Rational design of spontaneous reactions for protecting porous lithium electrodes in lithium-sulfur batteries

Perspectives on Advanced Lithium-Sulfur Batteries for Electric Vehicles and Grid-Scale Energy Storage

Intensive increases in electrical energy storage are being driven by electric vehicles (EVs), smart grids, intermittent renewable energy, and decarbonization of the energy economy. Advanced lithium-sulfur batteries (LSBs) are among the most promising candidates, especially for EVs and grid-scale energy storage applications. In this topical review, the recent progress and perspectives of practical LSBs are reviewed and discussed; the challenges and solutions for these LSBs are analyzed and proposed for future practical and large-scale energy storage applications. Major challenges for the shuttle effect, reaction kinetics, and anodes are specifically addressed, and solutions are provided on the basis of recent progress in electrodes, electrolytes, binders, interlayers, conductivity, electrocatalysis, artificial SEI layers, etc. The characterization strategies (including in situ ones) and practical parameters (e.g., cost-effectiveness, battery management/modeling, environmental adaptability) are assessed for crucial automotive/stationary large-scale energy storage applications (i.e., EVs and grid energy storage). This topical review will give insights into the future development of promising Li-S batteries toward practical applications, including EVs and grid storage.

Scalable Customization of Crystallographic Plane Controllable Lithium Metal Anodes for Ultralong-Lasting Lithium Metal Batteries

A formidable challenge to achieve the practical applications of rechargeable lithium (Li) metal batteries (RLMBs) is to suppress the uncontrollable growth of Li dendrites. One of the most effective solutions is to fabricate Li metal anodes with specific crystal plane, but still lack of a simple and high-efficient approach. Herein, a facile and controllable way for the scalable customization of polished Li metal anodes with highly preferred (110) and (200) crystallographic orientation (donating as polished Li(110) and polished Li(200), respectively) by regulating the times of accumulative roll bonding, is reported. According to the inherent characteristics of polished Li(110)/Li(200), the influence of Li atomic structure on the electrochemical performance of RLMBs is deeply elucidated by combining theoretical calculations with relative experimental proofs. In particular, a polished Li(110) crystal plane is demonstrated to induce Li+ uniform deposition, promoting the formation of flat and dense Li deposits. Impressively, the polished Li(110)||LiFePO4 full cells exhibit unprecedented cycling stability with 10 000 cycles at 10 C almost without capacity degradation, indicating the great potential application prospect of such textured Li metal. More valuably, this work provides an important reference for low-cost, continued, and large-scale production of Li metal anodes with highly preferred crystal orientation through roll-to-roll manufacturability.

Sulfur Vacancies and 1T Phase-Rich MoS2 Nanosheets as an Artificial Solid Electrolyte Interphase for 400 Wh kg-1 Lithium Metal Batteries

Constructing large-area artificial solid electrolyte interphase (SEI) to suppress Li dendrites growth and electrolyte consumption is essential for high-energy-density Li metal batteries (LMBs). Herein, chemically exfoliated ultrathin MoS2 nanosheets (EMoS2) as an artificial SEI are scalable transfer-printed on Li-anode (EMoS2@Li). The EMoS2 with a large amount of sulfur vacancies and 1T phase-rich acts as a lithiophilic interfacial ion-transport skin to reduce the Li nucleation overpotential and regulate Li+ flux. With favorable Young's modulus and homogeneous continuous layered structure, the proposed EMoS2@Li effectively suppresses the growth of Li dendrites and repeat breaking/reforming of the SEI. As a result, the assembled EMoS2@Li||LiFePO4 and EMoS2@Li||LiNi0.8Co0.1Mn0.1O2 batteries demonstrate high-capacity retention of 93.5% and 92% after 1000 cycles and 300 cycles, respectively, at ultrahigh cathode loading of 20 mg cm-2. Ultrasonic transmission technology confirms the admirable ability of EMoS2@Li to inhibit Li dendrites in practical pouch batteries. Remarkably, the Ah-class EMoS2@Li||LiNi0.8Co0.1Mn0.1O2 pouch battery exhibits an energy density of 403 Wh kg-1 over 100 cycles with the low negative/positive capacity ratio of 1.8 and electrolyte/capacity ratio of 2.1 g Ah-1. The strategy of constructing an artificial SEI by sulfur vacancies-rich and 1T phase-rich ultrathin MoS2 nanosheets provides new guidance to realize high-energy-density LMBs with long cycling stability.

