Mechanically Robust Current Collector with Gradient Lithiophilicity Induced by Spontaneous Lithium Ion Diffusion for Stable Lean-Lithium Metal Batteries.

Lean-lithium metal batteries represent an advanced version of the anode-free lithium metal batteries, which can ensure high energy density and cycling stability while addressing the safety concerns and the loss of energy density caused by excessive lithium metal. Herein, a mechanically robust carbon nanotube framework current collector with gradient lithiophilicity is constructed for a lean-lithium metal battery. Using the physical vapor deposition method, precise prelithiation of a carbon nanotube framework is achieved, eliminating its irreversible capacity, retaining the porous structure in the framework, and inducing the gradient lithiophilicity formation due to spontaneous lithium ion diffusion. The lithiophilic gradient and three-dimensional porous structure are characterized by time-of-flight secondary ion mass spectrometry (TOF-SIMS), scanning transmission electron microscopy (STEM), and corresponding electron energy loss spectroscopy (EELS), which enables the preferential deposition of lithium ions at the bottom of the carbon nanotube framework, thereby avoiding lithium losses associated with dead lithium. As a result, in the LiFePO4 full cell with an ultralow N/P ratio of 0.15, the initial Coulombic efficiency increases from 77.75 to 95.07%. Collaborating synergistically with the ultrathin (1.5 µm) lithium metal, serving as a gradual lithium supplement, the full cell with an N/P ratio of 1.43 demonstrates an 86% capacity retention after 500 cycles at 1C, far surpassing the copper-based counterparts (0.9%).

Ultrathin Cobalt Phthalocyanine@Graphene Oxide Layer-Modified Separator for Stable Lithium-Sulfur Batteries.

Rechargeable lithium-sulfur (Li-S) batteries have aroused great attention due to their high energy density and low cost. However, Li-S batteries suffer from rapid capacity decay owing to the shuttle effect of the intermediate polysulfides. To tackle this issue, functional separators with the ability to absorb polysulfides play a vital role to block them from passing through the separator. Herein, an ultrathin and lightweight layer of graphene oxide (GO) loaded with Co phthalocyanine (CoPc) is fabricated on a polypropylene (PP) separator. The thickness of CoPc@GO is about 200 nm with a low areal mass of 22 µg cm-2. CoPc is uniformly dispersed on GO sheets through π-π interactions, which inhibits the shuttle effect and facilitates the conversion of the intermediate polysulfides. In consequence, the battery with a CoPc@GO-PP separator exhibits good cycling stability with a low-capacity decay rate of 0.076% per cycle at 1 C over 400 cycles and a high specific capacity of 919 mA h g-1 after 250 cycles at 0.5 C.