DESC:FIELD OF THE INVENTION
[0001] The present disclosure relates to an anode-free metal batteries. In particular, the present disclosure provides a separator assembly for anode-free metal batteries, specially for Li and Na metal batteries.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] A typical lithium-ion battery may offer a limited energy density range (180- 300 Wh/kg) depending on its cathode and anode materials and its loadings. In pursuing enhanced energy density, a renaissance in the exploration of lithium metal anodes has been revived. A lithium metal battery could offer ~1.5 times (or >550 Wh/kg) more energy density than the lithium-ion battery with a conventional graphite host material. However, the cells with metallic anodes experience severe issues in terms of performance stability and safety. Significant issues like inevitable continuous electrolyte degradation and growth of metal dendrites resulting in short circuits and thermal runaways make its practical implementation a daunting challenge. Cathodes are the source of lithium in practical commercial batteries. Thus, reducing the Li metal foil thickness in an anode would eventually increase the energy density. However, manufacturing Li metal foil (<100µm thickness) on the bulk scale while maintaining chemical purity is an expensive and arduous challenge.
[0004] Hence, there is a need to develop a separator assembly to overcome the drawbacks of the anode-free metal batteries.

OBJECTS OF THE INVENTION
[0005] An object of the present invention is to provide a separator assembly for anode-free metal battery.
[0006] Another object of the present invention is to provide an anode-free metal battery.
[0007] Still another object of the present invention is to provide a cell architecture.
[0008] Yet another object of the present invention is to achieve high columbic efficiency, high-rate performance, and highly stable long-term cycling of the anode-free Li and Na metal batteries.

SUMMARY OF THE INVENTION
[0009] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0010] The present disclosure relates to anode-free metal batteries. In particular, the present disclosure provides a separator assembly for anode-free metal batteries, specially for Li and Na metal batteries.
[0011] An aspect of the present disclosure is to provide a separator assembly for anode-free metal battery comprising: a separator A; and a separator B, wherein the separator B is sandwiched between two separators of type A.
[0012] Another aspect of the present disclosure is to provide an anode-free metal battery comprising: a negative electrode; a positive electrode; a separator assembly as defined above; and an electrolyte.
[0013] Still another aspect of the present disclosure is to provide a cell architecture comprising: a positive casing (1); spacers (2, 6); a copper foil (3); a separator assembly (4) as defined above; a lithium/sodium foil (5); and a negative casing (7); wherein the spacers (2, 6) are arranged between the positive casing (1) and the negative casing (7), the copper foil (3) and a lithium/sodium foil (5) are arranged between the spacers (2, 6) and the separator assembly (4) of the present disclosure is disposed between the copper foil (3) and the lithium/sodium foil (5).
[0014] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The following drawings form part of the present specification and are included to further illustrate aspects of the present invention. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0016] FIG. 1 illustrates a schematic representation of charge storing mechanism in an anode free cell.
[0017] FIG. 2 illustrates a separator assembly, according to an embodiment of the present disclosure.
[0018] FIG. 3 illustrates a schematic representation of a cell architecture, according to an embodiment of the present disclosure.
[0019] FIG. 4 illustrates an exemplary plot of performance of the cell architecture Li?Cu.
[0020] FIG. 5 illustrates another exemplary plot of performance of the cell architecture of celgard 2500, celgard 2325, whatman GF-A (comparative example) and customized separator of the present invention.
[0021] FIG. 6 illustrates another exemplary plot of performance of the cell architecture Na?Cu.
[0022] FIG. 7 illustrates another exemplary plot of performance of the cell architecture Na?Cu.
[0023] FIG. 8 illustrates another exemplary plot of performance of the cell architecture Na?C@Al.

DETAILED DESCRIPTION OF THE INVENTION
[0024] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered 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.
[0025] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0026] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[0027] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0028] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it is individually recited herein.
[0029] All processes described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0030] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0031] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0032] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0033] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description that follows, and the embodiments described herein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0034] It should also be appreciated that the present invention can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.
[0035] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0036] The present disclosure relates to anode-free metal batteries. In particular, the present disclosure provides a separator assembly for anode-free metal batteries, specially for Li and Na metal batteries.
[0037] An embodiment of the present disclosure provides a separator assembly for anode-free metal battery comprising: a separator A; and a separator B, wherein the separator B is sandwiched between two separators of type A.
