2), the mass ratio of the hard carbon / silicon dioxide composite material to the chiral polymer is (1-3): (1-3), for example, it can be 1:1, 1:2, 1:3, 2:1, 2:3, 3:1, 3:2 or any value in the range formed by any two of the above ratios. Preferably, the mass ratio of the hard carbon / silicon dioxide composite material to the chiral polymer is (1-2): (1-2).

[0036] In the present invention, the sol-gel method uses silicate as raw material, water as solvent, ethanol as co-solvent, acid or base as catalyst, reaction temperature is 60-80° C., and reaction time is 2-12 h.

[0037] Further, the molar ratio of the silicate to ethanol and water is 1: (80-120): (10-50), for example, 1: 80: 10, 1: 90: 10, 1: 100: 10, 1: 110: 10, 1: 120: 10, 1: 90: 20, 1: 100: 20, 1: 110: 20, 1: 120: 20, 1: 80: 30, 1: 90: 30, 1: 100: 30, 1: 110: 30, 1: 120: 30, 1: 80: 40, 1: 90: 40, 1: 100: 40, 1:110:40, 1:120:40, 1:80:50, 1:90:50, 1:100:50, 1:110:50, 1:120:50 or any value in the range formed by any two of the above ratios.

[0038] Furthermore, the acid is at least one of HCl, HNO3, H3PO4, and CH3COOH; and the base is at least one of ammonia water, NaOH, and KOH.

[0039] Anthracite is a hard, dense and high-gloss coal variety with a high carbon content and low impurity content. In the present invention, the hard carbon is prepared using anthracite as a raw material, and the preparation method is as follows: the anthracite and the activator are evenly mixed, and then calcined, washed and dried in a protective gas atmosphere to obtain porous hard carbon. The activator is used to react with non-carbon atoms (ash) and some highly active disordered carbon in the raw coal to form a preliminary microporous structure; at the same time, as the activation proceeds, in addition to generating new micropores, the activator can also play a role in expanding the pores by etching the carbon atoms on the walls of the already formed micropores, thereby further increasing the pore volume.

[0040] Furthermore, the activator is selected from at least one of KOH, NaOH, K2CO3, ZnCl2, and H3PO4, preferably KOH or NaOH.

[0041] Furthermore, the mass ratio of the anthracite to the activator is 1: (1-5), for example, it can be 1: 1, 1: 2, 1: 3, 1: 4, 1: 5 or any value in the range formed by any two of the above ratios, preferably 1: (2-5).

[0042] Furthermore, the protective gas is selected from at least one of nitrogen, helium and argon.

[0043] Furthermore, the calcination temperature is 600-1200°C.

[0044] Furthermore, the washing includes acid washing, water washing and alcohol washing. The acid washing uses HCl, H2SO4 or HNO3 solution with a concentration of 0.5-2 mol / L; the alcohol washing is ethanol washing. The purpose of acid washing is to remove residual activator and byproducts of the reaction between the activator and anthracite; the purpose of alcohol washing is to improve the purity of the material and reduce the drying time.

[0045] In some preferred embodiments of the present invention, the anthracite needs to be pretreated before activation, and the pretreatment includes pre-carbonization, impurity removal and refinement. The purpose of pre-carbonization is to reduce the impurities on the surface of the anthracite while maintaining the original microstructure of the anthracite, thereby improving the chemical stability; the purpose of impurity removal is to remove the corresponding impurities, reduce the occurrence of side reactions in the electrochemical process, and further improve the electrochemical performance of the battery; the purpose of refinement is to reduce the van der Waals force that needs to be overcome when lithium / sodium ions are embedded, thereby improving the discharge capacity of the battery, while increasing the compaction density of the pole piece and improving the volume energy density of the battery.

[0046] Furthermore, the pre-carbonization is carried out in a protective gas atmosphere at a temperature of 400-800° C. for a time of 0.2-2 h.

[0047] Furthermore, the protective gas is selected from at least one of nitrogen, helium and argon.

