Influence of Morphology - LFP/C Nanoparticle Composites and Their Fast-Charging Performance

摘要

The scope of our research project is the optimization and enhancement of cathode materials for fast-charging applications, focusing on the well-known cathode material lithium iron phosphate (LFP). It is one of the most promising cathode materials for these applications. It is inexpensive, non-toxic and chemically as well as thermally stable with a reasonable specific capacity. Even though LFP is already used for commercial batteries, there is still a need to improve its properties. Its main drawbacks are low ionic and electronic conductivity. The key factor to enhance the electrochemical performance of LFP materials is the reduction of the lithium-ion diffusion length. LFP shows anisotropic lithium-ion diffusion, which takes place exclusively along its crystallographic b-axis. So far, only a few studies compared LFP materials with different particle morphologies. In these the LFP nanomaterials differ in morphology but also in particle size, so it is not surprising that the materials with the smallest dimension along the b-axis show the best electrochemical results. In our contribution, we present a study of the fast-charging ability LFP/C nanoparticle composites as a function of particle morphology and size. Throughout this variation, particle dimensions along the b-axis are kept in a comparable range. In addition, the influence of synthesis parameters and impurities are presented. For this purpose, we synthesized monodisperse LFP nanoparticles via a solvothermal approach. A thin carbon shell smaller than 10 nm was produced around each LFP particle by a resorcinol-formaldehyde resin coating and subsequent calcination. Electrochemical characterization focusing on fast-charging tests of all materials are carried out in commercial standardized electrochemical test cells (PAT-Cells, EL CELL) to reduce variation by cell test assembly to a minimum.