Although lithium ion batteries are the most promising candidates for plug-in hybrid electric vehicles, the use of cobalt (Co) in cathode materials yields a high battery cost. Mixed transition metal oxides have been considered to replace the standard LiCoO2 cathode materials, but these variations have negative impacts on performance.
Marca M. Doeff and James D. Wilcox of Berkeley Lab have developed a mixed transition metal oxide formulation using aluminum (Al) that allows the amount of Co to be reduced by more than one-half, compared to the standard Li[Ni1/3Co1/3Mn1/3]O2 formulation, and still achieve the power and energy density required for plug-in hybrid vehicles. The Berkeley Lab formulation yields up to three times the rate capability of variations without Al.
This invention also includes a process of manufacturing a layered oxide material with greater homogeneity than typically created, which contributes to its improved performance. A decrease in lithium ion mobility would be expected for layered oxides containing Al, because Al ions act like traps. However, the Al substitution creates a physical change in the layering of the structure that, to a large extent, appears to counter the expected trapping effect and allow better Li ion diffusion.
In addition, because Al is not electroactive, its addition prohibits the removal of all the lithium at the top of charge. This could potentially provide overcharge protection for large battery systems.