Cycling Stability Of Batteries Research Articles

High concentration in situ polymer gel electrolyte for high performance lithium metal batteries.

A high concentration gel polymer electrolyte (GPE) was prepared by simply using LiFSI-LiNO3 dissolved in 1,3-dioxolane. The Li‖Li cell achieves stable battery cycling for over 3200 h. Furthermore, the Li‖Cu cell demonstrates a high CE of 99.2%. Even at a high current density of 8 mA cm-2, a high CE of 98.5% was still achieved. Notably, in a Li‖LiFePO4 cell, this electrolyte enables high capacity retention of 94.5% and an average CE of 99.8% over 500 cycles, showing promising prospects for high-performance lithium metal batteries.

Tailoring Breathing Behaviour of Solid Electrolyte Interphases (SEIs) Unraveled by Cryo-TEM

The cycling stability of batteries is closely related to the dynamic evolution of solid electrolyte interphases (SEIs) in response to the discharging/charging processes. Here we utilize the state-of-the-art cryogenic transmission electron microscopy (cryo-TEM) and spectroscopy to probe the SEI breathing behaviour induced by discharging/charging on the conversion-type anode made of Fe2O3 quasi-cubes. The incorporation of the identical-location strategy allows us to track the evolution of same SEIs at different charge states, which unequivocally unravels SEI breathing featured by swelling (contracting) upon lithiation (de-lithiation), and the associated compositional change. Bare Fe2O3 anode develops an unstable SEI layer due to the intermixing with the lithiation product Li2O, which exhibits a large thickness variation upon breathing as well as excessive growth, causing substantial capacity fading within 100 cycles. A transition from organic to inorganic-type SEI is also identified upon cycling, which gives rise to significantly increased SEI resistance. To tailor the SEI behaviour, we apply N-doped carbon coating on Fe2O3 (Fe2O3@CN), which can effectively separate the lithiation product from SEI. A thinner and chemically more stable SEI layer develops on Fe2O3@CN, resulting in remarkably enhanced cycling stability compared to bare Fe2O3. Our work demonstrates the importance of understanding and optimizing the dynamic behaviour of SEIs to achieve better battery performance.

Modulation of Prelithiation Solution for Hard Carbon Anodes of Lithium-Ion Batteries

The increasing demand for high-energy and high-power lithium-ion batteries (LIBs) in portable gadgets and electric vehicles has led to exploration of high-performance silicon and hard carbon (HC) anodes to replace traditional graphite anodes. However, their practical application is hindered by low initial coulombic efficiency and large irreversible capacity, which decreases the total energy density. Prelithiation is a strategy to restore energy density by supplying additional Li ions. Chemical prelithiation, involving immersing the electrode in a reductive Li−aromatic hydrocarbon (arene) complex solution, is a standout method due to its safety, high efficiency, and practical feasibility. It not only restores the lost lithium but also aids in maintaining a more stable solid electrolyte interphase layer to guarantee battery cycling stability. The first part of our study addresses the issue of expensive and impractical arene complexes for prelithiation, we focus on using low-cost and commercially available aromatic compounds such as naphthalene and methyl-substituted naphthalene compounds. This study investigates the effects of electron-donating methyl groups on naphthalene on the prelithiation activity toward HC using density functional theory calculations. In the second part of this study, we use low-cost and easily available solvents such as ethylene glycol dimethyl ether, bis(2-methoxyethyl) ether, and triethylene glycol dimethyl ether for chemical prelithiation. Ether solvents have a desirable solvation effect with Li+, and the ether with low solvation power enhances the prelithiation activity. The degree of prelithiation is greatly affected by the reaction time, and the details of this relationship are rarely investigated. In the final part of our study, we conduct a detailed investigation on the effects of various reaction times on the prelithiation activity toward the HC anode. This study provides useful insights for effective prelithiation, in terms of choosing aromatic compounds, solvents, and reaction time.

