MnO2 Cathode Research Articles

High energy storage performance MnSe2 cathode by one-step deposition strategy in aqueous zinc-ion batteries

The directly synthesized MnO2 using ambient temperature aqueous solution deposition strategy has great application prospects as the cathode material for aqueous zinc-ion batteries, which strategy has the advantages of simple process, large-scale and reproducible production. However, the single MnO2 suffers many problems, such as poor practical energy density and serious capacity fading. In order to improve the capacity and cycling stability of the cathode, we designed to use the method of ambient temperature aqueous solution deposition strategy. Using this method and adding a reducing agent and selenide to the original raw materials for the preparation of MnO2, the crystalline state of MnSe2 materials was finally synthesized creatively. This in situ one-step deposition method for the synthesis of MnSe2 is a very simple process and can be prepared on a large scale in a short period of time, saving time and effort. Compared with the MnO2 cathode materials, the MnSe2 cathode can reach the high capacity of 452.4 mAh g−1 at a low current density of 0.1 A g−1, an excellent rate capability of 242.7 mAh g−1 at 2.0 A g−1. After 2000 cycles (2 A g−1) of charging and discharging, the Zn/MnSe2 battery can maintain a specific capacity of over 231.5 mAh g−1 and a superior cycling retention of 86.3%, with a coulombic efficiency remains above 98%. This work provides a new way to develop simple, high-capacity and long-life aqueous zinc-ion batteries.

High-Energy and Long-Lived Zn–MnO2 Battery Enabled by a Hydrophobic-Ion-Conducting Membrane

Alkaline Zn-MnO2 batteries feature high security, low cost, and environmental friendliness while suffering from severe electrochemical irreversibility for both the Zn anode and MnO2 cathode. Although neutral electrolytes are supposed to improve the reversibility of the Zn anode, the MnO2 cathode indeed experiences a capacity degradation caused by the Jahn-Teller effect of the Mn3+ ion, thus shortening the lifespan of the neutral Zn-MnO2 batteries. Theoretically, the MnO2 cathode undergoes a highly reversible two-electron redox reaction of the MnO2/Mn2+ couple in strongly acidic electrolytes. However, acidic electrolytes would inevitably accelerate the corrosion of the Zn anode, making long-lived acidic Zn-MnO2 batteries impossible. Herein, to overcome the challenges faced by Zn-MnO2 batteries, we propose a hybrid Zn-MnO2 battery (HZMB) by coupling the neutral Zn anode with the acidic MnO2 cathode, wherein the neutral anode and acidic cathode are separated by a proton-shuttle-shielding and hydrophobic-ion-conducting membrane. Benefiting from the optimized reaction conditions for both the MnO2 cathode and Zn anode as well as the well-designed membrane, the HZMB exhibits a high working voltage of 2.05 V and a long lifespan of 2275 h (2000 cycles), breaking through the limitations of Zn-MnO2 batteries in terms of voltage and cycle life.

Ag-Doping Effect on MnO2 Cathodes for Flexible Quasi-Solid-State Zinc-Ion Batteries

Rechargeable aqueous Zn/MnO2 batteries are very potential for large-scale energy storage applications owing to their low cost, inherent safety, and high theoretical capacity. However, the MnO2 cathode delivers unsatisfactory cycling performance owing to its low intrinsic electronic conductivity and dissolution issue. Herein, we design and synthesize a Ag-doped sea-urchin-like MnO2 material for rechargeable zinc-ion batteries (ZIBs). Doping Ag was found to reduce charge transfer resistance, increase the redox activity, and improve the cycling stability of MnO2. The unique sea-urchin-like structure maintains rich active sites for charge storage. As a result, the Ag-doped MnO2-based ZIB presents a high reversible specific capacity to 315 mA h g−1 at 50 mA g−1, excellent rate performance, and a capacity retention of 94.4% when cycling over 500 cycles. An ex situ TEM test demonstrates the low-dissolution property of Ag-doped MnO2. A flexible quasi-solid-state ZIB is successfully assembled using Ag-doped MnO2 on graphite paper, which shows a stable specific capacity of 171 mA h g−1 at 1 A g−1 when cycled over 600 cycles. Our investigation demonstrates the significant role played by Ag doping in enhancing the ZIB performance of MnO2, and gives some insight into developing advanced active materials by heteroatom doping.

