High-rate sodium ion battery

Abstract

The invention relates to a high-rate sodium ion battery, and belongs to the technical field of power grid frequency modulation. The battery cell of the sodium-ion battery comprises a positive plate, a negative plate and an electrolyte, an active material of the positive plate is graphene-coated potassium ion doped sodium ferric sulfate; the chemical formula of the potassium ion doped sodium ferric sulfate is Na < 6-2x-y > K < y > Fe < x > (SO4) 3; the active material of the negative plate is titanium sodium phosphate coated with secondary carbon; the primary particle size D90 of the titanium sodium phosphate coated with the secondary carbon is 100 nm to 800 nm; the porosity of the positive plate and the negative plate is independently 50-60%; the electrolyte consists of electrolyte salt, an additive and a solvent; the electrolyte salt comprises sodium hexafluorophosphate and sodium bis (fluorosulfonyl) imide; the additive is prepared from 1-ethyl-3-methylimidazolium bis (fluorosulfonyl) imine and sodium lignin sulfonate. The sodium ion battery has excellent specific capacity, cycling stability and rate capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid frequency regulation, and in particular relates to a high-rate sodium ion battery. Background Art

[0002] In the field of grid frequency regulation, the large-scale integration of renewable energy sources such as wind power and photovoltaics poses significant challenges to grid frequency stability due to the volatility, intermittency, and unpredictability of their output, placing higher demands on grid frequency regulation. Current energy storage frequency regulation methods have their own limitations: lithium-ion batteries have a limited cycle life and are susceptible to capacity degradation due to frequent charging and discharging; flywheel energy storage has low energy density and is only suitable for high-frequency, short-term frequency regulation; supercapacitors have a high self-discharge rate and poor long-term energy storage efficiency, making them only suitable for suppressing millisecond-level frequency fluctuations. Sodium-ion batteries, however, offer advantages such as low-temperature safety, rapid charge and discharge performance, fast startup, and zero-charge storage, making them highly suitable for frequency regulation applications and filling gaps in existing technologies. Therefore, the development of high-rate sodium-ion batteries is particularly necessary. Such high-rate sodium-ion batteries should have charge and discharge times in the second-to-minute range, high energy efficiency, and a long cycle life to fully meet the stringent requirements of grid frequency regulation technology and become a powerful solution.

[0003] However, at this stage, there are many problems with the positive and negative electrode materials of sodium ion batteries, which make it difficult to meet the requirements of high-rate sodium ion batteries. In terms of positive electrode materials, layered oxides, Prussian blue analogs, and polyanionic compounds generally have disadvantages such as low specific capacity, poor cycle stability, and poor rate performance. Negative electrode materials, such as hard carbon, are prone to induce sodium dendrite precipitation during high-rate charging, thereby affecting the safety and cycle life of the battery. To solve these problems, patent CN118336084A discloses a high-rate sodium ion battery, in which the active material of the negative electrode plate is a composite material of phosphorus carbon and hard carbon, thereby inhibiting sodium precipitation and gas production. Although this design helps to achieve high-rate fast charging, due to the sodium insertion potential problem of the negative electrode material, the carbon material still has the risk of sodium precipitation. Patent CN117334995A discloses a low-cost, ultra-long-life sodium ion battery, in which the positive and negative electrodes of the battery both use polyanionic materials with a NASICON-type three-dimensional skeleton structure as active materials, so that the battery capacity is mainly limited by the capacity of the negative electrode. This design fully utilizes the advantages of the stable lattice structure of polyanion materials and can achieve long-term application, but it is still insufficient in high-rate applications.

[0004] The development of high-power batteries requires comprehensive consideration of multiple aspects, including positive and negative electrode active materials, electrode plates, electrolyte, and battery structure. Specifically, the positive and negative electrode materials must possess high electrical conductivity, including both electronic and ionic conductivity. Furthermore, the design of the electrodes and electrolyte should focus on shortening ion diffusion paths to improve ion transport efficiency. Therefore, the development of a sodium-ion battery with excellent performance remains essential. Summary of the Invention

[0005] To this end, the technical problem to be solved by the present invention is to overcome the problems of low specific capacity, poor cycle stability, poor rate performance of the positive electrode material of sodium ion batteries in the prior art, and the easy occurrence of sodium dendrite precipitation in the negative electrode material during high-rate charging.

[0006] In order to solve the above technical problems, the present invention provides a high-rate sodium ion battery.

[0007] The object of the present invention is to provide a high-rate sodium ion battery, wherein the battery cell of the sodium ion battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte;

[0008] The active material of the positive electrode sheet is graphene-coated potassium ion-doped sodium ferric sulfate; the chemical formula of the potassium ion-doped sodium ferric sulfate is Na 6-2x-y K y Fe x (SO4)3, where 1.5<x<2, 0.01<y<0.2; under these conditions, potassium ion doping with sodium ferric sulfate can increase the lattice voids and improve the ion diffusion coefficient of the material;

[0009] The active material of the negative electrode sheet is secondary carbon-coated sodium titanium phosphate; the primary particle size D90 of the secondary carbon-coated sodium titanium phosphate is 100nm-800nm;

[0010] The porosity of the positive electrode sheet and the negative electrode sheet is independently 50%-60%. The in-situ foaming technology (using the chemical reaction in the slurry) is used to spontaneously form the electrode sheet with high porosity, which is conducive to improving the diffusion of electrolyte ions.

