A method for improving the performance of micro-expanded mesophase carbon microbeads in a dual-ion battery

Abstract

The application relates to a method for improving the performance of microswelling mesophase carbon microspheres in a dual-ion battery, and the specific steps are as follows: a carbonate electrolyte is selected, and the sodium salt concentration contained in the carbonate electrolyte is 0.5-3 mol / L; the application utilizes an electrochemical activation process, adds NaDFOB with a concentration of 0.01-0.2 mol / L into the carbonate electrolyte, makes the NaDFOB decompose in advance on the surface of the microswelling mesophase carbon microspheres, forms a stable artificial solid-phase electrolyte interface film, i.e., a pre-CEI film layer, the CEI film can play a barrier role, and can inhibit the serious oxidation side decomposition reaction between a large number of oxygen-containing functional groups in the graphite layer of the microswelling mesophase carbon microspheres and the electrolyte under high voltage; in addition, the pole piece with the artificial pre-CEI film layer after electrochemical activation can greatly weaken anion solvation intercalation, improve the coulomb efficiency of the dual-ion battery, has stable rate performance and cycle stability, and further improves the electrochemical performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dual-ion batteries, in particular to a method for improving the performance of micro-swelling mesophase carbon microspheres in dual-ion batteries. BACKGROUND

[0002] Currently, graphite is mainly used as the cathode (anode) material in dual-ion batteries. In addition to the limited capacity, the small interlayer spacing of graphite is not conducive to the deintercalation of large-sized anions during the charging and discharging process, which can easily cause the peeling of graphite layers and result in short cycle life. In addition, the working potential of graphite material in the dual-ion battery system is greater than 5V, and at this potential, the commonly used carbonate electrolyte will undergo serious oxidative side decomposition reactions, directly affecting the coulombic efficiency and cycle stability of the dual-ion battery.

[0003] The use of micro-swelling mesophase carbon microspheres as the cathode of dual-ion batteries has a larger interlayer spacing due to the presence of various oxygen-containing functional groups in the interlayer, which is more conducive to the intercalation of anions and provides higher capacity. After the electrochemical activation process at a high voltage of 5V, the highest working cutoff potential of this material is only 4.5V, which can provide a capacity higher than that of ordinary graphite anode materials.

[0004] During the electrochemical activation of micro-swelling mesophase carbon microspheres, the rich oxygen-containing functional groups in the interior of the material undergo intense and complex oxidative side decomposition reactions with carbonate electrolyte at a high voltage of 5V, resulting in extremely low coulombic efficiency and severe peeling of the graphite layers inside the carbon microspheres, which is not conducive to the normal operation of the subsequent dual-ion battery.

[0005] Therefore, there is an urgent need to develop a method for improving the cycle stability of micro-swelling mesophase carbon microspheres in dual-ion batteries. SUMMARY

[0006] The present application provides a method for improving the performance of micro-swelling mesophase carbon microspheres in dual-ion batteries to solve the problems of the prior art.

[0007] To solve the above technical problems, the present application is realized by the following technical scheme: a method for improving the performance of micro-swelling mesophase carbon microspheres in dual-ion batteries, the specific steps are as follows:

[0008] Step 1, preparation of anode and cathode sheets

[0009] Preparation of anode sheet:

[0010] A carbonate electrolyte is selected, and the concentration of sodium salt contained in the carbonate electrolyte is in the range of 0.5-3 mol / L;

[0011] The NaDFOB additive with a concentration of 0.01-0.2 mol / L is added to the carbonate electrolyte under vacuum, mixed and stirred for a period of time to obtain a clear and transparent electrolyte;

[0012] The micro-expanded mesophase carbon microspheres are mixed with the conductive agent and the binder to form a slurry, which is coated on the surface of the aluminum foil current collector, dried and compacted to obtain the positive electrode sheet;

[0013] The positive electrode sheet obtained above is assembled with the metallic sodium and the glass fiber separator into a dual-ion half battery using the clear and transparent electrolyte obtained above under vacuum, and is left to stand for a period of time;

