A method of formation of a secondary battery

Abstract

The present disclosure provides a method of formation of a secondary battery comprising a metal current collector, the method comprising: tap-charging the battery to a first potential (Va) greater than reduction potential of at least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; thermal aging the tap-charged battery to densify the solid electrolyte interphase layer; and performing consecutive charging on the aged battery to a second potential (Vb) enabling complete reduction of the electrolyte additive for the SEI layer formation; and discharging to a third potential (Vc) to obtain the battery, wherein tap-charging to the first potential (Va) partially reduces the electrolyte additive Further, the present disclosure provides a battery formed by the method as disclosed herein.

Description

A METHOD OF FORMATION OF A SECONDARY BATTERYFIELD OF INVENTION

[0001] The subject matter of the present disclosure broadly relates to the field of battery. Particularly, the present disclosure relates to a method of formation of a secondary battery.BACKGROUND OF THE INVENTION

[0002] Secondary batteries are widely used in electronic devices such as mobile phones, laptops, computers, camcorders, and electric vehicles, owing to recharging property. In particular, secondary lithium-ion batteries have a larger capacity than convention batteries such as nickel-cadmium (Ni-Cd) batteries or Ni-water bath batteries. Furthermore, in view of the higher energy density of the secondary Li-ion batteries, their utilization is exponentially increasing. To optimise the electrochemical performance of such secondary batteries, obtaining a stable and dense solid electrolyte interface (SEI) is a significant objective.

[0003] The solid electrolyte interphase (SEI) layer is a layer formed at the surface of the electrode in alkali metal ion batteries, including lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs) through the decomposition of the electrolyte. The SEI layer is crucial for battery performance and stability. Among the existing approaches to achieve a stable and dense SEI layer in LIBs, formation methods of charging are prevalent. However, the existing methods do not provide a battery with high charge-discharge capacity with improved coulombic efficiency and life cycle performance. All of the above properties are associated with achieving a stable, dense and uniform SEI layer in the battery.

[0004] Hence, there is a need in the art to develop a convenient method of formation of a secondary battery with stable, dense and uniform SEI layer.SUMMARY OF THE INVENTION

[0005] In an aspect of the present disclosure, there is provided a method of formation of a secondary battery comprising an anode, a lithium based cathode and an electrolyte having at least one electrolyte additive, the method comprising: a) tap-charging the battery to a first potential (Va) greater than reduction potential ofat least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; b) thermal aging the tap-charged battery to densify the solid electrolyte interphase layer; and c) performing consecutive charging on the aged battery to a second potential (Vb) enabling complete reduction of the electrolyte additive for the SEI layer formation; and discharging to a third potential (Vc) to obtain the battery, wherein tap-charging to the first potential (Va) partially reduces the electrolyte additive.

[0006] In another aspect of the present disclosure, there is provided a battery formed by the method as disclosed herein.

[0007] In yet another aspect of the present disclosure, there is provided a use of the battery formed by the method as disclosed herein, for manufacturing energy storage devices and electronic devices.

[0008] These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. 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 charge-discharge profile for the batteries formed by methods I, II and III, in accordance with an embodiment of the present disclosure.

[0011] Figure 2 depicts the differential capacity (dQ / dV) analysis for the batteries formed by methods I, II and III, in accordance with an embodiment of the present disclosure.

[0012] Figure 3A depicts the graphical representation of charge capacity and discharge capacity of batteries formed by the methods I, II and III, in accordance with an embodiment of the present disclosure.

[0013] Figure 3B depicts the charge-discharge capacities of the batteries formed by the methods I, II and III, in the (i) first cycle at 0.1 C c-rate, and (ii) second cycle; and (iii) coulombic efficiency by the methods I, II and III, in the first cycle and second cycle, in accordance with an embodiment of the present disclosure.

[0014] Figure 4 depicts the life cycle analysis of the batteries formed by the methods I, II and III, in accordance with an embodiment of the present disclosure.

[0015] Figure 5 depicts the graphical representation of delta V values exhibited by batteries formed by the methods I, II and III, in accordance with an embodiment of the present disclosure.

[0016] Figure 6 depicts the direct current internal resistance (DCIR) batteries formed by the methods I, II and III, in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION OF THE INVENTION

[0017] 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

[0018] 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.

[0019] 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.

[0020] 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”.

[0021] 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 elements or steps but not the exclusion of any other element or step or group of element or steps.

[0022] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0023] The term “w / w” means the percentage by weight, relative to the weight of the total composition, unless otherwise specified.

[0024] The term “at least one” is used to mean one or more and thus includes individual components as well as mixtures / combinations.

[0025] The term “secondary battery” refers to an electrochemical cell or combination of electrochemical cells wherein the cell reactions are reversible. Therefore, by passing current to flow into a secondary battery the chemical conditions within the electrochemical cell can be restored. In an aspect of the present disclosure, the secondary battery is prepared by assembling a dry lithium- based cathode and a dry anode in a package case, followed by injecting an electrolyte, soaked for a period and formed using the method as disclosed herein.

[0026] The term “electrolyte” refers to an ion-conducting and electron-insulating material used for the purpose of acting as a medium of ion conduction between an anode and a cathode of an electrochemical cell. In an aspect of the present disclosure, the electrolyte comprises a lithium salt dispersed in a solvent with one or more electrolyte additives.

[0027] The term “electrolyte additives” refers to an additional component added to an electrolyte in order to impart or enhance the electrochemical properties or prevent the detrimental effects in the electrolyte. The electrolyte additive is generally added to an electrolyte to facilitate ion conduction and / or to achieve a stable solid electrolyte interface (SEI) layer Examples of electrolyte additivesinclude but not limited to lithium bis(oxalato) borate (LiBOB), vinylene carbonate, 1, 3, 2-di oxathiolane 2,2-dioxide, succinonitrile, fluoroethylene carbonate, 1,3- propane sultone, 1,3,6-hexanetricarbonitrile, lithium difluoro(oxalato)b orate, and trimethylene sulfate.

