Patent Publication Number: US-2022223868-A1

Title: Anode-less lithium-sulfur (li-s) battery with lithium metal-free current

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority from U.S. Provisional Application No. 63/137,712 filed Jan. 14, 2021 and entitled “ANODE-LESS SOLID STATE LI-S BATTERIES,” the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to electrochemical energy storage systems and methods for manufacturing the same. Specifically, the present disclosure provides for manufacturing and using two-dimensional (2D) transition metal dichalcogenides (TMDs) to coat metals other than lithium for use in “anode-less” electrochemical energy storage systems. 
     BACKGROUND 
     There is a growing awareness that current lithium-ion battery technologies are reaching their limits in terms of storage and energy capabilities. However, there is still increasing demand for higher energy storage and longer lasting devices. For example, prevalent battery-based appliances (e.g., electric vehicles, mobile computing and telecommunications devices, aerospace transportation, specialized unmanned vehicles, etc.) require higher energy storage over conventional lithium-ion battery systems. This has challenged the research community to search for next-generation battery systems. 
     Lithium (Li) metal has been known as the “hostless” material to store Li ions (Li+) without the need for using intercalating and/or conducting scaffold techniques. For this reason, Li metal electrodes exhibit high theoretical specific capacity (˜3860 mAh g −1 ) and low redox potential (−3.04 V); thus, they are often regarded as the best choice to use for manufacturing/fabricating anodes for next-generation rechargeable Li batteries. However, Li metal anodes exhibit properties that cause multiple practical issues which inhibit their use. These properties are often associated with uncontrollable dendrite formation during repeated Li deposition/dissolution processes, which can lead to short circuiting the battery and potential overheating and fire. 
     Among various electrochemical energy storage systems, lithium-sulfur (Li—S) batteries have potential to be a next generation rechargeable battery because of their high theoretical energy density (approximately 2600 Wh kg − , which is five times higher than the approximately 387 Wh kW&#39; energy density of the conventional Li-ion batteries), low cost, and the natural abundance of sulfur and other chalcogens (e.g., selenium, tellurium, etc.). As an example, an Li—S battery may include an anode, cathode, separator, electrolyte, negative terminal, positive terminal, and casing. The anode may include a Li electrode coated with at least one layer of two-dimensional (2D) material, and the cathode may include sulfur powder as a sulfur electrode and/or a composite with carbon structures (e.g., carbon nanotubes (CNTs), graphene, porous carbons, free-standing three-dimensional (3D) CNTs, etc.). The separator may include polypropylene (PP), polyethylene (PE), or the like, and the electrolyte may include any number of electrolyte solutions (e.g., aqueous, non-aqueous, etc.) which may allow for transporting Li ions between the cathode and the anode. Example structures and operations of Li—S batteries are discussed in further detail in U.S. patent application Ser. No. 16/482,372, which is incorporated by reference herein. 
     While the low cost and abundance of sulfur make the concept of Li—S batteries alluring, there are several issues that generally prevent the widespread development of Li—S batteries. For example, sulfur is an insulating material, which provides for poor utilization of the active material and hinders electron transfer during the charge/discharge process. In addition, during the discharge process, Li may react with sulfur to form higher-order soluble polysulfides at the cathode, which creates shuttling of polysulfide between the anode and cathode during the cycling process. The shuttling effect may increase the internal resistance of the battery and contribute to capacity fading. Further, the formation of uncontrolled dendrites resulting from uneven deposition of Li metal may cause safety problems at higher C-rates as well as continuous evolution of a porous Li metal structure, which may lead to corrosion of the Li metal. While some approaches for Li—S batteries have been developed, issues of decreased cell efficiency and increased capacity fading still affect the performance of Li—S batteries when used with an Li anode. To address some of these issues, research has begun into using solid-state electrolytes (SSEs) in Li—S batteries. Although several types of SSEs have been tested in this context, issues of low ion flow, low Coulombic efficiency, and extensive dendrite growth have so far prevented widespread use of SSEs in Li—S batteries. 
     SUMMARY 
     Aspects of the present disclosure provide systems, devices, and methods of manufacturing lithium metal-free current collectors coated with two-dimensional (2D) transition metal dichalcogenide (TMD) materials (e.g., MoS 2 , MoSe 2 , MoWeTe 2 , BN—C, etc.) for use in place of lithium metal anodes in lithium-sulfur (Li—S) batteries. For example, instead of a typical lithium metal anode, a battery of the present disclosure may include a metal (e.g., aluminum or copper, as non-limiting examples), carbon material, or alloy (e.g., lithium alloy) current collector that operates as an anode for the battery. The current collector is “lithium metal-free,” such that the current collector does not include lithium metal (e.g., the current collector is formed from a different metal or from an alloy of lithium or another metal or from carbon materials and is not formed from metallic lithium). The 2D TMD material(s) act as a protective layer for the current collector to reduce or prevent lithium dendrite growth and to provide significant performance improvements as compared to other Li—S batteries. 
     In some aspects, one or more layers of 2D TMD material may be formed on a lithium metal-free current collector by deposition techniques such as sputtering or evaporation. The thickness of the layer(s) of the 2D TMD material may be controlled by controlling the deposition time, preferably such that the 2D TMD material has a thickness between 1 nanometer (nm) to 1000 nm. A dense, solid-state electrolyte (SSE) layer may be formed on the 2D TMD material. In some implementations, the SSE layer includes one or more layers of 2D TMD materials, preferably having a thickness between 10 nm and 200 micrometers (μm). Alternatively, the SSE layer may include other types of SSEs, such as garnet structures, perovskite structures, thiosilicate lithium super ionic conductor (thio-LISICON) materials, or solid polymer composite electrolytes, as non-limiting examples. A cathode may be provided in direct contact with the SSE layer. The cathode may include carbon material and sulfur powder or lithium sulfide (Li 2 S) powder. In some implementations, the carbon material includes structures (e.g., carbon nanotubes (CNTs) or the like), carbon nanofibers, or carbon powder that form a conductive matrix structure, and the sulfur powder or the Li 2 S powder is diffused within the conductive matrix structure. 
