A first principles investigation of new cathode materials for advanced lithium batteries

First principles calculations on the crystal and electronic structure of a layered Li(Ni_1/3Mn_1/3M_1/3)O₂ (M = Al, Ti, Cr, Fe and Mo) were undertaken as part of a search for new positive electrode materials for advanced lithium ion batteries. The formal charge of Ni, Mn and M (Ti and Mo) were estimated to be +2, +3 and +4, respectively, from electronic structures and interatomic distances. In the cases of the Al, Cr and Fe substitution, the compounds had trivalent M and tetravalent Mn ions. The solid-state redox reactions of Li(Ni_1/3Mn_1/3M_1/3)O₂ were calculated assuming a Li deinsertion scheme, and the reactions were shown to be Ni²⁺/Ni³⁺/Ni⁴⁺ and M³⁺/M⁴⁺ for the Cr and Fe substitution. Al substitution will lead to higher voltages, as fixed 3+ valence of Al forces more electron exchange with oxygen. The cases of Ti and Mo substitution, Ti and Ni ions do not participate in the redox reactions over the entire range, respectively. The substitutive cation-oxygen bonding has a more covalent character, when the redox energy of Ni is lowered, resulting in an increase in potential. As described above, the voltage profiles are very different because the types of metals are different and participate in electrochemical reactions according to the substituted.