High‐capacity cathode materials are requisite for constructing high‐energy‐density Li‐ion batteries. Although efforts are being concentrated on exploring ultra‐Ni‐rich layered oxides, the structural instability of these cathodes remains a hard nut to crack before reaching their practicality. Alternatively, raising the upper cutoff voltage of medium‐Ni oxides can equivalently increase the capacity, but it also devastates the structure. Here, a strategy is proposed to circumvent this dilemma by enriching the Li ions in medium‐Ni layered oxides, and meanwhile remaining Co‐free. Through surveying a range of compositions of Li 1+y Ni 1−3y Mn 2y O 2 (0.03≤ y≤0.15), a threshold for Li richness in this class of compounds is pinpointed, as represented by Li 1.12 Ni 0.64 Mn 0.24 O 2 , which is crucial to reach optimum capacity and cycling. This is delicately mediated by the proper amount of reversible anionic redox, as evidenced by electrochemistry and spectroscopy, that contributes to the structural stability even cycled to 4.5 V. We also found that the existence of additional Li ions in the lattice can effectively suppress the Li/Ni mixing, thereby weakening the necessity of Co in Ni‐based cathodes. As a result, Li 1.12 Ni 0.64 Mn 0.24 O 2 shows a capacity of ≈200 mA h g −1 that can be sustained for 100 cycles, which is further validated by an excellent long‐life full‐cell performance.

The ever-increasing demand for lithium-ion batteries has necessitated the development of high-performance cathode materials. However, previous studies have predominantly focused on crystal cathodes comprising the octahedral coordination of metal atoms and a well-ordered layered topology. This omits other cathode materials with other structures or coordination that could potentially surpass conventional counterparts in terms of performance. Here, using X-ray diffraction, resonant inelastic X-ray scattering and X-ray absorption near-edge spectra experiments, we investigated an amorphous Li-V-O-F cathode (a-LVOF) with tetrahedral coordination and elucidated an O-O formal redox mechanism at a moderate voltage of 4.1 V, without a conventional octahedral Li-O-Li configuration. The electrochemically amorphized material fosters randomly distributed VO4 units and scattered dangling oxygen bonds, which facilitated O-O binding. Moreover, a-LVOF demonstrates a high capacity of 230 mAh g-1. Our findings reveal a low-voltage O-O formal redox mechanism in an amorphized cathode material.

Li-rich layered oxides with reversible anionic redox offer exceptional capacity but suffer from high-voltage instability and oxygen loss at potentials exceeding 4.5 V. Here, a breakthrough in stabilizing oxygen redox is demonstrated through the design of a novel Ni-based Li-rich cathode material, Li1.2Ni0.708Mn0.092O2, synthesized under low-temperature atmospheric conditions. Structural characterization reveals an ordered superstructure phase that significantly enhances transition metal-oxygen covalency, lowering the oxygen redox activation potential by 100 mV compared to conventional Mn-based Li-rich cathodes. The material delivers a high reversible capacity of 260 mAh g(-1) with 80% capacity retention after 400 cycles, attributed to the synergistic stabilization of cationic (Ni3+/Ni4+) and anionic (O2-/On-) redox couples. The unique structural design mitigates lattice strain during cycling, as evidenced by minimal c-axis contraction (<1.08%) compared to conventional Ni-rich cathodes. This work establishes a new materials design principle for high-capacity Li-rich cathodes by engineering ordered superstructures that simultaneously enable low-voltage anionic redox and exceptional cycling stability, paving the way for next-generation high-energy lithium-ion batteries.

Li-rich Mn-based cathode materials exhibit a remarkable reversible specific capacity exceeding 250 mAh g-1, positioning them as the preferred choice for the next generation of high-energy density lithium-ion battery cathode materials. However, their inferior rate and cycling performance pose significant challenges. In this context, a Li-rich material incorporating an expanded fast Li-ion diffusion network has been successfully synthesized. This advancement involves the introduction of a single-layer of LiCo(Ni)O2 with high Li-ion diffusion coefficients into the crystal structure of Li-rich cathode, thereby enhancing the rate performance, achieving an impressive capacity of 212 mAh g-1 at 5 C. Furthermore, the single-layer LiCo(Ni)O2 can effectively isolates Li2MnO3 phase domains, thereby enhancing the structural stability during the anion redox process, consequently extending the electrochemical stability limits. Operating within a voltage range of 2.1-4.6 V, the capacity retention reaches 80% after 400 cycles, with a voltage decay of merely 0.74 mV per cycle. This innovative utilization of an expanded fast Li-ion diffusion network provides invaluable insights that will guide the development of strategies aimed at unlocking rate capability in layered oxide cathode materials.

To improve the interface stability between Li-rich Mn-based oxide cathodes and electrolytes, it is necessary to develop new polymer electrolytes. Here, we report an entanglement association polymer electrolyte (PVFH-PVCA) based on a poly (vinylidene fluoride-co-hexafluoropropylene) (PVFH) matrix and a copolymer stabilizer (PVCA) prepared from acrylonitrile, maleic anhydride, and vinylene carbonate. The entangled structure of the PVFH-PVCA electrolyte imparts excellent mechanical properties and eliminates the stress arising from dendrite growth during cycling and forms a stable interface layer, enabling Li//Li symmetric cells to cycle steadily for more than 4500 h at 8 mA cm −2 . The PVCA acts as a stabilizer to promote the formation of an electrochemically robust cathode–electrolyte interphase. It delivers a high specific capacity and excellent cycling stability with 84.7% capacity retention after 400 cycles. Li 1.2 Mn 0.56 Ni 0.16 Co 0.08 O 2 /PVFH-PVCA/Li full cell achieved 125 cycles at 1 C (4.8 V cut-off) with a stable discharge capacity of ~2.5 mAh cm −2 .

Nickel-rich layered transition metal oxides are leading cathode candidates for lithium-ion batteries due to their increased capacity, low cost and enhanced environmental sustainability compared to cobalt formulations. However, the nickel enrichment comes with larger volume change during cycling as well as reduced oxygen stability, which can both incur performance degradation. Here we show an ultrahigh-nickel cathode, LiNi0.94Co0.05Te0.01O2, that addresses all of these critical issues by introducing high valent tellurium cations (Te6+). The as-prepared material exhibits an initial capacity of up to 239 milliampere-hours (mAh) per gram and an impressive capacity retention of 94.5% after 200 cycles. The resulting Ah-level lithium metal battery with silicon-carbon anode achieves an extraordinary monomer energy density of 404 watt-hours (Wh) per kilogram with retention of 91.2% after 300 cycles. Advanced characterizations and theoretical calculations show that the introduction of tellurium serves to engineer the particle morphology for a microstructure to better accommodate the lattice strain and enable an intralayer Te-Ni-Ni-Te ordered superstructure, which effectively tunes the ligand energy-level structure and suppresses lattice oxygen loss. This work not only advances the energy density of nickel-based lithium-ion batteries into the realm of 400 Wh kg-1 but suggests new opportunities in structure design for cathode materials without trade-off between performance and sustainability. Increasing the Ni content to replace Co can increase the capacity and sustainability of cathode for batteries but leads to performance degradation issues. Here the authors address the structural and oxygen instabilities of Ni-rich cathodes by doping with tellurium.

Controlling multimetallic ensembles at the atomic level is significantly challenging, particularly for high-entropy alloys with more than five elements. Herein, we report an innovative ultrasmall (∼2 nm) PtFeCoNiCuZn high-entropy intermetallic (PFCNCZ-HEI) with a well-ordered structure synthesized by using the space-confined strategy. By exploiting these combined metals, the PFCNCZ-HEI nanoparticles achieve an ultrahigh mass activity of 2.403 A mgPt-1 at 0.90 V vs reversible hydrogen electrode for the oxygen reduction reaction, which is up to 19-fold higher than that of state-of-the-art commercial Pt/C. A proton exchange membrane fuel cell assembled with PFCNCZ-HEI as the cathode (0.03 mgPt cm-2) exhibits a power density of 1.4 W cm-2 and a high mass-normalized rated power of 45 W mgPt-1. Furthermore, theoretical calculations reveal that the outer electrons of the non-noble-metal atoms on the surface of the PFCNCZ-HEI nanoparticle are modulated to show characteristics of multiple active centers. This work offers a promising catalyst design direction for developing highly ordered HEI nanoparticles for electrocatalysis.

