A NiS@SnO2 heterojunction composite material, preparation method and application thereof

Abstract

The present invention relates to a NiS@SnO2 heterojunction composite material, a preparation method thereof and an application thereof, belonging to the technical field of lithium ion batteries. The composite material has a NiS core, and SnO2 is distributed in a granular lattice on the surface of NiS; the volume of the SnO2 particles accounts for 20% to 50% of the surface area of the NiS microspheres; the molar ratio of NiS to SnO2 is 0.2 to 0.4:1. First, nickel salt and a sulfur source are self-assembled into NiS microspheres with irregular surfaces through a hydrothermal reaction, and then the NiS microspheres are used as templates and added to a Sn(OH)2 suspension to deposit SnO2 on the surface, forming a NiS@SnO2 heterojunction composite material. While the composite material exerts the high ion / electron conductivity of the heterojunction structure, it can effectively solve the aggregation problem of nanoparticles and the volume expansion problem caused by the insertion / extraction of lithium ions.

Description

Technical Field

[0001] The invention relates to a NiS@SnO2 heterojunction composite material, a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. Background Art

[0002] As one of the common forms of energy utilization in daily life, electricity is a good way to store energy. In particular, lithium-ion batteries are considered to be the most promising energy storage devices due to their high energy density and long life. They have been widely used in smart phones, laptops, and new energy vehicles. However, commercial graphite and lithium titanate anode materials for lithium-ion batteries are currently limited in lithium storage applications due to their limited theoretical capacity. Many alternative anode materials with high energy density and cycle life have been developed, such as high-capacity, low-cost electrode materials such as metal oxides and metal sulfides. However, they are severely limited by the inherent conductivity and the severe volume expansion effect during lithiation / delithiation, which leads to particle pulverization. To improve the kinetics of ion / electron transfer, the most direct way is to reduce the size of metal oxides or metal sulfides to the nanoscale, which benefits from the extremely short distance of electron / ion diffusion. However, small-sized particles have a great tendency to aggregate during lithiation / delithiation cycles, which ultimately leads to performance degradation. An effective way is to prepare two or more materials with similar lattice structures into heterojunction materials. Among them, the core-shell structure is one of the most common heterojunction structures. However, the core-shell structures reported so far are mainly complete and tightly coated. Although this method utilizes the high ionic conductivity of the heterojunction to a certain extent and promotes the migration of lithium ions in the negative electrode material, this tightly coated heterojunction structure still has the problem of volume expansion caused by lithium ion embedding. Summary of the invention

[0003] In view of this, the object of the present invention is to provide a NiS@SnO2 heterojunction composite material, a preparation method and its application, which can effectively solve the aggregation problem of nanoparticles and the volume expansion problem caused by the insertion / extraction of lithium ions while giving full play to the high ionic / electronic conductivity of the heterojunction structure.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A NiS@SnO2 heterojunction composite material, wherein the composite material has NiS microspheres as the core, and SnO2 is distributed on the NiS surface in a granular lattice to increase the gap inside the material to accommodate the volume expansion caused by lithium ion embedding; wherein the volume of the SnO2 particles accounts for 20% to 50% of the surface area of ​​the NiS microspheres; and in the composite material, the molar ratio of NiS to SnO2 is 0.2 to 0.4:1.

[0006] Preferably, the particle size of the NiS microspheres is 1 μm to 2.5 μm, and the particle size of SnO2 is 10 nm to 50 nm.

[0007] A method for preparing the NiS@SnO2 heterojunction composite material of the present invention, the method steps comprising:

[0008] (1) NiS microspheres were prepared by hydrothermal method;

[0009] (2) A Sn(OH)2 suspension is prepared by a coprecipitation method: a tin salt is dissolved in anhydrous ethanol to obtain a solution I, and a strong alkaline hydroxide is dissolved in water with a purity higher than that of deionized water to obtain a solution II; the solution II is added dropwise to the solution I, the pH is adjusted to 10 to 14, and a Sn(OH)2 suspension is obtained by a coprecipitation reaction;

[0010] (3) adding the NiS microspheres to the Sn(OH)2 suspension, dispersing the NiS microspheres by ultrasound to obtain a mixture, heating the mixture to 160° C. to 200° C., and keeping the mixture warm for 4 h to 15 h; after the reaction is completed, cooling, solid-liquid separation, and collecting the solid to obtain a NiS@SnO2 heterojunction composite material;

[0011] Wherein, the molar ratio of the NiS microspheres to the tin salt is 1-2:4.

[0012] Preferably, in step (1), the NiS microspheres are prepared by the following method: dissolving a soluble nickel salt and a soluble sulfur source in water with a purity higher than that of deionized water to obtain a clear solution, standing for 10 min to 30 min, adding a regulator, stirring and mixing to obtain a mixed solution; heating the mixed solution to 160° C. to 200° C., keeping warm for 4 h to 16 h, and after the reaction is completed, separating the solid and the liquid, collecting the solid and drying it to obtain the NiS microspheres.

[0013] More preferably, the soluble nickel salt is nickel nitrate, nickel perchlorate or nickel chloride; the soluble sulfur source is thiourea, thioacetamide, ammonium sulfide or sodium thiosulfate.