     The present disclosure describes systems, devices, and methods of manufacture of electrochemical energy storage systems that provide benefits compared to conventional Li—S batteries. For example, an anode-less battery described herein includes an Li-metal-free current collector coated with at least one layer of 2D TMD material instead of a conventional Li-metal anode. The protective layer(s) of 2D TMD material reduce or prevent Li-dendrite growth due to the 2D TMD material&#39;s high ion transport and uniform Li-ion deposition properties. Reducing or preventing Li-dendrite growth reduces corrosion of the battery and prevents (or reduces the likelihood of) safety issues at higher C-rates. Because the current collector is Li-metal-free, the source of Li-ions within the battery is Li 2 S and polysulfides in the cathode and/or the pre-lithiated SSE layer. Due to trapping of polysulfides within a carbon matrix structure of the cathode, the polysulfides are converted faster, which decreases polysulfide loss due to diffusion. This decrease in polysulfide loss extends the cycle life and improves the energy density of the battery, thereby providing significant performance improvements as compared to other Li—S batteries. Additionally, using an Li-metal-free current collector instead of a conventional lithium anode reduces the weight and cost of the battery. 
     In a particular aspect, a battery includes a lithium metal-free current collector coated with at least one layer of a two-dimensional (2D) transition metal dichalcogenide (TMD) material. The battery also includes a cathode. The battery further includes a solid-state electrolyte in physical contact with both the at least one layer of the 2D TMD material and the cathode. 
     In another particular aspect, a method includes providing a lithium metal-free material. The method also includes depositing an interlayer material on the lithium metal-free material. The method includes depositing at least one layer of a 2D TMD material on the interlayer material. The method further includes depositing a solid-state electrolyte on the at least one layer of the 2D TMD material. 
     The foregoing has outlined rather broadly the features and technical advantages of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific aspects disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the scope of the disclosure as set forth in the appended claims. The novel features which are disclosed herein, both as to organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a cross-sectional view of an example of a lithium metal-free current collector coated with at least one layer of a two-dimensional (2D) transition metal dichalcogenide (TMD) material according to one or more aspects; 
         FIG. 2  illustrates views of an example of a cathode according to one or more aspects; 
         FIG. 3  illustrates an example of a battery system implemented with a 2D TMD-coated lithium metal-free current collector according to one or more aspects; 
         FIG. 4  depicts an illustrative schematic for fabricating a 2D TMD-coated lithium metal-free current collector according to one or more aspects; 
         FIG. 5  depicts another illustrative schematic for fabricating a 2D TMD-coated lithium metal-free current collector according to one or more aspects; 
         FIG. 6  is a flow diagram illustrating an example of a method for manufacturing a battery system with a 2D TMD-coated lithium metal-free current collector according to one or more aspects; 
         FIG. 7A  depicts an illustrative schematic for a symmetric cell test during discharge cycling according to one or more aspects; 
         FIG. 7B  illustrates scanning electron microscopy (SEM) images of components of the symmetric cell test after discharge cycling according to one or more aspects; 
         FIG. 8A  depicts an illustrative schematic for a symmetric cell test during charge cycling according to one or more aspects; 
         FIG. 8B  illustrates SEM images of components of the symmetric cell test after charge cycling according to one or more aspects; and 
         FIG. 9  illustrates images of a 2D TMD-coated, lithium metal-free current collector after multiple discharge cycles according to one or more aspects. 
     
    
    
     It should be understood that the drawings are not necessarily to scale and that the disclosed aspects are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular aspects illustrated herein. 
     DETAILED DESCRIPTION 
     Aspects of the present disclosure provide systems, devices, and methods of manufacturing “anode-less” electrochemical energy storage systems, such as lithium-sulfur (Li—S) batteries. As referred to herein, an anode-less battery is a battery that omits a metallic lithium anode that is included in conventional Li—S batteries. Instead of the metallic lithium anode, a battery in accordance with one or more aspects includes a lithium metal-free current collector coated with two-dimensional (2D) transition metal dichalcogenide (TMD) materials, which provides performance improvements compared to conventional Li—S batteries that include metallic lithium anodes. 
     Referring to  FIG. 1 , an example of a lithium metal-free current collector coated with at least one layer of a 2D TMD material according to one or more aspects is shown as an electrochemical energy storage system  100 . In some implementations, the electrochemical energy storage system  100  is included or integrated in a battery, such as a Li—S battery. For example, the electrochemical energy storage system  100  may be part of an anode-less Li—S battery or an Li—S battery having a lithium metal-free anode. Although described as an anode-less Li—S battery, in some implementations the battery may not include any lithium, and thus may also be referred to as an anode-less solid state battery that is similar to an Li—S battery. As shown in  FIG. 1 , the electrochemical energy storage system  100  includes a current collector  102 , an optional interlayer  104 , one or more layers of 2D TMD material (referred to herein as the 2D TMD layers  106 ), a solid-state electrolyte (SSE)  110 , and a cathode  120 . A second current collector (not shown) may be coupled to the cathode  120 . 
