Inhibition of Structural Transformation and Surface Lattice Oxygen Activity for Excellent Stability Li-Rich Mn-Based Layered Oxides

Operando Magnetism on Oxygen Redox Process in Li-Rich Cathodes

Oxide ions in lithium-rich layered oxides can store charge at high voltage and offer a viable route toward the higher energy density batteries. However, the underlying oxygen redox mechanism in such materials still remains elusive at present. In this work, a precise in situ magnetism measurement is employed to monitor real-time magnetization variation associated with unpaired electrons in Li1.2Mn0.6Ni0.2O2 cathode material, enabling the investigation on magnetic/electronic structure evolution in electrochemical cycling. The magnetization gradually decreases except for a weak upturn above 4.6 V during the initial charging process. According to the comprehensive analyses of various in/ex situ characterizations and density functional theory (DFT) calculations, the magnetization rebound can be attributed to the interaction evolution of lattice oxygen from π-type delocalized Mn─O coupling to σ-type O─O dimerization bonding. Moreover, the magnetization amplitude attenuation after long-term cycles provides important evidence for the irreversible structure transition and capacity fading. The oxygen redox mechanism concluded by in situ magnetism characterization can be generalized to other electrode materials with an anionic redox process and provide pivotal guidance for designing advanced high-performance cathode materials.

One-Step Realization of Layered/Spinel Heterostructures and Na Doping by Sodium Dodecyl Sulfate-Assisted Sol-Gel Method for Li-Ion Batteries

Li-rich layered oxide cathodes have attracted extensive attention due to their high energy density. However, due to the low initial Coulombic efficiency and the capacity fading and voltage fading during cycling, its practical application is still a great challenge. Here, we report the one-step realization of layered/spinel heterostructures and Na doping by the sodium dodecyl sulfate (SDS)-assisted sol-gel method. The spinel phase provides 3D diffusion channels for Li-ions, and sodium doping changes the layered lattice constant and expands the layer spacing. Therefore, the designed Li1.15Mn0.54Ni0.13Co0.13Na0.05O2 (SDS-2) cathode possesses excellent electrochemical performance such as higher initial Coulombic efficiency and rate capacity and also alleviates voltage decay. The initial discharge-specific capacity of SDS-2 is 298.8 mAh g-1 at 0.1 C, and the discharge-specific capacity can reach 111.7 mAh g-1 at 10 C. This strategy can provide new insights into the design and synthesis of high-performance Li-rich layered oxide cathode materials.

Functional Composite Dual-Phase In Situ Self-Reconstruction Design for High-Energy-Density Li-Rich Cathodes

The unique anionic redox mechanism provides, high-capacity, irreversible oxygen release and voltage/capacity degradation to Li-rich cathode materials (LRO, Li1.2Mn0.54Co0.13Ni0.13O2). In this study, an integrated stabilized carbon-rock salt/spinel composite heterostructured layers (C@spinel/MO) is constructed by in situ self-reconstruction, and the generation mechanism of the in situ reconstructed surface is elucidated. The formation of atomic-level connections between the surface-protected phase and bulk-layered phase contributes to electrochemical performance. The best-performing sample shows a high increase (63%) of capacity retention compared to that of the pristine sample after 100 cycles at 1C, with an 86.7% reduction in surface oxygen release shown by differential electrochemical mass spectrometry. Soft X-ray results show that Co3+ and Mn4+ are mainly reduce in the carbothermal reduction reaction and participate in the formation of the spinel/MO rock-salt phase. The results of oxygen release characterized by Differential electrochemical mass spectrometry (DEMS) strongly prove the effectiveness of surface reconstruction.

Interpretable Machine Learning To Accelerate the Analysis of Doping Effect on Li/Ni Exchange in Ni-Rich Layered Oxide Cathodes

In Ni-rich layered oxide cathodes, one effective way to adjust the performance is by introducing dopants to change the degree of Li/Ni exchange. We calculated the formation energy of Li/Ni exchange defects in LiNi0.8Mn0.1X0.1O2 with different doping elements X, using first-principles calculations. We then proposed an interpretable machine learning method combining the Random Forest (RF) model and the Shapley Additive Explanation (SHAP) analysis to accelerate identification of the key factors influencing the formation energy among the complex variables introduced by doping. The valence state of the doping element effectively regulates Li/Ni exchange defects through changing the valence state of Ni and the strength of the superexchange interaction, and COOPSU-SD and MagO were proposed as two indicators to assess superexchange interaction. The volume change also affects the Li/Ni exchange defects, with a larger volume reduction corresponding to fewer Li/Ni exchange defects.