Semi-Embedded Structured Bi Nanospheres for Boosted Self-Heating-Induced Healing of Li-Dendrites

It is reported that self-heating-induced healing on lithium metal anodes (LMAs) provides a mitigation strategy for suppressing Li dendrites. However, how to boost the self-heating-induced healing of Li-dendrites and incorporate it into Li-host design remains an imminent problem that needs to be solved. Herein, a new bismuth nanosphere semi-buried carbon cloth (Bi-NS-CC) material with a 3D flexible host structure is proposed. The ultrasmall Bi nanospheres are uniformly and densely distributed on carbon fiber, providing active sites to form uniform Li3 Bi alloy with molten lithium, thereby guiding the injection of molten metallic lithium into the 3D structure to form a self-supporting composite LMAs. The ingenious semi-embedded structure with strong interfacial C─Bi ensures superior mechanical properties. Interestingly, when the current density reaches up to 10 mA cm-2 , the lithium dendrites undergo self-heating. Carbon cloth as a host can quickly and uniformly transfer heat, which induces the uniform migration of Li on anodes. The semi-embedded structure with strong C─Bi ensures Bi nanospheres guide the formation of smooth morphology even under these harsh conditions (high-temperature, high-rate, etc.). Consequently, at 10 mA cm-2 /10 mAh cm-2 , the Li/Li3 Bi-NS-CC realizes ultra-long cycles of 1500 h and ultra-low overpotential of 15 mV in a symmetric cell.

Hierarchical Li electrochemistry using alloy-type anode for high-energy-density Li metal batteries

Exploiting thin Li metal anode is essential for high-energy-density battery, but is severely plagued by the poor processability of Li, as well as the uncontrollable Li plating/stripping behaviors and Li/electrolyte interface. Herein, a thickness/capacity-adjustable thin alloy-type Li/LiZn@Cu anode is fabricated for high-energy-density Li metal batteries. The as-formed lithophilic LiZn alloy in Li/LiZn@Cu anode can effectively regulate Li plating/stripping and stabilize the Li/electrolyte interface to deliver the hierarchical Li electrochemistry. Upon charging, the Li/LiZn@Cu anode firstly acts as Li source for homogeneous Li extraction. At the end of charging, the de-alloy of LiZn nanostructures further supplements the Li extraction, actually playing the Li compensation role in battery cycling. While upon discharging, the LiZn alloy forms just at the beginning, thereby regulating the following Li homogeneous deposition. The reversibility of such an interesting process is undoubtedly verified from the electrochemistry and in-situ XRD characterization. This work sheds light on the facile fabrication of practical Li metal anodes and useful Li compensation materials for high-energy-density Li metal batteries.

Engineering Strategies for Suppressing the Shuttle Effect in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are supposed to be one of the most potential next-generation batteries owing to their high theoretical capacity and low cost. Nevertheless, the shuttle effect of firm multi-step two-electron reaction between sulfur and lithium in liquid electrolyte makes the capacity much smaller than the theoretical value. Many methods were proposed for inhibiting the shuttle effect of polysulfide, improving corresponding redox kinetics and enhancing the integral performance of Li-S batteries. Here, we will comprehensively and systematically summarize the strategies for inhibiting the shuttle effect from all components of Li-S batteries. First, the electrochemical principles/mechanism and origin of the shuttle effect are described in detail. Moreover, the efficient strategies, including boosting the sulfur conversion rate of sulfur, confining sulfur or lithium polysulfides (LPS) within cathode host, confining LPS in the shield layer, and preventing LPS from contacting the anode, will be discussed to suppress the shuttle effect. Then, recent advances in inhibition of shuttle effect in cathode, electrolyte, separator, and anode with the aforementioned strategies have been summarized to direct the further design of efficient materials for Li-S batteries. Finally, we present prospects for inhibition of the LPS shuttle and potential development directions in Li-S batteries.

Demystifying the Salt-Induced Li Loss: A Universal Procedure for the Electrolyte Design of Lithium-Metal Batteries

