Negative-electrode-free secondary sodium battery and manufacturing method thereof

Abstract

The invention discloses a negative-electrode-free secondary sodium battery and a manufacturing method thereof, the negative-electrode-free secondary sodium battery comprises a negative current collector, an electrolyte, a diaphragm and a positive electrode, and the diaphragm is located between the negative current collector and the positive electrode; the electrolyte is positioned between the negative current collector and the positive electrode; the positive electrode comprises a positive electrode current collector and positive electrode active materials coated on two sides of the positive electrode current collector; the surface of the negative electrode current collector comprises a micro-structure, the micro-structure is a pit or a bulge, the micro-structure is micron-sized or nano-sized, and the surface of the negative electrode current collector is subjected to micro-etching treatment, so that sodium is conveniently deposited at the micro-structure on the surface of the negative electrode current collector and then is increased around the micro-structure, and the sodium is deposited more compactly; and more compact sodium deposition can improve the energy density, the cycling stability, the safety and other performances of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium batteries, and more specifically, to a negative electrode-free secondary sodium battery and a manufacturing method thereof. Background Art

[0002] Sodium-ion batteries are electrochemical devices that use sodium ions (Na+) to move between the positive and negative electrodes to store and release energy. Their basic working principle is similar to that of traditional lithium-ion batteries, but sodium ions have a larger ionic radius and a lower redox potential, which causes sodium-ion batteries to differ from lithium-ion batteries in material selection and electrochemical performance. During the charging process, sodium ions are released from the positive electrode material, migrate to the negative electrode through the electrolyte, and are embedded in the negative electrode material. At the same time, in order to maintain charge balance, electrons flow from the positive electrode to the negative electrode through an external circuit. The discharge process is the opposite. Sodium ions are released from the negative electrode and return to the positive electrode through the electrolyte, and electrons flow from the negative electrode to the positive electrode through an external circuit to provide power to external devices.

[0003] Compared with ordinary sodium batteries, negative electrode-free sodium ion secondary batteries have the following advantages:

[0004] 1. No chemically active metallic sodium negative electrode is used, which reduces the production environment requirements and the risk of production safety accidents;

[0005] 2. It has no voltage before the first charge, can be stored for a long time without self-discharge, and has a high safety index;

[0006] 3. No negative electrode active materials are used, and the volume energy density and mass energy density are extremely high.

[0007] The negative electrode-free design is expected to improve the energy density of the battery, making it suitable for applications with long battery life and lightweight. Summary of the invention

[0008] In view of this, the present invention provides a negative electrode-free secondary sodium battery and a manufacturing method thereof, so as to improve the energy density, cycle stability and safety of the battery.

[0009] In one aspect, the present invention provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein:

[0010] The separator is located between the negative electrode current collector and the positive electrode;

[0011] The electrolyte is located between the negative electrode current collector and the positive electrode;

[0012] The positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0013] The surface of the negative electrode current collector includes a microstructure, and the microstructure is a pit or a protrusion, and the microstructure is micrometer-scale or nanometer-scale.

[0014] The present invention performs micro-etching on the surface of the negative electrode current collector to facilitate sodium deposition at the microstructure on the surface of the negative electrode current collector, and then grows around the microstructure to make the sodium deposition denser. Denseer sodium deposition can improve the energy density, cycle stability, safety and other performance of the battery.

[0015] Optionally, the surface of the negative electrode current collector is plated with a protective layer, and the protective layer includes at least one of nickel, tin, antimony, bismuth, zinc, barium, cadmium, chromium, and strontium.

[0016] By plating tin on the surface of copper foil, the nucleation barrier of sodium is reduced. The nucleation barrier is a certain amount of energy required for atomic crystallization. The energy required for crystallization can be reduced when there are attachment sites. A protective layer is plated on the surface of the negative electrode current collector. The formed protective layer is relatively rough, which makes it easier to induce sodium to find deposition sites on the protective layer. The number of sodium attachment sites increases, which is conducive to atomic crystallization nucleation. Of course, during the deposition process, sodium will form alloys with elements such as nickel, tin, antimony, bismuth, zinc, barium, cadmium, chromium, and strontium. The formation of the alloy further reduces the nucleation barrier of sodium, making the deposition of sodium more uniform and stable.

[0017] Optionally, the negative electrode current collector includes one of copper foil, carbon-coated aluminum foil, or carbon-coated copper foil.

[0018] The present invention directly uses the negative electrode current collector as the negative electrode sheet, and deposits and strips the sodium metal in situ on the negative electrode current collector through positive electrode discharge, thereby forming a negative electrode-free secondary sodium battery, removing the negative electrode material in the traditional battery, thereby saving the cost of the negative electrode material. The negative electrode current collector, as the negative electrode sheet, dissolves in the electrolyte and forms sodium ions, achieving efficient material utilization and avoiding the loss and waste of traditional negative electrode materials during the charging and discharging process. Of course, due to the negative electrode-free design, the battery can accommodate more sodium ions, thereby improving the energy density of the battery.

[0019] Copper foil has excellent electrical conductivity, which can ensure efficient transmission of current in the negative electrode current collector, thereby improving the power output of the battery. In addition, due to its good ductility and flexibility, copper foil can adapt to the volume changes that may occur during the battery's charge and discharge process, preventing the current collector from breaking or deforming. Of course, copper foil has low reactivity with sodium ions, and can remain stable inside the battery to avoid adverse reactions with the electrolyte.

