Ceramic–Polymer–Carbon Composite Coating\non the Truncated Octahedron-Shaped LNMO Cathode for High Capacity\nand Extended Cycling in High-Voltage Lithium-Ion Batteries

Long-term electrochemical\ncycle life of the LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> (LNMO)\ncathode with liquid electrolytes (LEs)\nand the inadequate knowledge of the cell failure mechanism are the\neloquent Achilles’ heel to practical applications despite their\nlarge promise to lower the cost of lithium-ion batteries (LIBs). Herein,\na strategy for engineering the cathode–LE interface is presented\nto enhance the cycle life of LIBs. The direct contact between cathode-active\nparticles and LE is controlled by encasing sol–gel-synthesized\ntruncated octahedron-shaped LNMO particles by an ion–electron-conductive\n(ambipolar) hybrid ceramic–polymer electrolyte (IECHP) via\na simple slot-die coating. The IECHP-coated LNMO cathode demonstrated\nnegligible capacity fading in 250 cycles and a capacity retention\nof ∼90% after 1000 charge–discharge cycles, significantly\nexceeding that of the uncoated LNMO cathode (a capacity retention\nof ∼57% after 980 cycles) in 1 M LiPF<sub>6</sub> in EC:DMC\nat 1 C rate. The difference in stability between the two types of\ncathodes after cycling is examined by focused ion beam scanning electron\nmicroscopy and time-of-flight secondary ion mass spectrometry. These\nstudies revealed that the pristine LNMO produces an inactive layer\non the cathode surface, reducing ionic transport between the cathode\nand the electrolyte and increasing the interface resistance. The IECHP\ncoating successfully overcomes these limitations. Therefore, the present\nwork underlines the adaptability of IECHP-coated LNMO as a high-voltage\ncathode material in a 1 M LiPF<sub>6</sub> electrolyte for prolonged\nuse. The proposed strategy is simple and affordable for commercial\napplications.