A battery cathode material, a battery and a preparation method thereof

Abstract

The application belongs to the technical field of lithium-sulfur battery materials, and specifically discloses a battery positive electrode material, a battery and a preparation method thereof. The preparation method comprises the following steps: S1, adding cyanuric chloride, V·2Cl and carbon nanotubes CNT into a solvent to generate a solvothermal reaction, and growing a viologen-based conjugated porous polymer on the surface of the carbon nanotubes CNT in situ directional polymerization, denoted as TCV@CNT; S2, grinding and mixing the TCV@CNT and sublimed sulfur, and then adding the mixture into a reaction kettle, filling argon, and obtaining the battery positive electrode material through a melt diffusion method, denoted as S / TCV@CNT. Compared with the material physically mixed with TCV and carbon nanotubes (CNT), the synthesis method is simple and easy to repeat, raw materials are easy to obtain and cheap, the prepared positive electrode composite material (TCV@CNT) has faster electron transmission capacity, can catalyze the conversion of lithium polysulfide, accelerates the conversion rate of lithium polysulfide in the discharge and charging process, and improves the overall electrochemical performance of the lithium-sulfur battery.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and lithium-sulfur battery technology, and particularly to a battery cathode material, a battery, and a method for preparing the same. Background Technology

[0002] Due to limitations such as energy density, lithium-ion batteries can no longer meet the energy storage needs of future advanced transportation, portable devices, and residential applications. Lithium-sulfur (Li-S) batteries can provide 1675 mAh g⁻¹ based on active sulfur. -1 High theoretical specific capacity and 2600Wh / kg -1 The energy density and capacity of lithium-sulfur batteries are three to five times that of traditional lithium-ion batteries. Furthermore, sulfur is abundant and inexpensive in the Earth's crust, making lithium-sulfur batteries a promising next-generation rechargeable battery. However, the commercial application of lithium-sulfur batteries still faces many problems and challenges. Among them, the shuttle effect caused by the dissolution and migration of lithium polysulfides leads to rapid capacity decay and poor cycle stability. To address these issues, researchers have conducted extensive exploration and research on cathode materials.

[0003] Based on this, we constructed viologen-based conjugated porous polymers as cathode supports for lithium-sulfur batteries. Conjugated porous polymers are a class of porous organic polymer materials constructed through covalent bonds, possessing abundant polar functional groups and permanent pores. The network structure of conjugated porous polymers containing a large π-conjugated system is entirely composed of lightweight elements, exhibiting good electrochemical stability. In-situ polymerization growth on the surface of a conductor facilitates rapid electron transfer and achieves high specific capacity. The abundant viologen polar functional groups in viologen-based conjugated porous polymers can efficiently capture soluble lithium polysulfides, and the presence of lithiophilic and thiophilic groups can catalyze the redox conversion of lithium polysulfides, thereby suppressing the shuttle effect. Therefore, developing efficient, simple, easily synthesized, and reproducible viologen-based conjugated porous polymers as efficient sulfur cathode support materials is a research area that needs further investigation. Summary of the Invention

[0004] One objective of this invention is to provide a method for preparing a battery cathode material. The prepared battery cathode material has faster electron transport capability, can catalyze the conversion of lithium polysulfides, accelerate the conversion rate of lithium polysulfides during discharge and charging, and improve the overall electrochemical performance of lithium-sulfur batteries. The synthesis method is simple and easy to repeat, and the raw materials are cheap and readily available.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a battery positive electrode material, comprising the following steps:

[0006] S1. Take 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diammonium chloride, denoted as V·2Cl. Add cyanuric chloride, V·2Cl and carbon nanotubes (CNTs) to the solvent and mix them evenly. A solvothermal reaction occurs, and viologen-based conjugated porous polymers are in situ directionally polymerized and grown on the surface of carbon nanotubes (CNTs). The product is denoted as TCV@CNT.

[0007] S2. TCV@CNT and sublimed sulfur are ground and mixed and then added to a reaction vessel. The reaction vessel is filled with a protective gas, and TCV@CNT is sulfided by melt diffusion method to obtain the battery cathode material, denoted as S / TCV@CNT.

