Conductive grease based on ionic liquid modification and preparation method thereof

Abstract

The application discloses a kind of electrically conductive grease based on ionic liquid modification and preparation method thereof, including base grease and modified ionic liquid;The modified ionic liquid is obtained by in-situ functionalization reaction of BMIMPF6 with CF3I.This application controls the molar ratio (preferably 2:1) of BMIMPF6 and CF3I and reaction temperature (preferably 60 DEG C) accurately, and the modified ionic liquid with high conductivity (≥9.68 ms / cm) and excellent thermal stability (onset decomposition temperature ≥318 DEG C) is prepared.It can significantly reduce the volume wear rate (lowest to 6.84×10 7 mm³ / (N·m)) and friction coefficient of current-carrying friction pair by adding it to composite lithium-based grease with a certain mass fraction (preferably 0.5%-1.5%).The application effectively solves the problem that existing lubricating grease is prone to electric erosion and severe wear in the bearing of new energy vehicle electric drive system by forming a fluoride protective film and enhancing the internal polar network of the grease.

Description

Technical Field

[0001] This invention relates to the field of lubricating materials technology, specifically to a conductive lubricating grease based on in-situ functionalization modification of ionic liquid and its preparation method. Background Technology

[0002] With the rapid development of the new energy vehicle industry, its core "three-electric system" (battery, motor, and electronic control) has placed higher demands on the reliability and lifespan of key components. Bearings and other transmission components within the electric drive system must withstand both mechanical loads and the impact of electrical loads. When current passes through the bearing contact surface, it generates electrolytic corrosion phenomena such as Joule heating, arc discharge, and electrochemical corrosion, leading to localized melting and oxidation of the material surface, accelerating wear, and severely reducing the bearing's lifespan and the overall vehicle safety.

[0003] Currently, common lubricating greases include lithium-based greases, polyurea greases, and composite lithium-based greases. Lithium-based greases are widely used in automobiles and industrial equipment due to their low cost and good mechanical stability. Traditional lubricating greases perform well under no-current conditions, but their lubrication performance drops sharply under current-carrying conditions. Current can damage the molecular structure of the grease, leading to carbonization and failure, preventing the formation of an effective lubricating film. In recent years, ionic liquids have attracted widespread attention as a novel lubricating material. Ionic liquids are molten salts composed of organic cations and inorganic anions, exhibiting low volatility, high thermal stability, and good electrical conductivity. Adding ionic liquids to lubricating greases is expected to improve conductivity and anti-wear properties. However, the high cost of ionic liquids and the unresolved compatibility issues with lubricating greases limit their industrial application. Therefore, improving the performance of ionic liquids through modification techniques, optimizing their compounding with lubricating greases, and reducing costs have become current research hotspots.

[0004] This invention focuses on the lubrication problem in the transmission system of new energy vehicles. By compounding and modifying ionic liquids, a novel conductive grease is prepared, and its preparation process is optimized. The performance of the modified grease is verified on a current-carrying friction test bench, providing technical support for the design of lubrication materials for the transmission system of new energy vehicles. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a conductive grease based on ionic liquid modification and its preparation method. By in-situ functionalizing BMIMPF6 with CF3I, the conductivity, thermal stability, and anti-wear properties of the lubricating oil are improved. It is suitable for current-carrying friction pairs such as bearings in electric drive systems of new energy vehicles. Moreover, its preparation process is simple and controllable, making it suitable for industrial production.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a conductive grease modified with an ionic liquid, comprising a base grease and a modified ionic liquid dispersed in the base grease; The modified ionic liquid is a reaction product obtained by in-situ functionalization of BMIMPF6 with CF3I (trifluoroiodomethane); The molar ratio of BMIMPF6 to CF3I is 1:1 to 2:1, and the reaction temperature of the in-situ functionalization reaction is 50-70℃.

[0007] Furthermore, the modified ionic liquid has a mass fraction of 0.5-2% in the conductive grease.

[0008] Preferably, the modified ionic liquid has a mass fraction of 0.5-1.5% in the conductive grease. Most preferably, it is 1%. Too low a concentration will result in insignificant effects, while too high a concentration (e.g., >2%) will cause the coefficient of friction and wear rate to increase.

[0009] Furthermore, the molar ratio of BMIMPF6 to CF3I is 2:1, and the reaction temperature of the in-situ functionalization reaction is 60°C. The product under these conditions exhibits optimal electrical conductivity and wear resistance.

[0010] Furthermore, the base grease can be any type of grease commonly used in the art, preferably a composite lithium-based grease with good compatibility with ionic liquids.

[0011] As a base grease system, a conventional type of complex lithium-based grease can be selected, such as by heating and stirring the complex lithium soap thickener and base oil at 120-150℃ to form a homogeneous base grease system.

[0012] The conductive grease prepared by this invention exhibits excellent comprehensive performance: its conductivity can reach 7.23 ms / cm or higher, preferably 9.68 ms / cm or higher; and its volumetric wear rate under current-carrying conditions can be as low as 1.1 × 10⁻⁶. -6 mm 3 / (N·m) or less, preferably as low as 6.84×10 -7 mm 3 / (N·m) or less; the initial thermal decomposition temperature can reach above 304℃, preferably above 318℃.

