Preparation method and application of nano zinc sulfide with adjustable crystal structure

Abstract

The invention provides a preparation method and application of nano zinc sulfide with adjustable crystal structure, belonging to the technical field of nano zinc sulfide materials. The invention relates to a method for controlling the defect structure of zinc sulfide by utilizing the substituent structure of a mercapto surfactant. The increase in the number of carbon atoms of the mercapto surfactant and the presence of a branched chain can significantly reduce the particle size and defect degree of zinc sulfide. The increase in the coordination ability of the mercapto surfactant can reduce the defect degree and the particle size. The non-polar substituent group is too short, the particle size of zinc sulfide is mainly large particles with uneven distribution, and the material has a large number of surface defects and dislocation structures. The method can be applied to improving the electrochemical properties such as the first cycle coulomb efficiency of negative electrode materials of ion batteries, can increase the material conductivity and the ion transmission path in the material body, improve the electrochemical reaction kinetics and reversibility of zinc sulfide, and improve the material capacity and rate performance.

Description

Technical Field

[0001] The invention belongs to the technical field of nano zinc sulfide materials, and in particular relates to a preparation method and application of nano zinc sulfide with adjustable crystal structure. Background Art

[0002] Lithium-ion batteries convert electrical energy into chemical energy for storage through the reversible electrochemical reaction of Li+ at the positive and negative electrodes, and are the main energy supply device for existing new energy vehicles. However, existing lithium-ion batteries have the problem of short driving range and cannot meet the needs of long-distance travel, becoming the biggest obstacle to the popularization of new energy vehicles. Although directly increasing the number of single cells or battery modules can achieve an increase in driving range, it will increase the weight of the vehicle, affect the handling performance, and increase safety risks such as spontaneous combustion. In contrast, under the premise that the volume or mass of the vehicle battery remains unchanged, improving the energy density of the battery will significantly increase the average amount of electrical energy released per unit mass of the battery, which is an effective strategy to improve the driving range of new energy vehicles. It can be seen from the battery energy density formula that the energy density is linearly related to the battery capacity. The positive and negative electrodes of ion batteries are the carriers for electrochemical reactions, and their properties are the core factors affecting the battery capacity. The application of ternary materials has increased the theoretical capacity of the positive electrode from 160 mAh.g -1 Increased to 200 mAh.g -1 . Since there is little room for further improvement in the capacity of positive electrode materials, the development of high-capacity negative electrode materials has become the core of developing high-energy density batteries. Studies have shown that zinc sulfide is a type of electrode material that achieves energy storage through conversion reactions and alloying reactions. It has a theoretical capacity of up to 963 mAh.g-1 and a half-cell voltage platform of < 1.0 V. It is non-toxic, has abundant element reserves, and is low in cost. It is one of the most promising candidate negative electrode materials for high-energy density lithium-ion batteries. However, there is an irreversible electrochemical reaction during the first charging process of ZnS, and the first-week coulomb efficiency (ICE) is less than 60%. In addition, due to the conductivity of the particles, the actual capacity and rate performance are poor, which greatly reduces the low energy density of ion batteries. Therefore, studying the strategy to improve the first-week coulomb efficiency, capacity and rate performance of zinc sulfide is the key to building a high-energy density battery system. Studies have shown that cubic zinc sulfide and hexagonal zinc sulfide (wurtzite structure) exhibit different performances in energy storage. However, the wurtzite structure has diverse configurations, and there is no strategy to regulate the wurtzite-type structure and reveal its impact on the energy storage performance of zinc sulfide. Most of the existing ideas for regulating the zinc sulfide crystal structure are to achieve the transition between cubic zinc sulfide (sphalerite) and hexagonal (wurtzite) by controlling the roasting temperature. This process makes it difficult to achieve the targeted construction of wurtzite crystal polymorphic structures. Summary of the invention

[0003] In order to solve the above technical problems, solve the key technical problems that the existing zinc sulfide materials cannot be industrialized, and improve the problems of low first-week coulombic efficiency and poor capacity and rate performance of zinc sulfide used as negative electrode materials for alkali metal secondary batteries, this scheme provides a nano zinc sulfide with adjustable crystal structure and its preparation method and application, which is a new idea for crystal structure regulation. Different precursors are prepared by using thiol surfactants to obtain wurtzite with different crystal structures, which can be used to improve the electrochemical properties such as the first-week coulombic efficiency of negative electrode materials for ion batteries, increase the material's conductivity and the ion transmission path in the material body, improve the electrochemical reaction kinetics and reversibility of zinc sulfide, and improve the material's capacity and rate performance.

