Synthesis and enhanced electrochemical performance of LiNi0.5Mn1.5O4 materials with porous hierarchical microsphere structure by a surfactant-assisted method

LiNi0.5Mn1.5O4 cathode materials with porous hierarchical microsphere structure are prepared by surfactant-assisted coprecipitation-hydrothermal method followed by a two-step high-temperature calcination process. The effects of different surfactants (cationic CTAB, anionic SDBS, non-ionic PVP) on the crystalline structure, morphology and electrochemical properties of LiNi0.5Mn1.5O4 materials are systematically investigated. XRD results show that the addition of surfactants does not change the crystal structure but improves the crystallinity of LiNi0.5Mn1.5O4 materials. SEM shows that LiNi0.5Mn1.5O4 materials synthesized by the surfactant-assisted method exhibit hierarchical microsphere structure composed of truncated octahedral primary particles with reduced agglomeration, in stark contrast to the irregular structure and severe agglomeration of pristine sample. Among them, the LiNi0.5Mn1.5O4 material synthesized with CTAB exhibits porous hollow structure with the smallest primary particle size and uniform distribution. It is noteworthy that the primary particles of LiNi0.5Mn1.5O4 samples synthesized with different surfactants possess different surface planes. More specifically, LNMO–SDBS and LNMO–PVP particles display {111} and {100} surfaces, while LNMO–CTAB particle possesses extra {110} surfaces. Electrochemical results show that LNMO–CTAB sample exhibits the optimal rate performance, while LNMO–SDBS and LNMO–PVP samples show better cycling performance, which can be mainly attributed to the different morphologies, including the size, distribution and crystalline orientation of surface planes of primary particle, as well as secondary agglomeration degree.