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

Abstract

The invention belongs to the technical field of secondary batteries and preparation thereof, and relates to a charging method of a sodium ion battery, the sodium ion battery and application. The technical problems that in the prior art, a sodium ion battery is low in capacitance during low-temperature charging, and sodium precipitation of a negative electrode is serious are solved. The invention provides a charging method of a sodium-ion battery, which comprises the following steps: acquiring the constant volume capacity C0 of the sodium-ion battery at normal temperature, charging the battery to 0.5 time of the constant volume capacity C0, and acquiring the charging tail end voltage V1; standing the battery at a target low temperature in an empty electricity state, charging the battery to 0.5 times of C0, and obtaining a charging tail end voltage V2 of the battery; delta V is calculated to be equal to V2-V1, and when delta V is larger than or equal to X, the battery is charged to be fully charged by adopting a sectional charging method; and when delta V is less than X, the battery is firstly charged to 0.7 time C0, and then the battery is fully charged by adopting a sectional charging method. According to the invention, the low-temperature charging performance is optimized, the sodium-ion battery is charged to a fully charged state at a low temperature, the phenomenon of sodium precipitation of a negative electrode in a low-temperature charging process is avoided, and the safety of the battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries and preparation thereof, and in particular, relates to sodium ion batteries and charging methods and applications thereof. Background Art

[0002] As a new type of secondary battery technology, sodium-ion batteries have received widespread attention in recent years. It mainly relies on the movement of sodium ions between the positive and negative electrodes to complete the charging and discharging work. Sodium-ion batteries have the advantages of abundant resources, low cost, and environmental friendliness, which has attracted great attention for their application in extreme temperature conditions such as high altitude, deep sea, and aviation. Sodium-ion batteries show great application potential in low-temperature environments. Sodium-ion batteries in layered oxygen systems can show a discharge capacity retention rate of ≥90% at -20°C. However, in low-temperature environments, due to the poor low-temperature kinetics of the positive electrode materials of sodium-ion batteries, it is easy to cause electrolyte decomposition, thereby affecting the charge and discharge performance of sodium-ion batteries. The electrochemical impedance and polarization will increase sharply at low temperatures and high current densities, which can easily cause sodium precipitation at the negative electrode. Therefore, low-temperature charging is still a major challenge facing sodium-ion batteries.

[0003] Most of the existing technologies improve the low-temperature charging performance of sodium ions by changing the composition of the electrolyte. For example, the Chinese invention patent publication number is CN118352638A, the application date is April 17, 2024, and the name of the invention is "A low-temperature fast-charging sodium ion battery electrolyte and its preparation method." The electrolyte of this scheme includes a mixed solvent, a sodium salt and a modifier; the mixed solvent is a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1; the sodium salt is sodium hexafluorophosphate, and the molar concentration of the sodium salt is 1.0-1.5 mol / L; the modifier is a mixture of modifier A, modifier B and modifier C in a mass ratio of 10g:1.5-5.5g:10-25g, and the amount of the modifier added is 0.3-1.2% of the total mass of the low-temperature fast-charge sodium ion battery electrolyte; modifier A is 15-crown ether-5; modifier B is a fluorine-containing hyperbranched carboxylate; modifier C is boron-containing silicone oil. The electrolyte improves the low-temperature performance of the sodium ion battery by adding specific modifiers and realizes the rapid charging of the sodium ion battery, but the technical scheme needs to comprehensively consider its physical properties, chemical stability, cost, safety and environmental adaptability and other factors, which is relatively complicated, and the electrolyte is not suitable for all types of sodium ion batteries.