[0014] The dual-ion half battery obtained above is subjected to an electrochemical activation process, and is charged at a constant current with a maximum cutoff voltage of 5 V and a current density of 50-200 mA / g, and is subjected to charge-discharge cycles 1-6 times in a voltage window of 1.5-5 V;

[0015] The dual-ion half battery after electrochemical activation is disassembled under vacuum, and the micro-expanded mesophase carbon microsphere positive electrode sheet is taken out, washed and dried using the corresponding organic solvent to obtain a micro-expanded mesophase carbon microsphere positive electrode sheet with a thin and uniform and stable artificial solid electrolyte interphase (CEI) film layer;

[0016] The negative electrode sheet is prepared as follows:

[0017] The amorphous carbon material is mixed with the conductive agent and the binder to form a slurry, which is coated on the surface of the copper foil current collector, dried and compacted to obtain the negative electrode sheet;

[0018] Step two: the positive electrode sheet and the negative electrode sheet obtained in step one are assembled with the glass fiber separator, the positive and negative electrode shells, the spring sheet, the gasket, and the carbonate electrolyte in step one into a sodium-ion-based dual-ion full battery, and are left to stand for a period of time;

[0019] Step three: the dual-ion full battery obtained in step two is subjected to electrochemical performance testing.

[0020] Preferably, in step one, the sodium salt is selected from any one of sodium hexafluorophosphate and sodium perchlorate, and the organic solvent inside the carbonate electrolyte is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

[0021] Preferably, in step one, the magnetic stirrer is used for mixing and stirring, and the stirring time is 18-32 h.

[0022] Preferably, in step one, the dual-ion half battery assembled is left to stand for 18-32 h.

[0023] Preferably, in the step one, the amorphous carbon material is hard carbon, soft carbon or mixture of both in any ratio; wherein the hard carbon based material comprises at least one of biomass based hard carbon, phenolic resin based hard carbon and pitch based hard carbon, and the soft carbon based material comprises at least one of petroleum coke, needle coke, carbon fiber, coke, carbon microbead.

[0024] Preferably, in the step one, the conductive agent comprises at least one of conductive carbon black, conductive graphite, carbon nanotube.

[0025] Preferably, in the step one, the binder comprises at least one of polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF).

[0026] Preferably, in the step two, the assembled sodium ion based full cell is rested for 18-32h.

[0027] Preferably, in the step three, the electrochemical performance test comprises rate performance, cycle performance and alternating current impedance.

[0028] The beneficial effects of the present application are:

[0029] 1. The present application utilizes an electrochemical activation process, and adds 0.01-0.2mol / L of sodium difluoro(oxalato)borate (NaDFOB) in the electrolyte, so that it is decomposed in advance on the surface of the slightly expanded mesophase carbon microbeads, forming a stable artificial solid electrolyte interface-pre-CEI film layer. The CEI film can play a barrier role, inhibiting the serious oxidative side decomposition reaction between a large number of oxygen-containing functional groups in the graphite layer of the slightly expanded mesophase carbon microbeads and the electrolyte at high voltage. In addition, the electrode sheet with the artificial CEI film layer after electrochemical activation can greatly weaken the anion solvation intercalation, improve the coulombic efficiency of the dual-ion battery, and at the same time make the battery have stable rate performance and cycle stability, further improving the electrochemical performance of the battery.

[0030] 2. The present application optimizes the electrochemical activation process of the slightly expanded mesophase carbon microbeads by optimizing the electrolyte, and obtains a dual-ion battery cathode material with a thin and uniform stable artificial solid electrolyte film layer (CEI). The cathode and the hard carbon negative electrode are assembled to obtain a sodium-based dual-ion full cell with excellent electrochemical performance. Compared with the slightly expanded mesophase carbon microbead cathode material without optimized electrochemical activation process, the sodium-based dual-ion full cell has more stable rate performance and long cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram of the relationship between the electrochemical activation process time and voltage of each embodiment and the comparative example of the present application.

