Galvanostatic Charge-discharge Cycling Tests Research Articles

Superior compatibility of silicon nanowire anodes in ionic liquid electrolytes

Silicon nanowire anodes were investigated in lithium-metal cells using different electrolyte formulations based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide and N -trimethyl-N -butyl-ammonium bis(fluoro sulfonyl)imide ionic liquids. The lithium insertion process in the silicon anode was analyzed by cyclic voltammetry measurements, performed at different scan rates and for prolonged cycles, combined with impedance spectroscopy analysis. A galvanostatic charge-discharge cycling test was performed to analyze the electrochemical performances using different types of ionic liquids. A study of the Solid Electrolyte Interphase layer on the silicon nanowire electrode surface was carried out through X-ray photoelectron spectroscopy. In general, the silicon anodes in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide-based electrolytes show very good reversibility, reproducibility, and efficiency in the lithiation process, even at high scan rates, and exhibit a reversible capacity exceeding 1,000 mA h g-1 after 2,000 charge-discharge cycles, corresponding to 46% of the initial value.

On Synthesis and Electrochemical Performance of Na4Fe3(PO4)2(P2O7) Cathode for Sodium-Ion Batteries

Developing cost-effective and large-scale energy storage systems (ESSs) has been an important topic over the past years in order to implement efficient utilization of renewable electricity generated from sources like solar, wind, geothermal and tidal energy (1). Since the commercialization in 1991, lithium-ion batteries (LIBs) have been widely used in portable electronics, electric vehicles (EVs), and energy storage devices (2). However, there is an increase in demand for alternative energy sources based on abundant and low-cost materials due to the limited reserves and high costs of lithium compounds. In this context, sodium-ion batteries (SIBs) have received great attention because of their similarities to LIBs and the large abundance (2.3%) on earth, and low cost of sodium compounds (3). However, the energy density of most SIBs are lower that of LIBs, primarily due to the larger ionic radius and higher mass of Na+ ion compared to Li+ ions, as well as the lower electrochemical potential of sodium cells relative to lithium cells (4). Many efforts have been devoted to the development of high-performance cathode materials, including layered transition metal oxides, Prussian blue analogues (PBAs), sulfates, phosphates and pyrophosphates. Polyanionic compounds, in particular, are considered as promising cathode materials with regard to their high working voltage, structural stability, thermal stability and small volume change upon cycling (5). For example, iron phosphate-based materials have gained attention inspired by LiFePO4 for LIBs. However, the olivine NaFePO4 is predominantly produced through an ion exchange process (6). The maricite NaFePO4 is electrochemically inactive due to the lack of Na migration channels within its structure. On the other hand, Na2FeP2O7 shows long cycle life and structural stability with a low capacity because of its single electron diffusion process. Na4Fe3(PO4)2(P2O7) (NFPP) combines the benefits of both phosphate and pyrophosphate, offering potential advantages such as low-cost, environmental friendliness, high average working voltage (~ 3.1 V vs. Na+/Na), favorable theoretical capacity (129 mAh g-1), low volume change (< 4%) due to its open framework composed of [Fe3P2O13] layers connected by (P2O7)4- groups with 3D ion channels and low activation barriers for Na+ transport as well as structural and thermal stability. However, NFPP is susceptible to the formation of impurities such as NaFePO4 and Na2FeP2O7, which can arise from the synthesis temperature and adopted reaction materials, potentially restricting the electrochemical performance of NFPP. Additionally, the inherent insulating characteristics of the (PO4)3- group in NFPP may result in reduced electronic conductivity and slow ion diffusion, which hinders its practical application (7, 8). Therefore, various strategies have been developed to enhance conductivity such as nanosizing, carbon coating and metal ion doping.NFPP can be synthesized by various methods like solid-state, sol-gel, spray drying and combustion. In this study, we present our results on employing both sol–gel and combustion methods with distinct synthesis parameters. The structure, morphology and particle size of NFPP are characterized by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) techniques. The electrochemical performance of NFPP cathodes is investigated in both half- and full-cells via galvanostatic charge-discharge cycling tests. Keywords: sodium-ion batteries, cathode material, iron-based mixed phosphate, sol-gel synthesis, large scale M. Armand and J. M. Tarascon, Nature, 451, 652 (2008).J. B. Goodenough and K.-S. Park, Journal of the American Chemical Society, 135, 1167 (2013).B. Dunn, H. Kamath and J.-M. Tarascon, Science, 334, 928 (2011).M. H. Han, E. Gonzalo, G. Singh and T. Rojo, Energy & Environmental Science, 8, 81 (2015).P. Barpanda, L. Lander, S.-i. Nishimura and A. Yamada, Advanced Energy Materials, 8, 1703055 (2018).K. T. Lee, T. N. Ramesh, F. Nan, G. Botton and L. F. Nazar, Chemistry of Materials, 23, 3593 (2011).X. Wu, G. Zhong and Y. Yang, Journal of Power Sources, 327, 666 (2016).H. Kim, I. Park, S. Lee, H. Kim, K.-Y. Park, Y.-U. Park, H. Kim, J. Kim, H.-D. Lim, W.-S. Yoon and K. Kang, Chemistry of Materials, 25, 3614 (2013).

