Amorphous MoS x High-performance negative electrode sheet of material and preparation method and application thereof

Abstract

The present invention provides a high-performance negative electrode sheet based on amorphous MoS x material, a preparation method thereof and an application. The negative electrode sheet comprises an anode active material a-MoS2 / DT@CNTs composite material. The preparation method of the negative electrode sheet comprises the following steps: S1, mixing the anode active material, a conductive agent and a binder, fully grinding in an agate mortar, and then adding an appropriate amount of N-methylpyrrolidone to form a uniform slurry; S2, uniformly coating the slurry on a copper foil and drying to obtain a dried electrode sheet; S3, rolling and cutting the dried electrode sheet to obtain the negative electrode sheet. The method of the present invention for preparing the battery negative electrode sheet has low production cost, simple process and good processability, and exhibits excellent electrochemical performance and stability in the application of the negative electrode of sodium ion batteries, and has important application potential and commercial value.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method based on amorphous MoS x High-performance negative electrode sheet of the material and its preparation method and application. Background Art

[0002] Sodium-ion batteries (SIBs) are considered a promising alternative to lithium-ion batteries (LIBs) due to their abundant raw materials and low cost, especially for large-scale energy storage systems. However, the energy density and cycle stability of sodium-ion batteries still need to be improved compared with lithium-ion batteries, which is largely limited by the performance of the negative electrode materials.

[0003] Currently, graphite is widely used as the negative electrode material in commercial lithium-ion batteries, but its application in sodium-ion batteries is limited by the large ionic radius and low diffusion coefficient of sodium ions. Therefore, researchers are looking for negative electrode materials that are more suitable for sodium-ion batteries to achieve higher energy density and better cycle stability.

[0004] Amorphous MoS x The material is considered to be a potential negative electrode material for sodium-ion batteries due to its unique chemical and physical properties, such as high theoretical capacity, excellent electronic conductivity and ion diffusion. The amorphous structure provides more active sites and shorter ion diffusion paths, which helps to improve the insertion and extraction performance of sodium ions, thereby improving the charge and discharge performance of the battery. x The material shows great potential in the application of sodium ion battery negative electrode, but its practical application still faces some challenges. First, the structural stability of amorphous materials is poor, and it is easy to undergo structural changes during the charging and discharging process, resulting in rapid decay of battery capacity. Second, amorphous MoS x Side reactions between the material and the electrolyte may lead to battery capacity loss and cycle performance degradation. x The preparation of materials usually requires complex processes and high costs. Summary of the invention

[0005] The present invention provides a novel amorphous MoS x High-performance negative electrode sheet of material and preparation method and application thereof, which improves the amorphous MoS x The structural stability and electrochemical performance of the material solve the problem of poor material performance in the prior art. The present invention also provides the application of the negative electrode sheet in a sodium ion battery, which improves the electrochemical performance and stability of the sodium ion battery.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A negative electrode sheet comprises a negative electrode active material, wherein the negative electrode active material is an a-MoS2 / DT@CNTs composite material.

[0008] Preferably, the negative electrode active material loading of each negative electrode sheet is 0.9-1.1 mg cm -2 .

[0009] The present invention also provides a method for preparing a negative electrode sheet, comprising the following steps:

[0010] S1. Mix the negative electrode active material, the conductive agent and the binder, grind them thoroughly in an agate mortar, and then add an appropriate amount of N-methylpyrrolidone to mix into a uniform slurry;

[0011] S2, evenly apply the slurry on the copper foil, dry it, and obtain a dry electrode;

[0012] S3. Roll and cut the dried electrode sheet to obtain a negative electrode sheet.

[0013] Preferably, the mass ratio of the negative electrode active material, the conductive agent and the binder in S1 is 7:2:1-8:1:1.

[0014] Preferably, the mass ratio of the negative electrode active material, the conductive agent and the binder in S1 is 8:1:1.

[0015] Preferably, the conductive agent in S1 includes but is not limited to one or more of conductive carbon black (SP), acetylene black, carbon nanotubes (CNT), and Ketjen black.

[0016] Preferably, the binder in S1 includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, carboxymethyl cellulose, sodium alginate, polyacrylic acid and cross-linked polymer (aqueous dispersion of acrylonitrile multipolymer).

[0017] Preferably, the drying temperature in S2 is 90° C.-150° C., and the drying time is 35 min-180 min.

