Lithium battery

Abstract

The application provides an electrolyte, a preparation method thereof, a lithium battery and application. According to mass percentage, the electrolyte comprises 16.5-21% of lithium hexafluorophosphate, 0.5-2% of lithium difluoro(oxalato)borate, 0.1-2% of sodium hexafluorophosphate and 1-2% of a pyrrole ionic liquid, and the balance is a solvent. The compatibility of the electrolyte with lithium metal is improved. When the electrolyte is applied to the lithium battery, the phenomenon of gas expansion and uneven deposition can be improved, and the cycle performance and safety performance of the lithium battery are improved.

Description

[0001] The application is a divisional application, the original application number of which is: 202410548491.7, the application date of which is May 6, 2024, and the invention name of which is: electrolyte and preparation method thereof, lithium battery and application. TECHNICAL FIELD

[0002] The application relates to the technical field of electrolytes, in particular to an electrolyte and a preparation method thereof, a lithium battery and application. BACKGROUND

[0003] With the continuous development of portable electronic devices, electric vehicles and large-scale energy storage markets, the demand for lithium batteries also continues to grow. After years of development, lithium batteries have made great progress in performance indicators and have shown great application development potential, but there are still deficiencies in related technologies.

[0004] Taking a traditional carbonate system electrolyte containing lithium hexafluorophosphate as an example, the traditional carbonate system electrolyte has the problem of poor interface stability, and phenomena such as gas generation and uneven deposition based on the reaction between the electrolyte and lithium metal can cause the cycle performance of the lithium battery to decline, increasing the risk of swelling, explosion and other accidents, thereby limiting the large-scale application of lithium batteries in the field of power batteries. SUMMARY

[0005] The application provides an electrolyte and a preparation method thereof, a lithium battery and application.

[0006] In a first aspect, the application provides an electrolyte, which comprises, calculated in percentage by mass, 16.5-21% of lithium hexafluorophosphate, 0.5-2% of lithium difluoro(oxalato)borate, 0.1-2% of sodium hexafluorophosphate and 1-2% of a pyrrole ionic liquid, and the balance is a solvent.

[0007] The pyrrole ionic liquid has the structure shown in the following general formula (I):

[0008]

[0009] In the general formula (I), R1 and R2 are each independently selected from C1-C30 alkyl.

[0010] In a second aspect, the application provides a preparation method of an electrolyte for preparing the electrolyte as described in the first aspect, which comprises the step of mixing lithium hexafluorophosphate, lithium difluoro(oxalato)borate, sodium hexafluorophosphate, a pyrrole ionic liquid and a solvent according to the ratio to obtain the electrolyte.

[0011] In a third aspect, the application provides an electrolyte, which is the electrolyte according to the first aspect, or the electrolyte prepared by the preparation method of the electrolyte according to the second aspect.

[0012] In a fourth aspect, the application provides a lithium battery, which comprises a positive electrode, a negative electrode and a separator, and further comprises the electrolyte according to the first aspect.

[0013] Advantages:

[0014] The embodiments of the application improve the compatibility of the electrolyte with lithium metal by compounding lithium hexafluorophosphate, lithium difluoro(oxalato)borate, sodium hexafluorophosphate, a pyrrole ionic liquid and a solvent in a specific ratio, and the application of the electrolyte in a lithium battery can improve the phenomena of gas expansion and uneven deposition, and is beneficial to improving the cycle performance and safety performance of the lithium battery. BRIEF DESCRIPTION OF DRAWINGS

[0015] The technical solutions and other advantages of the application will be apparent from the following detailed description of the embodiments of the application, taken in conjunction with the accompanying drawings.

[0016] Figure 1 Figure 4 is a micrograph of the negative electrode of the lithium battery in Example 1 of the application after failure.

[0017] Figure 2 Figure 5 is a micrograph of the negative electrode of the lithium battery in Comparative Example 1 of the application after failure. DETAILED DESCRIPTION

[0018] The technical solutions and other advantages of the application will be apparent from the following detailed description of the embodiments of the application, taken in conjunction with the accompanying drawings.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art. In addition, all methods and materials similar or equivalent to those described herein can be used in the practice of the present application. The preferred methods and materials are presented by way of example only and not by way of limitation, as any method and material similar or equivalent to those described herein can be used in the practice or testing of the present application.

[0020] It should be noted that the sequence of the following embodiments is not limited as the preferred sequence of the embodiments, and various embodiments of the present application can exist in a range of forms, and it should be understood that the description in a range of forms is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values in the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers in the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) in the indicated range.

