Electrolyte, battery, battery pack and electric equipment

Abstract

The invention provides an electrolyte battery, a battery pack and electric equipment. The electrolyte comprises a sodium salt, a cosolvent and an electrolyte additive; the sodium salt comprises sodium monofluorophosphate; the cosolvent is prepared from ethoxypentafluorocyclotriphosphazene; the electrolyte additive comprises fluoroethylene carbonate; the molar ratio of sodium ions provided by the sodium monofluorophosphate in the total sodium ions of the electrolyte is 0.1%-20%. The electrolyte can improve the safety performance, the first coulombic efficiency and the capacity retention ratio of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrolyte, a battery, a battery pack and an electrical equipment. BACKGROUND

[0002] With the continuous rise of global energy demand, sodium-ion batteries have attracted much attention due to their low cost, abundant resources and other significant advantages, and have shown broad application prospects, especially in large-scale energy storage and electric vehicles. Although sodium-ion batteries have many advantages, they still face several technical challenges in practical application, such as low battery safety, low first coulomb efficiency and low capacity retention rate.

[0003] By adding electrolyte additives and other substances to the electrolyte, some of the problems of low battery safety, low first coulomb efficiency and low capacity retention rate can be improved to some extent, but it is still difficult to achieve the expected improvement of the above problems.

[0004] Therefore, there is an urgent need for an electrolyte that can improve the safety performance, first coulomb efficiency and capacity retention rate of the battery. SUMMARY

[0005] The present application provides an electrolyte, a battery, a battery pack and an electrical equipment, which can improve the safety performance, first coulomb efficiency and capacity retention rate of the battery.

[0006] The present application provides an electrolyte, which comprises a sodium salt, a co-solvent and an electrolyte additive.

[0007] The sodium salt comprises sodium monofluorophosphate.

[0008] The co-solvent comprises ethoxy pentafluorocyclotriphosphazene.

[0009] The electrolyte additive comprises fluoroethylene carbonate.

[0010] The molar proportion of sodium ions provided by the sodium monofluorophosphate in the total sodium ions in the electrolyte is 0.1% to 20%.

[0011] In some embodiments of the present application, the volume ratio of the ethoxy pentafluorocyclotriphosphazene to the fluoroethylene carbonate is (0.5-20):1.

[0012] In some embodiments of the present application, the volume proportion of the ethoxy pentafluorocyclotriphosphazene in the total volume of the electrolyte is 5% to 20%.

[0013] And / or, the volume proportion of the fluoroethylene carbonate in the total volume of the electrolyte is 1% to 10%.

[0014] In some embodiments of the present application, the sodium ions provided by the sodium monofluorophosphate account for 1% to 18% of the total sodium ions in the electrolyte.

[0015] In some embodiments of the present application, the ionic conductivity of the electrolyte is greater than 10 mS / cm.

[0016] In some embodiments of the present application, the acidity of the electrolyte is no more than 100 ppm.

[0017] In some embodiments of the present application, the sodium salt further comprises other sodium salts, and the other sodium salts comprise one or more of sodium hexafluorophosphate, sodium methylsulfonate, sodium trifluoromethylsulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0018] In some embodiments of the present application, the co-solvent further comprises other fluorine-containing co-solvents, and the fluorine-containing co-solvents comprise one or more of hexafluorocyclotriphosphazene, methoxy-pentafluorocyclotriphosphazene, (2,2,2-trifluoroethoxy)-pentafluorocyclotriphosphazene, phenoxy-pentafluorocyclotriphosphazene, di(ethoxy)-tetrafluorocyclotriphosphazene, tri(ethoxy)-trifluorocyclotriphosphazene, octafluorocyclotetraphosphazene, and poly(difluorophosphazene).

[0019] In some embodiments of the present application, the electrolyte additive further comprises other additives, and the other additives comprise at least one of trimethyl carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and trimethyl phosphate.

[0020] In some embodiments of the present application, the molar ratio of the sodium monofluorophosphate to the other sodium salts is 1: (4-1000).

[0021] In some embodiments of the present application, the volume ratio of the ethoxy-pentafluorocyclotriphosphazene to the other fluorine-containing co-solvents is (0.5-2): 1.

[0022] In some embodiments of the present application, the volume ratio of the fluoroethylene carbonate to the other additives is (0.5-3): 1.

