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Lithium-ion capacitors are energy storage devices between lithium-ion batteries and supercapacitors, which have both high energy density and high power density, and are considered as one of the most promising energy storage systems. In this paper, the research progress of carbon-based and lithium-embedded cathode materials in recent years was summarized, and the classification and modification methods of carbon-based and lithium-embedded electrode materials were introduced in detail. In order to further improve the performance of lithium-ion capacitors, researchers further optimized the cathode materials by means of microstructure regulation, surface modification, doping modification and composite materials, and carried out cathode and anode dynamic matching to comprehensively improve the electrochemical performance of lithium-ion capacitors. Finally, the research hotspots and development directions of cathode materials for lithium-ion capacitors in the future were reviewed in order to provide good electrochemical properties for the next generation of cathode materials for commercial applications.

A lithium ion capacitor is a kind of novel energy storage device with the combined merits of a lithium ion battery and a supercapacitor. In order to obtain a design scheme for lithium ion capacitor with as much superior performance as possible, the key research direction is the ratio of battery materials and capacitor materials in lithium ion capacitor composite cathode materials. In this work, an improved electrochemical model of a lithium ion capacitor is proposed, and the simulated results obtained from the model were validated based on experiments, including under the premise of fixed electrode quality, under the current applied to the battery material keeps unchanged, and under the current applied to the capacitor material keeps unchanged. Results show that the improved model can simulate the electrode properties of lithium ion capacitor with high precision, and 0.3~0.4 is recommended as the best volume ratio for improving the specific energy of lithium ion capacitor. [ABSTRACT FROM AUTHOR]

As a new generation of energy storage devices, lithium-ion capacitors (LICs) rationally combine high energy density and high power density, providing an alternative solution for multi-functional electronic equipment and state grid system. However, the dynamic mismatch between the battery-type anode and the capacitor-type cathode seriously limits its development and application. Herein, a high performance LIC simultaneously using carbon materials derived from Ethylenediaminetetraacetic Acid Ferric Sodium Salt (EDTA-Na-Fe) was prepared. By calcination of EDTA-Na-Fe in an inert atmosphere, nitrogen-doped carbon frameworks (NCF) can be obtained which possess a high reversible capacity and excellent rate-capability. Using this NCF as the anode and cathode of the LICs, the hybrid devices with a wide voltage window of 0.5-4.0 V are obtained. The employment of the same materials as the anode and cathode can largely simplify the fabrication process. The energy density of LICs can reach 193.4 Wh·kg-1 at a power density of 225 W·kg-1. This reasonable dynamic matching strategy can be helpful for the application of LICs.

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Research on the synthesis of activated carbon from coffee industrial waste has been successfully carried out using the pretreatment method. Samples are carried out by varying the calcination temperature (600 °C; 700 °C; 800 °C). Samples were tested for iodine to determine the surface area of activated carbon, characterized by Optical Microscopy (OM), conductivity behavior was studied by Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) testing to determine electrochemical performance. Iodine test results produce the highest surface area of 2614 m2/gr. Based on the morphological results using OM, the surface morphology looks relatively homogeneous. A lithium-ion capacitor cell with sample C1 as a carbon cathode synthesized by the steam hydrothermal method has the smallest semicircle with the highest conductivity of 14 × 10−5 S/cm and a specific capacitance of 31.25 F/g which indicates better electrochemical performance than other cells.

Copyright of Electronic Components & Materials is the property of Electronic Components & Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The lack of methods to modulate intrinsic textures of carbon cathode has seriously hindered the revelation of in-depth relationship between inherent natures and capacitive behaviors, limiting the advancement of lithium ion capacitors (LICs). Here, an orientated-designed pore size distribution (range from 0.5 to 200 nm) and graphitization engineering strategy of carbon materials through regulating molar ratios of Zn/Co ions has been proposed, which provides an effective platform to deeply evaluate the capacitive behaviors of carbon cathode. Significantly, after the systematical analysis cooperating with experimental result and density functional theory calculation, it is uncovered that the size of solvated PF6 − ion is about 1.5 nm. Moreover, the capacitive behaviors of carbon cathode could be enhanced attributed to the controlled pore size of 1.5–3 nm. Triggered with synergistic effect of graphitization and appropriate pore size distribution, optimized carbon cathode (Zn90Co10-APC) displays excellent capacitive performances with a reversible specific capacity of ~ 50 mAh g−1 at a current density of 5 A g−1. Furthermore, the assembly pre-lithiated graphite (PLG)//Zn90Co10-APC LIC could deliver a large energy density of 108 Wh kg−1 and a high power density of 150,000 W kg−1 as well as excellent long-term ability with 10,000 cycles. This elaborate work might shed light on the intensive understanding of the improved capacitive behavior in LiPF6 electrolyte and provide a feasible principle for elaborate fabrication of carbon cathodes for LIC systems.

Lithium ion capacitor (LIC) is an emerging technology that holds promise to bridge the energy‐to‐power gap between already market stablished lithium ion battery and electrochemical double‐layer capacitor technologies. Academic research is mainly focused on increasing energy, power and cycle life metrics, but next, pre‐lithiation strategy is the key that will open the final door, or not, towards industrialization and commercialization of the technology. Its relevance has only recently been thoroughly considered, but several strategies, all with their own particular set of assets, are already available within the state‐of‐the‐art. It is the right moment to make a retrospective review analysis of the pros and cons of each of the strategies, in order to draw the correct conclusions and look into the future with the best perspective. Despite some reviews newly considered the topic, they were all done in a broader framework, what finally waters down the importance of this critical step. Thus, this review aims to solely focus on the pre‐lithiation strategies that have been reported so far for LICs, from the first academic auxiliary lithium metal approach to the latest novel strategies. To conclude, challenges and requierements that the ideal pre‐lithiation strategy should fulfil in order to foster market uptake of LIC technology are also discussed. [ABSTRACT FROM AUTHOR]

