Negative electrode material, preparation method thereof and electrochemical energy storage device

Abstract

The invention provides a negative electrode material, a preparation method thereof and an electrochemical energy storage device. The negative electrode material comprises a SnS nanosheet and a carbon spherical shell coated outside the SnS nanosheet. The SnS nanosheet with the sheet structure can provide a larger specific surface area, the contact area with an electrolyte is increased, and the transmission path of lithium ions on a bulk phase and a solid-liquid interface is shortened, so that the transmission of the lithium ions between the negative electrode material and the electrolyte is more efficient; in addition, the sheet-shaped structure can cause electrons to be transmitted along the sheet-shaped plane direction, so that the electron transmission resistance is reduced; besides, the SnS nanosheet with the sheet structure can better buffer volume change caused by lithium ion intercalation and deintercalation in the charging and discharging process, and compared with other shapes, the SnS nanosheet with the sheet structure is less prone to structural collapse. In the negative electrode material, the microstructure of the SnS nanosheet is sheet-shaped, and the exterior of the sheet-shaped SnS nanosheet is coated with the carbon spherical shell, so that the negative electrode material has excellent electrochemical performance and cycling stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a negative electrode material, and in particular to a negative electrode material and a preparation method thereof and an electrochemical energy storage device. Background Art

[0002] The widespread use of electric vehicles and the development of renewable energy have driven the growing demand for high-energy-density secondary batteries. The development of high-performance electrode materials to replace traditional lithium-ion graphite anodes has become inevitable. Many lithium alloy materials have a higher energy density than graphite (372 mAh g -1 ) has a higher capacity, for example, silicon anode (3579mAh g -1 ), germanium negative electrode (1384mAh·g -1 ), tin negative electrode (994mAh g -1 ) etc. However, safety is also very important for batteries. Compared with silicon and germanium materials, the discharge voltage of tin is slightly higher (0.4-0.75V), which means that the safety risks caused by lithium dendrites are relatively reduced. Therefore, compared with silicon and germanium negative electrodes, tin negative electrodes have better safety.

[0003] The primary factor hindering the widespread use of tin-based anode materials is their rapid capacity loss during cycling, caused by volume expansion and material pulverization during lithium insertion and delithiation. Several existing strategies have been employed to overcome this limitation, including intercalation reactions, alloying reactions, and conversion reactions.

[0004] Intercalation reactions are gradually being eliminated due to their low theoretical capacity. Alloy reactions, on the other hand, offer a relatively low reaction potential, which contributes to a higher operating voltage for the full battery. Furthermore, the fast kinetics of alloy reactions can reduce voltage hysteresis, facilitating full utilization of stored charge. However, their enormous volume expansion can lead to material pulverization and capacity degradation.

[0005] For conversion reactions, unlike alloy reactions, Li2O and Li2S introduced by conversion reactions can be reversibly formed and decomposed, which can contribute a buffer layer to reduce volume expansion and bring about capacity stability; therefore, introducing heteroatoms such as O and S into tin materials to introduce conversion reactions is a feasible strategy.

[0006] In the prior art, the electrochemical properties of elemental Sn and SnO2 hybridized with O atoms were studied by the NaBH4 reduction method. The results showed that although elemental Sn had a high initial capacity, the capacity of elemental Sn decayed rapidly; SnO2 also had a high initial capacity, but SnO2 hybridized with O atoms had poor reversibility and low coulombic efficiency when used in lithium-ion batteries. In addition, the structure of SnO2 was not conducive to the diffusion of ions.

[0007] Compared with SnO2, SnS2 hybridized with S atoms has higher reversibility when used in lithium-ion batteries due to its weak MS bond; in addition, its unique layered structure has a large interlayer space (interlayer spacing of ), which is conducive to the diffusion of ions; moreover, SnS2 also has a high theoretical specific capacity (theoretical specific capacity can reach 1231mAh·g -1 However, SnS2 is prone to huge volume expansion during the electrode reaction process, and has low conductivity, which can easily cause the material to pulverize, resulting in a further decrease in capacity.

[0008] CN117580807A discloses a method for preparing a negative electrode material for a sodium ion battery and its application. Ammonia solution is added dropwise to a mixed solution containing a tin salt and a nickel salt, and heated to react to obtain NiSn(OH)6 nanospheres. The NiSn(OH)6 nanospheres are then dispersed in a solvent, and thioacetamide is added and heated to react to obtain flower-shaped nanospheres SnS2-NiS. The flower-shaped nanospheres SnS2-NiS, biochar, and a binder are mixed in water, heated to react, and solid-liquid separation is performed. The resulting solid is dried and then sintered under an inert atmosphere to obtain the negative electrode material for a sodium ion battery. However, the SnS2-based negative electrode material obtained by the preparation method disclosed in this publication has weak electrochemical properties.

[0009] Compared with SnS2, S-atom hybridized SnS also has higher reversibility and a large interlayer space (interlayer spacing of ), also has a high theoretical specific capacity (theoretical specific capacity is 1137mAh g -1 ); however, SnS has higher conductivity and relatively less volume expansion, and is more promising in lithium-ion batteries.

[0010] In the prior art, a SnS nanoparticle is prepared by a template-assisted self-assembly method and anchored in a three-dimensional cross-linked spherical graphene framework; in this structure, SnS achieves almost complete reversibility during the charge and discharge process, and its Li2S reversibility reaches 97%. In the prior art, a self-supporting polypyrrole / carbon nanotube-coated SnS nanobelt structure is also designed by an in-situ polymerization self-assembly method. The SnS nanobelt exhibits a high specific surface area and a short ion diffusion distance. The polypyrrole coating can inhibit the volume expansion of SnS, while the carbon nanotubes act as a conductive network. This structure is conducive to the transmission of electrons and ions due to its high conductivity and porous properties. However, the electrochemical performance of the SnS-based negative electrode materials obtained by these two methods disclosed in the prior art is insufficient, and the long-cycle stability cannot meet the requirements of practical applications.

[0011] CN117154038A discloses a lignin-based carbon-coated stannous sulfide composite material and its preparation method and application, comprising the following steps: (1) first mixing a tetravalent tin salt with acetic acid, and then mixing with thioacetamide; water and ethanol are also added as solvents to obtain a mixed solution; (2) adding lignin to the mixed solution, stirring and dissolving, performing a hydrothermal reaction, washing, and drying to obtain a SnS2 / C composite material; (3) calcining the obtained SnS2 / C composite material at 500-700°C under a protective atmosphere for 2-5 hours, washing, and drying to obtain a lignin-based carbon-coated stannous sulfide composite material. This disclosure uses industrial lignin as a carbon precursor and generates a reducing gas in situ to reduce SnS2 to SnS. The process is simple, cost-effective, and reduces fossil energy consumption. However, the electrochemical performance and cycle stability of the disclosed lignin-based carbon-coated stannous sulfide composite material still cannot meet the requirements of practical applications.

[0012] The anode materials disclosed in the prior art all have certain defects, and their electrochemical performance and cycle stability cannot meet the requirements of practical applications. Therefore, it is crucial to develop and design a new anode material, its preparation method, and electrochemical energy storage device. Summary of the Invention

[0013] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a negative electrode material, a preparation method thereof, and an electrochemical energy storage device. In the negative electrode material provided by the present invention, the microstructure of the SnS nanosheets is flaky, and the outside of the flaky SnS nanosheets is coated with a carbon shell. The negative electrode material has excellent electrochemical performance and cycle stability.

