Electrolyte for inhibiting low-temperature sodium precipitation of battery, preparation method of electrolyte, sodium-ion battery and electric equipment

Abstract

The invention provides an electrolyte for inhibiting low-temperature sodium precipitation of a battery, a preparation method of the electrolyte, a sodium-ion battery and electric equipment, and relates to the field of sodium-ion batteries. The electrolyte for inhibiting low-temperature sodium precipitation of the battery, provided by the invention, comprises an electrolyte solvent as a raw material, and the electrolyte solvent comprises an organic solvent and ethyl propionate; based on 100 wt% of the mass of the electrolyte solvent, the content of the organic solvent is 60-95 wt%, and the content of the ethyl propionate is 5-40 wt%. The electrolyte for inhibiting low-temperature sodium precipitation of the battery, provided by the invention, can still keep relatively good fluidity at relatively low temperature, so that sodium ion transmission is facilitated, relatively high ion transmission rate can be kept, and the overall performance of the battery is favorably improved.

Description

Technical Field

[0001] The present application relates to the field of sodium ion batteries, and in particular to an electrolyte for inhibiting low-temperature sodium precipitation in batteries and a preparation method thereof, a sodium ion battery, and electrical equipment. Background Art

[0002] Lithium-ion batteries are widely used in fields such as transportation, energy storage systems, military applications, and telecommunications. These wide applications require batteries to operate in a variety of harsh environments. One example is the use of batteries at low temperatures. In low temperature environments, the diffusion of metal ions in electrodes and electrolytes slows down, which increases the possibility of metal plating on the negative electrode. Metal plating is detrimental to the cycling performance of the battery due to the high surface reactivity of the metal with the electrolyte, which leads to the consumption of active sodium ions in the system. In addition, metal plating also affects the safety of operation due to the possibility of causing short circuits and thermal runaway.

[0003] Sodium-ion batteries are considered to be suitable candidates to compete with the already mature lithium-ion batteries due to their potential advantages, such as low cost and improved low-temperature performance. The Stokes radius of sodium ions is smaller than that of lithium ions, which inherently improves the ionic conductivity in the electrolyte. In addition, the lower desolvation energy of sodium ions also helps to reduce the resistance of the electrode / electrolyte interface, which is conducive to achieving high performance at low temperatures. However, even in sodium-ion batteries, the problem of sodium precipitation at low temperatures is prevalent.

[0004] Electrolyte optimization is one of the most important strategies to suppress sodium precipitation. By changing the types of solvents, salts, and additives used in the electrolyte, the physical and chemical properties of the electrolyte, such as viscosity, density, wettability, and ionic conductivity, can be fine-tuned. At low temperatures, the ionic conductivity of sodium ions drops sharply with decreasing temperature. In addition, sodium precipitation and slow ion diffusion exacerbate the problem by increasing charge transfer resistance and polarization during cycling. Therefore, how to suppress the phenomenon of low-temperature sodium precipitation by optimizing the electrolyte has become an urgent problem to be solved. Summary of the invention

[0005] The purpose of the present application is to provide an electrolyte for inhibiting low-temperature sodium precipitation in batteries, a preparation method thereof, a sodium ion battery, and electrical equipment to solve the above-mentioned problems.

[0006] To achieve the above objectives, this application adopts the following technical solutions:

[0007] In a first aspect, the present application provides an electrolyte for inhibiting low-temperature sodium precipitation in a battery, wherein the raw materials thereof include an electrolyte solvent, wherein the electrolyte solvent includes an organic solvent and ethyl propionate;

[0008] Calculated based on the mass of the electrolyte solvent itself being 100wt%, the content of the organic solvent is 60-95wt%, and the content of the ethyl propionate is 5-40wt%.

[0009] Optionally, the organic solvent includes ethyl methyl carbonate and propylene carbonate, and based on the mass of the electrolyte solvent itself being 100wt%, the content of the ethyl methyl carbonate is 40-60wt%, and the content of the propylene carbonate is 20-40wt%.

[0010] Optionally, the raw material further comprises sodium salt, the sodium salt comprises sodium hexafluorophosphate, and the concentration of the sodium salt is 12-17 wt%.

[0011] Optionally, the raw materials further include additives, and the additives include fluoroethylene carbonate and 1,3-propane sultone.

