Sputter-deposited TiOx_x thin film as a buried interface modification layer for efficient and stable perovskite solar cells

Despite perovskite solar cells (PSCs) based on a SnO2 hole-blocking layer (HBL) are achieving excellent performance, the non-perfect buried interface between the SnO2 HBL and the perovskite layer is still an obstacle in achieving further improvement in power conversion efficiency (PCE) and stability. The poor morphology with numerous defects and the energy level mismatch at the buried interface constrain the open circuit voltage and cause instability. Herein, a sputter-deposited TiOx thin film is used as a buried interface modification layer to address the aforementioned issues. Utilizing in situ grazing-incidence small-angle X-ray scattering (GISAXS) during the sputter deposition, we monitor and unveil the growth process of the TiOx thin film, identifying a 10 nm thickness optimum. The defects at the buried interface are passivated through tuning the growth, leading to a suppressed non-radiative recombination and improved PCE (from 22.19 % to 23.93 %). The evolution of the device performance and the degradation process of PSCs using operando grazing-incidence wide-angle X-ray scattering (GIWAXS) under the protocol ISOS-L-1I explains the enhanced stability introduced by the buried interface modification via a sputter-deposited TiOx thin layer. The perovskite decomposition process and the detrimental formation of PbI2 are both slowed down by the TiOx thin layer

Impact of CO2 activation on the structure, composition, and performance of Sb/C nanohybrid lithium/sodium-ion battery anodes

Antimony (Sb) has been regarded as one of the most promising anode materials for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) and attracted much attention in recent years. Alleviating the volumetric effect of Sb during charge and discharge processes is the key point to promote Sb-based anodes to practical applications. Carbon dioxide (CO2) activation is applied to improve the rate performance of the Sb/C nanohybrid anodes caused by the limited diffusion of Li/Na ions in excessive carbon components. Based on the reaction between CO2 and carbon, CO2 activation can not only reduce the excess carbon content of the Sb/C nanohybrid but also create abundant mesopores inside the carbon matrix, leading to enhanced rate performance. Additionally, CO2 activation is also a fast and facile method, which is perfectly suitable for the fabrication system we proposed. As a result, after CO2 activation, the average capacity of the Sb/C nanohybrid LIB anode is increased by about 18 times (from 9 mA h g−1 to 160 mA h g−1) at a current density of 3300 mA g−1. Moreover, the application of the CO2-activated Sb/C nanohybrid as a SIB anode is also demonstrated, showing good electrochemical performance

Carbon-emcoating architecture boosts lithium storage of Nb2O5

Intercalation transition metal oxides (ITMO) have attracted great attention as lithium-ion battery negative electrodes due to high operation safety, high capacity and rapid ion intercalation. However, the intrinsic low electron conductivity plagues the lifetime and cell performance of the ITMO negative electrode. Here we design a new carbon-emcoating architecture through single CO2 activation treatment as demonstrated by the Nb2O5/C nanohybrid. Triple structure engineering of the carbon-emcoating Nb2O5/C nanohybrid is achieved in terms of porosity, composition, and crystallographic phase. The carbon-embedding Nb2O5/C nanohybrids show superior cycling and rate performance compared with the conventional carbon coating, with reversible capacity of 387 mA h g−1 at 0.2 C and 92% of capacity retained after 500 cycles at 1 C. Differential electrochemical mass spectrometry (DEMS) indicates that the carbon emcoated Nb2O5 nanohybrids present less gas evolution than commercial lithium titanate oxide during cycling. The unique carbon-emcoating technique can be universally applied to other ITMO negative electrodes to achieve high electrochemical performance

Dental resin monomer enables unique NbO2/carbon lithium‐ion battery negative electrode with exceptional performance

