Effects of electrolyte additives and solvents on unwanted lithium plating in lithium-ion cells

Unwanted lithium plating on the graphite anode of lithium ion batteries can reduce the cycle life and safety of lithium ion batteries. Increased charging rates, lower temperatures, thicker electrodes, lower Li-ion diffusion constant and larger graphite particles all increase the propensity for unwanted lithium plating. In this work, a variety of electrolyte additives and electrolytes, which extend lifetime during low rate cycling, were used in Li[Ni_1/3Mn_1/3Co_1/3]O2/graphite (NMC111/graphite) pouch cells subjected to high rate charging at 20^◦C. It was found that additives and electrolytes which increased the negative electrode area-specific resistance, R_negative, decreased the onset current, I_u, for unwanted lithium plating. Here, the processes of ion desolvation, electron and ion transport through the solid electrolyte interphase and contact resistance are lumped into the R_negative. Under conditions where R_negative is the dominant factor determining when unwanted Li plating occurs, the onset current for lithium plating could be well predicted by the expression: I_u = 0.080 V x S/R_negative, where S is the geometric electrode surface area. R_negative is easily determined using negative electrode coin-type symmetric cells. This simple rule-of-thumb relation will help guide researchers seeking to select electrolyte additives that simultaneously increase lifetime and also allow fast charging.