Enabling Long‐term Cycling Stability of Na3V2(PO4)3/C vs. Hard Carbon Full‐cells

AbstractSodium‐ion batteries are becoming an increasingly important complement to lithium‐ion batteries. However, while extensive knowledge on the preparation of Li‐ion batteries with excellent cycling behavior exists, studies on applicable long‐lasting sodium‐ion batteries are still limited. Therefore, this study focuses on the cycling stability of batteries composed of Na3V2(PO4)3/C based cathodes and hard carbon anodes. It is shown that full‐cells with a decent stability are obtained for ethylene carbonate/propylene carbonate electrolyte and the conducting salt NaPF6. With cathode loadings of 1.2 mAh/cm2, after cell formation discharge capacities up to 92.6 mAh/g are obtained, and capacity retentions >90 % over 1000 charge/discharge cycles at 0.5 C/0.5 C are observed. It is shown that both, the additive fluoroethylene carbonate and impurities in the electrolyte, negatively affect the overall discharge capacity and cycling stability and should therefore be avoided. Remarkably, the internal resistances of well‐balanced and well‐built cells did not increase over 1500 cycles and 5 months of testing, which is a very promising result regarding the possible lifespan of the cells. The initial loss of active sodium ions in hard carbon remains a major problem, which can only be partially reduced by proper balancing.

Molten Sodium Batteries – Lewis Acidity of AlCl3/NaI Catholyte Impedes NaSICON Interface

Low temperature molten sodium batteries with sodium metal anodes, NaSICON solid-state separators, and sodium halide salt catholytes are low cost, earth-abundant technologies for grid-scale energy storage.1-3 We compared batteries with NaI/AlCl3-based molten salt catholytes of differing Lewis acidities at 110 °C. Batteries with >50 mol% AlCl3 (acidic catholytes) experienced a linear decline in energy efficiency during cycling, whereas batteries with >50 mol% NaI (basic catholytes) maintained 95% energy efficiency for 100 cycles (5 months) at 2.5 mA cm-2. A 3-electrode cell was developed, enabling electrochemical identification of the NaSICON-catholyte interface as the source of increased impedance. Complementary physical and chemical characterization of the NaSICON exposed to acidic and basic catholytes showed no changes in crystallinity, bulk morphology, or bulk chemical composition, but surface sensitive X-ray photoelectron spectroscopy (XPS) revealed subtle changes in the local NaSICON surface chemistry. In addition, Raman spectroscopy indicated that basic catholytes lack the dimer species Al2Cl6I- present in acidic catholytes. These results suggest that one means to enable efficient and stable battery cycling is maintaining Lewis-basic NaI/AlCl3, which avoids deleterious interactions at the NaSICON-catholyte interface. Recent progress towards achieving high cycling rates in these molten salt systems will also be shared.References L. J. Small, A. Eccleston, J. Lamb, A. C. Read, M. Robins, T. Meaders, D. Ingersoll, P. G. Clem, S. Bhavaraju and E. D. Spoerke, J. Power Sources, 360, 569 (2017).S. J. Percival, L. J. Small and E. D. Spoerke, J. Electrochem. Soc., 165, A3531 (2018).M. M. Gross, S. J. Percival, L. J. Small, J. Lamb, A. S. Peretti and E. D. Spoerke, ACS Appl. Energy Mater., 3, 11456 (2020). Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Bipolar Radicals as Active Material for Symmetrical Redox Flow Batteries

Redox-active organic molecules are increasingly investigated as charge-storage materials for redox-flow batteries (RFBs), but material crossover between posolyte/negolyte and chemical degradation are limiting factors in the performance of all-organic RFBs. Bipolar organic radicals can in principle be used to construct batteries with symmetrical electrolyte composition, which mitigates issues due to crossover. This presentation will describe studies to correlate molecular features with battery cycling stability using representative stable organic radicals (Blatter- and verdazyl-type compounds). We illustrate how an understanding of the reaction pathways that contribute to capacity fade can be used to improve battery longevity.

