A positive electrode chemical pre-sodiation reagent and method for a sodium-ion battery and a sodium-ion battery

Abstract

The present invention belongs to the technical field of pre-sodiation of cathode materials for sodium-ion batteries, and discloses a chemical pre-sodiation reagent and method for sodium-ion batteries and a sodium-ion battery. In the present invention, a chemical pre-sodiation solution is prepared with ethylene glycol diethyl ether and 2,2'-bipyridine and metallic sodium. The pre-sodiation solution is placed in a dry environment. Several cathode sheets are taken and immersed in the pre-sodiation solution. After a certain period of time, the cathode sheets are taken out, washed and dried to obtain a pre-sodiated cathode of a sodium-ion battery. The chemical pre-sodiation reagent used in the present invention has characteristics such as a suitable redox potential and good chemical stability, and can be applied to commercial sodium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a positive electrode chemical pre-sodiation reagent and method for a sodium-ion battery and a sodium-ion battery. Background Art

[0002] With the rapid growth of the energy storage market demand, sodium-ion batteries are regarded as a promising emerging energy storage technology due to their rich resources, low cost, and excellent low-temperature performance. However, one of the main challenges in the commercial application of sodium-ion batteries is the low initial sodium content of oxide cathode materials and their corresponding low initial Coulomb efficiency, which seriously affects the energy density and cycle stability of the full battery. To overcome these problems, in recent years, researchers have widely explored pre-sodiation strategies for oxide cathode materials. During the pre-sodiation process, additional sodium ions are pre-introduced into the cathode to increase the initial sodium content of the material, thereby improving its initial Coulomb efficiency and cycle stability.

[0003] So far, the main pre-sodiation strategies include sacrificial salt pre-sodiation, electrochemical pre-sodiation, and chemical pre-sodiation. Among them, the sacrificial salt pre-sodiation method introduces sodium salts into the battery. After one charge-discharge cycle, these sodium salts will decompose and release sodium ions, thereby achieving pre-sodiation. Electrochemical pre-sodiation is to introduce sodium ions into the electrode material through an external electrochemical device before battery assembly. This method can precisely control the degree and uniformity of pre-sodiation. The chemical pre-sodiation method is based on the spontaneous reaction between the pre-sodiation reagent and the electrode material to introduce sodium ions into the electrode material. Due to its simple operation, uniform reaction, and controllable process, the chemical pre-sodiation method has significant potential for scalable application. By selecting appropriate chemical pre-sodiation reagents and optimizing the reaction conditions, efficient pre-sodiation can be achieved, thereby improving the initial Coulomb efficiency and cycle performance of sodium-ion batteries.

[0004] Currently, the widely used chemical pre-sodiation reagents are polycyclic aromatic hydrocarbons, such as naphthalene, biphenyl, etc. These special organic compounds have conjugated large π bonds and can react with various alkali metals to form strongly reducing alkali metal-organic solutions, which have been widely used as pre-sodiation reagents for the positive and negative electrode materials of sodium-ion batteries. However, this kind of pre-sodiation reagent usually has an extremely low redox potential (about 0.1V vs. Na + / Na), which is prone to cause over-pre-sodiation and structural damage of the cathode material. In addition, the pre-sodiation process must be completed in a glove box atmosphere because this solvent has poor chemical stability, which severely limits its large-scale application. Therefore, how to design a cathode pre-sodiation reagent with controllable redox potential and chemical stability is still challenging. Summary of the Invention

[0005] The object of the present invention is to solve the problem of low initial Coulombic efficiency of the oxide cathode material for sodium-ion batteries, and to provide a chemical pre-sodiation reagent and method for the cathode of sodium-ion batteries. The chemical pre-sodiation reagent used in the present invention has characteristics such as appropriate redox potential and good chemical stability, and can be applied to commercial sodium-ion batteries.

[0006] Based on the above object, the technical solution of the present invention is as follows:

[0007] In the first aspect, an embodiment of the present invention provides a novel chemical pre-sodiation reagent for the cathode of a sodium-ion battery, which is prepared by using ethylene glycol diethyl ether and 2,2'-bipyridine and metallic sodium to prepare the chemical pre-sodiation reagent; the concentration of the solute in the 2,2'-bipyridine sodium solution is 0.001 mol L -1 ~2 mol L -1 .

