All-solid-state lithium batteries (ASSLBs) assembled with solid polymer electrolytes (SPEs) have been regarded as promising next-generation rechargeable batteries with improved safety and high energy densities. However, the Li dendrites and poor Li+ transport greatly inhibit their practical applications when coupled with relatively high loading cathodes. Herein, we combine a glass fiber (GF)-reinforced composite polymer electrolyte based on poly(ethylene oxide) (labeled as PEO@GF) to suppress Li dendrite growth with a freeze-casted vertically-aligned (VL) electrode to facilitate Li+ transport in the high loading cathode. Benefiting from the enhanced mechanical strength and uniformed Li deposition enabled by the implanted GF, the Li–Li symmetric cells exhibit significantly improved cycling stability up to 2000 h (0.2 mA cm−2, 0.2 mAh cm-2) and 1000 h (0.42 mA cm−2, 0.4 mAh cm−2), which are over one order of magnitude longer than those of the pure PEO electrolyte. Furthermore, VL-LiFePO4 (LFP) cathode divides the thick electrode into numerous vertically-aligned “thin electrodes”, which significantly decreases the Li+ transport distance and enables the Li | PEO@GF | VL-LFP cell with a high LFP loading of 10.5 mg cm-2 to deliver a high areal capacity of 1.52 mAh cm−2. The rational structure design of both electrolyte and electrode offers an opportunity for developing high-performance ASSLBs with high active material loadings.