Ultrathin, Smooth Li-Metal Anode Via Electrodeposition for Stable Cycling of Li-Betal Batteries Under Practical Conditions

Lithium (Li) metal anodes (LMAs) with high specific capacity (3860 mAh g–1) and lowest redox voltage (–3.04 V vs SHE) are considered superlative candidates for high energy batteries. Ultra-thin, large-area LMA is crucial for building Li-metal batteries (LMBs) that can deliver high volumetric and gravimetric energy density in practice. As the charging and discharging continue, the growth of Li dendrite is regarded as one of the significant challenges. The surface nature of LMAs is the main aspect of Li dendrite formation and interface reaction. However, most studies overlooked the initial condition of LMA surface. Native passivation layer (NPL) of commercial Li foils is inherently uneven composed of Li2CO3, LiOH, and Li2O, and its chemical nature is mostly determined under manufacturing conditions. Incomplete passivation at an initial stage can trigger sporadic Li dendrite growth and chemical/structural deterioration of LMAs, adversely affecting the cycling stability of LMBs.This work presents the electrochemical pre-passivation to build an electrolyte-derived native layer (electro-native layer, E-NPL) through Li electrodeposition method. Electrodeposited LMA (ed-LMA) was prepared by pre-deposition at the Cu foil using localized high-concentration electrolyte (LHCE) and post calendaring for smooth LMA surface. As-prepared ed-LMA has 4.13 mAh cm-2 of areal capacity with ~22 µm, and reduced roughness, which is much lower than that of manufactured LMA (m-LMA). Particularly, the E-NPL derived by LHCE can tailor the LMA surface by enriching the inorganic SEI compounds such as LiF, and N-SOx. In addition, decreased amount of passivated components such as Li2CO3, LiOH, and hydroxide were found in XPS analysis of the anodes. Compared to manufactured LMA (m-LMA), the ed-LMA exhibited lower overpotential for Li plating/stripping cycles and enhanced capacity retention. Benefiting from better compatibility with newly plated Li, it showed higher plating density without electric isolation from beneath Li surface, mitigating the anode swelling during subsequent cycling. We successfully demonstrated battery cycling stability of Li||NMC622 cells exploiting ed-LMA (195 cycle at 80% retention), superior to m-LMA (110 cycle at 80% retention) under stringent conditions.

Potential regulation of bipolar redox-active molecules with fused conjugation for high-voltage symmetric organic redox flow batteries

Bipolar redox-active organic molecules (ROMs) are emerging as promising active materials as both anolyte and catholyte for symmetric organic redox flow batteries (ORFBs) which moderating the detrimental electrolyte crossover. However, certain bipolar ROMs suffer seriously from irreversible redox reactions when their redox potential exceeds the electrochemical window of electrolyte, resulting in unpredictable side reactions and serious degradation of battery cycling stability. In this study, we propose that incorporating electron-withdrawing or electron-donating groups into the bipolar ROMs with fused conjugation is capable to tune their redox potentials simultaneously to make them compatible with different electrolytes without sacrificing the output voltage. As a demonstration, we have designed and synthesized a series of bipolar ROMs with fused conjugation based on phenoxazine derivatives (denoted as QPO, QPO-3OMe and DQPO). All the three molecules undergo highly reversible redox reactions in the given electrolyte systems with voltage gap of ca. 2.5 V between two half-reactions. Moreover, symmetric ORFBs based on the bipolar ROMs maintain decent electrochemical stability when cycled in a compatible electrolyte, which the electrochemical window fully covers the voltage gap of the bipolar ROMs. This study provides a strategy for the design of bipolar ROMs with fused conjugation and the regulation of compatibility between the ROMs and the electrolytes, thus contributing to developing symmetric ORFBs with higher voltage and better stability.

Modified ceramic coated polyethylene separator – A strategy for using lithium metal as anode with superior electrochemical performance and thermal stability

Herein, we report the Li-ion conducting composite material, Li0.57La0.29TiO3 (LLTO), coated on a microporous polyethylene separator to use in rechargeable Lithium-metal batteries. Since the LLTO contains structural Li-ions and the three-dimensional conducting channels within, it not only improved the ionic conductivity of coated separator but also improved the surface electrolyte wettability and suppressed the dendrite formation. As a result, the Lithium-metal battery cycling stability and safety features are increased. Consequently, the ceramic composite separator enabled a specific capacity of 105.6 mAhg−1 for Li/LiMn2O4 coin cell, and 80 % capacity retention is observed even after 500 cycles at 1C, indicating its promising practical potential application. This work provides a feasible and efficient modification strategy of separators for improving the cycling performance and safety of Lithium-metal batteries. In addition, the ceramic composite-coated separator could instill confidence in using Lithium metal as the attractive anode for high-capacity Li-air and Li‑sulfur batteries with enhanced thermal and cyclic stability.

