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.