Tin disulfide negative electrode material for lithium battery and preparation method of tin disulfide negative electrode material

Abstract

The invention discloses a tin disulfide negative electrode material for a lithium ion battery and a preparation method of the tin disulfide negative electrode material, and belongs to the technical field of lithium battery negative electrode materials. The preparation method comprises the following steps: dissolving sodium stannate (chlorine-free tin source) and thiourea (chlorine-free sulfur source) in deionized water, adjusting the pH value to 1-3 by dilute sulphuric acid, adding melamine (20% by mass of sodium stannate), and stirring to obtain a precursor solution; and transferring into a magnetic stirring autoclave, reacting at 180-220 DEG C for 6-10 hours, and carrying out centrifugal washing (alternating deionized water and absolute ethyl alcohol) and vacuum drying (at 50-70 DEG C, 7-12 hours) on the product to obtain the nitrogen-doped flower-like tin disulfide powder. The method puts an end to chloride ions, solves the problem of equipment corrosion, does not need complex post-treatment, and is short in process and low in cost; due to the nitrogen doping and layered structure, the product is excellent in cycling stability (the capacity retention rate of 300 circles is 97.6%) and rate performance, and an industrialization scheme is provided for a high-performance lithium battery negative electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode materials, in particular to a chlorine-free and nitrogen-doped tin disulfide (SnS2) negative electrode material and a process for preparing the material by one-step hydrothermal method. The material can effectively improve the electrochemical performance of lithium ion batteries and is suitable for the production and application of high-energy-density lithium ion batteries. BACKGROUND

[0002] The performance of lithium ion batteries depends largely on the characteristics of their negative electrode materials. The currently commercialized graphite negative electrode material has a low theoretical capacity (only 372 mAh / g) and is prone to lithium precipitation and structural damage during high-current charging and discharging, making it difficult to meet the needs of the next generation of high-energy-density lithium batteries. Therefore, it is crucial to develop new high-performance negative electrode materials.

[0003] Among the numerous new negative electrode materials, tin disulfide (SnS2) is considered a promising alternative to graphite due to its high theoretical capacity (about 645 mAh / g), suitable lithium ion intercalation potential, and environmental friendliness. However, SnS2 also faces severe challenges in practical applications: first, during the lithium ion intercalation and deintercalation processes, SnS2 undergoes a significant volume change (up to 300%), leading to the pulverization and shedding of active materials, which in turn causes rapid capacity decay; second, the intrinsic electrical conductivity is low, resulting in sluggish electrode reaction kinetics and poor rate performance.

[0004] To overcome the above-mentioned defects, common technical means include nanostructuring, carbon compounding, or element doping. Among them, the hydrothermal method is widely used to prepare SnS2 nanomaterials due to its simple operation and controllable morphology. However, existing hydrothermal synthesis techniques have the following outstanding shortcomings: (1) Strongly corrosive raw materials: stannous chloride (SnCl2) or tin tetrachloride (SnCl4) is commonly used as the tin source. These chloride salts are inherently highly corrosive and toxic, and their use, storage, and subsequent disposal pose safety and environmental hazards; (2) High equipment requirements and costs: the released chloride ions (Cl - ) in the high-temperature and high-pressure hydrothermal environment cause severe corrosion of the stainless steel reaction kettle body, forcing the reaction to be carried out in a polytetrafluoroethylene lining, which significantly increases equipment costs and energy consumption; (3) Complex composition and process: in order to improve the electrochemical performance of SnS2, carbon materials (such as graphene, carbon nanotubes) are often introduced or complex post-treatment (such as high-temperature carbonization) is performed, resulting in a long process flow, high cost, and possible introduction of impurity phases.

[0005] In summary, the prior art has not yet been able to provide a solution that combines "high-performance SnS2 material" and "low cost, low risk, simple process". Therefore, it is of great significance to develop a chlorine-free, short-process, low-cost preparation method to realize the intrinsic improvement of the structural stability and conductivity of SnS2 material, which promotes the industrial application of SnS2 negative electrode material. SUMMARY

[0006] In view of the problems of "raw material containing chlorine corroding equipment", "complex process and high cost", "poor material cycle stability and conductivity" and the like in the preparation of SnS2 negative electrode material in the prior art, the present application provides a tin disulfide negative electrode material for lithium battery and a preparation method thereof. The method is based on chlorine-free raw materials, realizes nitrogen doping through one-step hydrothermal method, has simple process, low cost and high safety, and can effectively inhibit the volume expansion of SnS2 in the cycle process, and significantly improve the conductivity and cycle stability.

