Electrolyte and sodium ion battery

Abstract

The invention provides an electrolyte and a sodium ion battery, the electrolyte comprises a solvent, an electrolyte and an additive, the additive comprises a first additive, and the first additive is selected from at least one of compounds as shown in a formula 1; wherein R1 and R2 are respectively and independently selected from an oxygen atom, C1-C3 alkylene or C1-C3 alkyleneoxy, at least one of R1 and R2 is C1-C3 alkylene or C1-C3 alkyleneoxy, n and m are respectively and independently 0 or 1, and n and m are not 0 at the same time; the electrolyte comprises a main salt, and the main salt comprises sodium bis (fluorosulfonyl) imide. Through the synergistic effect of the first additive and the sodium bis (fluorosulfonyl) imide, a good interfacial film can be formed on the surface of the electrode material, and impedance increase under a high-temperature condition can be inhibited. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the field of electrochemistry technology, and particularly to an electrolyte and a sodium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in fields such as consumer electronics, electric vehicles, and energy storage due to their high energy density and cycling performance. However, the rising price of lithium salts limits the development of lithium-ion batteries. Compared with lithium resources, sodium resources are abundant, with a crustal abundance of 2.64%, which is 440 times that of lithium resources. Moreover, sodium resources are widely distributed and easy to extract. After large-scale commercialization, the cost is low. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, which makes sodium-ion batteries more advantageous in terms of raw material cost compared to lithium-ion batteries. In addition to the cost advantage, compared with lithium-ion batteries, sodium-ion batteries also have the following advantages: 1) The energy density is better than that of lead-acid batteries and comparable to that of lithium iron phosphate batteries; 2) Good low-temperature performance, can be used in alpine regions; 3) Higher safety performance compared with ternary lithium-ion batteries and lithium iron phosphate batteries; 4) Environmentally friendly, in line with the sustainable development strategy.

[0003] However, there are still some problems and challenges in the practical application of sodium-ion batteries, such as serious gas generation, poor high and low temperature performance, etc. Therefore, it is particularly important to improve the performance of sodium-ion batteries. As an ion conductor that regulates electrochemical behavior and stabilizes the interface between the electrode and the electrolyte, the electrolyte affects the performance of sodium-ion batteries. The existing conventional electrolytes have poor thermal stability and low-temperature stability, and are prone to serious oxidative decomposition on the surface, resulting in the deterioration of capacity and cycling performance. The key to solving this problem lies in developing an electrolyte system with excellent high and low temperature performance. Summary of the Invention

[0004] The purpose of the present application is to provide an electrolyte and a sodium-ion battery to improve the low-temperature performance of sodium-ion batteries, and at the same time enhance the high-temperature performance of sodium-ion batteries by suppressing gas generation at high temperatures. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides an electrolyte, which includes a solvent, an electrolyte, and an additive. The additive includes a first additive, and the first additive is selected from at least one of the compounds shown in Formula 1;

[0006]

[0007] Wherein, R 1 and R 2 are each independently selected from an oxygen atom, a C1-C3 alkylene group, or a C1-C3 alkoxy group, and R 1 and R 2At least one of them is a C1-C3 alkylene group or a C1-C3 alkoxy group, n and m are each independently 0 or 1, and n and m are not both 0 at the same time; the electrolyte includes a main salt, and the main salt includes sodium bis(fluorosulfonyl)imide.

[0008] In some embodiments of the present application, the compound shown in Formula 1 is selected from at least one of the following compounds:

[0009]

[0010] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage content of the first additive is W1, and 0.03% ≤ W1 ≤ 3%; and / or, based on the mass of the electrolyte, the mass percentage content of sodium bis(fluorosulfonyl)imide is W2, and 6% ≤ W2 ≤ 18%.

[0011] In some embodiments of the present application, 0.5% ≤ W1 ≤ 2%.

[0012] In some embodiments of the present application, the mass ratio of sodium bis(fluorosulfonyl)imide to the first additive is (2-120):1.

[0013] In some embodiments of the present application, the electrolyte includes other sodium salts, and the other sodium salts are selected from sodium hexafluorophosphate; and / or, based on the mass of the electrolyte, the mass percentage content of the other sodium salts is W3, and 0% ≤ W3 ≤ 6%.

