Cation Doping Research Articles

Doping effects on the optoelectronic properties and the stability of Cs3Sb2I9: Density functional theory insights on photovoltaics and light-emitting devices

In this work, we address a knowledge gap regarding how cation and anion doping affect the stability and optoelectronic properties of Cs3Sb2I9 perovskites. We have employed Density Functional Theory (DFT) to investigate structures doped with Ag, In, Mo, Nb, Sc, Bi, Br and Cl in both 0D hexagonal P63/mmc and 2D trigonal P 3‾ m1 Cs3Sb2I9 polymorphs. Our results show that doping with either Sc, Bi, or In leads to negative decomposition energy and doping with Ag or In results in a reduced band gap while enhancing absorption, offering beneficial enhancements for LED and photovoltaic applications. Mo and Nb doping facilitate d-d transitions at lower energies, which is also significant for light emission applications. Conversely, halogen doping allows for fine-tuning the band gap with minimal changes in effective mass, accompanied by lattice parameter contraction, yielding more stable Sb-X bonds. Additionally, our analysis demonstrates that the 0D polymorph allows for easier dopant incorporation, leading to improved stability compared to the 2D structure. The results from this study offer important directions for experimentalists to explore in the development of efficient energy conversion materials.

Improving the electrochemical cycle stability of LiNi0.8Co0.1Mn0.1O2 via Al(H2PO4)3 treatment on its precursor

Ni-rich layered transition-metal oxides are important cathodes for lithium-ion batteries (LIBs). Unfortunately, they still suffer from capacity fading arising from structure transformation and side reactions. Cation doping and surface coating with a protective layer can alleviate the problem. Herein, a synergistic strategy of Al3+ doping near the surface and Li3PO4-LiAlO2 coating is adopted to modify LiNi0.8Co0.1Mn0.1O2 (NCM811), and it is carried out by using a simple Al(H2PO4)3 wet deposition method on its precursor. Structure and surface analysis show that Li3PO4-LiAlO2 is formed on the NCM surface and some Al3+ ions enter the near-surface lattice of cathode particles. Compared to NCM811, the modified-NCM811 exhibits slower impedance growth and better capacity retention (from 55.55 % to 75.09 % after 100 cycles) during cycling, which shows the strategy can effectively stabilize the interface and crystal structure.

Enhancing the Ammonia Catalytic Decomposition of Lanthanum Strontium Titanate Nickel Perovskite Catalysts via a Balanced Cation Doping and Deficiency Strategy

Enhancing the Ammonia Catalytic Decomposition of Lanthanum Strontium Titanate Nickel Perovskite Catalysts via a Balanced Cation Doping and Deficiency Strategy

Synthesis and Comprehensive Analytical Study of β-Li3PS4 Stabilization by Ca- and Ba-Codoped Li3PS4.

Sulfide-based solid electrolytes with high Li+ conductivity, such as Li3PS4, are key materials for the realization of all-solid-state Li+ batteries. One approach to achieving high Li+ conductivity is to combine crystalline-phase stabilization at high temperatures with the introduction of defects at room temperature. In this work, this approach was verified by codoping Li3PS4 with two kinds of divalent cations. The resulting structural changes were comprehensively investigated both experimentally and computationally. The high-temperature β-Li3PS4 phase of Li3PS4 could be stabilized at room temperature by adjusting the amount of Ca or Ba doping. The synthesized samples doped with divalent cations were found to have conductivities about 2 orders of magnitude higher than that of the γ-Li3PS4 phase at room temperature. The resultant Li+ conductivity at room temperature was also higher than that expected from interpolation of results for nondoped β-Li3PS4. It is believed that the structural changes produced by the divalent cation doping contribute to this increase in conductivity. The stability of the β-Li3PS4 phase with divalent cation doping was also demonstrated using density-functional-theory calculations for models with equivalent compositions to the synthesized samples. The Li+ positions obtained by structural optimization calculations showed the presence of diverse and disordered Li sites in the Ca-doped lattice. Such structural changes can contribute to cascade processes involving Li+ collisions, referred to as the "billiard-ball" mechanism, which cannot occur in nondoped β-Li3PS4. This series of experiments involving the synthesis and analyses of β-Li3PS4 with divalent cation doping provides a way to enhance Li+ conductivity through structural modification and optimization.