[0012] Optionally, the content of the additive is 1-5wt%, calculated based on the mass of the electrolyte for inhibiting low-temperature sodium precipitation of the battery as 100wt%.

[0013] Optionally, based on the mass of the electrolyte for inhibiting low-temperature sodium precipitation of the battery as 100wt%, the content of the fluoroethylene carbonate is 2-4wt%, and the content of the 1,3-propane sultone is 0.8-1.2wt%.

[0014] In a second aspect, the present application also provides a method for preparing an electrolyte for inhibiting low-temperature sodium precipitation in a battery, comprising: mixing raw materials to obtain an electrolyte for inhibiting low-temperature sodium precipitation in a battery.

[0015] Optionally, the method comprises:

[0016] Under the protection of an inert gas, the ethyl methyl carbonate and the propylene carbonate are mixed to obtain a first mixed solution;

[0017] adding the ethyl propionate to the first mixed solution to obtain a second mixed solution;

[0018] adding the additive to the second mixed solution and mixing them evenly to obtain a third mixed solution;

[0019] The sodium salt is added to the third mixed solution, and stirred until completely dissolved to obtain the electrolyte for inhibiting low-temperature sodium precipitation in the battery.

[0020] In a third aspect, the present application further provides a sodium ion battery, the raw materials of which include the electrolyte, the positive electrode, the negative electrode and the separator for inhibiting the low temperature sodium precipitation of the battery, and meet at least one of the following conditions:

[0021] a. The positive electrode current collector comprises aluminum foil;

[0022] b. The active material of the positive electrode includes NaNi x Fe y Mn z Cu 1-x-y-z O2, where 0≤x<1, 0≤y<1, 0≤z<1, and 0 <x+y+z≤1;

[0023] c. The negative electrode current collector comprises aluminum foil;

[0024] d. The active material of the negative electrode is hard carbon.

[0025] In a fourth aspect, the present application also provides an electrical device, including the above-mentioned sodium ion battery.

[0026] Compared with the prior art, the beneficial effects of this application include:

[0027] The present application provides an electrolyte for inhibiting low-temperature sodium precipitation in a battery and a sodium ion battery including the electrolyte. First, ethyl propionate has a lower freezing point, which can broaden the liquid temperature range of the electrolyte, so that the electrolyte can still maintain good fluidity at a lower temperature, which is beneficial to the transmission of sodium ions; secondly, it can effectively improve the conductivity of ions, especially at a lower temperature, it can maintain a higher ion transmission rate, which helps to improve the overall performance of the battery. In addition, through the solvent in the present application, the phenomenon of low-temperature sodium precipitation in the battery can be effectively suppressed, and the adverse reaction between sodium and the electrolyte can be reduced, thereby reducing the safety hazards of the battery in a low-temperature environment. Moreover, on the one hand, with the addition of ethyl propionate, the dielectric constant of the electrolyte can be increased while reducing the viscosity, which is beneficial to the transmission efficiency of sodium ions in the electrolyte; on the other hand, ethyl propionate and organic solvents can form a stable interface layer on the surface of the electrode, and the interface layer can inhibit the precipitation of sodium ions and reduce the growth of sodium dendrites, thereby reducing the adverse reaction between the electrode and the electrolyte, and finally improving the cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0029] Figure 1 Schematic diagram showing the relationship between the number of cycles and the capacity retention rate of sodium ion batteries using different electrolytes in Examples 1-3 and Comparative Examples 1-3;

[0030] Figure 2 A comparative schematic diagram of the relationship between the number of cycles and the coulombic efficiency of sodium ion batteries using different electrolytes in Examples 1-3 and Comparative Examples 1-3;

[0031] Figure 3 Schematic diagram of the degree of sodium precipitation at the negative electrode of the sodium ion batteries using different electrolytes after 100 cycles in Examples 1-3 and Comparative Examples 1-3;

[0032] Figure 4 dQdV curves of the sodium ion battery prepared in Example 1 after the 5th, 50th and 250th cycles at 0°C;

[0033] Figure 5 dQdV curves of the sodium ion battery prepared in Example 2 after the 5th, 50th and 250th cycles at 0°C;

[0034] Figure 6 dQdV curves of the sodium ion battery prepared in Example 3 after the 5th, 50th and 250th cycles at 0°C;

