A sodium-ion battery

Abstract

The application provides a sodium ion battery, which comprises an electrolyte, a positive electrode sheet, a negative electrode sheet and a diaphragm, the electrolyte comprises an electrolyte salt, an organic solvent and a combined additive, the combined additive comprises an additive A and an additive B; the additive A is a compound shown in formula I, the additive B is a compound shown in formula II, the additive A and the additive B synergistically inhibit the consumption of sodium salt, improve the stability of SEI, reduce the consumption of the electrolyte in the cycle process and improve the cycle performance. The application also provides a preparation method of the electrolyte and a sodium ion battery containing the electrolyte.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a sodium ion battery. BACKGROUND

[0002] As the best secondary battery in terms of comprehensive performance, lithium ion batteries have the characteristics of high energy density, excellent performance, good safety and low cost, and thus have large-scale applications in the fields of digital devices, automobiles, energy storage and the like. In lithium ion batteries, the positive active material and the lithium salt in the electrolyte are both prepared from lithium-containing compounds, wherein the positive active material accounts for about 40% of the total cost of lithium ion batteries, and the lithium salt accounts for about 50% of the total cost of electrolyte, so the price of lithium ore has a huge impact on the price of lithium ion batteries. China is very poor in lithium ore resources, and most of them depend on imports. Sodium, as one of the elements with the highest content in nature, widely exists in nature and is also one of the best elements for making batteries. Under this background, researchers invented sodium ion batteries.

[0003] The positive electrode of a sodium ion battery generally uses layered oxides, Prussian blue, Prussian white and the like, and the negative electrode generally uses hard carbon. The main disadvantage of sodium ion batteries is that the energy density is low, but they have excellent safety performance, and the cost is lower than that of the cheap lithium iron phosphate, and the concentration requirement of the electrolyte in the electrolyte is lower, Na cannot form an alloy with Al, so Al can be used as the current collector of the negative electrode, there is no risk of over-discharge, the safety is high, and it is very suitable for application in energy storage systems and two-wheeled vehicles which do not require high volume energy density.

[0004] However, the stability of the SEI of the sodium ion battery is worse than that of the lithium ion battery, gas is easily produced during the cycle process, and the cycle performance is poor, so it is urgent to develop a sodium ion battery which takes into account the cycle performance and other key performances. SUMMARY

[0005] The present application aims at at least solving one of the above-mentioned technical problems in the prior art. To this end, the present application provides a sodium ion battery which takes into account the cycle performance and other key performances.

[0006] The present application also provides a preparation method of a sodium ion battery electrolyte.

[0007] The present application provides a sodium ion battery, which comprises an electrolyte, a positive electrode sheet, a negative electrode sheet and a separator, wherein the electrolyte comprises an electrolyte salt, an organic solvent and a combined additive, the combined additive comprises an additive A and an additive B; the additive A is a compound represented by formula I, and the additive B is a compound represented by formula II:

[0008] The compound represented by formula I has the following structure:

[0009]

[0010] The compound shown in formula II has the following structure:

[0011]

[0012] In formula II, R1-R5 are each independently selected from one of a hydrogen atom, a C1-C 10 alkyl group, a C1-C 10 fluoroalkyl group, a C2-C 10 alkenyl group, a C2-C 10 fluoroalkenyl group, a C2-C 10 alkynyl group, a C2-C 10 fluoroalkynyl group, a C6-C 10 aromatic group, and a C6-C 10 halogenated aromatic group; and / or, R1-R5 are each independently selected from one of a halogen-containing alkyl group, a phenyl group, a biphenyl group, a naphthyl group, a pyridyl group, a thienyl group, a halogenated phenyl group, a halogenated biphenyl, a phenol group, an alkyl-containing phenol group, an alkenyl-containing phenol group, an alkynyl-containing phenol group, a nitrile-containing phenol group, a monohalogenated phenol group, and a polyhalogenated phenol group;

[0013] The sodium ion battery has a NP ratio of x; the positive electrode sheet comprises a positive electrode active material, a compaction density of the positive electrode active material is w g / cm 3 ; a mass percentage content of the additive A in the electrolyte is y%, a mass percentage content of the additive B in the electrolyte is z%, and w, x, y and z satisfy the following relationship: 0.2≤(w-x 2 ) / min[(y+z),(y / z)]≤5.