[0032] Figure 2is a CV curve schematic diagram of the electrochemical activation process of each embodiment and the comparative example of the present application;

[0033] Figure 3 is a cross-section schematic diagram of the electrode sheet under a microscope after electrochemical activation of the comparative example 1 of the present application;

[0034] Figure 4 is a cross-section schematic diagram of the electrode sheet under a microscope after electrochemical activation of the embodiment 1 of the present application;

[0035] Figure 5 is a surface schematic diagram of the electrode sheet under a scanning electron microscope after electrochemical activation of the embodiment 1 of the present application;

[0036] Figure 6 is a cross-section schematic diagram of the electrode sheet under a scanning electron microscope after electrochemical activation of the embodiment 1 of the present application;

[0037] Figure 7 is a schematic diagram of the pre-CEI film layer under a transmission electron microscope of the comparative example 1 of the present application;

[0038] Figure 8 is a schematic diagram of the pre-CEI film layer under a transmission electron microscope of the embodiment 1 of the present application;

[0039] Figure 9 is a schematic diagram of the double-ion half-cell rate and coulombic efficiency performance of the embodiment 1 and the comparative example 1 of the present application;

[0040] Figure 10 is a schematic diagram of the double-ion half-cell voltage-specific capacity charge-discharge curve of the embodiment 1 and the comparative example 1 of the present application;

[0041] Figure 11 is a schematic diagram of the long cycle performance of the double-ion half-cell at a current density of 100 mA / g of the embodiment 1 and the comparative example 1 of the present application;

[0042] Figure 12 is a schematic diagram of the long cycle performance of the double-ion half-cell at a current density of 500 mA / g of the embodiment 1 and the comparative example 1 of the present application;

[0043] Figure 13 is a schematic diagram of the impedance of the double-ion half-cell of the embodiment 1 and the comparative example 1 of the present application;

[0044] Figure 14 is a schematic diagram of the double-ion full-cell rate and coulombic efficiency performance of the embodiment 1 of the present application;

[0045] Figure 15 is a schematic diagram of the double-ion full-cell voltage-specific capacity charge-discharge curve of the embodiment 1 of the present application;

[0046] Figure 16is a schematic diagram of the long cycle performance of the dual-ion full battery of embodiment 1 of the present application;

[0047] Figure 17 is a schematic diagram of the electrochemical activation process of the dual-ion half battery of embodiment 1 and comparative example 1 of the present application. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0049] Embodiment 1

[0050] A method for improving the performance of micro-swelling mesophase carbon microspheres in a dual-ion battery, the specific steps are as follows:

[0051] Step one, preparation of positive and negative electrode sheets

[0052] Preparation of positive electrode sheet:

[0053] Selecting organic solvents as carbonate electrolyte of ethylene carbonate and methyl ethyl carbonate, and selecting 2mol / L sodium hexafluorophosphate as the sodium salt contained therein;

[0054] In a vacuum glove box, 0.02mol / L NaDFOB additive was added to the above-mentioned carbonate electrolyte, and mixed and stirred for 24h using a magnetic stirrer to obtain a clear and transparent electrolyte;

[0055] Mixing the micro-swelling mesophase carbon microspheres with the conductive agent and the binder to form a slurry, coating it on the surface of the aluminum foil current collector, drying and compacting, and then cutting it into an electrode sheet with a diameter of 13mm;

[0056] In a vacuum glove box, the above-mentioned electrode sheet was assembled into a dual-ion half battery with metallic sodium and a glass fiber separator using the above-mentioned clear and transparent electrolyte, and was left to stand for 24 hours;

[0057] The above-mentioned dual-ion half battery was subjected to an electrochemical activation process using an electrochemical instrument, and was charged at a constant current with a maximum cutoff voltage of 5V and a current density of 50mA / g, and was subjected to charge-discharge cycles 6 times in a voltage window of 1.5-5V;

[0058] The dual-ion half battery after electrochemical activation was disassembled in a vacuum glove box, and the micro-swelling mesophase carbon microsphere electrode sheet was taken out, washed and dried using the corresponding organic solvent, to obtain a micro-swelling mesophase carbon microsphere positive electrode sheet with a thin and uniform and stable artificial solid-phase electrolyte membrane layer (CEI);

[0059] Preparation of negative electrode sheet:

[0060] The biomass-based hard carbon material is mixed with a conductive agent and a binder into a slurry, coated on the surface of a copper foil current collector, and cut into a negative electrode sheet with a diameter of 13 mm after drying and compaction;

[0061] Step two, using the positive electrode sheet and the negative electrode sheet obtained in step one, a glass fiber separator, a positive and negative electrode shell, a spring sheet, a gasket, and the carbonate electrolyte in step one are assembled into a sodium ion-based dual-ion full battery, and left to stand for 24 hours;

[0062] Step three, the dual-ion full battery obtained in step two is subjected to electrochemical performance testing, including rate performance, cycle performance and AC impedance.