Lithium-rich Mn-based oxides have gained significant attention worldwide as potential cathode materials for the next generation of high-energy density lithium-ion batteries. Nonetheless, the inferior rate capability and voltage decay issues present formidable challenges. Here, a Li-rich material equipped with quasi-three-dimensional (quasi-3D) Li-ion diffusion channels is initially synthesized by introducing twin structures with high Li-ion diffusion coefficients into the crystal and constructing a "bridge" between different Li-ion diffusion tunnels. The as-prepared material exhibits monodispersed micron-sized primary particles (MP), delivering a specific capacity of 303 mAh g-1 at 0.1 C and an impressive capacity of 253 mAh g-1 at 1 C. More importantly, the twin structure also serves as a "breakwater" to inhibit the migration of Mn ions and improve the overall structural stability, leading to cycling stability with 85% capacity retention at 1 C after 200 cycles. The proposed strategy of constructing quasi-3D channels in the layered Li-rich cathodes will open up new avenues for the research and development of other layered oxide cathodes, with potential applications in industry.

Lithium-manganese-oxides have been exploited as promising cathode materials for many years due to their environmental friendliness, resource abundance and low biotoxicity. Nevertheless, inevitable problems, such as Jahn-Teller distortion, manganese dissolution and phase transition, still frustrate researchers; thus, progress in full manganese-based cathode materials (FMCMs) has been relatively slow and limited in recent decades. Recently, with the fast growth of vehicle electrification and large-scale energy-storage grids, there has been an urgent demand to develop novel FMCMs again; actually, new waves of research based on FMCMs are being created. Herein, we systematically review the history of FMCMs, correctly describe their structures, evaluate the advantages and challenges, and discuss the resolution strategies and latest developments. Additionally, beyond FMCMs, a profound discussion of current controversial issues, such as oxygen redox reaction, voltage decay and voltage hysteresis in Li2MnO3-based cathode materials, is also presented. This review summarizes the effectively optimized approaches and offers a few new possible enhancement methods from the perspective of the electronic-coordination-crystal structure for building better FMCMs for next-generation lithium-ion batteries.

Lithium-rich transition metal oxides (LLOs) can deliver high specific capacity over 250 mAh g-1 , stemming from additional contribution of oxygen redox. However, the formation of O(2-n)- (0 < n < 2) species and even oxygen gas during the deep oxidation stage leads to progressive structural transformation that cause voltage decay/hysteresis, sluggish kinetics, and poor thermostability, preventing real-world application of LLOs. Therefore, the substantive key relies on enhancing the anionic redox stability in LLOs. Here, a sulfuration procedure of LLOs (S-LLOs) is proposed, in which sulfur anions are incorporated into oxygen sites in the lattice structure and form polyanions on the surface. Proved by structural characterizations and density functional theory (DFT) calculations, sulfur anions in the interior lattice can reversibly participate in the redox process and enhance the integral coordination stability by mitigating undesired oxygen redox. Moreover, S polyanions at the surface form a protecting layer for interfacial stability. The electrochemical measurements indicate that S-LLO demonstrates a high discharge capacity of 307.8 mAh g-1 , an outstanding capacity retention rate of 91.5% after 200 cycles, along with excellent voltage maintenance, rate capability, and thermostability. The sulfuration process of LLOs with multianionic redox mechanism highlights a promising strategy to design novel high-energy-density cathode materials with superior cycling performance.

Bi-functional N -methylurea molecules participate in co-solvating the Li + ions enhancing the ionic conductivity, and deactivate the non-solvating polymer ethereal groups through the amide acceptor, providing a wide electrochemical window.

Layered Li-rich cathode materials with high reversible energy densities are becoming prevalent. However, owing to the activation of low-potential redox couples and the progressively irreversible structural transformation caused by the local adjustment of transition-metal ions in the intra/interlayer driven by anionic redox, continuous capacity degradation, and voltage decay emerge, thus greatly reducing the energy density and increasing the difficulty of battery system management. Herein, layered Li-rich cathode materials with higher intralayer configuration entropy have more local structural diversity and higher distortion energy, resulting in superior local structural adaptability with no drastic redox couple evolution, major local structural adjustment, or obvious layered-to-spinel phase transition. Consequently, the energy retention of the entropy-stabilization-strategy-enhanced Li-rich cathode materials is almost twice that of a typical Li-rich cathode material (Li1.20 Mn0.54 Ni0.13 Co0.13 O2 , T-LRM) after 3 months of cyclic testing. Moreover, when cycled at 1 C, the voltage degradation per cycle is less than 0.02%, that is, it results in a voltage loss of only 0.8 mV per cycle, which is excellent performance. This study paves the way for the development of Li-rich cathode materials with stabilized intralayer atomic arrangements and high local structural adaptability.

