Surface coating by mechanofusion modulates bulk charging pathways and battery performance of Ni-rich layered cathodes.

Ni-rich layered oxides as high-capacity battery cathodes suffer from degradation at high voltages. We utilize a dry surface modification method, mechanofusion (MF), to achieve enhanced battery stability. The simplicity, high yield, and flexibility make it cost-effective and highly attractive for processing at the industrial scale. The underlying mechanisms responsible for performance improvement are unveiled by a systematic study combining multiple probes, e.g., 3D nano-tomography, spectroscopic imaging, in situ synchrotron diffraction, and finite element analysis (FEA). MF affects the bulk crystallography by introducing partially disordered structure, microstrain, and local lattice variation. Furthermore, the crack initiation and propagation pattern during delithiation are regulated and the overall mechanical fracture is reduced after such surface coating. We validate that MF can alter the bulk charging pathways. Such a synergic effect between surface modification and bulk charge distribution is fundamentally important for designing next-generation battery cathode materials.

Large-Scale Synthesis of N,S Codoped Carbon-Modified Fe0.975S Composites as a Novel Anode for Lithium/Sodium Ion Batteries with Enhanced Performance.

To overcome obstacles hindering the commercialization of lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), we introduce a cost-effective single-step sulfurization strategy for synthesizing iron sulfide (Fe0.975S) nanohybrids, augmented by N,S codoped carbon. The resulting N,S codoped carbon-coated Fe0.975S (Fe0.975S@NSC) electrode exhibits exceptional potential as a highly reversible anode material for both LIBs and SIBs. With impressive initial discharge and charge capacities (1658.2 and 1254.9 mAh g-1 for LIBs and 1450.9 and 1077.1 mAh g-1 for SIBs), the electrode maintains substantial capacity retention (900 mA h g-1 after 1000 cycles for LIBs and 492.5 mA h g-1 after 600 cycles for SIBs at 1.0 A g-1). The LiMn2O4//Fe0.975S@NSC and Na3V2(PO4)3//Fe0.975S@NSC full batteries can maintain excellent reversible capacity and robust cycling stability. Ex situ and in situ X-ray diffraction, density functional theory (DFT) calculations, and kinetics analysis confirm the promising energy storage potential of the Fe0.975S@NSC composite.

Grafting a Polymer Coating Layer onto Li1.2 Ni0.13 Co0.13 Mn0.54 O2 Cathode by Benzene Diazonium Salts to Facilitate the Cycling Performance and High-Voltage Stability.

Li-rich Mn-based cathodes have been regarded as promising cathodes for lithium-ion batteries because of their low cost of raw materials (compared with Ni-rich layer structure and LiCoO2 cathodes) and high energy density. However, for practical application, it needs to solve the great drawbacks of Li-rich Mn-based cathodes like capacity degradation and operating voltage decline. Herein, an effective method of surface modification by benzene diazonium salts to build a stable interface between the cathode materials and the electrolyte is proposed. The cathodes after modification exhibit excellent cycling performance (the retention of specific capacity is 84.2% after 350 cycles at the current density of 1 C), which is mainly attributed to the better stability of the structure and interface. This work provides a novel way to design the coating layer with benzene diazonium salts for enhancing the structural stability under high voltage condition during cycling.

Universal Intercalation/Alloying Hybrid Mechanism with -ICOHP Criterion in MAX Toward Steadily Ascending Lithium-Ion Batteries.

Profiting from the unique atomic laminated structure, metallic conductivity, and superior mechanical properties, transition metal carbides and nitrides named MAX phases have shown great potential as anodes in lithium-ion batteries. However, the complexity of MAX configurations poses a challenge. To accelerate such application, a minus integrated crystal orbital Hamilton populations descriptor is innovatively proposed to rapidly evaluate the lithium storage potential of various MAX, along with density functional theory computations. It confirms that surface A-element atoms bound to lithium ions have odds of escaping from MAX. Interestingly, the activated A-element atoms enhance the reversible uptake of lithium ions by MAX anodes through an efficient alloying reaction. As an experimental verification, the charge compensation and SnxLiy phase evolution of designed Zr2SnC MAX with optimized structure is visualized via in situ synchrotron radiation XRD and XAFS technique, which further clarifies the theoretically expected intercalation/alloying hybrid storage mechanism. Notably, Zr2SnC electrodes achieve remarkably 219.8% negative capacity attenuation over 3200 cycles at 1 A g-1. In principle, this work provides a reference for the design and development of advanced MAX electrodes, which is essential to explore diversified applications of the MAX family in specific energy fields.