     Conventional lithium-ion batteries (LIBs) typically include two electrodes (e.g., an anode and a cathode), a separator disposed between the two electrodes, an electrolyte that is in contact with (and may surround portions of) the two electrodes, and two current collectors. Each current collector is coupled to a respective electrode and operates as an electrical conductor between the respective electrode and external circuits, as well as a support for any materials that coat the respective electrode. The anode of LIBs is typically formed of metallic lithium, and the cathode is formed of a conductive material. The current collectors are typically formed of metal, such as copper or aluminum, in order to conduct electricity between the respective electrode and external circuits powered by the LIB. 
     In contrast to many conventional LIBs, the electrochemical energy storage system  100  is anode-less (e.g., the electrochemical energy storage system  100  does not include an anode coupled to the current collector  102 ). Instead of being coupled to a metallic lithium anode, the current collector  102  (in conjunction with one or more other elements) may operate as an anode and a current collector by conducting electricity from external circuits to the electrochemical energy storage system  100  for storage or conducting stored energy from the electrochemical energy storage system  100  to external circuits. The current collector  102  is a lithium metal-free (Li-metal-free) current collector, also referred to as a metallic lithium-free (metallic-Li-free) current collector. To illustrate, the current collector  102  does not include lithium metal (e.g., metallic lithium). In some implementations, the current collector  102  may include a different metal, such as copper or aluminum (e.g., the current collector  102  may include a copper metal collector or an aluminum metal collector), as non-limiting examples. In some other implementations, the current collector  102  may include metallic alloys. For example, the current collector  102  may include lithium alloy (e.g., an alloy of lithium instead of metallic lithium), such that the current collector  102  is includes a lithium alloy collector. In some other implementations, the current collector  102  may include carbon materials. 
     The 2D TMD layers  106  may coat, or be disposed on, the current collector  102 . For example, the 2D TMD layers  106  may be formed by a deposition process, such as sputtering, evaporation, or electrochemical deposition, as non-limiting examples. The 2D TMD layers  106  may include one or more 2D TMD materials, such as molybdenum disulfide (MoS 2 ), tungsten disulfide (WS 2 ), molybdenum ditelluride (MoTe 2 ), molybdenum diselenide (MoSe 2 ), tungsten diselenide (WSe 2 ), titanium disulfide (TiS 2 ), tantalum disulfide (TaSe 2 ), niobium diselenide (NbSe 2 ), nickel ditelluride (NiTe 2 ), boron nitride (BN), composites thereof, or the like, or these compounds (or alloys) combined with one or more additional elements, such as molybdenum tungsten disulfide (MoWS 2 ), molybdenum tungsten ditelluride (MoWTe 2 ), molybdenum sulfur ditelluride (MoSTe 2 ), molybdenum sulfur diselenide (MoSSe 2 ), molybdenum rhenium disulfide (MoReS 2 ), niobium tungsten disulfide (NbWS 2 ), vanadium molybdenum ditelluride (VMoTe 2 ), tungsten sulfur diselenide (WS Se 2 ), tungsten tellurium disulfide (WTeS 2 ), tin selenium disulfide (SnSeS 2 ), or the like. It is appreciated that different materials may provide for different performance. As a non-limiting example, MoS 2  provides strong adhesion to Li metal; it also is readily transformed to metallic phase to reduce impedance. The 2D TMD layers  106  may include a single layer or multiple layers of 2D TMD material. If the 2D TMD layers  106  include multiple layers, each layer of the 2D TMD layers  106  may include the same type of 2D TMD material or at least one layer may be a different type of 2D TMD material than at least one other layer. In some implementations, the 2D TMD layers  106  may have a thickness between approximately 1 nanometer (nm) and approximately 1000 nm, which may be controlled by controlling a deposition duration, as further described herein. Because the 2D TMD layers  106  coat (or are disposed on) the current collector  102  and therefore prevent direct contact between the current collector  102  and the SSE  110 , the 2D TMD layers  106  may act as a protective layer for the current collector  102 . 
     In some implementations, the optional interlayer  104  is included and is disposed between the current collector  102  and the 2D TMD layers  106 . In implementations in which there are multiple layers in the 2D TMD layers  106 , the interlayer  104  is disposed between the current collector  102  and a first deposed layer (e.g., a bottom layer in the orientation shown in  FIG. 1 ) of the 2D TMD layers  106 . In some implementations, the interlayer  104  includes metal particles or one or more thin films, such as thin films of magnesium (Mg), silver (Ag), zinc (Zn), aluminum (Al), carbon (C), silicon (Si), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), molybdenum (Mo), tellurium (Te), tantalum (Ta), titanium (Ti), or the like. The interlayer  104  may provide additional protection for the current collector  102  (e.g., by providing an additional layer between the current collector  102  and the SSE  110 ) and/or may promote adhesion with the 2D TMD layers  106 . The combination of the current collector  102 , the 2D TMD layers  106 , and optionally the interlayer  104 , may be referred to as an anode replacement structure, or a lithium metal-free anode. 
