An electrolyte for lithium-ion battery

Abstract

The present disclosure provides an electrolyte comprising: an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt; and (c) an additive; wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4:1 to 6:1; and the additive is selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof. The present disclosure further provides an electrochemical cell comprising the electrolyte as disclosed herein.

Description

AN ELECTROLYTE FOR LITHIUM-ION BATTERY FIELD OF INVENTION

[0001] The present disclosure broadly relates to the field of batteries. Particularly, the present disclosure relates to an electrolyte for a lithium-ion battery (LIB).BACKGROUND OF THE INVENTION

[0002] Secondary batteries like lithium-ion batteries (LIBs), are the most commonly used energy supply units for portable electronic devices such as mobile phones, laptop computers and portable handheld power tools. The relevance of LIBs is increasing day-by-day, particularly in light of the growing demand for energy storage and sustainability along with high energy density and cyclic abilities of the LIBs. Electrolyte being a crucial component in batteries, plays a pivotal role in the electrochemical processes by facilitating the movement of ions between the electrodes. The ionic conductivity, voltage stability, temperature range, composition and the formation of solid-electrolyte interface (SEI) is critical to the overall performance, efficiency, and longevity of batteries, particularly in electrochemical cells.

[0003] Higher temperatures can initially improve ionic conductivity of the electrolyte. However, the performance of conventional electrolytes in lithium-ion batteries are detrimentally impacted by high temperatures. Elevated temperatures can lead to the thermal decomposition of organic solvents used in conventional electrolytes, such as carbonate-based solvents. At high temperatures, the lithium salt in the electrolyte becomes highly susceptible to decomposition, which results in the formation of unfavourable byproducts. Electrolyte degradation can increase internal resistance and reduce the longevity and cycle life of batteries. Further, it can destabilize the SEI layer on the anode, leading to increased capacity fading and decreased overall battery cycle life. Furthermore, temperature exceeding certain limits may lead to viscosity alterations that detrimentally impacts the ion transport.

[0004] Similarly, at low temperatures the ionic conductivity of the electrolyte decreases significantly, leading to reduced battery performance. It also results in increased internal resistance resulting in poorer battery efficiency and greatervoltage drop during discharge. The electrochemical reaction rates are slowed down at lower temperatures, which can lead to diminished capacity and longer charging times. Further, the electrochemical stability window may change at low temperatures, potentially leading to undesirable reactions of electrolytes. Furthermore, prolonged exposure to low temperatures can contribute to overall degradation in cycle life of lithium-ion batteries. Hence, exposing conventional electrolytes comprising lithium salts and organic solvent(s) to extreme temperatures are still a major concern.

[0005] Accordingly, there is a dire need in the state of art to develop an electrolyte which can overcome these issues and provide high ionic conductivity, better performance and electrochemical stability.SUMMARY OF THE INVENTION

[0006] In an aspect of the present disclosure, there is provided an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt and (c) an additive; wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4:1 to 6:1; and the additive is selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6, hexanetricarbonitrile (HTCN), or combinations thereof.

[0007] In another aspect of the present disclosure, there is provided an electrochemical cell comprising: a. a cathode; b. an anode and c. the electrolyte as disclosed herein.

[0008] These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The following drawings form a part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.

[0010] Figure 1 depicts the combinatorial cyclic voltammetry (combi CV) data for the electrolytes O-l, O-2, 0-3, 0-4, 0-5, 0-6, 0-8, and 0-10, in accordance with an embodiment of the present disclosure.

[0011] Figure 2 depicts the combined combi CV data plot of electrolytes 0-3, 0-7, 0-8, 0-9, and 0-10, at (a) 1stcycle and (b) 501stcycle measured at 0.1 mV / s scan rate, in accordance with an embodiment of the present disclosure.

[0012] Figure 3 depicts the combined combi CV data plot of electrolytes 0-3, 0-7, 0-8, 0-9, and 0-10, at (a) 1stcycle and (b) 500thcycle measured at 1 mV / s scan rate, in accordance with an embodiment of the present disclosure.

[0013] Figure 4 depicts electrochemical charge-discharge data for the electrolytes 0-3 and 0-5, in accordance with an embodiment of the present disclosure.

[0014] Figure 5 depicts digital images of the disassembled coin cells comprising (a) 0-3 and (b) 0-7 as electrolyte after cycling for 900 charge-discharge cycles, in accordance with an embodiment of the present disclosure.

[0015] Figure 6 depicts the electrochemical charge-discharge data for the electrolyte 0-3, in accordance with an embodiment of the present disclosure.

