Bulk Structure Stability Research Articles

Surface and Grain Boundary Coating for Stabilizing LiNi0.8Mn0.1Co0.1O2 Based Electrodes.

The widespread use of high-capacity Ni-rich layered oxides such as LiNi0.8Mn0.1Co0.1O2 (NMC811), in lithium-ion batteries is hindered due to practical capacity loss and reduced working voltage during operation. Aging leads to defective NMC811 particles, affecting electrochemical performance. Surface modification offers a promising approach to improve cycle life. Here, we introduce an amorphous lithium titanate (LTO) coating via atomic layer deposition (ALD), not only covering NMC811 surfaces but also penetrating cavities and grain boundaries. As NMC811 electrodes suffer from low structural stability during charge and discharge, We combined electrochemistry, operando X-ray diffraction (XRD), and dilatometry to understand structural changes and the coating protective effects. XRD reveals significant structural evolution during delithiation for uncoated NMC811. The highly reversible phase change in coated NMC811 highlights enhanced bulk structure stability. The LTO coating retards NMC811 degradation, boosting capacity retention from 86 % to 93 % after 140 cycles. This study underscores the importance of grain boundary engineering for Ni-rich layered oxide electrode stability and the interplay of chemical and mechanical factors in battery aging.

Enhanced Lithium Ion Diffusivity of Nanosized Li1.2Mn0.8O2 Cathode Material Via Na and Ti Co-Doping

Ionic doping is amongst the most effective modification methods capable of altering the local atomic environment, which in turn governs the redox reactions and electrochemical performance of Li-rich cathode materials. It has been demonstrated to improve bulk structural stability and suppress oxygen loss to some extent. Independently doping with Na and Ti has sparked interest in them however, very little is understood about their combined impact in a quest to address the structural complexities encountered during the operation of Li-rich cathodes. Herein, molecular dynamics simulations were carried out on both the bulk and nanospherical structures of Li1.2Mn0.8O2, Li1.2Mn0.72Ti0.08O2, and Li1.15Na0.05Mn0.72Ti0.08O2 whereNa+ doping in the Li-site and Ti in the Mn site. The temperature variations were between 300K and 2000 K. The findings of this study depict that bulk structures have diffusion coefficients that are orders of magnitude less than those of nanospherical structures. This strongly supports the unique capabilities of nanoparticles in reducing the Li-ion diffusion distance and increasing the contact area between the electrode and the electrolyte. In terms of variation in doped systems, it was observed that singly doping the layered structure with titanium slightly increases ionic diffusion in the Li-Rich structure whereas, co-doping the same structure yields even higher diffusion coefficients. These are possible results of enhanced interlayer spacing as Na generally has a larger ionic radius than Li. Furthermore, the co-doping may have contributed to structural stability wherein cationic mixing influenced by Mn migration in pure Li1.2Mn0.8O2 is largely reduced [1]. This places the two dopants at the pinnacle of capacity enhancement for the Li-rich electrode and sparks significant interest in further performance and structural stability studies.

Oxide Coating Role on the Bulk Structural Stability of Active LiMn2O4 Cathodes.

The protective coating of the electrode materials is a known source of improvement of the cycling performances in battery devices. In the case of the LiMn2O4 cathodes, the coating with a thin alumina layer has been proven to show performance efficiency. However, the precise mechanism of its effect on the performance improvement of the electrodes is still not clear. In this work we investigate alumina-coating-induced effects on the structural dynamics of the active materials in correlation to the modified solid electrolyte interface dynamics. The local structures of coated and uncoated samples at different galvanostatic points are studied by both soft X-ray absorption measurements at the Mn L-edges and O K-edge (in total electron yield mode) and hard X-ray absorption at the Mn K-edge (in transmission mode). The different probing depths of the employed techniques allowed us to study the structural dynamics both at the surface and within the bulk of the active material. We demonstrate that the coating successfully hinders the Mn3+ disproportionation and, hence, the degradation of the active material. Side products (layered Li2MnO3 and MnO) and changes in the local crystal symmetry with formation of Li2Mn2O4 are observed in uncoated electrodes. The role of alumina coating on the stability of the passivation layer and its consequent effect on the structural stability of the bulk active materials is discussed.

