Electrolyte for improving wide temperature range performance of lithium battery

Abstract

The invention relates to the technical field of lithium batteries, in particular to an electrolyte for improving the wide temperature range performance of a lithium battery. According to the electrolyte, under the action of a proper amount of components in a proper proportion, the ionic conductivity is improved, the desolvation energy, the viscosity and the eutectic point of the electrolyte are reduced to optimize the low-temperature performance, the oxidation stability at the high temperature is improved, the side reaction of the electrolyte at the high temperature is inhibited, and therefore the high-temperature and low-temperature performance is optimized at the same time. Meanwhile, the electrolyte effectively solves the compatibility problem of the nitrile solvent and the negative electrode in a wide temperature range, and the generated interfacial film has the characteristics of thinness, uniformity and compactness, so that the SEI film impedance can be effectively reduced at low temperature, the stability of the interfacial film can be kept at high temperature, and the impedance is prevented from being increased. A compact CEI film rich in N, F and other components is formed on a positive electrode interface, and the CEI film can effectively inhibit the structural stress damage of a positive electrode material in circulation and the dissolution of transition metal ions at a high temperature, so that the structural stability is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to an electrolyte for improving the wide-temperature-range performance of lithium batteries. Background Technology

[0002] As a high-efficiency energy storage device, the comprehensive performance of lithium batteries across a wide temperature range has become a key bottleneck restricting their widespread application in transportation and energy storage scenarios in extreme climates (such as frigid or hot regions). At low temperatures, the electrolyte viscosity increases significantly, and Li... + The migration rate decreases significantly, leading to a sharp increase in battery internal resistance, making low-temperature charging and discharging difficult, and severely reducing capacity and energy density; simultaneously, Li + The kinetic process is hindered at the electrode interface, and the charge transfer impedance increases significantly, causing Li + The intercalation reaction at the negative electrode becomes extremely slow, and lithium plating is highly likely to occur under high current. At high temperatures, the electrolyte's thermal stability decreases, making it prone to oxidative decomposition and gas generation. The electrode interface film (SEI / CEI) structure becomes unstable, easily dissolving or reforming, leading to continuous increase in internal resistance and loss of active materials, thus accelerating battery performance degradation. Therefore, optimizing the electrolyte formulation and developing film-forming additives for both positive and negative electrodes are effective strategies to simultaneously improve the low-temperature kinetics and high-temperature stability of lithium batteries and achieve wide-temperature-range applications. For example, patent application CN118693356 A relates to fast-charging electrolytes and lithium batteries. The fast-charging electrolyte includes: lithium salt, nitrile solvent, fluorinated diluent, and electrolyte additives, wherein the lithium salt concentration is 3~5 mol / L. The volume ratio of the nitrile solvent to the fluorinated diluent is (2~4):1. Further, the nitrile solvent includes acetonitrile, and the nitrile solvent also includes at least one of glutaronitrile and adiponitrile. The fluorinated diluent is at least one selected from 1H, 1H, 5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. The electrolyte additives include fluoroethylene carbonate and tris(2,2,2-trifluorofluoroethyl)borate. This patent relates to the performance of products under room temperature 5C testing conditions, but does not address the performance of products at higher rates or at low or even ultra-low temperatures. Patent CN 117393860 A relates to a fast-charging electrolyte, a battery filling method, and a battery; the electrolyte involved includes lithium salts, carbonate solvents, carboxylic acid ester solvents, vinylene carbonate, fluorocarbonate additives, phosphite additives, sulfur-containing additives, and fluorophenyl carboxylic acid ester additives. This technology improves the constant current charge ratio and 60°C storage performance of the product battery, and significantly improves the 45°C cycle performance, -10°C cycle performance, and low-temperature charging performance. However, it also does not address the electrical performance of products at higher rates or at low or even ultra-low temperatures. Summary of the Invention

[0003] The purpose of this invention is to provide an electrolyte and electrolyte additive for improving the wide-temperature-range performance of lithium batteries, in order to solve the problems mentioned in the background above, such as the obstruction of Li⁺ kinetics under low temperature or even ultra-low temperature conditions, resulting in a significant reduction in the charge and discharge rate performance of lithium-ion batteries; and the problems of electrolyte oxidation and decomposition, decreased interfacial film stability leading to impedance growth, damage to the cathode material structure, and cycle life decay at high temperatures.

