DESC:

FORM 2
The Patents Act 1970 (39 of 1970)
&
The Patent Rules 2003
NON-PROVISIONAL SPECIFICATION
(See Section 10 and rule 13)

TITLE
“POLYMER GARNET COMPOSITE SOLID STATE ELECTROLYTE AND METHOD OF SYNTHESIS THEREOF”

APPLICANT:
QPIVOLTA TECHNOLOGIES INDIA PVT LTD
No 18, Gayatri Krupa, Somanna Gardens, Vidyaranyapura Bangalore Karnataka India 560097

PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING NON-PROVISIONAL SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THIS INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:

A) CROSS- REFERENCE TO RELATED APPLICATION

This application claims the priority of the provisional application with serial number 202341015739 filed on 9th March 2023 with the title, “POLYMER GARNET COMPOSITE SOLID STATE ELECTROLYTE AND METHOD OF SYNTHESIS THEREOF” and the contents of which is incorporated in entirety.

B) TECHNICAL FIELD

[0001] The present invention is generally related to a field of battery technology. The present invention is particularly related to a polymer garnet composite solid state electrolyte and method of synthesis thereof. The present invention is more particularly related to a polymer garnet composite solid state electrolyte, with an on-site coagulated layer, providing good interfacial stability to the electrodes in a solid-state lithium battery system.

C) BACKGROUND OF THE INVENTION

[0002] Solid-state electrolytes can be classified into three categories based on their major sources, such as solid polymer electrolytes (major sources from polymers), solid state ceramic electrolytes (major sources from ceramics) and hybrid solid state electrolytes (mixture of polymer and ceramics). Solid polymer electrolytes is a mixture of polymer and lithium salt, which is highly flexible with good interfacial stability at electrodes but has poor ionic conductivity at a lower temperature, decreasing the lithium-ion transports. Ceramics-based solid-state electrolytes are oxides and sulfides, which have reasonable ionic conductivity (10-3- 10-4 S cm-1) but suffer from poor interfacial stability. The mixture of polymer and ceramics can be named as composite polymer electrolytes and this type of electrolytes can overcome the limitations of both polymer and ceramic type SSE. The presence of lithium in ceramics helps to enhance the lithium transportation and the flexible, smooth portion of the polymer phase provides good interfacial stability with the electrodes. Recently, researchers have been focused on polymer garnet composite electrolytes based on solid- state lithium-ion batteries due to the aforementioned reasons.
[0003] The commercial lithium battery consists of a celgard membrane separator with liquid electrolytes separated the two electrodes (anode and cathode). This system provides an unstable side reaction that leads to instability growth of the solid electrolytes interface layer. The formation of lithium dendrites and it grows rapidly at the lithium metal anode side which would reach another side of the electrode (cathode) further cycling for long cycles. This could result in short circuiting the device and also highly possible for the explosion of device due to the presence of liquid electrolytes in the system.
[0004] Furthermore, the current R&D focuses on development of lithium metal anode based rechargeable lithium batteries because of its high theoretical capacity (3680 mAh/g) and negative potential (- 3.06 V), and these properties help to obtain high energy density batteries to fulfill the current requirement in energy storage technologies. But this system (lithium metal anode and liquid electrolyte) has several issues including a continuous lithium stripping/plating process forms an unstable growth of solid electrolyte interface (SEI) layer on lithium metal anode which leads to obtaining a thick SEI layer. Continuous growth of lithium dendrites from the fragile SEI layer, and the formed lithium dendrites removed from the root could form a dead lithium at the lithium metal anode surface upon continuous cycling. Hence, the issues like SEI growth, lithium dendrites and dead lithium particles lead to results in decrease the discharge capacity or coulombic efficiency and also may be possible for short-circuiting a device which leads to explosion of the devices.
[0005] Solid-state electrolytes (SSE) categorized into three types based on their major sources, such as polymer-based SSE, ceramics-based SSE and hybrid SSE (mixture of polymer and ceramic). Polymer-based SSE (mixture of polymer and lithium salt) has good interfacial stability at electrodes, highly flexible but has poor ionic conductivity at a lower temperature which decreases the lithium-ion transports and results in poor cell performance. Ceramics-based (oxides and sulfides) have reasonable ionic conductivity (10-3 S cm-1) but suffer from poor interfacial stability. Garnet and Sulfide-based electrolytes are the most prominent electrolyte when compared to other solid-state electrolytes because of its sufficient ionic conductivity (10-3 S cm-1) to achieve good lithium-ion batteries but those electrolytes have poor interfacial stability with electrodes and thus restricts the commercialization of solid-state lithium batteries while using pristine form of solid electrolyte. Hybrid SSE could overcome the limitations of both polymer and ceramic type SSE. The presence of lithium in ceramics helps to enhance the lithium transportation and the flexibility, smooth portion of the polymer phase provides good interfacial stability with the electrodes. However, due to the dry surface of hybrid electrolytes reduces ionic mobility between the electrodes and leads to the poor cell capacity and cycle life.
[0006] Chen et al. developed three different kinds of garnet composite polymer electrolytes solid state lithium battery applications such as ceramic-in-polymer, intermediate and polymer-in-ceramic referring to PEO (polyethylene oxide)/garnet composite electrolytes for solid-state lithium batteries. From ceramic-in-polymer to polymer-in-ceramic, Nano Energy 46 (2018) 176-184. The various amounts of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) in polyethylene-oxide lithium bis trifluorosulfonyl imide (PEO8-LiTFSI) composite polymer electrolytes such as ceramic-in-polymer type electrolyte is a combination of minimal amount of ceramic and higher amount of polymer matrix, about 10 wt% of LLZTO, the intermediate type has an equal amount of ceramic-polymer mixture (50 wt% of LLZTO), and the polymer-in-ceramic type is a mixture of higher amount of ceramic and minimal amount of polymer matrix (80 wt% of LLZTO) is incorporated. The addition of LLZTO particles into the polymer matrix helps to enhance the segmental motion of the polymer chain and also reduces the crystalline phase of PEO which results in an obtained high amorphous phase. Among the various types, polymer in ceramic type electrolytes has stable stability and good cyclic performance than the contemporaries.
[0007] Yet another polymer ceramic composite electrolytes has been developed by Zheng and Hu (as referred in: “New insights into the compositional dependence of Li-ion transport in polymer–ceramic composite electrolytes, ACS applied materials & interfaces 10(4) (2018) 4113-4120”). Herein, the various percentages of Li7La3Zr2O12 (LLZO) (5, 20 & 50 wt %) incorporated into PEO-LiTFSI electrolytes have been prepared and studied. The higher amount of LLZO (50 wt%) composite electrolytes has slightly reduced the ionic conductivity than the 20 wt% of LLZO incorporated composite electrolytes which is due to the restriction of the ionic migrations by bulk LLZO. To overcome this issue, authors have introduced tetra ethylene glycol dimethyl ether (TEGDME) into the composite polymer electrolytes. TEGDME incorporated 50 wt% of LLZO-PEO-LiTFSI electrolyte has good ionic conductivity than the others. Also, it has a high charge carrier density because of active lithium ions contributed from LiTFSI salt, decomposed LLZO and bulk LLZO which results in achieving high ionic conductivity.
[0008] Furthermore, polydopamine has been used as a coating layer on Li6.4La3Zr1.4Ta0.6O12 (LLZTO) to improve the electrochemical performance of the device. The modified LLZTO incorporated PEO based composite polymer electrolytes (CPE) has been studied for solid-state lithium battery applications and compared it with the pristine LLZTO based CPE (as referred in “A dopamine modified Li6.4La3Zr1.4Ta0.6O12 /PEO solid-state electrolyte: enhanced thermal and electrochemical properties, Journal of Materials Chemistry A 7(27) (2019) 16425-16436”). The higher amounts of LLZTO were added into the polymer (PEO-LiTFSI) matrix, the higher percentage of garnet helps in achieving good electrochemical performance. However, the uniform dispersion of LLZTO throughout the polymer matrix is quite difficult because of its different surface energy compared to the undoped LLZTO. The surface energy plays a major role in the dispersion of one phase to another phase which could be reduced by agglomeration of LLZTO particles. The agglomerated LLZTO particles are difficult to disperse in a polymer solution and form uniformity. There is a huge difference in surface energy between LLZTO particles and PEO which leads to poor contact between them. To overcome this issue, the polydopamine has been used as a coating agent and coated on the LLZTO particle (PDA-LLZTO) which helps in avoiding aggregation in the solvent and results in uniform dispersion in the polymer matrix. PDA-LLZTO doped PEO based CPE has higher ionic conductivity, electrochemical stability and good cyclic stability than the pristine LLZO-PEO based CPE.
[0009] Hence, in the view of this, there is a need for an improved polymer garnet composite solid state electrolyte to mitigate the aforementioned drawbacks, and provide good interfacial stability compared to the existing lithium-ion battery system.
[0010] The above-mentioned shortcomings, disadvantages and problems are addressed herein, and which will be understood by reading and studying the following specification.