[0011] The electrolyte consists of an electrolyte salt, an additive and a solvent; the electrolyte salt includes sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI); the additive includes 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM-FSI) and sodium lignin sulfonate (SLS).

[0012] In one embodiment of the present invention, the weight proportion of graphene in the graphene-coated potassium ion-doped sodium ferric sulfate is 0.5%-10%, thereby improving the electron diffusion coefficient of the material.

[0013] In one embodiment of the present invention, the secondary carbon-coated sodium titanium phosphate includes sodium titanium phosphate, and a first carbon layer and a second carbon layer sequentially coated on the surface of the sodium titanium phosphate.

[0014] In one embodiment of the present invention, the weight proportion of the first carbon layer in the secondary carbon-coated sodium titanium phosphate is 0.1%-1%; the weight proportion of the second carbon layer is 1%-5%.

[0015] In one embodiment of the present invention, the theoretical capacity ratio of the active material of the negative electrode sheet to the active material of the positive electrode sheet is (0.7-0.98):1, which is beneficial to improving the cycle stability of the battery.

[0016] In one embodiment of the present invention, the method for preparing the graphene-coated potassium ion-doped sodium ferric sulfate comprises the following steps:

[0017] S1. Add an antioxidant and an iron source to water and stir evenly to obtain an antioxidant iron solution;

[0018] S2. Adding a sodium source, a potassium source, and a sulfur source to the antioxidant iron solution described in S1, and stirring uniformly to obtain a precursor solution;

[0019] S3, spray drying and sintering the precursor solution described in S2 to obtain potassium ion-doped sodium ferric sulfate;

[0020] S4. Evenly stir the potassium ion-doped sodium ferric sulfate and graphene solution described in S3, and spray dry to obtain the graphene-coated potassium ion-doped sodium ferric sulfate.

[0021] Furthermore, the antioxidant is selected from one or more of hydrogen peroxide, ascorbic acid and vitamin C;

[0022] The iron source is selected from one or more of iron powder, ferrous oxide, ferric oxide, ferric oxide, ferric hydroxide, ferrous hydroxyhydroxide, ferrous sulfate and ferric sulfate;

[0023] The sodium source is selected from one or more of sodium carbonate, sodium sulfate, sodium hydroxide, sodium oxalate and sodium acetate;

[0024] The potassium source is selected from one or more of potassium carbonate, potassium sulfate, potassium hydroxide, potassium oxalate and potassium acetate;

[0025] The sulfur source is selected from one or more of sodium sulfate, sodium bisulfate, anhydrous ferrous sulfate, ammonium sulfate and ammonium bisulfate.

[0026] In one embodiment of the present invention, the method for preparing the secondary carbon-coated sodium titanium phosphate comprises the following steps:

[0027] S1. Add a titanium source, a sodium source, a phosphorus source, an organic carbon source, and an inorganic carbon source to water and stir uniformly to obtain a precursor slurry; wherein the molar ratio of the titanium source, the sodium source, and the phosphorus source is 1:0.5:2;

[0028] S2. spray-drying and sintering the precursor slurry described in S1 to obtain primary carbon-coated sodium titanium phosphate;

[0029] S3, adding the primary carbon-coated sodium titanium phosphate and the organic carbon source described in S2 to water and stirring evenly to obtain a secondary carbon-coated sodium titanium phosphate slurry;

[0030] S4. Under a protective atmosphere, spray-drying and sintering the secondary carbon-coated sodium titanium phosphate slurry described in S3 to obtain the secondary carbon-coated sodium titanium phosphate.

[0031] Furthermore, the titanium source is titanium dioxide; the primary particle size D90 of the titanium dioxide is less than 300 nm; sodium titanium phosphate is synthesized on the basis of titanium dioxide, and only when the particle size of the basic raw material is nanometer-scale, the synthesized material can be nanometer-scale;

[0032] The sodium source is selected from one or more of sodium hydroxide, sodium carbonate, sodium sulfate, sodium dihydrogen phosphate and sodium acetate;

[0033] The phosphorus source is selected from one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus pentoxide;

[0034] The organic carbon source is selected from one or more of polyethylene glycol 400, citric acid, sucrose, glucose and polyacrylic acid; the organic carbon source also acts as a dispersant;

[0035] The inorganic carbon source is selected from acetylene black and / or graphite.

