An armored vehicle low-temperature sodium ion battery and a preparation method thereof

Abstract

The application relates to the technical field of sodium ion batteries, in particular to a low-temperature sodium ion battery for armored vehicles and a preparation method thereof, which comprises a positive electrode sheet, a negative electrode sheet, a diaphragm, an electrolyte and a shell, the negative electrode sheet comprises a current collector and a negative electrode material coated on the current collector, the negative electrode material is composed of a composite powder comprising a hard carbon material, tin-based alloy particles and carbon nanotubes, the carbon nanotubes form a three-dimensional conductive network, the tin-based alloy particles are embedded in the pores of the hard carbon material or attached to the surface of the hard carbon material and are connected with each other through the carbon nanotube network; the unique composite negative electrode structure provides a fast ion and electron transmission channel, cooperates with a fluorinated ester-based high-concentration electrolyte with low viscosity and high ionic conductivity, and synergistically reduces the electrochemical polarization at low temperature, so that the battery can still maintain more than 80% of the initial capacity at an extreme low temperature of -40 DEG C and can be normally started and discharged.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a low-temperature sodium-ion battery for armored vehicles and its preparation method. Background Technology

[0002] Sodium-ion batteries are considered an important supplement to lithium-ion batteries in the field of large-scale energy storage due to their abundant resources and low cost. In recent years, exploration of their application in the power supply of special vehicles has gradually increased. However, applying sodium-ion batteries to armored vehicles faces the following problems: First, it has poor low-temperature performance. Traditional sodium-ion batteries use carbonate-based electrolytes (such as EC / DEC), which have a sharp increase in viscosity and a sharp drop in ionic conductivity when the temperature is below -20°C. At the same time, the ion insertion / extraction kinetics of the negative electrode (such as hard carbon) become sluggish, resulting in severe capacity decay and inability to start normally.

[0003] Secondly, the high power output capability is insufficient. Armored vehicles need to provide ultra-high power (pulse discharge) instantaneously during tactical actions such as assault and hill climbing. Conventional sodium-ion battery designs focus on energy density, and the electrode electronic conductivity, ion migration speed, and tab design are all difficult to meet the requirements of continuous or pulse discharge above 5C, resulting in severe internal resistance and heat generation.

[0004] Finally, the requirements for environmental adaptability and reliability are stringent. Military equipment needs to operate stably in a wide temperature range of -40℃ to 60℃ and in a high-intensity vibration and shock environment. This places higher demands on the interface stability, structural integrity and thermal management of batteries than on civilian products. Existing technologies mostly focus on the improvement of single materials and lack a systematic design from electrode structure and electrolyte formulation to battery construction, making it difficult to meet the comprehensive performance indicators of military applications. In view of this, we propose a low-temperature sodium-ion battery for armored vehicles and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings mentioned in the background section and provide a low-temperature sodium-ion battery for armored vehicles and its preparation method.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A low-temperature sodium-ion battery for armored vehicles includes: a positive electrode, a negative electrode, a separator, an electrolyte, and a casing; The negative electrode sheet includes a current collector and a negative electrode material coated thereon. The negative electrode material is composed of a composite powder comprising hard carbon material, tin-based alloy particles, and carbon nanotubes. In this composite structure, the carbon nanotubes are cross-linked to form a three-dimensional conductive network. The tin-based alloy particles are embedded in the pores of the hard carbon material or attached to the surface of the interconnected carbon nanotube network. This design comprehensively utilizes the excellent structural stability and rapid surface sodium storage capacity of hard carbon, the high specific capacity of tin-based alloys, and the role of carbon nanotube networks in improving electronic conductivity and buffering volume expansion. Specifically, based on the total mass of the composite powder, the mass percentage of the hard carbon material is 60%-75%, the mass percentage of the tin-based alloy particles is 20%-35%, and the mass percentage of the carbon nanotubes is 2%-8%. The tin-based alloy particles are tin-antimony alloys or tin-silver alloys with an average particle size of 50 nm to 200 nm. The hard carbon material is resin-based hard carbon with a specific surface area of ​​200 m². 2 / g to 600 m 2 / g; The electrolyte comprises a solvent, a sodium salt, and a film-forming additive. The solvent is ethyl 2,2-difluoroacetate (DFEA), and the sodium salt is sodium difluorosulfonamide. The molar concentration of the sodium salt in the electrolyte is 2.0 mol / L to 3.5 mol / L, constituting a high-concentration electrolyte system. The film-forming additive includes triallyl phosphate or lithium difluorooxalate borate. The total mass percentage of the film-forming additive in the electrolyte is 0.5% to 3%. This electrolyte system has the characteristics of low freezing point, low viscosity, and weak binding energy with sodium ions. It can effectively reduce the desolvation energy barrier at low temperatures, promote ion transport, and form a dense and stable solid electrolyte interphase (SEI) film. Both the negative and positive electrode plates have a bitab structure, symmetrically arranged on both sides of the electrode plate, in order to reduce the internal resistance and local current density of the battery during high-rate discharge, reduce heat generation, and improve the uniformity of current distribution.

