High-safety sodium-ion battery, its capacity grading method, and applications

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] This invention relates to sodium-ion batteries, particularly high-safety sodium-ion batteries, a method for grading their capacity, and their applications. [Background technology]

[0002] Backup power batteries are typically lead-acid batteries, but due to heavy metal contamination, their sale is prohibited in many countries and regions. Furthermore, lead-acid batteries only have a cycle life of 3-5 years. Lithium-ion batteries, which are used on a large scale, undergo changes in their internal structure due to long-term float charging, primarily resulting in the following:

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

[0004] (2) The SEI film (solid electrolyte phase interface film) formed during the chemical conversion by the irreversible reaction between the negative electrode material and the electrolyte protects the negative electrode from corrosion of the electrolyte. When the negative electrode is fully charged during the float phase, 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, No. 1).

[0005] (3) During battery use and storage, the SEI film of the battery undergoes a similar reaction due to constant damage and reconstruction caused by the volume effect of the electrodes, irreversibly consuming lithium ions in the electrolyte and further reducing battery capacity (Reference: Float life and failure analysis of lithium iron phosphate / graphite batteries, "Batteries", October 2023, Vol. 53, No. 5).

[0006] This allows us to infer the instability of the crystal structure of the battery system active material and the existence of irreversible capacity in the battery's float due to the damage and reconstruction of the SEI film.

[0007] Conventional batteries undergo chemical conversion capacity grading before being assembled into a system. While this conventional process focuses on capacity and open-circuit voltage, batteries, which are storage modules in backup electrical systems, do not have a positive correlation between float performance and capacity / voltage. Using the conventional chemical conversion capacity grading process can introduce batteries with substandard float performance into the system, potentially leading to a reduced system lifespan. [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0009] The proposed technology to achieve the above objective is as follows: A capacity grading method for a high-safety sodium-ion battery, wherein when the high-safety sodium-ion battery functions as an energy storage module, capacity grading is performed in the following manner: S1, the assembled high-safety sodium-ion battery is charged and activated in a 40-50°C environment. S2, and a high-safety sodium-ion battery, are charged and discharged at 0.1C from 0.3V to 1.6V to calibrate their capacity, and it is determined whether the capacity meets the requirements based on the battery's rated capacity. S3, a high-safety sodium-ion battery that passed capacity requirements was charged to 1.3V with a 0.1C current, then switched to constant voltage charging and charged at a constant voltage for 40 hours. S4. After the high-safety sodium-ion battery enters the constant voltage charging phase, any two hours are selected from 30 to 40 hours, and the average capacity per hour is calculated as a percentage of the total battery capacity. ratio The system is characterized by performing capacity grading based on R, classifying products into Category A if R < 0.2‰, Category B if R = 0.2-0.4‰, and Category C if R > 0.4‰.

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

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

[0012] In the above-mentioned high-safety sodium-ion battery, the active materials for both the positive and negative electrodes are selected to be phosphate compounds having a rapid sodium ion conductivity structure.

[0013] In the above-mentioned 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 At least one of (PO4)2(P2O7), Na4Mn3(PO4)2(P2O7), and Na3MnTi(PO4)3 is selected, 0 <X<3であり、 The active material for the negative electrode is selected from at least one of NaTi2(PO4)3, Na3Fe2(PO4)3, and Na3MnTi(PO4)3.

[0014] In the above-described 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 above-mentioned high-safety sodium-ion battery, the electrolyte uses at least one of the following organic solvents: methyl ethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, and diethylene glycol dimethyl ether.

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

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

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

[0019] The present invention provides a highly safe sodium-ion battery, its applications, and a capacity grading method, which have the following beneficial effects.

[0020] (1) The negative electrode active material has a stable crystal structure. The change in the distance between the P-O atoms and the Fe-O atoms during charge and discharge of the phosphate compound is not large, and the volume change of this material during charge and discharge is small, about 6%. Therefore, it has extremely strong structural stability and fatigue resistance. Even in the case of overcharge, the phosphate compound does not generate free oxygen, has low reactivity with the organic electrolyte, and has excellent electrical safety performance. In addition, the P-O bond energy of the phosphate compound is high, there is no change below 400 °C, and it has excellent thermal stability.

