Li-Se Batteries Research Articles

State-Of-The-Art and Future Challenges in High Energy Lithium-Selenium Batteries.

Li-chalcogen batteries, especially the Li-S batteries (LSBs), have received paramount interests as next generation energy storage techniques because of their high theoretical energy densities. However, the associated challenges need to be overcome prior to their commercialization. Elemental selenium, another chalcogen member, would be an attractive alternative to sulfur owing to its higher electronic conductivity, comparable capacity density, and moreover, excellent compatibility with carbonate electrolytes. Unlike LSBs, the research and development of Li-Se batteries (LSeBs) have garnered burgeoning attention but are still in their infant stage, where a comprehensive yet in-depth overview is highly imperative to guide future research. Herein, a critical review of LSeBs, in terms of the underlying mechanisms, cathode design, blocking layer engineering, and emerging solid-state electrolytes is provided. First, the electrolyte-dependent electrochemistry of LSeBs is discussed. Second, the advances in Se-based cathodes are comprehensively summarized, especially highlighting the state-of-the-art Sex Sy cathodes, and mainly focusing on their structures, compositions, and synthetic strategies. Third, the versatile separators/interlayers optimization and interface regulation are outlined, with a particular focus on the emerging solid-state electrolytes for advanced LSeBs. Last, the remaining challenges and research orientations in this booming field are proposed, which are expected to motivate more insightful works.

Understanding the anchoring and catalytic effect of the Co@C2N monolayer in lithium-selenium batteries: a first-principles study.

The practical applications of lithium-selenium (Li-Se) batteries are impeded due to the low utilization of active selenium, sluggish kinetics, and volume change. The development of highly efficient host materials to suppress high-order polyselenide shuttling and accelerate Li2Se conversion is essential for Li-Se batteries. Herein, a theoretical design of a Co@C2N monolayer as a host material for ultra-high areal capacity Li-Se batteries is proposed by first-principles calculations. The investigations of the lowest energy configurations, binding energies, and the charge transfer indicate that the Co@C2N monolayer could alleviate the reciprocating motion of high-order polyselenides and improve the cycling performance. Further electronic property calculations show that the semi-metallic characteristics of the Co@C2N monolayer material are retained even after chemical adsorption with Se8 or Li2Sen molecules, which is beneficial for the utilization of active selenium. In addition, the crucial catalytic role of the Co@C2N monolayer is investigated and the results indicate that the Co@C2N monolayer could facilitate the formation and decomposition of Li2Se molecules during the discharge and charge processes. Our present work would not only provide a deep understanding on the anchoring and catalytic effect of the Co@C2N monolayer, but also demonstrate a general principle for the rational design and screening of advanced materials for high energy density Li-Se batteries.

A MOF-derived carbon host associated with Fe and Co single atoms for Li–Se batteries

Lithium–selenium (Li–Se) batteries are considered a promising energy storage material due to their high electronic conductivity and volume capacity.

Unraveling the superior anchoring of lithium polyselenides to the confinement bilayer C2N: an efficient host material for lithium-selenium batteries.

Carbonaceous materials with pores or bilayer spaces are a kind of potential host material to confine polyselenide diffusion and mitigate the shuttling effect. In the present work, a theoretical design of bilayer C2N (bi-C2N) as an efficient host material for lithium-selenium (Li-Se) batteries was explored by first-principles calculations. AA- and AB-stacking bilayer C2N could alleviate the dissolution of high-order polyselenides through a synergistic effect of physical confinement and strong Li-N bonds. Lithium polyselenides prefer to anchor on AA- and AB-stacking bilayer C2N instead of the commonly used electrolytes, showing their capabilities in suppressing the shuttle effect. Charge transfer occurs from Se8 and Li2Sen molecules (LiPSes) to AA- and AB-stacking bilayer C2N, giving rise to the formation of strong Li-N bonds. The AA- and AB-stacking LiPSes@C2N systems possess high electrical conductivities, which is beneficial for high electrochemical performance. In addition, the reversible conversion mechanisms of Li2Sen in the AA- and AB-stacking bilayer C2N are also investigated through the energy changes and decomposition reaction of the Li2Se molecule, and the results indicate that AA- and AB-stacking bilayer C2N facilitate the formation and decomposition of Li2Se by decreasing the active energy barriers and improving the selenium utilization rates. Our present work could shed some light on a possible strategy for designing highly efficient bilayer host materials for high performance Li-Se batteries.

