Electrochemical sodium supplement-based long-life negative-electrode-free sodium metal battery

Abstract

The invention belongs to the technical field of negative-electrode-free sodium metal batteries, and particularly discloses a long-service-life negative-electrode-free sodium metal battery constructed based on an electrochemical sodium supplementing strategy and an implementation method of the long-service-life negative-electrode-free sodium metal battery. According to the battery, an electrochemical pre-embedded sodium positive plate is used as a sodium-rich positive electrode, so that sodium source compensation of the negative-electrode-free sodium metal battery in the first cycle and the cycle process is realized, the charge-discharge performance of the battery is effectively improved, the energy density of the battery is improved, and the cycle life of the battery is prolonged.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of negative-electrode-free sodium metal batteries, in particular to a long-life negative-electrode-free sodium metal battery based on an electrochemical sodium supplementing strategy and a preparation method thereof. BACKGROUND

[0002] In recent years, sodium ion batteries have attracted extensive attention from the industry and the scientific research field due to the fact that the crust abundance of Na is 1180 times that of Li, the cost of sodium carbonate is only 1 / 60 of that of lithium carbonate, and the sodium ion battery has a similar insertion / extraction working principle to the lithium ion battery. However, the relative atomic mass, atomic radius and ionic radius of sodium are all greater than those of lithium, which means that the intrinsic energy density of the sodium ion battery is low. Moreover, due to thermodynamic reasons, the graphite negative electrode of the commercial lithium ion battery cannot be directly used in the sodium ion battery.

[0003] In the exploration of a large number of novel negative electrode materials, sodium metal is considered to be the best negative electrode material for sodium batteries due to its ultra-high theoretical specific capacity and low working potential (1166 mAh / g, -2.71 V vs. standard hydrogen electrode). However, the sodium metal negative electrode has poor electrochemical reaction reversibility and poor electrode cycle stability, and even in laboratory tests, an excessive amount of sodium metal needs to be added, which greatly reduces the energy density of the prepared sodium metal battery. In addition, the poor air stability of sodium metal and the low mechanical strength increase the manufacturing cost of the thin sodium. Therefore, there is still a large gap between the sodium metal negative electrode and practical application.

[0004] In view of the challenges of sodium metal battery manufacturing difficulty and low energy density, the concept of a negative-electrode-free sodium metal battery is proposed. Similar to the traditional battery, the negative-electrode-free sodium metal battery is composed of a negative electrode, a separator and a positive electrode, but only uses a current collector as a nominal negative electrode without coating an active material, and is therefore called a negative-electrode-free battery. Specifically, during charging, Na + is deposited on the negative electrode current collector from the positive electrode material, and the lost electrons of the positive electrode reach the negative electrode through the external circuit to achieve charge balance; during discharging, the sodium metal is dissolved into Na + which is embedded into the positive electrode material, and the electrons from the negative electrode return to the positive electrode through the external circuit to generate a discharge current to do work outside. The sodium of the entire battery comes entirely from the positive electrode material, and there is no excess sodium metal, so the energy density can be improved.

[0005] In the sodium metal battery without negative electrode, the deposition and stripping of sodium metal on the surface of the current collector are unstable, and the sodium metal is prone to fall off and accumulate into dead sodium during the charging and discharging process, causing rapid loss of active sodium and making the cycle life of the battery generally difficult to exceed 50 weeks, which cannot meet the actual application requirements. The existing solution is to preplate a layer of sodium metal on the current collector, and then assemble the battery. However, this method uses a current collector containing sodium metal during the assembly process of the battery, which is dangerous and difficult to realize commercialization. In addition, there are also methods of introducing self-sacrificial additives into the positive electrode material, but this method produces many by-products such as CO2 and NiO during the operation process. Based on the above engineering problems, it is urgent to develop a long-life sodium metal battery without negative electrode based on electrochemical sodium compensation. The electrochemically compensated sodium source can stably compensate for the active sodium consumed during the cycle process, maintain the structural integrity, avoid the introduction of harmful by-products, and thus realize higher reliability and longer service life. SUMMARY

[0006] To solve the problems raised in the background art, the present application provides a long-life sodium metal battery without negative electrode based on electrochemical sodium compensation, which is characterized by utilizing the low-potential reversible sodium intercalation characteristics of sodium vanadium phosphate positive electrode material to compensate for the first-cycle irreversible sodium loss of the sodium metal battery without negative electrode, and leaving excess active sodium on the negative electrode current collector to continuously compensate for the active sodium consumed due to interface side reactions in subsequent cycles.

