High-temperature-resistant and stable-circulation sodium metal battery electrolyte

Abstract

The application discloses a kind of high-temperature resistant stable cycle sodium metal battery electrolyte.The electrolyte includes ester solvent, sodium salt and film-forming additive;Wherein, in electrolyte, the concentration of sodium salt is 0.5~1.5mol / L;Film-forming additive in solvent is 2%‑8% in volume ratio;The composition of the ester solvent is carbonic acid ester solvent and phosphoric acid ester solvent;The carbonic acid ester solvent is vinyl carbonate, propylene carbonate or carbonic acid methyl ethyl ester;The phosphoric acid ester solvent is trimethyl phosphate (TMP), triethyl phosphate or tributyl phosphate;The sodium salt is sodium perchlorate.The electrolyte obtained by the application can stably resist the upper limit of voltage to reach 4.64 V and 4.55 V respectively, has more excellent anti-oxidation decomposition capacity, and has good cycle stability at normal temperature and high temperature.

Description

Technical Field

[0001] This invention relates to a high-temperature resistant and stable cycling sodium metal battery electrolyte, belonging to the field of electrochemical technology. Background Technology

[0002] With the large-scale advancement of the electrochemical energy storage industry, sodium-ion batteries have become a core technology route in large-scale energy storage, low-speed power and other fields due to the abundance and wide distribution of sodium resources, their outstanding cost advantages, smaller Stokes radius and lower desolvation energy in carbonate media, and superior rate and low-temperature performance compared to lithium-ion batteries.

[0003] However, performance degradation and safety risks at high temperatures are the core bottlenecks restricting the expansion of sodium-ion batteries. As the core carrier of ion transport, the thermal and interfacial stability of the electrolyte directly determines the battery's high-temperature operating capability. Currently, carbonate-based electrolytes are the mainstream choice for sodium-ion batteries. These solvents, with their high polarity and strong solvation ability, can effectively dissociate sodium salts and ensure high ionic conductivity at room temperature, making them the mainstream choice for industrial applications at this stage. However, carbonate solvents have a low intrinsic flash point and a narrow thermal stability window, making them prone to thermal degradation in the 100-150 °C range. This releases volatile and flammable byproducts and can also cause high-temperature dissolution and rupture of the solid electrolyte interphase (SEI) film on the electrode surface, leading to continuous consumption of electrolyte by side reactions and damage to the electrode structure. This results in rapid capacity decay and, in severe cases, even the risk of thermal runaway.

[0004] Therefore, overcoming the shortcomings of traditional carbonate electrolytes in high-temperature stability and developing an electrolyte system that can operate stably for a long time in high-temperature environments is a key technical challenge that urgently needs to be overcome in the field of sodium-ion batteries.

[0005] In the prior art: For example, Chinese patent application CN202410957108.3, entitled "A High-Temperature Sodium-Ion Electrolyte and a High-Safety Sodium-Ion Battery," discloses a sodium-ion battery electrolyte that can operate stably at high temperatures. This solution uses propylene carbonate as the sole solvent, combined with a 1.4M sodium hexafluorophosphate and sodium difluorosulfonyl imide composite sodium salt, and also incorporates various functional additives to improve the battery's high-temperature performance by optimizing the protective film on the electrode surface. While this solution optimizes the film formation at the electrode interface through the combination of functional additives, thus improving the battery's high-temperature cycle performance to some extent, it still suffers from an inherent defect that cannot be completely resolved by additives: the main solvent in this solution is a carbonate solvent, which is inherently a flammable liquid with a low flash point and high volatility. Even with the addition of small amounts of additives with flame-retardant properties, only limited performance improvement can be achieved, and the flammability of the main solvent itself cannot be changed. Under extreme high-temperature conditions, the electrolyte is still prone to thermal decomposition, generating large amounts of gas and even combustion, resulting in a high risk of battery thermal runaway and making it difficult to meet the high-safety-level requirements of high-temperature applications. Furthermore, the NaPF6 used in this design has weak chemical stability, decomposing even in the presence of trace amounts of moisture to generate highly corrosive acidic substances. The higher the ambient temperature, the faster this decomposition reaction occurs. The continuously generated corrosive substances gradually erode the cathode material, causing the dissolution and loss of metallic components, while also damaging the protective film structure on the electrode surface. Ultimately, this leads to a rapid increase in battery internal resistance, a sharp decline in energy storage capacity, and a significant shortening of the battery's high-temperature lifespan. Summary of the Invention