[0035] Figure 7 dQdV curves of the sodium ion battery prepared in Comparative Example 1 after the 5th, 50th and 250th cycles at 0°C;

[0036] Figure 8 dQdV curves of the sodium ion battery prepared in Comparative Example 2 after the 5th, 50th and 250th cycles at 0°C;

[0037] Fig. 9 dQdV curves of the sodium ion battery prepared in Comparative Example 3 after the 5th, 50th and 250th cycles at 0°C. DETAILED DESCRIPTION

[0038] As used herein:

[0039] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0040] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0041] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described in this article, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0042] In these examples, parts and percentages are by mass unless otherwise indicated.

[0043] "Parts by mass" refers to the basic unit of measurement for expressing the mass ratio of multiple components. 1 part can represent any unit mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that, unlike the mass parts, the sum of the mass of all components is not limited to 100 parts.

[0044] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0045] In order to better explain the technical solution provided by this application, before the embodiments, the technical solution is first described as a whole, as follows:

[0046] In a first aspect, the present application provides an electrolyte for inhibiting low-temperature sodium precipitation in a battery, wherein the raw materials include an electrolyte solvent, wherein the electrolyte solvent includes an organic solvent and ethyl propionate. Calculated based on the mass of the electrolyte solvent itself as 100wt%, the content of the organic solvent is 60-95wt%, and the content of the ethyl propionate is 5-40wt%.

[0047] Optionally, the content of the organic solvent can be 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, or any value between 60-95wt%; the content of the ethyl propionate can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, or any value between 4-40wt%.

[0048] In an optional embodiment, the organic solvent includes ethyl methyl carbonate and propylene carbonate, the content of ethyl methyl carbonate is 40-60wt%, and the amount of propylene carbonate is 20-40wt%. Propylene carbonate has high thermal stability and chemical inertness, can absorb and eliminate some reaction products, and ethyl methyl carbonate and propylene carbonate can form a stable interface layer on the electrode surface under the joint action of ethyl propionate, reducing the adverse reaction between the electrode and the electrolyte.

[0049] Optionally, the content of the ethyl methyl carbonate may be 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, or any value between 40-60wt%; the content of the propylene carbonate may be 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, or any value between 20-40wt%.

[0050] In an optional embodiment, the raw material further comprises sodium salt, the sodium salt comprises sodium hexafluorophosphate, and the concentration of the sodium salt is 12-17 wt %.

[0051] Optionally, the concentration of the sodium salt may be 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, or any value between 12-17wt%.

[0052] In an optional embodiment, the raw materials further include additives, and the additives include fluoroethylene carbonate and 1,3-propane sultone.

[0053] In an optional embodiment, the content of the additive is 1-5wt%, calculated based on the mass of the electrolyte for inhibiting low-temperature sodium precipitation of the battery as 100wt%.

[0054] Optionally, the content of the additive may be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any value between 1-5 wt%.

[0055] In an optional embodiment, based on the mass of the electrolyte for inhibiting low-temperature sodium precipitation of the battery as 100wt%, the ratio of the fluoroethylene carbonate to the 1,3-propane sultone is 2-4wt%:0.8-1.2wt%.

[0056] Optionally, the content of the fluoroethylene carbonate can be 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, or any value between 2-4wt%; the content of the 1,3-propane sultone can be 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, or any value between 0.8-1.2wt%.

[0057] In a second aspect, the present application provides a method for preparing an electrolyte for inhibiting low-temperature sodium precipitation in a battery, comprising: mixing raw materials to obtain an electrolyte for inhibiting low-temperature sodium precipitation in a battery.

[0058] Optionally, the method comprises:

[0059] Under the protection of inert gas, the ethyl methyl carbonate and the propylene carbonate are mixed to obtain a first mixed solution; ethyl propionate is added to the first mixed solution to obtain a second mixed solution; the additive is added to the second mixed solution and mixed evenly to obtain a third mixed solution; the sodium salt is added to the third mixed solution, and the mixture is stirred until completely dissolved to obtain the electrolyte for inhibiting low-temperature sodium precipitation in the battery.

[0060] In a third aspect, the present application also provides a sodium ion battery, the raw materials of which include the electrolyte, positive electrode, negative electrode and separator for inhibiting low-temperature sodium precipitation of the battery.

