Polyacrylonitrile-based gel polymer electrolyte membrane separators for lithium-sulfur batteries

Abstract

Polyacrylonitrile (PAN)-based gel polymer electrolyte (GPE) membrane separators for lithium-sulfur batteries. The PAN-based GPE membrane separators may include a freestanding electrospun nonwoven mat of PAN-based nanofibers. The PAN-based GPE membrane separators may include one or more inorganic nanoparticles dispersed therein. A lithium-sulfur battery including a freestanding PAN-based GPE membrane separator may be characterized by an electrolyte to sulfur (E / S) ratio of less than 4 µL / mg and a ratio of an areal capacity of the anode to that of the cathode (N / P ratio) of less than 2. A thickness of an example PAN-based GPE membrane separator may be less than 30 µm.

Description

POLYACRYLONITRILE-BASED GEL POLYMER ELECTROLYTE MEMBRANESEPARATORS FOR LITHIUM- SULFUR BATTERIESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Patent Application claims priority to U.S. Provisional Patent Application No. 63 / 559,397 entitled “POLYACRYLONITRILE-BASED GEL POLYMER ELECTROLYTE MEMBRANE SEPARATORS FOR LITHIUM-SULFUR BATTERIES” and filed on February 29, 2024, which is assigned to the assignee hereof. The disclosures of all prior Applications are considered part of and are incorporated by reference in this Patent Application.TECHNICAL FIELD

[0002] This disclosure relates generally to batteries, and, more particularly, to lithiumsulfur batteries that can provide high specific energy and energy density combined with long cycle life.DESCRIPTION OF RELATED ART

[0003] Recent developments in batteries allow consumers to use high-specific energy batteries such as Li-sulfur batteries in many new applications. However, further improvements in battery technology are desirable.SUMMARY

[0004] This summary is provided to introduce in a simplified form a selection of concepts that are further described below in the 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 limit the scope of the claimed subject matter.

[0005] In some implementations, a lithium-sulfur battery may include a free-standing anode including one or more of a lithium anode or a lithium- alloy anode, a cathode including one or more of sulfur, sulfur composites, or a sulfurized polymer, supported in a carbon material, a freestanding polyacrylonitrile (“PAN”)-based gel polymer electrolyte (“GPE”) membrane separator, and a liquid electrolyte. In some instances, the liquid electrolyte may include a fluorinated ether electrolyte. In some instances, an electrolyte to sulfur (“E / S”) ratio in an example lithium-sulfur battery including a freestanding PAN-based GPE membrane may be less than 4 pL / mg. In some other instances, a ratio of an areal capacity ofthe anode to that of the cathode (“N / P ratio”) in an example lithium-sulfur battery including a freestanding PAN-based GPE membrane may be less than 2. In some instances, a thickness of an example PAN-based GPE membrane may be less than 30 m. In some other instances, a porosity of an example PAN-based GPE membrane separator may be about 50%.

[0006] In some implementations, a freestanding PAN-based GPE membrane separator may include a nonwoven mat of PAN-based nanofibers made by electrospinning. In some instances, an average diameter of the PAN-based nanofibers may between about 0.15 pm and about 0.5 pm.

[0007] In some implementations, a lithium-sulfur battery including a freestanding PAN- based GPE membrane separator may include a lithium-magnesium (“Li-Mg”) alloy. In some instances, an example Li-Mg alloy may include a 90 wt% Li-10 wt% Mg alloy.

[0008] In some implementations, the cathode carbon material in a lithium- sulfur battery including a freestanding PAN-based GPE membrane separator may include carbon agglomerates characterized by a Raman spectroscopy signature having an ID / IG ratio between approximately 0.95 and 1.05. In some instances, the porous carbon agglomerates may be characterized by a Brunauer-Emmett-Teller (“BET”) surface area between approximately 50 m2 / g and 300 m2 / g measured using nitrogen gas. In some other instances, the porous carbon agglomerates may be characterized by an electrical conductivity of between about 500 S / m and 20,000 S / m when compressed at a pressure of about 12,000 pounds per square inch (psi).

[0009] In some implementations, a freestanding anode associated with a lithium-sulfur battery may include a dual-phase alloy including a Li-Mg alloy phase and a Li-x alloy phase. In some aspects, the Li-x alloy phase may include alloys of lithium and one of calcium, boron, tin, aluminum, indium, bismuth, antimony, or zinc. In some other aspects, the Li-x alloy phase may include a LizCa (also referred to herein as CaLiz) alloy phase. In some instances, the weight ratio of the Li-Mg alloy phase to the LizCa alloy phase may be between about 0.1 and about 20.

[0010] In some implementations, a dual-phase alloy including a Li-Mg alloy phase and a LizCa alloy phase may include a lithium content of between about 55 wt% and about 75 wt%, a magnesium content of between about 15 wt% and about 30 wt% and a calcium content of between about 2 wt% and about 30 wt%.

[0011] In some other implementations, a lithium- sulfur cathode discharge capacity target (for example, about 600 mAh / g) may be realized without sacrificing anode stability and cellformation cycle time using a Li-Mg alloy composite anode. In some implementations, a freestanding composite anode associated with a lithium-sulfur battery may include a Li-Mg alloy and a lithium-ion conducting material. In some aspects, the lithium-ion conducting material (also referred to herein as lithium-ion conductive fillers) may include one of lithium titanate (“LTO”), lithium lanthanum zirconium oxide (“LLZO”), lithium nitride (Li3N), or lithium phosphide (Li3P). In some other aspects, an example freestanding Li-Mg alloy composite anode may further include one of alumina (AI2O3) or titanium dioxide (TiCL). In some instances, the amount of the lithium-ion conducting material in the freestanding Li-Mg alloy composite anode may be between about 10 wt% and about 40 wt%. In some other instances, the weight ratio of the Li-Mg alloy composite anode to the lithium-ion conducting material may be between about 1 and about 9.

[0012] In some implementations, any one of the freestanding anodes described herein may include a polymer coating including one or more of pentaerythritol tetraacrylate (“PETEA”) or polyethylene glycol dimethacrylate (“PEGDMA”) disposed on the freestanding anode. The thickness of the freestanding anode may be about 100 pm. The thickness of the polymer coating may be between about 1 m and about 10 pm.

[0013] In some implementations, a lithium-sulfur battery may include any one of the freestanding anodes disclosed herein and a fluorinated ether electrolyte including about 50:25:25 (vol%) 1 ,2-dimethoxyethane (“DME”): 1,3-dioxolane (“DOL”): bis (2,2,2- trifluoroethyl) ether (“BTFE”) and including about 0.4 M lithium bis (trifluoromethanesulfonyl) (LiTFSI) and about 2 wt% LiNO3.

[0014] In some implementations, the fluorinated electrolyte in a Li-S battery including any one of the freestanding anodes described herein may include about 50:25:25 (vol%) DME : DOL: 1,1,2,2-tetraethoxyethane (“TEE”) and including about 0.4 M LiTFSI and about 2 wt% LiNO3.

[0015] In some implementations, the fluorinated electrolyte in a Li-S battery including any one of the freestanding anodes described herein may include about 50:25:25 (vol%) DME : DOL: 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (“TFETFE”) and including about 0.4 M LiTFSI and about 2 wt% LiNO3.

[0016] In some implementations, the fluorinated electrolyte in a Li-S battery including any one of the freestanding anodes described herein may include about 60:20:10:10 (vol%) DME : DOL: TEE: TFETFE and including about 0.4 M LiTFSI and about 2 wt% LiNO3.

[0017] In some implementations, the fluorinated electrolyte in a Li-S battery including any one of the freestanding anodes described herein may include about 50:25:25 (vol%) DME : DOL: l,l,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (“TTE”) and including about 0.4M LiTFSI and about 2 wt% LiNOs.

[0018] In some implementations, the fluorinated electrolyte in a Li-S battery including any one of the freestanding anodes described herein may include about 50:25:25 (vol%) DME : DOL: 1 fluorinated 1 ,4-dimethoxylbutane (FDMB) including about 0.4 M LiTFSI and about 2 wt% Li NO ;.

[0019] In some implementations, the fluorinated electrolyte in a Li-S battery including any one of the freestanding anodes described herein may include about 1.0 M LiTFSI in about 50:50 (vol%) DOL: BTFE.

[0020] In some implementations, an example lithium-sulfur battery may include a cathode disposed opposite to the anode. In some implementations, an example cathode may include one or more porous carbon layers including porous carbon agglomerates of porous carbon primary nanoparticles, wherein a respective porous carbon primary nanoparticle may include an inner porous shell disposed about a center of the respective porous carbon primary nanoparticle and enclosing an inner porous carbon region, an outer porous shell enclosing an outer porous carbon region disposed between the inner shell and the outer shell, and an interconnected porous network disposed in and in fluid communication with the inner and outer porous carbon regions.

[0021] In some aspects, the inner carbon region and the outer carbon region of example porous carbon primary nanoparticles may be characterized by an average pore size and an average pore density associated with each region. In some other aspects, the average pore size may decrease along a radial direction from the center to the outer porous shell.

[0022] In some instances, an example porous carbon primary nanoparticle may further include one or more intermediate porous shells disposed between the inner porous shell and the outer porous shell, wherein each of the intermediate porous shells encloses a respective intermediate porous carbon region.

[0023] In some aspects, the porous carbon agglomerates may be characterized by a Raman spectroscopy signature with an ID / IG ratio between about 0.95 and about 1.05. In some other aspects, the porous carbon agglomerates may be characterized by a Brunauer- Emmett-Teller (BET) surface area between approximately 50 m2 / g and 300 m2 / g measured using nitrogen gas. In some aspects, the porous carbon agglomerates may be characterizedby an electrical conductivity of between about 500 S / m and 20,000 S / m when compressed at a pressure of about 12,000 pounds per square inch (psi).

[0024] In some implementations, an example cathode for a lithium- sulfur battery may include porous carbon agglomerates of porous carbon primary nanoparticles, which include one or more interconnected bundles of electrically conductive graphene layers. In some aspects, the graphene layers may be arranged as one or more stacks connected to each other and defining a 3D porous scaffold structure including mesopores. In some other aspects, the one or more stacks may be disposed substantially orthogonal to each other. In some instances, the graphene layers may be characterized by a linear dimension of between approximately 50 nm and 200 nm. In some other instances, the graphene layers may include one or more of single layer graphene (“SLG”), few layer graphene (“FLG”), or many layer graphene (“MLG”). In some aspects, the porous carbon agglomerates may be characterized by an electrical conductivity of between about 500 S / m and 20,000 S / m when compressed at a pressure of about 12,000 pounds per square inch (psi).

[0025] In some implementations, the geometrical shape of any one of the Li-S batteries previously described may be cylindrical. The cylindrical battery may be about 18 mm in diameter and about 65 mm in length. In some implementations, the cylindrical battery may be about 21 mm in diameter and about 70 mm in length. In some implementations, the cylindrical battery may be about 46 mm in diameter and about 80 mm in length.

[0026] Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following figures may not be drawn to scale.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 shows a plot illustrating cathode discharge capacity of example lithiumsulfur coin cells including freestanding Li-Mg alloy anodes of varying Li-Mg compositions, according to some implementations.

[0028] Figure 2A shows an example X-ray diffraction (XRD) pattern of a dual-phase freestanding anode alloy including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations.

[0029] Figure 2B shows a scanning electron microscopy (SEM) micrograph of a cross section of an example dual-phase freestanding anode alloy including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations.

[0030] Figure 2C shows another SEM micrograph of an example dual-phase freestanding anode alloy including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations .

[0031] Figure 3 A shows a scanning electron microscopy (SEM) micrograph of a cross section of an example dual-phase freestanding anode alloy including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations.

[0032] Figures 3B-3C show SEM-energy dispersive X-ray spectroscopy (EDS) elemental dispersion images of an example dual-phase freestanding anode alloy including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations.

[0033] Figure 4 A shows voltage profiles of example lithium-sulfur half cells including a freestanding composite anode including a Li-Mg alloy and lithium titanate (“LTO”), according to some implementations.

[0034] Figures 4B-4C show SEM images and SEM-EDS elemental dispersion images of an example Li-Mg alloy anode and a freestanding composite anode including Li-Mg alloy / LTO, respectively, according to some implementations.

[0035] Figure 5 A shows a schematic diagram of an example porous carbon primary nanoparticle, according to some implementations.

[0036] Figure 5B shows a transmission electron microscopy (TEM) image showing aggregates of porous carbon primary nanoparticles, according to some implementations.

[0037] Figure 5C shows a TEM image of agglomerates of porous carbon primary nanoparticles, according to some implementations.

[0038] Figure 5D shows a TEM image of surface etched agglomerates of porous carbon primary nanoparticles, according to some implementations.

[0039] Figure 5E shows a schematic diagram of another example porous carbon primary nanoparticle, according to some implementations.

[0040] Figure 6 A shows a schematic diagram of agglomerates of porous carbon primary nanoparticles, according to some implementations.

[0041] Figure 6B shows a scanning electron microscopy (SEM) micrograph of agglomerates of porous carbon primary nanoparticles, according to some implementations.

[0042] Figure 6C shows a TEM micrograph of agglomerates of porous carbon primary nanoparticles, according to some implementations.