[0014] One of the technical solutions of the present application relates to a sodium ion battery, and at least has the following beneficial effects:

[0015] The present application uses additive A as an auxiliary solvent and a film-forming additive, optimizes the solvation structure, enhances the stability of SEI, reduces its dissolution in the cycle process, and at the same time reduces the content of Na x PO y F z , can increase the content of NaF, improve the stability of SEI, and inhibit the dissolution of SEI. In the SEI component of the sodium ion battery, NaF has the highest LUMO energy level, the electronic affinity is weak, the electronic driving force of SEI is low, and the energy band gap is large, which is beneficial to enhance the insulation ability of SEI and reduce the continuous growth of SEI.

[0016] The application introduces additive B as a film-forming additive on the basis of additive A, B structure contains B atom, has empty orbital, belongs to electron-deficient group, can form complex with additive A, and then forms stable ion complex with PF6 - , is beneficial to the dissociation of sodium salt, can improve the stability of PF6 - , reduces the decomposition of sodium salt in the cycle process, and prolongs the cycle life of sodium ion battery.

[0017] Meanwhile, additive A and B have synergistic effect, and need to maintain certain parameter relationship with the N / P ratio of sodium ion battery and the positive electrode compaction density, the comprehensive effect inhibits the consumption of sodium salt, improves the stability of SEI, reduces the consumption of electrolyte in the cycle process, and improves the cycle performance.

[0018] Compared with the prior art, the application has the following obvious advantages:

[0019] Additive A has one more F atom than common additive FEC, the LUMO energy is lower, is more easily reduced than FEC, can form film in the negative electrode preferentially, and can make the SEI film contain more NaF, thereby improving the stability of SEI film, additive B is introduced, B structure contains boron atom, has empty orbital, belongs to electron-deficient group, can form complex with additive A, and then forms stable ion complex with PF6 - , is beneficial to the dissociation of sodium salt, can improve the stability of PF6 - , reduces the decomposition of sodium salt in the cycle process, and prolongs the cycle life of sodium ion battery.

[0020] The sodium ion battery of the application can significantly improve the stability of nickel-iron-manganese sodium Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2 and negative electrode hard carbon, inhibit the dissolution of transition metal ions, improve the stability of SEI on the surface of hard carbon, inhibit the reaction of active end groups on the surface of hard carbon, reduce the loss of electrolyte solvent and Na + caused by active sites, and improve the room temperature / high temperature cycle performance, high temperature storage performance and thermal box performance of the battery.

[0021] In summary, by introducing additive A as auxiliary solvent and film-forming additive, the stability of SEI can be improved, the problem of fragile and easy decomposition of SEI caused by more low-lattice-energy compounds in SEI components can be solved, and the cycle performance can be improved. Additive B is introduced as a film-forming additive, the stability of sodium salt is improved, participates in film formation to improve the stability of SEI, and the cycle performance of sodium ion battery is improved.

[0022] The additive A and the additive B synergistically inhibit damage of the positive active material to the electrolyte, reduce consumption of the electrolyte during the cycle, and improve cycle performance.

[0023] The application improves the stability of SEI of the sodium ion battery by introducing difluorocarbonic acid ethylene ester as an auxiliary solvent and a film forming additive, pyridine boronic acid pinacol ester derivatives as a film forming additive, limiting the content percentage of the two additives, the N / P ratio of the battery and the positive electrode compaction density by a relational expression, and improving the stability of SEI of the sodium ion battery by synergistic effect

[0024] According to some embodiments of the application, the additive B has at least one of the structures B1 to B3, wherein:

[0025] The structure of B1 is:

[0026]

[0027] The structure of B2 is:

[0028]

[0029] The structure of B3 is:

[0030]

[0031] According to some embodiments of the application, the additive A is added in the electrolyte in an amount of 0.2wt% to 15wt%.

[0032] According to some embodiments of the application, the additive A is added in the electrolyte in an amount of 1wt% to 8wt%.

[0033] According to some embodiments of the application, the additive B is added in the electrolyte in an amount of 0.1wt% to 5wt%.

[0034] According to some embodiments of the application, the additive B is added in the electrolyte in an amount of 0.15wt% to 2.5wt%.

[0035] According to some embodiments of the application, the electrolyte further contains a solvent.

[0036] According to some embodiments of the application, the solvent is a mixture of ethylene carbonate, propylene carbonate, diethyl carbonate and dimethyl carbonate.

[0037] According to some embodiments of the application, the electrolyte further contains a sodium salt.

[0038] According to some embodiments of the present application, the sodium salt comprises at least one of sodium hexafluorophosphate (NaPF6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) and sodium bis(fluorosulfonyl)imide (NaFSI).

