Sodium-ion battery low-temperature electrolyte, sodium-ion battery and activation method of sodium-ion battery

Abstract

The invention provides a sodium-ion battery low-temperature electrolyte, a sodium-ion battery and an activation method of the sodium-ion battery, the sodium-ion battery low-temperature electrolyte comprises sodium salt, an interface type modification additive, a sodium-conducting framework additive and an organic solvent, the mass ratio of the interface type modification additive to the sodium-conducting framework additive is 1: (0.5-2), and the concentration of the sodium salt is 0.8-1.5 M; according to the low-temperature electrolyte of the sodium-ion battery, provided by the invention, a difunctional additive system is used, the estersil-containing compound is used as an interface modification type additive, and a stable SEI film rich in siloxane and sodium fluoride can be formed on the surface of a negative electrode through preferential reduction; the MOF material is used as a sodium-conducting framework additive, an ordered channel is provided for sodium ion transmission by using a regular pore channel structure of the MOF material, and the formed electrolyte has the advantage of high ionic conductivity and is convenient for industrial popularization.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a low-temperature electrolyte for sodium-ion batteries, a sodium-ion battery, and an activation method thereof. Background Technology

[0002] Sodium-ion batteries have broad prospects in large-scale energy storage due to their abundant resources and low cost. However, the problem of their performance degradation at low temperatures severely restricts their practical application. Existing technologies for improving the low-temperature performance of sodium-ion batteries mainly include electrolyte optimization, such as adding film-forming additives and using low-viscosity solvents.

[0003] CN120527452A discloses the use of triisopropyltrifluoromethanesulfonate as a single additive; Hunan Nafang New Energy uses triphenylphosphine bromide derivatives as an additive. Most of these methods rely on a single additive, making it difficult to balance interfacial stability and ion transport efficiency. Material modification: For example, Fujian Shiji Huana reduces internal resistance through the synergistic design of framework support materials and conductive fillers; Hunan Lifang New Energy develops nitrogen-doped carbon nanofiber anode materials supported by Na2Ti3O7. These methods are complex and costly. Activation process optimization: For example, the multi-stage gradient formation method proposed by Li Wei et al. includes pre-passivation, SEI film construction period, and stabilization period; Jiangsu Jihou Intelligent Technology improves cycle stability through the synergistic effect of positive and negative electrode active materials. Most of these processes are complex and time-consuming.

[0004] CN120914341A discloses a sodium-ion battery electrolyte and its preparation method. The electrolyte comprises a sodium salt, a composite solvent, additives, and an auxiliary agent. The sodium salt is a compound of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and modified sodium bis(oxalato)borate. The composite solvent consists of sulfolane, 1,3-propanediol dimethyl ether, dimethyl carbonate, fluoroethylene carbonate, and ethyl acetate. The additives are modified 1,3-propanesulfonyl lactone, trimethyl phosphate, and hydroquinone dimethyl ether. The auxiliary agent is nano-ZIF-8. This electrolyte, after being modified with hydrogen peroxide, exhibits highly efficient resistance to hydrofluoric acid. Simultaneously, the nano-ZIF-8 auxiliary agent, combined with the sodium salt, forms a synergistic effect to specifically remove hydrofluoric acid generated from the reaction of fluorinated sodium salt and water in the electrolyte, preventing hydrofluoric acid from damaging the negative electrode SEI film and thus improving the cycle life of the sodium-ion battery. However, sulfolane and 1,3-propanediol dimethyl ether are high-viscosity solvents. The electrolyte has poor fluidity at low temperatures, which restricts ion conduction and makes the performance of this technology unsatisfactory in low-temperature environments.

[0005] CN120300127A discloses a sodium-ion battery composite cathode, its preparation method, and a secondary sodium-ion battery made therefrom. The sodium-ion battery composite cathode sequentially comprises a current collector, a layered oxide layer, and a MOF layer. In preparing the sodium-ion battery composite cathode, the layered oxide layer and the MOF layer are formed using a dry method. This method improves the stability of the layered oxide in air and inhibits corrosion by the electrolyte by directly coating the surface of the manganese-based layered oxide layer with the MOF layer. Furthermore, by adding suitable sodium ion conductors and electron conductors to the MOF layer, sodium ion transport is promoted, while simultaneously adsorbing gaseous and solid byproducts of battery side reactions. The sodium ion conductors and electron conductors in the MOF layer ensure rapid transport of sodium ions and electrons, improving the activity of the cathode and thus achieving higher battery capacity, better rate performance, and longer cycle life. However, at low temperatures, the MOF layer may change from a channel conducive to ion and electron transport to a porous barrier requiring overcoming additional impedance due to decreased electrolyte wettability and reduced conductivity. Therefore, this method cannot guarantee the performance of the electrolyte at low temperatures.

