High-capacity and high-performance rechargeable batteries containing a cathode material layer having an improved surface roughness is provided. A cathode material layer is provided in which at least an upper portion of the cathode material layer is composed of nanoparticles (i.e., particles having a particle size less than 0.1 μm). In some embodiments, a lower (or base) portion of the cathode material layer is composed of particles whose particle size is greater than the nanoparticles that form the upper portion of the cathode material layer. In other embodiments, the entirety of the cathode material layer is composed of the nanoparticles. In either embodiment, a conformal layer of a dielectric material can be disposed on a topmost surface of the upper portion of the cathode material layer. The presence of the conformal layer of dielectric material can further improve the smoothness of the cathode material layer.