     The SSE  110  may be disposed on the 2D TMD layers  106 , as shown in  FIG. 1 . The SSE  110  may be deposited using sputtering, evaporation, or electrochemical deposition, as non-limiting examples, and, prior to deposition, the SSE  110  may include an aqueous electrolyte or a non-aqueous electrolyte. In some implementations, the SSE  110  may include one or more layers of 2D TMD material. For example, at least a portion of the SSE  110  may include MoS 2 , WS 2 , MoTe 2 , MoSe 2 , WSe 2 , TiS 2 , TaSe 2 , NbSe 2 , NiTe 2 , BN, composites thereof, or the like, or these compounds (or alloys) combined with one or more additional elements, such as MoWS 2 , MoWTe 2 , MoSTe 2 , MoSSe 2 , MoReS 2 , NbWS 2 , VMoTe 2 , WSSe 2 , WTeS 2 , SnSeS 2 , or the like. The 2D TMD material included in the SSE  110  may be the same as or different than the 2D TMD material included in the 2D TMD layers  106 . As a non-limiting example, the 2D TMD layers  106  may include MoS 2 , and the SSE  110  may include MoTe 2 . In some implementations in which the SSE  110  includes one or more layers of 2D TMD material, the SSE  110  may have a thickness between approximately 10 nm and approximately 1000 micrometers (μm), which may be controlled by controlling a deposition duration, as further described herein. In some other implementations, the SSE  110  may include other types of SSEs, such as one or more garnet structures, one or more perovskite structures, a thiosilicate lithium super ionic conductor (thio-LISICON) material, a solid polymer composite electrolyte, or the like. 
     The cathode  120  may include a carbon-based conductive material, such as, for example, carbon nanotube (CNT) paper, activated carbon, porous carbon structures or carbon nanotube structures in one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D) structures, carbon powder, carbon fibers, carbon nanofibers, graphite, graphene, graphene oxides, or other materials suitable for operations described herein. In some implementations, the cathode  120  includes a composite that includes carbon material in a matrix structure (e.g., a carbon matrix structure) and sulfur or lithium sulfide (Li 2 S) powders. For example, CNTs, carbon nanotubes, or carbon powder may form a conductive matrix structure, and the sulfur powder or the Li 2 S powder may be disposed within the conductive matrix structure. Illustrative examples of carbon matrix structures are shown herein with reference to  FIG. 2 . Additionally or alternatively, the cathode  120  may include a polysulfide, such as Li 2 S 8 , Li 2 S 6 , Li 2 S 4 , Li 2 S 2 , Li 2 S, or a mixture thereof, as non-limiting examples. 
     As described above, the electrochemical energy storage system  100  provides benefits compared to conventional LIBs and Li—S batteries. For example, the 2D TMD layers  106  reduce or prevent Li-dendrite growth at the current collector  102  due to the 2D TMD material&#39;s high ion transport and uniform Li-ion deposition properties. Reducing or preventing Li-dendrite growth reduces corrosion of the electrochemical energy storage system  100  (e.g., of the current collector  102 ), thereby preventing (or reducing a likelihood of) safety issues for the electrochemical energy storage system  100  at higher C-rates. Because the current collector  102  is Li-metal-free, the source of Li-ions within the electrochemical energy storage system  100  is Li 2 S and polysulfides in the cathode  120 , the SSE  110 , or both. The Li 2 S and polysulfides may be trapped within the carbon matrix structure of the cathode  120 , resulting in faster conversion of polysulfides, which decreases polysulfide loss due to diffusion. This decreased polysulfide loss extends the cycle life and improves energy density of the electrochemical energy storage system  100 , thereby providing significant performance improvements as compared to LIBs or other Li—S batteries. Additionally, using an Li-metal-free current collector (e.g., the current collector  102 ) instead of a conventional lithium anode reduces the weight and cost of the electrochemical energy storage system  100 . 
       FIG. 2  illustrates views of an example of a cathode according to one or more aspects. In some implementations, the cathode shown in  FIG. 2  may include or correspond to the cathode  120  of  FIG. 1 .  FIG. 2  depicts a molecular-structural view  200  of the cathode and a molecular-level view  210  of the cathode. Although described as a single cathode, the views  200  and  210  may correspond to different cathodes in other implementations. 
     In the molecular-structural view  200 , the cathode includes a conductive matrix structure  202  formed from carbon (or a carbon-based material), in addition to sulfur powder (representative sulfur  204 ) and ion-conductive particles (representative ion-conductive particle  206 ) that are disposed within the conductive matrix structure  202 . The conductive matrix structure  202  may be formed from a variety of carbon structures, such as CNTs, carbon nanofibers, or carbon powder, as non-limiting examples. As can be seen in  FIG. 2 , Li 2 S  208  (or polysulfide) particles that move toward or away from the cathode during charge cycles or discharge cycles may become trapped within the conductive matrix structure  202 . As illustrated in the molecular-level view  210 , sulfur molecules (e.g., representative sulfur  212 , which may include individual sulfur molecules and/or Li 2 S molecules that provide a source of Li-ions in the anode-free structure) and ion-conductive particles (e.g., representative ion-conductive particle  214 ) are disposed between adjacent carbon molecules (or carbon-based material molecules, such as representative carbon molecule  216 ) of the conductive matrix structure  202 . 
     Referring to  FIG. 3 , an example of a battery system implemented with a 2D TMD-coated lithium metal-free current collector according to one or more aspects is shown as a battery system  300 . In some implementations, the battery system  300  may include or correspond to the electrochemical energy storage system  100  of  FIG. 1 . In the implementation illustrated in  FIG. 3 , the battery system  300  (e.g., a Li—S battery (LSB) system) includes a current collector  302 , a cathode  306 , a separator  308 , an electrolyte  310 , a current collector  314 , and a casing  316 . The current collector  302  may be an Li-metal-free structure, for example, a collector made of Cu, Al, carbon materials, or a Li alloy, or other Li-metal-free conductive materials suitable for operations described herein. The current collector  302  may be coated with a 2D TMD layer  304  (or multiple 2D TMD layers), such as one or more layers of MoS 2 , WS 2 , MoTe 2 , MoSe 2 , WSe 2 , TiS 2 , TaSe 2 , NbSe 2 , NiTe 2 , BN, or the like, as non-limiting examples. Although not illustrated, an interlayer may be disposed between the current collector  302  and the 2D TMD layer  304 , similar to the interlayer  104  described with reference to  FIG. 1 . The cathode  306  may include CNT paper, activated carbon, porous carbon structures in 1D, 2D, or 3D structures, carbon powder, carbon fibers, carbon nanofibers, graphite, graphene, graphene oxides, or other materials suitable for operations described herein. In some implementations, the cathode  306  includes a composite that includes carbon material in a matrix structure (e.g., a carbon structure such as carbon powder, CNTs, carbon nanofibers, or the like) and sulfur or Li 2 S powders. 
