Method for reducing sodium ion battery positive electrode residual alkali and sodium ion battery

Abstract

The invention relates to the technical field of sodium-ion batteries, and particularly discloses a method for reducing residual alkali of a sodium battery positive electrode and a sodium-ion battery. The method comprises the following steps: calculating the addition amounts of organic acid and a water removal agent according to a stoichiometric ratio; uniformly mixing the organic acid, the water removal agent and the electrolyte in proportion to obtain a mixed electrolyte; injecting the mixed electrolyte into the battery cell; in the cell infiltration process, the organic acid reacts with the residual alkali to generate an organic acid sodium salt sodium supplementing agent, and water generated by acid-base neutralization is removed by utilizing a water removal agent; and discharging gas generated by acid-base neutralization in the cell formation stage. The organic acid is added in the battery cell liquid injection process, so that the generated residual alkali on the surface of the material can be eliminated, and the contact with air can be isolated to regenerate the residual alkali; in addition, residual alkali is converted into an organic acid sodium salt sodium supplementing agent in the cell infiltration process, so that the first-circle capacity can be improved; and meanwhile, water generated in the neutralization process is removed by utilizing a water removal agent, and gas byproducts can be discharged in the formation stage, so that the influence on the subsequent charge-discharge process is avoided.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a method for reducing residual alkali in the positive electrode of a sodium battery and a sodium-ion battery. Background Technology

[0002] Layered oxides, Prussian blue / white, and polyanion technologies are the main technical routes for the development of sodium-ion batteries. Among them, layered oxides have achieved mass production first due to their advantages such as high specific energy, high compaction, good rate performance, and high compatibility with ternary cathode materials. With the promotion of sodium-ion battery applications, layered oxides are facing technical bottlenecks such as severe gas generation and poor cycle stability, which are closely related to the residual alkali content of the cathode material.

[0003] The formation of residual alkali is due to the following reasons: first, the sodium source remaining during calcination reacts with H2O and CO2 in the air; second, in subsequent processes, Na+ in the bulk phase easily undergoes ion exchange with H+ in H2O molecules in the air, causing Na in the sodium ion cathode material lattice to continuously detach, resulting in an increase in residual alkali.

[0004] Currently, the industry commonly employs a process that mimics the ternary material washing technique, involving washing the sodium electrode cathode material with water, followed by coating and secondary sintering (washing + secondary sintering) to reduce the surface residual alkali content. Most published patents also require doping or coating during material synthesis through sintering. Therefore, current methods primarily reduce residual alkali during material preparation, which increases material processing costs and involves complex process control and operation.

[0005] High residual alkali content typically leads to problems such as slurry gelation, poor electrode coating, reduced rate capability, decreased cycle performance, and gas generation. While current market-ready materials offer good processing performance, preventing slurry gelation and ensuring stable coating, issues remain regarding gas generation and electrical properties. Therefore, further reducing residual alkali content to improve gas generation, increase capacity, and enhance cycle stability is crucial.

[0006] Patent application CN117699866A discloses adding organic acid after sintering the precursor and sodium salt, followed by grinding and mixing to achieve uniformity. Although this technical solution is a method to reduce residual alkali in the cathode by using organic acid, processing it during material synthesis often requires additional material production steps, making the process relatively complex, and it cannot prevent the regeneration of residual alkali during subsequent storage and use.

[0007] Furthermore, firstly, although the technical solution of patent application CN117699866A can also generate sodium supplement in situ, the energy consumption of the phase treatment process is higher; secondly, the water generated in situ will cause the subsequent bulk phase Na to precipitate again, generating new residual alkali; thirdly, the technical solution is to treat the material before it leaves the factory, and cannot reduce the residual alkali newly generated during the process from the time the material leaves the factory to the time of mixing and electrode assembly, that is, it cannot completely eliminate the residual alkali.

[0008] Based on this technical background, this invention studies a method for reducing residual alkali in sodium-ion batteries and a sodium-ion battery. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for reducing residual alkali in sodium-ion batteries and a sodium-ion battery. This method involves adding organic acid during the cell electrolyte injection process. This not only eliminates existing residual alkali on the material surface but also effectively prevents contact with air from regenerating residual alkali, thus completely eliminating the impact of residual alkali on gas generation and electrical performance. Furthermore, the cell wetting process converts residual alkali into an organic acid sodium salt supplement, restoring the active sodium lost in the bulk phase and improving the initial charge / discharge capacity. Simultaneously, water generated during neutralization is removed using a dehydrating agent. Moreover, gaseous byproducts generated during neutralization can be discharged during the formation stage, avoiding any impact on subsequent charge / discharge processes.