[0004] To achieve the above objectives, the present invention provides the following technical solution: an electrolyte for improving the wide-temperature-range performance of lithium batteries, wherein the electrolyte comprises lithium salt, solvent, and electrolyte additives, and the concentration of Li element in the electrolyte is 0.5-3 mol / L; the electrolyte contains nitrile solvent, and the volume ratio of nitrile solvent to all solvents is 5%-50%, and the general structural formula of nitrile solvent is as follows:

[0005] .

[0006] As a preferred technical solution, R1 is a saturated hydrocarbon group and satisfies the condition that the number of carbon atoms is ≤6.

[0007] As a further preferred option, one or more of the following nitrile solvents can be used. .

[0008] This invention discloses an electrolyte for improving the wide-temperature-range performance of lithium batteries; the electrolyte additive includes a first additive and / or a second type of additive, wherein the structural formula of the first additive is as follows:

[0009] ;

[0010] The structural formula of the second additive is as follows:

[0011] .

[0012] Preferably, the content of additives in the electrolyte is 0.05~13.5%, and more preferably 0.45~13.5%.

[0013] Preferably, the content of the first additive in the electrolyte is 0.05wt% to 8wt%.

[0014] Preferably, the ratio of the first additive content to the second additive content is greater than or equal to 1.1. More preferably, it is 1.5-10, and even more preferably, 2-4, which naturally includes 2, 3, 4, etc. In the composition of the present invention, the first additive, as the main film-forming substance, is responsible for achieving the core function of a wide temperature range; while the second additive mainly plays a role in optimizing and improving the system formed by the first additive. To ensure sufficient long-term stability of the system, the amount of the first additive needs to be dominant. Preferably, the weight ratio of the first additive to the second additive is in the range of (1.5-10):1, and even more preferably, 2-4:1.

[0015] As a preferred technical solution, R2 in the first additive formula is one of the following structures: hydrocarbon group, unsaturated hydrocarbon group, fluorine group, and fluorine-containing saturated hydrocarbon group, and the carbon chain of the additive does not exceed five carbon atoms, and its structural formula can be one of the following structures:

[0016] .

[0017] As a preferred technical solution, R in the second additive formula 3~7 It is one of the following structures: hydrocarbon group, unsaturated hydrocarbon group, fluorine group, and F-containing saturated hydrocarbon group, and R 3~7 It contains at least two groups of F-containing groups, and its structural formula can be one of the following:

[0018] .

[0019] The present invention provides an electrolyte for improving the wide temperature range performance of lithium batteries; comprising one or more nitrile solvents and one or more electrolyte additives as described above, the electrolyte further comprising lithium salts and other organic solvents and other additives, wherein the total proportion of other additives in the electrolyte is ≤6wt%.

[0020] As a preferred technical solution, the lithium salt is one or more of the following lithium salts in combination: lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium di(oxalateborate) (LiBOB), lithium di(fluorooxalateborate) (LiDFOB), and lithium perchlorate (LiClO4).

[0021] As a preferred technical solution, other organic solvents can be one or more combinations of ester solvents, some of which are as follows: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl propionate (EP), ethyl acetate (EA), and methyl acetate (MA).

[0022] As a preferred technical solution, the electrolyte further includes additives other than the first and second additives. These other additives are preferably one or a combination of vinyl sulfate (DTD), vinylene carbonate (VC), and 1,3-propanesulfonate lactone (1,3-PS). The total proportion of these other additives in the electrolyte should be ≤6 wt%, and the ratio of the amount of the first and second additives (W3) to the sum of the amounts of the remaining additives (W4) should satisfy W3 / W4 > 1. In the composition of this invention, the first and second additives, as the main film-forming substances, are responsible for achieving the core function of a wide temperature range; while the remaining additives mainly optimize and improve the system formed by the first and second additives. To ensure sufficient long-term stability of the system, the amounts of the first and second additives must be dominant. Preferably, the ratio of the amount of the first and second additives (W3) to the sum of the amounts of the remaining additives (W4) should satisfy W3 / W4 > 1.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] This electrolyte, with appropriate amounts and proportions of its components, not only improves ionic conductivity and reduces electrolyte desolvation energy, viscosity, and eutectic point to optimize low-temperature performance, but also enhances oxidation stability at high temperatures and suppresses side reactions (such as decomposition and gas generation) at high temperatures, thus simultaneously optimizing both high and low-temperature performance. Furthermore, this electrolyte effectively solves the compatibility problem between nitrile solvents and the negative electrode over a wide temperature range. The resulting interfacial film is thin, uniform, and dense, effectively reducing SEI film impedance at low temperatures and maintaining interfacial film stability at high temperatures, preventing impedance growth. It forms a dense CEI film rich in N and F components at the positive electrode interface. This CEI film has high lithium-ion conductivity, significantly reducing the transport energy barrier and impedance, effectively improving battery kinetic performance over a wide temperature range. Simultaneously, this CEI film effectively suppresses structural stress damage and transition metal ion dissolution in the positive electrode material during cycling at high temperatures, ensuring structural stability. Attached Figure Description

