Nitrile low-temperature electrolyte and secondary battery

Abstract

The invention provides a nitrile low-temperature electrolyte and a secondary battery, and relates to the technical field of secondary batteries. The nitrile low-temperature electrolyte comprises a main lithium salt, a solvent and a functional additive, wherein the functional additive comprises at least one of phosphorus-sulfenyl compounds with the structural formula shown as the following formula: in the # imgabs0 # formula, M is Li or Na, x + y = 6, and n = 0-9. According to the nitrile low-temperature electrolyte, the phosphorus-sulfur compound is added as a functional additive, so that a good passivation effect on an electrode solid electrolyte interface film is realized, an interface film with a fast ion conductor function is generated, the compatibility of the nitrile compound to a negative electrode is improved, and the low-temperature performance and the rate capability of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a nitrile-based low-temperature electrolyte and a secondary battery. Background Art

[0002] Secondary batteries include various types such as lithium-ion batteries and sodium-ion batteries. Among them, lithium-ion batteries are extremely widely used. Currently, they are commonly used in various portable devices, such as mobile phones, tablet computers, digital cameras, etc., and have also been widely used in fields such as electric vehicles and aerospace. They have advantages such as high energy density and long cycle life. However, in a low-temperature environment, the electrolyte of lithium-ion batteries will solidify, the charge and discharge performance will be greatly reduced, the internal polarization of the battery will be serious, and there is a risk of internal short circuit and explosion. Therefore, the low-temperature performance is a bottleneck problem that plagues and restricts the continuous development of lithium-ion batteries.

[0003] Currently, commercial electrolytes are generally carbonate electrolyte systems composed of LiPF6 and mixed carbonate solvents. The carbonate solvents are mostly mixed solvents composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). These solvents have relatively high melting points and large viscosities under low-temperature conditions, which in turn leads to a decrease in conductivity and a sharp reduction in the discharge capacity of the battery. However, the traditional carbonate electrolyte system has a large viscosity, a relatively high desolvation energy, and poor ion-conducting ability for forming the electrode interface film. These three factors severely limit the improvement of the low-temperature performance of the existing electrolyte system. Chinese Patent with Application No. CN202411698029.1 discloses a low-temperature electrolyte for lithium batteries and a lithium battery. It introduces a compound containing amino-nitrile in the electrolyte system. This type of compound can preferentially decompose and passivate the negative electrode on the negative electrode side, and the generated LiN3 has a relatively low ion-passing impedance, improving the low-temperature performance of the battery; this nitrogen-containing compound can decompose on the surface of the negative electrode to form LiN3, but this type of compound is a neutral compound, and a large amount of lithium ions are consumed for the decomposition of LiN3 on the negative electrode side, seriously reducing the first-cycle Coulomb efficiency. Chinese Patent with Application No. CN202111199766.3 discloses a low-temperature electrolyte for lithium batteries and a lithium battery; this patent slows down the attenuation of the battery capacity at low temperature by improving the salt dissociation degree, lithium-ion migration rate, low-temperature ionic conductivity, and low-impedance solid electrolyte interface film; this technology has indeed achieved excellent results in improving the discharge capacity, but there are also certain shortcomings. For example, this technology mainly improves the discharge performance at low temperature, rather than charging in a low-temperature environment, while the actual operating scenario of lithium batteries is long-cycle charging and discharging cycles at low temperature.

[0004] Nitrile compounds have a relatively low desolvation energy and show potential for developing low-temperature electrolytes. However, nitrile solvents have poor resistance to reduction, and it is difficult to form a good interfacial film with the negative electrode, resulting in poor compatibility with the negative electrode, which limits their application in lithium battery electrolytes. Therefore, it is of great significance to develop a lithium-ion battery electrolyte that can operate at low temperatures and cover the entire high-low temperature range (-30°C to 80°C). Summary of the Invention

[0005] The object of the present invention is to provide a nitrile-based low-temperature electrolyte and a secondary battery in view of the deficiencies of the prior art. A nitrile compound is introduced into the electrolyte of the present invention, which improves the overall ionic conductivity of the electrolyte. A new type of phosphorus-sulfur-based functional additive is introduced, and this type of additive can form a solid electrolyte interface film (SEI) rich in phosphorus-sulfur-fluorine species on the negative electrode of the battery, effectively isolating the contact between the nitrile and the negative electrode active material, improving the compatibility of the nitrile-based electrolyte with the negative electrode, and solving the problem of poor low-temperature performance of the existing electrolyte system.

