Selective Nitridation Crafted a High-Density, Carbon-Free Heterostructure Host with Built-In Electric Field for Enhanced Energy Density Li-S Batteries.

To achieve both high gravimetric and volumetric energy densities of lithium-sulfur (Li-S) batteries, it is essential yet challenging to develop low-porosity dense electrodes along with diminishment of the electrolyte and other lightweight inactive components. Herein, a compact TiO2 @VN heterostructure with high true density (5.01 g cm-3 ) is proposed crafted by ingenious selective nitridation, serving as carbon-free dual-capable hosts for both sulfur and lithium. As a heavy S host, the interface-engineered heterostructure integrates adsorptive TiO2 with high conductive VN and concurrently yields a built-in electric field for charge-redistribution at the TiO2 /VN interfaces with enlarged active locations for trapping-migration-conversion of polysulfides. Thus-fabricated TiO2 @VN-S composite harnessing high tap-density favors constructing dense cathodes (≈1.7 g cm-3 ) with low porosity (<30 vol%), exhibiting dual-boosted cathode-level peak volumetric-/gravimetric-energy-densities nearly 1700 Wh L-1 cathode /1000 Wh kg-1 cathode at sulfur loading of 4.2 mg cm-2 and prominent areal capacity (6.7 mAh cm-2 ) at 7.6 mg cm-2 with reduced electrolyte (<10 µL mg-1 sulfur ). Particular lithiophilicity of the TiO2 @VN is demonstrated as Li host to uniformly tune Li nucleation with restrained dendrite growth, consequently bestowing the assembled full-cell with high electrode-level volumetric/gravimetric-energy-density beyond 950 Wh L-1 cathode+anode /560 Wh kg-1 cathode+anode at 3.6 mg cm-2 sulfur loading alongside limited lithium excess (≈50%).