Electrolyte and battery

Abstract

The application provides an electrolyte and a battery. The electrolyte comprises an electrolyte salt, a solvent, and at least one additive A as shown in formula (I): wherein at least one pair of R1 and R4 and R2 and R3 contains an amino group, and the other pair contains at least one of an amino group, a nitrile group and an isocyanate group. The electrolyte can make the battery have good cycle performance and storage performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery electrolyte, in particular to an electrolyte and a battery. BACKGROUND

[0002] Lithium ion batteries have been widely used in mobile terminal devices, electric vehicles and other fields. Sodium ion batteries are a kind of batteries similar to lithium ion batteries in energy storage mechanism, and the sodium resources are more abundant on the earth, which makes sodium ion batteries more likely to meet the low-cost demand of large-scale energy storage devices in the future.

[0003] Both lithium batteries and sodium batteries have certain performance deficiencies that affect their large-scale application. For example, a certain amount of moisture inevitably exists in the battery electrolyte, which will cause the hydrolysis of fluorine-containing electrolyte salts or other components in the electrolyte to generate HF. The presence of HF will exacerbate the dissolution of metal ions in the positive electrode material of the battery, and reduce the stability of the positive and negative electrode side interface film, thereby reducing the cycle performance and storage performance (especially high-temperature storage performance) of the battery.

[0004] Among them, adding a film-forming additive to the battery electrolyte has become one of the common means to improve the cycle performance of the battery, but it usually cannot guarantee that the battery has good cycle performance and high-temperature storage performance at the same time. SUMMARY

[0005] In view of this, the present application provides an electrolyte containing a specific additive to ensure that a lithium / sodium battery containing the electrolyte has good cycle performance and storage performance at the same time.

[0006] Specifically, the first aspect of the present application provides an electrolyte, which comprises an electrolyte salt, a solvent, and at least one additive A as shown in formula (I):

[0007]

[0008] In formula (I), at least one pair of R1 and R4 and R2 and R3 contains an amino group, and the other pair contains at least one of an amino group, a nitrile group and an isocyanate group.

[0009] The above-mentioned electrolyte contains additive A, which has a pyridine ring and contains amino, nitrile and isocyanate substituents on the pyridine ring. This makes additive A have good basicity, which can effectively reduce the content of HF in the electrolyte, thereby effectively inhibiting the dissolution of transition metal ions on the positive electrode side of the battery, improving the stability of the positive and negative electrode side interface film, and ensuring that the battery has good room temperature cycle performance and high-temperature storage performance.

[0010] The second aspect of the present application provides a battery in which the electrolyte of the first aspect of the present application is built-in. The battery can be a sodium ion battery or a lithium ion battery, etc.

[0011] The battery using the above electrolyte can better balance good room temperature cycle performance and high temperature storage performance, and low room temperature impedance. DETAILED DESCRIPTION

[0012] The electrolyte provided by the embodiments of the present application can make the battery have good cycle performance and storage performance.

[0013] Specifically, the electrolyte provided by the embodiments of the present application comprises an electrolyte salt, a solvent, and at least one additive A as shown in formula (I):

[0014]

[0015] In formula (I), at least one pair of R1 and R4 and R2 and R3 contains an amino group (-NH2), and the other pair contains at least one of an amino group (-NH2), a nitrile group (-CN), and an isocyanate group (-NCO).

[0016] The above electrolyte contains the additive A, which has a weakly basic pyridine ring in its structure, and the pyridine ring contains weakly basic substituents such as an amino group, a nitrile group, and an isocyanate group. This makes the additive A have good basicity, which can effectively reduce the content of HF in the electrolyte, thereby effectively inhibiting the dissolution of transition metal elements on the positive electrode side, improving the structural stability of the positive electrode material, and improving the stability of the interface film on the positive and negative electrode sides, ensuring that the cycle performance and high-temperature storage performance of the battery are good. In addition, while reducing the content of HF in the electrolyte, the additive A can also inhibit the formation of MF salt (M represents an active ion participating in energy storage / release in the battery, such as Li + or Na + ) with low conductivity on the surface of the negative electrode of the battery due to the presence of HF, thereby improving the rate performance of the battery.

