Sodium-ion battery low-temperature charging strategy exploration method and application thereof

Abstract

The invention relates to the technical field of sodium-ion batteries, in particular to an exploration method for a low-temperature charging strategy of a sodium-ion battery and application of the exploration method. The exploration method comprises the following steps: obtaining a low-temperature capacity retention ratio CR, a room-temperature capacity recovery rate CRR and a negative electrode sodium precipitation condition of the sodium-ion battery; when CR is greater than or equal to 99%, CRR is greater than or equal to 99% and no sodium is separated from the negative electrode, gradually increasing the preset cut-off voltage, and repeating the operation until at least one of CR is greater than or equal to 99%, CRR is greater than or equal to 99% and no sodium is separated from the negative electrode is not satisfied; and when at least one of CR > = 99%, CRR > = 99% and no sodium precipitation of the negative electrode is not satisfied, gradually reducing the preset cut-off voltage, and repeating the operation until CR > = 99%, CRR > = 99% and no sodium precipitation of the negative electrode are satisfied at the same time. According to the method, the proper charging rate and charging upper limit voltage of the sodium ion battery at the low temperature can be explored, so that a safe, rapid and reliable charging strategy of the sodium ion battery at the low temperature is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a method for exploring a low-temperature charging strategy for sodium ion batteries and an application thereof. Background Art

[0002] Sodium-ion batteries are one of the most promising secondary batteries after lithium-ion batteries. They have the characteristics of low raw material cost, excellent rate performance and low-temperature performance. Unlike lithium-ion batteries, sodium-ion batteries can also be charged to a certain extent in low-temperature environments. Low-temperature charging and discharging is one of the advantages of sodium-ion batteries, which allows sodium-ion batteries to abandon complex thermal management systems in the application of low-speed electric vehicles, electric vehicles and energy storage systems, thereby reducing costs.

[0003] However, in low temperature environments, if there is no appropriate charging rate and charging voltage upper limit, sodium precipitation may occur in sodium-ion batteries, reducing the cycle life of sodium-ion batteries.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The first object of the present invention is to provide a method for exploring a low-temperature charging strategy for a sodium ion battery, which can explore the appropriate charging rate and upper charging limit voltage of the sodium ion battery at low temperatures, thereby providing a safe, fast and reliable charging strategy for the sodium ion battery at low temperatures.

[0006] The second object of the present invention is to provide a method for exploring a low-temperature charging strategy for a sodium ion battery and its application in sodium ion batteries and electrical equipment containing the sodium ion batteries.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0008] The present invention provides a method for exploring a low-temperature charging strategy for a sodium ion battery, comprising the following steps:

[0009] S1: Obtain the low temperature capacity retention rate CR and room temperature capacity recovery rate CRR of the sodium ion battery:

[0010] At room temperature, the sodium ion battery is discharged at 0.5C to its discharge cut-off voltage, then charged at 0.5C / 0.05C constant current and constant voltage to its charge cut-off voltage, discharged at 0.5C to its discharge cut-off voltage, and cycled constant current and constant voltage charge-discharge x times to obtain an average discharge capacity C0;

[0011] After the sodium ion battery is left to stand for a first preset time at a preset temperature, the sodium ion battery is first charged at a preset rate constant current to a preset cut-off voltage, and then discharged at a 0.5C discharge current to its discharge cut-off voltage, and the charge and discharge are cycled n times to obtain each low-temperature charge capacity and each low-temperature discharge capacity, wherein the first low-temperature discharge capacity is LT-C1, and the nth low-temperature discharge capacity is LT-C n ;

[0012] After the sodium ion battery is left to stand at room temperature for a second preset time, the sodium ion battery is first charged at a constant current and constant voltage of 0.5C / 0.05C to its charge cut-off voltage, and then discharged at 0.5C to its discharge cut-off voltage, and the charge and discharge are cycled y times to obtain each room temperature charge capacity and each room temperature discharge capacity, wherein the first room temperature discharge capacity is AMB-C1;

[0013] At room temperature, after charging the sodium ion battery at 0.5C to a charging cut-off voltage, the sodium ion battery is disassembled to observe the sodium precipitation at the negative electrode;

[0014] Calculate CR and CRR, CR = LT-C n / LT-C1×100%, CRR=AMB-C1 / C0×100%;

[0015] S2: When CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode, gradually increase the preset cut-off voltage and repeat step S1 until at least one of CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is not satisfied; when at least one of CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is not satisfied, gradually reduce the preset cut-off voltage and repeat step S1 until CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode are satisfied at the same time;

[0016] In step S1, the preset temperature is less than the room temperature.