[0014] In some embodiments of the present application, the electrolyte includes other sodium salts and sodium bis(fluorosulfonyl)imide, and the mass ratio of the other sodium salts to sodium bis(fluorosulfonyl)imide is (0-1):1.

[0015] In some embodiments of the present application, the solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate, ethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dioxolane, ethyl acetate, ethyl propionate, and propyl propionate.

[0016] The second aspect of the present application provides a sodium ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte provided by the first aspect of the present application. The separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive electrode active material, and the positive electrode active material is selected from at least one of layered oxides, Prussian compounds, and polyanion compounds; preferably Na 3 V 2 (PO 4 ) 3 、Na 0.9 Mn 0.6 Fe 0.4 PO 4 、Na 4 Fe3 (PO 4 ) 2 (P 2 O 7 )、NaFePO 4 、 sodium ferrocyanide and NaNi X Me Y O 2 or at least one of them, Me is selected from two or three of Fe, Co, Mn and Al, and X + Y = 1.

[0017] In some embodiments of the present application, the negative electrode tab includes a negative electrode active material, and the negative electrode active material is selected from one or more of carbon-based materials, silicon-based materials, alloy materials, and organic materials; preferably hard carbon.

[0018] Advantages of the present application:

[0019] The present application provides an electrolyte and a sodium ion battery. The electrolyte includes a solvent, an electrolyte, and an additive. The additive includes a first additive, and the first additive is selected from at least one of the compounds shown in Formula 1; the electrolyte includes a main salt, and the main salt includes sodium bis(fluorosulfonyl)imide. Through the synergistic effect of the first additive and sodium bis(fluorosulfonyl)imide, it is possible to form a good interface film on the surface of the electrode material while suppressing the increase in impedance under high temperature conditions.

[0020] Of course, it is not necessary for any product or method implementing the present application to achieve all of the above-mentioned advantages simultaneously. Detailed embodiments

[0021] The technical solutions in the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0022] The first aspect of the present application provides an electrolyte, which includes a solvent, an electrolyte, and an additive. The additive includes a first additive, and the first additive is selected from at least one of the compounds shown in Formula 1;

[0023]

[0024] wherein, R 1 and R 2 are each independently selected from an oxygen atom, a C1-C3 alkylene group or a C1-C3 alkoxy group, and at least one of R 1 and R 2 is a C1-C3 alkylene group or a C1-C3 alkoxy group, n and m are each independently 0 or 1, and n and m are not both 0; the electrolyte includes a main salt, and the main salt includes sodium bis(fluorosulfonyl)imide.

[0025] Due to the relatively large size of sodium ions and the relatively large loss during insertion and extraction, the cycle reversibility of sodium-ion batteries and the stability of the interface film are poorer compared to lithium-ion batteries. Therefore, sodium-ion batteries have higher requirements for the ion transport ability. In addition, during the cycling process of sodium-ion batteries, the gas generation amount of the battery is relatively large, and the high-temperature storage performance needs to be improved. The inventors have found through research that the large π bond on the benzene ring in the compound shown in Formula 1 will affect the activity of the compound shown in Formula 1, reduce its energy barrier, and facilitate the ring-opening reaction of the sulfonate ester structure in the compound shown in Formula 1 during the formation stage of sodium-ion batteries, forming an interface film rich in inorganic sulfates, inorganic sulfites, sodium alkyl sulfonates, and sodium alkyl sulfates on the surface of the negative electrode sheet, which is beneficial to enhancing the stability at the interface between the negative electrode sheet and the electrolyte and improving the cycle performance and high-temperature storage performance of sodium-ion batteries.

[0026] Sodium bis(fluorosulfonyl)imide can be partially decomposed, thereby introducing components such as sodium nitride, sodium sulfate, and sodium fluoride into the SEI film or CEI film, reducing the electrode interface polarization, improving the stability of the SEI film or CEI film, and enabling sodium-ion batteries to exhibit excellent high-temperature performance. However, after hydrolysis, the bis(fluorosulfonyl)imide group is weakly basic, which will cause a deterioration effect during the high-temperature storage of sodium-ion batteries, resulting in the oxidative decomposition of the electrolyte on the surface of the positive electrode, the dissolution of transition metal ions in the positive electrode material, and the reduction of the stability of the positive electrode material structure and interface. The bis(fluorosulfonyl)imide group will also hydrolyze during the battery reaction to generate corrosive products, which will further damage the aluminum current collector and deteriorate the high-temperature cycle performance and high-temperature storage performance of the battery.

