High Voltage Window Research Articles

High-nickel and cobalt-free layered LiNi0.90Mn0.06Al0.04O2 cathode for lithium-ion batteries

In order to obtain superior cathode materials for lithium-ion batteries with lower cost and higher energy density, the research of nickel-based cathode materials trend towards high Ni, low Co or no Co composition. To demonstrate the feasibility of this compositional transformation, we introduce a Co-free LiNi0.90Mn0.06Al0.04O2 (NMA) cathode material with a Ni content of 90 mol%, ranging from LiNi0.90Co0.1O2 (NC) to low Co LiNi0.90Mn0.06Co0.04O2 (NMC) composition transformation. All samples were synthesized by an organic amine coprecipitation method. The results show that the NMA cathode can provide the first discharge specific capacity of 223.1 mAh g−1 at 0.1 C and 2.5–4.3 V, although is lower than that of NC and NMC, it has a higher average discharge voltage of 47 and 17 mV, respectively. At a high voltage window ranging from 2.5 to 4.5 V, the first discharge specific capacity up to 232.1 mAh g−1, and the capacity retention rate of 100 cycles at 0.5 C is as high as 93.3%, which is much higher than the 66.9% of the NC. The dQ dV−1 and discharge curves show that the NMA phase transition is gentler and the polarization is smaller during the high-voltage charge-discharge process, which also indicates that the destructive effect of Co on the layered structure is further enhanced at high potential. In conclusion, this work provides favorable support for NMA as a next-generation candidate for high-nickel and Co-free cathode materials.

Difluorophosphoric Acid Generation and Crossover Reactions in LiNixCoyMnzO2 Cathodes

Layered LiNixCoyMnzO2 (NCM) materials are one of the most widely utilized cathode materials for Lithium-ion batteries (LIB) with their high theoretical capacity and relatively high voltage window. Increasing the Nickel content and the cycling voltage can increase the capacity of these cells at a lower cost. But these high Nickel cathodes cycled to a higher upper cut off voltage have poor cycling stability. The cause of this rapid capacity decrease has been attributed to decomposition of the anode solid electrolyte interphase (SEI) from transition metal deposition on the anode surface and impedance growth on the cathode surface. Recent studies have also attributed this to acidic species generated from oxidative decomposition of the electrolyte and their crossover reactions degrading the SEI, particularly the Difluorophosphoric acid.In this study the role of transition metal dissolution and Difluorophosphoric acid generation has been investigated through various quantitative analysis techniques including, ICP-MS, XPS, quantitative solution NMR, and EIS. Full cells were constructed using graphite as the negative electrode and NCM cathodes with different Nickel contents as the positive electrode. These cells contain the same base electrolyte formulation (1.2M LiPF6 and EC: EMC, 3:7) and they were cycled at different temperatures and voltages to investigate the correlation between acid and transition metal concentration, cell voltage and capacity fade.

Graphene decorated LiMn2O4 electrode material for hybrid type energy storage devices

AbstractLithium‐ion capacitors (LICs) are becoming useful owing to their high energy and power densities. LICs show enhance capacitance than electric double‐layer capacitance (EDLC) and pseudocapacitors, due to their battery electrode material, which can operate over a higher voltage window. LiMn2O4 is fast emerging electrode material for energy storage devices. The major limitation associated with it is the low conductivity. Therefore, to simultaneously improve the electrical conductivity as well as the electrochemical performance, a novel strategy of decoration LiMn2O4 with graphene is being proposed. Graphene will improve electrical conductivity while contributing to EDLC and pseudocapacitance values. A cost‐effective synthesis protocol is utilized to obtain conical pyramid‐type particles. These particles were thoroughly characterized using a large number of experimental techniques. Cyclic voltammetry and charge‐discharge measurements were used to evaluate the electrochemical characteristics, in 0.0 to 1.2 V stable window, using 1M LiOH electrolyte. Graphene decorated LiMn2O4 electrode show improved cyclic stability and higher specific capacitances 250 F/g in comparison to LiMn2O4 electrode. The cycling stability of the electrode was above 90% up to 3000 cycles at a higher current density.