[0038] In an embodiment, the separator A has a material of polyolefins-based polymer. The polyolefins-based polymer is selected from a group consisting of polyethylene, polypropylene, polyethylene oxide, polyethylene terephthalate, poly(tetrafluoroethylene), polyvinyl chloride, polyamide or their laminates/blends/composites layers, anodic aluminum oxide, nylon and combination thereof. The separator A has also multilayer combinations such as polypropylene/polyethylene/polypropylene (PP/PE/PP) composite membrane.
[0039] In an embodiment, the separator A has a porosity in the range from 10-90%, the pore size in the range from 20 nm to 500 nm and the thickness is in the range of 0.01 microns to 30 microns. Preferably, the separator A has a porosity in the range from 30-60%, the pore size in the range from 20 nm to 200 nm and the thickness is in the range of 0.1 microns to 30 microns.
[0040] In an embodiment, the separator B is selected from a group consisting of a glass fiber separator or a foam type material with compression mechanical behavior. Materials for this layer can be any highly porous material endowed with foam-like mechanical features.
[0041] In an embodiment, the separator B has a porosity in the range from 10-90%, pore size in the range of 0.1 to 5 microns and the thickness in the range of 100 microns to 500 microns. Preferably, the separator B has a porosity in the range from 30-60%, pore size in the range of 0.5 to 2 microns and the thickness in the range of 150 microns to 300 microns.
[0042] In an embodiment, the pore size of separator B is bigger than the pore size of separator A.
[0043] In an embodiment, the separator A and the separator B are further coated with a material is selected from a group consisting of metals, inorganic, organic and hybrid materials and the thickness of the material layer is in the range of 1 to 100 nm.
[0044] In an embodiment, the separator assembly is applied to symmetric cell, half-cell or full cell or metal batteries configuration with a varieties of cathode and anode materials.
[0045] Another embodiment of the present disclosure provides an anode-free metal battery comprising: a negative electrode; a positive electrode; a separator assembly as defined above; and an electrolyte.
[0046] In an embodiment, the negative electrode is lithium or sodium.
[0047] In an embodiment, the positive electrode is a copper foil.
[0048] In an embodiment, the electrolyte is an ether-based electrolyte, which included 1M lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI) salt in a mixture of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) with 2 wt.% of lithium nitrate (LiNO3) as an additive, 1M sodium hexafluorophosphate (NaPF6) salt in a diethylene glycol dimethyl ether (Diglyme), and 1M lithium sodium hexafluorophosphate (LiPF6) salt in a diethylene glycol dimethyl ether (Diglyme).
[0049] The present disclosure can be implemented in numerous ways, including a new system, or a device, or a cell size or architecture.
[0050] Still another embodiment of the present disclosure provides a cell architecture comprising: a positive casing (1); spacers (2, 6); a copper foil (3); a separator assembly (4) as defined above; a lithium/sodium foil (5); and a negative casing (7); wherein the spacers (2, 6) are arranged between the positive casing (1) and the negative casing (7), the copper foil (3) and a lithium/sodium foil (5) are arranged between the spacers (2, 6) and the separator assembly (4) is disposed between the copper foil (3) and the lithium/sodium foil (5).
[0051] In an embodiment, the cell architecture is selected from a coin cell, Swagelok cell, split cell, cylindrical, pouch or prismatic cell.
[0052] FIG. 1 illustrates a schematic representation of charge storing mechanism in an anode free cell. In the conventional lithium/sodium ion batteries, the charge is stored using host anode materials. Specifically, the charge may be stored either by intercalation, conversion, or alloying. In an anode-free battery, due to the absence of host materials, ions may be directly electroplated onto the surface of the current collector. The life of such anode free batteries may mainly be limited by the inefficient plating and stripping process, or the percentage of ion reversibility (coulombic efficiency). The performance and life cycle are thwarted by the dendritic, uneven, and high surface area growth and parasitic reactions.
[0053] Several strategies have been explored to achieve better performance of lithium metal plating/stripping efficiency. Among several approaches, liquid electrolyte optimization, metallic host design, and artificial coatings are commonly practiced modifications. In some cases, 3D printed copper mesh may be used to distribute the electric field and accommodate electroplated lithium metal into the structure, inhibiting the dendritic shorts. Similarly, copper 3D current collectors in the form of copper foam, copper mesh, macropores copper, copper nanowire, laser structured copper, etc., may be used for homogenously distributed lithium-ion flux guided deposition. Additionally, surface coating of copper current collector with lithophilic material such as multilayer graphene, nitrogen-doped graphene, ZnO quantum dots, silver nanoparticles, etc., may function as the nucleating host, thereby minimizing the overpotential and assisting with homogenous deposition.