[0020] Carbon-coated aluminum foil can further improve the conductivity of the current collector and reduce the internal resistance of the battery by coating a layer of carbon material on the surface of the aluminum foil. The carbon coating can enhance the adhesion between the negative electrode active material and the current collector, prevent the active material from falling off during the charge and discharge process, thereby improving the cycle stability and service life of the battery, and can also protect the aluminum foil from being corroded or oxidized by the electrolyte, thereby extending the service life of the current collector.

[0021] The carbon-coated copper foil improves the adsorption capacity of the negative electrode current collector surface, making it easier for the metallic sodium released from the positive electrode to be evenly deposited on the negative electrode current collector surface.

[0022] Optionally, the positive electrode current collector includes one of aluminum foil, Goudain aluminum foil, or carbon-coated aluminum foil.

[0023] As a product of metal aluminum, aluminum foil has good electrical conductivity, which can effectively reduce the internal resistance of the battery and increase the power output of the battery. The thin thickness of aluminum foil can reduce the weight of the battery and increase the energy density of the battery. At the same time, aluminum foil has good plasticity, which is convenient for the assembly and production of batteries.

[0024] The Goudain aluminum foil may be specially treated to enhance its surface tension, making it easier for the electrolyte to form a uniform film on its surface, thereby improving the performance of the battery. Due to the enhanced surface tension, the Goudain aluminum foil may be more easily coated with active substances or other coating materials, thereby improving the manufacturing efficiency and performance of the battery;

[0025] Carbon-coated aluminum foil adds a layer of carbon coating on the surface of aluminum foil. This layer of carbon material (such as carbon black, graphite sheets, graphene, etc.) can serve as a bridge for electron transmission, improve the conductivity of the positive electrode sheet, and reduce the internal resistance of the battery. In addition, the carbon coating layer makes the surface of the aluminum foil evenly concave and convex, increasing the contact area between the active material in the electrolyte and the positive electrode current collector, so that electrons can be transferred and current can be collected faster during rapid charging and discharging of large currents. In addition, carbon-coated aluminum foil can also reduce the interface impedance and polarization of the current collector, improve the cycle life and rate performance of the battery, and the carbon coating layer can prevent the current collector from being corroded and oxidized, further extending the service life of the battery.

[0026] Optionally, the positive electrode active material includes 92-96% of a positive electrode main material, 1-6% of a conductive agent, 1-5% of a binder and 0.1-1% of a dispersant, wherein the positive electrode main material includes one of sodium ferric pyrophosphate and sodium nickel iron manganese oxide.

[0027] Sodium iron pyrophosphate is preferred for the positive electrode because the polyanion system has a more stable discharge voltage during the cycle, a lower exothermic reaction, good electrochemical reversibility, a smaller volume change during charge and discharge, stronger structural stability and excellent thermal stability, which helps to improve the safety performance of the battery. It makes them safer under high temperature or extreme conditions. Sodium iron pyrophosphate has a higher conductivity, which helps to improve the discharge performance of the battery, allowing the battery to release stored energy faster.

[0028] Sodium nickel iron manganese oxide has a high specific capacity, which means it can store more energy per unit mass or unit volume, thereby increasing the energy density of the battery.

[0029] The addition of conductive agent can improve the conductivity of positive electrode active materials, making the transmission of electrons in the positive electrode materials smoother, which helps to improve the power output and charge and discharge efficiency of the battery.

[0030] The function of the binder is to bond the positive electrode main material, conductive agent and other particles together to form a stable positive electrode structure, which helps prevent the positive electrode material from falling off and pulverizing during the charging and discharging process, and improves the stability and cycle life of the battery.

[0031] The addition of dispersants can improve the dispersibility of positive electrode materials, making the positive electrode active materials more evenly distributed in the electrolyte, which helps to improve the charge and discharge efficiency and energy density of the battery.

[0032] The positive electrode active material formula of the present invention combines the advantages of multiple materials, so that the battery has significant advantages in performance, safety, cost and application prospects.

[0033] Optionally, the diaphragm includes at least one of a polypropylene PP film, a polyethylene PE film, a non-woven fabric diaphragm, a glass fiber diaphragm, a ceramic diaphragm, a filter membrane, and a solid electrolyte diaphragm.

[0034] The separator in the present invention can effectively isolate the electrolyte between the positive and negative electrodes to prevent the battery from short circuiting, while allowing sodium ions to shuttle freely during the charging and discharging process.

[0035] Polypropylene PP film and polyethylene PE film have good chemical stability and can resist corrosion from most acids, alkalis, organic solutions and hot water, ensuring stable operation of the battery in a variety of environments. Non-woven fabric diaphragms have a high porosity, which is conducive to the rapid transmission of sodium ions and improves the charging and discharging efficiency of the battery. Glass fiber diaphragms can maintain stable performance in high temperature environments and are not easy to soften and deform, ensuring the safe operation of the battery under high temperature conditions. Glass fiber diaphragms have a high ionic conductivity and can quickly transfer ions, improving the charging and discharging efficiency of the battery.

[0036] Optionally, the electrolyte includes a solvent and a sodium salt, wherein:

[0037] The solvent is an ether solvent, including at least one of tetrahydrofuran, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and triethylene glycol dimethyl ether;

[0038] The sodium salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethylsulfonyl)imide, sodium iodide, sodium bromide, sodium thiocyanate, sodium chlorate, sodium carbonate, sodium oxalate, sodium ketomalonate, sodium diketosuccinate and sodium triketoglutarate, 2-cyclopropene-1-one-2,3-dihydroxy sodium, 3-cyclobutene-1,2-dione-3,4-dihydroxy sodium, 4-cyclopentene-1,2,3-trione-4,5-dihydroxy sodium, and 5-cyclohexene-1,2,3,4-tetraone-5,6-dihydroxy sodium.

