Non-aqueous electrolyte and potassium ion battery containing the same

Abstract

The application provides a non-aqueous electrolyte and a potassium ion battery containing the non-aqueous electrolyte. The non-aqueous electrolyte comprises an electrolyte salt, a non-aqueous organic solvent and an additive, the additive comprises a cyan compound and a potassium oxalate compound, and the structural formula of the cyan compound is shown as formula I. The additive of the non-aqueous electrolyte comprises the cyan compound and the potassium oxalate compound, can be modified at the interfaces of the positive electrode and the negative electrode respectively, the positive electrode CEI film reduces metal dissolution and improves material stability, avoids the migration of dissolved metal ions to the negative electrode to cause chemical corrosion to the SEI film, and the solid negative electrode SEI film provides a more stable sodium ion deposition interface, reduces the interface side reaction, and creates a more stable electrochemical environment for the positive electrode. Therefore, the two-way optimization is realized through the synergistic effect, the structural integrity and the interface stability of the full battery in the long cycle process are promoted, and finally the cycle life of the battery is significantly prolonged and the high and low temperature performance is overall improved. Formula I

Description

Technical Field

[0001] This invention relates to the field of energy storage device technology, particularly to secondary batteries, and even more particularly to a non-aqueous electrolyte and a potassium-ion battery containing the non-aqueous electrolyte. Background Technology

[0002] Modern society's high demands for energy storage have prompted the scientific community to actively explore new, more sustainable rechargeable battery systems. Potassium-ion batteries (PIBs) are particularly advantageous due to the abundance of potassium resources and their high potassium content. + PIBs have attracted much attention due to their low reduction potential (-2.93V) and high compatibility with commercial graphite and hard carbon anodes. However, in traditional carbonate electrolytes, PIBs face severe challenges such as dendrite growth, interface corrosion, and poor low-temperature performance. The unstable cathode electrolyte interface (CEI) usually leads to rapid capacity decay during long-term cycling, thus limiting their practical application.

[0003] Common electrolytes for potassium-ion batteries include 1 mol / L potassium bis(fluorosulfonyl)imide / 1,2-ethylene glycol dimethyl ether (1 M KFSI DME) and 1.5 mol / L KFSI / ethylene carbonate-diethyl carbonate (1.5 M KFSI EC / DEC). These electrolytes cannot fully release the negative electrode capacity, resulting in problems such as ion solvent co-intercalation and continuous capacity decay.

[0004] Therefore, there is an urgent need to develop a new type of electrolyte to meet the usage requirements of potassium-ion batteries, thereby expanding the practical application range of potassium-ion batteries. Summary of the Invention

[0005] Based on the above problems, the purpose of this invention is to provide a non-aqueous electrolyte and a potassium-ion battery. By optimizing the solvation environment of the electrolyte, a CEI / SEI with higher stability and durability is formed, thereby achieving high reversibility and long cycle stability of potassium, thus improving the cycle characteristics and high and low temperature performance of the potassium-ion battery.

[0006] To achieve the above objectives, the present invention provides a non-aqueous electrolyte comprising an electrolyte salt, a non-aqueous organic solvent, and additives, wherein the additives include a cyano compound and a potassium oxalate compound, and the structural formula of the cyano compound is shown in Formula 1.

[0007]