Achieving high open-circuit voltage in efficient kesterite solar cells via lanthanide europium ion induced carrier lifetime enhancement

Short carrier lifetimes is a key challenge limiting the open-circuit voltage (VOC) and power conversion efficiency (PCE) of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this work, for the first time, lanthanide europium (Eu) ions have been introduced into Ag-incorporated CZTSSe absorber layer, which can modify the selenization reaction pathway during the initial selenization process, leading to high-quality (Ag, Eu)-CZTSSe absorber with large compact crystal grains and benign surface potential fluctuations. This innovative absorber engineering can also optimize defects dynamics with less detrimental defects and defects-assisted non-radiative recombination. Thus, significantly enhanced minority carrier lifetimes from 0.97 to 3.15 ns can be achieved, representing one of the top values among various bulk and/or interface engineering treated CZTSSe. The champion CZTSSe thin-film solar cell exhibits an impressive VOC of 545.6 mV, accompanied with a stimulating increase in PCE from 10.68% to 13.30%. These findings underscore the potential of lanthanide cation doping to drive significant advancements in CZTSSe photovoltaic technology, and therefore promoting its further development and future applications.

Slug-flow synthesis of NCMA: Effect of substitution of cobalt with aluminum on the electrochemical performance of Ni-rich cathode for lithium-ion battery

Nickle-rich Li[Ni1-x-yCoxMny]O2 (x, y ≤ 0.1) (NCM) layered materials are known as promising cathode materials for next-generation lithium-ion batteries and electric vehicles owing to their high-reversible capacity and operating voltage of up to 3.6 vs Li/Li+. However, issues, such as irreversible phase transition, cation mixing, microcrack formation, thermal and structural stability of the material prevent its widespread adoption. Although, cation doping is a well-known technique to enhance the electrochemical performance of the NCM-based cathode material, the performance of the material is very sensitive to the doping amount. In this study, three Al-doped quaternary Ni-rich cathode materials Li[Ni0.85Co(0.1-x)Mn0.05Alx]O2 (where, x = 0–0.04) (NCMA) are synthesized through three-phase slug-flow based continuous manufacturing process followed by high temperature calcination to study the effect of Al-doping on the performance of the cathode material while reducing Co. The slug flow-based production platform has several advantages, like particle size uniformity, high production rate, and homogeneity in elemental distribution. It is found that with an increase in Al content, the specific capacity decreases but the cyclic stability and rate capability increases. Optimum Al-doping not only compensates for the adverse effect of low Co by decreasing the extent of cation mixing, but it also minimizes the electrode polarization and cracking of the particles.

A multifunctional dual cation doping strategy to stabilize high-voltage medium-nickel low-cobalt lithium layered oxide cathode

High-voltage medium-nickel low-cobalt lithium layered oxide cathode materials are intriguing for lithium-ion batteries (LIBs) applications because of their relatively low cost and high capacity. Unfortunately, high charging voltage induces bulk layered structure decline and interface environment deterioration, low cobalt content reduces lithium diffusion kinetics, severely limiting the performance liberation of this kind of cathode. Here, a multifunctional Al/Zr dual cation doping strategy is employed to enhance the electrochemical performance of LiNi0.6Co0.05Mn0.35O2 (NCM) cathode at a high charging cut-off voltage of 4.5 V. On the one hand, Al/Zr co-doping weakens the Li+/Ni2+ mixing through magnetic interactions due to the inexistence of unpaired electrons for Al3+ and Zr4+, thereby increasing the lithium diffusion rate and suppressing the harmful coexistence of H1 and H2 phases. On the other hand, they enhance the lattice oxygen framework stability due to strong Al-O and Zr-O bonds, inhibiting the undesired H2 to H3 phase transition and interface lattice oxygen loss, thereby enhancing the stability of the bulk structure and cathode-electrolyte interface. As a result, Al/Zr co-doped NCM (NCMAZ) shows a 94.2 % capacity retention rate after 100 cycles, while that of NCM is only 79.4 %. NCMAZ also exhibits better rate performance than NCM, with output capacities of 92 mAh/g and 59 mAh/g at a high current density of 5C, respectively. The modification strategy will make the high-voltage medium-nickel low-cobalt cathode closer to practical applications.