[0017] The specific explanation of the above "at least one pair of R1 and R4 and R2 and R3 contains an amino group, and the other pair contains at least one of an amino group, a nitrile group, and an isocyanate group" is as follows: R1 and / or R4 can contain an amino group, and R2 and / or R3 independently contain at least one of an amino group, a nitrile group, and an isocyanate group (R2 and R3 can be the same or different groups); or R2 and / or R3 can contain an amino group, and R1 and / or R4 independently contain at least one of an amino group, a nitrile group, and an isocyanate group (R1 and R4 can be the same or different groups). The amino group, the nitrile group, and the isocyanate group, etc. can be directly connected to the pyridine ring in formula (I), or can be connected to the pyridine ring in formula (I) through a certain linking group (such as an alkylene group, a cycloalkylene group, etc.).

[0018] In some embodiments of the present application, one pair of R1 and R4, R2 and R3 is amino, and the other pair is at least one of nitrile group, isocyanate group. At this time, R1, R4, R2 and R3 are all directly connected to the pyridine ring in formula (I). Specifically, R1 and R4 can be -NH2, R2 and R3 can be both -CN, or both -NCO, or one is -CN and the other is -NCO; or R2 and R3 can be -NH2, R1 and R4 can be both -CN, or both -NCO, or one is -CN and the other is -NCO.

[0019] In this case, under the premise that the presence of pyridine ring and amino group can ensure the good basicity of additive A, the nitrile group and isocyanate group can also complex the metal ions in the positive electrode material, form a protective film on the surface of the positive electrode, inhibit the interfacial side reaction between the positive electrode material and the electrolyte, inhibit the decomposition of the electrolyte and the dissolution of the positive electrode metal ions; and can reduce the damage to the negative electrode SEI film caused by the deposition of the positive electrode dissolved metal ions to the negative electrode side, thereby better improving the cycle performance and high-temperature storage performance of the battery, etc.

[0020] In the embodiments of the present application, the additive A includes at least one of the following compounds:

[0021]

[0022] Among the above-mentioned substances represented by formula (i-1) to (i-6), the improvement effect on the cycle performance, high-temperature storage performance of the battery containing the above-mentioned electrolyte, the reduction effect on the room temperature impedance of the battery, and the stabilization of the positive electrode interface and the reduction of the dissolution of the positive electrode transition metal element are more obvious than those of the substance represented by formula (i-7), and especially effective in inhibiting the dissolution of vanadium element in the vanadium-containing sodium positive electrode material.

[0023] In the embodiments of the present application, the total content of the above-mentioned additive A in the electrolyte is 0.01wt%-5wt%, for example, specifically 0.02wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt% and the like. The appropriate content of additive A can effectively improve the cycle performance and high-temperature storage performance of the battery containing the above-mentioned electrolyte, while not deteriorating the battery impedance and increasing the adverse reactions such as gas production. In some embodiments, the total content of additive A in the electrolyte is 1wt%-3wt%.

[0024] In some embodiments of the present application, the electrolyte further contains a film-forming additive. The film-forming additive can inhibit the battery electrode material (i.e. positive electrode material, negative electrode material) from falling off from the current collector, and help form a relatively stable electrolyte interface film. Among them, the above-mentioned negative film-forming additive can include one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), 1,3-propane sulfone lactone, sodium difluorophosphate (NaPO2F2), but not limited to this.

[0025] The battery electrolyte contains both the above-mentioned additive A and the film-forming additive. Under the synergistic cooperation of the two, the film composition components of the SEI film (solid electrolyte interface film) on the negative electrode side and the CEI film (cathode electrolyte interface film) on the positive electrode side of the battery are regulated, the high impedance components such as fluoride (such as LiF, NaF) of active ions are reduced, and the stability of the SEI film and the CEI film is further improved, thereby ensuring excellent cycle performance of the battery.

[0026] In embodiments of the present application, the total content of the film-forming additive in the electrolyte is 0.01wt%-7wt%, for example, specifically 0.02wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt%, 5.5wt%, 6.0wt%, 6.5wt%, 6.9wt% and the like. In some embodiments, the total content of the film-forming additive in the electrolyte is 1wt%-7wt%.

[0027] In some embodiments of the present application, the mass ratio of the film-forming additive to the additive A in the electrolyte is 1:(1-6). In this case, the synergistic cooperation between the film-forming additive and the additive A is better, and the improvement effect on the cycle performance, high-temperature storage performance and rate performance of the battery is more obvious. Specifically, the mass ratio can be specifically 1.2, 1.5, 2, 3, 4, 5, 5, 5.5, 6 and the like. In some embodiments, the mass ratio is 1:(1-5), further 1:(1.2-5), or 1:(1.2-3) and the like.

