Formation and capacity grading method of layer oxygen P-phase sodium ion battery

Abstract

The invention discloses a formation and capacity grading method of a layer oxygen P-phase sodium ion battery, and belongs to the technical field of sodium ion batteries. According to the layered oxygen P-phase sodium ion battery, a layered oxygen P-phase NaxMO2 material is used as a sodium ion battery positive electrode material, three-step stepped charging is adopted in the formation method, an SEI film can be denser and more uniform, and therefore the sodium battery has better ionic conductivity and cycling stability, and the capacity grading method is adopted, so that the lithium ion battery can be used for lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery lithium ion battery. The high-voltage characteristic of the P-phase layer oxygen material can be fully utilized, the sodium separation phenomenon of the sodium-ion battery under high voltage is avoided, and the cycle performance and the energy density of the sodium-ion battery are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion batteries, and in particular relates to a method for chemical composition and capacity of a layered oxygen P-phase sodium ion battery. Background Art

[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] There are currently three paths for the positive electrode materials of sodium-ion batteries: Prussian blue / anionic compounds / layered transition metal oxides. Among them, the layered oxygen sodium battery materials have two directions: P phase and O phase. The O-phase layered oxygen sodium-ion battery positive electrode material was verified first, but the upper limit voltage of the O-phase material is 3.6V, while the upper limit voltage of the P-phase material can reach 4.2V or even higher, which has a better application market. At the same time, the capacity division process of the O-phase material is obviously not suitable for the P-phase material due to the different upper limit voltage. The standard potential of lithium ions is -3.04V (VS SHE), and the standard potential of sodium ions is -2.7V. The standard potential of sodium ions is about 0.3V higher than that of lithium ions. Under the same battery voltage, the potential of the cathode and anode of the sodium-ion battery is 0.3V higher than that of the lithium-ion battery, that is, the anode potential of the sodium-ion battery at 4.2V is equivalent to 4.5V of the lithium-ion battery. Therefore, the capacity division process of the ternary lithium-ion battery is not suitable for the P-phase layered oxygen sodium-ion battery. Experiments have confirmed that the formation and capacity division process of the ternary materials of lithium-ion batteries will cause sodium precipitation in the sodium-ion battery, which seriously affects the cycle performance. At the same time, the structure of the layered oxygen P-phase material is highly stable and the negative electrode current collector of the sodium ion battery uses aluminum foil. When the sodium ion battery is discharged to a low voltage or even 0V, the negative electrode current collector will not be oxidized, and the sodium ions will not undergo electrochemical alloying reaction with the aluminum current collector. Experiments 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 difference in material potential between sodium-ion batteries and lithium-ion batteries and the difference in current collectors, it is necessary to design a chemical composition and capacity 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 object of the present invention is to provide a method for chemical composition and capacity of a layered oxygen P-phase sodium ion battery to solve the problems of low capacity and poor cycle performance of sodium ion batteries in the background technology.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for converting a layered oxygen P-phase sodium ion battery into a capacity-compounding battery comprises the following steps:

[0008] Step 1, placing the layer oxygen P-phase sodium ion battery after liquid injection at rest for the first time;

[0009] Step 2, forming the battery after the first static standing;

[0010] The specific steps of the formation are: under negative pressure of -70KPa, the current I1 is charged to 5%-15% SOC (state of charge), and then left to stand for several minutes; the current I2 is charged to 30%-40% SOC, and left to stand for several minutes; the current I3 is charged to 70%-80% SOC at constant current and constant voltage, and left to stand for several minutes;

[0011] Step 3, allowing the formed battery to rest for a second time;

[0012] Step 4, performing a capacity separation step on the battery after the second static condition;

[0013] The steps of the capacity division are as follows: constant current charging with current I4 to a cut-off voltage V1, and standing for several minutes; constant current discharging with current I5 to a cut-off voltage V2, and standing for several minutes, and recording the discharge capacity Q1; constant current charging with current I4 and constant current discharging with current I5, cycle once, and record the discharge capacity Q2; constant current charging with current I4 to 70%-80% SOC, and the capacity division is completed.

[0014] Furthermore, the temperature of the first standing in step 1 is 45±5° C. and the time is 12-24 hours.

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

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

[0017] Furthermore, the temperature of the second standing in step 3 is 45±5° C. and the time is 24-72 hours.

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

[0019] Furthermore, in step 4, the cut-off voltage V1 and the cut-off voltage V2 are based on the product specification, V1 = 4.25-4.30V, V2 = 2.0V.