Design of Boron Carbonitrides-Polyaniline (BCN-PANI) assembled supercapacitor with high voltage window

Boron carbonitrides (BCN) have been widely concerned in the field of energy storage and conversion. However, the energy storage mechanism of electrical double-layer behavior and their stacked-layer structure severely limit the improvement of capacitance, thereby hindering their further development in energy storage. Therefore, an ultrasonic-ball milling method was first chosen to obtain BCN nanosheets, together with a feasible way of polyaniline (PANI) modification performed to boost the capacitive reaction of BCN nanosheets. For the first time, a BCN-PANI-based symmetric supercapacitor device can reach a high voltage window of 3.0 V when 1 M Et4N·BF4 was chosen as the electrolyte. The working voltage of 3.0 V is three times that of a device with pure PANI with the ultrahigh energy density of 67.1 W h kg−1, superior to most of the reported PANI-based devices. The eminent electrochemical performance provides a promising strategy to pave the way for configuring carbon-based multiple composite electrodes for other energy storage devices.

Porous MgCo2O4 nanoflakes serve as electrode materials for hybrid supercapacitors with excellent performance

In this work, MgCo2O4 microspheres (MgCo2O4 MSs) and MgCo2O4 nanoflakes (MgCo2O4 NFs) were prepared by one-step and two-step synthetic method, respectively, and combined with a post annealing treatment. Both MSs and NFs electrode materials possessed porous structure and large specific surface areas. The electrochemical properties were evaluated using three-electrode as well as two-electrode systems. The MgCo2O4 NFs delivered a specific capacity of 375.5C g−1 at 1 A g−1 together with a high rate performance (74.9%) at 10 A g−1, while the MgCo2O4 MSs exhibited 276.3C g−1 at the current density of 1 A g−1. A hybrid supercapacitor (HSC) device was assembled with a cathode made from MgCo2O4 and an anode made from activated carbon (AC) for evaluation of real applications, and it was able to run over a high voltage window (1.75 V). This MgCo2O4 NFs//AC HSC delivered a high energy density (Ed, 35.4 W h kg−1) at 950.6 W kg−1, and at the highest power density (Pd) of 8905.0 W kg−1, it could still hold 25.8 W h kg−1. On the other hand, the MgCo2O4 MSs//AC HSC device exhibited an Ed of 32.4 W h kg−1 at a Pd of 1048.0 W kg−1. Both HSCs exhibited good long-term cycling stability due to no capacity decay over 6000 cycles at 6 A g−1. The excellent electrochemical performance demonstrates that these MgCo2O4 electrode materials, especially the MgCo2O4 NFs, have great application potential for electrochemical energy storage. This synthesis method is simple and is possibly to be applied in synthesizing other transition metal oxides (TMOs)-based electrode materials with large surface area and outstanding electrochemical performance.

A high energy density supercapacitor fabricated with aqueous polymer electrolyte based on soybean protein isolate grafted by polyacrylic acid

Soybean protein isolate (SPI) has good reactivity, hydrophilicity and film-forming properties, but its electrochemical performance is poor when used as a polymer electrolyte matrix. The graft-modification of the SPI using polyacrylic acid (PAA) allows the introduction of strong hydrophilic carboxyl groups into the SPI molecular chains. This enables the SPI to effectively absorb electrolytes in the subsequent electrolyte adsorption process, resulting in a modified polymer electrolyte. The resulting constructed supercapacitor can operate stably in a voltage window of 0–2 V and exhibit excellent electrochemical behavior with a high single electrode specific capacitance up to 293.08 F g−1 and an energy density of 38.76 W h kg−1 at a power density of 734.38 W kg−1, which is much better than SPI-based supercapacitor. This simple, low-cost and environmentally friendly approach has a great potential for the development of high-performance supercapacitor with high voltage window, high specific capacitance and high energy density.

