A sodium-ion battery and a preparation method and application thereof

Abstract

The application relates to the field of electrochemical energy storage technology, and discloses a sodium ion battery and a positive electrode material composed of the following components: graphene with a mass fraction of 5%-20%; transition metal sulfide with a mass fraction of 50%-70%; and ion sieve functional layer material; and a sodium ion battery preparation method, which comprises the following steps: graphene modification and dispersion: graphene powder is dispersed into a suspension through ultrasonic dispersion, and sodium persulfate and nitric acid are added to perform functionalization treatment on the graphene powder; and transition metal sulfide synthesis, which is applied to portable electronic devices, electric vehicles and large-scale energy storage systems. The sodium ion battery is prepared by compounding functionalized graphene and transition metal sulfide, combining the multi-dimensional network design of the ion sieve functional layer and the carbon nanofiber, optimizing the sodium ion transmission, conductivity and thermal management performance, and significantly improving the energy density, cycle stability and safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical energy storage, in particular to a sodium ion battery and a preparation method and application thereof. BACKGROUND

[0002] With the development of new energy technology, the importance of energy storage systems in energy conversion and power regulation is increasingly prominent. As a kind of energy storage device with abundant resources, low cost and environmental friendliness, sodium ion battery gradually attracts the attention of researchers. However, compared with lithium ion battery, the maturity of sodium ion battery technology is still low, and there are significant deficiencies in energy density, cycle life and operation safety and other key performances.

[0003] The current positive electrode material of sodium ion battery mainly uses metal oxide, metal sulfide and other active materials. However, due to the large ionic radius of sodium ion, its embedding and de embedding process is easy to cause material structure expansion or collapse. After a long time of cycle, the positive electrode material often appears the phenomenon of pulverization, which leads to the rapid decay of battery capacity. In addition, the traditional positive electrode material is also weak in electronic transmission ability, which limits the discharge capacity of the battery under high rate condition. These problems are common in sodium ion battery, which limits the performance improvement.

[0004] At the same time, the interface reaction between the electrolyte and the electrode of sodium ion battery also has an important influence on the performance. Because the migration rate of sodium ion is low, the byproduct is easy to form at the interface during the cycle process, which significantly increases the impedance. This phenomenon is particularly evident in high rate charge and discharge and long time cycle, which further reduces the utilization efficiency of sodium ion. In addition, the instability of electrolyte may also lead to the formation of sodium dendrite, which not only shortens the service life of the battery, but also significantly increases the safety risk.

[0005] The problem of thermal stability of sodium ion battery also needs to be solved. Under high rate charge or high temperature environment, local heat accumulation is more serious, which is easy to cause interface failure, material degradation and even thermal runaway. Although some researches try to introduce heat conducting materials or optimize electrolyte to alleviate the problem of heat management, these schemes are often difficult to balance the conductivity and stability, resulting in poor overall performance of the battery.

[0006] In summary, sodium ion battery has obvious shortcomings in the structural stability of positive electrode material, interface chemical stability, sodium ion migration efficiency and heat management ability. SUMMARY

[0007] In view of the shortcomings of the prior art, the present application provides a sodium ion battery and a preparation method and application thereof, which solves the technical problems of sodium ion battery in the conductivity of positive electrode material, interface stability, sodium ion migration efficiency and heat management performance.

[0008] To achieve the above object, the present application is implemented by the following technical solutions: a sodium ion battery, comprising:

[0009] A positive electrode material consisting of the following components:

[0010] Graphene, mass fraction 5%-20%;

[0011] Transition metal sulfide, mass fraction 50%-70%;

[0012] Ion sieve functional layer material, mass fraction 5%-15%;

[0013] Carbon-based nanofiber, mass fraction 5%-10%;

[0014] Binder, mass fraction 3%-5%;

[0015] Sodium metal negative electrode;

[0016] Electrolyte, the electrolyte is a solution of NaClO4 dissolved in EC and DMC solvents, the volume ratio of the solvents is 1:1, and the concentration is 0.5-1M.

[0017] Preferably, the transition metal sulfide includes one or more of nickel sulfide, cobalt sulfide, iron sulfide, or vanadium sulfide.

[0018] Preferably, the ion sieve functional layer material is a metal organic framework, including ZIF-8 or a derivative material thereof.

[0019] Preferably, the graphene is functionalized graphene modified by oxidation, and the surface contains hydroxyl and carboxyl groups.

[0020] Preferably, the carbon-based nanofiber is a carbon nanotube, and the carbon nanotube is compounded with the positive electrode material by a mechanical mixing method.