Synergetic enhancement of structural stability and kinetics of P’2-type layered cathode for sodium-ion batteries via cation–anion co-doping

The P’2-type layered oxides attract much attention as viable cathode materials for sodium-ion batteries (SIBs), due to their high specific capacity and environmental friendliness. Nevertheless, the sluggish Na+ diffusion kinetics and drastic capacity decay triggered by irreversible phase transition limit their large-scale application. In this study, we employ a synergistic optimization strategy involving cation and anion dopants to successfully restrain intergranular strain and tune local electronic structure, strengthening structural stability and electrochemical performance of the cathode material. Specifically, the Mg2+ dopant suppresses Na+/vacancy rearrangement and Mn-O anisotropic changes, while the F− dopant facilitates Na+ transport and alleviates phase evolution in high-voltage regions. Through this co-doping design, the modified electrodes display more alleviated voltage decay and exceptional capacity retention enhancements ranging from 6.57 % to 81.23 % after 750 cycles at 1000 mA g–1. This work provides novel perspectives on precise design of cathode materials, making layered oxides promising contenders for the next generation energy storage systems.

Performance improvement of Li-rich Mn-based materials with the submicron-sized single-crystal morphology and cationic doping

Lithium-rich manganese-based cathode materials (LRMCs) can be regarded as one of the most potential cathode materials for the next-generation high-energy Li-ion batteries due to the extra oxygen redox, which can greatly increase the actual output energy density of LRMCs. Nevertheless, the structure degradation and inevitable loss of oxygen will be triggered by the irreversible oxygen redox, which will cause a significant decline in cyclic performance and limited initial Coulombic efficiency, thus restricting their industrial applicability. Herein, the LRMCs with the submicron-sized single-crystal morphology and sodium doping are prepared by molten salt treatment with NaCl. On one hand, the submicron-sized single-crystal cathode effectively reduces the diffusion path for Li+ due to the smaller particle dimensions. On the other hand, Na+ doping expands the Li slab spacing, promoting the transport of Li+. The results show that the as-prepared material can purposefully alleviate oxygen release, improve structure stability, and increase the Li+ diffusion rate for the pristine LRMCs. Moreover, the as-prepared material in this study exhibits a higher reversible capacity of 282.8 mAh g−1 at 0.1 C and displays good cyclic performance, retaining a capacity rate of 80.9% after 200 cycles at 1 C. Therefore, this study offers a potential exploration for designing LRMCs with high energy density and excellent cyclic performance, which are achieved through building submicron-sized single-crystal morphology and introducing cationic doping.

Unveiling the tailorable electrochemical properties of zeolitic imidazolate framework-derived Ni-doped LiCoO2 for lithium-ion batteries in half/full cells

As a prevailing cathode material of lithium-ion batteries (LIBs), LiCoO2 (LCO) still encounters the tricky problems of structural collapse, whose morphological engineering and cation doping are crucial for surmounting the mechanical strains and alleviating phase degradation upon cycling. Hereinafter, we propose a strategy using a zeolitic imidazolate framework (ZIF) as the self-sacrificing template to directionally prepare a series of LiNi0.1Co0.9O2 (LNCO) with tailorable electrochemical properties. The rational selection of sintering temperature imparts the superiority of the resultant products in lithium storage, during which the sample prepared at 700 °C (LNCO-700) outperforms its counterparts in cyclability (156.8 mA h g−1 at 1 C for 200 cycles in half cells, 1 C = 275 mA g−1) and rate capability due to the expedited ion/electron transport and the strengthen mechanical robustness. The feasibility of proper Ni doping is also divulged by half/full cell tests and theoretical study, during which LNCO-700 (167 mA h g−1 at 1 C for 100 cycles in full cells) surpasses LCO-700 in battery performance due to the mitigated phase deterioration, stabilized layered structure, ameliorated electronic conductivity, and exalted lithium storage activity. This work systematically unveils tailorable electrochemical behaviors of LNCO to better direct their practical application.

Fluoride Doping Na3Al2/3V4/3(PO4)3 Microspheres As Cathode Materials for Sodium-Ion Batteries with Multielectron Redox.

