Unique Core–Shell Nanorod Arrays with Polyaniline Deposited into Mesoporous NiCo₂O₄ Support for High-Performance Supercapacitor Electrodes

Polyaniline (PANI), one of the most attractive conducting polymers for supercapacitors, demonstrates a great potential as high performance pseudocapacitor materials. However, the poor cycle life owing to structural instability remains as the major hurdle for its practical application; hence, making the structure-to-performance design on the PANI-based supercapacitors is highly desirable. In this work, unique core–shell NiCo₂O₄@PANI nanorod arrays (NRAs) are rationally designed and employed as the electrode material for supercapacitors. With highly porous NiCo₂O₄ as the conductive core and strain buffer support and nanoscale PANI layer as the electrochemically active component, such a heterostructure achieves favorably high capacitance while maintaining good cycling stability and rate capability. By adopting the optimally uniform and intimate coating of PANI, the fabricated electrode exhibits a high specific capacitance of 901 F g^–1 at 1 A g^–1 in 1 M H₂SO₄ electrolyte and outstanding capacitance retention of ∼91% after 3000 cycles at a high current density of 10 A g^–1, which is superior to the electrochemical performance of most reported PANI-based pseudocapacitors in literature. The enhanced electrochemical performance demonstrates the complementary contributions of both componential structures in the hybrid electrode design. Also, this work propels a new direction of utilizing porous matrix as the highly effective support for polymers toward efficient energy storage

Enhanced Pseudocapacitive Performance of α‑MnO₂ by Cation Preinsertion

Although the theoretical capacitance of MnO₂ is 1370 F g^–1 based on the Mn³⁺/Mn⁴⁺ redox couple, most of the reported capacitances in literature are far below the theoretical value even when the material goes to nanoscale. To understand this discrepancy, in this work, the electrochemical behavior and charge storage mechanism of K⁺-inserted α-MnO₂ (or K_<i>x</i>MnO₂) nanorod arrays in broad potential windows are investigated. It is found that electrochemical behavior of K_<i>x</i>MnO₂ is highly dependent on the potential window. During cyclic voltammetry cycling in a broad potential window, K⁺ ions can be replaced by Na⁺ ions, which determines the pseudocapacitance of the electrode. The K⁺ or Na⁺ ions cannot be fully extracted when the upper cutoff potential is less than 1 V vs Ag/AgCl, which retards the release of full capacitance. As the cyclic voltammetry potential window is extended to 0–1.2 V, enhanced specific capacitance can be obtained with the emerging of new redox peaks. In contrast, the K⁺-free α-MnO₂ nanorod arrays show no redox peaks in the same potential window together with much lower specific capacitance. This work provides new insights on understanding the charge storage mechanism of MnO₂ and new strategy to further improve the specific capacitance of MnO₂-based electrodes

Gradient Nitrogen Doping in the Garnet Electrolyte for Highly Efficient Solid-State-Electrolyte/Li Interface by N₂ Plasma

Solid-state lithium batteries (SSBs) have been widely researched as next-generation energy storage technologies due to their high energy density and high safety. However, lithium dendrite growth through the solid electrolyte usually results from the catastrophic interface contact between the solid electrolyte and lithium metal. Herein, a gradient nitrogen-doping strategy by nitrogen plasma is introduced to modify the surface and subsurface of the garnet electrolyte, which not only etches the surface impurities (e.g., Li2CO3) but also generates an in situ formed Li3N-rich interphase between the solid electrolyte and lithium anode. As a result, the Li/LLZTON-3/Li cells show a low interfacial resistance (3.50 Ω cm2) with a critical current density of about 0.65 mA cm–2 at room temperature and 1.60 mA cm–2 at 60 °C, as well as a stable cycling life for over 1300 h at 0.4 mA cm–2 at room temperature. A hybrid solid-state full cell paired with a LiFePO4 cathode exhibits excellent cycling durability and rate performance at room temperature. These results demonstrate a rational strategy to enable lithium utilization in SSBs

Flexible and Self-Standing Urchinlike V₂O₃@Carbon Nanofibers toward Ultralong Cycle Lifespan Lithium-Ion Batteries

In this study, V2O3@carbon nanofibers as flexible anode materials were synthesized via electrospinning. The electrode showed a specific discharge capacity with 495 mA h g–1 at 1000 mA g–1 after 1000 cycles. Surprisingly, the electrode fabricated from the V2O3@carbon nanofibers exhibited a specific capacity of 336 mA h g–1 at 5000 mA g–1. Even after 10,000 cycles, it still displayed a specific discharge capacity of 290 mA h g–1, indicating that it has outstanding capacity advantages and long-cycle lifespan. The large specific surface area and abundant active sites of urchinlike V2O3 were considered as the reasons for its outstanding electrochemical performance. The combination of V2O3 and the carbon nanofibers formed a complete conductive network that enhanced the conductivity of the sample, reduced the diffusion path of Li+, and eased the volume change during intercalation/deintercalation of Li+. These results not only demonstrated that the flexible V2O3@carbon nanofibers prepared herein have broad application prospects as an anode for LIBs but also offer a processing strategy for fabricating other state-of-the-art flexible electrode materials for energy storage systems