Modified current collector, benzyloxy helicene electrolyte additive, preparation method of benzyloxy helicene electrolyte additive, negative-electrode-free sodium metal battery and application of modified current collector and benzyloxy helicene electrolyte additive

Abstract

The invention provides a modified current collector, a benzyloxy helicene electrolyte additive, a preparation method of the benzyloxy helicene electrolyte additive, a negative-electrode-free sodium metal battery and application, and relates to the technical field of new energy batteries. Sodium fluoroaluminate in the modified current collector can passivate the current collector and inhibit oxidation corrosion of FSI-to aluminum, the sodium fluoroaluminate and an electrolyte have a synergistic effect to generate SEI rich in inorganic components, continuous corrosion of a carbon-coated aluminum foil is further inhibited, an Al-F bond passivation film regulates a sodium deposition path, dendritic crystal aggregation caused by too high local current density is avoided, and the service life of the current collector is prolonged. The deposition / stripping reversibility is improved; the modified current collector is cooperated with a benzyloxy helicene special electrolyte additive, so that uniform deposition of sodium ions can be promoted, the modified current collector can be cooperated with a sulfonyl imide salt electrolyte, the advantages of the sulfonyl imide salt electrolyte are exerted, a layer of passive film is formed on the surface of the aluminum metal current collector, and a carbon-coated aluminum foil is prevented from being corroded by sulfonyl imide groups.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of new energy batteries, in particular to a modified current collector, a benzyloxy spiro olefin electrolyte additive and a preparation method thereof, a negative electrode-free sodium metal battery and application. BACKGROUND

[0002] In the process of accelerating the transformation of global energy structure to low carbonization, developing high cost-effective battery technology has become a key breakthrough point to solve energy crisis and environmental problems. Sodium ion battery is becoming an important development direction of new type of electrochemical energy storage system due to its rich resource reserves (2.74% of the earth's abundance, much higher than 0.0065% of lithium) and controllable raw material cost (sodium salt price is only 1 / 10 of lithium salt). However, the industrialization process of this technology is facing a key material bottleneck - the existing hard carbon negative electrode material has a significant gap in key indicators such as specific capacity (<300 mAh / g vs. 360 mAh / g of graphite negative electrode), compaction density (<1.0 g / cm 3 vs. 1.6 g / cm 3 of graphite) and other indicators, which directly leads to the difficulty of breaking through the industry threshold of 140 Wh / kg of battery energy density.

[0003] The structural characteristics of hard carbon material are the fundamental reason for its limited performance: as an unordered carbon structure composed of cross-linked aromatic layers, its sodium storage sites are mainly distributed in micropores and surface defects. This special structure not only gives it a theoretical capacity of 530 mAh / g, but also faces three major technical obstacles in practical application: (1) high specific surface area (usually >10 m 2 / g) causes serious interface side reactions, resulting in a first cycle coulombic efficiency (ICE) generally lower than 80%; (2) disordered carbon layer stacking leads to tortuous ion diffusion paths, and significant rate performance degradation; (3) low material packing density limits the volume capacity of the electrode, which seriously restricts the improvement of battery energy density. Therefore, it is necessary to develop a new negative electrode material system to improve the energy density of sodium ion batteries.

[0004] The existing solution is to directly use a carbon-coated aluminum foil as a negative electrode, use the electroplating deposition and dissolution of sodium ions as a negative electrode reaction, and construct a negative electrode-free sodium metal battery to achieve extremely high energy density. However, the traditional carbon-coated aluminum foil has a low binding energy with sodium metal, which will cause uneven deposition of sodium metal during charging and low battery coulombic efficiency.

[0005] In addition, for high-voltage (>4.1V) anode-free systems such as anode-free sodium ferric sulfate (NFS) systems, the traditional NaPF6 electrolyte has poor thermal stability and chemical stability, is very sensitive to water, and is prone to decomposition to produce acidic substances such as HF, thereby causing the dissolution of transition metals on the surface of the positive electrode material and migration to the negative electrode surface, reducing the capacity and service life of the sodium ion battery. The sodium salt of sulfonimide is more stable to water and has better thermal stability and chemical stability, but it has strong corrosion ability to carbon-coated aluminum foil at high voltage, which limits its use in the NFS anode-free system, further restricting the industrialization process of the NFS high-voltage anode-free system.

