ABSTRACT

Niobates are regarded as prospective Li⁺-storage anode candidates due to the rich chemistry of niobium and crystal-structural openness. However, the exploration of niobates is still insufficient. In this study, we explore CuNb₃O₈ with a large theoretical capacity is 341.9 mAh g^–1 as a high-performance anode compound. The reversible redox reaction among Nb⁵⁺, Nb⁴⁺ and Nb³⁺ during lithiation/delithiation is confirmed by ex-situ XPS, and a large reversible capacity of 231.8 mAh g^–1 and safe lithiation potential of 1.53 V are achieved at 0.1 C. An intercalation-type Li⁺-storage mechanism is confirmed by in-situ XRD after the first lithiation process, guaranteeing the good cyclability from the second discharge–charge cycles. The Li⁺ diffusivity in CuNb₃O₈ is systematically and carefully studied. The galvanostatic intermittent titration technique tests show large Li⁺ diffusion coefficients of 1.2 × 10^–12/1.5 × 10^–12 cm² s^–1 during lithiation/delithiation, and the corresponding values obtained through the cyclic voltammetry technique are similar (2.2 × 10^–12/3.0 × 10^–12 cm² s^–1). Additionally, CuNb₃O₈ is successfully coupled with LiFePO₄, and the resultant CuNb₃O₈//LiFePO₄ full cell also exhibits good electrochemical properties, demonstrating the practicability of CuNb₃O₈ for large-scale energy-storage applications.

摘要

由于铌的丰富化学性质和晶体结构的开放性，铌酸盐被认为是潜在的锂离子存储^负极候选者。然而，铌酸盐的探索仍然不足。在本研究中，我们探索了具有大理论容量为 341.9 mAh g ^{-1的 CuNb} ₃ O ₈作为高性能负极化合物。异位XPS证实了锂化/脱锂过程中Nb ⁵⁺、Nb ⁴⁺和Nb ³⁺之间的可逆氧化还原反应，在0.1时实现了231.8 mAh g ^-1的大可逆容量和1.53 V的安全锂化电位C. 嵌入型 Li ⁺-存储机制在第一次锂化过程后通过原位XRD 确认，保证了第二次放电-充电循环的良好循环性。对CuNb ₃ O ₈中的Li ⁺扩散率进行了系统而仔细的研究。恒电流间歇滴定技术测试表明，锂化/脱锂过程中 Li ⁺扩散系数为 1.2 × 10 ^–12 /1.5 × 10 ^–12 cm ² s ^–1，通过循环伏安技术获得的相应值相似（2.2 × 10 ^–12 /3.0 × 10 ^–12厘米²秒^–1）。此外，CuNb ₃ O ₈与LiFePO ₄成功耦合，得到的CuNb ₃ O ₈ //LiFePO ₄全电池也表现出良好的电化学性能，证明了CuNb ₃ O ₈在大规模储能应用中的实用性。