Solid-state sodium-ion battery

Abstract

This invention relates to a solid-state sodium-ion battery, belonging to the field of solid-state battery technology. The solid-state sodium-ion battery of this invention uses carbon-coated NASICON-type cathode material as the positive electrode active material. The carbon coating on the surface of the NASICON-type cathode material can further enhance its conductivity, which is beneficial to improving the electrochemical performance of the battery. The coated carbon establishes a bridge between the NASICON-type cathode material and the solid electrolyte, acting as a buffer layer to effectively prevent direct contact between the cathode and the sulfide solid electrolyte. This effectively avoids both the low-voltage reduction decomposition of the cathode material and the high-voltage oxidative decomposition of the sulfide solid electrolyte. It can fill the electrochemical window gap between the cathode and electrolyte, promoting compatibility between the two, thereby enabling stable cycling of the solid-state sodium-ion battery over a wide voltage range.

Description

Technical Field

[0001] This invention relates to a solid-state sodium-ion battery, belonging to the field of solid-state battery technology. Background Technology

[0002] The sustainable development of commercial lithium-ion batteries is currently limited due to the scarcity and high cost of lithium resources. Sodium-ion batteries operate on a similar principle to lithium-ion batteries, and sodium resources offer advantages such as wide global distribution and low cost. Sodium-ion batteries are considered a next-generation commercial battery that can replace lithium-ion batteries. However, due to the limited availability and high cost of sodium... + The ionic radius is greater than that of Li + The ionic radius of Na, therefore Na + The transportation of these items is quite difficult.

[0003] In commercially available lithium-ion batteries, the flammability and volatility of organic electrolytes pose certain safety hazards. For sodium-ion batteries, the safety risks associated with organic electrolytes are even more severe. Therefore, developing solid-state sodium-ion batteries is of great significance for achieving safe, high-energy-density sodium-ion battery technology. Key aspects of developing high-energy-density solid-state sodium-ion batteries include: 1) using high-voltage, high-specific-capacity cathode materials; 2) ensuring seamless matching of the electrochemical window between the cathode material and the solid electrolyte; and 3) using sodium-ion conductivity of at least 1 mS·cm. -1 4) Reduce the amount of solid electrolyte used in the positive electrode region; 5) Develop low-cost battery preparation methods that are as compatible as possible with existing electrolyte battery industrial technology solutions.

[0004] Among existing high-voltage, high-specific-capacity cathode materials, polyanionic sodium-ion compounds with an open NASCION framework structure possess advantages such as relatively stable crystal structure, large specific capacity, high open-circuit voltage, and high sodium-ion conductivity, making them a class of cathode materials with significant application value. Currently reported NASCION-type materials include Na3Mn2(PO4)3, Na3V2(PO4)3, Na3MnTi(PO4)3, Na4MnZr(PO4)3, and Na3TiCr(PO4)3. However, NASCION-type materials exhibit poor electronic conductivity, leading to severe capacity decay at high rates. Furthermore, after long-term charging and discharging, especially at high currents, severe side reactions occur on the material surface, accelerating capacity decay.

[0005] Although both sulfide solid electrolytes and NASICON-type cathode materials have high sodium ion conductivity, their combined use can solve the Na+ problem. +The transport of sulfide-based solid electrolytes presents challenges, but their voltage tolerance is low, with an oxidation potential not exceeding 2V. Therefore, they cannot be directly matched with cathode materials whose reduction potential exceeds 2V (such as NASICON-type cathode materials). Otherwise, decomposition at the interface between the cathode material and the electrolyte would occur, leading to structural failure and battery degradation. Consequently, current high-voltage, high-specific-capacity cathode materials cannot be directly used with sulfide-based solid electrolytes. Summary of the Invention

[0006] The purpose of this invention is to provide a solid sodium-ion battery that solves the problem that the high-voltage, high-specific-capacity cathode materials in current solid sodium-ion batteries cannot be directly matched with sulfide-based solid electrolytes.