[0006] This invention addresses the limitations of existing sodium metal battery electrolytes, such as insufficient high-temperature thermal stability and significant safety risks, by developing a sodium metal battery electrolyte capable of stable cycling at high temperatures. This electrolyte employs a dual-main solvent system constructed from propylene carbonate and trimethyl phosphate, achieving synergistic and complementary performance. The carbonate solvent possesses characteristics such as high dielectric constant, strong sodium salt solubility, and a wide oxidation stability window, while exhibiting excellent wettability to both the cathode and separator, maintaining high ionic conductivity even at high temperatures. The phosphate solvent, introduced as an intrinsically flame-retardant main solvent component, imparts flame-retardant properties to the electrolyte at the solvent matrix level, significantly improving the electrolyte's thermal stability and battery safety performance, and suppressing the risk of thermal runaway at high temperatures. NaClO4 is selected as the sole sodium salt for the electrolyte to avoid decomposition and the generation of corrosive substances under high temperature conditions. For the additives, only DFEC or PFPN single fluorinated additives are used. This can weaken the combination of sodium ions and solvent through the hydrogen-like effect of fluorine atoms and reduce the desolvation energy barrier. It can also preferentially reduce and form a stable interface film rich in NaF on the negative electrode surface to inhibit sodium dendrites. This simplifies the formula and avoids the risk of interfacial side reactions caused by multiple additives.

[0007] The technical solution of this invention is as follows: A high-temperature resistant and stable cycling sodium metal battery electrolyte, comprising an ester solvent, a sodium salt, and a film-forming additive; In the electrolyte, the concentration of sodium salt is 0.5~1.5 mol / L; the volume ratio of film-forming additives in the solvent is 2%-8%. The ester solvent is composed of carbonate solvent with high dielectric constant and ionic conductivity and intrinsically flame-retardant phosphate solvent, and the volume ratio of carbonate electrolyte to phosphate solvent is 4:1 to 1:4. The carbonate solvent with high dielectric constant and ionic conductivity is propylene carbonate (PC). The intrinsically flame-retardant phosphate solvent is trimethyl phosphate (TMP). The sodium salt is sodium perchlorate (NaClO4), sodium bis(fluorosulfonyl)imide (NaFSI), or sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), preferably sodium perchlorate (NaClO4), and its concentration in the electrolyte is 1 mol / L.

[0008] The film-forming additive is one or more of the following: fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), tris(2,2,2-trifluoroethyl) phosphate (TFEP), and ethoxypentafluorocyclotriphosphazene (PFPN); When the ester solvent is preferably propylene carbonate (PC) and trimethyl phosphate (TMP) in a volume ratio of 1:1; The preferred film-forming additive is ethylene difluorocarbonate (DFEC) at a volume ratio of 2% in the electrolyte or ethoxypentafluorocyclotriphosphazene (PFPN) at a volume ratio of 5% in the electrolyte.

[0009] The sodium metal battery includes a positive electrode, a sodium metal negative electrode, a separator, and the sodium metal battery electrolyte that is resistant to low and high temperature stable cycling.

[0010] The positive electrode sheet comprises a positive current collector, a positive active material, a conductive agent, and a binder.

[0011] The positive electrode active material is a layered oxide with the structural formula NaM. x O y M is one or more of iron, copper, nickel, cobalt and manganese, and the values ​​of x and y are in the range of: 0.1≤x≤1.0, 1.5≤y≤2.5.

[0012] The positive electrode active material is O3 type NaNi1 / 3Fe1 / 3Mn1 / 3O2 (NFM111), which is coated on one side of the aluminum foil current collector.

