Three-electron Redox Reaction Research Articles

Benzoquinone-Lubricated Intercalation in Manganese Oxide for High-Capacity and High-Rate Aqueous Aluminum-Ion Battery.

Aqueous aluminum-ion batteries are attractive post-lithium battery technologies for large-scale energy storage in virtue of abundant and low-cost Al metal anode offering ultrahigh capacity via a three-electron redox reaction. However, state-of-the-art cathode materials are of low practical capacity, poor rate capability, and inadequate cycle life, substantially impeding their practical use. Here layered manganese oxide that is pre-intercalated with benzoquinone-coordinated aluminum ions (BQ-AlxMnO2) as a high-performance cathode material of rechargeable aqueous aluminum-ion batteries is reported. The coordination of benzoquinone with aluminum ions not only extends interlayer spacing of layered MnO2 framework but reduces the effective charge of trivalent aluminum ions to diminish their electrostatic interactions, substantially boosting intercalation/deintercalation kinetics of guest aluminum ions and improving structural reversibility and stability. When coupled with Zn50Al50 alloy anode in 2m Al(OTf)3 aqueous electrolyte, the BQ-AlxMnO2 exhibits superior rate capability and cycling stability. At 1Ag-1, the specific capacity of BQ-AlxMnO2 reaches ≈300mAhg-1 and retains ≈90% of the initial value for more than 800 cycles, along with the Coulombic efficiency of as high as ≈99%, outperforming the AlxMnO2 without BQ co-incorporation.

Electrochemical performance of Na4MnCr(PO4)3/C cathode affected by different transition metal dopants for sodium ion batteries

Na4MnCr(PO4)3 (NMCP) has been considered as one kind of privileged cathodes with high energy density for sodium ion batteries (SIBs) due to three-electron redox reaction during the insertion/extraction process. Nevertheless, its practical use is restricted by its low intrinsic conductivity and serious Jahn-Teller distortions. Herein, a facile doping strategy was presented to address the above issues, and the effects of different kinds and quantities of transition metal dopants on electrochemical performance of NMCP were systemically studied. The results reveal that Ni50-NMCP/C has the most effective doping composition, showing a discharge capacity of 143.0 mAh g−1 at 50 mA g−1 and long-term cyclic stability with capacity retention of 55.7 % at 1000 mA g−1 over 500 cycles, higher than those of the pristine NMCP (106.6 mAh g−1 at 50 mA g−1 and 38.8 % capacity retention at 1000 mA g−1). The substitution of Ni2+ for Mn2+ promotes electron conductivity and structural stability, rendering improved electrochemical performance. Moreover, the promising electrochemical performance of Ni50-NMCP/C//HC full cell demonstrates the anode's potential for use. This study indicates a quick way to understand the effects of elemental doping on NMCP and explore novel high energy and high stability cathodes for SIBs.

Reversible multielectron redox in NASICON cathode with high energy density for low-temperature sodium-ion batteries

The NASICON-type Na3V2(PO4)3 cathode based on vanadium multiple redox is particularly attractive for large-scale sodium-ion battery application. In this work, it was found that the reversible redox of V4+/V5+ can be activated by replacing a part of V3+ with Al3+, obtaining Na3V1.5Al0.5(PO4)3 with typical NASICON phase structure and offering a reversible specific capacity of 163 mAh g−1 through a three-electron redox reaction with a small volume change (2.62%). The most surprising thing is that in addition to favorable room temperature electrochemical performance, Na3V1.5Al0.5(PO4)3 also exhibits a superior low temperature (-20 °C) cycling stability with a capacity retention of 98.9% after 1000 cycles at 5 C. Thin and conformal CEI film as well as stable phase structure across a broad temperature range are responsible for this superior electrochemical property. A Na+ storage mechanism consisting of two-phase and solid-solution electrochemical reactions for Na3V1.5Al0.5(PO4)3 cathode is elucidated via ex-situ XRD structural analysis. DFT calculations indicate that Al3+ substitution could manipulate the localized electronic state and strengthen the oxygen ligand skeleton in the NASICON matrix. Hence, the Na3V1.5Al0.5(PO4)3 cathode renders a slight lattice variation upon the repeated desodiation and sodiation and enhanced Na+ diffusion rate along with low charge transfer resistance.

