High-safety sodium ion battery, and capacity grading method and application therefor

Abstract

To provide a capacity grading method for a high-safety sodium ion battery that can be used for a backup power supply system as an energy storage module.SOLUTION: A grading method includes: charging and activating an assembled high-safety sodium ion battery in a 40-50°C environment (step S1); charging / discharging the high-safety sodium ion battery at a 0.1 C with a voltage of 0.3-1.6 V to calibrate the capacity and determining whether or not the capacity is acceptable based on a battery rated capacity (step S2); charging the high-safety sodium ion battery with an accepted capacity at a 0.1 C current to 1.3 V and switching to constant voltage charging to charge for 40 hours at a constant voltage (step S3); and after the high-safety sodium ion battery is brought into the constant voltage charging step, selecting any two hours from 30-40th hour, and performing capacity grading based on a percentage R of an average capacity per hour occupying the total battery capacity (step S4).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sodium ion battery, in particular to a high-safety sodium ion battery and its capacity grading method and application. [Background technology]

[0002] Backup power batteries are usually lead-acid batteries, but due to heavy metal contamination, lead-acid batteries are banned from sale in many countries and regions. Furthermore, the cycle life of lead-acid batteries is only 3 to 5 years. Lithium-ion batteries, which are used on a large scale, undergo long-term float charging, causing their internal structure to change. The main types of lithium-ion batteries are as follows:

[0003] (1) Irreversible reactions between the positive electrode material and the electrolyte mainly occur in two types of materials, lithium manganese oxide and lithium nickel oxide, which are prone to structural defects. For example, an irreversible phase transition occurs in the lithium manganese oxide positive electrode during long-term charging.

[0004] (2) The SEI film (solid electrolyte interphase film) formed during the chemical formation process is an irreversible reaction between the negative electrode material and the electrolyte. This film protects the negative electrode from corrosion by the electrolyte. Since the negative electrode is fully charged during the floating stage, the reaction between the negative electrode and the electrolyte is LiyC6 → Liy-xC6 + xLi + Reactions such as +xe may occur (Reference: Summary of float research on lithium-ion batteries, Energy Storage Science and Technology, January 2021, Vol. 10, Issue 1).

[0005] (3) During battery use and storage, the SEI film of the battery is constantly damaged and rebuilt due to the volume effect of the electrodes, and similar reactions irreversibly consume lithium ions in the electrolyte, further resulting in a loss of battery capacity (Reference: Float Life and Failure Analysis of Lithium Iron Phosphate / Graphite Batteries, Battery, October 2023, Vol. 53, Issue 5).

[0006] This suggests the existence of irreversible capacity during battery float due to the instability of the crystalline structure of the battery active material and the damage and reconstruction of the SEI film.

[0007] Conventional batteries undergo chemical capacity grading before being assembled into a system. The conventional chemical capacity grading process focuses on capacity and open-circuit voltage, but for batteries that are storage modules in backup electrical systems, there is no positive correlation between float performance and capacity / voltage. Therefore, using the conventional chemical capacity grading process may result in batteries with unacceptable float performance being introduced into the system, which could result in a shortened system lifespan. Summary of the Invention [Problem to be solved by the invention]

[0008] The objective of the present invention is to overcome the deficiencies of the prior art and improve the battery consistency and service life of backup power systems, thereby providing a battery capacity grading method and application in the energy storage module of backup power systems for large-scale use in UPS systems, and also to provide a high-safety sodium ion battery that uses a highly stable lattice structure material as the active material, does not generate solid electrolyte membrane (SEI) film during operation, and can meet the technical requirements for long-term float. [Means for solving the problem]

[0009] The technical solution for achieving the above object is as follows: A capacity grading method for a high-safety sodium ion battery, when the high-safety sodium ion battery functions as an energy storage module, comprises: S1. Assemble the highly safe sodium-ion battery and charge it under a 40-50℃ environment. S2, and calibrate the capacity by charging and discharging the high-safety sodium-ion battery at 0.3V~1.6V at 0.1C, and determine whether the capacity is acceptable based on the battery rated capacity; S3: The high-safety sodium ion battery with qualified capacity is charged to 1.3V at 0.1C current, and then switched to constant voltage charging for 40 hours. S4: After the high-safety sodium-ion battery enters the constant voltage charging stage, any two hours between the 30th and 40th hours are selected, and capacity grading is performed based on the percentage R of the average capacity per hour to the total battery capacity, with the battery classified as Class A if R<0.2‰, Class B if R=0.2-0.4‰, and Class C if R>0.4‰.

