Anionic oxygen redox has aroused great interest in developing high-capacity Li-ion battery cathode materials. The fundamental understanding of this concept, compared to cationic redox, has promoted extensive studies on lithium transition metal oxides including those of 4d and 5d transition metals. Lithium ruthenium oxide has been found to exhibit a reversible anionic redox upon cycling. However, lithium-rich layered oxide with anionic redox is still facing great challenges, such as sluggish kinetics. Here we investigate the effect of cationic redox reaction on the kinetics of anionic reaction when they are strongly coupled. We report the cobalt-substituted lithium ruthenium oxide, where all Ru, Co, and O redox participate in the charge compensation mechanism in relatively defined voltage regions. The improved anionic kinetics is attributed to the fast cationic Co redox process that serves as a redox mediator. Our work sheds light on the potential direction to address the commonly believed sluggish anionic kinetics in high-capacity oxygen-redox cathode materials.
Since the development of Ti2.08Zr null matrix alloy by Sidhu et al. in 1956, only a handful of new null matrix alloys have been reported over the past 70 years. Most of them are not suitable to be utilized in applications due to the poor chemical/physical stabilities and the presence of strong short-range ordering in the structures. For the first time, a new family of V-based null matrix alloys V1–xMx (M = Al, Nb, Ta, Ni, Fe, Sn, and Mo; x < 0.1 in molar ratio) were synthesized by an arc melting method. The structural and physical properties were systematically evaluated. All of the alloys crystallize into a cubic body center structure with a space group of Im3̅m. Based on the neutron diffraction (ND), X-ray diffraction, and X-ray pair distribution function, the dopants (except Mo) and V atoms were atomically homogeneous and distributed into the 2a sites of Im3̅m. Small angle neutron scattering was used to probe the bulk neutron transparent properties and the possibilities of dopant clustering at the mesoscopic level. These conditions yield a specific feature in which the ND patterns of the alloys have no diffraction peaks. Hard X-ray absorption spectroscopy revealed that the valence states of V remained 0 in all investigated alloys. Nonetheless, a small degree of charge redistribution were observed. The Coulombic energies of configurations of supercells with different degrees of dopants clustering were also computed for comparison. Tensile tests were also conducted to evaluate the mechanical stress and strain properties. The high-temperature oxidation properties were examined by thermogravimetric analysis differential scanning calorimetry. Among the investigated samples, Nb-doped and Ni-doped V-based alloys show superior chemical and mechanical properties, which could be promising to be utilized to develop advanced in situ devices and high-temperature/pressure neutron scattering sample holders for ND and total scattering measurements.
Abstract Lithium‐rich manganese‐based layered oxides (LRM) have garnered considerable attention as cathode materials due to their superior performance. However, the inherent structural degradation and obstruction of ion transport during cycling lead to capacity and voltage decay, impeding their practical applications. Herein, an Sb‐doped LRM material with local spinel phase is reported, which has good compatibility with the layered structure and provides 3D Li + diffusion channels to accelerate Li + transport. Additionally, the strong Sb‐O bond enhances the stability of the layered structure. Differential electrochemical mass spectrometry indicates that highly electronegative Sb doping effectively suppresses the release of oxygen in the crystal structure and mitigates successive electrolyte decomposition, thereby reducing structural degradation of the material. As a result of this dual‐functional design, the 0.5 Sb‐doped material with local spinel phases exhibits favorable cycling stability, retaining 81.7% capacity after 300 cycles at 1C, and an average discharge voltage of 1.87 mV per cycle, which is far superior to untreated material with retention values of 28.8% and 3.43 mV, respectively. This study systematically introduces Sb doping and regulates local spinel phases to facilitate ion transport and alleviate structural degradation of LRM, thereby suppressing capacity and voltage fading, and improving the electrochemical performance of batteries.
Inspired by naturally occurring helical supramolecular architectures, a series of chiral conjugated phospholes with a cholesteryl pendant have been synthesized and characterized. The photophysically and electrochemically active conjugated phosphole species can act as dopants for the formation of chiral liquid crystals. The supramolecular structures were found to be tunable by careful choice of the conjugated headgroup as well as the rigidity of the linker of the new cholesteric phospholes.
