Design and Fabrication of Stretchable and Transparent Rechargeable Batteries

The main task of a battery is to store energy and supply power to electronic devices. Although the areas of application for batteries have expanded massively in recent years - from portable devices to e-mobility and stationary storage options - the basic structure of the battery has hardly changed: It consists of two electrodes with electrolyte and separator, which are housed in a more or less rigid casing. Compared to batteries, portable electronic devices are constantly changing their design, depending on fashion and consumer tastes, but also with the intention of implementing new mechanical properties that make the devices flexible, rollable, stretchable or perhaps even transparent. For fully integrated systems that contain the battery and thus do not require wiring to an external power source, the batteries must have similar physical properties, which requires a complete rethink of battery design, but also allows for certain trade-offs in electrochemical performance [1].<br/>In this talk, examples of the design and fabrication of a stretchable lithium-ion battery [2] and a transparent and stretchable zinc-ion battery [3] will be presented and discussed. In the Li-ion battery, all components (current collector, anode and cathode, electrolyte and packaging) were stretchable, making the battery flexible and twistable. The current collector was fabricated by depositing Ag microflakes as a conductive layer on a stretchable carbon-polymer composite. Anode (pre-lithiated V₂O₅) and cathode (LiMn₂O₄) powders were sprayed onto the silver flakes. A polyacrylamide 'water-in-salt' hydrogel was used as the electrolyte, which exhibited high ionic conductivity and excellent stretchability. The full cell battery worked even at a high strain of 50%. The second example concerns a transparent and stretchable Zn-ion battery with two electrodes featuring a hexagonal grid structure deposited on a polydimethylsiloxane (PDMS) substrate with a polyacrylamide (PAM) hydrogel electrolyte. In both electrodes, Au nanowires (NWs) were used as current collectors together with Zn for the anode and α-MnO₂ for the cathode. For the full cell battery, the PAM hydrogel was sandwiched between aligned films of PDMS+Au NWs/Zn and PDMS+Au NWs/α-MnO₂, showing a high transmittance of 73% and 65% at 550 nm without and with 50% strain, respectively. The battery provided a capacity of 176.5 mA h g⁻¹ after 120 cycles under varying strain conditions up to 50%.<br/><br/>[1] N. Mittal, L. Wehner, T. Liu, M. Niederberger, Multifunctional Batteries: Flexible, Transient and Transparent, ACS Cent. Sci. 2021, 7, 231<br/>[2] X. Chen, H. Huang, L. Pan, T. Liu, M. Niederberger, Fully Integrated Design of a Stretchable Solid-State Lithium-Ion Full Battery, Adv. Mater. 2019, 31, 1904648<br/>[3] T. Liu, X. Chen, E. Tervoort, T. Kraus, M. Niederberger, Design and Fabrication of Transparent and Stretchable Zinc Ion Batteries, ACS Appl. Energy Mater. 2021, 4, 6166