[0054] The SEI layer may play a key role in development of a high-performance battery. Hence, electrolyte formulation may be important, involving modifying the electrolyte composition, concentrations, and incorporation of additives. In some cases, a high concentration electrolyte (4 M LiFSI-DME) may be used, which enables the high coordination between the salt and solvent and forms a favorable SEI layer at the anode interface. Similarly, localized high concentration (1.1 M LiDFOB–DMMP/HFE) electrolytes may be used exhibiting the aggregated ion pair solvation and leading to the desired and robust SEI.
[0055] Besides the addition of KNO3 additives in the carbonate electrolytes, the use of TEP as an electrolyte cosolvent to dissolve LiNO3 in 1M LiDFOB in EC/DMS electrolyte, and a dual-salt electrolyte system (2M LiFSI+ 1M LiTFSI) in DME/DOL (1:1, v/v) have also been explored to reduce the anion to form a stable SEI preferentially.
[0056] However, compared to the electrodes and the electrolyte engineering, separator and other cell component modification have not been focused proportionately.
[0057] The present disclosure relates to a new design, implementation, testing and optimization of a multi-layer separator system for use in an anode-free battery. The separator is a passive part of the system and it’s the critical material regulating the ion flow and battery safety. Some of the battery separators' significant required properties or functions are (1) Electrically insulating and mechanically robust by separating the contact between the positive and the positive plates; (2) High wettability and electrolyte absorption capability; (3) Resistance to the electrolyte and its electrochemical stability; (4) Maintaining a specific pore size that facilitates fast ionic transport properties; (5) Homogenously distributed pores throughout the membrane that could generate distributed electric fields; and (6) Mechanically robust and should provide resistance and void-free interfacial contacts between the electrodes.
[0058] An anode-free battery offers even higher energy density than metal batteries by eliminating the complete lithium metal anode and using merely a current collector. With the anode-free configuration, gravimetric energy density ~1.65 times (or >720Wh/kg) and volume energy density ~2.2 times that of the conventional lithium-ion battery can be achieved. This design of the battery reduces energy consumption, time, and cost. Anode-free batteries are currently more focused upon and believed to support the future energy demand outlook.
[0059] Presently, polyolefins and glass fiber-based porous separators are commonly used in lithium-ion or sodium-ion battery technology. Operating a lithium-ion battery using such separators may not cause significant degradation to the battery performance. However, employing these separators in the anode-free design may not be conducive. Separators may need to be compatible with the plating/stripping process. Many different types of coatings for the separator and multilayer structure have been explored for the anode-free technology. Table-1 lists the exemplary separators and a review of their respective performances in the sodium and lithium anode-free batteries.

Table 1: Exemplary separators and a review of their respective performances in the sodium and lithium anode-free batteries.
Sl. No Cells Materials and (Methods) Electrolyte Best Performance
Current Density
(mA/cm2) Capacity
(mAh/cm2) Cycle Life
(hour) Avg. CE
(%)
1. Li||Cu Al doped LLZTO
(Coated on PP) 1.0M LiTFSI in DOL/DME (1:1) + 5wt% LiNO3
0.5
1
900
--
2. Li||Cu Polydopamine/Gr-CMC
(Surface functionalised PP) 1.0 M LiPF6 in (EC: DEC) (1:1 by volume) 0.5 1 400 >98
3. Li||Cu Three dimensionally ordered macro-porous
Polyimide
1M LiPF6 in EC 1 0.5 200 87.5
4. Li||Cu Polyacrylamide grafted graphene oxide molecular brushes
(Blade coated on PP) 1.0M LiTFSI in DOL/DME (1:1) + 1 wt.% LiNO3 1 1 300 98%
5. Li||Cu Carbon nanotubes (CNT)/cellulose nanofiber (CNF) composite layers
(Coated both side of glass-fibre
(GF)/CNF composite membrane)
1M LiPF6 in EC: DEC (1:1)

0.75

0.75

~110

~80
6. Li||Cu PVDF with LLZTO
(Coating on PP) 1.0M LiTFSI in DOL/DME (1:1) + 5wt% LiNO3 1 1 600 97.5
7. Li||Cu mesoporous silica thin films
(Stacking on an anodic aluminium oxide (AAO)) 1 M LiTFSI in DOL/DME (1:1) 10 5 250 >99.9
8. Li||Cu Lignosulfonate
(Film on PP) 1.0M LiTFSI in DOL/DME (1:1) + 2wt% LiNO3 1 1 320 96