Weaving 3D highly conductive hierarchically interconnected nanoporous web by threading MOF crystals onto multi walled carbon nanotubes for high performance Li–Se battery

Weaving 3D highly conductive interconnected hierarchically nanoporous web by threading MOF crystals onto multi walled carbon nanotubes for high performance lithium–selenium battery. • Pure MOF materials in Li–Se battery with highly superior performance. • 3D highly conductive hierarchical porous MIL-68 (Al)@MWCNTs web. • Novel Se cathode configurations. • Weaving the 3D highly conductive hierarchically interconnected nanoporous web. • Threading microporous metal organic framework MIL-68(Al) crystals. Lithium–selenium (Li–Se) battery has attracted growing attention. Nevertheless, its practical application is still impeded by the shuttle effect of the formed polyselenides. Herein, we report in-situ hydrothermal weaving the three-dimensional (3D) highly conductive hierarchically interconnected nanoporous web by threading microporous metal organic framework MIL-68(Al) crystals onto multi-walled carbon nanotubes (MWCNTs). Such 3D hierarchically nanoporous web (3D MIL-68 (Al)@MWCNTs web) with a very high surface area, a large amount of micropores, electrical conductivity and elasticity strongly traps the soluble polyselenides during the electrochemical reaction and significantly facilitates lithium ion diffusion and electron transportation. Molecular dynamic calculation confirmed the strong affinity of MIL-68 (Al) for the adsorption of polyselenides, quite suitable for Li–Se battery. Their hexahedral channels (1.56 nm) are more efficient for the confinement of polyselenides and for the diffusion of electrolytes compared to their smaller triangular channels (0.63 nm). All these excellent characteristics of 3D MIL-68 (Al)@MWCNTs web with suitable confinement of a large amount of selenium and the conductive linkage between MIL-68(Al) host by MWCNTs result in a high capacity of 453 mAh/g at 0.2C with 99.5% coulombic efficiency after 200 cycles with significantly improved cycle stability and rate performance. The 3D MIL-68 (Al)@MWCNTs web presents a good performance in Li–Se battery in term of the specific capacity and cycling stability and also in terms of rate performance compared with all the metal–organic framework (MOF) based or MOF derived porous carbons used in Li–Se battery.

High-performance Li–Se battery: Li2Se cathode as intercalation product of electrochemical in situ reduction of multilayer graphene-embedded 2D-MoSe2

Lithium–selenium (Li–Se) batteries are considered as promising candidates for next-generation battery technologies, as they have high energy density and low cost. A new class of electrochemical intercalation of interlayer MoSe2 to graphene (Gr) Li2Se based cathode materials for room temperature Li–Se batteries is reported. An advanced approach preparing spatially confined Li2Se cathode active materials inside carbon materials to minimize the shuttle effects of Se compounds is confirmed by XRD, XPS, TEM and electrochemical analysis studies. The starting chalcogenide Gr–MoSe2 were synthesized by applying a closed reflux system in diethylene glycol solvent, polypropylviologen as a carbon (C) precursor source, and selenoacetamide were used as Se precursor and followed by calcination under the Ar and N2 atmosphere to form Gr- layers between MoSe2 interlayers. Then, Mo in Gr–MoSe2 nanocomposites are electrochemically reduced (lithiation process) to give multi-layered graphene structures, and selenide compounds, Li2Se is generated inside graphene multi-layers, simultaneously in Li-Se battery. The capacity decay rate of the cell is 0.04% per cycle for 100 cycles, with nearly 100% coulombic efficiency throughout the cycling at current density of 1 Ag−1. Nyquist plots, were reported for electrochemical impedance Gr–MoSe2 as active materials after pretreatment step of 2 cycles (0.01–3 V) at 3 V and 0.01 V vs Li+/Li. Based on the conductivity of Gr–MoSe2 characteristics, reporting here also a new class of cathode of Li2Se, there is no conductive additive of carbon black to the active material.

