Temperature self-adaptive electrolyte for wide-temperature-range lithium battery

Abstract

The invention relates to the technical field of lithium battery electrolyte, in particular to temperature self-adaptive electrolyte for a wide-temperature-range lithium battery. The electrolyte comprises a lithium salt, a temperature-sensitive solvent, a temperature-insensitive solvent and an additive. In the electrolyte, the interaction strength of the temperature-sensitive solvent and the lithium ions can be obviously changed along with the change of the temperature, and the interaction strength of the temperature-insensitive solvent and the lithium ions is kept unchanged. At low temperature, the coordination ability of the temperature-sensitive solvent and lithium ions is stronger, the coordination ability of the temperature-sensitive solvent and lithium ions is gradually weakened along with temperature rise, and the coordination ability of the temperature-insensitive solvent and lithium ions is enhanced. The electrolyte shows obviously different solvated structures at low temperature and high temperature, and can realize low-temperature rapid electrochemical reaction kinetics and high-temperature electrochemical stability, thereby realizing excellent wide temperature range performance. The invention provides a new thought for designing the wide-temperature-range electrolyte, and the wide-temperature-range electrolyte has wide application value.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery electrolytes, and in particular to a temperature-adaptive electrolyte for wide-temperature-range lithium batteries. Background Art

[0002] Lithium batteries are one of the most widely used energy storage devices today, with advantages such as high energy density, low self-discharge, and stable cycling. In practical application scenarios such as portable electronic products, electric and hybrid vehicles, and space exploration, there are often large changes in external ambient temperature, which has led to an increasing demand for wide-temperature range lithium batteries. In low-temperature environments, lithium batteries have problems such as capacity decay, reduced power density, and difficulty in charging; while in high-temperature scenarios, lithium batteries are plagued by problems such as intensified interfacial side reactions and decreased cycling stability. In order to solve the bottleneck problem of lithium battery applications in wide-temperature scenarios, it is necessary to optimize the key component of lithium batteries, the electrolyte. Currently, commonly used electrolytes mainly use carbonate solvents with strong polarity, such as ethylene carbonate, to achieve full dissociation of lithium salts, form a relatively stable electrode-electrolyte interface, and improve the compatibility between the electrode and the electrolyte. However, these commonly used solvents have slow low-temperature kinetics and intensified side reactions at high temperatures.

[0003] Current strategies to address these issues often target low- and high-temperature applications separately, modifying solvents, lithium salts, or adding additives. However, the design approaches for high- and low-temperature electrolytes differ in many ways, sometimes even contradictory. Low-temperature solvents have weak solvation capabilities, posing risks such as low boiling points and flashover. High-temperature solvents or additives, on the other hand, can suffer from slow interfacial charge transfer at low temperatures.

[0004] Patent publication number CN118198491A proposes a preparation method and application of a wide-temperature battery electrolyte, which relies on fluorocarboxylic acid ester solvents and composite additives (such as methyl fluorosulfonyldifluoroacetate) to achieve wide-temperature performance through high-concentration lithium salts and diluents. It does not involve the dynamic adjustment mechanism of the solvation structure with temperature. Although the low-temperature (-60°C) conductivity is high, the high-temperature interface stability is insufficient, and it cannot take into account both the desolvation kinetics and interface stability at extreme temperatures.

[0005] Patent publication number CN112331917A proposes a wide-temperature range lithium-ion battery electrolyte, its preparation method, and application. The main purpose is to optimize the electrolyte components to improve the properties of the interface film to meet the discharge requirements within a wide temperature range. A fixed-ratio mixed solvent of cyclic carbonate and linear carbonate is used, and the interface film is improved by additives (VC / PS / LiPO2F2). However, the solvation structure does not change with temperature. The high viscosity of the cyclic solvent at low temperatures leads to poor dynamics. The linear solvent has insufficient film-forming stability at high temperatures, and the high-temperature (55°C) cycle capacity retention rate is only 80%.