[0028] In embodiments of the present application, the electrolyte salt is a sodium salt or a lithium salt. When the electrolyte salt is a sodium salt, the above-mentioned electrolyte is suitable for sodium ion batteries. When the electrolyte salt is a lithium salt, the above-mentioned electrolyte is suitable for lithium ion batteries.

[0029] In some embodiments, the electrolyte salt is a sodium salt. The sodium salt can include one or more of sodium hexafluorophosphate (NaPF6), sodium difluorophosphate (NaPF2O2), sodium nitrate (NaNO3), sodium perchlorate (NaClO4), sodium bis(oxalato)borate (NaBC4O8), sodium difluoro(oxalato)borate (abbreviated as NaDFOB, with a chemical formula of NaBC2F2O4), sodium bis(trifluoromethylsulfonyl)imide (with a molecular formula of NaN(SO2CF3)2), and sodium bis(fluorosulfonyl)imide (NaN(SO2F)2), and at least includes sodium hexafluorophosphate. The sodium hexafluorophosphate has good thermal stability, high ionic conductivity, and good film-forming effect as an electrolyte sodium salt in a sodium battery electrolyte. The concentration of the sodium hexafluorophosphate in the electrolyte can be 0.6-1.2 mol / L, for example, specifically 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, etc.

[0030] In some other embodiments of the present application, the electrolyte salt is a lithium salt. The lithium salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonate (LiSbF6), lithium perchlorate (LiClO4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(fluorosulfonyl)imide (abbreviated as LiFSI, with a molecular formula of LiN(SO2F)2), lithium bis(trifluoromethylsulfonyl)imide (abbreviated as LiTFSI, with a molecular formula of LiN(SO2CF3)2), lithium bis(perfluoroethylsulfonyl)imide (LiN(C2F5SO2)2), lithium trifluoromethylsulfonate (LiCF3SO3), and lithium perfluorobutylsulfonate (LiC4F9SO3). The content of the lithium salt in the electrolyte is not particularly limited and can be used in a conventional amount in the art. In some embodiments of the present application, the lithium salt includes lithium hexafluorophosphate. The lithium hexafluorophosphate has good thermal stability, high ionic conductivity, and good film-forming effect. The concentration of the lithium hexafluorophosphate in the electrolyte can be 0.6-1.2 mol / L, for example, specifically 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, etc.

[0031] In the embodiments of the present application, the solvent includes a carbonate solvent. The carbonate solvent can include at least one of cyclic carbonate and / or linear carbonate. The cyclic carbonate can include at least one of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, halogenated ethylene carbonate, etc. The linear carbonate can include at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate, etc. In some embodiments, the solvent includes cyclic carbonate and linear carbonate. The combination of the two types of carbonate solvents is conducive to ensuring that the electrolyte has high ionic conductivity, low viscosity, and good solubility of electrolyte. The volume ratio of the cyclic carbonate to the linear carbonate can be (2-8):(4-6). In some embodiments, the solvent includes PC, EMC, and DMC.

[0032] The embodiments of the present application also provide a battery in which the above-mentioned electrolyte of the embodiments of the present application is built-in. The battery containing the above-mentioned electrolyte has good normal-temperature cycle performance, good high-temperature storage performance, and good rate performance.

[0033] Specifically, the battery includes a battery shell, an electrode core accommodated in the battery shell, and the above-mentioned electrolyte of the embodiments of the present application. The electrode core includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet.

[0034] The preparation method of the battery includes: sequentially stacking the positive electrode sheet, the separator, and the negative electrode sheet to form the electrode core, accommodating the electrode core in the battery shell, injecting the above-mentioned electrolyte, and then sealing the battery shell to obtain the battery.

[0035] The negative electrode sheet, the positive electrode sheet, and the separator are all conventional choices in the battery field. The separator can include, but is not limited to, a single-layer PP (polypropylene) film, a single-layer PE (polyethylene) film, a double-layer film PP / PE, a double-layer film PP / PP, a three-layer PP / PE / PP, and other polymer separators, or a non-woven fabric, etc. Generally, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer can include a positive electrode active material, a binder, and an optional conductive agent. Similarly, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector. The negative electrode material layer can include a negative electrode active material, a binder, and an optional conductive agent.

