Formation and capacity-determination method of layered-oxygen p-phase sodium-ion battery

Abstract

The application discloses a formation and capacity grading method of a layered oxygen P-phase sodium ion battery, and belongs to the technical field of sodium ion batteries. The layered oxygen P-phase sodium ion battery refers to that a layered oxygen P-phase NaxMO2 material is used as a positive electrode material of the sodium ion battery. The formation method adopts three-step ladder charging, can make the SEI film more dense and uniform, and thus makes the sodium battery have better ion conductivity and cycle stability. The capacity grading method can fully utilize the high-voltage characteristics of the P-phase layered oxygen material and avoid the sodium precipitation phenomenon of the sodium ion battery under high voltage, and improves the cycle performance and energy density of the sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a method for the formation and capacity testing of a layered oxygen P-phase sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have broad application prospects in the fields of new energy storage and power, but their commercialization process still faces challenges due to performance limitations such as energy density and cycle life.

[0003] Currently, there are three main approaches to developing cathode materials for sodium-ion batteries: Prussian blue, anionic compounds, and layered transition metal oxides. Among these, layered oxygen sodium-ion battery materials include both P-phase and O-phase options. O-phase layered oxygen sodium-ion battery cathode materials have been validated first, but their upper voltage limit is 3.6V, while P-phase materials can reach 4.2V or even higher, making them more marketable. Furthermore, the capacity grading process for O-phase materials is clearly unsuitable for P-phase materials due to the different upper voltage limits. The standard potential of lithium ions is -3.04V (VS SHE), while that of sodium ions is -2.7V. Sodium ions have a standard potential approximately 0.3V higher than lithium ions. At the same battery voltage, the cathode and anode potentials of sodium-ion batteries are 0.3V higher than those of lithium-ion batteries. That is, at 4.2V, the anode potential in a sodium-ion battery is equivalent to 4.5V in a lithium-ion battery. Therefore, the capacity grading process for ternary lithium-ion batteries is not suitable for P-phase layered oxygen sodium-ion batteries. Experiments have shown that using the same formation and capacity grading processes for ternary lithium-ion materials results in sodium deposition in sodium-ion batteries, severely impacting cycle performance. Meanwhile, the high structural stability of the layered oxygen P-phase material and the use of aluminum foil as the negative electrode current collector in sodium-ion batteries mean that the negative electrode current collector will not be oxidized when the sodium-ion battery is discharged to a low voltage or even 0V. Moreover, sodium ions will not undergo an electrochemical alloying reaction with the aluminum current collector. Tests have confirmed that sodium-ion batteries can be used normally at higher and lower voltages, which is also very different from lithium batteries.

[0004] Therefore, considering the differences in material potential and current collector between sodium-ion batteries and lithium-ion batteries, it is necessary to design a formation and capacity testing method for layered oxygen P-phase sodium-ion batteries to further improve the capacity and cycle performance of sodium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the formation and capacity testing of a layered oxygen P-phase sodium-ion battery, in order to solve the problems of low capacity and poor cycle performance of sodium-ion batteries in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for forming and compatibility testing a layered oxygen P-phase sodium-ion battery includes the following steps:

[0008] Step 1: Allow the oxygen-filled P-phase sodium-ion battery to stand for the first time after the electrolyte injection is completed.

[0009] Step 2: Perform formation on the battery after the first settling period;

[0010] The formation process is as follows: under negative pressure of -70 kPa, constant current I1 is used to charge to 5%-15% SOC (state of charge), and then left to stand for several minutes; constant current I2 is used to charge to 30%-40% SOC, and then left to stand for several minutes; constant current I3 is used to charge to 70%-80% SOC, and then left to stand for several minutes.

