Developing high-performance Ni-rich cathode materials is a key pathway toward achieving single-cell energy densities exceeding 400 Wh kg-1. Among various candidates, 7-series high-Ni cathodes with approximately 70% Ni content have attracted growing attention because they offer a favorable balance between energy density and manufacturability when operated at high voltages (≥ 4.5 V). However, elevated charging voltages inevitably lead to excessive de-lithiation, resulting in severe stress concentration and strain accumulation within cathode particles. Such mechanical instability accelerates microcrack formation and propagation, ultimately causing particle fracture and rapid capacity fading.
To address this, a research team led by Professor Chunzhong Li from Key Laboratory for Ultrafine Materials of Ministry of Education, Shanghai Engineering Research Center of Hierarchical Nanomaterials, East China University of Science and Technology recently demonstrates an in-situ co-precipitation strategy to synthesize quinary full-concentration-gradient cathode, LiNi0.73Co0.05Mn0.20Al0.01B0.01O2. The study has been published in the journal of Science Bulletin.
In this design, boron occupies tetrahedral sites within the transition-metal layer, effectively suppressing heat-driven interdiffusion of transition metals during high-temperature lithiation and thereby mitigating the degradation of the concentration gradient. Meanwhile, aluminum preferentially locates at tetrahedral sites in the lithium layer, alleviating the inherent increase in Li/Ni mixing induced by heterogeneous elemental distribution. As a result, the synthesized quinary gradient cathode features a Mn-rich, Ni-poor surface and radially aligned primary particles. This unique structural configuration enhances surface chemical and mechanical stability while efficiently dissipating internal tensile and compressive stresses.
Benefiting from the synergistic effects of boron and aluminum, the quinary gradient cathode exhibits improved lattice oxygen stability, effectively suppressing O2 and CO2 evolution during charging to 4.5 V and mitigating distortion of the Ni–O coordination environment upon prolonged cycling. Electrochemical evaluations demonstrate that the material delivers a high specific capacity of 210.5 mAh g–1 with an initial Coulombic efficiency of 90.1%. Notably, pouch-type full cells operated between 2.7 and 4.5 V retain 87.3% of their capacity after 1700 ultra-long cycles, highlighting exceptional long-term durability. This work provides a practical and scalable strategy for addressing mechanical and interfacial instability in high-voltage Ni-rich cathodes, offering new insights for the development of next-generation, cost-effective, high-energy-density lithium-ion batteries.
