Charging method of sodium ion battery, sodium ion battery and application

Abstract

The application belongs to the field of secondary batteries and its preparation technology, and relates to a charging method of a sodium ion battery, the sodium ion battery and application. In view of the technical problems that the sodium ion battery in the prior art has low capacity when charging at low temperature and serious sodium precipitation in the negative electrode, the application provides a charging method of a sodium ion battery, which comprises the following steps: obtaining a constant volume capacity CO of the sodium ion battery at normal temperature, charging the battery to 0.5 times CO, and obtaining a charging end voltage V1; placing the battery in an empty state at a target low temperature, charging to 0.5 times CO, and obtaining a battery charging end voltage V2; calculating AV = V2-V1, when AV >= X, the battery is charged to full capacity by adopting a segmented charging method; and when AV < X, the battery is first charged to 0.7 times CO, and then the segmented charging method is adopted to charge to full capacity. The application optimizes the low-temperature charging performance, charges the sodium ion battery to a full-electric state at low temperature, avoids the phenomenon of negative electrode sodium precipitation in the low-temperature charging process, and improves the safety of the battery.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology and its preparation technology, specifically relating to sodium-ion batteries, their charging methods and applications. Background Technology

[0002] Sodium-ion batteries, as a novel rechargeable battery technology, have received widespread attention in recent years. They primarily rely on the movement of sodium ions between the positive and negative electrodes to complete charging and discharging. Sodium-ion batteries possess advantages such as abundant resources, low cost, and environmental friendliness, making their application in extreme temperature conditions such as high altitudes, deep seas, and aviation highly promising. Sodium-ion batteries exhibit significant application potential in low-temperature environments; sodium-ion batteries with a layered oxide system can maintain a discharge capacity retention rate of ≥90% at -20℃. However, in low-temperature environments, the poor low-temperature kinetics of the positive electrode material in sodium-ion batteries easily lead to electrolyte decomposition, thus affecting the charge-discharge performance of the battery. Electrochemical impedance and polarization increase sharply at low temperatures and high current densities, easily causing sodium deposition at the negative electrode. Therefore, low-temperature charging remains a major challenge for sodium-ion batteries.

[0003] Most existing technologies improve the low-temperature charging performance of sodium ions by changing the composition of the electrolyte. For example, Chinese invention patent publication number CN118352638A, application date April 17, 2024, invention title "A low-temperature fast-charging sodium ion battery electrolyte and its preparation method". The electrolyte in this scheme includes a mixed solvent, a sodium salt, and a modifier. The mixed solvent is a mixture of ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate in a volume ratio of 1:1:1. The sodium salt is sodium hexafluorophosphate with a molar concentration of 1.0–1.5 mol / L. The modifier is a mixture of modifier A, modifier B, and modifier C in a mass ratio of 10 g: 1.5–5.5 g: 10–25 g, and the amount of modifier added is 0.3–1.2% of the total mass of the low-temperature fast-charging sodium-ion battery electrolyte. Modifier A is 15-crown ether-5; modifier B is a fluorinated hyperbranched carboxylate; and modifier C is borosilicate oil. This electrolyte improves the low-temperature performance of sodium-ion batteries and enables fast charging by adding specific modifiers. However, this technical solution is complex and requires comprehensive consideration of various factors such as physical properties, chemical stability, cost, safety, and environmental adaptability. Furthermore, this electrolyte is not suitable for all types of sodium-ion batteries.

[0004] Existing technologies also include methods to improve the low-temperature charging performance of sodium-ion batteries without altering the battery itself, by changing the low-temperature charging method. For example, Chinese invention patent publication number CN117080593A, filed on September 6, 2023, entitled "A Charging Method for Improving the Low-Temperature Performance of Sodium-Ion Batteries," describes a charging method that includes the following steps: a first-stage capacitive charging, a low-temperature cycle, and a second capacitive charging. The low-temperature cycle involves using a bidirectional pulse method, controlling the operating temperature at -60℃ to -10℃, the frequency at 100Hz to 2000Hz, the forward current amplitude at 0.5C to 1.5C, the reverse current amplitude at 0.25C to 1.5C, and the duty cycle at 5% to 20%. While this technology improves the low-temperature cycle performance of sodium-ion batteries, using bidirectional pulse heating at low temperatures may increase internal electrochemical reactions, potentially increasing safety risks, especially if the battery already has defects or is aging.