[0011] Step 3: Allow the formed battery to stand for a second time;

[0012] Step 4: Perform capacity testing on the batteries after the second settling period;

[0013] The specific steps of the capacity grading process are as follows: charge with constant current I4 to the cutoff voltage V1, and let it stand for several minutes; discharge with constant current I5 to the cutoff voltage V2, and let it stand for several minutes, recording the discharge capacity Q1; charge with constant current I4 and discharge with constant current I5, repeat once, and record the discharge capacity Q2; charge with constant current I4 to 70%-80% SOC, and the capacity grading is completed.

[0014] Furthermore, in step 1, the temperature for the first settling period is 45±5℃, and the time is 12-24h.

[0015] Furthermore, in step 2, the currents I1, I2, and I3 increase sequentially, with I1 = 0.05C, I2 = 0.1C, and I3 = 0.2C.

[0016] Furthermore, the settling time in step 2 is 2-30 minutes; preferably, the settling time is 5 minutes.

[0017] Furthermore, in step 3, the temperature for the second settling period is 45±5℃, and the time is 24-72h.

[0018] Furthermore, in step 4, the currents I4 and I5 are based on the product specifications, with I4 = 0.5C and I5 = 0.5C.

[0019] Furthermore, in step 4, the cutoff voltages V1 and V2 are based on the product specifications, with V1 = 4.25-4.30V and V2 = 2.0V.

[0020] Furthermore, in step 4, the capacity is based on Q2, and the settling time is 2-30 minutes; preferably, the settling time is 5 minutes.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. This invention provides a method for the formation and capacity testing of a layered oxygen P-phase sodium-ion battery, using a layered oxygen P-phase sodium-ion battery. x MO2 material is used as the cathode material for sodium-ion batteries. During the formation process, a three-step stepped charging method is employed, which makes the SEI (solid electrolyte interphase) film more dense and uniform, thus giving the sodium battery better ionic conductivity and cycle stability. In the capacity grading process, constant current charging is used instead of the constant current / constant voltage charging commonly used in lithium batteries. This fully utilizes the high-voltage characteristics of the P-phase oxygen layer material and avoids sodium deposition in sodium-ion batteries under high voltage, improving the cycle performance of the sodium-ion battery. Furthermore, by adjusting the upper and lower limits of the capacity grading voltage, the capacity and energy density of the sodium battery can be further increased.

[0023] 2. In verifying the sodium deposition phenomenon in layered oxygen P-phase sodium batteries, this invention found that if layered oxygen P-phase sodium batteries are charged using the conventional 4.2V constant current and constant voltage charging of ternary lithium batteries, sodium deposition will occur, resulting in unsatisfactory cycle performance. However, using 4.2V constant current charging will not cause sodium deposition, but the lack of a constant voltage stage leads to a capacity loss of 5%-15%. Further verification showed that sodium batteries charged at 4.25V or even 4.3V constant current did not exhibit sodium deposition. Moreover, the capacity of 4.25V constant current charging reached 99.9% of the capacity of 4.2V constant current and constant voltage charging, and the capacity of 4.3V constant current charging even reached 104% of the capacity of 4.2V constant current and constant voltage charging. The reason is that, since the radius of sodium ions is larger than that of lithium ions, the disordered structure of the sodium ion anode hard carbon under high voltage makes sodium intercalation much more difficult than the layered structure of the lithium ion anode graphite. As a result, the constant current ratio of sodium ion batteries is much lower than that of lithium ion batteries. If constant current and constant voltage charging is used, the constant voltage period is too long, and the high voltage of sodium batteries (4.2V) is equivalent to that of lithium batteries (4.5V). At present, the electrolyte is in such a high voltage environment for a long time. The hard carbon anode and the electrolyte are not compatible and are prone to deterioration, resulting in sodium precipitation and poor cycle performance. Attached Figure Description

[0024] The present invention will now be further described with reference to the accompanying drawings.