[0036] In one embodiment of the present invention, the preparation method of the positive electrode sheet includes the following steps: mixing the active material, conductive agent, binder and solvent of the positive electrode sheet uniformly to obtain a slurry, and continuously adding a foaming agent and a catalyst and stirring uniformly to obtain a composite slurry; then coating the composite slurry on an aluminum foil, first heating it to 50°C-60°C at a rate not exceeding 5°C / min and heating it for 5min-10min, and then heating it to 60°C-80°C at a rate not exceeding 5°C / min and heating it for 10min-20min to obtain a positive electrode sheet; the total amount of the foaming agent and the catalyst is 10wt%-40wt% of the slurry; the molar ratio of the foaming agent and the catalyst is (2.5-3.5):1; the foaming agent and the catalyst react by heating to generate CO2 bubbles, forming uniform micropores; by controlling the heating rate, the sudden temperature rise can be prevented to cause the concentrated release of CO2, and the problem of uneven pore distribution can be avoided. Because the decomposition temperature of sodium bicarbonate is about 50℃ and it starts to produce gas significantly, keeping it at this temperature for 8 minutes can make the electrode heated evenly, while 60℃-80℃ can greatly accelerate the reaction rate and avoid side reactions caused by high temperature (such as carbonization of citric acid).

[0037] Furthermore, the conductive agent is selected from one or more of carbon nanotubes, acetylene black, conductive carbon black, conductive graphite, carbon fiber and graphene;

[0038] The binder is selected from one or more of polyolefins, fluorine-containing resins, polypropylene resins and rubbers;

[0039] The foaming agent is sodium bicarbonate;

[0040] The catalyst is citric acid;

[0041] The solvent is selected from one or more of water, N-methylpyrrolidone, ethanol and acetone.

[0042] Furthermore, the mass ratio of the active material, the conductive agent and the binder of the positive electrode sheet is (90-95):(2-8):(1-5).

[0043] In one embodiment of the present invention, the method for preparing the negative electrode sheet includes the following steps: uniformly mixing the active material, conductive agent, binder and solvent of the negative electrode sheet to obtain a slurry, further adding a pore-forming agent and stirring to obtain a composite slurry; then coating the composite slurry on aluminum foil, heating to 60°C-80°C at a rate not exceeding 5°C / min, and drying to obtain a negative electrode sheet; the amount of the pore-forming agent is 1wt%-5wt% of the slurry; and heating to decompose ammonia, carbon dioxide and water vapor in the pore-forming agent to form uniform micropores.

[0044] Furthermore, the conductive agent is selected from one or more of carbon nanotubes, acetylene black, conductive carbon black, conductive graphite, carbon fiber and graphene;

[0045] The binder is selected from one or more of polyolefins, fluorine-containing resins, polypropylene resins and rubbers;

[0046] The pore-forming agent is ammonium bicarbonate;

[0047] The solvent is selected from one or more of water, N-methylpyrrolidone, ethanol and acetone.

[0048] Furthermore, the mass ratio of the active material, the conductive agent and the binder of the negative electrode sheet is (90-95):(2-8):(1-5).

[0049] In one embodiment of the present invention, the molar ratio of sodium hexafluorophosphate to sodium bis(fluorosulfonyl)imide is (6-8):(4-2);

[0050] The mass ratio of the 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide to sodium lignin sulfonate is (0.1-5):(0.1-1); sodium lignin sulfonate is a bio-based surfactant that can improve the wettability and conductivity of the electrolyte; combined with the high ionic conductivity (>10mS / cm) of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, the diffusion coefficient of sodium ions and the conductivity of the electrolyte can be increased, thereby improving the high-rate performance of the battery.

[0051] In one embodiment of the present invention, the solvent is selected from one or more of ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate and diethylene glycol dimethyl ether.

[0052] In one embodiment of the present invention, the concentration of the electrolyte salt in the electrolyte is 1.0 mol / L-3.0 mol / L, and the weight proportion of the additive is 0.2%-6%.

[0053] The technical solution of the present invention has the following advantages over the prior art:

[0054] (1) The high-rate sodium ion battery described in the present invention uses graphene-coated potassium ion-doped sodium ferric sulfate as the active material of the positive electrode sheet, and controls the porosity of the positive electrode sheet to 50%-60%, which significantly improves the ion and electron diffusion capacity of the positive electrode material, thereby greatly improving the rate performance of the battery and achieving high-rate charge and discharge of 1C-100C.

[0055] (2) The high-rate sodium ion battery described in the present invention uses nano-scale secondary carbon-coated sodium titanium phosphate as the active material of the negative electrode sheet, and controls the porosity of the electrode sheet to 50%-60%, thereby improving the ion and electron transport performance of the negative electrode material and effectively improving the rate performance of the battery.

[0056] (3) The positive electrode sheet in the high-rate sodium ion battery described in the present invention adopts the in-situ foaming technology to not only produce uniform pores, but also the sodium citrate generated by the reaction can serve as a sodium supplement, synergistically acting with the sodium ions in the electrolyte, further improving the sodium ion transmission rate and the conductivity of the electrolyte, thereby improving the battery's rate performance.