[0017] Furthermore, the room temperature is 25°C; and / or the preset temperature is <25°C.

[0018] Furthermore, the gradient interval of gradually increasing the preset cut-off voltage or gradually decreasing the preset cut-off voltage is 0.1V.

[0019] Further, in step S2, when CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode, the preset cut-off voltage is gradually increased, and step S1 is repeated until at least one of CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is not satisfied, and the highest preset cut-off voltage satisfying CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is determined to be the highest safe charging voltage at the corresponding preset temperature and the corresponding preset rate; when at least one of CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is not satisfied, the preset cut-off voltage is gradually reduced, and step S1 is repeated until CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode are simultaneously satisfied, and the preset cut-off voltage when CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is determined to be the highest safe charging voltage at the corresponding preset temperature and the corresponding preset rate.

[0020] Furthermore, the preset rate is adjusted, and step S1 and step S2 are repeated to obtain the highest safe charging voltage under different preset rates.

[0021] Furthermore, the gradient interval of the preset magnification is adjusted to 0.1C.

[0022] Furthermore, the preset temperature is adjusted, and step S1 and step S2 are repeated to obtain the highest safe charging voltage at different preset temperatures.

[0023] Furthermore, the gradient interval of the preset temperature is adjusted to 10°C.

[0024] Furthermore, in step S1, x≥3.

[0025] Furthermore, in step S1, the first preset time is ≥5h.

[0026] Furthermore, in step S1, the preset magnification is 0.1C to 5C.

[0027] Further, in step S1, the preset cut-off voltage is a discharge cut-off voltage of the sodium ion battery ~ a charge cut-off voltage of the sodium ion battery.

[0028] Furthermore, in step S1, n≥10.

[0029] Furthermore, in step S1, the second preset time is ≥ 3 hours.

[0030] Furthermore, in step S1, y≥10.

[0031] The present invention further provides the application of the method for exploring the low-temperature charging strategy of the sodium ion battery in the sodium ion battery and the electrical equipment containing the sodium ion battery.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The method for exploring the low-temperature charging strategy of sodium ion batteries provided in the present invention can explore the appropriate charging rate and upper charging limit voltage of sodium ion batteries at low temperatures, thereby providing a safe, fast and reliable charging strategy for sodium ion batteries at low temperatures.

[0034] (2) The method for exploring the low-temperature charging strategy of sodium-ion batteries provided by the present invention can accurately analyze the low-temperature charging performance of sodium-ion batteries by comprehensively judging the low-temperature charging capability of sodium-ion batteries based on the low-temperature capacity retention rate CR, the room-temperature capacity recovery rate CRR, and the sodium precipitation situation.

[0035] (3) The method for exploring the low-temperature charging strategy of sodium ion batteries provided by the present invention can quickly analyze the maximum charging voltage at different rates at different temperatures through low-temperature cycling, then room temperature cycling, and disassembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 A schematic flow chart of a method for exploring a low-temperature charging strategy for sodium-ion batteries provided by the present invention. DETAILED DESCRIPTION

[0038] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0039] Unless otherwise specified, in the present invention, "the first aspect", "the second aspect", "the third aspect", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0040] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0041] If there is no special explanation, in the present invention, "one or more" or "at least one" refers to any one, any two or more of the listed items. Among them, "several" refers to any two or more of the listed items.