[0013] The conductive agent is selected from any one or a combination of at least two of Super P Li, acetylene black, conductive graphite, Ketjen black, graphene, or carbon fiber. Super P Li is preferred as the conductive agent.

[0014] The binder is one or more selected from polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), sodium alginate (SA), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). Polyvinylidene fluoride (PVdF) binder is preferred. The positive electrode current collector is aluminum foil. The above-mentioned O3-type NaNi1 / 3Fe1 / 3Mn1 / 3O2 (NFM111) positive electrode active material, Super P Li conductive agent, and polyvinylidene fluoride (PVdF) binder powder were thoroughly mixed at an optimal mass ratio of 8:1:1. Then, an appropriate amount of N-methylpyrrolidone (NMP) dispersant was added, and the mixture was thoroughly ground. The slurry was then uniformly coated onto the surface of an aluminum current collector to a thickness of 100 μm and heated in a vacuum environment at 80 °C for 12 h. After heating, the mixture was cut into positive electrode sheets with a diameter of 12 mm.

[0015] The sodium metal negative electrode sheet has a thickness of 1 mm, a diameter of 10 mm, and a circular shape.

[0016] The diaphragm is any one or a combination of at least two of Celgard 2500 diaphragm, Celgard 2325 diaphragm, or glass fiber diaphragm. Glass fiber diaphragm is preferred.

[0017] The essential features of this invention are: This invention mixes propylene carbonate and the flame-retardant solvent trimethyl phosphate in equal volume ratios. Trimethyl phosphate itself possesses excellent flame-retardant properties, and its direct addition as one of the main solvents significantly improves the overall flash point and flame resistance of the electrolyte, fundamentally reducing the safety risks of thermal runaway and fire in batteries under high-temperature environments. Sodium perchlorate (NaClO4) is selected as the sole sodium salt in the electrolyte system. NaClO4 exhibits extremely high dissociation in common sodium metal battery organic solvents such as carbonates, thus possessing high ionic conductivity in the PC system. Simultaneously, NaClO4 can construct a stable interfacial protective layer by controlling the interface of the sodium metal battery cathode. NaClO4 has a high HOMO energy level and preferentially decomposes on the cathode surface, forming a NaCl-rich CEI, reducing side reactions, thereby improving the battery's cycle stability and coulombic efficiency. This invention focuses on improving long-cycle performance at both high and normal temperatures. Therefore, trace amounts of fluorinated additives (DFEC and PFPN) are introduced. In the electrolyte, the H atom on the methyl group of the TMP molecule exhibits significant positive charge due to the influence of the electron-withdrawing P=O group within the molecule; the DFEC (or PFPN) molecule contains strongly electronegative fluorine atoms. A hydrogen-bond-like dipole interaction is formed between the two. This type of hydrogen bond weakens the interaction between the solvent molecules and Na+. + The coordination ability between them promotes the formation of anion-rich solvation structures. This anion-dominated solvation structure can effectively reduce the sodium ion desolvation energy barrier and accelerate the desolvation of sodium ions. + Transmission dynamics enabled long-term stable operation of the battery.

[0018] The beneficial effects of this invention are: 1. This invention introduces phosphate ester solvents into a traditional carbonate solvent system and combines them with fluorinated additives such as DFEC and PFPN. From a microscopic perspective, the fluorinated additives form a strong interaction with trimethyl phosphate (TMP) molecules. This interaction weakens the binding force between sodium ions and TMP solvent molecules, allowing more anions in the electrolyte to participate in the sodium ion encapsulation structure, forming an anion-dominated ionic solvation state and reducing the resistance of sodium ions to escaping the solvent molecule encapsulation. Electrochemical linear scan tests at a scan rate of 0.5 mV / s show that the optimized electrolyte can stably withstand voltages of 4.64 V and 4.55 V, respectively, which are higher than electrolytes using pure propylene carbonate (PC) as a single solvent. This indicates that the electrolyte system has superior antioxidant capacity and better chemical stability at high temperatures.