Electrode and Interface Design for High-Performance Lithium/Sodium-Selenium Batteries

Lithium/sodium-selenium (Li/Na-Se) batteries are promising energy storage systems due to their relatively low cost and high volumetric energy density of Se cathode. Rechargeable lithium-ion batteries (LIBs) play a critical role in portable devices, electric vehicles and large-scale stationary energy storage, due to their relatively high energy density and low cost among available technologies [1]. Sodium-selenium (Na-Se) batteries have also drawn much attention, because of the large abundance and low cost of sodium and decent energy density of Se [2]. As a cathode material, Se provides a moderate gravimetric capacity of 678 mAh g−1, a high volumetric capacity of 3270 mAh cm−3, and possesses a high electronic conductivity of 1 ×10 −3 S m−1 [3, 4]. These advantages of Se have stimulated growing research in developing Li-Se and Na-Se batteries over the past years. However, the practical application of these batteries has been hindered by the polyselenides dissolution (or shuttle effect phenomena), which could cause low Coulombic efficiency and poor cycling lifetime. Microporous carbon (MPC) has been fabricated through a facile carbonization method from polyvinylidene fluoride (PVDF) and used without any further activation as selenium host to produce MPC/Se composite employed as cathode in rechargeable lithium/sodium-selenium (Li/Na-Se) batteries and the electrochemical properties of the prepared cell have been investigated in Li-Se batteries. (figures 1 and 4).Basically, in linear carbonate-containing electrolytes, the metal readily decomposes at the anode side, causing capacity drop over cycling. To address this problem, electrolyte design should accompany manifested cathode structure. Hence, fluoroethylene carbonate (FEC) has been used as an additive in the electrolyte solution for stabilizing the capacity in Na-Se batteries. Our investigation showed that exceptional cell stability could be reached by using the FEC in carbonate-based electrolyte. In lithium/sodium-selenium batteries, diethyl carbonate (DEC) electrolyte decomposes in contact with metal, producing some radicals and metal alkyl carbonates. These radicals start a chain reaction, causing the destruction of over cycles. By adding the FEC to the electrolyte solution, this side reaction will be prohibited. [5] FEC readily decomposes on the surface of the metal prior to any reduction of linear carbonates, making the protective and stable surface film on the metal. This layer makes the capacity much more stable for the cell contains FEC in the electrolyte. For the cell without FEC in the electrolyte, the capacity starts to fade from initial cycles and continue fading during the cycling. In sodium/selenium batteries, at the current rate of 0.1 C, the cell contains no FEC in the electrolyte, showed a capacity of 317 and 245 mAh g-1 after 100 and 200 cycles, respectively. However, the cell with an electrolyte solution containing 3% FEC, showing excellent cyclability by way of delivering 382 and 350 mAh g-1 capacity at those above-mentioned cycles, respectively (figures 2 and 5). Another important finding was that the use of FEC additive could prevent the corrosion of metal anode from soluble polyselenides, and preserve the structural integrity of metal anode, contributing to the enhanced cycling stability and specific capacity of Na-Se batteries.The utilization of nanoscale Al2O3 surface coating by atomic layer deposition (ALD) to protect a MPC/Se cathode and reduce polyselenide dissolution was also investigated in another stage. It was found that Al2O3 surface coating effectively suppressed the polyselenide dissolution from the MPC/Se cathode, thus reducing the loss of Se active material and improving the overall performance of Na-Se batteries. Compared to the pristine MPC/Se, Al2O3-coated MPC/Se cathode exhibited improved discharge capacity, cycling stability, and rate capability in Na-Se batteries (figures 3 and 6). Keywords: Fluoroethylene carbonate; lithium/sodium−selenium batteries; ALD coating; carbonate-based electrolyte; microporous carbon

Electrochemical Activation for Improved Cycle Life of Li-Se Batteries

Recently, the lithium-selenium (Li-Se) batteries have received enormous interest as a promising candidate for next-generation rechargeable batteries. Although selenium is similar to sulfur because they belong to the same group (chalcogenides), Li-Se battery has an advantage beyond lithium-sulfur batteries. Selenium is less reactive and more controllable in an electrochemical cell. Moreover, it has a much higher electrical conductivity than sulfur, which enables high utilization of selenium. However, one problem is the dissolution of lithium polyselenides. The lithium polyselenides aggregate at the cathode surface, resulting in increased cell impedance. To solve this problem, many experiments have been suggested but they were difficult to conduct. Herein, a simple and facile method is introduced to improve cycle performance. Before the fully discharge process, the Li-Se cell was activated electrochemically. This activation leads to a significant improvement in cycle performance by the redistribution of selenium on the electrode.

