Freestanding and Sandwich MXene-Based Cathode with Suppressed Lithium Polysulfides Shuttle for Flexible Lithium-Sulfur Batteries.

Flexible lithium-sulfur (Li-S) batteries with high mechanical compliance and energy density are highly desired. This manuscript reported that large-area freestanding MXene (Ti3C2Tx) film has been obtained through a scalable drop-casting method, significantly improving adhesion to the sulfur layer under the continuously bent. Titanium oxide anchored on holey Ti3C2Tx (TiO2/H-Ti3C2Tx) was also produced by the well-controlled oxidation of few-layer Ti3C2Tx, which greatly facilitates lithium ion transport as well as prevents the shuttling of lithium polysulfides. Therefore, the obtained sandwich electrode has demonstrated a high capacity of 740 mAh g-1 at 2 C and a high capacity retention of 81% at 1 C after 500 cycles. Flexible Li-S batteries based on this sandwich electrode have a capacity retention as high as 95% after bending 500 times. This work provides effective design strategies of MXene for flexible batteries and wearable electronics.

Stabilized Solid Electrolyte Interphase Induced by Ultrathin Boron Nitride Membranes for Safe Lithium Metal Batteries.

Lithium-ion batteries (LIBs) are still facing safety problems, mainly due to dendrite growth on the anode that leads to combustion and explosion. Forming a stable solid electrolyte interface (SEI) layer is an effective way to suppress this. To induce the formation of stable SEI using simple methods at a low cost, we report an ultrathin and large-scale hexagonal boron nitride (h-BN)/polyimide (PI) layer that was coated on a commercial polypropylene (PP) separator. The formation of a stabilized SEI component induced by the h-BN coating layer is proposed, as suggested by theoretical calculations and confirmed by electrochemical analysis and spectroscopy. It effectively suppresses Li dendrite growth and reduces the consumption of active lithium. The separator also has good electrolyte wettability, excellent mechanical strength and thermal conductivity, and high thermal stability. When using the h-BN modified separator in a full cell, the capacity is extremely stable after long cycling and high temperature.

Stable Thiophosphate-Based All-Solid-State Lithium Batteries through Conformally Interfacial Nanocoating.

All-solid-state lithium batteries (ASLBs) are promising for the next generation energy storage system with critical safety. Among various candidates, thiophosphate-based electrolytes have shown great promise because of their high ionic conductivity. However, the narrow operation voltage and poor compatibility with high voltage cathode materials impede their application in the development of high energy ASLBs. In this work, we studied the failure mechanism of Li6PS5Cl at high voltage through in situ Raman spectra and investigated the stability with high-voltage LiNi1/3Mn1/3Co1/3O2 (NMC) cathode. With a facile wet chemical approach, we coated a thin layer of amorphous Li0.35La0.5Sr0.05TiO3 (LLSTO) with 15-20 nm at the interface between NMC and Li6PS5Cl. We studied different coating parameters and optimized the coating thickness of the interface layers. Meanwhile, we studied the effect of NMC dimension to the ASLBs performance. We further conducted the first-principles thermodynamic calculations to understand the electrochemical stability between Li6PS5Cl and carbon, NMC, LLSTO, NMC/LLSTO. Attributed to the high stability of Li6PS5Cl with NMC/LLSTO and outstanding ionic conductivity of the LLSTO and Li6PS5Cl, at room temperature, the ASLBs exhibit outstanding capacity of 107 mAh g-1 and keep stable for 850 cycles with a high capacity retention of 91.5% at C/3 and voltage window 2.5-4.0 V (vs Li-In).

One-Dimensional Hetero-Nanostructures for Rechargeable Batteries.