[0008] Further improvements to the preparation method of battery cathode materials:

[0009] Preferably, in step S1, cyanuric chloride, V·2Cl and carbon nanotubes (CNTs) are mixed in a mass ratio of 1:3.35:3.7, and then anhydrous ethanol and DMF are added as solvents, with the volume ratio of anhydrous ethanol to DMF in the solvent being 3:2.

[0010] Preferably, in step S1, the temperature of the solvothermal reaction is 120°C and the reaction time is 3 days. After cooling to room temperature, the mixture is filtered to obtain black powder TCV@CNT.

[0011] Preferably, in step S2, TCV@CNT and sublimed sulfur are ground and mixed at a mass ratio of 4:6.

[0012] Preferably, in step S2, the reactor is a polytetrafluoroethylene-lined stainless steel reactor, the reaction temperature in the reactor is 155°C, and the reaction time is 12 hours.

[0013] A second objective of this invention is to provide a battery positive electrode material prepared by the method described in any one of the above-mentioned battery positive electrode materials.

[0014] The third objective of this invention is to provide a lithium-sulfur battery made from the above-mentioned battery cathode material.

[0015] The fourth objective of this invention is to provide a method for preparing the above-mentioned lithium-sulfur battery, comprising the following steps: grinding and mixing the positive electrode material S / TCV@CNT and the binder PVDF at a mass ratio of 9:1, adding N-methylpyrrolidone, grinding evenly to obtain a paste mixture, scraping the paste mixture onto a carbon paper current collector, drying at 50-60°C for 10-12 hours to obtain a positive electrode sheet; assembling the positive electrode sheet, negative electrode sheet, and battery electrolyte in a glove box under a protective atmosphere to obtain a lithium-sulfur battery.

[0016] As a further improvement to the above-mentioned method for preparing lithium-sulfur batteries:

[0017] Preferably, the battery electrolyte contains 1.0 mol L. -1 LiTFSI and concentration 0.1 mol L -1 The LiNO3 solvent is a mixture of dioxolane DOL and ethylene glycol dimethyl ether DME in a 1:1 volume ratio.

[0018] Preferably, the separator used is the commercial Celgard 2400 type, and the negative electrode is a commercial lithium sheet.

[0019] The advantages of this invention compared to the prior art are as follows:

[0020] 1) This invention provides a method for preparing a battery cathode material. A viologen-based conjugated porous polymer is grown on the surface of carbon nanotubes (CNTs) through a solvothermal reaction of cyanuric chloride with V·2Cl, serving as a highly efficient sulfur host material (TCV@CNT). The battery cathode material (S / TCV@CNT) is then prepared by melt diffusion of TCV@CNT and sublimed sulfur. The raw materials for this material are readily available and inexpensive, and the synthesis method is simple and easily reproducible.

[0021] 2) When preparing TCV@CNT, cyanuric chloride, V·2Cl and carbon nanotubes (CNTs) are mixed in a mass ratio of 1:3.35:3.7. This allows the ligands to be polymerized and grown in situ on the CNT surface, avoiding the aggregation of low-conductivity viologen-based conjugated porous polymers, improving the interfacial electron transfer rate during battery charging and discharging, and helping to confine lithium polysulfides to the positive electrode side, thereby increasing battery capacity.

[0022] 3) When preparing TCV@CNT, anhydrous ethanol and DMF are mixed in a volume ratio of 3:2 as a solvent. This solvent is inexpensive and low in price.

[0023] 4) When preparing the battery cathode material S / TCV@CNT, TCV@CNT and sublimed sulfur are ground and mixed at a mass ratio of 4:6. Mixing according to this mass ratio can ensure the overall conductivity of the cathode material, improve the utilization rate of active sulfur, and alleviate the capacity decay during cycling.

[0024] 5) When preparing the battery cathode material S / TCV@CNT, the reason for choosing a PTFE-lined stainless steel reactor is that PTFE has excellent corrosion resistance, which can resist corrosive substances that may be generated during the reaction and protect the reactor from damage. The design of the reaction temperature and time is to place the active sulfur in a molten state, allowing it to be trapped inside the polymer pores, which is beneficial for the adsorption of lithium polysulfides during charging and discharging.

[0025] 6) The battery cathode material S / TCV@CNT prepared by this invention has faster electron transport capability and can catalyze the conversion of lithium polysulfides.

