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Summary Manganese dioxide is abundant, low-cost, and has the potential to be utilized as a semi-solid electrode for long-duration energy storage technologies such as flow batteries. However, the more stringent pumping requirements of semi-solid electrodes compared to the electrolytes of all-liquid flow battery might limit their techno-economic feasibility. Here, we developed a rechargeable MnO2 semi-solid electrode, performed electrochemical and rheological characterizations, and bottom-up techno-economic analysis of the Zn-MnO2 semi-solid flow battery (SSFB) system. The high power needed for pumping (ranging from 8% to 50% of the power output) leads to a system with high cost of power. Using our experimental results, we suggest strategies to minimize the pumping power requirement for Zn-MnO2 SSFB. As a result of the low cost of its chemical constituents, we show that a Zn-MnO2 SSFB can be cheaper than Li-ion and vanadium redox flow battery solutions for long discharge durations (e.g., >24 h per cycle).

Ni-rich positive electrodes for Li-ion batteries can provide enhanced initial discharge capacity yet suffer from significant capacity degradation upon cycling. Fluorination of Ni-rich NMC811 positive electrodes results in a capacity retention of more than 90% after 100 cycles upon cycling to 4.4 VLi. The increased cycling stability of F-modified NMC811 can be attributed to the modification of the oxide electronic structures, where density functional theory calculations shows that incorporating fluorine into the oxide lattice decrease the driving force of carbonate dissociation on the oxide surface. In situ infrared (IR) spectroscopy and ex situ X-ray photoelectron spectroscopy (XPS) further supports this argument by showing less carbonate oxidation for F-modified LiNi0.8Mn0.1Co0.1O2 (NMC811) than as-received NMC811 upon charging. The reduced carbonate oxidation is coupled with minimal salt decomposition on the electrode surface, as revealed by XPS. Further comparing in situ IR and XPS with that of the heat-treated NMC811 and Li2CO3 allows for decoupling the solvent decomposition products, where oxides are responsible for the vinylene carbonate formation with two hydrogens removed whereas surface metal carbonates promote dehydrogenated ethylene carbonate with just one hydrogen removed. This work points towards the importance of the anion engineering to increase the cycling stability of Ni-rich NMC positive electrodes.

A stable Zn metal electrode can develop rechargeable zinc metal batteries (RZMBs) which have the high theoretical capacity (820 mAh g−1), low redox potential, and intrinsic safety. However, the corrosion of Zn metal in aqueous electrolytes and Zn dendrite formation during the plating process lead to poor cycling and thus hinder the development of RZMBs. Here, we employed ionic liquid-based gel polymer (poly(vinylidene fluoride)-co-hexafluoropropylene, PVDF-HFP) and acetylene black (AB) to achieve a stable and flexible three-dimensional (3D) Zn/AB/PVDF-HFP film electrode with ionic and electronic conductive networks and high surface area, showing 26 times higher plating/stripping current than planar Zn plate. By developing a continuous structure between the ionic liquid-based gel polymer membrane and the flexible 3D Zn/AB/PVDF-HFP electrode, the low resistance, high rate capability and long cycle life (> 800 h) was obtained. Our work shows a flexible Zn film electrode and ionic liquid-based gel polymer electrolyte, could pave the path for rechargeable and high-cycle life thin-film RZMBs.

Summary Redox flow batteries have great system scalability and operational flexibility but relatively low energy density because of the limited solubility of redox molecules in the electrolytes. By storing energy in solid materials while producing power from redox fluids, the redox-targeting concept provides an effective way to significantly increase the energy density of flow batteries. Redox targeting generally involves multiple redox reactions between the molecules and materials, which inevitably brings about additional complexity in electrolyte composition and low voltage efficiency. The Nernstian-potential-driven redox-targeting reaction reported here considerably eliminates the voltage loss of a LiFePO 4 -based redox flow lithium battery. Driven by the Nernstian potential difference, the redox molecule, a ferrocene-grafted ionic liquid with standard potential identical to that of LiFePO 4 , reacts with the solid material both anodically and cathodically and exhibits near-unity material utilization, a voltage efficiency of 95%, and an energy density of 330 Wh/L (up to 942 Wh/L).

We demonstrate a redox flow lithium oxygen battery (RFLOB) using a pair of soluble redox catalysts, 2,5-di-tert-butyl-p-benzoquinone (DTBBQ) and tris{4-[2-(2-methoxyethoxy)ethoxy]phenyl}amine (TMPPA). The catalytic effects of DTBBQ on the oxygen reduction reaction (ORR) and TMPPA on the oxygen evolution reaction (OER) were investigated and unambiguously substantiated with various electrochemical, morphological, and spectroscopic characterization methods. It is observed that, upon discharging, oxygen is rapidly reduced by DTBBQ•– and Li2O2 is formed in the presence of Li+; upon charging, Li2O2 is oxidized by TMPPA•+, releasing oxygen. Such redox-mediated ORR and OER reactions enable the formation and oxidation of Li2O2 in a separate gas diffusion tank (GDT) other than on the cathode of the cell, thus obviating surface passivation and pore clogging of the electrode. The cell presents a high energy density with DTBBQ as the ORR redox catalyst and good rechargeability when paired with TMPPA as the OER redox c...

