Organic Electrolyte Additive: Dual Functions Toward Fast Sulfur Conversion and Stable Li Deposition for Advanced Li-S Batteries.

Lithium-sulfur (Li-S) battery is of great potential for the next generation energy storage device due to the high specific capacity energy density. However, the sluggish kinetics of S redox and the dendrite Li growth are the main challenges to hinder its commercial application. Herein, an organic electrolyte additive, i.e., benzyl chloride (BzCl), is applied as the remedy to address the two issues. In detail, BzCl can split into Bz· radical to react with the polysulfides, forming a Bz-S-Bz intermediate, which changes the conversion path of S and improves the kinetics by accelerating the S splitting. Meanwhile, a tight and robust solid electrolyte interphase (SEI) rich in inorganic ingredients namely LiCl, LiF, and Li2O, is formed on the surface of Li metal, accelerating the ion conductivity and blocking the decomposition of the solvent and lithium polysulfides. Therefore, the Li-S battery with BzCl as the additive remains high capacity of 693.2 mAh g-1 after 220 cycles at 0.5 C with a low decay rate of 0.11%. This work provides a novel strategy to boost the electrochemical performances in both cathode and anode and gives a guide on the electrolyte design toward high-performance Li-S batteries.

Microstructure-Dependent K+ Storage in Porous Hard Carbon.

Hard carbons (HCs) are emerging as promising anodes for potassium-ion batteries (PIBs) due to overwhelming advantages including cost effectiveness and outstanding physicochemical properties. However, the fundamental K+ storage mechanism in HCs and the key structural parameters that determining K+ storage behaviors remain unclear and require further exploration. Herein, HC materials with controllable micro/mesopore structures are first synthesized by template-assisted spray pyrolysis technology. Detailed experimental analyses including in situ Raman and in situ electrochemical impedance spectroscopy analysis reveal two different K+ storage ways in the porous hard carbon (p-HC), e.g., the adsorption mechanism at high potential region and the intercalation mechanism at low potential region. Both are strongly dependent on the evolution of microstructure and significantly affect the electrochemical performance. Specifically, the adequate micropores act as the active sites for efficient K+ storage and ion-buffering reservoir to relieve the volume expansion, ensuring enhanced specific capacity and good structural stability. The abundant mesopores in the porous structure provide conductive pathways for ion diffusion and/or electrolyte infiltration, endowing fast ionic/electronic transport kinetics. All these together contribute to the high energy density of activated carbon//p-HCs potassium ion hybrid capacitors (74.5 Wh kg-1 , at 184.4 W kg-1 ).

Improving Polysulfides Adsorption and Redox Kinetics by the Co4 N Nanoparticle/N-Doped Carbon Composites for Lithium-Sulfur Batteries.

Improved conductivity and suppressed dissolution of lithium polysulfides is highly desirable for high-performance lithium-sulfur (Li-S) batteries. Herein, by a facile solvent method followed by nitridation with NH3 , a 2D nitrogen-doped carbon structure is designed with homogeneously embedded Co4 N nanoparticles derived from metal organic framework (MOF), grown on the carbon cloth (MOF-Co4 N). Experimental results and theoretical simulations reveal that Co4 N nanoparticles act as strong chemical adsorption hosts and catalysts that not only improve the cycling performance of Li-S batteries via chemical bonding to trap polysulfides but also improve the rate performance through accelerating the conversion reactions by decreasing the polarization of the electrode. In addition, the high conductive nitrogen-doped carbon matrix ensures fast charge transfer, while the 2D structure offers increased pathways to facilitate ion diffusion. Under the current density of 0.1C, 0.5C, and 3C, MOF-Co4 N delivers reversible specific capacities of 1425, 1049, and 729 mAh g-1 , respectively, and retains 82.5% capacity after 400 cycles at 1C, as compared to the sample without Co4 N (MOF-C) values of 61.3% (200 cycles). The improved cell performance corroborates the validity of the multifunctional design of MOF-Co4 N, which is expected to be a potentially promising cathode host for Li-S batteries.

LifePo4 Coated Homogeneously with 3D Carbon Nanotube Conductive Networks for Enhanced Electrochemical Performance.