[0023] In some embodiments of the present application, the electrolyte further comprises a main solvent, and the main solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate.

[0024] In some embodiments of the present application, the main solvent comprises any two of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, and the volume ratio of any two of the main solvents is (0.4-1.5): 1.

[0025] The embodiments of the present application also provide a battery comprising the electrolyte as described above.

[0026] In some embodiments of the present application, the battery further comprises a positive electrode sheet comprising a positive electrode active material, wherein the positive electrode active material comprises one or more of transition metal oxides, polyanion compounds, organic polymers, and Prussian blue analogues.

[0027] In some embodiments of the present application, the battery further comprises a negative electrode sheet comprising a negative electrode active material, wherein the negative electrode active material comprises one or more of natural graphite, artificial graphite, petroleum coke, and silicon-carbon materials.

[0028] In some embodiments of the present application, the battery further comprises a positive electrode sheet comprising a positive electrode active material, wherein the positive electrode active material comprises one or more of transition metal oxides, polyanion compounds, organic polymers, and Prussian blue analogues.

[0029] In some embodiments of the present application, the battery further comprises a positive electrode sheet comprising a positive electrode active material, wherein the positive electrode active material comprises one or more of transition metal oxides, polyanion compounds, organic polymers, and Prussian blue analogues.

[0030] The electrolyte provided by the embodiments of the present application has high safety performance, high initial coulombic efficiency, and high capacity retention rate by virtue of the synergistic effect of sodium monofluorophosphate, ethoxy pentafluoro cyclo-triphosphazene, and fluoroethylene carbonate. DETAILED DESCRIPTION

[0031] The objects, technical solutions, and advantages of the present application will be more clearly understood from the following detailed description of the embodiments of the present application. It should be apparent that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of the present application.

[0032] In practical applications, sodium-ion batteries have the problems of low safety, low initial coulombic efficiency, and low capacity retention rate. The use of an electrolyte with good electrochemical stability, ionic conductivity, high-pressure resistance, and flame retardancy can effectively solve the above problems.

[0033] The inventors have found that sodium monofluorophosphate, as a new type of sodium salt, has good electrochemical stability and can improve the electrochemical stability of the electrolyte to some extent. However, the composition of the electrolyte is complex, and simply optimizing the concentration of sodium monofluorophosphate cannot improve the safety, initial coulombic efficiency, and capacity retention rate of the battery.

[0034] Therefore, in some embodiments of the present application, an electrolyte is provided, which comprises a sodium salt, a co-solvent, and an electrolyte additive. The sodium salt comprises sodium monofluorophosphate. The co-solvent comprises ethoxy pentafluoro cyclo-triphosphazene. The electrolyte additive comprises fluoroethylene carbonate. The molar proportion of sodium ions provided by sodium monofluorophosphate in the total sodium ions in the electrolyte is 0.1% to 20%.

[0035] The embodiment of the present application makes the sodium salt in the electrolyte include sodium monofluorophosphate and controls the molar proportion of sodium monofluorophosphate in the electrolyte, and adds the electrolyte additive fluoroethylene carbonate and the cosolvent ethoxy pentafluorocyclotriphosphazene in the electrolyte, so that the electrolyte has good electrochemical stability, ionic conductivity, high-pressure resistance and flame retardation, and the safety, first coulomb efficiency, capacity retention and other performances of the battery are improved.

[0036] The inventor found that a stable and uniform solid-state electrolyte interface film (SEI film) directly affects the safety, first coulomb efficiency, capacity retention and other performances of the battery. In detail, a stable SEI film can effectively improve the ionic conductivity, so that the battery has a high capacity retention and first coulomb efficiency; when the surface of the SEI film is uniform, the deposition of sodium metal can be avoided, and the occurrence of side reactions in the battery is reduced, so that the safety performance, first coulomb efficiency and capacity retention of the battery are improved. When the electrolyte of the embodiment of the present application includes sodium monofluorophosphate, the electrolyte additive fluoroethylene carbonate, the cosolvent ethoxy pentafluorocyclotriphosphazene, and the molar proportion of sodium ions provided by sodium monofluorophosphate in the total sodium ions in the electrolyte is 0.1% to 20%, the battery can form a SEI film with high uniformity and high stability, so that the safety performance, first coulomb efficiency and capacity retention of the battery are high. In detail, when the electrolyte of the embodiment of the present application has the above composition, the SEI film has good ionic conductivity and ion intercalation / deintercalation efficiency, so that the battery has a high first coulomb efficiency. At the same time, after the battery of the embodiment of the present application uses the electrolyte with the above composition, more inorganic fluorine is embedded in the SEI film, so that the SEI film can uniformly and stably cover the negative electrode surface, improve the problems such as battery gas generation caused by side reactions between the negative active material and the electrolyte, and can reduce the deposition of sodium metal on the negative electrode, greatly improving the safety performance and capacity retention of the battery. In addition, when the electrolyte has the above composition, the electrolyte has good flame retardation and high-pressure resistance, so that the safety performance of the battery is better.

