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A sodium polyacrylate (NaPAA) binder induces the formation of a stable and Na-ion conductive NaPO2F2-rich cathode–electrolyte interphase layer via a displacement reaction.

A uniform carbon-coated Na3V2(PO4)2O2xF3–2x (NVPOF/C) nanoparticle synthesized by a novel pyro synthesis method is utilized for sodium-ion batteries (SIBs) as a cathode. Remarkably, the electrochem...

In this study, a pseudo-layered Na super-ionic conductor of Na3V2(PO4)2F3 (NVPF)/C cathode for sodium-ion batteries is prepared successfully using a facile polyol refluxing process without any impurity phases. The X-ray diffraction and Rietveld refinement results confirm that NVPF possesses tetragonal NASICON-type lattice with a space group of P42/mnm. In this preparative method, polyol is utilized as a solvent as well as a carbon source. The presence of nanosized NVPF particles in the carbon network is confirmed by field-emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM). The existence of carbon is analyzed by Raman scattering and elemental analysis. When applied as a Na-storage material in a potential window of 2.0–4.3 V, the electrode exhibits two flat voltage plateaus at 3.7 and 4.2 V with an electrochemically active V3+/V4+ redox couple. In addition, Na3V2(PO4)2F3/C composite achieved a retention capacity of ~ 88% even after 1,500 cycles at 15 C. Moreover, at high current densities of 30 and 50 C, Na3V2(PO4)2F3/C cathode retains the specific discharge capacities of 108.4 and 105.9 mAh·g–1, respectively, revealing the structural stability of the material prepared through a facile polyol refluxing method.

Nickel vanadate (Ni3V2O8, NVO) nanoparticles (NPs) with a typical size of 30 nm were prepared through a zeolitic imidazolate framework (ZIF) intermediate precipitation method using water as a solvent. The intermediate and the NVO obtained after annealing the intermediate were systematically characterized using various techniques. When tested as an anode for Li-ion batteries (LIBs), the electrode displayed stable specific capacities of 940 and 305 mA h g− 1 at 1 and 5 A g− 1, respectively, after 400 and 1000 cycles. Additionally, a very high reversible capacity of 1024 mA h g− 1 was observed after 525 cycles, during which high current densities of 2 and 0.5 A g− 1 alternated every 100 cycles. The long cycling rate capability with repeated sets, confirm the structural stability of the material, which was prepared through a facile and eco-friendly procedure.

NiO nanoparticles with average particles size of 30 nm are synthesized using a one-pot metal–organic framework-combustion (MOF-C) technique, for use as an anode material in rechargeable lithium ion batteries (LIBs). The structural and electronic properties of these nanoparticles are studied using various techniques, including powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and N 2 adsorption/desorption studies. The as-synthesized NiO nanoparticles sustained reversible stable capacities of 748 and 410 mAh/g at applied current densities of 500 and 1000 mA/g, respectively, after 100 cycles. Furthermore, the anode displays a notable rate capability, achieving a stable capacity of ∼200 mAh/g at a high current density of 10 A/g. These results indicate that the size of the NiO nanoparticles and their high surface area influence their electrochemical properties. Specifically, this combustion strategy is clearly favorable for improving the cyclability and rate capability of various metal oxides in rechargeable battery electrodes.

P2-structure sodium manganese oxide is synthesized by a facile reduction reaction. We provide new data on the direct use of sodium manganese oxide instead of lithium analogues as a low-cost electrode for lithium/sodium hybrid ion batteries after an ion-exchange process. Ion exchange occurs in sodium manganese oxide through the electrolyte during cell stabilization, as observed by X-ray diffraction analysis. The self ion-exchanged material delivers a high discharge capacity of 195 mA h g −1 and a stable plateau at 3.0 V for 50 cycles with stable cyclability. In-situ X-ray diffraction and ex-situ X-ray absorption near edge structure studies also confirm reversible redox reactions and stable structural changes. The ex-situ inductively coupled plasma atomic emission spectroscopy analysis verifies that residual sodium ions in the structure act as pillars during cycling.

The solid electrolyte interphase (SEI) layer plays a crucial role in ensuring the safety and stability of batteries. The SEI layer is highly complex and it comprises organic and inorganic components due to the electrolyte decomposition and electrode dissolution. In this study, SEI layers were formed at various current rates using a full cell, and their chemical and electrochemical properties were investigated. SEIs formed at various current rates consisted of similar constituents; however, the composition of the constituents differed according to the current rate, indicating the effect of current rate on the SEI formation kinetics. The differential scanning calorimetry (DSC) thermograms showed that the SEI formed at a low current rate included a larger portion of components that decomposed at ∼100 °C than those formed at high current rates. In addition, in-depth X-ray photoelectron spectroscopy (XPS) also revealed this difference in composition according to the varying current rate. The anode cycled at a low current rate displayed a low charge transfer resistance. This study suggests that the physicochemical and electrochemical properties of SEIs differ depending on the formation conditions.

