Cyclic performance of Li-rich layered material Li1.1Ni0.35Mn0.65O2 synthesized through a two-step calcination method

Ultrathin interfacial modification of Li-rich layered oxide electrode/sulfide solid electrolyte via atomic layer deposition for high electrochemical performance batteries

Herein, Li-rich layered oxides (LLOs) are modified by sulfide solid electrolyte Li₁₀GeP₂S₁₂ (LGPS) with high ionic conductivity to enhance the diffusion of Li⁺ and an ultrathin Al₂O₃ layer is interposed between LLOs and LGPS through the atomic layer deposition (ALD) technique to inhibit the development of the highly resistive space-charge layer, the side reactions and structure transition of the composites, thus excellently promoting the electrochemical properties of the composites in liquid electrolyte. Among the different ALD cycles of Al₂O₃, 10 cycles of ultrathin Al₂O₃ layer achieves the greatest electrochemical performance. The beginning discharge capacity of LLOs@Al₂O₃/LGPS composites comes up to 233.4 mA h g^-1 with a capacity retention of 90.6% and a voltage retention of 97.3% after 100 cycles at 0.2 C. The composites also exhibit the optimal rate capability and a high energy density of 581 Wh kg^-1 at 1 C. The galvanostatic intermittent titration technique test indicates that the composites (LLOs@Al₂O₃/LGPS) possess the greatest Li⁺ diffusion coefficient (1.58 × 10^-10 cm² s^-1) compared to LLOs (0.85 × 10^-10 cm² s^-1) and LLOs/LGPS (1.10 × 10^-10 cm² s^-1). More importantly, charge curves at the beginning of the initial charge and electrochemical impedance spectroscopy curves clearly reveal the inhibition of the development of the highly resistive space-charge layer.

Boosting Cell Performance of LiNi0.8 Co0.15 Al0.05 O2 via Surface Structure Design

Although the high energy density and environmental benignancy of LiNi_0.8 Co_0.15 Al_0.05 O₂ (NCA) holds promise for use as cathode material in Li-ion batteries, present low rate capabilities, and fast capacity fade limit its broad commercial applications. Here, it is reported that surface modification of NCA cathode (R-3m) with 5 nm-thick nanopillar layers and Fm-3m structures significantly improves electrode structure, morphology, and electrochemical performance. The formation of nanopillar layers increases cycling and working voltage stability of NCA by shielding the host material from hydrofluoric acid and improves structural stability with the electrolyte. The modified NCA cathode exhibits an enhanced 89% capacity retention at a rate of 1 C over that of pristine NCA (75.2%) after 150 cycles and effectively suppresses working voltage fade (a drop of 0.025 V after 300 cycles) during repeated charge-discharge cycles. In addition, the diffusion barrier of Li ions in NCA crystals at 0.80 V is noticeably smaller than that of Li ions in pristine NCA (0.87 eV). These findings demonstrate that this unique surface structure design considerably enhances cycle and rate performance of NCA, which has potential applications in other Ni-rich layered cathode materials.

The Effects of Trace Yb Doping on the Electrochemical Performance of Li-Rich Layered Oxides

Layered lithium-rich cathode materials are one of the most promising cathode materials owing to their higher mass energy density than the commercial counterparts. A series of trace Yb-doped lithium-rich cathode materials Li_1.2 Mn_0.54 Ni_0.13 Co_0.13-x Yb_x O₂ (0≤x≤0.050) were synthesized and the effects were investigated by XRD, X-ray photoelectron spectroscopy, and high-resolution TEM. The participation of Yb ions in electrochemical reactions and the larger binding energy of Yb-O than M-O (M=Mn, Ni, Co), which expands the lithium layer spacing and stabilizes the oxygen stacking, resulted in excellent performance of materials doped with a limited Yb content (x≤0.005). However, higher doping amounts (x>0.005) significantly increased the charge-transfer impedance and led to a sharp deterioration in electrochemical performance. The reason lies in the large difference in ionic radius between the transition metals (Mn, Co, and Ni) and Yb. There is an upper limit to the amount of Yb ions in the lattice. If the amount of Yb is higher than the limit, excess Yb ions enter the Li layers instead of staying in the transition-metal layers or even segregate on the surface and form electrochemically inert oxides.