[0006] Patent publication number CN111342134A proposes a wide-temperature range non-aqueous electrolyte for lithium-ion batteries and a preparation method thereof. The solution uses a propylene carbonate / ethylene ester / ethyl methyl ester mixed solvent and phenyl methanesulfonate additives to balance high and low temperature performance through a fixed ratio. However, the solvent system is a static combination and cannot dynamically adjust its coordination capacity with temperature changes. Solvent side reactions still exist at high temperatures, and the ion conduction efficiency is limited at low temperatures. Summary of the Invention

[0007] In order to overcome the difficulties of current wide-temperature range electrolytes, the purpose of the present invention is to provide a temperature-adaptive electrolyte for wide-temperature range lithium batteries. By combining a temperature-sensitive solvent with an insensitive solvent, the adaptive change of the electrolyte solvation structure with temperature is achieved, solving the inherent problem of the contradiction between high and low temperature performance in the existing technology.

[0008] The technical solution of the present invention is:

[0009] A temperature-adaptive electrolyte for a wide-temperature-range lithium battery is prepared by mixing a lithium salt, a temperature-sensitive solvent, a temperature-insensitive solvent, and an additive in a molar ratio of 1:(1-15):(1-10):(0-5).

[0010] The temperature-adaptive electrolyte for a wide-temperature range lithium battery is prepared as follows: first, a lithium salt is dissolved in a temperature-sensitive solvent and a temperature-insensitive solvent, and stirred at 25 to 60°C until completely dissolved; additives are added according to specific needs, and the mixture is stirred evenly to obtain a temperature-adaptive electrolyte.

[0011] The temperature-adaptive electrolyte for the wide-temperature range lithium battery, wherein the lithium salt is one or more of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), and lithium nitrate.

[0012] The temperature-sensitive solvent of the temperature-adaptive electrolyte for the wide-temperature range lithium battery is one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2,2-dimethyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2-methyltetrahydrofuran-3-one, tetrahydropyran, and 2,2-bis(2-tetrahydrofuranyl)propane.

[0013] The temperature-insensitive solvent of the temperature-adaptive electrolyte for the wide-temperature range lithium battery is one or more of ethylene glycol dibutyl ether, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate.

[0014] The temperature-adaptive electrolyte for the wide-temperature range lithium battery, when additives are needed, is one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, and fluoroethylene carbonate.

[0015] The temperature-adaptive electrolyte for the wide-temperature range lithium battery has a solvation structure that spontaneously changes between -40 and 60°C.

[0016] The design concept of the present invention is:

[0017] The temperature-adaptive electrolyte for a wide-temperature-range lithium battery of the present invention comprises a lithium salt, a temperature-sensitive solvent, a temperature-insensitive solvent and an additive. In this type of electrolyte, the strength of the interaction between the temperature-sensitive solvent and lithium ions changes significantly with changes in temperature, while the strength of the interaction between the temperature-insensitive solvent and lithium ions remains unchanged. At low temperatures, the coordination ability of the temperature-sensitive solvent with lithium ions is stronger. As the temperature rises, the coordination ability of the temperature-sensitive solvent with lithium ions gradually weakens, resulting in an increase in the coordination of the temperature-insensitive solvent with lithium ions. The electrolyte exhibits significantly different solvation structures at low and high temperatures, which can achieve rapid interfacial reaction kinetics at low temperatures and electrochemical stability at high temperatures, thereby achieving excellent wide-temperature-range performance.

[0018] The present invention can realize the dynamic change of solvation structure with temperature in the same electrolyte by mixing two types of solvents, thereby adapting to wide temperature application scenarios. Among them, the first type of solvent is a temperature-sensitive solvent, which is a cyclic asymmetric molecule with a low molecular weight and a large distance between the positive and negative centers of the molecule, and is easily affected by molecular thermal motion. The second type of solvent is a temperature-insensitive solvent, which is a high-temperature thermally stable molecule with a high molecular weight and a close or even overlapping positive and negative centers of the molecule. The strength of the interaction with lithium ions does not change significantly with temperature. In the electrolyte, the two types of solvents have a competitive coordination relationship, and the coordination ability changes with the temperature change. At high temperatures, the molecular thermal motion is accelerated, the molecular motion rate of the temperature-sensitive solvent is faster, the molecular dipole orientation is disordered, and the lithium ion binding ability becomes weak, so that the temperature-insensitive solvent and the anion participate in the coordination more, and high-temperature stability is obtained; at low temperatures, the molecular thermal motion of the temperature-sensitive solvent slows down, and the average distance between the solvent and the lithium ions is reduced, ensuring the dissociation of lithium salts and the liquid phase diffusion of lithium ions, weakening the binding between lithium ions and the temperature-insensitive solvent, and promoting the kinetics of low-temperature desolvation reactions. The solvation structure that changes dynamically with temperature can be adapted to different temperature scenarios.