[0007] The long-life sodium metal battery without negative electrode of the present application first uses electrochemically pre-intercalated sodium vanadium phosphate as a positive electrode material to release active sodium ions in the lattice during the first charging process, and forms sodium metal in situ on the surface of the negative electrode current collector to provide a stable sodium source for subsequent cycles, dynamically compensating for the active sodium consumed due to interface side reactions, thereby significantly improving the cycle life and sodium utilization rate of the battery, while maintaining the structural integrity and process safety of the battery.

[0008] To achieve the above purpose, the present application provides the following technical solutions:

[0009] First, a half-cell is assembled with a sodium foil as the negative electrode and a positive electrode sheet as the positive electrode, and the battery is discharged to 0-1.5 V low voltage on a constant current charger, and then the battery is disassembled. The pre-intercalated sodium positive electrode sheet and the current collector foil are taken out to form a sodium metal battery without negative electrode.

[0010] During the first charging, the pre-intercalated sodium vanadium phosphate will preferentially release the sodium ions intercalated at low potential to form a layer of sodium metal on the negative electrode, and then the normal charging process is carried out. During the first discharging, the sodium metal on the negative electrode is stripped and re-intercalated into the positive electrode sodium vanadium phosphate, and the discharge cut-off voltage is set to be greater than 1.5 V to prevent further stripping of the negative electrode sodium source.

[0011] In the subsequent charge and discharge process, the discharge cut-off voltage is set to 1.5V or above, and the sodium metal formed on the negative side in the first cycle can continuously play the role of sodium source to compensate for the loss of active sodium in the charge and discharge process.

[0012] The application provides a pre-embedded sodium positive electrode sheet, and a preparation method thereof.

[0013] S01: Assembling sodium metal foil, a positive electrode sheet, a separator and electrolyte to obtain a half battery for standby;

[0014] S02: Discharging the half battery prepared in step S01 at a constant current of 0.01-5 C to 0-1.5 V; and disassembling the battery to obtain a pre-embedded sodium positive electrode sheet;

[0015] Further, in step S01, the positive electrode sheet comprises a sodium vanadium phosphate positive electrode sheet, a sodium vanadium oxyfluorophosphate, a sodium nickel-iron-manganese acid, a sodium nickel-manganese acid and a manganese-based anion redox positive electrode sheet.

[0016] Further, in step S01, the separator comprises a polypropylene separator, a polyethylene separator and a ceramic coating separator.

[0017] Further, in step S01, the electrolyte comprises an ether electrolyte and an ester electrolyte.

[0018] The application further provides a long-life negative electrode-free sodium metal battery based on electrochemical sodium supplement, which comprises the pre-embedded sodium positive electrode sheet.

[0019] The preparation method of the long-life negative electrode-free sodium metal battery based on electrochemical sodium supplement comprises the following steps:

[0020] S01: Assembling sodium metal foil, a positive electrode sheet, a separator and electrolyte to obtain a half battery for standby;

[0021] S02: Discharging the half battery prepared in step S01 at a constant current of 0.01-5 C to 0-1.5 V; and disassembling the battery to obtain a pre-embedded sodium positive electrode sheet;

[0022] S03: Assembling the pre-embedded sodium positive electrode sheet obtained by disassembling in step S02, a current collector foil and a separator to form a negative electrode-free sodium metal battery.

[0023] Further, in step S01, the positive electrode sheet comprises a sodium vanadium phosphate positive electrode sheet, a sodium vanadium oxyfluorophosphate, a sodium nickel-iron-manganese acid, a sodium nickel-manganese acid and a manganese-based anion redox positive electrode sheet.

