Stable Discharge Specific Capacity Research Articles

Low-carbon emitting Fe-cycle recovery of battery-grade FePO4 from biogas slurry for Li-battery application

Under the background of carbon peaking and carbon neutrality in China, anaerobic digestion of sludge to produce methane was an important way to recover biomass energy. But plenty of as-generated biogas slurry (BS) with high P concentration was valuable and difficult to dispose. Here, this work proposed a low-carbon emitting Fe-cycle strategy to recover battery-grade FePO4 from BS. At pH=1.0, the P-leaching rate of Fe-sludge (42.93 ± 1.49 mg g−1) generated by polymerized ferrous sulfate (an inorganic polymer coagulant) addition into BS was 93.46 ± 3.56% and high-purity FePO4 (99.0%) could further be obtained by Fe3+ supplement and pH adjustment (pH=2.0). The contents of all elements in recovered FePO4 product fully complied with the battery grade of national industry standard of China (HG/T 4701-2021). After battery-grade FePO4 precipitate separation, recovery solution (RS) with remaining Fe3+ was reutilized to remove 88.05 ± 1.77% of P when mixed with BS wit RS/BS ratio of 2:1, thus achieving a Fe cycle utilization. Meanwhile, the recovery cost of 5.42 $/kg P and CO2 emissions of 80.83 kg/kg P were lower than those of current FePO4 industrial production (14.60 $/kg P and 110.60 kg/kg P). Finally, the LiFePO4/C cathode material based on recovered FePO4 from BS exhibited stable discharge specific capacity of 84.6–100.2 mAh/g during 100 charge–discharge cycles. In general, this study successfully manifested the feasibility of novel Fe-cycle battery-grade FePO4 recovery strategy from wastewater, paving a viable low-carbon emitting pathway for future Li-battery manufacture industry.

Mesoporous carbon hollow spheres with controllable pore structure for efficient lithium and aluminum ion storage

Mesoporous carbon hollow nanospheres (MCHS), synthesized via a block copolymer-mediated supramolecular self-assembly process, serve as both anode materials for lithium-ion batteries (LIBs) and cathode materials for aluminum-ion batteries (AIBs). By adjusting the carbonization temperature and the dosage of the pore extender, 1,3,5-trimethylbenzene (TMB), insights into the relationships among pore structure, crystal structure, and electrochemical properties of MCHS in Li/Al-ion batteries are gained. Their exceptional properties, including hierarchically porous structure, large surface area, tailored inner voids, mesoporous shells, and high electronic conductivity, contribute to high specific capacity, improved rate performances, and remarkable electrochemical stability. Crystallographic insights reveal that highly porous MCHS facilitate the intercalation of ionic lithium and aluminum species into the carbon crystal lattices while maintaining structural integrity. The appropriate mesopore size significantly impacts the storage of lithium or aluminum ions, with relatively larger mesopore sizes being more beneficial for aluminum ion storage compared to lithium ions. The optimal MCHS exhibit a stable discharge specific capacity of 330.8 mAh·g−1 after 800 cycles at a current density of 372 mA·g−1 (1C) in LIBs and 41.6 mAh·g−1 after 500 cycles at 74.4 mA·g−1 in AIBs.

Mesoporous hollow Fe4[Fe(CN)6)]3 hierarchical nanocrystal architecture for advanced sodium-ion batteries

Prussian blue (PB) has been broadly recognized as promising cathode materials for sodium-ion batteries (SIBs) due to its large interstitial space and robust frame structure, whereas their applications are impeded by unsatisfied long-term cyclability and poor rate capability due to its inherent lattice defects. Herein, we report to fabricate the mesoporous hollow Fe4(Fe(CN)6)3 (one kind of PB) hierarchical nanocrystal architecture by the hydrothermal crystallization and HCl etching of the mesoporous precursor Fe4[Fe(CN)6]3 cubic particles, leading to high crystallinity and large specific surface area. The resultant Fe4[Fe(CN)6]3 cathode for SIBs exhibits a good reversibility and cycling stability with a capacity retention of 75.6 % at 0.5 C after 200 cycles as well as superb rate capability featuring a stable discharge specific capacity of 30.2 mAh g−1 at as high as 10 C, demonstrating the fast kinetics and low polarization of electrochemical reaction, which might be ascribed to the unique architecture and high crystallinity. This offers a new route to designing PB cathode of for SIBs with high rate capabilities.