Lithium (Li) metal electrodes show significantly different reversibility in the electrolytes with different salts. However, the understanding on how the salts impact on the Li loss remains unclear. Herein, using the electrolytes with different salts (e.g., lithium hexafluorophosphate (LiPF6), lithium difluoro(oxalato)borate (LiDFOB), and lithium bis(fluorosulfonyl)amide (LiFSI)) as examples, we decouple the irreversible Li loss (SEI Li+ and "dead" Li) during cycling. It is found that the accumulation of both SEI Li+ and "dead" Li may be responsible to the irreversible Li loss for the Li metal in the electrolyte with LiPF6 salt. While for the electrolytes with LiDFOB and LiFSI salts, the accumulation of "dead" Li predominates the Li loss. We also demonstrate that lithium nitrate and fluoroethylene carbonate additives could, respectively, function as the "dead" Li and SEI Li+ inhibitors. Inspired by the above understandings, we propose a universal procedure for the electrolyte design of Li metal batteries (LMBs): (i) decouple and find the main reason for the irreversible Li loss; (ii) add the corresponding electrolyte additive. With such a Li-loss-targeted strategy, the Li reversibility was significantly enhanced in the electrolytes with 1,2-dimethoxyethane, triethyl phosphate, and tetrahydrofuran solvents. Our strategy may broaden the scope of electrolyte design toward practical LMBs.

Caffeic Acid-Zinc Basic Salt/Chitosan Nanohybrid Possesses Controlled Release Properties and Exhibits In Vivo Anti-Inflammatory Activities

Caffeic acid (CA) exhibits a myriad of biological activities including cardioprotective action, antioxidant, antitumor, anti-inflammatory, and antimicrobial properties. On the other hand, CA presents low water solubility and poor bioavailability, which have limited its use for therapeutic applications. The objective of this study was to develop a nanohybrid of zinc basic salts (ZBS) and chitosan (Ch) containing CA (ZBS-CA/Ch) and evaluate its anti-edematogenic and antioxidant activity in dextran and carrageenan-induced paw edema model. The samples were obtained by coprecipitation method and characterized by X-ray diffraction, Fourier transform infrared (FT-IR), scanning electron microscope (SEM) and UV-visible spectroscopy. The release of caffeate anions from ZBS-CA and ZBS-CA/Ch is pH-dependent and is explained by a pseudo-second order kinetics model, with a linear correlation coefficient of R² ≥ 0.99 at pH 4.8 and 7.4. The in vivo pharmacological assays showed excellent anti-edematogenic and antioxidant action of the ZBS-CA/Ch nanoparticle with slowly releases of caffeate anions in the tissue, leading to a prolongation of CA-induced anti-edematogenic and anti-inflammatory activities, as well as improving its inhibition or sequestration antioxidant action toward reactive species. Overall, this study highlighted the importance of ZBS-CA/Ch as an optimal drug carrier.

Efficient Regulation of Polysulfides by Anatase/Bronze TiO2 Heterostructure/Polypyrrole Composites for High-Performance Lithium-Sulfur Batteries

Despite having ultra-high theoretical specific capacity and theoretical energy density, lithium-sulfur (Li-S) batteries suffer from their low Coulombic efficiency and poor lifespan, and the commercial application of Li-S batteries is seriously hampered by the severe "shuttle effect" of lithium polysulfides (LiPSs) and the large volume expansion ratio of the sulfur electrode during cycling. Designing functional hosts for sulfur cathodes is one of the most effective ways to immobilize the LiPSs and improve the electrochemical performance of a Li-S battery. In this work, a polypyrrole (PPy)-coated anatase/bronze TiO₂ (TAB) heterostructure was successfully prepared and used as a sulfur host. Results showed that the porous TAB could physically adsorb and chemically interact with LiPSs during charging and discharging processes, inhibiting the LiPSs' shuttle effect, and the TAB's heterostructure and PPy conductive layer are conducive to the rapid transport of Li⁺ and improve the conductivity of the electrode. By benefitting from these merits, Li-S batteries with TAB@S/PPy electrodes could deliver a high initial capacity of 1250.4 mAh g^-1 at 0.1 C and show an excellent cycling stability (the average capacity decay rate was 0.042% per cycle after 1000 cycles at 1 C). This work brings a new idea for the design of functional sulfur cathodes for high-performance Li-S battery.

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.

Advanced Composite Lithium Metal Anodes with 3D Frameworks: Preloading Strategies, Interfacial Optimization, and Perspectives

Lithium (Li) metal is regarded as the most promising anode candidate for next-generation rechargeable storage systems due to its impeccable capacity and the lowest electrochemical potential. Nevertheless, the irregular dendritic Li, unstable interface, and infinite volume change, which are the intrinsic drawbacks rooted in Li metal, give a seriously negative effect on the practical commercialization for Li metal batteries. Among the numerous optimization strategies, designing a 3D framework with high specific surface area and sufficient space is a convincing way out to ameliorate the above issues. Due to the Li-free property of the 3D framework, a Li preloading process is necessary before the 3D framework that matches with the electrolyte and cathode. How to achieve homogeneous integration with Li and 3D framework is essential to determine the electrochemical performance of Li metal anode. Herein, this review overviews the recent general fabrication methods of 3D framework-based composite Li metal anode, including electrodeposition, molten Li infusion, and pressure-derived fabrication, with the focus on the underlying mechanism, design criteria, and interfacial optimization. These results can give specific perspectives for future Li metal batteries with thin thickness, low N/P ratio, lean electrolyte, and high energy density (>350 Wh Kg^-1 ).

