Design And Synthesis Of Metal-oxo Cluster Based Hybrid Electrodes For High Performance Metal Ion Batteries

The vigorous development of the global economy has spurred the ever-growing demand for energy.The excessive use of non-renewable energy sources,such as coal,oil and natgas has caused severe global warming and environmental pollution problems.Exploring and developing new green energy sources is an effective strategy to solve environmental pollution problems and reduce fossil fuel consumption.Cost-effective energy storage devices with high-performance are vital to the popularity of renewable energy,making up for the intermittent and volatile nature of renewable energy and promoting the low-carbon energy transition.Lithium/sodium secondary batteries are considered to be the most promising energy storage devices.Lithium-ion batteries with high energy density and superb rate performance are widely used in portable/wearable electronic devices and electric vehicles.Sodium-ion batteries,as a potential replacement for lithium-ion batteries,are gradually being commercialized in virtue of their abundance,low cost and environmental benign.Aluminium-ion batteries are an emerging secondary battery with high abundance of aluminium resources and three electrons transfer properties of Al³⁺,making them as promising energy storage systems.Since electrode materials are decisive for the overall performance of metal-ion batteries,it is urgent to design and develop high performance electrode materials to satisfy the increasing demand for energy storage.Polyoxometalates（POMs）with nano-size and high redox activity are promising electrode materials.However,the disadvantages of easy agglomeration and poor electrical conductivity limit their practical applications.In this article,we concentrate on the structural design of electrode materials for POM-based metal-ion batteries,improving the conductivity and dispersion of electrode materials through three strategies,i.e.nanosizing,hybridization and self-assembly,achieving excellent rate performance and cycling stability,elucidating the influence of the matching relationship between the pore size and ionic radius of electrode materials on the battery performance,and providing a new idea for the development of POM-based electrodes.The chief research content of this thesis is as follows.（1）Mn₁₂-Ac crystals were synthesized by simple evaporative crystallization at room temperature for the study of anode materials for lithium-ion batteries.The micron-sized Mn₁₂-Ac crystals have poor electrical conductivity and severe volume change during charging and discharging,as well as poor rate performance and stability.By nanosizing the Mn₁₂-Ac crystals into nanoparticles with diameters of～45 nm,the specific surface area of the electrode material is increased,the diffusion distance of Li⁺is shortened,and the volume change during charging and discharging is alleviated.However,the nanosizing caused electron transport discontinuities and increment of the interfacial resistance.To further enhance the electron transfer,carbon nanotubes were chosen as the conductive substrate and Mn₁₂-Ac was anchored on the outer surface of carbon nanotubes to construct Mn₁₂-CNTs composites,which achieved a evenly dispersion of the POMs and effectively improved the ion/electron transport.The diffusion capacity contribution of Mn₁₂-CNTs composite at the scan rate of 0.2 m V s^-1 was 439.56 m Ah g^-1,which approached to the theoretical capacity value.（2）Two vanadium-boron cluster-based MOFs（SUT-10 and SUT-11）were successfully synthesized by a hydrothermal synthesis method at 100°C.The vanadium-boron cluster units self-assembled to three-dimensional porous MOFs,generating more active sites and improving the charge transfer kinetics.The experimental comparison revealed that SUT-10 with small pore size had better lithium storage performance in Li-ion batteries,while SUT-11 with larger pore size facilitated the fast transport of large Na⁺and Al³⁺,which exhibited higher specific capacity and better rate performance when applied in Na and Al-ion batteries.The capacity ratios of SUT-10 and SUT-11 decrease with the increment of carriers sizes,demonstrating that electrochemical performance can be optimized when the pore size of the electrode material matched the ion radius.