Multi-lithium salt composite organic electrolyte suitable for low temperature environment and application thereof

Abstract

The application discloses a kind of multi-lithium salt composite organic electrolyte suitable for low temperature environment, comprising: lithium salt system and organic solvent system;Wherein, the lithium salt system includes lithium tetrafluoroborate, lithium bisfluorosulfonylimide and lithium bis (oxalate) borate;Organic solvent system includes carbonate solvent, linear ether solvent and weak solvent molecule;The application aims at providing a kind of multi-lithium salt composite organic electrolyte suitable for low temperature environment, can have good ion transport capacity, interface stability and cycle life under low temperature environment, can maintain higher reversible capacity and stable charge-discharge platform, capacity decay rate is significantly slowed down, meet the application demand of high reliability and high stability of low temperature lithium ion battery.

Description

Technical Field

[0001] This invention relates to electrolyte technology, belonging to the field of lithium-ion battery material technology, and specifically to a multi-lithium salt composite organic electrolyte suitable for low-temperature environments and its application. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, high operating voltage, and long cycle life. Lithium-ion batteries mainly consist of three parts: the positive electrode, the negative electrode, and the electrolyte. The electrolyte, as a channel for the free movement of lithium / sodium ions, is the core material that determines the battery's energy density, safety, lifespan, and environmental adaptability. At low temperatures, the thermal motion of solvent molecules in the electrolyte weakens, their kinetic energy decreases, and they become more ordered, leading to a significant increase in electrolyte viscosity. Furthermore, the solvent dielectric constant decreases, and the slower rearrangement of solvent molecules to encapsulate lithium ions reduces the degree of lithium salt dissociation. This results in a substantial decrease in lithium ion migration rate and diffusion coefficient, leading to intensified battery polarization and a significant reduction in rate performance and reversible capacity. Simultaneously, lithium ion deposition on the negative electrode surface becomes more uneven at low temperatures, easily inducing lithium dendrite growth and posing safety hazards. In addition, the interfacial reaction kinetics between the electrolyte and electrode materials slow down at low temperatures, easily forming a non-uniform solid electrolyte interfacial film with poor mechanical stability, further deteriorating battery cycle stability. Under these conditions, the electrolyte is unsuitable for applications in cold regions, high latitudes, and aerospace, for example, it cannot maintain high ionic conductivity and stable electrochemical response in environments as low as -20°C. Traditional lithium-ion battery systems face severe performance degradation under these low-temperature conditions. Currently, the main methods for improving low-temperature performance include: 1. Increasing the proportion of linear ether solvents or low-viscosity solvents to reduce the overall viscosity of the electrolyte; 2. Using high-concentration or locally high-concentration electrolyte systems to enhance the lithium salt dissociation; 3. Introducing functional additives to improve interfacial film-forming properties. However, the following problems still exist: single lithium salt systems often struggle to balance ion transport performance and interface stability at low temperatures, while high-concentration electrolyte systems are costly and have poor fluidity, hindering practical engineering applications; some additives do not decompose sufficiently at low temperatures, potentially introducing additional side reactions. Therefore, there is an urgent need for an electrolyte system that can achieve efficient lithium-ion transport and stable interface control at low temperatures. Summary of the Invention

[0003] The purpose of this invention is to provide a multi-lithium salt composite organic electrolyte suitable for low-temperature environments. It can exhibit good ion transport capability, interface stability, and cycle life at low temperatures, maintain high reversible capacity and a stable charge-discharge platform, and significantly slow down the capacity decay rate, thus meeting the application requirements of low-temperature lithium-ion batteries for high reliability and high stability.

[0004] To achieve the above objectives, a multi-lithium salt composite organic electrolyte suitable for low-temperature environments is provided, comprising: a lithium salt system and an organic solvent system; The lithium salt system includes lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(oxalateborate). Organic solvent systems include carbonate solvents, linear ether solvents, and weak solvent molecules.

[0005] In some examples of the present invention, the organic solvent system includes propylene carbonate, 1,2-dimethoxyethane, and isobutyl isobutyrate.

[0006] In some examples of the present invention, the lithium salt system and the organic solvent system are prepared at a mass ratio of 1:(5 to 15).

[0007] In some examples of the present invention, the molar concentration of the lithium tetrafluoroborate is 0.5 to 1.0 mol / L, the molar concentration of the lithium difluorosulfonylimide is 0.1 to 0.4 mol / L, and the molar concentration of the lithium dioxaborate is 0.02 to 0.10 mol / L. The volume ratio of propylene carbonate, 1,2-dimethoxyethane and isobutyl isobutyrate is (15-35):(50-75):(5-15).