[0005] Therefore, it is necessary to design a feasible low-temperature charging method to ensure the normal charging and discharging of sodium-ion batteries under low-temperature conditions and to improve the sodium deposition phenomenon at the negative electrode during the charging process. Without changing the battery design, the low-temperature charging performance should be optimized to enable wider application in low-temperature environments. Summary of the Invention

[0006] 1. The problem to be solved

[0007] To address the technical problems of low capacity and severe sodium deposition on the negative electrode in existing sodium-ion batteries during low-temperature charging, this application provides a charging method for a sodium-ion battery; furthermore, this application also provides a sodium-ion battery; and this application also provides applications of the sodium-ion battery.

[0008] 2. Technical Solution

[0009] To achieve the above objectives, the provided technical solution is as follows:

[0010] The charging method for sodium-ion batteries includes the following steps:

[0011] S1. Obtain the constant capacity C0 of the sodium-ion battery at room temperature;

[0012] S2. Charge the sodium-ion battery to 0.5 times C0 at room temperature and obtain the charging end voltage V1;

[0013] S3. Place the sodium-ion battery in a depleted state at the target low temperature until the sodium-ion battery temperature stabilizes and reaches the target low temperature. Then charge the sodium-ion battery to 0.5 times C0 and obtain the charging terminal voltage V2 of the sodium-ion battery.

[0014] S4. Calculate ΔV, where ΔV = V2 - V1.

[0015] When ΔV≥X, the sodium-ion battery is charged to full capacity using a segmented charging method;

[0016] When ΔV < X, the sodium-ion battery is first charged to 0.7 times C0, and then charged to full capacity using a segmented charging method.

[0017] Furthermore, in step S1, the sodium-ion battery is charged and discharged multiple times, and the capacity of the last discharge is taken as the fixed capacity C0.

[0018] Repeated charge-discharge cycles can activate battery materials, contributing to the battery's stability and safety during long-term operation.

[0019] Preferably, in step S1, N charge-discharge cycles are performed, where N ≥ 3.

[0020] Preferably, the current is constant at 0.2C to 3.95V, then constant at 0.05C until the current drops to 0.05C. After resting for 30 minutes, the current is discharged at 0.2C to 2.0V, and then rested for another 30 minutes. The above steps are repeated 3 times. The discharge capacity of the third discharge is recorded as C0, and the charging capacity of the third charge is recorded as C1.

[0021] When N≥3, the actual usable capacity of the battery, C0, can be determined more accurately. This helps the battery management system (BMS) to control the charging and discharging process of the battery more accurately, avoid overcharging and over-discharging, and extend the battery's lifespan.

[0022] Furthermore, in step S3, the target low temperature is -10 to 0°C, and the settling time is ≥10h.

[0023] At low temperatures, the fluidity of the electrolyte decreases, and its compatibility with the electrodes deteriorates. Allowing the electrolyte to stand for at least 10 hours helps improve its compatibility with the electrode materials, thereby enhancing the transport capacity of sodium ions in the electrolyte and improving the battery's low-temperature charge-discharge performance to some extent. This also allows the battery to reach its target temperature and achieve a stable state.

[0024] Furthermore, in step S4, the segmented charging method specifically involves: each segment using constant current charging, and a rest period being set between each segment.

[0025] When charging at low temperatures, the battery's charging acceptance capacity decreases. By using segmented constant current charging combined with resting time, the battery temperature can be gradually increased, which can improve charging efficiency. When charging at low temperatures, sodium deposition is more pronounced, which can lead to irreversible loss of battery capacity. Segmented constant current charging can reduce sodium deposition, thereby reducing the loss of battery capacity.

