The Influence of Ultrathin Amorphous ALD Alumina and Titania on the Rate Capability of Anatase TiO_2 and LiMn_2O_4 Lithium Ion Battery Electrodes

摘要

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 Al_2O_3 and amorphous TiO_2. It is found that, on thin-film anatase TiO_2, the rate capability is unaffected by an amorphous TiO_2 coating since it does not pose an additional impedance on the system, while Al_2O_3 coatings are detrimental for the rate performance due to the 1.5 × 10~(12) Ω cm resistivity toward lithium ions. A thicker than 2 nm ALD Al_2O_3 film is found to block lithium transfer completely, resulting in a purely capacitive film. Solvent oxidation is studied on thin-film LiMn_2O_4. The authors demonstrate that both coatings can partially solve the solvent decomposition. However, the kinetic bottleneck posed by 1 nm Al_2O_3 is still greater than the uncoated LiMn_2O_4, leading to worsened rate capability. ALD TiO_2 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 TiO_2 films results in an improved rate capability for the ALD TiO_2 coated electrode.