Single “Swiss-roll” microelectrode elucidates the critical role of iron substitution in conversion-type oxides

Advancing the lithium-ion battery technology requires the understanding of electrochemical processes in electrode materials with high resolution, accuracy, and sensitivity. However, most techniques today are limited by their inability to separate the complex signals from slurry-coated composite electrodes. Here, we use a three-dimensional “Swiss-roll” microtubular electrode that is incorporated into a micrometer-sized lithium battery. This on-chip platform combines various in situ characterization techniques and precisely probes the intrinsic electrochemical properties of each active material due to the removal of unnecessary binders and additives. As an example, it helps elucidate the critical role of Fe substitution in a conversion-type NiO electrode by monitoring the evolution of Fe2O3 and solid electrolyte interphase layer. The markedly enhanced electrode performances are therefore explained. Our approach exposes a hitherto unexplored route to tracking the phase, morphology, and electrochemical evolution of electrodes in real time, allowing us to reveal information that is not accessible with bulk-level characterization techniques

Amorphous manganese dioxide with the enhanced pseudocapacitive performance for aqueous rechargeable zinc-ion battery

Aqueous rechargeable zinc-manganese dioxide batteries have attracted extensive attention due to their high energy density, low cost, and environmental friendliness. However, the crystalline MnO2 polymorphs suffer from substantial phase changes upon cycling, leading to structural collapse and poor long-term cycling performance. Here, a highly reversible amorphous manganese dioxide with structural defects is reported as the cathode for aqueous rechargeable zinc-ion batteries (ARZIBs). Because of the existence of the abundant structural defects and intrinsic isotropic nature, the A-MnO2-δ exhibits significant pseudocapacitive contribution and facilitated reaction kinetics. As expected, the A-MnO2-δ delivers a high specific capacity of 301 mAh g−1 at 100 mA g−1 and long cycle-life with a capacity retention of 78% over 1000 cycles at 1 A g−1, which is better than its crystalline counterparts. In addition, a reversible H+ and Zn2+ two-step insertion storage mechanism of the A-MnO2-δ electrode is demonstrated. This study not only suggests that amorphous manganese dioxide can serve as a stable cathode for ARZIBs but also provides significant guidance to realize other high-capacity and long-lifespan aqueous batteries by using the amorphous materials.National Research Foundation (NRF)This work was financially supported by the National Research Foundation of Singapore (NRF) Investigatorship Award Number NRFI2017-08/NRF2016NRF-NRFI001-22

3D hierarchical defect-rich NiMo3S4 nanosheet arrays grown on carbon textiles for high-performance sodium-ion batteries and hydrogen evolution reaction

A hierarchical hybrid nanostructure composed of NiMo3S4 nanosheet arrays with abundant exposed edges on flexible carbon textiles (denoted as NiMo3S4/CTs) has been designed and synthesized for sodium ion batteries (SIBs) and electrocatalytic hydrogen evolution reaction (HER). The novel NiMo3S4 nanostructure, formed by incorporating Ni2+ into Mo-S lattice, shows plenty of substantial defects and active sites, which are favorable for the improvement of the overall electrochemical performances for both SIBs and HER. When evaluated as the anode of SIBs, the NiMo3S4/CT electrode delivers a high specific capacity of ~ 480 mA h g−1 at a current density of 0.12 A g−1 and a high Coulombic efficiency of 100%. Moreover, the NiMo3S4/CT electrode shows an excellent long-term cycling performance with a high reversible capacity of ~ 302 mA h g−1 after 1000 cycles at 0.48 A g−1, showing a high capacity retention of 73.9%. Furthermore, as a HER catalyst, the NiMo3S4/CT hybrid nanostructure exhibits a low onset over-potential of 0.124 V, a small Tafel slope of 46.2 mV dec−1 as well as an excellent long-term stability, which are among the best values of current noble-metal-free electrocatalysts. These results may open up a new route to introduce more active defect sites to enhance the electrochemical performance of metal sulfides by incorporation of metal elements

Recent progress in heterostructured materials for room‐temperature sodium‐sulfur batteries

