Morphology-controlled two-step synthesis and electrochemical studies on hierarchically structured LiCoPO4

• LiCoPO4 micro- and nanocrystals were synthesized by novel two-step approach.
• Unique morphologies obtained by additive assisted microwave hydrothermal method.
• Investigation by XRD, SEM and electrochemical GCPL and IS techniques.
• Flower-like particles show enhanced discharge performance.
• Diffusion coefficients of lithiated and delithiated phase differ by factor of 100.

Olivine structured LiCoPO4 was synthesized by a novel two-step process involving the hydrothermal synthesis of recently discovered metastable tetragonal LiCoPO4tetra and its transformation to the olivine-like phase. The transformation process does not change the size and shape of the particles so that they can be tailored by appropriate choice of the synthesis parameters and addition of organic compounds in the first production step. Our results demonstrate a clear effect of the particle shape on the electrochemical performance. The material shows discharge capacities up to 107 mAh/g for flower-like secondary particles synthesized under the mediation of citric acid. Electrochemical impedance spectroscopy reveals a strong surface reaction during the delithiation process which is key for the capacity fade of LiCoPO4 battery materials and a difference of three orders of magnitude in the diffusion coefficient of lithiated and delithiated species is observed.

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