[0010] In the above-mentioned capacity grading method for high-safety sodium-ion batteries, the classified Class A batteries are used as energy storage modules in backup power systems, the classified Class B batteries are used as energy storage modules in industrial and commercial energy storage systems, and the classified Class B batteries are further used as energy storage modules in small energy storage systems.

[0011] The high-safety sodium ion battery, which is capacity graded using the above capacity grading method, is used as an energy storage module in a backup power system, and includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode and the negative electrode each comprise an active material, a conductive agent, and a binder. The active material of the positive electrode and the negative electrode each comprises a polyanion material with a very stable lattice structure, and no interfacial reaction occurs between the active material used by the positive electrode and the negative electrode and the electrolyte.

[0012] In the high-safety sodium ion battery, the active materials of the positive and negative electrodes are both selected to be phosphate compounds with a rapid sodium ion conducting structure.

[0013] In the above high safety sodium ion battery, the active material of the positive electrode is Na4Fe3(PO4)2(P2O7), Na4Fe 2.5 Ti 0.5 (PO4)2(P2O7), Na4Fe 3-x Mn x (PO4)2(P2O7), Na4Mn3(PO4)2(P2O7), Na3MnTi(PO4)3, <X<3であり、 The active material of the negative electrode is selected from at least one of NaTi2(PO4)3, Na3Fe2(PO4)3, and Na3MnTi(PO4)3.

[0014] In the high-safety sodium ion battery, no solid electrolyte phase interfacial film is formed at the interface between the negative electrode and the electrolyte, and no electrochemical interfacial film is formed at the interface between the positive electrode and the electrolyte.

[0015] In the high-safety sodium ion battery, the electrolyte uses at least one organic solvent selected from the group consisting of methyl ethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, and diethylene glycol dimethyl ether.

[0016] In the high-safety sodium-ion battery, the electrolyte uses at least one of sodium perchlorate, sodium bis(oxalic acid)borate, sodium bis(salicylic acid)borate, and sodium tetraphenylborate as an electrolyte salt.

[0017] In the high-safety sodium ion battery, the single battery capacity of the high-safety sodium ion battery is 100-350 Ah.

[0018] In the application of a high-safety sodium-ion battery as an energy storage module in a backup power system, if the capacity of a single battery of the high-safety sodium-ion battery after one hour of floating is less than 0.2‰ of the total battery capacity, it can be used as an energy storage module in the backup power system. [Effects of the Invention]

[0019] The high-safety sodium ion battery and its application and capacity grading method of the present invention have the following beneficial effects:

[0020] (1) The negative electrode active material has a stable crystalline structure. The change in the distance between the PO atoms and the Fe-O atoms of the phosphate compound during charging and discharging is minimal. The volume change of this material during charging and discharging is small, at approximately 6%, resulting in extremely strong structural stability and fatigue resistance. Even in the case of overcharging, the phosphate compound does not generate free oxygen and has low reactivity with organic electrolytes, resulting in excellent electrical safety. In addition, the phosphate compound has a high PO bond energy, and remains unchanged at temperatures below 400°C, providing excellent thermal stability.

[0021] (2) The battery system is stable, and both the positive and negative electrodes are made of ion-extraction materials. a) There is no "generation-dissolution-reconstruction" of the SEI film, and active sodium ions are not consumed. b) The ion-extraction materials do not generate sodium dendrites, and the current during long-term float operation is close to zero. Unlike overcharging lithium iron phosphate batteries, excessive lithium ions are released from the cathode material, forcing the excess lithium ions into the carbon anode structure or accumulating on the carbon surface to form lithium dendrites, gradually collapsing the structure of the positive electrode material and permanently damaging the electrode structure. (Reference: Applied Research on Environmentally Friendly Float-Type Lithium Iron Phosphate Batteries, Cen Kaijia, Popular Electric 2016 / 9) [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a 0.1C charge / discharge curve of a high-safety sodium ion battery of the present invention. [Figure 2] 1 shows current-voltage curves when the battery of Example 1 is floating. [Figure 3] FIG. 2 is an enlarged view of a current curve when the battery of Example 1 is floating. [Figure 4] 1 shows a capacity curve of the battery in a floating state in Example 1. [Figure 5] FIG. 10 is an enlarged view of a current curve when the battery floats in a comparative example. [Figure 6] 1 is a flowchart of a capacity grading method for a high-safety sodium ion battery. [Figure 7] A comparison of the float performance of different types of batteries. [Figure 8] Comparison of cycle performance of different types of batteries. DETAILED DESCRIPTION OF THE INVENTION

