FORM - 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
Title: ELECTROLYTES FOR LITHIUM ION BATTERIES
Applicant : IITB MONASH RESEARCH ACADEMY Nationality : INDIAN Address : NT Bombay
Powai, Mumbaj 400 076, India
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER, IN WHICH IT IS TO BE
PERFORMED

FIELD OF INVENTION
The present invention relates to electrolytes for lithium batteries. In particular, the present invention relates to electrolytes for lithium batteries operating at sub-zero temperatures. More particularly, the present invention relates to electrolytes using a single additive to facilitate the operation of lithium batteries at wide range of operating temperatures starting from high temperatures up to sub-zero temperatures.
BACKGROUND OF INVENTION
In recent times, the energy storage devices, especially batteries are required to power most of the electronic devices and electric vehicles. The operation of these batteries depends on the site temperature. The major components of the batteries are positive electrode, negative electrode and the electrolyte. In order to facilitate the batteries to operate over a wide range of temperatures, these essential components should remain unaffected by the operating temperatures. Though, the electrode components remain mostly stable over a wide range of temperatures, the electrolytes mostly used as liquids undergo a phase change. So, careful selection of the electrolyte ingredients plays a key role in determining the battery performance. In case of aqueous batteries such as lead acid batteries, the use of aqueous solution limits the usage of these batteries both at low and high temperatures. Even non-aqueous batteries such as lithium batteries which are dominating the current electronics market, have a limited use for operations at low temperatures especially below -10°C [1]. The limitations of low temperature operation could be due to the slow mobility of lithium ions in the system, which may also occur due to freezing of the electrolyte mixture at these temperatures [2-5]. As a result, altering the electrolyte mixture helps in increasing the freezing point of the electrolytes|2,6]. The most common electrolyte ingredient in a lithium battery is the lithium hexafluorophosphate salt dissolved in solvents such as Ethylene carbonate and linear carbonate solvents such as Dimethyl Carbonate / Diethyl carbonate or a mixture of both. Each of these electrolyte ingredients has a specific role in

the performance of battery which cannot be skipped from the composition, whereas there could be additives which can do the required job [2].
This concept was adopted in some of the existing works, where a mixture of organic solvents was added to the electrolytes which lower the freezing point of the electrolyte. Previous studies involved complex compositions, in which a number of organic solvents could be added to the electrolyte which may also interfere with the battery performance. The addition of these organic solvents also restricts their usage only to sub-zero temperatures due to the volatility and flammability of these organic solvents. The performance of lithium ion batteries at low temperatures under -20°C is a major challenge due to the freezing of the electrolyte and other lithium ion kinetics.
Therefore, there is an existing need for developing lithium ion batteries, which are configured to operate over a wide range of temperatures, i.e. from high temperatures of the order of over 50°C to much lower sub-zero temperatures, e.g. around -40°C.
PRIOR ART
CN 103107364 A discloses a low-temperature type lithium ion battery electrolyte. The electrolyte comprises lithium hexafluorophosphate UPF6 and a mixed solvent, wherein the concentration of the lithium hexafluorophosphate LiPF6 is 0.8-1.5mol/l, and the mixed solvent comprises the following components in percent by weight: 20-40 percent of ethylene carbonate (EC), 5-30 percent of ethyl methyl carbonate (EMC), 30-50 percent of methyl acetate (MA) and 0.5-5 percent of vinylene carbonate (VC). According to the electrolyte, the low-melting-point organic solvents, namely, EMC and MA and a film-forming agent, namely the VC, are added to the basic solvent, namely EC to ensure that the low temperature performance of the lithium ion battery is improved, the electrochemical property of the lithium ion battery under the low temperature condition is improved, and the application range of the lithium ion battery is greatly enlarged. However, this electrolyte includes a plurality of additives for low-temperature performance of the battery.