[0021] In the present application, the term "comprising" means "including but not limited to".

[0022] In the present application, the term "and / or" is used to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural.

[0023] In the present application, the term "at least one" means one or more, and "more" means two or more. The term "at least one", "at least one of the following" or similar expressions means any combination of these items, including any combination of single or multiple. For example, "at least one of a, b or c" or "at least one of a, b and c" can be expressed as a, b, c, a-b (i.e. a and b), a-c, b-c or a-b-c, wherein a, b and c can be single or multiple.

[0024] The embodiment of the present application provides a kind of electrolyte, according to mass percentage calculation, electrolyte includes 16.5%~21% lithium hexafluorophosphate, 0.5%~2% lithium difluorophosphate oxalate, 0.1%~2% sodium hexafluorophosphate and 1%~2% pyrrole ionic liquid, the rest is solvent;Wherein, pyrrole ionic liquid has the structure shown in the following general formula (I):

[0025]

[0026] In general formula (I), R11 and R2 are each independently selected from C1-C30 alkyl, and R1 and R2 are each independently selected from C1-C3 alkyl, C1-C5 alkyl, C1-C8 alkyl, C1-C10 alkyl, C1-C15 alkyl, or C1-C20 alkyl, for example.

[0027] In the electrolyte of the present embodiment, by compounding lithium hexafluorophosphate, lithium difluoro(oxalato)borate, sodium hexafluorophosphate, a pyrrolidinium ionic liquid, and a solvent in a specific ratio, the compatibility of the electrolyte with lithium metal is improved, and when the electrolyte is applied to a lithium battery, the phenomena of gas evolution and uneven deposition are improved, and the cycle performance and safety performance of the lithium battery are improved.

[0028] In the electrolyte, the pyrrolidinium ion in the pyrrolidinium ionic liquid can be reduced in preference to lithium ions, thereby reducing the ability of lithium dendrite growth and improving the uniformity of lithium deposition. The mass percentage of the pyrrolidinium ionic liquid may, for example, be 1%, 1.2%, 1.5%, 1.8%, 2%, or a value between any two of the foregoing, improving the uniformity of lithium deposition while avoiding a sharp increase in the viscosity of the electrolyte, and ensuring that the lithium battery to which the electrolyte is applied has good rate performance, cycle performance, and low-temperature performance.

[0029] To further improve the cycle performance of the lithium battery to which the electrolyte is applied, in some embodiments of the present application, the pyrrolidinium ionic liquid is selected from one or more of N-butyl-N-methylpyrrolidinium hexafluorophosphate (CAS No. 330671-29-9), N-propyl-N-methylpyrrolidinium hexafluorophosphate (CAS No. 327022-58-2), and N-ethyl-N-methylpyrrolidinium hexafluorophosphate (CAS No. 121057-90-7).

[0030] It should be noted that the applicant has found that if the pyrrolidinium ionic liquid in the electrolyte is replaced by an imidazolium ionic liquid and the mass percentage remains the same, the cycle performance of the lithium battery will decrease, and if a comparable cycle performance is to be obtained, the amount of the imidazolium ionic liquid needs to be increased, which increases the production cost.

[0031] The mass percentage of lithium hexafluorophosphate in the electrolyte may be, for example, 16.5%, 18%, 19%, 20%, 21%, or a value between any two of the foregoing; the mass percentage of lithium difluoro(oxalato)borate may be, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a value between any two of the foregoing; and the mass percentage of sodium hexafluorophosphate may be, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, or a value between any two of the foregoing.

[0032] The mass percentage of lithium hexafluorophosphate in the electrolyte is 16.5%-21%, which can make the viscosity of the electrolyte appropriate, and the electrolyte has good stability, and the lithium battery using the electrolyte has good rate performance, cycle performance, and low-temperature performance, ensuring that the "inflection point" of the lithium battery degradation trajectory is at a suitable time point. If the mass percentage of lithium hexafluorophosphate is too high, the viscosity of the electrolyte will increase, and the rate performance, cycle performance, and low-temperature performance of the lithium battery using the electrolyte will decrease; if the mass percentage of lithium hexafluorophosphate is too low, the stability of the electrolyte will decrease, and the "inflection point" of the lithium battery degradation trajectory will be advanced.

