Study on Structural Evolution of Synthetic Graphite Derived from Lignite Prepared by High Temperature–High Pressure Method

Ultrafine Graphite Scrap and Carbon Blocks Prepared by High-Solid-Loading Bead Milling and Conventional Ball Milling: A Comparative Assessment

A comparison between the physical characteristics of graphite ultrafine particles and the properties of graphite blocks prepared from graphite scrap using bead and conventional ball milling techniques is presented. Industrial-scale bead milling was used to prepare graphite scrap with an initial particle size d50 of 24 μm in the ultrafine range of <10 μm. Bead milling can significantly reduce the production time of ultrafine graphite from graphite scrap from 72 h by ball milling to 10 min. Ultrafine graphite scrap prepared from both ball milling and bead milling yields particles with a similar morphology, with a minor difference in crystalline size La and stacking height Lc observed. Carbon blocks were fabricated from both techniques, yielding carbon blocks with an almost identical microstructure and block density. Blocks from bead milling have slightly higher flexural strength as well as comparable hardness and resistivity. The block's flexural strength, hardness, and resistivity were 68.37 MPa, 99, and 36.9 μΩ·m, respectively, in a bead-milled carbon block and 61.86 MPa, 95.5, and 38.6 μΩ·m, respectively, for a ball-milled carbon block. Bead milling can be applied for the preparation of ultrafine graphite particles and graphite blocks with production that is 9 times faster for the same ultrafine graphite particle output and final product quality.

Reduced Graphene Oxide Derived from Low-Grade Coal for High-Performance Flexible Supercapacitors with Ultrahigh Cyclability

Preparation of reduced graphene oxide (RGO) from abundant and inexpensive low-grade coal is regarded as one of the most promising methods for utilizing this resource in a high-value and environmentally sustainable manner. As the main precursor for the fabrication of RGO, graphene oxide (GO) can be extracted from low-grade coal such as lignite, but its size is just in the range of tens to hundreds of nanometers, which limits its practical application. Herein, we demonstrate that large-size RGO sheets can be prepared in large quantities by the pretreatment of lignite using the high temperature-high pressure (HTHP) method. The RGO electrode after the reduction reaction by 50 mM NaBH₄ at 105 °C features porosity and high conductivity, which can facilitate high electrochemical reaction efficiency. Thus, we also demonstrate the use of lignite-derived RGO for supercapacitor electrode materials with high performance. The lignite-derived RGO supercapacitor can deliver outstanding volumetric capacitance (30.6 F cm^-3), high energy density (4.2 mW h cm^-3), excellent flexibility (79.5% retention of the initial capacitance at 180° bending), and a long lifespan (112.3% retention of the initial capacitance after 20,000 cycles). It is believed that the proposed large-size RGO based on reasonable optimization of inferior lignite will offer a new prospect for next-generation energy storage applications.