Antisite Defects Research Articles

Synthesis of Multifunctional Organic Molecules via Michael Addition Reaction to Manage Perovskite Crystallization and Defect

AbstractAdditive engineering plays a pivotal role in achieving high‐quality light‐absorbing layers for high‐performance and stable perovskite solar cells (PSCs). Various functional groups within the additives exert distinct regulatory effects on the perovskite layer. However, few additive molecules can synergistically fulfill the dual functions of regulating crystallization and passivating defects. Here, we custom‐synthesized 2‐ureido‐4‐pyrimidone (UPy) organic small molecules with diverse functional groups as additives to modulate crystallization and defects in perovskite films via the Michael addition reaction. Theoretical and experimental investigations demonstrate that the −OH groups in UPy exhibit significant effects in fixing uncoordinated Pb2+ ions, passivation of lead‐iodide antisite defects, alleviating hysteresis, and reducing non‐radiative recombination. Furthermore, the enhanced C=O and −NH2 motifs interact with the A‐site cation via hydrogen bonding, which relieves residual strain and adjusts crystal orientation. This strategy effectively controls perovskite crystallization and passivates defects, ultimately enhancing the quality of perovskite films. Consequently, the open‐circuit voltage of the UPy‐based p‐i‐n PSCs reaches 1.20 V, and the fill factor surpasses 84 %. The champion device delivers a power conversion efficiency of 25.75 %. Remarkably, the unencapsulated device maintained 96.9 % and 94.5 % of its initial efficiency following 3,360 hours of dark storage and 1,866 hours of 1‐sun illumination, respectively.

Catalytic Strategies Enabled Rapid Formation of Homogeneous and Mechanically Robust Inorganic‐Rich Cathode Electrolyte Interface for High‐Rate and High‐Stability Lithium‐Ion Batteries

AbstractLithium iron phosphate (LFP) cathode is renowned for high thermal stability and safety, making them a popular choice for lithium‐ion batteries. Nevertheless, on one hand, the fast charge/discharge capability is fundamentally constrained by low electrical conductivity and anisotropic nature of sluggish lithium ion (Li+) diffusion. On the other hand, the interface and internal structural degradation occurs when subjected to high‐rate condition. Herein, a multifunctional boron‐doping graphene/lithium carbonate (BG/LCO) nanointerfacial layer on surface of commercial LiFePO4 particles is designed, in which the BG layer catalyzes the rapid reaction of Li2CO3‐LiPF6 for homogeneous and mechanically robust inorganic LiF‐rich structure across the cathode‐electrolyte interphase (CEI), forms a conductive network to significantly enhance both electron and Li+ transport, and strengthens the FeO bonding to minimize both Fe loss and the formation of Fe‐Li antisite defects. Correspondingly, the modified LFP cathode achieves a high capability of 113.2 mAh g−1 at 10 C and extraordinary cyclic stability with 88.0% capacity retention over 1000 cycles as compared to the pristine LFP cathode with a capacity of only 94.0 mAh g−1 and 64.6% capacity retention. It also exhibits great enhancements of 20.1% and 3.7% at higher‐rate condition (room temperature/15 C) and the low temperature condition (−10 °C/1 C), respectively.

Dynamic Evolution of Antisite Defect and Coupling Anionic Redox in High-Voltage Ultrahigh-Ni Cathode.

High-voltage ultrahigh-Ni cathodes (LiNixCoyMn1-x-yO2, x≥0.9) can significantly enhance the energy density and cost-effectiveness of Li-ion batteries beyond current levels. However, severe Li-Ni antisite defects and their undetermined dynamic evolutions during high-voltage cycling limit the further development of these ultrahigh-Ni cathodes. In this study, we quantify the dynamic evolutions of the Li-Ni antisite defect using operando neutron diffraction and reveal its coupling relationship with anionic redox, another critical challenge restricting ultrahigh-Ni cathodes. We detect a clear Ni migration coupled with an unstable oxygen lattice, which accompanies the oxidation of oxygen anions at high voltages. Based on these findings, we propose that minimized Li-Ni antisite defects and controlled Ni migrations are essential for achieving stable high-voltage cycling structures in ultrahigh-Ni cathodes. This is further demonstrated by the optimized ultrahigh-Ni cathode, where reduced dynamic evolutions of the Li-Ni antisite defect effectively inhibit the anionic redox, enhancing the 4.5 V cycling stability.