[0004] To achieve the above purpose, this scheme first provides a method for preparing nano zinc sulfide with adjustable crystal structure, comprising the following steps:

[0005] S1. Mixing the zinc sulfate solution and the thiol surfactant at room temperature, centrifuging and freeze-drying the solid to obtain a thiol complex precursor;

[0006] S2, mixing the thiol complex precursor prepared in S1 with NaCl uniformly, heating under a nitrogen atmosphere and then calcining the mixture at the same temperature, washing the calcined product with high-frequency ultrasonic water, performing solid-liquid separation, and drying the product to obtain carbon composite nano zinc sulfide;

[0007] The polar groups of the mercapto surfactant are -S-, -S, -SH, -S-S-, , , , Any of the following, the non-polar group is C1~C 10 Alkyl, C5~C 10 Cyclic hydrocarbon groups, C5~C 10 Any one of a heterocyclic aromatic group and a phenyl group.

[0008] Preferably, the mercapto surfactant in step S1 includes any one of sodium salt of xanthate, potassium salt of xanthate, thiocarbamate, ammonium alkylthiophosphate, dithiophosphoric acid, thiourea, thiol, thiophene, mercaptobenzothiazole, mercaptobenzimidazole, mercaptobenzoxazole, acetylthiobenzamide, carbonylthioamide, and thioketone.

[0009] Preferably, in step S1, the room temperature is 15-35°C, the concentration ratio of the zinc sulfate solution to the thiol surfactant is 2:1, and the volume ratio is 1:1; the stirring speed is 200 rpm, and the time is 3 min; the centrifugal speed is 5000 r / min, and the time is 5 min; the freeze-drying temperature is -80°C, and the time is 12 h.

[0010] Preferably, in step S2, the mass ratio of the thiol complex precursor to NaCl is 1:1; the calcination temperature is 500-600° C. and the calcination time is 2-3 h.

[0011] Preferably, in the step S2, the particle size of NaCl is 0.010-0.037 mm; and the particle size of the carbon composite nano zinc sulfide is 2-100 nm.

[0012] Preferably, the carbon composite nano zinc sulfide includes any one of wurtzite, 2H-type wurtzite, 6H-type wurtzite, 8H-type wurtzite and 10H-type wurtzite.

[0013] Based on a general inventive concept, the present invention also provides nano zinc sulfide prepared by the above method.

[0014] Based on a general inventive concept, the present invention also provides an application of nano zinc sulfide for preparing negative electrode active materials for alkali metal or alkali metal ion batteries, wherein the alkali metal is at least one of lithium, sodium and potassium.

[0015] Based on a general inventive concept, the present invention also provides an application of nano zinc sulfide in regulating zinc sulfide crystals.

[0016] Based on a general inventive concept, the present solution also provides an application in regulating the defect types of zinc sulfide.

[0017] The principle of the adjustable nano zinc sulfide crystals of the present invention is as follows:

[0018] In the preparation process of thiol complex-based wurtzite structured nano zinc sulfide, the polar group-bonded atoms, central core atoms, connecting atomic composition or non-polar base structure of the thiol surfactant are used to affect the electron cloud density around the bonded atom S, adjust the precursor of zinc sulfide - the thiol complex, and regulate the crystal structure (wurtzite, 2H-type wurtzite, 10H-type wurtzite, etc.), defect structure (lattice fringe missing, surface defect, dislocation defect, point defect), particle size (2-100nm) and other properties and electrochemical performance (first-cycle coulomb efficiency, capacity and rate performance) of the thiol complex-based nano zinc sulfide.

[0019] The non-polar group and the polar group are the two main parts that constitute the mercapto surfactant. Due to the existence of the inductive effect, the substances in the non-polar group and the polar group affect the coordination ability of the chemically bonded atom S. The constituent elements of the polar group are closer to the S atom, so their influence on the coordination performance of the mercapto surfactant is more significant.

[0020] The polar group of the thiol surfactant is composed of bonding atoms, central core atoms and connecting atoms. The change of related atoms affects the electron cloud density around the bonding atom S and regulates its interaction with Zn2+ The coordination ability and coordination product (thiol complex precursor) can be optimized to achieve the crystal structure, defect structure and particle size of thiol complex-based zinc sulfide nanodots.

[0021] According to the lithium storage mechanism of the material, defects and dislocations are expected to cause additional lithium embedding capacity, making the actual lithium storage capacity of the material higher than the theoretical value. However, too many defects will reduce the stability of the material structure, causing the structure of the material to collapse during the charge and discharge cycle, and reducing the cycle life. The increase in the number of carbon atoms in the thiol surfactant will reduce the particle size of wurtzite, increase the thickness of the carbon layer, and reduce the defect structure. The smaller nanoparticle size will shorten the lithium ion diffusion path, increase the electrochemical reaction conversion rate of the material under high current density, and improve the material rate performance. The extension of the carbon chain and the presence of branches can reduce the wurtzite particle size, increase the thickness of the carbon layer, and reduce material defects. However, too long a carbon chain and too many branches will lead to too high a carbon content in the material, too many side reactions, and reduce the actual capacity and first-cycle coulomb efficiency of the material.

[0022] The non-polar group also has an inductive effect on the bonding element S. In addition, the increase of the non-polar group has a confining effect on the nano zinc sulfide during the calcination process. Therefore, the introduction of the branch chain and the increase in the number of carbon atoms will significantly reduce the particle size and defect level of the material, and increase the carbon content of the material, thereby affecting the electrochemical properties of the material. The study found that the regulated and optimized zinc sulfide material has a higher first-cycle coulomb efficiency, better rate performance and cycle stability in alkali metal secondary batteries.