SnO2 oxide cathode coating: The key ingredient for bi-based polymer quasi-solid-state batteries, enabling stable cycling of high-voltage solid-state LiNi0.5Mn1.5O4/lithium metal battery

The solid electrolytes are strongly considered as the next-generation electrolyte due to the natural safety compared with liquid electrolyte, however, the overall low-rate performance of all-solid-state batteries and large internal resistance have hindered the development of all-solid-state batteries. In this paper, SnO2 is grown in situ on LiNi0.5Mn1.5O4 (LNMO) to increase the specific capacity and stabilize the cycle performance. After the preparation of the cathode material, it is assembled with the solid electrolyte slurry prepared by PMMA-PVDF @ Li1.3Al0.3Ti1.7(PO4)3(LATP) to form an all-solid-state battery, which has good electrochemical performance, even at high rates. At a test temperature of 60 ℃, the initial specific capacity obtained at 0.2 C is 125 mAh·g−1. After 100 cycles, it drops to 105 mAh·g−1, with a capacity decay rate of 94.2 %, and the initial specific capacity at a rate of 0.5 C. After being 110 mAh·g−1, 500 cycles, the specific capacity remains at 95 mAh·g−1. The excellent performance of coating LNMO depends on the binding of SnO2 to Mn+. The good catalytic effect enables the high specific capacity of SnO2 and the high voltage window of LNMO to be displayed. After the coating of tin dioxide, the interface contact between the positive electrode and the solid electrolyte is improved. The appearance of SnO2 reduces the interface impedance of the quasi-solid-state battery from 276 Ω to 243 Ω. At the same time, the generation of space charge layer is suppressed. Combined with the prepared dual matrix [email protected], the working environment and cycle stability of the all-solid-state battery are improved, and the development of the all-solid-state battery is promoted.

High-voltage and wide temperature aqueous supercapacitors aided by deep eutectic solvents

• DES can expand the voltage and operating temperature range of aqueous supercapacitors; • DFT is applied for electrolyte design, optimization and theoretical calculation; • Adjusting the molar ratio of DES and water can influence on the structure and performance of electrolyte; • DES exhibits important potential for high-performance aqueous supercapacitors. For water supercapacitors, how to realize high voltage and wide temperature range operation is of great theoretical and practical significance. In this work, introducing a deep eutectic solvent (DES) composed of choline chloride (ChCl, as hydrogen bond acceptor) and ethylene glycol (EG, as hydrogen bond donor) into H 2 O (as co-hydrogen bond donor) produces DES-H 2 O electrolyte. Furthermore, density functional theory (DFT) can design and verify the DES system. The experimental results show that the molar ratio of DES plays a decisive role in the solvent structure and supercapacitor performance. When the molar ratio of ChCl, EG and H 2 O is 1:2:2, the DES structure is the most stable, the total energy is the largest (49.93 eV), also exhibiting the high voltage window of 2.4 V, and the wide temperature range of − 40 to 80 °C. In the meanwhile, superior capacitive performance also occurs with specific capacity of 202 F g −1 , energy density of 40.3 Wh kg −1 and cyclability (98.51% after 10,000 cycles) The present DES-H 2 O electrolyte has the advantages of low price, easy synthesis, good water resistance and high electrochemical performance, which makes it have large application potential in the field of supercapacitors.