[0037] The molar percentage of sodium ions provided by the sodium monofluorophosphate in the total sodium ions in the electrolyte is 0.1% to 20%. For example, the molar percentage of sodium ions provided by the sodium monofluorophosphate in the total sodium ions in the electrolyte is, for example, 0.1%, 1%, 5%, 10%, 15%, 20%, or a range formed by any two of them. It should be clear that other sodium salts are also included in the electrolyte, and the total sodium ions in the electrolyte are the sum of the sodium ions provided by the sodium monofluorophosphate and the sodium ions provided by other sodium salts. When testing the molar percentage of sodium ions provided by the sodium monofluorophosphate in the total sodium ions in the electrolyte, the anions of the sodium monofluorophosphate and the anions of other sodium salts can be tested using conventional testing methods in the art, and the molar percentage of sodium ions provided by the sodium monofluorophosphate in the total sodium ions in the electrolyte can be calculated according to the content of the anions in each sodium salt. The molar percentage of sodium ions provided by the sodium monofluorophosphate in the total sodium ions in the electrolyte can be tested by ion chromatography.

[0038] In some embodiments of the present application, the volume ratio of ethoxy pentafluoro cyclotriphosphazene to fluoroethylene carbonate is (0.5-20):1. For example, the volume ratio of ethoxy pentafluoro cyclotriphosphazene to fluoroethylene carbonate is, for example, 0.5:1, 1:1, 5:1, 10:1, 15:1, 20:1, or a range formed by any two of them. By further controlling the volume ratio of ethoxy pentafluoro cyclotriphosphazene to fluoroethylene carbonate, the embodiments of the present application are more conducive to the synergistic effect of sodium monofluorophosphate, ethoxy pentafluoro cyclotriphosphazene, and fluoroethylene carbonate, thereby better improving the chemical stability, ionic conductivity, high-pressure resistance, and flame retardancy of the electrolyte, and further improving the safety, first coulombic efficiency, capacity retention rate, and other properties of the battery. The above volume ratio can be determined by gas chromatography-mass spectrometry.

[0039] In order to make the electrolyte have better high-pressure resistance and flame retardancy to further improve the safety performance of the battery, in some embodiments, the volume percentage of ethoxy pentafluoro cyclotriphosphazene in the total volume of the electrolyte is 5% to 20%. For example, the volume percentage of ethoxy pentafluoro cyclotriphosphazene in the total volume of the electrolyte is, for example, 5%, 10%, 15%, 20%, or a range formed by any two of them.

[0040] In some embodiments, by controlling the volume percentage of fluoroethylene carbonate in the total volume of the electrolyte to be 1% to 10%, the ionic conductivity and electrochemical stability of the electrolyte are further improved, thereby making the SEI film form more stably and uniformly, and enabling the safety, first coulombic efficiency, capacity retention rate, and other properties of the battery to be further improved. For example, the volume percentage of fluoroethylene carbonate in the total volume of the electrolyte is, for example, 1%, 3%, 5%, 7%, 9%, 10%, or a range formed by any two of them.

[0041] In some embodiments of the present application, the molar proportion of sodium ions provided by sodium monofluorophosphate in the total sodium ions in the electrolyte is 1% to 18%, which can further improve the ionic conductivity and electrochemical stability of the electrolyte, and further make the SEI film more stable and uniform, so that the safety, initial coulombic efficiency, capacity retention rate and other performances of the battery can be further improved. For example, the molar proportion of sodium ions provided by sodium monofluorophosphate in the total sodium ions in the electrolyte is 1%, 3%, 6%, 9%, 10%, 15%, 18% or a range formed by any two of them.