Metal oxide anodes which can achieve high lithiation capacities by conversion mechanism are promising in lithium storage systems. The main obstacle to their practical applications is poor cycling performance. Regulating element ratio of multi-metal materials is effective for improving their electrochemical properties. Herein, optimized Mn–Ni–Co–O anode materials with long-cycle stability are reported. The improvement is associated with proper element ratio, which enables accelerated Li+ ion diffusion and high-stability LiF-rich solid electrolyte interphase (SEI) layer. As a result, (Ni 0 · 1 Co 0 · 3 Mn 0.6) 3 O 4 materials deliver lithiation capacities of 500 mAh g−1 after 1500 cycles at the current density of 1 A g−1. It is greatly better than other samples with different element ratio. Then, application properties of (Ni 0 · 1 Co 0 · 3 Mn 0.6) 3 O 4 materials are evaluated by assembled with active carbon and LiFePO 4 for energy storage devices, respectively. The obtained Li-ion capacitor exhibits high energy densities of 112 Wh kg−1 based on total mass of oxides and active carbon. The obtained Li-ion battery also shows good cycle stability. These results suggest lithiation capacity fade of metal oxide anodes can be mitigated by controlling their component contents. This low-cost and high effective way is to promote commercial applications of metal oxide anode materials in energy storage systems. [ABSTRACT FROM AUTHOR]

In order to inhibit the formation of lithium dendrites and solid electrolyte interface films, prevent the corrosion of electrolyte to lithium powder (Li) and improve the electrochemical properties of a lithium ion capacitor (LIC), the lithium powder was fluorinated at high temperature under the protection of nitrogen (N2) by using perfluororesin (CYTOP) as the fluorine source to obtain lithium/lithium fluoride powder (Li@LiF). Li@LiF was pre-embedded in the LIC-cathode sheet and assembled into the LIC. Scanning electron microscopy and x-ray diffraction were used to analyze and test the materials and electrode sheets. The electrochemical properties of the LIC were studied by constant-current charge and discharge (GCD) and electrochemical impedance spectroscopy. Experimental results showed that the lithium powder was successfully fluorinated, and that Li@LiF pre-embedded in the cathode can modify the electrochemical properties of the devices that store electrical charge. The specific capacitance of GCD reached 51.92 F g−1 at a current density of 50 mA g−1. In the range of 50 mA g−1 to 700 mA g−1, the smallest power density reached 68.51 Wh kg−1 and the highest energy density reached 1.02 kW kg−1. After 2000 invariant current charge and discharge cycles, the capacitance remained at about 96%. [ABSTRACT FROM AUTHOR]

High performance N-doping porous carbon (NDPC) are ideal electrode materials for Li-ion capacitors (LICs). However, the practical application of NDPC is extremely limited, which is mainly attributed to the typical methods for the scale preparation NDPC are time-consuming, high cost and low yield. Herein, we have developed a new route for high efficient, environment friendly, low cost and high yield fabrication of NDPC, using biomass waste as the carbon source and a novel eutectic salt as the activation agent. After a series of comparative experiments, the application of eutectic salt herein not only reduce the process time and cost, but also obviously enhance the yield, the specific surface area (SSA) and nitrogen-doping content of NDPC sample (labelled as NDPC-0.5). In combination of the rich N-doping level, larger SSA and interconnected porous structure, the NDPC-0.5 sample exhibit an excellent electrochemical performance as both cathode and anode materials for a LIC, with specific discharge capacities of ∼60 and 290 mAh g−1 at a current density of 5 A g−1. The resultant NDPC-0.5//NDPC-0.5 LIC device delivers a high energy density of 116.9 Wh kg−1 at 500 W kg−1, with a capacity retention of 81% after 8000 cycles at 2 A g−1. Image 1 [ABSTRACT FROM AUTHOR]

Li4Ti5O12‐TiO2 (LTO‐TO) composite is coated on carbon foam (CF) for anode of lithium ion capacitors (LICs). The resulting CF@LTO‐TO electrodes with varied mass loadings of LTO‐TO exhibit much improved rate performance compared to pristine LTO electrode. Specifically, asymmetric LICs based on activated carbon cathode and CF@LTO‐TO anode (AC//CF@LTO‐TO) with 25 wt% of LTO‐TO delivers a specific capacity of 65 mAh g−1 at 300 C. In addition, the self‐discharge rates of the LICs are evaluated. It is found that AC//CF@LTO‐TO LIC with 45 wt% of LTO‐TO shows much reduced self‐discharge rate (open circuit voltage drops from 2.5 to 1.1 V in 144 hours) relative to AC//CF@LTO‐TO with different LTO‐TO mass loadings. The results of this study suggest that the introduction of TO in LTO anode can affect both the rate performance and the self‐discharge behavior, which may be due to the fast faradaic reaction kinetic of TO and the rich LTO‐TO grain boundary interfaces. [ABSTRACT FROM AUTHOR]

Highlights: Pore size and graphitization engineering of carbon cathode were orientated-designed by regulating the molar ratios of Zn/Co ions. Zn90Co10-APC and its assembled PLG//Zn90Co10-APC LIC both deliver the excellent electrochemical performances.The lack of methods to modulate intrinsic textures of carbon cathode has seriously hindered the revelation of in-depth relationship between inherent natures and capacitive behaviors, limiting the advancement of lithium ion capacitors (LICs). Here, an orientated-designed pore size distribution (range from 0.5 to 200 nm) and graphitization engineering strategy of carbon materials through regulating molar ratios of Zn/Co ions has been proposed, which provides an effective platform to deeply evaluate the capacitive behaviors of carbon cathode. Significantly, after the systematical analysis cooperating with experimental result and density functional theory calculation, it is uncovered that the size of solvated PF6− ion is about 1.5 nm. Moreover, the capacitive behaviors of carbon cathode could be enhanced attributed to the controlled pore size of 1.5–3 nm. Triggered with synergistic effect of graphitization and appropriate pore size distribution, optimized carbon cathode (Zn90Co10-APC) displays excellent capacitive performances with a reversible specific capacity of ~ 50 mAh g−1 at a current density of 5 A g−1. Furthermore, the assembly pre-lithiated graphite (PLG)//Zn90Co10-APC LIC could deliver a large energy density of 108 Wh kg−1 and a high power density of 150,000 W kg−1 as well as excellent long-term ability with 10,000 cycles. This elaborate work might shed light on the intensive understanding of the improved capacitive behavior in LiPF6 electrolyte and provide a feasible principle for elaborate fabrication of carbon cathodes for LIC systems. [ABSTRACT FROM AUTHOR]