[0014] To achieve this object, the present invention adopts the following technical solutions:

[0015] In a first aspect, the present invention provides a negative electrode material, comprising SnS nanosheets and a carbon shell coating the SnS nanosheets.

[0016] In the negative electrode material provided by the present invention, the SnS nanosheets with a sheet structure can provide a larger specific surface area, increase the contact area with the electrolyte, and shorten the transmission path of lithium ions in the bulk phase and the solid-liquid interface, thereby making the transmission of lithium ions between the negative electrode material and the electrolyte more efficient, thereby improving the charge and discharge performance of the battery; in addition, the sheet structure causes electrons to be transmitted along the sheet plane direction, reducing the electron transmission resistance and improving the energy conversion efficiency of the battery prepared with the negative electrode material; in addition, the SnS nanosheets with a sheet structure can better buffer the volume change caused by the insertion and extraction of lithium ions during the charge and discharge process, and are less likely to undergo structural collapse compared to other shapes, thereby extending the cycle life of the battery.

[0017] In the negative electrode material provided by the present invention, the microstructure of the SnS nanosheet is flaky, and the outside of the flaky SnS nanosheet is coated with a carbon spherical shell. The negative electrode material has excellent electrochemical performance and cycle stability.

[0018] In a second aspect, the present invention provides a method for preparing the negative electrode material according to the first aspect, the preparation method comprising:

[0019] (1) coating the exterior of NiSn(OH)6 with a carbon source to obtain NiSn(OH)6 having an exterior coating layer;

[0020] (2) using a sulfur source to sulfidize the NiSn(OH)6 with a coating layer obtained in step (1) to convert the NiSn(OH)6 inside the coating layer into NiS-SnS2 nanosheets, and then pickling to remove NiS in the NiS-SnS2 nanosheets to obtain SnS2 nanosheets coated with the coating layer;

[0021] (3) Carbonizing and reducing the coating layer-coated SnS2 nanosheets obtained in step (2) by heat treatment to obtain the negative electrode material.

[0022] Preferably, the method for preparing the NiSn(OH)6 in step (1) comprises: mixing nickel salt, tin salt, ammonia water and solvent to obtain the NiSn(OH)6.

[0023] Preferably, the nickel salt comprises any one of nickel acetate, nickel chloride, nickel sulfate, nickel nitrate, nickel bromate, nickel sulfamate or nickel fluoroborate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of nickel acetate and nickel chloride, a combination of nickel sulfate and nickel nitrate, a combination of nickel bromate and nickel sulfamate, or a combination of nickel acetate, nickel sulfate and nickel fluoroborate.

[0024] Preferably, the tin salt comprises any one or a combination of at least two of potassium stannate, stannous chloride, stannous chloride, stannous sulfate, stannous fluoroborate or stannous nitrate. Typical but non-limiting combinations include a combination of potassium stannate and stannous chloride, a combination of stannous chloride and stannous sulfate, a combination of stannous fluoroborate and stannous nitrate, or a combination of potassium stannate, stannous chloride and stannous nitrate.

[0025] Preferably, the solvent comprises water.

[0026] Preferably, the mixing includes: first mixing nickel salt and solvent to obtain a nickel salt solution; second mixing tin salt and solvent to obtain a tin salt solution; third mixing the obtained nickel salt solution and tin salt solution to obtain a mixed liquid, and then fourth mixing ammonia water with the obtained mixed liquid; after solid-liquid separation, performing a first post-treatment on the obtained solid to obtain the NiSn(OH)6.

[0027] Preferably, the first mixing method includes stirring.

[0028] Preferably, the second mixing method includes stirring.

[0029] Preferably, the concentration of the nickel salt solution is 0.02 to 0.03 g / mL, for example, 0.020 g / mL, 0.021 g / mL, 0.022 g / mL, 0.023 g / mL, 0.024 g / mL, 0.025 g / mL, 0.026 g / mL, 0.027 g / mL, 0.028 g / mL, 0.029 g / mL or 0.030 g / mL, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0030] Preferably, the concentration of the tin salt solution is 0.03 to 0.05 mol / L, for example, 0.030 mol / L, 0.032 mol / L, 0.034 mol / L, 0.036 mol / L, 0.038 mol / L, 0.040 mol / L, 0.042 mol / L, 0.044 mol / L, 0.046 mol / L, 0.048 mol / L or 0.050 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the concentration of the ammonia water is 25-28 wt %.

[0032] Preferably, the volume ratio of the nickel salt solution to the tin salt solution in the third mixture is (1-1.5):1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0033] Preferably, the volume ratio of the mixed liquid to the ammonia water in the fourth mixing is (4-4.5):1, for example, it can be 4:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1 or 4.5:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0034] Preferably, the third mixing method includes: adding a tin salt solution to the obtained nickel salt solution while stirring the obtained nickel salt solution at a speed of 1600 to 2000 r / min, and continuing to stir at a speed of 1600 to 2000 r / min for 30 to 90 seconds after all the tin salt solution is added. For example, it can be 30 seconds, 35 seconds, 40 seconds, 45 seconds, 50 seconds, 55 seconds, 60 seconds, 65 seconds, 70 seconds, 75 seconds, 80 seconds, 85 seconds or 90 seconds, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0035] In the present invention, the obtained nickel salt solution is stirred at a speed of 1600 to 2000 r / min. The speed may be, for example, 1600 r / min, 1650 r / min, 1700 r / min, 1750 r / min, 1800 r / min, 1850 r / min, 1900 r / min, 1950 r / min or 2000 r / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0036] In the present invention, after all the tin salt solution is added, stirring is continued at a speed of 1600 to 2000 r / min. The speed may be, for example, 1600 r / min, 1650 r / min, 1700 r / min, 1750 r / min, 1800 r / min, 1850 r / min, 1900 r / min, 1950 r / min or 2000 r / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, the volume ratio of the nickel salt solution to the tin salt solution in the third mixture is (1-1.5):1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0038] Preferably, the fourth mixing method includes: adding ammonia water to the obtained mixed liquid while stirring the obtained mixed liquid at a speed of 1600-2000 r / min, and continuing to stir at a speed of 1600-2000 r / min for 20-30 minutes after the ammonia water is completely added, and then stirring at a speed of 600-800 r / min for 4-8 hours.

[0039] In the fourth mixing of the present invention, while stirring the obtained mixed liquid at a speed of 1600 to 2000 r / min, ammonia water is added to the obtained mixed liquid. The stirring speed can be, for example, 1600 r / min, 1650 r / min, 1700 r / min, 1750 r / min, 1800 r / min, 1850 r / min, 1900 r / min, 1950 r / min or 2000 r / min, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0040] In the present invention, after the ammonia solution is completely added, stirring is continued at a speed of 1600 to 2000 r / min. The speed can be, for example, 1600 r / min, 1650 r / min, 1700 r / min, 1750 r / min, 1800 r / min, 1850 r / min, 1900 r / min, 1950 r / min or 2000 r / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0041] In the present invention, stirring is continued for 20 to 30 minutes after the ammonia solution is completely added, for example, it can be 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes or 30 minutes, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0042] In the present invention, after the ammonia solution is completely added, stirring is carried out for 20 to 30 minutes, and then stirring is carried out at a speed of 600 to 800 r / min. The speed can be, for example, 600 r / min, 625 r / min, 650 r / min, 675 r / min, 700 r / min, 725 r / min, 750 r / min, 775 r / min or 800 r / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0043] In the present invention, the stirring time is 4 to 8 hours, for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] Preferably, the volume ratio of the mixed liquid to the ammonia water in the fourth mixing is (4-4.5):1, for example, it can be 4:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1 or 4.5:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0045] Preferably, the solid-liquid separation comprises centrifugation.