[0026] Furthermore, the charging current of each segment decreases sequentially, and the charging current of each segment is 0.5 times that of the previous segment.

[0027] By gradually reducing the charging current, charging efficiency and battery life can be improved while ensuring charging safety, reducing battery aging, and preventing sodium deposition on the negative electrode.

[0028] Furthermore, the settling time is 1 hour.

[0029] Setting a 1-hour rest period allows the battery time to release the heat generated during charging, reducing sodium deposition and thus minimizing capacity loss. It also avoids the problem of high polarization caused by continuous charging of the battery cells.

[0030] Furthermore, when ΔV < X, the battery is charged at a constant current of 0.1C to 0.7 times C0, and then segmented charging begins at a current of 0.05C; when ΔV ≥ X, the battery begins segmented charging at a current of 0.05C.

[0031] When ΔV < X, the battery polarization is not significant. Charging to 0.7 times C0 using a 0.1C current can improve the battery's charge acceptance in low-temperature environments, allowing the battery to be charged with more power at lower temperatures. At the same time, it can effectively avoid sodium deposition, protect battery safety, and shorten the overall charging time.

[0032] When ΔV≥X, the battery is polarized to a certain extent. If a 0.1C current is used for charging, the polarization phenomenon will increase. However, if the battery is charged in stages with a current of 0.05C, the charging efficiency can be improved and sodium deposition on the negative electrode can be avoided.

[0033] Furthermore, X is 0.25.

[0034] Using 0.25 as a value to judge the degree of battery polarization, when ΔV≥0.25, the battery is polarized to a certain extent, and when ΔV<0.25, the battery polarization is not significant, thus different charging methods are adopted.

[0035] A sodium-ion battery, wherein the sodium-ion battery is manufactured using any of the charging methods described herein.

[0036] The application of sodium-ion batteries is to use them in the manufacture of electric vehicles.

[0037] 3. Beneficial effects

[0038] Compared with existing known technologies, the technical solution provided by this invention has the following beneficial effects:

[0039] (1) The charging method for sodium-ion batteries of this invention addresses the issue of severe battery polarization at low temperatures. Since battery polarization is highly correlated with the choice of charging strategy, the method obtains the charging terminal voltage V1 at room temperature and the target low-temperature charging terminal voltage V2. The difference between V2 and V1 is used to determine the battery polarization at low temperatures, allowing for the selection of a suitable charging strategy. Different segmented charging methods are used based on the magnitude of the difference. When charging to 0.5 times C0, battery polarization is low, making it easy to determine the battery polarization at low temperatures, while ensuring that the charging time for the remaining battery capacity at low temperatures is not too long. This solution is applicable to sodium-ion batteries with a layered oxide system. Without altering the original battery design, it determines the polarization of individual battery cells based on the voltage difference between low and room temperatures, selecting the optimal charging method to fully charge the sodium-ion battery at low temperatures and avoiding sodium deposition at the negative electrode during low-temperature charging, thus improving battery safety. It has broad applicability, adapting to different types of sodium-ion batteries with layered oxide systems, providing flexible charging solutions for users with different needs.

[0040] (2) The sodium-ion battery of the present invention uses the above-described charging method during its preparation. Enhanced safety: By avoiding sodium deposition at the negative electrode during low-temperature charging, the safety of the battery is improved. Sodium deposition can damage the internal structure of the battery, increasing safety risks; the sodium-ion battery of the present invention effectively avoids this problem. Optimized charging efficiency: The polarization of the battery cells is determined based on the voltage difference between the charging terminals at low and normal temperatures, and the optimal charging method is selected. This helps to improve charging efficiency, reduce energy loss during charging, and thus extend the battery's lifespan. Achievement of full charge: This method can charge the sodium-ion battery to full charge at low temperatures, which is particularly important for electric vehicles used in low-temperature environments, as low temperatures may affect the battery's charging performance and range.

