Inheritance of spherical morphology and optimization of assembled structures during preparation of LiMnPO4 cathodes for high electrochemical properties

Abstract

Microspherical structures of cathodes facilitate high tap densities and good cycling stabilities, but their inferior rate capabilities due to low surface permeability for the electrolyte, remains a hurdle. An effective strategy to address this issue would be the optimization of the assembled microspheres structure. In this work, LiMnPO₄ hollow microspheres assembled by radially aligned nanoprisms with fully exposed (010) facets are prepared by the solvothermal method using Li₃PO₄ as the self-sacrificed templates to improve the rate capability. By simply varying ammonium based salts during the solvothermal reaction, the nanoprisms-randomly assembled and the wedges-radially assembled microspheres are also fabricated. A plausible formation mechanism is carefully proposed. When the three kinds of microspheres are evaluated by charge/discharge measurements, their electrochemical properties are highly dependent on the variation of the assembled structures. In particular, microspheres with radially aligned nanoprisms exhibit high rate capabilities, delivering discharge capacities of 125 mA h g⁻¹ at 1C and 113 mA h g⁻¹ at 2C. These results originate from the unique structure of the microspheres, which not only ensures rapid electrolyte penetration to the interior of the shells due to the radial pore channels, but also guarantees fast Li⁺ insertion into the nanoprisms owing to their fully exposed (010) facets.