High Rate and Long Cycle Life Anodes Via ALD TiO2 Coatings on Mesoporous Activated Carbons
Authors: Xing Weibing , Buettner-Garrett Josh , Krysiak Mike , Kelly Joe , King David M 
Published: February 2020

Titanium dioxide (TiO2), a candidate as anode active material for lithium ion batteries, has attracted much attention from researchers due to its safety characteristics arising from its high electrochemical potential (~1.5V) vs. Li/Li+, low cost, material availability and environmental benignity. However, low electric conductivity, sluggish Li+ diffusivity and poor cycle performance of TiO2 have limited its wide acceptance in practical rechargeable lithium ion batteries. Various strategies such as TiO2-C-nano metal composites [1], nanofibers [2], and TiO2 flakes [3], have been investigated in literature work. While these studies led to improved performance to various degrees, they were limited either in rate (<20C) or cycle life (<100 cycles) or both. A recent work [4] involved atomic layer deposition (ALD) of TiO2on graphene powders and demonstrated vastly improved rate and cycle capabilities of the resulting materials.

Here we present an alternative and promising method of preparing extremely high rate and long cycle life anodes via ALD coatings of TiO2on mesoporous activated carbon (AC) electrodes.

Figure 1 shows charge and discharge voltages between 1.5V and 3.0V (vs. Li/Li+) of an ALD TiO2-AC and a mesoporous AC baseline coin half cell versus specific capacity based on total active materials. Conventional carbonate-based lithium ion electrolyte was used. The ALD TiO2-AC cell demonstrated nearly five-fold capacity increase against the baseline with voltage profiles typical of nano TiO2. The contribution of ALD TiO2to the observed capacity is ~83%, which leads to ~73 mAh/g specific capacity. The relatively low specific capacity is because of the 1.5V cutoff voltage used in this study.

Figure 2 shows rate performance of ALD TiO2-AC vs. AC baseline half cells. The ALD TiO2-AC demonstrated very high rate capability, e.g. delivering 70% of low rate capacity at 400C rate, surpassing that of AC baseline.

Figure 3 shows excellent cycle stability of ALD TiO2-AC half cell with 80% capacity retention after 800 cycles.

The remarkable electrochemical performance demonstrated from ALD TiO2-AC is attributed to ALD enabled TiO2nano structure. Such nano structure is responsible for facile lithium insertion/extraction leading to extremely high rate capability and long cycle life due to stress/stain free nano architecture. The results in this study suggest a promising material processing methodology for high rate and long cycle life anodes for lithium ion batteries used in applications that require fast rate capability, when implemented with high throughput, high volume ALD processes.

Figure 1. Charge and discharge voltage profiles of ALD TiO2-AC/Li vs. AC/Li baseline half cells.

Figure 2. Rate capability tests of ALD TiO2-AC/Li vs. AC baseline half cells.

Figure 3. Cycle life test of an ALD TiO2-AC/Li cell.

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