[0004] There are also existing technologies that do not change the sodium ion battery itself, but improve the low-temperature charging performance of sodium ions by changing the low-temperature charging method of the sodium ion battery. For example, the Chinese invention patent publication number is CN117080593A, the application date is September 6, 2023, and the invention name is "A charging method for improving the low-temperature performance of sodium ion batteries". The charging method of this scheme includes the following steps: a first constant volume, a low-temperature cycle and a second constant volume in sequence; wherein, the low-temperature cycle process includes: using a bidirectional pulse method, controlling the operating temperature to -60℃~-10℃, the frequency to 100Hz~2000Hz, the forward current amplitude to 0.5C~1.5C, the reverse current amplitude to 0.25C~1.5C, and the duty cycle to 5%~20%. This technical solution improves the low-temperature cycle performance of sodium ion batteries, but the use of bidirectional pulse heating at low temperatures may increase the electrochemical reaction inside the battery, which may increase safety risks, especially when the battery is already defective or aged.

[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 improve the sodium precipitation phenomenon at the negative electrode during the charging process. Without changing the battery design, the low-temperature charging performance can be optimized to enable it to be more widely used in low-temperature environments. Summary of the invention

[0006] 1. Problems to be solved

[0007] Aiming at the technical problems of low capacity of sodium ion batteries in the prior art when charged at low temperatures and serious sodium precipitation at the negative electrode, the present application provides a charging method for a sodium ion battery; further, the present application also provides a sodium ion battery; and at the same time, the present application also provides an application of the sodium ion battery.

[0008] 2. Technical solution

[0009] In order to achieve the above purpose, the technical solution provided is:

[0010] A method for charging a sodium ion battery comprises the following steps:

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

[0012] S2, charging the sodium ion battery to 0.5 times C0 at room temperature, and obtaining a charging terminal voltage V1;

[0013] S3, placing the sodium ion battery at a target low temperature in an empty state until the temperature of the sodium ion battery stably reaches the target low temperature, charging the sodium ion battery to 0.5 times C0, and obtaining the charging terminal voltage V2 of the sodium ion battery;

[0014] S4, calculate ΔV, wherein ΔV=V2-V1,

[0015] When ΔV≥X, the sodium ion battery is charged to full power by 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 power by a segmented charging method.

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

[0018] Through multiple charge and discharge cycles, the battery materials can be activated, which helps to ensure the stability and safety of the battery in long-term operation.

[0019] Preferably, in step S1, N times of charging and discharging are performed, where N≥3.

[0020] Preferably, charge at a constant current of 0.2C to 3.95V, then switch to constant voltage charging until the current drops to 0.05C, leave it for 30 minutes, then discharge at a current of 0.2C to 2.0V, leave it for another 30 minutes, repeat the above steps 3 times, take the third discharge capacity and record it as C0, and the third charge capacity is recorded as C1.

[0021] When N ≥ 3, the actual available capacity of the battery, i.e. C0, can be determined more accurately, which helps the battery management system (BMS) to more accurately control the battery charging and discharging process, avoid overcharging and over-discharging, and extend the battery life.

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

[0023] At low temperatures, the fluidity of the electrolyte will decrease, and its compatibility with the electrode will also deteriorate. Standing for ≥10 hours will help improve the compatibility of the electrolyte and electrode materials, thereby increasing the transport capacity of sodium ions in the electrolyte and improving the low-temperature charge and discharge performance of the battery to a certain extent. On the other hand, the battery reaches the target temperature and reaches a stable state.

[0024] Furthermore, in step S4, the segmented charging method is specifically as follows: each segment is charged with a constant current, and a rest time is set between each segment.

[0025] When charging at low temperatures, the battery's charging acceptance capacity will decrease. By combining segmented constant current charging with a rest period, the battery temperature can gradually rise, which can improve the charging efficiency. When charging at low temperatures, the sodium precipitation phenomenon is more significant, which will lead to irreversible loss of battery capacity. Segmented constant current charging can reduce the sodium precipitation phenomenon, thereby reducing the loss of battery capacity.

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

[0027] By gradually reducing the charging current, we can improve the charging efficiency and battery life while ensuring charging safety, reduce battery aging, and avoid sodium precipitation at the negative electrode.

