  Cobalt is used in Li-ion batteries, but it is expensive and could be replaced
by nickel to deliver better performance at a lower cost. With this motivation,
we discuss how the character of redox orbitals of LiNiO$_2$ can be ascertained
through x-ray Compton scattering measurements combined with parallel
first-principles simulations. Our analysis reveals the nature of hole states in
Li-doped NiO resulting from the hybridization of O 2$p$ and Ni 3$d$ orbitals.
Our study also gives insight into the ferromagnetic ground state and provides a
pathway toward the rational design of next-generation battery materials.
