Reduced liquid content in in-situ polymerized quasi-solid-state sodium batteries enabled by robust electrode–electrolyte interface

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Quasi-solid-state batteries (QSSBs) are an intermediate development step from liquid batteries toward all-solid-state batteries, and the diminish of liquid content in QSSBs is of practical significance. However, in sodium batteries with a metallic Na anode, large interfacial resistance is a bottleneck restricting rate capability and further decrease of liquid content in QSSBs. In this work, we demonstrate the construction of a robust anode–electrolyte interface with facilitated charge transfer process and enhanced chemical stability for in-situ polymerized QSSBs, realized by a 3D Na/Na-Sn composite anode. The Na-Sn alloys uniformly distributed in Na matrix not only possess lower Na+ diffusion barrier intrinsically, but also contribute to a stereo surface with increased electrochemical surface area, which is beneficial to accommodating volume variations during sodiation/desodiation. Importantly, the in-situ polymerization process is highly compatible with the 3D composite anode without sacrificing of interfacial geometric contact. As a result, in QSSBs with a Na3V2(PO4)3 cathode, by replacing metallic Na anode with the Na/Na-Sn composite anode, liquid content in quasi-solid-state electrolyte can be appropriately reduced (e.g., from 70% to 50%) while maintaining similar level of electrochemical performance, i.e. high discharge specific capacity (109.5 mAh g−1 at 0.5 C) and good cyclic stability (96.5% capacity retention after 650 cycles), showing high practical significance.