[0039] According to some embodiments of the present application, the sodium salt is added in the electrolyte in an amount of 8wt% to 20wt%.

[0040] According to some embodiments of the present application, the electrolyte further comprises an additive.

[0041] According to some embodiments of the present application, the additive comprises one of fluoroethylene carbonate (FEC), 1,3-propane sultone, tris(trimethylsilyl)borate (TMSB) and tris(trimethylsilyl)phosphate (TMSP).

[0042] According to some embodiments of the present application, the additive is added in the electrolyte in an amount of 0.1wt% to 20wt%.

[0043] According to some embodiments of the present application, the method for preparing the electrolyte comprises the following steps: mixing the components of the electrolyte in a proportion.

[0044] The method for preparing the electrolyte does not require expensive equipment and complex process control, the reaction condition is not harsh, the raw material is easy to obtain, the production cost is low, and the industrial production is easy.

[0045] According to some embodiments of the present application, the negative electrode hard carbon suitable for the sodium ion battery is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2.

[0046] The sodium ion battery of the present application can significantly improve the stability of Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2and the negative electrode hard carbon, inhibit the dissolution of transition metal ions, improve the stability of the SEI on the surface of the hard carbon, inhibit the reaction of active end groups on the surface of the hard carbon, reduce the loss of electrolyte solvent and Na + loss caused by active sites, and thus improve the room temperature / high temperature cycle performance, high temperature storage performance and hot box performance of the battery.

[0047] The sodium ion battery of the present application, since the electrolyte of the present application is used, at least has all the beneficial effects of the electrolyte. Specifically:

[0048] The sodium ion battery of the present application optimizes the solvation structure by using additive A as an auxiliary solvent and a film-forming additive, and enhances the stability of the solid electrolyte interface (SEI). This helps to reduce the dissolution of SEI during the cycle process and improve the stability of SEI.

[0049] The sodium ion battery of the present application can reduce the content of Na x PO y F z in the SEI film by optimizing the electrolyte composition, thereby increasing the content of NaF, improving the stability of SEI, and inhibiting the dissolution of SEI.

[0050] The sodium ion battery of the present application has a higher LUMO energy level and a weaker electron affinity due to NaF, which helps to enhance the insulation capacity of SEI and reduce the continuous growth of SEI, thereby improving the battery performance.

[0051] The sodium ion battery of the present application contains B atoms in additive B as a film-forming additive, forms a complex with

[0052] PF6, and forms a stable ionic complex. This helps to dissociate the sodium salt and improve the stability of PF6, reduce the decomposition of sodium salt during the cycle process, and prolong the cycle life of the sodium ion battery.

[0053] The synergistic effect of additives A and B in the sodium ion battery of the present application helps to inhibit the consumption of sodium salt, improve the stability of SEI, reduce the consumption of electrolyte during the cycle process, and thereby improve the cycle performance.

[0054] According to some embodiments of the present application, the NP ratio of the sodium ion battery is x, the positive electrode compaction density is w g / cm 3 , the mass percentage content of additive A is y%, and the mass percentage content of additive B is z%, and the following relationship should be satisfied between w, x, y and z: 0.5≤(w-x 2 ) / min[(y+z),(y / z)]≤4.

[0055] In the above relationship, "min" means the smaller one between (y+z) and (y / z). For example, y is 1 and z is 3, then y+z=4 and y / z=1 / 3, and the value of / min[(y+z),(y / z)] is 1 / 3. For another example, y is 3 and z is 1, then y+z=4 and y / z=3, and the value of / min[(y+z),(y / z)] is 3.

[0056] According to some embodiments of the present application, the value range of w is 2.8-3.2 g / cm 3 .

[0057] According to some embodiments of the present application, x is in the range of 1.038-1.048.

[0058] According to some embodiments of the present application, y is in the range of 0.2-15%.

[0059] According to some embodiments of the present application, z is in the range of 0.1-5%.

[0060] According to some embodiments of the present application, the sodium-ion battery further comprises a cathode electrode sheet, an anode electrode sheet and a separator film.

[0061] According to some embodiments of the present application, the cathode electrode sheet comprises an aluminum foil current collector and a cathode film sheet.

[0062] According to some embodiments of the present application, the cathode film sheet comprises a cathode active material lithium nickel-iron-manganese oxide Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2, a conductive agent Super-P and a binder polyvinylidene fluoride PVDF.

[0063] According to some embodiments of the present application, the anode electrode sheet comprises an aluminum foil current collector and an anode film sheet.

