Energy Materials

The formation of a stable cathode-electrolyte interphase (CEI) is critical for the performance of lithium–sulfur (Li–S) batteries with carbonate-based electrolytes, as it suppresses parasitic polysulfide reactions and enables solid-state sulfur conversion. In nanoporous carbon hosts, the CEI together with nanopore confinement plays a key role in capacity retention and long-term cycling. Yet, its spatial formation, stability, and contribution to electrochemical performance remain poorly understood, partly due to challenges in characterization caused by beam and air sensitivity. Here, we employ cryogenic transmission electron microscopy (cryo-TEM) with electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and electrochemical testing together with galvanostatic intermittent titration technique measurements to elucidate how carbon particle size affects CEI formation and electrochemical performance. We find that the CEI is not a uniform surface film but extends heterogeneously into the particle bulk. Mass transport during the first discharge dictates CEI development, and larger particles suffer from inactive regions due to the preferential CEI formation only in the outer regions of the particles. During extended cycling, charge transfer resistance at confined CEI/active material/carbon interfaces emerges as the dominant performance-limiting factor. These findings show that particle size controls CEI formation during initial discharge, offering guidance for designing carbon hosts from nano- to micrometer length scales in Li–S battery cathodes.

In this work, hierarchically porous materials have been prepared by the self-assembly and pore formation of different amphiphilic block copolymers (BCPs) in the vicinity of cellulose paper sheets. For this, polystyrene-block-polysolketal methacrylate (PS-b-SMA) as a linear BCP and polymethyl methacrylate-block-polysolketal methacrylate (PMMA-b-SMA)n as a star-shaped BCP were prepared using living anionic polymerization. Under mild acidic conditions, the amphiphilic properties were revealed by converting the PSMA block segment to poly(dihydroxypropyl methacrylate) (PDHPMA). The BCPs were incorporated onto cellulose linters fiber-based sheets by a self-assembly and nonsolvent-induced phase separation (SNIPS) process. The resulting porous materials have been further modified with 3-aminopropyltriethoxysilane (APTES) and 3,3,3-trifluoropropyl dimethyl chlorosilane (TFPCS) using a vapor-phase modification approach. This strategy enabled further tuning of the surface properties of the resulting porous structures to adjust surface polarity. The characteristics of the modified porous materials were confirmed at the microscopic scale by solid-state nuclear magnetic resonance (NMR) combined with selectively enhanced dynamic nuclear polarization (DNP) and Fourier transform infrared (FTIR) spectroscopy. The influence of APTES and TFPCS was further analyzed at the macroscopic level using water contact angle (WCA) measurements and water permeance testing, where changes were observed for both modifiers. Using this convenient strategy, the fabrication of functional porous cellulose composite materials is demonstrated, paving the way for a new family of cellulose-based porous materials.

The development of efficient carbon-based materials is crucial for overcoming the performance limitations of traditional electrodes in capacitive deionization (CDI). However, the practical performance of heteroatom-doped carbon electrodes for desalination in complex multi-ion water matrices remains largely unexplored. In this work, we studied the ion selectivity toward Li+ and the removal efficiency of nitrogen‑sulfur co-doped and boron-doped carbon electrodes in brackish water, using multi-salt cation solutions containing monovalent (Li+, Na+, K+) and divalent (Ca2+, Mg2+) ions. These modifications enhanced charge distribution, wettability, and ion diffusion within the electrodes. As a result, the N,S-AC electrode exhibited pronounced lithium selectivity in brackish water, while the B-AC electrode delivered higher adsorption capacity. The B-AC electrode achieved both high capacity and enhanced lithium selectivity even under strong competition from Na+, Mg2+, and Ca2+. These findings demonstrate the distinct and complementary roles of N,S-co-doping and B-doping, offering valuable insights into how heteroatom engineering can advance CDI performance.

Transition metal oxalates have been proven to be a promising electrode material for lithium-ion batteries. Here, we have designed a series of multi-phase transition metal oxalates with different structures and compositions by simply adjusting the proportions of five transition metal elements. Among them, the multi-phase mixture (MC2O4·2H2O – CuC2O4 – MC2O4·2H2O, M = Mn, Fe, Co, Ni, Cu) provides a more stable framework for the material during lithiation and delithiation, effectively alleviating the structural collapse during the cycling process. In addition, the electron transport and fast charge compensation processes of multiple electrochemically active metal pairs also contribute to the improvement of performance. Therefore, the multi-phase transition metal oxalate TMOx-2 electrode with an additional CuC2O4 phase exhibits high reversible capacity and long-term cycling stability. After 400 cycles at 100 and 500 mA/g, the specific discharge capacities are 827 mAh/g and 498 mAh/g, respectively. Constructing multi-metal, multi-phase systems by combining different transition metals enables control over potential, reaction pathways, and stability of high-performance electrodes.

Supercapacitors are efficient and versatile energy storage devices, offering remarkable power density, fast charge/discharge rates, and exceptional cycle life. As research continues to push the boundaries of their performance, electrode fabrication techniques are critical aspects influencing the overall capabilities of supercapacitors. Herein, we aim to shed light on the advantages offered by dry electrode processing for advanced supercapacitors. Notably, our study explores the performance of these electrodes in three different types of electrolytes: organic, ionic liquids, and quasi-solid states. By examining the impact of dry electrode processing on various electrode and electrolyte systems, we show valuable insights into the versatility and efficacy of this technique. The supercapacitors employing dry electrodes demonstrated significant improvements compared with conventional wet electrodes, with a lifespan extension of +45% in organic, +192% in ionic liquids, and +84% in quasi-solid electrolytes. Moreover, the increased electrode densities achievable through the dry approach directly translate to improved volumetric outputs, enhancing energy storage capacities within compact form factors. Notably, dry electrode-prepared supercapacitors outperformed their wet electrode counterparts, exhibiting a higher energy density of 6.1 Wh cm−3 compared with 4.7 Wh cm−3 at a high power density of 195 W cm−3, marking a substantial 28% energy improvement in the quasi-solid electrolyte.

