Lithium-Ion Capacitors: A Review of Design and Active Materials

Fluorine-Free Lithium-Ion Capacitor with Enhanced Sustainability and Safety Based on Bio-Based ƴ-Valerolactone and Lithium Bis(Oxalato)Borate Electrolyte

In this work, the properties of a novel electrolyte based on the combination of bio-based ƴ-valerolactone (GVL) solvent with lithium bis(oxalato)borate (LiBOB) salt and its use for lithium-ion capacitors (LICs) are presented. It is shown that the 1 m LiBOB in GVL electrolyte displays good transport properties, high thermal stability, and the ability to prevent anodic dissolution. Its impact on the performance of both battery-type and capacitive-type electrodes is evaluated. In this regard, special attention is paid to the filming properties associated with LiBOB and GVL decomposition at the electrode surfaces. To the best of the authors' knowledge, the full-cell devices assembled in this study are the first example of a fluorine-free LIC. These devices exhibit a favorable energy-to-power ratio, delivering 80 Wh kg-1 AM at 10 000 W kg-1 AM along with excellent cycling stability, retaining 80% of the initial capacitance after 25 000 cycles. Furthermore, post-mortem analysis of the LIC electrodes is conducted to gain deeper insights into the degradation mechanisms within the device.

High-Performance Li-Ion and Na-Ion Capacitors Based on a Spinel Li4Ti5O12 Anode and Carbonaceous Cathodes

Lithium-ion hybrid capacitors (LICs) have become promising electrochemical energy storage systems that overcome the limitations of lithium-ion batteries and electrical double-layer capacitors. The asymmetric combination of these devices enhances the overall electrochemical performance by delivering simultaneous energy and power capabilities. Lithium titanate (Li4Ti5O12, LTO), a spinel zero-strain material, has been studied extensively as an anode material for LIC applications because of its high-rate capability, negligible volume change, and enhanced cycling performance. Here, the different synthetic methods and modifications of the intercalation-type LTO to enhance the overall electrochemical performance of LICs are mainly focused. Moreover, the cathodic part (i.e., the activated carbon derived from various sources, including natural products, polymers, and inorganic materials) is also dealt with as it contributes substantially to the overall performance of the LIC. Not only do the anode and cathode, but also the electrolytes have a substantial influence on LIC performance. The electrolytes used in LTO-based LICs as well as in flexible and bendable configurations are also mentioned. Overall, the previous work along with other available reports on LTO-based LICs in a simplified way is analyzed.

Characterization of Activated Carbon from Rice Husk for Enhanced Energy Storage Devices

The production of activated carbon (AC) from lignocellulosic biomass through chemical activation is gaining global attention due to its scalability, economic viability, and environmental advantages. Chemical activation offers several benefits, including energy efficiency, reduced carbonization time, and lower temperature requirements. In this study, potassium hydroxide (KOH) was employed for chemical activation, resulting in activated carbon with a high specific surface area of ~3050 m2/g. The structural analysis revealed the presence of graphitized carbon in the activated carbon matrix, accounting for over 15%. The X-ray diffraction (XRD) technique was employed to investigate the activated carbon derived from rice husk (RH). The potential applications of activated carbon obtained from rice husks through chemical activation were explored, including its use for heavy metal removal, elimination of organic pollutants, and as an active material in hybrid energy storage devices. Furthermore, a scaling methodology for the production of activated carbon was proposed, facilitating its industrial implementation.

Interphase stabilized electrospun SnO2 fibers as alloy anode via restricted cycling for Li-ion capacitors with high energy and wide temperature operation

The second-generation supercapacitor comprises the hybridized energy storage mechanism of Lithium-ion batteries and electrical double-layer capacitors, i.e, Lithium-ion capacitors (LICs). The electrospun SnO₂ nanofibers are synthesized by a simple electrospinning technique and are directly used as anode material for LICs with activated carbon (AC) as a cathode. However, before the assembly, the battery-type electrode SnO₂ is electrochemically pre-lithiated (Li_xSn + Li₂O), and AC loading is balanced with respect to its half-cell performance. First, the SnO₂ is tested in the half-cell assembly with a limited potential window of 0.005 to 1 V vs. Li to avoid the conversion reaction of Sn⁰ to SnO_x. Also, the limited potential window allows only the reversible alloy/de-alloying process. Finally, the assembled LIC, AC/(Li_xSn + Li₂O), displayed a maximum energy density of 185.88 Wh kg^-1 with ultra-long cyclic durability of over 20,000 cycles. Further, the LIC is also exposed to various temperature conditions (-10, 0, 25, & 50 °C) to study the feasibility of using them in different environmental conditions.