[0057] (4) The SEI film in the high-rate sodium-ion battery described in the present invention is primarily formed on the surface of the negative electrode material, rather than on the overall structure of the negative electrode sheet. It has a significant impact on the performance, safety, and cycle life of the battery. By optimizing the electrolyte composition and charging conditions, a stable and high-performance SEI film can be formed, thereby improving the overall performance of the battery.

[0058] (5) The negative electrode of the high-rate sodium ion battery described in the present invention has no SEI film, and there is no dendrite "generation-dissolution-reconstruction" process, which avoids the consumption of active sodium ions and improves the safety and cycle life of the battery.

[0059] (6) The high-rate sodium ion battery described in the present invention uses a negative electrode material with stable chemical properties to control the battery capacity, and the rich positive electrode material ensures the stability of the battery cycle and long cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0061] Figure 1 This is a charge and discharge performance diagram of the sodium ion battery of Example 1 of the present invention at 1C. DETAILED DESCRIPTION

[0062] The present invention will be further described below with reference to specific embodiments so that those skilled in the art can better understand and implement the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. It should be understood that the specific embodiments are only used to illustrate the present invention, and the embodiments are not intended to limit the present invention.

[0063] In the present invention, unless otherwise defined, technical and scientific terms used herein have the same meanings as commonly understood by one skilled in the art to which the present invention belongs.

[0064] In the present invention, unless stated otherwise, the term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0065] In the present invention, unless otherwise stated, the experimental methods used in the examples of the present invention are conventional methods unless otherwise stated, and the materials, reagents, etc. used are all commercially available unless otherwise stated.

[0066] In the present invention, unless otherwise specified, the process parameters of the spray drying involved in the embodiments of the present invention are: an air inlet temperature of about 200°C, and an air outlet temperature of about 120°C.

[0067] In the present invention, unless otherwise specified, the reaction equation during the in-situ foaming process of the positive electrode sheet in the embodiments of the present invention is: 3NaHCO3+C6H8O7=C6H5O7Na3+3H2O+3CO2↑.

[0068] In the present invention, unless otherwise specified, the separator used in the embodiments of the present invention is a polypropylene film with a thickness of 9+3+3+3 μm.

[0069] Example 1

[0070] The high-rate sodium ion battery and its preparation method of this embodiment specifically include the following steps:

[0071] S1. Preparation of positive electrode sheet

[0072] S11. Preparation of graphene-coated potassium ion-doped sodium ferric sulfate:

[0073] 2.12 g of ascorbic acid was added to deionized water and stirred and dispersed for 30 minutes; then 52 g of ferrous sulfate heptahydrate was added and stirred and dispersed for 1 hour to obtain an antioxidant iron solution.

[0074] 15.695 g of sodium sulfate and 0.44 g of potassium sulfate were added to the antioxidant iron solution and stirred for 2 h to obtain a precursor solution.

[0075] The precursor solution was slowly added dropwise to 200 mL of deionized water and then spray-dried to form granules. The granules were then sintered at 350 ° C for 18 h in an inert reducing atmosphere (a mixture of nitrogen and hydrogen, with a volume percentage of hydrogen of 10%) to obtain potassium ion-doped sodium iron sulfate Na. 2.21 K 0.05 Fe 1.87 (SO4)3.

[0076] The potassium ion-doped sodium ferric sulfate powder was crushed and added into a graphene aqueous solution containing 1.87 g of graphene, and stirred evenly. The graphene-coated potassium ion-doped sodium ferric sulfate with a graphene content of 4 wt% was obtained by spray drying.

[0077] S2. Preparation of positive electrode sheet

[0078] 1.2g of binder PVDF and 60g of solvent NMP were added to a blender in sequence, stirred at 4000rpm and 70rpm for 3h, 1.6g of conductive agent SuperP and 0.4g of conductive agent CNT were added in sequence for high-speed mixing, with an interval of 1h, 36.8g of graphene-coated potassium ion-doped sodium ferric sulfate was added and stirred for 6h to obtain 100g of slurry; 12.6g (12.6%) of foaming agent sodium bicarbonate and 9.6g (9.6%) of catalyst citric acid were added and stirred for 2h to obtain a composite slurry; the composite slurry was evenly coated on an aluminum foil with a thickness of 12μm, the wet thickness of the composite slurry was 195μm, the temperature was first increased to 50℃ at a rate of 3℃ / min and heated for 8min, then increased to 70℃ at a rate of 3℃ / min and heated for 15min, dried and cut with a die to obtain a positive electrode sheet.

[0079] S2. Preparation of negative electrode sheet

[0080] S21. Preparation of secondary carbon-coated sodium titanium phosphate:

[0081] Titanium dioxide with a primary particle size D90 of approximately 250 nm is added to deionized water and ultrasonically dispersed uniformly. Then, diammonium hydrogen phosphate, sodium dihydrogen phosphate, acetylene black and polyethylene glycol 400 are added and ultrasonically dispersed uniformly to obtain a precursor slurry, wherein the molar ratio of titanium element, sodium element and phosphorus element is 1:0.5:2, the amount of polyethylene glycol 400 is 0.3% of the target product mass, and the amount of acetylene black is 0.5% of the target product mass.