[0046] Preferably, the first post-treatment includes: washing the solid obtained by solid-liquid separation, quenching with liquid nitrogen and vacuum freeze-drying for 10 to 15 hours, for example, it can be 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] Preferably, the NiSn(OH)6 is spherical and / or cubic in shape.

[0048] Preferably, the coating in step (1) comprises: first mixing a first reaction solvent, NiSn(OH)6 and a carbon source to obtain NiSn(OH)6 having a coating layer on the outside.

[0049] Preferably, the first reaction solvent comprises Tris-HCl buffer solution and / or Bis-Tris buffer solution.

[0050] Preferably, the Tris-HCl solution buffer is prepared from tris(hydroxymethylaminomethane), tris(hydroxymethylaminomethane hydrochloride) and water. The Tris-HCl solution buffer is a buffer in the prior art. All Tris-HCl solution buffers disclosed in the prior art are applicable in this application.

[0051] Preferably, the Bis-Tris buffer solution is prepared from bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane and water. The Bis-Tris buffer solution is a buffer solution in the prior art. All Bis-Tris buffer solutions disclosed in the prior art are applicable in this application.

[0052] Preferably, the carbon source in step (1) comprises 6-hydroxydopamine hydrochloride and / or tannic acid.

[0053] Preferably, the mass ratio of NiSn(OH)6 to the carbon source in the first mixture is 1:(0.8~1.2), for example, it can be 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.1, 1:1.15 or 1:1.2, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] Preferably, the solid-liquid ratio of NiSn(OH)6 to the first reaction solvent in the first mixture is 1:(1.5-2.5), for example, it can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4 or 1:2.5, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable. The unit of solid-liquid ratio is mg / mL.

[0055] Preferably, the first mixing method includes stirring at a speed of 600 to 800 r / min for 10 to 14 hours, for example, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours or 14 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] The stirring speed in the first mixing of the present invention is 600-800 r / min. The speed can be, for example, 600 r / min, 620 r / min, 640 r / min, 660 r / min, 680 r / min, 700 r / min, 720 r / min, 740 r / min, 760 r / min, 780 r / min or 800 r / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0057] Preferably, the first mixing further includes solid-liquid separation and a second post-treatment performed in sequence to obtain NiSn(OH)6 with a coating layer on the outside.

[0058] Preferably, the solid-liquid separation method includes centrifugation.

[0059] Preferably, the second post-treatment includes: washing the solid obtained by solid-liquid separation, quenching with liquid nitrogen and vacuum freeze-drying for 10 to 15 hours, for example, it can be 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0060] Preferably, the sulfurization treatment in step (2) comprises: performing a second mixing of the second reaction solvent, the sulfur source and the NiSn(OH)6 with the coating layer obtained in step (1), and then performing a hydrothermal reaction.

[0061] Preferably, the second reaction solvent comprises water.

[0062] Preferably, the sulfur source in step (2) comprises any one or a combination of at least two of thioacetamide, thiourea, lithium sulfide, hydrosulfuric acid, potassium sulfide, sodium sulfide or ammonium sulfide. Typical but non-limiting combinations include a combination of thioacetamide and thiourea, a combination of thiourea and lithium sulfide, a combination of lithium sulfide and hydrosulfuric acid, a combination of hydrosulfuric acid and potassium sulfide, a combination of potassium sulfide and sodium sulfide, a combination of sodium sulfide and ammonium sulfide, or a combination of thioacetamide, thiourea and lithium sulfide.

[0063] Preferably, the mass ratio of the sulfur source in the second mixture to the NiSn(OH)6 having an external coating layer obtained in step (1) is (1 to 1.5):1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0064] Preferably, the solid-liquid ratio of NiSn(OH)6 with a coating layer on the outside obtained in step (1) to the second reaction solvent in the second mixture is 1:(1-1.5), for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable. The unit of solid-liquid ratio is mg / mL.

[0065] Preferably, the second mixing method includes: adding the sulfur source and the NiSn(OH)6 with a coating layer on the outside obtained in step (1) into a second reaction solvent.

[0066] Preferably, the temperature of the hydrothermal reaction is 160-200° C., and the time is 10-14 hours.

[0067] The temperature of the hydrothermal reaction in the present invention is 160-200°C, for example, it can be 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or 200°C, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0068] The time in the present invention is 10 to 14 hours, for example, it can be 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours or 14 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0069] Preferably, the second mixing further includes solid-liquid separation and a third post-treatment performed in sequence to obtain NiS-SnS2 nanosheets coated with a coating layer.

[0070] Preferably, the solid-liquid separation method includes centrifugation.

[0071] Preferably, the third post-treatment includes: washing the solid obtained by solid-liquid separation, quenching with liquid nitrogen and vacuum freeze-drying for 10 to 15 hours, for example, it can be 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0072] Preferably, the pickling method used in step (2) includes: mixing the pickling agent, the pickling solvent and the NiS-SnS2 nanosheets with a coating layer on the outside after sulfurization for a third time, and then condensing and refluxing to obtain SnS2 nanosheets coated with the coating layer.

[0073] Preferably, the pickling agent comprises ethylenediaminetetraacetic acid and / or ethylenediaminetetraacetic acid salt.

[0074] Preferably, the EDTA salt comprises any one of disodium EDTA, tetrasodium EDTA, disodium calcium EDTA or sodium ferric EDTA, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of disodium EDTA and tetrasodium EDTA, a combination of disodium calcium EDTA and sodium ferric EDTA, a combination of disodium EDTA, tetrasodium EDTA and disodium calcium EDTA, or a combination of tetrasodium EDTA, disodium calcium EDTA and sodium ferric EDTA.

[0075] Preferably, the pickling solvent comprises water.

[0076] Preferably, the mass ratio of the pickling agent in the third mixture to the NiS-SnS2 nanosheets with a coating layer on the outside after sulfurization treatment is (5-9):1, for example, it can be 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1 or 9:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0077] Preferably, the solid-liquid ratio of NiS-SnS2 nanosheets with a coating layer on the outside after sulfurization treatment to the pickling solvent in the third mixture is 1:(7.5~9), for example, it can be 1:7.5, 1:7.6, 1:7.7, 1:7.8, 1:7.9, 1:8, 1:8.1, 1:8.2, 1:8.3, 1:8.4, 1:8.5, 1:8.6, 1:8.7, 1:8.8, 1:8.9 or 1:9, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable. The unit of solid-liquid ratio is mg / mL.

[0078] Preferably, the condensation reflux temperature is 100-120° C., and the time is 4-8 hours.

[0079] The condensation reflux temperature in the present invention is 100-120°C, for example, it can be 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0080] The condensation reflux time in the present invention is 4 to 8 hours, for example, it can be 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0081] Preferably, the third mixing further includes solid-liquid separation and a third post-treatment performed in sequence to obtain SnS2 nanosheets coated with a coating layer.

