La-Ce双掺杂调控电子结构及离子传输增强Na4Fe3(PO4)2P2O7正极的超快储钠性能OA

The low cost and high theoretical capacity of Na4Fe3(PO4)2P2O7(NFPP)make it an ideal candidate material for sodium-ion battery cathodes;however,the presence of NaFePO4,which is electrochemically inactive and exhibits poor electronic conductivity,is a common issue during synthesis,limiting the application of NFPP.Herein,we report a synergistic La-Ce dual-doping strategy that simultaneously addresses both critical challenges by engineering the electronic structure and stabilizing the crystal lattice of NFPP.First-principles density functional theory(DFT)simulations indicate the La3+and Ce3+ions preferentially substitute Fe sites in the NFPP lattice.This substitution suppresses the nucleation and growth of NaFePO4 impurities effectively via modification of the local thermodynamic environment,while simultaneously bringing about substantial changes in the electronic structure.Specifically,the hybridization between La/Ce 4f orbitals and Fe 3d-O 2p orbitals dramatically narrows the band gap,while simultaneously strengthening the Fe-O covalent bonds to enhance structural stability.Na4Fe2.91La0.03Ce0.03(PO4)2P2O7(La-Ce-NFPP)exhibited a high-rate capacity of 92.47 mAh g-1 at 20C,and reached 93.76%capacity retention after 3000 cycles at 10C.La-Ce dual-doping reduces the unit cell volume variation from 4.63%(NFPP)to 3.05%(La-Ce-NFPP),as evidenced by in situ XRD testing,this confirms that the doping optimizes Na⁺ diffusion pathways and mitigates structural strain during phase transitions.Furthermore,the La-Ce-NFPP//hard carbon full cell shows superior cycling stability,achieving 94.9%capacity preservation after 200 cycles,demonstrating great potential for practical applications.