Effective and Low-Cost In Situ Surface Engineering Strategy to Enhance the Interface Stability of an Ultrahigh Ni-Rich NCMA Cathode

Machine learning-assisted precision inverse design research of ternary cathode materials: A new paradigm for material design

The Li+ diffusion rate directly affects the cathode rate performance, and it is inefficient to precision design cathode materials with excellent rate performance using the Edison approach method. Here, a new paradigm for the precision design of ternary cathode materials is exploited. The data of Ni-Co-Mn ternary (NCM) cathode materials doped with Li sites and transition metal (TM) sites, respectively, were extracted from publications, and the model Gradient Boosted Regression (GBR), which can accurately reveal the relationship between physical characterization variables and Li+ diffusion rate, was trained. Subsequently, the inverse design of the synthetic experimental parameters was carried out based on the desired target Li+ diffusion rate with the GBR model and particle swarm optimization (PSO) algorithm. A global search of the crystal structure is then performed using the Universal Structure Predictor: Evolutionary Xtallography (USPEX) code based on the parameters of the reverse design. Finally, first-principle calculations are performed to verify Li+ diffusion rate of the searched structures. The theoretical calculations show that the Li+ diffusion rates of the designed materials Ce-NCM and Li/Ni@Ce-NCM are 8.66 × 10-9 cm2/s, and 9.67 × 10-9 cm2/s, respectively, which are better than the target values (1.23 × 10-10 cm2/s). The density functional theory (DFT) calculations of charge transfer density indicate that moderate Li/Ni mixing induces a built-in electric field, which facilitates Li+ diffusion in the NCM cathode materials. This work demonstrates the potential of accurate inverse design of ternary cathode materials, advances the research process of ternary cathode materials, and provides a reference for the design of cathode materials and its counterparts. This work will open new avenues for designing cathode materials and counterparts, potentially revolutionizing traditional trial-and-error experiments.

Oxygen Vacancies Driven by Co in the Deeply Charged State Inducing Intragranular Cracking of Ni-Rich Cathodes

Intragranular cracking within the material structure of Ni-rich (LiNixCoyMn1 - x - y, x ≥0.9) cathodes greatly threatens cathode integrity and causes capacity degradation, yet its atomic-scale incubation mechanism is not completely elucidated. Notably, the physicochemical properties of component elements fundamentally determine the material structure of cathodes. Herein, a diffusion-controlled incubation mechanism of intragranular cracking is unraveled, and an underlying correlation model with Co element is established. Multi-dimensional analysis reveals that oxygen vacancies appear due to the charge compensation from highly oxidizing Co ions in the deeply charged state, driving the transition metal migration to Li layer and layered to rock-salt phase transition. The local accumulation of two accompanying tensile strains collaborates to promote the nucleation and growth of intragranular cracks along the fragile rock-salt phase domain on (003) plane. This study focuses on the potential risks posed by Co to the architectural and thermal stability of Ni-rich cathodes and is dedicated to the compositional design and performance optimization of Ni-rich cathodes.

Understanding Electrochemical Performance Enhancement with Quaternary NCMA Cathode Materials

Ni-rich cathode materials show promise for use in lithium-ion batteries. However, a significant obstacle to their widespread adoption is the structural damage caused by microcracks. This research paper presents the synthesis of Ni-rich cathode materials, including LiNi0.8Co0.1Mn0.1O2 (referred to as NCM) and Li(Ni0.8Co0.1Mn0.1)0.98Al0.02O2 (referred to as NCMA), achieved through the high-temperature solid-phase method. Electrochemical (EC) testing results reveal the impressive EC performance of NCMA. NCMA exhibited a discharge capacity of 141.6 mAh g-1 and maintained a cycle retention rate of up to 74.92% after 300 cycles at a 1 C rate. In contrast, the NCM had a discharge capacity of 109.7 mAh g-1 and a cycle retention rate of 61.22%. Atomic force microscopy showed that the Derjaguin-Muller-Toporov (DMT) modulus value of NCMA exceeded that of NCM, signifying a greater mechanical strength of NCMA. Density functional theory calculations demonstrated that the addition of aluminum during the delithiation process led to the mitigation of anisotropic lattice changes and the stabilization of the NCMA structure. This improvement was attributed to the relatively stronger Al-O bonds compared to the Ni(Co, Mn)-O bonds, which reduced the formation of microcracks by enhancing NCMA's mechanical strength.