[0043] Figure 7 shows a schematic diagram depicting an example lithium-sulfur cylindrical battery, according to some implementations.

[0044] Figure 8A shows a plot illustrating cathode discharge capacity of lithium-sulfur coin cells including dual-phase freestanding anodes including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations.

[0045] Figure 8B shows another plot illustrating cathode discharge capacity of lithiumsulfur coin cells including dual-phase freestanding anodes including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations.

[0046] Figure 9A shows a plot illustrating the rate capability test performance of lithiumsulfur symmetric cells including a freestanding composite anode including a Li-Mg alloy and LTO, according to some implementations.

[0047] Figure 9B shows a plot illustrating corrosion current after lithium stripping measured using lithium- sulfur symmetric cells including a freestanding composite anode including a Li-Mg alloy and LTO, according to some implementations.

[0048] Figure 9C shows a plot illustrating corrosion current after lithium plating measured using lithium- sulfur symmetric cells including a freestanding composite anode including a Li-Mg alloy and LTO, according to some implementations.

[0049] Figure 10 shows a plot illustrating cathode discharge capacity of lithium- sulfur coin cells including a freestanding composite anode including a Li-Mg alloy and LTO, according to some implementations.

[0050] Figure 11 shows a SEM micrograph of a freestanding PAN-based GPE membrane separator made by electrospinning, according to some implementations.

[0051] Figure 12A shows a plot illustrating cathode discharge capacity of lithium- sulfur coin cells including various membrane separators, according to some implementations.

[0052] Figure 12B shows a plot illustrating capacity retention of lithium- sulfur coin cells including various membrane separators, according to some implementations.

[0053] Figure 13A shows a plot illustrating cathode discharge capacity of lithium-sulfur coin cells including various membrane separators, according to some implementations.

[0054] Figure 13B shows a plot illustrating capacity retention of lithium-sulfur coin cells including various membrane separators, according to some implementations.

[0055] Figure 14 shows a plot illustrating cathode discharge capacity of lithium-sulfur coin cells including various membrane separators, according to some implementations.

[0056] Figure 15A shows a plot illustrating cathode discharge capacity of lithium- sulfur coin cells including freestanding PAN-based GPE membrane separators, according to some implementations.

[0057] Figure 15B shows a plot illustrating capacity retention of lithium- sulfur coin cells including freestanding PAN-based GPE membrane separators, according to some implementations.

[0058] Like reference numbers and designations in the various drawings indicate like elements.DETAILED DESCRIPTION

[0059] The following description is directed to some example implementations for the purpose of describing the innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. The described implementations can be implemented in batteries for a variety of applications and may be tailored to compensate for various performance related deficiencies. As such, the disclosed implementations are not to be limited by the examples provided herein, but rather encompass all implementations contemplated by the attached claims. Additionally, well-known elements of the disclosure will not be described in detail or will be omitted so as not to obscure the relevant details of the disclosure.

[0060] Various aspects of the novel compositions and methods are described more fully herein with reference to the accompanying drawings. These aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Although some examples and aspects are described herein, manyvariations and permutations of these examples fall within the scope of the disclosure. Although some benefits and advantages of the various aspects are mentioned, the scope of the disclosure is not intended to be limited to benefits, uses, or objectives. The detailed description and drawings are merely illustrative of the disclosure rather than limiting, the scope of the disclosure being defined by the appended claims and equivalents thereof.

[0061] In this disclosure, a primary carbon nanoparticle may be considered as a spheroidal shaped, non-discreet component or building block of an aggregate, separable from the aggregate only by fracturing. A plurality of primary carbon nanoparticles produced by one or more methods including thermal cracking of a hydrocarbon gas, may be coalesced, or joined to form aggregates of primary carbon nanoparticles. A carbon aggregate may be considered as a discrete, colloidal entity that is the smallest dispersible unit, composed of coalesced primary carbon nanoparticles. The primary carbon nanoparticles may be connected together by one or more of van der Waals forces, covalent bonds, ionic bonds, metallic bonds, or by other physical or chemical interactions. A plurality of aggregates may be considered as an agglomerate. Agglomerates of primary carbon nanoparticles may be produced from one or more methods including thermal cracking of a hydrocarbon gas. An example porous carbon agglomerate of primary carbon nanoparticles may be characterized by a principal dimension of at least about 1 pm.

[0062] In this disclosure, “graphene” refers to an allotrope of carbon in the form of atomic-scale, hexagonal lattice in which one atom forms each vertex. The carbon atoms in graphene may be sp2hybridized carbon atoms. Additionally, graphene has a Raman spectrum with two main peaks: a G-mode at approximately 1580 cm1and a D mode at approximately 1350 cm'1(when using a 532 nm excitation laser). As used herein, carbonaceous materials may refer to materials containing or formed of one or more types or configuration of carbon.

[0063] Commercialization of lithium- sulfur (“Li-S”) batteries has been hampered by limited discharge / charge cycling of less than approximately 100 cycles. Root cause analysis suggests that lithium-metal anode failure is a primary reason for cell failure. During cycling, the lithium-metal anode experiences significant volume change caused by repeated stripping (during discharge) and plating (during charge) of lithium. This volume change negatively impacts anode stability, and in particular, the stability of unsupported (or freestanding) lithium-metal anodes. In a freestanding lithium-metal anode, the anode is not supported on a metal substrate such as a copper current collector. Anode stability is further impacted by anunstable electrode-electrolyte interface and pulverization of the anode caused by volume changes during cycling, because lithium has a high oxidation potential (about 3.04V) and can react with almost any electrolyte solution, either in a solvent or in a salt form, to form a solid electrolyte interphase (“SEI”) layer.

[0064] The SEI layer is electronically insulating but ionically conductive to Li+ions. As such, once the SEI layer is formed, additional undesirable reaction between the lithium-metal anode and electrolyte may be blocked or partially blocked by the SEI layer. However, the SEI layer is generally non-uniform, which results in non-uniform current distribution during plating, and may cause uneven (or non-uniform) lithium deposition and anode cracking during cycling. Fresh lithium metal-anode may be exposed to the electrolyte resulting in the undesirable consumption of lithium for re-formation of the SEI layer. The localized non- uniform lithium deposition and stripping may manifest as dendrites during plating and pits during stripping at the anode during charge / discharge cycles. Dendrites may cause serious safety problems and reduce the cyclability of lithium-ion batteries. Additionally, dendrites may be dislodged from the anode to form ‘dead’ zones of lithium. Lithium dendrites may penetrate through polyolefin separators or even polymer / solid electrolyte separators disposed between the anode and the cathode of a battery, and negatively impact the safety and performance of lithium-ion batteries.

[0065] The above problems are further exacerbated in Li-S batteries, which include sulfur confined in a porous carbon cathode as the active cathode material. Sulfur reacts with lithium ions forming polysulfides. During the discharge cycle, Li ions migrate from the anode to the cathode through the electrolyte where sulfur is reduced to lithium sulfide ( Li 2S ). The sulfur reduction to Li2S is complex and may involve the formation of several intermediate Li polysulfides (Li2Sx, 8 < x < 1). Polysulfides (“Li-PS”) may be formed during the battery discharge cycle as:Ss — > Li2Ss — >■ Li2S6 — > Li2S4 — > Li2S3 — > Li2S2 — > Li2S

[0066] Ideally, the Li-PS compounds would oxidize back to sulfur during the charge cycle. In practice, Li-PS compounds leak out from the porous carbon cathode as they are highly soluble in the electrolyte, which results in loss of sulfur and reduction in cathode capacity. While sulfur and Li2S are relatively insoluble in most electrolytes, many intermediate polysulfides (“Li-PS”) are soluble and cause irreversible loss of active sulfur from the cathode. The dissolution of Li-PS in the electrolyte requires a large amount of electrolyte (E / S > 3 pL / mg), which reduces battery specific energy. The higher polysulfides(LizS and Li 280 ) may diffuse to the anode and may get reduced to lower polysulfides (LLSG and IJ2S4), which subsequently get oxidized at the cathode. At the anode, the polysulfides participate in SEI formation, increase the unevenness of SEI, and aggravate the corrosion of the Li metal anode. This cyclic process commonly known as the polysulfide “shuttle effect” results in poor coulombic efficiency, and progressive leakage of active sulfur material from the cathode which also reduces the life cycle of the battery. Further, the conversion of elemental sulfur to LiiSx sulfur compounds is accompanied by large volumetric expansion at the cathode (which could be as high as 80%), which subjects the cathode to significant mechanical stresses resulting in rapid cathode degradation.

[0067] Additionally, the “shuttle effect” is responsible for self-discharge of Li-S batteries, because of the slow dissolution of Li-PS during battery dormancy. Battery self-discharge reduces battery life and causes safety issues. The repeated volume change and the corrosion reactions at the anode continuously consume active Li and form massive “dead Li,” which may be detached during cycling, leading to poor recyclability of Li-S battery. As previously noted, often the anode contributes to cell failure, either via electrolyte consumption of Li due to corrosion or its depletion during cycling. These challenges limit the commercial viability of high- specific energy Li-S batteries having dense cathodes, limited electrolyte, and limited anode capacity (or low N / P ratio). The N / P ratio may be defined as the ratio of reversible capacity (mAh) of the negative electrode (anode) to that of the positive electrode (cathode) assuming complete utilization of sulfur.

[0068] Accordingly, to mitigate the loss of conductivity due to dissolved Li-PS an excess amount of electrolyte is used in Li-S batteries. Additionally, to mitigate lithium-metal loss due to SEI formation, pitting, and dendrite formation, an excess of lithium-metal is required at the anode. These requirements frustrate attempts to reach or exceed the specific energy target of 500 W-h / kg in Li-S batteries. Li-S batteries generally require an electrolyte to sulfur ratio (“E / S ratio”) of approximately 5 pL / mg, and a N / P ratio of greater than 2. For comparison, the N / P ratio in commercial Li-ion batteries is between approximately 1.03 and 1.2. While the N / P ratio is important to offset the likely higher loss of anode material during cycling, the areal capacity (mAh / cm2) is also critical to reduce the current density and hence failure rate on the anode.

[0069] Li-S battery anodes generally use a current collector including copper as an anode support. Copper adds significant weight to Li-S batteries and reduces the specific energy of the battery. Copper is also susceptible to corrosion by polysulfides. Accordingly, there issignificant interest in developing substrate-free or freestanding anodes. However, freestanding anode in Li-S batteries is challenging due to the morphological and instability issues with the lithium-metal (100% lithium) anode. Freestanding anode alloy compositions that are stable under cyclic conditions in Li-S batteries and at low E / S ratios of approximately less than or equal to 5 for coin cells, and less than or equal to 3 for pouch cells are needed. Freestanding anode compositions that are stable under cyclic conditions in Li-S batteries and at N / P ratios of approximately less than 2 to realize battery specific energy of 500 W-h / kg are also needed.

[0070] The polysulfide shuttle effect in lithium-sulfur batteries may be mitigated by using a cathode including carbon materials characterized by an interconnected porous structure to physically trap the polysulfides at the cathode. Alternately, polysulfides may be chemically adsorbed in the cathode porous surfaces by impregnating the cathode carbon materials with nanometals. The polysulfide shuttle effect may also be mitigated by using lithium-alloy anodes and employing one or more anode coatings that block polysulfides from reaching the anode active material.

[0071] Alternately, the polysulfide shuttle effect may be mitigated by using freestanding gel polymer electrolyte (“GPE”) membrane separators disposed between the anode and the cathode. These separators may also block polysulfides from reaching the anode.Accordingly, a combination of methods and battery design elements may be used to mitigate the polysulfide shuttle effect. Novel thin GPE membrane separators for lithium-sulfur batteries are desired to realize cathode discharge capacities of at least 600 mAh / g at capacity retention of greater than 70% and at E / S ratios of < 4 and N / P ratio < 2 while improving cyclic stability.

[0072] In some implementations, Li-alloys may be used as freestanding anodes instead of pure-lithium metal anodes to overcome the previously described anode instability issues related to volume change during cycling, and the high reactivity of the Li-metal anodes with the electrolyte and with polysulfides. Lithium may alloy with several metals including one or more of silicon, tin, magnesium, or aluminum. Li-alloy anodes may have higher electrode potential compared to lithium deposition and may hinder corrosion at the anode caused by reactions between the anode and polysulfides and electrolytes. Meanwhile, the alloying element may function as a lithium host for lithium deposition or plating (during the charge cycle) absorb volume changes during cycling and help to stabilize the anode. The alloyingelement may form a stable surface film over the anode, which may reduce the non-uniform deposition of lithium during plating.

[0073] Some alloying elements with lithium may reduce the Li-S battery capacity (mAh) or voltage, and subsequently reduce battery specific energy. Additionally, some alloying elements, for example, silicon (Si), tin (Sn), and germanium (Ge), may undergo severe volume changes during lithiation (plating, during charge cycle) and de-lithiation (stripping during discharge) and may not be suitable candidates for a Li-S battery anode. With elements such as silicon and tin, lithium may form intermetallic compounds of the type LixMy, which have a high degree of ionic bonding, and are subsequently, brittle, and fragile. Some other lithium alloys such as lithium-aluminum alloys are reversible only over a limited composition range and may not be suitable for Li-S battery use.