[0016] Figure 7 depicts the capacity retention data for the electrolytes (a) 0-3 and (b) 0-5 at 10°C, in accordance with an embodiment of the present disclosure.

[0017] Figure 8 depicts the capacity retention data for the electrolytes (a) 0-3 and (b) 0-5 at 25°C, in accordance with an embodiment of the present disclosure.

[0018] Figure 9 depicts the capacity retention data for the electrolytes (a) 0-3 and (b) 0-5 at 45°C, in accordance with an embodiment of the present disclosure.

[0019] Figure 10 depicts the capacity retention data for the electrolytes 0-1, 0-2, 0-3, 0-4, 0-5, 0-6, at (a) 25°C and (b) 45°C, in accordance with an embodiment of the present disclosure.

[0020] Figure 11 depicts the electrochemical charge-discharge data of the cells comprising electrolyte 0-3 (a) for first cycle at scan rate 0.1 mV / s, (b) for first cycleat scan rate ImV / s and (c) for 60thcycle at scan rate ImV / s, in accordance with an embodiment of the present disclosure.

[0021] Figure 12 depicts the electron dispersion spectroscopic (EDS) images (a) layered image, (b) map sum spectrum, and (c) elemental mapping, for the cycled cells, in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION OF THE INVENTION

[0022] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps, features, compositions, and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features. Definitions

[0023] For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are delineated here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below.

[0024] The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0025] The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

[0026] Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

[0027] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0028] The term “organic solvent” as used herein refers to carbon-based compounds such as hydrocarbons, alcohols, esters, carbonates, ethers, ketones, and aromatic compounds, used to dissolve metal salts and promote ion flow in an electrolyte. Examples of organic solvents include, but not limited to ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) or combinations thereof.

[0029] The term “lithium salt” refers to any salt form of lithium, having lithium cation with a counter anion. The lithium-based salts in an electrolyte form a solid electrolyte interphase (SEI) on the electrolyte -anode interface and also facilitate ionic mobility from anode to cathode. The lithium salt comprises a primary lithium salt and a secondary lithium salt. Examples of lithium salts include but not limited to lithium hexafluorophosphate (LiPFe), lithium bis(fluorosulfonyl) imide (LiFSI), lithium fluorosulfonyl (trifluoromethanesulfonyl)imide (LiFTFSI), lithium difluoro(oxalate)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), and lithium bis(oxalate)borate (LiBOB).

[0030] The term “active material” refers to the active constituent of an electrode, which comprises the particles that undergo oxidation or reduction, resulting in reversible ion storage. In an aspect of the present disclosure, the active material includes but not limited to synthetic graphite, natural graphite, silicon, lithium nickel manganese cobalt oxides (NMC), lithium nickel cobalt aluminium oxides (NCA), or combinations thereof.

[0031] The term “additive” refers to a substance that is incorporated into the electrolyte formulation to enhance or modify various characteristics of the electrolyte, including ionic conductivity, electrochemical stability, viscosity, thermal stability, and overall efficiency in electrochemical applications. The additives facilitate the ion mobility and improve the battery performance by regulating SEI layer formation and electrode stripping behaviour. Additives added in an electrolyte comprises cathode additive and anode additive. In an aspect of thepresent disclosure, the additive is selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), and 1,3,6 hexanetricarbonitrile (HTCN).

[0032] The term “ionic conductivity” refers to the measure of the ability of electrolyte to conduct electric current through the movement of ions within the solution, which influences the efficiency and performance of electrochemical devices and is typically expressed in units of Siemens per centimetre (S / cm) or milli Siemens per centimetre (mS / cm). In an aspect of the present disclosure, the ionic conductivity of the electrolyte is in a range of 10.5 to 12.5 mS / cm.

[0033] The term “electrochemical cell” refers to a device that converts chemical energy into electrical energy or vice versa through electrochemical reactions. It consists of two electrodes, namely an anode and a cathode, separated by an electrolyte that facilitates ion transport between the electrodes. In an aspect of the present disclosure, the electrochemical cell comprises an anode, a cathode and the electrolyte as disclosed herein.

[0034] The term “capacity retention” refers to the ability of an electrochemical cell, to maintain its operational capacity under defined charge and discharge cycling conditions and over extended periods. It is used for assessing the longevity and performance stability of the device. It is expressed as a percentage of the initial capacity. In an aspect of the present disclosure, the electrochemical cell exhibits a capacity retention of 90 to 100%.

