Selenium/g-C3N4 with a Solid Li4Ti5O12 Blocking Layer for Selective Li+ Ion Diffusion in Long-Lived Li-Se Batteries

A durableLi-Se battery is fabricated by implementing arational and facile design strategy for the cathode. The cathode consistsof a Se/graphitic carbon nitride (g-C3N4) compositecombined with a solid lithium titanate (Li4Ti5O12, LTO) layer applied as a solid coating over the separator.The solid LTO layer has pores large enough to allow Li+ ions to diffuse through to the anode during charging but small enoughto effectively block the polyselenides formed during the dischargingcycle and confine them to the cathode, thus inhibiting capacity fadeand improving the operational lifespan. The micrometer-thick LTO barrierlayer affords selective diffusion of Li+ ions, with anaverage Li+ diffusion coefficient of 6 x 10(-11) cm(2) s(-1), enabling reasonably fast iontransport and kinetics. Simultaneously, g-C3N4, which is rich with active heteroatom (N) sites, also affords avery high Li+ ion adsorption, leading to an improved capacitycompared to pristine Se. The Se/g-C3N4/LTO@separator-Li+/Li cell delivers a superior capacity (750 versus 538 mAhg(-1) at 0.1 C-rate), rate capability (39% versus22% capacity retention ongoing from 0.1 to 2 C-rate), and cycle life(498 versus 283 mAh g(-1) reversible capacity after400 cycles) compared to the equivalent cell devoid of the LTO layer.Extended long-term cycling metrics showed a 310 mAh g(-1) reversible capacity at 2 C, with 78% retention after 1600 cycles,and reiterated the potential it has for scale-up and even commercialapplications.