[0021] A sodium ion battery preparation method, comprising the following steps:

[0022] Modification and dispersion of graphene: graphene powder is dispersed into a suspension by ultrasonic dispersion, and sodium persulfate and nitric acid are added for functionalization treatment;

[0023] Synthesis of transition metal sulfide: the functionalized graphene suspension is mixed with a precursor solution containing a transition metal salt and a sulfur source, and a composite material is synthesized by high-temperature solid-phase reaction under inert gas protection;

[0024] Introduction of ion sieve functional layer: the transition metal sulfide composite material is mixed with a MOF precursor, and an ion sieve functional layer is formed by a solvothermal reaction;

[0025] Preparation of electrode sheet: the composite material is mixed with carbon-based nanofiber, binder and conductive agent into slurry, coated on the current collector, and pressed into sheet after drying to make the positive electrode sheet;

[0026] Battery assembly: the positive electrode sheet, sodium metal negative electrode and electrolyte are assembled into a sodium ion battery

[0027] Preferably, the treatment temperature of the functionalized graphene suspension is 50-80 DEG C, and the treatment time is 2-3h.

[0028] Preferably, the temperature of the high-temperature solid-phase reaction is 300-400 DEG C, and the time is 4-6h.

[0029] Preferably, the temperature of the solvothermal reaction is 150-200 DEG C, and the time is 6-12h.

[0030] According to the sodium ion battery, it is applied to portable electronic equipment, electric vehicles and large-scale energy storage systems.

[0031] The application provides a sodium ion battery and a preparation method and application thereof.

[0032] 1. The application adopts the technical scheme of compounding graphene with transition metal sulfide and introducing an ion sieve functional layer, realizes efficient sodium ion transmission and optimized conductive network, significantly improves the energy density and rate performance of the battery compared with the insufficient conductivity caused by single active material in the prior art, and solves the deficiency that the traditional positive electrode material is prone to decay.

[0033] 2. The application constructs an ion sieve functional layer on the surface of the composite material by a solvothermal method, accurately screens sodium ions and inhibits side reactions, effectively reduces the capacity loss of the battery in multiple charge-discharge cycles, and greatly improves the cycle stability compared with the prior art without optimizing the interface structure, and overcomes the technical defect that the interface side reaction is serious.

[0034] 3. The application adds carbon nanofiber in the positive electrode to construct a multi-dimensional heat-conducting and conductive network, optimizes the material distribution and heat management capability, realizes the stability under high-rate charge-discharge conditions, improves the thermal stability and safety performance of the battery compared with the safety hazard caused by insufficient heat management in the prior art, and solves the problem of thermal runaway in extreme environment. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a method flowchart of the application. DETAILED DESCRIPTION

[0036] With reference to the drawings of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0037] Please refer to the drawings of the present application Figure 1 The present application provides a sodium ion battery, comprising:

[0038] A positive electrode material consisting of the following components:

[0039] Graphene, mass fraction 5%-20%;

[0040] Transition metal sulfide, mass fraction 50%-70%;

[0041] Ion sieve functional layer material, mass fraction 5%-15%;

[0042] Carbon-based nanofiber, mass fraction 5%-10%;

[0043] Binder, mass fraction 3%-5%;

[0044] Sodium metal negative electrode;

[0045] Electrolyte, the electrolyte is a solution of NaClO4 dissolved in EC and DMC solvents, the volume ratio of the solvents is 1:1, and the concentration is 0.5-1M.

[0046] The transition metal sulfide includes one or more of nickel sulfide, cobalt sulfide, iron sulfide, or vanadium sulfide.

[0047] The ion sieve functional layer material is a metal organic framework, including ZIF-8 or a derivative material thereof.

[0048] The graphene is functionalized graphene modified by oxidation, and the surface contains hydroxyl and carboxyl groups.

[0049] The carbon-based nanofiber is a carbon nanotube, and the carbon nanotube is compounded with the positive electrode material by a mechanical mixing method.

[0050] A sodium ion battery preparation method, comprising the following steps:

[0051] Modification and dispersion of graphene: graphene powder is dispersed by ultrasonic to form a suspension, and sodium persulfate and nitric acid are added for functionalization treatment;

[0052] Synthesis of transition metal sulfide: the functionalized graphene suspension is mixed with a precursor solution containing a transition metal salt and a sulfur source, and a composite material is synthesized by high-temperature solid-phase reaction under inert gas protection.

