CN118507872A - A battery formation process method and its application in sodium ion battery - Google Patents

Abstract

The embodiment of the present invention relates to a battery formation process method and its application in sodium ion batteries. The battery formation process method comprises: discharging the assembled sodium ion full battery to a negative potential before the normal charge and discharge cycle to perform battery formation, so that an interface film component mainly composed of inorganic substances generated by electrolyte reduction is formed on the positive electrode side of the battery, and the inorganic substances include NaF. Through the process of discharging to a negative potential in advance, the method can form an interface film component mainly composed of inorganic NaF generated by electrolyte reduction on the positive electrode side, which is different from the interface component mainly composed of organic substances generated by electrolyte oxidation on the positive electrode side during conventional charging. In subsequent cycles, the interface is more stable and not easy to decompose, thereby improving the battery cycle performance.

Description

A battery formation process method and its application in sodium ion battery

Technical Field

The present invention relates to the technical field of secondary batteries, and in particular to a battery formation process method and application thereof in sodium ion batteries.

Background Art

The research and development of positive and negative electrode materials and electrolytes in sodium-ion batteries has always been a top priority, which directly affects the comprehensive performance of sodium-ion batteries, such as energy density and cycle life. Among them, the stable electrode/electrolyte interface constructed by the electrolyte and the positive and negative electrode system is an important key to determine whether the battery can be stably cycled. In addition to the selection of positive and negative electrode materials and electrolyte formulas, the battery formation process also greatly affects the construction of the initial electrode interface, and plays an equally important role in the performance of the subsequent battery operation process.

The cathode electrolyte interphase (CE I) film is mainly obtained by oxidation of the electrolyte during battery charging, and is often dominated by organic components. It is easy to decompose or dissolve in the electrolyte during high voltage or long battery cycles, resulting in problems such as interface instability and exposure of active substances, which greatly affects the high-voltage stability, energy density and cycle stability of the battery. The interface components on the negative electrode side are derived from electrolyte reduction and are rich in a large number of inorganic components, which can effectively slow down the decomposition of the interface.

Summary of the invention

The purpose of the present invention is to provide a battery formation process method and its application in sodium ion batteries. The formation process utilizes the over-discharge characteristic of sodium ion batteries, discharges the battery to a negative potential, or charges to a positive potential after the positive and negative electrodes are reversed, so as to realize the formation process of sodium ion batteries, and forms an interface film component mainly composed of inorganic NaF generated by electrolyte reduction on the positive electrode side, so that the interface is more stable and not easy to decompose in subsequent cycles, thereby improving the battery cycle performance. This method can only be used in sodium ion batteries and cannot be used in lithium ion batteries. It is a simple and unique formation method for sodium ion batteries.

To this end, in the first aspect, an embodiment of the present invention provides a battery formation process method, which comprises: discharging the assembled sodium ion full battery to a negative potential before a normal charge and discharge cycle for battery formation, so that an interface film component mainly composed of inorganic substances generated by electrolyte reduction is formed on the positive electrode side of the battery, and the inorganic substance includes NaF.

Preferably, the specific method of discharging to a negative potential includes:

Under the condition that the positive and negative electrodes of the battery are connected in a positive direction, the battery is discharged to a negative potential; wherein the discharge cut-off voltage is between -5V and 0V, excluding 0V; or,

Under the condition that the positive and negative poles of the battery are reversed, the battery is charged to a positive potential; wherein the charging cut-off voltage is between 0-5V, excluding 0V.

Preferably, -5V≤discharge cut-off voltage≤-3V; or, 3V≤charge cut-off voltage≤5V

Preferably, the specific method of discharging to a negative potential includes:

When the positive and negative electrodes of the battery are connected in a positive direction, the battery is discharged to a negative potential; wherein the discharge specific capacity is ≥ 4 mAh/g; or,

Under the condition that the positive and negative electrodes of the battery are reversed, the battery is charged to a positive potential; wherein the charging specific capacity is ≥4mAh/g.

Preferably, the positive electrode of the sodium ion full battery includes: any one of layered oxides, tunnel-type oxides, polyanion compounds, Prussian blue materials, Prussian white materials or organic materials; the negative electrode includes: any one of carbon-based materials, titanium-based materials, and alloy materials; the electrolyte includes: carbonate electrolyte and/or ether electrolyte.

Preferably, the discharge rate to the negative potential is 0.01C-1C.

Preferably, the process of discharging to a negative potential includes one or more discharge processes, and the rate and cutoff condition of each discharge process are the same or different.

