Surface and interface engineering of electrode materials for lithium-ion batteries

Experimental and Theoretical Insights on Interface Engineered FeS/rGO as Anode for Fast-Charging Lithium- and Sodium-Ion Batteries

Interface engineering facilitates the development of stable energy storage devices that can endure the severe changes encountered during operation. In the context of fast-charging anodes for lithium- and sodium-ion batteries (LIBs and SIBs), the interface needs to promote charge/ion transfer processes, enhance Li-/Na-ion storage capacity, and ensure good reversibility in order to function efficiently at high rates. Herein, a simple synthetic strategy is reported to design interfaces between transition metal sulfides and carbonaceous supports to generate high-performance fast-charging anodes. FeS/rGO nanostructures are synthesized via a simple solid-state annealing method by employing FeOOH/rGO, a metastable precursor, which is annealed at 600 °C in the presence of H₂S gas. Interface engineering between FeS and rGO significantly improved the electrochemical performance, particularly demonstrated by stable capacities at high rates (625 mAh g⁻¹ at 5 A g⁻¹ for LIBs and 708 mAh g⁻¹ at 10 A g⁻¹ for SIBs). The high-rate charge storage is primarily governed by capacitive processes. Density functional theory (DFT) calculations attributed the enhanced performance of the FeS/rGO anode to a lower diffusion energy barrier for Li- and Na-ion diffusion at the interface along with the presence of a built-in electric field at the heterointerface.

Design principle of disordered rocksalt type overlithiated anode for high energy density batteries

Rechargeable lithium-ion batteries with high energy density and fast-charging capability are vital for commercial applications. Disordered rocksalt (DRX) materials with a cation/anion ratio greater than one, achieved through additional lithium insertion, have emerged as promising high-rate anode candidates. Inspired by the previously reported Li3+xV2O5 (0 ≤ x ≤ 2) anode, a comprehensive search was conducted for all potential redox centers using high-throughput density functional theory (DFT) computations. This study examined 23 redox centers in a prototype formula Li3+xV2O5 (0 ≤ x ≤ 2) with the DRX structure, analyzing aspects such as voltage curve, theoretical capacity, energy density, phase stability, electronic conductivity, and volumetric change during cycling. Promising candidates were identified with redox centers including V, Cr, Nb, Mn, and Fe, marking them as potential anode materials. Additionally, this research revealed the origin of the low voltage in DRX anodes and proposed a method to optimize the average voltage by tuning the relative energies among structures with varying lithium contents. This work provides compositional design principles for the new promising DRX anode of LIBs with high energy density, fast-charging capability, and good cycling stability.

Self-Assembled Molecular Layers as Interfacial Engineering Nanomaterials in Rechargeable Battery Applications

Rechargeable batteries have transformed human lives and modern industry, ushering in new technological advancements such as mobile consumer electronics and electric vehicles. However, to fulfill escalating demands, it is crucial to address several critical issues including energy density, production cost, cycle life and durability, temperature sensitivity, and safety concerns is imperative. Recent research has shed light on the intricate relationship between these challenges and the chemical processes occurring at the electrode-electrolyte interface. Consequently, a novel approach has emerged, utilizing self-assembled molecular layers (SAMLs) of meticulously designed molecules as nanomaterials for interface engineering. This research provides a comprehensive overview of recent studies underscoring the significant roles played by SAML in rechargeable battery applications. It discusses the mechanisms and advantageous features arising from the incorporation of SAML. Moreover, it delineates the remaining challenges in SAML-based rechargeable battery research and technology, while also outlining future perspectives.

Ultrasensitive electrochemical sensor based on synergistic effect of Ag@MXene and antifouling cyclic multifunctional peptide for PD-L1 detection in serum

A sensing interface co-constructed from the two-dimensional conductive material (Ag@MXene) and an antifouling cyclic multifunctional peptide (CP) is described. While the large surface area of Ag@MXene loads more CP probes, CP binds to Ag@MXene to form a fouling barrier and ensure the structural rigidity of the targeting sequence. This strategy synergistically enhances the biosensor's sensitivity and resistance to contamination. The SPR results showed that the binding affinity of the CP to the target was 6.23 times higher than that of the antifouling straight-chain multifunctional peptide (SP) to the target. In the 10 mg/mL BSA electrochemical fouling test, the fouling resistance of Ag@MXene + CP (composite sensing interface of CP combined with Ag@MXene) was 30 times higher than that of the bare electrode. The designed electrochemical sensor exhibited good selectivity and wide dynamic response range at PD-L1 concentrations from 0.1 to 50 ng/mL. The lowest detection limit was 24.54 pg/mL (S/N = 3). Antifouling 2D materials with a substantial specific surface area, coupled with non-straight chain antifouling multifunctional peptides, offer a wide scope for investigating the sensitivity and antifouling properties of electrochemical sensors.

Understanding the Role of Zinc Hydroxide Sulfate and its Analogues in Mildly Acidic Aqueous Zinc Batteries: A Review

Mildly acidic aqueous zinc batteries (AZBs) have attracted tremendous attention for grid storage applications with the expectation to tackle the issues of Li-ion batteries on high cost and poor safety. However, the performance, particularly energy density and cycle stability of AZBs are still unsatisfactory when compared with LIBs. To help the development of AZBs, a lot of effort have been made to understand the battery reaction mechanisms and precedent microscopic and spectroscopic analyses have shown flake-like large particles of zinc hydroxide sulfate (ZHS) and its analogues formed on the surfaces of cathodes and anodes in sulfate and other electrolyte systems during cycling. However, because of the complexity of the thermodynamics and kinetics of aqueous reactions to understand different battery conditions, controversies still exist. This article will review the roles of ZHS discussed in recent representative references aiming to shine light on the fundamental mechanisms of AZBs and pave ways to further improve the battery performance.