[0024] Further, in step S01, the separator comprises a polypropylene separator, a polyethylene separator and a ceramic coating separator, and the electrolyte comprises an ether electrolyte and an ester electrolyte.

[0025] Further, in step S03, the separator includes a polypropylene separator, a polyethylene separator, and a ceramic-coated separator.

[0026] Further, in step S03, the current collector foil includes a copper foil, an aluminum foil, a carbon-coated aluminum foil, and a carbon-coated copper foil.

[0027] Further, in step S03, the activation current of the negative electrode-free sodium metal battery is 0.01 C-0.5 C, the cycle current is 0.5 C-10 C, and the lower limit voltage and the upper limit voltage of charging and discharging can be 1.5-3.2 V and 3.6-4.5 V, respectively.

[0028] Compared with the prior art, the beneficial effects of the present application are:

[0029] (1) Sodium compensation in situ without damage: the present application provides a long-life negative electrode-free sodium metal battery based on electrochemical sodium compensation. The battery uses a pre-embedded sodium positive electrode sheet as a sodium-rich positive electrode to compensate for the sodium source of the negative electrode-free sodium metal battery during the first cycle and the cycle process, effectively improving the charge and discharge performance of the battery and improving its energy density and cycle life. Through the design of "electrochemical sodium compensation" in the present application, the battery maintains structural integrity while improving cycle life, and the cycle life can be improved from about 50 weeks of traditional to 2500 weeks (70% capacity retention rate), which is increased by ~50 times. The process is simple, environmentally friendly, and has little effect on the battery system, providing a new engineering design route for high-energy-density, long-cycle-stability negative electrode-free sodium metal batteries.

[0030] (2) Innovative dynamic sodium source management: excess active sodium is left on the negative current collector after the first charging, and can be released on demand in subsequent cycles to inhibit the formation of dead sodium. The first cycle coulombic efficiency reaches 99.5%, and the sodium metal loss during long-term cycling is reduced by about 80% compared to traditional methods, achieving true "in situ, dynamic, controllable, and continuous" sodium compensation.

[0031] (3) No by-products, safe and reliable: the present battery innovatively avoids the use of high-activity sodium or self-sacrificial additives, and has no CO2, NiO, etc. By-products are generated, which has no effect on the battery structure and subsequent cycle performance. Soft package dry cells can be assembled in dry room or outdoor, reducing the operation risk and production difficulty.

[0032] (4) Simple process, great industrialization potential: battery assembly, liquid injection, charging and discharging, and disassembly can be completed under normal conditions, without high temperature and high pressure treatment or additional material synthesis. It is easy to operate and has low cost, excellent process compatibility and large-scale production application value. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 XRD pattern of the sodium vanadium phosphate positive electrode material used in Example 1;

[0034] Figure 2 Cycle capacity-voltage curve of the sodium metal battery without negative electrode after electrochemical sodium supplement;

[0035] Figure 3 Long cycle capacity retention rate graph of the sodium metal battery without negative electrode after electrochemical sodium supplement;

[0036] Figure 4 Long cycle capacity retention rate graph of the sodium metal battery without negative electrode after electrochemical sodium supplement; DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0038] Embodiment 1

[0039] A sodium vanadium phosphate positive electrode sheet with a diameter of 10 mm, a copper foil current collector with a diameter of 12 mm, a sodium metal sheet with a diameter of 12 mm, and a polypropylene separator with a diameter of 16 mm were used to assemble a sodium vanadium phosphate half-battery in an argon-filled glove box (H2O < 0.01 ppm, O2 < 0.01 ppm) according to the order of “2032 type negative electrode shell, 12 mm sodium metal sheet, 20 μL electrolyte, 16 mm polypropylene separator, 20 μL electrolyte, 10 mm sodium vanadium phosphate positive electrode sheet, 2032 type positive electrode shell”. The internal pressure of the battery can be adjusted by adding shims and springs according to the remaining space inside the 2032 type battery. The electrolyte used was a 1 mol / L NaPF6 Diglyme mixed solution (Suzhou Duoduo Chemical Technology Co., Ltd., NP-005). Figure 1 The XRD pattern of the sodium vanadium phosphate electrode used is shown in the figure. The results show that the diffraction peak intensity of the sodium vanadium phosphate is high, indicating that the crystallinity is high. The amorphous carbon coating diffraction peaks on the surface of the sodium vanadium phosphate appear at 16.08° and 32.98°.

