Review of Hybrid Ion Capacitors: From Aqueous to Lithium to Sodium

The underestimated charge storage capability of carbon cathodes for advanced alkali metal-ion capacitors

Li-ion capacitors (LICs) are emerging as complementary energy storage devices to Li-ion batteries to satisfy some specific applications where high power density and long cycle life are required. Due to the wide usage of LICs, LICs with promising energy density are urgently needed; however, at this stage, the achievement of this type of LICs is the main challenge. In this study, we increased the energy density of LICs via both material optimization and charge storage mechanism exploration. Moreover, porous carbon with a high surface area of over 2800 m² g^-1 was fabricated from alkali lignin via a traditional KOH activation method assisted by self-activation. A wide voltage window of 1.0-4.8 V was applied where the synergistic storage of anions and cations was achieved. This shows that a deep discharge down to 1.0 V is necessary for the complete desorption of anions, which also triggers the adsorption of cations (Li⁺), resulting in increased capacity. However, a compromise must be made in the energy efficiency due to intensified battery polarization upon deep discharging. Furthermore, considering the natural abundance of sodium and potassium over lithium, Na- and K-ion capacitors have been investigated for sustainable development using the as-prepared carbon materials.

Direct Structure-Performance Comparison of All-Carbon Potassium and Sodium Ion Capacitors

A hybrid ion capacitor (HIC) based on potassium ions (K+) is a new high-power intermediate energy device that may occupy a unique position on the Ragone chart space. Here, a direct performance comparison of a potassium ion capacitor (KIC) versus the better-known sodium ion capacitor is provided. Tests are performed with an asymmetric architecture based on bulk ion insertion, partially ordered, dense carbon anode (hard carbon, HC) opposing N- and O-rich ion adsorption, high surface area, cathode (activated carbon, AC). A classical symmetric "supercapacitor-like" configuration AC-AC is analyzed in parallel. For asymmetric K-based HC-AC devices, there are significant high-rate limitations associated with ion insertion into the anode, making it much inferior to Na-based HC-AC devices. A much larger charge-discharge hysteresis (overpotential), more than an order of magnitude higher impedance R SEI, and much worse cyclability are observed. However, K-based AC-AC devices obtained on-par energy, power, and cyclability with their Na counterpart. Therefore, while KICs are extremely scientifically interesting, more work is needed to tailor the structure of  "Na-inherited" dense carbon anodes and electrolytes for satisfactory K ion insertion. Conversely, it should be possible to utilize many existing high surface area adsorption carbons for fast rate K application.

NASICON-Structured NaTi2(PO4)3 for Sustainable Energy Storage

Several emerging energy storage technologies and systems have been demonstrated that feature low cost, high rate capability, and durability for potential use in large-scale grid and high-power applications. Owing to its outstanding ion conductivity, ultrafast Na-ion insertion kinetics, excellent structural stability, and large theoretical capacity, the sodium superionic conductor (NASICON)-structured insertion material NaTi2(PO4)3 (NTP) has attracted considerable attention as the optimal electrode material for sodium-ion batteries (SIBs) and Na-ion hybrid capacitors (NHCs). On the basis of recent studies, NaTi2(PO4)3 has raised the rate capabilities, cycling stability, and mass loading of rechargeable SIBs and NHCs to commercially acceptable levels. In this comprehensive review, starting with the structures and electrochemical properties of NTP, we present recent progress in the application of NTP to SIBs, including non-aqueous batteries, aqueous batteries, aqueous batteries with desalination, and sodium-ion hybrid capacitors. After a thorough discussion of the unique NASICON structure of NTP, various strategies for improving the performance of NTP electrode have been presented and summarized in detail. Further, the major challenges and perspectives regarding the prospects for the use of NTP-based electrodes in energy storage systems have also been summarized to offer a guideline for further improving the performance of NTP-based electrodes.

Strongly Coupled Pyridine-V2 O5 ·nH2 O Nanowires with Intercalation Pseudocapacitance and Stabilized Layer for High Energy Sodium Ion Capacitors

Developing pseudocapacitive cathodes for sodium ion capacitors (SICs) is very significant for enhancing energy density of SICs. Vanadium oxides cathodes with pseudocapacitive behavior are able to offer high capacity. However, the capacity fading caused by the irreversible collapse of layer structure remains a major issue. Herein, based on the Acid-Base Proton theory, a strongly coupled layered pyridine-V₂ O₅ ·nH₂ O nanowires cathode is reported for highly efficient sodium ion storage. By density functional theory calculations, in situ X-ray diffraction, and ex situ Fourier-transform infrared spectroscopy, a strong interaction between protonated pyridine and VO group is confirmed and stable during cycling. The pyridine-V₂ O₅ ·nH₂ O nanowires deliver long-term cyclability (over 3000 cycles), large pseudocapacitive behavior (78% capacitive contribution at 1 mV s^-1 ) and outstanding rate capability. The assembled pyridine-V₂ O₅ ·nH₂ O//graphitic mesocarbon microbead SIC delivers high energy density of ≈96 Wh kg^-1 (at 59 W kg^-1 ) and power density of 14 kW kg^-1 (at 37.5 Wh kg^-1 ). The present work highlights the strategy of realizing strong interaction in the interlayer of V₂ O₅ ·nH₂ O to enhance the electrochemical performance of vanadium oxides cathodes. The strategy could be extended for improving the electrochemical performance of other layered materials.

Metal-ion batteries meet supercapacitors: high capacity and high rate capability rechargeable batteries with organic cathodes and a Na/K alloy anode

Organic polymers were used with a NaK-based anode to make ultrafast stable batteries with high energy densities.

Towards establishing standard performance metrics for batteries, supercapacitors and beyond

Electrochemical energy storage (EES) materials and devices should be evaluated against clear and rigorous metrics to realize the true promises as well as the limitations of these fast-moving technologies.

A rough endoplasmic reticulum-like VSe2/rGO anode for superior sodium-ion capacitors

A rough endoplasmic reticulum-like VSe₂/rGO were designed to tackle the sluggish sodium ion storage and severe volume expansion in a sodium ion capacitor.

Homologous Hierarchical Porous Hollow Carbon Spheres Anode and Bowls Cathode Enabling High-Energy Sodium-Ion Hybrid Capacitors

It is a highly expected avenue to construct dual-carbon sodium-ion hybrid capacitors (SIHCs) using hierarchical porous carbon with interconnected pores, high accessible surface area, and disordered carbon frameworks for ameliorating the sluggish kinetics of SIHCs. In this work, a novel dual-carbon SIHCs system with homologous enhanced kinetics hierarchical porous hollow carbon spheres (HPCS) and hierarchical porous hollow carbon bowls (HPCB) as the anode and cathode is constructed for the first time. In a Na half-cell configuration, the HPCS anode synthesized through a facile one-pot in-situ template route demonstrates a superior reversible capacity as well as outstanding rate capability and cycleability, and the HPCB cathode fabricated by chemical activation of HPCS exhibits excellent capacitive behaviors. Thanks to superior properties and structures of the anode and cathode, the constructed novel dual-carbon SIHCs present an exceptionally high energy/power density (128.5 Wh kg^-1 and 11.9 kW kg^-1), along with a long cycling lifespan with retained morphology. This study on the kinetics of enhanced dual-carbon SIHCs opens a new avenue for optimizing the microstructure of hierarchical porous carbon and constructing new type of high-performance SIHCs systems.