[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] On the one hand, a nitrile-based low-temperature electrolyte, comprising a main lithium salt, a solvent, and a functional additive;

[0008] Among them, the functional additive comprises at least one of phosphorus-sulfur-based compounds represented by the structural formula (I):

[0009]

[0010] In formula (I), M is Li or Na, x + y = 6, and n = 0 to 9.

[0011] Preferably, the phosphorus-sulfur-based compound is selected from at least one of the following compounds:

[0012]

[0013]

[0014] Among them, M is Li or Na.

[0015] Furthermore, the functional additive further comprises other functional additives, and the other functional additives are selected from any one or a combination of phosphates, borates, nitrates, sulfonimide salts, carbonates, phosphates, sulfates, sulfone ethers and sulfoxides, inorganic lithium compounds.

[0016] Preferably, the other functional additives are selected from any one or a combination of lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, bis(oxalato)phosphate lithium, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium fluoroalkoxytrifluorophosphate, lithium bis(fluorosulfonyl)imide, fluoroethylene carbonate, vinylene carbonate, 1,3 - propanesultone, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, dimethyl sulfoxide, dimethyl sulfonate, lithium fluoride, lithium oxide, lithium nitride, lithium carbonate, lithium nitrate.

[0017] Preferably, the functional additive is a combination of a phosphorus - sulfur - based compound and other functional additives, and the mass ratio of the phosphorus - sulfur - based compound to the other functional additives is 1:(0.3 - 2), more preferably 1:1.5.

[0018] Further, the functional additive accounts for 0.1% - 5% of the total mass of the nitrile - based low - temperature electrolyte.

[0019] Further, the main lithium salt is selected from any one or a combination of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluorophosphate, lithium difluoro(oxalato)phosphate; preferably a combination of any one or more of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0020] Further, the concentration of the main lithium salt in the nitrile - based low - temperature electrolyte is 0.8 mol / L - 8 mol / L.

[0021] Further, the solvent comprises any one or a combination of nitrile solvents represented by the structural formula as shown in formula (II):

[0022]

[0023] In formula (II), n = 0 - 8, and R1, R2, and R3 are each independently selected from a hydrogen atom, a cyano group, or an alkyl group having 1 - 8 carbon atoms.

[0024] Preferably, the nitrile solvent is selected from any one or a combination of acetonitrile, propionitrile, isobutyronitrile, trimethylacetonitrile, butyronitrile, succinonitrile, valeronitrile, adiponitrile, 2 - methylmalononitrile.

[0025] Further, the solvent further comprises other solvents, and the other solvents are selected from any one or a combination of carbonate esters, γ - butyrolactone, sulfolane, organic acid esters having 1 - 4 carbon atoms.

[0026] Preferably, the other solvent is selected from any one or a combination of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, methyl trifluoroethyl carbonate, γ-butyrolactone, sulfolane, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0027] More preferably, the other solvent is selected from any one or a combination of propylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, methyl trifluoroethyl carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, methyl acetate, methyl propionate, and γ-butyrolactone.

[0028] Further, the solvent is a combination of a nitrile solvent having the structural formula shown in Formula (II) and another solvent, and the volume ratio of the two is (10 - 60):(30 - 90).

[0029] Further, the total volume of the solvent is 10 - 99% of the total volume of the nitrile-based low-temperature electrolyte.

[0030] On the other hand, the method for preparing the above-mentioned nitrile-based low-temperature electrolyte includes the following steps:

[0031] Mix the first solvent and the second solvent, add the main lithium salt and mix well, then add the functional additive, and stir until clear to obtain the electrolyte.

[0032] On yet another hand, the application of the above-mentioned nitrile-based low-temperature electrolyte in secondary batteries.