[0014] More preferably, the molar ratio of the soluble sulfur source to the soluble nickel salt is 3 to 6:1.

[0015] More preferably, the Ni in the clear solution 2+ The concentration is 0.03mol / L~0.06mol / L.

[0016] More preferably, the regulator is an alcohol having a boiling point greater than or equal to 120° C. and a molar ratio of C to hydroxyl of 1:1, such as ethylene glycol or glycerol.

[0017] More preferably, the volume ratio of the regulator to water in the mixed solution is 5:1-2.

[0018] Preferably, in step (2), the tin salt is SnCl2 or SnSO4; and the strong alkaline hydroxide is NaOH or KOH.

[0019] Preferably, in step (2), the concentration of solution I is 0.1 mol / L to 0.4 mol / L; the concentration of solution II is 0.4 mol / L to 1 mol / L.

[0020] Preferably, in step (2), the heating rate is 2°C / min to 5°C / min.

[0021] A lithium-ion battery, wherein the negative electrode material of the battery adopts the NiS@SnO2 heterojunction composite material described in the present invention.

[0022] Beneficial Effects

[0023] The present invention provides a NiS@SnO2 heterojunction composite material, which uses NiS microspheres as the deposition site of SnO2 nanoparticles to construct a NiS@SnO2 heterojunction composite material, effectively increasing the specific surface area of ​​metal sulfide or metal oxide, reducing the fatigue stress caused by volume change during lithiation / delithiation, and extending the service life. At the same time, the irregular grain boundaries of the heterojunction interface provide a low-energy barrier migration path for the migration of lithium ions, improving the electronic / ionic conductivity; the material can simultaneously take into account high specific capacity and long cycle stability.

[0024] The present invention provides a method for preparing a NiS@SnO2 heterojunction composite material, firstly, a nickel salt and a sulfur source are self-assembled into NiS microspheres with irregular surfaces through a hydrothermal reaction, and then the NiS microspheres are added into a Sn(OH)2 suspension as a template, and SnO2 is deposited on the surface to form a NiS@SnO2 heterojunction composite material. The composite material prepared by the method is a core-shell structure, which can increase the specific surface area and active sites of the material, thereby improving the lithium storage capacity of the composite material. At the same time, the loose lattice arrangement of SnO2 provides a stress buffer for the volume change during the lithiation / delithiation process, which can adapt to the volume change, thereby improving the structural stability of the material. At the same time, the method can also control the structure of the NiS@SnO2 heterojunction composite material. The method effectively alleviates the stress caused by ion insertion and removal and the problem of poor electronic / ionic conductivity inherent in the intrinsic conductivity of metal sulfides or metal oxides. NiS microspheres with uneven surfaces were obtained by hydrothermal reaction self-assembly method, and the irregular surface structure provided more active sites for NiS microspheres; Sn(OH)2 suspension was prepared by coprecipitation method, and NiS microspheres were used as templates to deposit uniformly on their surface, with Ni elements partially replacing Sn elements and O elements partially replacing S elements, thereby obtaining NiS@SnO2 heterojunction materials with high purity, good crystal form, and complete and controllable structure. In particular, by controlling the concentration of the precursor solution and the reaction time, the size of NiS and SnO2 microspheres can be controlled, realizing the controllable structure of NiS@SnO2 heterojunction composite materials.

[0025] In the method of the present invention, by controlling the molar ratio of the raw materials in each step, the reaction can be ensured to be fully carried out. By controlling the temperature and time of the hydrothermal reaction, the size of the NiS microspheres and the SnO2 nanoparticles can be regulated. If the reaction temperature is too high or the reaction time is too long, the morphology of the NiS@SnO2 heterojunction composite material is easily destroyed, thereby affecting the cycle stability and specific capacity of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The schematic diagram is a synthesis process and structure diagram of the NiS@SnO2 heterojunction composite material of the present invention;

[0027] Figure 2 This is an X-ray diffraction (XRD) diagram of the NiS@SnO2 heterojunction composite material described in Example 1 of the present invention.

[0028] Figure 3 1 and 2 are XRD diagrams of NiS described in Comparative Example 1 of the present invention and SnO2 described in Comparative Example 2.

[0029] Figure 4 This is a scanning electron microscope (SEM) image of the NiS@SnO2 heterojunction composite material described in Example 1 of the present invention.

[0030] Figure 5 This is the SEM image of NiS described in Comparative Example 1 of the present invention.

[0031] Figure 6 This is a transmission electron microscope (TEM) image of SnO2 described in Comparative Example 2 of the present invention.

[0032] Figure 7 This is a Raman spectrum of the NiS@SnO2 heterojunction composite material described in Example 1 of the present invention.

[0033] Figure 8 This is a cyclic stability diagram of the NiS@SnO2 heterojunction composite material described in Example 1 of the present invention.

[0034] Fig. 9 This is a rate performance diagram of the NiS@SnO2 heterojunction composite material described in Example 1 of the present invention.

[0035] Fig.10 is the Li calculated in the confined range based on the CI-NEB method + The migration energy barriers of the materials described in Comparative Examples 1 and 2 and Example 1.