Lithium ion capacitors made using prelithiated coalesced carbon onion based anode showed excellent high energy and power performance with time constant in the order of ∼1.45s. The interconnected carbon onion microstructure facilitated both rapid electron and ion transport thereby minimizing the overall resistance. Additionally, high specific capacitance was achieved through control of pore size distribution in high surface area carbons derived from polyfurfuryl alcohol based polymer blends. The fabricated capacitors can be charged and discharged in less than 30s between 2.2V − 4V with energy efficiencies >90%. The maximum achievable energy density was 120 Wh/kg with the capacitor retaining 77 Wh/kg even at a high power density of 11 kW/kg. The capacitors also demonstrated excellent cycling stability with 80% capacitance retention over 21000 cycles along with good thermal stability up to 60 °C. Image 1 [ABSTRACT FROM AUTHOR]

Activated carbon (AC) was acidified with dilute sulfuric acid (H2SO4) as an acidifying agent to obtain acidified activated carbon (HAC). The positive electrode was prepared by mixing HAC with a conductive agent (SP) or polyvinylidene fluoride. Carbon nanotubes and mesocarbon microbeads, as negative materials, were prelithiated and used as the negative eletrode. The positive electrode and negative electrode were assembled into the lithium ion capacitor. Materials and electrodes were characterized by scanning electron microscopy; elemental analysis, chemical bond analysis and specific surface area analysis of acidified activated carbon were made by x-ray energy spectrum analysis, an intelligent Fourier transform infrared spectrometer and specific surface space as well as a porosimetry analyzer (BET); The electrochemical capability of lithium ion capacitors was tested by constant current charge and discharge as well as electrochemical impedance. From the results, it can be concluded that the activated carbon acidified successfully grafted with hydroxyl (OH) and carboxyl (COOH) functional groups has increased the surface area by about 60% compared with AC. Under this situation, the charge and discharge current density is 50 mA/g. Also the capacitor has a mass ratio of 40.17 F/g, whose maximum power density is 0.98 kW/kg (700 mA/g) and maximum energy density is 52.34 Wh/kg (50 mA/g). Impedance tests showed that it has low impedance characteristics; the capacitance retention rate is above 60% after 2000 cycles of charge and discharge; the energy density can still reach 21.68 Wh/kg with a power density of 0.98 kW/kg. The electrochemical capability of the lithium ion capacitor was improved with acidified activated carbon as positive electrode. [ABSTRACT FROM AUTHOR]

An efficient, convenient and flexible polyvinylidene fluoride/tetrabutylammonium hexafluorophosphate hierarchical nanofiber membrane (PVDF/TBAPF6 HNM) was successfully fabricated by one-step electrospinning and used as the separator of Li-ion capacitor (LIC). The PVDF/TBAPF6 HNMs displayed high ion conductivity of 4.28 × 10−3 S/cm, high mechanical strength, porosity, wettability and excellent thermal performance. Furthermore, the separator of PVDF/TBAPF6 HNM possessed lower interfacial resistance (134Ω) and better electrochemical stability, which exhibits better capacity retention and coulombic efficiency, compared with the commercial celgard 2340 separator. We believe that the gel polymer PVDF/TBAPF6 HNMs separator will have great potential in the field of the separator of LIC. The PVDF/TBAPF6 nanofiber gel membrane with hierarchical structure exhibited excellent cycle performance due to the effect of TBAPF6 and hierarchical structure. Image 100 • A hierarchical nanofiber membrane (HNM) was fabricated by electrospinning. • The HNM possessed good mechanical property and excellent thermal stability. • The HNMs showed superior ion conductivity (4.28*10−3 S/cm). • The HNMs exhibited long cycle stability and excellent interfacial compatibility. [ABSTRACT FROM AUTHOR]

Activated carbon (AC) has been utilized for various applications including as an electrode for supercapacitor, i.e., electric double-layer capacitor (EDLC) as well as hybrid capacitor such as lithium ion capacitor. In this research, salacca peel was used as a raw material for AC. It was chosen among other biomass wastes because it is abundant and is still considered as a waste. The hydrothermal carbonization was conducted at 5 MPa, temperature of 200–250 °C, and 5 h in subcritical water, which is a green dehydrating agent. The effect of parameters (temperature and addition of citric acid as a catalyst) on the hydrochar and AC product was investigated. The hydrochar from hydrothermal carbonization was activated by chemical activation using potassium hydroxide (KOH) as an activated agent to enhance the surface area and porosity. The morphology of both hydrochar and AC was measured by scanning electron microscopy (SEM), its chemical transformation was measured by Fourier transform infrared spectroscopy (FTIR) while the surface area and pore size distribution were measured by nitrogen adsorption at 77.35 K. The electrochemical performance of activated carbon from salacca peel as well as commercial activated carbon using a coin cell in a Li half-cell system was evaluated by CV, GCD, and EIS. The results show that the presence of citric acid contributes to higher specific capacitance in the rate performance test of LIC at different current density as well as in long rate stability test. [ABSTRACT FROM AUTHOR]

Modelling and numerical simulations play a vital role in the design and optimization of electrochemical energy storage devices. In this study, a general physics-based model is developed to describe Hybrid Asymmetric Capacitors (HACs). A one-dimensional cell is constructed with one faradaic electrode, a separator and a capacitive electrode. The model is validated using a commercial Lithium Ion Capacitor (LIC). Galvanostatic charge and discharge processes are simulated with a maximum mean relative error of 7.8%. This suggest that this simple Ohmic model captures the key electrochemical phenomena occurring inside the LIC cell. Image 1 • A general physics-based model is developed in 1D to simulate HAC. • A commercial LIC is used to validate the general ohmic model. • Numerical results reproduce accurately experimental electrical features of the LIC. • Maximum mean relative error achieved in galvanostatic processes is less than 7.8%. [ABSTRACT FROM AUTHOR]