2D Se-Rich ZnSe/CoSe2@C Heterostructured Composite as Ultrastable Anodes for Alkaline-Ion Batteries.

2D transitional metal selenide heterostructures are promising electrode materials for potassium-ion batteries (PIBs) owing to the large surface area, high mechanical strength, and short diffusion pathways. However, the cycling performance remains a significant challenge, particularly concerning the electrochemical conversion reaction. Herein, 2D Se-rich ZnSe/CoSe2@C heterostructured composite is fabricated via a convenient hydrothermal approach followed by selenization process, and then applied as high-performance anodes for PIBs. For example, the capacity delivered by the heterostructured composite is mainly contributed to the synergistic effect of conversion and alloy/de-alloy processes aroused by K+, where K+ may highly insert or de-insert into Se-rich ZnSe/CoSe2@C. The obtained electrode delivers an outstanding reversible charge capacity of 214 mA h g-1 at 1 A g-1 after 4000 cycles for PIBs, and achieves 262 mAh g-1 when coupled with a PTCDA cathode in the full cell. The electrochemical conversion mechanism of the optimized electrode during cycling is investigated through in situ XRD, Raman, and ex situ HRTEM. In addition, the heterostructured composite as anodes also displays excellent electrochemical performances for sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs). This work opens up a new window for investigating novel electrode materials with excellent capacity and long durability.

Fabrication of a Stable and Highly Effective Anode Material for Li-Ion/Na-Ion Batteries Utilizing ZIF-12.

Transition metal selenides (TMSs) are receiving considerable interest as improved anode materials for sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs) due to their considerable theoretical capacity and excellent redox reversibility. Herein, ZIF-12 (zeolitic imidazolate framework) structure is used for the synthesis of Cu2Se/Co3Se4@NPC anode material by pyrolysis of ZIF-12/Se mixture. When Cu2Se/Co3Se4@NPC composite is utilized as an anode electrode material in LIB and SIB half cells, the material demonstrates excellent electrochemical performance and remarkable cycle stability with retaining high capacities. In LIB and SIB half cells, the Cu2Se/Co3Se4@NPC anode material shows the ultralong lifespan at 2000 mAg-1, retaining a capacity of 543 mAhg-1 after 750 cycles, and retaining a capacity of 251 mAhg-1 after 200 cycles at 100 mAg-1, respectively. The porous structure of the Cu2Se/Co3Se4@NPC anode material can not only effectively tolerate the volume expansion of the electrode during discharging and charging, but also facilitate the penetration of electrolyte and efficiently prevents the clustering of active particles. In situ X-ray difraction (XRD) analysis results reveal the high potential of Cu2Se/Co3Se4@NPC composite in building efficient LIBs and SIBs due to reversible conversion reactions of Cu2Se/Co3Se4@NPC for lithium-ion and sodium-ion storage.

Phosphorous and Nitrogen Dual-Doped Carbon as a Highly Efficient Electrocatalyst for Sodium-Oxygen Batteries.

