Unraveling the Dual Functionality of High‐Donor‐Number Anion in Lean‐Electrolyte Lithium‐Sulfur Batteries

Minimizing electrolyte use is essential to achieve high practical energy density of lithium–sulfur (Li–S) batteries. However, the sulfur cathode is more readily passivated under a lean electrolyte condition, resulting in low sulfur utilization. In addition, continuous electrolyte decomposition on the Li metal anode aggravates the problem, provoking rapid capacity decay. In this work, the dual functionalities of NO₃^? as a high‐donor‐number (DN) salt anion is presented, which improves the sulfur utilization and cycling stability of lean‐electrolyte Li–S batteries. The NO₃^? anion elevates the solubility of the sulfur species based on its high electron donating ability, achieving a high sulfur utilization of above 1200 mA h g^?1. Furthermore, the anion suppresses electrolyte decomposition on the Li metal by regulating the lithium ion (Li⁺) solvation sheath, enhancing the cycle performance of the lean electrolyte cell. By understanding the anionic effects, this work demonstrates the potential of the high‐DN electrolyte, which is beneficial for both the cathode and anode of Li–S batteries.     

Toward a Reversible Calcium‐Sulfur Battery with a Lithium‐Ion Mediation Approach

Calcium represents a promising anode for the development of high‐energy‐density, low‐cost batteries. However, a lack of suitable electrolytes has restricted the development of rechargeable batteries with a Ca anode. Furthermore, to achieve a high energy density system, sulfur would be an ideal cathode to couple with the Ca anode. Unfortunately, a reversible calcium‐sulfur (Ca‐S) battery has not yet been reported. Herein, a basic study of a reversible nonaqueous room‐temperature Ca‐S battery is presented. The reversibility of the Ca‐S chemistry and high utilization of the sulfur cathode are enabled by employing a Li⁺‐ion‐mediated calcium‐based electrolyte. Mechanistic insights pursued by spectroscopic, electrochemical, microscopic, and theoretical simulation (density functional theory) investigations imply that the Li⁺‐ions in the Ca‐electrolyte stimulate the reactivation of polysulfide/sulfide species. The coordination of lithium to sulfur reduces the formation of sturdy Ca‐S ionic bonds, thus boosting the reversibility of the Ca‐S chemistry. In addition, the presence of Li⁺‐ions facilitates the ionic charge transfer both in the electrolyte and across the solid electrolyte interphase layer, consequently reducing the interfacial and bulk impedance of Ca‐S batteries. As a result, both the utilization of active sulfur in the cathode and the discharge voltage of Ca‐S batteries are significantly improved.     

A Dual‐Carbon Battery Based on Potassium‐Ion Electrolyte

Although potassium‐ion batteries (KIBs) have been considered to be promising alternatives to conventional lithium‐ion batteries due to large abundance and low cost of potassium resources, their development still stays at the infancy stage due to the lack of appropriate cathode and anode materials with reversible potassium insertion/extraction as well as good rate and cycling performance. Herein, a novel dual‐carbon battery based on a potassium‐ion electrolyte (named as K‐DCB), utilizing expanded graphite as cathode material and mesocarbon microbead as anode material is developed. The working mechanism of the K‐DCB is investigated, which is further demonstrated to deliver a high reversible capacity of 61 mA h g^‐1 at a current density of 1C over a voltage window of 3.0–5.2 V, as well as good cycling performance with negligible capacity decay after 100 cycles. Moreover, the high working voltage with medium discharge voltage of 4.5 V also enables the K‐DCB to meet the requirement of some high‐voltage devices. With the merits of environmental friendliness, low cost and high energy density, the K‐DCB shows attractive potential for future energy storage application.     