[0018] Preferably, the drying temperature in S2 is 120° C. and the drying time is 60 min.

[0019] Preferably, in S4, rolling is performed by a roller press to increase the compaction density of the pole piece, and the pole piece after rolling is cut into a diameter of 10-25 mm.

[0020] Preferably, the diameter of the negative electrode sheet in S4 is 14 mm.

[0021] The present invention also provides a sodium ion battery, comprising a positive electrode sheet, a separator, an electrolyte and the negative electrode sheet.

[0022] The sodium ion battery is assembled as follows: the prepared negative electrode sheet is used as the negative electrode, the positive electrode is a high-purity sodium sheet (diameter 15.6mm, thickness 0.4-0.5mm), the separator is glass fiber (Whatman, 18mm), and the electrolyte is 1M NaClO4 (dissolved in a mixed solvent of EC: DMC: EMC = 1:1:1). The negative electrode sheet, electrolyte, separator, electrolyte and high-purity sodium sheet are assembled in order, and then sealed with a hydraulic sealing machine to obtain a sodium ion battery.

[0023] The present invention also provides a method for preparing the a-MoS2 / DT@CNTs composite material, which is used to manufacture the negative electrode sheet, comprising the following steps:

[0024] (1) Add CNTs to deionized water and stir for 10-50 minutes to obtain a CNTs solution;

[0025] (2) Add (NH4)6Mo7O to the CNTs solution 24 4H2O, C2H5NS and C8H4Na2O4, stir for 10-50min to form a mixed solution;

[0026] (3) transferring the mixed solution to a 100 mL polytetrafluoroethylene-lined autoclave and reacting at 180° C. for 0.5-5 h to obtain a black product;

[0027] (4) collecting the black product after the reaction in step (3), and washing it three times with deionized water and anhydrous ethanol respectively;

[0028] (5) The washed reactants are placed in an oven at 60-80°C and dried for 5-24 hours to obtain a-MoS2 / DT@CNTs composite material.

[0029] Preferably, in step (2), (NH4)6Mo7O 24 The molar ratio of 4H2O, C2H5NS and C8H4Na2O4 is 1:1:0.05-1:20:0.5.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] The present invention adopts disodium terephthalate (DT), a conjugated carboxylic acid organic molecule with a carbon-oxygen double bond, as a molecular model and combines it with an amorphous MoS2 nanocomposite (a-MoS2 / DT@CNTs). The DT molecules are embedded in the a-MoS2 molecular layer, successfully expanding the interlayer spacing to It provides more space for the embedding of sodium ions. DT molecules themselves have the property of storing sodium, and can achieve synergistic sodium storage with a-MoS2, thereby improving the sodium storage capacity of the material. As the negative electrode material of sodium battery, at 50mA g -1 The charge and discharge test was carried out at a current density of 1.34 Å, and the specific capacity of the 20th cycle reached 619 mAh g -1 , only 7.47% loss compared with the theoretical specific capacity. After 100 cycles, a-MoS2 / DT@CNTs still has 412 mAh g -1 High reversible specific capacity. At 1000mA g -1 Under high rate conditions, a-MoS2 / DT@CNTs exhibited a high rate performance of 459 mAh g -1 The capacity of the a-MoS2 / DT@CNTs nanocomposite material of the present invention demonstrates its excellent rate performance. In summary, the a-MoS2 / DT@CNTs nanocomposite material of the present invention exhibits excellent electrochemical performance and stability in the application of the negative electrode of sodium ion batteries, and has important application potential and commercial value.

[0032] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The rate performance and cycle performance results of the composite materials provided in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention are as follows, wherein: Figure 1 a in the figure is the scan rate of 0.2 mV s -1 When, the first four CV cycle curves of the a-MoS2 / DT@CNTs composite nanomaterial provided in Example 1 are shown in FIG. Figure 1 b is the CV cycle curve of a-MoS2@CNTs provided in Comparative Example 1. Figure 1 c is the a-MoS2 / DT@CNTs provided in Example 1 at 50 mAg -1 The results of the constant current charge and discharge (GCD) test of SIBs at a current density of Figure 1 d in is a comparison diagram of the first-cycle GCD curves of a-MoS2 / DT@CNTs and MoS2 / DT@CNTs samples provided in Example 1 and Comparative Example 2;

