Origin of structural degradation in Li-rich layered oxide cathode.

Li- and Mn-rich (LMR) cathode materials that utilize both cation and anion redox can yield substantial increases in battery energy density1-3. However, although voltage decay issues cause continuous energy loss and impede commercialization, the prerequisite driving force for this phenomenon remains a mystery3-6 Here, with in situ nanoscale sensitive coherent X-ray diffraction imaging techniques, we reveal that nanostrain and lattice displacement accumulate continuously during operation of the cell. Evidence shows that this effect is the driving force for both structure degradation and oxygen loss, which trigger the well-known rapid voltage decay in LMR cathodes. By carrying out micro- to macro-length characterizations that span atomic structure, the primary particle, multiparticle and electrode levels, we demonstrate that the heterogeneous nature of LMR cathodes inevitably causes pernicious phase displacement/strain, which cannot be eliminated by conventional doping or coating methods. We therefore propose mesostructural design as a strategy to mitigate lattice displacement and inhomogeneous electrochemical/structural evolutions, thereby achieving stable voltage and capacity profiles. These findings highlight the significance of lattice strain/displacement in causing voltage decay and will inspire a wave of efforts to unlock the potential of the broad-scale commercialization of LMR cathode materials.

Nanoscale Ultrafine Zinc Metal Anodes for High Stability Aqueous Zinc Ion Batteries.

Aqueous Zn batteries (AZBs) are a promising energy storage technology, due to their high theoretical capacity, low redox potential, and safety. However, dendrite growth and parasitic reactions occurring at the surface of metallic Zn result in severe instability. Here we report a new method to achieve ultrafine Zn nanograin anodes by using ethylene glycol monomethyl ether (EGME) molecules to manipulate zinc nucleation and growth processes. It is demonstrated that EGME complexes with Zn2+ to moderately increase the driving force for nucleation, as well as adsorbs on the Zn surface to prevent H-corrosion and dendritic protuberances by refining the grains. As a result, the nanoscale anode delivers high Coulombic efficiency (ca. 99.5%), long-term cycle life (over 366 days and 8800 cycles), and outstanding compatibility with state-of-the-art cathodes (ZnVO and AC) in full cells. This work offers a new route for interfacial engineering in aqueous metal-ion batteries, with significant implications for the commercial future of AZBs.

Correlating Rate-Dependent Transition Metal Dissolution between Structure Degradation in Li-Rich Layered Oxides.

Understanding the mechanism of the rate-dependent electrochemical performance degradation in cathodes is crucial to developing fast charging/discharging cathodes for Li-ion batteries. Here, taking Li-rich layered oxide Li1.2 Ni0.13 Co0.13 Mn0.54 O2 as the model cathode, the mechanisms of performance degradation at low and high rates are comparatively investigated from two aspects, the transition metal (TM) dissolution and the structure change. Quantitative analyses combining spatial-resolved synchrotron X-ray fluorescence (XRF) imaging, synchrotron X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques reveal that low-rate cycling leads to gradient TM dissolution and severe bulk structure degradation within the individual secondary particles, and especially the latter causes lots of microcracks within secondary particles, and becomes the main reason for the fast capacity and voltage decay. In contrast, high-rate cycling leads to more TM dissolution than low-rate cycling, which concentrates at the particle surface and directly induces the more severe surface structure degradation to the electrochemically inactive rock-salt phase, eventually causing a faster capacity and voltage decay than low-rate cycling. These findings highlight the protection of the surface structure for developing fast charging/discharging cathodes for Li-ion batteries.

LiMgPO4 -Coating-Induced Phosphate Shell and Bulk Mg-Doping Enables Stable Ultra-High-Voltage Cycling of LiCoO2 Cathode.