Preparation of MOF/polypyrrole and flower-like MnO2 electrodes by electrodeposition: High-performance materials for hybrid capacitive deionization defluorination

Fluorine pollution has become a global public health problem due to its adverse health effects. Adsorption is the primary method for removing fluoride from drinking water. However, the adsorption method has disadvantages such as difficulty in recovering the adsorbent, and the need to add additional chemicals for regeneration, thereby causing secondary pollution, which limits further industrial applications. Capacitive deionization (CDI), as an emerging water treatment technology, has attracted widespread attention due to its advantages of simple operation, low energy consumption and less environmental impact. In this study, a polypyrrole (PPy) film was prepared on a graphite substrate by electrodeposition, and then metal-organic framework Ce/Zn-BDC-NH2 (CZBN) was deposited on the PPy film by electrophoretic deposition to obtain CZBN/PPy electrode was obtained. The CZBN/PPy anode was then coupled with the MnO2 cathode for capacitive removal of fluoride in a CDI cell. Both CZBN/PPy and MnO2 electrodes exhibit pseudocapacitive behavior, which can selectively and reversibly intercalate F− (CZBN/PPy) and Na+ (MnO2) ions. As expected, the CZBN/PPy-MnO2 system exhibits excellent fluorine removal performance. In 1.2 V, 100 mg/L F− solution, the F− removal capacity can reach 55.12 mg/g. It has high F− selectivity in the presence of some common anions, and can maintain high F− removal ability even after five adsorption regeneration processes. The mechanism of F− removal was studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). F− was mainly removed by electrostatic interaction and ion exchange with hydroxyl. The excellent defluorination performance of the CZBN/PPy-MnO2 system makes it have good practical application prospects.

Synergistically coupling of graphene quantum dots with Zn-intercalated MnO2 cathode for high-performance aqueous Zn-ion batteries

Synergistically coupling of graphene quantum dots with Zn-intercalated MnO2 cathode for high-performance aqueous Zn-ion batteries

Investigation of physical and electrochemical properties of Ni-doped Tunnel/P2 hybrid Na0.44MnO2 cathode material for sodium-ion batteries

The increasing demand for energy in recent years has accelerated the efforts to increase the efficiency of energy storage systems. Although lithium-ion batteries are very popular in energy storage systems, the dramatic increase in costs due to the decrease in lithium resources has greatly increased the interest in sodium-ion batteries. Na0.44MnO2 has recently received increasing attention due to the fact that the tunnel structures in the crystal structure are suitable for the diffusion of Na ions. However, rapid structural degradation is an important problem that must be overcome to move into practical applications. In this study, the tunnel/P2 hybrid type Na0.44MnO2 was synthesized by a one-step heat treatment with the Ni substitution to Mn sites for improving cyclic performance. It was demonstrated by various physical analyses, that biphasic hybrid material starts forming with Ni substitution, and Ni occupied the Mn sites in the P2 phase. Electrochemical measurements provide that after 100 cycles at 0.3C, while Na0.44MnO2 has 77% capacity retention, 1% and 5% Ni substituted samples have 86.4% and 77.3%, respectively. The results show that tunnel-P2 hybrid cathode materials can be developed for practical applications in sodium-ion batteries.

Interface engineering enabled high-performance layered P3-type K0.5MnO2 cathode for low-cost potassium-ion batteries

Mn-based layered oxides exhibit high theoretical capacity and are environmentally friendly. However, the Mn2+ dissolution and structural degradation during the cycling process result in performance decay. Herein, interface engineering using an artificial Al2O3 coating layer was proposed to improve the performance of the K0.5MnO2 material. This Al2O3 protective layer acts as a barrier to avoid direct contact between the active material and the electrolyte, which could improve the Coulombic efficiency by inhibiting the side reactions, and boost the cycling stability via suppressing the Mn2+ dissolution. In addition, the Al2O3 coating layer modified K0.5MnO2 electrode exhibits highly reversible structure evolution, which could be attributed to the mitigation of structural degradation. As a result, the K0.5MnO2@Al2O3 cathode delivers a high capacity (95.3 mAh g‒1 at 50 mA g‒1) and long lifespan (53% capacity over 300 cycles).