Pilot-scale phosphorus recovery from biogas slurry to produce battery-grade FePO4: Chemical enhanced primary treatment coupled adsorption process

Recovering phosphorus (P) from wastewater was expected to bring win–win profits for environmental protection and clean energy industries. Ferric phosphate (FePO4) was a key raw material for lithium-ion battery production for new energy vehicles, which was a more valuable and promising product for recovering P from wastewater. There were challenges in recovering high-purity FePO4 from wastewater with complex components, especially in achieving large-scale recovery. Here, a pilot-scale platform, the Chemical Enhanced Primary Treatment (CEPT) coupled Fe@aminated-polyacrylonitrile (Fe-NH2-PAN) adsorption, was established for recovering battery-grade FePO4 from biogas slurry. The platform stably removed over 80% of PO43− from biogas slurry during long-term operation, the removed PO43− was enriched in chemical sludge and Fe-NH2-PAN, and then was leached into H2SO4 solution. FePO4 crystal was successfully recovered from the leaching solution (822.35 ± 15.91 mg/L PO43−) with a recovery rate of over 75%. Importantly, the lithium-ion battery prepared from recovered FePO4 exhibited excellent and stable electrochemical performance (with stable discharge specific capacity of 100.4–106.7 mAh/g at 1.0 C). This study provides a new path for large-scale P recovery in WWTPs.

Copper/cobalt metal-organic framework composites for advanced anode material of lithium-ion battery

In this paper, two new types of metal-organic frameworks (MOFs) materials, namely Cu-IM and Co-MOF, have been successfully applied to the anode of lithium-ion batteries with LiPF6 (EC: DMC = 1:1, volume) electrolyte additive. Cu-IM and Co-MOF employed imidazole (IM) and 2-methylimidazole (2-MeIM) as organic ligands, respectively. The results revealed the synthesized MOFs exhibited high initial discharge specific capacities (Cu-IM: 1964.5 mAh g−1, Co-MOF: 1423.3 mAh g−1) as well as low internal resistances (Cu-IM: 146 Ω; Co-MOF: 236 Ω). To alleviate the issue of capacity decay in single MOFs, we attempted the dual-MOFs materials through the rational design of interfacial/surface properties and microstructure. Compared to Cu-IM, the prepared Cu-IM/Co-MOF composites have a higher specific surface area and pore volume. Furthermore, the charge transfer resistance of Cu-IM/Co-MOF composites (141 Ω) was lower than that of Cu-IM and Co-MOF respectively. After a heat treatment to Cu-IM/Co-MOF composites, the electrochemical performance of obtained Cu-IM/Co-MOF 250 dual-MOFs composites have been significantly improved. The Cu-IM/Co-MOF 250 dual-MOFs composites demonstrated excellent cycling stability and high discharge specific capacities at various current densities. The composites displayed stable discharge specific capacity retention of 834 mAh g−1 (50 mA g−1, 75 cycles), 710.5 mAh g−1 (200 mA g−1, 50 cycles), and 392.5 mAh g−1 (500 mA g−1, 50 cycles), highlighting their promising performance for energy storage applications. The synthesized Cu-IM/Co-MOF 250 dual-MOFs composites demonstrates exceptional cycling performance and rate capability, implying that it has the promising prospects as anode material for lithium-ion batteries.

Nitrogen-doped porous carbon encapsulates multivalent cobalt-nickel as oxygen reduction reaction catalyst for zinc-air battery

In this study, we present a bimetallic ion coexistence encapsulation strategy employing hexadecyl trimethyl ammonium bromide (CTAB) as a mediator to anchor cobalt–nickel (CoNi) bimetals in nitrogen-doped porous carbon cubic nanoboxes (CoNi@NC). The fully encapsulated and uniformly dispersed CoNi nanoparticles with the improved density of active sites help to accelerate the oxygen reduction reaction (ORR) kinetics and provide an efficient charge/mass transport environment. Zinc-air battery (ZAB) equipped CoNi@NC as cathode exhibits an open-circuit voltage of 1.45 V, a specific capacity of 870.0 mAh g−1, and a power density of 168.8 mW cm−2. Moreover, the two CoNi@NC-based ZABs in series display a stable discharge specific capacity of 783.0 mAh g−1, as well as a large peak power density of 387.9 mW cm−2. This work provides an effective way to tune the dispersion of nanoparticles to boost active sites in nitrogen-doped carbon structure, and enhance the ORR activity of bimetallic catalysts.