[0082] Preferably, the solid-liquid separation method includes centrifugation.

[0083] Preferably, the third post-treatment includes: washing the solid obtained by solid-liquid separation, quenching with liquid nitrogen and vacuum freeze-drying for 10 to 15 hours, for example, it can be 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0084] Preferably, the heat treatment includes heating and holding in sequence in a protective atmosphere; the holding temperature is 400-450° C., and the holding time is 1-3 hours.

[0085] The insulation temperature described in the present invention is 400-450°C, for example, it can be 400°C, 405°C, 410°C, 415°C, 420°C, 425°C, 430°C, 435°C, 440°C, 445°C or 450°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0086] The insulation time in the present invention is 1 to 3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0087] Preferably, the heating rate is 1 to 5°C / min, for example, it can be 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min or 5°C / min, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0088] Preferably, the protective atmosphere comprises nitrogen and / or an inert gas.

[0089] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises:

[0090] (1) mixing nickel salt and water by stirring to obtain a nickel salt solution with a concentration of 0.02 to 0.03 g / mL; mixing tin salt and water by stirring to obtain a tin salt solution with a concentration of 0.03 to 0.05 g / mL; while stirring the obtained nickel salt solution at a speed of 1600 to 2000 r / min, adding the tin salt solution to the obtained nickel salt solution, the volume ratio of the nickel salt solution to the tin salt solution is (1 to 1.5):1, and after all the tin salt solution is added, continuing to stir at a speed of 1600 to 2000 r / min for 30 to 90 seconds to obtain a mixed solution; and then stirring at a speed of 1600 to 2000 r / min for 30 to 90 seconds to obtain a mixed solution. min while stirring the obtained mixed solution, adding ammonia water with a mass fraction of 25 to 28 wt % to the obtained mixed solution, with the volume ratio of the mixed solution to the ammonia water being (4 to 4.5):1, and after the ammonia water is completely added, continuing to stir at a speed of 1600 to 2000 r / min for 20 to 30 minutes, and then continuing to stir at a speed of 600 to 800 r / min in a water bath heating environment of 80 to 120° C. for 4 to 8 hours; then centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 10 to 15 hours are carried out in sequence to obtain NiSn(OH)6 in the shape of spheres and / or cubic blocks;

[0091] The method comprises the following steps: stirring and mixing a Tris-HCl buffer solution and / or a Bis-Tris buffer solution with the obtained NiSn(OH)6 and 6-hydroxydopamine hydrochloride and / or tannic acid at a speed of 600 to 800 r / min for 10 to 14 hours, wherein the mass ratio of NiSn(OH)6 to 6-hydroxydopamine hydrochloride and / or tannic acid during the stirring and mixing is 1:(0.8 to 1.2), and the solid-liquid ratio of NiSn(OH)6 to the Tris-HCl buffer solution and / or the Bis-Tris buffer solution is 1:(1.5 to 2.5), and the unit of the solid-liquid ratio is mg / mL; centrifugation washing, liquid nitrogen quenching, and vacuum freeze drying for 10 to 15 hours are sequentially performed to obtain NiSn(OH)6 with a coating layer on the outside;

[0092] (2) adding a sulfur source and the NiSn(OH)6 with an external coating layer obtained in step (1) into water, wherein the mass ratio of the sulfur source to the NiSn(OH)6 with an external coating layer is (1-1.5):1, and the solid-liquid ratio of the NiSn(OH)6 with an external coating layer to water is 1:(1-1.5), and the unit of the solid-liquid ratio is mg / mL; then performing a hydrothermal reaction at 160-200°C for 10-14h to convert the NiSn(OH)6 inside the coating layer into NiS-SnS2 nanosheets; then performing centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 10-15h in sequence to obtain NiS-SnS2 nanosheets coated with the coating layer;

[0093] Ethylenediaminetetraacetic acid and / or ethylenediaminetetraacetic acid salt, water and NiS-SnS2 nanosheets coated with a coating layer are mixed to remove NiS from the NiS-SnS2 nanosheets, wherein the mass ratio of ethylenediaminetetraacetic acid and / or ethylenediaminetetraacetic acid salt to the NiS-SnS2 nanosheets coated with the coating layer is (5-9):1, and the solid-liquid ratio of the NiS-SnS2 nanosheets coated with the coating layer to water is 1:(7.5-9), and the unit of the solid-liquid ratio is mg / mL; after the mixing is completed, condensation reflux is performed at 100-120° C. for 4-8 hours; and then centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 10-15 hours are performed in sequence to obtain SnS2 nanosheets coated with the coating layer;

[0094] (3) The SnS2 nanosheets coated with the coating layer obtained in step (2) are placed in nitrogen and / or inert gas, heated to 400-450°C at a rate of 1-5°C / min and kept warm for 1-3 hours to carbonize and reduce the obtained negative electrode material.

[0095] In a third aspect, the present invention provides an electrochemical energy storage device, comprising the negative electrode material described in the first aspect.

[0096] Preferably, the electrochemical energy storage device comprises a lithium ion battery, a sodium ion battery or a potassium ion battery.

[0097] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0098] Compared with the prior art, the present invention has the following beneficial effects:

[0099] (1) In the negative electrode material provided by the present invention, the sheet-like SnS nanosheets can provide a larger specific surface area, increase the contact area with the electrolyte, and shorten the transmission path of lithium ions in the bulk phase and the solid-liquid interface, thereby making the transmission of lithium ions between the negative electrode material and the electrolyte more efficient, thereby improving the charge and discharge performance of the battery; in addition, the sheet-like structure causes electrons to be transmitted along the sheet plane direction, reducing the electron transmission resistance and improving the energy conversion efficiency of the battery prepared with the negative electrode material; in addition, the sheet-like SnS nanosheets can better buffer the volume change caused by the insertion and extraction of lithium ions during the charge and discharge process, and are less likely to collapse compared to other shapes, thereby extending the cycle life of the battery;

[0100] (2) In the negative electrode material provided by the present invention, the microstructure of the SnS nanosheets is flaky, and the outside of the flaky SnS nanosheets is coated with a carbon shell. The negative electrode material has excellent electrochemical performance and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 is a SEM image of the negative electrode material provided in Example 1.

[0102] Figure 2 This is a TEM image of the negative electrode material provided in Example 1.

[0103] Figure 3 is the XRD pattern of the negative electrode material provided in Example 1. DETAILED DESCRIPTION

[0104] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0105] Example 1

[0106] This embodiment provides a negative electrode material, which includes SnS nanosheets and carbon shells covering the SnS nanosheets.

