Sodium-ion battery electrolyte, battery, battery pack and electric equipment

Abstract

The invention provides a sodium-ion battery electrolyte, a battery, a battery pack and electric equipment, the sodium-ion battery electrolyte comprises a first additive and a second additive, the first additive is a non-sodium metal cation compound, the second additive is a halogenated organic ester compound, and the second additive is a non-sodium metal cation compound. Halogen atoms in the second additive comprise at least one of chlorine, bromine and iodine. Under the synergistic effect of the first additive and the second additive, the sodium-ion battery electrolyte provided by the invention can significantly reduce impedance and improve cycle stability.

Description

Technical Field

[0001] The present invention relates to a sodium ion battery electrolyte, in particular to a sodium ion battery electrolyte, a battery, a battery pack and an electrical device, belonging to the field of secondary batteries. Background Art

[0002] With global concern about climate change, countries are setting carbon neutrality goals and promoting the development of clean energy sources such as wind and solar power. Secondary batteries, as the core of energy storage systems, can effectively address the intermittent nature of renewable energy. Furthermore, the widespread adoption of portable electronic devices such as smartphones and laptops is driving demand for high-performance secondary batteries.

[0003] The unique advantages of sodium-ion batteries hold broad application prospects in areas such as large-scale energy storage and low-speed electric vehicles. With continued technological advancements, sodium-ion batteries are expected to become an important complement to, or even a replacement for, lithium-ion batteries. However, their development still faces challenges. For one thing, side reactions between the electrolyte and the electrode materials during charge and discharge consume active materials and increase impedance. Furthermore, excessive SEI film growth and dendrite growth can affect the cycling performance of sodium-ion batteries during operation.

[0004] The performance of sodium-ion batteries can be optimized by adjusting the type of additives in the sodium-ion battery electrolyte. However, current research on sodium-ion battery electrolyte additives mainly focuses on a single function, and has limited effect on reducing impedance and improving cycle performance of sodium-ion batteries. Summary of the Invention

[0005] The present invention provides a sodium ion battery electrolyte. Under the synergistic effect of a non-sodium metal cation compound and a halogenated organic ester compound, the sodium ion battery electrolyte can form a uniform and stable SEI film, thereby inhibiting the decomposition of the sodium ion battery electrolyte, reducing the impedance of the sodium ion battery, and improving the cycle stability.

[0006] The present invention also provides a sodium ion battery, which includes the above-mentioned sodium ion battery electrolyte and thus has lower impedance and excellent cycle stability.

[0007] The present invention also provides a battery pack, which includes the above-mentioned sodium ion battery and has good performance.

[0008] The present invention also provides an electrical device, which includes the above-mentioned sodium ion battery or battery pack and has good performance.

[0009] On the one hand, the present invention provides a sodium ion battery electrolyte, comprising a first additive and a second additive, wherein the first additive is a non-sodium metal cation compound, the second additive is a halogenated organic ester compound, and the halogen atoms in the second additive include at least one of chlorine, bromine, and iodine.

[0010] In the sodium ion battery electrolyte described above, the chemical formula of the first additive is XY n , wherein X is selected from at least one of Li, K, Rb, Ca, Mg, Sb, Mn, Fe, Co, Ni, Zn, and Cu, and Y is selected from NO3 - PF6 - , TFSI, FSI, at least one of which n is 1 to 4;

[0011] And / or, the second additive is selected from at least one of chloroethylene carbonate, bromoethylene carbonate, fluorobromoethylene carbonate, ethyl chlorobenzoate, ethyl bromoacrylate, ethyl bromoacetate, and methyl bromobenzoate.

[0012] In the sodium ion battery electrolyte as described above, the mass ratio of the first additive to the second additive is (2-1):(1-4).

[0013] The sodium ion battery electrolyte as described above, based on the total mass of the sodium ion battery electrolyte, the mass percentage of the first additive is 0.01% to 5%;

[0014] And / or, based on the total mass of the sodium ion battery electrolyte, the mass percentage of the second additive is 0.01% to 5%.

[0015] The sodium ion battery electrolyte as described above further includes a third additive, wherein the third additive includes at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, propenyl-1,3-sultone, vinyl sulfate, methylene methanedisulfonate, succinonitrile, adiponitrile, tris(trimethylsilyl)phosphite, trimethyl phosphate, and ethoxy(pentafluoro)cyclotriphosphazene;

[0016] The third additive accounts for 0.1% to 10% by mass of the sodium ion battery electrolyte.

