Sodium-ion battery electrolyte, electrolyte injection method and battery
By adding thiophene cyano compounds and phenyl phthalic anhydride compounds to sodium-ion batteries through a phased injection method, the problems of unstable SEI film and electrolyte decomposition in sodium-ion batteries were solved, the fast-charging cycle performance and stability of the batteries were improved, and the application requirements under high-rate conditions were met.
Patent Information
- Application Number
- CN202511505388.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-21
- Publication Date
- 2026-03-06
AI Technical Summary
The SEI film of sodium-ion batteries is unstable during charge and discharge, leading to continuous decomposition of the electrolyte, which affects the fast charge cycle performance. Furthermore, under high voltage and fast charging conditions, sodium salts and additives in the electrolyte react with trace amounts of water to generate HF, which corrodes the positive and negative electrode surfaces, causing battery failure.
A phased electrolyte injection method is adopted, in which thiophene cyano compounds and phenyl phthalic anhydride compounds are added to the first and second electrolyte injections respectively to form a synergistic effect, inhibit the dissolution of transition metals at the positive electrode interface, improve the fast charge cycle performance of the battery, and reduce the DCR growth rate and energy loss.
Through synergistic effects, the fast-charging cycle performance of sodium-ion batteries is improved, the increase in battery internal resistance is reduced, and the stability and fast-charging capability of the batteries are enhanced, meeting the application requirements under high-rate conditions.
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Figure CN121618052A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a sodium-ion battery electrolyte, an electrolyte injection method, and a battery. Background Technology
[0002] Sodium-ion batteries offer significant advantages over lithium-ion batteries, including stable raw material supply, low cost, high potential for fast charging and discharging, good low-temperature performance, and no risk of over-discharge. They have a broad market potential in low-energy-density electric passenger vehicles, two-wheeled electric vehicles, energy storage, and power tools. Furthermore, sodium-ion batteries can also be used in energy storage applications, such as renewable energy integration and industrial energy storage. Therefore, sodium-ion batteries are considered a highly promising supplementary energy storage technology for both electric vehicles and stationary energy storage.
[0003] As a crucial component of sodium-ion batteries, the electrolyte decomposes on the negative electrode surface, forming a solid electrode / electrolyte interface (SEI) film. However, the SEI film in sodium-ion batteries is unstable during charge and discharge, continuously dissolving and regenerating, leading to ongoing electrolyte decomposition and thus affecting the fast-charge cycle performance of sodium-ion batteries.
[0004] Furthermore, under high voltage and fast charging conditions, sodium salts and additives in the electrolyte will react with trace amounts of water in the electrolyte system to generate HF, which will not only accelerate the decomposition of the electrolyte, but also corrode the positive and negative electrode surfaces, damage the electrode structure, and cause transition metals to dissolve, ultimately leading to battery failure.
[0005] Currently, improving the fast-charging cycle performance of sodium-ion batteries mainly focuses on two aspects. One is to conduct research on the modification of cathode materials, optimizing the carbon content through doping, coating and other means to improve the conductivity of the materials. The other is to conduct research on the modification of electrolytes, mainly by introducing new film-forming additives to form a uniform and dense SEI film to ensure the fast-charging cycle performance of the battery. Summary of the Invention
[0006] Based on the technical problems existing in the background art, the present invention proposes a sodium-ion battery electrolyte, an electrolyte injection method, and a battery.
[0007] The present invention provides a sodium-ion battery electrolyte, comprising a primary electrolyte and a secondary electrolyte. The primary electrolyte comprises a first sodium salt, a first solvent, and a first additive. The secondary electrolyte comprises a second sodium salt, a second solvent, and a second additive. The first additive comprises a thiophene cyano compound, and the second additive comprises a phenyl phthalic anhydride compound.
[0008] The sodium-ion battery electrolyte of the present invention is prepared by adding thiophene cyano compounds and phenyl phthalic anhydride compounds to the first and second electrolyte injections, respectively. The two compounds work synergistically to suppress the dissolution of transition metals at the positive electrode interface, improve the fast-charging cycle performance of the battery, reduce the DCR growth rate during the fast-charging cycle, reduce energy loss and heat generation, and meet the fast-charging application requirements of sodium-ion batteries under high-rate conditions.
[0009] Preferably, the structural formula of the thiophene cyano compound is shown in Formula I:
[0010]
[0011] Formula I
[0012] In Formula I, R1 to R3 are independently selected from hydrogen atoms, halogen atoms, phenyl groups, cyano groups, five- or six-membered heterocycles, and substituted or unsubstituted C atoms. 1~5 One or more of alkyl, alkenyl, and alkynyl groups.