Rechargeable batteries are regarded as one of the most practical electrochemical energy storage devices that are able to convert and store the electrical energy generated from renewable resources, and they function as the key power sources for electric vehicles and portable electronics. The ultimate goals for electrochemical energy storage devices are high power and energy density, long lifetime, and high safety. To achieve the above goals, researchers have tried to apply various morphologies of nanomaterials as the electrodes to enhance the electrochemical performance. Among them, one-dimensional (1D) materials show unique superiorities, such as cross-linked structures for external stress buffering and large draw ratios for internal stress dispersion. However, a homogeneous single-component electrode material can hardly have the characteristics of high electronic/ionic conductivity and high stability in the electrochemical environment simultaneously. Therefore, designing well-defined functional 1D hetero-nanostructures that combine the advantages and overcome the limitations of different electrochemically active materials is of great significance. This Account summarizes fabrication strategies for 1D hetero-nanostructures, including nucleation and growth, deposition, and melt-casting and electrospinning. Besides, the chemical principles for each strategy are discussed. The nucleation and growth strategy is suitable for growing and constructing 1D hetero-nanostructures of partial transition metal compounds, and the experimental conditions for this strategy are relatively accessible. Deposition is a reliable strategy to synthesize 1D hetero-nanostructures by decorating functional layers on 1D substrate materials, on the condition that the preobtained substrate materials must be stable in the following deposition process. The melt-casting strategy, in which 1D hetero-nanostructures are synthesizes via a melting and molding process, is also widely used. Additionally, the main functions of 1D hetero-nanostructures are summarized into four aspects and reviewed in detail. Appropriate surface modification can effectively restrain the structure deterioration and the regeneration of the solid-electrolyte interphase layer caused by the volume change. A porous or semihollow external conducting material coating provides advanced electron/ion bicontinuous transmission. Suitable atomic heterogeneity in the crystal structure is beneficial to the expansion and stabilization of the ion diffusion channels. Multiphase-assisted structural design is also an accessible way for the sulfur electrode material restriction. Moreover, some outlooks about the further industrial production, more effective and cheaper fabrication strategies, and new heterostructures with smaller-scale composition are given in the last part. By providing an overview of fabrication methods and performance-enhancing mechanisms of 1D hetero-nanostructured electrode materials, we hope to pave a new way to facile and efficient construction of 1D hetero-nanostructures with practical utility.

Mesoporous NiS2 Nanospheres Anode with Pseudocapacitance for High-Rate and Long-Life Sodium-Ion Battery.

It is of great importance to exploit electrode materials for sodium-ion batteries (SIBs) with low cost, long life, and high-rate capability. However, achieving quick charge and high power density is still a major challenge for most SIBs electrodes because of the sluggish sodiation kinetics. Herein, uniform and mesoporous NiS2 nanospheres are synthesized via a facile one-step polyvinylpyrrolidone assisted method. By controlling the voltage window, the mesoporous NiS2 nanospheres present excellent electrochemical performance in SIBs. It delivers a high reversible specific capacity of 692 mA h g-1 . The NiS2 anode also exhibits excellent high-rate capability (253 mA h g-1 at 5 A g-1 ) and long-term cycling performance (319 mA h g-1 capacity remained even after 1000 cycles at 0.5 A g-1 ). A dominant pseudocapacitance contribution is identified and verified by kinetics analysis. In addition, the amorphization and conversion reactions during the electrochemical process of the mesoporous NiS2 nanospheres is also investigated by in situ X-ray diffraction. The impressive electrochemical performance reveals that the NiS2 offers great potential toward the development of next generation large scale energy storage.

A High-Rate V2 O5 Hollow Microclew Cathode for an All-Vanadium-Based Lithium-Ion Full Cell.

V2O5 hollow microclews (V2O5-HMs) have been fabricated through a facile solvothermal method with subsequent calcination. The synthesized V2O5-HMs exhibit a 3D hierarchical structure constructed by intertangled nanowires, which could realize superior ion transport, good structural stability, and significantly improved tap density. When used as the cathodes for lithium-ion batteries (LIBs), the V2O5-HMs deliver a high capacity (145.3 mAh g(-1)) and a superior rate capability (94.8 mAh g(-1) at 65 C). When coupled with a lithiated Li3VO4 anode, the all-vanadium-based lithium-ion full cell exhibits remarkable cycling stability with a capacity retention of 71.7% over 1500 cycles at 6.7 C. The excellent electrochemical performance demonstrates that the V2O5-HM is a promising candidate for LIBs. The insight obtained from this work also provides a novel strategy for assembling 1D materials into hierarchical microarchitectures with anti-pulverization ability, excellent electrochemical kinetics, and enhanced tap density.