Thin Film Composite Membranes with Regulated Crossover and Water Migration for Long-Life Aqueous Redox Flow Batteries.

Redox flow batteries (RFBs) are promising for large-scale long-duration energy storage owing to their inherent safety, decoupled power and energy, high efficiency, and longevity. Membranes constitute an important component that affects mass transport processes in RFBs, including ion transport, redox-species crossover, and the net volumetric transfer of supporting electrolytes. Hydrophilic microporous polymers, such as polymers of intrinsic microporosity (PIM), are demonstrated as next-generation ion-selective membranes in RFBs. However, the crossover of redox species and water migration through membranes are remaining challenges for battery longevity. Here, a facile strategy is reported for regulating mass transport and enhancing battery cycling stability by employing thin film composite (TFC) membranes prepared from a PIM polymer with optimized selective-layer thickness. Integration of these PIM-based TFC membranes with a variety of redox chemistries allows for the screening of suitable RFB systems that display high compatibility between membrane and redox couples, affording long-life operation with minimal capacity fade. Thickness optimization of TFC membranes further improves cycling performance and significantly restricts water transfer in selected RFB systems.

Tailoring Conversion-Reaction-Induced Alloy Interlayer for Dendrite-Free Sulfide-Based All-Solid-State Lithium-Metal Battery.

Utilization of lithium (Li) metal anodes in all-solid-state batteries employing sulfide solid electrolytes is hindered by diffusion-related dendrite growth at high rates of charge. Engineering ex-situ Li-intermetallic interlayers derived from a facile solution-based conversion-alloy reaction is attractive for bypassing the Li0 self-diffusion restriction. However, no correlation is established between the properties of conversion-reaction-induced (CRI) interlayers and the deposition behavior of Li0 in all-solid-state lithium-metal batteries (ASSLBs). Herein, using a control set of electrochemical characterization experiments with LixAgy as the interlayer in different battery chemistries, this work identifies that dendritic tolerance in ASSLBs is susceptible to the surface roughness and electronic conductivity of the CRI-alloy interlayer. This work thereby tailors the CRI-alloy interlayer from the typical mosaic structure to a hierarchical gradient structure by adjusting the pit corrosion kinetics from the (de)solvation mechanism to an adsorption model, yielding a smooth organic-rich outer layer and a composition-regulated inorganic-rich inner layer composed mainly of lithiophilic LixAgy and electron-insulating LiF. Ultimately, desirable roughness, conductivity, and diffusivity are integrated simultaneously into the tailored CRI-alloy interlayer, resulting in dendrite-free and dense Li deposition beneath the interlayer capable of improving battery cycling stability. This work provides a rational protocol for the CRI-alloy interlayer specialized for ASSLBs.

Small Molecules, Great Powers: Chemistry of Small Organo‐Chalcogenide Molecules in Rechargeable Li‐Sulfur Batteries

AbstractSmall organic chalcogenides molecules are receiving more attention in conjunction with the development of rechargeable lithium metal batteries (LMBs) especially lithium–sulfur (Li−S) batteries due to their abundant resources, reversible redox, high capacities, tunable structures, unique functional adjustability, and strong interaction with congener polysulfides. In this review, the working principles are generalized of small organo‐chalcogenide molecules in three important parts of batteries: electrolyte, interface, and cathode. First, in terms of regulating kinetics in electrolyte, small organo‐chalcogenide molecules can not only act as redox mediator to accelerate the redox kinetics of sulfur, but also change the inherently slow solid–solid process to form a faster redox pathway, which will bring light to the development of cryogenic Li−S batteries. Second, for interface chemistry, the introduction of small organo‐chalcogenide molecules can construct more elastic and stable anodic single‐SEI or cathodic/anodic dual‐SEI, thus effectively improving the cycling stability of batteries. Third, small organo‐chalcogenide molecules can be used as cathode materials in the form of liquid phase, solid phase, or precursor of polymers. Finally, advised optimizations are proposed about further mechanism deciphering, battery configuration design, machine learning, thereby providing direction to bridge the gap between rational modulation and practical battery implementation for small organo‐chalcogenide molecules.