[0008] Formula 1 The additives in the non-aqueous electrolyte of this invention include cyano compounds and potassium oxalate compounds. The cyano compounds, as shown in Formula 1, undergo in-situ polymerization under electrochemical conditions based on specific adsorption, thereby constructing a dense, uniform CEI (cathode-electrolyte interface) film with excellent interfacial compatibility on the surface of the cathode material. This film layer can suppress the oxidative decomposition of the electrolyte under high voltage and side reactions on the electrode surface, effectively widening the battery's operating voltage window, enhancing the stability of the crystal structure of the cathode material (such as Prussian blue cathode material) during cycling, alleviating lattice stress caused by metal ion insertion / extraction, and suppressing mechanical damage to the material. More importantly, this interface layer can efficiently block the dissolution of metal ions, fundamentally improving the intrinsic structural stability and cycle reversibility of the cathode. Simultaneously, potassium oxalate compounds are introduced, which preferentially reduce and decompose on the negative electrode surface to construct an SEI (solid electrolyte interface) film with both high mechanical strength and high ionic conductivity. This film effectively regulates the uniform deposition of metal ions, inhibits the growth of metal dendrites, and completely avoids the risk of internal short circuits caused by dendrites piercing the separator, greatly improving battery safety performance. It also optimizes the metal ion transport kinetics at the interface, reduces interface impedance, and thus significantly improves the battery's fast charge / discharge capability and performance under low-temperature conditions. In short, the additives, including cyano compounds and potassium oxalate compounds, can be modified at the positive and negative electrode interfaces, respectively. The positive electrode SEI film reduces metal dissolution, improves material stability, and prevents dissolved metal ions from migrating to the negative electrode and causing chemical corrosion of the SEI film. The robust negative electrode SEI film provides a more stable sodium ion deposition interface, reduces interfacial side reactions, and creates a more stable electrochemical environment for the positive electrode. Therefore, through the synergistic effect of the two, bidirectional optimization is achieved, jointly promoting the structural integrity and interface stability of the full battery during long-cycle processes, ultimately resulting in a significant extension of battery cycle life and an overall improvement in high and low temperature performance.

[0009] As one technical solution of the present invention, the potassium oxalate salt compound is selected from at least one of potassium oxalate borate salt and potassium oxalate phosphate salt.

[0010] As a technical solution of the present invention, the potassium oxalate salt compound is selected from at least one of compounds one to four.

[0011]

[0012] Compound 1, Compound 2, Compound 3, Compound 4 As a technical solution of the present invention, based on the mass of the electrolyte salt, the non-aqueous organic solvent and the additive being 100%, the mass percentage of the cyano compound is 0.1~2.0%.

[0013] As a technical solution of the present invention, based on the mass of the electrolyte salt, the non-aqueous organic solvent and the additive being 100%, the mass percentage of the potassium oxalate compound is 0.1~1.0%.

[0014] As one technical solution of the present invention, the electrolyte salt is a potassium salt, which is selected from at least one of potassium hexafluorophosphate, potassium perchlorate, potassium tetrafluoroborate, potassium trifluoromethanesulfonate, potassium bis(trifluoromethanesulfonyl)imide, potassium bis(oxalate-borate), potassium difluorophosphate, potassium di(oxalate-borate), potassium di(oxalate-difluorophosphate), and potassium bis(oxalate-imide).

[0015] As one technical solution of the present invention, the electrolyte salt is selected from potassium hexafluorophosphate and / or potassium difluorosulfonyl imide.

[0016] As one technical solution of the present invention, the non-aqueous organic solvent includes at least one of chain carbonates, cyclic carbonates and carboxylic acid esters.

[0017] A second aspect of this invention provides a potassium-ion battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, wherein the electrolyte is selected from the aforementioned non-aqueous electrolytes. The non-aqueous electrolyte used in the potassium-ion battery of this invention contains a cyano compound and a potassium oxalate salt compound. Through the synergistic effect of these two compounds, a highly stable and durable SEI (Sediment Injection) can be formed while optimizing the solvation environment of the electrolyte, thereby achieving high reversibility and long-cycle stability of potassium, thus improving the high-rate characteristics and high / low-temperature performance of the potassium-ion battery.

[0018] As a technical solution of the present invention, the positive electrode material comprises a Prussian blue analogue, the chemical formula of which is K. x Fe[Fe(CN)6], 0 <x<2。 Detailed Implementation

[0019] The non-aqueous electrolyte of this invention can improve the rate capability and high / low temperature performance of potassium-ion batteries. The potassium-ion battery of this invention may include a positive electrode material, a negative electrode material, and a non-aqueous electrolyte.

[0020] The positive electrode material may include layered oxides (such as potassium cobaltate, potassium manganate, and potassium nickel cobalt manganate), polyanionic phosphates, and Prussian blue analogs (potassium phosphate, potassium pyrophosphate, and potassium fluorophosphate). The chemical formula for Prussian blue analogs is K2. x Fe[Fe(CN)6], 0 <x<2。

[0021] The negative electrode material is selected from at least one of carbon-based materials, titanium-based materials, and alloy materials. The carbon-based material is selected from at least one of artificial graphite, natural graphite, soft carbon, and hard carbon. The titanium-based material is selected from K₂Ti₃O₇, K... 0.6 [Cr 0.6 Ti0.4 O2, Li4Ti5O 12 KTiOPO4, KSICON, KTi2(PO4)3. Alloy materials are alloys formed by Sn, Sb, and In.