Abstract In this work, a lithium ion capacitor (LIC) based on carbon electrodes prepared from furfuryl alcohol-derived polymers is presented. While furfuryl alcohol is not a new carbon precursor, it has been evaluated in the past mainly for negative electrodes with Li-ion insertion. Here we describe both an activated carbon (AC) and a hard carbon (HC) made from the same furfuryl alcohol-derived polymers, for both electrodes of the LIC. The polymerization technique used to make carbon from the furfuryl alcohol precursor is different from all the methods described earlier, and is flexible enough to make soft, high surface area AC, as well as a denser, low surface area HC. The HC and the HC-based negative electrode used in this study are targeted at a high-energy and high-power LIC application by specifically reducing the carbon particle size to sub-micrometric levels, using a HC with a specific surface area of ∼300 m2 g−1 and keeping the electrode mass loading to <2 mg cm−2. The HC delivers a stable capacity of ∼400 mAh g−1 vs. Li+/Li at C/10, with excellent capacity retention of 50% at 10C (>200 mAh g−1) and 25% at 50C (∼100 mAh g−1). The AC used for the capacitor-type positive electrode was activated to a specific surface area of ∼1670 m2 g−1. For comparison purposes, a symmetric electric double layer capacitor (EDLC) using the same AC, in a 1.5 M Et 4 NBF 4 (acetonitrile) electrolyte, was also fabricated. Overall, the LIC showed considerably higher energy density over its EDLC counterpart, delivering a maximum energy density (based on the total electrode active mass weight) of 150 Wh kg−1 AM at a power density of 150 W kg−1 AM , with a 66% retention of the initial energy at the highly demanding 10,000 W kg−1 AM power peak point. Additionally, long cycle life was measured, with 83% capacitance retention after 10,000 cycles. Graphical abstract Image 1 Highlights • Synthesis of Hard Carbon and Activated Carbon from furfuryl alcohol. • Development of ultrafast performing Hard Carbon (<100 mAh g−1 at 50C). • Fabrication of Lithium Ion Capacitor with mass balance 1:2 (HC:AC). • Fabrication of Lithium Ion Capacitor exceeding 100 Wh Kg−1 AM at 10 KW Kg−1 AM. • Lithium Ion Capacitor with 83% capacity retention after 10,000 cycles. [ABSTRACT FROM AUTHOR]

Supercapacitors means electrochemical capacitors are being considered these days to be a good alternative for the conventional power sources (fuel cells and batteries) in many applications because of their high power density, long cycle life and less charging and discharging time. This review article presents an overview of different types of supercapacitors (electrical double-layer capacitors (EDLCs), pseudocapacitors and hybrid supercapacitors. The device configurations (symmetric, asymmetric and hybrid), the mechanism of charge storing at the surface (ion adsorption for EDLCs and fast surface redox reactions for pseudocapacitors) and the effect of electrode material (activated carbon, carbon aerogels, carbon fabrics, carbide-derived carbons, carbon nanotubes (CNTs), graphene, biomass, etc. for EDLCs and conducting polymers and insertion type compounds for pseudocapacitors) and electrolytes are crucial. Electrolytes used in the supercapacitors also play important role to determine its operating voltage range, energy density, power density, etc. Both the classes of electrolytes, liquid electrolytes (aqueous, organic, ionic liquids) and solid electrolytes (polymer-based electrolytes) are also discussed in the last section of this review. The voltage range, energy density and power density ultimately define their use for different applications namely heavy electric vehicles and portable electronic devices. [ABSTRACT FROM AUTHOR]

Abstract Lithium-ion capacitors are considered as a promising energy storage device to combine the high energy of lithium-ion batteries and high power of supercapacitors, and it is urgently required to evaluate the energy storage capability of lithium-ion capacitors from practical perspectives. In this work, a pouch-type lithium-ion capacitor is constructed using commercial SiO x /graphite as anode and activated carbon as cathode. Due to the outstanding tap density and electrical conductivity of SiO x /graphite anode, the reversibility and charge storage of lithium-ion capacitor pouch is greatly improved, which can function stably within a wide voltage window of 1–4 V to achieve a maximum gravimetric energy and power density of 29.3 Wh kg−1 and 6 kW kg−1, respectively (based on the total weight of pouch). Moreover, the volumetric energy and power density of this pouch also reach 50 Wh L−1 and 10 kW L−1 (based on the total volume of pouch), respectively. The achievement of both gravimetric and volumetric energy performances promises a bright future for of lithium-ion capacitors toward electrical applications where large energy-storage in limited space is demanded. Highlights • A pouch-type lithium-ion capacitor (LIC) is constructed using SiO x /graphite as anode. • High gravimetric and volumetric energy storage can be reached by this LIC. • This LIC may find applications where large energy in limited space is demanded. [ABSTRACT FROM AUTHOR]

Lithium ion capacitor (LIC) is a promising energy storage system that can simultaneously provide high energy with high rate (high power). Generally, LIC is fabricated using capacitive cathode (activated carbon, AC) and insertion‐type anode (graphite) with Li‐ion based organic electrolyte. However, the limited specific capacities of both anode and cathode materials limit the performance of LIC, in particular energy density. In this context, we have developed "two in one" synthetic approach to engineer both cathode and anode from single precursor for high performance LIC. Firstly, we have engineered a low cost 1D polypyrrole nanopipes (PPy‐NPipes), which was utilized as cathode material and delivered a maximum specific capacity of 126 mAh/g, far higher than that of conventional AC cathodes (35 mAh/g). Later, N doped carbon nanopipes (N‐CNPipes) was derived from direct carbonization of PPy‐NPipes and successfully applied as anode material in LIC. Thus, a full LIC was fabricated using both pseudo‐capacitive cathode (PPy‐NPipes) and anode (N‐CNPipes) materials, respectively. The cell delivered a remarkable specific energy of 107 Wh/kg with maximum specific power of 10 kW/kg and good capacity retention of 93 % over 2000 cycles. Thus, this work provide a new approach of utilization of nanostructured conducting polymers as a promising pseudocapacitive cathode for high performance energy storage systems. Lithium ion capacitor based on N‐doped carbon nanopipes anode and polypyrrole nanopipes cathode. Cyclic voltammetry curves shows that N‐CNPipes and PPy‐NPipes electrodes work in different working potential windows such as 0.01–3 V and 1.5–4.5 V (vs. Li/Li+), respectively. [ABSTRACT FROM AUTHOR]