Flexible additive free H2V3O8 nanowire membrane as cathode for sodium ion batteries.

Sodium ion batteries (SIBs) have emerged as a potential candidate to succeed lithium ion batteries (LIBs), because of the abundant sodium resources on earth. Layered vanadium oxides are regarded as the promising candidates for SIBs because of their large interlayer spacing, high theoretical specific capacity, abundant sources and low cost. In this paper, a vanadium oxide hydrate (H2V3O8) nanowire membrane is presented as a flexible cathode for SIBs without addition of any other additives (binders or conductive compounds). Such a freestanding flexible membrane exhibits a high specific capacity of 168 mA h g(-1) at 10 mA g(-1), and its high capacity is maintained well after 100 cycles. It is found that the capacitive charge storage accounts for a relatively large proportion of the total capacity, whereas the crystal structure of H2V3O8 is highly reversible during the sodiation/desodiation processes. This research demonstrates that the H2V3O8 nanowire is an exceptional candidate for SIBs.

Three-Dimensional Interconnected Vanadium Pentoxide Nanonetwork Cathode for High-Rate Long-Life Lithium Batteries.

Three-dimensional interconnected vanadium pentoxide nanonetworks as cathodes for rechargable lithium batteries are successfully synthesized via a quick gelation followed by annealing. The interconnected structure ensures the electron transport of each unit. And their inner porous structure buffer the volume change over long-term repeated lithium ion insertion/extraction cycles, leading to the high-rate long-life cycling performance.

Amorphous vanadium oxide matrixes supporting hierarchical porous Fe3O4/graphene nanowires as a high-rate lithium storage anode.

Developing electrode materials with both high energy and power densities holds the key for satisfying the urgent demand of energy storage worldwide. In order to realize the fast and efficient transport of ions/electrons and the stable structure during the charge/discharge process, hierarchical porous Fe3O4/graphene nanowires supported by amorphous vanadium oxide matrixes have been rationally synthesized through a facile phase separation process. The porous structure is directly in situ constructed from the FeVO4·1.1H2O@graphene nanowires along with the crystallization of Fe3O4 and the amorphization of vanadium oxide without using any hard templates. The hierarchical porous Fe3O4/VOx/graphene nanowires exhibit a high Coulombic efficiency and outstanding reversible specific capacity (1146 mAh g(-1)). Even at the high current density of 5 A g(-1), the porous nanowires maintain a reversible capacity of ∼500 mAh g(-1). Moreover, the amorphization and conversion reactions between Fe and Fe3O4 of the hierarchical porous Fe3O4/VOx/graphene nanowires were also investigated by in situ X-ray diffraction and X-ray photoelectron spectroscopy. Our work demonstrates that the amorphous vanadium oxides matrixes supporting hierarchical porous Fe3O4/graphene nanowires are one of the most attractive anodes in energy storage applications.

A 3D Framework with Li3 N-Li2 S Solid Electrolyte Interphase and Fast Ion Transfer Channels for a Stabilized Lithium-Metal Anode.

The Li-metal anode has been recognized as the most promising anode for its high theoretical capacity and low reduction potential. However, the major drawbacks of Li metal, such as high reactivity and large volume expansion, can lead to dendrite growth and solid electrolyte interface (SEI) fracture. An in situ artificial inorganic SEI layer, consisting of lithium nitride and lithium sulfide, is herein reported to address the dendrite growth issues. Porous graphene oxide films are doped with sulfur and nitrogen (denoted as SNGO) to work as an effective lithium host. The SNGO film enables the in situ formation of an inorganic-rich SEI layer, which facilitates the transport of Li-ions, improves SEI mechanical strength, and avoids SEI fracture. In addition, COMSOL simulation results reveal that the microchannels fabricated by the 3D printing technique further shorten the Li-ion transfer pathways and homogenize heat and stress distribution in the batteries. As a result, the assembled anode shows low capacity fading of 0.1% per cycle at 2 C rate with the sulfur cathode. In addition, the high lithium utilization of the SNGO host enables the anode to provide a stable capacity at low negative/positive electrode ratios under 3 in LiS batteries.