[0023] The substituents and elemental composition in the polar groups of mercapto surfactants induce differential inductive effects. The greater the inductive effect, the greater the electron cloud shift. The smaller the electronegativity of the atoms connected to the surfactant, the smaller the electron cloud shift caused by the inductive effect, which increases the coordination ability of the bonded atom S. The faster the coordination reaction, the smaller the size of the zinc sulfide crystallites in the coordination product. The non-polar substituent R has the following effects on the complex: 1) affects the carbon content in the complex, 2) affects the coordination ability of the bonded atom S to the metal ion through the inductive effect and the spatial effect, and 3) hydrocarbon chain association strengthens the polymerization between the complexes. Therefore, the structure of the non-polar group of the mercapto surfactant will affect the particle size of the carbon composite sulfide nanodots and the thickness of the carbon layer.

[0024] Dibutylammonium dithiophosphate and Zn 2+The crystal growth of ZnS generated by the complex is incomplete and the crystallinity is not high. -C(=S)S-xanthate type surfactant can generate 6H wurtzite, 8H wurtzite, and 10H wurtzite. The crystal structure of zinc sulfide induced by -NC(=S)S-surfactant is wurtzite and 2H wurtzite. The polar group structure has a significant effect on the crystal structure of ZnS, proving that the closer the polar element is to the chemical bonding element S in the structure of the mercapto surfactant, the greater the influence on the crystal structure of the material. The zinc sulfide generated by the mercapto surfactant with stronger coordination ability has better electrochemical properties.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) This solution changes the idea of ​​controlling the crystal structure of zinc sulfide by calcination temperature in the industry. It provides for the first time a method for preparing materials based on precursors to achieve the material performance regulation. It provides a new idea that can more accurately achieve the regulation of the crystal structure, defect structure and particle size structure of zinc sulfide. It has guiding significance for the targeted regulation of the electrochemical properties of materials. Not only that, it can also unexpectedly improve the performance of materials.

[0027] (2) This scheme innovatively uses the substituent structure of the mercapto surfactant to control the defect structure of zinc sulfide. The increase in the number of carbon atoms of the mercapto surfactant and the presence of the branched chain can significantly reduce the particle size and defect level of zinc sulfide. The increase in the coordination ability of the mercapto surfactant will reduce the defect level and particle size. The non-polar substituent group is too short, the zinc sulfide particle size is mainly large particles with uneven distribution, and the material has a large number of surface defects and dislocation structures.

[0028] (3) The present invention also provides the application of carbon composite nano zinc sulfide materials, which are used as electrode materials for preparing batteries and their negative electrodes, including alkali metal batteries or alkali metal ion batteries, and can significantly improve the electrochemical performance of ion battery negative electrode materials. The electrochemical performance includes first-cycle coulomb efficiency, capacity, cycle life, rate performance, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 FTIR spectrum of sodium dimethyldithiocarbamate, a precursor of the thiol complex in Example 1;

[0031] Figure 2is a SEM image of the thiol complex precursor in Example 1;

[0032] Figure 3 is the XRD spectrum of nano zinc sulfide in Example 1;

[0033] Figure 4 TEM and HRTEM images of nano zinc sulfide in Example 1; (a) is a TEM image (scale bar 200 nm), (b) is a TEM image (scale bar 20 nm), (c) is a HRTEM image (scale bar 5 nm), and (d) is a HRTEM image (scale bar 2 nm);

[0034] Figure 5 This is the EPR diagram of nano zinc sulfide in Example 1;

[0035] Figure 6 0.1A g of nano zinc sulfide in Experimental Example 1 -1 The charge and discharge cycle curves at the current density of ;

[0036] Figure 7 This is the charge and discharge cycle curve of nano zinc sulfide under step current density in Experimental Example 1;

[0037] Figure 8 The nano zinc sulfide in Experimental Example 1 at 10 A g -1 The charge and discharge cycle curves at the current density of ;

[0038] Fig. 9 is the FTIR spectrum of the thiol complex precursor isobutyl zinc xanthate in Example 2;

[0039] Fig.10 The SEM images of nano zinc sulfide in Example 2, (a) is a SEM image at a scale of 20 μm, and (b) is a SEM image at a scale of 5 μm;

[0040] Fig.11 is the XRD pattern of nano zinc sulfide in Example 2;

[0041] Fig.12 TEM and HRTEM images of nano zinc sulfide in Example 2, (a) is the TEM image, (b) is the HRTEM image;

[0042] Fig.13 FTIR spectrum of the thiol complex precursor sodium dibutyl dithiophosphate in Example 3;

[0043] Fig.14 The SEM images of nano zinc sulfide in Example 3, (a) is a SEM image at a scale of 50 μm, and (b) is a SEM image at a scale of 20 μm;

[0044] Fig.15 This is the XRD diagram of the nano zinc sulfide material in Example 3;

[0045] Fig.16 TEM and HRTEM images of nano zinc sulfide in Example 3, (a) is the TEM image, (b) is the HRTEM image;

[0046] Fig.17 This is the EPR diagram of the nano zinc sulfide material in Example 3;

[0047] Fig.18 This is the EPR diagram of nano zinc sulfide in Example 6;

[0048] Fig.19 This is the EPR diagram of nano zinc sulfide in Example 7;

[0049] Fig. 20 This is the EPR diagram of nano zinc sulfide in Example 8. DETAILED DESCRIPTION

[0050] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0051] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0052] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the examples are commercially available.