[0010] To achieve the above objectives, a first aspect of the present invention provides a method for reducing residual alkali in a sodium-ion battery cathode and a sodium-ion battery, comprising: Calculate the amount of organic acid and dehydrating agent to be added based on the stoichiometric ratio; The organic acid, dehydrating agent and electrolyte are mixed evenly in a certain proportion to obtain a mixed electrolyte; The mixed electrolyte is injected into the battery cell; During the cell immersion process, the organic acid reacts with the residual alkali to generate an organic acid sodium salt sodium supplement, and the water generated by acid-base neutralization is removed by the dehydrating agent; During the cell formation stage, the gas generated by the acid-base neutralization is discharged.

[0011] A second aspect of the present invention provides a sodium-ion battery that reduces residual alkali using the method described above.

[0012] The beneficial effects of this invention include: (1) The method for reducing residual alkali in sodium-ion batteries proposed in this invention treats the residual alkali on the surface of the positive electrode during the electrolyte injection process. This not only eliminates the surface residual alkali that has already been generated, but also eliminates concerns about Na+ residue since it has already been incorporated into the battery casing. + The dissolved substance reacts with H2O and CO2 in the air to generate new residual alkali. Compared with the existing technology that reduces the residual alkali of the positive electrode during the material synthesis stage, the removal of residual alkali is relatively thorough.

[0013] (2) The method for reducing residual alkali in sodium-ion cathode proposed in this invention uses organic acid to convert residual alkali into sodium replenishing agent, which "restores" the sodium lost in the bulk phase, which is beneficial to replenish the active sodium consumed in the formation of SEI in the first cycle, thereby improving the capacity and cycle performance in the first cycle.

[0014] (3) The method for reducing residual alkali in sodium battery cathode proposed in this invention eliminates the influence of water generated during neutralization on the battery cell system by adding a dehydrating agent.

[0015] (4) The method for reducing residual alkali in sodium electrode proposed in this invention allows the gaseous byproducts generated during the neutralization and dehydration processes to be discharged during the formation stage, thus avoiding the impact on subsequent charging and discharging processes.

[0016] (5) The method for reducing residual alkali in sodium cathode proposed in this invention avoids the residual alkali treatment in the material synthesis process of the prior art, reduces the material production process, simplifies the processing process, and solves the problem that the prior art cannot avoid the generation of residual alkali in the subsequent storage and use of materials.

[0017] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings.

[0019] Figure 1 This is a schematic flowchart of the method for reducing residual alkali in sodium electrode cathodes proposed in this invention.

[0020] Figure 2 This is a flowchart illustrating a specific implementation of the method for reducing residual alkali in sodium-ion cathodes proposed in this invention. Detailed Implementation

[0021] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0022] This invention provides a method for reducing residual alkali in sodium electrode positive electrodes, such as... Figure 1 As shown, it includes: Calculate the amount of organic acid and dehydrating agent to be added based on the stoichiometric ratio; Organic acid, dehydrating agent and electrolyte are mixed evenly in proportion to obtain mixed electrolyte; Inject the mixed electrolyte into the battery cell; During the cell immersion process, organic acids react with residual alkali to generate sodium organic acid salts as a sodium supplement, and the water generated by acid-base neutralization is removed using a dehydrating agent. During the cell formation stage, gases generated during acid-base neutralization are discharged.

[0023] In this invention, the residual alkali on the positive electrode surface is treated during the electrolyte injection process. This not only eliminates the existing surface residual alkali, but also eliminates concerns about Na+ because the electrolyte is already encased in the casing. + The dissolved substance reacts with H2O and CO2 in the air to generate new residual alkali. Compared with the existing technology that reduces the residual alkali of the positive electrode during the material synthesis stage, the removal of residual alkali is relatively thorough.

[0024] According to the present invention, the organic acid includes at least one selected from oxalic acid, squaric acid, citric acid, ascorbic acid, urea acid and pyruvic acid; The dehydrating agent includes at least one of hexamethyldisilazane, trimethylchlorosilane, trimethylsilylphosphine, acetic anhydride, and phthalic anhydride; The residual alkali is sodium carbonate and / or sodium hydroxide.