[0033] In the electrolyte, sodium hexafluorophosphate is used to introduce sodium ions to stabilize lithium metal, i.e., because the original potential of sodium ions is higher than that of lithium ions, during the formation of the solid electrolyte interface (SEI) of the lithium battery, sodium ions are more easily reduced to form a precipitate, and the potential difference can guide sodium ions and lithium ions to spontaneously occupy different regions, thereby forming a SEI layer with higher uniformity and higher density. Too much or too little sodium hexafluorophosphate in the electrolyte will cause the cycle performance of the lithium battery to decrease.

[0034] In the electrolyte, too much or too little lithium difluoro(oxalato)borate will cause the cycle performance of the lithium battery to decrease. Too much lithium difluoro(oxalato)borate will cause the capacity of the lithium battery to decrease, thereby degrading the cycle performance; too little lithium difluoro(oxalato)borate will degrade the cycle performance of the electrolyte and accelerate the drying of the electrolyte.

[0035] In some embodiments of the present application, the molar ratio of lithium hexafluorophosphate to sodium hexafluorophosphate in the electrolyte is 1:(0.02-0.05), which can be 1:0.02, 1:0.03, 1:0.04, 1:0.05, or a value between any two of the foregoing values; and / or, the molar ratio of lithium hexafluorophosphate to lithium difluoro(oxalato)borate is 1:(0.023-0.056), which can be 1:0.023, 1:0.03, 1:0.04, 1:0.05, 1:0.056, or a value between any two of the foregoing values. By reasonably adjusting the ratio among lithium hexafluorophosphate, sodium hexafluorophosphate, and lithium difluoro(oxalato)borate, the loss of lithium hexafluorophosphate during the operation of the lithium battery can be reduced, which is conducive to improving the stability of the SEI layer, thereby further improving the cycle performance of the lithium battery.

[0036] In some embodiments of the present application, the solvent is selected from one or more of vinyl carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, butylene carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, fluoroethylene carbonate, and diethyl carbonate.

[0037] In order to further improve the compatibility of the electrolyte with lithium metal, thereby further improving the cycle performance of the lithium battery using the electrolyte, in some embodiments of the present application, the solvent is composed of vinyl carbonate, diethyl carbonate, dimethyl carbonate, and fluoroethylene carbonate.

[0038] It should be noted that the applicant found that if the vinyl carbonate in the solvent is replaced with propylene carbonate, and the mass percentages of each component in the solvent remain the same, the improvement in the cycle performance of the lithium battery using the electrolyte is limited.

[0039] Further, in some embodiments of the present application, in the solvent, the volume ratio of vinyl carbonate, diethyl carbonate, and dimethyl carbonate is 1:(2-3):(1-2).

[0040] Further, in some embodiments of the present application, the mass percentage of fluoroethylene carbonate in the total mass of the electrolyte is 10%-15%, which can be 10%, 11%, 12%, 13%, 14%, 15%, or a value between any two of the foregoing values. Fluoroethylene carbonate not only can act as a solvent, but also can act as a film-forming aid. Fluoroethylene carbonate can participate in the construction of SEI, reduce the side reaction between the electrolyte and lithium metal, and thereby improve the cycle performance of the lithium battery. If the addition amount of fluoroethylene carbonate is too much, serious gas production will occur, leading to non-uniformity of lithium migration and deposition, thereby reducing the cycle performance of the lithium battery; if the addition amount of fluoroethylene carbonate is too little, the stabilizing effect on SEI is limited.

[0041] The application further provides a preparation method of the electrolyte, which can be used to prepare any of the electrolytes described above, and comprises the following steps: mixing lithium hexafluorophosphate, lithium difluoro(oxalato)borate, sodium hexafluorophosphate, a pyrrole ionic liquid and a solvent according to a proportion to obtain the electrolyte.

[0042] To further improve the stability of the electrolyte and further improve the cycle performance of the lithium battery, in some embodiments of the application, the mixing of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, sodium hexafluorophosphate, the pyrrole ionic liquid and the solvent according to a proportion comprises the following steps: providing a solvent at room temperature, adding lithium hexafluorophosphate, lithium difluoro(oxalato)borate, sodium hexafluorophosphate and the pyrrole ionic liquid into the solvent, and mixing at room temperature. The mixing mode includes but is not limited to stirring, and the room temperature is, for example, 20-25℃.

[0043] The application further provides an application of the electrolyte, which is the electrolyte described above or prepared by the preparation method of the electrolyte described above.