     During operation of the battery system  300 , ion flow  320  illustrates the flow of discharging ions (e.g., Li+, etc.) from the current collector  302 , and ion flow  322  illustrates the flow of charging ions (e.g., Li+, etc.) from the cathode  306 . The separator  308  may be positioned between the current collector  302  and the cathode  306  and may include, for example, polypropylene (PP), polyethylene (PE), other materials suitable for operations discussed herein, or combinations thereof. The separator  308  preferably has pores through which ion flows  320  and  322  may pass. The electrolyte  310  may be positioned on either side of the separator  308 , between the current collector  302  and the cathode  306 , and may include any number of electrolyte solutions (e.g., aqueous, non-aqueous, etc.) which may allow for transporting ion flows  320  and  322  between the current collector  302  and the cathode  306 . For example, the electrolyte  310  may include various lithium salts (e.g., LiPF 6 , LiClO 4 , LiH 2 PO 4 , LiAlCl 4 , LiBF 4 , etc.) or other electrolyte material suitable for operations discussed herein. In some implementations, the electrolyte  310  may include one or more layers of a 2D TMD material. In some other implementations, the electrolyte  310  may include a type of SSE, such as one or more garnet structures, one or more perovskite structures, a thio-LISICON material, a solid polymer composite electrolyte, or the like. 
     The current collector  302  may operate as (or be used as a replacement for) a conventional metallic Li anode, and the current collector  314  may be attached to cathode  306 . In some implementations, the current collectors  302  and  314  may extend, through the casing  316 , from an interior region of the casing  316  to an exterior region of the casing  316 . Additionally, the current collectors  302  and  314  may correspond to negative and positive voltage terminals, respectively, and comprise conductive materials. As a non-limiting example, the current collector  302  may include copper metal and the current collector  314  may include aluminum metal. The casing  316  may include a variety of cell form factors. For example, implementations of the battery system  300  may be incorporated in a cylindrical cell (e.g., 13650, 18650, 18500, 26650, 21700, etc.), a polymer cell, a button cell, a prismatic cell, a pouch cell, or other form factors suitable for operations discussed herein. Further, one or more cells may be combined into larger battery packs for use in a variety of applications (e.g., cars, laptops, etc.). In certain implementations, microcontrollers and/or other safety circuitry may be used along with voltage regulators to manage cell operation and may be tailored to specific uses of the battery system  300 . 
     Referring to  FIG. 4 , a schematic for fabricating a 2D TMD-coated Li-metal-free current collector according to one or more aspects is shown a system  400 . The system  400  is configured to perform a sputtering process to fabricate the 2D TMD-coated Li-metal-free current collector. In some implementations, the system  400  may be used to fabricate one or more components of the electrochemical energy storage system  100  of  FIG. 1  or the battery system  300  of  FIG. 3 . As shown in  FIG. 4 , the system  400  includes a substrate  402  and target materials  404  for use during sputtering. The substrate  402  includes Li-metal free material(s), such as Cu, Al, carbon materials, or Li alloys as non-limiting examples. The target materials  404  include one or more 2D TMD materials, such as MoS 2 , WS 2 , MoWS 2 , or any of the other 2D TMD materials described herein. 
     During fabrication, one or more layers of 2D TMD material (e.g., the target materials  404 ) may be formed on the substrate  402  by sputtering  410 . In some implementations, the sputtering  410  may include forming an interlayer on the substrate  402  prior to deposition of the target materials  404 . For example, the sputtering  410  may include sputtering metallic materials as an interlayer, such as, for example, Si, Ge, Sn, Pb, Sb, Al, Ti, Ta, Mo, Nb, W, Hf, Ni, Co, Cd, and/or other metals suitable for forming Li alloys when a battery is cycling. After the interlayer is formed, the sputtering  410  includes sputtering the target materials  404  on a metallic-coated surface of the substrate  402  to form one or more layers of 2D TMD material. Using the target materials  404  (e.g., any of the aforementioned materials) as the target material for magnetron radio frequency (RF) sputtering, one or more successive layers of 2D TMD material may be deposited onto a current conducting material (e.g., the substrate  402  and the optional interlayer) to produce a 2D TMD-coated current collector. In some implementations, inert gas  412  such as, for example, argon plasma or pure (99.999% purity) argon, helium, or other gases with low reactivity with other substances may be fed into the system  400  via a gas inlet valve (not depicted) during the sputtering  410 . The sputtering  410  preferably occurs within the system  400  (e.g., within a chamber) at temperatures set between room temperature and approximately 500° C. In some implementations, the chamber may be evacuated, before each sputtering run, to a vacuum level of, e.g., ≤1×10 −6  Torr without plasma. In some implementations, the sputtering  410  may start when an RF power of 5-100 W is applied to the target materials  404  and one or more layers of transition metals alloys are consequently deposited on the substrate  402 . The sputtering duration of the sputtering  410  may be varied from 1 second to 500 seconds to adjust the thickness of the 2D TMD layer(s) deposited on the current collector (e.g., the substrate  402 ). For example, the sputtering duration may be controlled to result in a thickness of between approximately 1 nm and approximately 1000 nm. In some implementations, prior to deposition on the current collector, the target materials  404  may be pre-sputtered in the chamber for a pre-determined time to stabilize the deposition process. Although  FIG. 4  illustrates a sputtering process, in some other implementations, the 2D TMD layer(s) may be formed (e.g., deposited) using an evaporation process or another type of deposition process. 