[0025] According to the present invention, the actual amount of organic acid and dehydrating agent added is 90%-110% of the amount that should be added.

[0026] According to the present invention, the amount to be added should be calculated based on the measured content of residual alkali in the positive electrode material inside the battery cell and the stoichiometric ratio of the chemical reaction equation.

[0027] According to the present invention, the method of uniform mixing is at least one of stirring and ultrasonication.

[0028] According to the present invention, the immersion temperature of the battery cell is 25-45°C and the immersion time is 24-48h.

[0029] According to the present invention, the removal of the gas generated by acid-base neutralization is called vacuuming; The vacuuming time is 10-30 seconds, and the pressure of the pressure plate is 0.01-1 MPa.

[0030] In this invention, organic acids are used to convert residual alkali into sodium replenishing agents, which "restores" the sodium lost in the bulk phase. This helps to replenish the active sodium consumed in the formation of SEI during the first cycle, thereby improving the first cycle capacity and cycling performance.

[0031] According to the present invention, when the organic acid is oxalic acid, the equation for the acid-base neutralization reaction is: ; .

[0032] In this invention, by adding a dehydrating agent, the influence of water generated during the neutralization process on the battery cell system is eliminated. At the same time, the gaseous byproducts generated during the neutralization and dehydration processes can be discharged during the formation stage, avoiding any impact on the subsequent charging and discharging processes.

[0033] According to the present invention, when the dehydrating agent is hexamethyldisilazane, the equation for the reaction of removing water generated by acid-base neutralization is: .

[0034] This invention avoids the residual alkali treatment required in the material synthesis process of existing technologies, reduces material production steps, simplifies the processing, and solves the problem that residual alkali cannot be avoided in the subsequent storage and use of materials in existing technologies.

[0035] The method of this invention is also applicable to other batteries, such as lithium batteries.

[0036] The present invention also provides a sodium-ion battery that uses the above-described method to reduce residual alkali.

[0037] The present invention will be described in more detail below through embodiments.

[0038] Example 1

[0039] This embodiment provides a method for reducing residual alkali in sodium-ion batteries, such as... Figure 2 As shown, the specific steps include: A positive electrode sheet is prepared according to the method for preparing a sodium-ion battery positive electrode sheet. It is then stacked with a negative electrode sheet and a separator. After welding, top and side sealing, casing, and baking, a dry cell is obtained. Oxalic acid and hexamethyldisilazane (HMDS) are weighed at 102% and 100% of their respective required amounts and added to the electrolyte. They are then thoroughly mixed to obtain a mixed electrolyte. The mixed electrolyte is injected into the dry cell and sealed. The cell is then placed in an oven at 45°C for 24 hours to soak. After formation, degassing, and capacity testing, the first discharge specific capacity is obtained. Remove the battery cells for pretreatment, store them at 55°C for 7 days with full charge, and test the gas production. The battery cells were removed and subjected to 1C / 1C cycles to obtain the discharge specific capacity and capacity retention rate after 800 cycles.

[0040] Example 2

[0041] This embodiment provides a method for reducing residual alkali in a sodium electrode, the specific steps of which include: A positive electrode sheet is prepared according to the method for preparing a sodium-ion battery positive electrode sheet. It is then stacked with a negative electrode sheet and a separator. After welding, top and side sealing, casing, and baking, a dry cell is obtained. Oxalic acid and hexamethyldisilazane (HMDS) are weighed at 105% and 100% of their respective amounts and added to the electrolyte. They are then thoroughly mixed to obtain a mixed electrolyte. The mixed electrolyte is injected into the dry cell and sealed. The cell is then placed in an oven at 45°C for 24 hours to soak. After formation, degassing, and capacity testing, the first discharge specific capacity is obtained. Remove the battery cells for pretreatment, store them at 55°C for 7 days with full charge, and test the gas production. The battery cells were removed and subjected to 1C / 1C cycles to obtain the discharge specific capacity and capacity retention rate after 800 cycles.

