Ex-situ X-ray Photoelectron Spectroscopy Research Articles

Au-decorated WO3-based sensor for chemiresistive detection of NO2 at 80 °C

Nitrogen dioxide (NO2), a hazardous gas of acidic nature, is constantly released into the atmosphere by human activities. Based on the noble metal sensitization, the NO2 sensing performance of Au decorated WO3 sensors (Rg/Ra = 4.3@ 1 ppb, 746.0@ 5 ppm) was found to be superior to that of pristine WO3 (Rg/Ra = 1.2@ 1 ppb). In addition, the dynamic processes that occur in Au–WO3-3 during NO2 sensing reactions were analyzed using ex-situ X-ray photoelectron spectroscopy. Density functional theory containing adsorption energy, is further used to analyse mechanism accurate electron transfer sensing process. Furthermore, the effects of the oxygen partial pressure and relative humidity on the sensing performance of the sensors were studied. The enhanced sensing mechanisms of Au–WO3 sensors can be attributed to the electronic and chemical sensitization effects of Au, increased number of active sites, decrease in the activation energy of the sensing reactions and three-dimensional hierarchical structure, which boosts the adsorption of gas molecules and charge transfer efficiency.

Molybdenum-leaching induced rapid surface reconstruction of amorphous/crystalline heterostructured trimetal oxides pre-catalyst for efficient water splitting and Zn-air batteries

Crystalline and amorphous structure can entitle a catalyst with high stability and activity, respectively. Oxygen evolution reaction (OER) catalysts, which widely used in water electrolysis and rechargeable Zn-air batteries, often undergo a surface phase reconstruction process and generate amorphous active phases under applied anodic potential. Although widely known, few studies and strategies have been reported to rationally tune OER pre-catalysts for enhanced reaction kinetics. Herein, we report a trimetallic oxides (a/c-NiFeMoOx) OER per-catalyst with rationally tunable amorphous/crystalline heterostructure degrees by a precise-tuning component strategy. The best a/c-NiFeMoOx electrode exhibits an OER overpotential merely of 256 mV and a small cell-voltage of 1.52 V to reach 10 mA cm–2 for water electrolysis, respectively. It is find that Mo leaching with tailored amorphous/crystalline heterostructure via the rational tuned degree of amorphousness promotes a rapid surface reconstruction of the a/c-NiFeMoOx pre-catalyst to form (oxy)hydroxide active species, whilst operando Raman, ex-situ X-ray photoelectron spectroscopy and density functional theory (DFT) analysis show the ample oxygen vacancies generated by phase transition significantly accelerates the deprotonation of OH* and lower the O* ➝ OOH* free energy for a fast oxygen evolution kinetics. Additionally, the practical application of a/c-NiFeMoOx cathode in rechargeable Zn-air battery delivers a robust long-term cycling (over 840 cycles).

Rationally designed NASICON-type Na3.75V1.25Mn0.75(PO4)3 cathode towards long life-span sodium ion batteries

Owning to non-toxic and high working potential, Mn-substituted NASICON-type Na3+xMnxV2-x(PO4)3 cathodes have promising application in sodium ion batteries (SIBs). However, the poor cycling stability limits their further practical applications. Herein, a succession of carbon coated Na3.75Mn0.75V1.25(PO4)3 cathodes are constructed via a sol–gel combining with heating treatment. The effects of carbon content on the structure, electrochemical properties and sodium ion diffusion kinetics are investigated. The optimal composition, Na3.75Mn0.75V1.25(PO4)3/2VitC, displays an outstanding specific capacity and long-cycling stability. It releases a discharge capacity of 105.6 mAh g-1 with a high initial Coulombic efficiency of 97.5% at 0.2C. It can also deliver a high capacity of 92.6 mAh g-1 with a capacity retention of 88.3% at 5C over 2000 cycling, and the reversible capacity can achieve to 79.1 mAh g-1 with 78% capacity retention after 4000 cycles at high rate of 10C. Ex-situ X-ray diffraction and X-ray photoelectron spectroscopy reveal a biphasic reaction process and high structural reversibility during sodium ion insertion/extraction. The good multiplicity performances, excellent long cycle stability and low cost of the optimized Na3.75Mn0.75V1.25(PO4)3 composite indicate that it is a promising cathode material for SIBs.