[0061] In an optional embodiment, the current collector of the positive electrode comprises aluminum foil; the active material of the positive electrode comprises NaNi x Fe y Mn z Cu 1-x-y-z O2, where 0≤x<1, 0≤y<1, 0≤z<1, and 0 <x+y+z≤1。

[0062] In an optional embodiment, the current collector of the negative electrode comprises aluminum foil; and the active material of the negative electrode is hard carbon.

[0063] Fourthly, the present application also provides an electrical device, including the above-mentioned sodium ion battery, such as smart phones, tablet computers, laptops, smart watches, electric bicycles, electric vehicles, drones, etc.

[0064] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If specific conditions are not specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0065] Example 1

[0066] This embodiment provides an electrolyte for inhibiting low-temperature sodium precipitation in a battery, and the preparation method is as follows:

[0067] Taking the mass of the electrolyte solvent itself as 100wt%, 52.5wt% of ethyl methyl carbonate and 37.5wt% of propylene carbonate are mixed in a glove box filled with argon to obtain an ethyl methyl carbonate / propylene carbonate mixed solution; 10wt% of ethyl propionate is added to the ethyl methyl carbonate / propylene carbonate mixed solution to obtain an electrolyte solvent.

[0068] Taking the mass of the electrolyte for inhibiting low-temperature sodium precipitation of the battery as 100wt%, 3wt% of fluoroethylene carbonate and 1wt% of 1,3-propane sultone were added, and after stirring and mixing evenly, 14.2wt% of sodium hexafluorophosphate was added, and the mixture was stirred until the sodium hexafluorophosphate was completely dissolved to obtain the electrolyte for inhibiting low-temperature sodium precipitation of the battery.

[0069] This embodiment also provides a sodium ion battery, which is composed of a positive electrode, a negative electrode, an electrolyte for inhibiting low-temperature sodium precipitation of the battery, and a separator. The positive electrode active material is NaCu1 / 9Ni2 / 9Fe1 / 3Mn1 / 3O2, and the positive electrode current collector is aluminum foil; the negative electrode active material is hard carbon, and the negative electrode current collector is aluminum foil; the separator is a PE separator coated with Al2O3 particles on one side. The sodium ion battery is prepared according to conventional methods.

[0070] Example 2

[0071] This embodiment provides an electrolyte for inhibiting low-temperature sodium precipitation in a battery, and the preparation method is as follows:

[0072] Taking the mass of the electrolyte solvent itself as 100wt%, 46.67wt% of ethyl methyl carbonate and 46.67wt% of propylene carbonate are mixed in a glove box filled with argon to obtain an ethyl methyl carbonate / propylene carbonate mixed solution; 20wt% of ethyl propionate is added to the ethyl methyl carbonate / propylene carbonate mixed solution to obtain an electrolyte solvent.

[0073] Taking the mass of the electrolyte for inhibiting low-temperature sodium precipitation of the battery as 100wt%, 3wt% of fluoroethylene carbonate and 1wt% of 1,3-propane sultone were added, and after stirring and mixing evenly, 14.2wt% of sodium hexafluorophosphate was added, and the mixture was stirred until the sodium hexafluorophosphate was completely dissolved to obtain the electrolyte for inhibiting low-temperature sodium precipitation of the battery.

[0074] This embodiment also provides a sodium ion battery, which is composed of a positive electrode, a negative electrode, an electrolyte for inhibiting low-temperature sodium precipitation of the battery, and a separator. The positive electrode active material is NaCu1 / 9Ni2 / 9Fe1 / 3Mn1 / 3O2, and the positive electrode current collector is aluminum foil; the negative electrode active material is hard carbon, and the negative electrode current collector is aluminum foil; the separator is a PE separator coated with Al2O3 particles on one side. The sodium ion battery is prepared according to conventional methods.

[0075] Example 3

[0076] This embodiment provides an electrolyte for inhibiting low-temperature sodium precipitation in a battery, and the preparation method is as follows:

[0077] Taking the mass of the electrolyte solvent itself as 100wt%, 40.83wt% of ethyl methyl carbonate and 29.17wt% of propylene carbonate are mixed in a glove box filled with argon to obtain an ethyl methyl carbonate / propylene carbonate mixed solution; 30wt% of ethyl propionate is added to the ethyl methyl carbonate / propylene carbonate mixed solution to obtain an electrolyte solvent.

