Lithium manganese orthosilicate is an attractive cathode material providing high theoretical specific capacity (ca. 330 mAhg⁻¹) and reasonably high potential; however, it suffers from rapid capacity/voltage decay upon cycling. The origin of the poor cyclability is closely related to the structural instability of Li₂MnSiO₄ polymorphs, including layer exfoliation and pulverization during extended cycling. To address these problems, a gradient Na substitution method was developed to prepare Li₂MnSiO₄ cathode materials with a Na⁺-enriched surface pillaring layer and a moderately Na⁺-substituted core material. The results shows that the pillaring layer can effectively suppress the occurrence of layer exfoliation/collapse during delithiation/lithiation and prevent particle pulverization upon extended cycling. This corresponds to a high initial Coulombic efficiency (89.8%) and improved cyclability with a capacity retention (81.3%) after 200 cycles in Na-substituted materials. The gradient Na substitution process also results in improved Li⁺ diffusivity and rate performance in Na-substituted materials by shortening Lisingle bondLi distances. This gradient Na-doping method can be further applied to other structure-unstable polyanion-type cathode materials, such as phosphates, fluorophosphates and borates.