Air-stabilized pore structure engineering of antimony-based anode by electrospinning for potassium ion batteries

Due to the large ionic radius and associated slow reaction kinetics of potassium ions, it is a major challenge to find suitable anode materials for potassium-ion batteries. Herein, we design porous antimony-based nanofibres via a simple, low-cost and large scalable method to promote the electrochemical performance of potassium-ion batteries. Unlike those traditionally treated in inert atmospheres, using the different decomposition processes of polyacrylonitrile and polyvinylpyrrolidone in air, we obtain antimony trioxide embedded in porous carbon nanofibres (Sb2O3@PCN). The porous structure can promote the permeation of electrolyte into electrode materials and increase the active sites of the redox reaction. The porous carbonaceous fibre skeleton structure establishes a fast ion transport channel and enhances the kinetic performance. In a concentrated 5 M potassium bis(fluorosulfonyl)-imide/dimethyl carbonate electrolyte, Sb2O3@PCN exhibits a stable discharge specific capacity of 437.3 mAh g-1 at a current density of 100 mA g−1 after 50 cycles, which is much higher than that treated in a N2 atmosphere (247.5 mAh g-1). This method provides a new approach for the preparation of efficient potassium-ion battery electrode materials.

A facile in situ Mg surface chemistry strategy for conditioning-free Mg[AlCl4]2 electrolytes

Developing a simple and reliable strategy for modulating overpotential of Mg plating/stripping is crucial for realizing overall high performance of rechargeable Mg batteries, which have been demonstrated to be rather challenging. Herein, we report a facile LiI-assisted Mg surface chemistry to reduce Mg plating/stripping overpotential via in situ solubilization mechanism and ion conductive surface layer formation mechanism. As a result, we successfully formulate a new conditioning-free Mg[AlCl4]2-based Mg electrolyte system that improves Mg plating/stripping from the very first cycle. The overpotential of Mg plating/stripping of the as-prepared electrolyte with a LiI electrolyte additive is remarkably reduced to 240/240 mV at a current density of 1000 µA cm−2. Using this electrolyte, a rechargeable Mg battery coupled with PANi intercalated V2O5 (V2O5-PANi) cathode and Mg anode delivers a stable discharge specific capacity of nearly 50 mA h g−1 after an impressively prolonged cycle life of 500 cycles. Our finding provides a new inspiration of in situ Mg surface chemistry to activate Mg anode surface with high Mg ion conductivity.

A novel AlCl3-[EMIM][TF2N] electrolyte for rechargeable aluminum-ion battery

Owing to the high theoretical capacity, low price, easy availability of aluminum, the rechargeable aluminum-ion battery (AIB) is very suitable as an electrochemical energy storage device for large-scale power storage. High preference of rechargeable AIBs is depended on the suitable electrolytes. In this paper, a kind of novel ionic liquid electrolyte is prepared by mixing aluminum chloride (AlCl3) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TF2N]). This electrolyte possesses high electrical conductivity and a satisfactory oxidation voltage (2.50 V vs. Al/Al3+), which are more excellent than conventional AlCl3-based electrolytes. The Al|1.7AlCl3-[EMIM][TF2N]|carbon paper battery exhibits a stable discharge specific capacity of ~75 mAh⋅g-1 at 100 mA⋅g-1 with a near 100% coulombic efficiency, indicating that AlCl3-[EMIM][TF2N] ionic liquid is a promising electrolyte for high-voltage and high-performance aluminum-ion batteries.