[0074] In some implementations, alloying lithium with small amounts of magnesium (Mg) may improve the stability of Li-S battery anodes to reactions with the electrolyte and polysulfides and increase battery cycle life. In lithium-magnesium (“Li-Mg”) alloy anodes, the magnesium alloying element may provide structural integrity to the anode during volume changes associated with battery cycling, because magnesium does not undergo stripping and plating at the anode. Additionally, alloying lithium with small amounts of magnesium permits a free-standing anode design (without the need for a copper current collector substrate), which also increases battery specific energy.

[0075] Li and Mg have comparable atomic radii and form an extended single solid phase (body centered cubic structure or BCC) alloy over a wide composition range of about 11 .5- 100 wt% lithium in Li-Mg alloys. Therefore, the capacity of a Li-Mg alloy anode may be tuned over a broad range free of any alloy phase change considerations. The Li-Mg alloy may provide a scaffold-like structure, which may facilitate insertion and removal of Li+ions during the charge / discharge cycling of a Li-S battery. The volume change related to the insertion of one mole of Li into Mg may be about 80% as calculated using Li-Mg alloy lattice parameters, which is much lower than the volume change related to the interaction of lithium with other alloying elements such as silicon, tin, and antimony. Li-Mg alloys are very ductile, which permit straightforward fabrication of electrodes by rolling and annealing. At Li-rich compositions of approximately 90%, no loss in battery voltage may be observed when replacing a Li-anode (100% lithium) with a Li-Mg anode, because lithium stripping and plating may occur close to 0 V. Additionally, as magnesium is lithiophilic, dispersedmagnesium in Li-Mg anodes may serve as nucleation sites for uniform lithium deposition during the charge cycle.

[0076] Since Li-Mg alloy anodes form relatively stable SEI interface (compared to Li- anodes), a comparatively smooth anode surface morphology may be realized during the cyclic operation of a Li-S battery. Additionally, a Li-Mg alloy matrix, poor in lithium, and with high electric and ionic conductivity, may be formed after Li stripping to provide an excellent anode current collector and host for subsequent Li plating. Accordingly, Li-Mg alloy anodes may be freestanding and may not require a separate anode current collector.

[0077] As previously described, lithium has a high oxidation potential (of about 3.04V) and can react with almost any electrolyte solution, either in a solvent or in a salt form, to form a solid electrolyte interphase (“SEI”) layer. Lithium anode stability is further impacted by an unstable electrode-electrolyte interface and pulverization of the anode caused by volume changes during cycling. Alloying lithium with metals including magnesium may reduce stabilize the life of the anode in lithium-sulfur cells, but this increased stability often requires an increase in the number of formation cycles required to reach a target cathode discharge capacity.

[0078] Figure 1 shows a plot 100 illustrating cathode discharge capacity of example lithium-sulfur coin cells including freestanding Li-Mg alloy anodes of varying Li-Mg compositions, according to some implementations. Tests were conducted at C / 3 charge / discharge rate after initial formation cycles at a C / 20 rate for 2 cycles followed by a C / 10 rate for 1 cycle. The Mg content in the Li-Mg alloys was between about 10 wt% and 28 wt%. The thickness of the Li-Mg freestanding alloy anodes was about 100 pm. The cathode loading was approximately 7.5 mg / cm2. The cathode capacity in each case was approximately 4 mAh / cm2. A Celgard PP2075 separator was disposed between the cathode and anode. The anodes did not include any polymeric material coating. The electrolyte included about 50:25:25 (vol%) 1 ,2-dimethoxyethane (“DME”): 1,3-dioxolane (“DOL”): bis (2,2,2-trifluoroethyl) ether (“BTFE”) and including about 0.4 M LiTFSI and about 2 wt% LiNOs. The electrolyte-to-sulfur (“E / S”) ratio was about 5.

[0079] As can be seen in Figure 1 , initial cathode discharge capacity at C / 20 rate decreased as the Mg content in the Li-Mg alloy anodes increased beyond 12 wt%. With the 72Li-28Mg alloy anode (72 wt% Li and 28 wt% Mg), initial discharge capacity measured was less than 200 mAh / g, which is a 3x decrease in initial discharge capacity over the discharge capacity measured using the 90Li-10Mg alloy anode. With repeated formationcycles, the cells including the 85Li-15Mg alloy anode produced a discharge capacity comparable to that of the 90Li-10Mg anode. This extended formation cycling including about 25 cycles is not practical for several applications. Prolonged formation cycling through 40 cycles of cells including 72Li-28Mg alloy anode did not significantly increase the discharge capacity. As such, increased anode stability in Li-Mg alloy anodes may be realized at the expense of discharge capacity and formation cycling time. There is a need to realize improved anode stability with high discharge capacity of about 600 mAh / g and at formation cycles of less than about 5.

[0080] In some implementations, a freestanding anode associated with a lithium-sulfur battery may include a dual-phase alloy including a Li-Mg alloy phase and a Li-x alloy phase. In some aspects, the Li-x alloy phase may include alloys of lithium and one of calcium, boron, tin, aluminum, indium, bismuth, antimony, or zinc. In some other aspects, the Li-x alloy phase may include a LizCa (also referred to herein as CaLiz) alloy phase. In some instances, the weight ratio of the Li-Mg alloy phase to the LizCa alloy phase may be between about 0.1 and about 20.

[0081] In some implementations, a dual-phase alloy including a Li-Mg alloy phase and a LizCa alloy phase may include a lithium content of between about 55 wt% and about 75 wt%, a magnesium content of between about 15 wt% and about 30 wt% and a calcium content of between about 2 wt% and about 30 wt%. Cathode discharge capacity of example lithiumsulfur coin cells including a freestanding dual phase alloy anode including a Li-Mg alloy phase and a LizCa alloy is discussed below under Example 1.

[0082] Figure 2A shows an example X-ray diffraction (“XRD”) pattern 200A of a dualphase freestanding anode alloy including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations. The elemental composition of the example dual-phase anode alloy was about 55 wt% Li, about 17 wt% Mg and about 28 wt% Ca. As can be seen, the XRD pattern 200A confirms the presence of a Li-Mg alloy phase with a characteristic peak corresponding to the (110) plane based on the reference XRD fingerprint of the 90Li- lOMg alloy. Additionally, the XRD pattern 200A confirms the presence of a LizCa alloy phase with a fingerprint corresponding to the (100), (002), (101), (102), (110), (103), (200) and (112) planes based on the reference XRD fingerprint of the LizCa alloy.

[0083] Figure 2B shows a scanning electron microscopy (“SEM”) micrograph 200B of a cross section of an example dual-phase freestanding anode alloy including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations. The elementalcomposition of the example dual-phase anode alloy was about 55 wt% Li, about 17 wt% Mg and about 28 wt% Ca. As can be seen, discrete LizCa alloy 201 is dispersed in the Li-Mg alloy matrix.

[0084] Figure 2C shows another SEM micrograph 200C of an example dual-phase freestanding anode alloy including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations. SEM micrograph 200C was collected in the backscattered electron mode. As can be seen, Li2Ca alloy 201 is uniformly dispersed in the Li-Mg alloy matrix. These observations corroborate the XRD pattern of a dual-phase alloy (referring to Figure 2A) and confirms the presence of a dual alloy phase including a Li-Mg alloy phase and a LiiCa alloy phase in the example freestanding anode. Those skilled in the art will appreciate that the micrographs are shown by way of example only, and that other scales may exist without departing from the scope and spirit of the present implementations.

[0085] Figure 3A shows a scanning electron microscopy (SEM) micrograph 300A of a cross section of an example dual-phase freestanding anode alloy including a Li-Mg alloy phase and a Li2Ca alloy phase, according to some implementations. Figures 3B-3C show SEM-EDS elemental dispersion images 300B-300C of an example dual-phase freestanding anode including a Li-Mg alloy phase and a Li2Ca alloy phase, according to some implementations. The elemental composition of the example dual-phase anode alloy was about 55 wt% Li, about 17 wt% Mg and about 28 wt% Ca. Similar to micrograph 200A (referring to Figure 2A), micrograph 300A shows the dispersion of Li2Ca alloy in the Li-Mg alloy matrix. The elements examined during EDS analysis included magnesium (shown in EDS image 300B, K line) and calcium (shown in elemental dispersion image 300C, K line). Referring to Figure 3C, the discrete and substantially uniform distribution of calcium suggests no cross-contamination between the dual-phase alloys Li-Mg and Li2Ca.Additionally, the dual-phase alloys were produced at about 300 °C, which is much lower than the formation temperature of at least about 400 °C for a Mg-Ca alloy. As such, the above observations indicate that calcium is present as Li2Ca alloy 301 . The dual-phase alloy including Li-Mg alloy phase and a Li2Ca alloy phase is also substantially free of any unalloyed calcium. The uniform distribution of Mg (referring to Figure 3B) suggests that the Li2Ca phase is distributed in the Li-Mg alloy phase in the dual phase anode alloy.

[0086] In some implementations, any of the dual-phase freestanding anode alloys previously disclosed herein may include a polymer coating including one or more of pentaerythritol tetraacrylate (“PETEA”) or polyethylene glycol dimethacrylate (“PEGDMA”)disposed on the freestanding anode. The thickness of the coating layer may be between about 1 pm and about 10 pm.

[0087] In some other implementations, a lithium-sulfur battery target of high cathode discharge capacity (for example, about 600 mAh / g) may be realized without sacrificing anode stability and cell formation cycle time using a Li-Mg alloy composite anode. In some implementations, a freestanding composite anode associated with a lithium-sulfur battery may include a Li-Mg alloy and a lithium-ion conducting material. In some aspects, the lithium-ion conducting material (also referred to herein as lithium-ion conductive fillers) may include one of lithium titanate (“LTO”), lithium lanthanum zirconium oxide (“LLZO”), lithium nitride (LisN), or lithium phosphide (Li3P). In some other aspects, an example freestanding Li-Mg alloy composite anode may further include one of alumina (AI2O3) or titanium dioxide (TiCL). In some instances, the amount of the lithium-ion conducting material in the freestanding Li-Mg alloy composite anode may be between about 10 wt% and about 40 wt%. In some other instances, the weight ratio of the Li-Mg alloy composite anode to the lithium-ion conducting material may be between about 1 and about 9. Cathode discharge capacity of example lithium-sulfur coin cells including a freestanding dual phase alloy anode including a Li-Mg alloy phase and a Li2Ca alloy is discussed below under Example 3. Without being bound by any particular theory the lithium-ion conducting fillers may help in controlling the grain size of Li-Mg in the Li-Mg alloy and facilitate lithium-ion diffusion across grain boundaries.

[0088] Figure 4A shows voltage profiles 400A of example lithium-sulfur half cells including a freestanding composite anode including a Li-Mg alloy and lithium titanate (“LTO”), according to some implementations. The voltage profiles of the half cells with freestanding Li-Mg alloy anode and Li-Mg alloy / LTO composite anode were measured at charging current of 0.2 mA / cm2and discharge current of 1.3 mA / cm2. A copper foil was used as the cathode. A glass fiber (GF / A) separator was used between the cathode and anode. The anode did not include any polymeric material coating. The electrolyte included about 50:25:25 (vol%) DME: DOL: BTFE and including about 0.4 M LiTFSI and about 2 wt% LiNO v As shown in Figure 4A, with one discharge / charge cycle at C / 3 rate, the charge / discharge profiles of the symmetric cell including the Li-Mg alloy / LTO composite anode was flatter than that measured using the Li-Mg alloy anode.

[0089] Figures 4B-4C show SEM images and SEM-EDS elemental dispersion images 400B-400C of an example Li-Mg alloy anode and freestanding composite anode includingLi-Mg alloy / LTO, respectively, according to some implementations. The Li-Mg alloy anode sample and Li-Mg alloy / LTO composite anode sample corresponding to the tests associated with Figure 4A were examined under SEM-EDS imaging. Referring to Figure 4B, the Li-Mg alloy anode shows a Li-rich layer 401 disposed on a and a Li-Mg alloy layer 402. This stratified gradation in Li-Mg alloy composition could negatively impact anode stability. The EDS analysis targeted magnesium (K line). In contrast, referring to Figure 4C, the Li-Mg alloy / LTO composite anode showed uniform Mg distribution suggesting stripping and plating of lithium. This result suggests that Li-Mg alloy / LTO composite anode could favor improved anode stability compared to the Li-Mg alloy anode.

[0090] In some implementations, any of the freestanding Li-Mg alloy / lithium ion conducting material composite anodes previously disclosed herein may include a polymer coating including one or more of pentaerythritol tetraacrylate (“PETEA”) or polyethylene glycol dimethacrylate (“PEGDMA”) disposed on the freestanding anode. The thickness of the coating layer may be between about 1 pm and about 10 pm.

[0091] In some implementations, an example lithium-sulfur battery may include any one of the freestanding anodes previously described herein and a fluorinated ether electrolyte. The thickness of the freestanding anode may be about 100 pm. In some instances, a freestanding anode may include any one of the dual-phase alloy anodes including a Li-Mg alloy phase and a Li2Ca alloy phase. In some other instances, a freestanding anode may include any one of the Li-Mg alloy / lithium-ion conducting material composite anode.

