Suppression of lithium dendrites in all-solid-state lithium batteries by using a Janus-structured composite solid electrolyte

[Display omitted] •A Janus-structured IP/LLP CSE is designed with flexible IP layer and rigid LLP layer.•A LiI-rich SEI film with high ionic conductivity is perfectly formed in-situ in CSE.•The CSE can completely inhibit lithium dendrites by a “double insurance” mechanism.•Assembled Li||IP/LLP/IP||Li cell demonstrates stable Li plating/stripping for 2000 h.•Flexible I2-loaded IP layer facing Li can be extended to many types of electrolytes. All-solid-state lithium batteries (ASSLBs) have become one of the most promising next-generation energy storage devices owing to their high energy density and inherent safety. However, the uneven growth of lithium dendrites and large interface impedance between electrolyte and electrode easily lead to low coulombic efficiency and fast capacity fading. Here, we design and construct a novel Janus-structured composite solid electrolyte, viz. I2-PEO-LiTFSI (IP)/Li6.4La3Zr2Al0.2O12(LLZAO)-PEO-LiTFSI (LLP) (abbreviated as IP/LLP) for ASSLBs. The double-layer electrolyte closely contacts with Li anode with a flexible IP layer facing the Li anode, reducing the interfacial resistance and in-suit generating a stable SEI film. The SEI film is mainly composed of LiI with high ionic conductivity, which can effectively inhibit lithium dendrites, even if lithium dendrites accidentally insert into the electrolyte, they will also be swallowed by I2 loaded in the IP layer. Hence, such “double insurance” mechanism for inhibiting lithium dendrites is successfully realized, and the Li symmetric cell displays long-term stability at a current density of 0.2 mA cm−2 for 2000 h. Meanwhile, the assembled Li||IP/LLP||LiFePO4 all-solid-state battery still has a discharge specific capacity of 146.20 mAh g−1 after 500 cycles with a capacity decay rate of 0.024 % per cycle at 0.2 C, exhibiting superior long cycling stability. Afterwards, we also prove the creatively designed and prepared IP layer is of universality to suit for many composite solid electrolytes. The new findings show that Janus-structured composite solid electrolyte has potential to be a high-performance electrolyte for ASSLBs.