Development of NMC/LFP Cathode Material Blends for Lithium-Ion Batteries

The need for renewable energy is rapidly increasing, and the optimization of lithium-ion batteries is critical for the industry. Their high power and energy capability provides power for small consumables, such as watches, up to electric vehicles (EVs) and grid scale energy storage systems. Lithium-nickel-manganese-cobalt-oxide (NMC) is a favored cathode active material in EVs because of its high energy density and high voltage limits, with the challenge of inferior high rate performance than other chemistries. Lithium-iron-phosphate (LFP) is less common due to its lower voltage range but exhibits higher safety and better high rate performance, especially during pulses of high current demand. For this reason, blends of NMC and LFP can impart the high energy density of NMC, with the safety and pulsed performance of LFP.

The research conducted focuses on testing cathode materials by performing electrochemical and rate testing followed by electrochemical impedance spectroscopy (EIS). This experiment focused specifically on the cathode by assembling half-cells, which cycle the cathode against pure lithium. This allows any performance effects from the anode to be eliminated. The coin cells tested had NMC, LFP, or a blend of NMC/LFP as the primary material in the cathode. Blended cathodes were made with 70% NMC and 30% LFP. The EIS analysis allowed cell kinetics and transfer mechanisms to be assigned and compared between the two chemistries. The analysis attributed electrochemical features from both species, including the high voltage profiles from the NMC and the good pulse performance from the LFP.