Electrolyte, sodium ion battery, battery pack and energy storage system

Abstract

The invention provides an electrolyte, a sodium ion battery, a battery pack and an energy storage system, the electrolyte comprises a first additive, a second additive and a third additive, the first additive is fluoroethylene carbonate, the second additive is selected from at least one of sulfate compounds and sultone compounds, and the third additive is a first sodium salt; the mass percentage content of the first additive in the electrolyte is m1, the mass percentage content of the second additive in the electrolyte is m2, the mass percentage content of the third additive in the electrolyte is m3, m1 is 0.5%-3%, m2 is 0.1%-5%, and m3 is 0.2%-10%. Therefore, under the action of the three additives, not only can the positive electrode and the negative electrode be subjected to dual protection, but also the impedance of passive films formed on the surfaces of the positive electrode and the negative electrode can be reduced, and the ion transmission performance is improved, so that the performance of the sodium ion battery is improved.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to an electrolyte, a sodium-ion battery, a battery pack, and an energy storage system. Background Art

[0002] Sodium-ion batteries are favored in the energy storage field due to the advantages of rich sodium resources and relatively low theoretical cost compared to lithium-ion batteries. Currently, a sodium-ion battery generally includes a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is located between the positive electrode and the negative electrode, and the positive electrode, the negative electrode, and the separator are all immersed in the electrolyte. If the electrolyte decomposes on the surface of the positive electrode or the negative electrode, it will not only cause the loss of the positive electrode or the negative electrode, but also cause the loss of the electrolyte, damage the components of the electrolyte, affect the transmission of sodium ions, and ultimately lead to a reduction in the performance of the sodium-ion battery or even make it unusable. Therefore, how to design the electrolyte to improve the performance of the sodium-ion battery has become an urgent problem to be solved. Summary of the Invention

[0003] This application provides an electrolyte, a sodium-ion battery, a battery pack, and an energy storage system for improving the performance of a sodium-ion battery.

[0004] In a first aspect, an embodiment of this application provides a sodium-ion battery, which may include an electrolyte. The electrolyte includes a first additive, a second additive, and a third additive. The first additive is fluoroethylene carbonate, the second additive is selected from at least one of sulfate compounds and sulfonic acid lactone compounds, and the third additive is a first sodium salt. The mass percentage content of the first additive in the electrolyte is m1, the mass percentage content of the second additive in the electrolyte is m2, and the mass percentage content of the third additive in the electrolyte is m3. m1 is 0.5%-3%, m2 is 0.1%-5%, and m3 is 0.2%-10%.

[0005] The first additive and the second additive have a lower reaction potential, so they are easier to be reduced and less likely to be oxidized. Because the potential of the negative electrode is generally lower and the potential of the positive electrode is higher, the first additive and the second additive are more inclined to form a stable solid electrolyte film on the surface of the negative electrode. The solid electrolyte film can also be called a passivation film. The passivation film can effectively block the electrolyte from reacting with the negative electrode active material, thereby preventing the electrolyte from decomposing on the surface of the negative electrode; of course, even if the first additive and the second additive form a passivation film on the surface of the positive electrode, the film-forming effect is poor, and the protective effect on the positive electrode is limited. The third additive is easy to be reduced and oxidized, so the third additive tends to form a stable passivation film on both the positive and negative electrode surfaces and has a good film-forming effect. This can make up for the disadvantage of poor film-forming effect on the positive electrode surface, thereby effectively preventing the electrolyte from decomposing on the positive and negative electrode surfaces, and effectively realizing dual protection of the positive and negative electrodes. It is worth noting that although the third additive has a good film-forming effect when forming a passivation film on the positive electrode surface and the negative electrode surface, the use of only the third additive will result in a relatively single component in the passivation film. If the three additives are used at the same time, the types of components in the passivation film can be increased, so that the passivation film contains more types of substances and components, which will further increase the density and uniformity of the passivation film, thereby achieving dual protection of the positive and negative electrodes under the synergistic effect of the three additives.

[0006] Moreover, since the passivation film formed by the first additive and the third additive is an inorganic film, although this inorganic film has good stability, it has a large impedance and is not conducive to ion transmission; the presence of the second additive can reduce the impedance of this inorganic film and improve the ion transmission capacity, thereby improving the performance of the sodium ion battery under the synergistic effect of the three additives. In addition, due to the presence of the passivation film, the decomposition of the electrolyte on the positive and negative electrode surfaces can be inhibited, thereby improving the cycle stability of the electrolyte and increasing the life of the sodium ion battery.

[0007] Optionally, the mass percentage contents of the three additives may further satisfy the following relationship: m2 / (m1 + m3) is 0.1 - 3. If m2 / (m1 + m3) is small and less than 0.1, the film-forming effect on the positive electrode surface and the negative electrode surface is poor, resulting in a poor barrier effect of the formed passivation film and being unable to prevent the decomposition of the electrolyte on the positive electrode surface and the negative electrode surface. If m2 / (m1 + m3) is large and greater than 3, it means that the addition ratio of the second additive is large, which will instead cause an increase in the impedance of the passivation film, thereby resulting in a decrease in the capacity of the sodium-ion battery. Therefore, setting m2 / (m1 + m3) within a suitable range can protect the positive electrode and the negative electrode with the formed passivation film and avoid the decomposition of the electrolyte on the positive electrode surface and the negative electrode surface, thereby improving the cycle stability of the electrolyte and increasing the lifespan and performance of the sodium-ion battery. The mass percentage contents of the three additives may further satisfy the following relationship: m2 / (m1 + m3) is 0.4 - 2, such as but not limited to m2 / (m1 + m3) being: 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2. This can further improve the protection of the positive electrode and the negative electrode and further avoid the decomposition of the electrolyte on the positive electrode surface and the negative electrode surface, thereby further improving the cycle stability of the electrolyte and further increasing the lifespan and performance of the sodium-ion battery.

