Thermal runaway management

Abstract

The present invention provides a thermal management system for lithium-ion batteries with a maximum thermal dissipation of 5 mm at 100°C to rapidly dissipate heat generated during a thermal runaway event. 2 The present invention provides for the use of a Fischer-Tropsch derived working fluid having a kinematic viscosity of 1000 kJ / sec.

Description

[Technical Field]

[0001] The present invention relates to the use of immersion cooling fluids in the control and management of thermal runaway in electric batteries. [Background technology]

[0002] Up to 50% of all new passenger vehicle sales are expected to be electric vehicles by 2040. Current battery technology relies on lithium-ion batteries, which are likely to remain the dominant battery technology for at least the next 15 years.

[0003] One of the main concerns for potential electric vehicle buyers is "range anxiety" regarding the limited driving range of electric vehicles, the lack of convenient charging stations, and the time it takes to recharge the vehicle. Vehicle manufacturers and battery suppliers are focusing on developing more powerful lithium batteries that enable better driving range and have the ability to be recharged more quickly.

[0004] However, while driving range is important to consumers, thermal management of these powerful lithium-ion batteries is key to ensuring they remain safe and pose no risk to the vehicle's occupants. While thermal management is a key challenge for everyday vehicle operation, a pressing concern with lithium-ion batteries is preventing thermal runaway.

[0005] Lithium-ion batteries contain many cells, each of which contains a flammable liquid electrolyte. If a single cell shorts out, the electrolyte can burn, causing the cell to explode and expel the electrolyte. This creates pockets of extreme temperatures within the battery. If uncontrolled, the extreme temperatures can spread to nearby cells, causing further cell failure and destruction. This thermal runaway can produce smoke, fire, and possibly explosions, putting vehicle occupants at risk.

[0006] Therefore, managing thermal runaway is a major concern for electric vehicle manufacturers. Adding protective material between cells to prevent propagation requires taking up space and weight that could otherwise be used for additional cells.

[0007] The day-to-day thermal management of electric batteries has been the subject of considerable research. Historically, most cooling systems have used air passing over the heat source to manage excess heat. However, such systems are unable to manage the heat generated during thermal runaway in modern battery systems.

[0008] More advanced thermal management systems have been developed that use traditional water / glycol mixtures as heat transfer fluids. Battery blocks containing many individual battery cells are most effectively cooled by water / glycol mixtures. This is more efficient than air cooling and is becoming the dominant thermal management technology for use in currently sold electric vehicles. US2009 / 0023056, US2010 / 0025006, and US2011 / 021356, all in the name of Tesla Motors Inc., describe pipe systems in which approximately 11% of the cell surface is in direct contact with pipes containing the coolant. In these indirect thermal management systems, heat must pass through the pipe material, which is then transferred to the glycol / water. This limits the overall effectiveness of this heat transfer design, especially during a thermal runaway event.

[0009] Phase change materials (PCMs) are also used in some systems and are an effective means of absorbing heat as they change from a solid to a liquid state. PCMs are limited to the melting temperature of selected ones and are not suitable for thermal management at high ambient temperatures or during thermal runaway events.

[0010] Immersion cooling has been described for a variety of applications. It involves at least partially immersing a heat-generating component, such as a battery cell, in a working fluid. Heat from the heat-generating component is then removed into the working fluid, which can be circulated back to the heat exchanger using a pump. Various fluorinated hydrocarbons are described for this use, for example, in WO 2018 / 224908 in the name of 3M Innovative Properties Company. Summary of the Invention [Problem to be solved by the invention]

[0011] While these methods have been demonstrated for the everyday thermal management of lithium-ion batteries, the thermal management required during the propagation of thermal runaway is a different challenge, where heat must be rapidly dissipated to prevent catastrophic battery failure.