     In implementations in which an SSE is to be included in a battery with the 2D TMD-coated Li-metal-free current collector and includes one or more layers of 2D TMD material, at least a portion of the SSE may be formed using the same process described above with reference to  FIG. 4 . For example, the 2D TMD-coated current collector formed as shown in  FIG. 4  may be placed on the substrate  402 , and one or more layers of 2D TMD material may be deposited on the 2D TMD-coated current collector using the sputtering  410  described above. These one or more layers of 2D TMD material may be the same or different than the 2D TMD material that coats the current collector and may serve as at least a portion of an SSE. Alternatively, at least a portion of the SSE may be formed by an evaporation process or an electrochemical deposition process, as further described herein with reference to  FIG. 5 . In some other implementations, the SSE includes one or more garnet structures, one or more perovskite structures, a thio-LISICON material, a solid polymer composite electrolyte, or the like, and formation of the SSE may be accomplished by slip coating or spraying the 2D TMD-coated current collector, followed by a drying and sintering process. 
     Referring to  FIG. 5 , another schematic for fabricating a 2D TMD-coated Li-metal-free current collector according to one or more aspects is shown a system  500 . The system  500  is configured to perform an electrochemical deposition process to fabricate the 2D TMD-coated Li-metal-free current collector. In some implementations, the system  500  may be used to fabricate one or more components of the electrochemical energy storage system  100  of  FIG. 1  or the battery system  300  of  FIG. 3 . As shown in  FIG. 5 , the system  500  includes an electrode  502  (e.g., a counter electrode), a current collector material  504 , and a reference electrode  510 . 
     During fabrication, a material to be used as a current conductor, such as Cu, Al, carbon materials, or Li alloys, as non-limiting examples, may be provided as the current collector material  504 , and metal or metallic compounds or alloys may be used as the electrode  502  (e.g., the counter electrode) and the reference electrode  510 . As a particular, non-limiting example, the electrode  502  may include platinum (Pt), the current collector material  504  may include Cu or a Li alloy, and the reference electrode  510  may include silver (Ag) or silver chloride (AgCl). In some implementations, an aqueous electrolyte solution, such as between approximately 1 millimol (mM) and approximately 1 mol (M) of ammonium tetrathiomolybdate ((NH 4 ) 2 MoS 4 ) dissolved in de-ionized (DI) water, may be added to at least partially surround the electrode  502 , the current collector material  504 , and the reference electrode  510 . A bias voltage, such as between 1 v/cm and 100 v/cm, may be applied to the electrode  502 , the current collector material  504 , and the reference electrode  510  to cause the aqueous electrolyte to reduce on a surface of the current collector material  504  to form (e.g., dispose) one or more layers of 2D TMD material  506 . During at least one test run, at −1.0 v versus the reference electrode  510  (e.g., the Ag or AgCl reference), the (NH 4 ) 2 MoS 4  in the aqueous solution starts to reduce on the carbon materials by forming MoS 4   2−  ions, which get further reduced to a deposit of MoS 2  particles. During the at least one run, at low solution concentration of (NH 4 ) 2 MoS 4  (e.g., 10 −3  mM to 10 3  mM), the reduction process of MoS 4   2−  on the electrode  502  can be controlled by an applied electric field, such as from 1 v/cm to 100 v/cm. A deposition time of the process may be controlled from between 1 sec and 10 minutes to control a thickness of the one or more layers of 2D TMD material  506  (e.g., the MoS 2  film). For example, the deposition time may be controlled such that the thickness of the one or more layers of 2D TMD material  506  is between approximately 1 nm and 1000 nm. 
     In implementations in which an SSE is to be included in a battery with the 2D TMD-coated Li-metal-free current collector and the SSE includes one or more layers of 2D TMD material, at least a portion of the SSE may be formed using the same process described above with reference to  FIG. 5 . For example, the 2D TMD-coated current collector formed as shown in  FIG. 5  may be placed in the system  500  (e.g., in place of the current collector material  504 ), and one or more layers of 2D TMD material may be deposited on the 2D TMD-coated current collector using the reduction process described above. These one or more layers of 2D TMD material may be the same or different than the 2D TMD material (e.g., the one or more layers of 2D TMD material  506 ) that coats the current collector and may serve as at least a portion of an SSE. Alternatively, at least a portion of the SSE may be formed by an evaporation process or a sputtering process, as further described above with reference to  FIG. 4 . In some other implementations, the SSE includes one or more garnet structures, one or more perovskite structures, a thio-LISICON material, a solid polymer composite electrolyte, or the like, and formation of the SSE may be accomplished by slip coating or spraying the 2D TMD-coated current collector, followed by a drying and sintering process. 
     Referring to  FIG. 6 , a flow diagram of an example of a method for manufacturing a battery system with a 2D TMD-coated lithium metal-free current collector according to one or more aspects is shown as a method  600 . In some implementations, the operations of the method  600  may be stored as instructions that, when executed by one or more processors (e.g., one or more processors of a fabrication system, which may include or correspond to the system  400  of  FIG. 4 , the system  500  of  FIG. 5 , or components thereof), cause the one or more processors to perform the operations of the method  600 . In some implementations, the method  600  may be performed to manufacture a Li—S battery, such as the electrochemical energy storage system  100  of  FIG. 1  or the battery system  300  of  FIG. 3 . 
