Scalable, low-cost synthesis of high volumetric capacity LiMn0.5Fe0.5PO4 cathode for lithium-ion batteries†
Abstract
LiMnxFe1−xPO4 (LMFP) cathodes in lithium-ion batteries (LIBs) can improve the energy density by up to 15% compared to LiFePO4. However, the smaller primary particle size needed to overcome sluggish Mn2+/3+ redox kinetics results in lower electrode density, limiting the practical energy density of LMFP cells. We present here a scalable, wastewater-free synthesis of high energy density LMFP cathodes by employing a spinel LiMnFeO4 precursor obtained by a facile solid-state reaction. The LMFP synthesized with LiMnFeO4, referred to as S-LMFP, has uniform secondary particles formed via spray drying and greater tap density than LMFP synthesized with a conventional co-precipitation route, referred to as P-LMFP. While S-LMFP offers a lower specific capacity (147 mA h g−1) than P-LMFP (153 mA h g−1) at C/5 rate due to inferior Li+ diffusion kinetics during Mn2+/3+ redox, it exhibits a ∼15% higher electrode-level energy density due to its exceptional electrode packing density (2.6 g cm−3). Rate capability testing of LMFP cathodes with different electrode densities reveals that at low rates (<1C), electrode density is more important than specific capacity in determining the energy density of LMFP cathodes. Overall, this work highlights the complex tradeoff between Mn2+/3+ redox kinetics and electrode density, which dictates the practical energy density of LMFP cathodes. With further optimization of composition, particle size, and synthesis conditions, LMFP synthesized from LiMnFeO4 is promising to improve the energy density of the next generation of LIBs.