[0008] Optionally, the mass percentage content m1 of the first additive in the electrolyte may be further set to 1% - 2%, such as but not limited to m1 being 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%. The specific value can be set according to the actual situation and is not limited herein. The mass percentage content m2 of the second additive in the electrolyte may be further set to 1% - 3%, such as but not limited to m2 being 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%. The specific value can be set according to the actual situation and is not limited herein. The second additive is selected from at least one of sulfate compounds and sulfonic acid lactone compounds. The general formula structure of the sulfate compound is as follows:

[0009]

[0010] wherein, R 1Selected from H, or C1-C3 hydrocarbyl, the C1-C3 hydrocarbyl may be selected from C1-C3 alkyl, and the C1-C3 alkyl such as but not limited to: methyl, ethyl, propyl, isopropyl. n1 is selected from 1, 2 and 3. Based on this, the sulfate compounds may be selected from: ethylene sulfate, 4-methyl ethylene sulfite, 4-propyl ethylene sulfite, propylene sulfate, 4-methyl propylene sulfite, and 4-propyl propylene sulfite, etc., and further the sulfate compounds are selected from: ethylene sulfate, 4-methyl ethylene sulfite, propylene sulfate and 4-methyl propylene sulfite, etc.

[0011] The sultone compounds may be selected from the structure shown in formula a1 or the structure shown in formula a2 as follows:

[0012]

[0013] Wherein, R 2 -R 5 are each independently selected from H, or C1-C6 hydrocarbyl, the C1-C6 hydrocarbyl may be selected from C1-C3 hydrocarbyl, and the C1-C3 hydrocarbyl such as but not limited to: methyl, ethyl, propyl, isopropyl, vinyl, propenyl, isopropenyl, ethynyl, propynyl. n2 and n3 are each independently selected from 1, 2 and 3. Based on this, the sultone compounds may be selected from: 1,3-propane sultone, 1-propenyl-1,3-sultone, 1-propenyl-1-methyl-1,3-sultone, 1-propenyl-1,2-dimethyl-1,3-sultone, 1-propenyl-1-ethyl-1,3-sultone, 1-propenyl-1,2-diethyl-1,3-sultone, 1-butenyl-1,4-sultone, 1-butenyl-1-methyl-1,4-sultone, 1-butenyl-1,2-dimethyl-1,4-sultone, 1-butenyl-1-ethyl-1,4-sultone, etc.; further the sultone compounds are selected from: 1-propenyl-1,3-sultone, 1,3-propane sultone, etc.

[0014] The mass percentage content m3 of the third additive in the electrolyte may be further set to 0.5%-7%, such as but not limited to m3 being 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%. The specific value can be set according to the actual situation and is not limited here. The third additive is the first sodium salt, and the first sodium salt may be selected from at least one of the following: NaDFOB, NaTFOP, NaPO 2 F 2 、NaSbF 6 、NaAsF 6 、NaN(SO2 CF 3 ) 2 、NaC(SO 2 CF 3 ) 3 、NaN(SO 2 F) 2 、NaAlCl 4 、NaCF 3 SO 3 、Na 2 B 10 Cl 10 , and further, the first sodium salt may be selected from at least one of the following: NaDFOB, NaPO 2 F 2 、NaCF 3 SO 3 、NaN(SO 2 CF 3 ) 2 、NaN(SO 2 F) 2 . Among them, when the first sodium salt is selected as NaDFOB, the formed passivation film contains B-O, and B-O can reduce the impedance of the passivation film to improve the performance of ion transport, and can also make the passivation film have better stability and improve the stability of the sodium-ion battery. When the first sodium salt is selected as a sodium salt containing F, the formed passivation film contains fluoride, and the fluoride can also reduce the impedance of the passivation film, thereby improving the performance of ion transport.

[0015] The sum of the mass percentages of the three additives can be 2.5% - 12%, that is, m1 + m2 + m3 is 2.5% - 12%. This can avoid having a greater impact on the addition amounts of the second sodium salt and the organic solvent. For example, when the sum of the mass percentages of the three additives is relatively large, the addition amounts of the second sodium salt and the organic solvent will be relatively small, which may affect the transport ability of sodium ions in the electrolyte and increase the production cost of the electrolyte; when the sum of the mass percentages of the three additives is relatively small, it may not be able to protect the positive electrode and the negative electrode, and thus cannot avoid the decomposition of the electrolyte on the surfaces of the positive electrode and the negative electrode. Therefore, setting the sum of the mass percentages of the three additives within a suitable range can improve the lifespan and performance of the sodium-ion battery on the basis of ensuring the basic functions of the electrolyte.

[0016] Optionally, the electrolyte may further include a second sodium salt, and the solubility of the second sodium salt is higher than that of the first sodium salt, so that the content of the first sodium salt in the electrolyte is less and the content of the second sodium salt is more. The second sodium salt may be selected from at least one of the following: NaPF 6 , NaN(SO 2 C 2 F 5) 2 、NaClO 4 Further, the second sodium salt may be selected from: NaPF 6 and NaN(SO 2 C 2 F 5 ) 2 and at least one of the above. The molar concentration of the second sodium salt in the electrolyte can be set to 0.5 mol / L - 1.5 mol / L. Further, the molar concentration of the second sodium salt in the electrolyte can be 1 mol / L, so as to provide sufficient sodium ions, which is conducive to improving the capacity of the sodium-ion battery.