[0034] Figure 2 The results of the rate performance test of the SIBs of the sodium ion batteries provided in Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. Figure 2 Where a is the specific capacity of the sodium ion battery provided in Example 1 at different current densities, Figure 2 b in the figure is the GCD curve of the sodium ion battery provided in Example 1, Figure 2 c is the sodium ion battery provided in Example 1 at 50 mA g-1 GCD curve of 100 cycles under the condition;

[0035] Figure 3 is the kinetic analysis result of the sodium ion battery provided by Example 1 and Comparative Example 2, wherein, Figure 3 a in the figure is the EIS spectrum comparison result of Example 1 and Comparative Example 2, Figure 3 b in the figure is a function diagram of the impedance in Warburg inversely proportional to the square root of the angular frequency in Example 1 and Comparative Example 2, Figure 3 c in FIG. 1 is the GITT test result of Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0037] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0038] Example 1

[0039] Preparation of negative electrode active materials:

[0040] (1) Add 30 mg of CNTs to 20 mL of deionized water and stir for 30 min to obtain a CNTs solution;

[0041] (2) Add (NH4)6Mo7O to the CNTs solution 24 4H2O (0.5mmol, 618mg), C2H5NS (7mmol, 526mg) and C8H4Na2O4 (0.05mmol, 10.5mg) were stirred for 30min to form a mixed solution;

[0042] (3) The mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined autoclave and reacted at 180° C. for 2.5 h;

[0043] (4) collecting the black product after the reaction in step (3), and washing it three times with deionized water and anhydrous ethanol respectively;

[0044] (5) The washed reactant was placed in an oven at 60°C and dried for 12 h to obtain an a-MoS2 / DT@CNTs composite material.

[0045] The a-MoS2 / DT@CNTs composite material prepared above is used as a negative electrode active material to prepare a negative electrode sheet, including the following steps:

[0046] S1. Weigh the a-MoS2 / DT@CNTs composite material, acetylene black and polyvinylidene fluoride in a mass ratio of 7:2:1, grind them thoroughly in an agate mortar, and then add an appropriate amount of N-methylpyrrolidone to mix into a uniform slurry;

[0047] S2. Use an infrared drying coater to evenly coat the slurry on the copper foil and dry it at 90°C for 35 minutes to obtain a dry electrode;

[0048] S3, the roller press rolls the dried electrode sheet and cuts it to obtain a negative electrode sheet with a diameter of 14 mm. The negative electrode active material loading of each negative electrode sheet is 1 mg cm -2 .

[0049] The negative electrode sheet is used to prepare a sodium ion battery, comprising the following steps:

[0050] The button cell was assembled in a glove box (water and oxygen contents were both less than 0.01 ppm).

[0051] The prepared negative electrode sheet was used as the negative electrode, the positive electrode was a high-purity sodium sheet (diameter 15.6 mm, thickness 0.45 mm), the separator was glass fiber (Whatman, 18 mm), and the electrolyte was 1M NaClO4 (dissolved in a mixed solvent of EC: DMC: EMC = 1:1:1). The negative electrode sheet, electrolyte, separator, electrolyte and high-purity sodium sheet were assembled in order, and then sealed with a hydraulic sealing machine to obtain a sodium ion battery.

[0052] Comparative Example 1

[0053] The preparation method is the same as that of Example 1, except that in the preparation of the negative electrode active material, under the same synthesis method, C8H4Na2O4(DT) is not added to synthesize a-MoS2@CNTs as the negative electrode active material.

[0054] Comparative Example 2

[0055] The preparation method is the same as that of Example 1, except that in the preparation of the negative electrode active material, under the same synthesis method, C8H4Na2O4(DT) and CNTs are not added to synthesize a-MoS2 as the negative electrode active material.

[0056] Comparative Example 3

[0057] The preparation method is the same as that of Example 1, except that in the preparation of the negative electrode active material, the a-MoS2 / DT@CNTs composite material prepared in Example 1 is heated in a tubular furnace under an argon atmosphere at 5°C min -1The temperature was raised to 500 °C and maintained at this temperature for 2 h to make a-MoS2 / DT@CNTs crystallize into MoS2 / DT@CNTs as the negative electrode active material.

[0058] The effect was verified through the following tests:

[0059] 1. The electrochemical performance of the sodium ion batteries provided in Example 1 and Comparative Examples 1-3 was characterized and tested. The results are as follows Figure 1 shown.