Auxiliary coordination strategy designed poly(chloranil-squaricamide) cathode achieving enhanced specific capacity utilization and Zn2+ insertion/extraction for aqueous zinc ion batteries

High-performance organic cathodes with sustainable advantages are suitable for low-carbon and secure applications in aqueous zinc ion batteries (AZIB). Herein, we propose an improved auxiliary coordination facilitating Zn2+ insertion/extraction strategy to design a novel poly(chloranil-squaricamide) (PCSA) as AZIB cathode. The auxiliary coordination squaraine groups with appropriate Zn2+ coordination configuration can facilitate Zn2+ insertion/extraction, so that PCSA presents enhanced stable cycle performance and specific capacity utilization. Particularly, PCSA can perform maximum 98.4% specific capacity utilization and 93% capacity retention after 400 cycles under 0.02 A g−1, even under 0.1 A g−1 the capacity retention can still reach 80% after 1000 cycles. The ex-situ X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectra (FTIR) reveal that quinone units can undertake redox function in PCSA and the auxiliary coordination of the squaraine groups can facilitate Zn2+ insertion/extraction. The ex-situ XRD indicates that slight H+ is involved in the Zn2+ storage process. Such an auxiliary coordination strategy can provide a prospective design method to construct high-performance organic cathode materials for AZIB.

High capacity Mo7S8 nanosheets with electrodeposited alpha-Co(OH)2 thin layer as positive electrode in hybrid potassium dual-ion supercapacitors

Alpha-Co(OH)2 nanoflakes are grown on Mo7S8 electrodes by galvanostatic electrodeposition. The influence of various electrodeposition time durations on the electrochemical properties of alpha-Co(OH)2@Mo7S8 electrodes is compared. When the optimized deposition time is 1440 s, alpha-Co(OH)2@Mo7S8 composite electrode obtains the highest specific capacity of 484.8 C g−1, the lowest internal resistance of 1.96 Ω, the shortest time constant of 2.15 s, and the maximum diffusion coefficient of 2.27 × 10−14 cm2 s−1. The kinetic analysis of this electrode reveals the highest diffusion and the lowest non-diffusion contributions of 76.25% and 23.75% at 0.5 mV s−1, respectively. Ex-situ X-ray photoelectron spectroscopy shows that chemical valences of Mo and Co increased from +2 to +4 and from +2 to +3 after OH− insertion, respectively. The hybrid potassium dual-ion supercapacitor is assembled with alpha-Co(OH)2@Mo7S8 cathode (positive electrode) and molybdenum-phosphate-based MoPO@Mo7S8 anode (negative electrode). The device exhibits remarkable capacitance characteristics with a high specific energy of 59.4 Wh kg−1 at a specific power of 734 W kg−1 and a capacity-maintaining retention rate of 97.3% after 10,000 charge–discharge cycles.

Enhancing the lithium-ion storage capability of Cu2ZnSnS4 anodes via a nitrogen-doped conductive support

Achieving lithium-ion batteries with both excellent electrochemical performance and cycling stability is a top priority for their real-world applications. This work reports high-performance and stable Cu2ZnSnS4 (CZTS) anode materials encapsulated by nitrogen-doped carbon (CZTS@N-C) for advanced lithium-ion battery application. Ex-situ X-ray photoelectron spectroscopy and transmission electron microscopy revealed that the nitrogen-doped carbon network features a more conducive solid-electrolyte interphase that enables lower charge-transfer resistance and fast Li+ diffusion kinetics with negligible initial irreversible capacity loss. As a result, the CZTS@N-C electrode delivers a significantly enhanced capacity of 710 mAh g−1 with 73% capacity retention after 220 cycles at a current rate of 0.5 mA g−1 and superior rate performance compared to that of unmodified CZTS. Additionally, the study sheds light on the fast lithiation dynamics chemistry of CZTS@N-C through kinetics analysis, explored by in-situ Raman, ex-situ X-ray absorption, and in-situ electrochemical impedance. This study provides a new approach for fabricating high-performance, durable conductive polymer-encapsulated low-cost transition-metal-sulfide anode materials.