[0022] Non-aqueous electrolytes include electrolyte salts, non-aqueous organic solvents, and additives.

[0023] Based on the mass of electrolyte salt, non-aqueous organic solvent, and additives being 100%, the mass percentage of electrolyte salt is 10-25%, and further, it is 8-14%. For example, the mass percentage of electrolyte salt may be, but is not limited to, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 24%, and 25%. The mass percentage of electrolyte salt is not limited to the listed values; other unlisted values ​​within this range also apply. The electrolyte salt is selected from at least one of potassium hexafluorophosphate (KPF6), potassium perchlorate (KClO4), potassium tetrafluoroborate (KBF4), potassium trifluoromethanesulfonate (KCF3SO3), potassium bis(trifluoromethanesulfonyl)imide (KTFSI), potassium bis(oxalate)borate (KBC4O8), potassium difluorophosphate (KPO2F2), potassium difluorooxalateborate (KBF2C2O4), potassium difluorodioxalate phosphate (KDFBP), and potassium bis(fluorosulfonyl)imide (KFSI). Preferably, the electrolyte salt is selected from potassium hexafluorophosphate and / or potassium difluorosulfonyl imide. More preferably, the electrolyte salt is a mixture of potassium hexafluorophosphate and potassium difluorosulfonyl imide, wherein potassium difluorosulfonyl imide accounts for 10-60% of the electrolyte salt by mass. More preferably, potassium difluorosulfonyl imide accounts for 40-60% of the electrolyte salt by mass. As examples, potassium difluorosulfonyl imide accounts for 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, and 60% of the electrolyte salt by mass.

[0024] Non-aqueous organic solvents include at least one of linear carbonates, cyclic carbonates, and carboxylic acid esters. Linear carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and propylene carbonate (PC). Cyclic carbonates may be, but are not limited to, ethylene carbonate (EC), propylene carbonate, butyl carbonate (BC), amyl carbonate, vinyl carbonate (VC), or derivatives thereof. Carboxylic acid esters include, but are not limited to, cyclic carboxylic acid esters and linear carboxylic acid esters. Cyclic carboxylic acid esters may specifically include, but are not limited to, at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Linear carboxylic acid esters include, but are not limited to, at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0025] The additives include cyano compounds and potassium oxalate compounds. The structural formula of the cyano compounds is shown in Formula 1. The mass percentage of the cyano compounds is 0.1% to 2.0% based on 100% of the mass of the electrolyte salt, non-aqueous organic solvent, and additives. For example, the mass percentage of the cyano compounds may be, but is not limited to, 0.1%, 0.3%, 0.5%, 0.7%, 1.0%, 1.3%, 1.5%, 1.7%, and 2.0%, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0026]

[0027] Formula 1 CAS No.: 3245-46-5 The potassium oxalate compound is selected from at least one of potassium oxalate borate and potassium oxalate phosphate. Further, the potassium oxalate compound is selected from at least one of compounds one through four. The mass percentage of the potassium oxalate compound is 0.1% to 1.0%, and more specifically, the mass percentage of the potassium oxalate compound is 0.5% to 1.0%. As an example, the mass percentage of the potassium oxalate compound may be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0028]

[0029] Compound 1, Compound 2, Compound 3, Compound 4 The synthetic route for compound 1 can be as follows: Dissolve 35g of potassium tetrafluoroborate (CAS No. 14075-53-7) in 300mL of EMC, add 25g of anhydrous oxalic acid, stir for 30min, and slowly add 70g of trimethylchlorosilane dropwise at 40-50°C. After the addition is complete, keep the reaction at this temperature for 2h, then concentrate the EMC, add dichloromethane to crystallize, filter and dry.

[0030] Compound 2 can be synthesized by controlling the amount of anhydrous oxalic acid, following the same synthetic route as Compound 1.

[0031] The synthetic route for compound four is as follows: Dissolve 50 g of potassium hexafluorophosphate (CAS No. 17084-13-8) in 300 mL of EMC, add 54 g of anhydrous oxalic acid, stir for 30 min, and slowly add 145 g of trimethylchlorosilane dropwise at 40-50 °C. After the addition is complete, maintain the reaction temperature for 2 h, then concentrate the EMC, add dichloromethane to crystallize, filter and dry.