[0007] In order to achieve the above-mentioned purpose, the specific scheme adopted by the present application is as follows: On the one hand, the present application discloses a preparation method of a tin disulfide negative electrode material for lithium ion battery, comprising the following steps: (1) Dissolve sodium stannate and thiourea in deionized water respectively, adjust the pH value of the solution to 1-3, and obtain a mixed solution; (2) Add melamine to the mixed solution and stir until dissolved to obtain a precursor solution; wherein the addition amount of melamine is 20% of the mass of sodium stannate; (3) Put the precursor solution into a magnetic stirring autoclave, and stir at 180-220℃ for 6-10h, and cool to room temperature after reaction; (4) Centrifugal washing and drying the obtained product to obtain a tin disulfide powder material.

[0008] Further, in step (1), the molar ratio of tin element to sulfur element in sodium stannate and thiourea is 1:1-1:12.

[0009] Further, in step (1), dilute sulfuric acid is used to adjust the pH value of the solution.

[0010] Further, in step (4), the centrifugal washing is alternately washed with deionized water and anhydrous ethanol for at least 3 times.

[0011] Further, in step (4), the drying is vacuum drying, the drying temperature is 50-70℃, and the drying time is 7-12h.

[0012] On the other hand, the present application discloses a tin disulfide negative electrode material for lithium ion battery prepared by the above-mentioned method, which is nitrogen-doped tin disulfide and has a flower-like morphology with hexagonal sheet accumulation.

[0013] Furthermore, the average size of the hexagonal sheet is 2 μm.

[0014] The core advantage of this invention stems from the innovative design of the raw material system and the synergistic effect of the one-step hydrothermal process. Its working principle can be explained from the following three aspects: (1) The principle of solving corrosion and safety problems in chlorine-free raw material system Traditional hydrothermal methods use tin chloride as the tin source, and Cl is released during the reaction. - High temperature and pressure can cause strong corrosion to stainless steel reactors. This invention innovatively uses sodium stannate (Na2SnO3) instead of tin chloride as the tin source, and thiourea (CH4N2S) as the sulfur source. Neither raw material contains chlorine, thus eliminating the generation of Cl⁻ at the source. Therefore, the reaction can be carried out directly in a conventional stainless steel autoclave, eliminating the need for an expensive PTFE liner. This reduces equipment costs and maintenance difficulty, avoids the toxicity and corrosive risks of chloride salt raw materials, and improves the safety and economy of the process.

[0015] (2) The principle of melamine improving material properties Melamine (C3H6N6) is used as a nitrogen doping source, and its addition of 20% (relative to the mass of sodium stannate) is key to optimizing material properties. The specific working principle includes: (I) Improved conductivity: After nitrogen (N) is doped into SnS2 crystal, it will change the electronic structure around SnS2, introduce additional charge carriers, significantly reduce the electronic resistance of the material, accelerate the electrode reaction kinetics rate, and improve the rate performance of the battery. (II) Suppressing volume expansion: Nitrogen atoms bridge adjacent SnS2 layers through chemical bonds (such as Sn-N bonds), enhancing interlayer bonding and suppressing the slippage and peeling of SnS2 layers during cycling, thereby reducing volume expansion (significantly reduced from the traditional 300%), preventing active materials from pulverizing and falling off, and improving cycling stability. (III) Optimize interface performance: Nitrogen doping can adjust the interface characteristics between SnS2 and electrolyte, promote the formation of a uniform and dense solid electrolyte interface (SEI) film, reduce the continuous decomposition of electrolyte and loss of active lithium, reduce interface resistance, accelerate the transport of lithium ions at the electrode-electrolyte interface, and improve charge and discharge efficiency.