[0035] The term “wt%” or “% by weight” refers to the amount of a particular component with respect to total weight of the material in which said component is present. The terms shall be used interchangeably.

[0036] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, weight percentage in the range of 1 to 2% should be interpreted to include not only theexplicitly recited limits of 1 to 2% but also to include sub-ranges, such as 1.1% to 2% (w / w), 1.5 to 1.9% and so forth, as well as individual amounts, including fractional amounts, within the specified ranges, such as 1.8%, 1.5%, 1.3% and 1%.

[0037] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only. Functionally equivalent products, compositions, formulations, and methods are clearly within the scope of the disclosure, as described herein.

[0038] As discussed in the background, there are challenges in subjecting the conventional electrolytes to extreme temperatures. Conventional electrolytes majorly employ LiPFe as lithium salt. At elevated temperatures, LiPFe decomposes into lithium fluoride (LiF), phosphorus oxyfluoride (POF3), phosphorus pentafluoride (PF5), and hydrogen fluoride (HF). This is because of the high energy state of the LiPFe salt acquired at high temperature which makes it susceptible for the breaking of bonds. Furthermore, the reaction kinetics for the decomposition of LiPFe increase at higher temperatures, thereby accelerating the decomposition process. The generated HF reacts with various components of the electrolyte and the battery, resulting in further degradation of the electrolyte and a consequent reduction in battery performance. Further, it can lead to reduced ionic conductivity of the electrolyte, inefficient lithium-ion transport, and thus reduced power capacity, cycle life and energy density of the battery.

[0039] Accordingly, in the present disclosure, there is provided an electrolyte comprising a primary lithium salt (LiPFe) and secondary lithium salt, wherein the secondary lithium salt is a bulky lithium salt such as lithium bis(fluorosulfonyl) imide (LiFSI) and its similar lithium salts. The employment of lithium salts having fluorosulfonyl moi eties can be advantageous with respect to prevention of HF-mediated degradation and ion mobility. The LiFSI salt dissociate into Li+ions and SO2F2'ions which can react with HF molecules to form stable products such as LiF, FSO2NH2 and SO2F2. One molecule of LiFSI can scavenge two molecules of HF. This byproduct formation stabilizes LiPFe-based electrolytes and thereby effectively neutralizes the toxicity and corrosiveness of HF. Further, the electrolytecomprises a combination of additives that neutralizes the HF generated during battery operation, preventing its corrosive effects on the battery's components. As a result, the high ionic conductivity and electrochemical stability of the battery is maintained and thereby ensures higher capacity retention and prolonged cycle life at extreme temperature environments.

[0040] The present disclosure employs a secondary lithium salt such as LiFSI which is less prone to hydrolysis in comparison to LiPF6 and its resistance to hydrolysis helps to mitigate this risk consequently reducing the potential for degradation of LiPFe. LiFSI improves the ionic conductivity of electrolyte at lower temperatures, better ionic conductivity ensures that the electrolyte remains effective, promoting better performance and stability of LiPFe within the electrolyte. LiFSI is often compatible with a wider range of solvents compared to LiPFe. This compatibility results in more stable electrolyte formulations that are less prone to degradation at lower temperatures. LiFSI generally forms solvent shared ion pair (SIP) structure with solvents such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) which helps to maintain the higher ionic conductivity of electrolyte even at lower temperatures. SIP type of solvation structure exhibits higher ionic conductivity than Solvent separated ion pair (S2IP) solvation structure due to closer proximity of ions, than that observed in S2IP.

[0041] According to the present disclosure, there is provided an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt; and (c) an additive; wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4:1 to 6:1; and the additive is selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof.

[0042] In an embodiment of the present disclosure, there is provided an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt; and (c) an additive; wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of4:1 to 6:1; and the additive is selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof. In another embodiment of the present disclosure, the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4.2: 1 to 5.8:1; and the additive is selected from difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof. In yet another embodiment of the present disclosure, the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4.5:1 to 5.5:1; and the additive is a combination of difluoro(oxalato)borate (LiDFOB), and 1,3,6 hexanetricarbonitrile (HTCN).

[0043] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the primary lithium salt and secondary lithium salt in combination is in a concentration range of 0.8 to 1.4 M. In another embodiment of the present disclosure, the primary lithium salt and secondary lithium salt in combination is in a concentration range of 0.9 to 1.3 M. In yet another embodiment of the present disclosure, the primary lithium salt and secondary lithium salt in combination is in a concentration range of 1 to 1.25 M.

