Harnessing the kinetics of LiMn0.5Fe0.5PO4 in energy-dense layered-olivine blend cathodes for lithium-ion batteries

Abstract

Layered-olivine blends have been a topic of recent commercial and research interest due to their thermal stability, cycling stability, and low cost, but the low energy density of olivine cathodes remains a key challenge. Despite the low theoretical energy density of olivine cathodes, the practical energy density of layered-olivine blend cathodes depends strongly on the operating conditions. Herein, we explore how the performance of blends of Nb-incorporated LiNi_0.8Mn_0.1Co_0.1O₂ (Nb@NMC811) and LiMn_0.5Fe_0.5PO₄ (LMFP) depends on various operating conditions. With the help of a novel technique for rapidly comparing the energy density of cathodes for different operating conditions, it is found that the layered-olivine blends offer the most competitive energy density during high-rate, high-temperature, and low state-of-charge (SOC) operations. This observation is ascribed primarily to the redox buffer effect of the Fe^2+/3+ couple, which offers more facile Li⁺ transport kinetics than layered oxides at low operating voltages (<3.6 V vs. Li/Li⁺). Under high electrode loading conditions in full-cells, it is demonstrated that the layered-olivine blends can offer more competitive energy density compared to pure Nb@NMC811 with appropriate C-rate and temperature conditions. These findings reveal how operating conditions can further improve the cost benefit of layered-olivine blends.