Three-roll milling exfoliated graphite nanoplatelets with semi-graphitized hard carbon by Ni-catalyzed pyrolysis of phenolic resin for high-performance sodium-ion batteries

Sodium-ion batteries (SIBs) have gained increasing attention for commercial applications due to their low cost and environmental friendliness. However, developing high-performance and low-cost anode materials remains a significant challenge. This study presents a novel method for preparing graphite nanoplatelets (GNPs) exfoliated by three-roll milling with semi-graphitized hard carbon (SGHC), obtained through Ni-catalyzed pyrolysis of phenolic resin, for high-performance SIBs. The resulting Ni/GNPs@SGHC composite exhibited a larger layer spacing of GNPs (d₀₀₂ = 0.39 nm), while the addition of Ni(NO₃)₂·6H₂O caused the amorphous hard carbon to transform into a SGHC with a micropore structure, which enabled it to accommodate more Na⁺. As an anode material for SIBs, the specific capacity (SC) of x%-Ni/GNPs@SGHC initially increased and subsequently decreased with the increasing x. The 5.0%-Ni/GNPs@SGHC electrode showed excellent performance and ultra-long cycling stability, with an SC of 183 mA h g^-1, which was twice that of 0.0%-Ni/GNPs@SGHC (89 mA h g^-1) after 200 cycles at a current density of 1 A g^-1, and it maintained an SC of 96 mA h g^-1 after 7600 cycles at a high current density of 50 A g^-1. These results were attributed to the combination of high carbon content, nickel metal phase, and the unique structure of Ni/GNPs@SGHC. This work offers a promising strategy for the rational design of novel electrode materials for advanced energy storage devices.