An efficient and environmentally friendly coolant for direct cooling of batteries

Abstract

The present invention relates to the use of a composition consisting of 80% by weight or more and 100% by weight or less of a diester of butanediol and an aliphatic C4-C10 monocarboxylic acid for direct temperature control of a storage battery.

Description

[Technical Field]

[0001] The present invention relates to the use of a composition consisting of 80% by weight or more and 100% by weight or less of a diester of butanediol and an aliphatic C4-C10 monocarboxylic acid for direct temperature control of a storage battery. [Background technology]

[0002] The potential of modern mobility is largely based on the use of high-performance, safe energy storage, which forms the basis for the long-lasting, successful functionality of selected applications. For example, new functionalities in smartphones and tablets can only be successfully established on the market if the basic device can reliably provide them over a certain minimum period of use. This fundamental relationship is even more applicable to more energy-intensive areas of use, such as electric mobility, where various vehicle types can successfully replace existing options only if they can provide practical ranges and charging times under most environmental conditions. In particular, the development of efficient alkali-ion energy storage has contributed significantly to increasing the maximum range of purely electric vehicles in recent years. However, significant development is still needed to provide an alternative that is not only comparable to internal combustion engine-based mobility concepts but is also more environmentally friendly. To improve the efficiency of e-mobility, research and industry have primarily focused on improving the performance of the battery itself. However, there is still great potential in optimizing the integration of energy storage into the vehicle environment. For example, active temperature control of batteries can contribute to increased available energy and cycle count by providing a controllable and constant battery temperature. Furthermore, it is of course desirable for this active temperature control to occur under the most environmentally friendly conditions possible. This may mean, among other things, that the agents used for temperature control are not only effective, but also non-toxic, environmentally friendly, biodegradable, and have a low GWP ("global warming potential"). This bundle of application and environmental requirements is currently not yet fully met overall in the field of direct cooling or temperature control fluids for batteries.

[0003] The patent literature also contains several examples of the use of cooling fluids to cool electrical systems.

[0004] For example, WO2014116369A1 (Patent Document 1) describes a liquid cooling medium used for immersion cooling of electronic hardware devices. Such liquid cooling medium has a flash point of at least 190°C as determined in accordance with ASTM D92 and a viscosity of 27 centistokes ("cSt") or less at 40°C as determined in accordance with ASTM D445. Such liquid cooling medium can be used to maintain immersion cooling of devices such as computer servers, server motherboards, and microprocessors.

[0005] Furthermore, EP2520637A1 (Patent Document 2) discloses a base oil for cooling equipment, which contains 30 mass % or more of at least one of oleyl esters (oleate and oleyl alcohol ester) and oleyl ether, wherein the total number of terminal methyl groups, methylene groups and ether groups in the main chain of each of the oleyl esters and oleyl ethers is 23 or more, the total number of methyl branches and ethyl branches of each of the oleyl esters and oleyl ethers is 1 or less, and the base oil has a viscosity of 4 mm 2 / s~30mm 2 Base oils having kinematic viscosities in the range of 1 / s are disclosed.

[0006] JP2011063734A (Patent Document 3) provides an electric motor oil composition that has excellent electrical insulation properties, cooling performance, and thermo-oxidation stability, a high flash point from the perspective of safety, lubricity, and low-temperature startability, and that can also be used as a transmission fluid, and preferably has excellent biodegradability. The electric motor oil composition is produced by using, as a base oil, one or more esters synthesized from adipic acid and / or sebacic acid and an alcohol having 5 to 14 carbon atoms, and / or esters synthesized from neopentyl glycol and / or trimethylolpropane and a carboxylic acid having 5 to 14 carbon atoms, the esters having a hydroxyl value of 50 mgKOH / g or less, a total acid value of 2 mgKOH / g or less, and a flash point of 150°C or higher, and by adding an amine compound and / or a phenol compound in an amount of 0.01 to 3.0 wt% of the total composition.

[0007] Such solutions known from the prior art may still offer the potential for further improvement, especially with regard to the physical, biological and environmentally relevant properties of the temperature control fluid in direct contact with the battery. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] WO2014116369A1 [Patent Document 2] EP2520637A1 [Patent Document 3] JP2011063734A Summary of the Invention [Problem to be solved by the invention]

[0009] It is therefore an object of the present invention to at least partially overcome the drawbacks known from the prior art. In particular, it is an object of the present invention to provide compositions that have very good physical properties, such as low electrical conductivity, high heat capacity, excellent chemical stability and low viscosity, and also very good biological properties, such as rapid biodegradability, low water contamination potential, low (or no) toxicity to humans and low GWP. [Means for solving the problem]

[0010] Said problem is solved by the features of the independent claims, which are directed to the use according to the invention. Preferred embodiments of the invention are set out in the dependent claims, in the description or in the drawings, wherein further features mentioned or shown in the dependent claims or in the description or drawings may, individually or in any combination, form the subject of the invention, unless the context clearly indicates otherwise.

