Novel Nanodisperse Composite Cathode for Rechargeable Lithium/Polymer Batteries

Abstract

A novel approach to the design of a composite positive electrode for lithium/polymer cells based on a polyethylene oxide (PEO) polymer, manganese (II), and lithium hydroxide has been discovered. A chemical reaction leading to a stable suspension occurs when the precursor salts are added directly to a polymer solution. The electrode film is cast directly and then vacuum‐dried with no calcination step. The film is amorphous as‐prepared and has been named the nanodisperse composite cathode, or NCC. Film characterization with x‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy indicates that the Mn (II) has been oxidized to Mn (IV), which forms a complex with the PEO. This leads to highly disperse Mn sites within the polymer matrix and highly mobile Li ions within the PEO. Cells have been assembled with NCC films, electrolyte and lithium metal, and cycled at 85 to 105°C at current densities of 0.2 mA/cm2 between the voltage limits of 3.5 and 2.0 V. Discharge capacities as high as 340 mAh/g‐cathode film have been achieved on the first half‐cycle. The discharge capacity declines consistently during a formation process to steady values as high as 50 mAh/g‐cathode. This cathode capacity is equivalent to an active material capacity of 150 mAh/g in a composite cathode at a loading of 30 weight percent. The synthesis process for the NCC is simple, should be relatively easy to scale up, and should lead to an extremely useful composite cathode for a lithium polymer battery.