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Double perovskite (DP) oxides are promising electrode materials for symmetric solid oxide cells (SSOCs) due to their excellent electrochemical activity and stability. B-site cation doping in DP oxides affects the reversibility of phase transformation and exsolution, which plays a crucial role in the catalyst recovery. Yet, few studies have been conducted on this topic. In this study, the Sr2Fe1.5-xCoxMo0.5O6-δ (CSFM, x = 0, 0.1, 0.3, 0.5) DP system demonstrates modulated exsolution and phase transformation reversibility by manipulating the oxygen vacancy concentration. The correlation between Co-doping level and oxygen vacancy concentration is investigated to optimize the exsolution and phase transformation properties. Sr2Fe1.2Co0.3Mo0.5O6-δ (3CSFM) exhibits reversible transformation between DP and Ruddlesden-Popper phases with a high density of exsolved CoFe nanoparticles under redox atmospheres. The quasi-symmetric cell with 3CSFM shows a peak power density of 1.27 W cm-2 at 850 °C in H2 fuel cell mode and a current density of 2.33 A cm-2 at 1.6 V and 800 °C in H2O electrolysis mode. The 3CSFM electrode exhibits robust stability during continuous operation for ≈700 h. These results demonstrate the significant role of B-site doping in designing DP materials capable of dynamic phase transformation in diverse environments.
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Phase engineering is an effective strategy for modulating the electronic structure and electron transfer mobility of cobalt selenide (CoSe2) with remarkable sodium storage. Nevertheless, it remains challenging to improve fast-charging and cycling performance. Herein, a heterointerface coupling induces phase transformation from cubic CoSe2 to orthorhombic CoSe2 accompanied by the formation of MoSe2 to construct a CoSe2/MoSe2 heterostructure decorated with N-doped carbon layer on a 3D graphene foam (CoSe2/MoSe2@NC/GF). The incorporated Mo cations in the bridged o-CoSe2/MoSe2 not only act an electron donor to regulate charge-spin configurations with more active electronic states but also trigger the upshift of d/p band centers and a decreased ∆d-p band center gap, which greatly enhances ion adsorption capability and lowers the ion diffusion barrier. As expected, the CoSe2/MoSe2@NC/GF anode demonstrates a high-rate capability of 447 mAh g-1 at 2 A g-1 and an excellent cyclability of 298 mAh g-1 at 1 A g-1 over 1000 cycles. The work deepens the understanding of the elaborate construction of heterostructured electrodes for high-performance SIBs.
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A long-standing issue about the correct identification of an important starting reagent, iron(III) hexafluoroacetylacetonate, Fe(hfac)3 (1), has been resolved. The tris-chelated mononuclear complex was found to crystallize in two polymorph modifications which can be assigned as the low-temperature (1-L) monoclinic P21/n and the high-temperature (1-H) trigonal P-3. Low-temperature polymorph 1-L was found to transform to 1-H upon sublimation at 44â °C. Two modifications are clearly distinguished by powder X-ray diffraction (PXRD), single-crystal X-ray diffraction, differential scanning calorimetry (DSC), and melting-point measurements. On the other hand, the two forms share similar characteristics in direct analysis in real-time mass spectrometry (DART-MS), attenuated total reflection (ATR) spectroscopy, and some physical properties, such as color, volatility, sensitivity, and solubility. Analysis of the literature and some of our preliminary data strongly suggest that the appearance of two polymorph modifications for trivalent metal (both transition and main group) hexafluoroacetylacetonates is a common case for several largely used complexes not yet accounted for in the crystallographic databases.
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Nanoscale zero-valent iron (nZVI) has been extensively utilized in environmental remediation, but its reactivity in the presence of co-contaminants requires further investigation for effective application in complex environments. Here, we conducted batch removal experiments to systematically investigate the co-removal behaviors of Cd(II) and phosphate by nZVI. Results showed that nZVI can synergistically remove Cd(II) and phosphate in solution, with the removal efficiency of Cd(II) and phosphate in the binary system being approximately 2 and 5 times higher than those in the single system, respectively. Sequential removal experiments combined with characterization analysis revealed the co-sorption of Cd(II) and phosphate onto the corrosion product of nZVI mainly by forming the ternary complexes (≡Fe-P-Cd). The Fe(OH)2 formed as the initial nZVI corrosion product provides numerous active sites for immobilization of Cd(II) and phosphate. Such effective co-sorption of Fe(OH)2 inhibits its subsequent phase transformation to Fe3O4. Overall, our work sheds light on how nZVI, Cd(II), and phosphate interact in solution as well as highlights the influence of phase transformation on co-removal, which can broaden the potential applications of nZVI in the practical environment.
