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 LiCoO 2 (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%∼98% of the 2 nd 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. Recently, the all-solid-state lithium batteries (ASLBs) based on solid electrolyte are receiving significant attention for its safety by the displacement of the volatile and flammable liquid electrolyte.1-4 To develop high performance ASLBs, three critical issues must be considered: (1) get a high lithium ionic conductivity solid electrolyte of 10 −2 ∼10 −3 S cm −1 at room temperature and stability against chemical reaction with lithium anode, (2) lower the interfacial resistance between the electrodes and solid electrolyte, (3) solve the problem of poor Li ionic transportation among active material particles in the cathode. However, the third issue is often overlooked.The garnet-type inorganic oxide lithium ion conductor, nominal Li 7 La 3 Zr 2 O 12 (LLZO), is highly expected to be used as the solid electrolyte to accelerate the development of ASLBs.5-8 Recent reports reveal that doping with elements such as Ga 3+ and Ta 5+ can improve its room temperature conductivity to 0.4∼1.0 × 10 −3 S cm −1 .
9,10The LLZO system is reported to be stable with Li metal anode as well as possessing high electrochemical window (vs Li > 5 v). 11 The wide electrochemical window allows the use of high voltage cathode materials which may result in a potential high specific capacity for ASLBs.So far, the interfacial resistance between the electrodes and solid electrolyte has become the main contributor to the internal resistance of ASLBs, especially the resistance between cathode and solid electrolyte. Electrochemical performance of ASLBs based on LLZO solid electrolyte has been constructed by some groups using various methods aimed at reducing the interfacial resistance.12-15 Tan et al.12 reported a proto-type Li/LLZO/LiCoO 2 (LCO) cell whic...