RESUMEN
Zinc-ion batteries (ZIBs) are promising candidates for safe energy storage applications. However, undesirable parasitic reactions such as dendrite growth, gas evaluation, anode corrosion, and structural damage to the cathode under an acidic microenvironment severely affected cell performance. To resolve these issues, an MXene entrapped in an ionic liquid semi-solid gel polymer electrolyte (GPE) composite was explored. The molecular-level mixing of poly(vinylidene fluoride-co-hexafluoropropylene) (PVHF), zinc trifluoromethanesulfonate (Zn(OTF)2), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) ionic liquid, and Ti3C2Tx MXene provided a controlled Zn2+ shuttle toward the anode/cathode. Ti3C2Tx/EMIBF4/Zn(OTF)2/PVHF exhibited a breaking strength of 0.36 MPa with an associated extension of 23%. The Zn//Ti3C2Tx/EMIBF4/Zn(OTF)2/PVHF//Zn symmetric cell with continuous zinc plating/stripping exhibited excellent Zn2+ ion mobility toward the anode and cathode without undesired reactions. This was confirmed by post-mortem analysis after a symmetric cell compatibility test. The as-prepared GPE with a Na3V2(PO4)3 (NVP) cathode exhibited a high chemical diffusion coefficient of 1.14 × 10-7. It also showed an outstanding reversible capacity of 89 mAh g-1 at C/10 with an average discharge plateau voltage of 1.45 V, cycle durability, and controlled self-discharge. These results suggested that the Zn2+ ions in the Ti3C2Tx/EMIBF4/Zn(OTF)2/PVHF composite are reversibly labile in the anode and cathode directions.
RESUMEN
In the loop of numerous challenges and ambiguities, Li-O2 batteries are crawling to reach their commercialization phase. To achieve the progressive milestones, along with the developments in the architecture of cathodes, anodes, and electrolytes, understanding its failure mode is equally important. Under an unrestricted charge-discharge protocol, cyclability of nonaqueous Li-O2 batteries are limited to only a few cycles. This report examines an additive-free ether-based Li-O2 battery in the perspective of identifying the origin of possible side reactions and their affiliations to integral components of the battery. Structural and compositional changes during every charge-discharge sequence are studied using bottom-up sequential tear-down analysis. The substantial increase in impedance and corresponding decrease in capacities after every cycle are interrelated to the amount of electrode passivation resulting from the discharge products and electrolyte decomposition. From the tear-down analysis, it is approximated that, among the total capacity loss, ≈55% is attributed to the cathode, ≈28% of the loss corresponds to the anode, and ≈17% is attributed to the electrolyte, given that battery failure instigates from the "reactive oxygen species". Electrochemically formed Li2O2 via the superoxide pathway induces large decomposition overpotentials up to 4.6 V versus Li/Li+ because of its overrated reactivity with electrolytes and carbon supports. On the contrary, efficient decomposition of chemically formed Li2O2 below 3.9 V proves that the extra charge potential observed for electrochemically formed Li2O2 is in fact consumed for the decomposition of irreversibly formed side products via the superoxide pathway. Spontaneous reactivity of Li2O2 and trivial reactivity of Li2O highlight the need of advanced strategies to maneuver oxygen red-ox in selective pathways that unalter the electrolyte and electrodes, and the necessity of their synchronized performance for the evolution of practical Li-O2 batteries.
RESUMEN
Rechargeable zinc-air batteries are considered to be more sustainable and efficient candidates for safe, low-cost energy storage because of their higher energy density and the abundance of zinc resources. Recently Zn-air batteries have aroused significant research attention, however, because an unresolved impediment due to the notorious instability of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) kinetics of the cathode catalyst limit their practical application. Herein, we report the synthesis of non-precious MnCo2O4 nanospheres synergized with a graphene sheet as a bi-functional cathode catalyst for rechargeable Zn-air battery application using a one-pot probe sonochemical method. Structural characterization confirms that the MnCo2O4 nanospheres successfully anchored on graphene sheet. X-ray photoelectron spectroscopy revealed that the Mn and Co in the MnCo2O4 are in mixed valence states on the graphene sheet surface and the MnCo2O4-graphene sheet (MCO-GS) hybrid catalyst exhibits excellent OER and ORR activity compared with their individual counterparts. A rechargeable Zn-air battery using an MCO-GS catalyst reveals unique small charge-discharge overpotential, cycling stability and higher rate capability than a bare MnCo2O4 (MCO) catalyst. This superiority in electrocatalytic activity combined with simplicity of material synthesis, turn the MCO-GS hybrid into a promising catalyst for a rechargeable Zn-air battery.