Sodium-ion batteries (SIBs) are potential candidates for large energy storage usage because of the natural abundance and cheap sodium. Nevertheless, improving the energy density and cycling steadiness of SIB cathodes remains a challenge. In this work, F-doping Na3Al2/3V4/3(PO4)3(NAVP) microspheres (Na3Al2/3V4/3(PO4)2.9F0.3(NAVPF)) are synthesized via spray drying and investigated as SIB cathodes. XRD and Rietveld refinement reveal expanded lattice parameters for NAVPF compared to the undoped sample, and the successful cation doping into the Na superionic conductor (NASICON) framework improves Na+ diffusion channels. The NAVPF delivers an ultrahigh capacity of 148 mAh g-1 at 100mA g-1 with 90.8% retention after 200 cycles, enabled by the activation of V2+/V5+ multielectron reaction. Notably, NAVPF delivers an ultrahigh rate performance, with a discharge capacity of 83.6 mAh g-1 at 5000mA g-1. In situ XRD demonstrates solid-solution reactions occurred during charge-discharge of NAVPF without two-phase reactions, indicating enhanced structural stability after F-doped. The full cell with NAVPF cathode and Na+ preintercalated hard carbon anode shows a large discharge capacity of 100 mAh g-1 at 100mA g-1 with 80.2% retention after 100 cycles. This anion doping strategy creates a promising SIB cathode candidate for future high-energy-density energy storage applications.

Dual modification of phosphate toward improving electrochemical performance of LiNiO2 cathode materials

Lithium nickel oxide (LiNiO2) cathode materials are featured with high capacity and low cost for rechargeable lithium-ion batteries but suffer from severe structure and interface instability. Bulk doping together with surface coating has been proven to be an efficient approach to improve the inner structure and interfacial stability of the LiNiO2 cathode material. Nevertheless, the role of anion doping seems to be quite different from that of cation doping, and a deep insight will be desirable for the structure design of the LiNiO2 cathode material. In this paper, PO43−-doped and Li3PO4-coating of dual modification of LiNiO2 are achieved via a facile approach. It is demonstrated that the PO43− anions are doped into the tetrahedron vacant sites of the crystal structure, alleviating the phase transition and improving the reversibility of crystal structure. Besides, the Li3PO4 coating layer ameliorates the interface stability to restrain the side reactions. Therefore, the dual modification enhances overall structural stability of the material to provide excellent performance. Moreover, the consumption of the Li residues by the formation of Li3PO4 coating layer, and the enlarged interlayer spacing of the crystal structure by PO43− doping can facilitate the Li+ ions diffusion, resulting in a superior rate capability.

Low-valent cation doping and leaching to construct single-atom Cu decorated Cu-ZnIn2S4 with multiple defects for boosting photocatalytic H2 evolution

It is a promising means to enhance photocatalytic activity by ions doping, single-atom decoration, and vacancies introducing, yet a simple approach to realize their simultaneous appearance in one material remains a great challenge hitherto. Herein, an original strategy of low-valent cation doping and leaching is developed to construct Cu single atom (Cu SAs)-decorated and monovalent Cu ion (Cu+)-doped ZnIn2S4 photocatalyst (RCu-ZIS) with multiple defects. The Cu doping atoms and Cu/In/S vacancies clusters induce electron-poor zones, meanwhile, S vacancies and isolated Cu SAs result in electron-rich regions, thus forming some local electric field with different states of charge, which can act as electron-accepting and donating centers accelerating the transfer and separation of photocarriers. The optimized RCu-ZIS delivers a high visible-light-driven H2 evolution activity of 70.58 mmol·g−1·h−1 with an AQE of 12.24% at 420 nm. This work opens up an all-in-one modification strategy on redounding photocatalytic activity through rational structural fine-tuning.