[0017] Further, the electrolyte may further include an organic solvent. The organic solvent can be any solvent that can realize the function of the electrolyte well-known to those skilled in the art, such as but not limited to carbonate compounds. Among them, the carbonate compounds can include but not limited to: cyclic carbonate compounds, chain carbonate compounds and other carbonate compounds. The cyclic carbonate compounds can include but not limited to: ethylene carbonate, propylene carbonate and other cyclic carbonate compounds, and one or more of them; the chain carbonate compounds can include but not limited to: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and other chain carbonate compounds, and one or more of them. When the organic solvent includes cyclic carbonate compounds and chain carbonate compounds, the mass percentage of the cyclic carbonate compounds and the chain carbonate compounds can be set to 0.5 - 1.0.

[0018] Optionally, the sodium-ion battery further includes a positive electrode, and the positive electrode includes: a current collector and a positive electrode active material disposed on the current collector. The positive electrode active material includes: a layered transition metal oxide and a polyanion compound. Among them, the layered transition metal oxide has a high specific capacity and can meet the requirements of high energy density; the polyanion compound has good structural stability and a high voltage platform; when the positive electrode active material includes a layered transition metal oxide and a polyanion compound, the advantages of both can be combined to improve the performance of the sodium-ion battery.

[0019] Among them, the molecular general formula of the positive electrode active material is: Na α (M x Fe y Mn z )O 2 @Na β N γ (PO 4 ) 2 P 2 O 7, M is selected from at least one of Ni, Cu, Co, Ti, Mg, Li, Al, Zn, Ca, N is selected from at least one of Fe, Mn, Co, 0.8 ≤ α ≤ 1.1, 3 ≤ β ≤ 5, 2 ≤ γ ≤ 5, x + y + z = 1, Na α (M x Fe y Mn z )O 2 The mass ratio in the positive electrode active material is k1, Na β N γ (PO 4 ) 2 P 2 O 7 The mass ratio in the positive electrode active material is k2, k1 + k2 = 1, 0 < k2 < 0.5, further 0.01 < k2 < 0.3, still further 0.1 < k2 < 0.2, which can be specifically designed according to actual needs and is not limited herein. And, Na β N γ (PO 4 ) 2 P 2 O 7 can be of NASICON structure, or can also be of olivine structure or triclinic structure, which can be specifically selected according to actual needs and is not limited herein.

[0020] In a second aspect, the embodiments of the present application further provide an electrolyte for a sodium-ion battery. The electrolyte may include: a first additive, a second additive, and a third additive. The first additive is fluoroethylene carbonate, the second additive is selected from at least one of sulfate compounds and sulfonic acid lactone compounds, and the third additive is a first sodium salt; the mass percentage content of the first additive in the electrolyte is m1, the mass percentage content of the second additive in the electrolyte is m2, and the mass percentage content of the third additive in the electrolyte is m3. m1 is 0.5% - 3%, m2 is 0.1% - 5%, and m3 is 0.2% - 10%. Thus, under the action of the three additives, not only can the positive electrode and the negative electrode be protected doubly, but also the impedance of the passivation films formed on the surfaces of the positive electrode and the negative electrode can be reduced, and the ion transport performance can be improved, thereby improving the performance of the sodium-ion battery.

[0021] It should be understood that since the principle of solving problems by this electrolyte is similar to that of the aforementioned sodium-ion battery, the implementation and technical effects of this electrolyte can refer to the implementation and technical effects of the aforementioned sodium-ion battery, and the repeated parts will not be elaborated herein.

[0022] In a third aspect, an embodiment of the present application further provides a battery pack, which may include: a box body and a plurality of sodium-ion batteries. Each sodium-ion battery is disposed in the box body, and the sodium-ion battery is the sodium-ion battery described in the first aspect and any embodiment of the first aspect above. In this way, on the basis of improving the performance of the sodium-ion battery, the performance of the battery pack will also be improved.

[0023] It should be understood that since the principle of solving problems by this battery pack is similar to that of the aforementioned sodium-ion battery, the implementation and technical effects of this battery pack can refer to the implementation and technical effects of the aforementioned sodium-ion battery, and the repeated parts will not be elaborated.

[0024] In a fourth aspect, an embodiment of the present application further provides an energy storage system, which includes the battery pack and a power converter described in the third aspect above. The power converter is used to convert the alternating current output by an external AC power supply into direct current and output it to the battery pack, and / or the power converter is used to convert the direct current output by the battery pack into alternating current and output it to a load or the power grid. In this way, on the basis of improving the performance of the battery pack, the performance of the energy storage system will also be improved.

[0025] It should be understood that since the principle of solving problems by this energy storage system is similar to that of the aforementioned battery pack, the implementation and technical effects of this energy storage system can refer to the implementation and technical effects of the aforementioned battery pack, and the repeated parts will not be elaborated. Description of the Drawings

[0026] Figure 1 It is a schematic structural diagram of the energy storage system provided by an embodiment of the present application;

[0027] Figure 2 It is a schematic structural diagram of the battery pack provided by an embodiment of the present application;

[0028] Figure 3 It is a schematic structural diagram of the sodium-ion battery provided by an embodiment of the present application. Detailed Embodiments

[0029] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings.

