Capacity-expanding O/Cl-bridged catholyte boosts energy density in zero-pressure all-solid-state lithium batteries

Abstract The advancement of all-solid-state lithium batteries (ASSLBs) requires innovative breakthroughs in catholyte design to eliminate the need for external pressure and mitigate the adverse effects of inactive catholytes on energy density. Here, we present a capacity-expanding O/Cl-bridged catholyte (1.2LiOH-FeCl3) featuring an abundant, freely rotating FexOyClz framework, endowing it with polymer-like viscoelasticity and an impressive ionic conductivity (6.1 mS cm−1 at 25 °C). The polymer-like viscoelasticity creates a soft interface that alleviates volume changes during cycling, enabling zero-pressure ASSLBs to deliver a high capacity retention of 86.6% after 100 cycles, which is a 35.7% improvement compared to the rigid Li2ZrCl6 catholyte (50.9%). Moreover, the fast Li+ transport capability and variable-valence iron coordination center endow 1.2LiOH-FeCl3 catholyte delivering a capacity of 97.7 mAh g−1. When used as a catholyte alongside a LiFePO4 cathode material, it adds capacity by 31.3% (196.4 mAh g−1LFP vs. 149.6 mAh g−1LFP) and boosts energy density by 21.1% (609.4 Wh kg−1LFP vs. 503.4 Wh kg−1LFP) compared to Li2ZrCl6 catholyte. Beyond these properties, the 1.2LiOH-FeCl3 catholyte offers significant cost advantages, priced at just $2.6 kg−1 (16% of the cost of Li2ZrCl6), and supports scalable production at 60°C, making kilogram- to ton-level manufacturing feasible.