[0048] Furthermore, the impurity removal includes at least one of alkali washing, acid washing and water washing. The alkali washing temperature is 100-220°C, the time is 1-5 h, the alkali concentration is 0.5-2 mol / L, and the alkali is selected from one of KOH, NaOH, LiOH and RbOH; the acid washing temperature is 50-100°C, the time is 1-5 h, the acid concentration is 0.5-2 mol / L, and the acid is selected from at least one of HCl, H2SO4 and HNO3.

[0049] Furthermore, the refinement is carried out by ball milling, with a ball milling ratio of (5-40): 1, a rotation speed of 200-500 rpm, and a time of 3-12 h.

[0050] In the present invention, the chiral polymer is obtained by reacting a chiral inducing agent and a monomer under the action of an initiator.

[0051] Furthermore, the chiral inducing agent is one of N-lauroyl-L-glutamic acid, L-tartaric acid, and L-camphorsulfonic acid.

[0052] In the present application, the chiral polymer includes but is not limited to doped or undoped chiral polypyrrole, doped or undoped chiral polyaniline and doped or undoped chiral polythiophene; further, the monomer includes but is not limited to at least one of pyrrole, aniline and thiophene.

[0053] In the present application, the initiator is a peroxide initiator or an azo initiator.

[0054] Furthermore, the mass ratio of the chiral inducing agent to the monomer is 1: (1-5). For example, it can be 1: 1, 1: 1.5, 1: 2, 1: 2.5, 1: 3, 1: 3.5, 1: 4, 1: 4.5, 1: 5 or any value in the range of any two of the above ratios.

[0055] Further, the mass ratio of the hard carbon / silicon dioxide composite material to the monomer is (1~5): (1~5), for example, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1 or any value in the range of any two of the above ratios. Preferably, the mass ratio of the hard carbon / silicon dioxide composite material to the monomer is; preferably (1~2): (1~3).

[0056] In some preferred embodiments of the present invention, the N-lauroyl-L-glutamic acid is obtained by reacting L-glutamic acid with lauroyl chloride in the presence of an acid-binding agent and alkaline conditions. The types of the acid-binding agent may be known to those skilled in the art, including but not limited to at least one of sodium hydroxide, sodium carbonate, triethylamine, and pyridine; further preferably, the molar ratio of the L-glutamic acid to lauroyl chloride to the acid-binding agent is 1:1:(0.5-2.5).

[0057] The present invention provides application of the chiral polymer-coated hard carbon / silicon dioxide composite material in sodium ion batteries and lithium ion batteries.

[0058] The present invention also provides a sodium ion battery, comprising a positive electrode, a negative electrode and a separator, wherein the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises the chiral polymer-coated hard carbon / silicon dioxide composite material.

[0059] The present invention has no special limitation on the positive electrode and the separator of the sodium ion battery, which are known to those skilled in the art and will not be described in detail herein.

[0060] In the present invention, the negative electrode includes a negative electrode active material, a conductive agent and a binder. The types of the conductive agent and the binder are known to those skilled in the art.

[0061] The technical solution of the present invention is described in detail below through specific embodiments.

[0062] Example 1

[0063] Figure 1 The preparation flow chart of chiral polypyrrole coated hard carbon / silicon dioxide (C / SiO2@L-PPy) composite material is as follows:

[0064] (1) Pretreatment of anthracite

[0065] Weigh 5g of anthracite and place it in a tubular furnace. Heat it to 650℃ under a nitrogen atmosphere for pre-carbonization for 1h. Add the pre-carbonized anthracite into a 1mol / L potassium hydroxide (KOH) solution at 180℃ and stir for 2h. Then add the treated anthracite into a 1mol / L hydrochloric acid solution at 80℃ and stir for 2h. Then wash it with deionized water until it is neutral, dry it in an oven at 120℃, and ball mill it (ball milling ratio is 20:1, rotation speed is 300rpm, ball milling time is 6h) to obtain the pretreated anthracite (WYM).