[0012] Providing an improved thermal management system that can manage the kind of uncontrolled temperature spikes seen when lithium-ion cells fail would be highly advantageous and potentially life-saving. [Means for solving the problem]

[0013] The present invention provides a thermal management system for lithium-ion batteries with a maximum thermal dissipation of 5 mm at 100°C to rapidly dissipate heat generated during a thermal runaway event. 2 The present invention provides for the use of a Fischer-Tropsch derived working fluid having a kinematic viscosity of 1000 kJ / sec. [Brief explanation of the drawings]

[0014] [Figure 1] 1 shows a cross section of a typical battery setup with many cylindrical cells arranged in rows. [Figure 2] 1 shows a 1D electrostatic modeling system that forms part of the basis of the modeling system used in the examples. [Figure 3]1 illustrates the feedback loops used between the modeling systems used in the examples. [Figure 4] 1 is a charge-discharge cycle applied to each cell in the modeling system used in the examples. [Figure 5] 1 is a graph showing the results of an example. [Figure 6] 1 is a graph showing the results of an example. DETAILED DESCRIPTION OF THE INVENTION

[0015] The inventors have surprisingly found that using Fischer-Tropsch derived working fluids in thermal management systems provides improved control of thermal runaway events, which could not be predicted from a comparison of thermodynamic flow data for such working fluids and other known thermal fluids.

[0016] A Fischer-Tropsch derived working fluid comprises one or more Fischer-Tropsch derived base fluids. Fischer-Tropsch derived base fluids are known in the art. The term "Fischer-Tropsch derived" means that the base fluid is, or is derived from, a synthesis product of a Fischer-Tropsch process.

[0017] Fischer-Tropsch derived base fluids are often classified by the starting material in the Fischer-Tropsch process, i.e., "X-to-liquid" or "XTL," where X represents the starting material. Biomass-to-liquid (BTL), coal-to-liquid (CTL), gas-to-liquid (GTL), and power-to-liquid (PTL) processes are some examples of Fischer-Tropsch processes that produce base fluids. Preferably, the Fischer-Tropsch derived base fluid is a GTL (Gas-To-Liquid) base fluid. Suitable Fischer-Tropsch derived base fluids, including oils, that may be conveniently used in Fischer-Tropsch derived working fluids are, for example, those described in EP0776959, EP0668342, WO97021788, WO0015736, WO0014188, WO0014187, WO0014183, WO0014179, WO0008115, WO9941332, EP1029029, WO0118156 and WO0157166.

[0018] The Fischer-Tropsch derived base fluid for use in the present invention preferably has a viscosity of up to 4mm at 100°C. 2 / sec.

[0019] Particularly preferred Fischer-Tropsch derived base fluids for use in the working fluids herein have a viscosity of 2-4 mmH2O at 100°C. 2 Fischer-Tropsch derived base oils, e.g., GTL3 (approximately 3 mmHg at 100°C) having a kinematic viscosity in the range of 1 / 2 s. 2 / sec), which can be prepared according to the method described in WO02070631.

[0020] Another particularly preferred Fischer-Tropsch derived base fluid for use in the working fluids herein is a Fischer-Tropsch derived base fluid produced from a gas oil stream from a GTL process, preferably a dewaxed gas oil stream, the fluid having a viscosity of from 2.0 to 11 mmHg at 40°C. 2Preferably, the Fischer-Tropsch derived base fluid produced from a gas oil stream has a kinematic viscosity in the range of at least 2.1 mm / s at 40°C. 2 / sec, more preferably at least 2.2 mm 2 Preferably, the fluid has a kinematic viscosity of at most 10.0 mm / s at 40°C. 2 / sec, preferably up to 7.0mm 2 / sec, most preferably up to 6.0mm 2 / sec.

[0021] In one embodiment of the present invention, the working fluid comprises a mixture of two or more Fischer-Tropsch derived base fluids. For example, the working fluid may have a viscosity of 2-4 mmHg at 100°C. 2 The base oils may include both Fischer-Tropsch derived base oils having kinematic viscosities in the range of 1 / 2 s / sec and Fischer-Tropsch derived base fluids produced from gas oil streams.

[0022] The total amount of Fischer-Tropsch derived base fluid incorporated into the working fluid is preferably in the range of 60.0 to 99.9 wt. %, more preferably in the range of 65.0 to 98.0 wt. %, and most preferably in the range of 70.0 to 95.0 wt. %, based on the total weight of the working fluid.