[0013] This invention screened various ionic liquids (BMIMBF4, BMIMPF6, BMIMHF3) and selected BMIMPF6 as the base for modification, based on its optimal overall performance. Further research revealed that simply increasing the amount of BMIMPF6 (e.g., exceeding 1%) led to a decrease in the anti-wear performance of the grease due to agglomeration and disruption of the grease structure. Therefore, this invention proposes an innovative in-situ functionalization modification strategy. Reacting CF3I with BMIMPF6 significantly improves the conductivity and thermal stability of the product. More importantly, by precisely controlling the reactant molar ratio (especially 2:1) and reaction temperature (especially 60°C), optimal reaction degree and product structure can be obtained, resulting in excellent synergistic effects in the final grease: not only is the conductivity significantly increased from 1.51 ms / cm to 9.68 ms / cm, but the initial decomposition temperature also increases from 304.35°C to 318.18%, while the volumetric wear rate is reduced to 6.84 × 10⁻⁻⁻⁻⁶. 7 mm³ / (N·m) was reduced by 55.3% compared to unmodified composite lithium-based grease.

[0014] The present invention also provides a method for preparing the above-mentioned conductive grease, comprising the following steps: (1) Preparation of modified ionic liquid: BMIMPF6 and CF3I are weighed according to the ratio of 1:1 to 2:1, and placed in a sealed reaction vessel. The mixture is stirred and reacted under constant temperature conditions of 50-70℃ to obtain the modified ionic liquid. (2) Compounding: The modified ionic liquid obtained in step (1) is added to the base grease according to a predetermined mass fraction, mixed evenly, and then subjected to vacuum degassing treatment to obtain conductive grease.

[0015] Furthermore, in step (1), the reaction is carried out in an acetonitrile solvent system for 4-6 hours.

[0016] The acetonitrile solvent system is acetonitrile: BMIMPF6+CF3I with a ratio of (2:1) to (5:1).

[0017] Further, in step (1), after the reaction is complete, the mixture is cooled to room temperature and the washing solution is used to remove iodide ions.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention improves conductivity, thermal stability, and anti-wear performance by in-situ functionalizing BMIMPF6 with CF3I. After modification, the fluorine introduced into the grease forms a dense fluoride protective film at the friction interface, effectively isolating the friction pair surface and preventing electrolytic corrosion. At the same time, the reaction products enhance the polar network and ion migration channels inside the grease, which is the fundamental reason for the improved conductivity. In particular, the optimized process with a molar ratio of 2:1 and a temperature of 60°C brings excellent lubrication effect.

[0019] (2) The present invention effectively solves the problem of performance degradation of existing conductive greases at high concentrations, and provides a solution that achieves excellent performance with a low addition amount (1%), reducing costs and ensuring the colloidal stability of the grease.

[0020] (3) The preparation method of the present invention is simple, the reaction conditions are mild, and the key parameters (molar ratio and temperature) are easy to control, which has good prospects for industrialization. Attached Figure Description

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0022] Figure 1 The average coefficient of friction for different ionic liquids at a mass fraction of 1% in Example 1; Figure 2 The average coefficient of friction for different ionic liquids at a mass fraction of 3% in Example 1; Figure 3 The average coefficient of friction for different ionic liquids at a mass fraction of 5% in Example 1; Figure 4 The volumetric wear rate of different ionic liquids at a mass fraction of 1% in Example 1; Figure 5 The volumetric wear rate of different ionic liquids at a mass fraction of 3% in Example 1; Figure 6 The volumetric wear rate of different ionic liquids at a mass fraction of 5% in Example 1; Figure 7 The average coefficient of friction in Example 2 with a mass fraction of 0.5-2% BMIMPF6 modified grease; Figure 8 The volumetric wear rate of the BMIMPF6 modified grease in Example 2 with a mass fraction of 0.5-2%; Figure 9 The average coefficient of friction of the 1:1 modified grease of BMIMPF6 and CF3I at different temperatures in Example 3; Figure 10 The average coefficient of friction of the modified grease made by compounding BMIMPF6 and CF3I in a 2:1 ratio at different temperatures in Example 3; Figure 11 The volumetric wear rate of the 1:1 compound modified grease of BMIMPF6 and CF3I at different temperatures in Example 3; Figure 12 The volumetric wear rate of the modified grease, a mixture of BMIMPF6 and CF3I in a 2:1 ratio, was measured at different temperatures in Example 3. Figure 13 The average coefficient of friction in Example 4 is calculated using BMIMPF6 and CF3I modified grease with a mass fraction of 0.5-2%. Figure 14 The volumetric wear rate is given by the modified BMIMPF6 and CF3I grease in Example 4 at a mass fraction of 0.5-2%. Figure 15 For the 1% BMIMPF6 modified grease in Example 2: (a) Differential scanning calorimetry curve; (b) Thermogravimetric analysis curve; Figure 16 For the modified BMIMPF6 and CF3I grease (molar ratio 2:1, reaction temperature 60°C) in Example 4 at a mass fraction of 1%, (a) differential scanning calorimetry curve; (b) thermogravimetric analysis curve; Figure 17 The conductivity of the modified ionic liquids under different preparation processes in Example 3; Figure 18 Infrared images of lithium composite and two modified greases (lithium composite + BMIMPF6, lithium composite + BMIMPF6 + CF3I). Detailed Implementation

[0023] 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.