Stable cycling of LiCoO2 (LCO) cathode at high voltage is extremely challenging due to the notable structural instability in deeply delithiated states. Here, using the sol-gel coating method, LCO materials (LMP-LCO) are obtained with bulk Mg-doping and surface LiMgPO4 /Li3 PO4 (LMP/LPO) coating. The experimental results suggest that the simultaneous modification in the bulk and at the surface is demonstrated to be highly effective in improving the high-voltage performance of LCO. LMP-LCO cathodes deliver 149.8 mAh g-1 @4.60 V and 146.1 mAh g-1 @4.65 V after 200 cycles at 1 C. For higher cut-off voltages, 4.70 and 4.80 V, LMP-LCO cathodes still achieve 144.9 mAh g-1 after 150 cycles and 136.8 mAh g-1 after 100 cycles at 1 C, respectively. Bulk Mg-dopants enhance the ionicity of CoO bond by tailoring the band centers of Co 3d and O 2p, promoting stable redox on O2- , and thus enhancing stable cycling at high cut-off voltages. Meanwhile, LMP/LPO surface coating suppresses detrimental surface side reactions while allowing facile Li-ion diffusion. The mechanism of high-voltage cycling stability is investigated by combining experimental characterizations and theoretical calculations. This study proposes a strategy of surface-to-bulk simultaneous modification to achieve superior structural stability at high voltages.

Mitigating Jahn-Teller Effect in Layered Cathode Material Via Interstitial Doping for High-Performance Sodium-Ion Batteries.

Layered transition metal oxides are promising cathode materials for sodium-ion batteries due to their high energy density and appropriate operating potential. However, the poor structural stability is a major drawback to their widespread application. To address this issue, B3+ is successfully introduced into the tetrahedral site of Na0.67 Fe0.5 Mn0.5 O2 , demonstrating the effectiveness of small-radius ion doping in improving electrochemical performance. The obtained Na0.67 Fe0.5 Mn0.5 B0.04 O2 exhibits excellent cycling performance with 88.8% capacity retention after 100 cycles at 1 C and prominent rate performance. The structure-property relationship is constructed subsequently by neutron powder diffraction, in situ X-ray diffraction and X-ray absorption spectroscopy, which reveal that the Jahn-Teller distortion and the consequent P2-P2' phase transformation are effectively mitigated because of the occupancy of B3+ at the interstitial site. Furthermore, it is found that the transition metal layers are stabilized and the transition metal dissolution are suppressed, resulting in excellent cycling performance. Besides, the prominent rate performance is attributed to the enhanced diffusion kinetics associated with the rearrangement of Na+ . This work provides novel insight into the action mechanism of interstitial site doping and demonstrates a universal approach to improve the electrochemical properties of P2-type manganese-based sodium cathode materials.

Promoting Surface Electric Conductivity for High-Rate LiCoO2.

The cathode materials work as the host framework for both Li+ diffusion and electron transport in Li-ion batteries. The Li+ diffusion property is always the research focus, while the electron transport property is less studied. Herein, we propose a unique strategy to elevate the rate performance through promoting the surface electric conductivity. Specifically, a disordered rock-salt phase was coherently constructed at the surface of LiCoO2 , promoting the surface electric conductivity by over one magnitude. It increased the effective voltage (Veff ) imposed in the bulk, thus driving more Li+ extraction/insertion and making LiCoO2 exhibit superior rate capability (154 mAh g-1 at 10 C), and excellent cycling performance (93 % after 1000 cycles at 10 C). The universality of this strategy was confirmed by another surface design and a simulation. Our findings provide a new angle for developing high-rate cathode materials by tuning the surface electron transport property.

Simultaneous Formation of Interphases on both Positive and Negative Electrodes in High-Voltage Aqueous Lithium-Ion Batteries.

The formation of solid-electrolyte interphase (SEI) in "water-in-salt" electrolyte (WiSE) expands the electrochemical stability window of aqueous electrolytes beyond 3.0 V. However, the parasitic hydrogen evolution reaction that drives anode corrosion, cracking, and the subsequent reformation of SEI still occurs, compromising long-term cycling performance of the batteries. To improve cycling stability, an unsaturated monomer acrylamide (AM) is introduced as an electrolyte additive, whose presence in WiSE reduces its viscosity and improves ionic conductivity. Upon charging, AM electropolymerizes into polyacrylamide, as confirmed both experimentally and computationally. The in situ polymer constitutes effective protection layers at both anode and cathode surfaces, and enables LiMn2 O4 ||L-TiO2 full cells with high specific capacity (157 mAh g-1 at 1 C), long-term cycling stability (80% capacity retention within 200 cycles at 1 C), and high rate capability (79 mAh g-1 at 30 C). The in situ electropolymerization found in this work provides an alternative and highly effective strategy to design protective interphases at the negative and positive electrodes for high-voltage aqueous batteries of lithium-ion or beyond.