Na3V2(PO4)3 (NVP) is characterized by a robust 3D structural framework and a high operating potential; these properties have enabled it to be widely studied as a stable and high-energy density cathode material for sodium-ion batteries (SIBs). In the present study, we designed a Na3V1.6Cr0.4(PO4)3/C (NVCrP@C) cathode by implanting Cr into the crystal structure of NVP and simultaneously coating the surface of NVP with carbon for realizing high power density SIBs. The substitution of Cr to vanadium in the NVP structure significantly enhanced the structural stability of the electrode while the uniform and thin carbon layer improved the electrical conductivity. Interestingly, the NVCrP@C cathode showed high electrochemical activities with multiple V3+/4+/5+ redox reactions triggered by Cr3+ substitution in a wide voltage range (2.5–4.1 V). Consequently, the NVCrP@C cathode delivered excellent cycling stability over 500 cycles even at 15C-rate and power capability up to 70 C-rate. Results from the in-situ X-ray diffraction and ex-situ X-ray absorption near edge structure studies were combined to verify the detailed mechanism of the enhanced sodium storage in the NVCrP@C cathode.

This study aims to imitate the artificial structural degradation of a LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode and the electrochemical data for the analysis of spent batteries. Degraded NCM622 was obtained by controlling the charging cut off voltage, and the structural degradation was investigated using X-ray diffraction and inductively coupled plasma optical emission spectrometry. X-ray photoelectron spectroscopy results confirmed the cathode electrolyte interface on the surface of the electrode. Galvanostatic charge/discharge tests were performed using a cell with an overcharged NCM622 cathode, fresh anode, and fresh electrolyte to investigate the structural degradation effect on the cathode. The capacity of the higher overcharged electrode decreased with the higher IR drop and concentration polarization. This study demonstrates that structural degradation results in different discharge behaviors in lithium-ion batteries.

The present study reports on the one-pot synthesis of Ni3V2O8 (NVO) electrodes by a simple metal organic framework-combustion (MOF-C) technique for anode applications in Li-ion batteries (LIBs). The particle morphology of the prepared NVO is observed to vary as irregular rods, porous bitter gourd and hybrid micro/nano particles depending on the concentration of the framework linker used during synthesis. In specific, the orthorhombic phase and the unique bitter gourd-type secondary structure comprised of agglomerated nanoparticles and porous morphologies is confirmed using powder X-ray diffraction, electron microscopies, X-ray photoelectron spectroscopy and N2 adsorption–desorption measurements. When tested for lithium batteries as anode, the bitter gourd-type NVO electrode shows an initial discharge capacity of 1362 mA h g−1 and a reversible capacity of 822 mA h g−1 are sustained at a rate of 200 mA g−1 after 100 cycles. Moreover, at 2000 mA g−1, a reversible capacity of 724 mA h g−1 is retained after 500 cycles. Interestingly, the porous bitter gourd-shaped NVO electrode registered significantly high rate performance and reversible specific capacities of 764, 531 and 313 mA h g−1 at high rates of 1, 5 and 10 A g−1, respectively.

Zn3V2O8 (ZVO) with sheet-like morphology is synthesized by a simple green precipitation technique via a metal-organic framework (MOF) intermediate for use as an anode in high energy lithium-ion batteries (LIBs). This sheet-like morphology, enriched with highly porous features, is evident from transmission electron microscopy (TEM) and surface area measurements. When tested as a lithium half-cell electrode, the ZVO porous sheets delivered a reversible specific capacity of 1228 mA h g−1 at a current density of 0.3 A g−1 for 200 cycles. Interestingly, on applying two different high current densities of 1 and 3 A g−1, this porous ZVO material registered high capacities of 665 and 510 mA h g−1, initially for 30 and 50 cycles, respectively. On reducing the current density to 0.5 and 1 A g−1 for the two instances, both sustained stable capacities of 906 and 687 mA h g−1 in the 160th and 600th cycles, respectively. The fact that these porous sheets maintained a stable capacity as high as 370 mA h g−1 at the high applied current density of 5 A g−1 after 2000 discharge/charge cycles reveals the structural stability of the ZVO prepared by a simple green precipitation technique.

In the present study, a metal-organic framework (MOF) derived from a facile water-assisted green precipitation technique is employed to synthesize phase-pure cobalt vanadate (Co3V2O8, CVO) anode for lithium-ion battery (LIB) application. The material obtained by this eco-friendly method is systematically characterized using various techniques such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption measurements. By using as an anode, an initial discharge capacity of 1640mAhg-1 and a reversible capacity of 1194mAhg-1 are obtained at the applied current densities after the 240th cycle (2Ag-1 for 200 cycles followed by 0.2Ag-1 for 40 cycles). Moreover, a reversible capacity as high as 962mAhg-1 is retained at high current densities even after 240 cycles (4Ag-1 for 200 cycles followed by 2Ag-1 for 40 cycles), revealing the long life stability of the electrode. Significantly, CVO anode composed of fine nanoparticles (NPs) registered a substantial rate performance and reversible specific capacities of 275, 390, 543 and 699mAhg-1 at high reversibly altered current densities of 10, 5, 2, and 1Ag-1, respectively.