[0007] To achieve the above objectives, the technical solution adopted by the solid-state sodium-ion battery of the present invention is as follows:

[0008] A solid-state sodium-ion battery includes a positive electrode, a solid electrolyte, and a negative electrode. The positive electrode includes a positive current collector, a positive active material layer, and an electrolyte impregnated in the positive active material layer. The positive active material layer is composed of carbon-coated NASICON-type positive electrode material, a conductive agent, and a binder. The solid electrolyte is a sulfide solid electrolyte. The electrolyte mainly consists of an electrolyte and a solvent. The electrolyte is sodium perchlorate and / or sodium hexafluorophosphate.

[0009] The solid-state sodium-ion battery of this invention uses carbon-coated NASICON-type cathode material as the positive electrode active material. This not only maintains the high sodium-ion conductivity of both the sulfide-based solid electrolyte and the NASICON-type cathode material, but also allows the carbon coating on the surface of the NASICON-type cathode material to further enhance its conductivity, thus improving the battery's electrochemical performance. The coated carbon establishes a bridge between the NASICON-type cathode material and the solid electrolyte, acting as a buffer layer to effectively prevent direct contact between the cathode and the sulfide-based solid electrolyte. This effectively avoids both low-voltage reduction decomposition of the cathode material and high-voltage oxidative decomposition of the sulfide-based solid electrolyte. It also fills the electrochemical window gap between the cathode and electrolyte, promoting their compatibility and solving the problem of volume expansion of the cathode material due to long-term charge-discharge cycles, thereby improving the rate performance and cycle stability of the sodium-ion solid-state battery. By impregnating the carbon-coated NASICON-type cathode material with the electrolyte, the introduction of solid electrolyte into the cathode material region can be avoided. This breaks through the technical framework that requires solid-state batteries to incorporate a large amount of solid electrolyte into the composite material in the cathode region, effectively increasing the overall specific capacity of the cathode region. The solid-state sodium-ion battery of this invention has the advantages of high voltage, large specific capacity, stability, and safety, and can be stably cycled within a wide voltage range.

[0010] Preferably, the positive current collector is aluminum foil.

[0011] Preferably, the mass ratio of the carbon-coated NASICON-type cathode material, the conductive agent, and the binder is (5-8):(1-4):1. For example, the mass ratio of the carbon-coated NASICON-type cathode material, the conductive agent, and the binder is 7:2:1.

[0012] Preferably, the conductive agent is acetylene black and / or Super-P. Preferably, the binder is polyvinylidene fluoride binder and / or sodium carboxymethyl cellulose binder.

[0013] Preferably, the positive electrode sheet is prepared by a method comprising the following steps: coating a positive electrode active slurry onto a positive electrode current collector, drying to obtain a sheet-like positive electrode material, then dripping an electrolyte onto the surface of the sheet-like positive electrode material to wet the positive electrode active material layer, and allowing it to stand to obtain the final product; the positive electrode active slurry mainly consists of carbon-coated NASICON-type positive electrode material, a conductive agent, a binder, and an organic solvent. Preferably, the organic solvent is NMP. Preferably, the positive electrode active slurry is obtained by mixing carbon-coated NASICON-type positive electrode material, a conductive agent, a binder, and an organic solvent. Preferably, the mixing time is 6 hours. Preferably, the drying temperature is 70°C, and the drying time is 12 hours. Preferably, the standing time is 5 minutes. This invention uses a low-cost coating technology to prepare solid-state battery positive electrodes, greatly reducing the manufacturing cost of solid-state batteries. The preparation method of the positive electrode sheet of this invention is simple, uses environmentally friendly raw materials, has low cost, low equipment dependence, and has a wide range of applications.

[0014] Preferably, in the positive electrode active slurry, the ratio of the sum of the mass of the carbon-coated NASICON-type positive electrode material, the mass of the conductive agent, and the mass of the binder to the mass of the organic solvent is 1:2.

[0015] Preferably, the mass of the electrolyte in the electrolyte solution impregnating the positive electrode active material layer is 10% to 25% of the mass of the carbon-coated NASICON-type positive electrode material in the positive electrode active material layer; the concentration of the electrolyte in the electrolyte solution is 1 mol / L. Further, the mass of the electrolyte in the electrolyte solution impregnating the positive electrode active material layer is 25% of the mass of the carbon-coated NASICON-type positive electrode material in the positive electrode active material layer.

