A method for preparing a lithium-sulfur battery positive electrode by electroless nickel-phosphorus alloy plating on a leaf surface
By chemically plating nickel-phosphorus alloy onto the surface of tree leaves and then performing high-temperature carbonization, a porous carbon matrix material was prepared, which solved the problems of poor conductivity of the sulfur cathode and polysulfide migration in lithium-sulfur batteries, thereby improving the electrochemical performance and cycle stability of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HARBIN UNIV OF SCI & TECH
- Filing Date
- 2022-10-30
- Publication Date
- 2026-06-16
AI Technical Summary
In lithium-sulfur batteries, sulfur has poor conductivity as a cathode material, and the diffusion and migration of lithium polysulfide intermediates cause shuttle effect problems.
A lithium-sulfur battery cathode was prepared by electroless plating of nickel-phosphorus alloy onto the surface of tree leaves. Micro-grooves were formed by roughening the leaves with NaOH. Nickel ions and hypophosphate ions in the plating solution were embedded in the leaf surface and melted and diffused at high temperature to combine with sulfur, forming a porous carbon matrix material. The nickel-phosphorus alloy chemically adsorbed polysulfides and inhibited their migration.
It improves the electrochemical performance and cycle stability of lithium-sulfur batteries, enhances charge transport rate, reduces capacity decay, suppresses polysulfide diffusion and volume change, and improves conductivity and ion conductivity.
Smart Images
Figure CN115911285B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing lithium-sulfur battery cathodes using chemical plating of nickel-phosphorus alloy onto the surface of tree leaves. Background Technology
[0002] Among current energy storage systems, lithium-sulfur batteries are one of the most promising electrochemical systems because sulfur is inexpensive. When used as a cathode, sulfur has a theoretical specific capacity of 1675 mAh / g, and the theoretical energy density of batteries composed of sulfur can even reach 2600 Wh / kg. However, the practical application of lithium-sulfur batteries still faces some obstacles, including poor conductivity of sulfur in the cathode material and the shuttle effect caused by lithium polysulfide intermediates. To overcome these challenges, researchers have tried different strategies, such as preparing carbon-sulfur composite materials and mesoporous carbon materials. A large amount of research has focused on cathode materials. Many carbonaceous materials, metal oxides, metal sulfides, metal-organic frameworks, and MXenes have been developed as sulfur-based matrix materials. Among them, carbon materials with good conductivity and stability, such as graphite, graphene, mesoporous / microporous carbon, carbon nanotubes / nanofibers, and hollow carbon nanospheres, have been widely studied as sulfur-loaded cathode matrices for lithium-sulfur batteries. Generally, they can slow down the dissolution and deposition of polysulfides and overcome the shuttle effect to some extent. Summary of the Invention
[0003] The purpose of this invention is to solve the problems of poor conductivity of sulfur as a cathode material and the shuttle effect caused by the diffusion and migration of soluble lithium polysulfide intermediates, and to provide a method for preparing lithium-sulfur battery cathodes by chemically plating nickel-phosphorus alloy on the surface of leaves.
[0004] The present invention provides a method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves, which is carried out according to the following steps:
[0005] I. Pretreatment of Leaves
[0006] After soaking the leaves in ethanol, remove them and dry them in an oven at 40-80℃ for later use.
[0007] II. Leaf Surface Roughening Treatment
[0008] The leaves obtained in step one are soaked in NaOH solution to roughen the surface. After being taken out, they are washed with distilled water and dried for later use.
[0009] III. Leaf Surface Activation Treatment
[0010] Place the leaves obtained in step two into the prepared activation solution A and let them stand for 5-20 minutes. Then, take out the leaves and place them into the prepared activation solution B and let them stand for 5-20 minutes. After that, place the leaves into a beaker containing a mixture of activation solution A and activation solution B and activate them with ultrasound.