[0036] wherein, for sodium-ion batteries, the negative active material can include, but is not limited to, one or more of soft carbon, hard carbon, sodium titanate, and metals capable of alloying with sodium. The positive active material can include, but is not limited to, one or more of sodium vanadium phosphate (Na3V2(PO4)3), NaFePO4, NaCoPO4, sodium transition metal oxides (such as Na x CoO2, Na x MnO2, NaNi 0.33 Fe 0.33 Mn 0.33 O2, etc.

[0037] The above-mentioned battery can be used in 3C products (such as mobile phones, notebook computers, tablet computers, pen-input computers, e-book players, wearable devices, etc.), electric vehicles (such as electric cars, electric motorcycles, electric bicycles, etc.), and other electrical equipment; and can also be used in energy storage systems.

[0038] The technical solutions of the embodiments of the present application are further described below in multiple embodiments.

[0039] Embodiment 1

[0040] A preparation method of an electrolyte for a sodium-ion battery, comprising: mixing propylene carbonate (PC), methyl ethyl carbonate (EMC), and diethyl carbonate (DMC) in a volume ratio of 25:65:10 to obtain a mixed solvent; then adding a certain amount of sodium hexafluorophosphate (NaPF6) as an electrolyte sodium salt to the mixed solvent, and after the sodium salt is completely dissolved, adding a film-forming additive, vinyl sulfate (DTD), a film-forming additive, fluoroethylene carbonate (FEC), and an additive A as shown in the above formula (i-1), and stirring until all solid substances are completely dissolved to obtain the required electrolyte. In the electrolyte, the concentration of NaPF6 is 0.8 mol / L, the concentration of DTD is 1 wt%, the concentration of FEC is 5 wt%, and the concentration of the additive A as shown in formula (i-1) is 1 wt%.

[0041] A preparation method of a sodium-ion battery, comprising:

[0042] (1) Preparation of a positive electrode sheet: mixing positive active material Na3V2(PO4)3, conductive agent Super p, conductive agent carbon nanotube, and binder PVDF (polyvinylidene fluoride) in a mass ratio of 95:2.3:0.7:2 in a solvent to prepare a positive electrode slurry; coating the positive electrode slurry on both sides of a positive electrode current collector aluminum foil, with a surface density of 30 g / m 2 , and then performing cold pressing after drying at 85℃; then performing edge cutting, sheet cutting, and striping, and then drying at 85℃ for 4 hours under vacuum conditions, and welding the tabs to obtain the positive electrode sheet.

[0043] (2) Preparation of negative electrode sheet: The negative electrode active material—hard carbon, conductive agent Superp, binder CMC, and binder SBR (styrene-butadiene rubber emulsion) are mixed at a mass ratio of 95:1.5:1:2.5 to prepare a negative electrode slurry; the negative electrode slurry is coated on both sides of the positive electrode current collector copper foil, and after drying and rolling, a negative electrode sheet is obtained.

[0044] (3) Assembly of sodium-ion batteries: In a glove box, the positive electrode, separator, and negative electrode are stacked in sequence and wound into a square cell (thickness 4.7 mm, width 55 mm, length 60 mm). The cell is then installed into the battery casing and welded. Subsequently, the cell is vacuum-baked at 75°C for 10 hours to reduce the water content. Afterward, the electrolyte is injected into the battery casing, and the battery casing is sealed to produce a sodium-ion battery. After the battery was left to stand for 24 hours, it was formed and activated. Specifically, it was first charged at a constant current of 0.1C (180mA) to 4.2V, and then charged at a constant voltage of 4.2V until the current dropped to 0.05C (90mA). Then it was discharged at 0.2C (180mA) to 3.0V, and the above charging and discharging was repeated twice. Finally, the battery was charged at 0.2C (180mA) to 3.8V to obtain a battery that can be used for electrochemical performance testing.

[0045] Example 2

[0046] The electrolyte in Example 2 differs from that in Example 1 only in that the concentration of additive A shown in formula (i-1) in the electrolyte is 2 wt%.

[0047] A sodium-ion battery was prepared from the electrolyte of Example 2 according to the method described in Example 1.

[0048] Example 3

[0049] The electrolyte in Example 3 differs from that in Example 1 only in that the concentration of additive A shown in formula (i-1) in the electrolyte is 3 wt%.