Chiral Molecular Coating of a LiNiCoMnO2 Cathode for High-Rate Capability Lithium-Ion Batteries

The growing demand for energy has increased the need for battery storage, with lithium-ion batteries being widely used. Among those, nickel-rich layered lithium transition metal oxides [LiNi1-x-yCoxMnyO2 NCM (1 - x - y > 0.5)] are some of the promising cathode materials due to their high specific capacities and working voltages. In this study, we demonstrate that a thin, simple coating of polyalanine chiral molecules improves the performance of Ni-rich cathodes. The chiral organic coating of the active material enhances the discharge capacity and rate capability. Specifically, NCM811 and NCM622 electrodes coated with chiral molecules exhibit lower voltage hysteresis and better rate performance, with a capacity improvement of >10% at a 4 C discharge rate and an average improvement of 6%. We relate these results to the chirally induced spin selectivity effect that enables us to reduce the resistance of the electrode interface and to reduce dramatically the overpotential needed for the chemical process by aligning the electron spins.

Advanced TiO2/Al2O3 Bilayer ALD Coatings for Improved Lithium-Rich Layered Oxide Electrodes

Surface modification is a highly effective strategy for addressing issues in lithium-rich layered oxide (LLO) cathodes, including phase transformation, particle cracking, oxygen gas release, and transition-metal ion dissolution. Existing single-/double-layer coating strategies face drawbacks such as poor component contact and complexity. Herein, we present the results of a low-temperature atomic layer deposition (ALD) process for creating a TiO2/Al2O3 bilayer on composite cathodes made of AS200 (Li1.08Ni0.34Co0.08Mn0.5O2). Electrochemical analysis demonstrates that TiO2/Al2O3-coated LLO electrodes exhibit improved discharge capacities and enhanced capacity retention compared with uncoated samples. The TAA-5/AS200 bilayer-coated electrode, in particular, demonstrates exceptional capacity retention (∼90.4%) and a specific discharge capacity of 146 mAh g-1 after 100 cycles at 1C within the voltage range of 2.2 to 4.6 V. The coated electrodes also show reduced voltage decay, lower surface film resistance, and improved interfacial charge transfer resistances, contributing to enhanced stability. The ALD-deposited TiO2/Al2O3 bilayer coatings exhibit promising potential for advancing the electrochemical performance of lithium-rich layered oxide cathodes in lithium-ion batteries.

Rational Design of Ion-Conductive Layer on Si Anode Enables Superior-Stable Lithium-Ion Batteries

Silicon (Si) is considered a promising commercial material for the next-generation of high-energy density lithium-ion battery (LIB) due to its high theoretical capacity. However, the severe volume changes and the poor conductivity hinder the practical application of Si anode. Herein, a novel core-shell heterostructure, Si as the core and V3 O4 @C as the shell (Si@V3 O4 @C), is proposed by a facile solvothermal reaction. Theoretical simulations have shown that the in-situ-formed V3 O4 layer facilitates the rapid Li+ diffusion and lowers the energy barrier of Li transport from the carbon shell to the inner core. The 3D network structure constructed by amorphous carbon can effectively improve electronic conductivity and structural stability. Benefiting from the rationally designed structure, the optimized Si@V3 O4 @C electrode exhibits an excellent cycling stability of 1061.1 mAh g-1 at 0.5 A g-1 over 700 cycles (capacity retention of 70.0%) with an average Coulombic efficiency of 99.3%. In addition, the Si@V3 O4 @C||LiFePO4 full cell shows a superior capacity retention of 78.7% after 130 cycles at 0.5 C. This study opens a novel way for designing high-performance silicon anode for advanced LIBs.

Quantification of the Carbon-Coating Effect on the Interfacial Behavior of Graphite Single Particles

The effect of carbon coating on the interfacial charge transfer resistance of natural graphite (NG) was investigated by a single-particle measurement. The microscale carbon-coated natural graphite (NG@C) particles were synthesized by the simple wet-chemical mixing method using a phenolic resin as the carbon source. The electrochemical test results of NG@C using the conventional composite electrodes demonstrated desirable rate capability, cycle stability, and enhanced kinetic property. Moreover, the improvements in the composite electrodes were confirmed with the electrochemical parameters (i.e., charge transfer resistance, exchange current density, and solid phase diffusion coefficient) analyzed by a single-particle measurement. The surface carbon coating on the NG particles reduced the interfacial charge transfer resistance (Rct) and increased the exchange current density (i0). The Rct decreased from 81-101 (NG) to 49-67 Ω cm2 (NG@C), while i0 increased from 0.25-0.32 (NG) to 0.38-0.52 mA cm-2 (NG@C) after the coating process. The results suggested both electrochemically and quantitatively that the outer uniformly coated surface carbon layer on the graphite particles can improve the solid-liquid interface and other kinetic parameters, therefore enhancing the rate capabilities to obtain the high-power anode materials.