[0092] In some implementations, the fluorinated ether electrolyte may include one or more of lithium nitrate (LiNCL) or lithium bis (trifluoromethanesulfonyl) imide (“LiTFSI”).In some implementations, the concentration of LiTFSI in the fluorinated electrolyte may be between about 0.1M and about 2M. In some implementations, the concentration of LiNCL in the electrolyte may be between about 2 wt% and about 6 wt%.

[0093] In some implementations, an example fluorinated ether electrolyte may include about 50:25:25 (vol%) 1 ,2-dimethoxyethane (“DME”): 1,3-dioxolane (“DOL”): bis (2,2,2- trifluoroethyl) ether (“BTFE”) and including about 0.4 M LiTFSI and about 2 wt.-% LiN'Ov In some other implementations, an example fluorinated ether electrolyte may include about 50:25:25 (vol%) DME : DOL: TEE (1,1,2,2-tetraethoxyethane) and including about 0.4 M LiTFSI and about 2 wt% LiNOs.

[0094] In some implementations, an example electrolyte may include about 50:25:25 (vol%) DME : DOL: TFETFE (1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether) andincluding about 0.4 M LiTFSI and about 2 wt% L1NO3. In some other implementations, an example electrolyte may include about 60:20: 10: 10 (vol%) DME : DOL: TEE: TFETFE and including about 0.4 M LiTFSI and about 2 wt% LiNOv

[0095] In some implementations, an example electrolyte may include about 50:25:25 (vol%) DME : DOL: TTE (l,l,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether) and including about 0.4 M LiTFSI and about 2 wt% L1NO3. In some implementations, an example fluorinated ether electrolyte may include LiTFSI at concentrations of between about 0.1 M and about 1 M, and LiNCh concentrations of between about 1 wt% and 6 wt%. In some other implementations, an example fluorinated ether electrolyte may include about 50:25:25 (vol%) DME : DOL: 1 fluorinated 1,4-dimethoxylbutane (“FDMB”) and including about 0.4 M LiTFSI and about 2 wt% LiNOa. In some other implementations, the electrolyte may include about 1.0 M LiTFSI in about 50:50 (vol%) DOL: BTFE.

[0096] Additives such as lithium nitrate (LiNOs) in the electrolyte may dissociate to produce lithium cations (Li+). Alternately, additives such as LiTFSI in the electrolyte may dissociate to produce lithium cations (Li+) and TFSI” anions. Additives in the electrolyte that may dissociate to lithium ions may also include one or more of lithium lanthanum zirconium oxide (“LLZO”), oxinitrides (e.g., lithium phosphorus oxynitride or “UPON”), NASICON- type conductors (e.g., lithium aluminum titanium phosphate) or lithium tin phosphorus sulfide (“LSPS”).

[0097] In some example implementations, any one of the previously described freestanding dual phase Li-Mg alloy and Li-x alloy anodes or any of the Li-Mg alloy / Li-ion conducting material composite anodes in an example lithium-sulfur battery may be coated with a surface coating which may react with lithium in the alloy to form a protective layer and further improve the stability of the anode under cycling. In some aspects, the surface coating may include a poly vinylidene fluoride (“PVDF”) coating layer. The thickness of the PVDF coating layer may be between about 1 pm and about 10 pm.

[0098] Without being bound by any particular theory, PVDF may react with lithium in the freestanding Li-Mg alloy anode to form LiF ions dispersed in a polymeric matrix. The protective layer may improve and / or may be associated with an improvement of lithium ion (Li+) transport from and to the anode during cycling. Reducing lithium-containing dendritic growth from the anode of a Li-S battery may increase the charge rate, the discharge rate, the energy density, the cycle life, or any combination thereof. The polymeric matrix maypartially trap TFSI anions produced by the dissociation of additives such as LiTFSI in the electrolyte.

[0099] In some implementations, the surface coating for freestanding dual-phase Li-Mg alloy and Li-x alloy or any of the Li-Mg alloy / Li-ion conducting material composite anodes in an example lithium- sulfur battery may include one or more of a pentaerythritol tetraacrylate (“PETEA”) or polyethylene glycol dimethacrylate (“PEGDMA”). The thickness of the coating layer may be between about 1 pm and about 10 m. In other implementations, the surface coating for freestanding Li-Mg alloy anodes may include PETEA and PEGDMA. The thickness of the coating layer may be between about 1 pm and about 10 pm.

[0100] In some implementations, an example lithium-sulfur battery may include a cathode disposed opposite to the anode. As described below with reference to Figures 5A- 5E, in some implementations, an example cathode may include one or more porous carbon layers including porous carbon agglomerates of porous carbon primary nanoparticles, wherein a respective porous carbon primary nanoparticle may include an inner porous shell disposed about a center of the respective porous carbon primary nanoparticle and enclosing an inner porous carbon region, an outer porous shell enclosing an outer porous carbon region disposed between the inner shell and the outer shell, and an interconnected porous network disposed in and in fluid communication with the inner and outer porous carbon regions.

[0101] In some aspects, the inner carbon region and the outer carbon region of example porous carbon primary nanoparticles may be characterized by an average pore size and an average pore density associated with each region. In some other aspects, the average pore size may decrease along a radial direction from the center to the outer porous shell.

[0102] In some instances, an example porous carbon primary nanoparticle may further include one or more intermediate porous shells disposed between the inner porous shell and the outer porous shell, wherein each of the intermediate porous shells encloses a respective intermediate porous carbon region.

[0103] In some aspects, the porous carbon agglomerates may be characterized by a Raman spectroscopy signature with an ID / IG ratio between about 0.95 and about 1.05. In some other aspects, the porous carbon agglomerates may be characterized by a Brunauer- Emmett-Teller (BET) surface area between approximately 50 nr / g and 300 nr / g measured using nitrogen gas. In some aspects, the porous carbon agglomerates may be characterized by an electrical conductivity of between about 500 S / m and 20,000 S / m when compressed at a pressure of about 12,000 pounds per square inch (psi).

[0104] Figure 5A shows a schematic diagram 500A of an example porous carbon primary nanoparticle 505, according to some implementations. In some aspects, the porous primary carbon nanoparticle 505 may resemble carbon nano-onions (“CNOs”). As shown in the example of Figure 5A, the porous primary carbon nanoparticle 505 may include a core (inner) porous carbon region 511 defined by a first porosity and enclosed within an inner porous shell 513. The inner porous carbon region 511, which may also be referred to herein as the first porosity region, may include a plurality of first pores 501 dispersed therein. An outer porous carbon region 512, which may also be referred to herein as the second porosity region, may be disposed between the inner porous shell 513 and an outer porous shell 510 and may include a plurality of second pores 502 dispersed therein. The inner porous carbon region 511 and the outer porous carbon region 512 may be interconnected by one or more of the first pores 501 or one or more of the second pores 502, thereby interconnecting the first and second porosity regions. That is, the inner porous carbon region 511 may be configured to be in fluid communication with the outer porous carbon region 512 through an interconnected porous network. The inner porous carbon region 511 may be defined by a first pore density, and the outer porous carbon region 512 may be defined by a second pore density that is similar to or different than the first pore density.

[0105] Example porous primary carbon nanoparticle 505 may be characterized by an average size or principal dimension (diameter, length, width) of less than approximately 200 nm. In some implementations, an average pore size may gradually decrease along a radial direction from the center 516 of the nanoparticle 505 to the outer boundary 513 of the nanoparticle 505. In some implementations, porous primary carbon nanoparticle 505 may be characterized by a range of pore sizes and pore distributions in each region. The first pores 501 may be configured to retain poly sulfides 520, and the second pores 502 may provide pathways or channels for the transport of lithium ions (not shown for simplicity) into and from the porous primary carbon nanoparticles 505 and for pre-loading sulfur 524 into the nanoparticles.

[0106] Figure 5B shows a transmission electron microscopy (“TEM”) micrograph 500B of aggregates 540 of porous carbon primary nanoparticles 505, according to some implementations. Those skilled in the art will appreciate that the micrographs are shown by way of example only, and that other scales may exist without departing from the scope and spirit of the present implementations. Example carbon aggregates 540 may include an interconnected porous network disposed between adjacent carbon nanoparticles 505.Aggregate 540 may include a plurality of porous carbon primary nanoparticles 505 and, in some instances, may resemble a “string-of-pearls.” In some implementations, the size or principal dimension of aggregate 540 may be between about 50 nm and 500 nm.

[0107] Figure 5C shows a TEM image 500C of agglomerates 545 of porous primary carbon nanoparticles 505, according to some implementations. An agglomerate 545 of porous carbon primary nanoparticles 505 may be characterized by a Brunauer-Emmett- Teller (“BET”) surface area of between about 50 m2 / g and about 300 m2 / g measured using nitrogen gas. In some implementations, an example agglomerate 545 may be spherical in shape. In some implementations, an agglomerate 545 may be of any shape, including one or more of spherical, spheroidal, dumbbell, cylindrical, elongated cylindrical type, rectangular prism, disk, wire, or irregular.

[0108] Figure 5D shows a TEM image 500D of surface etched agglomerates 542 of porous primary carbon nanoparticles, according to some implementations. Example agglomerates 545 may be surface etched using methods that include CO2 etching to create pores on the external surface of the agglomerates 545 and to increase the surface area of the carbon agglomerates 545 to yield surface etched agglomerates 542. After etching, the surface etched agglomerates 542 may include three-dimensional graphene carbons (“3DG carbons”) including graphene layers interconnected as three-dimensional (“3D”) graphene structures (not shown for simplicity). The surface etched agglomerates 542 of porous primary carbon nanoparticles may be characterized by a Raman spectroscopy signature with an ID / IG ratio of approximately between 0.95 and 1.05. As previously noted, the surface etched agglomerates 542 may be assembled as rigid porous carbon agglomerates by processes including spray drying.

[0109] Figure 5E shows a schematic diagram 500E of another example porous primary carbon nanoparticle 505, according to some implementations. Example tri-zone porous primary nanoparticle 505 may include a first core (inner) carbon zone or region 551, nested within a second intermediate carbon zone or region 552, which in turn is nested within a third outer carbon zone or region 553. Example first zone 551 may include pores 561 having an average size or principal dimension (diameter, length width) of less than approximately 40 nm, the second zone 552 may include pores 562 having an average size or principal dimension of less than approximately 35 nm, and the third zone 553 may include pores 563 having an average size or principal dimension of less than approximately 30 nm. In some example implementations, pores 561 may be characterized as macropores, the pores 562 inthe intermediate region 552 may be characterized as mesopores, and the pores 563 in the outer region 552 as micropores.

[0110] In some implementations, the principal dimension DI of first zone 551 may be less than approximately 100 nm, the principal dimension D2 may be less than approximately 150 nm, and the principal dimension D3 of third zone 553 may be approximately 200 nm. The relative dimensions, porosities, and electrical conductivities of the first zone 551, the second zone 552, and the third zone 553 may be tuned to achieve a desired balance between minimizing the polysulfide shuttle effect and maximizing the specific capacity of a host battery. The first zone (inner core zone) 551 may have a density of carbons of less than approximately 1 g / cc. The third zone (outer zone) 553 bounded by the perimeter or outer shell 555 of particle 205 may have a density of carbons of approximately less than between 1 g / cc and 3.5 g / cc. The second zone (intermediate zone) 552 may have a density of carbons of between approximately 0.5 g / cc and 3 g / cc. Each of the zones 551, 552, and 553 may be characterized by an average pore size and an average pore density associated with each region. The average pore size associated with each of zones 551-553 may decrease along a radial direction from the center of the porous primary carbon nanoparticle 505 to the outer porous shell 555.

[0111] Agglomerates of porous primary carbon nanoparticles 505 may be surface etched using methods that include CO2 etching to create pores on the external surface of the agglomerates and to increase the surface area of the carbon agglomerates. After etching, the agglomerates may include three-dimensional graphene carbons (“3DG carbons”) including graphene layers interconnected as three-dimensional (“3D”) graphene structures. The resulting surface etched agglomerates of porous primary carbon nanoparticles 505 may be characterized by a Raman spectroscopy signature with an ID / IG ratio of approximately between 0.95 and 1.05. In some implementations, the resulting agglomerates may be produced by thermal cracking of hydrocarbon feedstock as disclosed in commonly -owned U.S. Pat. No. 9,862,602, U.S. Pat. No. 10,112,837, U.S. Pat. No. 11,053,121, and / or U.S. Pat. Pub. No. 2021 / 0292170, all of which are incorporated by reference herein in each of their entireties.

[0112] The porous carbon agglomerates as described above may be used to produce carbon-sulfur composites (“CSC”) by sulfurizing the carbon agglomerates. The sulfur to carbon weight ratio may be between approximately 1:5 and 10:1. The sulfur to carbon weight ratio may be about 3. A slurry including the carbon-sulfur composites and one ormore polymeric binders may be cast as one or more layers or films of carbon material on a suitable substrate to form the cathode in an example Li-S battery. The cathode substrate may include a cathode current collector. The cathode current collector may include aluminum. The carbon agglomerates may resist deformation under high shear mixing, and therefore produce films or layers of carbon of desired porosity, thickness, and packing density. In some implementations, the cathode may be characterized by a packing density of carbon material on the substrate (including sulfur, binder, and other constituents) of at least about 7 mg / cm2, which in turn increases the sulfur loading at the cathode and may reduce the N / P ratio in a Li-S battery.

