Electronic-ionic bi-functional conduction β-Li₃PS₄-coated graphene hollow spheres as a highly stable lithium metal...

Although Li metal is considered the most potential anode for Li based batteries, the repeatedly large volume variation and low Coulombic efficiency (CE) are still serious challenges for commercial application. Herein, the interconnect closed hollow graphene spheres with electronic-ionic bi-functional conduction network containing Li_4.4Sn nanoparticles loaded internally and β-Li₃PS₄ solid electrolyte layer coated externally (β-LPS/SG/Li_4.4Sn) is proposed to achieve uniform and dense Li deposition. Density functional theory (DFT) calculation and experimental results show that Li_4.4Sn owns larger Li binding energy and lower nucleation overpotential than spherical graphene (SG), thus being able to guide Li traversing and depositing inside the hollow spheres. The Tafel curves, Li⁺ diffusion activation energy and experimental results reveal that the β-Li₃PS₄ coating layer significantly improves the ionic conductivity of the negative skeleton, covers the defect sites on the SG surface, provides continuous ion transmission channels and accelerates Li⁺ migration rate. The synergy of both can inhibit the formation of dendritic Li and reduce side reaction between freshly deposited lithium and the organic electrolyte. It's found that Li is preferentially deposited within the SG, evenly deposited on the spherical shell surface until it's completely filled to obtain a dense lithium layer without tip effect. As a result, the β-LPS/SG/Li_4.4Sn anode exhibits a long life of up to 2800 h, an extremely low overpotential (∼13 mV) and a high CE of 99.8 % after 470 cycles. The LiFePO₄-based full cell runs stably with a high capacity retention of 86.93 % after 800 cycles at 1C. It is considered that the novel structure design of Li anode skeleton with electron-ionic bi-functional conduction is a promising direction to construct long-term stable lithium metal anodes.