Effects of Synthesis Conditions of Na0.44MnO2 Precursor on the Electrochemical Performance of Reduced Li2MnO3 Cathode Materials for Lithium-Ion Batteries

Li2MnO3 nanobelts have been synthesized via the molten salt method that used the Na0.44MnO2 nanobelts as both the manganese source and precursor template in LiNO3-LiCl eutectic molten salt. The electrochemical properties of Li2MnO3 reduced via a low-temperature reduction process as cathode materials for lithium-ion batteries have been measured and compared. Particularly investigated in this work are the effects of the synthesis conditions, such as reaction temperature, molten salt contents, and reaction time on the morphology and particle size of the synthesized Na0.44MnO2 precursor. Through repeated synthesis characterizations of the Na0.44MnO2 precursor, and comparing the electrochemical properties of the reduced Li2MnO3 nanobelts, the optimum conditions for the best electrochemical performance of the reduced Li2MnO3 are determined to be a molten salt reaction temperature of 850 °C and a molten salt amount of 25 g. When charge-discharged at 0.1 C (1 C = 200 mAh g-1) with a voltage window between 2.0 and 4.8 V, the reduced Li2MnO3 synthesized with reaction temperature of Na0.44MnO2 precursor at 850 °C and molten salt amounts of 25 g exhibits the best rate performance and cycling performance. This work develops a new strategy to prepare manganese-based cathode materials with special morphology.

Hierarchical porous loofah-like carbon with sulfhydryl functionality for electrochemical detection of trace mercury in water

Mercury is a common contaminant found in natural waters, which is highly toxic to human health. Thus, the facile and reliable monitoring of mercury in waters is of great significance. In this study, we fabricated a novel loofah-like hierarchical porous carbon with sulfhydryl functionality (S-LHC), and applied it as an ultrasensitive sensor for the electrochemical detection of mercury in water. The S-LHC was prepared through the direct pyrolysis of a triazole-rich metal-organic framework (MOF), followed by chemical modification using thioglycolic acid. The highly conductive N-doped carbon framework of S-LHC facilitated the electron transfer in mercury electrochemical sensing. Meanwhile, the open hierarchical pore structure and abundant sulfhydryl groups allowed the fast diffusion and effective enrichment of mercury ions. Consequently, the S-LHC sensor exhibited an exceptionally high sensitivity for mercury ions, with the mercury detection limit (0.36 nM) orders of magnitude lower than the regulated values in drinking water (typically 10∼30 nM). The constructed sensor also afforded good anti-interference ability and excellent stability for long-term detection of mercury in a variety of complex real water samples. The present study provides not only a facile method for mercury detection, but also a new idea for the construction of highly sensitive electrochemical sensors.

Turbulence induced shear controllable synthesis of nano FePO4 irregularly-shaped particles in a counter impinging jet flow T-junction reactor assisted by ultrasound irradiation

FePO4 (FP) particles with a mesoporous structure amalgamated by nanoscale primary crystals were controllably prepared using an ultrasound-intensified turbulence T-junction microreactor (UTISR). The use of this type of reaction system can effectively enhance the micro-mixing and remarkably improve the mass transfer and chemical reaction rates. Consequently, the synergistic effects of the impinging streams and ultrasonic irradiation on the formation of mesoporous structure of FP nanoparticles have been systematically investigated through experimental validation and CFD simulation. The results revealed that the FP particles with a mesoporous structure can be well synthesised by precisely controlling the operation parameters by applying ultrasound irradiation with the input power in the range of 0-900 W and the impinging stream volumetric flow rate in the range of 17.15-257.22 mL·min-1. The findings obtained from the experimental observation and CFD modelling has clearly indicated that there exists a strong correlation between the particle size, morphology, and the local turbulence shear. The application of ultrasonic irradiation can effectively intensify the local turbulence shear in the reactor even at low Reynolds number based on the impinging stream diameter (Re < 2000), leading to an effective reduction in the particle size (from 273.48 to 56.1 nm) and an increase in the specific surface area (from 21.97 to 114.97 m2·g-1) of FP samples. The FPirregularly-shaped particles prepared by UTISR exhibited a mesoporous structure with a particle size of 56.10 nm, a specific surface area of 114.97 m2·g-1and a total pore adsorption volume of 0.570 cm3·g-1 when the volumetric flow rate and ultrasound power are 85.74 mL·min-1and 600 W, respectively.

Recent advances in lithium-rich manganese-based cathodes for high energy density lithium-ion batteries

The development of society challenges the limit of lithium-ion batteries (LIBs) in terms of energy density and safety. Lithium-rich manganese oxide (LRMO) is regarded as one of the most promising cathode materials owing to its advantages of high voltage and specific capacity (more than 250 mA h g^-1) as well as low cost. However, the problems of fast voltage/capacity fading, poor rate performance and the low initial Coulombic efficiency severely hinder its practical application. In this paper, we review the latest research advances of LRMO cathode materials, including crystal structure, electrochemical reaction mechanism, existing problems and modification strategies. In this review, we pay more attention to recent progress in modification methods, including surface modification, doping, morphology and structure design, binder and electrolyte additives, and integration strategies. It not only includes widely studied strategies such as composition and process optimization, coating, defect engineering, and surface treatment, but also introduces many relatively novel modification methods, such as novel coatings, grain boundary coating, gradient design, single crystal, ion exchange method, solid-state batteries and entropy stabilization strategy. Finally, we summarize the existing problems in the development of LRMO and put forward some perspectives on the further research.