[0026] 7) The battery cathode material S / TCV@CNT prepared by this invention can be used in the preparation of lithium-sulfur batteries due to its properties.

[0027] 8) This invention also discloses a method for preparing a lithium-sulfur battery. A positive electrode is prepared using S / TCV@CNT, and after assembly with a separator, a negative electrode, and a battery electrolyte, a 2025-type button cell is obtained. The S / TCV@CNT positive electrode can be used to accelerate the conversion rate of lithium polysulfides during discharge and charging, thereby improving the overall electrochemical performance of the lithium-sulfur battery.

[0028] 9) The electrolyte of the lithium-sulfur battery used in this invention contains 1.0 mol L. -1 LiTFSI and concentration 0.1 mol L -1 The LiNO3 solvent is a mixture of DOL and DME in a 1:1 volume ratio; this is because LiTFSI is a lithium salt with high ionic conductivity, and its high concentration in the electrolyte (1.0 mol L) -1 It helps to improve the ion conduction rate of the battery, thereby improving the charge and discharge performance and power density of the battery; the addition of LiNO3 can act as an additive, which helps to form a stable protective film on the surface of lithium metal anode, reduce the formation and growth of lithium dendrites, thereby improving the cycle stability and safety of the battery; the mixed solvent system of DOL and DME has low viscosity and high dielectric constant, which is conducive to the migration of lithium ions and charge transfer, thereby improving the rate performance of the battery.

[0029] 10) This invention uses commercially available Celgard 2400 separators and commercially available lithium sheets because: the Celgard 2400 separator has excellent electrolyte wetting properties, which can effectively improve the battery's conductivity and power density, thereby enhancing the charge and discharge performance of the lithium-sulfur battery. This separator can maintain stable performance at high temperatures, is not easily deformed or melted, and improves the battery's safety and reliability. At the same time, its high strength and tear resistance can effectively prevent internal short circuits and leakage, extending the battery's cycle life. Attached Figure Description

[0030] Figure 1 Solid-state carbon NMR spectrum of viologen-based conjugated porous polymer (TCV) prepared in Example 1;

[0031] Figure 2 TEM image of TCV@CNT obtained in Example 1;

[0032] Figure 3 The CV curves are for the TCV@CNT in step S1 of Example 1, the TCV+CNT in Comparative Example 3, the untreated CNT, and the symmetrical cells assembled from the TCV of Comparative Example 3.

[0033] Figure 4 The S / TCV@CNT of Example 1, the S / TCV+CNT of Comparative Example 3, the S / CNT of Comparative Example 1, and the S / TCV of Comparative Example 2 were subjected to charge-discharge cycles at 0.2C. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0035] Comparative Example 1

[0036] This comparative example provides a method for preparing the positive electrode composite material S / CNT, and the specific steps are as follows:

[0037] Carbon nanotubes (CNTs) and sublimed sulfur were ground and mixed at a mass ratio of 4:6 and added to a polytetrafluoroethylene-lined stainless steel reactor filled with argon. The mixture was then kept at 155°C for 12 hours using a melt diffusion method. After cooling to room temperature, sulfurized carbon nanotubes, denoted as S / CNTs, were obtained.

[0038] Comparative Example 2

[0039] This comparative example provides a method for preparing the positive electrode composite material S / TCV, and the specific steps are as follows:

[0040] S1. Take 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diammonium chloride, denoted as V·2Cl. Add 0.03 mol of cyanuric chloride and 0.045 mol of V·2Cl to the solvent and mix well. The solvent is composed of 1.5 ml of anhydrous ethanol and 1 ml of DMF. The mixture is kept at 120°C for 3 days to undergo a solvothermal reaction. After cooling to room temperature, the mixture is filtered to obtain a brown powder, which is viologen-based conjugated porous polymer (TCV).

[0041] S2. TCV and sublimed sulfur are ground and mixed at a mass ratio of 4:6 and placed in a polytetrafluoroethylene-lined stainless steel reactor filled with argon. The mixture is kept at 155°C for 12 hours by melt diffusion method. After cooling to room temperature, a vulcanized viologen-based conjugated porous polymer, denoted as S / TCV, is obtained.