[0082] The precursor slurry was spray dried and then sintered at 700° C. for 4 h under a nitrogen atmosphere to obtain primary carbon-coated sodium titanium phosphate.

[0083] The primary carbon-coated sodium titanium phosphate was crushed and added to deionized water together with polyethylene glycol 400, and stirred evenly to obtain a secondary carbon-coated sodium titanium phosphate slurry; wherein the amount of polyethylene glycol 400 used was 2% of the mass of the target product.

[0084] The secondary carbon-coated sodium titanium phosphate slurry was spray-dried and then sintered at 400° C. for 6 h in a nitrogen atmosphere to obtain the secondary carbon-coated sodium titanium phosphate.

[0085] S22. Preparation of negative electrode sheet:

[0086] 1.2g of binder polyacrylic resin (LA132) and 60g of solvent water were added to a blender in sequence, stirred at 4000rpm and 70rpm for 3h, 2g of conductive agent SuperP was added in sequence and mixed at high speed for 2h, 36.8g of secondary carbon-coated sodium titanium phosphate was added and stirred for 6h to obtain 100g of slurry; 3g (3%) of pore-forming agent ammonium bicarbonate was added and stirred for 1h to obtain a composite slurry; the composite slurry was evenly coated on an aluminum foil with a thickness of 12μm, the wet thickness of the composite slurry was 178μm, and the temperature was raised to 60℃ for drying at a rate of 3℃ / min. After drying, it was cut with a knife die to obtain a negative electrode sheet.

[0087] S3. Preparation of electrolyte: The electrolyte salt, additive and solvent ethylene carbonate are uniformly mixed to obtain an electrolyte; wherein the concentration of the electrolyte salt in the electrolyte is 2.0 mol / L, and the weight proportion of the additive is 2.5%; the electrolyte salt is obtained by mixing sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI) in a molar ratio of 7:3; the additive is obtained by mixing 1-ethyl-3-methylimidazole bis(fluorosulfonyl)imide (EMIM-FSI) and sodium lignin sulfonate (SLS) in a mass ratio of 2:0.5.

[0088] S4. Assembly of sodium ion batteries: stack the positive electrode sheet, negative electrode sheet and separator in the order of "positive electrode sheet-separator-negative electrode sheet-separator" and wind them to obtain battery cells; place the battery cells in a 110°C forced air oven and bake them for 48 hours. Transfer the baked battery cells to a liquid injection room with a dew point environment of -30 degrees in a low dew point environment under a low dew point environment, and inject the above-mentioned sodium ion battery electrolyte, seal the battery cells, and then perform aging, formation, and capacity separation to obtain sodium ion batteries.

[0089] Test Example 1

[0090] Based on Example 1, the effects of different potassium doping amounts and graphene contents on the ion diffusion coefficient and ion resistivity were explored.

[0091] (1) Ion diffusion coefficient test (cm 2 s -1 ): The constant current intermittent titration technique (GITT) tests the dynamic diffusion behavior of active materials during the charge and discharge process. Generally, the Na ion diffusion coefficient is between 10 -7 cm 2 s -1 -10 -12 cm 2 s -1 The higher the ion diffusion coefficient, the faster the ion migration rate of the material during the charge and discharge process, and the more suitable it is for high-rate devices.

[0092] (2) Electronic resistivity test R (Ω·cm): The powder resistivity of the active material was tested using the ST2742C automatic powder resistivity tester. Under the same test conditions, the electronic conductivity of the positive and negative active material powders can be directly reflected. The curve between pressure (MPa) and resistivity (Ω·cm) was recorded, and the resistivity at a pressure of 60 MPa was used as a comparison between different samples.

[0093] Table 1 shows the relevant variables and the final measured performance:

[0094] Table 1

[0095]

[0096] As can be seen from Table 1, the doping of K ions and the composite of graphene conductive materials can improve the ion diffusion coefficient and electronic resistivity of the positive electrode material. Through the collaborative analysis of experimental group 1 and the comparative group, when 0.05% K doping and 4% graphene composite were implemented at the same time, the optimal ion diffusion coefficient (10 -8 cm 2 s -1 The researchers achieved a 100-fold increase in ion conductivity and a 6.3-fold increase in electronic conductivity compared to the undoped systems (Groups 2 and 3). This synergistic effect stems from the fact that potassium ion doping optimizes the energy barrier for bulk ion migration while the graphene network simultaneously enhances intercrystalline electron transport, forming a "continuous ion-electron dual conduction channel."