[0041] (3) Application of the sodium-ion battery of the present invention: The battery is applied to the manufacture of electric vehicles. Better environmental adaptability: Sodium-ion batteries exhibit excellent capacity retention in both high and low temperature environments, meaning that electric vehicles can operate under a wider range of climatic conditions, unaffected by extreme temperatures. Fast charging capability: Sodium-ion batteries enable fast charging, significantly reducing charging time and improving user convenience. Cost-effectiveness: The material cost of sodium-ion batteries is 30%–40% lower than that of lithium-ion batteries, helping to reduce the overall manufacturing cost of electric vehicles, making them more economical and promoting their widespread adoption. High safety: Sodium-ion batteries are less prone to thermal runaway under extreme conditions, exhibiting good safety performance, which is crucial for ensuring the safety of electric vehicle users. Long cycle life: Sodium-ion batteries have a long cycle life, which helps reduce maintenance costs and battery replacement frequency, improving the operating efficiency and economy of electric vehicles. Attached Figure Description

[0042] Figure 1 Flowchart of the segmented low-temperature charging method;

[0043] Figure 2 This is a photograph of the negative electrode interface after the battery is fully charged and disassembled in Example 1.

[0044] Figure 3 This is a photograph of the negative electrode interface after the battery is fully charged and disassembled in Example 2.

[0045] Figure 4 This is a photograph of the negative terminal interface after the battery in Comparative Example 1 has been fully charged and disassembled. Detailed Implementation

[0046] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments.

[0047] Example 1

[0048] The charging method for the sodium-ion battery in this embodiment, using a sodium-ion battery with a layered oxide system, includes the following steps:

[0049] S1. Obtain the constant capacity C0 of the battery at room temperature. Charge the battery with a constant current of 0.2C to 3.95V, then switch to constant voltage charging until the current drops to 0.05C. Let it rest for 30 minutes, then discharge it with a current of 0.2C to 2.0V, and let it rest for another 30 minutes. Repeat the above steps 3 times. Take the discharge capacity of the third time and record it as C0. Record the charge capacity of the third time as C1.

[0050] By conducting three charge-discharge cycles, the actual usable capacity of the battery, C0, can be determined more accurately. This also activates the battery materials, contributing to the battery's stability and safety during long-term operation. C1 represents the battery's charging capacity at room temperature and can be used to calculate the charging capacity ratio at low temperatures.

[0051] S2. At room temperature, charge the battery with a constant current of 0.2C to 0.5 times C0 to obtain the charging end voltage V1. After standing for 30 minutes, discharge the battery with a constant current of 0.2C to 2.0V.

[0052] S3. Place the battery in an empty state at the target temperature of -10℃ for 10 hours until the battery temperature stabilizes and reaches the target temperature. Then charge the battery at a constant current of 0.1C to 0.5 times C0 to obtain the battery charging end voltage V2.

[0053] Charging the battery at a constant current of 0.2C at room temperature can save charging time, while charging it at a constant current of 0.1C at low temperatures can improve the battery's charging acceptance in low-temperature environments, allowing the battery to be charged with more power at lower temperatures. At the same time, it can effectively avoid sodium deposition and protect battery safety. The reason for charging to 0.5 times C0 is that the battery polarization is lower at this point, and it also ensures that the charging time for the remaining battery power at low temperatures will not be too long. At low temperatures, it is difficult for the battery to be charged to C0, and as the charging power increases, the battery polarization will intensify, interfering with the judgment of the battery polarization at low temperatures.

[0054] S4. Calculate ΔV = V2 - V1 = 0.21. When ΔV < X, X is 0.25. First, charge the battery with a constant current of 0.1C to 0.7 times C0, let it rest for 1 hour, and then charge it to full capacity using a segmented charging method. The segmented charging method is as follows:

[0055] Charge the battery to 3.75V with a constant current of 0.05C and let it rest for 1 hour; then charge it to 3.85V with a constant current of 0.025C and let it rest for 1 hour; then charge it to 3.95V with a constant current of 0.0125C. The battery is now fully charged. Calculate the cumulative charging capacity C2.

