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As a new generation of capacitors, lithium-ion capacitors (LICs) have the same power density and cycle life as traditional electric double-layer capacitors, and 2-5 times the energy density. For the first time, in this paper we derive the mathematical formulas for the energy density of LICs. These formulas describe the relationship between the energy density of LICs and all the critical parameters, including the specific capacities of anode (negative) and cathode (positive) electrodes, the capacity ratio of anode to cathode electrodes, the maximum and minimum voltages of the LICs, the specific capacity of pre-lithiation source and the degree of the pre-lithiation and so on. These formulas provide not only a clear direction for future research in materials and devices of LICs, but also a useful tool for LIC design. [ABSTRACT FROM AUTHOR]

In this study, the importance of the preparation technique of Li4Ti5O12 (LTO) anode on its performance in a lithium-ion capacitor (LIC) application was investigated. These desired characteristics include energy density, rate capability, and cycle life. The samples were prepared using three approaches, and the same sol-gel synthesis procedure is applied to obtain phase-pure samples and keep the structural properties similar. The influence of these methods on the LTO anodes was then explored in both half-cell and full-cell LIC devices with an activated carbon (AC) cathode. It was observed that the samples had similar specific capacities and energy densities at low specific currents. However, significant differences were observed in the samples' morphological properties, the rate capability, and the full-cell cycle life performance. Electrochemical impedance spectroscopy was used to identify the electrochemical kinetics and revealed that the LIC with the best performance was influenced by the LTO anode having the least charge transfer and diffusion resistances prepared using a surfactant. This was due to the small particle size, good particle dispersion, and high specific surface area of the LTO anode. This result points to the importance of the choice of synthesis technique in LIC material's overall performance. [ABSTRACT FROM AUTHOR]

The lithium-ion capacitor (LIC) is a recent innovation in the area of electrochemical energy storage that hybridizes lithium-ion battery anode material and an electrochemical double layer capacitor cathode material as its electrodes. The high power compared to batteries and higher energy compared to capacitors has made it a promising energy-storage device for powering hand-held and portable electronic systems/consumer electronics, hybrid electric vehicles, and electric vehicles. The swelling and gassing of the LIC when subjected to abuse conditions is still a critical issue concerning the safe application in power electronics and commercial devices. However, it is imperative to carry out a thorough investigation that characterizes the safe operation of LICs. We investigated and studied the safety of LIC for commercial applications, by conducting a comprehensive abuse tests on LIC 200 F pouch cells with voltage range from 3.8 V to 2.2 V manufactured by General Capacitors LLC. The abuse tests include overcharge, external short circuit, crush (flat metal plate and blunt indentation), nail penetration test, and external heat test. [ABSTRACT FROM AUTHOR]

In recent years, an increased attention has been focused on Li-ion capacitors (LICs) which are high power hybrid devices. Various carbon materials (hard carbon (HC), soft carbon (SC) and graphite) have been investigated for use as the negative electrodes for LICs. The rate capabilities are compared by half cells with carbon anode as working electrode and lithium foil as counter electrode, and by LIC full cells with test current density up to 20 mA cm-2 . It is found that the LIC with HC and SC at 20 mA cm-2 can be maintained up to 72.5% and 70%, compared to that at 0.5 mA cm-2, which is better power performance than the graphite materials. LICs with both HC and SC as anodes displayed better cycle lifes than graphite anode. After 100,000 high-rate charge-discharge cycles, the capacity retention of the LIC with HC anode maintained higher than 85%. The Scanning electron microscopy (SEM) images, surface area and the pore size distribution are also studied and compared for the various carbon anode materials. [ABSTRACT FROM AUTHOR]

We proposed an electrochemical capacitor that consists of a battery/double-layer capacitor or a pseudocapacitor/pseudocapacitor electrode configuration, with charge transferring during the charge and discharge processes. This is fundamentally different from exiting capacitors including conventional double-layer electrochemical capacitors and asymmetrical cells. The ions in the proposed capacitors are shuttled between two electrodes during the charge and discharge cycle. The theoretical energy density of the proposed asymmetric capacitors is as high as 60 W h/kg vs less than 15 and 25 W h/kg for conventional double-layer capacitors and battery/double-layer capacitors, respectively. [ABSTRACT FROM AUTHOR]

The ac and dc performance and leakage current of Evans tantalum oxide-ruthenium oxide hybrid capacitors were characterized at room temperature. The RC time constants were in the range from 2 to 0.45 ms and dependent on the maximum operational voltage of the capacitor. The gravimetric and volumetric energy densities of hybrid capacitors were in the range of 0.074-0.233 J/g and 0.388-1.384 J/cm³, respectively. The gravimetric and volumetric power densities of hybrid capacitors were in the range of 19-259 W/g and 100-1540 W/cm³, respectively. A comparison of the performance between hybrid capacitors to conventional aluminum and tantalum electrolytic capacitors is made in this paper. [ABSTRACT FROM AUTHOR]

Lithium-ion capacitors (LICs) were investigated for high power, moderate energy density applications for operation in extreme environments with prolonged cycle-life performance. The LICs were assembled as three-layered pouch cells in an asymmetric configuration employing Faradaic pre-lithiated hard carbon anodes and non-Faradaic ion adsorption-desorption activated carbon (AC) cathodes. The capacity retention was measured under high stress conditions, while the design factor explored was electrolyte formulation using a set of carbonates and electrolyte additives, with a focus on their stability. The LIC cells were evaluated using critical performance tests under the following high stress conditions: long-term voltage floating-cycling stability at room temperature (2.2–3.8 V), high temperature storage at 3.8 V, and charge voltages up to 4.4 V. The rate performance of different electrolytes and additives was measured after the initial LIC cell formation for a 1C–10C rate. The presence of vinylene carbonate (VC) and tris (trimethylsilyl) phosphate (TMSP) were found to be essential to the improved electrochemical performance of the LIC cells under all testing conditions. [ABSTRACT FROM AUTHOR]

Abstract: A polymer gel electrolyte has been prepared based on polyvinyl alcohol, lithium salt and organic solvent N-methyl-2-pyrrolidone (NMP). This gel has the potential for use in secondary batteries and electrochemical capacitors. The conductivity of this gel electrolyte can be as high as 2×10−3–5.8×10−4 S/cm at room temperature. Functioning as separator and electrolyte, this gel system was used to evaluate the specific capacitance of an electrochemical capacitor with carbon nanotube films as the active electrodes. [Copyright &y& Elsevier]

Lithium ion capacitor is one of the most promising energy storage technologies with a higher power density and a longer cycling lifespan than Li-ion battery, but also a higher energy density than supercapacitor. However, the unbalanced electrochemical performance between the cathode and anode will inevitably result in unsatisfied power density and reduced cycling lifespan, which largely hinders its commercial applications. In order to eliminate the unbalanced kinetic behavior and cycling stability between the cathode and anode, in this study, we propose a practical and universal electrode matching approach for constructing high performance LIC systems. The effect of effective anode potential range on the performance of a typical LIC system was investigated. An optimal anode potential range is determined and then realized through pre-lithiation to pair with cathode, by which a much improved LIC with high energy density, large power density as well as long cycling lifespan is achieved. Based on the above findings, this approach brings some new insights on ideal anode material candidates for future LIC systems. • A practical and universal matching approach is proposed. • The approach for common lithium ion capacitor system is systemically demonstrated. • The approach brings new insight for anode candidates of lithium ion capacitors. [ABSTRACT FROM AUTHOR]