D) OBJECTS OF THE INVENTION:

[0011] The primary object of the present invention is to provide a polymer garnet composite solid state electrolyte and method for synthesis thereof.
[0012] Another object of the present invention is to provide a polymer garnet composite solid state electrolyte comprising solid polymer composite membrane used as an electrolyte cum separator, along with an artificial interfacial layer.
[0013] Yet another object of the present invention is to provide a method for synthesis of a polymer garnet composite solid state electrolyte, that provides good interfacial stability to the electrodes of the lithium-ion battery.
[0014] Yet another object of the present invention is to provide a method for synthesis of metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12), through solid state reaction.
[0015] Yet another object of the present invention is to provide a method for incorporating the metal doped LLZO with a garnet composite solid state electrolyte, by solution casting technique.
[0016] Yet another object of the present invention is to provide a method for synthesis of gel polymer electrolyte solution and on-site coagulation method.
[0017] Yet another object of the present invention is to provide a method for assembling the lithium metal battery.
[0018] Yet another object of the present invention is to provide a method for preparation of a cathode, to assemble in the lithium metal battery.
[0019] These and other objects and advantages of the embodiments herein will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

E) SUMMARY OF THE INVENTION

[0020] The following details present a simplified summary of the embodiments herein to provide a basic understanding of the several aspects of the embodiments herein. This summary is not an extensive overview of the embodiments herein. It is not intended to identify key/critical elements of the embodiments herein or to delineate the scope of the embodiments herein. Its sole purpose is to present the concepts of the embodiments herein in a simplified form as a prelude to the more detailed description that is presented later.
[0021] The other objects and advantages of the embodiments herein will become readily apparent from the following description taken in conjunction with the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
[0022] The various embodiments of the present invention provides a polymer garnet composite solid state electrolyte and method of synthesis thereof. The present invention provides a polymer garnet composite solid state electrolyte comprising solid polymer composite membrane used as an electrolyte cum separator, along with an artificial interfacial layer. The artificial interfacial layer is either coated on the surface of the polymer composite membrane or used as thin layer of membrane at the electrodes side. Hence, the present invention provides a highly conductive metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12) incorporated garnet composite solid state electrolyte, with good lithium-ion transference number. Furthermore, the present invention provides good interfacial stability with the electrodes, by forming an artificial layer on the garnet composite solid state electrolyte through an on-site coagulation method.
[0023] According to one embodiment of the present invention, a method for synthesis of a polymer garnet composite solid state electrolyte is provided. The method comprises synthesizing a highly conductive metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12) solid state electrolyte. The method further includes incorporating the metal doped LLZO with a garnet composite solid state electrolyte. The garnet composite solid state electrolyte has a good lithium-ion transferase number. Furthermore, the method involves coating an artificial layer of gel polymer electrolyte solution on the garnet composite solid state electrolyte using on-site coagulation method. The artificial layer provides good interfacial stability to the electrodes. Furthermore, the method involves assembling a lithium metal battery, in the order comprising first layer a cathode coated aluminum foil, second layer, the garnet composite polymer electrolyte along with the on-site coagulation method. The on-site coagulation technique is gel polymer liquid electrolyte solution injected on the garnet composite polymer electrolyte membrane, wherein the gel polymer solution becomes solid after standing for a while about 15 minutes, within the glove box. Finally, the third layer a lithium metal anode assembled to obtain the lithium metal battery.
[0024] According to one embodiment of the present invention, a method for synthesis of metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12) is provided. The metal doped LLZO is synthesized by solid state reaction, and the steps is disclosed herein. The method comprises procuring an stoichiometric amount of lithium hydroxide (LiOH), lanthanum oxide (La2O3), zirconium oxide (ZrO2) and metal dopants. The lanthanum oxide is preheated at 950 oC for 24 hours, prior to procuring. The metal dopants include Tantalum, Aluminium, Gallium, Tellurium and/or Niobium. The method further comprises mixing appropriate amount of LLZO with the metal dopants, in the presence of a solvent to obtain a composite mixture. The solvent includes isopropanol. The method further includes milling the obtained composite mixture for a long cycle about 9 hours with an interval of resting time about 15 minutes, and then drying the obtained milled sample in a vacuum oven at 373 K for 10 hours to evaporate the solvent. Further, the method includes sintering the obtained milled sample at 950 oC. The method further involves milling the sintered sample for 18 hours, with an interval of resting time and drying in a vacuum oven at 373 K for 10 hours to remove the solvent. Finally, the method involves grinding and sieving the dried powder to obtain particles of size around 100 nm.
[0025] According to one embodiment of the present invention, a method for incorporating the metal doped LLZO with a garnet composite solid state electrolyte is provided. The garnet composite polymer electrolyte includes polymer-lithium salt- metal doped LLZO, which is prepared by solution casting technique. The concentration of LLZO is above 50 %. The method comprises dissolving an appropriate amount of polymer in a solvent, until a homogenous solution is obtained. The polymer includes polyethylene oxide at a concentration of less than 50 wt %. The solvent includes acetonitrile. Further, adding lithium salt to the obtained homogenous solution, and stirred for 10 hours to obtain a polymer composite solution. The method further includes incorporating metal doped LLZO into the obtained polymer composite solution and stirred continuously for 8 hours to get a homogenous polymer composite solution. The metal doped LLZO is pre-heated at 100 oC for 12 hours, before incorporating with the polymer composite solution. Furthermore, the method involves casting the homogenous polymer composite solution on a teflon coated sheet, and drying in a vacuum oven at 60 oC for 12 hours, to remove the solvent, and to obtain a free standing polymer composite solid-state electrolyte.