Modulating Electron Conducting Properties at Lithium Anode Interfaces for Durable Lithium-Sulfur Batteries

The lithium (Li) ion and electron diffusion behaviors across the actual solid electrolyte interphase (SEI) play a critical role in regulating the Li nucleation and growth and improving the performance of lithium-sulfur (Li-S) batteries. To date, a number of researchers have pursued an SEI with high Li-ion conductivity while ignoring the Li dendrite growth caused by electron tunneling in the SEI. Herein, an artificial anti-electron tunneling layer with enriched lithium fluoride (LiF) and sodium fluoride (NaF) nanocrystals is constructed using a facile solution-soaking method. As evidenced theoretically and experimentally, the LiF/NaF artificial SEI exhibits an outstanding electron-blocking capability that can reduce electron tunneling, resulting in dendrite-free and dense Li deposition beneath the SEI, even with an ultrahigh areal capacity. In addition, the artificial anti-electron tunneling layer exhibits improved ionic conductivity and mechanical strength, compared to those of routine SEI. The symmetric cells with protected Li electrodes achieve a stable cycling of 1500 h. The LiF/NaF artificial SEI endows the Li-S full cells with long-term cyclability under conditions of high sulfur loading, lean electrolyte, and limited Li excess. This study provides a perspective on the design of the SEI for highly safe and practical Li-S batteries.

Dendrite-Free and Long-Cycling Lithium Metal Battery Enabled by Ultrathin, 2D Shield-Defensive, and Single Lithium-Ion Conducting Polymeric Membrane

Polymeric membranes are considered as promising materials to realize safe and long-life lithium metal batteries (LMBs). However, they are usually based on soft 1D linear polymers and thus cannot effectively inhibit piercing of lithium dendrites at high current density. Herein, single lithium-ion conducting molecular brushes (GO-g-PSSLi) are successfully designed and fabricated with a new 2D "soft-hard-soft" hierarchical structure by grafting hairy lithium polystyrenesulfonate (PSSLi) chains on both sides of graphene oxide (GO) sheets. The ultrathin GO-g-PSSLi membrane is further constructed by evaporation-induced layer-by-layer self-assembly of GO-g-PSSLi molecular brushes. Unlike conventional soft 1D linear polymeric structure, the rigid 2D extended aromatic structure of intralayer GO backbones can bear the shield effect of preventing the dendrites possibly generated at high current density from piercing. More importantly, such a shield effect can be significantly strengthened by layer-by-layer stacking of 2D molecular brushes. On the other hand, the 3D interconnected interlayer channels and the soft single lithium-ion conducting PSSLi side-chains on the surface of channels provide rapid lithium-ion transportation pathways and homogenize lithium-ion flux. As a result, LMBs with GO-g-PSSLi membrane possess long-term reversible lithium plating/striping (6 months) at high current density.

Development of quasi-solid-state anode-free high-energy lithium sulfide-based batteries

Anode-free lithium batteries without lithium metal excess are a practical option to maximize the energy content beyond the conventional design of Li-ion and Li metal batteries. However, their performance and reliability are still limited by using low-capacity oxygen-releasing intercalation cathodes and flammable liquid electrolytes. Herein, we propose quasi-solid-state anode-free batteries containing lithium sulfide-based cathodes and non-flammable polymeric gel electrolytes. Such batteries exhibit an energy density of 1323 Wh L^-1 at the pouch cell level. Moreover, the lithium sulfide-based anode-free cell chemistry endows intrinsic safety thanks to a lack of uncontrolled exothermic reactions of reactive oxygen and excess Li inventory. Furthermore, the non-flammable gel electrolyte, developed from MXene-doped fluorinated polymer, inhibits polysulfide shuttling, hinders Li dendrite formation and further secures cell safety. Finally, we demonstrate the improved cell safety against mechanical, electrical and thermal abuses.