     The method  600  includes providing a lithium metal-free material, at  602 . For example, the Li-metal-free material may include or correspond to the current collector  102  (e.g., Cu, Al, carbon materials, or Li alloy, as non-limiting examples) of  FIG. 1 . The method  600  includes depositing an interlayer material on the lithium metal-free material, at  604 . The interlayer material may include Si, Ge, Sn, Pb, Sb, Al, Ti, Ta, Mo, Nb, W, Hf, Ni, Co, or Cd, as non-limiting examples, and may be used to form an interlayer on the Li-metal-free material, which may include or correspond to the interlayer  104  of  FIG. 1 . The interlayer may improve the deposition of Li on the current collector during battery cycling. In some implementations, forming the interlayer is optional. The method  600  includes depositing at least one layer of a 2D TMD material on the interlayer material (or the lithium metal-free material if the interlayer is omitted), at  606 . For example, the at least one layer of the 2D TMD material may include or correspond to the 2D TMD layers  106  of  FIG. 1 . The method  600  includes depositing a solid-state electrolyte on the at least one layer of the 2D TMD material, at  608 . For example, the solid-state electrolyte may include or correspond to the SSE  110  of  FIG. 1 . 
     In some implementations, depositing the at least one layer of the 2D TMD material may include at least one of sputtering and evaporation. For example, the sputtering may include or correspond to the sputtering  410  of  FIG. 4 . In some such implementations, the sputtering uses Ar plasma, as described with reference to  FIG. 4 . Additionally or alternatively, the sputtering may be performed between room temperature and 500° C., as described with reference to  FIG. 4 . Additionally or alternatively, a deposition power of the sputtering may be between 5-100 W and a deposition time of the sputtering may be between 1-500 seconds, and the at least one layer of the 2D TMD material may have a thickness of approximately 1 nm to approximately 1000 nm, as described with reference to  FIG. 4 . 
     In some implementations, the solid-state electrolyte includes one or more layers of a 2D TMD material. In some such implementations, depositing the solid-state electrolyte includes at least one of sputtering, evaporation, or electrochemical deposition. For example, the sputtering may include or correspond to the sputtering  410  of  FIG. 4 , or the electrochemical deposition may include or correspond to the electrochemical deposition process described with reference to  FIG. 5 . In some such implementations, the one or more layers of the 2D TMD material have a thickness of approximately 1 nm to approximately 200 μm. 
     In some implementations, the solid-state electrolyte includes one or more garnet structures, one or more perovskite structures, a thio-LISICON material, or a solid polymer composite electrolyte. In some such implementations, depositing the solid-state electrolyte includes slip-coating or spraying the solid-state electrolyte on the at least one layer of the 2D TMD material, and performing a drying and sintering process on the solid-state electrolyte. 
     In some implementations, the method  600  may further include providing a cathode, forming a matrix structure from a carbon material on the cathode, depositing sulfur powder or Li 2 S powder on the matrix structure, and disposing the cathode in physical contact with the solid-state electrolyte. For example, the cathode may include or correspond to the cathode  120  of  FIG. 1 . The cathode may include (or have formed thereon) a conductive matrix structure of carbon material, such as the conductive matrix structure  202 , as further described above with reference to  FIG. 2 . Additionally or alternatively, the cathode may include a polysulfide, such as Li 2 S 8 , Li 2 S 6 , Li 2 S 4 , Li 2 S 2 , Li 2 S, or a mixture thereof, as non-limiting examples. 
     As described above with reference to  FIG. 6 , the method  600  may enable manufacture of a battery (e.g., a Li—S battery) that includes a Li-metal-free current collector instead of a metallic Li anode. Such a battery may experience reduced Li-dendrite growth and provide improved battery performance, such as enhanced cycle life and energy density, as compared to other Li—S batteries or LIB s. 
     Experimental Testing of 2D TMD-Coated, Li-Metal-Free Current Collectors 
     The following describes experimental implementations of 2D TMD-coated, Li-metal-free current collectors for use in Li—S batteries. The discussion further illustrates possible performance advantages afforded by the 2D TMD-coated, Li-metal-free current collectors, and batteries including the same, according to aspects described herein. It should be appreciated by those skilled in the art that the present application is not intended to be limited to the particular experimental implementations and results described below. 
     In an experimental implementation, an Li-metal-free current collector is formed from Cu and coated in MoS 2  (e.g., a 2D TMD material). The MoS 2 -coated Cu current collector is displaced within a half-cell for performing symmetric cell tests. The MoS 2 -coated Cu current collector is configured as a Li-metal-free anode, and the half-cell includes a counter electrode formed from MoS 2 -coated Li. A schematic illustration for a symmetric cell test during discharge cycling according to one or more aspects is provided in  FIG. 7A .  FIG. 7A  illustrates a half-cell  700  that includes a counter electrode  702  (e.g., Li+metal), a MoS 2  coating  704  (e.g., one or more layers of a 2D TMD material), a current collector  706  (e.g., Cu metal), and a MoS 2  coating  708  (e.g., one or more layers of a 2D TMD material). Prior to testing, the MoS 2  coating  708  is uniformly, or substantially uniformly, distributed on the current collector  706 . During discharge cycling, as shown in  FIG. 7A , Li metal is reduced from the counter electrode  702  and moves to the MoS 2 -coated Cu for storage between the MoS 2  coating  708  and the current collector  706 . After discharging, a thickness of the Li metal of the counter electrode  702  may be reduced from approximately 120 μm to approximately 110 μm, and the Li metal stored between the MoS 2  coating  708  and the current collector  706  may increase from 0 μm (e.g., the combination of the MoS 2  coating  708  and the current collector  706  is initially Li-metal-free) to approximately 10 μm.  FIG. 7B  shows a scanning electron microscopy (SEM) image  720  of the counter electrode  702  and the MoS 2  coating  704  and an SEM image  730  of the current collector  706  and the MoS 2  coating  708  after the discharge cycling. The SEM image  720  includes a side view  722  of MoS 2  and a side view  724  of Li, and the SEM image  730  includes a side view  732  of MoS 2 , a side view  734  of Cu, and a side view  736  of transferred Li. In the example of  FIG. 7B , the side view  736  of transferred Li has a thickness of approximately 10 μm. 