[0008] In the second aspect, an embodiment of the present invention provides a chemical pre-sodiation method in a non-glove box (dry room). The pre-sodiation solution described in any one of the first aspects is placed in the dry room environment, and several cathode plates are taken and immersed in the pre-sodiation solution. After 1 min to 10 min, the cathode plates are taken out, washed and dried to obtain a pre-sodiated cathode of a sodium-ion battery.

[0009] Preferably, the dry room environment directly affects the stability of the pre-sodiation solution, and the humidity and humidity need to be strictly controlled. The dew point range of the dry room is -20°C to -40°C, and the temperature is usually controlled between 20°C and 30°C.

[0010] Preferably, the pre-sodiation time is 5 min to 10 min.

[0011] In the third aspect, an embodiment of the present invention provides a sodium-ion battery including the pre-sodiated cathode plate. The pre-sodiated cathode plate of the sodium-ion battery, the separator, the electrolyte and the negative electrode plate are assembled in a glove box atmosphere, and finally a sodium-ion battery is prepared; wherein the separator is glass fiber; the solute in the electrolyte is 1M NaPF 6 , and the solvent is diethylene glycol dimethyl ether, and the negative electrode plate is a metallic sodium sheet or a hard carbon negative electrode.

[0012] Advantages and beneficial effects of the present invention:

[0013] The present invention selects the 2,2'-bipyridine sodium / ethylene glycol diethyl ether reagent with mild reaction and stable properties to perform pre-sodiation treatment on the cathode material of the sodium-ion battery. This method can be carried out in a normal temperature dry room, with simple operation, short process flow, rapid reaction, high safety, and is very easy to industrialize. At the same time, this pre-sodiated cathode can make up for the defect of insufficient sodium in itself, and effectively improve the initial Coulombic efficiency of the cathode. Description of the Drawings

[0014] Figure 1Cyclic voltammetry test curve graphs of pre-sodium solutions with different solutes (Na-Biph, Na-Bpy) obtained in Example 1 and Comparative Example 1;

[0015] Figure 2 Initial and first-cycle charge-discharge curve graphs of the oxide cathode material pre-sodiumed with Na-Bpy / DEE solution for 5 min obtained in Example 1;

[0016] Figure 3 Initial and first-cycle charge-discharge curve graphs of the oxide cathode material pre-sodiumed with Na-Bpy / DEE solution for 10 min obtained in Example 2;

[0017] Figure 4 Initial and first-cycle charge-discharge curve graphs of the oxide cathode material pre-sodiumed with Na-Bpy / DME solution for 5 min obtained in Comparative Example 2;

[0018] Figure 5 Initial and first-cycle charge-discharge curve graphs of the oxide cathode material pre-sodiumed with Na-Bpy / DME solution for 10 min obtained in Comparative Example 3;

[0019] Figure 6 Change graphs of pre-sodium solutions standing for 1 h in the drying room obtained in Example 3 and Comparative Example 4 (left is Na-Bpy / DME solution, right is Na-Bpy / DEE solution);

[0020] Figure 7 Initial and first-cycle charge-discharge curve graphs of the oxide cathode material pre-sodiumed with Na-Bpy / DEE solution in the drying room obtained in Example 3;

[0021] Figure 8 Initial and after pre-sodiuming with Na-Bpy / DEE solution in Example 3, P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 / / First-cycle charge-discharge curve graph of the hard carbon full cell;

[0022] Figure 9 Initial and after pre-sodiuming with Na-Bpy / DEE solution in Example 3, P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 / / Cycle graph of the hard carbon full cell;

[0023] Figure 10 Initial and first-cycle charge-discharge curve graphs of the oxide cathode material pre-sodiumed with Na-Bpy / DME solution in the drying room obtained in Comparative Example 4. Detailed implementation manners

[0024] The present invention will be described in detail and completely below in conjunction with the accompanying drawings. However, these embodiments do not mean to limit the protection scope of the present invention. Unless otherwise specified, the reagents used in the embodiments are all commercially available or obtained through conventional synthesis methods in the art.

[0025] Example 1

[0026] In a glove box, 10 mL of ethylene glycol diethyl ether (DEE) solvent was taken, 0.312 g of 2,2'-bipyridine (2,2'-Bipyridine, Bpy) was added, and magnetically stirred for 30 min to obtain a homogeneous and clear solution; 0.046 g of metallic sodium was added to the obtained solution, and magnetically stirred for 120 min to obtain a homogeneous dark purple chemical pre-sodiation solution Na-Bpy / DEE with a concentration of 0.2 mol L -1 The P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 positive electrode was placed in the pre-sodiation solution for 5 min. After the reaction was complete, it was washed three times with DEE and dried at 60 °C for 2 h.