[0024] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product instructions shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0025] The experimental testing method is as follows: Friction and Wear Test: Friction and wear tests were conducted using a reciprocating current-carrying tribological testing machine. The friction-reducing performance of the grease was analyzed by comparing the friction coefficients. The test temperature was room temperature, a ball-disc friction pair was used, and the lubricating medium was a composite lithium-based grease modified with ion liquid. The friction test time was 60 minutes, the reciprocating stroke was 5 mm, and the frequency was 4 Hz. The friction pair consisted of a steel ball and a rectangular A100 steel plate, with the steel ball diameter being 6 mm and the base plate size being 20 mm × 30 mm × 5 mm. The load was 10 N, and the current was 10 A.

[0026] Volumetric wear rate test: The samples before and after wear were weighed using an electronic balance (ME204, 0.1mg). The surface profile of the disc sample after wear was measured using a stylus profilometer, and the wear rate was calculated based on the wear track profile.

[0027] Microscopic analysis: The scanning electron microscope (SEM, JSM-650) and EDAX energy dispersive spectrometer (EDS, INCA energy) used for surface analysis and elemental determination of wear marks were provided by Xi'an Qinghua Company of Northern Special Energy Co., Ltd.

[0028] Thermal stability test: The composition of the grease before and after modification was analyzed by infrared spectroscopy. Its thermal stability and thermal decomposition temperature were characterized by DSC and TGA curves. The infrared spectrometer and differential scanning calorimeter were both from China Petroleum Lubricating Oil Company.

[0029] In-situ functionalization modification of ionic liquids was performed using a water bath heated magnetic stirrer from Licheng Technology Co., Ltd.

[0030] The conductivity of the ionic liquid was measured using an APT conductivity meter.

[0031] Example 1 Using three ionic liquids—BMIMBF4, BMIMBF6, and BMIMBF3—as additives, this study systematically investigated their modification effects and wear mechanisms on the anti-electro-erosion wear performance of composite lithium-based grease at different addition amounts. By comparing and analyzing the lubrication performance and conductivity of different ionic liquids, the optimal ionic liquid system was selected.

[0032] The three ionic liquids, BMIMBF4, BMIMPF6, and BMIMIHF3, were all provided by Shanghai Aladdin Biochemical Technology Co., Ltd. The purity of the ionic liquids is >97%, and their basic data sources and performance are shown in Table 1.

[0033] Table 1 type Molecular formula Molecular weight (g / mol) Density (g / cm³) Refractive index (nD) Boiling point (°C) Melting point (°C) Conductivity (ms / cm) <![CDATA[BMIMBF4]]> <![CDATA[C8H 15 BF4N2]]> 312.1 1.21 1.428 350 15 1.22 <![CDATA[BMIMPF6]]> <![CDATA[C8H 15 N2F6P]]> 284.2 1.38 1.435 350 6.5 1.51 <![CDATA[BMIMHF3]]> <![CDATA[C8H 15 F3IN2]]> 226.2 1.52 1.442 288 16 1.01 Using a lithium-based composite grease system, different ionic liquids (BMIMBF4, BMIMBF6, and BMIMBF3) were added to the base grease at mass fractions of 1%, 3%, and 5%, respectively. The ionic liquids were pre-dispersed with a small amount of anhydrous ethanol before addition to ensure uniform distribution within the grease. After mixing, the mixture was stirred at high speed for 30 min at room temperature, followed by vacuum degassing to remove air bubbles. Finally, modified grease samples with different ionic liquids and concentrations were prepared and labeled in the format of "ionic liquid type-concentration". All samples were sealed and stored to prevent oxidation and moisture absorption for subsequent performance testing and analysis.

[0034] 1. Tribological property analysis Figure 1 The friction coefficient of the composite lithium-based grease is calculated using three ionic liquids, BMIMBF4, BMIMBF6, and BMIMBF3, as additives at a mass fraction of 1%. The average friction coefficients of the three modified greases were 0.102, 0.083, and 0.098, respectively, with all modifications showing a decrease in average friction coefficient. Compared to the unmodified composite lithium, the average friction coefficients of the modified greases prepared from the three ionic liquids decreased by 1.17%, 18.87%, and 4.28%, respectively, indicating improved friction reduction performance. Overall, BMIMBF4 did not significantly improve the effect of electrolytic erosion damaging the lubricating oil film, leading to oil film rupture. BMIMPF6 showed the most significant modification effect, exhibiting the best friction reduction performance, with BMIMHF3 falling in between. Combined with conductivity analysis, the conductivity of the three ionic liquids was 1.22 ms / cm, 1.51 ms / cm, and 1.01 ms / cm, respectively. This is because BMIMPF6 has higher conductivity, reducing the contact resistance of the contact surface, resulting in reduced current heat and lowering the coupling effect of frictional heat and current heat during the experiment, thus making the grease relatively stable during the experiment.