[0044] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the primary lithium salt is in a concentration range of 0.96 to 1.028 M. In another embodiment of the present disclosure, the primary lithium salt is in a concentration range of 0.98 to 1.02 M. In yet another embodiment of the present disclosure, the primary lithium salt is in a concentration of IM.

[0045] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the secondary lithium salt is in a concentration range of 0.172 to 0.24 M. In another embodiment of the present disclosure, the secondary lithium salt is in a concentration range of 0.18 to 0.22 M. In yet another embodiment of the present disclosure, the secondary lithium salt is in a concentration of 0.2M.

[0046] In an embodiment of the present disclosure, there is provided an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt and (c) an additive; wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe) in a concentration range of 0.8 to 1.4 M; the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4: 1 to 6: 1; and the additive is selected fromvinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof.

[0047] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the lithium salt is selected from the group consisting of lithium bis(fluorosulfonyl) imide (LiFSI), lithium fluorosulfonyl(trifluoromethanesulfonyl)imide (LiFTFSI), lithium difluoro(oxalate)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), and lithium bis(oxalate)borate (LiBOB). In yet another embodiment of the present disclosure, the secondary lithium salt is selected from the group consisting of lithium bis (fluorosulfonyl) imide (LiFSI), lithium fluorosulfonyl (trifluoromethanesulfonyl) imide (LiFTFSI), and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). In yet another embodiment of the present disclosure, the secondary lithium salt is lithium bis(fluorosulfonyl) imide (LiFSI).

[0048] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the electrolyte comprises an organic solvent in a weight range of 75 to 85%, with respect to the total weight of the electrolyte. In another embodiment of the present disclosure, the electrolyte comprises an organic solvent in a weight range of 75 to 83%, with respect to the total weight of the electrolyte. In yet another embodiment of the present disclosure, the electrolyte comprises an organic solvent in a weight range of 76 to 82%, with respect to the total weight of the electrolyte.

[0049] In an embodiment of the present disclosure, there is provided an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt; (c) an additive; and (d) an organic solvent, wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4: 1 to 6: 1 ; and the additive is selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof.

[0050] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the organic solvent is selected from, ethylenecarbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), Butylene carbonate (BC), or combinations thereof. In another embodiment of the present disclosure, the organic solvent is a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC).

[0051] In an embodiment of the present disclosure, there is provided an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt selected from the group consisting of lithium bis (fluorosulfonyl) imide (LiFSI), lithium fluorosulfonyl (trifluoromethanesulfonyl) imide (LiFTFSI), lithium difluoro (oxalate) borate (LiDFOB), lithium bis (trifluorom ethanesulfonyl) imide (LiTFSI), lithium tetrafluoroborate (LiBF4), and lithium bis (oxalate) borate (LiBOB); (c) an additive selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof; and (d) 75 to 85% by weight of an organic solvent selected from, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or combinations thereof; wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4: 1 to 6: 1.

[0052] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the organic solvent is a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), in a weight ratio range of 23:4:73 to 27:6:67. In another embodiment of the present disclosure, the organic solvent is a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), in a weight ratio range of 24:4.5:71.5 to 26:5.5:68.5. In yet another embodiment of the present disclosure, the organic solvent is a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), in a weight ratio range of 24.5:4.5:71 to 25.5:5.5:69. In yet another embodiment of the present disclosure, the organic solvent is a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), in a weight ratio of 25:5:70.

[0053] In an embodiment of the present disclosure, there is provided an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt; (c) an additive selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof; and (d) 75 to 85% by weight of an organic solvent which is a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), in a weight ratio range of 23:4:73 to 27:6:67; wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4: 1 to 6: 1 and in a concentration in a range of 0.8 to 1.4 M.

[0054] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the additive is in a weight range of 5 to 7 %, with respect to the total weight of the electrolyte. In another embodiment of the present disclosure, the additive is in a weight range of 5.3 to 6.8 %, with respect to the total weight of the electrolyte. In another embodiment of the present disclosure, the additive is in a weight range of 5.5 to 6 %, with respect to the total weight of the electrolyte.

[0055] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the additive is a combination of 1.5 to 2.5% by weight of vinylene carbonate, 0.5 to 2% by weight of propane sultone, 0.5 to 1.5% by weight of lithium difluoro(oxalato)borate (LiDFOB), and 0.5 to 1.5% by weight of hexanetricarbonitrile (HTCN). In another embodiment of the present disclosure, the additive is a combination of 1.7 to 2.3% by weight of vinylene carbonate, 0.5 to 2% by weight of propane sultone, 1 to 1.5% by weight of lithium difluoro(oxalato)borate (LiDFOB), and 0.75 to 1.25% by weight of hexanetricarbonitrile (HTCN).

