Materials for 3D Battery Structures

Lithium ion batteries are widely applied in portable electronics due to their high energy density. The state-of-the-art materials and approaches lack in safety and lifetime, however. The safety can be improved by using solid state electrolyte instead of liquid. All-solid state batteries have also longer lifetimes. Additionally, by making the battery in 3D rather than planar, the energy density per footprint area can be remarkably increased. Complex surface structures are on the other hand challenging for most of the thin film deposition methods. Atomic layer deposition (ALD) is based on sequential self-limiting chemical reactions between gaseous source chemicals and the solid substrate. Films produced by ALD are therefore highly conformal, uniform, and pinhole free. Aims of the project The primary aim is to make an all-solid-state thin film battery in which all the battery constituents are prepared by atomic layer deposition. By ALD the complex nanostructures needed for high density 3D battery can be coated conformally, resulting safe and long-life operation of the battery. Key results of the project this far We have developed ALD process for lithium titanate spinel (Li4Ti5O12, LTO). It is a promising anode material especially suitable for all-solid-state batteries owing to its minimal volume change during charge-discharge operation. We are currently studying electrochemical properties of LTO material and optimizing its performance for the battery application. For the cathode side of the battery, we have developed ALD process for lithium manganese oxide spinel (LiMn2O4). It has already proven very good operational performance, both capacity and cycle life, under charge-discharge cycling. For the solid electrolyte, we have been studying novel lithium source chemicals to realize better controllability over composition and ion transport properties of the electrolyte material. As a model material, we have been studying lithium aluminate (LixAlyOz) deposited from two different ALD chemistries. In order to control the ALD film growth for the actual battery film stack, we have developed a system to mask the film growth. It has proven in functionality in preliminary testing of the thin film batteries. We have also done work in the basic understanding of atomic layer deposition of lithium containing compounds. During the year 2013, our activity in electrochemical impedance spectroscopy (EIS) has been increased and we are currently developing setup (substrate, thin film material, contact electrodes) for characterization of thin film electrolytes.

Lithium ion batteries have high energy densities and are therefore widely used in powering portable electronics. The use of lithium ion batteries in large-scale applications such as hybrid electric vahicles, load leveling, and energy storage is limited b y safety issues as well as their lifetime. The safety of lithium ion batteries can be improved by using solid-state electrolytes instead of liquid electrolytes. All-solid-state batteries have also improved lifetimes. The power density of lithium ion batte ries can be increased by making the structures three-dimensional (3D). In this project we will develop an all-solid-state 3D thin film lithium ion battery made by atomic layer deposition (ALD). ALD gives films with excellent conformality and uniformity and is therefore regarded as one of the best techniques to deposit films into 3D structures. Initial testing of the batteries will be done on planar structures. The 3D batteries will be made to 3D structures developed in collaboration with Sintef Inform ation and Communication Technology (ICT). Battery safety testing will be done in collaboration with Norwegian Defence Research Establishment (FFI) and scale-up in collaboration with Baldur Coating AS.