Non-aqueous electrolyte and sodium-ion battery thereof

Abstract

This invention discloses a non-aqueous electrolyte and its sodium-ion battery. The non-aqueous electrolyte of this invention comprises a sodium salt, a non-aqueous organic solvent, and additives, the additives including compound A as shown in structural formula I. Compound A in the non-aqueous electrolyte of this invention, with its isosorbide ester cyclic structure, endows the electrolyte with excellent oxidation resistance and weak solvation ability. Simultaneously, the fluorosulfonic acid group can effectively participate in the film-forming reaction at the electrode interface, increasing the content of inorganic components such as sulfur and fluorine in the SEI film, thereby significantly enhancing interfacial stability and effectively improving the room-temperature cycling performance and high-temperature storage performance of the sodium-ion battery. Structural formula I.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a non-aqueous electrolyte and its sodium-ion battery. Background Technology

[0002] Sodium-ion batteries, as a new generation of electrochemical energy storage system, have broad application prospects in large-scale energy storage due to their abundant resources and controllable costs. However, sodium-ion batteries still face many technical bottlenecks in practical applications, especially the insufficient interfacial compatibility between the electrolyte and electrode materials, which makes it difficult to meet commercialization requirements in terms of cycle life and high-temperature stability. Traditional electrolyte systems typically use a combination of carbonate solvents and sodium salts (such as NaPF6). This type of system easily forms an unstable solid electrolyte interphase (SEI) film in sodium-ion batteries, causing continuous interfacial side reactions and electrolyte decomposition, thereby affecting the long-term cycle performance of the battery.

[0003] In sodium-ion batteries, the reactivity between electrode materials and electrolytes is typically higher than in lithium-ion systems. If the SEI film has a porous structure or unstable composition, sodium ions will exacerbate interfacial side reactions during insertion and extraction, leading to decreased coulombic efficiency and capacity decay. Furthermore, conventional electrolyte systems often generate interfacial components dominated by organic matter during film formation. These SEI films have low mechanical strength and poor ionic conductivity, making it difficult to effectively suppress further electrolyte decomposition and sodium dendrite growth. Especially under high-temperature conditions, interfacial side reactions intensify, severely impacting the battery's cycle life and safety performance.

[0004] Currently, adding conventional film-forming additives (such as FEC and VC) can optimize the organic components of SEI films to some extent, but it is difficult to effectively control their inorganic component content. Studies have shown that SEI films rich in inorganic components such as sulfur and fluorine (such as NaF and Na2S) have higher ion conductivity and interfacial stability, which can significantly suppress side reactions and improve the high-temperature performance of batteries. However, traditional additives lack functional groups in their molecular structure that simultaneously possess oxidation resistance and weak solvation ability, making it difficult to directionally induce the enrichment of inorganic phases on the negative electrode surface, thus limiting further improvement in SEI film performance.

[0005] Therefore, there is an urgent need to develop a non-aqueous electrolyte and its sodium-ion battery to address the shortcomings of existing technologies. Summary of the Invention

[0006] In view of the above problems, the purpose of this invention is to provide a non-aqueous electrolyte and a sodium-ion battery thereof. The non-aqueous electrolyte contains compound A, whose molecular structure contains both an isosorbide ester cyclic structure and a fluorosulfonic acid group. The synergistic effect of these two components can effectively improve the room-temperature cycling performance and high-temperature storage performance of the sodium-ion battery.

[0007] To achieve the above objectives, the present invention provides a non-aqueous electrolyte comprising a sodium salt, a non-aqueous organic solvent, and an additive, wherein the additive comprises compound A as shown in structural formula I.

[0008] Structural formula I.

[0009] Compared with existing technologies, the additive in the non-aqueous electrolyte of this invention includes compound A as shown in structural formula I, compound A being isosorbide bis(fluorosulfonic acid) ester. On one hand, the introduction of isosorbide bis(fluorosulfonic acid) ester optimizes the electrolyte-electrode interface, forming a dense interface layer with high ionic conductivity containing sulfur and fluorine, effectively protecting the electrode material during long-term cycling. On the other hand, the cyclic isosorbide ester structure in isosorbide bis(fluorosulfonic acid) ester exhibits excellent oxidation resistance and weak solvation ability. Its unique spatial configuration effectively weakens the solvation effect of sodium ions. Simultaneously, the fluorosulfonic acid groups preferentially decompose at the reduction potential, directionally releasing sulfur and fluorine-containing active components at the electrode interface, promoting the formation of a stable SEI film rich in inorganic components such as NaF and Na2S. This inorganic-rich interface layer with high ionic conductivity significantly inhibits the continuous decomposition of the electrolyte, reduces active sodium loss, and thus effectively improves the room-temperature cycling performance and high-temperature storage performance of sodium-ion batteries.