[0019] The "solvation structure" of the present invention refers to the specific coordination configuration formed by lithium ions surrounded by solvent molecules in the electrolyte. It manifests as a dynamic complex structure formed by the interaction between lithium ions, surrounding solvent molecules, and anions. The dynamic changes in this structure directly affect the low-temperature desolvation reaction kinetics of lithium ions and the high-temperature thermal stability of the electrolyte, thereby affecting the electrochemical performance of the battery, including capacity, cycle life, rate capability, and performance at different temperatures.

[0020] The advantages and beneficial effects of the present invention are:

[0021] 1. In the prior art, the design concepts of high- and low-temperature electrolytes are independent of each other and even contradictory. At low temperatures, weak solvation ability is required to promote lithium ion desolvation, while at high temperatures, a thermally stable solvent is required to stabilize the interface. The present invention proposes a temperature-adaptive electrolyte for wide-temperature-range lithium batteries. This electrolyte combines a temperature-sensitive solvent with a temperature-insensitive solvent in a specific ratio. By utilizing the synergistic effect of the two types of solvents, the solvation structure of the electrolyte can spontaneously change with temperature changes, effectively solving the problem of existing electrolytes that are difficult to achieve wide-temperature-range performance.

[0022] 2. In the temperature-adaptive electrolyte of the present invention, the competitive coordination mechanism of two types of solvents is utilized, and the solvation structure of lithium ions can adaptively change with changes in temperature, thereby having a suitable solvation structure in a wide temperature range.

[0023] 3. In the temperature-adaptive electrolyte of the present invention, the chemical environment of lithium ions varies significantly at different temperatures. At high temperatures, the coordination ability of the temperature-sensitive solvent is weakened, and the temperature-insensitive solvent dominates the high-temperature interface stability. At low temperatures, the coordination ability of the temperature-sensitive solvent is enhanced, promoting lithium salt dissociation and ion transport.

[0024] 4. The temperature-adaptive electrolyte of the present invention can maintain excellent performance in a wide temperature range of -40 to 60°C, significantly improving the coulombic efficiency of the lithium metal negative electrode in a wide temperature range.

[0025] 5. The temperature-adaptive electrolyte of the present invention significantly improves the wide-temperature performance of various battery systems such as NCM811||graphite soft-pack batteries, lithium iron phosphate||lithium metal batteries, and NCM811||lithium metal batteries, including key indicators such as battery cycle stability, capacity retention rate, and average coulombic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure is a flow chart for preparing the temperature-adaptive electrolyte of the present invention.

[0027] Figure 2The in-situ Raman spectra of the control group electrolytes obtained by combining the temperature-sensitive solvent and lithium salt in the present invention are shown in Figure 1. (a) LiFSI / THF electrolyte, (b) LiFSI / MeTHF electrolyte.

[0028] Figure 3 The in-situ Raman spectra of the control electrolytes obtained by combining the temperature-insensitive solvent and lithium salt in the present invention are shown in Figure 1. (a) LiFSI / DBE electrolyte, (b) LiFSI / DEE electrolyte.

[0029] Figure 4 It is the chemical shift of the nuclear magnetic resonance lithium spectrum of the temperature-adaptive electrolyte of the present invention and the control group in the temperature range of -20 to 50°C.

[0030] Figure 5 The coulombic efficiency of lithium negative electrode deposition / dissolution using the temperature adaptive electrolyte of the present invention and the control group. -2 Current density and 1mAh cm -2 Average coulombic efficiency after 5 capacity cycles.

[0031] Figure 6 The coulombic efficiency of lithium negative electrode deposition / dissolution using the temperature adaptive electrolyte of the present invention and the control group. -2 Current density and 1mAh cm -2 Average coulombic efficiency after 5 capacity cycles.

