Wide-temperature-range lithium ion battery electrolyte, preparation method and application thereof

Abstract

The application relates to a wide-temperature-range lithium ion battery electrolyte as well as a preparation method and application thereof. The application belongs to the field of lithium ion battery electrolytes. The application is used for solving the technical problems that the existing lithium ion battery electrolyte is seriously prone to lithium precipitation at low temperature, seriously produces gas at high temperature, and has large volume expansion, thereby causing the narrow working temperature range of the lithium ion battery. The wide-temperature-range lithium ion battery electrolyte is prepared from a lithium salt and a mixed solvent, the mixed solvent is composed of 10-30vol% of fluoroethylene carbonate, 10-50vol% of fluoro phenyl acetonitrile and 20-80vol% of isobutyl formate. The working temperature range of the lithium ion battery assembled from the wide-temperature-range lithium ion battery electrolyte is -70-100 DEG C. The application solves the problems that the lithium battery electrolyte has high viscosity, high freezing point and poor conductivity in a low-temperature environment, and the electrolyte is decomposed and unstable at high temperature, so that lithium ions can be effectively transmitted in an extremely high or low temperature environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion battery electrolyte, and particularly relates to a wide-temperature-range lithium ion battery electrolyte as well as a preparation method and application thereof. BACKGROUND

[0002] At present, lithium ion batteries as power sources have been widely applied in the fields of portable electronic products and electric vehicles. In specific application scenarios such as national defense, polar exploration, aerospace, and the like, higher requirements are put forward for the chargeability of lithium battery packs below zero degrees and at high temperatures. At present, lithium batteries with graphite as a negative electrode material are widely applied due to low working potential and low cost, but the low-temperature chargeability is still a challenge. Under low-temperature conditions, the main factors affecting the electrochemical performance of the graphite negative electrode are: 1) low temperature leads to a decrease in the conductivity of the electrolyte and an increase in the viscosity of the electrolyte; 2) the interface resistance increases under low-temperature conditions, which reduces the speed of lithium ions passing through the electrode | electrolyte interface phase; 3) low temperature reduces the diffusion of lithium ions in the graphite. These problems significantly slow down the charge-discharge dynamics of the graphite negative electrode at low temperatures; in addition, the working potential between graphite (0.05 V vs. Li + / Li) and metal lithium is very close, and serious lithium precipitation occurs during low-temperature charging (lithium insertion into the graphite negative electrode), which is easy to form dendritic lithium.

[0003] At present, there are mainly three methods to improve the low-temperature chargeability of lithium batteries. The first strategy is to improve the working temperature of the battery through internal or external heating. The main disadvantage of this method is that auxiliary heating equipment is needed, which leads to additional energy input and introduces additional non-active weight, reduces energy efficiency, and increases the complexity of the system. The second method is to reduce the liquidus temperature of the electrolyte by adding some low-melting-point, low-viscosity co-solvents and / or additives. For commercial lithium ion batteries containing graphite, ethylene carbonate (EC) is often an indispensable electrolyte component due to its excellent ability to form a passivation solid electrolyte interface layer (SEI) on the graphite negative electrode. Unfortunately, EC has a very high melting point (35-38℃), which leads to solidification of most commercial electrolytes containing EC below-20℃, unless a low-melting-point co-solvent is added to replace some EC, such as methyl formate, ethyl acetate, and propylene carbonate. The third method is to optimize the structure of the graphite negative electrode to improve its low-temperature performance, such as preparing porous graphite nanosheets to improve the charge transfer dynamics of lithium and reduce the solid-state diffusion length.

[0004] Meanwhile, during the operation of the normal battery, the temperature rise usually brings irreversible side reactions and even thermal runaway. The conventional electrolyte in the lithium ion battery starts to decompose above 55℃, the solid electrolyte interface starts to decompose above 65℃, the risk of thermal runaway increases rapidly outside the working temperature range, and the above problems result in that the existing lithium ion battery can only work in a mild temperature range (-40~55℃), thereby greatly limiting the application of the lithium ion battery. SUMMARY

[0005] The present application provides a wide temperature range lithium ion battery electrolyte, a preparation method and application thereof to solve the technical problems of the existing lithium ion battery electrolyte, such as serious lithium precipitation at low temperature, serious gas production at high temperature, large volume expansion, and narrow working temperature range of the lithium ion battery.