[0013] Preferably, the thiophene cyano compound is selected from at least one of compounds 1 to 4:
[0014]
[0015] Compound 1 Compound 2
[0016]
[0017] Compound 3 Compound 4.
[0018] Thiophene cyano compounds combine thiophene and cyano groups. Thiophene forms a low-resistance polymer CEI film on the positive electrode surface, sulfur increases the flexibility of the interfacial film, and elements such as fluorine and oxygen enrich the interfacial film composition of the electrode / electrolyte, thereby improving the structural stability of the interfacial film. The cyano group has a strong coordination ability and can bind to the active sites on the electrode surface, masking the active ions on the positive electrode surface and reducing the decomposition of the electrolyte by the electrode under high-rate conditions.
[0019] The CAS number of compound 1 is 79505-22-9, the CAS number of compound 2 is 3002446-82-1, the CAS number of compound 3 is 2889358-89-6, and the CAS number of compound 4 is 2259315-07-4.
[0020] Preferably, the structural formula of the phenyl phthalic anhydride compound is shown in Formula II:
[0021]
[0022] Formula II
[0023] In Formula II, R4 to R7 are selected from hydrogen atoms, halogen atoms, benzene rings, substituted or unsubstituted C atoms, respectively. 1~5 It can be any one of alkyl, alkenyl, and alkynyl groups, and at least one of R4 to R7 is a functional group containing a benzene ring.
[0024] Preferably, the phenyl phthalic anhydride compound is selected from at least one of compounds 5 to 7:
[0025]
[0026] Compound 5 Compound 6
[0027]
[0028] Compound 7.
[0029] Phenyl phthalic anhydride compounds contain both benzene rings and anhydride functional groups. The benzene rings effectively protect the positive electrode interface, inhibiting the migration of transition metal ions at the positive electrode under fast charging conditions and the direct contact between the electrode interface and the electrolyte, thus improving the fast charging cycle stability of the battery. The anhydride readily undergoes a reduction film-forming reaction at the negative electrode interface, forming a stable SEI film that isolates the direct contact between the electrolyte and the electrode interface, alleviates electrolyte consumption, and reduces the irreversible loss of active sodium at the negative electrode interface under high-rate conditions, thereby improving the overall performance of the battery.
[0030] Compound 5 is 4-phenylethynylphthalic anhydride (CAS: 119389-05-8), compound 6 is tetraphenylphthalic anhydride (CAS: 4741-53-1), and compound 7 is 4-phenoxyphthalic anhydride (CAS: 21345-01-7).
[0031] Preferably, the first additive further includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and vinyl sulfate (DTD).
[0032] Vinylene carbonate (VC), fluoroethylene carbonate (FEC), and vinyl sulfate (DTD) are used as film-forming additives to help promote film formation on the positive electrode surface.
[0033] Preferably, the first sodium salt is selected from one or more of sodium hexafluorophosphate (NaPF6), sodium difluorosulfonamide (NaFSI), and sodium tetrafluoroborate (NaBF4).
[0034] The fluorine atoms in the first sodium salt have strong electron-withdrawing properties, which helps to enhance ion association and pairing, making sodium ions easier to dissociate and promoting the migration of sodium ions between the positive and negative electrodes, thus improving kinetic performance.
[0035] Preferably, the second sodium salt is selected from at least two of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium dioxolane borate (NaBOB), sodium difluorooxolane borate (NaODFB), sodium difluorosulfonamide (NaFSI), and sodium ditrifluoromethylsulfonamide (NaTFSI).
[0036] The second sodium salt provides a multi-anion coordination environment, which can regulate the solvation structure of sodium ions, resulting in more controllable dissolution behavior of sodium ions and thus optimizing their electrode intercalation / deintercalation behavior under high-rate conditions.
[0037] Preferably, the first solvent is a carbonate solvent, and the second solvent includes carbonate solvents and carboxylic acid ester solvents.
[0038] More preferably, the carbonate solvent includes cyclic carbonates and chain carbonates; the cyclic carbonate is selected from one or more of ethylene carbonate (EC), fluoroethylene carbonate (FEC), and propylene carbonate (PC); the chain carbonate is selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC); and the carboxylic acid ester solvent is selected from one or more of ethyl acetate (EA), methyl acetate (MA), propyl propionate (PP), and ethyl propionate (EP).
[0039] The solvent uses a mixture of cyclic carbonates, chain carbonates, and carboxylic acid esters instead of conventional carbonate organic solvents, which takes into account the requirements of dielectric constant, viscosity, and binding energy. It can form an anion-rich solvation structure, which helps to reduce the oxidation and decomposition of electrolyte solvent under fast charging conditions, while reducing HF generation and suppressing side reactions at the sodium-electrolyte interface.
