Huadong Yuan

Pillared Structure Design of MXene with Ultralarge Interlayer Spacing for High-Performance Lithium-Ion Capacitors

Two-dimensional transition-metal carbide materials (termed MXene) have attracted huge attention in the field of electrochemical energy storage due to their excellent electrical conductivity, high volumetric capacity, etc. Herein, with inspiration from the interesting structure of pillared interlayered clays, we attempt to fabricate pillared Ti3C2 MXene (CTAB-Sn(IV)@Ti3C2) via a facile liquid-phase cetyltrimethylammonium bromide (CTAB) prepillaring and Sn4+ pillaring method. The interlayer spacing of Ti3C2 MXene can be controlled according to the size of the intercalated prepillaring agent (cationic surfactant) and can reach 2.708 nm with 177% increase compared with the original spacing of 0.977 nm, which is currently the maximum value according to our knowledge. Because of the pillar effect, the assembled LIC exhibits a superior energy density of 239.50 Wh kg-1 based on the weight of CTAB-Sn(IV)@Ti3C2 even under higher power density of 10.8 kW kg-1. When CTAB-Sn(IV)@Ti3C2 anode couples with commercial AC cathode, LIC reveals higher energy density and power density compared with conventional MXene materials.

Ionic conductivity promotion of polymer electrolyte with ionic liquid grafted oxides for all-solid-state lithium–sulfur batteries

Recently, great attention has been paid to all-solid-state lithium–sulfur (Li–S) batteries for their high energy density and security. But large-scale application of this technology is hindered by the poor ionic conductivity of solid-state electrolytes and high interfacial resistance at ambient temperature. In addition, seeking an appropriate carbon matrix for solid-state Li–S batteries is challenging. Herein, with the purpose of addressing these problems, N-doped carbon nanosheets (N-CNs) as a matrix for optimizing a sulfur cathode was successfully prepared. Furthermore, we fabricated innovative poly(ethylene oxide) (PEO)-based solid-state polymer electrolytes (SSPEs) containing ionic liquid grafted oxide nanoparticles (IL@NPs), which showed high ionic conductivity at low temperatures. Additionally, the differences among IL@NPs based on ZrO2, TiO2, and SiO2 are compared. The electrolyte with IL@ZrO2 showed the highest ionic conductivity of 4.95 × 10−4, 2.32 × 10−4 S cm−1 at 50 and 37 °C, respectively. With advanced and innovative designs in both cathode and electrolyte, our solid-state Li–S battery exhibits improved electrochemical performance. The battery with SSPEs based on IL@ZrO2 delivered a high specific capacity of 986, 600 mA h g−1 at 50 and 37 °C, respectively. Its believed that this strategy, using IL@NPs added SSPEs and the N-CNs/S cathode, may shed light on prospective applications with all-solid-state Li–S batteries.

Enhanced sulfide chemisorption by conductive Al-doped ZnO decorated carbon nanoflakes for advanced Li–S batteries

Lithium–sulfur batteries have attracted significant attention recently due to their high theoretical capacity, energy density and cost effectiveness. However, sulfur cathodes suffer from issues such as shuttle effects, uncontrollable deposition of lithium sulfides species, and volume expansion of sulfur, which result in rapid capacity fading and low Coulombic efficiency. In recent years, metal-oxide nanostructures have been widely used in Li–S batteries, owing to their effective inhibition of the shuttle effect and controlled deposition of lithium sulfide. However, the nonconductive metal-oxides used in Li–S batteries suffer from extra diffusion process, which slows down the electrochemical reaction kinetics. Herein, we report the synthesis of carbon nanoflakes decorated with conductive aluminium-doped zinc oxide (AZO@C) nanoparticles, through a facile biotemplating method using kapok fibers as both the template and carbon source. A sulfur cathode based on the AZO@C nanocomposites shows better electrochemical performance than those of cathodes based on ZnO and Al2O3 with poor conductivity, with a stable capacity of 927 mAh·g−1 at 0.1C (1C = 1,675 mA·g−1) after 100 cycles. A reversible capacity of 544 mAh·g−1 after 300 cycles was obtained even after increasing the current density to 0.5C, with a 0.039% capacity decay per cycle under a sulfur loading of 3.3 mg·cm−2. Moreover, a capacity of 466 mAh·g−1 after 100 cycles at 0.5C could still be obtained when the sulfur loading was increased to 6.96 mg·cm−2. The excellent electrochemical performance of the AZO@C/S composite can be attributed to its high conductivity of the polar AZO host, which suppresses the shuttle effect while simultaneously improving the redox kinetics in the reciprocal transformation of lithium sulfide species.