Porous Bamboo‐Derived Carbon as Selenium Host for Advanced Lithium/Sodium–Selenium Batteries

Selenium (Se) has received extensive attention as the most competitive cathode material for next generation high‐energy batteries. However, the shuttle effect of polyselenide and volume change lead to inferior electrochemical properties. To solve these issues, a porous bamboo‐derived carbon (PBC) with abundant meso/micropores is prepared as a framework to effectively encapsulate elemental selenium. For Li–Se batteries, Se/PBC electrode delivers an outstanding capacity of 509 mAh g−1 after 200 cycles at 0.2 C (1 C = 675 mA g−1) with a low capacity fade of 0.036% per cycle. The Se/PBC composite also reveals a satisfied electrochemical performance for Na–Se batteries with an excellent capacity of 409 mAh g−1 after 200 cycles at 0.2 C. Moreover, Se/PBC electrode also presents excellent long‐term cycle performance and rate performance at 15 C for Li–Se batteries and 10 C for Na–Se batteries. The outstanding properties are attributed to the specific 3D structure and high conductivity of PBC, which significantly inhibits the shuttle effect and enhances the reaction kinetics. Herein, not only the great application potential of bamboo in energy storage systems is demonstrated, but also an effective approach and low‐cost strategy for improving the performance of lithium/sodium–selenium batteries is offered.

High stable rate cycling performances of microporous carbon spheres/selenium composite (MPCS/Se) cathode as lithium–selenium battery

Loading selenium (Se) into microporous carbon spheres (MPCS) for the use as a cathode material is an efficient method for reducing the volume expansion and dissolution of polyselenides in the lithium-selenium (Li–Se) batteries during cycling. In this study, we produced MPCSs from glucose using a simple and efficient hydrothermal synthesis method, followed by activation of the MPCS with KOH. Selenium particles were homodispersed in the micropores of MPCS by a typical melt-diffusion process. The obtained MPCS/Se composites used as a cathode of Li–Se batteries show high Se loading of nearly 45%, and high capacities as well as stable cycling performance in both carbonate-based LiPF6 electrolyte (565 mAh g−1 at 1 C after 500 cycles) and ether-based LiTFSI electrolyte (480 mAh g−1 at 1 C after 500 cycles). Notably, an outstanding rate capability in the carbonate-based electrolyte and a coulombic efficiency of nearly 100% in both types of electrolytes were observed. The microporous structure of the MPCS material with high conductivity contributes to the excellent electrochemical properties and rate capability, effectively alleviating volume expansion and suppressing dissolution of polyselenides.

Biomass-derived, 3D interconnected N-doped carbon foam as a host matrix for Li/Na/K-selenium batteries

Rechargeable alkali metal-Se batteries have attracted a lot of attention due to their high capacity and low cost. However, the shuttle effect and volume change during charge/discharge are the main obstacles for further development of high-performance alkali-Se rechargeable batteries. In order to solve these issues, herein a biomass-derived 3D interconnected foam-like N-doped porous carbon (FNDPC) is synthesized as a Se-container for metal-Se batteries. In this FNDPC@Se structure, stable porous carbon hosts can serve as chambers for Se reacting with Li+, Na+ or K+. As expected, the FNDPC@Se electrode exhibits an ultrahigh rate performance and excellent cycling stability during the reversible storage of alkali metal ions. For Na-Se batteries, the high specific capacity of 354.9 mAh g−1 is achieved even at a high current density of 20 A g−1 and there is 90.7% capacity retention after 500 cycles at 2.0 A g−1. For Li-Se batteries, FNDPC@Se can offer an impressive rate capability with specific capacities of 653.1 mAh g−1 at 0.1 A g−1 and 350.4 mAh g−1 at 20 A g−1. In contrast, the performance of FNDPC@Se in K-Se batteries is relatively lower than that in Li-Se and Na-Se batteries. Moreover, different energy-storage mechanisms for three types of ions are also revealed by cycling voltammetry (CV). Therefore, FNDPC is considered to be a promising carbon host for alkali-Se batteries, and our reported method provides possibilities for mass production of alkali-Se battery through the cheap raw materials.