[0042] In the first aspect, the present invention provides a method for exploring a low-temperature charging strategy for a sodium ion battery, such as Figure 1 The figure shows a flow chart of a method for exploring a low-temperature charging strategy for sodium-ion batteries, which specifically includes the following steps:

[0043] Step S1: obtaining the low temperature capacity retention rate CR and room temperature capacity recovery rate CRR of the sodium ion battery, and the obtaining method is as follows:

[0044] At room temperature, the sodium ion battery is discharged at 0.5C to its discharge cut-off voltage, and then charged at 0.5C / 0.05C constant current and constant voltage to its charge cut-off voltage, discharged at 0.5C to its discharge cut-off voltage, and the above constant current and constant voltage charge-discharge is cycled x times to obtain an average discharge capacity C0 for x times. Among them, charging at 0.5C / 0.05C constant current and constant voltage means charging at 0.5C constant current to the cut-off voltage, and then charging at constant voltage until the current is less than 0.05C. It can be understood that after x cycles, multiple groups of discharge capacities are obtained, and the average value is the average discharge capacity C0.

[0045] Further, the sodium ion battery is left to stand at a preset temperature for a first preset time, so that the difference between the battery temperature and the preset temperature is within an error range, wherein the error range is ±2°C. Then, the sodium ion battery is first charged at a preset rate constant current to a preset cut-off voltage, and then discharged at a 0.5C discharge current to its discharge cut-off voltage, and the charge and discharge process is cycled n times to obtain each low-temperature charge capacity and each low-temperature discharge capacity, wherein the first low-temperature discharge capacity is LT-C1, and the nth low-temperature discharge capacity is LT-C n The first preset time may be dynamically adjusted according to the temperature difference between the ambient temperature and the battery.

[0046] Further, the sodium ion battery is left to stand at room temperature for a second preset time so that the difference between the battery temperature and the room temperature is within an error range, wherein the error range is ±2°C. Then, the sodium ion battery is first charged to its charging cut-off voltage at 0.5C / 0.05C constant current and constant voltage, and then discharged to its discharge cut-off voltage at 0.5C, and the charge and discharge process is cycled y times to obtain each room temperature charging capacity and each room temperature discharge capacity, wherein the first room temperature discharge capacity is AMB-C1. Among them, the second preset time can be dynamically adjusted according to the ambient temperature and the temperature difference of the battery. Among them, charging with 0.5C / 0.05C constant current and constant voltage means charging with 0.5C constant current to the cut-off voltage, and then charging with constant voltage until the current is less than 0.05C.

[0047] It is understandable that between each charging and each discharging, a rest or a rest is performed, wherein the rest time may be 30 minutes.

[0048] Furthermore, at room temperature, after the sodium ion battery is charged at 0.5C to a charge cut-off voltage, the sodium ion battery is disassembled to observe the sodium precipitation at the negative electrode and determine whether sodium precipitation occurs.

[0049] Calculate CR and CRR, where the calculation method is as follows: CR = LT - C n / LT-C1×100%, CRR=AMB-C1 / C0×100%.

[0050] Step S2: judgment: when CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode are satisfied at the same time, the preset cut-off voltage is gradually increased, and step S1 is repeated until at least one of CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode is not satisfied; when at least one of CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode is not satisfied, the preset cut-off voltage is gradually reduced, and step S1 is repeated until CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode are satisfied at the same time.

[0051] Wherein, in step S1, the preset temperature is less than the room temperature.

[0052] The method for exploring the low-temperature charging strategy of a sodium ion battery provided by the present invention can explore the appropriate charging rate and upper charging limit voltage of the sodium ion battery at low temperatures, thereby providing a safe, fast and reliable charging strategy for the sodium ion battery at low temperatures.

[0053] The present invention can accurately analyze the low-temperature charging performance of the sodium ion battery by comprehensively judging the low-temperature charging capability of the sodium ion battery through the low-temperature capacity retention rate CR, the room-temperature capacity recovery rate CRR and the sodium precipitation situation.

[0054] Furthermore, the present invention can quickly analyze the maximum charging voltage at different rates at various temperatures through low-temperature cycling, room-temperature cycling, and disassembly.

[0055] In some specific embodiments, the room temperature is 25°C.

[0056] In some specific embodiments, the preset temperature is <25°C, including but not limited to 24°C, 20°C, 15°C, 10°C, 5°C, 1°C, 0°C, -1°C, -3°C, -5°C, -10°C, -15°C, -20°C, -25°C, -30°C, -35°C, -40°C, or any range between two of them. The present invention can explore the charging capacity of sodium ion batteries at low temperatures.