[0039] Compared with traditional ester electrolytes, the present invention uses ether solvents to form a thinner and more stable solid electrolyte interface on the electrode surface, which helps to reduce the irreversible capacity of the first cycle and the decomposition of the electrolyte in subsequent cycles.

[0040] Preferably, the sodium salt concentration is 0.5 mol / L to 2.0 mol / L, for example, the sodium salt concentration is 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or any value between 0.5 mol / L and 2.0 mol / L. In electrolytes of the same concentration, sodium salt electrolytes have higher ion conductivity than lithium salt electrolytes. In the sodium salt concentration range of 0.5 mol / L to 2.0 mol / L, the electrolyte can conduct sodium ions more effectively, thereby improving the rate performance and power output capacity of the battery.

[0041] Preferably, 90% sodium hexafluorophosphate and 10% sodium tetrafluoroborate are selected, wherein the 10% borate helps to form a negative electrode film and improve the stability of the battery cell.

[0042] Optionally, the electrolyte also includes functional additives, and the functional additives include at least one of fluoroethylene carbonate, ethylene carbonate, propylene carbonate, ethyl acetate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl acetate, propyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, acetophenone, maleic anhydride, citraconic anhydride, succinic anhydride, pyromellitic anhydride, styrene anhydride, glutaric anhydride, succinic anhydride, azelaic anhydride, N,N-dimethyltrifluoroacetamide, N,N-dimethylacrylamide, sulfate, sulfite, potassium nitrate, triethyl acetate, sodium difluorooxalatoborate, phosphorus oxide, and phosphorus sulfide.

[0043] The present invention adds functional additives to the electrolyte, which can improve the electrochemical stability of the electrolyte, improve the interface characteristics between the electrolyte and the electrode, and reduce the interface resistance.

[0044] On the other hand, the present invention also provides a method for manufacturing a negative electrode-free secondary sodium battery, which is used to manufacture the negative electrode-free secondary sodium battery, comprising the steps of:

[0045] The steps of assembling a sodium battery cell include:

[0046] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0047] Placing the separator between the negative electrode current collector and the positive electrode, placing the structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell shell, injecting the electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0048] The steps of forming the microstructure include:

[0049] Providing an external circuit, reversely connecting the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connecting the positive electrode of the external circuit to the negative electrode of the sodium battery cell, electrically connecting the negative electrode of the external circuit to the positive electrode of the sodium battery cell, charging the sodium battery cell so that a microstructure is formed on the surface of the negative electrode current collector, and performing secondary packaging of the sodium battery cell by evacuating air;

[0050] The steps of fractionation include:

[0051] The external circuit is positively connected to the positive and negative electrodes of the sodium battery cell, the positive electrode of the external circuit is electrically connected to the positive electrode of the sodium battery cell, and the negative electrode of the external circuit is electrically connected to the negative electrode of the sodium battery cell to perform capacity conversion.

[0052] Optionally, in the step of forming the microstructure, charging the sodium battery cell comprises charging at 0.01C for 10 min to 60 min, or charging from 0 V to 1.0 V to 2.0 V;

[0053] And / or, the composition includes charging to 3.4V with 0.1C constant current and constant voltage, charging for 10 hours, standing for 20 minutes, discharging to 1.5V with 0.2C constant current, standing for 20 minutes, then charging to 3.4V with 0.2C constant current and constant voltage, standing for 20 minutes, discharging to 1.5V with 0.2C constant current, standing for 20 minutes, and then charging to 2.5V with 0.2C constant current and constant voltage.

[0054] It should be noted that "C" represents the capacity of the battery (usually in Ah, i.e. ampere-hour). 0.1C charging means that the charging current is 0.1 times the battery capacity.

[0055] The upper limit of the formation voltage is reduced to 3.4V, which avoids the decomposition of ether electrolytes. Since the negative electrode is a foil, it does not need to be aged to form a stable SEI film interface, which shortens the process time of the battery cell and improves output efficiency.

[0056] Compared with the prior art, the negative electrode-free secondary sodium battery and the manufacturing method thereof provided by the present invention achieve at least the following beneficial effects:

[0057] The negative electrode-free secondary sodium battery of the present invention comprises a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the separator is located between the negative electrode current collector and the positive electrode; the electrolyte is located between the negative electrode current collector and the positive electrode; the positive electrode comprises the positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector; the surface of the negative electrode current collector comprises a microstructure, the microstructure is pits or protrusions, and the microstructure is micrometer-level or nanometer-level. By micro-etching the surface of the negative electrode current collector, sodium is easily deposited at the microstructure on the surface of the negative electrode current collector, and then grows around the microstructure, so that the sodium deposition is denser, and denser sodium deposition can improve the energy density, cycle stability, safety and other performances of the battery.

[0058] Of course, any product implementing the present invention does not necessarily need to achieve all of the technical effects described above at the same time.