[0032] Figure 7 The coulombic efficiency of lithium negative electrode deposition / dissolution using the temperature adaptive electrolyte of the present invention and the control group. -2 Current density and 1mAh cm -2 Average coulombic efficiency after 5 capacity cycles.

[0033] Figure 8 It is the capacity retention rate of a 1Ah NCM811||graphite soft-pack battery using the temperature-adaptive electrolyte of the present invention when cycled at 50°C at a rate of 1C.

[0034] Figure 9 The capacity and coulombic efficiency of the lithium iron phosphate||lithium metal battery using the temperature adaptive electrolyte of the present invention and the control group are cycled at a rate of 1C at 25°C.

[0035] Figure 10 The capacity and coulombic efficiency of the NCM811 lithium metal battery using the temperature-adaptive electrolyte of the present invention and the control group are cycled at a rate of 0.1C at -20°C. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with specific embodiments.

[0037] Example 1

[0038] like Figure 1 As shown, the preparation process of the temperature-adaptive electrolyte of the present invention is as follows:

[0039] First, lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in a temperature-sensitive solvent, tetrahydrofuran (THF), and a temperature-insensitive solvent, ethylene glycol dibutyl ether (DBE). The molar ratio of lithium salt to temperature-sensitive solvent to temperature-insensitive solvent was 1:6.2:3.6. The solution was stirred magnetically at 25°C until completely dissolved to obtain a temperature-adaptive electrolyte, designated LiFSI / THF-DBE. Raman spectra at different temperatures showed that the solvation structure of the electrolyte consisting only of lithium salt and temperature-sensitive solvent, such as THF or 2-methyltetrahydrofuran (MeTHF), changed significantly with temperature ( Figure 2 ); The electrolyte composed of lithium salt and temperature-insensitive solvent, such as DBE or ethylene glycol diethyl ether (DEE), has a solvation structure that remains stable at different temperatures ( Figure 3 The results of lithium nuclear magnetic resonance spectra at different temperatures also show that the chemical shift of the electrolyte containing only lithium salts and temperature-insensitive solvents DBE or DEE does not change much at different temperatures; the chemical shift of the electrolyte containing lithium salts and temperature-sensitive solvents THF or MeTHF changes more significantly; the chemical shift of the example electrolyte LiFSI / THF-DBE containing both types of solvents changes most significantly with temperature ( Figure 4 ).

[0040] The specific proportions of the control group electrolyte using only a single solvent mentioned above are as follows: an electrolyte composed of LiFSI and THF in a molar ratio of 1:12.3, denoted as LiFSI / THF; an electrolyte composed of LiFSI and MeTHF in a molar ratio of 1:10.0, denoted as LiFSI / MeTHF; an electrolyte composed of LiFSI and DBE in a molar ratio of 1:7.2, denoted as LiFSI / DBE; an electrolyte composed of LiFSI and DEE in a molar ratio of 1:7.2, denoted as LiFSI / DEE.

[0041] Example 2

[0042] The difference from Example 1 is that the ratio of the temperature-sensitive solvent to the temperature-insensitive solvent in Example 2 is different, and an additive is added. First, lithium bis(fluorosulfonyl)imide (LiFSI) is dissolved in a temperature-sensitive solvent tetrahydrofuran (THF) and a temperature-insensitive solvent ethylene glycol dibutyl ether (DBE), and the molar ratio of lithium salt to temperature-sensitive solvent to temperature-insensitive solvent is 1:4.1:2.4, and magnetic stirring is performed at 25°C until completely dissolved. The additive 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is then added to the solution, and the molar ratio of lithium salt to additive is 1:2.2 to obtain a temperature-adaptive electrolyte LiFSI / THF-DBE-TTE. Compared with the low-temperature electrolyte LiFSI / THF-TTE (molar ratio 1:8.2:2.2) that only uses the temperature-sensitive solvent THF and the additive TTE; or the high-temperature electrolyte LiFSI / DBE-TTE (molar ratio 1:4.8:2.2) that only uses the temperature-insensitive solvent DBE and the additive TTE, the lithium battery using this temperature-adaptive electrolyte can take into account the advantages of both.

