Singapore

As one of the most promising sustainable energy techniques, Li-O2 batteries have attracted tremendous interest. However, the sluggish cathode reactions and the unwanted side reactions by the reactive superoxide intermediates deleteriously compromise the attainable capacity and the reversibility. Herein, we introduce duroquinone (DQ) as a bifunctional soluble catalyst that facilitates electron transfer and stabilizes the aggressive superoxide intermediates. With the assistance of electron paramagnetic resonance (EPR), the prolonged lifetime by the quinone can be observed which proves the stabilization of the superoxide species. By enhancing the solvation of the superoxide species, the oxygen reduction turns from the surface to the solution mechanism in low donor number (DN) electrolyte. Consequently, the Li-O2 battery presents a significantly enlarged discharge capacity and the solution growth of micrometer-sized Li2O2 particles.

MATERIALS FOR HUMANITY (MH 21)

Bifunctional soluble catalyst promoting solution discharge of Li-O2 battery

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1) The aprotic Li–O2 battery are expected to be the promising next-generation candidates due to their extremely high theoretical gravimetric energy density. 2) However, to realize a commercial rechargeable Li–O2 technology confronts clogging and passivation of the cathode by insoluble nature of discharge product Li2O2 and high charge overpotential for its insulating nature. 3) Crown ethers have been attracting interests due to their ability to coordinate with Li+ , which enhances the ionic conductivity of the electrolyte and improves the battery performance. EXPERIMENTAL Here, we examined dibenzo-24-crown-8 derivative aldehyde (DB24C8-CHO) as an additive in TEGDME electrolyte solutions, which present a significantly low charge overpotential of 0.77 V, and an excellent cycle life (up to 213 cycles) at 500 mA g −1with a fixed capacity of 500 mAh·g -1.

A High-Performance Li–O2 Battery with dibenzo-24-crown-8 derivative aldehyde additives

The inability of the current energy storage system to meet the requirements of industry is driving the development of emerging battery devices. Rechargeable lithium-oxygen batteries are expected to be a possible solution for the development of alternative batteries with high energy density. However, the lithium-oxygen batteries are still in the prototype stage due to obstacles that are mainly related to the slow electrode dynamics, especially the high charge overpotential. To overcome these bottlenecks, the introduction of photo assistance into the lithium-oxygen system has attracted great research interest. Herein, we explored the application of WO3 with different crystal planes in photo-assisted lithium-oxygen batteries. At a current density of 0.04 mA cm-2, the 3-WO3-nanosheet shows a charge overpotential of about 3.1 V and is able to work for 95 cycles at 0.04 mAh cm-2.

Improving Lithium-Oxygen Battery Performance via Photocatalysis

Pore structure of hard carbon has a fundamental influence on the electrochemical properties in sodium-ion batteries (SIBs). Ultra-micropores (< 0.5nm) of hard carbon can function as ionic sieves to reduce the diffusion of slovated Na + but allow the entrance of naked Na + into the pores, which can reduce the interficial contact between the electrolyte and the inner pores without sacrificing the fast diffusion kinetics. Herein, a molten diffusion-carbonization method is proposed to transform the micropores (> 1 nm) inside carbon into ultra-micropores (< 0.5 nm). Consequently, the designed carbon anode displays an enhanced capacity of 346 mAh g -1 at 30 mA g -1 with a high ICE value of ~ 80.6% and most of the capacity (~90%) is below 1 V. Moreover, the high-loading electrode (~ 19mg cm-2 ) exhibits a good temperature endurance with a high areal capacity of 6.14 mAh cm-2 at 25℃ and 5.32 mAh cm-2 at -20 ℃. Based on the in-situ X-ray diffraction (XRD) and ex-situ solid-state nuclear magnetic resonance (NMR) results, the designed ultra-micropores provide the extra Na+ storage sites, which mainly contributes to the enhanced capacity. This proposed strategy shows good potential for the development of high-performance SIBs.

From Micropores to Ultra-micropores inside Hard Carbon: Towards Enhanced Capacity in Room/Low-Temperature Sodium-Ion Storage

Electromechanical Failure Mechanism of All-solid-state Li-ion Batteries based on a NASICON-type Solid-state Electrolyte 
Linchun He, Stefan Adams
Department of Materials Science and Engineering, National University of Singapore

All-solid-state lithium batteries (ASSLiB) are promising candidates for next-generation energy storage. Beyond design requirements and concerns of conventional batteries, the undeformable nature of solid-state electrolytes (SSEs)1 raises new issues for ASSLiBs such as poor interface bonding, limited contact area and cathode utilization.2 Moreover, volume changes of electrodes during Li-ion (de)intercalation are restricted by the SSE, resulting in large internal stresses that may drive crack creation. Such cracks reduce the utilization of electrodes and the available cross-section of the SSE for ion transport. Increased currents in the remaining connected regions turn this into a self-accelerating aging process. Hence it is essential to synergize understanding of the ion transport with insight into mechanochemical processes in the SSE or at its interfaces to overcome these obstacles.
Here, we demonstrate and analyze a model bulk ASSLiB with MnO2-CNT nanocomposite anode, high voltage LiNi0.5Mn1.5O4 cathode and ambient-stable Li1.5Al0.5Ge(PO4)3 (LAGP) as SSE. This ASSLiB has a discharge capacity of 82 mAh g-1 at 0.15 C at 23.8°C. Electrochemical impedance studies reveal a decrease in impedance by solid interface layer formation, followed by an increase over extended cycling. Electrochemical evaluation and first-principle calculations are used to explore the aging processes. Li4P2O7, Li3PO4, Ge5P6O25, AlPO4 and GeO are identified as products of the decomposition of LAGP, which is assisted by Li-ions and free electrons from voids and grain boundaries. Finite element method (FEM) simulations reveal that the volume expansion on forming the decomposition products causes maximum internal stresses of 2.5 to 125 GPa (for Li excess ratios from 0 to 6), resulting in crack formation and growth within the SSE on multiple cycling. 
1. C. Chen, Y. Sun, L. He et al., ACS Appl. Mater. Interfaces (2020).
2. L. He, C. Chen, M. Kotobuki et al., J. Mater. Chem. A 7, 9748 (2019).