[0042] When the electrolyte provided by the embodiments of the present application has the above composition, the ionic conductivity is greater than 10 mS / cm, so that the safety, initial coulombic efficiency, capacity retention rate and other performances of the battery can be further improved.

[0043] In addition, when the electrolyte of the embodiments of the present application has the above composition, the acidity of the electrolyte is not more than 100 ppm, at this time the electrolyte has better stability, which is beneficial to better improve the safety, initial coulombic efficiency, capacity retention rate and other performances of the battery.

[0044] In some embodiments, considering the further improvement of the ionic conductivity of the electrolyte, the sodium salt further includes other sodium salts, and the other sodium salts include one or more of sodium hexafluorophosphate, sodium methyl sulfonate, sodium trifluoromethyl sulfonate, and sodium bis(trifluoromethylsulfonyl)imide. The introduction of the above other sodium salts can provide more sufficient active metal ion source for the sodium ion battery system, so that the safety, initial coulombic efficiency, capacity retention rate and other performances of the battery can be further improved.

[0045] In some embodiments, the co-solvent further includes other fluorine-containing co-solvents, and the fluorine-containing co-solvents include one or more of hexafluorocyclotriphosphazene (HFPN), methoxy pentafluorocyclotriphosphazene, (2,2,2-trifluoroethoxy) pentafluorocyclotriphosphazene, phenoxy pentafluorocyclotriphosphazene, di(ethoxy) tetrafluorocyclotriphosphazene, tri(ethoxy) trifluorocyclotriphosphazene, octafluorocyclotetraphosphazene, and poly(difluorophosphazene). By adding the above other fluorine-containing co-solvents, the embodiments of the present application are beneficial to further improve the stability and uniformity of the SEI film, so that the safety, initial coulombic efficiency, capacity retention rate and other performances of the battery can be further improved.

[0046] In some specific embodiments, the electrolyte additive further includes other additives, and the other additives include at least one of trimethyl carbonate, difluoroethylene carbonate (DFEC), trifluoroethylene carbonate (TFEC), dimethyl carbonate, methyl ethyl carbonate, and trimethyl phosphate, which can better improve the electrochemical stability of the electrolyte, and further improve the safety, initial coulombic efficiency, capacity retention rate and other performances of the battery.

[0047] In some embodiments, when the molar ratio of sodium monofluorophosphate to other sodium salts is 1: (4-1000), the ionic conductivity of the electrolyte is further improved, and the performance of the battery, such as the initial coulombic efficiency and capacity retention rate, is further improved.

[0048] In some embodiments, when the volume ratio of ethoxy-pentafluoro-cyclotriphosphazene to other fluorine-containing co-solvents is controlled to be (0.5-2):1, the stability and uniformity of the SEI film can be more effectively improved, and the performance of the battery, such as safety, initial coulombic efficiency, capacity retention rate, and the like, can be further improved.

[0049] In some embodiments, when the volume ratio of fluoroethylene carbonate to other additives is controlled to be (0.5-3):1, the stability and uniformity of the SEI film can be more effectively improved, and the performance of the battery, such as safety, initial coulombic efficiency, capacity retention rate, and the like, can be further improved.

[0050] In the embodiments of the present application, the electrolyte further comprises a main solvent, and the main solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate. The above-mentioned main solvent has better solubility for sodium salts, can better improve the ionic conductivity of the electrolyte, and is conducive to improving the performance of the battery, such as the initial coulombic efficiency and capacity retention rate. In detail, either one of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate can be used as the main solvent, or two or more of the above-mentioned substances can be used as the main solvent. When there are two or more components in the main solvent, the volume ratio of each component can be determined according to actual needs.

[0051] In some embodiments, the main solvent comprises any two of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, and the volume ratio of any two main solvents is (0.4-1.5):1. For example, the volume ratio of any two of the above-mentioned main solvents is, for example, 0.4:1, 4.8:1, 1:1, 1.2:1, 1.5:1, or a range composed of any two of them. When the main solvent of the embodiments of the present application has the above-mentioned components, the performance of the battery, such as the initial coulombic efficiency and capacity retention rate, can be further improved.

