Flame-retardant electrolyte constructed by synergistic effect of phosphate-based solvent and double salt
By introducing phosphate ester solvent and strong binding energy auxiliary salt into the sodium-ion battery electrolyte, the problems of flammability and thermal stability of traditional electrolytes are solved, achieving high safety and long cycle stability of the battery, especially its excellent performance under high pressure and high temperature conditions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HEBEI UNIV OF TECH
- Filing Date
- 2026-03-10
- Publication Date
- 2026-05-29
AI Technical Summary
Traditional sodium-ion battery electrolytes have poor thermal stability and high flammability, posing serious safety hazards. They also pose significant safety risks to the batteries under harsh conditions such as mechanical shock, thermal shock, overcharging, and short circuits, and the batteries have poor cycle stability.
A flame-retardant electrolyte was constructed using a phosphate ester-based solvent and a dual salt synergistic effect. By introducing a phosphate ester solvent into a carbonate solvent and adding auxiliary salts with strong binding energy, such as NaDFOB and NaNO3, the interfacial binding energy was optimized, thereby improving the flame retardancy and stability of the electrolyte.
It significantly improves the safety and electrochemical performance of sodium-ion batteries, achieving long-cycle stability and excellent performance under high voltage. The battery also exhibits excellent thermal stability and electrochemical performance at high temperatures.
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Figure CN122118073A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a sodium-ion battery electrolyte, comprising a main salt, an auxiliary salt, and an organic solvent. Background Technology
[0002] With the increasing prominence of environmental protection and sustainable energy development, the research and development of energy storage batteries that combine high safety, low cost, and environmental friendliness has become a core focus of both academia and industry. Sodium-ion batteries possess an intrinsic cost advantage due to the high abundance of raw materials in the Earth's crust and mature smelting processes. They represent a promising electrochemical energy storage technology that can replace more expensive and resource-limited lithium-ion batteries, especially to meet the growing demand for large-scale energy storage systems. Sodium-ion batteries consist of four core components: a positive electrode, a negative electrode, a separator, and an electrolyte. Among these, the electrolyte not only determines the chemical composition and microstructure of the electrode / electrolyte interface but also directly regulates ion transport kinetics, the electrochemical stability window, and the applicable temperature range. Therefore, constructing high-performance electrolytes and systematically optimizing their design strategies are crucial for advancing the commercialization of sodium-ion batteries.
[0003] As an indispensable component of batteries, the electrolyte plays a crucial role in determining the electrochemical performance of sodium-ion batteries (SIBs). Sodium-ion battery electrolytes mainly consist of sodium salts, organic solvents, and additives. Traditional carbonate and ether electrolytes are highly volatile and flammable. When batteries encounter harsh conditions such as impacts, collisions, or overcharging, they can burn, ultimately leading to thermal runaway and serious safety hazards. They also form unstable interfacial films, causing dendrite formation and resulting in poor long-cycle stability. Liu Jianwen et al., in patent (CN115000509A), proposed a design concept for a sodium-ion battery electrolyte by adding perfluorohexanone (PFH) as a flame-retardant solvent and non-polar fluorinated ethers as co-solvents to a carbonate solvent. This provides inherent non-flammability, significantly improving battery safety. Furthermore, the addition of solvent-free fluorinated ethers further reduces free carbonate solvent, effectively mitigating the continuous decomposition of carbonates on the sodium metal anode, thereby improving battery cycle performance. However, perfluorohexanone and fluoroethers are expensive, which increases the cost of electrolytes. At the same time, the poor oxidation stability of fluoroethers limits the cycle performance of sodium-ion batteries under high voltage. Summary of the Invention
[0004] The purpose of this invention is to address the problems of poor thermal stability, high volatility, and high flammability of traditional carbonate and ether electrolytes, which pose significant safety hazards to batteries under harsh conditions such as mechanical shock, thermal shock, overcharging, and short circuits. This invention proposes a flame-retardant electrolyte constructed using a phosphate ester-based solvent and a dual-salt synergistic effect. This electrolyte introduces a phosphate ester solvent into a carbonate solvent, along with strong binding energy auxiliary salts such as NaDFOB and NaNO3 to optimize the interface. The synergistic effect of the phosphate ester solvent and the strong binding auxiliary salts achieves excellent flame retardancy while significantly improving the performance of sodium-ion batteries. The electrolyte of this invention exhibits stable long-term cycling performance in transition metal layered oxide cathode materials, demonstrating excellent performance; it also exhibits excellent high-voltage cycling performance in polyanionic cathode materials (phosphate-based); and it demonstrates excellent electrochemical performance in full cells assembled from layered cathodes and hard carbon anodes.