Sodium Sulfide Cathodes Superseding Hard Carbon Pre‐sodiation for the Production and Operation of Sodium–Sulfur Batteries at Room Temperature

This study demonstrates for the first time a room temperature sodium–sulfur (RT Na–S) full cell assembled based on a pristine hard carbon (HC) anode combined with a nanostructured Na₂S/C cathode. The development of cells without the demanding, time‐consuming and costly pre‐sodiation of the HC anode is essential for the realization of practically relevant RT Na–S prototype batteries. New approaches for Na₂S/C cathode fabrication employing carbothermal reduction of Na₂SO₄ at varying temperatures (660 to 1060 °C) are presented. Initial evaluation of the resulting cathodes in a dedicated cell setup reveals 36 stable cycles and a capacity of 740 mAh g_S^?1, which correlates to ≈85% of the maximum value known from literature on Na₂S‐based cells. The Na₂S/C cathode with the highest capacity utilization is implemented into a full cell concept applying a pristine HC anode. Various full cell electrolyte compositions with fluoroethylene carbonate (FEC) additive have been combined with a special charging procedure during the first cycle supporting in situ solid electrolyte interphase (SEI) formation on the HC anode to obtain increased cycling stability and cathode utilization. The best performing cell setup has delivered a total of 350 mAh g_S^?1, representing the first functional full cell based on a Na₂S/C cathode and a pristine HC anode today.     

Hard Carbon Anodes and Novel Electrolytes for Long‐Cycle‐Life Room Temperature Sodium‐Sulfur Full Cell Batteries

A novel combination of hard carbon anode sodium pre‐loading and a tailored electrolyte is used to prepare room temperature sodium‐sulfur full cell batteries. The electrochemical loading with sodium ions is realized in a specific mixture of diethyl carbonate, ethylene carbonate, and fluoroethylene carbonate electrolyte in order to create a first solid electrolyte interface (SEI) on the anode surface. Combining such anodes with a porous carbon/sulfur composite cathode results in full cells with a significantly decreased polysulfide shuttle when compared to half cells combined with metallic sodium anodes. Further optimization involves the use of Na₂S/P₂S₅ doped tetraethylene glycol dimethyl ether based electrolyte in the full cell for the formation of a second SEI, reducing polysulfide shuttle even further. More importantly, the electrochemical discharge processes in the cell are improved by adding this dissolved complexation agent to the electrolyte. As a result of this combination sodium‐sulfur cells with tailored cathode materials and electrolytes can achieve high discharge capacities up to 980 mAh g^?1_sulfur and 1000 cycles with 200 mAh g^?1_sulfur remaining capacity, at room temperature.     

Aqueous Electrochemical Energy Storage with a Mediator‐Ion Solid Electrolyte

This study presents a battery concept with a “mediator‐ion” solid electrolyte for the development of next‐generation electrochemical energy storage technologies. The active anode and cathode materials in a single cell can be in the solid, liquid, or gaseous form, which are separated by a sodium‐ion solid‐electrolyte separator. The uniqueness of this mediator‐ion strategy is that the redox reactions at the anode and the cathode are sustained by a shuttling of a mediator sodium ion between the anolyte and the catholyte through the solid‐state electrolyte. Use of the solid‐electrolyte separator circumvents the chemical‐crossover problem between the anode and the cathode, overcomes the dendrite‐problem when employing metal‐anodes, and offers the possibility of using different liquid electrolytes at the anode and the cathode in a single cell. The battery concept is demonstrated with two low‐cost metal anodes (zinc and iron), two liquid cathodes (bromine and potassium ferricyanide), and one gaseous cathode (air/O₂) with a sodium‐ion solid electrolyte. This novel battery strategy with a mediator‐ion solid electrolyte is applicable to a wide range of electrochemical energy storage systems with a variety of cathodes, anodes, and mediator‐ion solid electrolytes.     

“Water‐in‐Salt” Electrolyte Makes Aqueous Sodium‐Ion Battery Safe,Green, and Long‐Lasting

Narrow electrochemical stability window (1.23 V) of aqueous electrolytes is always considered the key obstacle preventing aqueous sodium‐ion chemistry of practical energy density and cycle life. The sodium‐ion water‐in‐salt electrolyte (NaWiSE) eliminates this barrier by offering a 2.5 V window through suppressing hydrogen evolution on anode with the formation of a Na⁺‐conducting solid‐electrolyte interphase (SEI) and reducing the overall electrochemical activity of water on cathode. A full aqueous Na‐ion battery constructed on Na_0.66[Mn_0.66Ti_0.34]O₂ as cathode and NaTi₂(PO₄)₃ as anode exhibits superior performance at both low and high rates, as exemplified by extraordinarily high Coulombic efficiency (>99.2%) at a low rate (0.2 C) for >350 cycles, and excellent cycling stability with negligible capacity losses (0.006% per cycle) at a high rate (1 C) for >1200 cycles. Molecular modeling reveals some key differences between Li‐ion and Na‐ion WiSE, and identifies a more pronounced ion aggregation with frequent contacts between the sodium cation and fluorine of anion in the latter as one main factor responsible for the formation of a dense SEI at lower salt concentration than its Li cousin.     