[0027] The pre-sodiated positive electrode sheet and the sodium sheet were assembled into a half-cell, and the loading of the positive electrode active material was ~1.5 mg cm -2 , and cyclic voltammetry tests were carried out in the voltage range of 1.5 V - 4.15 V at a scanning rate of 0.2 mV s -1 . Figure 1 (Upper) is the cyclic voltammetry test curve of the Na-Bpy / DEE pre-sodiation solution used in Example 1, and its oxidation-reduction potentials are 0.33 V and 0.40 V respectively.

[0028] The pre-sodiated positive electrode sheet and the sodium sheet were assembled into a half-cell, and the loading of the positive electrode active material was ~1.5 mg cm -2 , and constant current charge-discharge tests were carried out in the voltage range of 1.5 V - 4.15 V at a current density of 50 mA g -1 . Figure 2 is the first-cycle charge-discharge curve of the P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 electrode sheets before and after pre-sodiation for 5 min. Electrochemical tests show that the open-circuit voltage of the half-cell after pre-sodiation decreases from 2.826 V to 1.821 V. The first charge and discharge capacities of the initial P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 positive electrode are 86.4 mAh g -1 and 151.2 mAh g -1, and after pre-sodiation, P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 The first charge and discharge capacities of the positive electrode are 155.8 mAh g -1 and 153.0 mAh g -1 respectively, and the first Coulombic efficiency is increased from 57.14% to 100%.

[0029] Comparative Example 1

[0030] In a glove box, 10 mL of ethylene glycol diethyl ether (DEE) solvent was taken, 0.308 g of biphenyl (Biphenyl, Biph) was added, and magnetic stirring was carried out for 30 min to obtain a homogeneous and clear solution; 0.046 g of metallic sodium was added to the obtained solution, and magnetic stirring was carried out for 120 min to obtain a homogeneous dark blue chemical pre-sodiation solution Na-Biph / DEE with a concentration of 0.2 mol L -1 The P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 positive electrode was placed in the pre-sodiation solution for 5 min, and after the reaction was complete, it was washed three times with DEE and dried at 60 °C for 2 h.

[0031] The pre-sodiated positive electrode sheet and the sodium sheet were assembled into a half-cell, and the loading of the positive electrode active material was ~1.5 mg cm -2 , and cyclic voltammetry tests were carried out in the voltage range of 1.5 V - 4.15 V at a scanning rate of 0.2 mV s -1 . Figure 1 (below) is the cyclic voltammetry test curve of the Na-Biph / DEE pre-sodiation solution used in Comparative Example 1, and its redox potentials are 0.16 V and 0.20 V respectively. Compared with the Na-Bpy / DEE pre-sodiation solution of Example 1, the Na-Biph / DEE pre-sodiation solution has a lower redox potential, which is likely to cause over-pre-sodiation and structural damage of the positive electrode material. Therefore, the sodium biphenyl pre-sodiation solution is not suitable for pre-sodiation of layered oxide positive electrode materials.

[0032] Example 2

[0033] The difference from Example 1 is that the P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 positive electrode was placed in the pre-sodiation solution for 10 min.

[0034] The pre-sodiated positive electrode sheet and the sodium sheet were assembled into a half-cell, and the loading of the positive electrode active material was ~1.5 mg cm -2 , at 50 mA g -1At a current density, a constant current charge-discharge test was carried out in the voltage range of 1.5 V - 4.15 V. Figure 3 P2-Na after initial and pre-sodiation for 10 min used in Example 2 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 First charge-discharge curve of the electrode sheet. Electrochemical tests show that the open-circuit voltage of the half-cell after pre-sodiation decreased from 2.826 V to 1.793 V, and the initial P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 The first charge and discharge capacities of the positive electrode were 86.4 mAh g -1 and 151.2 mAh g -1 respectively, while for P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 the first charge and discharge capacities of the positive electrode were 184.7 mAh g -1 and 155.5 mAh g -1 respectively. As the pre-sodiation time increased, the first charge capacity further improved, and the electrochemical curve plateau of the positive electrode material remained consistent with the initial material, indicating that the Na-Bpy / DEE pre-sodiation solution could maintain the structural stability of the positive electrode material during long-term pre-sodiation.