The relative discharge capacity* is 55% (at -40°C, after holding for 16-24h at a C rate of C/20) whereas the relative capacity is 90% (at -20°C, at C/20). This is unlike the electrolyte of the present invention comprising of a single additive for sub-zero temperature operations.
*Relative capacity is the ratio of capacity obtained at specific temperatures to the capacity obtained at room temperatures.
CN 103378360 A discloses organic electrolyte capable of improving low-
temperature performance of a lithium manganese battery. A main salt of a
lithium salt is lithium perchlorate, an auxiliary salt of the lithium salt is selected
from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium
trifluoromethanesulfonate, lithium bis(oxalate) borate,lithium
bis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulfonyl)imide, lithium oxalyldifluoroborate and lithium iodide; an organic solvent is a mixed solvent of cyclic esters, linear esters, ethers and sulfones;; an additive is selected from an additive A and an additive B, wherein the additive A is selected from benzoic acid, phenylacetic acid, benzoic anhydride, phthalic anhydride, m-phthalic anhydride and terephthalic anhydride, and the additive B is selected from 2,6-di-tert-butyl-4-methylphenol, tert-butylhydroquinone and butylated hydroxyanisole. By adopting the organic electrolyte, the low-temperature discharging performance of the lithium manganese battery can be obviously improved, and the application range of lithium manganese battery can be effectively enlarged. However, this organic electrolyte includes a set of additiveswere testedfor improving the low-temperature performance of the lithium manganese battery. Moreover, the average relative capacity obtained for various set of additives used in this case is about 44.756% at - 20°C.
US 2005123835 discloses non-aqueous electrolytes having an extended temperature range for battery applications. The electrolyte comprises an electrolyte salt, e.g. LiPF6, a first non-aqueous solvent, and a second non-aqueous solvent having a structure of formula I or II. The electrolyte has higher ionic conductivity, lower freezing point, and lower vapor pressure at high temperature than commercial electrolytes. These non-aqueous electrolytes can be used, for example, in lithium-ion batteries. Methods of making lithium-

ion batteries are also described. However, the maximum relative capacity that can be achieved with this composition is about 63.6% at - 30°C, whereas when it was 53.8%, the Relative Capacity were 60.7% and 25.8%.
CN 103779605 A discloses a low-temperature lithium iron phosphate ion battery electrolyte which solves the problem of poor low-temperature performance of the lithium iron phosphate ion battery electrolyte in the prior art. The electrolyte consists of lithium hexafluorophate, a quaternary system organic solvent and an additive, wherein the quaternary system organic solvent is formed by mixing gamma-butyrolactone, ethylene carbonate, methyl ethyl carbonate and ethyl acetate according to the volume ratio of (1-2):(1-2):(1-2):(1-2), the additive is glycol dimethyl ether. In the electrolyte, the concentration of lithium hexafluorophate is 1-1.2mol/L, the substance amount ratio of lithium hexafluorophat to glycol dimethyl ether is 1:(3-4). The compatibility of the electrolyte and positive electrode material, namely, lithium iron phosphate is good, the viscosity at low temperature is low, the dielectric constant is high, and the low-temperature conductivity of the electrolyte is effectively improved, and the exertion of the electrochemical performance of the battery is ensured. Although the capacity retention is 92% at 30°C, it is only 89% at -10°C and 84% at -25°C respectively.
US 2016149263 A1 discloses a lithium ion battery cell includes a housing, a cathode disposed within the housing, wherein the cathode comprises a cathode active material, an anode disposed within the housing, wherein the anode comprises an anode active material, and an electrolyte disposed within the housing and in contact with the cathode and anode. The electrolyte includes a solvent mixture and a lithium salt serving as a primary lithium ion conductor in the electrolyte to allow for lithium ion intercalation and deintercalation processes at the cathode and the anode during charging and discharging of the lithium ion battery cell. The solvent mixture includes a cyclic carbonate and one or more non-cyclic carbonates. The lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI). The solvent mixture and LiFSI are configured to enhance the low temperature performance of the lithium ion battery cell at operating temperatures below 0°C. Electrolyte mixtures involving various salt,