[0060] Figure 1 The scan rate is 0.2 mV s -1 The first four CV cycle curves of the a-MoS2 / DT@CNTs composite nanomaterials provided in Example 1 are shown. During the initial cathode scan, three peaks appeared near 2.55, 1.45, and 0.63 V, of which the peaks near 2.55 V and 1.34 V were consistent with those of Na + Embedded into a-MoS2(MoS2+xNa + +xe - →Na x MoS2) and explains that Na + is hierarchically embedded; the peak at 0.63 V is consistent with the DT storage Na + Related (Na2C8H4O4+2Na + +2e - →Na4C8H4O4). It is worth noting that the curve has good reproducibility in the subsequent cycles, indicating that the a-MoS2 / DT@CNTs material has good electrochemical reversibility. Compared with a-MoS2@CNTs ( Figure 1 As for the CV cycle curve diagram of b), the reduction peak positions of the two are very close, and neither has a reduction peak near 0.63V, which proves that DT has the function of storing sodium ions in this composite structure.

[0061] The a-MoS2 / DT@CNTs provided in Example 1 were -1 The constant current charge and discharge (GCD) test of SIBs was carried out at a current density of , and the curves of the first five cycles are shown in Figure 1 Its first discharge and charge capacities are 1021.5 mAh g -1 and 678.2mAh g -1 The low reversibility of the first cycle is mainly due to the formation of SEI film by nanomaterials. In the second cycle, it has 621.3 mAh g -1 The reversible specific capacity and coulombic efficiency (CE) can reach 93.2%. The GCD curves of the second and fifth cycles almost completely overlap, indicating that the reversibility of amorphous MoS2 is very good. Figure 1 d in the figure is a comparison of the first GCD curves of the samples before and after calcination. From the curves, we can observe that the discharge platforms of a-MoS2@CNTs and MoS2@CNTs are completely different, and the charge / discharge curve before calcination does not have an obvious voltage platform. This is because MoS2 is an amorphous crystal structure with a large number of randomly arranged atoms and defect sites. Therefore, the active sites for sodium ion reactions are not discrete, resulting in no obvious charge / discharge platform during the charge and discharge process. In addition, from the GCD curve, we can conclude that the charge / discharge capacity of the sample after calcination is much lower than that of a-MoS2 / DT@CNTs, proving that amorphous MoS2 is conducive to the realization of Na + Rapid diffusion and storage.

[0062] 2. The sodium ion batteries prepared from the three negative electrode active materials a-MoS2 / DT@CNTs, a-MoS2@CNTs, and a-MoS2 provided in Example 1, Comparative Example 1, and Comparative Example 2 were used for the rate performance test of SIBs. The results are as follows Figure 2 .

[0063] like Figure 2 As shown in a, the sodium ion battery provided in Example 1 is 20, 50, 100, 200, 500 and 1000 mAg -1 The specific capacities at the current densities are 1021, 590, 557, 541, 501 and 459 mAh g -1 , its GCD curve is as follows Figure 2 As shown in b, when the current density returns to 50 mA -1 583mAh g can be restored -1 The reversible discharge capacity of the sodium ion battery provided in Comparative Example 1 is 99%, and the capacity retention rate is 99%. In contrast, the capacity of the sodium ion battery provided in Comparative Example 1 at the same rate current is lower than that of Example 1. This is because the insertion of DT expands the interlayer distance of a-MoS2, which can be used in a large amount of Na + In the process of shuttling back and forth, sufficient space is provided. Without the support of DT molecules, the high current density accelerates the destruction of the layer structure and the pulverization of the electrode material. However, in Comparative Example 1, at 20 and 50 mAg -1 The specific capacity of the samples was lower than that of the comparative example 2, which may be related to the reduction of active sites caused by doping CNTs. -1 In the 10 cycles, the capacity stability of Example 1 and Comparative Example 1 is higher than that of Comparative Example 2, indicating that the addition of CNTs can enhance the stability of the composite structure.