[0066] (2) Preparation of porous hard carbon materials

[0067] Weigh 2g WYM and 6g KOH, grind and mix them evenly in a mortar, then place them in a tubular furnace and heat them to 800°C under a nitrogen atmosphere for 2 h. After naturally cooling to room temperature, wash them with deionized water and ethanol until they are neutral, and place them in a 120°C oven to dry to obtain a porous hard carbon material (PCM).

[0068] (3) Preparation of hard carbon / silicon dioxide composites

[0069] 2 g PCM was weighed and mixed with 2.217 mL tetraethyl orthosilicate (TEOS), and then ultrasonically treated at 80°C for 30 min to obtain solution A; 0.1 mol / L ammonia water was added to deionized water (H2O) and ethanol (EtOH) in a molar ratio of 1:12 to obtain solution B with pH=9; solution B was heated to 75°C and quickly stirred with solution A at a stirring speed of 1000 rpm. The reaction time was 12 h, and the mixture was centrifuged, washed, and dried to obtain a hard carbon / silicon dioxide (C / SiO2) composite material.

[0070] (4) Preparation of chiral polypyrrole-coated hard carbon / silicon dioxide composites

[0071] Under ice bath conditions, L-glutamic acid, water, acetone and sodium hydroxide are mixed, stirred to dissolve the L-glutamic acid, the pH value is controlled to be 9, and then lauroyl chloride is slowly added dropwise, wherein the molar ratio of L-glutamic acid to lauroyl chloride is 1:1, and sodium hydroxide solution is simultaneously added dropwise during the reaction to keep the pH of the reaction system constant. The reaction is stopped after reacting for 2 hours, and then the pH is adjusted to neutral with a hydrochloric acid solution with a concentration of 1 mol / L. After standing for 12 hours, it is washed with petroleum ether and dried to obtain N-lauroyl-L-glutamic acid.

[0072] 1.2 g of the C / SiO2 composite material prepared above was added to a 50 mL ethanol solution containing 0.58 g N-lauroyl-L-glutamic acid and 2.477 mL pyrrole and stirred at a speed of 500 rpm. Subsequently, 8.44 g of ammonium persulfate was added and the reaction was stopped after 12 h of reaction. The solution was washed with deionized water and anhydrous ethanol alternately by suction until it became colorless and dried to obtain a C / SiO2@L-PPy composite material.

[0073] Figure 2 The XRD and EDS diagrams of WYM in Example 1 are shown in FIG. Figure 2 (a) is the XRD pattern of WYM before and after activation. Figure 2 (b) is the EDS diagram after WYM activation. Figure 2(a) It can be seen that the two diffraction peaks of 25.3° and 42.6° correspond to the two crystal planes (002) and (100), respectively, indicating that the hard carbon prepared in Example 1 is amorphous carbon. In addition to these two diffraction peaks, there are still some peaks before activation, which are impurity peaks. After activation, the impurity peaks basically disappear, indicating that the impurities are efficiently removed. Figure 2 (b) It can be seen that the content of hard carbon obtained after activation is as high as 96.93%, which corresponds to the XRD pattern. Figure 2 (b) It can also be seen that the impurities are mainly composed of Al2O3, SiO2 and FeS2.

[0074] Figure 3 The particle size distribution curve, SEM image, nitrogen adsorption / desorption curve and pore size distribution curve of PCM in Example 1 are shown in FIG. Figure 3 (a) is a SEM image of PCM magnified 150,000 times. Figure 3 (b) is the particle size distribution curve of PCM. Figure 3 (c) is the nitrogen adsorption / desorption curve of PCM (where the cross group curve is the adsorption curve, and the hollow group curve is the desorption curve). Figure 3 (d) is the pore size distribution curve of PCM. Figure 3 (b) It can be seen that the particle size distribution of WYM after KOH activation is mainly concentrated around 10 μm, and the particle size distribution is concentrated and the range is narrow. Figure 3 (a) It can be seen that WYM forms obvious holes after KOH pore formation; Figure 3 (c) It can be seen that the isotherm curves basically conform to the characteristics of type IV isotherms, that is, the two curves do not completely overlap and there is a hysteresis loop, but compared with the typical mesoporous material isotherm, this hysteresis loop is not obvious, which indicates that the pores of PCM are mainly mesoporous structures; at the same time, combined with Figure 3 (d) It can be seen that in addition to the mesoporous structure, PCM also has a small amount of micropores and macropores; the specific surface area of ​​PCM can reach 1440 m 2 Based on the above results, it can be proved that PCM has an ultra-high specific surface area and rich pore structure, which further provides a large number of storage and adsorption sites for sodium ions.