Monoclinic Li3V2(PO4)3 (LVP) has been considered a promising cathode material for lithium-ion batteries for the past decade because of its high average potential (>4.0 V) and specific capacity (197 mAh g–1). In this paper, we report a new monoclinic-orthorhombic Na1.1Li2.0V2(PO4)3/C (NLVP/C) composite cathode synthesized from monoclinic LVP via a soft ion-exchange reaction for use in Na+/Li+ hybrid-ion batteries. High-resolution synchrotron X-ray diffraction (XRD), thermal studies, and electrochemical data confirm room temperature stabilization of the monoclinic-orthorhombic NLVP/C composite phase. Specifically, we report the application of a monoclinic-orthorhombic NLVP/C composite as cathode material in a Na half-cell. The cathode delivered initial discharge capacities of 115 and 145 mAh g–1 at a current density of 7.14 mA g–1 in the 2.5–4 and 2.5–4.6 V vs Na/Na+ potential windows, respectively. In the lower potential window (2.5–4 V), the composite electrode demonstrated a two-step voltage plateau duri...

Rhombohedral Li 2 NaV 2 (PO 4 ) 3 is very attractive cathode material for lithium-ion battery (LIB) application due to its single voltage plateau at 3.7 V that provides a constant output power. Here, for the first time, we report a direct and simple synthesis of high performance carbon-coated rhombohedral Li 2 NaV 2 (PO 4 ) 3 (LNVP/C) nanoflake cathode using a pyro-synthesis technique. The cathode demonstrates long cycle stability (100% capacity retention over 300 cycles) and high rate capabilities (77 and 55 mAh g −1 at 6.4 and 12C, respectively). The present study may facilitate a simple and low-cost preparation technique towards high performance cathode materials for advanced LIB applications.

In this study, we report the cost-effective and simple synthesis of carbon-coated α-MnO2 nanoparticles (α-MnO2@C) for use as cathodes of aqueous zinc-ion batteries (ZIBs) for the first time. α-MnO2@C was prepared via a gel formation, using maleic acid (C4H4O4) as the carbon source, followed by annealing at low temperature of 270 °C. A uniform carbon network among the α-MnO2 nanoparticles was observed by transmission electron microscopy. When tested in a zinc cell, the α-MnO2@C exhibited a high initial discharge capacity of 272 mAh/g under 66 mA/g current density compared to 213 mAh/g, at the same current density, displayed by the pristine sample. Further, α-MnO2@C demonstrated superior cycleability compared to the pristine samples. This study may pave the way for the utilizing carbon-coated MnO2 electrodes for aqueous ZIB applications and thereby contribute to realizing high performance eco-friendly batteries.

In this work, we demonstrate the first use of a V-doped MnO2 nanoparticle electrode for zinc-ion battery (ZIB) applications. The V-doped MnO2 was prepared via a simple redox reaction and the X-ray diffraction studies confirmed the formation of pure MnO2, accompanied by an anisotropic expansion of MnO2 lattice, suggesting the incorporation of V-ions into the MnO2 framework. V doping of MnO2 not only increased the specific surface area but also improved the electronic conductivity. When Zn-storage properties were tested, the V-doped MnO2 electrode registered a higher discharge capacity of 266 mAh g−1 compared to 213 mAh g−1 for the pure MnO2 electrode. On prolonged cycling, the doped electrode retained 31% higher capacity than that of the bare MnO2 electrode and thereby demonstrated superior cycling performance. This study may pave the way towards understanding the enhancement of the energy storage properties via doping in electrodes of aqueous ZIB applications and also furthers the efforts for the practical realization of a potential eco-friendly battery system.

β-Mn 2 V 2 O 7 , for the first time, is synthesized by a simple and cost-effective zeolitic imidazolate framework precipitation technique using water as the sole solvent and reported for excellent electrochemical Li storage properties. The anode delivers specific capacities of 868 and 751 mA h g −1 at rates of 500 and 2000 mA g −1 after 180 and 400 cycles, respectively.