Abstract Lithium-ion capacitors (LICs) emerge as the promising energy storage devices owing to their enhanced power density compared to batteries and superior energy density to electric double-layer capacitors. However, the wide use of graphite anodes in LICs results in intrinsic problems such as sluggish reaction kinetics and dendritic Li plating problem, while Li 4 Ti 5 O 12 -based electrodes exhibit low energy storage capacity and excessively high insertion potential. Herein, our research uncovers the synthesis of novel Li 2 TiSiO 5 and carbon nanofibers (LTSO/C) via a morphology-preserved thermal transformation strategy as the high-performance anodes of LICs. LTSO/C electrodes with the unique 3D interconnected nanoarchitecture consisting of aggregation-free LTSO nanoparticles exbibit high-rate behavior (ca. 50% capacity retention from 0.1 to 10 A g−1), suitable Li+ insertion potential (0.1–1 V vs. Li/Li+), and high packing density of 1.93 g cm−3 (highly comparable to graphite and larger than Li 4 Ti 5 O 12). Moreover, analysis on reaction kinetics has revealed that such high-rate performance can be attributed to the pseudocapacitive charge storage mechanism of as-synthesized LTSO/C electrodes. Afterwards, novel LICs employing LTSO/C anodes to replace graphite and Li 4 Ti 5 O 12 further yield high working potential of 4.2 V and large gravimetric energy and power densities. These results thus suggest a great promise of the proposed materials selection and nanostructure design for ultrafast and stable energy storage devices. Graphical abstract fx1 Highlights • 3D interconnected fibrous nanostructure of LTSO/C is synthesized by electrospinning. • Such LTSO/C exhibit superior rate capability as anodes of lithium-ion capacitors. • The high-rate capability is attributed to pseudocapacitive charge storage mechanism. • Assembled full-cell lithium-ion capacitors have high working potential up to 4.2 V. [ABSTRACT FROM AUTHOR]

Pre-lithiation is a critical component to improve the performance of lithium-ion capacitors. However, the process of pre-lithiation may bring some safety problems or hazards for the capacitor itself, like the danger associated with the usage of metallic lithium or impairments of the cathode. In this work, a novel cathode pre-lithiation method is proposed to avoid those problems. In this strategy, lithium ions are stored in the cathode by capacitive adsorption in advance. And they are used as the lithium source to achieve the pre-lithiation in the first few cycles. Meanwhile, the degree of pre-lithiation can also be regulated by changing the charge voltage of the capacitive adsorption. The full LIC device pre-lithiated through this method has a specific capacity of 31.4 mAh g−1. In addition to providing potential solutions for hazards associated with metallic lithium or the performance of the cathode in the production of LICs, the study will also offer some insights through a new design of the cathode pre-lithiation method. [ABSTRACT FROM AUTHOR]

Highlights • SnO 2 coated with an ultrathin carbon film was prepared by a hydro thermal method. • Pre-lithitated SnO 2 @C was employed as an anode materials for lithium ion capacitors. • Electrodes mass ratio, cut-off voltage and the degree of pre-lithiation were controlled. Abstract A porous SnO 2 electrode with an ultra-thin 2-nm-thick coating of carbon (SnO 2 @C) was prepared by a hydrothermal method. The thin carbon layer acted as a relaxant layer alleviating the stress of the volume expansion of the SnO 2 active material during intercalation/de-intercalation of lithium ions. The pre-lithiated SnO 2 @C was employed as an anode material for a non-aqueous lithium-ion capacitor (LIC) using commercial activated carbon (YP-80F) as the cathode. Different states of discharge of the pre-lithiated SnO 2 @C anode were characterized. At different lithiation degrees, phase transformation and morphology changes of the SnO 2 active material affected the electrochemical performance of the LIC system. Shallow lithiation provided insufficient lithium ions to the activated carbon cathode, yielding poor specific energy. Excessively deep lithiation risked severe crack formation on the surfaces of the SnO 2 particles, affecting the electrochemical performance at high current densities. Other parameters, including the negative-to-positive electrode mass balance and cut-off voltage control, were also studied regarding their effects on performance. The fabricated LIC (SnO 2 @C/Activated carbon) delivered a maximum energy of 130 W h kg−1 and a maximum specific power of 6900 W kg−1. [ABSTRACT FROM AUTHOR]

The 20 kW class Proton Exchange Membrane (PEM) type Water Electrolyzer (Ely) system directly coupled with photovoltaic panels (PV) was developed. In this system the number of Ely cells is changeable during operation to truck maximum power point of the PV by adjusting operation voltage. Since neither DC/DC converters nor power conditioners are used in this system, there are no power conversion loss, however the input current into Ely fluctuates due to the fluctuation of the irradiation. Lithium ion capacitors (LiC) are incorporated into PV-Ely system in order to smooth the Ely input current, that would stabilize the pressure of generated hydrogen gas and extend the lifetime of the Ely cells. Before the examination using the facility, the simulation program for the 20 kW PV-ELY-LiC system was developed. The program can simulate the operation condition of the system each one second. The simulation program can be used to estimate the current smoothing effect by the LiC. The simulation program can also contribute to a preparatory experiment and tuning of parameters in the control program for the system. [ABSTRACT FROM AUTHOR]

Abstract Depending on the nature of a particular energy storage technology, an equivalent storage system will lead to a characteristic performance. In an extreme case the system will either provide high power (if based on capacitors) or high energy (if based on lithium ion batteries). On the other hand it will lack in energy or power, respectively. Therefore, a passive parallel connection of unlike energy storage technologies is very attractive to improve cycle life as well as power and energy density in comparison to single energy storage technologies. In this approach, different lithium ion technologies are connected with different supercapacitor technologies directly in parallel. Experimental and model-based investigations show, how the energy and power density characteristics of such systems differ from each other and which advantages can be achieved in comparison to commercial systems. [ABSTRACT FROM AUTHOR]