[0035] Comparative Example 2

[0036] The difference from Example 1 was that ethylene glycol diethyl ether (DEE) was replaced by ethylene glycol dimethyl ether (DME).

[0037] The pre-sodiated positive electrode sheet was assembled with a sodium sheet into a half-cell, and the positive electrode active material loading was ~1.5 mg cm -2 At a current density of 50 mA g -1 a constant current charge-discharge test was carried out in the voltage range of 1.5 V - 4.15 V. Figure 4 P2-Na after initial and pre-sodiation for 5 min used in Comparative Example 2 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 First charge-discharge curve of the electrode sheet. Electrochemical tests show that the open-circuit voltage of the half-cell after pre-sodiation decreased from 2.826 V to 1.825 V, and the initial P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 The first charge and discharge capacities of the positive electrode were 86.4 mAh g -1 and 151.2 mAh g -1, and after pre-sodiation, P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 The first charge and discharge capacities of the positive electrode are 154.9 mAh g -1 and 152.5 mAh g -1 respectively, and the first Coulombic efficiency is increased from 57.14% to 100%.

[0038] Comparative Example 3

[0039] The difference from Comparative Example 2 is that the P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 positive electrode was placed in the pre-sodium solution for 10 min.

[0040] The pre-sodiated positive electrode sheet and the sodium sheet were assembled into a half-cell, and the positive electrode active material loading was ~1.5 mg cm -2 , and a constant current charge and discharge test was carried out in the voltage range of 1.5 V - 4.15 V at a current density of 50 mA g -1 . Figure 5 The initial and pre-sodiated for 10 min P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 polar electrode first cycle charge and discharge curve diagram. Electrochemical tests show that the open circuit voltage of the half-cell after pre-sodiation decreases from 2.826 V to 1.761 V. The first charge and discharge capacities of the initial P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 positive electrode are 86.4 mAh g -1 and 151.2 mAh g -1 respectively, while the first charge and discharge capacities of the P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 positive electrode after pre-sodiation are 186.9 mAh g -1 and 101.3 mAh g -1 . As the pre-sodiation time increases, the first cycle charge capacity further increases; however, compared with the initial material, the electrochemical curve platform of the positive electrode material becomes smooth and the discharge capacity decreases significantly, indicating that the Na-Bpy / DME pre-sodium solution will damage the structural stability of the positive electrode material during the long-term pre-sodiation process.

[0041] Example 3

[0042] The difference from Example 1 is that the glove box was replaced with a drying room.

[0043] Figure 6 (The right bottle) shows the change of the Na-Bpy / DEE pre-sodium solution prepared in the drying room after standing for 1 h. It was observed that the pre-sodium solution remained consistent before and after standing for 1 h, with basically no change, indicating that the Na-Bpy / DEE pre-sodiation solution has good chemical stability.

[0044] The pre-sodiated positive electrode sheet and the sodium sheet were assembled into a half-cell in the drying room, and the loading of the positive active material was ~1.5 mg cm -2 , and a constant current charge-discharge test was carried out in the voltage range of 1.5 V - 4.15 V at a current density of 50 mA g -1 . Figure 7 The initial and pre-sodiated P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 polar electrode sheet for Example 3. Electrochemical tests showed that the open-circuit voltage of the half-cell after pre-sodiation decreased from 2.826 V to 1.833 V. The initial charge and discharge capacities of the P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 positive electrode were 86.4 mAh g -1 and 151.2 mAh g -1 , respectively, while the initial charge and discharge capacities of the pre-sodiated P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 positive electrode were 155.1 mAh g -1 and 153.5 mAh g -1 , respectively. The initial Coulombic efficiency increased from 57.14% to 100%. The results show that the Na-Bpy / DEE solution can achieve positive electrode pre-sodiation in the drying room and can better maintain the electrochemical performance.