[0030] It should be noted that the same reference numerals in the drawings of the present application represent the same or similar structures, and thus the repeated descriptions thereof will be omitted. The words expressing positions and directions described in the present application are all illustrated with reference to the drawings, but can be changed according to needs, and all the changes made are included in the protection scope of the present application. The drawings of the present application are only used to illustrate the relative position relationship and do not represent the true proportion.

[0031] To facilitate the understanding of the technical solution provided by the embodiments of the present application, the following first describes its application scenarios.

[0032] The technical solution provided by the embodiments of the present application can be widely applied in an energy storage system, which can be applied to, but is not limited to, scenarios such as household energy storage, site energy, intelligent photovoltaics, and data center energy, for storing electrical energy and supplying electrical energy outward. Refer to Figure 1 the schematic structural diagram of the energy storage system shown. The energy storage system may include: a battery cluster and a power converter 200. The battery cluster includes a plurality of battery packs 100 connected in series. Figure 1 Only one battery pack 100 is shown as an example. The power converter 200 can convert the alternating current output by an external alternating current power source (such as the power grid 300) into direct current and output it to the battery pack 100 in the battery cluster to charge the battery pack 100. It can also convert the direct current output by the battery pack 100 in the battery cluster into alternating current and output it to the load 400 or the power grid 300 to discharge the battery pack 100.

[0033] Refer to Figure 2 the schematic structural diagram of the battery pack 100 shown. The battery pack 100 may include: a box body 101 and a plurality of sodium-ion batteries 102. Each sodium-ion battery 102 is arranged in the box body 101. Each sodium-ion battery 102 can be connected in series, in parallel, or in a combination of series and parallel connections, so that the battery pack 100 has a higher capacity and a higher voltage, and thus can be applicable to various application scenarios. Among them, for each sodium-ion battery 102, as Figure 3 the schematic structural diagram of the sodium-ion battery 102 shown, the sodium-ion battery 102 may include: a positive electrode 11, a negative electrode 12, a separator 13, and an electrolyte 14. The separator 13 is arranged between the positive electrode 11 and the negative electrode 12, and the electrolyte 14 infiltrates the positive electrode 11, the separator 13, and the negative electrode 12. When the sodium-ion battery 102 is charged, sodium ions are removed from the positive electrode 11, pass through the separator 13, and are embedded in the negative electrode 12; when the sodium-ion battery 102 is discharged, sodium ions are removed from the negative electrode 12, pass through the separator 13, and are embedded in the positive electrode 11; therefore, the amount of sodium ions embedded in the negative electrode 12 during charging affects the charging capacity of the sodium-ion battery 102, and the amount of sodium ions embedded in the positive electrode 11 during discharging affects the discharging capacity of the sodium-ion battery 102. Thus, by improving the structures and manufacturing materials of the positive electrode 11 and the negative electrode 12, the charging capacity and the discharging capacity can be increased.

[0034] Continue to refer to Figure 3As shown, the positive electrode 11 may include: a current collector 11a and a positive electrode active material 11b provided on the current collector 11a. In currently common sodium-ion batteries 102, the positive electrode active material 11b mainly includes: layered transition metal oxides, Prussian blue analogs, polyanion compounds, etc. The layered transition metal oxides have a relatively high specific capacity and can meet the requirements of high energy density. However, during the insertion and extraction process of sodium ions, the layered transition metals are prone to structural changes or phase transitions, resulting in cycle attenuation of the sodium-ion battery 102. The polyanion compounds have good structural stability and less gas generation, but their energy density is relatively low. Therefore, adopting a composite positive electrode including layered transition metal oxides and polyanion compounds can combine the advantages of both and improve the performance of the sodium-ion battery 102. For example, but not limited to, the structural general formula of the layered transition metal oxide can be: Na α (M x Fe y Mn z )O 2 , and the structural general formula of the polyanion compound can be: Na β N γ (PO 4 ) 2 P 2 O 7 . The structural general formula of the formed composite positive electrode can be: Na α (M x Fe y Mn z )O 2 @Na β N γ (PO 4 ) 2 P 2 O 7 , where M is selected from at least one of Ni, Cu, Co, Ti, Mg, Li, Al, Zn, Ca; N is selected from at least one of Fe, Mn, Co; 0.8 ≤ α ≤ 1.1, 3 ≤ β ≤ 5, 2 ≤ γ ≤ 5, x + y + z = 1. The mass fraction of Na α (M x Fe y Mn z )O 2 in the composite positive electrode is k1, and the mass fraction of Na β N γ (PO 4 ) 2 P 2 O 7 in the composite positive electrode is k2, k1 + k2 = 1, 0 < k2 < 0.5, further 0.01 < k2 < 0.3, and still further 0.1 < k2 < 0.2. Specifically, it can be designed according to actual needs and is not limited here. Naβ N γ (PO 4 ) 2 P 2 O 7 It can be of NASICON structure, or olivine structure or triclinic structure, and can be specifically selected according to actual needs, which is not limited herein.

[0035] Moreover, different cathodes have different requirements for the electrolyte. By designing the components of the electrolyte, not only can the requirements of the cathode be met, but also the performance of the sodium-ion battery can be improved. For example, during the use of layered transition metal oxides, the gas generation amount is relatively high, and the battery potential is also relatively high. At this time, the electrolyte needs to have high oxidation resistance, and the components and contents of additives in the electrolyte are relatively large, so the composition of the corresponding electrolyte is relatively complex. The polyanion compound is the opposite of the layered transition metal oxide, so the composition of the corresponding electrolyte is relatively simple. However, the currently used electrolyte is applicable to a single-component cathode active material, and there is temporarily no matching electrolyte for the composite cathode including layered transition metal oxides and polyanion compounds.

[0036] Based on this, the embodiment of the present application provides an electrolyte applicable to a composite cathode including layered transition metal oxides and polyanion compounds. The electrolyte may include: a second sodium salt, an organic solvent, and a first additive, a second additive, and a third additive. The first additive is vinylene carbonate fluoride, the second additive is selected from at least one of sulfate compounds and sultone compounds, and the third additive is a first sodium salt; the mass percentage content of the first additive in the electrolyte is m1, the mass percentage content of the second additive in the electrolyte is m2, and the mass percentage content of the third additive in the electrolyte is m3. m1 is 0.5%-3%, m2 is 0.1%-5%, and m3 is 0.2%-10%.

[0037] The reaction potentials of the first additive and the second additive are relatively low, so they are relatively easy to be reduced and not easy to be oxidized. Since the potential of the negative electrode is generally low and the potential of the positive electrode is high, the first additive and the second additive tend to form a stable solid electrolyte film on the surface of the negative electrode. This solid electrolyte film can also be called a passivation film. The passivation film can effectively block the reaction between the electrolyte and the negative electrode active material, thereby avoiding the decomposition of the electrolyte on the surface of the negative electrode. Of course, even if the first additive and the second additive form a passivation film on the surface of the positive electrode, the film-forming effect is poor and the protective effect on the positive electrode is limited. The third additive is easy to be reduced and oxidized, so the third additive tends to form stable passivation films on both the positive electrode and the negative electrode surfaces and the film-forming effects are both good. This can make up for the disadvantage of the poor film-forming effect on the positive electrode surface, thereby effectively avoiding the decomposition of the electrolyte on the positive electrode surface and the negative electrode surface and effectively realizing the dual protection of the positive electrode and the negative electrode. It should be noted that although the film-forming effects of the third additive on the positive electrode surface and the negative electrode surface are both good, using only the third additive will result in a relatively single component in the passivation film. If the three additives are used simultaneously, the types of components in the passivation film can be increased, making the passivation film contain more types of substances and components. This will further increase the density and uniformity of the passivation film, thereby realizing the dual protection of the positive electrode and the negative electrode under the synergistic effect of the three additives.

[0038] Moreover, since the passivation film formed by the first additive and the third additive is an inorganic film, although this inorganic film has good stability but large impedance, which is not conducive to ion transport. The presence of the second additive can reduce the impedance of this inorganic film and improve the ion transport ability, thereby improving the performance of the sodium-ion battery under the synergistic effect of the three additives. In addition, due to the presence of the passivation film, the decomposition of the electrolyte on the positive electrode and the negative electrode surfaces can be inhibited, thereby improving the cycle stability of the electrolyte and the service life of the sodium-ion battery.

[0039] For the first additive: The mass percentage content m1 of the first additive in the electrolyte can be further set to 1%-2%. For example, but not limited to, m1 is 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%. The specific value can be set according to the actual situation and is not limited here. The first additive is fluoroethylene carbonate, and the structure of fluoroethylene carbonate is as follows:

[0040]

[0041] For the second additive: The mass percentage content m2 of the second additive in the electrolyte can be further set to 1% - 3%. For example but not limited to, m2 can be 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%. The specific value can be set according to the actual situation and is not limited herein. The second additive is selected from at least one of sulfate compounds and sultone compounds. The general formula structure of the sulfate compounds is as follows:

[0042]

[0043] Wherein, R 1 is selected from H, or a C1-C3 hydrocarbon group. The C1-C3 hydrocarbon group can be selected from C1-C3 alkyl groups, and the C1-C3 alkyl groups such as but not limited to are: methyl, ethyl, propyl, isopropyl. n1 is selected from 1, 2, and 3. Based on this, the sulfate compounds can be selected from one or more of ethylene sulfate, ethyl 4-methylsulfite, ethyl 4-propylsulfite, propylene sulfate, 4-methylpropylsulfite, and 4-propylpropylsulfite. Further, the sulfate compounds are selected from one or more of ethylene sulfate, ethyl 4-methylsulfite, propylene sulfate, and 4-methylpropylsulfite.

[0044] The sultone compounds can be selected from the structure shown in formula a1 or the structure shown in formula a2 as follows:

[0045]

[0046] Wherein, R 2 -R 5 are each independently selected from H, or a C1-C6 hydrocarbon group. The C1-C6 hydrocarbon group can be selected from C1-C3 hydrocarbon groups, and the C1-C3 hydrocarbon groups such as but not limited to are: methyl, ethyl, propyl, isopropyl, vinyl, propenyl, isopropenyl, ethynyl, propynyl. n2 and n3 are each independently selected from 1, 2, and 3. Based on this, the sultone compounds can be selected from one or more of 1,3-propane sultone, 1-propenyl-1,3-sultone, 1-propenyl-1-methyl-1,3-sultone, 1-propenyl-1,2-dimethyl-1,3-sultone, 1-propenyl-1-ethyl-1,3-sultone, 1-propenyl-1,2-diethyl-1,3-sultone, 1-butenyl-1,4-sultone, 1-butenyl-1-methyl-1,4-sultone, 1-butenyl-1,2-dimethyl-1,4-sultone, 1-butenyl-1-ethyl-1,4-sultone; Further, the sultone compounds are selected from one or more of 1-propenyl-1,3-sultone and 1,3-propane sultone.