LiFePO4 (LFP) microparticles coated homogeneously with three-dimensional (3D) carbon nanotube (CNT) conductive networks were successfully prepared via a simple and effective ball milling method by controlling Polyvinylidene fluoride (PVDF) content in cathode electrode slurry. Scanning electron microscopy (SEM) demonstrated that the electrical bridge between the LFP could be well modulated by varying the amount of the CNTs and PVDF. The LFP/CNTs composite with 3 wt% CNTs and 5 wt% PVDF, in which CNTs are embedded in the microspheres homogeneously, possesses the best 3D CNT conductive networks and exhibits the best electrochemical property with high capacity retention of 95.72% at 0.25 C after 50 cycles. Essentially, in comparison with those samples without CNT networks, this CNT network structure can greatly enhance the electrical conductivity, thus markedly improving the electrochemical performance. (LFP) microparticles coated homogeneously with three-dimensional (3D) carbon nanotube (CNT) conductive networks were successfully prepared via a simple and effective ball milling method by controlling Polyvinylidene fluoride (PVDF) content in cathode electrode slurry. Scanning electron microscopy (SEM) demonstrated that the electrical bridge between the LFP could be well modulated by varying the amount of the CNTs and PVDF. The LFP/CNTs composite with 3 wt% CNTs and 5 wt% PVDF, in which CNTs are embedded in the microspheres homogeneously, possesses the best 3D CNT conductive networks and exhibits the best electrochemical property with high capacity retention of 95.72% at 0.25 C after 50 cycles. Essentially, in comparison with those samples without CNT networks, this CNT network structure can greatly enhance the electrical conductivity, thus markedly improving the electrochemical performance.

Desolvation Synergy of Multiple H/Li-Bonds on an Iron-Dextran-Based Catalyst Stimulates Lithium-Sulfur Cascade Catalysis.

Traditional lithium-sulfur battery catalysts are still facing substantial challenges in solving sulfur redox reactions, which involve multistep electron transfer and multiphase transformations. Here, inspired by the combination of iron dextran (INFeD) and ascorbic acid (VC) as a blood tonic for the treatment of anemia, a highly efficient VC@INFeD catalyst is developed in the sulfur cathode, accomplishing the desolvation and enrichment of high-concentration solvated lithium polysulfides at the cathode/electrolyte interface with the assistance of multiple H/Li-bonds and resolving subsequent sulfur transformations through gradient catalysis sites where the INFeD promotes long-chain lithium polysulfide conversions and VC accelerates short-chain lithium polysulfide conversions. Comprehensive characterizations reveal that the VC@INFeD can substantially reduce the energy barrier of each sulfur redox step, inhibit shuttle effects, and endow the lithium-sulfur battery with high sulfur utilization and superior cycling stability even under a high sulfur loading (5.2 mg cm-2 ) and lean electrolyte (electrolyte/sulfur ratio, ≈7 µL mg-1 ) condition.

Fe/Fe3C Embedded in N-Doped Worm-like Porous Carbon for High-Rate Catalysis in Rechargeable Zinc-Air Batteries.

Designing low-cost preparation of high-activity electrocatalysts with excellent stability is the route one must take to fully realize large-scale application implementation of zinc-air batteries. 3D nitrogen-doped nanocarbons with transition metals or their derivatives encapsulated in show promising potential in the field of non-precious metal oxygen electrocatalysis. Herein, we report a simple, economical, and large-scale production method to construct worm-like porous nitrogen-doped carbon with in situ-grown carbon nanotubes and uniformly embedded Fe/Fe3C nanoparticles. It not only has high conductivity owing to the nitrogen-doped nature but also has ample active sites and electrolyte diffusion channels benefitting from the uniformly distributed heterostructural Fe/Fe3C nanoparticles and discrete hierarchically porous structures. When used as catalyst materials for a zinc-air battery, an energy density of 719.1 Wh kg-1 and a peak power density of 101.3 mW cm-2 at a 50 mA cm-2 discharge current density is achieved. Additionally, throughout charging and discharging for 200 cycles at a current density of 20 mA cm-2, the charge/discharge voltage gap is nearly constant.

Compact-Nanobox Engineering of Transition Metal Oxides with Enhanced Initial Coulombic Efficiency for Lithium-Ion Battery Anodes.

A novel strategy is proposed to construct a compact-nanobox (CNB) structure composed of irregular nanograins (average diameter ≈ 10 nm), aiming to confine the electrode-electrolyte contact area and enhance initial Coulombic efficiency (ICE) of transition metal oxide (TMO) anodes. To demonstrate the validity of this attempt, CoO-CNB is taken as an example which is synthesized via a carbothermic reduction method. Benefiting from the compact configuration, electrolyte can only contact the outer surface of the nanobox, keeping the inner CoO nanograins untouched. Therefore, the solid electrolyte interphase (SEI) formation is reduced. Furthermore, the internal cavity leaves enough room for volume variation upon lithiation and delithiation, resulting in superior mechanical stability of the CNB structure and less generation of fresh SEI. Consequently, the SEI remains stable and spatially confined without degradation, and hence, the CoO-CNB electrode delivers an enhanced ICE of 82.2%, which is among the highest values reported for TMO-based anodes in lithium-ion batteries. In addition, the CoO-CNB electrode also demonstrates excellent cyclability with a reversible capacity of 811.6 mA h g-1 (90.4% capacity retention after 100 cycles). These findings open up a new way to design high-ICE electrodes and boost the practical application of TMO anodes.