Electrolyte additive for a non-negative electrode alkali metal battery and use thereof

Abstract

This invention relates to the field of electrochemical energy storage technology, and in particular to an electrolyte additive for a negative electrode-free alkali metal battery and its application. It provides a silanoamine alkali metal salt with the general formula M[N(SiR1R2R3)2] as an electrolyte additive (M is Na / K / Li, R is C1-C6 alkyl, concentration 0.01-1.0M), and also discloses an electrolyte containing this additive, a negative electrode-free alkali metal battery, and a method for gas-free sodium replenishment. This additive can operate at 2.6-3.0V (vs. M). + Under conditions of oxidation and alkali replenishment without gas, this method induces the formation of a dense SEI film rich in fluorides and nitrides, providing both alkali replenishment and interface stabilization. Using this method, a sodium-ion coin cell without a negative electrode retains over 92.8% capacity after 100 cycles at 1C, and a 1.6Ah pouch cell retains 89.6% capacity after 500 cycles at 1C. No fire or explosion was observed during nail penetration testing, demonstrating process compatibility and broad applicability.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to an electrolyte additive for negative electrode-free alkali metal batteries and its application. Background Technology

[0002] Alkali metal ion batteries (such as sodium-ion and potassium-ion batteries) are considered an important complement to lithium-ion batteries in large-scale energy storage due to their high abundance in the Earth's crust and low cost. Among them, the anode-free metal battery (AFMB) configuration completely eliminates the initial negative electrode active material (such as metal or hard carbon), using only a bare current collector as the negative electrode substrate. During the first charge, alkali metal ions from the positive electrode are extracted and deposited on the current collector, forming a metal negative electrode in situ. This configuration maximizes the battery's energy density and reduces manufacturing costs.

[0003] However, the core challenge facing AFMBs lies in their limited alkali metal "stockpile". During cycling, continuous interfacial side reactions, reconstruction of the solid electrolyte interphase (SEI) membrane, and the formation of "dead" metals irreversibly consume the limited alkali metals from the cathode, leading to rapid capacity decay and shortened cycle life.

[0004] To compensate for the loss of active alkali metals, researchers have attempted to introduce "alkali metal compensating additives." Traditional compensating additives, such as oxalates, carbonates, citrates, or nitrites, are typically premixed in solid form in the positive electrode. However, these additives suffer from problems such as high decomposition potentials, potential window mismatch with commonly used electrolytes (especially ethers), and the generation of gases (such as CO2, O2, and NO2) during decomposition. Gas release can disrupt the integrity of the electrode structure and may react with the metal on the negative electrode side, further consuming the active material and forming a thick passivation layer.

[0005] Recently, electrolyte-soluble compensating additives (such as thiocyanates) have emerged, which can achieve compensation through simple electrolyte injection, making the operation convenient. However, such additives may still trigger unfavorable interfacial side reactions, forming an interfacial layer with poor ionic conductivity, or fail to effectively inhibit dendrite growth, thus limiting their long-term cycling stability in AFMBs.

[0006] Therefore, developing an electrolyte-soluble alkali metal compensating additive that can decompose at a suitable potential, does not produce gas, and simultaneously stabilizes the electrode interface is crucial for promoting the practical application of electrodeless alkali metal batteries. Summary of the Invention

[0007] To overcome the above-mentioned defects of the prior art, the present invention provides an electrolyte additive for a non-anode alkali metal battery and its application to solve the problems existing in the above-mentioned background art.

[0008] The present invention provides the following technical solutions: An electrolyte additive for a non-anode alkali metal battery, wherein the additive is a silylamino alkali metal salt represented by the general formula (I): Wherein, M is an alkali metal, selected from at least one of Na, K, and Li; R1, R2, and R3 are each independently selected from C1-C6 alkyl groups; the concentration of the additive in the electrolyte is 0.01M to 1.0M, preferably 0.05M to 0.5M.

[0009] Further, M is Na, and the additive is sodium bis(trimethylsilyl)amide (NaHMDS) or potassium bis(trimethylsilyl)amide (KHMDS), and the concentration is 0.1M to 0.3M.