[0010] Specifically, compound A of the present invention can be prepared according to the following synthetic route:

[0011] Preferably, the mass percentage of compound A in the non-aqueous electrolyte is 0.5% to 3.0%. Specifically, the mass percentage of compound A in the non-aqueous electrolyte can be, but is not limited to, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, or 3.0%.

[0012] Preferably, the sodium salt of the present invention is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium methanesulfonate (NaCH3SO3), sodium trifluoromethanesulfonate (NaCF3SO3), sodium bis(trifluoromethanesulfonyl)imide (NaN(CF3SO2)2), sodium di(oxalate)borate (C4BNaO8), sodium di(fluorooxalate)borate (C2BF2NaO4), sodium difluorophosphate (NaPO2F2), sodium di(fluoro)oxalate phosphate (NaDFBP), sodium bis(fluoromethanesulfonyl)imide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0013] Preferably, the mass percentage of the sodium salt in the non-aqueous electrolyte of the present invention is 8% to 20%. Specifically, the mass percentage of the sodium salt in the non-aqueous electrolyte may be, but is not limited to, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0014] Preferably, the non-aqueous organic solvent of the present invention is selected from at least one of cyclic carbonates, chain carbonates, cyclic and chain carboxylic esters, ether compounds and sulfone compounds.

[0015] Further, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte is 65% to 90%. Specifically, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte can be, but is not limited to, 65%, 70%, 75%, 78%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, and 90%. Among these, cyclic carbonates include, but are not limited to, ethylene carbonate, ethylene carbonate, propylene carbonate, and butyl carbonate; chain carbonates include, but are not limited to, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, methyl ethyl carbonate, methyl-n-propyl carbonate, n-butyl methyl carbonate, isobutyl methyl carbonate, tert-butyl methyl carbonate, ethyl-n-propyl carbonate, n-butyl ethyl carbonate, isobutyl ethyl carbonate, and tert-butyl ethyl carbonate, preferably dimethyl carbonate and diethyl carbonate. Dipropyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, methyl ethyl carbonate, methyl-n-propyl carbonate, particularly preferably dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; cyclic carboxylic acid esters include, but are not limited to, γ-butyrolactone, γ-valerolactone, γ-caprolactone, and ε-caprolactone; chain carboxylic acid esters include, but are not limited to, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, and isopropyl propionate. Esters, including but not limited to butyl propionate, isobutyl propionate, tert-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, and isopropyl isobutyrate; ether compounds include, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether; sulfone compounds include, but are not limited to, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, and isopropyl... methyl sulfone, n-butyl methyl sulfone, tert-butyl methyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, trifluoromethyl-n-propyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-tert-butyl sulfone, trifluoromethyl-n-butyl sulfone, trifluoromethyl-tert-butyl sulfone.

[0016] Preferably, the non-aqueous electrolyte of the present invention further includes an additive selected from at least one of vinylene carbonate (VC), vinylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), and vinyl sulfate (DTD).

[0017] Preferably, the mass percentage of the auxiliary agent in the non-aqueous electrolyte is 0.1% to 5%. Specifically, the mass percentage of the auxiliary agent in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%.

[0018] On the other hand, the present invention provides a sodium-ion battery, comprising a positive electrode material, a negative electrode material, and the aforementioned non-aqueous electrolyte.

[0019] Preferably, the positive electrode active material is selected from at least one of layered oxides, Prussian blue compounds, and polyanion-type compounds. Specifically, the chemical formula of the layered oxide can be Na x MO2, where 0.8 ≤ x ≤ 1.1, and M can be transition metals such as nickel, cobalt, iron, manganese, etc. The chemical formula of the Prussian blue compound can be Na x M(Fe(CN)6) y ·nH2O, where 1 < x ≤ 2, 0 < y ≤ 1, 0 < n < 14, and M can be transition metal ions such as Fe, Mn, Co, Ni, Cu, etc. The polyanion-type compound is composed of (XO4) n- anion units or their derivative groups (X m O 3m+1 ) n- (X = B, S, P, Si, As, Mo, W, etc.) and transition metal-oxygen polyhedron units (MO x ) to form a class of compounds with a structure. The polyanion-type compound can be a phosphate-type polyanion compound, a pyrophosphate-type polyanion compound, a fluorophosphate-type polyanion compound, or a sulfate-type polyanion compound. Preferably, the positive electrode active material is a polyanion-type compound. Further preferably, the positive electrode active material is sodium iron pyrophosphate Na4Fe3(PO4)2(P2O7), which has a three-dimensional framework structure that can provide a wide tunnel network for the transportation of sodium ions to promote ion migration to the electrode surface.