Tailoring Breathing Behavior of Solid Electrolyte Interphases Unraveled by Cryogenic Transmission Electron Microscopy

AbstractThe cycling stability of batteries is closely related to the dynamic evolution of solid electrolyte interphases (SEIs) in response to the discharging/charging processes. Here, the state‐of‐the‐art cryogenic transmission electron microscopy (cryo‐TEM) and spectroscopy are utilized to probe the SEI breathing behavior induced by discharging/charging on the conversion‐type anode made of Fe2O3 quasi‐cubes. The incorporation of the identical‐location strategy allows the tracking of the evolution of the same SEIs at different charge states. SEI breathing is shown to involve swelling (contracting) upon lithiation (de‐lithiation) driven by the reversible compositional change. Bare Fe2O3 anodes develop an unstable SEI layer due to the intermixing with the lithiation product Li2O, which exhibits a large thickness variation upon breathing as well as excessive growth. A transition from organic to inorganic‐type SEI is also identified upon cycling, which gives rise to significantly increased SEI resistance. To tailor the SEI behavior, N‐doped carbon coating is applied on Fe2O3 (Fe2O3@CN), which can effectively separate the lithiation product from SEI. A thinner and chemically more stable SEI layer develops on Fe2O3@CN, resulting in remarkably enhanced cycling stability compared to bare Fe2O3. This work demonstrates the importance of understanding and optimizing the dynamic behavior of SEIs to achieve better battery performance.

Realizing Holistic Charging–Discharging for Dendrite-Free Lithium Metal Anodes via Constructing Three-Dimensional Li+ Conductive Networks

Lithium (Li) metal is a promising candidate for next-generation anode materials with high energy densities. However, Li dissolution/deposition processes are limited at the upper surface in contact with the electrolyte, which brings a locally high current density and then results in dendritic Li growth. This restraint of the local surface reaction during cycling has not been solved by commonly used modification strategies. In this study, a three-dimensional (3D) Li+ conductive skeleton is activated from atomic layer deposition (ALD) coating Li3PO4 (LPO) on the surface of the Ni foam (LPNF). Then, the skeleton is efficiently constructed in the Li metal anode by the lower-temperature Li infusion. Ionic conductor LPO layers and electronic conductor Ni fibers supply charge transport channels between the electrolyte and the internal Li. The mixed conductive network realizes holistic charge transfer, which is proved by in situ scanning electron microscopy experiments. In virtue of dispersive dissolution/deposition and optimized electrochemical kinetics brought by a Li+ conductive network, the composited Li electrode presents an excellent symmetric battery cycling stability (over 1200 h) and enhanced rate performances (stable cycling even at 10.0 mA cm-2). When matching with a LiCoO2 (LCO) cathode, LCO||Li@LPNF full batteries exhibit a capacity retention of 80.8% over 250 cycles. During cycling, there was no evidence of dendrite growth and the remaining Li in the composited anode showed a smooth, compact, and well-combined condition with LPNF. Through constructing a 3D Li+ conductive network, the composited Li metal anode breaks through the limit of the local surface reaction; this work proposes a novel insight of realizing holistic charging/discharging for the dendrite-free Li metal anode.