Approaches to Combat the Polysulfide Shuttle Phenomenon in Li–S Battery Technology

Lithium–sulfur battery (LSB) technology has tremendous prospects to substitute lithium-ion battery (LIB) technology due to its high energy density. However, the escaping of polysulfide intermediates (produced during the redox reaction process) from the cathode structure is the primary reason for rapid capacity fading. Suppressing the polysulfide shuttle (PSS) is a viable solution for this technology to move closer to commercialization and supersede the established LIB technology. In this review, we have analyzed the challenges faced by LSBs and outlined current methods and materials used to address these problems. We conclude that in order to further pioneer LSBs, it is necessary to address these essential features of the sulfur cathode: superior electrical conductivity to ensure faster redox reaction kinetics and high discharge capacity, high pore volume of the cathode host to maximize sulfur loading/utilization, and polar PSS-resistive materials to anchor and suppress the migration of polysulfides, which can be developed with the use of nanofabrication and combinations of the PSS-suppressive qualities of each component. With these factors addressed, our world will be able to forge ahead with the development of LSBs on a larger scale—for the efficiency of energy systems in technology advancement and potential benefits to outweigh the costs and performance decay.

Lithium reduction reaction for interfacial regulation of lithium metal anode

The lithium metal anode (LMA) is regarded as a very promising candidate for next-generation lithium batteries. The interfacial issue plays a pivotal role in affecting the lithium plating/stripping behavior, Coulombic efficiency and cycling lifespan of an LMA. The lithium reduction reaction (LRR) is an advanced regulating technique for optimizing the LMA interphase, which intelligently utilizes lithium metal itself as an interphase precursor. This strategy also possesses moderate operating conditions, high efficiency, great convenience and scalability. In this review, the latest developments of LRRs in interfacial regulation for LMAs are summarized, focusing on the interfacial regulation mechanism and the construction of various inorganic/organic interfaces in lithium metal liquid/solid batteries. The target interface properties and corresponding influence factors during LRRs are investigated in detail. Besides this, the superiority and insufficiency of LRRs are discussed and possible directions for LRRs are presented. This review highlights in situ modification characteristics for anode interface regulation during the LRR and can be extended to other metal anodes such as sodium, potassium and zinc.

Lithium-Sulfur Batteries Meet Electrospinning: Recent Advances and the Key Parameters for High Gravimetric and Volume Energy Density

Lithium-sulfur (Li-S) batteries have been regarded as a promising next-generation energy storage technology for their ultrahigh theoretical energy density compared with those of the traditional lithium-ion batteries. However, the practical applications of Li-S batteries are still blocked by notorious problems such as the shuttle effect and the uncontrollable growth of lithium dendrites. Recently, the rapid development of electrospinning technology provides reliable methods in preparing flexible nanofibers materials and is widely applied to Li-S batteries serving as hosts, interlayers, and separators, which are considered as a promising strategy to achieve high energy density flexible Li-S batteries. In this review, a fundamental introduction of electrospinning technology and multifarious electrospinning-based nanofibers used in flexible Li-S batteries are presented. More importantly, crucial parameters of specific capacity, electrolyte/sulfur (E/S) ratio, sulfur loading, and cathode tap density are emphasized based on the proposed mathematic model, in which the electrospinning-based nanofibers are used as important components in Li-S batteries to achieve high gravimetric (WG ) and volume (WV ) energy density of 500 Wh kg-1 and 700 Wh L-1 , respectively. These systematic summaries not only provide the principles in nanofiber-based electrode design but also propose enlightening directions for the commercialized Li-S batteries with high WG and WV .

Two Birds with One Stone: Interfacial Engineering of Multifunctional Janus Separator for Lithium-Sulfur Batteries

Li-dendrite growth and unsatisfactory sulfur cathode performance are two core problems that restrict the practical applications of lithium-sulfur batteries (LSBs). Here, an all-in-one design concept for a Janus separator, enabled by the interfacial engineering strategy, is proposed to improve the performance of LSBs. At the interface of the anode/separator, the thin functionalized composite layer contains high-elastic-modulus and high-thermal-conductivity boron nitride nanosheets and oxygen-group-grafted cellulose nanofibers (BNNs@CNFs), by which the formation of "hot spots" can be effectively avoid, the Li-ion flux homogenized, and dendrite growth suppressed. Meanwhile, at the interface between the separator and the cathode, the homogenously exposed single-atom Ru on the surface of reduced graphene oxide (rGO@Ru SAs) can "trap" polysulfides and reduce the activation energy to boost their conversion kinetics. Consequently, the LSBs show a high capacity of 460 mAh g^-1 at 5C and ultrastable cycling performance with an ultralow capacity decay rate of 0.046% per cycle over 800 cycles. To further demonstrate the practical prospect of the Janus separator, a lithium-sulfur pouch cell using the Janus separator delivers a cell-level energy density of 310.2 Wh kg^-1 . This study provides a promising strategy to simultaneously tackle the challenges facing the Li anode and the sulfur cathode in LSBs.