[0075] Figure 4 The SEM images of the C / SiO2 composite material in Example 1 at different magnifications are shown; wherein, Figure 4 (a) is a SEM image of C / SiO2 composite material magnified 50,000 times. Figure 4 (b) is a SEM image of C / SiO2 composite material magnified 120,000 times. Figure 4 (a) and Figure 4 (b) It can be seen that nano-SiO2 has entered the pores of PCM and partially attached to the surface.

[0076] Assemble the battery:

[0077] The C / SiO2@L-PPy composite material, WYM and PCM obtained in Example 1 were used as negative electrode active materials to prepare negative electrode sheets for sodium ion batteries, and button half-cells were assembled. The specific steps are as follows:

[0078] A small amount of N-methyl-2-pyrrolidone (NMP) was added dropwise to polyvinylidene fluoride (PVDF), and the mixture was ground at 60°C to completely dissolve the PVDF. Active substance and carbon black (SP) were then added, with the mass ratio of active substance to SP and PVDF being 8:1:1. The mixture was homogenized at a speed of 2000 rpm for 30 min to form a uniform slurry. The slurry was evenly scraped onto an aluminum foil, dried in an oven at 80°C for 12 h, and then pressed and sliced ​​to obtain an electrode sheet.

[0079] Place the above electrode sheet in the glove box, and place the CR2032 positive electrode shell in the middle of the glove box, then place the electrode sheet in the positive electrode shell, then lay the glass fiber diaphragm on the surface of the electrode sheet, and drip 100μL electrolyte (1M NaClO4inDMC: EC=1:1 Vol%), then place the sodium sheet on top of the diaphragm, and finally stack the gasket and shrapnel on the surface of the sodium sheet in sequence, and then cover it with the negative electrode shell and seal it with a battery sealing device. The packaged battery can be measured after standing for 12 hours.

[0080] from Figure 5 It can be seen that the first coulombic efficiency of the sodium ion battery assembled with C / SiO2@L-PPy prepared in Example 1 as the negative electrode material is 72.06%, the first coulombic efficiency of the sodium ion battery assembled with PCM as the negative electrode material is 64.13%, and the first coulombic efficiency of the sodium ion battery assembled with WYM prepared in Example 1 as the negative electrode material is 50.11%; and the sodium ion battery assembled with C / SiO2@L-PPy as the negative electrode material has a discharge capacity of 280 mAh g after 100 cycles. -1 , showing good cycling stability, which is significantly better than PCM and WYM.

[0081] Examples 2 to 6 and Comparative Examples 1 to 3

[0082] The method of Example 1 was followed, except that the impurity removal method in step (1) was changed, as shown in Table 1.

[0083] The impurity content of the prepared porous hard carbon material was measured, and the results are shown in Table 1.

[0084] Table 1

[0085]

[0086] From Table 1 we can see that:

[0087] By comparing Example 1, Comparative Example 2 and Comparative Example 3, it can be seen that although only alkaline washing or acid washing can remove some impurities in anthracite, the impurity content is still relatively high.

[0088] Comparison of Example 1 and Comparative Example 1 shows that alkali solution plays a very important role in removing anthracite impurities at high temperature.

[0089] Comparing Examples 1 and 3, it can be seen that when the temperature of the KOH solution reaches above 180°C, the impurity content of the anthracite is not much different, both less than 5%. In this application, the heating temperature of the KOH solution is set to 180°C.