[0028] The term “c-rate” refers to the rate at which a battery is charged or discharged to a potential. A lower c-rate refers to a slower charging / discharging process. In an aspect of the present disclosure, there is provided a method of formation of a secondary battery, wherein tap-charging is carried out at a c-rate in a range of 0.01 to 0.04C. Lower c-rate is employed for tap-charging which facilitates maximum reduction of the electrolyte additives so as to obtain a stable, dense and uniform SEI layer in the secondary battery.

[0029] The term “tap-charging” refers to the process by which a battery is subjected to a specific voltage range at a particular c-rate to reduce the corrosion of copper (anode current collector) by increasing the voltage. Additionally, tap-charging is carried out to efficiently reduce the electrolyte additive in the electrolyte and initiate the solid electrolyte interface layer formation. In an aspect of the present disclosure, the tap charging is carried out to a potential (Va) greater than the reduction potential of the electrolyte additive to partially reduce the electrolyte additive and thereby partially form a solid electrolyte interphase (SEI) layer partially reducing the electrolyte additive.

[0030] The term “reduction potential” refers to the electrochemical potential at which a substance undergoes or starts to undergo reduction. In an aspect of the present disclosure the tap-charging is carried out to a potential (Va) greater than reduction potential of the electrolyte additive in the electrolyte.

[0031] The term “solid electrolyte interphase layer” or “SEI layer” refers to a layer formed on the electrode surface, or in the interface between the electrode and the electrolyte, which is essential for electrochemical reactions in batteries and critically affects the stability of battery. In an aspect of the present disclosure, the SEI layer is partially formed while tap-charging, densifies during thermal ageing, completely formed and stabilized while consecutive charging.

[0032] The term “thermal aging” refers to a process of subjecting a system to elevated temperatures for a specific period of time so as to facilitate the chemical reactions happening in the system. In an aspect of the present disclosure, thermal ageing is carried out at a temperature in a range of 40 to 50°C for a period in a range of 20 to 30 hours for the formation of the secondary battery by the method as disclosed herein.

[0033] The term “consecutive charging” refers to subjecting a system to charging process wherein the voltage is raised in consecutive cycles to a specific potential. In an aspect of the present disclosure, consecutive charging to a potential (Vb) is carried out to a voltage in a range of 2.8 to 4.2 V. The consecutive charging steps involve solvent reduction, lithium intercalation with SEI stabilization, stress minimalization at anode and distribution of charges.

[0034] The term “metal current collector dissolution” refers to the effect of corrosion of a metal current collector as a result of reacting with one or more reagents. In an aspect of the present disclosure, the secondary battery comprises a metal current collector which is an anodic current collector selected from copper foil, copper sheet or the like. The present disclosure provides a method of formation of a secondary battery wherein tap-charging to a first potential (Va) minimizes metal current collector dissolution, as the method employs tap-charging 4 hours after injecting the electrolyte into the battery.

[0035] The term “complete reduction” refers to the maximum reduction of a compound. In an aspect of the present disclosure, the battery is subjected to consecutive charging to a potential (Vb) in a range of 2.8 to 4.2 V to result in reduction of the electrolyte additives to an extent of at least 80%, at least 85%, at least 90% or at least 95%, with respect to the total amount of the electrolyte additives present in the electrolyte of the battery.

[0036] The term “potential” refers to the difference in charge between positive and negative terminals of an electrochemical cell or battery. In an aspect of the present disclosure, there is provided a method of forming a battery wherein the battery is tap-charged to a potential Va, thermally-aged, subjected to consecutive charging to a potential Vb, and discharged to a potential Vcnot more than 2.8V.

[0037] The term “discharging” refers to the process of allowing a system at a higher potential to gradually decrease its potential at a specific rate and finally achieve a lower potential. In an aspect of the present disclosure, discharging of the battery is carried out to a voltage range of 2.5 to 2.8 V.

[0038] The term “capacity retention” refers to the measure of ability of a battery to retain the capacity through increasing number of cycles. In an aspect of the present disclosure, a battery formed by the disclosed method exhibits a capacity retention in a range of 80 to 95%, for up to 300 cycles.

[0039] The term “initial coulombic efficiency” denoted as ICE, refers to the efficiency of an electrochemical cell exhibited during the first charging-discharging cycle. ICE is calculated using the formula,ICE= (Discharge Capacity / Charge Capacity) x 100%.In an aspect of the present disclosure, the battery formed by the method as disclosed herein, exhibits an initial coulombic efficiency in a range of 99.5 to 100%.

[0040] 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.

[0041] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.

[0042] 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.

[0043] As discussed in the background, there is a need in the art to develop a convenient method to form a secondary battery with a stable and dense SEI layer. The conventional formation methods employ higher voltages and longer duration to achieve a battery yet still possessing stability issues, which detrimentally affects the electrochemical performance and life-cycle of the battery. Furthermore, the existing methods also allow a battery to soak the electrolyte for a period of time after injecting the same into the dry battery. However, this soaking time leads to corrosion of the current collectors upon reaction with the solvents in the electrolyte, majorly copper foil which is used generally as anode current collector. To avoid this corrosion, the present disclosure provides a method of formation of a secondary battery wherein the battery is tap-charged to a higher potential after injecting the electrolyte into the dry battery and soaking for about 3 to 5 hours. The higher potential employed for tap-charging in the method of the present disclosure resulted in prevention of copper dissolution / corrosion and thereby mitigating issues of corrosion.