[0059] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0061] Figure 1 It is a structural schematic diagram of a negative electrode-free secondary sodium battery provided by the present invention;

[0062] Figure 2 This is a schematic structural diagram of another negative electrode-free secondary sodium battery provided by the present invention;

[0063] Figure 3 This is a schematic structural diagram of another negative electrode-free secondary sodium battery provided by the present invention;

[0064] Figure 4 This is a flow chart of a method for manufacturing a negative electrode-free secondary sodium battery provided by the present invention;

[0065] Figure 5This is a cycle diagram of 1000 cycles of 0.5C charge and discharge of a negative electrode-free secondary sodium battery;

[0066] Among them, 1-negative electrode current collector, 10-microstructure, 2-electrolyte, 3-separator, 4-positive electrode, 41-positive electrode current collector, 42-positive electrode active material, 5-protective layer. DETAILED DESCRIPTION

[0067] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0068] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0069] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0070] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0071] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0072] Reference Figure 1 and Figure 2 The negative electrode-free secondary sodium battery comprises a negative electrode current collector 1, an electrolyte 2, a separator 3 and a positive electrode 4, wherein:

[0073] The separator 3 is located between the negative electrode current collector 1 and the positive electrode 4;

[0074] The electrolyte 2 is located between the negative electrode current collector 1 and the positive electrode 4;

[0075] The positive electrode 4 includes a positive electrode current collector 41 and a positive electrode active material coated on both sides of the positive electrode current collector 41;

[0076] The surface of the negative electrode current collector 1 includes a microstructure 10 . The microstructure 10 is a pit or a protrusion. The microstructure 10 is at a micrometer level or a nanometer level.

[0077] Figure 1 In the figure, the microstructure 10 is a protrusion as an example for schematic illustration. Figure 2In the figure, the microstructure 10 is a pit as an example for schematic illustration. Optionally, the difficulty of manufacturing a nanometer-scale microstructure 10 is greater than that of manufacturing a micrometer-scale microstructure 10.

[0078] The present invention performs micro-etching on the surface of the negative electrode current collector 1 to facilitate sodium deposition at the microstructure 10 on the surface of the negative electrode current collector 1, and then grows around the microstructure 10, so that the sodium deposition is denser. The denser sodium deposition can improve the energy density, cycle stability, safety and other performance of the battery.

[0079] Reference Figure 3 The negative electrode-free secondary sodium battery comprises a negative electrode current collector 1, an electrolyte 2, a separator 3 and a positive electrode 4, wherein:

[0080] The separator 3 is located between the negative electrode current collector 1 and the positive electrode 4;

[0081] The electrolyte 2 is located between the negative electrode current collector 1 and the positive electrode 4;

[0082] The positive electrode 4 includes a positive electrode current collector 41 and a positive electrode active material coated on both sides of the positive electrode current collector 41;

[0083] The surface of the negative electrode current collector 1 includes a microstructure 10, which is a pit or a protrusion, and is at the micron level or nanometer level. The surface of the negative electrode current collector 1 is plated with a protective layer 5, and the protective layer 5 includes at least one of nickel, tin, antimony, bismuth, zinc, barium, cadmium, chromium, and strontium.

[0084] Figure 3 The negative electrode-free secondary sodium battery reduces the sodium nucleation barrier by plating a protective layer 5 on the surface of the negative electrode current collector 1.

[0085] Reference Figure 4 , Figure 4 The method for making a negative electrode-free secondary sodium battery comprises the following steps:

[0086] S101, the step of assembling a sodium battery cell comprises:

[0087] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0088] Placing the separator between the negative electrode current collector and the positive electrode, placing the structure formed by the negative electrode current collector, the separator and the positive electrode in the battery cell shell, injecting the electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0089] S102, the step of forming a microstructure includes:

[0090] Providing an external circuit, reversely connecting the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connecting the positive electrode of the external circuit to the negative electrode of the sodium battery cell, electrically connecting the negative electrode of the external circuit to the positive electrode of the sodium battery cell, charging the sodium battery cell so that a microstructure is formed on the surface of the negative electrode current collector, and performing secondary packaging of the sodium battery cell by evacuating air;

[0091] S103, the step of converting into a component comprises:

[0092] The positive connection connects the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connects the positive electrode of the external circuit to the positive electrode of the sodium battery cell, and electrically connects the negative electrode of the external circuit to the negative electrode of the sodium battery cell to perform capacity conversion.

[0093] The following are specific embodiments:

[0094] Embodiment 1:

[0095] The present embodiment provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator, a positive electrode material and a positive electrode current collector, wherein the positive electrode active material is coated on both sides of the positive electrode current collector, the positive electrode current collector and the negative electrode current collector are separated by the separator, and the surface of the negative electrode current collector comprises a microstructure, the microstructure is a protrusion, and the microstructure is at the micron level.

[0096] The positive electrode current collector is made of carbon-coated aluminum foil; the positive electrode active material includes 92% of the positive electrode main material, 6% of the conductive agent, 1% of the binder and 1% of the dispersant.

[0097] The main material of the positive electrode is sodium iron pyrophosphate. The diaphragm is polyethylene ceramic diaphragm.

[0098] The electrolyte includes an ether solvent, a sodium salt and a functional additive, wherein the ether solvent is selected from diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the sodium salt concentration is 0.5 mol / L, and its composition is 90% of sodium hexafluorophosphate and 10% of sodium tetrafluoroborate; the functional additive concentration is 0.01 mol / L, and the functional additive is selected from N,N-dimethyltrifluoroacetamide.

[0099] Carbon-coated copper foil is used as the negative electrode current collector.

[0100] The method for making a negative electrode-free secondary sodium battery comprises:

[0101] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0102] Placing a separator between the negative electrode current collector and the positive electrode, placing a structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell housing, and injecting an electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0103] The steps of forming the microstructure include:

[0104] Providing an external circuit, reversely connecting the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connecting the positive electrode of the external circuit to the negative electrode of the sodium battery cell, electrically connecting the negative electrode of the external circuit to the positive electrode of the sodium battery cell, charging the sodium battery cell, charging at 0.01C for 10 minutes, so that a microstructure is formed on the surface of the negative electrode current collector, and performing secondary packaging of the sodium battery cell by evacuating air;

[0105] Chemical composition and capacity process: connect the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connect the positive electrode of the external circuit to the positive electrode of the sodium battery cell, and electrically connect the negative electrode of the external circuit to the negative electrode of the sodium battery cell. Charge to 3.4V with 0.1C constant current and constant voltage for 10 hours. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, then charge to 3.4V with 0.2C constant current and constant voltage. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 2.5V with 0.2C constant current and constant voltage.

