KEY MATERIALS CHALLENGES FOR ELECTROCHEMICAL ENERGY STORAGE SYSTEMS

Batteries are in most people's mind devices to power small-scale mobile applications ranging from children's toys, cell phones and cameras to tablet computers and laptops, but we hardly think about the considerably wider range of electrochemical energy storage (EES) down to microbatteries that deliver milliwatts for smart-card devices or up via 10 30 kWh batteries powering electric drive vehicles to utility-scale stationary EES system that need to store tens to hundreds of MWh to locally balance demand in the power grid with energy supply from renewable sources. Currently it is the two latter applications, electromobility in battery electric vehicles (BEV) or plug-in hybrid electric vehicles (PHEV) and load leveling of power grids based on renewable sources, that appear to pose the key challenges to materials scientists and drive advancement of electrochemical energy storage technology. Due to their high energy density, rechargeable lithium ion batteries (LIBs) based on layered electrode materials [LiCoO2 as cathode (positive electrode), graphite as anode (negative electrode)] and organic liquid or polymeric gel electrolytes are the present-day choice as EES for small-scale portable appliances. LIBs possess high working voltage ( 3.6V) and thereby high energy-density compared to earlier rechargeable battery technologies such as Ni-Cd, NiMH and lead acid batteries. Global production (mostly in Asia) grows by 30% per year so that LIBs steadily increase their share of the also expanding battery market, that is estimated to reach 86 billion US$ in 2016. Road transportation constitutes a signi cant portion of energy consumption in Singapore as in most industrialized countries, 5 and the fast rise of vehicle population in developing countries is one of the main drivers of petroleum price increases. Provided that energy storage systems are technically and economically viable, high e±ciency electric vehicles (EV) have a number of advantages over current internal combustion engine cars: