Electrolyte for a Sodium-Free Battery and its Preparation Method, and Sodium-Free Battery

Abstract

This invention relates to the field of battery technology, and in particular to a sodium-free battery electrolyte, its preparation method, and a sodium-free battery. The electrolyte comprises a sodium salt and a solvent; the sodium salt includes a first anionic component and a second anionic component. The technical solution of this invention uses a weakly coordinated carborane anionic salt as the main salt as the first anionic component, which inherits its advantages of high reduction stability, promotion of organic enrichment / boron-containing ultrathin interface formation, and support for dense and uniform sodium deposition. By introducing a low content of the second anionic component, the interfacial chemistry during long-term cycling is preferentially controlled without significantly disrupting the solvation structure of the main salt, reducing the accumulation rate of boron-oxygen insulating species. This system does not rely on a thick inorganic film for "hard passivation" of the interface, but rather achieves synergy between the two anions, balancing ion transport, interfacial stability, and long lifetime.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a sodium-free negative electrode battery electrolyte, its preparation method, and a sodium-free negative electrode battery. Background Technology

[0002] Electrodeless sodium batteries are a type of rechargeable battery system that does not pre-place metallic sodium on the negative electrode side. Initially, they typically only have a negative electrode current collector. During the first charge, sodium ions are released from the positive electrode and deposited on the surface of the negative electrode current collector to form metallic sodium. In subsequent cycles, the sodium is reversibly deposited and stripped off. Because it eliminates the need for a pre-placed metallic sodium negative electrode, electrodeless sodium batteries offer significant advantages in terms of increasing battery energy density, simplifying battery structure, and reducing the risks associated with metallic sodium processing and assembly. Therefore, they have promising applications in the field of high-energy-density sodium batteries.

[0003] However, sodium-free batteries also face more severe interfacial stability issues than conventional sodium metal batteries. Since there is no excess metallic sodium in the system for compensation, any loss of active sodium during battery cycling caused by electrolyte decomposition, interfacial side reactions, or uneven deposition will directly weaken the battery's reversible capacity and cycle life. Especially during charge and discharge, the nucleation, growth, and stripping behavior of sodium on the surface of the negative electrode current collector is highly sensitive to the electrolyte properties. If the electrolyte cannot effectively regulate the interfacial reaction, it can easily lead to uneven sodium deposition, exacerbated local side reactions, continuous thickening of the interfacial film, and gradual accumulation of dead sodium.

[0004] Existing sodium-based battery electrolyte systems without a negative electrode typically suffer from the following problems in practical applications: First, interfacial side reactions are difficult to suppress effectively, and the electrolyte continues to decompose at the negative electrode interface, generating more insulating byproducts and causing an increase in interfacial impedance. Second, the sodium deposition / stripping process lacks reversibility, easily forming isolated sodium, dead sodium, or areas of electrical contact failure, leading to the continuous depletion of active sodium reserves. Third, as cycling progresses, the composition and structure of the interfacial film continue to evolve, and some byproducts accumulate on the negative electrode surface to form a dense or insulating layer, further hindering sodium ion transport and worsening subsequent deposition behavior. Fourth, traditional single-salt electrolyte systems often struggle to simultaneously achieve high reduction stability, uniform deposition capability, and interfacial stability during long-term cycling.

[0005] Therefore, for anode-free sodium batteries, the electrolyte not only needs to possess good ion conductivity and electrochemical stability, but also needs to continuously maintain a stable, thin interface layer that is conducive to sodium ion transport during cycling, while minimizing the accumulation of insulating byproducts and the formation of dead sodium. Especially under long-cycle conditions, how to further suppress interfacial side reactions, delay interface deterioration, and reduce irreversible loss of active sodium while ensuring uniform sodium deposition and highly reversible stripping has become a key technical problem restricting the performance improvement and practical application of anode-free sodium batteries. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a sodium-free battery electrolyte, its preparation method, and a sodium-free battery.

[0007] To achieve the above objectives, this application adopts the following solution: An electrolyte for a negative electrode-free sodium battery includes a sodium salt and a solvent; the sodium salt includes a first anionic component and a second anionic component; the first anionic component is a carborane anionic sodium salt; the second anionic component is a sodium salt additive capable of participating in interface regulation and inhibiting the accumulation of boron-oxygen insulating layer.

[0008] The first anionic component includes Na[HCB9H9], Na[HCB] 11 H 12 ]、Na[HCB 11 H 11 or one or more of its derivatives.

[0009] The concentration of the first anionic component is 0.2–2.0 mol / L, preferably 0.5–1.5 mol / L.

[0010] The second anionic component includes one or more of boron anion salt, sulfonamide-containing anion salt, phosphate-containing anion salt, nitrate-containing anion salt, difluorooxalate-borate anion salt, and difluorophosphate anion salt; preferably, the second anionic component includes one or more of NaNO3, NaDFOB, NaPO2F2, NaFSI, NaTFSI, and NaBOB.