[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: A flame-retardant electrolyte constructed by the synergistic effect of a phosphate ester-based solvent and two salts, the electrolyte comprising a sodium salt and an organic solvent; The solvent is composed of organic carbonate and phosphate solvent; based on the solvent being 100% of the total electrolyte volume, the volume of the phosphate solvent accounts for 40%-70% of the total electrolyte volume. The sodium salt comprises a main salt and a secondary salt. The main salt is sodium hexafluorophosphate (NaPF6) with a concentration of 0.70~1.00 mol / L; the secondary salt has a concentration of 0.01~0.30 mol / L. The carbonate solvent is an organic solvent containing C=O bonds: one or more of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC); The phosphate ester solvent is an organic solvent containing P=O bonds: one or both of trimethyl phosphate (TMP) and triethyl phosphate (TEP); The auxiliary salt is a sodium salt with a strong coordination ability with sodium ions and higher than that of sodium hexafluorophosphate, including sodium perchlorate (NaClO4), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), sodium difluorooxalate borate (NaDFOB), or sodium nitrate (NaNO3); preferably sodium difluorooxalate borate (NaDFOB).
[0006] Preferably, the concentration of the co-salt is 0.01-0.30 mol / L; A sodium-ion battery, which can be a half-cell or a full-cell battery; The half-cell is a battery composed of a sodium metal negative electrode and a positive electrode, a glass fiber membrane or a polyolefin membrane, a flame-retardant electrolyte constructed by the synergistic effect of the phosphate ester-based solvent and the dual salts. The full cell comprises a positive electrode, a hard carbon negative electrode, a glass fiber membrane or a polyolefin membrane, the phosphate ester-based solvent, and a flame-retardant electrolyte constructed by the synergistic effect of two salts. The positive electrode includes a positive electrode active material, which includes at least one of layered transition metal oxides and polyanionic compounds. The negative electrode includes a sodium metal half-cell negative electrode or a full-cell negative electrode, wherein the active material of the full-cell negative electrode is hard carbon (HC).
[0007] The chemical formula of the layered transition metal layered oxide is NaNi. x Fe y Mn z O2, 0<x≤1.5, 0<y≤1, 0<z≤0.75; The phosphate-based cathode material in the polyanionic compound has a chemical formula of at least one of NaFePO4, Na3V2(PO4)2F3, or Na3V2(PO4)3.
[0008] The essential features of this invention are: We selected sodium hexafluorophosphate (NaPF6), a commercially available solvent with low cost, high ionic conductivity, and high voltage stability, as the main salt. Secondly, we introduced a flame-retardant phosphate solvent into the carbonate solvent. The P=O functional groups in its molecular structure effectively inhibit combustion reactions, solving the safety issue of electrolyte flammability. It also broadens the electrochemical window, improving electrolyte stability. Furthermore, its excellent thermal stability prevents decomposition, enhancing the battery's high-temperature stability. To achieve good flame retardancy, more than 40% phosphate solvent is required. However, this high-content phosphate solvent electrolyte system has poor compatibility with the positive electrode, easily undergoing continuous decomposition and forming an unstable interfacial film. Therefore, we introduced a sodium salt with high conductivity, preferential decomposition to form a film, and strong coordination ability as an auxiliary salt. This improves the electrolyte's antioxidant capacity, optimizes the interfacial composition, and competes with the phosphate solvent for coordination, optimizing the solvation structure of the system and thus improving battery performance.
[0009] Specifically, the inherent non-flammability and thermal stability of phosphate solvents improve battery safety; the strong-binding co-salt improves the composition and structure of the positive and negative electrode interfaces while inhibiting excessive decomposition of the phosphate solvent; finally, sodium hexafluorophosphate, as a sodium salt with high antioxidant properties, plays a key role in improving the overall stability of the electrolyte and inhibiting electrolyte decomposition. The synergistic effect of sodium hexafluorophosphate and the strong-binding co-salt, when added to carbonate and phosphate solvents with strong flame retardancy and salt solubility, maintains suitable viscosity and ionic conductivity throughout the system, thus achieving a triple coupling effect of "flame retardancy-film formation-dilution".