[0023] Other components in the working fluid may include one or more additional base oils, including mineral oils and synthetic oils. Mineral oils include liquid petroleum oils and solvent- or acid-treated mineral oils of the paraffinic, naphthenic, or mixed paraffinic / naphthenic types, which may be further refined by hydrofinishing processes and / or dewaxing. Synthetic oils include hydrocarbon oils such as olefin oligomers (including polyalphaolefin base oils; PAOs), dibasic acid esters, polyol esters, polyalkylene glycols (PAGs), alkylbenzenes, alkylnaphthalenes, and dewaxed waxy isomerates.

[0024] In a preferred embodiment, the working fluid comprises one or more additional base oils selected from alkylbenzenes, alkylnaphthalenes, and mixtures thereof. When present, the one or more additional base oils selected from alkylbenzenes, alkylnaphthalenes, and mixtures thereof are present in an amount of 35 wt.% or less, based on the total weight of the working fluid. Preferably, the one or more additional base oils selected from alkylbenzenes, alkylnaphthalenes, and mixtures thereof are present in an amount ranging from 1 to 30 wt.%, based on the total weight of the working fluid.

[0025] In addition, additives may be included in the working fluid. Suitable additives include, but are not limited to, antioxidant additives, antistatic additives, corrosion inhibitors, pour point depressants, and viscosity index improvers. Any other oil additives common in the art may also be used. Antioxidants and antistatic additives are particularly preferred for inclusion in the working fluid.

[0026] Suitable antioxidant additives include hindered phenol antioxidant additives, sterically hindered monohydric, dihydric and trihydric phenols, sterically hindered dinuclear, trinuclear and polynuclear phenols.

[0027] Sterically hindered phenol antioxidants of particular interest are 2,6-di-tert-butylphenol (available from BASF under the trade name "IRGANOX™ L 140"), di-tert-butylated hydroxytoluene ("BHT"), methylene-4,4'-bis-(2,6-tert-butylphenol), 2,2'-methylenebis-(4,6-di-tert-butylphenol), 1,6-hexamethylene-bis-(3,5-di-tert-butyl-hydroxyhydrocinnamate) (available from BASF under the trade name "IRGANOX™ L109"), ((3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)methyl)thio)acetic acid, C 10 ~C 14isoalkyl esters (available from BASF under the trade name "IRGANOX™ L118"), 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid, C7-C9 alkyl esters (available from BASF under the trade name "IRGANOX™ L135"), tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxymethyl)methane (available from BASF under the trade name "IRGANOX™ 1010"), thiodiethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate) (available from BASF under the trade name "IRGANOX™ 1035"), octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate (available from BASF under the trade name "IRGANOX™ 1076"), and 2,5-di-tert-butylhydroquinone.

[0028] Particularly preferred antioxidants for use herein are di-tert-butylated hydroxytoluene ("BHT") and C7-C9 alkyl ester of 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid (available from BASF under the trade name "IRGANOX™ L135").

[0029] In one embodiment of the present invention, more than one antioxidant additive may be present in the working fluid. Optionally, additional amine antioxidants, such as alkylated or styrenated diphenylamines, may be added to the working fluid.

[0030] Examples of amine antioxidants include aromatic amine antioxidants, such as N,N'-di-isopropyl-p-phenylenediamine, N,N'-di-sec-butyl-p-phenylenediamine, N,N'-bis(1,4-dimethyl-pentyl)-p-phenylenediamine, N,N'-bis(1-ethyl-3-methyl-pentyl)-p-phenylene-diamine, N,N'-bis(1-methyl-heptyl)-p-phenylenediamine, N,N'-dicyclohexyl-p-phenylene-diamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di( Naphthyl-2-)-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-(1-methylheptyl)-N'-phenyl-p-phenylenediamine, N'-cyclohexyl-N'-phenyl-p-phenylenediamine, 4-(p-toluene-sulfamido)diphenylamine, N,N'-dimethyl-N,N'-di-sec-butyl-p-phenylenediamine, diphenylamine, N-allyldiphenylamine, 4-isopropanol diphenylamine, N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, octylated diphenylamines such as p,p'-di-tert-octyldiphenylamine, 4-n-butylaminophenol, 4-butyrylaminophenol, 4-nonanoylaminophenol, 4-dodecanoylaminophenol, 4-octadecanoylaminophenol, di(4-methoxyphenyl)amine, 2,6-di-tert-butyl-4-dimethylaminomethylphenol, 2,4'-diaminodiphenylmethane, 4,4'- Diaminodiphenylmethane, N,N,N',N'-tetramethyl-4,4'-diaminodiphenylmethane, 1,2-di(phenylamino)ethane, 1,2-di[(2-methylphenyl)amino]ethane, 1,3-di(phenylamino)propane, (o-tolyl)biguanide, di[4-(1',3'-dimethylbutyl)phenyl]amine, tert-octylated N-phenyl-1-naphthylamine, mixture of mono- and dialkylated tert-butyl- / tert-octyldiphenylamines, 2,3-dihydro-3,3-dimethyl-4H-1,4-benzothiazine, phenothiazine, N-allylphenothiazine, tert-octylated phenothiazine, 3,7-di-tert-octylphenothiazine. Possible amine antioxidants are also those of formulas VIII and IX of EP-A-1054052, which compounds are also described in US-A-4,824,601.