[0011] According to the present invention, the above-mentioned problems are solved by using a composition consisting of 80% by weight or more and 100% by weight or less of a diester of butanediol and an aliphatic C4-C10 monocarboxylic acid for direct temperature control of a storage battery.

[0012] Surprisingly, it has been found that compositions containing a major proportion of esters of butanediol and medium-chain monocarboxylic acids are very well suited for the direct cooling of storage batteries (e.g., in the form of alkali-ion batteries). The compositions exhibit very good chemical compatibility with the battery housing or the battery cells themselves and have low viscosities over a wide temperature range, which has a positive effect on the potential energy requirements for active circulation of the cooling fluid. The particularly advantageous viscosity characteristics of the compositions are observed both at higher and very low temperatures, which, together with low pour points, allow for an overall wide temperature use window for the fluid. The compositions are further characterized by a moderately low electrical conductivity and a high flash point. The compositions are non-toxic and, in particular, exhibit a significantly low GWP of 0 compared to other cooling media, such as FCKW (CFC). The proposed compositions are biodegradable, which results in a significantly improved environmental balance when used with the temperature control agent according to the present invention compared to other temperature control agents or refrigerants. The compositions of the present invention, based on a small selection of aliphatic diesters of butanediol, are also very chemically stable, ensuring a long service life even under harsh operating conditions. Furthermore, they are compatible with the majority of commonly used additives, allowing the esters to have additional chemical and physical properties specifically modified through the additives. These positive properties of the compositions in the present application are entirely surprising, since while the literature proposes suitable substance classes with a large number of possible members, the specifically disclosed members of these substance classes do not exhibit the balanced use profile described above in the applications claimed herein. In this regard, it is surprising that, within the vast group of proposed compounds, there exists a small group that is very well suited for temperature control, particularly cooling, of storage batteries (e.g., in the form of alkali-ion batteries), possessing balanced chemical, physical, and biological use properties. Furthermore, the temperature control agents of the present invention can contribute to the faster and safer market establishment of new battery-based electrical concepts.

[0013] The compositions according to the present invention are used for direct temperature control of storage batteries. The compositions according to the present invention are in direct contact with the battery housing or the battery cells themselves, and achieve temperature control of the storage battery or battery through this direct contact. Storage batteries are, in particular, electrically rechargeable energy storage devices that, in theory, exhibit reversible chemical electrode processes during charging and discharging. Therefore, temperature control of a battery via a separate temperature exchange surface that is not in direct thermal contact with the battery housing or battery is not in accordance with the present invention. Due to the fact that battery heating typically occurs during operation, the compositions essentially take on the task of cooling the battery or battery array under operating conditions. Typical operating temperatures can range, for example, from +80°C to -40°C. The compositions according to the present invention can be used to temperature control various battery types. Particularly advantageously, storage batteries based on the principle of storage and release of alkali ions or alkali metals or alkaline earth ions or alkaline earth metals in the anode or cathode can be temperature controlled. When alkali ions are used as the energy carrier, these batteries usually exhibit specific temperature control medium requirements regarding the amount of heat to be carried away, which are fully met by the compositions of the present invention. Even in the event of local overheating, direct cooling by the diesters of the present invention contributes to delaying it. Alkali ion batteries can have various specific structures (e.g., the use of high-voltage electrodes). The high dielectric strength of the temperature control fluid allows them to safely handle high voltages even in the event of a breakdown in the battery structure. Examples of alkali ion batteries are batteries based on the storage and release of lithium, sodium, potassium, or rubidium ions. Examples of alkaline earth ion batteries are batteries based on the storage and release of Be, Mg, or Ca ions.

