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• Compared with TiO 2 (1 0 1), Se(1 0 1) has a larger adsorption energy of [AlCl 4 ]−. • The porous nanosphere TiO 2 provides sites for the redox reaction of selenium. • TiO 2 @Se-rGO exhibits a discharge capacity of 225.8 mAh g−1 after 500 cycles. At present, because of the low energy density of aluminium-based batteries, rGO coated porous nanospheres TiO 2 @Se (TiO 2 @Se-rGO) was prepared by electrostatic effect as cathode material for Al-Se batteries. In Al-Se batteries, rGO coating has three functions: firstly, rGO uniform coating improves the dynamic properties of electrons and ions by increasing the diffusion or transfer rate; secondly, it avoids the diffusion of some selenides and dissolves them into the electrolyte to affect the electrochemical properties; lastly, the coating can stabilize the nanostructure and avoid the volume expansion or structural collapse during cycling. In addition, the porous nanosphere TiO 2 provides sites for the redox reaction of selenium, and can also avoid the dissolution of selenide. Most importantly, the density functional theory (DFT) shows that compared with TiO 2 (1 0 1), Se(1 0 1) has a larger adsorption energy of [AlCl 4 ]− and a smaller diffusion barrier of [AlCl 4 ]−. Therefore, TiO 2 @Se-rGO exhibits excellent electrochemical performance in Al-Se batteries. The initial discharge capacity reaches 1127.3 mAh g−1 at 0.2 A g−1, and the capacity is 208.7 mAh g−1 even at 1 A g−1. The discharge capacity is still as high as 225.8 mAh g−1 after 500 cycles at 0.5 A g−1. Therefore, TiO 2 @Se-rGO shows a clear advantage in the cathode material of aluminum-based batteries. [ABSTRACT FROM AUTHOR]

• Ti 3 C 2 @CTAB-Se is more conducive to the surface adsorption and diffusion of AlCl 4 −. • The Ti2+/Ti4+ and Se0/Sex+ undergo a reversible redox reaction in Ti 3 C 2 @CTAB-Se. • Ti 3 C 2 @CTAB-Se exhibits a reversible capacity of 583.7 mAh g−1 at 100 mA g−1. Recently, aluminum-based batteries have received extensive attention and research in various countries because of their absolute advantages in terms of cost, energy density, and safety performance compared to other metals-based batteries. Herein, we successfully synthesized composite two-dimensional layered structure (Ti 3 C 2 @CTAB-Se) through HF etching, CTAB expansion and subsequent selenium treatment. Through electrochemical and XPS analysis of Ti 3 C 2 @CTAB-Se, it is known that Ti2+/Ti4+ and Se0/Sex+ undergo a reversible redox reaction during charging/discharging. Moreover, it is surprisingly found by density functional theory (DFT) that Ti 3 C 2 O 2 after selenidation treatment is more conducive to the surface adsorption and diffusion of AlCl 4 − compared to Ti 3 C 2 O 2. Therefore, Ti 3 C 2 @CTAB-Se exhibits excellent electrochemical performance. It shows a reversible discharge specific capacity of 583.7 mAh g−1 at 100 mA g−1, and its capacity is still 132.6 mAh g−1 after 400 cycles. In addition, Ti 3 C 2 @CTAB-Se exhibits absolute advantages in both voltage and capacity for graphite-based, oxides, sulfide and other electrode materials in aluminum-based and other batteries cathode materials. Therefore, the advantages of this work in voltage and capacity will promote the development of aluminum batteries. [ABSTRACT FROM AUTHOR]

• The number of rings and the symmetry of molecular structure affect the redox reaction of organic compounds. • The DFT found that AlCl 2 + reacted with C=O in the batteries. • BDTO has a specific capacity of 238.6 mAh g−1 and is still 65.7 mAh g−1 after 500 cycles. Organic electrode materials have received extensive and long-term research and attention due to their safety, environmental friendliness, and lower price, and have also been used in aluminum-ion batteries (AIBs). The performance of existing applications in AIBs using organics as cathode materials still lags behind inorganics, especially in terms of battery capacity and voltage. Carbonyl groups have great potential as active sites for redox reactions in AIBs. Here, six carbonyl organic compounds were used as cathode for AIBs to investigate their performance differences and the factors affecting the performance. Through a combination of experiments and theoretical calculations (DFT), BDTO was first identified as the best performing cathode material in six organics, leading the organic materials with a high specific capacity of 236.8 mAh g−1 and 500 stable cycles. Moreover, it is proved that the symmetry of ring structure and molecular structure has an important influence on the properties of organic cathodes. These research results provide a direct reference for the selection and design of rational organic as cathode materials, which is an important step on the road to develop high-performance aluminum-organic batteries as soon as possible. [ABSTRACT FROM AUTHOR]

[Display omitted] • The multi-type cubic ComXn (X = O, S, Se) were prepared by ZIF induction. • The DFT confirmed that CoSe 2 is easier to the surface adsorption and diffusion of AlCl 4 −. • The discharge capacity of CoSe 2 remains 148.9 mAh g−1 at 500 mA g−1 after 500 cycles. Since the energy storage mechanism of metal oxides, sulfides and selenides as cathode materials for aluminum ion batteries (AIBs) is still unclear, we successfully prepared multi-type cubic Co m X n (X = O, S, Se) by ZIF induction to study and analyze the energy storage mechanism. Through ex-situ XRD and XPS characterization, it is found that Co 3 O 4 and Co 3 S 4 only cause the valence change of Co element for energy storage due to the insertion and extraction of Al3+, while in CoSe 2 , not only Co but also Se element is involved in the redox reaction. Besides, CoSe 2 exhibits higher operating voltage and excellent discharge capacity compared to Co 3 O 4 and Co 3 S 4. At 100 mA g−1, CoSe 2 exhibits two operating voltages at 0.8 V and 1.8 V, and its first discharge capacity is 785.6 mAh g−1, while the discharge voltage of Co 3 O 4 and Co 3 S 4 is only about 0.6 V, and the discharge capacities are 388.3 mAh g−1 and 579.7 mAh g−1, respectively. After 500 cycles, the discharge capacities of CoSe 2 are maintained at 148.9 mAh g−1 at 500 mA g−1. In addition, DFT proves that, compared with Co 3 O 4 and Co 3 S 4 , CoSe 2 is more conducive to the surface adsorption and diffusion of AlCl 4 −, which lays a key foundation for the research on the cathode materials of aluminum batteries. [ABSTRACT FROM AUTHOR]