Rechargeable Zinc-Air Batteries with an Ultralarge Discharge Capacity per Cycle and an Ultralong Cycle Life.

A conventional two-electrode rechargeable zinc-air battery (RZAB) has two major problems: 1) opposing requirements for the oxygen reduction (ORR) and oxygen evolution (OER) reactions from the catalyst at the air cathode; and 2) zinc-dendrite formation, hydrogen generation, and zinc corrosion at the zinc anode. To tackle these problems, a three-electrode RZAB (T-RZAB) including a hydrophobic discharge cathode, a hydrophilic charge cathode, and a zinc-free anode is developed. The decoupled cathodes enable fast ORR and OER kinetics, and avoid oxidization of the ORR catalyst. The zinc-free anode using tin-coated copper foam that induces the growth of (002)Zn planes, suppresses hydrogen evolution, and prevents Zn corrosion. As a result, the T-RZABs have a high discharge capacity per cycle of 800 mAh cm-2 , a low voltage gap between the discharge/charge platforms of 0.66 V, and an ultralong cycle life of 5220 h at a current density of 10 mA cm-2 . A large T-RZAB with a discharge capacity of 10 Ah per cycle with no obvious degradation after cycling for 1000 h is developed. Finally, a T-RZAB pack that has an energy density of 151.8 Wh kg-1 and a low cost of 46.7 US dollars kWh-1  is assembled.

Direct and green repairing of degraded LiCoO2 for reuse in lithium-ion batteries.

Traditional recycling processes of LiCoO2 rely on destructive decomposition, requiring high-temperature roasting or acid leaching to extract valuable Li and Co, which have significant environmental and economic concerns. Herein, a direct repairing method for degraded LiCoO2 using a LiCl-CH4N2O deep eutectic solvent (DES) was established. The DES is not used to dissolve LiCoO2 but directly serves as a carrier for the selective replenishment of lithium and cobalt. Replenishment of lithium restores LiCoO2 at different states of charge to a capacity of 130 mAh/g (at 0.1 C rate), while replenishing the cobalt increases the capacity retention rate of 90% after 100 cycles, which is comparable to pristine LiCoO2. The DES is collected and reused multiple times with a high repair efficiency. This process reduces energy consumption by 37.1% and greenhouse gas emissions by 34.8% compared with the current production process of LiCoO2, demonstrating excellent environmental and economic viability.

Toward an Understanding of the Reversible Li-CO2 Batteries over Metal-N4-Functionalized Graphene Electrocatalysts.

The lack of low-cost catalysts with high activity leads to the unsatisfactory electrochemical performance of Li-CO2 batteries. Single-atom catalysts (SACs) with metal-Nx moieties have great potential to improve battery reaction kinetics and cycling ability. However, how to rationally select and develop highly efficient electrocatalysts remains unclear. Herein, we used density functional theory (DFT) calculations to screen SACs on N-doped graphene (SAMe@NG, Me = Cr, Mn, Fe, Co, Ni, Cu) for CO2 reduction and evolution reaction. Among them, SACr@NG shows the promising potential as an effective electrocatalyst for the reversible Li-CO2 batteries. To verify the validity of the DFT calculations, a two-step method has been developed to fabricate SAMe@NG on a porous carbon foam (SAMe@NG/PCF) with similar loading of ∼8 wt %. Consistent with the theoretical calculations, batteries with the SACr@NG/PCF cathodes exhibit a superior rate performance and cycling ability, with a long cycle life and a narrow voltage gap of 1.39 V over 350 cycles at a rate of 100 µA cm-2. This work not only demonstrates a principle for catalysts selection for the reversible Li-CO2 batteries but also a controllable synthesis method for single atom catalysts.

