New-Tech Europe Magazine | Jan 2018

Solid-state batteries for wearable sensors and electric cars Prof. Philippe Vereecken, IMEC

The solid-state batteries that are on the market today are thin-film batteries which, on account of their limited capacity, can only be used for micro- storage, for example to provide power for sensors. But as a result of innovations in ma-terials and architecture, the design of solid-state batteries may be expanded to large storage systems, for example for electric cars or the smart grid. Philippe Vereecken, Principal Scientist and Program Manager ‘Electrochemical Storage’ at imec, explains imec’s roadmap that makes this development possible. Devel-oping a nano-composite electrolyte with high ion conductivity is an important link in achieving that aim. The current ‘wet’ Li-ion battery The introduction of the rechargeable Li-ion battery in 1991 brought about a general revolution in the battery landscape. As a result of its high energy den-sity, more energy could be stored

in a small volume, which meant that the en-ergy needed to power a device such as a laptop could be made portable. The emergence of this battery also enabled the rapid rise of smart, mobile elec- tronics. Philippe Vereecken: “Without the Li-ion battery, smart devices could never have been designed with such small and elegant form factor. Today, it is also chosen as a solution for systems that require more energy such as electric vehicles or as temporary local energy storage for the smart electricity grid. For these applications, other parameters are important, such as the storage capaci-ty (expressed in Ah) and the lifetime. For electric vehicles, the power (maxi-mum current flow) is also important: the car must be capable of accelerating quickly and we also want to recharge the vehicle in a short time. Current elec-tric cars drive entirely on Li-ion batteries.” To generate current, both electrons and lithium ions move from the negative to the positive electrodes. During

charging, they move in the opposite direc-tion. The amount of electrode material mainly determines the storage capacity. The electrolyte provides the ionic conductance between the electrodes and defines the power of the battery. Philippe Vereecken: “The liquid electrolytes which are used today have a number of limitations. For instance, the use of the liquid electrolyte requires the use of special housing, as well as a membrane between the porous anode and cathode. This puts restrictions on the dimen-sions and design of this ‘wet’ battery. The liquid electrolytes are typically also flammable and corrosive, which creates safety and health risks.” The solid-state Li-ion battery Several options are being explored for the battery of the future that over-comes these limitations without compromising on performance – or doing even better. Imec’s choice here is the concept of the (inorganic) solid-state battery. Philippe

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