[0047] For the third additive: The mass percentage content m3 of the third additive in the electrolyte can be further set to 0.5% - 7%. For example, but not limited to, m3 is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%. The specific value can be set according to the actual situation and is not limited herein. The third additive is the first sodium salt, and the solubility of the second sodium salt is higher than that of the first sodium salt, so that the content of the first sodium salt in the electrolyte is less and the content of the second sodium salt is more. The first sodium salt can be selected from at least one of the following: NaDFOB, NaTFOP, NaPO 2 F 2 、NaSbF 6 、NaAsF 6 、NaN(SO 2 CF 3 ) 2 、NaC(SO 2 CF 3 ) 3 、NaN(SO 2 F) 2 、NaAlCl 4 、NaCF 3 SO 3 、Na 2 B 10 Cl 10 , and further the first sodium salt can be selected from at least one of the following: NaDFOB, NaPO 2 F 2 、NaCF 3 SO 3 、NaN(SO 2 CF 3 ) 2 、NaN(SO 2 F) 2 . Among them, when the first sodium salt is selected from NaDFOB, the formed passivation film contains B - O, and B - O can reduce the impedance of the passivation film to improve the performance of ion transport, and can also make the passivation film have better stability and improve the stability of the sodium - ion battery. When the first sodium salt is selected from sodium salts containing F, the formed passivation film contains fluoride, and the fluoride can also reduce the impedance of the passivation film, thereby improving the performance of ion transport.

[0048] The mass percentage contents of the three additives can also satisfy the following relationship: m2 / (m1 + m3) is 0.1 - 3. If m2 / (m1 + m3) is small and less than 0.1, the film-forming effect on the positive electrode surface and the negative electrode surface is poor, resulting in a poor barrier effect of the formed passivation film and being unable to prevent the decomposition of the electrolyte on the positive electrode surface and the negative electrode surface. If m2 / (m1 + m3) is large and greater than 3, it means that the addition ratio of the second additive is large, which will instead cause an increase in the impedance of the passivation film, and further lead to a reduction in the capacity of the sodium-ion battery. Therefore, setting m2 / (m1 + m3) within a suitable range can enable the formed passivation film to protect the positive electrode and the negative electrode, and avoid the decomposition of the electrolyte on the positive electrode surface and the negative electrode surface, thereby improving the cyclic stability of the electrolyte and enhancing the lifespan and performance of the sodium-ion battery. The mass percentage contents of the three additives can further satisfy the following relationship: m2 / (m1 + m3) is 0.4 - 2, such as but not limited to m2 / (m1 + m3) being: 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2. This can further improve the protection of the positive electrode and the negative electrode, and further avoid the decomposition of the electrolyte on the positive electrode surface and the negative electrode surface, thereby further improving the cyclic stability of the electrolyte and further enhancing the lifespan and performance of the sodium-ion battery.

[0049] Moreover, the sum of the mass percentage contents of the three additives can be 2.5% - 12%, that is, m1 + m2 + m3 is 2.5% - 12%. This can avoid having a significant impact on the addition amounts of the second sodium salt and the organic solvent. For example, when the sum of the mass percentage contents of the three additives is large, it will lead to small addition amounts of the second sodium salt and the organic solvent, which may affect the transport ability of sodium ions in the electrolyte and increase the production cost of the electrolyte. When the sum of the mass percentage contents of the three additives is small, it may not be able to protect the positive electrode and the negative electrode, and thus cannot avoid the decomposition of the electrolyte on the positive electrode surface and the negative electrode surface. Therefore, setting the sum of the mass percentage contents of the three additives within a suitable range can, on the basis of ensuring the basic functions of the electrolyte, improve the lifespan and performance of the sodium-ion battery.

[0050] Of course, the types of the above three additives are all relatively common substances at present. Therefore, when using these substances to prepare the electrolyte, compared with relatively rare additives, it can not only reduce the production cost of the electrolyte, but also achieve mass supply, with good practicality.

[0051] For the second sodium salt: The second sodium salt can be selected from at least one of the following: NaPF 6 , NaN(SO 2 C 2 F 5 ) 2 , NaClO 4, further, the second sodium salt can be selected from: NaPF 6 and NaN(SO 2 C 2 F 5 ) 2 at least one of them. The molar concentration of the second sodium salt in the electrolyte can be set to 0.5 mol / L - 1.5 mol / L. Further, the molar concentration of the second sodium salt in the electrolyte can be 1 mol / L, so as to provide sufficient sodium ions, which is beneficial to improving the capacity of the sodium-ion battery.

[0052] For the organic solvent: The organic solvent can be any solvent that can realize the function of the electrolyte well-known to those skilled in the art, such as but not limited to carbonate compounds. Among them, the carbonate compounds can but not limited to include: cyclic carbonate compounds, chain carbonate compounds and other carbonate compounds. The cyclic carbonate compounds can but not limited to include: ethylene carbonate, propylene carbonate and other cyclic carbonate compounds, and can be one or more of them. The chain carbonate compounds can but not limited to include: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and other chain carbonate compounds, and can be one or more of them. When the organic solvent includes cyclic carbonate compounds and chain carbonate compounds, the mass percentage of the cyclic carbonate compounds and the chain carbonate compounds can be set to 0.5 - 1.0.

[0053] Next, the performance of the sodium-ion battery is tested in combination with specific examples.

[0054] Fabrication of the sodium-ion battery.