Lattice oxygen activation and local electric field enhancement by co-doping Fe and F in CoO nanoneedle arrays for industrial electrocatalytic water oxidation

Oxygen evolution reaction (OER) is critical to renewable energy conversion technologies, but the structure-activity relationships and underlying catalytic mechanisms in catalysts are not fully understood. We herein demonstrate a strategy to promote OER with simultaneously achieved lattice oxygen activation and enhanced local electric field by dual doping of cations and anions. Rough arrays of Fe and F co-doped CoO nanoneedles are constructed, and a low overpotential of 277 mV at 500 mA cm−2 is achieved. The dually doped Fe and F could cooperatively tailor the electronic properties of CoO, leading to improved metal-oxygen covalency and stimulated lattice oxygen activation. Particularly, Fe doping induces a synergetic effect of tip enhancement and proximity effect, which effectively concentrates OH− ions, optimizes reaction energy barrier and promotes O2 desorption. This work demonstrates a conceptual strategy to couple lattice oxygen and local electric field for effective electrocatalytic water oxidation.

Effect of alkali metal cation doping in graphitic carbon nitride towards photocatalytic generation of hydrogen peroxide under direct sunlight

H2O2, a powerful oxidant with a vast number of industrial applications, is being synthesized by the energy intensive anthraquinone process. Recently, H2O2 has been synthesized using H2O and O2 by photocatalysis. Graphitic carbon nitride (g-C3N4) is a popular low-cost photocatalyst that is known to produce H2O2. However, the properties g-C3N4 needs to be tailored to improve the yield of H2O2. We discuss such a modification of g-C3N4 by alkali metal cation doping. Among the Li+, Na+ and K+ ions, doping of 10 wt% of K+ in g-C3N4 increase the yield of H2O2 (200 μmol g−1 h−1) by 2.5 times as compared un-doped g-C3N4 under natural sunlight.

Competing Mechanisms Determine Oxygen Redox in Doped Ni-Mn Based Layered Oxides for Na-Ion Batteries.

Cation doping is an effective strategy for improving the cyclability of layered oxide cathode materials through suppression of phase transitions in the high voltage region. In this study, Mg and Sc are chosen as dopants in P2-Na0.67Ni0.33Mn0.67O2, and both have found topositively impact the cycling stability, but influence the high voltage regime in different ways. Through a combination of synchrotron-based methods and theoretical calculations it is shown that it is more than just suppression of the P2 to O2 phase transition that is critical for promoting the favorable properties, and that the interplay between Ni and O activity is also a critical aspect that dictates the performance. With Mg doping, the Ni activity can be enhanced while simultaneously suppressing the O activity. This is surprising because it is in contrast to what has been reported in other Mn-based layered oxides where Mg is known to trigger oxygen redox. This contradiction is addressed by proposing a competing mechanism between Ni and Mg that impacts differences in O activity in Na0.67MgxNi0.33- xMn0.67O2 (x<0<0.33). These findings provide a new direction in understanding the effects of cation doping on the electrochemical behavior of layered oxides.

Improved performance of kesterite Cu2ZnSn(S,Se)4 thin film solar cells by Ag/Ge co-doping

Cation doping is an important approach to improve the performance of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells. Since different cation dopant has different effects on the defects and crystallization of CZTSSe absorber, it is expected to achieve better device performance via the synergistic effects of double cation co-doping compared with the single cation doping. Herein, we investigated the effects of Ag/Ge co-doping on CZTSSe solar cells by doping Ge in an already optimized Ag-alloyed CZTSSe (ACZTSSe). It is found that incorporating a small amount of Ge can further improve the crystallinity and minority carrier lifetime of ACZTSSe. The low-temperature photoluminescence results reveal that the Ge doping primarily suppressed the SnZn defects in ACZTSSe, thereby further boosting the device performance. However, higher Ge doping concentration can lead to a discontinuous surface morphology, which is believed to be related with the relatively low melting temperature and double-layered structure of ACZTSSe absorber. The deteriorated surface morphology results in photocurrent loss in the near-infrared region and decreased fill factor. As the Ge doping ratio increases, there is a balance between the defects and morphology. A champion power conversion efficiency (PCE), 11.4%, was achieved for the Ag/Ge co-doped CZTSSe solar cells at Ge substitution rate of 3%. Compared with the single Ag doping, the average PCE was further promoted by 0.5% due to Ag/Ge co-doping.

Low-Electronegativity Cationic High-Entropy Doping to Trigger Stable Anion Redox Activity for High-Ni Co-Free Layered Cathodes in Li-Ion Batteries.

