Impedance Studies of the Thin Film LiMn[sub 2]O[sub 4]/Electrolyte Interface

Impedance measurements at thin-film electrodes in have been used to identify the spontaneous room temperature formation of at the interface at voltages of 3.7 and higher. The impedance of the films exhibited two time constants, at about 14 kHz and 60 to 200 Hz. The high frequency loop is dependent on film morphology and was attributed to the substrate/oxide interface. The low frequency behavior was dependent on both state-of-charge (SOC) and time at a given SOC. At full charge the impedance in this electrolyte was stable at room temperature over several days. At high lithium contents, film open-circuit voltage and impedance tended to grow logarithmically with time, with lower rates for lower content in the film. The increased impedance was removed by oxidation of the film to 4.5 V vs . The observations are consistent with a reversible disproportionation of part of the into and a lithium-deficient spinel. With extended constant current cycling part of the degrades to the and the process is no longer reversible. © 2001 The Electrochemical Society. All rights reserved.