A sodium ion battery

Abstract

The embodiment of the present application provides a sodium ion battery, which relates to the field of new energy. The sodium ion battery includes a battery cell and an electrolyte; the battery cell includes a plurality of positive and negative electrode sheets alternately stacked, the components of the positive and negative slurries attached to the surfaces of the positive and negative electrode sheets are set within a suitable range, and the electrolyte includes a main material, a solvent, and an auxiliary material; the main material contains sodium bis(trifluoromethanesulfonyl)imide; the auxiliary material includes at least one of sodium tetrafluoroborate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, vinyl sulfate, and trimethyl methyl phosphate. In the embodiment of the present application, the solvent and auxiliary materials in the electrolyte cooperate with each other, and are matched with specific positive electrode slurries and negative electrode slurries, which can improve the safety performance of the sodium ion battery and the battery capacity performance at high temperature, and is conducive to expanding the application scenarios of the sodium ion battery.

Description

Technical Field

[0001] The present application relates to the field of new energy, and specifically, to a sodium ion battery. Background Art

[0002] As an important component of new energy technology, lithium-ion batteries have become the most important energy carrier and are used in all aspects of society, such as energy storage facilities, power facilities, and home facilities, due to their high energy density, low self-discharge, environmental friendliness, no memory effect, and excellent cycle performance. However, the distribution of lithium resources is extremely uneven around the world, and my country's reserves are relatively small. The current surge in lithium carbonate prices has become the most prominent problem in the development of many lithium-ion manufacturing companies.

[0003] Compared with lithium-ion batteries, sodium-ion batteries have the advantages of low-cost and easy-to-obtain raw materials, good power performance, excellent high and low temperature performance, and better safety performance. They have good application prospects in the two-wheeled vehicle and small energy storage markets.

[0004] However, there are some outstanding problems in the development stage of current sodium-ion batteries, especially in terms of safety performance and battery capacity performance at high temperatures. For example, existing cylindrical sodium-ion batteries still cannot pass some safety test items, especially the 100% SOC puncture test of the battery cell; and the capacity retention rate of existing cylindrical sodium-ion batteries in high-temperature shelf tests is significantly lower than that of lithium-ion batteries; these problems have limited the application scope (scenario) of sodium-ion batteries to a certain extent. Summary of the invention

[0005] The embodiments of the present application can provide a sodium ion battery, which can improve the safety performance of the sodium ion battery and the battery capacity performance at high temperatures, and is conducive to expanding the application scenarios of the sodium ion battery.

[0006] The sodium ion battery provided in the embodiment of the present application includes a battery cell and an electrolyte; the battery cell includes a plurality of positive electrode sheets and negative electrode sheets alternately stacked, a positive electrode slurry is attached to the surface of each positive electrode sheet, a negative electrode slurry is attached to the surface of each negative electrode sheet, and a separator is provided between adjacent positive electrode sheets and negative electrode sheets; the positive electrode sheets and the negative electrode sheets are both made of aluminum foil; in terms of mass percentage, the positive electrode slurry includes 97.3% to 98.4% of a positive electrode active material, 0.3% to 0.5% of a conductive agent, and 1.2% to 2 .2% of binder; by mass percentage, the negative electrode slurry includes 96.5% to 97.4% of negative electrode active material, 0.2% to 0.4% of conductive agent, 1.0% to 1.2% of thickener, and 1.3% to 2.0% of binder; the components of the electrolyte include main ingredients, solvents, and auxiliary materials; the main ingredient contains sodium bistrifluoromethanesulfonyl imide; the auxiliary materials include at least one of sodium tetrafluoroborate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, vinyl sulfate, and methyl trimethyl phosphate.

[0007] In the above technical solution, the separator in the battery cell can separate the positive electrode sheet from the negative electrode sheet, prevent the positive electrode sheet from directly contacting the negative electrode sheet, and ensure that there is no short circuit inside the sodium ion battery. In addition, in the embodiment of the present application, the material of the positive electrode sheet and the negative electrode sheet is the same, and no potential difference is formed. The potential difference is formed by coating different types of slurries on the surface of the positive and negative electrode sheets, thereby forming a current and transmitting it to the outside.