[0113] In some implementations, the porous carbon agglomerates as disclosed herein may resist deformation under high shear mixing, and therefore produce films or layers of carbon of desired porosity, thickness, and packing density. In some implementations, the porous carbon agglomerates may resist deformation at shear rates of at least 500 s1during mixing of a slurry including the porous carbon agglomerates in a high shear mixer. The slurry may be disposed as one or more porous carbon layers on the cathode substrate (also referred to herein as the cathode current collector).

[0114] In some implementations, as described below with reference to Figures 6A-6C, an example cathode for a lithium-sulfur battery may include porous carbon agglomerates of porous carbon primary nanoparticles, which include one or more interconnected bundles of electrically conductive graphene layers. In some aspects, the graphene layers may be arranged as one or more stacks connected to each other and defining a 3D porous scaffold structure including mesopores. In some other aspects, the one or more stacks may be disposed substantially orthogonal to each other. In some instances, the graphene layers may be characterized by a linear dimension of between approximately 50 nm and 200 nm. In some other instances, the graphene layers may include one or more of single layer graphene (“SLG”), few layer graphene (“FLG”), or many layer graphene (“MLG”).

[0115] Figure 6A shows a schematic diagram of a mesoporous carbon nanoparticle 600A having an interconnected bundle of electrically conductive graphene layers arranged to form a 3D open porous scaffold structure, according to some implementations. Nanoparticle 600A and porous carbon agglomerates including nanoparticles 600A may be produced using a high throughput, low-cost, cracking of a hydrocarbon gas such as natural gas, in an atmospheric microwave plasma reactor. An example microwave plasma reactor is disclosed in commonly-owned U.S. Pat. No. 9,767,992, which is incorporated by reference herein in itsentirety. For example, the agglomerates may be formed in-flight and grown by adding additional carbon-based materials derived from incoming carbon-containing gas within a microwave-plasma reaction chamber.

[0116] The carbon nanoparticles 600A may include three-dimensional (“3D”) multimodal mesoporous carbon nanoparticles. A mesoporous material, as generally understood and as referred to herein, includes a material containing pores with diameters between 2 nm and 50 nm, according to IUPAC nomenclature. For the purposes of comparison, IUPAC defines microporous material as a material having pores smaller than 2 nm in diameter and defines macroporous material as a material having pores larger than 50 nm in diameter. In some instances, mesoporous carbon particle 600A may be characterized by a three- dimensional (“3D”) hierarchical porous structure including pores 680. In some aspects, at least a portion of the hierarchical porous structure may further define a 3D open porous scaffold structure 681.

[0117] The nanoparticle 600A may include one or more interconnected bundles 682 of electrically conductive graphene layers or sheets. Each interconnected bundle 682 may include one or more stacks 683 of graphene layers. Each stack 683 may include a plurality of graphene layers 686 that are generally stacked horizontally as more clearly shown in stack 684. One or more stacks 683 of graphene layers 686 may be arranged to form a 3D porous scaffold structure 681 including mesopores. That is, a plurality of stacks 683 of electrically conductive graphene layers 686 may be sintered together to define the 3D open porous scaffold structure 681 (which includes mesopores 680 in the example of Figure 6A). In some implementations, one or more of the stacks 683 may be connected substantially orthogonal to each other. The open porous scaffold structure 681 may be configured to provide electrical conduction between contact points (not shown for simplicity) of the stacks of graphene layers 686. In some implementations, each graphene layer 686 may be characterized by a diameter or linear dimension (“La”) of between about 50 nm to about 200 nm. In some implementations, the graphene stack 683 may include few layer graphene (“FLG”), which may be composed of 5 to 15 layers of graphene.

[0118] A plurality of porous carbon primary nanoparticles 600A may be coalesced or joined to form porous carbon agglomerates of porous carbon primary nanoparticles. In this disclosure, three-dimensional graphene carbons (“3DG carbons”) include porous carbon agglomerates of mesoporous nanoparticles 600A. In some implementations, the example 3DG carbons described herein may be characterized by a Brunauer-Emmett-Teller (“BET”) surface area measured using nitrogen gas of about 50 to 300 m2 / g. In some implementations,the 3DG carbons may be characterized by a graphene to amorphous carbon ratio of between about 1% and 95%. In some implementations, the 3DG carbons may be characterized by a carbon purity of at least 99.9%. The 3DG carbons may be characterized by an electrical conductivity of between about 500 S / m and about 20,000 S / m when compressed at pressure of about 12,000 pounds per square inch (“psi”). The open porous scaffold structure 681, while confining sulfur, may also provide a host scaffold-type structure to manage volume expansion due to the formation of long chain polysulfides.

[0119] In some implementations, sulfur may be confined in the pores 680 of open porous scaffold structure 681. In some implementations, sulfur may also be confined in the scaffold structure spaces 685 formed by orthogonally joined stacks 683 of graphene layers 684.

[0120] In some implementations, the porous carbon primary nanoparticles 600A may include a plurality of interconnected crinkled 3D graphene sheets, a plurality of non-hollow carbon spherical particles (“NHCS”), flat graphene, wrinkled graphene, or a plurality of carbon nano-onions (“CNOs”). In some implementations, the porous carbon primary nanoparticles 600A may include wavy or flexible graphene layers that resemble crinkled paper and may be produced using microwave processes. The graphene layers may be flexible as they may be fused with each other at sp3type defects in a sp2graphene lattice structure.

[0121] Figure 6B shows a SEM micrograph 600B of porous carbon agglomerates 402, according to other implementations. In some instances, plasma-based processing conditions applied or performed in a reactor such as a microwave reactor may be adjusted with a high degree of tunability to achieve of porous carbon agglomerates and graphene-on-graphene densification to yield the complex 3D carbons 602. The porous carbon agglomerates 602 may be surface etched using methods such as CO2 etching to create pores on the external surface of the aggregates and to increase the surface area of the aggregates.

[0122] The porous carbon agglomerates described herein and characterized using Raman spectroscopy show a high degree of order and uniformity of structure. In this disclosure, “graphene” refers to an allotrope of carbon in the form of a two-dimensional, atomic-scale, hexagonal lattice in which one atom forms each vertex. The carbon atoms in graphene may be sp2hybridized carbon atoms. Additionally, graphene has a Raman spectrum with two main peaks: a G-mode at approximately 1580 cm1and a D mode at approximately 1350 cm1(when using a 532 nm excitation laser). The porous carbon agglomerates may be characterized by a Raman spectroscopy signature having an ID / IG ratio between approximately 0.95 and approximately 1.05.

[0123] Figure 6C shows a TEM micrograph 600C of porous carbon agglomerates, according to some implementations. As shown, the 3D few-layer graphene (“FLG”) structure 604 may be considered to be a porous carbon aggregate at a 50 nm scale. Those skilled in the art will appreciate that the micrographs are shown by way of example only, and that other scales may exist without departing from the scope and spirit of the present implementations.

[0124] Any one of the Li-S battery cathode or anode implementations previously described herein may be configured or disposed for use in cylindrical batteries, prismatic batteries, pouch cells, or any other suitable geometrical shape. A Li-S cylindrical battery may comport with the dimensions of an 18650 battery (about 18 mm diameter x about 65 mm length), a 21700 (about 21 mm diameter x about 70 mm length) battery or a 4680 (about 46 mm diameter x about 80 mm length) battery. In some implementations, a Li-S battery may have a prismatic form factor that can comport with the dimensions of a CP3553 battery. For example, an example Li-S battery may have a height between approximately 56 mm and approximately 58 mm, a length between approximately 34 mm and approximately 36 mm, and a width between approximately 6 mm and approximately 8 mm.

[0125] Figure 7 shows a schematic diagram 700 depicting an example cylindrical battery 700, according to some implementations. Battery 700 may include a shell 710 and a jelly roll 720. Shell 710 may have a longitude axis indicated as AA’ in Figure 4, and jelly roll 720 may be disposed along the longitudinal axis AA’ within shell 710. Jelly roll 720 may have a cross section in a circle, a rectangle, a square, a triangle, or any other geometric shapes. Jelly roll 720 may include an anode 722, a first barrier layer (or separator layer) 724, a cathode 726, and a second barrier layer 728, each in the form of a rollable sheet. Anode 722, first barrier layer 724, cathode 726, and the second barrier layer 728 may be laminated on top of one another. As such, anode 722 and cathode 726 may be separated by the first and the second barrier layers to avoid undesirable short circuiting within battery 700. In some other implementations, a center pin or mandrel (not shown in Figure 7 for simplicity) may be attached to an inner edge of anode 722, and the lamination of cathode-first barrier layer- anode-second barrier layer may be radially wound or rolled around the center pin to form the jelly roll 720. Anode current collector 702 (in the event the anode is not a free-standing anode) and cathode current collectors 704 may be integrated into the anode and cathode layers, respectively.

[0126] In some implementations, anode 722, first barrier layer 724, cathode 726, and second barrier layer 728 may share the same dimensions, and the sheets may be aligned withone another during the rolling process so that there are no sheets protruding from the jelly roll 720. Either anode 722 or cathode 726 current collectors may include a current collector tab, which may protrude out after the sheets are wounded into the jelly roll 720. Tab 723 may connect the anode 722 or the cathode 726 to a negative or positive terminal (not shown in Figure 7 for simplicity), respectively, via any suitable process including a mechanical welding process. In some implementations, tab 723 may be the cathode current collector tab. The anode current collector (not shown for simplicity) may be disposed at the outer edge of the jelly roll 720, and the cathode current collector tab 723 may be disposed approximately in the center of the jelly roll 720.

[0127] In some implementations, either electrode (e.g., the anode 722 or the cathode 726) may be arranged in a misalignment with the other electrode and the first and the second barrier layers 724 and 728 during the rolling process so that a portion 725 may protrude out of the jelly roll 720. In some aspects, an electron conductive glue (not shown in Figure 7 for simplicity) may be disposed within shell 710 at the top and bottom of shell 710. The protruding portion 725 may be connected to the negative or positive terminal of shell 710 via electron conductive glue, and thereby eliminates the need for a mechanical welding process. In some implementations anode 722, anode current collector (not shown), first barrier layer 724, cathode 726, cathode current collector 704 and the second barrier layer 728 may be laminated on top of one another. A center pin or mandrel (not shown in Figure 7 for simplicity) may be configured as the cathode terminal and may be attached to the cathode current collector 704. When disposed as a jelly roll, the anode current collector may be disposed at the outer edge of the jelly roll 720, and the cathode current collector 404 may be disposed approximately in the center of the jelly roll 720.

[0128] In various implementations, anode 722 may be any suitable material that is typically used as an anode in a Li-S battery. For example, anode 722 may be a lithium foil or a lithium substrate. In some instances, anode 722 may include a current collector to support the lithium foil or the lithium substrate. In some aspects, the anode 722 may include freestanding Li-alloy anodes.

[0129] In some implementations, cathode 726 may include one or more layers of films or CSC including any of the previously described rigid porous carbon agglomerates including metal nanoparticles. Cathode 726 may be disposed on cathode current collector 704. The cathode films may coat both sides of a current collector, such as an aluminum foil, to provide the maximum cathode capacity. The cathode CSC including any of the previously describedrigid porous carbon agglomerates having metal nanoparticles may include multiple pores to micro-confine sulfur as the cathode electroactive material. The electroactive material (sulfur) may constitute approximately between 60 wt% and 90 wt% of the cathode films. The electroactive material of the cathode 726 may include other suitable sulfur-containing materials, such as lithium sulfide.

[0130] Battery 700 may have electrolyte (not shown in Figure 7 for simplicity) incorporated into the jelly roll 720. In some implementations, battery 700 may have a liquid electrolyte that may be added to shell 710 after jelly roll 720 is disposed in shell or casing 710. In some other implementations, battery 700 may include a non-aqueous electrolyte such as solid-state electrolyte, gel electrolyte, or polymer film electrolyte incorporated into jelly roll 720. For example, between the first and the second barrier layers 724 and 728, one barrier layer may function as a separator and the other one may function as a non-aqueous electrolyte film. In some other implementations, each of the first and second barrier layers 724 and 728 may function as both a separator and a non-aqueous electrolyte film. The electrolyte may include any one of the electrolyte compositions previously described herein.

[0131] In some implementations, a microporous monolayer polypropylene membrane may be used as a separator disposed between the anode 722 and the cathode 726. The porosity of an example separator (e.g., CelgardR2500) may be about 55%. The separator may have a similar ionic conductivity as the electrolyte but may serve to reduce lithium dendrite formation. The separator may be formed from a ceramic containing material that does not chemically react with metallic lithium. As a result, the separator with ceramic containing material may be used to control lithium-ion transport through the pores dispersed across the separator, while concurrently preventing a short-circuit by impeding the flow or passage of electrons through the electrolyte. The separator layer may include a mechanical strength enhancer coated and / or deposited on the anode. The mechanical strength enhancer may provide structural support for the battery, may prevent lithium dendrite formation from the anode, and / or may prevent protrusion of lithium dendrite throughout the battery. In some exemplary implementations, ceramic particles may be impregnated in the microporous monolayer polypropylene membrane. In some exemplary implementations, the separator may include a ceramic coated separator.