[0027] In this application, the first additive and sodium bis(fluorosulfonyl)imide are used in combination. The intermediate product obtained from the ring-opening reaction of the compound of Formula 1 has a benzene ring. Under the conjugation of the large π bond on the benzene ring, the intermediate-state radical formed by the ring-opening reaction of the compound shown in Formula 1 can combine with the bis(fluorosulfonyl)imide group to form a stable conjugated compound, reducing the damage of the hydrolysis of sodium bis(fluorosulfonyl)imide to the positive electrode material and inhibiting the side reaction between the positive electrode material interface and the electrolyte. Through the synergistic effect of sodium bis(fluorosulfonyl)imide and the first additive, while a good interface film can be formed on the surface of the electrode material, the increase in impedance under high-temperature conditions can be inhibited.

[0028] In some embodiments of this application, the compound shown in Formula 1 is selected from at least one of the following compounds:

[0029]

[0030] By selecting the compound shown in Formula 1 within the scope of the present application, it is beneficial to enhance the stability at the interface between the negative electrode sheet and the electrolyte, and is beneficial to further improve the cycle performance and high-temperature storage performance of the secondary battery. Preferably, the first additive is selected from the compound shown in Formula 1-1. The intermediate product formed after the bond breakage of the compound shown in Formula 1-1 has more sites, which is more conducive to forming a stable interface film at the electrode and the electrolyte liquid surface, thereby further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0031] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage content of the first additive is W1, 0.03% ≤ W1 ≤ 3%, preferably 0.5% ≤ W1 ≤ 2%; and / or, based on the mass of the electrolyte, the mass percentage content of sodium bis(fluorosulfonyl)imide is W2, 6% ≤ W2 ≤ 18%. For example, based on the mass of the electrolyte, the mass percentage content of the first additive can be 0.03%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a range composed of any two of these values; based on the mass of the electrolyte, the mass percentage content of sodium bis(fluorosulfonyl)imide can be 6%, 8%, 10%, 12%, 14%, 16%, 18% or a range composed of any two of these values. Controlling the mass percentage contents of the first additive and sodium bis(fluorosulfonyl)imide within the scope of the present application is beneficial to further enhance the stability at the interface between the negative electrode sheet and the electrolyte, and improve the cycle performance and high-temperature storage performance of the sodium-ion battery.

[0032] In some embodiments of the present application, the mass ratio of sodium bis(fluorosulfonyl)imide to the first additive is (2 - 120):1. For example, the mass ratio of sodium bis(fluorosulfonyl)imide to the first additive can be 2:1, 10:1, 30:1, 50:1, 70:1, 100:1, 120:1 or a range composed of any two of these values. Controlling the mass ratio of sodium bis(fluorosulfonyl)imide to the first additive within the scope of the present application is beneficial to the further synergistic effect between the two, and further improve the cycle performance and high-temperature storage performance of the sodium-ion battery.

[0033] In some embodiments of the present application, the electrolyte includes other sodium salts, and the other sodium salts are selected from sodium hexafluorophosphate; and / or, based on the mass of the electrolyte, the mass percentage content of the other sodium salts is W3, 0% ≤ W3 ≤ 6%. For example, based on the mass of the electrolyte, the content of the other sodium salts can be 0%, 1%, 2%, 3%, 4%, 5%, 6% or a range composed of any two of these values. The electrolyte includes the electrolyte within the above range and regulates the mass percentage content of the other sodium salts within the scope of the present application, which can make the electrolyte have a high ionic conductivity and good electrochemical stability, and can further improve the cycle performance and high-temperature storage performance of the sodium-ion battery.