[0016] (3) The principle of achieving short process and high performance in one-step hydrothermal method The present application introduces tin source (sodium stannate), sulfur source (thiourea) and nitrogen doping source (melamine) into the same hydrothermal reaction system at one time, synchronously completes the crystallization, morphology control and nitrogen doping process of SnS2 through chemical reaction under high temperature and high pressure environment. Compared with the two-step method of "synthesizing SnS2 and then carrying out nitrogen doping (additional high temperature heat treatment is needed)" in the traditional process, the present application does not need raw material pretreatment and product post-treatment (such as high temperature carbonization), and the process flow is greatly shortened. At the same time, one-step reaction can ensure that nitrogen elements are uniformly doped in SnS2 crystals, avoid uneven doping or impurity introduction caused by subsequent treatment, and ensure the stability of material performance; in addition, the omission of post-treatment process also significantly reduces energy consumption and time cost, and is more suitable for large-scale industrial production.

[0017] Through the synergistic innovation of raw material system, process design and doping strategy, compared with the prior art, the present application has the following remarkable beneficial effects, and all effects are directly related to the specific selection of raw materials and step design: (1) Safety is improved, and equipment cost is reduced: the present application innovatively selects sodium stannate (chlorine-free) to replace the traditional chlorine-containing tin source (stannous chloride, tin tetrachloride), and matches thiourea (chlorine-free) as the sulfur source, which eliminates the generation of chloride ions (Cl - ) from the source. On the one hand, it avoids the corrosion of Cl - to the reaction kettle under high temperature and high pressure hydrothermal environment, so that the reaction can be directly carried out in a conventional stainless steel autoclave without using expensive and low heat transfer efficiency polytetrafluoroethylene lining, which greatly reduces the equipment investment cost; on the other hand, it eliminates the toxicity and strong corrosive risk of chloride raw materials, simplifies the process of raw material storage, transportation and subsequent waste treatment, and significantly improves the safety of the production process.

[0018] (2) Process is simplified, and production efficiency is improved: the one-step hydrothermal method is used to simultaneously complete the synthesis and nitrogen doping of tin disulfide (SnS2), without the need for pretreatment of raw materials (such as tin source purification) and post-treatment of products (such as high temperature carbonization, carbon material compounding, etc.), which greatly shortens the process flow. Among them, the centrifugal washing link is carried out by deionized water and anhydrous ethanol alternately, which can completely remove the residual ions and unreacted raw materials in the product; the setting of vacuum drying parameters (temperature 50-70℃, time 7-12h) ensures the drying effect while considering the material stability, avoiding excessive drying damage to the crystal structure. The whole process not only greatly compresses the production cycle, but also reduces the energy consumption by omitting the post-treatment process (especially high temperature carbonization), and does not need to add additional surfactants or carbon materials, which further simplifies the operation and controls the production cost, and is more suitable for large-scale industrial production.

[0019] (3) Material cycle stability is significantly improved: with melamine of 20% of the mass of sodium stannate as a nitrogen-doped source, the prepared SnS2 forms a flower-like layered structure with hexagonal sheet layers (average size 2 pm) stacked. Nitrogen elements bridge SnS2 layers through chemical bonds, effectively inhibiting interlayer slip and volume expansion (from the traditional 300%) during the cycle; at the same time, the layered stacked structure can further buffer the volume change to avoid active material pulverization and shedding. Experimental data (Example 1) show that at a current density of 500 mA / g, the discharge specific capacity of the material is still 491.4 mAh / g after 300 cycles, and the capacity retention rate is as high as 97.6%, which is much better than the comparative example 1 without nitrogen doping (the capacity is only 377.6 mAh / g after 140 cycles, and the capacity retention rate is less than 34%).

[0020] (4) Material conductivity and rate performance are optimized: nitrogen doping can change the electronic structure of SnS2, introduce additional carriers, reduce electronic resistance, and accelerate the electrode reaction kinetics rate. This enables the material to maintain stable performance under high current charge and discharge scenarios. Experimental data (Example 1) show that even at a high current density of 2.0 A / g, the material still has stable discharge specific capacity; when the current density returns to 0.1 A / g from 2.0 A / g, the capacity quickly recovers to a high level and the overall trend is smooth, proving that it has excellent rate performance and can meet the demand for large current applications such as electric vehicle fast charging.