[0023] In order to enable those skilled in the art to better understand the technical solution of the present invention, the following detailed description of specific embodiments is given with reference to the accompanying drawings.

[0024] In an embodiment of the present invention, a high-safety sodium-ion battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode and the negative electrode each comprise an active material, a conductive agent, and a binder. The active materials of the positive electrode and the negative electrode each comprise a polyanion material with a highly stable lattice structure, and no interfacial reaction occurs between the active materials used in the positive electrode and the negative electrode and the electrolyte. The capacity of the battery after floating for one hour is less than 0.4‰ of the total battery capacity.

[0025] [Table 1]

[0026] Example 1: The high-safety sodium-ion battery used Na4Fe3(PO4)2(PO2O7) as the positive electrode active material and NaTi2(PO4)3 as the negative electrode active material, with the conductive agent being acetylene black, and the binder being a 5 wt.% PVDF (polyvinylidene difluoride) solution in MNP (N-methylpyrrolidone). The ratio of active material:conductive agent:binder was 90:5:5. The sheet was prepared by manual application, and the pouch-type battery of Example 1 was assembled and tested. The electrolyte salt in the electrolyte solution was sodium perchlorate with a concentration of 1 mol / kg, and the solvent was propylene carbonate.

[0027] See Figure 1. The battery of Example 1 was charged and discharged at 0.1C from 0.3V to 1.6V to calibrate the capacity, and the charge and discharge curve is shown in Figure 1, which revealed that the capacity of the battery cell was 520mAh.

[0028] See Figures 2 and 3. The battery in Example 1 was charged in a constant current-constant voltage float charge mode, with the current at constant current set to 50 mA (0.1 C) and the voltage at constant voltage set to 1.3 V. The constant voltage charge time was 168 hours. As can be seen from Figure 2, which shows the current-voltage curve during the float phase, after the charge mode was switched to constant voltage charge, the charge current began to decrease from 50 mA and essentially stabilized after 20 hours of constant voltage charge (reaching a total charge time of 30 hours), remaining less than 0.1 mA for most of the time (>98%) during the float phase. Referring to Figure 3, when the calibration capacity of the entire battery was 520 mAh, the capacity after one hour of floating was 0.19‰ of the total battery capacity.

[0029] See Figure 4. After the battery of Example 1 was activated, it was charged and discharged normally 10-20 times and then used. The capacity of the battery at the float stage remained unchanged, again verifying that no side reactions such as electrolyte reaction or active material dissolution occurred in the battery system, and no additional capacity replenishment was required during the float process.

[0030] Example 2: The highly safe sodium ion battery is made up of the positive and negative electrode active materials shown in Table 1. 2.5 Ti 0.5 Using (PO4)2(P2O7) as the positive electrode active material and NaTi2(PO4)3 as the negative electrode active material, a sheet was produced by manual application with reference to the method in Example 1, and a pouch-type battery of Example 2 was assembled and tested. The battery cell capacity was 530mAh, and the capacity after 1 hour of floating was 0.16‰ of the total battery capacity.

[0031] Example 3: The highly safe sodium ion battery is made up of the positive and negative electrode active materials shown in Table 1.2.5 Mn 0.5 Using (PO4)2(P2O7) as the positive electrode active material and Na3MnTi(PO4)3 as the negative electrode active material, a sheet was produced by manual application with reference to the method in Example 1, and a pouch-type battery of Example 3 was assembled and tested. The battery cell capacity was 515mAh, and the capacity after 1 hour of floating was 0.23‰ of the total battery capacity.

