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High-voltage layered oxide cathodes attract great attention for sodium-ion batteries (SIBs) due to the potential high energy density, but high voltage usually leads to rapid capacity decay. Herein, a stable high-voltage NaLi0.1Ni0.35Mn0.3Ti0.25O2cathode with a ribbon-ordered superlattice is reported, and the intrinsic coupling mechanism between structure evolution and the anion redox reaction (ARR) is revealed. Li introduction constructs a special Li–O–Na configuration activating reversible nonbonded O 2p (|O2p)-type ARR and regulates the structure evolution way, enabling the reversible Li ions out-of-layer migration instead of the irreversible transition metal ions out-of-layer migration. The reversible structure evolution enhances the reversibility of the bonded O 2p (O2p)-type ARR and inhibits the generation of oxygen dimers, thus suppressing the irreversible molecular oxygen (O2)-type ARR. After the structure regulation, the structure evolution becomes reversible, |O2p-type ARR is activated, O2p-type ARR becomes stable, and O2-type ARR is inhibited, which largely suppresses the capacity degradation and voltage decay. The discharge capacity is increased from 154 to 168 mA h g–1, the capacity retention after 200 cycles significantly increases from 35 to 84%, and the voltage retention increases from 78 to 93%. This study presents some guidance for the design of high-voltage, O3-type oxide cathodes for high-performance SIBs.

To realize concurrently the high-energy density and excellent cycling stability, maximum utilization of redox couple, minimization of detrimental phase transition, and structural degradation of O3-type layered oxide cathodes are critical for developing Na-ion batteries. Ni2+/Ni4+redox couple showing multielectron reaction and higher redox potential is favorable to increase the energy density. However, the Jahn-Teller distortion of Ni3+generated upon (dis)charging results in a strong anisotropy in the local crystal structure that causes irreversible interlayer bending and chemo-mechanical cracks of the cathode particles, compromising the electrochemical properties eventually. In this work, we show a slight multielement doping strategy that enlarges the amount of active redox components while minimizing the inactive contents. The results show that the uniform distribution of multiple components can help increase the disorder degree of atom arrangement and alleviate the structural changes and detrimental anisotropy cracks. As a proof of concept, a multielement-doped O3-type Na0.9Ni0.25Cu0.05Mg0.05Zn0.05Fe0.05Al0.05Mn0.40Ti0.05Sn0.05O2oxide is rationally prepared that presents better chemo-mechanical stability and delayed O3-P3 phase transition behavior. Compared to the high Ni-content Na0.9Ni0.35Fe0.2Mn0.45O2cathode, this as-prepared multielement material delivers a reversible capacity of about 120 mAh/g in the voltage range of 2–4.0 V, superior cycling stability with 90% of capacity retention after 500 cycles, and excellent rate capability (more than 70% of initial capacity at 5.0 C). This work indicates that the multielement doping method is highly suitable for the development of advanced Na-ion layered oxide cathodes.

Ce2Fe14B compound has a great potential to serve as a novel permanent magnet alternative thanks to the abundant and inexpensive rare-earth element (cerium), while its low magnetocrystalline anisotropy and energy product severely restrict its applications. In this work, a novel strategy combining melt-spinning and electron-beam exposure (EBE) aiming for fabricating high-performance Ce-Fe-B magnetic materials is reported to solve the above-mentioned problem. Remarkably, this strategy facilitates developing a suitable grain boundary configuration without using any additional heavy rare-earth element. Under the optimal EBE condition, the maximum energy product ((BH)max) of pure Ce-Fe-B alloy is 6.5 MGOe, about four times higher than that obtained after conventional rapid thermal processing method for the same precursor. The enhanced intergranular magnetostatic coupling effect in the EBE sample is validated by mapping the first-order-reversal-curve (FORC) diagrams. The in-situobservation of magnetic domain wall motion for Ce-Fe-B alloy using Lorentz transmission electron microscopy reveals that the boundary layers are very effective in pinning the motion of domain walls, leading to the increased coercivity under EBE, and this pinning effect is further verified by micromagnetic simulations. Our results suggest that CeFeB materials using EBE could be a promising candidate after further processing, which could fill the performance “gap” between hexaferrite and Nd-Fe-B-based magnets.