[0044] In addition, a major challenge faced by the battery is the reactivity of electrode binder with the electrolyte which detrimental to the electrochemical performance of the battery. To stop the binder reactivity, complete passivation of anode surface is required. So, the present disclosure provides a method that facilitated stabilization of the battery by forming stable SEI on the anode surface which stops the binder reactivity. The presence of electrolyte additives such as LiBOB efficiently passivates the anode surface at a lower voltage.

[0045] Furthermore, the method as disclosed in the present disclosure facilitates reduction of electrolyte additives and solvent via two steps, partially at tap-charging step and completely via charging to potential Vb. This step-by-step reduction is carried out along with the step of a thermal ageing. The consecutive reduction results in complete reduction and utilisation of the electrolyte additives and solvent to result in maximum SEI layer components. Moreover, the thermal ageing step placed in between the reduction steps of tap-charging and consecutive charging to potential Vb, result in achieving a dense and stable SEI layer. Furthermore, thethermal ageing step facilitates stabilization of SEI layer by removal of unstable species when charged via consecutive charging step to a potential of 4.2V.

[0046] Accordingly, the present disclosure provides a method of formation of a secondary battery comprising an anode, a lithium-based cathode, and an electrolyte having at least one electrolyte additive, the method comprising: a. tap-charging the battery to a first potential (Va) greater than reduction potential of at least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; b. thermal aging the tap-charged battery to densify the solid electrolyte interphase layer; and c. performing consecutive charging on the aged battery to a second potential (Vb) enabling complete reduction of the electrolyte additive for the SEI layer formation; and discharging to a third potential (Vc) to obtain the battery, wherein tap-charging to the first potential (Va) partially reduces the electrolyte additive.

[0047] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein tap-charging the battery to a first potential (Va) is carried out to a voltage in a range of 1.7 to 2.65 V. In another embodiment of the present disclosure, the tap-charging the battery to a first potential (Va) is carried out to a voltage in a range of 1.8 to 2.6V. In yet another embodiment of the present disclosure, the tap-charging the battery to a first potential (Va) is carried out to a voltage in a range of 1.9 to 2.4V. In still another embodiment of the present disclosure, the tap-charging the battery to a first potential (Va) is carried out to a voltage in a range of 2 to 2.2V. In a further embodiment of the present disclosure, the tap-charging the battery to a first potential (Va) is carried out to a voltage in a range of 2.05 to 2.15V.

[0048] In an embodiment of the present disclosure, there is provided a method of formation of a secondary battery comprising an anode, a lithium-based cathode, and an electrolyte having at least one electrolyte additive, the method comprising:a. tap-charging the battery to a first potential (Va) in a range of 1.7 to 2.65 V greater than reduction potential of at least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; b. thermal aging the tap-charged battery to densify the solid electrolyte interphase layer; and c. performing consecutive charging on the aged battery to a second potential (Vb) enabling complete reduction of the electrolyte additive for the SEI layer formation; and discharging to a third potential (Vc) to obtain the battery, wherein tap-charging to the first potential (Va) partially reduces the electrolyte additive.

[0049] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein thermal ageing is carried out at a temperature in a range of 40 to 50°C for a period in a range of 20 to 30 hours. In another embodiment of the present disclosure, the thermal ageing is carried out at a temperature in a range of 42 to 48°C for a period in a range of 22 to 26 hours. In yet another embodiment of the present disclosure, the thermal ageing is carried out at a temperature in a range of 44 to 46°C for a period in a range of 23 to 25 hours.

[0050] In an embodiment of the present disclosure, there is provided a method of formation of a secondary battery comprising an anode, a lithium-based cathode, and an electrolyte having at least one electrolyte additive, the method comprising: a. tap-charging the battery to a first potential (Va) in a range of 1.7 to 2.65 V greater than reduction potential of at least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; b. thermal aging the tap-charged battery at a temperature in a range of 40 to 50°C for a period in a range of 20 to 30 hours to densify the solid electrolyte interphase layer; and c. performing consecutive charging on the aged battery to a second potential (Vb) enabling complete reduction of the electrolyte additive for the SEI layer formation; and discharging to a third potential (Vc) to obtain the battery,wherein tap-charging to the first potential (Va) partially reduces the electrolyte additive.

[0051] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein consecutive charging to a second potential (Vb) is carried out to a voltage in a range of 2.8 to 4.2 V, followed by subjecting to constant currentconstant voltage.

[0052] In an embodiment of the present disclosure, there is provided a method of formation of a secondary battery comprising an anode, a lithium-based cathode, and an electrolyte having at least one electrolyte additive, the method comprising: a. tap-charging the battery to a first potential (Va) in a range of 1.7 to 2.65 V greater than reduction potential of at least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; b. thermal aging the tap-charged battery at a temperature in a range of 40 to 50°C for a period in a range of 20 to 30 hours to densify the solid electrolyte interphase layer; and c. performing consecutive charging on the aged battery to a second potential (Vb) in a range of 2.8 to 4.2 V, followed by subjecting to constant currentconstant voltage, enabling complete reduction of the electrolyte additive for the SEI layer formation; and discharging to a third potential (Vc) to obtain the battery, wherein tap-charging to the first potential (Va) partially reduces the electrolyte additive.

[0053] In an embodiment of the present disclosure, there is provided a method of formation of a secondary battery comprising an anode, a lithium-based cathode, and an electrolyte having at least one electrolyte additive, the method comprising: a. tap-charging the battery to a first potential (Va) in a range of 1.7 to 2.65 V greater than reduction potential of at least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; b. thermal aging the tap-charged battery at a temperature in a range of 40 to 50°C for a period in a range of 20 to 30 hours to densify the solid electrolyte interphase layer; andc. performing consecutive charging on the aged battery to a second potential (Vb) in a range of 2.8 to 4.2 V, followed by subjecting to constant currentconstant voltage enabling complete reduction of the electrolyte additive for the SEI layer formation; and discharging to a third potential (Vc) to obtain the battery, wherein tap-charging to the first potential (Va) partially reduces the electrolyte additive.