[0020] Preferably, the negative electrode active material is selected from at least one of carbon-based negative electrode materials, metal alloy-based negative electrode materials, metal oxides, metal sulfides, titanium-based negative electrode materials, and organic negative electrode materials. Specifically, the carbon-based negative electrode material can be hard carbon and soft carbon. The metal alloy-based negative electrode material can be antimony (Sb), tin (Sn), lead (Pb), and their alloys, etc. The metal oxide can be Fe2O3, CuO, Sb2O3, etc. The metal sulfide can be Cu2S, Ni3S2, FeS2, etc. The titanium-based negative electrode material can be Na2Ti6O 12Examples of suitable anode materials include Na₂Ti₃O₇ and NaTi₂(PO₄)₃. Organic anode materials can be organic polymers with N-type doping properties and some small organic molecule compounds with conjugated structures, such as polythiophene derivatives, poly(p-phenylene), sodium organic carboxylate, and quinone compounds. Preferably, the active anode material is hard carbon. Detailed Implementation

[0021] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0022] Example 1 (1) Preparation of non-aqueous electrolyte In an argon-filled glove box (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in a weight ratio of EC:EMC:PC = 1:1:1 to prepare 86.5 g of non-aqueous organic solvent. Then, 0.5 g of compound A was added, dissolved, and stirred thoroughly. After that, 13.0 g of sodium hexafluorophosphate was added and mixed evenly to obtain a non-aqueous electrolyte.

[0023] (2) Preparation of positive electrode Na4Fe3(PO4)2(P2O7), binder PVDF and conductive agent SuperP are mixed evenly at a mass ratio of 96:2:2 to prepare a sodium-ion battery positive electrode slurry of a certain viscosity. The mixed slurry is coated on both sides of aluminum foil, dried and rolled to obtain the positive electrode sheet.

[0024] (3) Preparation of negative electrode Hard carbon material is mixed with conductive agent SuperP, thickener CMC and binder SBR (styrene-butadiene rubber latex) in a mass ratio of 95:3:2 to form a slurry. The mixture is then coated on both sides of copper foil, dried and rolled to obtain the negative electrode sheet.

[0025] (4) Preparation of sodium-ion batteries The positive electrode, separator, and negative electrode are wound together to form a soft-pack battery cell, which is then packaged in a polymer aluminum-plastic film and filled with the sodium-ion battery non-aqueous electrolyte prepared above. After formation, capacity testing, and other processes, a sodium-ion battery is manufactured.

[0026] The non-aqueous electrolyte formulations for Examples 2-11 and Comparative Examples 1-3 are shown in Table 1. The steps for preparing the electrolyte and manufacturing the battery are the same as in Example 1.

[0027] Table 1. Non-aqueous electrolyte formulations for Examples 2-11 and Comparative Examples 1-3

[0028] In Table 1, EA refers to ethyl acetate; the structural formulas of compounds B and C are shown below:

[0029] Compound B

[0030] Compound C The non-aqueous electrolytes prepared in Examples 1-11 and Comparative Examples 1-3 were tested for oxidation resistance and weak solvation performance. The sodium-ion batteries prepared were subjected to high-temperature storage test and room-temperature cycling test, respectively. The specific test conditions are as follows, and the performance test results are shown in Table 2.

[0031] (1) High-temperature storage performance test Under normal temperature (25℃) conditions, a sodium-ion battery was subjected to one 0.5C / 0.5C charge and discharge cycle (battery discharge capacity recorded as C0), with an upper limit voltage of 3.4V. The battery was then placed in a 60℃ oven for 30 days, removed, and placed in a 25℃ environment for a 0.5C discharge, with the discharge capacity recorded as C1. The sodium-ion battery was then subjected to another 0.5C / 0.5C charge and discharge cycle (battery discharge capacity recorded as C2). The capacity retention rate and capacity recovery rate of the sodium-ion battery were calculated using the following formulas.

[0032] Capacity retention rate = C1 / C0 × 100% Capacity recovery rate = C2 / C0 × 100% (2) Room temperature cycling performance test The sodium-ion battery was charged at a constant current of 1C to a voltage of 3.6V, then charged at a constant voltage of 3.6V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 1.5V. The first discharge capacity of the battery was recorded as C0. This constitutes one charge-discharge cycle. After 300 cycles, the discharge capacity was recorded as C1. The capacity retention rate of the sodium-ion battery was calculated using the following formula.

[0033] Capacity retention rate = C1 / C0 × 100% (3) Oxidation resistance The oxidation resistance of lithium-ion battery electrolytes was tested using a three-electrode linear sweep voltammetry (LSV) method. A platinum electrode was used as the working electrode, a lithium foil as the reference electrode, and a lithium foil as the counter electrode. The three-electrode test system was assembled in an argon glove box. Before testing, the platinum electrode surface was polished, cleaned, and dried to ensure cleanliness. The assembled three-electrode system was allowed to stand for 2 hours at room temperature (25°C) to reach a stable state. Subsequently, linear sweep voltammetry was performed using an electrochemical workstation, with a scanning voltage range of 3.0–7.0 V vs. Li / Li. +The scan rate was 1.0 mV / s, and the current-voltage variation curve was recorded. When the current density reached 0.1 mA / cm²... 2 The corresponding potential is recorded as the oxidation decomposition potential of the electrolyte. The higher the oxidation decomposition potential, the better the oxidation stability of the electrolyte.