9. Li||Cu SnO2
(Sputtered on Celgard) 1.0M LiTFSI in DOL/DME (1:1) + 0.2wt% LiNO3 1 1 500 >97
10. Li||Cu Electro spun polyimide (PI) separators 1.2M LiPF6 in EC: DMC (1:1) 1 1 240 --
11. Li||Cu Zn nanoparticles
(Sputtered on PP) 1.0M LiTFSI in DOL/DME (1:1) + 2wt% LiNO3 1 1 400 --
12. Li||Cu GO/ZIF-8-modified separator (Coated on Celgard) 1M LiTFSI in DOL and DME (1:1 v/v) + 2 % mass ratio of LiNO3 1 3 ~342 >96.5
13. Li||Cu SiO microparticles with high binding
polyacrylate acid (SiO@PAA)
(Coated on PE) 1.0M LiTFSI in DOL/DME (1:1) + 1wt% LiNO3

1

1
400
~97.2
14. Na||Cu Dual Separator-dual electrolyte 1M NaPF6 sulfolane/FEC electrolyte (In GF)
And
1M NaPF6 Diglyme (In PP) 0.5
1 0.5
1 1120
420 97.22
95.60
15. Li||Cu Customized tri-layer arrangement
(Present application) 1.0M LiTFSI in DOL/DME (1:1) + 2wt% LiNO3 0.5
1
2 1
1
1 ~2700
800
500 98.52
97.9
97.38
Na||Cu Customised tri-layer arrangement
(Present application) 1M NaPF6 in Diglyme 0.5 1 ~2700 99.85
Na|| C@Al Customised arrangement
(Present application) 1M NaPF6 in Diglyme 0.5 1 >3500 99.82
[0060] The present disclosure provides a method of placing multiple separators and its arrangement after understanding the behavior of both polymer and glass-fiber separators in the anode-free coin cell. The cell with these customized separators exhibits improved performance. This process doesn’t require any pre- or post-modification on partitions. Further, the disclosure provides use of only bare current collector foils without pre-treatment.
[0061] FIG. 2 illustrates a separator assembly, according to an embodiment of the present disclosure. In some embodiments, the present disclosure further provides a separator that overcomes specific challenges associated with Li/Na metal plating/stripping process. The separator may provide high columbic efficiency, high-rate performance, and highly stable long-term cycling of the anode-free Li and Na metal batteries. The enhancement in the performance may be attributed to the improved interfacial contact between the separator and the electrode, which facilitates uniform ion transfer all through the plating area, leading to the non-dendritic growth of the metal.
[0062] A tri-layer arrangement of separators is proposed to achieve the above mentioned objective, which includes of a specific assembly of two separators, namely separator A and separator B. The separator B is sandwiched between two separators of type A. Separator A is a polypropylene separator. Materials for this layer can be selected from any of the polyolefins-based polymer separators that include, without limitations, polyethylene (PE), polypropylene (PP), or its multilayer combinations such as polypropylene/polyethylene/polypropylene (PP/PE/PP) composite membrane. The porosity of the separator can vary from 30-60%, and the pore size can range from 20nm to 200nm. The preferred thickness of this layer is less than 30 microns. Separator B is a commercial glass fiber separator. Materials for this layer can be any highly porous material endowed with foam-like mechanical features. The pore size of the separator layer B can be bigger than the pore size of layer A. The recommended pore size and thickness is around 0.5 – 2 microns and 150-300 microns, respectively.
[0063] Further, the disclosure provides a functioning lithium and sodium anode-free battery including lithium/sodium as the negative electrode, copper foil as the positive electrode, along with the separator, and the electrolyte. The arrangement of the separators provides stress compensation during metal plating/striping, homogeneous distribution of ionic flux, and better interfacial contacts between the separator and the electrode, resulting in long cycling with stable coulombic efficiency and fast charging. Keeping in view the performance, time and resources consumed, the process is instant, compelling, and convincing.
[0064] FIG. 3 illustrates a schematic representation of a cell architecture, according to an embodiment of the present disclosure. The cell architecture includes a positive casing (1) and a negative casing (7). Spacers (2, 6) are arranged between the positive and negative casings (1, 7). Further, a copper foil (3) and a lithium/sodium foil (5) are arranged between the spacers (2, 6). The separator assembly (4) of the present disclosure is disposed between the copper foil (3) and the lithium/sodium foil (5).