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Abstract: Lithium ion capacitors (LICs), which are hybrid electrochemical energy storage devices combining the intercalation/deintercalation mechanism of a lithium‐ion battery (LIB) electrode with the adsorption/desorption mechanism of an electric double‐layer capacitor (EDLC) electrode, have been extensively investigated during the past few years by virtue of their high energy density, rapid power output, and excellent cycleability. In this review, the LICs are defined as the devices with an electrochemical intercalation electrode and a capacitive electrode in organic electrolytes. Both electrodes can serve as anode or cathode. Throughout the history of LICs, tremendous efforts have been devoted to design suitable electrode materials or develop novel type LIC systems. However, one of the key challenges encountered by LICs is how to balance the sluggish kinetics of intercalation electrodes with high specific capacity against the high power characteristics of capacitive electrode with low specific capacitance. Herein, the developments and the latest advances of LIC in material design strategies and key techniques according to the basic scientific problems are summarized. Perspectives for further development of LICs toward practical applications are also proposed. [ABSTRACT FROM AUTHOR]

Ionic liquid (IL) electrolytes have been applied to lithium ion capacitors (LICs) composed of porous three-dimensional (3D) current collector. LIC cells containing IL electrolytes showed reversible charge-discharge potential profiles and their capacity degradation was hardly observed during 3000 cycles. In particular, a cell with 1-ethyl-3-methyl imidazolium bis(fluorosulfonyl)imide (EMImFSI) containing lithium FSI (LiFSI) as Li salt kept over 90% of its initial capacity even after 3000 cycles. The EMImFSI-based IL electrolyte system (LiFSI/EMImFSI) also provided better rate performance than that of a conventional LiPF 6 -based organic electrolyte system. Considering high-temperature (60 °C) characteristics in the IL system and LiPF 6 -based system, charge-discharge operation in LiFSI/EMImFSI was stable compared to that in the LiPF 6 -based solvent system. Moreover, the LIC cell with LiFSI/EMImFSI was stably cycled even at 0 °C and its discharge capacity was superior to that of the LiPF 6 -based solvent electrolyte at 0 °C. [ABSTRACT FROM AUTHOR]

Lithium-ion capacitor (LIC) is a novel electrochemical energy storage device that bridges the performance gap between the electrical double-layer capacitor and lithium ion battery. In this work, we fabricated lithium-ion capacitors (LICs) with activated carbon (AC) positive electrode and pre-lithiated hard carbon (HC) negative electrode. The effect of low temperature on the electrochemical performance of LIC is investigated by the galvanostatic charging-discharging, electrochemical impedance tests, rate performance and cycle performance testing. The electrolyte viscosity increases, the ionic conductivity decreases and ionic migration becomes slow in the charge-discharge process with the decrease of temperature, causing the increase of resistance and the electrochemical polarization, which is responsible for the attenuation of LIC electrochemical performance. LIC at the temperature of −20 °C exhibits the optimal low temperature electrochemical performance, high energy density up to 76.6 Wh kg −1 and power density as high as 5.8 kW kg −1 (based on active material mass of two electrodes), excellent capacity retention of 80.1% after 5000 cycles. [ABSTRACT FROM AUTHOR]

Hard carbon is emerging as a highly promising material for power-demanded energy storage devices. Recently, introducing heteroatom such as oxygen is confirmed to be available to improve the capacity. However, it remains a significant challenge to achieve simultaneously superior high-rate capability and long-term cycling stability. Here we demonstrate that the surface oxo-funcitionalized hard carbon spheres (o-HCS, 4.2 m 2  g −1 ) derived from mild oxidative approach enhance pseudocapacitance lithium-ion storage with improved Li-ion diffusivity and thus exhibit high-rate capacity and long cycle life in both Li-ion batteries and Li-ion capacitors. The o-HCS electrode delivers specific capacity of around 275 mAh g −1 at 744 mA g −1 (2C) and capacity retention of above 92.0% and about 86.5% after 1100 and 1700 cycles, respectively. Impressively, it delivers above 110 mAh g −1 at extreme high current density of 14.88 A g −1 (40C). As well, o-HCS electrode in Li-ion capacitor shows a capacitance of 34.8 F g −1 (corresponding to 48.5 Wh kg −1 and 3.6 kW kg −1 ) at the current density of 3720 mA g −1 , and after 7000 cycles the capacity retention is 96% (∼0.057% decay per cycle). [ABSTRACT FROM AUTHOR]

Thermally curable hybrid ionogel electrolytes consisting of epoxy-functionalized POSS, amine-terminated polypropylene glycol, and ionic liquid electrolyte, 1 M LiTFSI in BMPTFSI were fabricated to give ionic conducting epoxy networks with cubic inorganic star networks crosslinked with lithium ion dissociating polypropylene glycol linkers. Characterization of these hybrid ionogels revealed high ion conduction, exceptional thermal stability, and electrochemical stability. Lithium ion capacitors fabricated with these hybrid ionogels revealed exceptional performance on par with the neat liquid ionic liquid electrolyte, and far superior over ionogels fabricated with conventional organic crosslinkers, due to the mechanical robustness and lithium ion dissociative character imparted by the POSS and PPG functionalities. [ABSTRACT FROM AUTHOR]

Hybrid capacitor configurations are now of increasing interest to overcome the current energy limitations of supercapacitors. In this work, we report a lithium ion capacitor (LIC) entirely based on graphene. On the one hand, the negative –battery-type- electrode consists of a self-standing, binder-free 3D macroporous foam formed by reduced graphene oxide and decorated with tin oxide nanoparticles (SnO 2 -rGO). On the other hand, the positive –capacitor-type- electrode is based on a thermally expanded and physically activated reduced graphene oxide (a-TEGO). For comparison purposes, a symmetric electrical double layer capacitor (EDLC) using the same activated graphene in 1.5 M Et 4 NBF 4 /ACN electrolyte is also assembled. Built in 1 M LiPF 6 EC:DMC, the graphene-based LIC shows an outstanding, 10-fold increase in energy density with respect to its EDLC counterpart at low discharge rates (up to 200 Wh kg −1 ). Furthermore, it is still capable to deliver double the energy in the high power region, within a discharge time of few seconds. [ABSTRACT FROM AUTHOR]