[0054] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein consecutive charging to a potential (Vb) comprises the steps of solvent reduction and lithium intercalation with SEI stabilization.

[0055] In another embodiment of the present disclosure, consecutive charging to a potential (Vb) comprises the steps of solvent reduction, lithium intercalation with SEI stabilization, stress minimalization at anode and distribution of charges.

[0056] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein discharging is carried out to a voltage range of 2.5 to 2.8 V. In another embodiment of the present disclosure, discharging is carried out to a voltage range of 2.6 to 2.8 V. In yet another embodiment of the present disclosure, discharging is carried out to a voltage range of 2.7 to 2.8 V.

[0057] In an embodiment of the present disclosure, there is provided a method of formation of a secondary battery comprising an anode, a lithium-based cathode, and an electrolyte having at least one electrolyte additive, the method comprising: a. tap-charging the battery to a first potential (Va) in a range of 1.7 to 2.65 V greater than reduction potential of at least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; b. thermal aging the tap-charged battery at a temperature in a range of 40 to 50°C for a period in a range of 20 to 30 hours to densify the solid electrolyte interphase layer; and c. performing consecutive charging on the aged battery to a second potential (Vb) in a range of 2.8 to 4.2 V, followed by subjecting to constant currentconstant voltage enabling complete reduction of the electrolyte additive forthe SEI layer formation; and discharging to a third potential (Vc) in a range of 2.5 to 2.8 V to obtain the battery, wherein the metal current collector is an anodic current collector; and wherein tapcharging to the first potential (Va) partially reduces the electrolyte additive.

[0058] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein the electrolyte additive is in a weight range of 2.5 to 6% (w / w) with respect to total weight of the electrolyte; and is selected from lithium bis(oxalato) borate (LiBOB), vinylene carbonate (VC), 1,3,2-dioxathiolane 2,2- di oxide (DTD), lithium difluorophosphate (LFO), succinonitrile, fluoroethylene carbonate, 1,3-propane sultone, 1,3,6-hexanetricarbonitrile, lithium difluoro(oxalato)borate, trimethylene sulfate, or combinations thereof. In another embodiment of the present disclosure, the electrolyte additive is in a weight range of 5 to 6% (w / w) with respect to total weight of the electrolyte; and is a combination of lithium bis(oxalato) borate (LiBOB), vinylene carbonate (VC), 1,3,2- dioxathiolane 2,2-dioxide (DTD), and lithium difluorophosphate (LFO).

[0059] In an embodiment of the present disclosure, there is provided a method of formation of a secondary battery comprising an anode, a lithium-based cathode, and an electrolyte having at least one electrolyte additive, the method comprising: a. tap-charging the battery to a first potential (Va) in a range of 1.7 to 2.65 V greater than reduction potential of at least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; b. thermal aging the tap-charged battery at a temperature in a range of 40 to 50°C for a period in a range of 20 to 30 hours to densify the solid electrolyte interphase layer; and c. performing consecutive charging on aged battery to a second potential (Vb) in a range of 2.8 to 4.2 V, followed by subjecting to constant currentconstant voltage enabling complete reduction of the electrolyte additive for the SEI layer formation; and discharging to a third potential (Vc) in a range of 2.5 to 2.8 V to obtain the battery, wherein tap-charging to the first potential (Va) partially reduces the electrolyte additive.

[0060] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein the electrolyte comprises a lithium salt selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, or lithium bis(trifluoromethanesulfonyl)imide; and a solvent selected from ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate or combinations thereof. In another embodiment of the present disclosure, the electrolyte comprises a lithium salt lithium hexafluorophosphate; and a solvent comprising ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0061] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein the lithium-based cathode comprises (a) 96 to 98% by weight of a cathode active material selected from tin-based alloys, lithium nickel manganese cobalt oxide (Li-NMC), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel cobalt aluminium oxide (Li-NCA), lithium iron phosphate (LiFePCh), lithium nickel cobalt oxide (LiNiCoCh) or combinations thereof; (b) 0.5 to 2% by weight of a first binder selected from polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride, or combinations thereof; and optionally (c) 0.5 to 2% by weight of a conductive material selected from carbon black, graphite, activated carbon, graphene, single-walled carbon nanotube, multiwalled carbon nanotube carbon nanofiber, or combinations thereof. In another embodiment of the present disclosure, the lithium-based cathode comprises (a) 96.5 to 97.5% by weight of a cathode active material selected from lithium nickel manganese cobalt oxide (Li-NMC), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), or combinations thereof; (b) 1 to 2% by weight of a first binder selected from polyvinylidene fluoride, polytetrafluoroethylene or combinations thereof; and optionally (c) 1 to 2% by weight of a conductive material selected from carbon black, graphite, or combinations thereof.

[0062] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein the anode comprises (a) 95 to 97% by weight of an anode active material selected from graphite, hard carbon, lithium titanate (LTO), silicon- graphite, lithium metal, titanium oxide (TiCh), niobium-titanium oxide (NTO), orcombinations thereof; (b) 0.5 to 4% by weight of a second binder selected from styrene butadiene rubber, carboxymethyl cellulose or combinations thereof; and optionally (c) 0.5 to 2% by weight of a conductive carbon selected from carbon black, graphite, activated carbon, graphene, or combinations thereof. In another embodiment of the present disclosure, the anode comprises (a) 95.5 to 96.5% by weight of an anode active material selected from graphite, silicon-graphite, or combinations thereof; (b) 2 to 3% by weight of a second binder selected from styrene butadiene rubber, carboxymethyl cellulose or combinations thereof; and (c) 1 to 2% by weight of a conductive carbon selected from carbon black, graphite, or combinations thereof.