[0010] The beneficial effects of this invention are as follows: The sodium-ion battery electrolyte provided by this invention incorporates a phosphate ester solvent into a traditional carbonate electrolyte, giving the electrolyte inherent flame retardancy and improving battery safety. The addition of sodium salts (NaClO4, NaFSI, NaTFSI, NaDFOB, or NaNO3) with high conductivity and preferential decomposition for film formation enhances the electrolyte's antioxidant capacity and improves interfacial composition. During the charge and discharge process of the sodium-ion battery, anions in the electrolyte preferentially undergo reduction / oxidation at the positive and negative electrode interfaces, generating a passivation layer rich in fluorine, boron, and phosphorus at the positive electrode interface. This inhibits transition metal dissolution and improves the battery's cycle stability. Example 1, after 500 cycles, still retains 92% of its capacity, nearly 70% higher than Comparative Example 1; even at a high voltage of 4.2V, the half-cell assembled based on the electrolyte of Example 1 exhibits a capacity of 153.1 mAh g⁻¹ in the first cycle. -1 The electrolyte exhibits high discharge capacity, retaining 83% of its initial capacity after 200 cycles, demonstrating excellent stability. Furthermore, when a half-cell is assembled using sodium vanadium phosphate cathode (Na3V2(PO4)3) and sodium metal anode, the battery using the electrolyte from Example 1 retains a high capacity retention of 93% after 2000 cycles at 4.5V. Applying the electrolyte of this invention to sodium-ion batteries demonstrates excellent flame-retardant properties. Sodium-ion batteries using this electrolyte not only exhibit excellent electrochemical performance but also significantly improved safety, showing broad application prospects. Attached Figure Description
[0011] To more clearly illustrate the optimization results in this invention, the accompanying drawings used in the prior art will be described below.
[0012] Figure 1 This is a schematic diagram of the flammability test of the present invention; Figure 2 This is the transition metal layered cathode (NaNi) tested in Example 1 of this invention. 1 / 3 Fe 1 / 3 Mn 1 / 3Cyclic performance and coulombic efficiency of a half-cell assembled with O2 and sodium metal anode at 1C rate and 2-4.0V; Figure 3 This is the transition metal layered cathode (NaNi) tested in Example 1 of this invention. 1 / 3 Fe 1 / 3 Mn 1 / 3 Cyclic performance and coulombic efficiency of a half-cell assembled with O2 and sodium metal anode at 1C rate and 2-4.2V; Figure 4 This is the transition metal layered cathode (NaNi) tested in Example 1 of this invention. 1 / 3 Fe 1 / 3 Mn 1 / 3 Cyclic performance and coulombic efficiency of a full cell assembled with O2 and hard carbon anode (HC) at 1C rate; Figure 5 This is a graph showing the cycle performance and coulombic efficiency of a half-cell assembled with sodium vanadium phosphate cathode Na3V2(PO4)3 and sodium metal anode tested in Example 1 of this invention at a 1C rate. Detailed Implementation
[0013] The technical solution of the present invention will be further illustrated below through specific embodiments.
[0014] In the embodiments of this invention, sodium hexafluorophosphate is abbreviated as NaPF6, sodium perchlorate as NaClO4, sodium bis(fluorosulfonyl)imide as NaFSI, sodium bis(trifluoromethylsulfonyl)imide as NaTFSI, sodium difluorooxalate borate as NaDFOB, sodium nitrate as NaNO3, propylene carbonate as PC, ethylene carbonate as EC, diethyl carbonate as DEC, dimethyl carbonate as DMC, methyl ethyl carbonate as EMC, trimethyl phosphate as TMP, and triethyl phosphate as TEP.
[0015] Example 1: This embodiment provides a flame-retardant phosphate ester-based electrolyte. The preparation steps of the electrolyte include: in an argon-filled glove box (moisture content < 0.01 ppm, oxygen content < 0.01 ppm), mixing the corresponding solvents in a predetermined ratio and stirring continuously, and slowly adding a predetermined amount of electrolyte sodium salt to the mixed solvent to obtain the electrolyte of Example 1. The amount of each component added in the electrolyte is shown in Table 1.