Electrochemical performance of copper phosphosulfide (Cu3PS4) towards magnesium ion storage

Rechargeable magnesium batteries are good alternates for large scale energy storage applications and development of electrolytes as well as electrode materials are being pursued. In the present study, a cost-effective electrode material made of naturally abundant elements, Cu3PS4 is proposed for rechargeable magnesium battery. The electrochemical performance of Cu3PS4 is evaluated in different potential ranges. Further enhancement in the performance is achieved by using a carbon nanotube composite. The optimized electrode can deliver high capacity of 130 mAh g−1 at 50 mA g−1 current density and high cycling stability of 500 cycles with 80 % capacity retention at 1000 mA g−1 current density at room temperature. The possible mechanism for Mg2+ storage is probed by ex-situ X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS).

Corrosion behavior of a compositionally complex alloy utilizing simultaneous Al, Cr, and Ti passivation

The corrosion behavior of the Al0.3Cr0.5Fe2Mn0.25Mo0.15Ni1.5Ti0.3 compositionally complex dual-phase alloy was explored in a variety of electrolytes. Comparable corrosion resistance to 316L stainless steel and Ni-Cr binaries was observed in NaCl despite lower Cr concentrations. Individual elemental fates during corrosion were identified by combinations of in-situ atomic emission spectroelectrochemistry and ex-situ X-ray photoelectron spectroscopy with high-resolution surface analysis and depth profiling. A potentiostatically grown passive film was enriched in Al(III), Cr(III), Ti(IV), and Mo(VI). Al-Ti and Cr-Ti layers were suggested but significant Al, Cr, and Ti mixing was present. Proposed benefits of Al-Cr-Ti coexistence are addressed.

Regulating the electrochemical activity of Fe-Mn-Cu-based layer oxides as cathode materials for high-performance Na-ion battery

Fe-Mn based layer oxides cathode materials have attracted widespread attention as a potential candidate for sodium-ion batteries (SIBs) owing to the earth abundance, cost-effectiveness and acceptable specific capacity. However, the irreversible phase transition often brings rapid capacity decay, which seriously hinders the practical application in large-scale energy storage. Herein, we design a nickel-doped Na0.70Fe0.10Cu0.20Ni0.05Mn0.65O2 (NFCNM-0.05) cathode material of SIBs with activated anionic redox reaction, and then inhibit the harmful phase transition. The ex-situ X-ray diffraction patterns demonstrate the NFCNM-0.05 always keeps the P2 phase during the sodiation/desodiation process, indicating a high structure stability. The ex-situ X-ray photoelectron spectroscopy implies the redox reactions between O2− and O− occur in the charging process, which offers extra specific capacity. Thus, the NFCNM-0.05 electrode delivers a high initial discharge capacity of 148 mA h g−1 and remains a prominent cycling stability with an excellent capacity retention of 95.9% after 200 cycles at 1 C. In addition, the electrochemical impedance spectroscopy and galvanostatic intermittent titration technique show the NFCNM-0.05 electrode possesses fast ion diffusion ability, which is beneficial for the enhancement of rate performance. Even at 10 C, the NFCNM-0.05 can offer a reversible discharge capacity of 81 mA h g−1. DFT calculation demonstrates the doping of appropriate amount of Ni ions is benefit for the enhancement of the electrochemical performance of the layer oxides. This work provides an effective strategy to enhance the electrochemical performance of Fe-Mn based cathode materials of SIBs.

