Rational design of bamboo mat-like 3D Ni foam@NiO@PPy nanoarray electrode for binder-free, high-loading and high-areal capacity lithium storage

Achieving high capacity and good cyclability of transition metal oxides anodes remains a challenge for lithium-ion batteries (LIBs) because of their poor conductivity and severe volume change. In this work, a bamboo mat-like nanoarray electrode consisting of NiO nanoarray interlayer and polypyrrole (PPy) coating layer growing directly on three-dimensional nickel foam (3D NF) conductive substrate (denoted as 3D NF@NiO@PPy) is reported to overcome the challenge. The 3D NF current collector can provide more active growth sites and thus achieve high loading (about 5.5 mg cm^–2). The bamboo mat-like NiO nanoarray reduces the Li⁺ ions diffusion path and enhances the contact surface areas with the electrolyte, which can improve the electrochemical properties. The in-situ growth PPy coating can not only effectively suppress the volume expansion of NiO during the charge and discharge process, but also effectively improve the electrical conductivity of the electrode within a certain thickness range. Benefiting from this unique structure, the as-obtained 3D NF@NiO@PPy binder-free nanoarray electrode exhibits stable cycle performance and high reversible areal capacity of 4.90 mA h cm^-2 at 0.5 mA cm^-2. Remarkably, a large reversible capacity of 1.10 mA h cm^-2 is also achieved even after 200 cycles at a relatively high current density of 2.5 mA cm^-2. This work proposes a feasible strategy to enhance the capacity and stability of NiO anode and provides a new way for the practical application of self-supporting electrodes.