Army

Li-ion battery cathodes

Lithium manganese oxide spinel with cobalt and chlorine offers low-toxicity, comparable capacity, and low-cost

Energy

Lithium-Ion (Li-ion) batteries are widely used because of their high-specific energy, high-energy density, and excellent charge retention. Many Li-ion batteries utilize a manganese dioxide (MnO2) cathode which has high-energy density and low material cost.

Unfortunately, MnO2 is subject to degradation which causes capacity fading. This is due to mechanical (insertion/extraction of Li in the cathode lattice) stress-strain induced fractures on the MnO2 crystal structures during cycling. The elevated temperature may also lead to cathode degradation.  All of this leads to limited cycle life and limited rate capability for lithium electrochemical systems. An additional limiting factor for lithium manganese-based materials is the time required to process the raw materials and synthesize the desired product. Conventional methods require multiple mixing, grinding and calcining steps, which take days to complete.

Army researchers have made excellent steps in an improvement of lithium manganese materials with a charge transfer catalyst coated and chlorine modified lithium manganese compound. The immediate benefits are improved rate capability, under-voltage tolerance, and high-rate durability. These benefits are accomplished while avoiding problems associated with loss of reversibility and without suffering from the limitations associated with rigid current limits and rigid stoichiometry control. More specifically, this material shows:

  • Full reversibility between 4.5 V and 2.0 V
  • Low-charge/discharge overpotential between 4.5 V and 3.5 V
  • A high-specific capacity of 240 mAh/g of active material
  • High-rate charge and discharge

Furthermore, the relatively low temperatures of the preparation method of the material afford better process control, and the fabrication time is significantly lower than that of the conventional lithium manganese-based materials.

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