[0035] As the mass fraction increases, the friction coefficients of the three ionic liquids, BMIMBF4, BMIMBF6, and BMIMBF3, at a 3% mass fraction are as follows: Figure 2As shown in the figure, the average friction coefficients of the three ionic liquids generally showed an increasing trend, increasing by 2.85%, 23.51%, and 1.56%, respectively. BMIMPF6 showed the largest change, while BMIMHF3 showed the smallest. Overall, based on physicochemical property analysis, the density of BMIMHF3 is 1.52 g / cm³, while the densities of the other two ionic liquids are 1.21 g / cm³ and 1.38 g / cm³, respectively. With the increase of the amount of ionic liquid added, its dispersion uniformity in the grease decreased, resulting in excessively high local concentrations and agglomeration. Agglomerated ionic liquids may not be able to effectively form a uniform lubricating film, but instead produce uneven frictional contact on the friction surface, causing the friction coefficient to fluctuate more. The friction coefficient fluctuation of BMIMHF3 is more severe compared to the 1% mass fraction, which is because the density of BMIMHF3 is too high compared to the other two ionic liquids, making the agglomeration phenomenon more obvious.

[0036] like Figure 3 When the mass fraction of the three ionic liquids, BMIMBF4, BMIMPF6, and BMIMIHF3, reaches 5%, the average friction coefficient is lowest for BMIMHF3 (0.104), followed by the other two (0.105 and 0.107). BMIMPF6 exhibits the worst friction-reducing performance at the highest mass fraction, showing a 2.8% increase in friction coefficient compared to a 3% mass fraction. This is because BMIMPF6 has a larger molecular weight (312.1 g / mol) than BMIMBF4 and BMIMHF3, leading to more severe agglomeration at higher mass fractions. Overall, the average friction coefficient of the three ionic liquids further increases. Analysis of the trends suggests that, besides agglomeration, this may be directly related to the grease concentration: ionic liquids have strong fluidity, and high concentrations may disrupt the colloidal structure of the grease, affecting its rheological properties and mechanical stability. This leads to a decrease in grease viscosity, preventing the formation of a stable lubricating film on the friction surface, resulting in drastic fluctuations in the friction coefficient during friction and wear, and ultimately an increase in the average friction coefficient.

[0037] Figure 4 The volumetric wear rates of three ionic liquids, BMIMBF4, BMIMPF6, and BMIMIHF3, at a mass fraction of 1% were shown. The volumetric wear rate of BMIMBF4 was 1.53 × 10⁻⁶. -6 mm 3 ×(N·m) -1 Compared to before modification, it increased by 8.5%; the best performance after modification was achieved with BMIMPF6, with a volumetric wear rate of 1.07 × 10⁻⁶. -6 mm 3 ×(N·m) -1Compared to before modification, it decreased by 24.11%; the volumetric wear rate of BMIMHF3 was 1.41 × 10⁻⁶. -6 mm 3 ×(N·m) -1 Compared to the other two ionic liquids, it was at a mid-level, but the modification effect was still poor, with a 5.7% increase in volumetric wear rate compared to the unmodified version. Overall, at a mass fraction of 1%, only BMIMPF6 showed improved anti-wear performance after modification with different ionic liquids, while BMIMBF4 showed the worst.

[0038] The volumetric wear rates exhibited by the modified greases prepared from three ionic liquids at a 3% mass fraction are as follows: Figure 5 As shown, BMIMPF6 still exhibits the lowest volumetric wear rate, at 1.53 × 10⁻⁶. -6 mm 3 ×(N·m) -1 Compared to a 1% mass fraction, this represents a 43% increase, but compared to the unmodified grease, it represents an 8.5% increase. The modified grease with the highest volumetric wear rate is BMIMHF3, with a volumetric wear rate increasing to 2.01 × 10⁻⁶. -6 mm 3 ×(N·m) -1 The year-on-year growth rate was 42.6%, while BMIMBF4 showed the smallest change at 9.2%. Overall, as the mass fraction increased, the modification effect of each ionic liquid on the anti-wear performance gradually deteriorated, and the volumetric wear rate showed an increasing trend. BMIMPF6 still showed the best anti-wear performance at a mass fraction of 3%. With the increase of mass fraction, the anti-wear performance of BMIMHF3 decreased the most significantly, while BMIMBF4 was least affected by the mass fraction.

[0039] Figure 6 The volumetric wear rates of three ionic liquids at a 5% mass fraction were shown, with the volumetric wear rates of the three ionic liquids being 1.61 × 10⁻⁶. -6 mm 3 ×(N·m) -1 1.67×10 -6 mm 3 ×(N·m) -1 and 2.08×10 -6 mm 3 ×(N·m) -1As the mass fraction further increased, the volumetric wear rate of BMIMBF4 showed a decreasing trend, decreasing by 3.6% year-on-year, while the other two ionic liquids showed a further increasing trend, increasing by 9.2% and 3.5% respectively. The volumetric wear rate of BMIMPF6 was most affected by concentration. Overall, at a mass fraction of 5%, BMIMBF4 showed the best anti-wear effect, while the effect of BMIMPF6 deteriorated with further increases in mass fraction, and BMIMHF3 still showed the worst anti-wear performance.

[0040] Example 2 BMIMPF6 exhibited the best tribological properties in the above performance comparison, but its anti-wear performance gradually weakened as the mass fraction increased. In order to explore the optimal compounding concentration of BMIMPF6 modified grease, this example further investigates the effect of BMIMPF6 at four addition concentrations of 0.5%, 1%, 1.5% and 2% on the tribological properties of the modified grease.

[0041] Figure 7 The friction coefficients of BMIMPF6 modified grease at mass fractions of 0.5%, 1%, 1.5%, and 2% are shown. The average friction coefficient histogram shows that the average friction coefficient first decreases and then increases with increasing mass fraction, with a trough at 1%, indicating that this mass fraction is the optimal concentration for improving the lubrication performance of BMIMPF6 modified lithium composite grease.