[0032] Comparative Example: Referring to FIG. 5 and Table 1 for the positive and negative electrode active materials, Na4Fe3(PO4)2(P2O7) was used as the positive electrode active material and hard carbon was used as the negative electrode active material. A sheet was produced by manual application using the method in Example 1. When the battery calibration capacity was 550 mAh, the current in the float stage was shown in FIG. 5. It was found that the current in the float stable stage was large, greater than 2 mA, and the battery capacity ratio was greater than 3.6‰. This is mainly because the solvent undergoes a reduction reaction on the surface of the hard carbon anode, and the SEI film constantly undergoes modification and repair reactions. However, when NaTi2(PO4)3 is used as the anode, its sodium embedding potential (2.1V) is much higher than the sodium deposition potential (0V), so no SEI occurs (Reference: Analysis and Improvement of the Causes of Expansion in Lithium-Ion Battery Float Tests, Li Huifang, Gao Junkui, Li Fei, Huang Jiajian, Power Technology, 2023 / 12). This meets the long-standing technical requirements for float, allowing it to be used in large-scale UPS systems.

[0033] See Figure 6. 200 square-case batteries with a rated capacity of 260 Ah were assembled using the active material and electrolyte in Example 1, and the capacity was graded according to the following method: S1. Charging and activating the assembled battery in a 40-50℃ environment. S2: Calibrate the capacity of the battery by charging and discharging it at 0.1C between 0.3V and 1.6V. If the capacity is greater than 260Ah, it is determined to be passed. The number of passed batteries is 193. S3: The battery whose capacity is approved is charged to 1.3V at 0.1C current, and then switched to constant voltage charging for 40 hours. S4: Any two hours were selected from the 30th to 40th hours of the constant voltage charging stage of the battery, and capacity grading was performed based on the percentage R of the average capacity per hour to the total battery capacity.

[0034] See Figures 7 and 8. R<0.2‰ was classified as Class A, R=0.2-0.4‰ as Class B, and R>0.4‰ as Class C. A total of 142 Class A products, 27 Class B products, and 24 Class C products were obtained. To verify the classification effect, a total of 12 random Class A, B, and C product batteries were connected in series and assembled into a small module with a rated voltage of 12V. A performance test was conducted using a simulated UPS. The specific test method was as follows: After capacity grading of the batteries, they were float-discharged at 1.3V for 14 days, and then calibrated by two charge-discharge cycles at 0.1C. This cycle was repeated. As can be seen from Figure 7, over a total of 15 cycles over 8 months, the calibrated capacity of the Class A batteries showed almost no decay. The capacity retention of the Class B batteries was 91.5%, while the capacity retention of the Class C batteries was the worst at 87.4%. This was because differences between individual batteries during the manufacturing process were magnified during long-term floating at high voltage charging states, resulting in, for example, micro-short circuits in the batteries, which reduced the capacity of individual batteries and affected the module capacity.

[0035] To compare whether there is a difference between cycle and float, a total of 12 randomly selected Class A, Class B, and Class C batteries were connected in series at the same time, assembled into a small module with a rated voltage of 12V, and cycle tested. The specific test method was as follows: After capacity grading of the battery, it was subjected to 1C charge / discharge cycles at a voltage of 0.3-1.6V, and every 500 cycles, 2 cycles of charge / discharge at 0.1C were performed to calibrate the capacity, and this was repeated. As can be seen from Figure 8, the order of decay is still Class A, followed by Class B, and then Class C. However, the capacity retention rate of Class B batteries (the capacity retention rate is the same at 1C and 0.1C) is 96.5%, and the capacity retention rate of Class C batteries (the capacity retention rate is the same at 1C and 0.1C) is 90.3%. Therefore, Class B and Class C batteries are not suitable for assembling into energy storage modules for use as UPS, but they can function as energy storage systems for charging and discharging. According to the decay rates of Class B and Class C batteries, when the capacity decays to 70%, the number of cycles is 20,000 and 7,000, respectively. Class B batteries can be used as energy storage modules in industrial and commercial energy storage systems, while Class C batteries can be used in small energy storage systems such as electric vehicles or street lights.

[0036] Based on the capacity grading method for high-safety sodium ion batteries of the present invention, when the high-safety sodium ion battery is used as an energy storage module in a backup power system, Class A batteries with R<0.2‰ can be selected and assembled; when the high-safety sodium ion battery is used as an energy storage module in an industrial or commercial energy storage system, Class B batteries with R=0.2-0.4‰ can be selected and assembled; and for small power supply systems (<20KWh) such as electric bicycles or street lights, Class C batteries with R>0.4‰ can be selected and assembled.