Towards Self-Powered WSN: The Design of Ultra-Low-Power Wireless Sensor Transmission Unit Based on Indoor Solar Energy Harvester

The current revolution in communication and information technology is facilitating the Internet of Things (IoT) infrastructure. Wireless Sensor Networks (WSN) are a broad category of IoT applications. However, power management in WSN poses a significant challenge when the WSN is required to operate for a long duration without the presence of a consistent power source. In this paper, we develop a batteryless, ultra-low-power Wireless Sensor Transmission Unit (WSTx) depending on the solar-energy harvester and LoRa technology. We investigate the feasibility of harvesting ambient indoor light using polycrystalline photovoltaic (PV) cells with a maximum power of 1.4 mW. The study provides comprehensive power management design details and a description of the anticipated challenges. The measured power consumption of the developed WSTx was 0.02109 mW during the sleep mode and 11.1 mW during the operation mode. The harvesting system can harvest energy up to 1.2 mW per second, where the harvested energy can power the WSTx for six hours with a maximum power efficiency of 85.714%.

Impact of Full Prelithiation of Si-Based Anodes on the Rate and Cycle Performance of Li-Ion Capacitors

The impact of full prelithiation on the rate and cycle performance of a Si-based Li-ion capacitor (LIC) was investigated. Full prelithiation of the anode was achieved by assembling a half cell with a 2 µm-sized Si anode (0 V vs. Li/Li+) and Li metal. A three-electrode full cell (100% prelithiation) was assembled using an activated carbon (AC) cathode with a high specific surface area (3041 m2/g), fully prelithiated Si anode, and Li metal reference electrode. A three-electrode full cell (87% prelithiation) using a Si anode prelithiated with 87% Li ions was also assembled. Both cells displayed similar energy density levels at a lower power density (200 Wh/kg at ≤100 W/kg; based on the total mass of AC and Si). However, at a higher power density (1 kW/kg), the 100% prelithiation cell maintained a high energy density (180 Wh/kg), whereas that of the 87% prelithiation cell was significantly reduced (80 Wh/kg). During charge/discharge cycling at ~1 kW/kg, the energy density retention of the 100% prelithiation cell was higher than that of the 87% prelithiation cell. The larger irreversibility of the Si anode during the initial Li-ion uptake/release cycles confirmed that the simple full prelithiation process is essential for Si-based LIC cells.

A Comprehensive Review of Lithium-Ion Capacitor Technology: Theory, Development, Modeling, Thermal Management Systems, and Applications

This review paper aims to provide the background and literature review of a hybrid energy storage system (ESS) called a lithium-ion capacitor (LiC). Since the LiC structure is formed based on the anode of lithium-ion batteries (LiB) and cathode of electric double-layer capacitors (EDLCs), a short overview of LiBs and EDLCs is presented following the motivation of hybrid ESSs. Then, the used materials in LiC technology are elaborated. Later, a discussion regarding the current knowledge and recent development related to electro-thermal and lifetime modeling for the LiCs is given. As the performance and lifetime of LiCs highly depends on the operating temperature, heat transfer modeling and heat generation mechanisms of the LiC technology have been introduced, and the published papers considering the thermal management of LiCs have been listed and discussed. In the last section, the applications of LiCs have been elaborated.

Facile In Situ Synthesis of Co(OH)2-Ni3S2 Nanowires on Ni Foam for Use in High-Energy-Density Supercapacitors

Ni3S2 nanowires were synthesized in situ using a one-pot hydrothermal reaction on Ni foam (NF) for use in supercapacitors as a positive electrode, and various contents (0.3-0.6 mmol) of Co(OH)2 shells were coated onto the surfaces of the Ni3S2 nanowire cores to improve the electrochemical properties. The Ni3S2 nanowires were uniformly formed on the smooth NF surface, and the Co(OH)2 shell was formed on the Ni3S2 nanowire surface. By direct NF participation as a reactant without adding any other Ni source, Ni3S2 was formed more closely to the NF surface, and the Co(OH)2 shell suppressed the loss of active material during charging-discharging, yielding excellent electrochemical properties. The Co(OH)2-Ni3S2/Ni electrode produced using 0.5 mmol Co(OH)2 (Co0.5-Ni3S2/Ni) exhibited a high specific capacitance of 1837 F g-1 (16.07 F cm-2) at a current density of 5 mA cm-2, and maintained a capacitance of 583 F g-1 (16.07 F cm-2) at a much higher current density of 50 mA cm-2. An asymmetric supercapacitor (ASC) with Co(OH)2-Ni3S2 and active carbon displayed a high-power density of 1036 kW kg-1 at an energy density of 43 W h kg-1 with good cycling stability, indicating its suitability for use in energy storage applications. Thus, the newly developed core-shell structure, Co(OH)2-Ni3S2, was shown to be efficient at improving the electrochemical performance.