[0006] In view of this, the present application is proposed. SUMMARY

[0007] In view of the problems of the existing anode-free battery negative electrode carbon-coated aluminum foil current collector, the first object of the present application is to provide a modified current collector for anode-free sodium battery (also referred to as negative electrode current collector in the present application), aiming to provide a modified current collector that promotes uniform deposition of sodium ions and adapts to sulfonimide electrolyte.

[0008] The second object of the present application is to provide a benzyloxy-spiroolefin electrolyte additive and a preparation method thereof, aiming to improve ion transport rate, reduce interfacial side reactions with modified current collector, and further promote uniform deposition of sodium ions.

[0009] The third object of the present application is to provide an anode-free sodium metal battery, preferably a high-voltage NFS anode-free sodium metal battery containing a modified current collector, aiming at the problems of the existing high-voltage NFS anode-free battery negative electrode carbon-coated aluminum foil current collector. Compared with the negative electrode of conventional negative electrode active material, the negative electrode current collector of anode-free sodium battery has greater difficulty in controlling sodium dendrites, sodium uniform induction, and sodium expansion, and it is more difficult to adapt to high surface load and high-voltage positive electrode to assemble a high-performance anode-free battery.

[0010] The fourth object of the present application is to provide the application of the modified current collector and the benzyloxy-spiroolefin electrolyte additive in the anode-free sodium metal battery In order to achieve the above-mentioned objects of the present application, the following technical solutions are adopted: A modified current collector for anode-free sodium metal battery, comprising a planar current collector and a modified layer composite on the surface of the planar current collector; the modified layer comprises the following components by weight: modified material 30~80 parts, conductive agent 10~60 parts, and binder 10~20 parts.

[0011] Further, the modified material is sodium fluoroaluminate, which contains at least one of Na5Al3F 14 , Na3AlF6.

[0012] Further, the particle size of the modified material is 50-1000 nm.

[0013] Further, the conductive agent includes at least one of conductive carbon black, natural graphite, artificial graphite, carbon nanotube, graphene, and graphene nanosheet.

[0014] Further, the binder includes at least one of PVDF, CMC, SBR, and PAA.

[0015] Further, the modified layer is a coating layer coated on the surface of the planar current collector.

[0016] Further, the modified layer is a single-layer structure, and the thickness of the modified layer is less than or equal to 150 μm; preferably 15-80 μm; further preferably 35-65 μm; and more further 48-54 μm.

[0017] Further, the planar current collector is a conductive metal foil, and the conductive metal foil is a carbon-coated aluminum foil.

[0018] A benzyloxy-spiro olefin electrolyte additive, the structural formula of which is: .

[0019] A preparation method of the above-mentioned benzyloxy-spiro olefin electrolyte additive, including the following steps: , wherein MeOH is methanol, and PPA is polyphosphoric acid.

[0020] Further, including the following steps: , wherein MeOH is methanol, DMSO is dimethyl sulfoxide, Ethanol is ethanol, and PPA is polyphosphoric acid.

[0021] A negative electrode-free sodium metal battery including the above-mentioned modified current collector; the negative electrode-free sodium metal battery includes an electrode core sequentially compounded of a positive electrode, a barrier layer, and the above-mentioned modified current collector.

[0022] Further, the positive electrode active material of the positive electrode is at least one of sodium ferric sulfate (NFS) and sodium nickel-iron-manganese acid.

[0023] Further, the positive electrode is a high-face-load positive electrode, and the loading amount of the positive electrode active material is greater than 15 mg·cm -2 , preferably 15-25 mg·cm -2 .

[0024] Further, the barrier layer is a separator or a solid-state electrolyte.

[0025] Further, the negative electrode-free sodium metal battery further comprises an electrolyte for soaking the battery cell, and the electrolyte comprises the following components by weight: 10-15 parts of sodium salt, 81.5-85 parts of organic solvent, and 2-5.5 parts of additive.