solvent and additive compositions were checked at low temperatures of -20 and -30°C. The maximum relative capacity is 65% at -30°C which employs 3-methoxypropionitrile as a major additive in addition to the other salt and solvent ingredients.
CN 103078136 A discloses a lithium ion battery electrolyte, mainly relates to a low-temperature rate lithium ion battery electrolyte, and belongs to the lithium ion battery field. The low-temperature rate lithium ion battery electrolyte is characterized in that the low-temperature rate lithium ion battery electrolyte is prepared through mixing an electrolyte lithium salt, a non-aqueous organic solvent, a film forming additive, a low-melting-point and low-viscosity additive and a low-temperature conductive additive; and the structural formula 1 of the low-temperature conductive additive is shown in the specification, and R in the structural formula 1 can be a hydrocarbyl group selected from CH3, C2H3, C6H6 and the like, or a derivative thereof, and can also be a nitrogen-containing a heteroaryl group selected from C5H5N and the like, or a derivative thereof.; The low-temperature rate lithium ion battery electrolyte has the advantages of reasonable component ratio, guarantee of good cycle performances at normal temperature, increase of the rate discharge performance and the conductivity at a low temperature, and effective widening of the application range of a lithium ion battery in a low temperature environment. However, this lithium ion battery electrolyte comprises a plurality of additives unlike the electrolyte of the present invention prepared with a single additive. The ionic conductivities of various additive added compositions used in this patent range from 0.87-1.37 mS/cm at -40°C whereas, the 18650 battery performance was tested at -20°C and it was observed that the maximum relative capacity in this system is 84%.
US 6153338 A discloses an alkali metal secondary electrochemical cell, and preferably a lithium ion cell, activated with a quaternary solvent system, is described. The solvent system comprises a quaternary mixture of dialkyl carbonates and cyclic carbonates, and preferably dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and ethylene carbonate. Lithium ion cells activated with this electrolyte have good room temperature cycling

characteristics and excellent low temperature discharge behavior. However, the relative capacity at -20°C is only 70% and the relative capacity at 0°C is 95%.
US 2013157147 A1 discloses electrolytes for lithium based batteries are described with good temperature tolerance over appropriate temperature ranges for uses in vehicles. In particular, the electrolytes are suitable for high voltage operation over 4.4V and can provide high rate performance. The electrolytes generally comprise a solvent that is a mixture of ethylene carbonate, dimethyl carbonate and ethylmethyl carbonate. Alternatively, a solvent combination of fluoroethylene carbonate and dimethyl carbonate was used. A primary lithium salt is includes at a concentration greater than about 1.05M. The electrolyte generally also comprises a lithium salt additive. The electrolytes can provide some battery capacity down to at least -40° C. while providing good performance also at elevated temperatures of 45° or more, and the corresponding batteries can be cycled to several thousand cycles. However, the relative capacity at -30°C and -40°C are only 40% and 25% respectively.
CN 103151558 A discloses an ester-based ionic liquid electrolyte solution for a low temperature lithium ion battery. The electrolyte solution contains a lithium salt, non-aqueous solvents, an additive and an ionic liquid. With a wide liquid range, the ionic liquid can still maintain good liquid properties at a low temperature. The adding of the ionic liquid can effectively improve the low temperature performance of the lithium ion battery, thus widening the operating temperature range of the electrolyte solution. The invention aims to overcome the defects of low temperature problem and potential safety hazards in the electrolyte solution composed of an organic solvent and a lithium salt in the prior art, and provides the ester-based ionic liquid electrolyte solution for a low temperature lithium ion battery. The charging of the batteries were carried out at room temperatures by taking them out of the testing chamnber and the discharge was carried out at room temperatures.However, the discharge capacity of the battery composed of the electrolyte solution at a temperature of - 40°C is about 60% of its discharge capacity at 25°C.

US 9466857 B1 discloses electrolyte solutions including additives or combinations of additives that provide low temperature performance and high temperature stability in lithium ion battery cells. However, this electrolyte also includes a plurality of additives for low-temperature performance of the battery.
NON-PATENT LITERATURE
An article entitled: The low temperature performance of Li-ion batteries [1] by S.S. Zhang, K.Xu, T.R. Jow and published in Journal of Power Sources. 115 (2003) 137-140 discusses that a symmetric cell was adopted to analyze low temperature performance of Li-ion battery and results have shown that impedances of both Li-ion and symmetric cells are mainly composed of bulk resistance (Rb), surface layer resistance (Rs\) and charge-transfer resistance (Rct). Among these three components, Rct is most significantly increased and becomes predominant as temperature falls under -10°C. Therefore, the poor low temperature performance of Li-ion battery is due to the substantially high Rct of the graphite and cathode. Comparing impedance spectra of the symmetric cells, it was found that at -30°C the delithiated graphite and lithiated cathode, both of which correspond to a discharged state in a Li-ion battery, have a much higher Rct than when charged. This means that the Li-ion battery in the discharged state suffers a higher polarization. Therefore, it was demonstrated that at low temperatures, the charging of a discharged Li-ion battery is more difficult than discharging of a charged battery,
Another article entitled: Electrolytes for Low-Temperature Lithium Batteries Based on Ternary Mixtures of Aliphatic Carbonates [2] by M.C. Smart, B.V. Ratnakumar, S. Surampudi and published in the Journal of Electrochemical Society 146(2) 486-492 (1999), discusses the low-temperature performance of lithium-ion cells being mainly limited by the electrolyte solution, which not only determines the ionic mobility between electrodes but also strongly affects the nature of surface films formed on the carbonaceous anode. The surface films provide kinetic stability to the electrode (toward electrolyte) and permit charge (electron) transfer across them, which in turn determines the cycle life and rate