[0026] According to one embodiment of the present invention, a method for synthesis of gel polymer electrolyte solution is provided. In the gel polymer electrolyte solution, comprising a polymer, lithium salt, succinonitrile as a plasticizer and garnet is synthesized in argon atmosphere in the glove box. The method comprises dissolving an appropriate amount of a polymer and lithium salt in liquid electrolyte, and stirred continuously for 10 hours to obtain a composite liquid electrolyte homogenous solution. The amount of polymer used is 3 % and 1M of lithium salt based liquid electrolyte is used. Besides, the liquid electrolytes include 1M LiFSI (Lithium bis fluorosulfonyl imide)/ LiTFSI (Lithium bis trifluorosulfonyl imide) in carbonate solvents. The method further includes incorporating succinonitrile at concentration of 10 wt % and garnet at a concentration of 10 wt % to the obtained composite liquid electrolyte homogenous solution, and then mixing thoroughly for 8 hours to obtain a homogenous gel polymer electrolyte solution. The succinonitrile and garnet helps to provide good interfacial stability with the electrodes.
[0027] According to one embodiment of the present invention, the succinonitrile is used as a plasticizer to improve the ionic conductivity and stability (mechanical and electrochemical) of the composite polymer electrolytes. The introduction of higher oxidative potential of succinonitrile into the composite electrolytes helps to obtain higher voltage cathode batteries and thus leads to achieve high energy density batteries and also prolonged cycle life. The optimized amount of succinonitrile incorporation forms a good interfacial stability with the electrodes and while adding beyond the optimized amount succinonitrile leads to form a thick SEI layer which results in reducing the performance and cycle life of the device.
[0028] According to one embodiment of the present invention, the polymer employed in the lithium battery system should be a low glass transition temperature, amorphous in nature, low cohesive energy and high dielectric constants. However, only few polymers can fulfill the above requirements needed for practical use. The polymer used comprises polyethylene oxide (PEO) & its copolymer, polymethyl methacrylate (PMMA) & its copolymer, polyacrylonitrile (PAN) & its copolymer and polyvinylidene fluoride (PVDF) & its copolymer.
[0029] According to one embodiment of the present invention, the onsite coagulation method involves injecting the gel polymer electrolyte solution into the free-standing polymer composite solid-state electrolyte to form an artificial layer. The on-site coagulation method helps to provide a good interfacial stability with the electrodes and which results in achieving a prolonged cyclic stability.
[0030] According to one embodiment of the present invention, assembling the lithium metal battery is provided. The lithium metal batteries are assembled in the following order, a single layer cell consisting of a cathode, garnet composite polymer electrolyte and lithium metal anode. The first layer in the lithium metal batteries includes a cathode coated with aluminium foil. The second layer includes the garnet composite polymer electrolyte along with onsite coagulation technique. The on-site coagulation technique is gel polymer liquid electrolyte solution injected on the garnet composite polymer electrolyte membrane, wherein the gel polymer solution becomes solid after standing for a while about 15 minutes, within the glove box. Finally, the third layer includes a lithium metal anode assembled to obtain the lithium metal battery.
[0031] According to one embodiment of the present invention, a method for preparation of a cathode in the lithium metal battery is provided. The method comprises mixing together a catholyte at a concentration of less than 5% wt, active material comprising LFP (Lithium iron Phosphate), NMC (Lithium Nickel Manganese Cobalt oxide), NCA (Lithium Nickel Cobalt Aluminium oxide), and activated carbon to obtain a homogenous mixture. The catholyte is used in minimal amount, about less than 5 wt% instead of polymer binder in the cathode preparation, as catholyte serves as both the role binder as well as improving the performance. The introduction of catholyte into the cathode slurry leads to enhanced conductivity and also improves the interfacial stability. Furthermore, the method involves casting the homogenous mixture on an aluminum foil, and drying in a vacuum oven to obtain a solvent free coated sheet. The method further involves calendaring and punching the solvent free coated sheet in to required size of cathode.
[0032] From the foregoing discussion, it is apparent that the present invention provides a polymer garnet composite solid state electrolyte comprising solid polymer composite membrane used as an electrolyte cum separator, along with an artificial interfacial layer. The artificial interfacial layer is either coated on the surface of the polymer composite membrane or used as thin layer of membrane at the electrodes side. Hence, the present invention provides a highly conductive metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12) incorporated garnet composite solid state electrolyte, with good lithium-ion transference number. Furthermore, the present invention provides good interfacial stability with the electrodes, by forming an artificial layer on the garnet composite solid state electrolyte through an on-site coagulation method. The present invention mitigates the poor electrochemical & cyclic stability of nickel rich cathodes and the formations of lithium dendrites at lithium metal anode by the solid-state electrolyte system. The solid-state electrolyte has a high electrochemical potential window and is more than sufficient than nickel rich cathodes. The deployed artificial layer in the present invention leads to reduced growth or formation of lithium dendrites and this results in highly safer, enhanced cycle life and capacity of the battery system.
[0033] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0034] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent in reference to the drawings and the following detailed description.

F) BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0036] FIG. 1 illustrates a flowchart on the method for synthesis of a polymer garnet composite solid state electrolyte, according to an embodiment of the present invention.
[0037] FIG. 2 illustrates a flowchart on the method for synthesis of metal doped LLZO, according to an embodiment of the present invention.
[0038] FIG. 3 illustrates a flowchart on the method for incorporating the metal doped LLZO with a garnet composite solid state electrolyte, according to an embodiment of the present invention.
[0039] FIG. 4 illustrates a flowchart on the method for method for synthesis of gel polymer electrolyte solution and on-site coagulation method, according to an embodiment of the present invention.
[0040] FIG. 5 illustrates a block diagram of an assembly of a lithium metal battery, according to an embodiment of the present invention.
[0041] FIG. 6 illustrates an X-Ray diffraction (XRD) study in LLZTO (Lithium Lanthanum Zirconium Tantalum Oxide), according to an embodiment of the present invention.
[0042] FIG. 7 illustrates an ionic conductivity analysis on LLZTO, according to an embodiment of the present invention.
[0043] Although the specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.

G) DETAILED DESCRIPTION OF THE DRAWINGS:

[0044] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0045] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure can be practiced without these specific details.
[0046] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0047] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0048] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however, that it is not intended to limit the disclosure to the forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.
[0049] The various embodiments of the present invention provides a polymer garnet composite solid state electrolyte and method of synthesis thereof. The present invention provides a polymer garnet composite solid state electrolyte comprising solid polymer composite membrane used as an electrolyte cum separator, along with an artificial interfacial layer. The artificial interfacial layer is either coated on the surface of the polymer composite membrane or used as thin layer of membrane at the electrodes side. Hence, the present invention provides a highly conductive metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12) incorporated garnet composite solid state electrolyte, with good lithium-ion transference number. Furthermore, the present invention provides good interfacial stability with the electrodes, by forming an artificial layer on the garnet composite solid state electrolyte through an on-site coagulation method.
[0050] According to one embodiment of the present invention, a method for synthesis of a polymer garnet composite solid state electrolyte is provided. The method comprises synthesizing a highly conductive metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12) solid state electrolyte. The method further includes incorporating the metal doped LLZO with a garnet composite solid state electrolyte. The garnet composite solid state electrolyte has a good lithium-ion transferase number. Furthermore, the method involves coating an artificial layer of gel polymer electrolyte solution on the garnet composite solid state electrolyte using on-site coagulation method. The artificial layer provides good interfacial stability to the electrodes. Furthermore, the method involves assembling a lithium metal battery, in the order comprising first layer a cathode coated aluminum foil, second layer, the garnet composite polymer electrolyte along with the on-site coagulation method. The on-site coagulation technique is gel polymer liquid electrolyte solution injected on the garnet composite polymer electrolyte membrane, wherein the gel polymer solution becomes solid after standing for a while about 15 minutes, within the glove box. Finally, the third layer a lithium metal anode assembled to obtain the lithium metal battery.
[0051] According to one embodiment of the present invention, a method for synthesis of metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12) is provided. The metal doped LLZO is synthesized by solid state reaction, and the steps is disclosed herein. The method comprises procuring a stoichiometric amount of lithium hydroxide (LiOH), lanthanum oxide (La2O3), zirconium oxide (ZrO2) and metal dopants. The lanthanum oxide is pre-heated at 950 oC for 24 hours, prior to procuring. The metal dopants include Tantalum, Aluminium, Gallium, Tellurium and/or Niobium. The method further comprises mixing appropriate amount of LLZO with the metal dopants, in the presence of a solvent to obtain a composite mixture. The solvent includes isopropanol. The method further includes milling the obtained composite mixture for a long cycle about 9 hours with an interval of resting time about 15 minutes, and then drying the obtained milled sample in a vacuum oven at 373 K for 10 hours to evaporate the solvent. Further, the method includes sintering the obtained milled sample at 950 oC. The method further involves milling the sintered sample for 18 hours, with an interval of resting time and drying in a vacuum oven at 373 K for 10 hours to remove the solvent. Finally, the method involves grinding and sieving the dried powder to obtain particles of size around 100 nm.
[0052] According to one embodiment of the present invention, a method for incorporating the metal doped LLZO with a garnet composite solid state electrolyte is provided. The garnet composite polymer electrolyte includes polymer-lithium salt- metal doped LLZO, which is prepared by solution casting technique. The concentration of LLZO is above 50 %. The method comprises dissolving an appropriate amount of polymer in a solvent, until a homogenous solution is obtained. The polymer includes polyethylene oxide at a concentration of less than 50 wt %. The solvent includes acetonitrile. Further, adding lithium salt to the obtained homogenous solution, and stirred for 10 hours to obtain a polymer composite solution. The method further includes incorporating metal doped LLZO into the obtained polymer composite solution and stirred continuously for 8 hours to get a homogenous polymer composite solution. The metal doped LLZO is pre-heated at 100 oC for 12 hours, before incorporating with the polymer composite solution. Furthermore, the method involves casting the homogenous polymer composite solution on a teflon coated sheet, and drying in a vacuum oven at 60 oC for 12 hours, to remove the solvent, and to obtain a free-standing polymer composite solid-state electrolyte.
