A monocrystalline orthorhombic Na0.44Mn0.9Li0.1O2 cathode with outstanding stability and negligible structural strain for sodium-ion batteries

Abstract

The application of sodium ion batteries (SIBs) in future large-scale energy storage equipment has been facing great challenges due to their unstable cathode materials. Herein, a monocrystalline orthorhombic Na_0.44Mn_0.9Li_0.1O₂ cathode with high crystallinity has been designed and synthesized via a simple sol–gel method. The wide tunnel structure of Na_0.44Mn_0.9Li_0.1O₂ can not only adapt to structural strain in the electrochemical process, but also provide a rapid migration path for Na⁺. Furthermore, the introduction of Li promotes the transformation from trivalent manganese to tetravalent manganese so that the structural distortion caused by the Jahn–Teller effect is effectively alleviated. High Na⁺ mobility and low Na⁺ diffusion resistance are further evidence of its excellent rate performance. As a consequence, the Na_0.44Mn_0.9Li_0.1O₂ electrode delivers an initial discharge capacity of 111.71 mA h g⁻¹ at 1 C with an excellent retention of 80% after 900 cycles. So far, to the best of our knowledge, the as-synthesized Na_0.44Mn_0.9Li_0.1O₂ cathode shows the most excellent stability at 1 C. Such a material with superior stability and high rate performance is suggested to be one of the promising cathodes for SIBs.