[0032] Compound 3 can be synthesized by controlling the amount of anhydrous oxalic acid, following the same synthetic route as compound 4.

[0033] To further illustrate the purpose, technical solution, and beneficial effects of this invention, the following will provide a further description of the invention in conjunction with specific embodiments. It should be noted that, for other raw materials in the embodiments and comparative examples where specific conditions are not specified, they can be carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used where the manufacturer is not specified are all commercially available conventional products.

[0034] Example 1 1.1 Preparation of Electrolyte Electrolyte was prepared in a vacuum glove box under an argon atmosphere with a moisture content of <1 ppm. Propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed thoroughly in a weight ratio of PC:EMC:DEC = 1:1:1. This mixture was used as the organic solvent. A cyano compound and a potassium oxalate salt compound were then added to obtain a mixed solution. The mixed solution was sealed and packaged, then frozen in a freezer (-4°C) for 2 hours. After removal, potassium hexafluorophosphate was slowly added to the mixed solution, and the mixture was thoroughly mixed to obtain the electrolyte.

[0035] 1.2 Preparation of the positive electrode sheet Prussian blue cathode material KFe[Fe(CN)6], binder PVDF and conductive agent SuperP are mixed in a mass ratio of 95:1:4 to form a slurry, which is then coated on both sides of aluminum foil, dried and rolled to obtain a cathode sheet.

[0036] 1.3 Preparation of negative electrode sheet Artificial graphite was mixed with conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) in a mass ratio of 95:1.5:1.0:2.5 to form a slurry. The mixture was then coated on both sides of copper foil, dried, and rolled to obtain the negative electrode sheet.

[0037] 1.4 Preparation of potassium-ion batteries: A square cell is made by stacking positive electrode, separator and negative electrode, using polymer packaging, filling with the electrolyte prepared above, and then producing a potassium-ion battery with a capacity of 1000mAh after formation, capacity grading and other processes.

[0038] The composition and content of the electrolytes in Examples 1-10 and Comparative Examples 1-3 are shown in Table 1. The preparation processes of the potassium-ion battery electrolytes, positive electrode sheets, negative electrode sheets, and potassium-ion batteries in Examples 2-10 and Comparative Examples 1-3 are the same as those in Example 1.

[0039] Table 1. Composition of the electrolytes in Examples 1-10 and Comparative Examples 1-3

[0040] The potassium-ion batteries prepared in Examples 1-10 and Comparative Examples 1-3 were subjected to performance tests under the following conditions, and the results are shown in Table 2.

[0041] (1) First Coulomb efficiency test Potassium-ion batteries were placed in a high-temperature, high-pressure formation chamber and subjected to a three-step formation process at 25°C and 0.28 MPa (4 cells). The first step involved a constant current of 0.05C for 60 minutes, recording the charging capacity C1. The second step involved a constant current of 0.1C for 120 minutes, recording the charging capacity C2. The third step involved a constant current of 0.2C for 240 minutes, recording the charging capacity C3. The upper limit voltage was 3.5V. The batteries were then resealed using a rotary sealing machine. They were then charged at room temperature with a constant current of 0.5C until the voltage reached 3.5V, followed by a constant voltage charge at 3.5V until the current reached 0.05C. Finally, they were discharged at a constant current of 1C until the voltage reached 1.5V, and the initial discharge capacity C0 was recorded.

[0042] Initial Coulomb efficiency = C0 / (C1+C2+C3)×100% (2) Room temperature cycle test of potassium-ion battery Place the potassium-ion battery in a 25°C constant temperature chamber and let it stand for 30 minutes to allow it to reach a constant temperature. Charge the battery at a constant current of 1C until the voltage reaches 3.5V, then charge it at a constant voltage of 3.5V until the current reaches 0.05C. Next, discharge the battery at a constant current of 1C until the voltage reaches 1.5V. Record the discharge capacity of the battery in the first cycle; this constitutes one charge-discharge cycle. Repeat this cycle for 400 cycles, recording the discharge capacity of the first and last cycles. Calculate the capacity retention rate using the following formula.