[0007] Preferably, the diaphragm is a polyethylene-based diaphragm coated with ceramic particles (such as alumina or boehmite), the ceramic particles including alumina or boehmite, and the coating thickness is 2 to 5 micrometers to enhance the thermal stability and mechanical strength of the diaphragm.

[0008] Preferably, the positive electrode includes a current collector and a positive electrode material coated thereon, wherein the positive electrode material is a layered oxide (such as...). ) or polyanionic compounds (such as ).

[0009] Preferably, the current collector of the negative electrode is a copper foil with a roughened surface to enhance the adhesion of the slurry, and the material of the bipolar tab is nickel or nickel-plated copper.

[0010] A method for preparing a low-temperature sodium-ion battery for armored vehicles includes the following steps: S1. Preparation of negative electrode material: Hard carbon material, tin-based alloy particles and carbon nanotubes are placed in a ball mill jar in a predetermined ratio and mixed by high-energy ball milling under argon protection for 4-10 hours to obtain a uniform composite powder. S2. Preparation of negative electrode sheet: The composite powder obtained in step S1, the conductive agent (such as SuperP) and the binder are dispersed in deionized water or N-methylpyrrolidone (NMP) solvent at a mass ratio of (85-92):(3-8):(5-10), and stirred at high speed to prepare a negative electrode slurry. The binder is preferably a mixture of polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC-Na). The negative electrode slurry is uniformly coated on the current collector and dried at 80-120℃. Then, it is cold-pressed under a pressure of 10-50 MPa. Finally, the bipolar tabs are welded to obtain the negative electrode sheet. S3. Electrolyte preparation: In an argon atmosphere glove box with both moisture and oxygen content below 10 ppm, sodium difluorosulfonamide (NaFSI) is dissolved in ethyl 2,2-difluoroacetate solvent and magnetically stirred until completely dissolved to prepare a solution with a concentration of 2.0-3.5 mol / L. Then, the measured film-forming additive is added and the mixture is stirred until homogeneous to obtain the electrolyte. S4. Battery Assembly: The positive electrode, separator, and negative electrode are stacked or wound in sequence to form a battery cell. The battery cell is installed in an aluminum-plastic composite film shell or a metal shell, and the electrolyte prepared in step S3 is injected. After vacuum sealing and standing for 12-24 hours, a formation process is carried out: first, it is charged at a constant current rate of 0.05C to 2.0V, then charged at a constant current rate of 0.1C to 3.8V, and finally charged at a constant voltage of 3.8V until the current drops below 0.02C. After formation, an aging process is carried out: the battery is placed in an environment of 45-60℃ for 24-72 hours to obtain the low-temperature sodium-ion battery for armored vehicles.

[0011] Compared with the prior art, the beneficial effects of the present invention are: 1. The unique composite negative electrode structure of this invention provides a fast ion and electron transport channel. Combined with a low-viscosity, high-ionic-conductivity fluorinated ester-based high-concentration electrolyte, it synergistically reduces electrochemical polarization at low temperatures, enabling the battery to maintain more than 80% of its initial capacity even at extreme low temperatures of -40℃, and to start discharging normally. 2. The low-temperature sodium-ion battery of this invention has excellent high rate and pulse discharge capabilities. The three-dimensional carbon nanotube network and bipolar tab design in the negative electrode greatly reduce the overall internal resistance and electron transport path of the battery, enabling the battery to support continuous discharge and instantaneous pulse discharge of up to 5C and above, meeting the high power requirements of armored vehicles for acceleration, obstacle crossing, etc. 3. The carbon nanotube network of this invention effectively buffers the volume expansion of tin-based alloys during cycling. The high-concentration electrolyte and film-forming additives promote the formation of a robust SEI film, which together stabilizes the electrode structure. The ceramic-coated separator and the optimized electrolyte system also improve the thermal stability of the battery. Detailed Implementation