capability of lithium-ion cells. Aiming at enhancing low-temperature cell performance, the electrolyte solutions based on different ratios of alkyl carbonate solvent mixtures, i.e., ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were studied in terms of electrolyte conductivity, film resistance, film stability, and kinetics of lithium intercalation and deintercalation at various temperatures. Electrolytes based on the ternary mixtures of EC, DEC, and DMC emerged as the preferred combination as compared to the binary analogues, both in terms of conductivity and surface film characteristics, especially at low temperatures. Therefore, this study demonstrated a synergistic effect of high durability from the DMC-based solutions and improved low-temperature performance from the DEC-based electrolytes.
The article entitled: Effects of SEI on the kinetics of lithium intercalation [3] by B.V. Ratnakumar, M.C. Smart, S. Surampudi, and published in the Journal of Power Sources. 97-98 (2001) 137-139 also discusses that the electrochemical stability of electrolytes at lithium, or lithium-intercalating anodes is achieved via ionically conducting surface films termed as solid electrolyte interphase (SEI). Since the lithium deposition or intercalation process occurs on the electrode covered with the SEI, the characteristics of the SEI determine the kinetics of lithiation/delithiation, stability of the interface, and thus, the overall cell performance, especially at low temperatures. In this paper, the significance of the SEI characteristics over the solution properties was reiterated by using a few illustrative examples from the research on low temperature Li ion battery electrolytes at JPL. The examples specifically include the beneficial aspects of a ternary carbonate mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) compared to the binary mixtures (of EC and either DMC or DEC) and quaternary solutions with appropriate co-solvents, such as alkyl esters. However, this paper relates to solid electrolyte interphase (SEI), unlike the liquid electrolyte in accordance with the present invention prepared with a single additive.
The paper entitled: A low-temperature electrolyte for lithium and lithium-ion batteries [4] by E.J. Plichta, W.K. Behl and published in the Journal of Power

Sources. 88 (2000) 192-196, discusses that an electrolyte consisting of 1 M solution of lithium hexafluorophosphate in 1:1:1 ethylene carbonate (EC)-dimethyl carbonate (DMC)-ethyl methyl carbonate (EMC) is used for low temperature applications of lithium and lithium-ion cells. This new electrolyte has good conductivity and electrochemical stability. Lithium and lithium-ion cells using this new electrolyte are found to be operable at temperatures down to -40°C. This paper also reports on the electrochemical stability of aluminum metal, which is used as a substrate for the positive electrodes in lithium-ion cells, in the new electrolyte. However, this electrolyte includes three different constituents, viz. EC, DMC and EMC, mixed for obtaining a low-temperature of the lithium and lithium-ion batteries.
The paper entitled: Limits of Low-Temperature Performance of Li-Ion Cells [5 by C.K. Huang, J.S. Sakamoto, J. Wolfenstine, S. Surampudi and published in the Journal of Electrochemical Society, 147 (2000) 2893. doi:10.1149/1.1393622, discloses the results of electrode and electrolyte studies in that a poor low-temperature (<-30°C) performance of Li-ion cells is mainly caused by the carbon electrodes and not the organic electrolytes and solid electrolyte interphase, as was suggested previously. The paper suggests that the main causes for the poor performance in the carbon electrodes are (/') the low value and concentration dependence of the Li diffusivity and (/'/') limited Li capacity. However, it was observed that only 0.8 M LiPF6 electrolyte consisting of EC:DEC:DMC:EMC electrolyte in a ratio of 3:5:4:1 was found suitable for low-temperature electrochemical performance, unlike the electrolyte of the present invention consisting of a single additive.
The paper entitled: Identification of solid electrolyte interphase formed on graphite electrode cycled in trifluoroethyl aliphatic carboxylate-based electrolytes for low-temperature lithium-ion batteries [6] by W. Lu, S. Xiong, K. Xie, Y. Pan, C. Zheng, and published in Ionics (Kiel) 22 (2016) 2095-2102, discusses that trifluoroethyl aliphatic carboxylates with different length of carbon-chain in acyl groups have been introduced into carbonate-based electrolyte as co-solvents for improve the low-temperature performance of lithium-ion batteries, both in capacity retention and lowering polarization of