[0016] This invention does not limit the use of sulfide solid electrolytes; any sulfide solid electrolyte used in solid sodium-ion batteries is applicable to this invention. For example, the sulfide solid electrolyte is Na... 11 Sn2PS 12 Or Na3PS4.

[0017] Preferably, the NASICON-type cathode material in the carbon-coated NASICON-type cathode material is Na. a M n (PO4) b The following conditions apply: 1.5 ≤ a ≤ 3, 1 ≤ n ≤ 4, 2 ≤ b ≤ 3.5; M is a transition metal selected from one or any combination of Ti, Mn, V, Fe, and Cr. Preferably, the transition metal is Ti and Mn. Further, the NASICON-type cathode material is Na3MnTi(PO4)3.

[0018] Preferably, a = b = 3; the carbon-coated NASICON-type cathode material is prepared by a method comprising the following steps: heating and stirring a solution containing an organic carbon source, a transition metal salt and sodium dihydrogen phosphate to form a gel, then drying and pulverizing it in sequence, and then heating it in an inert atmosphere.

[0019] Preferably, the solution containing an organic carbon source, a transition metal salt, and sodium dihydrogen phosphate is prepared by a method comprising the following steps: mixing an organic carbon source solution with a transition metal salt or a transition metal salt solution to obtain a solution containing an organic carbon source and a transition metal salt, and then mixing the solution containing the organic carbon source and the transition metal salt with a sodium dihydrogen phosphate solution.

[0020] Preferably, the organic carbon source is selected from one or any combination of citric acid, glucose, and sucrose. Preferably, the molar ratio of carbon in the organic carbon source to the molar ratio of the transition metal element in the transition metal salt is (6-9):1. For example, the molar ratio of carbon in the organic carbon source to the molar ratio of the transition metal element in the transition metal salt is 6:1.

[0021] Preferably, the metal element in the transition metal salt is selected from one or any combination of Ti, Mn, V, Fe, and Cr. Preferably, the transition metal salt is manganese acetate tetrahydrate and / or diammonium di(2-hydroxypropionic acid) hydroxide titanium. Preferably, the transition metal salt is composed of manganese acetate tetrahydrate and diammonium di(2-hydroxypropionic acid) hydroxide titanium. Preferably, the molar ratio of manganese acetate tetrahydrate to diammonium di(2-hydroxypropionic acid) hydroxide titanium is 1:1. Preferably, diammonium di(2-hydroxypropionic acid) hydroxide titanium is added in the form of a diammonium di(2-hydroxypropionic acid) hydroxide titanium solution. Preferably, the mass fraction of the diammonium di(2-hydroxypropionic acid) hydroxide titanium solution is 50%.

[0022] Preferably, the organic carbon source is citric acid; the molar ratio of citric acid, manganese acetate tetrahydrate and di(2-hydroxypropionic acid)diammonium hydroxide titanium is (10-15):5:5.

[0023] Preferably, the concentration of the sodium dihydrogen phosphate solution is 1.5 mol / L.

[0024] Preferably, the temperature used for the heat treatment is 650°C; the heating rate to the temperature used for the heat treatment is 5°C / min; and the heat treatment time is 8 hours.

[0025] Preferably, the inert atmosphere is argon.

[0026] Preferably, the Na 11 Sn2PS 12 The electrolyte precursor mixture is prepared by a method comprising the following steps: pressing a mixture of sodium sulfide, sulfur powder, phosphorus pentasulfide, and tin powder, and then sintering the pressed mixture in an inert atmosphere. Preferably, the particle size of the electrolyte precursor mixture is less than 400 mesh. Preferably, the pressing is performed using a cold press. Preferably, the pressed mixture is in the form of a disc. Preferably, the sintering temperature is 500°C, the sintering time is 8 hours, and the heating rate to the sintering temperature is 1°C / min. Preferably, the electrolyte precursor mixture is prepared by a method comprising the following steps: sequentially grinding and filtering a mixture of sodium sulfide, sulfur powder, phosphorus pentasulfide, and tin powder. Preferably, the grinding is ball milling. Preferably, the inert atmosphere used for sintering the pressed mixture is argon.