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

[0029] By setting the rest time of 1h, the battery can have time to release the heat generated during the charging process, reduce the sodium precipitation phenomenon, and thus reduce the loss of battery capacity. On the other hand, it can avoid the problem of high polarization degree caused by continuous charging of the battery cell.

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

[0031] When ΔV<X, the battery polarization is not large. Using 0.1C current to charge to 0.7 times C0 can improve the battery's charging acceptance in a low temperature environment, allowing the battery to be charged with more electricity at a lower temperature. At the same time, it can effectively avoid sodium precipitation, protect battery safety, and shorten the charging time overall.

[0032] When ΔV≥X, the battery is polarized to a certain extent. If it is charged with a current of 0.1C, the polarization of the battery will increase. If the battery is directly charged in stages with a current of 0.05C, the charging efficiency of the battery can be improved and sodium precipitation at the negative electrode can be avoided.

[0033] Furthermore, the X is 0.25.

[0034] Use 0.25 as a value to judge the polarization degree of the battery. When ΔV ≥ 0.25, the battery is polarized to a certain extent. When ΔV < 0.25, the battery is not polarized much, so different charging methods are adopted.

[0035] A sodium ion battery, wherein during the preparation process of the sodium ion battery, any one of the charging methods is used.

[0036] Application of sodium ion batteries: applying the sodium ion batteries to the preparation of electric vehicles.

[0037] 3. Beneficial effects

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

[0039] (1) The charging method of the sodium ion battery of the present invention, because the battery polarization is serious at low temperature, and the polarization of the battery has a high correlation with the selection of the charging strategy, obtains the charging terminal voltage V1 at room temperature and the charging terminal voltage V2 at the target low temperature, and judges the polarization of the battery at low temperature by the difference between V2 and V1, and then selects the appropriate charging strategy, and uses different segmented charging methods according to the value of the difference. When charging to 0.5 times C0, the battery polarization is low, and it is easy to judge the polarization of the battery at low temperature, while ensuring that the charging time of the remaining battery power at low temperature will not be too long. This scheme is suitable for sodium ion batteries of layered oxygen system. On the basis of not changing the original design of the battery, the polarization of the battery cell can be judged according to the difference in charging terminal voltage at low temperature and room temperature, and the optimal charging method can be selected to charge the sodium ion battery to a full charge state at low temperature, and avoid the phenomenon of sodium precipitation at the negative electrode during low temperature charging, thereby improving the safety of the battery. It has a wide range of applicability, can adapt to sodium ion batteries of different types of layered oxygen systems, and provide flexible charging solutions for users with different needs.

[0040] (2) The sodium ion battery of the present invention uses the above-mentioned charging method during preparation. Improved safety: The safety of the battery is improved by avoiding the phenomenon of sodium precipitation at the negative electrode during low-temperature charging. The phenomenon of sodium precipitation may cause damage to the internal structure of the battery and increase safety risks. The sodium ion battery of the present invention can effectively avoid this problem. Optimized charging efficiency: The polarization of the battery cell is judged based on the voltage difference at the charging terminal at low temperature and normal temperature, and the optimal charging method is selected, which helps to improve the charging efficiency and reduce energy loss during the charging process, thereby extending the service life of the battery. Achievement of a fully charged state: This method can charge the sodium ion battery to a fully charged state at low temperature, which is particularly important for using electric vehicles in low temperature environments, because low temperature environments may affect the charging performance and endurance of the battery.

[0041] (3) Application of the sodium ion battery of the present invention, wherein the battery is applied in the preparation of electric vehicles. Better environmental adaptability: Sodium ion batteries have excellent capacity retention rates in both high and low temperature environments, which means that electric vehicles can operate under a wider range of climatic conditions and are not restricted by extreme temperatures. Fast charging capability: Sodium ion batteries can achieve fast charging capabilities, which greatly reduces the charging time of electric vehicles and improves user convenience. Cost-effectiveness: The material cost of sodium ion batteries is 30% to 40% lower than that of lithium ion batteries, which helps to reduce the overall manufacturing cost of electric vehicles, making electric vehicles more economical and thus promoting the popularization of electric vehicles. High safety: Sodium ion batteries are not prone to thermal runaway under extreme conditions and have good safety performance, which is crucial to ensuring the safety of electric vehicle users. Long cycle life: Sodium ion batteries have a long cycle life, which helps to reduce the maintenance cost and battery replacement frequency of electric vehicles and improve the operating efficiency and economy of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a flow chart of a segmented low-temperature charging method;

