Additional file 1: Figure S1. of Tailoring the Mesoscopic TiO2 Layer: Concomitant Parameters for Enabling High-Performance Perovskite Solar Cells

SEM images showing the TiO2 nanostructures with the PbI2 pre-coating and MAPbI3(Cl) infiltration into the PS-templated TiO2. Figure S2. The effect of PS ratio and the concentration of precursor solution on the X-ray diffraction of MAPbI3(Cl) perovskite. Figure S3. Cross-sectional back scattered electron images exhibiting the MAPbI3(Cl) perovskite infiltration in the porous TiO2 layer. Figure S4. Cross-sectional elemental distributions from energy dispersive X-ray spectroscopy (SEM-EDS) showing the Sn, Ti, O, Pb, and I distributions for different porous TiO2 scaffolds. Figure S5. Microstructures of MAPbI3(Cl) on the TiO2 blocking layer. Figure S6. Photovoltaic parameters with the average and the standard deviation in each condition. Figure S7. Ideal one-diode model for the perovskite solar cell. Figure S8. Current density vs. bias under dark and the corresponding fitting results. Figure S9. The effect of TiO2 blocking layer by sputter deposition on the performance of the perovskite solar cell. Figure S10. Morphology comparison by the spin-coating and sputter deposition

Copolymerization of Polythiophene and Sulfur To Improve the Electrochemical Performance in Lithium–Sulfur Batteries

We first report on the copolymerization of sulfur and allyl-terminated poly­(3-hexylthiophene-2,5-diyl) (P3HT) derived by Grignard metathesis polymerization. This copolymerization is enabled by the conversion of sulfur radicals formed by thermolytic cleavage of S₈ rings with allyl end-group. The formation of a C–S bond in the copolymer is characterized by a variety of methods, including NMR spectroscopy, size exclusion chromatography, and near-edge X-ray absorption fine spectroscopy. The <b>S-P3HT</b> copolymer is applied as an additive to sulfur as cathode material in lithium–sulfur batteries and compared to the use of a simple mixture of sulfur and P3HT, in which sulfur and P3HT were not covalently linked. While P3HT is incompatible with elementary sulfur, the new <b>S-P3HT</b> copolymer can be well dispersed in sulfur, at least on the sub-micrometer level. Sulfur batteries containing the <b>S-P3HT</b> copolymer exhibit an enhanced battery performance with respect to the cycling performance at 0.5C (799 mAh g^–1 after 100 cycles for <b>S-P3HT</b> copolymer versus only 544 mAh g^–1 for the simple mixture) and the C-rate performance. This is attributed to the attractive interaction between polysulfides and P3HT hindering the dissolution of polysulfides and the charge transfer (proven by electrochemical impedance spectroscopy) due to the homogeneous incorporation of P3HT into sulfur by covalently linking sulfur and P3HT

Conformal Polymeric Multilayer Coatings on Sulfur Cathodes via the Layer-by-Layer Deposition for High Capacity Retention in Li–S Batteries

We report on the conformal coating of thickness-tunable multilayers directly onto the sulfur (S₈) cathodes by the layer-by-layer (LbL) deposition for the significant improvement in the performances of Li–S batteries even without key additives (LiNO₃) in the electrolyte. Poly­(ethylene oxide) (PEO)/poly­(acrylic acid) (PAA) multilayers on a single poly­(allylamine hydrochloride) (PAH)/PAA priming bilayer, deposited on the S₈ cathodes, effectively protected from the polysulfide leakage, while providing a Li⁺ ion diffusion channel. As a result, PAH/PAA/(PEO/PAA)₃ multilayer-coated cathodes exhibited the highest capacity retention (806 mAh g^–1) after 100 cycles at 0.5 C, as well as the high C-rate capability up to 2.0 C. Furthermore, the multilayer coating effectively mitigated the polysulfide shuttle effect in the absent of LiNO₃ additives in the electrolyte

Visualization of the Phase Propagation within Carbon-Free Li₄Ti₅O₁₂ Battery Electrodes