[0027] Preferably, the negative electrode includes a copper mesh layer and a sodium metal layer loaded on one side of the copper mesh, the copper mesh layer facing the solid electrolyte. Attached Figure Description

[0028] Figure 1 This diagram illustrates the voltage, capacity, volume changes, and activation energy of different NASCION-type cathode materials; among them, Figure 1 a represents Na, a type of NASCION cathode material. x A schematic diagram showing the voltage of MnTi(PO4)3 as a function of x; Figure 1 b is Na, a NACSION-type cathode material. x A schematic diagram showing the change in capacity of MnTi(PO4)3 as x. Figure 1 c represents Na, a NACSION-type cathode material. x Schematic diagram of the volume change of MnTi(PO4)3 as a function of x; Figure 1 d represents Na, a NASCION-type cathode material. x A schematic diagram showing the variation of the activation energy of MnTi(PO4)3 with x (x = 2, 3, and 3.5);

[0029] Figure 2 The diagram shows the structure of the solid sodium-ion battery in Example 1; where the reference numerals are as follows: 1-negative electrode shell, 2-spring sheet, 3-negative electrode pad, 4-negative electrode sheet, 5-solid electrolyte sheet, 6-positive electrode sheet, 7-positive electrode pad and 8-positive electrode shell;

[0030] Figure 3 The images shown are SEM and TEM images of Na3MnTi(PO4)3@C prepared in Example 1; wherein, Figure 3 a is a SEM image of Na3MnTi(PO4)3@C prepared in Example 1; Figure 3 b is a TEM image of Na3MnTi(PO4)3@C prepared in Example 1 (NMTP represents Na3MnTi(PO4)3, Carbon represents carbon);

[0031] Figure 4 These are SEM images of Na3MnTi(PO4)3@C prepared in Examples 2 and 5; wherein, Figure 4 a is a SEM image of Na3MnTi(PO4)3@C prepared in Example 2; Figure 4 b is a SEM image of Na3MnTi(PO4)3@C prepared in Example 5;

[0032] Figure 5 The impedance diagrams for the solid sodium-ion batteries of Example 1 and Comparative Example 1 are shown.

[0033] Figure 6 This is a schematic diagram of the rate performance of the solid sodium-ion battery in Example 1;

[0034] Figure 7 This is a schematic diagram of the cycle performance of the solid sodium-ion battery in Example 1;

[0035] Figure 8 This is a schematic diagram of the symmetrical battery performance of the solid sodium-ion batteries in Example 1 and Comparative Example 2. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0037] The inventors based their work on NASCION-type cathode materials (Na2MnTi(PO4)3, Na3MnTi(PO4)3, Na... 3.5 Theoretical calculations of the electrochemical stability of MnTi(PO4)3 and sulfide solid electrolytes revealed that the reduction potential of the NASCION-type cathode material is higher than the oxidation potential of the sulfide solid electrolyte, indicating that the two do not meet the chemical compatibility conditions for a seamless electrochemical window and are not suitable for direct contact. The calculation method is as follows: Na... x The voltage, specific capacitance, and volume changes corresponding to MnTi(PO4)3 (1≤x≤4) are calculated as follows: Figure 1As shown, the results indicate that, while maintaining structural integrity (containing at least one Na), the maximum voltage can reach 3.98V, and its volume change is also very small. The values ​​of Na₂MnTi(PO₄)₃, Na₃MnTi(PO₄)₃, and Na₂MnTi(PO₄)₃ were calculated respectively. 3.5 The activation energy of MnTi(PO4)3 was found to be the lowest, which is favorable for the transport of sodium ions.