Lignin derived hierarchical porous carbon with extremely suppressed polyselenide shuttling for high-capacity and long-cycle-life lithium–selenium batteries

A low-cost scalable strategy is developed to fabricate lignin derived hierarchical porous carbon as a high-loading Se host. When combined with carbonate-based electrolyte, the high-capacity and long-term cycling Li–Se batteries were obtained. Lithium–selenium (Li–Se) batteries have attracted considerable attentions for next-generation energy storage systems owing to high volumetric capacity of 3265 mAh cm −3 and excellent electronic conductivity (~10 −5 S cm −1 ) of selenium. However, the shuttling effect and capacity fading prevent their wide applications. Herein we report a low-cost strategy for scalable fabrication of lignin derived hierarchical porous carbon (LHPC) as a new high-loading Se host for high-capacity and long-term cycling Li–Se batteries in carbonate electrolyte. The resulting LHPC exhibits three-dimensional (3D) hierarchically porous structure, high specific surface area of 1696 m 2 g −1 , and hetero-atom doping (O, S), which can effectively confine the Se particles into the micropores, and meanwhile, offer effective chemical binding sites for selenides from hetero-atoms (O, S). As a result, our Li–Se batteries based on Se@LHPC demonstrate high capacity of 450 mAh g −1 at 0.5 C after 500 cycles, with a low capacity fading rate of only 0.027%. The theoretical simulation confirmed the strong affinity of selenides on the O and S sites of LHPC effectively mitigating the Se losing. Therefore, our strategy of using lignin as the low-cost precursor of hierarchically porous carbon for high-loading Se host offers new opportunities for high-capacity and long-life Li–Se batteries.

Performance enhancement of Li–Se batteries by manipulating redox reactions pathway

Lithium–selenium (Li–Se) batteries are promising high-energy battery systems. However, they suffer from shuttling effects of soluble lithium polyselenide intermediates and poor cycling stability. Herein, we use diphenyl diselenide (DPDSe) as an electrolyte additive to alter the redox reactions of selenium. The Li|Se-DPDSe cell shows the maximum discharge capacity of 643 mAh/g at 0.3 °C in the first few cycles, which is 94.7% of the theoretical specific capacity. After 250 cycles, it still maintains a reversible capacity of 602 mAh/g, possessing 93.6% of the initial capacity with Coulombic efficiency of almost 100%. DPDSe brings a new electrochemical reduction pathway leading to a high discharge voltage plateau. In the charge process, some selenium atoms are integrated into the structure of DPDSe to form diphenyl triselenide which adheres to carbon nanotubes therefore reducing the loss of active material. This study reveals intriguing electrochemical reactions of organoselenides and provides guidance for the optimization of electrolyte for stable Li–Se batteries.

Melamine-based polymer networks enabled N, O, S Co-doped defect-rich hierarchically porous carbon nanobelts for stable and long-cycle Li-ion and Li-Se batteries

Li-Se battery is a promising energy storage candidate owing to its high theoretical volumetric capacity and safe operating condition. In this work, for the first time, we report using the whole organic Melamine-based porous polymer networks (MPNs) as a precursor to synthesize a N, O, S co-doped hierarchically porous carbon nanobelts (HPCNBs) for both Li-ion and Li-Se battery. The N, O, S co-doping resulting in the defect-rich HPCNBs provides fast transport channels for electrolyte, electrons and ions, but also effectively relieve volume change. When used for Li-ion battery, it exhibits an advanced lithium storage performance with a capacity of 345 mAh g−1 at 500 mA g−1 after 150 cycles and a superior rate capacity of 281 mAh g−1 even at 2000 mA g−1. Further density function theory calculations reveal that the carbon atoms adjacent to the doping sites are electron-rich and more effective to anchor active species in Li-Se battery. With the hierarchically porous channels and the strong dual physical–chemical confinement for Li2Se, the Se@ HPCNBs composite delivers an ultra-stable cycle performance even at 2 C after 1000 cycles. Our work here suggests that introduce of heteroatoms and defects in graphite-like anodes is an effective way to improve the electrochemical performance.

