Synergistic Structure and Iron-Vacancy Engineering Realizing High Initial Coulombic Efficiency and Kinetically...

Transition metal oxides with high capacity still confront the challenges of low initial coulombic efficiency (ICE, generally <70%) and inferior cyclic stability for practical lithium-storage. Herein, a hollow slender carambola-like Li_0.43 FeO_1.51 with Fe vacancies is proposed by a facile reaction of Fe³⁺ -containing metal-organic frameworks with Li₂ CO₃ . Synthesis experiments combined with synchrotron-radiation X-ray measurements identify that the hollow structure is caused by Li₂ CO₃ erosion, while the formation of Fe vacancies is resulted from insufficient lithiation process with reduced Li₂ CO₃ dosage. The optimized lithium iron oxides exhibit remarkably improved ICE (from 68.24% to 86.78%), high-rate performance (357 mAh g^-1 at 5 A g^-1 ), and superior cycling stability (884 mAh g^-1 after 500 cycles at 0.5 A g^-1 ). Paring with LiFePO₄ cathodes, the full-cells achieve extraordinary cyclic stability with 99.3% retention after 100 cycles. The improved electrochemical performances can be attributed to the synergy of structural characteristics and Fe vacancy engineering. The unique hollow structure alleviates the volume expansion of Li_0.43 FeO_1.51 , while the in situ generated Fe vacancies are powerful for modulating electronic structure with boosted Li⁺ transport rate and catalyze more Li₂ O decomposition to react with Fe in the first charge process, hence enhancing the ICE of lithium iron oxide anode materials.