Boosting the Energy Density of Aqueous Batteries via Facile Grotthuss Proton Transport.

The recent developments in rechargeable aqueous batteries have witnessed a burgeoning interest in the mechanism of proton transport in the cathode materials. Herein, for the first time, we report the Grotthuss proton transport mechanism in α-MnO2 which features wide [2×2] tunnels. Exemplified by the substitution doping of Ni (≈5 at.%) in α-MnO2 that increases the energy density of the electrode by ≈25 %, we reveal a close link between the tetragonal-orthorhombic (TO) distortion of the lattice and the diffusion kinetics of protons in the tunnels. Experimental and theoretical results verify that Ni dopants can exacerbate the TO distortion during discharge, thereby facilitating the hydrogen bond formation in bulk α-MnO2 . The isolated direct hopping mode of proton transport is switched to a facile concerted mode, which involves the formation and concomitant cleavage of O-H bonds in a proton array, namely via Grotthuss proton transport mechanism. Our study provides important insight towards the understanding of proton transport in MnO2 and can serve as a model for the compositional design of cathode materials for rechargeable aqueous batteries.

Unravelling H+ /Zn2+ Synergistic Intercalation in a Novel Phase of Manganese Oxide for High-Performance Aqueous Rechargeable Battery.

Aqueous Zn-MnO2 batteries using mild electrolyte show great potential in large-scale energy storage (LSES) application, due to high safety and low cost. However, structure collapse of manganese oxides upon cycling caused by the conversion mechanism (e.g., from tunnel to layer structures for α-, ß-, and γ-phases) is one of the most urgent issues plaguing its practical applications. Herein, to avoid the phase conversion issue and enhance battery performance, a structurally robust novel phase of manganese oxide MnO2 H0.16 (H2 O)0.27 (MON) nanosheet with thickness of ≈2.5 nm is designed and synthesized as a promising cathode material, in which a nanosheet structure combined with a novel H+ /Zn2+ synergistic intercalation mechanism is demonstrated and evidenced. Accordingly, a high-performance Zn/MON cell is achieved, showing a high energy density of ≈228.5 Wh kg-1 , impressive cyclability with capacity retention of 96% at 0.5 C after 300 cycles, as well as exhibiting rate performance of 115.1 mAh g-1 at current rate of 10 C. To the best current knowledge, this H+ /Zn2+ synergistic intercalation mechanism is first reported in an aqueous battery system, which opens a new opportunity for development of high-performance aqueous Zn ion batteries for LSES.

Numerical analysis of a multi-pass pumping Yb:YAG thick-disk laser with minimal heat generation.

A theoretical model is established to describe the dynamic behavior and fractional thermal load of a multi-pass pumping Yb:YAG thick-disk laser, which is pumped at 1030 nm and emits laser radiation at around 1048 nm. The fractional thermal load, the temperature of the thick-disk crystal, and the operational properties for different ambient temperatures and different output coupler transmissions are investigated in detail. The results show that the pump saturation effect and the laser threshold are sensitive to the ambient temperature and the output coupler transmission, which affect the fractional thermal load and the laser extraction efficiency. Furthermore, a new design scheme is proposed to realize "zero thermal load" throughout the output range by dynamically adjusting the output coupler transmission.

Analytical model of amplified spontaneous emission with different thickness anti-ASE caps for thin disk lasers.

The amplified spontaneous emission (ASE) effect is a major factor affecting large, high gain Yb:YAG thin disk lasers. In this paper, the analytical model is built to estimate the ASE photon flux density of thin disk crystals with different thickness anti-ASE caps. Theoretical analysis shows that it is unnecessary to use a critical thickness anti-ASE cap to suppress the ASE effect. At the same time, adjusting the coupler reflectivity of the resonator is an effective way to decrease the ASE effect and decrease the thickness of the anti-ASE cap to effectively suppress the ASE effect. This paper will better reveal how the anti-ASE cap suppresses the ASE effect.