[0044] The application further provides a lithium battery comprising a positive electrode, a negative electrode and a separator, and further comprising the electrolyte described above, which effectively improves the problems of gas expansion and uneven deposition, and improves the cycle performance and safety performance of the lithium battery.

[0045] In the embodiments of the application, the lithium battery can be a laminated structure formed by laminating the positive electrode, the negative electrode and the separator in a specific order, or can be a winding body formed by winding the laminated structure. According to the form, the lithium battery can be a laminated battery, a soft-packaged battery, a square battery, a cylindrical battery, a coin battery or a button battery; according to the material, the lithium battery can be a lithium battery, a lithium ion battery, a lithium-sulfur battery or a lithium-air battery.

[0046] In some embodiments of the present application, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector, the material of the positive electrode active material layer comprises a positive electrode active substance, a positive electrode binder and a positive electrode conductive agent. The material of the positive electrode current collector, the positive electrode active substance, the positive electrode binder and the positive electrode conductive agent can be conventional materials in the art, for example: the material of the positive electrode current collector comprises but is not limited to aluminum foil, platinum foil or palladium foil; the positive electrode active substance comprises but is not limited to one or more of lithium cobaltate, lithium manganate, lithium permanganate, lithium iron phosphate, lithium nickelate, lithium manganese phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganate and lithium nickel cobalt aluminum, it can be understood that the surface of the above-mentioned compounds as the positive electrode active substance can have a coating layer, the material of the coating layer comprises but is not limited to a carbon material; the positive electrode binder comprises but is not limited to one or more of vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate and polytetrafluoroethylene; the positive electrode conductive agent comprises but is not limited to one or more of carbon black, graphite and graphene.

[0047] The preparation method of the positive electrode can comprise the steps of: mixing the positive electrode active substance, the conductive agent, the binder and the first solvent to obtain a first mixture; then, coating the first mixture on the positive electrode current collector, and then sequentially performing a drying process and a rolling process to obtain a positive electrode plate. It should be noted that the first mixture can also be cast on a separate carrier to form a film layer, and then the film layer is separated from the carrier, and then the film layer is stacked on one side of the positive electrode current collector. The first solvent comprises but is not limited to N-methyl pyrrolidone, acetone and water.

[0048] In some embodiments of the present application, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, the material of the negative electrode active material layer comprises a negative electrode active substance, a negative electrode binder and a negative electrode conductive agent. The material of the negative electrode current collector, the negative electrode active substance, the negative electrode binder and the negative electrode conductive agent can be conventional materials in the art, for example: the material of the negative electrode current collector comprises but is not limited to aluminum foil, platinum foil or palladium foil; the negative electrode active substance comprises but is not limited to one or more of lithium, a metal that can be alloyed with lithium, a semi-metal, a transition metal oxide, a non-transition metal oxide and a carbon material, the metal that can be alloyed with lithium or the semi-metal comprises but is not limited to Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y1 alloy (Y1 is an alkali metal, an alkaline earth metal, a group 13-16 element, a transition metal, a rare earth element, or a combination thereof, except Si), and Sn-Y2 alloy (Y2 is an alkali metal, an alkaline earth metal, a group 13-16 element, a transition metal, a rare earth element, or a combination thereof, except Sn), the transition metal oxide comprises but is not limited to one or more of lithium titanium oxide, vanadium oxide, lithium vanadium oxide and titanium niobium oxide, the non-transition metal oxide comprises but is not limited to SnO2 and SiO xThe carbon material includes, but is not limited to, one or more of crystalline carbon (e.g., graphite) and amorphous carbon, the negative electrode binder can be the same as the positive electrode binder, and the negative electrode conductive agent can be the same as the positive electrode conductive agent. The preparation method of the negative electrode can refer to the preparation method of the positive electrode.

[0049] The material of the separator includes, but is not limited to, one or more of glass fiber, polyester, Teflon, polyethylene, polypropylene, and polytetrafluoroethylene.

[0050] The preparation method of the lithium battery in the embodiment of the present application includes, for example, the steps of: assembling the positive electrode, the negative electrode, and the separator to form a battery body, and then injecting the electrolyte into the inside of the battery body for infiltration to obtain the lithium battery.

[0051] The technical solutions and technical effects of the present application are described in detail below through specific examples, comparative examples, and experimental examples. The following examples are only part of the examples of the present application and do not specifically limit the present application.