[0106] Example 2

[0107] The present embodiment provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator, a positive electrode material and a positive electrode current collector, wherein the positive electrode active material is coated on both sides of the positive electrode current collector, the positive electrode current collector and the negative electrode current collector are separated by the separator, and the surface of the negative electrode current collector comprises a microstructure, the microstructure is a pit, and the microstructure is nanoscale.

[0108] The positive electrode current collector is made of carbon-coated aluminum foil; the positive electrode active material includes 96% of the positive electrode main material, 1% of the conductive agent, 2.9% of the binder and 0.1% of the dispersant. The positive electrode main material is sodium iron pyrophosphate. The diaphragm is a polyethylene ceramic diaphragm.

[0109] The electrolyte includes an ether solvent, a sodium salt and a functional additive. The ether solvent is selected from diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the sodium salt concentration is 2 mol / L, and its composition is 90% sodium hexafluorophosphate and 10% sodium tetrafluoroborate; the functional additive concentration is 0.05 mol / L. The functional additive is selected from N,N-dimethyltrifluoroacetamide.

[0110] Carbon-coated copper foil is used as the negative electrode current collector.

[0111] The method for making a negative electrode-free secondary sodium battery comprises:

[0112] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0113] Placing a separator between the negative electrode current collector and the positive electrode, placing a structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell housing, and injecting an electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0114] The steps of forming the microstructure include:

[0115] Providing an external circuit, reversely connecting the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connecting the positive electrode of the external circuit to the negative electrode of the sodium battery cell, electrically connecting the negative electrode of the external circuit to the positive electrode of the sodium battery cell, charging the sodium battery cell from 0V to 1.0V, so that a microstructure is formed on the surface of the negative electrode current collector, and performing secondary packaging of the sodium battery cell by evacuating air;

[0116] Chemical composition process: charge to 3.4V with 0.1C constant current and constant voltage for 10 hours. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 3.4V with 0.2C constant current and constant voltage. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 2.5V with 0.2C constant current and constant voltage.

[0117] Embodiment 3:

[0118] The present embodiment provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator, a positive electrode material and a positive electrode current collector, wherein the positive electrode active material is coated on both sides of the positive electrode current collector, the positive electrode current collector and the negative electrode current collector are separated by the separator, and the surface of the negative electrode current collector comprises a microstructure, the microstructure is a protrusion, and the microstructure is at the micron level.

[0119] The positive electrode current collector is made of carbon-coated aluminum foil; the positive electrode active material includes 93% of the positive electrode main material, 1.5% of the conductive agent, 5% of the binder and 0.5% of the dispersant. The positive electrode main material is sodium iron pyrophosphate. The diaphragm is a polyethylene ceramic diaphragm.

[0120] The electrolyte includes an ether solvent, a sodium salt and a functional additive, wherein the ether solvent is selected from diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the sodium salt concentration is 1 mol / L, and its composition is 90% sodium hexafluorophosphate and 10% sodium tetrafluoroborate; the functional additive concentration is 0.1 mol / L. The functional additive is selected from N,N-dimethyltrifluoroacetamide (to improve the electrochemical stability of the electrolyte, improve the interface characteristics between the electrolyte and the electrode, and reduce the interface resistance).

[0121] Carbon-coated copper foil is used as the negative electrode current collector.

[0122] The method for making a negative electrode-free secondary sodium battery comprises:

[0123] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0124] Placing a separator between the negative electrode current collector and the positive electrode, placing a structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell housing, and injecting an electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0125] The steps of forming the microstructure include:

[0126] Providing an external circuit, reversely connecting the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connecting the positive electrode of the external circuit to the negative electrode of the sodium battery cell, electrically connecting the negative electrode of the external circuit to the positive electrode of the sodium battery cell, charging the sodium battery cell, charging at 0.01C for 60 minutes, so that a microstructure is formed on the surface of the negative electrode current collector, and performing secondary packaging on the sodium battery cell by evacuating air;

[0127] Chemical composition process: charge to 3.4V with 0.1C constant current and constant voltage for 10 hours. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 3.4V with 0.2C constant current and constant voltage. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 2.5V with 0.2C constant current and constant voltage.

[0128] Example 4

[0129] The present embodiment provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator, a positive electrode material and a positive electrode current collector, wherein the positive electrode active material is coated on both sides of the positive electrode current collector, the positive electrode current collector and the negative electrode current collector are separated by the separator, the surface of the negative electrode current collector comprises a microstructure, the microstructure is a pit, and the microstructure is nanoscale; the surface of the negative electrode current collector is plated with tin.

[0130] The positive electrode current collector is made of carbon-coated aluminum foil; the positive electrode active material includes 94.7% of the positive electrode main material, 2% of the conductive agent, 3% of the binder and 0.3% of the dispersant. The positive electrode main material is sodium iron pyrophosphate. The diaphragm is a polyethylene ceramic diaphragm.

