Unraveling the fundamentals of Li-O(2) battery chemistry is crucial to develop practical cells with energy densities that could approach their high theoretical values. We report here a straightforward chemical approach that probes the outcome of the superoxide O(2)(-), thought to initiate the electrochemical processes in the cell. We show that this serves as a good measure of electrolyte and binder stability. Superoxide readily dehydrofluorinates polyvinylidene to give byproducts that react with catalysts to produce LiOH. The Li(2)O(2) product morphology is a function of these factors and can affect Li-O(2) cell performance. This methodology is widely applicable as a probe of other potential cell components.

We report a significant difference in the growth mechanism of Li 2 O 2 in Li-O 2 batteries for toroidal and thin-film morphologies which is dependent on the current rate that governs the electrochemical pathway. Evidence from diffraction, electrochemical, FESEM and STEM measurements shows that slower current densities favor aggregation of lithium peroxide nanocrystallites nucleated via solution dismutase on the surface of the electrode; whereas fast rates deposit quasi-amorphous thin films. The latter provide a lower overpotential on charge due to their nature and close contact with the conductive electrode surface, albeit at the expense of lower discharge capacity.

The possibility of achieving high-energy, long-life storage batteries has tremendous scientific and technological significance. An example is the Li-s cell, which can offer a 3-5-fold increase in energy density compared with conventional Li-ion cells, at lower cost. Despite significant advances, there are challenges to its wide-scale implementation, which include dissolution of intermediate polysulphide reaction species into the electrolyte. Here we report a new concept to mitigate the problem, which relies on the design principles of drug delivery. our strategy employs absorption of the intermediate polysulphides by a porous silica embedded within the carbon-sulphur composite that not only absorbs the polysulphides by means of weak binding, but also permits reversible desorption and release. It functions as an internal polysulphide reservoir during the reversible electrochemical process to give rise to long-term stabilization and improved coulombic efficiency. The reservoir mechanism is general and applicable to Li/s cathodes of any nature.

The lithium–O2 ‘semi-fuel’ cell based on the reversible reaction of Li and O2 to form Li2O2 can theoretically provide energy densities that exceed those of Li-ion cells by up to a factor of five. A key limitation that differentiates it from other lithium batteries is that it requires effective catalysts (or ‘promoters’) to enable oxygen reduction and evolution. Here, we report the synthesis of a novel metallic mesoporous oxide using surfactant templating that shows promising catalytic activity and results in a cathode with a high reversible capacity of 10,000 mAh g(−1) (∼1,000 mAh g(−1) with respect to the total electrode weight including the peroxide product). This oxide also has a lower charge potential for oxygen evolution from Li2O2 than pure carbon. The properties are explained by the high fraction of surface defect active sites in the metallic oxide, and its unique morphology and variable oxygen stoichiometry. This strategy for creating porous metallic oxides may pave the way to new cathode architectures for the Li–O2 cell.

With the increasing importance of electrifi ed transport, the need for high energy density storage is also increasing. Possible candidates include Li-O 2 batteries, which are the subject of rapidly increasing focus worldwide despite being in their infancy of understanding. This excitement owes to the high energy density of Li-O 2 (up to 2−3 kWh kg − 1 ), theoretically much higher compared to that of other rechargeable systems, and the open "semi-fuel" cell battery confi guration that uses oxygen as the positive electrode material. To bring Li-O 2 batteries closer to reality as viable energy storage devices, and to attain suitable power delivery, understanding of the underlying chemistry is essential. Several concepts have been proposed in the last year to account for the function and target future design of Li-O 2 batteries and these are reviewed. An overview is given of the efforts to understand oxygen reduction/ evolution and capacity limitations in these systems, and of electrode and electrolyte materials that are suitable for non-aqueous and hybrid (nonaqueous/ aqueous) cells.