[0006] In summary, existing technologies have the following limitations: most solutions use a single additive, making it difficult to achieve multifunctional electrolyte formulations; there is insufficient synergistic optimization of activation processes; the control over the composition and structure of the interface layer is not precise enough; and performance remains unsatisfactory under extreme low-temperature conditions (-30°C and below). Therefore, there is an urgent need in this field for a comprehensive solution that can precisely construct a high-ionic-conductivity interface layer at the electrode interface through the synergistic effect of electrolyte component design and activation process optimization. Summary of the Invention

[0007] The technical problem that this invention aims to solve is that existing electrolytes are difficult to achieve high performance under low temperature conditions, and single additives cannot achieve multiple functions.

[0008] To address the aforementioned technical problems, in a first aspect, the present invention provides a low-temperature electrolyte for sodium-ion batteries. The low-temperature electrolyte comprises a sodium salt, an interface-modifying additive, a sodium-conducting framework additive, and an organic solvent. The mass ratio of the interface-modifying additive to the sodium-conducting framework additive is 1:0.5~2 (e.g., 1:0.5, 1:0.7, 1:1, 1:1.5, or 1:2, etc.), and the concentration of the sodium salt is 0.8~1.5M (e.g., 0.8M, 0.9M, 1M, 1.2M, 1.4M, or 1.5M, etc.). Under the specific mass ratio of the present invention, it is beneficial to form a "continuous, interwoven, rapid ion transport network," ensuring that ions can smoothly converge from the electrode surface, thereby minimizing impedance at low temperatures.

[0009] The sodium-ion battery low-temperature electrolyte provided by this invention uses a dual-functional additive system. It contains silicone compounds as interface-modifying additives, which can preferentially reduce and form a stable SEI film rich in siloxanes and sodium fluoride on the negative electrode surface. The MOF material serves as a sodium-conducting framework additive, which provides an ordered channel for sodium ion transport using its regular pore structure. The resulting electrolyte has the advantage of high ionic conductivity.

[0010] Preferably, the sodium salt includes NaPF6 and / or NaClO4.

[0011] Preferably, the interface-modifying additive is tris(trimethylsilane) phosphate and / or tris(trimethylsilane) phosphite. Tris(trimethylsilane) phosphate (TMSP) and tris(trimethylsilane) phosphite (TMSPi), through their Si-OP-containing functional groups and highly reactive sites, can precisely regulate the formation mechanism, chemical composition, and physical properties of the SEI film (solid electrolyte interphase), fundamentally solving the problems of high interfacial impedance, severe side reactions, and poor cycle stability in sodium-ion batteries.

[0012] Preferably, the sodium-conducting skeleton additive includes ZIF-8 and / or UIO-66.

[0013] This invention uses MOF material as a sodium-conducting framework additive, utilizing its regular pore structure to provide an ordered channel for sodium ion transport.

[0014] Preferably, the particle size of the sodium-conducting skeleton additive is 50~200nm, for example, it can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 180nm or 200nm, etc.

[0015] Preferably, the mass of the interface-type modifying additive and the sodium-conducting framework additive accounts for 1% to 5% of the total mass of the sodium-ion battery low-temperature electrolyte, for example, 1%, 2%, 3%, 4%, or 5%. The quality control of the interface-type modifying additive and the sodium-conducting framework additive in this invention facilitates the formation of a complete, uniform, thin (nanoscale), and dense composite interface layer, effectively regulating ion transport without introducing significant additional impedance.

[0016] Preferably, the organic solvent comprises a mixture of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC), wherein the volume ratio of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and ethyl methyl carbonate is (2~4):(1~3):(0.5~2):(3~5), for example, 2:1:0.5:3, 3:2:0.5:3, 4:3:2:5, or 3:2:1:4, etc. This organic solvent can work synergistically with interface-modifying additives. The interface-modifying additives can remove hydrogen fluoride, preventing the hydrogen fluoride generated during defluorination of the organic solvent from corroding the electrode. Simultaneously, the organic components of the organic solvent can enhance the membrane flexibility, achieving a membrane structure with superior performance.

[0017] In a second aspect, the present invention provides a sodium-ion battery, the sodium-ion battery comprising the sodium-ion battery low-temperature electrolyte described in the first aspect.

[0018] Thirdly, the present invention provides an activation method for the sodium-ion battery described in the second aspect, the activation method comprising: (1) The sodium-ion battery low-temperature electrolyte is immersed in the electrode at low temperature to cause an interfacial reaction; (2) Then, under a medium temperature environment, the first stage of charging and the first stage of discharging are performed sequentially, and the first stage of charging and discharging are cycled 1 to 3 times to obtain the SEI film; (3) Continue to perform the second stage of charging and the second stage of discharging at low temperature, and cycle the second stage of charging and discharging 2 to 5 times to obtain the sodium-ion battery.

[0019] The method provided by this invention is a step-by-step activation process. Through the synergistic effect of a bifunctional additive system and the step-by-step activation process, the decomposition products of the bifunctional additives form a siloxane network, which can improve mechanical toughness and has the effect of elastic buffering and adapting to volume changes. The decomposition product of the electrolyte and salt, sodium fluoride, can also improve mechanical and thermal properties, so that the overall electrolyte has high mechanical stability, excellent chemical stability and high ionic conductivity. The step-by-step activation method precisely controls the composition and structure of the interface layer through a three-stage process of "low temperature standing - medium pressure formation - low temperature aging", forming an interface layer with both high ionic conductivity and excellent mechanical stability, so that sodium-ion batteries can still maintain excellent performance in extreme low temperature environments of -30℃ to -50℃.

[0020] Preferably, the low temperature in step (1) is -10~0℃, and the immersion time is 12~48h; step (1) allows the electrolyte to fully wet the electrode and cause an initial interface reaction.

[0021] The temperature of the medium-pressure environment in step (2) is 10~25℃, the first stage of charging rate is 0.05~0.2C, the first stage of charging is charging to a voltage of 2~3V; the first stage of discharging rate is 0.02~0.1C, the first stage of discharging is discharging to a voltage of 1~2V; step (2) can construct a stable SEI film.

[0022] In step (3), the low temperature is -20~0℃, the charging rate of the second stage is 0.1~0.5C, and the second stage of charging is charging to a voltage of 3~3.8V; the discharging rate of the second stage is 0.1~0.5C, and the second stage of discharging is discharging to a voltage of 1.5~2.5V. Step (3) enables the interface layer to tend to stabilize at low temperatures.

[0023] Implementing this invention has the following beneficial effects: The electrolyte and step-by-step activation method provided by this invention exhibit significant synergistic effects: bifunctional additives synergistically optimize interface properties through different mechanisms of action; interface-modifying additives form a stable SEI film; and sodium-conducting framework additives provide high-speed ion transport channels, solving the problem of limited functionality of single additives. Excellent low-temperature performance: Through the synergistic design of the electrolyte and activation process, the capacity retention rate of the battery at -30℃ is increased from approximately 40% in traditional methods to over 85%. Long cycle life: The formed interface layer structure is stable and effectively inhibits interface degradation during cycling, enabling the battery to retain over 80% of its capacity after 1000 cycles at -20℃. Strong process compatibility: Only adjustments to existing electrolyte formulations and formation processes are required; no changes to electrode materials or production lines are necessary, facilitating industrial-scale promotion. Attached Figure Description

[0024] Figure 1 This is a comparison curve of discharge capacity retention rate under -30℃ environment for Embodiment 1 and Comparative Examples 1-4 of the present invention.

[0025] Figure 2 This is a comparison curve of the -20℃ cycling performance of Example 1 of the present invention with Comparative Examples 1 and 4. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1 This embodiment provides a low-temperature electrolyte for a sodium-ion battery, a sodium-ion battery, and an activation method. Electrolyte preparation: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), dissolve NaPF6 in a mixed solvent of EC / PC / FEC / EMC (volume ratio 3:2:1:4) to prepare a basic electrolyte with a concentration of 1.0 M. Add a bifunctional additive system consisting of TMSP and ZIF-8 (particle size 100 nm) to this basic electrolyte, wherein the mass ratio of TMSP to ZIF-8 is 1:1, and the total addition amount is 3% of the total mass of the electrolyte. Stir well and set aside for use.

[0028] Battery assembly: Using hard carbon material as the negative electrode, Prussian white material as the positive electrode, and a microporous polyolefin separator, a CR2032 button cell is assembled.