Porous L 4 Ti 5 O 12 (LTO) nanoparticles were prepared by a precursor directed hydrothermal method followed by sintering. The influence of sintering temperature and graphene additives on the microstructure evolution and electrochemical properties of LTO for lithium ion capacitors (LICs) was investigated. Bare LTO with fine particle and porous microstructure can be obtained under low temperature sintering (600 °C), which can deliver a specific capacity of 65.2 mAh g −1 at the current rate of 20C. With increasing temperature, the LTO particles are inclined to grow with coarse particle and the agglomerate state, deteriorating the electrochemical performances (14.3 mAh g −1 at 20C). After introduction of graphene additives, LTO can be prepared with increased surface area, pore volume and electrical conductivity, which are beneficial for LTO to contact with electrolyte, shorten the lithium diffusion length and facilitate the electron and ion transport during lithiation/delithiation process, leading to the greatly improved electrochemical performances (102 mAh g −1 at 20C). The LICs full cell using the LTO/graphene anode and activated carbon cathode was also evaluated. The decent energy/power densities (maximum energy/power densities are 44.0 Wh kg −1 and 7200 W kg −1 , respectively) with excellent cycling stability (capacitance retention of 80% at a current density of 3.2 A g −1 after 10000 cycles) show the promising application perspective. [ABSTRACT FROM AUTHOR]

In this work, we are presenting both lithium and sodium ion capacitors (LIC and NIC) entirely based on electrodes designed from recycled olive pit bio-waste derived carbon materials. On the one hand, olive pits were pyrolized to obtain a low specific surface area semigraphitic hard carbon to be used as the ion intercalation (battery-type) negative electrode. On the other hand, the same hard carbon was chemically activated with KOH to obtain a high specific surface area activated carbon that was further used as the ion-adsorption (capacitor-type) positive electrode. Both electrodes were custom-made to be assembled in a hybrid cell to either build a LIC or NIC in the corresponding Li- and Na-based electrolytes. For comparison purposes, a symmetric EDLC supercapacitor cell using the same activated carbon in 1.5 M Et 4 NBF 4 /acetonitrile electrolyte was also built. Both LIC and NIC systems demonstrate remarkable energy and power density enhancement over its EDLC counterpart while showing good cycle life. This breakthrough offers the possibility to easily fabricate versatile hybrid ion capacitors, covering a wide variety of applications where different requirements are demanded. [ABSTRACT FROM AUTHOR]

Biomass-derived activated carbon electrode materials have been synthesized by carbonization and KOH activation processes from an agriculture waste − rice husk, composed of organic compound and silica. The surface area of activated carbon reached 1098.1 m2/g mainly including mesopores and macropores due to the template effect of silica in rice husk. Owing to the existence of mesopores and macropores, the as-obtained activated carbon materials can be used in aqueous supercapacitors, lithium-ion (Li-ion) capacitors and lithium-sulfur (Li-S) batteries. In KOH electrolyte, fast rate performance (as high as 2 V/s) was obtained due to the existence of ideal electrical double layer capacitance. In organic electrolyte, high voltage (2.5 V) was achieved. Activated carbon electrode for Li-ion capacitor also showed capacity of 17 mAh/g at 100 mA/g with the high voltage range of 2.5 V. The capacities of sulfur-activated carbon in Li-S batteries were 1230 and 970 mAh/g at the current densities of 0.1 and 0.2 C. The present results showed that activated carbon materials with mesopores were good host to immobilize polysulfides. [ABSTRACT FROM AUTHOR]

In order to improve the electrochemical performance of lithium titanium oxide, Li 4 Ti 5 O 12 (LTO), for the use in the lithium-ion capacitors (LICs) application, LTO/graphene composites were synthesized through a solid state reaction. The composite exhibited an interwoven structure with LTO particles dispersed into graphene nanosheets network rather than an agglomerated state pristine LTO particles. It was found that there is an optimum percentage of graphene additives for the formation of pure LTO phase during the solid state synthesis of LTO/graphene composite. The effect of graphene nanosheets addition on electrochemical performance of LTO was investigated by a systemic characterization of galvanostatic cycling in lithium and lithium-ion cell configuration. The optimized composite exhibited a decreased polarization upon cycling and delivered a specific capacity of 173 mA h g −1 at 0.1 C and a well maintained capacity of 65 mA h g −1 even at 20 C. The energy density of 14 Wh kg −1 at a power density of 2700 W kg −1 was exhibited by a LIC full cell with a balanced mass ratio of anode to cathode along with a superior capacitance retention of 97% after 3000 cycles at a current density of 0.4 A g −1 . This boost in reversible capacity, rate capability and cycling performance was attributed to a synergistic effect of graphene nanosheets, which provided a short lithium ion diffusion path as well as facile electron conduction channels. [ABSTRACT FROM AUTHOR]

High performance composite of nanosized Li 4 Ti 5 O 12 (LTO) and graphene nanosheets was fabricated using a novel atomic layer deposition (ALD) seeded process incorporated with hydrothermal lithiation for the first time. TiO 2 nanoislands as seeds were anchored on graphene by ALD process, triggering the unique structure formation of subsequent LTO. The synergistic effects of nanosized LTO and graphene endow the composite with a short lithium ion diffusion path and efficiently conductive network for electron and ion transport, boosting the excellent reversible capacity, rate capability, and cyclic stability as anode materials for lithium ion capacitors (LICs). The reversible capacity of 120.8 mA h g −1 at an extremely high current rate of 100 C was achieved successfully, and the electrode can be charged/discharged to about 70% of the theoretical capacity of LTO in 25 s. Meanwhile, the composite exhibited excellent cyclic stability of 90% capacity retention at 20 C with nearly 100% Coulombic efficiency after 2500 cycles. The sintering treatment after hydrothermal reaction has significant effects on the crystallinity, defect density, microstructure and electrochemical property of the composite, which is also supported by theoretical calculations. The results provide a versatile roadmap for synthesis of high performance LTO based composite and new insights into LICs. [ABSTRACT FROM AUTHOR]