Two-Plateau Li-Se Chemistry for High Volumetric Capacity Se Cathodes.

For Li-Se batteries, ether- and carbonate-based electrolytes are commonly used. However, because of the "shuttle effect" of the highly dissoluble long-chain lithium polyselenides (LPSes, Li2 Sen , 4≤n≤8) in the ether electrolytes and the sluggish one-step solid-solid conversion between Se and Li2 Se in the carbonate electrolytes, a large amount of porous carbon (>40 wt % in the electrode) is always needed for the Se cathodes, which seriously counteracts the advantage of Se electrodes in terms of volumetric capacity. Herein an acetonitrile-based electrolyte is introduced for the Li-Se system, and a two-plateau conversion mechanism is proposed. This new Li-Se chemistry not only avoids the shuttle effect but also facilitates the conversion between Se and Li2 Se, enabling an efficient Se cathode with high Se utilization (97 %) and enhanced Coulombic efficiency. Moreover, with such a designed electrolyte, a highly compact Se electrode (2.35 gSe cm-3 ) with a record-breaking Se content (80 wt %) and high Se loading (8 mg cm-2 ) is demonstrated to have a superhigh volumetric energy density of up to 2502 Wh L-1 , surpassing that of LiCoO2 .

High-Performance Li-Se Batteries Enabled Via All-in-One Designed Cathode

As an alternative to Li-S battery, a Li-Se battery is promising due to its high volumetric energy density. However, practical applications have been limited by complex fabrication and undesirable electrochemical process during charge-discharge which leads to poor cycling performance and low rate capability. To overcome these obstacles, we demonstrate a new design of “all-in-one” Se cathode, which is a one-piece body combined with a cathode and a solid polymer electrolyte. It is simply prepared by electrodeposition of Se on Ni-foam and subsequent coating of the solid polymer electrolyte without using any binders or conductive additives. All-in-one Se cathode can provide facile manufacturing process, prohibit undesirable electrochemical reaction, enhance ion pathway, and secure safety from advantages of solid polymer electrolyte. Li-Se batteries assembled with all-in-one Se cathode and Li-metal anode exhibited highly stable performance with a low capacity decay of 0.003% per cycle at 1 C over 3000 cycles.

In Batteria Polyaniline Coating: In Batteria Electrochemical Polymerization to Form a Protective Conducting Layer on Se/C Cathodes for High‐Performance Li–Se Batteries (Adv. Funct. Mater. 19/2020)

In Batteria Polyaniline Coating: In Batteria Electrochemical Polymerization to Form a Protective Conducting Layer on Se/C Cathodes for High‐Performance Li–Se Batteries (Adv. Funct. Mater. 19/2020)

Toward High Areal Capacity Lithium Batteries Via 3D Printing: From Liquid to Solid