graphite electrode. To identify the further influence of trifluoroethyl aliphatic carboxylates on graphite electrode, the components and properties of the surface film on graphite electrode cycled in different electrolytes were
investigated by using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The IR and XPS results show that the chemical species of the solid electrolyte interphase (SEI) on graphite electrode strongly depend on the selection of co-solvent. For instance, among those species, the content of RCOOLi increases with an increasing number of carbon atoms in RCOOCH2CF3molecule, wherein R was an alkyl with 1, 3, or 5 carbon atoms. It was suggested that the thickness and components of the SEI film play a crucial role on the enhanced low-temperature performance of the lithium-ion batteries. However, this paper relates to solid electrolyte interphase (SEI) film, unlike the liquid electrolyte in accordance with the present invention prepared with a single additive.
DISADVANTAGES OF THE PRIOR ART
The performance of Lithium batteries in the sub-zero temperatures is exceptional due to the freezing of the electrolytes as well as the limited diffusion of lithium in the system at those temperatures. In this scenario, literature suggests the use of number of organic solvent mixture as additives which can retard the freezing of electrolytes as well as the different synthesis route of electrode materials for the better diffusion of lithium ions in the system. The electrolyte compositions reported in the literature includes number of organic solvents most of which have very low boiling points which can restrict the performance only to low temperatures and complicate the working of these batteries at room temperatures as well as above room temperatures.
The plurality of organic solvents used in the prior art electrolytes although, helps in low temperature performance but most of the mixtures as a whole gets complicated at room temperatures due to the volatility and flammability of the organic solvents used in the electrolytes.

Moreover, the addition of too many organic solvents also complicates the commercial preparation of these electrolyte at large scales.
The addition of these organic solvent additives also limits the performance of these electrolytes to low temperatures, whereas the operations at ambient and above ambient temperatures such as 60°C is limited.
OBJECTS OF THE INVENTION
Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:
An object of the present invention is to provide an electrolyte for lithium batteries operating at sub-zero temperatures.
Another objective of this present invention is to provide an electrolyte which operate at potential limit of 4.4V vs. Li/Li+.
Another objective of this present invention is to provide an electrolyte that has better safety features than the conventional electrolytes even at room temperatures.
Another objective of this present invention is to provide an electrolyte composition that includes the conventional solid electrolyte interface film forming additives.
Another objective of the present invention is to provide a simple electrolyte composition for lithium batteries, which can help the easy preparation of these electrolytes in bulk at commercial scale.
Another objective of the present invention is to provide the electrolyte having a single additive for operating lithium batteries at wide range of temperatures (-40°C to 60°C).

These and other objects and advantages of the present invention will become more apparent from the following description when read with the accompanying
figures of drawing, which are, however, not intended to limit the scope of the present invention in any way.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided an electrolyte for Lithium ion batteries operating at sub-zero temperatures, wherein the electrolyte comprises a mixture of Lithium hexafluorophosphate salt dissolved in a solvent Ethylene Carbonate (EC) and the linear carbonate solvent Diethyl Carbonate and a single ionic liquid for maintaining the liquid state of the electrolyte at temperatures as low as - 40°C and having an improved ionic conductivity.
Typically, the electrolyte comprises N-Propyl-N-Methyl pyrrolidinium bis (fluorosulfonyl) imide as the single additive for improving the low-temperature performance thereof.
Typically, the solvents Ethylene Carbonate (EC) and Diethyl Carbonate are mixed in a ratio of 1:1.
Typically, the mixture of solvents Ethylene Carbonate (EC) and Diethyl Carbonate are added to the Lithium hexafluorophosphate (LiPF6) salt to make at least a concentration of 1M to obtain the electrolyte without the ionic liquid.
Typically, the concentration of Lithium hexafluorophosphate (LiPF6) salt is between 1-1.2 M.
Typically, 40% by weight of N-Propyl-N-Methylpyrrolidinium bis (fluorosulfonyl) imide is added to the obtained electrolyte without the ionic liquid.
Typically, any other metal salt replaces the Lithium hexafluorophosphate salt for a corresponding metal ion batteries.