[0010] An electrolyte comprising an organic solvent, an alkali metal salt, and the electrolyte additive according to any one of the above; the organic solvent is an ether solvent, selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,2-dimethoxyethane, and tetrahydrofuran; the alkali metal cation in the alkali metal salt is the same as the alkali metal M in the electrolyte additive, and is selected from one or more of hexafluorophosphate, perchlorate, bis(trifluoromethanesulfonyl)imide salt, bis(fluorosulfonyl)imide salt, and bis(pentafluoroethylsulfonyl)imide salt.

[0011] A non-anode alkali metal battery comprising a positive electrode, a negative electrode current collector, a separator disposed between the positive electrode and the negative electrode current collector, and an electrolyte, wherein the electrolyte is the above-mentioned electrolyte; the alkali metal battery is a non-anode sodium battery or a non-anode potassium battery; the positive electrode comprises a positive electrode active material capable of reversibly intercalating and deintercalating alkali metal ions; the negative electrode current collector is one of copper foil, aluminum foil, carbon-coated aluminum foil, and carbon-coated copper foil, and its surface can be modified with one or more of carbon nanomaterials, metal particles, nitrides, or phosphides.

[0012] Further, the positive electrode active material is a polyanionic compound, selected from one or more of phosphates, pyrophosphates, and sulfates, specifically or ; or the positive electrode active substance is a sodium-compensated P2-type layered oxide of the general formula (0.05 < x ≤ 0.4).

[0013] The electrolyte additive is used in the preparation of a negative electrode-free alkali metal battery. The additive is also used to: compensate for the loss of active alkali metals during battery cycling; participate in the formation or improvement of the solid electrolyte interphase (SEI) film on the surface of the negative electrode current collector of the battery, promote the formation of an inorganic SEI film rich in alkali metal fluorides and / or alkali metal nitrides; inhibit the growth of alkali metal dendrites and reduce the formation of "dead" alkali metals.

[0014] A method for sodium replenishment in a negative electrode-free alkali metal battery involves decomposing a silanol alkali metal salt additive in the electrolyte via electrochemical oxidation to achieve sodium compensation, and this compensation process does not produce gaseous byproducts; the silanol alkali metal salt additive is the compound of general formula (I).

[0015] Furthermore, the silanoamine alkali metal salt is sodium bis(trimethylsilyl)amino (NaHMDS), with a concentration of 0.1 M to 0.3 M in the electrolyte and an electrochemical oxidation potential of 2.6 V to 3.0 V vs. Na. + / Na.

[0016] Furthermore, the organic solvent is diethylene glycol dimethyl ether, the alkali metal salt is sodium hexafluorophosphate (NaPF6) at a concentration of 1M, and the electrolyte additive is 0.2M sodium bis(trimethylsilyl)amino (NaHMDS).

[0017] Furthermore, the battery is a sodium-filled pouch battery without a negative electrode, and the positive electrode uses a double-sided coated high-load electrode. Electrode, total load approximately The negative electrode current collector is carbon-coated aluminum foil (Al@C), and the battery operating voltage range is 1.5V to 3.8V.

[0018] The technical effects and advantages of this invention are as follows: No gas compensation: The silanol alkali metal salt additive of the present invention operates at a relatively low potential (e.g., for NaHMDS, approximately 2.6V to 3.0V vs. M). + Electrochemical oxidation occurs under / M) to achieve alkali metal compensation, and the process does not produce gaseous byproducts, thus avoiding electrode structure damage and safety hazards caused by gas release.

[0019] Dual function: This additive not only provides an additional source of active alkali metals, but also their oxidation products (such as HMDS) - Free radicals and their subsequent reaction products can effectively participate in the formation of interfacial films, inducing the formation of a thin, dense layer rich in inorganic substances (such as NaF, NaN) on the surface of the negative electrode current collector. This SEI film exhibits excellent mechanical properties and promotes uniform alkali metal deposition, inhibits dendrite and "dead" metal formation, and reduces electrolyte consumption in subsequent cycles.

[0020] Interface stability: By optimizing the composition and structure of the SEI film, the coulombic efficiency of alkali metal deposition / stripping is significantly improved, thereby greatly extending the cycle life of the anode-free battery.