[0040] Subsequently, the assembled sodium vanadium phosphate half-battery was deeply discharged to 1 V at a discharge rate of 0.1 C, and the sodium vanadium phosphate positive plate after pre-embedding sodium was taken out by disassembling the battery. A sodium metal battery without negative electrode with pre-embedded sodium sodium vanadium phosphate as the positive electrode was assembled in the order of "2032 type negative electrode shell, 12 mm copper foil, 20 μL electrolyte, 16 mm polypropylene separator, 20 μL electrolyte, pre-embedded sodium sodium vanadium phosphate positive plate, 2032 type positive electrode shell". Subsequently, the assembled sodium metal battery without negative electrode was tested by charging and discharging, the activation current was 0.1 C, the activation cycle number was 3 cycles, the cycle current was 1 C, and the charging and discharging voltage range was 2.0-4.0 V. Figure 2 The cycle charging and discharging specific capacity-voltage curve of the sodium metal battery without negative electrode after electrochemical sodium supplementation is shown, the charging and discharging platform voltage difference is low, and the capacity retention rate is high, indicating that the structure of the sodium vanadium phosphate material is not damaged after embedding sodium at low voltage. Figure 3 The long cycle capacity retention rate of the sodium metal battery without negative electrode is shown, and the capacity retention rate of the battery after 2500 cycles is 70 %, indicating that the cycle life of the sodium metal battery without negative electrode after electrochemical sodium supplementation is greatly improved.

[0041] Example 2

[0042] A sodium vanadium phosphate positive plate with a length of 65 mm and a width of 45 mm, a copper foil current collector with a length of 67 mm and a width of 47 mm, a sodium metal plate with a length of 67 mm and a width of 47 mm, and a polypropylene separator with a width of 80 mm were used to assemble a sodium vanadium phosphate soft pack half-battery in a lamination manner in an argon-filled glove box (H2O < 0.01 ppm, O2< 0.01 ppm). The electrolyte used was a 1 mol / L NaPF6 Diglyme mixed solution.

[0043] Subsequently, the assembled sodium vanadium phosphate soft pack half-battery was deeply discharged to 1 V at a discharge rate of 0.1 C, and the sodium vanadium phosphate positive plate after pre-embedding sodium was taken out by disassembling the battery. A sodium metal battery without negative electrode with pre-embedded sodium sodium vanadium phosphate as the positive electrode was assembled in the order of "2032 type negative electrode shell, 12 mm copper foil, 20 μL electrolyte, 16 mm polypropylene separator, 20 μL electrolyte, pre-embedded sodium sodium vanadium phosphate positive plate, 2032 type positive electrode shell". Subsequently, the assembled sodium metal battery without negative electrode was tested by charging and discharging, the activation current was 0.1 C, the activation cycle number was 3 cycles, the cycle current was 1 C, and the charging and discharging voltage range was 2.0-4.0 V, and the electrochemical performance was not much different from that of Example 1.

[0044] Example 3

[0045] A sodium vanadium phosphate positive electrode sheet with a length of 65 mm and a width of 45 mm, a copper foil current collector with a length of 67 mm and a width of 47 mm, a sodium metal sheet with a length of 67 mm and a width of 47 mm, and a polyethylene separator with a width of 80 mm were used to assemble a sodium vanadium phosphate soft-pack half-battery in a stacking manner in an argon-filled glove box (H2O < 0.01 ppm, O2 < 0.01 ppm). The electrolyte used was a 1 mol / L NaPF6 Diglyme mixed solution.

[0046] Subsequently, the assembled sodium vanadium phosphate soft-pack half-battery was deeply discharged to 1 V at a discharge rate of 0.1 C, and the sodium pre-intercalated sodium vanadium phosphate positive electrode sheet was removed. A negative electrode-free sodium metal soft-pack battery with the sodium pre-intercalated sodium vanadium phosphate as the positive electrode was assembled using the stacking method. Subsequently, the assembled negative electrode-free sodium metal soft-pack battery was subjected to charge-discharge tests, with an activation current of 0.1 C, an activation number of 3 cycles, a cycle current of 5 C, and a charge-discharge voltage range of 2.0-4.2 V. The electrochemical performance was similar to that of Example 1.