Construction of sticky ionic conductive buffer layer for inorganic electrolyte toward stable all-solid-state lithium metal batteries

Inorganic electrolyte based all-solid-state lithium metal batteries (LMBs) are considered the most promising secondary power storage device. However, there still exist significant interfacial issues, which hurdles its advancement in application seriously. Herein, we synthesize a sticky anion-immobilized oligomer ionic conductor (AIOC) to construct a buffer layer for inorganic electrolyte. The AIOC displays high ionic conductivity (2.21 × 10−5 S cm−1), large Li+ transference number (0.65) at 30 °C, which is beneficial to promote homogenous lithium deposition, moreover, it endows a wide electrochemical window of 4.3 V (vs. Li+/Li). Based on these merits, when AIOC serves as buffer layer for Li1.5Al0.5Ge1.5(PO4)3 (LAGP) electrolyte, the interfacial stability and compatibility between LAGP and lithium metal anode can be enhanced remarkably. Upon which, the interfacial resistance of lithium symmetrical cell can be declined sharply (5313 Ω→718 Ω). Enduring 100-h galvanostatic charge-discharge cycling test, the surficial morphologies and elemental constitutions of the lithium metal anode and LAGP electrolyte almost remain unchanged as before. As a result, a LiFePO4/Li all-solid-state cell with AIOC modified Li1.5Al0.5Ge1.5(PO4)3 electrolyte enables to achieve a reversible discharge capacity of 120.1 mAh g−1 at 0.5C with a notable capacity retention of 86.3% in 100 cycles at 50 °C.

High-Performance Structural Supercapacitors Based on Aligned Discontinuous Carbon Fiber Electrodes and Solid Polymer Electrolytes

This paper presents an investigation of the potential to use aligned discontinuous carbon fiber dry prepregs as electrodes in structural supercapacitors (SSCs). The high fiber-matrix interfacial bonding of the structural composite was achieved by adopting a solid polymer electrolyte, consisting of poly(vinylidene), lithium triflate, and epoxy. Processing of the SSC was carried out via dip-coating of the polymer electrolyte and then cured using a vacuum bag. The electrochemical performance of the SSCs was measured before and after mechanical loading. The microstructures of the SSCs as-fabricated and damaged under flexural loading were identified by μ-CT imaging. An SSC with a specific capacitance of 0.128 mF/cm2 (11.62 mF/g), a flexural strength of 47.49 MPa, and a flexural modulus of 8.48 GPa has been achieved, demonstrating significant improvements in mechanical properties over those of SSCs based on woven carbon fiber fabric-based electrodes. The mechanical behavior of the supercapacitors was evaluated by both quasi-static and cyclic flexural loading tests. The excellent electrochemical stability of the supercapacitors was validated by a capacitance retention of above 96% under galvanostatic charge-discharge cycling tests. The knowledge gained in this work will benefit future research in the optimization of SSC performance.

Surface modified TiO2/reduced graphite oxide nanocomposite anodes for lithium ion batteries

Anatase TiO2 nanoparticles with an average crystallite size of ~ 20 nm are synthesized through a sol-gel method. A composite anode for Li-ion batteries is prepared with the synthesized TiO2 nanoparticles and reduced graphite oxide (RGO) as the conductive carbon source. After the preparation of TiO2/RGO nanocomposite, a novel surface modification is carried out by the employment of H2O2 to enhance the overall electrochemical performance of nanocomposite anode (TiO2/RGO-P composite). The physical and chemical characterizations of the surface modified TiO2/RGO-P composites are performed with X-ray powder diffraction (XRPD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) analyses. The electrochemical performance of TiO2/RGO-P composite electrodes is investigated via galvanostatic charge-discharge cycling tests in a potential window of 1.0–3.0 V. Compared to the plain TiO2/RGO composite anode, the TiO2/RGO-P composite anode has higher reversible capacities and better cycling performance due to the enhanced and stable formation of 3D channels of TiO2 nanoparticles with RGO stemming from the surface modification with H2O2. The TiO2/RGO-P composite anode delivers reversible discharge capacities around 291 mA h g−1 at a rate of 100 mA g−1, whereas the value stays at 214 and 143 mA h g−1 for the plain TiO2/RGO composite and TiO2 nanoparticle without any RGO, respectively.

Pseudocapacitive properties of nickel oxide nanoparticles synthesized via ultrasonication approach

Here, nickel oxide (NiO) nanoparticles are prepared via an ultrasonication approach and tested for the pseudocapacitance performance. The crystalline structures, functional groups, and morphology of NiO nanoparticles are investigated using various experimental tools such as XRD, FT-IR, FESEM, and HRTEM respectively. Cyclic voltammetry (CV), galvanostatic charge-discharge cycling test, and electrochemical impedance spectroscopic (EIS) measurements were utilized to determine the pseudocapacitive properties of the NiO nanoparticles. Noticed high specific capacitance (423 F g−1) at 0.5 mA cm−2 current density and in addition achieved good capacitance retention (93%) even after continuous 2000 cycles illustrate excellent electrochemical stability of sonochemically prepared NiO nanoparticles compared to other preparation procedures.

Facile synthesis of CoWO4/RGO composites as superior anode materials for lithium-ion batteries

In this paper, a facile method has been developed to synthesize supported CoWO4 on the reduced graphene oxide (RGO) as high-performance anode material for Li-ion batteries. The composites with cuboid-like CoWO4 nanoparticles were prepared by directly adding graphene oxide into the precursor solution followed by a hydrothermal treatment. Different analytical methods like high-resolution TEM, XRD, TGA, and XPS characterizations were employed to illustrate structural information of the as-prepared CoWO4 and CoWO4/RGO composites. In addition, the Li-ion battery performance using the composites as anode materials was also discussed based on the detailed galvanostatic charge-discharge cycling tests. The result shows that the specific capacity of the as-prepared CoWO4/RGO composites can reach 533.3 mAh g−1 after 50 cycles at a current density of 100 mA g−1. During the whole cyclic process, the coulombic efficiency was maintained higher than 90%. Therefore, CoWO4, as an environment-friendly and cost-effective anode material, has promising potential for Li-ion batteries.

Chemical precipitation synthesis of KCoF3 for supercapacitor applications

A simple chemical precipitation method is applied to synthesize pure-phase KCoF3 with size in the range of 1–5 μm, which is further used as electrode material in supercapacitors. The cyclic voltammetry, electrochemical impedance spectroscopy measurements, and galvanostatic charge-discharge cycling test measurements are carried out for the KCoF3 electrode, and the results show a specific capacitance of 286 F⋅g−1 at 0.5 A⋅g−1 in 6.0 M KOH electrolyte. Particularly, KCoF3 electrode exhibits long cycling lifetime with 96% retention of initial capacitance after 1000 cycles at a current density of 5.0 A⋅g−1.

Sonochemical synthesis of Co2SnO4 nanocubes for supercapacitor applications

In this work, a simple sonochemical route was followed to synthesize cobalt stannate (Co2SnO4) nanocubes using stannous and cobalt chlorides as the precursors in alkaline medium at room temperature. The structure, composition and surface morphology of synthesized Co2SnO4 nanocubes have been characterized by using X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) indicates that the Co2SnO4 nanocubes are crystalline, single-phase without any impurity phase; the sizes of nanocubes are ∼100 nm. The cyclic voltammetry, galvanostatic charge-discharge cycling test, and electrochemical impedance spectroscopy (EIS) measurements are carried out for the Co2SnO4 nanocubes shows a specific capacitance 237 F g−1 at 0.5 mA cm−2 current density and in 1 M Na2SO4 electrolyte. Co2SnO4 nanocubes exhibit long cycling life with 80% retention of initial capacitance after 2000 cycles and the excellent rate capability at 15 mA cm−2 as much as 70% of that at 0.5 mA cm−2 suggest its potential use for supercapacitor applications.