Formation and Effect of Residual Lithium Compounds on Li-Rich Cathode Material Li1.35[Ni0.35Mn0.65]O2

Li-rich cathode materials are regarded as ideal cathode materials, owing to their excellent electrochemical capacity. However, residual lithium compounds, which are formed on the surface of the materials by reacting with moisture and carbon dioxide in ambient atmosphere, can impair the surface structure, injure the capacity, and impede the electrode fabrication using Li-rich materials. Exposure to air atmosphere causes the formation of residual lithium compounds; the formation of such compounds is believed to be related to humidity, temperature, and time during handling and storage. In this study, we demonstrated for the first time an artificial strategy for controlling time, temperature, and humidity to accelerate exposure. The formation and effect of residual lithium compounds on Li-rich cathode material Li_1.35[Ni_0.35Mn_0.65]O₂ were systematically investigated. The residual lithium compounds formed possessed primarily an amorphous structure and were partially coated on the surface. These compounds include LiOH, Li₂O, and Li₂CO₃. Li₂CO₃ is the major component in residual lithium compounds. The presence of residual lithium compounds on the material surface led to a high discharge capacity loss and large discharge voltage fading. Understanding the formation and suppressing the effect of residual lithium compounds will help prevent their unfavorable effects and improve the electrochemical performance.

Multiple Linkage Modification of Lithium-Rich Layered Oxide Li1.2Mn0.54Ni0.13Co0.13O2 for Lithium Ion Battery

A multiple linkage modification (MLM) method was investigated to comprehensively improve the properties of lithium-rich layered oxides. MLM Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ was successfully synthesized via continuous and appropriate heat treatment. The synthesized Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ particles were coated with a Li₂ZrO₃ layer and doped with Zr⁴⁺ by using a Zr compound as the MLM reagent. The Li₂ZrO₃ coating layer could protect materials from the corrosion of hydrogen fluoride, and the structure of the base materials was stabilized due to Zr⁴⁺ doping. In addition, the formation of Li₂ZrO₃ captured inactive residual lithium on the surface and absorbed lithium of host materials, thereby leading to the reduction in the Li/M ratio of materials and promoting the first-cycle Coulombic efficiency. The MLM material delivered the highest initial cycle Coulombic efficiency (∼85%), the best cycle and rate performance among bare and ZrO₂-coated particles. These results indicate that MLM is an important technique for improving the performance of electrode materials.

Comparative Investigation of 0.5Li2MnO3·0.5LiNi0.5Co0.2Mn0.3O2 Cathode Materials Synthesized by Using Different Lithium Sources

Lithium-rich manganese-based cathode materials has been attracted enormous interests as one of the most promising candidates of cathode materials for next-generation lithium ion batteries because of its high theoretic capacity and low cost. In this study, 0.5Li₂MnO₃·0.5LiNi_0.5Co_0.2Mn_0.3O₂ materials are synthesized through a solid-state reaction by using different lithium sources, and the synthesis process and the reaction mechanism are investigated in detail. The morphology, structure, and electrochemical performances of the material synthesized by using LiOH·H₂O, Li₂CO₃, and CH₃COOLi·2H₂O have been analyzed by using Thermo gravimetric analysis (TGA), X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The 0.5Li₂MnO₃·0.5LiNi_0.5Co_0.2Mn_0.3O₂ material prepared by using LiOH·H₂O displays uniform morphology with nano particle and stable layer structure so that it suppresses the first cycle irreversible reaction and structure transfer, and it delivers the best electrochemical performance. The results indicate that LiOH·H₂O is the best choice for the synthesis of the 0.5Li₂MnO₃·0.5LiNi_0.5Co_0.2Mn_0.3O₂ material.