A highly crystalline carbon-coated 0.66LiFePO4•0.33Li3V2(PO4)3 (LFP-LVP) nanocomposite was synthesized by a one-pot pyro-synthetic strategy using a polyol medium at low temperature. Prior to any additional heat treatment, electron microscopy confirmed the as-synthesized composite to consist of spherical particles with average diameters in the range of 30–60 nm. A crystal growth phenomenon and particle aggregation was observed upon heat treatment at 800 °C, thus resulting in an increase in the average particle size to 200–300 nm. When tested for a lithium-ion cell, the nanocomposite electrode demonstrated impressive electrochemical properties with higher operating potentials hence enhanced energy densities. Specifically, the composite cathode delivered a high reversible capacity of 156 mAh g−1 at 0.1 C and exhibited a remarkable reversible capacity of 119 mAh g−1, corresponding to an energy density of 46.88 Wh Kg−1 at 6.4 C. When cycling was performed at 6.4 C, the electrode could recover up to 85% of the capacity observed at low current density of 0.1 C, which indicates the excellent rate capability of the nanocomposite electrode. The enhanced performance was attributed to the inclusion of the high potential LVP phase constituent in the present cathode by a simple one-pot polyol-assisted pyro strategy.

A facile and scalable strategy was developed for in situ preparation of ultrafine molybdenum oxycarbide (MoOC) nanoparticles embedded in a porous N-doped carbon matrix by pyrolysis of molybdenum–imidazole frameworks in an argon atmosphere. The composite contains a high content (∼83 wt%) of electrochemical active material MoOC. When evaluated as an anode material for lithium-ion batteries, the as-obtained porous MoOC/N-doped C composite electrode exhibits high reversible lithium specific capacity (1217 mA h g −1 at 50 mA g −1 ), excellent rate capability (481 mA h g −1 at 1 A g −1 ), and good cycle stability (361 mA h g −1 at 2 A g −1 for 100 cycles). The superior lithium storage capability was ascribed to the unique structure with ultrafine and high-containing MoOC nanocrystals embedded in a porous N-doped carbon matrix. The porous N-doped carbon matrix can largely enhance the electronic conductivity of the composite, remarkably increasing rate capability. Meanwhile, the carbon matrix can effectively accommodate the volume change and reduce the aggregation of the MoOC nanoparticles during charge/discharge process, significantly enhancing cycle stability of the composite electrode. The superior electrochemical performance indicated that the attained porous MoOC/N-doped C composite could be a promising anode material for next generation high-performance lithium-ion batteries.

A monoclinic Li 3 V 2 (PO 4 )/C (LVP/C) with nanostructured morphology was synthesized via a one-step pyro-synthesis, for use as cathode material in rechargeable Li-ion batteries. Highly crystalline LVP/C nanoparticles can be obtained without additional heat treatment. The structural properties and morphology of the sample were studied using various analyses, including high resolution powder X-ray diffraction (HRPD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The LVP/C cathode exhibited initial discharge capacities of 139 and 190.3 mAh g −1 within the potential windows of 3–4.3 V and 3–4.8 V, respectively. These results indicate that the formation of nanosized particles and the presence of amorphous carbon layer influence the electrochemical properties LVP/C electrode. Specifically, the present pyro-synthesis strategy facilitates the production of LVP cathode materials with improved cyclability and rate capability under a very short reaction time.

Rechargeable zinc-ion batteries (ZIBs) with high energy densities appear promising to meet the increasing demand for safe and sustainable energy storage devices. However, electrode research on this low-cost and green system are faced with stiff challenges of identifying materials that permit divalent ion-intercalation/deintercalation. Herein, we present layered-type LiV3O8 (LVO) as a prospective intercalation cathode for zinc-ion batteries (ZIBs) with high storage capacities. The detailed phase evolution study during Zn intercalation using electrochemistry, in situ XRD, and simulation techniques reveals the large presence of a single-phase domain that proceeds via a stoichiometric ZnLiV3O8 phase to reversible solid–solution ZnyLiV3O8 (y > 1) phase. The unique behavior, which is different from the reaction with lithium, contributes to high specific capacities of 172 mAh g–1 and amounts to 75% retention of the maximum capacity achieved in 65 cycles with 100% Coulombic efficiency at a current density of 133 ...

Aqueous Zn-ion batteries (ZIBs) have emerged as promising and eco-friendly next-generation energy storage systems to substitute lithium-ion batteries. Therefore, discovering new electrode materials for ZIBs with high performance and unraveling their electrochemical reactions during Zn-ion insertion/extraction are of great interest. Here, we present, for the first time, tunnel-type β-MnO2 nanorods with exposed (101) planes, prepared via a facile microwave-assisted hydrothermal synthesis within only 10 min, for use as a high performance cathode for ZIBs. In contrast to its bulk counterpart, which showed no electrochemical reactivity, the present β-MnO2 nanorod electrode exhibited a high discharge capacity of 270 mA h g−1 at 100 mA g−1, high rate capability (123 and 86 mA h g−1 at 528 and 1056 mA g−1, respectively), and long cycling stability (75% capacity retention with 100% coulombic efficiency at 200 mA g−1) over 200 cycles. The Zn-ion storage mechanism of the cathode was also unraveled using in situ synchrotron, ex situ X-ray diffraction, ex situ X-ray photoelectron spectroscopy, and ex situ X-ray absorption spectroscopy. Our present study indicates that Zn intercalation occurred via a combination of solid solution and conversion reactions. During initial cycles, the β-MnO2 cathode was able to maintain its structure; however, after prolonged cycles, it transformed into a spinel structure. The present results challenge the common views on the β-MnO2 electrode and pave the way for the further development of ZIBs as cost-effective and environmentally friendly next-generation energy storage systems.