[0017] The sodium ion battery electrolyte as described above further includes an electrolyte salt, and the electrolyte salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium nitrate, and sodium chloride.

[0018] The sodium ion battery electrolyte as described above further includes a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, dimethyl sulfoxide, tetrahydrofuran, acetonitrile, and N,N-dimethylformamide.

[0019] In another aspect, the present invention provides a battery comprising the sodium ion battery electrolyte described above.

[0020] In another aspect, the present invention provides a battery pack comprising the sodium ion battery described above.

[0021] In another aspect, the present invention provides an electrical device comprising the sodium ion battery or the battery pack as described above.

[0022] The sodium ion battery electrolyte provided by the present invention includes a non-sodium metal cation compound as a first additive and a halogenated organic ester compound as a second additive. The inorganic component generated by the non-sodium metal cation compound on the electrode surface has high mechanical strength and ionic conductivity, and the components generated by the decomposition of the halogenated organic ester compound can fill the gaps between the inorganic components, forming a uniform and dense SEI film. This "inorganic-organic composite" SEI film has both high mechanical strength and good flexibility and ionic conductivity, which can effectively inhibit the decomposition of the sodium ion battery electrolyte and the degradation of the electrode material, reduce the battery impedance, and improve the cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Room temperature cycle performance curves of batteries prepared with the sodium ion battery electrolytes provided in Example 1 and Comparative Examples 1-3 of the present invention;

[0024] Figure 2 EIS curves of batteries prepared with the sodium ion battery electrolytes provided in Example 1 and Comparative Examples 1-3 of the present invention. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0026] At present, in order to improve battery performance, a single additive is usually added to the electrolyte of sodium-ion batteries. The effect of a single additive is limited, and impedance and cycle stability involve the complex coupling of multiple factors such as sodium-ion battery electrolyte phase transmission, interfacial reaction kinetics, and electrode material compatibility.

[0027] On one hand, the present invention provides a sodium ion battery electrolyte, comprising a first additive and a second additive, wherein the first additive is a non-sodium metal cation compound, the second additive is a halogenated organic ester compound, and the halogen atom in the second additive comprises at least one of chlorine, bromine, and iodine.

[0028] The sodium ion battery electrolyte provided by the present invention is used in a secondary battery system. Through the synergistic effect of the two additives, the performance of the sodium ion battery electrolyte is improved, and the impedance and cycle stability of the secondary battery can be significantly improved.

[0029] Specifically, a non-sodium metal cation compound is a compound formed by ionic bonding between a metal cation and a non-metal anion, wherein the metal cation referred to in the present invention does not include sodium ions. The non-sodium metal cation compound can regulate the solvation structure of sodium ions through coordination, thereby improving ion mobility and forming a stable interfacial film on the electrode surface.

[0030] Halogenated organic ester compounds are a class of organic ester compounds containing halogens (chlorine, bromine, and iodine). They are formed by the esterification reaction of alcohols (or phenols) and carboxylic acids and contain at least one halogen atom in the molecule. The halogenated organic ester compounds provided by the present invention have a strong electron-withdrawing effect, which can significantly improve the antioxidant capacity of sodium-ion battery electrolytes. They decompose on the electrode surface to form a uniform and stable SEI film, inhibiting the decomposition of the sodium-ion battery electrolyte.

[0031] The sodium ion battery electrolyte provided by the present invention is used in a sodium ion battery system, so that the sodium ion battery has lower impedance and relatively excellent cycle stability.

[0032] Common sodium-ion battery electrolyte additives such as fluoroethylene carbonate (FEC) mainly generate SEI film components of lithium fluoride (LiF) or sodium fluoride (NaF) after reduction and decomposition on the negative electrode surface, but they may be thin or uneven and may break during long-term cycling.

