Li Insertion into Li[sub 4]Ti[sub 5]O[sub 12] (Spinel)

(spinel) materials were prepared with Brunauer-Emmett-Teller surface areas ranging from 1.3 to 196 m2/g. The corresponding average particle sizes varied from ca. 1 μm to ca. 9 nm. Twenty-five different materials were tested as Li insertion hosts in thin-film electrodes (2-4 μm) made from a pure spinel. Trace amounts of anatase in were conveniently determined by cyclic voltammetry of Li insertion. Electrodes from nanocrystalline exhibited excellent activity towards Li insertion, even at charging rates as high as 250C. The charge capability at 50-250C was proportional to the logarithm of surface area for coarse particles (surface areas smaller than ca. 20 m2/g). With increasing charge/discharge rates, a narrowing plateau in performance was observed for materials with surface areas between ca. 20 to 100 m2/g. These materials can be charged/discharged nearly to the nominal capacity of (175 mAh/g) within a wide range of the rates. Very small particles exhibit a growing decrease of charge capability at 50-250C. The Li-diffusion coefficients, calculated from chronoamperometry, decrease by orders of magnitude if the average particle size drops from ca. 1 μm to ca. 9 nm. However, the sluggish transport in small particles is compensated by the increase in active electrode area. Materials having surface areas larger than ca. 100 m2/g also tend to show increased charge irreversibility. This could be caused by parasitic cathodic reactions, due to enhanced adsorption of reducible impurities (humidity) or the quality of the spinel crystalline lattice itself. The optimum performance of thin-film electrodes is achieved, if the parent materials have surface areas between ca. 20 to 110 m2/g, with the maximum peak at 100 m2/g. © 2003 The Electrochemical Society. All rights reserved.