Three-dimensional hierarchically porous MoS2 foam as high-rate and stable lithium-ion battery anode

Abstract

Architected materials that actively respond to external stimuli hold tantalizing prospects for applications in energy storage, wearable electronics, and bioengineering. Molybdenum disulfide, an excellent two-dimensional building block, is a promising candidate for lithium-ion battery anode. However, the stacked and brittle two-dimensional layered structure limits its rate capability and electrochemical stability. Here we report the dewetting-induced manufacturing of two-dimensional molybdenum disulfide nanosheets into a three-dimensional foam with a structural hierarchy across seven orders of magnitude. Our molybdenum disulfide foam provides an interpenetrating network for efficient charge transport, rapid ion diffusion, and mechanically resilient and chemically stable support for electrochemical reactions. These features induce a pseudocapacitive energy storage mechanism involving molybdenum redox reactions, confirmed by in-situ X-ray absorption near edge structure. The extraordinary electrochemical performance of molybdenum disulfide foam outperforms most reported molybdenum disulfide-based Lithium-ion battery anodes and state-of-the-art materials. This work opens promising inroads for various applications where special properties arise from hierarchical architecture.

Fig. 1. Printing 3D MoS₂ foam through dewetting-induced manufacturing.

a The manufacturing scheme illustrates the EHD setup and the structural evolution of the MoS₂ foam. b Demonstration of up-scalable manufacturing of MoS₂ foam on a 4-inch copper (Cu) substrate that comprises structural hierarchies over seven orders of magnitude, including (c) interconnected porous networks, (d) architected structure, (e) vortical truss unit cell, (f) nanopores and struts, (g) intertwined MoS₂ sheets, (h) tears and holes on the basal plane, and (i) S vacancies.

Fig. 2. Electrochemical performance of MoS₂ foam along with MoS₂ bulk, wrinkled film, and crumples.

a Rate capacity performance is measured at different current densities. b Galvanostatic discharge and charge profiles of MoS₂ foam were measured at the first 10 cycles. c Cycling stability comparison at the current density of 5 A g⁻¹. d The volumetric capacity of MoS₂ foam outperforms various state-of-the-art anodes and compares favorably to the current benchmark of 2D BP composite anodes, reproduced from ref. [20]. e Cycling performance of MoS₂ foam anodes was measured at current densities of 5 A g⁻¹ and 10 A g⁻¹ each for 1000 cycles.

Fig. 3. Structural stability and capacity retention of MoS₂ foam.

a SEM images of pre- (left panel) and post-compression (right panel) of MoS₂ foam to 50% of displacement demonstrate an excellent recovery behavior. b The load and displacement curve (displacement to 50%) displays a ductile-like feature with continuous serrated flow (gray arrows), attesting to the multistep deformation of the hierarchical structure. c The load and displacement curve (displacement to 10%) exhibits a resilient feature with great recoverability. d Li-ion diffusion and the associated concentration distribution within the architected MoS₂ at different state-of-charge (SOC). The highest concentration of scale bar at SOC = 100% is calculated from the theoretical capacity of pristine MoS₂. e Volume expansion at various SOC. About 70% at SOC = 100%. SEM images of (f) pristine MoS₂ foam and (g) MoS₂ foam after 1000 charge/discharge cycles prove the uniform formation of the SEI layer while the hierarchical structure remains intact.

Fig. 4. Pseudocapacitive charge storage contributes to the MoS₂ foam’s excellent rate capacity.

a Nyquist plots of MoS₂ foam and MoS₂ bulk electrode at a fully discharged state after ten cycles at 100 mA g⁻¹. b CV measurements feature the 2nd cycle of MoS₂ foam and MoS₂ bulk electrodes under 1 mV s⁻¹ in the voltage window between 0.01–3 V. c Capacitive effects are characterized by analyzing the CV curves at various sweep rates based on i = av^b, where the measured current i follows a power-law relationship with the sweep rate v. d Capacitive and diffusion-controlled charge storage contributions for architected MoS₂ cycled in a Li-ion electrolyte at a scan rate of 1 mV s⁻¹.

Fig. 5. In situ XANES tracking of Mo redox reaction in MoS₂ foam anode.

a Normalized operando Mo K-edge XANES spectra of architected MoS₂ foam electrode measured at different potentials (blue: the discharging process; red: the charging process). b Normalized operando Mo K-edge XANES spectra for the first cycle at open-circuit voltage (OCV, 2.86 V), the first fully discharge (0.01 V), and the first fully charge (3 V) of MoS₂, compared with MoO₃ and Mo metal foil reference materials. c The cyclic voltammograms of architected MoS₂ foam anode at a scan rate of 0.3 mV s⁻¹ and (d) the corresponding absorption edge energy shift (ΔE_edge) of architected MoS₂ foam at different potentials (labeled as colored dots in the cyclic voltammograms).