A Universal Thick Anode for Aqueous and Seawater Energy Storage Devices

Aqueous and seawater energy storage devices hold great potential for electrical grids application due to safety, affordability, and sustainability. However, their broader deployment has been constrained by the absence of a durable thick anode. Here, the first universal thick anode operating stably across 15 simple-ion and 3 complex-ion systems, including nonmetallic (H⁺, NH₄ ⁺), monovalent (Li⁺, Na⁺, K⁺), multivalent ions (Zn²⁺, Ca²⁺, Mg²⁺, Al³⁺), and seawater ions (>5 cations) is reported. Composed of polymer nanosheets and carbon nanotubes, this anode supports thick electrode fabrication (e.g., 100 mg cm^-2 and 1 mm) with low porosity/tortuosity, superior electrical conductivity, mechanical robustness, and chemical stability. Consequently, it achieves exceptionable cycle life (up to 380 000 cycles) in supercapacitors and ultrahigh areal capacities (6.5 mAh cm^-2) in batteries, even under practical/extreme conditions, attributed to the formation of a water-scarce, cation-rich electrical double-layer structure, as revealed by simulations. Compatible with sea salt-based electrolytes and paired with a metal-free cathode, the anode enables seawater batteries with thousands-cycle life and high energy/power density. Of universal ion storage, ultrahigh-loading capability, unlimited resources, and cost-effectiveness, this polymer electrode is promising for practical aqueous (seawater) energy devices.