Rational design of 3D N-doped carbon nanosheet framework encapsulated ultrafine ZnO nanocrystals as superior performance anode materials in lithium ion batteries

Abstract

Transition metal oxides have been extensively studied as anodes in lithium ion batteries due to their high specific capacity. However, they face some challenges to realize their practical applications owing to their inherent drawbacks of poor electronic conductivity and large volume expansion during charge/discharge. In this work, a facile synthesis of ultrafine ZnO nanocrystals encapsulated in a 3D N-doped carbon nanosheet framework (ZnO–NCNF) is reported to tackle these issues and improve the performance. The ZnO–NCNF-700 composite maintains a reversible capacity of 770 mA h g⁻¹ at 500 mA g⁻¹ after 1000 cycles. At 1000 mA g⁻¹, a capacity of 572 mA h g⁻¹ is retained after 750 cycles. Even at higher current density of 10 000 mA g⁻¹, it still possesses a capacity of 148 mA h g⁻¹. Moreover, it maintains the structural integrity and its ion-diffusion coefficient increases by over three orders of magnitude. Also, the LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811)/ZnO–NCNF-700 full cell maintains a capacity of 531 mA h g⁻¹ after 60 cycles. The superior electrochemical performance might be ascribed to the reduced charge-transfer resistance, boosted Li⁺ diffusivity, mitigated breakage and structural integrity that originated from the decreased particle size and NCNF architecture. This work provides more insight into the lithium storage of ultrafine ZnO nanocrystals as anode electrode materials, and opens a new and facile strategy for developing a promising ZnO anode material for practical applications in lithium ion batteries.