[0107] The preparation method of the negative electrode material is:

[0108] (1) A nickel salt and water are stirred to obtain a nickel salt solution with a concentration of 0.025 g / mL; a tin salt and water are stirred to obtain a tin salt solution with a concentration of 0.04 g / mL; while stirring the obtained nickel salt solution at a speed of 1800 r / min, a tin salt solution is added to the obtained nickel salt solution, the volume ratio of the nickel salt solution to the tin salt solution is 1.25:1, and after the tin salt solution is fully added, the mixture is stirred at a speed of 1800 r / min for 60 seconds to obtain a mixed solution; while stirring the obtained mixed solution at a speed of 1800 r / min, ammonia water with a mass fraction of 26 wt% is added to the obtained mixed solution, the volume ratio of the mixed solution to the ammonia water is 4.25:1, and after the ammonia water is fully added, the mixture is stirred at a speed of 1800 r / min for 25 minutes and then stirred at a speed of 700 r / min for 6 hours; washing, liquid nitrogen quenching and vacuum freeze drying for 12.5 hours are then carried out in sequence to obtain spherical NiSn(OH)6;

[0109] The Tris-HCl buffer solution, the obtained NiSn(OH)6 and 6-hydroxydopamine hydrochloride were stirred and mixed at a speed of 700 r / min for 12 hours, wherein the mass ratio of NiSn(OH)6 to 6-hydroxydopamine hydrochloride during the stirring and mixing was 1:1, and the solid-liquid ratio of NiSn(OH)6 to the Tris-HCl buffer solution was 1:2, and the unit of the solid-liquid ratio was mg / mL; then centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 12.5 hours were performed in sequence to obtain NiSn(OH)6 with a coating layer on the outside;

[0110] (2) adding thioacetamide and the NiSn(OH)6 with an external coating layer obtained in step (1) into water, wherein the mass ratio of thioacetamide to the NiSn(OH)6 with an external coating layer is 1.25:1, the solid-liquid ratio of the NiSn(OH)6 with an external coating layer to water is 1:1.25, and the unit of the solid-liquid ratio is mg / mL; then performing a hydrothermal reaction at 180°C for 12 hours to convert the NiSn(OH)6 inside the coating layer into NiS-SnS2 nanosheets; then performing centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 12.5 hours in sequence to obtain NiS-SnS2 nanosheets coated with the coating layer;

[0111] Ethylenediaminetetraacetic acid, water and coating layer coated NiS-SnS2 nanosheets were mixed to remove NiS from NiS-SnS2 nanosheets. During the mixing process, the mass ratio of ethylenediaminetetraacetic acid to coating layer coated NiS-SnS2 nanosheets was 7:1, and the solid-liquid ratio of coating layer coated NiS-SnS2 nanosheets to water was 1:8.25. The unit of solid-liquid ratio was mg / mL. After the mixing was completed, condensation reflux was performed at 110°C for 6 hours. Then, centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 12.5 hours were carried out in sequence to obtain coating layer coated SnS2 nanosheets.

[0112] (3) The SnS2 nanosheets coated with the coating layer obtained in step (2) are placed in a nitrogen atmosphere, heated to 425°C at a rate of 3°C / min, and then kept warm for 2 hours for carbonization and reduction to obtain the negative electrode material.

[0113] Example 2

[0114] This embodiment provides a negative electrode material, which includes SnS nanosheets and carbon shells covering the SnS nanosheets.

[0115] The preparation method of the negative electrode material is:

[0116] (1) mixing nickel salt and water by stirring to obtain a nickel salt solution with a concentration of 0.02 g / mL; mixing tin salt and water by stirring to obtain a tin salt solution with a concentration of 0.03 g / mL; while stirring the obtained nickel salt solution at a speed of 1600 r / min, adding tin salt solution to the obtained nickel salt solution, the volume ratio of the nickel salt solution to the tin salt solution is 1:1, and after the tin salt solution is fully added, continuing to stir at a speed of 1600 r / min for 90 seconds to obtain a mixed solution; while stirring the obtained mixed solution at a speed of 1600 r / min, adding ammonia water with a mass fraction of 25 wt% to the obtained mixed solution, the volume ratio of the mixed solution to the ammonia water is 4.5:1, and after the ammonia water is fully added, continuing to stir at a speed of 1600 r / min for 20 minutes, and then stirring at a speed of 800 r / min for 8 hours; after filtering, washing the obtained solid, quenching with liquid nitrogen and vacuum freeze-drying for 10 hours in sequence to obtain spherical NiSn(OH)6;

[0117] The Bis-Tris buffer solution, the obtained NiSn(OH)6 and tannic acid were stirred and mixed at a speed of 800 r / min for 14 hours, wherein the mass ratio of NiSn(OH)6 to tannic acid during the stirring and mixing was 1:0.8, and the solid-liquid ratio of NiSn(OH)6 to the Bis-Tris buffer solution was 1:2.5, and the unit of the solid-liquid ratio was mg / mL; then, centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 15 hours were performed in sequence to obtain NiSn(OH)6 with an external coating layer;

[0118] (2) adding a sulfur source and the NiSn(OH)6 with an external coating layer obtained in step (1) into water, wherein the mass ratio of the sulfur source to the NiSn(OH)6 with an external coating layer is 1.5:1, the solid-liquid ratio of the NiSn(OH)6 with an external coating layer to water is 1:1, and the unit of the solid-liquid ratio is mg / mL; then performing a hydrothermal reaction at 200°C for 10 hours to convert the NiSn(OH)6 inside the coating layer into NiS-SnS2 nanosheets; then performing centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 10 hours in sequence to obtain NiS-SnS2 nanosheets coated with the coating layer;

[0119] NiS in the NiS-SnS2 nanosheets was removed by mixing ethylenediaminetetraacetic acid, water and coating-coated NiS-SnS2 nanosheets. During the mixing process, the mass ratio of ethylenediaminetetraacetic acid to coating-coated NiS-SnS2 nanosheets was 9:1, and the solid-liquid ratio of coating-coated NiS-SnS2 nanosheets to water was 1:7.5. The unit of solid-liquid ratio was mg / mL. After the mixing was completed, condensation reflux was performed at 120°C for 4 hours. Then, centrifugal washing, liquid nitrogen quenching and vacuum freeze-drying for 10 hours were performed in sequence to obtain coating-coated SnS2 nanosheets.

[0120] (3) The SnS2 nanosheets coated with the coating layer obtained in step (2) are placed in a nitrogen atmosphere, heated to 450°C at a rate of 1°C / min, and then kept warm for 1 hour for carbonization and reduction to obtain the negative electrode material.

[0121] Example 3

[0122] This embodiment provides a negative electrode material, which includes SnS nanosheets and carbon shells covering the SnS nanosheets.

[0123] The preparation method of the negative electrode material is:

[0124] (1) A nickel salt and water are stirred to obtain a nickel salt solution with a concentration of 0.03 g / mL; a tin salt and water are stirred to obtain a tin salt solution with a concentration of 0.05 g / mL; while stirring the obtained nickel salt solution at a speed of 2000 r / min, a tin salt solution is added to the obtained nickel salt solution, the volume ratio of the nickel salt solution to the tin salt solution is 1.5:1, and after the tin salt solution is fully added, the mixture is stirred at a speed of 2000 r / min for 30 seconds to obtain a mixed solution; while stirring the obtained mixed solution at a speed of 2000 r / min, ammonia water with a mass fraction of 28 wt% is added to the obtained mixed solution, the volume ratio of the mixed solution to the ammonia water is 4:1, and after the ammonia water is fully added, the mixture is stirred at a speed of 2000 r / min for 30 minutes, and then stirred at a speed of 600 r / min for 4 hours; after filtering, the obtained solid is washed, liquid nitrogen quenched and vacuum freeze-dried for 15 hours to obtain spherical NiSn(OH)6;

[0125] The Tris-HCl buffer solution, the obtained NiSn(OH)6 and 6-hydroxydopamine hydrochloride were stirred and mixed at a speed of 600 r / min for 10 hours, wherein the mass ratio of NiSn(OH)6 to 6-hydroxydopamine hydrochloride during the stirring and mixing was 1:1.2, and the solid-liquid ratio of NiSn(OH)6 to the Tris-HCl buffer solution was 1:1.5, and the unit of the solid-liquid ratio was mg / mL; then centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 10 hours were performed in sequence to obtain NiSn(OH)6 with a coating layer on the outside;