Targeted Defect Repair and Multi-functional Interface Construction for the Direct Regeneration of Spent LiFePO4 Cathodes.

Due to the low economic benefits and environmental pollution of traditional recycling methods, the disposal of spent LiFePO4 (SLFP) presents a significant challenge. The capacity fade of SLFP cathode is primarily caused by lithium loss and formation of a Fe (III) phase. Herein, a synergistic repair effect is proposed to achieve defect repair and multi-functional interface construction for the direct regeneration of SLFP. Tannic acid (TA) forms a compact coating precursor for a carbon layer on SLFP with abundant functional groups and creates a mildly acidic environment to enhance the reducibility of thiourea (TU). Therefore, TU reduces Fe (III) to Fe (II) and repairs Li-Fe anti-site defects of SLFP, while at the same time acting as a source of N/S-doping elements for the carbon layer at a lower temperature (140°C). The multi-functional carbon layer improves the properties of the regenerated LiFePO4 (RLFP) due to the enhanced conductivity, structure maintenance and protection, and the improved kinetics of Li+ transport. Furthermore, the Fe─O and P─O bonds are strengthened, further enhancing the structural stability of the RLFP. Consequently, the RLFP demonstrates outstanding performance with a discharge capacity of 141.3 mAh g-1 and capacity retention of 72% after 1000 cycles at 1C.

Electronic Confinement-Restrained Anti-Site Defects in Sodium-Rich Phosphates Toward Multi-Electron Transfer and High Energy Efficiency.

Sodium (Na) super-ionic conductor structured Na3MnTi(PO4)3 (NMTP) cathodes have garnered interest owing to their cost-effectiveness and high operating voltages. However, the voltage hysteresis phenomenon triggered by anti-site defects ( -ASD), namely, the occupation of Mn2+ in the Na2 vacancies in NMTP, leads to sluggish diffusion kinetics and low energy efficiency. This study employs an innovative electronic confinement-restrained strategy to achieve the regulation of -ASD. Partial replacement of titanium (Ti) with electron-rich vanadium (V) favors strong electronic interactions with Mn2+, restraining Mn2+ migration. The results suggest that this strategy can significantly increase the vacancy formation energy and migration energy barrier of manganese (Mn), thus inhibiting -ASD formation. As proof of this concept, an Na-rich Na3.5MnTi0.5V0.5(PO4)3 (NMTVP) material is designed, wherein the electronic interaction enhanced the redox activity and achieved more Na+ storage under high-voltage. The NMTVP cathode delivered a reversible specific capacity of up to 182.7 mAh g-1 and output an excellent specific energy of 513.8Wh kg-1, corresponding to ≈3.2 electron transfer processes, wherein the energy efficiency increased by 35.5% at 30C. Through the confinement effect of electron interactions, this strategy provides novel perspectives for the exploitation and breakthrough of high-energy-density cathode materials in Na-ion batteries.

Investigation of structural and magnetic properties of Mg0.946Cu2.054O3 compound

The crystal structure of synthesized Mg0.946Cu2.054O3 compound was examined using Rietveld refinement of powder X-ray diffraction (XRD), revealing the presence of antisite defects in the form of substitution occupation of Mg atomic sites by Cu atoms upto ∼9 %. Detailed investigation by magnetic measurements around antiferromagnetic Néel transition around 95 K and below hints at the existence of paramagnetic component and short-range order due to presence of antisite defects, which is further supported by specific heat measurements.