3D Ordered Porous Nanostructure Confers Fast Charge Transfer Rate and Reduces the Electrode Polarization in Thick Electrode

Lithium batteries with high electrode thickness always possess a poor battery property due to electrode polarization along the thickness direction. Herein, a concept that the electrode polarization can be reduced through the fabrication of 3D ordered interconnected nanostructure in the electrode is put forward. A nitrogen-doped carbon photonic crystal (NCPC) with the ordered interconnected nanostructure is used in the electrode to prove the concept. NCPC can provide a fast charge transfer rate along the thickness direction and a uniform distribution for electrons and lithium ions, resulting in diminishing the concentration polarization and concentration gradient. When NCPC works for lithium-sulfur battery, the thick electrode achieves a fast charge transfer rate and a small voltage gap as well as the thin electrode. The 200 µm thick sulfur cathode obtains a specific capacity (87%) as high as 100 µm thick sulfur cathode. In contrast, the capacity ratio of the electrode made by the traditional coating method is only 45%.

Biomass-Derived Carbon/Sulfur Composite Cathodes with Multiwalled Carbon Nanotube Coatings for Li-S Batteries

Lithium sulfur (Li-S) batteries stand out among many new batteries for their high energy density. However, the intermediate charge–discharge product dissolves easily into the electrolyte to produce a shuttle effect, which is a key factor limiting the rapid development of Li-S batteries. Among the various materials used to solve the challenges related to pure sulfur cathodes, biomass derived carbon materials are getting wider research attention. In this work, we report on the fabrication of cathode materials for Li-S batteries based on composites of sulfur and biomass-derived porous ramie carbon (RC), which are coated with multiwalled carbon nanotubes (MWCNTs). RC can not only adsorb polysulfide in its pores, but also provide conductive channels. At the same time, the MWCNTs coating further reduces the dissolution of polysulfides into the electrolyte and weakens the shuttle effect. The sulfur loading rate of RC is 66.3 wt.%. As a result, the initial discharge capacity of the battery is 1325.6 mAh·g−1 at 0.1 C long cycle, and it can still maintain 812.5 mAh·g−1 after 500 cycles. This work proposes an effective double protection strategy for the development of advanced Li-S batteries.

Two steps synthesis of plum-shaped C@Ni/MnO nanofiber heterostructures for trapping and catalyzing polysulfides in lithium-sulfur batteries

Both spherical MnO as adsorbent and Ni nanoparticles as catalyzer, with highly exposed contact surface area in the carbon nanofibers, are successfully synthesized via electrospinning technology combined with carbothermal reduction. Compared with typical electrospun carbon nanofiber composites, the as-prepared C@Ni/MnO composite fibers as interlayer enable MnO and Ni to contact fully with polysulfides rather than provide local contact surface. With the sulfur loading of 1.6 mg cm^-2 and the approximately 0.1 g composite fibers as interlayer, the cathode shows initial capacity of 687.36 mAh g^-1 at 0.5C and superior capacity retention of 70%. This simple technical route leads a way to prepare nanoparticles with highly exposed contact surfaces partially embedded in the carbon nanofibers, which can be applied in electrocatalysis.

Thermodynamic Regulation of Dendrite-Free Li Plating on Li3Bi for Stable Lithium Metal Batteries

Rechargeable batteries with metallic lithium (Li) anodes are attracting ever-increasing interests because of their high theoretical specific capacity and energy density. However, the dendrite growth of the Li anode during cycling leads to poor stability and severe safety issues. Here, Li₃Bi alloy coated carbon cloth is rationally chosen as the substrate of the Li anode to suppress the dendrite growth from a thermodynamic aspect. The adsorption energy of a Li atom on Li₃Bi is larger than the cohesive energy of bulk Li, enabling uniform Li nucleation and deposition, while the high diffusion barrier of the Li atom on Li₃Bi blocks the migration of adatoms from adsorption sites to the regions of fast growth, which further ensures uniform Li deposition. With the dendrite-free Li deposition, the composite Li/Li₃Bi anode enables over 250 cycles at an ultrahigh current density of 20 mA cm^-2 in a symmetrical cell and delivers superior electrochemical performance in full batteries.