[0042] Comparative Example 3

[0043] This comparative example provides a method for preparing the positive electrode composite material S / TCV+CNT, and the specific steps are as follows:

[0044] S1. Take 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diammonium chloride, denoted as V·2Cl. Add 0.03 mol of cyanuric chloride and 0.045 mol of V·2Cl to the solvent and mix well. The solvent is composed of 1.5 ml of anhydrous ethanol and 1 ml of DMF. The mixture is kept at 120°C for 3 days to undergo a solvothermal reaction. After cooling to room temperature, the mixture is filtered to obtain a brown powder, which is viologen-based conjugated porous polymer (TCV).

[0045] S2. TCV, carbon nanotubes (CNTs), and sublimed sulfur were physically ground and mixed in a mass ratio of 1.33:2.66:6, and placed in a polytetrafluoroethylene-lined stainless steel reactor filled with argon. The mixture was kept at 155°C for 12 hours by melt diffusion method. After cooling to room temperature, a vulcanized viologen-based conjugated porous polymer and carbon nanotubes were prepared, denoted as S / TCV+CNT.

[0046] As a control, TCV and carbon nanotubes (CNTs) were physically ground and mixed at a mass ratio of 1.33:2.66 to obtain a blend of TCV and CNTs, denoted as TCV+CNT.

[0047] Example 1

[0048] This comparative example provides a method for preparing the positive electrode composite material S / TCV@CNT, and the specific steps are as follows:

[0049] S1. Take 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diammonium chloride, denoted as V·2Cl. Mix cyanuric chloride, V·2Cl and CNTs in a mass ratio of 1:3.35:3.7. Add 2.1 ml of anhydrous ethanol and 1.4 ml of DMF as solvents. The mixture undergoes a solvothermal reaction at 120°C for 3 days. After cooling to room temperature, filter to obtain a black powder. The black powder is a viologen-based conjugated porous polymer grown in situ on the surface of carbon nanotubes (CNTs) by directional polymerization, denoted as TCV@CNT.

[0050] S2. TCV@CNT and sublimed sulfur are ground and mixed at a mass ratio of 4:6, and placed in a polytetrafluoroethylene-lined stainless steel reactor filled with argon. The mixture is kept at 155°C for 12 hours by melt diffusion method. After cooling to room temperature, sulfurized TCV@CNT is obtained, which is the battery cathode material S / TCV@CNT.

[0051] The positive electrode composite materials (S / TCV@CNT, S / TCV+CNT, S / CNT, S / TCV) prepared in Comparative Examples 1-3 and Example 1 were ground and mixed with PVDF binder at a mass ratio of 9:1, and N-methylpyrrolidone (NMP) was added dropwise, and ground until uniform to a paste. The paste mixture was coated onto carbon paper current collector and dried at 60°C for 12 hours to be used as a positive electrode sheet; the selected battery electrolyte contained 1.0 mol L... -1 LiTFSI and concentration 0.1 mol L -1 The solvent is a mixture of DOL and DME in a 1:1 volume ratio; the separator is a commercial Celgard 2400 type; and the negative electrode is a commercial lithium sheet. The positive electrode, separator, negative electrode, and battery electrolyte are assembled in a glove box under a protective atmosphere to obtain a lithium-sulfur battery.

[0052] Performance testing:

[0053] 1) Electron micrographs of the test

[0054] Figure 1 This is the solid-state carbon NMR spectrum of viologen-based conjugated porous polymer (TCV); by Figure 1 It can be seen that the peak at 167 ppm in the TCV spectrum is the carbon peak on the triazine ring, and the other seven peaks can be attributed to the skeletal carbon peaks of the viologen derivative, proving that cyanuric chloride (TCT) and viologen derivative (V·2Cl) undergo a condensation reaction.

[0055] Figure 2 TEM image of TCV@CNT obtained in Example 1; Figure 2 The TEM images confirmed the successful growth of TCV on the CNT surface.

