Electrochemical interfacial catalysis in Co-based battery electrodes involving spin-polarized electron transfer.

Interfacial catalysis occurs ubiquitously in electrochemical systems, such as batteries, fuel cells, and photocatalytic devices. Frequently, in such a system, the electrode material evolves dynamically at different operating voltages, and this electrochemically driven transformation usually dictates the catalytic reactivity of the material and ultimately the electrochemical performance of the device. Despite the importance of the process, comprehension of the underlying structural and compositional evolutions of the electrode material with direct visualization and quantification is still a significant challenge. In this work, we demonstrate a protocol for studying the dynamic evolution of the electrode material under electrochemical processes by integrating microscopic and spectroscopic analyses, operando magnetometry techniques, and density functional theory calculations. The presented methodology provides a real-time picture of the chemical, physical, and electronic structures of the material and its link to the electrochemical performance. Using Co(OH)2 as a prototype battery electrode and by monitoring the Co metal center under different applied voltages, we show that before a well-known catalytic reaction proceeds, an interfacial storage process occurs at the metallic Co nanoparticles/LiOH interface due to injection of spin-polarized electrons. Subsequently, the metallic Co nanoparticles act as catalytic activation centers and promote LiOH decomposition by transferring these interfacially residing electrons. Most intriguingly, at the LiOH decomposition potential, electronic structure of the metallic Co nanoparticles involving spin-polarized electrons transfer has been shown to exhibit a dynamic variation. This work illustrates a viable approach to access key information inside interfacial catalytic processes and provides useful insights in controlling complex interfaces for wide-ranging electrochemical systems.

Vertically assembled nanosheet networks for high-density thick battery electrodes.

As one of the prevailing energy storage systems, lithium-ion batteries (LIBs) have become an essential pillar in electric vehicles (EVs) during the past decade, contributing significantly to a carbon-neutral future. However, the complete transition to electric vehicles requires LIBs with yet higher energy and power densities. Here, we propose an effective methodology via controlled nanosheet self-assembly to prepare low-tortuosity yet high-density and high-toughness thick electrodes. By introducing a delicate densification in a three-dimensionally interconnected nanosheet network to maintain its vertical architecture, facile electron and ion transports are enabled despite their high packing density. This dense and thick electrode is capable of delivering a high volumetric capacity >1,600 mAh cm-3, with an areal capacity up to 32 mAh cm-2, which is among the best reported in the literature. The high-performance electrodes with superior mechanical and electrochemical properties demonstrated in this work provide a potentially universal methodology in designing advanced battery electrodes with versatile anisotropic properties.

Entropymetry for detecting microcracks in high-nickel layered oxide cathodes.

Electric vehicles (EVs) are imposing ever-challenging standards on the lifetime and safety of lithium-ion batteries (LIBs); consequently, real-time nondestructive monitoring of battery cell degradation is highly desired. Unfortunately, high-nickel (Ni) layered oxides, the preferred LIB cathodes for EVs, undergo performance degradation originating from microcrack formation during cycling. Entropymetry is introduced as a real-time analytic tool for monitoring the evolution of microcracks in these cathodes along the state of charge. The entropy change of the layered cathode is associated with the lattice configuration and reflects the structural heterogeneity relevant to the evolution of these microcracks. The structural heterogeneity was correlated with peak broadening in in-situ X-ray diffractometry while varying the experimental conditions that affect crack formation such as the upper cutoff voltage during charging and the Ni-content of the active material. Entropymetry, proposed here as a nondestructive diagnostic tool, can contribute greatly to the safe and reliable operation of LIBs for EVs.

Lithiating magneto-ionics in a rechargeable battery.

Magneto-ionics, real-time ionic control of magnetism in solid-state materials, promise ultralow-power memory, computing, and ultralow-field sensor technologies. The real-time ion intercalation is also the key state-of-charge feature in rechargeable batteries. Here, we report that the reversible lithiation/delithiation in molecular magneto-ionic material, the cathode in a rechargeable lithium-ion battery, accurately monitors its real-time state of charge through a dynamic tunability of magnetic ordering. The electrochemical and magnetic studies confirm that the structural vacancy and hydrogen-bonding networks enable reversible lithiation and delithiation in the magnetic cathode. Coupling with microwave-excited spin wave at a low frequency (0.35 GHz) and a magnetic field of 100 Oe, we reveal a fast and reliable built-in magneto-ionic sensor monitoring state of charge in rechargeable batteries. The findings shown herein promise an integration of molecular magneto-ionic cathode and rechargeable batteries for real-time monitoring of state of charge.

In situ visualization of multicomponents coevolution in a battery pouch cell.