[0097] Comparing groups 1, 2, and 5, it can be seen that with the increase of potassium ion doping concentration, the ion diffusion rate increases by an order of magnitude; when the potassium doping amount increases from 0% to 0.03%, the ion diffusion coefficient increases from 10 -10 cm 2 s -1 -10 -12 cm 2 s -1 Increased to 10 -9 cm 2 s -1 -10 -11 cm 2 s -1 , an order of magnitude higher; when the doping amount continues to increase to 0.05%, the diffusion coefficient further jumps to 10 -8 cm 2 s -1 -10 -10 cm 2 s -1 This indicates that potassium ions establish a three-dimensional ion diffusion network by expanding the interlayer spacing of sodium ion transmission channels, and its doping concentration is positively correlated with the improvement of the diffusion coefficient.

[0098] Comparing Groups 1, 3, and 4 reveals a decreasing electronic resistivity with increasing graphene content. The electronic resistivities of Groups 3, 4, and 1 were 6846Ω·cm, 2832Ω·cm, and 1747Ω·cm, respectively. This demonstrates a gradient effect in the construction of graphene's two-dimensional conductive network: when the graphene content reaches 1%, the resistivity decreases by 58.6% compared to the blank group; when the content increases to 4%, the resistivity drops further by 85.4%. In particular, when the graphene content exceeds 1%, a continuous electron transport path forms between the layers, effectively reducing the grain boundary barrier and achieving a semiconductor-to-conductor transition.

[0099] Test Example 2

[0100] Based on Example 1, the effects of the primary particle size of the secondary carbon-coated sodium titanium phosphate and the contents of the first carbon layer and the second carbon layer on the ion diffusion coefficient and ionic resistivity were investigated.

[0101] Table 2 shows the relevant variables and the final measured performance:

[0102] Table 2

[0103]

[0104] As can be seen from Table 2, group 1 achieved an ion diffusion coefficient (10 -8 -10 -10 cm 2 s -1 ) and electronic resistivity (1984Ω·cm), indicating that the secondary carbon coating process and nanoparticle morphology control have a significant synergistic enhancement effect on the electrochemical performance.

[0105] Comparing groups 1, 2, and 3, it can be seen that as the particle size increases, the ion diffusion rate decreases; large particles lead to a longer ion transmission path, a reduced contact area between particles, and a significant increase in bulk grain boundary resistance, indicating the nonlinear enhancement of the ion diffusion rate by nano-sizing.

[0106] Comparison of groups 1, 4, 5, and 6 shows that the electronic conductivity of the material is higher when there is only one carbon coating or no carbon coating. When double carbon coating is performed, the resistivity decreases by 54.4%-76.7% compared with a single carbon layer and decreases by 79.9% compared with no carbon layer. The first carbon layer (0.8%) preferentially coats the particle surface to form a conductive base, and the second carbon layer (2%) fills the grain boundary gaps to form a continuous three-dimensional conductive network, effectively suppressing interfacial polarization.

[0107] Test Example 3

[0108] The positive electrode material adopts Group 1 in Table 1, and the negative electrode material adopts Group 1 in Table 2. Based on Example 1, the effects of different amounts of foaming agent, catalyst and pore-forming agent on porosity, ion diffusion coefficient and ionic resistivity are explored. The porosity of the positive and negative electrode materials is the core structural parameter that directly determines the upper limit of the battery's rate performance. In this test example, the 20C rate capacity retention rate of the full battery is used for characterization.

[0109] Porosity (%): The porosity is tested using the electrolyte infiltration method, simulating the electrolyte filling effect in an actual battery. The dry weight of the electrode (m1) is weighed, the electrode is immersed in the electrolyte, and vacuum pressurized to ensure complete infiltration. After removing and wiping the surface, the wet weight of the electrode (m2) is weighed to calculate the porosity. Porosity = [(m2-m1) / ρ 电 electrolyte] / (A×L)*100%; wherein, ρ electrolyte is 1.2g / cm 3 , A is the cross-sectional area of ​​the electrode (cm 2 ), L is the thickness of the electrode (cm).

[0110] 20C rate capacity retention rate: First, perform 1C charge and discharge for 3 cycles and record the average discharge capacity as C1. Then, perform 20C charge and discharge for 3 cycles and record the average discharge capacity as C20. 20C capacity retention rate = C20 / C1*100%.

[0111] Table 3 shows the relevant variables and the final measured performance:

[0112] Table 3

[0113]

[0114]

[0115] As can be seen from Table 3, for the positive electrode sheet, the porosity increases with the increase of the foaming agent and catalyst content; for the negative electrode sheet, the porosity increases with the increase of the pore-forming agent content. The increase in porosity shortens the diffusion distance of the electrolyte and improves the rate performance of the battery. At the same time, the pore gradient design of the positive electrode slightly higher than that of the negative electrode (ΔP = 1%-5%) can balance the Na ion intercalation and deintercalation kinetics and the uniformity of sodium deposition at the negative electrode, thereby suppressing electrode polarization at high rates.

[0116] Test Example 4

[0117] Based on Example 1, the effects of different EMIM-FSI contents, SLS contents, and NaPF6 / NaFSI molar ratios on the conductivity of the electrolyte were investigated.