[0036] Fig.11 This is a cycle stability diagram of NiS described in Comparative Example 1 of the present invention.

[0037] Fig.12 This is the cyclic stability diagram of SnO2 described in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below in conjunction with specific embodiments.

[0039] In the following examples or comparative examples:

[0040] (1) XRD test: D8 ADVANCE X-ray diffractometer from Bruker.

[0041] (2) SEM test: Zeiss Sigma-500 field emission scanning electron microscope.

[0042] (3) TEM test: JEOL JEM-2100F field emission transmission electron microscope.

[0043] (4) Raman spectroscopy: HR-800μ-Raman spectrometer.

[0044] (5) Inductively coupled plasma (ICP) test: Agilent ICPOES730 inductively coupled plasma spectrometer.

[0045] (6) Battery assembly: ① Preparation of pole piece: The materials described in the embodiment or comparative example, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 8:1:1. The specific steps are as follows: first, the materials described in the embodiment or comparative example and acetylene black are mixed, and ground for 30 minutes, then PVDF and N-methylpyrrolidone (NMP) are added, and the grinding is continued for 30 minutes to obtain a uniform slurry, and the slurry is applied on the current collector copper foil, and dried at 80°C for 24 hours to obtain a negative pole piece. ② Use a 16mm cutter to cut the negative electrode into a 16mm diameter electrode, select the electrode with uniform coating appearance, weigh it with a precision balance, and calculate the mass of the materials described in the embodiment or comparative example (the total mass minus the mass of the current collector multiplied by the parameter 0.8); bring the above-mentioned electrode into a glove box with an argon atmosphere to assemble a half-cell, put the negative electrode shell, lithium sheet, PP diaphragm, drip commercial electrolyte (LiPF6 / EC+DEC), cut electrode, gasket, and shrapnel in turn, that is, assemble the half-cell, and press it with a button battery sealing machine. The battery model is CR2025 button battery, PP is polypropylene, EC is ethylene carbonate, and DEC is diethyl carbonate. Take the battery out of the glove box and measure the electrochemical performance after standing for 24 hours.

[0046] (7) Half-cell performance test: On the Xinwei battery charge and discharge tester, the charge and discharge voltage range is 0.01~3V, and the current density is 200mA / g. The charge specific capacity, cycle efficiency and cycle stability of the button battery after 90 cycles are tested and analyzed. The coulomb efficiency of each cycle is above 95%, and after 90 cycles, it can still maintain a specific capacity of more than 300mAh / g; under the electrochemical workstation conditions of 0.01~3V, the rate performance diagram is measured at current densities of 0.1, 0.2, 0.5, 0.8, 1, 2, and 5A / g.

[0047] Example 1

[0048] A method for preparing a NiS@SnO2 heterojunction composite material specifically comprises the following steps:

[0049] (1) Preparation of NiS microspheres: 3 mmol Ni(NO3)2·6H2O and 12 mmol thiourea were dissolved in 50 mL deionized water to form a clear solution, which was allowed to stand for 30 min. Then 20 mL ethylene glycol was added, stirred for 5 min, and mixed to obtain a mixed solution. The mixed solution was transferred into a reactor and kept at 200°C for 8 h. After the reaction was completed, the reactor was cooled to room temperature and centrifuged. The solid was dried to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0050] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnCl2 was dissolved in 20 mL anhydrous ethanol to obtain solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to obtain solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 13 to prepare Sn(OH)2 suspension by coprecipitation reaction.

[0051] (3) Preparation of NiS@SnO2 heterojunction: 0.27g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1h to disperse the NiS microspheres to obtain a mixture; the mixture was transferred to a reactor and heated to 200°C for 10h; after the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0052] The synthesis process and structure of the NiS@SnO2 heterojunction composite material are as follows Figure 1 shown.

[0053] Figure 2 : is the XRD diagram of the NiS@SnO2 heterojunction composite material. The composite material has characteristic peaks of both NiS and SnO2, indicating that the composite material contains both NiS and SnO2.

[0054] Figure 4 The SEM image of the NiS@SnO2 heterojunction composite material shows that SnO2 nanoparticles are attached to the surface of NiS microspheres to form a core-shell structure. The particle size of the NiS microspheres is between 1μm and 2μm, the particle size of SnO2 is between 10nm and 50nm, and the volume of SnO2 particles on the surface of the NiS microspheres accounts for about 30%. The ICP test results show that the molar ratio of NiS to SnO2 in the composite material is 2.4:7.5.

[0055] Figure 7 : is the Raman spectrum of the NiS@SnO2 heterojunction composite material, and the results show that NiS phase and SnO2 phase exist in the composite material.

[0056] Figure 8 This is a charge and discharge cycle test (cycle number-discharge specific capacity, efficiency) of the NiS@SnO2 heterojunction composite material lithium-ion battery negative electrode material in a lithium half-cell. The results show that the composite material has good cycle stability during the charge and discharge process.

[0057] Fig. 9This is a rate diagram of the NiS@SnO2 heterojunction composite material. The results show that the composite material has good application ability under large current.