[0057] In some specific implementations, the preset temperature is less than 25° C. and greater than or equal to −40° C. This temperature range can cover the lowest temperature in most areas.

[0058] In some specific implementations, the gradient interval of gradually increasing the preset cut-off voltage or gradually decreasing the preset cut-off voltage is 0.1V.

[0059] In some specific embodiments, in step S2, when CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode, the preset cut-off voltage is gradually increased, and step S1 is repeated until at least one of CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is not satisfied, and the highest preset cut-off voltage that satisfies CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is determined to be the highest safe charging voltage at the corresponding preset temperature and the corresponding preset rate.

[0060] Furthermore, when at least one of CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode is not satisfied, the preset cut-off voltage is gradually reduced, and step S1 is repeated until CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode are satisfied at the same time, and the preset cut-off voltage when CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode is determined to be the highest safe charging voltage at the corresponding preset temperature and the corresponding preset rate.

[0061] In some specific implementations, the preset rate is adjusted, and step S1 and step S2 are repeated to obtain the highest safe charging voltage under different preset rates.

[0062] In some specific implementations, the gradient interval of the preset magnification is adjusted to 0.1C.

[0063] In some specific implementations, the preset temperature is adjusted, and step S1 and step S2 are repeated to obtain the highest safe charging voltage at different preset temperatures.

[0064] In some specific implementations, the preset temperature is adjusted to a gradient interval of 10°C.

[0065] The present invention provides a testing method for exploring the safe charging boundary of sodium ion batteries in a low temperature environment. Through charging tests at different temperatures, different rates, and different upper limit voltages, the optimal charging strategy for sodium ion batteries that is fast, safe, and reliable at low temperatures is found.

[0066] Based on the highest voltage that meets the above criteria at each temperature and rate, a charging strategy that meets the requirements can be formulated.

[0067] In some specific implementations, in step S1, x≥3, including but not limited to any point value of 3, 4, 5, 6, 7, 8, 10 or a range of values ​​between any two of them.

[0068] In some specific implementations, in step S1, the first preset time is ≥ 5 hours, including but not limited to any point value of 5 hours, 6 hours, 7 hours, and 8 hours, or a range of values ​​between any two of them. Only when the battery is left at the corresponding temperature for a sufficient period of time can the temperature from the outside to the inside of the battery be consistent with the ambient temperature.

[0069] In some specific embodiments, in step S1, the preset ratio is 0.1C to 5C, including but not limited to any point value of 0.1C, 0.3C, 0.5C, 0.8C, 1C, 1.3C, 1.5C, 2C, 2.5C, 3C, 3.5C, 4C, 4.5C, and 5C, or a range value between any two of them.

[0070] In some specific implementations, in step S1, the preset cut-off voltage is a discharge cut-off voltage of the sodium ion battery ~ a charge cut-off voltage of the sodium ion battery.

[0071] The range of the preset rate and the preset cut-off voltage is the normal usage range at room temperature. The purpose is to explore a charging strategy with greater charging capacity and faster charging speed at low temperatures without sacrificing battery life and performance.

[0072] In some specific implementations, in step S1, n≥10, including but not limited to any point value of 10, 11, 12, 13, 14, 15, 16, 18, 20, 23, 25, 28, 30, 33, 35, 38, 40, 42, 45, 48, 50 or a range value between any two of them. Preferably, n=10-50.

[0073] In some specific implementations, in step S1, the second preset time is ≥ 3 hours, including but not limited to any point value of 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours, or a range value between any two of them.

[0074] In some specific implementations, in step S1, y≥10, including but not limited to any point value of 10, 11, 12, 13, 15, 18, 20, 25, 30, 35, 40, 45, 50 or a range value between any two of them. Preferably, y=10-50.

[0075] In a second aspect, the present invention provides the application of the method for exploring the low-temperature charging strategy of sodium ion batteries in sodium ion batteries and electrical equipment containing the sodium ion batteries.