P2-type Na0.67Mn0.75Fe0.25O2cathode materials with low cost and high specific capacity have aroused much interest for sodium-ion batteries. Nevertheless, the cyclic and structural stabilities need to be improved for practical application. Herein, we tune the activity and reversibility of the cationic redox and the structure stability in Na0.67Mn0.75Fe0.25O2by doping Mg/Ca/F into multi-Na/TM/O sites, respectively. The capacity performance at a high rate and cyclic stability are significantly enhanced. The mechanism of the synergy has been revealed by means of an X-ray photoelectronic spectrometer, neutron powder diffraction, ex situ/in situX-ray diffraction, and so on. The improvement of the rate performance is mostly due to the broadening of the interlayer spacing caused by the element doping and the decrease of the Na-ion diffusion barrier, which facilitates Na-ion diffusion. The reduced transitional metal (TM)–O bond length demonstrates that the bonding energy has been strengthened, which benefits the structural stability and the cycling stability. Moreover, the synergy of multisite substitution suppresses the P2-OP4 phase transition at a high voltage and further improves the cycle stability. The Mg doping also activates Mn3+/Mn4+redox and increases the intensity of Mn3+/Mn4+redox. The ratio of Mn3+/Mn4+is reduced by Ca substitution. Therefore, the Jahn–Teller effect, which is harmful to the structural stability, is restrained. The insights into the synergy of multisite substitution proposed in this study may also be helpful in the design of other cathode materials.

LiCoO2can deliver more capacity under a high voltage but it suffers from a serious capacity decay due to the irreversible structure transition during Li+intercalation/extraction. Herein, we propose to mitigate the irreversible structural changes through modulating the crystal lattice by Ca-P dual-doping with Ca3(PO4)2. Both the cycling stability and high-rate capacity have been largely enhanced. At 5C and 10C, the capacity retention rate after 500 cycles is significantly enhanced from 4 and 2% (bare samples) to 70 and 73%, respectively. The enhancement can be mainly attributed to the synergy of Ca and P dual-doping. Ca doped in the Li site can act as a “pillar” to prevent the lithium layer from collapsing when Li extracts and inserts during the charging/discharging process. The doped P in the transition metal site can synergize with Ca to further stabilize the crystal structure of LiCoO2under a high voltage. This study offers some insights on modulating the lattice structure through dual-doping, which can also be extended to other layered structures of cathode materials.

A large linear negative thermal expansion (NTE) and expanded NTE temperature range (ΔTNTE) were obtained in magnetoelastic CrTe1–xSex(0 ≤ x≤ 0.15) compounds. For CrTe compound, its thermal expansion coefficient of volume (αV) was calculated to be −28.8 ppm K–1with the temperature ranging from 280 to 340 K. Substituting Te with Se atoms, the NTE behavior and magnetic properties can be well manipulated. With increasing Se in CrTe1–xSex(0 ≤ x≤ 0.15) compounds, the ΔTNTEincreases from 60 K (280–340 K for x= 0), to 80 K (240–320 K for x= 0.05), to 95 K (200–295 K for x= 0.1), and finally to 100 K (170–270 K for x= 0.15). Furthermore, a linear NTE remains independent of temperature for samples with x≤ 0.1. The relationship between tunable NTE and magnetic properties was analyzed in detail, indicating that the NTE in CrTe1–xSexcompounds originates from the magnetovolume effect (MVE).