[0011] IV. Chemical plating of leaves with nickel-phosphorus alloy
[0012] After washing the leaves obtained in step 3 with distilled water 3-6 times, they are placed in a chemical plating solution. The nickel-phosphorus alloy plating temperature is 60-85℃ and the plating time is 10-30 minutes. After washing with distilled water and drying at 30-60℃, the leaves are chemically plated with nickel-phosphorus alloy.
[0013] V. Carbonization treatment
[0014] The chemically plated nickel-phosphorus alloy leaves obtained in step four are subjected to carbonization treatment. The temperature is raised to 750-800℃ at 5-20℃ / min and held for 4-8 hours. The temperature is then naturally cooled to room temperature to obtain a lithium-sulfur battery positive electrode carrier material Ni-P@PC that utilizes the chemically plated nickel-phosphorus alloy on the leaf surface.
[0015] VI. Ni-P@PC loaded sulfur
[0016] The Ni-P@PC prepared in step 5 and sublimed sulfur were uniformly mixed at a certain mass ratio. The resulting mixture was then thoroughly ground in a mortar and transferred to a tube furnace. Under nitrogen protection, the mixture was heated to 150-180℃ and held for 10-16 hours to obtain the lithium-sulfur battery cathode composite material.
[0017] VII. Preparation of the positive electrode for lithium-sulfur batteries
[0018] The lithium-sulfur battery cathode composite material, conductive agent acetylene black, and binder prepared in step six are mixed in a certain mass ratio and stirred at room temperature for 10-16 hours. The resulting slurry is then coated onto aluminum foil and vacuum dried at 40-80°C.
[0019] VIII. Assembly of Lithium-Sulfur Batteries
[0020] In an argon-atmospheric glove box, the button cell is assembled in sequence according to the following order: positive electrode shell, prepared positive electrode sheet, electrolyte membrane, lithium sheet, and negative electrode shell. The assembly is completed after sealing with a sealing machine.
[0021] In step two, the concentration of NaOH is 100-150 g / L, and the soaking time is 10-30 min.
[0022] The activation solution A mentioned in step three is composed of 11-15 g / L potassium sodium tartrate, 2-5 g / L nickel sulfate and 10-20 g / L sodium hydroxide aqueous solution;
[0023] The activation solution B mentioned in step three is composed of a 10-20 g / L sodium borohydride aqueous solution;
[0024] The plating solution described in step four is composed of an aqueous solution of 10-15 g / L nickel sulfate, 10-15 g / L nickel acetate, 4-8 g / L sodium hydroxide, 4-8 g / L ammonium chloride, 16-25 g / L sodium citrate, and 16-25 g / L sodium hypophosphite.
[0025] This invention includes the following gain effects:
[0026] First, this invention uses NaOH to roughen the surface of the leaves, forming micro-grooves, which allows nickel ions (Ni) in the plating solution to... 2+ and hypophosphite H2PO2 - The groups are embedded in the microscopic grooves on the surface of poplar leaves, Ni 2+ In hypophosphate H2PO2 - Under the catalytic action of [a specific catalyst], it is reduced to elemental nickel. Subsequently, it is combined with sulfur using a high-temperature melt diffusion method to form a composite material. The introduction of the nickel-phosphorus alloy anchors polysulfides through chemical adsorption via polarity, preventing them from shuttling to the negative electrode and causing capacity decay, thus improving the battery's cycle stability and significantly enhancing its electrochemical performance. The nickel-phosphorus alloy not only inhibits polysulfides but also increases charge transport rate, accelerating the chemical reaction kinetics of lithium-sulfur batteries and reducing capacity decay. The nickel-phosphorus alloy forms a good synergistic relationship with the carbon mesh framework, giving the lithium-sulfur battery positive electrode excellent conductivity and ion conductivity, as well as excellent adsorption and catalytic properties for polysulfides. This allows for rapid carrier transport, and the polysulfides embedded and adsorbed in the carbon-nickel-phosphorus framework can be rapidly converted, reducing polarization and improving battery capacity and cycle life.