[0063] Example 2

[0064] A method for improving the performance of micro-expanded mesophase carbon microspheres in a dual-ion battery, the specific steps are as follows:

[0065] Step one, preparation of positive electrode sheet and negative electrode sheet

[0066] Preparation of positive electrode sheet:

[0067] An organic solvent is selected as a carbonate electrolyte of ethylene carbonate and methyl ethyl carbonate, and a sodium salt selected from 2 mol / L sodium hexafluorophosphate is contained;

[0068] In a vacuum glove box, the 0.05 mol / L NaDFOB additive is added to the above-mentioned carbonate electrolyte, and mixed and stirred for 24 hours using a magnetic stirrer to obtain a clear and transparent electrolyte;

[0069] The micro-expanded mesophase carbon microspheres are mixed with a conductive agent and a binder into a slurry, coated on the surface of an aluminum foil current collector, and cut into an electrode sheet with a diameter of 13 mm after drying and compaction;

[0070] In a vacuum glove box, the above-mentioned clear and transparent electrolyte is used to assemble the above-mentioned electrode sheet with metallic sodium and a glass fiber separator into a dual-ion half battery, and left to stand for 24 hours;

[0071] The above-mentioned dual-ion half battery is subjected to an electrochemical activation process using electrochemical instruments, the dual-ion half battery is charged at a constant current, the highest cutoff voltage is set to 5V, the current density is 50mA / g, and the charge-discharge cycle is performed 6 times in a voltage window of 1.5-5V;

[0072] The electrochemically activated dual-ion half battery is disassembled in a vacuum glove box, the micro-swelling mesophase carbon microsphere electrode plate is taken out, and the corresponding organic solvent is used for cleaning and drying to obtain a micro-swelling mesophase carbon microsphere positive electrode plate with a thin and uniform stable artificial solid electrolyte membrane layer (CEI);

[0073] The negative electrode plate is prepared:

[0074] The biomass-based hard carbon material is mixed with a conductive agent and a binder to form a slurry, which is coated on the surface of a copper foil current collector, dried and compacted, and then cut into a negative electrode plate with a diameter of 13 mm;

[0075] Step two, using the positive electrode plate and negative electrode plate obtained in step one, glass fiber separator, positive and negative electrode shell, spring sheet, gasket, and carbonate electrolyte in step one to assemble a sodium ion-based dual-ion full battery, and stand for 24 hours;

[0076] Step three, the dual-ion full battery obtained in step two is subjected to electrochemical performance test, and the electrochemical performance test includes rate performance, cycle performance and AC impedance.

[0077] Example 3

[0078] A method for improving the performance of micro-swelling mesophase carbon microspheres in a dual-ion battery, the specific steps are as follows:

[0079] Step one, preparation of positive electrode plate and negative electrode plate

[0080] The positive electrode plate is prepared:

[0081] The carbonate electrolyte is selected from organic solvents such as ethylene carbonate and methyl ethyl carbonate, and the sodium salt contained therein is selected from 2 mol / L sodium hexafluorophosphate;

[0082] In a vacuum glove box, 0.1 mol / L NaDFOB additive is added to the above-mentioned carbonate electrolyte, and mixed and stirred for 24 hours by a magnetic stirrer to obtain a clear and transparent electrolyte;

[0083] The micro-swelling mesophase carbon microspheres are mixed with a conductive agent and a binder to form a slurry, which is coated on the surface of an aluminum foil current collector, dried and compacted, and then cut into an electrode plate with a diameter of 13 mm;