Engineering the Active Sites of Graphene Catalyst: From CO2 Activation to Activate Li-CO2 Batteries.

As one of the CO2 capture and utilization technologies, Li-CO2 batteries have attracted special interest in the application of carbon neutral. However, the design and fabrication of a low-cost high-efficiency cathode catalyst for reversible Li2CO3 formation and decomposition remains challenging. Here, guided by theoretical calculations, CO2 was utilized to activate the catalytic activity of conventional nitrogen-doped graphene, in which pyridinic-N and pyrrolic-N have a high total content (72.65%) and have a high catalytic activity in both CO2 reduction and evolution reactions, thus activating the reversible conversion of Li2CO3 formation and decomposition. As a result, the designed cathode has a low voltage gap of 2.13 V at 1200 mA g-1 and long-life cycling stability with a small increase in the voltage gap of 0.12 V after 170 cycles at 500 mA g-1. Our work suggests a way to design metal-free catalysts with high activity that can be used to activate the performance of Li-CO2 batteries.

Engineering d-p Orbital Hybridization in Single-Atom Metal-Embedded Three-Dimensional Electrodes for Li-S Batteries.

Single-atom metal catalysts (SACs) are used as sulfur cathode additives to promote battery performance, although the material selection and mechanism that govern the catalytic activity remain unclear. It is shown that d-p orbital hybridization between the single-atom metal and the sulfur species can be used as a descriptor for understanding the catalytic activity of SACs in Li-S batteries. Transition metals with a lower atomic number are found, like Ti, to have fewer filled anti-bonding states, which effectively bind lithium polysulfides (LiPSs) and catalyze their electrochemical reaction. A series of single-atom metal catalysts (Me = Mn, Cu, Cr, Ti) embedded in three-dimensional (3D) electrodes are prepared by a controllable nitrogen coordination approach. Among them, the single-atom Ti-embedded electrode has the lowest electrochemical barrier to LiPSs reduction/Li2 S oxidation and the highest catalytic activity, matching well with the theoretical calculations. By virtue of the highly active catalytic center of single-atom Ti on the conductive transport network, high sulfur utilization is achieved with a low catalyst loading (1 wt.%) and a high area-sulfur loading (8 mg cm-2 ). With good mechanical stability for bending, these 3D electrodes are suitable for fabricating bendable/foldable Li-S batteries for wearable electronics.

Intercalation-Induced Conversion Reactions Give High-Capacity Potassium Storage.

Potassium ion batteries (PIBs) have shown great potential as a next-generation electrochemical energy storage system, due to the natural abundance of potassium and the relatively low redox potential of K ions. To accommodate the large ionic radius of K ions, conversion-type electrode materials are regarded as suitable candidates for K ion storage. However, the triggering mechanism of a conversion reaction in most anode materials of PIBs is unclear, which limits their further development. To reveal the mechanism, in this work, MoSe2, MoS2, and MoO2 were selected as model materials, guided by theoretical calculations, to investigate the K ion storage process. Through ex situ characterization, it was found that intercalation reactions preferentially occur in MoSe2 and MoS2, while an adsorption reaction preferentially occurs in MoO2. This is because of the larger interlayer spacing and lower K ion intercalation barrier in MoSe2 and MoS2 than in MoO2. The preferential intercalation reactions are able to induce a further conversion reaction by reducing the reaction barrier, thereby realizing high K ion storage capacities. As a result, the MoSe2-rGO and MoS2-rGO hybrids showed higher reversible capacities than the MoO2-rGO hybrid. By demonstrating a relationship between intercalation and the conversion reaction and understanding the mechanism, guidance is provided for selecting the electrode materials to obtain PIBs with high performance.