[0118] Conductivity (mS / cm): The conductivity of the electrolyte at 25°C was measured using a conductivity meter.

[0119] Table 4 shows the relevant variables and the final measured performance:

[0120] Table 4

[0121]

[0122] As can be seen from Table 4, groups 1, 2, and 5 have a significant synergistic regulatory effect on the electrolyte conductivity through the ratio of EMIM-FSI ionic liquid, SLS surfactant, and sodium salt.

[0123] Comparing groups 1, 2, and 3, it can be seen that the conductivity decreases by about 1.7 mS / cm for every 1% decrease in EMIM-FSI content. As the EMIM-FSI content decreases, the electrolyte conductivity decreases. This is because the high dissociation degree of EMIM-FSI can reduce the Na+ solvation energy, increase the ion migration number, and thus improve the conductivity of the electrolyte.

[0124] Comparing groups 1 and 4, it can be seen that the addition of SLS can increase the conductivity by 34.2%. This is because SLS is a bio-based surfactant that can improve the wettability and desolvation ability of the electrolyte, reduce the wetting angle of the electrolyte to the diaphragm, and shorten the penetration time.

[0125] Comparing groups 1, 5, 6, and 7, it can be seen that as the proportion of NaFSI increases, the conductivity of the electrolyte shows an upward trend. This is mainly due to the low viscosity and high dissociation degree of NaFSI. The low cost of NaPF6 and the high dissociation degree of NaFSI are used to form a low-cost, high-conductivity electrolyte, which is easy to achieve industrial mass production.

[0126] Test Example 5

[0127] Based on the above experiments, the effects of different active materials of positive and negative electrodes, different porosities, and different electrolytes on battery rate performance were explored.

[0128] Battery rate performance: The theoretical capacity of the active material of the negative electrode is 0.98 of that of the positive electrode; different sodium ion batteries are charged and discharged 5 times at rates of 1C, 10C, 20C, 50C, and 100C, with a charge and discharge voltage of 0.1V-2.2V, and then the specific capacity of the sodium ion battery after 5 cycles of charge and discharge at different rates is recorded (the specific capacity is calculated based on the negative electrode because the negative electrode controls it).

[0129] Figure 1 Table 5 shows the relevant variables and the final measured related performance:

[0130] Table 5

[0131] serial number positive electrode negative electrode Electrode porosity (%) electrolyte 1C 10C 20C 50C 100C Battery 1 1 group 1 group 1 group 1 group 98 95 89 72 45 Battery 2 1 group 6 groups 1 group 1 group 94 85 76 48 16 Battery 3 1 group 3 groups 1 group 1 group 95 86 77 49 17 Battery 4 2 groups 1 group 1 group 1 group 97 90 80 59 20 Battery 5 3 groups 1 group 1 group 1 group 97 90 80 59 20 Battery 6 1 group 1 group 4 groups 1 group 98 94 81 48 9 Battery 7 1 group 1 group 1 group 8 groups 94 84 64 51 32

[0132] from Figure 1 Table 5 shows the quantitative impact of the synergistic effect of "positive and negative electrode active material design, electrode pores, and electrolyte" on ultra-high rate (100C) performance. With a medium voltage of 1.56V and good symmetry in the charge-discharge curves, the battery exhibits excellent rate performance, with a capacity retention at 100C of 45% of that at 1C.

[0133] Comparing Battery 1 and Battery 2, it can be seen that when the active material of the negative electrode is not coated with carbon, electron transmission is hindered, the overall internal resistance of the battery increases, and the rate performance decreases.

[0134] Comparing Battery 1 and Battery 3, it can be seen that when the primary particle size of the active material of the negative electrode is too large, the sodium ion transmission rate is affected, the overall internal resistance of the battery increases, and the rate performance decreases.

[0135] Comparing Battery 1 with Batteries 4-5, it can be seen that when the active materials of the positive and negative electrodes have the same trend, whether the electronic conductivity is reduced (without graphene composite) or the ion transport rate is reduced (without potassium ion doping), it will lead to a decrease in rate performance; in addition, since the battery capacity is controlled by the negative electrode active material, the impact of the negative electrode will be greater.

[0136] Comparing Battery 1 and Battery 6, it can be seen that when the positive and negative electrodes are not subjected to porosity creation, the capacity drops sharply at high rates; because the size of the porosity limits the degree of electrolyte immersion, at low rates, the difference is not large, and as the rate increases, the differentiation becomes more and more obvious.

[0137] Comparing Battery 1 and Battery 7, it can be seen that the electrolyte conductivity is low, resulting in a proportional decrease in performance at high rates (greater than 10C).

[0138] Test Example 6

[0139] Based on Battery 1 in Test Example 5, the effect of the theoretical capacity ratio of active materials of different negative and positive electrodes on the battery cycle stability was investigated; the theoretical capacity of each positive and negative electrode was determined by assembling a sodium metal half-cell for testing; the half-cell assembly was to assemble the obtained positive or negative electrode sheet with a sodium metal sheet into a button cell, and then test it within the corresponding voltage range after filling the cell with liquid.