LiNi0.8 Co0.1 Mn0.1 O2 (NCM-811) exhibits the highest capacity in commercial lithium-ion batteries (LIBs), and the high Ni content (80 %) provides the only route for high energy density. However, the cationic structure instability arisen from the increase of Ni content (>80 %) limits the further increase of the capacity, and inevitable O2 release related to anionic structure instability hinders the utilization of anion redox activity. Here, by comparing various combinations of high-entropy dopants substituted Co element, we propose a low-electronegativity cationic high-entropy doping strategy to fabricate the high-Ni Co-free layered cathode (LiNi0.8 Mn0.12 Al0.02 Ti0.02 Cr0.02 Fe0.02 O2 ) that exhibits much higher capacity and cycling stability. Configurational disorder originated from cationic high-entropy doping in transition metal (TM) layer, anchors the oxidized lattice oxygen ((O2 )n- ) to preserve high (O2 )n- content, triggering the anion redox activity. Electron transfer induced by applying TM dopants with lower electronegativity than that of Co element, increases the electron density of O in TM-O octahedron (TM-O6 ) configuration to reach higher (O2 )n- content, resulting in the higher anion redox activity. With exploring the stabilization effect on both cations and anions of high-entropy doping and low-electronegativity cationic modified anion redox activity, we propose an innovative and variable pathway for rationally tuning the properties of commercial cathodes.

Synergistic Zinc(II) and Formate Doping of Perovskites: Thermal Phase Stabilization of α-FAPbI3 and Enhanced Photoluminescence Lifetime of FA0.8MA0.2PbI3 up to 3.7 µs.

Adding zinc (II) cations and formate anions improves the thermal phase stability of α-FAPbI3 materials, and the spin-coated thin films of such doped FAPbI3 (produced using MACl) show an increased emission lifetime of up to 3.7 μs on quartz (for FA0.8MA0.2PbI3). This work investigates the effects of zinc and formate on the phase stability and time-resolved photoluminescence of FAPbI3 perovskites for solar cell applications. Perovskite samples with varying concentrations of zinc and formate were made by incorporating different amounts of zinc formate and zinc iodide and were characterized with XRD. Doping levels of 1.7% Zn(II) and 1.0% formate (relative to Pb) seem optimal. The thermal phase stability of the doped perovskite powders (FAPbI3) and thin films (FA0.8MA0.2PbI3) was assessed. XRD of the thin films after 6 months shows only the alpha-phase. The time-resolved photoluminescence spectroscopy of the doped spin-coated perovskite samples (FA0.8MA0.2PbI3 produced using MACl) is reported. The results show that synergy between an anionic and a cationic dopant can take place, making the perovskite thermally more phase-stable (not converting to the yellow delta-phase) with a longer charge carrier lifetime. In order to produce good thin films by spin coating, the use of MACl was essential.

Ce-doped multi-phase NiMo-based phosphorus/sulfide heterostructure for efficient photo-enhanced overall water splitting at high current densities

NiMo-based electrocatalysts are widely regarded as promising electrocatalysts for overall water splitting (OWS). However, to solve the problem of slow reaction kinetics and serious deactivation at high current density, the reasonable design of NiMo-based electrocatalysts is still a great challenge. In this work, NiMo-based phosphorus/sulfide heterostructure electrocatalysts with different Ce doping ratios (5%/10%/15%Ce-NiMo-PS@NF) have been designed using the combination of cation doping and heterostructure engineering. The doping of Ce not only changes the electronic environment of the heterostructure, accelerates the electron transport at the heterostructure interface, but also enhances the light absorption capacity of the heterostructure. The experimental results show that 10%Ce-NiMo-PS@NF has the best photo-enhanced electrocatalytic activity (hydrogen evolution reaction (HER): η1000 = 250 mV, oxygen evolution reaction (OER): η1000 = 242 mV, and OWS: E1000 = 1.864 V). In addition, its solar-to-hydrogen (STH) efficiency in a photoelectric coupled water splitting system is as high as 18.68%. This study not only provides a new method for the synthesis of new heterostructure electrocatalysts, but also provides a reference for the rational use of light energy to enhance electrocatalytic activity.