[0008] In the embodiment of the present application, the applicant found that in the battery cell, the content of the conductive agent in the positive electrode slurry is controlled within the range of 0.3% to 0.5%, and the content of the conductive agent in the negative electrode slurry is controlled within the range of 0.2% to 0.4%, which can improve the safety performance of the battery without affecting the electrical performance of the battery, making it easy to pass the needle test. In addition, in the components of the electrolyte, the solvent can dissolve the main material and the auxiliary material. When the electrolyte is used in a sodium ion battery, the main material and the auxiliary material can play the role of transmitting ions so that the sodium ion battery can work normally; and the sodium bis(trifluoromethanesulfonyl imide) in the main material can improve the conductivity and thermal stability of the electrolyte. In addition, the auxiliary material can not only improve the battery performance of the sodium ion battery at high temperature, but also has a certain flame retardant effect, which can improve the safety performance of the sodium ion battery. Moreover, in the electrolyte of the embodiment of the present application, there is a synergistic effect between sodium bis(trifluoromethanesulfonyl imide) and the auxiliary material, which can further improve the safety performance of the sodium ion battery and the battery capacity performance at high temperature.

[0009] In addition, in the embodiments of the present application, the specific content of the conductive agent and the specific components of the electrolyte cooperate with each other and work synergistically to better improve the safety performance of the sodium ion battery and the battery capacity performance at high temperature, which is conducive to expanding the application scenarios of the sodium ion battery.

[0010] In a possible implementation, the main material also contains sodium hexafluorophosphate, and the mass ratio of sodium hexafluorophosphate to sodium bis(trifluoromethanesulfonyl)imide is not higher than 5:1.

[0011] In the above technical scheme, the sodium hexafluorophosphate in the electrolyte can play a good role in carrying sodium ions when dissolved in the electrolyte solvent, thereby ensuring the normal operation of the sodium ion battery; and the mass ratio of sodium hexafluorophosphate and sodium bis(trifluoromethanesulfonyl)imide is controlled within an appropriate range, which is beneficial to further improve the conductivity of the main material.

[0012] In a possible implementation, the components in the electrolyte are calculated by mass percentage, the amount of the main material is 10% to 15%, the amount of the solvent is 80% to 85%, and the amount of the auxiliary material is 1% to 10%.

[0013] In a possible implementation, the solvent includes, by volume percentage, 30% to 45% of ethylene carbonate, 35% to 45% of dimethyl carbonate, and 10% to 20% of ethylene glycol dimethyl ether.

[0014] In a possible implementation, the positive electrode active material is a layered transition metal oxide.

[0015] In the above technical solution, the transition metal oxide has a high gram capacity, which is conducive to improving the electrical performance of sodium ion batteries; and the reserves of transition metal elements are abundant, and the synthesis process of their oxides is simple, which is conducive to reducing the preparation cost of sodium ion batteries. In addition, the use of layered transition metal oxides as positive electrode active materials can be well compatible with existing lithium ion battery production processes.

[0016] In a possible implementation, the particle size distribution D50 of the positive electrode active material is 7.0-15.0 μm; and / or the tap density of the positive electrode active material is ≥2.2 g / cm 3 ; and / or, the specific surface area of ​​the positive electrode active material is 0.1 to 0.6 m 2 / g.

[0017] In a possible implementation, the negative electrode active material is hard carbon particles.

[0018] In the above technical solution, the hard carbon structure has high isotropy, which enables sodium ions to be embedded and removed from all angles, greatly improving the charge and discharge speed, rate and low-temperature performance of sodium-ion batteries. In addition, hard carbon does not have solvent co-embedding and significant lattice expansion and contraction, which greatly promotes the cycle and rate performance of sodium-ion batteries.

[0019] In a possible implementation, the particle size distribution D50 of the negative electrode active material is 5.0 to 9.0 μm;

[0020] and / or the specific surface area of ​​the negative electrode active material is 2.5 to 4.5 m 2 / g;

[0021] And / or, the compaction density of the negative electrode active material is 1.0 to 1.4 g / cm 3 .