[0008] In some examples of the present invention, the lithium salt system and the organic solvent system are prepared at a mass ratio of 1:10; The molar concentration of the lithium tetrafluoroborate salt is 0.75 mol / L, the molar concentration of the lithium difluorosulfonylimide salt is 0.2 mol / L, and the molar concentration of the lithium dioxaborate salt is 0.05 mol / L. Propylene carbonate, 1,2-dimethoxyethane, and isobutyl isobutyrate are in a volume ratio of 25:65:10.

[0009] Application of a multi-lithium salt composite organic electrolyte suitable for low-temperature environments in lithium-ion batteries.

[0010] Compared with existing technologies, this multi-lithium salt composite organic electrolyte suitable for low-temperature environments has the following advantages: 1. Through the synergistic effect of lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide and lithium bis(oxalate)borate, the solvation structure of lithium ions is effectively regulated, which significantly improves the degree of lithium salt dissociation under low temperature conditions, significantly reduces the lithium ion diffusion resistance, maintains high reversible capacity and stable charge and discharge platform, and significantly slows down the capacity decay rate, which is significantly better than traditional single lithium salt or conventional carbonate electrolyte systems. 2. Organic solvent systems include carbonate solvents, linear ether solvents, and weak solvent molecules. Linear ether solvents can reduce the overall viscosity of the electrolyte, while weak solvent molecules weaken the interaction between lithium ions and strong coordinating solvents, making the lithium ion desolvation process easier and significantly improving polarization behavior and rate performance under low temperature conditions. 3. Boron- and fluorine-containing lithium salts preferentially decompose at the electrode interface, inducing the formation of a stable interface film with uniform composition, dense structure, and mainly inorganic components. This effectively reduces the growth rate of interface impedance, suppresses lithium dendrite formation and side reactions under low-temperature conditions, and further improves the safety and long-term cycle performance of lithium batteries. Attached Figure Description

[0011] Figure 1 These are scanning electron microscope images of battery solution A in Example 1 of the present invention under conditions of 25°C and -20°C. Figure 2 This is the X-ray diffraction pattern of battery solution A in Embodiment 1 of the present invention; Figure 3 This is a constant current charge-discharge curve of battery fluid A in Embodiment 1 of the present invention; Figure 4 This is a long-cycle performance diagram of battery fluid A in Embodiment 1 of the present invention; Figure 5 These are scanning electron microscope images of battery solution A in Example 2 of the present invention under conditions of 25°C and -20°C. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0013] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0014] This invention relates to a multi-lithium salt composite organic electrolyte suitable for low-temperature environments, comprising: a lithium salt system and an organic solvent system; The lithium salt system includes lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(oxalateborate). Organic solvent systems include carbonate solvents, linear ether solvents, and weak solvent molecules; Specifically, multiple lithium salts are used in the lithium salt system. Due to the differences in their anionic structure, coordination ability and electrochemical decomposition behavior, they jointly participate in the construction of lithium ion solvation shell and synergistically regulate the interfacial film formation process under low temperature conditions, thereby reducing the desolvation energy barrier of lithium ions while ensuring the full dissociation of lithium salts. In organic solvent systems, carbonate solvents are used to provide a higher dielectric constant to ensure the dissolution and electrochemical stability window of lithium salts, linear ether solvents are used to reduce the viscosity of the system and improve the ion migration ability under low temperature conditions, and weak solvent molecules further regulate the solvation structure by weakening the interaction between lithium ions and strong coordinating solvents. This multi-lithium salt composite organic electrolyte, through the synergistic effect of the lithium salt system and the organic solvent system, enables lithium ions to form a solvated configuration that is more easily desolvated under low-temperature conditions. At the same time, during the charge and discharge process, it induces the preferential decomposition of boron-containing and fluorine-containing lithium salts at the electrode interface, forming a dense and stable interfacial film structure, thereby effectively suppressing side reactions and lithium dendrite growth. This allows the electrolyte to maintain high ionic conductivity and good cycle stability at temperatures of −20℃ and below, making it suitable for low-temperature lithium-ion battery energy storage systems.

[0015] In some examples of the present invention, the organic solvent system includes propylene carbonate, 1,2-dimethoxyethane, and isobutyl isobutyrate.

