The effect of electrolyte additives on both LaPO4-coated Li(Ni0.4Mn0.4Co0.2)O2 and uncoated Li(Ni0.4Mn0.4Co0.2)O2 in Li-ion pouch cells

• Electrolyte additives are more effective than a LaPO4 coating for improving lifetime.
• A LaPO4 coating is more valuable at 4.5 V.
• State-of-the-art electrolyte additives that improve high voltage lifetime are discussed.

The effectiveness of some selected electrolyte additive blends were systematically studied in Li[Ni0.4Mn0.4Co0.2]O2/graphite and 3 wt% LaPO4-coated Li[Ni0.4Mn0.4Co0.2]O2/graphite pouch cells using ex-situ gas measurements, ultra high precision coulometry, automated storage experiments, long-term cycling and electrochemical impedance spectroscopy. For cells tested to an upper cutoff potential of 4.4 V the LaPO4-coating provided no benefit when state-of-the-art electrolyte additives were used. For cells tested to 4.5 V, the LaPO4 coating appeared to limit electrolyte oxidation slightly and resulted in better capacity retention compared to uncoated cells for cells with state-of-the-art electrolyte additives. However, even for cells tested to 4.5 V, the benefits of the additives far outweighed the benefits of the coating. This suggests literature papers that compare the impact of coatings on positive electrode materials in cells that contain electrolytes without electrolyte additives have limited value.