Jae‐Kwang Kim

Sodium-metal halide and sodium-air batteries.

Impressive developments have been made in the past a few years toward the establishment of Na-ion batteries as next-generation energy-storage devices and replacements for Li-ion batteries. Na-based cells have attracted increasing attention owing to low production costs due to abundant sodium resources. However, applications of Na-ion batteries are limited to large-scale energy-storage systems because of their lower energy density compared to Li-ion batteries and their potential safety problems. Recently, Na-metal cells such as Na-metal halide and Na-air batteries have been considered to be promising for use in electric vehicles owing to good safety and high energy density, although less attention is focused on Na-metal cells than on Na-ion cells. This Minireview provides an overview of the fundamentals and recent progress in the fields of Na-metal halide and Na-air batteries, with the aim of providing a better understanding of new electrochemical systems.

A hybrid solid electrolyte for flexible solid-state sodium batteries

Development of Na-ion battery electrolyte with high-performance electrochemical properties and high safety is still challenging to achieve. In this study, we report on a NASICON (Na3Zr2Si2PO12)-based composite hybrid solid electrolyte (HSE) designed for use in a high safety solid-state sodium battery for the first time. The composite HSE design yields the required solid-state electrolyte properties for this application, including high ionic conductivity, a wide electrochemical window, and high thermal stability. The solid-state batteries of half-cell type exhibit an initial discharge capacity of 330 and 131 mA h g−1 for a hard carbon anode and a NaFePO4 cathode at a 0.2C-rate of room temperature, respectively. Moreover, a pouch-type flexible solid-state full-cell comprising hard carbon/HSE/NaFePO4 exhibits a highly reversible electrochemical reaction, high specific capacity, and a good, stable cycle life with high flexibility.

Metal-free hybrid seawater fuel cell with an ether-based electrolyte

In this work, the design of a new metal-free hybrid seawater fuel cell consisting of a flowing seawater cathode and a hard carbon anode was proposed. The electrochemical performance of the cell was investigated with two different electrolytes, i.e., 1 M NaClO4 in ethylene carbonate (EC)/propylene carbonate (PC), and 1 M NaCF3SO3 in tetraethylene glycol dimethyl ether (TEGDME). The TEGDME-based electrolyte showed a good cycle performance for 100 cycles, whereas EC/PC showed poor cycle stability after 30 cycles. Our results showed that a low conducting solid-electrolyte interphase (SEI) was formed with a thick layer, and the PVdF binder was degraded during the redox reaction when the EC/PC-based electrolyte was used. In contrast, the TEGDME-based electrolyte induced the formation of a more efficient SEI layer without degradation of the binder.

Eco‐friendly Energy Storage System: Seawater and Ionic Liquid Electrolyte

As existing battery technologies struggle to meet the requirements for widespread use in the field of large-scale energy storage, novel concepts are urgently needed concerning batteries that have high energy densities, low costs, and high levels of safety. Here, a novel eco-friendly energy storage system (ESS) using seawater and an ionic liquid is proposed for the first time; this represents an intermediate system between a battery and a fuel cell, and is accordingly referred to as a hybrid rechargeable cell. Compared to conventional organic electrolytes, the ionic liquid electrolyte significantly enhances the cycle performance of the seawater hybrid rechargeable system, acting as a very stable interface layer between the Sn-C (Na storage) anode and the NASICON (Na3 Zr2 Si2 PO12) ceramic solid electrolyte, making this system extremely promising for cost-efficient and environmentally friendly large-scale energy storage.