The present work reports on the development of layered-type Li x (Ni 1/3 Co 1/3 Mn 1/3 )O 2 ( x = 1.05 and 1.1) cathodes by a simple ambient temperature redox synthesis followed by post-heat treatments with added lithium source. The intermediate precursor (Ni 1/3 Co 1/3 Mn 1/3 O y ) was synthesized through redox reaction between KMnO 4 , CoCl 2 and NiCl 2 in aqueous KOH medium. Synchrotron XANES and ICP measurements were performed to confirm the changes in the oxidation states and successful control in stoichiometric ratio of ternary transition metal oxide (Ni 2+ 0.33 Co 3+ 0.35 Mn 4+ 0.32 O y ) during the redox reaction. Synchrotron X-ray diffraction studies of post lithiation confirmed the formation of a well-developed layer-type hexagonal phase of α-NaFeO 2 with least cation mixing, as observed from the estimated lattice parameters ( a = 2.858 A and c = 14.228 A), integrated intensity ratio ( I 003 / I 104 = 1.79), and c /3 a ratio (∼1.659) values. FE-SEM images revealed loosely agglomerated particles with average diameters of 60 nm in the intermediate product while the particle-size grows to a few hundred nanometers after lithiation at elevated temperatures. The electrochemical performances in the potential range of 3.0–4.3 V vs. Li/Li + at 14 mAg −1 indicated that reasonable specific capacities and cycle performances are registered for all the prepared cathodes. In particular, the Li 1.05 (Ni 1/3 Co 1/3 Mn 1/3 )O 2 composition demonstrated the highest capacity retention value (∼99%) after 50 cycles and better rate performances (104, 91, 76, and 67 mAhg −1 ) at high current densities (229, 457, 914, and 1429 mAg −1 respectively).

Herein, we report on a high-discharge-rate Na3V2(PO4)3-Ni2P/C (NVP-NP/C) composite cathode prepared using a polyol-based pyro synthesis for Na-ion battery applications. X-ray diffraction and electron microscopy studies established the presence of Na3V2(PO4)3 and Ni2P, respectively, in the NVP-NP/C composite. As a cathode material, the obtained NVP-NP/C composite electrode exhibits higher discharge capacities (100.8 mAhg–1 at 10.8 C and 73.9 mAhg–1 at 34 C) than the NVP/C counterpart electrode (62.7 mAhg–1 at 10.8 C and 4.7 mAhg–1 at 34 C), and the composite electrode retained 95.3% of the initial capacity even after 1500 cycles at 16 C. The enhanced performance could be attributed to the synergetic effect of the Ni2P phase and nanoscale NVP particles, which ultimately results in noticeably enhancing the electrical conductivity of the composite. The present study thus demonstrates that the Na3V2(PO4)3-Ni2P/C nanocomposite is a prospective candidate for NIB with a high power/energy density.

CV profile

Carbon-coated sodium iron pyrophosphate (Na₂FeP₂O 7 ) was prepared by a simple and low-cost pyro-synthesis route for further use as the cathode for Na-ion batteries. The X-ray diffraction (XRD) pattern of the sample annealed at 650℃ confirmed the pure triclinic phase of Na₂FeP₂O 7 . Electron microscopy studies revealed a cross linked plate shape morphology of the Na₂FeP₂O 7 sample. When tested for application in Na-ion battery, the Na₂FeP₂O 7 cathode showed two redox pairs in the potential window of 2.0-4.0 V. The cathode registered initial discharge and charge capacities of 80.85 and 90 mAh/g, respectively, with good cycling performance.

Mesoporous anatase TiO2 (MAT) with a disk-like morphology was prepared by direct pyrolysis of a titanium metal-organic framework [MIL-125(Ti)] in air. When employed as an anode material for lithium–ion batteries, the as-prepared MAT electrode exhibited superior lithium storage properties with negligible capacity loss at high discharge/charge rates. At 10C rate, the prepared electrode still delivered a high reversible capacity of 127 mA h g−1 after 1100 cycles. The superior battery performance could be attributed to the unique mesoporous structure that promoted Li+ diffusion and shortened the Li+ and e− transport length.