Lithium ion capacitor (LIC) is one of the most promising electrochemical energy storage devices, which offers rapid charging-discharging capability and long cycle life. We have fabricated LIC pouch cells using an electrochemically-driven lithium pre-doping method through a three-electrode pouch cell structure. The active materials of cathode and anode of LIC cell are activated carbon and pre-lithiated hard carbon, respectively. The electrochemical performances and the capacity fading behaviors of LICs in the voltage range of 2.0 − 4.0 V have been studied. The specific energy and specific power reach 73.6 Wh kg −1 and 11.9 kW kg −1 based on the weight of the active materials in both cathode and anode, respectively. Since the cycling performance is actually determined by hard carbon anode, the anode potential swings are emphasized. The capacity fading of LIC upon cycling is proposed to be caused by the increases of internal resistance and the consumption of lithium stored in anode. Finally, a large-capacity LIC pouch cell has been assembled with a maximum specific energy of 18.1 Wh kg −1 and a maximum specific power of 3.7 kW kg −1 based on the weight of the whole cell. [ABSTRACT FROM AUTHOR]

As an electrolyte solvent for lithium ion capacitors (LICs), tetrahydrofuran (THF) showed lots of advantages on increasing the discharge capacity, suppressing the potential drop at charged state, and improving the slope of discharge curve. Several electrochemical studies were conducted to verify these effects of THF on LICs. The open circuit potentials of AC/Li beaker-cells with THF were shifted to more positive potentials because of the lowered electrostatic potential of the electrolyte, the weakened solvation energy with LiBF 4 , and the easier adsorption of BF 4 − ions to AC electrode in aging step. Although the concentration of LiBF 4 decreased with adding THF, the electrolyte conductivity increased by the improved mobility of ions more than enough to compensate to the electrolyte conductivity decreasing by the reduced salt concentration. The capacitive resistance of activated carbon (AC)/Li cell was little changed by adding THF in fully charged state but was much smaller in fully discharged state than the reference condition. These results imply that THF seldom disturbed the behavior of BF 4 − ions but accelerated the mobility of Li + ions at AC electrode. [ABSTRACT FROM AUTHOR]

Lithium-ion capacitor (LIC) is a novel advanced electrochemical energy storage (EES) system bridging gap between lithium ion battery (LIB) and electrochemical capacitor (ECC). In this work, we report that sisal fiber activated carbon (SFAC) was synthesized by hydrothermal treatment followed by KOH activation and served as capacitive material in LIC for the first time. Different particle structure, morphology, specific surface area and heteroatoms affected the electrochemical performance of as-prepared materials and corresponding LICs. When the mass ratio of KOH to char precursor was 2, hierarchical porous structured SFAC-2 was prepared and exhibited moderate specific capacitance (103 F g −1 at 0.1 A g −1 ), superior rate capability and cyclic stability (88% capacity retention after 5000 cycles at 1 A g −1 ). The corresponding assembled LIC (LIC-SC2) with optimal comprehensive electrochemical performance, displayed the energy density of 83 Wh kg −1 , the power density of 5718 W kg −1 and superior cyclic stability (92% energy density retention after 1000 cycles at 0.5 A g −1 ). It is worthwhile that the source for activated carbon is a natural and renewable one and the synthesis method is eco-friendly, which facilitate that hierarchical porous activated carbon has potential applications in the field of LIC and other energy storage systems. [ABSTRACT FROM AUTHOR]

Although Li/CF x and Li/CF x MnO 2 have two of the highest energy densities of all commercial lithium primary batteries known to date, they are typically current-limited and therefore are not used in high-power applications. In this work, a Li/CF x MnO 2 battery (BA-5790) was hybridized with a 1000 F lithium ion capacitor to allow its use for portable electronic devices requiring 100 W 1-min pulses. An intelligent, power-management board was developed for managing the energy flow between the components. The hybrid architecture was shown to maintain the battery current to a level that minimized energy loss and thermal stress. The performance of the Li/CF x MnO 2 hybrid was compared to the standard Li/SO 2 battery (BA-5590). The hybrid was shown to deliver the same number of 100 W pulse cycles as two BA-5590 batteries, resulting in a weight savings of 30% and a volumetric reduction of 20%. For devices requiring 8 h of operational time or less, a 5-cell Li/CF x MnO 2 hybrid was found to be a lighter (55%) and smaller (45%) power source than the existing two BA-5590 battery option, and a lighter (42%) and smaller (27%) option than 1½ BA-5790 batteries alone. At higher power requirements (>100 W), further weight and size improvements can be expected. [ABSTRACT FROM AUTHOR]

We report the fabrication of a high energy-power density Li-ion hybrid supercapacitor (Li-HSC) using rice husk derived activated porous carbon as cathode and insertion type Li 4 Ti 5 O 12 (LTO) as anode. Nanoporous carbon chemically activated with KOH (RHDPC-KOH) and H 3 PO 4 (RHDPC- H 3 PO 4 ) exhibited high surface area and improved porosity characteristics. With optimized electrode mass loading, the fabricated Li-HSC exhibited excellent electrochemical properties with a maximum energy density of ∼57 Wh kg −1 and ∼37Wh kg −1 for LTO/RHDPC-KOH and LTO/RHDPC-H 3 PO 4 configuration respectively. The obtained energy density of 45 Wh kg −1 for RHDPC-KOH −based Li-HSC, even at a high power density of ∼4.3 kW kg −1 , is far superior to several porous carbon-based Li-ion capacitors reported. Furthermore, the device showed excellent cyclability with capacity retention of ∼92% of initial capacity even after 2000 cycles, at high current density of 2 Ag −1 . [ABSTRACT FROM AUTHOR]