Performance of lithium-ion capacitors using pre-lithiated multiwalled carbon nanotubes/graphite composite as negative electrode

Multiwalled carbon nanotubes have been synthesized by floating reactant method in a vertical tubular reactor. An internal short approach process was developed to achieve the pre-lithiated multiwalled carbon nanotube MWCNTs/graphite composite anodes. Lithium-ion capacitors (LICs) were composed of a pre-lithiated multiwalled carbon nanotubes/graphite composite anode and an activated carbon (AC) cathode. The electrochemical performance of LICs with different MWCNTs content was investigated through galvanostatic charge/discharge and electrochemical impedance. The results show that the charge–discharge performance of LICs was greatly improved with the addition of MWCNTs in anodes. LIC25 (25 wt% MWCNTs) was found to achieve the optimal electrochemical performance. The LIC25 hold a specific capacitance of 58.2 F/g at the current density of 100 mA/g. The maximum energy density and power density were up to 96 Wh/kg and 10.1 kW/kg, respectively, in the current range of 100~8000 mA/g. The continuous galvanostatic charge–discharge cycling tests revealed that the LIC25 maintained excellent capacity retention of 86% after 3000 cycles.

Enhanced cycle and rate performances of Li(Li0.05Al0.05Mn1.90)O4 cathode material prepared via a solution combustion method for lithium-ion batteries

A (Li, Al)-co-doped spinel Li(Li0.05Al0.05Mn1.90)O4 (LAMO) cathode material has been rapidly prepared by a solution combustion method. The structure of as-prepared samples was characterized by X-ray diffraction (XRD), which shows that (Li, Al)-co-doping does not change the intrinsic spinel structure of LiMn2O4. The morphology and particle size of the as-prepared samples were analyzed by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM), which indicate that the LAMO has high crystallinity, regular truncated octahedran morphology and uniform particle size distribution. The X-ray photoelectron spectrometer (XPS) measurement shows that (Li, Al)-co-doping increases the average valence of Mn. The cycle performance was evaluated by galvanostatic charge-discharge cycling test. The results show that LAMO maintains a high discharge specific capacity of 98.0mAhg−1 with a capacity retention of 82.4% after 1000cycles at 5C (1C=148mAhg−1) compared with that of 60.7mAhg−1 with a capacity retention of 60.4% for the pristine LiMn2O4 (LMO). Furthermore, LAMO exhibits obvious improvement of elevated-temperature cyclic performance, resulting in a superior capacity retention of 73.9% after 400cycles at 1C at 55°C with an initial discharge specific capacity of 107.2mAhg−1, which is much higher than that of 14.6% for the pristine LMO. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies certify that (Li, Al)-co-doping improves the reversibility and enhances kinetics process of electrode.

A hybrid electrochemical device based on a synergetic inner combination of Li ion battery and Li ion capacitor for energy storage

Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg−1. The cycle life test proves that HyLIC exhibits a good cycle life and an excellent coulombic efficiency. The present study shows that HyLIC, which is capable of achieving a high energy density, a long cycle life and an excellent power density, has the potential to achieve the winning combination of a high energy and power density.

Preparation of porous-structured LiFePO4/C composite by vacuum sintering for lithium-ion battery

The LiFePO4/C (LFP/C) composite as a cathode material for lithium-ion battery was synthesized by solid-state reaction under vacuum sintering condition (20–5Pa). The effects of vacuum sintering temperature and time on the phase composition, morphological structure, and electrochemical performance of LFP/C composite were investigated by X-ray diffraction, scanning electron microscopy, galvanostatic charge–discharge cycling test, and electrochemical impedance spectroscopy. The synthetic LFP/C composite possessed uniform particle-size distribution with porous architecture upon sintering at 650°C for 12h and thus exhibited the highest discharge capacity and best cycle performance. The complete decomposition of citric acid at a suitable temperature under vacuum condition resulted in the formation of porous structure. Compared with atmospheric argon sintering, vacuum sintering method led to the formation of porous architecture, the porous sample showed excellent cycle performance with less than 2% capacity loss after 80 cycles at 0.2C, and reached the discharge specific capacity of 87.6mAhg−1 at 10C rate, these are better than that of atmospheric argon sintering. The LFP/C composite prepared under vacuum sintering also reduced the optimum sintering temperature by nearly 100°C compared with that prepared under atmospheric argon sintering.