[0052] Example 1

[0053] The present embodiment provides an electrolyte and a lithium battery containing the electrolyte. According to the mass percentage, the electrolyte includes 19.5% of lithium hexafluorophosphate, 1% of lithium difluoro(oxalato)borate, 0.5% of sodium hexafluorophosphate, and 1.2% of N-propyl-N-methylpyrrolidinium hexafluorophosphate, and the balance is a solvent. The solvent is composed of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and fluoroethylene carbonate. The volume ratio of ethylene carbonate, diethyl carbonate, and dimethyl carbonate is 2:5:3. The mass of fluoroethylene carbonate accounts for 10% of the total mass of the electrolyte.

[0054] The preparation method of the electrolyte in the present embodiment includes the following steps:

[0055] S1.1. Mix ethylene carbonate, diethyl carbonate, dimethyl carbonate, and fluoroethylene carbonate according to the formula ratio, cool to room temperature, and obtain a solvent;

[0056] S1.2. Add lithium hexafluorophosphate, N-propyl-N-methylpyrrolidinium hexafluorophosphate, lithium difluoro(oxalato)borate, and sodium hexafluorophosphate to the solvent prepared in step S1.1 in the formula ratio, stir at room temperature until uniform, and obtain an electrolyte.

[0057] A 6.2 Ah soft-pack battery was produced in an argon-filled glove box using NCM811 as the positive electrode material (positive electrode loading of 3.2 mAh, the material of the positive electrode current collector was aluminum foil), lithium metal as the negative electrode material (thickness of the lithium metal layer was 20 pm, the material of the negative electrode current collector was copper foil), and a polyethylene film coated with Al2O3 on both sides (coating thickness of each side was 2 pm) as the separator, under the condition that the injection amount was 1.6 g / Ah, and then the electrolyte was injected into the battery to soak, thereby obtaining the lithium battery of the present embodiment.

[0058] Example 2

[0059] The electrolyte and the lithium battery containing the electrolyte of the present embodiment are different from the electrolyte of Example 1 in that the mass percentage of sodium hexafluorophosphate in the electrolyte is replaced with “0.1%”, and the mass percentage of the solvent is adaptively changed. It should be noted that the volume ratio of ethylene carbonate, diethyl carbonate and dimethyl carbonate and the mass percentage of fluoroethylene carbonate are the same as those of Example 1.

[0060] The preparation method of the electrolyte of the present embodiment is performed with reference to Example 1.

[0061] The lithium battery of the present embodiment is different from the lithium battery of Example 1 in that the electrolyte is the electrolyte of the present embodiment.

[0062] Example 3

[0063] The electrolyte and the lithium battery containing the electrolyte of the present embodiment are different from the electrolyte of Example 1 in that the mass percentage of sodium hexafluorophosphate in the electrolyte is replaced with “1%”, and the mass percentage of the solvent is adaptively changed. It should be noted that the volume ratio of ethylene carbonate, diethyl carbonate and dimethyl carbonate and the mass percentage of fluoroethylene carbonate are the same as those of Example 1.

[0064] The preparation method of the electrolyte of the present embodiment is performed with reference to Example 1.

[0065] The lithium battery of the present embodiment is different from the lithium battery of Example 1 in that the electrolyte is the electrolyte of the present embodiment.

[0066] Example 4

[0067] The embodiment provides a kind of electrolyte and lithium battery comprising electrolyte, compared with the electrolyte in embodiment 1, the difference of electrolyte in this embodiment is that the mass percentage of lithium difluoroborate in electrolyte is replaced by "0.5%", correspondingly, the mass percentage of solvent is adaptively changed.It should be noted that the volume ratio of ethylene carbonate, diethyl carbonate and dimethyl carbonate and the mass percentage of fluoroethylene carbonate are the same as in embodiment 1.

[0068] The preparation method of electrolyte in the embodiment is carried out with reference to embodiment 1.

[0069] Compared with the lithium battery in embodiment 1, the difference of lithium battery in this embodiment is that the electrolyte is the electrolyte of this embodiment.

[0070] Embodiment 5

[0071] The embodiment provides a kind of electrolyte and lithium battery comprising electrolyte, compared with the electrolyte in embodiment 1, the difference of electrolyte in this embodiment is that the mass percentage of lithium difluoroborate in electrolyte is replaced by "1.5%", correspondingly, the mass percentage of solvent is adaptively changed.It should be noted that the volume ratio of ethylene carbonate, diethyl carbonate and dimethyl carbonate and the mass percentage of fluoroethylene carbonate are the same as in embodiment 1.