[0012] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0013] The present invention will describe the above technical solution in detail through the following embodiments: A method for preparing a low-temperature sodium-ion battery for armored vehicles includes the following steps: 1. Preparation of negative electrode material: Weigh 70 grams of phenolic resin-based hard carbon with an average particle size of 5 μm (specific surface area 350 m²). 2 25 grams of tin-antimony (SnSb) alloy particles with an average particle size of 100 nanometers and 5 grams of multi-walled carbon nanotubes were placed together in the agate jar of a planetary ball mill. High-purity argon gas was introduced into the jar to positive pressure, and the mixture was ball-milled at a speed of 300 rpm for 6 hours to obtain the composite anode material. 2. Negative electrode preparation: 90g of the above-mentioned composite negative electrode material, 5g of conductive carbon black Super P, and 5g of binder (a mixture of polyacrylic acid PAA and sodium carboxymethyl cellulose CMC-Na in a mass ratio of 7:3) were added to 100g of deionized water and stirred in a vacuum planetary mixer at 2000 rpm for 2 hours to obtain a uniform slurry. The slurry was then uniformly coated onto a roughened 12μm thick copper foil with a coating surface density of 8 mg / cm². 2 The electrodes were dried in a vacuum oven at 100°C for 12 hours, then rolled under a pressure of 30 MPa, and finally nickel bipolar tabs were welded to symmetrical positions on both sides of the electrodes. 3. Electrolyte preparation: In <0.1 ppm, In an argon glove box with a concentration of <0.1 ppm, ethyl 2,2-difluoroacetate (DFEA) solvent was added to a beaker, followed by slow addition of sodium bis(fluorosulfonyl)imide (NaFSI) solid. The mixture was magnetically stirred until completely dissolved to prepare an electrolyte base solution with a NaFSI concentration of 3.0 mol / L. Subsequently, 1% of triallyl phosphate (TAP) and 1% of lithium difluorooxalate borate (LiDFOB) by mass of the base solution were added, and stirring was continued for 2 hours to obtain the final electrolyte solution. 4. Positive electrode preparation: Purchase commercially available layered oxides (such as...) (NFM) is used as the positive electrode material. NFM, conductive carbon black and polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) at a mass ratio of 92:4:4 to form a slurry. The slurry is coated on aluminum foil, dried and rolled to obtain the positive electrode sheet. 5. Battery Assembly: Stack the positive electrode, the PE separator coated with boehmite (3μm thick), and the negative electrode in sequence, pack them into an aluminum-plastic composite film shell, inject sufficient electrolyte prepared in step 3, vacuum heat seal, and let stand at 25°C for 24 hours, then perform formation: charge at a constant current of 0.05C (1C=120 mA / g, based on the mass of the positive electrode material) to 2.0V, then charge at a constant current of 0.1C to 3.8V, and finally charge at a constant voltage of 3.8V until the current <0.02C. After formation, place the battery in a 50°C oven for 48 hours to age, and obtain a soft-pack battery cell.

[0014] Example 2 The only difference between this embodiment and Embodiment 1 is that the negative electrode material ratio in step 1 of this embodiment is as follows: 65 grams of hard carbon of the same specification, 30 grams of tin-antimony (SnSb) alloy particles, and 5 grams of carbon nanotubes are weighed out, and all other conditions are the same.

[0015] Example 3 The only difference between this embodiment and Embodiment 1 is that in this embodiment, the electrolyte preparation in step 3 is as follows: a base electrolyte solution with a NaFSI concentration of 2.5 mol / L is prepared, and only 2% by mass of lithium difluorooxalate borate (LiDFOB) is added as a film-forming additive, while all other conditions are the same.

[0016] Example 4 The only difference between this embodiment and Embodiment 1 is that the ball milling mixing time in step 1 is adjusted to 8 hours; and in step 4, the positive electrode material is a polyanionic compound (such as...). The adhesive system remains unchanged; the aging process in step 5 is adjusted to aging at 60℃ for 24 hours, while other conditions remain the same.

[0017] Comparative Example 1 The only difference between this comparative example and Example 1 is that in step 1 of this comparative example, the negative electrode material is only 100 grams of phenolic resin-based hard carbon from the same batch, without the addition of tin-antimony (SnSb) alloy particles and carbon nanotubes, while all other conditions are the same.

[0018] Comparative Example 2 The only difference between this comparative example and Example 1 is that this comparative example uses 1.0 mol / L. Dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC = 1:1, volume ratio), without adding any special film-forming additives, and under all other conditions being the same.