[0064] Figure 2 c shows the Example 1 at 50 mA -1The GCD was cycled 100 times under the condition of 400V, and the specific capacity at the 20th cycle was 619 mAh g -1 The capacity retention rate is 70.5%, and it still has 412mAh g after 100 cycles. -1 The reversible specific capacity at 200mAg -1 After 100 cycles of GCD (SI), the sodium ion battery of Example 1 retained a discharge capacity of 306 mAh g -1 , which are higher than those in Comparative Example 1 (226 mAh g -1 ), Comparative Example 2 (147 mAh g -1 ) discharge capacity. This indicates that the synergistic effect between DT and MoS2 helps Na + Storage, can provide more active sites for a-MoS2 / DT@CNTs, so as to have a higher specific capacity. Rate performance, cycle stability and high specific capacity performance, the sodium ion battery provided in Example 1 has excellent rate performance, cycle stability and high specific capacity performance.

[0065] 3. Electrochemical impedance spectroscopy (EIS) was used to study the charge transfer mechanics of the sodium ion batteries provided in Example 1 and Comparative Example 2. The results are shown in Figure 3 shown.

[0066] Figure 3 a in the figure is the Nyquist plot of Example 1 and Comparative Example 2. The diameter of the semicircle in the high frequency region can reflect the charge transfer resistance (Rct) of the electrode. The larger the diameter, the greater the charge transfer resistance. The charge transfer resistance of Example 1 and Comparative Example 2 are 109 and 177 Ω respectively, indicating that Na + The redox reaction on the surface of a-MoS2 / DT@CNTs is faster. Therefore, Example 1 can release a higher capacity at a high current. In addition, the slope of the straight line in the low frequency region can reflect the Weber impedance, which is similar to Na + This is related to the diffusion process in the electrode material. Figure 3 The b in the equation is Z real With ω -1 / 2 The linear fit of the results shows that the slope obtained from the linear fit can be used to calculate the sodium ion diffusion rate constant D. The larger the D value, the greater the diffusion rate. The results show that the D values ​​of Example 1 and Comparative Example 2 are 1.53×10 -14 ,7.09×10 -16 cm2s -1 Since the interlayer spacing of Example 1 is larger than that of Comparative Example 2, Na + It encounters less resistance in the process of shuttling back and forth, thus having better diffusion performance.

[0067] The reasons for the excellent electrochemical performance of Example 1 were further analyzed from the perspective of sodium storage kinetics by constant current intermittent titration test (GITT). The GITT test conditions were as follows: -1 The battery was charged and discharged at a constant current of 10 min and then left to stand for 60 min. As is known to all, in the GITT test, the fewer the pulses, the smaller the charge / discharge capacity, the wider the pulse potential step, and the greater the polarization of the pulse process. Figure 3 Figure c shows the GITT diagram of Example 1 and Comparative Example 2. It can be seen that Example 1 has more pulses (148 vs. 87), which means that it can provide a larger capacity and a smaller polarization.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The negative electrode sheet contains a negative electrode active material, and the negative electrode active material is an a-MoS2 / DT@CNTs composite material; The negative electrode active material loading of each negative electrode sheet is 0.9-1.1 mg cm -2 ; The preparation of the a-MoS2 / DT@CNTs composite material comprises: (1) Add CNTs to deionized water and stir for 10-50 minutes to obtain a CNTs solution; (2) Add to the CNTs solution , and , stirring for 10-50 min to form a mixed solution; (3) The mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined autoclave and reacted at 180 °C for 0.5-5 h to obtain a black product; (4) Collecting the black product after the reaction in step (3), and washing it three times with deionized water and anhydrous ethanol respectively; (5) The washed reactants were placed in an oven at 60-80 °C and dried for 5-24 h to obtain a-MoS2 / DT@CNTs composite material; In step (2) , and The molar ratio is 1:1:0.05-1:20:0.

5.

2. A method for preparing a negative electrode sheet as claimed in claim 1, characterized in that: The steps include: S1. Mix the negative electrode active material, the conductive agent and the binder, grind them thoroughly in an agate mortar, and then add an appropriate amount of N-methylpyrrolidone to mix into a uniform slurry; S2, evenly apply the slurry on the copper foil, dry it, and obtain a dry electrode; S3, rolling and cutting the dried electrode sheet to obtain a negative electrode sheet; The mass ratio of negative electrode active material, conductive agent and binder in S1 is 7:2:1-8:1:1; In S2, the drying temperature is 90°C-150°C, and the drying time is 35 min-180 min; The diameter of the negative electrode sheet in S3 is 10-25 mm.

3. A sodium ion battery, characterized in that: The invention comprises a positive electrode sheet, a separator, an electrolyte and the negative electrode sheet as claimed in claim 1.

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