[0016] In some examples of the present invention, the lithium salt system and the organic solvent system are prepared at a mass ratio of 1:(5-15); In some examples of the present invention, the molar concentration of the lithium tetrafluoroborate is 0.5 to 1.0 mol / L, the molar concentration of the lithium difluorosulfonylimide is 0.1 to 0.4 mol / L, and the molar concentration of the lithium dioxaborate is 0.02 to 0.10 mol / L. The volume ratio of propylene carbonate, 1,2-dimethoxyethane and isobutyl isobutyrate is (15-35):(50-75):(5-15).

[0017] Preferably, the lithium salt system and the organic solvent system are prepared at a mass ratio of 1:10; The molar concentration of the lithium tetrafluoroborate salt is 0.75 mol / L, the molar concentration of the lithium difluorosulfonylimide salt is 0.2 mol / L, and the molar concentration of the lithium dioxaborate salt is 0.05 mol / L. Propylene carbonate, 1,2-dimethoxyethane, and isobutyl isobutyrate are in a volume ratio of 25:65:10.

[0018] Example 1

[0019] The lithium salt system and the organic solvent system were prepared at a mass ratio of 1:10; First, propylene carbonate, 1,2-dimethoxyethane, and isobutyl isobutyrate were mixed in a volume ratio of 25:65:10 to form a composite solvent. Then, under an inert gas environment, 0.75 mol / L lithium tetrafluoroborate, 0.2 mol / L lithium bis(fluorosulfonyl)imide, and 0.05 mol / L lithium bis(oxalate-borate) were dissolved in the composite solvent and stirred thoroughly at room temperature until the lithium salt system was completely dissolved in the composite solvent, thus preparing a transparent electrolyte A. Finally, the lithium-ion battery was used as a carrier to conduct cycle performance tests at 25℃ and −20℃. Specifically, LiCoO2 was selected as the positive electrode material, lithium sheet was selected as the negative electrode material, and polypropylene material was selected as the separator for combination. The transparent electrolyte A prepared above was then assembled to form lithium-ion battery A. like Figure 1 As shown, the deposited lithium is relatively denser and more continuous, and the porous / moss-like features are suppressed; at −20℃, the lithium surface remains denser and more uniform. The formation of a LiF-rich, inorganic-dominated SEI in electrolyte A promotes more uniform interfacial ion transport, reduces local current amplification, thereby suppressing dendrite growth and demonstrating superior low-temperature cycling stability; Figure 2As shown, the cathode circulating in electrolyte A retains stronger LiCoO2 diffraction intensity and significantly enhanced LiF-related peaks, which is consistent with the improved preservation of the cathode structure and the enhanced formation of the inorganic (LiF-rich) interface phase during low-temperature cycling; Figure 3 As shown, lithium-ion battery A exhibits clear, closely overlapping charge-discharge levels at both temperatures, with a smaller voltage gap and a more stable intermediate plateau potential. This indicates significantly reduced polarization, easier Li+ diffusion, and maintenance of charge transfer kinetics even at low temperatures. Figure 4 As shown, electrolyte A initially achieved a discharge capacity of 143.5 mAh g⁻¹, maintaining ~98.4% of its room temperature capacity. After 500 cycles, it still maintained 129.7 mAh⁻¹, or ~85.5% of its room temperature capacity, demonstrating high cycling stability.

[0020] At 25°C, lithium-ion battery A retains 138.6 mAh / g after 200 cycles at a 0.2C rate. −1 The discharge specific capacity is [value missing], and the coulombic efficiency is approximately 99.5%, demonstrating stable cycling behavior. Under the same rate and cycling conditions at −20℃, lithium-ion battery A still maintains 133.2 mAh g⁻¹ after 200 cycles. −1 The discharge specific capacity indicates that the electrolyte still has good cycle stability in low-temperature environments; In long-cycle testing, at 25°C, the initial discharge specific capacity of lithium-ion battery A was 145.8 mAh g. −1 It can still maintain 151.7 mAh g after 500 cycles. −1 The discharge specific capacity is high, and the capacity decay is slow; under −20℃ conditions, the initial discharge specific capacity of lithium-ion battery A reaches 143.5 mAh g. −1 This is equivalent to approximately 98.4% of its room temperature capacity, and it retains 129.7 mAh g after 500 cycles. −1 It has approximately 85.5% of its room temperature capacity, demonstrating excellent low-temperature long-cycle stability.