Layered double hydroxide-derived Fe-doped NiSe cathode toward stable and high-energy aluminum storage

Rechargeable aluminum-ion batteries (AIBs) are promising candidates for energy storage because of their low cost, high safety, and high-power density owing to the three-electron redox reaction. However, the applications of AIBs are hindered by their limited lifetime and practically achievable energy density. Herein, we present a novel Fe-doped Nickel selenide (Fe-NiSe) nanoflake cathode material, derived from a Ni–Fe layered double hydroxide, affording a long cycle life and high energy density. Synergism between the ultrafine nanostructure and Fe doping provided shorter ion diffusion pathways and created multiple active sites in the cathode. As a result, the prepared Fe–NiSe battery achieved an outstanding energy density of 402.5 W h kg−1 and an ultra-long lifespan of 13,500 cycles with a capacity decay of only 0.0026% per cycle. Furthermore, based on the mass of the entire pouch-type cell, the fabricated AIB delivered an energy density of 101.2 W h kg−1. This work paves the way for serviceable high-energy density AIBs.

Elevating Energy Density for Sodium-Ion Batteries through Multielectron Reactions.

It remains a great challenge to explore desirable cathodes for sodium-ion batteries to satisfy the ever-increasing demand for large-scale energy storage systems. In this Letter, we report a NASICON-structured Na4MnCr(PO4)3 cathode with high specific capacity and operation potential. The reversible access of the Mn2+/Mn3+ (3.75/3.4 V), Mn3+/Mn4+ (4.25/4.1 V), and Cr3+/Cr4+ (4.4/4.3 V vs Na/Na+) redox couples in a Na4MnCr(PO4)3 cathode endows a distinct three-electron redox reaction during the insertion/extraction process. The highly stable NASICON structure with a small volume variation upon cycling ensures long-time cycling stability (73.3% capacity retention after 500 cycles within the potential region of 2.5-4.6 V). The impedance analysis and interface characterization indicate that the evolution of a cathode electrolyte interphase at high potential is correlated with the capacity fading, while the robustness of the NASICON framework is redemonstrated.

Vanadium hexacyanoferrate with two redox active sites as cathode material for aqueous Zn-ion batteries

Aqueous rechargeable Zn-ion batteries (ARZIBs) are attractive due to their low cost, high safety and environmental friendliness. However, the development of ARZIBs still faces many challenges. One of the biggest challenges is to find suitable cathode materials for reversible Zn2+ ions insertion/extraction. In this work, we synthesize a Prussian blue analogue (PBA) with a new chemical composition, vanadium hexacyanoferrate (VHCF), via a simple co-precipitation method and study its performance as a cathode material for an aqueous rechargeable Zn-ion battery. The VHCF with two electrochemical redox active sites, V and Fe, delivers a three-electron redox reaction with a capacity of 187 mA h g−1 at current density of 0.5 A g−1. Even at a current rate of 5 A g−1, VHCF can still deliver a large capacity of 122 mA h g−1. The Zn//VHCF battery also exhibits a long cycle life of 1000 cycles with excellent capacity retention of 87.8% and a high Coulombic efficiency close to 100%. During the first charging process, the cubic structure of VHCF changes to a rhombohedral phase, a structure where the Zn2+ ions can be reversibly inserted into and extracted from in subsequent cycles. The promising performances make VHCF an attractive candidate as cathode material for ARZIBs system.

A Redox-Active 2D Metal-Organic Framework for Efficient Lithium Storage with Extraordinary High Capacity.

Metal-organic framework cathodes usually exhibit low capacity and poor electrochemical performance for Li-ion storage owing to intrinsic low conductivity and inferior redox activity. Now a redox-active 2D copper-benzoquinoid (Cu-THQ) MOF has been synthesized by a simple solvothermal method. The abundant porosity and intrinsic redox character endow the 2D Cu-THQ MOF with promising electrochemical activity. Superior performance is achieved as a Li-ion battery cathode with a high reversible capacity (387 mA h g-1 ), large specific energy density (775 Wh kg-1 ), and good cycling stability. The reaction mechanism is unveiled by comprehensive spectroscopic techniques: a three-electron redox reaction per coordination unit and one-electron redox reaction per copper ion mechanism is demonstrated. This elucidatory understanding sheds new light on future rational design of high-performance MOF-based cathode materials for efficient energy storage and conversion.

Beyond Lithium-Based Batteries.

