An interfacial compatible Ti ₄ P ₈ S ₂₉ polysulfide cathode with open channels for high‐rate solid‐state polymer sodium batteries

Abstract Solid‐state polymer sodium batteries (SPSBs) are promising candidates for achieving higher energy density and safe energy storage. However, interface issues between oxide cathode and solid‐state polymer electrolyte are a great challenge for their commercial application. In contrast, soft sulfur‐based materials feature better interface contact and chemical compatibility. Herein, an interfacial compatible polysulfide Ti 4 P 8 S 29 with robust Ti–S bonding and a highly active P–S unit is tailored as a high‐performance cathode for SPSBs. The Ti 4 P 8 S 29 cathode possesses a three‐dimensional channel structure for offering ample Na + diffusion pathways. The assembled poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP)‐based SPSBs deliver a discharge capacity of 136 mAh·g −1 at 0.5C after 200 cycles. Furthermore, a discharge capacity of 88 mAh·g −1 is retained after 600 cycles at a high rate of 2C, surpassing many cathode materials in SPSBs. A dual‐site redox of Ti 4+ /Ti 3+ and S − /S 2− is verified by X‐ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) tests. Interestingly, a refined locally‐ordered amorphous structure is unveiled by in situ and ex situ characterizations. The as‐formed electrode structure with lots of open channels and isotropic properties are more beneficial for ion diffusion on the interface of electrode and solid‐state polymer electrolytes (SPEs), leading to faster Na + diffusion kinetics. This work proposes a strategy of modulating open‐channel to boost conversion kinetics in polysulfide cathode and opens a new pathway for designing high‐performance SPSBs.