[0053] According to one embodiment of the present invention, a method for synthesis of gel polymer electrolyte solution is provided. In the gel polymer electrolyte solution, comprising a polymer, lithium salt, succinonitrile as a plasticizer and garnet is synthesized in argon atmosphere in the glove box. The method comprises dissolving an appropriate amount of a polymer and lithium salt in liquid electrolyte, and stirred continuously for 10 hours to obtain a composite liquid electrolyte homogenous solution. The amount of polymer used is 3 % and 1M of lithium salt based liquid electrolyte is used. Besides, the liquid electrolytes include 1M LiFSI (Lithium bis fluorosulfonyl imide)/ LiTFSI (Lithium bis trifluorosulfonyl imide) in carbonate solvents. The method further includes incorporating succinonitrile at concentration of 10 wt % and garnet at a concentration of 10 wt % to the obtained composite liquid electrolyte homogenous solution, and then mixing thoroughly for 8 hours to obtain a homogenous gel polymer electrolyte solution. The succinonitrile and garnet helps to provide good interfacial stability with the electrodes.
[0054] According to one embodiment of the present invention, the succinonitrile is used as a plasticizer to improve the ionic conductivity and stability (mechanical and electrochemical) of the composite polymer electrolytes. The introduction of higher oxidative potential of succinonitrile into the composite electrolytes helps to obtain higher voltage cathode batteries and thus leads to achieve high energy density batteries and also prolonged cycle life. The optimized amount of succinonitrile incorporation forms a good interfacial stability with the electrodes and while adding beyond the optimized amount succinonitrile leads to form a thick SEI layer which results in reducing the performance and cycle life of the device.
[0055] According to one embodiment of the present invention, the polymer employed in the lithium battery system should be a low glass transition temperature, amorphous in nature, low cohesive energy and high dielectric constants. However, only few polymer can fulfill the above requirements needed for practical use. The polymer used comprises polyethylene oxide (PEO) & its copolymer, polymethyl methacrylate (PMMA) & its copolymer, polyacrylonitrile (PAN) & its copolymer and polyvinylidene fluoride (PVDF) & its copolymer.
[0056] According to one embodiment of the present invention, the on- site coagulation method involves injecting the gel polymer electrolyte solution into the free-standing polymer composite solid-state electrolyte to form an artificial layer. The on-site coagulation method helps to provide a good interfacial stability with the electrodes and which results in achieving a prolonged cyclic stability.
[0057] According to one embodiment of the present invention, assembling the lithium metal battery is provided. The lithium metal batteries are assembled in the following order, a single layer cell consisting of a cathode, garnet composite polymer electrolyte and lithium metal anode. The first layer in the lithium metal batteries includes a cathode coated with aluminum foil. The second layer includes the garnet composite polymer electrolyte along with onsite coagulation technique. The on-site coagulation technique is gel polymer liquid electrolyte solution injected on the garnet composite polymer electrolyte membrane, wherein the gel polymer solution becomes solid after standing for a while about 15 minutes, within the glove box. Finally, the third layer includes a lithium metal anode assembled to obtain the lithium metal battery.
[0058] According to one embodiment of the present invention, a method for preparation of a cathode in the lithium metal battery is provided. The method comprises mixing together a catholyte at a concentration of less than 5% wt, active material comprising LFP (Lithium iron Phosphate), NMC (Lithium Nickel Manganese Cobalt oxide), NCA (Lithium Nickel Cobalt Aluminium oxide), and activated carbon to obtain a homogenous mixture. The catholyte is used in minimal amount, about less than 5 wt % instead of polymer binder in the cathode preparation, as catholyte serves as both the role binder as well as improving the performance. The introduction of catholyte into the cathode slurry leads to enhanced conductivity and also improves the interfacial stability. Furthermore, the method involves casting the homogenous mixture on an aluminum foil and drying in a vacuum oven to obtain a solvent free coated sheet. The method further involves calendaring and punching the solvent free coated sheet in to required size of cathode.
[0059] FIG. 1 illustrates a flowchart on the method for synthesis of a polymer garnet composite solid state electrolyte, according to an embodiment of the present invention. The method 100 comprises synthesizing a highly conductive metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12) solid state electrolyte at step 101. The method 100 further includes incorporating the metal doped LLZO with a garnet composite solid state electrolyte at step 102. The garnet composite solid state electrolyte has a good lithium-ion transferase number. Furthermore, the method 100 involves coating an artificial layer of gel polymer electrolyte solution on the garnet composite solid state electrolyte using on-site coagulation method at step 103. The artificial layer provides good interfacial stability to the electrodes. Furthermore, the method 100 involves assembling a lithium metal battery at step 104, in the order comprising first layer a cathode coated aluminum foil, second layer, the garnet composite polymer electrolyte along with the on-site coagulation method. The on-site coagulation technique is gel polymer liquid electrolyte solution injected on the garnet composite polymer electrolyte membrane, wherein the gel polymer solution becomes solid after standing for a while about 15 minutes, within the glove box. Finally, the third layer a lithium metal anode assembled to obtain the lithium metal battery.