[0072] The preparation method of electrolyte in the embodiment is carried out with reference to embodiment 1.

[0073] Compared with the lithium battery in embodiment 1, the difference of lithium battery in this embodiment is that the electrolyte is the electrolyte of this embodiment.

[0074] Embodiment 6

[0075] The embodiment provides a kind of electrolyte and lithium battery comprising electrolyte, compared with the electrolyte in embodiment 1, the difference of electrolyte in this embodiment is that the mass percentage of lithium difluoroborate in electrolyte is replaced by "2%", correspondingly, the mass percentage of solvent is adaptively changed.It should be noted that the volume ratio of ethylene carbonate, diethyl carbonate and dimethyl carbonate and the mass percentage of fluoroethylene carbonate are the same as in embodiment 1.

[0076] The preparation method of electrolyte in the embodiment is carried out with reference to embodiment 1.

[0077] Compared with the lithium battery in embodiment 1, the difference of lithium battery in this embodiment is that the electrolyte is the electrolyte of this embodiment.

[0078] Embodiment 7

[0079] The embodiment provides a kind of electrolyte and lithium battery comprising electrolyte, compared with the electrolyte in embodiment 1, the difference of electrolyte in this embodiment is that 1.2% N-propyl-N-methyl pyrrolidine hexafluorophosphate is replaced with "1.2% N-butyl-N-methyl pyrrolidine hexafluorophosphate".

[0080] The preparation method of electrolyte in this embodiment is carried out with reference to embodiment 1.

[0081] Compared with the lithium battery in embodiment 1, the difference of lithium battery in this embodiment is that the electrolyte is the electrolyte of this embodiment.

[0082] Embodiment 8

[0083] The embodiment provides a kind of electrolyte and lithium battery comprising electrolyte, compared with the electrolyte in embodiment 1, the difference of electrolyte in this embodiment is that 1.2% N-propyl-N-methyl pyrrolidine hexafluorophosphate is replaced with "1.2% N-butyl-N-methyl pyrrolidine hexafluorophosphate".

[0084] The preparation method of electrolyte in this embodiment is carried out with reference to embodiment 1.

[0085] Compared with the lithium battery in embodiment 1, the difference of lithium battery in this embodiment is that the electrolyte is the electrolyte of this embodiment.

[0086] Embodiment 9

[0087] The embodiment provides a kind of electrolyte and lithium battery comprising electrolyte, compared with the electrolyte in embodiment 1, the difference of electrolyte in this embodiment is that 1.2% N-propyl-N-methyl pyrrolidine hexafluorophosphate is replaced with "0.6% N-propyl-N-methyl pyrrolidine hexafluorophosphate".

[0088] The preparation method of electrolyte in this embodiment is carried out with reference to embodiment 1.

[0089] Compared with the lithium battery in embodiment 1, the difference of lithium battery in this embodiment is that the electrolyte is the electrolyte of this embodiment.

[0090] Embodiment 10

[0091] The embodiment provides a kind of electrolyte and lithium battery comprising electrolyte, compared with the electrolyte in embodiment 1, the difference of electrolyte in this embodiment is that 1.2% N-propyl-N-methyl pyrrolidine hexafluorophosphate is replaced with "2% N-propyl-N-methyl pyrrolidine hexafluorophosphate".

[0092] The preparation method of electrolyte in this embodiment is carried out with reference to embodiment 1.

[0093] Compared to the lithium battery in Example 1, the difference of the lithium battery in this example is that the electrolyte is the electrolyte of this example.

[0094] Comparative Example 1

[0095] This comparative example provides an electrolyte and a lithium battery containing the electrolyte. Compared to the electrolyte in Example 1, the electrolyte in this comparative example differs in that N-propyl-N-methylpyrrolidine hexafluorophosphate is omitted, and correspondingly, the mass percentage of the solvent is adapted accordingly. It should be noted that the volume ratio of ethylene carbonate, diethyl carbonate, and dimethyl carbonate, as well as the mass percentage of fluoroethylene carbonate, are the same as in Example 1.

[0096] The electrolyte in this comparative example was prepared according to Example 1.

[0097] Compared to the lithium battery in Example 1, the lithium battery in this comparative example differs in that the electrolyte is the electrolyte of this comparative example.

