Plasma-assisted ALD of LiPO(N) for solid state batteries

All solid state 3D batteries are pursued for their increased safety and high power capabilities. At present conformal coating of the solid electrolyte remains one of the key hurdles for the implementation of such devices. In the present work we investigate atomic layer deposition (ALD) as means of conformal deposition of lithium phosphate (Li₃PO₄) and nitrogen doped lithium phosphates (LiPON). These processes are characterized here to obtain the highest possible Li-ion conductivity. Li₃PO₄ is shown to yield a conductivity of 10−¹⁰ S/cm at 25°C. On the other hand, an optimized LiPON process gave rise to a Li-ion conductivity of 510−⁷ S/cm at 25°C. In addition, good conformality of the LiPON process was shown on high aspect ratio pillars. Furthermore, a solid state battery device was fabricated comprising a Li₄Ti₅O₁₂ cathode, a 70 nm thick ALD LiPON solid electrolyte and a metallic lithium anode. This finding indicates that a layer down to 70 nm can be made pinhole free.