[0052] In specific implementation, ethylene carbonate and dimethyl carbonate can be mixed in a volume ratio of 1:1 to be used as the main solvent, which can further improve the flowability of the electrolyte, so that the electrolyte has a high ionic conductivity, and the performance of the battery, such as the initial coulombic efficiency and capacity retention rate, can be better improved.

[0053] The embodiments of the present application also provide a battery comprising the above-mentioned electrolyte. The battery provided by the present application has the advantages corresponding to the above-mentioned electrolyte, which will not be repeated here.

[0054] In the embodiments of the present application, the coating, drying, rolling and other processes involved are conventional operations in the art, and the equipment used can be conventional equipment in the art, which is not particularly limited.

[0055] The battery is a sodium ion battery.

[0056] Generally, the battery includes an electrolyte, a cell, and a shell encapsulating the cell, the electrolyte is injected into the cell in the shell, and the cell includes a positive plate, a negative plate, and a separator between the positive plate and the negative plate. Among them, the cell can be a laminated cell, that is, the cell is formed by interleaving and stacking the positive plate, the separator and the negative plate; or the cell can also be a wound cell, that is, the cell is formed by stacking and winding the positive plate, the separator and the negative plate.

[0057] In some embodiments, the battery further includes a positive plate, the positive plate includes a positive active material, and the positive active material includes one or more of a transition metal oxide, a polyanion compound, an organic polymer, and a Prussian blue material.

[0058] Specifically, the positive plate includes a positive current collector and a positive active layer on at least one side surface of the positive current collector. Specifically, the positive active layer can be arranged on one side surface in the thickness direction of the positive current collector, or the positive active layer can be arranged on both opposite side surfaces in the thickness direction of the positive current collector.

[0059] The positive active layer includes the positive active material, a conductive agent and a binder. In the positive active layer, the mass percentage of the positive active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or a range formed by any two of them. The mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range formed by any two of them. The mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range formed by any two of them.

[0060] In the embodiments of the present application, the conductive agent in the positive active layer can be a conventional conductive material in the art. For example, the conductive agent in the positive active layer can include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNT), carbon fibers, graphene, acetylene black, and Ketjen black.

[0061] In the embodiments of the present application, the binder in the positive active layer can be a conventional binder in the art, for example, the binder in the positive active layer can include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, etc.

[0062] The embodiments of the present application can use a conventional positive current collector in the art, for example, the positive current collector includes an aluminum foil.

[0063] In the embodiments of the present application, the positive sheet can be prepared by a conventional method in the art, for example, by a coating method, specifically, the components for forming the positive active layer such as the positive active material, the conductive agent, and the binder can be dispersed in a solvent such as N-methylpyrrolidone (NMP) to prepare a positive slurry, which is then coated on the surface of the positive current collector, and after processes such as drying and rolling, the positive sheet is prepared. The coating, drying, rolling, etc. processes involved are conventional operations for preparing the positive sheet by the coating method, and are not particularly limited.

[0064] In some embodiments of the present application, the battery further includes a negative sheet, and the negative sheet includes a negative active material, and the negative active material includes one or more of natural graphite, artificial graphite, petroleum coke, and silicon-carbon material.

[0065] Specifically, the negative sheet includes a negative current collector and a negative active layer on at least one side surface of the negative current collector, and specifically, the negative active layer can be provided on one side surface of the negative current collector, or the negative active layer can be respectively provided on the opposite side surfaces of the negative current collector in the thickness direction.

[0066] Specifically, the negative active layer can include the above-mentioned negative active material, conductive agent, and binder, which can all be conventional materials in the art, for example, the conductive agent can include one or more of conductive carbon black, carbon nanotube (CNT), acetylene black, graphene, ketjen black, and carbon fiber; and the binder can include one or more of sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0067] The embodiments of the present application can use a conventional negative current collector in the art, for example, the negative current collector includes a copper foil.

[0068] In the embodiments of the present application, the negative electrode sheet can be prepared by conventional methods in the art, for example, by a coating method. Specifically, the negative electrode active material, the conductive agent, the binder and other components used for forming the negative electrode active layer can be dispersed in a solvent, for example, water, to prepare a negative electrode slurry, which is then coated on the surface of the negative electrode current collector, and then dried, rolled and subjected to other processes to prepare the negative electrode sheet. The coating, drying, rolling and other processes are conventional operations for preparing the negative electrode sheet by the coating method, and thus are not particularly limited.

