Search

Li–O2 batteries can provide greater gravimetric energy than Li-ion batteries but suffer from poor efficiency and cycle life due to the instability of aprotic electrolytes. In this study, we show that the apparent four-electron oxygen reduction to form Li2O in Li–O2 batteries with molten nitrate is facilitated by the electrochemical reduction of nitrate to nitrite, and subsequent chemical oxidation of nitrite to nitrate by molecular oxygen, instead of a four-electron oxygen reduction aided by disproportionation of Li2O2 generated from two-electron reduction of molecular oxygen. By examining a series of transition metal catalysts using experiments and computation, optimizing the surface binding of nitrate to enhance the kinetics of the electrochemical reduction of nitrate to nitrite, as well as increasing the kinetics of nitrite oxidation by O2 was shown to increase the discharge voltage and render the observed high-rate capability for NiO-based surfaces in Li–O2 batteries.

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).

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).

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.

Miniaturized energy storage devices have attracted considerable research attention due to their promising applications such as power-on-chip units in various smart electronic devices. In this work, a printable micro-supercapacitor (MSC) device was designed and fabricated wherein a novel three dimensional (3D) nanocomposite consisting of cobalt oxide (CoO) nanoflowers woven with carbon nanotubes (CNTs) networks were used as the active material. The CoO/CNT nanocomposites were synthesized via a high-throughput hydrothermal method. High capacitance of 17.4 F/cm 3 and energy density of ~3.48 mWh/cm 3 were achieved for the CoO/CNT MSC at a current density of 0.25 A/cm 3 . The high volumetric energy density is attributed to the widened operation voltage window ranging from 0 to 1.2 V. Moreover, the printed CoO/CNT MSCs also showed remarkable cycling stability with ~85% energy density retention after 1700 cycles and high mechanical flexibility which can function well even after bending up to 180°. As a result, the printed CoO/CNT MSC is a possible contender in future energy storage devices for low-cost on-chip power applications.