Facile synthesis of porous LiMn2O4 micro-/nano-hollow spheres with extremely excellent cycle stability as cathode of lithium-ion batteries

Small hollow nanostructures as a new morphology to improve stability of LiMn2O4cathodes in Li-ion batteries

Spinel LiMn₂O₄is a promising cathode material for lithium-ion batteries. However, bulk LiMn₂O₄commonly suffers from capacity fading due to the dissolution of Mn into the electrolyte during cycling. Moreover, bulk LiMn₂O₄exhibits a low Li⁺diffusion coefficient that limits the volume available to Li⁺storage. Herein, we report the synthesis of small hollow porous LiMn₂O₄nanostructures with a mean size of 51 nm exhibiting exposed (111) planes, assembled by nanoparticles of about 6 nm in size. The morphological features of these nanostructures ensure a large contact area between the material and the electrolyte, shorten the pathways for Li⁺diffusion and provide effective accommodation of the volume change during cycling. Therefore, these hollow nanostructures exhibit improved discharge capacity retention (nearly 82% after 200 cycles) and a greater Li⁺diffusion coefficient (3.46 × 10^-7cm s^-1) compared with that of bulk LiMn₂O_4.

Facile Controlled Synthesis of Spinel LiMn2O4 Porous Microspheres as Cathode Material for Lithium Ion Batteries

Although the electrochemical properties of porous LiMn₂O₄ microspheres are usually improved compared to those of irregular LiMn₂O₄ particles, the effects of the different synthesis conditions on the preparation of the porous LiMn₂O₄ microspheres are rarely discussed in detail. In the present work, porous LiMn₂O₄ microspheres were successfully synthesized by using molten LiOH and porous Mn₂O₃ spheres as a template. Multiple factors were considered in the preparation process, including reagent concentration, pH, adding mode, heating time, etc. The morphology of the MnCO₃ template was crucial for the preparation of porous LiMn₂O₄ microspheres and it was mainly affected by the concentration of reactants and the pH value of the solution during the precipitation process. During the lithiation of Mn₂O₃ microspheres, the heating temperature and the ratio between Mn₂O₃ and lithium salt were the most significant variables in terms of control over the morphology and purity of the LiMn₂O₄ microspheres. Furthermore, we demonstrated that the porous LiMn₂O₄ microspheres presented better rate capability and cyclability compared to commercial LiMn₂O₄ powder as cathode materials for lithium-ion batteries (LIBs). This study not only highlights the shape-controllable synthesis of LiMn₂O₄ microspheres as promising cathode materials, but also provides some useful guidance for the synthesis of porous LiMn₂O₄ microspheres and other LIB' electrode materials.