[0098] Comparative Example 2

[0099] This comparative example provides an electrolyte and a lithium battery containing the electrolyte. Compared with the electrolyte in Example 1, the electrolyte in this comparative example is different in that "1.2% N-propyl-N-methylpyrrolidine hexafluorophosphate" is replaced with "1.2% 1-ethyl-3-methylimidazolium hexafluorophosphate".

[0100] The electrolyte in this comparative example was prepared according to Example 1.

[0101] Compared to the lithium battery in Example 1, the lithium battery in this comparative example differs in that the electrolyte is the electrolyte of this comparative example.

[0102] Experimental Example

[0103] The performance of the lithium batteries in Examples 1 to 10, Comparative Examples 1 and 2 was tested. Specifically, each lithium battery after formation was subjected to a cycle test. Each lithium battery was charged at 25°C with a constant current at a rate of 0.33C to a voltage of 4.2V, and then discharged at a constant current at a rate of 0.5C until the voltage reached 3V. The above charge and discharge cycle was repeated 300 times, with a time interval of 10 minutes between two adjacent cycles. The capacity retention rate after 150 cycles at 25°C was obtained. Each lithium battery that completed the above cycle test was subjected to a national standard nail penetration test.

[0104] The test results are shown in Table 1 below:

[0105] Table 1

[0106]

[0107] As shown in Table 1, the lithium battery in Examples 1 to 10 has better comprehensive performance than the lithium batteries in Comparative Example 1 and Comparative Example 2, the lithium battery in Examples 1 to 10 has good cycle performance, and the lithium battery in Examples 1 to 10 can pass the needle test. For example, the capacity retention rate of the lithium battery in Example 1 after 150 cycles at 25°C is 11.8% higher than that of the lithium battery in Comparative Example 1, and the capacity retention rate of the lithium battery in Example 1 after 150 cycles at 25°C is 19.8% higher than that of the lithium battery in Comparative Example 2. The capacity retention rate of the lithium battery in Comparative Example 1 after 150 cycles at 25°C is higher than that of the lithium battery in Comparative Example 2, but the lithium battery in Comparative Example 1 does not pass the needle test.

[0108] In addition, the lithium batteries in Example 1 and Comparative Example 1 are subjected to the aforementioned cycle test after being formed, the aforementioned cycle test is stopped when the capacity retention rate is less than 80%, and then the morphology of the negative electrode of the lithium battery is observed by using a scanning electron microscope to obtain Figure 1 and Figure 2 In Figure 1 and Figure 2 , the A-surface lithium layer and the B-surface lithium layer are both film layers deposited on the copper foil layer in the long cycle of the lithium battery, and the A-surface lithium layer and the B-surface lithium layer each include an SEI layer.

[0109] Figure 1 In the lithium battery in Example 1, the thickness of the A-surface lithium layer is 49.6 μm to 51.4 μm, the thickness of the copper foil layer is 6.35 μm, the thickness of the B-surface lithium layer at a position is 55.4 μm, and Figure 1 In the lithium battery in Example 1, the sum of the thicknesses of the A-surface lithium layer, the copper foil layer, and the B-surface lithium layer at a position is 110 μm. Figure 2 In the lithium battery in Example 1, the thickness of the A-surface lithium layer at a position is 72.2 μm Figure 2 In the lithium battery in Example 1, the sum of the thicknesses of the A-surface lithium layer, the copper foil layer, and the B-surface lithium layer at a position is 110 μm. Figure 2 In the lithium battery in Example 1, the thickness of the A-surface lithium layer at a position is 72.2 μm Figure 2 In the lithium battery in Example 1, the sum of the thicknesses of the A-surface lithium layer, the copper foil layer, and the B-surface lithium layer at a position is 110 μm. Figure 1 and Figure 2 In the lithium battery in Example 1, the sum of the thicknesses of the A-surface lithium layer, the copper foil layer, and the B-surface lithium layer at a position is 110 μm.

[0110] It is shown that the gas generation and expansion of the lithium battery in Example 1 is obviously improved during the cycle test, the thickness of the film deposited on the copper foil is low and the deposition uniformity is relatively high after long cycle, and the cycle performance of the lithium battery in Example 1 is good, which can maintain a capacity retention rate of more than 90% after 150 cycles at 25°C. The lithium battery in Comparative Example 1 has obvious gas generation and expansion during the cycle test, the thickness of the film deposited on the copper foil is high and the surface roughness is high after long cycle, and there is a problem of uneven deposition, so the lithium battery in Comparative Example 1 fails to pass the needle test.