[0084] In a vacuum glove box, the above-mentioned electrode plate is assembled with metallic sodium and a glass fiber separator to form a dual-ion half battery using the above-mentioned clear and transparent electrolyte, and the assembly is left to stand for 24 hours;

[0085] The above obtained dual-ion half battery is subjected to an electrochemical activation process using an electrochemical instrument, and the dual-ion half battery is charged at a constant current, with a maximum cutoff voltage of 5V and a current density of 50mA / g, and is subjected to charge-discharge cycles 6 times in a voltage window of 1.5-5V;

[0086] The dual-ion half battery after electrochemical activation is disassembled in a vacuum glove box, and the micro-swelling mesophase carbon microsphere electrode sheet is taken out and cleaned and dried using a corresponding organic solvent to obtain a micro-swelling mesophase carbon microsphere positive electrode sheet with a thin and uniform and stable artificial solid electrolyte membrane layer (CEI);

[0087] The negative electrode sheet is prepared as follows:

[0088] The biomass-based hard carbon material is mixed with a conductive agent and a binder to form a slurry, which is coated on the surface of a copper foil current collector, dried and compacted, and then cut into a negative electrode sheet with a diameter of 13mm;

[0089] Step two, the positive electrode sheet and the negative electrode sheet obtained in step one are assembled into a sodium-ion-based dual-ion full battery together with a glass fiber separator, a positive and negative electrode shell, a spring sheet, a gasket, and the carbonate electrolyte in step one, and are left to stand for 24 hours;

[0090] Step three, the dual-ion full battery obtained in step two is subjected to electrochemical performance testing, including rate performance, cycle performance and AC impedance.

[0091] Comparative example 1

[0092] A method for improving the performance of micro-swelling mesophase carbon microspheres in a dual-ion battery, the specific steps are as follows:

[0093] Step one, preparation of positive electrode sheet and negative electrode sheet

[0094] The positive electrode sheet is prepared as follows:

[0095] An organic solvent is selected as a carbonate electrolyte, which is ethylene carbonate and methyl ethyl carbonate, and the sodium salt contained therein is selected as 2mol / L sodium hexafluorophosphate;

[0096] The micro-swelling mesophase carbon microspheres are mixed with a conductive agent and a binder to form a slurry, which is coated on the surface of an aluminum foil current collector, dried and compacted, and then cut into an electrode sheet with a diameter of 13mm;

[0097] In a vacuum glove box, the above obtained electrode sheet is assembled into a dual-ion half battery together with metallic sodium and a glass fiber separator using the above carbonate electrolyte, and is left to stand for 24 hours;

[0098] The above obtained dual-ion half battery is subjected to an electrochemical activation process using an electrochemical instrument, and the dual-ion half battery is charged at a constant current, with a highest cut-off voltage of 5 V and a current density of 50 mA / g, and is subjected to charge-discharge cycles 6 times in a voltage window of 1.5-5 V;

[0099] The dual-ion half battery after electrochemical activation is disassembled in a vacuum glove box, and the micro-swelling mesophase carbon microsphere electrode sheet is taken out and cleaned and dried using a corresponding organic solvent to obtain a micro-swelling mesophase carbon microsphere positive electrode sheet with a thick and non-uniform stable artificial solid electrolyte interphase (CEI) film layer;

[0100] The negative electrode sheet is prepared as follows:

[0101] The biomass-based hard carbon material is mixed with a conductive agent and a binder to form a slurry, which is coated on the surface of a copper foil current collector, dried and compacted, and then cut into a negative electrode sheet with a diameter of 13 mm;

[0102] Step two, the positive electrode sheet and the negative electrode sheet obtained in step one are assembled into a sodium-ion-based dual-ion full battery together with a glass fiber separator, a positive and negative electrode shell, a spring sheet, a gasket, and the carbonate electrolyte in step one, and are left to stand for 24 hours;

[0103] Step three, the dual-ion full battery obtained in step two is subjected to electrochemical performance testing, including rate performance, cycle performance and AC impedance.