Combining Nature‐Inspired,Graphene‐Wrapped Flexible Electrodes with Nanocomposite Polymer Electrolyte for Asymmetric Capacitive Energy Storage

Two kinds of free‐standing electrodes, reduced graphene oxide (rGO)‐wrapped Fe‐doped MnO₂ composite (G‐MFO) and rGO‐wrapped hierarchical porous carbon microspheres composite (G‐HPC) are fabricated using a frozen lake‐inspired, bubble‐assistance method. This configuration fully enables utilization of the synergistic effects from both components, endowing the materials to be excellent electrodes for flexible and lightweight electrochemical capacitors. Moreover, a nonaqueous HPC‐doped gel polymer electrolyte (GPE‐HPC) is employed to broad voltage window and improve heat resistance. A fabricated asymmetric supercapacitor based on G‐MFO cathode and G‐HPC anode with GPE‐HPC electrolyte achieves superior flexibility and reliability, enhanced energy/power density, and outstanding cycling stability. The ability to power light‐emitting diodes also indicates the feasibility for practical use. Therefore, it is believed that this novel design may hold great promise for future flexible electronic devices.     

High‐Performance Protonic Ceramic Fuel Cells with 1 µm Thick Y:Ba(Ce,Zr)O3 Electrolytes

This study demonstrates the effectiveness of using thin‐film electrolytes to enhance protonic ceramic fuel cells (PCFCs). The material tested in this study is yttrium‐doped barium cerate‐zirconate (BCZY), which is a representative electrolyte material of PCFCs. The thickness of the electrolyte membrane is as small as 1 µm and designed to minimize ohmic loss in proton transport pathways. Integration of this thin BCZY electrolyte is attempted on a multilayered anode comprised of two‐step supports with bulk nickel‐yttria stabilized zirconia cermet as a base and thin nickel‐BCZY as an anode functional layer atop the base. The compatibility of this support with the deposited thin electrolyte is able to be confirmed from the results of iterated tests. The power of the fabricated cell is greater than 1.1 W cm^?2 at 600 °C, which is a record high for PCFCs and is reproducible. In this paper, the origin of this high power is discussed and improvements that could be made to cell performance are further suggested.     

A Stable Graphitic,Nanocarbon‐Encapsulated,Cobalt‐Rich Core–Shell Electrocatalyst as an Oxygen Electrode in a Water Electrolyzer

The oxygen electrode plays a vital role in the successful commercialization of renewable energy technologies, such as fuel cells and water electrolyzers. In this study, the Prussian blue analogue‐derived nitrogen‐doped nanocarbon (NC) layer‐trapped, cobalt‐rich, core–shell nanostructured electrocatalysts (core–shell Co@NC) are reported. The electrode exhibits an improved oxygen evolution activity and stability compared to that of the commercial noble electrodes. The core–shell Co@NC‐loaded nickel foam exhibits a lower overpotential of 330 mV than that of IrO₂ on nickel foam at 10 mA cm^?2 and has a durability of over 400 h. The commercial Pt/C cathode‐assisted, core–shell Co@NC–anode water electrolyzer delivers 10 mA cm^?2 at a cell voltage of 1.59 V, which is 70 mV lower than that of the IrO₂–anode water electrolyzer. Over the long‐term chronopotentiometry durability testing, the IrO₂–anode water electrolyzer shows a cell voltage loss of 230 mV (14%) at 95 h, but the loss of the core–shell Co@NC–anode electrolyzer is only 60 mV (4%) even after 350 h cell‐operation. The findings indicate that the Prussian blue analogue is a class of inorganic nanoporous materials that can be used to derive metal‐rich, core–shell electrocatalysts with enriched active centers.     

Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes

Hard carbon (HC) is the state‐of‐the‐art anode material for sodium‐ion batteries (SIBs). However, its performance has been plagued by the limited initial Coulombic efficiency (ICE) and mediocre rate performance. Here, experimental and theoretical studies are combined to demonstrate the application of lithium‐pretreated HC (LPHC) as high‐performance anode materials for SIBs by manipulating the solid electrolyte interphase in tetraglyme (TEGDME)‐based electrolyte. The LPHC in TEGDME can 1) deliver > 92% ICE and ≈220 mAh g^?1 specific capacity, twice of the capacity (≈100 mAh g^?1) in carbonate electrolyte; 2) achieve > 85% capacity retention over 1000 cycles at 1000 mA g^?1 current density (4 C rate, 1 C = 250 mA g^?1) with a specific capacity of ≈150 mAh g^?1, ≈15 times of the capacity (10 mAh g^?1) in carbonate. The full cell of Na₃V₂(PO₄)₃‐LPHC in TEGDME demonstrated close to theoretical specific capacity of ≈98 mAh g^?1 based on Na₃V₂(PO₄)₃ cathode, ≈2.5 times of the value (≈40 mAh g^?1) with nontreated HC. This work provides new perception on the anode development for SIBs.     

A Sodium‐Ion Battery with a Low‐Cost Cross‐Linked Gel‐Polymer Electrolyte

The design of a sodium‐ion rechargeable battery with an antimony anode, a Na₃V₂(PO₄)₃ cathode, and a low‐cost composite gel‐polymer electrolyte based on cross‐linked poly(methyl methacrylate) is reported. The application of an antimony anode, on replacement of the sodium metal that is commonly used in sodium‐ion half‐cells, reduces significantly the interfacial resistance and charge transfer resistance of a sodium‐ion battery, which enables a smaller polarization for a sodium‐ion full‐cell Sb/Na₃V₂(PO₄)₃ running at relatively high charge and discharge rates. The incorporation of the gel‐polymer electrolyte is beneficial to maintain stable interfaces between the electrolyte and the electrodes of the sodium‐ion battery at elevated temperature. When running at 60 °C, the sodium‐ion full‐cell Sb/Na₃V₂(PO₄)₃ with the gel‐polymer electrolyte exhibits superior cycling stability compared to a battery with the conventional liquid electrolyte.     

A Hybrid Electrolytes Design for Capacity‐Equivalent Dual‐Graphite Battery with Superior Long‐Term Cycle Life

Based on cation/anion graphite intercalation chemistry (GIC) processes, dual‐graphite batteries promise to be an energy storage device of high safety and low cost. However, few single electrolyte systems can simultaneously meet the requirements of both high oxidative stability during high voltage anion‐GIC on cathode and high reversibility upon cation‐GIC on anode. Thus, in order to rigidly remedy the irreversible capacity loss, excessive electrode materials need to be fabricated within full cell, resulting in an imbalance toward capacity‐dependent mass loading proportion between both electrodes. This work introduces a hybrid (dual‐organic) electrolytes design strategy into this promising technology. Segregated by a Nafion‐based separator, an ionic liquid electrolyte within the cathodic side can endure high operation potentials, while high Li‐GIC reversibility can be achieved in a superconcentrated ether‐based electrolyte on the anode side. On a mechanistic level, various cation‐GIC processes conducted in different electrolyte systems are clearly revealed and are summarized based on systematical characterizations. More importantly, after synergistically tuning the advantage and drawback of each electrolyte in this hybrid system, the dual‐graphite full cell assembled with capacity‐equivalent graphite‐based electrodes (1:1 mass loading) demonstrates superior long‐term cycling stability with ultrahigh capacity retention for over 3000 cycles.     

Li3N as a Cathode Additive for High‐Energy‐Density Lithium‐Ion Batteries

The formation of a solid‐electrolyte interphase on the anode surface of an Li‐ion battery using an organic liquid electrolyte robs Li⁺ irreversibly form the cathode on the initial charge if the cells are fabricated in the discharged state. In order to increase the cathode capacity, the use of Li₃N as a sacrificial source of Li⁺ on the initial charge has been evaluated chemically and electrochemically as an additive to an LiCoO₂ cathode. Li₃N is shown to be chemically stable in a dry atmosphere as small particles with fresh surfaces and can increase the reversible capacities of a full cell without compromising the rate capability of the cells.     