[0006] One of the purposes of the present application is to provide a wide temperature range lithium ion battery electrolyte, which is prepared from a lithium salt and a mixed solvent, the mixed solvent is composed of 10-30vol% of fluoroethylene carbonate, 10-50vol% of fluoro phenyl acetonitrile and 20-80vol% of isobutyl formate, and the total volume fraction satisfies 100%.

[0007] Further limited, the lithium salt is lithium difluoro(oxalato)borate (LiDFOB), and the lithium salt concentration in the electrolyte is 0.1-1mol / L.

[0008] Further limited, the fluoro phenyl acetonitrile includes o-fluoro phenyl acetonitrile, m-fluoro phenyl acetonitrile, p-fluoro phenyl acetonitrile, difluoro phenyl acetonitrile, trifluoro phenyl acetonitrile, tetrafluoro phenyl acetonitrile and pentafluoro phenyl acetonitrile.

[0009] The second purpose of the present application is to provide a preparation method of a wide temperature range lithium ion battery electrolyte, which is carried out according to the following steps:

[0010] Step 1: drying treatment of the lithium salt;

[0011] Step 2: washing, drying and calcining the molecular sieve, and then immersing the molecular sieve in fluoroethylene carbonate, fluoro phenyl acetonitrile and isobutyl formate respectively to obtain dry fluoroethylene carbonate, fluoro phenyl acetonitrile and isobutyl formate respectively;

[0012] Step 3: adding the dry fluoroethylene carbonate, fluoro phenyl acetonitrile and isobutyl formate into the lithium salt in sequence, and stirring at room temperature to obtain the wide temperature range lithium ion battery electrolyte.

[0013] Further limited, the drying temperature in step 1 is 70-90℃, and the time is 24-48h.

[0014] Further limited, the moisture content of the lithium salt after drying in step 1 is less than 100ppm. ​

[0015] Further specify that in step 2, the device should be washed 4-6 times with anhydrous ethanol.

[0016] Further specifying, the drying temperature in step 2 is 70-90℃, and the time is 24-48h.

[0017] Further specifying, the calcination temperature in step 2 is 350-400℃, and the time is 2-4h.

[0018] Further specifying, the moisture content of the dried fluoroethylene carbonate, fluorophenylacetonitrile, and isobutyl formate in step 2 is all below 50 ppm.

[0019] Further specify that the stirring time in step 3 is 12-24 hours and the room temperature is 25-35℃.

[0020] The third objective of this invention is to provide a wide-temperature-range lithium-ion battery electrolyte for use in assembling lithium-ion batteries.

[0021] Furthermore, the operating temperature range of the lithium-ion battery is -70 to 100°C.

[0022] The significant advantages of this invention compared to existing technologies are:

[0023] This invention uses lithium difluorooxalate borate (LiDFOB) as a wide-temperature-range lithium salt as a lithium-ion donor and isobutyl formate (IF), fluoroethylene carbonate (FEC), and fluorophenylacetonitrile as a mixed solvent to prepare a wide-temperature-range electrolyte with low freezing point, low viscosity, high lithium-ion conductivity, and high temperature resistance. This electrolyte can effectively improve the transport and diffusion of lithium ions at extreme high and low temperatures, construct a stable solid-state electrolyte interface (SEI) and cathode electrolyte interface (CEI), and suppress the formation of lithium dendrites. Therefore, the electrolyte and the lithium-ion battery based on this electrolyte can operate stably and safely in a wide temperature range of -70 to 100°C. The specific advantages of this invention are as follows:

[0024] 1) This invention improves the electrolyte's resistance to high-voltage oxidation by introducing fluoroethylene carbonate (FEC) into the electrolyte, and is also beneficial for the formation of a film on the negative electrode.

[0025] 2) This invention significantly improves the high-temperature stability of the electrolyte by introducing fluorophenylacetonitrile with a stable benzene ring structure and a high-bond-energy cyano group into the electrolyte, while combining it with Li + Isobutyl formate, a co-solvent with high adsorption energy, is used in synergy with fluoroethylene carbonate to construct a multi-coordination system, which effectively improves the stability of the positive and negative electrode interfaces, thereby significantly broadening the operating temperature range of the electrolyte and lithium-ion battery, while also improving the working stability over a wide temperature range.