[0026] Further, the sodium salt is at least one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bis(oxalato)borate.

[0027] Further, the organic solvent is at least one of ethylene carbonate, methyl ethyl carbonate, and diethylene glycol dimethyl ether.

[0028] Further, the electrolyte additive is at least one of the above-mentioned benzyloxy spiro olefin, fluoroethylene carbonate, and sodium bisfluorosulfonylimide; preferably, the benzyloxy spiro olefin is compounded with FEC and / or NaFSI.

[0029] The above-mentioned modified current collector for the negative electrode-free sodium metal battery, the application of the above-mentioned benzyloxy spiro olefin electrolyte additive, the modified current collector is used as an electrode to prepare a negative electrode-free sodium metal battery; or the benzyloxy spiro olefin electrolyte additive is used as an electrolyte additive to prepare a negative electrode-free sodium metal battery.

[0030] Compared with the prior art, the application has the following beneficial effects: 1. The modified current collector for the negative electrode-free sodium metal battery, the F in the coating layer of the composite modified current collector is sodium fluoroaluminate. - The current collector can be passivated to generate an AlF3 layer with extremely high chemical stability, and the AlF3 passivation film can block the charge transfer between the aluminum matrix and FSI - in the electrolyte, reduce the oxidation potential of aluminum under high pressure, and thereby inhibit the oxidation corrosion of aluminum by FSI - in the electrolyte.

[0031] 2. In the negative electrode-free sodium metal battery, the sodium fluoroaluminate in the modified current collector cooperates with the electrolyte to generate a solid-state electrolyte interface (SEI) rich in inorganic components (such as NaF and AlF3) during charging and discharging, further inhibits the continuous corrosion of the carbon-coated aluminum foil, the Al-F bond passivation film regulates the sodium deposition path, avoids the aggregation of dendrites caused by excessive local current density, and improves the deposition / detachment reversibility.

[0032] 3. In the negative electrode-free sodium metal battery, the sodium fluoroaluminate coated modified carbon-coated aluminum foil current collector is matched with a special benzyloxy spiro olefin electrolyte additive, and under high voltage, the carbon-hydrogen bond of the benzyloxy group is protonated to generate a benzyl cation intermediate, and the oxygen atom of the benzyloxy group can weakly solvate Na +This reduces the desolventization energy barrier and increases the ion migration rate. The decomposed helicene is attached to the sodium fluoroaluminate solid electrolyte coating modified current collector. The hydrophobicity of the helicene repels electrolyte solvent molecules and works synergistically with the sodium fluoroaluminate current collector coating layer to reduce side reactions.

[0033] 4. The sodium metal battery without negative electrode of the present invention, through the composite modified current collector and the special electrolyte additive benzyloxyspirene, can not only promote the uniform deposition of sodium ions, but also work synergistically with sulfonylimide salt electrolyte to give full play to the advantages of sulfonylimide salt electrolyte, and form a passivation film on the surface of aluminum metal current collector to prevent sulfonylimide groups from corroding the carbon-coated aluminum foil. Attached Figure Description

[0034] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 This is a diagram showing the surface corrosion of the positive electrode sheet of the battery in Embodiment 1 of the present invention after 300 cycles at 45°C. Figure 2 This is a diagram showing the surface corrosion of the positive electrode sheet after the battery of Comparative Example 2 of this invention has undergone 300 cycles. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0037] A modified current collector for a negative electrode-free sodium metal battery includes a planar current collector and a modified layer composited on the surface of the planar current collector; the modified layer includes the following components in parts by weight: 30-80 parts of modified material, 10-60 parts of conductive agent, and 10-20 parts of binder; preferably 40-80 parts of modified material, 10-50 parts of conductive agent, and 10-20 parts of binder; more preferably 60-70 parts of modified material, 10-30 parts of conductive agent, and 10-20 parts of binder.

[0038] This invention can efficiently adapt to the application requirements of sodium-anode-free batteries, especially high-area-load positive-electrode sodium-anode-free batteries, even with low modified material content, and can exhibit excellent stability.

