The drastic need for development
of power and electronic equipment
has long been calling for energy storage materials that possess favorable
energy and power densities simultaneously, yet neither capacitive
nor battery-type materials can meet the aforementioned demand. By
contrast, pseudocapacitive materials store ions through redox reactions
with charge/discharge rates comparable to those of capacitors, holding
the promise of serving as electrode materials in advanced electrochemical
energy storage (EES) devices. Therefore, it is of vital importance
to enhance pseudocapacitive responses of energy storage materials
to obtain excellent energy and power densities at the same time. In
this Review, we first present basic concepts and characteristics about
pseudocapacitive behaviors for better guidance on material design
researches. Second, we discuss several important and effective material
design measures for boosting pseudocapacitive responses of materials
to improve rate capabilities, which mainly include downsizing, heterostructure
engineering, adding atom and vacancy dopants, expanding interlayer
distance, exposing active facets, and designing nanosheets. Finally,
we outline possible developing trends in the rational design of pseudocapacitive
materials and EES devices toward high-performance energy storage.
Aqueous zinc ion batteries are promising secondary batteries
for
next-generation electrochemical energy storage. In this work, we report
a hybrid electrolyte system with 3 M Zn(OTf)2 as zinc salt
and 1 M urea + 0.3 M LiOAc as hybrid solute additives for highly reversible
aqueous zinc ion batteries. In this electrolyte system, partial coordinated
water molecules of Zn2+ are replaced, and the original
hydrogen bond network of the bulk electrolyte also suffers from interruption.
Moreover, the introduction of lithium acetate solves the aggravated
self-corrosion caused by urea on the one hand and inhibits the growth
of dendrites through the electrostatic shielding effect on the other.
Benefiting from this multifunctional synergistic effect, dendrite-free
Zn plating/stripping for 600 h at 4.8 mA cm–2 (20%
depth of discharge) and highly reversible plating/stripping at ∼99.7%
Coulombic efficiency with a high cumulative plating capacity of 1600
mAh is achieved.
Sodium ion batteries (SIBs) are expected to take the
place of lithium
ion batteries (LIBs) as next-generation electrochemical energy storage
devices due to the cost advantages they offer. However, due to the
larger ion radius, the reaction kinetics of Na+ in anode
materials is sluggish. SnS2 is an attractive anode material
for SIBs due to its large interlayer spacing and alloying reactions
with high capacity. Calcination is usually employed to improve the
crystallinity of SnS2, which could affect the Na+ reaction kinetics, especially the pseudocapacitive storage.
However, excessively high temperature could damage the well-designed
nanostructure of SnS2. In this work, we uniformly grow
SnS2 nanosheets on a Zn-, N-, and S-doped carbon skeleton
(SnS2@ZnNS). To explore the optimal calcination
temperature, SnS2@ZnNS is calcined at three typical
temperatures (300, 350, and 400 °C), and the electrochemical
performance and Na+ storage kinetics are investigated specifically.
The results show that the sample calcined at 350 °C exhibited
the best rate capacity and cycle performance, and the reaction kinetics
analysis shows that the same sample exhibited a stronger pseudocapacitive
response than the other two samples. This improved Na+ storage
capability can be attributed to the enhanced crystallinity and the
intact nanostructure.
Compared with lithium‐ion batteries (LIBs), aqueous zinc batteries (AZIBs) have received extensive attention due to their safety and cost advantages in recent years. The cathode determines the electrochemical performance of AZIBs to a large extent. Vanadium‐based materials exhibit excellent capacity when used as AZIB cathodes. However, unexpected structural stress is inevitably induced during cycling and high current densities, which can gradually lead to structural deterioration and capacity decay. In fact, the stress/strain distribution in nanomaterials is crucial for electrochemical performance. In this work, the optimized stress distribution of the hierarchical hollow structure is verified by the finite element simulation of COMSOL software firstly. Guided by this model, a simple solvothermal method to synthesize hierarchical hollow vanadium oxide nanospheres (VO‐NSs), consisting of ≈10 nm ultrathin nanosheets and ≈500 nm hollow inner cavities, is employed. And a highly disordered structure is introduced to the VO‐NSs by in situ electrochemical oxidation, which can also weaken the structural stress during Zn2+ insertion and extraction. Benefiting from this unique structure, VO‐NSs exhibit high‐rate and stable Zn2+ storage capability. The strategy of engineering‐driven material design provides new insights into the development of AZIB cathodes.
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