[0042] Figure 8 Two-dimensional wear track profiles and volumetric wear rates of BMIMPF6 modified grease at mass fractions of 0.5%, 1%, 1.5%, and 2% are presented. The wear track depths at the four mass fractions were 2.7 μm, 2.65 μm, 3.4 μm, and 3.5 μm, respectively, with the shallowest track at 1% and the deepest at 1.5%, representing a 28.3% increase. The wear track widths were 0.34 mm, 0.27 mm, 0.265 mm, and 0.305 mm, respectively. While the 1.5% mass fraction showed the greatest depth, its width was relatively small, followed by the 1% mass fraction. The 0.5% mass fraction grease had the largest wear track width. Overall, the 1% wear track profile was more uniform, while the 1.5% track was elongated. The volumetric wear rate histogram shows that the volumetric wear rates at the four mass fractions were 1.54 × 10⁻⁶, respectively. -6 mm 3 ×(N·m) -1 1.07×10 -6 mm 3 ×(N·m) -1 1.50×10 -6 mm 3 ×(N·m)-1 and 1.56×10 - 6 mm 3 ×(N·m) -1 The second group had the lowest volumetric wear rate, indicating that 1% mass fraction also has the best anti-wear performance; while the fourth group had the worst anti-wear performance, that is, at 2% content, the volumetric wear rate increased by 45.8% year-on-year; overall, the volumetric wear rate showed a trend of first decreasing and then increasing with the increase of mass fraction, which corresponds to the trend of friction coefficient that reflects the wear reduction performance mentioned above.

[0043] Example 3 The above investigation revealed that the conductive grease prepared by adding 1% BMIMPF6 ionic liquid to the composite lithium-based grease exhibits excellent tribological properties under current-carrying conditions. This is fundamentally due to the improved conductivity and thermal stability of the grease itself, as well as the combined effect of the fluoride protective film formed by the fluorine element during friction and wear. To further improve the tribological properties of the conductive grease, this embodiment introduces CF3I to react with BMIMPF6, performing in-situ functionalization modification. While introducing the fluorine element, its conductivity and thermal stability are also improved, thereby preparing a conductive grease with even better performance.

[0044] The preparation process of the conductive grease after in-situ functionalization modification with ionic liquid is as follows: BMIMPF6 and CF3I were weighed separately at molar ratios of 1:1 and 2:1 and placed in sealed reaction vessels. An appropriate amount of acetonitrile was added to prepare the reaction system. The mixture was placed in a constant-temperature water bath and heated at 50℃, 60℃, and 70℃ respectively, while simultaneously stirring at a constant speed using a magnetic stirrer. The reaction time was 5 hours. To prevent CF3I volatilization, the reaction vessel was sealed throughout the process. After the reaction, the mixture was cooled to room temperature, and the solution was washed to remove iodide ions, yielding a colorless or transparent modified ionic liquid. The reaction products were analyzed by infrared spectroscopy to verify the degree of reaction between BMIMPF6 and CF3I and the structure of the products. The conductivity was measured using a conductivity meter.

[0045] Finally, the modified ionic liquid was added to the composite lithium grease at a mass fraction of 1% to prepare the conductive grease after in-situ functionalization of the ionic liquid, which was used for subsequent performance testing and analysis.

[0046] Figure 9The study demonstrated the friction coefficients of modified greases prepared at different temperatures with a BMIMPF6 to CF3I molar ratio of 1:1. From the perspective of average friction coefficient, the friction coefficient at 70℃ was the lowest, at 0.097, representing a 16.8% increase compared to the 1% BMIMPF6 condition. The worst performance was observed at 1:1 and 60℃, with a friction coefficient of 0.111, an increase of 33.7%. Overall, the average friction coefficients of the three groups at a 1:1 molar ratio were all higher than those without CF3I, but the three friction coefficient curves were more stable without sustained drastic fluctuations, indicating improved stability of the grease during lubrication.

[0047] When the molar ratio of BMIMPF6 to CF3I changes to 2:1, under the same conditions, the friction coefficients of the modified grease prepared after reaction at different temperatures are as follows: Figure 10 As shown, when the preparation process is 2:1 at 50℃, the friction coefficient increases significantly, making it the worst in terms of friction reduction performance among all modifications. The fluctuation range is twice as long as that without CF3I modification, with an average friction coefficient of 0.171. However, with increasing reaction temperature, the other two preparation processes at a 2:1 molar ratio exhibit excellent friction coefficients. At 60℃, the average friction coefficient is 0.102, the lowest among the three processes; and at 70℃, the average friction coefficient is 0.105. Overall, the average friction coefficient of the modified greases prepared at all three reaction temperatures is higher than that without CF3I. However, the latter two friction coefficients are very stable, with the grease prepared at 60℃ showing the best friction coefficient and the one prepared at 50℃ showing the worst. Considering all six preparation processes, the 2:1 process at 60℃ exhibits the most stable lubrication performance, while the 1:1 process at 70℃ shows the lowest average friction coefficient; both possess good friction reduction properties.