[0056] In an embodiment of the present disclosure, there is provided an electrolyte as disclosed herein, wherein the electrolyte exhibits an ionic conductivity in a range of 10.5 to 12.5 mS / cm. In another embodiment of the present disclosure, the electrolyte exhibits an ionic conductivity in a range of 11.5 to 12.3 mS / cm. In yetanother embodiment of the present disclosure, the electrolyte exhibits an ionic conductivity in a range of 12 to 12.2 mS / cm.

[0057] In an embodiment of the present disclosure, there is provided an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt; and (c) an additive; wherein the additive is a combination of 1.5 to 2.5% vinylene carbonate, 1 to 2% propane sultone, 0.5 to 1.5% lithium difluoro(oxalato)borate (LiODFB), and 0.5 to 1.5% 1,3,6 hexanetricarbonitrile (HTCN); and 76.75 to 82.75% by weight of an organic solvent selected from, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a weight ratio range of 20:5 :75 to 30:5:65; wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4: 1 to 6: 1; wherein the electrolyte exhibits an ionic conductivity in a range of 10.5 to 12.5 mS / cm.

[0058] In an embodiment of the present disclosure, there is provided an electrolyte comprising: (a) a primary lithium salt; (b) a secondary lithium salt; (c) 5 to 7% by weight of an additive; and (d) 75 to 85% by weight of an organic solvent, wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4:1 to 6:1; and the additive is selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof.

[0059] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: (a) a cathode; (b) an anode and (c) the electrolyte as disclosed herein.

[0060] In an embodiment of the present disclosure, there is provided an electrochemical cell as disclosed herein, wherein the cathode comprises a cathode active material selected from lithium nickel manganese cobalt oxides (NMC), lithium nickel cobalt aluminium oxides (NCA), or combinations thereof. In another embodiment of the present disclosure, the cathode active material is lithium nickel manganese cobalt oxides (NMC).

[0061] In an embodiment of the present disclosure, there is provided an electrochemical cell as disclosed herein, wherein the anode comprises an anode active material selected from synthetic graphite, natural graphite, silicon or combinations thereof. In another embodiment of the present disclosure, the anode active material is synthetic graphite.

[0062] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: (a) a cathode comprising a cathode active material selected from lithium nickel manganese cobalt oxides (NMC), lithium nickel cobalt aluminium oxides (NCA), or combinations thereof; (b) an anode comprising an anode active material selected from synthetic graphite, natural graphite, silicon or combinations thereof; and (c) the electrolyte comprising (i) a primary lithium salt; (ii) a secondary lithium salt; and (iii) an additive selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof; wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4: 1 to 6: 1.

[0063] In an embodiment of the present disclosure, there is provided an electrochemical cell as disclosed herein, wherein the cell exhibits a capacity retention of 90 to 100%, at a temperature in a range of 10 to 50°C, after 300 cycles. In another embodiment of the present disclosure, the cell exhibits a capacity retention of 93 to 99.5%, at a temperature in a range of 10 to 45°C, after 300 cycles.

[0064] Although the subject matter has been described in considerable detail with reference to certain examples and implementations thereof, other implementations are possible.EXAMPLES

[0065] The disclosure will now be illustrated with following examples, which is intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosurebelongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices, and materials are described herein. It is to be understood that this disclosure is not limited to the particular methods, and experimental conditions described, as such methods and conditions may apply.Materials and methods

[0066] For the purpose of the present disclosure, the following raw materials were used.1. Lithium salts such as, LiPFe (primary lithium salt) and LiFSI (secondary lithium salt).2. Additives such as vinylene carbonate (VC), propane sultone (PS), lithium difluoro (oxalato) borate (LiDFOB), and 1,3,6 hexanetricarbonitrile (HTCN); 3. Organic solvents such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or combinations thereof; and4. Synthetic graphite (anode active material) and Lithium nickel manganese cobalt NMC 811 (cathode active material).EXAMPLE 1Preparation of electrolyte solutions

[0067] Electrolyte of the present disclosure was prepared by mixing organic solvents such as ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (ECZEMC / DMC) in a volume ratio 25±2: 5±1 : 70±3 respectively, followed by addition of IM of LiPFe and 0.2M LiFSI (lithium -based salts). To the obtained blend, additives comprising 2 wt% of vinylene carbonate (VC), 1.5 wt% of 1,3-propane sultone (PS), 1 wt% of lithium difluoro (oxalato) borate (LiDFOB), and 1 wt% of 1,3,6 hexanetricarbonitrile (HTCN) were added to result in an electrolyte O-3.