A Li-ion battery cathode with target stoichiometry LiTi 0.08 Fe 0.92 PO 4 was prepared by doping a high amount of Ti 4+ into the olivine structure using solid-state reaction at 700 °C. Synchrotron X-ray diffraction studies confirmed the presence of a major olivine phase and NASICON-type ion-conducting Li 3 Fe 2 (PO) 4 and Li 2 TiFe(PO 4 ) 3 impurities. Further, the calculated lattice parameter values appear to confirm Ti-doping in LiFePO 4 . Electron microscopy and particle distribution studies not only revealed a slightly increased average particle-size and particle fragmentation but also confirmed a fair distribution of Ti 4+ ions in the prepared sample. The LiTi 0.08 Fe 0.92 PO 4 cathode delivered high specific capacities and good capacity retentions (≤2% capacity loss after 50 cycles) for lithium battery applications. Besides, the cathode delivered impressive rate capabilities as specific capacities of 160 and 110 mA h g −1 at 0.2 and 11.4 C, respectively, were retained. Although the average particle-size was slightly higher, the presence of ion-conducting NASICON-type species appear to contribute to the enhanced electrical conductivity and hence to the cathode performance of LiTi 0.08 Fe 0.92 PO 4 .

Tunnel-type α-MnO2 with a nanorod morphology was prepared via a simple solvent-free synthesis method for use in aqueous zinc-ion battery (ZIB). This synthesis method produced α-MnO2 with a high BET surface area of 153 m2 g−1. α-MnO2 electrode demonstrated remarkable zinc storage properties (first and second discharge capacities of 323 and 270 mAh g−1 at 16 mA g−1) with good capacity retentions and rate capability. After charging within only 60 s, the α-MnO2 nanorod cathode delivered a considerable discharge capacity of 115 mAh g−1 when cycled at current density of 16 mA g−1.

The present study reports on the direct synthesis of LiFePO 4 nanoparticles and graphene nanosheets to form a composite cathode (LFP/GNs) in a one-step microwave-assisted polyol reaction. The polyol reaction induced by microwave irradiation for a few minutes produces nanocrystalline LFP and graphene nanosheets simultaneously from lithium, iron and phosphorus and carbon (5 wt% of graphite oxide) sources, respectively, used as starting precursors. Powder X-ray diffraction (XRD), electron microscopy, and atomic force microscopy (AFM) studies on microwave-reacted sample obtained using just graphite oxide confirms the formation of graphene nanosheets separately. Whereas, electron microscopy studies on the LFP/GNs composite reveals that olivine nanoparticles of average sizes ranging between 5 and 20 nm are well-dispersed on the graphene nanosheets. Electrochemical measurements reveal that the LiFePO 4 /GNs nanocomposite cathodes registered enhanced discharge capacities (79 and 108 mAh g −1 for the as-prepared and annealed composite cathodes, respectively) at 32 C rates with good capacity retention capabilities. The AC impedance measurements confirm that the enhanced cathode properties of the LFP/GNs nanocomposite are ascribed to the improved electronic conductivity of the graphene nanosheets and the nano-sized particles. The slightly better electrochemical properties of the annealed LFP/GNs are attributed to its higher crystallinity.

A nanostructured Mn3 O4 /C electrode was prepared by a one-step polyol-assisted pyro-synthesis without any post-heat treatments. The as-prepared Mn3 O4 /C revealed nanostructured morphology comprised of secondary aggregates formed from carbon-coated primary particles of average diameters ranging between 20 and 40 nm, as evidenced from the electron microscopy studies. The N2 adsorption studies reveal a hierarchical porous feature in the nanostructured electrode. The nanostructured morphology appears to be related to the present rapid combustion strategy. The nanostructured porous Mn3 O4 /C electrode demonstrated impressive electrode properties with reversible capacities of 666 mAh g-1 at a current density of 33 mA g-1 , good capacity retentions (1141 mAh g-1 with 100 % Coulombic efficiencies at the 100th cycle), and rate capabilities (307 and 202 mAh g-1 at 528 and 1056 mA g-1 , respectively) when tested as an anode for lithium-ion battery applications.

A sponge network-shaped Mn3O4 material is synthesized by a one-pot metal organic framework-combustion (MOF-C) technique for Li-ion battery anodes with improved performance. The as-synthesized ordered sponge network morphology is characterized by various techniques, such as powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and N2 adsorption–desorption measurements. The one-pot synthesized Mn3O4 material shows a uniform amorphous graphitic carbon coating with few-nanometer thickness on the surface. This anode shows an initial discharge capacity of 1186 mA h g−1 and a reversible capacity of 768 mA h g−1 is maintained at an applied current density of 200 mA g−1 after 100 cycles. Sustained reversible capacities of 651 and 592 mA h g−1 are measured for the other two different current densities of 500 and 700 mA g−1, respectively, after 120 cycles, demonstrating the high stability of the anode. This unique morphology appears to contribute to the significantly high rate performance, as observed from the retained reversible capacity of 155 mA h g−1 at a very high current density of 10 000 mA g−1, which is maintained for the next two subsequent sequences with a notable recovered capacity of 700 mA h g−1 for an intermediate current density of 400 mA g−1 after 175 cycles.