[0038] Example 1

[0039] A schematic diagram of the solid-state sodium-ion battery in this embodiment is shown below. Figure 2 As shown, it includes a negative electrode shell 1, a spring sheet 2, a negative electrode pad 3, a negative electrode sheet 4, a solid electrolyte sheet 5, a positive electrode sheet 6, a positive electrode pad 7, and a positive electrode shell 8. The positive electrode 6 comprises a positive electrode current collector, a positive electrode active material layer, and an electrolyte impregnated in the positive electrode active material layer. The positive electrode current collector is aluminum foil. The positive electrode active material layer consists of carbon-coated NASICON-type positive electrode material, a conductive agent, and a binder in a mass ratio of 7:2:1. The carbon-coated NASICON-type positive electrode material is carbon-coated Na3MnTi(PO4)3, the conductive agent is acetylene black, and the binder is polyvinylidene fluoride (PVDF). The mass of the electrolyte in the electrolyte impregnated in the positive electrode active material layer is 25% of the mass of the carbon-coated NASICON-type positive electrode material in the positive electrode active material layer. The electrolyte consists of an electrolyte and a solvent. The electrolyte is sodium perchlorate, and the solvent consists of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1. The concentration of the electrolyte in the electrolyte is 1 mol / L. The solid electrolyte is a sulfide solid electrolyte, and the sulfide solid electrolyte is Na... 11 Sn2PS 12 The negative electrode consists of a copper mesh layer and a sodium metal layer loaded on one side of the copper mesh, with the copper mesh layer facing the solid electrolyte.

[0040] The solid-state sodium-ion battery of this embodiment is prepared by a method including the following steps:

[0041] 1. Preparation of sulfide solid electrolyte sheets:

[0042] (1) Place sodium sulfide, sulfur powder, phosphorus pentasulfide, and tin powder into a ball mill jar, then add an appropriate amount of grinding balls, and seal the ball mill jar completely. Then, ball mill the sealed ball mill jar in a horizontal ball mill at a speed of 550 r / min for 10 h. During the ball milling process, every 2 h, put the ball mill jar into the glove box, scrape off the powder on the inner wall of the ball mill jar, and then continue ball milling.

[0043] (2) After ball milling, remove the grinding balls and powder from the ball mill jar, filter the powder with a 400-mesh sieve, collect the powder with a particle size of less than 400 mesh, and obtain an electrolyte precursor mixture.

[0044] (3) Then the electrolyte precursor mixture is cold-pressed using a cold press to form a disc with a diameter of 13 mm.

[0045] (4) Place the pressed discs into a transparent sealed container, then place the sealed container containing the discs into a muffle furnace in a glove box for sintering in an argon atmosphere. The sintering temperature is 500℃, the heating rate to the sintering temperature is 1℃ / min, and the sintering time is 8h. The resulting sheet-like sintered material is the sulfide (Na₂O₃). 11 Sn2PS 12 Solid electrolyte sheet.

[0046] 2. Preparation of carbon-coated NASICON-type cathode material:

[0047] (1) Add 0.01 mol of organic carbon source to a beaker containing 20 mL of deionized water, and then place the beaker in a water bath at 70 °C and heat until the organic carbon source is completely dissolved to obtain an organic carbon source solution. The organic carbon source is citric acid.

[0048] (2) Then, add 0.005 mol of manganese acetate tetrahydrate and an aqueous solution containing 0.005 mol of diammonium di(2-hydroxypropionic acid) dihydrogen phosphate titanium with a mass fraction of 50% to the beaker containing the organic carbon source solution. Stir until the manganese acetate tetrahydrate dissolves. Then add 10 mL of 1.5 mol / L sodium dihydrogen phosphate (NaH2PO4) solution to the beaker and continue heating and stirring to obtain a yellow transparent gel. Stop stirring and then remove the beaker from the water bath and place it in a 65°C drying oven to dry for 12 h to obtain a block.

[0049] (3) Grind the block into powder, and then heat the obtained powder in an argon atmosphere. The temperature used for the heating treatment is 650℃, the heating rate from room temperature to the temperature used for the heating treatment is 5℃ / min, and the heating treatment time is 8h. The nanoparticles obtained after the heating treatment are carbon-coated NASICON type cathode materials. The NASICON type cathode material in the carbon-coated NASICON type cathode material is Na3MnTi(PO4)3. The obtained carbon-coated NASICON type cathode material is labeled as Na3MnTi(PO4)3@C.