[0048] The volumetric wear rate of the modified lithium-based grease at different reaction temperatures was as follows: (BMIMPF6 to CF3I molar ratio 1:1) Figure 11 As shown, the volumetric wear rates under the three manufacturing processes are 1.36 × 10⁻⁶. -6 mm 3 ×(N·m) -1 1.1×10 - 6 mm 3 ×(N·m) -1 1.38×10 -6 mm 3 ×(N·m) -1 The lowest volumetric wear rate was at 60℃, compared to 1.07 × 10¹⁰ for the unmodified variety. -6 mm 3×(N·m) -1 The difference was only 0.03, while the other two preparation processes increased by 27.1% and 30% year-on-year, respectively. Based on the above, it can be seen that with a molar ratio of 1:1, a preparation temperature of 60℃ is the optimal temperature for improving the anti-wear performance of the modified grease.

[0049] Figure 12 The volumetric wear rate of the modified lithium-based composite grease at different reaction temperatures was shown when the molar ratio of BMIMPF6 to CF3I was 2:1. The volumetric wear rate at 50℃ was 1.89 × 10⁻⁶. -6 mm 3 ×(N·m) -1 The volumetric wear rate was the worst among different preparation processes, increasing by 76.6% compared to the process without in-situ modification; the volumetric wear rate was lowest at 60℃, at 6.84×10⁻⁶. -7 mm 3 ×(N·m) -1 This represents an order of magnitude improvement, a 36.01% reduction compared to the same period last year, and a 55.3% improvement in volumetric wear rate under the same operating conditions as unreinforced lithium. The volumetric wear rate at 70℃ is slightly higher than at 60℃, at 7.03 × 10⁻⁶. -7 mm 3 ×(N·m) -1 However, it still exhibits excellent anti-wear performance, with volumetric wear rate increasing by 31.8% and 54% year-on-year. In summary, BMIMPF6 and CF3I exhibit the best anti-wear performance at a molar ratio of 2:1 and a reaction temperature of 60℃, making them conductive greases with excellent tribological properties.

[0050] Example 4 In this embodiment, a modified ionic liquid was prepared by reacting BMIMPF6 and CF3I at a molar ratio of 2:1 and a reaction temperature of 60°C. The tribological properties of greases prepared from the modified ionic liquid at concentrations of 0.5%, 1%, 1.5%, and 2% were further investigated. By systematically comparing the coefficient of friction, volumetric wear rate, and conductivity of the greases at different concentrations, the influence of the concentration on the grease performance was clarified, providing experimental basis for optimizing grease formulations.

[0051] Figure 13The friction coefficients of conductive greases prepared with modified ionic liquid at mass fractions of 0.5%, 1%, 1.5%, and 2% were determined. The average friction coefficients for the four mass fractions were 0.102, 0.099, 0.103, and 0.107, respectively. The 1% mass fraction showed the lowest average friction coefficient, but it was not significantly different from the other three concentrations. The 2% mass fraction showed the highest average friction coefficient, representing a 7% year-on-year increase. Overall, the friction coefficient showed a trend of first decreasing and then increasing. The friction coefficient curves for the four mass fractions were relatively stable, indirectly confirming that 60℃ at a 2:1 ratio is the optimal parameter for preparing the modified conductive grease.

[0052] Figure 14 The volumetric wear rate was calculated when the modified liquid was added at concentrations of 0.5%, 1%, 1.5%, and 2% (by mass fraction). The volumetric wear rate at all four mass fractions was within 10%. -7 mm 3 ×(N·m) -1 All of these results were superior to those of modified greases with 1% BMIMPF6 added, with volumetric wear rates reduced by 14.1%, 36%, 25.4%, and 8.3% respectively, further validating the superiority of the preparation process parameters through anti-wear performance. The volumetric wear rate, consistent with the coefficient of friction, showed a trend of first decreasing and then increasing, indicating that the optimal concentration is between 0.5% and 1.5%, around 1%. Overall, selecting a 2:1 molar ratio, preparing the modified liquid at 60℃, and using a 1% mass fraction to prepare the modified grease were indeed the optimal parameters and concentrations, exhibiting the best tribological properties compared to other preparation process parameters and addition concentrations.

[0053] Thermal stability analysis Thermal stability is one of the important physicochemical properties affecting the wear resistance of grease under current-carrying conditions. To further explore the mechanism by which BMIMPF6 ionic liquid improves the wear resistance of composite lithium-based grease, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed on the modified grease at a mass fraction of 1% in Example 2, which showed the best performance. Figure 15 As shown.

[0054] Comparing the thermal stability characterization of the composite lithium-based grease, the DSC curves show that after adding 1% BMIMPF6, the DSC endothermic peak shifted slightly forward to 216.45°C, and the initial transition temperature decreased to 205.75°C. This phenomenon indicates that the introduction of the ionic liquid caused some disturbance to the grease structure, resulting in a slightly earlier thermal transition temperature range. This is because BMIMPF6 has a certain degree of fluidity, which affects the viscosity of the grease, making the microstructure more prone to flow or melting. This may allow the system to enter the thermal response state earlier, helping the grease to quickly establish a lubricating film in the early stages of operation. The TGA curves showed a more significant modification effect. The initial decomposition temperature of the grease modified with the ionic liquid was 304.35℃, which was 21.84℃ higher than the initial decomposition temperature of 282.51℃ for the composite lithium, representing a year-on-year increase of 7.73%. This directly indicates that the ionic liquid improved the thermal stability of the grease. Although the mass loss was significant (97.73%), this likely allows the grease to release more additives within this temperature range, enhancing its lubrication performance. Simultaneously, BMIMPF6 itself possesses an excellent polar structure, which can form stronger resistance to thermal decomposition in the grease system, improving the grease's lubrication stability at high temperatures. In summary, the introduction of BMIMPF6 not only effectively modulates the thermal response behavior of the grease but also significantly improves its thermal stability, providing a good guarantee for its lubrication stability under medium- and high-temperature current-carrying conditions.