[0058] Fig.10 is the migration energy barrier of the NiS@SnO2 heterojunction composite material calculated in the confined range based on the CI-NEB method. The results show that Li + The NiS@SnO2 heterojunction composite material has a lower migration energy barrier and is more conducive to transmission.

[0059] Example 2

[0060] A method for preparing a NiS@SnO2 heterojunction composite material specifically comprises the following steps:

[0061] (1) Preparation of NiS microspheres: 3 mmol Ni(NO3)2·6H2O and 12 mmol thiourea were dissolved in 50 mL deionized water to form a clear solution, and then allowed to stand for 30 min; then 20 mL ethylene glycol was added, stirred for 5 min, and mixed evenly to obtain a mixed solution. The mixed solution was transferred into a reactor and kept at 180°C for 12 h. After the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0062] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnCl2 was dissolved in 20 mL anhydrous ethanol to obtain solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to obtain solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 13 to prepare Sn(OH)2 suspension by coprecipitation reaction.

[0063] (3) Preparation of NiS@SnO2 heterojunction: 0.27g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1h to disperse the NiS microspheres to obtain a mixture; the mixture was transferred to a reactor and heated to 180°C for 12h; after the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0064] The XRD test results of the NiS@SnO2 heterojunction composite material show that the composite material has characteristic peaks of both NiS and SnO2.

[0065] The SEM test results of the NiS@SnO2 heterojunction composite material show that SnO2 nanoparticles are attached to the surface of NiS microspheres to form a core-shell structure.

[0066] The Raman spectrum test results of the NiS@SnO2 heterojunction composite material show that NiS phase and SnO2 phase exist in the composite material.

[0067] The half-cell assembled in this example shows similar cycle stability and rate performance as those in Example 1. This indicates that within the allowable range, changes in reaction temperature and reaction time have almost no effect on the morphology and electrochemical properties of the NiS@SnO2 heterojunction composite material.

[0068] Example 3

[0069] A method for preparing a NiS@SnO2 heterojunction composite material specifically comprises the following steps:

[0070] (1) Preparation of NiS microspheres: 3 mmol Ni(NO3)2·6H2O and 12 mmol thiourea were dissolved in 50 mL deionized water to form a clear solution, and then allowed to stand for 30 min; then 20 mL ethylene glycol was added, stirred for 5 min, and mixed evenly to obtain a mixed solution. The mixed solution was transferred into a reactor and kept at 160°C for 15 h. After the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0071] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnCl2 was dissolved in 20 mL anhydrous ethanol to obtain solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to obtain solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 13 to prepare Sn(OH)2 suspension by coprecipitation reaction.

[0072] (3) Preparation of NiS@SnO2 heterojunction: 0.27g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1h to disperse the NiS microspheres to obtain a mixture; the mixture was transferred to a reactor and heated to 160°C for 15h; after the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0073] The XRD test results of the NiS@SnO2 heterojunction composite material show that the composite material has characteristic peaks of both NiS and SnO2.

[0074] The SEM test results of the NiS@SnO2 heterojunction composite material show that SnO2 nanoparticles are attached to the surface of NiS microspheres to form a core-shell structure.

[0075] The Raman spectrum test results of the NiS@SnO2 heterojunction composite material show that NiS phase and SnO2 phase exist in the composite material.

[0076] The half-cell assembled in this example shows similar cycle stability and rate performance as those in Example 1. This indicates that within the allowable range, changes in reaction temperature and reaction time have almost no effect on the morphology and electrochemical properties of the NiS@SnO2 heterojunction composite material.

[0077] Example 4

[0078] A method for preparing a NiS@SnO2 heterojunction composite material specifically comprises the following steps:

[0079] (1) Preparation of NiS microspheres: 4 mmol Ni(ClO4)2·6H2O and 16 mmol thiourea were dissolved in 50 mL deionized water to form a clear solution, and then allowed to stand for 20 min; then 10 mL ethylene glycol was added, stirred for 5 min, and mixed to obtain a mixed solution. The mixed solution was transferred into a reactor and kept at 200°C for 8 h. After the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0080] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnSO4 was dissolved in 30 mL anhydrous ethanol to obtain solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to obtain solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 13 to prepare Sn(OH)2 suspension by coprecipitation reaction.

[0081] (3) Preparation of NiS@SnO2 heterojunction: 0.54 g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1 h to disperse the NiS microspheres to obtain a mixture; the mixture was transferred to a reactor and heated to 200°C for 8 h; after the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0082] The XRD test results of the NiS@SnO2 heterojunction composite material show that the composite material has characteristic peaks of both NiS and SnO2.

[0083] The SEM test results of the NiS@SnO2 heterojunction composite material show that SnO2 nanoparticles are attached to the surface of NiS microspheres to form a core-shell structure.

[0084] The Raman spectrum test results of the NiS@SnO2 heterojunction composite material show that NiS phase and SnO2 phase exist in the composite material.

[0085] The half-cell assembled in this example shows similar cycle stability and rate performance as those in Example 1. This indicates that within the allowable range, changes in the type, amount and reaction time of the nickel source and tin source have almost no effect on the morphology and electrochemical properties of the NiS@SnO2 heterojunction composite material.