Cystic adventitial disease of the popliteal artery: report of two cases.

Cystic adventitial disease (CAD) of the popliteal artery is a rare vascular disorder in which a mucin-containing cyst develops in the adventitial layer of the artery. We report two such cases, each of which was treated differently. The first case was of a 49-year-old man, treated by excision of the involved arterial segment and interposition of an autologous saphenous vein graft. The second case was of a 36-year-old man, treated by local excision of the affected arterial segment and interposition with prosthetic bypass grafting. Both patients presented with rapidly progressing intermittent claudication of the lower extremities, but without remarkable evidence of atherosclerotic disease. Physical examination revealed diminished or absent popliteal, posterior tibial and dorsalis pedis pulses in the lower extremities. Color Doppler ultrasound of the popliteal artery revealed hypoechoic cystic lesions surrounding the vessel, and popliteal arterial stenosis, in both patients. Surgery resulted in immediate improvement of the arterial pulse distal to the lesion. Both patients recovered uneventfully. Thus, resection of the involved artery segment and interposition bypass grafting, using either patient or prosthetic veins, offers favorable results for CAD of the popliteal artery.

Alleviating Structure Collapse of Polycrystalline LiNixCoyMn1-x-yO2 via Surface Co Enrichment.

The structure collapse issues have long restricted the application of polycrystalline LiNixCoyMn1-x-yO2 (NCM) at high voltages beyond 4.4 V vs Li/Li+. Herein, for LiNi0.55Co0.12Mn0.33O2 (P-NCM), rapid surface degradation is observed upon the first charge, along with serious particle fragmentation upon repeated cycles. To alleviate these issues, a surface Co enrichment strategy is proposed [i.e., Co-enriched NCM (C-NCM)], which promotes the in situ formation of a robust surface rock-salt (RS) layer upon charge, serving as a highly stable interface for effective Li+ migration. Benefiting from this stabilized surface RS layer, Li+ extraction occurs mainly through this surface RS layer, rather than along the grain boundaries (GBs), thus reducing the risk of GBs' cracking and even particle fragmentation upon cycles. Besides, O loss and TM (TM = Ni, Co, and Mn) dissolution are also effectively reduced with fewer side reactions. The C-NCM/graphite cell presents a highly reversible capacity of 205.1 mA h g-1 at 0.2 C and a high capacity retention of 86% after 500 cycles at 1 C (1 C = 200 mA g-1), which is among the best reported cell performances. This work provides a different path for alleviating particle fragmentation of NCM cathodes.

Closed-Loop Direct Upcycling of Spent Ni-Rich Layered Cathodes into High-Voltage Cathode Materials.

Facing the resource and environmental pressures brought by the retiring wave of lithium-ion batteries (LIBs), direct recycling methods are considered to be the next generation's solution. However, the contradiction between limited battery life and the demand for rapidly iterating technology forces the direct recovery paradigm to shift toward "direct upcycling." Herein, a closed-loop direct upcycling strategy that converts waste current collector debris into dopants is proposed, and a highly inclusive eutectic molten salt system is utilized to repair structural defects in degraded polycrystalline LiNi0.83Co0.12Mn0.05O2 cathodes while achieving single-crystallization transformation and introducing Al/Cu dual-doping. Upcycled materials can effectively overcome the two key challenges at high voltages: strain accumulation and lattice oxygen evolution. It exhibits comprehensive electrochemical performance far superior to commercial materials at 4.6 V, especially its fast charging capability at 15 C, and an impressive 91.1% capacity retention after 200 cycles in a 1.2 Ah pouch cell. Importantly, this approach demonstrates broad applicability to various spent layered cathodes, particularly showcasing its value in the recycling of mixed spent cathodes. This work effectively bridges the gap between waste management and material performance enhancement, offering a sustainable path for the recycling of spent LIBs and the production of next-generation high-voltage cathodes.