A porous TiN/N-doped carbon composite electrode prepared via a metal–organic framework strategy exhibited high reversible lithium specific capacity (561 mA h g−1 at 50 mA g−1), excellent rate capability (281 mA h g−1 at 2 A g−1), and good cycle stability (310 mA h g−1 at 2 A g−1 for 400 cycles).

The present study reports on a highly rate capable NASICON-structured NaTi2(PO4)3/reduced graphene oxide (NTP/rGO) composite electrode synthesized by polyol-assisted pyro synthesis for Na-ion batteries (NIBs). X-ray diffraction (XRD) studies confirmed the presence of a rhombohedral NaTi2(PO4)3 phase in the composite while Raman spectroscopy studies helped to identify the existence of rGO in the composite. Electron microscopy studies established that NaTi2(PO4)3 nanoparticles of average sizes ranging between 20 and 30 nm were uniformly distributed and embedded in the GO sheets. When tested for sodium storage properties, the obtained NTP/rGO composite electrode registered high rate capacities (95 mA h g−1 at 9.2C and 78 mA h g−1 at 36.8C) when compared to that of the NTP/C electrode (∼1 mA h g−1 at 9.2 and 36.8C). Further, the NTP/rGO composites delivered a reversible capability of 62 mA h g−1 at 20C after 1000 cycles. The enhanced performance of the composite electrode can be attributed to the nano-sized NaTi2(PO4)3 particles with shorter diffusion path lengths. These particles embedded in the rGO sheets with enhanced electrolyte/electrode contact areas ultimately lead to an improvement in the electrical conductivity at high current densities. Ex situ XANES studies confirmed reversible Na-ion intercalation/de-intercalation into/from NTP/rGO. The study thus demonstrates that the NaTi2(PO4)3/rGO nanocomposite electrode is a promising candidate for the development of high power/energy density anodes for NIBs.

A porous, cobalt vanadate (Co3V2O8) microsphere electrode with a cubic crystalline phase is synthesized using a novel one-pot synthesis with a metal–organic framework (MOF) based combustion strategy for use in high energy lithium ion batteries. The simple synthesis presented in this paper facilitates the evolution of a porous secondary microsphere morphology from primary aggregates of 20–50 nm particle sizes. This unique morphology appears to be derived from the Co-V–MOF intermediate network formed in situ during synthesis. The Co3V2O8 microsphere electrode displayed excellent cyclabilities at high current densities. In particular, a specific discharge capacity of 940 mA h g−1 after 100 cycles at 1 A g−1 and the highest known capacity of 650 mA h g−1 after 400 cycles at 5 A g−1 are sustained by the prepared microsphere electrode. The enhanced rate performance is mainly attributed to the unique morphology in addition to the nanoscale dimension of the electrode. Ex situ investigations confirmed that the high structural stability of the electrode facilitates minimum volume change during the electrochemical reaction under high discharge/charge rates. Furthermore, the present one-pot synthetic protocol appears to be promising for the production of phase pure, mixed metal oxide nanostructured electrodes for a wide range of applications including energy storage.

Energy storage devices remain critical to meet the increasing demands of the modern society. Rechargeable lithium ion batteries (LIBs) are a crucial finding in this century to compensate the energy demand in the present day. As device performance is intimately correlated with the material properties, production of functional energy storage nanomaterials endowed with exceptional physico-chemical properties in view of their particle-size confinement has become critically significant. Low- or moderate-temperature synthetic strategies that are versatile, easily scalable, and efficiently produce size-tuned and efficient materials are essential. In the recent past, combustion-based synthetic process has emerged as one of the promising strategies for developing customized energy storage nanomaterials due to rapid synthesis and ease of preparations in a large scale, etc. In the present review, the advancements in the design and chemistry of these strategies in developing a wide range of high voltage cathode materials for LIBs have been discussed. Among the various combustion techniques, this study will focus mainly on solution combustion, sol-gel based combustion and polyol-based pyro-synthesis. The versatility of these processes to provide tailored particle morphologies and particle sizes at the nanoscale and their effects on the material performance in various applications, particularly in energy storage, is also discussed.

Pyrite (FeS2) is a promising electrode material for lithium ion batteries (LIBs) because of its high natural availability, low toxicity, cost-effectiveness, high theoretical capacity (894 mA h g-1) and high theoretical specific energy density (1270 W h kg-1, 4e-/FeS2). Nevertheless, the use of FeS2 in electrochemical capacitors was restricted due to fast capacity fading as a result of polysulfide (S/Sn2-) formation during the initial electrochemical cycling. In order to avoid the formation of polysulfides, we employed the strategy of utilizing an ether based electrolyte (1.0 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/diglyme (DGM)). Herein, we introduce FeS2/C as the Faradaic electrode for a non-aqueous hybrid electrochemical capacitor (NHEC) in combination with activated carbon (AC) as a non-Faradaic electrode, and 1.0 M LiTFSI/DGM as a non-aqueous electrolyte. Specifically, FeS2/C nanoparticles have been prepared via the sulfidation of a room temperature synthesized Fe-based MOF (metal organic framework) precursor. The fabricated FeS2/C∥AC NHEC, operating within the chosen voltage window of 0-3.2 V, delivered energy densities in the range of 63-9 W h kg-1 at power densities of 152-3240 W kg-1. Remarkable cycling stability with stable energy density retention for 2500 cycles at high power densities (729, 1186 and 3240 W kg-1) was observed.