[0027] Secondly, this invention uses a method of carbonizing poplar leaves coated with nickel-phosphorus alloy to prepare porous carbon matrix materials. The veins of the poplar leaves are clearly visible, and the structure is well-defined. The natural carbon skeleton that the poplar leaves provide has a high specific surface area, which can provide a good environment for sulfur loading, achieve uniform distribution of sulfur on the matrix material, and has adsorption and catalytic effects, which can reduce the migration of soluble polysulfides to the negative electrode and reduce the battery capacity decay.
[0028] Finally, carbonized poplar leaves improve the conductivity and ion conductivity of the active material sulfur. The porous structure generated by high-temperature carbonization provides ample sulfur storage space, effectively suppressing the shuttle effect caused by the diffusion of polysulfides. The resulting carbon skeleton with excellent mechanical properties reduces the volume change before and after the reaction, providing an effective conductive network. This effectively suppresses the volume expansion caused by the formation of lithium sulfide from the active material sulfur in the cathode during the electrochemical reaction, thereby improving electrochemical performance. Attached Figure Description
[0029] For ease of explanation, the lithium-sulfur battery cathode material prepared by chemically plating nickel-phosphorus alloy on the surface of leaves in this invention is referred to as Ni-P@PC composite material, and the biomass carbon materials at carbonization temperatures of 600℃, 700℃, and 800℃ are referred to as PC1, PC2, and PC3.
[0030] Figure 1 The image shows the XRD pattern of a Ni-P@PC composite material used in a method for preparing a lithium-sulfur battery cathode by chemically plating nickel-phosphorus alloy onto the surface of tree leaves.
[0031] Figure 2 A 2000x SEM image of Ni-P@PC used in a method for preparing lithium-sulfur battery cathodes by chemically plating nickel-phosphorus alloy onto the surface of tree leaves.
[0032] Figure 3 A 1000x SEM image of Ni-P@PC used in a method for preparing lithium-sulfur battery cathodes by chemically plating nickel-phosphorus alloy onto the surface of tree leaves.
[0033] Figure 4 EDS image of Ni-P@PC for a method of preparing lithium-sulfur battery cathode by chemically plating nickel-phosphorus alloy on the surface of leaves;
[0034] Figure 5 Capacity-voltage curves of biomass carbon materials at carbonization temperatures of 600℃, 700℃, and 800℃ are presented for the first charge-discharge of a method for preparing a lithium-sulfur battery cathode using a chemical nickel-phosphorus alloy plating on the surface of tree leaves.
[0035] Figure 6 This is a charge-discharge cycle curve of biomass carbon material at 0.2C under a carbonization temperature of 600℃, which is used to prepare the positive electrode of a lithium-sulfur battery by chemically plating nickel-phosphorus alloy on the surface of tree leaves.
[0036] Figure 7 This is a charge-discharge cycle curve of biomass carbon material at 0.2C under a carbonization temperature of 700℃, which is used to prepare the positive electrode of a lithium-sulfur battery by chemically plating nickel-phosphorus alloy on the surface of tree leaves.
[0037] Figure 8 This is a charge-discharge cycle curve of biomass carbon material at 0.2C under a carbonization temperature of 800℃, which is used to prepare the positive electrode of a lithium-sulfur battery by chemically plating nickel-phosphorus alloy on the surface of tree leaves.
[0038] Figure 9 Electrochemical impedance spectroscopy (EIS) plots of PC and S / Ni-P@PC before cycling, for a method of preparing lithium-sulfur battery cathodes by chemically plating nickel-phosphorus alloy onto leaf surfaces;
[0039] Figure 10Electrochemical impedance spectroscopy (EIS) plots of PC and S / Ni-P@PC after cycling, based on a method for preparing lithium-sulfur battery cathodes using chemical nickel-phosphorus alloy plating on leaf surfaces.
[0040] Figure 11 Capacity-voltage curves of PC and Ni-P@PC during the first charge-discharge cycle for a method of preparing lithium-sulfur battery cathodes by chemically plating nickel-phosphorus alloy onto the surface of leaves.