[0040] More preferably, the second solvent is a combination of propylene carbonate (PC), ethyl methyl carbonate (EMC), and ethyl acetate (EA).
[0041] Preferably, the first sodium salt accounts for 8% to 15% of the mass of the electrolyte; the first solvent accounts for 80% to 89% of the mass of the electrolyte; and the first additive accounts for 3% to 5% of the mass of the electrolyte.
[0042] Preferably, the thiophene cyano compound accounts for 0-2% of the mass of a single electrolyte solution.
[0043] Preferably, the second sodium salt accounts for 10% to 20% of the mass of the second electrolyte; the second solvent accounts for 70% to 87% of the mass of the second electrolyte; and the second additive accounts for 3% to 10% of the mass of the second electrolyte.
[0044] By adjusting the content of different sodium salts, solvents, and additives, the overall performance of the battery can be optimized. Quality control of sodium salts and solvents ensures both electrolyte conductivity and improved electrolyte wettability on the electrodes, ensuring unimpeded sodium ion transport and minimal increase in polarization during battery cycling. Additives can form a relatively stable SEI film on the hard carbon surface of the negative electrode, coating the electrode surface and improving electrode stability. Simultaneously, the synergistic effect of co-deposition of different additives helps reduce film-forming impedance, preventing an increase in internal battery resistance and improving the battery's fast-charging and cycle performance.
[0045] Preferably, the mass ratio of the first and second electrolyte injections is (80~85):(15~20).
[0046] By combining first and second electrolytes with different compositions, and by optimizing and adjusting the quality of the electrolytes, the interfacial impedance and fast-charge cycle performance of the electrolytes can be effectively improved. This can also eliminate the influence on the initial film-forming impedance to a certain extent, suppress the film-forming consumption of the first additive throughout the battery's life cycle, and further improve battery performance.
[0047] The present invention also proposes a method for injecting electrolyte into a sodium-ion battery, comprising the following steps: injecting a first electrolyte into the sodium-ion battery, performing a first formation of the sodium-ion battery, injecting a second electrolyte into the sodium-ion battery, and performing a second formation of the sodium-ion battery.
[0048] Preferably, the first formation includes constant voltage charging of the sodium-ion battery after the first electrolyte injection, with a voltage of 3.7V, a charging time of 12 hours, and a formation temperature of 45°C.
[0049] Preferably, the second formation includes constant current charging of the sodium-ion battery after the second electrolyte injection, with a current of 0.33C, a cutoff voltage of 3.6V, and a formation temperature of 25°C.
[0050] A sodium-ion battery includes a positive electrode, a negative electrode, a separator, and the electrolyte described above.
[0051] The sodium-ion battery provided by this invention contains the above-mentioned electrolyte, which helps to meet the fast-charging application requirements of sodium-ion batteries under high-rate conditions.
[0052] Preferably, the electrolyte is injected using the above-described injection method.
[0053] Preferably, the positive electrode comprises a positive electrode material, which is selected from one or more of transition metal layered oxides, polyanionic compounds, and Prussian blue compounds.
[0054] More preferably, the transition metal layered oxide is NaFe. 1 / 3 Ni 1 / 3 Mn 1 / 3 O2.
[0055] Preferably, the negative electrode comprises a negative electrode material, which is selected from one or more of hard carbon, soft carbon, expanded graphite, phosphorus-carbon composite material, and expanded graphite / hard carbon composite material.
[0056] More preferably, the negative electrode material is hard carbon.
[0057] Preferably, the diaphragm is selected from one or more of polyethylene (PE), polypropylene (PP), and composite ceramic membrane (CCS).
[0058] More preferably, the composite ceramic membrane is a polypropylene (PP) membrane coated with a nano-alumina coating.
[0059] The beneficial effects of this invention are as follows:
[0060] The electrolyte provided by this invention employs a solvent combination with high dielectric constant and moderate binding energy, which can form a solvated structure rich in anions. This ensures high conductivity of the electrolyte, achieves a stable electrode interface, reduces HF generation, and suppresses side reactions at the sodium-electrolyte interface. Furthermore, by adding compounds of formula I and formula II to the first and second electrolyte injections respectively, the two compounds work synergistically to suppress the dissolution of transition metals at the positive electrode interface, improve the fast-charging cycle performance of the battery, reduce the DCR growth rate during fast-charging cycles, reduce energy loss and heat generation, and meet the fast-charging application requirements of sodium-ion batteries under high-rate conditions. Attached Figure Description
[0061] Figure 1 The content of transition metal dissolution in sodium-ion batteries proposed in this invention. Detailed Implementation
[0062] The technical solution of the present invention will be described in detail through specific embodiments.