Sodium-oxygen batteries have been regarded as promising energy storage devices due to their low overpotential and high energy density. Its applications, however, still face formidable challenges due to the lack of understanding about the influence of electrocatalysts on the discharge products. Here, a phosphorous and nitrogen dual-doped carbon (PNDC) based cathode is synthesized to increase the electrocatalytic activity and to stabilize the NaO2 superoxide nanoparticle discharge products, leading to enhanced cycling stability when compared to the nitrogen-doped carbon (NDC). The PNDC air cathode exhibits a low overpotential (0.36 V) and long cycling stability (120 cycles). The reversible formation/decomposition and stabilization of the NaO2 discharge products are clearly proven by in-situ synchrotron X-ray diffraction and ex-situ X-ray diffraction. Based on the density functional theory calculation, the PNDC has much stronger adsorption (-2.85 eV) for NaO2 than that of NDC (-1.80 eV), which could efficiently stabilize the NaO2 discharge products.

NiFe and CoFe nanocatalysts supported on highly dispersed alumina-silica: Structure, surface properties, and performance in CO2 methanation.

The hydrogenation of CO2 to CH4 has gained considerable interest in terms of sustainable energy and environmental mitigation. In this regard, the present work aims to investigate the adsorptive concentration and CO2 methanation performance over CoFe and NiFe bimetallic catalysts supported on fumed alumina-silica SA96 support at 170-450 °C and under atmospheric pressure. The catalysts were prepared by wet impregnation method, subjected to calcination and further reduced with hydrogen, and their performance in CO2 methanation was investigated in a hydrogen-rich 2%CO2-55%H2-43%He gas mixture. In this study, we describe the crystal and mesoporous structures of the prepared catalysts by in-situ XRD and ex-situ nitrogen adsorption, evaluate the NiFe and CoFe metal surface states before and after catalysis by XPS, visualize the surface morphology by SEM, estimate the catalytic activity by gas chromatography, and investigate the adsorbed surface species, showing the presence of *HCOO/*HCO and *CO intermediates, determine two possible pathways of CH4 formation on the studied catalysts by temperature-programmed desorption mass spectrometry, and correlate the structural and surface properties with high CO2 conversions up to 100% and methanation selectivities up to 72%. The latter is related to changes in the elemental chemical states and surface composition of CoFe and NiFe nanocatalysts induced by treatment under reaction conditions, and the surface reconstruction during catalysis transfers the part of active 3d transition metals into the pores of the SA96 support. Our thorough characterization study with complementary techniques allowed us to conclude that this high activity is related to the formation of catalytically active Ni/Ni3Fe and Co/CoFeOx nanoscale crystallites under H2 reduction and their maintenance under CO2 methanation conditions. The successfully applied combination of CO2 chemisorption and thermodesorption techniques demonstrates the ability to adsorb the CO2 molecules by supported NiFe and CoFe nanocatalysts and the pure alumina-silica SA96 support.

Metal Ion-Induced Porous MXene for All-Solid-State Flexible Supercapacitors.

MXenes are normally used for energy storage applications. However, large nanosheets and restacking are detrimental to the ion diffusion and thus limit its rate capability. Here, a strategy to prepare flexible and porous MXene-M supercapacitor electrodes can simultaneously enlarge the interlayer spacing between layers and create holes in the layers. As a result, Ti3C2Tx-Mn presents an excellent lifespan, with still 248 F g-1 after 100 000 cycles at a current density of 100 A g-1. Moreover, Ti3C2Tx-Mn-based symmetric all-solid-state supercapacitor exhibits outstanding volumetric energy up to 52.4 mWh cm-3 and retains 38.4 mWh cm-3 at an ultrahigh volumetric power density of 55.3 W cm-3. We believe this work provides an idea for the later regulation of MXene layer spacing and the design of porous structures, and can be widely used in the next-generation high-energy density and power density practical applications.

Asymmetric Lithium Extraction and Insertion in High Voltage Spinel at Fast Rate.

Spinel-structured ordered-LiNi0.5Mn1.5O4 (o-LNMO) has experienced a resurgence of interest in the context of reducing scarce elements such as cobalt from the lithium-ion batteries. O-LNMO undergoes two two-phase reactions at slow rates. However, it is not known if such phenomenon also applies at fast rates. Herein, we investigate the rate-dependent phase transition behavior of o-LNMO through in operando time-resolved X-ray diffraction. The results indicate that a narrow region of the solid solution reaction exists for charge and discharge at both slow and fast rates. The overall phase transition is highly asymmetric at fast rates. During fast charge, it is a particle-by-particle mechanism resulting from an asynchronized reaction among the particles. During fast discharge, it is likely a core-shell mechanism involving transition from Li0+xNi0.5Mn1.5O4 to Li1+xNi0.5Mn1.5O4 in the outer layer of particles. The Li0.5Ni0.5Mn1.5O4 phase is suppressed during fast discharge and appears only through Li redistribution upon relaxation.