[0104] The coulombic efficiency data of the electrochemical activation process of each of the above examples and comparative examples at different numbers of cycles is shown in Table 1 below:

[0105] Table 1 Comparison of coulombic efficiency at different numbers of cycles in the electrochemical activation process

[0106]

[0107] As can be seen from Table 1, compared with Comparative Example 1, the coulombic efficiency of each cycle is greatly improved after adding the additive sodium difluorooxalate borate (NaDFOB) in Examples 1-4. Figure 2 Corresponding obvious changes can also be observed in the CV curves.

[0108] After electrochemical activation, the interface of the electrode sheet is observed under a microscope, as shown in Figure 3 and Figure 4 It can be seen that the peeling of the graphite layer is significantly inhibited in Example 1 compared with Comparative Example 1. Figure 5 and Figure 6 It can be seen that the organic matter on the surface of the micro-swelling mesophase carbon microspheres in the electrode sheet of Example 1 is uniformly attached. Figure 7 andFigure 8 It can be seen that the pre-CEI film layer of Example 1 is thin and uniform.

[0109] In the electrochemical performance, Example 1 has obvious rate and cycle performance improvement compared with Comparative Example 1. Figure 9 In the electrochemical performance, Example 1 has obvious rate and cycle performance improvement compared with Comparative Example 1. Figure 10 It can be seen that, at a current density of 2 A / g, Example 1 can maintain a specific capacity of 94.5 mAh / g, while Comparative Example 1 only has 52.2 mAh / g, and the specific capacity of Example 1 is improved. Figure 11 At a small current density of 100 mA / g, Example 1 can cycle 1000 times and the capacity is maintained stable, while the battery capacity of Comparative Example 1 has been severely attenuated at 650 cycles. Figure 12 At a large current density of 500 mA / g, the capacity of Example 1 is maintained at 70% after 2000 cycles, while Comparative Example 1 has been attenuated to 30% after 2000 cycles. Figure 13 In addition, the impedance of Example 1 is also obviously reduced compared with Comparative Example 1.

[0110] After electrochemical activation, Example 1 of the present application forms a stable artificial solid electrolyte interface film, which is matched with biomass-based hard carbon material to form a sodium-ion-based dual-ion full battery, and the rate performance, charge-discharge curve and cycle performance thereof are respectively as shown in Figure 14 , Figure 15 , Figure 16 , Figure 14 which indicates that the rate performance thereof is excellent, and at a current density of 20C, the specific capacity can still reach 60 mAh / g. Figure 15 which indicates that at a current density of 0.5C, the maximum specific capacity can reach 140.6 mAh / g. Figure 16 which indicates that after 300 cycles, the reversible specific capacity can still be maintained at 114.6 mAh / g.

[0111] The present application utilizes an electrochemical activation process, and 0.01-0.2 mol / L of sodium difluoro(oxalato)borate (NaDFOB) is added to the electrolyte, so that it is decomposed in advance on the surface of the slightly expanded mesophase carbon microspheres to form a stable artificial solid electrolyte interface film, i.e., a pre-CEI film layer; the CEI film layer can play a barrier role to inhibit the serious oxidation side decomposition reaction between a large number of oxygen-containing functional groups in the graphite layer of the slightly expanded mesophase carbon microspheres and the electrolyte at high voltage; in addition, the electrode sheet with the pre-CEI film layer after electrochemical activation can greatly weaken the anion solvation intercalation, and improve the coulombic efficiency and cycle stability of the dual-ion battery.

[0112] The sodium-ion-based dual-ion battery of the application has a thin and uniform stable artificial solid-phase electrolyte interface-pre-CEI film layer micro-swelling intermediate phase carbon microsphere positive electrode sheet in the process of electrochemical activation by selecting a specific carbonate electrolyte and optimization, and effectively improves the rate performance, cycle stability and coulomb efficiency of the battery by selecting biomass-based hard carbon, phenolic resin-based hard carbon, pitch-based hard carbon and other hard carbon-based materials as the negative electrode material. Therefore, the sodium-ion-based dual-ion battery of the application has the advantages of high specific energy and high stability, and provides a new possibility for the development of new energy storage technology.

