Ni2P electrocatalysts decorated hollow carbon spheres as bi-functional mediator against shuttle effect and Li dendrite for Li-S batteries

Highlights: • Ni₂P decorated hollow carbon spheres (Ni₂P-HCS) were constructed as bi-functional mediator for Li-S batteries. • As the interlayer, Ni₂P-HCS has strong interaction and efficient electrocatalysis toward polysulfides. • As the Li host, lithiated Ni₂P-HCS (mixed ion-electron conductor Li₃P/Ni) enables regulated Li deposition. • Catalytic effectiveness value was proposed to evaluate the catalytic efficiency of diverse catalysts more intuitively. Lithium-sulfur (Li-S) batteries are promising candidates for next-generation energy storage devices, while shuttle effect and Li dendrite growth severely obstruct the practical applications. Herein, well-dispersed Ni₂P electrocatalysts decorated hollow carbon spheres (Ni₂P-HCS) are constructed as high-efficiency bi-functional mediator for Li-S batteries. Benefiting from polar surface and high electrical conductivity, Ni₂P-HCS possesses strong interaction and efficient electrocatalysis toward polysulfides. Moreover, regulated Li deposition behavior is realized on lithiated Ni₂P-HCS surface ascribed to its lithiophilicity and as-formed mixed ion-electron conducting host composed of Li₃P and Ni. As a result, the assembled Li-S full cells with Ni₂P-HCS used as interlayer and Li host exhibit excellent rate capability (755.5 mAh g⁻¹ at 2 C) and long-term cycling stability (capacity fading rate of 0.05% per cycle at 1 C after 500 cycles). Importantly, high areal capacity (6.67 mAh cm⁻²) with high sulfur loading of 5.9 mg cm⁻² at low E/S ratio (6.8 μL mg⁻¹) is achieved. The loading coefficient and catalytic effectiveness value (CEV) are proposed to evaluate catalytic efficiency of electrocatalysts. This work exploits the potential of metal phosphides in concurrently solving challenges for S cathode and Li anode, and offers insight into developing high-efficiency electrocatalysts for advanced Li-S batteries.