[0029] Stepwise activation: Low-temperature standing: Place the assembled battery in an environment of -5℃ for 24 hours; Medium voltage formation: Transfer to a 15°C environment, charge to 2.5V with a constant current of 0.1C, then discharge to 1.5V with a constant current of 0.05C, repeat 2 times; Low temperature aging: In an environment of -10℃, it is charged and discharged 3 times at a constant current of 0.2C, with an upper limit charging voltage of 3.5V and a lower limit discharging voltage of 2.0V.

[0030] Example 2

[0031] The difference between this embodiment and Embodiment 1 is that the mass ratio of TMSPi to ZIF-8 in the bifunctional additive system is 1:0.5, and the total amount added is 2% of the total mass of the electrolyte.

[0032] Example 3

[0033] The difference between this embodiment and Embodiment 1 is that the mass ratio of TMSPi to ZIF-8 in the bifunctional additive system is 1:2, and the total amount added is 5% of the total mass of the electrolyte.

[0034] Example 4

[0035] This embodiment provides a low-temperature electrolyte for a sodium-ion battery, a sodium-ion battery, and an activation method. Electrolyte preparation: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), dissolve NaClO4 in a mixed solvent of EC / PC / FEC / EMC (volume ratio 3:1:2:5) to prepare a basic electrolyte with a concentration of 1.2 M. Add a bifunctional additive system consisting of TMSPi and UIO-66 (particle size 100 nm) to this basic electrolyte, wherein the mass ratio of TMSPi to UIO-66 is 1:1, and the total addition amount is 3% of the total mass of the electrolyte. Stir well and set aside for use.

[0036] Battery assembly: Using hard carbon material as the negative electrode, Prussian white material as the positive electrode, and a microporous polyolefin separator, a CR2032 button cell is assembled.

[0037] Stepwise activation: Low-temperature standing: Place the assembled battery in an environment of -2℃ for 36 hours; Medium voltage formation: Transfer to a 20°C environment, charge at a constant current of 0.2C to 2.8V, then discharge at a constant current of 0.1C to 1.2V, repeat 3 times; Low temperature aging: In an environment of -15℃, it is charged and discharged at a constant current of 0.3C for 4 cycles, with an upper limit charging voltage of 3.5V and a lower limit discharging voltage of 2.0V.

[0038] Example 5

[0039] This embodiment provides a low-temperature electrolyte for a sodium-ion battery, a sodium-ion battery, and an activation method. Electrolyte preparation: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), dissolve NaPF6 in a mixed solvent of EC / PC / FEC / EMC (volume ratio 2:3:2:3) to prepare a basic electrolyte with a concentration of 0.8 M. Add a bifunctional additive system consisting of TMSPi and UIO-66 (particle size 200 nm) to this basic electrolyte, wherein the mass ratio of TMSPi to UIO-66 is 1:1, and the total addition amount is 3% of the total mass of the electrolyte. Stir well and set aside for use.

[0040] Battery assembly: Using hard carbon material as the negative electrode, Prussian white material as the positive electrode, and a microporous polyolefin separator, a CR2032 button cell is assembled.

[0041] Stepwise activation: Low-temperature standing: Place the assembled battery in an environment of -5℃ for 24 hours; Medium voltage formation: Transfer to a 15°C environment, charge to 2.5V with a constant current of 0.1C, then discharge to 1.5V with a constant current of 0.05C, repeat 2 times; Low temperature aging: In an environment of -10℃, it is charged and discharged 3 times at a constant current of 0.2C, with an upper limit charging voltage of 3.5V and a lower limit discharging voltage of 2.0V.

[0042] Comparative Example 1 Except for the absence of bifunctional additives in the electrolyte, the other steps are exactly the same as in Example 1.

[0043] Comparative Example 2 The electrolyte is the same as in Example 1 (containing bifunctional additives), but the activation process is changed to direct charge-discharge cycling at 0.1C at room temperature of 25°C, instead of step-by-step activation.

[0044] Comparative Example 3 The electrolyte was only modified by adding TMSPi (interface modification additive) and not by adding ZIF-8 (sodium-conducting framework additive). The rest of the steps were exactly the same as in Example 1.

[0045] Comparative Example 4 The difference between this comparative example and Example 1 is that the TMSPi and ZIF-8 dual additive system is replaced with an equal mass of vinylene carbonate (VC) and ZIF-8 dual additive system.