[0043] Figure 2 This is a physical picture of the negative electrode interface of the battery in Example 1 after it is fully charged;

[0044] Figure 3 This is a physical picture of the negative electrode interface of the battery in Example 2 after it is fully charged;

[0045] Figure 4 This is a physical picture of the negative electrode interface after the battery in Comparative Example 1 is fully charged and disassembled. DETAILED DESCRIPTION

[0046] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with embodiments.

[0047] Example 1

[0048] The charging method of the sodium ion battery of this embodiment, using a sodium ion battery of a layered oxygen system, comprises the following steps:

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

[0050] Through three times of charge and discharge, the actual available capacity of the battery, namely C0, can be determined more accurately, and the battery material can be activated at the same time, which is helpful for the stability and safety of the battery in long-term operation. C1 is the battery charging capacity at room temperature, which can be used to calculate the charging capacity ratio at low temperature.

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

[0052] S3, leaving the battery in an empty state at a target temperature of -10°C for 10 hours until the battery temperature reaches the target temperature, and then charging the battery at a constant current of 0.1C to 0.5 times C0, to obtain the battery charging terminal voltage V2;

[0053] At room temperature, the battery is charged at a constant current of 0.2C, which can save charging time. At low temperature, the battery is charged at a constant current of 0.1C, which can improve the battery's charging acceptance in a low temperature environment, allowing the battery to be charged with more power at a lower temperature. At the same time, it can effectively avoid the phenomenon of sodium precipitation and protect the battery safety. The reason for charging to 0.5 times C0 is that the battery polarization is low at this time, and at the same time, it ensures that the charging time of the remaining battery power at low temperature will not be too long. It is difficult for the battery to be charged to C0 at low temperatures, and as the charging power increases, the battery polarization will increase, 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 to 0.7 times C0 at a constant current of 0.1C, leave it for 1 hour, and then charge it to full power by segmented charging method. The segmented charging method is as follows:

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

[0056] Since the battery polarization is serious at low temperature, and the polarization of the battery is highly correlated with the choice of charging strategy, the difference between the charging terminal voltage V2 at low temperature and the charging terminal voltage V1 at normal temperature is mainly based on the difference between the normal charging terminal voltage at normal temperature and the severe low temperature polarization, to judge the polarization of the battery at low temperature, and then select the appropriate charging strategy. When ΔV = 0.21, that is, ΔV < 0.25, it means that the polarization of the battery is not large, and it can continue to be charged to 0.7 times C0 at a constant current of 0.1C, saving charging time. The remaining 0.3 times C0 capacity adopts a segmented charging system. By gradually reducing the charging current, it can improve the charging efficiency and battery life while ensuring charging safety, and reduce battery aging. By setting a 1h standby time, the battery can have time to release the heat generated during the charging process, reduce the sodium precipitation phenomenon, and thus reduce the loss of battery capacity. On the other hand, it avoids the problem of high polarization caused by continuous charging of the battery cell.