[0033] In the present invention, the first additive is a non-sodium metal compound. Na ions are the main carriers in the sodium ion battery electrolyte, and their concentration has been optimized by sodium salts (such as NaPF6). The additional addition of sodium ions will lead to concentration polarization, affecting the ion migration efficiency. The introduction of other metal cations can optimize the electrode interface through the adsorption-catalysis mechanism, form a more uniform adsorption layer, and inhibit the growth of dendrites. In addition, the non-sodium metal cation compound reduces the solvation energy of the active metal ions through coordination and increases the migration rate of the active metal ions, while the halogen atoms (such as Br, Cl) have a strong electron-withdrawing effect, which can reduce the HOMO energy level of the ester compound and improve its antioxidant capacity. This dual regulatory effect significantly reduces the impedance of the sodium ion battery electrolyte, thereby enhancing the SEI film stability of the battery, reducing the generation of dendrites, and inhibiting the decomposition of the sodium ion battery electrolyte, thereby improving the cycle performance.

[0034] Furthermore, in one embodiment of the present invention, the chemical formula of the first additive is XY n , wherein X is selected from at least one of Li, K, Rb, Ca, Mg, Sb, Mn, Fe, Co, Ni, Zn, and Cu, and Y is selected from NO3 - PF6 - , TFSI, FSI, at least one of which n is 1 to 4;

[0035] Wherein, X is a metal cation; Y is an anion; and n is an integer, specifically one of 1, 2, 3, and 4, representing the number of anions to satisfy the charge balance of the compound.

[0036] The value of n depends on the charge of the metal cation X and the charge of the anion Y, for example, Li + (+1) and PF6 - (-1) combination, n = 1, the chemical formula is LiPF6; Mg 2+ (+2) with TFSI - (-1) combination, n = 2, the chemical formula is Mg (TFSI) 2; Al 3+ When (+3) combines with NO3-(-1), n=3 and the chemical formula is Al(NO3)3.

[0037] The above-mentioned non-sodium metal cation compounds can optimize the ionic conductivity, electrochemical stability and interfacial properties of sodium ion battery electrolytes by selecting appropriate combinations of metal cations and anions, and are suitable for a variety of electrochemical energy storage devices.

[0038] In another specific embodiment, the second additive is selected from at least one of chloroethylene carbonate, bromoethylene carbonate, fluorobromoethylene carbonate, ethyl chlorobenzoate, ethyl bromoacrylate, ethyl bromoacetate, and methyl bromobenzoate.

[0039] The above-mentioned type of halogenated organic ester compounds can form a more stable SEI film, further improving the cycle stability of the battery and reducing impedance.

[0040] Furthermore, in a specific embodiment, the mass ratio of the first additive to the second additive is (2-1):(1-4).

[0041] In detail, the mass ratio of the first additive to the second additive includes but is not limited to 2:1, 1:1, 1:2, 1:3, 1:4 or a range between any two thereof.

[0042] The mass ratio of the first additive to the second additive can be controlled by adjusting the amount of the first additive and the second additive added during the preparation of the sodium ion battery electrolyte. By adjusting the ratio of the metal cation compound to the halogenated organic ester compound, it helps to form a more stable sodium ion battery electrolyte environment, reduce the performance degradation of the battery during the charge and discharge process, reduce dendrites caused by side reactions, improve the cycle stability of the battery, and reduce impedance.

[0043] Furthermore, based on the total mass of the sodium ion battery electrolyte, the mass percentage of the first additive is 0.01% to 5%; in detail, the mass percentage of the first additive includes but is not limited to 0.01%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range consisting of any two thereof.

[0044] By controlling the content of the first additive between 0.01% and 5%, the impedance of the sodium ion battery electrolyte can be precisely adjusted while avoiding precipitation or side reactions caused by the first additive, forming a stable ionic environment, and improving the battery's cycle performance through synergistic action with the second additive.

[0045] In another specific embodiment, based on the total mass of the sodium ion battery electrolyte, the mass percentage of the second additive is 0.01% to 5%.

[0046] In detail, the mass percentage of the second additive includes but is not limited to 0.01%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two thereof.

[0047] Controlling the mass percentage of the second additive within the above range can improve the interface properties between the sodium ion battery electrolyte and the electrode, promote the formation of a more stable solid electrolyte interface (SEI) layer, effectively utilize materials, reduce production costs, and ensure the performance improvement of the sodium ion battery electrolyte.