Converting Carbon Dioxide into Carbon Nanotubes by Reacting with Ethane.

The urgency to mitigate environmental impacts from anthropogenic CO2 emissions has propelled extensive research efforts on CO2 reduction. The current work reports a novel approach involving transforming CO2 and ethane into carbon nanotubes (CNTs) using earth-abundant metals (Fe, Co, Ni) at 750 °C. This route facilitates long-term carbon storage via generating high-value CNTs and produces valuable syngas with adjustable H2/CO ratios as byproducts. Without CO2, direct pyrolysis of ethane undergoes rapid deactivation. The participation of CO2 not only enhances the durability of the catalyst, but also contributes about 30 % of the CNTs production, presenting a viable solution to CO2 challenges. The CNT morphology depends on the catalyst used. Co- and Ni-based catalysts produce CNT with a 20 nm diameter and micrometer length, whereas Fe-based catalysts yield bamboo-like structures. This work represents a pioneering effort in utilizing CO2 and ethane for CNT production with potential environmental and economic benefits.

Construction of Co1-x S Nanoparticles Embedding in N-Doped Amorphous Carbon@Graphene with Enhanced Li-Ion Storage.

Cobalt sulfide is deemed a promising anode material, owing to its high theoretical capacity (630 mAh g-1 ). Due to its low conductivity, fast energy decay, and the huge volume change during the lithiation process limits its practical application. In this work, a simple and large-scale method are developed to prepare Co1-x S nanoparticles embedding in N-doped carbon/graphene (CSCG). At a current density of 0.2 C, the reversible discharge capacity of CSCG maintains 937 mAh g-1 after 200 cycles. The discharge capacity of CSCG maintains at 596 mAh g-1 after 500 cycles at the high current density of 2.0 C. The excellent performance of CSCG is due to its unique structural features. The addition of rGO buffered volume changes while preventing Co1-x S from crushing/aggregating during the cycle, resulting in multiplier charge-discharge and long cycle life. The N-doped carbon provides a simple and easy way to achieve excellent performance in practical applications. Combined with density functional theory calculation, the presence of Co-vacancies(Co1-x ) increases more active site. Moreover, N-doping carbon is beneficial to the improve adsorption energy. This work presents a simple and effective structural engineering strategy and also provides a new idea to improve the performance of Li-ion batteries.

Single-Phase Precursors for the Preparation of Spinel Ferrites via Oxalate Route: the Study of Cobalt Ferrite Synthesis.

This work explores the benefits of single-phase oxalate precursors for the preparation of spinel ferrites by thermal decomposition. A direct comparison between the genuine oxalate solid solution and the physical mixture of simple oxalates is presented using the case study of cobalt ferrite preparation. The mixing of metal cations within a single oxalate structure could be verified prior to its thermal decomposition by several non-destructive experimental techniques, namely Mössbauer spectroscopy, X-ray powder diffraction (XRD) and energy-dispersive X-ray spectroscopy. In situ XRD experiments were conducted to compare the decomposition processes of the solid solution and the physical mixture. Additionally, the decomposition products of the FeCo oxalate solid solution were studied ex situ by means of N2 adsorption, Mössbauer spectroscopy and XRD. The results obtained for different reaction temperatures demonstrate the possibilities to easily control the physical properties of the prepared oxides.

A Composite of Two Dimensional GeSe2 /Nitrogen-Doped Reduced Graphene Oxide for Enhanced Capacitive Lithium-Ion Storage.

