Facile Synthesis of Nanosized Lithium-Ion-Conducting Solid Electrolyte Li1.4Al0.4Ti1.6(PO4)3 and Its Mechanical Nanocomposites with LiMn2O4 for Enhanced Cyclic Performance in Lithium Ion Batteries.

Nanoparticles of fast lithium-ion-conducting solid electrolyte Li1.4Al0.4Ti1.6(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).