[0086] Example 5

[0087] A method for preparing a NiS@SnO2 heterojunction composite material specifically comprises the following steps:

[0088] (1) Preparation of NiS microspheres: 6 mmol Ni(NO3)2·6H2O and 24 mmol thiourea were dissolved in 50 mL deionized water to form a clear solution, and then allowed to stand for 10 min; then 20 mL ethylene glycol was added, stirred for 5 min, and mixed to obtain a mixed solution. The mixed solution was transferred into a reactor and kept at 200°C for 8 h. After the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0089] (2) Preparation of Sn(OH)2 suspension: 6 mmol SnCl2 was dissolved in 30 mL anhydrous ethanol to obtain solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to obtain solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 13 to prepare Sn(OH)2 suspension by coprecipitation reaction.

[0090] (3) Preparation of NiS@SnO2 heterojunction: 0.54 g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1 h to disperse the NiS microspheres to obtain a mixture; the mixture was transferred to a reactor and heated to 200°C for 8 h; after the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0091] The XRD test results of the NiS@SnO2 heterojunction composite material show that the composite material has characteristic peaks of both NiS and SnO2.

[0092] The SEM test results of the NiS@SnO2 heterojunction composite material show that SnO2 nanoparticles are attached to the surface of NiS microspheres to form a core-shell structure.

[0093] The Raman spectrum test results of the NiS@SnO2 heterojunction composite material show that NiS phase and SnO2 phase exist in the composite material.

[0094] The half-cell assembled in this example shows similar cycle stability and rate performance as those in Example 1. This indicates that within the allowable range, the changes in the amounts of nickel source, sulfur source and tin source and the reaction time have almost no effect on the morphology and electrochemical properties of the NiS@SnO2 heterojunction composite material.

[0095] Example 6

[0096] A method for preparing a NiS@SnO2 heterojunction composite material specifically comprises the following steps:

[0097] (1) Preparation of NiS microspheres: 3 mmol Ni(NO3)2·6H2O and 12 mmol sodium thiosulfate were dissolved in 50 mL deionized water to form a clear solution, and then allowed to stand for 30 min; then 20 mL propylene glycol was added, stirred for 5 min, and mixed evenly to obtain a mixed solution. The mixed solution was transferred into a reactor and kept at 200°C for 8 h. After the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0098] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnCl2 was dissolved in 20 mL anhydrous ethanol to obtain solution I, and 10 mmol KOH was dissolved in 20 mL deionized water to obtain solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 10 to prepare Sn(OH)2 suspension by coprecipitation reaction.

[0099] (3) Preparation of NiS@SnO2 heterojunction: 0.27g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1h to disperse the NiS microspheres to obtain a mixture; the mixture was transferred to a reactor and heated to 200°C for 8h; after the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0100] The XRD test results of the NiS@SnO2 heterojunction composite material show that the composite material has characteristic peaks of both NiS and SnO2.

[0101] The SEM test results of the NiS@SnO2 heterojunction composite material show that SnO2 nanoparticles are attached to the surface of the NiS microspheres to form a core-shell structure; wherein the size of the SnO2 nanoparticles is slightly reduced compared with that of Example 1.

[0102] The Raman spectrum test results of the NiS@SnO2 heterojunction composite material show that NiS phase and SnO2 phase exist in the composite material.

[0103] The half-cell assembled in this embodiment shows similar rate performance to that of Example 1, and the cycle stability is improved compared with that of Example 1. It shows that reducing the size of SnO2 nanoparticles and increasing the gap between SnO2 nanoparticles by reaction time can help improve the electrochemical performance of NiS@SnO2 heterojunction composite materials. It shows that reducing the size of SnO2 nanoparticles and increasing the gap between SnO2 nanoparticles by reaction time can help improve the electrochemical performance of NiS@SnO2 heterojunction composite materials. Within the allowable range, changes in the type, amount, pH and reaction time of the sulfur source, regulator have almost no effect on the morphology and electrochemical properties of the NiS@SnO2 heterojunction composite material, or slightly enhance the electrochemical performance by controlling the size of the SnO2 nanoparticles.

[0104] Example 7

[0105] A method for preparing a NiS@SnO2 heterojunction composite material specifically comprises the following steps:

[0106] (1) Preparation of NiS microspheres: 3 mmol Ni(NO3)2·6H2O and 12 mmol thioacetamide were dissolved in 50 mL deionized water to form a clear solution, and then allowed to stand for 30 min; then 20 mL propylene glycol was added, stirred for 5 min, and mixed evenly to obtain a mixed solution. The mixed solution was transferred into a reactor and kept at 200°C for 8 h. After the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0107] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnCl2 was dissolved in 20 mL anhydrous ethanol to obtain solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to obtain solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 13 to prepare Sn(OH)2 suspension by coprecipitation reaction.

[0108] (3) Preparation of NiS@SnO2 heterojunction: 0.54 g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1 h to disperse the NiS microspheres to obtain a mixture; the mixture was transferred to a reactor and heated to 200°C for 8 h; after the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0109] The XRD test results of the NiS@SnO2 heterojunction composite material show that the composite material has characteristic peaks of both NiS and SnO2.