[0078] Taking the mass of the electrolyte for inhibiting low-temperature sodium precipitation of the battery as 100wt%, 3wt% of fluoroethylene carbonate and 1wt% of 1,3-propane sultone are added, stirred and mixed evenly, and then 14.2wt% of sodium hexafluorophosphate is added, and stirred until the sodium hexafluorophosphate is completely dissolved to obtain the electrolyte for inhibiting low-temperature sodium precipitation of the battery.

[0079] This embodiment also provides a sodium ion battery, which is composed of a positive electrode, a negative electrode, an electrolyte for inhibiting low-temperature sodium precipitation of the battery, and a separator. The positive electrode active material is NaCu1 / 9Ni2 / 9Fe1 / 3Mn1 / 3O2, and the positive electrode current collector is aluminum foil; the negative electrode active material is hard carbon, and the negative electrode current collector is aluminum foil; the separator is a PE separator coated with Al2O3 particles on one side. The sodium ion battery is prepared according to conventional methods.

[0080] Comparative Example 1

[0081] This comparative example provides a conventional electrolyte, and the preparation method is as follows:

[0082] The difference between this comparative example and Example 1 is that ethyl propionate is not added to the electrolyte solvent. Ethyl methyl carbonate and propylene carbonate are mixed in a glove box filled with argon to obtain a conventional electrolyte solvent; based on the mass of the conventional electrolyte itself being 100wt%, 3wt% of fluoroethylene carbonate and 1wt% of 1,3-propane sultone are added, and after stirring and mixing evenly, 14.2wt% of sodium hexafluorophosphate is added, and the mixture is stirred until the sodium hexafluorophosphate is completely dissolved to obtain a conventional electrolyte.

[0083] This comparative example also provides a sodium ion battery, which is composed of a positive electrode, a negative electrode, an electrolyte for inhibiting low-temperature sodium precipitation of the battery, and a diaphragm. The positive electrode active material is NaCu1 / 9Ni2 / 9Fe1 / 3Mn1 / 3O2, and the positive electrode current collector is aluminum foil; the negative electrode active material is hard carbon, and the negative electrode current collector is aluminum foil; the diaphragm is a PE diaphragm coated with Al2O3 particles on one side. The sodium ion battery is prepared according to a conventional method.

[0084] Comparative Example 2

[0085] This comparative example provides an electrolyte, and the preparation method is as follows:

[0086] The difference between this comparative example and Example 1 is that the organic solvent ethyl propionate is replaced by diethyl carbonate, and the mass of the organic solvent remains unchanged; ethyl methyl carbonate and propylene carbonate are mixed in a glove box filled with argon to obtain a mixed solution; based on the mass of the electrolyte solvent itself as 100wt%, 15wt% of diethyl carbonate is added to the mixed solution to obtain an electrolyte solvent.

[0087] Based on the electrolyte mass as 100wt%, 3wt% of fluoroethylene carbonate and 1wt% of 1,3-propane sultone were added, and after stirring and mixing evenly, 14.2wt% of sodium hexafluorophosphate was added, and the mixture was stirred until the sodium hexafluorophosphate was completely dissolved to obtain a conventional electrolyte.

[0088] This comparative example also provides a sodium ion battery, which is composed of a positive electrode, a negative electrode, an electrolyte for inhibiting low-temperature sodium precipitation of the battery, and a diaphragm. The positive electrode active material is NaCu1 / 9Ni2 / 9Fe1 / 3Mn1 / 3O2, and the positive electrode current collector is aluminum foil; the negative electrode active material is hard carbon, and the negative electrode current collector is aluminum foil; the diaphragm is a PE diaphragm coated with Al2O3 particles on one side. The sodium ion battery is prepared according to a conventional method.

[0089] Comparative Example 3

[0090] This comparative example provides an electrolyte for inhibiting low-temperature sodium precipitation in a battery, and the preparation method is as follows:

[0091] The only difference between Comparative Example 1 and Comparative Example 3 is that 1 wt% of succinonitrile is added as an additive; ethyl methyl carbonate and propylene carbonate are mixed in a glove box filled with argon to obtain a mixed solution; and an electrolyte solvent is obtained based on the mass of the electrolyte solvent itself as 100 wt%.