We discuss the latest developments in alternative battery systems based on sodium, magnesium, zinc and aluminum. In each case, we categorize the individual metals by the overarching cathode material type, focusing on the energy storage mechanism. Specifically, sodium-ion batteries are the closest in technology and chemistry to today’s lithium-ion batteries. This lowers the technology transition barrier in the short term, but their low specific capacity creates a long-term problem. The lower reactivity of magnesium makes pure Mg metal anodes much safer than alkali ones. However, these are still reactive enough to be deactivated over time. Alloying magnesium with different metals can solve this problem. Combining this with different cathodes gives good specific capacities, but with a lower voltage (<1.3 V, compared with 3.8 V for Li-ion batteries). Zinc has the lowest theoretical specific capacity, but zinc metal anodes are so stable that they can be used without alterations. This results in comparable capacities to the other materials and can be immediately used in systems where weight is not a problem. Theoretically, aluminum is the most promising alternative, with its high specific capacity thanks to its three-electron redox reaction. However, the trade-off between stability and specific capacity is a problem. After analyzing each option separately, we compare them all via a political, economic, socio-cultural and technological (PEST) analysis. The review concludes with recommendations for future applications in the mobile and stationary power sectors.

Aluminium-poly(3,4-ethylenedioxythiophene) rechargeable battery with ionic liquid electrolyte

Aluminium is one of the promising negative electrode materials for modern batteries. It is environmentally abundant, affordable and recyclable, and its three-electron redox reaction offers high theoretical specific energy and power. However, the development of a suitable positive electrode continues to limit the practical performance of aluminium batteries. In this study, the application of a 3D conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) as a potential positive electrode material is reported. The battery performance, C-rate versus capacity extraction and successive charge/discharge cycling of a full cell (aluminium (-); PEDOT (+); EMImCl-AlCl3 ionic liquid electrolyte) is investigated. The design of the PEDOT electrode (using 3D reticulated vitreous carbon as substrate) is studied, and is supported by microstructure characterisation. The aluminium-PEDOT battery provides 50–64 Wh kg−1 specific energy and 32–40 W kg−1 specific power. The battery has a coulombic efficiency >95%, stable operation over 100 cycles and charge rates up to 80C. In summary, direct and meaningful progress has been made towards achieving useful capacity and cycling stability from aluminium batteries intended for future energy storage.

Stabilization of Hexaaminobenzene in a 2D Conductive Metal-Organic Framework for High Power Sodium Storage.

Redox-active organic materials have gained growing attention as electrodes of rechargeable batteries. However, their key limitations are the low electronic conductivity and limited chemical and structural stability under redox conditions. Herein, we report a new cobalt-based 2D conductive metal-organic framework (MOF), Co-HAB, having stable, accessible, dense active sites for high-power energy storage device through conjugative coordination between a redox-active linker, hexaaminobenzene (HAB), and a Co(II) center. Given the exceptional capability of Co-HAB for stabilizing reactive HAB, a reversible three-electron redox reaction per HAB was successfully demonstrated for the first time, thereby presenting a promising new electrode material for sodium-ion storage. Specifically, through synthetic tunability of Co-HAB, the bulk electrical conductivity of 1.57 S cm-1 was achieved, enabling an extremely high rate capability, delivering 214 mAh g-1 within 7 min or 152 mAh g-1 in 45 s. Meanwhile, an almost linear increase of the areal capacity upon increasing active mass loading up to 9.6 mg cm-2 was obtained, demonstrating 2.6 mAh cm-2 with a trace amount of conducting agent.

Chromium Doped Li2RuO3 As a Positive Electrode with Superior Electrochemical Performance for Lithium Ion Batteries