[0069] The electrolyte in the embodiments of the present application can use the electrolyte described above, or can further comprise other functional additives on the basis of the electrolyte described above, and thus is not particularly limited.

[0070] In the embodiments of the present application, the separator is used to separate the positive electrode sheet and the negative electrode sheet to avoid short circuit caused by the contact between the positive electrode sheet and the negative electrode sheet. The separator in the embodiments of the present application can be conventional separators in the art, and thus is not particularly limited. For example, the separator material can be a separator prepared from one or more of high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide and polyvinylidene fluoride.

[0071] In the embodiments of the present application, the battery cell can be packaged by using conventional casing materials in the art, for example, soft packaging materials such as aluminum plastic film, but is not limited thereto.

[0072] In the embodiments of the present application, the positive electrode sheet, the separator and the negative electrode sheet and other components can be assembled into a battery by conventional methods in the art. For example, the positive electrode sheet, the separator and the negative electrode sheet can be arranged in an interleaved and stacked manner to prepare a jelly-roll type battery cell (or a wound type battery cell). Then, the battery cell is placed in a casing (an outer package), and then subjected to conventional processes such as liquid injection (i.e., injection of the electrolyte) and packaging to prepare the battery.

[0073] The embodiments of the present application also provide a battery pack comprising at least two batteries described above. The battery pack has the advantages corresponding to the electrolyte described above, and thus is not described in detail.

[0074] Generally, the battery pack comprises a plurality of batteries described above, which are connected to form the battery pack as single batteries. The batteries can be electrically connected by conventional methods in the art, for example, in series, in parallel or in a mixed connection mode comprising the above connection modes, and thus are not particularly limited.

[0075] The embodiments of the present application also provide a power consumption device comprising the battery described above or the battery pack described above. The power consumption device has the advantages corresponding to the electrolyte described above, and thus is not described in detail.

[0076] The power consumption equipment of the embodiment of the present application can be a conventional power consumption equipment in the field, for example, a power equipment (such as an electric vehicle, an electric automobile), an electronic equipment (such as a mobile phone, a tablet computer, a notebook computer, a digital camera, etc.), a wearable equipment (such as a watch, a bracelet, a VR glasses, etc.), an energy storage power station, etc., and no special limitation is made thereto.

[0077] The technical solutions of the present application are further illustrated below in combination with specific embodiments.

[0078] Embodiment 1

[0079] The electrolyte of the present embodiment comprises the following components:

[0080] Sodium salt: sodium monofluorophosphate and sodium hexafluorophosphate, the concentration of sodium ions is 1 mol / L, and the proportion of sodium ions provided by sodium monofluorophosphate in the total sodium ions is 1%.

[0081] Main solvent: ethylene carbonate (EC) and diethyl carbonate (DEC), the volume ratio is 2:1.

[0082] Co-solvent: ethoxy pentafluorocyclophosphazene (PFPN), the volume ratio is 10% (based on the total volume of the electrolyte, the total volume of the electrolyte includes the volume of the main solvent, the co-solvent and the electrolyte additive).

[0083] Electrolyte additive: fluoroethylene carbonate (FEC), the volume ratio is 2% (based on the total volume of the electrolyte, the total volume of the electrolyte includes the volume of the main solvent, the co-solvent and the electrolyte additive).

[0084] Embodiments 2-16 and Comparative Examples 1-5 differ from Embodiment 1 in the types and molar ratios of sodium salts, the proportion of sodium ions provided by sodium monofluorophosphate in the total sodium ions (the sodium ion proportion in the table), the types and volume ratios of main solvents, the volume ratios of PFPN and FEC, the types and volume ratios of co-solvents, the volume proportion of co-solvents in the total volume of the electrolyte (the volume proportion of co-solvents in the table), the compositions and volume ratios of electrolyte additives, the volume proportion of electrolyte additives in the total volume of the electrolyte (the volume proportion of electrolyte additives in the table), etc. Among the above electrolyte components, except for the volume proportions of electrolyte additives and co-solvents, the remaining components are main solvents. See Table 1 for details.

