Electrolyte and sodium ion battery

Abstract

The invention discloses an electrolyte and a sodium ion battery, the electrolyte comprises an additive, a sodium salt and an organic solvent, the additive comprises at least one of a first additive with a structure as shown in a formula I and a second additive with a structure as shown in a formula II; according to the electrolyte provided by the invention, the cycle performance and the rate capability of the sodium ion battery are improved through the combined action of the first additive and the second additive, and the two active groups of silica and anhydride in the first additive and the second additive can spontaneously react with trace water and hydrofluoric acid in the electrolyte, so that the trace water and hydrofluoric acid in the sodium ion battery can be uniformly dispersed. Meanwhile, a compact and stable interfacial film is formed on the positive electrode and the negative electrode, and electrolyte decomposition and excessive metal dissolution are inhibited, so that the loss of active substances and the improvement of resistance are reduced, and the electrochemical performance of the sodium-ion battery is further improved.

Description

Technical Field

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

[0002] Sodium-ion batteries are rich in resources and low in cost, showing great application potential in the fields of large-scale energy storage and electric / hybrid electric transportation. However, sodium-ion batteries are restricted in their wide application due to poor rate performance, cycling performance, and low initial efficiency. Modulating the electrolyte is one of the effective means to improve the performance of sodium-ion batteries, and the introduction of functional additives is a key factor in enhancing the performance of sodium-ion batteries.

[0003] Electrolyte additives play a key role in lithium-ion batteries. They can improve the electrochemical performance of the battery, including capacity retention and rate performance. Additives such as VC (vinyl carbonate), PS (acrylate), FEC (fluoroethylene carbonate), and DTD (1,3-dithiolane) affect the properties of the electrolyte through different mechanisms, thereby enhancing the battery performance. Although additives can improve the battery performance, there are also challenges, such as reducing the ionic conductivity of the electrolyte, increasing the viscosity of the electrolyte, affecting the safety and cost-effectiveness of the battery, etc.

[0004] Therefore, it is necessary to develop an electrolyte that can effectively improve the cycling performance and rate performance of sodium-ion batteries. Summary of the Invention

[0005] The object of the present invention is to provide an electrolyte that can effectively improve the cycling performance and rate performance of sodium-ion batteries in view of the deficiencies of the prior art.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An electrolyte, comprising an additive, a sodium salt, and an organic solvent, wherein the additive comprises at least one of a first additive having a structure shown in Formula I and a second additive having a structure shown in Formula II;

[0008]

[0009] Wherein, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14 are each independently selected from one of H, a halogen atom, an alkyl group having 1-10 carbon atoms, an unsaturated hydrocarbon group having 2-10 carbon atoms, an alkoxy group having 1-10 carbon atoms, and an alkanoyl group having 2-10 carbon atoms, and the H in the alkyl group, the unsaturated hydrocarbon group, the alkoxy group, and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group.

[0010] Preferably, a third additive is further included, and the third additive is selected from at least one of ethylene carbonate, fluoroethylene carbonate, vinylene ethylene carbonate, 1,3 - propane sultone, propylene sulfite, ethylene sulfate, 4 - methyl ethylene sulfate, succinic anhydride, adiponitrile, and 1,3,6 - hexanetricarbonitrile.

[0011] Preferably, the total mass of the silicon - oxygen groups in the first additive and the second additive accounts for 20 - 24% of the total mass W1 of the first additive and the second additive, and the total mass of the anhydride groups in the first additive and the second additive accounts for 24 - 28% of the total mass W2 of the first additive and the second additive.

[0012] Preferably, the first additive accounts for 1 - 5 wt% of the total mass of the electrolyte, and the second additive accounts for 1 - 5 wt% of the total mass of the electrolyte.

[0013] Preferably, the third additive accounts for 1 - 5 wt% of the total mass of the electrolyte.

[0014] Preferably, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and methyl tert - butyl ether.

[0015] Preferably, the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, and sodium perchlorate.

[0016] Preferably, the organic solvent accounts for 60% - 85% of the total mass of the electrolyte.

[0017] Preferably, the sodium salt accounts for 0.1% - 15.0% of the total mass of the electrolyte.