[0053] Introducing ion sieve functional layer: mixing transition metal sulfide composite material with MOF precursor, forming ion sieve functional layer through solvothermal reaction;

[0054] Preparation of electrode sheet: mixing composite material with carbon-based nanofiber, binder and conductive agent into slurry, coating on current collector, drying and pressing into sheet to make positive electrode sheet;

[0055] Battery assembly: assembling positive electrode sheet, sodium metal negative electrode and electrolyte into sodium ion battery.

[0056] The treatment temperature of functionalized graphene suspension is 50-80℃, and the treatment time is 2-3h.

[0057] The temperature of high-temperature solid-phase reaction is 300-400℃, and the time is 4-6h.

[0058] The temperature of solvothermal reaction is 150-200℃, and the time is 6-12h.

[0059] According to a kind of sodium ion battery, it is applied to portable electronic equipment, electric vehicle and large-scale energy storage system.

[0060] Example 1: preparation of positive electrode material with nickel sulfide as core and battery assembly

[0061] Graphene modification and dispersion:

[0062] 10g high-purity graphene was added to 200mL deionized water, ultrasonic dispersion for 30min (power 400W), forming a suspension.

[0063] 2g sodium persulfate and 5mL nitric acid were added, the temperature was kept at 70℃, and stirring was carried out for 2h.

[0064] After centrifugal separation, it was washed with deionized water for 3 times, and dried to obtain functionalized graphene.

[0065] Transition metal sulfide synthesis:

[0066] 5g functionalized graphene was taken and added to 50mL nickel nitrate (0.1M) and 25mL thiourea (0.05M) solution.

[0067] After uniform stirring, it was heated to 350℃ under argon protection for 4h.

[0068] After cooling, it was washed and vacuum dried for 24h to obtain graphene-nickel sulfide composite material.

[0069] Introducing ion sieve functional layer:

[0070] 2 g of the composite was mixed with 50 mL of ethanol solution containing ZIF-8 precursor.

[0071] The composite with the functional layer was obtained by solvothermal reaction at 150℃ for 8 h.

[0072] After washing again, it was dried for standby.

[0073] Electrode preparation:

[0074] The composite 7 g, carbon nanotubes 2 g, binder 1 g were mixed, and an appropriate amount of NMP was added. After stirring for 6 h, the slurry was prepared.

[0075] The slurry was coated on a copper foil, dried, and then pressed into a sheet to make a positive electrode sheet.

[0076] Battery assembly:

[0077] The positive electrode sheet, sodium metal negative electrode, and NaClO4-EC / DMC (1M) electrolyte were assembled into a coin cell in a glove box.

[0078] The cycle performance was tested by constant current charge and discharge.

[0079] Example 2: Fast charging sodium ion battery based on cobalt sulfide

[0080] Preparation of functionalized graphene suspension:

[0081] 15 g of graphene was added to 300 mL of water, and the ultrasonic power was 300 W. The treatment time was 45 min.

[0082] 1 g of sodium persulfate and 3 mL of nitric acid were added, and the reaction was carried out at 60℃ for 3 h.

[0083] After centrifugal separation, the oxidized modified graphene was dried.

[0084] Synthesis of cobalt sulfide composite:

[0085] A 0.2M cobalt nitrate solution of 100 mL was prepared, and 10 g of functionalized graphene and 20 mL of sodium sulfide (0.1M) were added.

[0086] The graphene-cobalt sulfide composite was obtained by reacting at 400℃ under argon protection for 6 h.

[0087] MOF functional layer modification:

[0088] ZIF-8 precursor was dissolved in ethanol, and the composite was added. The solvothermal reaction was carried out at 120℃ for 10 h.

[0089] After drying, the material with complete structure was obtained.

[0090] Electrode sheet preparation and battery assembly:

[0091] Composite material 6g, carbon nanofiber 3g and conductive carbon black 1g were mixed, coated on copper foil, dried, and pressed into electrode sheet.

[0092] The negative electrode used sodium metal sheet, and the electrolyte used NaClO4(0.5M).

[0093] Assembled button cell.

[0094] Example 3: Iron sulfide-based high-safety sodium-ion battery

[0095] Preparation of functionalized graphene:

[0096] 20g graphene was added to 500mL water, ultrasonic power 500W, treatment time 30min.

[0097] 3g sodium persulfate was added, the temperature was kept at 50℃, and stirring was carried out for 1.5h.

[0098] Centrifugal washing, drying and standby.

[0099] Preparation of iron sulfide:

[0100] 5g of functionalized graphene was mixed with FeCl3 solution (0.1M, 50mL) and sodium sulfide (0.05M, 25mL).

