In Situ Co-O Bond Reinforcement of the Artificial Cathode Electrolyte Interphase in Highly Delithiated LiCoO2 for High-Energy-Density Applications

Preventing the Distortion of CoO6 Octahedra of LiCoO2 at High-Voltage Operation of Lithium-Ion Battery: An Organic Surface Reinforcement

Lithium cobalt oxide (LiCoO₂, LCO) has been widely used in electronic markets due to its high energy density and wide voltage range applications. Recently, high-voltage (HV, >4.5 V) operation has been required to obey the requirements of high energy density and cycle life in several applications such as electric vehicles and energy storage. However, the HV operation causes structure instability due to the over de-lithiation of LCO, as well as decomposing common carbonate solvents, thereby incurring the decay of battery performance. Moreover, a distortion of the CoO₆ octahedra of LCO during de-lithiation induces a rehybridization of the Co 3d and O 2p orbitals. According to above reasons, decreasing the Co-O covalent bond promptly triggers high risks that significantly limit further use of LCO. In this research, an organic surface reinforcement by using bismaleimide-uracil (BU) that electrochemically forms a cathode electrolyte interphase (CEI) on LCO was explored. The results of electrochemical impedance spectroscopy and battery performance, such as the c-rate and cyclability tests, demonstrated that the modified CEI formed from BU significantly prevents the distortion of CoO₆ octahedra. X-ray photoelectronic spectroscopy and in situ XAS indicated less LiF formation and higher bond energy of Co-O improved. Finally, the differential scanning calorimetry showed the onset temperature of decomposition of LCO was extended from 245 to 270 °C at 100% state of charge, which is about a 25 °C extension. The exothermic heat of LCO decreased by approximately 30% for high-safety use. This research confirms that the BU is eligible for high voltage (>4.5 V) LCO and presents outstanding electrochemical properties and safety performances.

Suppressed Lattice Oxygen Release via Ni/Mn Doping from Spent LiNi0.5Mn0.3Co0.2O2 toward High-Energy Layered-Oxide Cathodes

LiCoO₂ has suffered from poor stability under high voltage as a result of insufficient Co-O bonding that causes lattice oxygen release and lattice distortions. Herein, we fabricated a high-voltage LiCoO₂ at 4.6 V by doping with Ni/Mn atoms, which are obtained from spent LiNi_0.5Mn_0.3Co_0.2O₂ cathode materials. The as-prepared high-voltage LiCoO₂ with Ni/Mn substitutional dopants in the Co layer enhances Co-O bonding that suppresses oxygen release and harmful phase transformation during delithiation, thus stabilizing the layered structure and leading to a superior electrochemical performance at 4.6 V. The pouch cell of modified LiCoO₂ exhibits a capacity retention of 85.1% over 100 cycles at 4.5 V (vs graphite). We found that our strategy is applicable for degraded LiCoO₂, and the regenerated LiCoO₂ using this strategy exhibits excellent capacity retention (84.1%, 100 cycles) at 4.6 V. Our strategy paves the way for the direct conversion of spent batteries into high-energy-density batteries.