Synthesis of Diphenylalanine/Cobalt Oxide Hybrid Nanowires and Their Application to Energy Storage

We report the synthesis of novel diphenylalanine/cobalt(II,III) oxide (Co3O4) composite nanowires by peptide self-assembly. Peptide nanowires were prepared by treating amorphous diphenylalanine film with aniline vapor at an elevated temperature. They were hybridized with Co3O4 nanocrystals through the reduction of cobalt ions in an aqueous solution using sodium borohydride (NaBH4) without any complex processes such as heat treatment. The formation of peptide/Co3O4 composite nanowires was characterized using multiple tools, such as electron microscopies and elemental analysis, and their potential application as a negative electrode for Li-ion batteries was explored by constructing Swagelok-type cells with hybrid nanowires as a working electrode and examining their charge/discharge behavior. The present study provides a useful approach for the synthesis of functional metal oxide nanomaterials by demonstrating the feasibility of peptide/Co3O4 hybrid nanowires as an energy storage material

First-Principles Investigations on Sodium Superionic Conductor Na₁₁Sn₂PS₁₂

Sodium superionic conductors are key components of solid-state sodium ion batteries, which are regarded as promising alternative energy storage options for large-scale application. Recently, a new crystalline sodium superionic conductor Na11Sn2PS12 was reported with a remarkably high ionic conductivity over 1 mS/cm at room temperature. Herein, we report the comprehensive first-principles investigations on this new sodium superionic conductor. Our ab initio molecular dynamics simulations confirm the intrinsically fast and isotropic diffusion of sodium ions in Na11Sn2PS12 involving all the sodium sites. From a series of first-principles calculations, we propose a sodium diffusion mechanism and discuss the effects of various defects or substitutions on the diffusion kinetics, which may aid in further development of this class of materials. Moreover, we argue that the inherent vacant sites (Wyckoff position 8b), whose presence has been claimed to be critical for the fast sodium diffusion in this material, are less likely to contribute to the sodium diffusion. Finally, the thermodynamic stability and chemical compatibility of Na11Sn2PS12 are comparatively explored. Our theoretical study provides a more comprehensive understanding of Na11Sn2PS12-type conductors as well as helpful guidance on their optimal design for application in solid-state batteries

Redesign of Li₂MP₂O₇ (M = Fe or Mn) by Tuning the Li Diffusion in Rechargeable Battery Electrodes

Defects in crystals such as antisites generally lead to the deterioration of the ionic conductivity of solid-state ionic conductors. Herein, using first-principles calculations, we demonstrate that the Li diffusion in Li₂MP₂O₇ (M = Fe or Mn), a promising battery material, is sensitively affected by the presence of Li/M antisites; however, unexpectedly, the antisites significantly promote Li diffusion. The calculations reveal that the presence of antisites reduces the barrier of Li hopping and opens new paths for Li diffusion in the Li₂MP₂O₇ crystal. In our experimental verification, we succeeded in synthesizing crystalline Li₂MnP₂O₇ with varying Li/Mn antisite contents and demonstrated that the inclusion of antisites results in improved power capability with faster Li diffusion for Li-ion battery electrodes. We believe that this unexpected finding of increasing the ionic conductivity by introducing antisite defects broadens our understanding of solid-state ionic conductors and provides a new strategy for improving Li diffusion in conventional electrode materials for Li rechargeable batteries

Multicomponent Olivine Cathode for Lithium Rechargeable Batteries: A First-Principles Study

The in-depth study of the multicomponent effect on the structural and electrochemical properties of olivine cathodes is conducted using state-of-the-art first-principles calculations. The distribution of multiple transition metals in olivine structure alters local crystal structure and electronic structure, affecting its kinetic and thermodynamic properties. We find that local structure change, such as the reduced Jahn−Teller effect of Mn, significantly enhances both Li mobility and electron (polaron) conductivity when the redox Mn element neighbors Fe or Co. The unexpected one-phase Li insertion/extraction reaction of the multicomponent olivine cathode is explained with respect to the multiple interactions of M/Li or M/vacancy (M = transition metals). The redox potential of each transition metal also could shift as a result of charge redistribution and the relative energy change from the multiple M/Li interactions. Implications of multicomponent olivine as a useful strategy for tailoring the electrochemical properties of olivine compounds are discussed for designing better-performing Li rechargeable batteries

Pyrrolinium-Substituted Persistent Zwitterionic Ferrocenate Derivative Enabling the Application of Ferrocene Anolyte

Here, we report the imidazolium-/pyrrolinium-substituted persistent zwitterionic ferrocenate derivatives, which were characterized by electron paramagnetic resonance (EPR) and 57Fe Mössbauer spectroscopy. Additional theoretical studies on these zwitterionic ferrocenate derivatives clearly explain the origin of their thermal stability and the orbital interactions between iron and imidazolium-/pyrrolinium-substituted zwitterionic cyclopentadienyl ligand. Exploiting the facile Fe­(II/I) redox chemistry, we successfully demonstrated that the pyrrolinium-substituted ferrocene derivative can be applied as an example of derivatized ferrocene anolyte for redox-flow batteries. These zwitterionic ferrocenate derivatives will not only deepen our understanding of the intrinsic chemistry of ferrocenate but have the potential to open the way for the rational design of metallocenate derivatives for various applications