[0090] By comparing Examples 1, 4, and 5, it can be seen that from Example 4 (60°C) to Example 1 (80°C), the pickling temperature increased, and the impurity content in the anthracite decreased from 3.01 to 2.57, but when the pickling temperature was further increased to 100°C (Example 5), the impurity content in the anthracite did not change significantly, so the pickling heating temperature was set to 80°C.

[0091] Comparing Example 1 with Example 6, it can be seen that extending the alkali washing time and the acid washing time to 4 hours has little effect on the impurity content of the anthracite. In order to save time, the heating time for alkali washing and acid washing is set to 2 hours.

[0092] Examples 7 to 12 and Comparative Example 4

[0093] The method of Example 1 was followed, except that the mass ratio of anthracite to KOH or the type of activator in step (2) was changed. The specific surface area of ​​the prepared PCM was measured. The results are shown in Table 2.

[0094] Table 2

[0095]

[0096] From Table 2 we can see that:

[0097] It can be seen from Examples 1, 7 to 9 that if KOH is used to make pores, the specific surface area of ​​anthracite increases with the increase in the amount of activator. When the mass ratio of anthracite to KOH is 1:3, the maximum specific surface area of ​​anthracite can reach 1480.75 m 2 / g. However, it should be noted that the larger the amount of KOH used in this process, the better. When the amount of KOH used exceeds 3 times the amount of anthracite, the structure of the hard carbon material will collapse, resulting in a decrease in the specific surface area. Therefore, considering all factors, the best effect is when the mass ratio of anthracite to KOH is set at 1:3.

[0098] It can be seen from Examples 11 and 12 that when H3PO4 and ZnCl2 are used as activators to pore anthracite, the specific surface areas of the PCM obtained are 956.37 m 2 / g and 1087.11m 2 Although the specific surface area of ​​ZnCl2 pores is also large, chlorine gas will be produced during the reaction, which is dangerous. Therefore, KOH is the preferred material as the activator in the present invention.

[0099] From Comparative Example 4, it can be concluded that if water vapor pores are used, the specific surface area of ​​the PCM obtained is only 249.82 m 2 / g, which indicates that the pore-forming effect of water vapor is not ideal.

[0100] Embodiments 13 to 22

[0101] The method of Example 1 was followed, except that the condition parameters of the sol-gel method in step (3) were changed, as shown in Table 3.

[0102] The particle size of the prepared nano-silicon dioxide was measured, and the results are shown in Table 3.

[0103] Table 3

[0104]

[0105] It can be seen from Table 3 that: with the increase of TEOS concentration, the particle size distribution of nano-silica fluctuates only within a very small range, which shows that within this concentration range, the effect of TEOS concentration on the particle size distribution is very small; the increase of water content will promote the hydrolysis of TEOS, and the particle size of nano-silica will increase; while the increase of ethanol dosage, the particle size of nano-silica gradually decreases, which may be because the addition of ethanol increases the volume of the entire system, thereby reducing the concentration of reactants in the hydrolysis and polycondensation reactions, further reducing the hydrolysis and polycondensation reaction rates; with the increase of reaction temperature, the particle size of nano-silica gradually decreases. This is because with the increase of temperature, the nucleation rate increases and the condensation rate decreases. At the same time, with the increase of temperature, the concentration of ammonia water will decrease, and the rate of hydrolysis and condensation of silica gel will decrease accordingly, thereby further reducing the particle size of nano-silica.

[0106] Examples 23 to 26 and Comparative Example 5

[0107] The method of Example 1 is followed, except that the amount of TEOS in step (3) is changed, thereby changing the mass ratio of C to SiO2 in the prepared C / SiO2 composite material.

[0108] Comparative Example 5 is to fully mix the porous hard carbon prepared in step (2) of Example 1 with commercial SiO2 (particle size of 10 nm) to obtain a C / SiO2 composite material.

