No abstract

Prediction of the birefringence values of borate is very essential for developing new optical materials in UV range. In this paper, the birefringence values of five lead borates, Pb

The high-voltage spinel LiNi 0.5 Mn 1.5 O 4 cathode material suffers from the rapid degradation of electrochemical cycling performance at elevated temperatures, which prevents its successful commercialization. Herein, we show that coating the surface of this material with Ta 2 O 5 , which has high resistance against hydrofluoric acid (HF) attack, is an effective way to improve its electrochemical cycling performance. A Ta 2 O 5 -coated LiNi 0.5 Mn 1.5 O 4 half-cell shows a capacity retention of ∼93% and a Coulombic efficiency of ∼98% after 100 cycles at 55 °C, compared to the corresponding values of ∼76% and ∼95% measured for the bare LiNi 0.5 Mn 1.5 O 4 half-cell. The detailed structural analysis of the Ta 2 O 5 -coated LiNi 0.5 Mn 1.5 O 4 shows that a small amount of Ta 5+ ions diffuse into the 16c site on the cathode surface during the coating process, as directly observed by Cs corrected scanning transmission electron microscopy. The modification of the LiNi 0.5 Mn 1.5 O 4 surface with Ta 5+ , together with the residual Ta 2 O 5 coating, stabilizes the surface structure during cycling, leading to reduced Ni and Mn dissolution as well as formation of the solid electrolyte interface (SEI). In contrast, LiNi 0.5 Mn 1.5 O 4 coated with HF scavengers, such as Al 2 O 3 , shows only limited improvement in cycling performance after prolonged cycling at 55 °C, due to the consumption of the surface coating by reaction with HF, which leaves LiNi 0.5 Mn 1.5 MnO 4 unprotected against HF attack. KEYWORDS: lithium ion batteries, LiNi 0.5 Mn 1.5 O 4 , coating, Ta 2 O 5 , scanning transmission electron microscopy (STEM)