The Transition from Planar to Curved and Flexible Batteries

There is currently an enormous drive in research, development, production and marketing of Li-ion batteries for smartphone, tablets, portable electronics and of course hybrid and full electric vehicles (1-3).  The design of the portable electronics is currently being limited by the requirement to accommodate rigid planar batteries. Capacities can of course be increased, but this increases the bulk design, size and weight of the battery. For future portable devices, particularly wearable technology devices, there will be a need to transition from traditional planar cells to curved and flexible cells (4-6). One approach towards the development of curved and flexible cells is through the development of a sprayable battery process (7-9).

In this work we detail the preparation of sprayable paints using the most commonly used commercial cathode and anode materials, LiCoO₂ and graphite respectively as well as a sprayable separator. Initially the component paints were sprayed on to rigid current collectors. The resulting layered cells were tested in split cells to confirm their successful operation. The paints were then applied to curved current collectors leading the transition from a rigid planar cell to a flexible cell. Through detailed electrochemical investigations we compare the electrochemical performance of the layered cells in split cells, and in pouch cells on curved and flexible current collectors. Our approach initially uses commercial cathode and anode materials to confirm the successful operation of non-planar cells. We also investigate the use of a promising alternative cathode material in the form of V₂O₅ polycrystalline nanorods (poly-NRs) (10). Through galvanostatic cycling and cyclic voltammetry the electrochemical performance of poly-NRs in a full Li-ion cell in both planar and non-planar arrangements is demonstrated.

Acknowledgements

This research was supported through a Science Foundation Ireland Technology Innovation and Development Award under contract no 13/TIDA/E2761.

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