[0056] 2) Cyclic voltammetry test of symmetrical cells

[0057] The TCV@CNTs from step S1 of Example 1, the TCV+CNTs from Comparative Example 3, the untreated CNTs, and the TCV from Comparative Example 3 were ground and mixed with PVDF at a mass ratio of 9:1, and an appropriate amount of NMP was added to form a mixed slurry. The slurry was coated onto a carbon paper current collector as the working electrode and counter electrode. The electrolyte (0.2M Li2S6 solution) for the symmetric cell was obtained by dissolving elemental sulfur (S8) and Li2S in a commercial electrolyte at a molar ratio of 5:8. The assembled symmetric cell was subjected to CV testing on an electrochemical workstation. The voltage range of the CV curve was -1.5 to 1.5 V, and the scan rate was 10 mV s. -1 .

[0058] Figure 3 CV curves for symmetrical cells assembled from TCV@CNT, TCV+CNT, CNT, and TCV, respectively; by Figure 3It can be seen that the symmetric cell assembled by TCV@CNT has the highest reduction initiation potential and peak current, showing the highest rate of lithium polysulfide conversion, indicating that the nanopolymer TCV@CNT grown in situ on the CNT surface can promote the redox conversion of lithium polysulfides more efficiently.

[0059] 3) Cyclic stability test:

[0060] The battery cycle stability test was conducted on the Wuhan Landian multi-channel battery testing system. The voltage range for the battery charge and discharge test was 2.8 to 1.7V, and the test was carried out at a current of 0.2C.

[0061] Figure 4 Charge-discharge cycles of S / TCV@CNT, S / TCV+CNT, S / CNT, and S / TCV at 0.2C; by Figure 4 It can be seen that the S / TCV@CNT cathode exhibits the highest initial discharge specific capacity and the lowest specific capacity decay rate within 100 charge-discharge cycles, proving the excellent electrochemical performance of TCV@CNT.

[0062] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for preparing a battery cathode material, characterized in that, Includes the following steps: S1. Take 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diammonium chloride, denoted as V·2Cl. Mix cyanuric chloride, V·2Cl and carbon nanotubes (CNTs) in a mass ratio of 1:3.35:3.

7. Then add anhydrous ethanol and DMF in a volume ratio of 3:

2. Mix evenly to undergo a solvothermal reaction. Viologen-based conjugated porous polymers are in situ directionally polymerized and grown on the surface of carbon nanotubes (CNTs). The product is denoted as TCV@CNT. S2. TCV@CNT and sublimed sulfur are ground and mixed and then added to a reaction vessel. The reaction vessel is filled with a protective gas, and TCV@CNT is sulfided by melt diffusion method to obtain the battery cathode material, denoted as S / TCV@CNT.

2. The method for preparing the battery cathode material according to claim 1, characterized in that, In step S1, the solvothermal reaction temperature is 120 °C and the reaction time is 3 days. After cooling to room temperature, the mixture is filtered to obtain black powder TCV@CNT.

3. The method for preparing the battery cathode material according to claim 1, characterized in that, In step S2, TCV@CNT and sublimed sulfur are ground and mixed at a mass ratio of 4:

6.

4. The method for preparing the battery positive electrode material according to claim 1, characterized in that, In step S2, the reactor is a polytetrafluoroethylene-lined stainless steel reactor, the reaction temperature in the reactor is 155 °C, and the reaction time is 12 h.

5. A battery positive electrode material prepared by the method of any one of claims 1-4.

6. A lithium-sulfur battery made from the battery cathode material of claim 5.

7. A method for preparing a lithium-sulfur battery according to claim 6, characterized in that, The process includes the following steps: grinding and mixing the battery positive electrode material S / TCV@CNT and the binder PVDF at a mass ratio of 9:1, adding N-methylpyrrolidone, grinding evenly to obtain a paste mixture, scraping the paste mixture onto a carbon paper current collector, drying at 50~60 ℃ for 10~12 hours to obtain a positive electrode sheet; assembling the positive electrode sheet, negative electrode sheet, and battery electrolyte in a glove box under a protective atmosphere to obtain a lithium-sulfur battery.

8. The method for preparing a lithium-sulfur battery according to claim 7, characterized in that, The battery electrolyte contains 1.0 mol L. -1 LiTFSI and concentration 0.1 mol L -1 The LiNO3 solvent is a mixture of dioxolane DOL and ethylene glycol dimethyl ether DME in a 1:1 volume ratio.

9. The method for preparing a lithium-sulfur battery according to claim 7, characterized in that, The separator used is the commercial Celgard 2400 type, and the negative electrode is a commercial lithium sheet.

Images