MOF-derived porous carbon nanofibers wrapping Sn nanoparticles as flexible anodes for lithium/sodium ion batteries

Facile synthesis of flexible electrodes with high reversible capacity plays a key role in meeting the ever-increasing demand for flexible batteries. Herein, we incorporated Sn-based metal-organic framework (Sn-MOF) templates into crosslinked one-dimensional carbon nanofibers (CNFs) using an electrospinning strategy and obtained a hierarchical porous film (Sn@C@CNF) after a carbothermal reduction reaction. Merits of this modification strategy and its mechanism in improving the electrochemical performance of Sn nanoparticles (NPs) were revealed. Electrospun CNFs substrate ensured a highly conductive skeleton and excellent mechanical toughness, making Sn@C@CNF a self-supported binder-free electrode. Serving as a self-sacrificing template, Sn-MOF provided Sn NPs and derived into porous structures on CNFs after pyrolysis. The hierarchical porous structure of the carbon substrate was beneficial to enhancing the Li+/Na+ storage of the active materials, and the carbon wrappings derived from polyacrylonitrile (PAN) nanofibers and the MOF skeleton could jointly accommodate the violent volume variation during cycling, enabling Sn@C@CNF to have excellent cycle stability. The Sn@C@CNF anode exhibited a stable discharge specific capacity of 610.8 mAh g−1 under 200 mA g−1 for 180 cycles in lithium ion batteries (LIBs) and 360.5 mAh g−1 under 100 mA g−1 after 100 cycles in sodium ion batteries (SIBs). As a flexible electrode, Sn@C@CNF demonstrated a stable electromechanical response to repeated ‘bending-releasing’ cycles and excellent electrochemical performance when assembled in a soft-pack half-LIB. This strategy provided promising candidates of active materials and fabrication methods for advanced flexible batteries.

The electrochemical performanceand multielectron reaction mechanism of NiV2O6 as anovel anode material for lithium-ion batteries

Based on the existence of multiple valence states of Ni and V, the single-phase nickel vanadium bimetal oxide NiV2O6 is successfully synthesized by asimple sol-gel method. Benefiting from the multielectron reaction of nickel (Ni) and vanadium (V), as novel anode materials of lithium-ion batteries (LIBs), the NiV2O6 electrode exhibits excellent electrochemical performance. After activation, attributed to the decrease in the particle size and an increased pseudocapacitance contribution, the electrode material exhibits a highly stable reversible capacity. At a small current density of 0.1 A g−1, a stable discharge specific capacity of around 1200 mA h g−1 can be observed, which is more than three times the capacity of the commercial graphite anode. Using electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) measurement methods, we discuss the function of the activation process. To explore the discharge/charge process, based on in situ X-ray diffraction (XRD) measurements, combined with the X-ray photoelectron spectroscopy (XPS) and SEM results, we analyze the charge/discharge reaction mechanism of the NiV2O6 electrode in detail for the first time. In addition, a full cell is employed to confirm the practicality of the NiV2O6 anode material.

Preparation of room temperature liquid metal negative electrode for lithium ion battery in one step stirring

As a new type of self-healing material, room-temperature liquid metal (RLM) composed of Ga, In, Sn is a promising anode in lithium-ion batteries (LIBs). However it is difficult to prepare an electrode slurry with pure RLM directly. Here, a simple high-speed stirring method successfully prepared the RLM electrode slurry. The RLM in the slurry evenly distributed in the form of liquid particles, and no aggregation occurred. The stable discharge specific capacity of RLM is 350 mAh g−1. Electrochemical tests show that RLM electrodes have excellent cycle stability and reversible capacity retention rate at different current densities.

Three-dimensional porous carbon skeleton supporting Si nanosheets as anode for high-performance lithium ion batteries

Si nanosheets (NSs) are synthesized by the arc-discharge plasma and successfully anchored onto the surface of porous carbon (PC) substrate via physical adhesion assisted with ultrasonic blending. The PC matrix is obtained by high-temperature calcination of the mixture of glucose and calcium carbonate, followed by acid washing for removal of the oxidization products. The contents of Si NSs loaded are fixed at Si/PC = 1:9, 3:7, and 5:5 (in mass), respectively. It is found that the anode with the optimum composition of 30 wt% Si NSs exhibits the best electrochemical performances, owing to a homogeneous dispersion of Si NSs on the PC substrate without severe aggregation, typically a stable discharge specific capacity of 1252 mAh·g−1 with the coulombic efficiency of 99.58% at the current density of 100 mA·g−1 after 100 cycles while retains the capacity of 850 mAh·g−1 even at a high current density of 1 A·g−1 after 800 cycles. In comparison with the entire Si NSs electrode, the best Si/PC composite anode shows two times higher in the capacity retention ability and the excellent rate performance, due to the electrical contribution and large specific surface/pore volume of the PC matrix, which also plays positive roles in mass infiltration of electrolyte and rapid transport/diffusion of electrons/Li+ ions inside the electrodes.