[0041] Figure 12 The charge-discharge cycle curves of PC and Ni-P@PC at 0.2C are shown for a method of preparing lithium-sulfur battery cathodes by chemically plating nickel-phosphorus alloy on the surface of tree leaves. Detailed Implementation
[0042] The present invention will be further described below with reference to the preferred embodiments, but the scope of protection of the present invention is not limited to the following embodiments.
[0043] Experimental drugs
[0044]
[0045]
[0046] Experimental equipment
[0047]
[0048] Specific Implementation Method 1: One method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves according to this implementation method is carried out according to the following steps:
[0049] I. Pretreatment of Leaves
[0050] After soaking the leaves in ethanol, remove them and dry them in an oven at 40-80℃ for later use.
[0051] II. Leaf Surface Roughening Treatment
[0052] The leaves obtained in step one are soaked in NaOH solution to roughen the surface. After being taken out, they are washed with distilled water and dried for later use.
[0053] III. Leaf Surface Activation Treatment
[0054] Place the leaves obtained in step two into the prepared activation solution A and let them stand for 5-20 minutes. Then, take out the leaves and place them into the prepared activation solution B and let them stand for 5-20 minutes. Repeat the above steps. After that, place the poplar leaves into a beaker containing a mixture of activation solution A and activation solution B and activate them with ultrasound.
[0055] IV. Chemical plating of leaves with nickel-phosphorus alloy
[0056] After washing the leaves obtained in step 3 with distilled water 3-6 times, put them into the chemical plating solution. The nickel-phosphorus alloy plating temperature is 60-85℃. Adjust the pH during the plating process. The plating time is 10-30 minutes. Wash with distilled water and dry at 30-60℃ for later use. This gives you the chemically plated nickel-phosphorus alloy leaves.
[0057] V. Carbonization treatment
[0058] The chemically plated nickel-phosphorus alloy leaves obtained in step four are subjected to carbonization treatment. The temperature is raised to 750-800℃ at 5-20℃ / min and held for 4-8 hours. The temperature is then naturally cooled to room temperature to obtain a lithium-sulfur battery positive electrode carrier material Ni-P@PC that utilizes the chemically plated nickel-phosphorus alloy on the leaf surface.
[0059] VI. Ni-P@PC loaded sulfur
[0060] The Ni-P@PC prepared in step 5 and sublimed sulfur were uniformly mixed at a certain mass ratio. The resulting mixture was then thoroughly ground in a mortar and transferred to a tube furnace. Under nitrogen protection, the mixture was heated to 150-180℃ and held for 10-16 hours to obtain the lithium-sulfur battery cathode composite material.
[0061] VII. Preparation of the positive electrode for lithium-sulfur batteries
[0062] The lithium-sulfur battery cathode composite material prepared in step six, the conductive agent acetylene black, and the binder are mixed in a certain mass ratio and stirred at room temperature for 10-16 hours. The resulting slurry is then coated onto aluminum foil and vacuum dried at 40-80°C. VIII. Assembly of the Lithium-Sulfur Battery
[0063] In an argon-atmospheric glove box, the button cell is assembled in sequence according to the following order: positive electrode shell, prepared positive electrode sheet, electrolyte membrane, lithium sheet, and negative electrode shell. The assembly is completed after sealing with a sealing machine.
[0064] In step two, the concentration of NaOH is 100-150 g / L, and the soaking time is 10-30 min.
[0065] The activation solution A mentioned in step three is composed of 11-15 g / L potassium sodium tartrate, 2-5 g / L nickel sulfate and 10-20 g / L sodium hydroxide aqueous solution;
[0066] The activation solution B mentioned in step three is composed of a 10-20 g / L sodium borohydride aqueous solution;
[0067] The plating solution described in step four is composed of an aqueous solution of 10-15 g / L nickel sulfate, 10-15 g / L nickel acetate, 4-8 g / L sodium hydroxide, 4-8 g / L ammonium chloride, 16-25 g / L sodium citrate, and 16-25 g / L sodium hypophosphite.
[0068] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the leaves mentioned in step one are poplar leaves. Everything else is the same as in Specific Implementation Method One.
