Practical Pathways to Higher Energy Density LMFP Battery Cathodes

Abstract

The design of new lithium-ion battery cathode materials must balance many factors: performance, cost, manufacturability, safety, critical mineral usage, and geopolitical constraints. Recently, commercialized LiMnxFe1-xPO4 (LMFP) materials offer good energy density and stability, low material cost, and excellent safety characteristics, avoiding the use of Co or Ni. Within this material set lies a wide variety of potential formulations (Mn/Fe ratio) exhibiting varied cathode properties and challenges. In this work, we assessed three commercially available LMFP materials with Mn content in the range of 60-80% in full cell format, confirming the role of the Mn/Fe ratio on specific capacity, energy density, and electrochemical stability. High Mn content increased the average discharge voltage while maintaining specific discharge capacity, with 80% Mn providing an 18% boost to initial gravimetric energy density over LFP. However, worse kinetics and increased capacity fade rate resulted in the reduction and eventual elimination of this energy density advantage after 100 cycles. A blend cathode (LMFP and LiNi0.8Mn0.1Co0.1O2, NMC811) was also evaluated, exhibiting characteristics of both material types. An initial 23% boost to energy density over LMFP alone was diluted following NMC-dominated degradation in early cycles, but enhanced capacity retention over NMC811 alone remained in long-term cycling. This work highlights the potential advantages of these newly commercialized materials while identifying outstanding challenges to widespread adoption and exploitation.