Lei Yang,Xinyu Wang,Chunliu Zhu,Haozhi Wang,Jing Shi,Jingwei Chen,Weiqian Tian,Yue Zhu,Minghua Huang,Jingyi Wu,Huanlei Wang
Molybdenum sulfide (MoS 2 ) is a prospective anode material for potassium-ion batteries, owing to its large interlayer spacing and superior theoretical capacity. Nevertheless, its practical application is hindered by sluggish kinetics and inferior structural stability, which limit its potassium storage performance. Herein, we employ hollow hard-soft carbon bowls (HSCB), consisting of soft carbon uniformly coated on hard carbon bowls, as nanoreactors to confine few-layered MoS 2 nanosheets. The mesoporous carbon shells of HSCB enhance electrolyte penetration and enable rapid charge transfer and robust structural protection, while the mechanical coupling induced by pore filling, alongside the exist of C S Mo chemical bonds, further reinforces the structural integrity of MoS 2 . Additionally, the creation of few-layered MoS 2 structures and MoS 2 /carbon heterostructures promotes efficient K-ion adsorption and diffusion. Notably, there is a strong linear relationship between MoS 2 content and electrochemical performance, including initial Coulomb efficiency, rate performance, and reaction kinetics. Consequently, the optimized MoS 2 /HSCB anode demonstrating a superior reversible capacity of 630 mAh g −1 at 0.1 A g −1 , an exceptional rate capacity of 251 mAh g −1 at 10 A g −1 , and excellent cycling stability, retaining 369 mAh g −1 at 0.5 A g −1 after 700 cycles. Remarkably, a potassium-ion hybrid capacitor assembled with MoS 2 /HSCB anode achieves superior energy/power densities of 122 Wh kg −1 /11266 W kg −1 , along with splendid capacity retention of 89.5 % after 5000 cycles. This work not only offers an innovative approach for the structural engineering of high-performance sulfide-based composite materials but also elucidates the impact of sulfide content on electrochemical performance.
There is always a mutual inhibition relationship between porosity and electrical conductivity . Rational design of hard-soft carbon to regulate the graphitization degree is an effective strategy to solve this problem. Herein, we reported an efficient method to synthesize hard-soft carbon by grafting polyaniline (PANI) onto carboxymethyl chitosan (CMC), followed by calcination with potassium oxalate. The CMC-PANI derived carbon (CPC) exhibits an interconnected framework with a high specific surface area. The graphitization degree can be controlled by the grafting ratio of PANI. The highly uniform distribution of hard-soft carbon increases the electrical conductivity which permits fast electrons/ions transfer. Benefiting from these features, CPC-3 delivers an enhanced specific capacitance of 337 F g −1 at 1 A g −1 . The CV curves of the assembled symmetric supercapacitors (SCs) have no obvious distortion even at the scan rate of 500 mV s −1 , indicating a favorable rate capability. The SCs manifest the maximum energy density of 28.72 Wh Kg −1 at a power density of 450 W kg −1 , as well as excellent cycle stability with 97.5 % capacity retention after 5000 cycles at 10 A g −1 . This work affords a new sight to prepare uniformly distributed hard-soft carbon materials for SCs with high cycle stability and rate performance.
Carbon-based materials are the most prospective anodes. Typically, a single carbon-based material is applied to different energy storage systems (EESs) without modification. However, the microcrystal structure of carbon plays a decisive role in the energy storage performance, and therefore, it should be adjusted when applied to different EESs. Here, a hierarchical porous carbon monomer monolith (HPCM) embedded with carbon nanotubes blooming on ZIF-67 was designed as a soft–hard carbon-based freestanding thick electrode for achieving high-energy lithium-ion and sodium-ion batteries. HPCM is resorcinol–formaldehyde (RF) resin-derived carbon, mainly composed of hard carbon, which has outstanding mechanical properties, a high surface area, and high porosity. Carbon nanotubes (CNTs) derived from ZIF-67 have extraordinary electronic conductivity, which provides soft carbon. High-temperature CO2 etching was performed to adjust the microcrystal structure, and the lithium/sodium storage performance of the electrode was evaluated. After CO2 etching, the materials lose almost half their weight (mainly hard carbon), and pseudocapacitive contribution decreases for both lithium-ion and sodium-ion batteries, whereas the specific capacity increases for lithium-ion batteries and decreases for sodium-ion batteries. Capacities of 5.96 mAh cm–2 (areal) and 132.48 mAh cm–3 (volumetric) were achieved for lithium storage, and those for sodium storage were 2.31 and 51.24 mAh cm–3, respectively. In summary, it is significant to adjust the microcrystal structure of carbon-based electrodes, and this study provides related experience for lithium and sodium storage.
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