[0039] Preferably, the modified layer of the modified current collector faces the positive electrode direction.

[0040] Preferably, the modified material is sodium fluoroaluminate, containing Na5Al3F 14 At least one of Na3AlF6. A modified current collector containing the modified material is suitable for the application requirements of a cathodeless sodium battery, can induce uniform deposition of sodium metal, effectively suppress sodium dendrites, and its application in a cathodeless sodium battery can significantly improve its electrochemical performance.

[0041] The F in the modified sodium fluoroaluminate material of this invention - It can passivate the current collector and generate an AlF3 layer with extremely high chemical stability. The AlF3 passivation film can block the interaction between the aluminum substrate and FSI in the electrolyte. - The charge transfer reduces the oxidation potential of aluminum under high voltage, thereby inhibiting FSI in the electrolyte. - Oxidative corrosion of aluminum. Both sodium salt NaTFSI and additive NaFSI in the electrolyte can generate FSI-type groups (fluorosulfonyl imides). Fluorosulfonyl imide groups include both FSI and TFSI groups, and in this field, the fluorosulfonyl imide group is often replaced by FSI.

[0042] Preferably, the particle size of the modified material is 50~1000nm, including but not limited to 50nm, 100nm, 200nm, 500nm, 600nm, 700nm, 800nm, and 1000nm.

[0043] Preferably, the planar current collector is a conductive metal foil, and the conductive metal foil is a carbon-coated aluminum foil.

[0044] Preferably, the conductive agent includes at least one of conductive carbon black, natural graphite, artificial graphite, carbon nanotubes, graphene, and graphene nanosheets.

[0045] Preferably, the adhesive includes at least one of PVDF (polyvinylidene fluoride), CMC (carboxymethyl cellulose), SBR (styrene-butadiene rubber), and PAA (polyacrylic acid).

[0046] Preferably, the modified layer is a coating layer applied to the surface of the planar current collector. The coating layer is obtained by slurrying the binder, conductive agent and modified material with a solvent, applying it to the surface of the planar current collector, and then drying it.

[0047] Preferably, the modified layer is a single-layer structure, and the thickness of the modified layer is less than or equal to 150 μm; more preferably 15~80 μm; further preferably 35~65 μm; and even more preferably 48~54 μm.

[0048] By controlling the composition and structure of the modified current collector and further controlling the thickness of the modified layer, this invention can further improve the synergy between materials and structure, which helps to make it more suitable for the application requirements of negative electrodeless batteries and enable it to exhibit better electrochemical performance.

[0049] A benzyloxyspiroene electrolyte additive, wherein the structural formula of the benzyloxyspiroene is: .

[0050] A method for preparing a benzyloxyspiroene electrolyte additive includes the following steps: , MeOH is methanol, and PPA is polyphosphoric acid; Preferably, the method includes the following steps: , MeOH is methanol, DMSO is dimethyl sulfoxide, Ethanol is ethanol, and PPA is polyphosphoric acid.

[0051] A sodium metal battery without a negative electrode, comprising the modified current collector described above; The negative electrode-free sodium metal battery of the present invention, except for the modified current collector described in the present invention, can have conventional components and structures; the negative electrode-free sodium metal battery of the present invention refers to a sodium metal battery that eliminates or removes the negative electrode active material; the negative electrode-free sodium metal battery of the present invention, except for the modified current collector described in the present invention, can have known components, parts, and structures.

[0052] Preferably, the negative electrode-free sodium metal battery comprises a cell consisting of a positive electrode, a barrier layer, and the modified current collector described above, which are sequentially composited.

[0053] The positive electrode described in this invention can be a conventional positive electrode in the industry, which includes a current collector and a positive electrode material loaded on its surface. The positive electrode material includes conventional positive electrode active materials, binders and conductive agents.

[0054] Preferably, the positive electrode active material is at least one of sodium ferric sulfate (NFS) and sodium nickel iron manganate; in the positive electrode material of the present invention, the composition and ratio of the positive electrode active material, binder and conductive agent can all be conventional.