[0021] (2) The battery system is stable. Both the positive and negative electrodes are ion-extrusion type materials. a) There is no "formation-dissolution-reconstruction" of the SEI film and it does not consume active sodium ions. b) In the ion-extrusion type material, the generation of sodium dendrites does not exist, and the current during long-term float is close to zero. Unlike the case of overcharging of a lithium iron phosphate battery, where too many lithium ions are released from the cathode material and the extra lithium ions are forced into the carbon anode structure or deposited on the carbon surface to form lithium dendrites, gradually sinking the structure of the positive electrode material and causing permanent damage to the electrode structure does not occur (Reference: Applied Research on Environmentally Friendly Floating Lithium Iron Phosphate Batteries, Cen Kaijia, Popular Electric Power 2016 / 9).

Brief Description of the Drawings

[0022] [Figure 1] It is the 0.1C charge-discharge curve of the high-safety sodium-ion battery of the present invention. [Figure 2] It is the current-voltage curve during the float of the battery of Example 1. [Figure 3] It is an enlarged view of the current curve during the float of the battery of Example 1. [Figure 4] It is the capacity curve during the float of the battery of Example 1. [Figure 5] It is an enlarged view of the current curve during the float of the battery of the comparative example. [Figure 6] It is a flowchart of the capacity grading method for the high-safety sodium-ion battery. [Figure 7] It is a comparison of the float performance of different types of batteries. [Figure 8] This is a comparison of the cycle performance of different types of batteries. [Modes for carrying out the invention]

[0023] In order to enable those skilled in the art to better understand the technical concept of the present invention, specific embodiments thereof will be described in detail below with reference to the drawings.

[0024] In the embodiments of the present invention, the highly safe sodium-ion battery comprises a positive electrode, a negative electrode, and an electrolyte. Both the positive and negative electrodes consist of an active material, a conductive agent, and a binder. The active materials of both the positive and negative electrodes are polyanionic materials with a very stable lattice structure, and no interfacial reaction occurs between the active material used in the positive and negative electrodes and the electrolyte. The capacity of the battery alone when floated 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, referring to the positive and negative electrode active materials in Table 1, used Na4Fe3(PO4)2(P2O7) as the positive electrode active material and NaTi2(PO4)3 as the negative electrode active material. The conductive agent was acetylene black, and the binder was a 5 wt.% PVDF (polyvinylidene difluoride) MNP (N-methylpyrrolidone) solution. The ratio of active material:conductive agent:binder was 90:5:5. Sheets were manufactured by manual coating, and the pouch-type battery of Example 1 was assembled and tested. The electrolyte salt in the electrolyte solution was sodium perchlorate at a concentration of 1 mol / kg, and the solvent was propylene carbonate.

[0027] Please refer to Figure 1. The battery of Example 1 was charged and discharged at 0.1C from 0.3V to 1.6V to calibrate its capacity. The charge-discharge curve is shown in Figure 1, and the capacity of the battery cell was determined to be 520mAh.

[0028] Please refer to Figures 2 and 3. In Example 1, the battery used a constant current-constant voltage float charging mode. The current during constant current charging was set to 50mA (0.1C), and the voltage during constant voltage charging was set to 1.3V. The constant voltage charging time was 168 hours. As can be seen from Figure 2, which is the current-voltage curve during the float phase, after the charging mode switched to constant voltage charging, the charging current began to decrease from 50mA and stabilized after 20 hours of constant voltage charging (total charging time reached 30 hours). During the float phase, the current was less than 0.1mA for most of the time (>98%). Referring to Figure 3, when the total calibration capacity of the battery was 520mAh, the capacity after 1 hour of float charging was 0.19‰ of the total battery capacity.

[0029] Please refer to Figure 4. After the activation of the battery in Example 1 was completed, it was charged and discharged normally 10-20 times before use. Upon re-verification that there was no change in the battery's capacity during the float phase and that no side reactions such as electrolyte reactions or active material dissolution occurred in the battery system, no additional capacity replenishment was required during the float process.

[0030] Example 2: High-safety sodium-ion batteries, referring to the positive electrode active material and negative electrode active material in Table 1, use Na4Fe 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 manufactured by manual coating method referring to the method in Example 1, and the pouch-type battery of Example 2 was assembled and tested. The capacity of the battery cell was 530mAh, and the capacity after 1 hour of float was 0.16‰ of the total battery capacity.