[0126] (2) adding a sulfur source and the NiSn(OH)6 with an external coating layer obtained in step (1) into water, wherein the mass ratio of the sulfur source to the NiSn(OH)6 with an external coating layer is 1:1, and the solid-liquid ratio of the NiSn(OH)6 with an external coating layer to water is 1:1.5, and the unit of the solid-liquid ratio is mg / mL; then performing a hydrothermal reaction at 160°C for 14 hours to convert the NiSn(OH)6 inside the coating layer into NiS-SnS2 nanosheets; then performing centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 15 hours in sequence to obtain NiS-SnS2 nanosheets coated with the coating layer;

[0127] NiS in the NiS-SnS2 nanosheets was removed by mixing ethylenediaminetetraacetic acid, water, and coating-coated NiS-SnS2 nanosheets. During the mixing process, the mass ratio of ethylenediaminetetraacetic acid to coating-coated NiS-SnS2 nanosheets was 5:1, and the solid-liquid ratio of coating-coated NiS-SnS2 nanosheets to water was 1:9. The unit of solid-liquid ratio was mg / mL. After the mixing was completed, condensation reflux was performed at 100°C for 8 hours. Then, centrifugal washing, liquid nitrogen quenching, and vacuum freeze-drying for 15 hours were performed in sequence to obtain coating-coated SnS2 nanosheets.

[0128] (3) The SnS2 nanosheets coated with the coating layer obtained in step (2) are placed in an argon atmosphere, heated to 400°C at a rate of 5°C / min and kept warm for 3 hours to perform carbonization and reduction to obtain the negative electrode material.

[0129] Example 4

[0130] This embodiment provides a negative electrode material, which is the same as that of Example 1 except that the mass ratio of NiSn(OH)6 to 6-hydroxydopamine hydrochloride in the stirring and mixing in step (1) of the method for preparing the negative electrode material is 1:1.5.

[0131] Example 5

[0132] This embodiment provides a negative electrode material, which is the same as that of Example 1 except that the mass ratio of NiSn(OH)6 to 6-hydroxydopamine hydrochloride in the stirring and mixing in step (1) of the method for preparing the negative electrode material is 1:0.5.

[0133] Example 6

[0134] This embodiment provides a negative electrode material, which is the same as that of Example 1 except that in step (2) of the method for preparing the negative electrode material, the mass ratio of thioacetamide to NiSn(OH)6 with an external coating layer is 0.8:1.

[0135] Example 7

[0136] This embodiment provides a negative electrode material, which is the same as that of Example 1 except that in step (2) of the method for preparing the negative electrode material, the mass ratio of thioacetamide to NiSn(OH)6 with an external coating layer is 1.8:1.

[0137] Example 8

[0138] This embodiment provides a negative electrode material, which is the same as Example 1 except that in step (2) of the method for preparing the negative electrode material, the mass ratio of ethylenediaminetetraacetic acid to the NiS-SnS2 nanosheets coated with the coating layer is 12:1.

[0139] Example 9

[0140] This embodiment provides a negative electrode material, which is the same as Example 1 except that in step (2) of the method for preparing the negative electrode material, the mass ratio of ethylenediaminetetraacetic acid to the NiS-SnS2 nanosheets coated with the coating layer is 3:1.

[0141] Example 10

[0142] This embodiment provides a negative electrode material, which is the same as that of embodiment 1 except that the temperature is raised to 450°C and then kept warm in step (3) of the method for preparing the negative electrode material, that is, the holding temperature is 350°C.

[0143] Example 11

[0144] This embodiment provides a negative electrode material, which is the same as that of embodiment 1 except that the temperature is raised to 450°C and then kept warm in step (3) of the method for preparing the negative electrode material, i.e., the holding temperature is 550°C.

[0145] Comparative Example 1

[0146] This comparative example provides a negative electrode material, which is the same as Example 1 except that the carbon shell coating the outside of the negative electrode material is omitted, that is, the preparation method of the negative electrode material is omitted: "the Tris-HCl buffer solution is stirred and mixed with the obtained NiSn(OH)6 and 6-hydroxydopamine hydrochloride at a speed of 700 r / min for 12 hours, and the mass ratio of NiSn(OH)6 to 6-hydroxydopamine hydrochloride during the stirring and mixing is 1:1, and the solid-liquid ratio of NiSn(OH)6 to Tris-HCl solution buffer is 1:2, and the unit of the solid-liquid ratio is mg / mL; and then centrifugal washing, liquid nitrogen quenching and vacuum freeze-drying for 12.5 hours are performed in sequence to obtain NiSn(OH)6 with a coating layer on the outside."

[0147] Comparative Example 2

[0148] This comparative example provides a negative electrode material, which is the same as Example 1 except that the negative electrode material is a coating layer coated with SnS2 nanosheets, that is, step (3) in the preparation method of the negative electrode material is omitted.

[0149] Comparative Example 3

[0150] This comparative example provides a negative electrode material, wherein the negative electrode material includes a block of SnS and a granular carbon material generated by pyrolysis of lignin attached to the surface of the block of SnS;

[0151] The preparation method of the negative electrode material is:

[0152] (1) Add 3 mL of acetic acid to 1 g of tin chloride pentahydrate (SnCl4·5H2O), add 0.5 g of thioacetamide to the resulting solution, stir until uniformly dispersed, and then add 10 mL of ethanol and 40 mL of water to the resulting solution to obtain a mixed solution A;

[0153] (2) Add 0.5 g of sodium lignin sulfonate to the solution obtained in step (1), stir to dissolve, and then add to a reactor and react at 160°C for 12 h. The resulting material is centrifuged and washed with water and alcohol three times to obtain SnS2 / C;

[0154] (3) The powder obtained in step (2) was calcined at 500° C. for 3 h under a protective atmosphere, washed, and dried to obtain a negative electrode material.

[0155] The negative electrode material provided in Example 1 was tested using a scanning electron microscope, and the SEM image of the negative electrode material was obtained as shown in FIG. Figure 1 As shown;

[0156] The negative electrode material provided in Example 1 was tested using a transmission electron microscope, and the TEM image of the negative electrode material was obtained as shown in FIG. Figure 2 shown.

[0157] The negative electrode material provided in Example 1 was tested using an X-ray diffractometer, and the XRD pattern of the negative electrode material was obtained as shown in FIG. Figure 3 shown.

[0158] A battery was prepared using the negative electrode materials provided in the above embodiments and comparative examples. The method for preparing the battery was as follows: the negative electrode materials obtained in the above embodiments and comparative examples were used as negative electrode active materials, metallic lithium was used as a counter electrode, the negative electrode active material, acetylene black, and hydroxymethyl cellulose were added to water in a ratio of 8:1:1, stirred for 12 hours, and then coated on a copper foil. The mixture was transferred to a vacuum oven and heated at 75°C for 13 hours to obtain a negative electrode sheet. The negative electrode active material loading on the negative electrode sheet was 1.9 mg cm -2 ; Then, a microporous polypropylene membrane was used as a separator and a LiPF solution with a concentration of 1 mol / L was used as an electrolyte to assemble a CR2032 button battery.

