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

Abstract

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 2 O 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 2 O 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 2 O 3 film is found to block lithium transfer completely, resulting in a purely capacitive film. Solvent oxidation is studied on thin‐film LiMn 2 O 4 . The authors demonstrate that both coatings can partially solve the solvent decomposition. However, the kinetic bottleneck posed by 1 nm Al 2 O 3 is still greater than the uncoated LiMn 2 O 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.