[0055] To demonstrate whether the overall thermal stability of the in-situ functionalized ionic liquid-modified lithium-based grease synthesized by the chemical reaction of BMIMPF6 and CF3I is further improved under high-temperature friction conditions generated by electric current, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed on a group of greases from Example 4 that exhibited the best performance at a 1% mass fraction, with a molar ratio of 2:1 and a reaction temperature of 60°C. The results are as follows. Figure 16As shown in the DSC curve, the endothermic peak of this grease is located at 218.55°C, and the initial thermal transition temperature is 208.66°C, both higher than that of the unreacted BMIMPF6-added sample. The waveforms are also sharper and more compact, indicating a more stable combination of the reaction product and the thickener, a more concentrated thermal transition process, better structural stability and endothermic efficiency, and faster thermal response characteristics. Thermogravimetric analysis (TGA) further verifies its excellent thermal stability: the initial thermal decomposition temperature of this sample is as high as 318.18°C, 14°C higher than that of the unreacted BMIMPF6-added sample. Its mass loss rate is 98%, slightly higher than the unreacted BMIMPF6-added sample, but the increase is minimal. This demonstrates that the modified ionic liquid formed after the reaction of BMIMPF6 and CF3I possesses better thermal stability, significantly delaying the onset of thermal decomposition under high-temperature conditions, effectively increasing the thermal failure threshold of the entire system, and providing a more reliable guarantee for its stable operation in high-temperature conductive lubrication scenarios.

[0056] Electrical conductivity analysis The conductivity of the modified ionic liquids prepared under different preparation processes in Example 3 was tested and analyzed, such as... Figure 17As shown, measurements revealed that the modified ionic liquid prepared at a 2:1 ratio and 60℃ exhibited a conductivity as high as 9.68 ms / cm, while the conductivity of pure BMIMPF6 was only around 1.51 ms / cm. Comparing the conductivity and anti-wear properties of greases prepared at different molar ratios and reaction temperatures, the greases prepared at 2:1 ratio and 50℃ and 70℃ showed conductivity of 7.23 ms / cm and 8.94 ms / cm, respectively. Although the anti-wear properties of the greases prepared at 2:1 ratio and 70℃ were close to those at 2:1 and 60℃, their conductivity was slightly lower, indicating that 60℃ is the optimal reaction temperature, achieving the best balance between conductivity and anti-wear properties. Furthermore, at a 1:1 molar ratio, the conductivity of the greases prepared at 50℃, 60℃, and 70℃ were 3.56 ms / cm, 4.12 ms / cm, and 2.54 ms / cm, respectively. Although the conductivity of these groups showed some improvement, the increase was small, indicating that the 1:1 molar ratio is not the optimal reaction ratio of BMIMPF6 and CF3I. Moreover, their anti-wear performance was inferior to that of pure BMIMPF6 grease, suggesting that the increase in conductivity is not a single factor improving the grease's performance under current-carrying conditions. During current-carrying friction, grease not only needs good lubrication performance but also needs to effectively conduct current to avoid electrolytic corrosion and wear caused by local charge accumulation. High-conductivity grease can form a uniform current distribution on the friction surface, reducing local electrolytic corrosion and thus significantly reducing the wear rate. In this experiment, the significant increase in conductivity of the greases prepared at 2:1 and 60℃ conditions is due to the formation of more conductive networks or ion migration channels in their modified ionic liquid, thereby improving the overall conductivity. In summary, the significant improvement in conductivity is one of the key reasons for the excellent anti-wear performance of the grease at 2:1 ratio and 60℃.

[0057] Infrared spectroscopy analysis of reaction products Figure 18The images show FTIR analysis of the composite lithium and its two modified greases (the best-performing grease at 1% mass fraction in Example 2 (composite lithium + BMIMPF6), and the best-performing grease at 1% mass fraction in Example 4 (composite lithium + BMIMPF6 + CF3I) with a molar ratio of 2:1 and a reaction temperature of 60°C). All three spectra show significant CH stretching vibration peaks at 2924 cm⁻¹ and 2853 cm⁻¹, indicating that the alkyl chain structure remains stable. This suggests that although the greases are modified, the basic framework is relatively stable, and the base oil components have not undergone significant decomposition. In the grease with added BMIMPF6, a significant medium-strong absorption peak appears in the wavenumber region of approximately 840–860 cm⁻¹, significantly enhanced compared to the unmodified sample. This peak is attributed to the characteristic stretching vibration of the PF bond in the PF6- ion, indicating that BMIMPF6 has been successfully incorporated into the grease system. The successful introduction of the PF6- ion is the main reason for the enhanced conductivity of this group of greases. A new absorption peak appeared in the 1265 cm⁻¹ region, which is a characteristic peak of the stretching vibration of the CF bond. This peak exhibits strong electronegativity and steric repulsion, effectively altering the micro-polarity distribution of the grease and providing chemical inertness and resistance to electrolytic corrosion to the lubricating film. In the 3200–3700 cm⁻¹ region, all three groups of samples showed absorption peaks of the stretching vibration of OH / NH groups. The unmodified sample showed an absorption peak at 3645 cm⁻¹, exhibiting characteristics of a strong hydrogen bond network. Meanwhile, in BMIM... + The introduction of ions caused a blue shift in the absorption peak at 3739 cm⁻¹, indicating that some O–H / N–H groups in the system have broken free from their original hydrogen bonds and are in a relatively free state. This behavior can promote the free migration of ions and improve the conductivity of the grease.