Niobium dioxide (NbO2) features a high theoretical capacity and an outstanding electron conductivity, which makes it a promising alternative to the commercial graphite negative electrode. However, studies on NbO2 based lithium-ion battery negative electrodes have been rarely reported. In the present work, NbO2 nanoparticles homogeneously embedded in a carbon matrix are synthesized through calcination using a dental resin monomer (bisphenol A glycidyl dimethacrylate, Bis-GMA) as the solvent and a carbon source and niobium ethoxide (NbETO) as the precursor. It is revealed that a low Bis-GMA/NbETO mass ratio (from 1:1 to 1:2) enables the conversion of Nb (V) to Nb (IV) due to increased porosity induced by an alcoholysis reaction between the NbETO and Bis-GMA. The as-prepared NbO2/carbon nanohybrid delivers a reversible capacity of 225 mAh g−1 after 500 cycles at a 1 C rate with a Coulombic efficiency of more than 99.4% in the cycles. Various experimental and theoretical approaches including solid state nuclear magnetic resonance, ex situ X-ray diffraction, differential electrochemical mass spectrometry, and density functional theory are utilized to understand the fundamental lithiation/delithiation mechanisms of the NbO2/carbon nanohybrid. The results suggest that the NbO2/carbon nanohybrid bearing high capacity, long cycle life, and low gas evolution is promising for lithium storage applications

Spatial Effects between Two 3D Self-Supported Carbon-Nanotube-Based Skeleton as Binder-Free Cathodes for Lithium-Sulfur Batteries

In this manuscript a deep comparison of the spatial effect is conducted between vertically-aligned carbon nanotube array (CNTA) and 3D inter-connected carbon nanotube sponge (CNTS) based self-supported and adhesive free cathode material for lithium-sulfur battery. Melt impregnation (M-CNTA/S and M-CNTS/S) and solution penetration (S-CNTA/S and S-CNTS/S) methods are separately carried out to introduce sulfur into two carbon nanotube-based matrix. Besides, random distributed carbon nanotube powders (RCNT)-based cathode made through a slurry coating process is also prepared for comparison. As a result, the aligned CNTA skeleton has the most efficient transfer paths and regular nanometer-sized gaps, which greatly benefit the directional transmission of electrons, better rate performance, smaller cell resistance and long cyclic stability. Especially, the cell made by M-CNTA/S delivers an outstanding high-rate performance of 3 C -859.3 mAh g(-1), 5 C -833.1 mAh g(-1)and 10 C -702.8 mAh g(-1), with a capacity retention of 77 % and coulombic effciency (similar to 100 %) after 200 cycles at a rate of 3 C. Meanwhile, the interconnected CNTS has a larger pore diameter and 3D conductive network, which benefits higher sulfur loading and electrochemical activity of sulfur. In particular, the M-CNTS/S with a sulfur content up to 60 wt %, achieves an impressive multiplier performance of 0.5 C 1285 mAh g(-1), 1 C 1030 mAh g(-1)and 3 C 900 mAh g(-1). The retention of the capacity reaches around 88 % after 100 charge-discharge cycles at 3 C. The current observation reveals the crucial effects from the spatial structure and sulfur impregnation method on the performance of carbon nanotube/sulfur (C/S)-based cathodes for lithium-sulfur batteries, which serves as important guidance for the development of high-performance cathode materials

Ultrathin 2D Mesoporous TiO2/rGO Heterostructure for High-Performance Lithium Storage

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Lithium-ion batteries (LIBs) have been widely applied and studied as an effective energy supplement for a variety of electronic devices. Titanium dioxide (TiO2), with a high theoretical capacity (335 mAh g−1) and low volume expansion ratio upon lithiation, has been considered as one of the most promising anode materials for LIBs. However, the application of TiO2 is hindered by its low electrical conductivity and slow ionic diffusion rate. Herein, a 2D ultrathin mesoporous TiO2/reduced graphene (rGO) heterostructure is fabricated via a layer-by-layer assembly process. The synergistic effect of ultrathin mesoporous TiO2 and the rGO nanosheets significantly enhances the ionic diffusion and electron conductivity of the composite. The introduced 2D mesoporous heterostructure delivers a significantly improved capacity of 350 mAh g−1 at a current density of 200 mA g−1 and excellent cycling stability, with a capacity of 245 mAh g−1 maintained over 1000 cycles at a high current density of 1 A g−1. The in situ transmission electron microscopy analysis indicates that the volume of the as-prepared 2D heterostructures changes slightly upon the insertion and extraction of Li+, thus contributing to the enhanced long-cycle performance

In Situ Incorporation of Super-Small Metallic High Capacity Nanoparticles and Mesoporous Structures for High-Performance TiO2/SnO2/Sn/Carbon Nanohybrid Lithium-Ion Battery Anodes