In a second aspect, an embodiment of the present invention provides an application of a battery formation process method in a sodium ion battery, wherein the sodium ion battery is formed according to the battery formation process method described in the first aspect above.

In a third aspect, an embodiment of the present invention provides a sodium ion battery formed according to the battery formation process method described in the first aspect above.

The battery formation process provided by the embodiment of the present invention can form an interface film component mainly composed of inorganic NaF generated by electrolyte reduction on the positive electrode side by first discharging the sodium ion battery to a negative potential. This is different from the interface component mainly composed of organic matter formed on the positive electrode side by electrolyte oxidation during conventional charging. In subsequent cycles, the interface is more stable and not easy to decompose, thereby improving the battery cycle performance. This method is a formation method unique to sodium ion batteries, which can achieve simple and efficient interface regulation and is very beneficial to the needs of the actual battery production formation process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a discharge curve of a positive half-cell of a battery provided in Example 1 of the present invention;

FIG2 is a negative electrode half-cell charging curve of a battery provided in Example 1 of the present invention;

FIG3 is a full battery formation process curve provided in Example 1 of the present invention;

FIG4 is a full battery cycle performance diagram of Example 1 of the present invention and Comparative Example 1;

FIG5 is a graph showing the full battery cycle performance of Example 5 of the present invention and Comparative Example 4;

FIG6 is a comparison diagram of the cycle performance of Example 1 of the present invention and Comparative Example 1;

FIG. 7 is a comparison chart of the cycle performance of Example 5 of the present invention and Comparative Example 4.

DETAILED DESCRIPTION

The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

The embodiment of the present invention provides a battery formation process method, which includes: discharging the assembled sodium ion full battery to a negative potential before the normal charge and discharge cycle, wherein the discharge rate to the negative potential is 0.01C-1C, for battery formation, so that an interface film component mainly composed of inorganic NaF generated by electrolyte reduction is formed on the positive electrode side of the battery. The above-mentioned process of discharging to the negative potential includes one or more discharge processes, and the rate and cutoff conditions of each discharge process are the same or different.

The specific executable operations include:

Connect the positive and negative electrodes of the battery and discharge the battery to a negative potential; wherein the discharge cut-off voltage is between -5V and 0V, excluding 0V; or,

Reverse the positive and negative poles of the battery and charge the battery to a positive potential (equivalent to discharging under positive connection conditions); wherein the charging cut-off voltage is between 0-5V, excluding 0V.

Preferably, -5V≤discharge cut-off voltage≤-3V; or, 3V≤charge cut-off voltage≤5V.

In addition to directly controlling the cut-off voltage, it can also be achieved through the charge and discharge specific capacity.

Connect the positive and negative electrodes of the battery and discharge the battery to a negative potential; wherein the discharge specific capacity is ≥ 4 mAh/g; or,

Reverse the positive and negative poles of the battery and charge the battery to a positive potential (equivalent to discharging under positive connection conditions); wherein the charge specific capacity is ≥4mAh/g.

The battery formation process method proposed in the present invention can be applied to all types of sodium ion full batteries, and its specific composition may include but is not limited to the materials listed below.

The positive electrode comprises: any one of layered oxides, tunnel oxides, polyanion compounds, Prussian blue materials, Prussian white materials or organic materials;

The negative electrode includes: any one of a carbon-based material, a titanium-based material, and an alloy material;

The electrolyte includes: a carbonate electrolyte and/or an ether electrolyte.

Since both the positive and negative electrodes of the sodium ion battery use aluminum foil as the current collector, it has the characteristic of being over-dischargeable, so the sodium ion battery can be directly discharged to a negative potential, or the positive and negative electrodes can be reversed and then charged for formation. Through the process of first discharging to a negative potential, the present method can form an inorganic component-rich CE I film mainly composed of inorganic NaF generated by electrolyte reduction on the positive electrode side. Compared with conventional charge and discharge batteries, only an organic-based CE I film is formed on the positive electrode side. The inorganic-based CE I obtained through the formation process is more stable and not easy to decompose, thereby effectively improving the cycle stability of the sodium ion battery.

In order to better understand the technical solution of the present invention, the following is described with specific examples and compared with comparative examples. It should be understood that the specific materials used in the following disclosed embodiment descriptions are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention.