One step in-situ synthesis of Na3V2(PO4)3/Na3V3(PO4)4 biphase coexisted cathode with high energy density by inducing of polyvinylpyrrolidone for sodium ion batteries

The low voltage platform (∼3.4 V) and energy density of Na3V2(PO4)3 are far from the requirement of practical applications. Herein, Na3V2(PO4)3/Na3V3(PO4)4 biphase coexisted cathode is synthesized by a sol-gel method in one step. It exhibits an extra stable and sustained high voltage plateau (∼3.9 V) derived from the Na3V3(PO4)4. Polyvinylpyrrolidone (PVP) acts as a structural guiding agent to induce the formation of Na3V3(PO4)4 and behaves as a chelating agent to facilitate the synthesis of Na3V2(PO4)3. Nitrogen atoms on five-membered rings in PVP are reductive to make the reaction of V5+/V3+ faster and more complete. Furthermore, PVP decomposes into clusters and free radicals to form uniform carbon with relatively ordered structure. The generated nitrogen-doped carbon coating formed by PVP possesses more beneficial defects to accelerate the transport of electrons, resulting in superior kinetic characteristics. Ex-situ X-ray photoelectron spectroscopy demonstrates the reversible V3+/V4+ redox pair features both at voltage of 3.4 and 3.9 V, further indicating the biphase coexistence of Na3V2(PO4)3/Na3V3(PO4)4. Correspondingly, Na3V2(PO4)3/Na3V3(PO4)4 biphase material submits a capacity of 119.17 mAh g−1 at 0.1C and delivers an impressive energy density of 471.19 Wh kg−1. This novel biphase cathode significantly improves the energy density of Na3V2(PO4)3 to promote its practical application.

Surface redox pseudocapacitance boosting Fe/Fe3C nanoparticles-encapsulated N-doped graphene-like carbon for high-performance capacitive deionization

The practical application of carbon anode in capacitive deionization (CDI) is greatly hindered by their poor adsorption capacity and co-ion effect. Herein, an N-doped graphene-like carbon (NC) decorated with Fe/Fe3C nanoparticles composite (Fe/Fe3C@NC) with large specific surface area and plentiful porosity is fabricated via a facile and scalable method, namely sol–gel method combined with Fe-catalyzed carbonization. As expected, it exhibits superior CDI performance as a Cl-storage electrode, with Cl- adsorption capacity as high as 102.3 mg g−1 at 1000 mg L−1 Cl- concentration and 1.4 V voltage, and a stable capacity of 68.5 mg g−1 for 60 cycles in 500 mg L−1 Cl– concentration and 100 mA g−1 current density. More importantly, on the basis of electrochemical tests, ex-situ X-ray diffraction, ex-situ X-ray photoelectron spectroscopy (XPS), and XPS analysis with argon ion depth etching, it is revealed that the chlorine storage mechanism of the Fe/Fe3C@NC electrode is dominated by the surface-related redox pseudocapacitance behavior of Fe2+/Fe3+ couple occurring on or near the surface, enabling fast and reversible ion storage. This work proposes an economical and environmentally friendly general method for the design and development of high-performance Cl-storage electrodes for CDI, and offers an in-depth insight into the Cl- storage mechanism of Fe decorated carbon electrodes, further promoting the development of CDI technology.

Film-forming mechanism of 1,3-propanediolcyclic sulfate as a bifunctional additive for 4.45 V graphite/LiCoO2 batteries

Increasing the cutoff voltage is efficient to increase the energy density of LiCoO2-based lithium-ion batteries to meet consumers' demand for electronic devices. However, higher cut-off voltage may lead to continuous decomposition of electrolyte and shorten the battery's cycle life. Herein, 1,3-propanediolcyclic sulfate (PCS) is designed as a film-forming additive to improve the electrochemical performance of high-voltage graphite/LiCoO2 cells. The combined density functional theory (DFT) calculations and experimental results indicate that PCS participates in the film formation on both LiCoO2 cathode and graphite anode side to regulate the interfacial reaction and inhibit the corresponding gas production. Thus, the capacity retention of 4.45 V graphite/LiCoO2 pouch cells cycled at 45 °C after 300 cycles is elevated from 59.5% to 80.1% by incorporating 1.0 wt% PCS additive into the base electrolyte. It is found that PCS follows the C-O bond breaking mechanism on the positive electrode and S-O bond breaking mechanism on the negative electrode, respectively. In addition, PCS may undergo H-transfer reaction at the cathode in the first cycle because the -O-SO2- group appears as oxidation product in ex-situ X-ray photoelectron spectroscopy (XPS) results. This finding provides new insights for understanding the mechanism of PCS acting as a high-voltage additive.