[0037] In conclusion, the high-safety sodium ion battery and its application and capacity grading method of the present invention use a high-stability lattice structure material as the active material, and the battery does not generate a solid electrolyte membrane (SEI) film during operation, and can meet the technical requirements for long-term float, so that it can be used on a large scale in UPS systems.

[0038] Those skilled in the art should recognize that the above examples are merely for the purpose of illustrating the present invention and are not intended to limit the present invention. Any changes or modifications to the above examples that fall within the substantial spirit of the present invention are within the scope of the claims of the present invention.

Claims

1. 1. A method for capacity grading a sodium-ion battery functioning as an energy storage module, comprising: Step S1: activating the sodium ion battery in an environment of 40-50°C; Then, in step S2, the sodium ion battery is charged and discharged at 0.1C and a voltage of 0.3V to 1.6V to calibrate the capacity, and the sodium ion battery is determined to be acceptable based on the rated capacity of the sodium ion battery. If the sodium ion battery is determined to be passed, charging the sodium ion battery to 1.3V at 0.1C current, and then switching to constant voltage charging for 40 hours in step S3; and step S4, after the sodium-ion battery enters the constant voltage charging stage, selecting any two hours from the 30th hour to the 40th hour of the constant voltage charging, and performing capacity grading on the sodium-ion battery based on the value of R (R is the ratio of the average capacity per hour during the constant voltage charging period to the total capacity of the sodium-ion battery), so that if R<0.2‰, the sodium-ion battery is classified as Class A, if R=0.2-0.4‰, the sodium-ion battery is classified as Class B, and if R>0.4‰, the sodium-ion battery is classified as Class C.

2. 2. The capacity grading method for sodium ion batteries according to claim 1, wherein the sodium ion batteries classified as Class A can be used as energy storage modules in backup power supply systems, and the batteries classified as Class B can be used as energy storage modules in industrial and commercial energy storage systems, and can also be used as energy storage modules in small energy storage systems.

3. 2. The capacity grading method for a sodium ion battery according to claim 1, wherein the sodium ion battery comprises a positive electrode, a negative electrode, and an electrolyte, the positive electrode and the negative electrode each comprising an active material, a conductive agent, and a binder, the active materials of the positive electrode and the negative electrode each being made of a polyanion material, and no interfacial reaction occurs between the electrolyte and the active materials used by the positive electrode and the negative electrode.

4. The capacity grading method for a sodium ion battery according to claim 3, characterized in that the active materials of the positive and negative electrodes are both phosphate compounds with a rapid conduction structure of sodium ions.

5. The active material of the positive electrode is Na ４ Fe ３ (P.O. ４ ) ２ (P ２ O ７ ), Na ４ Fe ２．５ Ti ０．５ (P.O. ４ ) ２ (P ２ O ７ ), Na ４ Fe ３－ｘ Mn ｘ (P.O. ４ ) ２ (P ２ O ７ ), Na ４ Mn ３ (P.O. ４ ) ２ (P ２ O ７ ) and Na ３ MnTi(PO ４ ) ３ and 0<X<3; The active material of the negative electrode is NaTi ２ (P.O. ４ ) ３ , Na ３ Fe ２ (P.O. ４ ) ３ and Na ３ MnTi(PO ４ ) ３ 5. The capacity grading method for a sodium ion battery according to claim 4, wherein the capacity grading is selected from at least one of the following:

6. 6. The capacity grading method for a sodium-ion battery according to claim 5, wherein no solid electrolyte phase is generated during operation of the battery, and no electrochemical interfacial phase is generated at the interface between the positive electrode and the electrolyte.

7. 4. The capacity grading method for a sodium ion battery according to claim 3, wherein the electrolyte uses at least one of methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, and diethylene glycol dimethyl ether as an organic solvent.

8. 4. The capacity grading method for a sodium ion battery according to claim 3, wherein the electrolyte uses at least one of sodium perchlorate, sodium bis(oxalic acid)borate, sodium bis(salicylic acid)borate, and sodium tetraphenylborate as an electrolyte salt.

9. The capacity grading method for a sodium ion battery according to claim 3, wherein the monomer battery capacity of the sodium ion battery is 100-350 Ah.

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