LiFePO4 nanoplates with {010} exposed active planes prepared by hydrothermal method

It is well known that lithium-ion transport in olivine LiFePO4 is through one-dimensional (1D) channels along the [010] direction. Therefore, the crystal structure of LiFePO4 should be controlled to shorten Li+ diffusion pathway and orient {010} facets. In this work, LiFePO4 nanoplates with preferred growth {010} active facets are synthesized by hydrothermal method in the presence of NH4 + and ascorbic acid. The effects of organic additive on the morphologies and structures are characterized by XRD and SEM. It is recognized that organic additive plays a critical role in crystal growth in hydrothermal reaction and a rational mechanism is speculated. In addition, LiFePO4/C is prepared by mixing procedure of LiFePO4 nanoplates with 30 wt% ascorbic acid and carbonized at 600 °C for 5 h in Ar atmosphere. The resulting LiFePO4/C sample is used as cathode materials for lithium-ion batteries. The electrochemical performances are evaluated by galvanostatic charge–discharge cycling tests and cyclic voltammetry. LiFePO4/C displays a high initial discharge capacity of 163.62 mAh/g at 0.1C (1C = 170 mA/g) between 2.5 and 4.2 V.

Innovative Oxygen Selective Membrane for Li-Air Battery Operating in Ambient Air

The demand for high-energy storage systems is constantly increasing, as is the interest to explore alternatives to commercially available batteries. The rechargeable Li-air battery represents an exciting opportunity to design batteries that may satisfy some of the requirements of our future by coupling the light Li metal with the inexhaustible source of O2 of the surrounding air, resulting in high theoretical specific energy density. Currently, most of the researches on the Li-air battery comprise a cell fed with pure O2 allowing that way to maintain long-term operation, owing to the high O2 concentration free of contaminants. However, for many practical applications such as EV, air is the only viable option to supply the battery. In this context, moisture and gases other than O2 may cause side reactions and corrosion. Herein, we report a facile strategy to fabricate an effective oxygen selective membrane with poly(vinylidene fluoride co-hexafluoropropylene) (PVDF-HFP) via non-solvent induced phase separation, casted as a 240 micron thin sheets for cell protection in ambient air condition. The use of different additives helps enhancing the barrier properties as well as the membrane specificity toward O2. For instance, sacrificial silica nanoparticles (SiO2 NPs) were incorporated into the precursor solution to create a controlled alveolar-like structure inside the membrane. The membrane was loaded with polydimethylsiloxane (PDMS) under vacuum. Another kind of additive considered is the cyclodextrine. Indeed, thanks to their unique structure, cyclodextrines are able to form host-guest complexes with hydrophobic molecules such as our polymer matrix. Nanosponges based on cyclodextrines were prepared and added to the polymer precursor solution before membrane casting. The as prepared membranes showed higher oxygen permeability and lower water permeability. Galvanostatic charge-discharge cycling tests of a Li-air pouch cell in a potential/time controlled mode showed an outstanding cycling life superior to 1500h with more than 150 cycles.

An influence of carbon matrix origin on electrochemical behaviour of carbon-tin anode nanocomposites

Electrode materials in which tin nanograins are encapsulated in carbon matrix obtained from different origin (starch or modified polymer) were examined. Morphology of the C/Sn composites was observed using transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) analysis in different states of charge (SOC) at initial cycle together with a long term galvanostatic charge-discharge cycling tests allowed determining the influence of carbon coating origin on the electrochemical behaviour of C/Sn nanocomposites. X-ray photoelectron spectroscopy (XPS) measurements of C/Sn materials before cycling and after first cycle were performed to observe changes in surface composition of the material which occur during electrochemical reaction. The results of surface characterization as well as electrochemical studies of C/Sn nanocomposites indicated that the origin of carbon precursor has a major impact on the composites’ morphology and electrochemical behaviour. Long term galvanostatic charge-discharge cycling tests proved that the carbon obtained from MPNVF precursor allows better encapsulation of tin nanograins in the buffer matrix. Furthermore, according to the XPS studies carbon coating based on MPNVF is more chemically stable versus electrolyte, which contributes directly to the improved protection of active material against physical damage. The charge capacity of MPNVF-based composite was 589mAhg−1 after 70 cycles, which constitutes 59% of theoretical metallic tin capacity.

Synthesis and electrochemical properties of spinel Li(Li0.05Cu0.05Mn1.90)O4 by a flameless combustion method

A (Li, Cu)-co-doped cathode material Li(Li0.05Cu0.05Mn1.90)O4 was prepared by a flameless combustion synthesis at 500 °C for 3 h and then two-stage calcination at 700 °C for 6 h. Physical and electrochemical performances were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), galvanostatic charge–discharge cycling test, cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS) to investigate the influence of Li and Cu substitution on the lithium ion batteries. Li(Li0.05Cu0.05Mn1.90)O4 not only exhibited the initial discharge capacity of 106.9 mAh g−1 with a high retention of 89.2% after 500 cycles at 1.0 C but also retained 63.5% capacity after 1500 cycles at 5.0 C. Besides, a good rate capability at different current densities from 0.5 C to 5.0 C can be acquired. The (Li, Cu)-co-doped sample had excellent cycling stability in comparison with the LiMn2O4 cathode.