[0131] The electrolyte includes an ether solvent, a sodium salt and a functional additive, wherein the ether solvent is selected from diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the sodium salt concentration is 1 mol / L, and its composition is 90% of sodium hexafluorophosphate and 10% of sodium tetrafluoroborate; the functional additive concentration is 0.04 mol / L, and the functional additive is selected from N,N-dimethyltrifluoroacetamide (to improve the electrochemical stability of the electrolyte, improve the interface characteristics between the electrolyte and the electrode, and reduce the interface resistance).

[0132] Carbon-coated copper foil is used as the negative electrode current collector.

[0133] The method for making a negative electrode-free secondary sodium battery comprises:

[0134] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector, and tin is plated on the surface of the negative electrode current collector;

[0135] Placing a separator between the negative electrode current collector and the positive electrode, placing a structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell housing, and injecting an electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0136] The steps of forming the microstructure include:

[0137] Providing an external circuit, reversely connecting the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connecting the positive electrode of the external circuit to the negative electrode of the sodium battery cell, electrically connecting the negative electrode of the external circuit to the positive electrode of the sodium battery cell, charging the sodium battery cell from 0V to 2.0V, so that a microstructure is formed on the surface of the negative electrode current collector, and performing secondary packaging of the sodium battery cell by evacuating air;

[0138] Chemical composition process: charge to 3.4V with 0.1C constant current and constant voltage for 10 hours. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 3.4V with 0.2C constant current and constant voltage. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 2.5V with 0.2C constant current and constant voltage.

[0139] Embodiment 5:

[0140] The present embodiment provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator, a positive electrode material and a positive electrode current collector, wherein the positive electrode active material is coated on both sides of the positive electrode current collector, the positive electrode current collector and the negative electrode current collector are separated by the separator, the surface of the negative electrode current collector comprises a microstructure, the microstructure is a protrusion, the microstructure is at the micron level, and the surface of the negative electrode current collector is tin-plated.

[0141] The positive electrode current collector is made of Goudain aluminum foil; the positive electrode active material includes 94.7% of the positive electrode main material, 2% of the conductive agent, 3% of the binder and 0.3% of the dispersant. The positive electrode main material is sodium nickel iron manganese oxide. The diaphragm is a polyethylene ceramic diaphragm.

[0142] The electrolyte includes an ether solvent, a sodium salt and a functional additive. The ether solvent is selected from diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the sodium salt concentration is 1 mol / L, and its composition is 90% sodium hexafluorophosphate and 10% sodium tetrafluoroborate; the functional additive concentration is 0.1 mol / L. The functional additive is selected from N,N-dimethyltrifluoroacetamide (to improve the electrochemical stability of the electrolyte, improve the interface characteristics between the electrolyte and the electrode, and reduce the interface resistance).

[0143] Carbon-coated copper foil is used as the negative electrode current collector.

[0144] The method for making a negative electrode-free secondary sodium battery comprises:

[0145] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector, and tin is plated on the surface of the negative electrode current collector;

[0146] Placing a separator between the negative electrode current collector and the positive electrode, placing a structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell housing, and injecting an electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0147] The steps of forming the microstructure include:

[0148] Providing an external circuit, reversely connecting the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connecting the positive electrode of the external circuit to the negative electrode of the sodium battery cell, electrically connecting the negative electrode of the external circuit to the positive electrode of the sodium battery cell, charging the sodium battery cell, charging at 0.01C for 35 minutes, so that a microstructure is formed on the surface of the negative electrode current collector, and performing secondary packaging of the sodium battery cell by evacuating air;

[0149] Chemical composition process: charge to 3.4V with 0.1C constant current and constant voltage for 10 hours. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 3.4V with 0.2C constant current and constant voltage. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 2.5V with 0.2C constant current and constant voltage.

[0150] Example 6

[0151] The present embodiment provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator, a positive electrode material and a positive electrode current collector, wherein the positive electrode active material is coated on both sides of the positive electrode current collector, the positive electrode current collector and the negative electrode current collector are separated by the separator, and the surface of the negative electrode current collector comprises a microstructure, the microstructure is a pit, and the microstructure is nanoscale.

[0152] The positive electrode current collector is made of carbon-coated aluminum foil; the positive electrode active material includes 94.7% of the positive electrode main material, 2% of the conductive agent, 3% of the binder and 0.3% of the dispersant. The positive electrode main material is sodium iron pyrophosphate. The diaphragm is a polyethylene ceramic diaphragm.

[0153] The electrolyte includes ether solvent, sodium salt and functional additive. The ether solvent is selected from diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the sodium salt concentration is 1 mol / L, and its composition is 90% sodium hexafluorophosphate and 10% sodium tetrafluoroborate; the functional additive concentration is 0.1 mol / L, and the functional additive is N,N-dimethyltrifluoroacetamide (to improve the electrochemical stability of the electrolyte, improve the interface characteristics between the electrolyte and the electrode, and reduce the interface resistance).

[0154] Carbon-coated aluminum foil is used as the negative electrode current collector.

[0155] The method for making a negative electrode-free secondary sodium battery comprises:

[0156] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0157] Placing a separator between the negative electrode current collector and the positive electrode, placing a structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell housing, and injecting an electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0158] The steps of forming the microstructure include:

[0159] Providing an external circuit, reversely connecting the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connecting the positive electrode of the external circuit to the negative electrode of the sodium battery cell, electrically connecting the negative electrode of the external circuit to the positive electrode of the sodium battery cell, charging the sodium battery cell from 0V to 1.5V, so that a microstructure is formed on the surface of the negative electrode current collector, and performing secondary packaging of the sodium battery cell by evacuating air;

[0160] Chemical composition process: charge to 3.4V with 0.1C constant current and constant voltage for 10 hours. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 3.4V with 0.2C constant current and constant voltage. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 2.5V with 0.2C constant current and constant voltage.