[0101] Under argon protection, the temperature was raised to 300℃ and kept for 5h to generate graphene-iron sulfide composite material.

[0102] Introduction of functional layer and carbon fiber:

[0103] ZIF-8 precursor (mass ratio 1:1) was added to the above composite material, and solvent thermal reaction was carried out at 150℃ for 6h.

[0104] Carbon nanofiber was added in proportion to form a complete positive electrode material.

[0105] Electrode and battery assembly:

[0106] The positive electrode slurry was coated on aluminum foil, dried to prepare electrode sheet.

[0107] Sodium metal negative electrode, electrolyte NaClO4(1M) dissolved in EC / DMC.

[0108] Assembled into button cell.

[0109] Example 4: Vanadium sulfide-based energy storage system battery

[0110] Preparation of functionalized graphene:

[0111] 10g graphene was added to 200mL water at 60℃, and ultrasonic treatment was carried out for 40min.

[0112] Add 2g sodium persulfate, react for 2h, dry after centrifugation to obtain modified graphene.

[0113] Vanadium sulfide synthesis:

[0114] Mix NH4VO3(10g) with thiourea(5g) and stir well in graphene suspension.

[0115] React for 4h under inert atmosphere at 400℃ to obtain graphene-vanadium sulfide composite.

[0116] Functional layer construction and electrode preparation:

[0117] Modify the functional layer by ZIF-8, solvothermal treatment at 150℃ for 6h.

[0118] Add carbon nanotubes to form a composite positive electrode slurry, coat the current collector and dry to press a sheet.

[0119] Battery assembly and testing: assemble the positive sheet, sodium metal negative electrode and NaClO4 electrolyte into a button cell and perform high current charge and discharge performance test.

[0120] Comparative Example 1: graphene is not functionalized

[0121] Corresponding Example: Example 1 (nickel sulfide core positive electrode material)

[0122] Graphene dispersion: directly use non-functionalized graphene, take 10g and add to 200mL deionized water, ultrasonic dispersion for 30min (power 400W).

[0123] No sodium persulfate and nitric acid treatment.

[0124] Transition metal sulfide synthesis: mix non-treated graphene with nickel nitrate (0.1M, 50mL) and thiourea (0.05M, 25mL), heat to 350℃ under argon protection for 4h to generate graphene-nickel sulfide composite.

[0125] Subsequent steps: maintain the same ion sieve functional layer introduction, electrode sheet preparation and battery assembly process as Example 1.

[0126] Comparative Example 2: no ion sieve functional layer

[0127] Corresponding Example: Example 2 (cobalt sulfide core positive electrode material)

[0128] Functionalized graphene preparation: take 15g graphene and functionalize according to the method of Example 2.

[0129] Cobalt sulfide composite synthesis: functionalized graphene was reacted with cobalt nitrate (0.2 M, 100 mL) and sodium sulfide (0.1 M, 20 mL) at 400 °C under argon for 6 h following the procedure of Example 2.

[0130] Composite without functional layer: without introducing ZIF-8 functional layer modification, the graphene-cobalt sulfide composite was directly used to prepare the cathode slurry.

[0131] Subsequent steps: electrode sheet preparation and battery assembly were consistent with Example 2.

[0132] Comparative Example 3: without adding carbon-based nanofiber

[0133] Corresponding Example: Example 3 (iron sulfide core-based cathode material)

[0134] Functionalized graphene preparation: the functionalization treatment method of Example 3 was referred to.

[0135] Iron sulfide composite synthesis: functionalized graphene was mixed with FeCl3solution (0.1 M, 50 mL) and sodium sulfide (0.05 M, 25 mL) and reacted at 300 °C under argon for 5 h.

[0136] Without carbon-based nanofiber: during the preparation of the cathode slurry, only 7 g of composite, 1 g of binder, and 2 g of conductive carbon black were used, without adding carbon-based nanofiber.

[0137] Subsequent steps: other steps were consistent with Example 3, including electrode sheet preparation and battery assembly.

[0138] Comparative Example 4: traditional electrolyte system (without optimization)

[0139] Corresponding Example: Example 4 (vanadium sulfide core-based energy storage system battery)

[0140] Functionalized graphene preparation: the same functionalization treatment as Example 4.

[0141] Vanadium sulfide composite synthesis: vanadium sulfide composite was prepared by mixing NH4VO3(10 g) and thiourea (5 g) in a graphene suspension and then following the procedure of Example 4 at 400 °C for 4 h.