[0018] In addition, the present invention also provides a sodium - ion battery, including a battery cell wound by a negative electrode sheet, a positive electrode sheet, and a separator, an electrolyte, and a housing for encapsulating the battery cell and the electrolyte, wherein the electrolyte is the above - mentioned electrolyte.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The electrolyte provided by the present invention improves the cycling performance and rate performance of sodium-ion batteries through the combined action of two additives, namely a first additive and a second additive. Among them, the two active groups, namely silicon oxide and anhydride, in the first additive and the second additive can spontaneously react with trace water and hydrofluoric acid in the electrolyte, and at the same time form a dense and stable interface film on the positive and negative electrodes, inhibiting the decomposition of the electrolyte and the dissolution of excessive metals, thereby reducing the loss of active substances and the increase in resistance, and further improving the electrochemical performance of sodium-ion batteries. And the synergistic use of a third additive forms a more uniform, dense and smaller-impedance SEI film, thus further improving the cycling performance and rate storage performance of the battery. Detailed embodiments

[0021] To make the technical solutions and advantages of the present invention clearer, the following will describe the technical solutions of the present invention clearly and completely in conjunction with specific embodiments. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] According to the first aspect of the present application, the present application provides an electrolyte, which includes an additive, a sodium salt and an organic solvent, and the additive includes at least one of a first additive having the structure shown in Formula I and a second additive having the structure shown in Formula II;

[0023]

[0024] Wherein, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14 are each independently selected from one of H, a halogen atom, an alkyl group with 1-10 carbon atoms, an unsaturated hydrocarbon group with 2-10 carbon atoms, an alkoxy group with 1-10 carbon atoms and an alkanoyl group with 2-10 carbon atoms, and the H in the alkyl group, the unsaturated hydrocarbon group, the alkoxy group and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group and a sulfonic acid group.

[0025] Among them, the two active groups, namely silicon oxide and anhydride, in the first additive and the second additive can spontaneously react with trace water and hydrofluoric acid in the electrolyte, and at the same time form a dense and stable interface film on the positive and negative electrodes, inhibiting the decomposition of the electrolyte and the dissolution of excessive metals, thereby reducing the loss of active substances and the increase in resistance, and further improving the electrochemical performance of sodium-ion batteries.

[0026] In some embodiments, the first additive may be selected from

[0027] any one of them.

[0028] In some embodiments, the second additive may be selected from

[0029]

[0030] In some embodiments, a third additive is further included, and the third additive is selected from at least one of ethylene carbonate, fluoroethylene carbonate, vinylene ethylene carbonate, 1,3 - propane sultone, propylene sulfite, ethylene sulfate, 4 - methyl ethylene sulfate, succinic anhydride, adiponitrile, and 1,3,6 - hexanetricarbonitrile. Among them, when the first additive, the second additive, and the third additive are used synergistically, an SEI film that is more uniform, denser, and has a smaller impedance can be formed, thus further improving the cycle performance and rate storage performance of the battery.

[0031] In some embodiments, the total mass of the silicon - oxygen groups in the first additive and the second additive accounts for 20 - 24% of the total mass W1 of the first additive and the second additive. For example, it can be 20%, 21%, 22%, 23%, or 24%; the total mass of the anhydride groups in the first additive and the second additive accounts for 24 - 28% of the total mass W2 of the first additive and the second additive. For example, it can be 24%, 25%, 26%, 27%, or 28%.

[0032] Among them, when W1 and W2 exceed this range, the interfacial film formed by the participation of the silicon - oxygen group and the anhydride group will be thicker and have a greater impedance (RSEI is larger), which is not conducive to the cycle and rate performance. When W1 and W2 are lower than this range, the interfacial film formed by the participation of the silicon - oxygen group and the anhydride group will be relatively thinner, and it is easy to decompose and break under cycling and high rates. The repair of the interfacial film consumes active lithium ions and electrolyte, thereby leading to the deterioration of the cycle and rate.

[0033] In some embodiments, the first additive accounts for 1 - 5 wt% of the total mass of the electrolyte. For example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%; the second additive accounts for 1 - 5 wt% of the total mass of the electrolyte. For example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0034] In some embodiments, the third additive accounts for 1 - 5 wt% of the total mass of the electrolyte. For example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0035] In some embodiments, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and methyl tert - butyl ether.

[0036] In some embodiments, the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, and sodium perchlorate.

[0037] In some embodiments, the organic solvent accounts for 60%-85% of the total mass of the electrolyte, and can be, for example, 60%, 65%, 70%, 75%, 80%, or 85%.

[0038] In some embodiments, the sodium salt accounts for 0.1%-15.0% of the total mass of the electrolyte, and can be, for example, 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, or 15%.

[0039] According to the second aspect of the present application, the present application provides a sodium-ion battery, including a battery cell wound by a negative electrode sheet, a positive electrode sheet, and a separator, an electrolyte, and a housing for encapsulating the battery cell and the electrolyte, wherein the electrolyte is the above-mentioned electrolyte.