[0025] Figure 1 This is a schematic diagram of the battery cycle count after formation and capacity testing in Embodiment 1 of the present invention;

[0026] Figure 2 This is a schematic diagram of the negative electrode interface of the battery after being fully charged following the formation and capacity testing in Embodiment 1 of the present invention;

[0027] Figure 3 This is a schematic diagram of the battery cycle count after formation and capacity testing in Comparative Example 1 of the present invention;

[0028] Figure 4This is a schematic diagram of the negative electrode interface of the battery after being fully charged in Comparative Example 1 of the present invention. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] In the following examples and comparative examples, the positive electrode active material of the sodium-ion battery is P-phase NaNiFeMnO2, and the negative electrode active material is hard carbon.

[0031] Example 1

[0032] A method for forming and compatibility testing a layered oxygen P-phase sodium-ion battery includes the following steps:

[0033] Step 1: Place the oxygen-filled P-phase sodium-ion battery at 45°C for the first settling period of 24 hours.

[0034] Step 2: Perform formation on the battery after the first settling period;

[0035] The specific formation process is as follows: under a constant negative pressure of -70 kPa throughout the process, charge to 5% SOC with a constant current of I1 = 0.05 C and let stand for 5 min; charge to 30% SOC with a constant current of I2 = 0.1 C and let stand for 5 min; charge to 75% SOC with a constant current of I3 = 0.2 C and let stand for 5 min.

[0036] Step 3: Place the formed battery at 45°C for a second settling period of 48 hours.

[0037] Step 4: Perform capacity testing on the batteries after the second settling period;

[0038] The specific steps of the capacity grading process are as follows: Charge the battery with a constant current of I4 = 0.5C until the cutoff voltage V1 = 4.25C, and let it stand for 5 minutes; discharge the battery with a constant current of I5 = 0.5C until the cutoff voltage V2 = 2.0V, and let it stand for 5 minutes; charge the battery again with a constant current of I4 = 0.5C until the cutoff voltage V1 = 4.25C, and let it stand for 5 minutes; discharge the battery again with a constant current of I5 = 0.5C until the cutoff voltage V2 = 2.0V, and let it stand for 5 minutes, recording the discharge capacity Q; charge the battery with a constant current of I4 = 4.25C until it reaches 75% SOC, and let it stand for 5 minutes. The capacity grading process is then complete. Q is used as the basis for battery capacity screening, and self-discharge screening is performed at 75% SOC.

[0039] Comparative Example 1

[0040] A method for forming and compatibility testing a layered oxygen P-phase sodium-ion battery includes the following steps:

[0041] Step 1: Place the oxygen-filled P-phase sodium-ion battery at 45°C for the first settling period of 24 hours.

[0042] Step 2: Perform formation on the battery after the first settling period;

[0043] The specific formation process is as follows: under a constant negative pressure of -70 kPa throughout the process, charge to 5% SOC with a constant current of I1 = 0.05 C and let stand for 5 min; charge to 30% SOC with a constant current of I2 = 0.1 C and let stand for 5 min; charge to 75% SOC with a constant current of I3 = 0.2 C and let stand for 5 min.

[0044] Step 3: Place the formed battery at 45°C for a second settling period of 48 hours.

[0045] Step 4: Perform capacity testing on the batteries after the second settling period;

[0046] The specific steps of the capacity grading process are as follows: charge the battery with a constant current and constant voltage of I4 = 0.5C until the cutoff voltage V1 = 4.2C, and let it stand for 5 minutes; discharge the battery with a constant current of I5 = 0.5C until the cutoff voltage V2 = 2.0V, and let it stand for 5 minutes; charge the battery with a constant current and constant voltage of I4 = 0.5C again until the cutoff voltage V1 = 4.2C, and let it stand for 5 minutes; discharge the battery with a constant current of I5 = 0.5C again until the cutoff voltage V2 = 2.0V, and let it stand for 5 minutes, and record the discharge capacity Q; charge the battery with a constant current of I4 = 4.2C until it reaches 75% SOC, and let it stand for 5 minutes, and the capacity grading is completed. Use Q as the basis for battery capacity grading screening, and perform self-discharge screening at 75% SOC.

