高熵P2/O3双相正极的协同设计助力高性能钠离子电池OA

P2-type layered transition metal oxides(P2-NaxTMO2)have emerged as promising cathodes for sodium-ion batteries(SIBs)owing to their superior cycling stability and excellent rate capability.However,their practical application is significantly hindered by two major challenges.Firstly,irreversible phase transitions occur during high-voltage operation,which disrupt the structural integrity and deteriorate electrochemical performance.Secondly,their inherently low theoretical specific capacity fails to meet modern energy demands.To tackle these challenges,this study proposes a novel synergistic strategy that integrates high-entropy engineering with a biphasic P2/O3 structural design.An innovative cathode material,Na0.70Ni0.25Mn0.35Co0.15Fe0.05Ti0.20O2(denoted as Na0.70NMCFT),was successfully synthesized via a high-temperature solid-state reaction.This material design critically incorporates five distinct transition metal cations into the transition metal(TM)layer,constructing a stabilized high-entropy configuration.Careful optimization of both the five TM elements and the sodium content was essential to precisely regulate the synthesis and formation of the desired integrated P2/O3 biphasic structure within this high-entropy host.Comprehensive structural characterization unequivocally confirms the successful construction of this tailored architecture.X-ray diffraction(XRD)and transmission electron microscopy(TEM)collectively confirm the successful construction of the P2/O3 biphasic architecture.The high-entropy engineering stabilizes the P2 phase through configurational entropy,effectively suppressing irreversible phase transitions and Na+/vacancy ordering during cycling,as evidenced by smoother charge/discharge profiles and ex-situ XRD analysis under high potentials.Meanwhile,the introduced O3 phase compensates for capacity shortages and improves cycling stability,working in tandem with the P2 phase.Critically,the interaction between the two phases enables a highly reversible transition between P2/O3-P2/P3,further enhancing the overall performance.Under the combined action of the high-entropy and biphasic strategies,Na0.70NMCFT exhibits optimal electrochemical performance.It delivers an initial discharge capacity of 102.08 mAh g-1 at 1C,retaining 88.15%after 200 cycles,demonstrating exceptional cycling stability.Moreover,even at 10C,Na0.70NMCFT still has an initial discharge specific capacity of 85.67 mAh g-1 and a capacity retention of up to 70%after 1,000 cycles.Kinetic analyses further reveal that Na0.70NMCFT possesses the lowest charge transfer resistance and the highest sodium-ion diffusion coefficient among the materials studied.In conclusion,this work demonstrates that the rational design of biphasic high-entropy cathodes can synergistically achieve superior rate capability,cycling stability,and maintain high theoretical capacity.It not only overcomes the key bottlenecks of P2-type oxides but also paves the way for the development of advanced SIB cathodes,establishing a new paradigm for the engineering of high-performance cathode materials in the field of sodium-ion batteries.