[0050] A sodium-ion battery was prepared from the electrolyte of Example 3 according to the method described in Example 1.

[0051] Example 4

[0052] The electrolyte in Example 4 differs from that in Example 1 only in that additive A is the substance shown in formula (i-7), and its concentration in the electrolyte is still 1 wt%.

[0053] A sodium-ion battery was prepared from the electrolyte of Example 4 according to the method described in Example 1.

[0054] Example 5

[0055] The electrolyte of Example 5 differs from that of Example 1 only in that the additive A is a substance represented by formula (i-3), the concentration of which in the electrolyte is still 1 wt%.

[0056] A sodium-ion battery was prepared from the electrolyte of Example 5 according to the method described in Example 1.

[0057] Example 6

[0058] The electrolyte of Example 6 differs from that of Example 1 only in that the additive A is a substance represented by formula (i-2), the concentration of which in the electrolyte is still 1 wt%.

[0059] A sodium-ion battery was prepared from the electrolyte of Example 6 according to the method described in Example 1.

[0060] Example 7

[0061] The electrolyte of Example 7 differs from that of Example 1 only in that the additive A is a substance represented by formula (i-4), the concentration of which in the electrolyte is still 1 wt%.

[0062] A sodium-ion battery was prepared from the electrolyte of Example 7 according to the method described in Example 1.

[0063] Example 8

[0064] The electrolyte of Example 8 differs from that of Example 1 only in that the concentration of the additive A represented by formula (i-1) in the electrolyte is 5 wt%.

[0065] A sodium-ion battery was prepared from the electrolyte of Example 8 according to the method described in Example 1.

[0066] Example 9

[0067] The electrolyte of Example 9 differs from that of Example 1 only in that the concentration of the additive A represented by formula (i-1) in the electrolyte is 0.01 wt%.

[0068] A sodium-ion battery was prepared from the electrolyte of Example 9 according to the method described in Example 1.

[0069] Example 10

[0070] The electrolyte of Example 10 differs from that of Example 3 only in that no film-forming additive is contained in the electrolyte. That is, the content of DTD and FEC in the electrolyte is both 0.

[0071] A sodium-ion battery was prepared from the electrolyte of Example 10 according to the method described in Example 1.

[0072] Example 11

[0073] The electrolyte of Example 11 differs from that of Example 3 only in that the content of the film-forming additive in the electrolyte is changed, wherein the content of DTD is 0.005%, and the content of FEC is 0.005%.

[0074] The electrolyte of Example 11 was prepared into a sodium ion battery according to the method described in Example 1.

[0075] Example 12

[0076] The electrolyte of Example 12 differs from that of Example 3 only in that the content of the film-forming additive in the electrolyte is changed, wherein the content of DTD is 0.5wt%, and the content of FEC is 0.5wt%.

[0077] The electrolyte of Example 12 was prepared into a sodium ion battery according to the method described in Example 1.

[0078] Example 13

[0079] The electrolyte of Example 13 differs from that of Example 3 only in that the composition of the film-forming additive in the electrolyte is changed, specifically the concentration of VC is 2wt%, and the concentration of FEC is 5wt%.

[0080] The electrolyte of Example 13 was prepared into a sodium ion battery according to the method described in Example 1.

[0081] Example 14

[0082] The electrolyte of Example 14 differs from that of Example 3 in that the sodium salt in the electrolyte contains not only NaPF6, but also sodium difluoro(oxalato)borate (abbreviated as NaDFOB), and the concentration of NaDFOB in the electrolyte is 0.2mol / L.

[0083] The electrolyte of Example 14 was prepared into a sodium ion battery according to the method described in Example 1.

[0084] In order to highlight the beneficial effects of the embodiments of the present application, the following Comparative Examples 1-4 are provided.

[0085] Comparative Example 1

[0086] Comparative Example 1 differs from Example 1 in that the electrolyte does not contain the additive A represented by formula (i-1), i.e., the content of the additive A is 0.

[0087] The electrolyte of Comparative Example 1 was prepared into a sodium ion battery according to the method described in Example 1.

[0088] Comparative Example 2

[0089] The electrolyte of Comparative Example 2 differs from that of Example 1 only in that the additive A represented by formula (i-1) in Example 1 is replaced by a 2,6-diaminopyridine additive, which has a concentration of 1 wt% in the electrolyte.