[0063] Unless otherwise specified, all materials and reagents used in the following examples and comparative examples are commercially available.
[0064] Example 1
[0065] Prepare one injection of electrolyte:
[0066] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) was slowly added to the first solvent, and after NaPF6 was completely dissolved, vinylene carbonate (VC), vinyl sulfate (DTD) and compound 3 were added to obtain the final product;
[0067] One electrolyte consists of the following components by mass percentage: 13% sodium hexafluorophosphate (NaPF6), 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD) and 0.2% compound 3, with the solvent to be made up to 100%.
[0068] Preparation of two-stage electrolyte:
[0069] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) are mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) are slowly added to the second solvent until the sodium salts are completely dissolved to obtain the final product.
[0070] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI), and solvent to bring the total to 100%.
[0071] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0072] Preparation of positive electrode:
[0073] NaFe, the positive electrode material 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, binder (PVDF), and conductive agent (SP) were dispersed in NMP organic solvent at a mass ratio of 96:2:2. The mixture was stirred under vacuum until stable and homogeneous, and then uniformly coated onto a 15μm thick carbon-coated aluminum foil. After the aluminum foil was dried at room temperature, it was transferred to a 120℃ forced-air oven for 1 hour of drying. Then, it was cold-pressed and die-cut to form a positive electrode sheet.
[0074] Preparation of negative electrode:
[0075] Hard carbon (HC), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive agent (SP) were mixed together in a mass ratio of 96:1:2:1 and dispersed in deionized water. The mixture was stirred until stable and homogeneous using a vacuum mixer to form a negative electrode slurry. The negative electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 12 μm. After the aluminum foil was air-dried at room temperature, it was transferred to a 120°C forced-air oven for drying for 1 hour. Finally, it was cold-pressed and die-cut to form a negative electrode sheet.
[0076] Preparation of sodium-ion batteries:
[0077] The positive electrode, separator (the separator used is a polypropylene PP film coated with nano-alumina coating, wherein the thickness of the PP film is 12μm and the thickness of the nano-alumina coating is 4μm), and negative electrode are stacked in sequence to obtain a bare cell according to the process of stacked battery. Then the bare cell is placed in an aluminum-plastic film for pre-encapsulation, injected with the prepared electrolyte, and then encapsulated to obtain the required soft pack battery.
[0078] One-time electrolyte injection: One injection of electrolyte is injected into the battery and vacuum sealed. The battery is then placed in a 45°C environment and left to stand for 24 hours to fully wet the electrolyte, thus obtaining a one-time electrolyte-injected battery cell.
[0079] Primary formation: The above-mentioned primary liquid-filled battery cell is charged under constant voltage of 3.7V for 12 hours and at a formation temperature of 45℃ to obtain a primary formed battery cell.
[0080] Secondary electrolyte injection: A second electrolyte is injected into the primary formed cell, vacuum-sealed, and placed in a 25°C environment for 24 hours to fully wet the cell, thus obtaining a secondary electrolyte-injected cell.
[0081] Secondary formation: The above-mentioned secondary electrolyte-filled cells are charged with a constant current of 0.33C, a cutoff voltage of 3.6V, and a formation temperature of 25℃ to obtain sodium-ion batteries.
[0082] Example 2
[0083] Prepare one injection of electrolyte:
[0084] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) was slowly added to the first solvent, and after NaPF6 was completely dissolved, vinylene carbonate (VC), vinyl sulfate (DTD) and compound 3 were added to obtain the final product;
[0085] One electrolyte consists of the following components by mass percentage: 13% sodium hexafluorophosphate (NaPF6), 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD) and 1% compound 3, with solvent to make up to 100%.
[0086] Preparation of two-stage electrolyte:
[0087] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) are mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) are slowly added to the second solvent, and after the sodium salts are completely dissolved, vinylene carbonate (VC) is added to obtain the final product;
[0088] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI), and solvent to bring the total to 100%.
[0089] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0090] The preparation methods for the positive electrode, negative electrode, and sodium-ion battery are the same as in Example 1.
[0091] Example 3
[0092] Prepare one injection of electrolyte:
[0093] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) is slowly added to the first solvent, and after the NaPF6 is completely dissolved, vinylene carbonate (VC), vinyl sulfate (DTD) and compound 3 are added to obtain the final product;
[0094] One electrolyte consists of the following components by mass percentage: 13% sodium hexafluorophosphate (NaPF6), 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD) and 2% compound 3, with solvent to make up to 100%.
[0095] Preparation of two-stage electrolyte:
[0096] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) are mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) are slowly added to the second solvent, and after the sodium salts are completely dissolved, vinylene carbonate (VC) is added to obtain the final product;
[0097] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI), and solvent to bring the total to 100%.