Lanthanide perovskite oxides have attracted much attention as an oxygen reduction and evolution catalyst because of their high chemical stability and composition adjustability. A defect strategy has been applied to enhance their electrocatalytic activity with the modulation of the crystal/electronic structure. However, the intrinsic roles of the defects, particularly A-site vacancies, are poorly understood. Herein, we prepare LaxNiO3with various ratios of A-site vacancies by a facile nonstoichiometric strategy, which has boosted the dual-function catalytic activity of LaNiO3. More importantly, the enhancement mechanism of A-site-deficient LaxNiO3as an oxygen redox catalyst has been unveiled. Induced vacancy defects on the A sites raise a compression strain in the NiO6octahedron, exerting a positive enhancement on Ni–O covalency. Furthermore, the egelectron filling in the active cation Ni and the overlapping state of Ni 3d–O 2p hybridization have also been optimized, in which renovation will further boost the catalytic ability of oxygen redox processes. This work not only clarifies the intrinsic roles of A-site deficiency in the structure and electrocatalytic activities of perovskite oxides but also presents some insights into the design and exploration of high-activity catalysts by cation defect modulation.

Nanoscale permanent magnetic materials, which possess excellent magnetic and mechanical properties, thermal stability, and corrosion resistance, have become a research hotspot for permanent magnets. In reality, however, the obtained maximum energy product, (BH)max, is not satisfactory in comparison with the theory limit, especially for exchange-coupled nanocomposite magnets. The construction of an ideal microstructure still remains a challenge in the synthesis and preparation of nanoscale permanent magnets. This work reported the impact of rapid thermal process (RTP) with electron-beam heating on the microstructures of Nd12.5-xFe80.8+xB6.2Nb0.2Ga0.3(x = 0, 2.5) nanocomposites. It was found that the crystallization time was greatly reduced, from 15 min under the conventional annealing conditions to 0.1 s under the RTP. For Nd2Fe14B single-phase materials, the crystallization temperature of the RTP ribbons decreased by about 248 °C compared with that of the ribbons produced by the conventional annealing method. A synergetic crystallization of the Nd2Fe14B and α-Fe phases was observed under the RTP, which restrained not only the shape, size distribution, and compositions of the hard and the soft phases, but also the interface between them. This modification effect became more obvious as the fraction of Fe increased. Due to the improvement in the uniformity of the Nd2Fe14B and α-Fe phases, and their grain size distribution, better magnetic properties were achieved using RTP in comparison with the conventional annealing method.

The Ce-substituted (Nd1−xCex)12.2Fe81.6B6.2(x = 0.0, 0.2, 0.4, 0.6) nanocrystalline ribbons were prepared by annealing amorphous ribbons from melt spinning. It is found that all ribbons are in a multiphase state consisting of α-Fe phase, Nd(Ce)-rich phases and RE2Fe14B (RE = Nd, Ce) phases. However, the coercivity of all annealed ribbons can reach a considerably high value without doping any heavy rare earth or other coercivity enhanced elements. A strong intergranular exchange coupling appears in these nanocrystalline ribbons. The Nd12.2Fe81.6B6.2ribbons with multiphase have a coercivity of about 11.3 kOe, and the coercivity decreases slightly with increasing Ce content. A coercivity of 7.5 kOe can be obtained when 60 at% of Nd is replaced by Ce (x = 0.6) due to the grain refinement and the strong intergranular exchange coupling. This provides a practical approach of fabricating high coercivity Ce-substituted Nd-Fe-B materials.

In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ −10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RLof −53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites.

To understand what and how structural properties affect battery performance, and to optimize the structural properties accordingly are of crucial importance to improve the performance of cathode materials for advanced Li-ion batteries. Herein, we investigated the influence of Li-enrichment in Li1+x(Ni0.8Co0.2)1-xO2transition metal (TM) oxide cathodes, obtained by sintering Ni0.8Co0.2(OH)2precursor with different amount of Li sources. Compared with stoichiometric Li1+x(Ni0.8Co0.2)1-xO2(i.e. x = 0, Li:TM = 1:1), the improvements of cycling stability and rate performance were observed in material with moderate degree of Li-enrichment with respect to TMs (i.e. x = 0.019, Li:TM = 1.04:1). Further increase in Li:TM ratio up to 1.07 diminishes the electrochemical performance. Multi-scale structural characterizations including neutron diffraction and aberration-corrected transmission electron microscopy measurements show that the Li-enrichment leads to a monotonical increase in both Li/Ni exchange ratio and Li slab space. Based on the results, we argue that, in material with moderate Li-enrichment, larger Li slab space can facilitate the diffusion of Li ions and a certain amount of Li/Ni disordering can also mitigate the contraction of layered structure, therefore resulting in an optimized electrochemical performance; while in material with excessive Li:TM ratio, the diffusion path can be partially blocked due to the presence of redundant Ni ions in Li layers.