[0022] In a possible implementation, the diaphragm is a polyethylene ceramic coated diaphragm, and aluminum oxide nanomaterials are attached to the surface of the diaphragm.

[0023] In the above technical solution, the polyethylene ceramic coated diaphragm can improve the processing and safety performance of the sodium ion battery to a certain extent; and the surface of the diaphragm is attached with aluminum oxide nanomaterials, which can make the diaphragm have excellent thermal conductivity, good wettability and excellent flame retardant properties.

[0024] In a possible implementation, the thickness of the separator is 12-18 μm.

[0025] In the above technical solution, the thickness of the diaphragm is controlled within the range of 12 to 18 μm, which can improve the heat resistance and mechanical properties of the diaphragm without affecting the transmission of sodium ions, ensure that the diaphragm is not easily damaged, thereby reducing the probability of internal short circuit in the sodium ion battery and improving the safety performance of the sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 The figure is a diagram showing the capacity change of the sodium ion batteries in Example 3 and Comparative Example 2 during the cycle test. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0029] The electrolyte and sodium ion battery of the embodiments of the present application are described in detail below.

[0030] The electrolyte components in the embodiment of the present application include a main material, a solvent, and an auxiliary material. In this embodiment, based on mass percentage, the amount of the main material is 10% to 15%, the amount of the solvent is 80% to 85%, and the amount of the auxiliary material is 1% to 10%.

[0031] The solvent can dissolve the main material and the auxiliary material. When the electrolyte is used in a sodium ion battery, the main material and the auxiliary material can play the role of transporting ions so that the sodium ion battery can work normally. Therefore, as an example, in the embodiment of the present application, the main material contains sodium hexafluorophosphate and sodium bis(trifluoromethanesulfonyl imide. When sodium hexafluorophosphate is dissolved in the electrolyte solvent, it can play a good role in carrying sodium ions and ensure the normal operation of the sodium ion battery; sodium bis(trifluoromethanesulfonyl imide) can improve the conductivity and thermal stability of the electrolyte, and more specifically, in this embodiment, the mass ratio of sodium hexafluorophosphate and sodium bis(trifluoromethanesulfonyl imide is not more than 5:1. By controlling the mass ratio of sodium hexafluorophosphate and sodium bis(trifluoromethanesulfonyl imide within a suitable range, it is beneficial to further improve the conductivity of the main material.

[0032] In this embodiment, the solvent includes 30% to 45% of ethylene carbonate, 35% to 45% of dimethyl carbonate, and 10% to 20% of ethylene glycol dimethyl ether by volume to better dissolve the main ingredients and auxiliary ingredients.

[0033] The auxiliary materials can not only improve the battery performance of the sodium ion battery at high temperature, but also have a certain flame retardant effect, which can improve the safety performance of the sodium ion battery. The auxiliary materials include at least one of sodium tetrafluoroborate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, vinyl sulfate, and trimethyl methyl phosphate. The applicant has found that these auxiliary materials can also form a synergistic effect with sodium bis(trifluoromethanesulfonyl)imide and the auxiliary materials, which can further improve the safety performance of the sodium ion battery and the battery capacity performance at high temperature.

[0034] The structure of the sodium ion battery in the embodiment of the present application is as follows:

[0035] The sodium ion battery comprises a battery cell and the above-mentioned battery electrolyte; the battery cell comprises a plurality of positive electrode sheets and negative electrode sheets alternately stacked, a positive electrode slurry is attached to the surface of each positive electrode sheet, a negative electrode slurry is attached to the surface of each negative electrode sheet, and a diaphragm is arranged between adjacent positive electrode sheets and negative electrode sheets to separate the positive electrode sheets from the negative electrode sheets, prevent the positive electrode sheets from directly contacting the negative electrode sheets, and ensure that a short circuit does not occur inside the sodium ion battery.

[0036] Although sodium-ion batteries have similar principles to lithium batteries, they still have many differences. For example, in sodium-ion batteries, the positive and negative electrodes are both made of aluminum foil, and the two do not form a potential difference just through the electrodes. Instead, they form a potential difference by coating the surface with different types of slurries, which then form current and transmit it to the outside. Therefore, the performance of the slurry is crucial to the electrical performance of sodium-ion batteries.