[0064] According to some embodiments of the present application, the anode film sheet comprises an anode active material hard carbon, a conductive agent carbon nanotube CNT, a thickening agent sodium carboxymethyl cellulose (CMC) and a binder polyacrylic acid SBR. DETAILED DESCRIPTION

[0065] The following are specific embodiments of the present application, and the technical solutions of the present application are further described in conjunction with the embodiments, but the present application is not limited to these embodiments.

[0066] In some embodiments of the present application, a sodium-ion battery is provided, comprising an electrolyte, a positive electrode sheet, a negative electrode sheet and a separator film, the electrolyte comprising an electrolyte salt, an organic solvent and a combined additive, the combined additive comprising an additive A and an additive B; the additive A is a compound represented by Formula I, and the additive B is a compound represented by Formula II:

[0067] The compound represented by Formula I has the following structure:

[0068]

[0069] The compound represented by Formula I has a CAS number of 311810-76-1.

[0070] The compound represented by Formula II has the following structure:

[0071]

[0072] In formula II, R1-R5 are each independently selected from one of a hydrogen atom, a C1-C 10 alkyl group, a C1-C 10 fluoroalkyl group, a C2-C 10 alkenyl group, a C2-C 10 fluoroalkenyl group, a C2-C 10 alkynyl group, a C2-C 10 fluoroalkynyl group, a C6-C 10 aromatic group, and a C6-C 10 halogenated aromatic group; and / or, R1-R5 are each independently selected from one of a halogen-containing alkyl group, a phenyl group, a biphenyl group, a naphthyl group, a pyridyl group, a thienyl group, a halogenated phenyl group, a halogenated biphenyl, a phenol group, an alkyl-containing phenol group, an alkenyl-containing phenol group, an alkynyl-containing phenol group, a nitrile-containing phenol group, a monohalogenated phenol group, and a polyhalogenated phenol group;

[0073] A sodium ion battery has an NP ratio of x; a positive electrode sheet includes a positive electrode active material, a compaction density of the positive electrode active material is wg / cm 3 ; a mass percentage content of the additive A in the electrolyte is y%, a mass percentage content of the additive B in the electrolyte is z%, and w, x, y and z satisfy the following relationship: 0.2≤(w-x 2 ) / min[(y+z), (y / z)]≤5.

[0074] It can be understood that the electrolyte of the application uses the additive A as an auxiliary solvent and a film-forming additive, optimizes the solvation structure, enhances the stability of the SEI, reduces the dissolution of the SEI in the cycle process, and reduces the content of Na x PO y F z , can increase the content of NaF, improve the stability of the SEI, and inhibit the dissolution of the SEI. In the SEI components of the sodium ion battery, NaF has the highest LUMO energy level, the electronic affinity is weak, the electronic driving force of the SEI is low, and the energy gap is large, which is beneficial to enhance the insulation ability of the SEI and reduce the continuous growth of the SEI.

[0075] It can also be understood that the electrolyte of the application introduces the additive B as a film-forming additive, the B structure contains B atoms and has an empty orbital, which belongs to an electron-deficient group, and can form a complex with the additive A, and then form a stable ionic complex with PF6 - , which is beneficial to the dissociation of the sodium salt, and can improve the stability of PF6 - , reduce the decomposition of the sodium salt in the cycle process, and prolong the cycle life of the sodium ion battery.

[0076] The electrolyte of the present application, the synergistic effect of additives A and B, inhibits the consumption of sodium salt, improves the stability of SEI, reduces the consumption of electrolyte in the cycle process, and improves the cycle performance.

[0077] Specifically, compared with the prior art, the present application has the following remarkable advantages:

[0078] Additive A has more F atoms than the commonly used additive FEC, and its LUMO energy is lower, so it is easier to be reduced than FEC, and thus can form a film preferentially at the negative electrode, and at the same time, the SEI film can contain more NaF, thereby improving the stability of the SEI film. At the same time, additive B is introduced, which contains boron atoms in its structure and has an empty orbital, belonging to an electron-deficient group, and can form a complex with additive A, and then PF6 - forms a stable ionic complex, which is beneficial to the dissociation of sodium salt, and at the same time can improve the stability of PF6 - , reduce the decomposition of sodium salt in the cycle process, and prolong the cycle life of sodium ion battery.

[0079] The sodium ion battery electrolyte of the present application can significantly improve the stability of nickel-iron-manganese sodium Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2 and the negative electrode hard carbon, inhibit the dissolution of transition metal ions, and improve the stability of the SEI on the surface of hard carbon, inhibit the reaction of active end groups on the surface of hard carbon, reduce the loss of electrolyte solvent and Na + loss caused by active sites, thereby improving the room temperature / high temperature cycle performance, high temperature storage performance and hot box performance of the battery.