[0026] 3) The electrolyte system of the present invention, which combines fluoroethylene carbonate, fluorophenylacetonitrile and isobutyl formate, achieves a high voltage of 4.4V for the high-nickel cathode. In addition, it effectively improves the electrochemical cycle performance of lithium metal batteries and full batteries based on traditional electrode materials such as lithium cobalt oxide, high-nickel cathode, lithium titanate and commercial graphite in extreme high and low temperature environments.

[0027] 4) The wide-temperature-range lithium-ion battery electrolyte of the present invention is the first to use LiDFOB as the lithium salt and fluoroethylene carbonate, isobutyl formate and fluorophenylacetonitrile as solvents, which effectively improves the viscosity, freezing point, lithium-ion conductivity and wettability with the separator of the electrolyte.

[0028] 5) This invention proposes a method for preparing a wide-temperature-range electrolyte for lithium-ion batteries. The process is simple, inexpensive, and easy to implement. It will help improve the shortcomings of energy loss in lithium metal batteries and full batteries at high and low temperatures. It can also effectively improve the problems of high viscosity, high freezing point, poor conductivity, and decomposition and instability of lithium battery electrolytes at low temperatures, enabling lithium ions to be effectively transported in extreme high and low temperature environments.

[0029] 6) Using NCM811 as the positive electrode material and lithium sheet as the negative electrode, the lithium-ion battery based on the electrolyte of this invention can be stably and reversibly charged and discharged at -70°C, with a specific capacity of 100mAh / g and a charge-discharge cycle of up to 40 times; at a high temperature of 80°C, the capacity retention rate is as high as 78% after 500 cycles. This wide-temperature range lithium battery will be applied in key fields such as aerospace, special equipment and uncontrollable temperature environments. Attached Figure Description

[0030] Figure 1 The viscosity test results are shown in the graph for the wide-temperature range electrolyte of Example 1 and the commercial electrolyte of Comparative Example 1.

[0031] Figure 2 for Figure 1 A magnified view of a portion of the image;

[0032] Figure 3 The differential scanning calorimetry results are shown for the wide-temperature-range electrolyte of Example 1 and the commercial electrolyte of Comparative Example 1.

[0033] Figure 4 Thermogravimetric analysis results of the wide-temperature-range electrolyte of Example 1 and the commercial electrolyte of Comparative Example 1 are shown in the figure.

[0034] Figure 5 The graph shows the lithium-ion conductivity test results of the wide-temperature-range electrolyte of Example 1 and the commercial electrolyte of Comparative Example 1.

[0035] Figure 6The graph shows the test results of lithium-ion transference number and contact angle with the membrane for the wide-temperature range electrolyte of Example 1 and the commercial electrolyte of Comparative Example 1.

[0036] Figure 7 The graphs show the charge-discharge test results of NCM811 / Li batteries using the wide-temperature-range electrolyte of Example 1 and the commercial electrolyte of Comparative Example 1 at different temperatures.

[0037] Figure 8 The graph shows the charge-discharge test results of the NCM811 / Li battery using the wide-temperature-range electrolyte of Example 1 at –70°C.

[0038] Figure 9 The graphs show the charge-discharge test results of NCM811 / Li batteries using the wide-temperature-range electrolyte of Example 1 and the commercial electrolyte of Comparative Example 1 at a high temperature of 80°C.

[0039] Figure 10 The graph shows the charge-discharge test results of the graphite / NCM811 full cell using the wide-temperature-range electrolyte of Example 1 at -50°C. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0042] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in the following embodiments, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0043] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In this specification and claims, range definitions may be combined and / or interchanged, unless otherwise stated, these ranges include all subranges contained therein.

[0044] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0045] All reactants used in the following examples are commercially available products. The lithium difluorooxalate borate has a molecular weight of 143.77, the fluoroethylene carbonate has a molecular weight of 106.05, and the isobutyl formate additive IF has the structural formula H(CH3)2CH2OCHO, a molecular weight of 102.13, and a density of 0.89 g / cm³. 3 The viscosity is 0.68 × 10⁻⁶. -3 mPa·s, melting point -95.8℃.

[0046] Example 1: A method for preparing a wide-temperature-range lithium-ion battery electrolyte according to this example, the preparation method is carried out according to the following steps:

[0047] Step 1: Drying the lithium salt:

[0048] Lithium difluorooxalate borate (LiDFOB) was placed in a vacuum transition chamber of a glove box, with the temperature of the transition chamber set to 80°C, and dried for 24 hours. The moisture content was measured to be less than 100 ppm using a moisture analyzer, and the dried lithium difluorooxalate borate was obtained. After cooling, it was transferred to a glove box for later use.