[0110] The SEM test results of the NiS@SnO2 heterojunction composite material show that SnO2 nanoparticles are attached to the surface of NiS microspheres to form a core-shell structure; wherein the size of the NiS particles is slightly reduced compared with that of Example 1.

[0111] The Raman spectrum test results of the NiS@SnO2 heterojunction composite material show that NiS phase and SnO2 phase exist in the composite material.

[0112] The half-cell assembled in this example shows similar cycle stability and rate performance as those in Example 1. This indicates that within the allowable range, the types of nickel source and sulfur source, the amount of NiS microspheres in step (3), and the change in reaction time have almost no effect on the morphology and electrochemical properties of the NiS@SnO2 heterojunction composite material. However, with the change in the reaction time in step (1), the size of the NiS microspheres can be controlled.

[0113] Example 8

[0114] A method for preparing a NiS@SnO2 heterojunction composite material specifically comprises the following steps:

[0115] (1) Preparation of NiS microspheres: 3 mmol Ni(NO3)2·6H2O and 12 mmol ammonium sulfide were dissolved in 50 mL deionized water to form a clear solution, and then allowed to stand for 30 min; then 20 mL propylene glycol was added, stirred for 5 min, and mixed evenly to obtain a mixed solution. The mixed solution was transferred into a reactor and kept at 200°C for 8 h. After the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0116] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnCl2 was dissolved in 20 mL anhydrous ethanol to obtain solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to obtain solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 14 to prepare Sn(OH)2 suspension by coprecipitation reaction.

[0117] (3) Preparation of NiS@SnO2 heterojunction: 0.27g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1h to disperse the NiS microspheres to obtain a mixture; the mixture was transferred to a reactor and heated to 200°C for 8h; after the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0118] The XRD test results of the NiS@SnO2 heterojunction composite material show that the composite material has characteristic peaks of both NiS and SnO2.

[0119] The SEM test results of the NiS@SnO2 heterojunction composite material show that SnO2 nanoparticles are attached to the surface of NiS microspheres to form a core-shell structure; wherein the size of the NiS particles is slightly reduced compared with that of Example 1.

[0120] The Raman spectrum test results of the NiS@SnO2 heterojunction composite material show that NiS phase and SnO2 phase exist in the composite material.

[0121] The half-cell assembled in this example shows similar cycle stability and rate performance as those in Example 1. This indicates that within the allowable range, the type of sulfur source and the change of pH have almost no effect on the morphology and electrochemical properties of the NiS@SnO2 heterojunction composite material.

[0122] Example 9

[0123] A method for preparing a NiS@SnO2 heterojunction composite material specifically comprises the following steps:

[0124] (1) Preparation of NiS microspheres: 1mmol Ni(NO3)2·6H2O, 1mmol Ni(ClO4)2·6H2O, 1mmol NiCl2 and 12mmol thiourea were dissolved in 50mL deionized water to form a clear solution, and then allowed to stand for 30min; then 20mL propylene glycol was added, stirred for 5min, and mixed evenly to obtain a mixed solution. The mixed solution was transferred into a reactor and kept at 200°C for 8h. After the reaction was completed, the reactor was cooled to room temperature, centrifuged in a centrifuge, and the solid was dried to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0125] (2) Preparation of Sn(OH)2 suspension: 2mmol SnCl2 and 2mmol SnSO4 were dissolved in 20mL anhydrous ethanol to obtain solution I, and 10mmol NaOH was dissolved in 20mL deionized water to obtain solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 13 to prepare Sn(OH)2 suspension by coprecipitation reaction.

[0126] (3) Preparation of NiS@SnO2 heterojunction: 0.27g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1h to disperse the NiS microspheres to obtain a mixture; the mixture was transferred to a reactor and heated to 200°C for 8h; after the reaction was completed, the reactor was cooled to room temperature, centrifuged, and the solid was dried to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0127] The XRD test results of the NiS@SnO2 heterojunction composite material show that the composite material has characteristic peaks of both NiS and SnO2.

[0128] The SEM test results of the NiS@SnO2 heterojunction composite material show that SnO2 nanoparticles are attached to the surface of NiS microspheres to form a core-shell structure; wherein the size of the NiS particles is slightly reduced compared with that of Example 1.

[0129] The Raman spectrum test results of the NiS@SnO2 heterojunction composite material show that NiS phase and SnO2 phase exist in the composite material.

[0130] The half-cell assembled in this example shows similar cycle stability and rate performance as those in Example 1. This indicates that within the allowable range, the change of the types of nickel source and tin source has almost no effect on the morphology and electrochemical properties of the NiS@SnO2 heterojunction composite material.

[0131] Comparative Example 1

[0132] Preparation of NiS microspheres: 3mmol Ni(NO3)2·6H2O and 12mmol thiourea were dissolved in 50mL deionized water, and ultrasonicated for 30min to form a transparent cheng solution; 20ml ethylene glycol was added to the mixed solution, stirred for 5min, and mixed evenly. The mixed solution was transferred into a reactor and kept at 200℃ for 8h. After the reaction was completed, the reactor was cooled to room temperature, and NiS microspheres were obtained by filtering in a fume hood or centrifuging using a centrifuge. The heating rate of the hydrothermal reaction was 5℃ / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0133] The XRD test results of the NiS microspheres are as follows Figure 3 The SEM test results of the NiS microspheres are shown in Figure 5 shown.