[0014] The composition consists of 80% by weight or more and 100% by weight or less of a diester of butanediol and an aliphatic C4-C10 monocarboxylic acid. Therefore, the composition consists predominantly or entirely of chemical compounds belonging to the ester group. The ester is a compound of butanediol (COH), a dialcohol, i.e., a dihydric aliphatic alcohol, which can exist in the form of different stereoisomers: 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, or a mixture of at least two isomers from this list. The dihydric alcohol is esterified with one or two monocarboxylic acids, with dehydration, the monocarboxylic acids having 4 to 10 carbon atoms. The monocarboxylic acid chain is an aliphatic chain containing neither unsaturated nor aromatic moieties. At least a monoester, but especially a complete (di)ester, is formed; complete esterification is preferred, but not mandatory, for all butanediol used. The positive properties of the use of the butanediol esters are particularly evident when the composition contains a high weight percentage of the diester. A significantly lower ester concentration can be disadvantageous in this case, since the positive physical and chemical properties of the composition can no longer be maintained. However, small amounts of additives, such as corrosion inhibitors, viscosity-adjusting additives, dyes, or antioxidants, may be added within the above ranges as long as they do not significantly alter the properties. Preferably, the composition also contains the esters of the present invention in an amount of 85% by weight or more and 100% by weight or less, more preferably 87.5% by weight or more and 100% by weight or less, or even 90% by weight or more and 100% by weight or less.

[0015] In a preferred embodiment of the use, the butanediol can be 1,3-butanediol. Due to its chemical and physical properties, 1,3-butanediol (1,3BG) has been found to be particularly suitable for direct temperature control of batteries. In contrast to other stereoisomers, 1,3BG esters exhibit particularly low pour points, particularly high flash points, and good thermal properties. Furthermore, the viscosity profile of 1,3BG esters is particularly favorable because they provide low absolute viscosities and only a slight increase in viscosity as a function of decreasing temperature. In this respect, active circulation of the composition can be achieved with little energy consumption, even at low temperatures, due to its low viscosity.

[0016] In a further preferred embodiment of the use, the monocarboxylic acid may be 80 mol % or more of a linear monocarboxylic acid. To obtain a particularly advantageous viscosity profile, a high flash point, and a very low pour point, butanediol can be esterified using a high proportion of unbranched, i.e., linear, monocarboxylic acids. These butanediol esters using linear monocarboxylic acids can have lower viscosities, especially compared with esters of branched aliphatic monocarboxylic acids or esters of other diols. This situation is particularly advantageous in terms of energy when forced convection of the temperature control agent is performed via a pump.

[0017] In a further preferred embodiment of the use, the monocarboxylic acid may have 80 mol % or more odd carbon atoms. In particular, a high proportion of odd-numbered monocarboxylic acids may be used for esterification with butanediol to obtain a high flash point and a very low pour point. These BG esters from odd-numbered monocarboxylic acids may exhibit physical properties that allow the composition to be handled safely even under harsh use conditions, compared to esters from even-numbered monocarboxylic acids.

[0018] According to a preferred feature of the use, the monocarboxylic acid can be selected from the group consisting of C5 to C9 monocarboxylic acids. In particular, the medium range of C chain lengths of the monocarboxylic acids can provide particularly advantageous physical and chemical properties with respect to esterification with butanediol. The compositions are chemically very stable and exhibit suitable viscosity profiles at very low and very high temperatures. The compositions also have very low pour points and, at a sufficient degree of esterification, very low electrical conductivity. Preferably, the group of monocarboxylic acids may be selected from C5 to C8 monocarboxylic acids or C5 to C7 monocarboxylic acids. Within these groups, very good and uniform physical and electrical properties are obtained.

[0019] In a further preferred embodiment of the use, the monocarboxylic acid can be selected from the group consisting of linear C5 or C7 monocarboxylic acids or mixtures thereof. These BG esters with odd carbon numbers and medium carbon chain ranges exhibit particularly low viscosity even at very low temperatures. These compounds are biodegradable and non-toxic to humans.

[0020] In a preferred embodiment of the use, the composition may consist of 95% by weight or more and 100% by weight or less of diesters. A high degree of esterification of the composition can improve the electrical and physical properties, especially for the use according to the invention. A high degree of esterification can ensure very low conductivity and an appropriate viscosity profile. The degree of esterification can be determined, for example, spectroscopically or, preferably, chemically via the hydroxyl number.

[0021] In a further preferred embodiment of the use, the monocarboxylic acid may be composed of 95 mol % or more of linear C7 monocarboxylic acids. In particular, C7-esters and even C7-diesters of butanediol can provide the composition with particularly advantageous physical properties, including very good thermal and electrical properties. This also applies in particular to diesters of 1,3-BG. The composition is chemically very stable under use conditions and exhibits good biodegradability. Overall, a temperature control fluid is obtained that has a significantly better and more balanced property profile than known alternatives and is very environmentally friendly.

[0022] In a further embodiment of the use, the diester can be a diester of 1,3-butanediol, in which 95 mol % or more of the 1,3-butanediol is esterified with a linear C7 monocarboxylic acid. The favorable chemical and physical properties of the composition are obtained particularly when a very high degree of esterification is achieved. This correlation is particularly obtained when an unbranched monocarboxylic acid is used. The diester can be a complete ester of BG, particularly 1,3BG. However, the degree of esterification of the diester can be 96 mol % or more, even 97.5 mol % or more, or even 99 mol % or more of the esterifiable alcohol groups. The degree of esterification can be determined using chemical methods known to those skilled in the art.