[0016] Table 1
[0017] Note: Calculated based on a total solvent volume and additive volume of 100 vt.%. The sum of the total volumes of all solvents and additives listed in the table represents the total volume of the solvent. The concentrations of the main salt and auxiliary salt mentioned are the concentrations in the electrolyte. The same applies to the following examples.
[0018] Example 2: The other steps are the same as in Example 1, except that the content of phosphate ester solvent is changed to 40%, the content of carbonate solvent 1 is changed to 30%, the content of carbonate solvent 2 is changed to 30%, the main salt and its concentration remain unchanged, and the auxiliary salt and its concentration remain unchanged.
[0019] Example 3: The other steps are the same as in Example 1, except that the phosphate ester solvent content is changed to 50%, the carbonate solvent 1 content is changed to 25%, the carbonate solvent 2 content is changed to 25%, the main salt and its concentration remain unchanged, and the auxiliary salt and its concentration remain unchanged.
[0020] Example 4: The other steps are the same as in Example 1, except that the phosphate ester solvent content is changed to 70%, the carbonate solvent 1 content is changed to 15%, the carbonate solvent 2 content is changed to 15%, the main salt and its concentration remain unchanged, and the auxiliary salt and its concentration remain unchanged.
[0021] Example 5: The other steps are the same as in Example 1, except that the phosphate ester solvent and its content remain unchanged, the carbonate solvent and its content remain unchanged, the main salt and its concentration remain unchanged, and the auxiliary salt concentration is changed to 0.05 mol / L.
[0022] Example 6: The other steps are the same as in Example 1, except that the phosphate ester solvent and its content remain unchanged, the carbonate solvent and its content remain unchanged, the main salt and its concentration remain unchanged, and the auxiliary salt concentration is changed to 0.10 mol / L.
[0023] Example 7: The other steps are the same as in Example 1, except that the phosphate ester solvent and its content remain unchanged, the carbonate solvent and its content remain unchanged, the main salt and its concentration remain unchanged, and the concentration of the auxiliary salt is changed to 0.30 mol / L.
[0024] Example 8: The other steps are the same as in Example 1, except that the phosphate ester solvent and its content remain unchanged, the carbonate solvent and its content remain unchanged, the main salt and its concentration remain unchanged, and the auxiliary salt is replaced with NaClO4 with a concentration of 0.05 mol / L.
[0025] Example 9: The other steps are the same as in Example 1, except that the phosphate ester solvent and its content remain unchanged, the carbonate solvent and its content remain unchanged, the main salt and its concentration remain unchanged, and the auxiliary salt is replaced with NaTFSI with a concentration of 0.05 mol / L.
[0026] Example 10: The other steps are the same as in Example 1, except that the phosphate ester solvent and its content remain unchanged, the carbonate solvent and its content remain unchanged, the main salt and its concentration remain unchanged, and the auxiliary salt is replaced with NaFSI with a concentration of 0.05 mol / L.
[0027] Example 11: The other steps are the same as in Example 1, except that the phosphate ester solvent and its content remain unchanged, the carbonate solvent and its content remain unchanged, the main salt and its concentration remain unchanged, and the auxiliary salt is replaced with NaNO3 with a concentration of 0.05 mol / L.
[0028] Example 12: The other steps are the same as in Example 1, except that the phosphate ester solvent is replaced with TMP, while the content remains the same; the carbonate solvent and its content remain the same; the main salt and its concentration remain the same; and the auxiliary salt and its concentration remain the same.
[0029] Example 13: The other steps are the same as in Example 1, except that the phosphate ester solvent is replaced with TMP, the content remains the same, the carbonate solvent 1 and its content remain the same, the carbonate solvent 2 is replaced with PC, the content remains the same, the main salt and its concentration remain the same, and the auxiliary salt and its concentration remain the same.
[0030] Example 14: The other steps are the same as in Example 1, except that the phosphate ester solvent is replaced with TMP with the same content, the carbonate solvent 1 is replaced with PC with the same content, the carbonate solvent 2 and its content remain unchanged, the main salt and its concentration remain unchanged, and the auxiliary salt and its concentration remain unchanged.
[0031] Comparative Example 1: The composition of the electrolyte in this comparative example is shown in Table 2 below: Table 2
[0032] Note: Calculated based on a total solvent volume and additive volume of 100 vt.%. The total volume of solvents and additives listed in the table is the sum of their total volumes.
