Design and synthesis of high-energy-density heterostructure Na0.7MnO2–Li4Mn5O12 cathode material for advanced lithium batteries

Abstract

The heterostructures, xNa_0.7MnO₂–yLi₄Mn₅O₁₂(0 < x < 1, 0 < y ≤ 1), were synthesized by a solid-phase method. X-Ray diffraction (XRD) analyses revealed that the as-prepared samples were heterostructures Na_0.7MnO₂ and Li₄Mn₅O₁₂. Electron microscopy was used to study the lattice fingerprint area of 0.6Na_0.7MnO₂–0.4Li₄Mn₅O₁₂ that showed (111) crystal surface of Li₄Mn₅O₁₂ and (002) crystal surface of Na_0.7MnO₂. With different molar ratios of lithium and sodium, Li₄Mn₅O₁₂ and Na_0.7MnO₂ in the formed heterostructure will change accordingly, during the synthesis process. The XPS data also showed that Mn³⁺/Mn⁴⁺ in the materials presented different ratios. The heterostructure, 0.6Na_0.7MnO₂–0.4Li₄Mn₅O₁₂, exhibits superior high-rate capability and excellent cycle performance. The rate discharge capacity of 0.6Na_0.7MnO₂–0.4Li₄Mn₅O₁₂ was maintained at 163.25 mA h g⁻¹ at 500 mA g⁻¹. When cycled at 100 mA g⁻¹, the discharge capacity was maintained at 189.80 mA h g⁻¹ after 50 cycles. The construction of heterostructure can take the advantage of the high capacity of the layered structure of Na_0.7MnO₂ and the stable spinel structure of Li₄Mn₅O₁₂, which can form a synergistic effect and improve the electrochemical performance of cathode materials.