Li+/Ni2+ disorder as an intrinsic structure defect in Ni-based layered oxides cathodes for lithium-ion batteries plays a crucial role on the overall electrochemical performances. However, the nature of Li+/Ni2+ disorder on the structure and property is still poorly understood. Herein, we design and synthesize layered LiNi1/3Co1/3Mn1/3O2 cathode materials with a different Li+/Ni2+ mixing degree, and focus on unveiling the influence mechanism of Li+/Ni2+ disorder on the surface/bulk structural evolution and the charge compensation mechanism by neutron, synchrotron radiation and electrochemical impedance techniques. High Li+/Ni2+ disorder increases the side reactions between electrolyte and electrode surface and aggravates the variation of local environment of Mn cations with (de)lithiating, which is largely responsible for the degradation of the initial capacity, rate capability and cycling performance. Interestingly, Li+/Ni2+ disorder can also relieve the electrostatic interaction between the cationic and anionic ions by enlarging the LiO6 octahedron and TMO6 octahedron, and locks the surrounding oxygen slabs by forming strong covalent bonds between antisite Ni and coordinated O ions, which alleviates the variations of the lattice parameters during charging/discharging. This study presents some new insights into designing high performance layered oxide cathodes through regulating Li+/Ni2+ disorder.

Li4Ti5O12 (LTO) has attracted great interest as an anode material due to the "zero strain" during Li+ insertion and extraction. But the intrinsic ionic diffusion coefficient and electronic conductivity are very poor. Herein, a strategy of Mg2+ and Zr4+ co-doping has been proposed to modulate the crystal structure and improve the electrochemical performances. More importantly, the synergic roles of Mg/Zr co-doping has been unveiled based on the analysis of X-ray diffraction, Neutron powder diffraction, X-ray photoelectron spectroscopy, and electrochemical measurements. Firstly, Mg-Zr co-doping expands the lattice parameter, cell unit volume and even Li-O bond length, which reduces Li+ migration barrier and benefits to Li+ insertion/extraction. Secondly, Ti-O shrinkage induced by Mg-Zr co-doping enhances the structure stability and subsequently the cycle performance. Thirdly, Mg-Zr co-doping promotes more Ti4+/Ti3+ which facilitates electron conductivity. Moreover, Mg-Zr co-doping also decreases the polarization and charge transfer impedance. Li3.8Mg0.2Ti4.9Zr0.1O12 delivers a discharge capacity of 180.5, 150.7, 110.4 and 78.9 mAh/g at 0.2C, 1C, 5C and 10C, respectively. Moreover, the capacity retention is greatly increased from 57.9% of LTO to 98.59% at 10C after 500 cycles.

Exploiting advanced layered transition metal oxide cathode materials is of great importance to rechargeable sodium batteries. Layered oxides are composed of negatively charged TMO2slabs (TM = transition metal) separated by Na+diffusion layers. Herein, we propose a novel insight, for the first time, to control the electrochemical properties by tuning Coulombic repulsion between negatively charged TMO2slabs. Coulombic repulsion can finely tailor the d-spacing of Na ion layers and material structural stability, which can be achieved by employing Na+cations to serve as effective shielding layers between TMO2layers. A series of O3-type NaxMn1/3Fe1/3Cu1/6Mg1/6O2(x= 1.0, 0.9, 0.8, and 0.7) have been prepared, and Na0.7Mn1/3Fe1/3Cu1/6Mg1/6O2shows the largest Coulombic repulsion between TMO2layers, the largest space for Na ion diffusion, the best structural stability, and also the longest Na–O chemical bond with weaker Coulombic attraction, thus leading to the best electrochemical performance. Meanwhile, the thermal stability depends on the Na concentration in pristine materials. Ex situ X-ray absorption (XAS) analysis indicates that Mn, Fe, and Cu ions are all electrochemically active components during insertion and extraction of sodium ion. This study enables some new insights to promote the development of advanced layered NaxTMO2materials for rechargeable sodium batteries in the future.