Currently, over 60% of the world's population lives in cities. Urban living has many advantages but there are also challenges regarding the need for smart urbanization. The next generation of tunable 2D nanomaterials, called MXenes, is the critical enabling technology that can bring the current urban thinking to the next level, called a smart city. The smart city is a novel concept based on a framework of self-sufficient technologies that are interactive and responsive to citizens’ needs. In this perspective, MXene-enabled technologies for sustainable urban development are discussed. They can advance self-sufficient, adaptive, and responsive buildings that can minimize resource consumption, solving the deficiency of essential resources such as clean energy, water, and air. MXenes are at the cutting edge of technological limitations associated with the Internet of Things (IoT) and telemedicine, combining diverse properties and offering multitasking. It is foreseen that MXenes can have a bright future in contributing to the smart city concept. Therefore, the roadmap is presented for demonstrating the practical feasibility of MXenes in the smart city. Altogether, this study promotes the role of MXenes in advancing the well-being of citizens by raising the quality of urban living to the next level.

A multi-scale model is crucial for combining experiments and simulations to reveal the energy storage mechanism. As novel electrode materials, conductive metal–organic frameworks (c-MOFs) provide an ideal platform for understanding the energy storage process in supercapacitors. However, the prevailing circuit models lack consideration of the distinctive transmission path of c-MOFs, which hinders accurate descriptions of c-MOF supercapacitors. By proposing a concept for representing the c-MOF electrode as a crystal–matrix electrode according to the crystallinity, we developed a universal multi-scale circuit model considering crystal shape and porosity to describe the impedance and capacitance of c-MOF electrodes. For supercapacitors with c-MOF electrodes and ionic liquid electrolytes, results predicted from the new multi-scale circuit model, based on microscale parameters obtained from molecular dynamics simulations, demonstrate quantitative agreement with experimental data for electrodes with different crystallinities.

The significant demand for energy storage systems has spurred innovative designs and extensive research on lithium-ion batteries (LIBs). To that end, an in-depth examination of utilized materials and relevant methods in conjunction with comparing electrochemical mechanisms is required. Lithium titanate (LTO) anode materials have received substantial interest in high-performance LIBs for numerous applications. Nevertheless, LTO is limited due to capacity fading at high rates, especially in the extended potential range of 0.01–3.00 V versus Li+/Li, while delivering the theoretical capacity of 293 mAh g−1. This study demonstrates how the performance of the LTO anode can be improved by modifying the manufacturing process. Altering the dry and wet mixing duration and speeds throughout the manufacturing process leads to differences in particle sizes and homogeneity of dispersion and structure. The optimized anode at 5 A g−1 (≈17C) and 10 A g−1 (≈34C) yielded 188 and 153 mAh g−1 and retained 73% and 68% of their initial capacity after 1000 cycles, respectively. The following findings offer valuable information regarding the empirical modifications required during electrode fabrication. Additionally, it sheds light on the potential to produce efficient anodes using commercial LTO powder.

As we turn the page to a new year, it is a fitting moment to reflect on 2024, a year marked by remarkable strides in sustainable energy research and innovation. Energy Advances has been privileged to serve as a platform for groundbreaking studies that aim to address critical global challenges in energy generation, storage, and sustainability. This editorial revisits some of the year’s highlights, celebrates key accomplishments, and looks ahead to the exciting prospects of 2025. In 2024, we were delighted to hold the Energy Advances Editorial Board meeting in person at our London office, Burlington House. The day was filled with exciting discussions about the success and future of the journal. We were also fortunate to have Editorial Board members Matthew Suss, Raymond Wong and Michael Naguib attending in person.

Materials containing imidazole have been used as promising substances in the fields of life sciences, environmental science, and electrochemistry. In this study, tailored core–shell particles that respond to acidic solutions and fluorine-containing hydrophobic anions were synthesized through starved-feed emulsion polymerization. Imidazole, which responds to proton acids and hydrophobic anions, was incorporated as a functional moiety into the shell of the particles. The soft and viscoelastic matrix was composed of the copolymer, poly((n-butyl acrylate)-co-(1-vinylimidazole)), allowing for control of the hydrodynamic diameter of the core–shell particles due to the balance between hydrophilic and hydrophobic properties. The size comparison of monodisperse particles in the colloid state was investigated using dynamic light scattering (DLS) and transmission electron microscopy (TEM). Changes in the glass transition temperature, depending on the copolymer ratio, were calculated using the Fox equation. The particles were melt-sheared after extrusion to produce viscoelastic opal films, arranging the particles into colloidal crystal stacks showing vivid structural colors. The optical features changed in response to acidic solutions and hydrophobic anions and were examined using in situ ultraviolet–visible (UV–vis) spectroscopy. The degree of hydrophilicity of the film was compared through contact angle measurements. The manufactured smart opal film can be applied as an affordable sensor that exhibits optical color changes in response to acidic pH and hydrophobic anions.