In accordance with the present invention, there is also provided a method of preparation of the electrolyte for Lithium ion batteries operating at sub-zero temperatures as claimed in claims 1 to 7, comprises the following method steps:
(a) Mixing Ethylene carbonate with Diethyl carbonate in a ratio of 1:1;
(b) Adding Lithium hexafluorophosphate (LiPF6) salt to above mixture to obtain a solution of at least 1M concentration;
(c) Stirring the above solution for 24 hours to obtain the electrolyte without the ionic liquid (solution A);
(d) Adding 40% by weight of the salt N-Propyl-N-Methylpyrrolidinium bis (fluorosulfonyl) imide to the above solution A; and
(e) Stirring the above mixture for 24 hours at room temperature to obtain the electrolyte for Lithium ion batteries operating at sub-zero temperatures, preferably between -30°C and 60°C.
Typically, the concentration of the solution obtained in method step (b) is between 1-1.2 M.
Typically,50% Relative discharge capacity is obtained at -30°C for a charging time of 10 hours at a current rate of 0.053mA/cm2.
DESCRIPTION OF THE INVENTION
A particular percentage of ionic liquid in the conventional lithium ion battery electrolyte helps to achieve an electrolyte which can stay as liquid with better ionic conductivity at low temperatures of about -40°C. An electrolyte which could stay as liquid above -40°C as well as which helps in lithium ion conduction can be prepared according to the present invention.

In the system in accordance with the present invention, a single additive is used to help in the performances from -40°C to +60°C. Table 1 below shows the current composition and the physical properties of the electrolyte prepared in accordance with the present invention by using a single additive to help in operations in a wide temperature range, e.g. from -40°C to +60°C.
Table 1

S. No. Chemical Compound Melting Point (°C) Boiling Point (°C)/L Flash Point
<°C) (Closed Cup)
1. Lithium hexafluorophosphate 200
2. N-Propyl-N-Methylpyrrolidinium bis (fluorosulfonyl) imide
(ionic liquid) 12
3. Ethylene Carbonate (EC) 34-37 243 150
4. Diethyl Carbonate (DC) -43 126-128 33
In addition, the low temperature performance (at -40°C) prefers slow charging as the kinetics is quite limited and most commonly found charging time is as high as 20-10 hours. But in the present case, even fast charging times could be adopted and a reasonable percentage of the capacity can be obtained in comparison with the capacity obtained as a result of 10 hours charging as shown in Table 2 below, which shows the rate capability of the electrolytes at -30°C. Rate capability is the percentage ratio of the discharge capacity obtained when the battery was charged at a particular higher rate (short time duration) to the discharge capacity obtained when the battery was charged with a charging time of 10 h.
Table 2

S.No. Charging Time Discharging Time (h) Rate capability* at -30°C (%)
1. 10 10 100
2. 6 6 72
3. 2.5 2.5 50
4. 1.2 1.2 36

5. | 0.5 0.5 21
This invention can be commercialized as electrolyte composition and its application at low temperature application for lithium-ion batteries which are used in all mobile electronic devices, (e.g. mobile phones, cameras and all defense-related equipment requiring operation at sub-zero temperatures.
A wide range of applications are possible using this electrolyte composition including electrochemical capacitors, robotics, electric transports, micro grids etc. The potential size of the market, with a particularly emphasis to Australian, Indian, Global markets, is large. Since lithium-ion batteries dominate the world, this invention is a boon for Indian as well as international market to power the low temperature (sub-zero) operations of electronic devices. Therefore, a number of applications are possible by using this electrolyte composition, e.g. in Hybrid super capacitors, lithium ion capacitors, lithium/ lithium ion battery used in robotics, drone application, aviation sector, electric transports and micro grids etc.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present invention will be briefly described with reference to the accompanying drawings, wherein:
FIGURE 1 shows the Differential Scanning Calorimetry (DSC) curves for lithium battery electrolytes depicting the role after the addition of ionic liquid in different electrolyte mixtures.
FIGURE 2 shows the graphical representation of the ionic conductivity of the electrolytes with and without ionic liquid from - 40°C to 60°C.
FIGURE 3a shows the actual photographs of the electrolytes at -40°C an electrolyte without ionic liquid in the conductivity cell.