[0055] Components of the electrolyte: A second sodium salt with a molar concentration of 0.5 mol / L - 1.5 mol / L is used, a mixture of cyclic carbonate compounds and chain carbonate compounds is used as the organic solvent, and the mass percentage of the cyclic carbonate and the chain carbonate is 0.5 - 1.0. The first additive is fluoroethylene carbonate, the second additive includes sulfate compounds and sultone compounds, and the third additive is the first sodium salt.

[0056] The manufacturing process of the positive electrode includes: weighing the composite positive electrode active material, SuperP and PVDF according to a certain mass ratio, and dispersing them in N-methyl-2-pyrrolidone as a dispersant to obtain a positive electrode slurry; uniformly coating the positive electrode slurry on both sides of the current collector, drying, rolling and vacuum drying, and then welding the electrode tabs to obtain the positive electrode. Among them, SuperP is a conductive agent and PVDF is an adhesive.

[0057] The manufacturing process of the negative electrode includes: weighing the negative electrode active material, SuperP, SBR, and CMC according to a certain mass ratio, and dispersing them in deionized water to obtain a negative electrode slurry; coating the negative electrode slurry on both sides of the current collector, followed by drying, calendaring, and vacuum drying, and then welding the tab to obtain the negative electrode. Among them, SuperP is a conductive agent, and SBR and CMC are binders.

[0058] The preparation and formation process of the battery cell includes: placing a separator with a certain thickness between the positive electrode and the negative electrode, and then winding or laminating the sandwich structure composed of the positive electrode, negative electrode, and separator to prepare the battery cell. Then, putting the wound core into a packaging bag and baking it in a vacuum at a suitable temperature to obtain a dry battery cell to be filled with electrolyte. Subsequently, in a drying room, injecting the electrolyte into the battery cell, performing vacuum packaging, and then leaving it at a suitable temperature for a certain period of time, and then performing formation and constant volume to obtain a sodium-ion battery.

[0059] Performance testing.

[0060] The test method for the storage capacity retention rate when stored at 60°C for 30 days may include: at room temperature, repeating the following process three times for the sodium-ion battery. The process includes: first, charging at a constant current of 0.2C to 3.95V, then charging at a constant voltage of 0.05C until cutoff, leaving it for 30 minutes, and then discharging at a constant current of 0.2C to 2.0V, leaving it for 30 minutes. Record the discharge capacity each time after performing the above process, and then average the discharge capacities corresponding to the three processes to obtain the average discharge capacity C0 of the sodium-ion battery. Then, first charge at a constant current of 0.5C to 3.95V, then charge at a constant voltage of 0.05C until cutoff, and then place the charged sodium-ion battery in an oven at 60°C and take it out after storing for 30 days. After the sodium-ion battery cools to room temperature, repeat the above process three times for the sodium-ion battery. Record the discharge capacity each time after performing the above process, and then average the discharge capacities corresponding to the three processes to obtain the average discharge capacity C1 of the sodium-ion battery. Finally, calculate the storage capacity retention rate of the sodium-ion battery when stored at 60°C for 30 days, that is, C1 / C0*100%.

[0061] The test method for the cycle capacity retention rate when cycling charge and discharge at 45°C for 200 cycles includes: at 45°C, first charge the sodium-ion battery at a constant current rate of 0.5C to 3.95V, then charge at a constant voltage rate of 0.05C until cutoff, let it stand for 30 minutes, then discharge at a constant current rate of 0.5C to 2.0V, let it stand for 30 minutes, record the discharge capacity, and the first recorded discharge capacity is denoted as the initial capacity D1. Repeat this process for cycle performance testing, record the capacity after 200 cycles as D200, and calculate the cycle capacity retention rate when cycling charge and discharge at 45°C for 200 cycles, that is, D200 / D1*100%.

[0062] After the above test process, Table 1 is obtained. Table 1 shows the components of the electrolyte and the performance of the sodium-ion battery in Examples 1 to 12, as well as Comparative Examples 1 and 2. Among them, the component ratio in the solvent refers to the mass percentage of cyclic carbonate compounds and chain carbonate compounds, the cycle capacity retention rate refers to the cycle capacity retention rate of the sodium-ion battery when cycling charge and discharge at 45°C for 200 cycles, and the storage capacity retention rate refers to the storage capacity retention rate of the sodium-ion battery when stored at 60°C for 30 days.

[0063] Table 1

[0064]

[0065] It can be found from the results shown in Table 1 above:

[0066] (1) Comparing Examples 1 to 3 with Comparative Examples 1 and 2, the component ratio in the solvent and the concentration of the second sodium salt are the same, only the value of m2 / (m1+m3) is different. When m2 / (m1+m3) is in the range of 0.4 - 2, both the cycle capacity retention rate and the storage capacity retention rate are above 95%. When m2 / (m1+m3) is outside the range of 0.4 - 2, both the cycle capacity retention rate and the storage capacity retention rate decrease, indicating that when the value of m2 / (m1+m3) is smaller or larger, it will lead to a decrease in the capacity retention rate. When m2 / (m1+m3) is in the range of 0.4 - 2, the capacity retention rate of the sodium-ion battery is higher, thus indicating that when m2 / (m1+m3) is in the range of 0.4 - 2, the performance of the sodium-ion battery is better and more stable.

[0067] (2) The test results of Examples 4 to 9 show that when the component ratio in the solvent and m2 / (m1+m3) remain unchanged, as the concentration of the second sodium salt increases continuously, both the cycle capacity retention rate and the storage capacity retention rate show a trend of first increasing and then decreasing. When the concentration of the second sodium salt is 1.1 mol / L, the cycle capacity retention rate and the storage capacity retention rate reach the maximum, indicating that the performance of the sodium-ion battery is optimal when the concentration of the second sodium salt is near 1.1 mol / L.