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The emergence of multi-principal element alloys (MPEAs) heralds a transformative shift in the design of high-performance alloys. Their ingrained chemical complexities endow them with exceptional mechanical and functional properties, along with unparalleled microscopic plastic mechanisms, sparking widespread research interest within and beyond the metallurgy community. In this overview, a unique yet prevalent mechanistic process in the renowned FeMnCoCrNi-based MPEAs is focused on: the dynamic bidirectional phase transformation involving the forward transformation from a face-centered-cubic (FCC) matrix into a hexagonal-close-packed (HCP) phase and the reverse HCP-to-FCC transformation. The light is shed on the fundamental physical mechanisms and atomistic pathways of this intriguing dual-phase transformation. The paramount material parameter of intrinsic negative stacking fault energy in MPEAs and the crucial external factors c, furnishing thermodynamic, and kinetic impetus to trigger bidirectional transformation-induced plasticity (B-TRIP) mechanismsï¼ are thorougly devled into. Furthermore, the profound significance of the distinct B-TRIP behavior in shaping mechanical properties and creating specialized microstructures c to harness superior material characteristics is underscored. Additionally, critical insights are offered into key challenges and future striving directions for comprehensively advancing the B-TRIP mechanism and the mechanistic design of next-generation high-performing MPEAs.
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Our previous work (Mol Pharm, 20 (2023) 3427) showed that crystalline excipients, specifically anhydrous dibasic calcium phosphate (DCPA), facilitated the dehydration of carbamazepine dihydrate (CBZDH) and the formation of an amorphous product phase during the mixing stage of continuous tablet manufacturing. Understanding the mechanism of this excipient-induced effect was the object of this study. Blending with DCPA for 15 min caused pronounced lattice disorder in CBZDH. This was evident from the 190% increase in the apparent lattice strain determined by the Williamson-Hall plot. The rapid dehydration was attributed to the increased reactivity of CBZDH caused by this lattice disorder. Lattice disorder in CBZDH was induced by a second method, cryomilling it with DCPA. The dehydration was accelerated in the milled sample. Annealing the cryomilled sample reversed the effect, thus confirming the effect of lattice disorder on the dehydration kinetics. The hardness of DCPA appeared to be responsible for the disordering effect. DCPA exhibited a similar effect in other hydrates, thereby revealing that the effect was not unique to CBZDH. However, its magnitude varied on a case-by-case basis. The high shear powder mixing was necessary for rapid and efficient powder mixing during continuous drug product manufacturing. The mechanical stress imposed on the CBZDH, and exacerbated by DCPA, caused this unexpected destabilization.
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Investigating the structural evolution and phase transformation of iron oxides is crucial for gaining a deeper understanding of geological changes on diverse planets and preparing oxide materials suitable for industrial applications. In this study, in-situ heating techniques are employed in conjunction with transmission electron microscopy (TEM) observations and ex-situ characterization to thoroughly analyze the thermal solid-phase transformation of akaganéite 1D nanostructures with varying diameters. These findings offer compelling evidence for a size-dependent morphology evolution in akaganéite 1D nanostructures, which can be attributed to the transformation from akaganéite to maghemite (γ-Fe2O3) and subsequent crystal growth. Specifically, it is observed that akaganéite nanorods with a diameter of â¼50 nm transformed into hollow polycrystalline maghemite nanorods, which demonstrated remarkable stability without arresting crystal growth under continuous heating. In contrast, smaller akaganéite nanoneedles or nanowires with a diameter ranging from 20 to 8 nm displayed a propensity for forming single-crystal nanoneedles or nanowires through phase transformation and densification. By manipulating the size of the precursors, a straightforward method is developed for the synthesis of single-crystal and polycrystalline maghemite nanowires through solid-phase transformation. These significant findings provide new insights into the size-dependent structural evolution and phase transformation of iron oxides at the nanoscale.