[0019] 2. The fluoride ions in the fluorinated additive of this invention can preferentially undergo a reduction reaction on the negative electrode side, forming a negative electrode electrolyte interface film (SEI) rich in NaF, an inorganic component. This inorganic SEI film has a high inhibition of dendrite growth, and this stable SEI improves the cycle stability of the battery. The Na||NNFMO sodium metal battery assembled with the electrolyte prepared by adding the fluorinated additive DFEC performs well at room temperature (25°C) at 300 mA g. -1 At a current density of [value missing], it still retains 103.1 mAh g after 1000 cycles. -1 The discharge specific capacity and capacity retention rate were 84.39%, while the Na||NNFMO sodium metal battery assembled with an electrolyte containing PFPN, a fluorinated additive, showed a discharge specific capacity of 300 mA g at room temperature (25℃). -1 At a current density of [value missing], it still retains 96.82 mAh g after 1000 cycles. -1 The discharge specific capacity and capacity retention rate were 74.68%, both significantly higher than those of electrolytes using PC as the sole solvent, PC and TMP mixed solvents, and conventional commercial electrolytes. Simultaneously, the battery exhibited excellent rate performance: a 10 C (1C = 150 mAh g⁻¹) Na||NNFMO sodium metal battery assembled using the electrolytes described in Examples 1 and 2 was successfully tested. -1 ) still have 73.8 mAhg -1 and 99.1 mAh g -1 The discharge specific capacity is much higher than that of Comparative Example 1.

[0020] 3. The introduction of TMP and fluorinated solvents also effectively improved the high-temperature performance of the battery. At 60 °C, the Na||NNFMO sodium metal battery assembled using the electrolyte of Example 2 achieved a 2C (1C = 150 mAh g) performance. -1 At this setting, the discharge specific capacity after 350 cycles is 118.56 mAh g. -1 The capacity retention rate was 88.36%; the battery assembled with the electrolyte of Comparative Example 2 (1C = 150 mAh g) was 2C. -1 At this setting, the discharge specific capacity after 350 cycles is 94.33 mAh g. -1 The capacity retention rate was 72.89%; the battery assembled with the electrolyte of Comparative Example 1 failed after 20 cycles. Meanwhile, the battery in Example 1 exhibited good rate performance: the Na||NNFMO sodium metal battery assembled using the electrolyte described in Example 1 reached 10 C (1C = 150 mAh g⁻¹). -1 ) still have 73.8 mAh g -1 .

[0021] In summary, the high-temperature resistant electrolyte formulated according to this invention enables the safe and stable operation of sodium metal batteries at both room temperature and high temperature. This provides a reliable electrolyte design approach for the practical application of high-safety sodium metal batteries. Attached Figure Description

[0022] Figure 1 Linear sweep voltammetry curves at room temperature obtained in Examples 1 and 2 and Comparative Example 1; Figure 2 The current density obtained in Examples 1 and 2 and Comparative Example 1 is 30 mA g at room temperature. -1 The first-week charge-discharge curve of the Na||NNFMO sodium metal battery.

[0023] Figure 3 The samples obtained in Examples 1 and 2, Comparative Examples 1, 2 and 3 at 300 mA g -1 The room-temperature cycling diagram of the Na||NNFMO sodium metal battery at the given current density.

[0024] Figure 4 The table shows the room temperature rate capability of Na||NNFMO sodium metal batteries obtained in Examples 1 and 2 and Comparative Example 1 at a current density of .

[0025] Figure 5 In Examples 1 and 2, and Comparative Example 1, the concentration was 300 mA g. -1 The first-week charge-discharge curves of the Na||NNFMO sodium metal battery at 60 °C under the given current density.

[0026] Figure 6 The values ​​obtained in Examples 1 and 2, and Comparative Examples 1 and 2, at 300 mA g -1 High-temperature cycling diagram of Na||NNFMO sodium metal battery at 60 °C under a given current density.