A new high voltage alluaudite sodium battery insertion material

Large-scale stationary storage forms a key sector that can be economically served by sodium-ion batteries. In realizing practical sodium-ion batteries, discovery and development of novel cathodes is essential. In this spirit, alluaudite-type Na2Fe2(SO4)3 was reported in 2014 to have the highest Fe3+/Fe2+ redox potential (∼3.8 V vs. Na). This finding led to reports on various PO43− and SO42− based alluaudite compounds exhibiting high energy densities. In 2017, MoO42− based alluaudite, Na2.67Mn1.67(MoO4)3, was found as a 3.45 V cathode material. Exploring molybdenum chemistry further, this work reports alluaudite type Na3.36Co1.32(MoO4)3 (NCMo) as a novel versatile electroactive cathode for Li-ion and Na-ion batteries. It was synthesized by a wet solution-combustion route with a restricted annealing duration of 1 min at 600 °C. Calorimetric study revealed the formation enthalpy from component oxides (ΔH°f,ox = −575.49 ± 7.75 kJ/mol) to be highly exothermic. Unlike the sulfate class of alluaudites, this material is highly stable in air and moisture (ΔHds = 537.42 ± 0.78 kJ/mol). Having an ionic conductivity of 6.065 × 10−8 S/cm (at 50 °C), it offers a pseudo two-dimensional Na+ migration pathway. Without any material optimization, NCMo was found to work as a high-voltage insertion cathode (ca. 4.0 V vs. Na/Na+ and 4.1 V vs. Li/Li+) in sync with theoretically predicted potential of 3.98 V (vs. Na/Na+). Ex-situ X-ray diffraction and photoelectron spectroscopy studies revealed the occurrence of solid-solution redox mechanism solely involving Co3+/Co2+ redox centre. It benchmarks Na3.36Co1.32(MoO4)3 as a novel electrochemically active Mo-based alluaudite-type polyanionic cathode insertion material.

Mechanistic insights into efficient peroxymonosulfate activation by NiCo layered double hydroxides

The efficient removal of organic refractory pollutants such as dyes and antibiotics in wastewater is crucial for protecting the environment and human health. In this work, a NiCo-layered double hydroxide (NiCo-LDH) with a uniform microspherical, hierarchical structure and a high surface area was successfully synthesized as an effective peroxymonosulfate (PMS) activator for the degradation of various organic dyes and antibiotics. The influence of various parameters on the catalytic activity of the NiCo-LDH was determined. Radical scavenger studies unveiled the major reactive oxygen species (ROSs) generated in the NiCo-LDH/PSM system to be 1O2, SO4•−, and O2•−. Ex-situ X-ray photoelectron spectroscopy (XPS) analysis uncovered the role of Co sites and oxygen vacancy as active sites and revealed the reversible redox properties of NiCo-LDH based on Co2+/Co3+ cycles. The activation mechanism and Rhodamine B (RhB) degradation pathways were experimentally studied and proposed. The NiCo-LDH is highly versatile, reusable and stable as shown by post-catalysis characterizations. This work shows the excellent catalysis performances and provides insights into the activation mechanism of PMS by NiCo-LDH for organic pollutant remediation.

Ultrahigh level heteroatoms doped carbon nanosheets as cathode materials for Zn-ion hybrid capacitor: The indispensable roles of B containing functional groups

Heavily heteroatoms doped carbons are highly attractive for electrochemical energy storage and electrocatalysis applications. We report herein a versatile coordination chemistry strategy for the producing of B, N co-doped carbon nanosheets (BCN-Mg) with an ultrahigh doping level (15.26 % for N, 10.18 % for O, and 3.21 % for B) though pyrolysis of nitrogen-rich Mg-based complex in the presence of boric acid. In this protocol, hexamethylenetetramine, which acts as both carbon and nitrogen source, can easily complex with magnesium ion to form a nitrogen-rich Mg-based complex in aqueous solution due to the presence of plentiful amino groups with strong complexation capability. Benefiting from the ultrahigh doping level and moderate specific surface area of 428 m2 g−1, the as-obtained B, N co-doped carbon nanosheets display a high specific capacity of 130.7 mA h g−1 (at 0.1 A g−1), and good stability of 87.3 % after 10,000 cycles when serves as the cathode for aqueous Zn-ion hybrid capacitors. More importantly, change details of the N and B containing functional groups during the charge-discharge process have been fully evaluated by ex-situ X-ray photoelectron spectroscopy characterization technique and density functional theory calculations. This work not only offers a new way to develop B, N co-doped carbon nanosheets with an ultrahigh doping level but also shed some new insight on the roles of heteroatoms containing functional groups for electrochemical energy storage applications.