[0034] In some embodiments of the present application, the electrolyte includes other sodium salts and sodium bis(fluorosulfonyl)imide, and the mass ratio of the other sodium salts to sodium bis(fluorosulfonyl)imide is (0 - 1):1. For example, the mass ratio of the other sodium salts to sodium bis(fluorosulfonyl)imide can be 0:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, or any range composed of any two of these values. The electrolyte solution includes the electrolyte within the above range, and the mass ratio of the other sodium salts and sodium bis(fluorosulfonyl)imide is adjusted within the range of the present application. Sodium bis(fluorosulfonyl)imide can improve the kinetic performance of the electrolyte solution, and to a greater extent reduce the electrode interface polarization, further improving the high-temperature cycle performance of the sodium-ion battery; the other sodium salts are fully dissolved in the organic solvent, and an electrolyte solution with more stable chemical properties and higher conductivity can be formed, so that the sodium-ion battery exhibits better electrochemical performance.

[0035] In some embodiments of the present application, the electrolyte solution further includes other additives, and the other additives are selected from at least one of sodium bis(oxalato)borate, sodium perchlorate, and sodium difluoro(oxalato)borate.

[0036] In some embodiments of the present application, the solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate, ethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dioxolane, ethyl acetate, ethyl propionate, and propyl propionate. The present application has no special limitation on the mass of the solvent, as long as it can meet the purpose of the present application. For example, based on the mass of the electrolyte solution, the mass percentage content of the solvent is W4, and 73% ≤ W4 ≤ 93.97%. The electrolyte solution includes the solvent within the above range, which can make the electrolyte solution have appropriate viscosity, high ionic conductivity, and good electrochemical stability, and can further improve the cycle performance and high-temperature storage performance of the sodium-ion battery.

[0037] The second aspect of the present application provides a sodium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte solution provided by the first aspect of the present application. The separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive electrode active material, and the positive electrode active material is selected from at least one of layered oxides, Prussian compounds, and polyanion compounds; preferably Na 3 V 2 (PO 4 ) 3 、Na 0.9 Mn 0.6 Fe 0.4 PO 4 、Na 4 Fe 3 (PO 4 ) 2 (P 2O 7 )、NaFePO 4 、sodium ferrocyanide and NaNi X Me Y O 2 at least one of them, Me is selected from two or three of Fe, Co, Mn and Al, and X + Y = 1. Usually, during the charge and discharge process of the sodium-ion battery, the metal active ions (sodium ions) are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is arranged between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through. The sodium-ion battery of the present application includes the electrolyte provided in the first aspect of the present application, which is beneficial to form a stable interface film on the positive and negative electrodes, further improve the diffusion ability of sodium ions at the electrode interface, further reduce the impedance, and improve the low-temperature performance, high-temperature cycle performance and high-temperature storage performance of the sodium-ion battery. The positive electrode plate includes the positive electrode active material within the scope of the present application, which is beneficial to improve the cycle performance and high-temperature storage performance of the sodium-ion battery.

[0038] The positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its own thickness direction, or can be provided on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the positive electrode current collector, or can be a partial area of the surface of the positive electrode current collector. The present application has no special limitation, as long as the purpose of the present application can be achieved. The present application has no special limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector can be an aluminum foil, an aluminum alloy foil or a composite positive electrode current collector. The above-mentioned composite positive electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base. The material of the above-mentioned polymer material base layer can include but is not limited to at least one of polypropylene (PP), polyethylene terephthalate (PET) or polybutylene terephthalate (PBT). The material of the above-mentioned metal layer can include but is not limited to at least one of aluminum, aluminum alloy, nickel or nickel alloy. The present application has no special limitation on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 50 μm to 250 μm, and the thickness of the positive electrode current collector is 7 μm to 20 μm.

[0039] The positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. There are no particular limitations on the types of the positive electrode conductive agent and the positive electrode binder in this application, as long as the objectives of this application can be achieved. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, carbon dots, or carbon fibers. The above carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin. There are no particular limitations on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer in this application, and those skilled in the art can select according to actual needs as long as the objectives of this application can be achieved.