[0090] The electrolyte of Comparative Example 2 was prepared into a sodium-ion battery according to the method described in Example 1.

[0091] Comparative Example 3

[0092] The electrolyte of Comparative Example 3 differs from that of Example 1 only in that the additive A represented by formula (i-1) in Example 1 is replaced by a 2,6-dicyanopyridine additive, which has a concentration of 1 wt% in the electrolyte.

[0093] The electrolyte of Comparative Example 3 was prepared into a sodium-ion battery according to the method described in Example 1.

[0094] Comparative Example 4

[0095] The electrolyte of Comparative Example 4 differs from that of Example 1 only in that the electrolyte does not contain the additive A represented by formula (i-1), nor does it contain the film-forming additives DTD and FEC.

[0096] The sodium-ion batteries of each of the above examples and comparative examples were respectively subjected to the following performance tests:

[0097] a) Battery normal-temperature rated capacity test: at normal temperature (25°C), each sodium battery was charged at 0.33C constant current and constant voltage to an upper limit voltage of 4.5V, and then charged at 4.5V constant voltage to a cutoff current of 0.05C; after standing for 30 min; then discharged at 0.33C constant current to a lower limit voltage of 3.0V, and after standing for 30 min; repeat the above charging and discharging steps 3 times, and record the capacity discharged in the third time as C0, in Ah.

[0098] b) Battery direct current internal resistance (DCIR) test at 25°C: at 25°C, each sodium battery was first charged at 1C constant current to a voltage of 4.5V, and then charged at constant voltage to a cutoff current of 0.05C; then discharged at 1C0 to a battery capacity of 0.5C0 (i.e., the state of charge (SOC) of the battery is adjusted to 50% SOC), and after standing for 10 min, record the battery voltage after standing for 10 min as V1; then discharge the battery at 1.5C0 for 30s, and record the battery voltage after discharging as V2, and calculate the DCIR of the battery. Wherein, DCIR = (V1-V2) / 1.5C0.

[0099] c) Normal temperature cycle performance test: at normal temperature (25 °C), each battery is first charged at 0.5C constant current to 4.5V, then charged at 4.5V constant voltage to the cutoff current of 0.05C; then the battery is discharged at 1C constant current to the cutoff potential of 3V, and the first discharge capacity C1 is recorded. Repeat the above charging and discharging steps for a certain number of cycles until the capacity retention rate of the battery (i.e. the ratio of the discharge capacity after a certain number of cycles to C1) is below 80%, and the cycle number n is recorded as the service life of the battery.

[0100] d) Vanadium (V) element dissolution test: disassemble each battery that reaches the cycle life in step (c) above, take out the negative electrode sheet, soak in a solvent, dry, scrape off the powder, and test the collected powder negative electrode material using an inductively coupled plasma spectrometer (ICP) to measure the vanadium (V) content in the powder material to obtain the vanadium (V) content dissolved from the positive electrode to the negative electrode side.

[0101] e) 60 °C storage for 14 days capacity retention rate test: after each battery is cycled at 25 °C at a rate of 0.33C for 2 times, each battery is charged at 0.33C to full charge state, and then each battery in full charge state is stored at a high temperature environment of 60 °C for 14 days, and then discharged at 25 °C at a rate of 0.33C. The obtained discharge capacity is divided by the above discharge capacity C0 to obtain the discharge capacity retention rate after high temperature storage, to evaluate the high temperature storage performance of the battery.

[0102] f) Rate performance test: at 25 °C, each battery is charged at 0.33C constant current and constant voltage to 4.5V, and then discharged at 4C to the lower limit voltage of 3V to obtain the discharge capacity C 4c , wherein the ratio of the C 4c to the aforementioned C0 is the 4C capacity retention rate of the battery.

[0103] The performance test results of each battery are summarized in Table 1 below.

[0104] Table 1

[0105]

[0106] From the comparison of Examples 1, 4, 5, 6, 7 and Comparative Examples 1-3 in Table 1, it can be seen that in the case of containing the same amount of conventional film-forming additives in the electrolyte, the other additives in the electrolyte are the additives A provided by the present application, which have better improvement effects on the normal temperature cycle performance, high temperature storage performance and normal temperature impedance of sodium batteries than the additives 2,6-dinitrile pyridine and 2,6-dinitrile pyridine used in Comparative Examples 2-3, and they are all better than Comparative Example 1 which does not contain other additives. In addition, Examples 1, 4-7 and Comparative Examples 1-3 are also higher than Comparative Example 4 which does not contain conventional film-forming additives and additive A in the electrolyte.