(Digital Presentation) Fundamental Insights into Electrodeposition of Mixed Chromium Metal-Carbide-Oxides from Trivalent Chromium – Formate Electrolytes

Recent restrictions on industrial usage of hexavalent chromium under new REACH legislation have further sparked the development of hexavalent chromium-free chromium plating processes. An industrially important development in this field is Trivalent Chromium Coating Technology (TCCT®), a chromium electroplating technology for packaging steel developed at Tata Steel. In this process, aqueous trivalent chromium electrolytes rather than hexavalent chromium electrolytes are employed for the electrodeposition of metallic chromium. However, to deposit metallic chromium from a trivalent chromium electrolyte, it is necessary to incorporate a complexing agent given the kinetic inertness of aqueous trivalent chromium complexes. Formate plays this role in the TCCT® process yielding coatings comparable to the conventional hexavalent chromium-based process [1-4].However, understanding the mechanism and kinetics of chromium electrodeposition from this system is quite limited. Fundamental knowledge of the deposition process is key for industrial process optimization. Essential to determining the reaction mechanism and kinetics is the identification of the chemical species involved in the reaction. Using a hybrid multiscale experimental and computational approach, insights into chromium complexation in the bulk electrolytes and how this speciation influences the composition of the deposit have been gained.Samples electroplated in electrolytes of varied formate concentrations were characterized using X-ray Fluorescence (XRF) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). Results from these analyses show that metallic chromium is only deposited when the electrolyte contains formate ions. In the absence of formate, only oxide and carbide species are deposited. The characterization results also show a current efficiency of the TCCT process of ~ 40%. From observations from surface characterization as well as spectroscopic analysis and density functional theory (DFT) and ab initio molecular dynamics studies (AIMD) of the bulk electrolyte, the coordination and complexation of formate ion in the chromium complex responsible for metallic chromium deposition have also been identified. Voltammetric studies coupled with ex-situ XPS and scanning electron microscopy (SEM) surface characterization also lead to a clear definition of the reaction mechanism of metallic chromium deposition that the incorporation of formate in trivalent chromium electrolytes makes possible.

Zero volt storage of Na-ion batteries: Performance dependence on cell chemistry!

Sodium-ion batteries (NIBs) are regaining their importance in recent years as a sustainable complementary energy storage device for Li-ion batteries. Although, they cannot compete in terms of energy density with respect to Li-ion, they present a few advantages, namely the 0 V stability that makes them safe during external short and/or over-discharge. When the cell is discharged to 0 V, the negative electrode potential shoots up high during which the copper current collector in use for Li-ion cells could oxidize, dissolve and leads to internal short. In contrast, Na-ion cells utilize an aluminium current collector that is strongly resistant against oxidation, hence enabling their 0 V stability. However, apart from the current collector stability, the negative electrode potential rise could cause interphase instability which is not well elucidated. Hence, herein, we explored two different Na-ion chemistries, namely polyanionic Na3V2(PO4)2F3-hard carbon and sodium layered oxide-hard carbon using different electrolyte formulations. Combined impedance analyses, ex-situ X-ray photoelectron spectroscopy (XPS) and operando optical sensing indicate the 0 V discharge involves SEI degradation thereby deteriorating the cell performance, the extent of which depends on the positive electrode potential and the electrolyte in use. Overall, the 0 V stability is not an in-built property of Na-ion cells and a careful selection of cell chemistry is mandatory to achieve 0 V stable Na-ion cells.