High-Rate Organic Cathode Constructed by Iron-Hexaazatrinaphthalene Tricarboxylic Acid Coordination Polymer for Li-Ion Batteries

The sluggish ion-transport in electrodes and low utilization of active materials are critical limitations of organic cathodes, which lead to the slow reaction dynamics and low specific capacity. In this study, the hierarchical tube is constructed by iron-hexaazatrinaphthalene tricarboxylic acid coordination polymer (Fe-HATNTA), using HATNTA as the self-engaged template to coordinate with Fe2+ ions. This Fe-HATNTA tube with hierarchical porous structure ensures the sufficient contact between electrolyte and active materials, shortens the diffusion distance, and provides more favorable transport pathways for ions. When employed as the cathode for rechargeable Li-ion batteries, Fe-HATNTA delivers a high specific capacity (244 mAh g-1 at 50 mA g-1 , 91% of theoretical capacity), excellent rate capability (128 mAh g-1 at 9 A g-1 ), and a long-term cycle life (73.9% retention over 3000 cycles at 5 A g-1 ). Moreover, the Li+ ions storage and conduction mechanisms are further disclosed by the ex situ and in situ characterizations, kinetic analyses, and theoretical calculations. This work is expected to boost further enthusiasm for developing the hierarchical structured metal-organic coordination polymers with superb ionic storage and transport as high-performance organic cathodes.

Dynamic Investigation of Battery Materials via Advanced Visualization: From Particle, Electrode to Cell Level

Li-ion batteries, the most-popular secondary battery, are typically electrochemical systems controlled by ion-insertion dynamics. The battery dynamics involve mass transport, charge transfer, ion-electron coupled reactions, electrolyte penetration, ion solvation, and interfacial evolution. However, it is difficult for the traditional electrochemical methods to capture the accurate and individual details of the dynamic processes in "black box" batteries; instead, only the net result of multi-factors on the whole scale. Recently, different advanced visualization techniques have been developed, which provide powerful tools to track and monitor the internal real-time dynamic processes, giving intuitive details and fine information at various scales from crystal lattice, single particle, electrode to cell level. Here, the recent progress on the investigation of electrochemical dynamics in battery materials are reviewed, via developed techniques across wide timescales and space-scales, including the dynamic process inside the active particle, kinetics issues at the electrode/electrolyte interface, dynamic inhomogeneity in the electrode, and dynamic transportation at the cell level. Finally, the fundamental principles to improve the battery dynamics are summarized and new technologies for future more stringent conditions are highlighted. In prospect, this review opens sight on the battery interior for a clearer, deeper, and more thorough understanding of the dynamics.

Structural Characteristics and Electrochemical Performance of N,P-Codoped Porous Carbon as a Lithium-Ion Battery Anode Electrode

Biomass-derived heteroatom-doped carbons have been considered to be excellent lithium ion battery (LIB) anode materials. Herein, ultrathin g-C₃N₄ nanosheets anchored on N,P-codoped biomass-derived carbon (N,P@C) were successfully fabricated by carbonization in an argon atmosphere. The structural characteristics of the resultant N,P@C were elucidated by SEM, TEM, FTIR, XRD, XPS, Raman, and BET surface area measurements. The results show that N,P@C has a high specific surface area (S _BET = 675.4 cm³/g), a mesoporous-dominant pore (average pore size of 6.898 nm), and a high level of defects (I _D/I _G = 1.02). The hierarchical porous structural properties are responsible for the efficient electrochemical performance of N,P@C as an anode material, which exhibits an outstanding reversible specific capacity of 1264.3 mAh/g at 100 mA/g, an elegant rate capability of 261 mAh/g at 10 A, and a satisfactory cycling stability of 1463.8 mAh/g at 1 A after 500 cycles. Because of the special structure and synergistic contributions from N and P heteroatoms, the resultant N,P@C endows LIBs with electrochemical performance superior to those of most of carbon-based anode materials derived from biomass in the literature. The findings in this present work pave a novel avenue toward lignin volarization to produce anode material for use in high-performance LIBs.

Crystallographically Textured Electrodes for Rechargeable Batteries: Symmetry, Fabrication, and Characterization

The vast of majority of battery electrode materials of contemporary interest are of a crystalline nature. Crystals are, by definition, anisotropic from an atomic-structure perspective. The inherent structural anisotropy may give rise to favored mesoscale orientations and anisotropic properties whether the material is in a rest state or subjected to an external stimulus. The overall perspective of this review is that intentional manipulation of crystallographic anisotropy of electrochemically active materials constitute an untapped parameter space in energy storage systems and thus provide new opportunities for materials innovations and design. To that end, we contend that crystallographically textured electrodes, as opposed to their textureless poly crystalline or single-crystalline analogs, are promising candidates for next-generation storage of electrical energy in rechargeable batteries relevant to commercial practice. This perspective is underpinned first by the fundamental─to a first approximation─uniaxial, rotation-invariant symmetry of electrochemical cells. On this basis, we show that a crystallographically textured electrode with the preferred orientation aligned out-of-plane toward the counter electrode represents an optimal strategy for utilization of the crystals' anisotropic properties. Detailed analyses of anisotropy of different types lead to a simple, but potentially useful general principle that "P_ec//P_c" textures are optimal for metal anodes, and "P_ec//S_c" textures are optimal for insertion-type electrodes.

