The dependence of differential capacity versus voltage (dQ/dV) of Li/NCA half cells on temperature and testing current (C-rate) was studied. Kinetic hindrance of lithium diffusion at both low (∼3.5 V vs Li/Li + ) and high states of charge (∼4.17 V) was observed. In-situ X-ray diffraction measured the volume changes of the NCA lattice versus state of charge. NCA/graphite pouch cells were cycled in various voltage ranges to explore the impacts of depth of discharge (DOD) ranges and the kinetic hindrance regions in NCA on cell failure. dV/dQ analysis, full cell impedance and symmetric cell impedance analysis as well as half-cell studies of recovered electrodes were performed after 0, ∼400 and 800 charge-discharge cycles. The contributions of active mass loss and shift loss (from loss of Li inventory) to the capacity fade of NCA/graphite cells under various testing conditions were determined. The increase in positive electrode charge transfer impedance with cycle number was proportional to the increase of positive electrode active mass loss. There was no strong correlation between positive electrode active mass loss and lattice volume change. NCA active mass loss during cycling can be minimized when the dQ/dV peaks at ∼3.5 and 4.17 V (vs. Li/Li + ), that show kinetic hindrance, are partially or completely avoided.

The use of electrolyte additives is an important method to improve lithium-ion cell lifetime and performance without significantly affecting costs. This work evaluates two organic anhydrides, glutaric anhydride (GA) and citraconic anhydride (CA), as additives in Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 (NMC622)/graphite and Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 (NMC532)/graphite pouch cells, using ultrahigh precision coulometry and high-temperature storage. The additives were tested singly and in binary blends. GA-based additive blends give high coulombic efficiencies (CEs) and good storage performance. However, GA leads to substantial impedance during formation. Most notably, GA is extremely effective at suppressing gas during cell formation and storage. Whereas CA-containing blends yield good CEs, they show rapid voltage drop during storage. Both additives may provide specific benefits for target applications. Long-term cycling data indicates that GA is a negative electrode SEI-forming additive that is useful for capacity retention and limiting cell impedance growth when used as a binary blend with vinylene carbonate or lithium difluorophosphate. These results are also intended to facilitate comparison between chemically related additives in order to better understand the underlying chemistry behind their function in lithium-ion cells.