Kaiming Liao

A self-defense redox mediator for efficient lithium–O2 batteries

Redox mediators (RMs) have become focal points in rechargeable Li–O2 battery research to reduce overpotentials in oxygen evolution (charge) reactions. In this study, we found an evidence for the shuttle effect arising in dimethyl sulfoxide (DMSO) with a LiI RM through the visual observation of the diffusion of soluble I3− towards a Li anode where it reacted chemically to produce LiI, which can be only partly dissolved, leading to the loss of both the RM and electrical energy efficiency. Therefore, we proposed a self-defense redox mediator (SDRM) of InI3 to counter this problem. During charging, the In3+ is reduced electrochemically on the Li anode prior to Li+, forming a much stable indium layer to resist the synchronous attack by the soluble I3−. The pre-deposited indium layer can also reduce the growth of dendrites from the Li anode surface. As a result, the electrical energy efficiency and the cycling performance of the Li–O2 cells were improved significantly.

Nanoporous Ru as a Carbon‐ and Binder‐Free Cathode for Li–O2 Batteries

Porous carbon-free cathodes are critical to achieve a high discharge capacity and efficient cycling for rechargeable Li-O2 battery. Herein, we present a very simple method to directly grow nanoporous Ru (composed of polycrystalline particles of ∼5 nm) on one side of a current collector of Ni foam via a galvanic replacement reaction. The resulting Ru@Ni can be employed as a carbon- and binder-free cathode for Li-O2 batteries and delivers a specific capacity of 3720 mAh gRu (-1) at a current density of 200 mA gRu (-1) . 100 cycles of continuous discharge and charge are obtained at a very narrow terminal voltage window of 2.75∼3.75 V with a limited capacity of 1000 mAh gRu (-1) . The good performance of the nanoporous Ru@Ni cathode can be mainly attributed to the effective suppression of the by-products related to carbon or binder, the good adhesion of the catalyst to the current collector, and the good permeation of O2 and electrolyte into the active sites of the nanoporous Ru with the open pore system. This new type electrode provides a snapshot toward developing high-performance carbon- and binder-free Li-O2 batteries.

An oxygen cathode with stable full discharge–charge capability based on 2D conducting oxide

A two-dimensional conducting oxide nanosheet, which was prepared by a two-step process involving exfoliation and heat treatment, was employed as a Li–O2 cathode without adding any conductive additives. The 2D nanostructures in the Li–O2 cathode can provide a large surface-to-mass ratio, increase the electrode–electrolyte contact area and facilitate oxygen diffusion and electron transmission. The as-synthesized conducting oxide nanosheet of RuO2 enables the Li–O2 cathode to be operated under full discharge–charge conditions, and to deliver a high specific capacity of ∼900 mA h g−1 with stable discharge–charge overpotentials (0.15/0.59 V) over 50 cycles.

A long-life lithium ion oxygen battery based on commercial silicon particles as the anode

Lithium–oxygen (Li–O2) batteries with Li metal as anodes suffer from serious safety problems because of the formation of Li dendrites during the discharge and charge cycles. In this study, for the first time, we developed a long-life Li ion O2 battery based on commercial silicon particles as a substitute for Li metal as the anode. This was realized after determining the detailed cause of the fading performance of these batteries based on unoptimized Si anodes. The batteries can achieve as many as 100 discharge–charge cycles with low overpotentials, indicating excellent cycling stability. The durable solid electrolyte interphase (SEI) film built on the silicon anode surface was proved to play a critical role. The composition of the SEI film grown in glyme-based electrolyte was originally analyzed, and the resulting strong resistibility of the unique SEI film towards oxygen crossover effects endows these batteries with stable cycling ability. Moreover, a storage experiment confirmed the potential long-term operation of these batteries. These encouraging results imply an accessible solution to address problems related to Li metal for the realization of practical Li–O2 batteries.

Facile in Situ Preparation of Graphitic-C3N4@carbon Paper As an Efficient Metal-Free Cathode for Nonaqueous Li–O2 Battery

The rechargeable Li-O2 batteries with high theoretical specific energy are considered to be a promising energy storage system for electric vehicle application. Because of the prohibitive cost, limited supply, and weak durability of precious metals, the developments of novel metal-free catalysts become significant. Herein, the graphitic-carbon nitride@carbon papers have been produced by a facile in situ method and explored as cathodes for Li-O2 batteries, which manifest considerable electrocatalytic activity toward oxygen reduction reaction and oxygen evolution reaction in nonaqueous electrolytes because of their improved electronic conductivity and high nitrogen content. The assembled Li-O2 batteries using graphitic-carbon nitride@carbon papers as cathodes deliver good rate capability and cycling stability with a capacity retention of more than 100 cycles.

Stabilization of polysulfides via lithium bonds for Li–S batteries

One of the most vexing challenges in Li–S batteries is the polysulfide shuttle. Using a combined theoretical and experimental approach, we show that g-C3N4 coated carbon can provide effective anchoring sites for lithium polysulfides, potentially having implications for the design of electrodes for practical Li–S batteries.

Reducing the charging voltage of a Li–O2 battery to 1.9 V by incorporating a photocatalyst

We here present a photoassisted rechargeable Li–O2 battery by integrating a g-C3N4 photocatalyst to address the overpotential issue of conventional non-aqueous Li–O2 batteries. The high charging overpotential of a Li–O2 battery is compensated by the photovoltage, and finally an ultralow charging voltage of 1.9 V is achieved, which is much lower than that of any other conventional non-aqueous Li–O2 batteries. It is also worth noting that the charging voltage is even much lower than the discharging voltage (∼2.7 V), resulting in 142% energy efficiency (output electric energy/input electric energy, not including solar energy).

Lowering the charge voltage of Li–O2 batteries via an unmediated photoelectrochemical oxidation approach

We here demonstrate an unmediated photoelectrochemical oxidation approach to address the overpotential issue of Li–O2 batteries during the charge process. We show that photoexcited holes from the photoelectrode provide a direct oxidation of solid Li2O2, without the use of a redox mediator. The Li–O2 battery composed of carbon nitride on carbon paper as a cathode and also as a photoelectrode exhibits an ultralow charge voltage of 1.96 V resulting in a ‘negative’ overpotential and good cycling performance. These results could represent a new and promising avenue for the future development of photo-charging all-solid-state batteries.