Stabilizing Co-free Li-rich cathodes with LaF₃ coating and ionic liquid electrolytes: A pathway to high-performance...

The rapid development of cobalt-free, lithium-rich layered cathode materials is hindered by poor interfacial stability, oxygen evolution, and irreversible structural transitions during cycling, particularly at high voltages. This study aims to overcome these limitations by implementing a dual-interface engineering strategy combining surface modification and electrolyte optimization to enhance the electrochemical performance and stability of cobalt-free, lithium-rich Li_1.2Ni_0.2Mn_0.6O₂ (LRNMO) cathode materials. The cathodes were synthesized using a Taylor-Couette flow reactor and subsequently coated with a uniform LaF₃ nanolayer, which effectively suppressed transition metal dissolution and oxygen loss. Electrochemical testing revealed significant improvements in capacity retention, Coulombic efficiency, and high-rate capability for LaF₃-coated LRNMO compared to uncoated samples. The LaF₃ coating significantly improved Li⁺ diffusion kinetics, reducing polarization and enhancing electrochemical reversibility. In-situ X-ray diffraction and electrochemical impedance spectroscopy analyses provided insights into structural transformations and interfacial stability during cycling, confirming the protective role of LaF₃ coatings in stabilizing the cathode structure. To further enhance performance under elevated voltage and temperature conditions, a high-concentration fluorinated hybrid ionic liquid electrolyte was employed. This electrolyte formulation substantially mitigated decomposition reactions and promoted the formation of a stable cathode-electrolyte interphase. In-situ differential electrochemical mass spectrometry confirmed the suppression of gas evolution, underscoring the enhanced oxidative stability of the system. The combined approach of LaF₃ surface modification and hybrid ionic liquid electrolyte integration enables excellent electrochemical performance at 4.8 V, highlighting a promising pathway for the development of high-energy-density, cobalt-free lithium-ion batteries with prolonged cycle life and improved safety.