[0021] Process compatibility: As an electrolyte additive, it can be introduced through conventional electrolyte injection processes without changing existing electrode preparation or battery assembly processes, making it easy to achieve industrial application.

[0022] Universality: This strategy is applicable to different alkali metal systems (sodium, potassium) and different cathode materials, and has a wide range of applicability. Attached Figure Description

[0023] Figure 1 This is a comparison graph showing the cycle performance of the negative electrode-free sodium batteries of Example 1 and Comparative Examples 1 and 2 at a 1C rate. Figure 2 A needle penetration test diagram of an Ah-grade sodium-filled soft-pack battery without a negative electrode using the additive of the present invention. Figure 3 A voltage-temperature curve of an Ah-grade negative electrode-free sodium soft-pack battery using the additive of the present invention during a nail penetration test. Figure 4 The XPS spectra of the negative electrode surfaces of Example 1 and Comparative Example 1 after 50 cycles are shown. Detailed Implementation

[0024] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0025] Example 1: Preparation of electrolyte and negative electrode-free sodium coin cell Basic electrolyte (Pristine): In an argon glove box, dissolve 1M NaPF6 in diethylene glycol dimethyl ether (DEGDME) solvent and stir until homogeneous.

[0026] Electrolyte with additives: Add 0.2M sodium bis(trimethylsilyl)amino (NaHMDS) to the above basic electrolyte and stir until homogeneous.

[0027] Positive electrode preparation: Active material NFPP, conductive carbon black, carbon nanotubes and binder PVDF are mixed in N-methylpyrrolidone (NMP) at a mass ratio of 92:3:1:4 to form a slurry, which is then coated on carbon-coated aluminum foil, dried, rolled and cut into positive electrode sheets.

[0028] Battery assembly: Using Al@C (graphite-coated aluminum foil) as the negative electrode current collector, Whatman GF / A glass fiber separator, and injecting 80 μL of the above-mentioned electrolyte containing additives, the CR2032 coin cell is assembled in an argon glove box.

[0029] Comparative Example 1 The same basic electrolyte and battery assembly process as in Example 1 were used, but instead of adding NaHMDS, 0.1M NaSCN was added as an additive.

[0030] Comparative Example 2 The same basic electrolyte and battery assembly process as in Example 1 were used, but no compensating additives were added to the electrolyte. Instead, 10 wt% NaNO2 was incorporated as a positive electrode compensator during the preparation of the positive electrode slurry.

[0031] Performance testing The negative electrodeless sodium batteries assembled in Example 1 and Comparative Examples 1 and 2 were tested at a 1C rate (1C = 100 mAg). -1 A constant current charge-discharge test was performed at a voltage range of 1.5V-3.8V. The results are as follows: Figure 1 As shown, the battery of Example 1 exhibits excellent cycle stability, with a capacity retention rate of over 92.8% after 100 cycles. In contrast, the batteries of Comparative Example 1 (NaSCN) and Comparative Example 2 (NaNO2) showed faster capacity decay, with capacity retention rates of 84.3% and 81.7%, respectively, after 100 cycles.

[0032] Interface Analysis The battery was disassembled after 50 cycles, and the negative electrode current collector was analyzed by XPS. Results ( Figure 4 The results show that the NaF signal is stronger in the F1s spectrum of the negative electrode surface of Example 1. This indicates that the decomposition products of NaHMDS participate in the formation of an inorganic-rich and highly stable SEI film. In contrast, a thicker interface layer with higher impedance formed by sulfur-containing species was detected on the negative electrode surface of Comparative Example 1 (NaSCN).

[0033] Pouch batteries and safety testing High-load NFPP cathode with double-sided coating (total loading ~30 mg / cm³) -2 Sodium-based, electrodeless pouch cells with a capacity of approximately 1.6 Ah were assembled using Al@C current collectors and an electrolyte containing 0.4 M NaHMDS. After 500 cycles at 1C, the battery retained 89.6% of its capacity. A nail penetration test was performed on the fully charged pouch cells. Figure 2 The battery voltage dropped rapidly to 0V, but the highest temperature only rose to about 65°C. No fire or explosion occurred, demonstrating good safety performance.

