A Janus Li1.5Al0.5Ge1.5(PO4)3 with high critical current density for high-voltage lithium batteries.

• Dual interlayers are constructed in situ on both sides of the LAGP. • Janus LAGP is compatible with both Li metal and high-voltage cathodes. • The critical current density can be significantly increased to 5.4 mA cm−2. • The solid-state NCM811/Li battery exhibits excellent rate and cycling performance. The application of Li 1.5 Al 0.5 Ge 1.5 (PO 4) 3 (LAGP) is hindered by chemical instability with lithium (Li) metal and poor interfacial compatibility with high-voltage cathodes. Herein, an in-situ Janus LAGP is fabricated to solve the above two issues simultaneously. On the cathodic side, a succinonitrile-based interlayer with good oxidation stability is applied to facilitate ion transport at the interface and inside the cathode. On the anodic side, Fluoroethylene carbonate (FEC)-based polymer interlayer is chosen to ameliorate side reactions on LAGP/Li interface and inhibit the dendrite growth. Consequently, the Li symmetric cell with the Janus LAGP possesses a high critical current density of 5.4 mA cm−2 and operates stably for over 500 h at a high current density of 1.0 mA cm−2. Moreover, the Janus LAGP exhibits excellent ionic conductivity (4.76 × 10−4 S cm−1), wide electrochemical window (0–5.2 V vs. Li+/Li) and stable interfacial compatibility with high-voltage cathodes. The solid-state lithium battery (LiNi 0.8 Co 0.1 Mn 0.1 O 2 /Li) delivers a maximum discharge capacity of 178 mAh g−1 with a retention of 85.7% after 100 cycles at 0.5C. Notably, when the mass loading is increased to 10.0 mg cm−2, the battery delivers a maximum discharge capacity of 134.1 mAh g−1 (1.52 mAh) at 0.5C, and the capacity remains 76.1% after 100 cycles. [ABSTRACT FROM AUTHOR]