[0111] In summary, the electrolyte of the embodiments of the present application applied to the lithium battery can improve the compatibility of the electrolyte with lithium metal, effectively improve the phenomena of gas generation and expansion and uneven deposition, thereby improving the cycle performance and safety performance of the lithium battery.

[0112] The embodiments of the present application are described in detail above, and specific examples are applied in this paper to describe the principles and implementation modes of the present application. The above description of the embodiments is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed, and the content of the specification should not be understood as a limitation of the present application.

Claims

1. A lithium battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode comprises a negative electrode active material, the negative electrode active material comprising one or more of lithium monomer, metal that can be alloyed with lithium, semi-metal, transition metal oxide, non-transition metal oxide, and carbon material; The electrolyte comprises, in terms of mass percentage, 16.5% to 21% of lithium hexafluorophosphate, 0.5% to 2% of lithium difluoro(oxalato)borate, 0.1% to 2% of sodium hexafluorophosphate, and 1% to 2% of pyrrole-based ionic liquid, and the balance being solvent; The pyrrole-based ionic liquid has the structure shown in the following general formula (I): (Ⅰ) ； In the general formula (I), R1 and R2 are each independently selected from C1 to C30 alkyl.

2. The lithium battery of claim 1, wherein, The R1 and the R2 are each independently selected from C1 to C10 alkyl; and / or The negative electrode active material comprises at least one of lithium monomer and metal that can be alloyed with lithium.

3. The lithium battery according to claim 1 or 2, characterized in that, The R1 and the R2 are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, or tert-butyl; and / or The pyrrole-based ionic liquid is selected from one or more of N-butyl-N-methyl pyrrolidinium hexafluorophosphate, N-propyl-N-methyl pyrrolidinium hexafluorophosphate, and N-ethyl-N-methyl pyrrolidinium hexafluorophosphate.

4. The lithium battery of claim 1, wherein, The solvent is selected from one or more of vinyl carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, butylene carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, fluoro-vinyl carbonate, and diethyl carbonate.

5. The lithium battery of claim 4, wherein, The solvent consists of vinyl carbonate, diethyl carbonate, dimethyl carbonate, and fluoro-vinyl carbonate.

6. The lithium battery of claim 5, wherein, In the solvent, the volume ratio of vinyl carbonate, diethyl carbonate, and dimethyl carbonate is 1:(2 to 3):(1 to 2).

7. The lithium battery of claim 4, wherein, The proportion of the mass of the fluoro-vinyl carbonate in the total mass of the electrolyte is 10% to 15%.

8. The lithium battery of claim 1, wherein, In the electrolyte, the molar ratio of lithium hexafluorophosphate to sodium hexafluorophosphate is 1:(0.02 to 0.05), and / or the molar ratio of lithium hexafluorophosphate to lithium difluoro(oxalato)borate is 1:(0.023 to 0.056).

9. The lithium battery of claim 1, wherein, The metal that can be alloyed with lithium or semi-metal comprises Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y1 alloy, and Sn-Y2 alloy; wherein Y1 is alkali metal, alkaline earth metal, group 13 to 16 element, transition metal, rare earth element, or a combination thereof, except for Si; Y2 is alkali metal, alkaline earth metal, group 13 to 16 element, transition metal, rare earth element, or a combination thereof, except for Sn; and / or The transition metal oxide comprises one or more of lithium titanium oxide, vanadium oxide, lithium vanadium oxide, and titanium niobium oxide; and / or The non-transition metal oxide includes Sn02and SiO x one or more of Sn02, SiO, and Ti02, wherein 0 < x < 2; and / or The carbon material comprises one or more of crystalline carbon and amorphous carbon; and / or The negative electrode further comprises a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, the negative electrode active material layer comprising the negative electrode active material.

10. The lithium battery of claim 9, wherein, The crystalline carbon comprises graphite.

11. The lithium battery of claim 1, wherein, The positive electrode comprises a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector.

12. The lithium battery of claim 1, wherein, The material from which the separator is made includes one or more of glass fiber, polyester, Teflon, polyethylene, polypropylene, and polytetrafluoroethylene.

13. The lithium battery of claim 1, wherein, The lithium battery includes a laminated battery, a soft-pack battery, a prismatic battery, a cylindrical battery, a coin-type battery, or a button-type battery; and / or The lithium battery includes a lithium-ion battery, a lithium-sulfur battery, or a lithium-air battery.

Images