Morphology-controlled microwave-assisted solvothermal synthesis of high-performance LiCoPO4 as a high-voltage cathode material for Li-ion batteries

• Published in: Journal of power sources Vol. 342; pp. 214 - 223
• Main Authors: Ludwig, Jennifer, Marino, Cyril, Haering, Dominik, Stinner, Christoph, Gasteiger, Hubert A., Nilges, Tom
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 28-02-2017
• Subjects: High-voltage cathode; Lithium cobalt phosphate; Lithium-ion batteries; Microwave synthesis; Morphology control; Solvothermal synthesis; Lithium-ion batteries; Lithium cobalt phosphate; Microwave synthesis; Morphology control; High-voltage cathode; Solvothermal synthesis
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2016.12.059

High-performance particles of the high-voltage cathode material LiCoPO4 for Li-ion batteries are synthesized by a simple and rapid one-step microwave-assisted solvothermal route at moderate temperatures (250 °C). Using a variety of water/alcohol 1:1 (v:v) solvent mixtures, including ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TTEG), polyethylene glycol 400 (PEG), and benzyl alcohol (BA), the focus of the study is set on optimizing the electrochemical performance of the material by controlling the particle size and morphology. Scanning electron microscopy studies reveal a strong influence of the co-solvent on the particle size and morphology, resulting in the formation of variations between square, rhombic and hexagonal platelets. According to selected area electron diffraction experiments, the smallest crystal dimension is in the [010] direction for all materials, which is along the lithium diffusion pathways of the olivine crystal structure. The anisotropic crystal orientations with enhanced Li-ion diffusion properties result in high initial discharge capacities and gravimetric energy densities (up to 141 mAh g−1 at 0.1 C and 677 Wh kg−1 for LiCoPO4 obtained from TEG), excellent rate capabilities, and cycle life for 20 cycles.
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•Preparation of LiCoPO4 platelets by simple microwave-assisted solvothermal process.•Influence of solvent on morphology and electrochemical performance is investigated.•Co-solvent plays a key role in tuning the size, shape and orientation of crystals.•LiCoPO4 from triethylene glycol co-solvent shows best electrochemical performance.•Discharge capacity of 141 mAh g−1 and energy density of 677 Wh kg−1 are reached.