 Birnessite MnO2, a hydrated layered manganese dioxide with a layered structure, is a promising candidate for sodium-ion batteries because of a significant interlayer distance for the reversible insertion of sodium ions. This work proposes to improve the electrochemical performance of layered manganese dioxide by metal cation doping. Nickel-doped layered MnO2 (0.05–0.15 wt%) prepared by a sol–gel method using a chelate agent of fumaric acid showed a gradual increase of interlayer distance with an increase of Ni-doping amount. Moreover, ex situ XRD results during the first cycle confirmed a stabilization of the layered structure during the sodium insertion. During the charge–discharge test, the initial capacity of 15% Ni layered MnO2 was 140 mAh/g, with small capacity fade over 20 cycles.