[0159] The constant current charge and discharge tests of each obtained CR2032 button battery were carried out using a Blue Electric test system, and the charge and discharge specific capacity and the first efficiency were obtained as shown in Table 1. The capacity retention rate of the battery after 100 cycles at 0.2 A / g is shown in Table 1, and the capacity retention rate after 500 cycles at 2 A / g is shown in Table 1.

[0160] Table 1

[0161]

[0162] From Table 1, we can get:

[0163] (1) The lithium-ion batteries prepared using the negative electrode materials in Examples 1 to 3 have a high charge-discharge specific capacity and a high initial efficiency, which shows that the lithium-ion batteries have excellent electrochemical properties. In addition, the lithium-ion batteries exhibit a high capacity retention rate after 100 cycles and 200 cycles, which shows that the lithium-ion batteries also have excellent cycle stability.

[0164] (2) By comparing Example 1 with Examples 4 and 5, it can be seen that the mass ratio of NiSn(OH)6 to the carbon source in step (1) of the method for preparing the negative electrode material of the present invention will affect the performance of the negative electrode material and the lithium ion battery; when the mass ratio of NiSn(OH)6 to the carbon source is 1:(0.8~1.2), the lithium ion battery shows better performance. This is because when the carbon source is less, part of the NiSn(OH)6 is not coated with the carbon shell. After subsequent calcination, the conductivity of the prepared negative electrode material is poor, the internal resistance increases, resulting in a decrease in rate performance and a decrease in charge and discharge efficiency. In addition, the prepared negative electrode material cannot fully participate in the reaction due to its poor conductivity, and the actual capacity is far lower than the theoretical value. The buffering capacity is weak and the volume expansion cannot be effectively suppressed. The material is prone to pulverization and structural collapse. During the cycle, the contact between the negative electrode material and the current collector fails, and the capacity decays rapidly. , the interface side reaction is aggravated, the negative electrode material is directly exposed to the electrolyte, which triggers the continuous growth of SEI film, consumes lithium ions and electrolyte, reduces the first effect, and shortens the cycle life; when the carbon source is more, the carbon shell of NiSn(OH)6 is thicker. After subsequent calcination, the carbon shell of the prepared negative electrode material is too thick, and the energy density is reduced. In addition, due to the low specific capacity of the carbon material itself, the excessive carbon proportion leads to a decrease in the overall capacity, and the lithium storage capacity per unit mass or volume is limited, which makes it difficult to meet the high energy density demand, and the ion diffusion is hindered. In addition, the excessively thick carbon layer also extends the lithium ion diffusion path, and the polarization is significant at high rates. Some SnS nanosheets are over-wrapped by the carbon layer, resulting in a decrease in the utilization rate of the SnS nanosheets and an increase in the process cost. In addition, the excessive carbon source also pushes up the material cost, which is especially unfavorable for large-scale production. In addition, a too thick carbon layer requires annealing at a higher temperature, which increases energy consumption and is prone to side reactions.

[0165] (3) By comparing Example 1 with Examples 6 and 7, it can be seen that the mass ratio of the sulfur source to the NiSn(OH)6 with an external coating layer in step (2) of the method for preparing the negative electrode material of the present invention will affect the performance of the negative electrode material and the lithium ion battery; when the mass ratio of the sulfur source to the NiSn(OH)6 with an external coating layer is (1 to 1.5):1, the lithium ion battery shows better performance. This is because when the sulfur source is insufficient, it will lead to incomplete sulfurization, unreacted oxide phase will remain in the product, and structural defects will be generated, thereby causing performance degradation; when the sulfur source is excessive, it will trigger the generation of by-products, and the excess sulfur will react with the metal hydroxide to generate non-target phases, which will also lead to morphological degradation and cost waste;

[0166] (4) By comparing Example 1 with Examples 8 and 9, it can be seen that the mass ratio of the pickling agent and the NiSn(OH)6 with a coating layer on the outside after sulfurization in step (2) of the preparation method of the negative electrode material of the present invention will affect the performance of the negative electrode material and the lithium ion battery; when the mass ratio of the pickling agent to the NiS-SnS2 nanosheets coated with the coating layer after sulfurization is (5-9):1, the lithium ion battery shows better performance. This ratio can effectively remove the target impurities while maintaining the structural integrity and electrochemical activity of the material; too little pickling agent will lead to the target sulfide residue, causing the electrochemical polarization to increase, the interface impedance to increase and the metal ion redeposition to pollute the surface; excessive pickling agent will destroy the synergistic structure of the bimetallic sulfide, dissolve non-target components and form a pickling agent residual impurity layer, which hinders charge transfer;

[0167] (5) By comparing Example 1 with Examples 10 and 11, it can be seen that the terminal temperature of the heating in step (3) of the preparation method of the negative electrode material of the present invention, that is, the holding temperature, will affect the performance of the negative electrode material and the lithium ion battery; when the holding temperature is 400-450°C, the lithium ion battery shows more excellent performance. This temperature range can balance the conductivity, mechanical strength and integrity of the carbon layer and the active material, and achieve high cycle performance and capacity retention rate; if the temperature is too low, the carbon layer is incompletely carbonized, resulting in poor conductivity and loose structure, which cannot buffer volume expansion, causing electrode pulverization and excessive growth of SEI film, and reducing cycle life; if the temperature is too high, the carbon layer is excessively graphitized, the brittleness increases, the flexibility decreases, the active material grains coarsen and an inactive phase is generated, which weakens the lithium storage capacity and structural stability;

[0168] (6) By comparing Example 1 with Comparative Examples 1 to 3, it can be seen that in the negative electrode material provided by the present invention, the sheet-like SnS nanosheets can provide a larger specific surface area and increase the contact area with the electrolyte, thereby making the transmission of lithium ions between the negative electrode material and the electrolyte more efficient, thereby improving the charge and discharge performance of the battery; in addition, the sheet-like structure causes electrons to be transmitted along the sheet plane direction, reducing the electron transmission resistance and improving the energy conversion efficiency of the battery prepared with the negative electrode material; in addition, the sheet-like SnS nanosheets can better buffer the volume change caused by the insertion and extraction of lithium ions during the charge and discharge process, and are less likely to cause structural collapse than other shapes, thereby extending the cycle life of the battery; in the negative electrode material provided by the present invention, the microstructure of the SnS nanosheets is sheet-like, and the outside of the sheet-like SnS nanosheets is coated with a carbon shell, and the negative electrode material has excellent electrochemical properties and cycle stability.

[0169] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A negative electrode material, characterized in that The negative electrode material includes SnS nanosheets and carbon spherical shells covering the SnS nanosheets.

2. A method for preparing the negative electrode material according to claim 1, characterized in that: The preparation method comprises: (1) coating the exterior of NiSn(OH)6 with a carbon source to obtain NiSn(OH)6 having an exterior coating layer; (2) using a sulfur source to sulfidize the NiSn(OH)6 with a coating layer obtained in step (1) to convert the NiSn(OH)6 inside the coating layer into NiS-SnS2 nanosheets, and then pickling to remove NiS in the NiS-SnS2 nanosheets to obtain SnS2 nanosheets coated with the coating layer; (3) Carbonizing and reducing the coating layer-coated SnS2 nanosheets obtained in step (2) by heat treatment to obtain the negative electrode material.