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Exploring advanced electrocatalyst for the oxygen evolution reaction (OER) is of great importance in pursuing efficient and sustainable hydrogen production via electrolytic water splitting. Considering the structure-activity-stability relationship for designing advanced OER catalysts, two-dimensional (2D) porous catalyst with single crystallinity is deemed to be an ideal platform which could simultaneously endow enriched active sites, facile mass and charge transport ability as well as robust structural stability. Herein, we proposed a facile 2D confined topotactic phase transformation approach, which realizes the fabrication of highly porous single-crystalline Co3O4 nanosheets with in-situ surface modification of amorphous Co-Pi active species. Benefitted from the highly exposed undercoordinated cobalt sites, facilitated mass transport and facile 2D charge transfer pathway, the Co-Pi/Co3O4 hybrid porous nanosheets display enhanced OER activity with obvious pre-oxidation-induced activation. In addition, the operational stability was significantly improved owing to the strengthened structural stability which effectively buffers the internal strains and avoids the structural collapse during the electrochemical process. This work proposed a facile and mild method for the synthesis of amorphous/single-crystalline hybrid porous materials, and the achievement of synergistic modulation of active site density and charge transfer ability via targeted microstructural construction will shed light on catalyst design in the future.
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The In-Bi-Sn low-temperature solder alloys are regarded as potential candidates for cryogenic and space exploration applications. This study investigates the variations in the mechanical properties and microstructures of two different compositions: In15wt%Bi35wt%Sn and In30wt%Bi20wt%Sn, after exposure to a low-temperature environment (-20 °C) for 10 months. An increase in the ultimate tensile strength was observed across all the tested samples and a decrease in elongation to failure was observed in In30wt%Bi20wt%Sn. Changes in the microstructure were identified through scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The impact of this low-temperature environment is described, considering the varying proportions and compositions of the three phases (BiIn2(Sn), γ-InSn4(Bi), and ß-In3Sn(Bi)) present within the alloys and their contribution to the mechanical properties.
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This study aimed to investigate the amorphization capabilities of levofloxacin hemihydrate (LVXh), a fluoroquinolone drug, using a polymer excipient, Eudragit® L100 (EL100). Ball milling (BMing) was chosen as the manufacturing process and multiple mill types were utilized for comparison purposes. The product outcomes of each mill were analyzed in detail. The solid-state of the samples produced was comprehensively characterized by Powder X-ray Diffraction (PXRD), In-situ PXRD, Differential Scanning Calorimetry (DSC), Solid-State Fourier Transform Infrared Spectroscopy (FT-IR), and Dynamic Vapor Sorption (DVS). The crystallographic planes of LVXh were investigated by in-situ PXRD to disclose the presence or absence of weak crystallographic plane(s). The mechanism of LVXh:EL100 system formation was discovered as a two-step process, first involving amorphization of LVXh followed by an interaction with EL100, rather than as an instantaneous process. DVS studies of LVXh:EL100 samples showed different stability properties depending on the mill used and % LVXh present. Overall, a more sustainable approach for achieving full amorphization of the fluoroquinolone drug, LVXh, was accomplished, and advancements to the fast-growing world of pharmaceutical mechano- and tribo-chemistry were made.
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Improvements in phase stability and dielectric characteristics can broaden the applications of zirconia in ceramics. Herein, a series of Y2O3-stabilized zirconia (YSZ) ceramics are synthesized using solid-state sintering, followed by an investigation into their phase evolution, grain size, dielectric constant, and breaking field. As the Y2O3 content increases from 0 wt% to 4 wt%, the as-grown YSZ ceramics undergo a distinct phase transformation, transitioning from monoclinic to monoclinic + tetragonal and further to monoclinic + tetragonal + cubic, before finally returning to monoclinic + cubic. Significant changes occur in the internal microstructure and grain size of the ceramics as the phase composition alters, resulting in a reduction in grain size from 3.17 µm to 0.27 µm. Moreover, their dielectric constants exhibit an increasing trend as the Y2O3 content increases, rising from 3.92 to 13.2. Importantly, the dielectric breakdown field of these YSZ ceramics shows a similar variation to the phase evolution, ranging from 0.11 to 0.15 MV/cm. This study sheds light on the phase evolution and dielectric properties of YSZ ceramics, offering an efficient strategy for enhancing their dielectric performances.