Interfacial Designing of MnO2 Half‐Wrapped by Aromatic Polymers for High‐Performance Aqueous Zinc‐Ion Batteries

AbstractDue to the excellent specific capacity and high working voltage, manganese oxide (MnO2) has attracted considerable attention for aqueous zinc‐ion batteries (AZIBs). However, the irreversible structural collapse and sluggish ionic diffusion lead to poor rate capability and inferior lifespan. Herein, we proposed a novel organic/inorganic hybrid cathode of carbon‐based poly(4,4′‐oxybisbenzenamine)/MnO2 (denoted as C@PODA/MnO2) for AZIBs. Various in/ex situ analyses and theoretical calculations prove that PODA chains with C=N groups can provide a more active surface/interface for ion/electron mobility and zinc ion storage in the hybrid cathode. More importantly, newly formed Mn−N interfacial bonds can effectively promote ion diffusion and prevent Mn atoms dissolution, enhancing redox kinetics and structural integrity of MnO2. Accordingly, C@PODA/MnO2 cathode exhibits high capacity (321 mAh g−1 or 1.7 mAh cm−2 at 0.1 A g−1), superior rate performance (88 mAh g−1 at 10 A g−1) and excellent cycling stability over 2000 cycles. Hence, rational interfacial designs shed light on the development of organic/inorganic cathodes for advanced AZIBs.

Interfacial Designing of MnO2 Half-Wrapped by Aromatic Polymers for High-Performance Aqueous Zinc-Ion Batteries.

Due to the excellent specific capacity and high working voltage, manganese oxide (MnO2 ) has attracted considerable attention for aqueous zinc-ion batteries (AZIBs). However, the irreversible structural collapse and sluggish ionic diffusion lead to poor rate capability and inferior lifespan. Herein, we proposed a novel organic/inorganic hybrid cathode of carbon-based poly(4,4'-oxybisbenzenamine)/MnO2 (denoted as C@PODA/MnO2 ) for AZIBs. Various in/ex situ analyses and theoretical calculations prove that PODA chains with C=N groups can provide a more active surface/interface for ion/electron mobility and zinc ion storage in the hybrid cathode. More importantly, newly formed Mn-N interfacial bonds can effectively promote ion diffusion and prevent Mn atoms dissolution, enhancing redox kinetics and structural integrity of MnO2 . Accordingly, C@PODA/MnO2 cathode exhibits high capacity (321 mAh g-1 or 1.7 mAh cm-2 at 0.1 A g-1 ), superior rate performance (88 mAh g-1 at 10 A g-1 ) and excellent cycling stability over 2000 cycles. Hence, rational interfacial designs shed light on the development of organic/inorganic cathodes for advanced AZIBs.

Effect of dopants and microstructure on the electrochemical cyclic stability of layered P2-type Na0.67MnO2 prepared by different chemical routes: An experimental and theoretical study

High specific capacity layered transition metal oxide, NaxMnO2 is considered a potential cathode for sodium-ion batteries (SIBs). However, its poor capacity retention due to irreversible phase transitions during sodium ion insertion/extraction remains a critical challenge for practical applications. Herein, we report Fe and Co co-doped P2-type Na0.67MnO2 cathode material prepared via different facile chemical routes to understand the effect of dopants and microstructure on its electrochemical cyclic stability. The Rietveld refinement analysis depicts an increase in lattice parameter c of Fe and Co doped materials as compared to parent material; thereby favouring sodium-ion storage (in turn enhancing and stabilizing specific capacity). XPS analysis confirms the presence of Mn in both 3+ and 4+ oxidation states; whereas Fe and Co in 3+ oxidation states occupy Mn3+ in Na0.67MnO2. Both experiment and ab initio magnetic calculations show a reduction in Mn3+ content after Fe and Co doping, reducing the tendency for Jahn-Teller distortion. This is concomitant with Fe and Co doping showing improved cyclic stability when cycled under similar conditions. At 0.1 C (where 1 C = 174 mAh g−1), Fe and Co-doped Na0.67MnO2 showed significant improvement with higher discharge specific capacities of 80 and 103 mAh g−1 even after 60th cycle when compared to 36 mAh g−1 after 25th cycle for the parent material Na0.67MnO2.