A composite of two-dimensional (2D) GeSe2 nanosheets dispersed on N-doped reduced graphene oxide (GeSe2 /N-rGO) is fabricated via a simple hydrothermal method combined with post-selenization process. The high electronic conductivity and the substantial void spaces of the wrinkled N-rGO can improve the electrical conductivity of the active material and accommodate the volume evolution of GeSe2 nanosheets during the (de)lithiation processes, while GeSe2 nanosheets can reduce ion diffusion length effectively. Meanwhile, the unique layered structure is beneficial to the contact of the active material and electrolyte, and the reversibility of conversion reaction has also been improved. Furthermore, kinetics analysis reveals a pseudocapacitance-dominated Li+ -storage mechanism at high rates. In-situ X-ray diffraction analysis discloses that the conversion reaction has played a certain part in Li+ -storage. Thus, the GeSe2 /N-rGO composite delivers excellent rate capability and good long-term stability with a high reversible capacity of 711.0 mA h g-1 after 2000 cycles at 1 A g-1 .

Ten Thousand-Cycle Ultrafast Energy Storage of Wadsley-Roth Phase Fe-Nb Oxides with a Desolvation Promoting Interfacial Layer.

Developing advanced electrode materials with enhanced charge-transfer kinetics is the key to realizing fast energy storage technologies. Commonly used modification strategies, such as nanoengineering and carbon coating, are mainly focused on electron transfer and bulk Li+ diffusion. Nonetheless, the desolvation behavior, which is considered as the rate-limiting process for charge-storage, is rarely studied. Herein, we designed a nitridation layer on the surface of Wadsley-Roth phase FeNb11O29 (FNO-x@N) to act as a desolvation promoter. Theoretical calculations demonstrate that the adsorption and desolvation of solvated Li+ is efficiently improved at FNO-x@N/electrolyte interphase, leading to the reduced desolvation energy barrier. Moreover, the nitridation layer can also help to prevent solvent cointercalation during Li+ insertion, leading to advantageous shrinkage of block area and reduced volume change of lattice cell during cycling. Consequently, FNO-x@N exhibits a high-rate capacity of 129.7 mAh g-1 with negligible capacity decay for 10 000 cycles.

Solvent Co-Intercalation-Induced Activation and Capacity Fade Mechanism of Few-/Multi-Layered MXenes in Lithium Ion Batteries.

MXenes attract tremendous research efforts since their discovery in 2011 due to their unique physical and chemical properties, allowing for application in various fields. One of them is electrochemical energy storage due to their pseudocapacitive (=redox) behavior, high electronic conductivity, and charge storage versatility regarding the cationic species (e.g., Li+ ). MXenes typically display stable charge/discharge cycling behavior over hundreds of cycles in numerous electrolytes, however, a drastic loss of reversible capacity is detectable during the initial cycles. Furthermore, an electrochemical "activation" is also reported in the literature, especially for free-standing electrodes. Here, these electrochemical phenomena are investigated by electrochemical and analytical means to decipher the responsible mechanism by comparing few-layered and multi-layered Ti3 C2 Tx . A change in the pseudocapacitive behavior of MXenes during cycling can be explained by in situ X-ray diffraction studies, revealing solvent co-intercalation in the first cycle for the morphologically different MXenes. This co-intercalation is responsible for the capacity decay detected in the first cycles and is also responsible for the ongoing "activation" occurring in later cycles.

Insight into the capacity decay mechanism of cycled LiNi0.5Co0.2Mn0.3O2cathodes viain situx-ray diffraction.