[0057] Example 2

[0058] The charging method of the sodium ion battery of this embodiment, using a sodium ion battery of a layered oxygen system, comprises the following steps:

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

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

[0061] S3, leaving the battery in an empty state at a target temperature of -10°C for 10 hours until the battery temperature reaches the target temperature, and then charging the battery at a constant current of 0.1C to 0.5 times C0, to obtain the battery charging terminal voltage V2;

[0062] S4. Calculate ΔV=V2-V1=0.32. When ΔV≥X, X is 0.25. The battery is charged to full power by a segmented charging method. The specific segmented charging method is as follows:

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

[0064] Since the battery will be polarized at low temperatures, the difference between the charging terminal voltage V2 at low temperatures and the charging terminal voltage V1 at normal temperatures is used to judge the polarization of the battery at low temperatures. When ΔV = 0.32, that is, ΔV ≥ 0.25, it means that the battery is polarized to a certain extent and cannot continue to be charged at a constant current of 0.1C. Instead, it is necessary to directly adopt a segmented charging method to fully charge the battery. By combining segmented constant current charging with a shelf time, the battery temperature gradually rises, which can improve the charging efficiency. The currents for segmented charging are 0.05C, 0.025C, 0.025C, 0.0125, and 0.0125, respectively, to ensure that the battery polarization is low during low temperature charging, avoid sodium precipitation at the negative electrode, and save charging time overall.

[0065] By Example 1, Example 2 and Figure 1It can be seen that 0.25 is used as a value to judge the polarization degree of the battery. When ΔV<0.25, it means that the polarization of the battery is not large. It can continue to charge at low temperature to 70% SOC (i.e. 0.7 times C0), and then adopt segmented charging (i.e. step charging) to full charge, which is shorter than directly charging from 50% SOC (i.e. 0.5 times C0) to full charge. 0.7 times C0 is a value between 0.5 times C0 and 1 times C0. If it is charged directly to C0, it will cause serious polarization of the battery cell and even sodium precipitation. Charging to 0.7 times C0 is on the one hand to ensure that the polarization degree of the battery is low and the negative electrode does not precipitate sodium, and on the other hand to shorten the entire low-temperature charging time. The remaining 0.3 times C0 capacity adopts a segmented charging system. When ΔV≥0.25, it means that the battery is polarized to a certain extent. At this time, directly adopting a segmented charging method to charge to full charge can further improve the battery charging efficiency and avoid sodium precipitation at the negative electrode.

[0066] SOC (state of charge) is the state of charge of the 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] The sodium-ion battery of Example 1 or Example 2 is applied to electric vehicles, with wide temperature adaptability: excellent high and low temperature performance, enabling electric vehicles to operate stably under a variety of climatic conditions. Fast charging: supports fast charging, significantly reduces charging waiting time, and improves user convenience. Economy: The material cost is lower than that of lithium batteries, which helps to reduce the manufacturing cost of the entire vehicle and improve the affordability of electric vehicles. High safety: It is less likely to have thermal runaway under extreme conditions, which enhances the safety of electric vehicles. Long life: Longer cycle life reduces the need for maintenance and battery replacement, and improves operating efficiency and economy.

[0068] Comparative Example 1

[0069] The sodium ion battery charging method of this comparative example uses a sodium ion battery of a layered oxygen system, comprising the following steps:

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

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

[0072] S3, place the battery in an empty state at the target temperature of -10℃ for 10 hours until the battery temperature reaches the target temperature, charge the battery at a constant current of 0.1C to 3.95V, and then switch to constant voltage charging until the current drops to 0.05C. At this point, the battery charging is complete, and the cumulative charging capacity C2 is recorded.

[0073] Comparative Example 2

[0074] The low-temperature charging method of the sodium ion battery of this comparative example uses a sodium ion battery of a layered oxygen system, comprising the following steps:

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

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

[0077] S3, leaving the battery in an empty state at a target temperature of -10°C for 10 hours until the battery temperature reaches the target temperature, and then charging the battery at a constant current of 0.1C to 0.5 times C0, to obtain the battery charging terminal voltage V2;

[0078] S4, calculate ΔV=V2-V1=0.38, when ΔV≥X, X is 0.25, the battery is first charged to 0.7 times C0 with a constant current of 0.1C, left for 1 hour, and then charged to full power by a segmented charging method. The segmented charging method is as follows: charge to 3.75V with a constant current of 0.05C, leave for 1 hour; then charge to 3.85V with a constant current of 0.025C, leave for 1 hour; then charge to 3.95V with a constant current of 0.0125C, the battery charging is now complete, and the cumulative charging capacity C2 is calculated.