[0069] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the soaking time in step one is 24 hours. Everything else is the same as in Specific Implementation Method One or Two.
[0070] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the concentration of the NaOH solution in step two is 140 g / L, and the soaking time is 5-10 min. Everything else is the same as in Specific Implementation Methods One to Three.
[0071] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the above steps are repeated 4-8 times. Everything else is the same as in Specific Implementation Methods One to Four.
[0072] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the ultrasonic activation time in step three is 10-20 minutes. Everything else is the same as in Specific Implementation Methods One to Five.
[0073] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the pH is adjusted to 9-11 during the plating process described in step four. Everything else is the same as in Specific Implementation Methods One to Six.
[0074] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the pH value in step four is adjusted using a mixed solution of 4-6 g / L sodium hydroxide and 4-6 g / L ammonium chloride. Everything else is the same as in Specific Implementation Methods One to Seven.
[0075] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the mass ratio of Ni-P@PC and sublimed sulfur in step six is 2:8. Everything else is the same as in Specific Implementation Methods One to Eight.
[0076] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the mass ratio of the lithium-sulfur battery cathode composite material, conductive agent acetylene black, and binder prepared in step seven is 7:2:1. Everything else is the same as in Specific Implementation Methods One to Nine.
[0077] The beneficial effects of the present invention were verified through the following experiments:
[0078] One method of this experiment, which involves chemically plating a nickel-phosphorus alloy onto the surface of tree leaves and then carbonizing it as the positive electrode for a lithium-sulfur battery, was carried out according to the following steps:
[0079] I. Pretreatment of Leaves
[0080] After soaking poplar leaves in ethanol for 24 hours, they were placed in a petri dish and dried in an oven at 60°C for later use.
[0081] II. Leaf Surface Roughening Treatment
[0082] The poplar leaves obtained in step one were soaked in 140g / L NaOH solution for 15min for surface roughening treatment. The leaves after soaking in NaOH were removed, washed with distilled water, and dried for later use.
[0083] III. Leaf Surface Activation Treatment
[0084] Place the poplar leaves obtained in step 2 into the prepared activation solution A and let them stand for 5 minutes. Then, take out the leaves and place them into the prepared activation solution B and let them stand for 5 minutes. Repeat the steps more than 4 times. After that, place the poplar leaves into a beaker containing a mixture of activation solution A and activation solution B and perform ultrasonic activation for 10 minutes.
[0085] Activation solution A is prepared by uniformly mixing and dissolving 11.2 g / L potassium sodium tartrate, 2.1 g / L nickel sulfate, and 20 g / L sodium hydroxide in water;
[0086] Activation solution B is prepared by dissolving 20 g / L sodium borohydride in water;
[0087] IV. Chemical plating of leaves with nickel-phosphorus alloy
[0088] After washing the poplar leaves obtained in step 3 with distilled water 3-6 times, they are placed in a chemical plating solution. The nickel-phosphorus alloy plating temperature is 80-85℃, the plating time is 15 minutes, and the pH is controlled at 9-11. The pH is controlled by ammonium chloride and sodium hydroxide. After the chemical plating is completed, the leaves are washed with distilled water 3-6 times and dried at 30℃ for later use, thus obtaining chemically plated nickel-phosphorus alloy leaves.
[0089] The plating solution is prepared by uniformly mixing 10 g / L nickel sulfate, 10 g / L nickel acetate, 4 g / L sodium hydroxide, 4 g / L ammonium chloride, 16 g / L sodium citrate and 16 g / L sodium hypophosphite;
[0090] V. Carbonization treatment
[0091] The chemically plated nickel-phosphorus alloy leaves obtained in step four are subjected to carbonization treatment, heated to 800℃ at 5℃ / min and held for 4 hours, and then naturally cooled to room temperature to obtain a lithium-sulfur battery positive electrode carrier material Ni-P@PC using chemically plated nickel-phosphorus alloy on the leaf surface.