[0132] In a cylindrical Li-ion battery, the dense packing of the various layers in the jelly roll 720 and volume changes during discharge-charge cycling may cause mechanical stresses and ageing of the battery 700. As previously described, volume changes may result fromnon-uniform lithium plating and dendrite formation at the anode, polysulfide “shuttle effect” and growth of solid electrolyte interfaces. Dendrites may even cause fires due to localized heating. Also, pit formation on the anode 722 leads to non-homogenous transport of Li ions from the anode 722 to the cathode 726 and also to fracture of the protective coating / layers disposed on the anode. Similarly, during the charging cycle, lithium dendrites may be formed on the metal anodes due to non-homogenous transport and deposition of Li ions from the cathode to the anode. Pitting and / or dendrite formation leads to uneven stresses and volumetric expansion of the jelly roll 720, which over time causes the layers of the roll 720 to lose intimate contact with one another to exacerbate these issues and lead to accelerated degradation / capacity fade. Cathodes may include any one of the previously described CSC materials including any of the previously described porous carbon agglomerates. Freestanding anodes may include any one of the Li-Mg alloy compositions.

[0133] In some implementations, thin freestanding polyacrylonitrile (“PAN”)-based gel polymer electrolyte (“GPE”) membrane separators made by electrospinning may replace commercial Celgard® separators in lithium-sulfur batteries to realize superior battery cyclic performance even at low E / S ratios. As used herein, a “freestanding” membrane refers to an unsupported membrane. Without being bound by any particular theory, the lithium-sulfur battery coin cells using thin PAN-based GPE membrane separators may improve both battery discharge capacity at capacity retention of greater than 70%, and cycle-life, while using low electrolyte amounts (E / S ratio < 4) by mitigating the polysulfide shuttle effect that is common in lithium- sulfur batteries. PAN-based GPE membrane separators may provide an increased stability towards polysulfides on the cathode side of lithium- sulfur batteries and also a stability (lower reactivity) to the lithium or Li-Mg alloy anode side. PAN-based GPE membrane separators may minimize polysulfide crossover from the cathode to the anode and may also decrease electrolyte consumption or reactivity at the anode, thereby improving anode stability.

[0134] In some implementations, the anode thickness may be reduced in lithium sulfur batteries including freestanding PAN-based GPE membrane separators, because of the mitigation of anode-electrolyte and / or anode-polysulfide side reactions by the PAN-based GPE membranes. A reduction in anode thickness may result in a reduction of the weight of the anode, resulting in a ratio of an areal capacity of the anode to that of the cathode (N / P ratio) of less than 2. As such, battery cyclic life may be improved at capacity retention of > 70% without sacrificing the specific energy (W-h / kg) of lithium- sulfur batteries.

[0135] In some implementations, lithium-sulfur cells including freestanding PAN-based GPE membrane separators may be operated over a wide range of E / S ratios. In some aspects, lithium-sulfur batteries including freestanding PAN-based GPE membrane separators may be designed with a E / S ratio of less than 5 pL / mg in coin cells, which suggests that the E / S ratio may be below 3.5 pL / mg in lithium-sulfur pouch cells. The E / S ratio has a significant impact on specific energy (W-h / kg) of lithium-sulfur batteries. Decreasing the E / S ratio by about 0.5 may result in an increase in specific energy by about 40 W-h / kg.

[0136] In contrast to the example freestanding PAN-based GPE membrane separators described herein, lithium-sulfur batteries including GPE membranes made of other polymers including Polyvinylidene fluoride (“PVDF”), Poly (vinylidene fluoride-co- hexafluoropropylene) (“PVDF-HFP”), and ether and / or ester-based polymers, for example, Polymethyl methacrylate (“PMMA”), Polyethylene Glycol (“PEGs”), and Polyethylene oxides (“PEOs”) are typically prone to early cell failure issues and rapid capacity degradation.

[0137] In some implementations, the example PAN-based GPE membrane separators described herein may be made by electrospinning. In some instances, a thickness of an example thin PAN-based GPE membrane may be less than 30 pm. In some other instances, a thickness of an example thin PAN-based GPE membrane may be about 20 pm. In some implementations, the porosity of an example PAN-based GPE membrane separator may be about 50%. In contrast, GPE membranes produced using conventional wet chemistry methods are comparatively more dense (porosity < 50%) and / or thick GPE membranes, which require batteries to be designed with higher E / S ratios to allow for increased electrolyte uptake in the GPE membranes, which in turn results in an undesirable decrease in the specific energy (W-h / kg) of batteries.

[0138] In some implementations, a lithium-sulfur battery may include a free-standing anode including one or more of a lithium anode or a lithium-alloy anode, a cathode including one or more of elemental sulfur, sulfur composites, or a sulfurized polymer supported in a carbon material, a freestanding PAN-based GPE membrane separator disposed as a separator between the anode and the cathode and a liquid electrolyte. In some instances, example sulfur composites may include one or more of sulfur-dehydrogenated polyacrylonitrile (“S- DPAN”) or a sulfur-polyacrylonitrile-carbon composite. In some other instances, the carbon material in the example sulfur composites may include one or more of graphene, graphene oxides, or carbon black. In some instances, the sulfur composites may include inorganicadditives including one or more of magnesium nickel oxides (“MNO”), titanium oxide, or zirconium oxide.

[0139] In some implementations, an example lithium-sulfur battery including a freestanding PAN -based GPE membrane separator may be characterized by an electrolyte to sulfur (“E / S”) ratio of less than 4 pL / mg. In some instances, an example lithium-sulfur battery including a freestanding PAN-based GPE membrane separator may be characterized by a ratio of an areal capacity of the anode to that of the cathode (“N / P ratio”) of less than 2.

[0140] Figure 11 shows a SEM micrograph 1100 of a freestanding PAN-based GPE membrane separator made by electrospinning, according to some implementations. As can be seen, the membrane separator made by electrospinning may include a nonwoven mat 1001 of PAN-based nanofibers 1102. In some instances, an average diameter of the PAN-based nanofibers may between about 0.15 pm and about 0.5 pm

[0141] In some implementations, an example freestanding PAN-based GPE membrane separator may include one or more inorganic nanoparticles dispersed therein. In some instances, the one or more inorganic nanoparticles may include one or more of titanium oxide (TiCb), silica (SiOs), zirconia (ZrO ), alumina (AI2O3), lanthanum oxide (LmCh), boron nitride, or Lithium lanthanum zirconium oxide (“LLZO”). Other suitable solid electrolytes may also be used as additives in the freestanding PAN-based GPE membrane separators. In some other instances, an amount of the one or more nanoparticles dispersed in the PAN- based GPE membrane may be between about 1 wt% and about 10 wt%. Without being bound by any particular theory, the inorganic nanoparticle fillers or additives may provide one or more of structural rigidity to the freestanding PAN-based GPE membrane, improve resistance to penetration by dendrites originating from the anode, improve adsorption of polysulfides dissolved in the electrolyte, or increase lithium-ion conductivity.

[0142] In some implementations, example freestanding PAN-based GPE membrane separators may include copolymers including one or more of poly(acrylonitrile-vinyl acetate), poly(acrylonitrile- vinyl acetate-methyl methacrylate), or poly(vinylidene fluoride-co- hexafluoropropylene)-polyacrylonitrile. In some other implementations, example PAN-based GPE membrane separators may be disposed as a plurality of membrane layers. In some instances, a composition of each layer in the plurality of membrane layers may substantially be the same. In some other instances, the one or more layers in the plurality of membrane layers may be characterized by a unique composition associated with each layer. The uniquecompositions may include any of the PAN -based GPE membrane compositions described herein.

[0143] In some other implementations, an example PAN-based GPE membrane separator may include carbonaceous particles dispersed therein. As used herein, carbonaceous particles may refer to particles containing or formed of one or more types or configurations of carbon. In some instances, the carbonaceous particles may include graphene. Without being bound by any particular theory, graphene may reduce the polysulfide shuttle effect by accelerating polysulfide reaction at the cathode side of the freestanding PAN-based GPE membrane separator.

[0144] In some implementations, the anode in an example lithium-sulfur battery including a freestanding PAN-based GPE membrane may include a lithium-magnesium (“Li- Mg”) alloy. In some instances, an example Li-Mg alloy may include a 90 wt% Li-10 wt% Mg alloy.

[0145] In some implementations, an example Li-Mg alloy anode may include any one of the Li-Mg alloy compositions previously disclosed herein. In some instances, a magnesium content in the Li-Mg alloy may be between about 15 wt% and about 30 wt%. In some other instances, the freestanding anode may include a composite of a Li-Mg alloy and a lithium-ion conducting material. In some instances, the lithium-ion conducting material includes one or more of lithium titanate (LTO), lithium lanthanum zirconium oxide (LLZO), lithium nitride (LiaN), or lithium phosphide (LLP).

[0146] In some implementations, an amount of the lithium-ion conducting material may be between about 10 wt% and about 40 wt%. In some other implementations, a weight ratio of the Li-Mg alloy to the lithium-ion conducting material may be between about 1 and about 9. In some other implementations, an example Li-Mg alloy anode may further include one or more of alumina (AI2O3) or titanium dioxide (TiCL). The thickness of the freestanding anode may be about 100 pm.

[0147] In some implementations, any of the freestanding anodes previously disclosed herein may include a polymer coating including one or more of pentaerythritol tetraacrylate (“PETEA”) or polyethylene glycol dimethacrylate (“PEGDMA”) disposed on the freestanding anode. The thickness of the coating layer may be between about 1 pm and about 10 pm.

[0148] In some implementations, the liquid electrolyte in an example lithium-sulfur battery including a freestanding PAN-based GPE membrane may include a fluorinated etherelectrolyte. In some instances, an example fluorinated ether electrolyte may include one or more of about (a) 50:25:25 (vol%) 1 ,2-dimethoxy ethane (“DME”): 1,3-dioxolane (“DOL”): bis (2,2,2-trifluoroethyl) ether (“BTFE”) and including about 0.4 M LiTFSI and about 2 wt% LiNO3, (b) about 50:25:25 (vol%) DME : DOL: 1,1,2,2-tetraethoxyethane (“TEE”) and including about 0.4 M LiTFSI and about 2 wt% LiNO3, (c) about 50:25:25 (vol%) DME : DOL: 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFETFE) and including about 0.4 M LiTFSI and about 2 wt% LiNO3. (d) about 60:20:10: 10 (vol%) DME : DOL: TEE: TFETFE and including about 0.4 M LiTFSI and about 2 wt% LiNO3, (e) about 50:25:25 (vol%) DME : DOL: l,l,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and including about 0.4M LiTFSI and about 2 wt% LiNO3, (f) about 50:25:25 (vol%) DME : DOL: 1 fluorinated 1 ,4-dimethoxylbutane (“FDMB”) including about 0.4 M LiTFSI and about 2 wt% LiNO3, or (g) about 1.0 M LiTFSI in about 50:50 (vol%) DOL: BTFE.

[0149] In some implementations, the cathode in an example lithium-sulfur battery including a freestanding PAN-based GPE membrane separator may include one or more of elemental sulfur, composites of sulfur, or sulfurized polymer, supported in a carbon material (also referred to herein as a carbonaceous material). The sulfurized polymer may include sulfurized polyacrylonitrile (“SPAN”).

[0150] In some implementations, the cathode in an example lithium-sulfur battery including a freestanding PAN-based GPE membrane separator may include a carbon material including porous carbon agglomerates of porous carbon primary nanoparticles. In some instances, a respective porous carbon primary nanoparticle may include an inner porous shell disposed about a center of the respective porous carbon primary nanoparticle and enclosing an inner porous carbon region, an outer porous shell enclosing an outer porous carbon region disposed between the inner porous shell and the outer porous shell, and an interconnected porous network disposed in fluid communication with the inner and outer porous carbon regions. Additional details were previously described herein with respect to Figures 5A-5D. In some other instances, the inner porous carbon region and the outer porous carbon region may be characterized by an average pore size and an average pore density associated with each region. The average pore size may decrease along a radial direction from the center to the outer porous shell. In some instances, a porous carbon primary nanoparticle may further include one or more intermediate porous shells disposed between the inner porous shell and the outer porous shell. Additional details were previously described herein with respect toFigure 5E. Each of the intermediate porous shells encloses a respective intermediate porous carbon region.

[0151] In some implementations, porous carbon agglomerates may be characterized by a Raman spectroscopy signature having an ID / IG ratio between approximately 0.95 and 1.05. In some instances, the porous carbon agglomerates may be characterized by a Brunauer- Emmett-Teller (“BET”) surface area between approximately 50 m2 / g and 300 m2 / g measured using nitrogen gas. In some other instances, the porous carbon agglomerates may be characterized by an electrical conductivity of between about 500 S / m and 20,000 S / m when compressed at a pressure of about 12,000 pounds per square inch (psi).