[0048] Furthermore, the sodium ion battery electrolyte provided by the present invention also includes a third additive, and the third additive includes at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, propenyl-1,3-sultone, vinyl sulfate, methylene methanedisulfonate, succinonitrile, adiponitrile, tris(trimethylsilyl)phosphite, trimethyl phosphate, and ethoxy(pentafluoro)cyclotriphosphazene;

[0049] The third additive accounts for 0.1% to 10% of the mass percentage of the sodium ion battery electrolyte.

[0050] Specifically, the third additive can promote the formation of a stable and uniform SEI layer on the electrode surface, reduce side reactions between the sodium-ion battery electrolyte and the electrode, and improve the battery's cycle life and efficiency. Furthermore, the diversity of the third additive allows for the selection of suitable compounds or combinations thereof based on specific battery application requirements to achieve specific performance improvements. This flexibility enables sodium-ion battery electrolytes to adapt to different types of batteries and application scenarios.

[0051] In detail, the mass percentage of the third additive in the sodium ion battery electrolyte includes but is not limited to 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two thereof.

[0052] Furthermore, the sodium ion battery electrolyte provided by the present invention also includes an electrolyte salt, and the electrolyte salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium nitrate, and sodium chloride.

[0053] The choice of electrolyte salt type directly affects the ionic conductivity, electrochemical window, thermal stability and compatibility with electrode materials of sodium ion battery electrolytes.

[0054] It is understandable that different electrolyte salts have different electrochemical stability windows, and a suitable electrolyte salt can be selected according to the specific application requirements of the battery.

[0055] An appropriate electrolyte salt concentration can be selected according to actual conditions. For example, in one embodiment, the electrolyte salt concentration is 0.1 mol / L to 10 mol / L.

[0056] Furthermore, in a specific embodiment of the present invention, the sodium ion battery electrolyte also includes a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, dimethyl sulfoxide, tetrahydrofuran, acetonitrile, and N,N-dimethylformamide.

[0057] The mass percentages of the electrolyte salt, solvent, and third additive in the sodium ion battery electrolyte can be adjusted according to actual needs. For example, in one specific embodiment, the mass percentage of the electrolyte salt in the sodium ion battery electrolyte is 1% to 20%, the mass percentage of the solvent in the sodium ion battery electrolyte is 65% to 98.98%, and the mass percentage of the third additive in the sodium ion battery electrolyte is 0 to 5%.

[0058] In another aspect, the present invention provides a sodium ion battery comprising the sodium ion battery electrolyte described above.

[0059] Since the sodium ion battery provided by the present invention includes the above-mentioned sodium ion battery electrolyte, it has low impedance and good cycle performance during actual use.

[0060] It is understood that the battery provided by the present invention includes, in addition to the above-mentioned solid electrolyte, a positive electrode sheet, a negative electrode sheet, and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The sodium ion battery electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuits between the positive and negative electrodes, while allowing ions to pass through.

[0061] The present invention does not strictly limit the positive electrode active material in the positive electrode sheet. The positive electrode active material can be at least one of layered metal oxides (NaCoO2, NaNiO2 and NaFeO2, etc.), polyanion compounds (sodium iron phosphate (NaFePO4), sodium vanadium phosphate (Na3V2(PO4)3), etc.), and Prussian blue materials.

[0062] The present invention is not strictly limited to the negative electrode active material in the negative electrode sheet, and can be at least one of the currently commonly used negative electrode active materials, such as graphite, hard carbon, soft carbon, mesophase carbon microbeads, silicon-based negative electrode materials (mainly including silicon monoxide, silicon-carbon negative electrode), tin-based negative electrode materials (mainly including tin, tin alloy), etc.

[0063] In another aspect, the present invention provides a battery pack comprising the sodium ion battery described above, thereby having good ionic conductivity and cycle stability.

[0064] In another aspect, the present invention provides an electrical device comprising the sodium ion battery or the battery pack as described above.

[0065] The present invention is not limited to the specific types of electrical equipment, and can include large energy storage cabinets, electric vehicles, mobile phones, smart homes, robots, drones, electronic cigarettes, speakers, and any other equipment that requires batteries to power it.

[0066] The electrical equipment provided by the present invention includes the above-mentioned battery or battery pack, and thus has good performance.

[0067] The sodium ion battery electrolyte provided by the present invention is described in detail below through specific examples.