[0031] The total amount of the one or more antioxidant additives present in the working fluid is preferably at least 0.1 wt. %, more preferably at least 0.15 wt. %, and preferably at most 3.0 wt. %, more preferably at most 2.0 wt. %, based on the total weight of the working fluid.

[0032] Suitable antistatic additives include those selected from those containing alkyl-substituted naphthalene sulfonic acids, benzotriazoles and substituted benzotriazoles.

[0033] The substituted benzotriazole compounds may be represented by formula (I):

[0034] [ka] In the formula, R 4 is hydrogen or a group represented by the formula (II) [ka] or a group represented by formula (III): [ka] During the ceremony, c is 0, 1, 2 or 3; R 1 and R 2 are hydrogen or the same or different straight or branched chain alkyl groups of 1 to 18 carbon atoms, preferably branched chain alkyl groups of 1 to 12 carbon atoms, and R 3 is a linear or branched chain C 1~4 is an alkyl group, preferably R 3is methyl or ethyl, C is 1 or 2, and R 5 is a methylene or ethylene group, and R 6 and R 7 are the same or different alkyl groups of 3 to 15 carbon atoms, preferably 4 to 9 carbon atoms.

[0035] Preferred compounds are 1-[bis(2-ethylhexyl)aminomethyl]benzotriazole, methylbenzotriazole, dimethylbenzotriazole, ethylbenzotriazole, ethylmethylbenzotriazole, diethylbenzotriazole, and mixtures thereof. Other preferred compounds include (N-bis(2-ethylhexyl)-aminomethyl-tolutriazole, unsubstituted benzotriazole, and 5-methyl-1H-benzotriazole.

[0036] Preferred alkyl-substituted naphthalene sulfonic acids include di-C8-C10, branched, C-rich, alkyl naphthalene sulfonic acids, such as those commercially available as "STADIS 450" from Innospec.

[0037] The content of the antistatic additive in the working fluid herein is preferably greater than 0.5 mg / kg, more preferably greater than 1 mg / kg, based on the total weight of the working fluid. The practical upper limit may vary depending on the particular application of the lubricating composition. This concentration may be up to 3 wt. % based on the total weight of the working fluid, but preferably ranges from 1 mg / kg to 1 wt. %. However, such compounds may be advantageously used at concentrations less than 1000 mg / kg, more preferably less than 300 mg / kg, based on the total weight of the working fluid.

[0038] The working fluid preferably has a pour point, measured in accordance with ISO 3016, of -40°C or less, more preferably -50°C or less.

[0039] The working fluid also preferably has a flash point according to ASTM D93 of at least 100°C, more preferably at least 110°C, most preferably at least 120°C, and preferably at most 240°C.

[0040] The working fluid preferably has a viscosity of at least 2.0 mmHg at 40°C measured in accordance with ISO 3104. 2 / sec, more preferably at least 2.1 mm2 / sec, and most preferably at least 2.2 mm 2 The working fluid preferably has a kinematic viscosity of up to 22.0 mm / s at 40°C. 2 / sec, preferably up to 11.0mm 2 / sec, most preferably up to 10.0 mm 2 / sec.