RESUMEN
With an anticipation of their use in electric vehicles, Li-O2 batteries are found to be attractive despite their complex chemistry and drawbacks. To be successful, cathode materials that are robust enough to overcome the sluggish kinetics of the charge-discharge reactions are essential. This work reports sonochemically synthesized porous MnCo2 O4 /graphene (MCO/G) as a hybrid cathode material in nonaqueous Li-O2 batteries. The MCO/G hybrid is synthesized in less than four hours and offers a strong synergistic coupling between the MnCo2 O4 nanospheres and graphene sheets. It catalyzes the oxygen reduction through a three-electron-transfer process and initiates the oxygen evolution at 1.55â V vs. RHE in basic medium. A small charge-discharge voltage hysteresis of 0.8â V and a cycle life of 250â cycles at a limited capacity of 1000â mAh g-1 in a tetraglyme-based nonaqueous Li-O2 battery is demonstrated. The porous channels created on the sonochemically synthesized cathode facilitates easy oxygen adsorption onto the active sites to accommodate more discharge products following its decomposition. It exhibits a better rate capability in comparison to the widely used Vulcan carbon and benchmark Pt/C catalysts. The excellent cyclability, rate capability, and low overpotential demonstrates MnCo2 O4 /graphene composite as a promising cathode candidate for Li-O2 batteries. The porous nanosphere architecture with internal oxygen diffusion pathways and peripheral conductive graphene extensions fulfils the requirements that a robust cathode is expected to have to overcome the harsh Li-O2 battery conditions and to serve as a high-rate-capable cathode for Li-O2 batteries.
RESUMEN
Oxygen removal from high capacity Li-rich layered oxide Li1.17Ni0.17Mn0.5Co0.17O2 affects the charge transfer process during cycling. During de-lithiation, oxygen removal takes place with the reduction in oxygen binding energy. Co substitution affects oxygen removal by shifting the O-p orbital closer to the Fermi energy. A convex hull plot is used to analyse single-phase and two-phase reactions during de-lithiation in Li1.17Ni0.17Mn0.5Co0.17O2 and Li2MnO3. Experimentally, the single-phase and two-phase reactions are identified based on the characteristics of the charge curve. In the charge transfer process more than 80% of lithium charge is transferred to oxygen in both the compounds. Effective charge and cyclic voltammetry reveal the redox centers in the compounds which help to understand the role of oxygen and transition metals in de-lithiation. A detailed explanation of oxygen removal and the charge transfer mechanism of Li1.17Ni0.17Mn0.5Co0.17O2 and Li2MnO3 is provided in the current experimental and density functional theory based study.
RESUMEN
A theoretical and experimental diffusivity study of Li2MnO3 and Li1.17Ni0.17Mn0.67O2 has been carried out to investigate the effect of Mn, Ni and surrounding atoms on Li+ diffusion and to understand how the Li+ diffusion trajectory changes with different charge spheres. It is observed that due to the presence of Ni in Li1.17Ni0.17Mn0.67O2, the activation energy reduces in all the possible diffusion paths, which helps in faster Li+ diffusion. This study brings a new physical insight into Li+ diffusion based on elliptical and straight diffusion trajectories. In Li1.17Ni0.17Mn0.67O2, the Li+ diffusion mechanism in different paths based on 2b, 2c and 4h Wyckoff sites of Li has been discussed. Experimentally, the galvanostatic intermittent titration technique is adopted to identify the diffusion coefficient of Li+. The diffusion coefficient of both the compounds varies in different voltage ranges. For L2MnO3, diffusion varies from 10-11 to 10-13 cm2 s-1, whereas for Li1.17Ni0.17Mn0.67O2, diffusion varies from 10-9 to 10-11 cm2 s-1 in the voltage range of 3.7-4.7 V.
RESUMEN
In the quest to tackle the issue of surface degradation and voltage decay associated with Li-rich phases, Li-ion conductive Li2ZrO3 (LZO) is coated on Li1.2Ni0.13Mn0.54Co0.13O2 (LNMC) by a simple wet chemical process. The LZO phase coated on LNMC, with a thickness of about 10 nm, provides a structural integrity and facilitates the ion pathways throughout the charge-discharge process, which results in significant improvement of the electrochemical performances. The surface-modified cathode material exhibits a reversible capacity of 225 mA h g-1 (at C/5 rate) and retains 85% of the initial capacity after 100 cycles. Whereas, the uncoated pristine sample shows a capacity of 234 mA h g-1 and retains only 57% of the initial capacity under identical conditions. Electrochemical impedance spectroscopy reveals that the LZO coating plays a vital role in stabilizing the interface between the electrode and electrolyte during cycling; thus, it alleviates material degradation and voltage fading and ameliorates the electrochemical performance.