[0152] In some implementations, the cathode in an example lithium-sulfur battery including a freestanding PAN-based GPE membrane separator may include porous carbon agglomerates of porous carbon primary nanoparticles, each nanoparticle including one or more interconnected bundles of electrically conductive graphene layers. Additional details were previously described herein with respect to Figures 6A-6C. In some instances, the graphene layers may be arranged as one or more stacks connected to each other and defining a 3D porous scaffold structure including mesopores. In some other instances, the one or more stacks may be disposed substantially orthogonal to each other. In some instances, the graphene layers may be characterized by a linear dimension of between approximately 50 nm and 200 nm. The graphene layers may include one or more of single layer graphene (“SLG”), few layer graphene (“FLG”), or many layer graphene (“MLG”).

[0153] In some implementations, any one of the PAN-based GPE membrane separator compositions previously disclosed herein may be deposited by electrospinning on to polyethylene-polypropylene (“PE-PP”) separators. Example PE-PP separators include the Celgard® (made by Asahi Kasei) separators. In some other instances, any one of the PAN- based GPE membrane compositions previously disclosed herein may be deposited by electrospinning on to any other porous separators that are inert to chemical or electrochemical reactions that typically occur within a battery. In some instances, an example porous separator including one or more of polyethylene or polypropylene may be characterized by a porosity of about 50% and a thickness of between about 5 pm and about 20 pm.

[0154] In some implementations, an example lithium-sulfur battery may include a freestanding anode including one or more of a lithium anode or a lithium- alloy anode, a cathode including one or more of elemental sulfur, composites of sulfur, or sulfurized polymer, supported in a carbon material, a porous separator coated with a PAN-based GPEmembrane, and a liquid electrolyte. The example lithium- sulfur battery may be characterized by an electrolyte to sulfur (E / S) ratio of less than 4 pL / mg. In some instances, an example porous separator may include a porous material including polyethylene and / or polypropylene. In some other instances, an example porous separator may be characterized by a porosity of about 50%. In some implementations, an example PAN-based GPE membrane may include a nonwoven mat of PAN-based nanofibers deposited on the porous separator by electrospinning. Any one of the PAN-based GPE membranes previously described herein may be deposited on a porous separator by electrospinning. In some instances, an example porous separator may include a Celgard® PP 2075 microporous monolayer membrane material.EXAMPLES

[0155] In the examples described below, the electrolyte used in the Li-S battery implementations include about 50:25:25 (vol%) DME: DOL: BTFE and including about 0.4 M LiTFSI and about 2 wt% LiNOc For symmetric half-cell Li-S battery tests, the example electrolyte may include about IM lithium polysulfides, LizSe.EXAMPLE 1. Cathode discharge capacity of lithium-sulfur coin cells including a freestanding dual-phase alloy anode including Li-Mg alloy and a Li;Ca alloy at C / 3 discharge rate.

[0156] Figure 8 A shows a plot 800A illustrating cathode discharge capacity of lithiumsulfur coin cells including freestanding dual-phase anodes including a Li-Mg alloy phase and a LiiCa alloy phase, according to some implementations. Cathode discharge capacity at C / 3 rate of example lithium-sulfur coin cells was compared to cells including 72Li-28Mg alloy (72 wt% lithium, 28 wt% magnesium) anode. Four dual-phase alloys including Li-Mg-Ca contents (wt%) of (a) 61% Li, 21% Mg, 18% Ca, (b) 55% Li, 17% Mg, 28% Ca, (c) 67% Li, 25% Mg, 8% Ca, and (d) 70% Li, 26% Mg and 4% Ca were evaluated as freestanding anode alloy candidates. The weight ratio of Li-Mg alloy to the LiiCa alloy was between about 0.1 and about 20. The anode thickness in each case was about 100 pm. Formation cycles included 2 discharge / charge cycles at C / 20 rate and 1 cycle at C / 10 rate. The cathode loading was approximately 7.5 mg / cm2. The cathode capacity in each case was approximately 4 mAh / cm2. A Celgard PP2075 separator was used between the cathode and anode. The anode did not include any polymeric material coating. The E / S ratio was about 5.

[0157] Referring to Figure 8A, the cells with dual-phase alloy anodes including 61% Li, 21% Mg, 18% Ca, and 55% Li, 17% Mg, 28% Ca provided a discharge capacity of at least 400 mAh / g at about 150 cycles when compared to the 72Li-28Mg alloy, which required about 100 formation cycles to reach a discharge capacity of about 400 mAh / g.

[0158] To examine the effect of calcium content on discharge capacity, alloys were prepared with calcium content varying from 2 at% (atomic %) to 10 at % in the dual- phase alloy including Li-Mg alloy and LizCa alloy. Figure 8B shows another plot 800B illustrating cathode discharge capacity of lithium-sulfur coin cells including dual-phase freestanding anodes including a Li-Mg alloy phase and a LizCa alloy phase, according to some implementations. As can be seen, calcium content of at least 5 at% is required to realize a discharge capacity of about 600 mAh / g. Without being bound by any particular theory, it appears that increasing the calcium content in the example dual-phase alloy anodes results in a significant boost in discharge capacity even with Mg-rich Li-Mg alloy in the dual-phase alloy.EXAMPLE 2. Rate capability tests of lithium- sulfur symmetric cells including a including a freestanding composite anode including a Li-Mg alloy and LTO.

[0159] Figure 9A shows a plot 900A illustrating the rate capability test performance of lithium-sulfur symmetric cells including a freestanding composite anode including a Li-Mg alloy and LTO, according to some implementations. The rate capability test in the symmetric cells were conducted at areal current densities from 0.4 mA / cm2to 13 mA / cm2. In the symmetric cells, Li-Mg or Li-Mg / LTO electrodes were separated by a Celgard PP2075 separator. Rate capability tests may be used to monitor voltage loss at increasing current densities. Negligible voltage loss or polarization suggests that the cell is capable of high discharge capacities. As can be seen from Figure 9A, the cells with Li-Mg / LTO composite anodes show negligible voltage loss across current densities from 0.4 mA / cm2to 13 mA / cm2compared to cells with Li-Mg alloy anodes. At a current density of 13 mA / cm2, the symmetric cells the Li-Mg / LTO composite anodes showed a voltage loss of only about 0.12 V, which is about a third of the overpotential of about 0.3V measured using the symmetric cells using Li-Mg anodes.

[0160] Figure 9B shows a plot 900B illustrating corrosion current after lithium stripping measured using lithium- sulfur symmetric cells including a freestanding composite anode including a Li-Mg alloy and LTO, according to some implementations. Figure 9C shows a plot 900C illustrating corrosion current after lithium plating measured using lithium- sulfursymmetric cells including a freestanding composite anode including a Li-Mg alloy and LTO, according to some implementations. The corrosion currents after stripping and plating were obtained using Tafel plots (not shown). Referring to Figure 9B, the corrosion current after stripping in cells with Li-Mg anodes and Li-Mg / LTO composite anode is not significantly different. Additionally, the significantly higher corrosion current associated with cells including lithium-metal anodes indicate that cells with Li-Mg anodes may result in better cyclic stability compared to cells with lithium-metal anodes.

[0161] Referring to Figure 9C, the corrosion current after lithium plating suggests that the low reactivity of the Li-Mg / LTO composite anode may be a promising candidate for increasing the cyclic stability in lithium-sulfur batteries. As previously discussed with reference to Figure 9A, the cells with Li-Mg / LTO composite anodes also showed negligible voltage loss across current densities from 0.4 mA / cm2to 13 mA / cm2indicative of high discharge capacities.EXAMPLE 3. Cathode discharge capacity of lithium-sulfur coin cells including a freestanding Li-Mg / LTO composite anode at C / 3 discharge rate.

[0162] Figure 10 shows a plot 1000 illustrating cathode discharge capacity of lithiumsulfur coin cells including a freestanding Li-Mg / LTO composite anode including a Li-Mg alloy and LTO, according to some implementations.

[0163] Cathode discharge capacity at C / 3 rate of example lithium-sulfur coin cells with Li-Mg / LTO composite anodes was compared with cells including 72Li-28Mg alloy anode (72 wt% lithium, 28 wt% magnesium) and cells with 90Li-10Mg alloy (90 wt% lithium, 10 wt% magnesium) alloy anode. Two Li-Mg / LTO composite anode compositions were evaluated: 72Li-28Mg / LTO and 90Li-10Mg / LTO. The anode thickness in each case was about 100 pm. Formation cycles included 2 discharge / charge cycles at C / 20 rate and 1 cycle at C / 10 rate. The cathode loading was approximately 7.5 mg / cm2. The cathode capacity in each case was approximately 4 mAh / cm2. A Celgard PP2075 separator was used between the cathode and anode. The anode did not include any polymeric material coating. The E / S ratio was about 5. The anode did not include any polymeric material coating.

[0164] Referring to Figure 10, the cells with 72Li-28Mg / LTO composite anodes were characterized by higher reactivity and improved cycling through about 200 cycles compared to the performance of the 72Li-28Mg alloy anode. The cells with 72Li-28Mg / LTO composite anodes also had better cyclic stability than the cells with the 90Li-10Mg / LTO anodes indicating that the addition of LTO resulted in improving cyclic stability at highdischarge capacities of about 600 mAh / g and confirm the observations associated with Figures 9A-9C. Optimizing the Li-Mg composition (for example, increasing Mg content) and screening of lithium-ion conductive fillers may further improve the cyclic stability of lithium-sulfur batteries without sacrificing discharge capacity.EXAMPLE 4. Cathode discharge capacity and capacity retention of lithium- sulfur coin cells including various membrane separators at C / 3 discharge rate.

[0165] Figure 12A shows a plot 1200A illustrating cathode discharge capacity of lithiumsulfur coin cells including various membrane separators, according to some implementations. Figure 12B shows a plot 1200B illustrating capacity retention of lithium-sulfur coin cells including various membrane separators, according to some implementations. The lithiumsulfur battery coin cells included a 90wt% Li- 10 wt% Mg alloy anode and were cycled at C / 3 charge / discharge rate. The electrolyte included about 50:25:25 (vol%) DME: DOL: BTFE and including about 0.4 M LiTFSI and about 2 wt% LiNOv The freestanding PAN-based GPE membrane separators were produced by electrospinning and were characterized by a thickness of about 20 pm - 40 pm. For comparison, the Celgard® PP2075 separator used in reference lithium- sulfur cells was about 20 pm thick. Coin cells using Celgard® separators were also cycled at C / 3 charge / discharge rate. The cathode loading was about 5 mg / cm2.The E / S ratio was about 5 pL / mg. As can be seen, the coin cells with the PAN-based GPE membrane separators outperformed the coin cells with the Celgard® separator as cathode discharge capacity of greater than 550 mAh / g at capacity retention greater than 80% (target capacity retention is 70%) was measured through 100 cycles.EXAMPLE 5. Cathode discharge capacity and capacity retention of lithium-sulfur coin cells including various membrane separators at asymmetric charge / discharge rates.

[0166] Figure 13A shows a plot 1300A illustrating cathode discharge capacity of lithiumsulfur coin cells including various membrane separators, according to some implementations. Figure 13B shows a plot 1300B illustrating capacity retention of lithium-sulfur coin cells including various membrane separators, according to some implementations. During these tests, the lithium-sulfur coin cells were asymmetrically cycled at C / 5 charge rate and C / 3 discharge rate. Asymmetric cyclic testing protocol was used because the PAN-based GPE membrane separators absorb or trap polysulfides and are characterized by a higher impedance compared to commercial Celgard® separators. Accordingly, cells including PAN-based GPE membrane separators may require a slower charge rate to urge polysulfides to move back to the cathode during the charge cycle. The lithium-sulfur coin cells including the Celgard®PP2075 separators were cycled at C / 3 discharge rate. The freestanding PAN-based GPE membrane separators were produced by electrospinning and were characterized by a thickness of about 30 pm - 50 pm. In all other aspects, the lithium-sulfur cell design was similar to that previously described with respect to Example 4. As can be seen, the coin cells with the PAN-based GPE membrane separators outperformed the coin cells with the Celgard® separator as cathode discharge capacity of about 600 mAh / g at capacity retention greater than 80% (target capacity retention was 70%) was measured through 100 cycles.

[0167] The lithium- sulfur battery cyclic tests results described in Examples 4 and 5 demonstrate that thin PAN-based GPE membrane separators made by electrospinning may replace commercial Celgard® separators in lithium-sulfur batteries to realize superior battery cyclic performance even at low E / S ratios.EXAMPLE 6. Cathode discharge capacity and capacity retention of lithium- sulfur coin cells including various membrane separators at asymmetric charge / discharge rates.

[0168] Figure 14 shows a plot 1400 illustrating cathode discharge capacity of lithiumsulfur coin cells including various membrane separators, according to some implementations. During these tests, the lithium- sulfur coin cells were asymmetrically cycled at C / 10 charge rate and C / 3 discharge rate. The freestanding GPE membranes included PVDF-HFP / PEO dual layer membranes with ZrO: inorganic additives and were produced using wet chemistry (20 pm - 30 pm thick), and using electrospinning (20 pm thick). In addition, PAN-based GPE membranes (about 60 pm thick) with TiO2 inorganic additives were produced by electrospinning. The E / S ratio in the cells using the dual-layer PVDF-HFP / PEO GPE membranes was about 6 pL / mg - 7.5 pL / mg. The E / S ratio in the cells using the PAN-based GPE membrane was about 5 pL / mg. The lithium-sulfur battery coin cells included a 90wt% Li-10 wt% Mg alloy anode, and were cycled at C / 10-C / 3 charge / discharge rate. The electrolyte in the coin cells included about 50:25:25 (vol%) DME: DOL: BTFE and including about 0.4 M LiTFSI and about 2 wt% LiNO3. The cathode loading was about 7.5 mg / cm2.