[0050] 3. Preparation of the positive electrode:

[0051] (1) Carbon-coated NASICON-type cathode material, acetylene black, and PVDF in a mass ratio of 7:2:1 were added to solvent NMP and stirred at room temperature for 6 hours to obtain a uniform cathode active slurry. The cathode active slurry was then coated onto aluminum foil and dried in a 70°C forced-air drying oven for 12 hours to obtain a sheet-like cathode material. The mass ratio of PVDF to NMP was 1:20, and the thickness of the cathode active material layer on the sheet-like cathode material was 15 mm.

[0052] (2) Cut the sheet-like positive electrode material into a positive electrode sheet with a diameter of 13 mm, and then add electrolyte to the surface of the positive electrode sheet to wet the positive electrode active material layer. The mass of the electrolyte in the electrolyte impregnated in the positive electrode active material layer is 25% of the mass of the carbon-coated NASICON type positive electrode material on the positive electrode sheet. After standing for 5 minutes, the positive electrode sheet is obtained.

[0053] 4. Assembly of solid-state sodium-ion batteries:

[0054] Place the positive electrode sheet and the sulfide solid electrolyte sheet in a glove box. Place the positive electrode pad and then the positive electrode sheet (with the positive electrode active material layer facing upwards) on the positive electrode shell. Then place the sulfide (Na...) 11 Sn2PS 12 A solid electrolyte sheet is placed on top of the positive electrode active material layer on the positive electrode sheet. Then, metallic sodium loaded on a copper mesh is placed on top of the electrolyte sheet as the negative electrode sheet (copper mesh facing the solid electrolyte). Then, a negative electrode pad, a spring sheet, and a negative electrode shell are placed in sequence on one side of the negative electrode sheet to assemble the battery, thus obtaining a solid sodium ion battery.

[0055] Example 2

[0056] The only difference between the solid sodium-ion battery in this embodiment and the solid sodium-ion battery in Example 1 is that, in the preparation process of carbon-coated NASICON type cathode material, the amount of organic carbon source used in step (1) is 0.005 mol.

[0057] Example 3

[0058] The only difference between the solid sodium-ion battery in this embodiment and the solid sodium-ion battery in Example 1 is that, in the preparation process of carbon-coated NASICON type cathode material, the amount of organic carbon source used in step (1) is 0.0075 mol.

[0059] Example 4

[0060] The only difference between the solid sodium-ion battery in this embodiment and the solid sodium-ion battery in Example 1 is that, in the preparation process of carbon-coated NASICON type cathode material, the amount of organic carbon source used in step (1) is 0.0125 mol.

[0061] Example 5

[0062] The only difference between the solid sodium-ion battery in this embodiment and the solid sodium-ion battery in Example 1 is that, in the preparation process of carbon-coated NASICON type cathode material, the amount of organic carbon source used in step (1) is 0.015 mol.

[0063] Example 6

[0064] The only difference between the solid sodium-ion battery in this embodiment and the solid sodium-ion battery in Example 1 is that, in the preparation process of the positive electrode sheet, the mass of the electrolyte in the electrolyte solution impregnated in the positive electrode active material layer in step (2) is 10% of the mass of the carbon-coated NASICON type positive electrode material on the disc.

[0065] Example 7

[0066] The only difference between the solid sodium-ion battery in this embodiment and the solid sodium-ion battery in Example 1 is that, in the preparation process of the positive electrode sheet wetted with electrolyte, the mass of the electrolyte in the positive electrode active material layer in step (2) is 15% of the mass of the carbon-coated NASICON type positive electrode material on the disc.

[0067] Example 8

[0068] The difference between the solid sodium-ion battery in this embodiment and the solid sodium-ion battery in Example 1 is that, in the preparation process of the positive electrode sheet wetted with electrolyte, the mass of the electrolyte in the positive electrode active material layer in step (2) is 20% of the mass of the carbon-coated NASICON type positive electrode material on the disc.

[0069] Comparative Example 1

[0070] The only difference between the solid sodium-ion battery in this comparative example and the solid sodium-ion battery in Example 1 is that, in the preparation process of the positive electrode sheet impregnated with electrolyte, the mass of electrolyte impregnated in the positive electrode active material layer in step (2) is 0.

