The Influence of Ultrathin Amorphous ALD Alumina and Titania on the Rate Capability of Anatase TiO2 and LiMn2O4 Lithium Ion Battery Electrodes

Interface modification is a heavily investigated method of extending the lifetime of lithium ion batteries. While many studies have explored the effect of interface coating on the lifetime, the rate capability is often overlooked. In this study, the authors investigated the influence of ultrathin (< 10 nm) atomic layer deposition (ALD) coatings of amorphous Al2O3 and amorphous TiO2. It is found that, on thin-film anatase TiO2, the rate capability is unaffected by an amorphous TiO2 coating since it does not pose an additional impedance on the system, while Al2O3 coatings are detrimental for the rate performance due to the 1.5 x 10(12) cm resistivity toward lithium ions. A thicker than 2 nm ALD Al2O3 film is found to block lithium transfer completely, resulting in a purely capacitive film. Solvent oxidation is studied on thin-film LiMn2O4. The authors demonstrate that both coatings can partially solve the solvent decomposition. However, the kinetic bottleneck posed by 1 nm Al2O3 is still greater than the uncoated LiMn2O4, leading to worsened rate capability. ALD TiO2 on the other hand can prevent most of the solvent decomposition, resulting in smoother electrodes. The absence of the decomposition layer and lithium conducting properties of the ALD TiO2 films results in an improved rate capability for the ALD TiO2 coated electrode.