Co9S8@MnO2 core–shell defective heterostructure for High-Voltage flexible supercapacitor and Zn-ion hybrid supercapacitor

Flexible and wearable energy storage devices have drawn increasing attention owing to the rapid development of smart and portable electronic gadgets. Herein, vertically oriented Co9S8@MnO2 core–shell heterostructure nanotube arrays are in situ grown on the carbon cloth surface and activated by oxygen vacancy engineering via a fast NaBH4 reduction method. The introduction of oxygen vacancy can effectively improve the conductivity, reaction kinetics and thus increase the capacitance performance. The as-prepared high-active electrode material can assemble into high-performance flexible supercapacitor and Zn-ion hybrid supercapacitor. The assembled flexible all-solid asymmetric supercapacitors (AAS) show a wide potential window of 2.4 V, the excellent areal capacitance of 0.8058F cm−2 at 2 mA cm−2, high energy density of 92.14 Wh kg−1 and power density of 342.86 W kg−1. Further, the assembled Zn-ion hybrid supercapacitor has a higher energy density of 198.857 Wh kg−1, which is about twice than that of AAS devices. This work provides a rational strategy for design energy storage devices with high energy density and voltage window.

Controllable synthesis of Co/Ni basic carbonate composite via regulating Co/Ni ratio with super rate performance for asymmetric solid-state supercapacitor

Under the high current density, high cyclability and good rate performance are two major challenges for the applications of supercapacitor. How to control the composition and structure of the electrode materials is the key factor to solve these two problems. In this work, the controllable morphology Co/Ni Basic Carbonate Composites (CNBCC) were synthesized by one-step hydrothermal regulating the ratio of Co to Ni. Impressively, benefiting to its special sea urchin structure, the composite with the 1:1 ratio of Co to Ni exhibited remarkable electrochemical performance with specific capacitance (at 1 A g−1, 1682 F g−1), superior rate capability (at 1–30 A g−1, 79.3%) and cycling stability (2000 cycles, 96%). Further, a solid-state asymmetric supercapacitor Co1Ni1//AC (ASC) was constructed with a high voltage window (1.7 V). The ASC displayed a high energy density of 42.5 Wh kg−1 at power density 849.7 W kg−1, while still remained at 20.6 Wh kg−1 at a power density of 25511 W kg−1. In addition, the ASC had good flexibility, and their CV curves hardly changed after being bent into different angles; the two ASC in series could light a yellow LED for 25 min.

Novel preparation of attapulgite-reduced graphene oxide hydrogel composite and its application in flexible solid-state supercapacitors

After graphite oxide assisted the liquid phase shear exfoliation of attapulgite, the good dissociation and dispersion of attapulgite rod crystals are realized. Due to the spatial hindrance effect of attapulgite, which prevents the stacking of RGO sheets, the attapulgite-reduced graphene oxide three-dimensional porous hydrogel with abundant pore structure enables rapid transfer of electrolyte ions and exhibits good electrochemical performance and rate performance. The assembled flexible solid-state supercapacitor has a high operating voltage window and good flexibility and cycle stability. At a current density of 0.1 mA cm−2, it has an area specific capacitance of 127.33 mF cm−2. A series of solid-state supercapacitors can be used as the power supply for LED lights.

Diphenyl diselenide as a bifunctional electrolyte additive in a high-voltage LiNi0.8Mn0.1Co0.1O2/graphite battery

To increase the practical energy density and capacity of high-nickel cathode materials, it is crucial to develop a novel electrolyte additive that can enhance the unstable electrolyte/electrode interface over a wide operating voltage range. In this study, diphenyl diselenide (DPDS) is selected as a bifunctional electrolyte additive for high-voltage LiNi0.8Mn0.1Co0.1O2 (NMC811)/graphite batteries, considering the energy levels of its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). DPDS is oxidized and reduced prior to the decomposition of ethylene carbonate (EC) and diethyl carbonate (DEC), forming protective layers on both electrode surfaces. The DPDS-driven layers prevent parasitic reactions, maintain the structural stability of electrodes, and reduce active lithium loss. As a result, in the high voltage window of 2.8–4.5 V, DPDS enhances the capacity retention of NMC811/graphite batteries from 68.0% to 82.0% after 200 cycles at 1C. This paper provides an understanding of the DPDS operating principle in high voltage NMC811/graphite full cells to achieve high energy density.

Ultrathin Polypyrrole Layers Boosting MoO3 as Both Cathode and Anode Materials for a 2.0 V High-Voltage Aqueous Supercapacitor.

