Lessons Using an Electrochemical Method to Produce Lithium Manganese Oxide Cathodes for Lithium-Ion Batteries

Abstract

Lithium manganese oxide (LMO) has been a well-studied Li-ion battery cathode material for for many years. It offers high thermal stability for high-temperature battery applications and a prolonged cycle life compared to other materials. LMO also has an acceptably high energy density from a naturally abundant, inexpensive, and environmentally benign material, i.e. manganese (Mn). The cathodes for LIBs are conventionally synthesized via solid-state reaction techniques, which require harsh and complex conditions including high temperature (> 700oC) and high pressure. The resulting powders are incorporated into a slurry that is cast onto a current collector using a binder, additives, and solvent. Though this results in high-performing electrodes, it also usually increases the production cost. Another approach that is gaining traction to make LMOs is electrodeposition. Electrodeposition can allow for the direct synthesis of the active material on the current collector without using any binder or additives. Using electrodeposition not only could eliminate the mass and volume of inactive material but also reduce the cost of electrode fabrication. It also can facilitate recycling by depositing the active material from lower purity, material-digested streams.A few reports in the literature have discussed the electrochemical preparation of LMO cathode from the following steps: electrodeposition of manganese oxide (s) (MnxOy) onto a substrate followed by chemical lithiation and heat treatment of MnxOy [1,2]. Although a few reports showed the active materials with reasonable capacity, it is presently unknown what LiMnxOy phase or phases are active and which MnxOy is responsible. However, without sufficient physicochemical investigation, multiple works have postulated that the LMO is created from crystalline MnO2 or Mn3O4. It is also not known what the typical active phase yield is or what physical structures or conditions are responsible for increased capacity. If electrodeposition-to-LMO is to become a viable commercial pathway, a rational understanding of the solid-state chemistry for the LMO formation is needed.This talk will discuss the deposition and lithiation of multiple manganese oxide phases – linking the chemistry and morphology of the surface features to their charge/discharge properties. It will be shown that traditional crystalline phases are not responsible for the formation of LMOs. It will also be shown that the LMOs do not fully delithiate during charging. Lastly, the precise morphology of the active phase – separated out through new processing approaches – will be identified. The composition, structure, and crystallinity of the Mn oxides and LMOs were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The resulting LMO electrodes were incorporated into coin cells, cycled – achieving a capacity of 261 mAh g-1, and post-characterized.References J. Rana, M. Stan, R. Kloepsch, J. Li, G. Schumacher, E. Welter, I. Zizak, J. Banhart, and M. Winter, Adv. Energy Mater., 4, 1300998 (2014).Z. Quan, S. Ohguchi, M. Kawase, H. Tanimura, and N. Sonoyama, J. Power Sources, 244, 375 (2013).