[0056] Because battery polarization is severe at low temperatures, and the degree of battery polarization is highly correlated with the choice of charging strategy, the difference between the charging terminal voltage V2 at low temperatures and the charging terminal voltage V1 at room temperature (primarily the difference between the normal charging terminal voltage at room temperature and the voltage under severe low-temperature polarization) is used to determine the battery polarization at low temperatures, thus selecting an appropriate charging strategy. When ΔV = 0.21, i.e., ΔV < 0.25, it indicates that the battery polarization is not significant, and it can continue to be charged at a constant current of 0.1C to 0.7 times C0, saving charging time. The remaining 0.3 times C0 capacity is charged in stages. By gradually reducing the charging current, charging safety can be ensured while improving charging efficiency and battery lifespan, reducing battery aging. Setting a 1-hour rest period allows the battery time to release the heat generated during charging, reducing sodium deposition and thus reducing battery capacity loss. Furthermore, it avoids the problem of high polarization caused by continuous charging of the cell.

[0057] Example 2

[0058] The charging method for the sodium-ion battery in this embodiment, using a sodium-ion battery with a layered oxide system, includes the following steps:

[0059] S1. Obtain the constant capacity C0 of the battery at room temperature. Charge the battery with a constant current of 0.2C to 3.95V, then switch to constant voltage charging until the current drops to 0.05C. Let it rest for 30 minutes, then discharge it with a current of 0.2C to 2.0V, and let it rest for another 30 minutes. Repeat the above steps 3 times. Take the discharge capacity of the third time and record it as C0. Record the charge capacity of the third time as C1.

[0060] S2. At room temperature, charge the battery with a constant current of 0.2C to 0.5 times C0 to obtain the charging end voltage V1. After standing for 30 minutes, discharge the battery with a constant current of 0.2C to 2.0V.

[0061] S3. Place the battery in an empty state at the target temperature of -10℃ for 10 hours until the battery temperature stabilizes and reaches the target temperature. Then charge the battery at a constant current of 0.1C to 0.5 times C0 to obtain the battery charging end voltage V2.

[0062] S4. Calculate ΔV = V2 - V1 = 0.32. When ΔV ≥ X, X is 0.25. The battery is charged to full capacity using a segmented charging method, as detailed below:

[0063] The battery is charged at a constant current of 0.05C to 3.55V and left to rest for 1 hour; then charged at a constant current of 0.025C to 3.65V and left to rest for 1 hour; then charged at a constant current of 0.025C to 3.75V and left to rest for 1 hour; then charged at a constant current of 0.0125C to 3.85V and left to rest for 1 hour; then charged at a constant current of 0.0125C to 3.95V and left to rest for 1 hour. The battery is now fully charged. Calculate the cumulative charging capacity C2.

[0064] Because batteries exhibit polarization at low temperatures, the difference between the low-temperature charging terminal voltage V2 and the room-temperature charging terminal voltage V1 is used to determine the degree of battery polarization at low temperatures. When ΔV = 0.32, or ΔV ≥ 0.25, it indicates that the battery is polarized to some extent and cannot continue to be charged at a constant current of 0.1C. Instead, a segmented charging method should be used to charge the battery to full capacity. By combining segmented constant current charging with a resting period, the battery temperature can be gradually restored, thereby improving charging efficiency. The current during segmented charging is 0.05C, 0.025C, 0.025C, 0.0125C, and 0.0125C respectively. This ensures that the battery polarization is low during low-temperature charging, avoids sodium deposition on the negative electrode, and saves overall charging time.