[0042] Example 3

[0043] This embodiment provides a method for reducing residual alkali in a sodium electrode, the specific steps of which include: A positive electrode sheet is prepared according to the method for preparing a sodium-ion battery positive electrode sheet. It is then stacked with a negative electrode sheet and a separator. After welding, top and side sealing, casing, and baking, a dry cell is obtained. Oxalic acid and hexamethyldisilazane (HMDS) are weighed at 102% and 105% of their respective required amounts and added to the electrolyte. They are then thoroughly mixed to obtain a mixed electrolyte. The mixed electrolyte is injected into the dry cell and sealed. The cell is then placed in an oven at 45°C for 24 hours to soak. After formation, degassing, and capacity testing, the first discharge specific capacity is obtained. Remove the battery cells for pretreatment, store them at 55°C for 7 days with full charge, and test the gas production. The battery cells were removed and subjected to 1C / 1C cycles to obtain the discharge specific capacity and capacity retention rate after 800 cycles.

[0044] Example 4

[0045] This embodiment provides a method for reducing residual alkali in a sodium electrode, the specific steps of which include: A positive electrode sheet is prepared according to the method for preparing a sodium-ion battery positive electrode sheet. It is then stacked with a negative electrode sheet and a separator. After welding, top and side sealing, casing, and baking, a dry cell is obtained. Citric acid and hexamethyldisilazane (HMDS) are weighed at 102% and 100% of their respective required amounts and added to the electrolyte. They are then thoroughly mixed to obtain a mixed electrolyte. The mixed electrolyte is injected into the dry cell and sealed. The cell is then placed in an oven at 45°C for 24 hours to soak. After formation, degassing, and capacity testing, the first discharge specific capacity is obtained. Remove the battery cells for pretreatment, store them at 55°C for 7 days with full charge, and test the gas production. The battery cells were removed and subjected to 1C / 1C cycles to obtain the discharge specific capacity and capacity retention rate after 800 cycles.

[0046] Example 5

[0047] This embodiment provides a method for reducing residual alkali in a sodium electrode, the specific steps of which include: A positive electrode sheet is prepared according to the method for preparing a sodium-ion battery positive electrode sheet. It is then stacked with a negative electrode sheet and a separator. After welding, top and side sealing, casing, and baking, a dry cell is obtained. Oxalic acid and acetic anhydride are weighed at 102% and 100% of their respective required amounts and added to the electrolyte. They are then thoroughly mixed to obtain a mixed electrolyte. The mixed electrolyte is injected into the dry cell and sealed. The cell is then placed in an oven at 45°C for 24 hours to soak. After formation, degassing, and capacity testing, the first discharge specific capacity is obtained. Remove the battery cells for pretreatment, store them at 55°C for 7 days with full charge, and test the gas production. The battery cells were removed and subjected to 1C / 1C cycles to obtain the discharge specific capacity and capacity retention rate after 800 cycles.

[0048] Comparative Example 1

[0049] This comparative example provides a method for reducing residual alkali in sodium electrode positive electrodes, the specific steps of which include: A positive electrode sheet is prepared according to the method for preparing a sodium-ion battery positive electrode sheet. It is then stacked with a negative electrode sheet and a separator. After welding, top and side sealing, casing, and baking, a dry cell is obtained. Conventional electrolyte is injected into the dry cell and sealed. It is then placed in an oven at 45°C for 24 hours to soak. After formation, degassing, and capacity testing, the first discharge specific capacity is obtained. Remove the battery cells for pretreatment, store them at 55°C for 7 days with full charge, and test the gas production. The battery cells were removed and subjected to 1C / 1C cycles to obtain the discharge specific capacity and capacity retention rate after 800 cycles.

[0050] Comparative Example 2

[0051] A comparative example provides a method for reducing residual alkali in sodium-ion batteries, the specific steps of which include: A positive electrode sheet is prepared according to the method for preparing a sodium-ion battery positive electrode sheet. The positive electrode sheet is stacked with a negative electrode sheet and a separator. After welding, top and side sealing, casing, and baking, a dry cell is obtained. Oxalic acid is weighed at 102% of the required amount and added to the electrolyte. The mixture is thoroughly mixed to obtain a mixed electrolyte. The mixed electrolyte is injected into the dry cell and sealed. The cell is then placed in an oven at 45°C for 24 hours to soak. After formation, degassing, and capacity testing, the first discharge specific capacity is obtained. Remove the battery cells for pretreatment, store them at 55°C for 7 days with full charge, and test the gas production. The battery cells were removed and subjected to 1C / 1C cycles to obtain the discharge specific capacity and capacity retention rate after 800 cycles.