[0023] In a preferred embodiment of the use, the monocarboxylic acid may consist of 95 mol % or more of linear C5 monocarboxylic acids. In particular, C5 monocarboxylic acids as the ester component can result in diester compositions that exhibit particularly advantageous viscosity profiles, including very low viscosity indexes, low pour points, and high flash points.

[0024] In a further embodiment of the use, the diester can be a diester of 1,3-butanediol, the 1,3-butanediol being esterified with at least 95 mol % of a linear C5 monocarboxylic acid. In particular, the monocarboxylic acid having a total carbon number within the mid-C range exhibits a very balanced viscosity profile with a low pour point. Compositions of these diesters exhibit thermal properties and good chemical resistance, even at very low and high temperatures.

[0025] In a further preferred embodiment of the use, the diester content, based on the molar amount of alcohol, as determined by GC, can be 95 mol% or more and 100 mol% or less. In particular, the very high content of diesters in BG can contribute to particularly suitable physical and chemical properties for use in, for example, direct cooling of Li-ion batteries. Sufficient heat capacity for cooling or heating can be achieved via convection or active circulation of a temperature-controlled fluid with little energy consumption. This can improve or increase the energy balance, electrical performance, and number of cycles under constant power of the battery operation.

[0026] According to a preferred feature of the use, the content of monoester, based on the molar amount of alcohol, as determined by GC, can be 0 mol% or more and 2.5 mol% or less. A low proportion of monoester in the composition can contribute to improving the electrical properties of the composition, for example, in terms of the conductivity of the composition. A composition can be obtained that has a very low conductivity and is significantly superior in terms of electrical operational safety compared to commonly used water / glycol mixtures. The molar content of monoester is relative to the sum of the monoester and diester present.

[0027] According to a preferred feature of the use, the accumulator can be a Li-ion accumulator. It has been found that the composition of the present invention is particularly suitable for cooling or temperature control of Li-ion batteries or their electrical usage profiles. It is able to delay and safely compensate for temperature peaks that normally occur during power output and charging. This can therefore improve the electrical performance of the entire system as a whole.

[0028] In a preferred embodiment of the use, the Li-ion storage battery can be used to drive a vehicle. The composition according to the invention can particularly contribute to extending the electrical performance of the Li-ion storage battery operating in the vehicle. The waste heat generated can be safely discharged even under changing environmental conditions and with widely different load and charging profiles. This is particularly true for the temperature control of large battery arrays, where the low electrical conductivity of the composition according to the invention makes it possible to achieve a significantly improved safety profile even in the event of an accident. Vehicles within the meaning of the invention are partially or fully electrically driven means of transport, such as airplanes, bicycles, scooters, motorcycles, autorickshaws, rail vehicles, passenger cars, or vehicles for freight transport, mining, agriculture, or forestry.

[0029] In a further preferred embodiment of the use, the composition can be used simultaneously for cooling storage batteries (for example in the form of alkali ion batteries) and for lubricating moving parts in vehicles. Due to their particularly advantageous thermal and viscosity properties, the compositions according to the invention can be used not only for cooling but also for lubricating moving parts. [Example]

[0030] example I. Preparation of esters for use according to the invention The esters according to the invention are prepared by reacting the corresponding monocarboxylic acid with one or more stereoisomers of butanediol, in which a molar ratio of monocarboxylic acid to alcohol of, for example, 1 to 2.5 (monocarboxylic acid to dialcohol) or more can be selected.

[0031] The reaction is carried out in the presence of a water-adding solvent in the absence of a catalyst at a pressure ranging from 50 mbar to atmospheric pressure. The reaction time depends on the desired degree of esterification and can be, for example, 5 hours or more.