[0068] Similarly, other electrolytes were prepared using organic solvents as shown in below Table 1.Table 1Other additives include: fluoroethylene carbonate (FEC), tris (trimethyl silyl) phosphite (TMS) etc.

[0069] The electrolytes 0-3 and 0-5 were subjected to ionic conductivity measurements. The results are shown below Table 2.Table 2

[0070] The electrolyte 0-3 showed enhancement in ionic conductivity, in comparison to the O-5.EXAMPLE 2Preparation of an electrochemical cell

[0071] An electrochemical cell, specifically a battery, and more specifically, a lithium-ion battery was prepared. The lithium-ion battery includes an anode comprising synthetic graphite (anode active material), a cathode comprising NMC811 (cathode active material), disposed to face the anode, and the electrolyte prepared by the process as explained in Example 1 was placed between the cathode and anode.

[0072] The electrochemical cell was analysed with respect to the electrode voltage vs. current studies, discharge and charge capacities at different cycles and temperature and capacity retention studies. For the purpose of analysis, 2032- coin type cells were made for each electrolyte prepared by the process as explained in Example 1 and shown in Table 1.EXAMPLE 3Combinatorial Cyclic Voltammetry (CV) Studies

[0073] Combinatorial Cyclic Voltammetry (Combi CV) was carried for the coin cells comprising electrolytes provided in Table 1. The electrolytes were subjected to formation cycle at 0.1 c-rate, followed by Combi CV cycle of 0.1 mV / s for 2 cycles, ImV / s for 100 cycles and again 0.1 mV / s for 2 cycles, for 500 cycles, for 900 cycles and then for 1000 cycles.Upto 500 cycles:

[0074] The observations are provided in Figure 1 and Figure 2. From the combi CV data of electrolytes provided in Figure 1, it was observed that capacity fade was observed more in the case of electrolytes O-l, O-2, and O-4 after 500 cycles. Meanwhile, in the case of the electrolyte O-3 it was found to have lower capacity fade. O-l and O-2 showed higher capacity fading. Whereas, O-8 and 0-10 shows rapid capacity fade in the initial cycles.

[0075] Further, for comparative analysis, the combi CV data achieved for the first cycle at 0.1 mV / s scan rate of electrolytes O-3, O-7, 0-8, 0-9, and 0-10 were combined in a single plot (Figure 2 (a)). Additionally, the Figure 2 (b) shows the combined plot of 501stcycle combi CV data at 0.1 mV / s scan rate achieved for the above-mentioned electrolytes.

[0076] The combi CV data achieved for the first cycle at 1 mV / s scan rate of electrolytes 0-3, 0-7, 0-8, 0-9, and 0-10 were combined in a single plot and analysed (Figure 3 (a)). Additionally, the Figure 3 (b) shows the combined plot of 500thcycle combi CV data at 1 mV / s scan rate for the above-mentioned electrolytes.

[0077] As observed from the Figures of 2 and 3, the electrolytes 0-3, 0-7 and 0-9 comprising a primary lithium salt LiPFe and a secondary lithium salt LiFSI in a mole ratio of 5:1 was found to be best performing with lowest capacity fade. The electrolytes 0-7 and 0-10 having LiPFe and LiFSI in a mole ratio of 2:1 (0.8:0.4, less than the disclosed range of 4:1 to 6:1) showed comparatively higher capacity fade.Upto 900 cycles:

[0078] The coin cells comprising electrolytes 0-3 and 0-7 were then run for around 900 cycles at 0.1 mV / s and at ImV / s scan rates separately and the data obtained were combinedly plotted. Figure 4 shows the combi CV data obtained for electrolytes 0-3 and 0-7 (a) for their 901stcycle at 0.1 mV / s scan rate, and (B) for their 900thcycle at 1 mV / s scan rate. It was observed that both the electrolytes had a similar behaviour and not much deviation was observed in the performance. This suggested that increasing the concentration of LiFSI to deviate from the disclosed mole ratio range of 4:1 to 6:1, did not have much impact on the performance up until 900 cycles.

