All-solid-state lithium batteries (ASLBs) have been dramatically attracted recently for its ability of solving the safety issues in traditional lithium ion batteries using liquid electrolyte. However the poor Li+ transportation between the active material particles in the cathode greatly deteriorate the specific capacity of ASLBs. Herein, we design a composite cathode composed of polyethylene oxide (PEO) and LiCoO2 (LCO) in which a three-dimensional (3D) continuous Li+ conductive network forms. With the decrease of the LCO: PEO ratio, the 3D Li+ conductive network gradually becomes continuous, and the corresponding discharge capacity increase from 50 to 136 mAh g(-1). At LCO: PEO = 6: 1 and 4: 1, the corresponding ASLBs has a very high discharge capacity of 136 and 124 mAh g(-1), respectively, representing approximately 98% and 90% of the theoretical discharge capacity. The capacity retention after 5 cycles is 97%similar to 98% of the 2nd cycle, which confirms stable cycle performance of the battery. The FTIR results show that, in the composite cathode, the LCO particles transport Li+ cations by coordinating CO functional group in PEO chains. Compared with other optimized ASLBs based on LLZO solid elctrolyte, our battery has higher specific capacity while being tested under the highest current rate. (C) The Author(s) 2017. Published by ECS. All rights reserved.