[0021] Example 2

[0022] In this example, a conventional carbonate electrolyte system was selected to distinguish it from Example 1; That is, the conventional carbonate system electrolyte uses lithium tetrafluoroborate. Under an inert gas environment, 1.0 mol / L of lithium tetrafluoroborate is dissolved in a conventional carbonate organic solvent system and stirred thoroughly at room temperature until the lithium salt system is completely dissolved in the composite solvent to prepare a transparent electrolyte B. Using the same positive and negative electrode materials, separator type, battery structure and test conditions as in Example 1, the transparent electrolyte B prepared above was assembled to form lithium-ion battery B, and the cycle performance was tested at 25°C and −20°C using the lithium-ion battery as a carrier. like Figure 5 As shown, at 25°C, the lithium surface of lithium-ion battery B becomes severely rough and covered with uneven, porous / moss-like deposits with numerous protrusions; at −20°C, this morphological inhomogeneity is further aggravated, with larger agglomerated deposits and more severe topographic inhomogeneity observed, indicating that lithium nucleation and growth are uneven under low-temperature conditions. The initial discharge specific capacity of lithium-ion battery B is 122.5 mAh g. −1 The capacity gradually decreased with increasing cycle number, dropping to 90.5 mAh g after 500 cycles. −1 It exhibits a relatively obvious cycle degradation phenomenon; when subjected to low-temperature cycle testing at -20℃, the initial discharge specific capacity of lithium-ion battery B is 120.6 mAh g. −1 During cycling, polarization intensifies rapidly, the discharge plateau decreases significantly, and the discharge specific capacity drops sharply to 47.2 mAh g after 500 cycles. −1 It exhibits severe low-temperature cycling instability.

[0023] In summary, under identical conditions, conventional electrolytes using only lithium tetrafluoroborate as a single lithium salt are insufficient to maintain long-term stable cycling performance at low temperatures, further highlighting the significant advantages of the multi-lithium salt composite electrolyte described in Example 1 in terms of low-temperature cycling stability.

[0024] The foregoing description, with reference to preferred embodiments, details an exemplary embodiment of the multi-lithium salt composite organic electrolyte suitable for low-temperature environments proposed by the present invention. However, those skilled in the art will understand that various modifications and alterations can be made to the above specific embodiments without departing from the concept of the present invention, and various combinations can be made to the various technical features and structures proposed by the present invention without exceeding the protection scope of the present invention, which is determined by the appended claims.

Claims

1. A multi-lithium salt composite organic electrolyte suitable for low-temperature environments, characterized in that, include: Lithium salt systems and organic solvent systems; The lithium salt system includes lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(oxalateborate). Organic solvent systems include carbonate solvents, linear ether solvents, and weak solvent molecules.

2. The multi-lithium salt composite organic electrolyte suitable for low-temperature environments according to claim 1, characterized in that, The organic solvent system includes propylene carbonate, 1,2-dimethoxyethane, and isobutyl isobutyrate.

3. The multi-lithium salt composite organic electrolyte suitable for low-temperature environments according to claim 1, characterized in that, The lithium salt system and the organic solvent system are prepared at a mass ratio of 1:(5-15).

4. The multi-lithium salt composite organic electrolyte suitable for low-temperature environments according to claim 2, characterized in that, The molar concentration of the lithium tetrafluoroborate salt is 0.5–1.0 mol / L, the molar concentration of the lithium difluorosulfonylimide salt is 0.1–0.4 mol / L, and the molar concentration of the lithium dioxarate borate salt is 0.02–0.10 mol / L. Propylene carbonate, 1,2-dimethoxyethane and isobutyl isobutyrate are in a volume ratio of (15-35):(50-75):(5-15).

5. The multi-lithium salt composite organic electrolyte suitable for low-temperature environments according to claim 4, characterized in that, The lithium salt system and the organic solvent system were prepared at a mass ratio of 1:10; The molar concentration of the lithium tetrafluoroborate salt is 0.75 mol / L, the molar concentration of the lithium difluorosulfonylimide salt is 0.2 mol / L, and the molar concentration of the lithium dioxaborate salt is 0.05 mol / L. Propylene carbonate, 1,2-dimethoxyethane, and isobutyl isobutyrate are in a volume ratio of 25:65:

10.

6. The application of a multi-lithium salt composite organic electrolyte suitable for low-temperature environments as described in claims 2 to 5 in lithium-ion batteries.

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