Polyimide-derived carbon nanofiber membranes as free-standing anodes for lithium-ion batteries

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies. The influence of carbonization temperature on the physical-chemical characteristics of CNMs was investigated in detail. The electrochemical performances of CNMs as free-standing electrodes without any binder or conducting materials for lithium-ion batteries were also discussed. Furthermore, the surface state and internal carbon structure had an important effect on the nitrogen state, electrical conductivity, and wettability of CNMs, and then further affected the electrochemical performances. The CNMs/Li metal half-cells exhibited a satisfying charge–discharge cycle performance and excellent rate performance. They showed that the reversible specific capacity of CNMs carbonized at 700 °C could reach as high as 430 mA h g⁻¹ at 50 mA g⁻¹, and the value of the specific capacity remained at 206 mA h g⁻¹ after 500 cycles at a high current density of 1 A g⁻¹. Overall, the newly developed carbon nanofiber membranes will be a promising candidate for flexible electrodes used in high-power lithium-ion batteries, supercapacitors and sodium-ion batteries.

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies.

Competitive Doping Chemistry for Nickel-Rich Layered Oxide Cathode Materials

Chemical modification of electrode materials by heteroatom dopants is crucial for improving storage performance in rechargeable batteries. Electron configurations of different dopants significantly influence the chemical interactions inbetween and the chemical bonding with the host material, yet the underlying mechanism remains unclear. We revealed competitive doping chemistry of Group IIIA elements (boron and aluminum) taking nickel-rich cathode materials as a model. A notable difference between the atomic radii of B and Al accounts for different spatial configurations of the hybridized orbital in bonding with lattice oxygen. Density functional theory calculations reveal, Al is preferentially bonded to oxygen and vice versa, and shows a much lower diffusion barrier than B^III . In the case of Al-preoccupation, the bulk diffusion of B^III is hindered. In this way, a B-rich surface and Al-rich bulk is formed, which helps to synergistically stabilize the structural evolution and surface chemistry of the cathode.

Enabling the High-Voltage Operation of Layered Ternary Oxide Cathodes via Thermally Tailored Interphase

Layered ternary oxides LiNi_x Mn_y Co_z O₂ are promising cathode candidates for high-energy lithium-ion batteries (LIBs), but they usually suffer from the severe interfacial parasitic reactions at voltages above 4.3 V versus Li⁺ /Li, which greatly limit their practical capacities. Herein, using LiNi_1/3 Mn_1/3 Co_1/3 O₂ (NMC111) as the model system, a novel high-temperature pre-cycling strategy is proposed to realize its stable cycling in 3.0-4.5 V by constructing a robust cathode/electrolyte interphase (CEI). Specifically, performing the first five cycles of NMC111 at 55 °C helps to yield a uniform CEI layer enriched with fluorine-containing species, Li₂ CO₃ and poly(CO₃ ), which greatly suppresses the detrimental side reactions during extended cycling at 25 °C, endowing the cell with a capacity retention of 92.3% at 1C after 300 cycles, far surpassing 62.0% for the control sample without the thermally tailored CEI. This work highlights the critical role of temperature on manipulating the interfacial properties of cathode materials, opening a new avenue for developing high-voltage cathodes for Li-ion batteries.

Epitaxial growth of an atom-thin layer on a LiNi0.5Mn1.5O4 cathode for stable Li-ion battery cycling

Transition metal dissolution in cathode active material for Li-based batteries is a critical aspect that limits the cycle life of these devices. Although several approaches have been proposed to tackle this issue, this detrimental process is not yet overcome. Here, benefitting from the knowledge developed in the semiconductor research field, we apply an epitaxial method to construct an atomic wetting layer of LaTMO₃ (TM = Ni, Mn) on a LiNi_0.5Mn_1.5O₄ cathode material. Experimental measurements and theoretical analyses confirm a Stranski-Krastanov growth, where the strained wetting layer forms under thermodynamic equilibrium, and it is self-limited to monoatomic thickness due to the competition between the surface energy and the elastic energy. Being atomically thin and crystallographically connected to the spinel host lattices, the LaTMO₃ wetting layer offers long-term suppression of the transition metal dissolution from the cathode without impacting its dynamics. As a result, the epitaxially-engineered cathode material enables improved cycling stability (a capacity retention of about 77% after 1000 cycles at 290 mA g^-1) when tested in combination with a graphitic carbon anode and a LiPF₆-based non-aqueous electrolyte solution.

A limitation map of performance for porous electrodes in lithium-ion batteries

Driven by expanding interest in battery storage solutions and the success story of lithium-ion batteries, the research for the discovery and optimization of new battery materials and concepts is at peak. The generation of experimental (dis)charge data using coin cells is fast and feasible and proves to be a favorite practice in the battery research labs. The quantitative interpretation of the data, however, is not trivial and decelerates the process of screening and optimization of electrode materials and recipes. Here, we introduce the concept of polarographic map and demonstrate how it can be leveraged to quantify the contribution of different non-equilibrium phenomena to the performance limitation and total polarization of a lithium-ion cell. We showcase the accuracy and diagnostic power of this approach by preparing and analyzing the electrochemical performance of 54 sets of LiNixMnyCo1-x-yO2 electrodes with different formulations and designs discharged in a range of 0.2C-5C.

Iron-Based NASICON-Type Na4 Fe3 (PO4 )2 (P2 O7 ) Cathode for Zinc-Ion Battery: Zn2+ /Na+ Co-Intercalation Enabling High Capacity

The development of high-performance cathode materials for aqueous zinc-ion batteries (ZIBs) based on nontoxic and earth-abundant elements remains a great challenge. This study introduces the iron-based NASICON-type material Na₄ Fe₃ (PO₄ )₂ (P₂ O7) with carbon layer (NFPP@C) as a cathode material for ZIBs. When Zn²⁺ /Na⁺ dual ion electrolyte is employed, NFPP@C shows a high capacity of 114.4 mAh g^-1 with two voltage plateaus, excellent rate capability (95 mAh g^-1 at 2 A g^-1 ), and long-term cycling stability (66.4 mAh g^-1 after 1800 cycles at 1 A g^-1 ). The outstanding electrochemical performance is ascribed to the synergistic use of NFPP@C and dual ion electrolyte. The NASICON-structure and carbon layer of NFPP@C enable fast ion and electron transport, whereas Na⁺ in the electrolyte reduces the concentration gradient between the electrode and electrolyte, and thus inhibits excessive extraction of Na⁺ from NFPP, maintaining structural stability. Moreover, Zn²⁺ /Na⁺ co-intercalation in NFPP@C brings two potential platforms and enhanced capacity.