A TCO (transparent conductive oxide)-free redox-flow electrochromic window (RFEW) with considerably improved performance is demonstrated. The new RFEW employs Prussian blue (PB)/Prussian white (PW) as the electrochromic (EC) material, in which the decoloration/coloration is achieved by the redox targeting reactions of anthraquinone-2,6-disulfonate (AQDS) and FeCl3 with PB/PW, respectively. These redox molecules are electrochemically oxidized/reduced in an external stack cell and circulated through the window cavity. Hence, the costly TCO glass, indispensable in conventional EC windows, becomes redundant in RFEWs. Owing to the fast charge transfer kinetics of AQDS and Fe3+, the RFEW design investigated in this study presents substantially reduced response time. For a window with a size exceeding 100 cm2, coloration/decoloration switching with a change in absorbance by more than 80% is achieved within approximately 2 min. The static and dynamic optical characteristics of the window pane and the electrochemical behavior of the stack cell were examined in detail to understand the operation of the RFEW.

In this work, SnO2 quantum dots and graphene (G) nanocomposites (SnO2/G) were synthesized via a facile one-step hydrothermal method for the application of anode material in lithium ion batteries (LIBs). SnO2 quantum dots with a diameter ranging from 5 to 10 nm were uniformly anchored on graphene nanosheets. SnO2/G nanocomposites can deliver high specific capacities of 860 mAh g−1 after 50 cycles at a current density of 200 mA g−1, and 683 mAh g−1 at a current density of 1600 mA g−1. Compared to the pure SnO2, the excellent improved electrochemical performance of SnO2/G nanocomposites for lithium ion storage can be attributed to the stable structure and the improved electron conduction channel provided by graphene with functional groups (FGs), such as C-OH, C=O and C-OOH. In order to further improve the SnO2/G nancomposites electrochemical performance, carbon thin layers were coated by the reduction of C2H2 gas via CVD technology (SnO2/G-C). However, SnO2/G-C showed an inferior performance compared to that of the SnO2/G without carbon coating. Through X-ray photoelectron spectroscopy (XPS) analysis, it was found that function groups play a critical role on the stability of SnO2/G nanocomposites. Such observation may thus instruct the design and implementation of graphene/metal oxides nanocomposites for high-performance LIBs anode materials.

In this work, we succeeded in synthesis of spinel LiMn2O4 via a facile self-template method. The product displays a micro-/nanohybrid structure. Nanoparticles/plates act as the primary nanoblocks to build the secondary microarchitecture. There is the open space between the nanoblocks and the void space between the secondary structures. Electrochemical tests demonstrate that the as-synthesized sample exhibits superior rate capability and high-rate cycleability when contrasted with its solid counterpart. The initial discharge capacity is 126 mAh/g at 0.1 C, 110 mAh/g at 10 C, and 84 mAh/g at 20 C. The discharge capacity retention of about 80% is obtained after 800 cycles at 10 C. The high capacity and excellent cycling life of the material shows its potential for application as high-power batteries. The improved rate capability and cycleability can be attributed to its secondary structure that can facilitate fast Li-insertion/extraction and buffer the volume expansion/contraction upon cycling.

A Co(OH)2/graphene sheet-on-sheet hybrid has been fabricated by in situ one-step hydrothermal growth for electrochemical pseudocapacitors application. The hybrid delivers a specific capacitance of 436 F g−1 at a current density of 50 A g−1. Besides, it can keep a specific capacitance of 651 F g−1 after 10,000 cycles at 10 A g−1. The excellent performance can be ascribed to the high-quality graphene matrix, regular morphology and high crystallinity of Co(OH)2, and unique sheet-on-sheet structure of the hybrid, endowing enhanced transportation of electrons and Faradic redox reactions. The results demonstrate that the Co(OH)2/graphene hybrid with a sheet-on-sheet structure is promising for high-performance energy storage applications.

An all redox flow lithium battery with strikingly high energy density is successfully demonstrated., Redox flow batteries (RFBs) are considered one of the most promising large-scale energy storage technologies. However, conventional RFBs suffer from low energy density due to the low solubility of the active materials in electrolyte. On the basis of the redox targeting reactions of battery materials, the redox flow lithium battery (RFLB) demonstrated in this report presents a disruptive approach to drastically enhancing the energy density of flow batteries. With LiFePO4 and TiO2 as the cathodic and anodic Li storage materials, respectively, the tank energy density of RFLB could reach ~500 watt-hours per liter (50% porosity), which is 10 times higher than that of a vanadium redox flow battery. The cell exhibits good electrochemical performance under a prolonged cycling test. Our prototype RFLB full cell paves the way toward the development of a new generation of flow batteries for large-scale energy storage.

The catalytic role of germanium (Ge) was investigated to improve the electrochemical performance of tin dioxide grown on graphene (SnO(2)/G) nanocomposites as an anode material of lithium ion batteries (LIBs). Germanium dioxide (GeO(20) and SnO(2) nanoparticles (

In this work, we report the synthesis of MoO2 nanoparticles grown on three dimensional graphene (3DG) via the reduction of α-MoO3 nanobelts through a facile chemical vapor deposition (CVD) approach under argon protection gas environment. In this synthesis approach, the presence of hydrophobic 3DG promoted the Volmer-Weber growth of MoO2 nanoparticles (30-60 nm). The as-prepared MoO2-3DG nanocomposite was directly used as a binder-free anode electrode for lithium ion batteries (LIBs) without additives and exhibited excellent electrochemical performance. It delivered high reversible capacities of 975.4 mA h g(-1) and 537.3 mA h g(-1) at the current densities of 50 and 1000 mA g(-1), respectively. Moreover, the electrode also showed an increased capacity from 763.7 mA h g(-1) to 986.9 mA h g(-1) after 150 discharge and charge cycles at a current density of 200 mA g(-1). The enhanced electrochemical performance of MoO2-3DG nanocomposite electrode may be attributed to the synergistic effects of MoO2 nanoparticles and 3DG layers. This facile CVD synthesis process presents a feasible route for large-scale production of high performance, environmentally friendly electrode. In addition, this process also has the potential of being utilized in other materials for energy storage devices application.