[0065] In some embodiments, separator A is not restrictive to only the Polypropylene-based Celgard 2500 separator. Any commercial polymer-based separator which is previously used in commercial batteries with porosity in the range of 10-90% and pore-size 20-500 nm may be used as layer A. Recommended thickness of layer A is <30µm. However, this could vary, and that directly influences the cell performance. Non-limiting examples for layer A are single or multiple layers comprised of polypropylene, polyethylene, polyethylene oxide, polyethylene terephthalate, poly(tetrafluoroethylene), polyvinyl chloride, polyamide or their laminates/blends/composites layers, anodic aluminum oxide, nylon etc.
[0066] In some embodiments, separator B is a glass fiber separator. The layer has foam-like features. Any variety of microporous membranes based on cellulose or its glass fiber composite having a pore size in the range of 0.1– 5 micron and porosity 10-90% may be used. The thickness could vary in the range 10-500 microns.
[0067] In some embodiments, the layers may be electronically isolating and ionically conducting to the metal ions in the separator.
[0068] In some embodiments, the layer arrangement includes three layers in the separator. The following modifications may be formulated as follows,
• Separator A on the top and the bottom of separator B need not be of the same features but may belong to the polymer-based separator.
• Number of separators above and below the separator B is not restrictive to just a single separator of A. Any asymmetry in the top and bottom of layer B can be incorporated with respect to the number of layers and quality.
[0069] Coating of other materials on layer A and B by sputtering, blade casting, spraying, chemical dipping, chemical dry, or wet process etc. may be applied. The thickness of each of such layers may vary from 1-100 nanometers. The materials for such layers may be any metals, Inorganic, organic and hybrid materials, or molecules/frameworks comprising metal-organic, organic-inorganic molecules.
[0070] In some embodiments, layer A may also be realized in the form of coating on both side of layer B by several methods like electrospinning, spin coating, spray coating or any other existing coating processes.
[0071] In some embodiments, the tri-layer or multiple layer arrangement may also be synthesized through co-extruding, hot-press laminating and other industrial processes.
[0072] In some embodiments, asymmetry in the form of arrangement of the separator may be realized.
[0073] In some embodiments, layer A on the side of charge storing electrode (for e.g., copper foil) will always be present, but other side of layer A may be omitted depending on the format of the battery.
[0074] In some embodiments, the sandwich arrangement of separator can be applied at any length of scale varying between 10-1000 microns
[0075] The ratio of thickness of separator B to separator A could vary between 0.5 to 20.
[0076] In some embodiments, in the lithium anode-free cell, the electrolyte can be defined as the mixture of a single or/with multiple lithium salt and a single solvent or/with various solvents, which helps in the mobility of the ion during charge and discharge.
[0077] In some embodiments, the electrolyte in the sodium anode-free cell can be defined as a mixture of sodium salt and solvent, which helps the ion's mobility during charge and discharge.
[0078] In some embodiments, the lithium and sodium metal foil thickness in the negative electrode of the anode-free cells is not restricted. It may vary according to the need and application.
[0079] In some embodiments, the positive electrode may consist of any metal or sheet on which lithium and sodium can be plated. It may be any organic/inorganic coated metal foil which may or may not form alloy with the metal ion,
[0080] In some embodiments, the separator may also be applied to any coin cell and another type of cell, for example, Swagelok cell, split cell, cylindrical, pouch or prismatic cell or any structure
[0081] In some embodiments, the separator may also be applied to anode-free full cell with any cathode Li/Na compounds.
[0082] In some embodiments, the separator may also be applied to Li-Li and Na-Na symmetric cell and also Li/ Na metal batteries configuration.
[0083] In some embodiments, the operating temperature of the battery may vary from 20 °C to 60 °C, or it could directly depend on the stability range of the electrolyte used.
[0084] In some embodiments, the operating pressure of the battery could vary from 1 to 200 MPa, or it could directly depend on the cell types, cell formats, cathode thickness and electrolyte applied for fabricating battery.
[0085] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
EXAMPLES
[0086] The present invention is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.