Lithium-ion battery (LIB) is a broadly adopted technology for energy storage. With increasing demands to improve the rate capability, cyclability, energy density, safety, and cost efficiency, it is crucial to establish an in-depth understanding of the detailed structural evolution and cell-degradation mechanisms during battery operation. Here, we present a laboratory-based high-resolution and high-throughput X-ray micro-computed laminography approach, which is capable of in situ visualizing of an industry-relevant lithium-ion (Li-ion) pouch cell with superior detection fidelity, resolution, and reliability. This technique enables imaging of the pouch cell at a spatial resolution of 0.5 µm in a laboratory system and permits the identification of submicron features within cathode and anode electrodes. We also demonstrate direct visualization of the lithium plating in the imaged pouch cell, which is an important phenomenon relevant to battery fast charging and low-temperature cycling. Our development presents an avenue toward a thorough understanding of the correlation among multiscale structures, chemomechanical degradation, and electrochemical behavior of industry-scale battery pouch cells.

Lithiophilic Chemistry Facilitated Ultrathin Lithium for Scalable Prelithiation.

Prelithiation plays a crucial role in advancing the development of high-energy-density batteries, and ultrathin lithium (UTL) has been proven to be a promising anode prelithiation reagent. However, there remains a need to explore an adjustable, efficient, and cost-effective method for manufacturing UTL. In this study, we introduce a method for producing UTL with adjustable thicknesses ranging from 1.5 to 10 µm through blade coating of molten lithium on poly(vinylidene fluoride)-modified copper current collectors. By employing the transfer-printing method, prelithiated graphite and Si-C composite electrodes are prepared, which exhibit significantly improved initial Coulombic efficiencies of 99.60% and 99.32% in half-cells, respectively. Moreover, the energy densities of Li(NiCoMn)1/3O2 and LiFePO4 full cells assembled with the prelithiated graphite electrodes increase by 13.1% and 23.6%, respectively.

Ionic Pumping Effect at the Tailored Mesoporous Carbon Interface for an Extra-Stable Lithium Ion Battery at Low Temperatures.

Ion transportation at the interface significantly influences the electrochemical performance of the lithium ion battery, especially at high rates and low temperatures. Here, we develop a controlled self-assembly strategy for constructing a mesoporous carbon nanolayer with a uniform pore size and varied thicknesses on the two-dimensional monolayer MXene substrate. On the basis of the excellent electron conductivity of MXene, the mesoporous carbon layer is found with a voltage-driven ion accumulation effect, acting as an "ionic pump". The thicker mesoporous layer (∼2.28 nm) has the ability to accommodate a substantial quantity of ions, demonstrating enhanced ionic conductivity, remarkable cycling stability (192.8 mAh/g after 9400 cycles at 5.0 A/g), and outstanding rate capability at ambient and sub-zero temperatures (∼601 mAh/g at 0 °C and 0.05 A/g). This work provides valuable insights and guidance for the further development of high-performance electrode materials at high rates or low temperatures.

Cathode Electrolyte Interphase Engineering for Prussian Blue Analogues in Lithium-Ion Batteries.

The increasing use of low-cost lithium iron phosphate cathodes in low-end electric vehicles has sparked interest in Prussian blue analogues (PBAs) for lithium-ion batteries. A major challenge with iron hexacyanoferrate (FeHCFe), particularly in lithium-ion systems, is its slow kinetics in organic electrolytes and valence state inactivation in aqueous ones. We have addressed these issues by developing a polymeric cathode electrolyte interphase (CEI) layer through a ring-opening reaction of ethylene carbonate triggered by OH- radicals from structural water. This facile approach considerably mitigates the sluggish electrochemical kinetics typically observed in organic electrolytes. As a result, FeHCFe has achieved a specific capacity of 125 mAh g-1 with a stable lifetime over 500 cycles, thanks to the effective activation of Fe low-spin states and the structural integrity of the CEI layers. These advancements shed light on the potential of PBAs to be viable, durable, and efficient cathode materials for commercial use.

Reasonable Design and Deep Insight of Efficient Integrated Photorechargeable Li-Ion Batteries by Using a Cu/CuO/Cu2S Electrode.