[0107] In addition, from the comparison between Examples 1, 4, 5, 6, 7, it can be seen that when the content of the additive A is the same but the structural formula is different, the additive A represented by formula (i-7) containing only amino group in the structure has a slightly lower improvement effect on the comprehensive performance of the battery than the additive A containing one of nitrile group and isocyanate group and amino group in the structure (such as formula (i-1) to formula (i-4)).

[0108] From the comparison between Example 10 and Example 3, it can be known that the additive in the electrolyte is only the additive A in the present application, and compared with the electrolyte containing the additive A provided in the present application and the conventional film-forming additive, the improvement effect on the room temperature cycle performance and the high temperature storage performance of the sodium ion battery is reduced to a certain extent, which indicates that the two additives have a certain synergistic effect; but the effect of Example 10 is still obviously better than Comparative Examples 1-3.

[0109] From the comparison between Example 3 and Examples 11, 12, 13, it can be known that when the total additive amount of the conventional film-forming additive in the electrolyte is in the range of 0.01%-7% under the condition that the electrolyte contains the additive A of the present application, the room temperature cycle performance (including room temperature cycle life, vanadium element dissolution amount, etc.) of the battery can be improved.

[0110] From the comparison between Examples 1-3, 8-9, it can be seen that by adjusting the amount of the additive A represented by formula (i-1) in the electrolyte, the room temperature cycle stability, room temperature impedance, rate performance and high temperature storage performance of the battery can be adjusted. Moreover, when the mass ratio of the conventional film-forming additive to the additive A is in the range of 1:(1-6), the synergistic effect between the additive A provided in the present application and the conventional film-forming additive is better, and the improvement effect on the cycle performance, high temperature storage performance and rate performance of the battery is more obvious.

[0111] The above is an exemplary embodiment of the present application, which is described in more detail and in more detail, but it cannot be understood as limiting the scope of the present application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application.

Claims

1. An electrolyte, characterized by, The electrolyte comprises an electrolyte salt, a solvent, and at least one additive A as shown in formula (I): In formula (I), at least one pair of R1 and R4, R2 and R3 contains an amino group, and the other pair contains at least one of an amino group, a nitrile group, and an isocyanate group.

2. The electrolyte of claim 1, wherein One pair of R1 and R4, R2 and R3 is an amino group, and the other pair is at least one of a nitrile group and an isocyanate group.

3. The electrolyte of claim 2, wherein The additive A comprises at least one of the following compounds:

4. The electrolyte of claim 1, wherein The total content of the additive A in the electrolyte is 0.01wt%-5wt%.

5. The electrolyte according to any one of claims 1 to 4, wherein The electrolyte further comprises a film-forming additive; wherein the film-forming additive comprises one or more of fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, vinyl sulfate, 1,3-propane sulfone lactone, and sodium difluorophosphate.

6. The electrolyte of claim 5, wherein The total content of the film-forming additive in the electrolyte is 0.01wt%-7wt%.

7. The electrolyte of claim 5, wherein In the electrolyte, the mass ratio of the film-forming additive to the additive A is 1:(1-6).

8. The electrolyte of any one of claims 1 to 7, wherein The electrolyte salt is a sodium salt or a lithium salt.

9. The electrolyte of claim 8, wherein The sodium salt comprises one or more of sodium hexafluorophosphate, sodium difluorophosphate, sodium nitrate, sodium perchlorate, sodium bisoxalate borate, sodium difluoro oxalate borate, sodium bis-trifluoromethylsulfonylimide, and sodium bis-fluorosulfonylimide, and at least sodium hexafluorophosphate.

10. The electrolyte of claim 8, wherein The sodium salt comprises sodium hexafluorophosphate; the concentration of the sodium hexafluorophosphate in the electrolyte is 0.6mol / L-1.2mol / L.

11. The electrolyte of any one of claims 1 to 10, wherein The solvent comprises a carbonate solvent.

12. A battery, characterized by The battery comprises the electrolyte as claimed in any one of claims 1-11. The battery comprises the electrolyte as claimed in any one of claims 1-11.

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