Sequential Deposition of Integrated Cathode–Inorganic Separator–Anode Multilayers for High Performance Li-Ion Batteries

[Image: see text] A porous, spray-deposited Al(2)O(3)-based separator was developed to enable the direct deposition of an electrode/separator/electrode Li-ion battery full cell assembly in a single operation. The optimized sprayed separator consisted of 50 nm Al(2)O(3) particles, 1 wt % poly(acrylic acid), and 5 wt % styrene–butadiene rubber, deposited from an 80:20 vol % suspension of water and isopropanol. Separators between 5 and 22 μm thick had consistent and similar porosity of ∼58%, excellent wettability, thermal stability to at least 180 °C, adequate electrochemical stability and high effective ionic conductivity of ∼1 mS cm(–1) at room temperature in an EC/DMC electrolyte, roughly double that of a conventional polypropylene separator. A sequentially deposited three-layer LiFePO(4)/Al(2)O(3)/Li(4)Ti(5)O(12) full cell, the first of its kind, showed similar rate performance to an identical cell with a conventional polypropylene separator, with a capacity of ∼50 mAh g(–1) at 30 C. However, after cycling at 2 C for 400 cycles, Al(2)O(3) separator full cells retained 96.3% capacity, significantly more than conventional full cells with a capacity of 79.2% remaining.