In Situ Plastic-Crystal-Coated Cathode toward High-Performance Na-Ion Batteries

Cathode materials are critical for Na-ion batteries while facing challenges due to the instability of the structure and interfaces. In this work, we propose a strategy to achieve an in situ plastic-crystal Na3–3xAlxPO4 coating and bulk Al doping for an O3-NaNi0.4Fe0.2Mn0.4O2 cathode through a simple one-step method. Na3–3xAlxPO4 exhibits high ion transport performance due to its unique “paddle-wheel” mechanism. The in situ formed Na3–3xAlxPO4 could consume the residual alkali compounds and induce the formation of a Na-deficient phase, thus leading to enhanced Na+ transport kinetics. Furthermore, strong Al–O bonds formed in the bulk further enhance the crystal structure stability. In a full cell, the capacity retention rate reached 70% after 500 cycles, making its commercial operation possible. Altogether, these results suggest that the in situ plastic-crystal-coating strategy can significantly improve the surface and bulk structure stability of NaNi0.4Fe0.2Mn0.4O2, thus leading to improved electrochemical performance.

An effective co-modification strategy to enhance the cycle stability of LiNi0.8Co0.1Mn0.1O2 for lithium-ion batteries.

Ni-rich cathode materials suffer from rapid capacity fading caused by interface side reactions and bulk structure degradation. Previous studies show that Co is conducive to bulk structure stability and sulfate can react with the residual lithium (LiOH and Li2CO3) on the surface of Ni-rich cathode materials and form a uniform coating to suppress the side reactions between the cathode and electrolyte. Here, CoSO4 is utilized as a modifier for LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode materials. It reacts with the residual lithium on the surface of the NCM811 cathode to form Li-ion conductive Li2SO4 protective layers and Co doping simultaneously during the high-temperature sintering process, which can suppress the side reactions between the Ni-rich cathode and electrolyte and effectively prevent the structural transformation. As a result, the co-modified NCM811 cathode with 3 wt% CoSO4 exhibits an improved cycling performance of 81.1% capacity retention after 200 cycles at 1C and delivers an excellent rate performance at 5C of 187.4 mA h g-1, which is 10.2% higher than that of the pristine NCM811 cathode.

Enhancing the structure stability of Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode via encapsulating in negative thermal expansion nanocrystalline shell

Ni-rich cathode materials have attracted considerable attention due to the high electrochemical capacities and prominent price advantage, while their extensive applications are still impeded by the poor structure stability induced by the intrinsic Li+/Ni2+ cation mixing and mechanical stress accumulation upon cycling. To address these issues, a typical negative thermal expansion (NTE) material ZrV2O7 (ZVO) is firstly employed as coating layer on LiNi0.6Co0.2Mn0.2O2 (NCM622) particles to promote the electrochemical performances through enhancing the structure stability upon repeated cycling and operating at high temperature. The [email protected] wt% ZVO sample exhibits excellent cyclability (71.0% capacity retension after 500 cycles under 25 °C and 67.0% capacity retension after 200 cycles under 55 °C) and rate capability (60.7% at 5 C). Further in-situ XRD analysis confirms that the structure stability of NCM622 could be prominently stabilized both under electrochemical and thermal treatments after ZVO decoration. Intensive investigation implies the unique functionalities of ZVO in restraining the stress accumulation and volume expansion, thus contributing to the bulk structure stability and interface compatibility of modified NCM622, besides the traditional effect of surface deposition layers (physical separation between solid electrode/electrolyte and inhibited irreversible surface side reactions).