[0011] The concentration of the second anionic component is 0.005–0.30 mol / L, preferably 0.01–0.10 mol / L.

[0012] The second anionic component accounts for 0.5% to 25% of the total molar amount of anions, preferably 1% to 12%.

[0013] The solvent is an ether solvent, preferably one or more of DME, G2 (diethylene glycol dimethyl ether), G3 (triethylene glycol dimethyl ether), 1,3-dioxolane, and tetraethylene glycol dimethyl ether.

[0014] The present invention also includes a method for preparing the electrolyte for a negative electrode-free sodium battery, comprising the following steps: (1) dissolving the first anionic component in a solvent in an inert atmosphere to obtain the main electrolyte; (2) adding the second anionic component to the main electrolyte and stirring for 2 to 24 h to obtain a uniform and transparent dual anionic synergistic electrolyte.

[0015] The present invention also includes a negative electrode-free sodium battery, comprising a positive electrode, the electrolyte for the negative electrode-free sodium battery, a separator, and a negative electrode current collector.

[0016] The positive electrode is one or more of NFPP sodium iron pyrophosphate, Prussian blue, layered oxides, and polyanionic positive electrodes. Preferably, the negative electrode current collector includes carbon-coated aluminum foil, bare aluminum foil, copper foil, stainless steel foil, nickel foil, or a current collector whose surface is modified by carbon / metal / oxide; the negative electrode current collector does not contain pre-contained metallic sodium.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The technical solution of this invention uses a weakly coordinated carborane anionic salt as the main salt as the first anionic component, which can inherit its advantages of high reduction stability, promotion of organic enrichment / boron-containing ultrathin interface formation, and support for dense and uniform sodium deposition. By introducing a low content of the second anionic component, the interfacial chemistry in the long-term cycling stage is preferentially controlled without significantly destroying the solvation structure of the main salt, thereby reducing the accumulation rate of boron-oxygen insulating species. This system does not rely on a thick inorganic film to "hard passivate" the interface, but rather achieves a balance of ion transport, interfacial stability, and long lifetime through the synergy of the two anions. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0019] Example 1: Preparation of electrolyte for a negative electrode-free sodium battery, comprising the following steps: In an argon glove box, the first anionic component Na[HCB9H9] was dissolved in anhydrous DME to prepare a main electrolyte with a concentration of 1.0 mol / L. Then, NaNO3 was added to make the NaNO3 concentration 0.02 mol / L, and the mixture was stirred for 12 h to obtain a dual-anion synergistic electrolyte A.

[0020] Using NFPP as the positive electrode active material, the positive electrode surface capacity is 1.0 mAh / cm². 2 A 1 μm carbon-coated aluminum foil was used as the negative electrode current collector; a glass fiber separator was used. AC||NFPP coin cells were assembled with an electrolyte injection volume of 60 μL. The cells were formed at 0.1 C for 3 cycles at 25°C, followed by long-cycle testing at 2.0 C.

[0021] Other embodiments and comparative examples are shown in Table 1.

[0022] Example 2: Except for adjusting the second anion component to NaNO3 0.03 mol / L, the rest is the same as in Example 1, to obtain the dual anion synergistic electrolyte B, and to assemble an AC||NFPP full cell.

[0023] Example 3: Except for adjusting the second anion component to NaNO3 0.04 mol / L, the rest is the same as in Example 1, to obtain the dual anion synergistic electrolyte C, and to assemble an AC||NFPP full cell.

[0024] Example 4: Except for adjusting the second anion component to 0.05 mol / L NaNO3, the rest is the same as in Example 1, to obtain the dual anion synergistic electrolyte D, and to assemble an AC||NFPP full cell.

[0025] Example 5: Except for adjusting the second anion component to NaDFOB 0.04 mol / L, the rest is the same as in Example 1, and a dual anion synergistic electrolyte E is obtained, and an AC||NFPP full cell is assembled.

[0026] Example 6: Except for adjusting the second anion component to NaPO2F2 0.04 mol / L, the rest is the same as in Example 1, to obtain the dual anion synergistic electrolyte F, and to assemble an AC||NFPP full cell.

[0027] Example 7: Except for adjusting the second anion component to NaFSI 0.04 mol / L, the rest is the same as in Example 1, and a dual anion synergistic electrolyte G is obtained, and an AC||NFPP full cell is assembled.

[0028] Example 8: Based on Example 3, the solvent was adjusted to a mixed ether system of DME:G2=8:2 (volume ratio), the Na[HCB9H9] concentration remained at 1.0 mol / L, and the NaNO3 concentration was 0.04 mol / L, to obtain the dual anion synergistic electrolyte H, and an AC||NFPP full cell was assembled.

[0029] Example 9: Except for replacing the negative electrode current collector with copper foil instead of 1 μm carbon-coated aluminum foil, the rest is the same as in Example 2.