An aqueous supercapacitor is an emerging energy storage unit on account of its low cost, fast energy delivery rate, and long service life. The energy density of an aqueous supercapacitor can be enlarged via extending the voltage window of electrode materials, while the aqueous electrolyte remains thermodynamically constant at 1.23 V. Herein, an aqueous supercapacitor with a 2.0 V high-voltage window is realized by core-shell MoO3-x/polypyrrole (MP) nanocomposites as both cathode and anode materials. The ultrathin PPy layer on the MoO3 core not only improves the conductivity and cycle stability of the nanocomposites but also acts as a reductant, leading to the formation of oxygen vacancies in the MoO3 core. When used as a cathode material, the potential range of the as-obtained MP nanocomposite is up to 1.0 V. As an anode material, the stable potential range could reach -1.0 V. Due to the large potential range of the cathode and anode, the as-obtained 2.0 V aqueous supercapacitor shows a remarkably high delivery energy of 58.5 Wh kg-1. The synthesis of MP nanocomposites is simple and the electrode performance is significantly enhanced; thus, it is a suitable candidate for high-energy-density aqueous supercapacitors.

Interfacial Engineered Vanadium Oxide Nanoheterostructures Synchronizing High-Energy and Long-Term Potassium-Ion Storage.

Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy storage applications because of their high energy and power densities and the abundance of potassium sources. However, achieving KICs with high capacity and long lifespan remains challenging because the large size of potassium ions causes sluggish kinetics and fast structural pulverization of electrodes. Here, we report a composite anode of VO2–V2O5 nanoheterostructures captured by a 3D N-doped carbon network (VO2–V2O5/NC) that exhibits a reversible capacity of 252 mAh g–1 at 1 A g–1 over 1600 cycles and a rate performance with 108 mAh g–1 at 10 A g–1. Quantitative kinetics analyses demonstrate that such great rate capability and cyclability are enabled by the capacitive-dominated potassium storage mechanism in the interfacial engineered VO2–V2O5 nanoheterostructures. The further fabricated full KIC cell consisting of a VO2–V2O5/NC anode and an active carbon cathode delivers a high operating voltage window of 4.0 V and energy and power densities up to 154 Wh kg–1 and 10 000 W kg–1, respectively, surpassing most state-of-the-art KICs.

Composites of NiMoO4@Ni-Co LDH@NiCo2O4 on Ni foam with a rational microscopic morphology for high-performance asymmetric supercapacitors

The structural stability and high capacity of material enable a wide range of applications for asymmetric supercapacitors. In this work, we design a simple route to synthesize NiMoO4@Ni-Co LDH@NiCo2O4 composites on Ni foam. The NiMoO4@Ni-Co LDH@NiCo2O4 has a stable nanorod/nanosheet core-shell structure. In addition, the NiMoO4@Ni-Co LDH150@NiCo2O4 exhibits a high specific capacity of 1035 C g−1 and retained 80.6% of the original capacity after 5000 cycles. Moreover, the asymmetric supercapacitor is assembled by activated carbon and NiMoO4@Ni-Co LDH150@NiCo2O4 as two electrodes respectively, which shows a high energy density of 66.8 Wh kg−1 at a power density of 900 W kg−1. In the meantime, the asymmetric supercapacitor achieved a high voltage window of 1.8 V. The stable core-shell structure of NiMoO4@Ni-Co LDH@NiCo2O4 achieved a high energy density, which shows great potential for energy storage.