Impact of Catholyte Lewis Acidity at the Molten Salt–NaSICON Interface in Low-Temperature Molten Sodium Batteries

Low-temperature molten sodium batteries comprising molten sodium anodes, a NaSICON solid-state separator, and molten halide salt catholytes offer promise as low-cost, earth-abundant energy storage technologies. The emergence of a specific, high-voltage, sodium iodide (NaI)-based catholyte chemistry has prompted the evaluation of chemical and electrochemical properties of the molten salts, particularly at critical interfaces with high-performance NaSICON separators. Herein, batteries operated at 110 °C with NaI-AlCl3-based catholytes of differing Lewis acidities were evaluated. Batteries with >50 mol % AlCl3 (acidic catholytes) experienced a linear decline in energy efficiency during cycling, whereas batteries with >50 mol % NaI (basic catholytes) maintained >95% energy efficiency for 50 cycles (>80 days) at 2.5 mA cm–2. A three-electrode cell was developed, enabling identification of the NaSICON–catholyte interface as the source of increased battery impedance. Complementary physical and chemical characterization of the NaSICON exposed to acidic and basic catholytes showed no changes in crystallinity, bulk morphology, or bulk chemical composition, but surface sensitive X-ray photoelectron spectroscopy (XPS), however, revealed subtle changes in local NaSICON surface chemistry. In addition, Raman spectroscopy indicated that stably performing basic catholytes lack the dimer species Al2Cl6I– present in acidic catholytes. Select thermodynamic and formal charge assessments suggest that preferential interactions between these acidic dimeric species and the NaSICON surface may be responsible for the observed increases in electrochemical impedance and degraded battery performance. These results indicate that maintaining a Lewis basic catholyte avoids such potentially deleterious interactions, enabling efficient and stable battery cycling.

Molecular Self-Assembled Ether-Based Polyrotaxane Solid Electrolyte for Lithium Metal Batteries

Poly(ethylene oxide) has been widely investigated as a potential separator for solid-state lithium metal batteries. However, its applications were significantly restricted by low ionic conductivity and a narrow electrochemical stability window (<4.0 V vs Li/Li+) at room temperature. Herein, a novel molecular self-assembled ether-based polyrotaxane electrolyte was designed using different functional units and prepared by threading cyclic 18-crown ether-6 (18C6) to linear poly(ethylene glycol) (PEG) via intermolecular hydrogen bond and terminating with hexamethylene diisocyanate trimer (HDIt), which was strongly confirmed by local structure-sensitive solid/liquid-state nuclear magnetic resonance (NMR) techniques. The designed electrolyte has shown an obviously increased room-temperature ionic conductivity of 3.48 × 10-4 S cm-1 compared to 1.12 × 10-5 S cm-1 without assembling polyrotaxane functional units, contributing to the enhanced cycling stability of batteries with both LiFePO4 and LiNi0.8Co0.15Al0.05O2 cathode materials. This advanced molecular self-assembled strategy provides a new paradigm in designing solid polymer electrolytes with demanded performance for lithium metal batteries.

A Dendrite-Free Zn Anode Co-modified with In and ZnF2 for Long-Life Zn-Ion Capacitors.

Aqueous Zn (zinc) metal batteries have gotten a lot of interest and research because of their great volumetric capacity, low production cost, and high use safety. However, the coulombic efficiency of the Zn metal anode is low due to Zn dendrites formed during the charging and discharging processes of the battery, and the corrosion problem of the Zn anode in the electrolyte also reduces the battery's cycling stability and hinders its practical application. In this paper, InF3 has been used to decorate the surface of Zn foil, and In (indium) and ZnF2 coatings have been introduced to the surface of metal Zn simultaneously. After 1400 h of plating and stripping cycles, a symmetrical battery assembled from the modified Zn foil can still maintain a low voltage hysteresis of 30 mV. The Zn-ion capacitor assembled by the InF3-modified Zn foil (Zn@In&ZnF2) and activated carbon delivers an energy density of 33.5 Wh kg-1 and a power density of 1608 W kg-1 at a current density of 2 A g-1 and can still maintain almost 100% capacity after 10,000 cycles. This work is helpful to improve the cycling stability and the corrosion problem of aqueous Zn-based batteries.