Herein, Cu-foam-supported CuO nanowire arrays covered with Cu2S nanosheet substrates (Cu/CuO/Cu2S) are adopted as efficient photoelectrodes for photorechargeable lithium-ion batteries (PR-LIBs). The assembled PR-LIB exhibits remarkable solar energy conversion efficiency alongside superior lithium storage capabilities. Without an electrical power supply, the photocharged PR-LIB sustained a discharge process for 63.0 h under a constant current density of 0.05 mA cm-2. The corresponding solar-to-electrical energy conversion efficiency is 4.50%, which is an impressive achievement among recently reported contemporary technologies. Mechanism investigation shows that the Cu/CuO/Cu2S photogenerated carriers augment the extraction and insertion of Li+ according to different oxidation and reduction reactions in the charging and discharging reactions. This research delineates a refined model system and proposes innovative directions for developing efficient heterojunction photoelectrodes, significantly propelling the development of PR-LIB technology.

Balancing the Ion/Electron Transport of Graphite Anodes by a La-Doped TiNb2O7 Functional Coating for Fast-Charging Li-Ion Batteries.

A functional coating layer (FCL) is widely applied in fast-charging lithium-ion batteries to improve the sluggish Li+ transport kinetics of traditional graphite anodes. However, blindly increasing the Li+ conductivity for FCL reduces the overall electron conductivity of the anodes. Herein, we decoupled the effect of La-doping on TiNb2O7 (TNO) in terms of the phase evolution, Li+/electron transport, and lithiation behavior, and then proposed a promising La0.1TNO FCL with balanced Li+/electron transport for a fast-charging graphite anode. By optimizing the doping concentration of La, more holes are introduced into the TNO as electron carriers without causing lattice distortion, thus maintaining the fast Li+ diffusion channel in TNO. As a result, the graphite with La0.1TNO FCL delivers an excellent capacity of 220.2 mAh g-1 (96.3% retention) after 450 cycles at 3 C, nearly twice that of the unmodified one.

Photothermal Enhancement of Prussian Blue Cathodes for Li-Ion Batteries.

Photoenhanced batteries, where light improves the electrochemical performance of batteries, have gained much interest. Recent reports suggest that light-to-heat conversion can also play an important role. In this work, we study Prussian blue analogues (PBAs), which are known to have a high photothermal heating efficiency and can be used as cathodes for Li-ion batteries. PBAs were synthesized directly on a carbon collector electrode and tested under different thermally controlled conditions to show the effect of photothermal heating on battery performance. Our PBA electrodes reach temperatures that are 14% higher than reference electrodes using a blue LED, and a capacity enhancement of 38% was achieved at a current density of 1600 mA g-1. Additionally, these batteries show excellent cycling stability with a capacity retention of 96.6% in dark conditions and 94.8% in light over 100 cycles. Overall, this work shows new insights into the effects leading to improved battery performance in photobatteries.

Elucidating Heterogeneous Li Insertion Using Single-Crystalline and Freestanding Layered Oxide Thin Film.

The kinetics of interfacial ion insertion govern the uniformity of electrochemical reactions, playing a crucial role in lithium-ion battery performance. In two-dimensional lithium-conducting layered-oxide battery particles, variation in insertion rates across insertion channels remains unclear due to poorly defined crystal orientation at the solid-liquid interface and solid-state-lithium-diffusion length. This ambiguity complicates understanding inhomogeneous lithium-insertion channels activation. A systematic study requires crystallographically predefined interfaces and in situ lithium-concentration mapping. Here, we fabricated a freestanding, (104)-oriented-LiNi1/3Mn1/3Co1/3O2 single-crystal thin film using dissolution-induced release and performed in situ scanning-transmission-X-ray-microscopy to spatially resolve lithium-insertion at well-defined-interfaces. We observed heterogeneous lithium-concentration evolution due to channel-by-channel insertion rate variation, despite the potential for homogeneous lithium distribution via a solid-solution-phase at equilibrium in NMC111. Increasing current density exacerbates this heterogeneity, highlighting channel-by-channel variation. Our findings provide critical insights into battery electrode utilization and lifetime management, potentially guiding the design of more efficient and durable lithium-ion batteries.

Microcrystalline Nanofiber Electrode with Adaptive Intrinsic Structure and Microscopic Interface.

A strategy of microcrystalline aggregation is proposed to fabricate energy storage electrode with outstanding capacity and stability. Carbon-rich electrode (BDTG) functionalized with benzo[1,2-b:4,5-b']dithiophene units and butadiyne segments are prepared. The linear conjugate chains pack as microcrystalline nanofibers on nanoscale, which further aggregates to form a porous interpenetrating network. The microcrystalline aggregation feature of BDTG exhibit stable structure during long cycling test, revealing the following advantage in structure and property. The stretchable butadiyne linker facilitates reversible adsorption and desorption of Li with the aid of adjacent sulfur heteroatom. The alkyne-alkene transition exhibits intrinsic structural stability of microcrystalline region in BDTG electrodes. Meanwhile, alkynyl groups and sulfur heteroatoms on the surface of BDTG nanofibers participate in the formation of microscopic interface, providing a stable interfacial contact between BDTG electrodes and adjacent electrolyte. As a proof-of-concept, BDTG-based electrode shows high capacity (1430 mAh g-1 at 50 mA g-1) and excellent cycle performance (8000 cycles under 5 A g-1) in half-cell of lithium-ion batteries, and a reversible capacity of 120 mAh g-1 is obtained under the current density of 2 C in full-cell. This work shows microcrystalline aggregation is beneficial to realize adaptive intrinsic structure and interface contact during the charge-discharge process.