[0049] Step 2:

[0050] S1, will The molecular sieve was washed 5 times with anhydrous ethanol, then transferred to an oven and dried at 80°C for 24 hours. It was then calcined at 350°C for 3 hours in air atmosphere, cooled down, and then transferred to a glove box for later use.

[0051] S2: Fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate were added into three 20 mL glass bottles respectively, and then calcined molecular sieves were added into the three 20 mL glass bottles respectively, so that the calcined molecular sieves were immersed in the fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate respectively for 24 h, and the moisture content was detected to be less than 50 ppm by using a moisture detector, to obtain dry fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate respectively.

[0052] Step 3: In a glove box, a 20 mL glass empty bottle was prepared, and the dried lithium difluoro(oxalato)borate obtained in step 1 was added, followed by the dry fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate obtained in step 2, and stirring was performed at 25°C for 12 h to obtain a wide-temperature-range lithium ion battery electrolyte, wherein the concentration of the solute lithium difluoro(oxalato)borate in the wide-temperature-range lithium ion battery electrolyte was 1 mol / L, and the volume fractions of fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate in the mixed solvent were 20 vol%, 20 vol% and 60 vol% respectively.

[0053] Example 2: A preparation method of a wide-temperature-range lithium ion battery electrolyte according to the present embodiment was performed in the following steps:

[0054] Step 1: The lithium salt was subjected to drying treatment:

[0055] The lithium difluoro(oxalato)borate (LiDFOB) was placed in a glove box vacuum transition chamber, the temperature of the transition chamber was set to 80°C, and drying was performed for 24 h, and the moisture content was detected to be less than 100 ppm by using a moisture detector, to obtain dried lithium difluoro(oxalato)borate, which was transferred into a glove box after cooling.

[0056] Step 2:

[0057] S1, the molecular sieves were washed with anhydrous ethanol for 5 times, and then were transferred into an oven, dried at 80°C for 24 h, and calcined at 350°C for 3 h under air atmosphere, and were transferred into a glove box after cooling;

[0058] S2: Fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate were added into three 20 mL glass bottles respectively, and then calcined molecular sieves were added into the three 20 mL glass bottles respectively, so that the calcined molecular sieves were immersed in the fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate respectively for 24 h, and the moisture content was detected to be less than 50 ppm by using a moisture detector, to obtain dry fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate respectively.

[0059] Step 3: In the glove box, prepare a 20 mL glass empty bottle, add the dried lithium difluoro(oxalato)borate after step 1, then add the dried fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate obtained in step 2 in turn, stir at 25℃ for 12h, to obtain a wide temperature range lithium ion battery electrolyte, wherein the concentration of the solute lithium difluoro(oxalato)borate in the wide temperature range lithium ion battery electrolyte is 1mol / L, and the volume fractions of fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate in the mixed solvent are 20vol%, 30vol% and 50vol% in turn.

[0060] Example 3: A preparation method of a wide temperature range lithium ion battery electrolyte of the present embodiment, which is carried out in the following steps:

[0061] Step 1: Dry the lithium salt:

[0062] Put lithium difluoro(oxalate)borate (LiDFOB) into the glove box vacuum transition cabin, set the temperature of the transition cabin to 80℃, dry for 24h, use the moisture detector to detect that the moisture content is less than 100ppm, to obtain dried lithium difluoro(oxalate)borate, and then transfer it into the glove box after cooling.

[0063] Step 2:

[0064] S1, add Wash the molecular sieve with anhydrous ethanol for 5 times, then transfer it into the oven, dry at 80℃ for 24h, then calcine at 350℃ for 3h under air atmosphere, and then transfer it into the glove box after cooling;

[0065] S2: Add fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate into three 20mL glass bottles respectively, then add the calcined Molecular sieve into each of them respectively, so that the calcined Molecular sieve is immersed in fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate respectively, immerse for 24h, use the moisture detector to detect that the moisture content is less than 50ppm, to obtain dried fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate respectively.