[0046] The batteries provided in the above embodiments and comparative examples were subjected to performance tests: After the activated batteries were cycled 3 times at 0.2C at 25°C, they were moved to a low-temperature environment of -30°C to test their 0.2C discharge capacity, and the capacity retention rate was calculated. The results are shown in Table 1 below: Table 1

[0047] The discharge capacity retention rate comparison curves of Example 1 and Comparative Examples 1-4 at -30℃ are shown below. Figure 1 As shown in the figure. The comparison curves of the -20℃ cycling performance of Example 1 with Comparative Examples 1 and 4 are shown in the figure. Figure 2 As shown.

[0048] As shown in Table 1, at -30℃, the capacity retention rate of Comparative Example 1 (without additives) was only 38%; the capacity retention rate of Comparative Example 2 (activated at room temperature) was 52%; the capacity retention rate of Comparative Example 3 (single additive) was 65%; while the capacity retention rate of Example 1 using the scheme of this invention was as high as 86%. The performance of Comparative Example 4 (VC+ZIF-8) was much lower than that of Example 1 (TMSPi+ZIF-8), which proves that not a simple combination of any additive and MOF material can produce a synergistic effect. VC, as a common film-forming additive, has a different decomposition mechanism and product properties than TMSP / TMSPi, and cannot form a similar siloxane flexible network at the interface. Therefore, it is difficult to synergistically construct a high-performance composite interface layer with ZIF-8. This comparative result further highlights the necessity and innovation of the synergistic design of specific interface-type modifying additives (containing silicone ester compounds) and sodium-conducting framework additives (specific MOFs) in this invention.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-temperature electrolyte for sodium-ion batteries, characterized in that, The sodium-ion battery low-temperature electrolyte comprises sodium salt, interfacial modifying additive, sodium-conducting framework additive, and organic solvent. The mass ratio of the interfacial modifying additive to the sodium-conducting framework additive is 1:0.5~2, and the concentration of the sodium salt is 0.8~1.5M.

2. The sodium-ion battery low-temperature electrolyte according to claim 1, characterized in that, The interface-modifying additives are tris(trimethylsilane) phosphate and / or tris(trimethylsilane) phosphite.

3. The sodium-ion battery low-temperature electrolyte according to claim 1, characterized in that, The sodium-conducting skeleton additives include ZIF-8 and / or UIO-66.

4. The sodium-ion battery low-temperature electrolyte according to claim 3, characterized in that, The particle size of the sodium-conducting skeleton additive is 50~200nm.

5. The sodium-ion battery low-temperature electrolyte according to claim 1, characterized in that, The interface-type modifying additives and sodium-conducting framework additives account for 1% to 5% of the total mass of the sodium-ion battery low-temperature electrolyte.

6. The sodium-ion battery low-temperature electrolyte according to claim 1, characterized in that, The sodium salt includes any one or a combination of at least two of NaPF6, NaFSI, or NaClO4.

7. The sodium-ion battery low-temperature electrolyte according to claim 1, characterized in that, The organic solvent comprises a mixture of ethylene carbonate, propylene carbonate, fluoroethylene carbonate and methyl ethyl carbonate, wherein the volume ratio of ethylene carbonate, propylene carbonate, fluoroethylene carbonate and methyl ethyl carbonate is (2~4):(1~3):(0.5~2):(3~5).

8. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion battery low-temperature electrolyte according to any one of claims 1 to 7.

9. The activation method for a sodium-ion battery according to claim 8, characterized in that, The activation method includes: (1) The sodium-ion battery low-temperature electrolyte is immersed in the electrode at low temperature to cause an interfacial reaction; (2) Then, under medium pressure, the first stage of charging and the first stage of discharging are performed sequentially, and the first stage of charging and discharging are cycled 1 to 3 times to obtain the SEI film; (3) Continue to perform the second stage of charging and the second stage of discharging at low temperature, and cycle the second stage of charging and discharging 2 to 5 times to obtain the sodium-ion battery.

10. The activation method according to claim 9, characterized in that, The low temperature mentioned in step (1) is -10~0℃, and the soaking time is 12~48h; The temperature of the medium-pressure environment in step (2) is 10~25℃, the charging rate of the first stage is 0.05~0.2C, and the first stage of charging is charging to a voltage of 2~3V; the discharging rate of the first stage is 0.02~0.1C, and the first stage of discharging is discharging to a voltage of 1~2V; The low temperature mentioned in step (3) is -20~0℃, the charging rate of the second stage is 0.1~0.5C, and the second stage charging is charging to a voltage of 3~3.8V; the discharging rate of the second stage is 0.1~0.5C, and the second stage discharging is discharging to 1.5~2.5V.

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