Defect related anomalous mobility of small polarons in dielectric oxides at the example of congruent lithium niobate

Polarons play a major role in the description of optical, electrical and dielectrical properties of several ferroelectric oxides. The motion of those particles occurs by elementary hops among the material lattice sites. In order to compute macroscopic transport parameters such as charge mobility, normal (i.e. Fickian) diffusion laws are generally assumed. In this paper we show that when defect states able to trap the polarons for long times are considered, significant deviations from the normal diffusion behaviour arise. As an example of this behavior, we consider here the case of lithium niobate (LN). This can be considered as a prototypical system, having a rich landscape of interacting polaron types and for which a significant wealth of information is available in literature. Our analysis considers the case of a stoichiometric, defect-free lithium niobate containing a certain concentration of small electron polarons hopping on regular Nb sites, and compares it to the material in congruent composition, which is generally found in real-life applications and which is characterized by a large concentration of antisite NbLi defects. While in the first case the charge carriers are free polarons hopping on a regular Nb sublattice, in the second case a fraction of polarons is trapped on antisite defects. Thus, in the congruent material, a range of different hopping possibilities arises, depending on the type of starting and destination sites. We develop a formalism encompassing all these microscopic processes in the framework of a switching diffusion model which can be well approximated by a mobile–immobile transport model providing explicit expressions for the polaron mobility. Finally, starting from the Marcus–Holstein’s model for the polaron hopping frequency we verify by means of a Monte Carlo approach the diffusion/mobility of the different polarons species showing that, while free polarons obey the laws for normal diffusion as expected, bound polarons follow an anomalous diffusion behaviour and that in the case of the congruent crystal where mixed free and bound polaron transport is involved, our expressions indeed provide a satisfactory description.

Innovative In Situ Passivation Strategy for High-Efficiency Sb2(S,Se)3 Solar Cells.

An effective defect passivation strategy is crucial for enhancing the performance of antimony selenosulfide (Sb2(S,Se)3) solar cells, as it significantly influences charge transport and extraction efficiency. Herein, a convenient and novel in situ passivation (ISP) technique is successfully introduced to enhance the performance of Sb2(S,Se)3 solar cells, achieving a champion efficiency of 10.81%, which is among the highest recorded for Sb2(S,Se)3 solar cells to date. The first principles calculations and the experimental data reveal that incorporating sodium selenosulfate in the ISP strategy effectively functions as an in situ selenization, effectively passivating deep-level cation antisite SbSe defect within the Sb2(S,Se)3 films and significantly suppressing non-radiative recombination in the devices. Space-charge-limited current (SCLC), photoluminescence (PL), and transient absorption spectroscopy (TAS) measurements verify the high quality of the passivated films, showing fewer traps and defects. Moreover, the ISP strategy improved the overall quality of the Sb2(S,Se)3 films, and fine-tuned the energy levels, thereby facilitating enhanced carrier transport. This study thus provides a straightforward and effective method for passivating deep-level defects in Sb2(S,Se)3 solar cells.

Discovering the incorporation limits for wurtzite AlPyN1−y grown on GaN by metalorganic vapor phase epitaxy

We report on the growth of AlPN on GaN/sapphire templates by metalorganic vapor phase epitaxy using tertiarybutylphosphine (tBP) and NH3 as group-V precursors. P is easy to incorporate into the group-III lattice site, forming PAl anti-site defects and shrinking lattice constants that are even beyond AlN since Al is larger than P. We found that higher temperatures favor P incorporation on the N-sublattice, forming AlPyN1−y, while growth temperatures below 1000 °C result in dominant P incorporation on the Al-sublattice, forming PAl anisites. Similarly, larger NH3 flows stabilize GaN, leading to flat interfaces, but favor the formation of PAl. Furthermore, the P incorporation into AlPyN1−y is non-linear. At very low tBP flows, it initially increases to reach a maximum. Further increasing the tBP flow increases mostly the incorporation of P on the Al-sublattice, and the c-lattice constant decreases again. This leaves a small window of low V/III ratios below 5 and low P/N ratios of 1% or smaller, leading up to ∼4% P incorporation at typical growth temperatures of GaN. However, at such low V/III ratios, GaN is not stable even with N2 carrier gas and requires optimized switching sequences to minimize its decomposition and preserve flat interfaces. Eventually, a 10 nm coherent layer of AlP0.01N0.99 could be reproducibly grown on top of GaN channels with a smooth surface, an abrupt AlPN/GaN interface, and a two-dimensional electron gas with an electron mobility of ∼675 cm2/V s and a sheet carrier density of 1.5 × 1013 cm−2 at room temperature.