[0055] Preferably, the positive electrode is a high-area-load positive electrode, and the loading of the positive electrode active material is greater than 15 mg·cm³.-2 The preferred concentration is 15~25 mg·cm³. -2 including but not limited to 15 mg·cm -2 16mg·cm -2 17 mg·cm -2 18 mg·cm -2 19 mg·cm -2 20 mg·cm -2 21 mg·cm -2 22 mg·cm -2 23 mg·cm -2 24 mg·cm -2 25 mg·cm -2 The modified current collector of this invention is particularly suitable for high surface load positive electrodes that are difficult to adapt to in existing technologies.

[0056] Preferably, the barrier layer is a membrane or a solid electrolyte.

[0057] Preferably, the sodium metal battery without a negative electrode further includes an electrolyte for soaking the battery cell, the electrolyte comprising the following components by weight: 10-15 parts sodium salt, 81.5-85 parts organic solvent, and 2-5.5 parts additives.

[0058] Preferably, the sodium salt is at least one of sodium hexafluorophosphate (NaPF6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium bis(oxalatoborate) (NaBOB).

[0059] Preferably, the organic solvent is at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethylene glycol dimethyl ether (DEGDME).

[0060] Preferably, the electrolyte additive is at least one of the above-mentioned benzyloxyspirene, fluoroethylene carbonate (FEC), and sodium bis(fluorosulfonyl)imide (NaFSI); preferably, benzyloxyspirene is combined with FEC and / or NaFSI.

[0061] An application of a modified current collector for a negative electrode-free sodium metal battery is disclosed, which is used as an electrode to prepare a negative electrode-free sodium metal battery. Based on the characteristics of conventional negative electrode-free batteries, the modified current collector described in this invention can be used to prepare the required negative electrode-free sodium metal battery.

[0062] An application of a benzyloxyspiroene electrolyte additive, which is used as an electrolyte additive in the preparation of a sodium metal battery without a negative electrode.

[0063] Example 1 A method for preparing a sodium metal battery without a negative electrode includes the following steps: a. Preparation of modified current collector, namely sodium fluoroaluminate coated carbon-coated aluminum foil current collector: Sodium fluoroaluminate, conductive carbon black, and PVDF in a ratio of 7:2:1, with a total amount of 1g, are placed in a mortar and ground evenly. The mixture is then transferred to a beaker, and 40 drops of NMP (N...) are added dropwise. Methylpyrrolidone was stirred for 8 hours to obtain a modified mixed solution. The modified mixed solution was uniformly coated onto a clean carbon-coated aluminum foil current collector using a 50-micron scraper (coating thickness of 50±1μm). It was then placed in a vacuum drying oven to dry. The drying temperature could be controlled at 80±10℃ and the drying time could be 8~9 hours to obtain a sodium solid electrolyte composite coating current collector. b. Preparation of electrolyte: In an argon glove box with water and oxygen content ≤0.1ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were uniformly mixed at a mass ratio of 3:7 to obtain an organic solvent. Sodium hexafluorophosphate (NaPF6) was then slowly added to the organic solvent. After complete dissolution, fluoroethylene carbonate (FEC), sodium bis(fluorosulfonyl)imide (NaFSI), and benzyloxyspirene were added as additives. After stirring evenly, the electrolyte was obtained. The amounts of sodium hexafluorophosphate, organic solvent, FEC, NaFSI, and benzyloxyspirene used in the electrolyte were 13%, 81.5%, 2%, 3%, and 0.5% of the total mass of the electrolyte, respectively. c. Preparation of the positive electrode sheet: Sodium ferric sulfate (NFS), conductive agent carbon black (SuperP), and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 94:3:3. After mixing, N-methylpyrrolidone is added, controlling the theoretical solid content to 55%. The mixture is homogenized using a vacuum defoamer to obtain the positive electrode slurry. This slurry is then uniformly coated onto a 12μm thick carbon-coated aluminum foil (area density: 322.7 g / m²). 2 After drying, rolling, and cutting, positive electrode sheets are obtained. d. In an environment with a dew point temperature below -60℃, a soft-pack stacked battery is manufactured. The positive electrode, separator, and sodium fluoroaluminate coated carbonized aluminum foil current collector are stacked in sequence to ensure that the separator completely separates the positive and modified current collectors. The aluminum-plastic film is used to encapsulate and weld the tabs to form the battery to be injected with electrolyte. Before electrolyte injection, the moisture content of the battery is baked to below 300ppm. The electrolyte is then injected, and the battery undergoes one-sealing, formation, second sealing, and capacity testing to obtain a sodium metal battery without a negative electrode.

