Abstract
LTO (Li4Ti5O12) has been highlighted as anode material for next-generation lithium ion secondary batteries due to advantages such as a high rate capability, excellent cyclic performance, and safety. However, the generation of gases from undesired reactions between the electrode surface and the electrolyte has restricted the application of LTO as a negative electrode in Li-ion batteries in electric vehicles (EVs) and energy storage systems (ESS). As the generation of gases from LTO tends to be accelerated at high temperatures (40–60 °C), the thermal stability of LTO should be maintained during battery discharge, especially in EVs. To overcome these technical limitations, a thin layer of Al2O3 (~2 nm thickness) was deposited on the LTO electrode surface by atomic layer deposition (ALD), and an electrochemical charge-discharge cycle test was performed at 60 °C. The capacity retention after 500 cycles clearly shows that Al2O3-coated LTO outperforms the uncoated one, with a discharge capacity retention of ~98%. TEM and XPS analyses indicate that the surface reactions of Al2O3-coated LTO are suppressed, while uncoated LTO undergoes the (111) to (222) phase transformation, as previously reported in the literature.
Highlights
Lithium-ion batteries have been used as a power source for operating various small electronic devices, such as mobile phones and laptops
Recent studies showed that the transition-metal ions (Ti3+ and Ti4+ ) present on the Li4 Ti5 O12 (LTO) surface violently react with the electrolyte, causing the electrolyte solvent to decompose during electrochemical cycling, thereby deteriorating the long-term stability of electrodes made of LTO
atomic layer deposition (ALD) is the most effective approach compared to other deposition methods, since it allows one to adjust the thickness in Å units and uniformly deposit a protective layer [30–34]
Summary
Lithium-ion batteries have been used as a power source for operating various small electronic devices, such as mobile phones and laptops. Recent studies showed that the transition-metal ions (Ti3+ and Ti4+ ) present on the LTO surface violently react with the electrolyte, causing the electrolyte solvent to decompose during electrochemical cycling, thereby deteriorating the long-term stability of electrodes made of LTO. These reactions are accelerated in high-temperature environments, which has adverse effects on the cyclability of the electrode [24–26]. The stability of LTO electrodes has been enhanced by using carbon-based materials to separate LTO from the surrounding electrolyte, resulting in visibly reduced side reactions [27,28] These approaches were not quite effective to suppress gas evolution during electrode cycling, especially at elevated temperatures. Plane nor a change in the oxidation state of Ti was detected on the Al2 O3 -coated LTO, whereas a change in the interfacial phase of the uncoated LTO and shifts in the oxidation state (Ti3+ ) were observed after cycling
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