The miniaturization of portable electronic devices and urgent demand for long-range electric vehicles (EVs) drive researchers to seek for advanced lithium ion batteries (LIBs) as power sources with high energy densities. Traditional cathode materials (LiCoO2, LiMn2O4, LiFePO4 and their derivatives) with specific capacities less than 200 mA h g-1 are not able to fulfil the challenge. As one of the most promising alternatives, lithium-rich layered oxides (LRLOs) with exceptionally high capacities exceeding 250 mA h g-1 have been attracting extensive research interests for high energy density LIBs during the last decade.1-3 However, intrinsic disadvantages of voltage decay and capacity fade resulting from structural instability hinder practical use of LRLOs. Strategies such as ionic doping and surface engineering have been developed to improve electrochemical performance of LRLOs, but with limited understanding of the origins of their high capacity, voltage decay and capacity fade. Ru-based LRLOs stand out their counterparts for the good rate performance benefiting from low resistivity of Ru-based compounds. As the major component of Ru-based LRLOs, although Li2RuO3 exhibits large specific capacity and good rate capability, it suffers severely from capacity fade and voltage decay upon prolonged cycling. Herein in this work, for the first time, Cr has been employed as a dopant in Li2RuO3 compound and the correlation between Cr doping and electrochemical performance of Li2RuO3 is investigated. Elemental Cr is selected as dopant for plenty of reasons. Firstly, LiCrO2 possesses a layered structure with R-3m symmetry, which has similar oxygen stacking framework with Li2RuO3 layered structure. Besides, the ionic radius of Cr3+ (0.615 Å) is close to that of Ru4+ (0.62 Å). The similarity in crystal structure and ionic radius guarantees that the structure of Li2RuO3 is not destroyed by Cr doping. Secondly, Cr3+/Cr6+ three-electron redox reaction is electrochemically active which is expected to favor the capacity improvement of Li2RuO3 compound, as lots of literatures reported that Cr-doped Mn-based LRLOs showed enhanced reversible capacity because of the introduction of three-electron redox reaction of Cr3+/Cr6+. Thirdly, Singh and colleagues reported that Cr in the Cr-doped composite Li2MnO3-LiMn0.5Ni0.5O2 acts as a catalyst for the activation of Li2MnO3 component in the electrochemical reaction,4 which makes it reasonable to deduce that Cr activates anionic electrochemistry and thus contributes to capacity improvement. Based on the above considerations, we synthesized Cr-doped Li2RuO3 with different doping degrees (Li2RuO3, Li2Ru0.98Cr0.02O3, Li2Ru0.95Cr0.05O3 and Li2Ru0.9Cr0.1O3, denoted as LRO, LRO-Cr0.02, LRO-Cr0.05 and LRO-Cr0.1, respectively) by high-temperature sintering method. It is shown that with appropriate amount of Cr doping, the capacity, rate performance and cycling stability can be significantly improved for Li2RuO3 compound. Figure 1

Synthesis and electrochemical properties of Li1.3Nb0.3Cr0.4O2 as a high-capacity cathode material for rechargeable lithium batteries.

A cation-disordered Li-excess cathode material on the binary system xLi3NbO4-(1 - x)LiCrO2 (x = 0.43) has been successfully prepared by mechanical milling, and delivers a high reversible capacity of ∼362 mA h g-1, which originates from a highly reversible Cr3+/Cr6+ three-electron redox reaction with electrochemically inactive niobium ions.

Two-Dimensional Transition Metal Carbides (MXenes): A Large Family of Cathode Materials for Rechargeable Aluminum Batteries

Limited lithium resources in the Earth’s crust alongside the ever-growing demand for rechargeable batteries for portable electronics and electric vehicles (EVs) have led to extensive research on rechargeable battery systems beyond lithium-ion (Li-ion) technology. Among various possible technologies, multivalent-ion batteries offer the potential for cost-effective and safe energy storage devices with high energy density. However, the realization of multivalent-ion batteries depends on the development of electrolytes and cathode materials for these systems. Rechargeable aluminum batteries are promising alternative energy storage devices due to their low cost, abundance of Aluminum, and the potential for three-electron redox reaction leading to higher capacities. Aluminum has a theoretical volumetric capacity of 8040 mAh cm-3 (four times higher than that of lithium). Also, it can be easily handled in open air resulting in an enhanced cell fabrication options and elimination of some of the safety issues associated with lithium and sodium batteries [1]. Various materials have been studied as potential cathodes for Aluminum batteries, however, most suffer from problems such as low capacity, lack of distinct voltage plateaus, and low cycle life with significant capacity decay over 100 cycles. Herein, we are presenting several members of two-dimensional (2D) transition metal carbides (called MXenes) as potential cathode materials for rechargeable Aluminum batteries utilizing a mixture of AlCl3 and [EMIm]Cl as the electrolyte. MXenes are a family of 2D transition metal carbides and/or carbonitrides that are produced by selective removal of the A layer (i.e. Al) from MAX phases (i.e. Ti2AlC), a large family of hexagonal layered ternary carbides and carbonitrides [2, 3]. The MXene based Aluminum batteries work by electrochemical deposition and dissolution of aluminum at the anode and intercalation/de-intercalation of Al3+ ions between the layers of 2D MXene nanosheets. Among different studied MXene materials, Ti2CTx (Tx represents different functional groups such as O, OH, and F on the surface of MXene sheets) and V2CTx showed distinct charge and discharge plateaus with first discharge cycle capacity of as high as 200 mAh/g and 400 mAh/g, respectively at current density of 100 mA/g. The capacity of Ti2CTx dropped to around 60 mAh/g over 50 cycles, however, the V2CTxmaintained a reversible capacity of 200 mAh/g over 50 cycles with a high coulombic efficiency of ~95%. The MXene based Al-ion batteries were cycled in 1.7 V potential window and showed a good rate-capability. Our results show the high potential of MXenes as aluminum battery cathodes and open a new direction in search for high capacity cathode materials for these battery systems. Keywords: 2D, Transition Metal Carbides, MXenes, Aluminum battery