[0045] The pre-sodiated positive electrode sheet was assembled with a hard carbon negative electrode to form a full cell, and the loading of the positive active material was ~4 mg cm -2 , and a constant current charge-discharge test was carried out in the voltage range of 1.4 V - 4.05 V at a current density of 200 mA g -1 . Figure 8 The initial and pre-sodiated P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 / / The first charge-discharge curve of the hard carbon full cell. Electrochemical tests showed that the open-circuit voltage of the half-cell after pre-sodiation decreased from 0.198 V to -0.269 V. The initial P2-Na2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 / / The initial charge and discharge capacities of the hard carbon full cell are 89.4 mAh g -1 and 49.3 mAh g -1 , while after pre-sodiation, P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 / / The initial charge and discharge capacities of the hard carbon full cell are 179.9 mAh g -1 and 135.7 mAh g -1 , The results show that the full cell after pre-sodiation exhibits higher capacity compared to the non-pre-sodiated full cell. Figure 9 For P2-Na after pre-sodiation with Na-Bpy / DEE solution 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 / / The cycling performance of the hard carbon full cell, with a capacity of 0.5 Ah, and the capacity retention rate is ~100% after 40 cycles.

[0046] Comparative Example 4

[0047] The difference from Comparative Example 2 is that the glove box is replaced with a drying room.

[0048] Figure 6 (Left bottle) shows the change of the pre-sodiation solution of Na-Bpy / DME prepared in the drying room after standing for 1 h. It is observed that the pre-sodiation solution remains consistent before and after standing for 1 h, with basically no change, indicating that the Na-Bpy / DME pre-sodiation solution has good chemical stability.

[0049] The pre-sodiated positive electrode sheet is assembled with a sodium sheet into a half cell, and the positive electrode active material loading is ~1.5 mg cm -2 , and a constant current charge-discharge test is carried out in the voltage range of 1.5 V - 4.15 V at a current density of 50 mA g -1 . Figure 10 For the initial and P2-Na after pre-sodiation in the drying room used in Comparative Example 4 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 The first charge-discharge curve of the electrode sheet. Electrochemical tests show that the open circuit voltage of the half cell after pre-sodiation decreases from 2.826 V to 1.910 V, and the initial P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 The first charge and discharge capacities of the positive electrode are 86.4 mAh g-1 and 151.2 mAh g -1 , while after pre-sodiation, P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 The initial charge and discharge capacities of the cathode are 139.67 mAh g -1 and 129.05 mAh g -1 , respectively. The results show that the pre-sodiation of the cathode can be achieved with the Na-Bpy / DME solution in a dry room, but it is observed that its electrochemical curve is relatively smooth and the capacity shows attenuation.

[0050] In summary, the method of pre-sodiation of the cathode of a sodium-ion battery using the sodium 2,2'-bipyridine / ethylene glycol diethyl ether reagent has the best effect. This pre-sodiation solution has an appropriate redox potential, avoiding the destruction of the structural stability of the oxide cathode material. At the same time, the pre-sodiation process can be carried out in a normal-temperature dry room without affecting the subsequent electrochemical performance of the material. The P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O 2 cathode material has a high first-cycle efficiency and stable cycling performance, showing broad research prospects and application value.

[0051] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for pre-sodiumization of a sodium ion battery positive electrode chemical pre-sodiumization reagent, characterized in that: Ethylene glycol diethyl ether, 2,2'-bipyridine and metallic sodium are used to prepare a chemical pre-sodium reagent, wherein the chemical pre-sodium reagent is a 2,2'-bipyridine sodium solution, and the concentration of the solute in the 2,2'-bipyridine sodium solution is 0.001 mol L -1 ~2 mol L -1 , placing the pre-sodiumization reagent in a drying room, soaking the positive electrode sheet in the pre-sodiumization reagent, taking out the positive electrode sheet after 1min~10min, washing and drying, and obtaining a pre-sodiumized sodium ion battery positive electrode, wherein the dew point range of the drying room is -20℃~-40℃, the temperature range of the drying room is 20℃~30℃, and the active material of the sodium ion battery positive electrode is P2-Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2.

2. The method according to claim 1, characterized in that The pre-sodium time is 5min~10min.

3. A sodium ion battery, characterized in that: The invention comprises a pre-sodiumized sodium ion battery positive electrode, a separator, an electrolyte and a negative electrode sheet prepared by the method of any one of claims 1 to 2.

4. The sodium ion battery according to claim 3, characterized in that: The diaphragm is glass fiber, the solute in the electrolyte is 1M NaPF6, the solvent is diethylene glycol dimethyl ether; the negative electrode plate is a metal sodium plate or a hard carbon negative electrode.

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