Formulating Interfacial Impedances for Designing High-Energy and High-Power All-Solid-State Battery Cathodes.

All-solid-state batteries (ASSBs) are safe, high-energy-storage systems. However, despite the progress achieved in the development of high-ionic-conductivity solid electrolytes (SEs), the power performance of ASSBs remains low because of the high interfacial impedances in composite cathodes. Therefore, understanding the interfacial factors is crucial for obtaining high power ASSBs. This study provides a quantitative analysis of the influence of these factors using impedance spectroscopy measurements, which enables the elucidation of the interfacial impedance values of two key parameters, the grain-boundary resistance (ri,gb) and charge-transfer resistance (ri/e). Systematic investigation revealed an unexpected increase in the cathodic resistance with the decrease in the size of the cathode active material (CAM) particles, indicating that even high-reaction-surface-area CAMs yield low ri/e but high ri,gb values owing to their high porosity, resulting in a trade-off relationship. In contrast, this phenomenon is unlikely to occur in liquid-electrolyte-based batteries. Notably, we discuss how composite cathode design impacts performances of stable, high-power, and high-energy ASSBs.

Operando Observation of the De-Evolution/Evolution Process of Hydrated LiOH in Moisture-Assisted Li-O2 Batteries.

All-solid-state Li-O2 batteries that use ceramic electrolytes have been suggested to overcome the limitations posed by the decomposition of organic electrolytes. However, these systems show a low discharge capacity and high overpotential because the discharge product Li2O2 has low electronic conductivity. In this study, all-solid-state planar-type Li-O2 cells were constructed using a lithium anode, a Li1·3Al0·3Ti1·7(PO4) (LATP) inorganic solid electrolyte, and an air electrode composed of a Pt grid pattern. The discharge/charge process was observed in real time in a humidified O2 environment for the first time, which clarified both the hydration process of the discharge products and the charging process of the hydrated discharge products. The discharge product (LiOH) could be easily hydrated in water, which would facilitate ion transport, thereby increasing the discharge capacity and discharge voltage (vs Li/Li+; from 2.96 to 3.4 V). Thus, Li-O2 cells with a high energy density and a capacity of 3600 mAh/gcathode were achieved using a planar Pt-patterned electrode in a humidified O2 environment. This study is the first to demonstrate the hydration of the discharge products of a Li-O2 cell in humidified O2. Based on a thorough understanding of the hydration phenomenon/mechanism, our findings suggest new strategies for developing high-energy-density all-solid-state Li-O2 batteries using a simple, easy-to-manufacture planar Pt-patterned cathode.

Ion-channel aligned gas-blocking membrane for lithium-air batteries.

Lithium-metal-based batteries, owing to the extremely high specific energy, have been attracting intense interests as post-Li-ion batteries. However, their main drawback is that consumption/de-activation of lithium metal can be accelerated when O2 or S used in the cathode crosses over to the metal, reducing the lifetime of the batteries. In use of ceramic solid state electrolyte (SSE) separator, despite the capability of gas blocking, thick and heavy plates (~0.3 mm) are necessitated to compensate its mechanical fragility, which ruin the high specific energy of the batteries. Here, we demonstrate fabrication of a new membrane made of micron-sized SSE particles as Li-ion channels embedded in polymer matrix, which enable both high Li-ion conduction and gas-impermeability. Bimodal surface-modification was used to control the energy of the particle/polymer interface, which consequently allowed channel formation via a simple one-step solution process. The practical cell with the new membrane provides a cell-specific energy of over 500 Wh kg-1, which is the highest values ever reported.

Aqueous electrochemistry of poly(vinylanthraquinone) for anode-active materials in high-density and rechargeable polymer/air batteries.

A layer of poly(2-vinylanthraquinone) on current collectors underwent reversible electrode reaction at -0.82 V vs Ag/AgCl in an aqueous electrolyte. A repeatable charging/discharging cycles with a redox capacity comparable to the formula weight-based theoretical density at the negative potential suggested that all of the anthraquinone pendants in the layer was redox-active, that electroneutralization by an electrolyte cation was accomplished throughout the polymer layer, and that the layer stayed on the current collector without exfoliation or dissolution into the electrolyte during the electrolysis. The charging/discharging behavior of the polymer layer in the aqueous electrolyte revealed the capability of undergoing electrochemistry even in the nonsolvent of the pendant group, which offered insight into the nature of the anthraquinone pendants populated on the aliphatic chain. Charging/discharging capability of air batteries was accomplished by using the polymer layer as an organic anode-active material. A test cell fabricated using the conventional MnO(2)/C cathode catalyst exhibited a discharging voltage at 0.63 V corresponding to their potential gap and a charging/discharging cycle of more than 500 cycles without loss of the capacity.