[0041] The thermal conductivity of the working fluid at 20°C is preferably at least 0.135 w / mK, preferably at least 0.14 w / mK, most preferably at least 0.143 w / mK, measured according to ASTM D7896. The specific heat capacity of the working fluid at 20° C. according to ASTM D1269 is preferably at least 1.9 W / m*K, more preferably at least 2.0 W / m*K, and most preferably at least 2.1 W / m*K. [Detailed description of the drawings]

[0042] [Figure 1] Figure 1 shows a cross section of a battery. This cross section is numbered 1 to 10. The plate is shown to contain 10 individual cylindrical cells (cut-away view shown) attached to it. [Figure 2] Figure 2 is used as part of the modeling system used in the following examples. In Figure 2, 11 is the anode, 12 is the cathode, 13 represents discharge, and 14 represents charge. [Figure 3] Figure 3 shows the interactions between models used in the modeling process of the following example. In Figure 3, 15 represents the 3D flow model, 16 is the 3D thermal model, and 17 is the single particle model (SPM). FIG. 4 shows charge-discharge curves used in the model of the example. [Figure 5] Figures 5 and 6 show cell 1 (using the cell number from Figure 1) in Figure 5 and cell 2 (using the cell number from Figure 1) in Figure 6. A plot of temperature versus time is provided for cell 3 (using the cell number from Figure 1). [Figure 6] Figures 5 and 6 show cell 1 (using the cell number from Figure 1) in Figure 5 and cell 2 (using the cell number from Figure 1) in Figure 6. A plot of temperature versus time is provided for cell 3 (using the cell number from Figure 1).

[0043] The invention and figures will now be further described with reference to the following non-limiting examples. [Example]

[0044] 1. Modeling The software used for the modeling work was COMSOL Multiphysics version 5.4. The battery's electrochemistry, flow and heat transfer with the fluid surrounding the battery were achieved through the software's set of three physics modules: laminar flow; heat transfer in fluids; and single particle battery.

[0045] 1.1 Flow model The flow model was applied to the region where the fluid exists. This module calculates the flow by solving the Navier-Stokes equations:

number

number

[0046] The fluid was simulated with the incompressible flow option and without slip boundary conditions on the walls.

[0047] 1.2 Thermal model The thermal model calculated the heat transfer using the following energy conservation equation:

number

[0048] 1.3 Single particle model (SPM) The Single Particle Battery interface calculates voltage and current profiles assuming a single particle model (SPM) (see Figure 2) for both electrodes with diffusion and intercalation kinetics, considering the electrolyte as a lumped resistive element.

number

number

[0049] The current across the electrolyte is

number

[0050] The current across the electrodes is

number

[0051] The diffusion of the active material within the electrode is governed by Fick's law equation:

number

number

number

[0052] The heat generated by ohmic heating of the electrodes and electrolyte is

number

number

[0053] 1.4 Model combinations Thus, equations 1 and 2 define the flow model, equation 3 is the thermal model, and equations 4-9 represent the SPM of a single cell. Figure 3 shows how the different models are linked together. The SPM simulates the charge and mass transfer inside the cell, along with the temperature-dependent reaction kinetics at the electrodes. The average heat (Q) generated by an individual cell due to electrode reactions and electrical resistance is h ) was calculated from the SPM using Equations 8 and 9. Q h was fed as a heat source to a thermal model, which calculates the temperature distribution for the cylindrical cell and the fluid. The flow model is used to calculate the rate at which the coolant removes heat from the cell's surface. We linked the flow and thermal models in only one direction, where the velocity calculated by the flow model affects the temperature distribution in the fluid, but not the other way around. Once the temperature distribution is solved, we calculate the average temperature for each individual cell. This temperature is then fed back to the SPM, which links the two models as shown in the flow diagram (see Figure 3).

[0054] 1.5 Model Settings Our simulations involve 10 cylindrical cells, each with its own electrochemistry modeled by SPM. As shown in Figure 1, the cells are partially submerged in liquid coolant.

[0055] For all the experimental fluids considered, an inlet flow rate corresponding to a mass flow rate of 0.06 kg / s was defined.

[0056] Symmetry boundary conditions were used on the two sides perpendicular to the inlet-outlet flow direction so that the periodic images could capture the effect of the expansion pack like geometry.

