Composite TiO2/GeO2 for Higher Performance Inverse Opal Lithium-Ion Battery Electrodes
Authors: Carroll Aoife , O'Dwyer Colm 
Published: November 2022

With the ever-growing technology industry and the need for more sustainable energy, the race to develop better, more efficient, renewable materials for lithium ion batteries is at the forefront of research. Metal oxide materials for use as electrodes in lithium batteries have been promising in recent years, transition metal oxides are favourable due to their low cost and nanostructured metal oxides exhibit encouraging electrochemical properties.1-2 Photonic crystal structures, more specifically inverse opal (IO) structures, are porous, highly interconnected structures which have proven to have advantageous benefits such as increased surface area and lower ion diffusion distances.3

In this work we combine TiO2 and GeO2 in solution phase in two ratios, 2:1 and 5:1 in favour of TiO2. Titanium oxides have high working potentials, higher than graphite which is most commonly used today. TiO2 has previously shown excellent long life cyclability and has shown little structural strain during the lithiation/delithiation process.4 Germanium has a high theoretical capacity of 1384 mAh/g and high electrical conductivity however it is expensive for use as an anode.5 Previous reports have shown that by nano-structuring GeO2 into an inverse opal structure, it can behave like pure germanium during cycling beyond the initial reduction and lithitation cycles.6 By combining both materials, we were able to achieve high capacity values for both ratios, 3 times the capacity of titanium IOs on their own. Work is ongoing to investigate the optimal cost to benefit ratio of the TiO2/GeO2 composites. Initial capacity results showcase high capacity retention and voltage stability.

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Figure 1. (a) SEM image of a TiO2/GeO2 inverse opal (b) SEM image of TiO2/GeO2 IOs with EDX mapping overlay indicating position of titanium (green) and germanium (red). (c) and (d) Charge discharge profiles at 150 mA/g for the first 100 cycles for the 2:1 ratio and 5:1 ratio respectively.(e) Rate capability test for both ratios with specific currents ranging from 75 mA/g-450 mA/g.

Figure 1