[0085]

[0086] Test Example

[0087] The sodium ion battery electrolyte provided by the above embodiments and comparative examples is assembled into a square shell sodium ion battery according to the following method, respectively:

[0088] Positive electrode sheet preparation: The positive electrode active material (Na2Fe[Fe(CN)6]), polyvinylidene fluoride (PVDF) binder, and acetylene black (Super P) conductive agent were mixed in a mass ratio of 8:1:1, and a certain amount of N-methyl pyrrolidone (NMP) was added to prepare a positive electrode slurry. The solid content of the slurry was adjusted to about 50%. After the slurry was degassed and sieved, it was uniformly coated on the surface of an aluminum foil. After drying, rolling, and cutting, a positive electrode sheet was obtained.

[0089] Negative electrode sheet preparation: The negative electrode active material hard carbon (IC), butadiene-styrene rubber (SBR) / carboxymethyl cellulose (CMC) composite binder, and acetylene black (Super P) conductive agent were mixed in a mass ratio of 8:1, and deionized water was added to prepare a negative electrode slurry. The solid content was adjusted to about 45%, and the slurry was degassed and sieved before being uniformly coated on the surface of an aluminum foil. After drying, rolling, and cutting, a negative electrode sheet was obtained.

[0090] Square cell preparation: The negative electrode sheet, separator, and positive electrode sheet were stacked in order to form an electric core, which was then packaged in a square shell. After the electric core was baked to remove moisture, the electrolyte in the examples and comparative examples was injected into the square shell battery. After aging, formation, aging, and capacity distribution, square shell sodium ion batteries of Examples 1-8 and Comparative Examples 1-3 were obtained.

[0091] Capacity retention rate (1C cycle for 1000 cycles) test:

[0092] The capacity retention rate test is designed to evaluate the capacity decay of the battery during long-term charge and discharge cycles, thereby reflecting the cycle stability of the battery. First, square shell sodium ion batteries prepared from the electrolytes in the examples and comparative examples were selected according to the above method, and it was ensured that the batteries had completed the charge / discharge formation, aging, and capacity distribution processes. Then, a constant current charge / discharge test device was used for testing, with the charge and discharge current set to 1C (i.e., the charge and discharge current equal to the nominal capacity of the battery). During charging, the battery was charged from 0% to 100%, and during discharging, it was discharged from 100% to the minimum voltage. The test was continued for 1000 cycles, and the capacity of the battery was recorded after each charge and discharge. After 1000 cycles, the capacity retention rate was obtained by calculating the ratio of the final capacity to the initial capacity. The higher the capacity retention rate, the better the cycle stability of the battery and the slower the performance degradation. The test results are shown in Table 2.

[0093] Initial Coulombic Efficiency:

[0094] The first coulombic efficiency test is used to evaluate the battery's electrical energy conversion efficiency during the first charge and discharge process. First, select the square shell sodium ion batteries prepared by the electrolyte in Example 8 and the comparative example according to the above method, and ensure that the battery has undergone pre-treatment such as formation, aging and capacity distribution. Then, the first charge and discharge test is carried out. The battery is first charged from 0% to the maximum charging voltage (usually the rated charging voltage of the battery), and then discharged from 100% to the minimum discharge voltage of the battery (i.e. the lower limit of the discharge voltage of the battery). During the test, precise current and voltage monitoring equipment is used to record the capacity (first charge gram capacity C0 and first discharge gram capacity D0) and voltage data of the battery during the charging and discharging process. The higher the coulombic efficiency, the more efficient the battery can convert electrical energy, with lower internal resistance and better battery performance. The first coulombic efficiency is calculated according to D0 / C0. The test results are shown in Table 2.

[0095] Safety test of the puncture test:

[0096] The puncture test is mainly used to evaluate the safety of the battery when subjected to physical impact (such as puncture). First, select the square shell sodium ion batteries prepared by the electrolyte in Example and the comparative example according to the above method, and ensure that the battery has undergone pre-treatment such as formation, aging and capacity distribution. Then, use a standard steel needle or similar sharp object (5 mm diameter steel needle) to perform a puncture test on the battery. The battery is fixed on the test platform to ensure that there is no physical obstacle on the surface of the battery, and then the steel needle is inserted into the center of the battery cell at a standard speed. After the test, observe the reaction of the battery, mainly check whether there is abnormal situation such as fire, smoke, swelling, leakage, rupture or sharp temperature rise. If the battery remains stable after puncture and does not have abnormal reaction, it means that the battery has high safety. The puncture test can effectively verify the pressure resistance and safety of the battery under extreme physical conditions. The test results are shown in Table 2.

