Direct Solution-calcination synthesis of residual Li-free layered cathode materials for Li-ion batteries

[Display omitted] •Layered cathode material is successfully synthesized via direct solution calcination.•Residual compounds are successfully suppressed at solution-calcined LiCoO2 cathodes.•Solution-calcined cathodes deliver improved cycle performance and rate capability.•Phase evolution mechanism during calcination is elucidated via in-situ XRD analysis. Layered cathode materials have advanced existing Li-ion batteries by improving cell voltage and enabling facile charge transfer. Yet diverse synthetic issues such as particle inhomogeneity, Li residues, complicated processes, and large micron-scale particle sizes, need to be addressed. We report a direct solution-calcination strategy for the simple and scalable synthesis of layered cathode materials (i.e. LiCoO2) for Li-ion batteries. Polyvinylpyrrolidone (PVP) as functional agent is introduced to intimately bind and uniformize the metal precursors, thereby sufficiently eliminating surface Li residues and forming a uniform particle distribution. Compared with commercial LCO, solution-calcined LCO exhibits improved cycling stability and rate capability with suppressed phase transition. The structural phase evolution mechanism for solution-calcination is investigated using in-situ X-ray diffraction analysis. Overall, our research suggests a simple and versatile strategy for the synthesis of cathode materials; the proposed method is effective and avoids complicated synthesis steps and the formation of unwanted residual lithium compounds.