[0021] (5) High material purity and good performance stability: by strictly controlling the raw material ratio (molar ratio of tin element to sulfur element 1:1-1:12), ensuring that the reaction proceeds fully and reducing the generation of impurity phases; using dilute sulfuric acid to adjust the solution pH to 1-3 to provide a suitable acidic environment for SnS2 crystallization and promote regular crystal growth; combined with centrifugal washing (deionized water and anhydrous ethanol are alternately washed ≥3 times) to completely remove residual impurities. The finally prepared SnS2 powder has high purity, and clear lattice fringes can be observed by high-resolution transmission electron microscopy (HRTEM) without obvious impurity phases; the performance difference between batches is small, which can effectively guarantee the performance consistency during battery production. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The flowchart of the preparation process of the present application.

[0023] Figure 2 The FESEM image of the sample prepared in Example 1 shows its flower-like morphology.

[0024] Figure 3 The HRTEM image of the sample prepared in Example 1 shows its clear lattice fringes and layered structure.

[0025] Figure 4FESEM image of the sample prepared for Comparative Example 1 shows its flower-like morphology.

[0026] Figure 5 Cycle performance comparison chart of electrode materials prepared for different examples and comparative examples at a current density of 500 mA / g.

[0027] Figure 6 Rate performance chart of the electrode material prepared for Example 1. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described clearly and completely below in combination with specific examples. Obviously, the described examples are only some of the examples of the present application, but not all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0029] In a first aspect, the present application provides a preparation method of a tin disulfide negative material for lithium batteries, please refer to Figure 1 The preparation method includes the following four steps, which does not require chlorine-containing raw materials throughout, and the material synthesis and nitrogen doping are completed by one-step hydrothermal reaction: (1) Mixed solution preparation: sodium stannate (as a tin source, replacing traditional tin chloride) and thiourea (as a sulfur source) are respectively dissolved in deionized water, after stirring to complete dissolution, dilute sulfuric acid is used to adjust the pH value of the solution to 1-3, to obtain a uniform mixed solution; wherein the molar ratio of tin element (Sn) to sulfur element (S) in sodium stannate and thiourea is controlled to be 1:1-1:12, to ensure sufficient reaction and stable product composition; (2) Preparation of precursor solution: melamine (as a nitrogen doping source) is added to the above-mentioned mixed solution, and continuous stirring is performed until the melamine is completely dissolved, to form a precursor solution; wherein the addition amount of melamine is strictly controlled to be 20% of the mass of sodium stannate, which is the optimal doping amount verified by experiments, and can achieve the best balance of conductivity and structural stability; (3) One-step hydrothermal reaction: the precursor solution is transferred to a magnetic stirring autoclave (without polytetrafluoroethylene lining, a conventional stainless steel autoclave can be directly used), and kept under magnetic stirring at a temperature of 180-220℃ for 6-10h; after the reaction is completed, the product is cooled to room temperature naturally, so that the product is fully crystallized; (4) Product separation and drying: the mixed solution after reaction is centrifuged and washed, deionized water and anhydrous ethanol are used for alternating washing at least 3 times, to remove unreacted impurities and residual ions; then the washed precipitate is vacuum dried, the drying temperature is controlled to be 50-70℃, and the drying time is 7-12h, to finally obtain a tin disulfide powder material.

[0030] In still another aspect, the present application provides a tin disulfide negative material, the tin disulfide negative material for lithium ion battery prepared by the above method, having the following core characteristics: (1) the material is nitrogen-doped tin disulfide, nitrogen elements are uniformly distributed in the SnS2 crystal structure and combined with the SnS2 layer through chemical bonds; (2) the material presents a flower-like morphology, which is self-assembled and stacked by hexagonal lamellae, and the average size of the hexagonal lamellae is 2 μm; the layered stacking structure can effectively buffer the volume change in the cycle process and improve the structural stability.

[0031] The technical solutions of the present application are further described below in combination with specific examples and comparative examples. The raw materials used in the examples and comparative examples are all analytical pure or industrial grade reagents, specifically including: sodium stannate (Na2SnO3·3H2O), thiourea (CH4N2S), melamine (C3H6N6), dilute sulfuric acid (H2SO4, concentration 1 mol / L), deionized water, anhydrous ethanol (C2H5OH). The equipment used in the experiment is a 150 mL mini magnetic stirring autoclave (with real-time temperature and pressure display device and pressure relief valve), a high-speed centrifuge, a vacuum drying oven, a field emission scanning electron microscope (FESEM), a high-resolution transmission electron microscope (HRTEM), and a battery assembly device and test system for electrochemical performance test.