[0092] Based on the electrolyte mass as 100wt%, 3wt% of fluoroethylene carbonate and 1wt% of 1,3-propane sultone were added, and after stirring and mixing evenly, 14.2wt% of sodium hexafluorophosphate was added, and the mixture was stirred until the sodium hexafluorophosphate was completely dissolved to obtain a conventional electrolyte.

[0093] This comparative example also provides a sodium ion battery, which is composed of a positive electrode, a negative electrode, an electrolyte for inhibiting low-temperature sodium precipitation of the battery, and a diaphragm. The positive electrode active material is NaCu1 / 9Ni2 / 9Fe1 / 3Mn1 / 3O2, and the positive electrode current collector is aluminum foil; the negative electrode active material is hard carbon, and the negative electrode current collector is aluminum foil; the diaphragm is a PE diaphragm coated with Al2O3 particles on one side. The sodium ion battery is prepared according to a conventional method.

[0094] Experimental example

[0095] The electrical properties of the electrolytes and sodium ion batteries prepared in the embodiments and comparative examples were tested, and the electrical properties of the prepared sodium ion batteries are shown in Table 1.

[0096] Table 1 Electrical properties of sodium ion batteries

[0097]

[0098]

[0099] It can be seen that as the content of ethyl propionate in the electrolyte increases, the capacity retention rate increases. Example 3 with 30wt% ethyl propionate shows the highest number of cycles with 80% capacity retention rate. In addition, the coulombic efficiency during the cycle test also increases with the increase of ethyl propionate content in the electrolyte, which indicates that the addition of ethyl propionate increases the active sodium ions in the electrolyte, which is beneficial to improve the cycle performance, such as Figure 1 , Figure 2 shown.

[0100] The sodium ion batteries prepared in each embodiment and comparative example were pre-charged, stored at 45°C for 3 days at 100% SOC, and subjected to formation cycles before cycling. The cycle performance test at 0°C was performed by charging to 3.95V at 0.5C constant current, then charging at 3.95V constant voltage with a cutoff current of 0.05C, and then discharging to 1.5V at 1C constant current. dQdV was obtained from the charge and discharge curves of different cycles using Origin software. The battery was disassembled after 100 cycles to check the sodium precipitation of the negative electrode under different electrolytes. Figure 3 As shown, a large amount of sodium precipitation was observed on the negative electrode in the cycles in Comparative Example 1, Comparative Example 2, and Comparative Example 3. In Example 1, Example 2, and Example 3, as the content of ethyl propionate in the electrolyte increased, the amount of sodium precipitation was significantly reduced.

[0101] like Figures 4 to 9 As shown, Figure 4 dQdV curves of the sodium ion battery prepared in Example 1 after the 5th, 50th and 250th cycles at 0°C, Figure 5dQdV curves of the sodium ion battery prepared in Example 2 after the 5th, 50th and 250th cycles at 0°C, Figure 6 dQdV curves of the sodium ion battery prepared in Example 3 after the 5th, 50th and 250th cycles at 0°C, Figure 7 dQdV curves of the sodium ion battery prepared in Comparative Example 1 after the 5th, 50th and 250th cycles at 0°C, Figure 8 dQdV curves of the sodium ion battery prepared in Comparative Example 2 after the 5th, 50th and 250th cycles at 0°C, Fig. 9 The dQdV curves of the sodium ion battery prepared in Comparative Example 3 after the 5th, 50th and 250th cycles at 0°C. It can be seen that in the electrolyte of Comparative Example 1, the polarization increased by 0.3V after 250 cycles. In addition, an additional peak was observed at 3.7V, which was attributed to sodium precipitation. After 250 cycles, the peak shifted 0.13V to a low voltage, indicating that sodium precipitation occurred at a higher voltage in the negative electrode. In the electrolyte of Comparative Example 2, the polarization increased by 0.28V after 250 cycles. In addition, an additional peak was observed at 3.7V, which was attributed to sodium precipitation. After 250 cycles, the peak shifted 0.12V to a high voltage, indicating that sodium precipitation occurred at a lower voltage in the negative electrode. In the electrolyte of Comparative Example 3, the polarization increased by 0.36V after 250 cycles. In addition, an additional peak was observed at 3.7V, which was attributed to sodium precipitation. After 250 cycles, the peak shifted 0.06 V to a lower voltage, indicating that sodium precipitation occurred at a higher voltage in the negative electrode. In Example 1, the polarization increased by 0.29 V after 250 cycles, and the sodium precipitation only shifted by 0.06 V. In Examples 2 and 3, the polarization increased by 0.24 V and 0.21 V, respectively, and the sodium precipitation peak disappeared, further confirming the inhibitory effect on sodium precipitation in an electrolyte containing a large amount of ethyl propionate solvent.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0103] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present application and form different embodiments. For example, in the above claims, any one of the claimed embodiments may be used in any combination. The information disclosed in this background technology section is intended only to deepen the understanding of the overall background technology of the present application and should not be regarded as an admission or in any form of implication that the information constitutes prior art known to those skilled in the art.