[0080] In summary, by introducing additive A as an auxiliary solvent and film-forming additive, the stability of SEI can be improved, the problem of weak and easy decomposition of SEI caused by the presence of more low-lattice-energy compounds in SEI components can be reduced, and the cycle performance can be improved. By introducing additive B as a film-forming additive, the stability of sodium salt is improved, and additive B participates in film formation to improve the stability of SEI, thereby improving the cycle performance of sodium ion battery.

[0081] Additive A and additive B synergistically inhibit the damage of positive active material to electrolyte, reduce the consumption of electrolyte in the cycle process, and improve the cycle performance.

[0082] In some embodiments of the present application, additive B has at least one of the structures B1 to B3, wherein:

[0083]

[0084] The CAS number of B1 is: 754214-56-7.

[0085] The structure of B2 is:

[0086]

[0087] The CAS number of B2 is: 181219-01-2.

[0088] The structure of B3 is:

[0089]

[0090] The CAS number of B3 is: 844891-01-6.

[0091] In some embodiments of the present application, the additive A is added in the electrolyte in an amount of 0.2wt% to 15wt%.

[0092] In some embodiments of the present application, the additive A is added in the electrolyte in an amount of 1wt% to 8wt%.

[0093] In some embodiments of the present application, the additive B is added in the electrolyte in an amount of 0.1wt% to 5wt%.

[0094] In some embodiments of the present application, the additive B is added in the electrolyte in an amount of 0.15wt% to 2.5wt%.

[0095] In some embodiments of the present application, the electrolyte further contains a solvent.

[0096] In some embodiments of the present application, the solvent is a mixture of ethylene carbonate, propylene carbonate, diethyl carbonate and dimethyl carbonate.

[0097] In some embodiments of the present application, the electrolyte further contains a sodium salt. In some embodiments of the present application, the sodium salt includes at least one of sodium hexafluorophosphate (NaPF6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) and sodium bisfluorosulfonylimide (NaFSI).

[0098] In some embodiments of the present application, the sodium salt is added in the electrolyte in an amount of 8wt% to 20wt%.

[0099] In some embodiments of the present application, the electrolyte further contains an additive.

[0100] In some embodiments of the present application, the additive includes one of fluoroethylene carbonate (FEC), 1,3-propane sultone, tris(trimethylsilyl)borate (TMSB) and tris(trimethylsilyl)phosphate (TMSP).

[0101] In some embodiments of the present application, the additive is added in the electrolyte in an amount of 0.1wt% to 20wt%.

[0102] In some embodiments of the present application, the preparation method of the electrolyte comprises the following steps: mixing each component of the electrolyte according to the proportion.

[0103] It can be understood that the preparation method of the present application does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are easy to obtain, the production cost is low, and the industrial production is easy.

[0104] In some embodiments of the present application, the sodium ion battery adapted negative electrode hard carbon is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2.

[0105] The sodium ion battery of the present application can significantly improve the stability of Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2 and the negative electrode hard carbon, inhibit the dissolution of transition metal ions, and improve the stability of the SEI on the surface of the hard carbon, inhibit the reaction of active end groups on the surface of the hard carbon, reduce the loss of electrolyte solvent and Na + loss caused by active sites, thereby improving the room temperature / high temperature cycle performance, high temperature storage performance and hot box performance of the battery.

[0106] It can be understood that the sodium ion battery of the present application has at least all the beneficial effects of the electrolyte due to the use of the electrolyte of the present application. Specifically:

[0107] The sodium ion battery of the present application optimizes the solvation structure by using additive A as an auxiliary solvent and a film-forming additive, and enhances the stability of the solid electrolyte interface (SEI). This helps to reduce the dissolution of SEI during the cycle process and improve the stability of SEI.

[0108] The sodium ion battery of the present application can reduce the content of Na x PO y F z in the SEI film by optimizing the electrolyte composition, thereby increasing the content of NaF and improving the stability of SEI and inhibiting the dissolution of SEI.

[0109] The sodium ion battery of the present application has a higher LUMO energy level and a weaker electron affinity due to NaF, which helps to enhance the insulation ability of SEI and reduce the continuous growth of SEI, thereby improving the battery performance.

[0110] The sodium ion battery of the present application contains B atoms as a film-forming additive, forms a complex with

[0111] --PF6 forms a stable ionic complex. This helps to dissociate the sodium salt and improve the stability of PF6, reduce the decomposition of sodium salt during the cycle process, and prolong the cycle life of sodium ion battery.