[0142] Traditional electrolyte system: the electrolyte was NaPF6(1 M) dissolved in EC / DMC (1:1) solvent, without using the optimized NaClO4system.

[0143] Subsequent steps: electrode sheet preparation and battery assembly procedures were consistent with Example 4.

[0144] Comparative Example 5: using unmodified graphene with a single active material

[0145] Corresponding example: Example 1 (positive electrode material with nickel sulfide as the core)

[0146] Combination of graphene and nickel sulfide: without using functionalized graphene, only 10 g of ordinary graphene powder is mixed with a 0.1 M nickel nitrate solution to react under the condition of no sulfide precursor.

[0147] Single nickel sulfide active material: the prepared positive electrode material only contains nickel sulfide, without a graphene composite network.

[0148] Subsequent steps: keep consistent with the electrode sheet preparation and battery assembly of Example 1.

[0149] Experiment 1: battery cycle performance test

[0150] Experiment description:

[0151] Purpose of the experiment: to verify the energy density and cycle performance advantages of the technical solution of the present application using functionalized graphene and ion sieve functional layer material in sodium ion batteries.

[0152] Experimental equipment: constant current constant voltage charge-discharge tester, battery clamp, button cell test rack.

[0153] Experimental materials:

[0154] Example 1 (functionalized graphene + nickel sulfide + ion sieve functional layer)

[0155] Comparative Example 1 (non-functionalized graphene)

[0156] Comparative Example 2 (without ion sieve functional layer)

[0157] Experimental steps:

[0158] Sample preparation:

[0159] According to the descriptions of Example 1, Comparative Example 1 and Comparative Example 2, button cells are prepared respectively to ensure that the assembly of the positive electrode sheet, electrolyte and negative electrode sheet is complete and accurate.

[0160] Charge-discharge cycle:

[0161] The assembled button cell is installed on the test rack.

[0162] Set the constant current charge-discharge mode, the current density is 0.5C, and the charge-discharge voltage range is 2.0V to 4.2V.

[0163] Cycle test 500 times, record the discharge capacity and coulomb efficiency of each cycle.

[0164] Data recording and processing:

[0165] Measure and record the initial capacity of each battery, the remaining capacity after each cycle, and the capacity retention rate during the cycle test process.

[0166] Record the change of coulombic efficiency of each cycle.

[0167] Experimental data:

[0168] Table 1: Comparison of cycle test results (Example 1 and Comparative Example)

[0169] Cycle number Example 1 capacity (mAh / g) Comparative Example 1 capacity (mAh / g) Comparative Example 2 capacity (mAh / g) Initial value 145.3 122.5 133.8 50 140.6 109.3 120.1 100 138.9 98.7 112.5 150 135.7 91.4 102.8 200 132.5 85.9 93.4 300 128.4 76.3 81.9 400 122.9 68.7 72.3 500 120.2 62.5 65.1

[0170] Summary: The results of the cycle performance test show significant differences. The use of functionalized graphene in the positive electrode is obviously the key. Its high conductivity and the binding force of the modified surface hydroxyl and carboxyl groups make the nickel sulfide more stable during charging and discharging. The ion sieve functional layer further optimizes the interface transmission and reduces the side reactions caused by electrolyte decomposition. This combination allows the battery to maintain a high capacity over a long period of time, while the comparative example shows obvious degradation due to the lack of such design.

[0171] From another perspective, the use of non-functionalized graphene limits the electron migration rate of the positive electrode material. The results show that the initial capacity of the battery is low and the capacity decay rate is faster during the cycle process. This indicates that the functionalization of graphene not only improves the conductive network, but also improves the uniformity of the active material distribution, avoiding the problem of excessive local current density. The absence of the ion sieve functional layer enhances the electrolyte side reactions, further reducing the cycle stability.

[0172] Furthermore, as the number of cycles increases, the difference in coulombic efficiency begins to appear. The battery without the ion sieve functional layer has a poor selectivity of sodium ion migration, resulting in an increase in side reaction products, which affects the long-term capacity retention rate. It can be said that the synergy of the positive electrode material design is the core path to solve the cycle stability problem of sodium ion batteries. This synergy is achieved through functionalized graphene, transition metal sulfide, and ion sieve functional layer, which is unmatched by traditional design.

[0173] Experiment 2: Rate performance test

[0174] Experimental description:

[0175] Purpose of the experiment: To test the sodium ion transport efficiency and stability of the conductive network of the invention under high-rate charging and discharging conditions. By comparing with the comparative example, the improvement effect of functionalized graphene and carbon-based nanofibers on the rate performance is verified.