[0040] There are no particular limitations on the preparation method of the positive electrode sheet in this application, as long as the objectives of this application can be achieved. For example, the preparation method of the positive electrode sheet may include, but is not limited to, the following steps: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, positive electrode conductive agent, and positive electrode binder, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0041] In this application, the negative electrode tab includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The statement "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or can be disposed on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. There is no special limitation in this application, as long as the purpose of this application can be achieved. There is no special limitation on the negative electrode current collector in this application, as long as the purpose of this application can be achieved. For example, the negative electrode current collector can be copper foil, copper alloy foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam or copper foam or a composite negative electrode current collector. The above composite negative electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The material of the above polymer material base layer can include, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET) or polybutylene terephthalate (PBT). The material of the above metal layer can include, but is not limited to, at least one of copper, copper alloy, nickel or nickel alloy. There is no special limitation on the thickness of the negative electrode material layer and the negative electrode current collector in this application, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided negative electrode material layer is 50 μm to 180 μm, and the thickness of the negative electrode current collector is 3 μm to 15 μm.

[0042] In some embodiments of this application, the negative electrode tab includes a negative electrode active material, and the negative electrode active material is selected from one or more of carbon-based materials, silicon-based materials, alloy materials and organic materials; preferably hard carbon.

[0043] In some embodiments of this application, the negative electrode material layer may further include a negative electrode conductive agent and a negative electrode binder. There is no special limitation on the types of the negative electrode conductive agent and the negative electrode binder in this application, as long as the purpose of this application can be achieved. For example, the negative electrode conductive agent can include, but is not limited to, at least one of conductive carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, carbon dots or carbon fibers. The above carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. For example, the negative electrode binder can include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) or carboxymethyl chitosan (CMCS). In some embodiments of this application, the negative electrode material layer may also optionally include other additives, such as thickeners, and the thickeners can include, but are not limited to, sodium carboxymethyl cellulose (CMC-Na), etc.

[0044] The present application does not particularly limit the preparation method of the negative electrode sheet, as long as the object of the present application can be achieved. For example, the preparation method of the negative electrode sheet may include, but is not limited to, the following steps: dispersing the above components for preparing the negative electrode sheet, such as negative electrode active material, negative electrode conductive agent, negative electrode binder and other additives, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0045] The present application does not particularly limit the separator, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), glass fiber, polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), and polyamide (PA). The type of the separator may include at least one of a woven film, non-woven fabric, microporous film, composite film, rolled film or spun film. In the present application, the thickness of the separator is not particularly limited, as long as the object of the present application can be achieved. For example, the thickness of the separator may be 4 μm to 20 μm.

[0046] In the present application, the sodium ion battery further includes a housing for accommodating the positive electrode sheet, separator, negative electrode sheet and electrolyte, as well as other components known in the field of sodium ion batteries. The present application does not limit the above other components. The present application does not particularly limit the housing, and it may be a housing well-known in the art, as long as the object of the present application can be achieved. For example, the housing may be a hard shell housing or a flexible housing. The material of the hard shell housing may be metal. The present application does not limit the type of the metal, and a metal hard shell housing known in the art may be used, as long as the object of the present application can be achieved. The flexible housing may be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0047] The preparation process of the sodium ion battery of the present application is well-known to those skilled in the art, and the present application has no particular limitation. For example, the preparation process of the sodium ion battery may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator and negative electrode sheet in sequence, and performing operations such as winding and folding according to needs to obtain a wound structure electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain a sodium ion battery. Or, stacking the positive electrode sheet, separator and negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated structure electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain a sodium ion battery. In addition, an overcurrent protection element, a guide plate, etc. may be placed in the housing according to needs to prevent the pressure inside the sodium ion battery from rising and overcharging and discharging.

[0048] Examples

[0049] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0050] Testing methods and equipment:

[0051] 25°C Cycling Performance Test

[0052] The sodium-ion battery is left standing at 25°C for 30 minutes to reach a constant temperature, charged at a constant current of 1C until the voltage reaches 4.0V, then charged at a constant voltage of 4.0V until the cut-off current is 0.05C, and then discharged at a constant current of 1C until the voltage reaches 2.0V. Record the initial discharge capacity as C 1 , and this is taken as one charge-discharge cycle. Repeat the above charge-discharge cycle 500 times, and record the discharge capacity of the 500th cycle as C 500 .

[0053] 25°C Cycling Capacity Retention Rate (%) = C 500 / C 1 × 100%; The room temperature cycling performance of the sodium-ion battery is evaluated by the 25°C cycling capacity retention rate. The larger the 25°C capacity retention rate, the better the room temperature cycling performance of the sodium-ion battery.