[0092] VI. Ni-P@PC loaded sulfur
[0093] The Ni-P@PC prepared in step 5 and sublimed sulfur were uniformly mixed at a mass ratio of 2:8. The resulting mixture was then thoroughly ground in a mortar and transferred to a tube furnace. Under nitrogen protection, the mixture was heated to 155°C and held for 10-16 hours to obtain the lithium-sulfur battery cathode composite material.
[0094] VII. Preparation of the positive electrode for lithium-sulfur batteries
[0095] The lithium-sulfur battery cathode composite material, conductive agent acetylene black, and binder prepared in step six were mixed in a mass ratio of 7:2:1 and stirred at room temperature for 12 hours. The resulting slurry was then coated onto aluminum foil and dried under vacuum at 60°C.
[0096] VIII. Assembly of Lithium-Sulfur Batteries
[0097] In an argon-atmospheric glove box, the button cell is assembled in sequence according to the following order: positive electrode shell, prepared positive electrode sheet, electrolyte membrane, lithium sheet, and negative electrode shell. The assembly is completed after sealing with a sealing machine.
[0098] An XRD pattern of a Ni-P@PC composite material prepared by chemically plating nickel-phosphorus onto the surface of tree leaves and then carbonizing it into a lithium-sulfur battery cathode, as shown in the present invention. Figure 1 As shown, by Figure 1 Comparison with the standard diffraction card of C revealed that the material has a strongest peak at around 44°, which is the amorphous carbon PC generated after the carbonization of leaves. Comparison with the standard diffraction card of Ni3P revealed that the composite material corresponds to the (3 2 1), (2 0 2), and (5 3 2) crystal planes of Ni3P at 41°, 47°, and 76°. It can be concluded that the carbon of the leaves after high-temperature carbonization and plating with nickel-phosphorus alloy is well combined with nickel and phosphorus.
[0099] Figure 2 This is a SEM image of Ni-P@PC, a method for preparing lithium-sulfur battery cathodes using chemical plating of nickel-phosphorus alloy on the surface of tree leaves. After magnification of 2000 times, it can be seen that the nickel-phosphorus alloy coating is uniformly distributed on the surface of the carbon substrate.
[0100] Figure 3 This is a 1000x magnified SEM image of Ni-P@PC, a method for preparing lithium-sulfur battery cathodes using chemical plating of nickel-phosphorus alloy on the surface of tree leaves. It can be seen that nickel-phosphorus was successfully embedded on the surface of carbon material using chemical plating technology.
[0101] Figure 4The image shows the elemental distribution curve of Ni-P@PC, a method for preparing lithium-sulfur battery cathodes using chemical plating of nickel-phosphorus alloy on the surface of tree leaves. It can be seen that the surface contains approximately 43 wt% carbon, 49 wt% nickel, and 8 wt% phosphorus. The influence of different carbonization temperatures on the biomass carbon materials obtained from poplar leaves at different carbonization temperatures as cathode materials for lithium-sulfur batteries was investigated through analysis, as detailed below:
[0102] Figure 5 This is a method for preparing a lithium-sulfur battery cathode using chemical nickel-phosphorus alloy plating on the surface of tree leaves. The capacity-voltage curves of the biomass carbon material under carbonization temperatures of 600℃, 700℃, and 800℃ are shown. It can be seen that the polarization of the biomass carbon material at the carbonization temperature of 800℃ is 0.29V, which is significantly lower than the latter two. This is because the increase in temperature leads to an increase in graphite carbon content, which promotes improved conductivity, and the increase in pore size enhances the ability to confine polysulfides.
[0103] Figure 6 , Figure 7 and Figure 8 The graphs show the charge-discharge cycle curves of biomass carbon materials at 0.2C with carbonization temperatures of 600℃, 700℃, and 800℃, respectively. It can be seen that compared with the biomass carbon materials at carbonization temperatures of 600℃ and 700℃, the capacity decay of the biomass carbon material at carbonization temperature of 800℃ is significantly weaker with increasing cycle number. This indicates that the increase in temperature leads to an increase in porosity. At the same time, the synergistic effect of co-component formulation with nickel-phosphorus alloy enhances the inhibition of polysulfides and increases the utilization rate of active materials. Therefore, this invention selects 800℃ as the optimal carbonization temperature.