[0047] Performance tests were conducted on the batteries of Example 1 and the comparative example after capacity testing at room temperature (25-30°C):

[0048] In Example 1, the battery cycle count and capacity retention after formation and capacity testing are as follows: Figure 1 As shown (two parallel tests), the negative electrode interface after the battery is fully charged is as follows. Figure 2 As shown; by Figure 1 and Figure 2 It can be seen that no sodium is deposited at the negative electrode interface of the battery, and the number of cycles of the battery in the two parallel tests both reached more than 1500.

[0049] Comparative Example 1: Battery cycle life and capacity retention after composition and capacity adjustment are as follows Figure 3 As shown, the negative electrode interface after the battery is fully charged is as follows: Figure 4 As shown; by Figure 3 and Figure 4It can be seen that after the battery is fully charged, sodium deposition is obvious at the negative electrode interface, and the number of cycles at room temperature is less than 160.

[0050] The test results are summarized in Table 1:

[0051] Table 1

[0052] After filling the interface Sodium not precipitated Sodium precipitation Constant capacity 69Ah 69Ah Cycle life 1600 laps 84.5% 155 laps 88.7%

[0053] As can be seen from Example 1, Comparative Example 1 and the test results, in Example 1, constant current charging to 4.25V was used without adding a constant voltage section, while in Comparative Example 1, constant current and constant voltage charging to 4.2V was used in the capacity grading step. The effect of Comparative Example 1 is relatively poor. The reason is that the constant current ratio of the P phase of the sodium battery is low, the constant voltage section time is too long, the requirements for the electrolyte are high, and sodium is easily precipitated, resulting in unsatisfactory cycle performance.

[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for the formation and capacity testing of a layered oxygen P-phase sodium-ion battery, characterized in that, Includes the following steps: Step 1: Allow the oxygen-filled P-phase sodium-ion battery to stand for the first time after the electrolyte injection is completed. Step 2: Perform formation on the battery after the first settling period; The formation process is as follows: under negative pressure of -70 kPa, charge with constant current I1 to 5%-15% SOC, and then let stand. Charge the battery with a constant current I2 until it reaches 30%-40% SOC, then let it rest. Charge the battery with a constant current and constant voltage I3 until it reaches 70%-80% SOC, then let it rest. Step 3: Allow the formed battery to stand for a second time; Step 4: Perform capacity testing on the batteries after the second settling period; The specific steps of the capacity grading process are as follows: charge with constant current I4 to the cutoff voltage V1, and let it stand; discharge with constant current I5 to the cutoff voltage V2, and let it stand; repeat once, and record the discharge capacity Q. The current I4 is constant current charging until 70%-80% SOC is reached, and the capacity grading ends.

2. The method for forming and compatibility testing of a layered oxygen P-phase sodium-ion battery according to claim 1, characterized in that, In step 1, the temperature for the first settling period is 45±5℃, and the time is 12-24h.

3. The method for forming and compatibility testing of a layered oxygen P-phase sodium-ion battery according to claim 1, characterized in that, In step 2, the currents I1, I2, and I3 increase sequentially, with I1 = 0.05C, I2 = 0.1C, and I3 = 0.2C.

4. The formation and capacity testing method for a layered oxygen P-phase sodium-ion battery according to claim 1, characterized in that, The settling time in step 2 is 2-30 minutes.

5. The method for forming and compatibility testing of a layered oxygen P-phase sodium-ion battery according to claim 1, characterized in that, In step 3, the temperature for the second settling period is 45±5℃, and the time is 24-72h.

6. The formation and capacity testing method for a layered oxygen P-phase sodium-ion battery according to claim 1, characterized in that, In step 4, I4 = 0.5C and I5 = 0.5C.

7. The method for forming and compatibility testing of a layered oxygen P-phase sodium-ion battery according to claim 1, characterized in that, In step 4, V1 = 4.25-4.30V and V2 = 2.0V.

8. The formation and capacity testing method for a layered oxygen P-phase sodium-ion battery according to claim 1, characterized in that, The settling time in step 4 is 2-30 minutes.

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