Though considerable Mg-doped layered cathodes have been exploited, some new differences relative to previous reports can be concluded by doping a heavy dose of Mg via two rational strategies. Unlike the common unit cell of the P63/mmcgroup by X-ray diffraction, neutron diffraction reveals a large supercell of the P63group and enhanced ordering for Na11/18Mg1/18[Ni1/4Mg1/9Mn11/18]O2with Mg occupying both the Na and Mn sites. Compared with only one obvious voltage plateau of Na0.5[Ni0.25Mn0.75]O2(NNM), Na11/18Mg1/18[Ni1/4Mg1/9Mn11/18]O2(NMNMM) shows more severe voltage plateaus but with excellent electrochemical performance. Na0.5[Mg0.25Mn0.75]O2(NMM) with Mg only occupying the Ni site displays a highly reversible whole-voltage-range oxygen redox chemistry and smooth voltage curves without any voltage hysteresis. Cationic Ni2+/Ni4+couples are responsible for the charge compensations of NNM and NMNMM, while only the oxygen anionic reaction accounts for the capacity of NMM between 2.5 and 4.3 V. Interestingly, the Mn3+/Mn4+pair contributes all capacity for all cathodes between 1.5 and 2.5 V. All cathodes undergo a double-phase mechanism: an irreversible P2–O2 phase transition for NNM, an enhanced reversible P2–O2 phase transition for NMNMM, and a highly reversible P2–OP4 phase transition for NMM. In addition, the designed cathodes display excellent rate capability and long-term cycling stability but with a large difference in the various voltage ranges of 2.5–4.3 and 1.5–2.5 V, respectively. This work provides a good understanding of ion doping and some new insights into exploiting high-performance materials.

P2-type Na0.67Mn0.5Fe0.5O2(MF) has attracted great interest as a promising cathode material for sodium-ion batteries (SIBs) due to its high specific capacity and low cost. However, its poor cyclic stability and rate performance hinder its practical applications, which is largely related to lattice oxygen instability. Here, we propose to coat the cathode of SIBs with Li2ZrO3, which realizes the “three-in-one” modification of Li2ZrO3coating and Li+, Zr4+co-doping. The synergy of Li2ZrO3coating and Li+/Zr4+doping improves both the cycle stability and rate performance, and the underlying modification mechanism is revealed by a series of characterization methods. The doping of Zr4+increases the interlayer spacing of MF, reduces the diffusion barrier of Na+, and reduces the ratio of Mn3+/Mn4+, thus inhibiting the Jahn–Teller effect. The Li2ZrO3coating layer inhibits the side reaction between the cathode and the electrolyte. The synergy of Li2ZrO3coating and Li+, Zr4+co-doping enhances the stability of lattice oxygen and the reversibility of anionic redox, which improves the cycle stability and rate performance. This study provides some insights into stabilizing the lattice oxygen in layered oxide cathodes for high-performance SIBs.

The electrochemical performance and structural stability of sodium-ion battery is substantially dependent on the occupancy and distribution of Na+in cathode materials. However, it is challenging to simultaneously regulate the occupancy and optimize the distribution of Na+in cathodes for higher capacity and superior cyclability. Here we attempt to adjust the arrangement of Na+in layered cathode materials by applying a combination approach, including enhancing the Na content, disrupting transition metal ordering and strengthening Na+-TMn+electrostatic force. Through detailed structural characterizations on cathodes, it is revealed that the rearrangement of Na+at two distinct Wyckoff positions can be realized in Li/Ti-codoped Na2/3Ni1/3Mn2/3O2cathodes, contributing to outstanding rate performance and smooth kinetic process. In addition, the inhibited P2-O2 phase transition and intact lattice structure is closely related to the rearranged Na layer and strengthened transition metal slab, jointly resulting in excellent long cycling performance with 90.2% capacity retention after 200 cycles at 1 C (150 mA/g). This work sheds new light on the role of different Na sites and provides a universal and practical approach to adjusting the Na+distribution in P2-type cathode materials.