[0098] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0099] The preparation methods for the positive electrode, negative electrode, and sodium-ion battery are the same as in Example 1.
[0100] Example 4
[0101] Prepare one injection of electrolyte:
[0102] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) is slowly added to the first solvent, and after the NaPF6 is completely dissolved, vinylene carbonate (VC) and vinyl sulfate (DTD) are added to obtain the final product.
[0103] One electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI), 0.5% vinylene carbonate (VC) and 1% vinyl sulfate (DTD), with the solvent to be made up to 100%.
[0104] Preparation of two-stage electrolyte:
[0105] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) were mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) were slowly added to the second solvent, and after the sodium salts were completely dissolved, compound 7 was added to obtain the final product;
[0106] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI) and 3% compound 7, with the solvent to be made up to 100%.
[0107] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0108] The preparation methods for the positive electrode, negative electrode, and sodium-ion battery are the same as in Example 1.
[0109] Example 5
[0110] Prepare one injection of electrolyte:
[0111] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) is slowly added to the first solvent, and after the NaPF6 is completely dissolved, vinylene carbonate (VC) and vinyl sulfate (DTD) are added to obtain the final product.
[0112] One electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI), 0.5% vinylene carbonate (VC) and 1% vinyl sulfate (DTD), with the solvent to be made up to 100%.
[0113] Preparation of two-stage electrolyte:
[0114] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) were mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) were slowly added to the second solvent, and after the sodium salts were completely dissolved, compound 7 was added to obtain the final product;
[0115] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI) and 5% compound 7, with the solvent to be made up to 100%.
[0116] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0117] The preparation methods for the positive electrode, negative electrode, and sodium-ion battery are the same as in Example 1.
[0118] Example 6
[0119] Prepare one injection of electrolyte:
[0120] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) is slowly added to the first solvent, and after the NaPF6 is completely dissolved, vinylene carbonate (VC) and vinyl sulfate (DTD) are added to obtain the final product.
[0121] One electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI), 0.5% vinylene carbonate (VC) and 1% vinyl sulfate (DTD), with the solvent to be made up to 100%.
[0122] Preparation of two-stage electrolyte:
[0123] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) were mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) were slowly added to the second solvent, and after the sodium salts were completely dissolved, compound 7 was added to obtain the final product;
[0124] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI) and 10% compound 7, with the solvent to be made up to 100%.
[0125] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0126] The preparation methods for the positive electrode, negative electrode, and sodium-ion battery are the same as in Example 1.
[0127] Example 7
[0128] Prepare one injection of electrolyte:
[0129] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) was slowly added to the first solvent, and after NaPF6 was completely dissolved, vinylene carbonate (VC), vinyl sulfate (DTD) and compound 3 were added to obtain the final product;
[0130] One electrolyte consists of the following components by mass percentage: 13% sodium hexafluorophosphate (NaPF6), 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD) and 1% compound 3, with solvent to make up to 100%.
[0131] Preparation of two-stage electrolyte:
[0132] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) were mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) were slowly added to the second solvent, and after the sodium salts were completely dissolved, compound 7 was added to obtain the final product;
[0133] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI) and 5% compound 7, with the solvent to be made up to 100%.
[0134] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0135] The preparation methods for the positive electrode, negative electrode, and sodium-ion battery are the same as in Example 1.
[0136] Example 8
[0137] Prepare one injection of electrolyte:
[0138] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) was slowly added to the first solvent, and after NaPF6 was completely dissolved, vinylene carbonate (VC), vinyl sulfate (DTD) and compound 3 were added to obtain the final product;
[0139] One electrolyte consists of the following components by mass percentage: 13% sodium hexafluorophosphate (NaPF6), 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD) and 1% compound 3, with solvent to make up to 100%.
[0140] Preparation of two-stage electrolyte:
[0141] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) were mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) were slowly added to the second solvent, and after the sodium salts were completely dissolved, compound 7 was added to obtain the final product;
[0142] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI) and 3% compound 7, with the solvent to be made up to 100%.
[0143] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0144] The preparation methods for the positive electrode, negative electrode, and sodium-ion battery are the same as in Example 1.
[0145] Example 9
[0146] Prepare one injection of electrolyte:
[0147] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) was slowly added to the first solvent, and after NaPF6 was completely dissolved, vinylene carbonate (VC), vinyl sulfate (DTD) and compound 3 were added to obtain the final product;
[0148] One electrolyte consists of the following components by mass percentage: 13% sodium hexafluorophosphate (NaPF6), 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD) and 1% compound 3, with solvent to make up to 100%.