[0031] Example 3: High-safety sodium-ion batteries, referring to the positive electrode active material and negative electrode active material in Table 1, use Na4Fe2.5 Mn 0.5 (PO4)2(P2O7) was used as the positive electrode active material, and Na3MnTi(PO4)3 was used as the negative electrode active material. Referring to the method in Example 1, a sheet was manufactured by the manual coating method, and the pouch-type battery of Example 3 was assembled and tested. The capacity of the battery cell was 515 mAh, and the capacity after 1-hour floating was 0.23‰ of the total battery capacity.

[0032] Comparative Example: Referring to the positive electrode active material and negative electrode active material in FIG. 5 and Table 1, Na4Fe3(PO4)2(P2O7) was used as the positive electrode active material, and hard carbon was used as the negative electrode active material. Referring to the method in Example 1, a sheet was manufactured by the manual coating method. When the calibration capacity of the battery was 550 mAh, the current in the floating stage was shown in FIG. 5. It was found that the current in the floating stable stage was large, greater than 2 mA, and the ratio of the battery capacity was greater than 3.6‰. This is mainly because the solvent undergoes a reduction reaction on the surface of the hard carbon negative electrode, and the SEI film constantly undergoes modification and repair reactions. However, when NaTi2(PO4)3 is used as the negative electrode, its sodium insertion potential (2.1 V) is much higher than the sodium deposition potential (0 V), so there is no generation of SEI (Reference: Analysis of the causes of swelling and improvement of the floating test of lithium-ion batteries, Li Huifang, Gao Junkui, Li Fei, Huang Jiajian, Power Technology, 2023 / 12). It can meet the technical requirements of long-term floating and is thus used in large-scale UPS systems.

[0033] Please refer to FIG. 6. According to the active material and electrolyte in Example 1, 200 square-case batteries with a rated capacity of 260 Ah were assembled, and the formation capacity grading was carried out according to the following method. S1. The assembled batteries were charge-activated in an environment of 40 - 50 °C. S2. The batteries were charged and discharged at 0.1 C between 0.3 V and 1.6 V to calibrate the capacity. If the capacity was greater than 260 Ah, it was determined to be qualified. The number of qualified batteries was 193. S3: The batteries that passed capacity requirements were charged to 1.3V with a 0.1C current, and then switched to constant voltage charging for 40 hours. S4. Select any two hours from the 30th to 40th hour of the battery's constant voltage charging phase, and calculate the average capacity per hour as a percentage of the total battery capacity. ratio Capacity grading was performed based on R.

[0034] Please refer to Figures 7 and 8. The batteries were classified into three categories: Category A if R < 0.2‰, Category B if R = 0.2-0.4‰, and Category C if R > 0.4‰. A total of 142 Category A products, 27 Category B products, and 24 Category C products were obtained. To verify the classification effect, a total of 12 arbitrary Category A, Category B, and Category C batteries were connected in series and assembled into a small module with a rated voltage of 12V to simulate a "UPS" and perform performance tests. The specific test method was as follows: After grading the battery capacity, the batteries were discharged by floating at a voltage of 1.3V for 14 days, and then the capacity was calibrated by performing two charge-discharge cycles at 0.1C. This process was repeated. As can be seen from Figure 7, out of a total of 15 cycles over 8 months, the calibrated capacity of Category A batteries hardly decayed, the capacity retention rate of Category B batteries was 91.5%, and the capacity retention rate of Category C batteries was the worst at 87.4%. This was because individual battery differences during the manufacturing process were amplified during the long-term float of the battery's high-voltage charge state, leading to micro-short circuits in the battery, for example, reducing the capacity of a single battery and affecting the module capacity.