3D-printing has found wide applications in numerous research fields, ranging from mechanical engineering, medicine, and material science to chemistry. Among them, it is capable of fabricating electrodes with high active material loading and improved ion/electron conductivity, and is thereby a promising method to improve the energy and power density of energy storage systems. And this technique offers a fresh viewpoint in designing high loading cathodes and will arise interest in other energy storage devices such as Li-ion batteries, Li-S batteries, and Li-Se batteries, etc. In this talk, I will talk about 3D-printed high active material loading cathode applied in batteries: from liquid to solid.In the first part of this talk, I will introduce 3D-printed high S loading cathode applied in liquid-based Li-S batteries. Compared with conventional cathode fabrication method, a 3D-printed S cathode with grid structure, which could facilitate Li+/e- transport at the macro, micro and nano scale in Li-S batteries. Moreover, a thickness-independent S cathode structure is also proposed via converting thick electrode into thousands of vertically aligned thin electrode by 3D printing. And each thin electrode delivers a constant thickness of around 20 μm, which is not affected by the intrinsic thickness of electrode as well as sulfur loading. Compared with other high S loading Li-S batteries performace, this work demonstrate a similar electrochemical kinetics in spite of the total sulfur loading or thickness of the electrode. [1-2]In the second part of this talk, I will talk about 3D-printed ultra-high Se loading cathode applied in solid-state Li-Se batteries. Compared with other Li-Se work, this work exhibits excellent cycling stability and remarkable rate performance with the highest reported Se loadings of 20 mg cm-2, and also delivers the highest reported areal capacity of 12.99 mA h cm-2 under a current density of 3 mA cm-2. The 3D-printed Se cathodes with grid structure provide large spaces for polymer electrolyte impregnation to further build interconnected Li+ transport channels in thick electrodes, enabling fast Li+ transport in solid-state Li-Se batteries. [3] References [1] X. Gao, X. Sun* et al, Nano Energy , 2019, 56, 595-603.[2] X. Gao, X. Sun* et al, Energy Storage Mater. Doi.org/10.1016/j.ensm.2019.08.001.[3] X. Gao, X. Sun* et al, J. Mater. Chem. A , under revision. Figure 1

Electrode and Interface Design for High-Performance Lithium/Sodium-Selenium Batteries

Lithium/sodium-selenium (Li/Na-Se) batteries are promising energy storage systems due to their relatively low cost and high volumetric energy density of Se cathode. Rechargeable lithium-ion batteries (LIBs) play a critical role in portable devices, electric vehicles and large-scale stationary energy storage, due to their relatively high energy density and low cost among available technologies [1]. Sodium-selenium (Na-Se) batteries have also drawn much attention, because of the large abundance and low cost of sodium and decent energy density of Se [2]. As a cathode material, Se provides a moderate gravimetric capacity of 678 mAh g−1, a high volumetric capacity of 3270 mAh cm−3, and possesses a high electronic conductivity of 1 ×10 −3 S m−1 [3, 4]. These advantages of Se have stimulated growing research in developing Li-Se and Na-Se batteries over the past years. However, the practical application of these batteries has been hindered by the polyselenides dissolution (or shuttle effect phenomena), which could cause low Coulombic efficiency and poor cycling lifetime. Microporous carbon (MPC) has been fabricated through a facile carbonization method from polyvinylidene fluoride (PVDF) and used without any further activation as selenium host to produce MPC/Se composite employed as cathode in rechargeable lithium/sodium-selenium (Li/Na-Se) batteries and the electrochemical properties of the prepared cell have been investigated in Li-Se batteries. (figures 1 and 4).Basically, in linear carbonate-containing electrolytes, the metal readily decomposes at the anode side, causing capacity drop over cycling. To address this problem, electrolyte design should accompany manifested cathode structure. Hence, fluoroethylene carbonate (FEC) has been used as an additive in the electrolyte solution for stabilizing the capacity in Na-Se batteries. Our investigation showed that exceptional cell stability could be reached by using the FEC in carbonate-based electrolyte. In lithium/sodium-selenium batteries, diethyl carbonate (DEC) electrolyte decomposes in contact with metal, producing some radicals and metal alkyl carbonates. These radicals start a chain reaction, causing the destruction of over cycles. By adding the FEC to the electrolyte solution, this side reaction will be prohibited. [5] FEC readily decomposes on the surface of the metal prior to any reduction of linear carbonates, making the protective and stable surface film on the metal. This layer makes the capacity much more stable for the cell contains FEC in the electrolyte. For the cell without FEC in the electrolyte, the capacity starts to fade from initial cycles and continue fading during the cycling. In sodium/selenium batteries, at the current rate of 0.1 C, the cell contains no FEC in the electrolyte, showed a capacity of 317 and 245 mAh g-1 after 100 and 200 cycles, respectively. However, the cell with an electrolyte solution containing 3% FEC, showing excellent cyclability by way of delivering 382 and 350 mAh g-1 capacity at those above-mentioned cycles, respectively (figures 2 and 5). Another important finding was that the use of FEC additive could prevent the corrosion of metal anode from soluble polyselenides, and preserve the structural integrity of metal anode, contributing to the enhanced cycling stability and specific capacity of Na-Se batteries.The utilization of nanoscale Al2O3 surface coating by atomic layer deposition (ALD) to protect a MPC/Se cathode and reduce polyselenide dissolution was also investigated in another stage. It was found that Al2O3 surface coating effectively suppressed the polyselenide dissolution from the MPC/Se cathode, thus reducing the loss of Se active material and improving the overall performance of Na-Se batteries. Compared to the pristine MPC/Se, Al2O3-coated MPC/Se cathode exhibited improved discharge capacity, cycling stability, and rate capability in Na-Se batteries (figures 3 and 6). Keywords: Fluoroethylene carbonate; lithium/sodium−selenium batteries; ALD coating; carbonate-based electrolyte; microporous carbon