[0034] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An electrolyte additive for negative electrode-less alkali metal batteries, characterized in that, The additive is a silanol alkali metal salt of general formula (I): Wherein, M is an alkali metal selected from at least one of Na, K, and Li; R1, R2, and R3 are each independently selected from C1-C6 alkyl groups; the concentration of the additive in the electrolyte is 0.01M to 1.0M, preferably 0.05M to 0.5M.

2. The electrolyte additive for a negative electrode-free alkali metal battery according to claim 1, characterized in that, M is Na, and the additive is sodium bis(trimethylsilyl)amino (NaHMDS) or potassium bis(trimethylsilyl)amino (KHMDS), with a concentration of 0.1M to 0.3M.

3. An electrolyte, characterized in that, The electrolyte comprises an organic solvent, an alkali metal salt, and the electrolyte additive as described in claim 1 or 2; the organic solvent is an ether solvent selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,2-dimethoxyethane, and tetrahydrofuran; the alkali metal cation in the alkali metal salt is the same as the alkali metal M in the electrolyte additive, and is selected from one or more of hexafluorophosphate, perchlorate, bis(trifluoromethanesulfonyl)imide salt, bis(fluorosulfonyl)imide salt, and bis(pentafluoroethylsulfonyl)imide salt.

4. A negative electrode-free alkali metal battery, comprising a positive electrode, a negative electrode current collector, a separator disposed between the positive electrode and the negative electrode current collector, and an electrolyte, characterized in that, The electrolyte is the electrolyte according to claim 3; the alkali metal battery is a negative electrode-free sodium battery or a negative electrode-free potassium battery; the positive electrode contains a positive electrode active material capable of reversibly intercalating and deintercalating alkali metal ions; the negative electrode current collector is one of copper foil, aluminum foil, carbon-coated aluminum foil, and carbon-coated copper foil, and its surface may be modified with one or more of carbon nanomaterials, metal particles, nitrides, or phosphides.

5. The negative electrode-free alkali metal battery according to claim 4, characterized in that, The positive electrode active material is a polyanionic compound, selected from one or more of phosphates, pyrophosphates, and sulfates, specifically Na4Fe3(PO4)2P2O7 (NFPP) or Na3V2(PO4)3 (NVP); or the positive electrode active material is a sodium-compensated P2-type layered oxide with the general formula (0.05 < x ≤ 0.4).

6. The use of the electrolyte additive according to claim 1 or 2 in the preparation of a negative electrode-free alkali metal battery, characterized in that, The additive is also used to: compensate for the loss of active alkali metals during battery cycling; participate in the formation or improvement of the solid electrolyte interphase (SEI) film on the surface of the negative electrode current collector of the battery, promote the formation of an inorganic SEI film rich in alkali metal fluorides and / or alkali metal nitrides; inhibit the growth of alkali metal dendrites and reduce the formation of "dead" alkali metals.

7. A method for sodium replenishment in a negative electrode-free alkali metal battery, characterized in that, Sodium compensation is achieved by decomposing the silanol alkali metal salt additive in the electrolyte through electrochemical oxidation, and the compensation process does not produce gaseous byproducts; the silanol alkali metal salt additive is the compound of general formula (I) as described in claim 1 or 2.

8. The sodium supplementation method according to claim 7, characterized in that, The silanoamine alkali metal salt is sodium bis(trimethylsilyl)amino (NaHMDS), with a concentration of 0.1 M to 0.3 M in the electrolyte and an electrochemical oxidation potential of 2.6 V to 3.0 V vs. Na. + / Na.

9. The electrolyte according to claim 3, characterized in that, The organic solvent is diethylene glycol dimethyl ether, the alkali metal salt is sodium hexafluorophosphate (NaPF6) at a concentration of 1M, and the electrolyte additive is 0.2M sodium bis(trimethylsilyl)amino (NaHMDS).

10. The negative electrode-free alkali metal battery according to claim 4, characterized in that, The battery is a negative electrode-free sodium soft-pack battery. The positive electrode uses a double-coated high-load Na4Fe3(PO4)2P2O7 (NFPP) electrode sheet with a total loading of approximately 30 mg / cm³. -2 The negative electrode current collector is carbon-coated aluminum foil (Al@C), and the battery operating voltage range is 1.5V to 3.8V.

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