[0033] Comparative Example 2: The composition of the electrolyte in this comparative example is shown in Table 3 below: Table 3
[0034] Note: Calculated based on a total solvent volume and additive volume of 100 vt.%. The total volume of solvents and additives listed in the table is the sum of their total volumes.
[0035] Comparative Example 3: The composition of the electrolyte in this comparative example is shown in Table 4 below: Table 4
[0036] Note: Calculated based on a total solvent volume and additive volume of 100 vt.%. The total volume of solvents and additives listed in the table is the sum of their total volumes.
[0037] I. Battery Manufacturing 1. Cathode preparation: NaNi, the positive electrode active material 1 / 3 Fe 1 / 3 Mn 1 / 3 Prepare a mixture of O2 (NFM111), conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. Mix the weighed materials thoroughly in a mortar, then add N-methyl-2-pyrrolidone (NMP) and stir to obtain the positive electrode slurry. Coat the slurry evenly onto aluminum foil, achieving an areal density of 3.2 mg / cm³. 2 After drying and cutting, the positive electrode sheet is obtained.
[0038] 2. Anode Preparation The negative electrode of the half-cell is metallic sodium: a layer of sodium metal is cut off from a block of sodium metal, wrapped in plastic wrap, and then flattened, the oxide layer is scraped off, and cut to obtain individual sodium metal negative electrode sheets with a diameter of 10 mm.
[0039] The negative electrode active material for the full battery, consisting of hard carbon HC, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, is prepared. The weighed materials are then placed in a mortar and mixed thoroughly. N-methyl-2-pyrrolidone (NMP) is then added and stirred to obtain the negative electrode slurry. The slurry is then evenly coated onto copper foil, achieving an areal density of 1.5 mg / cm³. 2 After drying and cutting, the negative electrode sheet is obtained.
[0040] 3. Diaphragm preparation 14 mm diameter glass fiber was selected as the battery separator.
[0041] 4. Sodium-ion battery preparation The negative electrode shell, negative electrode sheet, separator, positive electrode sheet, gasket, spring sheet, and positive electrode shell are stacked together in sequence. Then, the R2032 button cell is pressed together under a pressure of 11.3 MPa, left to stand at room temperature for 8 hours, and then charged and discharged at a rate of 0.1 C for two cycles, followed by a long cycle at a rate of 1 C (1 C = 127 mAh / g), with a charge and discharge voltage range of 2.0-4.0 V.
[0042] II. Performance Testing In this embodiment, room temperature and normal temperature refer to 25°C.
[0043] 1. High-temperature cycling performance test The R2032 button cell was placed in an oven at a constant temperature of 60 ℃ and charged and discharged at a rate of 0.1 C for two cycles, and then charged and discharged at a rate of 1 C for a long cycle. The charge and discharge voltage range was 2.0-4.0 V.
[0044] 2. Room temperature cycling performance test Button half-cells with different electrolytes were charged to 4.0V at a current rate of 0.1C at room temperature (25 ℃), and then discharged to 2.0V. This cycle was repeated twice. Then, the cells were charged to 4.0V at a current rate of 1C, and then discharged to 2.0V. This cycle was repeated n times. The discharge specific capacity of each cycle was recorded. The capacity retention rate of the room temperature cycle was calculated using the following formula: Capacity retention rate of m cycles = Discharge specific capacity of the mth cycle / Discharge specific capacity of the 3rd cycle × 100%.
[0045] Button cells with different electrolytes were charged to 3.9V at a current rate of 0.1C at room temperature (25 ℃), and then discharged to 0.5V. This cycle was repeated twice. Then, the cells were charged to 3.9V at a current rate of 1C, and then discharged to 0.5V. This cycle was repeated n times. The discharge specific capacity of each cycle was recorded. The capacity retention rate of the room temperature cycle was calculated using the following formula: Capacity retention rate of m cycles = Discharge specific capacity of the mth cycle / Discharge specific capacity of the 3rd cycle × 100%.
[0046] 3. High-voltage cycling performance test Button half-cells with different electrolytes were charged to 4.2V at a current rate of 0.1C at room temperature (25 ℃), and then discharged to 2.0V. This cycle was repeated twice. Then, the cells were charged to 4.2V at a current rate of 1C, and then discharged to 2.0V. This cycle was repeated n times. The discharge specific capacity of each cycle was recorded. The capacity retention rate of the room temperature cycle was calculated using the following formula: Capacity retention rate of m cycles = Discharge specific capacity of the mth cycle / Discharge specific capacity of the 3rd cycle × 100%.