Understanding the Role of Imide-Based Salts and Borate-Based Additives for Safe and High-Performance Glyoxal-Based Electrolytes in Ni-Rich NMC811 Cathodes for Li-Ion Batteries.

Herein, the design of novel and safe electrolyte formulations for high-voltage Ni-rich cathodes is reported. The solvent mixture comprising 1,1,2,2-tetraethoxyethane and propylene carbonate not only displays good transport properties, but also greatly enhances the overall safety of the cell thanks to its low flammability. The influence of the conducting salts, that is, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), and of the additives lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFOB) is examined. Molecular dynamics simulations are carried out to gain insights into the local structure of the different electrolytes and the lithium-ion coordination. Furthermore, special emphasis is placed on the film-forming abilities of the salts to suppress the anodic dissolution of the aluminum  current collector and to create a stable cathode electrolyte interphase (CEI). In this regard, the borate-based additives significantly alleviate the intrinsic challenges associated with the use of LiTFSI and LiFSI salts. It is worth remarking that a superior cathode performance is achieved by using the LiFSI/LiDFOB electrolyte, displaying a high specific capacity of 164 mAh g-1 at 6 C and ca. 95% capacity retention after 100 cycles at 1 C. This is attributed to the rich chemistry of the generated CEI layer, as confirmed by ex situ X-ray photoelectron spectroscopy.

Silicon Nanowire Array Weaved by Carbon Chains for Stretchable Lithium-Ion Battery Anode.

To manufacture flexible batteries, it can be a challenge for silicon base anode materials to maintain structural integrity and electrical connectivity under bending and torsion conditions. In this work, 1D silicon nanowire array structures combined with flexible carbon chains consisting of short carbon nanofibers (CNFs) and long carbon nanotubes (CNTs) are proposed. The CNFs and CNTs serve as chain joints and separate chain units, respectively, weaving the well-ordered Si nanowire array into a robust and integrated configuration. The prepared flexible and stretchable silicon array anode exhibits excellent electrochemical performance during dynamic operation. A high initial specific capacity of 2856 mAh g-1 is achieved. After 1000 cycles, a capacity retention of 60% (1602 mAh g-1) is maintained. Additionally, the capacity attenuation is less than 1% after 100 bending cycles. This excellent cycling stability is obtained with a high Si loading of 6.92 mg cm-2. This novel approach offers great promise for the development of high-loading flexible energy-storage devices.

Emerging Processes for Sustainable Li-Ion Battery Cathode Recycling.

The colossal growth in the use of Li-ion batteries (LiBs) has raised serious concerns over the supply chain of strategic minerals, e.g., Co, Ni, and Li, that make up the cathode active materials (CAM). Recycling spent LiBs is an important step toward sustainability that can establish a circular economy by effectively tackling large amounts of e-waste while ensuring an unhindered supply of critical minerals. Among the various methods of LiB recycling available, pyro- and hydrometallurgy have been utilized in the industry owing to their ease of operation and high efficiency, although they are associated with significant environmental concerns. Direct recycling, a more recent concept that aims to relithiate spent LiBs without disrupting the lattice structure of the CAMs, has been realized only in the laboratory scale so far and further optimization is required before it can be extended to the bulk scale. Additionally, significant progress has been made in the areas of hydrometallurgy in terms of using ecofriendly green lixiviants and alternate sources of energy, e.g., microwave and electrochemical, that makes the recycling processes more efficient and sustainable. In this review, the latest developments in LiB recycling are discussed that have focused on environmental and economic viability, as well as process intensification. These include deep eutectic solvent based recycling, electrochemical and microwave-assisted recycling, and various types of direct recycling.

The Synergistic Effect of Aramid Nanofibers and Carbon Nanotubes on Micro-Silicon Anodes for Improved Stability and Conductivity.