Mg2B2O5 Nanowire Enabled Multifunctional Solid-State Electrolytes with High Ionic Conductivity, Excellent Mechanical Properties, and Flame-Retardant Performance

High ionic conductivity, satisfactory mechanical properties, and wide electrochemical windows are crucial factors for composite electrolytes employed in solid-state lithium-ion batteries (SSLIBs). Based on these considerations, we fabricate Mg2B2O5 nanowire enabled poly(ethylene oxide) (PEO)-based solid-state electrolytes (SSEs). Notably, these SSEs have enhanced ionic conductivity and a large electrochemical window. The elevated ionic conductivity is attributed to the improved motion of PEO chains and the increased Li migrating pathway on the interface between Mg2B2O5 and PEO-LiTFSI. Moreover, the interaction between Mg2B2O5 and -SO2- in TFSI- anions could also benefit the improvement of conductivity. In addition, the SSEs containing Mg2B2O5 nanowires exhibit improved the mechanical properties and flame-retardant performance, which are all superior to the pristine PEO-LiTFSI electrolyte. When these multifunctional SSEs are paired with LiFePO4 cathodes and lithium metal anodes, the SSLIBs show better rate performance and higher cyclic capacity of 150, 106, and 50 mAh g-1 under 0.2 C at 50, 40, and 30 °C. This strategy of employing Mg2B2O5 nanowires provides the design guidelines of assembling multifunctional SSLIBs with high ionic conductivity, excellent mechanical properties, and flame-retardant performance at the same time.

Tunable pseudocapacitance storage of MXene by cation pillaring for high performance sodium-ion capacitors

2D transition metal carbide materials called MXene have attracted significant interest in the field of electrochemical energy storage due to their high electrical conductivity and high volumetric capacity. However, the low capacity accompanied by sluggish sodiation kinetics of electrodes made from multi-layer MXene has limited their further application for sodium ion storage. The key challenge to overcome the abovementioned issue is to decrease the Na+ diffusion barrier and increase the active site concentration in MXene electrodes used for Na+ storage. In this study, a method to significantly improve the capacity and kinetics of Ti3C2 MXene for Na+ storage using facile alkali metal ion pillaring is reported. After Na+ pillaring, the MXene sheets (Na–Ti3C2) with incremental interlayer spacing exhibit a high reversible capacity of 175 mA h g−1 (∼170% of the original value) at 0.1 A g−1 and an excellent outstanding cycling stability for 2000 cycles at 2.0 A g−1 for sodium ion storage. By combining ex situ XPS with kinetics analysis, the increased number of active sites and lower Na+ diffusion barrier were confirmed after Na+ pillaring when compared with the cases of Ti3C2, Li–Ti3C2, and K–Ti3C2. The role of the terminal groups (–OH) in Na–Ti3C2 has also been confirmed by analysis of the electrochemical performance of the annealed Na–Ti3C2 samples (450 °C and 700 °C). The results show that the existence of –OH groups in Na–Ti3C2 can increase the number of Na+ storage active sites, but decrease the kinetics. By coupling the Na–Ti3C2 anode with an AC cathode, the assembled SIC device delivers a high energy density of 80.2 W h kg−1 and high power density (6172 W kg−1) with an ultra-long and stable cycling performance (capacity retention: ∼78.4 at 2 A g−1 after 15 000 cycles).

Enhancing Catalyzed Decomposition of Na2CO3 with Co2MnOx Nanowire-Decorated Carbon Fibers for Advanced Na–CO2 Batteries

The metal-CO2 batteries, especially Na-CO2, batteries come into sight owing to their high energy density, ability for CO2 capture, and the abundance of sodium resource. Besides the sluggish electrochemical reactions at the gas cathodes and the instability of the electrolyte at a high voltage, the final discharge product Na2CO3 is a solid and poor conductor of electricity, which may cause the high overpotential and poor cycle performance for the Na-CO2 batteries. The promotion of decomposition of Na2CO3 should be an efficient strategy to enhance the electrochemical performance. Here, we design a facile Na2CO3 activation experiment to screen the efficient cathode catalyst for the Na-CO2 batteries. It is found that the Co2MnO x nanowire-decorated carbon fibers (CMO@CF) can promote the Na2CO3 decomposition at the lowest voltage among all these metal oxide-decorated carbon fiber structures. After assembling the Na-CO2 batteries, the electrodes based on CMO@CF show lower overpotential and better cycling performance compared with the electrodes based on pristine carbon fibers and other metal oxide-modified carbon fibers. We believe this catalyst screening method and the freestanding structure of the CMO@CF electrode may provide an important reference for the development of advanced Na-CO2 batteries.