Recently, imec announced a major breakthrough in solid-state battery technology. The research center engineered a new solid electrolyte that has an exceptionally high conductivity of up to 10 mS/cm. According to imec’s Dr. Philippe Vereecken, there is even potential to reach 100 mS/cm, paving the way for a whole new generation of batteries for applications covering the spectrum from small portable electronics to electric vehicles and stationary grid storage. To create optimal solutions for these applications, with a higher energy density, faster charging time, longer lifetime, and an improved safety, imec’s researchers are now looking to further improve the innovative electrolytes and integrate them with thick-layered nanoparticle electrodes with innovative functional coatings.
Since the introduction of the rechargeable Li-ion battery in 1991, it has become the technology of choice for portable energy storage. With its available high energy density, it could store enough energy in a small volume to power the surge of portable electronic devices. But more and more, Li-ion technology is also chosen as the preferred solution to drive larger systems such as electric vehicles or stationary home batteries that store renewable energy and balance the smart electricity grid. These applications, however, place new demands on the battery technology that Li-ion cannot always fulfill.
For electric vehicles, e.g. a key consideration is to have batteries with as low a weight and volume as possible. That calls for an even higher energy density than is possible today. Also, the maximum current flow becomes more of an issue: the time to recharge critically depend on how fast energy can flow in and out of the battery. And as we consider economically critical applications such as grid storage and grid balancing, the cost and related high lifetime also become a key consideration.
Today’s Li-ion technology has some room to improve, but not enough to sustain the future requirements for all these applications. So we need innovation: new cathode and anode architectures with higher energy densities and new electrolytes that can deliver the necessary conductivity and that are safer.
Why use solid-state electrolytes?
An essential component of the battery is the electrolyte, the medium through which the Li-ions migrate between the anode and cathode. In today’s batteries, that electrolyte is a liquid. It fills the open spaces inside the porous membrane that is placed between the anode and the cathode. And it also soaks the powder electrodes, completely filling all pores and spaces and providing as much contact as possible between the electrodes and the electrolyte. Crucial for a battery’s properties is a high ion conductivity, i.e. the speed by which the ions can move about the electrolyte (expressed in mS/cm or milli-Siemens per centimeter). The higher that ion conductivity, the faster a battery can charge. And conversely the more power it can release.
Replacing the liquid electrolyte with a solid would allow removing the membrane and placing the electrodes much closer together, making the battery more compact and thus delivering a greater energy density. Until recently, however, the solid-state electrolytes didn’t have the required conductivity. One such electrolyte is LiPON (lithium-phosphate-salt doped with nitrogen), which has an intrinsic conductivity of only 10-7-10-6 S/cm. But that means the electrolyte layer can be no thicker than one micrometer. The only practical application of such solid-state electrolytes is therefore in planar thin-film batteries in which the ions have to travel only a short distance. Such batteries are great for micro-storage, e.g. in combination with energy scavenging for autonomous sensors , but for other applications their capacity is inadequate.
A breakthrough electrolyte
To engineer new solid electrolytes with an ion conductivity that is high enough to drive large-capacity cells, imec’s scientists have been looking towards composite materials. In November last year, a first result was announced: a new way to engineer nanocomposite materials that amplifies the ion conductivity to exceed that of liquid electrolytes.