Prussian blue analogues (PBAs) are appealing active materials for post-lithium electrochemical energy storage. However, PBAs are not generally suitable for non-aqueous Li-ion storage due to their instability upon prolonged cycling. Herein, we assess the feasibility of PBAs with various lithium content for non-aqueous Li-ion storage. We determine the crystal structure of the lithiated PBAs via neutron powder diffraction measurements and investigate the influence of water on structural stability and Li-ion migration through operando X-ray diffraction measurements and bond valence simulations. Furthermore, we demonstrate that a positive electrode containing Li2-xFeFe(CN)6⋅nH2O (0 ≤ x ≤ 2) active material coupled with a Li metal electrode and a LiPF6-containing organic-based electrolyte in coin cell configuration delivers an initial discharge capacity of 142 mAh g-1 at 19 mA g-1 and a discharge capacity retention of 80.7% after 1000 cycles at 1.9 A g-1. By replacing the lithium metal with a graphite-based negative electrode, we also report a coin cell capable of cycling for more than 370 cycles at 190 mA g-1 with a stable discharge capacity of about 105 mAh g-1 and a discharge capacity retention of 98% at 25 °C.
Ni-rich layered oxides (Ni content >60%) are promising cathode candidates for Li-ion batteries because of their high discharge capacity, high energy density, and low cost. However, fast capacity fading, poor thermal stability, and sensitivity to the ambient moisture still plague their mass application. In this work, we systematically investigate the effects of Mn content on the structure, morphology, electrochemical performance, and thermal stability of the Ni-rich cathode materials LiNi0.8–xCo0.1Mn0.1+xO2 (0.0 ≤ x ≤ 0.08). It is demonstrated that with the increase in Mn content and decrease in Ni content, the cycling stability of LiNi0.8–xCo0.1Mn0.1+xO2 to a cutoff charge voltage of 4.5 V is significantly improved. The high-Mn-content electrode LiNi0.72Co0.10Mn0.18O2 shows a capacity retention of 85.7% after 100 cycles at a 0.2 C rate at room temperature, much higher than those of the lower Mn-content samples LiNi0.80Co0.10Mn0.10O2 (64.0%) and LiNi0.76Co0.10Mn0.14O2 (72.9%). The improved capacity retention of the high-Mn-content electrode LiNi0.72Co0.10Mn0.18O2 is due to the stabilization of the electrode/electrolyte interface, as evidenced by the lower solid-electrolyte interphase (SEI) resistance and charge-transfer resistance. Furthermore, with the increase in Mn content and decrease in Ni content, the thermal stability of the Ni-rich cathode is also remarkably enhanced.
Recent reports on high capacities delivered by Li-excess transition-metal oxide cathodes have triggered intense interest in utilizing reversible oxygen redox for high-energy battery applications. To control oxygen electrochemical activities, fundamental understanding of redox chemistry is essential yet has so far proven challenging. In the present study, micrometer-sized Li1.3Nb0.3Mn0.4O2 single crystals were synthesized for the first time and used as a platform to understand the charge compensation mechanism during Li extraction and insertion. We explicitly demonstrate that the oxidation of O2– to On– (0 < n < 2) and O2 loss from the lattice dominates at 4.5 and 4.7 V, respectively. While both processes occur in the first cycle, only the redox of O2–/On– participates in the following cycles. The lattice anion redox process triggers irreversible changes in Mn redox, which likely causes the voltage and capacity fade observed on this oxide. Two drastically different redox activity regions, a single-phase behavior involving only Mn3+/4+ and a two-phase behavior involving O2–/On– (0 ≤ n < 2), were found in LixNb0.3Mn0.4O2 (0 < x < 1.3). Morphological damage with particle cracking and fracturing was broadly observed when O redox is active, revealing additional challenges in utilizing O redox for high-energy cathode development.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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