Invoking Hybrid‐Ion Correlation Electrochemistry to Enable Optimal Aqueous Zn‐Ion Batteries

Abstract As a generation beyond conventional batteries based on mono‐/poly‐valent ions, hybrid‐ion batteries (HIBs) offer more opportunities to build battery prototypes because they utilize the merits of multiple ions. However, the limited understanding of ionic correlations in these heterogeneous systems experimentally and theoretically brings a great challenge in exploring their performance limits. Here, an approach is proposed combining electrochemical phase‐field simulation with thermodynamic calculation, where ionic correlation in the electrolyte and electrode is addressed using the linearized Poisson‐Boltzmann equation embedded with Debye‐Hückel theory and ion‐occupied sub‐lattice model, to invoke the ionic electrodeposition and ( de )intercalation advantages. This approach is independent of specific HIB electrolytes or electrodes. A “Seesaw‐Inhibition” mechanism is uncovered, operating under hybrid‐ion concentration regulation to determine the electrodeposition morphology in three types of HIBs, and simultaneously predict a general ion competitive behavior during their intercalation. Following this, a prototype of Na 3 V 2 (PO 4 ) 3 ||1 M NaTfO+1 M Zn(TfO) 2 ||Zn aqueous HIB is built, surpassing pure Zn‐ion batteries by 32% in measured energy density (128.3 Wh kg −1 ) and exhibiting low capacity decay (0.10% per cycle over 300 cycles). The scalability of the approach for regulating hybrid‐ion electrochemistry demonstrates its practical viability for designing HIBs.