[0068] Example 1

[0069] The preparation method of the sodium ion battery electrolyte provided in this embodiment includes the following steps:

[0070] Ethylene carbonate, propylene carbonate and diethyl carbonate in a mass ratio of 1:1:1 are mixed uniformly at 25°C; vinylene carbonate and electrolyte salt NaPF6 are added at a mass ratio of 1% of the total mass of the sodium ion battery electrolyte, and the mixture is mixed uniformly at 25°C; a first additive (copper hexafluorophosphate) is added at a mass ratio of 0.05% of the total mass of the sodium ion battery electrolyte, and the mixture is mixed uniformly at 25°C; a second additive (fluorobromoethylene carbonate, FBrEC) is added at a mass ratio of 0.1% of the total mass of the sodium ion battery electrolyte, and the mixture is mixed uniformly at 25°C to obtain a sodium ion battery electrolyte.

[0071] The mass ratio of the first additive to the second additive is 1:2.

[0072] Example 2

[0073] The preparation method of the sodium ion battery electrolyte provided in this embodiment is basically the same as that in Example 1, except that copper hexafluorophosphate is replaced by nickel hexafluorophosphate.

[0074] Example 3

[0075] The preparation method of the sodium ion battery electrolyte provided in this embodiment is basically the same as that in Example 1, except that fluorobromoethylene carbonate is replaced by chloroethylene carbonate.

[0076] Example 4

[0077] The preparation method of the sodium ion battery electrolyte provided in this embodiment is basically the same as that in Example 1, except that the mass percentage of copper hexafluorophosphate in the sodium ion battery electrolyte is 0.03%, the mass percentage of the second additive (fluorobromoethylene carbonate) in the sodium ion battery electrolyte is 0.12%, and the mass ratio of the first additive to the second additive is 1:4.

[0078] Example 5

[0079] The preparation method of the sodium ion battery electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0080] The mass percentage of copper hexafluorophosphate in the sodium ion battery electrolyte is 0.1%, the mass percentage of the second additive (fluorobromoethylene carbonate) in the sodium ion battery electrolyte is 0.05%, and the mass ratio of the first additive to the second additive is 2:1.

[0081] Example 6

[0082] The preparation method of the sodium ion battery electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0083] The mass percentage of copper hexafluorophosphate in the sodium ion battery electrolyte is 0.025%, the mass percentage of the second additive (fluorobromoethylene carbonate) in the sodium ion battery electrolyte is 0.125%, and the mass ratio of the first additive to the second additive is 1:5.

[0084] Example 7

[0085] The preparation method of the sodium ion battery electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0086] The mass percentage of copper hexafluorophosphate in the sodium ion battery electrolyte is 0.1125%, the mass percentage of the second additive (fluorobromoethylene carbonate) in the sodium ion battery electrolyte is 0.0375%, and the mass ratio of the first additive to the second additive is 3:1.

[0087] Example 8

[0088] The preparation method of the sodium ion battery electrolyte provided in this embodiment includes the following steps:

[0089] Ethylene carbonate, propylene carbonate and diethyl carbonate in a mass ratio of 1:1:1 are mixed uniformly at 25°C; trimethyl phosphate and electrolyte salt lithium hexafluoroarsenate are added at a mass ratio of 5% of the total mass of the sodium ion battery electrolyte, and the mixture is mixed uniformly at 25°C; a first additive (magnesium bis(trifluoromethanesulfonyl)imide, Mg(TFSI)2) is added at a mass ratio of 5% of the total mass of the sodium ion battery electrolyte, and the mixture is mixed uniformly at 25°C; a second additive (bromoethylene carbonate) is added at a mass ratio of 5% of the total mass of the sodium ion battery electrolyte, and the mixture is mixed uniformly at 25°C to obtain a sodium ion battery electrolyte.

[0090] The mass ratio of the first additive to the second additive is 1:1.

[0091] Example 9

[0092] The preparation method of the sodium ion battery electrolyte provided in this embodiment includes the following steps:

[0093] Ethylene carbonate, propylene carbonate and diethyl carbonate in a mass ratio of 1:1:1 are mixed uniformly at 25°C; trimethyl phosphate and electrolyte salt lithium hexafluoroarsenate are added at a mass ratio of 5% of the total mass of the sodium ion battery electrolyte, and the mixture is mixed uniformly at 25°C; a first additive (magnesium nitrate) is added at a mass ratio of 0.01% of the total mass of the sodium ion battery electrolyte, and the mixture is mixed uniformly at 25°C; a second additive (ethyl chlorobenzoate) is added at a mass ratio of 0.01% of the total mass of the sodium ion battery electrolyte, and the mixture is mixed uniformly at 25°C to obtain a sodium ion battery electrolyte.