Double Crosslinked Lignin/Hydrogel Electrolyte with High Ion Conductivity and Super Ductility for High Voltage Window Supercapacitor

Double Crosslinked Lignin/Hydrogel Electrolyte with High Ion Conductivity and Super Ductility for High Voltage Window Supercapacitor

Superior pseudocapacitive performance and mechanism of self-assembled MnO2/MXene films as positive electrodes for flexible supercapacitors

Two-dimensional (2D) MXene materials have significant potential applications in electrochemical energy storage. A Ti3C2Tx MXene film can be used as a high-performance electrode for a flexible supercapacitor owing to its flexibility and excellent rate capability. However, Ti3C2Tx is usually only used as a negative electrode material because it can be easily oxidized under positive (anodic) potential. Herein, we report a simple filtration method to fabricate a hybrid cathode by mixing a colloidal solution of 2D Ti3C2Tx nanosheets and 1D MnO2 nanobelts to form an alternating MnO2/Ti3C2Tx stacked structure. Compared with pure Ti3C2Tx, the hybrid cathode has higher electrochemical stability toward anodic oxidation. The MnO2/Ti3C2Tx hybrid cathode delivers a high gravimetric capacitance of 315 F g−1 at 10 mV s−1 and a good rate capability of 166 F g−1 at 100 mV s−1. The high stability of the MnO2/Ti3C2Tx hybrid cathode is mainly attributed to the charge transfer-induced work function enlargement at the Ti3C2Tx and MnO2 heterointerface. Furthermore, a flexible asymmetric supercapacitor assembled using MnO2/Ti3C2Tx as the cathode and alkalized Ti3C2Tx as the anode delivers a high-voltage window up to 1.9 V. This work provides new insights for designing high-performance MXene-based cathode materials and devices for wearable electronics.

Maximizing Energy Density of Nanostructured Electrochemical Capacitors: From Proof of Concept to Reliable Manufacturing

Currently, portable energy storage devices are lacking in the overall performance characteristics needed to meet desired energy and power density performance demands. Furthermore, these performance demands for long-lasting energy storage devices for portable electronics continue to constantly increase. Batteries remain the main source of portable energy storage, but they generally lack the pulsed-power delivery capability required by many applications, as well as have limited cycle life. Thus, improvements in devices that show a high operational cycle life in addition to delivering high energy and power densities are extremely desirable over a wide range of physical sizes, footprints, and power delivery capabilities. Conventional electrostatic capacitors provide some of these benefits compared to batteries, including high power density and extended cycle life, but are lacking in the energy density capability required to replace batteries in many applications.Electrochemically-based double-layer capacitors (EDLCs) or ultracapacitors offer a promising solution to bridging the gap between maintaining the high-power density capability of electrostatic capacitors while providing a path to improving the energy density to be comparable to batteries –significantly broadening their applicability. An EDLC’s power density and energy density are based on the highly reversible surface charge adsorption-based mechanism of energy storage. This provides benefits in terms of high frequency responses as well as providing a route to supply power for longer duration pulses. Additionally, since the stored capacity is based on the surface charge adsorption-based energy storage, it provides an essentially indefinite lifespan as long as the materials do not degrade. However, current EDLC technologies still provide significantly lower energy density than is available from batteries. This energy density gap must be narrowed if the EDLCs are going to make further inroads toward replacing batteries.The capacitance and energy density are driven by the electrode’s available solution-accessible surface area. Thus, our approach to increasing the energy density of electrochemical capacitors is through the development of carbon nanotube-based electrode structures with a precise, highly controlled and ordered nanostructured porosity. To further improve power and energy density, these electrode structures are used in combination with an ionic liquid electrolyte with high voltage window, thus providing an increased operating voltage. While traditional electrode materials are generally comprised of randomly ordered porous structures, we have developed electrodes with an adjustable and highly controlled pore structure that provide very high surface area. These electrodes are produced using a nanotemplated approach that allows for preparation of high surface area aligned and vertically oriented carbon nanotube (CNT)-based electrodes. The templated approach has the added benefit of a achieving a greater areal CNT density than available in traditional carpet-grown CNT forests as well as providing more uniform and controllable CNT outer and inner diameters. The ability to control these dimensions allows for tailoring the electrode geometry for a specific electrolyte.Ionic liquids are becoming increasingly popular in a variety of applications as a result of their unique properties and highly tailorable chemistry. In electrochemical applications, their large voltage stability window, low vapor pressure, excellent thermal stability at temperatures above most organic solvents’ boiling points, and lower temperature conductivity make them an excellent electrolyte choice. Ionic liquids are ideal for use in higher temperature electronics applications, especially in small-scale microelectronics formats where confined spaces make efficient heat removal very difficult. By making use of ionic liquid electrolytes and optimizing the interaction of the electrolyte with our templated CNT electrodes, we have developed an energy storage technology with high-energy density and high-power density.In this talk, we will discuss the challenges and solutions to scaling up the fabrication and testing of reproducible, nanostructured electrodes from 3.14 cm2 or smaller single-sided lab cells to multiple 200 cm2 electrodes on both sides of an aluminum current collector. We will discuss the electrode fabrication scale-up and performance validation from small coin or disc cells tested in a glove box to larger area sealed pouch cells with integration of an optimized ionic liquid electrolyte. We discuss cell fabrication challenges and solutions including verifying the performance of the electrodes as they are scaled up, and the cell fabrication including ensuring the electrode and separator are reliably wetted with the ionic liquid electrolyte. The challenges of optimizing the practical tradeoff of electrode active depth and minimizing the current collector thickness as we move the electrode and overall cell design to a fully packaged cell while maintaining the optimized electrochemical performance characteristics will be discussed.[DISTRIBUTION STATEMENT A. Approved for public release; Distribution is unlimited 412TW-PA-21154]

