Advanced low-cobalt and cobalt-free high-nickel layered oxide cathodes for high-energy-density lithium-ion batteries

Abstract

The global electrification of the automotive sector has significantly accelerated the development and demand of high-energy-density lithium-ion batteries (LIBs). High-nickel layered oxides LiNi [subscript x] M [subscript 1-x] O2 (x ≥ 0.7; M = Mn, Co, Al, etc.) serve as promising cathode materials that can deliver such metrics, but face challenges due to material instabilities and high costs. Removing cobalt from cathode compositions can reduce costs and environmental impact but compromises structural stability and performance. This dissertation explores strategies to stabilize low-Co and Co-free, high-Ni cathodes, addressing their degradation mechanisms applied to various electrolyte and anode chemistries. First, a new Co-free cathode is introduced in LiNi [subscript 0.7] Mn [subscript 0.25] Al [subscript 0.05] O₂ and evaluated next to LiNi [subscript 0.7] Mn [subscript 0.15] Co [subscript 0.15] O₂ and LiNi [subscript 0.7] Mn [subscript 0.3] O₂ cathodes to distinguish the roles of Mn, Co, and Al in cycling stability. Al is shown to greatly improve rate capability, cyclability, and thermal stability, highlighting it as a promising Co-free dopant for high-Ni cathodes. Second, the Co-free LiNiO₂ cathode is dually modified with Mg and B elements to tune the interphase stability. Mg and B incorporations simultaneously bolster the structural integrity and surface stability of LiNiO₂, and correspondingly promote longer cycle life. The stabilization results in reduced cathode active loss and robust interphase passivation. Third, an advanced electrolyte known as a localized saturated electrolyte (LSE) is applied to stabilize LiNiO₂ in lithium-metal batteries. The LSE provides incredible cycling stability compared to the baseline LP57 electrolyte, owing to its unique solvation structure, which promotes beneficial inorganic-rich interphase formation in both electrodes. Fourth, the roles of Mn and Co are revisited to understand their impacts on the air-synthesizability of high-Ni cathodes. LiNi [subscript 0.7] Mn [subscript 0.3] O₂, LiNi [subscript 0.7] Mn [subscript 0.15] Co [subscript 0.15] O₂, and LiNi [subscript 0.7] Co [suscript 0.3] O₂ cathodes are calcined in air and oxygen atmospheres and evaluated through various electrochemical and material characterizations. Mn is shown to enhance air synthesizability by reducing the average Ni oxidation state, while Co worsens it by increasing the Ni oxidation state. Lastly, a localized high-concentration electrolyte (LHCE) is utilized to enhance the cycle life of the LiNi [subscript 0.9] Mn [subscript 0.05] Co [subscript 0.05] O₂ cathode with a prelithiated silicon oxide-graphite (SiO [subscript x] /Gr) composite anode. The prelithiated SiO [subscript x] /Gr anode with LHCE develops a robust artificial SEI that tolerates better the intrinsic Si volume expansion during cycling with the cathode. Additionally, the LHCE further enables the high-voltage operation of a low-Ni, low-Co LiNi [subscript 0.6] Mn [subscript 0.31] Co [subscript 0.07] Al [subscript 0.02] O₂ cathode, enhancing cost-effectiveness while maintaining high energy density. This application stabilizes both cathode and anode surfaces by forming beneficial fluorinated interphases that protect against electrolyte-surface degradation reactions in comparison to LP57.