[0047] 4. Ratio Performance Test The discharge specific capacities C0, C1, C2, C3, C4, and C5 of the button half-cell were measured at room temperature at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 5 C. The capacity retention rate of C5 was calculated as follows: n / C0×100%.
[0048] The results of the high-temperature cycling performance test, the room-temperature cycling performance test, and the high-pressure cycling performance test are shown in Table 5.
[0049] Table 5
[0050] As can be seen from Table 5, the sodium-ion battery using the electrolyte of the present invention has excellent high-voltage cycling, room-temperature cycling, and rate performance.
[0051] The comparison between Comparative Example 1 and Comparative Example 2 shows that introducing phosphate ester solvent (TEP) as the main solvent into the electrolyte further stabilizes the positive electrode interface of the battery, which in turn leads to a slight improvement in the long-cycle capacity retention rate of the half-cell.
[0052] A comparison between Comparative Example 1 and Comparative Example 3 shows a significant improvement in capacity retention. With the solvent remaining constant, introducing 0.2 mol / L NaDFOB as an auxiliary salt into the electrolyte significantly increased the NaF content in the interfacial film formed by the battery, leading to improved stability of the positive and negative electrode interfaces and enhanced long-cycle performance.
[0053] A comparison of Comparative Example 1 and Example 1 shows that when 0.2 mol / L NaDFOB co-salt and 60% vt. phosphate ester solvent (TEP) are synergistically introduced into the electrolyte, NaDFOB decomposes to form an interface film rich in B and F inorganic substances, which can stabilize the positive and negative electrode interfaces and significantly improve the long-term cycle stability of half-cells and full-cells. At the same time, the presence of TEP improves the thermal stability of the battery, and the electrochemical performance is also improved at high temperatures.
[0054] By comparing Comparative Example 2 and Example 1 with Example 6, it can be seen that, under the premise that the main salt concentration remains unchanged, by introducing the auxiliary salt NaDFOB and changing the auxiliary salt concentration to 0.10 mol / L, the electrochemical long-cycle performance is worse than that of Example 1 due to the low content of the auxiliary salt and some consumption during the cycle. However, the electrochemical stability is also improved compared with the blank electrolyte.
[0055] By comparing Comparative Example 2 and Example 1 with Example 5, it can be seen that, under the premise that the main salt concentration remains unchanged, by introducing the auxiliary salt NaDFOB and changing the auxiliary salt concentration to 0.05 mol / L, the content of the auxiliary salt is further reduced and it is exhausted during the cycle. The electrochemical long-cycle performance is worse than that of Example 1, but the electrochemical stability is also improved compared with the blank electrolyte.
[0056] By comparing Comparative Example 2 and Example 1 with Example 8, it can be seen that, under the premise of keeping the main salt concentration unchanged, replacing 0.2 mol / L NaDFOB with 0.05 mol / L NaClO4 as the auxiliary salt, NaClO4, as an auxiliary salt with strong binding energy, improves the stability of the electrolyte and helps with long-term cycling stability. However, due to the low concentration of NaClO4, it will be rapidly consumed during long-term cycling, so the electrochemical performance is worse than that of Example 1, but it is still better than the electrolytes of Comparative Example 1 and Comparative Example 2.
[0057] For Examples 9 and 10, NaDFOB in Example 1 was replaced with NaTFSI and NaFSI for long-term cycling. Although the performance was not as good as that of Example 1, a stable SEI / CEI rich in NaF was formed, which effectively protected the electrode. The performance was also improved compared with Comparative Examples 1 and 2.
[0058] By comparing Comparative Example 2 and Example 1 with Example 11, it can be seen that, under the premise of keeping the main salt concentration unchanged, replacing 0.2 mol / L NaDFOB with 0.05 mol / L NaNO3 as the auxiliary salt, NaNO3, as an auxiliary salt with strong binding energy, can improve the electrochemical window. At the same time, NaNO3 can decompose to form an interface rich in nitrogen compounds, which can significantly improve the stability of the electrolyte and the interface, and help stabilize the electrochemical long-cycle. However, due to the low solubility and concentration of NaNO3, it will be rapidly consumed during long-cycle, so the electrochemical performance is worse than that of Example 1, but it is better than the electrolytes of Comparative Example 1 and Comparative Example 2.