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In the current study, an improved method of adding Zn ion doping to the 0.5BZT-0.5BCT-based films with high pyroelectric properties was designed. Under different Zn ion doping ratios, the structure, dielectric constant, phase transition relationship and other characteristics of the test product were analyzed experimentally to obtain the optimal ratio parameters. The experimental results demonstrate that the dielectric properties of the 0.5BZT-0.5BCT-xZn-based films proposed in this study can be far superior to those of other films under the optimal preparation process. The optimal dielectric properties and ferroelectric properties are obtained when the doped data are 0.008. Considering the comprehensive dielectric and energy storage capacity, the optimal doping ratio is 0.01, which can take into account dielectric data and energy storage performance. The energy storage density is 1.842 J / c m 3 , and the energy storage efficiency exceeds 30%. From 0 to 0.02, the properties of the material, such as the hysteresis loop and phase transition relationship are excellent. The properties of the materials studied in this study are excellent, and they are excellent candidate materials for the future application of ferroelectric materials, and provide ideas for related work.
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Polyamorphic transformations driven by high-energy mechanical ball milling (nanomilling) are recognized in a melt-quenched glassy alloy of tetra-arsenic triselenide (As4Se3). We employed XRPD analysis complemented by thermophysical heat-transfer and micro-Raman spectroscopy studies. A straightforward interpretation of the medium-range structural response to milling-driven reamorphization is developed within a modified microcrystalline model by treating diffuse peak-halos in the XRPD patterns of this alloy as a superposition of the Bragg-diffraction contribution from inter-planar correlations, which are supplemented by the Ehrenfest-diffraction contribution from inter-atomic and/or inter-molecular correlations related to derivatives of thioarsenide As4Sen molecules, mainly dimorphite-type As4Se3 ones. These cage molecules are merely destroyed under milling, facilitating the formation of a polymerized network with enhanced calorimetric heat-transfer responses. Disruption of intermediate-range ordering, due to weakening of the FSDP (the first sharp diffraction peak), accompanied by an enhancement of extended-range ordering, due to fragmentation of structural entities responsible for the SSDP (the second sharp diffraction peak), occurs as an interplay between medium-range structural levels in the reamorphized As4Se3 glass alloy. Nanomilling-driven destruction of thioarsenide As4Sen molecules followed by incorporation of their remnants into a glassy network is proved by micro-Raman spectroscopy. Microstructure scenarios of the molecular-to-network polyamorphic transformations caused by the decomposition of the As4Se3 molecules and their direct destruction under grinding are recognized by an ab initio quantum-chemical cluster-modeling algorithm.
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Metal implants require an elastic modulus close to cortical bone (<30 GPa) to avoid stress shielding and ensure adequate load-bearing strength. The metastable ß-type Ti-25Nb-8Sn alloy has a low elastic modulus (52 GPa), but its yield strength (<500 MPa) needs enhancement. This study enhances Ti-25Nb-8Sn's elastic admissible strain through cold rolling and aging heat treatments, investigating the microstructure's impact on mechanical and corrosion properties. The results show that lower-temperature aging (<450 °C) leads to ω-phase precipitation, yielding a 300% increase in yield strength (>1900 MPa). However, this also increases the elastic modulus (~80 GPa), limiting the deformation ability. Higher-temperature aging (>500 °C) eliminates the ω phase, transforming it into α precipitates, resulting in a lower elastic modulus (~65 GPa) and improved deformation ability, with substantial yield strength (>1000 MPa). In summary, the optimal process conditions are determined as 90% cold rolling followed by aging treatment at 550 °C. Under these conditions, Ti-25Nb-8Sn achieves the most suitable yield strength (1207 MPa) and high corrosion resistance, retaining a relatively low elastic modulus (64.7 GPa) and high elastic admissible strain (1.93%). This positions it as an ideal material for biomedical implants.