[0053] Example 1 Preparation of carbon composite nano zinc sulfide.

[0054] S1. At 20° C., 0.02 M sodium diethyldithiocarbamate and 0.01 M zinc sulfate solution were mixed in a volume ratio of 1:1, stirred at a stirring speed of 200 rpm for 3 min, centrifuged at a speed of 4000 r / min for 5 min for solid-liquid separation, and the resulting complex was freeze-dried in a -80° C. freeze dryer for 12 h to obtain a thiol complex precursor;

[0055] S2. The thiol complex precursor prepared in S1 is uniformly mixed with 0.010 mm NaCl in a mass ratio of 1:1, the temperature is raised to 500° C. in a nitrogen atmosphere, and the mixture is kept warm and calcined for 2 h, and then washed with high-frequency ultrasonic water, solid-liquid separated, and dried to obtain carbon composite nano zinc sulfide.

[0056] The thiol complex precursor prepared in step S1 was subjected to FTIR spectroscopy detection, and the results were as follows Figure 1 As shown, the FTIR spectrum proves that the complex is zinc diethyldithiocarbamate (mercapto complex precursor).

[0057] The prepared carbon composite nano zinc sulfide was subjected to scanning electron microscopy (SEM), X-ray diffraction (XRD), TEM and EPR analysis. Figure 2-5 As shown, Figure 2 This is the SEM image of the thiol complex precursor, ethyl dithiocarbamate and Zn 2+ Strong coordination ability, fast coordination reaction speed, and short particle growth time. Therefore, zinc diethyldithiocarbamate has a smaller particle size, mainly distributed in the range of 200-300 nm, and the particle size is uniform; Figure 3 This is the XRD diagram of nano zinc sulfide. The peaks at 26.91º, 28.50º, 30.53º, 47.56º and 51.77º correspond to the (100), (002), (101), (110) and (103) crystal planes of 2H-type wurtzite (JCPDS No: 36-1450), respectively. No other peaks were detected, indicating that the material has a high purity. Figure 4 TEM measurements showed that the material had dislocation defects and a particle size of 5-15 nm. Figure 5 This is the EPR result of the material, proving the existence of O defects in the material.

[0058] Experimental Example 1 The properties of the carbon composite nano zinc sulfide prepared in Example 1 as a negative electrode composite material for a lithium ion battery were investigated.

[0059] The carbon composite nano zinc sulfide material prepared in Example 1 was used as a negative electrode composite material for lithium-ion batteries and was mixed evenly with carboxymethyl cellulose (CMC) and conductive carbon black in a mass ratio of 70:15:15. An appropriate amount of deionized water was added to make a slurry and applied to a copper foil. After the water evaporated, it was placed in a vacuum drying oven at 80°C for 12 hours, and then the copper foil coated with the active material was cut into a disc with a diameter of 12 mm. The disc with a diameter of 12 mm coated with the active material was used as the working electrode, the metal lithium was used as the counter electrode, and the Celgard 2400 composite membrane was used as the diaphragm. The button cell was assembled in an inert gas glove box. The electrode made of carbon-based zinc sulfide negative electrode material was 0.1 A·g -1 The charge and discharge performance curve at the current density is shown in Figure 6 The material’s first charge and discharge specific capacity is 925.6 / 1216.0 mAh g -1 The first cycle coulombic efficiency was 76.16%. It showed the best cycle stability, with a small attenuation of the reversible specific capacity in the first 6 cycles of charge and discharge, from 925.6 mAh g -1 Reduced to 915.7 mAh g -1After that, the capacity slowly increases with the increase of cycle number, and the reversible specific capacity is 978 mAh g at the 100th cycle. -1 , capacity retention is as high as 105.7%.

[0060] Figure 7 The charge-discharge cycle curve of the material under step current density (0.1, 1, 2, 5, 10, 15, 0.1 A g-1) is shown in the figure. -1 At current densities of 1.3, 1.7, 2.1, 3.5, 5.9, 1.1, 2.5, 5.9, 1.1, 2.5, 1.6, 1.8, 2.9, 3.5, 1.9, 2.9, 3.5, 1.6, 2.9, 3.5, 1.8, 2.9, 3.5, 1.9, 3.5, 1.8 ... -1 , 15.0 A g -1 The lithium storage capacity of the material at a current density of 0.1 A g -1 The specific capacity is only 45.4 mAhg at a high current of 15.0 Ag-1. -1 It can be seen that the material exhibits the best rate performance. When the current density is increased from 15.0 Ag -1 Return to 0.1 Ag -1 The specific capacity of the material is 1089.6 mAh g-1, indicating that the material still maintains a good structure under high current density.