Surface Engineering of a Mg Electrode via a New Additive to Reduce Overpotential

In nonaqueous Mg batteries, inactive adsorbed species and the passivation layer formed from the reactive Mg with impurities in the electrolyte seriously affect the Mg metal/electrolyte interface. These adlayers can impede the passage of Mg²⁺ ions, leading to a high Mg plating/stripping overpotential. Herein, we report the properties of a new additive, bismuth triflate (Bi(OTf)₃), for synthesizing a chlorine-free Mg electrolyte to enhance Mg plating/stripping from initial cycles. The beneficial effect of Bi(OTf)₃ can be ascribed to Bi/Mg₃Bi₂ formed in situ on the Mg metal surface, which increases the charge transfer during the on-off transition by reducing the adsorption of inactive species on the Mg surface and enhancing the resistance of the reactive surface to passivation. This simple method provides a new avenue to improve the compatibility between the Cl-free Mg electrolyte and the Mg metal anode.

Selective Permeable Lithium-Ion Channels on Lithium Metal for Practical Lithium-Sulfur Pouch Cells

Lithium metal batteries are considered a promising candidate for high-energy-density energy storage. However, the strong reducibility and high reactivity of lithium lead to low Coulombic efficiency when contacting oxidants, such as lithium polysulfide caused by the serious "shuttle effect" in lithium-sulfur batteries. Herein we design selectively permeable lithium-ion channels on lithium metal surface, which allow lithium ions to pass through by electrochemical overpotential, while the polysulfides are effectively blocked due to the much larger steric hindrance than lithium ions. The selective permeation of lithium ions through the channels is further elucidated by the molecular simulation and visualization experiment. Consequently, a prolonged cycle life of 75 cycles and high Coulombic efficiency of 99 % are achieved in a practical Li-S pouch cell with limited amounts of lithium and electrolyte, confirming the unique role the selective ion permeation plays in protecting highly reactive alkali metal anodes in working batteries.

Design Principles and Applications of Next-Generation High-Energy-Density Batteries Based on Liquid Metals

Increasing need for the renewable energy supply accelerated the thriving studies of Li-ion batteries, whereas if the high-energy-density Li as well as alkali metals should be adopted as battery electrodes is still under fierce debate for safety concerns. Recently, a group of low-melting temperature metals and alloys that are in liquid phase at or near room-temperature are being reported for battery applications, by which the battery energy could be improved without significant dendrite issue. Besides the dendrite-free feature, liquid metals can also promise various high-energy-density battery designs on the basis of unique materials properties. In this review, the design principles for liquid metals-based batteries from mechanical, electrochemical, and thermodynamical aspects are provided. With the understanding of the theoretical basis, currently reported relevant designs are summarized and analyzed focusing on the working mechanism, effectiveness evaluation, and novel application. An overview of the state-of-the-art liquid metal battery developments and future prospects is also provided in the end as a reference for further research explorations.

Binder-free and high-loading sulfurized polyacrylonitrile cathode for lithium/sulfur batteries

Sulfurized polyacrylonitrile (SPAN) is a promising active material for Li/S batteries owing to its high sulfur utilization and long-term cyclability. However, because SPAN electrodes are synthesized using powder, they require large amounts of electrolyte, conducting agents, and binder, which reduces the practical energy density. Herein, to improve the practical energy density, we fabricated bulk-type SPAN disk cathodes from pressed sulfur and polyacrylonitrile powders using a simple heating process. The SPAN disks could be used directly as cathode materials because their π–π structures provide molecular-level electrical connectivity. In addition, the electrodes had interconnected pores, which improved the mobility of Li⁺ ions by allowing homogeneous adsorption of the electrolyte. The specific capacity of the optimal electrode was very high (517 mA h g_electrode⁻¹). Furthermore, considering the weights of the anode, separator, cathode, and electrolyte, the Li/S cell exhibited a high practical energy density of 250 W h kg⁻¹. The areal capacity was also high (8.5 mA h cm⁻²) owing to the high SPAN loading of 16.37 mg cm⁻². After the introduction of 10 wt% multi-walled carbon nanotubes as a conducting agent, the SPAN disk electrode exhibited excellent cyclability while maintaining a high energy density. This strategy offers a potential candidate for Li/S batteries with high practical energy densities.

A simple synthesis procedure to prepare bulk-type SPAN electrodes toward the realization of Li/S batteries with enhanced practical energy densities.