[0112] The sodium ion battery of the present application, the synergistic effect of additives A and B helps to inhibit the consumption of sodium salt, improve the stability of SEI, reduce the consumption of electrolyte during the cycle process, and thus improve the cycle performance.

[0113] In some embodiments of the present application, the NP ratio of the sodium ion battery is x, the positive electrode compaction density is w g / cm 3 , the mass percentage content of additive A is y%, and the mass percentage content of additive B is z%, and the following relationship should be met between w, x, y and z: 0.2≤(w-x 2 ) / min[(y+z),(y / z)]≤5.

[0114] The above relationship is that "min" means between (y+z) and (y / z), and the smaller one is taken. For example, y is 1, z is 3, y+z=4, y / z=1 / 3, and the value of / min[(y+z), (y / z)] is 1 / 3. For another example, y is 3, z is 1, y+z=4, y / z=3, and the value of / min[(y+z), (y / z)] is 3.

[0115] In some embodiments of the present application, the value range of w is 2.8-3.2 g / cm 3 .

[0116] In some embodiments of the present application, the value range of x is 1.038-1.048.

[0117] In some embodiments of the present application, the value range of y is 0.2-15%.

[0118] In some embodiments of the present application, the value range of z is 0.1-5%.

[0119] In some embodiments of the present application, the sodium ion battery further comprises a cathode electrode sheet, an anode electrode sheet and a separator film.

[0120] In some embodiments of the present application, the cathode electrode sheet comprises an aluminum foil current collector and a cathode film sheet.

[0121] In some embodiments of the present application, the cathode film sheet comprises a cathode active material lithium nickel-iron-manganese oxide Na[Ni 1 / 3 Fe 1 / 3Mn 1 / 3 ]O2, a conductive agent Super-P and a binder polyvinylidene fluoride PVDF.

[0122] In some embodiments of the present application, the anode tab includes an aluminum foil current collector and an anode film.

[0123] In some embodiments of the present application, the anode film includes an anode active material hard carbon, a conductive agent carbon nanotube CNT, a thickening agent sodium carboxymethyl cellulose (CMC), and a binder polyacrylic acid SBR.

[0124] The technical solutions of the present application will be better understood in combination with the specific embodiments below.

[0125] It should be noted that all reagents in the examples are obtained from commercial channels.

[0126] Example 1

[0127] This embodiment provides an electrolyte. The specific preparation method is:

[0128] In an argon-filled glove box, EC, PC, DEC, DEC were mixed in a mass ratio of EC:PC:DMC:DEC = 20:20:50:10, then 12wt% of sodium hexafluorophosphate (NaPF6) based on the total weight of the electrolyte was slowly added to the mixed solution, and finally 1.5wt% of additive A, 1.5wt% of B1, 4wt% of 1,3-propanesulfonic acid lactone (PS) and 1wt% of tris(trimethylsilyl)borate (TMSB) based on the total weight of the electrolyte were added. After stirring uniformly, the sodium ion battery electrolyte of this embodiment was obtained.

[0129] Further, the positive electrode tab was prepared. The specific preparation method is:

[0130] The cathode film includes a cathode active material lithium nickel-iron-manganese oxide Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2, a conductive agent Super P, and a binder polyvinylidene fluoride PVDF. After mixing the substances in a weight ratio of active material NFM: conductive agent Super P: polyvinylidene fluoride PVDF = 97%:1.7%:1.3%, adding N-methyl pyrrolidone (NMP), and mixing uniformly, a sodium ion battery positive electrode slurry was prepared: the positive electrode slurry was coated on the current collector aluminum foil, dried at 85°C, then cold-pressed, and then edge cut, tabbed, and striped, and then dried at 85°C under vacuum conditions for 4h, and the tab was welded, to prepare a sodium ion battery positive electrode tab.

[0131] Further, the negative electrode tab was prepared. The specific preparation method is:

[0132] The anode diaphragm comprises anode active material hard carbon, conductive agent carbon nanotube CNT, thickening agent sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber SBR. After mixing the substances in a weight ratio of hard carbon: CNT: CMC: SBR = 96%: 1.3%: 1.2%: 1.5%, adding deionized water and mixing uniformly, a negative electrode slurry is prepared; the negative electrode slurry is coated on the current collector aluminum foil, dried at 85°C, then cold-pressed, followed by edge cutting, piece cutting, and slitting, and then dried at 85°C under vacuum for 12h to obtain a sodium ion battery negative electrode sheet.