[0134] The charge and discharge cycle test results of the NiS microspheres in the lithium half-cell are as follows Fig.11 As shown, the results show that the NiS microspheres have extremely poor cycle stability during charge and discharge.

[0135] Fig.10 is the migration energy barrier of the NiS microspheres calculated in the confined range based on the CI-NEB method. The results show that Li + The NiS microspheres have a high migration barrier, which is not conducive to transport.

[0136] Comparative Example 2

[0137] Preparation of SnO2: Dissolve 4mmol SnCl2 in 20mL anhydrous ethanol to obtain solution I, and dissolve 10mmol NaOH in 20mL deionized water to obtain solution II. Add solution II dropwise to solution I, adjust the pH to 13, and obtain a suspension of Sn(OH)2 by coprecipitation reaction. Transfer the suspension to a reactor and heat to 200℃ for 8h. After the reaction is completed, wait for the reactor to cool to room temperature and filter in a fume hood to obtain SnO2. The heating rate of the hydrothermal reaction is 5℃ / min, the centrifugation time is 10min / time, and the rotation speed is 8000rpm.

[0138] The XRD test results of SnO2 are as follows Figure 3 The TEM test results of SnO2 are shown in Figure 6 shown.

[0139] The charge and discharge cycle test results of SnO2 in lithium half-cell are as follows Fig.12 As shown, the results show that the cycle stability of SnO2 is extremely poor during the charge and discharge process.

[0140] Fig.10 is the migration energy barrier of the NiS microspheres calculated in the confined range based on the CI-NEB method. The results show that Li + The NiS microspheres have a high migration barrier, which is not conducive to transport.

[0141] Comparative Example 3

[0142] (1) Preparation of NiS microspheres: 3 mmol Ni(NO3)2·6H2O and 12 mmol thiourea were dissolved in 50 mL deionized water to form a transparent mixed solution, which was allowed to stand for 30 min. 20 mL ethylene glycol was added to the mixed solution, stirred for 5 min, and mixed evenly. The mixed solution was transferred into a reactor and kept at 200°C for 8 h. After the reaction was completed, the reactor was cooled to room temperature and filtered in a fume hood or centrifuged to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0143] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnCl2 was dissolved in 20 mL anhydrous ethanol to prepare solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to prepare solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 9 to obtain a Sn(OH)2 suspension by coprecipitation reaction.

[0144] (3) Preparation of NiS@SnO2 heterojunction: 0.27g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1h to disperse the NiS microspheres; the mixture was transferred to a reactor and heated to 200°C for 10h. After the reaction was completed, the reactor was cooled to room temperature and centrifuged to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0145] Comparative Example 4

[0146] (1) Preparation of NiS microspheres: 3 mmol Ni(NO3)2·6H2O and 12 mmol thiourea were dissolved in 50 mL deionized water to form a transparent mixed solution, which was allowed to stand for 30 min. 20 mL ethylene glycol was added to the mixed solution, stirred for 5 min, and mixed evenly. The mixed solution was transferred into a reactor and kept at 200°C for 8 h. After the reaction was completed, the reactor was cooled to room temperature and filtered in a fume hood or centrifuged to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0147] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnCl2 was dissolved in 20 mL anhydrous ethanol to prepare solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to prepare solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 15 to obtain a Sn(OH)2 suspension by coprecipitation reaction.

[0148] (3) Preparation of NiS@SnO2 heterojunction: 0.27g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1h to disperse the NiS microspheres; the mixture was transferred to a reactor and heated to 200°C for 10h. After the reaction was completed, the reactor was cooled to room temperature and filtered in a fume hood or centrifuged to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0149] Comparative Examples 3 and 4 changed the pH value in step (2), and found that during the operation of step (2), the clarity of the milky white suspension formed was higher than that of the embodiment, and the morphology of the composite material finally formed was the same as the NiS microspheres prepared in Comparative Example 1, which means that when the pH value exceeds the range specified in the embodiment, the NiS@SnO2 heterojunction composite material in which SnO2 nanoparticles are distributed in a lattice on the NiS microspheres cannot be obtained.

[0150] The electrochemical performance test results of Comparative Examples 3 and 4 are similar to those of the NiS microspheres described in Comparative Example 1.

[0151] Comparative Example 5

[0152] (1) Preparation of NiS microspheres: 3 mmol Ni(NO3)2·6H2O and 12 mmol thiourea were dissolved in 50 mL deionized water to form a transparent mixed solution, which was allowed to stand for 30 min. 20 mL ethylene glycol was added to the mixed solution, stirred for 5 min, and mixed evenly. The mixed solution was transferred into a reactor and kept at 200°C for 8 h. After the reaction was completed, the reactor was cooled to room temperature and filtered in a fume hood or centrifuged to obtain NiS microspheres. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10 min / time, and the rotation speed was 8000 rpm.