[0104] By analyzing biomass carbon materials that have undergone electroless plating, the impact of electroless plating on the performance of untreated biomass carbon materials as cathode materials for lithium-sulfur batteries was examined, as follows:
[0105] 1) Figure 9 The capacity-voltage curves for the first charge-discharge of PC and Ni-P@PC are shown. The reverse extension of the impedance (Rct) line of Ni-P@PC intersects the horizontal axis at a lower point than that of PC. This indicates that when nickel-phosphorus alloy is plated on the surface of the leaf carbon precursor, the nickel-phosphorus alloy covers the carbon, which increases the conductivity of the surface. The slope of the straight line in the low-frequency region is higher than that of PC, indicating that the lithium-ion diffusion resistance of Ni-P@PC composite material is smaller before cycling, the surface conductivity of the material is improved, and the carrier transport speed is increased.
[0106] Figure 10The capacity-voltage curves of Ni-P@PC after cycling are shown. Rct is only generated in the high-frequency region and is smaller than PC. At the same time, no other types of impedance are observed. This indicates that the "shuttle effect" generated by the chemical adsorption of polysulfides by the nickel-phosphorus alloy is weakened during cycling. At the same time, as the charge and discharge proceed, the carbon surface activity is activated, which improves the conductivity of the material and reduces the charge transfer impedance. This is because the nickel-phosphorus alloy and the carbon grid framework form a good compatibility and synergy, which gives the lithium-sulfur battery cathode excellent conductivity and ion conduction, as well as excellent adsorption and catalysis of polysulfides. This enables rapid carrier transport, and the polysulfides embedded and adsorbed in the carbon-nickel-phosphorus framework can be quickly converted to reduce polarization and improve battery capacity and cycle life.
[0107] 2) Figure 11 The capacity-voltage curves for the first charge-discharge of PC and Ni-P@PC show that the average polarization of the Ni-P@PC composite cathode is lower than that of PC. When the 30th cycle is performed, the potential difference of Ni-P@PC is only 0.29V, which is lower than that of PC. The introduction of nickel-phosphorus elements by chemical plating not only reduces battery polarization, but also significantly improves the chemical adsorption and catalytic effect of polysulfides when the carbon activity is fully activated by the nickel-phosphorus alloy, thus improving cycle stability.
[0108] 3) Figure 12 The charge-discharge cycle curves of PC and Ni-P@PC at 0.2C show that although the initial discharge specific capacity of PC is higher than that of Ni-P@PC, after 6 cycles, the capacity increases to 520 mAh / g. In the 50 cycles, the discharge specific capacity of Ni-P@PC is consistently higher than that of PC. After 50 cycles, the discharge specific capacities of PC and Ni-P@PC remain at reversible capacities of 261 mAh / g and 359 mAh / g, respectively, with capacity retention rates of 58.9% and 82.9%. This demonstrates that introducing nickel-phosphorus alloy into the carbon network framework through chemical plating effectively utilizes "polar-polar" chemical adsorption and bonding with polysulfides to fix them, while simultaneously increasing the carrier transport rate and catalyzing the rapid conversion of polysulfides, thus promoting battery stability.