Reducing Gases Triggered Cathode Surface Reconstruction for Stable Cathode-Electrolyte Interface in Practical All-Solid-State Lithium Batteries.

The interfacial compatibility between cathodes and sulfide solid-electrolytes (SEs) is a critical limiting factor of electrochemical performance in all-solid-state lithium-ion batteries (ASSLBs). This work presents a gas-solid interface reduction reaction (GSIRR), aiming to mitigate the reactivity of surface oxygen by inducing a surface reconstruction layer (SRL) . The application of a SRL, CoO/Li2 CO3 , onto LiCoO2 (LCO) cathode results in impressive outcomes, including high capacity (149.7 mAh g-1 ), remarkable cyclability (retention of 84.63% over 400 cycles at 0.2 C), outstanding rate capability (86.1 mAh g-1 at 2 C), and exceptional stability in high-loading cathode (28.97 and 23.45 mg cm-2 ) within ASSLBs. Furthermore, the SRL CoO/Li2 CO3 enhances the interfacial stability between LCO and Li10 GeP2 S12 as well as Li3 PS4 SEs. Significantly, the experiments suggest that the GSIRR mechanism can be broadly applied, not only to LCO cathodes but also to LiNi0.8 Co0.1 Mn0.1 O2 cathodes and other reducing gases such as H2 S and CO, indicating its practical universality. This study highlights the significant influence of the surface chemistry of the oxide cathode on interfacial compatibility, and introduces a surface reconstruction strategy based on the GSIRR process as a promising avenue for designing enhanced ASSLBs.

Constructing Matching Cathode-Anode Interphases with Improved Chemo-mechanical Stability for High-Energy Batteries.

Coupling Ni-rich layered oxide cathodes with Si-based anodes is one of the most promising strategies to realize high-energy-density Li-ion batteries. However, unstable interfaces on both cathode and anode sides cause continuous parasitic reactions, resulting in structural degradation and capacity fading of full cells. Herein, lithium tetrafluoro(oxalato) phosphate is synthesized and applied as a multifunctional electrolyte additive to mitigate irreversible volume swing of the SiOx anode and suppress undesirable interfacial evolution of the LiNi0.83Co0.12Mn0.05O2 (NCM) cathode simultaneously, resulting in improved cycle life. Benefiting from its desirable redox thermodynamics and kinetics, the molecularly tailored additive facilitates matching interphases consisting of LiF, Li3PO4, and P-containing macromolecular polymer on both the NCM cathode and SiOx anode, respectively, modulating interfacial chemo-mechanical stability as well as charge transfer kinetics. More encouragingly, the proposed strategy enables 4.4 V 21700 cylindrical batteries (5 Ah) with excellent cycling stability (92.9% capacity retention after 300 cycles) under practical conditions. The key finding points out a fresh perspective on interfacial optimization for high-energy-density battery systems.

Mechanochemically Robust LiCoO2 with Ultrahigh Capacity and Prolonged Cyclability.

Pushing intercalation-type cathode materials to their theoretical capacity often suffers from fragile Li-deficient frameworks and severe lattice strain, leading to mechanical failure issues within the crystal structure and fast capacity fading. This is particularly pronounced in layered oxide cathodes because the intrinsic nature of their structures is susceptible to structural degradation with excessive Li extraction, which remains unsolved yet despite attempts involving elemental doping and surface coating strategies. Herein, a mechanochemical strengthening strategy is developed through a gradient disordering structure to address these challenges and push the LiCoO2 (LCO) layered cathode approaching the capacity limit (256 mAh g-1, up to 93% of Li utilization). This innovative approach also demonstrates exceptional cyclability and rate capability, as validated in practical Ah-level pouch full cells, surpassing the current performance benchmarks. Comprehensive characterizations with multiscale X-ray, electron diffraction, and imaging techniques unveil that the gradient disordering structure notably diminishes the anisotropic lattice strain and exhibits high fatigue resistance, even under extreme delithiation states and harsh operating voltages. Consequently, this designed LCO cathode impedes the growth and propagation of particle cracks, and mitigates irreversible phase transitions. This work sheds light on promising directions toward next-generation high-energy-density battery materials through structural chemistry design.