[0061] Figure 8 For this material at 10 A g -1 The cycling performance diagram at high current density is 10 A g -1 After 3000 charge-discharge cycles at a high current density, the charge-discharge specific capacity is as high as 516.4 / 516.4 mAh g -1 , the Coulomb efficiency is 100%.

[0062] Example 2 Preparation of carbon composite nano zinc sulfide.

[0063] S1. At 20° C., 0.01 M potassium isobutyl xanthate and 0.02 M zinc sulfate solution were mixed in a volume ratio of 1:1, stirred at a stirring speed of 200 rpm for 3 min, centrifuged at a speed of 5000 r / min for 5 min for solid-liquid separation, and the resulting complex was freeze-dried in a -80° C. freeze dryer for 12 h to obtain a thiol complex precursor;

[0064] S2. The precursor prepared in S1 was mixed evenly with 0.010 mm NaCl in a mass ratio of 1:1, the temperature was raised to 500° C. in a nitrogen atmosphere, and the mixture was kept warm and calcined for 2 h, followed by high-frequency ultrasonic washing, solid-liquid separation, and drying to obtain carbon composite nano zinc sulfide.

[0065] The thiol complex precursor prepared in step S1 was subjected to FTIR spectroscopy detection, and the results were as follows Fig. 9 As shown, the FTIR spectrum proves that the complex is isobutyl zinc xanthate (precursor).

[0066] The prepared carbon composite nano zinc sulfide was subjected to electron microscopy scanning, X-ray diffraction, TEM and HRTEM analysis. Figure 10-12 shown.

[0067] Fig.10 This is a scanning electron micrograph of zinc isobutyl xanthate, a spherical polymer with a particle size of 5-20 μm. Under high magnification ( Fig.11 -b) It was observed that the basic unit of spherical isobutyl zinc xanthate is a nanometer-level lamellae, which are tightly bound to each other. Fig.11 This is the XRD diagram of the material. The sharp peaks at 27.33º, 28.58º, 47.72º, and 56.55º belong to the (102), (0010), (110), and (1110) crystal planes of wurtzite (Wurzite-10H: JCPDS No.12-0688). No other obvious peaks appear, indicating that it is a high-purity 10H-type wurtzite without other impurities, proving that the crystal structure of thiol complex-based zinc sulfide can be regulated by thiol surfactants. Fig.12 (a) is a TEM image of the material, showing that the diameter of ZnS particles is about 14-23nm. Fig.12 (b) is the HRTEM image in high-resolution mode, showing certain dislocation defects, proving that the polar base structure of the thiol complex can regulate the particle size and defect structure of zinc sulfide.

[0068] Experimental Example 2 The properties of the carbon composite nano zinc sulfide prepared in Example 2 as a negative electrode composite material for lithium ion batteries were investigated.

[0069] The battery was assembled using the method of Example 1 at 0.1 A·g -1 The charge and discharge performance at a current density of 10.5 and 14.8 mAh g -1 The first cycle coulombic efficiency was 71.10%. It showed the best cycle stability, and the reversible specific capacity decay was small in the first 6 cycles, from 925.6 mAh g -1 Reduced to 915.7 mAh g -1 After that, the capacity slowly increases with the increase of cycle number, and the reversible specific capacity is 978 mAh g at the 100th cycle. -1 , the capacity is maintained as high as 105.7%. This indicates that wurtzite with different crystal structures has different first-cycle coulombic efficiencies.

[0070] Example 3 Preparation of carbon composite nano zinc sulfide.

[0071] S1. At 20°C, 0.01M dibutyl ammonium dithiophosphate and 0.02M zinc sulfate solution were mixed in a volume ratio of 1:1, stirred at a stirring speed of 200 rpm for 3 min, centrifuged at a speed of 5000 r / min for 5 min for solid-liquid separation, and the resulting complex was freeze-dried in a -80°C freeze dryer for 12 h to obtain a thiol complex precursor;

[0072] S2. The precursor prepared in S1 was mixed evenly with 0.010 mm NaCl in a mass ratio of 1:1, the temperature was raised to 500° C. in a nitrogen atmosphere, and the mixture was kept warm and calcined for 2 h, followed by high-frequency ultrasonic washing, solid-liquid separation, and drying to obtain carbon composite nano zinc sulfide.

[0073] The thiol complex precursor prepared in step S1 was subjected to FTIR spectroscopy detection, and the results were as follows Fig.13 As shown, the FTIR spectrum proves that the complex is dibutyl zinc dithiophosphate (precursor).

[0074] The prepared carbon composite nano zinc sulfide was subjected to electron microscopy scanning, X-ray diffraction, TEM and HRTEM analysis. Figure 14-16 shown.

