Lithium aluminate (LAO) is known to be an effective filler for improving the conductivity of polyethylene-LiX (PEO-LiX) solid polymer electrolytes (SPEs), while succinonitrile (SN) is an excellent solid plasticizer with plastic crystalline organic molecules. In this work, LAO micro-rods are prepared via a simple hydrothermal method, and a novel PEO-based composite polymer electrolyte is developed by the addition of SN and LAO. The resulting optimal composite PEO:LiTFSI:SN(15%):LAO(10%) (PEOL-SPE) has a maximized ionic conductivity of 1.36x10(-5) Scm(-1)at 30 degrees C, and the membrane has a wide electrochemical window of 5.2V. The fabricated cell with LiFePO4 as the cathode, metallic lithium as the anode and PEOL-SPE as the electrolyte membrane delivers an impressive initial charge/discharge capacity of 153.1/141.3mAhg(-1) at 60 degrees C. The addition of 10wt% of the LAO micro-rods results in a favorable increase in the ionic conductivity, and no apparent blocking effect is observed to impede the electrochemical performance. These results bring to light the potential of micro-sized additives for use in lithium battery applications.