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It is critical to understand molecular ordering processes in small-molecule organic semiconductor (OSC) films in optimizing electronic device applications, although it is difficult to observe and investigate the ordering characteristics at a mesoscopic or device scale. Here, we report that friction force microscopy (FFM) allows visualizing the ordering transformation process from a thermodynamically metastable phase to a stable phase at a mesoscopic scale. We utilized 2-octyl-benzothieno[3,2-b]naphtho[2,3-b]thiophene (2-C8-BTNT) as a typical highly layered-crystalline OSC. We found that the friction force between an AFM tip and spin-coated OSC films significantly depends on whether local film states are in metastable monolayer phase or stable bilayer-type herringbone (b-LHB) phase that exhibits high carrier mobility. The formation of the stable b-LHB phase leads to lower friction than the metastable monolayer phase, clearly visualizing the molecular order. Force map (Fmap) analysis indicates that the lower friction in the b-LHB phase should be associated with the reduction of interfacial adhesion force. Notably, the observed results demonstrate that the spin-coated thin film changes from continuous film with the monolayer phase to rugged microcrystal grains with the b-LHB phase when left at ambient conditions. By contrast, an appropriate post-thermal annealing process facilitates the phase transformation without inducing such morphological changes. The technique provides a unique and effective tool for revealing the relationship between processing conditions and device performance in polycrystalline OSC films.
RESUMEN
Morphology, crystal phase, and its transformation are important structures that frequently determine electrocatalytic activity, but the correlations of intrinsic activity with them are not completely understood. Herein, using Co(OH)2 micro-platelets with well-defined structures (phase, thickness, area, and volume) as model electrocatalysts of oxygen evolution reaction, multiple in situ microscopy is combined to correlate the electrocatalytic activity with morphology, phase, and its transformation. Single-entity morphology and electrochemistry characterized by atomic force microscopy and scanning electrochemical cell microscopy reveal a thickness-dependent turnover frequency (TOF) of α-Co(OH)2. The TOF (≈9.5 s-1) of α-Co(OH)2 with ≈14 nm thickness is ≈95-fold higher than that (≈0.1 s-1) with ≈80 nm. Moreover, this thickness-dependent activity has a critical thickness of ≈30 nm, above which no thickness-dependence is observed. Contrarily, ß-Co(OH)2 reveals a lower TOF (≈0.1 s-1) having no significant correlation with thickness. Combining single-entity electrochemistry with in situ Raman microspectroscopy, this thickness-dependent activity is explained by more reversible Co3+/Co2+ kinetics and larger ratio of active Co sites of thinner α-Co(OH)2, accompanied with faster phase transformation and more extensive surface restructuration. The findings highlight the interactions among thickness, ratio of active sites, kinetics of active sites, and phase transformation, and offer new insights into structure-activity relationships at single-entity level.
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In recent years, two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been widely recognized as an ideal platform for surface-enhanced Raman scattering (SERS). Given their rich structural phases, phase transformation in 2D TMDCs is an efficient strategy to tailor their SERS performance. In this paper, we present the great SERS performance of multilayer 2M-WS2 and then investigate the effect of its phase transformation on SERS performance. It is observed that multilayer 2M-WS2 nanosheets undergo a thermally induced single-crystal phase transition from 2M-WS2 to 2H-WS2 upon thermal annealing or laser treatment. Distinguishing from the commercially available pure 2H-WS2 (P-2H-WS2), 2H-WS2 obtained by annealing and laser treatment still retain SERS properties comparable to those of 2M-WS2, among which the detection limits for CV molecules (10-8 M) are 3 orders of magnitude lower than that of P-2H-WS2 and the Raman intensity enhancements are â¼10-37 times higher. In contrast to the charge transfer (CT) mechanism governed by the Fermi level in metallic-phase 2M-WS2, 2H-WS2 obtained by phase transition exhibits accelerated CT facilitated by the bandgap reduction and reorganization resulting from the abundance of vacancies. This study introduces an interesting perspective and potential avenue for enhancing SERS through metal-to-semiconductor phase transitions in 2D TMDCs materials.