[0109] The obtained C / SiO2 composite material was used as the negative electrode active material of sodium ion battery. -1 The first coulombic efficiency at a current density of and the discharge specific capacity after 100 cycles are shown in Table 4.

[0110] Table 4

[0111]

[0112] It can be seen from Table 4 that the sodium ion battery prepared using the C / SiO2 composite material obtained in Example 1 as the negative electrode active material has the highest discharge specific capacity after 100 cycles, and the sodium ion battery prepared using the C / SiO2 composite material obtained in Examples 23 to 26 as the negative electrode active material has a first coulombic efficiency and a discharge specific capacity after 100 cycles lower than the first coulombic efficiency and discharge specific capacity of the sodium ion battery prepared using the C / SiO2@L-PPy composite material obtained in Example 1 as the negative electrode active material. This is mainly due to the fact that when the SiO2 content is too high, the volume expansion effect is particularly significant; however, when the SiO2 content gradually decreases, although the first coulombic efficiency of the battery has a certain recovery, it is not obvious, and the discharge specific capacity still gradually decreases.

[0113] By comparing Example 1 and Comparative Example 5, it can be concluded that compared with directly compounding porous hard carbon with SiO2, the hard carbon / silicon dioxide composite material obtained by in-situ generating silicon dioxide in the pores of hard carbon by using the sol-gel method has higher first coulombic efficiency and cycle performance after coating, and exhibits more excellent electrochemical performance.

[0114] Embodiments 27 to 32

[0115] The method of Example 1 is followed, except that: Examples 27 to 30 change the mass ratio of N-lauroyl chloride-L-glutamic acid (L-LGA) and pyrrole (Py) in step (4), and Examples 31 and 32 replace L-LGA with L-tartaric acid (L-TA) and L-camphorsulfonic acid (L-CSA), respectively.

[0116] The chiral polymer-coated C / SiO2 composite material was used as the negative electrode active material of sodium ion battery. -1 The first coulombic efficiency at a current density of and the discharge specific capacity after 100 cycles are shown in Table 5.

[0117] Table 5

[0118]

[0119] From Table 5 we can see that:

[0120] By comparing Example 1 with Examples 27 to 31, it can be concluded that the first coulombic efficiency and discharge specific capacity of the sodium ion battery increase with the increase of the mass ratio of L-LGA:Py. When the mass ratio of N-lauroyl chloride-L-glutamic acid to pyrrole increases from 1:1 to 1:3, the first coulombic efficiency and discharge specific capacity of the sodium ion battery are significantly improved; when the mass of pyrrole is further increased, the first coulombic efficiency and discharge specific capacity of the sodium ion battery do not change much.

[0121] After N-lauroyl chloride-L-glutamic acid was replaced with L-tartaric acid and L-camphorsulfonic acid, the first coulombic efficiency and discharge specific capacity of the sodium ion battery were slightly reduced. Therefore, the chiral inducer in the present invention is preferably N-lauroyl chloride-L-glutamic acid.

[0122] Embodiments 33 to 36

[0123] The method of Example 1 is followed, except that: Examples 33 to 36 change the dosage ratio of the C / SiO2 composite material to pyrrole in step (4), thereby changing the mass ratio of C / SiO2 to L-PPy in the prepared C / SiO2@L-PPy composite material, as shown in Table 6 for details.

[0124] The C / SiO2@L-PPy composites prepared with different mass ratios of C / SiO2 and L-PPy were used as negative electrode active materials for sodium ion batteries. -1 The first coulombic efficiency at the current density and the discharge specific capacity after 100 cycles are shown in Table 6.

[0125] Table 6

[0126]

[0127] It can be seen from Table 6 that: by comparing Examples 1, 33 and 34, it can be concluded that with the increase of the chiral polypyrrole content, the first coulombic efficiency and cycle performance of the obtained sodium ion battery gradually increase; however, when the mass of L-PPy exceeds twice the mass of C / SiO2, the first coulombic efficiency and discharge specific capacity of the sodium ion battery are both decreasing, which is mainly because the outermost layer of chiral polypyrrole is too thick, affecting the transmission of sodium ions.