[0032] Example 1 (1) Preparation of initial solution: 1 g of sodium stannate and 0.856 g of thiourea (molar ratio of tin element to sulfur element is 1:3) were accurately weighed and dissolved in 80 mL of deionized water, and stirred at room temperature for 30 min until the two raw materials were completely dissolved; then the pH value of the solution was slowly adjusted to 2 using dilute sulfuric acid, and the stirring was continued for 30 min to obtain a uniform mixed solution; (2) Preparation of precursor solution: 0.2 g of melamine (20% of the mass of sodium stannate) was added to the above mixed solution, and the stirring was continued at room temperature for 1 h until the melamine was completely dissolved, forming a clear and transparent precursor solution; (3) One-step hydrothermal reaction: the precursor solution was transferred to a 150 mL mini magnetic stirring autoclave, and after sealing, the magnetic stirring speed was set to 300 r / min, and the temperature was programmed to 200 ℃, and the reaction was carried out at this temperature for 8 h; after the reaction was completed, the heating device was turned off, and the autoclave was naturally cooled to room temperature; (4) Separation and drying of the product: the autoclave was opened, and the mixed solution after reaction was taken out and placed in a high-speed centrifuge for centrifugal separation at a speed of 12000 r / min, and each time for 5 min; after centrifugation, the supernatant was poured out, and the precipitate was washed with deionized water and anhydrous ethanol alternately, and the washing was repeated for 4 times; finally, the washed precipitate was placed in a vacuum drying oven and dried at a temperature of 60 ℃ for 12 h to obtain a white tin disulfide powder material.

[0033] Comparative Example 1 (tin disulfide material without melamine addition) (1) Initial solution preparation: 1 g of sodium stannate and 0.856 g of thiourea (molar ratio of tin element to sulfur element 1:3) were accurately weighed and dissolved in 80 mL of deionized water, stirred at room temperature for 30 min until completely dissolved; the pH value of the solution was adjusted to 2 with dilute sulfuric acid, and stirring was continued for 30 min to obtain a mixed solution; (2) Hydrothermal reaction: the mixed solution was directly transferred to a 150 mL mini magnetic stirring autoclave, the magnetic stirring speed was set to 300 r / min, the temperature was raised to 200°C and kept for 8 h; after the reaction was completed, it was naturally cooled to room temperature; (3) Product separation and drying: the subsequent centrifugal washing (12000 r / min, deionized water and anhydrous ethanol were alternately washed 4 times, 5 min each time), vacuum drying (60°C, 12h) steps were exactly the same as in Example 1, and finally the tin disulfide powder material was obtained.

[0034] Comparative Example 2 (tin disulfide material doped with low-dose melamine) (1) Initial solution preparation: 1 g of sodium stannate and 0.285 g of thiourea (molar ratio of tin element to sulfur element 1:1) were accurately weighed and dissolved in 80 mL of deionized water, stirred at room temperature for 30 min until completely dissolved; the pH value of the solution was adjusted to 1 with dilute sulfuric acid, and stirring was continued for 30 min to obtain a mixed solution; (2) Precursor solution preparation: 0.1 g of melamine (10% of the mass of sodium stannate) was added to the mixed solution, stirred at room temperature for 1 h until completely dissolved, forming a precursor solution; (3) Hydrothermal reaction and product treatment: the precursor solution was transferred to a 150 mL mini magnetic stirring autoclave, the stirring speed was 300 r / min, the temperature was raised to 180°C and kept for 10 h; after cooling, centrifugal washing (10000 r / min, alternately washed 4 times) and vacuum drying (60°C, 12h) were carried out according to the method of Example 1, to obtain a tin disulfide powder material.

[0035] Comparative Example 3 (tin disulfide material doped with high-dose melamine) (1) Initial solution preparation: 1 g of sodium stannate and 3.425 g of thiourea (molar ratio of tin element to sulfur element 1:12) were accurately weighed and dissolved in 80 mL of deionized water, stirred at room temperature for 30 min until completely dissolved; the pH value of the solution was adjusted to 3 with dilute sulfuric acid, and stirring was continued for 30 min to obtain a mixed solution; (2) Precursor solution preparation: 0.3 g of melamine (30% of the mass of sodium stannate) was added to the mixed solution, stirred at room temperature for 2 h until completely dissolved, forming a precursor solution; (3) Hydrothermal reaction and product processing: The precursor solution was transferred to a 150 mL micro magnetic stirring autoclave, stirred at 300 r / min, heated to 220 °C and kept at that temperature for 6 h; after cooling, it was centrifuged and washed (12000 r / min, 4 times alternately) and vacuum dried (60 °C, 12 h) according to the method in Example 1 to obtain tin disulfide powder material.