     A schematic illustration for a symmetric cell test during charge cycling according to one or more aspects is provided in  FIG. 8A .  FIG. 8A  illustrates a half-cell  800  that includes a counter electrode  802  (e.g., Li +  metal), a MoS 2  coating  804  (e.g., one or more layers of a 2D TMD material), a current collector  806  (e.g., Cu metal), and a MoS 2  coating  808  (e.g., one or more layers of a 2D TMD material). As described above with reference to  FIGS. 7A-7B , after discharge cycling, approximately 10 μm of Li metal is stored between the MoS 2  coating  808  and the current collector  806 . During charge cycling, as shown in  FIG. 8A , the stored Li metal is returned to the counter electrode  802 . After charging, a thickness of the Li metal of the counter electrode  802  increases from approximately 110 μm to approximately 120 μm, and the Li metal stored between the MoS 2  coating  808  and the current collector  806  is removed (e.g., the thickness is substantially 0 μm).  FIG. 8B  shows a SEM image  820  of the counter electrode  802  and the MoS 2  coating  804  and a SEM image  830  of the current collector  806  and the MoS 2  coating  808  after the charge cycling. The SEM image  820  includes a side view  822  of MoS 2  and a side view  824  of Li (which has returned to a thickness of approximately 120 μm), and the SEM image  830  includes a side view  832  of MoS 2 , a side view  834  of Cu, and a side view  836  of stored Li (which is reduced to substantially 0 μm/is substantially removed). 
       FIG. 9  illustrates images of the 2D TMD-coated, Li-metal-free current collector (e.g., the MoS 2 -coated Cu of  FIGS. 7A-8B ) after multiple discharge cycles. In the particular example of  FIG. 9 , the multiple discharge cycles include at least ten discharge cycles. As shown in  FIG. 9 , a cross-sectional SEM image  900  of the MoS 2 -coated Cu illustrates the structural differences between the layers of Li+, MoS 2 , and Cu. During subsequent discharge and charge cycles, the thickness of the Li returns to approximately the initial thickness, such as varying between approximately 118 μm and approximately 105 μm, at the MoS 2 -coated Cu, removing (e.g., substantially removing) the Li metal stored at the MoS 2 -coated Li.  FIG. 9  also includes an energy-dispersive X-ray spectroscopy (EDS) image  910  of the Cu, an EDS image  920  of the Mo, and an EDS image  930  of the S in the MoS 2 -coated Cu. During at least the first ten discharge and charge cycles, the MoS 2  film remains stable (e.g., a thickness remains substantially the same) on the Cu and Li metal. 
     Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to some other implementations without departing from the spirit or scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein. 
     Additionally, a person having ordinary skill in the art will readily appreciate, the terms “upper” and “lower” are sometimes used for ease of describing the figures, and indicate relative positions corresponding to the orientation of the figure on a properly oriented page, and may not reflect the proper orientation of any device as implemented. 
     Certain features that are described in this specification in the context of separate implementations also may be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also may be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination may in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one more example processes in the form of a flow diagram. However, other operations that are not depicted may be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations may be performed before, after, simultaneously, or between any of the illustrated operations. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, some other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results. 
     As used herein, including in the claims, various terminology is for the purpose of describing particular implementations only and is not intended to be limiting of implementations. For example, as used herein, an ordinal term (e.g., “first,” “second,” “third,” etc.) used to modify an element, such as a structure, a component, an operation, etc., does not by itself indicate any priority or order of the element with respect to another element, but rather merely distinguishes the element from another element having a same name (but for use of the ordinal term). The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically; two items that are “coupled” may be unitary with each other. the term “or,” when used in a list of two or more items, means that any one of the listed items may be employed by itself, or any combination of two or more of the listed items may be employed. For example, if a composition is described as containing components A, B, or C, the composition may contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination. Also, as used herein, including in the claims, “or” as used in a list of items prefaced by “at least one of” indicates a disjunctive list such that, for example, a list of “at least one of A, B, or C” means A or B or C or AB or AC or BC or ABC (that is A and B and C) or any of these in any combination thereof. The term “substantially” is defined as largely but not necessarily wholly what is specified—and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel—as understood by a person of ordinary skill in the art. In any disclosed aspect, the term “substantially” may be substituted with “within [a percentage] of” what is specified, where the percentage includes 0.1, 1, 5, and 10 percent; and the term “approximately” may be substituted with “within 10 percent of” what is specified. The phrase “and/or” means and or. 
     Although the aspects of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit of the disclosure as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular implementations of the process, machine, manufacture, composition of matter, means, methods and processes described in the specification. As one of ordinary skill in the art will readily appreciate from the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or operations, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding aspects described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or operations.