[0097] In addition, by using conventional test methods to test the electrolyte in Example and the comparative example, the ionic conductivity of the electrolyte is greater than 10 mS / cm, and the acidity is not more than 100 ppm.

[0098]

[0099] As shown in the table, compared with the comparative examples, the embodiments of the present application give consideration to the safety performance, the initial coulombic efficiency and the capacity retention rate of the battery by the synergistic effect of sodium monofluorophosphate, ethoxy pentafluorocyclo-triphosphazene and fluoroethylene carbonate, and by controlling the molar ratio of sodium ions provided by sodium monofluorophosphate in the total sodium ions in the electrolyte to be 0.1% to 20%. Compared with example 9 and example 10, by further controlling the volume ratio of the cosolvent in the electrolyte, the safety performance, the initial coulombic efficiency and the capacity retention rate of the battery are improved. Compared with example 11 and example 12, by further controlling the volume ratio of PFPN and FEC and the volume ratio of the electrolyte additive, the safety performance, the initial coulombic efficiency and the capacity retention rate of the battery are improved.

[0100] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte includes sodium salt, co-solvent, and electrolyte additive; The sodium salt includes sodium monofluorophosphate; The co-solvent includes ethoxypentafluorocyclotriphosphazene; The electrolyte additive includes fluoroethylene carbonate; The sodium ions provided by the sodium monofluorophosphate account for a molar ratio of 0.1% to 20% of the total sodium ions in the electrolyte.

2. The electrolyte according to claim 1, characterized in that The volume ratio of the ethoxy pentafluorocyclotriphosphazene to the fluoroethylene carbonate is (0.5-20):

1.

3. The electrolyte according to claim 1 or 2, characterized in that The volume proportion of the ethoxy pentafluorocyclotriphosphazene in the total volume of the electrolyte is 5% to 20%; And / or, the volume proportion of the fluoroethylene carbonate in the total volume of the electrolyte is 1% to 10%.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The sodium ions provided by the sodium monofluorophosphate account for 1% to 18% by mole of the total sodium ions in the electrolyte.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The ionic conductivity of the electrolyte is greater than 10 mS / cm; And / or, the acidity of the electrolyte does not exceed 100 ppm.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The sodium salt also includes other sodium salts, and the other sodium salts include one or more of sodium hexafluorophosphate, sodium methanesulfonate, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide; And / or, the co-solvent further comprises other fluorine-containing co-solvents, wherein the fluorine-containing co-solvent comprises one or more of hexafluorocyclotriphosphazene, methoxypentafluorocyclotriphosphazene, (2,2,2-trifluoroethoxy)pentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, di(ethoxy)tetrafluorocyclotriphosphazene, tri(ethoxy)trifluorocyclotriphosphazene, octafluorocyclotetraphosphazene, and poly(difluorophosphazene); And / or, the electrolyte additive further includes other additives, and the other additives include at least one of trimethyl carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and trimethyl phosphate.

7. The electrolyte according to claim 6, characterized in that The molar ratio of the sodium monofluorophosphate to the other sodium salt is 1:(4-1000); And / or, the volume ratio of the ethoxy pentafluorocyclotriphosphazene to the other fluorinated co-solvent is (0.5-2):1; And / or, the volume ratio of the fluoroethylene carbonate to the other additives is (0.5-3):

1.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The electrolyte further includes a main solvent, and the main solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate.

9. The electrolyte according to claim 8, characterized in that The main solvent includes any two of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, and the volume ratio of any two of the main solvents is (0.4-1.5):

1.

10. A battery, characterized in that: The battery comprises the electrolyte according to any one of claims 1 to 9.

11. The battery according to claim 10, characterized in that The battery further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material, wherein the positive electrode active material comprises one or more of a transition metal oxide, a polyanionic compound, an organic polymer, and a Prussian blue material; And / or, the battery further comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises one or more of natural graphite, artificial graphite, petroleum coke, and silicon-carbon material.

12. A battery pack, characterized in that: The battery pack comprises at least two batteries according to claim 10 or 11.

13. An electrical device, characterized in that: The electrical device comprises the battery according to claim 10 or 11, or the battery pack according to claim 12.

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