[0036] The materials of the products obtained in the examples and comparative examples are characterized below.

[0037] (I) Morphological and structural characterization The morphology and crystal structure of the tin disulfide powder materials prepared in Example 1 and Comparative Example 1 were analyzed using FESEM and HRTEM: Figure 2 As can be seen, the material obtained in Example 1 exhibits a uniform flower-like morphology, which is formed by the self-assembly and stacking of hexagonal sheet-like nanosheets. The average size of the hexagonal sheets is approximately 2 μm, and the particle distribution is relatively uniform with no obvious agglomeration. Figure 3 (HRTEM image) shows that the material has clear lattice fringes and a layered crystal structure. The lattice arrangement is regular and there are no obvious defects. This indicates that the prepared tin disulfide crystal structure is complete and well-dispersed, and also shows that nitrogen doping has not destroyed the integrity of the tin disulfide crystal structure. Figure 4 As can be seen, without the addition of melamine, the material obtained in Comparative Example 1 also exhibits a flower-like morphology formed by the stacking of hexagonal sheets, which is basically consistent with the morphology of Example 1. This indicates that the addition of melamine did not change the basic morphological characteristics of tin disulfide, but only affected its internal structure and performance through chemical doping.

[0038] (II) Electrochemical performance characterization (1) Battery preparation: The tin disulfide powder materials prepared in Example 1 and Comparative Examples 1-3 were used as negative electrode active materials, and were mixed with conductive agent (acetylene black) and binder (polyvinylidene fluoride) at a mass ratio of 8:1:1. N-methylpyrrolidone solvent was added to prepare a slurry, which was uniformly coated on copper foil current collector. After drying and rolling, a negative electrode sheet was prepared. A lithium metal sheet was used as the counter electrode, Celgard 2400 was used as the separator, and 1 mol / L LiPF6 (solvent EC:DMC:EMC=1:1:1, volume ratio) was used as the electrolyte. The CR2032 coin cell was assembled in an argon-protected glove box. The battery was then subjected to cycle performance test (current density 500 mA / g) and rate performance test (current density was 0.1 A / g, 0.2 A / g, 0.5 A / g, 1.0 A / g, 2.0 A / g, and finally returned to 0.1 A / g).

[0039] (2) Results Analysis: Based on the comparison chart of cycle performance ( Figure 5) can be seen that the initial discharge specific capacity of the product of Example 1 (blue curve) is 503.3 mAh / g, and after 100 cycles, it is 406.6 mAh / g, and after 200 cycles, the capacity tends to be stable, and after 300 cycles, it reaches 491.4 mAh / g, with a capacity retention rate of up to 97.6%; the initial discharge specific capacity of Comparative Example 1 (black curve) is 1123.2 mAh / g, but after 100 cycles, it decreases to 430.1 mAh / g, and after 140 cycles, it is only 377.6 mAh / g; the initial discharge specific capacity of Comparative Example 2 (red curve) is 1118.1 mAh / g, and after 100 cycles, it is only 266.2 mAh / g; the initial discharge specific capacity of Comparative Example 3 (green curve) is 1135.5 mAh / g, and after 100 cycles, it is 340.5 mAh / g, and the capacity decay of the latter three is much faster than that of Example 1. As can be seen from the rate performance graph Figure 6 ) can be seen that the capacity of the product of Example 1 slowly decreases at a current density of 0.1 A / g, and the capacity remains stable at 0.2 A / g, 0.5 A / g, 1.0 A / g and 2.0 A / g, and the capacity can recover to a high level after the current density returns to 0.1 A / g, and the rate performance is excellent.