[0043] Capacity retention rate = (Discharge capacity in the last cycle / Discharge capacity in the first cycle) × 100% (3) High-temperature storage test of potassium-ion batteries Under normal temperature (25℃) conditions, the lithium-ion battery was charged and discharged once at 0.5C / 0.5C (the battery discharge capacity was recorded as C0), with an upper limit voltage of 3.5V. Then, the battery was charged to 3.5V under constant current and constant voltage conditions at 0.5C, and the battery thickness was measured (the thickness was recorded as D0). The battery was placed in a 60℃ oven for 30 days, and then removed and the battery thickness was measured (the thickness was recorded as D1). The thickness expansion rate was calculated.

[0044] Thickness expansion rate = (D1 / D0) × 100% (4) Low-temperature discharge test At room temperature (25℃), the potassium-ion battery was charged and discharged once at 0.5C / 0.5C (the battery discharge capacity was recorded as C0), with an upper limit voltage of 3.5V. The battery was then placed in a low-temperature chamber at -10℃ and discharged at a constant current of 0.1C until the voltage reached 1.5V. The first discharge capacity of the battery was recorded as C1, which constitutes one charge-discharge cycle. The lithium-ion battery was then charged and discharged once at room temperature (25℃) once at 0.5C / 0.5C (the battery discharge capacity was recorded as C2). After 10 cycles, the capacity recovery rate was calculated.

[0045] Capacity recovery rate = (C2 / C0) × 100% Table 2 Performance test results of potassium-ion batteries in Examples 1-10 and Comparative Examples 1-3

[0046] As can be seen from the results in Table 2, compared with Comparative Examples 1-3, the additives in Examples 1-10, including cyano compounds and potassium oxalate compounds, can greatly improve the initial coulombic performance, high and low temperature performance and cycle performance of potassium batteries.

[0047] Comparing Examples 1 and 9-10, it can be seen that when KPF6 is combined with KFSI as the electrolyte salt, the electrochemical performance of the battery is significantly improved. This may be because the cyano compound can effectively inhibit the increase of the acid value of KFSI, so that the performance of KFSI can be stably exerted. Moreover, the higher the content of KFSI, the more obvious the performance difference.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that, The mixture includes electrolyte salts, non-aqueous organic solvents, and additives, wherein the additives include cyano compounds and potassium oxalate compounds, the structural formula of which is shown in Formula 1. Formula 1.

2. The non-aqueous electrolyte according to claim 1, characterized in that, The potassium oxalate compound is selected from at least one of potassium oxalate borate and potassium oxalate phosphate.

3. The non-aqueous electrolyte according to claim 1, characterized in that, The potassium oxalate compound is selected from at least one of compounds one through four. Compound 1, Compound 2, Compound 3, Compound 4.

4. The non-aqueous electrolyte according to claim 1, characterized in that, Based on the mass of the electrolyte salt, the non-aqueous organic solvent, and the additives being 100%, the mass percentage of the cyano compound is 0.1~2.0%.

5. The non-aqueous electrolyte according to claim 1, characterized in that, Based on the mass of the electrolyte salt, the non-aqueous organic solvent, and the additives being 100%, the mass percentage of the potassium oxalate compound is 0.1-1.0%.

6. The non-aqueous electrolyte according to claim 1, characterized in that, The electrolyte salt is a potassium salt, which is selected from at least one of potassium hexafluorophosphate, potassium perchlorate, potassium tetrafluoroborate, potassium trifluoromethanesulfonate, potassium bis(trifluoromethanesulfonyl)imide, potassium bis(oxalate-borate), potassium difluorophosphate, potassium difluorooxalate-borate, potassium difluorodioxalate-phosphate, and potassium bis(oxalate-imide).

7. The non-aqueous electrolyte according to claim 6, characterized in that, The electrolyte salt is selected from potassium hexafluorophosphate and / or potassium difluorosulfonamide.

8. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent includes at least one of chain carbonates, cyclic carbonates, and carboxylic acid esters.

9. A potassium-ion battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized in that, The electrolyte is selected from the non-aqueous electrolyte described in any one of claims 1 to 8.

10. The potassium-ion battery according to claim 9, characterized in that, The cathode material contains a Prussian blue analogue, the chemical formula of which is K. x Fe[Fe(CN)6], 0 <x<2。

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