Abstract Room‐temperature sodium‐sulfur (RT Na‐S) batteries are a promising next‐generation energy storage device due to their low cost, high energy density (1274 Wh kg−1), and environmental friendliness. However, RT Na‐S batteries face a series of vital challenges from sulfur cathode and sodium anode: (i) sluggish reaction kinetics of S and Na2S/Na2S2; (ii) severe shuttle effect from the dissolved intermediate sodium polysulfides (NaPSs); (iii) huge volume expansion induced by the change from S to Na2S; (iv) continuous growth of sodium metal dendrites, leading to short‐circuiting of the battery; (v) huge volume expansion/contraction of sodium anode upon sodium plating/stripping, causing uncontrollable solid‐state electrolyte interphase growth and “dead sodium” formation. Various strategies have been proposed to address these issues, including physical/chemical adsorption of NaPSs, catalysts to facilitate the rapid conversion of NaPSs, high‐conductive materials to promote ion/electron transfer, good sodiophilic Na anode hetero‐interface homogenized Na ions flux and three‐dimensional porous anode host to buffer the volume expansion of sodium. Heterostructure materials can combine these merits into one material to realize multifunctionality. Herein, the recent development of heterostructure as the host for sulfur cathode and Na anode has been reviewed. First of all, the electrochemical mechanisms of sulfur cathode/sodium anode and principles of heterostructures reinforced Na‐S batteries are described. Then, the application of heterostructures in Na‐S batteries is comprehensively examined. Finally, the current primary avenues of employing heterostructures in Na‐S batteries are summarized. Opinions and prospects are put forward regarding the existing problems in current research, aiming to inspire the design of advanced and improved next‐generation Na‐S batteries

Boosting Zn-Ion Storage Performance of Bronze-Type VO2 via Ni-Mediated Electronic Structure Engineering

Aqueous rechargeable zinc-ion batteries are emerging as attractive alternatives for post-lithium-ion batteries. However, their electrochemical performances are restricted by the narrow working window of materials in aqueous electrolytes. Herein, a Ni-mediated VO2–B nanobelt [(Ni)VO2] has been designed to optimize the intrinsic electronic structure of VO2–B and thus achieve much more enhanced zinc-ion storage. Specifically, the Zn/(Ni)VO2 battery yields a good rate capability (182.0 mA h g–1 at 5 A g–1) with a superior cycling stability (130.6 mA h g–1 at 10 A g–1 after 2000 cycles). Experimental and theoretical methods reveal that the introduction of Ni2+ in the VO2 tunnel structure can effectively provide high surface reactivity and improve the intrinsic electronic configurations, thus resulting in good kinetics. Furthermore, H+ and Zn2+ cointercalation processes are determined via in situ X-ray diffraction and supported by ex situ characterizations. Additionally, quasi-solid-state Zn/(Ni)VO2 soft-packaged batteries are assembled and provide flexibility in battery design for practical applications. The results provide insights into the interrelationships between the intrinsic electronic structure of the cathode and the overall electrochemical performance.National Research Foundation (NRF)Accepted versionR.C. and Y.C. contributed equally to this work. This work was financially supported by the National Research Foundation of Singapore (NRF) Investigatorship award number NRFI2017-08/NRF2016NRF-NRFI001-22. The authors thank Synchro-tron Light Research Institute (Public Organization), Muang, Nakhon Ratchasima, 30000, Thailand, for XANES measure-ments in Beamline 8

Surface modification of Na₂Ti₃O₇ nanofibre arrays using N-doped graphene quantum dots as advanced anodes for sodium-ion batteries with ultra-stable and high-rate capability

Both nanoscale surface modification and structural control play significant roles in enhancing the electrochemical properties of battery electrodes. Herein, we design a novel binder-free anode via N-doped graphene quantum dot (N-GQD) decorated Na₂Ti₃O₇ nanofibre arrays (Na₂Ti₃O₇ NFAs) directly grown on flexible carbon textiles (CTs) for high-performance sodium-ion batteries (SIBs). Three dimensional (3D) hierarchical Na₂Ti₃O₇ NFAs constructed from ultrathin Na₂Ti₃O₇ nanosheets provide a large specific surface area and shorter diffusion paths for both ions and electrons. More importantly, the unique N-GQD soft protection produces greatly increased surface conductivity and imparts stability to the nanofibre array structure, leading to fast Na-ion diffusion kinetics. As a result, the flexible 3D hierarchical Na₂Ti₃O₇@N-GQDs/CT electrode as a binder-free anode for a sodium half-battery delivers a high specific capacity of 158 mA h g⁻¹ after 30 cycles and retains ∼92.5% of this capacity after 1000 cycles at a high rate of 4C (1C = 177 mA g⁻¹). Furthermore, it can be assembled into a flexible full cell with Na₃V₂(PO₄)₃@NC/CTs as the cathode, which exhibits high levels of flexibility, excellent long-term cycling stability, and outstanding energy/power density. Our results open up a new approach for the surface modification strategy to enhance the performance of battery electrodes.This work is supported by the SUTD Digital Manufacturing and Design (DManD) Centre and International Design Centre (IDC)