Bonding Heterogeneity Leads to Hierarchical and Ultralow Lattice Thermal Conductivity in Sodium Metavanadate

Sodium metavanadate (NaVO₃) is a promising low-cost candidate as a cathode material for sodium-ion batteries (SIBs) owing to its high cycle performance. Its thermal transport, although being a central factor limiting its practical applications, remains scarce. Herein, we comprehensively investigate the intrinsic thermal transport properties of the two phases of NaVO₃ using the unified theory. Importantly, we identify a hierarchical thermal transport mechanism in NaVO₃ and the significant contribution of diffusive thermal transport. With the combined two channels, we reveal that NaVO₃ has the anisotropic and ultralow thermal conductivity κ, which is derived from the bonding heterogeneity with the coexistence of strong V-O bonds and weak Na-O bonds, implying the possibility of engineering the κ of SIBs by spatially tuning the sodium concentration distribution. Our work establishes a fundamental understanding of the intrinsic thermal transport of NaVO₃ and provides guidance toward designing tunable thermal conductivity cathode materials for SIBs.