[0075] Fig.14 This is a scanning electron microscope image of dibutyl zinc dithiophosphate. 2+ The coordination ability of dibutyl ammonium dithiophosphate is weak. The reason is that the coordination number of P in dibutyl ammonium dithiophosphate is 5. In addition to the double bond thioketone bond and single bond thioether bond formed with two S, two butyl groups are connected by two -O-. The negative induction effect of the two -O- is greater than that of one -O- in xanthate. Although the two butyl groups have a positive induction effect, due to the long distance from the chemically bonded atom, the influence on the chemical bonding ability of the S atom is not as great as that of -O-. In addition, the electronegativity of P is smaller than that of C. The dominant role of the negative induction effect of the central atom P and the two O atoms it carries leads to the S atom in dibutyl ammonium dithiophosphate and Zn 2+ The coordination ability of dibutyl ammonium dithiophosphate and Zn 2+ The reaction speed slows down, the crystal nucleation speed is slow at the beginning of the reaction, the number of crystal nuclei is small, and the growth time is sufficient, so it is easy to form particles with larger particle size. Fig.14 It shows that PZnAA presents a dense bulk structure with a size of about 50-100 μm. In addition, the non-polar group of dibutyl ammonium dithiophosphate is an isobutyl structure, and the presence of methyl side chains will also increase the degree of polymerization of the particles, resulting in further growth of the particle size.

[0076] Fig.15This is the XRD diagram of the material. The diffraction peaks at 27.60º, 28.14º, 28.55º, 28.81º and 29.61º correspond to the (013), (104), (1014), (015) and (106) crystal planes of ZnS (JCPDS No: 89-2195), respectively. The curve has a large amount of noise, indicating that the ZnS crystal growth is incomplete and the crystallinity is not high.

[0077] Compared with Examples 1-2, the polar group structure has a significant effect on the ZnS crystal structure, proving that the closer the polar element is to the chemical bonding element S in the structure of the thiol surfactant, the greater the influence on the crystal form of the material. According to the above research results, the degree of crystallinity of the thiol complex-based ZnS composite material is consistent with the order of the bond and atomic S coordination ability of the thiol surfactant.

[0078] Fig.16 This is a TEM image of a zinc dibutyl dithiophosphate-based material, which is composed of uniform nanodots with a particle size of about 25 nm. The HRTEM image shows that there is a local amorphous carbon layer with a thickness of about 2-3 nm, and the carbon layer is unevenly distributed in the SZnAA material. The lattice fringe spacing of SZnAA is 0.312 nm, which corresponds to the (0014) crystal plane of ZnS (JCPDS No: 89-2195). It is worth noting that there are a large number of defects such as dislocations, point defects, and missing lattice fringes on the SZnAA crystal plane. Excessive defects will cause structural changes, damage, and collapse of the material during the charge and discharge cycle, resulting in capacity decay during the charge and discharge process of the material. Fig.17 This is the EPR defect diagram of the material. Compared with Example 2, the material has more vacancy defects.

[0079] Experimental Example 3 The properties of the carbon composite nano zinc sulfide prepared in Example 3 as a negative electrode composite material for lithium ion batteries were investigated.

[0080] The battery was assembled using the method of Example 1 at 0.1 A g -1 At a current density of 1.344 W / m, the initial charge and discharge specific capacities of the materials were 708.3 / 1331.0 mAh g -1 The first cycle coulombic efficiency was only 53.21%. This was because there were many defective structures inside the dibutyl ammonium dithiocarbamate-based SZnAA. The lithium ion embedding process would produce more active sites and too many irreversible reactions. In addition, due to the poor crystal structure, the material had poor cycle stability. After 25 cycles, significant capacity decay began to occur. When the cycle reached 100 cycles, the charge-discharge specific capacity decayed to 364.6 / 379.1 mAh g -1 The materials are available in 0.1, 1.0, 2.0, 5.0, 10.0 and 15.0 A g -1At a current density of 15.0 Ag -1 The specific capacity is only 45.4 mAh g -1 , and when the current density returns to 0.1 A g -1 When the lithium storage capacity is increased, the lithium storage capacity is significantly reduced, indicating that the material has poor structural maintenance ability under high current density.

[0081] Example 4 Preparation of carbon composite nano zinc sulfide.

[0082] S1. At 20° C., 0.01 M sodium dimethyldithiocarbamate and 0.02 M zinc sulfate solution were mixed in a volume ratio of 1:1, stirred at a stirring speed of 200 rpm for 3 min, centrifuged at a speed of 5000 r / min for 5 min for solid-liquid separation, and the resulting complex was freeze-dried in a -80° C. freeze dryer for 12 h to obtain a thiol complex precursor;

[0083] S2. The precursor prepared in S1 was mixed evenly with 0.010 mm NaCl in a mass ratio of 1:1, the temperature was raised to 500° C. in a nitrogen atmosphere, and the mixture was kept warm and calcined for 2 h, followed by high-frequency ultrasonic washing, solid-liquid separation, and drying to obtain carbon composite nano zinc sulfide.

