Energy Storage Options for Self-powering Devices

Autonomous self-powered devices may use energy harvested from the environment. However, both the harvested power, and the demanded power are typically nonconstant and not matching. In order to enable a sustained energy efficient operation, an energy storage device as buffer is needed. In general, electric energy can be directly stored in capacitors or through an electrochemical conversion in batteries, which provide a significantly higher specific energy. Numerous different battery chemistries are commercially available and differ significantly in their characteristics. The performance of different commercially available batteries was investigated and is discussed with respect to the needs of self-powered small scale devices. In particular, specific energy and power are typical conflicting objectives for the design of a battery. Most batteries use a liquid electrolyte that is contained in a sealed housing. Typical shapes are coin cells, cylindrical, or prismatic cells. A new class of batteries uses a solid state electrolyte instead and has been commercialized as thin film battery. Through the use of a solid electrolyte, the degree of freedom for the design of the battery is dramatically increased. Moreover, safety, cycling stability, and working temperature range can be improved. Therefore, these types of batteries provide an interesting option for future self-powered devices. Materials and their impact on battery performance and manufacturing options for thin film solid state batteries are discussed.