[0064] Example 2 The difference between this embodiment and Example 1 is that the electrolyte additives in step b are FEC and NaFSI, and the amounts of sodium hexafluorophosphate, organic solvent, fluoroethylene carbonate, and sodium difluorosulfonyl imide in the electrolyte are 13%, 82%, 2%, and 3% of the total mass of the electrolyte, respectively; the rest is the same as in Example 1.

[0065] Example 3 The difference between this embodiment and Embodiment 1 is that the electrolyte additive in step b is FEC, and the amounts of sodium hexafluorophosphate, organic solvent, and fluoroethylene carbonate used are 13%, 85%, and 2% of the total mass of the electrolyte, respectively; the rest is the same as in Embodiment 1.

[0066] Example 4 The difference between this embodiment and Example 1 is that the sodium salt in the electrolyte is replaced by an equal mass of sodium hexafluorophosphate (NaPF6); the rest is the same as in Example 1.

[0067] Example 5 The difference between this embodiment and Example 1 is that the sodium salt in the electrolyte is replaced by an equal mass of a NaTFSI and NaBOB composition, with a NaTFSI to NaBOB mass ratio of 6:4; the rest is the same as in Example 1.

[0068] Example 6 A method for preparing a benzyloxyspiroene electrolyte additive includes the following steps: Step A: Preparation of compound 2:

[0069] 20.0 g (99 mmol) of 2,5-difluoroterephthalic acid (molecular weight 202.11) was dissolved in methanol (250 ml), and concentrated sulfuric acid (40 ml) was added. The mixture was slowly heated to 65 °C and refluxed for 12 h. After the reaction solution cooled to room temperature, 450 ml of distilled water was added, and the mixture was filtered. The solid was washed with distilled water, and the crude product was rapidly purified by column chromatography (ethyl acetate: petroleum ether = 1:10) to give 20.5 g of white solid methyl 2,5-difluoroterephthalate, with a yield of 90%. Step B, Preparation of compound 3:

[0070] In a flask, 5.0 g (21.7 mmol) of methyl 2,5-difluoroterephthalate (molecular weight 230.16), 9.5 g (42.5 mmol) of 4-benzyloxyindole (molecular weight 223.27), and 35.5 g (109 mmol) of cesium carbonate (molecular weight 325.8) were added sequentially. Then, 150 mL of DMSO was added as a solvent, and the mixture was slowly heated to 50 °C and reacted for 2 h. After the reaction solution cooled to room temperature, dilute hydrochloric acid was added to quench the reaction. The resulting mixed suspension was then poured into water (150 mL), and the aqueous layer was extracted with dichloromethane (50 mL × 3). The mixed organic layer was washed with water (150 mL), dried over magnesium sulfate, filtered, and the solvent was evaporated to dryness by vacuum distillation. The crude product was purified by column chromatography (dichloromethane:petroleum ether = 1:2) to give 13.1 g of methyl 2,5-dibenzyloxyindole terephthalate, a pale yellow solid, with a yield of 95%. Step C, Preparation of compound 4:

[0071] Methyl 2,5-dibenzyloxyindole terephthalate (molecular weight 636.7) (10 g, 15.7 mmol, 1.0 equiv) was dissolved in ethanol (100 mL), and sodium hydroxide (2.5 g, 62.8 mmol, 4 equiv) was dissolved in deionized water (50 mL). The methyl 2,5-dibenzyloxyindole terephthalate / ethanol and sodium hydroxide / deionized water solution were mixed, and the mixture was slowly heated to 100 °C and stirred for 12 h. After the reaction solution cooled to room temperature, dilute hydrochloric acid was added to quench the reaction. The resulting suspension was then poured into water (30 mL), and the aqueous layer was extracted with dichloromethane (50 mL × 3). The mixed organic layer was washed with water (30 mL), dried over magnesium sulfate, filtered, and the solvent was evaporated to dryness by vacuum distillation. The crude product was purified by column chromatography (dichloromethane:petroleum ether = 1:2) to give 8.0 g of solid product 2,5-dibenzyloxyindole terephthalic acid, with a yield of 84%. Step D, Preparation of compound 5:

[0072] 2,5-Dibenzyloxyindole terephthalic acid (molecular weight 608.7) (6.1 g, 10 mmol, 1 equiv) was dissolved in polyphosphoric acid (30 mL), and the mixture was slowly heated to 180 °C and stirred for 4 h. After the reaction solution cooled to room temperature, the resulting suspension was poured into water (50 mL), and the aqueous layer was extracted with dichloromethane (50 mL × 3). The mixed organic layer was washed with water (30 mL), dried on magnesium sulfate, filtered, and the solvent was evaporated to dryness by vacuum distillation. The crude product was purified by column chromatography (dichloromethane:petroleum ether = 1:1) to give 4.6 g of the target product compound 5 (i.e., benzyloxyspiroene electrolyte additive), with a yield of 80%.

[0073] Comparative Example 1 The difference between this comparative example and Example 1 is that ordinary carbon-coated aluminum foil current collector is used instead of the modified current collector; otherwise, it is the same as Example 1.

[0074] Comparative Example 2 The difference between this comparative example and Example 2 is that ordinary carbon-coated aluminum foil current collector is used instead of the modified current collector; The sodium salt in the electrolyte was replaced by sodium hexafluorophosphate (NaPF6) with an equal mass of NaTFSI; The rest is the same as in Example 2.

[0075] Comparative Example 3 The difference between this comparative example and Example 3 is that ordinary carbon-coated aluminum foil current collector is used instead of the modified current collector; The sodium salt in the electrolyte was replaced by sodium hexafluorophosphate (NaPF6) with an equal mass of NaTFSI and NaBOB composition, wherein the mass ratio of NaTFSI to NaBOB in the composition was 6:4. The rest is the same as in Example 3.

[0076] Performance testing: I. Cyclic performance tests were conducted at 45°C on the soft-pack experimental batteries obtained in Examples 1-3 and Comparative Examples 1-3, and the corrosion of the electrode sheets after cycling were confirmed.

[0077] 1. The method for testing room temperature cycling performance is as follows: The prepared soft-pack experimental battery was placed in an explosion-proof box at an ambient temperature of 45℃ and charged at a constant current of 1C to a voltage of 4.2V. Then, it was charged at a constant voltage of 4.2V to a current of 0.05C, followed by a constant current discharge of 1C to a voltage of 2.0V. The cycle was repeated for 200 cycles, and the capacity retention rate was recorded. The capacity retention rate (%) of the nth cycle was calculated as (discharge capacity of the nth cycle / discharge capacity of the first cycle) × 100%. The cycle performance test results are shown in Table 1.

[0078] 2. The method for confirming electrode corrosion is as follows: The batteries obtained in Examples 1-3 and Comparative Examples 1-3 were disassembled after being cycled at 45°C for 300 cycles. The corrosion status of the positive electrode surface was confirmed, and the batteries were classified into severe / slight / no corrosion according to the size of the corrosion area, as shown in Table 1. The corrosion status of the positive electrode surface in Example 1 is as follows: Figure 1 As shown. The surface corrosion of the positive electrode in Comparative Example 2 is as follows. Figure 2 As shown.