3. The preparation method according to claim 2, characterized in that The method for preparing the NiSn(OH)6 described in step (1) comprises: mixing nickel salt, tin salt, ammonia water and solvent to obtain the NiSn(OH)6; Preferably, the NiSn(OH)6 is spherical and / or cubic in shape.

4. The preparation method according to claim 2 or 3, characterized in that The coating in step (1) comprises: first mixing a first reaction solvent, NiSn(OH)6 and a carbon source to obtain NiSn(OH)6 with a coating layer on the outside; Preferably, the carbon source in step (1) includes 6-hydroxydopamine hydrochloride and / or tannic acid. Preferably, the mass ratio of NiSn(OH)6 to the carbon source in the first mixture is 1:(0.8-1.2); Preferably, the solid-liquid ratio of NiSn(OH)6 to the first reaction solvent in the first mixture is 1:(1.5-2.5), and the unit of the solid-liquid ratio is mg / mL.

5. The preparation method according to any one of claims 2 to 4, characterized in that The sulfurization treatment in step (2) comprises: performing a second mixing of a second reaction solvent, a sulfur source and the NiSn(OH)6 having an external coating layer obtained in step (1), and then performing a hydrothermal reaction; Preferably, the sulfur source in step (2) comprises any one or a combination of at least two of thioacetamide, thiourea, lithium sulfide, hydrosulfuric acid, potassium sulfide, sodium sulfide or ammonium sulfide; Preferably, the mass ratio of the sulfur source in the second mixture to the NiSn(OH)6 with a coating layer obtained in step (1) is (1-1.5):1; Preferably, the solid-liquid ratio of NiSn(OH)6 with a coating layer obtained in step (1) to the second reaction solvent in the second mixture is 1:(1-1.5), and the unit of the solid-liquid ratio is mg / mL; Preferably, the temperature of the hydrothermal reaction is 160-200° C., and the time is 10-14 hours.

6. The preparation method according to any one of claims 2 to 5, characterized in that: The pickling method of step (2) comprises: mixing a pickling agent, a pickling solvent and the NiS-SnS2 nanosheets with a coating layer on the outside after the sulfurization treatment for a third time, and then condensing and refluxing to obtain SnS2 nanosheets coated with the coating layer; Preferably, the pickling agent comprises ethylenediaminetetraacetic acid and / or ethylenediaminetetraacetic acid salt; Preferably, the mass ratio of the pickling agent in the third mixture to the NiS-SnS2 nanosheets having a coating layer after sulfurization is (5-9):1; Preferably, the solid-liquid ratio of the NiS-SnS2 nanosheets with a coating layer on the outside after sulfurization treatment to the pickling solvent in the third mixture is 1:(7.5-9), and the unit of the solid-liquid ratio is mg / mL; Preferably, the condensation reflux temperature is 100-120° C., and the time is 4-8 hours.

7. The preparation method according to any one of claims 2 to 6, characterized in that: The heat treatment includes heating and holding in a protective atmosphere in sequence; the holding temperature is 400-450°C and the holding time is 1-3 hours; Preferably, the heating rate is 1-5°C / min; Preferably, the protective atmosphere comprises nitrogen and / or an inert gas.

8. The preparation method according to claim 2, characterized in that The preparation method comprises: (1) mixing nickel salt and water by stirring to obtain a nickel salt solution with a concentration of 0.02 to 0.03 g / mL; mixing tin salt and water by stirring to obtain a tin salt solution with a concentration of 0.03 to 0.05 g / mL; while stirring the obtained nickel salt solution at a speed of 1600 to 2000 r / min, adding the tin salt solution to the obtained nickel salt solution, the volume ratio of the nickel salt solution to the tin salt solution is (1 to 1.5):1, and after all the tin salt solution is added, continuing to stir at a speed of 1600 to 2000 r / min for 30 to 90 seconds to obtain a mixed solution; and then stirring at a speed of 1600 to 2000 r / min for 30 to 90 seconds to obtain a mixed solution. min while stirring the obtained mixed solution, adding ammonia water with a mass fraction of 25 to 28 wt % to the obtained mixed solution, with the volume ratio of the mixed solution to the ammonia water being (4 to 4.5):1, and after the ammonia water is completely added, continuing to stir at a speed of 1600 to 2000 r / min for 20 to 30 minutes, and then continuing to stir at a speed of 600 to 800 r / min in a water bath heating environment of 80 to 120° C. for 4 to 8 hours; then centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 10 to 15 hours are carried out in sequence to obtain NiSn(OH)6 in the shape of spheres and / or cubic blocks; The method comprises the following steps: stirring and mixing a Tris-HCl buffer solution and / or a Bis-Tris buffer solution with the obtained NiSn(OH)6 and 6-hydroxydopamine hydrochloride and / or tannic acid at a speed of 600 to 800 r / min for 10 to 14 hours, wherein the mass ratio of NiSn(OH)6 to 6-hydroxydopamine hydrochloride and / or tannic acid during the stirring and mixing is 1:(0.8 to 1.2), and the solid-liquid ratio of NiSn(OH)6 to the Tris-HCl buffer solution and / or the Bis-Tris buffer solution is 1:(1.5 to 2.5), and the unit of the solid-liquid ratio is mg / mL; centrifugation washing, liquid nitrogen quenching, and vacuum freeze drying for 10 to 15 hours are sequentially performed to obtain NiSn(OH)6 with a coating layer on the outside; (2) adding a sulfur source and the NiSn(OH)6 with an external coating layer obtained in step (1) into water, wherein the mass ratio of the sulfur source to the NiSn(OH)6 with an external coating layer is (1-1.5):1, and the solid-liquid ratio of the NiSn(OH)6 with an external coating layer to water is 1:(1-1.5), and the unit of the solid-liquid ratio is mg / mL; then performing a hydrothermal reaction at 160-200°C for 10-14h to convert the NiSn(OH)6 inside the coating layer into NiS-SnS2 nanosheets; then performing centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 10-15h in sequence to obtain NiS-SnS2 nanosheets coated with the coating layer; Ethylenediaminetetraacetic acid and / or ethylenediaminetetraacetic acid salt, water and NiS-SnS2 nanosheets coated with a coating layer are mixed to remove NiS from the NiS-SnS2 nanosheets, wherein the mass ratio of ethylenediaminetetraacetic acid and / or ethylenediaminetetraacetic acid salt to the NiS-SnS2 nanosheets coated with the coating layer is (5-9):1, and the solid-liquid ratio of the NiS-SnS2 nanosheets coated with the coating layer to water is 1:(7.5-9), and the unit of the solid-liquid ratio is mg / mL; after the mixing is completed, condensation reflux is performed at 100-120° C. for 4-8 hours; and then centrifugal washing, liquid nitrogen quenching and vacuum freeze drying for 10-15 hours are performed in sequence to obtain SnS2 nanosheets coated with the coating layer; (3) The SnS2 nanosheets coated with the coating layer obtained in step (2) are placed in nitrogen and / or inert gas, heated to 400-450°C at a rate of 1-5°C / min and kept warm for 1-3 hours to carbonize and reduce the obtained negative electrode material.

9. An electrochemical energy storage device, characterized in that: The electrochemical energy storage device comprises the negative electrode material according to claim 1.

10. The electrochemical energy storage device according to claim 9, characterized in that: The electrochemical energy storage device includes a lithium ion battery, a sodium ion battery or a potassium ion battery.

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