[0066] Step 3: In the glove box, prepare a 20 mL glass empty bottle, add the dried lithium difluoro(oxalate)borate after step 1, then add the dried fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate obtained in step 2 in turn, stir at 25℃ for 12h, to obtain a wide temperature range lithium ion battery electrolyte, wherein the concentration of the solute lithium difluoro(oxalate)borate in the wide temperature range lithium ion battery electrolyte is 1mol / L, and the volume fractions of fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate in the mixed solvent are 20vol%, 40vol% and 40vol% in turn.

[0067] Embodiment 4: A preparation method of a wide-temperature-range lithium ion battery electrolyte according to the embodiment is performed in the following steps:

[0068] Step 1: Oven-drying treatment of lithium salt:

[0069] LiDFOB was placed in a glove box vacuum transition cabin, the temperature of the transition cabin was set to 80°C, and oven-drying was performed for 24 hours. A moisture detector was used to detect that the moisture content was less than 100 ppm, and oven-dried LiDFOB was obtained. After cooling, it was transferred into the glove box for standby.

[0070] Step 2:

[0071] S1, LiDFOB was oven-dried in the glove box, and the oven-drying temperature was set to 80°C. Oven-drying was performed for 24 hours. A moisture detector was used to detect that the moisture content was less than 100 ppm, and oven-dried LiDFOB was obtained. After cooling, it was transferred into the glove box for standby. The molecular sieve was washed with anhydrous ethanol for 5 times, and then transferred into an oven for oven-drying at 80°C for 24 hours. After cooling, it was transferred into the glove box for standby.

[0072] S2: Fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate were respectively added into three 20 mL glass bottles, and then the calcined molecular sieve was added into each of the three 20 mL glass bottles, so that the calcined molecular sieve was immersed in fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate respectively. Immersion was performed for 24 hours. A moisture detector was used to detect that the moisture content was less than 50 ppm, and dry fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate were respectively obtained.

[0073] Step 3: In the glove box, a 20 mL glass empty bottle was prepared, oven-dried LiDFOB obtained in step 1 was added, and then dry fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate obtained in step 2 were sequentially added. Stirring was performed at 25°C for 12 hours, and a wide-temperature-range lithium ion battery electrolyte was obtained. In the wide-temperature-range lithium ion battery electrolyte, the concentration of solute LiDFOB was 1 mol / L, and the volume fractions of fluoroethylene carbonate, fluoro phenylacetonitrile and isobutyl formate in the mixed solvent were 20 vol%, 60 vol% and 20 vol% respectively.

[0074] Comparative Example 1: Commercial electrolyte composition: 1M LiPF6, ethylene carbonate / dimethyl carbonate (EC / DMC = 1 / 1).

[0075] Test experiment:

[0076] The performance of the wide-temperature-range lithium ion battery electrolyte prepared in Embodiment 1 and the commercial electrolyte of Comparative Example 1 was characterized, and the specific test process was as follows:

[0077] (1) Viscosity test:

[0078] Test procedure: prepare 30 mL sample, use parallel plate measurement system of rheometer, fix 1000 s -1 constant shear rate, conduct viscosity test at -50-100℃.

[0079] Results are shown in Figures 1-2 and Table 1, from Figures 1-2 it can be seen that the viscosity of the commercial electrolyte rapidly increases to 930 mpa·s at -30℃, and turns into solidification state, while the viscosity of the wide temperature range electrolyte of Example 1 of the present application slowly increases from room temperature to -50℃, and the viscosity at -50℃ is only 73 mpa·s; in addition, the viscosity of the wide temperature range electrolyte of Example 1 of the present application is always lower than that of the commercial electrolyte of Comparative Example 1 in the range from room temperature to 100℃, which shows that the wide temperature range electrolyte of the present application can significantly improve the viscosity of the electrolyte at different temperatures, thereby improving the transmission capacity of lithium ions under high and low temperature conditions.

[0080] (2) Differential scanning calorimetry test:

[0081] Test procedure: use pure aluminum sealed pan to hold electrolyte, under nitrogen atmosphere, initial equilibrium temperature is -150℃, heat to 30℃ at a rate of 5℃ / min, conduct differential scanning calorimetry test.

[0082] Results are shown in Figure 3 and Table 1, from Figure 3 it can be seen that the freezing point of the wide temperature range electrolyte of Example 1 of the present application reaches -110℃, while the commercial electrolyte completely solidifies at -25℃, which shows that the wide temperature range electrolyte of Example 1 of the present application significantly reduces the freezing point of the electrolyte, which is conducive to meeting the application of the electrolyte in special extreme environments, so that the lithium ion battery can work normally.