Suppressed P2–P2′ phase transition of Fe/Mn-based layered oxide cathode for high-performance sodium-ion batteries

P2-type Fe/Mn-based layered oxide cathode has attracted enormous interest as a prospective candidate for sodium-ion batteries (SIBs) used in large-scale energy storage owing to its low cost, low toxicity, earth abundance and high theoretical specific capacity. However, the P2–P2′ phase transition associated with the Jahn–Teller effect of Mn 3+ at the end of the discharge process often appears, leading to severe capacity fading during charge-discharge process. Herein, we propose an effective strategy of using Al-doping to completely inhibit the harmful P2–P2′ phase transition by suppressing the Jahn–Teller effect of Mn 3+ , which has been verified by ex-situ and in-situ X-ray powder diffraction (XRD), high-resolution transmission electron microscope (HR-TEM) and ex-situ X-ray photoelectron spectroscopy (XPS). Consequently, Al-doped P2-Na 0.67 Fe 0.5 Mn 0.45 Al 0.05 O 2 electrode exhibits excellent cycling stability (92.8% capacity retention after 200 cycles at 1 C within 2.0–4.0 V). Meanwhile, Al-doping could widen interspacing of Na + layer to accelerate the migration of Na + , further improve rate capability (from 32 to 48% under the ratio of 5 to 0.1 C). This work provides a new sight to effectively suppress P2–P2′ phase transition for Fe/Mn-based layered oxide cathode.

Reversible anionic redox and spinel-layered coherent structure enable high-capacity and long-term cycling of Li-rich cathode

Initiating effective strategies to improve the reversibility of anionic redox and structural stabilization is crucial to the development and industrial application of Li-rich cathode materials (LRO), which are regarded as the preferred option of the cathode materials for the next-generation lithium-ion battery with high energy density. To remit the unexpected behavior of structural destruction and capacity attenuation, this paper proposes a strategy for maintaining high specific capacity and improving the reversible anionic redox and stable cyclic performance of LRO by introducing the spinel-layered coherent structure and S-anions. Proved by the ex-situ X-ray photoelectron spectroscopy, S-anions can regulate the anionic redox reversibility and thus enhance the reversible discharge capacity and initial Coulombic efficiency. Moreover, the structural stability is greatly improved by the introduction of spinel-layered coherent structure and S-anions in LRO, which has been confirmed by abundant structural characterizations. Besides, the results reveal that the optimized material exhibits a high reversible discharge capacity of 289.52 mAh/g and good cyclic performance with a retention rate of 88.21% after 200 cycles. Evidently, the structure design strategy for LRO based on the reversible anionic redox and spinel-layered coherent structure is a significant exploration, which will bring a new clew for the design of the cathode materials with high-energy–density and excellent electrochemical performance.

A cobalt-based coordination compound with high capacity as the anode of lithium-ion battery and its stepwise reaction mechanism

Metal-coordination compounds are regarded as the most promising electrodes for lithium-ion batteries compared to inorganic anode materials because they are environmentally benign, rich in coordination, abundant in active sites, and low cost. In contrast, their possible molecular structures and reaction mechanisms are still mysteries. Here, using a microwave-assisted solvothermal process, we created the Co-1,3,5-trioxy-2,4,6-Triamino-benzo (Co-TB) coordination compound, which exhibits a flower-like shape of tiny flakes with a typical crystal feature. When applied as the anode of lithium-ion battery (LIB), Co-TB has shown a high reversible capacity of 1092 mAh g−1 at 1 A g−1 after 800 cycles and remarkable rate performances (497 mAh g−1 at 5 A g−1). This is significantly better than pure TB with similar functional groups but without coordination cations. Based on several electrochemical characterization techniques, ex-situ X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and in-situ X-ray diffraction techniques, a possible molecular structure, and stepwise reaction mechanism are postulated. All of them have demonstrated that the stepwise redox reactions between Co-TB and Li relied on these reactions of Li+ ions and Co2+/various multiple organic functional groups in Co-TB, including CO, CN, and CC of benzene rings. The synthesized method and characterization approaches can be extended to study other organic metal-coordination compounds.