[0149] Preparation of two-stage electrolyte:
[0150] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) were mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) were slowly added to the second solvent, and after the sodium salts were completely dissolved, compound 7 was added to obtain the final product;
[0151] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI) and 10% compound 7, with the solvent to be made up to 100%.
[0152] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0153] The preparation methods for the positive electrode, negative electrode, and sodium-ion battery are the same as in Example 1.
[0154] Comparative Example 1
[0155] Prepare one injection of electrolyte:
[0156] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of PC:EMC = 3:7 to obtain the first solvent; sodium hexafluorophosphate (NaPF6) is slowly added to the first solvent, and after the NaPF6 is completely dissolved, vinylene carbonate (VC) and tris(trimethylsilane) phosphate (TMSP) are added to obtain the final product;
[0157] One electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI), 0.5% vinylene carbonate (VC) and 1% tris(trimethylsilane) phosphate (TMSP), with the solvent to be made up to 100%.
[0158] Preparation of two-stage electrolyte:
[0159] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethyl acetate (EA) are mixed in a mass ratio of EMC:PC:EA = 50:30:20 to obtain a second solvent; sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) are slowly added to the second solvent, and after the sodium salts are completely dissolved, vinylene carbonate (VC) is added to obtain the final product;
[0160] The second electrolyte consists of the following components by mass percentage: 10% sodium hexafluorophosphate (NaPF6), 3% sodium difluorosulfonamide (NaFSI) and 10% vinylene carbonate (VC), with the solvent to be made up to 100%.
[0161] The first and second electrolyte solutions are mixed evenly at a mass ratio of 85:15 to obtain the final electrolyte solution.
[0162] The preparation methods for the positive electrode, negative electrode, and sodium-ion battery are the same as in Example 1.
[0163] Comparative Example 2
[0164] The only difference between Comparative Example 2 and Comparative Example 1 is that Comparative Example 2 uses a single-injection method, and the electrolyte formula is detailed in Table 1. The rest is the same as Comparative Example 1.
[0165] The comparison of the embodiments and comparative examples is shown in Table 1:
[0166] Table 1
[0167]
[0168] Test case
[0169] (1) HF content test
[0170] Weigh 20-30g of the electrolytes prepared in Examples 1-9 and Comparative Example 1 into conical flasks, record the mass as m, and add 1-2 drops of methyl red-EMC solution as an indicator. At this point, the electrolyte turns pink. Then, titrate with 0.1M triethylamine solution until the solution suddenly changes from pink to yellow, and record the titration volume of the standard solution as V.
[0171] Calculate the HF content of the electrolyte using the following formula:
[0172] HF content (ppm) = 20.006 × 1000 × V × c / m;
[0173] Take 20-30g of the electrolyte prepared in Examples 1-9 and Comparative Example 1 and put it into a clean and dry aluminum-plastic bottle. After sealing, place it in a 25°C oven for 14 days. Then take out the electrolyte and measure the acidity of the electrolyte again according to the above method. The test results are shown in Table 2.
[0174] (2) Initial DCR
[0175] First, the experimental batteries from Examples 1-9 and the comparative examples were subjected to capacity testing and fully charged. Then, they were discharged to a state of charge of 50% (SOC). After resting for 30 minutes, the sampling voltage V0 at the start of discharge was recorded. Then, the batteries were discharged at a current of 1C for 18 seconds, and the sampling voltage V1 at the end of discharge was recorded. The initial DCR of the experimental batteries was calculated using the following formula:
[0176] DCR=(V1-V0) / I
[0177] (3) 4C fast charging cycle test
[0178] The experimental batteries were placed in a 25°C constant temperature chamber and subjected to a fast-charge cycle test for 500 cycles, following the steps of "charging to full capacity at a constant current of 4C, then charging at a constant voltage until the current ≤0.05C, and finally discharging to empty capacity at a constant current of 1C". The discharge capacity of the first cycle was taken as the initial capacity Q1, and the discharge capacity of the last cycle was taken as the final capacity Q2. The capacity retention rate after 500 fast-charge cycles was calculated using the following formula.