TiO2 is a promising lithium-ion battery anode due to its good operation safety enabled by its voltage profile. However, the intrinsically low electronic/ionic conductivity and moderate reversible capacity compromise its potential for practical applications. It is proposed in this work to incorporate super-small sized metallic high capacity tin-based nanoparticles into TiO2/carbon nanohybrids, coupled with in situ generation of mesoporous structures. Difunctional methacrylate resin monomers are used as the solvent and carbon source, followed by carbonization and hydrofluoric (HF) etching treatment. The precursors of TiO2, tin-based component, and SiOx porogen agent are homogeneously integrated into the cross-linking network at a molecular level. High reversible capacities, excellent rate capability, and good capacity retention are achieved simultaneously due to synergistic effects from the tin-based component bearing high capacity and good electron conductivity, and mechanical buffer medium of the mesoporous structures. Reversible capacities of 452 mAh g(-1) are achieved after 400 cycles at 200 mA g(-1). High rate capacity of 131 mAh g(-1) is maintained at 5 A g(-1). The overall capacities are increased by more than 2 times compared with the capacities of the tin-free TiO2/C and pristine TiO2/SnO2/Sn/SiOx/C nanohybrids

Operando Study Insights into Lithiation/Delithiation Processes in a Poly(ethylene oxide) Electrolyte of All-Solid-State Lithium Batteries by Grazing-Incidence X-ray Scattering.

Poly(ethylene oxide) (PEO)-based composite electrolytes (PCEs) are considered as promising candidates for next-generation lithium-metal batteries (LMBs) due to their high safety, easy fabrication, and good electrochemical stability. Here, we utilize operando grazing-incidence small-angle and wide-angle X-ray scattering to probe the correlation of electrochemically induced changes and the buried morphology and crystalline structure of the PCE. Results show that the two irreversible reactions, PEO-Li+ reduction and TFSI- decomposition, cause changes in the crystalline structure, array orientation, and morphology of the PCE. In addition, the reversible Li plating/stripping process alters the inner morphology, especially the PEO-LiTFSI domain radius and distance between PEO-LiTFSI domains, rather than causing crystalline structure and orientation changes. This work provides a new path to monitor a working battery in real time and to a detailed understanding of the Li+ diffusion mechanism, which is essential for developing highly transferable and interface-stable PCE-based LMBs

Diblock copolymer pattern protection by silver cluster reinforcement

Pattern fabrication by self-assembly of diblock copolymers is of significant interest due to the simplicity in fabricating complex structures. In particular, polystyrene-block-poly-4-vinylpyridine (PS-b-P4VP) is a fascinating base material as it forms an ordered micellar structure on silicon surfaces. In this work, silver (Ag) is applied using direct current magnetron sputter deposition and high-power impulse magnetron sputter deposition on an ordered micellar PS-b-P4VP layer. The fabricated hybrid materials are structurally analyzed by field emission scanning electron microscopy, atomic force microscopy, and grazing incidence small angle X-ray scattering. When applying simple aqueous posttreatment, the pattern is stable and reinforced by Ag clusters, making micellar PS-b-P4VP ordered layers ideal candidates for lithography

Tailored fabrication of quasi-isoporous and double layered αα-Fe2_2O3_3 thin films and their application in photovoltaic devices

A series of $\alpha-Fe_2O_3$ thin films with distinct morphologies are prepared via a facile polystyrene-block-polyethylene oxide templated sol–gel method. By tailoring the poor solvent contents and FeCl$_3$-to-polymer weight ratio in the sol–gel solutions, quasi-isoporous $\alpha-Fe_2O_3$ thin films with different substructures and thicknesses are obtained. Via a thermal annealing post-treatment, double layered structures are induced by a synergistic dewetting and Oswald ripening effect. Special focus is set on the $\alpha-Fe_2O_3$ thin films prepared with no annealing/annealing-medium $FeCl_3$ concentration, as they possess uniform periodic structures, which is suitable to be used as hole blocking modification layer of perovskite solar cells (PSCs). An improved power conversion efficiency (PCE) is obtained when the double layered $\alpha-Fe_2O_3$ thin film is applied as the hole blocking modification layer for PSCs. The improved PCE primarily originates from the increased $V_{OC}$, which probably benefits from the synergistic effect of the suppressed charge carrier recombination at the interfaces, the enhanced light transmittance as well as the superior electron extraction capacity