{'fraction_non_alphanumeric': 0.038028169014084505, 'fraction_numerical': 0.029577464788732393, 'mean_word_length': 5.518348623853211, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Improved electrochemical performance of lanthanum-modified Na3V2(PO4)3/C cathode materials for sodium-ion batteries

A series of lanthanum-doped Na3V2−xLax(PO4)3/C (0 ≤ x ≤ 0.03) composites have been fabricated via a simple sol–gel approach. The influences of La3+ substitution on the structure, morphology and electrochemical properties are systematically studied. Rietveld refinement is applied to explore the actual substitution site of La, which proves that La3+ ions successfully occupy the octahedral V sites. It is suggested that appropriate La doping will reduce the particle size and enhance the reversible capacity and rate capability. Among all the samples, the as-prepared Na3V1.99La0.01(PO4)3/C compound shows the highest electrochemical capability. It delivers a high initial specific capacity of 111.3 mA h g−1 at 0.2C and maintains a capacity of 108.1 mA h g−1 over 100 cycles, exhibiting much better electrochemical performance than the original Na3V2(PO4)3/C. In addition, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments suggest that low-level La doping can greatly decrease the polarization and increase electrical conductivity with fast reaction kinetics and a higher Na+ diffusion coefficient. The study presented here will provide considerable insights into rare earth element-doping tactics, which will facilitate the commercialization of sodium-ion batteries.