[0094] The mass ratio of the first additive to the second additive is 1:1.

[0095] Comparative Example 1

[0096] The preparation method of the sodium ion battery electrolyte provided in this comparative example is basically the same as that in Example 1, except that:

[0097] No first additive was added.

[0098] Comparative Example 2

[0099] The preparation method of the sodium ion battery electrolyte provided in this comparative example is basically the same as that in Example 1, except that:

[0100] No secondary additives were added.

[0101] Comparative Example 3

[0102] The preparation method of the sodium ion battery electrolyte provided in this comparative example is basically the same as that in Example 1, except that:

[0103] The first additive and the second additive were not added.

[0104] Test Case

[0105] The sodium ion battery electrolytes provided in all the embodiments and comparative examples were used in sequence to prepare a battery, comprising the following steps:

[0106] (1) Preparation of positive electrode sheet: The positive electrode active material NFPP, the conductive agent CNT (carbon nanotube), and the binder polyvinylidene fluoride are mixed in a solvent N-methylpyrrolidone (NMP) at a weight ratio of 94:4:2 to prepare a positive electrode slurry; the positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained after baking and rolling.

[0107] (2) Preparation of negative electrode sheet: Hard carbon (HC) as the negative electrode active material, conductive agent Super p, and binder CMC are mixed in water at a mass ratio of 96:2:2 to prepare a negative electrode slurry; the negative electrode slurry is coated on both sides of the positive electrode current collector copper foil, dried, and rolled to obtain a negative electrode sheet.

[0108] (3) Assembly of sodium ion battery: In a nitrogen-filled glove box, the positive electrode sheet, separator, and negative electrode sheet were stacked in order and wound into a square cell. The cell was then placed into a battery case and welded. The sodium ion battery electrolyte was then injected into the battery case, and the battery case was sealed to produce a sodium ion battery. After the battery was allowed to stand for 24 hours, it was formed to obtain a soft-pack sodium battery that can be used for electrochemical performance testing.

[0109] 1. Normal temperature cycle performance test

[0110] At room temperature (25°C), each soft-pack sodium battery is first charged at a constant current of 1C to a voltage of 3.5V, and then charged at a constant voltage to a cut-off current of 0.05C; then the battery is discharged at a constant current of 1C to a cut-off potential of 2V, and the first discharge capacity C1 is recorded. After repeating the above charging and discharging steps for 100 cycles, the ratio of the discharge capacity at the 1000th cycle to its C1 is recorded as the capacity retention rate of the 100 cycles. In addition, if the capacity retention rate of the batteries in some experimental groups is less than 80% after the number of cycles is less than 1000, the number of cycles is recorded as the life of the battery. The test results of the room temperature cycle performance of each battery are summarized in the following Table 1. Among them, Figure 1 The figure is a normal temperature cycle performance curve of the soft-pack sodium battery provided in Example 1 and Comparative Examples 1-3.

[0111] 2. Impedance test

[0112] At room temperature (25°C), each soft-pack sodium battery was first charged at a constant current of 1C to a voltage of 3.5V, and then charged at a constant voltage to a cutoff current of 0.05C; then the battery was discharged at a constant current of 1C for 30 minutes, and the electrochemical impedance spectroscopy (EIS) of each battery was tested using an electrochemical workstation. The specific test data are shown in Table 1.

[0113] Figure 2 The EIS curves of the soft-pack sodium batteries of Example 1 and Comparative Examples 1-3 are shown. The EIS curves are mainly composed of a semicircle in the high-frequency region and a slant line in the low-frequency region. The larger the diameter of the semicircle in the high-frequency region, the greater the charge transfer impedance of the battery.