Searching for an efficient, durable, and low cost catalyst toward oxygen reduction reaction (ORR) is of paramount importance for the application of fuel cell technology. Herein, PtFeCoNiCu high-entropy alloy nanoparticles (PFCNC-HEA) is reported as electrocatalyst toward ORR. It shows remarkable ORR catalytic mass activity of 1.738 A mg-1Pt at 0.90 V, which is 15.8 times higher than that of the state-of-art commercial Pt/C catalyst. It also exhibits outstanding stability with negligible voltage decay (3 mV) after 10k cycles accelerated durability test. High ORR activity is ascribed to the ligand effect caused by polymetallic elements, the optimization of the surface electronic structure, and the formation of multiple active sites on the surface. In the proton exchange membrane fuel cell setup, this cell delivers a power density of up to 1.380 W cm-2 with a cathodic Pt loading of 0.03 mgPt cm-2, demonstrating a promising catalyst design direction for highly efficient ORR.

The size and composition of colloidal lead sulfide (PbS) quantum dots (QDs) are closely related to their optoelectronic properties, such as the band structure, carrier transportation, resistivity toward surface oxidation, etc., and hence would greatly affect the device performance. In this work, we developed a simple electrochemical methodology for probing the microscopic composition of the PbS QDs capped with oleic acid (OA). Cathodic and anodic voltammetry of PbS-OA QDs dropcast onto an electrode surface corresponding to the reduction of lead(II) and the oxidation of sulfide was separately investigated to quantify the amount of lead and sulfur. The submonolayer QDs underwent complete electrolysis at low potential scan rates, while under high scan rates, the larger reduction to oxidation charge ratio reflects that probably, only the Pb(II)-rich surface layer was electrolyzed. Based on the controllable electrolysis, not only the surface composition was revealed, but also, a depth profile of the elemental distribution for PbS-OA QDs was proposed. In addition, the size-dependent composition of PbS-OA QDs was also successfully determined, demonstrating it as a powerful tool for quantifying the composition of QDs.

Li‐rich oxide (LRO) cathodes that exhibit anionic redox activity can boost the energy density of Li‐ion batteries. Oxygen redox in LROs can originate from the charge compensation of pure O 2p nonbonding (NB) states; however, the high charging voltages cause much safety concerns in practical applications. Exploiting new anionic redox modes that can be used at low voltages is thus imperative. In view of this, a further understanding of the anionic redox behavior with respect to metal‐ligand interactions in LROs is highly desired. In this study, by analyzing the orbital combinations of transition metals (TMs) and O in LROs, the prevalence of π‐type, σ‐type, and NB states is investigated. Highly covalent Li 2 RhO 3 with strong π‐type interactions is selected as a model material. Owing to the closer energy levels of O and Rh and the orbital vacancy of Rh 4+ , oxygen acts as a π‐electron donor to central Rh and exhibits high reactivity in the occupied anti‐bonding state, showing a novel low‐voltage O redox which is distinct from high‐voltage NB O redox. This π‐type oxygen redox mode expands the fundamental theories of anionic redox and provides a new design route to achieve high‐capacity Li‐rich cathode materials.

On the foundation of Li-Ni-Co-Mn quaternary phase diagram, a series of manganese-based cathode materials Li delta Ni0.25-zMn0.75-zCo2zOy (0 <= delta <= 1.75, z = 0, 0.05, 0.15 and 0.25) have been designed and systematically studied. These materials are synthesized via a carbonate co-precipitation route and followed by a solid-state reaction. The effects of cobalt and lithium contents on phase transformations morphologies, and electrochemical behaviors of the cathode materials are overall compared and evaluated. The results reveal that, with delta increases, structures of the materials present phase evolution from spinel phase (delta <= 0.5) to integrated composite of spinel and layered phase (Fd (3) over barm and R (3) over barm, 0.5 < delta < 1.5) and then to a pure layered phase (R (3) over barm and C2/m, delta >= 1.5). In addition, size of primary particle and roughness of the secondary particles are also affected by delta value. Moreover, it is found that the initial discharge capacity and cycle stability of the cathode materials can be improved by a proper amount of cobalt substitution for both spinel and layered structure. These studies on the Li-Ni-Mn-Co quaternary phase diagram provide a new insight into the research and development of the cathode materials for advanced lithium-ion batteries. (C) 2018 Published by Elsevier Ltd.