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

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention provides a method for preparing a layered oxygen P-phase sodium ion battery. x MO2 material is used as the positive electrode material of sodium ion battery; three-step stepped charging is adopted in the formation process, which can make the SEI (solid electrolyte interface membrane) membrane more dense and uniform, so that the sodium battery has better ionic conductivity and cycle stability; constant current charging is adopted in the capacity division process to replace the constant current and constant voltage charging commonly used in lithium batteries, so as to make full use of the high voltage characteristics of P-phase layer oxygen materials and avoid the sodium precipitation phenomenon of sodium ion batteries under high voltage, thereby improving the cycle performance of sodium ion batteries; in addition, by adjusting the upper and lower limit voltages of the capacity division, the capacity of the sodium battery can be further increased, and the energy density of the sodium battery can be increased.

[0023] 2. In the process of verifying the sodium precipitation phenomenon of the layer oxygen P-phase sodium battery, the present invention found that if the layer oxygen P-phase sodium battery adopts the conventional 4.2V constant current and constant voltage charging of the ternary lithium battery, sodium precipitation will occur and the cycle performance is not ideal. When using 4.2V constant current charging, sodium precipitation will not occur, but the lack of a constant voltage section causes a capacity loss of 5%-15%. Further verification is made that the sodium battery does not exhibit the sodium precipitation phenomenon when charged with a constant current of 4.25V or even 4.3V, and the 4.25V constant current charging capacity reaches 99.9% of the 4.2V constant current and constant voltage capacity, and the 4.3V constant current charging capacity even reaches 104% of the 4.2V constant current and constant voltage charging capacity. The reason is that, since the radius of sodium ions is larger than that of lithium ions, the disordered structure of the sodium ion negative electrode hard carbon under high voltage makes it much more difficult to embed sodium than the layered structure of the lithium ion negative electrode graphite. As a result, the constant current ratio of the sodium ion battery is much smaller than that of the lithium ion battery. If constant current and constant voltage charging is adopted, the constant voltage period is too long and the high voltage of the sodium battery 4.2V is equivalent to the 4.5V of the lithium battery. At this stage, the electrolyte is in such a high voltage environment for a long time, the negative electrode hard carbon and the electrolyte are not matched and are prone to deterioration, resulting in sodium precipitation and poor cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below in conjunction with the accompanying drawings.

[0025] Figure 1 This is a schematic diagram of the cycle number of the battery after the capacity is converted into battery capacity in Example 1 of the present invention;

[0026] Figure 2 is a schematic diagram of the negative electrode interface of the battery after being fully charged after being converted into capacity in Example 1 of the present invention;

[0027] Figure 3 Schematic diagram of the battery cycle number after capacity conversion in Comparative Example 1 of the present invention;

[0028] Figure 4It is a schematic diagram of the negative electrode interface of the battery after being fully charged after being capacitated in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In the following embodiments 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 converting a layered oxygen P-phase sodium ion battery into a capacity-compounding battery comprises the following steps:

[0033] Step 1, placing the layered oxygen P-phase sodium ion battery after liquid injection at 45°C for the first time, and the standing time is 24 hours;

[0034] Step 2, forming the battery after the first static standing;

[0035] The specific steps of the formation process are as follows: under the condition of negative pressure of -70KPa, the current I1 = 0.05C constant current charging to 5% SOC, and standing for 5 minutes; the current I2 = 0.1C constant current charging to 30% SOC, and standing for 5 minutes; the current I3 = 0.2C constant current charging to 75% SOC, and standing for 5 minutes;

[0036] Step 3, placing the formed battery at 45°C for a second resting time of 48 hours;

[0037] Step 4, performing a capacity separation step on the battery after the second static condition;

[0038] The specific steps of the capacity division are: constant current charging with current I4=0.5C to cut-off voltage V1=4.25C, standing for 5 minutes; constant current discharging with current I5=0.5C to cut-off voltage V2=2.0V, standing for 5 minutes; constant current charging with current I4=0.5C again to cut-off voltage V1=4.25C, standing for 5 minutes, constant current discharging with current I5=0.5C again to cut-off voltage V2=2.0V, standing for 5 minutes, and recording the discharge capacity Q; constant current charging with current I4=4.25C to 75% SOC, standing for 5 minutes, and the capacity division is completed, Q is used as the basis for battery capacity division screening, and self-discharge screening is performed at 75% SOC.

