High performance solid-state sodium batteries enabled by boron contained 3D composite polymer electrolyte

Practical application of solid-state batteries has been severely hindered by the relatively low ionic conductivity of electrolyte and high charge-transfer resistance between electrode and solid electrolyte . The development of novel materials and creation of new nanostructures are effective strategies to address the challenges. Here, an innovative 3D composite polymer electrolyte modified with anion-trapping boron (B-CPE) is reported for the first time as a solid electrolyte for sodium-ion batteries (SIBs). The B-CPE is prepared through in situ polymerization of polymer electrolyte inside a mechanically supporting matrix. It shows excellent ionic conductivity of 2.57 × 10 −4  S cm −1 at 40 °C, high Na + transference number of 0.66, and good interfacial compatibility with Na metal anode. Moreover, solid-state SIBs were assembled by one-step in situ solidification method to form “gentle” electrode/electrolyte contact, and it’s found that the charge-transfer efficiency has been significantly improved at the electrode/electrolyte interface as well as in cathode due to the formation of ion-conducting continuous polymer phase. Hence the B-CPE based solid-state SIBs exhibit outstanding electrochemical performances as the synergistic effect of high performance electrolyte and optimized cell structure. It delivers initial discharge capacity of 113.8 mAh g −1 and maintains 80.1% of capacity during 320 cycles under 0.2 C at 40 °C, and even 80.4% of the capacity retention after 700 cycles under 3 C. Notably, the battery achieves a significant improvement in rate capability owing to the introduction of boron moieties. This work opens new possibilities to fabricate high performance other rechargeable solid-state batteries.