[0071] Comparative Example 2

[0072] The only difference between the solid sodium-ion battery in this comparative example and the solid sodium-ion battery in Example 1 is that metallic sodium is used as the negative electrode during the assembly process of the solid sodium-ion battery.

[0073] Experimental Example 1

[0074] The Na3MnTi(PO4)3@C prepared in Example 1 was characterized by SEM and TEM, respectively, and the results are as follows: Figure 3 As shown. The Na3MnTi(PO4)3@C prepared in Examples 2 and 5 were then characterized by SEM, and the results are as follows. Figure 4 As shown. By Figure 3 and Figure 4It can be seen that the carbon and Na3MnTi(PO4)3@C prepared in Example 1 are well combined, while the Na3MnTi(PO4)3 particles in Na3MnTi(PO4)3@C prepared in Example 2 are sparsely distributed, and the Na3MnTi(PO4)3 particles in Na3MnTi(PO4)3@C prepared in Example 3 are relatively densely distributed. This indicates that adding too much or too little carbon source is not conducive to the transport of sodium ions.

[0075] Experiment Example 2

[0076] The impedance of the solid sodium-ion batteries in Example 1 and Comparative Example 1 was tested using a Chenhua electrochemical tester. The test conditions were as follows: the batteries were allowed to stand at room temperature for more than 4 hours before testing began. The impedance test frequency was 100-1MHz. Based on the impedance magnitude, Example 1 was determined to be the optimal battery. The test results are as follows: Figure 5 As shown, the results indicate that the impedance of the solid sodium-ion battery in Example 1 (<2000Ω) is significantly smaller than that of the solid sodium-ion battery in Comparative Example 1 (>5000Ω). This suggests that the electrolyte impregnated in the positive electrode can connect the positive electrode active material layer with the solid electrolyte, reducing the interfacial impedance and thus improving battery performance.

[0077] Experimental Example 3

[0078] The rate performance of the solid-state sodium-ion battery in Example 1 was tested using a LAND charge-discharge instrument. The test conditions were as follows: the battery was allowed to stand at room temperature for at least 4 hours before testing began. Charge-discharge cycles were performed at different rates from 0.05 to 2C, with each rate lasting 5 cycles. The voltage ranges were set to 1.5–3.5V and 1.5–4.1V. The test results are shown in Table 1 and... Figure 6 As shown, the results indicate that the solid sodium-ion battery of Example 1 can still be charged and discharged normally at a high rate of 2C, and can return to a low rate of charge and discharge.

[0079] Table 1 Rate performance of solid-state sodium-ion batteries in Example 1

[0080]

[0081]

[0082] Experiment Example 4

[0083] The cycle performance of the solid-state sodium-ion battery in Example 1 was tested using a LAND charge-discharge instrument. The test conditions were as follows: the battery was allowed to stand at room temperature for more than 4 hours before testing began, a fixed rate of 0.1C was set, and 160 charge-discharge cycles were performed. The test results are shown in Table 2 and... Figure 7 As shown, the results indicate that the capacity after 160 cycles is 82% of the capacity after 5 cycles.

[0084] Table 2 Cycle performance of solid sodium-ion batteries in Example 1

[0085] Cycle number <![CDATA[Charge specific capacity (mAh g -1 )]]> <![CDATA[Discharge specific capacity (mAh g -1 )]]> Coulomb efficiency (%) 2 116.1 114.8 101.13 3 110.7 102.9 107.58 4 101.9 107.2 95.07 5 93.8 92.6 101.28 10 91.6 91.1 100.48 20 87.8 87.3 100.57 30 85.3 85.1 100.23 40 83.7 83.3 100.51 50 83.2 83 100.25 60 82.9 82.7 100.26 61 82.6 82.6 99.99 70 82.2 82.2 99.91 80 81.4 81.4 99.94 90 82 81.3 100.78 100 81.5 81 100.7 110 80.9 81 99.84 120 80.7 80.7 100.05 130 80.5 80.1 100.38 140 79.6 79.8 99.7 150 79.3 79.1 100.26 160 76.9 77.8 98.85