[0179] Capacity retention rate = Q2 / Q1 * 100%
[0180] (4) DCR after 500 fast charging cycles
[0181] The DCR test method after 500 fast-charge cycles is the same as the initial DCR. The experimental batteries from Examples 1-9 and the comparative examples that underwent 500 fast-charge cycles were fully charged and then discharged to a 50% SOC state. After resting for 30 minutes, the sampling voltage V2 at the start of discharge was recorded. Then, the batteries were discharged at a 1C current I for 18 seconds, and the sampling voltage V3 at the end of discharge was recorded. The DCR of the experimental batteries after 500 fast-charge cycles was calculated using the following formula:
[0182] DCR=(V3-V2) / I
[0183] The test results of HF content, capacity retention rate and DCR after 500 cycles of 4C fast charging, and after being placed in a 25℃ oven for 14 days are shown in Table 2:
[0184] Table 2
[0185]
[0186] The only difference between Comparative Example 2 and Comparative Example 1 is that Comparative Example 2 involves a single electrolyte injection, while the electrolyte composition is a combination of a primary electrolyte injection and a secondary electrolyte injection. As shown in Table 2, the electrical performance of Comparative Example 1 is superior to that of Comparative Example 2. This is because NaFSI and EA are prone to decomposition at high temperatures, leading to battery capacity decay. Placing them in a secondary electrolyte injection (ambient temperature 25°C) avoids the side reactions caused by the high-temperature environment (45°C) of the primary electrolyte injection and formation process.
[0187] The difference between Comparative Example 1 and Examples 1-3 is that the electrolyte in Comparative Example 1 does not contain Compound 3. The results from Comparative Example 1 and Examples 1-3 show that adding Compound 3 to the electrolyte significantly improves fast-charge cycle performance and reduces the DCR of the battery after 500 fast-charge cycles; the effect is best when the content of Compound 3 in the electrolyte is 1%. This is because Compound 3 combines thiophene and cyano groups. Thiophene forms a low-resistance polymer CEI film on the positive electrode surface, sulfur increases the flexibility of the interfacial film, and elements such as fluorine and oxygen enrich the interfacial film composition, thereby improving the structural stability of the interfacial film. The cyano group has a strong coordination ability and can bind to active sites on the electrode surface, masking active ions on the positive electrode surface and reducing the decomposition of the electrolyte by the electrode under high-rate conditions.
[0188] The difference between Comparative Example 1 and Examples 4-6 is that the second-cell electrolyte does not contain compound 7. Compared to Comparative Example 1, Examples 4-6 show that the addition of compound 7 to the second-cell electrolyte significantly improves battery performance under high-rate conditions. The capacity retention improvement is most significant when the content of compound 7 in the second-cell electrolyte is 5%. This is because compound 7 contains both benzene rings and anhydride functional groups. The benzene rings effectively protect the positive electrode interface, inhibiting the migration of transition metal ions at the positive electrode under fast-charging conditions and the direct contact between the electrode interface and the electrolyte, thus improving the battery's fast-charging cycle stability. The anhydride readily undergoes a reduction film-forming reaction at the negative electrode interface, forming a stable SEI film that isolates the direct contact between the electrolyte and the electrode interface, alleviates electrolyte consumption, and reduces the irreversible loss of active sodium at the negative electrode interface under high-rate conditions, thereby improving the overall battery performance.
[0189] A comparison of Examples 7-9 with Comparative Examples 1 and 2 shows that using single-cell and double-cell electrolytes with different compositions can effectively improve the interfacial impedance and fast-charge cycle performance of the electrolyte, overcome the influence on the initial impedance, and further improve battery performance. The battery exhibits the best overall performance when 1% of Compound 3 is added to the single-cell electrolyte and 5% of Compound 7 is added to the double-cell electrolyte. This is because the introduction of the double-cell electrolyte method effectively improves the distribution of the electrolyte within the battery, allowing for more uniform wetting of the electrodes and separator, reducing performance differences caused by uneven electrolyte distribution. Simultaneously, a uniformly distributed electrolyte effectively reduces ion transport resistance within the battery, thereby lowering its internal resistance. Lower internal resistance means the battery can convert energy faster during charging and discharging, reducing energy loss and heat generation. This not only improves the battery's charging and discharging efficiency and extends its lifespan but also enhances its performance under rapid charging and discharging conditions. In addition, the second additive can, to some extent, eliminate the influence on the initial film-forming resistance and suppress the film-forming consumption of the first additive throughout the battery's entire life cycle.
[0190] Furthermore, as can be seen from the comparison of HF content between Examples 1-9 and Comparative Examples 1 and 2 in Table 1, the electrolyte prepared by the present invention has the function of removing water and acid, and can inhibit the increase of acidity in the electrolyte under fast charging conditions.
[0191] (5) Transition metal dissolution test
[0192] The experimental batteries from Examples 2, 5, 7, and Comparative Example 1, after 500 cycles of 4C fast charging, were disassembled, and a negative electrode was taken as a sample. Each sample was then thoroughly washed with dimethyl carbonate (DMC) solution. The negative electrode active material was then scraped off, and ICP testing was performed to determine the dissolution of transition metals (Ni, Fe, Mn). The test results are as follows: Figure 1 As shown.
