Changes in Mn3+/Mn4+ ratio, resistance values in electrochemical impedance spectra, and rate capability with increased lithium content in spinel LixMn2O4
Abstract Spinel-structured Li x Mn 2 O 4 (x = 1.0, 1.02, 1.04, and 1.06) cathode materials have been synthesized by a solid-state method using Mn 3 O 4 and Li 2 CO 3 as raw materials. The Mn 4+ content gradually decreases from 84.80% to 82.62% and then increases from 82.62% to 88.98%, when the Li content increases from 1.00 to 1.06. The rate capability of the LiMn 2 O 4 samples evidently increases as the lithium content increases from 1.00 to 1.06. Electrochemical impedance spectroscopy results indicate that the R ct values gradually increase from 58.33 Ω to 133.1 Ω and then decrease from 133.1 Ω to 68.79 Ω when the Li concentration increases from 1.00 to 1.06. The R sf values also increase from 25.67 Ω to 37.84 Ω and then decrease from 37.84 Ω to 16.69 Ω, when the Li concentration increases from 1.00 to 1.06. These changes in Mn 4+ content, R sf , and R ct with the increase in Li content are related to changes in the second phase in LiMn 2 O 4 .