ZnSe Microsphere/Multiwalled Carbon Nanotube Composites as High-Rate and Long-Life Anodes for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are considered as one of the most favorable alternative devices for sustainable development of modern society. However, it is still a big challenge to search for proper anode materials which have excellent cycling and rate performance. Here, zinc selenide microsphere and multiwalled carbon nanotube (ZnSe/MWCNT) composites are prepared via hydrothermal reaction and following grinding process. The performance of ZnSe/MWCNT composites as a SIB anode is studied for the first time. As a result, ZnSe/MWCNTs exhibit excellent rate capacity and superior cycling life. The capacity retains as high as 382 mA h g-1 after 180 cycles even at a current density of 0.5 A g-1. The initial Coulombic efficiency of ZnSe/MWCNTs can reach 88% and nearby 100% in the following cycles. The superior electrochemical properties are attributed to continuous electron transport pathway, improved electrical conductivity, and excellent stress relaxation.

VO2 Nanoflakes as the Cathode Material of Hybrid Magnesium-Lithium-Ion Batteries with High Energy Density.

The hybrid magnesium-lithium-ion batteries (MLIBs) combining the dendrite-free deposition of the Mg anode and the fast Li intercalation cathode are better alternatives to Li-ion batteries (LIBs) in large-scale power storage systems. In this article, we reported hybrid MLIBs assembled with the VO2 cathode, dendrite-free Mg anode, and the Mg-Li dual-salt electrolyte. Satisfactorily, the VO2 cathode delivered a stable plateau at about 1.75 V, and a high specific discharge capacity of 244.4 mA h g-1. To the best of our knowledge, the VO2 cathode displays the highest energy density of 427 Wh kg-1 among reported MLIBs in coin-type batteries. In addition, an excellent rate performance and a wide operating temperature window from 0 to 55 °C have been obtained. The combination of VO2 cathode, dual-salt electrolyte, and Mg anode would pave the way for the development of high energy density, safe, and low-cost batteries.

Top-Down Strategy to Synthesize Mesoporous Dual Carbon Armored MnO Nanoparticles for Lithium-Ion Battery Anodes.

To overcome inferior rate capability and cycle stability of MnO-based materials as a lithium-ion battery anode associated with the pulverization and gradual aggregation during the conversion process, we constructed robust mesoporous N-doped carbon (N-C) protected MnO nanoparticles on reduced graphene oxide (rGO) (MnO@N-C/rGO) by a simple top-down incorporation strategy. Such dual carbon protection endows MnO@N-C/rGO with excellent structural stability and enhanced charge transfer kinetics. At 100 mA g-1, it exhibits superior rate capability as high as 864.7 mAh g-1, undergoing the deep charge/discharge for 70 cycles and outstanding cyclic stability (after 1300 cyclic tests at 2000 mA g-1; 425.0 mAh g-1 remains, accompanying merely 0.004% capacity decay per cycle). This facile method provides a novel strategy for synthesis of porous electrodes by making use of highly insulating materials.

Mesoporous Li3VO4/C Submicron-Ellipsoids Supported on Reduced Graphene Oxide as Practical Anode for High-Power Lithium-Ion Batteries.

Despite the enormous efforts devoted to high-performance lithium-ion batteries (LIBs), the present state-of-the-art LIBs cannot meet the ever-increasing demands. With high theoretical capacity, fast ionic conductivity, and suitable charge/discharge plateaus, Li3VO4 shows great potential as the anode material for LIBs. However, it suffers from poor electronic conductivity. In this work, we present a novel composite material with mesoporous Li3VO4/C submicron-ellipsoids supported on rGO (LVO/C/rGO). The synthesized LVO/C/rGO exhibits a high reversible capacity (410 mAh g-1 at 0.25 C), excellent rate capability (230 mAh g-1 at 125 C), and outstanding long-cycle performance (82.5% capacity retention for 5000 cycles at 10 C). The impressive electrochemical performance reveals the great potential of the mesoporous LVO/C/rGO as a practical anode for high-power LIBs.