[0128] Comparative Example 6

[0129] The method of Example 1 is followed, except that the chiral polypyrrole (L-PPy) is replaced by an achiral polypyrrole (PPy), as shown in Table 7.

[0130] The obtained C / SiO2@L-PPy composites and C / SiO2@PPy composites were used as negative electrode active materials for sodium ion batteries, and the performance of sodium ion batteries at 0.1A g -1 The first coulombic efficiency at a current density of and the discharge specific capacity after 100 cycles are shown in Table 7.

[0131] Table 7

[0132]

[0133] It can be seen from Table 7 that the first coulombic efficiency and the discharge specific capacity after 100 cycles of the chiral polypyrrole-coated C / SiO2 composite material are higher than those of the achiral polypyrrole-coated C / SiO2 composite material. This is mainly because the chiral polypyrrole has better conductive properties than the achiral polypyrrole.

[0134] Figure 6 The SEM images of the C / SiO2@L-PPy composite material in Example 1 and the C / SiO2@PPy composite material in Comparative Example 6; wherein, Figure 6 (a) is a SEM image of C / SiO2@L-PPy composite material magnified 20,000 times. Figure 6 (b) is a SEM image of the C / SiO2@L-PPy composite material magnified 3,000 times. Figure 6 (c) is a SEM image of the C / SiO2@PPy composite material magnified 20,000 times. Figure 6 (d) is a SEM image of the C / SiO2@PPy composite material magnified 3,000 times. Figure 6 (a) It can be seen that the chiral polypyrrole formed by the in-situ polymerization reaction has a helical structure. This is precisely because the presence of N-lauroyl-L-glutamic acid small molecules gives polypyrrole chiral properties; this is consistent with Figure 6 (c) form a sharp contrast, Figure 6 (c) is a non-chiral polypyrrole-coated structure, and no chiral helical structure is generated on its surface; Figure 6 (b) It can be seen that the surface of C / SiO2 composite material is coated with chiral polypyrrole. Figure 4 In comparison, the number of exposed nano-SiO2 particles was significantly reduced after chiral polypyrrole was coated on the surface of C / SiO2 material; Figure 6 (d) It can be seen that although achiral polypyrrole also forms a thin film on the surface, the surface is not smooth and has protrusions. These protrusions will more easily react with the electrolyte to form an unstable SEI film, thereby reducing the initial discharge capacity of the battery.

[0135] Comparative Example 7

[0136] The method of Example 1 is followed, except that the method of compounding C / SiO2 and L-PPy in step (4) is changed. Example 1 is to generate L-PPy in situ on the surface of C / SiO2, while Comparative Example 7 is to synthesize L-PPy first and then mix L-PPy and C / SiO2, as shown in Table 8.

[0137] The obtained composite material was used as the negative electrode active material of sodium ion battery. -1 The first coulombic efficiency at a current density of and the discharge specific capacity after 100 cycles are shown in Table 8.

[0138] Table 8

[0139]

[0140] It can be seen from Table 8 that the in-situ generation of L-PPy on the surface of C / SiO2 can effectively reduce the specific surface area, thereby reducing the generation of unstable SEI film and improving the first coulombic efficiency; in comparison, the specific surface area of ​​the doped synthesized C / SiO2 / L-PPy is significantly larger than that of C / SiO2@L-PPy, which leads to an increase in the area of ​​the unstable SEI film and a decrease in the first coulombic efficiency. The discharge specific capacity after 100 cycles is also significantly lower than that of C / SiO2@L-PPy.

[0141] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A chiral polymer-coated hard carbon / silicon dioxide composite material, comprising a core and a shell, characterized in that: The core is a hard carbon / silicon dioxide composite material, the shell is a chiral polymer, and the hard carbon / silicon dioxide composite material is porous hard carbon filled with nano-silicon dioxide; The polymerization monomer of the chiral polymer is at least one of pyrrole, aniline and thiophene.