Sulfonated covalent organic framework modified separators suppress the shuttle effect in lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have gained intense research enthusiasm due to their high energy density. Nevertheless, the 'shuttle effect' of soluble polysulfide (a discharge product) reduces their cycling stability and capacity, thus restricting their practical application. To tackle this challenging issue, we herein report a sulfonated covalent organic framework modified separator (SCOF-Celgard) that alleviates the shuttling of polysulfide anions and accelerates the migration of Li⁺ions. Specifically, the negatively charged sulfonate can inhibit the same charged polysulfide anion through electrostatic repulsion, thereby improving the cycle stability of the battery and preventing the Li-anode from being corroded. Meanwhile, the sulfonate groups may facilitate the positively charged lithium ions to pass through the separator. Consequently, the battery assembled with the SCOF-Celgard separator exhibits an 81.1% capacity retention after 120 cycles at 0.5 C, which is far superior to that (55.7%) of the battery with a Celgard separator. It has a low capacity degradation of 0.067% per cycle after 600 cycles at 1 C, and a high discharge capacity (576 mAh g^-1) even at 2 C. Our work proves that the modification of a separator with a SCOF is a viable and effective route for enhancing the electrochemical performance of a LSB.

Dense-Stacking Porous Conjugated Polymer as Reactive-Type Host for High-Performance Lithium Sulfur Batteries

Commercialization of the lithium-sulfur battery is hampered by bottlenecks like low sulfur loading, high cathode porosity, uncontrollable Li₂ S_x deposition and sluggish kinetics of Li₂ S activation. Herein, we developed a densely stacked redox-active hexaazatrinaphthylene (HATN) polymer with a surface area of 302 m²  g^-1 and a very high bulk density of ca. 1.60 g cm^-3 . Uniquely, HATN polymer has a similar redox potential window to S, which facilitates the binding of Li₂ S_x and its transformation chemistry within the bulky polymer host, leading to fast Li₂ S/S kinetics. The compact polymer/S electrode presents a high sulfur loading of ca. 15 mg_s  cm^-2 (200-μm thickness) with a low cathode porosity of 41 %. It delivers a high areal capacity of ca. 14 mAh cm^-2 and good cycling stability (200 cycles) at electrolyte-sulfur (E/S) ratio of 5 μL mg_s ^-1 . The assembled pouch cell delivers a cell-level high energy density of 303 Wh kg^-1 and 392 Wh L^-1 .

On-Site Fluorination for Enhancing Utilization of Lithium in a Lithium-Sulfur Full Battery

The rechargeability of the lithium anode in lithium-sulfur (Li-S) batteries is an issue for this type of battery. In this work, we demonstrate a Li-S full battery comprising a protected anode scaffold and a Li₂S cathode. The stabilized performance is attained by an on-site fluorination strategy, using BiF₃ for the interfacial coating of the anode. Unlike previously reported LiF protective coating derived from the vapor/solution depositions, BiF₃ nanocrystals would be lithiated on-site to the anode surface and server as the protective layer. The chemically inertial Li₃Bi alloy can provide additional ion-conductive paths and stitch the LiF to form a seamless protective layer, thereby suppressing the dendrite propagation and parasitic reactions effectively. With the designed anode structures and compositions, the high-loading full battery (8.05 mg cm^-2) can achieve an exceptional utilization of both sulfur (898 mAh g_S^-1) and lithium (1533 mAh g_Li^-1) over 200 cycles, marking a step toward cyclable Li metal batteries at a high capacity.

Towards practical lithium-metal anodes

Lithium-ion batteries have had a tremendous impact on several sectors of our society; however, the intrinsic limitations of Li-ion chemistry limits their ability to meet the increasing demands of developing more advanced portable electronics, electric vehicles, and grid-scale energy storage systems. Therefore, battery chemistries beyond Li ions are being intensively investigated and need urgent breakthroughs toward commercial applications, wherein the use of metallic Li is one of the most intuitive choices. Despite several decades of oblivion due to safety concerns regarding the growth of Li dendrites, Li-metal anodes are now poised to be revived because of the advances in investigative tools and globally invested efforts. In this review, we first summarize the existing issues with regard to Li anodes and their underlying reasons and then highlight the recent progress made in the development of high-performance Li anodes. Finally, we propose the persisting challenges and opportunities toward the exploration of practical Li-metal anodes.

A highly-effective nitrogen-doped porous carbon sponge electrode for advanced K–Se batteries

A rechargeable K–Se battery is emerging as an energy storage system because of its much higher specific capacity than that of the traditional alkali metal-ion batteries, but is facing some critical issues and challenges.