[0079] The cells were then disassembled after subjecting to 900 cycles of electrochemical cycling. Digital images of the disassembled cells were captured (Figure 5) and electron diffraction spectroscopy (EDS) was carried out. However, when the cycled cells were characterised using EDS (Figure 12), it was found that the increase in concentration of LiFSI in 0-7 resulted in corrosion of the cellcomponents. The below table 3 shows the elemental composition obtained from EDS.Table 3

[0080] In 0-7, cell corrosion was observed which could be attributed to the high concentration of LiFSI content. The electron diffraction spectroscopy (EDS) confirmed the presence of Iron in those black regions of the cell components which was the result of corrosion of the stainless-steel components (such as current collector) of the coin cell. The electrolyte 0-7 comprising 0.8M LiPFe and 0.4M LiFSI (mole ratio = 2:1), revealed notable corrosion effects after subjecting to 900 cycles as shown in the digital images (Figure 5). It was observed that as the concentration of LiFSI increased, corrosion of the cell components intensified. Thus, it was concluded that elevating the concentration of LiFSI beyond the range of 0. IM to 0.2M contributed to the corrosion of cell components.Upto 1000 cycles:

[0081] The individual combi CV data of O-3 up to 1000 cycles at O.lmV / s and ImV / s are provided in Figure 6 (a) and (b) respectively. It was observed that, O-3 exhibited an appreciable performance up to 1000 cycles, with very less capacity fade.

[0082] LiPFe reacts with H2O to form HF, POF3 and LiF. One molecule of LiPFe can give 2 molecule of HF in presence of moisture. This reaction was controlled by LiFSI, by inhibiting the reaction of LiPFe with protic impurities and HF. LiFSI in appropriate amounts reacted with protic impurities to form F-SO2-NH2, which thereby resulted in better capacity retention in electrolyte O-3.EXAMPLE 4Characterization of the electrochemical cell

[0083] The electrochemical cells (coin cells) prepared as described in Example 2, were subjected to electrochemical analysis. The nominal capacity of the cells was evaluated through charge-discharge cycles conducted at a charging rate of 0.5C and a discharging rate of 1C, across a wide range of temperatures: 10°C, 25°C, and 45°C, as shown in Figure 7, Figure 8 and Figure 9 respectively.

[0084] From the life cycle performance of O-3 and O-5 electrolytes evaluated at 10°C, 25°C and 45°C, provided in Figure 7, Figure 8 and Figure 9 respectively, it was observed that, at 10°C drastic capacity fade was observed in the cell comprising O-5. Meanwhile, cycle life performance of the cells comprising 0-3 as the electrolyte was found to be more stable and exhibited a capacity retention above 95% over 300 cycles, when measured at 10°C. The electrolytes 0-3 and 0-5 exhibited almost similar and appreciable performance at 25°C and 45°C. At 45°C, 0-3 showed a better capacity retention than and 0-5 when observed at 200 cycles. However, 0-3 electrolyte had better capacity retention in comparison with 0-5 at all three temperatures. The inclusion of LiFSI in a concentration of 0.2M contributed to the better capacity retention performance of the cells comprising O-3 at low temperatures.

[0085] Furthermore, the combined capacity retention plot of analysis of cells comprising various electrolytes were carried out at 25°C (Figure 10 (a)) and 45°C (Figure 10 (b)). It was similarly observed that all the electrolytes comprising the lithium salts (LiPFe and LiFSI) in a mole ratio range of 4:1 to 6:1 showed better capacity retention of above 95% at 25°C, up to 300 cycles. At 25°C, the capacity retention was better for 0-3 after 300 cycles, similarly 0-4 also showed better performance, but the cycle life data had too many fluctuations which might be attributed to the side reactions occurring during the cycling. Thus, 0-3 cycle life performance was better at 25°C in comparison to all other electrolytes. Similarly, at 45 °C, 0-5 and 0-3 exhibited better capacity retention over 200 cycles. 0-3 and 0-5 seemed to be performing better at 25 °C and 45 °C. The main difference in theformulation of these two electrolytes was the variation in lithium salt as mentioned in the Table 1.EXAMPLE 5Analysis of the impact of the additive content in the electrolyte

[0086] To investigate the influence of additive concentration in the electrolyte performance, O-3 electrolyte was selected as the base electrolyte, with the additive percentages systematically varied in the electrolyte. The results are illustrated in Figure 11 (a), (b), and (c). Notably, the concentrations of all other additives were held constant (VC at 2%, PS at 1.5%, and HTCN at 1%), and the percentage of LiDFOB was varied between 1% and 2%. A decline in electrochemical performance was observed when weight % of LiDFOB was increased to 2% with respect to total weight of the electrolyte. The decline was observed as the total weight % of additive increased above 7%. This observation highlighted that even slight variation in the additive concentrations can significantly affect the performance characteristics of the electrolytes.ADVANTAGES OF THE PRESENT INVENTION