2. A method for preparing the chiral polymer-coated hard carbon / silicon dioxide composite material as claimed in claim 1, characterized in that: The following steps are involved: (1) Using silicate as raw material, silicon dioxide is in situ generated in the pores of hard carbon by a sol-gel method to obtain a hard carbon / silicon dioxide composite material; (2) coating the surface of the hard carbon / silicon dioxide composite material with a chiral polymer by an in-situ polymerization method to obtain a chiral polymer coated hard carbon / silicon dioxide composite material.

3. The method according to claim 2, characterized in that: In step (1), the mass ratio of the hard carbon to the silicate is (1-3): (1-3), wherein the mass of the silicate is calculated as silicon dioxide; In step (2), the mass ratio of the hard carbon / silicon dioxide composite material to the chiral polymer is (1~3): (1~3).

4. The method according to claim 2, characterized in that: The reaction temperature of the sol-gel method is 60-80° C., and the reaction time is 2-12 h.

5. The method according to claim 2, characterized in that: The hard carbon is prepared from anthracite as a raw material, and the preparation method thereof is as follows: the anthracite and an activator are uniformly mixed, and then calcined, washed, and dried in a protective gas atmosphere to obtain porous hard carbon; The activator is selected from at least one of KOH, NaOH, K2CO3, ZnCl2, and H3PO4; The mass ratio of the anthracite to the activator is 1: (1-5); The protective gas is selected from at least one of nitrogen, helium and argon; The calcination temperature is 600-1200°C.

6. The method according to claim 5, characterized in that: The anthracite needs to be pre-treated before activation, and the pre-treatment includes pre-carbonization, impurity removal and refinement; The pre-carbonization is carried out in a protective gas atmosphere at a temperature of 400-800° C. for a time of 0.2-2 h; The protective gas is selected from at least one of nitrogen, helium and argon; The impurity removal includes at least one of alkali washing, acid washing and water washing; The alkali washing temperature is 100-220°C, the time is 1-5 h, the alkali solution concentration is 0.5-2 mol / L, and the alkali is selected from one of KOH, NaOH, LiOH, and RbOH; The pickling temperature is 50-100°C, the time is 1-5 h, the acid concentration is 0.5-2 mol / L, and the acid is selected from at least one of HCl, H2SO4, and HNO3; The refinement is carried out by ball milling, with a ball milling ratio of (5-40): 1, a rotation speed of 200-500 rpm, and a time of 3-12 hours.

7. The method according to claim 2, characterized in that: The chiral polymer is obtained by reacting a chiral inducing agent and a monomer under the action of an initiator; The chiral inducing agent is one of N-lauroyl-L-glutamic acid, L-tartaric acid, and L-camphorsulfonic acid; The monomer is at least one of pyrrole, aniline and thiophene; The initiator is a peroxide initiator or an azo initiator; The mass ratio of the chiral inducing agent to the monomer is 1: (1-5); The mass ratio of the hard carbon / silicon dioxide composite material to the monomer is (1-5): (1-5).

8. The method according to claim 7, characterized in that: The N-lauroyl-L-glutamic acid is obtained by reacting L-glutamic acid and lauroyl chloride in the presence of an acid binding agent; The acid binding agent is at least one of sodium hydroxide, sodium carbonate, triethylamine and pyridine; The molar ratio of L-glutamic acid to lauroyl chloride and acid binding agent is 1:1:(0.5-2.5).

9. Use of the chiral polymer-coated hard carbon / silicon dioxide composite material according to claim 1 or the chiral polymer-coated hard carbon / silicon dioxide composite material obtained by the method according to any one of claims 2 to 7 in sodium ion batteries and lithium ion batteries.

10. A sodium ion battery comprising a positive electrode, a negative electrode and a separator, wherein the negative electrode comprises a negative electrode active material, characterized in that: The negative electrode active material comprises the chiral polymer coated hard carbon / silicon dioxide composite material according to claim 1 or the chiral polymer coated hard carbon / silicon dioxide composite material obtained by the method according to any one of claims 2 to 7.

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