[0193] Depend on Figure 1 It can be seen that, compared with Comparative Example 1, Examples 2, 5, and 7 show a significant reduction in the transition metal content of the negative electrode after fast charging cycles. This improvement is due, on the one hand, to the reduction of HF content in the electrolyte. HF, as a strong acid, is highly corrosive to the metal materials in the battery; therefore, reducing its content can effectively reduce the dissolution of transition metals. On the other hand, this is also closely related to the improved stability of the positive electrode structure. The electrolytes of Examples 1-9 correspond to a more stable and robust structure of the battery positive electrode material, thereby reducing the dissolution of transition metals during fast charging cycles.
[0194] In summary, the electrolyte provided by this invention, through a secondary electrolyte injection process, can suppress the dissolution of transition metals at the positive electrode interface, reduce HF generation, and improve the fast-charging cycle performance of the battery.
[0195] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A sodium-ion battery electrolyte, characterized in that, The one-injection electrolyte comprises a first sodium salt, a first solvent and a first additive, and the two-injection electrolyte comprises a second sodium salt, a second solvent and a second additive; the first additive comprises a thiophene cyano compound, and the second additive comprises a phenyl phthalic anhydride compound.
2. The sodium-ion battery electrolyte of claim 1, wherein, The thiophene cyano compound has a structural formula as shown in formula I. Formula I In the formula I, R1~R3are independently selected from a hydrogen atom, a halogen atom, a phenyl group, a cyano group, a five- or six-membered heterocycle, a substituted or unsubstituted C 1~5 one or more of an alkyl group, an alkenyl group, an alkynyl group; The phenyl phthalic anhydride compound has a structural formula as shown in formula II. Formula II In the above formula II, R4to R7are independently selected from a hydrogen atom, a halogen atom, a benzene ring, one or more of an alkyl group, an alkenyl group, an alkynyl group, and at least one of R4to R7is a functional group containing a benzene ring. 1~5 In the above formula II, R4to R7are independently selected from a hydrogen atom, a halogen atom, a benzene ring, one or more of an alkyl group, an alkenyl group, an alkynyl group, and at least one of R4to R7is a functional group containing a benzene ring.
3. The sodium-ion battery electrolyte according to claim 1 or 2, characterized in that, The thiophene cyano compound is at least one of compounds 1-4. Compound 1 Compound 2 Compound 3 Compound 4 The phenyl phthalic anhydride compound is at least one of compounds 5-7. Compound 5 Compound 6 Compound 7.
4. The sodium-ion battery electrolyte of claim 1, wherein, The first additive further comprises one or more of vinylene carbonate, fluoroethylene carbonate and vinyl sulfate.
5. The sodium-ion battery electrolyte of claim 1, wherein, The first sodium salt is at least one of sodium hexafluorophosphate, sodium bisfluorosulfonimide and sodium tetrafluoroborate, and the second sodium salt is at least two of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium dihydrogen bis (oxalate) borate, sodium difluoro (oxalate) borate, sodium bisfluorosulfonimide and sodium bis (trifluoromethyl) sulfonimide.
6. The sodium-ion battery electrolyte of claim 1, wherein, The first solvent is a carbonate solvent, and the second solvent comprises a carbonate solvent and a carboxylic acid ester solvent; the carbonate solvent comprises a cyclic carbonate and a chain carbonate; the cyclic carbonate is one or more of ethylene carbonate, fluoroethylene carbonate and propylene carbonate; the chain carbonate is one or more of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; and the carboxylic acid ester solvent is one or more of ethyl acetate, methyl acetate, propyl propionate and ethyl propionate.
7. The sodium-ion battery electrolyte of claim 1, wherein, The mass percentage of the first sodium salt in the one-injection electrolyte is 8-15%, the mass percentage of the first solvent in the one-injection electrolyte is 80-89%, the mass percentage of the first additive in the one-injection electrolyte is 3-5%, the mass percentage of the second sodium salt in the two-injection electrolyte is 10-20%, the mass percentage of the second solvent in the two-injection electrolyte is 70-87%, and the mass percentage of the second additive in the two-injection electrolyte is 3-10%.
8. The sodium-ion battery electrolyte of claim 1, wherein, The mass ratio of the one-injection electrolyte to the two-injection electrolyte is (80-85):(15-20).
9. A method for injecting the electrolyte of any one of claims 1 to 8 into a sodium-ion battery, characterized in that, The method comprises the following steps: The sodium ion battery is first injected with the one-injection electrolyte, and then the sodium ion battery is secondly injected with the two-injection electrolyte after the first formation of the sodium ion battery.
10. A sodium-ion battery, characterized in that, The sodium ion battery comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1-8.