Melanin as biological organic polymer with semiconductor properties is unique effective modifier for MnO2 cathode and increases the energy of Li-MnO2 battery

This article presents results on the modification of a composite mass based on MnO2 with an organic polymer – melanin. The main goal was to evaluate the possibility of increasing the efficiency of electrode processes during cycling and their stabilization. MnO2, synthesized chemically on the basis of Ukrainian manganese ores, was used for modification. This manganese dioxide has a high density (about 2.64 g/cm3), a high specific surface area (28 m2/g), and electronic conductivity also. The final product of the synthesis is γ-MnO2 powder with 5% admixture of γ-Mn2O3.

MnO2 cathode materials with high reversible stability through Li intercalating for aqueous zinc ion battery

Manganese oxides have been paid attention to storage energy with low price, high safety and environmentally friendly. Nevertheless, poorly cycling stability and low structure stability restrict their appliance. The metal doping is a potential method to enhance their electrochemical performance. Herein, a new strategy was proposed to optimize the cycling stability and rate performance of the pristine MnO2 by the simple lithium doped. The Li-doped MnO2 (Li-MnO2) not only relieved the manganese dissolution during charge-discharge process but also introduced oxygen defects boosting the electrochemical kinetics of MnO2. The prepared composite delivers a reversible specific capacity of 185 mAh g−1 at 0.1 A g−1 and 88 mAh g−1 at 1 A g−1, maintaining 88% of its initial capacity after 1000 cycles. This work may provide some new ideas for improving the stability of manganese-based zinc-ion batteries.

Interface Engineering of Aqueous Zinc/Manganese Dioxide Batteries with High Areal Capacity and Energy Density.

Commercialization of aqueous batteries is mainly hampered by their low energy density, owing to the low mass loading of active cathode materials. In this work, a MnO2 cathode structure (MnO2 /CTF) is designed to modify the MnO2 /collector interface for enhanced ion transportation properties. Such a cathode can achieve ultrahigh mass loading of MnO2 , large areal capacity, and high energy density, with excellent cycling stability and rate performance. Specifically, a 0.15mm thick MnO2 /CTF cathode can realize a mass loading of 20mg cm-2 with almost 100% electrochemical conversion of MnO2 , providing the maximum areal capacity of 12.08mA h cm-2 and energy density of 191W h kg-1 for Zn-MnO2 /CTF batteries when considering both cathode and anode. Besides the conventional low energy demonstrations, such a Zn-MnO2 /CTF battery is capable of realistic applications, such as mobile phones inourdaily life, which is a promising alternative for wearable electronics.

Highly Reversible Zn Metal Anodes Realized by Synergistically Enhancing Ion Migration Kinetics and Regulating Surface Energy

AbstractThe Zn metal anode suffers from uncontrollable dendrite formation and intricate parasitic reactions that dramatically impede the commercialization of aqueous Zn metal batteries (AZMBs). This st proposes synergistic strategies for facilitating Zn2+ migration kinetics and regulating surface energy to achieve dendrite‐free Zn deposition and suppressing self‐corrosion by covering Zn anode with multifunctional covalent organic frameworks possessing sulfonate‐rich (SO3H) covalently‐tethered nanochannels (SCOFs). Benefiting from the vital interplay between SO3H and Zn2+, the SCOFs coatings form ample Zn2+ accelerated transport channels to extract Zn2+ from the electrolyte quickly, thereby promoting rapid desolvation of hydrated Zn2+, enhancing ion replenishment capability, and guaranteeing a steady stream of Zn2+ flux for endowing uniform and compact nucleation. Additionally, the zincophilic SCOFs significantly reduce the surface energy of the Zn (002) crystal plane, inducing preferentially crystallographic (002) orientation electroplating growth. Consequently, the SCOFs‐coated Zn anodes (SCOFs@Zn) demonstrate an excellent lifespan up to 4000 h at 5 mA cm−2, 1 mAh cm−2, and 3000 h at 5 mA cm−2, 2 mAh cm−2. Meanwhile, the full cell paired with the MnO2 cathode sustains remarkable reversibility within 1000 cycles. The synergistic approach to manipulating ion migration and surface energy provides new insights into developing highly stable AZMBs.