[0087] The present disclosure provides an electrolyte for lithium-ion batteries that comprises of a combination of LiPFe and LiFSI as primary and secondary lithium salts, along with a blend of additives. The disclosed electrolyte addresses the issue of undesirable hydrofluoric acid (HF) formation, which can occur at elevated temperatures due to the decomposition of lithium salts. By incorporating LiPFe and LiFSI in disclosed mole ratio range of 4:1 to 5:1, along with the specified combination of additives in the disclosed weight range of 5 to 7%, the electrolyte effectively mitigates the toxicity and corrosiveness associated with HF, thereby tackling a significant challenge related to battery safety and longevity. Furthermore, the inclusion of these additives enhances the ability of the electrolyte to maintain high ionic conductivity and electrochemical stability, which facilitates efficient lithium-ion transport and promotes consistent capacity retention. The disclosed electrolyte also contributes to prolonged cycle life and improved energy density, making it particularly suitable for battery applications in extreme temperatureenvironments while minimizing the risk of degradation of the electrolyte and battery components. Additionally, the present disclosure encompasses an electrochemical cell that incorporates the disclosed electrolyte, featuring a combination of LiPFe and a secondary lithium salt (such as LiFSI), along with the disclosed combination of additives, resulting in improved electrochemical performance and stabilised capacity retention.

Claims

I / Wc Claim;1. An electrolyte comprising:(a) a primary lithium salt;(b) a secondary lithium salt; and(c) an additive;wherein the primary lithium salt is lithium hexafluorophosphate (LiPFe); the primary lithium salt and the secondary lithium salt are in a mole ratio range of 4: 1 to 6: 1 ; andthe additive is selected from vinylene carbonate, propane sultone, lithium difluoro(oxalato)borate (LiDFOB), 1,3,6 hexanetricarbonitrile (HTCN), or combinations thereof.

2. The electrolyte as claimed in claim 1, wherein the combination of the primary lithium salt and the secondary lithium salt are in a concentration range of 0.8 to 1.4 M.

3. The electrolyte as claimed in claim 1, wherein the secondary lithium salt is selected from the group consisting of lithium bis (fluorosulfonyl) imide (LiFSI), lithium fluorosulfonyl (trifluoromethanesulfonyl)imide (LiFTFSI), lithium difluoro (oxalate)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), and lithium bis(oxalate)borate (LiBOB).

4. The electrolyte as claimed in claim 1 , wherein the electrolyte comprises an organic solvent in a weight range of 75 to 85%, with respect to total weight of the electrolyte.

5. The electrolyte as claimed in claim 4, wherein the organic solvent is selected from ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), Butylene carbonate (BC), or combinations thereof.

6. The electrolyte as claimed in claim 4, wherein the organic solvent is a combination of ethylene carbonate (EC), ethyl methyl carbonate (EMC),and dimethyl carbonate (DMC), in a volume ratio range of 23:4:73 to 27:6:67.

7. The electrolyte as claimed in claim 1, wherein the additive is in a weight range of 5 to 7 %, with respect to the total weight of the electrolyte.

8. The electrolyte as claimed in claim 1 , wherein the additive is a combination of 1.5 to 2.5% by weight of vinylene carbonate, 0.5 to 2% by weight of propane sultone, 0.5 to 1.5% by weight of lithium difluoro(oxalato)borate (LiODFB), and 0.5 to 1.5% by weight of 1, 3, 6-hexanetricarbonitrile (HTCN).

9. The electrolyte as claimed in claim 1, wherein the electrolyte exhibits an ionic conductivity in a range of 10.5 to 12.5 mS / cm.

10. An electrochemical cell comprising:a. a cathode;b. an anode andc. an electrolyte as claimed in claim 1.

11. The electrochemical cell as claimed in claim 10, wherein the cathode comprises a cathode active material selected from lithium nickel manganese cobalt oxides (NMC) lithium nickel cobalt aluminium oxides (NCA), or combinations thereof.

12. The electrochemical cell as claimed in claim 10, wherein the anode comprises an anode active material selected from synthetic graphite, natural graphite, silicon or combinations thereof.

13. The electrochemical cell as claimed in claim 10, wherein the cell exhibits a capacity retention of 90 to 100%, at a temperature in a range of 10 to 50°C after 300 cycles.

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