Preparation And Energy Storage Mechanism Of Biomass Carbon Cathode Material For Non-aqueous Rechargeable Aluminum-ion Batteries

Due to the advantages of low cost,high performance and safety,non-aqueous rechargeable aluminum batteries（RABs）have shown great potential in the field of large-scale energy storage.Finding suitable cathode materials for RABs has always been one of the urgent issues to be solved.Although the commonly used carbonaceous cathode materials present outstanding electrochemical performance,the problem of high cost and high preparation difficulty desperately required to be solved.Biomass-derived hard carbon materials contain large interlayer distances,which indicate high possibility for ion intercalation on the surface of the material.In addition,hard carbon materials also have many advantages such as diverse structures,low cost,and simple preparation processes that can be used in large-scale production.However,resulting from the instability of the structure and unstable layered-structure,the problems of low capacity,low rate and severe capacity fading of hard carbon materials urgently need to be improved.In this paper,various of modification methods including high-temperature carbonization,high-speed ball milling,low-temperature hydrothermal,nitrogen doping,etc.were utilized to prepare high-performance positive electrodes for rechargeable aluminum batteries.The specific research contents are as follows:1.The pomegranate peel was used as a carbon source,the hard carbon materials of the pomegranate peel were prepared after carbonization at 900°C for 1 hour and high-speed ball milling.The results show that more graphite microcrystalline regions and pore structures are exposed on the surface of the hard carbon material by ball milling.In addition,graphite layer domains with interlayer spacing of 0.344 nm appear on the surface of the hard carbon material after ball milling for 5 minutes,which have the largest specific surface area,present the best electrochemical performance.At a current density of 150m A·g^-1,the capacity after 200 cycles was 120.3 m Ah·g^-1;at a current density of 200m A·g^-1,the capacity remained at 82.2 m Ah·g^-1 after 500 cycles.The energy storage process follows the insertion mechanism of carbonaceous materials,that is,Al Cl₄^-inserts into the surface of the material during charging and comes out during discharging.2.Using ball-milled hard carbon as a precursor,the hard carbon materials were intercalated by FeCl₃ through hydrothermal reaction and the electrochemical properties of high-layer spacing hard carbon materials were explored.As a result,a concentric layered structure was formed on the hard carbon surface,and the interlayer spacing of graphite domains was increased from 0.344 nm to 0.367 nm.The expansion of the layer spacing is beneficial to the deintercalation of Al Cl₄^-,and reduces the loss of the structure after multiple cycles,and improves the stability of the structure.At a current density of 1 A·g^-1,the discharge specific capacity after 1000 cycles is 83.6 m Ah·g^-1.3.Utilizing melamine as the nitrogen source,the hard carbon material after ball milling was doped with nitrogen by direct mixing and hydrothermal method,the effect of nitrogen doping on the energy storage behavior of hard carbon material was studied.The introduction of nitrogen atoms makes the electronegativity change of the hard carbon material show Lewis basicity,and combines with Cl^-in the electrolyte to form an ionic compound to participate in the subsequent charge and discharge process,effectively improving the surface activity of the hard carbon material and improving the reaction rate.Efficiency improves the capacitive performance of the material at high current densities.At a current density of 500 m A·g^-1,the discharge specific capacity is 149 m Ah·g^-1 after200 cycles,and 109.3 m Ah·g^-1 after 1000 cycles at a current density of 1 A·g^-1.