[0027] Figure 7 The high-temperature rate curves for Na||NNFMO sodium metal batteries at 60 °C are shown in Example 1 and Comparative Example 2. Detailed Implementation

[0028] The present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

[0029] Example 1: The following operations were performed in an argon-atmospheric glove box: 122.44 mg (1 mmol) of sodium perchlorate was weighed using a balance and dissolved in a mixed solvent of 500 μL trimethyl phosphate and 500 μL propylene carbonate. 20 μL (1 mmol) of ethylene difluorocarbonate was added to the mixed solvent to prepare a 1.0 M NaClO4 / PC:TMP (V:V, 1:1) + 2% vol. DFEC electrolyte, which was then used as the optimized electrolyte. The prepared electrolyte was thoroughly dissolved using a shaker and allowed to stand for 12 hours.

[0030] Example 2: The following operations were performed in an argon-atmospheric glove box: 122.44 mg (1 mmol) of sodium perchlorate was weighed using a balance and dissolved in a mixed solvent of 500 μL trimethyl phosphate and 500 μL propylene carbonate. 50 μL of ethoxypentafluorocyclotriphosphazene was added to the mixed solvent to prepare a 1.0 M NaClO4 / PC:TMP (V:V, 1:1) + 5% vol. PFPN electrolyte, which was used as the optimized electrolyte. The prepared electrolyte was thoroughly dissolved using a shaker and allowed to stand for 12 hours.

[0031] Comparative Example 1: The following operations were performed in an argon-atmospheric glove box: 122.44 mg (1 mmol) of sodium perchlorate was weighed using a balance and dissolved in a mixed solvent of 500 μL trimethyl phosphate and 500 μL propylene carbonate to prepare a 1.0 M NaClO4 / PC:TMP (V:V, 1:1) electrolyte as a control electrolyte. The prepared electrolyte was thoroughly dissolved using a shaker and allowed to stand for 12 hours.

[0032] Comparative Example 2: The following operations were performed in an argon-atmospheric glove box. 122.44 mg (1 mmol) of sodium perchlorate was weighed using a balance and dissolved in 1 mL of propylene carbonate to prepare a 1.0 M NaClO4 / PC electrolyte as a control electrolyte. The prepared electrolyte was thoroughly dissolved using a shaker and allowed to stand for 12 hours.

[0033] Comparative Example 3: Sodium-ion battery NaClO4 electrolyte (NC-097) was purchased through the Duoduo Chemical Reagents platform. The specific composition is 1.0M NaClO4 / EC:PC:DMC (V:V:V, 1:1:1) + 2% vol. FEC, which was used as a commercial comparison electrolyte.

[0034] Example 3: Completed in a glove box filled with high-purity argon gas, with the only variable being the type of electrolyte (corresponding to Example 1, Example 2, and Comparative Example 1, respectively). A half-cell without a positive electrode was assembled in the following order: negative electrode shell, 10 mm diameter circular sodium metal electrode, glass fiber separator, electrolyte, and matching CR2032 type gasket, spring, and positive electrode shell. After sealing with a sealing machine, it was allowed to stand for 8 hours. The electrochemical window of the electrolyte was tested using a Chenhua CHI660E electrochemical workstation with a linear scanning voltammetry method at a scan rate of 0.5 mV / s. -1 .

[0035] Figure 1 Linear sweep voltammetry curves of Na||NNFMO sodium metal batteries assembled using the electrolytes of Examples 1 and 2 are shown. The results indicate that the electrochemical windows of the batteries assembled using the electrolytes of Examples 1 and 2 are 4.64 V and 4.55 V, respectively. Compared to 4.46 V of Comparative Example 1, Examples 1 and 2 have wider electrochemical windows, indicating that the electrolytes of Examples 1 and 2 have superior oxidative stability.

[0036] Example 4: Purchase commercial O3-type layered oxide positive electrode active material sodium nickel iron manganate, with the specific molecular formula NaNi. 0.33 Fe 0.33 Mn 0.33 O2 was purchased from Shenzhen Huaxin New Materials Technology Co., Ltd.