[0083] (3) Thermogravimetric test:

[0084] Test procedure: use pure aluminum sealed pan to hold electrolyte, under nitrogen atmosphere, initial equilibrium temperature is 30℃, heat to 150℃ at a rate of 5℃ / min, conduct thermogravimetric test.

[0085] Results are shown in Figure 4 , from Figure 4 it can be seen that the residual mass of the wide temperature range electrolyte of Example 1 of the present application at 100℃ is 56.76%, which is higher than 47.47% of the commercial electrolyte, which shows that the wide temperature range electrolyte of Example 1 of the present application has lower volatility compared with the commercial electrolyte.

[0086] (4) Lithium ion conductivity test:

[0087] Test procedure: use parallel 1cm 2The platinum plate is 1 cm away from the other platinum plate, the electrolyte is immersed in the two platinum plate electrodes, and the conductivity is tested by an alternating current impedance method.

[0088] The results are shown in Table 1. Figure 5 As can be seen from Table 1, Figure 5 at a working temperature lower than -40℃, the lithium ion conductivity of the wide-temperature-range electrolyte of Example 1 of the present application is obviously higher than that of the commercial electrolyte, and the lithium ion conductivity at -70℃ is 4.5 x 10 4 times that of the commercial electrolyte.

[0089] (5) Lithium ion transference number and contact angle with the separator test:

[0090] The lithium ion transference number test process: by assembling a Li / Li battery, an R0 is obtained by an alternating current impedance test, then an I-t test is performed with a 10 mV voltage as ΔV to obtain an I0 and an I S , and an R S is obtained by an alternating current impedance test, and the transference number is calculated.

[0091] The separator contact angle test process: the separator is placed flat on a sample stage, 0.2 mL of electrolyte is added dropwise, and after the liquid is stable, a contact angle tester is used for photographing test.

[0092] The results are shown in Table 1. Figure 6 As can be seen from Table 1, Figure 6 the lithium ion transference number of the wide-temperature-range electrolyte of Example 1 of the present application is as high as 0.72, while the transference number of the commercial electrolyte is 0.39, and the electrolyte of Example 1 of the present application significantly improves the wettability with the separator, which is beneficial to improve the rate performance of the battery.

[0093] Table 1: electrolyte performance

[0094] Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Lithium ion conductivity (-70°C, mScm -1 )]]> 2.5 x 10 -6 ]]> 0.11 0.09 0.05 0.03 Freezing point (°C) –25 –110 –100 –92 –86 Minimum operating temperature (°C) –20 –70 –60 –40 –40 Maximum operating temperature (°C) 60 100 90 80 80

[0095] Application Example 1: NCM811 is used as a positive electrode material, lithium sheet is used as a negative electrode, and the wide-temperature-range lithium ion battery electrolyte prepared in Example 1 and the commercial electrolyte of Comparative Example 1 are used to assemble lithium ion batteries, which are counted as NCM811 / Li batteries.

[0096] The lithium ion batteries assembled by using the wide-temperature-range lithium ion battery electrolyte prepared in Example 1 and the commercial electrolyte of Comparative Example 1 are subjected to charge-discharge tests at different temperatures, and the results are as follows:

[0097] Figure 7 are charge-discharge test graphs of NCM811 / Li batteries using the wide-temperature-range electrolyte of Example 1 of the present application and the commercial electrolyte at different temperatures, and Figure 7 ​It can be seen that the electrochemical performance of the NCM811 / Li battery using the wide-temperature-range electrolyte of Example 1 of the present invention is significantly higher than that of the NCM811 / Li battery using the commercial electrolyte at different temperatures. Moreover, the NCM811 / Li battery using the commercial electrolyte can hardly discharge below -30°C, while the NCM811 / Li battery using the wide-temperature-range electrolyte of Example 1 of the present invention can charge and discharge at a minimum of -70°C. The NCM811 / Li battery using the wide-temperature-range electrolyte of Example 1 of the present invention can operate at a maximum of 100°C, while the NCM811 / Li battery using the commercial electrolyte cannot operate normally at 70°C.