[0037] In the embodiments of the present application, the applicant found that, whether it is the positive electrode slurry or the negative electrode slurry, as long as the content of the conductive agent in the slurry is appropriately reduced and then matched with the above-mentioned electrolyte, the safety performance of the battery can be improved without affecting the electrical performance of the battery, making it easy to pass the needle puncture test. In addition, in the sodium ion battery, by setting a specific content of the conductive agent, it can also cooperate with the above-mentioned electrolyte to better improve the safety performance of the sodium ion battery and the battery capacity performance at high temperature, which is conducive to expanding the application scenarios of the sodium ion battery.

[0038] Specifically, in the embodiment of the present application, the positive electrode slurry includes 97.3% to 98.4% of the positive electrode active material, 0.3% to 0.5% of the conductive agent, and 1.2% to 2.2% of the binder by mass percentage; the negative electrode slurry includes 96.5% to 97.4% of the negative electrode active material, 0.2% to 0.4% of the conductive agent, 1.0% to 1.2% of the thickener, and 1.3% to 2.0% of the binder by mass percentage.

[0039] It should be noted that the slurry generally needs to be dissolved in a specific dissolving liquid before it can be coated on the surface of the current collector electrode, and then the electrode coated with the slurry is rolled, cut and sliced ​​to form the electrode for preparing the battery cell. In the embodiment of the present application, whether it is the positive electrode slurry or the negative electrode slurry, the mass percentage of its specific components does not include the mass of the dissolving liquid, but is only the mass percentage of each component compared to the total solid component. In addition, in this embodiment, N-methylpyrrolidone and anhydrous oxalic acid are generally used to dissolve the positive electrode slurry, and deionized water is used to dissolve the negative electrode slurry.

[0040] As an example, in the present embodiment, the positive electrode active material in the positive electrode slurry is a layered transition metal oxide ("layered" means that the lattice of the metal oxide is layered); the transition metal oxide has a high gram capacity, which is beneficial to improving the electrical performance of the sodium ion battery; and the reserves of transition metal elements are abundant, and the synthesis process of their oxides is simple, which is beneficial to reducing the preparation cost of sodium ion batteries. In addition, the use of layered transition metal oxides as positive electrode active materials can be well compatible with existing lithium ion battery production processes. More specifically, in the present embodiment, the particle size distribution D50 of the positive electrode active material is 7.0~15.0μm; and / or, the tap density of the positive electrode active material is ≥2.2g / cm3 ; and / or, the specific surface area of ​​the positive electrode active material is 0.1 to 0.6 m 2 For the sake of comparison, in all the examples and comparative examples of the present application, the particle size distribution D50 of the transition metal oxide is 11 μm, and the tap density is 2.3 g / cm 3 The specific surface area of ​​the positive electrode active material is 0.4m 2 In addition, in this embodiment, the binder in the positive electrode slurry is generally a PVDF binder (PVDF is Polyvinylidene Difluoride, polyvinylidene fluoride resin), and the conductive agent is generally a conductive agent SP (i.e. conductive carbon black, SP represents super pure purity).

[0041] As an example, in the present embodiment, the negative electrode active material in the negative electrode slurry is hard carbon particles. The hard carbon structure has high isotropy, which enables sodium ions to be embedded and migrated from all angles, greatly improving the charge and discharge speed, rate and low temperature performance of the sodium ion battery. Moreover, the solvent co-embedding and significant lattice expansion and contraction phenomena that will not occur in hard carbon greatly promote the cycle and rate performance of sodium ion batteries. More specifically, in the present embodiment, the particle size distribution D50 of the negative electrode active material is 5.0~9.0μm; and / or, the specific surface area of ​​the negative electrode active material is 2.5~4.5m 2 / g; and / or, the compaction density of the negative electrode active material is 1.0 to 1.4 g / cm 3 For the sake of comparison, in all the examples and comparative examples of this application, the particle size distribution D50 of the transition metal oxide is 7 μm, and the compacted density is 1.2 g / cm 3 The specific surface area of ​​the negative electrode active material is 3.5m 2 / g. In addition, in this embodiment, the binder in the negative electrode slurry is generally an SBR binder (SBR is butadiene-styrene latex, butadiene styrene latex), the conductive agent is generally a conductive agent SP, and the thickener is generally CMC (Carboxymethyl cellulose, carboxymethyl cellulose).