[0076] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0077] Example 1

[0078] Taking 32140-MP10 sodium ion battery as an example, the method for exploring the optimal charging strategy of sodium ion battery at low temperature provided in this embodiment includes the following steps:

[0079] (1) At room temperature (25°C), a) the battery is discharged at a constant current of 0.5C to 2V and allowed to stand for 30 minutes, b) it is then charged at a constant current and voltage of 0.5C / 0.05C to 4V and allowed to stand for 30 minutes, c) it is discharged at a constant current of 0.5C to 2V and allowed to stand for 30 minutes, and steps b) to c) are cycled three times to obtain an average discharge capacity C0;

[0080] (2) the battery is left at a preset temperature of -10°C for a first preset time of 5 hours, so that the difference between the battery temperature and the preset temperature of -10°C is within an error range of ±2°C;

[0081] (3) Charge the battery at a preset rate of 0.1C constant current to a preset cut-off voltage of 3.6V, let it stand for 30 minutes, then discharge it at a standard discharge current of 0.5C to a cut-off voltage of 2V, and let it stand for 30 minutes;

[0082] (4) Step (3) is cycled for a fixed number of times 10 times, and the charging capacity of each time is obtained, LT-CHG-C1, LT-CHG-C2, LT-CHG-C3, ..., LT-CHG-C 10 , and discharge capacity LT-C1, LT-DIS-C2, LT-DIS-C3, ..., LT-DIS-C 10 ; The first low-temperature discharge capacity is LT-C1, and the nth low-temperature discharge capacity is LT-C n ;

[0083] (5) returning the battery to room temperature and leaving it at room temperature for a second preset time of 3 hours, so that the difference between the battery temperature and room temperature is within an error range;

[0084] (6) Charge to 4 V at 0.5 C / 0.05 C constant current and constant voltage, let stand for 30 min, discharge to 2 V at 0.5 C constant current, let stand for 30 min, cycle 10 times, and obtain the charge capacity AMB-CHG-C1, AMB-CHG-C2, AMB-CHG-C3, ..., AMB-CHG-C 10 , and discharge capacity AMB-C1, AMB-C2, AMB-C3, ..., AMB-C 10 ; The first room temperature discharge capacity is AMB-C1;

[0085] (7) At room temperature, perform standard charging on the above batteries (charge at 0.5C to the charging cut-off voltage specified by the product), disassemble the fully charged batteries, and observe whether there is sodium precipitation at the negative electrode;

[0086] (8) Calculate the low temperature capacity retention rate CR and room temperature capacity recovery rate CRR of the battery, where CR = LT-C n / LT-C1×100%, CRR=AMB-C1 / C0×100%, the results are shown in Table 1, which meets CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode (to improve accuracy, this scheme tests two groups of batteries, and Table 1 is the test results of the two groups of batteries).

[0087] The preset cut-off voltage was increased to 3.7 V, and the above test was repeated. The obtained CR, CRR and sodium precipitation of the negative electrode are shown in Table 1 below (to improve accuracy, this scheme tests two groups of batteries, and Table 1 is the test results of the two groups of batteries).

[0088] Table 1 CR, CRR and sodium precipitation at negative electrode

[0089]

[0090]

[0091] It can be found from Table 1 above that the maximum safe charging voltage of this type of battery at -10℃ and 0.1C is 3.6V.

[0092] Repeat the above test method by changing the preset rate in turn, and finally obtain the appropriate charging strategy at this temperature.

[0093] The above test was repeated by changing the preset temperatures in sequence, and finally a full-temperature charging strategy for sodium-ion batteries was obtained.