[0034] (4) Weak solvation properties Batteries with the same system were assembled using different electrolytes; the batteries were graphite||Li half-cells. After assembly, the batteries were left to stand at 25°C for 12 hours to allow the electrolyte to fully wet the electrodes. Then, 10 charge-discharge cycles were performed to form a negative electrode interface film. After formation, the batteries were adjusted to 50% SOC. The batteries were then placed in environments at different temperatures, 25°C and -20°C, and kept at these temperatures for at least 2 hours to allow the batteries to reach thermal equilibrium. EIS tests were performed at these temperatures, with a test frequency range of 100kHz to 10mHz and an AC disturbance voltage of 5 to 10mV. The charge transfer impedance Rct was obtained by fitting a Nyquist plot. A simplified equivalent circuit was used: Rs (Rct∣∣CPE) W Where Rs is the ohmic impedance; Rct is the charge transfer impedance; CPE is the constant phase element; and W is the diffusion impedance.

[0035] Calculate the low-temperature impedance growth factor: K = Rct(-20℃) / Rct(25℃) K represents the low-temperature impedance growth factor. A smaller K value indicates a smaller increase in Rct at low temperatures. + Desolvation is less affected by temperature, and electrolytes have better weak solvation performance.

[0036] Table 2 Performance test results of sodium-ion batteries in Examples 1-11 and Comparative Examples 1-3

[0037] As shown in Table 2, the sodium-ion batteries in Examples 1-11 exhibited superior high-temperature storage performance and room-temperature cycle capacity retention. This is primarily due to the simultaneous addition of compound A to the sodium-ion batteries in these examples. Compound A can create a weakly solvating and oxidation-resistant sodium-ion atmosphere and preferentially participates in film formation, thereby increasing the content of inorganic components sulfur and fluorine in the SEI film formed at the electrolyte-electrode interface, improving the stability of the SEI film, and thus effectively enhancing the room-temperature cycle performance and high-temperature storage performance of the sodium-ion battery. Examples 1-5 show that the performance of compound A gradually increases with increasing addition amount, but begins to decline when the addition amount exceeds 2%. Furthermore, Examples 1 and 9-11 demonstrate that compound A can be used in combination with other commonly used electrolyte additives, showing promise for large-scale application.

[0038] As shown in Comparative Example 2, when compound B is used, all battery performance deteriorates because compound B contains the active hydroxyl group. As shown in Comparative Example 3, when compound C is used, the battery performance is improved compared to Comparative Example 1, but all performance is still not as good as Example 1 containing compound A.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A nonaqueous electrolyte comprising a sodium salt, a nonaqueous organic solvent, and an additive, characterized in that, The additive includes compound A as shown in structural formula I. Structural formula I.

2. The nonaqueous electrolyte according to claim 1, characterized by The mass percentage of compound A in the non-aqueous electrolyte is 0.5-3%.

3. The nonaqueous electrolyte according to claim 1, wherein The sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium methanesulfonate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium di(oxalate)borate, sodium di(fluorooxalate)borate, sodium difluorophosphate, sodium di(fluorobis(oxalate))phosphate, sodium bis(trifluoromethanesulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

4. The non-aqueous electrolyte according to claim 1, characterized in that, The sodium salt constitutes 8% to 20% of the mass of the non-aqueous electrolyte.

5. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of cyclic carbonates, chain carbonates, cyclic carboxylic esters, chain carboxylic esters, ether compounds, and sulfone compounds.

6. The non-aqueous electrolyte according to claim 1, characterized in that, It also includes an additive selected from at least one of vinylene carbonate, vinylene carbonate, fluorovinyl carbonate, vinyl sulfite, 1,3-propanesulfonate lactone, and vinyl sulfate.

7. The non-aqueous electrolyte according to claim 5, characterized in that, The mass percentage of the additive in the non-aqueous electrolyte is 0.1-5%.

8. A sodium-ion battery, characterized in that, It includes positive electrode materials, negative electrode materials, and the non-aqueous electrolyte as described in any one of claims 1 to 7.

9. The sodium-ion battery according to claim 8, characterized in that, The positive electrode active material is selected from at least one of layered oxides, Prussian blue compounds, and polyanionic compounds.

10. The sodium-ion battery according to claim 8, characterized in that, The negative electrode active material is selected from at least one of carbon-based negative electrode materials, metal alloy negative electrode materials, metal oxides, metal sulfides, titanium-based negative electrode materials, and organic negative electrode materials.

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