Research On Aluminum Storage Properties Of High Performance Expanded Graphite Aluminum Ion Battery Cathode Materials

Expanded graphite（EG）has great potential for application because of its low price,good electrical conductivity and long-range ordered layered structure.However,the large size space（0.528 nm）of the intercalated anions Al Cl₄^-when expanded graphite is used as the cathode of aluminum ion battery（AIBs）makes the space for storing the guest ions insufficient and the ions diffusion paths limited,leading to its low discharge specific capacity and poor ions diffusion kinetics.In response to the above problems,this paper prepared expanded graphite with larger interlayer spacing and positive surface charge from the perspective of structural regulation and surface modification.Its electrochemical performance as anode for AIBs was investigated.The relationship between graphite interlayer spacing,surface charge modification and electro-chemical performance was explored,and the following main findings were obtained.（1）A porous structure,worm-like expanded graphite was prepared by temperature regulation using expandable graphite as raw material.The results showed that the interlayer spacing of expanded graphite（800-EG）obtained by heat treatment at 800°C was the largest,about 0.41 nm.（2）The 800-EG electrode has the largest interlayer spacing and the best electrochemical performance.At a current density of 1 A g^-1,its reversible capacity is 86 m Ah g^-1 for 4000 cycles;at a current density of 5A g^-1,its discharge specific capacity is 66 m Ah g^-1.There is no obvious capacity decay for 10,000 cycles and the coulombic efficiency is about100%.（3）The two-stage energy storage mechanism of 800-EG electrode,namely adsorption mechanism（0.5-1.5 V）and intercalation mechanism（1.5-2.5 V）,was revealed by electrochemical experiments and in-situ X-ray diffraction tests.（4）Based on the adsorption mechanism of EG material,positively charged expanded graphite materials（PDDA-EG）were prepared by using polydiallyldimethylammonium chloride（PDDA）throughπ-πelectrostatic interactions with the electron leaving domains of the expanded graphite backbone.PDDA-EG（1:1）electrode exhibited good electrochemical properties,with a reversible capacity of 104 m Ah g^-1 after 30,000 cycles at a current density of 5 A g^-1.（5）The PDDA-EG（1:1）electrode has abundant active positive charge,which makes it have large pseudo-capacitance effect in the voltage range of 0.5-2.5 V(the pseudo-capacitance contribution percentage is 95.79%at a scan rate of 5 m V s^-1),which leads to a further improvement of its rate performance.