This study reports the use of a layered-type birnessite δ-MnO2 nano-flake cathode for eco-friendly zinc-ion battery (ZIB) applications. The present δ-MnO2 was prepared via the simple low temperature thermal decomposition of KMnO4. The X-ray diffraction (XRD) pattern of the samples was well indexed to the δ-MnO2 phase. Field emission SEM and TEM images of the δ-MnO2 revealed flake-like morphologies with an average diameter of 200 nm. The electrochemical properties, investigated by cyclic voltammetry and constant current charge-discharge measurements, revealed that the nano-flake cathode exhibited first discharge capacity of 122 mAh g−1 under a high current density of 83 mA g−1 versus zinc. The discharge capacity thereafter increased until it reached 252 mAh g−1 in the fourth cycle. On the hundredth cycle, the electrode registered a discharge capacity of 112 mAh g−1. Coulombic efficiencies of nearly 100% were maintained on prolonged cycling and thereby indicate the long cycle stability of the δ-MnO2. Besides, the realization of specific capacities of 92 and 30 mAh/g at high current densities of 666 and 1333 mA g−1, respectively, clearly demonstrates the decent rate capabilities of δ-MnO2 nano-flake cathode. These results may facilitate the utilization of layered-type birnessite δ-MnO2 in ZIB applications. Keywords: Layered structure, Manganese dioxide, Aqueous zinc-ion batteries, Energy storage

Nanocrystalline LiFePO4/C has been synthesized under a very short period of time (90 sec) using a polyol-assisted microwave heating synthesis technique. The X-ray diffraction (XRD) data indicates that the rapidly synthesized materials correspond to phase pure olivine. Post-annealing of the as-prepared sample at 600 °C in argon atmosphere yields highly crystalline LiFePO4/C. The morphology of the samples studied using scanning electron microscopy (SEM) reveals the presence of secondary particles formed from aggregation of primary particles in the range of 30-50 nm. Transmission electron microscopy (TEM) images reveal a thin carbon layer coating on the surface of the primary particle. The charge/discharge studies indicate that the as-prepared and annealed LiFePO4/C samples delivered initial discharge capacities of 126 and 160 mA h g-1, respectively, with good capacity retentions at 0.05 mA cm-2 current densities. The post-annealing process indeed improves the crystallinity of the LiFePO4 nanocrystals, which enhances the electrode performance of LiFePO4/C.

In the present study, a nanorod-type α-MnO2 cathode is prepared by a facile hydrothermal method for rechargeable aqueous zinc-ion battery (ZIB) applications. Electron microscopy studies reveal rod shaped particles with approximately 20 nm of width and 200 nm of length. When tested for aqueous ZIBs, the α-MnO2 nanorod cathode exhibits an initial discharge capacity of 233 mA h/g at a current density of 83 mA/g with nearly 100% Coulombic efficiencies under prolonged cycling. Besides, the prepared cathode demonstrates decent rate capabilities at higher current densities (43.33 and 31.48 mA h/g at 1333 and 1666 mA/g, respectively). Ex-situ synchrotron XAS investigations clearly establish the reversibility of electrochemical Zn-insertion into the α-MnO2 nanorod cathode. The analyses also reveal that the host α-MnO2 structure demonstrates considerable structural stability during Zn-insertion/extraction. Further, a combination of ex-situ synchrotron XRD studies, visualization and pattern-fitting software programs not only confirm electrochemical Zn-insertion into the host α-MnO2 structure but also suggest that the unit cell volume of the [2×2] tunnels in the α-MnO2 host expands by approximately 3.12% during Zn-insertion. The present study thus paves the way for further development of eco-friendly ZIB as an ideal energy storage system due to its excellent safety and reliability.

Carbon-coated nano-sized LiMnPO4/C particles are synthesized by polyol method using low-cost glucose as the carbon source. The X-ray diffraction patterns of the synthesized samples are well indexed to the orthorhombic olivine-LiMnPO4 structure. The morphology studies using FE-SEM and HR-TEM images clearly illustrate thin layered carbon coatings on LiMnPO4 particles of sizes ranging between 50~100 nm. The LiMnPO4/C particles delivers an initial discharge capacity of 151 mA h g-1 at a current density of 1.6 mA g-1 in the voltage range of 2.5-4.3 V with impressive capacity retentions.