[0054] 45°C Cycling Performance Test

[0055] The sodium-ion battery is left standing at 45°C for 30 minutes to reach a constant temperature, charged at a constant current of 1C until the voltage reaches 4.0V, then charged at a constant voltage of 4.0V until the cut-off current is 0.05C, and then discharged at a constant current of 1C until the voltage reaches 2.0V. Record the initial discharge capacity as C m , and this is taken as one charge-discharge cycle. Repeat the above charge-discharge cycle 400 times, and record the discharge capacity of the 400th cycle as C 400 .

[0056] 45°C Cycling Capacity Retention Rate (%) = C 400 / C m × 100%; The high temperature cycling performance of the sodium-ion battery is evaluated by the 45°C cycling capacity retention rate. The larger the 45°C capacity retention rate, the better the high temperature cycling performance of the sodium-ion battery.

[0057] 55°C Storage Performance Test

[0058] The sodium-ion battery is left standing at 25°C for 30 minutes to reach a constant temperature, charged at a constant current of 1C until the voltage reaches 4.0V, then charged at a constant voltage of 4.0V until the cut-off current is 0.05C, and then discharged at a constant current of 0.5C until the voltage reaches 2.0V. Record the discharge capacity as C 0Then, it is charged at a constant current of 1C to 4.0V, and charged at a constant voltage of 4.0V until the cut-off current is 0.05C. The thickness of the sodium-ion battery is measured with a flat thickness gauge and denoted as d 0 Then, the sodium-ion battery is transferred to an explosion-proof oven at 55°C and left for 14 days. Then, the thickness of the sodium-ion battery is measured and denoted as d 1 After that, the sodium-ion battery is taken out and cooled to room temperature. At 25°C, the sodium-ion battery is discharged at a constant current of 0.5C until the voltage is 2.0V, and the discharge capacity is denoted as C n The thickness expansion rate at 55°C = (d 1 - d 0 ) / d 0 × 100%, and the storage capacity retention rate at 55°C = C n / C 0 × 100%.

[0059] The high-temperature storage performance of the sodium-ion battery is evaluated by the storage thickness expansion rate and the storage capacity retention rate at 55°C. The smaller the storage thickness expansion rate and the larger the storage capacity retention rate, the better the high-temperature storage performance of the sodium-ion battery

[0060] -20°C Discharge Performance Test

[0061] The sodium-ion battery is left at 25°C for 30 minutes to reach a constant temperature, charged at a constant current of 1C to a voltage of 4.0V, then charged at a constant voltage of 4.0V until the cut-off current is 0.05C, and then discharged at a constant current of 0.5C until the voltage is 2.0V. The initial discharge capacity is recorded as C 2 , then the sodium-ion battery is charged at a constant current of 1C to a voltage of 4.0V, and then charged at a constant voltage of 4.0V until the cut-off current is 0.05C. The sodium-ion battery is transferred to a -20°C thermostat and left for 4h, and then discharged at a constant current of 0.5C at -20°C until the voltage is 2.0V. The discharge capacity is denoted as C 3 .

[0062] The storage capacity retention rate at -20°C (%) = C 3 / C 2 × 100%; The low-temperature discharge performance of the sodium-ion battery is evaluated by the capacity retention rate at -20°C. The larger the capacity retention rate at -20°C, the better the low-temperature discharge performance of the sodium-ion battery

[0063] Example 1

[0064] <Preparation of Electrolyte>

[0065] In an inert atmosphere environment with a water content of less than 0.1 ppm and an oxygen content of less than 1 ppm, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate are mixed in a mass ratio of 3:6:1 to obtain a base solvent. Then, sodium bis(fluorosulfonyl)imide (NaFSI) as an electrolyte and a first additive (Formula 1-1) are added to the base solvent and mixed evenly to obtain an electrolyte solution. Among them, based on the mass of the electrolyte solution, the mass percentage content of NaFSI is 12%, and the mass percentage content of the first additive (Formula 1-1) is 0.02%.