[0019] Comparative Example 3 The only difference between this comparative example and Example 1 is that in steps 2 and 5 of this comparative example, both the negative electrode and the positive electrode adopt the traditional single-tab design, and the tabs are welded to the same side of the electrode sheet. All other conditions are the same.

[0020] Comparative Example 4 The only difference between this comparative example and Example 1 is that the negative electrode material ratio in step 1 of this comparative example is as follows: 50 grams of hard carbon of the same specification, 45 grams of tin-antimony (SnSb) alloy particles, and 5 grams of carbon nanotubes are weighed. The alloy content in this ratio exceeds the range defined in claim 2 of this invention, while all other conditions are the same.

[0021] Based on Examples 1-4 and Comparative Examples 1-4 above, soft-pack battery samples were prepared and their performance was tested. The specific performance testing steps are as follows: 1. Room temperature capacity and first-efficiency test (25℃): Procedure: After the battery has been left to stand in a constant temperature chamber at 25℃ for 2 hours, it is charged at a constant current of 0.1C to 3.8V, then charged at a constant voltage until the current is ≤0.02C. After standing for 5 minutes, it is discharged at a constant current of 0.1C to 2.0V. The initial charge capacity (Qc) and discharge capacity (Qd) are recorded, and the initial charge and discharge efficiency (first efficiency, CE=Qd / Qc×100%) is calculated. This cycle is repeated 3 times, and the discharge capacity of the 3rd cycle is taken as the rated capacity at room temperature (C0).

[0022] 2. Low-temperature discharge performance test (-40℃): Procedure: The battery that has completed the room temperature test is fully charged to 3.8V at 0.1C at 25℃, and then transferred to a -40℃ low temperature test chamber for constant temperature storage for 8 hours. After that, it is directly discharged to 2.0V at a constant current of 0.2C in the low temperature chamber, and the discharge capacity (C_low) is recorded. The low temperature capacity retention rate is calculated by the formula: (C_low / C0)×100%.

[0023] 3. High-rate discharge performance test (25℃): Procedure: The battery was fully charged to 3.8V at 0.1C at 25℃. After standing for 5 minutes, it was discharged at constant current to 2.0V at 1C, 3C, and 5C rates respectively. The discharge capacity at each rate (C_1C, C_3C, C_5C) was recorded. Rate performance was evaluated as C_5C / C_1C×100%. At the same time, during the 5C discharge, the temperature change at the center point of the battery surface was monitored using a thermocouple, and the maximum temperature rise (ΔT) was recorded.

[0024] 4. Cycle life test (25℃, 1C / 1C): Procedure: Charge the battery at 25°C with a constant current of 1C to 3.8V, then switch to constant voltage charging until the current is ≤0.02C. Let it stand for 2 minutes, then discharge it with a constant current of 1C to 2.0V. This is one charge-discharge cycle. Repeat this cycle until the discharge capacity decays to 80% of the discharge capacity of the first cycle. Record the number of cycles (N) at this point.

[0025] The specific data is shown in the table below: Note: Due to the different cathode materials, the capacity and voltage plateau of Example 4 are inherently different from those of the NFM-based system, which is normal.

[0026] The data in the table above shows that: All embodiments (1-4) of the present invention exhibited excellent capacity retention of over 80% at -40℃, which is far higher than that of the comparative examples using traditional hard carbon anodes (Comparative Example 1, 32.7%) or conventional electrolytes (Comparative Example 2, 41.5%), fully verifying the significant effect of the composite anode and special electrolyte in synergistically improving low-temperature performance.

[0027] Under high-rate (5C) discharge, the embodiment of the present invention exhibits high capacity retention (>90%) and low temperature rise (<16°C), which is superior to all comparative examples, especially comparative example 3 (without bipolar tabs), which has a significantly higher temperature rise during 5C discharge, demonstrating the key role of the bipolar tab structure in improving heat dissipation at high rates.

[0028] In terms of cycle life, Examples 1-4 all showed good stability, while Comparative Example 4 (imbalanced negative electrode ratio) had a high initial capacity but the fastest cycle decay, proving that controlling the ratio of composite negative electrode components within the range defined in the claims is crucial for maintaining long-term structural stability. Based on the data in the table above, Example 1 is preferred.