[0030] Example 10: Except for replacing the negative electrode current collector with stainless steel foil instead of 1 μm carbon-coated aluminum foil, the rest is the same as in Example 2.

[0031] Comparative Example 1: A single main salt electrolyte was used, namely 1.0 mol / L Na[HCB9H9] / DME, without the addition of a second anionic component, and the rest was the same as in Example 1.

[0032] Comparative Example 2: A conventional comparative electrolyte, namely 1.0 mol / L NaPF6 / DME, was used, and the rest was the same as in Example 1.

[0033] Electrochemical performance testing conditions: Cyclic test conditions: 25℃, AC||NFPP button cell; Formation: 0.1 C charge-discharge 3 cycles; Long cycle: 2.0C, voltage range 2.0~3.8 V; First cycle coulombic efficiency = First discharge capacity / First charge capacity × 100%; Capacity retention = nth cycle discharge capacity / 1st cycle discharge capacity × 100%.

[0034] Table 1

[0035]

[0036] The data above show that: (1) the single carborane main salt system has excellent cycling performance, but there is still a problem of boron oxide insulation layer accumulation after long cycling; (2) a low proportion of the second anion component will not destroy the basic advantages of the main salt, but will further improve the capacity retention in the 500-cycle stage; (3) the NaDFOB scheme performs best, indicating that it is more conducive to constraining the continuous generation of boron oxide in the interface; (4) the inventive point of this invention is not to simply improve the performance of the first cycle, but to delay the interface deterioration and sodium inventory loss in the middle and late stages, which is also the key difference from the existing single salt system; (5) using different current collectors, the dual anion synergistic electrolyte can still form a stable composite interface on the current collector surface, and the sodium deposition / stripping process has good reversibility.

[0037] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0038] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An electrolyte for a negative electrode-less sodium battery, characterized in that, It includes a sodium salt and a solvent; the sodium salt includes a first anionic component and a second anionic component; the first anionic component is a sodium carborane anionic salt; the second anionic component is a sodium salt additive that can participate in interface regulation and inhibit the accumulation of boron-oxygen insulating layer.

2. The electrolyte for a negative electrodeless sodium battery according to claim 1, characterized in that, The first anionic component includes Na[HCB9H9], Na[HCB] 11 H 12 ]、Na[HCB 11 H 11 or one or more of its derivatives.

3. The electrolyte for a negative electrodeless sodium battery according to claim 1, characterized in that, The concentration of the first anionic component is 0.2–2.0 mol / L, preferably 0.5–1.5 mol / L; more preferably 1 mol / L.

4. The electrolyte for a negative electrodeless sodium battery according to claim 1, characterized in that, The second anionic component includes one or more of boron anion salt, sulfonamide-containing anion salt, phosphate-containing anion salt, nitrate-containing anion salt, difluorooxalate-borate anion salt, and difluorophosphate anion salt; preferably, the second anionic component includes one or more of NaNO3, NaDFOB, NaPO2F2, NaFSI, NaTFSI, and NaBOB.

5. The electrolyte for a negative electrodeless sodium battery according to claim 1, characterized in that, The concentration of the second anionic component is 0.005–0.30 mol / L, preferably 0.01–0.10 mol / L, and more preferably 0.02–0.05 mol / L.

6. The electrolyte for a negative electrodeless sodium battery according to claim 1, characterized in that, The second anionic component accounts for 0.5% to 25% of the total molar amount of anions, preferably 1% to 12%.

7. The electrolyte for a negative electrodeless sodium battery according to claim 1, characterized in that, The solvent is an ether solvent, preferably one or more of DME, G2 (diethylene glycol dimethyl ether), G3 (triethylene glycol dimethyl ether), 1,3-dioxolane, and tetraethylene glycol dimethyl ether.

8. A method for preparing an electrolyte for a negative electrode-free sodium battery according to any one of claims 1-7, characterized in that, The process includes the following steps: (1) dissolving the first anionic component in a solvent in an inert atmosphere to obtain the main electrolyte; (2) adding the second anionic component to the main electrolyte and stirring for 2 to 24 hours to obtain a uniform and transparent dual anionic synergistic electrolyte.

9. A sodium battery without a negative electrode, characterized in that, Includes a positive electrode, an electrolyte for a negative electrodeless sodium battery as described in any one of claims 1-7, a separator, and a negative electrode current collector.

10. The sodium-ion battery without a negative electrode according to claim 9, characterized in that, The positive electrode is one or more of NFPP sodium iron pyrophosphate, Prussian blue, layered oxides, and polyanionic positive electrodes. Preferably, the negative electrode current collector includes carbon-coated aluminum foil, bare aluminum foil, copper foil, stainless steel foil, nickel foil, or a current collector whose surface is modified by carbon / metal / oxide; The negative electrode current collector does not contain pre-filled metallic sodium.

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