Sodium-ion hybrid capacitor (SIHC) is one of the most promising alternatives for large-scale energy storage due to its high energy and power densities, natural abundance, and low cost. However, overcoming the imbalance between slow Na+ reaction kinetics of battery-type anodes and rapid ion adsorption/desorption of capacitive cathodes is a significant challenge. Here, we propose the high-rate-performance NiS2@OMGC anode material composed of monodispersed NiS2 nanocrystals (8.8 ± 1.7 nm in size) and N, S-co-doped graphenic carbon (GC). The NiS2@OMGC material has a three-dimensionally ordered macroporous (3DOM) morphology, and numerous NiS2 nanocrystals are uniformly embedded in GC, forming a core–shell structure in the local area. Ultrafine NiS2 nanocrystals and their nano–microstructure demonstrate high pseudocapacitive Na-storage capability and thus excellent rate performance (355.7 mAh/g at 20.0 A/g). A SIHC device fabricated using NiS2@OMGC and commercial activated carbon (AC) cathode exhibits ultrahigh energy densities (197.4 Wh/kg at 398.8 W/kg) and power densities (43.9 kW/kg at 41.3 Wh/kg), together with a long life span. This outcome exemplifies the rational architecture and composition design of this type of anode material. This strategy can be extended to the design and synthesis of a wide range of high-performance electrode materials for energy storage applications.
Silicon (Si) is a potential high-capacity anode material for the next-generation lithium-ion battery with high energy density. However, Si anodes suffer from severe interfacial chemistry issues, such as side reactions at the electrode/electrolyte interface, leading to poor electrochemical cycling stability. Herein, we demonstrate the fabrication of a conformal fluorine-containing carbon (FC) layer on Si particles (Si-FC) and its in situ electrochemical conversion into a LiF-rich carbon layer above 1.5 V (vs. Li+/Li). The as-formed LiF-rich carbon layer not only isolates the active Si and electrolytes, leading to the suppression of side reactions, but also induces the formation of a robust solid–electrolyte interface (SEI), leading to the stable interfacial chemistry of as-designed Si-FC particles. The Si-FC electrode has a high initial Coulombic efficiency (CE) of 84.8% and a high reversible capacity of 1450 mAh/g at 0.4 C (1000 mA/g) for 300 cycles. In addition, a hybrid electrode consisting of 85 wt% graphite and 15 wt% Si-FC, and mass 2.3 mg/cm2 loading delivers a high areal capacity of 2.0 mAh/cm2 and a high-capacity retention of 93.2% after 100 cycles, showing the prospects for practical use.
The safe operating voltage and low volume variation of Li3VO4 (LVO) make it an ideal anode material for lithium (Li)-ion batteries. However, the insufficient understanding of the inner storage mechanism hinders the design of LVO-based electrodes. Herein, we investigate, for the first time, the Li-ion storage activity in LVO via Cl doping. Moreover, N-doped C coating was simultaneously achieved in the Cl doping process, resulting in synergistically improved reaction kinetics. As a result, the as-prepared Cl-doped Li3VO4 coated with N-doped C (Cl-LVO@NC) electrodes deliver a discharge capacity of 884.1 mAh/g after 200 cycles at 0.2 A/g, which is the highest among all of the LVO-based electrodes. The Cl-LVO@NC electrodes also exhibit high-capacity retention of 331.1 mAh/g at 8.0 A/g and full capacity recovery after 5 periods of rate testing over 400 cycles. After 5000 cycles at 4.0 A/g, the discharge capacity can be maintained at 423.2 mAh/g, which is superior to most LVO-based electrodes. The Li-ion storage activity in LVO via Cl doping and significant improvement in the high-rate Li-ion storage reported in this work can be used as references for the design of advanced LVO-based electrodes for high-power applications.
With the increasing scale of energy storage, it is urgently demanding for further advancements on battery technologies in terms of energy density, cost, cycle life and safety. The development of lithium-ion batteries (LIBs) not only relies on electrodes, but also the functional electrolyte systems to achieve controllable formation of solid electrolyte interphase and high ionic conductivity. In order to satisfy the needs of higher energy density, high-voltage (> 4.3 V) cathodes such as Li-rich layered compounds, olivine LiNiPO4, spinel LiNi0.5Mn1.5O4 have been extensively studied. However, high-voltage cathode-based LIBs fade rapidly mainly owing to the anodic decomposition of electrolytes, gradually thickening of interfacial passivation layer and vast irreversible capacity loss, hence encountering huge obstacle toward practical applications. To tackle this roadblock, substantial progress has been made toward oxidation-resistant electrolytes to block its side reaction with high-voltage cathodes. In this review, we discuss degradation mechanisms of electrolytes at electrolyte/cathode interface and ideal requirements of electrolytes for high-voltage cathode, as well as summarize recent advances of oxidation-resistant electrolyte optimization mainly from solvents and additives. With these insights, it is anticipated that development of liquid electrolyte tolerable to high-voltage cathode will boost the large-scale practical applications of high-voltage cathode-based LIBs.
The development of reliable and low-cost energy storage systems is of considerable value in using renewable and clean energy sources, and exploring advanced electrodes with high reversible capacity, excellent rate performance, and long cycling life for Li/Na/Zn-ion batteries and supercapacitors is the key problem. Particularly because of their diverse structure, high specific surface area, and adjustable redox activity, electrically conductive metal–organic frameworks (c-MOFs) are considered promising candidates for these electrochemical applications, and a detailed overview of the recent progress of c-MOFs for electrochemical energy storage and their intrinsic energy storage mechanism helps realize a comprehensive and systematic understanding of this progress and further achieve highly efficient energy storage and conversion. Herein, the chemical structure of c-MOFs and their conductive mechanism are first introduced. Subsequently, a comprehensive summarization of the current applications of c-MOFs in energy storage systems, namely supercapacitors, LIBs, SIBs, and ZIBs, is presented. Finally, the prospects and challenges of c-MOFs toward much higher-performance energy storage devices are presented, which should illuminate the future scientific research and practical applications of c-MOFs in energy storage fields.
Designing high-performance nanostructured electrode materials is the current core of electrochemical energy storage devices. Multi-scaled nanomaterials have triggered considerable interest because they effectively combine a library of advantages of each component on different scales for energy storage. However, serious aggregation, structural degradation, and even poor stability of nanomaterials are well-known issues during electrochemically driven volume expansion/contraction processes. The confinement strategy provides a new route to construct controllable internal void spaces to avoid the intrinsic volume effects of nanomaterials during the reaction or charge/discharge process. Herein, we discuss the confinement strategies and methods for energy storage-related electrode materials with a one-dimensional channel, two-dimensional interlayer, and three-dimensional space as reaction environments. For each confinement environment, the correlation between the confinement condition/structure and the behavioral characteristics of energy storage devices in the scope of metal–ion batteries (e.g., Li-ion, Na-ion, K-ion, and Mg-ion batteries), Li–S batteries (LSBs), Zn–air batteries (ZIBs), and supercapacitors. Finally, we discussed the challenges and perspectives on future nanomaterial confinement strategies for electrochemical energy storage devices.