Heterogeneous double-layered hybrid solid electrolyte with a concentration-gradient structure for high-performance all-solid-state lithium batteries

All-solid-state lithium batteries (ASSLBs) with hybrid solid electrolytes (HSEs) fabricated using composite structures consisting of polymers and oxides have received extensive attentions owing to their high energy densities and excellent stabilities. Herein, for the high-performance ASSLBs, we designed a double-layered hybrid solid electrolyte (DLHSE) containing 15 wt% LiTa2PO8 (LTPO) and 10 wt% Li6.28Al0.24La3Zr2O12 (LALZO) heterogeneous active fillers in a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix (LTPO 15% HSE and LALZO 10% HSE, respectively) via two-step casting method. For application in high-performance ASSLBs, LTPO 15% and LALZO 10% HSEs were contacted with cathode and lithium metal anode, respectively. Additionally, DLHSE demonstrated a high ionic conductivity of 8.7 × 10−4 S cm−1 at 25 °C, electrochemical oxidative stability (∼5.1 V) at 55 °C, and a high critical current density of >1.0 mA cm−2, resulting from its low interfacial resistance and high-density interior structure. ASSLB consisting of LiFePO4 (LFP), DLHSE, and lithium metal anode (LFP/DLHSE/Li) demonstrated an initial specific capacity of ∼151 mAh g−1 at 0.2 C and 25 °C and a specific capacity retention of 91% after 140 cycles of charge/discharge. Moreover, Li2MnO3/DLHSE/Li ASSLB demonstrated relatively stable cycling performance up to ∼4.4 V at 20 mA g−1 and 25 °C for 400 cycles of charge/discharge.