[0133] Further, a soft-pack battery is prepared. The specific preparation method is as follows:

[0134] The prepared positive electrode sheet (main active material Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2, Xiangtung New Energy), diaphragm (Shenzhen Xingyuan), and negative electrode sheet (active material hard carbon, Shenzhen Betrue) are stacked in order, with the diaphragm between the positive and negative electrode sheets, and then wound to obtain a bare cell; the bare cell is placed in an aluminum plastic film outer package, the electrolyte prepared above is injected into the dried battery, and then the battery is packaged, placed, formed, shaped, and separated to complete the preparation of the sodium ion soft-pack battery.

[0135] The NP ratio of the sodium ion battery is 1.044, and the positive electrode compaction density is 3.0g / cm 3 .

[0136] Example 2-7

[0137] Except that the electrolyte components are different, the remaining parameters and processes are consistent with those of Example 1.

[0138] Example 8

[0139] Except that the positive electrode compaction density is 2.9g / cm 3 , the remaining parameters and processes are consistent with those of Example 1.

[0140] Example 9

[0141] Except that the NP ratio is 1.040, the remaining parameters and processes are consistent with those of Example 1.

[0142] Comparative Examples 1-3

[0143] Except that the electrolyte components are different, the remaining parameters and processes are consistent with those of Example 1.

[0144] Comparative Example 4

[0145] Except that the positive electrode compaction density is 2.6g / cm 3 , the remaining parameters and processes are consistent with those of Example 1.

[0146] Comparative Example 5

[0147] The remaining parameters and processes were consistent with Example 1, except that the NP ratio was 1.02.

[0148] The specific proportions of each example and comparative example are shown in Table 1.

[0149] Table 1

[0150]

[0151]

[0152] Performance Test

[0153] The batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were subjected to relevant performance tests.

[0154] Normal temperature cycle performance test: in a 25℃ environment, the battery after being divided into groups was charged to 4.0V at 0.7C constant current and constant voltage, the cutoff current was 0.05C, then discharged to 2.0V at 0.5C constant current, and so on, after 700 cycles of charge and discharge, the 700th week cycle capacity retention rate was calculated, and the calculation formula was as follows:

[0155] The 700th week cycle capacity retention rate (%) = (the 700th week cycle discharge capacity / the first cycle discharge capacity) x 100%.

[0156] High temperature cycle performance test: in a 45℃ environment, the battery after being divided into groups was charged to 4.0V at 0.7C constant current and constant voltage, the cutoff current was 0.05C, then discharged to 2.0V at 0.5C constant current, and so on, after 700 cycles of charge and discharge, the 700th week cycle capacity retention rate was calculated, and the calculation formula was as follows:

[0157] The 700th week cycle capacity retention rate (%) = (the 700th week cycle discharge capacity / the first cycle discharge capacity) x 100%.

[0158] 85℃ 24h high temperature storage test: the battery was placed at room temperature to charge and discharge 1 time (4.0V-2.0V) at 0.5C, the discharge capacity C0of the battery before storage was recorded, then the battery was charged to 4.0V full state (100% SOC) at constant current and constant voltage, the thickness d1of the battery before high temperature storage was tested using PPG battery thickness tester (600g), the battery was placed in a 85℃ constant temperature oven for 24h, after storage was completed, the battery was taken out and the battery thickness d2after storage was tested, the thickness expansion rate of the battery after 85℃ storage for 24h was calculated; after the battery was cooled at room temperature for 24h, the battery was discharged to 2.0V at 0.5C constant current again, then charged to 4.0V at 0.5C constant current and constant voltage, the discharge capacity C1and charge capacity C2of the battery after storage were recorded, the capacity retention rate and recovery rate of the battery after 85℃ storage for 24h were calculated, the calculation formula is as follows:

[0159] Thickness expansion rate after 85℃ storage for 24h = (d2-d1) / d1x100%;

[0160] Capacity retention rate after 85℃ storage for 24h = C1 / C0x100%;

[0161] Capacity recovery rate after 85℃ storage for 24h = C2 / C0x100%.

[0162] The results of the above performance tests are shown in Table 2.

[0163] Thermal shock performance: discharge to 2.0V at a given current of 0.2C at 25℃ environmental conditions; stand for 5min; charge to 4.0V at a charge current of 0.2C, when the cell voltage reaches 4.0V, change to 4.0V constant voltage charging until the charge current ≤ cutoff current 0.05C; after standing for 1h, place the cell in an oven, increase the oven temperature to 135±2℃ at a speed of 5±2℃ / min, and keep for 60min before stopping, the judgment standard is that the cell does not catch fire and does not explode.