[0086] Experimental Example 5

[0087] The symmetric cell performance of the solid-state sodium-ion batteries in Example 1 and Comparative Example 2 was tested using a LAND charge-discharge instrument. The test conditions were as follows: the batteries were allowed to stand at room temperature for more than 4 hours before testing began; a constant capacity of 0.111 mAh was set; and different current densities ranging from 0.05 to 1 mA cm⁻¹ were used. -2 Perform charging and discharging. Test results are as follows: Figure 8 As shown, the results indicate that the symmetrical cell using metallic sodium as an electrode operates at 0.2 mA·cm⁻¹. -2 A short circuit occurred at a current density of 1 mA·cm⁻¹, while the symmetrical cell with sodium metal loaded on a copper grid showed a short circuit at 1 mA·cm⁻¹. -2 The fact that it can still charge and discharge normally under high current density indicates that the copper mesh effectively isolates the direct contact between metallic sodium and electrolyte, avoiding interfacial reactions.

Claims

1. A solid-state sodium-ion battery, characterized by, The system includes a positive electrode, a solid electrolyte, and a negative electrode. The positive electrode comprises a positive current collector, a positive active material layer, and an electrolyte impregnated in the positive active material layer. The positive active material layer is composed of carbon-coated NASICON-type positive electrode material, a conductive agent, and a binder. The solid electrolyte is a sulfide solid electrolyte. The electrolyte consists of an electrolyte and a solvent. The electrolyte is sodium perchlorate and / or sodium hexafluorophosphate. The NASICON-type positive electrode material in the carbon-coated NASICON-type positive electrode material is Na... a M n (PO4) b The following conditions are met: 1.5 ≤ a ≤ 3, 1 ≤ n ≤ 4, 2 ≤ b ≤ 3.5; M is a transition metal selected from one or any combination of Ti, Mn, V, Fe, and Cr; the sulfide solid electrolyte is Na. 11 Sn2PS 12 Or Na3PS4; the negative electrode includes a copper mesh layer and a sodium metal layer loaded on one side of the copper mesh, the copper mesh layer facing the solid electrolyte.

2. The solid-state sodium-ion battery of claim 1, wherein, The mass ratio of the carbon-coated NASICON-type cathode material, conductive agent, and binder is (5~8):(1~4):

1.

3. The solid-state sodium-ion battery as described in claim 1 or 2, characterized in that, The mass of the electrolyte in the electrolyte solution impregnated in the positive electrode active material layer is 10% to 25% of the mass of the carbon-coated NASICON type positive electrode material in the positive electrode active material layer; the concentration of the electrolyte in the electrolyte solution is 1 mol / L.

4. The solid-state sodium-ion battery as described in claim 1 or 2, characterized in that, The NASICON-type cathode material is Na3MnTi(PO4)3.

5. The solid-state sodium-ion battery as described in claim 4, characterized in that, The a=b=3; the carbon-coated NASICON-type cathode material is prepared by a method including the following steps: heating and stirring a solution containing an organic carbon source, a transition metal salt and sodium dihydrogen phosphate to form a gel, then drying and pulverizing it in sequence, and then heating it in an inert atmosphere.

6. The solid-state sodium-ion battery of claim 5, wherein, The ratio of the molar amount of carbon in the organic carbon source to the molar amount of transition metal in the transition metal salt is (6~9):

1.

7. The solid-state sodium-ion battery of claim 5, wherein, The heating treatment was performed at a temperature of 650°C; the heating rate to the heating treatment temperature was 5°C / min; and the heating treatment time was 8 hours.

8. The solid-state sodium-ion battery of claim 1 or 2, wherein, The conductive agent is acetylene black and / or Super-P; the binder is polyvinylidene fluoride binder and / or sodium carboxymethyl cellulose binder.

9. The solid-state sodium-ion battery of either claim 1 or 2, wherein, The Na 11 Sn2PS 12 It is prepared by a method including the following steps: pressing an electrolyte precursor mixture consisting of sodium sulfide, sulfur powder, phosphorus pentasulfide and tin powder, and then sintering the pressed material in an inert atmosphere.

10. The solid-state sodium-ion battery of claim 9, wherein, The sintering temperature is 500℃ and the sintering time is 8h.

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