Enhanced the electrochemical performances of LiNi0.7Co0.15Mn0.15O2 cathodes by the hybrid ZrO2-Li2ZrO3 layer

Electrode-electrolyte interface side reactions cause the fast capacity fading of Ni-rich cathode, especially at high cutoff voltages and high temperatures. This is the main obstacle for their commercial application. Herein, a hybrid ZrO2-Li2ZrO3 (LZO) coating layer was fabricated through a wet process on LiNi0.7Co0.15Mn0.15O2 (NCM) cathode materials. The structure and chemical composition of the ZrO2-Li2ZrO3 coating layer were studied by the characterizations of XRD, SEM, TEM, and XPS. The ZrO2-Li2ZrO3-coated LiNi0.7Co0.15Mn0.15O2 cathode improved cycling stabilities at both 25 and 55 °C in the case of high cutoff voltage. In detail, ZrO2-Li2ZrO3-coated NCM (LZO-NCM) delivers a 187.40 mAh g−1 with 83.4% capacity retention after 100 cycles at 1C over 3.0–4.5 V, and it is far higher than that of uncoated sample (71.4%). At elevated temperature (55 °C), the ZrO2-Li2ZrO3-coated sample also maintains 79% capacity retention after 100 cycles (3.0–4.5 V, 1C), which is higher than the 61.5% capacity retention of the pristine electrode. The hybrid ZrO2-Li2ZrO3 coating could not only keep the bulk structure stability but also prevent the electrochemical resistance which varies after cycles. Thereby, the electrochemical properties were improved significantly.

Ultra-Thin AlPO4 Layer Coated LiNi0.7Co0.15Mn0.15O2 Cathodes With Enhanced High-Voltage and High-Temperature Performance for Lithium-Ion Half/Full Batteries.

Side-reactions in LiNi1−x-yCoxMnyO2 (0≤−x+y≤1) cathode materials are one kind of the problems that would deteriorate the surface structure and the electrochemical stabilities of the cathodes, especially when they are working at high cut-off voltages and high temperatures. In this study, an ultrathin (~10 nm) AlPO4 coating layer was fabricated through a two-step “feeding” process on LiNi0.7Co0.15Mn0.15O2 (NCM) cathode materials. The structure and chemical composition of the AlPO4 coating were studied by XRD, SEM, TEM, and XPS characterizations. Further electrochemical testing revealed that the AlPO4-coated LiNi0.7Co0.15Mn0.15O2 cathode exhibited enhanced electrochemical stabilities in the case of high cut-off voltage at both 25 and 55°C. In detail, the AlPO4-coated LiNi0.7Co0.15Mn0.15O2 could deliver 186.50 mAh g−1 with 81.5% capacity retention after 100 cycles at 1C over 3–4.5 V in coin cell, far higher than the 71.4% capacity retention of the pristine electrode. In prismatic full cell, the coated sample also kept 89.5% capacity retention at 25°C and 81.1% capacity retention at 55°C even after 300 cycles (2.75–4.35 V, 1C), showing better cycling stability than that of the pristine NCM. The ultrathin AlPO4 coating could not only keep the bulk structure stability from the surface degradation, but also diminishes the electrochemical resistance varies after cycles, thereby supporting the coated cathodes with enhanced electrochemical stability.

(Sm,Zr)Fe12−xMx(M=Zr,Ti,Co)for Permanent-Magnet Applications:Ab InitioMaterial Design Integrated with Experimental Characterization

In rare-earth permanent magnets (REPM's), trade-off's between intrinsic magnetic properties are often encountered. A recent example is SmFe$_{12}$ where excellent magnetic properties can be achieved at the sacrifice of bulk structure stability. Bulk structure stability is sustained by the presence of the third substitute element as is the case with SmFe$_{11}$Ti, where Ti degrades magnetic properties. It is now in high demand to find out with which chemical composition a good compromise in the trade-off between structure stability and strong ferromagnetism is reached. We inspect the effects of representative substitute elements, Zr, Ti, and Co in SmFe$_{12}$ by combining ab initio data with experimental data from neutron diffraction. The trend in the intrinsic properties with respect to the concentration of substitute elements are monitored and a systematic way to search the best compromise is constructed. A certain minimum amount of Ti is identified with respect to the added amount of Co and Zr. It is found that Zr brings about a positive effect on magnetization, in line with recent experimental developments, and we argue that this can be understood as an effective doping of extra electrons.

