Thin-film Li-ion batteries produced by precise thickness control atomic layer deposition (ALD) method are promising, safe, and high-energy density sources for miniature devices. The paper presents a detailed analysis of the multilayer thin film cathode for microbatteries. Structures were obtained by combining several technological parameters to increase capacity, uniformity, and lifetime. The protective function of a nano-sized coating was demonstrated. The influence of coating application on cathode capacity was explained. The studied structure consists of Ni-rich cathode layer modified with an amorphous Li-Ta-O functional layer on a steel substrate with a Cr coating. The cathode and the functional layer were obtained by the ALD multilayer approach followed by heat treatment at 800 °C for a minute. According to XPS and TEM data, the composition of the cathode after annealing was LiNi_0.7Co_0.3O₂ well-defined structure without separation into Ni-rich and Co-rich layers, with texturing of crystallite pillars and with the absence of Fe. The Li-Ta-O films have a slight chemical composition gradient from Li₃Ta_1.2O₄ on the surface to Ta_1.7O₅ in bulk. The electrochemical characterization showed that combining the functional layer and cathode heat treatment preserves the electrochemical capacity (32 µAh·µm⁻¹·cm⁻²) and increases Coulomb efficiency.