Thermoelectric Performance Enhancement in Commercial Bi0.5Sb1.5Te3 Materials by Introducing Gradient Cu-Doped Grain Boundaries.

Modulated doping has always been a conventional and effective way to optimize thermoelectric (TE) materials. Unfavorably, the efficiency of conventional doping is always restricted by the strong interdependence of thermoelectric parameters. Here, an unconventional grain boundary doping strategy is reported to solve the above problem using commercial p-type Bi0.5Sb1.5Te3 as matrix materials. Decoupling of the three key TE parameters and large net get of the figure of merit (ZT) could be achieved in Bi0.5Sb1.5Te3 materials by introducing the gradient Cu-doped grain boundary. A high ZT of ∼1.40 at 350 K and a superior average ZT of ∼1.24 (300-475 K) are obtained in the as-prepared samples, projecting a maximum conversion efficiency of ∼8.25% at ΔT = 200 K, which are considerably greater than those of the commercial Bi0.5Sb1.5Te3 matrix and the traditional Cu-doped Bi0.5Sb1.5Te3 sample. This study gives deep insights to understand the relationships between the microstructure and the carrier/phonon transport behaviors and promotes a new strategy for improving the thermoelectric performance of commercial p-type Bi0.5Sb1.5Te3 materials.

Revealing the Grain-Boundary-Cracking Induced Capacity Decay of a High-Voltage LiCoO2 at 4.6 V.

During a practical battery manufacture process, the LiCoO2 (LCO) electrodes are usually rolled with high pressure to achieve better performance, including reducing electrode polarization, increasing compact density, enhancing mechanical toughness, etc. In this work, a high-voltage LCO (HV-LCO) is achieved via modulating a commercialized LCO with an Al/F enriched and spinel reinforced surface structure. We reveal that the rolling can more or less introduce risk of grain-boundary-cracking (GBC) inside the HV-LCO and accelerate the capacity decay when cycled at 3-4.6 V vs Li/Li+. In particular, the concept of interface structure is proposed to explain the reason for the deteriorated cycle stability. As the GBC is generated, the interface structure of HV-LCO alters from a surface spinel phase to a hybrid of surface spinel plus boundary layer phases, leading to the exposure of some the nonprotective layer phase against the electrolyte. This alternation causes serious bulk structure damage upon cycles, including expanding GBC among the primary crystals, forming intragranular cracks and inactive spinel phases inside the bulk regions, etc., eventually leading to the deteriorated cycle stability. Above all, we realize that it is far from enough to achieve a eligible high-voltage LCO via only applying surface modification. This work provides a new insight for developing more advanced LCO cathodes.

Exploiting Cation Intercalating Chemistry to Catalyze Conversion-Type Reactions in Batteries.

Effective harvest of electrochemical energy from insulating compounds serves as the key to unlocking the potential capacity from many materials that otherwise could not be exploited for energy storage. Herein, an effective strategy is proposed by employing LiCoO2, a widely commercialized positive electrode material in Li-ion batteries, as an efficient redox mediator to catalyze the decomposition of Na2CO3 via an intercalating mechanism. Differing from traditional redox mediation processes where reactions occur on the limited surface sites of catalysts, the electrochemically delithiated Li1-xCoO2 forms NayLi1-xCoO2 crystals, which act as a cation intercalating catalyzer that directs Na+ insertion-extraction and activates the reaction of Na2CO3 with carbon. Through altering the route of the mass transport process, such redox centers are delocalized throughout the bulk of LiCoO2, which ensures maximum active reaction sites. The decomposition of Na2CO3 thus accelerated significantly reduces the charging overpotential in Na-CO2 batteries; meanwhile, Na compensation can also be achieved for various Na-deficient cathode materials. Such a surface-induced catalyzing mechanism for conversion-type reactions, realized via cation intercalation chemistry, expands the boundary for material discovery and makes those conventionally unfeasible a rich source to explore for efficient utilization of chemical energy.