[0033] On yet another hand, a secondary battery includes a positive electrode active material, a negative electrode active material, a separator, and the above-mentioned nitrile-based low-temperature electrolyte.

[0034] Further, the positive electrode active material is a conventional positive electrode active material in the art without special limitations. For example, it can be any one or a combination of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt phosphate, lithium cobalt oxide, lithium-rich manganese-based, lithium nickel manganese cobalt oxide, and lithium nickel manganese oxide.

[0035] Further, the negative electrode active material is a conventional negative electrode active material in the art without special limitations. For example, it can be any one or a combination of metallic lithium, graphite, hard carbon, silicon carbon, tin-based, and carbon materials.

[0036] Further, the separator is a conventional separator material in the art without special limitations. For example, it can be any one of a cellulose separator, a high-porosity polyethylene separator, a high-porosity polypropylene separator, a glass fiber separator, a polyimide separator, a PEEK separator, a polyolefin non-woven separator, a PVDF separator, and a ceramic particle composite non-woven separator.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. In the nitrile-based low-temperature electrolyte of the present invention, the components interact with each other, solving the compatibility problem of nitrile compounds with the negative electrode, breaking through the barrier that restricts the low-temperature performance of the existing electrolyte system, having excellent low-temperature charging performance, and excellent long-cycle performance.

[0039] 2. In the nitrile-based low-temperature electrolyte of the present invention, by adding a phosphorus-sulfur-based compound as a functional additive, a good passivation effect on the solid electrolyte interface film (SEI) of the electrode is achieved, generating an interface film with fast ion conductor function, improving the compatibility of nitrile compounds with the negative electrode, and improving the low-temperature performance of the battery; using the phosphorus-sulfur-based compound in combination with other functional additives helps to further improve the low-temperature performance of the battery and can also improve its high-temperature performance and long-cycle performance.

[0040] 3. In the nitrile-based low-temperature electrolyte of the present invention, by adding other additives and cooperating with the functional additives, the organic and inorganic components in the SEI film are effectively regulated, the Young's modulus of the SEI film is increased, and an SEI film that is not easily broken during the cycle, has fast desolvation, and conducts ions is formed, improving the low-temperature performance of the battery. Description of the Drawings

[0041] Figure 1 is the long-cycle performance test of the Li / / Gr half-cell assembled in Example 1;

[0042] Figure 2 is the long-cycle performance test of the NCM811 / / Gr full-cell assembled in Example 2 at 25 °C;

[0043] Figure 3 is the long-cycle performance test of the NCM811 / / Gr full-cell assembled in Example 5 at -30 °C;

[0044] Figure 4 is the long-cycle performance test of the NCM811 / / Gr full-cell assembled in Example 6 at a high temperature of 80 °C. Detailed Embodiments

[0045] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way. The following content is merely an exemplary illustration of the scope claimed by the present invention. Those skilled in the art can make various changes and modifications to the invention of the present invention based on the disclosed content, and it should also fall within the scope claimed by the present invention.

[0046] In a specific embodiment of the present invention, the phosphorus-sulfur-based compound is prepared by the following method:

[0047] Dissolve lithium hexafluorophosphate and TMS fluorosulfonate in a solvent, react at 100 °C for 24 h, perform hot filtration and then add a poor solvent for recrystallization to finally obtain a white solid target product. The solvent and poor solvent used therein are all conventional selections in the art and are not particularly limited. The specific reaction formula of the phosphorus-sulfur-based compound is as follows:

[0048]

[0049] The present invention will be further described below by way of specific examples. All chemical reagents used in the examples of the present invention are obtained through conventional commercial channels unless otherwise specified.