[0042] As an example, the diaphragm in this embodiment is a polyethylene ceramic coated diaphragm, and aluminum oxide nanomaterials are attached to the surface of the diaphragm. The polyethylene ceramic coated diaphragm can improve the processing and safety performance of the sodium ion battery to a certain extent; and the aluminum oxide nanomaterials are attached to the surface of the diaphragm, which can make the diaphragm have excellent thermal conductivity, good wettability and excellent flame retardant properties. In addition, the thickness of the diaphragm in this embodiment is generally 12 to 18 μm, which can improve the heat resistance and mechanical properties of the diaphragm without affecting the transmission of sodium ions, and ensure that the diaphragm is not easily damaged, thereby reducing the probability of internal short circuits in sodium ion batteries and improving the safety performance of sodium ion batteries.

[0043] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0044] Example 1

[0045] This embodiment provides a sodium ion battery, and the preparation method thereof is as follows:

[0046] The positive electrode active material layered metal oxide, conductive agent SP, and binder PVDF are mixed with solvent N-methylpyrrolidone and anhydrous oxalic acid in a mass ratio of 97.6%, 0.4%, and 2.0%, respectively, to form a positive electrode slurry. The positive electrode slurry is coated on the surface of the current collector aluminum foil, and then rolled, cut, and sliced ​​to form a positive electrode sheet.

[0047] The negative electrode active material graphite, the conductive agent SP, the thickener CMC, the binder SBR according to the mass proportions of 96.8%, 0.3%, 1.2%, 1.7% respectively and the solvent deionized water are mixed to form a negative electrode slurry.

[0048] The negative electrode slurry is coated on the surface of the current collector aluminum foil, and then the negative electrode sheet is finally formed through rolling, slitting and sheeting. The positive electrode sheet, negative electrode sheet and separator are prepared by single-pole winding. The separator is a double-sided ceramic and glue 16μm PE film. Then the battery preparation is completed through assembly, electrolyte injection, sealing, formation, aging and capacity division processes.

[0049] The electrolyte comprises, by mass percentage, 12.5% ​​of a main material, 85% of a solvent and 2.5% of an auxiliary material.

[0050] The main material is sodium bis(trifluoromethanesulfonyl)imide; the solvent is ethylene carbonate, dimethyl carbonate and ethylene glycol dimethyl ether in a volume ratio of 40%:45%:15%; and the auxiliary materials are sodium tetrafluoroborate and fluoroethylene carbonate in a mass ratio of 1:2.

[0051] Example 2

[0052] This embodiment provides a sodium ion battery. The preparation of the sodium ion battery is different from that of the embodiment 1, mainly in that the electrolyte is different. Specifically, the composition of the electrolyte in this embodiment is as follows:

[0053] The main ingredients are sodium hexafluorophosphate and sodium bistrifluoromethanesulfonimide in a mass ratio of 5:1; the solvent is ethylene carbonate, dimethyl carbonate and ethylene glycol dimethyl ether in a volume ratio of 40%:45%:15%; and the auxiliary materials are sodium tetrafluoroborate and fluoroethylene carbonate in a mass ratio of 1:2.

[0054] Example 3

[0055] This embodiment provides a sodium ion battery. The preparation of the sodium ion battery is different from that of the embodiment 1, and the difference mainly lies in the difference of the electrolyte. Specifically, the composition of the electrolyte in this embodiment is as follows:

[0056] The main ingredients are sodium hexafluorophosphate and sodium bistrifluoromethanesulfonimide in a mass ratio of 5:1; the solvent is ethylene carbonate, dimethyl carbonate and ethylene glycol dimethyl ether in a volume ratio of 40%:45%:15%; the auxiliary materials are sodium tetrafluoroborate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, vinyl sulfate and trimethyl methyl phosphate in a mass ratio of 1:1:1:2:1:10.