[0066] <Preparation of the positive electrode plate>

[0067] Mix the positive electrode active material NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3 O 2 powder, conductive agent acetylene black, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 94:2.5:0.5:3, add N-methylpyrrolidone (NMP) as a solvent, and formulate it into a slurry with a solid content of 50 wt%. After vacuum stirring evenly, a positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 16 μm to obtain a positive electrode plate with a single-sided coated positive electrode material layer. Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode plate with a double-sided coated positive electrode material layer. After drying at 85 °C, it is cold-pressed, trimmed, sliced, slit, vacuum dried at 75 °C for 10 hours, and the tab is welded to make the positive electrode plate ready for use. Among them, the total thickness of the positive electrode plate is 174 μm, and the single-sided coating density of the positive electrode slurry is 15 mg / cm 2 。

[0068] <Preparation of the negative electrode plate>

[0069] Mix the negative electrode active material hard carbon, conductive agent conductive carbon black (Super P), binder styrene-butadiene rubber (SBR), and dispersant sodium carboxymethyl cellulose (CMC) in a mass ratio of 95:1.5:2:1.5, add deionized water as a solvent, and formulate it into a slurry with a solid content of 49 wt%. After vacuum stirring evenly with a vacuum mixer, a negative electrode slurry is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector aluminum foil with a thickness of 9 μm to obtain a negative electrode plate with a single-sided coated negative electrode material layer. Then, repeat the above steps on the other surface of the aluminum foil to obtain a negative electrode plate with a double-sided coated negative electrode material layer. After drying at 85 °C, it is cold-pressed, trimmed, sliced, slit, vacuum dried at 85 °C for 10 hours, and the tab is welded to make the negative electrode plate ready for use. Among them, the total thickness of the negative electrode plate is 144 μm, and the single-sided coating density of the negative electrode slurry is 6.4 mg / cm 2 。

[0070] <Preparation of the separator>

[0071] The separator is a PE + ceramic + PVDF (7 + 3 + 2) separator with a thickness of 12 μm.

[0072] <Preparation of Sodium-Ion Batteries>

[0073] Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator between the positive electrode sheet and the negative electrode sheet to isolate the positive electrode sheet and the negative electrode sheet, and then wind them. Connect the positive electrode tab to the positive electrode sheet and the negative electrode tab to the negative electrode sheet to obtain an electrode assembly. Place the electrode assembly in an aluminum foil packaging bag, and lead the positive electrode tab and the negative electrode tab from the internal space of the packaging bag to the external space of the packaging bag. After drying at 75 °C for 48 hours to remove moisture, perform hot pressing and sealing to obtain a battery cell to be injected with electrolyte. Inject the prepared electrolyte into the dried battery cell in a glove box, and after encapsulation, standing, formation, aging, and grading, obtain a sodium-ion battery.

[0074] The formation conditions are: temperature 45 °C, pressure 3 kg / cm 2 , constant current charge at 0.1C to 4.0V.

[0075] Examples 2 to 24

[0076] Except for adjusting the type and mass percentage content W1 of the first additive, the mass percentage content W2 of sodium bis(fluorosulfonyl)imide, and the mass percentage content W3 of other sodium salts according to Table 1, the rest are the same as in Example 1.

[0077] Among them, when the mass percentage content W1 of the first additive, the mass percentage content W2 of sodium bis(fluorosulfonyl)imide, and the mass percentage content W3 of other sodium salts change, the content of the base solvent changes accordingly.

[0078] Example 25

[0079] Except for adjusting the type of the negative electrode active material to artificial graphite, the rest are the same as in Example 20.

[0080] Example 26

[0081] Except for adjusting the type of the negative electrode active material to graphene composite material, the rest are the same as in Example 20.

[0082] Example 27

[0083] Except for adjusting the type of the positive electrode active material to NaNi 1 / 3 Mn 1 / 3 Co 1 / 3 O 2 otherwise, the rest are the same as in Example 20.

[0084] Example 28

[0085] Except for adjusting the type of the positive electrode active material to Na 0.9 Mn 0.6 Fe 0.4 PO 4 the rest is the same as that of Example 20.

[0086] Comparative Examples 1 to 2

[0087] Except for adjusting the mass percentage content W1 of the first additive, the mass percentage content W2 of sodium bis(fluorosulfonyl)imide, and the mass percentage content W3 of other sodium salt electrolytes according to Table 1, the rest is the same as that of Example 1.