[0025] Figure 1 The capacity efficiency graph shows the capacity efficiency of batteries assembled with the electrolytes obtained in Example 1 and Comparative Example 1 after 200 cycles under the conditions of 55°C / 3C charging and 5C discharging.

[0026] like Figure 1 As shown, under high-temperature cycling, the capacity retention rate of Example 1 is 66.8%, while the capacity of Comparative Example 1 drops significantly after 200 cycles. This indicates that our electrolyte system design effectively suppresses interfacial side reactions at high temperatures and forms an interfacial film with stronger thermal stability, significantly improving the cycle stability of the battery under high-temperature and high-rate conditions. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This application addresses the problem of insufficient wide-temperature-range performance of batteries and the poor improvement effect of existing additives. It proposes an electrolyte containing nitrile solvents and two electrolyte additives, namely a first additive containing F and sulfonic acid group structure and a second additive containing F and cyano group, and uses them to prepare a wide-temperature-range electrolyte.

[0029] To achieve the above objectives, the technical solution adopted in this invention is as follows: Nitrile solvents are used to improve the ionic conductivity and boiling point of the electrolyte, while reducing the electrolyte desolvation energy, viscosity, and eutectic point. Simultaneously, two novel electrolyte additives are used to optimize the positive and negative electrode interfaces and improve wide-temperature-range performance. Specifically, the first additive preferentially forms an SEI film containing inorganic components such as S and F on the negative electrode surface. This electrolyte film effectively solves the incompatibility problem between nitrile solvents and the negative electrode under wide-temperature-range conditions. Furthermore, this interfacial film is thin, uniform, and dense, reducing impedance at low temperatures and maintaining film stability at high temperatures, thereby improving the battery's wide-temperature-range charge-discharge capability. The second additive forms a dense CEI film rich in components such as N and F at the positive electrode interface. This CEI film has high lithium-ion conductivity, significantly reducing the transport energy barrier and impedance, effectively improving the battery's kinetic performance over a wide temperature range. It also effectively suppresses structural stress damage to the positive electrode material and the dissolution of transition metal ions during cycling, especially ensuring the stability of the positive electrode structure at high temperatures.

[0030] The electrolyte contains a nitrile solvent, which contains a cyano group and satisfies Formula 1, including but not limited to Formulas 1-1, 1-2, 1-3, 1-4, and 1-5.

[0031] Formula 1: Its specific structure can be one of the following, but is not limited to the following structures:

[0032] ;

[0033] Formula 1-1 Formula 1-2 Formula 1-3 Formula 1-4 Formula 1-5.

[0034] The first additive comprises a sulfonic acid group structure satisfying Formula 2, where R2 in Formula 2 is one of the following structures: a hydrocarbon group, an unsaturated hydrocarbon group, a fluorine group, or an F-containing saturated hydrocarbon, including but not limited to Formulas 2-1, 2-2, 2-3, and 2-4; the second additive is a molecule containing N and F, where R in Formula 3... 3~7 It has the following structures: hydrocarbon group, unsaturated hydrocarbon group, fluorine group and F-containing saturated hydrocarbon, including but not limited to formula 3-1, formula 3-2, formula 3-3 and formula 3-4.

[0035] Formula 2: Its specific structure can be one of the following, but is not limited to the following structures:

[0036] ;

[0037] Equation 2-1 Equation 2-2 Equation 2-3 Equation 2-4.