[0035] To compare whether there is a difference between cycle and float, a total of 12 arbitrary A, B, and C type batteries were connected in series at the same time and assembled into a small module with a rated voltage of 12V for cycle testing. The specific test method was as follows: After grading the battery capacity, a 1C charge / discharge cycle was performed at a voltage of 0.3-1.6V, and every 500 cycles, a 2-cycle charge / discharge at 0.1C was performed to calibrate the capacity, and this process was repeated. As can be seen from Figure 8, the order of decay is still A-type best, followed by B-type, and C-type worst. However, the capacity retention rate of B-type batteries (with the same capacity retention rate for 1C and 0.1C) is 96.5%, and the capacity retention rate of C-type batteries (with the same capacity retention rate for 1C and 0.1C) is 90.3%. Therefore, B-type and C-type 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 rate of B-type and C-type batteries, when the capacity decays to 70%, the number of cycles is 20,000 and 7,000, respectively. B-type batteries can be used as energy storage modules in industrial and commercial energy storage systems, while C-type batteries can be used in small-scale energy storage systems such as electric vehicles or streetlights.

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

[0037] Based on the above, the present invention provides a highly safe sodium-ion battery, its applications, and a capacity grading method, which utilize a highly stable lattice structure material as the active material. The battery does not generate a solid electrolyte membrane (SEI) during operation and can meet the technical requirements for long-term float, thereby enabling large-scale use in UPS systems.

[0038] Those skilled in the art should recognize that the above examples are merely for illustrative purposes and not intended to limit the present invention, and that any changes or modifications to the above examples, as long as they fall within the substantial spirit of the present invention, are all within the scope of the claims of the present invention.

Claims

1. A method for grading the capacity of a sodium-ion battery that functions as an energy storage module, Step S1 involves activating the sodium-ion battery in an environment of 40-50°C, Then, step S2 involves charging and discharging the sodium-ion battery at 0.1C with a voltage of 0.3V to 1.6V to calibrate its capacity and determining whether the sodium-ion battery has passed the test based on its rated capacity. If the sodium-ion battery is determined to be acceptable, step S3 involves charging the sodium-ion battery to 1.3V with a current of 0.1C, then switching to a constant voltage and charging for 40 hours. A method for grading the capacity of a sodium-ion battery functioning as an energy storage module, comprising step S4, which includes the following steps: after the sodium-ion battery enters the constant-voltage charging stage, any two hours are selected from the 30th to 40th hours of constant-voltage charging, and the sodium-ion battery is capacity graded based on the R value (where 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); if R < 0.2‰, the sodium-ion battery is classified as Category A; if R = 0.2 - 0.4‰, the sodium-ion battery is classified as Category B; and if R > 0.4‰, the sodium-ion battery is classified as Category C.

2. The sodium-ion battery capacity grading method according to Claim 1, characterized in that the sodium-ion battery classified as Category A can be used as an energy storage module for a backup power supply system, and the sodium-ion battery classified as Category B can be used as an energy storage module for a small energy storage system.

3. The sodium-ion battery comprises a positive electrode, a negative electrode, and an electrolyte, the positive electrode and the negative electrode both consist of an active material, a conductive agent, and a binder, the active materials of the positive electrode and the negative electrode are both manufactured from polyanionic materials, and no interfacial reaction occurs between the electrolyte and the active materials used by the positive electrode and the negative electrode, characterized in that the sodium-ion battery comprises a positive electrode, a negative electrode, and an electrolyte, the positive electrode and the negative electrode both consist of an active material, and the sodium-ion battery comprises a positive electrode, a negative electrode, and an electrolyte, the positive electrode and the negative electrode both consist of an active material, a conductive agent, and a binder a polyanionic material, and no interfacial reaction occurs between the electrolyte and the active materials used by the positive electrode and the negative electrode, the characteristic of the sodium-ion battery capacity grading method according to claim 1.

4. The method for grading the capacity of a sodium-ion battery according to claim 3, characterized in that the active materials of the positive electrode and the negative electrode are both phosphate compounds having a rapidly conductive structure of sodium ions.

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

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

7. The method for grading the capacity of a sodium-ion battery according to claim 3, characterized in that 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. The method for grading the capacity of a sodium-ion battery according to claim 3, characterized in that the electrolyte uses at least one of sodium perchlorate, sodium bis(oxalic acid)borate, sodium bis(salicylic acid)borate, and sodium tetraphenylborate as the electrolyte salt.

9. The sodium-ion battery capacity grading method according to claim 3, characterized in that the individual battery capacity of the sodium-ion battery is 100-350 Ah.

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