RESUMEN
The lithium and sodium storage behavior of porous carbon remains controversial, though it shows excellent cycling stability and rate performances. This Letter discloses the insertion, adsorption, and filling properties of porous carbon. 7Li nuclear magnetic resonance (NMR) spectroscopy recognized inserted and adsorbed lithium in this porous carbon but did not observe any other forms of lithium above 0.0 V vs. Li+/Li. In addition, although lithium insertion mainly takes place at low potentials, adsorption was found to be the main form of lithium storage throughout the investigated potential range. Such a storage feature is responsible for the excellent rate performance and high specific capacity of porous carbon. Raman spectroscopy further demonstrated the structural reversibility of the carbon in different potential ranges, verifying the necessity to optimize the potential range for a better cycling performance. These findings provide insights for the design and application of porous carbon.
RESUMEN
Lithium metal is an ideal anode material due to its high specific capacity and low redox potential. However, issues such as dendritic growth and low Coulombic efficiency prevent its application in secondary lithium batteries. The use of three-dimensional (3D) porous current collector is an effective strategy to solve these problems. Herein, commercial carbon nanotube (CNT) sponge is used as a 3D current collector for dendrite-free lithium metal deposition to improve the Coulombic efficiency and the cycle stability of the lithium metal batteries. The high specific surface area of the CNT increases the density of the lithium nucleation sites and ensures the uniform lithium deposition while the "pre-lithiation" behavior of the porous CNT enhances its affinity with the deposited lithium. Meanwhile, the lithium plating/stripping on the sponge maintains high Coulombic efficiency and high cycling stability due to the robust structure of graphitic-amorphous carbon composite in the ether-based electrolyte. Our findings exhibit the feasibility of using CNT sponge as a 3D porous current collector for lithium deposition. They shed light on designing and developing advanced current collectors for the lithium metal electrode and will promote the commercialization of the secondary lithium batteries.
RESUMEN
Low storage capacity and poor cycling stability are the main drawbacks of the electrode materials for sodium-ion (Na-ion) batteries, due to the large radius of the Na ion. Here we show that micro-structured molybdenum disulfide (MoS2 ) can exhibit high storage capacity and excellent cycling and rate performances as an anode material for Na-ion batteries by controlling its intercalation depth and optimizing the binder. The former method is to preserve the layered structure of MoS2 , whereas the latter maintains the integrity of the electrode during cycling. A reversible capacity of 90 mAh g(-1) is obtained on a potential plateau feature when less than 0.5 Na per formula unit is intercalated into micro-MoS2 . The fully discharged electrode with sodium alginate (NaAlg) binder delivers a high reversible capacity of 420 mAh g(-1) . Both cells show excellent cycling performance. These findings indicate that metal chalcogenides, for example, MoS2 , can be promising Na-storage materials if their operation potential range and the binder can be appropriately optimized.
RESUMEN
MXene nanosheets have been used for preparing highly flexible integrated electrodes due to their two-dimensional (2D) morphology, flexibility, high conductivity, and abundant functional groups. However, restacking of 2D nanosheets inhibits the ion transport in MXene electrodes, limiting their thickness, rate performance, and energy storage capacity. Here, we employed a natural sedimentation method instead of the conventional vacuum-assisted filtration to prepare flexible Ti3C2Tx MXene films with enlarged interlayer spacing, which facilitates the access of the lithium ions to the interlayers and thus leads to a greatly enhanced electrochemical performance. The naturally sedimented flexible film shows a double lithium storage capacity compared to the conventional vacuum-filtered MXene film, along with improved rate performance and excellent cycle stability.
RESUMEN
Silicon is a promising anode material with high capacity for lithium-ion batteries (LIBs) but suffers from poor conductivity and large volume change during charge/discharge. Herein, by using two-dimensional conductive MXene as a multifunctional binder instead of conventional insulating polymer binders such as poly(vinylidene fluoride) or carboxymethylcellulose sodium (PVDF and CMC, respectively), a free-standing, flexible Si@C film was fabricated by simple vacuum filtration and directly used as anode for LIBs. In the MXene-bonded Si@C film, MXene constructed a three-dimensional conductive framework in which Si@C nanocomposites were embedded. Its loose and porous structure provided much space to buffer the large volume expansion of Si@C nanoparticles and thus led to significantly superior cycle stability compared with conventional CMC- and PVDF-bonded Si@C electrodes. Moreover, the porous structure and the metallically conductive MXene offered fast ion transport and outstanding conductivity of the MXene-bonded Si@C film, which were favorable for its rate performance. These results promise good potential of the MXene-bonded Si@C film electrode for LIBs.
RESUMEN
With the high energy density of 2600 W h kg-1, lithium-sulfur (Li-S) batteries have been considered as one of the most promising energy storage systems. However, the serious capacity fading resulting from the shuttle effect hinders its commercial application. Encapsulating small S2-4 molecules into the pores of ultramicroporous carbon (UMC) can eliminate the dissolved polysulfides, thus completely inhibiting the shuttle effect. Nevertheless, the sulfur loading of S2-4/UMC is usually not higher than 1 mg cm-2 because of the limited pore volume of UMC, which is a great challenge for small sulfur cathode. In this paper, by applying ultralight 3D melamine formaldehyde-based carbon foam (MFC) as a current collector, we dramatically enhanced the areal sulfur loading of the S2-4 electrode with good electrochemical performances. The 3D skeleton of MFC can hold massive S2-4/UMC composites and act as a conductive network for the fast transfer of electrons and Li+ ions. Furthermore, it can serve as an electrolyte reservoir to make a sufficient contact between S2-4 and electrolyte, enhancing the utilization of S2-4. With the MFC current collector, the S2-4 electrode reaches an areal sulfur loading of 4.2 mg cm-2 and performs a capacity of 839.8 mA h g-1 as well as a capacity retention of 82.5% after 100 cycles. The 3D MFC current collector provides a new insight for the application of Li-S batteries with high areal small sulfur loading and excellent cycle stability.
RESUMEN
Different guest species, including amorphous carbon, polyvinyl pyrrolidone (PVP), ethylene diaminetrimolybdate (EDA) derived small molecules, have been successfully intercalated into a nano-scaled MoS2 (nano-MoS2). These guest species bridge the MoS2 slabs through chemical bonding and their host-guest interactions influence the structure and electrochemical performance of the nano-MoS2. When applied in lithium (Li) and sodium (Na) ion batteries, these MoS2 nanostructures exhibit distinguished intercalation thermodynamics and cycling performances. These findings shed light on the design of MoS2 nanostructures and other two-dimensional layer-structured materials.