[0038] Formula 3: Its specific structure can be one of the following, but is not limited to the following structures:

[0039] ;

[0040] Formula 3-1 Formula 3-2 Formula 3-3 Formula 3-4.

[0041] This solution provides an electrolyte for improving the wide-temperature-range performance of lithium batteries. In addition to the aforementioned nitrile solvents and electrolyte additives, the electrolyte also includes lithium salts and other organic solvents and additives. The lithium salt is one or more of the following: lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium dioxolane borate (LiBOB), lithium difluorooxolane borate (LiDFOB), and lithium perchlorate (LiClO4). The organic solvent is one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl propionate (EP), ethyl acetate (EA), and methyl acetate (MA).

[0042] The electrolyte must contain one or more of the aforementioned nitrile solvents, accounting for 5%-50% of the total volume of all solvents. The additives added to the electrolyte must include a first additive and a second additive. The content of the first additive must be in the range of 0.5wt% to 8wt%, and the ratio of the first additive content to the second additive content must be greater than or equal to 1.1. Furthermore, other additives that do not satisfy Formulas 2 and 3, such as DTD, VC, and 1,3-PS, may be added to the electrolyte. The total amount of these additives must be ≤6wt%, and the ratio of the amount of the first and second additives (W4) to the total amount of the remaining additives (W5) must satisfy W4 / W5 > 1.

[0043] Example 1: The invented additive and electrolyte were used in a 1Ah rated capacity pouch cell with NCM523||graphite as the positive and negative electrode system, with an electrolyte injection coefficient of 3.5 g / Ah. The electrolyte formulation adopted was: 1M / L LiPF6, with a solvent system of EC:PN:DEC:FEC = 4:3:2:1 Vol%, adding 3wt% of the first additive (Formula 1-2) and 1wt% of the second additive (Formula 2-1). All electrolyte preparation processes were carried out at room temperature in a glove box filled with Ar (water content <1ppm, oxygen content <1ppm). The organic solvents EC (ethylene carbonate), PN (pentafenone formula 1-4), DEC (diethyl carbonate), and FEC (fluoroethylene carbonate) were mixed and stirred for 10 min according to the above volume percentages. Then, the electrolyte lithium salt LiPF6 was added according to the solvent volume and lithium salt formulation concentration and stirred for 10 min. Finally, the first and second additives were added according to the formulation and stirred for 10 min to obtain a wide temperature range electrolyte.

[0044] The electrolyte and battery preparation methods of Examples 2-9 and Comparative Examples 1-2 are the same as those of Example 1, except that the positive and negative electrode material systems of the batteries are different and the electrolyte formulations are different. The specific implementation methods are shown in the table below.

[0045] Table 1: Specific Implementation Schemes of Examples and Comparative Examples

[0046] ;

[0047] The battery was charged to 4.3V at a rate of 1C at room temperature, and then discharged to 2V at a rate of 1C at room temperature. The discharge capacity is denoted as C0.

[0048] The battery was charged to 4.3V at a rate of 1C at room temperature, and then discharged to 2V at a rate of 0.2C at -40℃. The discharge capacity is denoted as C1.

[0049] The battery was charged to 4.3V at a rate of 1C at room temperature, and then discharged to 2V at a rate of 20C at room temperature. The discharge capacity is denoted as C2.

[0050] The battery was charged and discharged at 1C for 1000 cycles at room temperature, with a voltage range of 2-4.3V. The discharge capacity of the first cycle was recorded as C3, and the discharge capacity of the 1000th cycle was recorded as C4.

[0051] The battery was subjected to 200 cycles of charging at 3C and discharging at 55°C, with a voltage range of 2-4.3V. The discharge capacity of the first cycle was recorded as C5, and the discharge capacity of the 200th cycle was recorded as C6.

[0052] Five animals were tested from each group, and the average value was taken. The specific results are shown in Tables 2, 3, 4, and 5.