Controlling the phenolic resin-based amorphous carbon content for enhancing cycling stability of Si nanosheets@C anodes for lithium-ion batteries

Carbon-coated Si nanosheets (Si NSs@C) nanocomposites with different carbon contents are successfully controlled and synthesized by the method of DC arc-discharge plasma, followed by phenolic resin pyrolysis at high temperature. The electrochemical performances of these nanocomposites as the anodes of lithium-ion batteries (LIBs) are investigated. The Si NSs with an average size of 31 nm and a thickness of 2.4 nm are surrounded by phenolic resin-derived amorphous carbon, forming a cladding structure. In the nanocomposites, Si NSs play a leading role in the reaction with Li+ ions, while the amorphous carbon mainly provides a highly conductive matrix for good contact among Si NSs active phases, which further facilitates the diffusion and transport of Li+ ions and electrons. The carbon matrix can also protect Si NSs from direct contact with the electrolyte, to ensure the formation of stable SEI films in cycles. Electrochemical performances indicate that the Si NSs@C nanocomposite electrode with the carbon content of 66.4 wt% delivers a stable discharge specific capacity of 822 mAh g−1 at a current density of 100 mA g−1 after 200 cycles and a better rate capability, confirming the predominant role of the controlled carbon content in the enhancement of the cycling stability of such Si-based anodes for LIBs.

Low-Cost Room-Temperature Synthesis of NaV3O8·1.69H2O Nanobelts for Mg Batteries.

Potentially safe and economically feasible magnesium batteries (MBs) have attracted tremendous research attention as an alternative to high-cost and unsafe lithium ion batteries. In the current work, for the first time, we report a novel room-temperature approach to dope the atomic species sodium between the vanadium oxide crystal lattice to obtain NaV3O8·1.69H2O (NVO) nanobelts. The synthesized NVO nanobelts are used as electrode materials for MBs. The MB cells demonstrate stable discharge specific capacity of 110 mA h g-1 at a current density of 10 mA g-1 and a high cyclic stability, that is 80% capacity retention after 100 cycles, at a current density of 50 mA g-1. Moreover, the effects of cutoff voltages (ranging from 2 to 2.6 V) on their electrochemical performance were investigated. The reason for the limited specific capacity of MBs is attributed to the trapping of Mg ions inside the NVO lattices. This work opens up a new pathway to explore different electrode materials for MBs with improved electrochemical performance.

Cactus-like iron diphosphide@carbon nanotubes composites as advanced anode materials for lithium-ion batteries

The ball-cactus-like iron diphosphide@carbon nanotubes (FeP2@CNTs) composites are synthesized via a simple chemical vapor deposition (CVD) with two-step heating method. SEM, TEM, XRD and Raman spectrum confirm that FeP2 and CNTs exist as the core and the surrounding spines of the ball-cactus-like composite, respectively, for FeP2@CNTs synthesized under suitable conditions. With optimized FeP2@CNTs composite containing ball-catus-like structure as the anode of LIBs, the assembled batteries exhibit an initial coulombic efficiency of 91.6%. Furthermore, this kind of battery delivers a stable and high discharge specific capacity of 736.2 mAh g−1 at 0.1 C (1 C = 1365 mA g−1) after 100 cycles. Even at a higher rate of 2.5 C, it still delivers a stable discharge specific capacity of 650.2 mAh g−1 within 100 cycles with negligible capacity fading, much higher than the reported results to date. This excellent electrochemical performance of FeP2@CNTs composite is attributed to the cladding of FeP2 with CNTs, which prevent the large volume changes of FeP2 and improve the electrical conductivity of composites.