[0058] Based on BMIMPF6, the compound grease incorporating CF3I exhibits higher peak intensities in the 840–860 cm⁻¹ region, indicating a higher degree of PF6⁻ participation and better incorporation during the compounding process. New absorption peaks appear at 496 cm⁻¹ and 416 cm⁻¹. Considering the presence of some metal elements in the grease, these peaks are presumably derived from metal-fluorine coordination bonds, such as Ca-F or Zn-F, or weak absorption peaks of CI or PI bonds. The I⁻ peaks are likely derived from the reaction products of CF3I. Such low-wavenumber peaks are often associated with heavy elements or polar structures. Combined with the significantly enhanced conductivity, this suggests that such structures strengthen the internal polar network of the grease, facilitating the formation of microscopic ion channels and improving electron or ion migration efficiency. Similarly, in the 3200–3700 cm⁻¹ region, the unmodified sample exhibits an absorption peak at 3215 cm⁻¹, while in the CF3I group sample, this main peak undergoes a significant red shift to 3176 cm⁻¹, indicating further enhancement of hydrogen bonding, tighter intermolecular interactions, and increased system polarity. Simultaneously, the sample shows a slight blue shift near 3647 cm⁻¹, which, although subtle, indicates a higher degree of ion free migration compared to the unmodified sample, further validating the fundamental reason for the enhanced conductivity.

[0059] This invention introduces three ionic liquids—BMIMBF4, BMIMPF6, and BMIMHF3—to modify a composite lithium-based grease. Experiments revealed that the anti-friction performance of the grease decreases with increasing ionic liquid content. Between 1% and 5% content, the average coefficient of friction increases by 7.5%, and the volumetric wear rate increases by 54.06%. BMIMBF6 exhibits the lowest coefficient of friction (0.097) and the lowest volumetric wear rate (1.07 × 10⁻⁶). -6 mm 3 ×(N·m) -1 The volumetric wear rate decreased by 24.11% year-on-year. CF3I was introduced into BMIMPF6 for in-situ functionalization modification with ionic liquid. The optimal process parameters for preparation were determined to be a molar ratio of 2:1 and a preparation temperature of 60℃. Under this process, the conductivity of the in-situ modified liquid increased from 1.25 ms / cm to 9.68 ms / cm; the volumetric wear rate of the modified grease decreased to 6.84 × 10⁻⁶. -7 mm 3 ×(N·m) -1 Compared with composite lithium, it is reduced by 55.3%; its initial decomposition temperature under thermogravimetric analysis increased to 318.18℃; both modified greases showed the presence of fluorine (F) on the wear surface, indicating that an fluorine compound protective film was formed during the wear process. This phenomenon is the key reason for maintaining the film stability of the grease.

[0060] 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. A conductive lubricating grease modified with ionic liquid, characterized in that, It includes a base grease and a modified ionic liquid dispersed in the base grease; The modified ionic liquid is a reaction product obtained by in-situ functionalization of BMIMPF6 with CF3I; The molar ratio of BMIMPF6 to CF3I is 1:1 to 2:1, and the reaction temperature of the in-situ functionalization reaction is 50-70℃.

2. The conductive grease according to claim 1, characterized in that, The modified ionic liquid has a mass fraction of 0.5-2% in the conductive grease.

3. The conductive grease according to claim 2, characterized in that, The modified ionic liquid has a mass fraction of 0.5-1.5% in the conductive grease.

4. The conductive grease according to claim 1, characterized in that, The molar ratio of BMIMPF6 to CF3I is 2:1, and the reaction temperature of the in-situ functionalization reaction is 60℃.

5. The conductive grease according to claim 1, characterized in that, The base grease is a complex lithium-based grease.

6. A method for preparing a conductive lubricating grease as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Preparation of modified ionic liquid: BMIMPF6 and CF3I are weighed according to the ratio of 1:1 to 2:1, and placed in a sealed reaction vessel. The mixture is stirred and reacted under constant temperature conditions of 50-70℃ to obtain the modified ionic liquid. (2) Compounding: The modified ionic liquid obtained in step (1) is added to the base grease according to a predetermined mass fraction, mixed evenly, and then subjected to vacuum degassing treatment to obtain conductive grease.

7. The preparation method according to claim 6, characterized in that, In step (1), the reaction is carried out in an acetonitrile solvent system for 4-6 hours.

8. The preparation method according to claim 7, characterized in that, In step (1), after the reaction is complete, the mixture is cooled to room temperature and the washing solution is used to remove iodide ions.

9. The application of a conductive grease as described in any one of claims 1-5 in the bearings of an electric drive system for new energy vehicles, for reducing or preventing electrical erosion and frictional wear of the bearings under current-carrying conditions.

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