[0088] Among them, when the mass percentage content W1 of the first additive, the mass percentage content W2 of sodium bis(fluorosulfonyl)imide, and the mass percentage content W3 of other sodium salts change, the content of the base solvent changes accordingly.

[0089]

[0090]

[0091] It can be seen from Examples 1 to 11 and Comparative Example 1 that by adding the first additive to the electrolyte and controlling the type and content of the first additive within the scope of the present application, the sodium-ion battery has a high cycle capacity retention rate, storage capacity retention rate, and a low storage thickness expansion rate. It can be seen from Examples 12 to 19 and Comparative Example 2 that by adding sodium bis(fluorosulfonyl)imide to the electrolyte and controlling the content of sodium bis(fluorosulfonyl)imide within the scope of the present application, through the synergistic effect of the first additive and sodium bis(fluorosulfonyl)imide, it is beneficial to improve the cycle performance and storage performance of the sodium-ion battery. It can be seen from Examples 20 to 24 that by adding sodium bis(fluorosulfonyl)imide as the main salt to the electrolyte, and adding sodium hexafluorophosphate as other sodium salts, and regulating the mass ratio of sodium hexafluorophosphate to sodium bis(fluorosulfonyl)imide within the scope of the present application, the electrolyte can have a high ionic conductivity and good electrochemical stability, thereby further improving the cycle performance and storage performance of the sodium-ion battery. It can be seen from Examples 1 to 28 that by using the negative electrode active material and the positive electrode active material within the scope of the present application, the sodium-ion battery has high cycle performance and storage performance.

[0092] The above are only the preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. An electrolyte comprising a solvent, an electrolyte and an additive, wherein the additive comprises a first additive, and the first additive is selected from at least one of the compounds represented by Formula 1; in, R1 and R2 are independently selected from oxygen atoms, C1-C3 alkylene groups or C1-C3 alkyleneoxy groups, and at least one of R1 and R2 is C1-C3 alkylene groups or C1-C3 alkyleneoxy groups, and n and m are independently 0 or 1, and n and m are not 0 at the same time; The electrolyte includes a main salt, and the main salt includes sodium bis(fluorosulfonyl)imide.

2. The electrolyte according to claim 1, wherein The compound represented by Formula 1 is selected from at least one of the following compounds:

3. The electrolyte according to claim 1, wherein Based on the mass of the electrolyte, the mass percentage of the first additive is W1, 0.03%≤W1≤3%; And / or, based on the mass of the electrolyte, the mass percentage of the sodium bis(fluorosulfonyl)imide is W2, 6%≤W2≤18%.

4. The electrolyte according to claim 1, wherein 0.5％≤W1≤2％。 5. The electrolyte according to claim 1, wherein The mass ratio of the sodium bis(fluorosulfonyl)imide to the first additive is (2-120):

1.

6. The electrolyte according to claim 1, wherein The electrolyte includes other sodium salts, and the other sodium salts are selected from sodium hexafluorophosphate; And / or, based on the mass of the electrolyte, the mass percentage of the other sodium salt is W3, 0%≤W3≤6%.

7. The electrolyte according to any one of claims 1 to 6, wherein the electrolyte comprises other sodium salts and sodium bis(fluorosulfonyl)imide, and the mass ratio of the other sodium salts to the sodium bis(fluorosulfonyl)imide is (0-1):

1.

8. The electrolyte according to claim 7, wherein the solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, propylene carbonate, ethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dioxolane, ethyl acetate, ethyl propionate and propyl propionate.

9. A sodium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte according to any one of claims 1 to 8, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material is selected from at least one of a layered oxide, a Prussian compound and a polyanion compound; preferably Na3V2(PO4)3, Na 0.9 Mn 0.6 Fe 0.4 PO4, Na4Fe3(PO4)2(P2O7), NaFePO4, sodium ferrocyanide and NaNi X Me Y At least one of O2, Me is selected from 2 or 3 of Fe, Co, Mn and Al, and X+Y=1.

10. The sodium ion battery according to claim 9, wherein the negative electrode plate comprises a negative electrode active material, and the negative electrode active material is selected from one or more of carbon-based materials, silicon-based materials, alloy materials and organic materials; preferably hard carbon.

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