[0098] Figure 8 The following is a charge-discharge test chart of the NCM811 / Li battery using the wide-temperature-range electrolyte of Example 1 of this invention at -70°C. Figure 8 It can be seen that the NCM811 / Li battery using the wide-temperature-range electrolyte of Example 1 of the present invention can operate stably for 40 cycles at -70℃, with a discharge specific capacity as high as 100mAh g. -1 .

[0099] Figure 9 The graphs show the charge-discharge test results of the NCM811 / Li battery using the wide-temperature-range electrolyte of Example 1 of this invention and a commercial electrolyte at a high temperature of 80°C. Figure 9 It can be seen that the NCM811 / Li battery using the wide-temperature-range electrolyte of Example 1 of the present invention can work stably at a high temperature of 80°C, and the capacity retention rate is as high as 78% after 500 cycles; while the NCM811 / Li battery using commercial electrolyte can hardly work at a high temperature of 80°C, and the capacity decays to zero in less than 20 cycles.

[0100] Application Example 2: Using NCM811 as the positive electrode material and graphite as the negative electrode, a full cell is assembled using the wide-temperature-range lithium-ion battery electrolyte prepared in Example 1, which is called a graphite / NCM811 full cell.

[0101] The graphite / NCM811 full cell assembled using the wide-temperature-range lithium-ion battery electrolyte prepared in Example 1 of this invention was subjected to charge-discharge tests at -50°C, and the results are as follows: Figure 10 As shown, from Figure 10 As can be seen, since the commercial electrolyte used in the graphite / NCM811 full cell cannot function properly at -50℃, its discharge performance at -50℃ is omitted. However, the graphite / NCM811 full cell using the wide-temperature-range electrolyte of Example 1 of this invention can operate stably for 20 cycles at -50℃, with a discharge specific capacity as high as 108 mAh g⁻¹. -1 .

[0102] The above merely describes preferred specific embodiments of the present application, which are based on different implementations of the overall concept of the present application, and the protection scope of the present application is not limited thereto. Any changes or replacements that are easily conceived by those skilled in the art within the technical scope disclosed by the present application shall be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A wide temperature range lithium ion battery electrolyte, characterized in that, It is prepared from a lithium salt and a mixed solvent composed of 20 vol% fluoroethylene carbonate, 20 vol% fluoroacetonitrile and 60 vol% isobutyl formate, and has a working temperature range of -70-100 DEG C when assembled into a lithium ion battery, wherein the lithium salt is LiDFOB, and the lithium salt concentration in the electrolyte is 0.1-1 mol / L.

2. The wide temperature range lithium ion battery electrolyte of claim 1, wherein, The fluoroacetonitrile includes o-fluoroacetonitrile, m-fluoroacetonitrile, p-fluoroacetonitrile, difluoroacetonitrile, trifluoroacetonitrile, tetrafluoroacetonitrile and pentafluoroacetonitrile.

3. The preparation method of the wide-temperature-range lithium ion battery electrolyte according to any one of claims 1-2, characterized in that, The method is performed according to the following steps: Step 1: drying treatment of the lithium salt; Step 2: washing, drying and calcining 4 Å molecular sieves, and then immersing them in fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate respectively to obtain dried fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate respectively; Step 3: adding the dried fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate into the lithium salt in sequence, and stirring at room temperature to obtain the wide-temperature-range lithium ion battery electrolyte.

4. The production method according to claim 3, characterized by, The drying temperature in step 1 is 70-90 DEG C, and the time is 24-48 h, and the moisture content of the lithium salt after drying is less than 100 ppm.

5. The preparation method according to claim 3, characterized in that, In step 2, the 4-6 times of washing is performed with anhydrous ethanol, the drying temperature is 70-90 DEG C, the time is 24-48 h, the calcining temperature is 350-400 DEG C, and the time is 2-4 h.

6. The preparation method according to claim 3, characterized in that, In step 2, the moisture contents of the dried fluoroethylene carbonate, fluoroacetonitrile and isobutyl formate are all less than 50 ppm.

7. The preparation method according to claim 3, characterized in that, In step 3, the stirring time is 12-24 h, and the room temperature is 25-35 DEG C.

8. Use of the wide-temperature-range lithium-ion battery electrolyte according to any one of claims 1-2, characterized in that, The electrolyte is used for assembling a lithium ion battery.

9. Use according to claim 8, characterized in that, The working temperature range of the lithium ion battery is -70-100 DEG C.

Images