Soft,Highly Elastic,and Discharge‐Current‐Controllable Eutectic Gallium–Indium Liquid Metal–Air Battery Operated at Room Temperature

Based on a liquid metal (eutectic alloy with 90 wt% gallium and 10 wt% indium) anode, a soft, highly elastic, discharge‐current‐controllable, cable‐shaped liquid metal–air battery operated at 25 °C, with effective reactions of Ga ? 3e^? → Ga³⁺ and O₂ + 2H₂O + 4e^? → 4OH^? is presented. In the liquid metal electrode, indium is used not only to inhibit the corrosion of gallium in the alkaline electrolyte but also to maintain the liquid state of the anode at room temperature. Thus, the liquid anode can be easily injected into (or extracted from) the battery cavity, leading to an easily renewable anode. In addition, the cable‐shaped battery shows a pressure‐responsive discharge current, owing to the soft, deformable battery body. Due to the liquid anode and flexible carbon fiber‐based cathode, the battery is highly flexible (bending radius < 1 mm) and easily recovers from any degree of bending without electrochemical performance impairment. With its elastic polyacrylic acid‐based gel electrolyte, the battery shows high elasticity, stretching by up to 100% (from 12 to 24 cm), excellent shape recovery from stretched states, and a discharge performance retention of 98.87%. Moreover, this paper provides the possibility to develop a deformable battery based on the liquid metal material.     

Metalorganic Quantum Dots and Their Graphene‐Like Derivative Porous Graphitic Carbon for Advanced Lithium‐Ion Hybrid Supercapacitor

Lithium‐ion hybrid supercapacitors (LICs) are considered as a promising candidate in energy storage systems. Taking the factor of sluggish kinetics behavior, battery‐type anode plays a significant role in improving the performance of LICs. Here, onion‐shaped graphene‐like derivatives are synthesized via carbonization of metalorganic quantum dots (MQDs) accompanied with in situ catalytic graphitization by reduced metal. Notably MQDs, exhibiting water‐soluble character and ultrafine particles (2.5–5.5 nm) morphology, are prepared by the amidation reaction. The carbonized sample exhibits highly graphitic tendency with graphitization degree up to 95.6%, and shows graphene‐like porous structure, appropriate amorphous carbon decoration characteristic, as well as N‐doping and defective nature. When employed as anode material in LICs, it shows high energy density of 83.7 Wh kg^–1 and high power density of 6527 W kg^–1 when the mass ratio of cathode to anode is 1:1 and the operating voltage ranges from 2.0 to 4.0 V. It also possesses the long cyclic stability with the energy density retention maintains at 97.3% after 10 000 cycles at 5.0 A g^–1. In addition, the energy density is further increased by altering cathode/anode mass ratio and extending working voltage. This work provides a novel strategy to develop unique carbon materials for energy storage.     

Designing Safe Electrolyte Systems for a High‐Stability Lithium–Sulfur Battery

Safety, nontoxicity, and durability directly determine the applicability of the essential characteristics of the lithium (Li)‐ion battery. Particularly, for the lithium–sulfur battery, due to the low ignition temperature of sulfur, metal lithium as the anode material, and the use of flammable organic electrolytes, addressing security problems is of increased difficulty. In the past few years, two basic electrolyte systems are studied extensively to solve the notorious safety issues. One system is the conventional organic liquid electrolyte, and the other is the inorganic solid‐state or quasi‐solid‐state composite electrolyte. Here, the recent development of engineered liquid electrolytes and design considerations for solid electrolytes in tackling these safety issues are reviewed to ensure the safety of electrolyte systems between sulfur cathode materials and the lithium‐metal anode. Specifically, strategies for designing and modifying liquid electrolytes including introducing gas evolution, flame, aqueous, and dendrite‐free electrolytes are proposed. Moreover, the considerations involving a high‐performance Li⁺ conductor, air‐stable Li⁺ conductors, and stable interface performance between the sulfur cathode and the lithium anode for developing all‐solid‐state electrolytes are discussed. In the end, an outlook for future directions to offer reliable electrolyte systems is presented for the development of commercially viable lithium–sulfur batteries.     