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Sodium-ion batteries (SIBs) have emerged as a compelling alternative to lithium-ion batteries (LIBs), exhibiting comparable electrochemical performance while capitalizing on the abundant availability of sodium resources. In SIBs, P2/O3 biphasic cathodes, despite their high energy, require furthur improvements in stability to meet current energy demands. This study introduces a systematic methodology that leverages the meta-heuristically assisted NSGA-II algorithm to optimize multi-element doping in electrode materials, aiming to transcend conventional trial-and-error methods and enhance cathode capacity by the synergistic integration of P2 and O3 phases. A comprehensive phase analysis of the meta-heuristically designed cathode material Na0.76Ni0.20Mn0.42Fe0.30Mg0.04Ti0.015Zr0.025O2 (D-NFMO) is presented, showcasing its remarkable initial reversible capacity of 175.5 mAh g-1 and exceptional long-term cyclic stability in sodium cells. The investigation of structural composition and the stabilizing mechanisms is performed through the integration of multiple characterization techniques. Remarkably, the irreversible phase transition of P2âOP4 in D-NFMO is observed to be dramatically suppressed, leading to a substantial enhancement in cycling stability. The comparison with the pristine cathode (P-NFMO) offers profound insights into the long-term electrochemical stability of D-NFMO, highlighting its potential as a high-voltage cathode material utilizing abundant earth elements in SIBs. This study opens up new possibilities for future advancements in sodium-ion battery technology.
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Bimetallic lanthanide metal-organic frameworks (bi-Ln-MOFs) exhibit great appeal for ratiometric luminescent sensors due to their unique advantages. Specially, the low-lying energy of the empty 4f band of Ce4+ ions benefits Ce-MOFs with robust and broad fluorescent emission. Therefore, constructing ratiometric sensors based on Ce-MOFs is of significance but remains a challenge. Here, a two-dimensional (2D) bi-Ln-MOF is fabricated using Eu3+/Ce4+ and 5-boronoisophthalic acid (5-bop) via a crystal phase transformation strategy to construct a ratiometric luminescent Hg2+ sensor. Due to the lower energy gap of Ce4+ compared to Eu3+ and the corresponding stronger energy-absorption ability, the Ce4+ in bi-Ln-MOF shows a stronger and broader fluorescent emission than that of Eu3+. The substitution of the boric acid group in the bi-Ln-MOF by Hg2+ amplifies the difference between the two lanthanide ions. Therefore, the fluorescence intensity of Ce4+ increases whereas that of Eu3+ decreases accordingly, a behavior distinct from individual Eu-MOF or Ce-MOF performance. This novel bi-Ln-MOF sensor not only achieves a wide linear response range from 0.5 to 120 µM with a low detection limit of 167 nM for Hg2+, but also demonstrates exceptional selectivity and stability. The intriguing sensing mechanism of energy competition and the novel synthesis approach for 2D bi-Ln-MOF are anticipated to broaden the application possibilities of bi-Ln-MOFs for designing ratiometric sensors.
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The aggravated mechanical and structural degradation of layered oxide cathode materials upon high-voltage charging invariably causes fast capacity fading, but the underlying degradation mechanisms remain elusive. Here we report a new type of mechanical degradation through the formation of a kink band in a Mg and Ti co-doped LiCoO2 cathode charged to 4.55 V (vs Li/Li+). The local stress accommodated by the kink band can impede crack propagation, improving the structural integrity in a highly delithiated state. Additionally, machine-learning-aided atomic-resolution imaging reveals that the formation of kink bands is often accompanied by the transformation from the O3 to O1 phase, which is energetically favorable as demonstrated by first-principles calculations. Our results provide new insights into the mechanical degradation mechanism of high-voltage LiCoO2 and the coupling between electrochemically triggered mechanical failures and structural transition, which may provide valuable guidance for enhancing the electrochemical performance of high-voltage layered oxide cathode materials for lithium-ion batteries.