Electrochemical Performance of Lithium-Ion Hybrid Supercapacitors based on Activated Carbon and Nanoplatelet Li4Ti5O12 Insertion Electrode Synthesized by Nanoscission Technique

ABSTRACTElectrochemical performance of hybrid supercapacitor (HSC) utilizing surface sculpted Li4Ti5O12 (LTO) insertion electrode having nanoplatelet-like morphology and activated carbon (AC) electrode is investigated for energy storage application. Cyclic voltammetry (CV) at variable scan rates 0.5 to 60 mV.s-1 in the 0-3.2 V range show pseusocapacitive behavior and fast rate of current change indicating rapid Faradaic kinetics. Nyquist impedance study show charge transfer resistance due to kinetic effects of electron transfer and Li+ de-intercalation process at the LTO anode. Low capacity (0.2 C-1C) charge-discharge (CD) curves show high Coulomb efficiency with marginal reduction at high 5-10 C rates due to irreversibility of adsorbed PF6 anions at the electrolyte-AC interface. Galvanostatic CD cycling tests over 50 cycles at different C-rates show decline in storage capacity due to electrode polarization effects. Reduction, broadening and shift of the Raman line at 678 cm-1 from Ti-O bonds in TiO6 octahedra after cycling indicates Li insertion reactions in functioning of hybrid supercapacitor. The hybrid supercapacitor cells have shown energy density, 29 Wh.kg-1 and power density, 350 W.kg-1.

High performance lithium-ion hybrid capacitors with pre-lithiated hard carbon anodes and bifunctional cathode electrodes

Lithium-ion hybrid capacitor is a type of energy storage device that bridge the gap between lithium-ion battery and electrical double layer capacitor. We have developed a facile approach to achieve the pre-lithiation of carbonaceous anode, and then fabricated lithium-ion hybrid capacitors with bifunctional cathode containing capacitor material (activated carbon) and battery material (LiNi0.5Co0.2Mn0.3O2). The hybrid capacitor with 25 wt.% LiNi0.5Co0.2Mn0.3O2 addition in bifunctional cathode (denoted as LAN25) exhibits excellent rate capability and high energy density. The rate capability of LAN25 is comparable to that with pure AC cathode (denoted as LAC), while the volumetric energy density is 1.36 times higher than the latter one. The continuous galvanostatic charge–discharge cycling tests reveal that the lithium-ion hybrid capacitor remains more than 98% capacity after 20,000 cycles, and nearly 100% coulombic efficiency over entire cycles. The superior performance is ascribed to the synergy effect of the active components in bifunctional cathode and the effective pre-lithiation of hard carbon anode. The present work makes the study of lithium-ion hybrid capacitor easily accessible and broadens roads to hybrid devices with high energy density, high power density and long cycle life.

Amphiphilic carbonaceous material-intervened solvothermal synthesis of LiFePO4

LiFePO4 samples with preferred facets on the ac plane were prepared by the solvothermal method with or without well-dispersed amphiphilic carbonaceous material (ACM). The effects of ACM on the particle morphology, crystal orientation and electrochemical reactivity of the prepared LiFePO4 nanoparticles were investigated in detail. ACM serves a dual purpose. One purpose is facilitating the plate-like morphologies of LiFePO4 nanoparticles parallel to the bPnma axis by decreasing the surface energy of (010) facets of newly created LiFePO4 nuclei. The other purpose is suppressing crystal growth along the [010] direction by adhering onto the (010) surface of LiFePO4 nanoplates. Furthermore, ACM coating was performed and optimized using a carbon coating precursor. The electrochemical properties of the prepared LiFePO4 particles were characterized by cyclic voltammetry (CV) and galvanostatic charge–discharge cycling tests. After the optimized coating of ACM, the ACM-intervened LiFePO4 composite was observed to deliver discharge capacities of 151.3 mAh g−1 at 1C and 132.2 mAh g−1 at 10C. Even after 1000 cycles at a high rate of 10C, the LiFePO4 cathode could maintain 80% of its initial capacity.