[0029] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A low-temperature sodium-ion battery for armored vehicles, comprising: The positive electrode, negative electrode, separator, electrolyte, and casing are characterized in that: The negative electrode sheet includes a current collector and a negative electrode material coated thereon. The negative electrode material is composed of a composite powder including hard carbon material, tin-based alloy particles and carbon nanotubes, wherein the carbon nanotubes form a three-dimensional conductive network, and the tin-based alloy particles are embedded in the pores of the hard carbon material or attached to its surface and interconnected with each other through the carbon nanotube network. The electrolyte comprises a solvent, a sodium salt, and a film-forming additive. The solvent is ethyl 2,2-difluoroacetate, the sodium salt is sodium difluorosulfonamide, and the molar concentration of the sodium salt in the electrolyte is 2.0 mol / L to 3.5 mol / L. Both the negative electrode and the positive electrode have bipolar tabs, which are symmetrically arranged on both sides of the electrode.

2. The low-temperature sodium-ion battery for armored vehicles as described in claim 1, characterized in that: Based on the total mass of the composite powder, the hard carbon material accounts for 60%-75% of the mass, the tin-based alloy particles account for 20%-35% of the mass, and the carbon nanotubes account for 2%-8% of the mass.

3. The low-temperature sodium-ion battery for armored vehicles as described in claim 2, characterized in that: The tin-based alloy particles are tin-antimony alloys or tin-silver alloys, with an average particle size of 50 nanometers to 200 nanometers; the hard carbon material is resin-based hard carbon with a specific surface area of ​​200 m². 2 / g to 600 m 2 / g.

4. The low-temperature sodium-ion battery for armored vehicles as described in claim 1, characterized in that: The film-forming additive includes triallyl phosphate or lithium difluorooxalate borate, and the total mass percentage of the film-forming additive in the electrolyte is 0.5% to 3%.

5. The low-temperature sodium-ion battery for armored vehicles as described in claim 3, characterized in that: The diaphragm is a polyethylene-based diaphragm coated with ceramic particles, including alumina or boehmite, and the coating thickness is 2 to 5 micrometers.

6. The low-temperature sodium-ion battery for armored vehicles as described in claim 1, characterized in that: The positive electrode includes a current collector and a positive electrode material coated thereon, wherein the positive electrode material is a layered oxide or a polyanionic compound.

7. The low-temperature sodium-ion battery for armored vehicles as described in claim 1, characterized in that: The current collector of the negative electrode is a copper foil with a roughened surface, and the material of the bipolar tab is nickel or nickel-plated copper.

8. A method for preparing a low-temperature sodium-ion battery for armored vehicles as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Preparation of negative electrode material: Hard carbon material, tin-based alloy particles and carbon nanotubes are mixed in a predetermined ratio by high-energy ball milling under an inert atmosphere for 4-10 hours to obtain the composite powder. S2. Preparation of negative electrode sheet: The composite powder, conductive agent and binder are dispersed in a solvent at a mass ratio of (85-92):(3-8):(5-10) to prepare a negative electrode slurry. The slurry is uniformly coated on the current collector, dried and cold-pressed, and then the bipolar tabs are welded to obtain the negative electrode sheet. S3. Electrolyte preparation: In an inert atmosphere glove box with both moisture and oxygen content below 10 ppm, sodium difluorosulfonamide is dissolved in ethyl 2,2-difluoroacetate to prepare a solution with a concentration of 2.0-3.5 mol / L. Then, film-forming additives are added and mixed evenly to obtain the electrolyte. S4. Battery assembly: The positive electrode, separator, and negative electrode are stacked or wound in sequence to form a battery cell. The battery cell is installed in the battery casing and injected with the electrolyte prepared in step S3. After vacuum sealing, standing, formation and aging processes, the low-temperature sodium-ion battery for armored vehicles is obtained.

9. The method for preparing a low-temperature sodium-ion battery for armored vehicles as described in claim 8, characterized in that: In step S2, the adhesive is a mixture of polyacrylic acid and sodium carboxymethyl cellulose, the drying temperature is 80°C to 120°C, and the cold pressing pressure is 10 MPa to 50 MPa.

10. The method for preparing a low-temperature sodium-ion battery for armored vehicles as described in claim 8, characterized in that: In step S4, the formation process adopts a stepped current charging method, first charging to 2.0V with a constant current of 0.05C, then charging to 3.8V with a constant current of 0.1C, and then charging at a constant voltage of 3.8V until the current drops below 0.02C; the aging process is carried out at a temperature of 45°C to 60°C for 24 to 72 hours.

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