Example 1
[0087] For the separator A, two number polypropylene separator (Celgard 2500, pore size: 64 nm), and for separator B, one glass-fiber partition (Whatman GF-A, pore size: 1600nm) were kept in the electrolyte for proper soaking. To use in the coin cell (2032 type), the diameter of the separator was held at 19 mm. Separator B was sandwiched between layers of A. Since the separators are wet, they will stick together correctly when stacked due to the electrolyte's surface tension. The coin cell batteries (2032 type) were fabricated inside an Argon-filled glove box (O2 content < 0.1 ppm, H2O range < 0.1 ppm). Anode (negative) electrode was lithium metal (~100 microns), cathode (positive) electrode was copper foil (25 micron). An ether-based electrolyte was used, which included 1M lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI) salt in a mixture of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) with 2 wt.% of lithium nitrate (LiNO3) as an additive. The diameters of the anode and cathode electrodes were 10 mm and 14 mm, respectively. The separator, which was already soaked in the electrolyte, was placed between the positive and negative electrodes while assembling. Around 50 microliters of excess electrolyte were added later.
[0088] In order to test the cell's performance, a certain capacity of lithium was plated on copper foil by discharging the enclosure. Further, the charging step was programmed to see the reversibility percentage of the ions, and the processes are called plating and stripping, respectively. The processes continued until the cell failed and is called the life cycle. The percentage ratio of plated and stripped ions in each cycle was calculated as the coulombic efficiency of the cell.
[0089] FIG. 4 illustrates an exemplary plot of performance of the cell of example 1. A cell with the capacity of 1 mA/cm2 was plated at the current density of 0.5 mA/cm2, 1mA/cm2, and 2mA/cm2. The cells could run 2700 hours, 800 hours, and 420 hours, respectively.
Example 2
[0090] In this example, a comparative study of a commercial separator with the customized separator is demonstrated in a lithium anode-free half-cell. The customized separators were stacked according to example 1. For the commercial separators, polymer-based separators Celgard 2500, Celgard 2325, and glass fiber separator (GF-A) were punched into 19 mm diameter and soaked in electrolyte. Four-coin cell batteries 2032 type were prepared inside an Argon-filled glove box (O2 content < 0.1 ppm, H2O content < 0.1 ppm). Anode (negative) electrode was lithium metal (~100µm), cathode (positive) electrode was copper foil (25µm). The sizes of the anode and cathode electrodes were 10 mm and 14 mm, respectively. An ether-based electrolyte was used, which included 1M lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) salt in a mixture of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) with 2wt.% of lithium nitrate (LiNO3) as an additive. Four different cells were made by just varying the separator as mentioned below,
• Cell A: With polymer separator Celgard 2500;
• Cell B: With polymer separator Celgard 2325;
• Cell C: With a glass-fiber separator Whatman GF-A; and
• Cell D: With the customized separator.
[0091] In order to test the comparative performance of the customized separator with the commercial separators, the cells were tested for deposition current limit, starting from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12mA/cm2 for five cycles each.
[0092] FIG. 5 illustrates an exemplary plot of performance of the cells of example 2. The electrochemical data shows that the cells with single separators performed poorly at a high current rate. In contrast, the customized separator was able to sustain even at a very high current density of 12mA/cm2, which is helpful for the fast-charging battery.
Example 3
[0093] In this example, sodium plating/stripping is demonstrated on copper foil using the customized separator. The customized separators were stacked according to example 1. For sodium anode free cells, the coin cell batteries 2032 type were fabricated inside an Argon-filled glove box (O2 content < 0.1 ppm, H2O content < 0.1 ppm). Anode (negative) electrode was sodium metal (~100µm), cathode (positive) electrode was copper foil (25 micron). An ether-based electrolyte comprised of 1M sodium hexafluorophosphate (NaPF6) salt in a Diethylene glycol dimethyl ether (Diglyme) was used. The sizes of the anode and cathode electrodes were 10 mm and 14 mm, respectively. The separator that was soaked in the electrolyte, was placed between the positive and negative electrodes while assembling. Around 50 microliters of excess electrolyte were added later.
[0094] FIG. 6 illustrates an exemplary plot of performance of the cells of example 3. The cell was tested at the current density of 0.5mA/cm2, equivalent to 1mAh/cm2, plated to the Cu foil, and stripped back by charging it to 1V. The cell could run for a minimum of 2700 hours.