FIGURE 3b shows the actual photographs of the electrolytes at -40°C an electrolyte with an ionic liquid in the conductivity cell.
FIGURE 3c and 3d shows a bar-chart for the cycling temperatures v/s the relative capacity obtained at sub-zero temperature set against the actual photograph of the electrolyte at -40°C.
FIGURE 4a shows a graphical representation of discharge capacity at -30 C v/s cycle number for cell cycled with lithium titanium oxide and lithium iron phosphate electrodes.
FIGURE 4b shows a graphical representation of the Specific Discharge
0
Capacity (SDC) at -30 C for the cell cycled with lithium titanium oxide and lithium iron phosphate electrodes for 10h.
DETAILED DESCRIPTION OF THE FIGURES/DRAWINGS
In the following, the present invention will be described in more details with reference to the accompanying drawings without limiting the scope and ambit of the present invention in any way.
FIGURE 1 shows the Differential Scanning Calorimetry (DSC) curves for lithium battery electrolytes depicting the addition of ionic liquid in different electrolyte mixtures, i.e. (1) electrolyte without any ionic liquid (Red curve); (2) N-Propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (ionic liquid) (Green curve); and (3) electrolyte (Blue curve). The phase change behavior of these electrolytes was tested, which demonstrates that after adding an ionic liquid, a negligible phase change occurs in solution B as compared to their parent compounds which explains that the present invention can stay as liquid for subzero temperatures than their parent compounds.
FIGURE 2 shows the graphical representation of the ionic conductivity of the electrolytes with ionic liquid (3) and without ionic liquid (1) from - 40°C to 60°C.

The graph is plotted for the log values of the ionic conductivity on Y axis against the temperature (K) and 1000/T(K-1) on X axis. It should be noted that the electrolytes with addition of ionic liquid show a better ionic conductivity value at subzero temperatures as compared to the conventional electrolyte.
FIGURE 3a shows the actual photographs of the electrolytes at -40°C an electrolyte without ionic liquid in the conductivity cell.
FIGURE 3b shows the actual photographs of the electrolytes an electrolyte at -40°C with an ionic liquid in the conductivity cell. It is evident from the above figures that the electrolyte with ionic liquid (Figure 3b) remains in liquid state, whereas the electrolyte without ionic liquid (Figure 3a) gets frozen.
FIGURE 3c and 3d shows the graphical representation using a bar-chart for the cycling temperatures on Y axis plotted against the relative capacity (in %) obtained at sub-zero temperature (253K and 243K).
FIGURE 4a shows a graphical representation of the Discharge capacity (DC)
at -30°C for the cell cycled with Lithium titanium oxide and Lithium iron phosphate electrodes for ten hours. It is a graph of the discharge capacity v/s cycle number.
FIGURE 4b shows a graphical representation of the Specific Discharge
capacity (SDC) at -30°C for the cell cycled with Lithium titanium oxide and Lithium iron phosphate electrodes for ten hours. It is a graph of the specific discharge capacity at -30°C with respect to anodic mass loading in the electrodes. Since the relative capacity is the ratio of average capacity at -30°C to the average capacity at room temperature, it was calculated for cells at -20°C and at -30°C. It is evident from the above graphs that this safe and simple composition performs better as compared to the existing literatures as discussed with reference to Figure 3 below.