[0043] Taking the performance of lithium metal anode as an example, the temperature adaptive electrolyte shows excellent performance under high temperature, room temperature and low temperature conditions. At 50 ° C, the lithium metal battery using this electrolyte has a high current density of 0.5 mA cm -2 Current density and 1mAh cm -2 The average coulombic efficiency after 5 capacity cycles reaches 99.1%, which is slightly better than that of high-temperature electrolyte and significantly better than that of low-temperature electrolyte ( Figure 5 ). At 25 °C, the lithium metal anode using the temperature-adaptive electrolyte was charged at 0.5 mA cm -2 Current density and 1mAh cm -2 The average coulombic efficiency after 5 capacity cycles reaches 99.4% ( Figure 6 ). At -20 ° C, the lithium metal negative electrode of this electrolyte was charged at 0.5 mA cm -2 Current density and 1mAh cm -2 The average coulombic efficiency after 5 capacity cycles reaches 99.2%, which is slightly better than that of low-temperature electrolyte and significantly better than that of high-temperature electrolyte ( Figure 7 ).

[0044] In addition, the temperature-adaptive electrolyte also exhibits good performance when applied to full batteries of different systems under wide temperature conditions. At 50°C, a 1Ah capacity NCM811|| graphite soft-pack battery using this electrolyte was cycled 200 times at a current of 1A, with a capacity retention rate of approximately 81.6% and an average coulombic efficiency of 99.9% ( Figure 8At 25°C, the lithium iron phosphate||lithium metal battery using this electrolyte was charged and discharged 250 times at a rate of 1C, with a capacity retention rate of about 89.7% and an average coulombic efficiency of 99.9% ( Figure 9 At -20°C, the NCM811|| lithium metal battery using this electrolyte was charged and discharged at a rate of 0.1C. The discharge capacity was equivalent to 82.5% of that at room temperature. After 200 cycles, the capacity retention rate was about 100%, and the average coulombic efficiency was 99.9% ( Figure 10 ).

[0045] The results of the examples show that by combining temperature-sensitive and temperature-insensitive solvents, the present invention achieves an adaptive transformation of the electrolyte solvation structure with temperature changes, thereby optimizing the electrolyte solvation structure within the temperature range of -40 to 60°C. It also improves thermal stability at high temperatures and electrochemical reaction kinetics at low temperatures, significantly improving the wide-temperature performance of lithium batteries. Therefore, the present invention provides a new approach to the design of wide-temperature electrolytes and has broad application value.

[0046] The purpose of the above embodiments is to better illustrate and demonstrate the design concept and application effects of the present invention, and it is not intended to limit the scope of protection claimed by the present invention. Any modification or change based on the design concept of the present invention is included in the scope of protection claimed by the present invention.

Claims

1. A temperature-adaptive electrolyte for a wide temperature range lithium battery, characterized in that: The electrolyte is prepared by mixing lithium salt, a temperature-sensitive solvent, a temperature-insensitive solvent and an additive in a molar ratio of 1:(1-15):(1-10):(0-5).

2. The temperature-adaptive electrolyte for a wide temperature range lithium battery according to claim 1, characterized in that The preparation process of the temperature-adaptive electrolyte is as follows: first, dissolve the lithium salt in a temperature-sensitive solvent and a temperature-insensitive solvent, and stir at 25-60°C until completely dissolved; add additives according to specific needs, stir evenly, and obtain the temperature-adaptive electrolyte.

3. The temperature-adaptive electrolyte for a wide temperature range lithium battery according to claim 1, characterized in that The lithium salt is one or more of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), and lithium nitrate.

4. The temperature-adaptive electrolyte for a wide temperature range lithium battery according to claim 1, characterized in that The temperature sensitive solvent is one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2,2-dimethyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2-methyltetrahydrofuran-3-one, tetrahydropyran, and 2,2-di(2-tetrahydrofuryl)propane.

5. The temperature-adaptive electrolyte for a wide temperature range lithium battery according to claim 1, characterized in that: The temperature-insensitive solvent is one or more of ethylene glycol dibutyl ether, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate.

6. The temperature-adaptive electrolyte for a wide temperature range lithium battery according to claim 1, characterized in that: When additives are required, the additives are one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, and fluoroethylene carbonate.

7. The temperature-adaptive electrolyte for a wide temperature range lithium battery according to claim 1, characterized in that: The solvation structure of the electrolyte changes spontaneously between -40 and 60°C.

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