[0037] Preparation of NNFMO positive electrode sheet: Inside a glove box filled with high-purity argon gas, commercially available NaNi was taken. 0.33 Fe 0.33 Mn 0.33 O2, as the positive electrode active material, is mixed with conductive agent Super P Li conductive carbon black and binder polyvinylidene fluoride (PVdF) at a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) is added to the above mixture as a binder, and the mixture is thoroughly ground and stirred until a uniform, particle-free positive electrode slurry is formed. The obtained positive electrode slurry is uniformly coated on the surface of aluminum foil current collector, and the coating thickness is controlled to be 100 μm. After coating, the slurry is transferred to a glove box compartment for drying at a temperature of 80 ℃ for 8 h. The dried electrode is cut into circular electrode sheets with a diameter of 12 mm, which are the NNFMO positive electrode sheets.

[0038] All assembly operations were performed in a glove box protected by high-purity argon gas, with water and oxygen content both below 0.01 ppm. Sodium metal electrodes (1 mm thick, 10 mm in diameter) and glass fiber separators were stacked sequentially from the negative electrode side to the positive electrode side. Electrolytes corresponding to Examples 1, 2, Comparative Examples 1, and 2 were dripped onto the separators to wet them. Then, the aforementioned NNFMO positive electrode was stacked, followed by CR2032 stainless steel gaskets and CR2032 spring sheets. Finally, the CR2032 positive electrode shell was placed on top, and the battery was sealed using a sealing machine to obtain the corresponding CR2032 sodium metal button cell. Charge-discharge tests were performed on the Land CT2001A battery testing system. The charge-discharge cycle test conditions for this example were 25°C and 30 mA g. -1 It is charged and discharged at a constant current density, with a voltage range of 2.0-4.0 V.

[0039] Figure 2 The first-week charge-discharge curves of Na||NNFMO sodium metal batteries assembled using the electrolytes of Examples 1 and 2 are shown. The batteries assembled using the electrolytes of Examples 1 and 2 exhibit first-week coulombic efficiencies as high as 93.56% and 92.32%, respectively, significantly higher than those of the electrolyte described in Comparative Example 1.

[0040] Example 5: All assembly operations were performed in a glove box protected by high-purity argon gas, with water and oxygen content both below 0.01 ppm. Sodium metal electrodes (1 mm thick, 10 mm in diameter) and glass fiber separators were stacked sequentially from the negative electrode side to the positive electrode side. Electrolytes corresponding to Examples 1, 2, Comparative Examples 1, and 2 were dripped onto the separators to wet them. Then, the aforementioned NNFMO positive electrode was stacked, followed by a CR2032 stainless steel gasket and a CR2032 spring sheet. Finally, the CR2032 positive electrode shell was placed on top, and the batteries were sealed using a sealing machine to obtain the corresponding CR2032 sodium metal button cell. The cycle performance of the batteries was tested using the Land CT2001A battery testing system.

[0041] Figure 3 The diagram shows the cycling performance of Na||NNFMO sodium metal batteries in the electrolytes of Examples 1 and 2, and Comparative Examples 1, 2, and 3. The batteries assembled with the electrolytes of Examples 1 and 2 exhibited capacity retention rates of 84.39% and 74.68%, respectively, after 1000 cycles. In contrast, the electrolytes of Comparative Examples 1 and 3 showed a sharp decline in cycling performance. In particular, the capacity retention rate of the electrolyte in Comparative Example 2 was only 48.19% after 200 cycles. Therefore, the electrolyte of Example 1 demonstrates superior cycling stability at room temperature and shows great application potential.

[0042] Example 6: All assembly operations were performed in a glove box protected by high-purity argon gas, with water and oxygen content both below 0.01 ppm. Sodium metal electrodes (1 mm thick, 10 mm in diameter) and glass fiber separators were stacked sequentially from the negative electrode side to the positive electrode side. Electrolytes corresponding to Examples 1, 2, Comparative Examples 1, and 2 were dripped onto the separators to wet them. Then, the aforementioned NNFMO positive electrode was stacked, followed by a CR2032 stainless steel gasket and a CR2032 spring sheet. Finally, the CR2032 positive electrode shell was placed on top, and the cells were sealed using a packaging machine to obtain the corresponding CR2032 sodium metal button cell. The rate performance of the cells was tested using the Land CT2001A battery testing system.