[0057] Comparative Example 1

[0058] This comparative example provides a sodium ion battery, and the preparation method thereof is as follows:

[0059] The layered metal oxide, conductive agent SP, and binder PVDF are mixed with solvent N-methylpyrrolidone and anhydrous oxalic acid in a mass ratio of 97.3%, 0.7%, and 2.0% respectively to form a positive electrode slurry. The positive electrode slurry is coated on the surface of the current collector aluminum foil, and then rolled, cut, and made into a sheet to form a positive electrode sheet.

[0060] The negative electrode active material graphite, conductive agent SP, thickener CMC, binder SBR are mixed with solvent deionized water in a mass ratio of 96.5%, 0.6%, 1.3%, 1.6% respectively to form a negative electrode slurry. The negative electrode slurry is coated on the surface of the current collector aluminum foil, and then rolled, cut and sliced ​​to form a negative electrode sheet.

[0061] The positive electrode sheet, negative electrode sheet and separator are wound in a bipolar ear manner to prepare a winding core. The separator is a PE (Polyethylene) film with a thickness of 16μm and coated with ceramic on both sides. The battery is then assembled, injected with electrolyte, sealed, formed, aged and divided into different capacities.

[0062] The electrolyte in this comparative example is the same as that in Example 1.

[0063] Comparative Example 2

[0064] This comparative example provides a sodium ion battery, and the preparation method thereof is as follows:

[0065] The positive electrode active material layered metal oxide, conductive agent SP, and binder PVDF are mixed with solvent N-methylpyrrolidone and anhydrous oxalic acid in a mass ratio of 97.0%, 1.0%, and 2.0%, respectively, to form a positive electrode slurry. The positive electrode slurry is coated on the surface of the current collector aluminum foil, and then rolled, cut, and made into a positive electrode sheet.

[0066] The negative electrode active material graphite, conductive agent SP, thickener CMC, binder SBR are mixed with solvent deionized water in a mass ratio of 96.2%, 0.9%, 1.2%, 1.7% respectively to form a negative electrode slurry. The negative electrode slurry is coated on the surface of the current collector aluminum foil, and then rolled, cut and sliced ​​to form a negative electrode sheet. The positive electrode sheet, negative electrode sheet and separator are prepared by bipolar ear winding. The separator is an ordinary PE film without ceramic coating, and the film thickness is 16μm.

[0067] The battery preparation is completed through the processes of assembly, electrolyte injection, sealing, formation, aging and capacity division.

[0068] The electrolyte comprises 12.5% ​​of a main material, 85% of a solvent and 2.5% of an auxiliary material by mass percentage. The main material is sodium hexafluorophosphate; the solvent is ethylene carbonate and dimethyl carbonate in a volume ratio of 2:3; and the auxiliary material is fluoroethylene carbonate.

[0069] Application Examples

[0070] Six sodium ion batteries were provided for each embodiment and each comparative example, and then the sodium ion batteries in embodiments 1 to 3 and comparative examples 1 to 2 were subjected to a shelf performance test and a safety performance test, respectively. The test methods and test results are as follows:

[0071] Shelf performance test: 0.5C constant current and constant voltage charging to 3.95V, cut-off current 0.05C; 60℃ shelf for 7 days, 0.5C constant current discharge to 1.5V, test the battery capacity of the embodiment and the comparative example before and after shelf.

[0072] Safety performance test: 0.5C constant current and constant voltage charging to 3.95V, current cut-off 0.05C. At 23±2℃, fix the thermocouple on the surface of the fully charged battery and place it in a fume hood, pierce the center of the largest surface with a 3mm diameter stainless steel needle at a speed of 20mm / s, and keep it for 1h.