New Insight into the Role of Mn Doping on the Bulk Structure Stability and Interfacial Stability of Ni‐Rich Layered Oxide

AbstractNickel‐rich layered oxides have developed into appealing cathode materials for lithium‐ion batteries in recent years for the sake of high energy density and low cost, but they suffer from severe capacity deterioration during long‐term cycling. Herein, Mn‐doped nickel‐rich Li(Ni0.88Co0.09Al0.03)1‐δMnδO2 (δ=0, 0.01, 0.02) cathode materials with a nanoscale NixMn1−xO‐type pillar layer are synthesized using a facile high‐shear dry mixing and high‐temperature calcination process in this study. The as‐fabricated M0.01−NCA electrode with a NixMn1−xO‐type layer about 20 nm exhibits excellent cycle performance compared with the pristine in coin‐cells and in pouch cells (the long‐term cycle number is four times that of the pristine). Detailed investigation of the fading mechanism is performed by HRTEM, ex‐situ XRD, XPS et al. The enhanced performance is directly related to the synergetic effects of bulk inactive Mn4+ doping and the increased nanoscale NixMn1−xO‐type pillar layer. The Mn dopants stabilize the lattice structure thus decreasing the microcracks, and the pillar layer protects the cathode from parasitic reactions with electrolytes during long‐term cycling. This work gives a new insight into the role of Mn doping on the enhanced structure of nickel‐rich layered oxides.

Electronic Origins of Anomalous Twin Boundary Energies in Hexagonal Close Packed Transition Metals.

Density-functional-theory calculations of twin-boundary energies in hexagonal close packed metals reveal anomalously low values for elemental Tc and Re, which can be lowered further by alloying with solutes that reduce the electron per atom ratio. The anomalous behavior is linked to atomic geometries in the interface similar to those observed in bulk tetrahedrally close packed phases. The results establish a link between twin-boundary energetics and the theory of bulk structural stability in transition metals that may prove useful in controlling mechanical behavior in alloy design.

Degradation of Spark Plasma Sintered Yttria Stabilized Zirconia (YSZ) and CeO2‐YSZ Ceramics in Supercritical Water

Zirconia ceramics are often considered in the nuclear industry for high temperature applications due to their radiation resistance, chemical inertness, high thermal stability and low thermal conductivity. However, wide application of zirconia ceramics is hindered by their degradation behavior in aqueous media. In this research, moderately dense 8 mol% Yttria Stabilized Zirconia (YSZ) as well as YSZ based ceramics containing 5, 10 and 15 mol% CeO2 were fabricated via Spark Plasma Sintering (SPS). Sintered ceramics were subjected to static degradation testing in supercritical water at 400°C and 31 MPa. The weight loss and microstructural changes of the ceramics associated with supercritical water exposure were studied, and the results suggest that the addition of CeO2 significantly reduced the degradation rate and improved the bulk structural stability of the ceramic composite. This behavior was attributed to the enhanced stabilization of the zirconia lattice, preventing the evolution of the undesirable monoclinic‐ZrO2 phase.

Structural stability and energetics of As, Sb and Bi microclusters: empirical many-body potential energy function calculation

The structural stability and energetics of As, Sb and Bi microclusters having 3–7 atoms have been investigated by using a recently developed empirical many-body potential energy fuction (PEF), which comprises two- and three-body atomic interactions. The PEF satisfies both bulk cohesive energy per atom and bulk structural stability exactly. It has been found that the most stable structures of As3, Sb3 and Sb4 microclusters are in linear form with D∞h symmetry, Bi7 is in hexagonal pyramid form with D6v symmetry. The rest of the microclusters prefer the planar form.