Polymer‐in‐“Quasi‐Ionic Liquid” Electrolytes for High‐Voltage Lithium Metal Batteries

Due to the limited oxidation stability (<4 V) of ether oxygen in its polymer structure, polyethylene oxide (PEO)‐based polymer electrolytes are not compatible with high‐voltage (>4 V) cathodes, thus hinder further increases in the energy density of lithium (Li) metal batteries (LMBs). Here, a new type of polymer‐in‐“quasi‐ionic liquid” electrolyte is designed, which reduces the electron density on ethereal oxygens in PEO and ether solvent molecules, induces the formation of stable interfacial layers on both surfaces of the LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) cathode and the Li metal anode in Li||NMC batteries, and results in a capacity retention of 88.4%, 86.7%, and 79.2% after 300 cycles with a charge cutoff voltage of 4.2, 4.3, and 4.4 V for the LMBs, respectively. Therefore, the use of “quasi‐ionic liquids” is a promising approach to design new polymer electrolytes for high‐voltage and high‐specific‐energy LMBs.     

Impact of initial biofilm growth on the anode impedance of microbial fuel cells

Electrochemical impedance spectroscopy (EIS) was used to study the behavior of a microbial fuel cell (MFC) during initial biofilm growth in an acetate-fed, two-chamber MFC system with ferricyanide in the cathode. EIS experiments were performed both on the full cell (between cathode and anode) as well as on individual electrodes. The Nyquist plots of the EIS data were fitted with an equivalent electrical circuit to estimate the contributions of various intrinsic resistances to the overall internal MFC impedance. During initial development of the anode biofilm, the anode polarization resistance was found to decrease by over 70% at open circuit and by over 45% at 27 microA/cm(2), and a simultaneous increase in power density by about 120% was observed. The exchange current density for the bio-electrochemical reaction on the anode was estimated to be in the range of 40-60 nA/cm(2) for an immature biofilm after 5 days of closed circuit operation, which increased to around 182 nA/cm(2) after more than 3 weeks of operation and stable performance in an identical parallel system. The polarization resistance of the anode was 30-40 times higher than that of the ferricyanide cathode for the conditions tested, even with an established biofilm. For a two-chamber MFC system with a Nafion 117 membrane and an inter-electrode spacing of 15 cm, the membrane and electrolyte solution dominate the ohmic resistance and contribute to over 95% of the MFC internal impedance. Detailed EIS analyses provide new insights into the dominant kinetic resistance of the anode bio-electrochemical reaction and its influence on the overall power output of the MFC system, even in the high internal resistance system used in this study. These results suggest that new strategies to address this kinetic constraint of the anode bio-electrochemical reactions are needed to complement the reduction of ohmic resistance in modern designs.     

Multifunctional Silanization Interface for High‐Energy and Low‐Gassing Lithium Metal Pouch Cells

Lithium (Li) metal has attracted unprecedented attention as the ultimate anode material for future rechargeable batteries, but the electrochemical behavior (such as Li dendrites and gassing problems) in real Li metal pouch cells has received little attention. To achieve realistic high‐energy Li metal batteries, the designed solid electrolyte interface to suppress both Li dendrites and catastrophic gassing problems is urgently needed at cell level. Here, an efficient multifunctional silanization interface (MSI) is proposed for high‐energy Li metal pouch cells. Such an MSI not only guides uniform nucleation and growth of Li metal but also suppresses interfacial parasitic reactions between Li metal and electrolyte. As a result, under harsh conditions (negative to positive electrode capacity ratio of 2.96 and electrolyte weight to cathode capacity ratio of 2.7 g Ah^?1), a long‐running lifespan (over 160 cycles with a capacity retention of 96% at 1 C), and low‐gassing behavior of realistic high‐energy Li metal pouch cell (1 Ah, 300 Wh kg^?1) is achieved. This work opens a promising avenue toward the commercial applications of high‐energy Li metal batteries.