Surface Functionalization of Two-Dimensional MXene Nanosheets to Tailor Sulfur-Host Architecture for Metal-Sulfur Batteries

Practicality of lithium-sulfur batteries is severely hindered by the notorious polysulfide-shuttle phenomenon, leading to rapid capacity fade. This issue is aggravated with increase in sulfur loading, causing low-coulombic efficiency and cycle life. Herein, we present a facile strategy to combine hydrophobic sulfur and hydrophilic, conductive Ti3C2Tz-MXene via one-step surface functionalization using di(hydrogenated tallow) benzylmethyl ammonium chloride (DHT). The latter renders the Ti3C2Tz surface hydrophobic, making it readily dispersible in sulfur dissolved in a carbon disulfide (CS2) solvent. By evaporating the solvent, we conformally coat the DHT-Ti3C2Tz (DMX) with sulfur. The developed composite, with higher available active area, enables effective trapping of lithium polysulfides (LiPs) on the electroactive sites within the cathode, leading to improvement in electrochemical performance at higher sulfur loadings. The DMX/S cathodes function with high sulfur loading of ∼10.7 mg·cm−2 and deliver a stable areal capacity of ∼7 mAh·cm−2 for 150 cycles in the standard ether electrolyte. Moreover, a DMX/S cathode in a pouch-cell configuration retains ∼770 mAh·g−1 after ∼200 cycles at 0.2C (85.5% retention). Postmortem spectroscopic studies elucidate the nature of the LiPs-MXene interaction and the effect of surface functionalization towards improved performance. To further demonstrate the applicability of such uniquely functionalized MXene sheets, we study them as a host to confine sulfur (S8) triggering a quasi-solid state redox mechanism enabling the use of commercialization-friendly carbonate electrolyte in metal-sulfur batteries. We demonstrate that the multilayer MXene structure provides tunable spacing for S8 confinement and its unique interlayer spacing prevents adverse polysulfide-carbonate reactions resulting in stable battery cycling.

Al–Li alloys as bifunctional sacrificial lithium sources for prelithiation of high-energy-density Li-ion batteries

The low initial Coulombic efficiency of anodes such as Si@C can seriously affect the capacity of high-energy-density Li-ion batteries (LIBs). Supplement the initial irreversible lithium loss in the anode through prelithiation technology is the only way to realize the next generation of LIBs. In this work, we report the study of Al–Li alloy (ALA) as a prelithiation additive for LIBs cathodes. As a bifunctional sacrificial lithium source, ALA can not only provide an additional capacity of 1068 mAhg−1 to supplement the initial active lithium consumption, but also form aluminum and aluminum oxide to stabilize the cathode interface after the delithiation to improve the battery cycling stability. Therefore, the initial charge capacity of LiCoO2 (LCO) and LiNi0.6Co0.2Mn0.2O2 (NCM622) electrodes can be increased to 12.5%–18.5% by adding 2%–4% ALA. In addition, the energy density of the NCM811/Si@C pouch cell prelithiated by ALA can reach 541 Wh kg−1, which means that the cathode can maximize the capacity (from 189 mAh g−1 to 205 mAh g−1). In conclusion, this work develops a more inexpensive and efficient cathode prelithiation additive for next-generation LIBs.

VSe2/MXene composite with hierarchical three-dimensional structure encapsulated in dopamine as an anode for potassium-ion batteries

Potassium-ion batteries (PIBs) receive intensive interest because of the natural abundance of potassium sources and their potency to achieve high energy density. VSe2 is one of the promising electrode materials equipped with a huge interlayer distance, which can accommodate more K+ ions and reduce the structural distortion caused by the diffusion of K+ ions. But the problem of self-aggregation of VSe2 hinder its further application. Therefore, taking advantage of excellent electrical conductivity and mechanical strength of MXene, VSe2/MXene@C composites with a hierarchical three-dimensional structure are designed. Especially, VSe2 nanosheets are anchored on MXene substrates by strong covalent bonds, bridging with an oxygen atom. In addition, coating the carbon layer can avoid the deterioration of VSe2/MXene and improve the capacity and cycling stability of batteries effectively. As a result, the VSe2/MXene@C exhibits an excellent reversible capacity of 302.4 mAh g−1 with a coulombic efficiency of 99.49% at 200 mA g−1 after 200 cycles, long-term cycling performance of 138.7 mAh g−1 at 1 A g−1 after 500 cycles, and superior rate performance of 106.9 mAh g−1 at 2 A g−1. With outstanding electrochemical performance, the VSe2/MXene@C shows promise to become an excellent anode material for potassium-ion batteries(PIBs).