[0052] Comparative Example 3

[0053] A comparative example provides a method for reducing residual alkali in sodium-ion batteries, the specific steps of which include: A positive electrode sheet is prepared according to the method for preparing a sodium-ion battery positive electrode sheet. It is then stacked with a negative electrode sheet and a separator. After welding, top and side sealing, casing, and baking, a dry cell is obtained. Oxalic acid and hexamethyldisilazane (HMDS) are weighed at 150% and 100% of their respective amounts and added to the electrolyte. They are then thoroughly mixed to obtain a mixed electrolyte. The mixed electrolyte is injected into the dry cell and sealed. The cell is then placed in an oven at 45°C for 24 hours to soak. After formation, degassing, and capacity testing, the first discharge specific capacity is obtained. Remove the battery cells for pretreatment, store them at 55°C for 7 days with full charge, and test the gas production. The battery cells were removed and subjected to 1C / 1C cycles to obtain the discharge specific capacity and capacity retention rate after 800 cycles.

[0054] The performance test results of the sodium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-3 of this application are shown in Table 1.

[0055] Table 1: Performance test results of sodium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-3

[0056] As can be seen from the test results in Table 1, adding appropriate amounts of organic acid and dehydrating agent to the electrolyte can significantly improve the initial charge and discharge capacity of the battery, reduce gas generation during storage, and improve long-term cycle performance. The battery cell without any added organic acid and dehydrating agent has the lowest initial capacity. The battery cell with only added organic acid has improved initial charge and discharge capacity because the residual alkali is converted into a sodium replenishing agent, but its performance will be lower than that of the example cell because no dehydrating agent is added. In addition, if the organic acid is excessive, the excess acidic substances in the electrolyte will also have a negative impact on the battery cell system.

[0057] In summary, by adding appropriate amounts of organic acids and dehydrating agents to the electrolyte, injecting it into the battery cell, and undergoing processes such as wetting and degassing, the prepared sodium-ion battery cell exhibits significant improvements in capacity, cycle performance, and gas production.

[0058] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for reducing residual alkali in a sodium electrode, characterized in that, include: Calculate the amount of organic acid and dehydrating agent to be added based on the stoichiometric ratio; The organic acid, dehydrating agent and electrolyte are mixed evenly in a certain proportion to obtain a mixed electrolyte; The mixed electrolyte is injected into the battery cell; During the cell immersion process, the organic acid reacts with the residual alkali to generate an organic acid sodium salt sodium supplement, and the water generated by acid-base neutralization is removed by the dehydrating agent; During the cell formation stage, the gas generated by the acid-base neutralization is discharged.

2. The method according to claim 1, characterized in that, The organic acid includes at least one of oxalic acid, squaric acid, citric acid, ascorbic acid, urea acid, and pyruvic acid; The dehydrating agent includes at least one of hexamethyldisilazane, trimethylchlorosilane, trimethylsilylphosphine, acetic anhydride, and phthalic anhydride; The residual alkali is sodium carbonate and / or sodium hydroxide.

3. The method according to claim 1, characterized in that, The actual amount of organic acid and dehydrating agent added is 90%-110% of the amount that should be added.

4. The method according to claim 3, characterized in that, The required amount should be calculated based on the measured content of residual alkali in the positive electrode material inside the battery cell and the stoichiometric ratio of the chemical reaction equation.

5. The method according to claim 1, characterized in that, The method for achieving uniform mixing is at least one of stirring and ultrasonication.

6. The method according to claim 1, characterized in that, The battery cell is immersed at a temperature of 25-45℃ for 24-48 hours.

7. The method according to claim 1, characterized in that, The process of removing the gas generated during acid-base neutralization is called vacuuming. The vacuuming time is 10-30 seconds, and the pressure of the pressure plate is 0.01-1 MPa.

8. The method according to claim 2, characterized in that, When the organic acid is oxalic acid, the equation for the acid-base neutralization reaction is: ； 。 9. The method according to claim 2, characterized in that, When the dehydrating agent is hexamethyldisilazane, the equation for the reaction that removes water generated by acid-base neutralization is: 。 10. A sodium-ion battery, characterized in that, The method described in any one of claims 1-9 reduces residual alkali.

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