[0176] Experimental equipment: electrochemical workstation, constant current and constant voltage charge and discharge tester, battery clamp and test rack.

[0177] Experimental materials:

[0178] Example 2 (functionalized graphene + cobalt sulfide + carbon-based nanofiber)

[0179] Comparative Example 3 (without carbon-based nanofiber)

[0180] Comparative Example 5 (unmodified graphene with single cobalt sulfide)

[0181] Experimental procedure:

[0182] Sample preparation:

[0183] Button cells were prepared according to the procedures of Example 2, Comparative Example 3 and Comparative Example 5, ensuring the consistency of the quality of the positive electrode sheet, electrolyte, and negative electrode sheet.

[0184] Rate performance test:

[0185] The button cell was installed on the test rack and connected to the electrochemical workstation.

[0186] The constant current charge-discharge mode was set, and the current density was gradually increased: 0.5C (low rate), 1C, 2C, 5C, 10C (high rate).

[0187] Three charge-discharge cycles were performed at each rate, and the discharge specific capacity and coulombic efficiency were recorded.

[0188] The capacity change trend was observed by continuing to test 10 cycles at 10C.

[0189] Data recording:

[0190] The discharge capacity and coulombic efficiency change at each rate were measured and recorded.

[0191] The differences in capacity retention rate under different rate conditions were analyzed.

[0192] Experimental data:

[0193] Table 2: Comparison of specific capacity and efficiency under different rate conditions

[0194] Current density (C) Example 2 specific capacity (mAh / g) Comparative Example 3 specific capacity (mAh / g) Comparative Example 5 specific capacity (mAh / g) 0.5 137.6 122.4 109.8 1 132.1 115.7 97.5 2 125.8 106.3 85.1 5 110.2 89.7 62.5 10 92.4 73.2 45.8 10 (10 cycles) 88.6 66.8 40.2

[0195] Summary: Under high rate conditions, the performance differences of the batteries immediately appear. The functionalized graphene of the present invention provides a highly uniform conductive network, while the addition of carbon-based nanofibers enhances the transmission efficiency of electrons and ions. This multi-dimensional conductivity is obviously crucial for high-rate charge and discharge. Comparative Example 3 lacks the support of carbon-based nanofibers, and the electrochemical polarization increases, resulting in a rapid decrease in capacity after the rate is increased. Even worse, Comparative Example 5 uses unmodified graphene, and the active material is not evenly distributed, limiting the sodium ion transmission path, making it almost impossible to maintain reasonable performance at high rates.

[0196] The interface problem is amplified by the insufficient transport efficiency at high current density. The ion migration path in Example 2 is apparently optimized, and the introduction of polar groups on the functionalized graphene surface stabilizes the structure of sulfide, so that it does not collapse significantly during fast charging and discharging. Comparative Example 5 shows that the diffusion of sodium ions in the material is significantly hindered, resulting in a serious lack of utilization of the active area. This problem is particularly prominent at high rates.

[0197] In addition, the role of carbon-based nanofibers is not just to provide additional conductive paths. After continuous cycling at 10C, the capacity of Example 2 can still be maintained, while the capacity of Comparative Example 3 decays significantly. This shows that the high thermal conductivity of carbon fibers significantly improves the problem of local heat accumulation in the electrode. This thermal management advantage plays an irreplaceable role in actual high-rate applications, especially in portable electronic devices and energy storage systems.

[0198] Experiment 3: Thermal stability test

[0199] Experiment Description:

[0200] Purpose of the experiment: To verify the effect of the multi-dimensional thermal conduction network design of ion sieve functional layer and carbon-based nanofibers in the present application on improving the thermal stability and cycle performance of sodium ion batteries in high temperature environments.

[0201] Experimental equipment: constant temperature oven, constant current and constant voltage charge and discharge tester, thermal imager.

[0202] Experimental materials:

[0203] Example 3 (functionalized graphene + iron sulfide + ion sieve functional layer + carbon-based nanofiber)

[0204] Comparative Example 2 (without ion sieve functional layer)

[0205] Comparative Example 4 (unoptimized electrolyte system)

[0206] Experimental steps:

[0207] Sample preparation:

[0208] Prepare button cells according to Example 3, Comparative Example 2 and Comparative Example 4, respectively, to ensure the consistency of the battery assembly.

[0209] Thermal stability test:

[0210] Place the button cells in the following two environments, respectively:

[0211] Room temperature (25°C);

[0212] High temperature (80°C in the constant temperature oven).