[0153] (2) Preparation of Sn(OH)2 suspension: 4 mmol SnCl2 was dissolved in 20 mL anhydrous ethanol to prepare solution I, and 10 mmol NaOH was dissolved in 20 mL deionized water to prepare solution II. Solution II was added dropwise to solution I, and the pH was adjusted to 13 to obtain a Sn(OH)2 suspension by coprecipitation reaction.

[0154] (3) Preparation of NiS@SnO2 heterojunction: 0.27g of the NiS microspheres were added to the Sn(OH)2 suspension, and ultrasonicated for 1h to disperse the NiS microspheres; the mixture was transferred to a reactor and heated to 200°C for 48h. After the reaction was completed, the reactor was cooled to room temperature and filtered in a fume hood or centrifuged to obtain a NiS@SnO2 heterojunction composite material. The heating rate of the hydrothermal reaction was 5°C / min, the centrifugation time was 10min / time, and the rotation speed was 8000rpm.

[0155] In this comparative example, by significantly extending the time of the hydrothermal reaction in step (3), the number and size of SnO2 particles are increased, so that they can contact each other to form a complete shell layer, and a NiS@SnO2 heterojunction composite material with a complete core-shell structure is obtained. When the electrochemical performance is tested, its cycle stability is between that of the NiS microspheres prepared in comparative example 1 and the SnO2 nanosheets prepared in comparative example 2. According to the high volume expansion characteristics of SnO2, the lattice structure obtained in the embodiment can better adapt to the Li + Volume expansion caused by embedding.

[0156] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A method for preparing a NiS@SnO2 heterojunction composite material, characterized in that: The method steps include: (1) Preparation of NiS microspheres by hydrothermal method; (2) A Sn(OH)2 suspension is prepared by a coprecipitation method: a tin salt is dissolved in anhydrous ethanol to obtain solution I, and a strong alkaline hydroxide is dissolved in water with a purity higher than that of deionized water to obtain solution II; solution II is added dropwise to solution I, and the pH is adjusted to 10-14, and a Sn(OH)2 suspension is obtained by a coprecipitation reaction; (3) adding the NiS microspheres to the Sn(OH)2 suspension, dispersing the NiS microspheres by ultrasound to obtain a mixture, heating the mixture to 160°C to 200°C, and keeping the mixture warm for 4h to 15h; after the reaction is completed, cooling, solid-liquid separation, and collecting the solid to obtain a NiS@SnO2 heterojunction composite material; Wherein, the molar ratio of the NiS microspheres to the tin salt is 1-2:4; The composite material has NiS microspheres as the core, and SnO2 is distributed on the NiS surface in a granular lattice; wherein the volume of the SnO2 particles accounts for 20% to 50% of the surface area of ​​the NiS microspheres; in the composite material, the molar ratio of NiS to SnO2 is 0.2 to 0.4:

1.

2. The method for preparing a NiS@SnO2 heterojunction composite material according to claim 1, characterized in that: The particle size of the NiS microspheres is 1 μm to 2.5 μm, and the particle size of SnO2 is 10 nm to 50 nm.

3. The method for preparing a NiS@SnO2 heterojunction composite material according to claim 1, characterized in that: In step (1), the NiS microspheres are prepared by the following method: dissolving a soluble nickel salt and a soluble sulfur source in water with a purity higher than that of deionized water to obtain a clear solution, standing the solution for 10 min to 30 min, adding a regulator, stirring and mixing the solution to obtain a mixed solution; heating the mixed solution to 160° C. to 200° C., keeping the temperature for 4 h to 16 h, separating the solid from the liquid after the reaction is completed, collecting the solid and drying it to obtain the NiS microspheres.

4. The method for preparing a NiS@SnO2 heterojunction composite material according to claim 3, characterized in that: The soluble nickel salt is nickel nitrate, nickel perchlorate or nickel chloride; the soluble sulfur source is thiourea, thioacetamide, ammonium sulfide or sodium thiosulfate; the regulator is an alcohol with a boiling point greater than or equal to 120° C. and a molar ratio of C to hydroxyl of 1:

1.

5. The method for preparing a NiS@SnO2 heterojunction composite material according to claim 3, characterized in that: The molar ratio of the soluble sulfur source to the soluble nickel salt is 3 to 6:1; the Ni in the clear solution 2+ The concentration is 0.03mol / L~0.06mol / L; the volume ratio of the regulator to water in the mixed solution is 5:1~2.

6. The method for preparing a NiS@SnO2 heterojunction composite material according to claim 1, characterized in that: In step (2), the tin salt is SnCl2 or SnSO4; and the strong alkaline hydroxide is NaOH or KOH.

7. The method for preparing a NiS@SnO2 heterojunction composite material according to claim 1, characterized in that: In step (2), the concentration of solution I is 0.1 mol / L to 0.4 mol / L; the concentration of solution II is 0.4 mol / L to 1 mol / L.

8. The method for preparing a NiS@SnO2 heterojunction composite material according to claim 1, characterized in that: In step (2), the heating rate is 2°C / min to 5°C / min.

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