High-rate Electrochemical Energy Storage Research Articles

Core–shell ultramicroporous@microporous carbon nanospheres as advanced supercapacitor electrodes

Core–shell ultramicroporous@microporous carbon nanospheres were developed as advanced supercapacitor electrodes for high rate electrochemical energy storage.

Non-covalently functionalizing a graphene framework by anthraquinone for high-rate electrochemical energy storage

Anthraquinone (AQ) with electrochemically reversible redox couples is selected to functionalize graphene framework (GF) through non-covalent modification and the composite achieves high specific capacitance, good rate capability and long cycle life.

Pseudocapacitive oxide materials for high-rate electrochemical energy storage

Electrochemical energy storage technology is based on devices capable of exhibiting high energy density (batteries) or high power density (electrochemical capacitors). There is a growing need, for current and near-future applications, where both high energy and high power densities are required in the same material. Pseudocapacitance, a faradaic process involving surface or near surface redox reactions, offers a means of achieving high energy density at high charge–discharge rates. Here, we focus on the pseudocapacitive properties of transition metal oxides. First, we introduce pseudocapacitance and describe its electrochemical features. Then, we review the most relevant pseudocapacitive materials in aqueous and non-aqueous electrolytes. The major challenges for pseudocapacitive materials along with a future outlook are detailed at the end.

High-rate electrochemical energy storage through Li+ intercalation pseudocapacitance

Pseudocapacitance is commonly associated with surface or near-surface reversible redox reactions, as observed with RuO2·xH2O in an acidic electrolyte. However, we recently demonstrated that a pseudocapacitive mechanism occurs when lithium ions are inserted into mesoporous and nanocrystal films of orthorhombic Nb2O5 (T-Nb2O5; refs 1,2). Here, we quantify the kinetics of charge storage in T-Nb2O5: currents that vary inversely with time, charge-storage capacity that is mostly independent of rate, and redox peaks that exhibit small voltage offsets even at high rates. We also define the structural characteristics necessary for this process, termed intercalation pseudocapacitance, which are a crystalline network that offers two-dimensional transport pathways and little structural change on intercalation. The principal benefit realized from intercalation pseudocapacitance is that high levels of charge storage are achieved within short periods of time because there are no limitations from solid-state diffusion. Thick electrodes (up to 40 μm thick) prepared with T-Nb2O5 offer the promise of exploiting intercalation pseudocapacitance to obtain high-rate charge-storage devices.

Cathodic ALD V2O5 thin films for high-rate electrochemical energy storage

Atomic layer deposition (ALD) is attractive for next-generation electrical energy storage in forming passivation layers and more recently active storage material. Here we report a detailed study of ALD V2O5 as a high capacity cathode material, using vanadium tri-isopropoxide (VTOP) precursor with both O3 and H2O as oxidant. The O3-based process produces polycrystalline films with generally higher storage capacity than the amorphous films resulting from the H2O-based process over extended cycling (100 cycles). High capacities are achieved in V2O5 because of the ability to incorporate up to three Li per V2O5 formula unit. To address the central need for both high power and high energy, we identified the crucial tradeoff between higher gravimetric capacity with thinner films and higher material mass with thicker films. For the thickness regime 10–120 nm, we chose areal energy and power density as a useful metric for this tradeoff and found that it is optimized at 60 nm for the O3-VTOP ALD V2O5 films. We believe the control of material quality, thickness, and conformality achievable with ALD processes is valuable as new nanoarchitectures for electrochemical energy storage come into sight.

Multifunctional Metal Oxide-Carbon Nanoarchitectures as Designer Electrode Platforms for High-Rate Electrochemical Energy Storage Devices

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