[0063] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein the battery exhibits a charge capacity in a range of 23 to 27 Ah and a discharge capacity in a range of 23 to 25 Ah. In another embodiment of the present disclosure, the battery exhibits a charge capacity in a range of 23.25 to 26.9 Ah and a discharge capacity in a range of 23.4 to 25 Ah.

[0064] In yet another embodiment of the present disclosure, the battery exhibits a formation cycle charge capacity in a range of 26.26 to 26.8 Ah and a formation cycle discharge capacity in a range of 23.45 to 24 Ah.

[0065] In an embodiment of the present disclosure, there is provided a method as disclosed herein, wherein the battery exhibits capacity retention in a range of 80 to 95%. In another embodiment of the present disclosure, the battery exhibits a capacity retention in a range of 80 to 90%. In yet another embodiment of the present disclosure, the battery exhibits a capacity retention in a range of 82 to 88%, for up to 300 cycles.

[0066] In an embodiment of the present disclosure, there is provided a battery formed by method as disclosed herein.

[0067] In an embodiment of the present disclosure, there is provided a use of the battery formed by the method as disclosed herein, for manufacturing energy storage devices and electronic devices.

[0068] Although the subject matter has been described in considerable detail with reference to certain examples and implementations thereof, other implementations are possible.EXAMPLES

[0069] 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 disclosure belongs. 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 particular methods, and experimental conditions described, as such methods and conditions may apply.Materials and methods

[0070] The Neware systems, BTS (Battery Testing System) software, is used for testing batteries by monitoring and controlling charging and discharging processes, as well as conducting various electrochemical analyses.Example 1Preparation of dry battery

[0071] The present example provides the process of preparation of battery.

[0072] A dry lithium-based cathode comprising an aluminium foil current collector coated with a cathode composite was prepared. The cathode composite was prepared using known methods by mixing 97% by weight of nickel manganese cobalt (NMC; cathode active material), 1.5 % by weight of poly vinylidene fluoride (PVDF; first binder), 0.75 % by weight of carbon black (Super P; conductive carbon), and 0.75% by weight of multi-walled carbon nanotube (MWCNT; conductive material).

[0073] A dry anode comprising a copper foil current collector coated with an anode composite was prepared. The anode composite was prepared using known methods by mixing comprising 96% by weight of graphite (anode active material), 1.8% byweight of styrene butadiene rubber (SBR; second binder), 1.5% by weight of carboxymethyl cellulose (CMC; second binder) and 0.7% by weight of carbon black (Super P; conductive carbon).

[0074] An electrolyte was prepared by adding 5% by weight of electrolyte additive, specifically, 2% by weight of vinylene carbonate (VC), 1% by weight of 1,3,2- dioxathiolane 2,2-dioxide (DTD), 1% by weight of lithium bis(oxalato)borate (LiBOB), and 1% by weight of lithium difluorophosphate (LFO) in a 1.2 M solution of LiPFe dissolved in a solvent mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume percentage ratio of 25:5:70.

[0075] A dry battery was prepared by assembling the cathode prepared by the process as explained above, and the anode prepared by the process as explained above, with a polyethylene sheet coated on both sides with boehmite (separator) in between the cathode and anode and the electrolyte was injected into a package case and sealed. The cathode and anode were assembled such that the separator / electrolyte was arranged in between the electrodes.Example 2Formation of secondary batteryA. Method I

[0076] The dry battery prepared by the process as explained in Example 1 was taken and allowed to soak for 4 hours and tap-charged the battery to a potential (Va) of 2.1V at a c-rate of 0.025C. The electrolyte additive, majorly lithium bis(oxalato) borate (LiBOB) having a reduction potential in a range of 1.7 to 2 V. vinylene carbonate (VC) having a reduction potential in a range of 2.6 to 2.8V, 1,3,2- dioxathiolane 2,2-dioxide (DTD) having a reduction potential in a range of 2.4 to 2.5V and lithium difluorophosphate (LFO) had a reduction potential in a range of 2.8 to 2.9V. Hence, the tap-charging was performed to a potential (Va), greater than reduction potential of the electrolyte additive LiBOB majorly so as to partially reduce LiBOB to partially form a solid electrolyte interphase (SEI) layer inside the battery in between the cathode and the electrolyte. The dry battery was tap-chargedto a higher first potential (Va~2. IV) 4 hours after injecting the electrolyte to avoid corrosion of the copper foil (metal current collector) of the anode.

[0077] The tap-charged battery was then subjected to thermal aging at a temperature of 45 °C for 24 hours, to densify and integrate so as to result in a homogeneous SEI layer. The aged battery was then subjected to consecutive charging to a potential (Vb) in a range of 2.8 to 4.2 V via four steps so as to enable complete reduction of the electrolyte additives such as LiBOB and LFO to form electrolyte additive reduction products such as LiF and result in completion of the SEI layer formation. The dry battery was then as given below: a. In step 1 of consecutive charging, the dry battery was charged to a potential Vciof 3.4V and the solvent reduction occurred to result in solvent reduction products such as Li2CO3; b. Followed by step 1, in step 2 the dry battery was then charged to a potential VC2 of 3.6V which enabled lithium-ion intercalation into the SEI layer; c. Following the step 2, in step 3 the battery was charged to a potential VC3 of 4.05 V to achieve the critical rest potential after two phase changes (Hl-M) and (M-H2) in cathode; and d. Following the step 3, the battery was charged to a potential VC4 of 4.2Vto facilitate the battery in gaining work of capacity and charge distribution.