[0047] Example 4

[0048] A sodium vanadium oxyfluorophosphate positive electrode sheet with a diameter of 10 mm, a carbon-coated aluminum foil current collector with a diameter of 12 mm, a sodium metal sheet with a diameter of 12 mm, and a polypropylene separator with a diameter of 16 mm were used to assemble a sodium vanadium oxyfluorophosphate half-battery in the order of “2032-type negative electrode shell, 12 mm sodium metal sheet, 20 μL electrolyte, 16 mm polypropylene separator, 20 μL electrolyte, 10 mm sodium vanadium oxyfluorophosphate positive electrode sheet, and 2032-type positive electrode shell” in an argon-filled glove box (H2O < 0.01 ppm, O2 < 0.01 ppm). The internal pressure of the battery can be adjusted by adding shims and springs according to the remaining space inside the 2032-type battery. The electrolyte used was a 1 mol / L NaPF6 Diglyme mixed solution.

[0049] Subsequently, the assembled sodium vanadium oxyfluorophosphate half-battery was deeply discharged to 1 V at a discharge rate of 0.1 C, and the sodium pre-intercalated sodium vanadium phosphate positive electrode sheet was removed. A negative electrode-free sodium metal battery with the sodium pre-intercalated sodium vanadium oxyfluorophosphate as the positive electrode was assembled in the order of “2032-type negative electrode shell, 12 mm carbon-coated aluminum foil, 20 μL electrolyte, 16 mm polypropylene separator, 20 μL electrolyte, sodium pre-intercalated sodium vanadium oxyfluorophosphate positive electrode sheet, and 2032-type positive electrode shell”. Subsequently, the assembled negative electrode-free sodium metal button cell was subjected to charge-discharge tests, with an activation current of 0.1 C, an activation number of 1 cycle, a cycle current of 1 C, and a charge-discharge voltage range of 2.5-4.3 V. Figure 4The long cycle capacity retention of the pre-sodium intercalated sodium vanadium oxyfluorophosphate sodium (SR-NVPOF) sodium metal battery without negative electrode is demonstrated, with a 500-cycle capacity retention of 94%, and excellent cycle performance.

[0050] Example 5

[0051] A nickel iron manganese sodium positive electrode sheet with a diameter of 10 mm, a carbon-coated aluminum foil current collector with a diameter of 12 mm, a sodium metal sheet with a diameter of 12 mm, and a polypropylene separator with a diameter of 16 mm were used. In an argon-filled glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), a nickel iron manganese sodium half-battery was assembled in the order of "2032 type negative electrode shell, 12 mm sodium metal sheet, 20 μL electrolyte, 16 mm polypropylene separator, 20 μL electrolyte, 10 mm nickel iron manganese sodium positive electrode sheet, 2032 type positive electrode shell". The pressure inside the battery can be adjusted by adding shims and springs according to the remaining space inside the 2032 type battery. The electrolyte used was a 1 mol / L NaPF6 Diglyme mixed solution.

[0052] Subsequently, the assembled nickel iron manganese sodium half-battery was deeply discharged to 1 V at a discharge rate of 0.1 C, and the nickel iron manganese sodium positive electrode sheet after pre-intercalation of sodium was removed. A sodium metal battery without negative electrode with pre-intercalation of sodium nickel iron manganese sodium as the positive electrode was assembled in the order of "2032 type negative electrode shell, 12 mm carbon-coated aluminum foil, 20 μL electrolyte, 16 mm polypropylene separator, 20 μL electrolyte, pre-intercalation of sodium nickel iron manganese sodium positive electrode sheet, 2032 type positive electrode shell". Subsequently, the assembled sodium metal button cell without negative electrode was subjected to charge-discharge test, with an activation current of 0.1 C, an activation number of 3 cycles, a cycle current of 1 C, and a charge-discharge voltage range of 2.0-4.0 V. Figure 4 The long cycle capacity retention of the pre-sodium intercalated sodium nickel iron manganese (SR-NFM) sodium metal battery without negative electrode is demonstrated, with a 300-cycle capacity retention of 77%.