Example 1

With NaCu _1/9 Ni _2/9 Fe _1/3 Mn _1/3 O ₂ as the positive electrode, hard carbon as the negative electrode, 1 mol/L NaPF ₆ @ethylene carbonate (EC)/diethyl carbonate (DEC) (volume ratio 1:1) as the electrolyte, and sodium difluorooxalate borate (NaDFOB) accounting for 2wt% of the electrolyte mass as the electrolyte additive, a sodium ion full battery was assembled, and the assembled sodium ion full battery was first discharged at a rate of 0.02C, with a cut-off condition of specific capacity ≥5mAh/g, and a voltage of about -3V at the end of discharge. Subsequently, the battery was charged to 4V at a rate of 0.1C and cycled twice in the range of 1-4V, and then the subsequent cycle was carried out at a rate of 2C in the voltage range of 1-4V, and the capacity retention rate was about 80% after 500 cycles.

Figure 1 is the first-week discharge curve of the positive electrode half-cell of Example 1, which corresponds to the electrochemical behavior of the positive electrode side when discharged to a negative potential during the formation process. It can be seen that a discharge platform appears at about 1.2V (vs Na ⁺ /Na), proving that an interface film component formed by electrolyte reduction is generated. Through the process of first discharging to a negative potential, an interface film component mainly composed of inorganic NaF generated by electrolyte reduction can be formed on the positive electrode side. It is different from the interface component mainly composed of organic matter generated by electrolyte oxidation formed on the positive electrode side during conventional charging. In subsequent cycles, the interface is more stable and not easy to decompose, thereby improving the battery cycle performance.

FIG2 is a charging curve of the negative electrode half-cell of Example 1, which corresponds to the electrochemical behavior of the negative electrode side during the formation of the full battery. It can be seen that almost no capacity is generated, proving that the formation behavior has almost no effect on the negative electrode side.

FIG3 is a curve of the full battery of Example 1 discharged to a negative potential, representing its formation process. It can be seen that a platform appears at around -3 V, which corresponds to the electrochemical process in which the electrolyte is reduced on the positive electrode side to form an interface film.

FIG. 4 is a curve showing the full battery formation process of Example 1 and the charge and discharge in the first week after formation.

Example 2

The same sodium ion full battery as in Example 1 was first discharged at a rate of 0.02C, with a cut-off condition of specific capacity ≥ 4 mAh/g, and a voltage of about -3 V at the end of discharge. Subsequently, the battery was charged to 4 V at a rate of 0.1C and cycled twice in the range of 1-4 V, and then subsequently cycled at a rate of 2C in the voltage range of 1-4 V, with a capacity retention rate of about 80% after 500 cycles.

Example 3

The same sodium ion full battery as in Example 1 was first discharged at a rate of 0.02C, with a cut-off condition of specific capacity ≥ 5 mAh/g, and a voltage of about -3 V at the end of discharge. Subsequently, the battery was charged to 4.2 V at a rate of 0.1C, and cycled twice in the range of 1-4.2 V, and then subsequently cycled at a rate of 2C in the voltage range of 1-4.2 V, with a capacity retention rate of about 71% after 500 cycles.

Example 4

The same sodium ion full battery as in Example 1 was first discharged at a rate of 0.05C, with a cut-off condition of specific capacity ≥ 5 mAh/g, and a voltage of about -3 V at the end of discharge. Subsequently, the battery was charged to 4 V at a rate of 0.1C and cycled twice in the range of 1-4 V, and then subsequently cycled at a rate of 2C in the voltage range of 1-4 V, with a capacity retention rate of about 75% after 500 cycles.

Example 5

The same positive and negative electrode materials as in Example 1 were used, and the electrolyte was replaced with 1 mol/L NaPF ₆ @ diethylene glycol dimethyl ether (DEGDME), without electrolyte additives. The assembled sodium ion full battery was first discharged at a rate of 0.1C, with a cutoff condition of specific capacity ≥ 4 mAh/g, and a cutoff voltage of about -3.4V during discharge. Subsequently, the battery was charged to 4V at a rate of 0.1C and cycled at 1.5-4V for 2 weeks, followed by subsequent cycles at a rate of 1C within the range of 1.5-4V, with a capacity retention rate of about 90% after 200 weeks.

Comparative Example 1

The difference from Example 1 is that without going through the formation process, the sodium ion full battery is directly cycled twice at a rate of 0.1C and a voltage range of 1-4V, and then subsequent cycles are performed at a rate of 2C and a voltage range of 1-4V. After 500 cycles, the capacity retention rate is only 72%, which is lower than the capacity retention rate of Example 1, indicating that the formation process has an improving effect on the cycle stability. Figure 5 is the first week charge and discharge curve of the full battery of Comparative Example 1, and the cycle performance comparison of Example 1 and Comparative Example 1 is shown in Figure 6.