[0060] FIG. 2 illustrates a flowchart on the method for synthesis of metal doped LLZO, according to an embodiment of the present invention. The method 200 comprises procuring an stoichiometric amount of lithium hydroxide (LiOH), lanthanum oxide (La2O3), zirconium oxide (ZrO2) and metal dopants at step 201. The lanthanum oxide is pre-heated at 950 oC for 24 hours, prior to procuring. The metal dopants include Tantalum, Aluminium, Gallium, Tellurium and/or Niobium. The method 200 further comprises mixing appropriate amount of LLZO with the metal dopants, in the presence of a solvent to obtain a composite mixture at step 202. The solvent includes isopropanol. The method 200 further includes milling the obtained composite mixture for a long cycle about 9 hours with an interval of resting time about 15 minutes, and then drying the obtained milled sample in a vacuum oven at 373 K for 10 hours to evaporate the solvent at step 203. Further, the method 200 includes sintering the obtained milled sample at 950 oC at step 204. The method 200 further involves milling the sintered sample for 18 hours, with an interval of resting time and drying in a vacuum oven at 373 K for 10 hours to remove the solvent at step 205. Finally, the method 200 involves grinding and sieving the dried powder to obtain particles of size around 100 nm at step 206.
[0061] FIG. 3 illustrates a flowchart on the method for incorporating the metal doped LLZO with a garnet composite solid state electrolyte, according to an embodiment of the present invention. The method 300 comprises dissolving an appropriate amount of polymer in a solvent, until a homogenous solution is obtained at step 301. The polymer includes polyethylene oxide at a concentration of less than 50 wt %. The solvent includes acetonitrile. Further, adding lithium salt to the obtained homogenous solution, and stirred for 10 hours to obtain a polymer composite solution at step 302. The method 300 further includes incorporating metal doped LLZO into the obtained polymer composite solution and stirred continuously for 8 hours to get a homogenous polymer composite solution at step 303. The metal doped LLZO is pre-heated at 100 oC for 12 hours, before incorporating with the polymer composite solution. Furthermore, the method 300 involves casting the homogenous polymer composite solution on a teflon coated sheet and drying in a vacuum oven at 60 oC for 12 hours, to remove the solvent, and to obtain a free-standing polymer composite solid-state electrolyte at step 304.
[0062] FIG. 4 illustrates a flowchart on the method for method for synthesis of gel polymer electrolyte solution and on-site coagulation method, according to an embodiment of the present invention. The method 400 comprises dissolving an appropriate amount of a polymer and lithium salt in liquid electrolyte, and stirring continuously for 10 hours to obtain a composite liquid electrolyte homogenous solution at step 401. The amount of polymer used is 3 % and 1M of lithium salt based liquid electrolyte is used. Besides, the liquid electrolytes include 1M LiFSI (Lithium bis fluorosulfonyl imide)/ LiTFSI (Lithium bis trifluorosulfonyl imide) in carbon solvents. The method 400 further includes incorporating succinonitrile at concentration of 10 wt % and garnet at a concentration of 10 wt% to the obtained composite liquid electrolyte homogenous solution at step 402, and then mixing thoroughly for 8 hours to obtain a homogenous gel polymer electrolyte solution at step 403. The succinonitrile and garnet helps to provide good interfacial stability with the electrodes. Furthermore, the on-site coagulation method involves injecting the gel polymer electrolyte solution into the free-standing polymer composite solid-state electrolyte to form an artificial layer at step 404. The on-site coagulation method helps to provide a good interfacial stability with the electrodes and which results in achieving a prolonged cyclic stability.
[0063] FIG. 5 illustrates a block diagram of an assembly of a lithium metal battery, according to an embodiment of the present invention. The lithium metal battery 500 is assembled in the following order, a single layer cell consisting of a cathode 501, garnet composite polymer electrolyte 502 and lithium metal anode 503. The first layer in the lithium metal battery includes a cathode 501 coated with aluminum foil. The second layer includes the garnet composite polymer electrolyte 502 along with on-site coagulated layer 504 formed through on-site coagulation technique. The on-site coagulation technique is gel polymer liquid electrolyte solution injected on the garnet composite polymer electrolyte membrane 502, wherein the gel polymer solution becomes solid after standing for a while about 15 minutes, within the glove box. Finally, the third layer includes a lithium metal anode 503 assembled to obtain the lithium metal battery 500.
[0064] FIG. 6 illustrates an X-Ray diffraction (XRD) study in LLZTO (Lithium Lanthanum Zirconium Tantalum Oxide), according to an embodiment of the present invention. FIG. 6 600 illustrates the XRD studies analyzed on the structure of LLZTO sample. The XRD studies illustrates that the obtained sharp peaks implies that the crystalline nature of LLZTO has been formed and further denotes that the cubic phase matches with the standard cubic garnet phase.
[0065] FIG. 7 illustrates an ionic conductivity analysis on LLZTO, according to an embodiment of the present invention. FIG. 7 700, illustrates the cole-cole plot impedance of the LLZTO. The impedance measurement is carried out to determine the ionic conductivity of LLZTO solid state electrolyte. The cell is fabricated along with the solid electrolyte sandwiching between two stainless steel electrodes. The FIG. 7 700 illustrates that the impedance plot of LLZTO electrolyte has a semicircle at lower frequency region and the inclined straight line at higher frequency regions. The semicircle intercepted on x-axis provides the value of bulk resistance (1300 Ohm). Furthermore, ionic conductivity of the LLZTO electrolyte is found to be 2.108 x 10-4 S cm-1 at room temperature.
[0066] The foregoing examples and illustrative implementations of various embodiments have been provided merely for explanation and are in no way to be construed as limiting the present invention. While the present invention has been described with reference to various embodiments, illustrative implementations, drawings, and techniques, it is understood that the words, which have been used herein, are words of description and illustration, rather than words of limitation.
[0067] Further, although the present invention has been described herein with reference to particular means, materials, embodiments, techniques, and implementations, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
[0068] It will be understood by those skilled in the art, having the benefit of the teachings of this specification, that the present invention is capable of modifications and other embodiments may be affected and changes may be made thereto, without departing from the scope and spirit of the present invention.