Understanding the Failure Mechanisms of LiNixCoyMnzO2 Cathodes through Surface Reactions with the Electrolyte

Layered LiNixCoyMnzO2 (NCM) cathodes are one of the most widely used cathode materials for Lithium-ion batteries (LIB) with a high theoretical capacity and relatively high voltage window. Increasing the Nickel content and the cycling voltage can increase the capacity and the energy density at a lower cost, but these high Nickel cathodes cycled to a higher cut off voltage have poor cycling stability. The cause of this rapid capacity decrease has been attributed to continuous growth of the anode solid electrolyte interphase (SEI) due to transition metal deposition on the anode surface and impedance growth on the cathode surface. Recent studies have also attributed acid mediated electrolyte degradation reactions that degrade the SEI with extended cycling for this rapid capacity fade.In this study merits of these 3 theories are being investigated through various quantitative analysis techniques including, ICP-MS, solution NMR, XPS and EIS. Full cells were constructed using graphite as the negative electrode and NCM cathodes with different Nickel contents. These cells contain the same base electrolyte formulation (1.2M LiPF6 and EC: EMC, 3:7) and they were cycled at different temperatures and voltages to compare the correlation between nickel content, voltage and capacity fade.

(Invited) Design Principles of High Voltage Asymmetric Supercapacitors Based on Electrode Energetics

As the global appetite for clean energy is growing like never before, energy storage devices like supercapacitors are attracting considerable attention. With the advent of nanotechnology and the development of advanced materials, many researchers are focused on developing new nanomaterials and nanostructures to improve the energy storage capacity of these interesting devices. However, a major limitation for its widespread application as an energy storage device is its inferior energy density compared to Li-ion batteries, though their power density is much higher. An approach to achieve high energy density is to increase the voltage output of supercapacitors. Developing high-performing asymmetric supercapacitors is a viable direction to achieve this goal. To develop asymmetric supercapacitors, two different materials are used as anode and cathode. Currently, clear guidelines to select these two different materials are missing. A reason for this void is the complex involvement of multiple factors related to electrodes and electrolytes that determine the voltage window. In this talk, the importance of the work-function of electrodes in designing a high voltage asymmetric supercapacitor will be discussed. This would help understand the energetics of electrode-electrolyte interaction, which governs the output voltage window while the supercapacitor is in operation. It enables to better design supercapacitors with higher voltage window and thus increased energy density. We will also talk about the electrode-electrolyte interaction and the influence of hydrogen and oxygen evolution overpotential on the voltage of asymmetric supercapacitors.