[0043] Figure 4 Rate performance graphs of Na||NNFMO sodium metal batteries assembled using the electrolytes of Examples 1 and 2, and the electrolyte of Comparative Example 1. Batteries of Examples 1 and 2 are shown at 10 C (1C = 150 mAh g⁻¹). -1 At a current density of ), it still has 73.8 mAh g. -1 and 99.1 mAh g -1 The discharge specific capacity of the sample is much higher than that of the comparative sample 1. This indicates that the battery has better sodium ion transport kinetics.

[0044] Example 7: All assembly operations were performed in a glove box protected by high-purity argon gas, with water and oxygen content both below 0.01 ppm. Sodium metal electrodes (1 mm thick, 10 mm in diameter) and glass fiber separators were stacked sequentially from the negative electrode side to the positive electrode side. Electrolytes corresponding to Examples 1, 2, Comparative Examples 1, and 2 were dripped onto the separators to wet them. Then, the aforementioned NNFMO positive electrode was stacked, followed by CR2032 stainless steel gaskets and CR2032 spring clips. Finally, the CR2032 positive electrode shell was placed on top, and the battery was sealed using a sealing machine to obtain the corresponding CR2032 sodium metal button cell. Charge-discharge tests were conducted on the Land CT2001A battery testing system at 60 °C with a charge of 300 mA g. -1 It is charged and discharged at a constant current density, with a voltage range of 2.0-4.0 V.

[0045] Figure 5 The first-week charge-discharge curves of the Na||NNFMO sodium metal battery assembled using the electrolyte of Example 2 and Comparative Example 1 are shown. The results indicate that the first-week discharge specific capacity of the battery is 133.61 mAh g⁻¹. -1 In the first week, the Coulomb efficiency was 90.61%.

[0046] Example 7: All assembly operations were performed in a glove box protected by high-purity argon gas, with water and oxygen content both below 0.01 ppm. Sodium metal electrodes (1 mm thick, 10 mm in diameter) and glass fiber separators were stacked sequentially from the negative electrode side to the positive electrode side. Electrolytes corresponding to Examples 1, 2, Comparative Examples 1, and 2 were dripped onto the separators to wet them. Then, the aforementioned NNFMO positive electrode was stacked, followed by a CR2032 stainless steel gasket and a CR2032 spring sheet. Finally, the CR2032 positive electrode shell was placed on top, and the batteries were sealed using a sealing machine to obtain the corresponding CR2032 sodium metal button cell. The batteries were placed in a 60 °C constant temperature oven, and their high-temperature cycle performance was tested using a LandCT2001A battery testing system.

[0047] Figure 6 The figure shows the high-temperature cycling performance of the Na||NNFMO sodium metal batteries assembled using the electrolyte of Example 2, and Comparative Examples 1 and 3, at 60 °C. As shown in the figure, at 300 mA g... -1 At high current density, the capacity retention rate remains as high as 88.36% after 350 cycles. Therefore, this electrolyte achieves stable long-term cycling under normal temperature, high temperature and rapid charge-discharge conditions.

[0048] Example 8: All assembly operations were performed in a glove box protected by high-purity argon gas, where the water and oxygen content were both below 0.01 ppm. Sodium metal electrodes (1 mm thick, 10 mm in diameter) and glass fiber separators were stacked sequentially from the negative electrode side to the positive electrode side. Electrolytes corresponding to Examples 1, 2, Comparative Examples 1, and 2 were dripped onto the separators to wet them. Then, the aforementioned NNFMO positive electrode was stacked, followed by CR2032 stainless steel gaskets and CR2032 spring sheets. Finally, the CR2032 positive electrode shell was placed on top, and the batteries were sealed using a sealing machine to obtain the corresponding CR2032 sodium metal button cell. The batteries were placed in a 60 °C constant temperature oven, and their rate performance was tested using a LandCT2001A battery testing system.