The electrochemical reactions occurring in batteries involve the transport of ions and electrons among the electrodes, the electrolyte, and the current collector. In Li-ion battery electrodes, this dual functionality is attained with porous composite electrode structures that contain electronically conductive additives. Recently, the ability to extensively cycle composite electrodes of Li₄Ti₅O₁₂ without any conductive additives generated questions about how these structures operate, the answers to which could be used to design architectures with other materials that reduce the amount of additives that do not directly store energy. Here, the changes occurring in carbon-free Li₄Ti₅O₁₂ electrodes during lithiation were studied by a combination of ex situ and operando optical microscopy and microbeam X-ray absorption spectroscopy (μ-XAS). The measurements provide visualizations of the percolation of lithiated domains through the thick (∼40-μm) structure after a depth of discharge of only 1%, followed by a second wave of propagation starting with regions in closest contact with the current collector and progressing toward regions in contact with the bulk electrode. These results emphasize the interplay between the electronic and ionic conductivities of the phases involved in a battery reaction and the formation of the phases in localized areas in the electrode architecture. They provide new insights that could be used to refine the design of these architectures to minimize transport limitations while maximizing energy density

Monodisperse Sn Nanocrystals as a Platform for the Study of Mechanical Damage during Electrochemical Reactions with Li

Monodisperse Sn spherical nanocrystals of 10.0 ± 0.2 nm were prepared in dispersible colloidal form. They were used as a model platform to study the impact of size on the accommodation of colossal volume changes during electrochemical lithiation using ex situ transmission electron microscopy (TEM). Significant mechanical damage was observed after full lithiation, indicating that even crystals at these very small dimensions are not sufficient to prevent particle pulverization that compromises electrode durability

Ultrathin Lithium-Ion Conducting Coatings for Increased Interfacial Stability in High Voltage Lithium-Ion Batteries

Ultrathin conformal coatings of the lithium ion conductor, lithium aluminum oxide (LiAlO₂), were evaluated for their ability to improve the electrochemical stability of LiNi_0.5Mn_1.5O₄/graphite Li-ion batteries. Electrochemical impedance spectroscopy confirmed the ion conducting character of the LiAlO₂ films. Complementary simulations of the activation barriers in these layers match experimental results very well. LiAlO₂ films were subsequently separately deposited onto LiNi_0.5Mn_1.5O₄ and graphite electrodes. Increased electrochemical stability was observed, especially in the full cells, which was attributed to the role of the coatings as physical barriers against side reactions at the electrode–electrolyte interface. By comparing data from full cells where the coatings were applied to either electrode, the dominating failure mechanism was found to be the diffusion of transition metal ions from the cathode to the anode. The LiNi_0.5Mn_1.5O₄/graphite full cell with less than 1 nm LiAlO₂ on the positive electrode exhibited a discharge capacity of 92 mAh/g at C/3 rate. The chemical underpinnings of stable performance were revealed by soft X-ray absorption spectroscopy. First, both manganese and nickel were detected on the graphite electrode surfaces, and their oxidation states were determined as +2. Second, the ultrathin coatings on the anode alone were found to be sufficient to significantly reduce this deleterious process

The Formation Mechanism of Fluorescent Metal Complexes at the Li_<i>x</i>Ni_0.5Mn_1.5O_4−δ/Carbonate Ester Electrolyte Interface

Electrochemical oxidation of carbonate esters at the Li_<i>x</i>Ni_0.5Mn_1.5O_4−δ/electrolyte interface results in Ni/Mn dissolution and surface film formation, which negatively affect the electrochemical performance of Li-ion batteries. Ex situ X-ray absorption (XRF/XANES), Raman, and fluorescence spectroscopy, along with imaging of Li_<i>x</i>Ni_0.5Mn_1.5O_4−δ positive and graphite negative electrodes from tested Li-ion batteries, reveal the formation of a variety of Mn^II/III and Ni^II complexes with β-diketonate ligands. These metal complexes, which are generated upon anodic oxidation of ethyl and diethyl carbonates at Li_<i>x</i>Ni_0.5Mn_1.5O_4−δ, form a surface film that partially dissolves in the electrolyte. The dissolved Mn^III complexes are reduced to their Mn^II analogues, which are incorporated into the solid electrolyte interphase surface layer at the graphite negative electrode. This work elucidates possible reaction pathways and evaluates their implications for Li⁺ transport kinetics in Li-ion batteries