H) ADVANTAGES OF THE INVENTION:

[0069] The present invention provides a polymer garnet composite solid state electrolyte and method of synthesis thereof. The present invention provides a polymer garnet composite solid state electrolyte comprising solid polymer composite membrane used as an electrolyte cum separator, along with an artificial interfacial layer. The artificial interfacial layer is either coated on the surface of the polymer composite membrane or used as thin layer of membrane at the electrodes side. Hence, the present invention provides a highly conductive metal doped LLZO (Lithium Lanthanum Zirconium oxide, Li7La3Zr2O12) incorporated garnet composite solid state electrolyte, with good lithium-ion transference number. Furthermore, the present invention provides good interfacial stability with the electrodes, by forming an artificial layer on the garnet composite solid state electrolyte through an on-site coagulation method. The present invention mitigates the poor electrochemical & cyclic stability of nickel rich cathodes and the formations of lithium dendrites at lithium metal anode by the solid-state electrolyte system. The solid-state electrolyte has a high electrochemical potential window and is more than sufficient than nickel rich cathodes. The deployed artificial layer in the present invention leads to reduced growth or formation of lithium dendrites and this results in highly safer, enhanced cycle life and capacity of the battery system.
[0070] Moreover, the higher amount of garnet incorporated composite polymer electrolytes could be highly applicable in the development of solid-state lithium batteries. And also, incorporation of artificial layers on the composite electrolyte leads to the form a good interfacial stability with electrodes which helps in obtaining a good battery system. Furthermore, the on-site coagulation technique involving coating a composite liquid mixture on the garnet composite polymer electrolyte membrane and forming an artificial layer on the membrane which has been formed after injection of liquid mixture and standing for a while, provides good interfacial stability with the electrodes and which results in achieving a prolonged cyclic stability.
[0071] Furthermore, the LiTFSI/ LiFSI comprising imide-based salt is used alternative to the existing LiPF6 salt-based electrolytes to overcome the issue of electrolytes in the existing lithium-ion batteries. LiPF6 salt-based electrolytes does not provide high energy storage battery system because of its poor thermal stability resulting in decomposition product of counteracts leading to a thermal runaway which results in battery failure (explosive device). Hence, the introduced LiTFSI/ LiFSI salt-based electrolytes is used in the battery system due to its good solubility and thermal stability. However, the LiTFSI/LiFSI has a drawback of being highly corrosive with Al current collector. While combining the mixed salts of LiPF6 or borate-based salts and LiTFSI/ LiFSI could overcome the aforementioned issues and also achieve enhanced ionic migrations and form a good stability with electrodes.
[0072] In addition, the garnet enriched composite polymer electrolyte has been synthesized by solution casting technique. Garnet ratios plays an important role in the conductivity, stability, nature of the membrane and electrochemical performance. While adding beyond the optimized ratio of garnet into the polymer matrix leads to decrease the ionic mobility, interfacial stability with the electrodes and forming a thick SEI layer, which results in decrease of the specific capacity and cycle life. Therefore, the synthesized polymer garnet composite solid state electrolyte, along with on-site coagulated layer is highly conductive, mechanically stable with good flexibility and also possess good lithium-ion transference numbers.
[0073] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.
[0074] It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
[0075] Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0076] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.
[0077] The scope of the embodiments of the present invention is ascertained by the claims to be submitted at the time of filing the complete specification.