[0032] II. Physical properties of the esters compared to esters not according to the invention In principle, different diols can be used for esterification with monocarboxylic acids. The literature mentions esters along with other compounds that are considered suitable for use as coolants or lubricants. The table below lists the viscosity, pour point and flash point as a function of temperature for different diols reacted with aliphatic C5-C7 monocarboxylic acids:

[0033] [Table 1]

[0034] Tricyclodecane dimethanol diesters (TCD-DM) have high flash points and rather moderate pour points, but the viscosity of these esters at 20°C is 50 mmHg at 20°C. 2 / sec, which is in the undesirably high range. Compared to neopentyl glycol-diester (NPG) and 1,3-BG-ester, TCD-DM-diester has the highest viscosity. Neopentyl glycol-diester (NPG) shows a flash point comparable to that of 1,3-BG-diester, but the pour point and viscosity are both lower for 1,3-BG-diester. The difference in viscosity between NPG-diester and 1,3-BG-diester is particularly noticeable in the temperature range of ≦0°C. The measured values are shown in the table below. They show that the viscosity of 1,3-BG-diester in the low temperature range is much lower than that of NPG-diester:

[0035] [Table 2]

[0036] Compared to other esters, 1,3BG diesters are characterized by a sufficient flash point, a low pour point, and a very low advantageous viscosity. Furthermore, their thermal properties, such as thermal conductivity as determined according to ASTM D 7896, can be characterized as very good. For this reason, 1,3BG diesters are particularly suitable for use as temperature control agents or coolants for directly cooling storage batteries, such as alkali-ion batteries, compared to other esters.

[0037] III. Electrical Properties and Environmental Aspects of the Esters of the Invention The conductivity of the full esters of BG and monocarboxylic acids usable according to the present invention, determined according to CEI 60247, is typically in the range of less than 10 nS / m. The GWP potential of the compounds is in the range of 0. The compounds are biodegradable. For example, the degradability determined according to Sturm, CO2 evolution, OECD 301B can be more than 60% in 28 days. This results in a classification as readily biodegradable. The compounds are not toxic to humans.

[0038] IV. Physical Properties of the Esters According to the Invention For the different 1,3BG-esters the following data are obtained as a function of the monocarboxylic acid C chain length:

[0039] [Table 3]

[0040] To safely use a temperature control agent or coolant in direct contact with a battery cell, the composition should have a high flash point, a low pour point, and a low viscosity. As can be seen from the composition of different diesters as a function of the C chain length of the monocarboxylic acid used, diesters with very short C chain lengths produce compositions with too low a flash point, in the range of 110°C. Diesters of monocarboxylic acids with very long chain lengths provide very high flash points, but these diesters only exhibit unsatisfactory pour points and significantly too high viscosities.

[0041] In particular, diesters of 1,3BG with monocarboxylic acids having a medium C-chain length have very good properties for direct cooling of storage batteries, such as alkali-ion batteries. Despite their very low viscosity, these compositions have remarkably low pour points, high flash points, and good thermal properties. Therefore, these monocarboxylic acids with carbon numbers of C4 to C10, especially C5 to C7, are suitable for efficient cooling of, for example, Li-ion batteries.

Claims

1. 1. Use of a composition comprising 80% by weight or more and 100% by weight or less of a diester of butanediol and an aliphatic C4-C10 monocarboxylic acid for direct temperature control of a storage battery.

2. The use according to claim 1, wherein the butanediol is 1,3-butanediol.

3. 3. The use according to claim 1, wherein 80 mol % or more of the monocarboxylic acids are linear monocarboxylic acids.

4. 2. The use according to claim 1, wherein at least 80 mole percent of the monocarboxylic acids have an odd number of carbon atoms.

5. 2. The use according to claim 1, wherein the monocarboxylic acid is selected from the group consisting of C5 to C9 monocarboxylic acids.

6. 2. The use according to claim 1, wherein the monocarboxylic acid is selected from the group consisting of linear C5 or C7 monocarboxylic acids or mixtures thereof.

7. 2. The use according to claim 1, wherein the composition comprises at least 95% and at most 100% by weight of the diester.

8. 2. The use according to claim 1, wherein at least 95 mole % of the monocarboxylic acids consist of linear C7 monocarboxylic acids.

9. 2. The use according to claim 1, wherein the diester is a diester of 1,3-butanediol, and 95 mol % or more of the 1,3-butanediol is esterified with a linear C7 monocarboxylic acid.

10. 2. The use according to claim 1, wherein at least 95 mol% of the monocarboxylic acids consist of linear C5 monocarboxylic acids.

11. 11. The use according to claim 10, wherein the diester is a diester of 1,3-butanediol, and 95 mol % or more of the 1,3-butanediol is esterified with a linear C5 monocarboxylic acid.

12. 2. The use according to claim 1, wherein the content of diester based on the molar amount of alcohol, as determined by GC, is 95 mol % or more and 100 mol % or less.

13. 2. The use according to claim 1, wherein the content of monoesters based on the molar amount of alcohol, as determined by GC, is ≧0 mol % and ≦2.5 mol %.

14. 2. The use according to claim 1, wherein the accumulator is a Li-ion accumulator.

15. 15. The use according to claim 14, wherein the Li-ion storage battery is used to drive a vehicle.