Design, fabrication and characterization of all-solid-state three-dimensional rechargeable lithium on-chip batteries with silicon rod structured electrode.

摘要

Planar solid-state thin film batteries are widely used as an energy source for MEMS/CMOS devices but unfortunately have a low energy density. Recent technological advances have realized improved battery performance by reconfiguring electrode materials from the typical 2-D battery design of commercial technology into 3-D architectures. Such battery configurations more effectively utilize the highly limited space on board by increasing the power capabilities of batteries without increasing their footprint. Si is a highly attractive anode material for Li batteries due to its high theoretical charge capacity. A major drawback, however, is the mechanical failure of Si as an electrode material due to volume expansion. As Si expands and contracts up to 400% upon insertion and extraction of Li during cycling, the material is pulverized resulting in rapid capacity fading. In principle, a reduction in the size of the Si material (i.e. from micro- to nano-sized crystals) should mitigate the reversibility problem since a smaller Si crystallite will undergo less internal stresses that lead to pulverization of materials. In this work, a 3-D MEMS-fabricated Li battery incorporating structured Si rods is designed, fabricated and tested. A simple, quick and repeatable micro/nano rod array fabrication process for the battery anodes is developed using traditional MEMS technology. The testing results of the 3-D Li battery showed a fair degree of repeatability and revealed that structured Si rod arrays achieve a high first cycle coulombic efficiency as well as high continued cycling coulombic efficiency. High capacity with high reversibility was observed for this Li battery. Long cycle life with little fading was also achieved by using rod-structured electrodes. Performance of batteries with different rod dimensions is also reported.