[0039] Comparative Example 1

[0040] A method for converting a layered oxygen P-phase sodium ion battery into a capacity-compounding battery comprises the following steps:

[0041] Step 1, placing the layered oxygen P-phase sodium ion battery after liquid injection at 45°C for the first time, and the standing time is 24 hours;

[0042] Step 2, forming the battery after the first static standing;

[0043] The specific steps of the formation process are as follows: under the condition of negative pressure of -70KPa, the current I1 = 0.05C constant current charging to 5% SOC, and standing for 5 minutes; the current I2 = 0.1C constant current charging to 30% SOC, and standing for 5 minutes; the current I3 = 0.2C constant current charging to 75% SOC, and standing for 5 minutes;

[0044] Step 3, placing the formed battery at 45°C for a second resting time of 48 hours;

[0045] Step 4, performing a capacity separation step on the battery after the second static condition;

[0046] The specific steps of the capacity division are: constant current and constant voltage charging with current I4=0.5C to a cut-off voltage V1=4.2C, and standing for 5 minutes; constant current discharge with current I5=0.5C to a cut-off voltage V2=2.0V, and standing for 5 minutes; constant current and constant voltage charging with current I4=0.5C again to a cut-off voltage V1=4.2C, and standing for 5 minutes, constant current discharge with current I5=0.5C again to a cut-off voltage V2=2.0V, and standing for 5 minutes, and recording the discharge capacity Q; constant current charging with current I4=4.2C to 75% SOC, and standing for 5 minutes, the capacity division is completed, and Q is used as the basis for battery capacity division screening, and self-discharge screening is performed at 75% SOC.

[0047] At room temperature (25-30°C), the performance of the batteries of Example 1 and the comparative example after capacity division was tested:

[0048] The cycle number and capacity retention rate of the battery after capacity conversion in Example 1 are as follows: Figure 1 As shown (tested twice in parallel), the negative electrode interface after the battery is fully charged is as follows Figure 2 shown by Figure 1 and Figure 2 It can be seen that there is no sodium precipitation at the negative electrode interface of the battery, and the number of cycles of the two parallel test batteries reaches more than 1500 cycles;

[0049] The battery cycle number and capacity retention rate after the battery was converted into capacity in Comparative Example 1 are as follows: Figure 3 As shown in Figure 2, the negative electrode interface of the battery after full charge is as follows: Figure 4 shown by Figure 3 and Figure 4It can be seen that after the battery is fully charged, sodium precipitation is obvious at the negative electrode interface, and the number of cycles at room temperature is less than 160.

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

[0051] Table 1

[0052] Example 1 Comparative Example 1 Full screen No sodium precipitation Sodium Constant capacity 69Ah 69Ah Cycle life 1600 laps 84.5% 155 laps 88.7%

[0053] It can be seen from Example 1, Comparative Example 1 and the test results that in Example 1, constant current charging without adding a constant voltage section is used to charge to 4.25V, and in Comparative Example 1, constant current and constant voltage charging is used to charge to 4.2V in the capacity division step. The effect of Comparative Example 1 is relatively poor. The reason is that the P-phase constant current ratio of the sodium battery is low, the constant voltage section time is too long, the electrolyte requirements are high, sodium is easily precipitated, and the cycle performance is not ideal.

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

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

Claims

1. A method for preparing a layered oxygen P-phase sodium ion battery, characterized in that: The following steps are involved: Step 1, placing the layer oxygen P-phase sodium ion battery after liquid injection at rest for the first time; Step 2, forming the battery after the first static standing; The specific steps of the formation process are: under negative pressure of -70KPa, charge to 5%-15% SOC with constant current I1, and let stand; The current I2 is charged at a constant current to 30%-40% SOC, and then left to stand; The current I3 is charged at constant current and constant voltage to 70%-80% SOC, and then left to stand; Step 3, allowing the formed battery to rest for a second time; Step 4, performing a capacity separation step on the battery after the second static condition; The specific steps of capacity division are: constant current charging with current I4 to cut-off voltage V1, and then standing still; constant current discharge with current I5 to cut-off voltage V2, and then standing still; one cycle, and record the discharge capacity Q; The current I4 is used for constant current charging to 70%-80% SOC, and the capacity division is completed.

2. The method for preparing a layered oxygen P-phase sodium ion battery according to claim 1, characterized in that: The temperature of the first standing in step 1 is 45±5° C. and the time is 12-24 hours.

3. The method for preparing a layered oxygen P-phase sodium ion battery according to claim 1, characterized in that: In step 2, current I1, current I2, and current I3 increase in sequence, I1=0.05C, I2=0.1C, and I3=0.2C.

4. The method for preparing a layered oxygen P-phase sodium ion battery according to claim 1, characterized in that: The standing time in step 2 is 2-30 min.

5. The method for preparing a layered oxygen P-phase sodium ion battery according to claim 1, characterized in that: The temperature of the second standing in step 3 is 45±5° C. and the time is 24-72 hours.

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

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

8. The method for preparing a layered oxygen P-phase sodium ion battery according to claim 1, characterized in that: The standing time in step 4 is 2-30 min.

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