[0078] After four steps of consecutive charging, the battery was then subjected to constant current-constant voltage (CCCV) in a constant voltage of 4.2V up to a cut off charge of 0.01C. The battery was then discharged to a potential (Vc) of 2.75 V at a c-rate of 0.1C, to obtain the secondary battery I.

[0079] During the tap-charging step, lithium got extracted from the cathode structure with minimal changes, resulting in less stress on the anode. As more lithium was removed from cathode, the cathode active material underwent several phase transitions, starting from the original hexagonal layered structure (Hl) with high lithium content and moving to phases monoclinic (M), hexagonal (H2) and hexagonal (H3). The hexagonal (Hl) transition to the monoclinic (M) phase occurred without significant lithium loss in cathode, but as more lithium was removed from the cathode, the shift from monoclinic (M) to hexagonal (H2) causedchanges in the c-axis due to oxygen layer repulsion. At higher states of charge, further lithium removal led to the formation of the H3 phase of the cathode active material, resulting in significant structural changes and contraction of the c-axis. These phase transitions of the cathode active material in line with more lithium extraction parallelly imparted a stress on the anode during lithium intercalation. Therefore, as the structural changes happened in the cathode, it caused fluctuations in lithium intercalation into the anode, potentially leading to stress and strain on the anode material. However, as the tap-charging step of the method disclosed herein was charged to a potential of 2.1V, it resulted in minimising the stress on anode while lithium intercalation, and thus resulting in stable and dense SEI layer formation.B. Method II

[0080] For comparative purposes, the secondary battery was formed by another method wherein tap-charging was carried out 4 hours after injecting the dry battery with the electrolyte. This 4 hour period allowed the battery to soak the electrolyte. However, this soaking period resulted the copper foil current collector of anode to corrode and detrimentally affect the electrochemical performance of the battery.

[0081] The below method II explains the comparative method of formation of secondary battery. The electrolyte prepared by the process as explained in Example 1 was injected into the dry battery prepared by the process as explained in Example 1 and allowed for soaking for a period of 4 hours. Followed by soaking, the battery was tap-charged to a potential (Va) of 1.5V at a c-rate of 0.05C. The tap-charged battery was then subjected to thermal aging at a temperature of 45°C for 24 hours, to densify, integrate and thereby result in a homogeneous SEI layer. The thermally- aged battery was then subjected to consecutive charging to a potential (Vb) in a range of 2.8 to 4.2 V via three steps. After the consecutive charging steps, the battery was then subjected to constant current-constant voltage (CCCV) in a constant voltage of 4.2V. Followed by subjecting to CCCV, the battery was then discharged to a potential (Vc) of 2.75 V, to form the battery via method II.C. Method III

[0082] For comparative purposes, the secondary battery was formed by another method wherein tap-charging was carried out 4 hours after injecting the dry battery with the electrolyte, and the consecutive charging was carried out via three steps to higher potentials (Vb) at higher c-rates.

[0083] The below method III explains the comparative method of formation of secondary battery. The dry battery prepared by the process as explained in Example 1 was taken and the electrolyte prepared by the process as explained in Example 1 was injected into the dry battery followed by allowing for soaking for a period of 4 hours. Followed by soaking, the battery was tap-charged to a potential (Va) of 1 ,5V at a c-rate of 0.05C. The tap-charged battery was then subjected to thermal aging at a temperature of 45 °C for 24 hours, to densify, integrate and thereby result in a homogeneous SEI layer. The thermally-aged battery was then then subjected to consecutive charging to a potential (Vb) of up to 4.2 V via three steps. After the consecutive charging steps, the battery was then subjected to constant currentconstant voltage (CCCV) in a constant voltage of 4.2V. followed by subjecting to CCCV, the battery was then discharged to a potential (Vc) of 2.75V, to obtain the battery from method III. The detailed parameters for each step of the method III are provided in Table 1.Table 1EXAMPLE 3Electrochemical analysis of the batteries formed by methods I, II and III

[0084] The batteries formed using methods I, II and III were analysed for their electrochemical analysis using charge-discharge profile using the instrument battery testing system (BTS 4000), 5V 80Amps. The discharge capacities exhibited by the batteries were analysed. It was found that the batteries formed by the methods I, and II exhibited higher discharge capacities owing to the two-step reduction of electrolyte additives leading to complete reduction and formation of stable SEI layer which led to high discharge capacities. The method I provided a battery with higher coulombic efficiency (CE) value of 99.61%, in comparison to the other methods. Hence, the methods I and II were comparatively analysed further for the reaction mechanisms involved in the formation method.

[0085] The voltage vs capacity curve derived from the charge-discharge profile for the batteries formed by methods I, II and III are combinedly depicted in Figure 1. From the Figure 1, it was observed that the battery formed by the method I showed better charge capacity in comparison to batteries formed using methods II and III.

[0086] The differential capacity (dQ / dV) analysis was performed for the methods I, II and III to analyse the degradation mechanisms inside the electrodes or electrolyte of the battery. Figure 2 depicts the differential capacity (dQ / dV) analysis for the methods I, II and III. The dQ / dV curve represented the additive reduction regime and the solvent reduction regime that occurred in the electrolytes during the methods I, II, and III. In tap-charging step of method I, the battery was charged up to 2.1V. After this, during thermal aging period (or rest phase), the voltage dropped due to the relaxation within the battery. After the voltage drop, the second charging phase began from this lower voltage, bringing the battery back up again. This resulted in two distinct lines during the charging process.

