Facile Synthesis of Nanosized Lithium-Ion-Conducting Solid Electrolyte Li_1.4Al_0.4Ti_1.6(PO₄)₃ and Its Mechanical Nanocomposites with LiMn₂O₄ for Enhanced Cyclic Performance in Lithium Ion Batteries

Abstract

Nanoparticles of fast lithium-ion-conducting solid electrolyte Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) are prepared by a modified citric-acid-assisted sol-gel method that involves a two-step heat treatment in which the dry gel is calcined first in argon and then in air. The obtained LATP exhibits smaller particle size (down to 40 nm) with a narrower size distribution and less aggregation than LATP prepared by a conventional sol-gel method because of a polymeric network that preserves during LATP crystallization. It has a high relative density of 97.0% and a high room-temperature conductivity of 5.9 × 10^-4 S cm^-1. The as-prepared superfine LATP is further used to composite with a spinel LiMn₂O₄ cathode in lithium ion batteries by simple grinding. This noncoating speckled layer over the LiMn₂O₄ particle surface has a minimal effect on the electronic conductivity of the electrode while offering excellent ionic conductivity. The cycling stability and rate capability of LiMn₂O₄ are greatly improved at both ambient and elevated temperatures. After 100 cycles at 25 and 55 °C, the capacity retentions are 96.0% and 89.0%, respectively, considerably higher than the values of pristine LiMn₂O₄ (61.0% at 25 °C; 51.5% at 55 °C) and mechanical LiMn₂O₄ composite with LATP made by a conventional sol-gel method (85.0% at 25 °C; 71.4% at 55 °C).