[0065] From Example 1, Example 2 and Figure 1It can be seen that using 0.25 as a value to judge the degree of battery polarization, when ΔV < 0.25, it indicates that the battery polarization is not significant. In this case, it can continue to be charged at low temperature to 70% SOC (i.e., 0.7 times C0), and then use segmented charging (i.e., stepped charging) to full charge. This method is faster than directly charging from 50% SOC (i.e., 0.5 times C0) to full charge in stages. 0.7 times C0 is a value between 0.5 times C0 and 1 times C0. Charging directly to C0 can lead to severe cell polarization and even sodium deposition. Charging to 0.7 times C0 ensures a low degree of battery polarization and prevents sodium deposition on the negative electrode, while also shortening the overall low-temperature charging time. The remaining 0.3 times C0 capacity is then charged in stages. When ΔV ≥ 0.25, it indicates that the battery is polarized to some extent. In this case, directly using a segmented charging method to full charge further improves battery charging efficiency and avoids sodium deposition on the negative electrode.

[0066] SOC (state of charge) is the state of charge of a battery. The range of SOC is 0% to 100%. When SOC is 0%, it means that the battery is fully discharged; when SOC is 100%, it means that the battery is fully charged.

[0067] Applying the sodium-ion batteries of Example 1 or Example 2 to electric vehicles offers several advantages: Wide temperature range adaptability: Excellent high and low temperature performance enables stable operation of electric vehicles under diverse climatic conditions. Fast charging: Supports fast charging, significantly reducing charging waiting time and improving user convenience. Economic efficiency: Lower material costs compared to lithium batteries help reduce overall vehicle manufacturing costs and improve the affordability of electric vehicles. High safety: Less prone to thermal runaway under extreme conditions, enhancing the safety of electric vehicles. Long lifespan: Longer cycle life reduces maintenance and battery replacement needs, improving operating efficiency and economics.

[0068] Comparative Example 1

[0069] This comparative example of a low-charging method for sodium-ion batteries, using a layered oxide system, includes the following steps:

[0070] S1. Obtain the constant capacity C0 of the battery at room temperature. Charge the battery with a constant current of 0.2C to 3.95V, then switch to constant voltage charging until the current drops to 0.05C. Let it rest for 30 minutes, then discharge it with a current of 0.2C to 2.0V, and let it rest for another 30 minutes. Repeat the above steps 3 times. Take the discharge capacity of the third time and record it as C0. Record the charge capacity of the third time as C1.

[0071] S2. At room temperature, charge the battery with a constant current of 0.2C to 0.5 times C0 to obtain the charging end voltage V1. After standing for 30 minutes, discharge the battery with a constant current of 0.2C to 2.0V.

[0072] S3. Place the battery in a depleted state at the target temperature of -10℃ for 10 hours until the battery temperature stabilizes and reaches the target temperature. Then, charge the battery at a constant current of 0.1C until it reaches 3.95V, then switch to constant voltage charging until the current drops to 0.05C. The battery charging is now complete. Record the cumulative charging capacity C2.

[0073] Comparative Example 2

[0074] This comparative example uses a sodium-ion battery with a layered oxide system and includes the following steps:

[0075] S1. Obtain the constant capacity C0 of the battery at room temperature. Charge the battery with a constant current of 0.2C to 3.95V, then switch to constant voltage charging until the current drops to 0.05C. Let it rest for 30 minutes, then discharge it with a current of 0.2C to 2.0V, and let it rest for another 30 minutes. Repeat the above steps 3 times. Take the discharge capacity of the third time and record it as C0. Record the charge capacity of the third time as C1.

[0076] S2. At room temperature, charge the battery with a constant current of 0.2C to 0.5 times C0 to obtain the charging end voltage V1. After standing for 30 minutes, discharge the battery with a constant current of 0.2C to 2.0V.

[0077] S3. Place the battery in an empty state at the target temperature of -10℃ for 10 hours until the battery temperature stabilizes and reaches the target temperature. Then charge the battery at a constant current of 0.1C to 0.5 times C0 to obtain the battery charging end voltage V2.