[0068] (3) The test results of Example 1, Examples 10 to 12 show that, when the concentration of the second sodium salt and m2 / (m1 + m3) remain unchanged, as the component ratio in the solvent continuously increases, both the cycle capacity retention rate and the storage capacity retention rate first increase and then decrease. When the component ratio in the solvent is 4:6, the cycle capacity retention rate and the storage capacity retention rate reach the maximum, indicating that the performance of the sodium-ion battery is optimal when the component ratio in the solvent is 4:6.

[0069] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present application without departing from the spirit and scope of the embodiments of the present application. Thus, if these modifications and variations of the embodiments of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these changes and modifications.

Claims

1. A sodium-ion battery, characterized in that, it includes an electrolyte, and the electrolyte includes: a first additive, a second additive, and a third additive. The first additive is fluoroethylene carbonate, the second additive is selected from at least one of sulfate compounds and sultone compounds, and the third additive is a first sodium salt; the mass percentage content of the first additive in the electrolyte is m1, the mass percentage content of the second additive in the electrolyte is m2, and the mass percentage content of the third additive in the electrolyte is m3. m1 is 0.5%-3%, m2 is 0.1%-5%, and m3 is 0.2%-10%.

2. The sodium-ion battery according to claim 1, characterized in that, m2 / (m1 + m3) is 0.1 - 3.

3. The sodium-ion battery according to claim 2, characterized in that, m2 / (m1 + m3) is 0.4 - 2.

4. The sodium-ion battery according to any one of claims 1-3, characterized in that, m1 is 1% - 2%.

5. The sodium-ion battery according to any one of claims 1-4, characterized in that, m2 is 1% - 3%.

6. The sodium-ion battery according to any one of claims 1-5, characterized in that, m3 is 0.5% - 7%.

7. The sodium-ion battery according to any one of claims 1-6, characterized in that, m1 + m2 + m3 is 2.5% - 12%.

8. The sodium-ion battery according to any one of claims 1-7, characterized in that, the general formula structure of the sulfate compound is as follows: Wherein, R 1 is selected from H, or a C1-C3 hydrocarbyl group, and n1 is selected from 1, 2, and 3.

9. The sodium-ion battery according to any one of claims 1-8, characterized in that, the sultone compound is selected from the structure shown in formula a1 or the structure shown in formula a2 as follows: wherein, R 2 -R 5 each independently selected from H, or C1-C6 hydrocarbyl, and n2 and n3 are each independently selected from 1, 2, and 3.

10. The sodium-ion battery according to any one of claims 1-9, characterized in that, the electrolyte further includes a second sodium salt, and the solubility of the second sodium salt is higher than the solubility of the first sodium salt.

11. The sodium-ion battery according to claim 10, characterized in that, The second sodium salt is selected from at least one of the following: NaPF 6 , NaN(SO 2 C 2 F 5 ), 2 , NaClO 4 .

12. The sodium-ion battery according to any one of claims 1-11, characterized in that, The first sodium salt is selected from at least one of the following: NaDFOB, NaTFOP, NaPO 2 F 2 , NaSbF 6 , NaAsF 6 , NaN(SO 2 CF 3 ) 2 , NaC(SO 2 CF 3 ) 3 , NaN(SO 2 F) 2 , NaAlCl 4 , NaCF 3 SO 3 , Na 2 B 10 Cl 10 .

13. The sodium-ion battery according to any one of claims 1-12, characterized in that, the sodium-ion battery further includes a positive electrode, and the positive electrode includes: a current collector and a positive electrode active material disposed on the current collector. The positive electrode active material includes: a layered transition metal oxide and a polyanion compound.

14. The sodium-ion battery according to claim 13, characterized in that, The molecular general formula of the positive electrode active material is: Na α (M x Fe y Mn z )O 2 @Na β N γ (PO 4 ) 2 P 2 O 7 , M is selected from at least one of Ni, Cu, Co, Ti, Mg, Li, Al, Zn, Ca; N is selected from at least one of Fe, Mn, Co; 0.8 ≤ α ≤ 1.1, 3 ≤ β ≤ 5, 2 ≤ γ ≤ 5, x + y + z = 1. The mass ratio of Na α (M x Fe y Mn z )O 2 in the positive electrode active material is k1, and the mass ratio of Na β N γ (PO 4 ) 2 P 2 O 7 in the positive electrode active material is k2, k1 + k2 = 1, and 0 < k2 < 0.

5.

15. An electrolyte for a sodium-ion battery, characterized in that, it includes: a first additive, a second additive, and a third additive. The first additive is fluoroethylene carbonate, the second additive is selected from at least one of sulfate compounds and sultone compounds, and the third additive is a first sodium salt; The mass percentage content of the first additive in the electrolyte is m1, the mass percentage content of the second additive in the electrolyte is m2, and the mass percentage content of the third additive in the electrolyte is m3. m1 ranges from 0.5% to 3%, m2 ranges from 0.1% to 5%, and m3 ranges from 0.2% to 10%.

16. A battery pack, characterized in that, it includes: a box body and a plurality of sodium ion batteries as described in any one of claims 1-14, and each of the sodium ion batteries is disposed in the box body.

17. An energy storage system, characterized in that, the energy storage system includes the battery pack as described in claim 16 and a power converter. The power converter is configured to convert the alternating current output by an external AC power supply into direct current and output it to the battery pack, and / or the power converter is configured to convert the direct current output by the battery pack into alternating current and output it to a load or the power grid.

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