[0087] For methods III and II, the reduction of LiBOB was visible by prominent peaks at -1.8V and -2.45V. But for method I, the peak at -2.45V got suppresseddue to the effective reduction at -1.8V. This meant that the initial reduction of additive LiBOB was effective in comparison to other methods. Hence, the SEI stabilization was considered to be effective when the battery was formed by method I. Further the SEI stabilization via densification and homogenous distribution of compounds were achieved due to immediate tap charging after electrolyte injection, followed by thermal ageing which are critical steps in the method.

[0088] Figure 3A depicts the graphical representation of charge capacity and discharge capacity of batteries formed by the methods I, II and III. It was observed that the battery formed by method I showed highest charge capacity of 26.73 Ah and an improved discharge capacity of 23.51 Ah.

[0089] Figure 3B depicts the initial capacity test for the batteries formed by the methods I, II and III, wherein c-rate for charging and discharging are 0.1C c-rate for in the (i) first cycle, and (ii) second cycle. It was observed that the charge and discharge capacities of the battery formed by method I was 23.36Ah and 23.31 Ah, respectively. In comparison to the charge-discharge capacities of the batteries formed by methods II and III, the method I was found to provide a battery with much higher capacities as well as improved capacity retention in the proceeding cycles. Figure 3B (iii) depicts the coulombic efficiency (CE) of first and second cycles exhibited by the batteries formed by methods I, II and III. The battery formed by method I showed a higher 99.89% in the first cycle and 99.94% in the second cycle, which was comparatively better than the batteries formed by other methods II and III.

[0090] Overall, the method I was found to provide a battery with better stability and increased initial coulombic efficiency (ICE). Reduction of electrolyte additive sufficiently occurred in the method I than the similar method Ila. The method I also facilitated complete reduction of solvent and electrolyte additives of the electrolyte via two steps (tap-charging and charging to potential Vb) followed by densification of the SEI layer via thermal ageing. However, the similar method Ila allowed for reduction of solvent and electrolyte additives only at tap-charging which was followed by thermal aging for densification of the SEI layer. Therefore, the reduction of electrolyte additives was incomplete or partial in the battery formed bythe method II which resulted in an unstable SEI layer providing a battery with lower coulombic efficiency (CE)% value. Thermal ageing step in the methods of formation, enabled removing soluble unstable species which consequently stabilized the SEI layer. Therefore, the method I of the present disclosure comprising the combined steps of tap-charging, thermal ageing, consecutive charging to a potential of Vb via four consecutive charging steps and subjecting to constant current-constant voltage followed by discharging resulted in a formed battery with improved electrochemical properties.Life cycle analysis

[0091] The life cycle analysis of the batteries formed by methods I, II and III was carried out at 45°C with charge step at 0.5C rate and discharge step at 1C with 30 minutes rest time after both the steps. Figure 4 depicts the life cycle measurement data for the batteries formed by methods I, II and III. The method I was found to provide a battery with better life cycle than the other methods. The enhanced life cycle for the battery formed by the method I was attributed to the formation of a stable, dense and unform SEI layer. The reduction of electrolyte additives such as LiBOB completely occurred in the method I than the similar method II. The method I facilitated complete reduction of solvent and electrolyte additives of the electrolyte via two steps specifically by tap-charging and consecutive charging to potential Vb. Consequently, the life cycle data for the battery formed by method I showed flattening of the curve by virtue of which the battery was able to run 1000 cycles more with -80% capacity retention, specifically about more than 86.6% for up to 300 cycles. Meanwhile, the batteries formed by methods II and III showed a cycle efficiency of below 85% for up to 300 cycles.

[0092] The formation of a stable and robust SEI layer on the anode surface prevented the direct contact of the anode with the electrolyte. Therefore, further reduction of electrolyte led to minimize the irreversible loss of lithium from the cathode. The reduction of LiBOB additive formed dense boron containing polymer species, solid lithium oxalate (Li2C2O4) and some amount of lithium carbonate (Li2CO3). Along with these products, the soluble oxalatoborates (or) boron containing semicarbonates were also formed. Hence, the partial reduction ofLiBOB during tap-charging step saved the EC (ethylene carbonate; solvent) from the reduction which helped the cell for long run with enough electrolyte. In addition, thermal ageing after the LiBOB reduction made the SEI layer denser by eliminating the soluble by products formed. Eventually, at anode side a dense and stable inorganic first layer of SEI was formed by the reduction of the additives LiBOB and LFO. Further, other additives like VC, DTD also participated in the SEI growth during the consecutive charging steps, with low charge transfer resistance. Overall, these additives made the SEI more conductive (i.e. DTD and VC) and robust (i.e. VC). In addition to this, the corrosion inhibition in the initial step also limits the loss of conductivity and particle peel-off from the copper current collector, which in turn helped in maintaining the capacity / energy density and hence, improved the life cycle of the battery formed by the method I.Delta V measurement

[0093] The batteries formed by methods I, II and III were analysed for their delta V values. The potential difference (Delta V) for the batteries was measured to analyse the existence of parasitic reactions which led to a higher delta V value. After the formation method, the cells were charged up to 50% state-of-charge (SoC) and kept for 72 hrs of rest. The difference between the voltage measured before the 72 hrs of rest period (VI) and after (V2) is the Delta V.VI - V2 = Delta V.

