Achieving Ultrafast Monovalent ZnCl⁺ Ion Transport in MOF-Based Zn Ion Solid-State Electrolyte through Polyanion...

Solid-state transport of high-valence ions is a huge challenge, such as the transport of divalent zinc ions. Herein, a polyanion strategy is proposed to decrease divalent Zn²⁺ to monovalent ZnCl⁺, realizing ultrafast ion transport in solid-state electrolyte. An amorphous metal-organic framework (ZGB-MOF) is designed and constructed as the matrix for solid-state electrolyte. The ZGB-MOF matrix is obtained by the Zn²⁺/Ga³⁺ competitive coordination process, enriching O-Ga-Cl polyanion clusters, nanopores and C═O/oxygen vacancies active sites. The polyanion property of Ga³⁺ and physical limiting domains of nanopores promote the formation of ZnCl⁺. Abundant C═O and oxygen vacancies provide more transport sites, decreasing transport energy barriers for ZnCl⁺ (only 0.12 eV). Eventually, the obtained Zinc ion solid-state electrolyte (ZGBC) achieves high ionic conductivity of 5.2 × 10^-3 S cm^-1 and high transference number of 0.873. More importantly, the ZGBC electrolyte exhibits wide electrochemical window (up to 2.88 V) and high charging voltage (2.4 V), and achieves dendrite-free deposition of Zn-metal and stabilization of cathode materials. Full cells with ZGBC electrolyte and zinc hexacyanoferrate cathode exhibit excellent cycling stability, with no capacity degradation after 5000 cycles. This discovery could trigger new waves of enthusiasm for exploring new ion transport mechanisms beyond divalent Zn²⁺ transport.