[0161] Refer to Table 1 below, which shows the test results of negative electrode-free secondary sodium batteries of Examples 1 to 6.

[0162] Table 1 Test results of negative electrode-free secondary sodium batteries of Examples 1 to 6

[0163]

[0164] In summary, Example 4 has high peel strength and adhesion, low resistivity and membrane resistance, high capacity and initial efficiency, and the best overall performance.

[0165] Comparative Example 1

[0166] Comparative Document 1 provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator, a positive electrode material and a positive electrode current collector, wherein the positive electrode active material is coated on both sides of the positive electrode current collector, and the positive electrode current collector and the negative electrode current collector are separated by a separator.

[0167] The positive electrode current collector is made of Gundam aluminum foil; the positive electrode active material includes 94.7% of the positive electrode main material, 2% of the conductive agent, 3% of the binder and 0.3% of the dispersant. The positive electrode main material is sodium iron pyrophosphate. The diaphragm is a polyethylene ceramic diaphragm.

[0168] The electrolyte solvent is an ester solvent. The ester solvent is dimethyl carbonate. The sodium salt concentration is 1 mol / L, and its composition is 90% sodium hexafluorophosphate and 10% sodium tetrafluoroborate.

[0169] Carbon-coated copper foil is used as the negative electrode current collector.

[0170] The method for making a negative electrode-free secondary sodium battery comprises:

[0171] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0172] Placing a separator between the negative electrode current collector and the positive electrode, placing a structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell housing, and injecting an electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0173] Chemical composition process: charge to 3.4V with 0.1C constant current and constant voltage for 10 hours. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 3.4V with 0.2C constant current and constant voltage. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 2.5V with 0.2C constant current and constant voltage.

[0174] Comparative Example 2

[0175] Comparative Document 2 provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator, a positive electrode material and a positive electrode current collector, wherein the positive electrode active material is coated on both sides of the positive electrode current collector, and the positive electrode current collector and the negative electrode current collector are separated by a separator.

[0176] The positive electrode current collector is made of Gundam aluminum foil; the positive electrode active material includes 94.7% of the positive electrode main material, 2% of the conductive agent, 3% of the binder and 0.3% of the dispersant. The positive electrode main material is sodium iron pyrophosphate; the diaphragm is a polyethylene ceramic diaphragm.

[0177] The electrolyte includes an ether solvent, a sodium salt and a functional additive. The ether solvent is selected from diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether. The sodium salt concentration is 1 mol / L, and its composition is 90% of sodium hexafluorophosphate and 10% of sodium tetrafluoroborate.

[0178] The concentration of the functional additive is 0.1 mol / L. The functional additive is N,N-dimethyltrifluoroacetamide.

[0179] Carbon-coated copper foil is used as the negative electrode current collector.

[0180] The method for making a negative electrode-free secondary sodium battery comprises:

[0181] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0182] Placing a separator between the negative electrode current collector and the positive electrode, placing a structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell housing, and injecting an electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0183] Chemical composition and content process:

[0184] It takes 10 hours to charge to 3.9V with 0.1C constant current and constant voltage. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 3.6V with 0.2C constant current and constant voltage. After standing for 20 minutes, discharge to 1.5V with 0.2C constant current. After standing for 20 minutes, charge to 2.5V with 0.2C constant current and constant voltage.

[0185] Comparative Example 3:

[0186] Comparative Document 3 provides a negative electrode-free secondary sodium battery, comprising a negative electrode current collector, an electrolyte, a separator, a positive electrode material and a positive electrode current collector, wherein the positive electrode active material is coated on both sides of the positive electrode current collector, and the positive electrode current collector and the negative electrode current collector are separated by a separator.

[0187] The positive electrode current collector is made of Gundam aluminum foil; the positive electrode active material includes 94.7% of the positive electrode main material, 2% of the conductive agent, 3% of the binder and 0.3% of the dispersant. The positive electrode main material is sodium iron pyrophosphate. The diaphragm is a polyethylene ceramic diaphragm.

[0188] The electrolyte includes an ether solvent and a sodium salt. The ether solvent is selected from diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether. The sodium salt has a concentration of 1 mol / L and is composed of 90% sodium hexafluorophosphate and 10% sodium tetrafluoroborate.

[0189] Aluminum foil is used as the negative electrode current collector.

[0190] The method for making a negative electrode-free secondary sodium battery comprises:

[0191] Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector;

[0192] Placing a separator between the negative electrode current collector and the positive electrode, placing a structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell housing, and injecting an electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure;

[0193] Chemical composition process: Charge to 3.4V with 0.1C constant current and constant voltage for 10 hours, let it stand for 20 minutes, discharge to 1.5V with 0.2C constant current, let it stand for 20 minutes, then charge to 3.4V with 0.2C constant current and constant voltage, let it stand for 20 minutes, discharge to 1.5V with 0.2C constant current, let it stand for 20 minutes, then charge to 2.5V with 0.2C constant current and constant voltage

[0194] Reference Figure 5 , Figure 5 This is the cycle diagram of the battery cell charging and discharging at 0.5C for 1000 cycles. Figure 5 In order to distinguish the capacity retention rates corresponding to different embodiments, different colors are used to represent each embodiment. Figure 5 The horizontal axis is the cycle number, and the vertical axis is the capacity retention rate. Figure 5 It can be clearly seen that Example 4 has the best cycle performance, and the 1000-cycle capacity retention rates of Examples 5 and 6 are both greater than 90%, basically around 95%, and the long-term performance of the battery is excellent. However, the capacity retention rates of Comparative Examples 1, 2, and 3 all dropped significantly after 1000 cycles.