[0079] Table 1. Performance comparison of pouch cells obtained in Examples 1-3 and Comparative Examples 1-3

[0080] As shown in Table 1, the modified current collectors in Examples 1-3 resulted in virtually no corrosion of the carbon-coated aluminum foil on the pouch cells. Furthermore, Example 1, in conjunction with the benzyloxyspirene special electrolyte additive, improved ion transport performance, thereby enhancing the 45°C cycle performance. In contrast, Comparative Examples 1-3, which used ordinary carbon-coated aluminum foil as the current collector without a negative electrode, exhibited severe corrosion of the carbon-coated aluminum foil and poor high-temperature cycle performance (the cycle performance data in Table 1 are based on 45°C; the trend of performance changes at normal and high temperatures is consistent, with high temperatures accelerating corrosion). This demonstrates that the modified current collector in this invention, in conjunction with the benzyloxyspirene electrolyte additive, inhibited the corrosion of the carbon-coated aluminum foil and improved the battery's electrochemical performance.

[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A modified current collector for a negative electrode-free sodium metal battery, characterized by, The planar current collector and a modified layer compounded on the surface of the planar current collector; the modified layer comprises the following components by weight: modified material 30-80 parts, conductive agent 10-60 parts, and binder 10-20 parts.

2. The modified current collector for a negative electrode-free sodium metal battery according to claim 1, characterized in that, The modifying material is sodium fluoroaluminate, comprising at least one of Na5Al3F 14 10, Na3AlF6.

3. The modified current collector for a negative electrode-free sodium metal battery according to claim 1 or 2, characterized in that, At least one of the following technical features is included: (1) The particle size of the modified material is 50-1000 nm; (2) The conductive agent includes at least one of conductive carbon black, natural graphite, artificial graphite, carbon nanotubes, graphene, and graphene nanosheet; (3) The binder includes at least one of PVDF, CMC, SBR, and PAA; (4) The modified layer is a coating layer coated on the surface of the planar current collector; (5) The modified layer has a single-layer structure, and the thickness of the modified layer is less than or equal to 150 μm; preferably 15-80 μm; further preferably 35-65 μm; and more further 48-54 μm; (6) The planar current collector is a conductive metal foil, and the conductive metal foil is a carbon-coated aluminum foil.

4. A benzyloxy-spiro olefin electrolyte additive characterized in that, The structural formula of the benzyloxy spiro olefin is: 。 5. The preparation method of the benzyloxyspiroene electrolyte additive as described in claim 4, characterized in that, The method comprises the following steps: ， wherein MeOH is methanol, and PPA is polyphosphoric acid.

6. A sodium metal battery without a negative electrode, characterized by The modified current collector according to any one of claims 1-3; the negative-electrode-free sodium metal battery comprises an electrode core compounded in sequence of a positive electrode, a barrier layer, and the modified current collector.

7. The sodium metal battery without a negative electrode according to claim 6, wherein At least one of the following technical features is included: (1) The positive electrode active material of the positive electrode is at least one of sodium iron sulfate and sodium nickel manganese acid; (2) the positive electrode is a high surface loading positive electrode, and the loading of the positive electrode active material is greater than 15 mg·cm -2 , preferably 15~25 mg·cm -2 ; (3) The barrier layer is a separator or a solid-state electrolyte.

8. The sodium metal battery without negative electrode according to claim 6, wherein The negative-electrode-free sodium metal battery further comprises an electrolyte for soaking the electrode core, and the electrolyte comprises the following components by weight: sodium salt 10-15 parts, organic solvent 81.5-85 parts, and additive 2-5.5 parts.

9. The sodium metal battery without a negative electrode according to claim 8, wherein, At least one of the following technical features is included: (1) The sodium salt is at least one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bisoxalate borate; (2) The organic solvent is at least one of ethylene carbonate, methyl ethyl carbonate, and diethylene glycol dimethyl ether; (3) The electrolyte additive is at least one of the benzyloxy spiro olefin, fluoroethylene carbonate, and sodium bisfluorosulfonylimide according to claim 4; preferably the benzyloxy spiro olefin is compounded with FEC and / or NaFSI.

10. The use of the modified current collector for the anode-free sodium metal battery according to any one of claims 1-3, the use of the benzyloxy-spiro olefin electrolyte additive according to claim 4, characterized in that, The modified current collector is used as an electrode to prepare a negative-electrode-free sodium metal battery; or the benzyloxy spiro olefin electrolyte additive is used as an electrolyte additive to prepare a negative-electrode-free sodium metal battery.

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