Reconfiguring Sodium Intercalation Process of TiS₂ Electrode for Sodium-Ion Batteries by a Partial Solvent Cointercalation

Titanium disulfide (TiS2), a first-generation cathode in lithium batteries, has also attracted a broad interest as a sodium-ion battery electrode due to fast sodium intercalation kinetics and large theoretical capacity. However, the reversibility of sodium de/intercalation is far inferior to that of lithium because of the unfavorable intermediate phase formation. Herein, we demonstrate that reconfiguring sodium intercalation via partial solvent cointercalation alters the phase-transition paths for the entire reactions of NaxTiS2 (0 x < 1), detouring the formation of the unfavorable intermediates. Additionally, it unexpectedly results in a remarkable enhancement of sodium intercalation reversibility, boosting the cycle stability (1000 cycles) accompanying high power capability (10C rate). Comparative investigations reveal that the sodium intercalation in ether-based electrolyte involves a preintercalation of solvent molecules, which is subsequently dissimilar to the bare sodium intercalation in conventional electrolytes. Rediscovery of the intercalation behavior of TiS2 offers a new insight in revisiting the reversibility and kinetics of the commonly known electrodes for batteries

Core–Shell Structure of Mo-Based Nanoparticle/Carbon Nanotube/Amorphous Carbon Composites as High-Performance Anodes for Lithium-Ion Batteries

For large-scale energy storage devices, lithium-ion batteries (LIBs) are leading candidates for applications in electric vehicles. However, further research efforts are needed to maximize their capacity and stability. In this report, a core–shell structure of molybdenum-based nanoparticle/carbon nanotube (CNT)/carbon is synthesized successfully through facile hydrothermal/annealing processes and applies for anode materials in LIBs. The good conductivity of the CNT core and the uniform nanoparticle of molybdenum-based compounds in the buffer matrix of the amorphous carbon shell result in a high capacity of 810 mA h g–1 for anode LIBs, an excellent stability for 500 cycles, and a Coulombic efficiency of ∼98%. Our study reveals that ultrafine nanoparticles of molybdenum-based compounds can enhance the pseudocapacitance. The conductivity of the CNT is the main contributor to the improved stability for lithium-ion storage at a high current density. This approach can be used for further improvement of structural design and material synthesis for anode LIBs

Na₃V(PO₄)₂: A New Layered-Type Cathode Material with High Water Stability and Power Capability for Na-Ion Batteries

We introduce Na₃V­(PO₄)₂ as a new cathode material for Na-ion batteries for the first time. The structure of Na₃V­(PO₄)₂ was determined using X-ray diffraction and Rietveld refinement, and its high water stability was clearly demonstrated. The redox potential of Na₃V­(PO₄)₂ (∼3.5 V vs Na/Na⁺) was shown to be sufficiently high to prevent the side reaction with water (Na extraction and water insertion), ensuring its water stability in ambient air. Na₃V­(PO₄)₂ also exhibited outstanding power capability, with ∼79% of the theoretical capacity being delivered at 15C. First-principles calculation combined with electrochemical experiments linked this high power capability to the low activation barrier (∼433 meV) for the well-interconnected two-dimensional Na diffusion pathway. Moreover, outstanding cyclability of Na₃V­(PO₄)₂ (∼70% retention of the initial capacity after 200 cycles) was achieved at a reasonably fast current rate of 1C

Theoretical Evidence for Low Charging Overpotentials of Superoxide Discharge Products in Metal–Oxygen Batteries

Li–oxygen and Na–oxygen batteries are some of the most promising next-generation battery systems because of their high energy densities. Despite the chemical similarity of Li and Na, the two systems exhibit distinct characteristics, especially the typically higher charging overpotential observed in Li–oxygen batteries. In previous theoretical and experimental studies, this higher charging overpotential was attributed to factors such as the sluggish oxygen evolution or poor transport property of the discharge product of the Li–oxygen cell; however, a general understanding of the interplay between the discharge products and overpotential remains elusive. Here, we investigated the charging mechanisms with respect to the oxygen evolution reaction (OER) kinetics, charge-carrier conductivity, and dissolution property of various discharge products reported in Li–oxygen and Na–oxygen cells. The OER kinetics were generally faster for superoxides (i.e., LiO₂ and NaO₂) than for peroxides (i.e., Li₂O₂ and Na₂O₂). The electronic and ionic conductivities were also predicted to be significantly higher in superoxide phases than in peroxide phases. Moreover, systematic calculations of the dissolution energy of the discharge products in the electrolyte, which mediate a solution-based OER reaction, revealed that the superoxide phases, particularly NaO₂, exhibited markedly low dissolution energy compared with the peroxide phases. These results imply that the formation of superoxides instead of peroxides during discharge may be the key to improving the energy efficiency of metal–oxygen batteries in general