Chemisorption effect enables high-loading zinc-iodine batteries

Rechargeable Zn-I2 batteries featuring intrinsic safety and high energy density demonstrate promising energy storage prospects. However, the poor interface stability of the Zn anode and the undesirable shuttle effect severely hinder the device stability due to the diffusive characteristics of the soluble polyiodides in aqueous media. Here, a synergetic physicochemical strategy that combines physical constraints and chemical absorption was proposed by developing a composite host matrix with a core/porous-sheath structure, which can effectively confine iodine species. Initial I- ions bind securely with carboxylated multi-walled carbon nanotubes (c-MCNTs) to form the C-I bonds through chemical interactions. Furthermore, the pore structure of microporous carbon (MPC) not only restricts the iodine species in the pores through physisorption (secondary adsorption) but also facilitates the diffusion of Zn2+. The as-prepared carbon nanotubes coated with microporous carbon (glucose as the carbon source, and its ratio to CNT is 12:1) can serve as a host material (CNT@MPC12), and adsorb iodide ions to derive CNT@MPC12-I-. As a result, the developed aqueous Zn battery with CNT@MPC12-I- cathode delivers superior reversible rate capacity (0.35 mA h cm-2 at 20 mA cm-2) and remarkable cycling performance (12,000 cycles at 10 mA cm-2). Notably, such cathode can also exhibit an impressive capacity retention of 97% after 8600 cycles, even at an ultrahigh loading mass of 16.05 mg cm-2. As such, our strategy can be extended to design other metal I2 batteries with high loading and long-life expectancy.