Long Cycle Life, Highly Ordered SnO₂/GeO₂ Nanocomposite Inverse Opal Anode Materials for Li-Ion Batteries

Nanocomposite SnO₂/GeO₂ inverse opals (IOs) provide long cycle life with excellent capacity retention when tested as anode materials for Li-ion batteries. It is demonstrated that the electrochemical performance of SnO₂ is significantly improved via the engineering of a nanocomposite of nanoparticles of tetragonal SnO₂ and hexagonal GeO₂ into a highly ordered, porous inverse opal architecture. By introducing a GeO₂ component, the SnO₂/GeO₂ IOs demonstrate stepwise lithium storage processes to improve cycling stability by mitigating capacity fade from material volume variations in a material that already improves cycling repose by its architecture. This results in higher capacity and better capacity retention. SnO₂/GeO₂ IOs achieve a reversible capacity of ≈880 and 690 mAh g⁻¹ after the 50th and 250th cycles, respectively, at a specific current of 150 mA g⁻¹. SnO₂/GeO₂ IOs are capable of delivering high specific capacities (average value of ≈570 mAh g⁻¹) with stable capacity retention over 750 cycles at a specific current of 450 mA g⁻¹. Tailoring the composition of nanocomposite metal-oxide anodes to exploit the combination of conversion and alloying mechanisms enables stable binder-free Li-ion anodes. Nanoscaling the walls of the ordered macroporous structure provides efficient reversible redox lithiation mechanisms involving the oxides of Sn and Ge, which are simpler to prepare.