Nanostructure and Advanced Energy Storage: Elaborate Material Designs Lead to High-Rate Pseudocapacitive Ion Storage

Abstract

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.

Understanding Rapid Intercalation Materials One Parameter at a Time

“…Many definitions include faradaic reactions, reversibility (e.g., mirror like CV profiles), and a lack of diffusion limitations, that is, surface-limited kinetics. [52,[54][55][56][57]61] We support this generally agreed upon and broadest definition. Costentin has argued that "pseudocapacitance" is an incorrect notion where such reported box-like (redox pseudocapacitive) CV curves should be interpreted as EDLC and peak-like (intercalation pseudocapacitive) curves should be interpreted as normal battery-like intercalation undergoing slow charge transfer or ohmic drop.…”

“…The cyclic voltammetry (CV) characteristics of these materials fall broadly into two camps, [52,53] 1) surface redox pseudocapacitance which has dominant box-like character (RuO 2 , MnO 2 ) (Figure 2a) and 2) intercalation pseudocapacitance which has dominant peak-like character (TiO 2 (B), 2b). There is debate about the fundamental nature of these responses, [52,[54][55][56][57][58][59][60][61] including rigorous theoretical arguments that the first camp is attributed principally to EDLC [60] and a separate suggestion of a continuum between Faradaic and EDLC. [62] If indeed charge storage were dominated by EDLC, then the term pseudocapacitance [60] would be inaccurate.…”

“…Others have reported similar non-pseudocapacitive responses for T-Nb 2 O 5 such as large capacity reductions at modest charge rates [71] or a plateau-like state of charge responses. [72] The only other material described as being an intrinsic intercalation pseudocapacitor is bronze-TiO 2 [52,61] which has principally been investigated as nanoscale materials with conductive additives to make up for its low electronic conductivity. [73] For example, bronze-TiO 2 can exhibit significant capacity loss at rates of just 1C [74] which is not consistent with an intrinsic absence of diffusion limitations.…”

Balanced Crystallinity and Nanostructure for SnS2 Nanosheets through Optimized Calcination Temperature toward Enhanced Pseudocapacitive Na+ Storage

“…In the high-frequency region, SnS 2 @​ZnNS-350 exhibited the smallest semicircle, indicating the lowest charge-transfer resistance ( R ct ) . Generally, the power-law equation, i = av b , can be used to evaluate capacitive storage and diffusion-controlled storage of sodium ions. , Although the b values of the three samples are all between 0.5 and 1 (Figures c, S10, and S11), it is worth noting that the b value of SnS 2 @​ZnNS-300 is significantly lower than those of the other two samples, which indicates that the low crystallinity caused by the lower calcination temperature does not facilitate pseudo­capacitive Na + storage. Furthermore, we compared the capacitive contributions of the three samples by another equation of i = k 1 v + k 2 v 1/2 .…”

Laser Processing of Flexible In-Plane Micro-supercapacitors: Progresses in Advanced Manufacturing of Nanostructured Electrodes

“…10 It is worth noting that the asymmetric in-plane MSCs could maximize the working voltage of the whole device (>1.2 V in aqueous electrolytes) by making full use of the various potential windows of electrodes. 46 Regarding energy storage nanomaterials, they can be divided into three types of electrode materials, 47,48 as shown in Figure 2. EDLCs with capacitive electrode materials usually exhibit a potential-independent current and, therefore, show approximate rectangular cyclic voltammetry (CV) curves (Figure 2A,B).…”