[0084] The composite nano zinc sulfide obtained in this example is 2H-type wurtzite (JCPDS No: 36-1450), and the material particle size is between 15 and 20 nm, which proves that the reduction of the carbon chain of the non-polar group will lead to an increase in the material particle size.

[0085] Experimental Example 4 The properties of the carbon composite nano zinc sulfide prepared in Example 4 as a negative electrode composite material for lithium ion batteries were investigated.

[0086] The battery material was assembled using the method of Example 1 at 0.1 A·g -1 When charged at a current density of 1.5 Å, the material's first coulombic efficiency was 83.69%, and its reversible specific capacity was 855 mAh g at the 100th cycle. -1 , indicating that the increase in particle size will improve the first-cycle coulombic efficiency of the material, because the increase in particle size will reduce the specific surface area of ​​the material and reduce irreversible adsorption. However, because the increase in particle size will extend the lithium ion diffusion path, the capacity of the material will decrease.

[0087] Example 5 Preparation of carbon composite nano zinc sulfide.

[0088] S1. At 20°C, 0.01M sodium dibutyl dithiocarbamate and 0.02M zinc sulfate solution were mixed in a volume ratio of 1:1, stirred at a stirring speed of 200 rpm for 3 min, centrifuged at a speed of 5000 r / min for 5 min for solid-liquid separation, and the resulting complex was freeze-dried in a -80°C freeze dryer for 12 h to obtain a thiol complex precursor;

[0089] S2. The precursor prepared in S1 was mixed evenly with 0.010 mm NaCl in a mass ratio of 1:1, the temperature was raised to 500° C. in a nitrogen atmosphere, and the mixture was kept warm and calcined for 2 h, followed by high-frequency ultrasonic washing, solid-liquid separation, and drying to obtain carbon composite nano zinc sulfide.

[0090] In this example, 2H-type wurtzite (JCPDS No: 36-1450) was obtained, and the particle size of the material was between 4 and 10 nm, which proved that the extension of the carbon chain of the non-polar group can reduce the particle size of the material.

[0091] Experimental Example 5 The properties of the carbon composite nano zinc sulfide prepared in Example 5 as a negative electrode composite material for lithium ion batteries were investigated.

[0092] The battery material was assembled using the method of Example 1 at 0.1 A·g -1 When charged at a current density of 1.34 Å, the material's first coulombic efficiency was 75.21%, and its reversible specific capacity was 1031 mAh g at the 100th cycle. -1 , indicating that the reduction of particle size will reduce the first-cycle coulombic efficiency of the material, but because the reduction of particle size will improve the lithium ion diffusion kinetics, the capacity of the material will be improved.

[0093] Example 6 Preparation of carbon composite nano zinc sulfide.

[0094] S1. At 20°C, 0.01M sodium ethyl xanthate and 0.02M zinc sulfate solution were mixed in a volume ratio of 1:1, stirred at a stirring speed of 200 rpm for 3 min, centrifuged at a speed of 5000 r / min for 5 min for solid-liquid separation, and the resulting complex was freeze-dried in a -80°C freeze dryer for 12 h to obtain a thiol complex precursor;

[0095] S2. The precursor prepared in S1 was mixed evenly with 0.010 mm NaCl in a mass ratio of 1:1, the temperature was raised to 500° C. in a nitrogen atmosphere, and the mixture was kept warm and calcined for 2 h, followed by high-frequency ultrasonic washing, solid-liquid separation, and drying to obtain carbon composite nano zinc sulfide.

[0096] In this example, 10H wurtzite (Wurzite-10H: JCPDS No.12-0688) was obtained, and the particle size was uneven, ranging from 18 to 76 nm. Fig.18This is the EPR defect map of the material.

[0097] Experimental Example 6 The properties of the carbon composite nano zinc sulfide prepared in Example 6 as a negative electrode composite material for lithium ion batteries were investigated.

[0098] The battery was assembled using the method of Example 1 at 0.1 A·g -1 The charge and discharge performance at a current density of 1.5 % and the reversible specific capacity at the 100th cycle is 366.1 mAh g -1 , indicating that as the particle size increases, the lithium storage capacity of the material decreases. This may be because the diffusion path of lithium ions becomes larger as the particle size increases, resulting in the actual amount of ZnS participating in the reaction being lower than the theoretical value. In addition, if the ZnS particle size is too large, the cyclic stability of the material will deteriorate.

[0099] Example 7 Preparation of carbon composite nano zinc sulfide.

[0100] S1. At 20°C, 0.01M potassium butyl xanthate and 0.02M zinc sulfate solution were mixed in a volume ratio of 1:1, stirred at a stirring speed of 200 rpm for 3 min, centrifuged at a speed of 5000 r / min for 5 min for solid-liquid separation, and the resulting complex was freeze-dried in a -80°C freeze dryer for 12 h to obtain a thiol complex precursor;

[0101] S2. The precursor prepared in S1 was mixed evenly with 0.010 mm NaCl in a mass ratio of 1:1, the temperature was raised to 500° C. in a nitrogen atmosphere, and the mixture was kept warm and calcined for 2 h, followed by high-frequency ultrasonic washing, solid-liquid separation, and drying to obtain carbon composite nano zinc sulfide.

