ABSTRACT
The battery safety and cost remain major challenges for developing next-generation rechargeable batteries. All-solid-state sodium (Na)-ion batteries are a promising option for low-cost as well as safe rechargeable batteries by using abundant resources and solid electrolytes. However, the operation of solid-state batteries is limited due to the low ionic conductivity of solid electrolytes. Therefore, it is essential to develop new compounds that feature a high ionic conductivity and chemical stability at room temperature. Herein, we report a potassium-substituted sodium superionic conductor solid electrolyte, Na3-xKxZr2Si2PO12 (0 ≤ x ≤ 0.2), that exhibits an ionic conductivity of 7.734 × 10-4 S/cm-1 at room temperature, which is more than 2 times higher than that of the undoped sample. The synchrotron powder diffraction patterns with Rietveld refinements revealed that the substitution of large K-ions resulted in an increased unit cell volume, widened the Na diffusion channel, and shortened the Na-Na distance. Our work demonstrates that substituting a larger cation on the Na site effectively widens the ion diffusion channel and consequently increases the bulk ionic conductivity. Our findings will contribute to improving the ionic conductivity of the solid electrolytes and further developing safe next-generation rechargeable batteries.
ABSTRACT
Layered transition metal oxides, in particular P2-type ones, are considered as promising cathode materials for sodium-ion batteries on account of their high specific capacity and rate capability. Nevertheless, conventional layered compounds involve detrimental phase transformation throughout repeated cycles, which results in electrochemical performance degradation. Therefore, finding structurally stable layered compounds, featuring minimal phase transition has been a key theme of the sodium-ion battery research. Here lithium substituted Fe/Mn-based P2/O3 layered oxide-Na0.67 Li0.2 Fe0.2 Mn0.6 O2 -that overcomes the inherited structural instability, is reported. In situ synchrotron-based diffraction measurements and DFT calculations are utilized, in order to identify the association between P2/O3 biphasic structure and electrochemical performances. The lithium honeycomb ordering within the P2/O3 biphasic layered compound effectively constrains the undesirable phase transitions; more specifically, both P2-Z phase transition and Jahn-Teller distortion are suppressed throughout wide potential range of 1.5-4.5 V. The DFT calculation further discovers that the presence of honeycomb ordering is crucial for achieving the structural stability by forming Na-vac-Li and Na-Li-Na pairing at highly charged state. The results highlight that the synergetic effect of P2/O3 biphasic structure and lithium substitution can provide an effective strategy toward achieving electrochemically stable layered cathode material for sodium-ion batteries.
ABSTRACT
Lead-free piezoelectric 0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Zr0.2Ti0.8)O3 (BCTZ) nanoparticles (NPs) composed of earth-abundant elements were adopted for use in a flexible composite-based piezoelectric energy harvester (PEH) that can convert mechanical deformation into electrical energy. The solid-state synthesized BCTZ NPs and silver nanowires (Ag NWs) chosen to reduce the toxicity of the filler materials were blended with a polydimethylsiloxane (PDMS) matrix to produce a piezoelectric nanocomposite (p-NC). The naturally flexible polymer-based p-NC layers were sandwiched between two conductive polyethylene terephthalate plastic substrates to achieve a flexible energy harvester. The BCTZ NP-based PEH effectively generated an output voltage peak of â¼15 V and a current signal of â¼0.8 µA without time-dependent degradation. This output was adequate to operate a liquid crystal display (LCD) and to turn on six blue light emitting diodes (LEDs).