[0213] Set constant current charge-discharge conditions: 0.5C current density, voltage range 2.0V to 4.2V.

[0214] Record the discharge capacity and capacity retention rate under each environment.

[0215] Use a thermal imager to monitor the surface temperature distribution of each battery in a high-temperature environment, and record the thermal management performance.

[0216] Data recording and analysis:

[0217] Analyze the discharge capacity, capacity retention rate and thermal distribution under high-temperature conditions, and compare the differences in battery stability.

[0218] Experimental data:

[0219] Table 3: Thermal stability test results under different conditions

[0220] Cycle number Ambient temperature Example 3 capacity (mAh / g) Comparative Example 2 capacity (mAh / g) Comparative Example 4 capacity (mAh / g) Initial value Room temperature 138.5 122.7 128.3 25 Room temperature 134.3 114.8 119.6 50 Room temperature 129.8 108.5 113.2 100 Room temperature 124.7 99.3 102.4 Initial value 80℃ 137.4 121.5 127.6 25 80℃ 128.6 99.8 107.5 50 80℃ 122.4 86.2 91.8 100 80℃ 117.9 75.6 80.3

[0221] Summary: Under high-temperature conditions, the thermal stability of the battery becomes a key issue. The experiment shows that the performance of Example 3 is significantly better than that of the comparative example. The synergistic effect of functionalized graphene and iron sulfide improves the interface stability, while the ion sieve functional layer reduces the gas generated by side reactions. This design reduces the risk of thermal runaway, allowing the battery to maintain stable capacity under high temperature. Comparative Example 2 lacks an ion sieve functional layer, and the interface side reaction is more serious, resulting in a rapid decline in capacity in a high-temperature environment.

[0222] In addition, the introduction of carbon-based nanofibers plays a crucial role in thermal management. Thermal imaging data shows that the temperature distribution of Example 3 is more uniform, and the local overheating phenomenon is significantly reduced. In contrast, Comparative Example 4, without an optimized electrolyte system, has increased interface impedance and more prominent thermal accumulation problems. In the long run, this thermal management capability plays a key protective role in the safety and life of the battery in a high-temperature environment.

[0223] Fundamentally, the stability of Example 3 is due to the synergy of material design. Functionalized graphene enhances the dispersibility and conductivity of the positive electrode material, the ion sieve functional layer optimizes the sodium ion migration channel, and the carbon-based nanofiber provides an additional thermal conduction path. This multi-dimensional synergistic design is not achievable by traditional single optimization strategies. The experimental results further prove that the technical solution of the present invention can achieve stable and reliable performance in high-temperature energy storage scenarios, and is suitable for energy storage applications under complex working conditions.

[0224] Experiment 4: Large-scale energy storage simulation test

[0225] Experimental description:

[0226] Experimental purpose: To simulate the application scenario of sodium-ion batteries in large-scale energy storage systems, test the energy efficiency and stability, and verify the performance advantages of the invention in long-term operation.

[0227] Experimental equipment: constant-current discharge simulation system, battery constant-current charging device, simulated energy storage load (50W), temperature monitoring module.

[0228] Experimental materials:

[0229] Example 4 (functionalized graphene + vanadium sulfide + ion sieve functional layer + optimized electrolyte system)

[0230] Comparative Example 4 (unoptimized electrolyte system)

[0231] Comparative Example 5 (single vanadium sulfide + unmodified graphene)

[0232] Experimental steps:

[0233] Sample preparation:

[0234] According to the flow of Example 4, Comparative Example 4 and Comparative Example 5, button cells were prepared respectively.

[0235] Energy storage simulation test:

[0236] Connect each group of batteries to the simulated energy storage load, set the constant current charging and constant power discharge cycle conditions:

[0237] Constant current charging current density: 0.5C.

[0238] Discharge power: 50W.

[0239] Run continuously for 72h, record the energy efficiency, capacity retention rate and surface temperature change during operation.

[0240] Data recording and processing:

[0241] Record the discharge capacity, energy efficiency and temperature fluctuation of the battery every hour.

[0242] Compare the long-term performance of different samples in simulated energy storage applications.