Lithium Molybdenum Oxyfluorides As High-Capacity Positive Electrodes for Rechargeable Lithium Batteries

The demand for the increase in energy density of rechargeable lithium batteries are still growing. Recently, the use of two-electron redox of vanadium ions coupled with a high electronegativity anion in the crystal lattice is proposed as an effective strategy to enhance the energy density of positive electrode materials.[1] Theoretical capacities of lithium insertion materials depend on both total extractable lithium ions and electron numbers in the structure of positive electrodes. Therefore, in addition to the lithium-enrichment in the structure, the use of multi-electron redox processes for transition metals is expected to be an important strategy to further increase energy density of positive electrode materials. We have recently proposed a new lithium-excess oxide, Li9/7Nb2/7Mo3/7O2, which delivers a large reversible capacity of ca. 290 mAh g-1 based on highly reversible three-electron redox of Mo3+/Mo6+.[2] Three-electron redox of molybdenum ions is expected to be a promising system to further increase energy density of positive electrode materials with less transition metal ions. Nevertheless, redox potential of Mo3+/Mo6+in the oxide framework structure is relatively low for positive electrodes. In this study, to increase in the redox potential of three-electron redox reaction of Mo3+/Mo6+, a mixed anion system, oxyfluorides, is targeted. Crystal structures and electrode performance of a new series of xLiF–LiMoO2 binary system, Li1+x MoO2F x , as oxyfluoride positive electrodes are systematically examined. The highest theoretical capacity based on Mo3+/Mo6+ is expected for x = 2 (Li3MoO2F2) in this binary system. Li3MoO2F2 was prepared by mechanical milling from LiMoO2 and LiF. A mixture of LiMoO2 and LiF was mechanically milled with a ZrO2 container and balls. Li3MoO2F2 is found to crystallize into an anion-/cation-disordered rocksalt structure with low crystallinity. Electrochemical properties of Li3MoO2F2 before and after mechanical milling are compared in Figure 1. The sample after mechanical milling delivers a large reversible capacity of ca. 280 mAh g-1, which nearly corresponds to that of theoretical capacity based on the two-electron redox reaction of Mo3+/Mo5+. However, higher average voltage for the molybdenum oxyfluoride is evidenced compared with those of oxides.[2] From these results together with structural and electrochemical data of Li1+x MoO2F x (x= 0.5, 1, and 1.5), we will discuss the feasibility of molybdenum oxyfluoride materials with multi-electron redox reactions as positive electrode materials for rechargeable lithium batteries.

New Lithium-Excess High-Capacity Positive Electrode Materials with Reversible Three-Electron Redox Reaction of Mo3+/Mo6+

The demand for the increase in energy density of lithium batteries is steadily growing. The use of three-electron redox of transition metals is expected to be an important strategy to further increase the energy density of positive electrode materials with less transition metal ions. Recently, our group has reported that Mo3+ ions are diluted in lithium-excess oxides, Li2Ti4+O3, Li3Nb5+O4, and Li4Mo6+O5, which have higher lithium contents, and proposed as a new series of high-capacity electrode materials.[1] For instance, Li9/7Nb2/7Mo3/7O2 delivers a large reversible capacity of ca. 280 mAh g-1, which nearly corresponds to the theoretical capacity based on Mo3+/Mo6+. In this study, this concept is extended into other lithium-excess compounds, and the use of Li3PO4 is targeted. A new binary system with Mo3+ is prepared according to the chemical formula of x Li3PO4 – (1 – x) LiMoO2. Since the molar mass of P is much smaller than that of Nb, the P-based samples are expected to deliver higher reversible capacity. Crystal structures and electrode performance in this binary system are systematically examined. A mixture of Li3PO4 and LiMoO2 was mechanically ball milled at room temperature with a ZrO2 container and balls. The samples of x = 0.4 (Li9/7P2/7Mo3/7O2) and 0.6 (Li11/8P3/8Mo1/4O2) show a relatively small reversible capacities in Li cells (Figure 1). In contrast, the sample of x = 0.2 (Li7/6P1/6Mo2/3O2) delivers the highest reversible capacity of ca. 330 mAh g-1with relatively higher operating voltage compared with the samples without P ions.[1] From these results, we will discuss the possibility of a new series of high-capacity positive electrode materials with Mo3+ions for rechargeable lithium batteries. Reference [1] S. Hoshino, et al., and N. Yabuuchi, ACS Energy Letters, 2, 733 (2017). Figure 1