[0057] The flow model was first solved to obtain a steady-state flow solution. Because we coupled the flow model in only one direction, this steady-state solution was used for the time-dependent simulations. The time-dependent temperature field was then calculated by first initializing the first cell in the configuration to an initial temperature of 673 Kelvin. All cells were initialized in a fully charged state and subjected to charge-discharge cycling at a 2-C rate, with minimum and maximum operating voltages set to 3.5 and 4.3 volts, respectively. The time-dependent solver was simulated for a duration of 4000 seconds, corresponding to the charge-discharge curves (see Figure 4).

[0058] Example 1 and Comparative Example 2 The combined mathematical model described above was used to simulate two fluids and analyze their performance to prevent thermal runaway conditions inside the battery pack. Fluid 1 (Example 1) is a Fischer-Tropsch derived working fluid consisting of a Fischer-Tropsch derived diesel fuel, and Fluid 2 (Comparative Example 2) is Novec 7300 (a hydrofluoroether commercially available from 3M).

[0059] The properties of each fluid are shown in Table 1 below. [Table 1]

[0060] FIG. 5 shows the maximum temperature of the first cell (1) as a function of time, which is initialized to 673 K at time t=0 seconds. The temperature is somewhat lower in Example 1 of the present invention (which uses a Fischer-Tropsch derived working fluid), i.e., cell (1) reaches a lower temperature at any given time in Example 1.

[0061] FIG. 6 shows the maximum temperature of the third cell (3) as a function of time. Heat from the first cell (1) is carried away by the coolant flow, resulting in an increase in the temperature of the third cell (3). FIG. 6 clearly shows that at any given time and at a fixed mass flow rate of both coolants, the temperature of the third cell (3) is much lower in Example 1 compared to Comparative Example 2. This plot clearly shows that using the fluid of the present invention is much better at preventing the propagation of thermal runaway from one cell to another within a battery pack. The fluid of Example 1 is able to dissipate heat much faster than the fluid of Comparative Example 2. This potentially extends battery life and avoids thermal hot spots to prevent fires / explosions in extreme situations.

Claims

1. Up to 5mm at 100°C for rapid dissipation of heat generated during a thermal runaway event in a thermal management system for lithium-ion batteries. ２ Use of a Fischer-Tropsch derived working fluid having a kinematic viscosity of 100 / s.

2. The Fischer-Tropsch derived working fluid comprises a Fischer-Tropsch derived base fluid, the base fluid having a viscosity of up to 4 mm at 100° C. ２ 2. The use according to claim 1, wherein the base oil is a GTL base oil having a kinematic viscosity of 100 / s.

3. 2. The use according to claim 1, wherein the Fischer-Tropsch derived working fluid comprises a Fischer-Tropsch derived base fluid, the base fluid produced from a dewaxed light oil stream in a Fischer-Tropsch process and having a kinematic viscosity in the range of 1 to 10 mm / s at 40°C.

4. The use according to any one of claims 1 to 3, wherein the total amount of Fischer-Tropsch derived base fluid incorporated in the working fluid is in the range of 60.0 to 99.9 wt.%.

5. 5. Use according to any one of claims 1 to 4, wherein the Fischer-Tropsch derived working fluid also comprises one or more additional base oils selected from alkylbenzenes, alkylnaphthalenes, esters and mixtures thereof.

6. 6. Use according to any one of claims 1 to 5, wherein the Fischer-Tropsch derived working fluid also comprises an antioxidant additive selected from the group of hindered phenol antioxidant additives, sterically hindered mono-, di- and trihydric phenols, sterically hindered di-, tri- and polynuclear phenols.

7. The antioxidant additive is di-tert-butylated hydroxytoluene ("BHT") and 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid. ７ ~C ９ 7. The use according to claim 6, wherein the aryl ester is selected from alkyl esters.

8. 8. Use according to any one of claims 1 to 7, wherein the Fischer-Tropsch derived working fluid also comprises an antistatic additive selected from those containing alkyl substituted naphthalene sulfonic acids, benzotriazoles and substituted benzotriazoles.

9. 9. The use according to claim 8, wherein the content of said antistatic additive in said working fluid herein is more than 0.5 mg / kg and not more than 3% by weight.

10. The use according to any one of claims 1 to 9, wherein the thermal conductivity of the working fluid at 20°C is at least 0.135 w / mK.

Images