[0079] Table 1 Battery charging capacity data of examples and comparative examples

[0080] C0(Ah) C1(Ah) C2(Ah) Charge capacity ratio (%) 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] It can be seen from the data in Table 1 that the low-temperature charging capacity ratios of the sodium ion batteries obtained by using the charging method of the present application in Examples 1 and 2 are higher than the ratios of the conventional charging system in Comparative Example 1. When ΔV ≥ 0.25, the charging capacity ratio of Example 2 is higher than the method of first charging to 0.7 times C0 and then adopting segmented charging in Comparative Example 2, because in Comparative Example 2, ΔV = 0.38, the battery polarization is large at low temperatures, and continuing to charge to 0.7 times C0 with a current of 0.1C will increase the battery polarization phenomenon, resulting in sodium precipitation at the negative electrode and a decrease in the charging capacity. The segmented low-temperature charging method involved in the present application solves the technical problem of low charging capacity of sodium ion batteries at low temperatures, and can ensure the low-temperature charging efficiency of the battery under different polarization states.

[0083] After the batteries of Example 1, Example 2 and Comparative Example 1 were fully charged and disassembled to observe the sodium precipitation at the negative electrode interface, the sodium ion batteries in Example 1 and Example 2 did not show the phenomenon of sodium precipitation after being fully charged and disassembled (such as Figure 2 , Figure 3 As shown), while in Comparative Example 1, strip-shaped sodium precipitation appeared on the negative electrode surface (as shown Figure 4 As shown), it shows that the charging method of the present application solves the technical problem of sodium precipitation during charging of sodium ion batteries at low temperatures and improves battery safety.

[0084] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person skilled in the art, several modifications, improvements and substitutions can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A method for charging a sodium ion battery, characterized in that: The following steps are involved: S1. Obtaining the constant capacity C0 of the sodium ion battery at room temperature; S2, charging the sodium ion battery to 0.5 times C0 at room temperature, and obtaining a charging terminal voltage V1; S3, placing the sodium ion battery at a target low temperature in an empty state until the temperature of the sodium ion battery stably reaches the target low temperature, charging the sodium ion battery to 0.5 times C0, and obtaining the charging terminal voltage V2 of the sodium ion battery; S4, calculate ΔV, wherein ΔV=V2-V1, When ΔV≥X, the sodium ion battery is charged to full power by a segmented charging method; When ΔV<X, the sodium ion battery is first charged to 0.7 times C0, and then charged to full power by a segmented charging method.

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

3. The method for charging a sodium ion battery according to claim 1, wherein: In step S3, the target low temperature is -10 to 0°C, and the standing time is ≥ 10 hours.

4. The method for charging a sodium ion battery according to claim 1, wherein: In step S4, the segmented charging method is specifically as follows: each segment is charged with a constant current, and a rest time is set between each segment.

5. The method for charging a sodium ion battery according to claim 4, characterized in that: The charging current of each segment decreases successively, and the charging current of each segment is 0.5 times of the previous segment.

6. The method for charging a sodium ion battery according to claim 4, characterized in that: The holding time is 1 hour.

7. The method for charging a sodium ion battery according to any one of claims 1 to 6, characterized in that: When the ΔV is less than X, the battery is charged at a constant current of 0.1C to 0.7 times C0, and then starts segmented charging at a current of 0.05C; when the ΔV is greater than or equal to X, the battery starts segmented charging at a current of 0.05C.

8. The method for charging a sodium ion battery according to claim 7, characterized in that: The X is 0.

25.

9. A sodium ion battery, characterized in that: During the preparation of the sodium ion battery, the charging method according to any one of claims 1 to 8 is used.

10. Application of sodium ion battery, characterized in that: The sodium ion battery according to claim 9 is applied in the preparation of electric vehicles.

Images