[0053] It should be noted that, in the present text, relational terms such as first and second and the like can only be used to distinguish one entity or operation from another entity or operation, without necessarily requiring or implying any such actual relationship or order between these entities or operations. Moreover, the terms "comprising", "containing" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such a process, method, article or apparatus.

[0054] It should be noted that the above content only illustrates the technical idea of the present application, and cannot limit the protection scope of the present application. For ordinary skilled in the art, without departing from the principle of the present application, a number of improvements and refinements can be made, which fall within the protection scope of the claims of the present application.

Claims

1. A pre-intercalated sodium positive electrode, characterized in that, The preparation method includes the following steps: S01: Assemble a half-cell by combining sodium metal foil, positive electrode, separator, and electrolyte for later use; S02: Discharge the half-cell prepared in step S01 with a constant current of 0.01-5 C to 0-1.5 V; disassemble the cell to obtain a pre-sodium-embedded positive electrode sheet; In step S01, the positive electrode includes sodium vanadium phosphate positive electrode, sodium vanadium fluoride phosphate, sodium nickel iron manganese oxide, sodium nickel manganese oxide, and manganese-based anion redox positive electrode.

2. The pre-intercalated sodium positive electrode according to claim 1, characterized in that, In step S01, the diaphragm includes a polypropylene diaphragm, a polyethylene diaphragm, and a ceramic-coated diaphragm.

3. The pre-intercalated sodium positive electrode according to claim 1, characterized in that, In step S01, the electrolyte includes ether electrolyte and ester electrolyte.

4. A long-life, electrodeless sodium metal battery based on electrochemical sodium replenishment, characterized in that, The sodium metal battery without a negative electrode comprises the pre-intercalated sodium positive electrode sheet as described in any one of claims 1 to 3.

5. The method for preparing a long-life, electrodeless sodium metal battery based on electrochemical sodium supplementation as described in claim 4, characterized in that, Includes the following steps: S01: Assemble a half-cell by combining sodium metal foil, positive electrode, separator, and electrolyte for later use; S02: Discharge the half-cell prepared in step S01 with a constant current of 0.01-5 C to 0-1.5 V; disassemble the cell to obtain a pre-sodium-embedded positive electrode sheet; S03: Disassemble the pre-embedded sodium positive electrode obtained in step S02 and assemble it with current collector foil and separator to form a sodium metal battery without negative electrode. In step S01, the positive electrode includes sodium vanadium phosphate positive electrode, sodium vanadium fluoride phosphate, sodium nickel iron manganese oxide, sodium nickel manganese oxide, and manganese-based anion redox positive electrode.

6. The method for preparing a long-life, electrodeless sodium metal battery based on electrochemical sodium supplementation according to claim 5, characterized in that, In step S01, the diaphragm includes a polypropylene diaphragm, a polyethylene diaphragm, and a ceramic-coated diaphragm, and the electrolyte includes an ether electrolyte and an ester electrolyte.

7. The method for preparing a long-life, electrodeless sodium metal battery based on electrochemical sodium supplementation according to claim 5, characterized in that, In step S03, the diaphragm includes a polypropylene diaphragm, a polyethylene diaphragm, and a ceramic-coated diaphragm.

8. The method for preparing a long-life, electrodeless sodium metal battery based on electrochemical sodium supplementation according to claim 5, characterized in that, In step S03, the current collector foil includes copper foil, aluminum foil, carbon-coated aluminum foil, and carbon-coated copper foil.

9. The method for preparing a long-life, electrodeless sodium metal battery based on electrochemical sodium supplementation according to claim 5, characterized in that, In step S03, the activation current of the negative electrode-free sodium metal battery is 0.01 C-0.5 C, the cycle current is 0.5 C-10 C, and the lower and upper limits of the charge / discharge voltage can be 1.5~3.2 V and 3.6~4.5 V, respectively.

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