Effect of hydrothermally doped-Nb on structure and cycling stability of Li(Ni0.96Co0.04)O2

Nb5+ ions are hydrothermally incorporated into the hydroxide precursor of Li(Ni0.96Co0.04)O2 before lithiation. The hydrothermal doping of Nb results in particle size refinement and produces short- and long-ranged cation ordering that has not been observed in a Ni-rich layered cathode. The cation-ordered structure stabilizes the delithiated structure while the particle size refinement helps to absorb the strain energy generated during the H2 → H3 phase transformation near the charge end. 0.5 mol%-doped Li[Ni0.956Co0.039Nb0.005]O2 retains 96 % of the initial capacity after 100 cycles, which is remarkable despite its ultra-high Ni content. The cathode also delivers a discharge capacity of 227 mA h g−1. By contrast, the Li[Ni0.95Co0.04Al0.01]O2 maintains only 82 % of the initial capacity after 100 cycles. This finding highlights the importance of exploring different doping methods and the need to control and moderate the antisite defects which stabilize the delithiated structure to improve the cycling stability of ultra-high Ni-rich layered cathodes to a commercially viable level.

Dynamic Evolution of Antisite Defect and Coupling Anionic Redox in High‐Voltage Ultrahigh‐Ni Cathode

AbstractHigh‐voltage ultrahigh‐Ni cathodes (LiNixCoyMn1−x−yO2, x≥0.9) can significantly enhance the energy density and cost‐effectiveness of Li‐ion batteries beyond current levels. However, severe Li−Ni antisite defects and their undetermined dynamic evolutions during high‐voltage cycling limit the further development of these ultrahigh‐Ni cathodes. In this study, we quantify the dynamic evolutions of the Li−Ni antisite defect using operando neutron diffraction and reveal its coupling relationship with anionic redox, another critical challenge restricting ultrahigh‐Ni cathodes. We detect a clear Ni migration coupled with an unstable oxygen lattice, which accompanies the oxidation of oxygen anions at high voltages. Based on these findings, we propose that minimized Li−Ni antisite defects and controlled Ni migrations are essential for achieving stable high‐voltage cycling structures in ultrahigh‐Ni cathodes. This is further demonstrated by the optimized ultrahigh‐Ni cathode, where reduced dynamic evolutions of the Li−Ni antisite defect effectively inhibit the anionic redox, enhancing the 4.5 V cycling stability.

Amino Group-Aided Efficient Regeneration Targeting Structural Defects and Inactive FePO4 Phase for Degraded LiFePO4 Cathodes.

It is urgent to develop efficient recycling methods for spent LiFePO4 cathodes to cope with the upcoming peak of power battery retirement. Compared with the traditional metallurgical recovery methods that lack satisfactory economic and environmental benefits, the direct regeneration seems to be a promising option at present. However, a simple direct lithium replenishment cannot effectively repair and regenerate the cathodes due to the serious structural damage of the spent LiFePO4. Herein, the spent LiFePO4 cathodes are directly regenerated by a thiourea-assisted solid-phase sintering process. The density functional theory calculation indicates that thiourea has a targeted repair effect on the antisite defects and inactive FePO4 phase in the spent cathode due to the associative priority of amino group (─NH2) in thiourea with Fe ions: Fe3+─N > Fe2+─N. Meanwhile, the pyrolysis products of thiourea can also create an optimal reducing atmosphere and inhibit the agglomeration of particles in the high temperature restoration process. The regenerated LiFePO4 exhibits an excellent electrochemical performance, which is comparable to that of commercial LiFePO4. This targeted restoration has improved the efficiency of direct regeneration, which is expected to achieve large-scale recycling of spent LiFePO4.