TECHNICAL ADVANTAGES & ECONOMIC SIGNIFICANCE
The electrolyte composition for operating lithium batteries from high temperatures to sub-zero temperatures and prepared by using a single additive in accordance with the present invention has the following technical and economic advantages:
• Unrestricted operations from high temperatures to sub-zero temperatures, which was not possible with addition of multiple organic solvents in conventional electrolytes.
• Simple electrolyte composition.
• Addition of a single additive helps in the lithium battery performance over wide operating temperatures right from - 30°C to + 60°C.
• Facilitates charging and discharging of the lithium ion batteries with this electrolyte composition at sub-zero temperature of - 30°C with good rate capabilities which was not possible with conventional electrolytes usually frozen at this low temperature.
Throughout this specification, the word "comprise", or variations such as "comprises" or "comprising", shall be understood to implies including a described element, integer or method step, or group of elements, integers or method steps, however, does not imply excluding any other element, integer or step, or group of elements, integers or method steps.
The exemplary embodiments described in this specification are intended merely to provide an understanding of various manners in which this embodiment may be used and to further enable the skilled person in the relevant art to practice this invention. The description provided herein is purely by way of example and illustration.

Although the embodiments presented in this disclosure have been described in terms of its preferred embodiments, the skilled person in the art would readily recognize that these embodiments can be applied with modifications possible within the spirit and scope of the present invention as described in this specification by making innumerable changes, variations, modifications, alterations and/or integrations in terms of materials and method used to configure, manufacture and assemble various constituents, components, subassemblies and assemblies, in terms of their size, shapes, orientations and interrelationships without departing from the scope and spirit of the present invention.
While considerable emphasis has been placed on the specific features of the preferred embodiment described here, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other changes in the preferred embodiment of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation

WE CLAIM:
1. An electrolyte for Lithium ion batteries operating at sub-zero temperatures, wherein the electrolyte comprises a mixture of Lithium hexafluorophosphate salt dissolved in a solvent Ethylene Carbonate (EC) and a linear carbonate solvent such a Diethyl Carbonate and a single ionic liquid for maintaining the liquid state of the electrolyte at temperatures as low as - 40°C and having an improved ionic conductivity
2. Electrolyte for Lithium ion batteries as claimed in claim 1, wherein the electrolyte comprises N-Propyl-N-Methylpyrrolidinium bis (fluorosulfonyl) imide as the single additive for improving the low-temperature performance thereof.
Electrolyte for Lithium ion batteries as claimed in claim 1, wherein the solvents Ethylene Carbonate (EC) and Diethyl Carbonate or Dimethyl Carbonate are mixed in a ratio of 1:1.
Electrolyte for Lithium ion batteries as claimed in claim 3, wherein the mixture of solvents Ethylene Carbonate (EC) and Diethyl Carbonate or Dimethyl Carbonate is added to the Lithium hexafluorophosphate (LiPF6) salt to make at least a concentration of 1M to obtain the electrolyte without the ionic liquid.
5. Electrolyte for Lithium ion batteries as claimed in claim 4, wherein the concentration of Lithium hexafluorophosphate (LiPF6) salt is between 1-1.2 M.
6. Electrolyte for Lithium ion batteries as claimed in claim 4 or 5, wherein 40% by weight of N-Propyl-N-Methylpyrrolidinium bis (fluorosulfonyl) imide is added to the obtained electrolyte without the ionic liquid.

7. Electrolyte for Lithium ion batteries as claimed in claim 4 to 6, wherein any
other metal salt replaces the Lithium hexafluorophosphate salt for a
corresponding metal ion batteries.
8. A method of preparation of the electrolyte for Lithium ion batteries operating
at sub-zero temperatures as claimed in claims 1 to 7, comprises the
following method steps:
(f) Mixing Ethylene carbonate with Diethyl carbonate in a ratio of 1:1;
(g) Adding Lithium hexafluorophosphate (LiPF6) salt to above mixture to obtain a solution of at least 1M concentration;
(h) Stirring the above solution for 24 hours to obtain the electrolyte without the ionic liquid (solution A);
(i) Adding 40% by weight of the salt N-Propyl-N-Methyl pyrrolidinium bis (fluorosulfonyl) imide to the above solution A; and
(j) Stirring the above mixture for 24 hours at room temperature to obtain the electrolyte for Lithium ion batteries operating at sub-zero temperatures, preferably between -30°C and 60°C.
9. Method as claimed in claim 8, wherein the concentration of the solution obtained in method step (b) is between 1-1.2 M.
10. Method as claimed in claim 8 and 9, wherein 50% Relative discharge capacity is obtained at -30°C for a charging time of 10 hours at a current rate of 0.053mA/cm2.