[0050] Example 1

[0051] Mix propylene carbonate, diethyl carbonate and acetonitrile (a nitrile solvent) in a volume ratio of 1:7:2 and stir evenly. Add 2.06 g of lithium bis(fluorosulfonyl)imide to 10 mL of the above solvent at a concentration of 1.1 mol / L, and then add functional additive compound 1 (the addition amount of compound 1 is 1.5% of the total mass of the electrolyte), and stir the electrolyte until it is clear to obtain an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0052] Among them, the structural formula of compound 1 is:

[0053] Assemble the above electrolyte into a Li / / graphite half-cell (Li / / Gr half-cell) and perform a negative electrode compatibility test in a voltage range of 0 - 2 V and a rate of 0.1C / 0.1C. Figure 1 The specific capacity-voltage curve of the electrolyte prepared for Example 1 in the Li / / graphite half-cell, where the graphite electrode surface loading is 5.8 mg cm -2 . From Figure 1 It can be seen that this electrolyte system can cycle normally, the electrolyte has good compatibility with the negative electrode, and no common decomposition phenomenon of nitrile electrolytes occurs.

[0054] Example 2

[0055] Mix other solvents propylene carbonate, diethyl carbonate and nitrile solvent acetonitrile in a volume ratio of 1:7:2 and stir evenly. Add 2.06 g of lithium bis(fluorosulfonyl)imide into 10 mL of the above solvents at a concentration of 1.1 mol / L, then add functional additive compound 2 (the addition amount of compound 2 is 1% of the total mass of the electrolyte), and stir the electrolyte until it is clear to obtain an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0056] Among them, the structural formula of compound 2 is:

[0057] Assemble a LiNi 0.8 Co 0.1 Mn 0.1 / / graphite full cell (NCM811 / / Gr full cell), and perform long-cycle performance tests with a charge-discharge tester in a voltage range of 3 - 4.3 V, a rate of 1C / 1C, and a test temperature of 25 °C. Figure 2 The electrolyte prepared in Example 2 in the LiNi 0.8 Co 0.1 Mn 0.1 / / graphite full cell. The long-cycle results at a temperature of 25 °C and a positive electrode active material loading of 19.8 mg cm -2 . From Figure 2 it can be seen that the electrolyte has excellent long-cycle performance, good compatibility with the positive and negative electrodes, and no common decomposition phenomenon of nitrile electrolytes occurs.

[0058] Example 3

[0059] Mix other solvents propylene carbonate, methyl trifluoroethyl carbonate and nitrile solvent propionitrile in a volume ratio of 1:8:1 and stir evenly. Add 2.06 g of lithium bis(fluorosulfonyl)imide into 10 mL of the above solvents at a concentration of 1.1 mol / L, then add functional additive compound 3 (the addition amount of compound 3 is 0.1% of the total mass of the electrolyte), and stir the electrolyte until it is clear to form an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0060] Among them, the structural formula of compound 3 is:

[0061] Example 4

[0062] The difference from Example 1 is that the functional additive is replaced with an equal amount of compound 4, and the structural formula of compound 4 is as follows:

[0063]

[0064] Example 5

[0065] Mix other solvents propylene carbonate, diethyl carbonate and nitrile solvent acetonitrile in a volume ratio of 1:7:2 and stir evenly. Add 2.06 g of lithium bis(fluorosulfonyl)imide to 10 mL of the above solvent at a concentration of 1.1 mol / L; then add compound 2 and vinylene carbonate with a mass ratio of 1.5:1 (the total addition amount of vinylene carbonate and compound 2 is 1% of the total mass of the electrolyte) as functional additives, and stir the electrolyte until it is clear to form an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0066] Use the above electrolyte to assemble a LiNi 0.8 Co 0.1 Mn 0.1 / / graphite full cell (NCM811 / / Gr full cell), and conduct long-cycle performance tests on a charge-discharge tester, with a voltage range of 3 - 4.3 V, a rate of 0.3C / 0.3C, and a test temperature of -30°C. Figure 3 The long-cycle results of the NCM811 / / Gr full cell assembled for this example, with a positive electrode active material loading of 19.8 mg cm -2 . From Figure 3 It can be seen that this electrolyte system has excellent low-temperature long-cycle performance.