[0094] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for exploring a low-temperature charging strategy for sodium-ion batteries, characterized in that: The steps include: S1: Obtain the low temperature capacity retention rate CR and room temperature capacity recovery rate CRR of the sodium ion battery: At room temperature, the sodium ion battery is discharged at 0.5C to its discharge cut-off voltage, then charged at 0.5C / 0.05C constant current and constant voltage to its charge cut-off voltage, discharged at 0.5C to its discharge cut-off voltage, and cycled constant current and constant voltage charge-discharge x times to obtain an average discharge capacity C0; After the sodium ion battery is left to stand for a first preset time at a preset temperature, the sodium ion battery is first charged at a preset rate constant current to a preset cut-off voltage, and then discharged at a 0.5C discharge current to its discharge cut-off voltage, and the charge and discharge are cycled n times to obtain each low-temperature charge capacity and each low-temperature discharge capacity, wherein the first low-temperature discharge capacity is LT-C1, and the nth low-temperature discharge capacity is LT-C n ; After the sodium ion battery is left to stand at room temperature for a second preset time, the sodium ion battery is first charged at a constant current and constant voltage of 0.5C / 0.05C to its charge cut-off voltage, and then discharged at 0.5C to its discharge cut-off voltage, and the charge and discharge are cycled y times to obtain each room temperature charge capacity and each room temperature discharge capacity, wherein the first room temperature discharge capacity is AMB-C1; At room temperature, after charging the sodium ion battery at 0.5C to a charging cut-off voltage, the sodium ion battery is disassembled to observe the sodium precipitation at the negative electrode; Calculate CR and CRR, CR = LT-C n / LT-C1×100%, CRR=AMB-C1 / C0×100%; S2: When CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode, gradually increase the preset cut-off voltage and repeat step S1 until at least one of CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is not satisfied; when at least one of CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is not satisfied, gradually reduce the preset cut-off voltage and repeat step S1 until CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode are satisfied at the same time; In step S1, the preset temperature is less than the room temperature.

2. The method for exploring the low temperature charging strategy of sodium ion batteries according to claim 1, characterized in that: The room temperature is 25°C; and / or the preset temperature is <25°C.

3. The method for exploring the low temperature charging strategy of sodium ion batteries according to claim 1 is characterized in that: The gradient interval of gradually increasing the preset cut-off voltage or gradually decreasing the preset cut-off voltage is 0.1V.

4. The method for exploring the low temperature charging strategy of sodium ion batteries according to claim 1, characterized in that: In step S2, when CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode, the preset cut-off voltage is gradually increased, and step S1 is repeated until at least one of CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is not satisfied, and the highest preset cut-off voltage satisfying CR≥99%, CRR≥99% and no sodium is precipitated at the negative electrode is determined to be the highest safe charging voltage at the corresponding preset temperature and the corresponding preset rate; When at least one of CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode is not satisfied, the preset cut-off voltage is gradually reduced, and step S1 is repeated until CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode are satisfied at the same time, and the preset cut-off voltage when CR≥99%, CRR≥99% and no sodium precipitation at the negative electrode is determined to be the highest safe charging voltage at the corresponding preset temperature and the corresponding preset rate.

5. The method for exploring the low temperature charging strategy of sodium ion batteries according to claim 4 is characterized in that: Adjusting the preset rate, and repeating step S1 and step S2 to obtain the highest safe charging voltage under different preset rates; Preferably, the gradient interval of adjusting the preset magnification is 0.1C.

6. The method for exploring the low temperature charging strategy of sodium ion batteries according to claim 4, characterized in that: Adjusting the preset temperature, and repeating step S1 and step S2 to obtain the highest safe charging voltage under different preset temperatures; Preferably, the preset temperature is adjusted in gradient intervals of 10°C.

7. The method for exploring the low temperature charging strategy of sodium ion batteries according to claim 1, characterized in that: In step S1, x≥3.

8. The method for exploring the low temperature charging strategy of sodium ion batteries according to claim 1, characterized in that: In step S1, at least one of the following conditions is met: (1) The first preset time is ≥ 5 hours; (2) The preset magnification is 0.1C to 5C; (3) The preset cut-off voltage is a discharge cut-off voltage of the sodium ion battery ~ a charge cut-off voltage of the sodium ion battery; (4) The n is ≥10.

9. The method for exploring the low temperature charging strategy of sodium ion batteries according to claim 1, characterized in that: In step S1, at least one of the following conditions is met: (1) The second preset time is ≥ 3 hours; (2) Said y≥10.

10. Application of the method for exploring the low-temperature charging strategy of a sodium ion battery according to any one of claims 1 to 9 in a sodium ion battery and an electrical device containing the sodium ion battery.

Images