Enhancing the cut-off voltage of high-nickel layered oxide cathodes is an efficient way to obtain higher energy density of lithium-metal batteries (LMBs). However, the phase transition of the cathode materials and the uncontrolled decomposition of the electrolytes at high voltage can lead to irreversible dissolution of transition metal ions, which might cause the crossover effects on the lithium metal anodes. Nonetheless, the mechanism and electrolyte dependence of the crossover effects for Li metal anodes are still unclear. Herein, we investigate the crossover effects between LiNi_0.8Mn_0.1Co_0.1O₂ and Li-metal anode in two electrolyte systems. For ether-based electrolyte, its poor oxidation stability results in massive dissolution of transition metal ions, leading to dendrite growth on anode and rapid cells failure. Conversely, ester-based electrolyte exhibits good electrochemical performances at 4.5 V with little crossover effect. This study provides an idea for electrolyte systems selection for high-voltage LMBs, and verifies that the crossover effect should not be neglected in LMBs.

Nitriles as efficient electrolyte additives are widely used in high-voltage lithium-ion batteries. However, their working mechanisms are still mysterious, especially in practical high-voltage LiCoO₂ pouch lithium-ion batteries. Herein, we adopt a tridentate ligand-containing 1,3,6-hexanetricarbonitrile (HTCN) as an effective electrolyte additive to shed light on the mechanism of stabilizing high-voltage LiCoO₂ cathode (4.5 V) through nitriles. The LiCoO₂/graphite pouch cells with the HTCN additive electrolyte possess superior cycling performance, 90% retention of the initial capacity after 800 cycles at 25 °C, and 72% retention after 500 cycles at 45 °C, which is feasible for practical application. Such an excellent cycling performance can be attributed to the stable interface: The HTCN molecules with strong electron-donating ability participate in the construction of cathode-electrolyte interphase (CEI) through coordinating with Co ions, which suppresses the decomposition of electrolyte and improves the structural stability of LiCoO₂ during cycling. In summary, the work recognizes a coordinating-based interphase-forming mechanism as an effective strategy to optimize the performance of high voltage LiCoO₂ cathode with appropriate electrolyte additives for practical pouch batteries.