[0067] Example 6

[0068] Mix other solvents propylene carbonate, methyl trifluoroethyl carbonate and nitrile solvent acetonitrile in a volume ratio of 1:7:2 and stir evenly. Add 2.06 g of lithium bis(fluorosulfonyl)imide to 10 mL of the above solvent at a concentration of 1.1 mol / L; then add compound 2 and vinylene carbonate with a mass ratio of 1.5:1 (the total addition amount of vinylene carbonate and compound 2 is 1% of the total mass of the electrolyte) as functional additives, and stir the electrolyte until it is clear to form an electrolyte with a lithium salt concentration of 1.1 mol / L.

[0069] Use the above electrolyte to assemble a LiNi 0.8 Co 0.1 Mn 0.1 / / graphite full cell and conduct tests. Conduct long-cycle performance tests on a charge-discharge tester, with a voltage range of 3 - 4.3 V, a rate of 1C / 1C, and a test temperature of 80°C. Figure 4 The long-cycle results of the electrolyte prepared in Example 4 in LiNi 0.8 Co 0.1 Mn 0.1 / / graphite full cell, with a positive electrode active material loading of 19.8 mg cm -2 . From Figure 4 It can be seen that this electrolyte system has excellent high-temperature long-cycle performance.

[0070] Example 7

[0071] The difference from Example 5 is that the functional additive is Compound 2 and vinylene carbonate with a mass ratio of 1:2, and the total amount of the functional additive remains unchanged.

[0072] Example 8

[0073] The difference from Example 5 is that the functional additive is Compound 2 and vinylene carbonate with a mass ratio of 1:0.3, and the total amount of the functional additive remains unchanged.

[0074] Example 9

[0075] The difference from Example 5 is that the functional additive is Compound 2 and vinylene carbonate with a mass ratio of 1:0.1, and the total amount of the functional additive remains unchanged.

[0076] Example 10

[0077] The difference from Example 5 is that the functional additive is Compound 2 and vinylene carbonate with a mass ratio of 1:3, and the total amount of the functional additive remains unchanged.

[0078] Example 11

[0079] The difference from Example 5 is that the functional additive is only vinylene carbonate, and the addition amount of vinylene carbonate is 1% of the total mass of the electrolyte.

[0080] Example 12

[0081] The difference from Example 5 is that the solvent is propylene carbonate, diethyl carbonate and acetonitrile with a volume ratio of 1:8.5:0.5, and the total amount remains unchanged.

[0082] Example 13

[0083] The difference from Example 5 is that the solvent is propylene carbonate, diethyl carbonate and acetonitrile with a volume ratio of 1:2:7, and the total amount remains unchanged.

[0084] Example 14

[0085] The difference from Example 5 is that the solvent is only acetonitrile, and the total amount remains unchanged.

[0086] Example 15

[0087] The difference from Example 5 is that the solvent is only propylene carbonate and diethyl carbonate with a volume ratio of 1:7, and the total amount remains unchanged.

[0088] Test Example

[0089] The batteries assembled in the above Examples and Comparative Examples were subjected to long cycle performance tests on a charge-discharge tester in a voltage range of 3.0 - 4.2V, and the charge / discharge rate was 1C for both. The results are shown in Table 1 below:

[0090] Table 1 Capacity retention rate after 100 cycles

[0091]

[0092]

[0093] The results show that in Example 11, only vinylene carbonate, another functional additive, was added. The battery assembled with it had a low capacity retention rate after 100 cycles at low and high temperatures, and poor long-cycle performance at low and high temperatures. Compared with Example 11, in Examples 1-4, a phosphorus-sulfur-based compound was added, and its capacity retention rate after 100 cycles at low and high temperatures was increased to over 90%, making up for the defect of poor long-cycle performance of conventional functional additives at low and high temperatures. Compared with Examples 1-4, in Examples 5-8, the capacity retention rate after 100 cycles at low and high temperatures was further increased, indicating that there is a certain synergistic effect between the phosphorus-sulfur-based compound and vinylene carbonate. As functional additives together, they help to significantly improve the long-cycle performance and low-temperature and high-temperature resistance of the battery.