Despite the continuous development of energy storage, the challenges faced by micro-silicon anode pulverization have yet to be effectively addressed. In this work, the aramid nanofibers (ANFs) are in situ protonated on the surface of silicon micro-particles (SMPs), and also act as surfactants to bundle the carbon nanotubes (CNTs) to form ANF/CNT networks on SMPs (ANF/CNT/SMPs) at the same time. The results demonstrate that the dual-coating not only inhibits expansion and enhances structural stability but also improves conductivity, thereby promoting the cycling stability of micro-silicon anodes. The ANF/CNT/SMP anode shows cycling stability of 454 mAh g-1 at 0.2 A g-1 after 200 cycles. The expansion in thickness of the ANF/CNT/SMP electrode can be reduced by 51.5% after 100 cycles compared with the SMP electrode. The findings provide a novel approach for mitigating expansion in micro-silicon anodes through the combined coating of ANFs and CNTs.

Breaking the Temperature Limit of Lithium-Ion Batteries With Carbon Nanotube-Based Electrodes and "Constructive Alliance" Electrolyte Strategy.

Lithium-ion batteries (LIBs) are paramount in energy storage in consumer electronics and electric vehicles. However, a narrow operating temperature range severely constrains their evolution. In this study, a wide-temperature operating LIB system is constructed utilizing carbon nanotube (CNT)-based electrodes and a "constructive alliance" electrolyte. The unique microstructure of the CNT current collector, with high electrical and thermal conductivity, accelerates the reaction kinetics of active materials at subzero temperatures and optimizes the thermal management of the entire electrode at elevated temperatures. Furthermore, a strategy employing the "constructive alliance" electrolyte is proposed, demonstrating that a simple combination of commercially available electrolytes can enhance resilience to harsh thermal conditions. Molecular dynamics simulations and density functional theory calculations reveal that the hybrid electrolyte predominantly adopts aggregate solvation structures and possesses low Li+ desolvation barriers regardless of thermal variations. Consequently, the assembled Li4Ti5O12//LiCoO2 full cell, with a negative/positive electrode material ratio of 1.2, exhibits outstanding electrochemical performance in the wide temperature range of -40 and 60 °C. This innovative strategy overcomes challenges in wide-temperature electrolyte research and offers promise for next-generation wide-temperature LIBs.

Mussel-Inspired Polymer Binders for Organic Electrodes.

The development of polymer binders is necessary to meet the growing demands of modern energy storage technologies. While catechol-containing materials are proven successful in silicon anodes, their application in organic batteries remains unexplored. In this contribution, the synthesis of four polymers are described with nearly identical side chain composition but varying backbone structures. The materials are used to investigate the effect of polymer backbone structure on the binding abilities of catechol-containing materials. Comparative analysis with the commonly used polyvinylidene fluoride (PVDF) binder aims to address two critical questions: 1) Can catechol-rich polymers replace PVDF for use in organic cathodes? and 2) Does the choice of polymer backbone affect the performance of the battery?. The investigation reveals that supramolecular interactions, such as π-π stacking and coordination bonding, are pivotal features of catechol binders. Among the catechol-rich polymers, the polyacrylate binder stands out, likely attributed to its high flexibility. Additionally, introducing an oxygen atom into a catechol-rich polynorbornene enhances lithium-ion conductivity and rate performance. Overall, the findings highlight the viability of catechol-containing polymers as organic cathode binders, and that the choice of polymer backbone is a crucial factor for their use as lithium-ion battery binder materials.

High-Performance Single-Crystal Lithium-Rich Layered Oxides Cathode Materials via Na2WO4-Assisted Sintering.

Single-crystal lithium-rich layered oxides (LLOs) with excellent mechanical properties can enhance their crystal structure stability. However, the conventional methods for preparing single-crystal LLOs, require large amounts of molten salt additives, involve complicated washing steps, and increase the difficulty of large-scale production. In this study, a sodium tungstate (Na2WO4)-assisted sintering method is proposed to fabricate high-performance single-crystal LLOs cathode materials without large amounts of additives and additional washing steps. During the sintering process, Na2WO4 promotes particle growth and forms a protective coating on the surface of LLOs particles, effectively suppressing the side reactions at the cathode/electrolyte interface. Additionally, trace amounts of Na and W atoms are doped into the LLOs lattice via gradient doping. Experimental results and theoretical calculations indicate that Na and W doping stabilizes the crystal structure and enhances the Li+ ions diffusion rate. The prepared single-crystal LLOs exhibit outstanding capacity retention of 82.7% (compared to 65.0%, after 200 cycles at 1 C) and a low voltage decay rate of 0.76 mV per cycle (compared to 1.80 mV per cycle). This strategy provides a novel pathway for designing the next-generation high-performance cathode materials for Lithium-ion batteries (LIBs).