[0040] Among them, the separator can be selected from various separators used in sodium-ion batteries well-known to those skilled in the art, such as polypropylene microporous membranes, polyethylene felts, glass fiber felts, or ultra-fine glass fiber papers.

[0041] Among them, the positive electrode includes a current collector and an active material layer provided on the current collector. The active material layer includes, but is not limited to, a chemical formula such as Na 0.67 Mn x A y B z O 2±δ , in the molecular formula, A is one or more of Co, Ni, and Cr, B is one or more of Mg, Al, Ca, Ti, Cu, Zn, and Ba, 0.6 < x < 1, 0 < y < 0.1, 0.6 < x + y < 0.8, z > 0, x + y + z = 1, 0 ≤ δ ≤ 0.1. The positive electrode active material can also be, for example, Na 1.845 Mn[Fe(CN) 6 0.961 ·1.988H 2 O, Na 3 V 2 (PO 4 ) 2 O 2 F, Na 3 V 1.95 Mn 0.05 (PO 4 ) 2 F 3 、Na 3 V 1.95 Mn​0.05 (PO 4 ) 2 O 2 F, Na 3 V 2 (PO 4 ) 2 F 3 and Na 2.95 Li 0.05 V 2 (PO 4 ) 2 O 2 F, etc. or a combination of one or more thereof. The positive electrode active material may also be subjected to a modification treatment, and the method for modifying the positive electrode active material should be known to those skilled in the art. For example, methods such as coating and doping can be used to modify the positive electrode active material, and the materials used for the modification treatment can be a combination of one or more of, including but not limited to, Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive electrode current collector is usually a structure or component for collecting current, and the positive electrode current collector can be various materials suitable for use as a positive electrode current collector of a sodium ion battery in the art. For example, the positive electrode current collector can be, including but not limited to, a metal foil, etc., and more specifically can be, including but not limited to, an aluminum foil, etc.

[0042] Among them, the negative electrode includes a current collector and an active material layer provided on the surface of the current collector. The active material layer can be one or several of, including but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming an alloy with sodium, etc. Among them, the graphite can be selected from one or several of artificial graphite, natural graphite, and modified graphite; the silicon-based materials can be selected from one or several of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys; the tin-based materials can be selected from one or several of elemental tin, tin oxides, and tin alloys. The negative electrode current collector is usually a structure or component for collecting current, and the negative electrode current collector can be various materials suitable for use as a negative electrode current collector of a sodium ion battery in the art. For example, the negative electrode current collector can be, including but not limited to, a metal foil, etc., and more specifically can be, including but not limited to, a copper foil, etc.

[0043] To make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be further described in detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

[0044] Example 1

[0045] (1) Preparation of the electrolyte

[0046] In a glove box filled with nitrogen (O 2 <2 ppm, H2 Prepare an organic electrolyte solution with O < 3 ppm. Mix sodium salt, organic solvent, first additive, second additive, and third additive in weight portions of 14 parts, 81.5 parts, 1 part, 1 part, and 2.5 parts respectively to obtain the electrolyte solution. Among them, the organic solvent consists of EC (ethylene carbonate), PC (propylene carbonate), and EMC (ethyl methyl carbonate) in a weight ratio of 20:30:50, with a total of 81.5 parts. Among them, the third additive is 1 part of FEC, 1 part of PS, and 0.5 part of NaPO 2 F 2 which consists of a total of 2.5 parts;

[0047] Among them, the first additive is selected from The second additive is selected from

[0048]

[0049] (2) Preparation of the positive electrode sheet

[0050] Disperse the positive electrode material NFPP (sodium pyrophosphate phosphate, Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 )), binder PVDF, and conductive agent Super-P in a mass ratio of 95:3:2 in NMP organic solvent. Stir it with a vacuum mixer until it is stable and homogeneous, and evenly coat it on an aluminum foil with a thickness of 12 μm. After drying the aluminum foil at room temperature, transfer it to a forced-air oven at 120 °C and dry it for 1 h, and then make a positive electrode sheet through cold pressing and die cutting.

[0051] (3) Preparation of the negative electrode sheet

[0052] Mix hard carbon, binder PVDF, and conductive agent Super-P in a mass ratio of 97:2:1, disperse them in deionized water, and evenly coat them on an aluminum foil with a thickness of 10 μm. After drying the aluminum foil at room temperature, transfer it to a forced-air oven at 120 °C and dry it for 1 h, and then make a negative electrode sheet through cold pressing and die cutting.

[0053] (4) Preparation of the separator

[0054] Use a polyethylene (PE) polymer film as the separator.