Crystal Channel Engineering for Rapid Ion Transport: From Nature to Batteries

Ion transport behaviours through cell membranes are commonly identified in biological systems, which are crucial for sustaining life for organisms. Similarly, ion transport is significant for electrochemical ion storage in rechargeable batteries, which has attracted much attention in recent years. Rapid ion transport can be well achieved by crystal channels engineering, such as creating pores or tailoring interlayer spacing down to the nanometre or even sub-nanometre scale. Furthermore, some functional channels, such as ion selective channels and stimulus-responsive channels, are developed for smart ion storage applications. In this review, the typical ion transport phenomena in the biological systems, including ion channels and pumps, are first introduced, and then ion transport mechanisms in solid and liquid crystals are comprehensively reviewed, particularly for the widely studied porous inorganic/organic hybrid crystals and ultrathin inorganic materials. Subsequently, recent progress on the ion transport properties in electrodes and electrolytes is reviewed for rechargeable batteries. Finally, current challenges in the ion transport behaviours in rechargeable batteries are analysed and some potential research approaches, such as bioinspired ultrafast ion transport structures and membranes, are proposed for future studies. It is expected that this review can give a comprehensive understanding on the ion transport mechanisms within crystals and provide some novel design concepts on promoting electrochemical ion storage capability in rechargeable batteries.

Synthesis of truncated octahedral zinc-doped manganese hexacyanoferrates and low-temperature calcination activation for lithium-ion battery

Owing to their open three-dimensional framework structure, Prussian blue analogues (PBAs) have attracted increasing interest as anode materials for future lithium-ion batteries (LIBs). However, some disadvantages, such as inferior stability and short cycle life, hinder its utilization significantly. Hence, we develop a simple method to prepare a unique truncated octahedral ZnMnFe-PBA with exposed {111} crystal facets. The doping of Zn into Mn-based PBA enhances structural stability and improves the electronic conductivity. Meanwhile, low-temperature calcination not only improves the electrochemical activity but also preserves the porosity to enable mass transfer. When the ratio of Mn:Zn is 90:10 and the calcination temperature is 100 °C, sample Z10-100 displays high capacity and excellent cycle life (∼510.6 mA h g^-1 at 0.1 A g^-1, 168.9 mA h g^-1 after 5000 cycles at 1.0 A g^-1 with 99.9% capacity retention). The significant improvements in cycle stability and cycle life are attributable to transition metal ion doping and effective low-temperature calcination activation, which provide a facile approach for the synthesis of low-cost and efficient electrode materials.

Influence of Carbonate Solvents on Solid Electrolyte Interphase Composition over Si Electrodes Monitored by In Situ and Ex Situ Spectroscopies

A solid electrolyte interphase (SEI) layer on Si-based anodes should have high mechanical properties to adapt the volume changes of Si with low thickness and good ionic conductivity. To better understand the influence of carbonate solvents on the SEI composition and mechanism of formation, systematic studies were performed using dimethyl carbonate (DMC) or propylene carbonate (PC) solvent and LiPF₆ as a salt. A 1 M LiPF₆/EC-DMC was used for comparison. The surface chemical composition of the Si electrode was analyzed at different potentials of lithiation/delithiation and after a few cycles. Ex situ X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry results demonstrate that a thinner and more stable SEI layer is formed in LiPF₆/DMC. The in situ Fourier transform infrared spectroscopy proves that the coordination between Li⁺ and DMC is weaker, and fewer DMC molecules take part in the formation of the SEI layer. The higher capacity retention during 60 cycles and less significant morphological modifications of the Si electrode in 1 M LiPF₆/DMC compared to other electrolytes were demonstrated, confirming a good and stable interfacial layer. The possible surface reactions are discussed, and the difference in the mechanisms of formation of SEI in these three various electrolytes is proposed.

Se4P4nanoparticles confined within porous carbon as a lithium-ion battery anode with superior electrochemical performance

The exploration of advanced anode materials through rational structure/phase design is the key to developing high-performance rechargeable batteries. Herein, tetraphosphorus tetraselenide (Se₄P₄) nanoparticles confined within porous carbon (named SeP@C) are developed for lithium-ion batteries. The designed SeP@C shows a set of structural/compositional advantages as lithium-ion battery anodes including high electrical conductivity, low ion diffusion barrier, and relieved lithiation stress. Consequently, the SeP@C electrode displays superior comprehensive lithium storage performance, e.g., high reversible capacity (640.8 mA h g^-1at 0.1 A g^-1), excellent cycling stability (500 cycles with respective capacity retention of over or nearly 100%), and good rate capability, representing a comparable lithium storage performance in reported phosphide-based anodes. More significantly, it shows excellent energy storage properties in lithium-ion full cells which can light up 85 red LEDs for over 3.2 h. This work offers an advanced electrode construction guidance of phosphorous-based anodes for the development of high-performance energy storage devices.