[0053] Table 2: Low-temperature discharge performance of the examples and comparative examples

[0054] ;

[0055] Table 3: Room temperature rate discharge performance of the examples and comparative examples

[0056] ;

[0057] Table 4: Room temperature cycling performance of the examples and comparative examples

[0058] ;

[0059] Table 5: High-Temperature Cycling Performance of Examples and Comparative Examples

[0060] ;

[0061] As can be seen from the experimental results in Tables 2-5 above, the battery using the electrolyte of the example performs better than the comparative example in low-temperature discharge, room-temperature rate discharge, room-temperature cycling and high-temperature cycling tests.

[0062] Specifically, after using the nitrile solvent and additives, the low-temperature discharge capability is improved by approximately 10% compared to batteries without the nitrile solvent and additives. The room-temperature rate discharge capability is improved by approximately 20% compared to batteries without the nitrile solvent and additives, the capacity retention rate after 1000 cycles at room temperature is improved by approximately 15%, and the capacity retention rate after 200 cycles at high temperature is improved by approximately 50%. Furthermore, changes to the solvent system, the structure and concentration of the additives, the type and concentration of the lithium salt, or the addition of other additives all maintain the improvement effect of this invention on room-temperature / low-temperature rate charge-discharge performance. This invention effectively enhances the low-temperature charge-discharge performance of lithium batteries. Simultaneously, the embodiments also verify the operation of this invention in different cathode material systems, showing good performance and indicating that the additive has a certain degree of universality.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An electrolyte for improving the wide-temperature-range performance of lithium batteries, characterized in that: The electrolyte comprises lithium salt, solvent, and electrolyte additives. The concentration of Li in the electrolyte is 0.5-3 mol / L. The electrolyte contains nitrile solvents, and the volume percentage of nitrile solvents in the total solvent is 5%-50%. The general structural formula of the nitrile solvent is as follows: ； The electrolyte additive includes a first type of additive and / or a second type of additive, wherein the structural formula of the first additive is as follows: ； The structural formula of the second additive is as follows: ； The additive content in the electrolyte is 0.05%~13.5%; When the first additive and the second additive are added simultaneously, the ratio of the content of the first additive to the content of the second additive is greater than or equal to 1.

1.

2. The electrolyte for improving the wide-temperature-range performance of lithium batteries according to claim 1, characterized in that: R1 is a saturated hydrocarbon group and satisfies the condition that the number of carbon atoms is ≤6.

3. The electrolyte for improving the wide-temperature-range performance of lithium batteries according to claim 1, characterized in that: Nitrile solvents are selected from at least one of the following structural formulas; 。 4. The electrolyte for improving the wide-temperature-range performance of lithium batteries according to claim 1, characterized in that: The content of the first additive in the electrolyte is 0.05wt%~8wt%.

5. The electrolyte for improving the wide-temperature-range performance of lithium batteries according to claim 1, characterized in that: The ratio of the first additive content to the second additive content is 1.5-10.

6. The electrolyte for improving the wide-temperature-range performance of lithium batteries according to claim 1, characterized in that: In the first additive formula, R2 is one of the following structures: hydrocarbon group, unsaturated hydrocarbon group, fluorine group, and fluorine-containing saturated hydrocarbon group, and the carbon chain of the additive does not exceed five carbon atoms, and its structural formula is one of the following structures: ； R in the second additive formula 3~7 It is one of the following structures: hydrocarbon group, unsaturated hydrocarbon group, fluorine group, and F-containing saturated hydrocarbon group, and R 3~7 It contains at least two groups of F-containing groups, and its structural formula is one of the following: 。 7. The electrolyte for improving the wide-temperature-range performance of lithium batteries according to claim 1, characterized in that: The electrolyte also includes other additives, and the total proportion of other additives in the electrolyte is ≤6wt%; the other additives are selected from one or more of vinyl sulfate, vinylene carbonate and 1,3-propanesulfonate lactone.

8. The electrolyte for improving the wide-temperature-range performance of lithium batteries according to claim 1, characterized in that: The lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, and lithium perchlorate.

9. The electrolyte for improving the wide-temperature-range performance of lithium batteries according to claim 1, characterized in that: The electrolyte also includes other organic solvents, which are ester solvents selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, ethyl acetate, and methyl acetate.

10. An electrolyte for improving the wide-temperature-range performance of lithium batteries according to claim 1, characterized in that: In the electrolyte, the ratio of the amount of the first additive and the second additive, and W3 to the sum of the amounts of the remaining additives, W4, should satisfy W3 / W4 > 1.

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