Entropy engineering promotes thermoelectric performance while realizing P–N switchable conduction in BiSbSe1.5Te1.5

BiSbSe1.5Te1.5, a typical multi-layered compound, can be utilized to fabricate p-n junctions with the identical chemical composition by regulating the antisite defects and anion vacancies via defect engineering. However, the thermoelectric performance of n-type BiSbSe1.5Te1.5 is limited due to poor electrical transport properties. Entropy engineering is a novel strategy for expanding the space of performance optimization in materials science, including the field of thermoelectric. Herein, we realize a largely enhanced thermoelectric performance for n-type BiSbSe1.5Te1.5 by employing entropy engineering. Both mass field fluctuations and stress variations field are introduced simultaneously in the lattice, leading to additional phonon scattering. Moreover, nano-laminate structure, nanoscale interstices and holes are formed in the samples. All of these defects and nanoscale structures are especially efficient on trapping phonons. As a result, the optimizing electrical transport properties while maintaining low thermal conductivity are achieved, showcasing a peak ZT of 0.54 at 475 K and a remarkable average ZT of 0.45 between 300 and 550 K for n-type BiSbSe1.25Te1.75.These findings not only provide a way to enhance the thermoelectric performance of n-type BiSbSe1.5Te1.5 but also push forward the promise of the applications in fabricating well-matched p-n junctions using thermoelectric materials with the identical chemical composition.

Defect-driven ion storage on hexagonal boron nitride for fire-safe and high-performance lithium-ion batteries

The mass market adoption of electric vehicles has increased the risk of safety concerns, such as overheating and flammability. Rational design of fire-safe and high-capacity anodes with thermal tolerance, capable of fast-charging and long cycle-life, is crucial for the development of next generation Li-ion batteries operating under extreme conditions. Here we report a defect engineered hexagonal boron nitride (hBN) anode to mediate the safety dilemma. We demonstrate that the defects generated via cryomilling catalyze the reversible LiF formation and enable the pseudocapacitive type Li-ion storage on hBN. The non-flammability and excellent thermal tolerance of hBN allows high specific capacity (880 mAh/g @ 25 mA/g), rate performance (480 mAh/g @ 5 A/g) and stable cycling (5000 cycles) at 60 °C. The Li-ion full-cell with the defective hBN anode and the conventional cathode (LiNiMnCoO2) delivers significantly higher energy (400 Wh kg−1) and power density (1 kW kg−1) when compared to graphite/LiNiMnCoO2 full-cells (121 Wh kg−1 and 250 W kg−1). First-principles calculations confirm that nitrogen antisite (NBVN) defects are responsible for the electrochemical activation of otherwise inactive hBN. The strategy of defect-induced electrochemical activation opens up new avenues in the design of high-performance electrode materials for numerous secondary batteries.

Synthesis of Multifunctional Organic Molecules via Michael Addition Reaction to Manage Perovskite Crystallization and Defect.

Additive engineering plays a pivotal role in achieving high-quality light-absorbing layers for high-performance and stable perovskite solar cells (PSCs). Various functional groups within the additives exert distinct regulatory effects on the perovskite layer. However, few additive molecules can synergistically fulfill the dual functions of regulating crystallization and passivating defects. Here, we custom-synthesized 2-ureido-4-pyrimidone (UPy) organic small molecules with diverse functional groups as additives to modulate crystallization and defects in perovskite films via the Michael addition reaction. Theoretical and experimental investigations demonstrate that the -OH groups in UPy exhibit significant effects in fixing uncoordinated Pb2+ ions, passivation of lead-iodide antisite defects, alleviating hysteresis, and reducing non-radiative recombination. Furthermore, the enhanced C=O and -NH2 motifs interact with the A-site cation via hydrogen bonding, which relieves residual strain and adjusts crystal orientation. This strategy effectively controls perovskite crystallization and passivates defects, ultimately enhancing the quality of perovskite films. Consequently, the open-circuit voltage of the UPy-based p-i-n PSCs reaches 1.20 V, and the fill factor surpasses 84%. The champion device delivers a power conversion efficiency of 25.75%. Remarkably, the unencapsulated device maintained 96.9% and 94.5% of its initial efficiency following 3,360 hours of dark storage and 1,866 hours of 1-sun illumination, respectively.

Highly stoichiometry-deviating chalcopyrite quantum dots: synthesis and copper defects-correlated photophysical properties.