[0073] The results of the shelf performance test and safety performance test are shown in the following table:

[0074] Table 1 Shelf performance test results of Examples 1 to 3 and Comparative Examples 1 to 2:

[0075]

[0076] It can be seen from Table 1 that, compared with the comparative example, the sodium ion battery in the embodiment has little change in battery capacity after being placed at high temperature, and the sodium ion battery in the embodiment is not easy to catch fire after being punctured by a needle, but the sodium ion battery in the comparative example will catch fire after being punctured by a needle, and has good safety performance.

[0077] In addition, the cycle performance test of Example 3 and Comparative Example 2 was also carried out. The test method was 1C cycle test: 1C constant current constant voltage charging to 3.95V, cut-off current 0.05C, 1C constant current discharge to 1.5V, the test environment was 23±2℃, and the test results were as follows: Figure 1 shown.

[0078] As can be seen from the figure, compared with Comparative Example 2, after 2000 cycles, the battery capacity of Example 3 can be maintained at more than 80%, and its cycle test performance is much better than that of Comparative Example 2.

[0079] The above are only embodiments of the present application and are not intended to limit the scope of protection of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A sodium ion battery, characterized in that: It includes a battery cell and an electrolyte; The battery cell comprises a plurality of positive electrode sheets and negative electrode sheets alternately stacked, a positive electrode slurry is attached to the surface of each positive electrode sheet, a negative electrode slurry is attached to the surface of each negative electrode sheet, and a separator is arranged between adjacent positive electrode sheets and negative electrode sheets; the positive electrode sheets and the negative electrode sheets are both made of aluminum foil; The positive electrode slurry comprises, by mass percentage, 97.3% to 98.4% of a positive electrode active material, 0.3% to 0.4% of a conductive agent, and 1.2% to 2.2% of a binder; The negative electrode slurry comprises, by mass percentage, 96.5% to 97.4% of a negative electrode active material, 0.2% to 0.4% of a conductive agent, 1.0% to 1.2% of a thickener, and 1.3% to 2.0% of a binder; The components of the electrolyte include solvent, main material and auxiliary material; the main material contains sodium bis(trifluoromethanesulfonyl)imide, and the auxiliary material includes at least one of sodium tetrafluoroborate, vinylene carbonate, propylene sulfite, fluoroethylene carbonate, vinyl sulfate and trimethyl methyl phosphate.

2. The sodium ion battery according to claim 1, characterized in that The main material also contains sodium hexafluorophosphate, and the mass ratio of sodium hexafluorophosphate to sodium bis(trifluoromethanesulfonyl)imide is not higher than 5:

1.

3. The sodium ion battery according to claim 1, characterized in that: The components in the electrolyte are calculated by mass percentage, the amount of the main material is 10% to 15%, the amount of the solvent is 80% to 85%, and the amount of the auxiliary material is 1% to 10%.

4. The sodium ion battery according to claim 1, characterized in that Calculated by volume percentage, the solvent includes 30% to 45% of ethylene carbonate, 35% to 45% of dimethyl carbonate, and 10% to 20% of ethylene glycol dimethyl ether.

5. The sodium ion battery according to claim 1, characterized in that: The positive electrode active material is a layered transition metal oxide.

6. The sodium ion battery according to claim 1 or 5, characterized in that: The particle size distribution D50 of the positive electrode active material is 7.0 to 15.0 μm; And / or, the tap density of the positive electrode active material is ≥2.2 g / cm 3 ; And / or, the specific surface area of ​​the positive electrode active material is 0.1 to 0.6 m 2 / g.

7. The sodium ion battery according to claim 1, characterized in that: The negative electrode active material is hard carbon particles.

8. The sodium ion battery according to claim 1 or 7, characterized in that: The particle size distribution D50 of the negative electrode active material is 5.0 to 9.0 μm; And / or, the specific surface area of ​​the negative electrode active material is 2.5 to 4.5 m 2 / g; And / or, the compaction density of the negative electrode active material is 1.0 to 1.4 g / cm 3 .

9. The sodium ion battery according to claim 1, characterized in that: The diaphragm is a polyethylene ceramic glue-coated diaphragm, and aluminum oxide nanomaterials are attached to the surface of the diaphragm.

10. The sodium ion battery according to claim 1, characterized in that: The thickness of the separator is 12-18 μm.

Images