[0094] It can also be seen that in Example 14, only another solvent was added, and its low-temperature long-cycle performance was significantly lower than that of Example 5, with poor low-temperature performance. In Example 13, acetonitrile was used as the solvent, and its capacity retention rate after 100 cycles at low temperature was over 90%, showing better low-temperature resistance than Example 14. However, the capacity retention rate after 100 cycles at 80 °C was significantly lower than that of Example 5. It can be seen that using only acetonitrile as the solvent can improve the low-temperature resistance of the electrolyte, but has no effect on the high-temperature performance. When acetonitrile is used in combination with other solvents, there is a certain synergistic effect, which helps to improve the high-temperature performance of the electrolyte.

[0095] In the examples of this application, only several types of phosphorus-sulfur-based compounds are exemplified. It can be understood that as long as all phosphorus-sulfur-based compounds satisfy their structural general formula, they can achieve the technical effects of this application, break through the barrier of the existing electrolyte system that limits low-temperature performance, improve low-temperature charging performance, and improve high-temperature long-cycle performance. However, since there are many phosphorus-sulfur-based compounds that satisfy the shown structure, this application does not list them one by one. Those skilled in the art can infer that the compounds with the above structure can all achieve the above effects on the basis of clarifying the technical concept of this application, so as to achieve the above effects. In addition, for other materials in the electrolyte such as solvents and functional additives, no matter which one or several of them are used, they can achieve the effects of this application. There are many types of them, and this application does not list them one by one either. Although only several of them are exemplified in the above examples, it does not constitute a limitation to this application.

[0096] The above description of the embodiments is provided to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those who are familiar with the technology in this field can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A nitrile-based low-temperature electrolyte, characterized in that, It contains a main lithium salt, a solvent and a functional additive; wherein, the functional additive contains at least one of phosphorus-sulfur compounds with a structural formula as shown in formula (I): In formula (I), M is Li or Na, x + y = 6, and n = 0-9.

2. The nitrile-based low-temperature electrolyte according to claim 1, wherein The functional additive is selected from any one of the following compounds: Wherein, M is Li or Na.

3. The nitrile-based low-temperature electrolyte according to claim 2, wherein The functional additive further contains other functional additives, and the other functional additives are selected from any one or a combination of phosphates, borates, nitrates, sulfonimide salts, carbonates, phosphates, sulfates, sulfone ethers and sulfoxides, inorganic lithium compounds.

4. The nitrile-based low-temperature electrolyte according to claim 3, wherein The functional additive is a combination of a phosphorus-sulfur compound and other functional additives, and the mass ratio of the two is 1:(0.3-2); the total amount of the functional additive is 0.1%-5% of the total mass of the nitrile-based low-temperature electrolyte.

5. The nitrile-based low-temperature electrolyte according to claim 1, characterized in that, The main lithium salt is selected from any one or a combination of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluorophosphate, lithium difluorooxalate phosphate.

6. The nitrile-based low-temperature electrolyte according to claim 1, characterized in that, The solvent contains any one or a combination of nitrile solvents with a structural formula as shown in formula (II): In formula (II), n = 0-8, and R1, R2, and R3 are each independently selected from a hydrogen atom, a cyano group, or an alkyl group with 1-8 carbon atoms; Preferably, the nitrile solvent is selected from any one or a combination of acetonitrile, propionitrile, isobutyronitrile, trimethylacetonitrile, butyronitrile, succinonitrile, valeronitrile, adiponitrile, 2-methylmalononitrile.

7. The nitrile-based low-temperature electrolyte according to claim 6, wherein The other solvent is selected from any one or a combination of carbonates, γ-butyrolactone, sulfolane, organic acid esters with 1-4 carbon atoms.

8. The nitrile-based low-temperature electrolyte according to claim 6 or 7, characterized in that, The solvent is a combination of a nitrile solvent with a structural formula as shown in formula (II) and other solvents, and the volume ratio of the two is (10-60):(30-90); the total volume of the solvent is 10-99% of the total volume of the nitrile-based low-temperature electrolyte.

9. Application of the nitrile-based low-temperature electrolyte according to any one of claims 1-8 in a secondary battery.

10. A secondary battery, characterized in that, It includes a positive electrode active material, a negative electrode active material, a separator, and the nitrile-based low-temperature electrolyte according to any one of claims 1-8.

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