Single Nanorod Devices for Battery Diagnostics: A Case Study on LiMn2O4

This paper presents single nanostructure devices as a powerful new diagnostic tool for batteries with LiMn2O4 nanorod materials as an example. LiMn2O4 and Al-doped LiMn2O4 nanorods were synthesized by a two-step method that combines hydrothermal synthesis of β-MnO2 nanorods and a solid state reaction to convert them to LiMn2O4 nanorods. λ-MnO2 nanorods were also prepared by acid treatment of LiMn2O4 nanorods. The effect of electrolyte etching on these LiMn2O4-related nanorods is investigated by both SEM and single-nanorod transport measurement, and this is the first time that the transport properties of this material have been studied at the level of an individual single-crystalline particle. Experiments show that Al dopants reduce the dissolution of Mn3+ ions significantly and make the LiAl0.1Mn1.9O4 nanorods much more stable than LiMn2O4 against electrolyte etching, which is reflected by the magnification of both size shrinkage and conductance decrease. These results correlate well with the better cycling performance of Al-doped LiMn2O4 in our Li-ion battery tests: LiAl0.1Mn1.9O4 nanorods achieve 96% capacity retention after 100 cycles at 1C rate at room temperature, and 80% at 60 °C, whereas LiMn2O4 shows worse retention of 91% at room temperature, and 69% at 60 °C. Moreover, temperature-dependent I−V measurements indicate that the sharp electronic resistance increase due to charge ordering transition at 290 K does not appear in our LiMn2O4 nanorod samples, suggesting good battery performance at low temperature.