Protonated layered titanate anode at 0.008 V enables 1.75 V rocking-chair aqueous zinc-ion batteries with 87% energy efficiency

Aqueous zinc-ion batteries (AZIBs) with metallic Zn anodes face significant challenges, including dendrite growth, low Zn utilization, and parasitic side reactions. Inspired by rocking-chair design of lithium-ion batteries, developing intercalative anodes offers a promising strategy to address these issues. However, existing anode materials exhibit limited diversity, high redox potentials (≥ 0.3 V vs. Zn²⁺/Zn), and low energy efficiency, constraining the development of rocking-chair zinc-ion batteries. Herein, we report protonated layered titanate (H₂Ti₃O₇) that demonstrates an ultra-low redox potential of 0.008 V vs. Zn²⁺/Zn. The anode delivers a reversible capacity of 78 mAh·g⁻¹ at 0.2 A·g⁻¹, along with superior rate performance and remarkable cycling stability. In situ X-ray diffraction (XRD) analysis reveals a two-phase reaction mechanism during Zn²⁺ (de)intercalation. When coupled with a zinc hexacyanoferrate (KZnHCF) cathode, the full cell achieves a high output voltage of 1.75 V, long-term cycling stability of 3000 cycles, and an exceptional energy efficiency of 87% that far exceeds commercial lead-acid batteries. This work provides a highly promising anode candidate for the realization of high-voltage, high-energy-efficiency, and dendrite-free AZIBs.