[0164] Table 2

[0165]

[0166] From the test results of examples 1-7 and comparative examples 1-4 in table 2, it can be seen that the introduction of additive A in the electrolyte system can effectively improve the cycle performance and high temperature performance of sodium ion battery, and the effect is very significant.

[0167] Additive A as an auxiliary solvent and a film-forming additive, optimizes the solvation structure, enhances the stability of SEI, reduces its dissolution in the cycle process, and at the same time reduces the Na x PO y F zThe content of NaF is increased, the stability of SEI is improved, and the dissolution of SEI is inhibited. In the SEI component of the sodium ion battery, NaF has the highest LUMO energy level, the electron affinity is weak, the electron driving force of SEI is low, and the energy band gap is large, which is beneficial to enhance the insulation capacity of SEI and reduce the continuous growth of SEI.

[0168] At the same time, the additive B is introduced, the B structure contains B atoms, has an empty orbital, belongs to an electron-deficient group, can form a complex with the additive A, and then reacts with PF6 - to form a stable ion complex, which is beneficial to the dissociation of the sodium salt, and can improve the stability of PF6 - , reduce the decomposition of the sodium salt in the cycle process, and prolong the cycle life of the sodium ion battery. A and B have a synergistic effect, inhibit the consumption of the sodium salt, improve the stability of SEI, reduce the consumption of the electrolyte in the cycle process, and improve the cycle performance.

[0169] The above describes the present application in detail in combination with the embodiments, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge range possessed by those skilled in the art without departing from the purpose of the present application.

Claims

1. A sodium-ion battery, characterized in that, The electrolyte, the positive electrode sheet, the negative electrode sheet and the separator, the electrolyte comprising electrolyte salt, organic solvent and combined additive, the combined additive comprising additive A and additive B; the additive A is a compound shown in formula I, and the additive B is a compound shown in formula II. The compound shown in formula I has the following structure: ， The compound shown in formula II has the following structure: ， In formula II, R1to R5are each independently selected from one of a hydrogen atom, a C1-C 10 alkyl group, a C2-C 10 alkenyl group, a C2-C 10 fluoroalkenyl group, a C2-C 10 alkynyl group, a C2-C 10 fluoroalkynyl group, a C6-C 10 aromatic group, a C6-C 10 halogenated aromatic group, a halogen-containing alkyl group, a pyridyl group, a thienyl group, a halogenated biphenyl group, a biphenyl group, an alkyl-containing phenol group, an alkenyl-containing phenol group, an alkynyl-containing phenol group, and a nitrile-containing phenol group. The NP ratio of the sodium ion battery is x; the positive electrode plate comprises a positive electrode active material, and a compacted density of the positive electrode active material is w g / cm 3 ; a mass percentage content of the additive A in the electrolyte is y%, a mass percentage content of the additive B in the electrolyte is z%, and w, x, y and z need to satisfy the following relationship: 0.2≤(w-x 2 ) / min[(y+z), (y / z)]≤5, wherein the value range of w is 2.8~3.2 g / cm 3 ; the value range of x is 1.038~1.048; the value range of y is 0.2~15%; and the value range of z is 0.1~5%.

2. The sodium-ion battery of claim 1, wherein, In formula II, R1-R5 are each independently selected from one of C1-C10 fluoroalkyl, phenyl, naphthyl, phenol, monohalogenated phenol, polyhalogenated phenol and halogenated phenyl.

3. The sodium-ion battery of claim 1, wherein, The compound shown in formula II is at least one of B1 to B3 structures, wherein: The structure of B1 is: ， The structure of B2 is: ， The structure of B3 is: 。 4. The sodium-ion battery of claim 1, wherein, The electrolyte further contains sodium salt.

5. The sodium-ion battery of claim 4, wherein, The sodium salt includes at least one of sodium hexafluorophosphate, sodium bis-trifluoromethanesulfonimide and sodium bisfluorosulfonimide.

6. The sodium-ion battery of claim 4, wherein, The addition amount of the sodium salt in the electrolyte is 8wt%-20wt%.

7. The sodium-ion battery of any one of claims 1-6, wherein, The preparation method of the electrolyte comprises the following steps: mixing each component of the electrolyte according to the proportion.

8. The sodium-ion battery of any one of claims 1-6, wherein, The sodium ion battery adapted negative electrode hard carbon is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2.

Images