One-Pot Spray Engineering to Design Na0.44MnO2 Cathode Electrodes for High-Rate and Cycle-Stable Na-Ion Batteries

To improve the practical performance of Na-ion batteries, electrode structure engineering provides a new route to improve the electrochemical efficiency of the cathode active material. In this study, we suggest a new route of one-pot spray engineering to design Na0.44MnO2 cathodes to realize high-rate and cycle-stable Na-ion battery performance. This technique adjusts the electrode structure from a dense to an open sponge-like morphology during layer-by-layer deposition of the materials. The sponge-like cathode results in improved ion insertion and transport kinetics, thus accelerating the rate capability with increased capacity and high-rate cycling capability (100.1 mAh/g and 90.2% cycling retention after 100 cycles at 5 C). These results highlight the potential for design engineering of cathode structures to achieve high-rate and cycle-stable performance for Na-ion batteries.

Unlocking the High Capacity Ammonium-Ion Storage in Defective Vanadium Dioxide.

Aqueous ammonium-ion storage has been considered a promising energy storage competitor to meet the requirements of safety, affordability, and sustainability. However, ammonium-ion storage is still in its infancy in the absence of reliable electrode materials. Here, defective VO2 (d-VO) is employed as an anode material for ammonium-ion batteries with a moderate transport pathway and high reversible capacity of ≈200 mAh g-1 . Notably, an anisotropic or anisotropic behavior of structural change of d-VO between c-axis and ab planes depends on the state of charge (SOC). Compared with potassium-ion storage, ammonium-ion storage delivers a higher diffusion coefficient and better electrochemical performance. A full cell is further fabricated by d-VO anode and MnO2 cathode, which delivers a high energy density of 96Wh kg-1 (based on the mass of VO2 ), and a peak energy density of 3254W kg-1 . In addition, capacity retention of 70% can be obtained after 10 000 cycles at a current density of 1 A g-1 . What's more, the resultant quasi-solid-state MnO2 //d-VO full cell based on hydrogel electrolyte also delivers high safety and decent electrochemical performance. This work will broaden the potential applications of the ammonium-ion battery for sustainable energy storage.

(Invited) Flexible and Safe Zinc Alkaline Solid-State Rechargeable Battery for Wearable Applications

Wearable electronics are one of the most rapidly growing industries, due to their extended use in everyday applications resulting in an increased demand for portable energy storage devices. Despite immense success in commercialization of Lithium-ion batteries (LIBs), conventional LIBs suffer from issues of cost and safety. The expanding need for cheaper, and safer energy storage devices led explorations towards alternatives. After careful considerations, Zinc (Zn)-Manganese dioxide (MnO2) based alkaline system was chosen to be investigated in this work due to its low cost, inherent safety, and high theoretical energy density. However, challenges associated with making the aforementioned system rechargeable and highly performing still remains. The work in this study is directed towards enhancing the overall performance of the Zn-MnO2 alkaline battery in addition to making it suitable for flexible and wearable applications. A highly ionically conducting polymer electrolyte ({5}CP) with excellent physical and electrochemical stability primarily comprising biopolymer chitosan is prepared by using a time and energy-efficient technique. Incorporation of this polymer electrolyte with Zn anode and MnO2 cathode enabled the successful preparation of a physically flexible cell. To obtain high cyclability and performance of the system; issues of inactive phase formations (MnxOy, ZnMnxOy), low active material availability, pronounced shape changes at the anode surface, and zincate ion transfer towards cathode were overcome by enhancing the electrochemically active layers in the system. The assembled cell comprising the enhanced fabricated layers; (i.e. a Zinc/Stainless steel mesh composite anode, a hierarchical binder-free bismuth and copper additives based MnO2 cathode, and a chitosan-based polymer electrolyte with calcium hydroxide additive) indicated excellent rate capabilities (486 mAh/g @ 0.1 A/g, 78% of the theoretical 2-electron capacity on MnO2), long cycling stabilities (70% retention over 1000 cycles), and good energy densities (155 – 400 Wh/kg @ 0.1 – 1 A/g). Moreover, a number of destructive tests such as being bent, hammered, pressurized, and punctured were conducted on the pouch cell fabricated using the above-mentioned layers to analyze the cells’ safety, reliability, and robustness. Results indicated not much deterioration in capacities. Additionally, when the cell was bent and tested for long performance; a stable discharge capacity (270 mAh/g @ 1 A/g) was obtained after 250 cycles, thus attesting to excellent cycling stability. The successful working of the fabricated cell was validated by lighting up an LED. The successful findings presented in this study can chart new pathways to the development of safe, flexible, cost-effective, and more environmentally responsible alternative energy storage sources for wearables.