[0195] Although some specific embodiments of the present invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A negative electrode-free secondary sodium battery, characterized in that: It includes a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein: The separator is located between the negative electrode current collector and the positive electrode; The electrolyte is located between the negative electrode current collector and the positive electrode; The positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector; The surface of the negative electrode current collector includes a microstructure, and the microstructure is a pit or a protrusion, and the microstructure is micrometer-scale or nanometer-scale.

2. The negative electrode-free secondary sodium battery according to claim 1, characterized in that: The surface of the negative electrode current collector is plated with a protective layer, and the protective layer includes at least one of nickel, tin, antimony, bismuth, zinc, barium, cadmium, chromium, and strontium.

3. The negative electrode-free secondary sodium battery according to claim 1, characterized in that: The negative electrode current collector includes one of copper foil, carbon-coated aluminum foil, or carbon-coated copper foil.

4. The negative electrode-free secondary sodium battery according to claim 1, characterized in that: The positive electrode current collector includes one of aluminum foil, Goudain aluminum foil, or carbon-coated aluminum foil.

5. The negative electrode-free secondary sodium battery according to claim 1, characterized in that: The positive electrode active material comprises 92-96% of a positive electrode main material, 1-6% of a conductive agent, 1-5% of a binder and 0.1-1% of a dispersant, wherein the positive electrode main material comprises one of sodium iron pyrophosphate and sodium nickel iron manganese oxide.

6. The negative electrode-free secondary sodium battery according to claim 1, characterized in that: The diaphragm includes at least one of a polypropylene (PP) film, a polyethylene (PE) film, a non-woven fabric diaphragm, a glass fiber diaphragm, a ceramic diaphragm, a filter membrane, and a solid electrolyte diaphragm.

7. The negative electrode-free secondary sodium battery according to claim 1, characterized in that: The electrolyte comprises a solvent and a sodium salt, wherein: The solvent is an ether solvent, including at least one of tetrahydrofuran, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and triethylene glycol dimethyl ether; The sodium salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethylsulfonyl)imide, sodium iodide, sodium bromide, sodium thiocyanate, sodium chlorate, sodium carbonate, sodium oxalate, sodium ketomalonate, sodium diketosuccinate and sodium triketoglutarate, 2-cyclopropene-1-one-2,3-dihydroxy sodium, 3-cyclobutene-1,2-dione-3,4-dihydroxy sodium, 4-cyclopentene-1,2,3-trione-4,5-dihydroxy sodium, and 5-cyclohexene-1,2,3,4-tetraone-5,6-dihydroxy sodium.

8. The negative electrode-free secondary sodium battery according to claim 1, characterized in that: The electrolyte also includes functional additives, wherein: The functional additives include at least one of fluoroethylene carbonate, ethylene carbonate, propylene carbonate, ethyl acetate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl acetate, propyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, acetophenone, maleic anhydride, citraconic anhydride, succinic anhydride, pyromellitic anhydride, styrene anhydride, glutaric anhydride, succinic anhydride, azelaic anhydride, N,N-dimethyltrifluoroacetamide, N,N-dimethylacrylamide, sulfate, sulfite, potassium nitrate, triethyl acetate, sodium difluorooxalate borate, phosphorus oxide, and phosphorus sulfide.

9. A method for manufacturing a negative electrode-free secondary sodium battery, used for manufacturing a negative electrode-free secondary sodium battery as claimed in any one of claims 1 to 8, characterized in that: Includes steps: The steps of assembling a sodium battery cell include: Providing a negative electrode current collector, an electrolyte, a separator and a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material coated on both sides of the positive electrode current collector; Placing the separator between the negative electrode current collector and the positive electrode, placing the structure formed by the negative electrode current collector, the separator and the positive electrode in a battery cell shell, injecting the electrolyte so that the electrolyte is located between the negative electrode current collector and the positive electrode and around the structure; The steps of forming the microstructure include: Providing an external circuit, reversely connecting the external circuit to the positive and negative electrodes of the sodium battery cell, electrically connecting the positive electrode of the external circuit to the negative electrode of the sodium battery cell, electrically connecting the negative electrode of the external circuit to the positive electrode of the sodium battery cell, charging the sodium battery cell so that a microstructure is formed on the surface of the negative electrode current collector, and performing secondary packaging of the sodium battery cell by evacuating air; The steps of fractionation include: The external circuit is positively connected to the positive and negative electrodes of the sodium battery cell, the positive electrode of the external circuit is electrically connected to the positive electrode of the sodium battery cell, and the negative electrode of the external circuit is electrically connected to the negative electrode of the sodium battery cell to perform capacity conversion.

10. The manufacturing method according to claim 9, characterized in that: In the step of forming the microstructure, charging the sodium battery cell comprises charging at 0.01C for 10 to 60 minutes, or charging from 0V to 1.0V to 2.0V; And / or, the composition includes charging to 3.4V with 0.1C constant current and constant voltage, charging for 10 hours, standing for 20 minutes, discharging to 1.5V with 0.2C constant current, standing for 20 minutes, then charging to 3.4V with 0.2C constant current and constant voltage, standing for 20 minutes, discharging to 1.5V with 0.2C constant current, standing for 20 minutes, and then charging to 2.5V with 0.2C constant current and constant voltage.

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