Nanocomposite of ultra-small MoO2 embedded in nitrogen-doped carbon: In situ derivation from an organic molybdenum complex and its superior Li-Ion storage performance

MoO₂ is a promising anode material for lithium-ion batteries, however, the lithiation of bulk MoO₂ is usually limited to addition-type reaction at room temperature, and the conversion reaction is hindered because of the sluggish kinetics. Herein, a nanocomposite of MoO₂ embedded in nitrogen-doped carbon (MoO₂/NC) is synthesized through the in situ thermolysis of an organic molybdenum complex MoO₂(acac)(phen) (acac = acetylacetone, phen = 1,10-Phenanthroline). Owing to the fact that [MoO₂]²⁺ can be strongly chelated by phen, the molybdenum source in the MoO₂(acac)(phen) precursor is highly dispersed, leading to the formation of ultra-small MoO₂ nanoparticles in the nanocomposite, which can facilitate the conversion reaction. Moreover, the NC matrix can guarantee a high electrical conductivity and effectively accommodate the volume changes triggered by the conversion reaction. Consequently, the MoO₂/NC nanocomposite exhibits outstanding electrochemical properties, including large reversible capacity of 950 mA h g^-1 at 0.1 A g^-1, high-rate capability of 605 mA h g^-1 at 2 A g^-1, and excellent cycling stability over 500 cycles as an anode material for lithium-ion batteries.

3D tremella-like nitrogen-doped carbon encapsulated few-layer MoS2 for lithium-ion batteries

MoS₂ is regarded as an attractive anode material for lithium-ion batteries due to its layered structure and high theoretical specific capacity. Its unsatisfied conductivity and the considerable volume change during the charge and discharge process, however, limits its rate performance and cycling stability. Herein, 3D tremella-like nitrogen-doped carbon encapsulated few-layer MoS₂ (MoS₂@NC) hybrid is obtained via a unique strategy with simultaneously poly-dopamine carbonization, and molybdenum oxide specifies sulfurization. The three-dimensional porous nitrogen-doped carbon served both as a mechanical supporting structure for stabilization of few-layers MoS₂ and a good electron conductor. The MoS₂@NC exhibits enhanced high rate performance with a specific capacity of 208.7 mAh g^-1 at a current density of 10 A g^-1 and stable cycling performance with a capacity retention rate of 85.7% after 1000 cycles at 2 A g^-1.

Optimized atomic layer deposition of homogeneous, conductive Al2O3 coatings for high-nickel NCM containing ready-to-use electrodes

Atomic layer deposition (ALD) derived ultrathin conformal Al₂O₃ coating has been identified as an effective strategy for enhancing the electrochemical performance of Ni-rich LiNi_xCo_yMn_zO₂ (NCM; 0 ≤x, y, z < 1) based cathode active materials (CAM) in Li-ion batteries. However, there is still a need to better understand the beneficial effect of ALD derived surface coatings on the performance of NCM based composite cathodes. In this work, we applied and optimized a low-temperature ALD derived Al₂O₃ coating on a series of Ni-rich NCM-based (NCM622, NCM71.51.5 and NCM811) ready-to-use composite cathodes and investigated the effect of coating on the surface conductivity of the electrode as well as its electrochemical performance. A highly uniform and conformal coating was successfully achieved on all three different cathode compositions under the same ALD deposition conditions. All the coated cathodes were found to exhibit an improved electrochemical performance during long-term cycling under moderate cycling conditions. The improvement in the electrochemical performance after Al₂O₃ coating is attributed to the suppression of parasitic side reactions between the electrode and the electrolyte during cycling. Furthermore, conductive atomic force microscopy (C-AFM) was performed on the electrode surface as a non-destructive technique to determine the difference in surface morphology and conductivity between uncoated and coated electrodes before and after cycling. C-AFM measurements on pristine cathodes before cycling allow clear separation between the conductive carbon additives and the embedded NCM secondary particles, which show an electrically insulating behavior. More importantly, the measurements reveal that the ALD-derived Al₂O₃ coating with an optimized thickness is thin enough to retain the original conduction properties of the coated electrodes, while thicker coating layers are insulating resulting in a worse cycling performance. After cycling, the surface conductivity of the coated electrodes is maintained, while in the case of uncoated electrodes the surface conductivity is completely suppressed confirming the formation of an insulating cathode electrolyte interface due to the parasitic side reactions. The results not only show the possibilities of C-AFM as a non-destructive evaluation of the surface properties, but also reveal that an optimized coating, which preserves the conductive properties of the electrode surface, is a crucial factor for stabilising the long-term battery performance.

Atomic/molecular layer deposition for energy storage and conversion

Energy storage and conversion systems, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting, have played vital roles in the reduction of fossil fuel usage, addressing environmental issues and the development of electric vehicles. The fabrication and surface/interface engineering of electrode materials with refined structures are indispensable for achieving optimal performances for the different energy-related devices. Atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques, the gas-phase thin film deposition processes with self-limiting and saturated surface reactions, have emerged as powerful techniques for surface and interface engineering in energy-related devices due to their exceptional capability of precise thickness control, excellent uniformity and conformity, tunable composition and relatively low deposition temperature. In the past few decades, ALD and MLD have been intensively studied for energy storage and conversion applications with remarkable progress. In this review, we give a comprehensive summary of the development and achievements of ALD and MLD and their applications for energy storage and conversion, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting. Moreover, the fundamental understanding of the mechanisms involved in different devices will be deeply reviewed. Furthermore, the large-scale potential of ALD and MLD techniques is discussed and predicted. Finally, we will provide insightful perspectives on future directions for new material design by ALD and MLD and untapped opportunities in energy storage and conversion.