,CLAIMS:WE CLAIM:

1. A method for on-site coagulation of a polymer garnet composite solid-state electrolyte for a solid-state lithium metal battery, comprising:

a. synthesizing a metal doped LLZO solid-state electrolyte;

b. incorporating the said metal doped LLZO with a garnet composite solid-state electrolyte;

c. coating an artificial layer of gel polymer electrolyte solution on the garnet composite solid-state electrolyte using an on-site coagulation technique; and

d. assembling a solid-state lithium metal battery, comprising:
1. a cathode coated aluminium foil as the first layer;
2. the garnet composite polymer electrolyte along with the on-site coagulation technique as the second layer; and
3. a lithium metal anode as the third layer.

2. The method of claim 1, wherein the method for synthesizing a metal doped LLZO solid-state electrolyte, comprising:

a. procuring stoichiometric amounts of lithium hydroxide (LiOH), lanthanum oxide (La2O3), zirconium oxide (ZrO2), and metal dopants, wherein the composition is Li6.4La3Zr1.4Ta0.6O12;

b. mixing an appropriate amount, higher than 50% of LLZO, with the metal dopants in the presence of a solvent to obtain a composite mixture;

c. milling the obtained composite mixture for a long cycle of 30 min with a predefined interval of resting time of 15 min, followed by drying to evaporate the solvent;

d. sintering the obtained milled sample at a specific temperature, i.e., at 950 °C.

e. milling the sintered sample for a long cycle of 30 min with a predefined interval of resting time of 15 min and drying in a vacuum oven to remove the solvent.

f. grinding and sieving the dried powder to obtain particles of a specific size, i.e., particle size of the sample in the nanometer scale of 100 nm.

3. The method of claim 1, wherein the method for incorporating the metal doped LLZO with a garnet composite solid-state electrolyte, comprising:

a. dissolving an appropriate amount, lesser than 30% of polymer in a solvent until a homogenous solution is obtained;

b. adding lithium salt to the obtained homogenous solution and stirring to obtain a polymer composite solution;

c. incorporating metal doped LLZO into the polymer composite solution and stirring to get a homogenous polymer composite solution; and

d. casting the homogenous polymer composite solution on a teflon coated sheet and drying in a vacuum oven to obtain a free-standing polymer composite solid-state electrolyte.

4. The method of claim 1, wherein the method for synthesis of a gel polymer electrolyte solution and on-site coagulation method, comprising:

a. dissolving an appropriate amount, lesser than 30% of a polymer and lithium salt in liquid electrolyte and stirring to obtain a composite liquid electrolyte homogenous solution;

b. incorporating succinonitrile and garnet into the composite liquid electrolyte homogenous solution and mixing thoroughly to obtain a homogenous gel polymer electrolyte solution; and

c. injecting the gel polymer electrolyte solution into the free-standing polymer composite solid-state electrolyte to form an artificial layer.

5. The method of claim 4, wherein the liquid electrolytes include 1M LiFSI (Lithium bis fluorosulfonyl imide) or LiTFSI (Lithium bis trifluorosulfonyl imide) in carbonate solvents.

6. The method of claim 1, wherein the on-site coagulation technique comprises injecting a gel polymer liquid electrolyte solution onto the garnet composite polymer electrolyte membrane, and wherein the gel polymer solution becomes solid after standing for 15 minutes within a glove box.

7. The method of claim 1, wherein the method for preparing the cathode for the said solid-state lithium metal battery, comprising the steps of:

a. utilizing upto 5% of catholyte in lieu of polymer binder in the cathode preparation process, and wherein the catholyte acts as both a binder and enhances performance by improving conductivity and interfacial stability;

b. mixing upto 90% of active material selected from the group consisting of lithium iron phosphate (LFP), lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA), and activated carbon with a minimal amount of catholyte solution until a homogeneous mixture is achieved; and

c. casting the homogeneous mixture onto a copper foil and drying it in a vacuum oven to obtain a solvent-free coated sheet, followed by calendaring and punching the dried electrode sheets into a desired size.

8. The method of claim 7, wherein the catholyte comprises a polymer-lithium salt-garnet solution, and wherein the minimal amount of catholyte used is optimized to improve conductivity and interfacial stability while minimizing binder content.

9. The method of claim 7, wherein the active material comprises at least one of the following combinations:

a. lithium iron phosphate and activated carbon;

b. lithium nickel manganese cobalt oxide and activated carbon; and

c. lithium nickel cobalt aluminum oxide and activated carbon.

Dated this 08th day of March 2024

For, QPIVOLTA TECHNOLOGIES PRIVATE LIMITED
BY THEIR AGENT

(DR. BABITHA THARAPPAN)
IN/PA-1614
ATV-LEGAL