Ji Eun Wang

A flexible energy harvester based on a lead-free and piezoelectric BCTZ nanoparticle–polymer composite

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 ∼15 V and a current signal of ∼0.8 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).

Piezoelectric energy harvesting from a PMN–PT single nanowire

Flexible piezoelectric generators constructed using one-dimensional nanostructures are well known for their efficient energy harvesting. Herein, we have fabricated a flexible piezoelectric energy harvester (PEH) consisting of a single 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 nanowire (PMN–PT NW) using a facile transferring approach onto a Au electrode-patterned plastic substrate. The well-developed device effectively harvested the maximum output signals (9 mV and 1.5 nA) originating from a single PMN–PT nanowire under mechanical bending/unbending motions. The designed PEH is also expected to be utilized as a versatile tool to evaluate the performance of a one-dimensional nanostructure.

Facile hydrothermal synthesis of BaZrxTi1−xO3 nanoparticles and their application to a lead-free nanocomposite generator

A facile form of hydrothermal synthesis was utilized to obtain BaZrxTi1−xO3 (BZT) nanoparticles (NPs) with a wide range of Zr concentrations. The amorphous B-site precursor prepared by the hydrolysis of alkoxide using an ammonia solution, efficiently promotes the reaction with the A-site precursor solution. Subsequently, the BZT NPs were adopted for a flexible piezoelectric energy harvester (PEH) by employing a simple, low-cost, and scalable spin-casting method. The output performance achieved by the fabricated flexible PEH depends on the Zr/Ti ratio inside a piezoelectric nanocomposite. The BZT NP-embedded PEH with Zr concentration of 32 mol% generated a stable output voltage of ∼20 V and a current signal of 400 nA without performance decay.

New Insight to Na Intercalation with Li Substitution on Alkali Site and High Performance of O3-type Layered Cathode Material for Sodium Ion Batteries

Lithium was substituted on the alkali site of an O3-type layered structure as cathode material for sodium-ion batteries (SIBs). Role of Li in Na intercalation and high performance is reported for the first time. The behavior of Na during intercalation is a critical factor that determines electrochemical performance. Although transition-metal oxides with layered structures have been studied extensively for SIBs, the focus has been on substitution at transition metal sites rather than at the alkali site. Here, substitution of Li at the alkali site of Nax[FeyMn1−y]O2 (0 ≤ x, y ≤ 1) layered materials is reported for the first time. The substituted element at the alkali site can directly interfere with the behavior of Na during intercalation. In situ XRD, synchrotron powder XRD, neutron powder diffraction, ex situ XANES, and DFT calculation revealed that Li at alkali sites stabilized the layered structure during the electrochemical reaction and assisted Na intercalation by lowering the energy barrier for Na-hopping. Contrary to common understanding, Li substituted material showed an improved cyclic and rate performance in spite of the smaller interlayer spacing of the O3-type layered structure. The result provides new insight into the role of a substituted element at the alkali site and shows that the Li at the alkali site is a key factor for achieving high performance of a layered cathode material.