A high-voltage LiCoO2cathode material has been increasingly studied due to its high capacity; however, the structural instability of this material results in poor cycling performance at high voltages, restricting its application. We use a controlled Mg doping strategy to modulate the crystal and electronic structure of the material and unravel the different effects of Mg occupation at Li and Co sites on the structure and electrochemical performance of LiCoO2. Mg substitution at Li sites provides much better electrochemical performance than Mg substitution at Co sites. Compared with bare LiCoO2, the substitution of Mg for Li and Co significantly enhances the capacity retention from 0.5% to 58.6% and 85.6% (500 cycles at 5C), respectively. Mg substitution at Li sites provides a "pillar' to stabilize the layered structure and increases the interlayer spacing (I(LiO2)) to reduce the energy barrier for Li+migration. The stress and strain on the crystal structure caused by the substantial expansion and contraction during cycling are alleviated, while the stability of oxygen in the Li0.96Mg0.04CoO2sample is enhanced; additionally, the destruction of the CoO6octahedron is also significantly inhibited, all of which confirm the increase in stabilization due to the Mg substitution in LiCoO2. This study offers some insights on the distinct effects of the same dopant at different crystal sites, which is instructive to develop a precisely controlled doping strategy.

Li4Ti5O12(LTO) has attracted great interest as an anode material due to the “zero strain” during Li+insertion and extraction. But the intrinsic ionic diffusion coefficient and electronic conductivity are very poor. Herein, a strategy of Mg2+and Zr4+co-doping has been proposed to modulate the crystal structure and improve the electrochemical performances. More importantly, the synergic roles of Mg/Zr co-doping has been unveiled based on the analysis of X-ray diffraction, Neutron powder diffraction, X-ray photoelectron spectroscopy, and electrochemical measurements. Firstly, Mg-Zr co-doping expands the lattice parameter, cell unit volume and even Li-O bond length, which reduces Li+migration barrier and benefits to Li+insertion/extraction. Secondly, Ti-O shrinkage induced by Mg-Zr co-doping enhances the structure stability and subsequently the cycle performance. Thirdly, Mg-Zr co-doping promotes more Ti4+/Ti3+which facilitates electron conductivity. Moreover, Mg-Zr co-doping also decreases the polarization and charge transfer impedance. Li3.8Mg0.2Ti4.9Zr0.1O12delivers a discharge capacity of 180.5, 150.7, 110.4 and 78.9 mAh/g at 0.2C, 1C, 5C and 10C, respectively. Moreover, the capacity retention is greatly increased from 57.9% of LTO to 98.59% at 10C after 500 cycles.

Li+/Ni2+disorder as an intrinsic structure defect in Ni-based layered oxides cathodes for lithium-ion batteries plays a crucial role on the overall electrochemical performances. However, the nature of Li+/Ni2+disorder on the structure and property is still poorly understood. Herein, we design and synthesize layered LiNi1/3Co1/3Mn1/3O2cathode materials with a different Li+/Ni2+mixing degree, and focus on unveiling the influence mechanism of Li+/Ni2+disorder on the surface/bulk structural evolution and the charge compensation mechanism by neutron, synchrotron radiation and electrochemical impedance techniques. High Li+/Ni2+disorder increases the side reactions between electrolyte and electrode surface and aggravates the variation of local environment of Mn cations with (de)lithiating, which is largely responsible for the degradation of the initial capacity, rate capability and cycling performance. Interestingly, Li+/Ni2+disorder can also relieve the electrostatic interaction between the cationic and anionic ions by enlarging the LiO6octahedron and TMO6octahedron, and locks the surrounding oxygen slabs by forming strong covalent bonds between antisite Ni and coordinated O ions, which alleviates the variations of the lattice parameters during charging/discharging. This study presents some new insights into designing high performance layered oxide cathodes through regulating Li+/Ni2+disorder.