Fabrication and interfacial characterization of Ni-rich thin-film cathodes for stable Li-ion batteries

Lithium-Ion Conductive Coatings for Nickel-Rich Cathodes for Lithium-Ion Batteries

Nickel (Ni)-rich cathodes are among the most promising cathode materials of lithium batteries, ascribed to their high-power density, cost-effectiveness, and eco-friendliness, having extensive applications from portable electronics to electric vehicles and national grids. They can boost the wide implementation of renewable energies and thereby contribute to carbon neutrality and achieving sustainable prosperity in the modern society. Nevertheless, these cathodes suffer from significant technical challenges, leading to poor cycling performance and safety risks. The underlying mechanisms are residual lithium compounds, uncontrolled lithium/nickel cation mixing, severe interface reactions, irreversible phase transition, anisotropic internal stress, and microcracking. Notably, they have become more serious with increasing Ni content and have been impeding the widespread commercial applications of Ni-rich cathodes. Various strategies have been developed to tackle these issues, such as elemental doping, adding electrolyte additives, and surface coating. Surface coating has been a facile and effective route and has been investigated widely among them. Of numerous surface coating materials, have recently emerged as highly attractive options due to their high lithium-ion conductivity. In this review, a thorough and comprehensive review of lithium-ion conductive coatings (LCCs) are made, aimed at probing their underlying mechanisms for improved cell performance and stimulating new research efforts.

Influence of the SEI Formation on the Stability and Lithium Diffusion in Si Electrodes

Silicon (Si) is an attractive anode material for Li-ion batteries (LIBs) due to its high theoretical specific capacity. However, the solid-electrolyte interphase (SEI) formation, caused by liquid electrolyte decomposition, often befalls Si electrodes. The SEI layer is less Li-ion conductive, which would significantly inhibit Li-ion transport and delay the reaction kinetics. Understanding the interaction between the SEI components and Li-ion diffusion is crucial for further improving the cycling performance of Si. Herein, different liquid electrolytes are applied to investigate the induced SEI components, structures, and their role in Li-ion transport. It is found that Si electrodes exhibit higher discharge capacities in LiClO₄-based electrolytes than in LiPF₆-based electrolytes. This behavior suggests that a denser and more conductive SEI layer is formed in LiClO₄-based electrolytes. In addition, a coating of a Li₃PO₄ artificial SEI layer on Si suppresses the formation of natural SEI formation, leading to higher capacity retentions. Furthermore, galvanostatic intermittent titration technique (GITT) measurements are applied to calculate Li-ion diffusion coefficients, which are found in the range of 10^-23-10^-19 m²/s.

Low-Cost Al-Doped Layered Cathodes with Improved Electrochemical Performance for Rechargeable Sodium-Ion Batteries

O3-NaNi0.25Fe0.5Mn0.25O2 layered oxide is considered one of the most promising cathode candidates for sodium-ion batteries because of its advantages, such as its large capacity and low cost. However, the practical application of this material is limited by its poor cyclic stability and insufficient rate capability. Here, a strategy to substitute the Fe3+ in NaNi0.25Fe0.5Mn0.25O2 with Al3+ is adopted to address these issues. The substitution of Fe3+ with Al3+ enhances the framework stability and phase transition reversibility of the parent NaNi0.25Fe0.5Mn0.25O2 material by forming a stronger TM-O bond, which improves the cycling stability. Moreover, partial Al3+ substitution increases the interslab distance, providing a spacious path for Na+ diffusion and resulting in fast diffusion kinetics, which lead to improved rate capability. Consequently, the target NaNi0.25Fe0.5-xAlxMn0.25O2 sample with optimal x = 0.045 exhibits a remarkable electrochemical performance in a Na-ion cell with a large reversible capacity of 131.7 mA h g-1, a stable retention of approximately 81.6% after cycling at 1C for 100 cycles, and a rate performance of 81.3 mA h g-1 at 10C. This method might pave the way for novel means of improving the electrochemical properties of layered transitional-metal oxides and provide insightful guidance for the design of low-cost cathode materials.

Regulation of Surface Defect Chemistry toward Stable Ni-Rich Cathodes

Surface reconstruction of Ni-rich layered oxides (NLO) degrades the cycling stability and safety of high-energy-density lithium-ion batteries (LIBs), which challenges typical surface-modification approaches to build a robust interface with electrochemical activity. Here, a strategy of leveraging the low-strain analogues of Li- and Mn-rich layered oxides (LMR) to reconstruct a stable surface on the Ni-rich layered cathodes is proposed. The new surface structure not only consists of a gradient chemical composition but also contains a defect-rich structure regarding the formation of oxygen vacancies and cationic ordering, which can simultaneously facilitate lithium diffusion and stabilize the crystal structure during the (de)lithiation. These features in the NLO lead to a dramatic improvement in electrochemical properties, especially the cyclability under high voltage cycling, exhibiting the 30% increase in capacity retention after 200 cycles at the current density of 1 C (3.0-4.6 V). The findings offer a facile and effective way to regulate defect chemistry and surface structure in parallel on Ni-rich layered structure cathodes to achieve high-energy density LIBs.