Comparative Example 2

The difference from Example 4 is that, without going through the formation process, the assembled sodium ion full battery is directly cycled twice at a rate of 0.1C and a voltage range of 1-4.2V, and then subsequent cycles are performed at a rate of 2C and a voltage range of 1-4.2V. After 500 cycles, the capacity retention rate is only 61%, which is lower than the capacity retention rate of Example 1, indicating that the formation process has an improving effect on the high-voltage cycle stability of the battery.

Comparative Example 3

The assembled sodium ion full battery based on carbonate electrolyte was first discharged at a rate of 0.02C, with a cut-off condition of specific capacity ≥ 10 mAh/g, and a voltage of about -4 V at the end of discharge. Subsequently, the battery was charged to 4 V at a rate of 0.1C, and cycled twice in the range of 1-4 V, and then subsequently cycled at a rate of 2C in the voltage range of 1-4 V. After 500 cycles, the capacity retention rate was about 67%, which was lower than the cycle capacity retention rates of Example 1 and Comparative Example 1, indicating that the excessive cut-off capacity of the formation process has a negative effect on the cycle stability.

Comparative Example 4

The difference from Example 5 is that without going through the formation process, the assembled sodium ion full battery based on the ether-based electrolyte is directly cycled twice at a rate of 0.1C and a voltage range of 1.5-4V, and then subsequent cycles are performed at a rate of 1C and a voltage range of 1.5-4V. After 200 cycles, the capacity retention rate is only 66%, which is lower than the capacity retention rate of Example 5, indicating that the formation process also has an improving effect on the cycle stability in the ether-based electrolyte. The cycle performance comparison of Example 5 and Comparative Example 4 is shown in Figure 7.

The capacity retention rates after cycles of all the above embodiments and comparative examples are summarized in Table 1.

Table 1

It can be seen that the battery formation process method of the present invention can achieve better cycle performance. The battery formation process method of the present invention is applicable to various sodium ion full batteries.

The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims (9)

1. A battery formation process method, characterized in that the process method comprises: discharging the assembled sodium ion full battery to a negative potential before the normal charge and discharge cycle to perform battery formation, so that an interface film component mainly composed of inorganic substances generated by electrolyte reduction is formed on the positive electrode side of the battery, and the inorganic substance includes NaF. 2. The battery formation process according to claim 1, characterized in that the specific method of discharging to a negative potential comprises: Under the condition that the positive and negative electrodes of the battery are connected in a positive direction, the battery is discharged to a negative potential; wherein the discharge cut-off voltage is between -5V and 0V, excluding 0V; or, Under the condition that the positive and negative poles of the battery are reversed, the battery is charged to a positive potential; wherein the charging cut-off voltage is between 0-5V, excluding 0V. 3. The battery formation process according to claim 2, characterized in that -5V≤discharge cut-off voltage≤-3V; or 3V≤Charging cut-off voltage≤5V. 4. The battery formation process according to claim 1, characterized in that the specific method of discharging to a negative potential comprises: When the positive and negative electrodes of the battery are connected in a positive direction, the battery is discharged to a negative potential; wherein the discharge specific capacity is ≥ 4 mAh/g; or, Under the condition that the positive and negative electrodes of the battery are reversed, the battery is charged to a positive potential; wherein the charging specific capacity is ≥4mAh/g. 5. The battery formation process according to claim 1 is characterized in that the positive electrode of the sodium ion full battery comprises: any one of layered oxides, tunnel-type oxides, polyanion compounds, Prussian blue materials, Prussian white materials or organic materials; the negative electrode comprises: any one of carbon-based materials, titanium-based materials, and alloy materials; the electrolyte comprises: carbonate electrolyte and/or ether electrolyte. 6. The battery formation process according to claim 1, characterized in that the discharge rate to the negative potential is 0.01C-1C. 7. The battery formation process according to claim 1, characterized in that the process of discharging to a negative potential includes one or more discharge processes, and the rate and cutoff conditions of each discharge process are the same or different. 8. Application of a battery formation process method in a sodium ion battery, characterized in that the sodium ion battery is formed according to the battery formation process method according to any one of claims 1 to 7. 9. A sodium ion battery formed according to the battery formation process method described in any one of claims 1 to 7.