[0102] This scheme obtains 10H wurtzite (Wurzite-10H: JCPDS No.12-0688), which is concentrated around 40 nm, indicating that the longer the carbon chain of xanthate, the smaller the particle size of the prepared material. This further proves that the increase of carbon chain and the addition of branched hydrocarbon chain structure help to prevent the aggregation of sulfide crystallites under high temperature conditions, which is conducive to the acquisition of nano-sized sulfide. Fig.19 This is the EPR defect diagram of the material. Compared with Example 2 and Example 6, the vacancy defects of the material are less than that of sodium ethyl xanthate, and more than that of the material obtained from sodium isobutyl xanthate, indicating that the increase of the carbon chain and the introduction of the branched hydrocarbon chain structure are beneficial to reducing the defects of the material.

[0103] Experimental Example 7 The properties of the carbon composite nano zinc sulfide prepared in Example 7 as a negative electrode composite material for lithium ion batteries were investigated.

[0104] The battery was assembled using the method of Example 1 at 0.1 A·g -1 The charge and discharge performance at a current density of 1.5 % and the reversible specific capacity at the 100th cycle is 639.6 mAh g-1 .

[0105] Example 8 Preparation of carbon composite nano zinc sulfide.

[0106] S1. At 20° C., 0.01 M potassium isopentyl xanthate and 0.02 M zinc sulfate solution were mixed in a volume ratio of 1:1, stirred at a stirring speed of 200 rpm for 3 min, centrifuged at a speed of 5000 r / min for 5 min for solid-liquid separation, and the resulting complex was freeze-dried in a -80° C. freeze dryer for 12 h to obtain a thiol complex precursor;

[0107] S2, the precursor prepared in S1 was mixed with 0.010mm NaCl in a mass ratio of 1:1, heated to 500℃ in a nitrogen atmosphere, kept warm for 2h, washed with high-frequency ultrasonic water, separated solid and liquid, and dried to obtain carbon composite nano zinc sulfide. This scheme obtained 10H wurtzite (Wurzite-10H: JCPDS No.12-0688) with a particle size of about 16 nm. Fig. 20 is the EPR defect map of the material. Compared with Example 2, the defect concentration of the material is lower, which further illustrates that the increase in carbon chain length will reduce the particle size and defect concentration of the material.

[0108] Experimental Example 8 The properties of the carbon composite nano zinc sulfide prepared in Example 8 as a negative electrode composite material for lithium ion batteries were investigated.

[0109] The battery was assembled using the method of Example 1 at 0.1 A·g -1 The charge and discharge performance at a current density of 1.547 W / m was 702.3 mAh g at the 100th cycle. -1 .

[0110] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and changes obtained without departing from the technical concept of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing nano zinc sulfide with adjustable crystal structure, characterized in that: The following steps are involved: S1. Mixing the zinc sulfate solution and the thiol surfactant at room temperature, centrifuging and freeze-drying the solid to obtain a thiol complex precursor; S2, mixing the thiol complex precursor prepared in S1 with NaCl uniformly, heating under a nitrogen atmosphere and then calcining the mixture at the same temperature, washing the calcined product with high-frequency ultrasonic water, performing solid-liquid separation, and drying the product to obtain carbon composite nano zinc sulfide; The mercapto surfactant includes sodium diethyldithiocarbamate, potassium isobutyl xanthate, dibutyl ammonium dithiophosphate, sodium dimethyldithiocarbamate, sodium dibutyldithiocarbamate, sodium ethyl xanthate, potassium butyl xanthate, and potassium isopentyl xanthate; In the step S2, the particle size of NaCl is 0.010 mm to 0.037 mm; the particle size of the carbon composite nano zinc sulfide is 2 to 100 nm; In the step S2, the mass ratio of the thiol complex precursor to NaCl is 1:1; the calcination temperature is 500-600° C. and the calcination time is 2-3 hours.

2. The preparation method according to claim 1, characterized in that: In the step S1, the room temperature is 15-35°C, the concentration ratio of the zinc sulfate solution to the thiol surfactant is 2:1, and the volume ratio is 1:1; the stirring speed is 200 rpm, and the time is 3 min; the centrifugal speed is 5000 r / min, and the time is 5 min; the freeze-drying temperature is -80°C, and the time is 12 h.

3. The preparation method according to claim 1, characterized in that: The carbon composite nano zinc sulfide includes any one of 2H-type wurtzite and 10H-type wurtzite.

4. Use of nano zinc sulfide prepared by the preparation method according to any one of claims 1 to 3 in regulating zinc sulfide crystals.

5. Use of nano zinc sulfide prepared by the preparation method according to any one of claims 1 to 3 in regulating the defect types of zinc sulfide.

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