[0094] The battery formed by method II showed higher delta V value of 9.8mV than that of method I which showed a delta V value of 9.6mV, as depicted in Figure 5. It was hence understood that there were lesser parasitic reactions during thermal aging step of the method I. For the battery formed by method III, the capacity was found to be low which was considered to be the reason behind low delta V of 8.87mV. Therefore, the method I which provided a battery with higher capacity and moderately lesser parasitic reactions was the preferable method.Direct current Internal Resistance (DCIR) Measurement

[0095] DCIR measurement is the analysis of internal resistance of a battery against a direct current supply. DCIR measures the ohmic series DC outputresistance of the battery. The ohmic resistance of a battery depends on the current collectors, the electrode (cathode / anode) active materials, electrolyte, and other connections (like tab welds, contact resistances, and safety elements). After the formation method was completed, the battery was rested for 3 days of conditioning. Then for DCIR measurement, the battery was charged to 50% state of charge (SoC) at 0.1C rate and 30 minutes rest was provided. The discharge current pulse of 1C was given for 10 seconds to the battery. V3 value was measured as the voltage recorded before 1C pulse and V4 value was measured as the voltage recorded after 1C pulse. Therefore, the applied current (at 1C) = DCIR x I = (V3-V4) / I

[0096] Figure 6 depicts the DCIR measurement of the batteries formed by the methods I, II and III. The slightly higher DCIR value of 6.02mQ obtained for method I was due to more additive reductions of electrolyte additive LiBOB, which in turn stabilized the SEI layer.ADVANTAGES OF THE PRESENT DISCLOSURE

[0097] The method disclosed in the present disclosure employs a tap charging step to a higher potential, which reduces corrosion of metallic parts of the battery. The tap-charging is carried out to a voltage higher than the reduction potential of the electrolyte additives at a very low c-rate, thereby facilitating partial reduction of the electrolyte additives to form the SEI layer. Subsequently after to tap-charging the method of the present disclosure employs a thermal ageing step which results in the densification of the formed SEI layer. Further to the thermal ageing step, the battery is then subjected to consecutive charging to a potential Vb of up to 4.2 V to complete the SEI layer formation by reducing the electrolyte additives and solvent to a great extent. The battery is consecutively charged to a potential Vb to achieve a stabilised SEI layer with complete reduction of solvent and electrolyte additives. Thus, the present disclosure provides a convenient method of formation of a secondary battery, wherein a stable and dense SEI layer is formed in the battery which leads to higher charge-discharge capacities with better capacity retention.

Claims

I / We Claim:

1. A method of formation of a secondary battery comprising an anode, a lithium-based cathode, and an electrolyte having at least one electrolyte additive, the method comprising: a) tap-charging the battery to a first potential (Va) greater than decomposition potential of the at least one electrolyte additive to partially form a solid electrolyte interphase (SEI) layer; b) thermal aging the tap-charged battery of (a) to densify the solid electrolyte interphase layer; and c) performing consecutive charging on the aged battery to a second potential (Vb) enabling complete reduction of the electrolyte additive for the SEI layer formation; and discharging to a third potential (Vc) to obtain the battery, wherein tap-charging to the first potential (Va) partially reduces the electrolyte additive.

2. The method as claimed in claim 1 , wherein tap-charging the battery to a first potential (Va) is carried out to a voltage in a range of 1.7 to 2.65 V.

3. The method as claimed in claim 1, wherein thermal ageing is carried out at a temperature in a range of 40 to 50°C for a period in a range of 20 to 30 hours.

4. The method as claimed in claim 1 , wherein consecutive charging to a second potential (Vb) is carried out to a voltage in a range of 2.8 to 4.2 V, followed by subjecting to constant current-constant voltage.

5. The method as claimed in claim 1, wherein discharging is carried out to a voltage range of 2.5 to 2.8 V.

6. The method as claimed in claim 1, wherein the electrolyte additive is in a weight range of 2.5 to 6% (w / w) with respect to total weight of the electrolyte; and is selected from lithium bis(oxalato) borate (LiBOB), vinylene carbonate, 1,3,2-dioxathiolane 2,2-dioxide (DTD), lithium difluorophosphate (LFO), succinonitrile, fluoroethylene carbonate, 1,3-propane sultone, 1,3,6-hexanetricarbonitrile, lithium difluoro(oxalato)borate, trimethylene sulfate, or combinations thereof.

7. The method as claimed in claim 1, wherein the electrolyte comprises a lithium salt selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, or lithium bis(trifluoromethanesulfonyl)imide; and a solvent selected from ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate or combinations thereof.

8. The method as claimed in claim 1, wherein the lithium -based cathode comprises (a) 96 to 98% by weight of a cathode active material selected from tin-based alloys, lithium nickel manganese cobalt oxide (Li-NMC), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel cobalt aluminium oxide (Li-NCA), lithium iron phosphate (LiFePC ), lithium nickel cobalt oxide (LiNiCoCh) or combinations thereof;(b) 0.5 to 2% by weight of a first binder selected from polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride, or combinations thereof; and optionally (c) 0.5 to 2% by weight of a conductive material selected from carbon black, graphite, activated carbon, graphene, singlewalled carbon nanotube, multi-walled carbon nanotube carbon nanofiber, or combinations thereof.

9. The method as claimed in claim 1, wherein the anode comprises (a) 95 to 97% by weight of an anode active material selected from graphite, hard carbon, lithium titanate (LTO), silicon-graphite, lithium metal, titanium oxide (TiCh), niobium-titanium oxide (NTO), or combinations thereof; (b) 0.5 to 4% by weight of a second binder selected from styrene butadiene rubber, carboxymethyl cellulose, or combinations thereof; and optionally(c) 0.5 to 2% by weight of a conductive carbon selected from carbon black, graphite, activated carbon, graphene, or combinations thereof.

10. The method as claimed in claim 1, wherein the battery exhibits a charge capacity in a range of 23 to 27 Ah and a discharge capacity in a range of 23 to 25 Ah.

11. The method as claimed in claim 1, wherein the battery exhibits capacity retention in a range of 80 to 95%.

12. A battery formed by the method as claimed in claim 1.

13. Use of the battery as claimed in claim 12, for manufacturing energy storage devices and electronic devices.

Images