[0113] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A method for improving the performance of a slightly exfoliated mesophase carbon microbead in a dual-ion battery, characterized by, The specific steps are as follows: Step one, preparation of positive and negative electrode sheets Preparation of positive electrode sheet: A carbonate electrolyte is selected, and the concentration of sodium salt contained in the carbonate electrolyte is 0.5-3 mol / L; Under vacuum conditions, the NaDFOB additive with a concentration of 0.01-0.2 mol / L is added to the above-mentioned carbonate electrolyte and mixed and stirred for a period of time to obtain a clear and transparent electrolyte; The micro-expanded mesophase carbon microspheres are mixed with conductive agents and binders to form a slurry, which is coated on the surface of an aluminum foil current collector, dried and compacted to obtain an electrode sheet; Under vacuum conditions, the above-mentioned electrode sheet is assembled with metallic sodium and a glass fiber separator into a dual-ion half battery using the clear and transparent electrolyte obtained above, and is left to stand for a period of time; The dual-ion half battery obtained above is subjected to an electrochemical activation process, and the dual-ion half battery is charged at a constant current, with the highest cutoff voltage set to 5V and the current density set to 50-200 mA / g, and is subjected to charge-discharge cycling 1-6 times in a voltage window of 1.5-5V; The dual-ion half battery after electrochemical activation is disassembled under vacuum conditions, and the micro-expanded mesophase carbon microsphere electrode sheet is taken out, washed and dried using a corresponding organic solvent to obtain a micro-expanded mesophase carbon microsphere positive electrode sheet with a thin and uniform and stable artificial solid-state electrolyte film layer CEI; Preparation of negative electrode sheet: The amorphous carbon material is mixed with conductive agents and binders to form a slurry, which is coated on the surface of a copper foil current collector, dried and compacted to obtain a negative electrode sheet; Step two, the positive and negative electrode sheets obtained in step one are assembled into a sodium-ion-based dual-ion full battery together with a glass fiber separator, positive and negative electrode shells, a spring sheet, a gasket, and the carbonate electrolyte in step one, and are left to stand for a period of time; Step three, the dual-ion full battery obtained in step two is subjected to electrochemical performance testing.

2. The method for improving the performance of the slightly expanded mesophase carbon microbeads in the dual-ion battery according to claim 1, characterized in that: In step one, the sodium salt is selected from any one of sodium hexafluorophosphate and sodium perchlorate, and the organic solvent inside the carbonate electrolyte is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

3. The method for improving the performance of the slightly expanded mesophase carbon microbeads in the dual-ion battery according to claim 1, characterized in that: In step one, the magnetic stirrer is selected for mixing and stirring, and the stirring time is 18-32 h.

4. The method for improving the performance of the slightly expanded mesophase carbon microbeads in the dual-ion battery according to claim 1, characterized in that: In step one, the assembled dual-ion half battery is left to stand for 18-32 h.

5. The method for improving the performance of the slightly expanded mesophase carbon microbeads in the dual-ion battery according to claim 1, characterized in that: In step one, the amorphous carbon material includes hard carbon, soft carbon or a mixture of the two in any proportion; the hard carbon-based material includes at least one of biomass-based hard carbon, phenolic resin-based hard carbon and pitch-based hard carbon, and the soft carbon-based material includes at least one of petroleum coke, needle coke, carbon fiber, coke, and carbon microspheres.

6. The method for improving the performance of the slightly expanded mesophase carbon microbeads in the dual-ion battery according to claim 1, characterized in that: In step one, the conductive agent includes at least one of conductive carbon black, conductive graphite and carbon nanotubes.

7. The method for improving the performance of the slightly expanded mesophase carbon microbeads in the dual-ion battery according to claim 1, characterized in that: In step one, the binder includes at least one of polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose and polyvinylidene fluoride.

8. The method for improving the performance of the slightly expanded mesophase carbon microbeads in the dual-ion battery according to claim 1, characterized in that: In step two, the assembled sodium-ion-based dual-ion full battery is left to stand for 18-32 h.

9. The method for improving the performance of the slightly expanded mesophase carbon microbeads in the dual-ion battery according to claim 1, characterized in that: In step three, the electrochemical performance testing includes rate performance, cycle performance and AC impedance.

10. A sodium-ion based bi-ion full cell, characterized by: The method is prepared by any one of claims 1-9.

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