Polyvinylpyrrolidone-assisted synthesis of ultrathin multi-nanolayered Cu2Nb34O87−x for advanced Li+ storage

The ultrathin multi-nanolayered structure with ultrathin monolayer thickness (<10 nm) and certain interlayer spacing can significantly shorten Li + paths and alleviate the volume effect for Li + -storage materials. However, unlike layered materials such as MXene and MoS 2 , shear ReO 3 -type niobates have difficulty forming ultrathin multi-nanolayered structures due to their crystal structures, which still remains a challenge. Herein, by a polyvinylpyrrolidone (PVP)-assisted solvothermal method , we first synthesize ultrathin multi-nanolayered Cu 2 Nb 34 O 87−x with oxygen vacancies composed of ultrathin nanolayers (2–10 nm in thickness) and interlayer spacing (1–5 nm). Oxygen vacancies can radically enhance the inherent electronic/ionic conductivity and Li + diffusion coefficient of this material. The PVP-induced formation mechanism of this material is expounded in detail. The well-preserved ultrathin multi-nanolayered structure and excellent multi-electron electrochemical reversibility (Nb 5+  ↔ Nb 4+  ↔N b 3+ and Cu 2+  ↔ Cu + ) of this material during cycling are fully verified. Based on an ultrathin multi-nanolayered structure and oxygen vacancies, this material as the anode of lithium-ion batteries is highly competitive among reported shear ReO 3 -type Cu-Nb-O anodes, displaying a high reversible capacity (315.3 mAh g −1 after 300 cycles at 1 C), durable cycling stability (85.7 % capacity retention after 1000 cycles at 10 C), and outstanding rate performance. Moreover, the application of this material to lithium-ion capacitors generates a large energy density (97.9 Wh kg −1 at 87.5 W kg −1 ) and a high power density (17,500 W kg −1 at 12.6 Wh kg −1 ), thus further indicating its fast faradaic pseudocapacitive behavior for practical applications. The results of this work indicate a breakthrough in synthesizing ultrathin multi-nanolayered shear ReO 3 -type niobates.