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Surface coating is a crucial method to mitigate the aging problem of high‐Ni cathode active materials (CAMs). By avoiding the direct contact of the CAM and the electrolyte, side reactions are hindered. Commonly used techniques like wet or ALD coating are time consuming and costly. Therefore, a more cost‐effective coating technique is desirable. Herein, a facile and fast dry powder coating process for CAMs with nanostructured fumed metal oxides are reported. As the model case, the coating of high‐Ni NMC (LiNi0.7Mn0.15Co0.15O2) by nanostructured fumed Al2O3 is investigated. A high coverage of the CAM surface with an almost continuous coating layer is achieved, still showing some porosity. Electrochemical evaluation shows a significant increase in capacity retention, cycle life and rate performance of the coated NMC material. The coating layer protects the surface of the CAM successfully and prevents side reactions, resulting in reduced solid electrolyte interface (SEI) formation and charge transfer impedance during cycling. A mechanism on how the coating layer enhances the cycling performance is hypothesized. The stable coating layer effectively prevents crack formation and particle disintegration of the NMC. In depth analysis indicates partial formation of LixAl2O3/LiAlO2 in the coating layer during cycling, enhancing lithium ion diffusivity and thus, also the rate performance. [ABSTRACT FROM AUTHOR]

The separator and electrolyte are critical to the cycle performance and safety of lithium-ion batteries (LIBs). Selecting a proper combination of separator and electrolyte is thus imperative to develop LIBs that assure long cycle life and enhanced safety. In this work, we deliberately select their good combinations and demonstrate that in-situ thermal cross-linking promoted by reactive Al 2 O 3 particles coated on polyethylene (PE) separator to form the cross-linked network is a potential solution for enhancing both cycling performance and battery safety. The cost for making the reactive Al 2 O 3 -coated separator can be significantly reduced by employing an eco-friendly water-soluble binder. When the Al 2 O 3 particles are coated onto the PE separator, the reactive Al 2 O 3 -coated separator exhibits enhanced electrolyte wettability and thermal stability. Trimethylolpropane trimethacrylate is chosen as a cross-linking agent and its conversion is investigated by 1H nuclear magnetic resonance (NMR) analysis. The lithium-ion cell assembled with reactive Al 2 O 3 -coated separator exhibits stable cycling behavior at 55 °C and excellent thermal safety at 200 °C, demonstrating that the reactive Al 2 O 3 -coated PE is a safer and more reliable separator that ensures good cycling performance and safety. • A reactive Al 2 O 3 -coated separator is prepared using a water-soluble binder. • A reactive separator promotes the in-situ cross-linking of gel precursor in the cell. • The reactive separator exhibits enhanced electrolyte wettability and thermal safety. • The cell with reactive separator exhibits good cycling performance and less leakage. [ABSTRACT FROM AUTHOR]

The thermal instability of conventional polyolefin separators and the high flammability of organic electrolytes are the primary safety-related concerns of high-energy-density lithium-ion batteries. To address these issues, reactive Al 2 O 3 nanostructured materials are coated onto a polyethylene (PE) separator to promote the formation of gel electrolyte and enhance the thermal stability of the separator. The Al 2 O 3 nanostructured materials are surface-treated by 3-methacryloxypropyl trimethoxysilane to induce radical polymerization with tetra(ethylene glycol) diacrylate (TEGDA) in liquid electrolyte. The three-dimensional network formed by cross-linking reactive alumina nanostructured materials and TEGDA reduces the electrolyte leakage from the cell and enhances the interfacial adhesion between separator and electrodes. Thermal shrinkage of the reactive alumina-coated separator is also significantly reduced at 140 °C, providing enhanced thermal stability. In addition to improved thermal safety, lithium-ion cells employing a reactive alumina-coated PE separator exhibit stable cycling at both ambient and high temperatures. • Reactive alumina-coated separator is prepared to promote gel electrolyte formation. • Thermal stability of alumina-coated separator is significantly enhanced at 140 oC. • The cell with reactive separator exhibits good cycling stability and enhanced safety. • The reactive Al 2 O 3 coated-separator is promising for enhancing the battery safety. [ABSTRACT FROM AUTHOR]