| AVS 64th International Symposium & Exhibition | |
| Thin Films Division | Monday Sessions |
| Session TF+EM-MoM |
| Session: | ALD for Energy Conversion, Storage, and Electrochemical Processes |
| Presenter: | David Stewart, University of Maryland, College Park |
| Authors: | D. Stewart, University of Maryland, College Park A.J. Pearse, University of Maryland, College Park K. Gregorczyk, University of Maryland, College Park G. Rubloff, University of Maryland, College Park |
| Correspondent: | Click to Email |
Atomic layer deposition (ALD) is excellent for depositing conformal thin films on high aspect ratio substrates, and due to the good thickness control and uniformity, ALD allows us to push the limits of thin film batteries. To produce solid-state lithium ion batteries on such substrates new processes for anodes, high-capacity cathodes, and solid-electrolytes must continue to be developed and characterized. Sn and SnO2 have been well studied as alloy/conversion electrodes in the literature, while the properties of Sn3N4 and SnOxNy have yet to be explored in any detail. To study the differences in the electrochemical performance of SnO2, Sn3N4, and SnOxNy, an ALD process was developed that allows for highly tunable N/O ratios. In this study tetrakis(dimethylamido)tin (TDMA(Sn)) was used as the metal-organic precursor in combination with remote nitrogen plasma (pN) and H2O was used to introduce oxygen content. For the pure nitride phase, a broad temperature window was found between 150-250 °C, over which the growth rate per cycle (GPC) was ~ 0.55 Å. While only very short pulse times (< 1 s) were required for saturation of the TDMA(Sn), relatively long pN exposures (> 20 s) were required for GPC saturation. We then showed that by varying H2O super cycles the relative concentration of O and N in the film can be controlled between 0% N and 95% N.
To study the electrochemical performance of these materials solid-state half-cells were constructed using SnO2, Sn3N4, and SnOxNy thin films versus thermally evaporated Li. A 100 nm thin film of LiPON was deposited as the solid electrolyte by thermal ALD [1]. This electrolyte layer is thick enough to provide good electrical insulation and thin enough to allow fast ionic diffusion, however when cycled to voltages below 0.4 V vs Li/Li+ the half-cells shorted, possibly due to mechanical breakdown of the LiPON layer from significant volume expansion of the anodes during the alloying reaction with Li. The Li2O matrix formed from SnO2 is expected to be more stable, but with lower ionic conductivity than the Li3N matrix formed from Sn3N4. Galvanostatic intermittent titration and electrochemical impedance spectroscopy were used to analyze the ionic conductivity of the anodes before and after the initial conversion reaction and as a function of N/O ratio. The high capacity of the SnOxNy electrodes in combination with the excellent ionic conductivity and mechanical properties of the ALD LiPON makes these films attractive for applications in 3D Li-ion batteries.