[0114] Table 1

[0115]

[0116]

[0117] From Table 1 and Figure 1 From the comparison between Example 1 and Comparative Examples 1-3, it can be seen that the sodium battery assembled with the sodium ion battery electrolyte of Example 1 has a capacity retention rate of 93.69% after 1000 cycles at 1C at room temperature. When only the second additive is added to the sodium ion battery electrolyte (Comparative Example 1) or the first additive (Comparative Example 2), although the cycle performance of the battery is improved compared to the cycle performance of the battery of Comparative Example 3 without the addition of the first additive and the second additive, the capacity retention rate is not higher than 86.57% after 1000 cycles, which shows that the effect of adding the first additive and the second additive alone on the battery cycle performance is significantly worse than that of the battery containing both, which also illustrates from the side that the first additive and the second additive can play a synergistic role. In addition, it can be seen from the data of Examples 6 and 7 that when the ratio of the first additive and the second additive is too high or too low, although the battery performance is slightly improved compared to the battery without the additive, the capacity retention rate of 1000 cycles is slightly lower than the battery capacity retention rate provided by Examples 1-5.

[0118] From the comparison between Examples 1 to 3 and Examples 4 to 7, it can be seen that when the total amount of the first additive and the second additive is the same, when the mass ratio of the first additive to the second additive is 1:2, the synergistic effect between them is better, and the effect of improving the cycle performance of the battery is more obvious. In addition, when the mass ratio of the first additive to the second additive is between 2:1 and 1:4, the synergistic effect of the two can be better exerted to improve the electrochemical performance of the battery.

[0119] In addition, from Figure 2It can also be seen from the EIS curves of the soft-pack sodium batteries of Example 1 and Comparative Examples 1-3 that the diameter of the semicircle in the high-frequency region of the EIS curve of the sodium battery of Example 1 is very small, indicating that the impedance of the battery is small, which is conducive to charge transfer and ion diffusion in the electrode material during charging and discharging, and the cycle performance is good, which is better than that of other embodiments and comparative examples.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sodium ion battery electrolyte, characterized in that The method comprises a first additive and a second additive, wherein the first additive is a non-sodium metal cation compound, the second additive is a halogenated organic ester compound, and the halogen atom in the second additive comprises at least one of chlorine, bromine and iodine.

2. The sodium ion battery electrolyte according to claim 1, characterized in that The chemical formula of the first additive is XY n , wherein X is selected from at least one of Li, K, Rb, Ca, Mg, Sb, Mn, Fe, Co, Ni, Zn, and Cu, and Y is selected from NO3 - PF6 - TFSI - 、FSI - At least one of, n is 1 to 4; And / or, the second additive is selected from at least one of chloroethylene carbonate, bromoethylene carbonate, fluorobromoethylene carbonate, ethyl chlorobenzoate, ethyl bromoacrylate, ethyl bromoacetate, and methyl bromobenzoate.

3. The sodium ion battery electrolyte according to claim 2, characterized in that The mass ratio of the first additive to the second additive is (2-1):(1-4).

4. The sodium ion battery electrolyte according to any one of claims 1 to 3, characterized in that Based on the total mass of the sodium ion battery electrolyte, the mass percentage of the first additive is 0.01% to 5%; And / or, based on the total mass of the sodium ion battery electrolyte, the mass percentage of the second additive is 0.01% to 5%.

5. The sodium ion battery electrolyte according to any one of claims 1 to 4, characterized in that Also included is a third additive, the third additive comprising at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, propylene sulfate, propenyl-1,3-sultone, vinyl sulfate, methylene methanedisulfonate, succinonitrile, adiponitrile, tris(trimethylsilyl)phosphite, trimethyl phosphate, and ethoxy(pentafluoro)cyclotriphosphazene; The third additive accounts for 0.1% to 10% by mass of the sodium ion battery electrolyte.

6. The sodium ion battery electrolyte according to any one of claims 1 to 5, characterized in that The electrolyte salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium nitrate, and sodium chloride.

7. The sodium ion battery electrolyte according to any one of claims 1 to 6, characterized in that The invention also includes a solvent, which includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, dimethyl sulfoxide, tetrahydrofuran, acetonitrile, and N,N-dimethylformamide.

8. A battery, characterized in that: The invention relates to a sodium ion battery electrolyte comprising the sodium ion battery electrolyte according to any one of claims 1 to 7.

9. A battery pack, characterized in that: A battery comprising the battery of claim 8.

10. An electrical device, characterized in that: Comprising the battery according to claim 8 or the battery pack according to claim 9.

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