LiF-MO (M=Co, Fe, Ni) Nanocomposite Thin Film as Anode Materials for Lithium-ion Battery

To investigate the electrochemical performance of MO (M=Co, Fe, Ni) nanostructures on lithium insertion and extraction, size-controlled LiF-MO nanocomposite thin-film electrodes, consisting of metallic M and M oxide (MO) nanoparticles in an amorphous, inert LiF matrix, were designed and fabricated using a RF sputtering system with metallic M and LiF mixture targets. The structural and electrochemical properties of nanocomposite thin-film electrodes were characterized using TEM, SAED, XRD, XPS, and electrochemical measurements. The results showed that MO particles with average particle sizes of ca.10nm were well-dispersed in LiF matrix to form a kind of homogeneous LiFMO nanocomposite by the sputtering method. The inert medium of LiF provides an effective matrix to prevent the crystallization and agglomeration of MO during the deposition and electrochemical cycling of the thin film electrode, and then the well-formed nanophase structure in the nanocomposite thin-film electrodes leads to an excellent electrochemical cycling performance with the stable discharge specific capacity above 300mAh/g.

Synthesis and electrochemical performance of spherical-like Li2FeSiO4/C/SP cathode material for lithium-ion batteries

The novel spherical Li2FeSiO4/C/SP is successfully synthesized by two-step precipitation method. The structure and morphology of the as-prepared samples are characterized by means of XRD, SEM, TEM and HRTEM. The results show that the product is consisted of spherical Li2FeSiO4 microparticles coated with carbon layer and dispersive nanoparticle which is conductive carbon black. The growth mechanism of the spherical Li2FeSiO4/C/SP composites is discussed in particularly. The electrochemical performance is demonstrated by the electrochemical impedance spectra and charge–discharge curves. The product presents excellent electrochemical performance. This is the result of the uniform spherical morphology improved lithium-ion diffusion rate (1.271×10−12cm2s−1) by shortening diffusion pathways of lithium ion, and the carbon coating enhance the electronic conductivity. It is found that the spherical Li2FeSiO4/C/SP composites show a high capacity as 171.8mAhg−1 at 0.1C and high coulombic efficiency as 93.6%. The outstanding high-rate capability is also presented as 113.7mAhg−1 at 5C. Moreover, it exhibits very stable discharge specific capacity at different current densities from 0.2 to 5C. These indicate that the spherical Li2FeSiO4/C/SP is a very promising candidate for cathode material in lithium-ion batteries.

Hierarchical shuttle-like Li2FeSiO4 as a highly efficient cathode material for lithium-ion batteries

We successfully synthesized the novel hierarchical shuttle-like Li2FeSiO4 using one step hydrothermal method with ethylene glycol assisted. The growth mechanism of the shuttle-like Li2FeSiO4 constructed of nanosingle crystals was discussed and its electrochemical performance as a cathode material for lithium ion battery was investigated. Astonishingly, the 1st discharge specific capacity of the new material without carbon coating was 180.6 mA h g−1 at 0.1 C with a remarkably high Coulombic efficiency of 97.5%, and an improved high-rate capability (71.0 mA h g−1 at 2 C) was offered which is comparable to the commonly carbon-coated Li2FeSiO4. Moreover, it exhibited a very stable discharge specific capacity at current densities from 0.1 to 2 C. Its excellent electrochemical performance can be ascribed to the significantly improved diffusion coefficient of lithium ions (5.6421 * 10−11 cm2 s−1), which was greatly larger than the reported carbon-coated Li2FeSiO4 nanocomposites and diatomic metallic ions (Ni2+, Cu2+, Zn2+) doped Li2FeSiO4. These indicate the shuttle-like Li2FeSiO4 is a very promising cathode material for lithium-ion batteries.

Poly(tetrahydrobenzodithiophene): High discharge specific capacity as cathode material for lithium batteries

Abstract A novel thioether containing conjugative polymer, poly(tetrahydrobenzodithiophene) (PTBDT), with high discharge specific capacity as the cathode material for lithium batteries, has been synthesized chemically. The polymer has been characterized by elemental analysis, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The cyclic voltammogram of the polymer shows multiple redox peaks. The charge–discharge tests show stable discharge specific capacity about 560 mAh g −1 and the maximal capacity of 820 mAh g −1 , and discharge voltage about 2.3 V. The results indicate that the thioether bonds of the polymer are involved in the electrode reaction. It is tentatively proposed that the thioether cations are formed during the redox reaction on the cathode. The reversible redox reaction on thioether bonds that is a multi-electron process offers a high specific capacity, and low discharge voltages.