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John Wang

Bio: John Wang is an academic researcher from HRL Laboratories. The author has contributed to research in topics: Battery (electricity) & Lithium. The author has an hindex of 21, co-authored 45 publications receiving 8302 citations. Previous affiliations of John Wang include University of California, Los Angeles & Amazon.com.

Papers
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TL;DR: In this paper, the capacitive effects of nanostructured materials for electrochemical energy storage have been investigated over a dimensional regime where both capacitive and lithium intercalation processes contribute to the total stored charge.
Abstract: The advantages in using nanostructured materials for electrochemical energy storage have largely focused on the benefits associated with short path lengths. In this paper, we consider another contribution, that of the capacitive effects, which become increasingly important at nanoscale dimensions. Nanocrystalline TiO2 (anatase) was studied over a dimensional regime where both capacitive and lithium intercalation processes contribute to the total stored charge. An analysis of the voltammetric sweep data was used to distinguish between the amount of charge stored by these two processes. At particle sizes below 10 nm, capacitive contributions became increasingly important, leading to greater amounts of total stored charge (gravimetrically normalized) with decreasing TiO2 particle size. The area normalized capacitance was determined to be well above 100 μF/cm2, confirming that the capacitive contribution was pseudocapacitive in nature. Moreover, reducing the particle size to the nanoscale regime led to faster...

3,572 citations

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TL;DR: It is shown that the capacitive charge-storage properties of mesoporous films of iso-oriented alpha-MoO(3) are superior to those of either Mesoporous amorphous material or non-porous crystalline MoO( 3).
Abstract: Capacitive energy storage is technologically attractive because of its short charging times and its ability to deliver more power than batteries. The capacitive charge-storage properties of mesoporous films of MoO3 with iso-oriented grains now lead to pseudocapacitive materials that offer increased energy density while still maintaining high power density.

2,643 citations

Journal ArticleDOI
TL;DR: Experimental results indicated that the capacity loss was strongly affected by time and temperature, while the DOD effect was less important, and attempts in establishing a generalized battery life model that accounts for Ah throughput, C-rate, and temperature are discussed.

1,077 citations

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TL;DR: The synthesis and pseudocapacitive characteristics of block copolymer templated anatase TiO(2) thin films synthesized using either sol-gel reagents or preformed nanocrystals as building blocks are described, providing a new class of pseudocAPacitive materials, which offer increased charge storage without compromising charge storage kinetics.
Abstract: The advantages in using nanoscale materials for electrochemical energy storage are generally attributed to short diffusion path lengths for both electronic and lithium ion transport. Here, we consider another contribution, namely the charge storage from faradaic processes occurring at the surface, referred to as pseudocapacitive effect. This paper describes the synthesis and pseudocapacitive characteristics of block copolymer templated anatase TiO2 thin films synthesized using either sol−gel reagents or preformed nanocrystals as building blocks. Both materials are highly crystalline and have large surface areas; however, the structure of the porosity is not identical. The different titania systems are characterized by a combination of small- and wide-angle X-ray diffraction/scattering, combined with SEM imaging and physisorption measurements. Following our previously reported approach, we are able to use the voltammetric sweep rate dependence to determine quantitatively the capacitive contribution to the ...

851 citations

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TL;DR: In this paper, the aging and degradation of graphite/composite metal oxide cells were examined, and non-destructive electrochemical methods were used to monitor the capacity loss, voltage drop, resistance increase, lithium loss and active material loss during the life testing.

358 citations


Cited by
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Journal ArticleDOI
TL;DR: 2D nanosheets, composed of a few Ti 3 C 2 layers and conical scrolls, produced by the room temperature exfoliation of Ti 3 AlC 2 in hydrofl uoric acid are reported, which opens a door to the synthesis of a large number of other 2D crystals.
Abstract: Currently, however, there are relatively few such atomically layered solids. [ 2–5 ] Here, we report on 2D nanosheets, composed of a few Ti 3 C 2 layers and conical scrolls, produced by the room temperature exfoliation of Ti 3 AlC 2 in hydrofl uoric acid. The large elastic moduli predicted by ab initio simulation, and the possibility of varying their surface chemistries (herein they are terminated by hydroxyl and/or fl uorine groups) render these nanosheets attractive as polymer composite fi llers. Theory also predicts that their bandgap can be tuned by varying their surface terminations. The good conductivity and ductility of the treated powders suggest uses in Li-ion batteries, pseudocapacitors, and other electronic applications. Since Ti 3 AlC 2 is a member of a 60 + group of layered ternary carbides and nitrides known as the MAX phases, this discovery opens a door to the synthesis of a large number of other 2D crystals. Arguably the most studied freestanding 2D material is graphene, which was produced by mechanical exfoliation into single-layers in 2004. [ 1 ] Some other layered materials, such as hexagonal BN, [ 2 ] transition metal oxides, and hydroxides, [ 4 ] as well as clays, [ 3 ] have also been exfoliated into 2D sheets. Interestingly, exfoliated MoS 2 single layers were reported as early as in 1986. [ 5 ] Graphene is fi nding its way to applications ranging from supercapacitor electrodes [ 6 ] to reinforcement in composites. [ 7 ] Although graphene has attracted more attention than all other 2D materials combined, its simple chemistry and the weak van der Waals bonding between layers in multilayer structures limit its use. Complex, layered structures that contain more than one element may offer new properties because they

6,846 citations

Journal ArticleDOI
01 Aug 2014-Science
TL;DR: Perovskite films received a boost in photovoltaic efficiency through controlled formation of charge-generating films and improved current transfer to the electrodes and low-temperature processing steps allowed the use of materials that draw current out of the perovskites layer more efficiently.
Abstract: Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

5,789 citations

Journal ArticleDOI
24 Jun 2011-Science
TL;DR: This work synthesized a porous carbon with a Brunauer-Emmett-Teller surface area, a high electrical conductivity, and a low oxygen and hydrogen content that has high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes.
Abstract: Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp 2 -bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

5,486 citations

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TL;DR: In this article, a review of the key technological developments and scientific challenges for a broad range of Li-ion battery electrodes is presented, and the potential/capacity plots are used to compare many families of suitable materials.

5,057 citations

Journal ArticleDOI
TL;DR: This Review introduces several typical energy storage systems, including thermal, mechanical, electromagnetic, hydrogen, and electrochemical energy storage, and the current status of high-performance hydrogen storage materials for on-board applications and electrochemicals for lithium-ion batteries and supercapacitors.
Abstract: [Liu, Chang; Li, Feng; Ma, Lai-Peng; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;cheng@imr.ac.cn

4,105 citations