In Situ High‐Temperature Phase Elucidation of Secondary Particles and Segregating Nanoparticles with Surface Coating‐Networking Architecture for High‐Voltage Cathode Life at High Rate

Spinel LiMn_1.5Ni_0.5O₄ cathode being with surface modified primary nanoparticles by precursor structural advancement enables multiple diffusion pathways and least diffusion length to fast Li⁺ transport for stable high-voltage cathode life at high discharge rate. Results confirm a strong potential for use as a highly durable, cobalt-free, high-voltage cathode capable of high-rate discharge in LIBs.

Abstract

Secondary microparticles are synthesized using a Mn_1.5Ni_0.5(OH)₂CO₃ precursor, which undergoes thermal decomposition and calcination, releasing CO₂ and H₂O gaseous species. In situ high-temperature phase elucidation confirms the least degree of disordered phase LiMn_1.5Ni_0.5O₄ cathode without rock-salt impurity phase and having insignificant content of Mn³⁺ to stable Fd 3¯$\bar{3}$ m structure. Raman spectrum shows a band at 590 cm⁻¹ (F_2g ⁽³⁾) without splitting, confirming spinel compound derived with disordered phase. Microscopic analyses reveal secondary microparticles and segregated primary nanoparticles having surface coating-conducting network architecture. Cyclic voltammograms of primary nanoparticles show well-resolved two redox peaks at 4.7 V compared to secondary microparticles, confirming superior kinetic reversibility for Ni²⁺ to Ni³⁺ and Ni³⁺ to Ni⁴⁺ redox process. At 20C discharge, segregated primary nanoparticles exhibit a discharge flat voltage profile at 4.3 V and deliver a high reversible capacity of 100 mAh g⁻¹ for the 12th cycle and 86 mAh g⁻¹ for the 1000th cycle, while secondary microparticles deliver 70 mAh g⁻¹ for 12th cycle and declined its cycle operation at 250th cycle with the capacity of < 5 mAh g⁻¹. Results confirm a strong potential for use as a highly durable, cobalt-free, high-voltage cathode capable of high-rate discharge in LIBs.