[0040] (3) Reason analysis: the performance of Example 1 (20% sodium stannate is added to melamine) is excellent, and the key lies in the multiple roles played by melamine as a nitrogen doping source: nitrogen atoms bridge SnS2 layers through chemical bonds, enhance the interlayer bonding force, effectively inhibit the interlayer slip and volume expansion during the cycle process, avoid the pulverization and shedding of active materials; at the same time, nitrogen doping changes the electronic structure around SnS2, introduces electron donor characteristics, significantly improves the electronic conductivity of the material, and reduces the electrode reaction polarization; in addition, nitrogen doping can also optimize the interface performance of the material and the electrolyte, promote the formation of a uniform and dense solid electrolyte interface (SEI) film, reduce the continuous decomposition of the electrolyte and the loss of active lithium. And at the beginning of the cycle, part of the nitrogen doping sites may be temporarily occupied by Li + or by-products, and as the cycle progresses, these sites gradually release and participate in charge storage, causing the material capacity to show a gradual activation rising trend. In contrast, without nitrogen doping (Comparative Example 1) or with low-dose nitrogen doping (0.1 g of melamine, Comparative Example 2), the volume expansion of SnS2 material is not effectively inhibited, and repeated charging and discharging easily causes the particles to pulverize, resulting in poor contact between the active material and the current collector; at the same time, due to the lack of sufficient nitrogen doping to improve the conductivity, the electrode reaction polarization is intensified, ultimately causing the capacity to rapidly decay. Excessive nitrogen doping (0.3 g of melamine, Comparative Example 3) is also not conducive to performance improvement: excessive nitrogen may cover the active surface of SnS2 in the form of non-active agglomerates, hindering the diffusion of Li +Diffusion inside the material; and too high doping concentration will introduce too many lattice defects, accelerate the collapse of SnS2 crystal structure, and thus lead to worse cycle performance than Example 1. This further confirms that the 20% (0.2g) melamine addition amount is the optimal value to achieve the best balance between nitrogen doping effect and SnS2 structure stability.

[0041] In conclusion, by designing a chlorine-free raw material system and a key dopant melamine and its optimal addition amount, the three major problems of corrosion, conductivity and structural stability are ingeniously solved in a simple hydrothermal step, providing a high-performance, low-cost, and industrialized SnS2 negative electrode material and its preparation method. The preparation process is simple and easy to operate, does not need to add common surfactants, and the equipment is safe. The hydrothermal product can be directly used as a lithium battery negative electrode material without subsequent heating treatment process, and has good charge and discharge cycle performance.

[0042] The above only describes preferred embodiments of the present application and is not intended to limit the present application in any form. Any equivalent transformation or modification according to the essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing a tin disulfide negative material for lithium ion batteries, characterized by, The method comprises the following steps: (1) dissolving sodium stannate and thiourea in deionized water respectively, adjusting the pH value of the solution to 1-3 to obtain a mixed solution; (2) adding melamine into the mixed solution and stirring until the melamine is dissolved completely to obtain a precursor solution; wherein the amount of the melamine added is 20% of the mass of the sodium stannate; (3) placing the precursor solution in a magnetic stirring autoclave, stirring at 180-220 ℃ for 6-10 h, and cooling to room temperature after the reaction is completed; (4) centrifuging and washing the obtained product, and drying to obtain a tin disulfide powder material.

2. The method for preparing a tin disulfide anode material for lithium-ion batteries according to claim 1, characterized in that, In step (1), the molar ratio of tin to sulfur in the sodium stannate and the thiourea is 1:1-1:

12.

3. The method for preparing a tin disulfide anode material for lithium-ion batteries according to claim 1, characterized in that, In step (1), dilute sulfuric acid is used to adjust the pH value of the solution.

4. The method for preparing a tin disulfide anode material for lithium-ion batteries according to claim 1, characterized in that, In step (4), the centrifugal washing is performed by using deionized water and anhydrous ethanol alternately for at least 3 times.

5. The method for preparing a tin disulfide anode material for lithium-ion batteries according to claim 1, characterized in that, In step (4), the drying is vacuum drying, the drying temperature is 50-70 ℃, and the drying time is 7-12 h.

6. A tin disulfide negative material for lithium ion batteries produced by the method according to any one of claims 1 to 6, characterized by The material is nitrogen-doped tin disulfide, and has a flower-like morphology in which hexagonal platelets are stacked.

7. The tin disulfide negative material for lithium ion batteries according to claim 6, characterized in that, The average size of the hexagonal platelets is 2 μm.

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