To improve the electrochemical performances and thermal stability of Ni, Co-containing Li-rich materials, Li1.2(Ni0.25Co0.25Mn0.5)0.8O2 is redesigned into Li1.2[(Co0.5Mn0.5)1/2(Ni0.5Mn0.5)1/2]0.8O2 with a novel core-shelled structure for the first time. Subsequently, this core-shelled material is prepared successfully via co-precipitation and solid state method. The core-shelled structure of Li1.2[(Co0.5Mn0.5)1/2(Ni0.5Mn0.5)1/2]0.8O2 is certified by Energy Disperse X-ray Spectrum (EDS) on the cross-section of the single particle. Different from the conventional core-shelled structure design of Li-rich materials, in which Mn-rich materials act as core and Ni-rich materials act as shell, the novel core-shelled structure of Li1.2[(Co0.5Mn0.5)1/2(Ni0.5Mn0.5)1/2]0.8O2 incorporates the advantages of Co-rich core and Ni-rich shell. Subsequently, improved cyclability, rate capability and thermal stability are obtained in Li1.2[(Co0.5Mn0.5)1/2(Ni0.5Mn0.5)1/2]0.8O2.

The drawbacks of Li-rich layered oxides, such as large initial irreversible capacity, phase transformation and electrochemical performance degradation, are closely related to the surface states of the Li-rich layered oxide. To overcome these problems, a new surface modification method to the Li-rich layered oxide is proposed, in which the fast lithium-ion conductor (Li-La-Ti-O composite, LLTO) is coated on the surface of Li1.2Ni0.13Co0.13Mn0.54O2 (LRO) particles. SEM, EDS and HRTEM analyses reveal that an entire and homogeneous coating layer is formed. Electrochemical performances display that the LLTO coated samples, especially the LRO-LLTO5 material, exhibit better cycle stability, higher rate capabilities and less voltage decay. To investigate the origins of enhanced electrochemical performances for LLTO coated samples, the electrode processes at various cycles and the structural stability of the samples are studied by EIS and DSC. The protective effect of LLTO coating layer to the bulk crystallographic structure of cathode material is revealed by HRTEM images. Our study shows that the reduced interface impedances and definitely protective effect resulting from the complete and homogeneous LLTO coating layer are responsible for the enhanced electrochemical performances of the LLTO coated samples.

The LiCoO2 thin film electrodes were prepared by radio-frequency(RF) magnetron sputtering.By study of magnetron sputtering power,a LiCoO2 film electrode,prepared without post-annealing,has a discharge capacity of 60 μAh/(cm2·μm).The structure and morphology of LiCoO2 films were analyzed by XRD patterns and SEM images.The results of analysis show that the preferred orientation and crystallized degree of polycrystalline LiCoO2 films is decided by the power of magnetron sputtering,which determines the electrochemical performance of LiCoO2 films.The LiCoO2 films,prepared at an appropriate magnetron sputtering power without post-annealing process,still have good specific capacity and cycle performance.And the aluminum films were prepared as current collector by magnetron sputtering,instead of noble metals,such as platinum and gold,which brings a dramatic decrease of the film positive electrode cost.

The discharge performance of the water-stable lithium electrode (WSLE) is improved by introducing the surface modification of the glass-ceramic plate (LAGP and LATP). The water-stable lithium electrodes are prepared with the NASICON-type glass-ceramic plates as protection layer, and using organic electrolyte as interlayer. The glass-ceramic plates with ionic conductivity of 4 x 10(-4)-5.7 x 10(-4) S cm(-1) are water-stable and 300-500 mu m thick. The modified layer is deposited onto the glass-ceramic plates by RF magnetron sputtering from a Li4Ti5O12 target. The modified layer is analyzed by XRD, SEM-EDX, Raman and XPS. The Li-air test-cells are assembled with an SCE as reference electrode in aqueous solution. In the Li-air test-cells, the AC impedance and constant polarization potential measurements are carried out to identify the improvement of modification. The impedance of interface between the glass-ceramic plate and organic electrolyte decreases about 20-50%. Consequently, the discharge current is promoted about 70-80%. Then, by introducing interfacial modification of glass-ceramic plate, the power performance of WSLE, is remarkably promoted. (C) 2013 Elsevier B.V. All rights reserved.