[0169] As can be seen, the coin cells including the freestanding PAN-based GPE membrane outperformed the other coin cells including the dual-layer PVDF-HFP / PEO GPE membranes. The cells including the freestanding PVDF-HFP / PEO dual layer membranes were made using wet chemistry methods shorted within 50 cycles. The cells including the freestanding PVDF-HFP / PEO dual-layer membrane made by electrospinning were cycled to more than 200 cycles but at cathode discharge capacity of less than 400 mAh / g. In contrast, the cells including freestanding PAN-based GPE membranes formed by electrospinning werecycled to about 190 cycles at relatively lower E / S ratio of 5 |iL / mg but at significantly higher cathode discharge capacities of about 500 mAh / g.EXAMPLE 7. Cathode discharge capacity and capacity retention of lithium-sulfur coin cells including PAN-based GPE membrane at E / S ratio of 4.

[0170] Figure 15A shows a plot 1500A illustrating cathode discharge capacity of lithiumsulfur coin cells including freestanding PAN-based GPE membrane separators, according to some implementations. Figure 15B shows a plot 1500B illustrating capacity retention of lithium-sulfur coin cells including freestanding PAN-based GPE membrane separators, according to some implementations. During these tests, the lithium-sulfur coin cells were asymmetrically cycled at C / 10 charge rate and C / 3 discharge rate. The freestanding PAN- based GPE membrane separators were produced by electrospinning and were characterized by a thickness of about 20 pm - 40 pm. The E / S ratio was about 4 pL / mg. In all other aspects, the lithium- sulfur cell design was similar to that previously described with respect to Example 4. As can be seen, stable cyclic activity through about 100 cycles was observed at cathode discharge capacity of about 600 mAh / g and at capacity retention of greater than 80%.EXAMPLE 8. Representative electrochemical properties of freestanding PAN-based GPE membranes made by electrospinning.

[0171] Table 1 summarizes representative electrochemical properties of freestanding PAN-based GPE membrane separators made by electrospinning, according to some implementations The corresponding properties of a commercial Celgard® PP2075 separator are also shown for comparison.Table 1. Representative electrochemical properties of freestanding PAN-based GPE membrane separators made by electrospinning.

[0172] In Table 1, “Io” denotes initial polarization current, “ISs” denotes steady state polarization current, “Zo” and “Zss” denote initial impedance and steady state impedance, respectively, “AV” denotes voltage applied across a test cell to collect impedance and current data, “T+” denotes lithium-ion transference number, and “o” denotes ionic conductivity. Tests were conducted in symmetric cells. As can be seen, at a lithium-ion transference number comparable to that of a commercial Celgard® PP2075 membrane, and at a comparable thickness of 20 pm, the ionic conductivity of the freestanding PAN-based GPE membrane including TiCb inorganic additives was about 6-times greater than that of the Celgard® membrane.

[0173] As used herein, a phrase referring to “at least one of” or “one or more of’ a list of items refers to any combination of those items, including single members. For example, “at least one of: a, b, or c” is intended to cover the possibilities of: a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c. Unless otherwise specified in this disclosure, for construing the scope of the term “about” or “approximately,” the error bounds associated with the values (dimensions, operating conditions etc.) disclosed is ± 10% of the values indicated in this disclosure. The error bounds associated with the values disclosed as percentages is ± 1 % of the percentages indicated. The word “substantially” used before a specific word includes the meanings “considerable in extent to that which is specified,” and “largely but not wholly that which is specified.”

[0174] Various modifications to the implementations described in this disclosure may be readily apparent to persons having ordinary skill in the art, and the generic principles defined herein may be applied to 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.

[0175] Additionally, various features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. As such, although features may be described above in combination with one another, and even initially claimed as such, one or more features from a claimedcombination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0176] 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 flowchart or flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In some 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 can generally be integrated together in a single product or packaged into multiple products.

Claims

AMENDED CLAIMS received by the International Bureau on 22 October 2025 (22.10.2025)1. A lithium-sulfur battery including: a freestanding anode including one or more of lithium or a lithium-alloy; a cathode including one or more of elemental sulfur, sulfur composites, or a sulfurized polymer supported in a carbon material; and a porous separator coated with a polyacrylonitrile (PAN) -based GPE membrane and disposed between the freestanding anode and the cathode.

2. The lithium-sulfur battery of claim 1, further comprising a liquid electrolyte, wherein an electrolyte to sulfur (E / S) ratio of the lithium-sulfur battery is less than 4 pL / mg.

3. The lithium-sulfur battery of claim 1, wherein the PAN-based GPE membrane includes copolymers including one or more of poly(acrylonitrile-vinyl acetate), poly (acrylonitrile- vinyl acetate-methyl methacrylate), or poly (vinylidene fluoride-co- hexafluoropropylene)-polyacrylonitrile.

4. The lithium-sulfur battery of claim 1 , wherein a ratio of an areal capacity of the anode to an areal capacity of the cathode (N / P ratio) is less than 2.

5. The lithium-sulfur battery of claim 1, wherein a thickness of the PAN-based GPE membrane is less than 30 pm.

6. The lithium-sulfur battery of claim 1, wherein a thickness of the PAN-based GPE membrane is about 20 pm.

7. The lithium-sulfur battery of claim 1, wherein a porosity of the PAN-based GPE membrane is about 50 %.

8. The lithium-sulfur battery of claim 1, wherein the PAN-based GPE membrane includes a nonwoven mat of PAN-based nanofibers made by electrospinning.

9. The lithium-sulfur battery of claim 8, wherein an average diameter of the PAN-based nanofibers is between about 0.15 pm and about 0.5 pm.

10. The lithium-sulfur battery of claim 1, wherein the PAN-based GPE membrane includes one or more inorganic nanoparticles dispersed therein.

11. The lithium-sulfur battery of claim 10, wherein the one or more inorganic nanoparticles include one or more of titanium oxide (TiCh), silica (SiCh), zirconia (ZrCh), alumina (AI2O3), lanthanum oxide (LmCh), boron nitride, or Lithium lanthanum zirconium oxide (LLZO).

12. The lithium-sulfur battery of claim 10, wherein an amount of the one or more inorganic nanoparticles dispersed in the PAN-based GPE membrane is between about 1 wt% and about 10 wt%.

13. The lithium-sulfur battery of claim 1, wherein the PAN-based GPE membrane includes carbonaceous particles dispersed therein.

14. The lithium-sulfur battery of claim 13, wherein the carbonaceous particles include graphene.

15. The lithium-sulfur battery of claim 1, wherein the PAN-based GPE membrane includes a plurality of membrane layers.

16. The lithium-sulfur battery of claim 15, wherein a composition of each layer of the plurality of membrane layers is substantially the same.

17. The lithium-sulfur battery of claim 15, wherein at least some of the plurality of membrane layers are characterized by unique compositions.

18. The lithium-sulfur battery of claim 1, wherein the lithium-alloy includes a lithium-magnesium (Li-Mg) alloy.

19. The lithium-sulfur battery of claim 18, wherein the Li-Mg alloy includes a 90 wt% Li-10 wt% Mg alloy.

20. The lithium-sulfur battery of claim 18, wherein a magnesium content in the Li-Mg alloy is between about 15 wt% and about 30 wt%.

21. The lithium-sulfur battery of claim 1, wherein the freestanding anode includes a composite of a Li-Mg alloy and a lithium-ion conducting material.

22. The lithium-sulfur battery of claim 21, wherein an amount of the lithium-ion conducting material is between about 10 wt% and about 40 wt%.

23. The lithium-sulfur battery of claim 21, wherein the lithium-ion conducting material includes one or more of lithium titanate (LTO), lithium lanthanum zirconium oxide (LLZO), lithium nitride (LisN), or lithium phosphide (LiaP).

24. The lithium-sulfur battery of claim 21, wherein a weight ratio of the Li-Mg alloy to the lithium-ion conducting material is between about 1 and about 9.

25. The lithium-sulfur battery of claim 21, wherein the Li-Mg alloy further includes one or more of alumina (AI2O3) or titanium dioxide (TiCL).

26. The lithium-sulfur battery of claim 1, wherein the liquid electrolyte includes a fluorinated ether electrolyte.

27. The lithium-sulfur battery of claim 26, wherein the fluorinated ether electrolyte includes one or more of: about 50:25:25 (vol%) 1 ,2-dimethoxyethane (DME): 1,3-dioxolane (DOL): bis (2,2,2- trifluoroethyl) ether (BTFE) and including about 0.4 M LiTFSI and about 2 wt% LiNCL; about 50:25:25 (vol%) DME : DOL: 1,1,2,2-tetraethoxyethane (TEE) and including about 0.4 M LiTFSI and about 2 wt% LiNOc about 50:25:25 (vol%) DME : DOL: 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFETFE) and including about 0.4 M LiTFSI and about 2 wt% LiNOv about 60:20:10:10 (vol%) DME : DOL: TEE: TFETFE and including about 0.4 MLiTFSI and about 2 wt% LiNOqabout 50:25:25 (vol%) DME : DOL: l,l,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and including about 0.4M LiTFSI and about 2 wt% LiNCh; about 50:25:25 (vol%) DME : DOL: 1 fluorinated 1,4-dimethoxylbutane (FDMB) including about 0.4 M LiTFSI and about 2 wt% LiNOc or about 1.0 M LiTFSI in about 50:50 (vol%) DOL: BTFE.

28. The lithium-sulfur battery of claim 1, wherein the sulfurized polymer includes sulfurized polyacrylonitrile (SPAN).

29. The lithium-sulfur battery of claim 1, wherein the carbon material includes porous carbon agglomerates of porous carbon primary nanoparticles.

30. The lithium-sulfur battery of claim 29, wherein a respective porous carbon primary nanoparticle includes: an inner porous shell disposed about a center of the respective porous carbon primary nanoparticle and enclosing an inner porous carbon region; an outer porous shell enclosing an outer porous carbon region disposed between the inner porous shell and the outer porous shell; and an interconnected porous network disposed in fluid communication with the inner and outer porous carbon regions.

31. The lithium-sulfur battery of claim 30, wherein the inner porous carbon region and the outer porous carbon region are characterized by an average pore size and an average pore density.

32. The lithium-sulfur battery of claim 31, wherein the average pore size decreases along a radial direction from the center to the outer porous shell.

33. The lithium-sulfur battery of claim 30, wherein the respective porous carbon primary nanoparticle further includes one or more intermediate porous shells disposed between the inner porous shell and the outer porous shell, wherein each of the intermediate porous shells encloses a corresponding intermediate porous carbon region.

34. The lithium-sulfur battery of claim 29, wherein the porous carbon agglomerates are characterized by a Raman spectroscopy signature having an ID / IG ratio between approximately 0.95 and 1.05.

35. The lithium-sulfur battery of claim 29, wherein the porous carbon agglomerates are characterized by a Brunauer-Emmett-Teller (BET) surface area between approximately 50 m2 / g and 300 m2 / g measured using nitrogen gas.

36. The lithium-sulfur battery of claim 29, wherein the porous carbon agglomerates are characterized by an electrical conductivity of between about 500 S / m and 20,000 S / m when compressed at a pressure of about 12,000 pounds per square inch (psi).

37. The lithium-sulfur battery of claim 29, wherein a respective porous carbon primary nanoparticle includes one or more interconnected bundles of electrically conductive graphene layers.

38. The lithium-sulfur battery of claim 37, wherein the one or more electrically conductive graphene layers are arranged as one or more stacks connected to each other and collectively define a 3D porous scaffold structure including mesopores.

39. The lithium-sulfur battery of claim 38, wherein the one or more stacks are disposed substantially orthogonal to each other.

40. The lithium-sulfur battery of claim 37, wherein the one or more electrically conductive graphene layers are characterized by a linear dimension of between approximately 50 nm and 200 nm.

41. The lithium-sulfur battery of claim 37, wherein the one or more electrically conductive graphene layers include one or more of single layer graphene (SLG), few layer graphene (FLG), or many layer graphene (MLG).

42. A lithium-sulfur battery including: a freestanding anode including one or more of lithium or a lithium-alloy;a cathode including one or more of elemental sulfur, sulfur composites, or sulfurized polymer supported in a carbon material; a porous separator coated with a polyacrylonitrile (PAN)-based GPE membrane; and a liquid electrolyte, wherein an electrolyte to sulfur (E / S) ratio in the lithium-sulfur battery is less than 4 pL / mg.

43. The lithium-sulfur battery of claim 42, wherein the porous separator includes a porous material including one or more of polyethylene or polypropylene.

44. The lithium-sulfur battery of claim 42, wherein a porosity of the porous separator is about 50%.

45. The lithium-sulfur battery of claim 42, wherein the PAN-based GPE membrane includes a nonwoven mat of PAN-based nanofibers made by electrospinning.

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