Here in this work, we demonstrate a turn to composite electrodes formed from micro/nano size particles typical of today’s battery electrodes. We use atomic layer deposition (ALD) to create highly controlled, thin protective layers on composite FeOF conversion electrodes, testing their efficacy by cycling in batteries. ALD protection layers, the solid-electrolyte LiPON (lithium-phosphous oxynitride), were directly deposited on the electrodes in controlled inert ambient conditions. The porous structure of composite materials allows vapor-phase ALD techniques to penetrate into electrodes to form effective protection layer. We observed that the ALD protected composite conversion electrode exhibits superior cyclability (capacity retention) and high energy (round-trip) efficiency, with decreased overpotentials.
Detailed investigation was further performed to understand the mechanisms of superior reversibility for ALD protected composite electrodes, and surprisingly, based on solid-state NMR electron energy loss spectroscopy (EELS) and electrochemical data, we observed that the ALD protection layer allows extra Li insertion to form an extended insertion-like phase for Li storage, which largely increases the capacity for highly reversible insertion regime before it turns into conversion phase transformation. This observation provides a new insight on protection layer altering the phase diagram during Li insertion, and provides technological impact on utilizing high capacity conversion electrode.
This interfacial engineering approach can be applied to many commercial electrode systems (e.g. LTO, LMO, V2O5…., etc.) to show beneficial effects to the battery performance that we will briefly discuss in this talk.
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