Layered LiNixCoyMn1-x-yO2(NCM) is expected to dominate the future cathode technology of the automotive industry, due to its high energy density and low cost. Despite its excellent prospects, however, the severe capacity decay of NCM cathodes has prevented this promising material from achieving further success. The mechanism underlying this phenomenon is controversial and has been generally understood as arising from the complex structural changes that take place upon Li-(de)intercalation. However, deeper insight has not been available due to unclear structural kinetics, in particular, in cycled NCM cathodes. For this study, we conductedin situhigh-energy synchrotron x-ray diffraction (XRD) measurements on a typical LiNi0.5Co0.2Mn0.3O2(NCM523) cathode that had been operated for 90 cycles, then compared the results with those collected from a fresh NCM532 electrode. It was revealed that the H1-H2 phase transition that only occurs at the first cycle is irreversible. Remarkably, thec-contraction triggered by the H2-H3 transition, which is expected to be the major cause of intergranular cracks in electrodes, became even more profound after cycling. Combining the above results with electrochemical testing and microscopic imaging, we discuss the interplay between structural dynamics and performance degradation in NCM532 in detail. This study provides key evidence for a mechanically induced capacity decay mechanism, which is expected to be extended to NCM materials with various compositions.

In Situ Analysis Reveals the Role of 2D Perovskite in Preventing Thermal-Induced Degradation in 2D/3D Perovskite Interfaces.

Engineering 2D/3D perovskite interfaces is a common route to realizing efficient and stable perovskite solar cells. Whereas 2D perovskite's main function in trap passivation has been identified and is confirmed here, little is known about its 2D/3D interface properties under thermal stress, despite being one of the main factors that induces device instability. In this work, we monitor the response of two typical 2D/3D interfaces under a thermal cycle by in situ X-ray scattering. We reveal that upon heating, the 2D crystalline structure undergoes a dynamical transformation into a mixed 2D/3D phase, keeping the 3D bulk underneath intact. The observed 3D bulk degradation into lead iodide is blocked, revealing the paramount role of 2D perovskite in engineering stable device interfaces.

Domino Effect: Gold Electrocatalyzing Lithium Reduction to Accelerate Nitrogen Fixation.

Green production of NH3 , especially the Li-mediated electrochemical N2 reduction reaction (NRR) in non-aqueous solutions, is attracting research interest. Controversies regarding the NRR mechanism greatly impede its optimization and wide applications. To understand the electrocatalytic process, we treated Au coated carbon fibrous paper (Au/CP) as the model catalyst. In situ XRD confirmed the transformation of lithium intermediates during NRR. Au greatly improved electron transfer kinetics to catalyze metallic Li formation, and accordingly highly accelerated spontaneous NRR. The Faradaic efficiency of NRR on Au/CP reached 34.0 %, and NH3 yield was as high as 50 µg h-1 cm-2 . Our research shows that the key step of Li-mediated non-aqueous NRR is electrocatalytic Li reduction and offers a novel electrocatalyst design method for Li reduction.

Nb2 O5 /RGO Nanocomposite Modified Separators with Robust Polysulfide Traps and Catalytic Centers for Boosting Performance of Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) have shown great potential for application in high-density energy storage systems. However, the performance of LSBs is hindered by the shuttle effect and sluggish reaction kinetics of lithium polysulfides (LiPSs). Herein, heterostructual Nb2 O5 nanocrystals/reduced graphene oxide (Nb2 O5 /RGO) composites are introduced into LSBs through separator modification for boosting the electrochemical performance. The Nb2 O5 /RGO heterostructures are designed as chemical trappers and conversion accelerators of LiPSs. Originating from the strong chemical interactions between Nb2 O5 and LiPSs as well as the superior catalytic nature of Nb2 O5 , the Nb2 O5 /RGO nanocomposite possesses high trapping efficiency and efficient electrocatalytic activity to long-chain LiPSs. The effective regulation of LiPSs conversion enables the LSBs enhanced redox kinetics and suppressed shuttle effect. Moreover, the Nb2 O5 /RGO nanocomposite has abundant sulfophilic sites and defective interfaces, which are beneficial for the nucleation and growth of Li2 S, as evidenced by analysis of the cycled separators. As a result, LSBs with the Nb2 O5 /RGO-modified separators exhibit excellent rate capability (816 mAh g-1 at 3 A g-1 ) and cyclic performance (628 mAh g-1 after 500 cycles). Remarkably, high specific capacity and stable cycling performance are demonstrated even at an elevated temperature of 50 °C or with higher sulfur loadings.