NiFe saponite as a new anode material for high-performance lithium-ion batteries

Abstract

NiFe saponite (NF-SAP) with Na⁺ pillaring was investigated for the first time, as a new anode material for high-performance lithium-ion batteries (LIBs). In this material, non-metallic element Si and metallic elements Fe and Ni all act as active components (providing capacity) and undergo valence state changes during electrochemical progress. Si changes between Si²⁺ and Si⁴⁺, while Fe and Ni transform between a nearly metallic state and Fe^x+ and Ni^y+ (0 < x < 3, 0 < y < 2). In the fully lithiated state, Ni–Ni bonds appear but only Fe–O bonds can be observed in NF-SAP. The NF-SAP/Li half cell delivers a gradually increasing specific capacity in the initial hundreds of cycles (maximum capacity of 815 mA h g⁻¹ at the 350th cycle) and maintains a capacity of 646 mA h g⁻¹ after 1000 cycles at 500 mA g⁻¹. The pre-pillaring effect of Na⁺ is responsible for the good Li⁺ storage performance, which leads to the decrease of Li⁺ transport hindrance and high contribution of pseudocapacitance. Furthermore, a full cell of LiMn₂O₄/NF-SAP was assembled, which shows an initial specific capacity of 104 mA h g⁻¹ at 100 mA g⁻¹ and maintains a capacity of 68% after 50 cycles, demonstrating the bright application prospects of NF-SAP as a promising anode material. This work shows a new kind of anode for LIBs and provides an in-depth understanding of its energy-storage mechanism. Considering the easy preparation, low cost and environment-friendly characteristics of NF-SAP, this kind of material is applicable to large-scale energy storage.