[0243] Experimental data:

[0244] Table 4: Comparison of energy storage simulation test results

[0245] Time (h) Example 4 energy efficiency (%) Comparative Example 4 energy efficiency (%) Comparative Example 5 energy efficiency (%) 1 91.5 87.2 83.6 6 90.8 83.5 78.2 12 89.7 80.1 73.4 24 87.3 76.8 69.7 36 85.9 72.3 64.5 48 84.5 68.9 59.8 60 83.1 64.7 55.3 72 82.4 60.2 50.9

[0246] Summary: In the simulation test of energy storage system, the performance of the pros and cons quickly emerged. The performance of Example 4 is obviously superior, and the optimized electrolyte system effectively improves the migration rate of sodium ions and the interface stability. Combined with functionalized graphene and ion sieve functional layer, this design significantly improves energy efficiency, which remains above 80% after 72h operation. The counter example 4 has a higher impedance due to the unoptimized electrolyte, and the energy loss increases significantly, resulting in a rapid decline in efficiency. As for the counter example 5, the combination of single active material and unmodified graphene hinders the migration of sodium ions, resulting in low efficiency and faster decay.

[0247] The test results of temperature fluctuations are more intuitive. The thermal management design of Example 4 benefits from the multidimensional heat conduction network of carbon-based nanofibers, and the temperature change on the surface of the battery remains uniform when the load fluctuates. In contrast, the temperature of Counter Example 4 rises sharply, and local hot spots are obvious. Counter Example 5 of unmodified graphene exposes its weaknesses under high load conditions, with serious heat accumulation and difficulty in dissipation, showing potential safety hazards.

[0248] From a mechanistic point of view, the design of the present application is the result of multi-level cooperation. Optimizing the electrolyte reduces the interfacial impedance and improves the transmission rate of sodium ions; the high conductivity and stability of functionalized graphene provide good support for the positive electrode; the ion sieve functional layer precisely filters sodium ions, reducing side reactions. In addition, the thermal management of carbon-based nanofibers is indispensable, and this material cooperative design provides more reliable performance guarantee for energy storage systems. The experimental results prove that the present application has significant advantages in practical application scenarios and is an ideal choice for large-scale energy storage.

[0249] Although embodiments of the present application have been shown and described, it will be understood by those having ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A sodium-ion battery, characterized in that, Comprise: A positive electrode material consisting of: Graphene, 5%-20% by mass; Transition metal sulfide, 50%-70% by mass; Ion sieve functional layer material, 5%-15% by mass; Carbon-based nanofiber, 5%-10% by mass; Binder, 3%-5% by mass; Sodium metal negative electrode; Electrolyte, the electrolyte is a solution of NaClO4 dissolved in EC and DMC solvents, the volume ratio of the solvents is 1:1, and the concentration is 0.5-1M; The transition metal sulfide comprises one or more of nickel sulfide, cobalt sulfide, iron sulfide, or vanadium sulfide; The ion sieve functional layer material is a metal organic framework, and the metal organic framework is ZIF-8; The graphene is functionalized graphene modified by oxidation, and the surface contains hydroxyl and carboxyl groups.

2. The sodium-ion battery of claim 1, wherein, The carbon-based nanofiber is a carbon nanotube, and the carbon nanotube is compounded with the positive electrode material by a mechanical mixing method.

3. A method of preparing a sodium-ion battery, characterized by, Comprise the following steps: Modification and dispersion of graphene: graphene powder is dispersed into a suspension by ultrasonic dispersion, and sodium persulfate and nitric acid are added for functionalization treatment; Synthesis of transition metal sulfide: the functionalized graphene suspension is mixed with a precursor solution containing transition metal salt and sulfur source, and a composite material is synthesized by high-temperature solid-phase reaction under inert gas protection; Introduction of ion sieve functional layer: the transition metal sulfide composite material is mixed with ZIF-8 precursor, and an ion sieve functional layer is formed by solvothermal reaction; the temperature of the solvothermal reaction is 150-200°C, and the time is 6-12h; Preparation of electrode sheet: the composite material is mixed with carbon-based nanofiber, binder, and conductive agent to form a slurry, which is coated on a current collector, dried, and then pressed into a sheet to form a positive electrode sheet; Battery assembly: the positive electrode sheet, sodium metal negative electrode, and electrolyte are assembled into a sodium ion battery.

4. The method for preparing a sodium-ion battery according to claim 3, characterized in that, The treatment temperature of the functionalized graphene suspension is 50-80°C, and the treatment time is 2-3h.

5. The method of claim 3, wherein the sodium-ion battery is prepared by the steps of: The temperature of the high-temperature solid-phase reaction is 300-400°C, and the time is 4-6h. ​ 6. The sodium ion battery according to any one of claims 1-2 is applied in portable electronic devices, electric vehicles, and large-scale energy storage systems.

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