Electromechanical Failure Mechanism of All-solid-state Li-ion Batteries based on a NASICON-type Solid-state Electrolyte

Understanding the alkali interaction with the organic functional groups is significant for molecular-level design of potential anode materials.In this work,we investigate the chemical and electronic interactions between Li/Na and PTCDA/PTCDI during the deposition processes. The change of molecular electronic structures has been studied by X-ray photo electron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), synchrotron-based near edge X-ray absorption fine structure (NEXAFS), and corroborated by density functional theory (DFT) calculations.

Alkali Metal Storage Mechanism in Organic Semiconductor of PTCDA and PTCDI

Perovskite materials have attracted much attention due to their alternative structure and outstanding catalytic performance of OER and ORR. In this work, we synthesize a series of different ratio of Se-doped LCO, which greatly improved the conductivity of LCO. At the optimized Se-doping level(Se60%-LCO), the rechargeable lithium-oxygen battery has high specific capacity and long cycle life. With the good semiconductor characteristics of LaCoO3, the photo-electrochemical process is assisted by photoelectric double synergistic effect, which greatly improves the electrochemical performance of the battery. This work shows that the catalytic activity of oxide perovskite enhanced by Se doping combined with photo assistance, which make LaCoO3 a promising bifunctional catalyst.

Engineering Oxygen Vacancies of Oxide Perovskite by Selenium Doping for Electrocatalysis in Photo-assisted Li−O2 Batteries

Sodium-ion batteries (SIBs) have attracted growing interest as a promising energy storage technique due to their safety, low cost and excellent cycling performance. Among various electrode materials, phthalocyanine complexes (Pcs) is a kind of organometallic complexes (OMCs) with adjustable structure of organic moieties and metal active sites of inorganic moieties that possess promising redox activity in batteries. In this work, we investigate the interaction of Na atoms with CuPc and F16CuPc thin films by in-situ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) in an ultra-high vacuum (UHV) system, corroborated by the density functional theory (DFT) calculations. Na atoms are found to interact with inner pyrrole N ahead of outer aza N, for which process is accompanied by the reduction from Cu(II) to Cu(I). Na deposition leads to a charge transfer to CuPc that successfully fills up the lowest unoccupied molecular orbitals (LUMO) of CuPc. The role of fluorine groups is also investigated. F with high electronegativity can attract Na atoms to interact with outer aza N, and the proposed charge transfer from Na to F16CuPc as well as reduction of central Cu are also affected by the intense Na-F interaction. The microscopic-scale insights we obtained from the in-situ XPS and UPS characterization can be applied to other alkali ion-OMCs model systems, and will give comprehensive guidance for designing OMCs with required configurations and advanced features for next-generation energy storage devices.

Mechanism study of sodium storage in phthalocyanine based electrode materials

Stabilizing the active half-metallic LiO2 as discharge product is an effective approach to reduce the charge overpotential and enhance the stability of Li-O2 batteries. Here we developed a Rh nanoparticle decorated reduced graphene oxide (Rh/rGO) cathode to induce the formation of mixed discharge products of LiO2 and Li2O2. The as-assembled Li-O2 battery exhibited large discharge capacity (16157 mAh/g at 100 mA/g), long cycle life (136 cycles at 100 mA/g with capacity limited to 500 mAh/g) and reduced charge overpotential. The improved battery performance is ascribed to the intermetallic phase LiRh3 that stabilized crystalline LiO2 as substrate. Additionally, the high oxygen reduction reaction (ORR) catalytic activity of cathode material is determined to be crucial to stabilize crystalline LiO2 even with the presence of LiRh3. These results provide further insight into LiO2 based Li-O2 batteries and potential application of such template-assisted approach.

Rh/rGO stabilized LiO2 as Discharge Product in Lithium Oxygen Battery

In this work, in situ vertical growth of Sb2S3 on top of ultrathin TiO2 /CdS as the electron transport layer (ETL) by a solution method is demonstrated. The planar heterojunction solar cell using [hk1]-oriented Sb2S3 achieves a power conversion efficiency of 6.4%, performing at almost 20% higher than devices based on a [hk0]-oriented absorber. The main highlights of this work are summarized below: 1. In-situ growth of vertically oriented Sb2S3 on ETL by a facile solution method is realized 2. A convincing and enlightening crystal growth model is proposed. 3. Direct evidences are shown to reveal the relationship between crystal orientation of Sb2S3 and device performance 4. High efficient planar heterojunction Sb2S3 solar cell was obtained, performing almost 20% higher compared to device based on [hk0]-oriented absorber.

In Situ Growth of [hk1]-Oriented Sb2S3 for Solution Processed Planar Heterojunction Solar Cell with 6.4% Efficiency

Silver bismuth iodide has been studied comprehensively for its potential as light harvesters, owing to their low toxicity and environment conviviality. However, they often suffer with low efficiencies as compared to conventional light harvesters and hence there is a broad room for improvement. Here we propose doping the standard AgBiI4 composition with tin (Sn), to improve the relative absorbance and thereby potentially improving the efficiencies. It is observed that the addition of Sn did not alter the structural properties significantly, while it works on the orientation of the crystal growth during thin film synthesis, leading to ordered and uniform films. An improvement in absorption coefficient was observed, which can be considered to improve the performances of devices fabricated with AgBiI4 as light harvesters.

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