Surface Engineering of Nanostructured Electrodes and Electrolytes for Solid-State Battery Applications

Lithium ion secondary batteries are widely used to power portable electronics such as laptops, mobile phones, etc. and have become an integral part of our daily lives. As technology advances, batteries with a high capacity and long lifetime are demanded for increasingly diverse applications. Solid-state lithium ion batteries using solid electrolytes offer a promising avenue to meet these demands for the following reasons. First, solid-state batteries are easy to miniaturize and can be produced in a thin-film form. Second, solid electrolytes are more stable than any other electrolyte system and circumvent the well know safety issues with lithium ion batteries. However, current solid-state battery capacity is limited by significant interfacial impedance due to the nature of the solid electrolyte/electrode interface. Realization of a commercially viable solid-state battery will require significant progress in minimizing interfacial impedances.

Incorporating nanotechnology processes into the lithium ion battery system has helped enhance the performance of several lithium ion battery chemistries. Nanostructuring a lithium ion battery’s anode and cathode allows for vastly increased electrode surface area available for the battery system, thereby reducing the impact of interfacial impedance. High surface area nanostructured electrodes can be produced by using an RF magnetron sputter coater to deposit the electrode material onto a nanoporous Anodized Aluminum Oxide (AAO) membrane with nanopores of 200 nm in diameter. This research uses a nanostructured SnO₂ anode against a bulk LiCoO₂ cathode and a polyethylene-oxide (PEO) based solid polymer electrolyte. The electrolyte is similarly nanostructured by confining it in the nanopores of an AAO membrane. By melting a film of the electrolyte onto an AAO membrane under vacuum, the polymer is forced into the AAO nanopores, forming a nanocomposite electrolyte membrane. The confinement of the electrolyte increases its ionic conductivity to levels comparable to liquid electrolytes.

A functioning room-temperature solid-state lithium ion cell has been developed using the nanostructured SnO₂ anode, LiCoO₂ cathode, and PEO nanocomposite electrode. The cell was investigated using galvanostatic cell cycling and scanning electron microscopy (SEM). The cell achieved a specific discharge capacity of 125 mAh/g (89% of theoretical capacity) and a capacity retention of 20% after 20 cycles.