Claims

1. An electrolyte for inhibiting low-temperature sodium precipitation in a battery, characterized in that: The raw materials include electrolyte solvent, and the electrolyte solvent includes organic solvent and ethyl propionate; Calculated based on the mass of the electrolyte solvent itself being 100wt%, the content of the organic solvent is 60-95wt%, and the content of the ethyl propionate is 5-40wt%.

2. The electrolyte for inhibiting low-temperature sodium precipitation in a battery according to claim 1, characterized in that: The organic solvent includes ethyl methyl carbonate and propylene carbonate. Based on the mass of the electrolyte solvent itself being 100wt%, the content of the ethyl methyl carbonate is 40-60wt%, and the content of the propylene carbonate is 20-40wt%.

3. The electrolyte for inhibiting low-temperature sodium precipitation in a battery according to claim 1, characterized in that: The raw materials also include sodium salt, which includes sodium hexafluorophosphate, and the concentration of the sodium salt is 12-17wt%.

4. The electrolyte for inhibiting low-temperature sodium precipitation in a battery according to claim 1, characterized in that: The raw materials also include additives, which include fluoroethylene carbonate and 1,3-propane sultone.

5. The electrolyte for inhibiting low-temperature sodium precipitation in a battery according to claim 4, characterized in that: Calculated based on the mass of the electrolyte for inhibiting low-temperature sodium precipitation of the battery as 100wt%, the content of the additive is 1-5wt%.

6. The electrolyte for inhibiting low-temperature sodium precipitation in a battery according to claim 5, characterized in that: Calculated based on 100wt% of the mass of the electrolyte for inhibiting low-temperature sodium precipitation of the battery, the content of the fluoroethylene carbonate is 2-4wt%, and the content of the 1,3-propane sultone is 0.8-1.2wt%.

7. A method for preparing an electrolyte for inhibiting low-temperature sodium precipitation in a battery according to any one of claims 1 to 6, characterized in that: include: The raw materials are mixed to obtain an electrolyte that inhibits low-temperature sodium precipitation in the battery.

8. The method for preparing an electrolyte for inhibiting low-temperature sodium precipitation in a battery according to claim 7, characterized in that: include: Under the protection of an inert gas, ethyl methyl carbonate and propylene carbonate are mixed to obtain a first mixed solution; adding ethyl propionate to the first mixed solution to obtain a second mixed solution; adding an additive to the second mixed solution and mixing them evenly to obtain a third mixed solution; Sodium salt is added to the third mixed solution, and stirred until completely dissolved to obtain the electrolyte for inhibiting low-temperature sodium precipitation in the battery.

9. A sodium ion battery, characterized in that: The raw materials include the electrolyte for inhibiting low-temperature sodium precipitation of the battery according to any one of claims 1 to 6, the positive electrode, the negative electrode and the separator, and meet at least one of the following conditions: a. The positive electrode current collector comprises aluminum foil; b. The active material of the positive electrode includes NaNi x Fe y Mn z Cu 1-x-y-z O2, where 0≤x<1, 0≤y<1, 0≤z<1, and 0 <x+y+z≤1; c. The negative electrode current collector comprises aluminum foil; d. The active material of the negative electrode is hard carbon.

10. An electrical equipment, characterized in that: Including the sodium ion battery as described in claim 9.

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