Copper indium selenide (CISe) is a prototype infrared semiconductor with low toxicity and unique optical characteristics. Its quantum dots (QDs) accommodate ample intrinsic point defects which may actively participate in their rather complex photophysical processes. We synthesize CISe QDs with similar sizes but with distinct highly stoichiometry-deviating atomic ratios. The synthesis condition employing Se-rich precursors yields the Cu-deficient CISe QDs with special photophysical properties. The photoluminescence exhibits monotonic red shift from 680 to 775 nm when the ratio of Cu's proportion to In's decreases. The luminescence is found to stem from the copper vacancy and antisite defects. The CISe QDs exhibit Raman activity at 5.6, 6.9, and 8.7 THz that is separately assigned to Cu-Se and In-Se optical phonon modes and surface mode.

A comparative first-principles study on the physical properties of Gd2Zr2O7 weberite and pyrochlore

A comparative analysis of the physical properties of Gd2Zr2O7 weberite and pyrochlore is conducted using first-principles methods. The structural characteristics of Gd2Zr2O7 pyrochlore and weberite are examined at the atomic site, local coordination, and lattice parameter levels. The findings from ab initio molecular dynamics simulations and experimental data confirm the existence and stability of the Gd2Zr2O7 weberite structure at 300 K. The formation of cation antisite defects is calculated to be more facile in the weberite lattice compared to pyrochlore. The formation energy of vacancy defects is strongly correlated to the distinct defect configurations. The calculations further highlight that Gd2Zr2O7 weberite exhibits mechanical properties comparable to pyrochlore. The insulating nature, chemical bonding characteristics, and charge states of individual atoms in weberite and pyrochlore are elucidated through analysis of the partial density of states and Bader charges.

Nondisassembly Repair of Degraded LiFePO4 Cells via Lithium Restoration from the Solid Electrolyte Interphase.

The disposal of degraded batteries will be a severe challenge with the expanding market demand for lithium iron phosphate (LiFePO4 or LFP) batteries. However, due to a lack of economic and technical viability, conventional metal extraction and material regeneration are hindered from practical application. Herein, we propose a nondisassembly repair strategy for degraded cells through a lithium restoration method based on deep discharge, which can elevate the anodic potential to result in the selective oxidative decomposition and thinning of the solid electrolyte interphase (SEI) on the graphite anode. The decomposed SEI acts as a lithium source to compensate for the Li loss and eliminate Li-Fe antisite defects for degraded LFP. Through this design, the repaired pouch cells show improved kinetic characteristics, significant capacity restoration, and an extended lifespan. This proposed repair scheme relying on SEI rejuvenation is of great significance for extending the service life and promoting the secondary use of degraded cells.

(Invited) Unlocking High-Performance Zero-Cobalt Cathode Active Materials: High-Entropy Doping and Pre-CAM Microstructure Optimization

Our recent work, published in Nature (610, 67–73, 2022) and Nature Energy (695–702, 2023), demonstrates the effectiveness of high-entropy doping (HE) in tackling the stability-capacity challenge of zero-cobalt layered cathode active materials (CAMs). While the HE Ni-80% (HE-N80) CAM exhibits competitive discharge capacity, it slightly lags behind NMC-811. This presentation delves into the broader applicability of the HE strategy and highlights the crucial role of pre-CAM microstructure optimization.Through pre-CAM microstructure optimization, we significantly reduce layered CAMs' anti-site defects, leading to a notable enhancement in discharge capacity. This optimization strategy increases the discharge capacity of the HE-N80 cathode from 210 mAh/g to 220 mAh/g under 0.1C charging and 2.5-4.4V voltage window. Moreover, cycling stability sees a substantial improvement, with a 99.5% capacity retention at 0.5C after 100 cycles. The effectiveness of this methodology extends to CAMs with higher nickel content, as demonstrated by discharge capacities of 225 mAh/g for zero-cobalt HE-N85 and 235 mAh/g for zero-cobalt HE-N90 under the same conditions.

Viable Strategy for Suppressing Antisite Defects and Band Tailing States in Solution-Processed Kesterite Solar Cells via IIIA Incorporation: Case of Aluminum

Viable Strategy for Suppressing Antisite Defects and Band Tailing States in Solution-Processed Kesterite Solar Cells via IIIA Incorporation: Case of Aluminum