Understanding the Dual-Phase Synergy Mechanism in Mn2O3-Mn3O4 Catalyst for Efficient Li-CO2 Batteries

Rechargeable Li-CO₂ batteries have been receiving intense interest because of their high theoretical energy density and environmentally friendly CO₂ fixation ability. However, due to the sluggish CO₂ reduction/evolution reaction (CRR/CER) kinetics, the current Li-CO₂ batteries still suffer from severe polarization and poor cycling stability. Herein, we designed and in situ synthesized sea urchinlike Mn₂O₃-Mn₃O₄ nanocomposite and explored the synergistic effect between Mn₂O₃ and Mn₃O₄ during charge-discharge process in Li-CO₂ batteries. It is found that Mn₃O₄ can effectively promote the kinetics of CRR process, and Mn₂O₃ can induce the nucleation of Li₂CO₃ and promote its decomposition (CER). Benefiting from the dual-phase synergy, the Mn₂O₃-Mn₃O₄ cathode combines the respective catalytic advantages of the both and delivers a high full discharge capacity of 19 024 mAh g^-1, a low potential gap of 1.24 V, and durable cycling stability (1380 h) at a current density of 100 mA g^-1. Moreover, based on experimental results and density functional theory (DFT) calculations, a charge-discharge process model of the Mn₂O₃-Mn₃O₄ cathode was established to display the electrochemical reaction mechanism. We hope that this design strategy can encourage further studies for efficient cathode catalysts to accelerate the practical application of Li-CO₂ batteries and even the metal-air batteries.

Interface engineering of Co3O4 nanowire arrays with ultrafine NiO nanowires for high-performance rechargeable alkaline batteries

Interface engineering multi-component core-shell nanostructures with highly efficient and reversible faradaic reactions for energy conversion storage devices is still a challenge. Here, Co₃O₄ nanowires@NiO ultrafine nanowires on Ni foam were well fabricated via coating the NiO ultrafine nanowires on porous Co₃O₄ nanowire arrays. The combination of structural and compositional advantages endows the Co₃O₄@NiO core-shell composites with excellent electrochemical performance, such as a favorable specific capacity of 0.71 mA h cm^-2 at 3 mA cm^-2, excellent rate capability and 85% retention rate up to 10,000 cycles. Rechargeable alkaline batteries with the Co₃O₄@NiO core-shell composites and AC as cathode and anode, respectively, had a high specific capacity of 0.51 mA h cm^-2 and stable cycling ability (81% retention after 5000 cycles). The hierarchical core-shell heterostructure electrode exhibits excellent electrochemical performance, making it a very promising material for next-generation energy storage device applications.

Hierarchical Fusiform Microrods Constructed by Parallelly Arranged Nanoplatelets of LiCoO2 Material with Ultrahigh Rate Performance

The past few decades have witnessed the unprecedented success of the commercialized LiCoO₂ layered cathode in consumer electronics, but it still faces the poor rate capability and cycling performance because of its hexagonal layered α-NaFeO₂ structure and the high energy of electrochemically active crystal planes. In a bid to address these problems, we report the delicate design and synthesis of hierarchical fusiform LiCoO₂ microrods constructed by directionally assembled nanoplatelets along the [001] direction via a self-template route (PAHF-LCO). Remarkably, it is the first time that almost all the exposed surfaces of layered cathodes are dominated by the consistent {010} facets, which enable the express channels of Li⁺ diffusion to penetrate throughout the entire fusiform microrods. The as-obtained PAHF-LCO cathode material delivers specific capacities of 113 and 106 mA h g^-1 at 10 and 20 C after 200 cycles, respectively. Even under the high rate of 50 C, the discharge capacity initializes around 105 mA h g^-1 and ends around 80 mA h g^-1 after 200 cycles. The improvement mechanisms to the high-rate performance through crystal habit tuning have also been unraveled. The enhanced electrochemical performance can be attributed to the hierarchical fusiform structure as well as the coordinated crystal orientation of {010} facets.

Lithium-Oxygen Batteries and Related Systems: Potential, Status, and Future

The goal of limiting global warming to 1.5 °C requires a drastic reduction in CO₂ emissions across many sectors of the world economy. Batteries are vital to this endeavor, whether used in electric vehicles, to store renewable electricity, or in aviation. Present lithium-ion technologies are preparing the public for this inevitable change, but their maximum theoretical specific capacity presents a limitation. Their high cost is another concern for commercial viability. Metal-air batteries have the highest theoretical energy density of all possible secondary battery technologies and could yield step changes in energy storage, if their practical difficulties could be overcome. The scope of this review is to provide an objective, comprehensive, and authoritative assessment of the intensive work invested in nonaqueous rechargeable metal-air batteries over the past few years, which identified the key problems and guides directions to solve them. We focus primarily on the challenges and outlook for Li-O₂ cells but include Na-O₂, K-O₂, and Mg-O₂ cells for comparison. Our review highlights the interdisciplinary nature of this field that involves a combination of materials chemistry, electrochemistry, computation, microscopy, spectroscopy, and surface science. The mechanisms of O₂ reduction and evolution are considered in the light of recent findings, along with developments in positive and negative electrodes, electrolytes, electrocatalysis on surfaces and in solution, and the degradative effect of singlet oxygen, which is typically formed in Li-O₂ cells.