[0055] (5) Preparation of the battery

[0056] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, wind them to obtain an electrode assembly; place the electrode assembly in a packaging shell, inject the electrolyte solution into the packaging shell and seal it, and finally obtain a sodium-ion battery.

[0057] Among them, the preparation steps of Examples 2-6 and Comparative Examples 1-4 are the same as those of the Example, except that the parameters in the electrolyte are different. In Example 6, the first additive is The remaining specific parameters are shown in Table 1 below.

[0058] Table 1

[0059]

[0060]

[0061] The sodium-ion batteries prepared in the above Examples and Comparative Examples were tested, and the obtained data are shown in Table 2 below.

[0062] (1) Capacity retention rate test:

[0063] The battery was placed in an oven at a constant temperature of 25°C / 85°C for 4 hours, then charged at a constant current of 1C to 3.25V, then charged at a constant voltage until the current dropped to 0.05C, and then discharged at a constant current of 1C to 1.5V. Such cycles were carried out, and the initial capacity of the battery and the discharge capacity of the last cycle (the 5000 / 2000th cycle) were recorded.

[0064] Capacity retention rate = discharge capacity of the last cycle (the 5000 / 2000th cycle) / initial capacity × 100%.

[0065] (2) Rate performance test:

[0066] The battery was charged at a constant current of 0.5C to 3.25V in an environment of 25°C, charged at a constant voltage until the current dropped to 0.02C, and then discharged at constant currents of 0.2C / 3C / 5C / 10C / 20C to 1.5V respectively, and the discharge capacity of the battery cell was recorded;

[0067] Capacity retention rate at different rates = discharge capacity at different rates / initial capacity at 0.2C × 100%.

[0069] Table 2

[0070]

[0071] It can be seen from the data of Examples 1-6 and Comparative Examples 1-6 that when the first additive and the second additive are not contained, the cycle performance and rate performance of the sodium-ion battery are poor. When only the first additive or the second additive is contained, although the cycle performance and rate performance of the sodium-ion battery are both partially improved, the improvement value is small. Only when the first additive, the second additive and the third additive are added simultaneously, a more uniform, dense and smaller-impedance SEI film is formed on the sodium-ion battery, so the cycle performance and rate storage performance of the battery are further improved.

[0072] When the siloxy group is within the preset range of 20% - 24% and the anhydride group is within the preset range of 24% - 28%, the cycle rate is better and the performance improvement is significant. When the siloxy group is less than 20% and the anhydride group is less than 24%, it will lead to the deterioration of the cycle and rate. When the siloxy group is higher than 24% and the anhydride group is higher than 28%, it will also lead to the deterioration of the cycle and rate.

[0073] Based on the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions or variations made by those skilled in the art on the basis of the present invention fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. An electrolyte, characterized in that: It comprises an additive, a sodium salt and an organic solvent, wherein the additive comprises at least one of a first additive having a structure shown in Formula I and a second additive having a structure shown in Formula II; Wherein, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13 and R14 are independently selected from one of H, a halogen atom, an alkyl group having 1 to 10 carbon atoms, an unsaturated hydrocarbon group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms and an alkanoyl group having 2 to 10 carbon atoms, and H in the alkyl group, the unsaturated hydrocarbon group, the alkoxy group and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group and a sulfonic acid group.

2. The electrolyte according to claim 1, characterized in that The invention also includes a third additive, which is selected from at least one of ethylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, propylene sulfite, vinyl sulfate, 4-methylethylene sulfate, succinic anhydride, adiponitrile and 1,3,6-hexanetrinitrile.

3. The electrolyte according to claim 1, characterized in that The total mass of the siloxy groups in the first additive and the second additive accounts for 20-24% of the total mass W1 of the first additive and the second additive, and the total mass of the anhydride groups in the first additive and the second additive accounts for 24-28% of the total mass W2 of the first additive and the second additive.

4. The electrolyte according to claim 1, characterized in that The first additive accounts for 1-5 wt % of the total mass of the electrolyte, and the second additive accounts for 1-5 wt % of the total mass of the electrolyte.

5. The electrolyte according to claim 2, characterized in that The third additive accounts for 1-5 wt % of the total mass of the electrolyte.

6. The electrolyte according to claim 1, characterized in that The organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and methyl tert-butyl ether.

7. The electrolyte according to claim 1, characterized in that The sodium salt is selected from at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate and sodium perchlorate.

8. The electrolyte according to claim 1, characterized in that The organic solvent accounts for 60%-85% of the total mass of the electrolyte.

9. The electrolyte according to claim 1, characterized in that The sodium salt accounts for 0.1%-15.0% of the total mass of the electrolyte.

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

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