High Performance Separator and Hydrogel Based on Aramid Fibers for Zn Ion Batteries

Aqueous zinc-ion batteries (ZIBs) have received much attention recently because they are environmentally friendlier, safer, and cheaper than the current Li-ion batteries. Rechargeable ZIBs are not only regarded as promising alternative energy storage systems, but have the potential to replace Li-ion batteries in many applications. Unfortunately, the formation of the dendrites on the Zn anodes, hydrogen evolution and side reactions are overwhelming challenges for the commercialization of ZIBs. Conventional strategies often focused on anode protection and the design of the electrolyte additive, but neglected the importance of the separator. In this presentation, a uniform porous separator constructed from the commercial material Kevlar (para-aramid), a type of strong synthetic fiber, was developed for aqueous ZIBs. Derived from the high-strength aramid, the separator demonstrated excellent tensile strength compared to the conventional glass fiber separators. Therefore, the developed separator shows good protection to the Zn anode by preventing Zn dendrite growth and prolonged the lifetime of the Zn symmetric cell. In addition, aramid fiber was used to construct an anti-freeze hydrogel for aqueous ZIBs, which played the roles of both separator and electrolyte. The hydrogel could significantly inhibit zinc dendritic growth and other side reactions even when operating below 0 °C. When paired with a MnO2 cathode, the hydrogel based cell shows excellent electrochemical performance in a wide range of temperatures. This work opens a gate for the development of separators and hydrogel electrolytes based on aramid fibers.

Regulating the plating process of zinc with highly efficient additive for long-life zinc anode

The Zn-ion batteries (ZIBs) are considered as one of the most compelling candidates for large-scale energy storage due to their high capacity, cost-effectiveness, high output potential, safety, and eco-friendliness. However, the application of ZIBs is being seriously hindered by the dendritic formation on Zn electrode surfaces, which always leads batteries to circuit-short and failure. We report a discovery regarding the use of polyvinylpyrrolidone (PVP), a non-ionic polymer, as a highly efficient electrolyte additive to induce uniform Zn plating. Various characterizations reveal that PVP molecules are electrostatically adsorbed on zinc protrusions during zinc ion plating, inhibiting the development of zinc protrusions and guiding uniform plating of Zn2+. The Zn anode using PVP-additive electrolyte has a long plating/stripping cycle life of 1000 h at a current density of 0.5 mA cm−2. When coupled with a MnO2 cathode, the full cell of Zn–MnO2 with PVP-additive electrolyte achieves boosted stability (89.1% capacity retention after 500 cycles) than that with normal electrolyte (30.1% capacity retention after 158 cycles). The results of the study suggest new ideas for inexpensive and efficient electrolyte engineering strategies for high-performance ZIBs.

Toward highly reversible aqueous zinc-ion batteries: nanoscale-regulated zinc nucleation via graphene quantum dots functionalized with multiple functional groups

Rechargeable aqueous Zn-ion batteries have a promising application potential and represent competitive candidates in the field of large-scale energy storage. However, Zn metal is prone to uncontrolled dendrite formation, hydrogen evolution, and corrosion, all of which limit the reversibility of the corresponding batteries. Herein, a novel kind of nanosized and functionalized graphene quantum dots (F-GQDs) is decorated on a Zn anode via in situ electrochemical induction. These quantum dots (∼5 nm) can regulate Zn plating/stripping at the nanoscale. Furthermore, the high electronegativity of polar functional groups (–OH, –COOH, –NH2, and -SCN) on the GQDs results in strong Zn2+ affinity and the F-GQDs endow the Zn anode with high hydrophilicity, low nucleation energy barrier, and an evenly distributed electrical field. As a result, the F-GQDs-decorated Zn anode achieves superior Zn plating/stripping for greater than 450 h at 10 mA cm−2 and 5 mAh cm−2, with a low voltage hysteresis of 81 mV. Moreover, when coupled with MnO2 cathodes, the F-GQDs-decorated Zn enables the fabrication of Zn||MnO2 full batteries with significantly enhanced rate capability and long-term cycling performance (capacity retention of 78.6 % at 1 A/g after 500 cycles).