Structural Characterization of a Solid Electrolyte for 3D Microbatteries

Three-dimensional (3D) microbatteries have gained attention as viable compact power sources with applications in wearable and implantable microelectronics, and IoT functions. A key innovation from our lab is electrophoretic deposition (EPD) of all thin-film layers, enabling conformal deposition of electrodes and solid electrolytes on complex-shape, high-aspect-ratio perforated silicon and polymer substrates. This leads to a large capacity gain per footprint area of battery, compared with wafer surface deposition.

Using EPD, we prepared a novel composite polymer-in-ceramic electrolyte composed of 87% lithium aluminum germanium phosphate (Li_1.5Al_0.5Ge_1.5(PO₄)₃, LAGP), 13% polyethyleneimine (LAGP−PEI), saturated by LiI salt to produce high concentrations of mobile Li⁺ and I^- ions.

Solid state ^6,7Li, ²⁷Al, and ³¹P magic angle spinning nuclear magnetic resonance (MAS NMR) measurements showed structural changes the LAGP-PEI-LiI composite compared with base LAGP material, including the conversion of about 1/3 of the crystalline compound into an amorphous phase containing both two-fold and three-fold coordinated P, and a change in the ratio of five-fold to six-fold coordinated Al. ⁷Li NMR diffusometry revealed faster Li ion diffusion in the LAGP-PEI-LiI composite than in base LAGP.