[0059] As attached Figure 1 As shown, our configured Example 1 exhibits excellent flame retardant properties, significantly improving battery safety and achieving zero self-extinguishing time; under 2-4.0V ambient pressure, as... Figure 2 The assembled half-cells were subjected to long-term cycling. Example 1 retained 92% of its capacity after 500 cycles, an improvement of nearly 70% compared to Comparative Example 1. Comparative Example 1 experienced rapid capacity decay due to severe side reactions at the electrolyte / electrode interface; even at a high voltage of 4.2V, such as... Figure 3 The half-cell assembled based on the electrolyte of Example 1 has a first-cycle strength of 153.1 mAh g⁻¹. -1 The high discharge capacity of the electrolyte, retaining 83% of its initial capacity after 200 cycles, demonstrates excellent stability, while Comparative Example 1, due to its poor stability, almost failed to cycle. To further explore the practical application capabilities of the electrolyte, a full cell was assembled, such as... Figure 4As shown, Example 1 achieved an excellent capacity retention of 74% after 500 cycles, while the battery using the electrolyte in Comparative Example 1 had almost no discharge capacity. Finally, to demonstrate the universality of our invented electrolyte, the positive electrode material was changed, and a half-cell was assembled using a sodium vanadium phosphate positive electrode (Na3V2(PO4)3) and a sodium metal negative electrode. The battery using the electrolyte in Example 1 still maintained a high capacity retention of 93% after 2000 cycles at a high voltage of 4.5V, while Comparative Example 1 stopped cycling after 1000 cycles because it could not withstand the high voltage. Figure 5 As shown.
[0060] The present invention has been illustrated with the above embodiments to explain the detailed method of the present invention. However, the present invention is not limited to the detailed method described above, that is, it does not mean that the present invention must rely on the detailed method described above to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.
[0061] Matters not covered in this invention are common knowledge.
Claims
1. A flame-retardant electrolyte constructed by the synergistic effect of a phosphate ester-based solvent and two salts, characterized in that, The electrolyte includes sodium salts and organic solvents; The solvent consists of organic carbonate and phosphate solvent; the volume of the phosphate solvent accounts for 40%-70% of the total volume of the electrolyte. The sodium salt comprises a main salt and a secondary salt. The main salt is sodium hexafluorophosphate with a concentration of 0.70~1.00 mol / L; the secondary salt has a concentration of 0.01~0.30 mol / L. The carbonate solvent is an organic solvent containing C=O bonds: one or more of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate; The phosphate ester solvent is an organic solvent containing P=O bonds; The auxiliary salt is sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium difluorooxalate borate, or sodium nitrate.
2. The flame-retardant electrolyte constructed by the synergistic effect of the phosphate ester-based solvent and the dual salt as described in claim 1, characterized in that, It is sodium difluorooxalate borate.
3. The flame-retardant electrolyte constructed by the synergistic effect of the phosphate ester-based solvent and the dual salt as described in claim 1, characterized in that, The phosphate solvent is one or both of trimethyl phosphate and triethyl phosphate.
4. A sodium-ion battery, characterized in that, Sodium-ion batteries can be either half-cells or full-cells; The half-cell is a battery composed of a sodium metal negative electrode and a positive electrode, a glass fiber membrane or a polyolefin membrane, and a flame-retardant electrolyte constructed by the synergistic effect of the phosphate ester-based solvent and the dual salt as described in claim 1. The full cell comprises a positive electrode, a hard carbon negative electrode, a glass fiber membrane or a polyolefin membrane, a flame-retardant electrolyte constructed by the synergistic effect of the phosphate ester-based solvent as described in claim 1 and the dual salts; The positive electrode of the full cell or half cell is at least one of layered transition metal oxides and polyanionic compounds.
5. The sodium-ion battery as described in claim 4, characterized in that, The chemical formula of the layered transition metal layered oxide is NaNi. x Fe y Mn z O2, 0<x≤1.5, 0<y≤1, 0<z≤0.75; The phosphate-based cathode material in the polyanionic compound has a chemical formula of at least one of NaFePO4, Na3V2(PO4)2F3, or Na3V2(PO4)3.