Reversible Three-Electron Redox Reaction of Mo3+/Mo6+ for Rechargeable Lithium Batteries

To increase the energy density of lithium batteries, the development of high-capacity positive electrode materials is essential. Herein, we propose the use of a three-electron redox reaction of Mo3+/Mo6+ for a new series of high-capacity lithium insertion materials. In this study, a binary system of LiMoO2–Li3NbO4 is targeted, and nanosize and metastable Li9/7Nb2/7Mo3/7O2 is successfully prepared by a mechanical milling process. The sample delivers a large reversible capacity of ∼280 mAh g–1 in a Li cell with good capacity retention. On the basis of these results, the future possibility of high-capacity electrode materials with a three-electron Mo3+/Mo6+ redox reaction is discussed.

New Lithium-Excess High-Capacity Positive Electrode Materials with Mo3+/Mo6+ three-Electron Redox

The demand for the increase in energy density of lithium batteries are steadily growing. The use of three-electron redox of transition metals is expected to be a plausible strategy to further increase the energy density of positive electrode materials with less transition metal ions. Historically, three-electron redox reaction of transition metals is reported only for Cr3+/Cr6+, e.g., Li1.2Cr0.4Mn0.4O2.[1] In this study, the reaction of Mo3+/Mo6+ is targeted as electrode materials. Since conventional layered system, LiMo3+O2, has one mole of Li in the formula unit, only one-electron redox of Mo3+/Mo4+ is used. Therefore, Mo3+ is diluted in lithium-excess oxide, Li3NbO4 [2] as the model material, according to the chemical formula of x LiMoO2 – (1 – x) Li3NbO4 binary system. The highest reversible capacity based on Mo3+/Mo6+ is expected with x = 0.6 (Li9/7Nb2/7Mo3/7O2) in this binary system. Our trials to synthesize Li9/7Nb2/7Mo3/7O2 were, however, failed by conventional solid-state reaction. Mixtures of LiMoO2 and Li3NbO4 were obtained regardless of different synthesis conditions. Therefore, Li9/7Nb2/7Mo3/7O2 was prepared by mechanochemical route from LiMoO2 and Li3NbO4 as precursors. A mixture of LiMoO2 and Li3NbO4 was mechanically ball-milled at room temperature with a ZrO2 container and balls. XRD patterns of LiMoO2, Li3NbO4, and Li9/7Nb2/7Mo3/7O2 prepared by ball-milling are compared in Figure 1a. An X-ray diffraction pattern of Li9/7Nb2/7Mo3/7O2 is assigned to a cation disordered rocksalt structure with low crystallinity. Electrochemical properties of Li9/7Nb2/7Mo3/7O2 before and after mechanical-milling were examined in Li cells as shown in Figure 1b. The sample before mechanical-milling shows initial discharge capacity of ca. 80 mAh g-1, and a voltage profile is the same with LiMoO2. On the other hand, the sample after mechanical-milling delivers a reversible capacity of ca. 290 mAh g-1, which nearly corresponds to that of theoretical capacity based on the redox reaction of Mo3+/Mo6+. Moreover, three-electron redox of Mo is supported by X-ray absorption spectroscopy without the contribution of Nb for charge compensation. From these results, we will discuss the possibility of a new series of high-capacity positive electrode materials with three-electron redox of Mo3+/Mo6+ for rechargeable lithium batteries.

Simulation of square-wave voltammograms of three-electron redox reaction

The theory of square-wave voltammetry of three-electron electrode reaction that consists of one-electron transfer which is followed by the simultaneous transfer of two electrons is developed. If the first step is irreversible and the second one is quasireversible, the extremes of components may be widely separated, resulting in the net response with two peaks. This phenomenon could appear and disappear as the frequency is increased. It is proposed that the particular frequency is measured, at which the two peak currents of the net response are identical. For this critical frequency and the standard signal parameters, the relationship between the standard rate constant of the first step, the transfer coefficient of this step and the difference between standard potentials of two steps is calculated.