Claims
1. A method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves, characterized in that... A method for preparing lithium-sulfur battery cathodes using chemical plating of nickel-phosphorus alloy on the surface of tree leaves is carried out according to the following steps: I. Pretreatment of Leaves After soaking the leaves in ethanol, remove them and place them in an oven at 40-80℃ to dry for later use. II. Leaf Surface Roughening Treatment The leaves obtained in step one are soaked in NaOH solution to roughen the surface. After being taken out, they are washed with distilled water and dried for later use. III. Leaf Surface Activation Treatment Place the leaves obtained in step two into the prepared activation solution A and let them stand for 5-20 minutes. Then, take out the leaves and place them into the prepared activation solution B and let them stand for 5-20 minutes. Repeat the above steps. After that, place the poplar leaves into a beaker containing a mixture of activation solution A and activation solution B and activate them with ultrasound. IV. Chemical plating of leaves with nickel-phosphorus alloy After washing the leaves obtained in step 3 with distilled water 3-6 times, put them into the chemical plating solution. The nickel-phosphorus alloy plating temperature is 60-85℃. Adjust the pH during the plating process. The plating time is 10-30 minutes. Wash with distilled water and dry at 30-60℃ for later use. This gives you the chemically plated nickel-phosphorus alloy leaves. V. Carbonization treatment The chemically plated nickel-phosphorus alloy leaves obtained in step four are subjected to carbonization treatment. The temperature is raised to 750-800℃ at 5-20℃ / min and held for 4-8 hours. The temperature is then naturally cooled to room temperature to obtain a lithium-sulfur battery positive electrode carrier material Ni-P@PC that utilizes the chemically plated nickel-phosphorus alloy on the leaf surface. VI. Ni-P@PC loaded sulfur The Ni-P@PC prepared in step 5 and sublimed sulfur were uniformly mixed at a certain mass ratio. The resulting mixture was then thoroughly ground in a mortar and transferred to a tube furnace. Under nitrogen protection, the mixture was heated to 150-180℃ and held for 10-16 hours to obtain the lithium-sulfur battery cathode composite material. VII. Preparation of the positive electrode for lithium-sulfur batteries The lithium-sulfur battery cathode composite material, conductive agent acetylene black, and binder prepared in step six are mixed in a certain mass ratio and stirred at room temperature for 10-16 hours. The resulting slurry is then coated onto aluminum foil and vacuum dried at 40-80°C. VIII. Assembly of Lithium-Sulfur Batteries In an argon-atmospheric glove box, the button cell is assembled in sequence according to the following order: positive electrode shell, prepared positive electrode sheet, electrolyte membrane, lithium sheet, and negative electrode shell. The assembly is completed after sealing with a sealing machine. In step two, the concentration of NaOH is 100-150 g / L, and the soaking time is 5-30 min. The activation solution A mentioned in step three is composed of 11-15 g / L potassium sodium tartrate, 2-5 g / L nickel sulfate and 10-20 g / L sodium hydroxide aqueous solution; The activation solution B mentioned in step three is composed of a 10-20 g / L sodium borohydride aqueous solution; The plating solution described in step four is composed of an aqueous solution of 10-15 g / L nickel sulfate, 10-15 g / L nickel acetate, 4-8 g / L sodium hydroxide, 4-8 g / L ammonium chloride, 16-25 g / L sodium citrate, and 16-25 g / L sodium hypophosphite.
2. The method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves according to claim 1, characterized in that... The leaves mentioned in step one are poplar leaves.
3. The method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves according to claim 1, characterized in that... The soaking time described in step one is 24 hours.
4. The method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves according to claim 1, characterized in that... The concentration of the NaOH solution mentioned in step two is 140 g / L.
5. The method for preparing a lithium-sulfur battery cathode by chemically plating nickel-phosphorus alloy onto the surface of tree leaves according to claim 1, characterized in that... The above steps are repeated 4-8 times as described in step three.
6. The method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves according to claim 1, characterized in that... The ultrasonic activation time in step three is 10-20 minutes.
7. The method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves according to claim 1, characterized in that... In step four, the pH is adjusted to 9-11 during the plating process.
8. The method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves according to claim 1, characterized in that... The pH value mentioned in step four is adjusted using a mixed solution of 4-6 g / L sodium hydroxide and 4-6 g / L ammonium chloride.
9. A method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves according to claim 1, characterized in that... The mass ratio of Ni-P@PC to sublimed sulfur in step six is 2:
8.
10. A method for preparing a lithium-sulfur battery cathode using chemical plating of nickel-phosphorus alloy on the surface of tree leaves according to claim 1, characterized in that... The mass ratio of the lithium-sulfur battery cathode composite material, conductive agent acetylene black, and binder prepared in step seven is 7:2:1.