Example 4
[0095] In this example, sodium plating/stripping is demonstrated using a customized separator with another grade of A. For the separator A, two polypropylene separators (Celgard PP2068, pore size: 58 nm, thickness: 20 µm), and for layer B, one glass-fiber partition (Whatman GF-A, pore size:1600nm) were kept in the electrolyte for proper soaking. For use in the coin cell, the diameter of the separators was held at 19 mm. Layer B was then sandwiched between layers of separator type A. Since the separators are wet, they stick together correctly when stacked due to the electrolyte's surface tension. The fabrication of coin cell remains same as in example 3.
[0096] FIG. 7 illustrates an exemplary plot of performance of the cells of example 4. The cell was tested at the current density of 0.5mA/cm2, a capacity equivalent to 1mAh/cm2 was plated to the Cu foil and stripped back by charging it to 1V. The cell could run for a minimum of 2400 hours.
Example 5
[0097] In this example, sodium plating/stripping is demonstrated on commercial carbon-coated aluminum foil using a customized separator. The customized separators were stacked according to example 1. The coin cell batteries 2032 type were fabricated inside an Argon-filled glove box (O2 content < 0.1 ppm, H2O content < 0.1 ppm). Anode (negative) electrode was sodium metal (~100µm), and the cathode (positive) electrode was commercial carbon coated aluminum foil (20µm) from MTI. An ether-based electrolyte comprised of 1M lithium sodium hexafluorophosphate (LiPF6) salt in a Diethylene glycol dimethyl ether (Diglyme) was applied for coin cell fabrication. The sizes of the anode and cathode electrodes were 10 mm and 14 mm, respectively. The separator, which was already soaked in the electrolyte, was placed between the positive and negative electrodes while assembling. Around 50 microliters of excess electrolyte were added later.
[0098] FIG. 8 illustrates an exemplary plot of performance of the cells of example 5. The cell was tested at the current density of 0.5mA/cm2, a capacity equivalent to 1mAh/cm2 was plated onto the carbon-coated aluminum foil and stripped back by charging it to 1V. The cell could run for a minimum of 3500 hours.
[0099] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.
,CLAIMS:1. A separator assembly for anode-free metal battery comprising:
a separator A; and
a separator B,
wherein the separator B is sandwiched between two separators of type A.
2. The separator assembly as claimed in claim 1, wherein the separator A has a material of polyolefins-based polymer.
3. The separator assembly as claimed in claim 1, wherein the polyolefins-based polymer is selected from a group consisting of polyethylene, polypropylene, polyethylene oxide, polyethylene terephthalate, poly(tetrafluoroethylene), polyvinyl chloride, polyamide or their laminates/blends/composites layers, anodic aluminum oxide, nylon and combination thereof.
4. The separator assembly as claimed in claim 1, wherein the separator A has a porosity in the range from 10-90%, the pore size in the range from 20 nm to 500 nm and the thickness is in the range of 0.01 microns to 30 microns.
5. The separator assembly as claimed in claim 1, wherein the separator B is selected from a group consisting of a glass fiber separator or a foam type material with compression mechanical behavior.
6. The separator assembly as claimed in claim 1, wherein the separator B has a porosity in the range from 10-90%, pore size in the range of 0.1 to 5 microns and the thickness in the range of 100 microns to 500 microns.
7. The separator assembly as claimed in claim 1, wherein the pore size of separator B is bigger than the pore size of separator A.
8. The separator assembly as claimed in claim 1, wherein the separator A and the separator B are further coated with a material is selected from a group consisting of metals, inorganic, organic and hybrid materials and the thickness of the material layer is in the range of 1 to 100 nm.
9. The separator assembly as claimed in claim 1, wherein the separator assembly is applied to symmetric cell, half-cell or full cell or metal batteries configuration with a varieties of cathode and anode materials.
10. An anode-free metal battery comprising:
a negative electrode;
a positive electrode;
a separator assembly as claimed in claim 1; and
an electrolyte.
11. A cell architecture comprising:
a positive casing (1);
spacers (2, 6);
a copper foil (3);
a separator assembly (4) as claimed in claim 1;
a lithium/sodium foil (5); and
a negative casing (7);
wherein the spacers (2, 6) are arranged between the positive casing (1) and the negative casing (7), the copper foil (3) and a lithium/sodium foil (5) are arranged between the spacers (2, 6) and the separator assembly (4) is disposed between the copper foil (3) and the lithium/sodium foil (5).
12. The cell architecture as claimed in claim 11, wherein the cell architecture is selected from a coin cell, Swagelok cell, split cell, cylindrical, pouch or prismatic cell.