[0049] Figure 7 The graph shows the high-temperature rate performance of the Na||NNFMO sodium metal battery assembled using the electrolyte of Example 1 at 60 °C. The battery assembled using Example 1 exhibits good rate performance at 10C (1C = 150 mA g). -1 Under these conditions, the battery still has 75.7 mA g. -1 The specific discharge capacity.

[0050] Matters not covered in this invention are common knowledge.

Claims

1. A sodium metal battery electrolyte with high temperature resistance and stable cycling, characterized in that, The electrolyte includes ester solvents, sodium salts, and film-forming additives; In the electrolyte, the concentration of sodium salt is 0.5~1.5 mol / L; the volume ratio of film-forming additives in the solvent is 2%-8%. The ester solvent is composed of carbonate solvent with high dielectric constant and ionic conductivity and intrinsically flame-retardant phosphate solvent, and the volume ratio of carbonate electrolyte to phosphate solvent is 4:1 to 1:

4. The carbonate solvent with high dielectric constant and ionic conductivity is propylene carbonate (PC). The intrinsically flame-retardant phosphate solvent is trimethyl phosphate (TMP). The sodium salts are sodium perchlorate (NaClO4), sodium bis(fluorosulfonyl)imide (NaFSI), or sodium bis(trifluoromethyl)sulfonyl)imide (NaTFSI).

2. The high-temperature resistant and stable cycling sodium metal battery electrolyte as described in claim 1, characterized in that, The film-forming additive is one or more of the following: fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), tris(2,2,2-trifluoroethyl) phosphate (TFEP), and ethoxypentafluorocyclotriphosphazene (PFPN).

3. The high-temperature resistant and stable cycling sodium metal battery electrolyte as described in claim 1, characterized in that, The volume ratio of propylene carbonate (PC) to trimethyl phosphate (TMP) is 1:1; the sodium salt is sodium perchlorate (NaClO4), and its concentration in the electrolyte is 1 mol / L.

4. The high-temperature resistant and stable cycling sodium metal battery electrolyte as described in claim 1, characterized in that, The film-forming additive is ethylene difluorocarbonate or ethoxypentafluorocyclotriphosphazene; the volume ratio of ethylene difluorocarbonate (DFEC) in the electrolyte is 2%; the volume ratio of ethoxypentafluorocyclotriphosphazene (PFPN) in the electrolyte is 5%.

5. A sodium metal battery, characterized in that, Includes positive electrode, sodium metal negative electrode, separator, and sodium metal battery electrolyte that is resistant to low and high temperature stable cycling. The positive electrode sheet comprises a positive current collector, a positive active material, a conductive agent, and a binder; The positive electrode active material is a layered oxide with the structural formula NaM. x O y M is one or more of iron, copper, nickel, cobalt and manganese, and the values ​​of x and y are in the range of: 0.1≤x≤1.0, 1.5≤y≤2.5; The conductive agent is selected from any one or a combination of at least two of Super P Li, acetylene black, conductive graphite, Ketjen black, graphene, or carbon fiber; the positive electrode current collector is aluminum foil. The adhesive is one or more of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), sodium alginate (SA), and carboxymethyl cellulose (CMC); The sodium metal negative electrode sheet has a thickness of 1 mm and is circular in shape; The diaphragm is any one or a combination of at least two of Celgard 2500 diaphragm, Celgard 2325 diaphragm, or glass fiber diaphragm.

6. The sodium metal battery as described in claim 5, characterized in that, The positive electrode active material is O3 type NaNi1 / 3Fe1 / 3Mn1 / 3O2 (NFM111), which is coated on one side of the aluminum foil current collector; The method for preparing the positive electrode sheet includes the following steps: The above-mentioned O3-type NaNi1 / 3Fe1 / 3Mn1 / 3O2 (NFM111) positive electrode active material, Super P Li conductive agent and polyvinylidene fluoride (PVdF) binder powder were thoroughly mixed at a mass ratio of 8:1:

1. Then, N-methylpyrrolidone (NMP) dispersant was added. After grinding, the slurry was coated on the surface of the aluminum current collector with a coating thickness of 100 μm and heated in a vacuum environment at 80 °C for 12 h.

Images