[0140] Cycle stability: Place the sodium ion battery on the battery cycle test equipment and perform a 20C charge and 20C discharge cycle test on the sodium ion battery at room temperature. The capacity of the first cycle is recorded as Q 初始 , record the capacity Q after 50,000 cycles 50000圈 Calculate the capacity retention rate of each battery after 50,000 cycles = (Q 50000圈 / Q 初始 )×100%.

[0141] Table 6 shows the relevant variables and the final measured performance:

[0142] Table 6

[0143]

[0144]

[0145] As can be seen from Table 6, as the theoretical capacity ratio of the negative electrode active material to the positive electrode active material increases, the capacity control of the full battery shifts from negative electrode control to positive electrode control, and the cycling performance decreases. When the battery capacity is controlled by a chemically stable negative electrode material, the abundant positive electrode material ensures the stability of the battery cycle and a long cycle life. However, when the positive electrode is used for control, due to the lower chemical stability of the positive electrode material compared to the negative electrode, ion extraction and material dissolution occur during the cycling process, resulting in a decrease in cycling performance.

[0146] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A high-rate sodium ion battery, characterized in that The sodium ion battery cell comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; The active material of the positive electrode sheet is graphene-coated potassium ion-doped sodium ferric sulfate; the chemical formula of the potassium ion-doped sodium ferric sulfate is Na 6-2x-y K y Fe x (SO4)3, where 1.5<x<2, 0.01<y<0.2; The active material of the negative electrode sheet is secondary carbon-coated sodium titanium phosphate; the primary particle size D90 of the secondary carbon-coated sodium titanium phosphate is 100nm-800nm; The porosity of the positive electrode sheet and the negative electrode sheet is independently 50%-60%; The electrolyte solution consists of an electrolyte salt, an additive and a solvent; the electrolyte salt includes sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide; and the additive includes 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide and sodium lignin sulfonate.

2. The high-rate sodium ion battery according to claim 1, characterized in that The weight proportion of graphene in the graphene-coated potassium ion-doped sodium ferric sulfate is 0.5%-10%.

3. The high-rate sodium ion battery according to claim 1, characterized in that The secondary carbon-coated sodium titanium phosphate includes sodium titanium phosphate, and a first carbon layer and a second carbon layer sequentially coated on the surface of the sodium titanium phosphate.

4. The high-rate sodium ion battery according to claim 3, characterized in that The weight proportion of the first carbon layer in the secondary carbon-coated sodium titanium phosphate is 0.1%-1%; the weight proportion of the second carbon layer is 1%-5%.

5. The high-rate sodium ion battery according to claim 1, characterized in that The theoretical capacity ratio of the active material of the negative electrode sheet to the active material of the positive electrode sheet is (0.7-0.98):

1.

6. The high-rate sodium ion battery according to claim 1, characterized in that The preparation method of the positive electrode sheet comprises the following steps: uniformly mixing the active material, conductive agent, binder and solvent of the positive electrode sheet to obtain a slurry, further adding a foaming agent and a catalyst and stirring uniformly to obtain a composite slurry; then coating the composite slurry on aluminum foil, first heating the temperature to 50-60°C at a rate not exceeding 5°C / min and heating for 5-10 minutes, then heating the temperature to 60-80°C at a rate not exceeding 5°C / min and heating for 10-20 minutes to obtain the positive electrode sheet; the total amount of the foaming agent and the catalyst is 10wt%-40wt% of the slurry; and the molar ratio of the foaming agent to the catalyst is (2.5-3.5):

1.

7. The high-rate sodium ion battery according to claim 1, characterized in that The method for preparing the negative electrode sheet comprises the following steps: uniformly mixing the active material, conductive agent, binder and solvent of the negative electrode sheet to obtain a slurry, further adding a pore-forming agent and stirring to obtain a composite slurry; then coating the composite slurry on aluminum foil, heating the slurry to 60°C-80°C at a rate not exceeding 5°C / min and drying the slurry to obtain the negative electrode sheet; the amount of the pore-forming agent used is 1wt%-5wt% of the slurry.

8. The high-rate sodium ion battery according to claim 1, characterized in that The molar ratio of sodium hexafluorophosphate to sodium bis(fluorosulfonyl)imide is (6-8):(4-2); The mass ratio of the 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide to sodium lignin sulfonate is (0.1-5):(0.1-1).

9. The high-rate sodium ion battery according to claim 1, characterized in that The solvent is selected from one or more of ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate and diethylene glycol dimethyl ether.

10. The high-rate sodium ion battery according to claim 1, characterized in that The concentration of the electrolyte salt in the electrolyte is 1.0 mol / L-3.0 mol / L, and the weight proportion of the additive is 0.2%-6%.

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