Molten Lithium Battery for Space Applications

Solid-state electrolytes (SEs) have gained much interest lately as a potential for mitigating the various issues inherent in a most energy dense lithium metal (anode) based batteries such as lithium ion, lithium sulfur (Li-S), and lithium oxygen. Notable high energy next generation cathodes such as sulfur have their own issues with a liquid electrolyte based system, where the polysulfides discharge product dissolve into the electrolyte causing both: a loss of cathode active material and an unwanted shuttling of the polysulfides over the polymer separator to the lithium anode limiting their practical use. Moreover, the formation of lithium dendrites in lithium batteries is yet another challenging issue that not only limits battery cycle-life but also poses safety risks. The use of SEs can potentially address most of the issues related to next generation lithium batteries such as Li-S batteries, but getting rid of dendrite issues may not be addressed completely. One way to eliminate the dendrite issue is to use molten lithium as an anode.The National Aeronautics and Space Administration (NASA) has an ambitious plan to explore one of the most challenging planets in our solar system: Venus. The surface temperature of Venus can reach as high as 465°C and at same time, the Venus atmosphere is filled with corrosive gases such as carbon dioxide, sulfur dioxide, carbon monoxide, etc. A battery for such a challenging space mission can be built only if battery components (especially the electrolyte) is stable beyond 500°C and must be stable with molten lithium and sulfur electrodes for at least hours or days if not months—longer is better. Last but not the least, yet another challenge is containment of gaseous sulfur inside the battery container at such a high temperature. The potential to replace sulfur with selenium may mitigate the issue but at cost of reduced energy density.Under a NASA funded project, the University of Dayton Research Institute (UDRI) is developing molten lithium sulfur (Li-S) or lithium-selenium (Li-Se) batteries with the help of a high temperature solid ceramic electrolyte (SCE) that can enable a operating temperature >465°C for several hours. UDRI has been working on a high temperature SCE such as phosphate-based Li1+ xAlxGe2- x(PO4)3 (LAGP) ceramic electrolyte material1 that is stable beyond 500°C and also shows broad electrochemical window (up to 5V) that is sufficient for a molten Li-S or Li-Se battery operation; provided LAGP is stable with Li and S or Se in such harsh conditions and temperature. Unfortunately, LAGP is not stable with Li (forms a highly resistive interface layer between LAGP and electrode) and its stability with sulfur or Se, needs to be determined.Under the NASA project, UDRI has been developing interface materials between LAGP and electrodes for Li-S and Li-Se cells that can be stable at wide temperature range (room temperature to 500°C). The presentation will include progress on high temperature (up to 465°C) i) SCE, ii) SCE/Li interface materials, iii) SCE/S interface material, iv) SCE/Se interface material, v) impedance and open circuit voltage of Li-S or Li-Se cells at 465°C, and vi) cycle-life of Li-S or Li-Se cells at 465°C. To the authors knowledge, there is no such report (molten Li-S or Li-Se cells that can function at 465°C) that exists in literature.B. Kumar, D. Thomas, J. Kumar, “Space-Charge-Mediated Superionic Transport in Lithium Ion Conducting Glass–Ceramics,” J. Electrochem. Soc. 156, A506 (2009)