[0078] S4. Calculate ΔV = V2 - V1 = 0.38. When ΔV ≥ X, X is 0.25. First, charge the battery with a constant current of 0.1C to 0.7 times C0, let it rest for 1 hour, and then charge it to full capacity using a segmented charging method. The segmented charging method is as follows: charge the battery with a constant current of 0.05C to 3.75V, let it rest for 1 hour; then charge the battery with a constant current of 0.025C to 3.85V, let it rest for 1 hour; then charge the battery with a constant current of 0.0125C to 3.95V. The battery is now fully charged. Calculate the cumulative charging capacity C2.

[0079] Table 1. Battery charging capacity data for examples and comparative models.

[0080] Example 1 72.16 72.35 66.13 91.40 Example 2 72.12 72.31 64.54 89.25 Comparative Example 1 72.18 72.38 52.16 72.06 Comparative Example 2 72.11 72.33 57.72 79.80

[0081] Note: C0: Discharge capacity at room temperature, C1: Charge capacity at room temperature, C2: Charge capacity at low temperature, Charge capacity ratio: C2 / C1*100%.

[0082] As shown in Table 1, the low-temperature charging capacity ratios of sodium-ion batteries obtained using the charging method of this application in Examples 1 and 2 are both higher than those obtained using the conventional charging regime in Comparative Example 1. When ΔV ≥ 0.25, the charging capacity ratio of Example 2 is higher than that of Comparative Example 2, which first charges to 0.7 times C0 and then uses a segmented charging method. This is because in Comparative Example 2, ΔV = 0.38, the battery polarization is greater at low temperatures. Continuing to charge at a current of 0.1C to 0.7 times C0 would increase battery polarization, leading to sodium deposition on the negative electrode and a decrease in charging capacity. The segmented low-temperature charging method of this application solves the technical problem of low charging capacity of sodium-ion batteries at low temperatures and can ensure low-temperature charging efficiency of the battery under different polarization states.

[0083] After fully charging the batteries of Example 1, Example 2, and Comparative Example 1, they were disassembled at the negative electrode interface to observe sodium deposition. No sodium deposition was observed in the sodium-ion batteries of Example 1 and Example 2 after full-charge disassembly (e.g., ...). Figure 2 , Figure 3 As shown), while in Comparative Example 1, strip-shaped sodium deposition appeared on the negative electrode surface (as shown). Figure 4 As shown in the figure, the charging method of this application solves the technical problem of sodium precipitation during charging of sodium-ion batteries at low temperatures, thereby improving battery safety.

[0084] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A charging method for a sodium-ion battery, characterized in that: Includes the following steps: S1. Obtain the constant capacity C0 of the sodium-ion battery at room temperature; S2. Charge the sodium-ion battery to 0.5 times C0 at room temperature and obtain the charging end voltage V1; S3. Place the sodium-ion battery in a depleted state at a target low temperature until the sodium-ion battery temperature stabilizes and reaches the target low temperature. Then charge the sodium-ion battery to 0.5 times C0 and obtain the charging terminal voltage V2 of the sodium-ion battery. The target low temperature is -10~0 ℃, and the standing time is ≥10 h. S4. Calculate ΔV, where ΔV = V2 - V1. When ΔV≥0.25, the sodium-ion battery is charged to full capacity using a segmented charging method; When ΔV < 0.25, the sodium-ion battery is first charged at a constant current of 0.1 C to 0.7 times C0, and then charged to full capacity using a segmented charging method; The segmented charging method specifically involves constant current charging for each segment, with a rest period of 1 hour between each segment.

2. The charging method for a sodium-ion battery according to claim 1, characterized in that: In step S1, the sodium-ion battery is charged and discharged multiple times, and the capacity of the last discharge is taken as the fixed capacity C0.

3. The charging method for a sodium-ion battery according to claim 1, characterized in that: When ΔV < 0.25, the charging current of each segment decreases sequentially, and the charging current of each segment is 0.5 times that of the previous segment.

4. A sodium-ion battery, characterized in that: The sodium-ion battery is manufactured using the charging method described in any one of claims 1-3.

5. The application of sodium-ion batteries, characterized by: The sodium-ion battery of claim 4 is applied to the manufacture of electric vehicles.

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