Electrochemical Reactivity with Lithium of Spinel-type ZnFe_2–<i>y</i>Cr_<i>y</i>O₄ (0 ≤ <i>y</i> ≤ 2)

Members of the spinel solid solution series ZnFe_2–<i>y</i>Cr_<i>y</i>O₄ (<i>y</i> = 0, 0.5, 1.0, 1.5, and 2) were synthesized using high-energy ball milling followed by annealing at 1000 °C. The structural study of the samples was performed by Fourier transform infrared spectroscopy (FTIR), X-ray absorption spectroscopy (XAS), and powder X-ray diffraction (XRD). While XRD verified the formation of single spinel phases with lattice parameters reduced by increasing Cr substitution, FTIR and XAS provided insight into the subsequently increased covalence of the chemical bonding of the spinels. The mixed transition-metal spinel oxides were employed as working electrodes in Li metal batteries. In agreement with the literature, the spinel oxides experience amorphization during the first discharge, as shown by ex situ XRD and selected area electron diffraction (SAED). The electrochemical activity of the spinel oxides was found to diminish with Cr content so that ZnCr₂O₄ is completely inactive even when the material is nanosized and in the presence of a large amount of conductive additive. Comparison with mixtures of ZnO and Cr₂O₃ led to the conclusion that the conducting band of the ternary oxide, which would be injected with electrons during reduction, is raised with respect to the individual binary oxides to the point that the overpotential required to drive a conversion reaction displaces the experimental electrochemical potential to be extremely close to, or even lower than, that of Li metal

Electrochemical Reduction of a Spinel-Type Manganese Oxide Cathode in Aqueous Electrolytes with Ca²⁺ or Zn²⁺

In this report, the feasibility of reversible Ca²⁺ or Zn²⁺ intercalation into a crystalline cubic spinel Mn₂O₄ cathode has been investigated using electrochemical methods in an aqueous electrolyte. A combination of synchrotron XRD and XANES studies identified the partial structural transformation from a cubic to a tetragonally distorted spinel Mn₃O₄, accompanied by the reduction of Mn⁴⁺ to Mn³⁺ and Mn²⁺ during discharge. TEM/EDX measurements confirmed that practically no Ca²⁺ was inserted upon discharge. However, non-negligible amounts of Zn were detected after Mn₂O₄ was reduced in the Zn²⁺ electrolyte, but through the formation of secondary phases that, in some cases, appeared adjacent to the surface of a cathode particle. This report aims to identify bottlenecks in the application of manganese oxide cathodes paired with Ca or Zn metal anodes and to justify future efforts in designing prototype multivalent batteries

Elemental Sulfur and Molybdenum Disulfide Composites for Li–S Batteries with Long Cycle Life and High-Rate Capability

The practical implementation of Li–S technology has been hindered by short cycle life and poor rate capability owing to deleterious effects resulting from the varied solubilities of different Li polysulfide redox products. Here, we report the preparation and utilization of composites with a sulfur-rich matrix and molybdenum disulfide (MoS₂) particulate inclusions as Li–S cathode materials with the capability to mitigate the dissolution of the Li polysulfide redox products via the MoS₂ inclusions acting as “polysulfide anchors”. In situ composite formation was completed via a facile, one-pot method with commercially available starting materials. The composites were afforded by first dispersing MoS₂ directly in liquid elemental sulfur (S₈) with sequential polymerization of the sulfur phase via thermal ring opening polymerization or copolymerization via inverse vulcanization. For the practical utility of this system to be highlighted, it was demonstrated that the composite formation methodology was amenable to larger scale processes with composites easily prepared in 100 g batches. Cathodes fabricated with the high sulfur content composites as the active material afforded Li–S cells that exhibited extended cycle lifetimes of up to 1000 cycles with low capacity decay (0.07% per cycle) and demonstrated exceptional rate capability with the delivery of reversible capacity up to 500 mAh/g at 5 C